Field of the invention The present invention relates to the manufacturing of face masks aiming at filtering unwanted particles and/or aerosols.

Background

Surgical or medical face masks aim a suppressing transmission of air borne particles or aerosols from a wearer to the environment or from the environment to the wearer. These may be worn in operating theatres or other medical settings, or to reduce inhalation of unwanted substances in unhealthy air environment. In case of exhibiting appropriate microbial barrier function, can also be effective in reducing the emission of infective agents from the nose and mouth of an asymptomatic carrier or a patient with clinical symptoms. The medical face masks may fall under the Medical Device Regulation - under the European standard EN 14683 type II or, with additional splash protection type HR . The European Standard EN 14683 specifies requirements and test methods for medical face masks to limit the emission and transmission of infective agents.

Surgical masks should not be confused with respirators, for which more stringent fit and filtering performance is required. Modern surgical masks are often from non-woven material and are intended to be discarded after each use. Often the design includes a three- ply material, especially a melt-blown web as primary filtering layer sandwiched between carrier webs, such as spunbonded webs. Surgical masks may comprise pleats or folds to allow better fit on a wearer when covering chin, mouth and nose. A face mask may be secured on a wearer by straps, often elasticated straps, that may form closed loops to be fitted either around the ears or the back of the head. Alternatively straps, typically non elastic straps are connected to the mask and have loose ends that may be tied or otherwise connected to each other around the head or neck of a wearer. Optionally, the mask may comprise a stiffening means in the upper portion to allow adaptation to the shape of the nose so as to enhance fit. As one of many disclosures, US20140182602A1 describes such a face mask with a pleated nonwoven material and straps connected thereto.

It is also well known to employ nonwoven materials as filtering elements, in particular melt-blown structures are being widely used, typically in combination with spunbonded webs, that provide better strength and hence better usability than the relatively friable melt- blown webs. There is also ample disclosure of suitable materials to be used as filtering material, whereby filtering performance - balanced versus breathing resistance, as can be measured by pressure drop of air - is strongly dependent on fiber fineness and basis weight. US5645057A discloses a melt-blown web comprising a plurality of thermoplastic microfine fibers, exhibiting an average fiber diameter of less than 1.5 microns, preferably from 0.8 to 1.3 microns, and basis weights of less than 10 g/m ² , providing comparable performance to prior art materials exhibiting fiber diameters of typically 1.8 to 3 microns at basis weights of 20 to 40 g/m ² .

Whilst face mask materials may be produced from a great variety of materials, polypropylene based materials are often preferred for cost and availability reasons.

It is further known to enhance the filtering performance by using certain resins, waxes, compounds and plastics as coatings on the filter material to attract particles with an electrostatic charge that holds them on the filter material surface, a technique also sometimes referred to as “electret”, see e.g., CN1544724A for a particular execution employing 3-5 weight -% tourmaline with average particle size not greater than 0.5 pm in the extruded polymer.

Typically, nonwovens suitable for being employed in face masks are manufactured by two processes.

In a first approach, the layers for the composite web in the mask are produced separately to be then combined into a pre-cursor web by adhesive, heat- or ultrasonic bonding.

In a second approach, the laminate structure is made in a single nonwoven making process, such as by producing a first carrier layer of spunbonded fibers to which one or more melt- blown fiber layer(s) is/are added, further complemented by another spunbonded layers. Both of these techniques are broadly described in the art and available in industrial application. For economic reasons, the pre-cursor webs are made on large production units, often having a width of several meters. Before converting the pre-cursor in the face mask production site, these materials are slit to the appropriate width for a face mask.

However, in particular in view of increased air pollutions in certain regions but also in view of epidemic or even pandemic occurrence of health threatening pathogens, there is still a need for improving the efficiency and economy of such masks and their manufacturing

Summary

In a first aspect, the present invention is a pre-cursor nonwoven laminate web for the manufacture of face masks, exhibiting x-(length) direction, y-(width), and z-(thickness) direction, and extending essentially endless in x-direction. The web comprises a first spunbonded web, a second spunbonded web, essentially coextensive with the first spunbonded web, and one or more melt-blown web(s) sandwiched between the spunbonded webs. The webs are connected to each other without adhesive, and the melt-blown web(s) exhibit(s) a width less than the one of the spunbonded webs.

The pre-cursor nonwoven laminate may further satisfy one or more of the conditions selected from the group consisting of the materials of the webs are polyolefins, preferably polypropylene or polyethylene; the basis weight of the spunbonded webs is less than about 15 g/m ² , preferably less than about 10 g/m ² and more than about 5 g/m ² ; the basis weight of the one or more melt-blown webs together is more than about 20 g/m ² , preferably more than about 30 g/m ² more preferably more than about 40 g/m ² and less than about 100 g/m ² ; the spunbonded fibers exhibit an average fiber diameter of more than about 3 pm, preferably more than about 10 pm, and less than about 30 pm, preferably less than about 20 pm; the melt-blown fibers exhibit an average fiber diameter of less than about 5 pm, preferably less than about 3 pm, more preferably less than about 1.5 pm, and more than about 0.8 pm; the pre-cursor web exhibits a cross-directional extension or width of less than about 300 mm, preferably less than about 200 mm; the width of the melt-blown layers is less than 95%, preferably less than 90%, more preferably less than 95% and more than about 75%, preferably more than about 80% of the width of the spunbonded layers; the melt-blown fibers are treated by high-voltage treatment (Electret), optionally comprising a charge enhancing additive.

In another aspect, the present invention is a process for the manufacture of a pre-cursor nonwoven laminate web for the manufacture of face masks, wherein the laminate comprises a first spunbonded web, a second spunbonded web, essentially coextensive with the first spunbonded web, and a melt-blown web sandwiched between the spunbonded webs. The process comprises the steps of a) providing a first and a second spunbonding unit, each comprising, polymer supply, extruder, polymer pump, spunlaying unit a melt-blowing unit; a web receiving unit; b) extruding first and a second spunbonded web at essentially same width, c) extruding a melt-blown web such that the melt-blown web is sandwiched between the spunbonded web; d) collecting the web sandwich on a lay-down system; e) feeding the web sandwich to a further process step of an interim storage unit or a further processing unit; wherein the extruding of the melt-blown web is executed such that the width of the melt- blown web is less than the width of the spunbonded webs.

Optionally, the process may further comprise one or more steps selected from the group consisting of: selecting a polyolefin for the materials for the webs, preferably polypropylene or polyethylene; adjusting the basis weight of the spunbonded webs to less than about 15 g/m ² , preferably less than about 10 g/m ² and more than about 5 g/m ² ; adjusting the basis weight of the one or more melt-blown webs together to more than about 20 g/m ² , preferably more than about 30 g/m ² more preferably more than about 40 g/m ² and less than about 100 g/m ² ; adjusting the spunbonded fibers to exhibit an average fiber diameter of more than about 3 pm, preferably more than about 10 pm, and less than about 30 pm, preferably less than about 20 pm; adjusting the melt-blown fibers to exhibit an average fiber diameter of less than about 5 pm, preferably less than about 3 pm, more preferably less than about 1.5 pm, and more than about 0.8 pm; adjusting the pre-cursor web to a cross-directional extension or width of less than about 300 mm, preferably less than about 200 mm; adjusting the width of the melt-blown layers to less than 95%, preferably less than 90%, more preferably less than 95% and more than about 75%, preferably more than about 80% of the width of the spunbonded layers; treating the melt-blown fibers by high-voltage treatment (Electret), optionally adding a charge enhancing additive.

In yet another aspect, the present invention is a surgical face mask, comprising such a pre cursor web, further comprising fixation elements.

In an even further aspect, the present invention is a process for the manufacture of a face mask, comprising the steps of - providing

- a pre-cursor laminate web forming unit;

- a fixation means supply;

- a mask converting unit;

- a packing unit;

- forming a pre-cursor nonwoven pre-cursor laminate web;

- feeding continuously the pre-cursor laminate web to the mask converting unit;

- separating and spacing apart web pieces from the laminate web;

- connecting the fixation means to the pre-cursor laminate.

The present invention also relates to a process for the manufacture of an essentially continuous sequence of face masks, where the face masks exhibiting varying pre determined basis weights of melt-blown material the process being essentially uninterrupted upon the variation of basis weight.

Brief description of the Figures

Fig. 1 depicts general details of a face mask.

Fig. 2A to D show certain details of exemplary executions according to the present invention.

Fig. 3A and B depict schematically process set up and respective equipment for executing the present invention.

Figures are not to scale, and same numerals refer to same or equivalent elements.

Detailed description

The present invention relates to a surgical face mask, to non-woven pre-cursor materials for such masks as well as to manufacturing of such masks or pre-cursors.

For the purpose of general explanation but without intending any limitation to the present invention, Fig. 1 depicts schematically such a face mask 100 in general terms. The face mask 100 is adapted to be placed over chin, mouth, and nose of a wearer (not shown). The mask comprises upper (102) and lower (108) margins as well as left (104) and right (107) margins, and corresponding upper left (112) and right (122) and lower left (118) and right (128) comers, all relative to a wearer during use. The mask comprises a mask panel 200, executed as a web material, as may be positioned in a pleated manner, indicated by pleats 210. The mask panel further exhibits a first, inner, wearer oriented surface 220, and an opposite second or outer surface 230.

Further the mask comprises fixation straps 250, extending from the comers of the mask and adapted to be connected around the head of a wearer. The mask further comprises peripheral strips at the margins of the panel. At the left (104) and right (107) side margins, the peripheral strips 105, 106 are attached such that - in addition to reinforcing the margins - they fix the pleated structure, allowing to fold open in the center portion of the panel, thereby creating a three dimensional shape upon donning. At the lower margin 108 of the panel, an optional peripheral strip 109 may also reinforce the structure. At the upper margin 102 of the panel, an optional peripheral strip 103 may also be executed as the lower one, or - as shown - as a wider upper strip to better adapt to the shape of the nose region of a wearer. Optionally, a stiffening means (not shown) may be integrated in the central portion of the upper margin, as may be formed to the shape of the nose of the wearer upon donning. Fig. 2A depicts a cross-sectional view of a mask panel web material 300 for a mask panel 200, exhibiting a y- or width direction 306 aligned with the horizontal axis or left-to-right orientation of a wearer, and a x- or length direction aligned with the longitudinal axis (perpendicular to the paper plane) or upper - lower orientation of a wearer. Further, the web exhibits a z- or thickness direction 308, perpendicular to the x- and y- direction.

The term “web material” refers to an essentially endless material in one direction, i.e. the longitudinal extension, or the length, or the x-direction in Cartesian coordinates relative to the web material. Often, though not necessarily, the web materials will have a thickness dimension (i.e. the z-direction) which is significantly smaller than the longitudinal extension (i.e. in x-direction). The webs exhibit lateral side margins and often, though not necessarily, the width of web materials (the y-direction) will be significantly larger than the thickness, but less than the length. Often, though not necessarily, the thickness and the width of such materials is essentially constant along the length of the web. Within the context of the present invention, such web materials are non- woven materials. A web material travels through process steps or an equipment along a web path along the machine direction of the process step or equipment, which is typically aligned with the longitudinal extension or x-direction of the web.

A web material suitable for panel web material for the present invention is composed of several sub-layer materials, in particular of non-woven sub-layers. Such sub-layers may be of the same type, or be different, such as by differing in composition, thickness, basis weight, or physical, including mechanical, or chemical treatment of the sub-web materials. Preferably the sub-layers comprise materials that are thermally compatible to provide a coherent structure once combined. Preferred materials are polyolefins, in particular polypropylenes.

Referring again to the exemplary structure depicted in Fig. 2A, the panel web 300 is executed as a tri-layer structure, wherein the outer sub-layers 320, 330 provide mechanical properties such as strength or softness, whilst the one or more inner layers - here only on layer 310 shown - provide the particle or aerosol retention or filtering function.

The inner layer 310 may well be made as one or more layers of “melt-blown” materials, made of thermoplastic fine fibers. The fine fibers of melt-blown web 310 typically have an average fiber diameter of less than about between 2 and 4 pm, though often also less than about 1.5 pm, and typically more than about 0.8 pm, but less than about 20pm. The basis weight of such a melt-blown layer may be as low as about 10 g/m ² , or more than about 20 g/m ² or more than about 30 g/m ² , but typically less than about 80 g/m ² .

The outer material layers 320, 330 can be made with from spunbonded fibers, exhibiting fiber diameter of between about 1 and 50 pm, though often between about 15 and 35 pm and basis weights of mostly more than about 5 or 8 pm, or less than about 30 g/m ² or even less than 20 g/m ² . The layers may be essentially identical in composition, fiber size and basis weight, or may be different, e.g., to allow a softer surface 220 towards the wearer. The structure as described in Fig. 2A is often referred to as “SMS” referring to a tri-layer structure of spunbonded (S) - melt blown (M) - spunbonded (S) technologies, each well known in the art. However, it is also within the scope of the present invention to employ structures with more than three layers, e.g., having two MB layers (SMMS), as depicted in Fig. 2D, or more than 2 S layers, and so on.

Within the context of the present invention and as will be discussed in more detail herein below, it is important that the inner layer 310 is not coextensive with the outer layers, but leaves free regions 350’ and 350” on either side to the inner or retention layer 310.

The principle for manufacturing such tri-layer laminates is generally well known in the art, e.g., for barrier fabrics suitable in absorbent articles. Typically, and as schematically depicted in the left portion of Fig. 3A and B, a manufacturing equipment 1000 comprises fiber forming units 1100, 1200, and 1300 arranged along the machine or x-direction of the process (1004) as well as of the resulting web (304).

The fiber forming units comprise polymer supply units (1110, 1210, 1310, respectively), extruder (1120, 1220, 1320, respectively) and polymer pumps (1130, 1230, 1330, respectively). Further, in processing direction 1004, first spunbonding fibers 1250 are ejected from first spunbonding head or beam 1240 and deposited as first outer web 320 onto a lay down belt 1410 of a laydown unit 1400, supported by lay-down suction box 1420. The width of the web 320 is adjusted to match the width of the final face mask. Next along the direction 1004 of processing is a melt-blowing die head 1140, spraying fine fibers 1150 onto the web 320, thereby forming the inner or retention layer 310 at a width less than the one the web 320, corresponding to the width of the retention layer in the finished mask, thereby leaving melt-blown free regions 350’ and 350” along both sides of the web 320. Further downstream, a second spunbond head or beam 1340 deposits fibers 1350 forming a second spunbonding web 330 onto the inner layer 310, at a lay down width equal to the one of first spunbond layer 320, thus wider than the inner layer 310.

This is in contrast to conventional SMS (or similar) processes, whereby the widths of the created sub-layers are not only essentially identical but also significantly larger than the width of a single mask, often extending over several meter.

Also, in contrast to such conventional methods, the resulting tri- or multi-layer web panel web material 300 is not wound up or otherwise prepared for storage and delivery to a separate converting unit, but rather delivered as pre-cursor material for the mask directly and continuously to further processing steps of compressing 1450 and optionally pleating 1500, if pleats 210 are desired. Also, subsequent masks 100’, 100” may be cut in the same unit 1500, and optionally spaced apart by mask spacing 290. This is beneficial, if straps 250 are to be supplied from a strap supplies, here shown as 1610, and directed by guide rolls 1620’ and 1620” to overlay the pleated panel web material. The straps 250 and the panel web material 300 may be connected by a combining and connecting unit 1700, as may apply adhesive or energy, preferably and as indicated ultrasonic energy with a sonotrode 1710 and an anvil 1720.

Optionally a further strap material may be applied (not shown in Fig. 2), or the cross- directionally extending margins 102 and 108 may be reinforced, e.g. by the same connecting unit 1700. Similarly, a stiffening material 260 may be connected at the upper margin 102 of the mask 100 (not shown in Fig. 3).

The mask is further transferred to a final cut unit 1800 for separating the straps and packing the resulting face mask 100.

Thus the mask and relating manufacturing method provide benefits over the prior art in that material savings can be realized by using less of the melt-blown material, without majorly compromising on performance, as the filtering effect in the periphery is less relevant but also enhanced by the connecting. The consequential reduction in air permeability, and hence reduced breathability, is also of low relevance in the peripheral regions along the margins.

Considering a typical mask width 190 mm and a 15 mm MB-free portion along each of the margins, a saving of over 15 weight % of MB material can be realized.

On the process side, the manufacturing speed is determined by the converting speed, which may more than 20 m/min, or between 30 and 35 m/min but typically less than 100 m/min, or even less than 50 m/min, which does not pose particular problems for the web forming sections. Yet a further advantage is that when it is desired to produce masks with same dimensions but differing filtering performance, and hence differing basis weights of the retention layer. Referring to Fig. 2B, a panel web material 300 with retention layer 310, as depicted in Fig. 2A, can be seen in cross-sectional view of a mask, further comprising straps 250 and connecting regions 255’ and 255”. A similar structure is shown in Fig. 2C, with the inner retention layer 310 exhibiting a higher basis weight (indicated by higher thickness). A change over to a different basis weight may be readily achieved by the push of a button. This is in contrast to conventional approaches, where such a change over requires a more time consuming material change with shut down periods.

Alternatively, two retention layers 310’ and 31”, as shown in Fig. 3D may be employed to achieve higher MB basis weight. Such an alternative may also enhance the homogeneity of the total retention layer 310, as variations in the two layers 310’ and 31” tend to level out to a certain degree. Also the change over from a single to dual MB beam (and conversely) may be achieved very readily.

Optionally, the retention performance of the melt blown material may be enhanced by applying electro-charge enhancing materials via a further supply unit 2010 to the polymer for the melt-blowing step. Such additives known in the art, such as certain resins, waxes, e.g. - without limitation - magnesium stearate or 3 to 5 weight % of tourmaline 3-5% with average particle size not greater than 0.5mum, optionally supported by coupling agents or dispersants. These particles may be further electrically charged by high voltage electrode 2020 in Fig 3A and B, and a counteracting grounding 2030.

A skilled person will also realize that for the converting part of the process alternative techniques may be applied without departing from the invention, such as separating consecutive masks 100’, 100” or their respective pre-cursors, and rotating these before attaching straps. Similarly, the execution of the straps may be differently applied, e.g. each a single strap being connected to both upper comers 112 and 122 and lower corners 118 and 128 of the mask, respectively, for being worn around the head, or being connected to the left (112 and 118) and right (122, 128) comers for being worn around the ears.

Further even though certain executions are described independently from each other, the skilled person will also realize that combinations are also within the scope of the invention.