FR2864567A1 - Masking web for temporary ceilings, comprises perforated nonwoven containing holes with reinforced edges - Google Patents

Abstract

The web (NM) comprises a perforated nonwoven containing holes with reinforced edges formed by consolidating the fibres (F) around them in order to define cells. A three-dimensional textile masking web for forming temporary ceilings is mounted horizontally under tension and has a structure which is traversed by interconnected openings which form open tubular cavities. The web comprises a perforated nonwoven containing holes with reinforced edges formed by consolidating the fibres around them in order to define cells. Independent claims are also included for the following: (A) Method for making the masking web by perforating a nonwoven in order to form a network of holes and then compacting the fibres around these holes; (B) Machine for making the masking web, comprising a matrix (100) containing a network (101) of pyramid-shaped protrusions surrounded by forming channels (102) for defining the reinforced edges around the holes in the web; and (C) False ceiling comprising these masking webs and a means for securing and tensioning the webs.

Description

Field of the invention

  The invention relates to a ply of flexible product mas-quant for the realization of temporary false ceilings, this sheet being laid taut and including continuous false ceilings for exhibition halls.

  STATE OF THE ART The techniques for producing temporary false ceilings in the exhibition halls are very important in order to solve several ephemeral architecture problems. Indeed, these halls are generally very high ceiling to be able to accommodate the presentations of the largest products, (the big parts of the industry). But the majority of exhibitions concern smaller objects (consumer goods). For the latter, it is useful to establish in the hall, a temporary intermediate false ceiling, which will reduce the visible height by masking the upper parts where annoying utilitarian elements are always present. This significantly improves the quality of the exhibition by creating volumes in harmony with the size and nature of the products to be showcased. In addition, the fixed lighting of the halls is almost always dazzling and inappropriate, false ceilings will mitigate or transform them, for example by creating luminescent white ceilings. We will have the opportunity to make customized lighting very popular as a means of mise-en-scene.

  But in addition to their aesthetic importance, these false ceilings must satisfy all the obligations of safety and economy, which is particularly complex.

  Most exhibition hall ceilings are currently equipped with a regular mesh of smoke detectors, automatic smoke extraction systems and / or a network of automatic fire extinguishers. However, for these installations to work, when the exposures are installed, it is essential that the column of hot gases which is established vertically from the initial hearth, reaches and triggers, by rising, the extinguisher head installed in the ceiling, the closest to the vertical of this fireplace. This is then extinguished by the jets of water, sprinklers from top to bottom. It is therefore necessary that the hot, ascending gases and the downward jets of water not be stopped or deflected by a horizontal obstacle, as would a conventional ceiling. The correct operation of the smoke detectors presents, for the same reasons, the same requirements. Along with the extinction of fires, the evacuation of fumes released by a fire is doubly important, because in addition to being harmful, these fumes can also hide the sight of emergency access access signposts. create panic.

  These technical requirements complicate the realization of false ceilings. In addition to being economic and fire-resistant, they must also be permeable to gases and liquids, while masking the upper parts of the halls.

  Today, two types of techniques are used: - two-dimensional textile web techniques, using more or less complex stretched fabrics, flat, in flexible layers by juxtaposition of edges placed at edges, techniques of false three-dimensional, honeycomb ceilings forming horizontally open mesh, consisting of panels of lightweight materials forming screens suspended vertically.

  The techniques of planar velums to a two-dimensional sheet.

  1. The classic awnings. This simplest and oldest technique consists in stretching light fabrics, generally sheets of cotton fabric of about 100 gr / m2, flame retarded, usually horizontally. The strips are joined by seams. This technique is easy, economical and aesthetic. It was used a lot, but being not permeable, it is only allowed for false ceilings of small dimensions.

  2. Flat awnings in openwork textiles. These fire-resistant awnings are stretched horizontally and their weave has sufficiently wide open mesh, like a net, to allow the upward passage of hot gases and down the jets of water extinguishers, But as these fabrics must also beings sufficiently opaque to perform the function of masking, they must answer two contradictory conditions: if these awnings are sufficiently masking, they are not sufficiently permeable and if they are sufficiently permeable, they are not enough masking enough. According to certain regulations in force, open meshes for flat textiles must be at least 3x3 or 4x2 mm apart.

  3. Flat, stretched canopies with fusible lines. This technique uses the principle of assembling thin textile panels, plans ,. sufficiently opaque and fire-resistant, joined by lines of fusible material at a relatively low temperature, (# 60 C).

  The panels are generally made of mesh fabric mesh opacity and sufficient fire resistance, joined during their manufacture by mesh lines made with a fusible thread. These textile webs, once tensioned, realize false ceilings masking, aesthetic and a good degree of security. The textile, relatively elastic, allows implementation under tension in both directions of its plan. At the beginning of a fire, the fusible lines dissociate the live panels causing openings, by shrinkage, allowing both the evacuation of hot fumes to the extractors, the triggering of fire extinguishers and the extinction of the fireplaces, because this textile is very permeable to water. The temperature of 60 C is lower than that of the triggering of permanent fire extinguishers, (# 70 C). This technique is aesthetic, however it does not always allow sufficient evacuation of all fumes, especially when they have a temperature below 60 C, the minimum operating temperature of this technique. Because the opening temperature of 60 C, can not be lowered, without causing untimely openings that would hinder the operation of false ceiling.

  Three-dimensional false ceilings or honeycomb techniques.

  1. These false ceilings are not continuous. They operate on the principle of normal horizontal vision. They are composed of cells open horizontally, vertically limited by panels of thin materials, rigid or semi-flexible, and assembled in a regular network generally horizontal. These false ceilings are completely open and therefore perfectly permeable to vertical flows. Their masking capacity is a function of the horizontal dimensions of their voids and the vertical height of their screens. This technique is used in the traditional construction of buildings, in the form of rigid grilles, generally square bases, made of lacquered aluminum sheet strips. In this form, the cells measure about 1 decimeter, horizontally. This technique is effective but too expensive to be used in temporary exhibitions. However, the same principle is exploited by suspending non-woven screens or fabrics vertically in large formats, which also makes their use difficult and expensive in exhibitions.

  Figures 1 and 2 show the operating principle of the honeycomb technique. Figure 1 is a vertical sectional view, according to CD of the horizontal section, Figure 2. In these figures, a flat false ceiling ply is shown, horizontally, in front of and higher than the observer placed A. This false ceiling mesh consists of masking vertical bands, light and fire resistant.

  To describe, understand and define the functioning of the 3D false ceiling, it is essential to refer to the analysis of the principle of the usual human vision. It is indeed recognized that the usual vision of a spectator on a horizontal surface, is exercised mainly horizontally. This habitual vision is inscribed in a cone whose axis is horizontal and the normal apex in the middle of the segment joining the two eyes of the spectator. This cone has an opening of 30 vertically (Figure 1) and 60 horizontally, (Figure 2). The underside of the false ceiling for the viewer located at A will be completely masking from point 1/1 and beyond. The 1/1 point represents the beginning of the usual view of the observer at A; if the observer unconsciously raises his head, the ceiling will no longer seem completely masking, between the point 1/1 and the portion of space above him. This case is of little importance, because experience shows that even in this case, the viewer will keep the impression of having visited an exhibition with a masking ceiling, continuous over the entire surface. This peculiarity of visual memory linked to human behavior is exploited in the design and production of three-dimensional false ceilings (false 3D ceilings). In exceptional situations the angle α may be different from the usual angle of 15 depending on the need for upward or downward viewing to view large objects.

  For the observer at A, Figure 1 shows the usual horizontal plane of vision, which is the locus of the axes of the cones delimiting the usual vision. Under this plane, the line AF represents the lower limit of the cone of vision (or solid angle) if the observer pivots around its vertical axis A'A '.

  Above the horizontal plane, the line AG represents the upper boundary of the usual cone of vision from point A. This line AG has already been described. Above this line AG is a partially masked zone corresponding, for a pivoting of the observer around its vertical axis A'A ', to a cone of non-perception, of an opening of 120. This cone of non-vision accompanies the visitor and defines, on the contrary, the upper limits of the usual vision.

  In Figures 1 and 2, the square meshes of the false ceiling are diagonally illustrated with respect to the viewer's axis of vision.

  This arrangement is the most unfavorable for masking.

  The half-angle of vision which according to the indications given above is an angle a = 15 above the horizontal plane, corresponds, for an observer to the upper limit of his usual vision; this angle defines the principle of optimum scrolling of a false 3D ceiling.

  OBJECT OF THE INVENTION The object of the present invention is to develop a sheet of light masking product for producing temporary false ceilings as well as false ceilings, offering vertical permeability to gases and water whatever their temperature. masking power satisfactory, an attractive aesthetic appearance, industrial manufacture, a possibility of prefabrication of tablecloths, economy and ease of installation by suspension and tension, a variety of colors, a possibility of improving the fire resistance.

  DISCLOSURE AND ADVANTAGES OF THE INVENTION For this purpose the present invention relates to a masking sheet for the production of temporary ceilings, laid horizontally stretched, characterized in that it is formed of a sheet structure provided with through orifices, joined, forming tubular cavities emerging through the web structure, the height of these cavities being equal to at least the largest diagonal of the horizontal section of each orifice, multiplied by the tangent of the usual vertical half-angle of vision.

  The walls of the tubular cavities may be made in the mass of the material constituting the web, for example son or foam or non-woven fibers that are perforated.

  The false ceilings according to the invention not only have the advantage of masking the equipment located above the false ceiling but also to improve the stationary lighting hall, too often inappropriate to substitute more suitable lighting. Thus, the false ceilings according to the invention make it possible to attenuate the direct lighting of luminous sources located above the false ceiling if the false ceiling is in a matt black material. It will then be possible to create special adapted lighting. It is also possible to use the false ceiling as a light diffuser that regulates the luminous flux and spreads it over a larger area. The false ceilings thus become luminescent ceilings if the light sources above illuminate white and translucent sheets by manufacturing.

  The false ceiling according to the invention makes it possible to attenuate and transform the fixed lighting of the halls which are currently dazzling and inappropriate. The false ceiling can be a luminescent white ceiling. In general, it allows custom lighting popular as a means of staging.

  The vertical angle of vision according to the present invention is currently commonly accepted in architecture, ergonomics or in neighboring areas of staging, aesthetics and vision and is 30 in a vertical plane, along a horizontal axis that is to say an angle of 15 upwards or an angle of 15 directed downwards always with respect to the horizontal direction. It is recalled that the cone of vision is defined according to current considerations by a substantially elliptical section whose small vertical axis corresponds to a viewing angle of 30 in the vertical plane on either side of a horizontal bisector and for a angle of 60 in this horizontal plane.

  As already indicated, only the vertical half angle α = 15 above the horizontal axis is to be taken into account, the angle in the horizontal plane being arbitrary since the observer can turn his head around a vertical axis and look at the false ceiling in any direction.

  In a particularly advantageous manner, the ply is formed from a sheet of open-celled, open-celled textile product, in particular of prismatic section constituting tubular cavities, passing through the ply, the height of the cavities being equal to at least the largest diagonal of the horizontal section of the mesh multiplied by the tangent of the vertical half-angle of vision.

  The expression open integral cells, of prismatic section in the sense of the present invention, generally denotes a structure in the form of a web, provided with through orifices, contiguous forming open cavities.

  The sides of the cells or opaque walls may consist of vertical son, horizontal, coated or not. It can also be a textile with a resistant frame and a pleating material.

  The layer of masking textile product and consequently the false ceiling made with such plies have an exceptional vertical permeability since in plane projection, the only non-permeable surface occupied by the ply is that constituted by the sum of the slices or thicknesses of the walls of the walls. alveoli. This allows the rise of gases and in particular hot gases in case of fire. This rise is done vertically through the sheet and likewise the water or the extinguishing liquid emitted by the nozzles and in particular the automatic nozzles placed above the sheet can go down vertically, that is to say in the direction opposite that of the rise of hot gases and smoke to directly reach the fire. This permeability obviously also favors the very rapid and direct evacuation of the fumes to the top of the halls and possibly to the extractors.

  The tablecloth offers the masking power required, equivalent to that of the best current masking ceilings and this regardless of the orientation of the horizontal axis of vision relative to a vertical axis, with very important security improvements. The observer can look in one direction or turn his head around the vertical axis to look in another direction, his usual horizontal gaze will always be hidden under the normal viewing angle. In addition, even if he raises the head with a direction of non-horizontal vision, he will not see the space directly above the masking layer the vision will be veiled or attenuated by the stitches creating a partial veiling effect.

  The regular false ceiling is industrializable, it has the advantage of offering a pleasant aesthetic appearance by its fine and regular structure. The product webs can easily be assembled by prefabrication, seams or welds.

  The laying is particularly easy and economical given the lightness of the product and the reduced means necessary for the attachment of the strips or assemblies les on two sides of the surface to be covered. The web may be manufactured with a wide variety of processes and colors by dyeing the yarns or the produced textile product. The resulting surface may be decorative and / or constitute an advertising surface.

  It is also possible to improve the fire resistance by the choice of yarn or the treatment of the web after weaving.

  According to a particularly advantageous characteristic, the tubular cavities are formed by a lower mesh textile web in the horizontal plane composed of open cells and a web in the horizontal plane also with open cells, the cells of the two webs being connected by construction wires. , realizing the occultation forming the walls of the cells.

  This embodiment constitutes a resistant structure and little extensible in both directions of the web, the longitudinal direction and the transverse direction, the connection between the cells by the occultation son not having to offer tensile strength to stretch the tablecloth.

  According to another advantageous characteristic, the meshes are of rectangular section, in particular square, of which two sides are parallel to the edge of the sheet.

  The rectangular and in particular square shape of the meshes with two sides parallel to the longitudinal direction of the lé is very interesting because the tension is exerted directly in the longitudinal direction of the walls of the meshes and in the transverse direction that is to say perpendicular, when the strips are assembled. The result is a perfectly stretched ceiling, which concerns most of the requirements for the establishment of false ceilings on surfaces that are themselves rectangular. The square also has the advantage of having two equal orthogonal diagonals which have a better efficiency for masking, unlike the rectangle.

  According to another advantageous characteristic, fusible lines are integrated in the sheet. This makes it possible, in case of exceeding the melting temperature of these fuse lines, an opening of large longitudinal slots in the layers substantially canceling the pressure drop with respect to the gases and liquids at the crossing of the layers in case of recovery of hot gases of high temperature.

  Finally and as already indicated, the invention also relates to false ceilings formed of textile webs as defined above and having means for fixing and tensioning webs, for example the use of support cables placed in hems or welds in the junctions of the webs.

  Drawings The present invention will be described below in more detail with the aid of the accompanying drawings, in which: - Figure 1 is a vertical section of the usual scheme of view of a false ceiling, - Figure 2 is a view in plan of the usual scheme of view of a false ceiling, - Figure 3 is a schematic perspective view of principle on a greatly enlarged scale of a sheet of masking textile product according to the invention, - Figure 4 is a detailed view to very enlarged scale of a first embodiment of a sheet of masking textile product according to the invention, - Figure 5 is a perspective view on a very enlarged scale similar to that of Figure 4 of another embodiment of embodiment of a layer of masking textile product; FIG. 6 shows another example of masking fabric according to the invention, represented on a greatly enlarged scale; FIGS. 7 and 8 are explanatory side views of the operation of the FIG. 9 to 12 show other embodiments of masking layers, - FIG. 13 shows a diagram of the installation of mats of masking textile product or masking layers producing a false ceiling. DESCRIPTION OF EMBODIMENTS The definition of the usual angle of vision, which is valid for the vast majority of exhibitions, commonly accepted in architecture, ergonomics or more generally in psychology, is that of an angle of 30 in a vertical plane around a horizontal axis and an angle of 60 in a horizontal plane.

  It is important to obtain a false ceiling masking to take into account the usual viewing angle or normal vision of 30 in a vertical plane relative to a horizontal axis. The half-angle directed downwards does not intervene and only intervenes the angle of 15 in the vertical half-plane above the horizontal axis of usual vision.

  But this angle currently accepted as usual viewing angle can be modified according to particular considerations, for example for the presentation of objects of great height, the angle of vision is taken with respect to an inclined direction that is to say to say that it is increased by this particular inclination angle, the masking layer being always horizontal.

  According to Figure 3, the invention relates to a sheet of masking N textile product intended in particular for the realization of false masking ceilings or temporary false ceilings especially for exhibition halls. The sheet N is intended to be laid stretched usually horizontally, the horizontal direction corresponding to the horizontal plane P according to Figure 3.

  This sheet N is formed of open cells, of generally prismatic, polygonal or curvilinear base section forming open tubular cavities CT crossing the sheet N in the green direction () V with respect to the horizontal direction P. The alveoli or their CT cavities are contiguous and thus define an array of tubular cavities all of axis V, vertical.

  These CT cavities have dimensions defined by their larger horizontal diagonal DG corresponding for example to the diameter of the circle circumscribing the polygon formed by the mesh or more generally to the possibly mixtiligne curve formed by the section of the mesh.

  The height H of the tubular cavity CT is chosen as a function of the greatest horizontal diagonal DG of the mesh by the following relation: H = tga.DG, a being the usual half-angle of vision, defined previously. In FIG. 3, the triangle formed by the diagonal DG and the height H has for vertex SO one of the vertices SO, S1, S2, S3, S4, S5 of the prismatic section of the mesh. Any line of usual vision boundary passing through this peak SO and meeting one side of the cell closer to SO than the top S3 opposite to the summit SO, will meet this side at a height less than the height H. The tubular cavity thus formed will be perfectly masking in the sense of the masking effect defined for false ceilings or structures of the same type.

  The value of the coefficient (tangent a) for an angle of 15 is (tg 15) 0.267.

  The height H corresponds substantially to a quarter of the largest diagonal DG, which results in a layer of masking textile product of relatively small thickness if, for the cell, a dimension of the order of 3 to 4 mm is chosen. the thickness of the ply then being of the order of 1 mm.

  The open cells with prismatic section forming the tubular cavities CT are delimited by substantially vertical faceted sides F0, F1, F2, F3, F4, F5. These facets are opaque or translucent depending on the nature of the material constituting these facets and the direct or indirect lighting in the environment of the N web. These facets are generally perfectly opaque.

  FIG. 3 shows, by way of example, a layer of masking textile product whose cells have a hexagonal section to emphasize the possibilities of the invention. As indicated above, this section can be of very variable form, provided that the ratio between the largest horizontal diagonal and the height of each mesh or prismatic through cavity obtained is respected. This section may also be rounded, circular or more generally prismatic or curvilinear.

  FIG. 4 shows an example of a masking fabric sheet composed of tubular cavities formed by open cells with a prismatic section.

  In fact this sheet of textile product mesh 100, represented schematically and on a very enlarged scale, consists of a lower web 101 and an upper web 102 joined by occultation threads 103. The lower web 101 is formed of prismatic cells 110 delimited by sides 111. Here and by way of example these cells 110 are of hexagonal shape. The cells 110 are contiguous and the sides 111 are in each case common to two cells 110.

  The upper web 102 has a structure identical to or at least close to that of the lower web 101. The meshes 120 of the upper web 102 are also of polygonal section, for example hexagonal. They are delimited by the sides 121 each time common to two meshes contiguous 120. These meshes are joined to the meshes 110 of the lower veil 101 by occultation son 103 shown directed vertically. In fact, their orientation does not matter, it matters only the density of these yarns chosen as a function of their diameter in order to form facets 131 delimiting the prismatic cavities and which are opaque. For the purposes of the drawing, the vertices of the meshes 110 of the lower veil 101 and those of the meshes 120 of the upper veil 102 are connected by darker lines. In fact, these traits have no particular meaning. In some cases it may be vertical reinforcement son but in general these son are not distinguishable from other intermediate son 103.

  The height of the threads 103 with respect to the largest diagonal of the meshes 110/120 corresponds to the occultation condition defined above: the height is equal to the largest diagonal DG multiplied by the tangent of the angle a.

  FIG. 5 shows another embodiment of a layer of masking textile product 200 also formed in this case of a lower web 201 and an upper web 202 joined by occultation wires forming the walls of the through-tube cavities. the masking layer.

  The principle of orientation (horizontal / vertical) is the one defined previously. The sheet is supposed to be horizontal and the through cavities open in the vertical direction.

  Like the previous figures, the scale adapted for this drawing is greatly exaggerated with respect to the real dimensions.

  In this example, the lower web 201 is formed of meshes 210 rectangular or more particularly square section whose sides 211 are preferably directed parallel to the longitudinal direction of the web and the others in the transverse direction and preferably perpendicular. Meshes 210 are also joined in both directions.

  The upper web 202 is formed of cells 220 of identical size or close to that of the cells 210 of the lower web 201. These cells 220 are delimited by son 221 directed in the longitudinal direction and in the transverse direction of the web. As before, these wires 221 or sides of the cells have the same references for the different sides.

  The faces 231 of the through-tubular cavities are formed by wires connecting the sides of the cells. These son are for example vertical orientation. The distribution density of the yarns is chosen according to the characteristics of the yarns (opacity of the yarns, diameter) and the covering thickness required. These walls 231 are usually opaque.

  Figure 6 shows a perspective view of a masking layer portion formed by weaving without adding filling material. This sheet forms cells 210 delimited by the wires 211, 212. The masking effect is clearly explained in this figure. The angle a is defined by the horizontal line SHO and the rising right SG '. This angle intercepts the wire 212 whose apparent thickness H meets the definition given above to be masking when viewed from the point S or in a direction passing through the point S. At the crossing of two son 211, 212 , the height is equal to 2H, so that the masking effect is further accentuated. This masking effect is of the same order of magnitude when the cell 210 is viewed diagonally with respect to the S'HO direction which passes under the wire 211 and above the wire 212. In virtually all the orientations of FIG. aiming around a vertical axis passing through the point S, the half-angle of vision a will be occupied by the double layer of the son 211, 212 of the fabric. It is practically only in the orientation shown in FIG. 7 that the half-angle of vision a encounters only one wire 211. The superposition of the two wires is indicated schematically for a vision starting from the point S 'giving the horizontal line S'HO and an angle α 'between this straight line and the line S'G passing above the wire 212. This angle a' is practically twice the half-angle of vision a corresponding to the view of the thickness of the wire 212 from the point S. This situation is clearly explained in the side views of Figures 7 and 8.

  FIG. 9 shows another embodiment of a sheet with cavities 310 formed of crossed wires 311, 312. FIG. 10 shows a sheet with cavities 410 formed by a double crossing of wires 411, 413 and 412, 414 by overlays. FIG. 11 shows cavities 510 formed by a band structure 511, 512 of a certain height, obtained for example by fusion or coating at the junctions. Figure 12 shows another embodiment of a web with cells 610 formed of a reinforcing mesh composed of thickened son 613, 612 613, 614 in both directions of the wire 611, 612.

  FIG. 13 shows a very schematic plan view of a false ceiling masking with strips 300 assembled or juxtaposed and fixed to both sides of the hall by fastening means 301 such as hooks on which the strips are stretched. . The strips 300 can be assembled along their side 302 for example by stitching or welding with or without hem for the passage of support cables. They can also be left free. In the case where the strips are assembled, it is possible to also stretch the false ceiling in the direction perpendicular to the transverse direction by means of hooking means and tension 303.

  According to the invention, the web is formed of woven textile product or textile for glued webs. The web may also be formed of a web of foam or nonwoven or plastic material provided with perforations.

Claims (10)

  1) Masking sheet for the production of temporary ceilings, laid horizontally, characterized in that it is formed of a sheet-like structure (N) provided with through-holes, contiguous, forming open tubular cavities (CT), through the web structure, the height (H) of these cavities (CT) being at least equal to the largest horizontal diagonal (DG) of the section of each orifice, multiplied by 10 the tangent of the usual half-angle of vision.   2) Masking cloth according to claim 1, characterized in that it is formed of a ply (N) of woven fabric, knitted textile or textile for bonded plies, open-celled, integral, constituting tubular cavities ( CT), crossing the sheet, the height (H) of the cavities being at least equal to the largest horizontal diagonal of the section of the cell multiplied by the tangent of the usual viewing half-angle.   3) Masking sheet according to claim 1, characterized in that the tubular cavities are formed by a lower web (101, 201) composed of open cells (110, 210) and an upper web (102) also with open cells ( 120, 220), the cells of the two webs (101, 102) being superposed and connected by occultation walls (103, 203) forming the sides of the cavities (CT).   4) masking sheet according to claim 1 or 2, characterized in that the cells (210, 220) are of rectangular section, including square, two sides are parallel to the edge of the web (200).   5) Masking cloth according to claim 1 or 2, characterized in that the cells are of polygonal section, in particular hexagonal.   6) masking sheet according to claim characterized in that fusible lines are integrated in the sheet.   7) masking sheet according to claim 2, characterized in that the sides of the cells consist of vertical son, son horizontal son coated.   8) Masking cloth according to claim 1, characterized in that it is formed of a sheet of foam or nonwoven or plastic material provided with perforations.   9) masking sheet according to claim 8, characterized in that the foam web or nonwoven fabric is provided with a resistant integral frame.   10) False ceiling formed of masking layers according to claims 1 to 4, characterized by means for fixing and tensioning (301, 303) webs (300).