JP2012223663A - Filtering material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a filtering material developing performances such as collecting efficiency of fine particle, pressure drop, strength in good balance.SOLUTION: The filtering material comprising a nonwoven cloth containing synthetic resin fiber and fibrillated lyocell fiber as essential components is characterized in that the ratio of the fibers having the maximum peak between 0.00 to 1.00 mm and having fiber length of 1.00 mm or more in a fiber length distribution histogram is 50% or more. It is preferable to have the peak between 1.50 to 3.50 mm other than the maximum peak.

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 two main types of liquid filter media structures. 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, then molded into a predetermined shape to produce a filter, and combined with other parts to be used in a filter It is.

  Conventionally, as a filter medium for a liquid filtration filter used in an electric discharge machine or an IC production process, a sheet obtained by impregnating a mixed pulp sheet of natural pulp and organic fibers with a phenol resin or the like, a polyester nonwoven fabric, and the like have 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, organic fibers fibrillated to 1 μm or less, ultrafine organic fibers having a fiber diameter of 1 to 5 μm, and organic fibers having a fiber diameter of 5 μm or more, and an organic fiber having a fiber diameter of 5 μm or more. A “surface filtration type” filter medium for liquid filtration in which part or all of the fibers are fibrous organic binders and the filter medium density is 0.25 to 0.8 g / cm ³ has been proposed (for example, Patent Document 2). reference). In the filter medium of Patent Document 2, the fibrillated organic fiber expresses the collection efficiency of solid particles, and the content with other organic fibers is limited to suppress pressure loss and efficiently reduce a large amount of liquid. So that it can be processed in time.

  Since the filter medium of Patent Document 2 has a problem that it cannot be fold-folded because the thickness is very thin and not hard, the present applicants improve the strength and waist (stiffness). There has been proposed a filter medium for liquid filtration in which the above-mentioned filter medium layer that is thin and excellent in surface filtration performance and a support layer that has high liquid permeability, high strength, and good fold-foldability are combined and integrated (for example, (See Patent Document 3).

  As filter media using fibrillated fibers, filter media using lyocell fibers with controlled beating degree (Canadian freeness, CSF) have been proposed (see, for example, Patent Documents 4 to 6). Since the lyocell fiber is manufactured by solvent spinning, the cellulose crystals are oriented in the longitudinal direction of the fiber, and fibrillation is easy. In addition, when the filter medium is produced by the wet papermaking method, there is an advantage that the lyocell fibers are bonded by hydrogen bonding, and the strength of the filter medium can be improved.

  However, as is clear from Photo 3 of Non-Patent Document 1 (CSF = 370 ml), the fibrillated lyocell fiber is composed of a fibril fiber branched and connected from the fiber trunk, and a fibrillated fiber completely detached from the trunk. Both are present. Focusing on the fact that the form of fibrillation is not the same even in the fibrillated state showing the same CSF value, the fibrillated lyocell fiber with a fiber diameter of 1 μm or less detached from the trunk, the fiber diameter of 1 μm from the trunk with a fiber diameter of 2 μm or more Technology that optimizes properties such as filter media uniformity, solid particle collection efficiency, and pressure loss by using a filter media containing fibrillated lyocell fibers with the following branches, either singly or in two fibrillated states. Is disclosed (for example, see Patent Document 7).

  However, in the technique of Patent Document 7 in which the fibrillation state of the lyocell fiber is adjusted by the fiber diameter, there is still room for improvement in performance such as the collection efficiency of fine particles, pressure loss, and strength of the filter medium.

JP 2000-70628 A Japanese Patent No. 2633355 Japanese Patent No. 3305372 JP-A-11-70305 JP 2000-153116 A JP 2001-300225 A JP 2004-188409 A

“High Strength Cellulose Fibers for Papermaking Applications of Courtauds Fibers”, Non-woven Fabric Information, August 10, 1995, p. 22-24

  The subject of this invention is providing the filter medium which expressed performances, such as the collection efficiency of a fine particle, a pressure loss, and the intensity | strength of a filter medium, with sufficient balance.

As a result of intensive studies to solve the above problems, the present inventors have
(1) It consists of a nonwoven fabric containing synthetic resin fibers and fibrillated lyocell fibers as essential components, and has a maximum frequency peak between 0.00 and 1.00 mm in the fiber length distribution histogram of fibrillated lyocell fibers. A ratio of fibers having a fiber length of 1.00 mm or more is 50% or more,
(2) In the fiber length distribution histogram of fibrillated lyocell fiber, the filter medium according to (1) above having a peak between 1.50 and 3.50 mm in addition to the maximum frequency peak,
I found.

  The filter medium (1) of the present invention comprises a nonwoven fabric containing synthetic resin fibers and fibrillated lyocell fibers as essential components. In the fiber length distribution histogram of fibrillated lyocell fibers, the ratio of the fibers having a maximum frequency peak between 0.00 and 1.00 mm and having a fiber length of 1.00 mm or more is 50% or more, Since the fibrillated lyocell fiber is entangled with the synthetic resin short fiber, the surface is smooth, and the uniformity is excellent, so that the balance of collection efficiency, pressure loss, and strength is improved.

  In the fiber length distribution histogram of the fibrillated lyocell fiber, the filter medium (2) having a peak between 1.50 and 3.50 mm in addition to the maximum frequency peak has better uniformity required as a filter medium. The balance between collection efficiency, pressure loss and strength is further improved.

It is an example of the fiber length distribution histogram of the fibrillated lyocell fiber [1] which has a maximum frequency peak between 0.00-1.00 mm. It is an example of the fiber length distribution histogram of the fibrillated lyocell fiber [2] which has a peak between 1.50 and 3.50 mm besides a maximum frequency peak.

  Hereinafter, the filter medium of the present invention will be described in detail.

  The filter medium of the present invention comprises a nonwoven fabric containing synthetic resin short fibers and fibrillated lyocell fibers as essential components. As shown in FIG. 1, in the fiber length distribution histogram of fibrillated lyocell fibers, 0.00 The ratio of fibers having a maximum frequency peak between ˜1.00 mm and having a fiber length of 1.00 mm or more is 50% or more. In terms of increasing the collection efficiency, the ratio of fibers having a maximum frequency peak between 0.30 and 0.70 mm in the fiber length distribution histogram and having a fiber length of 1.00 mm or more is 55% or more. Is preferred. A higher proportion of fibers having a fiber length of 1.00 mm or more is desirable, but about 75% is sufficient.

  The fiber length and the fiber length distribution histogram of the fibrillated lyocell fiber of the present invention are shown in JAPAN TAPPI Paper Pulp Test Method No. It was measured using Kajaani Fiber Lab V3.5 (manufactured by Metso Automation) according to 52 “Fiber length test method for paper and pulp (automatic optical measurement method)”.

  The “fiber length” and “fiber length distribution” in the present invention mean “length weighted fiber length” and “length weighted fiber length distribution” measured and calculated according to the above.

  In addition, “lyocell” of fibrillated lyocell fiber is a term defined in ISO standard and Japanese JIS standard, and refers to “cellulose fiber obtained by spinning in an organic solvent directly without passing through a cellulose derivative”. This is also called “solvent-spun cellulose fiber”.

  Lyocell fibers are beater and dispersion equipment such as beaters, PFI mills, single disc refiners (SDR), double disc refiners (DDR), ball mills and dyno mills used to disperse and pulverize pigments, etc. Can be fibrillated. By adjusting the types of beating / dispersing equipment and processing conditions (fiber concentration, temperature, pressure, rotation speed, refiner blade shape, gap between refiner plates, number of treatments), the fiber length and fiber length of the target lyocell A distribution can be achieved.

  In the fiber length distribution histogram of the fibrillated lyocell fiber, it is preferable to have a peak between 1.50 and 3.50 mm in addition to the above maximum frequency peak as shown in FIG. More preferably, it has a peak between .25 mm, and more preferably between 2.00 and 3.00 mm. By having a peak in this range, it is preferable because both the collection efficiency and strength of the filter medium can be achieved. When the fiber length of the peak is shorter than 1.50 mm, tearing may occur due to insufficient filter medium strength. Moreover, when it exceeds 3.50 mm, the collection efficiency of a filter medium may not improve.

  The modified drainage degree of the fibrillated lyocell fiber is more preferably 0 to 250 mL, and further preferably 0 to 160 mL. When the modified drainage is more than 250 mL, the collection efficiency of the filter medium may be lowered.

  The modified freeness in the present invention was measured in accordance with JIS P811, except that an 80 mesh wire net having a wire diameter of 0.14 mm and an aperture of 0.18 mm was used as a sieve plate, and the sample concentration was 0.1%. It is a value.

  In the case of lyocell fiber, the fiber length becomes shorter as the microfabrication progresses. In particular, when the sample concentration is low, the entanglement between fibers decreases and the fiber network is difficult to form. It slips through the hole in the board. That is, in the case of the solvent-spun cellulose refined, an accurate freeness cannot be measured by the measuring method of JIS P8121. More specifically, the lyocell fiber is easily finely divided in parallel to the long axis of the fiber by the refining treatment, and since the uniformity of the fiber diameter in each fiber after division is high, the shorter the average fiber length, It is considered that the fibers are less likely to be entangled and it is difficult to form a fiber network. Therefore, in the present invention, in order to measure the exact freeness of the lyocell fiber, an 80-mesh wire net having a wire diameter of 0.14 mm and an aperture of 0.18 mm is used as the sieve plate, and the sample concentration is 0.1%. Used the modified freeness measured according to JIS P8121.

  The length-weighted average fiber length of the fibrillated lyocell fiber is preferably 0.20 to 2.00 mm, more preferably 0.40 to 1.80 mm, and further preferably 0.50 to 1.50 mm. If the length-weighted average fiber length is less than 0.20 mm, the fiber may be detached from the papermaking wire due to fiber dropping or insufficient entanglement. If it is longer than 2.00 mm, the fibers may be twisted to become lumpy, and the uniformity of the filter medium may be reduced.

  In the filter medium of the present invention, the content mass ratio between the synthetic resin short fibers and the fibrillated lyocell fibers is preferably 98/2 to 20/80, more preferably 95/5 to 30/70, and 90/10 to 40 /. 60 is more preferable. When the content ratio of the fibrillated lyocell fiber is less than 2% by mass, the uniformity and the collection efficiency may not be improved. Moreover, when the content ratio of the fibrillated lyocell fiber exceeds 80% by mass, the water resistance is insufficient, and the filter medium may peel off.

  In the present invention, the resins constituting the synthetic resin short fibers include polyolefin resins, polyester resins, polyvinyl acetate resins, ethylene-vinyl acetate copolymer resins, polyamide resins, acrylic resins, and polyvinyl chloride resins. Resin, polyvinylidene chloride resin, polyvinyl ether resin, polyvinyl ketone resin, polyether resin, polyvinyl alcohol resin, diene resin, polyurethane resin, phenol resin, melamine resin, furan resin, urea resin Examples thereof include resins, aniline resins, unsaturated polyester resins, alkyd resins, fluorine resins, and silicone resins. Among these, the use of a polyester resin, an acrylic resin, or a polyolefin resin is preferable because a filter medium having a high effect of suppressing damage to the filter medium and having excellent uniformity can be obtained.

  The synthetic resin short fiber may be a fiber (single fiber) made of a single resin, or may be a fiber (composite fiber) made of two or more kinds of resins. Moreover, the synthetic resin short fiber contained in the filter medium of the present invention may be one kind or a combination of two or more kinds.

  As the synthetic resin short fiber, a heat-fusible short fiber that functions as a binder may be used. Examples of the heat-fusible short fibers include core-sheath type, eccentric type, side-by-side type, sea-island type, orange type, multiple bimetal type composite fiber, or unstretched single fiber, but the point of increasing the strength of the filter medium Therefore, it is particularly preferable to use a core-sheath type polyester binder fiber.

  The fineness of the synthetic resin short fiber is preferably 0.007 to 4.4 dtex, more preferably 0.02 to 3.3 dtex, and further preferably 0.04 to 2.2 dtex. When the fineness of the synthetic resin short fiber exceeds 4.4 dtex, the uniformity of the filter medium may not be ensured. Moreover, when the fineness of the synthetic resin short fiber is less than 0.007 dtex, stable production of the fiber becomes difficult.

  The fiber length of the synthetic resin short fiber is preferably 1 mm or more and 15 mm or less, more preferably 1 mm or more and 10 mm or less, and further preferably 1 mm or more and 7 mm or less. If the fiber length exceeds 15 mm, the formation may be poor. On the other hand, when the fiber length is less than 1 mm, the mechanical strength of the filter medium may be lowered.

  The filter medium of the present invention is a paper machine for producing general paper or wet nonwoven fabric, for example, a long net paper machine, a circular net paper machine, or an inclined wire type paper machine, or these paper machines are the same or different. Manufactured on a combination paper machine etc. where more than the machine is installed online. The wet paper manufactured by the paper machine is dried by a dryer such as an air dryer, a Yankee dryer, a cylinder dryer, a suction drum dryer, or an infrared dryer.

The filter medium of the present invention can be integrated with the support layer as a filter medium layer, and can be advantageously used as a composite filter medium. The support layer is an organic fiber having a fiber diameter of 5 μm or more, includes at least one of polyolefin-based, polyamide-based, polyester-based, acrylic-based, vinylon-based, and regenerated fiber-based fibers, and 20 to 150 g / m ^2. It is preferable to use a support layer composed of a basis weight of. Furthermore, by containing 1 to 70% by mass of at least one kind of fibrous organic binder such as polyester, polyolefin, vinyl chloride, vinyl acetate or vinylon, a support layer having high strength can be obtained. In addition, this support layer is not limited to those obtained with a wet paper machine, but depending on the use, spunbond, melt blow, needle punch, spunlace, etc. made of polyester, nylon, polyethylene, polypropylene, cotton, rayon, etc. The sheet manufactured by the dry method can be used. The composite filter medium can be produced by a paper making method using a combination paper machine. After forming one layer, it can also be produced by a method of casting a slurry in which fibers are dispersed on the layer. Moreover, when using the support body layer manufactured by the dry method, the filter medium layer and support body layer which were manufactured with the paper machine may be laminated | stacked with a paper machine, and may be laminated | stacked using another processing machine.

  The composite filter media obtained by laminating and integrating the filter media and the support layer provide waist (stiffness), water resistance, and pleatability that could not be obtained only with the filter media, for electric discharge machines, engine oils, It is suitable as a filter medium for filters for liquid filtration, such as for fuel, oil / water separation, and hydraulic equipment. In this case, it is preferable to use the filter medium layer as the upstream side because the surface layer filtration mechanism can be expressed. However, when the particle diameter in the target liquid is large, it may be preferable to set the support layer upstream.

Filter media basis weight of the present invention is preferably from 5 to 100 g / ^{m 2,} more preferably 7~80g / ^{m 2,} more preferably 10 to 50 g / ^{m 2.} When it exceeds 100 g / m ² , the pressure loss becomes too high or the thickness becomes excessive, and when a composite filter medium is used, it is difficult to obtain a composite effect, and when it is less than 5 g / m ² , the uniformity. May be difficult to obtain, and a large variation may be easily generated on the surface after the composite filter medium is formed. The basis weight means the basis weight based on the method defined in JIS P8124 (paper and paperboard—basis weight measurement method).

  10-500 micrometers is preferable, as for the thickness of the filter medium of this invention, 20-400 micrometers is more preferable, and 30-300 micrometers is more preferable. If it exceeds 500 μm, the filter medium alone will occupy the majority of the filter, and it will be difficult to obtain the effect of the composite. There is a fear. In addition, thickness means the value measured by the method prescribed | regulated to JISB7502, ie, the value measured by the outside micrometer at the time of 5N load.

In the filter medium of the present invention, the density of the filter medium 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 filter medium layer, and the life may be shortened. Conversely, if it exceeds 0.8 g / cm ³ , the pressure loss may increase.

The support layer improves the mechanical strength without impairing the filtration efficiency of the composite filter medium. The density of the support layer is preferably 0.05 to 0.50 g / cm ³ . If the density of the support layer is less than 0.05 g / cm ^3, the mechanical strength of the composite filter media, may workability is deteriorated, when it exceeds 0.50 g / cm ^3, if the filtration resistance increases is there. Moreover, it is preferable that the density of the whole filter medium is 0.1-0.6 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 increases, so that the area of the filter medium that can be incorporated into the unit decreases, and as a result, the life of the filter may be shortened.

  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 can be appropriately blended as needed as long as the characteristics of the filter medium are not impaired. . Further, the filter medium and the composite filter medium can contain a thermoplastic resin in order to impart mechanical strength and water resistance. Examples of the thermoplastic resin include acrylic, vinyl acetate, epoxy, synthetic rubber, urethane, polyester, vinyl chloride, vinylidene chloride latex, polyvinyl alcohol, starch, phenol resin, and the like. These can be used alone or in combination of two or more.

  The amount of the thermoplastic resin contained in the filter medium and the composite filter medium is suitably 0.01 to 10% by mass with respect to the filter medium. When it exceeds 10% by mass, the pressure loss of the filter medium increases. Moreover, if it is less than 0.01 mass%, compared with the filter medium and composite filter medium which do not contain a thermoplastic resin, mechanical strength and water resistance do not improve.

  The state in which the thermoplastic resin is contained in the filter medium and the composite filter medium may be any state of only the filter medium layer, both the filter medium layer and the support layer, and only the support layer. However, when the filter medium layer contains a thermoplastic resin, the space of the filter medium layer is blocked, the trapping ability of the solid particles is reduced, and the pressure loss is increased. Therefore, the filter medium layer is preferably contained only in the support layer.

  The method of incorporating the thermoplastic resin into the filter medium and the composite filter 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 support body layer, it is preferable to use a spray system and a gravure coating system. After containing the thermoplastic resin, it is dried with an air dryer, Yankee dryer, cylinder dryer, suction drum dryer, infrared dryer or the like.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to a present Example. In the examples, all parts and percentages are by mass unless otherwise specified.

<Physical properties of fibrillated lyocell fiber>
About the fibrillated lyocell fiber used in the example below,
(1) Ratio of fibers having a fiber length of 1.00 mm or more: “Fiber ratio of 1.00 mm or more”
(2) Fiber length of maximum frequency peak in fiber length distribution histogram: “Fiber length of maximum frequency peak”
(3) Fiber length of peaks other than the maximum frequency peak: “fiber length of second peak”
(4) Length-weighted average fiber length: “Average fiber length”
(5) Freeness measured according to JIS P8121, except that an 80-mesh wire mesh with a wire diameter of 0.14 mm and an aperture of 0.18 mm was used as the sieve plate, and the sample concentration was 0.1%: “Freeness "
As shown in Table 1.

Example 1
45 parts of oriented and crystallized polyethylene terephthalate (PET) short fibers having a fineness of 0.3 dtex and a fiber length of 3 mm, a heat-sealable binder fiber (core-sheath type, polyester fiber) 30 having a fineness of 2.2 dtex and a fiber length of 5 mm Part, unfibrillated lyocell single fiber (fiber diameter 12 μm, fiber length 6 mm, manufactured by Coatles Co., Ltd.) and treated with a double disc refiner, 25 parts of fibrillated lyocell fiber A are mixed together to produce a pulper. The mixture was disaggregated in water and stirred with an agitator to prepare a uniform papermaking slurry (1% concentration). This slurry for paper making is made up by a wet method using a circular paper machine, and a non-woven fabric strength is expressed by bonding a heat-fusible binder fiber with a cylinder dryer at 130 ° C., and a filter medium having a basis weight of 20 g / m ² . Was made.

Example 2
A filter medium was prepared in the same manner as in Example 1 except that lyocell fiber B was blended in place of lyocell fiber A in Example 1.

Example 3
A filter medium was produced in the same manner as in Example 1 except that lyocell fiber C was blended instead of lyocell fiber A in Example 1.

Example 4
A filter medium was produced in the same manner as in Example 1 except that lyocell fiber D was blended instead of lyocell fiber A in Example 1.

Example 5
A filter medium was prepared in the same manner as in Example 1 except that lyocell fiber E was blended instead of lyocell fiber A in Example 1.

Example 6
A filter medium was prepared in the same manner as in Example 1 except that lyocell fiber F was blended in place of lyocell fiber A in Example 1.

Example 7
A filter medium was prepared in the same manner as in Example 1 except that lyocell fiber G was blended in place of lyocell fiber A in Example 1.

Example 8
A filter medium was prepared in the same manner as in Example 1 except that lyocell fiber H was blended instead of lyocell fiber A in Example 1.

Example 9
A filter medium was prepared in the same manner as in Example 1 except that lyocell fiber I was blended instead of lyocell fiber A in Example 1.

Example 10
60 parts of oriented PET crystal short fibers with a fineness of 0.1 dtex and fiber length of 3 mm, 30 parts of heat-fusible binder fiber (core-sheath type, polyester fiber) with a fineness of 2.2 dtex and fiber length of 5 mm, fibrillated Untreated lyocell monofilament (fiber diameter 12 μm, fiber length 6 mm, manufactured by Coatles Co., Ltd.) was mixed together with 10 parts of fibrillated lyocell fiber B obtained by using a double disc refiner and disaggregated in pulper water. A uniform papermaking slurry (1% concentration) was prepared under stirring by an agitator. This slurry for paper making is made up by a wet method using a circular paper machine, and a non-woven fabric strength is expressed by bonding a heat-fusible binder fiber with a cylinder dryer at 130 ° C., and a filter medium having a basis weight of 30 g / m ² . Was made.

Example 11
10 parts of PET short fibers oriented and crystallized with a fineness of 0.3 dtex and fiber length of 3 mm, 30 parts of heat-fusible binder fiber (core-sheath type, polyester fiber) with a fineness of 2.2 dtex and fiber length of 5 mm, fibrillated Untreated lyocell monofilament (fiber diameter 12 μm, fiber length 6 mm, manufactured by Coatles Co., Ltd.) was mixed together with 60 parts of fibrillated lyocell fiber I obtained using a double disc refiner and disaggregated in pulper water. A uniform papermaking slurry (1% concentration) was prepared under stirring by an agitator. This slurry for paper making is made up by a wet method using a circular paper machine, a heat-bondable binder fiber is adhered by a cylinder dryer at 130 ° C. to develop a nonwoven fabric strength, and a filter medium having a basis weight of 10 g / m ² . Was made.

Example 12
In order to form a filter medium layer, 45 parts of PET short fibers oriented and crystallized with a fineness of 0.3 dtex and a fiber length of 3 mm, a heat-fusible binder fiber with a fineness of 2.2 dtex and a fiber length of 5 mm (core-sheath type, polyester) Together with 30 parts of fibrillated lyocell fiber (fiber diameter 12 μm, fiber length 6 mm, manufactured by Coatles Co., Ltd.) using a double disc refiner. The mixture was mixed and disaggregated in water of a pulper. Under stirring by an agitator, a uniform papermaking slurry (1% concentration) was prepared and stored in a stock tank having a stirring device.

Subsequently, in order to form a support layer, 50 parts of PET-based short fibers having a fineness of 0.6 dtex and a fiber length of 5 mm were crystallized, and a heat-fusible binder fiber (core sheath) having a fineness of 2.2 dtex and a fiber length of 5 mm. 50 parts of polyester fiber (type, polyester fiber) are mixed together, disaggregated in pulper water, and stirred with an agitator to prepare a uniform papermaking slurry (1% concentration). What is a slurry for a filter media layer? Separately, it was stored in a stock tank with a stirring device. Using a combination machine of an inclined wire paper machine and a circular net paper machine, the support layer is an inclined wire paper machine, the filter medium layer is a circular net paper machine, the support layer is 50 g / m ² in dry mass, and the filter medium layer is 20 g / After forming the m ² paper wetting wet paper, it was hot-pressure dried so that the support layer side was in contact with a 130 ° C. Yankee dryer, and a composite filter medium with a basis weight of 70 g / m ² was obtained.

Example 13
In order to form a filter medium layer, 45 parts of PET short fibers oriented and crystallized with a fineness of 0.3 dtex and a fiber length of 3 mm, a heat-fusible binder fiber with a fineness of 2.2 dtex and a fiber length of 5 mm (core-sheath type, polyester) Fiber) 30 parts, unfibrillated lyocell monofilament (fiber diameter 12 μm, fiber length 6 mm, manufactured by Coatles) and mixed with fibrillated lyocell fiber B25 part obtained by using a double disc refiner Then, the pulper was disaggregated in water, and a uniform papermaking slurry (1% concentration) was prepared under stirring by an agitator, and stored in a stock tank having a stirring device.

Subsequently, in order to form a support layer, 50 parts of PET-based short fibers having a fineness of 0.6 dtex and a fiber length of 5 mm were crystallized, and a heat-fusible binder fiber (core sheath) having a fineness of 2.2 dtex and a fiber length of 5 mm. 50 parts of polyester fiber (type, polyester fiber) are mixed together, disaggregated in pulper water, and stirred with an agitator to prepare a uniform papermaking slurry (1% concentration). What is a slurry for a filter media layer? Separately, it was stored in a stock tank with a stirring device. Using a combination machine of an inclined wire paper machine and a circular net paper machine, the support layer is an inclined wire paper machine, the filter medium layer is a circular net paper machine, the support layer is 50 g / m ² in dry mass, and the filter medium layer is 20 g / After forming the m ² paper wetting wet paper, it was hot-pressure dried so that the support layer side was in contact with a 130 ° C. Yankee dryer, and a composite filter medium with a basis weight of 70 g / m ² was obtained.

(Comparative Example 1)
A filter medium was produced in the same manner as in Example 1 except that lyocell fiber J was blended instead of lyocell fiber A in Example 1.

(Comparative Example 2)
A filter medium was produced in the same manner as in Example 1 except that lyocell fiber K was blended instead of lyocell fiber A in Example 1.

(Comparative Example 3)
A filter medium was prepared in the same manner as in Example 1 except that lyocell fiber L was blended instead of lyocell fiber A in Example 1.

<Evaluation>
The filter media and composite filter media obtained in Examples and Comparative Examples were evaluated as follows, and Table 2 shows the evaluation results of pressure loss, particle collection efficiency, and strength.

[Pressure loss] (Unit: Pa)
According to JIS B9908, it measured on the conditions of the surface wind speed of 5.3 cm / sec. The pressure loss is preferably as low as possible. “◎” is less than 150 Pa, “◯” is 150 Pa or more and less than 200 Pa, “Δ” is 200 Pa or more and less than 250 Pa, and “X” is 250 Pa or more.

[Collection efficiency] (Unit:%)
According to JIS B9908, it measured on the conditions of the surface wind speed of 5.3 cm / sec. The particles to be measured were measured using a particle counter (trade name “KC-11”, manufactured by Rion Co., Ltd.) with respect to particles having a particle diameter of 0.25 to 0.35 μm using atmospheric dust. . The higher the collection efficiency, the better. "◎" if 50% or more, "○" if 40% or more and less than 50%, "△" if 30% or more and less than 40%, if less than 30%. It was set as “x”.

[Strength]
The filter media and composite filter media of Examples and Comparative Examples were cut into a strip shape having a width of 50 mm. The test piece was mounted on a 40 mmφ fixed frame installed on a tabletop material testing machine (trade name: STA-1150, manufactured by Orientec Co., Ltd.), and the tip was rounded (curvature: 1.6) with a diameter of 1.0 mm. The metal needle (manufactured by Orientec Co., Ltd.) was lowered at a constant speed of 50 mm / min. The maximum load (g) at this time was measured and used as the puncture strength. Measure the puncture strength at 5 or more locations for one sample, and the minimum puncture strength among all the measured values is “◎◎” if it is 100 g or more, “◎” if it is 50 g or more and less than 100 g, and 40 g or more and less than 50 g If it is, it is indicated by “◯”, if it is 30 g or more and less than 40 g, it is indicated by “Δ”, and if it is less than 30 g, it is indicated by “x”.

[Applicability to pleating]
The filter medium and the composite filter medium are cut into a machine flow direction (MD) of 30 cm and a horizontal direction of 20 cm, and a mountain fold and a valley fold are repeated every 5 cm so as to cross the flow direction. On the folded filter medium, a diameter of 5 cm and a length of 30 cm. Then, a cylindrical metal roll having a weight of 3 kg is slowly rolled to make a crease and a bellows shape. The crease is clear and has no distortion, and if the crease is not deformed even if it is pushed, it is considered good. The pleatability was evaluated for the filter media and composite filter media obtained in Examples 1, 3, 12 and 13.

  From the comparison between Examples 1 to 11 and Comparative Examples 1 to 3, the filter media obtained in Examples 1 to 11 were made of nonwoven fabric containing synthetic resin short fibers and fibrillated lyocell fibers, and fibrillated lyocell. In the fiber length distribution histogram of fibers, since the ratio of fibers having a maximum frequency peak between 0.00 and 1.00 mm and having a fiber length of 1.00 mm or more is 50% or more, the surface smoothness is The result was high, excellent in uniformity, and a good balance between collection efficiency and pressure loss.

  On the other hand, in the filter medium obtained in Comparative Example 1, the maximum frequency peak in the fiber length distribution histogram of the fibrillated lyocell fiber is out of the range of 0.00 to 1.00 mm. Lower results. Moreover, since the filter medium obtained in Comparative Example 2 had a fiber ratio of 1.00 mm or more less than 50%, the strength was low and the pressure loss was larger than that of the Example. Furthermore, since the maximum frequency peak of the filter medium obtained in Comparative Example 3 greatly deviated from between 0.00 and 1.00 mm, the collection efficiency was lower than that of the Examples.

  From the comparison of Examples 1 to 9, in the fiber length distribution histogram of the fibrillated lyocell fiber, when it has a peak between 1.50 and 3.50 mm in addition to the maximum frequency peak, the strength is also high, and the collection efficiency Was also good. In Example 4 where the fiber length of the peak other than the maximum frequency peak is shorter than 1.50 mm, the strength tends to be slightly reduced. Further, in Example 9 where the fiber length of the peak other than the maximum frequency peak is longer than 3.50 mm, the collection efficiency tends to be slightly deteriorated.

  Examples 12 and 13 were composite filter media in which the filter media of Example 1 and Example 3 and the support layer were laminated and integrated, and were satisfied with pressure loss, collection efficiency, and strength. In addition, since the composite filter media of Example 12 and Example 13 are integrated with the support layer, in the pleating processability evaluation, the crease is clear and has no distortion, and does not deform even when the crease is pushed, and the pleat processability is high. It was excellent.

  The filter medium of the present invention can be suitably used as a filter medium for a liquid filtration filter.

Claims (2)

  It consists of a non-woven fabric containing synthetic resin fibers and fibrillated lyocell fibers as essential components, and has a maximum frequency peak between 0.00 and 1.00 mm in the fiber length distribution histogram of fibrillated lyocell fibers. A filter medium, wherein the proportion of fibers having a fiber length of 0.000 mm or more is 50% or more.   2. The filter medium according to claim 1, wherein in the fiber length distribution histogram of the fibrillated lyocell fiber, there is a peak between 1.50 and 3.50 mm in addition to the maximum frequency peak.