MXPA01004279A - - Google Patents

Description

FIBROUS TRAM BLOWED BY UNIFORM FUSION, METHODS AND APPARATUS FOR ELABORATION DESCRIPTION OF THE INVENTION The present invention relates to fibrous webs blown by melting multiple layers, methods and apparatus for the manufacture thereof. BACKGROUND OF THE INVENTION The fabrication of meltblown fibrous webs has been discussed in several references, including, Wente, Van A., Superfine Thermoplastic Fibers, 48 Industrial Eng. And Chem. 1342-46 (1956); Report No. 4364 of Naval Research Laboratories, published on May 25, 1954, entitled Manufac t ure of Superfi ne Organi c Fibers, by Wente, V.A., Boone, C.D., and Fluharty, E L.; and US Patent No. 3,971,373 to Braun. During the manufacture of meltblown fibrous webs, a thermoplastic polymer or resin is usually extruded through a row of small holes from side to side in a high velocity gaseous flow which attenuates the material arising from the fibers. The gaseous flow creates a turbulence that randomly entangles the fibers to form a coherent nonwoven web in a collector. The collector can be a Ref .: 128742 movable flat belt or a rotating cylindrical screen or drum. The resulting nonwoven web is transferred from the collector to a temporary storage roll. The known processes have coupling drawbacks, that is, they can produce a significant loss as a derivative of the process and can also produce non-uniform cuts of the screen. The loss (also referred to as waste) normally occurs at the edges of the web during the processing of the meltblown fibrous webs. The loss or waste results because the edges of the weft are normally "lightened or reduced", which means that the edges are tapered or diminished and do not have the same weight and density as the central portion of the weft. The lightening or reduction originates from the dispersion of the fiber at the edges of the weft. To eliminate this variation in weight and density, the edges of the weft are normally cut and then discarded as loss, while the central portion of the weft is retained for further processing. Discarded material is added to the costs of the process, especially when online processing of the plot is desired.

The known meltblown fibrous webs or fabrics are usually monolayer fabrics or fabrics which, by definition, have only one layer. Monolayer meltblown fibrous webs often suffer from non-uniformity over their transverse web due, for example, to variations in the hole diameter. Variations in the diameter of the hole can cause non-uniform fiber deposition which, in turn, causes variations in the basis weight in the cross-sectional dimension. The basis weight is the weight per unit area of the monolayer web, and is usually adjusted by varying the extrusion rate of the polymer or the collector velocity or both. For example, if a higher basis weight plot is desired, the collector speed can be reduced and / or the extrusion rate can be increased. Reciprocally, if a lower basis weight web is desired, the collector speed may be increased and / or the extrusion rate may be decreased. A process for overcoming variations in the basis weight includes the lamination of multiple plots together using agents such as adhesives or resins and / or by physical processing such as welding. Variations in multiple frames then preferably averaged non-uniformities such that the minimum acceptable basis weight is achieved over the total laminated web. A disadvantage of this process is that some areas of the weft can have an excessive basis weight and unnecessary amounts of the weft material. The unnecessary material, as well as the rolling and / or processing agents needed to laminate the wefts to form the multiple weft products, they are added to the production costs and increasing the complexity. In addition, the solders and / or agents used to laminate the layers can adversely affect the formability and flexibility of the resulting articles. Efforts to employ tubular fibrous web processes to achieve a uniform web have typically involved fibrous web formation blown by tubular fusion and compression of the tube to obtain a uniform web without lightened or reduced edges. Alternatively, the tubular web can be cut longitudinally for the tube to open, whereby a uniform web is produced with two machine-cut edges. Two processes are described in U.S. Patent Nos. 3,909,174 (Blair et al.) And 4,032,688 (Pall). A disadvantage of these processes is that variations in the thickness of the weft can often be helical by nature. As a result, cutting the weft longitudinally frequently causes bound variations in the density of the weft, which are located at an angle, usually called the "deflection angle" with respect to the centerline of the weft.

BRIEF DESCRIPTION OF THE INVENTION The present invention is directed to overcoming the drawbacks already mentioned in the known methods for manufacturing the meltblown fibrous webs. In one aspect, the present invention provides a new apparatus for the fabrication of a meltblown fibrous web. The new apparatus includes (i) a manifold having a generally cylindrical forming surface and (ii) a source that is capable of directing meltblown fibers to the forming surface. The generally cylindrical forming surface can rotate about a longitudinal axis and can simultaneously move parallel to the longitudinal axis, such that a selected point on the forming surface can move in a helical pattern about and along the longitudinal axis from a first end of the manifold to a second end of the collector. The helical model defines a helix angle with respect to the longitudinal axis. The device it also includes (iii) a separator that can separate a blown fibrous web by tubular fusion formed on the forming surface in a direction generally parallel to the helix angle. The separator therefore converts the fibrous web blown by tubular fusion into a fibrous web blown by non-tubular or uniform melting. In a second aspect, the present invention provides a method of making a meltblown fibrous web using a collector having a generally cylindrical forming surface. The forming surface is rotated about a longitudinal axis and simultaneously moves longitudinally in the direction of the longitudinal axis such that a selected point on the forming surface moves in a helical pattern about and along the longitudinal axis from a first end of the manifold to a second end of the collector. The helical model defines a helix angle with respect to the longitudinal axis. The meltblown fibers are directed to the forming surface as the forming surface rotates and moves longitudinally, such that a fibrous web blown by tubular fusion is formed on the forming surface. The fibrous web blown by tubular fusion is then separated along a direction generally parallel to the helix angle to convert the fibrous web blown by tubular fusion into a fibrous web blown by non-tubular or uniform melting. In a third aspect, the present invention provides a multi-layer meltblown fibrous web having a plurality of interconnected layers containing the meltblown fibers. At least one of the layers containing the fiber has a less heavy edge. The plot also has two separate edges. The less heavy edge is located between the separated edges, and the separated edges and the less heavy edge are generally parallel to each other. The multi-layer meltblown fibrous web can be used in a variety of items such as filters for masks or respirators. The multilayer meltblown fibrous webs of the present invention are produced in a manifold having a forming surface in the general shape of a cylinder where the forming surface rotates about the longitudinal axis of the cylinder. While the forming surface rotates as such, it simultaneously proceeds parallel to and along the longitudinal axis. As a result, any particular point on the training surface moves as along a helical path during the elaboration of the frame. A source of melt-blown fiber is directed into the forming surface along at least a portion of the longitudinal extent of the manifold, whereby a layer of meltblown fibers is formed on the forming surface. The forming surface normally completes at least one turn on the longitudinal axis in the time required to advance the forming surface along the length of the meltblown fiber source. Where the forming surface completes two or more turns in the time required to advance the forming surface along the length of the collector, a multi-layered tubular web will be constructed on the forming surface. Because the forming surface rotates about the longitudinal axis while simultaneously advancing parallel to the longitudinal axis, the lightened or reduced edges are formed in each layer of melt blown fibers in a helical pattern on the cylindrical forming surface. A separator is used to separate the fibrous web blown by tubular fusion in a direction oriented at an oblique angle with respect to the axis longitudinal of the cylindrical formation surface. The oblique angle is equal to the helix angle formed by the lightened or reduced edges during processing of the meltblown fibrous web. The uniform meltblown fibrous web formed after separating the blown fibrous web from tubular multilayer along the helix angle includes two separate edges having a thickness substantially equal to the thickness of the remainder of the web and does not require cut or an additional process before the use of the frame in other processes. By separating the blown fibrous web from multi-layer tubular melting in a direction generally parallel to the helix angle to produce a uniform multi-layer meltblown fibrous web, variations in the density or weight of the meltblown fibrous web caused by Lightened or reduced edges, are parallel to the edges of the uniform weft formed. This is in direct contrast to the known tubular fused fibrous webs that are cut longitudinally, causing the lightened or reduced edges to cross the web at a deflection angle with respect to the center line of the uniform web.

The fibrous webs of the present invention are different from the known webs due to their multilayer composition wherein the lightened or reduced edges are incorporated in the web and are generally arranged parallel to the separate edges of the web. Because meltblown fibrous articles are usually formed from multiple layers of meltblown fibers, variations in the basis weight contributed by the lightened or reduced edges can be significantly reduced. The layers of the weft that end at the lightened or reduced edges form only a fraction of the overall basis weight of the weft as a whole. In addition, any variation in the basis weight contributed by the non-uniformities through the die or dies used to form the articles may also be reduced due to the nature of the multiple layers of the articles. The helical nature of the process will naturally displace the variations over the width of the weft in such a way that normally they will not be aligned along the thickness of the weft. Because the process causes the least heavy edge to be included in the resulting screen, the invention is advantageous in that the production of waste originating from the Previous need to remove the lighter edge of the product. These and other characteristics and advantages of meltblown fibrous webs, of the apparatus and methods for making them - are discussed in detail below.

GLOSSARY With reference to the invention, the following terms are defined as follows: "collector" means an apparatus that is capable of collecting melt blown fibers, "less heavy edge" means the portion of a blown fibrous web layer by melting where the density and basis weight of the web are reduced due to fiber dispersion; "forming surface" means the portion of a collector where the meltblown fibers are deposited after leaving a source of meltblown fiber; "helical model" means the model formed in the shape of a helix, in other words, similar to the path followed by the thread of a screw; "helix angle" means the angle formed by the helical model in relation to a plane perpendicular to the longitudinal axis; "interconnected layers" means the layers of meltblown fiber that are interconnected, for example, the interwoven fiber between the fibers in the different layers, an agent introduced to connect the layers (for example, a resin, adhesive, etc.). .), and / or processing (for example, by spindle, welding, etc.); "intermediate layer" means a layer of foundry fiber located between the first and second layers of a fibrous web blown by melting multiple layers; "longitudinal axis" means the central axis on which the cylindrical formation surface rotates; "machine direction" means the direction of travel of the forming surface during the formation of a fibrous web blown by tubular fusion; "meltblown fiber layer" and its variations means a fibrous non-woven structure containing meltblown fibers and possibly other ingredients formed in a manifold or other surface during a step before a source of fibers blown by fusion; "meltblown fibrous web" means a fibrous non-woven structure containing meltblown fibers and possibly other ingredients and having sufficient integrity to be manageable by itself as a mat; and "separated edge" means an edge of a fibrous web blown by melting multiple layers that is physically separated from another edge of the web by any convenient method, for example, by cutting, tearing, etc., BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a perspective view of a portion of a fibrous web blown by multi-layer melting 10 according to the present invention having two separate edges 12 and 14. Figure 2 is a sectional view enlarged, schematic cross section of the fibrous web blown by multiple layer fusion 10 of Figure 1 taken along line 2-2. Figure 3 is an enlarged, exploded, schematic cross-sectional view of the fibrous web Blown by alternative multiple layer fusion 110 according to the present invention. Figure 4 illustrates a breathing mask 16 that includes the multi-layer melt blown fibrous web as a filter according to the present invention. Figure 5 is a perspective view of an apparatus including a manifold 30 useful in the manufacture of a fibrous web blown by multiple layers according to the present invention. Figure 6 is a view of a preferred forming surface used in a manifold 30 for the apparatus of Figure 5, taken along line 6-6 of Figure 5. Figure 6A is a sectional view enlarged partial cross-section illustrating the energy transfer system used to rotate the bands 40a and 40b in the apparatus of Figures 5 and 6. Figure 6B is a schematic end view of the energy transfer system used to supply the energy to the axes 42 that rotate the bands 40a and 40b along the longitudinal axis 32 and rotate the manifold 30 completely on the longitudinal axis 32. Figure 6C is a sectional view Enlarged partial transverse of the nested bands 40a and 40b in the collector 30 of Figure 5, taken along the line 6C-6C. Figure 7 is a schematic diagram of a tubular multi-layer meltblown fibrous web 280 according to the present invention and an apparatus 230 for forming this web according to the invention. Figures 8A-8C are enlarged, schematic cross-sectional views of the meltblown fibrous webs of alternative multiple layers 210, 210 *, and 210"according to the present invention, Figure 9 is a schematic diagram of a 5: alternate tubular multiple layer meltblown fibrous web 380 according to the present invention Figure 10 is a schematic diagram of another tubular multi-layer meltblown fibrous web 480 according to the present invention. is a schematic diagram of an in-line industrial process using a multi-layer meltblown fibrous web 510 in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention provides multi-layer meltblown fibrous articles where the meltblown fiber layers can terminate at a lighter edge which is generally parallel to the machine direction of the blown fiber layers. merge in the article. The less heavy edge of each meltblown fiber layer does not need to be cut and can be incorporated into the article. In several cases, the multi-layer meltblown fibrous article is provided in the form of a web having a central line aligned with the machine direction and located between two separate edges. In the form of a frame, the lightened or reduced edges are generally parallel to the center line of the frame. The meltblown fibers used in the present invention can be essentially any size or diameter, proportioned such that the fibers can be meltblown to produce wefts and articles as discussed herein. The preferred meltblown fibers can be microfibers, depending on the application. "Microfibers" are fibers that have an average diameter of approximately 10 micrometers (μm) or less, measured generally transverse to the longest dimension of the fiber. Microfibers can offer improved filtration efficiency and other beneficial properties when used in various articles. In some applications, it may be desired that the melt blown fibers be oriented to increase the strength of the weft. Examples of processes useful in the formation of oriented meltblown fibers can be found in U.S. Patent Nos. 4,988,560 (Meyer et al.) And 5,141,699 (Meyer et al.). The fibers may be made from a single homogeneous polymeric material, or they may include one or more polymers in, for example, a two-component form as described in U.S. Patent 4,547,420 (Krueger et al.) Or U.S. Patent 4,729,371 (Krueger et al.). The electrical charge can be imparted to non-woven melt-blown fibrous webs to improve their filtration function using the techniques described in, for example, US Patent No. 5,496,507 (Angadjivand et al.), The North American Patent No. 5,057,710 (Nishiura et al.), The Patent North American No. 4,592,815 (Nakao), and US Patent No. 4,215,682 (Kubik et al.).

Fibers that include polypropylene may be convenient for receiving and retaining a persistent electrical charge. Another polymer that may be convenient for making the electric meltblown fibers is poly (4-methyl-1-pentene) alone or in combination with polypropylene. The fiber materials may contain additives to improve filtration function, such as the additives described in US Pat. Nos. 5,025,052 and 5,099,026 (Crater et al.), And Patent Application No. 08 / 514,866 (Rousseau et al.), And it may also have low levels of extractable hydrocarbons to improve execution; for example, see Patent Application Serial No. 08 / 941,945 (Rousseau et al.). Fibrous webs can also be manufactured to have increased oily drizzle resistance as discussed in U.S. Patent Nos. 5,411,576 and 5,472,481 (Jones et al.), And in US Patent Applications 08 / 941,270 and 08 / 941,864 (Rousseau et al. collaborators), or they can be made together with other layers to inhibit the liquid passage as described in US Pat. No. 5,706,804 (Baumann et al.). As described in several patents cited in this paragraph, the fibers may contain certain processable fusion fluorocarbons, for example, fluorochemical oxazolidinones and piperazines and compounds or oligomers containing perfluorinated moieties. The use of the additives can be particularly beneficial for the function as a filter of an electrically charged web. The following discussions assume that the methods of making the screen and the apparatus used in the method are operating in a continuous process in a safe state where the collector moves at a constant speed both rotationally and longitudinally. During the process changes, however, some of the spatial relationships can not be maintained. For example, if the helix angle is altered by changes in the rotational speed of the collector or the speed at which the tubular web advances along the collector, the lightened or reduced edges can not be parallel to the separate edges. until the process returns to a firm state and the spatial relationships are restored. Even during process changes, however, the lightened or reduced edges may still be generally parallel to the separated edges. Figure 1 illustrates a portion of a fibrous web 10 blown by melting multiple layers illustrative The weft 10 may be provided in a continuous length in the machine direction, or may be considered to have an endless length in the machine direction during processing. The weft 10 preferably includes a central line 11 and two separate edges 12 and 14 which are formed during the processing of the uniform weft 10 from a tubular weft as discussed below. The separated edges 12 and 14 are preferably generally parallel to the center line of the frame 11 and to each other. further, the machine direction, as defined by the movement of a selected point on the collector forming surface used to make the weft 10, is also preferably parallel to the center line 11 and the separated edges 12 and 14. The thickness or The basis weight of the web is preferably generally constant between the separated edges. This characteristic of the meltblown fibrous webs of the invention is in direct contrast to the webs formed by conventional processes wherein the thickness or basis weight generally narrows close to the edges of the web.

The separated edges 12 and 14 are described as straight lines in Figure 1, but edges 12 and 14 could be provided in other shapes as sinusoidal or other wave forms. In any case, however, the edges of the frame 12 and 14 will generally extend in directions that are parallel to the center line of the frame 11. The techniques used to form the separate edges 12 and 14 may vary. In some cases the edges may be split using techniques including, but not limited to, blade cutting, laser cutting, water jet cutting, ultrasonic cutting, hot wire cutting, flame cutting, etc. As an alternative for splitting, the edges of the weft 12 and 14 can be formed in a rotary die cutting process, or they can be formed by controlled tearing of the weft in a predetermined pattern. For example, it may be useful to punch, fold, or otherwise modify the tubular web before tearing to aid in controlling the direction of tearing. Figure 2 illustrates several layers in the fibrous web 10 blown by melting multiple layers. The relative dimensions and characteristics described in Figure 2 are exaggerated for purposes of illustration. The frame 10 preferably includes a plurality of interconnected layers of meltblown fibers, with each layer sequentially deposited as will be described in detail below. The layers included in the weft 10 are a first layer 20, the intermediate layers 22 and 24, and a second layer 26. The first layer 20 and the second layer 26 include the lightened or reduced edges 21 and 27, respectively. The lightened or reduced edges 21 and 27 are the result of the meltblown fiber deposition process wherein the basis weight is gradually reduced to zero at the edges of the meltblown fiber layer provided by the blown fiber source. fusion. In the meltblown fiber process for the known uniform web, the lightened or reduced edges will be located on the outer side edges of the formed web, where they will normally be cut from the web and discarded as waste material. In the present invention, however, the lightened or reduced edges 21 and 27 are incorporated into the fibrous web 10 blown by melting multiple layers in such a way that a weft 10 having two separate edges 12 and 14 is produced, whereby less a less heavy edge is located between the two separated 12 and 14 and parallel to edges 12 and 14, and at least a pair of interconnected layers of meltblown fibers. In a preferred multi-layer meltblown fibrous web, each layer is preferably interconnected by the fiber interwoven at least to the immediately adjacent layer. In the illustrated frame 10, the blown fibers are interwoven by melting the first layer 20 preferably with the meltblown fibers of the intermediate layer 22, which, in turn, are interwoven with the blown fibers by melting the intermediate layer 24. , which are interwoven with the meltblown fibers in the second layer 26. In addition, the layers that are not immediately adjacent to one another can also be interconnected depending on the thickness of the layer, the fibers to be deposited, and the process used to deposit the layers. fibers. For example, the meltblown fibers in the first layer 20 could be interwoven with the meltblown fibers both in the intermediate layer 22 as well as the intermediate layer 24 in some cases if, for example, each layer were thin enough to allow this interweaving happens. A preferred mechanism by which the fibrous web layers 10 blown by melting multiple layers are interconnected, is preferably in the same way in which the individual layers are formed. In other words, the process involves directing a source of meltblown fibers into at least one layer or layers of meltblown fibers already formed. The fibers blown by melting the different layers 20, 22, 24 and 26 of the fibrous web blown by melting multiple layers are preferably interwoven by the same process used to weave the individual fibers forming each layer. As a result, there is usually no need for any additional material or processing required to jointly connect the various layers to form a fibrous web 10 blown by multi-layered finishing. For example, no additional adhesive, resin, etc., or any processing, such as spot welding, may be required to jointly secure the various layers 20, 22, 24 and 26. In some cases, additional agents may sometimes be used. or processing steps to desirably assist in interconnecting the meltblown fiber layers to form the finished web 10. For example, a resin, adhesive or other agents may be introduced into each layer or between adjacent layers to aid interconnection of the layer.

The cross-sectional view taken in Figure 2 is taken in the direction of the cut line 2-2 through the weft 10 (along the edges 12 and 14) and, as a result, the direction of the section The cross section shown in Figure 2 is also generally in the direction of the machine. When viewed along the machine direction, the cross-sectional view of the fibrous web 10 blown by multi-layer melting in Figure 2 illustrates another feature of the present invention, namely, the spatial relationship of the lightened edges. or reduced 21 and 27 to the separated edges 12 and 14. In the fibrous web 10 blown by melting multiple layers, the lightened or reduced edges 21 and 27 are parallel to the separate edges 12 and 14 of the fibrous web 10 blown by melting (also see Figure 1). This is in direct contrast to other tubular shaped webs that are cut longitudinally to form a fibrous web blown by uniform melting. In these webs, the lightened or reduced edges that are formed during the processing of the tubular webs extend at an angle through the web, whereby a deflection angle is formed with respect to the center line of the uniform web. This is the result of longitudinally cutting the tubular web. At the moment invention, however, the tubular multi-layer meltblown fibrous web is helically cut and the resulting uniform multilayer meltblown fibrous web 10 incorporates the lightened or reduced edges extending parallel to the separated edges 12 and 14. Other characteristic of the meltblown fibrous webs 10 is the multi-layered construction of the finished web 10. Although only two intermediate layers 22 and 24 are described in Fig. 2, each of these intermediate layers 22, 24 could be formed by themselves of a plurality of separate layers such that the fibrous web 10 blown by melting multiple layers could be formed of 3, 4, 5, 6, 7 or more sequentially formed layers of melt blown fibers including the first and second layers and thus minus an intermediate layer. By providing a fibrous web 10 blown by multi-layer melting, variations of the percentage in density or basis weight are significantly reduced as a result of the lightened or reduced edges 21 and 27. For two frames having the same overall basis weight, a number Larger layers can be used advantageously because increasing the number of layers usually reduces variations in the interwoven in the basis weight of the plot. In a construction, the basis weight of each individual layer is generally reduced to compensate for the increased number of layers. For example, the fibrous web 10 blown by multi-layer melting preferably includes at least one intermediate layer between the first and second layers 20 and 26. More preferably, the meltblown fibrous web 10 includes approximately four or more layers. intermediates between the first and second layers 20 and 26. These preferences, however, vary based on the desired use of the multi-layer meltblown web 10 and a variety of other factors such as the desired total basis weight, the basis weight minimum of each layer, etc. Returning to Figure 1, a portion of the multi-layer meltblown fibrous web 10 can be die cut, stamped, or otherwise separated from the weft 10 to provide a fibrous article blown by multi-layer melting. Articles 18 may show the unique characteristics for multi-layer meltblown fibrous articles 18 which were made from a multi-layer meltblown fibrous web 10. Among those features is that Article 18 includes a plurality of layers as described above. In addition, without taking into account the shape of the fibrous article blown by melting multiple layers 18, the melt blown fibers in each of the layers normally show a detectable machine direction indicative of the helical movement of the collector in which the weft 10 was formed. In addition, the machine directions shown by the meltblown fibers in each of the layers in the meltblown fibrous article of multiple layers 18 are usually parallel to each other because the layers are formed in the same collector. The collector machine direction, wherein a meltblown fibrous web 10 is formed, can be determined in a method based on the tension force of the web. The tensile force of the weft 10 is generally greater in the transverse direction of the weft than in the downward direction thereof (corresponding to the centerline of the weft as described above). As a result, any less heavy edge in the articles 18 blown by melting multiple layers will generally be oriented transverse to the axis of maximum tension force. The machine direction can also be determined based on the shapes of bunches or cords of fiber in the layers of fiber-blown fiber. When meltblown fibrous webs are formed, it is normal for some fibers to adhere and form bunches or fiber cords. The fiber bundles normally extend in the weft in the form of an arch with the apex of the arch pointing in the direction of the weft downwards. Examination of a meltblown fibrous web 10 or article 18 in, for example, a light table should reveal the orientation of the fiber bunches. Depending on which portion of the web 10 the multi-layer melt-blown fibrous articles 18 are taken, these may also include one or more of the lightened or reduced edges 21 and 27 incorporated in the web 10 as described above. These lightened or reduced edges 21 and 27 will generally be visible by being parallel to the machine directions defined by the meltblown fibers in each of the layers constituting the fibrous articles blown by multi-layer melting 18. Figure 3 describes a cross-sectional view of another fibrous web blown by multi-layer melting 110. As with Figure 2, this figure is also a schematic diagram where several proportions have been exaggerated for illustrative purposes. The weft 110 includes a first portion 120 of meltblown fibers and a second portion 122 of meltblown fibers. The first and second portions 120 and 122 preferably each include a less heavy edge of melt blown fibers in the end layers of the portions of the meltblown fibrous web of multiple layers 110 as described above with respect to the blown fibrous web by multi-layer melting 110. These lightened or reduced edges preferably extend parallel to the separate edges 112 and 114 of the meltblown fibrous web of multiple layers as also discussed above with respect to the multi-layer meltblown fibrous web. 10. Each of the first and second portions 120 and 122 may include one or more sequentially applied layers of meltblown fibers. Located between the first and second portions of the meltblown fibrous web is an intermediate portion 124 of the fibrous web blown by multi-layer melting 110. The intermediate portion 124 may also include one or more materials instead of the blown fibers. fusion. The other materials could be of the nature of films, particulates, fibers, liquids, and combinations thereof. For example, intermediate portion 124 may include activated carbon to help remove gaseous and / or vaporous contaminants (see, for example, US Patent 3,971,373 to Braun). In another variation, the intermediate portion 124 could include a membrane having desirable properties such as limited permeability, etc. The intermediate portion 124 of the multilayer meltblown fibrous web 110 could comprise or consist essentially of these other materials, or the intermediate portion 124 can include the additional materials / layers in addition to one or more layers of meltblown fibers. The weft 110 may also incorporate one or more elements such as a fiber or yarns 128 which extend generally parallel to the separate edges 112 and 114 of the weft 110. Examples of suitable elements 128 include monofilament lines, woven yarns, strips, etc. . The additional elements 128 can be provided to improve the strength of the weft 110 or to provide a line along where the weft 110 can tear, fold, etc. If the materials instead of the meltblown fibers in the intermediate portion 124 and / or in the elements 128 are not inherently interconnected to or merged with the meltblown fibers in the rest of the fibrous web blown by multi-layer melting 110, it may be desirable to provide one or more agents or perform other process steps (such as welding) to help in the union of the fibers blown by fusion to these materials. For example, it may be desired to provide adhesives, resins, etc. To assist in the sufficient bonding of the meltblown fiber layers 120 and 122 to the materials instead of the meltblown fibers in the intermediate portion 124 and / or elements 128. Alternatively or in addition to these agents, the intermediate portion 124 of the multi-layer meltblown fibrous web 110 may include some meltblown fibers at least to aid in catching, binding, or interweaving the different materials in place of the meltblown fibers in the meltblown fibrous web multiple layers 110. Inventive multilayer meltblown fibrous articles, such as article 18 illustrated in Figure 1 above, can be incorporated into a variety of different products wherein the properties of the inventive articles can be exploited. A type of product where the fibrous articles Multilayer melt blown can be incorporated is a mask placed on the breathing steps of a person to prevent the entry of contaminants into the respiratory tract of the user and / or to protect other persons or things from exposure to pathogens or other contaminant expelled by the user during respiration. As used in connection with the present invention, the term "mask" means a device adapted to serve these purposes and includes masks for the breathing and filtering face. Figure 4 discloses one embodiment of a mask 16 that includes a porous mask body 17 and retention straps 19. The mask body 17 may include a multi-layer meltblown fibrous article of this invention as a filter medium for the filtration of particles. The mask body typically includes a support structure as a forming layer that supports the filter medium. In other respirators, a substantial portion of the mask body can be constructed of a material that is substantially impermeable to air (see, for example, U.S. Patent No. 5,062,421 to Burns et al. Which describes a face piece of elastomeric rubber or in the US Patent No. 35,062 de Brostro et al.). In these masks, the inventive multi-layer melt-blown articles can be used as a particulate filter that is supported on the filter cartridges. Masks having the dome-shaped configuration shown in Figure 4 are described in, for example, U.S. Patent No. 5,307,796 to Kronzer et al., U.S. Patent No. 4,807,619 to Dyrud et al., And U.S. Patent No. 4,536,440 from Berg. The masks of the invention can assume other configurations, such as flat masks, alternative dome-shaped masks, and masks that include filtration assemblies. For example, see US Patents Nos. Re 28,102 (Mayhew); 3,971,373 (Braun); 4,215,682 (Kubik et al.), 4,419,993 (Peterson); 4,547,420 (Krueger et al.); 4,729,371 Krueger et al); 4,795,668 (Krueger et al.); and 4,827,924 (Japtunich). Figure 5 illustrates a portion of an apparatus for forming the meltblown fibrous webs of multiple layers. The portion of the apparatus illustrated in Figure 5 includes a manifold 30 which provides a surface of generally cylindrical shape that rotates about the longitudinal axis 32 in the direction 34. of rotating about the longitudinal axis 32, the forming surface of the collector 30 also preferably moves longitudinally along the length of the longitudinal axis 32 in the direction of the arrow 36. As a result, any selected point on the forming surface of the manifold 30 moves in a generally helical pattern on and along the longitudinal axis 32 from a first end of the manifold 42 to a second end of the manifold 44. The illustrated apparatus also includes a source 38 of meltblown fibers that are directed into the collector forming surface 30. The source 38 preferably extends along at least a portion of the longitudinal extension of the collector 30 with one end of the source 38 to be located near of the first collector end 31 and the opposite end of the source 38 is located at a distance under the length of the collector 30 closest to the second collector end 33. The preferred source 38 of meltblown fibers is a die, although essentially any other source of melt blown fibers is contemplated including, but not limited to, hair sources, spinning machines, etc. A preferred die directs fibers blown by melting on the forming surface of the collector 30 along a generally straight line which is generally parallel to the longitudinal axis 32. The fibers can be directed into the collector 30 using the techniques known as those described by Wente, Van A., "Superfine Thermoplastic Fibers," Industrial Ingineering and Chemistry, Vol. 48, pages 1342-1346 (1956), Report No. 4364 of Naval Research Laboratories, published May 25, 1954, entitled Manufac t ure of Superfine Organi c Fibers, by Wente, VA; Boone, C.D .; and Fluharty, E.L., and U.S. Patent No. 3,971,373 (Braun). Generally, the fibers are directed to the collector 30 by a high velocity gaseous flow (usually air) which attenuates the material extruded into the fibers. One preferred manifold 30 includes a forming surface that includes a plurality of rotating bands. The webs rotate such that the webs formed in the collector 30 move toward the second collector end 33. FIG. 6 describes a view of the collector 30 of FIG. 5 from the direction of line 6-6 in FIG. 5. The surface The formation of the collector 30 includes several rotating bands 40a and 40b, which rotate in the direction indicated by the arrow 36 to the outside of the collector 30. In other words, the bands 40a and 40b rotate from a first collector end 31 to a second collector end 33. As shown in Figure 6A, the forming surface of the collector 30 is composed of a series of bands alternating long 40a and short strips 40b to allow the space of the energy transfer components necessary to transfer the energy to the driving rolls 41a and 41b, support the ends of the long bands 40a and 40b, respectively. The bands 40a and 40b are described in an adjacent flat relationship, in other words, as if the cylinder had been unwound, to well illustrate the energy transfer components. As can be seen, each energy input shaft 42 includes an outer drive gear 43 used to supply power to a first right angle gearbox 44 which includes a generator shaft 45 which supplies power to a drive roll 41a. The gearbox 44 also includes a second generator shaft 46 for supplying power to a distribution band 49 that transfers the energy to a transfer shaft 48. The transfer shaft 48 supplies power to a second right-angle gearbox 50 that includes a generator shaft 51 that rotates the driving roller 41b that drives the short band 40b. As a result, each of the energy input axes 42 drives one of the long bands 40a and an adjacent shortband 40b in the preferred collector apparatus 30. The components used to transfer the energy to the energy input axes 42 and the The corresponding sprockets 43 are illustrated in Figure 6B where an end view describes the arrangement of the output input shafts 42 and the sprockets 43 in the manifold 30. The drive sprockets 43 are positioned on the longitudinal axis 32. of the collector 30 as seen in Figure 6B. The web drive sprocket 54 rotates about the longitudinal axis 32 and transfers energy to the individual drive sprockets 43 by means of two chains 55 and 56 that rotate with the rotation of the band drive sprocket 54. The wheel The toothed belt drive 54 is preferably operatively connected to a drive gearwheel 57 which is driven by a belt drive motor 58 which uses a separate chain 59. As the motor 58 drives the chain 59, the drive gearwheel 57 rotates , where, in turn, rotates the band drive sprocket 54. The sprocket of The belt drive 54 drives the chains 55 and 56 which drive the energy input shafts 42 by means of the drive sprockets 43. The collection of belts 40a and 40b forming the cylindrical collector 30 rotates about the longitudinal axis 32 using the master drive sprocket 60, which receives the energy from the main drive motor 62 by means of the drive chain 61. The main drive sprocket 60 is operatively linked to the central axis 52, the center of which is co-extensive with the 32 longitudinal axis. The band drive sprocket 54 and the drive sprocket 57 preferably mount to the central shaft 52, but rotate independently thereof by the use of supports located between the central shaft 52 and the belt drive sprocket 54 / the wheel toothed drive 57. Because the manifold 30 includes separate drive systems for driving the strips 40a and 40b along the longitudinal axis 32 and simultaneously rotating the manifold 30 on the longitudinal axis 32, the propeller angle of the propeller can be controlled. the helix formed by the movement of a selected point on the collector formation surface . Alternatively, a single drive system could be used to energize the rotation of the bands 40a and 40b and the rotation of the collector 30 on the longitudinal axis 32, with changes between the relative speeds of the movement made by the gear speed settings. The use of two separate drive systems, however, provides the ability to quickly change the ratio without the time out of service of the machine. The strips 40a and 40b are preferably placed with a relatively small opening between their adjacent edges such that, as the melt blown fibers are directed to the collector forming surface 30 of the source 38, they are capable of forming a supporting layer of fibers blown by fusion. The maximum opening between the edges of adjacent bands 40a and 40b is preferably about 3 millimeters or less. The larger openings may also possibly depend on the materials constituting the meltblown fibers, the sizes of the meltblown fibers, the deposition rate on the forming surface, the distance between the meltblown source and of the forming surface, the temperature of the forming surface, etc.

In order to achieve that the small opening between the adjacent bands 40a and 40b, the bands are preferably nested within each other. As seen in Figure 6C, a partial enlarged cross-sectional view of the manifold 30 taken along the line 6C-6C in Figure 5, the short strips 40b are partially located within the long strips 40a within the interior of the cylinder formed by the bands. The number of layers in the meltblown fibrous web is, in the apparatus including only one source 38 of meltblown fibers, a function of the relative rotational speed of the collector 30 on axis 32, the speed of the translation movement of the collector forming surface 30 in the direction 36, and of the distance along the axis 32 on which the source 38 deposits the meltblown fibers on the forming surface of the collector 30. For example, if If a multilayer meltblown fibrous web having approximately six layers of meltblown fibers is desired, then the relative rotational speed of the collector 30 on axis 32 as compared to the translation speed 36 will be preferable such that any particular point on the surface of the collector 30 between the source 38 and the collector formation surface passes approximately six times during its helical movement on and along the collector 30. Changing one or more of the factors listed above, may impact the number of meltblown fiber layers provided in any meltblown fibrous web multilayer produced using the apparatus and methods of the present invention. Figure 7 also schematically illustrates a tubular multi-layer meltblown fibrous web 280 and a cylindrical collector 230 where the web is formed. Figure 7 shows a source 238 of meltblown fibers and a separator 270 in addition to the tubular web 280. The tubular web 280 is preferably formed in a collector 230 similar to the collector 30 described above. The tubular web 280 is advanced along the longitudinal axis 232 in a direction 236 while simultaneously rotating about the axis 232 during formation in the collector. The simultaneous rotational and longitudinal movement of the manifold 230 under the source 238 of the meltblown fibers forms the lightened or reduced edges 221 and 227 as seen in Figure 7 in the tubular meltblown fibrous web 280. The helical nature of the first less heavy edge 221, is illustrated in Figure 7 where, over the source 238, the first less heavy edge 221 extends from the outermost or furthest left portion of the source 238 while, after turning over the collector, the same first less heavy edge 221 is located a short distance through of the length of the source 238 (along the axis 232). Similarly, at the opposite or further to the right end of the source 238 of meltblown fibers, the second lighter edge 227 associated with the uniform multilayer meltblown fibrous web 210 is seen to extend outwardly from the source 238. towards the surface of the tubular web 280. Figure 7 also describes a separator 270 that separates the fibrous web blown by tubular fusion 280 into a uniform or flat web 210 having two separate edges 212 and 214. The angle α, wherein the separator 270 operates in the tubular meltblown fibrous web 280, is substantially equal to the helix angle provided by the ratio between the rotation of the collector 230 and the resulting tubular web 280 on the longitudinal axis 232 in combination with the translation movement 236 a along the longitudinal axis 232. The helix angle is also the angle followed by the lightened or reduced edges 221 and 227 with the axis 232.

Although the separator 270 is illustrated near one end of the manifold 230 in Figure 7, the separator 270 may be located away from the manifold 230 according to the present invention. Even when it is located away from the 230 collector, however, the separator 270 preferably separates the meltblown fibrous web from tubular multiple layers 280 along a direction generally parallel to the helix angle as discussed above. As a result, the uniform multilayer meltblown fibrous web 210 will have a generally constant width between the separated edges 212 and 214. In addition, the meltblown fibrous web 210 also incorporates the lightened or reduced edges produced by the source 238 that on the other hand it will be cut from the plot and it will be deleted. The second lighter edge 227 is seen in the view of Figure 7 and the first lighter edge is located on the opposite surface of the meltblown fibrous web 210. After the separation operation performed by the separator 270, the uniform multilayer meltblown fibrous web 210 may be wound on a roll for use in other processes or the web 210 may be transferred directly into a web. processing process wherein the multilayer meltblown fibrous web 210 is used. Because the web 210 has two separate edges 212 and 214, there is no need for additional edge cutting or treating with the remaining material as described previously, which facilitates its use in online production processes. The separator 270 can be provided in various forms, and essentially any device that is capable of separating the screen is contemplated by this invention. Examples of suitable spacers 270 in the form of cutters include, but are not limited to: knives, lasers, water jet, ultrasonic horns, hot wires, flames, etc. Other contemplated separators may include rotary dies, lasers, water or fluid injection jets, and other devices or operations designed to separate a blown fibrous web from tubular multiple layers along a helical path. Figure 7 also shows a vacuum source 290 connected to a distributor 292 located at one end of the manifold 230. The distributor 292 is connected to the vacuum source 290 by the line 294. The distributor 292 is preferably located in a end of the generally cylindrical surface of the manifold 230. The weft 280 is preferably formed in the manifold 230 under slightly negative air pressure provided by the vacuum source 290 to help remove the air and other gases normally used in directing the fibers melt blown towards the collector forming surface 230. The forming surface is preferably permeable and, as a result, a negative pressure condition within the volume defined by the forming surface can be communicated through the forming surface. The uniform multilayer meltblown fibrous web 210 produced in the manifold 230 includes multiple layers of meltblown fibers in which the lightened or reduced edges 221 and 227 are incorporated in the web 210 between the separate edges 212 and 214. The exact location of the lightened or reduced edges 221 and 227 is, however, the variable based on several factors. Figures 8A-8C illustrate a variety of possible relationships within the meltblown fibrous webs of uniform multilayer 210 formed by the operation of the collector apparatus 230. The width of each layer formed by the source of the fibers melt blown 238 (as measured along the longitudinal axis 232) must be at least as long as the distance over which a point on the forming surface moves in a full revolution of the forming surface. This distance, in other words, the distance over which a point on the formation surface travels in a complete turn of the formation surface, is sometimes called the precession speed. If the width of each melt-blown fiber layer is less than the precession speed, then gaps will be produced between the layers in the longitudinal direction. For simplicity in the following discussion, the width of the meltblown fiber layers will be assumed to be equal to the length of the meltblown fiber source 238. The actual width of the meltblown fiber layers on the surface of formation may, however, vary from meltblown fiber source length 238 by various processing techniques involving the direction of air flow, etc. The spatial relationships between the lightened or reduced edges and the location of the lightened or reduced edges between the separated edges may vary based on the relationship between the length of the melt-blown fiber source 238 along the longitudinal axis 232 as compared to the maximum width w of the fibrous web blown by uniform multilayer melting 210 between the separated edges, where the maximum width of the frame 210 is determined by the precession speed of the collector. The maximum width of the frame 210 is referred to on the understanding that the frame 210 can be separated into two or more narrower frames, provided so that the cumulative width of the narrower frames can not exceed the maximum width w which is a function of the precession ratio under steady-state operating conditions. The weft 210 illustrated in Figure 8A includes the lightened or reduced edges 221 and 227 located directly therebetween through the thickness of the weft 210. In this arrangement, the ratio of the longitudinal extension 1 (see Figure 7) of the source 238 (Figure 7) The width w of the frame 210 is an integral relation, in other words, l: w is approximately 1: 1, 2: 1, 3: 1, etc. Figure 8B illustrates the alignment of the lightened or reduced edges 221 'and 227' that can occur at any point across the width of the frame 210 'and is determined only by the original location of the separator 270 where the separation of the tubular web 280. The web 210 'is also formed by a system in which the proportion of the longitudinal extension of the fiber source blown by the width tv' of the web 210 'is an integral relationship, in other words , 1: 1, 2: 1, 3: 1, etc. Where the longitudinal extent of the source of the meltblown fibers is less than the width of the separated web, a different ratio is obtained between the lightened or reduced edges. As seen in Figure 8C, the multilayer meltblown fibrous web 210"includes the lightened or reduced edges 221" and 227"that are spaced across the width of the web 210". To obtain the frame 210"with the lightened or reduced edges separated 221" / 227", the width w" of the weft is smaller than the longitudinal extension of the meltblown fiber source. The lightened or reduced edges 221"/ 227" do not align vertically through the thickness of the weft 210"because the ratio of the longitudinal extent of the meltblown fiber source 238 (Figure 7) to the width w" of the frame 210"is not an integral relation, in other words, this ratio is, for example, 1.6: 1, 2.2: 1, 3.1: 1, etc. Although the various apparatuses and methods have been described with, for example, the use of a fiber source melt blown, the present invention can also be practiced with more than one meltblown fiber source. In addition, various other materials may be incorporated into the multilayer meltblown fibrous webs of the present invention by the addition of other sources of other materials. Once the variation is described in Figure 9 where a meltblown fiber source 338 is used to deposit the meltblown fibers in a transverse rotary collector 330. A secondary source 390 also shows how to deposit a different layer 392 in a portion of the collector forming surface 330. Because a portion of the tubular multi-layer meltblown fibrous web 380 has already been deposited on the surface of the collector 330, the additional material or materials 392 provided by the source 390 secondary particles are preferably located on the surface of at least one layer of meltblown fibers. In addition, because the secondary source 390 ends short of the straight end of the primary source 338 of the meltblown fibers, an outer layer of meltblown fibers is deposited on the surface of the layer 392 as it passes under the source 338 of the meltblown fibers at least before reaching the separator 370 where the tubular web 380 is separated along the helix angle to form a uniform multilayer meltblown fibrous web 310 having the separated edges 312 and 314. The apparatus and process described in Figure 9 will be useful for producing frames similar to the screen 110 described in Figure 3. In this situation, the material or materials provided by the secondary source 390 could be another of the meltblown fibers provided by the primary source 338. For example, the secondary source can deposit activated carbon, materials necessary to form a membrane within the tubular web 380, etc. Alternatively, the secondary source 390 can also provide only meltblown fibers to help provide meltblown fibrous webs of multiple layers having increased numbers of layers in the collectors having shorter longitudinal extensions. Other variations that may be introduced in multi-layer meltblown fibrous webs made using one or more sources of meltblown fibers include variations in color of the webs, variations in fiber composition, variations in size and / or distribution of the fiber along the thickness of the weft, and others.

A process for providing a meltblown fibrous web of graded density multiple layers 410 is illustrated in Figure 10 wherein a collector 430 is used in relation to three sources of the meltblown fibers 438a, 438b and 438c (collectively called sources 438). Each of the sources 438 is directed to a different portion of the manifold 430 and forms a different layer of meltblown fibers in the tubular multi-layer meltblown fibrous web 480. Although all the sources 438 can provide meltblown fibers that have the same properties, it may be advantageous for each of the sources 438 to provide melt blown fibers having different properties. In this situation, the layers formed by each of the sources 438 may have different densities, different fiber compositions, or other properties. Where each layer of meltblown fibers has a different density from adjacent layers, the apparatus 430 can be used to make a meltblown fibrous web of multiple layers of graded density 410 where the least heavy edge produced by each of the sources of meltblown fibers 438 is incorporated into the weft 410 as described above.

The continuous nature of the processes of forming fibrous webs blown by melting multiple layers as described herein is advantageous when the webs are processed in line. A system is illustrated in Figure 11 where the collector 530 is used in combination with the conversion stations 540 and 550. The frame 510 produced by the collector 530 is directly guided in the first conversion station 540 where one or more are performed conversion operations followed by the conversion station 550 where one or more additional conversion operations are performed to produce the multi-layer melt blown fiber articles 518 such as. masks or other items in an online process. The foregoing specific embodiments are illustrative of the practice of the invention. This invention can be practiced properly in the absence of any element or article specifically described in this document. Full descriptions of all patents, patent applications, and publications are incorporated herein by reference as if they were incorporated individually. Various modifications and alterations of this invention will be clear to those skilled in the art without departing from the scope of this invention, and should It is to be understood that this invention is not unduly limited to the illustrative embodiments indicated herein. It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is the conventional one for the manufacture of the objects or products to which it refers.

Claims (17)

1. Having described the invention as above, the content of the following claims is claimed as property: 1. An apparatus for making a meltblown fibrous web or fabric, the apparatus is characterized in that it comprises: (i) a collector comprising a generally of cylindrical shape which can rotate about a longitudinal axis and which can move simultaneously parallel to the longitudinal axis such that a selected point on the forming surface can move in a helical pattern on and along the longitudinal axis from a first end of the manifold to a second end of the collector, the helical model defines a helix angle with respect to the longitudinal axis; (ii) a source that is capable of directing the meltblown fibers in the forming surface; and (iii) a separator that can separate a meltblown tubular fibrous web formed in the forming surface in a direction generally parallel to the helix angle to convert the web tubular fibrous melt blown in a non-tubular fibrous web blown by melting.
2. 2. The apparatus according to claim 1, characterized in that it comprises a first drive system that can rotate the collector forming surface on the longitudinal axis and a second drive system that can move the forming surface along the longitudinal axis, such that the rotational speed of the collector can be controlled independently of the longitudinal speed to vary the helix angle.
3. 3. The apparatus according to claims 1-2, characterized in that the source comprises a die that is capable of extruding the microfibers.
4. 4. The apparatus according to claims 1-3, characterized in that it comprises a secondary source which directs a second material to the collector forming surface.
5. 5. A method for making a meltblown fibrous web, characterized in that it comprises: providing a manifold that includes a surface of generally cylindrical shape; rotating the forming surface on a longitudinal axis and simultaneously moving the forming surface longitudinally in the direction of the longitudinal axis such that a selected point on the forming surface moves in a helical pattern on and along the longitudinal axis from a first end from the collector to a second end of the collector, the helical model defines a helix angle with respect to the longitudinal axis; directing the meltblown fibers to the forming surface as the forming surface rotates and moves longitudinally, where a fibrous web blown by tubular fusion is formed on the forming surface; and separating the blown fibrous web by tubular fusion along in a direction generally parallel to the helix angle to convert the blown fibrous web by tubular fusion into a fibrous web blown by non-tubular fusion.
6. 6. The method according to claim 5, characterized in that the selected point on the forming surface rotates about the longitudinal axis at least about twice in the time required for the selected point to move along the entire longitudinal extent of the forming surface.
7. 7. The method according to claims 5-6, characterized in that the meltblown fibers are microfibers.
8. 8. The method according to claims 5-7, characterized in that it comprises imparting a persistent electric charge on the microfibers to produce an electrically charged web.
9. 9. A method for making a filter, characterized in that it comprises placing the electrically charged web produced by the method according to claim 8 in a support structure.
10. 10. A method for making a mask, characterized in that it comprises: carrying out the method according to claim 9, wherein the support structure is a porous structure in the shape of a dome.
11. 11. A multi-layer meltblown fibrous web characterized in that it comprises: a plurality of interconnected meltblown fiber layers, at least one of the meltblown fiber layers includes a less heavy edge; and two separate edges; wherein the less heavy edge is located between the separated edges, and also where the separated edges and the less heavy edge are generally parallel to each other.
12. 12. The screen according to claim 11, characterized in that the melt-blown fibers in each of the melt-blown fiber layers define a machine direction, and furthermore in which the machine directions of each of the blown fiber layers by fusion they are parallel to each other.
13. 13. The frame according to claims 11-12, characterized in that all the meltblown fiber layers include a lighter edge, and furthermore where the lightened or reduced edges are parallel to the separate edges of the weft.
14. 14. The screen according to claims 11-13, characterized in that the plurality of melt-blown fiber layers comprise at least one intermediate melt blown fiber layer located between two different meltblown fiber layers.
15. 15. The screen according to claims 11-14, characterized in that it includes at least 3 intermediate layers located between the first and second layers where each includes a less heavy edge.
16. 16. The screen according to claims 11-15, characterized in that the fiber layers contain electrically charged microfibers.
17. 17. A mask that is configured to fit at least on the nose and mouth of a user and that has a filter element disposed in the same as the air that is desired to be inhaled passes through the filter element before being inhaled, the filter element characterized in that it comprises the screen according to claim 16.