US 3769115 A
A method for the production of a fibrous sheet material by passing a stream of gas containing suspended fibres through a gaspermeable forming surface to form a fibrous layer thereon and bonding the fibres to each other or to a reinforcing material by means of a foamed binder.
Description (OCR text may contain errors)
United States Patent [191 Rasmussen et al.
[ METHOD FOR THE PRODUCTION OF A FIBROUS SHEET MATERIAL Inventors: Torben Borup Rasmussen, Tousvej;
Kjeld Dossiug Ottosen, l-lolmevej; Torsten Bengt Persson, Lystrup, all of Denmark Karl Kristian Kobs Kroyer Vestre Kongevej, Aarhus-Viby, Denmark Filed: Nov. 14, 1968 Appl. No.: 776,859
 Foreign Application Priority Data Nov. 15, 1967 Denmark 5701/67  US. Cl. 156/62.2, 156/78  Int. Cl B32b 23/12  Field of Search 156/72, 78, 79, 62.2; 264/ 121  References Cited UNITED STATES PATENTS 3,158,668 11/1964 Johnson 264/121 Primary ExaminerReuben Epstein Attorney-Watson, Cole, Grindle and Watson  ABSTRACT A method for the production of a fibrous sheet material by passing a stream of gas containing suspended fibres through a gaspermeable forming surface to form a fibrous layer thereon and bonding the fibres to each other or to a reinforcing material by means of a foamed binder.
4 Claims, 4 Drawing Figures Pmminumsolsrs I 3.769.115 sum 10F 3 PAIENTEDncI 30 ms 3,769,115 SHEET 20F 3 ATTORNEY PAIENTEUnmso 1915 3,769.1 1s SHEET 3 [IF 3 METHOD FOR THE PRODUCTION OF A FIBROUS SHEET MATERIAL BACKGROUND OF THE INVENTION This invention relates to a method for the production of a fibrous sheet material by passing a stream of gas containing suspended fibres through a gaspermeable forming surface to form a fibrous layer thereon and bonding the fibres to each other or to a reinforcing material by means of a binder.
In the production of fibrous sheet materials by the well known wet process which is used within the paper industry hydrogen bonds between the fibres are created during the formation of the fibrous layer from the aqueous suspension f fibres. These hydrogen bonds ensure together with the binder good strength properties of the final wet process products.
When preparing similar products in a dry'process no or only a few hydrogen bonds are created because the dry fibres which are very irregular do not get into so close contact that hydrogen bonds between the fibres can be established. Consequently, the type of binder and the way in which said binder is applied to the fibrous material are of great importance for obtaining the desired strength of the end products prepared by a dry process.
It has been attempted to apply the binder to the fibrous product as a mist generated in one or more spray nozzles. This form of application has many advantages but also many drawbacks. Thus, one of the drawbacks is that is is difficult to obtain a uniform distribution of said binder. Furthermore, a spraying cabin with a suction device is necessary in order to prevent the escape of binder particles which may stick to other parts of the apparatus and which may also be injurious to the health of the operators. Finally, it is necessary to clean the spray nozzles which tend to be choked at regular intervals.
Also an impregnating technique has been used. Such a technique presents the advantage that the binder penetrates deeper into the material than when the binder is sprayed onto the fibrous material. Furthermore, both sides of the product can be treated in one step. How'- ever, a method of impregnating has the drawback that great amounts of solvent such as water are introduced into the product and consequently, special measures for removing said solvent are required.
It is the object of the present invention to improve the well known methods of applying a binder to a fibrous material.
SUMMARY OF THE INVENTION According to the invention the binder used is a foamed binder.
One of the most important advantages realized by using a foamed binder is that it may be applied to the fibrous material with a considerably lower content of solvent than by the impregnating method and at the same time the dosage and the distribution of the binder can easily be controlled.
By using a foamed binder the health problems which are encountered when spraying the binder onto the fibrous material are avoided.
The size of the foam bubbles is important because the smaller the foam bubbles are the more coherent the layer of binder will be. The size of the bubbles depends not only on the manner in which the foam has been produced but also on the additives used. As an example of such an additive, foam stabilizers may be mentioned.
When using a reinforcing net as the gaspermeable forming surface to obtain an end product comprising said reinforcing net a foamed binder may be applied to the net before the application of the fibres.
The use of a foamed binder consisting of very small bubbles results in a complete encirclement of the threads of said net by the binder. This is especially advantageous if certain types of synthetic fibre scrims are used as reinforcing material because it is very difficult to cause the binder to adhere to the threads of said synthetic fibre scrims.
' The foamed binder is preferably applied to the fibrous sheet material by passing said sheet material through a trough-like funnel, the bottom of which comprises two lips adjustable relative to the plane in which the fibrous sheet material is passed through said funnel. When filling the foam into such a funnel the binder is automatically applied to the sheet material as it moves through said funnel.
' The application of binder to the surface of the sheet material will often'be insufficient to avoid a delamination of said sheet material. Thus, the binder should be introduced into the fibrous material itself. According to the invention the tendency of delamination is avoided by sucking or pressing the foam applied into the fibrous layer. When suction is used it is preferred that the sheet material after a foam layer has been applied is passed over a suction box to cause the binder to penetrate the fibrous layer.
The application of the foam layer is preferably carried out by passing the fibrous layer under an inclined doctors knife and by introducing the foam under said knife. To avoid an undesirable reduction of the voluminosity of the fibrous materialthe pressure exerted by said scraping knife should not be too high.
The foamed binder may be pressed into the fibrous material by mechanical means.
By using a foamed binder having a ratio of binder volume to gas volume of about 1:17, 20 grams of binder on dry basis may be applied per metre of fibrous material.
In a preferred embodiment of the method according to the invention a reinforcing net material is used and.
a layer of binder is subsequently applied to both sides of said reinforcing net material, whereafter fibrous layers formed by passing a stream of gas containing suspended fibres through ,a g'aspermeable surface to form a fibrous layer thereon are applied to both sides of said reinforcing net material, whereafter the product thus formed is subjected to a compression.
By applying a binder onto the reinforcing net material an improved penetration of the binder into the fibrous layer can be obtained and at the same time avoid the use of a means to be brought into direct contact with the binder otherwise necessary for the further treatment of the product. This method is particularly suitable when the fibrous layers used have many free fibre ends. By bringing these fibre ends in contact with the reinforcing net material a bonding similar to that of a zip fastener is obtained and the strength of the product is consequently increased.
The compression is preferably carried out by passing the reinforcing net material and the fibrous layers applied thereto through slots in the top and the bottom of a closed box and by supplying air under pressure to the box at both sides of the fibrous sheet material. The air streams thus created compress the material and contact between the fibrous sheet material and the apparatus used is avoided.
BRIEF DESCRIPTION OF THE DRAWINGS DESCRIPTION OF THE PREFERRED EMBODIMENTS.
The apparatus shown in FIG. 1 comprises two hammer mills each mounted at the top of a shaft 2. Suction boxes 2 which are connected with suction pipes 4 are mounted below the bottom of said shafts 2. The upper run of an endless perforated belt 5 mounted for rotation on two rollers 6 is located in the area between the lower edge of the shaft 2 and the suction box 3. The apparatus shown also comprises a roller 7 on which a reinforcing net material 8 is wound. The net material is passed through a trough-formed funnel 9 having at its bottom two adjustable lips 10. The apparatus also comprises two endless screens 11 mounted on rollers 12 and a set of embossing rollers 13.
The operation of the apparatus is as follows:
Two fibrous layers are formed on the endless belts 5 and are subsequently passed onto the screens 11. The two fibrous layers are subsequently brought into contact with the reinforcing net material 8, to which a foamed binder has been applied on both sides in the trough-shaped funnel 9. When passing between the vertical runs of the screens 11 the fibrous layers are pressed against the reinforcing net material without bringing the screens into direct contact with the binder applied.
The composite product is then passed into the nip between the set of embossing rollers 13 which maybe heated to obtain a final curing of the binder. The binder used may also be of an expanding type and may be activated when the composite fibrous product is in the area between the vertical runs of the screens 13, for example by supplying heat to said screens.
By proper adjustment of the lips of the troughshaped funnel the thickness of the foamed layer applied to the sides of the reinforcing material can be con trolled.
Another way of applying a foamed binder onto a fibrous sheet material is shown in FIG. .2, which shows an apparatus comprising an endless gaspermeable screen which is mounted on two rollers 21. An inclined scraper plate 22 is located above said screen. A suction box 24 which is connected with a suction pipe 25 is mounted below the upper run of the screen 20. The operation of the apparatus shown is as follows:
A fibrous layer is introduced on the screen in the direction shown on the drawing and is caused to pass under the scraper plate 22. A foamed binder 23, which is continuously supplied to the area below said inclined scraper plate 22, is then applied to the surface of the fibrous layer in an amount which depends on-the distance between the lower edge of said scraper plate 22 and the screen 20. During the passage across the suction box 24 the binder layer applied is sucked into the fibrous layer so as to bond the fibres together.
The apparatus shown in FIG. 3 comprises two hammer mills 51 each located at one end of a shaft 52. At the opposite end of said shaft 52 a suction box 53 is provided and one run of an endless screen 54 mounted on two parallel rollers 55 moves in a path between the shaft 52 and the suction box 53. A reinforcing web material 57 which is wound from a roll 56 passes through a trough-formed funnel 58 having a bottom comprising two adjustable lips 59 forming a slot in the bottom of said funnel. The apparatus shown also comprises two guide rollers 60 and a compartment 61 mounted below said guide rollers 60 and having an upper slot 62 and a lower slot 63 located in the same vertical plane. Each end of the compartment 61 is connected with an air inlet pipe 64 connected with a common blower not shown. In the compartment 61 a number of screens 65 are mounted on both sides of the slots 62 and 63. An endless steel belt 66 mounted on three rollers 67, 68 and 69 is located below the compartment 61. The roller 67 co-operates with another roller 70 and similarly the roller 68 co-operates with a roller 71. An endless steel belt is mounted on said rollers 70 and 71.
The apparatus also comprises an auxiliary endless belt 72 mounted on two rollers 73 and 74 and two guide rollers 75 and 76.
The apparatus shown operates in the following manner:
.A gas stream containing suspended fibres are supplied to the hammer mills 51 from which they pass into the shafts 52. By means of the suction boxes 53 firous layers'are deposited on the screens 54. These fibrous layers are passed down between the guide rollers 60 and at the same time the reinforcing net material 57 is passed through the trough-shaped funnel 58, in which foamed binder is applied to both sides. The two fibrous layers and the reinforcing material are then united in the compartments 61, in which streamsof air are directed against the composite material from both sides. When theweb has passed through the compartment 612 it is introduced in the nip between the rollers 70 and 67 and subsequently between the nip of the rollers 71'and 68. During the further movement between the endless belts 66 and 72 the fibrous web material may be heated, e.g., by resistance heating of one of the belts. Thus, the binder applied to the reinforcing net has been partially cured when the web material passes into the nip between the rollers 75 and 76.
By blowing oppositely directed streams of air against the composite material in the compartment 61 through air inlets 64 the fibrous layers are pressed into contact with the net without using mechanical means. In the construction shown a compression of the fibrous layers and the reinforcing net is obtained even when the streams of air introduced in opposite ends of the compartment is different. In this case the distance between the web material and the edge of the compartment in that side of the compartment in which the pressure is lowest will be decreased. Thus, the area in which the air supplied can escape to the surroundings will also be decreased and consequently the air pressure will increase. Thus, after some time the web material will find an equilibrium position.
The apparatus shown in FlG. 4 comprises an endless perforated belt 81 mounted on three rollers 82, 83, and
84. A hammer mill 8S and a shaft 86 is located above the belt 81 and on the opposite side thereof a suction box 87 is mounted. Another hammer mill 88 with a shaft 89 and a co-operating suction box 90 are located between the rollers 83 and 84. A reinforcing net material 91 stored on a roll 92 passes over a roller 93 and through a trough-formed funnel 94 containing a foamed binder 95. At the lower end of the funnel 94 adjustable lips 96 are provided controlling the amount of binder applied to the reinforcing net 91 during its passage through the funnel 94.
A layer of fibres is formed on the belt 81 by means of the hammer mill 85, the shaft 86 and the suction box 87, and this layer is transported towards the rollers 83. At the time the reinforcing net 91 is passed from the roll 92 through the funnel 94 in which foamed binder is applied to both sides of the net. At the roller 83 the fibrous layer formed is united with the reinforcing net 91 and the composite material is passed into the area between the shaft 89 and the suction box 90, in which a layer of fibres is deposited on the opposite side of the reinforcing net 91. After formation of said fibrous layer the product formed can be embossed and the binder can be cured before it is wound up on a roll 97.
The apparatus shown presents the advantage that the fibrous layer formed under the shaft 86 is thrown against the reinforcing net 91 when said. fibrous layer passes around the roller 83 especially when operating at high speeds. in this way the fibres are brought into 6 intimate contact with the binder applied in the funnel 94.
1. A method of making a fibrous sheet material consisting of a reinforcing net material and at least one layer of short fibers bonded to one another and to the reinforcing net material, the method comprising the steps of directing a stream of gas containing suspended fibers toward a forming surface having apertures therein, allowing the gas to pass therethrough but retaining the major portion of the fibers so as to form on the side of the forming surface to which the fibercontaining gas stream is supplied, a layer of haphazardly located fibers, supplying a foamed binder to at least one side of the reinforcing net, and directing the fibrous layer on to the one side of the reinforcing net.
2. A method according to claim 1, in which'said foamed binder is rolled into the fibrous layer. I
3. A method as in claim 1, wherein said binder is applied onto both sides of said forming surface, that fibrous layers are subsequently applied to said reinforcing net and that the composite product thus formed is compressed.
4. A method as in claim 3, in which the composite material is compressed by passing through slots in the top and the bottom of a closed compartment in which air streams are directed against the composite material from both sides.