Abstract: A sheet manufacturing apparatus includes a sheet forming portion that forms a sheet using a material including fibers, a transport portion that transports the sheet, a cutting portion that cuts one edge portion and the other edge portion of the sheet positioned in a direction intersecting a transport direction of the sheet, a first coarse crushing portion that coarsely crushes a first surplus portion generated by cutting the one edge portion by the cutting portion, and a second coarse crushing portion that coarsely crushes a second surplus portion generated by cutting the other edge portion by the cutting portion.

Abstract: Methods of producing a multi-ply paper product are provided. The methods comprise applying coagulant and/or hybrid coagulant-flocculant composition to an upper ply substrate disposed adjacent and above a lower ply substrate in an amount such that a portion of the coagulant and/or the hybrid coagulant-flocculant composition passes through the upper ply substrate. Preferably, the lower ply substrate has a greater freeness than the upper ply substrate. The methods of the present disclosure preferably allow for efficient use of RDF chemicals while making use of the innate freeness differences between the upper and lower ply substrates.

Abstract: The present disclosure offers an improvement in papermaking methods and products, by providing a tissue sheet and a method to obtain a tissue sheet, with improved absorbency at a given basis weight. Thus, by way of example, the present disclosure provides a single ply tissue sheet having a basis weight greater than about 50 gsm and a specific vertical absorbent capacity greater than about 6.0 g/g.

Abstract: Treatment liquid is sprayed onto a fibrous web surface by one or more spray boxes (21, 22, 23) having a spray chamber (4) and spray nozzles (1) in the travel direction of the fibrous web before a nip (N1 . . . N7; N8; N9) formed between them by two nip means (11 . . . 18) provided with a movable surface, and air and/or treatment medium mist is removed from the spray chamber and after having added treatment liquid the fibrous web is pressed in this nip. The spray chamber (4) is formed between a first spray box (21, 22, 23; 24; 25) and any successive first nip means (13; 52, 53; 62, 63) and second nip means (13; 52, 53; 62, 63), the fibrous web is guided supported by the surface of the first nip means to the spray chamber and the fibrous web is supported thereon during the spraying of treatment liquid.

Abstract: A multi-layer web formation section has two successive wire units (300, 310) with a common wire (11). A first headbox (100) supplies fiber pulp to the first wire unit (300) forming a first partial web (W1). A second headbox (110) supplies a new fiber pulp layer to the forward end of the second wire unit (310) atop the first partial web. A first non-pulsating dewatering zone (Z1b) in the forward end of a two-wire stretch of the second wire unit (310) has a first formation shoe (200b) with a curved cap (201) placed on the side of the new layer having openings (202) extending through the cap (201) with an under-pressure (P) affecting therethrough. A two-wire stretch of the second wire unit (310) has a second pulsating dewatering zone (Z2b) formed by fixed dewatering lists (210b), between which there are gaps (220b) and an under-pressure (Pb) affecting in these.

Abstract: A multiply former apparatus is disclosed for forming a base, top and intermediate ply. The apparatus includes a fourdrinier wire for receiving thereon the base ply. A first twin wire former is provided for forming the intermediate ply, the first former cooperating with the fourdrinier wire. A second twin wire former forms the top ply, the second former cooperating with the fourdrinier wire. The second former includes a third looped wire which cooperates with a fourth looped wire for defining therebetween a second forming section for forming the top ply. A vacuum box is disposed upstream relative to a further vacuum device such that the fourth wire is disposed between the vacuum box and the third wire. The vacuum box assists in removing water from the second forming section for increasing a capacity of the apparatus.

Abstract: A multi-layer web formation section has at least two successive wire units (300, 310). First and second headboxes (100, 110) supply pulp suspension jets to the forward end of the first wire unit (300) and the second wire unit respectively to form a first partial web (W1) and a second partial web (W2) which are joined at a joint (N1) between the second wire unit (310) and a bottom wire (11). A first non-pulsating dewatering zone (Z1b) in the forward end of a two-wire stretch of the second wire unit (310) is formed by a fixed formation shoe (200b) having a curved cap (201) placed against one side, having openings with an under-pressure applied. A two-wire stretch of the second wire unit (310) has a second pulsating dewatering zone (Z2b), formed by fixed dewatering lists (210b) in the cross machine direction with gaps (220b) therebetween with an under-pressure (Pb) applied.

Abstract: A web-forming section of a paper or board machine has a first web-forming unit with a first fiber layer (W1) formed on a first wire (10); a second web-forming unit with a second fiber layer (W2) formed on a second wire (30); and a couch shoe (39) over a curved deck (40) of which the fiber layers (W1, W2) are guided for joining them together. The second fiber layer (W2) is brought to the couch shoe (39) at an angle (?) of less than 20°, advantageously less than 15° in relation to the approach direction of the first fiber layer (W1). The couch shoe (39) is provided with underpressure and the radius of curvature of its deck (40) is usually larger than the radius of curvature of a guide roll (38) preceding it. By the couch shoe, the fiber layers can be joined together wetter than usual.

Abstract: A fibrous web including a back liner having a higher fines side with a higher fines content, a top liner having a higher fines side with a higher fines content and at least one middle layer having a higher fines side with a higher fines content, and a lower fines side with a lower fines content, at least one middle layer and the top liner being couched together, the back liner having the higher fines side in contact with the lower fines side of at least one middle layer.

Abstract: A papermaking or other industrial fabric formed from a base fabric and having a seam where a first end of the base fabric is attached to a second end of the base fabric. At least one preformed coil is used to attach the first end of the base fabric to the second end.

Abstract: The equipment for the production of a paper web material comprises: a first former (1) for forming a first layer (S1) consisting of a slurry containing fibers and water; a second former (2) for forming a second layer (S2) consisting of a slurry containing fibers and water; a third former (3) for forming a third layer (S3) consisting of a slurry containing fibers and water; and a creping device (50A, 50B) for wet creping of the third layer.

Abstract: A method of making a multilayer paper web, wherein at least two paper sheets are formed and dried separately to a dry content of no more than 80% by weight, imparting a three-dimensional pattern of alternating raised and recessed portions in the paper sheets during drying, combining the paper sheets into a multilayer web, in which void volumes are created between the raised and recessed portions of the combined sheets and drying the multilayer web.

Abstract: A machine for the manufacture of a multi-layer fibrous web includes at least two fibrous web layers and at least two formers; the fibrous web layers each having a lower fines side with a lower fines content and a higher fines side with a higher fines content; and the formers include a first former and a second former, at least one of the two formers being a gap former, with the second former including a couch roll defining a couching zone whereat the lower fines side of the first fibrous web layer is brought into contact with the lower fines side of the second fibrous web layer.

Abstract: A machine for the production of a multi-layer fiber stock web, specifically a paper or cardboard web, whereby a first and a second layer are couched as a result of being delivered by an associated forming belt or wire to a couching element around which a second forming belt, or wire delivering the second layer is guided. This second forming belt, or wire impacts/runs onto the couching element before the second layer, which is supported by it, makes contact with the first layer. The second layer, at least in the location where it comes into contact with the first layer, is retained through suction force to the second forming belt wire.

Abstract: The present invention relates to a system and method of making paperboard and paperboard corrugation that negates the steps of winding rolls of containerboard on machine reels of separate paper machines, subsequent rewinding and slitting of paperboard and unwinding rolls of containerboard on separate corrugators.

Abstract: The present invention relates to the manufacture of a multi-layered board having a stable, and moisture-resistant surface. To accomplish this and other advantages of the invention, an improved binder system is used in the production of the surface layers of a multi-layered board which combines an. excellent resin penetration inside the wood constituents of the board's surface layers, with a strength, durability and resistance to ambient water and moisture. The improved binder system used in the production of the board surface layers according to this invention involves contacting wood pieces with a binder composition comprised of a curable powdery aldehyde resin and a curable isocyanate resin in the substantial absence of free water to provide a composite mixture that can be formed into a surface layer for assembly and lamination together with other wood and resin composite layers.

Abstract: A board machine and method for making a multilayer cardboard web, in which a first layer of the web having a printable surface is formed in a first forming unit and carried on an extended forming wire thereof through a couching unit where the first layer is couched with one or more additional layers, the multilayer web then being carried on the extended wire to a pick-up point. An upper press felt of a double-felted press picks up the web at the pick-up point such that the printable surface faces downward and contacts the lower press felt through the nip of the press. The lower felt is smoother than the upper felt, and the lower felt contacts the lower press roll for a minimum sector angle beyond an exit of the nip to ensure that the web follows the lower felt.

Abstract: A process for increasing the tactile properties of a base web without adversely affecting the strength of the web is disclosed. In general, the process includes the steps of placing a base web in between a first moving conveyor and a second moving conveyor. The conveyors are then wrapped around a shear inducing roll which creates shear forces that act upon the base web. The shear forces disrupt the web increasing the softness and decreasing the stiffness of the web. The shear inducing roll typically has a relatively small diameter. In some applications, more than one shear inducing roll may be incorporated into the system.

Abstract: A method for making a paper sheet comprising at least one region which is thinner than the rest of the sheet. According to the method, a first paper layer (3) is formed on a wire in a first wet end of a paper-making machine, a second paper layer (5) is formed on a wire in a second wet end of the paper-making machine, one of the two paper layers has a number of localized tinner regions (8) so that the thickness (e2) of said paper layers in said regions is up to 50% less than the thickness (et) of the rest of the sheet, and the two layers are joined together and dried. The resulting paper may be used in banknotes or checks.

Abstract: An embossed multiple ply paper product and process for producing such product displaying aesthetically pleasing decorative attributes and exhibiting functional characteristics of softness, absorbency, and drape. The decorative attributes comprise embossed patterns of indicia displaying a high quality cloth-like appearance for a softer, more quilted look. The plies are joined in a face-to-face arrangement by selective bonds which are limited to the indicia, in order to produce more permanent decorative figures that inhibit dissipation caused by compressive forces, humidity, absorption, etc.

Abstract: The present invention is a method of making an ultra soft, multi-ply tissue from non-premium furnish using wet press technology and the product produced thereby.

Abstract: A multi-ply web forming method and apparatus are disclosed for forming a top ply onto a base ply. A fiber suspension jet is by means of a secondary headbox (21; 21′, 26) delivered into a twin-wire roll nip created by two tensioned wires (16, 22; 16′, 22′; 22, 27) one of which (16; 16′, 22) carries the moist base ply.

Abstract: A multi-ply fiber web forming apparatus includes a lower forming fabric defining a lower forming fabric run. A first headbox is positioned above the lower forming fabric for discharging a fiber suspension onto the lower forming fabric. An upper forming fabric defines an upper forming fabric run. A second headbox is positioned above the upper forming fabric for discharging a fiber suspension onto the upper forming fabric. A wet forming box is positioned below the lower forming fabric for applying a liquid to the lower forming fabric. A transfer roll is positioned above the upper forming fabric. The transfer roll and the wet forming box are positioned in close opposing relationship to each other, whereby each of the lower forming fabric and the upper forming fabric pass therebetween in a transfer area.

Abstract: An embossed multiple ply paper product having a nested latticework embossment pattern providing a cloth-like, quilted appearance and a process for embossing and bonding such multiple ply paper product. The multiple ply paper product comprises a latticework of cells composed of n rows of embossment elements nested within an interfacing latticework of cells composed of n+1 rows of embossment elements.

Abstract: The present invention relates to the manufacture of a hydrophilic, humectant, soft, pliant single-ply or multi-ply absorbent papers to which an organic permanent or temporary wet strength agent has been added. Novel absorbent papers having temporary or permanent wet strength properties are shown. These are useful as bathroom tissue and napkins. These products are suitably also prepared using through air drying methods with or without the use of a Yankee dryer, and the products exhibit a unique combination of properties designed to appeal to consumer preferences. In many applications, these products need not be creped, and in that case they do not have the serpentine configuration.

Abstract: An embossed multiple ply paper product and process for producing such product displaying aesthetically pleasing decorative attributes and exhibiting functional characteristics of softness, absorbency, and drape. The decorative attributes comprise embossed patterns of indicia displaying a high quality cloth-like appearance for a softer, more quilted look. The plies are joined in a face-to-face arrangement by selective bonds which are limited to the indicia, in order to produce more permanent decorative figures that inhibit dissipation caused by compressive forces, humidity, absorption, etc.

Abstract: The invention relates to a method of producing visible, preferably transparent or translucent, continuous streaks and/or delimited fields in paper in conjunction with forming a paper web in a paper machine. The method is characterized by essentially preventing dewatering of paper stock/paper fibres on one or more surfaces of a wire in the forming unit of a paper machine in conjunction with forming a paper web in the machine, and by applying a special stock that contains fibres which differ from the other fibre material deposited on the wire, optionally together with an arbitrary filler and/or binder. The invention also relates to a valuable document, such as a banknote, produced from the aforedescribed paper.

Abstract: In order to meet higher demands for the properties of paperboard products an improved method and machine for the manufacture of paperboard are proposed according to the present invention in which a core of a paperboard web is formed in a second forming unit from a stock with a consistency of 1.5-6.0% being supplied to the fourdrinier wire of a fourdrinier former carrying a back layer formed previously in a first forming unit, from a headbox for high consistency stock and being dewatered upon being enclosed between the fourdrinier wire and a top wire in said second forming unit, and in which an underliner is formed in a third forming unit of stock with a consistency of 0.3-1.4% being supplied to the fourdrinier wire carrying the back layer and core, from a headbox for stock of low consistency.

Abstract: A multiple ply tissue paper structure is disclosed. The multiple ply tissue paper has at least two plies having discrete low density regions dispersed throughout a continous relatively high density network. One of the plies has more of the discrete low density regions per square inch than does the other ply. In one embodiment, the two plies have different calipers and macrodensities.

Abstract: An inorganic board consisting of a cured base mat and a cured surface mat is manufactured by forming a surface mat by the dry method on a base mat formed by a paper making method, embossing the composite mat, and curing the embossed composite mat. Ridges each having an enlarged top are formed on the surface of the base mat when a plural number of single mats formed by the paper making method are rolled and laminated around a making roll having a surface on which a plural number of ring grooves are formed. The ridges of the base mat engage the surface mat since each ridge has an enlarged top to improve the interlaminate strength between a cured base mat and a cured surface mat of the resulting inorganic board.

Abstract: A paper machine forming section with two wire forming units. One of the two forming units is a twin wire web forming unit having a headbox, two wire loops arranged in sandwich-like manner and a drainage element for each of the wire loops. The first web-forming unit has a first section including a curved suction drainage element or roll in the first lower wire loop; a second section with opposing drainage ledges, wherein the drainage ledges are stationary on the upper side and the drainage ledges are developed resiliently pressable on the bottom side; the drainage ledges of the upper and lower sides are arranged staggered with respect to each other in the direction of travel of the wire, and at least the ledges of the upper side are developed with suction; a third section which has at least one suction wire separating element on one side. The second web-forming unit is a hybrid former with a single wire.

Abstract: A paper machine forming section with two twin-wire sections for forming a multilayer paper web. Each twin wire web-forming unit consisting of a headbox, two wire loops arranged to define a common wire path for molding the web being formed in sandwich-like manner and drainage elements for each of the wire loops. The common wire path of each web-forming unit has a first section including a curved suction drainage element or roll in the first lower wire loop; a second section including opposing drainage ledges, wherein the drainage ledges are stationary on the upper side and the drainage ledges are developed resiliently pressable on the bottom side; the drainage ledges of the upper and lower sides are arranged staggered with respect to each other in the direction of travel of the wire, and at least the ledges of the upper side are developed with suction; and a third section which has at least one suction wire separating element on one side.

Abstract: An oriented strand board product is provided. The board is comprised of a baseboard having three wood strand layers, the wood strands being oriented in space with respect to a board-forming machine such that a core layer is comprised of wood strands oriented generally in a random or cross-machine direction and each adjacent layer is comprised of coarse and fine wood strands oriented generally in the machine direction and wherein the wood strands comprising each adjacent layer are formed with the coarsest strands located nearest the core layer and the finest strands are located nearest the outer surfaces of each outer board layer. The OSB board product is clad with a dry felted wood fiber overlay on one planar surface of the baseboard.

Abstract: Process and apparatus for the continuous production of gypsum fiber plates in which the fiber component is dewatered and rediluted with water recovered from the gypsum-fiber suspension after it has been spread on a belt, passed over at least two suction boxes and densified on the last suction box by a densifying device engaging the filter cake layer from the top.

Abstract: An oriented strand board (OSB)-fiberboard composite structure is comprised of a baseboard having three wood strand layers, the wood strands being oriented in space with respect to a board forming machine such that a core layer is comprised of wood strands oriented generally in a random or cross-machine direction and each adjacent layer is comprised of coarse and fine wood strands oriented generally in the machine direction. In a preferred embodiment, the wood strands comprising each adjacent OSB layer are formed with the coarsest strands located nearest the core layer and the finest strands are located nearest the outer surfaces of each outer board layer. The OSB-fiberboard composite product is clad with a wood fiber overlay on one major surface of the baseboard. The composite board is manufactured without warping, by providing particular OSB layer thicknesses, such that the lower OSB layer is about 25% to about 35% thicker than the OSB layer bonded to the fiberboard.

Abstract: A multi-ply paper web is formed by bringing a top ply liner into ply-bonding engagement with a base ply web (W.sub.B) traveling on a base ply forming wire (36). The top ply liner (W.sub.T) is formed between two co-running forming wires (10, 20) in a convex upwardly/concave downwardly curved, substantially horizontal forming zone. Dewatering in the forming zone is effected by applying sub-atmospheric air pressure solely beneath the lower surface of the top ply liner (W.sub.T) being formed. Water is removed from the upper surface of the top ply liner (W.sub.T) solely by wire tension, gravity and centrifugal force created by passing the co-running forming wires (10, 20) over the convex upwardly curved path of travel. This permits a greater concentration of pulp stock fines to remain in the upper surface of the top ply liner (W.sub.T) to effect greater ply-bonding affinity with the base ply (W.sub.B) when the two plies (W.sub.T, W.sub.B) are brought together and bonded.

Abstract: A papermaking apparatus that can form a paper web having a good fiber formation is disclosed. A plurality of vertically adjustable forming rolls are provided on the top surface of an endless felt couch between a lead-in roll and a couch roll, and stationary forming bars are provided on the bottom surface of a wire screen. The endless felt couch and the wire screen, between which paper stock is interposed, are caused to move by undulation to generate pulses, which in turn apply shear force onto the paper web to dewater the paper web while facilitating fiber dispersion on the paper web.

Abstract: Apparatus for forming multilayered paper includes an endless loop of felt and at least two short wire units provided beneath the loop of felt. Each short wire unit has a fixed dehydrator having a forming shoe, at least part of the upper surface of which is curved, and a short wire traveling over the curved part of the upper surface of the forming shoe. The endless loop of felt is engaged with the short wire on the curved upper surfaces of the forming shoes of the fixed dehydrators. Stock is ejected from a head box onto each short wire unit and is moved between the endless loop of felt and the short wire of the unit where the stock is dehydrated to thereby form a paper layer. Each of a forming roll and a couch roll guiding the felt into engagement with the short wire, and a felt roll disposed beneath the felt downstream of the short wire unit, can be moved vertically.

Abstract: Multi-ply facial tissue paper products comprising biodegradable chemical softener compositions and a combination of a wet strength binder, either permanent and/or temporary, and a dry strength binder is disclosed.The multi-ply facial tissue paper products contain a biodegradable chemical softening composition comprising a mixture of a biodegradable quaternary ammonium compound and a polyhydroxy compound. The multi-ply facial tissue paper products also contain an effective amount of a wet strength binder, either permanent and/or temporary, and a dry strength binder to control linting and/or to offset the loss in tensile strength, if any, resulting from the use of the biodegradable chemical softening compositions. The use of both wet strength binder, either permanent and/or temporary, and dry strength binder also improves the retention of the chemical softening composition in the sheet.

Abstract: An oriented strand board product is provided. The board is comprised of a baseboard having three wood strand layers, the wood strands being oriented in space with respect to a board forming machine such that a core layer is comprised of wood strands oriented generally in a random or cross-machine direction and each adjacent layer is comprised of coarse and fine wood strands oriented generally in the machine direction and wherein the wood strands comprising each adjacent layer are formed with the coarsest strands located nearest the core layer and the finest strands are located nearest the outer surfaces of each outer board layer. The OSB board product is clad with a dry felted wood fiber overlay on one planar surface of the baseboard.

Abstract: Disclosed herein is agricultural paper to be made into pots for raising seedlings. It is made up of a first layer made chiefly of natural pulp and a second layer made of synthetic fibers having a basis weight of 3-15 g/m.sup.2, said first layer and second layer being joined to each other by the wet papermaking process which intertwines the fibers of the two layers at their joining interface. The second layer is formed by fusion bonding composite synthetic fibers of polymers having different plasticizing temperatures.

Abstract: A method for manufacturing multilayer board in which the pulp suspension forming a surface layer (12) is fed onto the horizontal section of a first, inner wire (1). The pulp suspension forming an intermediate layer (11) is supplied onto said web layer, which is already formed, in or in front of a tapering gap (6) constituted by the first wire and a second, outer wire (4). Both of the wires and the web layers (11, 12) between them are guided over a curved surface (3). After this the first wire and both of the web layers are guided against a third wire (8) onto the horizontal section of which the pulp suspension forming the other surface layer (13) is supplied. The consistency of the pulp suspension forming the intermediate layer (11) is remarkably higher than that of the pulp suspensions forming the surface layers (12, 13).

Abstract: A method of producing a multi-ply paperboard comprising at least one ply high bulk fibers sandwiched between at least two plies of conventional papermaking fibers. In a preferred embodiment, high bulk fibers characterized by twists, kinks and curls are produced by mechanical deformation without substantial fibrillation or breakage of the fibers, as by dry hammermilling or wet milling of the fibers. An aqueous foam furnish is preferred for laying the ply containing high bulk fibers.

Abstract: A multi-ply paper web forming apparatus utilizes first and second forming wires which travel in a co-running path for a portion of their length and which form a throat into which an aqueous slurry of paper pulp fibers is introduced. The slurry is dewatered between the co-running first and second forming wires upwardly and downwardly to quickly produce a substantially formed, but still moist, top ply web which is carried on the second forming wire onto a base ply web which has previously been formed on the wire of a single wire former. The first surface of the top ply web is brought into ply bonding engagement with the surface of the base ply web to produce a composite multi-ply web which has superior overall ply bond, retention and dryness before leaving the web forming section of a papermaking machine.

Abstract: A backstand threading device to be mounted on a paper sheeter to permit an operator to move the device and himself along the length of the paper sheeter to thread each of the plurality of webs moving through the paper sheeter.

Abstract: A process for manufacturing of kraft paper, especially kraft sack paper, on a multi-wire machine in which the web is dried by a combined cylinder drying and free drying and is optionally creped or micro-creped and optionally also glazed. By forming the web into two or more layers which are couched together in the wire part of the machine and subsequent shrinkage in order to obtain a stretch at break of at least 2.5% in the machine direction and of at least 5% in the tranverse direction, improved strength properties are provided.

Abstract: An aqueous slurry comprising fibrous particles of a heat-resistant aromatic polymer and short fibers made of said polymer or insulating inorganic short fibers, or a mixture thereof, is made into a wet web and, after adjusting the water content to 50 to 95 weight %, said wet web is laid up in a desired number of layers, and then the laminate is dewatered and dried for integration under pressure at a temperature not exceeding the softening point of said aromatic polymer, thereby obtaining an oil-impregnatable insulating board with high strength and capable of uniform impregnation of oil therein.

Abstract: A method and mechamism of removing an edge of a paper web formed on a traveling foraminous wire from stock issuing from the slice of a headbox including a blade positioned parallel to the machine direction and located to separate the edge from the flow of stock issuing from the slice opening before it engages the traveling wire and collecting the edge material separated and conveying it away so that the material can be used.

Abstract: A duplicating stencil is produced by placing an electrostatically-produced image on a substrate in contact with an ink-impervious surface layer of a stencil blank, bonding the image to the surface layer by the application of heat and/or pressure and stripping the substrate from the stencil blank to remove the surface layer in the image area. The surface layer may comprise a synthetic resin composition containing a finely dispersed pigment and is attached to the porous base tissue of the stencil blank by an adhesive. Bonding of the image to the surface layer and possibly also fixing of the image to the substrate in the same operation can be effected by means of infra-red heating.

Abstract: A laminated structure of sheets of fibrous cellulosic and polymeric materials is prepared upon a multiple plane table cardboard manufacturing machine by forming a sheet of cellulosic fibers from a pulp thereof on at least one of the plane tables of the machine, forming a sheet of polyolefinic fibrids from a pulp thereof on a second plane table of the machine, and forming a cellulosic fiber-polyolefinic fibrid sheet from a pulp thereof on a third plane table of the machine, joining those sheets in superposed position so that the sheet of cellulosic fibers is in the middle, drying the superposed sheets, and then calendering the dry superposed sheets at a temperature not lower than that necessary to melt at least partially the polyolefinic fibrids.