JP2016137459A - Nonwoven fabric for filter, and filter medium for filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve a nonwoven fabric for a filter having high strength even in the case of a low basis weight, and having a uniform tone; and to provide a filter medium for a liquid filter or a filter medium for an air filter having a long life, and hardly broken even under a high pressure.SOLUTION: In a nonwoven fabric for a filter, which is wet type nonwoven fabric containing non-fusible stretched polyethylene terephthalate fibers and thermo-fusible binder fibers, a fiber length of the stretched polyethylene terephthalate fibers is 7-12 mm, and a fiber length of the binder fibers is 1-12 mm.SELECTED DRAWING: None

Description

  The present invention relates to a filter non-woven fabric, a filter medium for liquid filter for efficiently removing particles contained in the liquid and obtaining a clean liquid, and a filter medium for air filter for collecting dust in the air. It relates to filter media.

  There are roughly two structures of the filter medium for liquid filters. One is an “internal filtration type”, which is a filter medium structured to trap solid particles inside the filter medium. The other is a “surface filtration type”, which is a filter medium having a structure of capturing solid particles on the surface of the filter medium (see, for example, Patent Document 1). In addition, the filter medium is subjected to pleating to increase the surface area of the filter medium, and then formed into a predetermined shape to produce a liquid filter, which is used in combination with other components in a filter.

  Conventionally, filter media for liquid filters used in electrical discharge machines and IC production processes, filter media for various types of liquids such as automotive engine oil, fuel, etc., mixed pulp of natural pulp and organic fibers, phenol resin, etc. Sheets impregnated with polyester, polyester nonwoven fabric (spunbond), and the like are used, but have disadvantages such as low filtration efficiency and short life. In addition, a porous sheet such as a fluororesin is available as a high-performance filter medium. However, since it is expensive, it is limited to special applications and is not suitable as a filter medium for treating a large amount of liquid.

As one of the filter media for solving these problems, 5 to 40% by mass of organic fibers fibrillated to 1 μm or less, 5 to 60% by mass of ultrafine organic fibers having a fiber diameter of 1 to 5 μm, and organic fibers having a fiber diameter of 5 μm or more. Surface filtration type liquid filtration comprising 20 to 70% by mass and part or all of the organic fiber having a fiber diameter of 5 μm or more is a fibrous organic binder, and the density of the filter medium is 0.25 to 0.8 g / cm ^3. Filter media have been proposed (see Patent Document 2). In this filter medium, the fibrillated organic fiber expresses the collection efficiency of solid particles and limits the content with other organic fibers to suppress pressure loss and efficiently process a large amount of liquid in a short time. To be able to.

  The above filter medium has a problem that it cannot be folded because it is very thin and not hard. Therefore, the above filter medium is thin and excellent in surface filtration performance in order to improve strength and waist (stiffness). An integrated filter medium for liquid filtration has been proposed by combining layers and a high-strength, high-strength, and foldable support layer. (See Patent Document 3).

  In recent years, as the processing speed of the filtration area processing machine is increased, the processing waste is refined, and further, the pressure applied to the filter medium is increased more and more, and the life time tends to be shortened. Therefore, in order to fold many filter media into the filter unit for the purpose of improving the life time, a filter media that exhibits high strength even at a low basis weight is required.

JP 2000-70628 A Japanese Patent No. 2633355 Japanese Patent No. 3305372

  An object of the present invention is to provide a filter nonwoven fabric for air filters and a filter medium for liquid filters and air filters that have a high strength even at low basis weights, have a uniform texture, have a long life, and are not easily damaged even at high pressures. It is in.

As a result of intensive studies to solve the above problems, the present inventor,
(1) A wet nonwoven fabric containing non-meltable stretched polyethylene terephthalate fiber and heat-meltable binder fiber, the stretched polyethylene terephthalate fiber has a fiber length of 7 to 12 mm, and the binder fiber has a fiber length of 1 to 1 A non-woven fabric for a filter of 12 mm,
(2) A filter medium for a filter formed by integrating the non-woven fabric for a filter according to (1) above as a rough layer and laminating with a dense layer;
(3) The filter medium for a filter according to (2), wherein the wet tensile strength in the CD direction is 0.8 kN / m or more,
(4) The filter medium according to the above (2) or (3), wherein the dense layer contains fibrillated organic fibers,
I found.

  As a means of improving the strength of wet nonwoven fabrics containing non-meltable stretched polyethylene terephthalate fibers and heat-meltable binder fibers, the length of each fiber is increased to increase the adhesion point between stretched polyethylene terephthalate fibers and binder fibers. A method is mentioned. However, if the fiber length is too long, the water dispersibility is lowered, and depending on the papermaking conditions, the formation becomes uneven and the strength is reduced. In the non-woven fabric for filter (1) of the present invention, by setting the fiber lengths of the stretched polyethylene terephthalate fiber and the binder fiber to suitable ranges, even if there are many adhesion points between the stretched polyethylene terephthalate fiber and the binder fiber, the formation is good. A filter nonwoven fabric that is uniform and excellent in strength is obtained.

  The filter non-woven fabric (1) excellent in strength (1) is made into a rough layer, and is laminated and integrated with the dense layer so that the filter medium (2) is not easily broken even at high pressure, and is excellent in filtration performance. In the filter medium (3) having a wet tensile strength in the CD direction of 0.8 kN / m or more, it is difficult for tearing to occur due to water pressure. Furthermore, in the filter medium (4) for a filter, it is preferable that a dense fiber network is obtained by containing fibrillated organic fibers in the dense layer, and the filtration performance is further improved.

  Hereinafter, the nonwoven fabric for filter and the filter medium for filter of the present invention will be described in detail. The non-woven fabric for filter of the present invention is a wet non-woven fabric containing non-meltable stretched polyethylene terephthalate fiber and heat-meltable binder fiber, and the stretched polyethylene terephthalate fiber has a fiber length of 7 to 12 mm. It is a nonwoven fabric for filters having a fiber length of 1 to 12 mm. In the present invention, “non-melting” means the property of maintaining the shape without being almost melted by heat (drying process, thermal calendaring, etc.) applied in the manufacturing process of the nonwoven fabric for filters. The term “meltability” means a property of melting by heating in a drying process at the time of manufacturing a nonwoven fabric and losing the original fiber form. The fiber length of the stretched polyethylene terephthalate fiber (hereinafter sometimes referred to as “stretched PET fiber”) is 7 to 12 mm, more preferably 7 to 10 mm. When the fiber length is less than 7 mm, On the other hand, if the fiber length exceeds 12 mm, the water dispersibility of the fiber is impaired, the formation becomes uneven, and the strength of the nonwoven fabric decreases. Decreases.

  The fiber diameter of the stretched PET fiber is preferably 0.3 dtex to 4.0 dtex, and more preferably 0.6 to 3.0 dtex. If the fineness is less than 0.3 dtex, sufficient rigidity cannot be obtained, and the pleatability may be impaired. On the other hand, if the fineness is larger than 4.0 dtex, the rigidity may be too high and the suitability for pleating may be impaired, or the formation may be poor.

  The content of the stretched PET fiber is preferably 10 to 80% by mass, more preferably 15 to 70% by mass, and still more preferably 20 to 60% by mass in terms of the nonwoven fabric mass ratio. If the content of the stretched PET fiber is less than 10% by mass, the strength may decrease. On the other hand, if the content exceeds 80% by mass, the content of the binder fiber may be relatively low and the strength may be insufficient. There is.

  The binder fiber in the nonwoven fabric for filters of the present invention is a fiber having a property of being melted by heat treatment (for example, drying treatment, thermal calendar treatment, etc.) at the time of producing the nonwoven fabric for filters. Examples of the binder fiber include single fibers, and composite fibers such as core-sheath fibers (core-shell type), parallel fibers (side-by-side type), and radially divided fibers. Since the composite fiber hardly forms a film, the strength can be improved while maintaining the space of the composite filter medium. For example, polypropylene fiber, combination of polypropylene (core) and polyethylene (sheath), combination of polypropylene (core) and ethylene vinyl alcohol (sheath), combination of polypropylene (core) and vinyl acetate alcohol (sheath), polypropylene (core) and A combination of polyethylene (sheath), a combination of high melting point polyester (core) and low melting point polyester (sheath), and the like can be mentioned. From the viewpoint of increasing the strength of the nonwoven fabric, in particular, a core-sheath type polyester binder fiber should be used. Is preferred. In addition, single fibers (fully fused type) composed only of low melting point resins such as polyethylene, and hot water soluble binder fibers such as hot water soluble polyvinyl alcohol fibers are easy to form a film in the heating process. Can be used as long as they are not hindered.

  The fiber length of the binder fiber is 1 to 12 mm, and more preferably 3 to 10 mm. Binder fibers having a fiber length of less than 1 mm are more likely to fall off the web during the paper making process, resulting in a decrease in the point of adhesion with stretched PET fibers and a decrease in strength of the nonwoven fabric. Moreover, when the fiber length of binder fiber exceeds 12 mm, water dispersibility will be impaired, formation will become non-uniform | heterogenous, and the intensity | strength of a nonwoven fabric will fall.

  The fiber diameter of the binder fiber is preferably 3 to 20 μm, and more preferably 5 to 18 μm. If the fiber diameter is less than 3 μm, the adhesion between the fibers tends to be insufficient, and the strength may decrease. On the other hand, if the fiber diameter exceeds 20 μm, the formation may be impaired.

  The content of the binder fiber is preferably 20 to 90% by mass and more preferably 30 to 80% by mass in terms of the nonwoven fabric mass ratio. If the binder fiber is less than 20% by mass, the adhesion between the fibers tends to be insufficient, and the strength may be insufficient. If it exceeds 90% by mass, the filtration resistance increases, which may cause problems in practice.

  The non-woven fabric for filters of the present invention may contain non-binder fibers that are non-meltable other than stretched PET fibers, if necessary. Specifically, examples of the synthetic fiber include polyester, polyolefin, polyamide, polyacryl, vinylon, vinylidene, polyvinyl chloride, polyester, benzoate, polyclar, and phenol fibers. Natural fiber includes hemp pulp, cotton linter, lint; regenerated fiber is lyocell fiber, rayon, cupra; semi-synthetic fiber is acetate, triacetate, promix; inorganic fiber is alumina fiber, 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-mentioned fibers, wood fibers such as conifer pulp and hardwood pulp, woods such as bamboo pulp, bamboo pulp, kenaf pulp, and herbs can be used as plant fibers. Moreover, as long as the said fiber is a range which does not inhibit liquid permeability and air permeability, it may be fibrillated at all. Furthermore, pulp fibers obtained from waste paper, waste paper, and the like can also be used. Moreover, the fiber which has irregular cross sections, such as T type, Y type, and a triangle, can also be contained.

The basis weight of the nonwoven fabric for filters of the present invention is not particularly limited, but is preferably ^{30~70g / m 2, 40~60g / m} 2 is more preferable. If it is less than 30 g / m ² , sufficient rigidity may not be obtained, and pleatability may be impaired. On the other hand, when it exceeds 70 g / m ² , it becomes too rigid and there is a risk of impairing the pleatability.

The filter medium of the present invention comprises the filter nonwoven fabric of the present invention, and the filter nonwoven fabric of the present invention is used as a coarse layer, and is laminated and integrated with a dense layer having a higher density than the coarse layer. Filter media can be used advantageously. The dense layer preferably contains at least one kind selected from polyolefin-based, polyamide-based, polyester-based, acrylic-based, vinylon-based, and regenerated fiber-based non-binder fibers having a fiber diameter of 20 μm or less. Moreover, it is preferable that the basic weight of a dense layer is 5-50 g / m < ² >. Furthermore, it is preferable to contain 5 to 60% by mass of at least one selected from polyester-based, polyolefin-based, vinyl chloride-vinyl acetate-based, vinylon-based binder fibers, etc., whereby a dense layer with high surface strength can be obtained. . This dense layer can be produced by a wet paper machine, but depending on the application, an electrospinning method comprising a material such as polyester, polyamide, polyolefin, or cellulose, spunbond, melt blow, needle punch A sheet produced by a method such as spunlace can be used.

The “fiber diameter” as used in the present invention refers to the fiber diameter of a value converted into a true circular diameter having the same cross-sectional area when the cross section of the fiber is an ellipse or a polygon, and is referred to in the present invention. The “average fiber diameter” indicates a mass average fiber diameter calculated by ΣDi ² Ni / ΣDiNi when Ni fibers having a fiber diameter Di exist.

  In the filter medium for a filter of the present invention, the wet tensile strength is preferably 0.8 kN / m or more, and more preferably 1.0 kN / m or more. The wet tensile strength refers to a physical property value according to JIS-8135 and JIS-8113. Specifically, after a sample having a width of 15 mm and a length of 200 mm is immersed in pure water at 20 ° C. for 5 minutes, it is a physical property value measured using a Tensilon measuring machine, and when actually used as a filter material for a liquid filter, This relates to the difficulty of breaking the filter due to water pressure. If the wet tensile strength in the CD direction is less than 0.8 kN / m, tearing may occur due to water pressure. The upper limit of the wet tensile strength is not particularly limited, but is preferably 5.0 kN / m or less. When it exceeds 5.0 kN / m, there is a problem that it is difficult to cut when cutting after pleating.

  The filter medium of the present invention obtained by laminating and integrating the coarse layer and the dense layer prevents the filter medium from being broken by pressure, has excellent filtration performance, for electric discharge machines, for engine oil, for fuel, It can be suitably used as a filter medium for liquid filters for oil-water separation, hydraulic equipment, and the like. In this case, the surface layer filtration mechanism can be developed by using the dense layer as the upstream side. Further, depending on the conditions used or the intended effect, the internal filtration mechanism can be developed with the coarse layer upstream.

  The filter medium of the present invention is used for an air filter for liquid crystal, bio, pharmaceutical, food industry clean rooms, clean benches, etc., an air filter for air conditioning, an air filter for an air purifier, a gas turbine or a steam turbine. It can also be suitably used for industrial air filters suitable for collecting particles in air or gas.

  The dense layer constituting the filter medium of the present invention preferably contains fibrillated organic fibers. This is preferable because the dense fiber network becomes more homogeneous and the filtration performance is improved.

  The fibrillated organic fiber used in the present invention refers to a fiber mainly having a fiber portion that is very finely divided in a direction parallel to the fiber axis, and at least a part of the fiber diameter is 1 μm or less. . In the present invention, it is preferable that the aspect ratio of the length and width is distributed in the range of 20: 1 to 100,000: 1 and the Canadian standard freeness is in the range of 0 ml to 500 ml.

  As the fibrillated organic fiber used in the present invention, celluloses such as natural cellulose, regenerated cellulose such as lyocell and rayon are preferable, and lyocell which is regenerated cellulose is particularly preferable. Also, aramid fibers such as wholly aromatic polyamide, polyester fibers such as wholly aromatic polyester, polyimide, polyamideimide, polyetheretherketone, polyphenylene sulfide, polybenzimidazole, poly-p-phenylenebenzobisthiazole, poly-p -Heat-resistant fibers made of phenylene benzobisoxazole, polytetrafluoroethylene, acrylic resins, etc. are also preferable because they can further improve heat resistance, and among these, aramid fibers such as para-type wholly aromatic polyamides and acrylonitrile that are particularly easily fibrillated An acrylic fiber such as a copolymer of acrylate and acrylate is preferred. These may be used alone or in combination of two or more.

  In the present invention, in order to obtain fibrillated organic fibers, for example, short fibers are dispersed in water at an appropriate concentration, and this is given shearing force by a refiner, a beater, a mill, a grinding device, or a high-speed rotary blade. Rotating blade type homogenizer, double cylindrical high speed homogenizer that generates shearing force between a cylindrical inner blade that rotates at high speed and a fixed outer blade, ultrasonic crusher that is refined by ultrasonic impact, high pressure A finer process may be performed by passing through a homogenizer or the like and adjusting conditions such as the shape of the blade, the flow rate, the number of treatments, the treatment speed, and the treatment concentration.

  In the present invention, in order to express the filter medium uniformity, solid particle capturing ability, pressure loss, etc. in a well-balanced manner, (A) A fibrillated organic material having a fiber diameter of 1 μm or less is separated from the trunk by applying a shearing force. It is preferable that the fibers and (B) two fibrillated organic fibers of a fibrillated organic fiber in which a branch portion having a fiber diameter of 1 μm or less is generated from a trunk portion having a fiber diameter of 2 μm or more by applying a shearing force.

In the filter medium of the present invention, the density of the dense layer is preferably 0.1 to 0.8 g / cm ³ . When the density is less than 0.1 g / cm ³ , particles are likely to be clogged in the dense layer, and the life may be shortened. Conversely, if it exceeds 0.8 g / cm ³ , the filtration resistance may become too high. The density of the coarse layer is preferably lower than the density of the dense layer and 0.05 to 0.6 g / cm ³ . When the density of the coarse layer is less than 0.05 g / cm ³ , the filter medium may have insufficient strength or the pleatability may be impaired. Conversely, if it exceeds 0.6 g / cm ³ , the filtration resistance may become too high. Moreover, it is preferable that the density of the whole filter material for filters is 0.1-0.6 g / cm < ³ >. When the density of the entire filter medium is less than 0.1 g / cm ³ , reliability may be lowered due to generation of pinholes or the like.

  Moreover, when the filter medium for a filter of the present invention contains a thermoplastic resin, the rigidity is preferably improved. Examples of the thermoplastic resin include acrylic, vinyl acetate, epoxy, synthetic rubber, urethane, polyester, vinylidene chloride, polyvinyl alcohol, starch, phenol resin, and the like. Can be used with more than one type.

  The amount of the thermoplastic resin contained in the filter medium of the present invention is preferably 0.01 to 10% by mass with respect to the filter medium. When it exceeds 10 mass%, the pressure loss of the filter medium for a filter may become too large. Moreover, if less than 0.01 mass%, compared with the filter medium which does not contain a thermoplastic resin, rigidity may not change.

  The state in which the thermoplastic resin is contained in the filter medium for the liquid filter may be only the dense layer, both the dense layer and the coarse layer, or only the coarse layer. However, if a thermoplastic resin is contained in the dense layer, the space of the dense layer is blocked, the solid particle capturing ability is reduced, and pressure loss may be increased. preferable.

  The method of incorporating the thermoplastic resin into the filter medium is not particularly limited, and examples thereof include a size press method, a tab size press method, a spray method, an internal addition method, and a gravure coating method. In order to make it contain only in a rough layer, it is preferable to use a spray system and a gravure coating system.

  In the filter medium of the present invention, additives such as a cross-linking agent, a water repellent, a dispersant, a yield improver, a paper strength agent, and a dye may be appropriately blended as long as the characteristics of the filter medium are not impaired as necessary. Can do.

  The filter non-woven fabric and filter medium of the present invention are a paper machine in which a papermaking method such as a long mesh, a circular mesh, or an inclined wire is installed alone, or two or more of the same or different types of these papermaking methods are online. It can be manufactured by an installed combination paper machine. The produced wet paper (web) is dried with a dryer. After drying, a thermoplastic resin is optionally contained and dried with an air dryer, cylinder dryer, suction drum dryer, infrared dryer or the like. In addition, when using a dense layer produced by a dry method, a rough layer produced by a paper machine and a dense layer produced by a dry method may be laminated by a paper machine, or a separate calender device, thermal calender device, bonding You may laminate | stack using processing machines, such as a matching apparatus.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to the examples. In the examples, all parts and percentages are by mass unless otherwise specified.

<PET fiber 1>
A PET fiber 1 was a drawn polyethylene terephthalate fiber having a fineness of 0.3 dtex and a fiber length of 7 mm.

<PET fiber 2>
The drawn polyethylene terephthalate fiber having a fineness of 0.6 dtex and a fiber length of 7 mm was used as the PET fiber 2.

<PET fiber 3>
The drawn polyethylene terephthalate fiber having a fineness of 1.7 dtex and a fiber length of 10 mm was designated as PET fiber 3.

<PET fiber 4>
A drawn polyethylene terephthalate fiber having a fineness of 2.2 dtex and a fiber length of 10 mm was designated as PET fiber 4.

<PET fiber 5>
The drawn polyethylene terephthalate fiber having a fineness of 3.3 dtex and a fiber length of 12 mm was used as the PET fiber 5.

<PET fiber 6>
The drawn polyethylene terephthalate fiber having a fineness of 0.6 dtex and a fiber length of 5 mm was used as the PET fiber 6.

<PET fiber 7>
The drawn polyethylene terephthalate fiber having a fineness of 2.2 dtex and a fiber length of 15 mm was designated as PET fiber 7.

<PET fiber 8>
A drawn polyethylene terephthalate fiber having a fineness of 0.1 dtex and a fiber length of 3 mm was designated as PET fiber 8.

<Acrylic fiber 1>
The acrylic fiber 1 was an acrylic fiber having a fineness of 0.1 dtex and a fiber length of 3 mm.

<Binder fiber 1>
Polyester core-sheath type heat-sealing fiber having a fiber diameter of 5 μm, a fiber length of 1 mm, a core part of polyethylene terephthalate (melting point 253 ° C.), and a sheath part of polyethylene terephthalate-isophthalate copolymer (softening point 75 ° C.) It was set to 1.

<Binder fiber 2>
A polyester core-sheath type heat-sealable fiber having a fiber diameter of 10 μm, a fiber length of 5 mm, a core part of polyethylene terephthalate (melting point 253 ° C.), and a sheath part of polyethylene terephthalate-isophthalate copolymer (softening point 75 ° C.) is a binder fiber. 2.

<Binder fiber 3>
A polyester core-sheath type heat-sealing fiber having a fiber diameter of 15 μm, a fiber length of 10 mm, a core part of polyethylene terephthalate (melting point 253 ° C.), and a sheath part of a polyethylene terephthalate-isophthalate copolymer (softening point 75 ° C.) is a binder fiber. It was set to 3.

<Binder fiber 4>
A polyester core-sheath type heat-sealing fiber having a fiber diameter of 18 μm, a fiber length of 12 mm, a core part of polyethylene terephthalate (melting point 253 ° C.), and a sheath part of polyethylene terephthalate-isophthalate copolymer (softening point 75 ° C.) is a binder fiber. It was set to 4.

<Binder fiber 5>
A polyester core-sheath type heat-seal fiber having a fiber diameter of 5 μm, a fiber length of 0.8 mm, a core part of polyethylene terephthalate (melting point 253 ° C.), and a sheath part of a polyethylene terephthalate-isophthalate copolymer (softening point 75 ° C.). Binder fiber 5 was obtained.

<Binder fiber 6>
A polyester core-sheath type heat-sealing fiber having a fiber diameter of 15 μm, a fiber length of 15 mm, a core part of polyethylene terephthalate (melting point 253 ° C.), and a sheath part of a polyethylene terephthalate-isophthalate copolymer (softening point 75 ° C.) It was set to 6.

<FB fiber 1>
A fibrillated lyocell fiber obtained by repeatedly treating a non-fibrillated lyocell single fiber (1.7 dtex × 4 mm, manufactured by Coatles Co., Ltd.) 60 times using a double disc refiner was designated as FB fiber 1.

<FB fiber 2>
A fibrillated para-type wholly aromatic polyamide fiber obtained by treating a para-type wholly aromatic polyamide having a fiber diameter of 10 μm and a fiber length of 3 mm with a double disc refiner 60 times was designated as FB fiber 2.

(Examples 1 to 5 and Comparative Examples 1 and 2)
After pouring water into a 2 m ³ dispersion tank, it is blended at the ratio shown in Table 1, and dispersed for 5 minutes at a dispersion concentration of 0.2% by mass to prepare a fiber dispersion for coarse layer (nonwoven fabric for filter) and a fiber for dense layer A dispersion was prepared.

Using an inclined / circular mesh type paper machine, a web (wet paper) is formed on the inclined wire so that the coarse layer has a dry mass of 40 g / m ² , and the dense layer has a dry mass of 20 g / m ² on the circular wire. After forming the web to m ² and laminating both webs before drying, they are dried and integrated while pressing the touch roll at a pressure of 400 N / cm ² with a cylinder dryer having a surface temperature of 130 ° C., The filter media of Examples 1 to 5 and Comparative Examples 1 and 2 were obtained.

(Example 6)
Using an inclined paper machine, a web was formed so as to have a dry mass of 40 g / m ² , and a coarse layer dried while pressing a touch roll with a pressure of 400 N / cm ² with a cylinder dryer having a surface temperature of 130 ° C. A polyethylene terephthalate nonwoven fabric (fiber diameter 0.8 μm, basis weight 20 g / m ² ) produced by a melt blow method as a dense layer was laminated and integrated by embossing to obtain a filter medium of Example 6.

  The following evaluation was performed on the filter media obtained in Examples and Comparative Examples, and the results are shown in Table 1.

Test 1 (basis weight)
The basis weight was measured according to JIS P8124.

Test 2 (thickness)
The thickness was measured according to JIS P8118.

Test 3 (wet tensile strength in the CD direction)
Cut into a 15 mm width in the MD direction and a length of 200 mm in the CD direction, and immersed in pure water at 20 ° C. for 5 minutes, the test piece was then used using a desktop material testing machine (trade name: STA-1150, manufactured by Orientec Co., Ltd.) The sample was stretched under the conditions of a gripping interval of 100 mm and a tensile speed of 20 mm / min, and the load value at the time of cutting was defined as the wet tensile strength, and evaluated according to the following criteria.

A: The wet tensile strength is 0.8 kN / m or more.
○: Wet tensile strength is 0.6 kN / m or more and less than 0.8 kN / m.
X: The wet tensile strength is less than 0.6 kN /.

Test 4 (collection efficiency)
According to JIS B9908, DOP aerosol (dioctyl phthalate, particle size: 0.3 to 0.5 μm) particles are generated, and air containing the particles is aerated at a wind speed of 5.3 cm / second, The particle concentration (unit time, number of particles per unit flow rate) of the air on the downstream side was measured with a particle counter (KC-11, manufactured by Rion Co., Ltd.), and the collection efficiency was calculated from Equation 1 below.

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

  The higher the collection efficiency, the better. If it is 40% or more, it can be used as a filter medium, more preferably 60% or more.

Test 5 (pressure test)
The filter media obtained in Examples 1 to 6 and Comparative Examples 1 and 2 were coated with an acrylic resin only by a gravure coating method so that the adhesion amount after dry weight was 1.0 g / m ^2. After that, a filter was produced by pleating. The cement dispersion was pumped into the filter prepared above, and the pressure at which the filter was damaged was measured.

  As shown in Table 1, the filter media of Examples 1 to 6 have a rough layer of a nonwoven fabric for a filter containing stretched polyethylene terephthalate fibers having a fiber length of 7 to 12 mm and binder fibers having a fiber length of 1 to 12 mm. Therefore, it showed high wet tensile strength. Further, the filter using the filter medium showed a high value in the pressure resistance test.

  From the comparison between Examples 1 and 5 and Examples 2 to 4 and 6, the filters using the filter media of Examples 2 to 4 and 6 having a wet tensile strength of 0.8 kN / m or more have a wet tensile strength of 0.00. The high value of the pressure resistance test was higher and better than the filters using the filter media of Examples 1 and 5 of less than 8 kN / m.

  When Example 1-5 was compared with Example 6, Example 1-5 which contained the fibrillated organic fiber in the dense layer showed high collection efficiency.

  Comparative Example 1 in which the fiber length of the stretched polyethylene terephthalate fiber was less than 7 mm and the fiber length of the binder fiber was less than 1 mm, and the comparative example in which the fiber length of the stretched polyethylene terephthalate fiber and the binder fiber was greater than 12 mm. The filter medium 2 had a low wet tensile strength, and the filter using the filter medium showed a low value in the pressure resistance test.

  The non-woven fabric for filter of the present invention is a process of cutting, polishing, etching, etc. of processing waste contained in the machining fluid of an electric discharge machine used for metal sculpture, cutting, etc., and substrate wafer in IC production Can be suitably used for various filter materials for liquid filters, such as filter media for liquid filters, automobile engine oil, fuel, etc. for efficiently removing processing waste contained in ultrapure water used in . Moreover, it can be used conveniently also as a filter medium for air filters which collects dust in the air.

Claims (4)

  It is a wet nonwoven fabric containing non-meltable stretched polyethylene terephthalate fibers and heat-meltable binder fibers, the stretched polyethylene terephthalate fibers have a fiber length of 7 to 12 mm, and the binder fibers have a fiber length of 1 to 12 mm. Nonwoven fabric for filters.   A filter medium for a filter obtained by forming the filter nonwoven fabric according to claim 1 as a coarse layer and laminating and integrating with a dense layer.   The filter medium for a filter according to claim 2, wherein the wet tensile strength in the CD direction is 0.8 kN / m or more.   The filter medium for a filter according to claim 2 or 3, wherein the dense layer contains fibrillated organic fibers.