Manufacture of non-woven fibrous material from a foamed furnish

Abstract

Non-woven fibrous material is manufactured from a foamed fibre dispersion fed to a foraminous support and the invention resides in forming the foamed fibre dispersion by applying a vacuum to the underside of the support to recover a major part of the liquid from the dispersion on the support, delivering the recovered liquid to a mixer and mixing the recovered liquid in the mixer with fibres, a air, and a surface active agent to obtain a mixture thereof which is fed to a foaming device in which the foamed fibre dispersion is formed for feeding to the support.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to the manufacture of non-woven fibrous material, for example paper.

2. Description of the Prior Art

It is known to manufacture paper and other nonwoven fibrous material by depositing a suspension of fibres in a liquid, usually water, onto a foraminous support, called the wire, of a paper-making machine, which allows the liquid to drain through while retaining most of the fibres in the form of a web in which the fibres lie intermeshed, all substantially in the plane of the web. Due to the random nature of the process of deposition, and also because of the natural tendency of most fibres to form flocs, or clumps, the web is usually not uniform but contains areas which are particularly thin or light, or which are particularly thick or heavy. The degree of uniformity, or the lack of uniformity, of the web, may be controlled to some extent by the exercise of the machine operator's skill and by the design of the machine. In particular, the formation of acceptably uniform webs from fibres which have an excessive tendency to flocculate, or clump together, such as long synthetic fibres, or long, lightly beaten cotton or wood fibres, or other long natural fibres from animal, vegetable or mineral sources, requires that the fibres be dispersed in very large volumes of liquid. The subsequent drainage of such large volumes of liquid cannot be accomplished on conventional paper-making machines but requires costly modifications thereto.

A less common known method of manufacturing fibrous material is that in which fibres are first dispersed in a liquid medium of high viscosity, such as an aqueous solution of sugar, or of natural gums, the dispersion then being drained through the wire of a paper-making machine thereby to form a fibrous web on the wire.

This method has the advantage that when the dispersing action ceases, the fibres very quickly cease their motion in the liquid medium, and become immobile before they can become flocculated and clumped together to any appreciable extent. Thus, the fibres in such a liquid medium remain well dispersed until the liquid medium is drained from the dispersion and the web formed. However, due to the always high viscosity of the liquid medium initial dispersion of fibres therein is difficult, and its drainage through the forming web and through the supporting wire is slow and difficult, so that this known method is not well suited to the large-scale continuous manufacture of fibrous material.

It has also been proposed to add a surface active agent to the water conventionally used in the water-laying of fibrous webs on a paper-making machine, and by agitation produce a foamed fibre dispersion having an air content of at least 65% by volume to assist in the formation of a uniform fibrous web and, more especially, a uniform fibrous web comprising fibres longer than those conventionally employed in the water-laying manufacture of fibrous webs on a paper-making machine, i.e. fibres having a length in excess of about 3 mm.

Known methods of forming such a foamed fibre dispersion involve subjecting water containing surface active agent to a vigorous shearing action, for example by the use of apparatus comprising a casing for containing the water, and an impeller mounted within the casing for rotation relative thereto such that the water is subjected to a vigorous shearing action between blades of the impeller and an inner surface of the casing. With the use of such apparatus fibres can be added either to the water prior to foaming thereof or to foam already formed in the apparatus.

Known foamed fibre dispersion forming apparatus as described above, while being effective to form dispersions having required properties, has the disadvantage that it comprises relatively moving parts, i.e. the impeller and the casing, and thus requires an input of power to provide the necessary movement. Further, the relative movement of the parts results in wear in the apparatus.

SUMMARY

It has now been discovered, firstly that fibrous material having a higher degree of uniformity of fibre dispersion throughout the material than can be produced at the same weight consistency using only water as the dispersion medium, can be manufactured using a foamed liquid medium having an air content above a lower limit less than 65%; secondly that there is an air content level for the foamed liquid medium above which although the dispersion of fibres in the foamed liquid medium is more uniform than can be obtained at the same weight consistency using only water as the dispersion medium, nevertheless the fibres in the foamed liquid medium have a tendency to agglomerate; and thirdly that the size distribution of the bubbles in the foamed liquid medium is of considerable importance.

It has also been discovered that not all foamed liquid media comprising air bubbles dispersed in a liquid containing a surface active agent are useful for dispersing fibres, and in fact that certain foamed liquid media can be used to produce agglomeration of fibres (and particles) rather than dispersion thereof, albeit that the overall fibre dispersion may be better than could be obtained at the same weight consistency using water only as the dispersion medium.

It has been further discovered that an important parameter in relation to the dispersion/agglomeration properties of a foamed liquid medium of the kind under consideration is the volume percentage of air therein, and that the possible volume percentage of air range (i.e. 0% to about 99.9%) can be divided into three sub-ranges two of which, namely up to about 55% and over about 75%, can be used to effect agglomeration of fibres and/or particles, and the other, namely from about 55% to about 75%, can be used to effect substantially uniform dispersion of generally discrete fibres.

The volume percentage of air required to effect the most uniform dispersion of any particular fibres and/or particles is generally dependent upon the shape, size, physical properties and concentration of the fibres and/or particles. The relationship between the size of the fibres and/or particles and the arithmetic mean diameter of the air bubbles is also relevant in determining the most uniform dispersion of any particular fibres and/or particles.

It has been ascertained that at all volume percentages of air, fibres normally occupy only the liquid between the air bubbles; that is that fibres do not penetrate the air bubbles. Thus, factors determining whether a particular foamed liquid medium will effect dispersion or agglomeration of fibres apart from the volume percentage or air therein are the number, shape and size of the air bubbles in the medium.

When the foamed liquid medium contains a volume percentage of air of between about 55 and 75%, the fibres are dispersed substantially, uniformly throughout the foamed liquid medium.

When the volume percentage of air in a foamed liquid medium is less than about 55%, the air is contained in a relatively few relatively wide diameter range bubbles which divide the medium into pockets of liquid in which the fibres collect, and as the viscosity of the liquid (normally water) is relatively low, the fibres are free to move and thus agglomerate within the liquid pockets.

When the volume percentage of air in a foamed liquid medium is greater than about 75% and the bubbles have a substantially uniform size distribution, the packing density of the bubbles is so high that the bubbles are deformed from their normally spherical shape into polyhedrally shaped bubbles. In a medium containing such bubbles, surface tension effects result in forces in the planes of the inter-bubble lamellae, the forces being directed towards the line of intersection of the lamellae and into the points of intersection of the lines of intersection of the lamellae. These forces move fibres into the lines of intersection of the lamellae and the fibres become aligned in bundles in these lines.

However, although when using a foamed liquid medium having a volume percentage of air above 75% therein there is some degree of fibre agglomeration, nevertheless the overall fibre dispersion in a web produced using such a foam can be better than can be obtained at the same fibre weight consistency using only water as the dispersion medium.

Work has shown that as the volume percentage of air in a foamed liquid medium increases, firstly the number of bubbles per unit volume of the medium increase; secondly the arithmetic mean diameter of the bubbles decreases; and thirdly the range of bubble diameters decreases. The inherent desirable viscosity properties of the foamed liquid medium produced in accordance with the present invention derive from not only the number of bubbles therein per unit volume, but also from the substantially uniform size of the bubbles.

The effect on the viscosity of the medium of the bubble size distribution is thought to result from the fact that the volume percentage of air required for close packing of the bubbles is less if the bubbles have a substantially uniform size distribution.

The chemical nature of the surface active agent used is not critical provided that it is able to produce a foamed liquid medium having the specified properties. The surface active agent may be anionic, cationic, or nonionic, and it has been found that proprietary surface active agents such as that sold under the name "ACE" liquid, this being an anionic substance, by Industrial Soaps Ltd., that sold as "TEXOFOR (Registered Trade Mark) FN 15," a non-ionic substance by Glover Chemicals Ltd., and that sold as "AMINE Fb19," a cationic substance, by Float-Ore Ltd. are all suitable. Other surface active agents that have been used are oxtylphenoxypolyethoxy ethanol, and commercial grade dodecyl benzene sulfonate.

The arithmetic mean diameter of the bubbles in a foamed liquid medium can be determined by plunging a microscope slide cooled to about - 70.degree.C into the medium, and then removing the slide with a sample of the medium frozen thereto and placing the slide into a freezing stage of a microscope. Photomicrographs at say 100 .times. magnification can then be taken and the arithmetic mean diameter of the visible bubbles then determined therefrom. This method has the advantage that a sample of the medium is taken from within the medium mass, and it is no only the outer layer of bubbles that is examined.

It is a main object of the present invention to provide such a method of and apparatus for manufacturing non-woven fibrous material from a foamed fibre dispersion, which method and apparatus permits liquid, generally in a foamed condition, recovered by vacuum boxes to be recirculated to a mixer in which a gas/water/fibre/surface active agent dispersion is formed preparatory to being converted into a foamed fibre dispersion, having required properties, thereby reducing wastage of surface active agent, reducing operating and maintenance costs, and substantially reducing the need for effluent treatment.

According to one aspect of the invention there is provided a method of manufacturing non-woven fibrous material, for example paper, by feeding to a foraminous support from a foaming device a foamed fibre dispersion formed by the foaming device, said method including the steps of forming the foamed fibrous dispersion which is fed to the support by recovering a major part of the foamed water from foamed fibre dispersion on the support by connecting the input side of a vacuum-creating device to the underside of the support and the output side to a mixer, introducing fibres into the mixer, together with recovered foamed water, a air and surface active agent, and following mixing thereof in the mixer feeding the air/water/fibre/surface active agent mixture to the foaming device.

According to another aspect of the invention there is provided in a machine for manufacturing non-woven fibrous material, which machine includes a foraminous support on which the material is formed, apparatus comprising a closed foaming device arranged to form a foamed fibre dispersion and to feed the dispersion for deposition on the support; a mixer; vacuum-creating means to drain liquid from foamed water from foamed fibre dispersion on the support, the negative pressure side of the vacuum-creating means being connected to the underside of the support and the positive pressure side being connected to the mixer; means operable to deliver to the mixer foamed water drained from foamed fibre dispersion on the support; and means connecting the mixer with the foaming device to deliver thereto a water/fibre/air/surface active agent mixture formed in the mixer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates diagrammatically apparatus for carrying into effect the method according to the invention,

FIG. 2 illustrates diagrammatically, in plan, one form of apparatus for forming a foamed fibre dispersion, and

FIG. 3 is a section diagrammatically illustrating a part of the apparatus of FIG. 2.

DESCRIPTION OF PREFERRED EMBODIMENT

Referring to the drawings, the reference 1 indicates a foraminous support, being the wire of a Fourdrinier paper-making machine, on which there is deposited from a head box 2 a foamed fibre dispersion, not shown, from which a non-woven fibrous material is formed by draining water, generally in a foamed condition, from the dispersion through the foraminous support 1. Draining is effected, in known manner by vacuum-creating means 3 and 4 the negative pressure sides of which are connected to the underside of the support 1. As can be seen from FIG. 1, the vacuum-creating means 3 and 4 are spaced apart along the support and between the means 3 and 4 the support 1 passes over what are known as table rolls 5. Some drainage, about 20%, takes place as the dispersion passes over the rolls 5 and the water so drained falls into a wire pit 6 from which it overflows over a weir 7 into a hog pit 8 in which it is slushed by an agitator 9 and from which it is pumped by a pump 10 into a broke tank 11. The vacuum-creating means are associated respectively with what are usually termed wet vacuum boxes 12 and dry vacuum boxes 13.

The positive pressure sides of the vacuum-creating means are respectively connected by pipes 14 and 15 with a pipe 16 in which drained foamed water containing surface active agent meets and becomes infused with a mixture of air/water/fibres/surface active agent fed to the pipe 16 by a pump 17 at a pressure of about 25 to 30 pounds per square inch. The pipe 16 is connected with an in-line mixer 18, of any suitable kind which effects a coarse mixing of the mixture to provide a fairly homogeneous mixture which passes from the mixer through an inlet pipe 19 to an in-line foaming device 20 in which a foamed fibre dispersion, having desired properties as referred to above, is formed for delivery through an outlet pipe 21 to the head box 2. The foaming device may be of any suitable closed kind, but is preferably of the kind described below with reference to FIG. 2 because this does not utilise any mechanical moving parts, it is not open to atmosphere, and it is possible to admit metered quantities of air and surface active agent to a water/fibre dispersion as the latter approaches the mixer.

As is usual in the manufacture of non-woven fibrous material, the fibre is first beaten with water in a conventional beater 22, such as a Hollander beater, to form stock having a consistency of about 4% by weight based on bone dry fibre. The stock is pumped by a pump 23 to chests 24 where it is held to provide bulk storage for the apparatus, the fibre being kept substantially uniformly in suspension by conventional agitators 25. From the chests 24 the stock is pumped along a line 26 by a pump 27 to a refiner 28 from which the stock passes to a thickener 29. The thickener serves to de-water the stock so that it leaves the thickener at a consistency which is usually between 20% and 30% by weight based on bone dry fibre, but should be sufficiently high to minimise the input of fresh water into the apparatus while achieving the required dryness for the web that is removed from the foraminous support 1 prior to drying. Water extracted from the stock in the thickener 29 is removed through a drain pipe 30 and may either go to drain or be re-directed for reuse in the beater 22. The thickened stock is delivered to a pulper 31 in which it is mixed by conventional agitating means 32 with water which is stored in a tank 33 which receives drained foamed water from pipe 14 through a valve 34, and with broke pumped to tank 33 from the broke tank 11 by a pump 35, passing if desired through a broke deflaker 36.

Surface active agent may, if desired, be added to the water in tank 33 but it is preferred to admit both air and surface active agent to the water/fibre dispersion as it flows through a pipe 37 to the pipe 16. The pump 17 is included in pipe 37 and the air and surface active agent are delivered into pipe 37, preferably on the output side of pump 17, through metering devices 38, 39 respectively. A deflaker 40 which serves to disperse clumps of fibres is also included in pipe 37.

The preferred kind of foaming device 20 mentioned above comprises a plurality of foam-forming pipes 41, which may consist of flexible tubes, each of which has at least one internal region of constricted cross-section formed by a tubular insert 42 which may be circular or of other desired cross-section. An inlet manifold, formed by a housing 43, and an outlet manifold, formed by a housing 44, are connected one to the other by the foam-forming pipes 41. The inlet manifold is connected to the inlet pipe 19 by a flange 45 and the outlet manifold is connected to the outlet pipe 21 by a flange 46. Each foam-forming pipe 41 extends laterally from a housing and is coiled, as at 47, between the ends thereof connected respectively to the inlet and the outlet housing. In a preferred embodiment the housings 43, 44 are circular and the foam-forming pipes extend radially therefrom.

Each end of each of the foam-forming pipes is connected to a housing 43, 44 through a manually operable valve 48 connected to a stub pipe 49 extending laterally from the housing. The tubular inserts 42 are connected to the valves 48 and the foam-forming pipes 41 are fitted over the inserts 42 as illustrated in FIG. 3.

One end 50 of the inlet housing 43 is open to communicate with the inlet pipe 19 and the end of the housing opposite said open end is closed by a plug 51, FIG. 3, having a conical configuration 52 extending into the housing to prevent the formation of air pockets in the inlet housing 43.

There may be forty-eight foam-forming pipes 41 arranged in four ranks or banks each of twelve pipes and the housings 43, 44 are preferably independently supported so that little or no vibration is transmitted between the inlet and outlet manifolds. Generally before using the foam-forming apparatus to make any particular kind of product the number of foam-forming pipes to be used is selected by manipulation of the valves 48. If desired, the number of foam-forming pipes 41 in use can be changed during operation of the apparatus by manipulation of the valves 48.

When the foam-forming apparatus is in operation a mixture of air, water and fibre, and surface active agent fed to the manifold 41 is substantially equally divided into each foam-forming pipe and the tubular inserts 42 set up turbulence in the mixture which effects foaming and dispersion of the fibres, to provide a foamed fibre dispersion having desired properties as referred to above.

From the foregoing description it will be understood that recovered drained liquid is continuously recycled through a loop formed by the pipes 14, 15, 16 mixer 18, pipe 19, and foaming device 20, thus reducing the quantity of "make-up" surface active agent required, and that by using the described preferred form of foaming device it is possible, by metering air and surface active agent into the approach flow system, to provide control over the air content and thus the viscosity of the foam.

Claims

I claim:

1. A process for manufacturing a non-woven fibrous material from a foamed fiber dispersion fed to a foraminous support from a foaming device wherein the amount of surface active agent required is reduced, the process comprising:

establishing an air/water/fibers/surface active agent mixture provided by a mixer;

delivering said mixture to a closed foaming device and effecting foaming thereof by the creation of turbulence without the use of moving mechanical means to establish said foamed fiber dispersion;

feeding said foamed fiber dispersion to said foraminous support;

recovering, by vacuum draining through vacuum box means, a major part of the liquid, generally in a foamed condition, from said foamed fiber dispersion on said foraminous support;

recirculating said liquid so recovered generally in a foamed condition directly from said vacuum box means to said mixer;

introducing into said mixer, together with said recirculated liquid, fibers, water and metered quantities of air and make-up surface active agent;

directing the contents of said mixer to said foaming device; and

repeating said feeding, recovering, recirculating, introducing and directing steps.

2. The method according to claim 1 including the step of dispersing clumps of fibers following introduction of metered quantities of air and surface active agent and prior to passage to the mixer.

3. A closed circuit system for manufacturing non-woven fibrous material from a foamed fiber dispersion wherein the amount of surface active agent required is reduced, the system comprising:

a mixer for establishing an air/water/fibers/surface active agent mixture;

a closed foaming device, downstream of said mixer, for effecting foaming of said mixture by the creation of turbulence without the use of moving mechanical means;

pipe means for deliverying said mixture from said mixer to said closed foaming device;

feeding means for feeding said foamed fiber dispersion effected by said closed foaming device to a foraminous support on which said non-woven fibrous material is formed;

vacuum drain means, including vacuum box means, for recovering a major part of the liquid, generally in a foamed condition, from said foamed fiber dispersion on said foraminous support;

a pulper connected by pulp delivery pipe means to said mixer;

pump means operable to recycle said liquid so recovered generally in a foamed condition directly from said vacuum box means through said pulp delivery pipe means to said mixer; and metering means operable to introduce into said pulp delivery pipe means upstream of said mixer metered quantities of air and make-up surface active agent.

4. The system according to claim 3 including a deflaker in said pulp delivery pipe means, downstream of said metering means and upstream of said mixer, for effecting dispersion of fiber clumps passing through said pulp delivery pipe means.