METHOD AND APPARATUS FOR MAKING A FIBROUS PRODUCT

Abstract: In a method for making a fibrous product from vegetable-based cellulosic fibers, an air flow (A) is used for forming a mat on an advancing forming platform (1). The mat is bonded by means of thermally bondable binder fibers, such as thermoplastic fibers intertwined with the cellulosic fibers such that, upon being brought to a binding state through the action of heat, said binder fibers bond the cellulosic fibers to each other in the mat. The thermally bondable binder fibers intertwined with cellulosic fibers are subjected to the action of heat already in air flow (A) carrying the fibers onto forming platform (1) by setting temperature of the air flow sufficiently high.

Description: Method and apparatus for making a fibrous product The present invention relates to a method as set forth in the preamble of the appended claim 1 for making a fibrous product as well as to an apparatus as set forth in the preamble of the appended claim 10 for making a fibrous product. International publication No. WO 82/03359 discloses a method for making a moldable mat from wood fibers such that the wood fibers are intertwined with thermally bondable binder fibers which bond the fibers together upon melting and setting. The mat is formed by using a so-called dry process on a moving belt by means of an air flow, which transports the fibers onto the belt and travels through the mat. This is followed by a mat bonding process by carrying the thus formed mat through an oven, having a sufficiently high temperature for softening the binder fibers, which are of thermoplastic plastics material, and bringing them in an adhesive state for bonding the wood fibers to each other. The above method is not only capable of producing mats by using binders that are not hazardous in view of safety at work and environment but can also be used for readily manufacturing products that can be subsequently molded into a desired shape by the application of heat, since the thermoplastic characteristics of binder fibers can be used for re-softening such fibers, whereby the mat is subjected to re-shaping and subsequent cooling for bringing said fibers to set the mat in a re-shaped form. The use of wood fibers and other cellulosic fibers of vegetable origin for manufacturing products made of fibers is attractive in the sense that the question is about reclaimable natural raw materials, which are abundantly available, pleasant to handle as a material, and do not create health hazards. A fibrous mat manufactured from these fibers is also an effective heat insulation. However, this is the very feature that causes a problem in manu¬ facturing the product, if the above process is to be employed. When treating the product in an oven, it is namely necessary to give the oven a considerable length for heat to penetrate also in the interior of a mat-shaped product for bonding the fibers. If the purpose is to manufacture products of considerable thickness, it would be necessary to make the ovens unreasonably long for bonding the mat properly also in its middle sections upon leaving the oven. Another alternative would be a drastic increase of temperature which would, however, lead to damages in the surface structure of a product, since the thermoplastic fibers included therein would then melt or fuse completely away as globular drops not capable of bonding the fibers together and the mat would break up. It is obvious that the above processes are not feasible in terms of energy consumption, either. An object of the invention is to eliminate the above drawbacks and to provide a method as well as an apparatus, whereby it is possible to employ wood fibers for making quite thick fibrous mats having excellent thermal insulation capacity. In order to achieve this object, a method of the invention is primarily characterized by what is set forth in the characterizing section of the appended claim 1. When the thermally bondable binder fibers intertwined with cellulosic fibers of vegetable origin are subjected to heat bringing them to a binding state as early as in the air flow carrying said fibers onto a processing platform by setting the air flow temperature sufficiently high, the heat insulation characteristics of the fibers do not present a problem. Thermally bondable binder fibers bond wood fibers to each other already at the manufacturing stage of a mat. In practice, this facilitates the manufacture of even a very thick mat, since fresh fibers bonding into a mat can be stacked basically in quantities as large as may be desired on top of a mat previously formed at the manufac¬ turing site of a mat. The appended non-independent claims 2-9 disclose other preferred embodiments for a method of the invention. For example, a mat can be compressed to a desired extent by the application of an air flow as it is still in a moldable state after manufacturing. In further processing, the mat is preferably molded into a building element insulation in view of making full use of the health protecting quali¬ ties of the product. An apparatus of the invention is in turn characterized by what is set forth in the characterizing section of the appended claim 10. An air chamber, in which a mat is formed on a conveying platform, receives an air duct from a heater for heating the binder fibers to an adhesive state already in the air chamber. Thus, the apparatus does not require a long oven for thermally bonding the product. The appended non-independent claims 11-14 disclose other preferred alternative embodiments for an apparatus of the invention. The invention will now be described in more detail with reference made to the accompanying drawings, in which fig. 1 is a cut-away side view of a mat forming assembly included in an apparatus of the invention, fig. 2 is a cut-away plan view of the assembly shown in fig. 1, fig. 3 shows one example of a finished product in a cut-away view, fig. 4 is a larger-scale view of a detail included in the assembly shown in fig. 1. fig. 5 illustrates schematically the operating prin¬ ciple for an entire apparatus. Fig. 1 illustrates a mat forming assembly, including a feeding mechanism 11 for fibers. The feeding mechanism may comprise either a per se known vertical device 11a for bringing the fibers by means of an air flow, or a horizontal conveyor lib, whose inlet end is provided with per se known pretreating means for fibers. The bottom end of feeding mechanism 11 is provided with a feeding roll 2 having studs on its surface in a dense pattern. Facing towards the surface of feeding roll 2 is a horizontal narrow slit orifice at the end of a first air conduit 3. Below the slit orifice is located an inlet for a second air conduit 4, with a constriction point formed between its bottom wall and the surface of feeding roll 2. Downstream of this constriction point there is an obliquely declining, expanding air chamber 6, having its lower end closed with an air permeable forming platform 1. On the opposite side of forming platform 1 lies a collecting chamber 10. The forming platform 1 is formed of an endless belt, extended around cylinders and adapted to travel across chamber 6. Downstream of chamber 6 said forming platform travels across a second air chamber 8, providing a bottom surface therefor. The inlet end of first air conduit 3 is provided with mutually parallel fans 12 for producing a uniform air flow across the entire width of duct 6. These fans 12 are shown by dash lines in fig. 2. A duct serving as the inlet end of second air conduit 4 is also provided with a fan 13, which is adapted to blow air heated by a heater 7 into said second air conduit 4. Heater 7 can be for example a conventional gas burner. The mat-forming process in the apparatus is such that a mixture of cellulosic fibers and thermally bondable binder fibers is delivered by means of the feeding mechanism towards feeding roll 2. Fig. 4 shows the subsequent mat- forming process in more detail. The rotating feeding roll 2 includes studs 2a, indicated in the figure as the outer¬ most layer of the feeding roll, for picking up and carrying the fibers further. In the rotating direction of the feeding roll, the fibers arrive next in the range of action of a horizontal slit orifice 3a, located at the end of first air conduit 3 and extending across the width of said roll. A high-speed air flow Al discharging from the slit orifice disengages the fibers from feeding roll 2 while rushing along the roll surface and carries them across the inlet 4a of second air conduit 4 into a constriction point 2b between the bottom" wall of said inlet 4a and the surface of feeding roll 2. After the constriction point, the fibers are completely disengaged from feeding roll 2 and proceed into an air chamber 6, having a cross-section which expands in the advancing direction of fibers and having a width which is constant and corresponds to the width of a mat to be manufactured. The expansion or flare of the chamber is achieved in a manner such that the front and rear walls, extending in the axial direction of feeding roll 2, i.e. in the lateral direction of a mat being manufactured, diverge from each other. Said second air conduit 4 is used for delivering air as an air flow A2 into said inlet 4a. The temperature of this second air flow A2 is higher than that of said first air flow Al supplied through said first air conduit 3. As a result of the ejector effect produced by constriction point 2b, this air flow A2 merges into air flow Al and blends therewith for an air flow A carrying fibers to the outlet end of air chamber 6. The supply rate of this higher- temperature air flow A2 is arranged to be such that the temperature of air flow A carrying the fibers in air chamber 6 is sufficient to cause a change on the surface of thermally bondable binder fibers blended with cellulosic fibers to a degree that makes them capable of bonding the fibers into a mat, such as the softening of the surface of the thermoplastic fibers. These binder fibers are well exposed to the action of air, since they travel in the air flow in bare condition. The outlet or trailing end of air chamber 6 is closed by a forming platform 1, which travels across the chamber and can be a woven wire felt or a like air-permeable flat piece of material. The fibers hitting the bottom at the inlet of a conveyor, i.e. downstream of the air chamber front wall, immediately build up a bonded mat and an identically bonded mat of a continuously increas¬ ing thickness begins to gather on top of that. Since the resulting mat is porous in nature, said air flow A is able to progress through the mat and said forming platform 1 therebelow into a collecting chamber 10 on the opposite side. Fig. 1 illustrates the subsequent processing of a mat. Downstream of chamber 6 in the traveling direction of forming platform 1 is mounted a packing cylinder 14, whose distance from forming platform 1 is adjustable. The packing cylinder prevents the passage of air in the traveling direction of forming platform 1 out of the air chamber from above the mat. Downstream of the packing cylinder, said forming platform 1 carries the mat into a second air chamber 8 located above forming platform 1. The top end of air chamber 8 is provided with an air conduit 9. The second air chamber 8 has a flaring or expanding configuration towards forming platform 1 in the flowing direction of an air current supplied from air conduit 9, i.e. the chamber walls located on the inlet and outlet side of the forming platform are diverging from each other. For example, the pressure of an air flow B supplied into the chamber can be applied for further compressing the mat to a desired degree for providing a desired value for its density. Thus, the air flow is delivered through the porous mat and the forming platform 1 supporting it from below and into a second collecting chamber 15 located on the opposite side. Thus, said air flow B supplied into second air chamber 8 has such a temperature that for example thermoplastic binder fibers still remain in an adhesive softened state where the fibers allow the deformation of the mat for shaping or molding the mat to a desired density such that the deforma¬ tion is permanent. Downstream of second chamber 8, the mat is transferred from forming platform 1 onto a conveyor 16 for carrying the bonded mat-shaped product forward for further processing. If a product of a particularly low density is desired, the further processing effected by means of second air chamber 8 can be omitted. The product density can also be controlled already during a mat-forming operation by means of the flow rate of air current A advancing in air cham¬ ber 6, said flow rate dictating the force by which the fibers strike into a mat configuration. Fig. 5 illustrates schematically one possible arrangement for air flows in the invention. The air currents are circulated such that the mat-forming air flow or current A arriving in collecting chamber 10 is delivered by way of fan 12 into first air conduit 3. During this period the air flow has time to cool to such a degree that the first air flow Al discharging from air conduit 3 through slit orifice 3a is below the temperature capable of bringing the binder fibers to a binding state. Thus, this air flow Al only serves for detaching the fibers from feeding roll 2. However, it can be used for providing a preheating, whereby the air flow A2 discharging from air conduit 4 need not be given a particularly high temperature. Said air flow A2 is delivered into second air conduit 4 from heater 7 by means of fan 13. The air conduit 4 branches for an air conduit 9 connected to second air chamber 8, whereby some of the heated air flow Al blown by the fan is extracted as an air flow B performing the further processing of a mat. This also secures that in the further processing said air flow B has a sufficiently high temperature and, since it originates from air conduit 4, which only contains the flow of heated air, its temperature is in fact higher than that of air chamber 6. However, this air does not cause too big a change in the state of the binder fibers, such as melting of thermoplastic fibers, as those are surrounded by cellulosic fibers serving as heat insulation and, on the other hand, the flow rate of air per unit area remains quite low due to the extent of chamber 8. The air flow B received in second collecting chamber 15 on the other side of forming platform 1 is circulated back to heater 7 by way of an air conduit 18. The chamber 8 also receives air carried along with a mat from chamber 6. This air advances through collecting chamber 15 merging with the return air flowing to heater 7. In order to maintain the air balance, some of the air progressing in first air conduit 3 is delivered out along a duct 17. This is compen- sated for by delivering to heater 7 not only circulated air but also compensation air from outside. Air can also be circulated from duct 17 to heater 7, but this degree of circulation is determined by impurities accumulated in the air during the mat manufacturing process. Fig. 5 further illustrates normal measuring and regulation equipment for setting the temperatures of air flows as desired. The method according to the invention is not limited to the apparatus described hereinabove, and its basic prin¬ ciples can be summarized as follows: a) Mixing of the cellulosic fibers and the thermally bondable fibers together in a suitable ratio. b) Introducing the cellulosic fibers and the thermally bondable fibers to a flow of gaseous medium to form a mixture distributed uniformly in the medium. c) Elevating the temperature of the gaseous medium to an area bringing the thermally bondable fibers to a binding state where they are capable of forming bonds between the thermally bondable fibers and cellulosic fibers. d) Forming a mat on a suitable forming support by means of the gaseous medium from tihe cellulosic fibers and the thermally bondable fibers intertwined with them and being in the binding state. Fig. 3 shows one preferred fibrous p r oduct, which is manufactured by using a flexible mat prepared according to the invention and having a density of appr. 18-25 kg/m 3 . The product comprises a flat rigid building element 5, wherein the mat is fitted as a layer 5c for providing a heat insulation between an outer lining 5a and an inner lining 5e of the building element. The layer 5c can also be made of a plurality of superimposed mats such that the layer will have a thickness of 10-20 cm. In the example shown in fig. 3, the surface of insulation layer 5c facing the outer lining is provided with a windscreen made of a non-woven fabric, with a ventilation gap remaining between the outer lining and the windscreen. Accordingly, the side facing the inner lining is provided with a vapour barrier sheet 5d, which can comprise a plastic sheet or film laminated on the surface of insulation layer 5c. The vapour barrier 5d is covered with inner lining 5e made of gypsum board. Also other final product forms are conceivable for a mat manufactured according to the invention. Thus, when the question is about mats having a density higher than that of a heat insulation mat, such mats can be used the same way as chipboard. Suitable raw materials for use as a mat include all vege- table-based cellulosic fibers, especially fibers based on woody-stem plants, such as mechanically manufactured pulp. Thus, the density of a mat can be controlled by selecting the degree of beating for fibers. Furthermore, the fibers may originate from any variety of wood, but fibers obtained from trees and bushes of the family Salicaceae, such as willows and aspen, are especially preferred due to the length thereof as they can be readily intertwined together. Other conceivable raw materials include cotton or jute either alone or as a mixture with wood fibers. The thermally bondable binder fiber may comprise any thermoplastic polymer, such as e.g. polypropylene or polyester. It is also possible to employ bicomponent fibers containing parts consisting of polymer softening at a lower temperature. The temperature of air current A flowing in air chamber 6 can be set according to the softening point of a binder fiber material and this point, at which the surface of fibers softens to an adhesive or tacky state, is within the range of 100°...200°C on the most commonly used thermo¬ plastic polymer materials. The thermally bondable fibers can also include any fiber types that become bonded by virtue of a change in their structure effected by heat, such as phenol-based fibers. The mat structure can also be controlled by selecting the proportions between binder fiber and cellulosic fiber, but the basic raw material for the structure of a product consists of a vegetable-based cellulosic fiber, which always makes up most of the total mass of a mat. An apparatus of the invention has been used for manufactur¬ ing a variety of mats from spruce-based wood fibers as well as polyester fibers. The flow rate of an air current upstream of the air chamber has been in this case 42 m/s and the surface speed of feeding roll 2 has then been appr. 10 m/s slower. The polyester fibers used as binder fibers have covered 15-20 % of the total amount of supplied fibers. The resulting mats have had weights per unit area within the range of 40 g/m 2 - 3000 g/m 2 , the former grammage being that of paper webs. The invention is thus applicable also to the manufacturing of thin products, the advantage being that the bonding can be effected simultaneously when the mat is formed on the support. Densities obtained range from 18 kg/m 3 to 400 g/m 3 , the former density relating primarily to glass- or rockwool used as heat insulation and the latter relating to chipboard. The resulting products have excellent heat insulation qualities for the reason that vegetable-based cellulosic fibers have a low coefficient of heat transfer and such fibers are capable of producing a fluffy mat suitable for insulation purposes. In addition, the resulting mats can be further processed for improving certain properties. For example, the mats can be subjected to a fire protection and anti-mildew treatment. The fibers supplied for mat forming can also be treated this way.

Claims: Claims 1. A method for making a fibrous product, wherein a flow (A) of gaseous medium is used for forming a mat from vegetable-based cellulosic fibers on an advancing forming platform (1) and the mat is bonded by means of thermally bondable binder fibers intertwined with the cellulosic fibers such that, upon being brought to a binding state through the action of heat, said binder fibers bond the cellulosic fibers to each other in the mat, characterized in that the thermally bondable binder fibers intertwined with cellulosic fibers are subjected to heat bringing them to a binding state already in said flow (A) carrying the fibers onto forming platform (1) by setting temperature of the flow sufficiently high. 2. A method as set forth in claim 1, wherein the fibers are delivered into the flow (A) of gaseous medium by means of a feeding roll (2) or a like, characterized in that the fibers are disengaged or released from feeding roll (2) or the like by means of a first flow (Al) of gaseous medium which is thereafter supplemented by a higher-temperature second flow (A2) of gaseous medium, as a result of which the temperature of a combined flow (A) of gaseous medium produced by said first and second flows (Al, A2) increases such that the binder fibers are brought to a binding state. 3. A method as set forth in claim 1 or 2, characterized in that, after being formed by means of the flow (A) of gaseous medium on forming platform (1) , said mat is processed further by delivering a flow (B) of gaseous medium through the mat while the mat is supported from the side opposite to the flowing direction of gaseous medium. 4. A method as set forth in claim 3, characterized in that the further processing comprises increasing the mat density by means of a pressure produced by the flow (B) of gaseous medium against the mat. 5. A method as set forth in any of claims 2, 3 or 4 , characterized in that said fibers-releasing first flow (Al) of gaseous medium and said higher-temperature second flow (A2) of gaseous medium are supplied along their own conduits (3, 4) and the flows are circulated such that, after flowing through forming platform (1) , some of the flow (A) used for the formation of a mat is delivered into the conduit (3) for fibers-releasing flow (Al) for preheating said flow. 6. A method as set forth in any of claims 3, 4 or 5, characterized in that some of the higher-temperature flow (A2) of gaseous medium progressing in the conduit (4) is delivered to the further processing of a mat, whereby that flow makes up at least some of the flow (B) of gaseous medium delivered through the mat. 7. A method as set forth in any of the preceding claims, characterized in that the thermally bondable fibers are thermoplastic fibers. 8. A method as set forth in any of the preceding claims, characterized in that the resulting mat is fitted as a heat insulation (5c) in a building element (5) between its outer lining (5a) and inner lining (5e) . 9. A method as set forth in claim 8, characterized in that a gypsum board is fitted as said inner lining (5e) . 10. An apparatus for making a fibrous product, comprising a chamber (6) for gaseous medium, having an inlet end provided with a conduit (3, 4) and an outlet end which is closed by a forming platform (1, adapted to be movable, said apparatus further comprising means (11, 2) for feeding vegetable-based cellulosic fibers and thermally bondable binder fibers into the chamber (6) for forming a mat on forming platform (1) by means of a flow (A) of gaseous medium supplied from the conduit (3, 4) as well as means for heating the thermally bondable binder fibers such that, upon being brought to a binding state through the action of heat, said fibers bond the cellulosic fibers to each other in the mat, characterized in that the apparatus includes a heater (7) of gaseous medium, from which is extended a conduit (4) to the chamber (6) for heating the binder fibers to the binding state already in said cham¬ ber (6) . 11. An apparatus as set forth in claim 10, comprising at the inlet end of the chamber (6) a feeding roll (2) or a like, characterized in that the inlet end of the chamber (6) is provided with a first conduit (3) for gaseous medium extended towards said feeding roll (2) or the like for releasing the fibers therefrom, whereby a second conduit for gaseous medium, which is formed of the above-mentioned conduit (4) associated with the heater, is extended to the chamber (6) at a location which in the flowing direction of the gaseous medium lies downstream of an inlet point (3a) of said first conduit (3) . 12. An apparatus as set forth in claim 10 or 11, charac¬ terized in that, in the advancing direction of said forming platform (1) , said chamber (6) is followed by a second chamber (8) including a mat-supporting platform prefer¬ ably provided by the same forming platform (1) coming out of the preceding chamber, and said second chamber (8) is provided with a duct (9) for delivering a flow (B) of gaseous medium through the mat. 13. An apparatus as set forth in claim 11 or 12, charac¬ terized in that, in the supplying direction of the gaseous medium, said first conduit (3) is in communication with a collecting chamber (10) located on the side of forming platform (1) opposite to said chamber (6) . 14. An apparatus as set forth in claim 12 or 13, charac¬ terized in that said conduit (4) between the heater (7) and the chamber (6) branches for the duct (9) connected to said second chamber (8) .

Inventors: NIEMINEN JORMA, NIEMINEN, JORMA
Applicants: NIEMINEN JORMA, SCANWOVEN AB OY, OY SCANWOVEN AB
Application year: 1993
Main classification: B27N3
IPC codes: B27N3