JP2010125410A - Coated filter medium for liquid filtration - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a coated filter medium for liquid demonstrating well-balanced performances of a collection efficiency of fine particles and pressure loss. <P>SOLUTION: The coated filter medium for liquid has a coated layer containing a pigment and an organic polymer on one face of a base material having gas permeability. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a filter medium used for a liquid filtration filter or the like for efficiently removing solid particles contained in a liquid to obtain a clean liquid.

  There are roughly two types of structures for the filter medium for liquid filtration. 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, these filter media are subjected to pleating "folding process" to increase the surface area of the filter media and then molded into a predetermined shape to produce a filter, which is used in combination with other components in a filter It is.

  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 phenolic resin or the like into a mixed sheet of natural pulp and organic fibers, a polyester nonwoven fabric, or the like has been used. However, these have problems such as low filtration efficiency of solid particles 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, the present applicants have 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 fiber diameters. It consists of 20 to 70% by mass of organic fibers having a diameter of 5 μm or more, and part or all of the organic fibers 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 . A “surface filtration type” filter medium for liquid filtration was proposed to solve the above problem (see, for example, Patent Document 2). This “surface filtration type” filter medium suppresses pressure loss and reduces the amount of liquid by limiting the content of the organic fibers that have been fibrillated to collect solid particles and limiting the content with other organic fibers. It is possible to process efficiently in a short time.

  The above-mentioned “surface filtration type” filter medium has a problem that it cannot be fold-folded because the thickness is very thin and not hard. Therefore, the present applicant intends to improve strength and waist (stiffness). In addition, the above-mentioned filter medium layer that is thin and excellent in surface filtration performance and a filter layer for liquid filtration that integrates and integrates a support layer with good liquid permeability, high strength, and pleat foldability, have been devised. Even now, it is usefully used in industry (for example, see Patent Document 3).

  However, with the increase in precision of cutting machines and electric discharge machines, the particle size of solid particles such as cutting waste is further reduced and is in the submicron order. In addition, the processing fluid is being closed in consideration of the environment. In order to circulate and use the processing fluid, it is important to clean the liquid after filtration. Therefore, it is required to increase the collection efficiency of solid particles (hereinafter referred to as “fine particles”) that are finer than before.

  Under such circumstances, in the “internal filtration type” filter medium, attempts have been made to increase the collection efficiency by incorporating powder into the filter medium. For example, a filter medium characterized by high adsorption and absorption capacity and high porosity has been proposed by filling liquid filter paper based on cellulose fibers with powder organic substance (powder) (for example, Patent Document 4). reference). Also, for liquid filtration, a polyolefin fibrillated synthetic fiber, a heat-adhesive synthetic composite fiber, glass fibers having an average fiber diameter of 2 μm or less, and inorganic powder having an average particle diameter of 10 μm or less are dispersed and mixed in a slurry and made by a wet papermaking method. A filter paper has been proposed (see, for example, Patent Document 5). “Internal filtration type” filter media that improve the collection efficiency with such powders have low initial filtration performance. Fine particles flow in the initial stage of use, and if fine particles are collected thereafter, pressure loss occurs. There was a problem that became higher. In addition, the powder easily drops from the filter medium. In particular, as described in Patent Document 5, when the inorganic powder is made by the wet papermaking method, there is a problem that the inorganic powder falls off the papermaking wire (for example, patents). Reference 4).

  As described above, in the “surface filtration type” filter medium, as in Patent Documents 1 to 3, by limiting the content of fibrillated organic fibers and other organic fibers, the collection efficiency is increased. Although it was balanced with pressure loss, it was necessary to increase the basis weight of the filter media layer containing the fibrillated organic fibers to increase the capture efficiency of solid particles of submicron order by this method. In the present situation, the water is not sufficiently squeezed to obtain a uniform texture, and only a filter medium having a high pressure loss can be obtained.

JP 2000-70628 A Japanese Patent No. 2633355 Japanese Patent No. 3305372 JP-A-10-237798 JP-A-7-256021

  An object of the present invention is to provide a coating material for liquid filtration that exhibits well-balanced performances such as collection efficiency of fine particles and pressure loss.

As a result of intensive studies to solve the above problems, the present inventors have
(1) A coating material for liquid filtration, characterized in that a coating layer comprising a pigment and an organic polymer is provided on one surface of a base material having air permeability,
(2) The coated filter medium for liquid filtration according to the above (1), wherein the substrate having air permeability is a nonwoven fabric or paper,
(3) The coated filter material for liquid filtration according to the above (1) or (2), wherein the base material having air permeability is a nonwoven fabric containing organic fibers,
(4) The liquid filtration coating material according to any one of (1) to (3), which is used with the coating layer surface set on the upstream side, has been found.

  In the coated filter material for liquid filtration of the present invention, a coating layer of a pigment and an organic polymer is provided on one surface of a substrate having air permeability. When the pigment and organic polymer are impregnated in the whole or inside of the base material, not only surface filtration but internal filtration results in not only improving the initial filtration performance but also increasing the pressure loss of the filter medium, shortening the life. Resulting in. On the other hand, when the coating layer is provided on one surface of the substrate as in the present invention, the pressure loss does not increase, and the pigment and the organic polymer may be present uniformly on the substrate surface. It becomes possible. In addition, surface filtration is possible from the beginning of use, and the collection efficiency of fine particles is improved. That is, the coated filter medium for liquid filtration of the present invention can express performance such as collection efficiency of fine particles and pressure loss in a well-balanced manner.

  This will be described in detail below.

  The liquid filtration coating material of the present invention is achieved by controlling the pore diameter on the substrate surface to be small by providing a coating layer on a breathable substrate in order to efficiently perform surface filtration. Is.

The base material having air permeability is used for air filter filter media, liquid filter media, or laminated and bonded to them, and has a fragile air permeability of 0.3 cc / cm ² / sec or more. , and the preferably 0.5cc ^/ cm 2 ^/ sec or more, more preferably 1.0cc ^/ cm 2 ^/ sec or more. The present invention is a coated filter material for liquid filtration, but instead of the liquid permeability test, an air permeability test using the air permeability A method (Fragile type method) of JIS L 1096 was applied. Specifically, the base material having air permeability is not particularly limited, but has air permeability such as a woven fabric, a knitted fabric, a nonwoven fabric, a porous film, paper, etc. Nonwoven fabric and paper are preferred. Nonwoven fabrics include spunbond, meltblown, chemical bond, needle punch, spunlace, electrospinning and other dry nonwoven fabrics, and wet nonwoven fabrics made by papermaking. In order to ensure air permeability, the paper is preferably made so as to have a low density by a treatment such as suppressing the beating degree of wood pulp, mixing linter pulp, or pre-crosslinking the pulp.

The substrate may be a single layer or a multilayer structure of two or more layers, but a two-layer structure is preferred. In the case of a two-layer structure, a dense structure is preferable, and the coating layer is preferably provided on the dense layer surface. The basis weight of the substrate is preferably although not particularly limited 20 to 300 g / ^{m 2,} more preferably 30~180g / ^{m 2.} If it is less than 20 g / m ² , the paper may be cut when it is processed into a filter or when a coating layer is formed. Moreover, when 300 g / m < ² > is exceeded, liquid flow resistance may become high, thickness may increase and a filter medium of a prescribed amount may not be accommodated in a filter unit.

  Although the raw material used for a base material is not specifically limited, Organic fibers, such as natural fiber, a regenerated fiber, a synthetic fiber, a semi-synthetic fiber, and an inorganic fiber are mentioned. Examples of natural fibers include wood pulp such as conifer pulp and hardwood pulp, wood pulp such as straw pulp, bamboo pulp, kenaf pulp, linter, lint, and herbs. Regenerated fibers include rayon, cupra, and lyocell fiber. Is mentioned. Examples of synthetic fibers include polyolefin, polyamide, polyacrylic, vinylon, vinylidene, polyvinyl chloride, polyester, nylon, polyolefin, benzoate, polyclar, and phenol fibers. Examples include acetate, triacetate, and promix, which are used alone or in combination. These organic fibers may be fibrillated at all. Furthermore, pulp fibers obtained from waste paper, waste paper, and the like are also included. Further, fibers having an irregular cross section such as a T-shape, Y-shape, or triangle can be included for ensuring air permeability and liquid permeability. Examples of the inorganic fiber include glass fiber, alumina fiber, lock fiber, and stainless fiber. Of these, alumina fibers and micro glass fibers are preferable, and micro glass fibers are more preferable.

  The organic fiber may be a heat-fusible binder fiber. By incorporating a heat-fusible binder fiber and increasing the temperature of the filter medium above the melting temperature of the heat-fusible binder fiber, the mechanical strength of the base material is improved. For example, a base material can be manufactured by a wet papermaking method, and a heat-fusible binder fiber can be melted in a subsequent drying step. Examples of the heat-fusible binder fiber that can be used for the base material of the present invention 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 mechanical strength can be improved while maintaining the space of the filter medium. Examples of the heat-fusible binder fiber include a short fiber of polypropylene, a combination of polypropylene (core) and polyethylene (sheath), a combination of polypropylene (core) and ethylene vinyl alcohol (sheath), a high melting point polyester (core) and low A combination of melting point polyester (sheath) can be mentioned. In addition, monofilaments (total melt type) composed only of low melting point resins such as polyethylene and hot water-soluble binders such as polyvinyl alcohols tend to form a film in the drying process of the filter medium, but do not impair the properties. Can be used in a range.

  A coating layer of a pigment and an organic polymer is provided on one surface of the substrate. When providing the coating layer, it is preferable that fine fibers are mixed on one surface of the substrate on which the coating layer is provided in order to prevent the coating layer from being deeply settled. Although it does not specifically limit with a fine fiber, A fiber diameter is a fiber of 10 micrometers or less, Preferably it is 7 micrometers or less, More preferably, it is 4 micrometers or less.

  The pigments used in the coating layer in the present invention are synthetic amorphous silica, light calcium carbonate, heavy calcium carbonate, kaolin, calcined kaolin, talc, calcium sulfate, barium sulfate, titanium dioxide, zinc oxide, zinc sulfide, carbonic acid. White inorganic pigments such as zinc, satin white, aluminum silicate, diatomaceous earth, calcium silicate, magnesium silicate, colloidal silica, colloidal alumina, pseudoboehmite, aluminum hydroxide, alumina, lithopone, zeolite, hydrous halloysite, magnesium carbonate, magnesium hydroxide Styrenic plastic pigments, acrylic plastic pigments, polyethylene, microcapsules, organic pigments such as melamine resins, and the like are used alone or in combination.

  The average secondary particle size of the pigment by the Coulter counter method is not particularly limited, but the particle size is preferably 50 μm or less, more preferably 20 μm or less in order to smoothly form the coating layer of the filter medium. If the average secondary particle diameter exceeds 50 μm, the pigment may settle in the mixed solution of the organic polymer and the pigment, the coating property may deteriorate, and a uniform coating layer may not be obtained. The shape of the pigment is not particularly limited, but is preferably an indeterminate shape that is difficult to close, a spherical shape, a rod shape, a needle shape, or the like from the viewpoint of ensuring liquid permeability.

  The organic polymer used in the present invention is a polyvinyl alcohol or a silanol-modified product thereof, a carboxylated product, a cationized product, a derivative such as an acetoacetylated product, a conjugated diene such as a styrene-butadiene copolymer or a methyl methacrylate-butadiene copolymer. Copolymer, acrylic polymer such as acrylic acid ester and methacrylic acid ester polymer or copolymer, vinyl polymer such as ethylene-vinyl acetate copolymer, vinyl chloride-vinyl acetate copolymer, or Examples of these various polymers include functional group-modified polymers such as carboxy groups and other functional group-containing monomers, polyurethane resin polymers, polyester polymers, and starches, and these can be used alone or in combination of two or more. In view of water resistance, powder retention, liquid permeability, etc., it is preferable to use an acrylic polymer, a polyurethane resin polymer, a polyester polymer, or the like. These organic polymers may be used in the form of latex.

  The content of the organic polymer in the coating layer is preferably from 5 to 70% by mass with respect to the pigment because good coating layer strength is obtained. More preferably, it is 10-60 mass%.

  Furthermore, for the coating layer, as additives, crosslinking agents, pigment dispersants, thickeners, fluidity improvers, antifoaming agents, foam suppressors, mold release agents, sizing agents, penetrating agents, coloring dyes, coloring Pigments, fluorescent brighteners, ultraviolet absorbers, antioxidants, preservatives, antibacterial agents, wet strength enhancers, dry strength enhancers, and the like can be appropriately blended.

  Various methods such as various blade coaters, roll coaters, air knife coaters, comma coaters, bar coaters, rod blade coaters, curtain coaters, short dwell coaters, size presses, etc. are provided as methods for providing a coating layer containing a pigment and an organic polymer. Can be used on-machine or off-machine. It is preferable to use a curtain coater or an air knife coater that provides a coating layer having a uniform thickness without uneven coating.

  After application of the coating layer, the back surface may be sprayed with humidified air or humidified steam to correct the curl. Further, the smoothness of the coating layer surface may be improved by calendar processing using a machine calendar, a super calendar, a soft calendar, or the like.

The coating amount of the coating layer is not particularly limited, but is preferably 0.5 to 40 g / m ² because a good coating layer can be formed. More preferably from 1 to 20 g / ^{m 2.} If it is less than 0.5 g / m ² , a uniform coating layer may not be obtained. If it exceeds 40 g / m ² , the liquid permeability may be lowered.

  The coated filter medium for liquid filtration of the present invention has water resistance and pleat processability, and is suitable for a filter medium for liquid filtration such as for electric discharge machines, engine oil, fuel, oil-water separation, and hydraulic equipment. Become. In this case, it is preferable that the surface layer filtration mechanism can be expressed by using the coating layer surface as the upstream side. However, when the particle diameter in the target liquid is large, it may be preferable to set the opposite surface of the coating layer upstream.

In the coated filter medium for liquid filtration of the present invention, the density of the filter medium is preferably 0.1 to 0.8 g / cm ³ . When the density of the entire filter medium is less than 0.1 g / cm ^3, the thickness of the filter medium is increased, so that the area of the filter medium that can be incorporated into the unit is reduced, and as a result, the life of the filter is shortened. On the other hand, when it exceeds 0.8 g / cm ³ , the liquid permeability may be lowered and the life may be shortened.

  The invention is explained in more detail by means of examples. Hereinafter, unless otherwise specified, the parts and ratios described in the examples are based on mass.

<Preparation of mixture of pigment and organic polymer>
70% by weight of heavy calcium carbonate pulverized to an average particle size of 1.5 μm using a mill and 30% by weight of acrylic polymer latex (trade name: Nippon LX842, manufactured by Nippon Zeon Co., Ltd.) were put into a dispersion tank, and dispersed water And the mixture was stirred for 10 minutes to prepare a mixed solution of a pigment and an organic polymer having a solid concentration of 15% by mass.

Example 1
A polyester spunbonded non-woven fabric (basis weight 100 g / m ² , trade name: Axter, manufactured by Toray Industries, Inc.) as a breathable base material is mixed with a mixture of pigment and organic polymer to a solid content of 10 g / m ² . Coating was performed using a tabletop air knife coater and dried to obtain a coated filter material for liquid filtration of Example 1.

(Comparative Example 1)
A polyester spunbonded nonwoven fabric (basis weight 100 g / m ² , trade name: ACSTER, manufactured by Toray Industries, Inc.) was used as the filter medium for liquid filtration of Comparative Example 1.

(Example 2)
A two-layer wet nonwoven fabric (basis weight 70 g / m ² , trade name: HF-V, Mitsubishi Paper Industries) comprising a filter medium layer (dense layer) and a support layer (coarse layer) having the structure described in Patent Document 3. The filter medium for liquid filtration of Example 2 was obtained in the same manner as in Example 1 except that the base material having air permeability was used and a coating layer was provided on the surface of the filter medium layer.

(Comparative Example 2)
A wet nonwoven fabric having a two-layer structure (basis weight 70 g / m ² , trade name: HF-V, manufactured by Mitsubishi Paper Industries Co., Ltd.) was used as the filter medium for liquid filtration of Comparative Example 2.

(Example 3)
<Preparation of base material>
40% by mass of NBKP beaten to a Canadian freeness of 500 ml, 40% by mass of commercially available linter pulp, heat-fusible binder fiber (core-sheath type, polyester fiber, diameter 15 μm, fiber length: 5 mm, manufactured by Unitika) Disperse in water at a ratio of 20% by mass, collect the dispersion so that the dry mass is 70 g / m ² , make paper using a standard square hand-made paper machine, and then dry with a cylinder dryer to make it air permeable. The base material which has was produced. The mixed liquid of the pigment and the organic polymer prepared in Example 1 is coated using a table air knife coater so as to have a solid content of 10 g / m ² , and dried to obtain a coated filter material for liquid filtration of Example 3. It was.

(Comparative Example 3)
Only the base material of Example 3 was used as the filter medium for liquid filtration of Comparative Example 3.

(Comparative Example 4)
The base material of Example 3 was impregnated on the whole base material using an impregnation apparatus so that the mixed liquid of the pigment and the organic polymer prepared in Example 1 had a solid content of 10 g / m ² and dried. No. 4 filter medium for liquid filtration was obtained.

  The following evaluations were performed on the liquid filtration (coated) filter media obtained in Examples and Comparative Examples, and the results are shown in Table 1.

Test 1 (thickness)
According to JIS L 1096, the thickness was measured with a thickness gauge for nonwoven fabric.

Test 2 (basis weight, density)
Basis weight and density were calculated according to JIS P 8124 and 8118.

Test 3 (initial filtration efficiency) (unit:%)
Using the filter medium for liquid filtration of Examples 1 to 3 and the filter medium for liquid filtration of Comparative Examples 1 to 4, JIS Type 8 powder and JIS Type 11 powder were mixed at a ratio of 1: 1, and 0 A sample diluted with water to a concentration of 0.05% by mass was used as a test liquid, and the filter medium was wetted with water. Then, 100 ml of the test liquid was set on the upstream side of the filter medium coating layer, and the filtration area was 14 cm ^2. The solution was filtered under the condition of differential pressure ΔP = 320 mmHg, and the number of particles of 3 to 10 μm in the solution before and after filtration was measured with an in-liquid fine particle counter (trade name: KL-01) manufactured by Rion. In the filter medium for liquid filtration of Comparative Example 2, the filter medium layer was set on the upstream side.

Test 4 (initial filtration rate) (unit: cc / cm ² / min)
The filtration rate was obtained from the filtration time during the filtration performance test in Test 3.

Test 5 (turbidity of filtrate)
Observe the degree of turbidity of the filtered liquid (filtrate) obtained in Test 3 visually, ◎ for very high transparency, ◯ for high transparency, △ for slightly turbid, very turbid Were evaluated in 4 grades.

Test 6 (Life test)
Filtration was repeated 10 times using the test solution of Test 3, and then the filtration efficiency and filtration rate were measured in the same manner as in the above test.

Test 7 (Pleated workability)
Samples were processed into pleats, and those with very good workability were evaluated in four stages: ◎, good ones, slightly bad Δ, bad ones.

Test 8 (initial filtration efficiency 2) (unit:%)
Using the coating material for liquid filtration of Examples 1 to 3 and the filtering material for liquid filtration of Comparative Example 2, JIS Type 8 powder and JIS Type 11 powder were mixed at a ratio of 1: 1, 0.05 The sample diluted in water to a concentration of 1% was used as the test liquid, and the filter medium was wetted with water. Then, 100 ml of the test liquid was set downstream of the filter medium coating layer, the filtration area was 14 cm ² , and the differential pressure The mixture was filtered under the condition of ΔP = 320 mmHg, and the number of particles of 3 to 10 μm in the solution before and after filtration was measured with an in-liquid fine particle counter (trade name: KL-01) manufactured by Lion. In the filter medium for liquid filtration of Comparative Example 2, the support layer was set on the upstream side.

Test 9 (initial filtration rate 2) (unit: cc / cm ² / min)
The filtration rate was obtained from the filtration time during the filtration performance test in Test 8.

Test 10 (turbidity of filtrate 2)
Observe the degree of turbidity of the filtered liquid (filtrate) obtained in Test 8 visually, ◎ for very high transparency, ◯ for high transparency, △ for slightly turbid, very turbid Were evaluated in 4 grades.

Test 11 (Life test 2)
Filtration was repeated 10 times using the test solution of Test 8, and then filtration efficiency 2 and filtration rate 2 were measured in the same manner as in the above test.

  Compared with the filter medium for liquid filtration of Comparative Example 1, the coated filter medium for liquid filtration of Example 1 had good initial filtration efficiency and filtration efficiency in the life test, and the filtrate was less turbid. Compared with the liquid filtration filter medium of Comparative Example 2, the liquid filtration coating medium of Example 2 had good initial filtration efficiency and filtration efficiency in the life test, and the filtrate was less turbid. Compared with the filter material for liquid filtration of Comparative Example 3, the coated filter material for liquid filtration of Example 3 had good initial filtration efficiency and filtration efficiency in the life test, and the filtrate was less turbid. The filter material for liquid filtration of Comparative Example 4 in which the pigment and the organic polymer are contained in the base material having air permeability has a lower initial filtration efficiency than the coated filter material for liquid filtration of Example 3, Not only the filtrate was slightly turbid, but also the filtration efficiency and filtration rate were low in the life test.

  When the coating layer of the filter medium for liquid filtration of the present invention is set and filtered on the upstream side, compared to the case where the coating layer is set and filtered on the downstream side, the life tends to be longer, It is preferable to use the coating layer side set upstream.

Claims (4)

  A coating material for liquid filtration, wherein a coating layer comprising a pigment and an organic polymer is provided on one surface of a breathable substrate.   The coated material for liquid filtration according to claim 1, wherein the base material having air permeability is a nonwoven fabric or paper.   The coated filter material for liquid filtration according to claim 1 or 2, wherein the substrate having air permeability is a nonwoven fabric containing organic fibers.   The coating filter medium for liquid filtration according to any one of claims 1 to 3, wherein the coating layer surface is set upstream and used.