Method for manufacturing a hydrophobic fiber, fiber, yarn and textile fabric

Abstract

The invention relates to a method for manufacturing a hydrophobic fiber (1), comprising the following steps in the indicated order: - melt spinning an intermediate product (1Z) having a circular cross section from two different plastics materials, wherein a cross section of a part of the intermediate product (1Z) formed from a first of the plastics materials has a core (2) with protrusions (3) pointing radially outward from the core and wherein the first plastics material has a hydrophobic surface, and wherein a second of the plastics materials fills up intermediate spaces (4) between the protrusions (3); - cooling the intermediate product (1Z); - stretching the intermediate product (1Z); - producing a hydrophilic surface of the intermediate product (1Z); - removing the second plastics material from the intermediate product (1Z) to form the fiber (1). With said fiber (1), superhydrophobic textiles can be manufactured. The invention further relates to a hydrophobic fiber (1) and to a fabric or yarn manufactured from said fiber (1).

Description

[0001] Process for producing a hydrophobic fiber, fiber, yarn and textile fabric

[0002] The invention relates to a method for producing a hydrophobic fiber, a corresponding fiber and a yarn and / or textile fabric produced from such fibers.

[0003] In the context of this invention, the term “fiber” as a structure means, as a technical textile term, either fiber or filament, depending on whether the structure is finite or endless.

[0004] Hydrophobicity is a desired property in many areas.

[0005] One example of surface engineering is shipbuilding, where hydrophobic exterior surfaces significantly reduce gliding resistance in the underwater area. This allows recreational boats to achieve higher speeds or, in the commercial sector, significant fuel cost savings.

[0006] In the textile sector, water-repellent properties are often desirable, for example, in rainwear, swimwear, surgical clothing, wound dressings, or filter cloths. In these cases, breathability of the textile is also usually desired.

[0007] To achieve hydrophobicity in textiles, it is known to use per- or polyfluorinated alkyl compounds (PFAS). These achieve good hydrophobicity in the treated textiles, but have several disadvantages. Permanent hydrophobicity cannot be achieved. PFAS are poorly degradable, toxic, and accumulate in organisms. Disposal is difficult. A global ban on these substances is therefore being sought.

[0008] WO 97 / 47801 A1 discloses a permeable hydrophobic substrate coated with a hydrophilic polymeric material. This material is stable in the temperature range from 10°C to 50°C and does not affect the surface tension of a liquid. No structure of the substrate is discernible. It is intended for use in diapers, for example, but is unsuitable for conventional textiles.

[0009] WO 2005 / 005679 A2 discloses a superhydrophobic substrate in which a plurality of short nanofibers are arranged on a surface. These nanofibers contain exogenous hydrophobic material and are made of inorganic material. They are mechanically unstable, making the substrate unsuitable for textiles.

[0010] EP 2 254 709 B1 discloses an article with a hydrophobic surface on which filaments are arranged, each of which has at least one hydrophilic region. This is intended to replicate the so-called Salvinia effect. The article is not suitable for textiles.

[0011] EP 4 098 799 A1 discloses textiles with a microstructured surface. This surface is intended to interact adhesively with a surface consisting of a mixture of hydrophilic and hydrophobic material.

[0012] EP 2 087 153 B1 describes a fiber for a filter medium that has a cross-sectional configuration of at least twelve projections extending from a core. The projections are irregularly shaped. Overall, good filter properties are intended to be achieved. Hydrophobic properties are not described.

[0013] US 2018 / 0030622 A1 discloses a fiber with radial protrusions in its cross-section and a corresponding groove between two adjacent protrusions. The protrusions have a truncated cone-shaped cross-section with a very small height compared to their diameter. This is intended to facilitate further processing and improve the comfort and durability of textiles made from the fibers. Hydrophobic properties are not achieved.

[0014] Salvinia is a worldwide distributed aquatic plant that occurs as a floating fern on the surface of bodies of water and rice fields, for example. Salvinia is highly hydrophobic, and its surface remains dry even when submerged underwater. Its mechanism of action is based on surface chemistry and surface structure. A multitude of fine hairs are arranged on the surface. The surface, and essentially the hairs themselves, are hydrophobic due to the deposition of wax; only the free tips of the hairs are hydrophilic. The hydrophobic surfaces provide the water-repellent effect. The hydrophilic tips, on the other hand, attract water, which leads to the formation of an air cushion. This air cushion is stabilized by the attracted water. The tips form a loose lattice that traps air and prevents it from escaping.

[0015] It is a first object of the invention to provide a process which allows the production of a superhydrophobic fibre.

[0016] The first problem is solved by the features of claim 1. First, an intermediate product with a circular cross-section is formed from two different plastics by melt spinning. A cross-section of a part of the intermediate product formed from a first of the plastics has a core with webs pointing radially outward from it, and a second of the plastics fills the spaces between the webs. This creates a closed fiber as the intermediate product, i.e., a fiber with a largely smooth surface. This enables the (final, finished) fiber to have a hydrophilic surface exclusively on the radially outer surfaces of the webs, while the remaining surfaces retain the hydrophobic properties of the first plastic. The shape of the part made from the first plastic creates a micro-roughness in the final product that allows air pockets in the textile and thus improves hydrophobicity.

[0017] The intermediate product is then cooled in the usual way so that the plastics solidify and can be further processed.

[0018] The intermediate product is then stretched in a known manner to reduce its diameter and improve the mechanical properties of the fiber.

[0019] A hydrophilic surface is then created on the intermediate product. This can be achieved, for example, by applying a suitable substance and / or by creating a nanoroughness.

[0020] Finally, the second plastic is extracted from the intermediate product. This can be achieved by chemical, thermal, and / or mechanical means. It may be advisable to first perform the extraction process on the yarn or textile fabric.

[0021] Overall, the invention creates a fiber that mimics the so-called Salvinia effect and is superhydrophobic (meaning a contact angle greater than 120°). This is because air can permanently accumulate in the interstices. This, together with the hydrophilic finish of the radially outer surfaces, causes water droplets to form a large contact angle of more than 120° on the surface of the fiber. This prevents the fiber from becoming wetted by liquid.

[0022] The subclaims relate to the advantageous embodiment of the invention.

[0023] In one embodiment, an intrinsically hydrophobic plastic is used as the first plastic. This allows the required hydrophobic surface property of the first plastic to be achieved in a simple manner, without the need for additional processing steps. Suitable plastics in this regard include polyethylene terephthalate (PET), polyolefin, and polyamide.

[0024] In a further embodiment, a nanoroughness is created on the hydrophobic surface, at least in the region of the outer periphery of the fiber. This can be achieved, for example, by adding suitable nanoparticles to the first plastic before or during melt spinning. The nanoroughness, in conjunction with the microroughness, results in improved air entrapment and, in better adhesion of the hydrophobin coating. Alternatively, the nanoroughness is created on the surface of the intermediate product before the hydrophilic surface is created, so that it affects the outer periphery of the fiber.

[0025] In a further embodiment, the hydrophilic surface is created by coating it with (deposits of) hydrophobin. Hydrophobins are proteins that have a bifunctional molecular structure: one end of the structure is hydrophobic, and the other end is hydrophilic. This allows them to attach to hydrophobic surfaces with the hydrophobic end, or vice versa. Coating surfaces with hydrophobin therefore reverses the wetting behavior. Hydrophobin is non-toxic, biodegradable, synthetically produced, difficult to wash off, and inexpensive. It can be easily applied to the intermediate product.

[0026] In an alternative embodiment, the hydrophilic surface is created by plasma treatment with hexamethyldisiloxane. This treatment is performed dry, thus saving the energy required for wet treatment. A rough, superhydrophilic surface with a water droplet contact angle of less than 10° is achieved.

[0027] In a further embodiment, the fibers are crimped. This results in a higher volume of the yarn and / or textile during further processing. Crimping can occur before or after the second plastic is removed.

[0028] In a further embodiment, the fibers are processed into staple fibers. This gives the yarn and / or textile produced from the fiber a feel similar to natural fibers.

[0029] A second object of the invention is to provide a superhydrophobic fiber.

[0030] The second problem is solved by the features of claims 8 and 9. The statements made regarding the method apply accordingly.

[0031] In one design, eight of the ridges are arranged. These ensure good microroughness for air entrapment and thus very high hydrophobicity.

[0032] A third object of the invention is to create a superhydrophobic yarn or fabric. The above statements regarding the process and the fiber apply accordingly. The fabric has a wide range of applications.

[0033] The invention is further explained with reference to the attached schematic drawing. Figure 1 shows, at a greatly enlarged scale, an idealized perspective view of a fiber section, and Figure 2 shows an exemplary cross-section of the fiber, at a further enlarged scale.

[0034] Figure 1 shows a section of a fiber 1 - in an upper part in a finished form 1F and in a lower left part as an intermediate product 1Z.

[0035] As can be seen from the figures, the fiber 1 produced by a method according to the invention comprises a core 2 with a plurality of webs 3 integrally formed thereon, here eight. A diameter Di of a sheath of a cross-section of the fiber 1 is approximately 20 pm. Other diameters Di are also suitable.

[0036] The core 2 has a circular cross-section whose diameter D2 is 5 pm to 15 pm.

[0037] The webs 3 are formed radially away from the core 2 and are evenly spaced apart. Each of the webs 3 has a trapezoidal cross-section, wherein, in deviation from the strictly geometric trapezoidal shape, a radially outer and a radially inner side each have the shape of a circular arc. This radially outer side is longer than the radially inner side for each embodiment. Each web 3 has a height H of 5 pm to 15 pm, which corresponds to half the difference between the diameter Di of the envelope and the diameter D2 of the core. A length Li of the inner side is 0.3 pm to 3.0 pm and a length L2 of the outer side is 1.0 pm to 4.5 pm.

[0038] Deviating from the illustrated embodiment, the number of webs 3 can be five to sixteen. This depends on the diameter D1 of the envelope and the dimensional ratios of the core 2 and the webs 3.

[0039] The core 2 and the webs 3 are made of a first plastic, e.g., poly-s-caprolactone (PCL) or semi-crystalline polyethylene terephthalate (PET) or polyolefin (PE6). These first plastics are intrinsically hydrophobic. Substances that impart nanoroughness to the surface of the fiber 1 can be added to the first plastic. These substances include, for example, fine-grained silicon dioxide or other organic or inorganic nanoparticles. Dyes can also be added.

[0040] As can be seen from 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 spaces between the webs 3, so that the intermediate product 1Z has an overall circular cross-section with the diameter Di of the sheath. The arrangement of the second plastic in the intermediate product 1Z is necessary to ensure that a hydrophilic finish is applied exclusively to the outer sides of the webs 3, thus ensuring that the remaining surfaces of the fiber 1 remain hydrophobic. The second plastic is, for example, polycaprolactone (PCL), which is easy to process for reuse.

[0041] A ratio of the height H of one of the webs 3 to the width L of the webs 3 and to the mutual spacing of the webs 3 - the latter two relative to the area of ​​the sheath of the fiber 1 - is 1:1:1 to 1:6:6 and depends essentially on the fineness of the fiber 1. The ratio of the width L to the spacing can also vary.

[0042] As can be seen from Figure 2, the radially outer sides of the webs 3 have a coating 5 that creates a hydrophilic surface. The coating consists, for example, of hydrophobin or hexamethyldisiloxane.

[0043] Fiber 1 can be used to produce a superhydrophobic yarn or textile fabric that exhibits the properties of the Salvinia fern. The textile fabric can be, for example, a woven fabric, a knitted fabric, or a nonwoven.

[0044] To produce fiber 1, the intermediate product 1Z is first manufactured by bicomponent spinning. For this purpose, the components, namely the first plastic and the second plastic, optionally with additives, are present separately in granulate form. The first plastic is fed into a first extruder and the second plastic into a second extruder, where the plastics are melted separately and fed under pressure to a spinning pack. In this spinning pack, the plastics are filtered, distributed, and extruded through a plurality of spinnerets in the desired shape described above as intermediate product 1Z in thin strands. After leaving the spinnerets, the intermediate product 1Z, i.e. the strands, are cooled so that the melting temperature of the two plastics is below the melting point.

[0045] The strands are then drawn between heated godets to reduce the diameter of the intermediate product 1Z and increase the strength.

[0046] The drawn strands are provided with a hydrophilic finish 5 to create a hydrophilic surface.

[0047] For this purpose, they are either refined with hydrophobin, e.g. by immersion in a trough followed by dosing and then drying.

[0048] Alternatively, the hydrophilic surface can be created by plasma treatment with, for example, hexamethyldisiloxane. Depending on the application of fiber 1, the intermediate 1Z can be crimped in a known manner.

[0049] Subsequently, the second plastic is removed from the intermediate product 1Z. This can be done by chemical and / or thermal and / or mechanical methods. As a result, the threads 1 are formed, with the radially outer sides of the webs 3 having the finishing 5.

[0050] Depending on the use of the fiber 1, which may be crimped, these can be cut or torn into pieces of predetermined length to form staple fibers.

[0051] The processes of crimping, removing the second plastic and cutting or tearing do not have a fixed order.

[0052] Depending on the use of fiber 1 or the staple fibers, they are spun into the yarn.

[0053] Fiber 1, or the staple fibers, or the yarn, is processed into a textile fabric in a known manner. This results in an improvement in the hydrophobic properties compared to fiber 1.

[0054] List of reference symbols

[0055] 1 fiber

[0056] 1Z Intermediate

[0057] 1F Finished form 2 Core

[0058] 3 bridge

[0059] 4 gap

[0060] 5 Finishing

[0061] The diameter of the envelope

[0062] D2 Diameter of the core

[0063] H Height of the bridge

[0064] Li Length of the inner side L2 Length of the outer side

Claims

Patent claims 1. A method for producing a hydrophobic fiber (1), comprising the following steps in the specified order: - melt spinning an intermediate product (1Z) having a circular cross-section from two different plastics, wherein a cross-section of a part of the intermediate product (1Z) formed from a first of the plastics has a core (2) with webs (3) pointing radially outwards from the core, and wherein the first plastic has a hydrophobic surface, and wherein a second of the plastics fills spaces (4) between the webs (3); - Cooling the intermediate product (1Z); - stretching of the intermediate product (1Z); - producing a hydrophilic surface of the intermediate product (1Z) by finishing; - dissolving the second plastic from the intermediate product (1Z) to form the fiber (1).

2. Method according to claim 1, characterized in that an intrinsically hydrophobic plastic is used as the first plastic.

3. Method according to claim 1 or 2, characterized in that a nanoroughness is produced on the hydrophobic surface at least in the region of an outer circumference of the fiber.

4. Method according to one of claims 1 to 3, characterized in that the hydrophilic surface is produced by coating with hydrophobin.

5. Method according to one of claims 1 to 3, characterized in that the hydrophilic surface is produced by plasma treatment with hexamethyldisiloxane.

6. Method according to one of claims 1 to 5, characterized in that the fibers (1) are crimped.

7. Method according to one of claims 1 to 6, characterized in that the fibers (1) are processed into staple fibers.

8. Hydrophobic fiber (1), characterized in that it is manufactured according to the method of claims 1 to 7.

9. Hydrophobic fibre (1) made of plastic, characterised by the following features: the plastic forms a core (2) in cross-section with a multiplicity of molded, radially outward-pointing webs (3); Surfaces of an outer circumference of the fiber (1) are hydrophilic and remaining (outer) surfaces of the fiber (1) are hydrophobic.

10. Fiber (1) according to claim 8 or 9, characterized in that eight of the webs 3 are arranged.

11. Fiber (1) according to claim 9 or 10, characterized in that the plastic is intrinsically hydrophobic.

12. Fiber (1) according to one of claims 9 to 11, characterized in that the surfaces of the outer periphery have a hydrophilic finish (5).

13. Textile fabric or yarn made from fibers (1) of claims 8 to 12.

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