METHOD FOR PRODUCING A POLYMER NONWOVEN FABRIC

Description

[0001] The invention relates to a method for producing a polymer nonwoven fabric. Furthermore, the invention relates to the use of a nonwoven semi-finished product on which the polymer nonwoven fabric is based, as well as to the use of the polymer nonwoven fabric.

[0002] Polymer nonwovens are used in many different applications today. They are often referred to as "nonwovens" to distinguish them from other "textiles," particularly woven and knitted fabrics, based on their structure. In principle, such polymer nonwovens can be used for fiber reinforcements, for example, as a surface laminate layer to create the smoothest possible surface with minimal fiber undulations, or as an approximately isotropic reinforcement layer. They are also used as filter material, for example, in respiratory masks, but also in vacuum cleaner bags or replaceable filters.

[0003] Applications involving the purpose of liquid absorption and / or transfer are also interesting. Here, they are used, for example, in (baby) diapers and similar products as so-called acquisition distribution layers ("ADL"). Their task is to absorb liquid due to their high absorbency and release it evenly to a storage medium behind it, usually a gel.

[0004] Particularly for the latter purpose, comparatively voluminous nonwoven structures are sought. Layered structures are known from the prior art, for example, from US 2019 / 0 388 263 A1 or US 2019 / 0 183 690 A1, in which such a polymer nonwoven is bonded at several points to an elastic carrier material while the latter is in a stretched state. Upon subsequent relaxation, the carrier material contracts, causing the polymer nonwoven to "puff up" by forming waves or folds.

[0005] In addition, ADLs are often made from carded fibers, which is comparatively complex.

[0006] The invention is based on the object of improving the production of a polymer nonwoven fabric.

[0007] This object is achieved according to the invention by a method having the features of claim 1. Furthermore, this object is achieved according to the invention by using a nonwoven semi-finished product according to claim 11 and by using a polymer nonwoven fabric according to claim 12. Further advantageous and inventive embodiments and further developments of the invention are set out in the subclaims and the following description.

[0008] The process according to the invention is used to produce a polymer nonwoven fabric. According to the process, a polymer blend of a thermoplastic elastomer (hereinafter referred to as "TPE") and another thermoplastic material is first prepared. Fibers are produced ("spun") from this polymer blend, and a semi-finished nonwoven fabric is formed therefrom, in particular during this process. The polymer nonwoven fabric is produced by subsequently mechanically stretching the semi-finished nonwoven fabric. Subsequent relaxation (i.e., removal of the mechanical stretching) produces (caused) an increase in volume.

[0009] In other words, to produce the polymer nonwoven, a nonwoven (semi-finished product) made from the polymer blend (especially a conventional spunbond) is stretched and then relaxed again. This stretching and subsequent relaxation process causes the nonwoven to experience the aforementioned increase in volume. The effect of the volume increase is primarily due to a plastic and thus irreversible stretching of the portions of the other thermoplastic material within the fibers formed by the polymer blend, whereas the TPE portions elastically recover. This results in the bending of the plastically deformed portions and thus of the entire fiber, which leads to an increase in volume in the nonwoven.

[0010] Preferably, only one type of fiber is used, namely the one formed from the polymer blend. The nonwoven semi-finished product is therefore not a laminate, a multi-fiber nonwoven, or the like. Particularly preferably, this type of fiber, i.e., the fibers for the nonwoven semi-finished product, are formed solely from the polymer blend.

[0011] This approach has the advantage that the nonwoven semi-finished product has a thickness typical for (spunbonded) nonwovens – especially immediately after production – and thus offers particularly good storage and transport properties. In contrast to conventional voluminous polymer nonwovens, which already reach their target volume – especially their target thickness – during production, the formation of the target volume can be easily and advantageously shifted to the location of further processing, since only stretching of the nonwoven semi-finished product is required, in contrast to comparatively complex lamination processes.

[0012] In a preferred process variant, a thermoplastic polyurethane (hereinafter referred to as "TPU") is used as the TPE.

[0013] In a suitable process variant, the additional thermoplastic material used is one that has a solubility parameter difference of greater than 1, preferably greater than 2 J cm 3 1 2 has.

[0014] In another advantageous process variant, a thermoplastic incompatible with the TPE, in particular TPU, is used as the additional thermoplastic material. "Incompatible" is understood here and below in particular to mean that the additional thermoplastic material does not form a common phase with the TPE, in particular TPU, in the polymer blend, but rather exists as an independent phase alongside the TPE, in particular TPU, phase. This is achieved or enabled in particular due to the solubility parameter difference described above. In particular, a polypropylene (PP) or a polyethylene (PE) is used.

[0015] Preferably, a material that is stiffer, in particular comparatively inelastic, than TPE, in particular TPU (in particular a conventional thermoplastic - a "non-TPE thermoplastic") is used.

[0016] In a suitable process variant, the additional thermoplastic material is added to the TPE or TPU in a proportion of 1.5 to 30 wt.%, in particular 5 to 20 wt.%.

[0017] In another advantageous process variant, the fibers formed from the polymer blend are stretched during their production, at least during the formation of the semi-finished nonwoven product, in particular so that fibrils of the separated phases of the additional thermoplastic material are formed during the spinning process. Put simply, the separated phases of the additional thermoplastic material form "microfibers" within the fibers formed from the polymer blend, i.e., a type of "subfiber" embedded in the TPE.

[0018] In particular, the fibers are produced using a so-called "melt-blown" process, and the semi-finished nonwoven product is formed during the deposition of the produced fibers. TPU, in particular, has the advantage that the fibers are self-binding during deposition, thus enabling the cohesion of the semi-finished nonwoven product. This is primarily due to the fact that the fibers in the melt-blown process are still sticky due to the hot gas supply during deposition. This advantageously eliminates the need for typical post-consolidation processes such as air-through drying, calendering, needle punching, etc.

[0019] Alternatively, the fibers and the semi-finished nonwoven fabric can also be formed using other spinning processes, particularly melt spinning. Here, too, the fibers are drawn during their production, i.e., during the spinning process. In this case, the fibers (especially randomly placed fibers) are subjected to conventional post-consolidation to form the semi-finished nonwoven fabric. This post-consolidation—e.g., local (point-based) calendering, air-through drying, or needle punch—takes place before the subsequent (or later) drawing of the semi-finished nonwoven fabric, which serves to increase its volume.

[0020] In another advantageous process variant, the mechanical stretching of the nonwoven semi-finished product also increases the pore size. In other words, the pores of the nonwoven semi-finished product are enlarged (especially also or in addition to the volume). This, in turn, is advantageous for the use of the polymer nonwoven as an ADL.

[0021] In a particularly useful process variant, the thickness of the nonwoven semi-finished product is increased by 2 to 10 times, particularly up to 8 times, compared to the initial thickness of the nonwoven semi-finished product due to mechanical stretching and thus also the increase in volume. This can, for example, reduce the space required for storage and / or transport, or conversely, allow a larger quantity of semi-finished product to be stored or transported.

[0022] In mechanical stretching, in a suitable process variant, in particular for adjusting the volume and property changes of the nonwoven semi-finished product described above, the nonwoven semi-finished product is stretched by at least 20, 25 or 50 percent and up to 80 percent, in particular up to 75 percent (in particular compared to its initial length).

[0023] The additional thermoplastic material is preferably selected in such a way that it remains plastically deformed at these degrees of deformation (i.e. the percentage stretching mentioned above), whereas the TPE recovers elastically.

[0024] Tests were conducted, among others, with a TPU of the Elasto-Ilan brand (registered trademark of BASF Polyurethanes GmbH), type 1180A, and as an additional (thermoplastic) plastic, a polypropylene (PP) of the HL504FB type (Borealis AG) with a 5 wt.% content, or a PP of the Moplen brand (registered trademark of LyondellBasell Industries Holdings BV), type HP561r with a 20 wt.% content. After mechanical stretching – here with stretching values ​​of approximately 25 and 38 percent – ​​a nonwoven thickness of approximately five to eight times was observed.

[0025] For example, with an initial thickness of the nonwoven semi-finished product of 0.85 millimeters, a thickness of approximately 6.58 millimeters was determined for the polymer nonwoven after stretching.

[0026] The invention also provides for the use of the above-described semi-finished nonwoven product for producing a polymer nonwoven, in particular for use as an ADL. Thus, the semi-finished nonwoven product, as described above, is formed from fibers produced from the polymer blend formed from TPE, in particular TPU, and another thermoplastic material. According to the invention, the semi-finished nonwoven product is mechanically stretched and subsequently relaxed, thereby causing the volume increase of the semi-finished nonwoven product and producing the polymer nonwoven, which is then preferably used as an ADL.

[0027] The invention also provides - in addition or alternatively to the use of the polymer nonwoven fabric as ADL - the use of the polymer nonwoven fabric produced according to the method described above as a carrier of catalyst, activated carbon, superabsorbent particles and / or the like.

[0028] The uses according to the invention as well as the method according to the invention described above share all the method steps described above and thus also the resulting physical characteristics and advantages.

[0029] The conjunction "and / or" is to be understood here and in the following in particular in such a way that the features linked by this conjunction can be formed both together and as alternatives to one another.

[0030] An embodiment of the invention is explained in more detail below with reference to a drawing. In the drawings: Fig. 1 shows a schematic representation of individual process steps of the process, and Fig. 2 shows a schematic flow diagram of a process for producing a polymer nonwoven fabric.

[0031] Corresponding parts are always provided with the same reference symbols in all figures.

[0032] Based on Fig. 1 and 2 The following describes a process for producing a polymer nonwoven fabric, abbreviated to nonwoven fabric 1. For this purpose, in a first process step S1, a polymer blend of a thermoplastic elastomer, specifically a thermoplastic polyurethane (TPU) and a polypropylene (PP), is prepared. In the present exemplary embodiment, PP is added to the TPU at a weight fraction of 5%. The polymer blend is fed to a spinning device 4 by means of an extruder 2. Optionally, blending (i.e., the creation of the polymer blend) also takes place in this extruder 2.

[0033] In a second process step S2, fibers 6 are spun from the polymer blend by means of the spinning device 4, specifically using a melt-blown process. Upon deposition of the fibers 6, a nonwoven semi-finished product (here referred to as "semi-finished product 8") is directly produced. Specifically, the semi-finished product 8 is already a nonwoven in the true sense of the word, i.e., it consists of randomly deposited and interconnected fibers 6. The cohesion of the fibers 6 in the semi-finished product 8 is made possible by the melt-blown process, which is made possible by the still "hot" fibers 6 and the resulting still sticky TPU components.

[0034] The finished semi-finished product 8 can now be (temporarily) stored or transported to a location for further processing.

[0035] In a third process step S3, which can and should preferably take place at the site of further processing, the semi-finished product 8 is mechanically stretched. The semi-finished product 8 is stretched by approximately 40%. After stretching, the semi-finished product 8 is relieved of stress. During the relief, the volume of the semi-finished product 8 increases, which is reflected in a multiplication, e.g., by a factor of 5, of the thickness. The semi-finished product 8 treated in this way forms the target product, the nonwoven fabric 1. This can be used, for example, as a so-called acquisition distribution layer, e.g., in diapers or the like. Furthermore, the nonwoven fabric 1 can also be used as a carrier for catalyst, activated carbon, and / or superabsorbent particles.

[0036] The subject matter of the invention is not limited to the exemplary embodiment described above. Rather, further embodiments of the invention can be derived by those skilled in the art from the above description. List of reference symbols

[0037] 1Nonwoven fabric 2Extruder 4Spinning device 6Fiber 8Semi-finished product S1Process step S2Process step S3Process step

Claims

1. Process for producing a polymer nonwoven (1), in which process - a polymer blend of a thermoplastic polymer and a further thermoplastic material is provided, - the polymer blend is used to produce fibres (6) and these are used to form a semifinished nonwoven product (8), and - the polymer nonwoven (1) is produced by mechanical stretching of the semifinished nonwoven product (8) and subsequent relaxation in order to achieve an increase in volume.

2. Process according to Claim 1, wherein the thermoplastic elastomer employed is a thermoplastic polyurethane.

3. Process according to Claim 1 or 2, wherein the further thermoplastic material employed is one having a difference in solubility parameter with respect to components of the thermoplastic elastomer of greater than 1, preferably of greater than 2 J cm 3 1 / 2 .

4. Process according to any of Claims 1 to 3, wherein the further thermoplastic material employed is a thermoplastic which is incompatible with the thermoplastic elastomer, for example a polypropylene or a polyethylene.

5. Process according to any of Claims 1 to 4, wherein the further thermoplastic material is added to the thermoplastic elastomer with a proportion of 1.5% to 30% by weight, especially 5% to 20% by weight.

6. Process according to any of Claims 1 to 5, wherein the fibres (6) are stretched in the forming of the semifinished nonwoven product (8).

7. Process according to any of Claims 1 to 6, wherein the semifinished nonwoven product (8) is produced in a meltblown process.

8. Process according to any of Claims 1 to 7, wherein the mechanical stretching increases a pore size.

9. Process according to any of Claims 1 to 8, wherein the thickness of the semifinished nonwoven product (8) is increased owing to the mechanical stretching by 2 to 10 times, especially by up to 8 times.

10. Process according to any of Claims 1 to 9, wherein the semifinished nonwoven product (8) is stretched by 20 up to 80 per cent, especially 25 to 75 per cent.

11. Use of a semifinished nonwoven product (8) formed from fibres (6) produced from a polymer blend which is formed from a thermoplastic elastomer and a further thermoplastic material in order to produce a polymer nonwoven (1), especially an acquisition / distribution layer formed therefrom, wherein mechanical stretching of the semifinished nonwoven product (8) and subsequent relaxation cause an increase in volume of the semifinished nonwoven product (8) and produce the polymer nonwoven (1).

12. Use of a polymer nonwoven (1) produced by a process according to any of Claims 1 to 10 as support for catalyst particles, activated carbon particles and / or superabsorbent particles.