JP2008238088A - Filter medium for filtering liquid - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a filter medium for filtering a liquid having a high initial filtration efficiency and a long life. <P>SOLUTION: The filter medium for filtering a liquid is characterized in that PF value (Y) and repellency (X) satisfy the following equation 1: Y≤50e<SP>-0.0065X</SP>[wherein e is Napier's number (the base of natural logarithm) and is approximately 2.71828], with PF value (Y) determined from the following equation: PF value (Y)=Log<SB>10</SB>ä(DOP transmissivity (%))/100}×(-100)/ä(pressure drop (Pa))/9.81} wherein pressure drop (Pa) represents a pressure drop in a filter medium in a gas phase measured according to JIS B9908 under a condition of a face wind velocity of 5.3 cm/second and DOP transmissivity represents transmissivity of monodispersed dioctyl phthalate (DOP) particles of 0.3 μm, and with repellency (X) measured according to the measurement method specified in MIL-STD-282. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a filter medium for liquid filtration that separates and captures fine particles contained in a liquid. More specifically, ultra-pure used in processes such as cutting, polishing, and etching of processing waste contained in the machining fluid of electrical discharge machines used for metal engraving and cutting, etc. The present invention relates to a filter medium for efficiently removing processing waste contained in water and obtaining a clear liquid.

  When evaluating the performance of the filter medium, the indispensable items are filtration efficiency and filtration resistance. As a filter medium, it is desirable that the filtration efficiency is as high as possible and the filtration resistance is as low as possible, but these two performances are contradictory. That is, if the filter medium has a dense structure, the filtration efficiency can be increased, but in this case, the filtration resistance increases. Conversely, if the filtration resistance is reduced, the filtration efficiency is lowered.

  There are roughly two types of filter media structures, one is an “internal filtration type”, which is a filter media with a structure that traps solid particles inside the filter media. The other is a “surface filtration type”, which is a filter medium structured to trap solid particles on the surface of the filter medium.

  Conventionally, as a filter medium for liquid filtration used in an electric discharge machine or an IC production process, a sheet obtained by impregnating a natural pulp and organic fiber with a phenol resin or the like, a polyester nonwoven fabric, or the like has been used. However, these have problems such as low filtration efficiency and short life. Moreover, although a porous sheet such as a fluorine-based resin is available as a high-performance filter medium, it is expensive and 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, it has been proposed that a part is thermocompression-bonded so that the burst strength when wet with water is 5 kgf / cm ² or more. (Patent Document 1)
However, the thermocompression bonding has a drawback that the filter medium gap in the thermocompression-bonded portion is crushed and the filtration efficiency is lowered.

Also, it is a filter medium for liquid filtration in which the filtration layer and the support layer are combined and integrated, and a proposal is made that the wet tensile strength in the transverse direction is 0.98 kN / m or more by adding a binder to the support layer. Has been. (Patent Document 2)
However, when the binder is applied only to the support layer, the pore structure of the filter medium becomes non-uniform, the filtration is not performed uniformly in the filter medium, and the initial filtration accuracy varies greatly. .

Moreover, it is a filter filter medium for liquids having a two-layer structure, and the substrate is composed of 1 to 80% by weight of liquid crystalline polymer pulp and 20 to 99% by weight of organic fibers having a fiber diameter of 5 μm or more, and the support layer has fibers It has been proposed to include one or more organic fibers having a diameter of 5 μm or more and a fiber length of 5 mm or more, and to control the ratio of the thickness of the filter medium layer to the support layer, the maximum pore diameter, and the collection efficiency. (Patent Document 3)
However, since it has a two-layer structure, the formation of cake is abrupt and the initial filtration is good, but there are problems such as short life.

  Further, a filter medium comprising 20 to 80% by weight of ultrafine organic fiber and ultrafine inorganic fiber having a fiber diameter of 5 μm or less and 80 to 20% by weight of organic fiber and inorganic fiber having a fiber diameter of 5 μm or more has been proposed. (Patent Document 4)

  In addition, a filter medium with less strength reduction has been proposed by controlling the formation of the sheet. (Patent Document 5)

However, with the recent increase in the flow rate of liquid filtration, the amount of processing waste generated per fixed time has become very large and clogging has come early. Reality.
JP-A-11-165209 JP 2003-38918 A JP 2006-61789 A JP 2002-85918 A WO2006-008828

  The present invention provides a filter medium for liquid filtration having a high initial filtration efficiency and a long life.

  As a result of intensive studies to solve the above problems, the present inventors have found that in order to increase the life and the processing flow rate of the filtrate, the PF value obtained from the pressure loss and permeability of the filter medium in the gas phase, The inventors have found that controlling the water repellency of the filter medium is the most important, and have completed the present invention.

That is, the present invention is as follows from the pressure loss of the filter medium in the gas phase measured under a surface wind speed of 5.3 cm / sec according to JIS B9908 and the transmittance of monodisperse dioctyl phthalate (DOP) particles of 0.3 μm. PF value (Y) calculated by the formula
PF value (Y) = Log ₁₀ {(DOP transmittance (%)) / 100} × (-100) / {(pressure loss (Pa) /9.81)
When,
The value calculated from the water repellency (X) measured according to the measurement method described in MIL-STD-282 is
Equation 1 below
[Equation 1]
Y ≦ 50e ^−0.0065X
[Where e is the Napier number (the base of the natural logarithm) and is approximated by 2.71828. ]
It is related with the filter medium for liquid filtration characterized by satisfying these.

  One embodiment of the present invention relates to the above-mentioned filter medium for liquid filtration, wherein the filter medium is a fiber layer filter medium and a synthetic resin binder is added.

  In another embodiment of the present invention, the filter medium is a fiber layer filter medium, and the synthetic resin binder to be applied is at least one of acrylic, vinyl acetate, styrene-butadiene, urethane, and nylon binders. A filter medium for liquid filtration characterized by being selected.

  Yet another embodiment is a filter medium for liquid filtration characterized by being provided with a surfactant.

  By controlling the type, pressure loss, DOP permeability, and water repellency of the synthetic resin binder used in the filter medium for liquid filtration, a filter medium for liquid filtration with a high initial filtration efficiency and a long life can be obtained.

  Details of the present invention will be described below.

As an important requirement of the filter medium of the present invention, in order to satisfy the improvement of the initial filtration efficiency and the life and the increase of the flow rate of the filtered water at the same time, the surface air velocity in the gas phase is 5.3 cm / sec in accordance with JIS B9908. PF value (Y) determined from the measured pressure loss of the filter medium in the gas phase and the transmittance of dioctyl phthalate (DOP) particles 0.3 μm monodisperse measured in the gas phase, and MIL-STD-282 The value calculated from the water repellency (X) measured in accordance with the measurement method described is the following formula 1
[Equation 2]
Y ≦ 50e ^−0.0065X
[Where e is the Napier number (the base of the natural logarithm) and is approximated by 2.71828. ]
It is necessary to apply to. However, the value of X is 0 ≦.

  When the PF value (Y) obtained from the pressure loss and transmittance of the filter medium is lower than the value obtained from the water repellency (X), the initial filtration efficiency and the life are improved, and the processing flow rate of the filtrate is increased. Are brought at the same time. On the contrary, when the initial filtration efficiency is high, the life and the processing flow rate of the filtrate are remarkably lowered when the initial filtration efficiency is high.

The PF value used here is the pressure loss of the filter medium in the gas phase measured at a surface wind speed of 5.3 cm / sec in the gas phase in accordance with JIS B9908 with respect to the filter medium having an area of 100 cm ² , and 0 It is obtained from the following relational expression of transmittance of 3 μm dioctyl phthalate (DOP) particles.

PF value = {Log ₁₀ (DOP transmittance (%) / 100) × (−100)} / (pressure loss (Pa) /9.81)
DOP permeability (%) = (number of particles after filtration) / (number of particles before filtration) × 100
The configuration of the filter medium is not limited as long as the filter medium satisfies the above requirements, and the best mode will be described.

  In the present invention, the filter medium constituting fibers include inorganic fibers, organic synthetic fibers, natural fibers, and derivatives thereof. Specifically, examples of the inorganic fiber include glass fiber, carbon fiber, lock fiber, and stainless fiber. Examples of the organic synthetic fiber include polyolefin, polyamide, polyester, and vinylon. Examples of natural fibers and derivatives thereof include pulp, hemp, linter, cotton, and straw.

  In addition, a part or all of the organic synthetic fiber may be a heat-sealable composite fiber, a wet heat-dissolving fiber such as vinylon fiber, or a so-called fibrous organic binder.

  Examples of the heat-sealable composite fiber include polyolefin-based composite fibers, and examples include a core-sheath type (core-shell type) and a parallel type (side-by-side type), but are not limited thereto. Representative composite fibers include, for example, a combination of polypropylene (core) and polyethylene (sheath), a combination of polypropylene (core) and ethylene vinyl alcohol (sheath), and a combination of polyester (core) and polyethylene (sheath). .

  Moreover, there is no problem even if two or more kinds of fibrous organic binders having different compositions are used.

  When these fibers are formed into a sheet, paper making methods such as a dry method and a wet method are generally used. Examples of the dry paper machine include a melt blow method, a spun bond method, and a spun lace method. In addition, examples of the wet type paper machine include a long net paper machine, a circular net paper machine, and an inclined wire paper machine, but the uniformity of the formation of the sheet largely affects the particle transmittance. The web is preferably formed into a sheet by a wet method with a good sheet formation.

  The application of the synthetic resin binder in the present invention is particularly important for obtaining the effects of the present invention.

  The synthetic resin binder used in the present invention is a liquid or viscous synthetic resin binder such as latex, solution or emulsion, and particularly preferably a latex binder. Among these, acrylic latex, vinyl acetate latex, urethane latex, styrene-butadiene latex, and NBR latex can be used alone or in combination of two or more.

  However, the use of these synthetic resin binders is not a problem as long as the relationship of Formula 1 is not impaired, but it is preferable to limit the amount to 20% by mass or less per substrate. When it exceeds 20 mass%, the film of the synthetic resin binder increases at the intersection with the filter medium fiber, the pressure loss and water repellency of the filter medium in the gas phase become too large, and the relationship of Formula 1 is impaired.

  If there is a risk of impairing the relationship of Formula 1 by applying a synthetic resin binder to the filter medium, the contact angle on the dry film surface of the synthetic resin binder is measured in advance. It is preferable to select one having good wettability.

  Moreover, in order to maintain the relationship of Formula 1, it is more effective to use a surfactant for the purpose of reducing water repellency with respect to a filter material having high water repellency using the synthetic resin latex.

  Examples of the surfactant used in the present invention include fatty acid series, higher alcohol series, betaine series, and acetylene series.

  With regard to the application of the surfactant to the filter medium, it is preferable to keep the addition rate to a minimum in order to minimize foaming due to elution during filtration, and it is preferable to limit the addition to 1% by mass or less per filter medium. Preferably, it is 0.01-1 mass% per filter medium, More preferably, it is 0.03-0.5 mass%.

  The method for applying the surfactant to the filter medium is preferably applied at the time of papermaking in the production stage of the filter medium, but the manufactured filter medium can be dipped in a surfactant-containing aqueous solution and dried.

  In addition, when forming a sheet from the web, there is no problem in pressing the web, heating by drying, improving the uniformity of the surface of the sheet by calendaring, etc., as long as the relationship of Formula 1 is not impaired.

  As a method for drying, there are a cylinder binder, a through dryer, an infrared dryer, and the like.

  However, the drying temperature depends on the type of heat-sealing fiber to be used, but a range of 60 ° C to 170 ° C is desirable. When the temperature is less than 60 ° C., poor adhesion between the fibers or between the fibers and the synthetic resin binder easily occurs, resulting in insufficient strength. Further, at a temperature higher than 170 ° C., the film formation and curing by the fibrous binder or the synthetic resin binder of the base material proceed, and the water repellency increases too much, so that the relationship of Formula 1 is impaired.

  Examples of the calendering method include roll combinations such as steel / steel, steel / resin, and steel / cotton. Moreover, there is no problem in using these two or more types as long as the relationship of Formula 1 is not impaired.

[Example]
EXAMPLES The present invention will be specifically described below with reference to examples. However, the present invention is not limited to the examples. In addition, about the mass per unit area in a Example and a comparative example, the pressure loss of the filter medium in a gaseous phase, 0.3 micrometer DOP transmittance | permeability, PF value, water repellency, initial stage filtration efficiency, and the measurement of the life were measured with the following method. .

The mass per unit area measured according to the present invention was measured according to JIS L1096. The pressure loss of the filter medium in the gas phase was measured using a manometer when the air was passed through a filter paper having an effective area of 100 cm ^{2 at} a surface wind speed of 5.3 cm / sec. As for 0.30 μm DOP transmittance, air containing polydisperse DOP particles generated by a Ruskin nozzle is passed through a filter paper having an effective area of 100 cm ^{2 at} a surface wind speed of 5.3 cm / sec. Measurement was performed using a counter. The PF value was determined from the above pressure loss and DOP transmittance using the following formula.

PF value = Log ₁₀ (DOP transmittance (%) / 100) × (−100) / {(pressure loss) /9.81}
The water repellency was measured according to MIL-STD-282.
The initial filtration efficiency was obtained by diluting 8 kinds of test dust powders defined in JIS Z8901 with water to a concentration of 500 ppm as a test liquid. 100 ml of this test liquid was filtered with an effective area of 14 cm ² and a differential pressure of 320 mmH ₂ O, and the liquid before and after filtration was heated and weighed until it was completely dry, and the value calculated from the following formula was used as the initial filtration efficiency.

Initial filtration efficiency (%) = [{(particle mass before filtration) − (particle mass after filtration)} / (particle mass before filtration)] × 100
When the initial filtration efficiency exceeds 80%, it is very good, and when it exceeds 50%, there is no problem in actual use. However, if it is less than 50%, turbidity is at a level that can be visually confirmed, which hinders practical use.

Life was obtained by filtering the test liquid 10 times repeatedly, performing the 11th filtration in the same manner as the above test, and measuring the filtration time at that time to calculate the filtration rate (unit: cc / cm ² · min). The greater the value of the filtration rate, the better the life, and the better the life is 4 cc / cm ² · min.

A polyester fiber having a fiber diameter of about 5 μm (0.3 Tex × 5 mm manufactured by Teijin Fibers Limited) and a polyester heat-bonding binder fiber having a fiber diameter of about 12 μm (Ester 4080 1.7 decitex × 5 mm manufactured by Unitika Co., Ltd.) in a mass ratio of 60 : Mixing so as to have a fiber composition of 40, creating an aqueous slurry, and forming a sheet having a basis weight of 68 g / m ² from these slurry using a paper machine. As a synthetic resin binder, acrylic latex (Dai Nippon Ink Chemical Co., Ltd. Boncoat SFA-33) was applied to the substrate so as to be 15% by mass, dried at 130 ° C., pressure loss 25 Pa, 0.3 μm DOP transmittance. Was 97.7%, the PF value was 0.40, and the water repellency was 700 mm.

  60:40 fiber by mass of glass fiber having a fiber diameter of about 3 μm (# 110 made by Johns Manville) and polyester heat-fusing binder fiber having a fiber diameter of about 12 μm (Ester 4080 1.7 decitex × 5 mm made by Unitika) It mixed so that it might become a mixing | blending, an aqueous slurry was created, and the pressure loss was 30 Pa, 0.3 micrometer DOP transmittance | permeability was 62.4% like Example 1 except having provided 10 mass% of synthetic resin binders, A filter medium for liquid filtration having a PF value of 6.7 and a water repellency of 250 mm was obtained.

  A glass fiber having a fiber diameter of about 0.7 μm (# 106 manufactured by Johns Manville) and a polyester heat-fusing binder fiber having a fiber diameter of about 12 μm (Ester 4080 1.7 decitex × 5 mm manufactured by Unitika Co., Ltd.) in a mass ratio of 40:60. In the same manner as in Example 1 except that an aqueous slurry was prepared and 5% by mass of a synthetic resin binder was added, the pressure loss was 250 Pa, and the 0.3 μm DOP transmittance was 0.40. %, A PF value of 9.4 and a water repellency of 200 mm were obtained.

  A glass fiber having a fiber diameter of about 0.7 μm (# 106 manufactured by Johns Manville) and a polyester heat-fusing binder fiber having a fiber diameter of about 12 μm (Ester 4080 1.7 decitex × 5 mm manufactured by Unitika Co., Ltd.) in a mass ratio of 40:60. Except for adding 10% by mass of a synthetic resin binder and 0.3% by mass of an acetylene surfactant (Olfin STG manufactured by Nissin Chemical Industry). In the same manner as in Example 1, a filter medium for liquid filtration having a pressure loss of 245 Pa, a 0.3 μm DOP transmittance of 58.1%, a PF value of 10.1, and a water repellency of 230 mm was obtained.

  A glass fiber having a fiber diameter of about 0.7 μm (# 106 manufactured by Johns Manville) and a polyester heat-fusing binder fiber having a fiber diameter of about 12 μm (Ester 4080 1.7 decitex × 5 mm manufactured by Unitika Co., Ltd.) in a mass ratio of 40:60. In the same manner as in Example 1 except that an aqueous slurry was prepared and 2% by mass of a synthetic resin binder was added, the pressure loss was 230 Pa, and the 0.3 μm DOP transmittance was 0.15. %, A PF value of 12.1, and a water repellency of 150 mm were obtained.

[Comparative Example 1]
A polyester fiber having a fiber diameter of about 5 μm (0.3 Tex × 5 mm manufactured by Teijin Fibers Limited) and a polyester heat-bonding binder fiber having a fiber diameter of about 12 μm (Ester 4080 1.7 decitex × 5 mm manufactured by Unitika Co., Ltd.) in a mass ratio of 60 : Mixing so as to have a fiber composition of 40, creating an aqueous slurry, and forming a sheet having a basis weight of 68 g / m ² from these slurry using a paper machine. As a synthetic resin binder, an olefin latex (Zyxen A manufactured by Mitsui Chemicals, Inc.) is applied to a substrate so as to be 15% by mass, dried at 130 ° C., a pressure loss is 25 Pa, and a 0.3 μm DOP transmittance is 97.8. %, A PF value of 0.38, and a water repellency of 900 mm were obtained.

[Comparative Example 2]
60:40 fiber by mass of glass fiber having a fiber diameter of about 3 μm (# 110 made by Johns Manville) and polyester heat-fusing binder fiber having a fiber diameter of about 12 μm (Ester 4080 1.7 decitex × 5 mm made by Unitika) The mixture was mixed so as to form an aqueous slurry, and the pressure loss was 30 Pa, 0 in the same manner as in Comparative Example 1, except that 5% by mass of the synthetic resin binder was added to the olefin latex (Zyxen A manufactured by Mitsui Chemicals). A filter medium for liquid filtration having a 3 μm DOP transmittance of 60.4%, a PF value of 7.2, and a water repellency of 330 mm was obtained.

[Comparative Example 3]
A glass fiber having a fiber diameter of about 0.7 μm (# 106 manufactured by Johns Manville) and a polyester heat-fusing binder fiber having a fiber diameter of about 12 μm (Ester 4080 1.7 decitex × 5 mm manufactured by Unitika Co., Ltd.) in a mass ratio of 40:60. In the same manner as in Comparative Example 1, except that an aqueous slurry was prepared and an acrylic latex (Doncoat SFA-33 manufactured by Dainippon Ink Chemical Co., Ltd.) was added in an amount of 10% by mass. A filter medium for liquid filtration having a pressure loss of 250 Pa, a 0.3 μm DOP transmittance of 0.64%, a PF value of 8.6, and a water repellency of 450 mm was obtained.

[Comparative Example 4]
A glass fiber having a fiber diameter of about 0.7 μm (# 106 made by Johns Manville) and a polyester heat-fusing binder fiber having a fiber diameter of about 12 μm (Ester 4080 1.7 decitex × 5 mm made by Unitika) in a mass ratio of 60:40 In the same manner as in Comparative Example 1 except that 2% by mass of an olefin-based latex (Zyxen A manufactured by Mitsui Chemicals) was added, an aqueous slurry was prepared by mixing so as to have a fiber composition of A filter medium for liquid filtration having a 0.3 μm DOP transmittance of 0.014%, a PF value of 12.6, and a water repellency of 250 mm was obtained.

  The filter medium for liquid filtration prepared in Examples 1 to 5 satisfied the relationship of Formula 1 and had good initial filtration efficiency and life.

  In Comparative Example 1, the synthetic resin binder was an olefin latex, and the PF value exceeded the value obtained from Formula 1, so that the initial filtration efficiency and life were significantly reduced.

  Comparative Example 2 has the same fiber composition as Example 2, but the synthetic resin binder is an olefin latex and the PF value exceeds the value obtained from Formula 1, so the initial filtration efficiency and life are remarkably high. Declined.

  Comparative Example 3 was the same fiber formulation and synthetic resin binder as Example 4, but had high water repellency and the PF value exceeded the value obtained from Formula 1, so that the initial filtration efficiency was good. However, the life was significantly reduced.

  In Comparative Example 4, since the PF value exceeded the value obtained from Formula 1, the initial filtration efficiency was good, but the life was significantly reduced.

Claims (4)

From the pressure loss of the filter medium in the gas phase measured under conditions of a surface wind speed of 5.3 cm / sec in accordance with JIS B9908 and the transmittance of monodisperse dioctyl phthalate (DOP) particles of 0.3 μm, the following formula is used. PF value (Y)
PF value (Y) = Log ₁₀ {(DOP transmittance (%)) / 100} × (-100) / {(pressure loss (Pa) /9.81)
When,
The value calculated from the water repellency (X) measured according to the measurement method described in MIL-STD-282 is
Equation 1 below
[Equation 1]
Y ≦ 50e ^−0.0065X
[Where e is the Napier number (the base of the natural logarithm) and is approximated by 2.71828. ]
A filter medium for liquid filtration, characterized by satisfying   2. The filter medium for liquid filtration according to claim 1, wherein the filter medium is a fiber layer filter medium and is provided with a synthetic resin binder.   In the filter medium, the filter medium is a fiber layer filter medium, and at least one of an acrylic, vinyl acetate, styrene-butadiene, urethane, and nylon binder is selected as the synthetic resin binder. The filter medium for liquid filtration according to claim 1 or 2.   The filter medium for liquid filtration according to any one of claims 1 to 3, wherein a surfactant is added to the filter medium.