SE503058C2 - 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

The object of the present invention is to provide a simplified process for the production of paper and other carrier webs, where dispersion of carriers in the carrier medium, supply of the carrier dispersion to the wire and recirculation of the carrier medium, which has passed through the wire, take place in a simple manner. circulation process. The carrier medium can be either liquid or foam. This has been solved according to the invention by dosing dry direkt fibers directly in the carrier medium, possibly after wetting, and dispersing the i fibers in the carrier medium in the dispersing vessel to form the äld berm, which is fed to said wire and that the carrier medium is recycled to dispersed after passing through the wire. a simple cycle. The dry fibrers are dosed at an adapted rate directly into the dispersing vessel where they are dispersed in the carrier diet recycled from the wire. The prepared fiber dispersion is transported to the wire without further dilutions. A simple, easily controlled process with short contact times between the carrier and the carrier medium is hereby achieved.

Bl ... |.

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

Fig. 1 is a fate diagram of the method according to the invention applied to a wet forming process.

Fig. 2 is a corresponding fl fate diagram of the process applied to a foaming process.

El .. E .. l With reference to Iiïgl, which shows a wet forming process, for example for the production of paper, preferably tissue paper so-called (issue, cellulose is fed in the form of easily de fi degradable roll mass 10 down into a dispersing vessel, a so-called pulper 11 The pulp 11 is intensively dispersed and mixed with the pulps in water with the possible addition of chemicals. The correct fiber concentration is obtained by controlling the dosing of the roll 10 into the pulp 11. The roll is fed at a controlled speed between a feed roll pair. 12 possibly with a combined basis weight meter, after which it is passed through a pre-wetting channel 13 before it is coarsely shredded into the pulp 11. The coarse shredding of the pulp takes place, for example, between a so-called pair of spike rollers. In case the roll mass has a fairly even basis weight, the dosing can only take place via the feed rate. Variations in the roll mass 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.

In the pulper 11, by means of a rotor 15, an intensive dispersion and mixing of the masses in the water takes place. An äld berm with the desired concentration, which is preferably in the range 0.1-1.5% by weight, is obtained in the pulp. The fiber stock is pumped by means of the pump 16 to the headbox 17 of 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 fiber stock is dewatered in a known manner on a wire 18 and passed through conventional press and drying sections (not shown). Any creping of the paper web occurs in the case of tissue paper to be produced.

The water which passes through the wire 18 to the suction box 19 is pumped by means of the pump 20 back to the pulper 11, which also functions as a rear water tank, and is thus circulated in a simple circulation process between the pulp and the paper machine. Alternatively, the system has a separate backwater tank, which acts as a communicating vessel with the pulper 11. A certain addition of fresh water to the system takes place at 21 to replace the water that accompanies the fiber web to the drying section.

Fig. 2 shows a process solution for a so-called foam-forming process. The foam is generated by adding a surfactant to the water in the pulp 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 foam production, however, is that there is access to air.

The surfactant may be of any suitable type, anionic, cationic, non-ionic or amphoteric. GB patent 1,329,409 discloses surfactants suitable for foaming fiber 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.

Suitable surfactant dosage to obtain a relatively stable foam, which is able to maintain a substantially even dispersion of fibers. The foam is set in each individual case and depends on such factors as type of surfactant, water hardness, water temperature and 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 mainly 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 formation process, a ball foam is usually used, ie the air contents are between 40 - 70%. The small air bubbles act as spacers between different fibers, while the higher apparent 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 mm.

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 in a manner similar to that described above by means of a feed roller pair 112. The pre-wetting channel and the coarse shredder have been omitted from the drawing for the sake of simplicity, but are preferably also exemplified herein.

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 pulp is used for the two types of fiber. In some cases, it may be appropriate to have separate pulpers for different types of fibers, due to the fact that these may require different processing or that one wants to use different types of fibers for so-called layer formation, which is described below.

In the example shown, the pulper / foam generator 111 is concentrically placed 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 there is an intensive dispersion and mixing of the fibers. 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 131 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.

The foam with the included bristles is pumped to the headbox 117 by means of a suitable pump 133. The pump must be able to handle large amounts of air and at the same time be able to lant long synthetic fibers, if any, without spinning effects occurring. A few different pump types meet these requirements. An example is a conventional piston pump. One: in-at is a vacuum pump of the water type, for example of the brand Helivac 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 Litföriiigsexeniplet 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-fiber dispersion is distributed over the machine width of the headbox 117 and fills the space bounded by the ends of the headbox and the downwardly sloping upper part. The foam is sucked through the wire 1 18 with the help of the vacuum pump 120 and the finished sheet remains on the wire.

It is also conceivable to use -sheet layer forming with different fiber types- or mixtures in different layers. The different types of bearings are then fed separately to the headbox, which in that case is of the multilayer type.

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. Spray 134 serves as a washing zone to minimize the surfactant content of the finished sheet.

Fresh water can also be added at other places in the system, for example during the pre-wetting 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 119 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.

Foam deposited in a vessel will eventually transition from ball foam to polyhedral foam, which types of foam have been described previously. Thus, in the foam tank 128, liquid will drain to the bottom of the tank, while the lighter polyhedral foam accumulates in the top of the tank.

Tensideii is accumulated in the contact surface between air and water. The surfactant 10 15 20 25 30 35 few fl 7 »tends to remain in the lighter foam and is thus concentrated towards the top of the tank.

The liquid phase in the bottom of the foam tank 128 flows over to the pulper 111 via the communicating tube 129 in the bottom of the tank. Likewise, the foam of 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 its air content must therefore be reduced before being dropped into the pulp 111. high speed propeller 136 mounted in the tube 130 mechanically breaks the larger air enclosures 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.

The volume of the foam tank 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 pulper / 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. Some surfactant and water are added to replace the amount that comes with the sheet after reforming.

The pulper / foam generator 111 and the foam tank 128 do not, of course, need to be arranged as an integrated unit, as shown, but can be separated from each other. However, even in this case, they must communicate with each other in the manner described. The formed fibrous sheet may be subjected to subsequent processing steps, for example "hydroiangangling", ie an entanglement of the fibers by means of very fine water jets, or only dried.

Fibers of many different kinds and in different blending ratios can be used both in the wet forming process in Fig. 1 or the foaming process in Fig. 2. Thus, mixtures of pulp fibers and synthetic fibers, eg polyester, polypropylene, rayon, lyocell etc. can be used.

As an alternative to synthetic fibers, natural fibers with a long fiber length, over 12 mm, can be used, such as seed hair fibers, eg cotton, kapok and milkweed; leaf fibers, such as sisal, abaca, pineapple, New Zealand hemp; or bast fibers, such as flax, hemp, ramie, jute, kenaf. Varying fiber lengths can be used and with foam forming technology longer fibers can be used than is possible in conventional wet laying of fiber webs. An additional advantage of foam forming is that it is possible to produce materials with lower basis weights than is the case with wet laying. As a substitute for pulp fibers, plant fibers with a short fiber length can be used. such as esparto grass, reed canary grass and straw from straw.

With certain types of fibers, an adhesive may be desirable to provide additional strength to the material. Suitable binders include starch-based binders, polyvinyl alkoliol, latex, etc., which are used to increase the strength of nonwoven materials.

The invention is not limited to the embodiments shown. It is thus understood, for example, that the wet forming process according to Fig. 1 may also include other fibers, for example a mixture of pulp and synthetic fibers, for the production of wet-formed nonwoven, and that the foam forming process according to Fig. 2 is also suitable for the production of e.g. pulp fibers only.

Claims (12)

10 15 20 25 30 Pgtçntkray A process for producing a fi ber or paper web, forming a äld berm by dispersing dry cellulosic fibers optionally in combination with synthetic fibers and optionally after pre-wetting, in a carrier medium, such as liquid or foam, in a dispersing vessel (1 1; 111) to form a berm, which is fed to a wire (18; 11b) on a paper machine, and that the carrier medium, after passing through the wire, is recycled to the dispersing vessel in a simple cycle, characterized in that cellulose burrs in the form of easily defibratable roll mass (10; 110) dosed directly into the dispersing vessel (11; 11) Method according to claim 1, characterized in that in addition to the fibers, only fresh water and any chemicals are supplied to the carrier medium cycle in order to replace the amount leaving the cycle with the fi berber or paper web after formation. A method according to claim 1 or 2, characterized in that. that the dispersing vessel (1 1; 111) also functions as a rear water tank 4. A method according to claim 1 or 2, characterized in that the dispersing vessel (11; 1111) acts as a communicating vessel with a rear water tank included in the circuit. A method according to claim 1, characterized in that the roll mass (10; 110) is dosed by the feed rate optionally in combination with basis weight measurement. A method according to claim 5, characterized in that the roll mass (10; 110) is pre-wet and coarsely shredded before it is fed to the carrier medium dispersing vessel (1 1; 111). Method according to one or more of the preceding claims, characterized in that synthetic fibers in a dosed amount are blown into a stream of air into the dispersing vessel (1 1; 111). 10 15 20 25 IO Method according to one or more of the preceding claims, characterized in that the carrier medium consists of foam which is generated by adding a surfactant to the water in the dispersing vessel (111). A method according to claim 8, characterized in that the dispersing vessel (111) communicates with a foam tank (128) to which the foam which has passed the wire (118) is passed and in which foam tank (128) 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 the liquid from the bottom of the foam tank is led over to the dispersing vessel (111) via a first pipeline (129) and that the foam passes via a second pipeline (130) in the top of the foam tank over to the dispersing vessel. A method according to claim 9, characterized in that said second pipeline (130) is provided with means (136) which mechanically break larger air bubbles in the foam and thereby release bound air from the foam. Method according to claim 9 or 10, characterized in that in connection with said second pipeline (130) a control valve (137) is arranged for regulating the pressure in the foam tank (128). A method according to claim 9, 10 or 11, characterized in that the dispersing vessel (111) and the foam tank (128) form an integrated unit in such a way that the dispersing vessel is arranged inside the foam tank.