Elastic single-layer melt-blown nonwoven fabric, and face mask made thereof

Abstract

The present invention relates to a melt-blown nonwoven fabric comprising filaments of thermoplastic polyurethane having an average fineness of not more than 2.5 μm. The invention also relates to a method for producing such a melt-blown nonwoven fabric, the method comprising the following steps: a) producing a melt-blown nonwoven fabric having a basis weight of 50 to 150 g / m2 by applying flowing air to the exterior of a thermoplastic polyurethane melt extruded through a die, and attenuating said melt before the filaments thus formed are deposited onto a support, and b) flat calendering the melt-blown nonwoven fabric produced in step a). The present invention also relates to a face mask composed of the melt-blown nonwoven fabric.

Description

[0001] Elastic single-layer meltblown nonwoven fabric and face mask made of it

[0002] The present invention relates to an elastic single-layer meltblown nonwoven fabric, a method for producing such a meltblown nonwoven fabric and a face mask made of such a meltblown nonwoven fabric, and in particular to a face mask that meets the FFP2 standard.

[0003] During the COVID-19 pandemic, there has been a sharp increase in demand for face masks and respiratory masks that meet the FFP2 standard according to EN 149. Such a face mask must be characterized by a high filter efficiency, i.e. a high degree of separation for small particles, such as viruses with a diameter of 0.06 to 0.40 pm. To meet this requirement, common face masks are multi-layered, with the outer cover layers usually providing mechanical protection and the inner layers, usually two inner layers, providing the actual filtration performance. Typically, at least the inner layers of the face masks are composed of a meltblown nonwoven fabric. The meltblown nonwoven fabric is usually electrostatically charged and consists of polypropylene filaments with an average fineness of 1.5 to 3 pm.Due to this low filament fineness, the meltblown nonwoven fabric has small pore sizes and thus high separation rates for small particles.

[0004] The filtering effect of an FFP2 face mask is based on four different effects: the sieve effect, the inertia effect, the diffusion effect, and the electrostatic effect. While the sieve effect retains the particles to be filtered due to their larger diameter compared to the average pore size of the filaments of the meltblown nonwoven fabric, medium-sized particles cannot follow the air flow through the capillary layer system of the meltblown nonwoven fabric due to the inertia effect and therefore remain stuck to the filaments of the meltblown nonwoven fabric. With the diffusion effect, the tumbling movements of very small particles cause the particles to adhere to the filaments of the meltblown nonwoven fabric, whereas the electrostatic effect, resulting from the electrostatic charging of the filaments, significantly enhances the effects of the inertia and diffusion effects.

[0005] In addition to the high degree of separation for small particles, FFP2 face masks must also be characterized by sufficiently high air permeability to allow adequate breathing. However, the two aforementioned properties—separation efficiency and air permeability—are diametrically opposed in the sense that most measures to increase the separation efficiency of small particles, such as reducing filament fineness, lead to a reduction in air permeability, and vice versa. The only measure that increases the separation efficiency and does not reduce the air permeability of the meltblown nonwoven fabric is the electrostatic charging of the filaments. This is the main reason why the filaments of the meltblown nonwoven fabric are electrostatically charged in almost all known FFP2 masks.However, the electrostatic charging of the filaments is associated with the considerable disadvantage that the electrostatic charge decreases significantly during storage of the face masks and is eventually lost, meaning that the corresponding face masks only have a comparatively short shelf life.

[0006] A further disadvantage of conventional face masks is that the multi-layer structure makes it necessary to weld the individual layers together at their edges. This welding is usually done using ultrasonic welding. However, the resulting seams pose two problems: firstly, the seams are stiff and hard, which can lead to skin irritation, and secondly, the material is sealed at these points, meaning these areas are no longer available as a filter surface through which air can pass. In addition, a good fit requires the face mask to be shaped, e.g., by means of a center cut, which requires an additional joint in the middle of the face mask. To secure the face masks to the head, they usually have elastic cords that are threaded around the head or around the ears.However, the elastic cords are made of a different material than the face mask itself—rubber—which makes these face masks difficult to recycle. Furthermore, the necessary tensile force of the elastic cords, which is a result of the rigid construction of the face masks, makes them uncomfortable to wear.

[0007] The object of the present invention is to avoid the above disadvantages and to provide a meltblown nonwoven fabric which is suitable for a single-layer and one-piece face mask which meets the FFP2 standard according to EN 149 and is also characterized by long durability, good wearing comfort and good recyclability.

[0008] According to the invention, this object is achieved by a meltblown nonwoven fabric comprising filaments of thermoplastic polyurethane with an average fineness of maximum 2.5 pm.

[0009] This solution is based on the surprising discovery that a meltblown nonwoven made of thermoplastic polyurethane filament with a maximum average fineness of 2.5 pm is suitable for a face mask that meets the FFP2 standard, even with a single-layer structure and without electrostatic charge. Such a meltblown nonwoven is particularly characterized by its high elasticity, which even makes it possible to make the carrying strap for attaching the face mask to the wearer's head from the meltblown nonwoven. In addition to the resulting high level of comfort, this also offers the further advantage that the face mask, including the carrying strap, can be manufactured in one piece from the meltblown nonwoven, eliminating the need for external materials such as rubber cords and thus leading to high recyclability.Since electrostatic charging of the meltblown nonwoven fabric is not required for the face mask made from it to meet the FFP2 standard, the face mask also has a very long shelf life.

[0010] For the purposes of the present invention, a meltblown nonwoven is understood to mean a nonwoven produced using one of the known meltblown processes, regardless of whether it is a flat, 2-dimensional nonwoven or a voluminous nonwoven. Processes for producing such meltblown nonwovens are described, for example, in US 4,375,446, US 4,380,570, US 3,849,241, US 4,824,451, and DE 17 85 712 C3.

[0011] According to the invention, the filaments of the meltblown nonwoven fabric have an average fineness of a maximum of 2.5 pm. In the context of the present invention, the average filament fineness or filament diameter is measured as follows: Images of a randomly selected nonwoven sample consisting of filaments are taken using a high-resolution light or scanning electron microscope at a magnification of 1000x. Two diagonals are drawn in each image, and the intersection points of filaments lying in the focal plane are then marked with the diagonals. In this process, multiple measurements resulting from multiple intersections of a diagonal by a filament are eliminated. For each of the intersection points, the distance of the outer edges orthogonal to the filament's longitudinal axis is then determined using image analysis software, such as that included as standard in Keyence digital microscopes.This value is then converted into a unit of length, e.g., in pm, using the corresponding scale, unless the image analysis software automatically generates the unit. To obtain a statistically meaningful result, at least 40 diameter values ​​should be present in the evaluation table. The statistical data of the sample are then determined, with the median—i.e., the 1 / 2 quantile—and not the mean of the diameter distribution being relevant. The determined median of the diameter distribution is then the average fineness.

[0012] Since the effects of the meltblown nonwoven fabric according to the invention are due to the filament or filaments made of thermoplastic polyurethane, each with an average fineness of not more than 2.5 μm, it is preferred according to the invention that the meltblown nonwoven fabric is composed of at least 50 wt.% one or more filaments made of thermoplastic polyurethane, each with an average fineness of not more than 2.5 μm. Good results are achieved in particular when the meltblown nonwoven fabric is composed of at least 80 wt.%, particularly preferably at least 90 wt.%, further preferably at least 95 wt.%, most preferably at least 99 wt.% one or more filaments made of thermoplastic polyurethane, each with an average fineness of not more than 2.5 μm. Most preferably, the meltblown nonwoven fabric consists of one or more filaments made of thermoplastic polyurethane, each with an average fineness of not more than 2.5 μm, i.e.The melt-blown nonwoven fabric is composed of 100% by weight of one or more filaments of thermoplastic polyurethane, each with an average fineness of maximum 2.5 pm.

[0013] With regard to air permeability as well as manufacturability, it is proposed in a further development of the inventive concept that the average fineness of the at least one filament made of thermoplastic polyurethane be at least 1.0 μm. Good results are obtained in particular when the average fineness of the at least one filament made of thermoplastic polyurethane is 1.5 to 2.5 μm and very particularly preferably 1.5 to 2.0 μm. According to a particularly preferred embodiment of the present invention, the basis weight of the meltblown nonwoven fabric is 50 to 150 g / m 2 . Good results are obtained especially when the meltblown nonwoven fabric has a basis weight of 60 to 120 g / m 2, more particularly preferably from 70 to 110 g / m 2 , most preferably from 80 to 100 g / m 2 and most preferably from 85 to 95 g / m 2 , such as 90 g / m 2 In particular, this combination of basis weight with the aforementioned medium fineness of the thermoplastic polyurethane filaments results in a good balance between filter performance and air permeability of the meltblown nonwoven fabric.

[0014] Furthermore, it is preferred that the meltblown nonwoven fabric has a density of 180 to 260 kg / m 3 and particularly preferably from 200 to 230 kg / m 3 has.

[0015] With regard to its suitability as a material for an FFP2 face mask, it is also preferred that the meltblown nonwoven fabric has an air permeability measured in accordance with DIN ISO 9237 of at least 150 mm / s, preferably of at least 160 mm / s, and particularly preferably of at least 170 mm / s. The higher the air permeability, the easier it is to breathe through the meltblown nonwoven fabric. However, excessively high air permeabilities lead to reduced filter performance of the meltblown nonwoven fabric. For this reason, it is preferred that the meltblown nonwoven fabric has an air permeability of 150 mm / s to 230 mm / s, and particularly preferably of 150 mm / s to 190 mm / s. In addition, the structure according to the invention provides the protective mask with a larger airflow area, which ensures good breathing conditions even at air permeabilities of 150 mm / s.

[0016] To ensure excellent wearing comfort, it is proposed, in a further development of the inventive concept, that the meltblown nonwoven fabric made of thermoplastic polyurethane exhibit an elongation at break of up to 400%. As explained above, the meltblown nonwoven fabric according to the invention achieves its results even when it is a single-layer fabric. Therefore, it is preferred that the meltblown nonwoven fabric be a single-layer fabric. Good results are achieved in particular when it has a thickness of 0.2 to 0.6 mm, and particularly preferably 0.3 to 0.45 mm.

[0017] In principle, the filaments of the meltblown nonwoven fabric can be made of any thermoplastic polyurethane that has a melting point suitable for extrusion and a sufficiently low viscosity in the melted state for the meltblown process. The melting point of the thermoplastic polyurethane is preferably between 190 and 235°C. Suitable commercially available thermoplastic polyurethanes are Desmopan 588E from Covestro AG, Leverkusen, Germany, and E 1154 D from BASF SE, Ludwigshafen, Germany.

[0018] According to a further, particularly preferred embodiment of the present invention, the meltblown nonwoven fabric or the filaments of the meltblown nonwoven fabric are not electrostatically charged.

[0019] A further subject of the present invention is a process for producing a meltblown nonwoven fabric described above, which comprises the following steps: a) producing a meltblown nonwoven fabric with a basis weight of 50 to 150 g / m 2by extruding a melt of thermoplastic polyurethane through a nozzle and exposing it to flowing air on the outside and stretching it, before the filaments formed thereby are deposited on a carrier, and b) flat calendering the meltblown nonwoven fabric produced in step a). The features described above as being preferred for the meltblown nonwoven fabric according to the invention also apply to the features to be achieved with the process according to the invention. Therefore, it is preferred, for example, that the meltblown nonwoven fabric after step b) has a basis weight mentioned above as being preferred, a density mentioned above as being preferred, an air permeability mentioned above as being preferred, an elasticity or elongation at break mentioned above as being preferred and / or a thickness mentioned above as being preferred.In addition, it is preferred that the meltblown nonwoven fabric after step b), as stated above as preferred, is single-layered and is not electrostatically charged.

[0020] The meltblown nonwoven fabric can be produced in step a) using any of the known meltblown processes, such as, for example, a process described in US 4,375,446, US 4,380,570, US 3,849,241, US 4,824,451 or DE 17 85 712 C3.

[0021] Preferably, the melt of thermoplastic polyurethane extruded through the nozzle in step a) is produced by extruding the thermoplastic polyurethane in an extruder and has a temperature of 220 to 260°C, and preferably of 235 to 260°C. The aforementioned, comparatively high polymer melt temperature has proven advantageous in achieving the highest possible stretch ratio in step a).

[0022] In addition, in order to achieve the highest possible stretch ratio in step a), it has proven advantageous to provide a comparatively wide air gap and a comparatively high process air flow in step a). For this reason, it is preferred to generate the flowing air through an air gap in step a), wherein the air gap has a width of 0.9 to 1.3 mm and preferably of 1.0 to 1.2 mm, and the flowing air has a standard volume flow per meter of working width of 1,200 to 2,000 Nm 3 / h / m and preferably from 1,400 to 1,800 Nm 3 / h / m.

[0023] Good results are obtained in particular when the flowing air in step a) has a temperature of 250 to 310 °C and preferably of 270 to 290 °C.

[0024] In a further development of the inventive concept, it is proposed that in step a) the melt of thermoplastic polyurethane extruded through the nozzle and exposed to flowing air on the outside is deposited on a screen belt, the distance between the nozzle and the screen belt being 100 to 300 mm and preferably 160 to 200 mm.

[0025] According to a further, particularly preferred embodiment of the present invention, the thermoplastic polyurethane melt extruded through the nozzle and exposed to flowing air on the outside is stretched in step a) by a factor of 10,000 to 30,000, and preferably 15,000 to 25,000. The stretching is the quotient of the filament speed and the speed of the polymer flow in the capillaries of the meltblown nozzle.

[0026] The meltblown nonwoven fabric produced as an intermediate product in step a) has good air permeability, but not necessarily the filter performance required to meet the FFP2 standard or the required separation efficiency for small particles. The filter performance is increased by flat calendering in step b). Good results are achieved in particular when the meltblown nonwoven fabric produced in step a) is flat calendered in step b) at a pressure of 0.5 to 5.0 N / mm 2 and preferably from 1.0 to 3.0 N / mm 2 and at a temperature of 150 to 190°C, and preferably 150 to 170°C, such as 160°C. Furthermore, it is preferred if the meltblown nonwoven fabric is subjected to flat calendering in step b) for 1 to 5 seconds, and more preferably for 2 to 3 seconds.

[0027] The above value ranges for the three process parameters pressing pressure, pressing temperature, and pressing time in step b) are exemplary preferred value ranges. It should be noted that these three process parameters are closely related to each other, so that combinations other than the above-mentioned value ranges can also produce useful results.

[0028] According to a preferred embodiment of the present invention, the flat calendering in step b) takes place in a press nip formed by two smooth rolls to enable continuous processing. However, pressing in a flat press is also conceivable.

[0029] Another object of the present invention is a face mask which contains a meltblown nonwoven fabric as described above.

[0030] Preferably, the face mask is made of a melt-blown nonwoven fabric described above and therefore does not contain any additional material.

[0031] Good results are achieved particularly when the meltblown nonwoven fabric of the face mask has a thickness of 0.2 to 0.6 mm and preferably 0.25 to 0.4 mm.

[0032] Continuing the inventive concept, it is proposed that the face mask include a carrying strap or a retaining cord and be made of one piece, i.e., the carrying strap or the retaining cord is made of the same meltblown nonwoven fabric as the rest of the face mask. Such a face mask is therefore not only easy to manufacture, but also offers the advantage of being comfortable to wear and excellent recyclability. The direct transition from the mask to the carrying strap area also results in a better seal between the mask and the wearer's cheeks, which also provides better protection for those with beards.

[0033] Continuing the inventive concept, it is proposed that the meltblown nonwoven be continuously processed using a feed system in a flat press. The flat press tools are designed such that the areas for the subsequent masks, which are intended to have improved filter properties, have narrower press gaps, resulting in a thickness reduction of between 5% and 25%, and can be heated to a temperature of 125 to 170°C. The areas that influence the wearing properties, on the other hand, are not pressed heavily or not at all and are also not exposed to temperatures of 20 to 125°C, or only to lower temperatures of 20 to 125°C, in order to ensure optimal elastic properties of the TPU meltblown nonwoven. At the same time, the press can be equipped with cutting edges on the contours of the masks to achieve direct assembly.

[0034] In a further development of the inventive concept, it is proposed that the pressing tools are contoured in such a way that an optimized shape of the masks is achieved, which further increases the tightness and wearing comfort.

[0035] The present invention is described below with reference to these explanatory but non-limiting figures.

[0036] Fig. 1 shows schematically a section of the punching pattern for producing single-layer TPU meltblown FFP2 protective masks according to the invention according to an embodiment of the present invention.

[0037] The punching pattern 10 shown in Figure 1 shows four one-piece face masks 12, each comprising a face area 14 and two carrying straps 16.

[0038] The present invention will now be described by way of illustrative but non-limiting examples.

[0039] Example 1

[0040] A meltblown nonwoven fabric made of filaments of the thermoplastic polyurethane Desmopan 588E from Covestro AG, Leverkusen, Germany with a basis weight of 90 g / m 2 and with a density of 220 kg / m 3 manufactured using the meltblown process described, for example, in US Pat. No. 4,375,446. A pilot plant from FTG GmbH was used, which has a plant width of 200 mm. The melt was extruded through the nozzle at a temperature of 260°C. The nozzle had capillaries with a diameter of 0.3 mm, the flowing air was guided through an air gap with a width of 1.0 mm, and the flowing air had a volume flow of 400 Nm. 3 / h and a temperature of 300 °C. This stretched the thermoplastic polymer by a factor of 20,000. The resulting meltblown nonwoven fabric was then placed in DIN A4 size between two preheated, smooth steel plates, which were then pressed together in a hydraulic press. This flattened the nonwoven fabric. The temperature of the steel plates was 160 °C, and the press pressure was 1 N / mm 2 and the residence time of the meltblown nonwoven between the plates was 5 seconds. A face mask was punched from the resulting meltblown nonwoven and its properties were measured. The face mask exhibited a separation efficiency of 98.4% in the finest measurement class of 0.3 to 0.5 μm and an air permeability of 160 mm / s measured according to DIN ISO 9237. For FFP2 masks, a value of 150 mm / s must not be exceeded. The meltblown nonwoven had a density of 220 kg / m 3and a basis weight of 90 g / m 2 on.

[0041] The separation efficiency was determined using a test bench constructed from a pipe system. At the inlet of the pipe system were the inlet opening and a medical nebulizer to generate an aerosol-air mixture. At the end, a fan was attached, which created a negative pressure in the pipe system through suction. In the middle of the pipe system, a sample chamber was installed, in which the sample was clamped in such a way that flow was ensured. Particle sensors were located in front of and behind the sample chamber. These determined the respective particle number in five size classes (namely 0.3 to 0.5 pm, 0.5 to 1.0 pm, 1.0 to 2.5 pm, 2.5 to 4.0 pm, and 4.0 to 10.0 pm). The separation efficiency in the classes was determined by calculating the differences between the measurement results in the respective classes of both sensors with reference to the respective initial values ​​(AG = (MEbefore / MEafter) / MEbefore in %).

[0042] In comparison, certified FFP2 masks purchased from retailers tested showed a separation efficiency of 93 to 95% and air permeabilities of 135 to 165 mm / s.

[0043] Example 2 Example 1 was repeated, except that E 1154 D from BASF SE, Ludwigshafen, Germany, was used as the thermoplastic polyurethane. The face mask exhibited a separation efficiency of 97.9% in the finest measurement class of 0.3 to 0.5 μm and a measured air permeability of 162 mm / s. The meltblown nonwoven had a density of 230 kg / m³. 3 and a basis weight of 87 g / m 2 on.

[0044] Reference symbol list 10 punching patterns

[0045] 12 face mask

[0046] 14 Facial area of ​​the face mask

[0047] 16 carrying straps

Claims

Patent claims 1 . Meltblown nonwoven fabric comprising filaments of thermoplastic polyurethane with an average fineness of maximum 2.5 pm.

2. Meltblown nonwoven fabric according to claim 1, characterized in that it is composed of at least 50 wt.%, preferably at least 80 wt.%, particularly preferably at least 90 wt.%, further preferably at least 95 wt.%, very particularly preferably at least 99 wt.% and most preferably 100 wt.% of one or more filaments of thermoplastic polyurethane each having an average fineness of at most 2.5 pm.

3. Meltblown nonwoven fabric according to claim 1 or 2, characterized in that the average fineness of the at least one filament made of thermoplastic polyurethane is 1.0 to 2.5 pm and preferably 1.5 to 2.5 pm.

4. Meltblown nonwoven fabric according to at least one of the preceding claims, characterized in that it has a basis weight of 50 to 150 g / m 2 , preferably from 60 to 120 g / m 2 , particularly preferably from 70 to 110 g / m 2 , most preferably from 80 to 100 g / m 2 and most preferably from 85 to 95 g / m 2 has.

5. Meltblown nonwoven fabric according to at least one of the preceding claims, characterized in that it has a density of 180 to 260 kg / m 3 and preferably from 200 to 230 kg / m 3 has.

6. Meltblown nonwoven fabric according to at least one of the preceding claims, characterized in that it has an air permeability measured according to DIN ISO 9237 of at least 150 mm / s, preferably of at least 160 mm / s and particularly preferably of at least 170 mm / s.

7. Meltblown nonwoven fabric according to at least one of the preceding claims, characterized in that the at least one filament made of thermoplastic polyurethane has an elongation at break of up to 400%.

8. Meltblown nonwoven fabric according to at least one of the preceding claims, characterized in that it is single-layered and not electrostatically charged.

9. A process for producing a meltblown nonwoven fabric according to at least one of the preceding claims, comprising the following steps: a) producing a meltblown nonwoven fabric having a basis weight of 50 to 150 g / m 2 by extruding a melt of thermoplastic polyurethane through a nozzle and applying flowing air to the outside and stretching it before the filaments thus formed are deposited on a carrier, and b) flat calendering the meltblown nonwoven fabric produced in step a).

10. The method according to claim 9, characterized in that the melt of thermoplastic polyurethane extruded through the nozzle in step a) is produced by extrusion of the thermoplastic polyurethane in a Extruder and has a temperature of 220 to 260°C and preferably 235 to 260°C.

11. Method according to claim 9 or 10, characterized in that in step a) the flowing air is generated through an air gap, wherein the air gap has a width of 0.9 to 1.3 m and preferably of 1.0 to 1.2 mm and the flowing air has a volume flow of 1,200 to 2,000 m 3 / s and preferably from 1,400 to 1,800 m 3 / s.

12. The method according to at least one of claims 9 to 11, characterized in that in step a) the melt of thermoplastic polyurethane extruded through the nozzle and exposed to flowing air on the outside is deposited on a screen belt, the distance between the nozzle and the screen belt being 100 to 300 mm and preferably 160 to 200 mm.

13. The method according to at least one of claims 9 to 12, characterized in that the melt of thermoplastic polyurethane extruded through the nozzle and exposed to flowing air on the outside is stretched in step a) by a factor of 10,000 to 30,000 and preferably 15,000 to 25,000.

14. Method according to at least one of claims 9 to 13, characterized in that the meltblown nonwoven fabric produced in step a) is heated in step b) at a pressure of 0.5 to 5.0 N / mm 2 and preferably by 1.0 to 3.0 N / mm 2and flat calendered at a temperature of 150 to 190°C and preferably 150 to 170°C.

15. The method according to at least one of claims 9 to 14, characterized in that the flat calendering in step b) takes place in a press nip formed by two smooth rolls.

16. A method according to at least one of claims 9 to 15, characterized in that the meltblown nonwoven fabric is continuously processed by means of a feed system in a flat press, the tools of which are designed such that the areas for the subsequent masks, which are intended to have the improved filter properties, have narrower press nips, which result in a thickness reduction of between 5% and 25%, and are heated to a temperature of 125 to 170°C, and the areas that influence the wearing properties are pressed less strongly or not at all and are exposed to temperatures of 20 to 125°C.

17. A face mask containing a meltblown nonwoven fabric according to at least one of claims 1 to 8.

18. Face mask according to claim 17, characterized in that it consists of a meltblown nonwoven fabric according to at least one of claims 1 to 8.

19. A face mask according to claim 17 or 18, characterized in that it comprises a retaining cord and is in one piece.

20. Face mask according to at least one of claims 17 to 19, characterized in that the meltblown nonwoven fabric has a thickness of 0.2 to 0.6 mm and preferably 0.25 to 4.0 mm.

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