JP7634254B2 - Wire for water treatment filters - Google Patents

Description

The present invention relates to a wire made of thermoplastic resin for use in filters for filtering and separating water.

Traditionally, filters have been used to filter wastewater and separate water from solids. Metals and synthetic resins are used as filter materials, but synthetic resin filters are advantageous in terms of corrosion resistance and light weight. Synthetic resin filters are used in various forms such as films or sheets with fine holes, woven fabrics, and nonwoven fabrics, but woven fabrics are superior in terms of filter strength, and woven fabrics made of synthetic resin wires with large wire diameters are preferably used, especially when the water flow rate is high or the object to be filtered is highly abrasive. Various thermoplastic resins are used as materials for synthetic resin wires, but polyester and polyamide wires are advantageous in terms of mechanical properties, heat resistance, chemical resistance, and economy. Of these, polyester wires have the advantage of excellent dimensional stability in water, while polyamide wires have the advantage of excellent abrasion resistance. In addition, various types of dirt adhere to the wire during filtration, and such dirt must be removed. However, polyamide wire has good soil release properties (ease of removing dirt) against water-based dirt because polyamide itself is hydrophilic. Patent Document 1 proposes a technology of disposing a cured product of epoxidized polyamide on the surface of a papermaking machine fabric, which is said to have anti-fouling properties that make it difficult for dirt to adhere and easy to wash off any dirt that does adhere. As a method of disposing a cured product of epoxidized polyamide on the surface of a fabric, a method of melt-kneading a composition containing epoxidized polyamide with a polymer and weaving the melt-spun fibers, and a method of impregnating, coating, or spraying a composition containing epoxidized polyamide as a solution in water or various organic solvents onto a fabric are disclosed.

Patent application No. 2002-68712

In the technology disclosed in the above-mentioned Patent Document 1, in the method of melt-kneading a composition containing an epoxylated polyamide with a polymer and weaving the melt-spun fibers, there are significant concerns about heat resistance and breakage during spinning, and in the method of impregnating, coating, or spraying a woven fabric with a composition containing an epoxylated polyamide as a solution in water or various organic solvents, there are concerns about the durability of the coating film containing epoxylated polyamide attached to the surface of the woven fabric due to friction during use in filtration.

The objective of the present invention is to provide a wire that constitutes a water treatment filter, which has the mechanical properties and durability required for practical use, while also having good soil release properties.

The present invention solves the above-mentioned problems by providing a continuous wire made of a thermoplastic resin, the cross section of which has a two-layer structure made of a core and a coating surrounding the core,
The core is made of polyamide,
the coating portion is composed of a resin composition containing a polyamide and a polyetheresteramide block copolymer , the resin composition containing 60 to 97% by mass of polyamide and 3 to 40% by mass of the polyetheresteramide block copolymer ;
The gist of the invention is a wire for water treatment filters, characterized in that the wire has a wire diameter of 0.15 mm or more, a tensile strength of 5 N or more and 300 MPa or more in a wet state, and a tensile strength of 5 N or more and 300 MPa or more after dry heat treatment at 180°C for 30 minutes.
The present invention also provides a continuous wire made of a thermoplastic resin, the cross section of which has a two-layer structure consisting of a core and a coating surrounding the core,
The core is made of polyamide,
the coating portion is composed of a resin composition containing polyamide and polyoxyalkylene group-containing polyvinyl alcohol, the resin composition containing 60 to 97% by mass of polyamide and 3 to 40% by mass of polyoxyalkylene group-containing polyvinyl alcohol;
The gist of the invention is a wire for water treatment filters, characterized in that the wire has a wire diameter of 0.15 mm or more, a tensile strength of 5 N or more and 300 MPa or more in a wet state, and a tensile strength of 5 N or more and 300 MPa or more after dry heat treatment at 180°C for 30 minutes.

According to the present invention, a wire for a water treatment filter has a two-layer structure consisting of a core and a coating surrounding the core , and the coating is made of a resin composition obtained by blending a polyamide resin with a polyetheresteramide block copolymer or a polyoxyalkylene group-containing polyvinyl alcohol. This imparts a high degree of hydrophilicity to the wire surface, and provides a water treatment filter that combines practical mechanical properties and durability and has excellent soil release properties.

The present invention relates to a continuous wire that constitutes a water treatment filter, the continuous wire being made of a thermoplastic resin, and the cross section (transverse section) of the wire cut perpendicularly to its axial direction has a two-layer structure consisting of a core and a coating surrounding the core. The number of cores is preferably one, but may be multiple. When there are multiple cores, multiple independent cores exist within the coating, and the cores form islands and the coating forms a sea, forming a so-called sea-island structure. When there are multiple cores, the number of cores is preferably about 2 to 6.

The external cross-sectional shape of the wire is not particularly limited and may be circular, elliptical, polygonal, etc., but a circular cross section is preferred in terms of the mechanical properties and versatility that can be obtained.

The thermoplastic resin disposed in the core is polyamide from the viewpoints of mechanical properties and heat resistance.

The polyamide to be placed in the core is not particularly limited as long as it has an amide group in the molecule, and examples include polyamide 6, polyamide 66, polyamide 69, polyamide 46, polyamide 610, polyamide 1010, polyamide 11, polyamide 12, polyamide 6T, polyamide 9T, polyamide 10T, polymetaxylene adipamide, and copolymers or blends of these components.

The relative viscosity of the polyamide in the core is preferably 2.5 or more, and more preferably 3.0 or more, in order to obtain a practical strength and elongation. The relative viscosity of the polyamide is measured at a concentration of 1 g/dl and a temperature of 25°C using 96% sulfuric acid as a solvent.

The thermoplastic resin in the core may contain other thermoplastic resins in small amounts within the range that achieves the object of the present invention. For example, polyester may be added to the polyamide thermoplastic resin in the core, or other thermoplastic resins such as polyolefin, acrylic resin, vinyl acetate resin, vinyl chloride resin, vinylidene chloride resin, polytetrafluoroethylene, silicone resin, or polyurethane may be added alone or in combination.

In addition, various additives may be added to the thermoplastic resin disposed in the core as desired. For example, dyes, pigments, dispersants, compatibilizers, spreaders, plasticizers, viscosity modifiers, flame retardants, lubricants, ultraviolet absorbers, infrared absorbing materials, microwave absorbing materials, light stabilizers, antioxidants, pH adjusters, antibacterial agents, preservatives, fillers, heat resistance agents, antistatic agents, conductive materials, thermally conductive materials, crystal nucleating agents, etc. can be added. In particular, adding a compatibilizer to improve adhesion with the coated part is preferable because it makes the coated part less likely to peel off. As the compatibilizer, various block copolymers and graft copolymers can be used. Examples of block copolymers include block copolymers having blocks of polyester, polyether, polyamide, polystyrene, polyethylene, polypropylene, polybutadiene, polyacrylic acid, etc. Examples of graft copolymers include those using polyester, polyolefin, etc. as the main chain and vinyl polymer, maleic anhydride, glycidyl group, carboxylic acid group, etc. as the side chain. The amount of compatibilizer added is preferably 20% by mass or less. If the amount added exceeds 20% by mass, the physical properties of the thermoplastic resin that is the base of the core will be significantly impaired, which is not preferable.

In the wire of the present invention, the coating surrounding the thermoplastic resin of the core is a resin composition containing polyamide and polyether ester amide block copolymer or polyoxyalkylene group-containing polyvinyl alcohol . The polyamide is not particularly limited as long as it has an amide group in the molecule, and examples thereof include polyamide 6, polyamide 66, polyamide 69, polyamide 46, polyamide 610, polyamide 1010, polyamide 11, polyamide 12, polyamide 6T, polyamide 9T, polyamide 10T, polymetaxylene adipamide, and copolymers or blends of these components. In addition, the relative viscosity of the polyamide is preferably 2.5 or more, more preferably 3.0 or more, in order to obtain a practical strength and elongation. The relative viscosity of the polyamide resin is measured using 96% sulfuric acid as a solvent at a concentration of 1 g/dl and a temperature of 25°C.

The resin composition of the coating portion contains 60 to 97% by mass of polyamide and 3 to 40% by mass of polyetheresteramide block copolymer or polyoxyalkylene group-containing polyvinyl alcohol . If the content of polyamide exceeds 97% by mass, or if the content of polyetheresteramide block copolymer or polyoxyalkylene group-containing polyvinyl alcohol is less than 3% by mass, the hydrophilicity of the coating portion is insufficient, and a wire having good soil releasability, which is the objective of the present invention, cannot be obtained. On the other hand, if the content of polyamide is less than 60% by mass, or if the content of polyetheresteramide block copolymer or polyoxyalkylene group-containing polyvinyl alcohol exceeds 40% by mass, the wire does not have a practical strength, and the productivity and handling of the wire are insufficient.

Other thermoplastic resins may be added to the resin composition of the coating portion in small amounts as long as the object of the present invention is achieved. For example, polyolefin, acrylic resin, vinyl acetate resin, polyester, vinyl chloride resin, vinylidene chloride resin, polytetrafluoroethylene, silicone resin, or polyurethane may be added alone or in combination.

The polyamide in the covering may contain various additives as desired. Examples of additives include the same ones as those added to the thermoplastic resin in the core described above.

The composite ratio (area ratio) of the core and coating of the wire of the present invention is preferably core:coating = 100:5-200, and may be appropriately selected taking into consideration the wire diameter and required mechanical properties, etc. However, in order to obtain both improved physical properties derived from the core and hydrophilicity derived from the coating, it is more preferable that the core:coating = 100:10-100.

The wire diameter of the wire of the present invention is 0.15 mm or more. If it is less than 0.15 mm, when the wire of the present invention is used to make a water treatment filter, it will not be able to withstand damage and wear caused by high loads during water treatment. The upper limit of the wire diameter is not particularly limited as long as it can be woven into a filter, but it is sufficient to have the wire diameter be about 1 mm.

In order to obtain resistance when used as a filter in water and resistance to processing heat such as heat setting in weaving using the wire, the wire has a tensile strength of 5N or more when a tensile test is performed in a wet state and after dry heat treatment at 180°C for 30 minutes. If it is less than 5N, it is not suitable as a water treatment filter because it cannot withstand the tension applied during use. A more preferable tensile strength is 30N or more, and even more preferably 60N or more. The higher the tensile strength, the better, but an upper limit of about 1000N is considered sufficient. If the wire diameter is large, the strength (N) as a wire will be high even if the strength (MPa) per unit cross-sectional area is low, but the strength per unit cross-sectional area (tensile strength when a tensile test is performed in a wet state and tensile strength after dry heat treatment at 180°C for 30 minutes) is 300MPa or more, and more preferably 400MPa or more. In the present invention, the tensile test in a wet state means that the sample (wire) is placed in a container, the container is filled with tap water (20±2°C), the sample is immersed in water for 24 hours or more, the immersed sample is then removed from the water, and immediately (within 1 minute) the sample is measured with a tensile tester, and a load is applied until it breaks. In addition, the tensile test after dry heat treatment at 180°C for 30 minutes means that the sample is left unloaded in a hot air dryer heated to 180°C, removed after 30 minutes, and stored under standard conditions (temperature 20±2°C, relative humidity 65±4%) for 24 hours or more, and then measured with a tensile tester and a load is applied until it breaks. The conditions for the tensile test are grip interval 250 mm, tensile speed 300 mm/min, n=5, and the average values of maximum strength and elongation at break are calculated, and the average values are the tensile strength and breaking elongation.

The wire of the present invention has a breaking elongation of 15 to 55%, and more preferably 20 to 50%, when subjected to a tensile test in a wet state. If it is less than 15%, the wire becomes more brittle and its durability against bending fatigue decreases, which is undesirable. If it exceeds 55%, the rigidity of the woven fabric decreases, resulting in insufficient filter precision, which is undesirable.

An example of a method for manufacturing a wire having a two-layer structure according to the present invention is described below. The resin or resin composition (basically in pellet form) to be placed in each of the core and coating is prepared, and the spinning temperature is set to about 260-290°C. The resin or resin composition is melt-spun from a core-sheath composite spinneret using an extruder-type spinning device, and the spun material is cooled in a warm water bath at about 10-60°C to obtain an undrawn wire. This undrawn wire is stretched in a water bath at about 60-90°C (stretching ratio of about 2.5-4.5 times), and then stretched in a hot air atmosphere at 100-300°C (stretching ratio of about 1.1-2.5 times). This is followed by a relaxation heat treatment of about 2.5-30% in a hot air atmosphere at about 150-300°C to obtain the wire for water treatment filters according to the present invention. To adjust the handling properties and surface properties, textile oils and the like may be applied online before or after stretching, or a coating film may be applied in a post-process by coating or dipping. In addition, post-processing such as plasma treatment may be performed to adjust the affinity with water and processability.

The present invention will now be described in detail with reference to examples. The evaluation methods used in the examples are as follows.

1. Wire diameter measurement The continuous wire was measured at 20 points at 50 cm intervals, and the average value of the measurements was taken as the wire diameter (mm).

2. Tensile test (dry)
Since the continuous wire is usually wound, a required amount was unwound and left at room temperature for 24 hours or more, and then a load was applied until the wire broke using a tensile tester, and the maximum strength and breaking elongation were measured. The conditions for the tensile test were a gripping distance of 250 mm, a pulling speed of 300 mm/min, and the average values measured for n=5 were taken as the maximum strength (N) and the breaking elongation (%).

3. Tensile test (wet)
Since continuous wire is usually wound, a required amount was unwound, the sample (wire) was placed in a container, the container was filled with tap water (20±2°C), and the sample was immersed in water for 24 hours or more, and then the immersed sample was taken out of the water and immediately (within 1 minute) measured with a tensile tester, a load was applied until the sample broke, and the maximum strength and breaking elongation were measured. The conditions of the tensile test were a gripping distance of 250 mm, a pulling speed of 300 mm/min, and the average values measured with n=5 were taken as the maximum strength (N) and the breaking elongation (%).

4. Tensile test (after heat treatment)
Since the continuous wire is usually wound up, the necessary amount was unwound, and the sample was placed in a hot air dryer heated to 180°C without load, and after 30 minutes it was taken out and left for 24 hours or more under standard conditions (temperature 20±2°C, relative humidity 65±4%), after which it was measured with a tensile tester, a load was applied until it broke, and the maximum strength and breaking elongation were measured. The conditions for the tensile test were grip interval 250 mm, tensile speed 300 mm/min, and the average values measured for n=5 were taken as the maximum strength (N) and breaking elongation (%).

5. Abrasion resistance (flexion type abrasion test)
The wear body was a metal round bar with a diameter of 20 mm with sandpaper #600 attached to the side. A sample (wire) was brought into contact with the wear body at an angle of 90 degrees, and a predetermined load was applied to one end of the sample, which was rubbed back and forth with a stroke width of 120 mm and a stroke speed of 35 strokes/min. The number of reciprocations until the sample broke was measured. Four samples were measured, and the average of the obtained numbers was taken as the wear number for wear resistance. The predetermined load was 1.89 kg per cross-sectional area ( ^mm2 ) of the sample. For example, if the wire diameter was 0.45 mm, a load of 300 g was used.

6. Pull-out test (soil release properties)
A circular hole with a diameter of 4 mm was opened in a resin board (thickness 5 mm), a continuous wire of sufficient length (about 20 cm) was conducted in the center of the hole, and the continuous wire was left at least 15 cm on the upper surface side of the resin board, and wood putty (manufactured by Cemedine Co., Ltd., product name "Wood Putty A Tamo White") was filled in, and the wood putty was left at room temperature to dry. If the volume of the wood putty decreased due to drying while it was left, additional wood putty was filled in so that the upper and lower surfaces of the filled wood putty and the upper and lower surfaces of the resin board were almost the same. Finally, after the additional filling, the resin plate was left for 2 days or more to thoroughly dry the wood putty, and the wire sticking out from the underside of the resin plate and the excess wood putty were cut with a cutter along the underside of the resin plate, and the resin plate with the wire fixed by the wood putty was fixed horizontally to the lower end of the tensile tester, while the wire sticking out at least 15 cm from the upper surface of the resin plate was lifted vertically and fixed with a capstan chuck. When fixing with the capstan chuck, the chuck distance (distance from the upper surface of the resin plate to the capstan chuck) of the wire (sample) was 100 mm, the tensile speed was 100 mm/min, and n=5, and the maximum strength in the tensile test was measured, and the average value was taken as the pull-out strength (N). The smaller the pull-out strength value, the easier it is to remove firmly stuck dirt, and the soil release property was evaluated.

Example 1
In order to obtain a continuous wire having a composite cross section in which the core is surrounded by the covering, PA6 chips (polyamide 6, relative viscosity 3.5) were prepared as the resin composition for the core, and PA6 chips (polyamide 6, relative viscosity 3.5) and polyether ester amide block copolymer were blended in a mass ratio of 95/5 as the resin composition for the covering. Then, melt-spun at a temperature of 270°C using a normal extruder-type melt composite spinning device. The core and covering were weighed and spun so that the volume ratio of the core to the covering was 7/3. The spun wire was cooled in a warm water bath at 25°C to obtain an undrawn wire. This undrawn wire was drawn in a first stage at a draw ratio of 3.0 in a hot water bath at 80° C. without being wound up, then drawn in a second stage (draw ratio of 1.6) while passing through a heating zone at 175° C. so that the total draw ratio became 4.8, and then passed through a heating zone at 175° C. for a 9% relaxation heat treatment to obtain a continuous wire with a two-layer structure. The obtained continuous wire had a diameter of 0.45 mm and an area ratio of the core/coating in the cross section of 7/3.

Example 2
A continuous wire was obtained in the same manner as in Example 1, except that the chip blend ratio of the resin composition of the coating was polyamide 6/ polyether ester amide block copolymer = 90/10. The obtained continuous wire had a diameter of 0.45 mm and an area ratio of the core/coating in the cross section of 7/3.

Example 3
A continuous wire was obtained in the same manner as in Example 2, except that a polyoxyalkylene group-containing polyvinyl alcohol was used instead of the polyether ester amide block copolymer in Example 2. The obtained continuous wire had a diameter of 0.45 mm and an area ratio of the core portion/coating portion in the cross section of 7/3.

Comparative Example 1
Using only the PA6 chips used in Example 1, a normal extruder-type melt spinning device was used to melt-spin at a temperature of 270°C. The spun wire was cooled in a warm water bath at 25°C to obtain an undrawn wire. Without winding, this undrawn wire was subjected to a first-stage drawing at a draw ratio of 3.0 times in a warm water bath at 80°C, and then to a second-stage drawing (draw ratio of 1.6 times) while passing through a heating zone at 175°C so that the total draw ratio became 4.8 times, and then to a 9% relaxation heat treatment by passing through a heating zone at 175°C to obtain a single-phase continuous wire made of only polyamide. The obtained continuous wire had a diameter of 0.45 mm.

The physical properties of the obtained continuous wires of Examples 1 to 3 and Comparative Example 1 are shown in Table 1.

The continuous wires of Examples 1 to 3 have practically sufficient tensile strength and tensile strength in both dry and wet conditions, as compared with the continuous wire of Comparative Example 1 made only of polyamide, and also have good abrasion resistance equivalent to that of Comparative Example 1. Furthermore, the pull-out strength of Examples 1 to 3 is smaller than that of Comparative Example 1, and the soil release properties are improved. This is considered to be due to the improved hydrophilicity of the wire surface in the continuous wire of the Examples, and the improved adhesion to the wood putty that is applied as dirt. From these measurement results, the wires of Examples 1 to 3 can provide a water treatment filter that has the mechanical properties and durability required for practical use, while improving the hydrophilicity of the wire surface, thereby improving the processability and soil release properties.

Claims (2)

A continuous wire made of a thermoplastic resin, the cross section of which has a two-layer structure consisting of a core and a coating surrounding the core,
The core is made of polyamide,
the coating portion is composed of a resin composition containing a polyamide and a polyetheresteramide block copolymer , the resin composition containing 60 to 97% by mass of polyamide and 3 to 40% by mass of the polyetheresteramide block copolymer ;
The wire for water treatment filters has a wire diameter of 0.15 mm or more, a tensile strength of 5 N or more and 300 MPa or more in a wet state, and a tensile strength of 5 N or more and 300 MPa or more after dry heat treatment at 180°C for 30 minutes. A continuous wire made of a thermoplastic resin, the cross section of which has a two-layer structure consisting of a core and a coating surrounding the core,
The core is made of polyamide,
the coating portion is composed of a resin composition containing polyamide and polyoxyalkylene group-containing polyvinyl alcohol , the resin composition containing 60 to 97% by mass of polyamide and 3 to 40% by mass of polyoxyalkylene group-containing polyvinyl alcohol ;
The wire for water treatment filters has a wire diameter of 0.15 mm or more, a tensile strength of 5 N or more and 300 MPa or more in a wet state, and a tensile strength of 5 N or more and 300 MPa or more after dry heat treatment at 180°C for 30 minutes.