JP2023128277A - Filter medium for liquid filter - Google Patents

Abstract

To provide a filter medium for a liquid filter, that efficiently removes particles in a liquid and is superior in pleating processability, water pressure resistance and oil pressure resistance.SOLUTION: A filter medium for a liquid filter is a laminate comprising: a melt-blown nonwoven fabric with an average fiber diameter of 1.0-4.0 μm; and a wet type nonwoven fabric composed of fibers with a fiber diameter of 5 μm or larger. In the filter medium for a liquid filter, the melt-blown nonwoven fabric and the wet type nonwoven fabric are bonded according to partial thermal-compression bonding.SELECTED DRAWING: None

Description

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

Filter media for liquid filters is mainly pleated to increase the surface area of the filter media, and then molded into a predetermined shape to create a liquid filter, which is used by combining it with other parts and setting it in a filter machine. .

Methods for producing filter media include melt blowing, spunbonding, wet papermaking, electrospinning, biaxial stretching, and the like, and each method is used to take advantage of its characteristics. As a filter medium for a liquid filter, a filter medium produced by a melt blow method is suitably used. However, the filter medium produced by the melt-blowing method has a very low density, has fiber fluff on the surface, and fibers are likely to come off due to abrasion or the like. Furthermore, since it is flexible and has low rigidity, pleatability is also low. Pressure treatment of melt-blown filter media with heated rolls solves problems such as fluffing and separation of fibers, but the density of the filter media increases and the voids become smaller, resulting in a decrease in the amount of liquid passing through and shortened filtration life. There was a problem in that it caused a decline.

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

In addition, the melt-blown filter medium is used as the main filtration nonwoven fabric, and a nonwoven fabric (wet-processed nonwoven fabric) made by a wet paper-making 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 for auxiliary filtration. It is disclosed that a cylindrical filter in which a main filtration nonwoven fabric and a pre-auxiliary filtration nonwoven fabric are laminated adjacent to each other as a nonwoven fabric and arranged around a porous tube can have a long filtration life and can be manufactured with good workability. (For example, see Patent Document 2). However, in order to have an auxiliary filtration function, the auxiliary filtration nonwoven fabric contains ultrafine fibers with low rigidity and a fiber diameter of 4 μm or less, so when pleated, there is a problem that the folded part cannot be processed sharply. There was a problem that it was difficult to maintain the shape.

In addition, the fiber layer I (Example 1: polypropylene ultrafine fiber nonwoven fabric produced by melt-blown method) is composed of ultrafine fibers with an average fiber diameter of 10 to 1000 nm, and the heat-fusible composite fibers have an average fiber diameter of 5 to 100 μm. Fiber layer II (Example 1: Mixing ratio of polyethylene terephthalate fiber with a fiber diameter of 14 μm and sheath/core type heat-fusible composite fiber of copolymerized polyester/polyethylene terephthalate = sheath/core = copolymerized polyester/polyethylene terephthalate = In a fiber laminate containing a 40/60 (w/w) mixed fiber (paper-made nonwoven fabric), contact between the ultrafine fibers and the heat-fusible conjugate fibers is made by melting the heat-fusible conjugate fibers of fiber layer II. The points are fused together, and the formed fusion points create a fiber laminate in which the fiber layer I and the fiber layer II are laminated and integrated. , it is possible to minimize the deterioration of the original properties of ultrafine fibers while compensating for the disadvantages of low mechanical strength and rigidity of the fiber layer I composed of ultrafine fibers. In addition to being able to significantly improve processability into products, fiber laminates have high gas and liquid permeability, excellent pressure resistance and durability, making them suitable as high-performance and long-life filter media. It is disclosed that it can be used for (for example, see Patent Document 3). However, in order to form the fiber layer II composed of heat-fusible conjugate fibers with a papermaking nonwoven fabric (wet-processed nonwoven fabric), it is necessary to use a Yankee dryer or the like at a temperature exceeding the melting temperature of the heat-fusible conjugate fibers that make up the nonwoven fabric. It is necessary to use heat and pressure drying. Heat-fusible composite fibers that have been heated above their melting temperature will not re-melt unless exposed to a higher temperature than the temperature that the heat-fusible composite fibers were exposed to. When pleated, there were cases where problems with delamination occurred. In order to fuse the fiber layer I and the fiber layer II by melting the heat-fusible conjugate fiber of the fiber layer II, processing at a higher temperature is required. Therefore, when processed at high temperatures, the ultrafine fibers may melt, causing problems such as the ultrafine fibers being cut or the fibers being fused together.

In addition, a nonwoven fabric layer A made of a melt-blown nonwoven fabric mainly composed of a thermoplastic resin (average single fiber diameter is 3.3 μm, polyethylene terephthalate (PET) resin) and a short fiber nonwoven fabric mainly composed of a thermoplastic resin (Example 5: A nonwoven fabric made by laminating at least one nonwoven fabric layer B consisting of a short fiber nonwoven fabric (wet-laid nonwoven fabric) made by a small paper machine for testing, in which the mass ratio of stretched PET fibers and unstretched PET fibers is 50/50. A laminate, in which the layers of the nonwoven fabric laminate are bonded by fusion at fiber intersection points, the product of basis weight and air permeability is a certain level or more, and the apparent density is 0.10 to 0.40 g/cm ³ It has been disclosed that the nonwoven fabric laminate has excellent air permeability, strength, and uniformity of formation, and that when used as a filter, the pressure loss is small and the filter life is long (for example, (See Patent Document 4). However, the stiffness of the short fiber nonwoven fabric is insufficient, and the pleated nonwoven fabric laminates are deformed by water pressure or hydraulic pressure, resulting in liquid flow resistance (hereinafter referred to as "structural pressure loss") that occurs when the flow path interval through which liquid flows is blocked. In some cases, this may cause a problem in which the amount of water increases.

Japanese Patent Application Publication No. 2010-19151 Japanese Patent Application Publication No. 2001-321620 International Publication No. 2015/046564 pamphlet JP 2018-204133 Publication

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

The above problem is a laminate containing a melt-blown nonwoven fabric with an average fiber diameter of 1.0 to 4.0 μm and a wet-laid nonwoven fabric made of fibers with a fiber diameter of 5 μm or more, in which the melt-blown nonwoven fabric and the wet-laid nonwoven fabric are partially bonded by thermocompression. This problem can be solved by using a liquid filter material made of bonded materials.

According to the present invention, the melt-blown nonwoven fabric has excellent pleatability, and even when high water pressure or high hydraulic pressure is applied to the filter medium, the melt-blown nonwoven fabric is not damaged, and the deformation caused by water pressure or oil pressure causes the flow path interval through which liquid flows to be blocked. A filter medium for a liquid filter that suppresses an increase in structural pressure loss and efficiently removes particles in a liquid can be obtained.

As a method of increasing the collection efficiency of a 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. Furthermore, in order to increase the filtration life, it is important to maintain the low density characteristic of the melt-blown nonwoven fabric. To this end, a filter medium design that solves the problems of fluffing and fiber separation of low-density melt-blown nonwoven fabrics, provides pleatability, and can withstand high water pressure or high hydraulic pressure is required.

The filter medium for liquid filters of the present invention solves these problems and has various aptitudes, and is a wet-laid nonwoven fabric made of a melt-blown nonwoven fabric with an average fiber diameter of 1.0 to 4.0 μm and a fiber with a fiber diameter of 5 μm or more. It is a laminate including a melt-blown nonwoven fabric and a wet-laid nonwoven fabric bonded together by partial thermocompression bonding, and is a filter medium for a liquid filter.

Raw material resins for melt-blown nonwoven fabrics include, for example, polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyamide (PA), polyacrylonitrile (PAN), and polyvinidene 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 preferred because it improves pleatability. Furthermore, polybutylene terephthalate tends to have better pleatability than polypropylene, and is also suitable for applications that require heat resistance.

The average fiber diameter of the fibers of the melt-blown nonwoven fabric is 1.0 to 4.0 μm, preferably 1.2 to 3.0 μm. If the average fiber diameter is less than 1.0 μm, the liquid passing resistance will be high and the life of the liquid filter will be shortened, and if it exceeds 4.0 μm, the filtration performance will be insufficient.

The average fiber diameter of a melt-blown nonwoven fabric is determined by photographing five arbitrary locations on the nonwoven fabric using an electron microscope, measuring the diameters of 20 fibers per photo for the five photographs obtained, and calculating the diameter of a total of 100 fibers. It was calculated by averaging.

The basis weight of the melt-blown nonwoven fabric is preferably 5 to 100 g/m ² , more preferably 7 to 70 g/m ² . If the basis weight of the melt-blown nonwoven fabric is less than 5 g/m ² , the filtration performance may be insufficient, and if it exceeds 100 g/m ² , the liquid passage resistance may become high and the life of the liquid filter may be shortened.

A crystal nucleating agent, a matting agent, a pigment, a fungicide, an antibacterial agent, a flame retardant, a hydrophilic agent, a light stabilizer, etc. may be added to the raw material resin of the melt-blown nonwoven fabric as long as the effects of the present invention are not impaired. good.

The melt-blown non-woven fabric is obtained by a known melt-blown non-woven fabric manufacturing method using the aforementioned raw material resins such as polypropylene and polybutylene terephthalate. Specifically, the raw resin is melted, discharged from a spinning nozzle, and exposed to high-temperature, high-pressure gas to make the raw resin into fine fibers. A melt-blown nonwoven fabric can be produced by collecting and depositing it on a collector.

As conditions for producing the melt-blown nonwoven fabric, for example, the spinning nozzle hole diameter is preferably 0.15 to 0.4 mm, the spinning temperature is preferably 200 to 340°C, and the temperature of the high-temperature high-pressure gas is: The temperature is preferably higher than the spinning temperature and lower than (spinning temperature + 60°C), and the speed of high-temperature, high-pressure gas per 1 m width (discharge air volume) is preferably 2 to 30 m ³ /min/m, and the surface of the nozzle spinneret is The distance (DCD) from the wire mesh conveyor to the wire mesh conveyor is preferably 3 to 55 cm, and the mesh width of the collector such as the wire mesh conveyor or perforated drum is preferably 5 to 200 mesh.

Wet-processed nonwoven fabrics are produced by 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 screen using a papermaking machine. Therefore, since the fibers are uniformly dispersed, the texture of wet-laid nonwoven fabrics is better than that of dry-laid nonwoven fabrics such as melt-blown nonwoven fabrics and spunbond nonwoven fabrics. In liquid filter media made by laminating melt-blown non-woven fabric and wet-laid non-woven fabric, when high water pressure or oil pressure is applied to the filter medium, the melt-blown non-woven fabric pressed against the wet-laid non-woven fabric is supported by the uniformly textured wet-laid non-woven fabric. The melt-blown nonwoven fabric is prevented from digging into the voids of the wet nonwoven fabric, and the deterioration of filtration performance due to the digging can be suppressed. Further, since 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, excellent pleatability is obtained, and an increase in structural pressure loss can be suppressed.

As a method of increasing the rigidity, there is a method of increasing the basis weight of the wet-laid nonwoven fabric. However, increasing the basis weight leads to a decrease in liquid permeability and increases the thickness, which causes the problem of reducing the area of the filter media that can be incorporated into the filter unit. In this case, the flow path interval through which the liquid flows is blocked, resulting in an increase in structural pressure loss. Therefore, the wet-laid nonwoven fabric of the present invention is required to have high rigidity regardless of the basis weight. In order to increase the rigidity of a wet-laid nonwoven fabric, the selection and combination of fibers that make up the wet-laid nonwoven fabric are important.

When the fibers constituting the wet-laid nonwoven fabric are thick, the rigidity 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, more preferably 7 μm or more, and still more preferably 10 μm or more. If the fiber diameter is less than 5 μm, liquid permeability may be reduced, the stiffness of the wet-laid nonwoven fabric may be insufficient, pleatability may be reduced, or structural pressure loss may increase due to deformation of the filter medium.

The fiber diameter of the fibers constituting the wet-laid non-woven fabric is measured using an electron microscope using an electron microscope to determine the fiber diameter of each fiber constituting the wet-laid non-woven fabric (for each fiber with almost the same material, fineness, fiber length, etc., in each purchased unit). It was determined by taking twice as many photographs, measuring the fiber diameters of 30 fibers that were in focus in the three photographs, and averaging them.

"Wet-laid nonwoven fabric made of fibers with a fiber diameter of 5 μm or more" means that the fiber diameters of all the fibers constituting the wet-laid nonwoven fabric are 5 μm or more. The fibers constituting the wet-laid nonwoven fabric include main fibers and binder fibers.

In the present invention, the main fibers are fibers that do not easily melt or soften during heat treatment (e.g., drying treatment, heat calendar treatment, etc.) during wet nonwoven fabric production, and maintain their fiber shape even after heat treatment. .

Examples of synthetic fibers as main fibers include polyester-based, polyolefin-based, polyamide-based, polyacrylic-based, vinylon-based, vinylidene, polyvinyl chloride, polyester-based, benzoate, polychlal, and phenol-based fibers. Natural fibers include hemp pulp with little film, cotton linter, and lint; recycled fibers include lyocell fiber, rayon, and cupro; semi-synthetic fibers include acetate, triacetate, and promix; inorganic fibers include alumina fiber, alumina・Fibers include silica fiber, rock wool, glass fiber, microglass fiber, zirconia fiber, potassium titanate fiber, alumina whisker, and aluminum borate whisker. In addition to the above-mentioned fibers, as plant fibers, wood pulps such as softwood pulp and hardwood pulp, woody plants such as straw pulp, bamboo pulp, and kenaf pulp, and herbaceous plants can also be used. In particular, polyester fibers and vinylon fibers are preferred in order to increase rigidity. It is preferable that the degree of stretching of the main fiber is higher, since the stiffness can be increased.

The fiber diameter of the main fiber is 5 μm or more, more preferably 5 to 30 μm, and even more preferably 7 to 25 μm. When the fiber diameter of the main fibers is less than 5 μm, the stiffness of the wet-laid nonwoven fabric is low, pleatability cannot be obtained, and the resistance to liquid passage becomes high. On the other hand, if the fiber diameter of the main fiber exceeds 30 μm, the voids in the wet-laid nonwoven fabric become too large, and when high water pressure is applied to the filter medium, the melt-blown nonwoven fabric may dig into the voids of the wet-laid nonwoven fabric, resulting in a decrease in filtration performance. .

The fiber length of the main fiber is preferably 3 to 20 mm, more preferably 3 to 15 mm. When the fiber length of the main fiber is less than 3 mm, the main fiber may fall off from the papermaking mesh, and when the fiber length of the main fiber exceeds 20 mm, the texture may deteriorate.

The content of the main fiber is preferably 20 to 80% by mass, more preferably 30 to 70% by mass, and 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 wet-laid nonwoven fabric may lack voids and the resistance to liquid passage may increase. If the content of the main fiber exceeds 80% by mass, the content of the binder fiber will be relatively low, and there is a possibility that the rigidity will be insufficient.

In order to increase the tensile strength and stiffness of the wet-laid nonwoven fabric, it is preferable that the wet-laid nonwoven fabric contains binder fibers. By adhering the intersections between the binder fibers or the intersections between the binder fibers and the main fibers, the tensile strength and rigidity 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 calender treatment, etc.) during production of wet-laid nonwoven fabric.

Examples of the binder fibers include composite fibers such as core-shell fibers, side-by-side fibers, and radially split fibers; and single fibers. Since composite fibers are difficult to form a film, the strength can be improved while retaining the spaces of the wet-laid nonwoven fabric. Examples of combinations of core-sheath fibers include polypropylene (core) and polyethylene (sheath), polypropylene (core) and ethylene vinyl alcohol (sheath), polypropylene (core) and vinyl acetate alcohol (sheath), and polyester. Examples include a combination of (core) and polyethylene (sheath), a combination of high melting point polyester (core) and low melting point polyester (sheath), etc. Examples of single fibers include polyethylene fibers, propylene fibers, undrawn polyester fibers, and the like. In order to increase the tensile strength and rigidity of the nonwoven fabric, it is particularly preferable to use a polyester core-sheath fiber that is a combination of a high melting point polyester (core) and a low melting point polyester (sheath). In addition, fully melting type single fibers made only of low melting point resins such as polyethylene fibers and hot water soluble binder fibers such as hot water soluble polyvinyl alcohol fibers tend to form a film during the heating process, but their characteristics It can be used as long as it does not inhibit.

The fiber length of the binder fibers is preferably 3 to 12 mm, more preferably 3 to 10 mm. When the fiber length of the binder fibers is less than 3 mm, the fibers tend to fall off from the papermaking screen during the papermaking process, the number of bonding points with other fibers decreases, and the rigidity may decrease. Furthermore, if the fiber length of the binder fiber exceeds 12 mm, the water dispersibility will be impaired and the texture will become uneven. It may bite into bad parts and reduce filtration performance.

The fiber diameter of the binder fiber is 5 μm or more, more preferably 5 to 20 μm, and even more preferably 7 to 18 μm. If the fiber diameter of the binder fiber is less than 5 μm, the resistance to liquid passage increases. On the other hand, if the fiber diameter of the binder fiber exceeds 20 μm, the number of bonding points with other fibers will decrease, and the rigidity may decrease.

The content of the binder fiber is preferably 20 to 80% by mass, more preferably 30 to 70% by mass, and preferably 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, adhesion between fibers tends to be insufficient, and rigidity may become insufficient. When the binder fiber content exceeds 80% by mass, the liquid passage resistance becomes high, which may cause practical problems.

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

The basis weight of the wet-laid nonwoven fabric of the present invention is not particularly limited, but is preferably from 5 to 100 g/m ² , more preferably from 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 , liquid passage resistance may increase and the life of the liquid filter may be shortened.

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

Furthermore, by including a thermoplastic resin in the wet-laid nonwoven fabric, the rigidity of the wet-laid nonwoven fabric can be improved. Examples of the thermoplastic resin include acrylic, vinyl acetate, epoxy, synthetic rubber, urethane, polyester, vinylidene chloride, polyvinyl alcohol, starch, and phenol resin. These thermoplastic resins may be used alone or in combination of two or more. The thermoplastic resin is not an essential component, and if sufficient rigidity can be obtained with the fibers alone, the thermoplastic resin is not necessary.

When the wet-laid nonwoven fabric contains a thermoplastic resin, the content thereof is preferably 0.01 to 10% by mass based on the wet-laid nonwoven fabric. If the content of the thermoplastic resin exceeds 10% by mass, the liquid flow resistance of the wet-laid nonwoven fabric may become too large. Furthermore, if the content of the thermoplastic resin is less than 0.01% by mass, the stiffness may not change as compared to a wet-laid nonwoven fabric that does not contain a thermoplastic resin.

Methods for incorporating the thermoplastic resin into the wet-laid nonwoven fabric include, but are not particularly limited to, methods such as a size press method, a tab size press method, a spray method, an internal addition method, and a gravure coating method.

Examples of methods for laminating melt-blown nonwoven fabrics and wet-laid nonwoven fabrics include ultrasonic heat fusion, heat fusion using a hot embossing roll, bonding using a reactive adhesive, and thermal lamination using hot melt resin. Illustrated. In the present invention, a lamination method of joining by partial thermocompression bonding is used, and specifically, an ultrasonic heat fusion method and a heat fusion method using hot embossing are preferably used. The lamination method, which involves joining by partial thermocompression bonding, eliminates problems in cases where the composition of the fibers that make up the melt-blown nonwoven fabric and the wet-laid nonwoven fabric are different, or when they are strongly adhered, and eliminates the problem of delamination after pleating, and improves shape retention. It can be suitably used when it is desired to increase the Partial thermocompression bonding refers to, for example, in the case of ultrasonic heat fusion, only a portion of the laminated nonwoven fabric is melted and bonded using ultrasonic heat and pressure. This means that all the fibers that form the melt-blown nonwoven fabric and the fibers that form the wet-laid nonwoven fabric are melt-bonded. In addition, partial thermocompression bonding using a heat fusion method using heat embossing is a method of thermocompression bonding by passing laminated nonwoven fabrics under pressure between a heated heat roll with a flat surface and a heat roll with an uneven surface. Only the portion that passed through the convex portion of the nonwoven fabric was bonded by thermocompression. In the case of the thermal fusion method using hot embossing, the layers are bonded by softening or melting the binder fibers contained in the wet nonwoven fabric and deforming it by pressure. Therefore, the hot roll temperature during hot embossing is preferably higher than the softening temperature or melting point of the binder fibers, and preferably lower than the melting point of the main fibers contained in the wet-laid nonwoven fabric.

EXAMPLES Hereinafter, the present invention will be specifically explained with reference to Examples, but the present invention is not limited to these Examples. In addition, all parts and percentages in the examples are based on mass unless otherwise specified.

<Melt-blown nonwoven fabric 1>
Using a melt-blown nonwoven fabric manufacturing device, a melt-blowing nozzle die with a spinning nozzle hole diameter of 0.2 mm and a pitch of 0.8 mm was heated to a temperature of 240°C, and a polypropylene resin (melt flow rate (MFR): 1200 g/10 minutes, measured DCD (resin temperature: 230°C) is supplied to the die, polypropylene fiber is discharged from the nozzle, and heated air (260°C, 8m ³ /min/m) is blown out from both sides of the nozzle. 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 (distance from 150 mm to a wire mesh conveyor).

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

<Melt-blown nonwoven fabric 3>
Using a melt-blown nonwoven fabric manufacturing device, a melt-blowing nozzle die with a spinning nozzle hole diameter of 0.2 mm and a pitch of 0.8 mm was heated to a temperature of 240°C, polypropylene resin (manufactured by ExxonMobil, Achieve 6936) was supplied to the die, and the nozzle was heated to 240°C. Polypropylene fibers are discharged from the nozzle along with heated air (260°C, 16 m ³ /min/m) blown from both sides of the nozzle, and the wire mesh moves at DCD (distance from the surface of the spinneret to the wire mesh conveyor): 300 mm. A melt-blown nonwoven fabric 3 having a basis weight of 10 g/m ² and an average fiber diameter of 0.8 μm was obtained by spraying on a conveyor.

<Melt-blown nonwoven fabric 4>
After drying the polyethylene terephthalate resin at 150°C for 24 hours in a nitrogen atmosphere using a melt-blown nonwoven fabric production device, a melt-blowing nozzle die arranged with a spinning nozzle hole diameter of 0.4 mm and a pitch of 0.8 mm was heated to a temperature of 300°C. , polyethylene terephthalate resin is supplied to the die, polyethylene terephthalate fiber is discharged from the nozzle, and heated air (320°C, 8 m ³ /min/m) is blown out from both sides of the nozzle. A melt-blown nonwoven fabric 4 having a basis weight of 20 g/m ² and an average fiber diameter of 3.3 μm was obtained by spraying onto a wire mesh conveyor moving at a distance of 150 mm (distance to a wire mesh conveyor).

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

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

<Main fiber 3>
The main fiber 3 was a drawn polyester fiber having a fiber diameter of 14.3 μm and a fiber length of 5 mm.

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

<Main fiber 5>
As a sea-island type fiber, a fiber (fineness: 1.65 dtex, fiber length: 3 mm) manufactured by a composite spinning method was prepared, in which 25 island components made of polypropylene were present in a sea component made of poly-L-lactic acid. . Next, this sea-island type fiber was 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 type fiber. : 1.8 μm, fiber length 3 mm) was used as the main fiber 5.

<Main fiber 6>
The main fiber 6 was an acrylic fiber with a fiber diameter of 4.0 μm and a fiber length of 3 mm.

<Main fiber 7>
The main fiber 7 was a drawn polyester fiber having a fiber diameter of 9.8 μm and a fiber length of 6 mm.

<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 being polyester (melting point 253° C.), and the sheath portion being polyethylene terephthalate-isophthalate copolymer (softening point 75° C.).

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

<Binder fiber 3>
Binder fiber 3 was a core-sheath fiber having a fiber diameter of 16 μm and a fiber length of 5 mm, the core component of which was polyester (melting point 253° C.), and the sheath portion of which was made of polyethylene terephthalate-isophthalate copolymer (softening point 75° C.).

<Binder fiber 4>
Binder fiber 4 was an undrawn PET fiber with a fiber diameter of 14.3 μm and a fiber length of 6 mm.

(Production of wet nonwoven fabric)
After pouring water into a ^2m3 dispersion tank, main fibers and binder fibers were added in the proportions shown in Table 1, and dispersed for 5 minutes at a dispersion concentration of 0.2% by mass to form a uniform paper under stirring with an agitator. 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 to a dry mass of 20 g/ ^m2 , and touch roll it with a Yankee dryer with a surface temperature of 130°C. was dried under a pressure of 400 N/cm ² to obtain wet-laid nonwoven fabrics 1 to 9.

After pouring water into a ^2m3 dispersion tank, main fibers and binder fibers were added in the proportions shown in Table 1, and dispersed for 5 minutes at a dispersion concentration of 0.2% by mass to form a uniform paper under stirring with an agitator. 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 to a dry weight of 40 g/ ^m2 , and touch roll it with a Yankee dryer with a surface temperature of 130°C. was dried under a pressure of 400 N/cm ² to obtain a wet nonwoven fabric 10 and a wet nonwoven fabric 11.

After pouring water into a ^2m3 dispersion tank, main fibers and binder fibers were added in the proportions shown in Table 1, and dispersed for 5 minutes at a dispersion concentration of 0.2% by mass to form a uniform paper under stirring with an agitator. 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 to a dry weight of 20 g/ ^m2 , and touch roll it with a Yankee dryer with a surface temperature of 110°C. was dried under a pressure of 400 N/cm ² to obtain a wet-laid nonwoven fabric 12.

(Preparation of filter medium for liquid filter)
Melt-blown nonwoven fabrics (MB) 1 and 2 and wet-laid nonwoven fabrics (WL) 1 to 9 were stacked in three layers in the combinations shown in Table 2 to form wet-laid nonwoven fabric/melt-blown nonwoven fabric/wet-laid nonwoven fabric, and then ultrasonic heat fusion was performed. The liquid filter media of Examples 1 to 9 and Comparative Examples 1 and 2 were produced by bonding using a device.

Melt-blown nonwoven fabric (MB) 1 and wet-laid nonwoven fabric (WL) 10 are stacked in two layers in the combination shown in Table 2 to form a melt-blown nonwoven fabric/wet-laid nonwoven fabric, and then joined using an ultrasonic heat fusion device, A filter medium for a liquid filter according to Example 10 was produced.

Melt-blown nonwoven fabric (MB) 3 and wet-laid nonwoven fabric (WL) 11 were stacked in two layers in the combination shown in Table 2 to form a melt-blown nonwoven fabric/wet-laid nonwoven fabric, and then passed through a paper machine's Yankee dryer (surface temperature 120°C). Heat treatment was performed to produce a liquid filter medium of Comparative Example 3.

Two sets of belt conveyors made of Teflon (registered trademark) resin belts woven with glass fiber as a core material were arranged one above the other so that the clearance between the belts was zero. Melt-blown non-woven fabric (MB) 4 and wet-laid non-woven fabric (WL) 12 are stacked in two layers in the combination shown in Table 2 to form a melt-blown non-woven fabric/wet-laid non-woven fabric, and passed through this belt conveyor at a speed of 1 m with the entire surface gripped. /min, passed through a heat treatment zone with a length of 1 m in which the upper and lower belt surface temperatures were heated to 145° C., and was heated for 60 seconds to produce a filter medium for a liquid filter of Comparative Example 4.

<Evaluation>
The melt-blown nonwoven fabrics, wet nonwoven fabrics, and liquid filter media obtained in Examples and Comparative Examples were subjected to the following measurements and evaluations, and the results are shown in Tables 1 and 2.

[Basic weight] (Unit: g/m ² )
The basis weight was measured based on the method specified in JIS P8124:2011 (paper and paperboard - basis weight measurement method).

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

[Pressure loss] (Unit: Pa)
Measurements were made in accordance with JIS B9908:2011 Format 1 at a surface wind speed of 5.3 cm/sec. The lower the pressure loss, the better; less than 50 Pa is rated "◎", 50 Pa or more and less than 100 Pa is rated "○", 100 Pa or more and less than 200 Pa is rated "△", and 200 Pa or more is rated "x". The liquid filter media of Examples 1 to 9 and Comparative Examples 1 and 2 were evaluated using wet-laid nonwoven fabric (WL) as the upstream material. The liquid filter media of Example 10 and Comparative Examples 3 and 4 were evaluated using melt-blown nonwoven fabric (MB) as the upstream material.

[Collection efficiency] (unit: %)
Measurements were made in accordance with JIS B9908:2011 Format 1 at a surface wind speed of 5.3 cm/sec. The particles to be measured were atmospheric dust, and the collection efficiency of particles with a particle size of 0.3 to 0.5 μm was measured using a particle counter (trade name "KC-11", manufactured by Rion Corporation). , the collection efficiency was calculated from Equation 1 below. The liquid filter media of Examples 1 to 9 and Comparative Examples 1 and 2 were evaluated using wet-laid nonwoven fabric (WL) as the upstream material. The liquid filter media of Example 10 and Comparative Examples 3 and 4 were evaluated using melt-blown nonwoven fabric (MB) as the upstream material.

(Formula 1)
η1=(1-C2/C1)×100
η1: 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 trapping efficiency, the better; if it is 50% or more, it is marked "○", if it is 30% or more and less than 50%, it is marked "Δ", and if it is less than 30%, it is marked "x".

To measure liquid filtration efficiency and liquid filtration rate, a JIS Class 8 powder diluted and dispersed in pure water to a concentration of 0.05% was used as a test liquid, and the measurements were performed in the following manner.

[Liquid filtration efficiency] (unit: %)
Liquid filtration efficiency is determined by moistening the liquid filter medium with pure water, using a vacuum filtration device, setting the liquid filter medium in a filtration holder with a filtration area of 14 cm ² , and placing 100 ml of the test liquid in the filtration holder. After pouring, the test liquid is filtered under reduced pressure with a differential pressure ΔP=200 mmHg, and after completely filtering the test liquid, 100 ml of the test liquid is poured into the same holder and filtered under reduced pressure under the same conditions. Vacuum filtration was repeated a total of 10 times, and at the 10th vacuum filtration, the number of 3-10 μm particles in the test liquid before and after was measured using a particle counter in liquid (KL-01) manufactured by Rion Co., Ltd., and the following formula was used: 2, the liquid filtration efficiency was calculated. The liquid filter media of Examples 1 to 9 and Comparative Examples 1 and 2 were evaluated using wet-laid nonwoven fabric (WL) as the upstream material. The liquid filter media of Example 10 and Comparative Examples 3 and 4 were evaluated using melt-blown nonwoven fabric (MB) as the upstream material.

(Formula 2)
η2=(1-C2/C1)×100
η2: 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, ``○'' if it is 50% or more and less than 70%, ``△'' if it is 30% or more and less than 50%, and ``△'' if it is less than 30%. I marked it with an “×”.

[Liquid filtration rate] (unit: cc/cm ² /min)
Liquid filtration rate: The liquid filtration rate was obtained from the 10th filtration time of the above liquid filtration efficiency test. The larger the value of the liquid filtration rate, the less clogging of the filter medium and the shorter the time required for filtration, resulting in a better filter medium. The liquid filter media of Examples 1 to 9 and Comparative Examples 1 and 2 were evaluated using wet-laid nonwoven fabric (WL) as the upstream material. The liquid filter media of Example 10 and Comparative Examples 3 and 4 were evaluated using melt-blown nonwoven fabric (MB) as the upstream material.

The higher the liquid filtration rate, the better; ``◎'' if it is 15 cc/cm <sup>2</sup> /min or more, ``○'' if it is 10 cc/cm ² /min or more and less than 15 cc/cm ² /min, and 5 cc/cm ² /min or more. If it was less than 10 cc/cm ² /min, it was rated "Δ", and if it was less than 5 cc/cm ² /min, it was rated "x".

[Pleating processability]
Pleating is a process of folding many liquid filter media into a bellows shape in order to fold them into a liquid filter. During actual use, water pressure and hydraulic pressure are applied to the pleated filter material folded into the liquid filter. Pleating property is evaluated by evaluating the occurrence of delamination of the filter medium, mesh opening, deformation of the filter medium, etc. when water pressure or oil pressure is applied. A filter medium with good pleatability means that it has excellent water pressure resistance and oil resistance, and is capable of suppressing an increase in structural pressure loss due to filter medium deformation.

Cut the filter medium for liquid filter into 30 cm in the flow direction (MD) and 20 cm in the cross direction (CD) of the papermaking process, repeat mountain folds and valley folds every 5 cm across the flow direction, and place the filter medium on the folded filter medium to a diameter of 5 cm. A cylindrical metal roll with a length of 30 cm and a weight of 3 kg is slowly rolled to create creases and form a bellows shape. If the crease is clear and there is no distortion, and there is no deformation even when the crease is pressed, it is marked as good. If it is slightly deformed, but there is no problem in use, it is marked as "△." If there is deformation or peeling between layers. were marked as "x" because of problems in use. Also, those that were extremely hard and were better than "○" were rated "◎".

The liquid filter media of Examples and Comparative Examples are liquid filter media formed 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, it is found that the liquid filter medium of Comparative Example 1 using a wet-laid nonwoven fabric containing main fibers with a fiber diameter of 1.8 μm (less than 5 μm in fiber diameter) has a fiber diameter of 5 μm. Compared to the liquid filter media of Examples 1 to 10 using wet-laid nonwoven fabrics made of the above-mentioned fibers, the pressure loss is high and the stiffness is insufficient, resulting in poor pleatability and unusable level. Liquid filtration rates were also low. The liquid filter medium of Comparative Example 2 using a wet-laid nonwoven fabric containing main fibers with a fiber diameter of 4.0 μm (less than 5 μm) is different from that of Examples 1 to 10 using a wet-laid nonwoven fabric consisting of fibers with a fiber diameter of 5 μm or more. Compared to filter media for liquid filters, the pleatability was poor and it was at an unusable level.

The liquid filter material of Comparative Example 3, in which a melt-blown nonwoven fabric and a wet-laid nonwoven fabric were laminated by heat treatment using a paper machine's Yankee dryer, had very poor adhesion between the layers of the melt-blown nonwoven fabric and the wet-laid nonwoven fabric, and the pleatability was evaluated. Previous delamination was observed.

The filter medium for liquid filter of Comparative Example 4 was evaluated for pleatability, using unstretched PET fiber as the binder fiber of the wet-laid nonwoven fabric, and heat-treating and laminating the melt-blown nonwoven fabric and the wet-laid nonwoven fabric by sandwiching the adhesive between Teflon belts. Although no delamination was observed before, partial delamination was observed after evaluation of pleatability, and the deformation was so significant that it was at an unusable level.

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

The liquid filter material of the present invention can be used to remove machining debris contained in the machining fluid of electrical discharge machines used for metal engraving and cutting, and for cutting, polishing, etching, etc. of substrate wafers in IC production. It can be suitably used as a liquid filter for efficiently removing processing debris contained in ultrapure water used in a process to obtain a clean liquid, a liquid filter for automobile engine oil, fuel, etc.

Claims (1)

It is a laminate containing a melt-blown nonwoven fabric with an average fiber diameter of 1.0 to 4.0 μm and a wet-laid nonwoven fabric made of fibers with a fiber diameter of 5 μm or more, and the melt-blown nonwoven fabric and the wet-laid nonwoven fabric are joined by partial thermocompression bonding. A filter medium for liquid filters.