Method for producing a polymer nonwoven fabric

Abstract

Method for producing a polymer nonwoven fabric (1), wherein according to the method - a polymer blend of a thermoplastic elastomer and another thermoplastic material is provided, - fibers (6) are produced from the polymer blend and a nonwoven semi-finished product (8) is formed therefrom, and - the polymer nonwoven fabric (1) is produced by generating a volume increase through mechanical stretching of the nonwoven semi-finished product (8) and subsequent relaxation.

Description

The invention relates to a method for producing a polymer nonwoven fabric. The invention further relates to a use of a nonwoven semi-finished product on which the polymer nonwoven is based, and to a use of the polymer nonwoven.Polymer nonwoven (fabrics) are nowadays used in many different applications. They are also frequently referred to as "nonwovens" in order to distinguish them from other "textiles", in particular woven fabrics and knitted fabrics, in terms of their structure. In principle, such polymer nonwovens can be used in the context of fiber reinforcements, for example as a superficial laminate layer, in order to form a surface which is as smooth as possible with little markings of fiber undulations, or as an approximately isotropic reinforcing layer. They are also used as filter material, for example in respirators, but also, for example, in vacuum cleaner bags or replaceable filters.However, applications with the purpose of liquid absorption and / or transfer are also interesting. Here, they are used, for example, in the field of (baby) diapers or the like as what is known as the acquisition distribution layer ("ADL"). The object of this is to absorb liquid on account of good absorbency and to deliver it in a two-dimensional distribution to a storage medium lying behind it, usually a gel.Comparatively voluminous nonwoven structures are sought, in particular for the latter purpose. From the prior art, for example from U.S. Pat. No. 2019) / 0 388 263 A1 or also U.S. Pat. No. 2019) / 0 183 690 A1 layer structures are known in which such a polymer nonwoven is bonded at a plurality of points to an elastic carrier material while the latter is in a stretched state. Upon subsequent relaxation, the carrier material contracts, whereby the polymer nonwoven is "aufplustert" by corrugation or wrinkling.In addition, ADLs are frequently also produced from carded fibers, which is comparatively complicated.The object of the invention is to improve the production of a polymer nonwoven.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 a use of a nonwoven semi-finished product according to claim 11 and by a use of a polymer nonwoven according to claim 12.The process of the invention is used to produce a polymer nonwoven. According to the method, a polymer blend of a thermoplastic elastomer (referred to below as "TPE") and a further thermoplastic material is first provided. Fibers are produced ("spun") from this polymer blend and a nonwoven semi-finished product is formed therefrom, in particular in this case. The polymer nonwoven is produced by subsequently mechanically stretching the nonwoven semi-finished product. By subsequent relaxation (i.e. removal of the mechanical stretching), an increase in volume is thereby produced (caused).In other words, to produce the polymer nonwoven, a (in particular conventional spun) nonwoven (semi-finished product) formed from the polymer blend is stretched and subsequently relaxed again. As a result of this stretching and subsequent relaxation, the nonwoven experiences the aforementioned volume increase. The effect of the volume increase is based in particular on a plastic and thus irreversible expansion of the fractions of the further thermoplastic material within the fibers formed by the polymer blend, whereas the fractions of the TPE elastically recover. This results in the plastically deformed portions and thus the entire fiber bending, which leads to an increase in volume in the nonwoven.Preferably, only one type of fiber, namely that formed from the polymer blend, is used. The nonwoven semi-finished product is therefore not a laminate, a multifiber nonwoven or the like.This procedure has the advantage that the semi-woven material semi-finished product has a thickness which is conventional for (spin) fleeces-in particular directly after the production of the fleece-and thus has particularly good storage and transport properties. In contrast to conventional bulky polymer nonwovens which already reach their target volume-in particular their target thickness-during their production, the formation of the target volume can be easily and advantageously shifted to the location of the further processing, since only an expansion of the nonwoven semi-finished product is necessary, in contrast to comparatively complicated laminating processes.In a preferred process variant, a thermoplastic polyurethane (referred to below as "TPU") is used as TPE.In an expedient process variant, the further thermoplastic material used is one which has a solubility parameter difference of greater than 1, preferably greater than, the components of the TPE (usually formed as a (block) copolymer).In a further expedient process variant, a thermoplastic incompatible with the TPE, in particular TPU, is used as further thermoplastic material. Here and in the following, "incompatible" is understood in particular to mean that the further thermoplastic material does not form a common phase with the TPE, in particular TPU, in the polymer blend, but rather is present as an independent phase alongside the TPE, in particular TPU, phase. This is achieved or made possible in particular on the basis of the solubility parameter difference described above. In particular, a polypropylene (PP) or a polyethylene (PE) is used.Preferably, a material that is more rigid than the TPE, in particular TPU, in particular comparatively inelastic, is also used.In an expedient process variant, the further thermoplastic material is added to the TPE or TPU in a proportion of from 1.5 to 30% by weight, in particular from 5 to 20% by weight.In addition, in a further expedient process variant, the fibers formed from the polymer blend are drawn during their production, at least during the formation of the nonwoven semi-finished product, in particular so that fibrils of the separated phases of the further thermoplastic material are formed in the spinning process. Expressed in terms of palaative terms, the precipitated phases of the further thermoplastic material form "smallest fibers" within the fibers formed from the polymer blend, that is to say a type of "subfibers" embedded in the TPE.In particular, the fibers are produced by means of a so-called "melt-blown" process and the nonwoven semi-finished product is also formed during the deposition of the produced fibers. In this case, the TPU in particular has the advantage that the fibers are self-bonding during deposition and it is thus possible to enable the non-woven semi-finished product to be held together. This is particularly due to the fact that the fibers are still tacky during the meltblown process due to the hot gas supply during the deposition. Typical post-consolidation processes such as air through drying, calendering, needle punch, etc. are advantageously not required as a result.Alternatively, a formation of the fibers and the nonwoven semi-finished product by means of other spinning methods, in particular by means of melt spinning, is likewise possible. Here too, the fibers are drawn during their production, i.e. in the scope of the spinning process. In this case, in particular, a conventional post-consolidation of the fibers deposited (in particular upon one another) to form the semifinished nonwoven product takes place. This post-consolidation-for example local (point) calendering, air through drying or needle punch-takes place before the subsequent (or later) stretching of the semi-woven product, which serves to increase the volume.In a further expedient process variant, a pore size is also increased by the mechanical stretching of the nonwoven semi-finished product. In other words, the pores of the nonwoven semi-finished product (in particular likewise or additionally to the volume) are enlarged. This is in turn advantageous for the use of the polymer nonwoven as ADL.In a particularly expedient method variant, the thickness of the nonwoven semi-finished product is increased by 2 to 10 times, in particular by 8 times, in particular in comparison with the starting thickness of the nonwoven semi-finished product, owing to the mechanical stretching and thus also the volume increase. As a result, for example, the space required for storage and / or transport can be reduced, or conversely a larger quantity of semi-finished product can be stored or transported.In the case of mechanical stretching, in an expedient process variant, in particular for setting the above-described changes in volume and property of the semifinished nonwoven product, the semifinished nonwoven product is stretched by at least 20, 25 or 50 percent and up to 80 percent, in particular up to 75 percent (in particular with respect to its starting length).The further thermoplastic material is preferably selected in such a way that it remains plastically deformed at these degrees of deformation (i.e. the abovementioned percentage stretches), whereas the TPE elastically resets.Experiments were carried out inter alia using a TPU of the trade name Elasto-Ilan (registered trade name of BASF Polyurethanes GmbH), type 1180A and, as further (thermoplastic) plastic, a polypropylene (PP) of the type HL504FB (Borealis AG) with a proportion of 5% by weight or a PP of the trade name Moplen (registered trade name of LyondellBasell Industries Holdings B.V.), type HP561r with a proportion of 20% by weight. After the mechanical stretching--here with stretching of about 25 and 38 percent--an about five to even about eight times the thickness of the nonwoven could be established.For example, with a starting 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.The invention also provides for the use of the above-described nonwoven semi-finished product for producing a polymer nonwoven, in particular for use as an ADL. Consequently, the nonwoven semi-finished product is formed, as described above, from fibers which are produced from the polymer blend which is formed from TPE, in particular TPU, and a further thermoplastic material. According to the invention, the nonwoven semi-finished product is mechanically stretched and subsequently relaxed, whereby the volume increase of the nonwoven semi-finished product is caused and the polymer nonwoven fabric, which is then preferably used as ADL, is produced.The invention provides--additionally or alternatively to the use of the polymer nonwoven as ADL--also the use of the polymer nonwoven produced according to the method described above as a carrier of catalyst particles, activated carbon particles, superabsorbent particles and / or the like.The uses according to the invention and the method according to the invention described above share all the method steps described above and thus also the resulting physical features and advantages.The conjunction "and / or" is to be understood here and in the following in particular in such a way that the features linked by means of this conjunction can be formed both jointly and as alternatives to one another.An exemplary embodiment of the invention is explained in more detail below with reference to a drawing. Shown therein are: FIG. 1 shows a schematic illustration of individual method steps of the method, and FIG. 2 shows a schematic flow diagram of a method for producing a polymer nonwoven fabric.Corresponding parts are always provided with the same reference numerals in all figures.With reference to FIGS. 1 and 2, a method for producing a polymer nonwoven fabric, nonwoven fabric 1 for short, is illustrated below. For this purpose, in a first process step S 1, a polymer blend of a thermoplastic elastomer, specifically a thermoplastic polyurethane (TPU) and a polypropylene (PP), is provided. In the present exemplary embodiment, PP is added to the TPU at a proportion by weight of 5%. The polymer blend is fed by means of an extruder 2 to a spinning device 4. Optionally, the blending (i.e. the production of the polymer blend) is also carried out only in this extruder 2.By means of the spinning device 4, fibers 6 are spun from the polymer blend in a second method step S 2 by means of the spinning device 4, specifically by means of a "melt-blown" process. When depositing the fibers 6, a non-woven semi-finished product (here for short: "semi-finished product 8") is directly produced. Specifically, the semi-finished product 8 is already a nonwoven in the actual sense, i.e. wirelessly laid and interconnected fibers 6.The finished semi-finished product 8 can now be stored (temporarily) or transported to a location for further processing.In a third method step S 3, which can and should preferably take place at the location of the further processing, the semi-finished product 8 is mechanically stretched. The semi-finished product 8 is stretched by about 40%. After stretching, the semifinished product 8 is relieved again. During the relief, an increase in the volume of the semi-finished product 8 occurs, which results in a multiplication, for example by 5 times, of the thickness. The semi-finished product 8 treated in this way forms the target product, the nonwoven fabric 1, which can be used, for example, as a so-called acquisition distribution layer, for example in diapers or the like. Furthermore, however, the nonwoven 1 can also be used as a carrier of catalyst, activated carbon and / or superabsorbent particles.The subject matter of the invention is not limited to the embodiment described above. Rather, further embodiments of the invention can be derived from the above description by the person skilled in the art.List of reference characters1 Non-woven fabric 2 Extruder 4 Spinning device 6 Fiber 8 Semi-finished product S 1 Method step S 2 Method step S 3 Method step

Claims

Method for producing a polymer nonwoven (1), wherein according to the method - a polymer blend of a thermoplastic elastomer and a further thermoplastic material is provided, - fibers (6) are produced from the polymer blend and a nonwoven semi-finished product (8) is formed therefrom, and - the polymer nonwoven (1) is produced in that an increase in volume is produced by mechanical stretching of the nonwoven semi-finished product (8) and subsequent relaxation.Method according to Claim 1, wherein a thermoplastic polyurethane is used as thermoplastic elastomer.Method according to Claim 1 or 2, wherein the further thermoplastic material used is one which has a solubility parameter difference of greater than 1, preferably greater than 2 ( J c m 3 ) 1 2 with respect to components of the thermoplastic elastomer.Method according to one of Claims 1 to 3, wherein a thermoplastic incompatible with the thermoplastic elastomer, for example a polypropylene or a polyethylene, is used as further thermoplastic material.Method according to one of Claims 1 to 4, wherein the further thermoplastic material is added to the thermoplastic elastomer in a proportion of from 1.5 to 30% by weight, in particular from 5 to 20% by weight.Method according to one of Claims 1 to 5, wherein the fibers (6) are drawn during the formation of the semi-woven material (8).Method according to one of Claims 1 to 6, wherein the nonwoven semi-finished product (8) is produced in a meltblown process.The method of any one of claims 1 to 7, wherein the mechanical stretching increases a pore size.Method according to one of Claims 1 to 8, wherein the thickness of the nonwoven semi-finished product (8) is increased by 2 to 10 times, in particular by 8 times, owing to the mechanical stretching.Method according to one of claims 1 to 9, wherein the semi-woven semi-finished product (8) is stretched by 20 up to 80 percent, in particular 25 to 75 percent.Use of a nonwoven semi-finished product (8) formed from fibers (6) produced from a polymer blend formed from a thermoplastic elastomer and a further thermoplastic material for producing a polymer nonwoven (1), in particular an acquisition distribution layer formed therefrom, wherein a volume increase of the nonwoven semi-finished product (8) is produced by mechanical stretching of the nonwoven semi-finished product (8) and subsequent relaxation and the polymer nonwoven (1) is produced.Use of a polymer nonwoven (1) produced by a method according to any of Claims 1 to 10 as support for catalyst, activated carbon and / or superabsorbent particles.

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