Flow path material for liquid separation device

Abstract

The present invention provides a flow path material for liquid separation devices, the flow path material being not susceptible to collapsing when a high pressure is applied thereto, while being suppressed in decrease in the flow rate.　A flow path material for liquid separation devices, the flow path material being formed of a tricot fabric that contains thermoplastic sheath-core composite fibers that are configured from two kinds of polyester resins having different melting or softening points, wherein: with respect to the thermoplastic sheath-core composite fibers, a high-melting-point component is arranged in the core part, and a low-melting-point component is arranged in the sheath part; the tricot fabric is obtained by rigidifying thermoplastic sheath-core composite fibers in a tricot knitted fabric by bonding the thermoplastic sheath-core composite fibers to each other, the tricot knitted fabric being weaved by a knitting machine having two reeds, using the thermoplastic sheath-core composite fibers for the front yarns and the back yarns; the wale density of the tricot fabric is 45-70 wales / inch (2.54 cm), and the course density of the tricot fabric is 40-70 courses / inch (2.54 cm); and if the tricot fabric is heat-pressed at 90°C and 4.0 MPa for three minutes, the change ratio in the thickness of the tricot fabric before and after pressing is 10% or less.

Description

Technical Field

[0001] The present invention relates to a flow path material for a liquid separation device that supports the back surface side of a semipermeable membrane that receives pressure from a stock solution in a liquid separation device used for concentrating and separating various liquids.

Background Art

[0002] As a liquid separation device using a semipermeable membrane, generally, the semipermeable membrane is formed in a cylindrical shape, and a flow path material that forms a flow path for passing the permeate inside the membrane by applying pressure from the outside is inserted, and the end of the flow path material is fixed to a hollow shaft and wound. A typical one uses a spiral-type liquid separation membrane module. In such a liquid separation membrane module, a stock solution at a high pressure higher than the reverse osmotic pressure is passed outside the membrane, and the permeate that has passed through the membrane is taken out through the inside of the membrane. Since the cylindrical separation membrane is pressurized from the outside at a high pressure, the flow path material inserted as the flow path for the permeate will be crushed, deteriorating the liquid flow. Therefore, generally, the flow path material itself is made rigid so that it can withstand deformation even when pressurized from the outside inside the separation membrane. Such liquid separation membrane modules have been put into practical use as water treatment devices for boiler water pretreatment, wastewater reuse, seawater desalination, and production of ultrapure water.

[0003] Conventionally, fabrics such as woven fabrics and knitted fabrics have been used for such flow path materials for permeated water, and particularly those having a structure with fine grooves on the surface have been used. These fabrics were impregnated with epoxy resin, melamine resin, etc. to be rigid so as not to deform even by the pressure applied to the stock solution through the membrane. In that case, in order not to be crushed even at a high pressure, it was necessary to adhere resin up to nearly half of the weight of the fabric. However, problems have occurred due to elution of the impregnated resin in applications that require high-purity permeated water or applications that treat high-temperature liquids. In particular, when the stock solution to be treated is a food liquid or a medical liquid, sterility is required. Therefore, in order to prevent contamination by miscellaneous bacteria before or after the start of the membrane separation treatment, sterilization with hot water is performed, and at that time, the elution of the resin impregnated in the flow path material has been a problem.

[0004] To solve the aforementioned problems, a channel material has been proposed in which thermoplastic synthetic fibers consisting of low-melting-point and high-melting-point components are knitted on a three-reed tricot knitting machine, and the ridges are made of thermoplastic synthetic fibers whose fineness is 1.2 times or more thicker than the fibers that make up the base fabric, and the knitted fabric is then heat-treated to make it rigid (Patent Document 1). However, this channel material has the problem of low productivity and high cost because it uses a three-reed machine and thermoplastic synthetic fibers of fine and thick fines. There was also the problem that the thickness of the channel material could not be reduced.

[0005] To solve the problems described in Patent Document 1, techniques have been proposed to create a back half structure using a tricot knit fabric made of core-sheath composite fibers with a two-reed (Patent Document 2), and to set the well density of the tricot knit fabric, made of core-sheath composite fibers with a total fineness of 30 to 90 dtex, to 35 to 45 threads / inch (2.54 cm) and the coarse density to 35 to 55 threads / inch (2.54 cm) (Patent Document 3).

[0006] Furthermore, since the osmotic pressure of 3.5% by mass sodium chloride in seawater is 2.8 MPa, considering the increase in salinity due to the cross-flow method in reverse osmosis desalination, it is necessary to pressurize the spiral element with a pressure of at least 4-6 MPa. In that case, there is a concern that the support structure coated with the membrane will collapse, and the channel material for the permeate water will collapse due to prolonged pressurization, resulting in a decrease in flow rate. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Special Publication No. 3-66008 [Patent Document 2] Patent No. 3559475 [Patent Document 3] WO2017 / 131031 publication [Overview of the project] [Problems that the invention aims to solve]

[0008] However, both Patent Documents 2 and 3 have the drawback that when used as flow channel materials for high-pressure operation, the flow channel becomes blocked by the pressure, resulting in insufficient flow rate. Furthermore, the three prior studies mentioned above all describe how, by knitting thermoplastic core-sheath composite fibers in a single tricot structure and then heat-setting them, the entire tricot fabric is hardened, preventing the flow path from becoming blocked and the flow rate from decreasing even when pressurized with the reverse osmotic pressure required for seawater desalination. However, none of these studies compared or examined the maintenance of the flow path cross-sectional area under actual reverse osmotic pressure. In other words, the susceptibility of the flow channel material to crushing under pressure was not considered. Furthermore, while there is a method for inspecting the thickness of the flow channel material after pressurization at room temperature, this requires prolonged pressurization, and conducting multiple inspections would be quite time-consuming and costly.

[0009] Furthermore, when testing the ease of crushing at room temperature, it was difficult to verify the ease of crushing because the material used for the flow channel is composed of thermoplastic polymers, and therefore exhibits behavior of returning to its original shape when the pressure is removed. Therefore, it was not easy to find a configuration and conditions for the flow channel material that would be least likely to collapse when subjected to high pressure, and would minimize the reduction in flow rate.

[0010] The present invention has been made to solve the aforementioned problems, and its objective is to provide a flow channel material for a liquid separation device that is less likely to collapse when high pressure is applied to the flow channel material and that reduces the decrease in flow rate. [Means for solving the problem]

[0011] Until now, there have been no studies comparing and examining the maintenance of the cross-sectional area of ​​a flow path and the flow rate under conditions equivalent to actual reverse osmosis. The inventors have discovered a method for easily determining the degree of collapse of a flow channel material when subjected to high pressure for a long period of time. Specifically, by measuring the thickness of the flow channel material before and after pressurizing the resin constituting the flow channel material for permeate water at a temperature above its glass transition temperature, the ease with which it collapses can be easily measured. Furthermore, using this method, the inventors have identified the configuration and conditions of the flow channel material that are least likely to collapse and result in the least reduction in flow rate when subjected to high pressure, leading to the present invention.

[0012] In other words, the object of the present invention is a flow channel material for a liquid separation device made of a tricot fabric containing thermoplastic core-sheath composite fibers composed of two types of polyester resins with different melting points, wherein the glass transition temperatures of the two types of polyester resins are 90°C or lower, and in the thermoplastic core-sheath composite fibers, the high-melting-point component is arranged in the core and the low-melting-point component is arranged in the sheath, and the high-melting-point component is polyethylene terephthalate, and A high melting point component and the low melting point component This is achieved by a fluid channel material for a liquid separation device, wherein the melting point difference of the material is 60°C or more, the thermoplastic core-sheath composite fiber is a core-sheath type composite multifilament with a fineness of 44 dtex or more, the tricot fabric is a tricot knit fabric knitted using the thermoplastic core-sheath composite fiber as the front yarn and back yarn on a two-reed knitting machine, the thermoplastic core-sheath composite fiber is bonded to each other and made rigid, the well density is 45-70 threads / inch (2.54 cm), the coarse density is 40-70 threads / inch (2.54 cm), the thickness is 0.2 mm or more, and the percentage change in thickness of the tricot fabric before and after hot pressing at 90°C and 4.0 MPa for 3 minutes is 10% or less.

[0013] Furthermore, it is preferable that the total fineness of the front and back yarns of the thermoplastic core-sheath composite fiber constituting the tricot fabric is 110 to 200 dtex, the difference in runner length between the front and back yarns is 5 cm or less, and the thickness of the tricot fabric is 0.2 to 0.3 mm.

[0014] Furthermore, in tricot fabric, one of the two reeds forms the sinker loop portion, which is the base fabric (back yarn), and the other reed forms the needle loop portion, which is the convex portion (front yarn). Preferably, the ratio of the width of the portion between the convex portions (groove width) to the width of the convex portions (ridge width) (groove width / ridge width) is 0.4 to 0.7.

[0015] Furthermore, in the thermoplastic core-sheath composite fibers that make up the tricot, it is preferable that the difference in total fineness between the convex portion (front yarn) and the base material portion (back yarn) is 20 dtex or more. [Effects of the Invention]

[0016] The flow channel material for liquid separation devices of the present invention is a flow channel material for liquid separation devices that has high compressive resistance, making it difficult to collapse when high pressure is applied to the flow channel material, and which also has low flow rate reduction. [Modes for carrying out the invention]

[0017] The flow channel material for the liquid separation apparatus of the present invention consists of a tricot fabric containing thermoplastic core-sheath composite fibers composed of two types of polyester resins with different melting or softening points. In the thermoplastic core-sheath composite fiber described above, the high-melting-point component is located in the core, and the low-melting-point component is located in the sheath. The difference in melting points between the two components is preferably 60°C or higher. In this invention, the difference between the melting point and the softening point in the case where there is no melting point but there is a softening point is also referred to as the melting point difference.

[0018] Preferred polyesters as the low melting point component include those mainly composed of terephthalic acid and ethylene glycol, and as copolymerization components, aliphatic dicarboxylic acids such as oxalic acid, malonic acid, azelaic acid, adipic acid, and sebacic acid, aromatic dicarboxylic acids such as phthalic acid, isophthalic acid, and naphthalenedicarboxylic acid, and / or alicyclic dicarboxylic acids such as hexahydroterephthalic acid, and one or more combinations of glycols such as aliphatic, alicyclic, or aromatic diols including diethyl glycol, polyethylene glycol, propylene glycol, hexanediol, paraxylene glycol, and bis-hydroxyethoxyphenylpropane, contained in a predetermined ratio, and a copolymerized ester added with oxyacids such as parahydroxybenzoic acid at a ratio of 50 mol% or less as desired is suitable.

[0019] Among these, in particular, a polyester obtained by adding and copolymerizing isophthalic acid to terephthalic acid and ethylene glycol is suitable. And in such an isophthalic acid copolymerized polyester, a copolymerized product with 10 to 30 mol% of the isophthalic acid component is preferable from the viewpoints of ease of heat-sealing and knitting property. By changing the copolymerization ratio of the above component monomers, it may be adjusted to a desired softening point.

[0020] Examples of the high melting point component include homopolyesters such as polyethylene terephthalate, polybutylene terephthalate, and polytrimethylene terephthalate.

[0021] In the present invention, a core-sheath type composite polyester multifilament using an isophthalic acid copolymerized polyester as the low melting point component of the sheath part and a homopolyester as the high melting point component of the core part is optimal. Also, linear fatty acid diols such as 1,4-butanediol, 1,6-hexanediol, and 1,9-nonanediol may be used together with isophthalic acid. The ratio of the core part / sheath part is preferably set to 5 / 1 to 1 / 5 on a volume basis, and particularly preferably set to 3 / 1 to 1 / 2.

[0022] In the core-sheath type composite multifilament, the fineness is preferably 44 to 110 dtex, the number of filaments is preferably 18 to 36, and the fineness of a single filament is preferably 1.2 to 6.2 dtex. When the fineness is less than 44 dtex, the yarn is too thin and is likely to be crushed under the pressure applied from above the loop and cannot withstand the pressure. When the total fineness exceeds 110 dtex, the fabric thickness becomes large, the fabric becomes hard, and it tends to be unsuitable as a flow path material for permeating water.

[0023] The tricot fabric in the present invention is a tricot knitted fabric knitted using the thermoplastic core-sheath composite fiber as the front yarn and the back yarn of a two-bar knitting machine, in which the thermoplastic core-sheath composite fibers are adhered to each other to be rigidified. The thermoplastic core-sheath composite fibers used for the front yarn and the back yarn may be fibers having the same or different core-sheath component compositions, but it is preferable that they have the same melting point or softening point.

[0024] It is preferable that the well density of the tricot fabric is 45 to 70 per inch (2.54 cm) and the course density is 40 to 70 per inch (2.54 cm). When the well density is 45 or more per inch (2.54 cm) and the course density is 40 or more per inch (2.54 cm), there are many convex portions of the needle loops in a certain area, and it tends to be resistant to the pressure applied from above the loop and not easily crushed. When the well density is 70 or less per inch and the course density is 70 or less per inch, the fabric thickness does not increase, the fabric does not easily become hard, and it is suitable as a flow path material for permeating water.

[0025] Also, the product of the well density and the course density of the tricot fabric is preferably 2700 or more, more preferably 3000 or more. When the product of the well density and the course density of the tricot fabric is less than 2700, the convex portions of the needle loops in a certain area of the tricot fabric decrease, and it tends to be unable to withstand the pressure applied from above the loop and be easily crushed. Furthermore, it is preferable that the product of the well density and coarse density of the tricot fabric be 4900 or less. When the product of the well density and coarse density of tricot fabric exceeds 4900, the fabric tends to be thicker and harder, making it unsuitable as a channeling material for permeable water.

[0026] Examples of knitting structures for tricot fabric include single tricot knits such as double denby knit, back half knit, and half tricot knit, with the double denby knit being preferred. In double tricot knitting, the fabric is thick and stiff, making it unsuitable as a channel material for permeable water.

[0027] Furthermore, the total fineness of the front and back yarns of the thermoplastic core-sheath composite fiber constituting the tricot fabric is preferably 110 to 200 dtex. If the total fineness of the front and back threads of the thermoplastic core-sheath composite fibers that make up the tricot fabric is less than 110 dtex, the strength of the convex portion of the needle loop will be weak, and it will tend to collapse easily when pressure is applied from above the loop. Also, if the total fineness of the front and back threads of the thermoplastic core-sheath composite fibers that make up the tricot fabric exceeds 200 dtex, the fabric will be thick and stiff, and will tend to become unsuitable as a channel material for permeable water.

[0028] The difference in runner length between the front and back threads of the tricot fabric is preferably 5 cm or less. If the difference in runner length between the front and back threads of tricot fabric exceeds 5 cm, the balance between the sinker loop portion (the base fabric) and the needle loop portion (the raised portion) becomes poor, which can cause the tricot fabric to tear during heat setting or make it impossible to adjust to the desired texture.

[0029] Furthermore, the thickness of the tricot fabric is preferably 0.2 to 0.3 mm. If the thickness of the tricot fabric is less than 0.2 mm, there will be insufficient void space between the sinker loop portion (the base tissue) and the needle loop portion (the convex part) of the tricot channel material, making it impossible to ensure sufficient flow rate. If the thickness of the tricot fabric exceeds 0.3 mm, the fabric becomes too thick and rigid, making it less suitable as a channel material for permeate water.

[0030] In the thermoplastic core-sheath composite fibers that make up the tricot fabric, it is preferable that the difference in total fineness between the front yarn and the back yarn is 20 dtex or more. If the difference in total fineness between the front yarn and the back yarn is less than 20 dtex, the strength of the convex part of the needle loop and the strength of the base fabric of the sinker loop will be weakened, making the loop prone to collapsing when pressure is applied from above. Furthermore, it is preferable that the difference in total fineness between the front yarn and the back yarn be 70 dtex or less. Note that the total fineness of the front yarn and the total fineness of the back yarn can be higher or lower.

[0031] When the tricot fabric is heat-pressed at 90°C and 4.0 MPa for 3 minutes, the change in thickness of the tricot fabric before and after pressure application must be 10% or less. When tricot fabric is heat-pressed at 90°C and 4.0 MPa for 3 minutes, a change in thickness of the tricot fabric before and after pressure application exceeding 10% indicates that the strength of the convex portion of the needle loop is weak, and that it is easily crushed when pressure is applied from above. Furthermore, it is preferable that the percentage change in the thickness of the tricot fabric before and after applying pressure when heat-pressed at 90°C and 4.0 MPa for 3 minutes is 6% or less. Furthermore, regarding the resin constituting the channel material for permeate water, the strain caused by the pressure can be fixed by applying pressure to the resin at a temperature above its glass transition temperature. By utilizing this, the ease of crushing can be easily measured by measuring the thickness of the channel material before and after pressurization. In this invention, a polyester resin is used, and since the glass transition temperature of polyester resin is approximately 80°C, hot pressing is performed at 90°C.

[0032] In the present invention, the tricot fabric uses two reeds, with one reed forming the sinker loop portion (ground fabric) and the other reed forming the needle loop portion (convex portion). Preferably, the ratio of the width of the portion between the convex portions (groove width) to the width of the convex portion (ridge width) (groove width / ridge width) is 0.4 to 0.7. In this case, preferably the groove width is 100 to 200 μm and the ridge width is 150 to 350 μm. If the ratio of the width of the space between the convex parts of the needle loop (groove width) to the width of the convex part (ridge width) (groove width / ridge width) is less than 0.4, there will be insufficient void space between the ground tissue portion of the sinker loop portion of the tricot flow channel material and the convex portion of the needle loop portion, making it impossible to secure sufficient flow rate. If the ratio of the width of the space between the convex parts of the needle loop (groove width) to the width of the convex part (ridge width) (groove width / ridge width) exceeds 0.7, the strength of the convex portion of the needle loop will weaken, making it prone to collapsing when pressure is applied from above. The width of the portion between the convex parts of the needle loop (groove width) and the width of the convex part (ridge width) can be adjusted according to the knitting density, the total fineness of the thermoplastic core-sheath composite fiber used, and the heat-setting conditions to obtain the desired width and ratio.

[0033] The tricot fabric according to the present invention is manufactured, for example, by the following method. A tricot knit fabric is produced by using thermoplastic core-sheath composite fibers as the front and back yarns of a two-reed tricot knitting machine. The resulting tricot knit fabric is heat-set to bond the thermoplastic core-sheath composite fibers together, making it rigid and obtaining a tricot fabric. The gauge of the tricot knit fabric is preferably 28 or higher. Furthermore, the heat setting can be performed using a pin tenter heat treatment machine, a cylinder dryer, or the like.

[0034] The above tricot fabric can be suitably used as a permeable channel material for a liquid separation device. The channel material for a liquid separation device of the present invention does not collapse even when pressurized at a high pressure of 4 to 6 MPa for a long period of time, and exhibits minimal flow rate reduction. [Examples]

[0035] The present invention will be described in detail below with reference to examples, but the present invention is not necessarily limited thereto. The measurement methods for various properties and the evaluation criteria for the tricot fabric used in these examples are as follows.

[0036] (1) Percentage change in thickness of tricot fabric before and after heat pressing (%) Using a tabletop hot press (Techno Supply Co., Ltd., small press model G-12), tricot fabric was heat-pressed at 90°C and 4.0 MPa for 3 minutes. The thickness of the tricot fabric was measured before and after pressurization, and the percentage change in thickness was calculated using the following formula. Percentage change in thickness (%) = {(Thickness before pressurization - Thickness after pressurization) / Thickness before pressurization} × 100

[0037] (2) Groove width (μm), ridge width (μm) of tricot fabric Using an optical microscope, planar and cross-sectional photographs of the tricot fabric were taken, and the groove width and ridge width were measured.

[0038] (3) Thickness of tricot fabric (mm) The thickness of the tricot fabric was measured using a Peacock Dial Gauge (H-30 model, manufactured by Ozaki Seisakusho Co., Ltd., with a 0.01 division scale and a 30mm diameter probe).

[0039] (4) Density (books / inch (2.54 cm)) The number of courses and welts per inch (2.54 cm) of tricot fabric were measured according to the knitting density specified in JIS L 1096 8.6.2.

[0040] (5) Flow rate reduction rate Thickness: 100 μm, Density: 0.8 g / cm³ 2 A liquid separation membrane was prepared by forming a 50 μm thick porous cellulose acetate membrane on a polyester wet nonwoven fabric, and a 700 μm thick polypropylene net was prepared as a channel material for the raw water. A channel forming material made of tricot fabric was placed on the permeable surface of the liquid separation membrane, and the channel material for the raw water was placed on the raw water side to create a spiral-shaped liquid separation membrane module. Raw water (a 3.5 wt% concentration NaCl aqueous solution) was then supplied to the liquid separation membrane module at a pressure of 5 MPa, and the system was operated to achieve a salt removal rate of 99.5% or more. The rate of decrease in permeate flow rate after 240 hours of use was measured.

[0041] [Example 1] A thermoplastic core-sheath composite fiber A (84 dtex / 24 f) was obtained by copolymerizing polyethylene terephthalate (melting point: 260°C) with 25% mol% isophthalic acid as the acid component of polyethylene terephthalate to obtain a low-melting-point copolymer polyester (melting point: 190°C) as the sheath, with a core / sheath ratio of 7 / 3 by volume. The composite fiber was used as the front yarn, and a thermoplastic core-sheath composite fiber B (56 dtex / 24 f) with a similar resin combination was used as the back yarn, and knitted into a double Denby structure (closed stitches) on a 36-gauge two-reed tricot knitting machine.

[0042] The obtained tricot knit fabric was heat-set in a pin tenter set to 200°C for 1 minute to obtain a tricot fabric channel material with a well density of 50 threads / inch (2.54 cm) and a coarse density of 60 threads / inch (2.54 cm). The percentage change in thickness of the obtained tricot fabric before and after heat pressing was 5.6%.

[0043] [Example 2] A flow channel material was obtained in the same manner as in Example 1, except that the well density of the processed roll after heat setting for 1 minute in a pin tenter was 70 threads / inch (2.54 cm) and the coarse density was 45 threads / inch (2.54 cm).

[0044] The percentage change in thickness of the obtained tricot fabric before and after heat pressing was 5.7%.

[0045] [Example 3] A channel material was obtained in the same manner as in Example 1, except that the gauge of the tricot knitting machine was set to 28 gauge, and the well density of the processed roll after heat setting for 1 minute with a pin tenter was 45 threads / inch (2.54 cm) and the coarse density was 70 threads / inch (2.54 cm).

[0046] The percentage change in thickness of the obtained tricot fabric before and after heat pressing was 8.5%.

[0047] [Example 4] A channel material was obtained in the same manner as in Example 1, except that the knitted structure was a half-tricot structure.

[0048] The percentage change in thickness of the obtained tricot fabric before and after heat pressing was 8.7%.

[0049] [Example 5] A channel material was obtained in the same manner as in Example 1, except that the knitted structure was a back half structure.

[0050] The percentage change in thickness of the obtained tricot fabric before and after heat pressing was 7.1%.

[0051] [Comparative Example 1] A flow channel material was obtained in the same manner as in Example 1, except that the well density of the processed material after heat setting in a pin tenter for 1 minute was 75 threads / inch (2.54 cm) and the coarse density was 35 threads / inch (2.54 cm).

[0052] The percentage change in thickness (%) before and after heat pressing of the resulting tricot fabric was 10.6%.

[0053] [Comparative Example 2] A flow channel material was obtained in the same manner as in Example 1, except that the well density of the processed material after heat setting in a pin tenter for 1 minute was 35 threads / inch (2.54 cm) and the coarse density was 75 threads / inch (2.54 cm).

[0054] The percentage change in thickness (%) before and after heat pressing of the resulting tricot fabric was 13.1%.

[0055] [Table 1]

[0056] <Result> [Examples 1-5] The percentage change in thickness before and after heat pressing of the tricot fabric was 10.0% or less, and the rate of decrease in flow rate was also 5% or less. When evaluated as a flow channel material, it was at a level that allowed for stable use over a long period of time.

[0057] [Comparative Examples 1-2] The percentage change in thickness (%) before and after heat pressing of the tricot fabric exceeded 10%. Furthermore, the flow rate reduction rate exceeded 5%, and when evaluated as a flow channel material, the flow rate was too low to be suitable for practical use.

Claims

1. A flow channel material for a liquid separation device, comprising a tricot fabric containing thermoplastic core-sheath composite fibers composed of two types of polyester resins with different melting points, wherein the glass transition temperatures of the two types of polyester resins are 90°C or lower, and in the thermoplastic core-sheath composite fibers, the high-melting-point component is arranged in the core and the low-melting-point component is arranged in the sheath, the high-melting-point component is polyethylene terephthalate, the difference in melting points between the high-melting-point component and the low-melting-point component is 60°C or higher, and the thermoplastic core-sheath composite fiber is a core-sheath type composite multifilament with a fineness of 44 dtex or higher. The tricot fabric is a flow channel material for a liquid separation device, wherein the thermoplastic core-sheath composite fibers are bonded to each other and made rigid in a tricot knitted fabric knitted on a two-reed knitting machine using the thermoplastic core-sheath composite fibers as the front yarn and back yarn, the well density is 45 to 70 threads / inch (2.54 cm), the coarse density is 40 to 70 threads / inch (2.54 cm), the thickness is 0.2 mm or more, and the percentage change in thickness of the tricot fabric before and after heat pressing at 90°C and 4.0 MPa for 3 minutes is 10% or less.

2. The flow channel material for a liquid separation apparatus according to claim 1, wherein the sum of the total fineness of the thermoplastic core-sheath composite fibers of the front yarn and the thermoplastic core-sheath composite fibers of the back yarn constituting the tricot fabric is 110 to 200 dtex, the difference in runner length between the front yarn and the back yarn is 5 cm or less, and the thickness of the tricot fabric is 0.2 to 0.3 mm.

3. The tricot fabric is characterized in that one of the two reeds forms the base fabric portion which is the sinker loop portion, and the other reed forms the convex portion which is the needle loop portion, and the ratio of the width of the portion between the convex portions (groove width) to the width of the convex portion (ridge width) (groove width / ridge width) is 0.4 to 0.7, as described in claim 1 or 2.

4. The flow channel material for a liquid separation apparatus according to any one of claims 1 to 3, characterized in that the difference in total fineness between the thermoplastic core-sheath composite fibers of the front yarn and the thermoplastic core-sheath composite fibers of the back yarn constituting the tricot fabric is 20 dtex or more.

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