Filter material for liquid filters and method for producing same

Abstract

To provide a filter medium for a liquid filter having a low pressure loss, high filtration efficiency and a long filtration life, and a method for manufacturing the same.SOLUTION: A filter medium for a liquid filter contains fibrillated lyocell fibers, and heat-fusible fibers having a fiber diameter of 35 μm or more, wherein at least the fibrillated lyocell fibers have a wet non-woven fabric forming a network structure. A method for manufacturing a filter medium for a liquid filter includes the steps of: preparing a raw material slurry containing fibrillated lyocell fibers, and heat-fusible fibers having a fiber diameter of 35 μm or more; paper-making the raw material slurry, and forming a wet sheet; and drying the wet sheet, and obtaining a dry sheet formed into the filter medium for the liquid filter.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a filter medium for a liquid filter, which is used to remove solid particles contained in a liquid to obtain a clean liquid, and a manufacturing method thereof. [Background technology]

[0002] As the filter material used to remove solid particles contained in liquid, the filter material made of paper or nonwoven fabric made of natural fiber, organic synthetic fiber or inorganic fiber etc. is widely used.In order to obtain the filter material with high filtering efficiency, it is effective to use the filter material that is densely packed with fine diameter fibers, but if the fiber diameter is too thin or the fiber packing is too dense, the pressure loss increases, it becomes difficult to secure the amount of liquid passing through, and there is a problem that the filter life, that is, the filtering time until reaching a predetermined pressure loss, is reduced.

[0003] As the fibers constituting the filter medium for liquid filters, fibrillated lyocell fibers are widely used because they provide high filtration efficiency. For example, a filter medium containing fibrillated lyocell fibers with a fiber diameter of 1 μm or less and organic fibers with a fiber diameter of 1 to 30 μm (see, for example, Patent Document 1) and a filter medium containing about 20 to about 80% by weight of bicomponent staple fibers and about 10 to about 50% by mass of fibrillated lyocell staple fibers (see, for example, Patent Document 2) have been proposed. However, there is a demand for a filter medium that has a higher filtration efficiency and a longer filtration life while maintaining a low pressure loss. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2004-188409 A [Patent Document 2] Special Publication No. 2021-521000 Summary of the Invention [Problem to be solved by the invention]

[0005] As mentioned above, there is a demand for a filter medium that can filter the solid particles contained in liquid with high efficiency while maintaining low pressure loss and has a long filter life, but it is difficult to obtain a filter medium that has these characteristics in the past.Therefore, the object of the present disclosure is to provide a filter medium for liquid filters that has low pressure loss, high filter efficiency and long filter life, and a method for manufacturing the same. [Means for solving the problem]

[0006] The filter material for liquid filters according to the present invention is characterized in that it comprises fibrillated lyocell fibers and heat-fused fibers having a fiber diameter of 35 μm or more, and has a wet-laid nonwoven fabric in which at least the fibrillated lyocell fibers form a network structure.

[0007] In the air filter material according to the present invention, the fibrillated lyocell fiber preferably has an average fiber diameter of 0.3 μm or more, a maximum fiber diameter of 8 μm or less, and a length-weighted average fiber length of 1 mm or more, thereby achieving high filtration efficiency.

[0008] In the liquid filter medium according to the present invention, the wetlaid nonwoven fabric may include a form containing non-thermal fusion fibers that are not fibrillated, thereby making it possible to obtain a filter medium with a good balance of physical properties.

[0009] In the filter medium for liquid filters according to the present invention, the blending amount of the fibrillated lyocell fibers is preferably 20 to 80 parts per 100 parts of the total fiber mass constituting the filter medium, which can reduce pressure loss while ensuring sufficient filtration efficiency.

[0010] In the filter medium for liquid filtering according to the present invention, the blending amount of the heat-fusible fibers is preferably 20 to 80 parts per 100 parts of the total fiber mass constituting the filter medium, which allows the strength of the filter medium to be ensured while obtaining sufficient filtering efficiency.

[0011] In the liquid filter medium according to the present invention, the heat-sealing fiber is preferably a composite heat-sealing fiber having a non-heat-sealing component that does not melt when heated and a heat-sealing component that melts when heated. The composite heat-sealing fiber is also added to the network structure formed by the fibrillated lyocell fiber, so that the strength of the filter medium can be ensured while sufficient filtering efficiency can be obtained.

[0012] In the filter medium for liquid filters according to the present invention, the blending amount of the non-thermal fusion fibers is preferably a maximum of 70 parts per 100 parts of the total fiber mass constituting the filter medium. This makes it possible to obtain a filter medium with well-balanced physical properties. The fibers constituting the filter medium include only the fibrillated lyocell fibers and the heat-sealed fibers having a fiber diameter of 35 μm or more. This may also be the case.

[0013] In the filter material for liquid filtering according to the present invention, the non-thermal fusible fibers preferably have a fiber diameter of 5 μm or more, which can prevent the pressure loss from becoming too high.

[0014] The method for producing a filter material for liquid filters according to the present invention is characterized by comprising the steps of: preparing a raw material slurry containing fibrillated lyocell fibers and heat-fused fibers having a fiber diameter of 35 μm or more; making the raw material slurry into a wet sheet; and drying the wet sheet to obtain a dry sheet that will become the filter material for liquid filters. The heat-fusible fibers are preferably fibers containing a heat-fusible component that melts when heated in the step of obtaining the dry sheet. Effect of the Invention

[0015] According to the present disclosure, it is possible to obtain a filter medium for liquid filters that has low pressure loss, high filtration efficiency, and a long filtration life. [Brief description of the drawings]

[0016] [Figure 1] 1 is a graph comparing the relationship between pressure loss and filtration efficiency in Examples and Comparative Examples. [Diagram 2] 1 is a graph comparing the relationship between pressure loss and filter life in Examples and Comparative Examples. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Next, the present invention will be described in detail with reference to the embodiments, but the present invention is not limited to these descriptions. Various modifications of the embodiments may be made as long as the effects of the present invention are achieved.

[0018] The lyocell fiber in this embodiment is a regenerated cellulose fiber spun by an organic solvent spinning method using N-methylmorpholine-N-oxide as a solvent. In the organic solvent spinning method, cellulose is dissolved in an organic solvent as it is and spun, so that the molecular breakage is small, the average degree of polymerization is higher than other regenerated cellulose fibers, the fiber has high rigidity, and the cross-sectional shape of the fiber is close to a circle. This rigidity and cross-sectional shape make it easier to maintain the voids in the filter medium. In addition, the fibrillated lyocell fiber after beating also maintains the above-mentioned rigidity and cross-sectional shape characteristics. Furthermore, when fibrillated by beating, the surface area of ​​the fiber that contributes to particle collection is increased, thereby increasing the filtration efficiency.

[0019] As a method for beating the lyocell fiber to fibrillate it, a beating machine such as a Niagara beater, a PFI mill, a single disc refiner, a double disc refiner, etc. In beating, it is preferable to beat the lyocell fiber without applying too strong a load so as not to shorten the fiber length of the lyocell fiber too much.

[0020] As the beating of the lyocell fiber proceeds, the fiber is cut and the fiber length is shortened. If the fiber length is too short, it may fill the voids after the sheet is formed, which may increase the pressure loss. The fibrillated lyocell fiber used in this embodiment preferably has a length-weighted average fiber length of 1 mm or more, more preferably 1 to 3 mm, and even more preferably 1 to 2 mm.

[0021] The length-weighted average fiber length of the fibrillated lyocell fiber was measured according to ISO 16065-2:2007 "Determination of fiber length by automated optical analysis-Part 2".

[0022] The fibrillation of the Lyocell fiber progresses by beating, and the fiber diameter becomes smaller. The average fiber diameter of the fibrillated Lyocell fiber used in this embodiment is preferably 0.3 μm or more, more preferably 0.3 to 1.0 μm, and even more preferably 0.3 to 0.8 μm. If the average fiber diameter is less than 0.3 μm, the fibers are cut as the fibrillation progresses, and the voids in the filter medium cannot be maintained, which may increase the pressure loss. On the other hand, if the average fiber diameter exceeds 1.0 μm, the surface area of ​​the fiber that contributes to particle collection becomes small, and the filtration efficiency may decrease.

[0023] The maximum fiber diameter of the fibrillated lyocell fiber is preferably 8 μm or less, more preferably 6 μm or less, and even more preferably 4 μm or less. If the maximum fiber diameter exceeds 8 μm, the surface area of ​​the fiber that contributes to particle collection becomes small, and the filtration efficiency may decrease.

[0024] In addition, in this embodiment, the fiber diameter is measured by taking a photograph of the surface of the filter medium using an electron microscope, drawing a straight line horizontally on the obtained electron microscope photograph, and measuring the fiber diameter at the intersection of the straight line and the fiber. The average fiber diameter is the arithmetic mean value of 200 measurement points.

[0025] The amount of fibrillated lyocell fiber in this embodiment can be adjusted appropriately according to the properties required for the filter medium, but when the total fiber mass constituting the filter medium is 100 parts, it is preferably 20 to 80 parts, more preferably 30 to 70 parts. If the amount of fibrillated lyocell fiber is too small, it may be difficult to obtain sufficient filtering efficiency. If the amount of fibrillated fiber is too large, the structure of the filter medium may become dense, and the pressure loss may increase.

[0026] The heat-fusible fiber in this embodiment is a fiber containing a heat-fusible component that melts when heated in the manufacturing process of the wet nonwoven fabric. The addition of the heat-fusible fiber can impart strength to the wet nonwoven fabric by melt adhesion. The melt adhesion includes a form in which the heat-fusible fiber is point-bonded to the fibrillated lyocell fiber. Examples of the heat-fusible fiber include polyvinyl alcohol fiber, polyester fiber, polyolefin fiber, etc. The form of the heat-fusible fiber includes a side-by-side type heat-fusible fiber in which a melting part and a non-melting part are combined side by side, a core-sheath type heat-fusible fiber having a non-melting core part and a melting sheath part, and a full melt type heat-fusible fiber that melts as a whole and contributes to adhesion between main fibers such as glass fibers. Among these, composite type heat-fusible fibers including side-by-side type heat-fusible fibers and core-sheath type heat-fusible fibers are preferred, which are made of a non-heat-fusible component that does not melt when heated and a heat-fusible component that melts when heated, and core-sheath type heat-fusible fibers having a non-heat-fusible component as the core and a heat-fusible component as the sheath are more preferred. Examples of non-heat-fusible components include polyesters, polyolefins, polyamides, polyurethanes, polyacrylonitriles, cellulose-based polymers, etc., among which polyesters such as polyethylene terephthalate and polyolefins such as polypropylene are preferred. Examples of heat-fusible components include polyesters, polyolefins, poly(ethylene-vinyl acetate), poly(ethylene-vinyl alcohol), etc., among which polyesters such as copolymerized polyethylene terephthalate and polyolefins such as polyethylene are preferred.

[0027] The heat-fusible fibers may be any one of side-by-side type heat-fusible fibers, core-sheath type heat-fusible fibers, and full-fusion type heat-fusible fibers, or may be two or three types. Examples of two types include a combination of side-by-side type heat-fusible fibers and core-sheath type heat-fusible fibers, a combination of side-by-side type heat-fusible fibers and full-fusion type heat-fusible fibers, or a combination of core-sheath type heat-fusible fibers and full-fusion type heat-fusible fibers.

[0028] When the heat-sealed fiber is in a wet state, it maintains the shape it had when it was mixed, but when the heat-sealed fiber is heated in the heat-drying process, it melts in part or in whole, and bonds with the fibrillated Lyocell fiber or the non-fibrillated non-heat-sealed fiber, which is the main fiber, or bonds with each other. The melted heat-sealed fiber contained in the filter material that has been subjected to the heat-drying process maintains the shape of the fiber, or although there are some broken parts, the shape of the fiber can be observed, and only the shape of a dot or line is observed. More specifically, when the fully melted heat-sealed fiber is heated, it melts in its entirety, and bonds with the fibrillated Lyocell fiber or the non-fibrillated non-heat-sealed fiber, or bonds with each other. The fully melted heat-sealed fiber that has been melted may have parts that are broken, crushed, bent, or otherwise deformed, but the shape of the fiber can be observed, and only the shape of a line or dot is observed. In this embodiment, the only difference between the fully melted heat-fusible fibers is that they are fibrous before and after the heating and drying process, whereas the fully melted heat-fusible fibers have traces of fibrous form, so the fully melted heat-fusible fibers before melting and the melted fully melted heat-fusible fibers are referred to as "fully melted heat-fusible fibers". When the side-by-side heat-fusible fibers or the core-sheath type heat-fusible fibers are heated, the melting part of the side-by-side heat-fusible fibers or the sheath part of the core-sheath type heat-fusible fibers melts and bonds with the fibrillated lyocell fibers, or the side-by-side heat-fusible fibers bond with each other, or the core-sheath type heat-fusible fibers bond with each other. In the melted side-by-side heat-fusible fibers or the melted core-sheath type heat-fusible fibers, the unmelted part of the side-by-side heat-fusible fibers or the core part of the core-sheath type heat-fusible fibers maintain the shape of the fibers. In this embodiment, since the side-by-side type heat-fusion fiber or the core-sheath type heat-fusion fiber is fibrous both before and after the heating and drying process, both the side-by-side type heat-fusion fiber or the core-sheath type heat-fusion fiber before melting and the melted side-by-side type heat-fusion fiber or the core-sheath type heat-fusion fiber are referred to as "side-by-side type heat-fusion fiber or the core-sheath type heat-fusion fiber". When the binder resin is heated by the heating and drying process, it melts or the emulsion particles fuse together to form a film, and it spreads over the entire filter medium and distributes in a flat shape.

[0029] The heat-sealed fibers in this embodiment are fibers with a fiber diameter of 35 μm or more, preferably 35 to 80 μm, and more preferably 38 to 50 μm. By having a fiber diameter of 35 μm or more, a filter medium having a high filtration efficiency and a long filtration life can be obtained when compared with a heat-sealed fiber having a smaller diameter at the same pressure loss. The reason for this is unclear, but it is presumed to be due to the difference in the effect on the fine network structure formed by the fibrillated lyocell fiber. On the other hand, if the fiber diameter exceeds 80 μm, there is a risk that sufficient strength of the filter medium cannot be obtained. Of the heat-sealed fibers contained in the filter medium for liquid filters in this embodiment, the heat-sealed fibers with a fiber diameter of 35 μm or more are preferably 80 mass% or more, more preferably 90 mass% or more, and even more preferably 100 mass%.

[0030] The liquid filter medium according to the present embodiment includes fibrillated lyocell fibers and heat-sealed fibers having a fiber diameter of 35 μm or more, and has a wet nonwoven fabric in which at least the fibrillated lyocell fibers form a network structure. Here, the term "at least" is defined because in the following several aspects, the fibrillated lyocell fibers are necessarily included as fibers constituting the network structure. In the first aspect, when the heat-sealed fibers are full-melt heat-sealed fibers and are melted as a whole to play a role of binding, a network structure of the fibrillated lyocell fibers exists in the wet nonwoven fabric. Here, the fibers are bonded together by the melted heat-sealed fibers. In the second aspect, when the heat-sealed fibers are full-melt heat-sealed fibers and are partially melted to play a role of binding while retaining the fiber shape, a network structure formed by the fibrillated lyocell fibers and the heat-sealed fibers that maintain a part of the fiber shape exists in the wet nonwoven fabric. Here, the fibers are bonded together by the remaining melted heat-sealed fibers. In the third embodiment, when non-fibrillated non-thermal fusion fibers are blended and the thermal fusion fibers are full-melt type thermal fusion fibers that melt as a whole and play a role of binding, a network structure formed by fibrillated lyocell fibers and non-thermal fusion fibers exists in the wet nonwoven fabric. Here, the fibers are bonded to each other by the melted thermal fusion fibers. In the fourth embodiment, when non-fibrillated non-thermal fusion fibers are blended and the thermal fusion fibers are full-melt type thermal fusion fibers that melt partially and play a role of binding while retaining the fiber shape, a network structure formed by fibrillated lyocell fibers, non-thermal fusion fibers, and thermal fusion fibers that maintain a part of the fiber shape exists in the wet nonwoven fabric. Here, the fibers are bonded to each other by the remaining melted thermal fusion fibers. In the fifth embodiment, when the thermal fusion fibers are composite type thermal fusion fibers, a network structure formed by fibrillated lyocell fibers and composite type thermal fusion fibers exists in the wet nonwoven fabric. In a sixth embodiment, when non-fibrillated non-thermal fusion fibers are blended and the thermal fusion fibers are composite thermal fusion fibers, a network structure formed by fibrillated lyocell fibers, non-thermal fusion fibers, and composite thermal fusion fibers exists in the wetlaid nonwoven fabric.The fiber diameter of the heat-fused fiber is the same or has an increase of up to +40% compared to before melting, in all cases where the fiber shape is maintained, the fiber shape can be observed although there are interrupted parts, and only the shape of dots or lines is observed.

[0031] The amount of heat-sealing fiber in this embodiment can be adjusted according to the properties required for the filter medium, but when the total fiber mass of the filter medium is 100 parts, it is preferably 20 to 80 parts, more preferably 30 to 70 parts. If the amount of heat-sealing fiber is too small, it may be difficult to obtain the strength of the filter medium required during processing and use. If the amount of heat-sealing fiber is too large, the amount of fibrillated lyocell is reduced, and it may be difficult to obtain sufficient filtering efficiency.

[0032] In this embodiment, non-fibrillated non-thermal fusion fibers can be used. The non-thermal fusion fibers referred to here are fibers made of non-thermal fusion components that do not melt when heated in the manufacturing process of the wet-laid nonwoven fabric. Examples of non-thermal fusion fibers include synthetic fibers such as polyester, polyolefin, polyamide, polyurethane, and polyacrylonitrile, natural fibers such as wood pulp, cotton linter pulp, hemp pulp, kenaf pulp, and mercerized pulp obtained by alkali treatment of wood pulp, and regenerated fibers such as viscose rayon fibers spun by the viscose method using cellulose as a raw material, and lyocell fibers spun by the organic solvent spinning method.

[0033] The non-thermofusible fibers in this embodiment preferably have a fiber diameter of 5 μm or more, more preferably 5 to 30 μm, and even more preferably 8 to 25 μm. If the fiber diameter is too small, the pressure loss may be too high. If the fiber diameter is too large, the filtration efficiency may be reduced.

[0034] The amount of non-thermofusible fibers in this embodiment can be adjusted as appropriate depending on the physical properties required for the filter medium, but is preferably 0 to 70 parts, and more preferably 5 to 50 parts, relative to 100 parts of the total fiber mass constituting the filter medium.

[0035] In this embodiment, a filter aid such as diatomaceous earth, celite, perlite, etc. may be blended by utilizing the powder retention ability of the fibrillated lyocell fiber, within a range that does not impair the effects of the present invention. These filter aids can be contained in an amount of about 1 to 40% by mass based on the fibrillated lyocell fiber.

[0036] The basis weight of the filter medium in this embodiment is not particularly limited, but is preferably 20 to 400 g / m 2 , more preferably 30 to 300 g / m 2 It is.

[0037] The filter medium of the present embodiment is manufactured by using a wet papermaking method.Here, the fiber that constitutes the filter medium is dispersed in water using a dispersing machine such as a pulper, the obtained raw material slurry is deposited on a wire and dehydrated to form a sheet, and the obtained wet sheet is dried using a dryer such as a hot air dryer or a cylinder dryer to obtain the filter medium as a dry sheet that becomes the filter medium for liquid filters.The drying temperature is preferably 80 to 180°C, more preferably 100 to 160°C.

[0038] In this embodiment, papermaking aids such as dispersants, defoamers, thickeners, retention aids, and paper strength agents may be used in the production using a wet papermaking method as long as the effects of the present invention are not impaired.

[0039] The liquid filter medium according to this embodiment can be used as a filter medium with the obtained wetlaid nonwoven fabric alone, but a reinforcing material such as a nonwoven fabric may be bonded to the wetlaid nonwoven fabric.

[0040] The method for producing a filter material for liquid filters according to the present embodiment includes the following aspects. (1) The fibrillated lyocell fiber has an average fiber diameter of 0.3 μm or more, a maximum fiber diameter of 8 μm or less, and a length-weighted average fiber length of 1 mm or more; (2) The wetlaid nonwoven fabric contains non-thermofusible fibers that are not fibrillated. (3) The amount of the fibrillated lyocell fiber is 20 to 80 parts per 100 parts of the total fiber mass constituting the filter medium; (4) The amount of the heat-fusible fiber is 20 to 80 parts per 100 parts of the total fiber mass constituting the filter medium. (5) The heat-fusible fiber is a composite heat-fusible fiber having a non-heat-fusible component that does not melt when heated and a heat-fusible component that melts when heated. (6) The amount of the non-thermofusible fiber is 0 to 70 parts per 100 parts of the total fiber mass constituting the filter medium; or (7) The non-thermofusible fibers have a fiber diameter of 5 μm or more. EXAMPLES

[0041] The present invention will be described below with reference to specific examples, but the present invention is not limited to these examples. In the examples, "parts" refers to the solid mass ratio of the fibers in the raw material slurry, and the total amount of all the fibers is taken as 100 parts.

[0042] <Example 1> Lyocell fiber (fineness 1.7 dtex (fiber diameter 12 μm), fiber length 4 mm, manufacturer: Lenzing AG) was beaten using a Niagara beater to obtain fibrillated lyocell fiber with an average fiber diameter of 0.7 μm, a maximum fiber diameter of 3.5 μm, and a length-weighted average fiber length of 1.1 mm. Next, 50 parts of the obtained fibrillated lyocell fiber and 50 parts of core-sheath type heat-fused PET fiber (product name: Melty 4080, fineness 17 dtx (fiber diameter 40 μm), fiber length 10 mm, manufacturer: Unitika Co., Ltd.) were used as raw fibers and disintegrated in water in a standard disintegrator to obtain a raw material slurry. The obtained raw material slurry was made into paper in a manual papermaking device to obtain a wet paper. The obtained wet paper was dried in a rotary dryer at 130° C. and had a basis weight of 140 g / m2 As a result, a filter medium for liquid filters of 100 g was obtained.

[0043] <Example 2> As raw fibers, 50 parts of the fibrillated lyocell fiber obtained in Example 1, 40 parts of core-sheath type heat-fused PET fiber (product name: Melty 4080, fineness 17 dtx (fiber diameter 40 μm), fiber length 10 mm, manufacturer: Unitika Co., Ltd.), and 10 parts of non-heat-fused PET fiber (product name: N081, fineness 1.6 dtx (fiber diameter 12 μm), fiber length 5 mm, manufacturer: Unitika Co., Ltd.) as non-fibrillated non-heat-fused fiber were used, and a 141 g / m2 spunbonded woven fabric was produced in the same manner as in Example 1. 2 As a result, a filter medium for liquid filters of 100 g was obtained.

[0044] <Example 3> As raw fibers, 50 parts of the fibrillated lyocell fiber obtained in Example 1, 40 parts of core-sheath type heat-bonded PET fiber (product name: Melty 4080, fineness 17 dtx (fiber diameter 40 μm), fiber length 10 mm, manufacturer: Unitika Ltd.), and 10 parts of lyocell fiber (fineness 1.7 dtx (fiber diameter 12 μm), fiber length 4 mm, manufacturer: Lenzing AG) as a non-fibrillated non-heat-bonded fiber were used, and a 142 g / m2 spunbonded woven fabric was produced in the same manner as in Example 1. 2 As a result, a filter medium for liquid filters of 100 g was obtained.

[0045] <Example 4> As raw fibers, 25 parts of the fibrillated lyocell fiber obtained in Example 1 and 75 parts of core-sheath type heat-fused PET fiber (product name: Melty 4080, fineness 17 dtx (fiber diameter 40 μm), fiber length 10 mm, manufacturer: Unitika Co., Ltd.) were used, and a 142 g / m2 spunbonded woven fabric was prepared in the same manner as in Example 1. 2 As a result, a filter medium for liquid filters of 100 g was obtained.

[0046] <Example 5> As raw fibers, 75 parts of the fibrillated lyocell fiber obtained in Example 1 and 25 parts of core-sheath type heat-bonded PET fiber (product name: Melty 4080, fineness 17 dtx (fiber diameter 40 μm), fiber length 10 mm, manufacturer: Unitika Co., Ltd.) were used, and a 140 g / m2 spunbonded woven fabric was prepared in the same manner as in Example 1. 2 As a result, a filter medium for liquid filters of 100 g was obtained.

[0047] <Example 6> As raw fibers, 20 parts of the fibrillated lyocell fiber obtained in Example 1, 20 parts of core-sheath type heat-bonded PET fiber (product name: Melty 4080, fineness 17 dtx (fiber diameter 40 μm), fiber length 10 mm, manufacturer: Unitika Ltd.), and 60 parts of lyocell fiber (fineness 1.7 dtx (fiber diameter 12 μm), fiber length 4 mm, manufacturer: Lenzing AG) as a non-fibrillated non-heat-bonded fiber were used, and a 140 g / m2 spunbonded woven fabric was produced in the same manner as in Example 1. 2 As a result, a filter medium for liquid filters of 100 g was obtained.

[0048] <Comparative Example 1> As raw fibers, 50 parts of the fibrillated lyocell fiber obtained in Example 1 and 50 parts of core-sheath type heat-fused PET fiber (product name: Melty 4080, fineness 1.7 dtx (fiber diameter 13 μm), fiber length 5 mm, manufacturer: Unitika Co., Ltd.) were used, and a 140 g / m2 spunbonded woven fabric was prepared in the same manner as in Example 1. 2 As a result, a filter medium for liquid filters of 100 g was obtained.

[0049] <Comparative Example 2> As raw fibers, 50 parts of the fibrillated lyocell fiber obtained in Example 1, 40 parts of core-sheath type heat-fused PET fiber (product name: Melty 4080, fineness 1.7 dtx (fiber diameter 13 μm), fiber length 5 mm, manufacturer: Unitika Co., Ltd.), and 10 parts of non-heat-fused PET fiber (product name: N081, fineness 1.6 dtx (fiber diameter 12 μm), fiber length 5 mm, manufacturer: Unitika Co., Ltd.) as a non-heat-fused fiber that was not fibrillated were used, and a 141 g / m2 basis weight was produced in the same manner as in Example 1. 2 As a result, a filter medium for liquid filters of 100 g was obtained.

[0050] <Comparative Example 3> As raw fibers, 50 parts of the fibrillated lyocell fiber obtained in Example 1, 40 parts of core-sheath type heat-bonded PET fiber (product name: Melty 4080, fineness 1.7 dtx (fiber diameter 13 μm), fiber length 5 mm, manufacturer: Unitika Ltd.), and 10 parts of lyocell fiber (fineness 1.7 dtx (fiber diameter 12 μm), fiber length 4 mm, manufacturer: Lenzing AG) as a non-fibrillated non-heat-bonded fiber were used, and a 140 g / m2 basis weight was produced in the same manner as in Example 1. 2 As a result, a filter medium for liquid filters of 100 g was obtained.

[0051] <Comparative Example 4> As raw fibers, 25 parts of the fibrillated lyocell fiber obtained in Example 1 and 75 parts of core-sheath type heat-bonded PET fiber (product name: Melty 4080, fineness 1.7 dtx (fiber diameter 13 μm), fiber length 5 mm, manufacturer: Unitika Co., Ltd.) were used, and a 141 g / m2 spunbonded woven fabric was prepared in the same manner as in Example 1. 2 As a result, a filter medium for liquid filters of 100 g was obtained.

[0052] <Comparative Example 5> As raw fibers, 75 parts of the fibrillated lyocell fiber obtained in Example 1 and 25 parts of core-sheath type heat-bonded PET fiber (product name: Melty 4080, fineness 1.7 dtx (fiber diameter 13 μm), fiber length 5 mm, manufacturer: Unitika Co., Ltd.) were used, and a 142 g / m2 spunbonded woven fabric was prepared in the same manner as in Example 1. 2 As a result, a filter medium for liquid filters of 100 g was obtained.

[0053] <Comparative Example 6> As raw fibers, 20 parts of the fibrillated lyocell fiber obtained in Example 1, 20 parts of core-sheath type heat-bonded PET fiber (product name: Melty 4080, fineness 1.7 dtx (fiber diameter 13 μm), fiber length 5 mm, manufacturer: Unitika Ltd.), and 60 parts of lyocell fiber (fineness 1.7 dtx (fiber diameter 12 μm), fiber length 4 mm, manufacturer: Lenzing AG) as a non-fibrillated non-heat-bonded fiber were used, and a 140 g / m2 basis weight was produced in the same manner as in Example 1. 2 As a result, a filter medium for liquid filters of 100 g was obtained.

[0054] The filter media for liquid filters obtained in the examples and comparative examples were evaluated by the following methods.

[0055] <Basic weight [g / m 2 ]> Basis weight was measured according to JIS P 8124:2011.

[0056] <Thickness [mm]> The thickness was measured using a digital thickness gauge (manufacturer: Sagawa Corporation) in accordance with JIS P 8118; 1998. The measurement pressure was 50 kPa.

[0057] <Density [g / cm 3 ]> The density was measured according to JIS P 8118;1998.

[0058] <Pressure loss [Pa]> Pressure loss is for an effective area of ​​100 cm 2 The differential pressure when air was passed through the liquid filter medium at a surface velocity of 5.3 cm / sec was measured using a differential pressure gauge (product name: Manostar Gauge, manufacturer: Yamamoto Electric Works, Ltd.).

[0059] <Filtration efficiency [%]> Filtration efficiency is 12.5 cm2 effective area 2 A water dispersion (hereinafter referred to as the stock solution) of test particles (product name: Green Densic GC#8000, manufacturer: Showa Denko Co., Ltd.) with a mass concentration of 100 ppm was passed through the filter medium for liquid filters at a filtration flow rate of 20 ml / min, and 50 ml of filtrate was collected 1 minute after the start of the flow. The turbidity [%] of the stock solution and the filtrate was measured using a turbidity meter (product name: COH400, manufacturer: Nippon Denshoku Kogyo Co., Ltd.), and the filtration efficiency was calculated using the formula shown in Equation 1.

[0060] (Number 1) Filtration efficiency [%] = (raw solution turbidity [%] - filtrate turbidity [%]) / (raw solution turbidity [%]) x 100

[0061] <Filtration life [min]> In the measurement of the filtration efficiency, the upstream pressure of the filter medium was measured using a pressure gauge (product name: KDM30, manufacturer: Krone Co., Ltd.), and the time required for the pressure to reach 100 kPa from the start of liquid passage was measured. <Tensile strength [kN / m]> The tensile strength was measured using a universal testing machine (product name: Autograph AGS-X, manufacturer: Shimadzu Corporation) in accordance with JIS P 8113-2006 "Paper and paperboard-Test methods for tensile properties-Part 2: Constant speed extension method."

[0062] The evaluation results of the filter media for liquid filters performed by the above-mentioned methods are shown in Tables 1 and 2. Based on the results of Examples 1 to 6 and Comparative Examples 1 to 6, the relationship between pressure loss and filtration efficiency is shown in Figure 1, and the relationship between pressure loss and filtration life is shown in Figure 2.

[0063] [Table 1]

[0064] [Table 2]

[0065] From the results in Tables 1 and 2 and Figs. 1 and 2, it was found that in the relationship between pressure loss and filtration efficiency and between pressure loss and filtration life, the Examples had higher filtration efficiency and longer filtration life than the Comparative Examples.

Claims

1. A filter medium for liquid filters, comprising a wet-laid nonwoven fabric containing fibrillated lyocell fibers and heat-fused fibers having a fiber diameter of 35 μm or more, and in which at least the fibrillated lyocell fibers form a network structure.

2. 2. The filter medium for liquid filters according to claim 1, wherein the fibrillated lyocell fibers have an average fiber diameter of 0.3 μm or more, a maximum fiber diameter of 8 μm or less, and a length-weighted average fiber length of 1 mm or more.

3. 3. The filter medium for liquid filters according to claim 1, wherein the wetlaid nonwoven fabric contains non-thermally fused fibers that are not fibrillated.

4. 4. The filter medium for liquid filters according to claim 1, wherein the amount of the fibrillated lyocell fibers is 20 to 80 parts per 100 parts of the total fiber mass constituting the filter medium.

5. 5. The filter medium for liquid filters according to claim 1, wherein the blending amount of the heat-fusible fibers is 20 to 80 parts per 100 parts of the total fiber mass constituting the filter medium.

6. The heat-fusible fiber is a composite type heat-fusible fiber having a non-heat-fusible component that does not melt when heated and a heat-fusible component that melts when heated. The filter material for liquid filters according to any one of claims 1 to 5.

7. 4. The filter medium for liquid filters according to claim 3, wherein the blending amount of the non-thermal fusible fibers is a maximum of 70 parts per 100 parts of the total fiber mass constituting the filter medium.

8. A filter material for liquid filters as described in claim 1 or 2, characterized in that the fibers constituting the filter material include only the fibrillated lyocell fibers and the heat-fused fibers having a fiber diameter of 35 μm or more.

9. 8. The filter medium for liquid filters according to claim 3 or 7, wherein the non-thermal fusible fibers have a fiber diameter of 5 μm or more.

10. A step of preparing a raw material slurry containing fibrillated lyocell fiber and a heat-fusible fiber having a fiber diameter of 35 μm or more; forming a wet sheet from the raw slurry; and drying the wet sheet to obtain a dry sheet which will become a filter material for liquid filters.

11. A method for manufacturing a filter material for liquid filters as described in Claim 10, characterized in that the heat-sealed fibers are fibers containing a heat-sealed component that melts when heated in the process of obtaining the dry sheet.

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