Methods for producing hydrophobic fibers, fibres, yarns and woven fabrics

Abstract

The present invention relates to a method for producing a hydrophobic fiber (1), comprising the following steps in the specified order: The present invention includes the steps of melt-spinning a circular cross-section intermediate product (1Z) from two different plastics (wherein a cross section of the intermediate product (1Z) formed from the first plastic has a core (2) with bars (3) radiating outward therefrom, the first plastic having a hydrophobic surface, and the second plastic filling the gaps (4) between the bars (3)), cooling the intermediate product (1Z), stretching the intermediate product (1Z), creating a hydrophilic surface on the intermediate product (1Z), and extracting the second plastic from the intermediate product (1Z) to form a fiber (1). This fiber (1) can be used to produce superhydrophobic textile products. The present invention also relates to hydrophobic fibers (1) and fabrics or yarns produced from the fibers (1).

Description

[Technical Field]

[0001] The present invention relates to a method for producing hydrophobic fibers, the corresponding fibers, and yarns and / or woven fabrics produced from such fibers. [Background technology]

[0002] In the context of the present invention, the term "fiber" as a textile term means either a fiber or a filament, depending on whether the structure is finite or infinite.

[0003] Hydrophobicity is a desirable property in many sectors. One example of surface technology is boat construction: providing a hydrophobic exterior surface on the underwater part of the hull significantly reduces skid resistance. This allows sports boats to reach higher speeds and can result in significant fuel cost savings in the commercial sector.

[0004] In the field of textiles, water resistance is a highly desirable property, for example in waterproof clothing, swimwear, surgical gowns, wound dressings, or filter fabrics. Breathability of textiles is also usually desirable.

[0005] To impart hydrophobic properties to textiles, for example, modification with per- or polyfluoroalkyl substances (PFAS) is known. Although these per- or polyfluoroalkyl substances produce excellent hydrophobic properties in the treated textiles, they have several drawbacks: they do not provide permanent hydrophobicity; PFAS are persistent, toxic, and bioaccumulative; they are difficult to dispose of, which is why a global ban on these substances is being pursued.

[0006] WO 97 / 47801 A1 discloses a permeable hydrophobic substrate coated with a hydrophilic polymeric material. This material is stable in the temperature range of 10°C to 50°C and does not impair the surface tension of liquids. The structure of this substrate is not clearly stated. It is intended for use in, for example, diapers, but is not suitable for use in ordinary textile products.

[0007] WO 2005 / 005679 A2 discloses a superhydrophobic substrate having a plurality of short nanofibers disposed on its surface. These nanofibers contain exogenous hydrophobic material and are composed of inorganic materials. Due to their mechanical instability, this substrate is also unsuitable for textile applications.

[0008] EP 2 254 709 B1 discloses an object with a hydrophobic surface on which filaments are arranged in at least one hydrophilic area, intended to simulate the so-called salvinia effect. This object is not suitable for textile applications.

[0009] From EP 4 098 799 A1, a textile product is known which has a microstructured surface, which is intended to adhesively interact with a surface consisting of a mixture of hydrophilic and hydrophobic materials.

[0010] EP 2 087 153 B1 describes a fiber for a filter medium that has a core and a cross section with at least 12 projections. The projections are irregularly shaped. Overall, good filtering properties are intended to be achieved. Hydrophobic properties are not described.

[0011] US 2018 / 0030622 A1 discloses a fiber having radial projections in its cross section and corresponding grooves between two adjacent projections. The projections have a cross section in the shape of a truncated cone with a very small height compared to its diameter. This is intended to facilitate further processing and improve the wear comfort and durability of textile products made from the fiber. Hydrophobic properties are not achieved.

[0012] Salvinia is an aquatic plant found worldwide, for example as a floating fern on the surface of water or in rice paddies. Salvinia is highly hydrophobic, and its surface remains dry even after being submerged in water. The mechanism by which it functions is based on surface chemistry and structure. Multiple fine hairs are arranged on the surface. The surface, and in fact the hairs, are hydrophobic due to their wax content; only the free ends of the hairs are hydrophilic. The hydrophobic surface creates a water-repellent effect. Meanwhile, the hydrophilic tips attract water, which creates an air cushion. The latter is stabilized by the attracted water. The tips form a loose lattice that traps air and prevents it from escaping. Summary of the Invention

[0013] A first object of the present invention is to provide a method that allows for the production of superhydrophobic fibers.

[0014] The first object is achieved by the features of claim 1. First, an intermediate product with a circular cross section is formed by melt spinning two different plastics. The cross section of a portion of the intermediate product formed from the first plastic has a core with bars pointing radially outward from it, and the second plastic fills the gaps between the bars. Thus, a closed fiber is created as the intermediate product, i.e., a fiber with a substantially uniform surface. This allows the (final, finished) fiber to have a hydrophilic surface only on the radially outer surfaces of the bars, while the remaining surface retains the hydrophobic properties of the first plastic. The shape of the portion made from the first plastic creates micro-roughness in the final product. This micro-roughness traps air within the textile, improving its hydrophobicity.

[0015] The intermediate product is then cooled in the usual manner to solidify the plastic and allow it to be further processed.

[0016] The intermediate product is then drawn in known manner to reduce its diameter and improve the mechanical properties of the fibers.

[0017] The intermediate product is then given a hydrophilic surface, which can be done, for example, by finishing it with a corresponding substance and / or by creating a nano-roughness.

[0018] Finally, the second plastic is extracted from the intermediate product. This can be done by chemical, thermal, and / or mechanical means. In some cases, it may make sense to perform the extraction only on the yarn or woven fabric.

[0019] Overall, the present invention produces a fiber that mimics the so-called Salvinia effect and is superhydrophobic (meaning that it has a contact angle greater than 120°). This is because, combined with the hydrophilic finish of the radially outer surface, air can permanently accumulate in the gaps and water droplets have a large contact angle of greater than 120° on the surface of the fiber, preventing the fiber from becoming wetted by liquids.

[0020] The dependent claims relate to advantageous embodiments of the invention.

[0021] In one embodiment, an inherently hydrophobic plastic is used as the first plastic. This method allows the first plastic to easily obtain the required hydrophobic surface properties without the need for additional process steps. In this regard, suitable plastics include, for example, polyethylene terephthalate (PET), polyolefins, and polyamides.

[0022] In a further embodiment, nano-roughness is created on the hydrophobic surface, at least in the region of the periphery of the fiber. This can be achieved, for example, by adding suitable nanoparticles to the first plastic before or during melt spinning. The nano-roughness, together with the micro-roughness, improves air entrapment on the one hand and causes better adhesion of the hydrophobin layer on the other. Alternatively, the nano-roughness is created on the surface of the intermediate product before the hydrophilic surface is created, and the nano-roughness is associated with the periphery of the fiber.

[0023] In a further embodiment, the hydrophilic surface is produced by finishing with hydrophobin. Hydrophobin is a protein with a bifunctional molecular structure (one end is hydrophobic and the other end is hydrophilic). Thus, hydrophobin attaches to hydrophobic surfaces with its hydrophobic end and vice versa. Finishing a surface with hydrophobin therefore reverses the wettability. Hydrophobin is non-toxic, biodegradable, synthetically manufacturable, resistant to wash-off, and affordable. It can be easily applied to intermediate products.

[0024] In an alternative embodiment, the hydrophilic surface is created by plasma finishing with hexamethyldisiloxane. This finishing is performed dry, thus saving the energy required for wet finishing. A rough, superhydrophilic surface is created, with a water droplet contact angle of less than 10°.

[0025] In a further embodiment, the fibers are crimped to obtain a higher volume of the yarn or textile during further processing. Crimping can be performed before or after the second plastic is extracted.

[0026] In a further embodiment, the fibers are processed into staple fibers, so that yarns and textile products produced from the fibers have a similar feel to natural fibers.

[0027] A second objective of the present invention is to create a superhydrophobic fiber.

[0028] The second object is solved by the features of claims 8 and 9. The same applies as stated with regard to the method.

[0029] In one embodiment, eight bars are arranged, which ensure a good micro-roughness for trapping air and therefore a very high hydrophobicity.

[0030] A third object of the present invention is to create a superhydrophobic yarn or fabric. Similar statements regarding the method and fiber apply. The fabric can be used in a variety of ways.

[0031] The invention will be explained in more detail using the accompanying schematic drawing, which is here greatly enlarged. [Brief explanation of the drawings]

[0032] [Figure 1] FIG. 1 shows in perspective an idealized portion of a fiber. [Figure 2] FIG. 2 shows an exemplary cross-sectional view of a fiber at a larger scale. DETAILED DESCRIPTION OF THE INVENTION

[0033] FIG. 1 shows a portion of a fiber 1, depicted at the top as finished form 1F and at the bottom left as intermediate product 1Z.

[0034] As can be seen, the fiber 1 produced by the method according to the invention comprises a core 2 with a plurality of, here eight, integrally formed bars 3. The diameter D1 of the cross-sectional envelope of the fiber 1 is approximately 20 μm. Other diameters D1 are also suitable.

[0035] The core 2 has a circular cross section with a diameter D2 of 5 μm to 15 μm.

[0036] The bars 3 are formed on the core 2 and point radially outward from it. They are equally spaced apart. Each bar 3 has a trapezoidal cross section. Unlike a strict geometric trapezoid, the radially outer and radially inner sides are each arc-shaped. In each embodiment, the radially outer side is longer than the radially inner side. Each bar 3 has a height H of 5 μm to 15 μm, which corresponds to half the difference between the envelope diameter D1 and the core diameter D2. The length of the inner side L1 is 0.3 μm to 3.0 μm, and the length of the outer side L2 is 1.0 μm to 4.5 μm.

[0037] Contrary to the exemplary embodiment shown, the number of bars 3 can be between 5 and 16. This depends largely on the envelope diameter D1 and the dimensional ratio of the core 2 and bars 3.

[0038] The core 2 and the bars 3 are made of a first plastic, such as poly-ε-caprolactone (PCL) or semi-crystalline polyethylene terephthalate (PET) or polyolefin (PE6). These first plastics are essentially hydrophobic. Materials that induce nano-roughness on the surface of the fibers 1 can be added to the first plastic. These materials are, for example, corresponding fine particles of silicon dioxide or other organic or inorganic nanoparticles. Furthermore, dyes can also be added.

[0039] As can be seen in Figure 1, the intermediate product 1Z comprises, in addition to the first plastic, a second plastic as an auxiliary component. The second plastic fills the gaps between the bars 3, and the entire intermediate product 1Z has a circular cross-section with an envelope of diameter D1. The placement of the second plastic in the intermediate product 1Z is necessary to ensure that the hydrophilic finish is applied only to the outer sides of the bars 3, while the remaining surfaces of the fibers 1 remain hydrophobic. The second plastic is, for example, polycaprolactone (PCL), which can be efficiently processed for recycling.

[0040] The ratio of the height H of one of the bars 3 to the width L of that bar 3 and the spacing between the bars 3 (the latter two relating to the area of ​​the envelope of the fibre 1) is between 1:1:1 and 1:6:6, depending mainly on the thinness of the fibre 1. Therefore, the ratio of the width L to the spacing may also vary.

[0041] As can be seen in Figure 2, the radially outer side of the bar 3 has a finish 5 as a coating that creates a hydrophilic surface, the finish consisting for example of hydrophobin or hexamethyldisiloxane.

[0042] From this fiber 1, a superhydrophobic yarn or fabric can be produced, which has the properties of salvinia fern. The fabric can be, for example, a woven fabric, a knitted fabric, or a nonwoven fabric.

[0043] To produce fiber 1, intermediate product 1Z is first produced by bicomponent spinning. For this purpose, the components, specifically the first and second plastics, are present in separate granular form, along with optional additives. The first plastic is fed into a first extruder, and the second plastic into a second extruder, where they are melted separately and fed under pressure into a spin pack. In this spin pack, the plastics are filtered, distributed, and extruded through multiple spinnerets into thin strands of the desired shape described above as intermediate product 1Z. After leaving the spinnerets, intermediate product 1Z, i.e., the strands, are cooled below the melting points of the two plastics.

[0044] The strands are then stretched between heated godet rollers to reduce the diameter and increase the strength of the intermediate product 1Z.

[0045] The drawn strands are given a hydrophilic finish 5 to create a hydrophilic surface.

[0046] For this purpose, they are finished with hydrophobin, for example by immersion in a trough followed by weighing and drying.

[0047] Alternatively, a hydrophilic surface may be produced by plasma finishing, for example with hexamethyldisiloxane.

[0048] Depending on the use of the fibre 1, the intermediate product 1Z can be crimped in a known manner.

[0049] The second plastic is then removed from the intermediate product 1Z, which can be obtained by chemical and / or thermal and / or mechanical methods.

[0050] As a result, a thread 1 is formed and the radially outer side of the bar 3 has a finish 5 .

[0051] The optionally crimped fiber 1 can be cut or torn to length to form staple fibers, depending on its use.

[0052] The process of crimping, removing the second plastic, and cutting or tearing occurs in no particular order.

[0053] The fibers 1 or staple fibers, depending on their use, are spun to form yarns.

[0054] Fiber 1 or staple fibers or yarns are processed in a known manner to form a woven fabric, which provides enhanced hydrophobic properties compared to Fiber 1.

[0055] Reference Symbol List 1. Fiber 1Z Intermediate product 1F Completed form 2 cores 3 Bar 4. Gap 5. Finishing D1 envelope diameter D2 Core Diameter H Bar height L1 medial lateral length L2 outer side length

Claims

1. A method for producing a hydrophobic fiber (1), comprising the following steps in the specified order: A process for melt-spinning an intermediate product (1Z) of circular cross section from two different plastics, wherein a cross section of a portion of the intermediate product (1Z) formed from a first plastic has a core (2) with bars (3) pointing radially outward therefrom, the first plastic having a hydrophobic surface, and the second plastic filling the gaps (4) between the bars (3); Cooling the intermediate product (1Z); A step of stretching the intermediate product (1Z); generating a hydrophilic surface of the intermediate product (1Z) by finishing, Extracting the second plastic from the intermediate product (1Z) to form fibers (1).

2. 10. The method of claim 1, wherein an inherently hydrophobic plastic is used as the first plastic.

3. 3. The method according to claim 1 or 2, wherein nano-roughness is generated on the hydrophobic surface at least in the region of the periphery of the fiber.

4. 4. The method according to any one of claims 1 to 3, wherein the hydrophilic surface is generated by coating with hydrophobin.

5. 4. The method according to any one of claims 1 to 3, wherein the hydrophilic surface is produced by plasma finishing with hexamethyldisiloxane.

6. 6. The method according to any one of claims 1 to 5, wherein the fibers (1) are crimped.

7. 7. The method according to any one of claims 1 to 6, wherein the fibres (1) are processed into staple fibres.

8. A hydrophobic fiber (1) produced according to the method of claims 1 to 7.

9. The following characteristics: Plastic hydrophobic fiber (1): In cross section, the plastic forms a core (2) having a plurality of bars (3) formed therein and pointing radially outward; The outer surface of the fiber (1) is hydrophilic, and The remaining (outer) surface of the fiber (1) is hydrophobic.

10. 10. The fiber (1) according to claim 8 or 9, wherein eight bars (3) are arranged.

11. 11. The fiber (1) according to claim 9 or 10, wherein the plastic is essentially hydrophobic.

12. A fiber (1) according to any one of claims 9 to 11, wherein the outer surface of the fiber (1) has a hydrophilic finish (5).

13. Woven fabric or yarn made from the fibers (1) according to claims 8 to 12.

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