SE503059C2 - Nonwoven material prodn. by hydro-entangling fibre web - Google Patents

Abstract

Prodn. of a nonwoven material by hydroentangling a fibre web comprises: (1) metering dry natural and/or synthetic fibres into a dispersion vessel (111), possibly after pre-wetting; (2) dispersing the fibres in a foamable liq. comprising water and a surfactant for forming a foamed fibre dispersion; (3) applying the dispersion to a wire (118) and draining; and (4) directly after the forming, subjecting the fibre web to hydroentangling, wherein the foamable liq., after passing through the wire, is recirculated to the dispersion vessel in a simple closed circuit. Also claimed is the obtd. nonwoven material.

Description

ff! Purpose and main features of the invention The object of the present invention is to provide a simplified process for producing a nonwoven material having high absorbency, strength and uniformity. This has been achieved by forming a foamed fiber dispersion by dispersing natural and / or synthetic fibers in a foamable liquid comprising water and a surfactant in a dispersing vessel, after which the foamed fiber dispersion is applied to a wire and drained, and the formed direct bond is formed. to the formation is subjected to hydro- - _ _ entangling.

By combining these two previously known techniques in the manner described, a flexible, space- and energy-efficient process has been achieved, with which one can produce a spunlace material of a surprisingly high quality.

Description of the drawings The invention will be described in more detail below with reference to a pair of exemplary embodiments shown in the accompanying drawings.

Fig. 1 is a flow chart of the method according to the invention.

Fig. 2 shows a modified embodiment of the dispersing vessel and the foam tank. Fig. 1 shows a process solution for a foam-forming process according to the invention. The foam is generated by adding a surfactant to the water in a pulper 111, where an intensive stirring and air entrainment takes place. Further foam generation takes place in the process through the turbulence created in pumps and at the wire 118. A prerequisite for shell generation, however, is that there is access to air. 10 15 20 25 35 f. F; ff, n f; The surfactant may be of any suitable type, anionic, cationic, non-ionic or amphoteric. GB patent 1,329,409 discloses surfactants suitable for scouring fibrous webs. However, there are several other surfactants available that are suitable for the purpose. The choice of surfactant can, for example, be influenced by factors such as the chemical composition of any other additives to the fiber stock, such as wet strength agents, binders, creping chemicals, etc.

Appropriate surfactant dosage for obtaining. a relatively stable foam, which is able to maintain a substantially even dispersion of the fibrous foam is set in each individual case and is dependent on such factors as the type of surfactant, the hardness of the water, the water temperature and the type of fibers. A suitable surfactant content in the water is in the range 0.02-1.0% by weight, but preferably below 0.2% by weight.

The properties of the foam vary with the amount of bound air. At air concentrations up to about 70-80%, the air is in the form of small spherical air bubbles surrounded by free water, so-called ball foam. At higher air concentrations, the foam turns into a so-called polyhedral foam, where the water is in the thin lamellae between different air bubbles. The latter type of foam makes the foam very stiff and difficult to handle. In a foam forming process, a ball foam is usually used, i.e. the air contents are between 40 - 70%. The small air bubbles act as a distance sensor between different fibers, at the same time as the higher viscosity compared to water dampens the turbulence in the liquid and reduces the collision frequency between different fibers and the resulting flocculation. The bubble size of the foam is affected by factors such as the type of stirrer in the pulper / foam generator 111, stirring speed and the amount and type of surfactant. A suitable average diameter of the bubbles is between 0.02 and 0.2 IIIIII.

In the example shown, a mixture of cellulose fibers and synthetic fibers is used. The cellulosic fibers in the form of easily defibratable roll mass 110 are dosed into the pulper / foam generator 111 at a controlled speed between a pair of feed rollers 112 with a combined basis weight meter, after which it is passed through a pre-wetting channel before being coarsely torn into the pulp 111. a so-called spike whale pair.

The pre-wetting of the pulp with fresh water is desirable to facilitate dispersion in the pulp. For the sake of simplicity, the pre-wetting line and the coarse shredder have been omitted from the drawing. In case the roll mass has a fairly even basis weight, the dosing can only take place via the feed speed. Any basis weight variations of the roll can also be compensated for by varying the machine speed in the paper machine, so that the basis weight of the formed sheet is kept substantially constant.

The synthetic fibers are usually provided in the form of bales 122, which are opened in a known manner by bale openers 123, dosed by means of a wave band 124 and deposited on a collecting wire 125. From the collecting wire the fibers are sucked through a blow line 126 and dosed into the pulper / foam generator 111 via a condenser 127.

Equipment for dosing pulp fibers and synthetic fibers other than those shown can of course be used.

In the example shown, the same pulps are used for the two fiber types, due to the fact that these may require different processing or that it is desired to use different types of fibers for so-called multilayer forming, which is described below.

The pulper / foam generator 111 is concentrically located inside a larger tank, the foam tank 128. While the pulper 111 is open upwards, the foam tank 128 is closed. The two vessels communicate with each other via tubes 129, 130 at the bottom and top.

In the pulper / foam generator 111 an intensive dispersion and mixing of the fibers takes place. At the same time, foam is generated using the surfactant present in the water. To prevent the foam from rising upwards and forming a growing foam layer on top, it is important to maintain a foam circulation between the top and bottom of the pulper / foam generator 111.

With a suitably designed rotor assembly 13 1 a fully formed vortex is obtained which gives the desired circulation. The pulper volume is adjusted to be able to even out rapid variations in the fiber dosage. A suitable berry concentration is 0.1-1.5% by weight. 10 15 20 H25 30 35 -a ._ | The lye content of the foam can be measured by weighing a known volume of foamed dispersion. This can be done by continuously recording the weight of a certain length of the line between the pulper / foam generator 11 and the headbox 117. Calibration of the measuring scale is done by the weight of said volume filled with the liquid in question without air mixture being allowed to correspond to 0% air, while the same volume filled with only air may correspond to 100% air content. Adjustment of the lulla content can take place, for example, by means of the surfactant additive, the agitator has the heat in the pulper / foam generator 111 and / or by allowing compressed air into the pump 133.

The foam with the incoming fi letters is pumped by means of a suitable pump 133 to the headbox 117 on a paper machine, which in the example shown is of the Fourdrinier type. However, the type of paper machine is of secondary importance to the invention, which can also be applied to, for example, suction breast rolling machines and double-wire machines. The pump must be able to handle large amounts of heat and at the same time be able to handle long synthetic cases that occur, without any germination effects occurring. Some different pump types meet these requirements. An example is a conventional piston pump. Another is a vacuum pump of the water ring type, for example of the Helivac brand manufactured by Berendsen Teknik AS. Another example is a pump type manufactured by Disc fl o Corp, which has a rotating disc package with radial slots.

In the exemplary embodiment shown, headbox 117 and suction box 119 can be considered as an integrated unit. The formation of the fiber track is completely closed, ie there is no free liquid surface. A dewatered and pre-formed sheet emerges from the headbox 117.

The foam dispersion is distributed over the machine width of the headbox 1 17 and fills the space bounded by the headboard ends and the downwardly sloping top. The foam is sucked through the wire 118 by means of the vacuum pump 120 and the wire-shaped sheet remains on the wire.

It is also conceivable to use so-called layer formation with different type of mixture in different layers. The different fi ber types are then fed separately to the headbox, which in this case is of the íler layer type. rf. .,. 10 15 20 25 30 35 ...- ._- fi o To maintain the water balance in the system, the water that disappears with the sheet after molding must be replaced. One way to do this is by means of a spreader 134 across the formed fiber web. The spout 134 also serves as a washing zone to minimize the content of surfactant in the formed sheet prior to hydroentangling. Fresh water can also be added at other places in the system, for example during the pre-hydrogenation step. A separate suction box 135 but connected to the same circulation stage as above, the make-up conveys the water to the foam tank 128.

The foam sucked through the wire 118 is conveyed via the suction box 19 and the vacuum pump 120 to the top of the foam tank 128. The foam also carries some unavoidable leakage air. The foam tank 128 acts as a buffer tank for the foam.

Foams deposited in a vessel will eventually transition from ball foam to polyhedral foam, which types of foam are described above. Thus, in the foam tank 128, liquid will drain to the bottom of the tank, while the lighter foam accumulates at the top of the tank. The surfactant is accumulated in the contact surface between air and water. It is therefore likely that the surfactant tends to remain in the lighter foam and thus concentrate towards the top of the tank.

The liquid phase in the bottom of the foam tank 128 flows over to the pulp 111 via the communicating tube 129 in the bottom of the tank. Likewise, the foam in the top of the foam tank 128 will be forced out via the tube 130 in the top of the tank due to the overpressure generated by the vacuum pump 120. This light foam is very stable and above all voluminous and must therefore be reduced before being dropped into the pulp 111. propeller 136 mounted in the tube 130 mechanically breaks the larger air inclusions and releases some of the large amount of air that is bound.

In the upper connecting pipe 130 between foam tank 128 and pulper 111 is also arranged a control valve 137 by means of which the pressure in the foam tank 128 and thus also the level in the pulper 111 can be kept constant.

By the described arrangement a closed foam loop is obtained which is opened in a controlled manner between the foam tank 128 and the pulp 111. 10 15 20 ~ 25 30 35 ÄH? - flfifl The foam tank volume should be dimensioned so that the residence time of the foam in the tank is about 45-180 seconds , preferably 60-120 seconds. A large part of the liquid quantity will then be able to drain to the bottom of the tank 128 and then flow over to the pulp. At the same time, the tank must be able to accommodate the lighter foam in the upper part of the tank. A suitable ratio between total volume and imagined liquid volume in the tank is about 4-8, preferably about 6.

The foam thus circulates between the pulp / foam generator 111, the headbox 117, the wire 118, the suction box 119 and back to the pulper / foam generator 111 via the foam tank 128 in a simple circulation step. A certain addition of surfactant and water takes place to replace the amount that comes with the sheet after formation. The make-up water additive can be controlled, for example, by measuring the differential pressure in the foam tank 128. The surfactant content of the foamed fiber dispersion is suitably determined by a surface tension meter.

The pulper / foam generator 111 and the foam tank 128 do not, of course, have to be arranged as an integrated unit, but can, as shown in Fig. 2, be separated from each other. However, even in this case they communicate with each other via pipelines 129 and 130. As mentioned above, the system may contain two or fl your pulpers / foam generators which, however, can all communicate with the same foam tank.

The shaped fi berark hydroentanglass directly adjacent to the formation in a entangling station 138 while still being supported by the wire 118.

The entangling station 138 comprises several rows of nozzles 139 from which very high water jets under high pressure are directed towards the ban berbanan and causes an entanglement thereof, i.e. a entanglement of av brema.

Appropriate pressure in the entangling nozzles is adapted to fiber material, basis weights, etc.

For a further description of the hydroentangling - or as it is also called the spunlace technique - reference is made to CA patent 841 938.

The entangled ñber web is dewatered over suction boxes140 and then taken to a drying station for drying before the finished material is rolled up. The water from the entangling nozzles is removed via the suction boxes 140 and pumped to a water purification process before being recirculated to the entangling station 138. The described plant is an in-line plant, where the the foam-shaped fi berban which constitutes the base material for the hydroentangling is entangled in direct connection with the foaming, either using the same wire 118, as shown in Fig. 1 or with different wires for foaming and hydroentangling, for example in the case of a hollow patterned material in connection with the entangling.

Preferably, the material is entangled from both sides.

The formation of the foam-shaped fiber web can of course take place with other process solutions than the one shown here. Examples of other such processes are shown, for example, in GB 1,329,409 and US 4,443,297.

Fibers of many different types and in different mixing ratios can be used. Thus, mixtures of pulp and synthetic fibers, eg polyester, polypropylene, rayon, lyocell, etc. can be used. As an alternative to synthetic fibers, natural fibers with a long length, over 12 mm, can be used, such as seed hair fibers, such as cotton, kapok and milkweed; blad fi brer t ex sisal, abaca, ananas, New Zealand hamp; or bast fi brer eg flax, hemp, ramie, jute, kenaf. Varying fiber lengths can be used and with foam forming technology you can use longer fi widths than is possible with conventional wet laying of fiber webs. Long fi bres, about 18-30 mm, are an advantage in hydroentangling, as they increase the strength of the material in both dry and wet conditions. An additional advantage of foam forming is that it is possible to produce materials with a lower basis weight than is the case with wet laying. As a substitute for pulses, plants with short lengths can be used, such as esparto grass, reed canary grass and straw from cereals.

With certain types of fibers, an adhesive may be desirable to provide additional strength to the material. Suitable binders include starch-based binders, polyvinyl alcohol, latex, etc., which are used to increase the strength of nonwoven materials. Example 1 A run was made on a F ourdrinier machine at a machine speed of 20 m / min using a fiber mixture consisting of 50% pulp fibers of bleached softwood sulphate and 50% polypropylene fibers 1.4 dtex / 18 mm. An berber dispersion with a berry concentration of 0.34% by weight was prepared in a pulp to which a nonionic surfactant was also added at a concentration of 0.06%.

The residence time in the pulp was 34 sec. The air content of the foamed ñber dispersion fed to the headbox was 54%. The dry matter of the formed fibrous web was 30%. This was subjected immediately after the formation to double-sided hydroentangling, ie the outer web was entangled from both sides. The number of entangling strips was 3 / passage. The hole diameter in the nozzles was 120 pm and the number of holes was 1700 / m. The entangling pressure was 95 bar. The entangled fiber web was pressed and dried with hot air at 10 ° C.

The properties before the produced material are reported in Table 1.

Example 2 A second run was made using a blend consisting of 70% bleached sulphate pulp fibers and 1.0 dtex / 18 mm polypropylene blanks. The fiber concentration was 0.20% by weight. The surfactant additive was the same as in Example 1. The residence time in the pulp was 40 sec. and the air content of the foamed fiber dispersion fed to the headbox was 53%. The entanglement was carried out in a manner similar to Example 1.

The properties of the material produced are reported in Table 1.

Example 3 A third run was performed using a fiber blend consisting of 50% bleached softwood sulphate pulp and 50% Tencelñer (lyocell) 1.7 dtex / 12 mm. The fiber concentration was 0.36% by weight and the residence time in the pulp was 26 sec. The air content of the foamed fiber dispersion fed to the headbox was 51%. The entangling was carried out in the same manner as in Example 1.

The properties of the material produced are reported in Table 1.

(TP el: 'JJ - ~.

CI! f) Example 4 Another run was made using a fiber mixture consisting of 60% pulp of bleached softwood sulphate and 40% Tencel fi 1.7dtex / 12 mm. The fiber concentration was 0.18% by weight and the residence time in the pulp was 27 seconds. The luit content of the foamed fiber dispersion that tzillfórdes headbox was 49%. The entangling was carried out in a similar manner as in Example 1.

The properties of the material produced are reported in Table 1. 11 Iahelll Ex. 1 Ex. 2 Ex. 3 Ex. 4 50/50 mass / 70/30 mass! 50/50 mass / 60/40 mass! PP 1.4x1 PP 1.0x18 Tencel 1.7x12 Tencel 13x12 Surface weight g / m2 79 43 74 39 SCAN-P 6:75 Thickness pm 486 326 362 299 SCAN -P 47:83 Elongation at break L% 67 22 14 22 SCAN-P 38:80 Elongation at break T% sCAN-P aszso 1 18 115 42 50 D ka wïgftåm 3061 1037 3036 890 scAN-P sæso Tensile strength wrr TN / m 955 139 711 seen SCAN -P 38:80 Tensile strength wet LN / m 2099 123 2505 350 SCAN-P 58:86 Tensile strength wet N / m 358 18 627 174 sCAN-P 58:86 Absorption 5 sec w / g 4.2 4.9 3.6 4.9 SIS 25 12 28 (food) Total absorption w / g 4.2 5 3.6 4.9 SIS 25 12 28 (mod )

Claims (9)

10 15 20 25 30 35 | 2 Patent claims A method for producing a nonwoven material by hydroentangling a fibrous web, characterized by drying synthetic and / or natural fibers, possibly. after a pre-wetting, is dosed directly into a dispersing vessel (III) and the fibers are dispersed in a foamable liquid comprising water and surfactant to form a foamed fiber dispersion which is applied to a wire (118) and dewatered and that the fibrous web formed after the dewatering immediately after forming is subjected to hydroentangling, while the foamable liquid, after passing through the wire, is recycled to the dispersing vessel via a foam tank (128) in a simple cycle. Method according to claim 1, characterized in that in addition to the fibers, only fresh water, surfactant and any other chemicals are supplied to the carrier medium cycle to replace the amount leaving the cycle with the fiber or paper web after formation. A method according to claim 2, characterized in that fresh water is sprayed (134) on the formed fiber web before the hydro entanglement and that it is supplied via a suction box (135) to the circuit after passing through the fiber web. 10 15 20 25 30 35 Method according to one or more of the preceding claims, characterized in that the foamed liquid removed by the wire (118) is passed to a closed foam tank (128) in which a drainage of liquid to the bottom of the foam tank takes place, while the lighter foam accumulates in the top of the foam tank. , that liquid from the bottom of the foam tank is passed over to the dispersing vessel (III) via a first pipeline (129) and that the foam via a second pipeline (130) in the top of the foam tank passes over to the dispersing vessel, where fibers are added and dispersed in the foamable liquid. A method according to claim 4, characterized in that the foam in or near said second pipeline (130) is mechanically processed so that larger air bubbles in the foam are broken, whereby, bound air is released from the foam. Method according to claim 5, characterized in that the pressure in the foam tank (128) is kept substantially constant by means of a control valve (137) arranged in or in connection with said second pipeline (130). Nonwoven material, characterized in that it is produced by hydroentangling a foam-shaped fibrous web according to the method set out in claim 1. Nonwoven material according to claim 7, characterized in that the constituent fibers consist of natural fibers or mixtures of natural fibers and synthetic fibers. Nonwoven material according to claim 8, characterized in that the wadding material is natural fibers with a length exceeding 12 mm.