FI65459C - FRAMEWORK FOR THE FRAMEWORK OF FIXED FIBERS - Google Patents

Description

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Patent and Registration Board · .... .........,. .

_ ^ *. . (44) Date of dispatch and date of hearing.

Patent- och regletentyreleen '' Amekan uti «* d och utLakrHtM puMimrad 31.01.6U

(32) (33) (31) P> ry4 «*» y muolkaua BagW prtortwc 07. OU.72 29.03.73 English-England (GB) 16210/72 I62IO / 72 Complete Spec.

(71) Wiggins Teape Research & Development Limited, Gateway House, 1 Watling Street, London ECUP UAU, England-England (GB) (72) Neil George Douglas Robertson, Marlow, Buckinghamshire, England-England (GB) (7U) Oy Kolster This invention relates to a method and apparatus for preparing a foamed fiber suspension from air and a dispersion of fibers in a surfactant-containing liquid, a nonwoven fabric, and an apparatus for preparing a foamed fiber suspension from an air and fiber dispersion in a surfactant-containing liquid. .

It is known to make paper and other nonwoven fibrous material by precipitating a fibrous suspension in a liquid, usually water, on a perforated substrate called a wire, in a paper machine, whereby the liquid can drain away and most of the fibers remain on the wire in a web where the fibers are in contact. all essentially at the level of the track. Due to the random nature of the precipitation process, and because most fibers have an inherent tendency to form flocs or clusters, the web is not usually uniform, but has particularly thin or light regions or particularly thick or heavy regions. The degree of track uniformity or lack thereof can be adjusted to some extent by the skill of the machine operator and the machine model. When it is necessary to form sufficiently uniform webs of fibers / which have a very high tendency to form flocs or cluster together, such as long man-made fibers or long, lightly struck cotton or wood fibers or other long natural fibers obtained from animals, plants or minerals, the fibers must be dispersed in very large volumes of liquids. Subsequent removal of these large amounts of liquid cannot be performed on conventional papermaking machines, but requires expensive modifications in these.

A less known method of making a fibrous material is one in which the fibers are first dispersed in a high viscosity liquid, such as an aqueous solution of sugar or natural gums, after which the dispersion is dried through a paper machine wire to form a fiber web on the wire.

This method has the advantage that when the dispersing effect ceases, the movement of the fibers in the liquid ceases very quickly and the fibers are immobile before they can flocculate and group together to a considerable extent.

The fibers thus remain well dispersed in such a liquid until the liquid is removed from the dispersion and a web is formed. Because the liquid always has a high viscosity, it is difficult to initially disperse the fibers and exits through a slow and difficult-to-form web and a supporting wire, so that this known method is not very suitable for large, continuous production of fibrous material.

It has also been proposed to add a surfactant to the water normally used for the introduction of fibrous webs into water in a paper machine, and to produce a foamed fiber distillate with an air content of at least 65% by volume by mixing, which helps to produce a uniform web and especially a uniform fiber web. are longer than those commonly used in the water production of fibrous webs in a paper machine, i. the length of the fibers is more than about 3 mm.

In known methods for forming such a foamed fiber dispersion, the surfactant-containing water is subjected to a strong frictional effect, e.g. by using a device comprising a housing for water and an impeller mounted inside the housing 3 65459 so that it can rotate relative to it. strong frictional effect between the impeller blades and the inner surface of the housing. When using such a device, the fibers can be added either to the water before foaming or to the foam already formed in the device.

Although the known foamed fiber dispersion forming device described above effectively forms dispersions with the required properties, it has the disadvantage that it has relatively moving parts, i. impeller and housing, and thus requires a power supply to effect the required movement. In addition, the relative movement of the parts results in wear of the device.

First, it has now been found that a fibrous material having a higher degree of uniformity of the fiber dispersion throughout the material than can be obtained by the same weight using only water as a dispersant can be prepared using a foamed liquid having an air content exceeding a lower limit of less than 65%; second, that there is a value of the air content of the foamed liquid above which the fibers tend to accumulate in the foamed liquid, although the fiber dispersion in the foamed liquid is more uniform than can be obtained by the same weight using only water as a dispersant; and third, that the size distribution of the bubbles in the foamed liquid is of considerable importance.

It has also been found that not all liquids containing gas bubbles dispersed in a surfactant-containing liquid are useful for dispersing fibers, and in fact certain liquids can be used to cause fibers (and particles) to accumulate rather than disperse, although the dispersion of fibers as a whole may be better. than can be obtained with the same weight using only water as a dispersant.

In addition, it has been found that an important parameter for the dispersion / accumulation properties of the foamed liquid type in question is the volume percentage of gas in the liquid and that the potential gas volume range (i.e. 0- to about 99.9%) can be divided into three sub-ranges, namely two, namely up to about 55% and above about 75%, may be used to cause accumulation of fibers and / or particles, and a third, namely, a range of about 4 65459 55 to about 75%, may be used to effect substantially uniform dispersion of the discrete fibers.

The percentage by volume of gas required to achieve the most uniform dispersion of certain fibers and / or particles generally depends on the shape, size, physical properties and concentration of the fibers and / or particles. The relationship between the size of the fibers and / or particles and the arithmetic mean diameter of the gas bubbles is also important in determining the most uniform dispersion of certain fibers and / or particles.

It has been ascertained that at all volume percentages of the gas, the fibers are normally present only in the liquid between the gas bubbles, i. the fibers do not penetrate the gas bubbles. Thus, in addition to the volume percentage of the gas it contains, the factors that determine whether a particular foamed liquid causes the fibers to disintegrate or accumulate are the number, shape, and size of the gas bubbles in the material.

When the foamed liquid contains a gas having a volume percentage of about 55 to 75%, the fibers disperse substantially uniformly throughout the foamed liquid.

When the volume percentage of gas in the foamed liquid is less than about 55%, the gas is present in relatively few bubbles of relatively large diameter that divide the liquid into liquid pockets where the fibers accumulate, and when the viscosity of the liquid (normally water) is relatively low, the fibers can move freely. and thus accumulate in fluid pockets.

When the volume percentage of gas contained in the foamed liquid is more than 75% and the size of the bubbles is substantially evenly distributed, the packing density of the bubbles is so large that the shape of the bubbles changes from a normal spherical shape to a polygonal shape. As a result of the surface tensioning effects, the material containing such bubbles has forces in the planes of the lamellae between the bubbles, which forces are directed towards the intersection line of the lamellae and to the intersection points of the intersection lines of the lamellae. These forces transfer the fibers to the cutting lines of the lamellae and the fibers are directed together into bundles along these lines.

Although some accumulation of fibers occurs when a liquid containing more than 75% by volume of gas is used, the overall dispersion of the fibers in a web made using such foam may still be better than that which can be achieved by the same weight using only water as a dispersant. .

The work has shown that as the volume percentage of gas contained in the foamed liquid increases, first, the number of bubbles per unit volume of the substance decreases, second, the arithmetic mean diameter of the bubbles increases, and third, the diameter range of the bubbles decreases. The characteristic, desirable viscosity properties of the foamed liquid prepared in accordance with the present invention result not only from the number of bubbles contained per unit volume, but also from the substantially uniform size of the bubbles.

The effect of bubble size on the viscosity of the substance is believed to be due to the fact that the volume percentage of gas required for dense packaging of the bubbles is smaller if the size of the bubbles is substantially evenly distributed.

The chemical nature of the surfactant used is not critical as long as it is capable of providing a foamed liquid having certain properties. The surfactant may be anionic, cationic or non-ionic, and it has been found that special surfactants, such as the liquid sold under the name "ACE", which is an anionic substance, are manufactured by Industrial Soaps Ltd. ., sold under the name "Texofor (registered trademark) FN 15", a non-ionic substance manufactured by Glover Chemicals Ltd., and sold under the name "Amine Fb 19", a cationic substance manufactured by Float-Ore Ltd., are other suitable surfactants used include oxylphenoxypolyethoxyethanol and commercially available dodecylbenzenesulfonate.

The arithmetic mean diameter of the bubbles in the foamed liquid can be determined by immersing a slide cooled to about -70 ° C in the medium, and then removing the glass along with the sample of material frozen therein and placing the slide in a freezing stage of a microscope. Micrographs can then be taken at approximately 100x magnification and these are then used to determine the arithmetic mean diameter of the visible bubbles. This method has the advantage that the substance is sampled from inside the substance mass and does not examine only the outermost bubble layer.

6 65459

It is an object of the present invention to provide a method and apparatus for preparing a foamed weft dispersion for use in the manufacture of a nonwoven fibrous material which does not contain moving parts, and further combines with means for controlling manufacture to obtain foamed fiber dispersions having have desirable properties which follow from the above.

The method according to the invention is known for pumping a dispersion of air and fibers in a surfactant-containing liquid from the inlet piping through a plurality of pipes in the outlet piping, each allowing only a small dispersion volume to pass through, each having at least one inner region defined by varying cross-sections. zones so as to form a cross-sectional choke in the pipes, thereby creating turbulence in the pipes and causing the formation of foam without the use of moving mechanical parts.

According to the invention, there is further provided a device characterized by an inlet piping, an outlet piping, a plurality of pipes connecting the inlet piping to the outlet piping, each allowing only a small dispersion volume to pass through and having at least one vortex generating area defined by a large forming a cross-sectional constriction, and a pump adapted to pump the dispersion through and out of the inlet piping and pipes.

An advantage of the device according to the invention is that it can be placed in line between the source of air-dispersed fibers dispersed in air and surfactant and a perforated substrate for drying the foamed fiber dispersion in the device without the need for any pump means which could damage the foamed fiber dispersion. between the perforated base. The foamed fiber dispersion can be fed directly from the device of the invention to the perforated substrate only by a flow spreader, e.g. a tube shaped to spread the flow from the device over the entire width of the perforated substrate, but is preferably fed to a closed or open paper machine pressure vessel.

7 65459

Embodiments of the device according to the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 shows a plan view of a form of device; Fig. 2 shows an end view of the device of Fig. 1; Fig. 3 shows a cross-sectional view of the connection between the inlet piping of the device and the foam-forming pipe; Fig. 4 is a plan view schematically showing another form of device; Fig. 5 is a cross-sectional view schematically showing a portion of the device of Fig. 4; and Figure 6 shows a block diagram of a portion of a nonwoven fiber manufacturing system incorporating an apparatus according to the invention.

The device shown in Figures 1 to 3 comprises a plurality of foam-forming tubes 1, each of which has at least one internal region with a reduced cross-sectional area formed by a tubular si-2 which may have a circular or other desired cross-sectional shape. The inlet piping formed by the inlet pipe 3 and the outlet piping formed by the outlet pipe 4 are connected to each other by foam-forming pipes 1.

The inlet pipes 3 and the outlet pipes 4 can have an inside diameter of 15.24 cm 3000 rpm. for flow, the foam-forming tubes may have an inside diameter of 1.87 cm and the tubular core may have an inside diameter of 1.27 cm. The foam-forming pipes 1 in this embodiment are straight pipes extending between the inlet and outlet pipes 3, 4 at a distance from each other and substantially parallel, the length of the pipes 1 being about 3.05 m and the distance between their axes being about 15.87 cm.

Attached to each inlet and outlet pipe 3, 4 are guided flanged parts 5 and the other end of the foam-forming pipe 1 is located in the guide 6 of each said part, as shown in Fig. 1. Each end of the foam-forming tube 1 is fixed in its guide 6, as shown in Fig. 3, by two cooperating sleeves 7, 8, which are nested and of which the inner sleeve 7 is fixed to the end of the tube 1 and the outer sleeve 8 and the outer sleeve 8 is fixed to the guide 6.

65459

Each end of each inlet and outlet pipe 3, 4 is provided with an apertured flange portion 9 for connecting the opposite ends of the pipes together to the inlet pipe and the outlet pipe, respectively, as will be explained below.

Of the foam-forming tubes 1 shown in Fig. 1, every second is provided with change-over valves 10 by means of which the production of the device can be adjusted.

In the embodiment of the device shown schematically in Figures 4 and 5, the housings 11, 12 form inlet and outlet pipes and each foam-forming pipe 1 extends laterally from the housing and is formed as a coil 13 between the ends connected to the inlet and outlet housing respectively. In the preferred embodiment, the housings 11, 12 are round and the foam-forming tubes extend radially therefrom.

Each end of each foam-forming tube is connected to the housing 11, 12 via a manual valve 14 connected to a pipe nozzle 15 extending laterally from the housing. In this embodiment, the tubular inserts 2 are connected to the valves 14 and the foam-forming tubes 1, which can be formed from hoses, are arranged on the inserts as shown in Fig. 5.

The other end 16 of the inlet housing 11 is open so that a dispersion of air and fibers in the surfactant-containing liquid can flow into the housing, and the opposite end is closed with a plug, Fig. 5 having a conical shape 17 and extending into the housing so that no air pockets and to obtain a substantially uniform flow through the foam-forming tubes 1. The other end of the housing 12 is also open to allow flow of the foamed fiber dispersion from the housing.

In this embodiment, 48 foam-forming tubes 1 can be used, arranged in four rows or series of twelve tubes each, and the housings 11, 12 are preferably supported separately so that little or no vibration is transferred between the inlet and outlet piping. Before the device is used to make a particular product, the number of foaming tubes to be used is generally selected using valves 14. If desired, the number of foaming tubes used can be changed during operation of the device using valves 14.

65459

When the device shown in Figures 4 and 5 operates / enters, the mixture of air, fibers, surfactant and liquid fed to the inlet piping 11 is distributed substantially evenly throughout the foam-forming tubes 1 and the tubular inserts 2 provide a vortex in the mixture which affects the formation of the foamed fiber dispersion. desired properties as explained above.

Figure 6 schematically shows the use of a device according to the invention in a system for producing a nonwoven fibrous material. The system includes a closed, in-line mixer 18, e.g., a closed container containing a rotating vane, in which an initial dispersion of air and fibers is formed in a liquid, usually water, containing a surfactant. From mixer 18, the dispersion is fed under pressure, about 1.76 to 2.11 kg / cm, by pump 19 to inlet pipe 20, inlet piping 2 or 11, as the situation requires.

The foamed fiber dispersion exits the outlet piping 4 or 12 through the outlet pipe 23 and is further fed to a perforated substrate 24 which is a wire of a Fourdrinier paper machine. The foamed fiber dispersion dries on a perforated substrate 24 under the action of a vacuum which is coupled below the substrate 24 and is provided by a vacuum system 25. Some of the liquid generally in the foamed state for reuse and new fibers, either dry or dispersed, are fed to mixer 18 via line 28 to be dispersible in the reused liquid. A compressor 22 or the like supplies compressed air to the measuring device 21 and the device 21 supplies the measured air volumes to the pipe 28. The measuring device 21 indicates the amount of air supplied and this is adjusted so that the foamed fiber dispersion to be formed contains the required air volume as a volume percentage.

The above description of the device according to the invention refers to the preparation of a foamed fiber dispersion from an initially substantially non-foamed fiber dispersion in a liquid containing a surfactant and air; it is obvious that the mixer described in connection with Fig. 6 causes some foaming in the mixture passing through it, the device according to the invention acting adjustable to obtain a foamed fiber dispersion having the desired properties.

10 65459

From the description of the reuse of a generally foamy liquid removed from a foamed fiber dispersion on a perforated substrate, it is further noted that a fiber dispersion in a foamed state may be fed to the apparatus or mixer of the invention, although not in the foamed state required to feed the dispersion to the hole.

Claims (4)

11 65459 A method for preparing a foamed fiber suspension from a dispersion of air and fibers in a surfactant-containing liquid for producing a nonwoven fibrous material, characterized by pumping an air and fiber dispersion in the surfactant-containing liquid from the outlet (11) outlet (11) ) through a plurality of tubes (1), each of which allows only a small volume of dispersion to pass through, each having at least one inner region (2) defined by zones of alternating decreasing cross-section so as to create cross-sectional constriction in the tubes, creating parts. Device for carrying out the method according to claim 1, characterized by an inlet piping (11), an outlet piping (12), a plurality of pipes (1) connecting the inlet piping (11) to the outlet piping (12), each allowing only a small dispersion volume and having at least one a swirling region (2) defined by zones of alternating decreasing and increasing cross-section so as to form a cross-sectional constriction in the pipe, and a pump (19) adapted to pump the dispersion through the inlet piping (11) and pipes (1) and out of the outlet pipe 12 Device according to Claim 2, characterized in that each pipe (1) has a loop-shaped part (13) between the outlet piping (12) and the area (2) with a reduced cross-section. Device according to Claim 2 or 3, characterized in that each region with a reduced cross-section is formed by an inner (2) in the tube (1).