JP7715577B2 - Channel material for liquid separation equipment - Google Patents

Description

The present invention relates to a flow path material for a liquid separator used to concentrate or separate various liquids, which supports the back side of a semipermeable membrane that receives pressure from the raw liquid.

A typical liquid separation device using a semipermeable membrane is a spiral-type liquid separation membrane module, in which the semipermeable membrane is formed into a cylindrical shape, pressure is applied from the outside, a channel material is inserted inside the membrane, and the end of the channel material is fixed to a hollow shaft and wrapped around it. In such a liquid separation membrane module, a raw liquid at a pressure higher than the reverse osmosis pressure is passed through the outside of the membrane, and the permeated liquid that passes through the membrane is extracted through the inside of the membrane. Because the cylindrical separation membrane is pressurized from the outside at high pressure, the channel material inserted as the channel for the permeated liquid is crushed, impairing the flow of liquid. Therefore, the channel material itself is generally made rigid to withstand deformation so that it does not crush even when pressure is applied from the inside of the separation membrane. Such liquid separation membrane modules are put to practical use in pretreatment of boiler water, recycling of wastewater, and water production systems for seawater desalination and ultrapure water production.

Traditionally, fabrics such as woven and knitted fabrics have been used as flow path materials for permeate water, particularly those with fine grooves on the surface. These fabrics have been impregnated with epoxy resin or melamine resin to make them rigid and prevent deformation when pressure is applied to the raw liquid through the membrane. In this case, to prevent collapse under high pressure, the resin must be applied to nearly half the weight of the fabric. However, in applications requiring high-purity permeate water or applications involving the treatment of high-temperature liquids, problems arise due to the elution of the impregnated resin. In particular, when the raw liquid to be treated is food-grade or medical liquid, it must be sterilized. For this reason, sterilization with hot water is performed before or after membrane separation treatment to prevent bacterial contamination, and the elution of the resin impregnated into the flow path material during this process poses a problem.

To solve the above problems, a new channel material has been proposed (Patent Document 1). This material is made by knitting thermoplastic synthetic fibers consisting of low-melting point and high-melting point components on a three-reed tricot knitting machine, with the ribs made of thermoplastic synthetic fibers that are at least 1.2 times thicker than the fibers making up the base weave. This knitted fabric is then heat-treated to stiffen the ribs (Patent Document 1). However, because this channel material uses a three-reed knitting machine and both thin and thick thermoplastic synthetic fibers, it suffers from low productivity and high costs. Another problem is that the thickness of the channel material cannot be reduced.

To solve the problems of Patent Document 1, a technology has been proposed for creating a back-half weave in a tricot knit fabric made of core-sheath composite fibers using a two-reed system (Patent Document 2), and a technology for achieving a welting density of 35-45 threads/2.54 cm and a course density of 35-55 threads/2.54 cm in a tricot knit fabric made of core-sheath composite fibers with a total fineness of 30-90 dtex (Patent Document 3).

In addition, the osmotic pressure of 3.5% sodium chloride in seawater by mass is 2.8 MPa, so when considering the increase in salinity due to the crossflow method in reverse osmosis desalination, a pressure of at least 4 to 6 MPa must be applied inside the spiral element. In this case, there is a concern that the support on which the membrane is applied will collapse, and the permeate flow channel material will be crushed by prolonged pressure, resulting in a decrease in flow rate. Depending on the operating conditions, extremely high pressures of 7.0 MPa or more can be applied, and under conditions of 7.0 MPa or higher, the flow channel material is even more susceptible to crushing due to prolonged pressure.

Special Publication No. 3-66008 Patent No. 3559475 WO2017/131031 publication

However, both Patent Documents 2 and 3 have the drawback that when used as a flow path material for high-pressure operation, the flow path is blocked by pressure, resulting in insufficient flow rate.
Furthermore, all of the three prior art documents mentioned above describe how thermoplastic sheath-core composite fibers are knitted into a single tricot weave and heat-set to harden the entire tricot fabric, thereby preventing blockage of flow channels and a decrease in flow rate even when pressurized with the reverse osmosis pressure required for seawater desalination. However, none of these documents compare or examine the maintenance of the cross-sectional area of the flow channels under actual reverse osmosis pressure.
In other words, the ease with which the flow path material collapses under pressure has not been considered. Also, there is a method for inspecting the thickness of the flow path material after pressurization at room temperature, but this requires applying pressure for a long period of time, and performing multiple inspections requires considerable effort and cost.

Furthermore, when testing the ease of crushing at room temperature, the flow path material is made of a thermoplastic polymer, which returns to its original shape when pressure is removed, making it difficult to verify the ease of crushing.
Therefore, it has not been easy to find the configuration and conditions of the flow path material that are least likely to collapse when high pressure is applied to the flow path material and that minimize the decrease in flow rate.

The present invention was made to solve the above problems, and its purpose is to provide a flow path material for a liquid separation device that is thin, does not easily collapse when high pressure is applied to the flow path material, and has little reduction in flow rate.

Until now, there has been no comparison or study of the maintenance of the cross-sectional area of the flow channel and the flow rate at that time under conditions equivalent to those under actual reverse osmosis pressure.
The present inventors have discovered a method for easily determining the degree of collapse of a flow path material when pressurized at high pressure for a long period of time. Specifically, the collapse susceptibility of a resin constituting a permeate flow path material can be easily determined by measuring the thickness of the flow path material after pressurizing the resin at a temperature above its glass transition temperature and before pressurization. Furthermore, using this method, the inventors have discovered the configuration and conditions of a flow path material that are least likely to collapse and result in the least decrease in flow rate when high pressure is applied to the flow path material, and have arrived at the present invention.

That is, the object of the present invention is achieved by a flow path material for a liquid separator, which comprises a tricot fabric containing thermoplastic sheath-core composite fibers constituted by two types of polyester resins having different melting points or softening points, wherein in the thermoplastic sheath-core composite fibers, a high-melting point component is disposed in the core and a low-melting point component is disposed in the sheath, the high-melting point component being polyethylene terephthalate, and the difference in melting points between the two components being 60°C or more, the tricot fabric is a tricot knitted fabric consisting only of front yarns and back yarns, the front yarns and the back yarns being the thermoplastic sheath-core composite fibers , the thermoplastic sheath-core composite fibers being bonded to each other to form a rigid tricot fabric, the tricot fabric having a well density of 50 to 68 threads/2.54 cm and a course density of 50 to 68 threads/2.54 cm, and wherein when the tricot fabric is hot-pressed at 90°C and 7.0 MPa for 3 minutes, the change in thickness of the tricot fabric before and after pressing is 14% or less.

It is also preferred that the sum of the total fineness of the front yarn and back yarn of the thermoplastic core-sheath composite fiber constituting the tricot fabric is 80 to 140 dtex, the difference in runner length between the front yarn and the back yarn is 40 cm or less, and the thickness of the tricot fabric is 0.18 to 0.26 mm .

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 ground weave portion (back yarn) be 20 dtex or less.

Furthermore, the core/sheath ratio of the thermoplastic bicomponent fibers in the front yarn and back yarn constituting the tricot fabric is preferably 60/40 to 80/20 by volume.

The tricot fabric is made up of a base structure (back yarn) that forms the sinker loop section on one of the two reeds, and a convex section (front yarn) that forms the needle loop section on the other reed, and it is preferable that the ratio of the width of the section between the convex sections (groove width) to the width of the convex section (rib width) (groove width/rib width) is 0.4 to 0.8.

The flow path material for a liquid separator of the present invention is thin and has high compression resistance, making it difficult to collapse when high pressure is applied to the flow path material, and exhibits little decrease in flow rate, particularly even under high-pressure conditions of 7.0 MPa or more.

The flow path material for a liquid separator of the present invention is made of a tricot fabric containing thermoplastic core-sheath composite fibers made of two types of polyester resins having different melting points or softening points.
In the thermoplastic sheath-core composite fiber, the high-melting point component is disposed in the core and the low-melting point component is disposed in the sheath. The difference in melting points between the two components is preferably 60° C. or more. In the present invention, the difference between the softening point and the high-melting point component is also referred to as the melting point difference when the fiber has no melting point but a softening point.

Preferable polyesters for the low-melting-point component include copolymer esters primarily composed of terephthalic acid and ethylene glycol, with copolymerization components containing, in specified proportions, one or more of the following glycols: 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 aliphatic, alicyclic, or aromatic diols such as diethyl glycol, polyethylene glycol, propylene glycol, hexanediol, paraxylene glycol, and bishydroxyethoxyphenylpropane; and optionally, hydroxy acids such as parahydroxybenzoic acid, added in a proportion of up to 50 mol %.

Among the above, polyesters copolymerized with terephthalic acid and ethylene glycol and isophthalic acid are particularly suitable. Among these isophthalic acid copolymer polyesters, those copolymerized with 10 to 30 mol% isophthalic acid are preferred in terms of ease of fusion bonding and knitting. The desired softening point can be achieved by changing the copolymerization ratio of the above component monomers.

Examples of the high-melting point component include homopolyesters such as polyethylene terephthalate, polybutylene terephthalate, and polytriethylene terephthalate.

In the present invention, a core-sheath bicomponent polyester multifilament is optimal, using isophthalic acid copolymerized polyester as the low-melting-point component of the sheath and homopolyester as the high-melting-point component of the core. Also, a linear fatty acid diol such as 1,4-butanediol, 1,6-hexanediol, or 1,9-nonanediol may be used together with isophthalic acid. The core/sheath ratio is preferably set to 60/40 to 80/20 by volume, with 68/32 to 75/25 being particularly preferred. A ratio of 60/40 to 80/20 ensures that the sheath, which is the low-melting-point component, is not too thin, allowing for sufficient adhesion between the sheaths when fused and fixed. Furthermore, the high proportion of the core, which is the high-melting-point component, ensures sufficient fiber strength, allowing the fiber to withstand pressures of 7.0 MPa or more without crushing.

In the core-sheath type composite multifilament, the total fineness is preferably 30 to 110 dtex, the number of constituent fibers is 10 to 50, and the single yarn fineness is preferably 1.0 to 6.2 dtex.
If the total fineness is less than 30 dtex, the yarn is too thin and cannot withstand pressure when pressure is applied from above the loop, making it prone to being crushed, while if the total fineness exceeds 110 dtex, the fabric becomes thick and hard, making it unsuitable as a flow path material for permeate water.

The tricot fabric of the present invention is a tricot knitted fabric knitted using the thermoplastic sheath-core composite fibers as the front yarn and back yarn of a two-bar knitting machine, and the thermoplastic sheath-core composite fibers are bonded to each other to make them rigid.
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.

The tricot fabric preferably has a wale density of 50 to 68 threads/2.54 cm and a course density of 50 to 68 threads/2.54 cm.
When the well density is 50/2.54 cm or more and the course density is 50/2.54 cm or more, there are many convex portions of the needle loops in a given area, and when pressure is applied from above, the loops tend to withstand the pressure and be less likely to collapse.Furthermore, when the well density is 68/2.54 cm or less and the course density is 68/2.54 cm or less, the thickness of the fabric does not increase and the fabric is less likely to harden, making it suitable for use as a flow path material for permeate water.

The product of the well density and the course density of the tricot fabric is preferably 2700 or more, and more preferably 3000 or more.
If the product of the well density and course density of the tricot fabric is less than 2700, the convex portion of the needle loops in a given area of the tricot fabric will be reduced, and when pressure is applied from above the loops, they will tend to be unable to withstand the pressure and will be easily crushed.
The product of the well density and the course density of the tricot fabric is preferably 4,600 or less.
When the product of the well density and the course density of the tricot fabric exceeds 4600, the fabric becomes thick and hard, and tends to become unsuitable as a permeate flow path material.

Examples of knitted structures for tricot fabrics include single tricot knits such as double Denbigh structure, back half structure, and half tricot structure, and among these, double Denbigh structure and half tricot structure are preferred.
Double tricot knit fabric tends to be thick and stiff, making it unsuitable as a permeate flow path material.

The total fineness of the front yarn and back yarn of the thermoplastic core-sheath composite fiber constituting the tricot fabric is preferably 80 to 140 dtex.
If the total fineness of the front yarn and back yarn of the thermoplastic sheath-core composite fiber constituting the tricot fabric is less than 80 dtex, the strength of the convex portion of the needle loop will be weak, and when pressure is applied from above the loop, the convex portion will tend to be easily crushed without being able to withstand the pressure.Also, if the total fineness of the front yarn and back yarn of the thermoplastic sheath-core composite fiber constituting the tricot fabric is more than 140 dtex, the fabric will tend to be thick and hard, making it unsuitable as a flow path material for permeate water.

The difference in runner length between the front yarn and the back yarn of the tricot fabric is preferably 40 cm or less.
If the difference in runner length between the front yarn and the back yarn of the tricot fabric exceeds 40 cm, the balance between the base part of the fabric (the sinker loop part) and the raised part (the needle loop part) will be poor, and the tricot fabric may tear when heat-set, or it may not be possible to adjust it to the target strength.

The thickness of the tricot fabric is preferably 0.18 to 0.26 mm.
If the thickness of the tricot fabric is less than 0.18 mm, the gap between the ground structure portion, which is the sinker loop portion of the tricot channel material, and the convex portion, which is the needle loop portion, is small, and sufficient flow rate cannot be ensured.If the thickness of the tricot fabric exceeds 0.26 mm, the fabric becomes thick and hard, and tends to become unsuitable as a channel material for permeate water.

In the thermoplastic core-sheath composite fibers constituting the tricot fabric, the difference in total fineness between the front yarn and the back yarn is preferably 20 dtex or less.
If the difference in total fineness between the front yarn and the back yarn is greater than 20 dtex, the strength of the convex part of the needle loop and the strength of the ground structure of the sinker loop will be weakened, and when pressure is applied from above the loop, the fabric will be unable to withstand the pressure and will be easily crushed. Also, the thickness of the fabric will be easily uneven, making it unsuitable as a permeate flow path material.
It does not matter whether the total fineness of the front yarns or the total fineness of the back yarns is larger.

When the tricot fabric is heat-pressed at 90° C. and 7.0 MPa for 3 minutes, the change in thickness of the tricot fabric before and after application of pressure must be 14% or less.
When tricot fabric is heat-pressed at 90°C and 7.0 MPa for 3 minutes, the change in thickness of the tricot fabric before and after pressure application exceeds 14%, which indicates that the strength of the convex part of the needle loop is weak and that when pressure is applied from above the loop, it cannot withstand the pressure and is easily crushed.
Furthermore, it is more preferable that the change in thickness of the tricot fabric before and after application of pressure when hot-pressed at 90° C. and 7.0 MPa for 3 minutes is 7% or less.
Furthermore, the strain caused by pressure on the resin constituting the permeate flow path material can be fixed by applying pressure to the resin while the resin is heated to a temperature equal to or higher than the glass transition temperature, and by utilizing this, the ease of crushing can be easily measured by measuring the thickness of the flow path material after and before pressure is applied. In the present invention, a polyester resin is used, and since the glass transition temperature of polyester resin is about 80°C, the resin is heat-pressed at 90°C.

The tricot fabric of the present invention uses two reeds, one of which forms the base structure portion, which is the sinker loop portion, and the other reed forms the convex portion, which is the needle loop portion.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 preferably 0.4 to 0.8.In this case, the groove width is preferably 100 to 200 μm, and more preferably 110 to 190 μm.The ridge width is preferably 150 to 350 μm, and more preferably 240 to 300 μm.
If the ratio (groove width/ridge width) of the width between the convex portions of the needle loops (groove width) to the width of the convex portions (ridge width) is less than 0.4, the gap formed by the base structure portion, which is the sinker loop portion of the tricot channel material, and the convex portion, which is the needle loop portion, is small, and sufficient flow rate cannot be ensured. If the ratio (groove width/ridge width) of the width between the convex portions of the needle loops (groove width) to the width of the convex portion (ridge width) exceeds 0.8, the strength of the convex portion of the needle loop is weakened, and when pressure is applied from above the loop, it is likely to collapse without being able to withstand the pressure. In addition, when pressure is applied, the separation membrane is likely to fall into the groove, which tends to reduce the flow rate.
The height of the groove is preferably 80 to 120 μm. If the height of the groove is 80 μm or more, a sufficient flow rate can be ensured, and if it is 120 μm or less, the groove is less likely to collapse when high pressure is applied.
The height and width (groove width) of the portions (grooves) between the convex portions of the needle loop and the width of the convex portions (rib width) can be adjusted depending on the knitting density, the total fineness of the thermoplastic core-sheath composite fiber used, and the heat setting conditions to achieve the desired width and ratio thereof.

The tricot fabric according to the present invention is produced, for example, by the following method.
A tricot knitted fabric is produced using thermoplastic sheath-core composite fibers as the front and back yarns of a two-bar tricot knitting machine. The resulting tricot knitted fabric is heat-set to bond the thermoplastic sheath-core composite fibers together and stiffen them, yielding a tricot fabric. The gauge number of the tricot knitted fabric is preferably 28 or more.
The heat setting may be carried out using a pin tenter heat treatment machine, a cylinder dryer or the like.

The tricot fabric can be suitably used as a flow path material on the water permeation side of a liquid separation device. The flow path material for a liquid separation device of the present invention has a sufficient flow rate despite its thin thickness, and in particular does not collapse even when pressurized for a long period of time at a high pressure of 7.0 MPa or more, and there is little decrease in flow rate.

The present invention will be explained in more detail below using examples, but the present invention is not necessarily limited to these. The methods for measuring various properties and the evaluation criteria for tricot fabric used in these examples are as follows:

(1) Change in thickness (%) of tricot fabric before and after heat pressing
A tricot fabric was hot-pressed using a tabletop hot press (Techno Supply Co., Ltd., small press G-12 model) at 90°C and 7.0 MPa for 3 minutes. The thickness of the tricot fabric was measured before and after pressing, and the percentage change in thickness was calculated using the following formula.
Thickness change rate (%) = {(thickness before pressure - thickness after pressure) / thickness before pressure} × 100

(2) Tricot fabric groove width (μm) and ridge width (μm)
Planar and cross-sectional photographs of the tricot fabric were taken using an optical microscope, and the groove width and ridge width were measured.

(3) Thickness of tricot fabric (mm)
The thickness of the tricot fabric was measured using a Peacock Dial Gauge (manufactured by Ozaki Seisakusho Co., Ltd., H-30 type, 0.01 scale, measuring probe 30 mmφ).

(4) Density (pieces/2.54 cm)
According to JIS L 1096 8.6.2 Knit density, the number of wales and the number of courses in a 2.54 cm section of the tricot fabric were measured.

(5) Flow Rate Reduction Rate The H-value, which is also described in U.S. Patent Application Publication No. 2005/0173333, was measured using a known method. Unlike U.S. Patent Application Publication No. 2005/0173333, the flow rate under a predetermined pressure was measured as the H-value (ml/min). The flow rate reduction rate was calculated from the H-value (ml/min) when pressurized to 5.5 MPa and the H-value (ml/min) when pressurized to 7.0 MPa and then again to 5.5 MPa.
A flow rate reduction rate of 5% or less was evaluated as ⊚, a flow rate reduction rate of more than 5% but not more than 12% was evaluated as ◯, and a flow rate reduction rate of more than 12% was evaluated as x.

[Example 1]
A thermoplastic core-sheath composite fiber (44 dtex/24f) was obtained by using polyethylene terephthalate (melting point: 260°C) as the core and a low-melting point copolymer polyester (melting point: 190°C) obtained by copolymerizing 25% mol% isophthalic acid as the acid component of polyethylene terephthalate as the sheath, with a core/sheath ratio of 72/28 on a volume basis. This composite fiber was used as the front yarn, and the same thermoplastic composite fiber was used for the back yarn. The fiber was knitted into a double Denbigh structure (closed loop) on a 36-gauge, two-reed tricot knitting machine with a front yarn runner length of 112.0 cm and a back yarn runner length of 112.0 cm.

The resulting tricot knit fabric was heat-set for 1 minute in a pin tenter set at 200°C to obtain a tricot fabric channel material with a well density of 60 threads/2.54 cm and a course density of 60 threads/2.54 cm. The change in thickness (%) of the resulting tricot fabric before and after heat pressing was 6.4%.

[Example 2]
A channel material was obtained in the same manner as in Example 1, except that the well density of the processed fabric after heat setting for 1 minute in a pin tenter was 65 wells/2.54 cm.

The percent change in thickness of the resulting tricot fabric before and after heat pressing was 10.0%.

[Example 3]
A flow path material was obtained in the same manner as in Example 1, except that a thermoplastic core-sheath composite fiber (56 dtex/12 f) with the same resin combination as in Example 1 was used as the front yarn, and knitted into a half structure on a 36-gauge two-reed tricot knitting machine with a runner length of 127.5 cm for the front yarn and a runner length of 94.0 cm for the back yarn.

The percent change in thickness of the resulting tricot fabric before and after heat pressing was 13.5%.

[Example 4]
A flow path material was obtained in the same manner as in Example 1, except that a thermoplastic core-sheath composite fiber (56 dtex/48 f) with the same resin combination as in Example 1 was used as the front yarn, and knitted into a half structure on a 36-gauge two-reed tricot knitting machine with a runner length of 127.5 cm for the front yarn and a runner length of 94.0 cm for the back yarn.

The change in thickness (%) of the obtained tricot fabric before and after the hot press was 8.0%.
[Comparative Example 1]

A thermoplastic core-sheath composite fiber (56 dtex/24 f) with the same resin combination as in Example 1 was used as the front yarn, and knitted into a half weave on a 36-gauge, two-reed tricot knitting machine with a front yarn runner length of 127.5 cm and a back yarn runner length of 94.0 cm. A channel material was obtained in the same manner as in Example 1, except that the well density of the processed fabric after heat setting for 1 minute in a pin tenter was 70 threads/2.54 cm.

When the resulting tricot fabric was heat-pressed, the change in thickness (%) before and after treatment was 13.1%.

[Comparative Example 2]
A channel material was obtained in the same manner as in Example 1, except that a thermoplastic core-sheath composite fiber (56 dtex/24 f) having the same resin combination as in Example 1 was used as the front yarn and knitted into a queen's coat stitch on a 36-gauge two-reed tricot knitting machine with a runner length of 94 cm for the front yarn and a runner length of 127.5 cm for the back yarn.

When the resulting tricot fabric was heat-pressed, the change in thickness (%) before and after treatment was 15%.

<Results>
[Examples 1 to 4]
When the tricot fabric was heat-pressed, the change in thickness (%) before and after the treatment was 14% or less, and the flow rate reduction rate at that time was also 12% or less. When evaluated as a flow path material, this was at a level that could be used stably for a long period of time even under high-pressure conditions.

[Comparative Examples 1 and 2]
In Comparative Example 1, the change in thickness (%) before and after heat pressing of the tricot fabric was 14% or less, but the thickness of the flow path material was greater than 0.26 mm. In Comparative Example 2, the change in thickness (%) exceeded 14%. Furthermore, the flow rate reduction rate at that time exceeded 12%, and when evaluated as a flow path material, the flow rate was low and it was not suitable for practical use.

Claims (5)

A flow path material for a liquid separator, comprising a tricot fabric containing thermoplastic sheath-core composite fibers constituted by two types of polyester resins having different melting points or softening points, wherein in the thermoplastic sheath-core composite fibers, a high-melting point component is disposed in the core and a low-melting point component is disposed in the sheath, the high-melting point component being polyethylene terephthalate, and the difference in melting points between the two components being 60°C or more, the tricot fabric is a tricot knitted fabric consisting only of front yarns and back yarns, the front yarns and the back yarns being the thermoplastic sheath-core composite fibers, the thermoplastic sheath-core composite fibers being bonded to each other and rigidified, the tricot fabric having a well density of 50 to 68 threads/2.54 cm and a course density of 50 to 68 threads/2.54 cm, and wherein when the tricot fabric is hot-pressed at 90°C and 7.0 MPa for 3 minutes, the change in thickness of the tricot fabric before and after pressing is 14% or less. The flow path material for a liquid separator according to claim 1, wherein the combined total fineness of the thermoplastic core-sheath composite fiber of the front yarn and the thermoplastic core-sheath composite fiber of the back yarn constituting the tricot fabric is 80 to 140 dtex, the difference in runner length between the front yarn and the back yarn is 40 cm or less, and the thickness of the tricot fabric is 0.18 to 0.26 mm. A flow path material for a liquid separator according to claim 1 or 2, characterized in that the difference in total fineness between the thermoplastic core-sheath composite fibers of the front yarns and the thermoplastic core-sheath composite fibers of the back yarns constituting the tricot fabric is 20 dtex or less. A flow path material for a liquid separator according to any one of claims 1 to 3, characterized in that the core/sheath ratio of the thermoplastic core-sheath composite fibers of the front yarn and back yarn constituting the tricot fabric is 60/40 to 80/20 on a volume basis. The tricot fabric is a flow path material for a liquid separator described in any one of claims 1 to 4, characterized in that one of the two reeds forms a base weave portion that is a sinker loop portion, and the other reed forms a convex portion that is a 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 0.8.