NZ751104B2 - Process and apparatus for wetlaying nonwovens - Google Patents

Abstract

There is a need for a process and apparatus for producing nonwoven sheet material allowing the use of higher proportions of relatively long fibres and the use of a higher levels of fibres compared to the amount of water used in the wet-laying process, while avoiding the need for expensive and high-maintenance pumps. A process and an apparatus for producing a nonwoven sheet material is disclosed. The process comprises a) providing a three-phase (gas-liquid-solid) suspension containing water, natural and/or man-made fibres, a surfactant, and 20-50 vol.% of air, b) depositing the suspension onto a moving carrier sieve to produce a fibrous web on the carrier, c) removing aqueous residue of the suspension through the carrier sieve, e) recycling the aqueous residue to step a), and before step e), subjecting the aqueous residue to a step d) of phase separation, in which the aqueous residue is conveyed through one or more phase separation tanks in an essentially horizontal direction while providing a depressurised headspace above the aqueous residue, the phase-separation resulting in reducing the air content of the aqueous residue to below 20 vol.%. aintenance pumps. A process and an apparatus for producing a nonwoven sheet material is disclosed. The process comprises a) providing a three-phase (gas-liquid-solid) suspension containing water, natural and/or man-made fibres, a surfactant, and 20-50 vol.% of air, b) depositing the suspension onto a moving carrier sieve to produce a fibrous web on the carrier, c) removing aqueous residue of the suspension through the carrier sieve, e) recycling the aqueous residue to step a), and before step e), subjecting the aqueous residue to a step d) of phase separation, in which the aqueous residue is conveyed through one or more phase separation tanks in an essentially horizontal direction while providing a depressurised headspace above the aqueous residue, the phase-separation resulting in reducing the air content of the aqueous residue to below 20 vol.%.

Description

P6058078PCT 20160901 PROCESS AND TUS FOR WETLAYING NONWOVENS Technical Field The present disclosure relates to a process for producing a fibre-containing nonwoven sheet material and to an apparatus for incorporating the fibre into the sheet al through foam formation.

Background Absorbent nonwoven materials are used for wiping various types of spills and dirt in industrial, medical, office and household applications. They typically include a ation of thermoplastic polymers (synthetic fibres) and cellulosic pulp for absorbing both water and other hydrophilic substances, and hydrophobic nces (oils, fats). The nonwoven wipes of this type, in addition to having sufficient absorptive power, are at the same time strong, flexible and soft.

They can be produced by ing a pulp-containing mixture on a polymer web, followed by dewatering and hydroentangling to anchor the pulp onto the polymer and final drying. Absorbent nonwoven materials of this type and their production processes are disclosed e.g. in WO2005/042819.

An improvement in wet-laying fibrous nonwovens involves using a foam instead of a purely aqueous slurry, since this results in a reduced consumption of water and in a d capital investment. WO96/02701 and WO96/02702 se a method of producing a hydroentangled nonwoven al by foam formation of a fibrous web, followed by spraying the ormed web with water.

WO98/27276 discloses a method of producing a nonwoven sheet material wherein a slurry of fibre, surfactant in water and air is pumped onto a wire material to allow the fibre to be attached to the wire material so as to produce a non-woven web of fibre onto the wire material, and the fibrefree slurry is then recycled to the foam production stage. The pumps used for orting the foam are degassing pumps, in order to prevent the pumps from being stuck by the ce of air. Thus, WO98/27276 employs a short ation using high flows (40,000 l/min) in the formation loop and a much smaller long circulation of 3,500 l/min for dosing fibres to be transported to the short circulation, where it is diluted to contain the desired conditions (50-80% of air) for g the web.

The process is used for producing sheet al of more than two meters wide.

[0005] EP 0481746 discloses a process of producing a fibrous sheet material by foam formation, in which surfactant is recovered from the spent foam, by removing bubbles and draining liquid from the foam and returning the surfactant-rich foam to the foam laying step. This process also involves both a short circulation (formation loop) and a long circulation (foam conditioning loop, i.e. extracting surfactants and removing surplus water) in the formation and dewatering s.

[0006] The prior art processes for producing pulp-containing nonwovens using foam formation use high air ts in the order of 50-80 vol.%. Such high air levels are more difficult to pump, P6058078PCT 20160901 because they make the foam more easily compressible. Also, these high air levels cause the foam to collapse easily at low flow rates. Hence prior art processes demand high flow rates to maintain the high air content. As a consequence, pumps, tanks and piping need to be scaled up and energy ption is high. Furthermore, the prior art processes, such as described in WO 98/27276 and EP0481746, use different circulations, making the processes complicated.

There is a need for a process and an equipment for producing non-woven sheet material allowing to use higher proportions of relatively long fibres and to use higher levels of fibres compared to the amount of water used in the wet-laying process, while avoiding the need for expensive and aintenance pumps.

Summary It is desired to provide a process for producing a, preferably hydroentangled, ent fibre-containing nonwoven material using a three-phase fibre-containing suspension, i.e. a foam, and efficiently upgrading and recycling aqueous residue of the suspension.

It is also desired to provide an apparatus for degassing and recycling aqueous residues from the deposition three-phase sions.

The presently disclosed process and the apparatus have the age of providing only one circulation for adding and mixing fibres, foam formation of the fibrous web, dewatering and recirculation of the drained flow. The degassing (deaeration) makes recirculation easier and more energy efficient, and allows the use of less demanding pumps. Main benefits are thus: a less complicated solution, low capital costs, energy efficiency and adaptation to short fibres of up to 25 In ance with a first aspect of the present invention, there is provided a process of producing a nonwoven sheet material of natural and/or man-made fibres, comprising: a) providing a three-phase iquid-solid) suspension containing water, natural and/or man-made , a tant, and 20-50 vol.% of air, b) depositing the suspension onto a moving carrier sieve to produce a fibrous web on the carrier, c) removing aqueous residue of the suspension through the carrier sieve, e) recycling the aqueous residue to step a), and before step e), subjecting the aqueous residue to a step d) of phase tion, in which the aqueous e is conveyed through one or more phase separation tanks in an essentially ntal direction while providing a depressurised headspace above the aqueous residue, the separation resulting in reducing the air t of the aqueous residue to below vol.%.

[0012] In accordance with a second aspect of the present invention, there is provided an apparatus for ing and recycling aqueous residues comprising: P6058078PCT 20160901 (1) one or more dewatering units, a dewatering unit comprising: 1a. a suction box capable of awing a residual fluid of an aqueous suspension deposited on a r sieve through said r sieve; 1b. a phase separation tank having a lower section and an upper section, the lower section forming a liquid flow passage and being in fluid connection with said suction box at one side and being in fluid connection with a liquid withdrawal system at an opposite side, the upper section forming a headspace and having a gas outlet, (2) one or more ters, an exhauster being connected to one or more of the gas outlets of the headspace, and being e of awing gas from the phase separation tank.

Brief description of the drawings The accompanying Figure 1 diagrammatically depicts an installation for producing an absorbent fibre-containing nonwoven sheet material of the t disclosure.

[0014] Figure 2 diagrammatically shows the phase separation process and equipment used in the production of the sheet material in more detail.

Detailed description of ular embodiments The invention pertains to a process of producing nonwoven materials as defined in appended claim 1. The invention furthermore pertains to an apparatus suitable for degassing recycling spent foam from a foam formation process as defined in appended claim 16.

The present process of producing a nonwoven sheet material includes the following steps: a) ing a three-phase (gas-liquid-solid) suspension containing air, water, s al and a tant, b) depositing the suspension onto a moving carrier sieve to produce a fibrous web on the carrier, c) removing aqueous residue of the suspension through the carrier sieve, d) conveying the aqueous residue through one or more phase separation tanks in an essentially horizontal direction while providing a depressurised headspace above the aqueous residue, e) recycling the aqueous residue resulting from step d) to step a).

In particular embodiments, in step a) of this process, a gas-liquid-solid sion is prepared in which the air content is between 20 and 50 vol.%, while the air content of the aqueous residue is reduced in step d) to below 20 vol.% for ease of pumping, and the air content is restored to n 20 and 50 vol.% in the mixing step a).

In particular ments, the s material of the suspension provided in step a) includes natural and/or man-made fibres, especially short fibres of between 1 and 25 mm average length. Part or all of the natural short fibres may include cellulosic pulp, which can have fibre lengths of between 1 and 5 mm. The cellulosic (pulp) fibres may constitute at least 25 wt.%, 40-95 wt.%, or 50-90 wt.%, of the short fibres to be provided in step a). Instead or in addition, the short fibres P6058078PCT 20160901 may include man-made staple fibres having fibre lengths of between 4 and 25 mm, or between 5 and 20 mm. The staple fibre length may also be bimodal, one part having an average length 5-10 mm and another part having an e length of 15-20 mm. The staple fibres may constitute at least 3 wt.%, or 5-50 wt.% of the short fibres to be provided in step a).

[0019] The three-phase suspension can contain a surfactant, in particular a non-ionic tant.

In ular embodiments, the suspension contains n 0.01 and 0.2 wt.% of surfactant.

Further s of the ition and the provision of the suspension are ted below.

The process of the present disclosure can be a peed wet-laying process, in which the three-phase suspension can be deposited in step b) at a rate of between 2.1 and 6 m3/min (35-100 l/sec; 126-360 m3/h) for a formed web having a width of 1 m.

In step c), aqueous residue of the suspension is removed through the carrier sieve, for example by suction. In an advantageous embodiment, depositing step b) and removing step c) are repeated after step c) as steps b’) and c’), respectively, i.e. the deposition of fibre-containing suspension and the corresponding removal of aqueous residue thereof is performed in two stages: b) and c) followed by b’) and c’). Aqueous residue from step c’) is also subjected to step d), wherein it is conveyed to one or more phase separation tanks, which can be distinct from the one or more phase separation tanks through which s residue from step c) is ed.

The second stage (and even an additional stage if desired) of removal of aqueous residue (c’) (and even an additional stage (c“) if d), can be carried out using multiple suction boxes, e.g. 2-3, each one being connected to a distinct phase separation tank. In this embodiment of repeated steps b) + c) and b’) + c’) the phase suspension can be deposited in equal amounts, but the amount in the first step (b) can be larger than in the second step (b’), for example 55-85% in step b) and 15-45% in step b’), the rates corresponding to e.g. 1-5 m3/min for the first deposition and a formed web having a width of 1 m, and 0.3-2.9 m3/min for the second deposition and a formed web having a width of 1 m. This corresponds to depositing about 5-25 kg fibres per min (and per m width) or 6-18 kg fibres per min and per m, and to a carrier sieve running speed of 1-8 m/sec, or 2.5-6 m/sec.

In an embodiment, the present process includes a further step, prior to step b), of depositing a polymer web, which contains at least 50 wt.% of synthetic filaments, in an way known as such in the art, e.g. by a spun-laid, air-laid or carding process step, and further illustrated below.

In another embodiment, the present process includes an optional step of depositing a polymer layer on the deposited (combined) fibrous web after step b). After the deposition of the fibrous web (containing short ) and the r web, the combined web can contain e.g. n 10 and 60 wt.%, or between 15 and 45 wt.%, of the synthetic filaments on dry matter basis of the combined web.

An important step of the present disclosure is the phase separation of step d), reducing the air content of the s residue (spent web-forming suspension) to below 20 vol.%, below vol.%, or below 10 vol.%. This is achieved by removing and collecting the aqueous residue P6058078PCT 20160901 through the carrier by means of suction, using a suction box array which can be divided in multiple suction boxes, such as 2-8 suction boxes, or 3-6 suction boxes. Such ity of suction boxes can also be considered as tments of a single suction box (array). The suction boxes (or compartments) can be arranged consecutively along the direction of movement of the carrier, and the residue ted in each suction box can advantageously be conveyed to a distinct phase separation tank. A low pressure in the headspace of the separation tanks reduces the air content of the aqueous residue, and at the same time assists in the suction step c). A low re can e.g. be an ressure of 0.05-0.5 bar compared to ambient pressure, the nominal pressure in the separation tanks being in the range of 0.5-0.95 bar, especially 95 bar. Deaeration is further enhanced by breaking the foam, e.g. by introducing turbulence by means of a fan or by spraying with water. After recycling the deaerated aqueous residue by pumping and entering the roducing step a), the air content is restored to the required level, in particular to between 20 and 40 vol.%, in step a). The working of the deaeration is further illustrated below with reference to accompanying Figure 2.

[0025] Thus, in particular embodiments, multiple phase separation tanks, i.e. at least 2, up to e.g. 8, or 3-6, are used, for e one separation tank for each point of suction (suction box) of aqueous residue. If desired, ent pressures may be applied in the multiple separation tanks.

For ce, the pressure in the headspace of the phase separation tank into which residue from the most upstream ) of the suction boxes is conveyed may be between 0.01 and 0.1 bar higher than the pressure in the headspace of the phase separation tank into which residue from the most downstream (last) of the suction boxes is conveyed.

The process can contain further steps after step b) of producing a fibrous web on the moving carrier sieve said as follows.

Advantageously, the fibrous web as ted on the moving carrier is subsequently pre- ated by flushing with water in an additional step f). This can be achieved by using multiple water jets which are arranged essentially perpendicular to the web (in particular vertical). The amount of water can be expressed in relation to amount of suspension applied, the amount then being between 0.0005 and 0.05 m3 of water per m3 of d suspension, or 0.001-0.03 m3, or 0.02 m3, or even 0.003-0.01 of water per m3 of suspension. Alternatively, the amount of water applied in step f) can be independently defined relative to the formed sheet material, the amount then being between 0.8 and 20 litres of water per kg of formed sheet material, or between 1 and 10 l/kg, or even between 1.2 and 5 l/kg of formed sheet material. As a r alternative, the amount of water applied in step f) can be expressed in time units, e.g. between 10 and 250 litres of water per min per m width of formed web, or between 13 and 170 l/min.m, or even n 17 and 50 l/min.m. Such amounts of pre-integrating water are especially suitable for a high-speed process as described above. The pressure of the jets can be n 2.5 and 50 bar, between 4 and 20 bar, or between 5 and 10 bar. Spent flushing water is removed through the carrier and can be added to the recycle stream of step e). Prior to the recycle, the removed flushing water can advantageously be conveyed through a further phase separation tank and then fed to step e) or P6058078PCT 20160901 directly to step a). The tegrating and removing step f) can also be carried out in at least two stages f1) and f2).

The spent flushing water that is removed in step f) can be used for spraying water through the headspace of the one or more phase separation tanks of step d), in addition to or instead of being recycled to the production of the suspension (pulper); sprayed water can then be collected in the aqueous residue and recycled.

In many instances it will be desirable to further treat the fibrous web. One important further treatment is hydroentanglement, in which the fibrous web, as such, or combined with a synthetic continuous filament layer, is integrated by high-pressure water jets. In particular embodiments, the hydroentangling is performed on a different moving r sieve from the carrier on which the fibrous web is laid.

Thus, step b) of depositing the three-phase sion and optional step f) of pre- integrating the deposited web, can be med on a first moving r sieve. The process then additionally includes, after step b), or after step f) if pre-integration is included: g) transferring the fibrous web from the first moving carrier used in steps b) and c) to a second moving carrier, the second moving carrier having a porosity which is lower than the porosity of the first moving r sieve, h) hydroentangling the fibrous web on the second moving carrier, i) drying the hydroentangled sheet; j) optionally ting, conditioning, dimensioning and/or packaging the dried sheet to produce a ready-for-use sheet material.

In step g), the porosities of the first and second moving carrier sieves (wires) can be such that that the permeability of the first moving carrier is 250-750 cfm (cubic foot per min) (= 7.1-21.2 m3/min), or 400-600 cfm (= 11.3-17.0 ), while the bility of the second moving carrier can be 100 - 350 cfm (= 2.8-9.9 m3/min), or 150-250 cfm (= 4.2-7.1 m3/min). Embodiments of steps h), i) and j) are bed further below.

The present apparatus for degassing and recycling aqueous residues includes: (1) one or more ring units, a dewatering unit including: 1a. a suction box (12) capable of withdrawing a residual fluid of an s suspension deposited on a carrier sieve through said carrier sieve; 1b. a phase tion tank (14) having a lower section and an upper section, the lower section forming a liquid flow passage and being in fluid connection with said suction box (12) at one side and being in fluid tion with a liquid awal system (16) at an opposite side, the upper section forming a headspace and having a gas outlet, (2) one or more exhausters (17), an exhauster being connected to one or more of the gas outlets of the headspace, and being capable of withdrawing gas from the phase separation tank.

More in particular, the apparatus for degassing and recycling aqueous residues may include: P6058078PCT 20160901 (1) one or more dewatering units, a dewatering unit including: 1a. a suction box (12) capable of withdrawing and g a al fluid of an aqueous suspension deposited on a carrier sieve through said carrier sieve; - a suction line (13) connected to a fluid exit of the suction box; - optionally a valve capable of regulating the fluid flow throu gh the suction line; 1b. a phase separation tank (14) having a lower section and an upper section, the lower section forming a liquid flow passage and being in fluid connection with said n box (12) through a fluid inlet connected to the n line (13) at one side, and being in fluid connection with a liquid withdrawal system (16) through a liquid outlet at an opposite side, the upper section forming a headspace and having a gas outlet, the fluid inlet and the liquid outlet being positioned in a manner allowing an essentially horizontal liquid flow through the tank while maintaining the headspace above the liquid, the tank being equipped in such a manner that a sub-atmospheric gas pressure in the tank will enhance the flow of fluid entering the tank from the suction box, 1c. a liquid withdrawal system including - a return line (16) connected to the liquid outlet of the phas e separation tank (14), capable of returning liquid from the phase separation tank to a common container for aqueous suspension, - a pump (18) capable of withdrawing liquid from the phase sepa ration tank through the return line (16); - a valve capable of regulating the liquid flow through the ret urn line; (2) one or more ters, an ter being connected to one or more of the gas outlets of the one or more phase separation tanks through a gas exit line (17) and e of withdrawing gas from the phase separation tank, the gas exit line optionally including a valve capable of regulating the gas flow through exit lines.

The phase tion tank can be equipped with a means for promoting breakdown of the foam, such as a fan or a sprayer. In case of a sprayer, the tank further es (iv) a spray liquid inlet and (v) a spraying device connected to the spray liquid inlet, the spraying device (v) being capable of spraying aqueous liquid in the headspace of the tank. The spray liquid can be an aqueous liquid, i.e. largely or wholly consisting of water, possibly containing agents assisting in breaking the foam.

There can be a single ring unit, but, in particular embodiments, there is a plurality, i.e. two or more. The plurality of dewatering units can be from 2 up to e.g. 8, or even up to 10. In certain embodiments, the apparatus has 3-6 dewatering units.

[0036] The apparatus can further include a modified dewatering unit instead of one of or in addition to the plurality of dewatering units. In the modified dewatering unit, a suction box is e of withdrawing flushing water from a flushing (pre-integration) device to be used in step f) bed above. The unit can further e a further exhauster, which is connected to the gas exit line of P6058078PCT 01 the modified dewatering unit and which may not be connected to at least one of the gas exit lines of the plurality of dewatering units.

In the present sure, the indications “between x and y” and “from x to y” and “of x-y”, wherein x and y are numerals, are considered to be synonymous, the inclusion or exclusion of the precise end points x and y being of theoretical rather than practical meaning.

Further details of particular embodiments of the various steps and materials to be applied are described below.

Materials and process steps a. Carrier and r web

[0039] A moving carrier sieve on which the s composition can be applied, can be a forming fabric, which can be a running belt-like wire having at least the breadth of the sheet material to be produced, which fabric allows ng of liquid h the fabric, i.e. which is semipermeable. In an embodiment, a r web can first be deposited on the carrier by laying de fibres on the r. The fibres can be short or long distinct (staple) fibres and/or continuous filaments. The use or co-use of filaments is preferred in certain ments. In another embodiment, a polymer layer can be deposited on the fibrous web obtained in steps b) and c), but before step g). It is also le to first deposit a polymer layer, ed by depositing the aqueous suspension to form a fibrous web on the polymer web and to deposit a further polymer layer on the fibrous web.

Filaments are fibres that in proportion to their diameter are very long, in principle endless, during their production. They can be produced by melting and extruding a thermoplastic polymer through fine nozzles, followed by cooling, for example using an air flow, and solidification into strands that can be treated by drawing, stretching or crimping. The filaments may be of a thermoplastic material having sufficient nt properties to allow g, drawing and stretching. Examples of useful synthetic polymers are polyolefins, such as polyethylene and polypropylene, polyamides such as nylon-6, polyesters such as poly(ethylene terephthalate) and polylactides. Copolymers of these polymers may of course also be used, as well as natural polymers with thermoplastic properties. Polypropylene is a particularly suitable thermoplastic manmade fibre. Fibre diameters can e.g. be in the order of 1-25 µm. Staple fibres can be of the same man-made materials as filaments, e.g. polyethylene, polypropylene, polyamides, polyesters, polylactides, cellulosic fibres, and can have lengths of e.g. 2-40 mm. In particular embodiments, the polymer web contains at least 50 wt.% of thermoplastic (synthetic) nts, or at least 75 wt.% of synthetic filaments. The combined web contains between 15 and 45 wt.% of the synthetic filaments on dry solids basis of the combined web. b. Three-phase fibre suspension

[0041] The aqueous suspension is obtained by mixing short fibres and water in a mixing tank. The short fibres can include natural fibres, in particular cellulosic fibres. Among the le cellulosic fibres are seed or hair fibres, e g cotton, flax, and pulp. Wood pulp fibres are especially well suited, and both softwood fibres and hardwood fibres are suitable, and also recycled fibres can be used.

P6058078PCT 20160901 The pulp fibre lengths can vary between 0.5 and 5, from 1 to 4 mm, or from around 3 mm for od fibres to around 1.2 mm for hardwood fibres and a mix of these lengths, or even shorter, for recycled fibres. The pulp can be introduced as such, i.e. as pre-produced pulp, e.g. supplied in sheet form, or produced in situ, in which case the mixing tank is commonly referred to as a pulper, which involves using high shear and possibly pulping chemicals, such as acid or alkali.

In addition or instead of the natural fibres, other natural or man-made materials can be added to the suspension, such as in particular other short fibres. Staple ade) fibres of variable length, e.g. 5-25 mm, can suitably be used as additional fibres. The stable fibres can be man-made fibres as described above, e.g. polyolefins, polyesters, polyamides, actic acid), or cellulose derivatives such as lyocell. The staple fibres can be colourless, or coloured as desired, and can modify further properties of the ontaining suspension and of the final sheet product.

Levels of additional (man-made) , in particular staple fibres, can suitably be between 3 and 100 wt.%, between 5 and 50 wt.%, between 7 and 30 wt.%, or between 8 and 20 wt.% on the basis of the dry solids of the aqueous suspension.

[0043] When using polymer fibres as additional material, it is usually ary to add a surfactant to the pulp-containing suspension. Suitable surfactants include anionic, cationic, non-ionic and amphoteric surfactants. Suitable examples of anionic surfactants include long-chain (lc) (i.e. having an alkyl chain of at least 8 carbon atoms, in particular at least 12 carbon atoms) fatty acid salts, lc alkyl sulfates, lc alkylbenzenesulfonates, which are optionally ethoxylated. Examples of cationic surfactants include lc alkyl ammonium salts. Suitable examples of nic surfactants include ethoxylated lc fatty alcohols, ethoxylated lc alkyl amides, lc alkyl glycosides, lc fatty acid amides, mono- and diglycerides etc.. Examples of amphoteric (zwitterionic) surfactants include lc alkylammonio-alkanesulfonates and choline-based or atidylamine-based surfactants. The level of surfactant (on the basis of the aqueous suspension) can be between 0.005 and 0.2, between 0.01 and 0.1, or between 0.02 and 0.08 wt.%.

For an effective application of the aqueous suspension the suspension contains air, i.e. it is a three-phase sion used as a foam. The amount of air introduced into the suspension (e.g. by stirring the suspension) can be n 15 and 60 vol.% of the final suspension (including the air). The air content of the three-phase suspension can be between 20 and 50 vol.%, between 20 and 45 vol.%, between 25 and 40 vol.%, or between 30 and 38 vol.%. The more air is present in the foam, often the higher levels of tants are required. The term “air” is to be interpreted broadly as any xious gas, typically containing at least 50% of molecular nitrogen, and r varying levels of molecular oxygen, carbon dioxide, noble gases etc. Further information about foam formation as such can be found e.g. in WO03/040469. b. Deposition of the fibre suspension The s suspension ning short fibres is ted on the carrier, either directly or on a polymer web, e.g. using a head box, which guides and spreads the sion evenly over the width of the r or the web in the direction of the running fabric, causing the suspension to partly penetrate into the polymer web. The speed of application of the aqueous suspension, which P6058078PCT 20160901 is the running speed of the moving carrier sieve (wire) and thus lly the same as the speed of laying the polymer web, can be high, e.g. between 1 and 8 m/sec (60-480 m/min), especially between 3 and 5 m/sec.

The aqueous suspension can also be deposited in two or more stages (b) and (b’), by using two or more head boxes. Where a polymer web is first applied, the aqueous fibre sion can be applied onto the polymer web in two or more separate steps at the same side of the polymer web. This results in part of the solids of the sion entering on and in the polymer web as a result of the deposition and uent removal of surplus water and air, and consequently the ing part(s) of the suspended solids to be even more evenly spread over the width of the web.

The total amount of liquid circulated by the wet-laying or foam laying for a formed web having a width of 1 m can be in the order of 1200-5400 kg/min, 1800-4500 kg/min, or 2100-3600 kg/min (20-90, 30-75, or 35-60 kg/sec). In case of two deposition stages, e.g. between 25 and 90, in ular between 50 and 85 % may be applied in the first stage, and the remaining part in the second and optional further stages. The amount that is drained off via the web having a width of 1 m, i.e. the part that is not recycled, will be in the order of 20-57 kg/min of liquid (36-66 kg/min including solid material). c-d-e. Removal and recycling of aqueous residue after the application of the suspension Surplus liquid and gas phase are sucked through the web and the fabric in step c), leaving the short fibres and other solids in and on the web. The spent liquid and gas are separated, and processed according to the present sure and, in particular embodiments, the liquid having an air t below 20 vol.%, or below 15 vol.%, is ed to the mixing tank for producing fresh aqueous fibre suspension, as described in more detail below.

When the aqueous fibre suspension is applied in two or more te steps (b), b’) and possibly b”), etc.), using two or more head boxes, the laying steps are separated by a suction step c) and followed by a suction step (c’, c”). The removal of aqueous residue in the first removal step c) can be such that the water t of the combined web before the second pulp application step is not more than 85 wt.%, or between 60 and 75 wt.%. Thus, the dry solids content of the fibrous web after the first ation step can be at least 15 wt.%, or between 25 and 40 wt.%. Where two or more removal steps are applied following distinct deposition steps, each removal step can be performed using multiple suction boxes, each suction box optionally being connected to a distinct phase separation tank. Advantageously, 2-5 suction boxes are used for the first removal step c), and 1-3 n boxes are used for the second removal step c’), and e.g. 1-2 suction boxes for a third or further removal step c“). f. Pre-integrating After the formation of the fibrous web, optionally combined with a polymer web, the fibrous web can be subjected, in a particular embodiment, to pre-integration, by flushing (rinsing) the web with water jets, in particular at a level of e.g. 0.001-0.03 m3 of water per m3 of applied three-phase P6058078PCT 20160901 suspension, or at a ently defined rate as described above with reference to step f). The water jets can form a row of perpendicular cal) jets covering the width of the moving web and can have a pressure of 2.5-50 bar. The water used for tegration can be fresh water, having low dissolved matter levels. Part of the water can be supplied by recycling flushed water, optionally after (micro)filtration. In an embodiment, part of the collected flushed water is fed to the s suspension in step a) and the remainder of the collected flushed water is recycled to the preintegration step f).

The pre-integrating and collecting step f) may be carried out in multiple stages, e.g. two stages f1) and f2), or even three stages f1), f2), f3), or even more stages, using multiple series of water jets, each series ng the entire width of the web g the sheet material. In the event of multiple pre-integration stages, it may be advantageous to e flushed water collected from the first stage f1), which will contain vely high levels of surfactant, to the three-phase (foam) suspension in step a) and at least a part of the flushed water collected from the second or last stage f2), which will contain lower levels of surfactant, to the first pre-integration step f1). The more specific distribution of collected flushed water to the suspension-forming stage and to the preintegration , can be chosen so as to have optimum quality of the suspension and the pre-integrating water in combination with minimum use of raw materials, including water and tant. g. Hydroentangling Subsequently to the wet-laying or aying steps b) and c), the fibrous web can be subjected to hydroentanglement, i.e. to needle-like water jets covering the width of the running web. In particular embodiments, the hydroentangling step (or steps) is performed on a different carrier (running wire), which is more dense (smaller sieve openings) than the carrier on which the fibre-containing suspensions (and optionally first the polymer web) are ted. In certain embodiments, the ntangling step includes the use of multiple hydroentanglement jets shortly sequencing each other. The pressure applied may be in the order of 20-200 bar. The total energy supply in the hydroentangling may step be in the order of 100-400 kWh per ton of the treated material, measured and ated as described in CA 841938, pages 11-12. The skilled person is aware of further technical s of hydroentanglement, as described e.g. in CA 841938 and WO96/02701. h. Drying The combined, hydroentangled web can be dried, e.g. using further suction and/or oven drying at temperatures above 100°C, such as between 110 and 150°C. i. Further processing The dried nonwoven can be further treated by adding additives, e.g. for enhanced strength, scent, printing, colouring, patterning, impregnating, wetting, cutting, folding, rolling, etc. as determined by the final use of the sheet material, such as in industry, medical care, household applications.

P6058078PCT 20160901 End product The nonwoven sheet material as produced can have any shape, but frequently it will have the form of gular sheets of between less than 0,5 m up to several meters. Suitable examples include wipes of 40 cm x 40 cm. Depending on the intended use, it may have various thicknesses of e.g. between 100 and 2000 µm, or from 250 to 1000 µm. The thickness can be determined as described below. Along its section, the sheet material may be essentially homogenous, or it may gradually change from relatively pulp-rich at one surface to relatively pulp-depleted at the opposite surface (as a result of e.g. wet-laying or foam-laying pulp at one side of the polymer web only), or, alternatively, from relatively pulp-rich at both surfaces to vely pulp-depleted in the centre (as a result of e.g. wet-laying or foam-laying pulp at both sides of the polymer web – either or both in multiple steps at the same side). In a ular embodiment, the nonwoven material as produced has front and back surfaces of different composition, in that the pulp-containing suspension is applied at the same side in each separate step, and/or hydroentanglement is performed only at one side. Other structures are equally feasible, including structures not containing filaments.

The composition can also vary within rather broad ranges. As an advantageous example, the sheet material may contain between 25 and 85 wt.% of (cellulosic) pulp, and between 15 and 75 wt.% of de (non-cellulosic) polymer material, r as (semi)continuous filaments or as relatively short (staple) fibres, or both. In a more detailed example, the sheet material may contain between 40 and 80 wt.% of pulp, between 10 and 60 wt.% of filaments and between 0 and 50 wt.% of staple fibres, or, more particular examples, between 50 and 75 wt.% of pulp, between and 45 wt.% of filaments and between 3 and 15 wt.% of staple fibres. As a result of the present process, the nonwoven sheet material has few if any deficiencies, combined with low residual levels of surfactant. In ular embodiments, the end product contains less than 75 ppm of the tant, less than 50 ppm, or less than 25 ppm of -soluble) surfactant. All these contents are on dry matter basis, unless otherwise specified.

Figures The accompanying figure 1 shows equipment for carrying out the process described herein. If used, thermoplastic polymer is fed into a heated g device 1 to produce filaments 2, which are deposited on a first running wire 3 to form a r layer. A mixing tank 4 has inlets for pulp 5, staple fibre 6, air 7, water 8, and surfactant (not shown). The resulting pulp-containing suspension (foam) 9 is fed to the head box 10 through inlet 24. A suction box 12 (or a plurality thereof) below the moving wire removes most of the liquid (and gaseous) residue of the spent pulpcontaining suspension, which is fed to one or more phase separation tanks 14 (only one shown), through line 13, equipped with a valve. The suspension is allowed to degas in the phase tion tank by means of an underpressure (vacuum) produced by a gas exhauster (not shown) in gas exit (line) 17. r 15 is provided in the headspace of the phase tion tank to enhance the phase separation by spraying water on the foam, thereby ng the foam. The resulting aqueous liquid is returned to the mixing tank through line 16. A tegration device 25 can produce a 78PCT 20160901 water jet 26 for pre-integrating the combined web 19, and the spent water is collected in suction box 27 and carried off through line 28, ultimately to the mixing tank 4. The combined pulp-polymer web 19 can be transferred to a second running wire 20 and subjected to multiple hydroentanglement steps through devices 21 producing water jets 22, with water suction boxes 23, the water being discharged and further recycled (not shown). The hydroentangled web 29 is then dried in drier 30 and the dried web 31 is r processed (not shown).

Figure 2 illustrates the cycle of the three-phase suspension including the deaeration process and equipment in more detail. In the figures, the same ts or parts have the same nce numerals. Figure 2 shows a set of four suction boxes 121-124 below the moving carrier 3 and the head box 10. The four suction boxes collect essentially all aqueous residue passing the moving sieve. The collected residues are conveyed to the corresponding separation tanks 141- 144, via lines 131-134, which are equipped with controllable valves. The separation tanks have liquid outlet lines 161-164 provided with pumps 181-184 at a lower part of the tanks and gas outlet lines 171-174 at an upper part of the tank. The gas outlet lines 4 are provided with control valves 71-74 and are combined to a gas line 176, a vacuum fan 42 and a gas exhaust 178. The tanks 141-144 are furthermore provided with sprayers 151-154, fed with spraying liquid - in this example aqueous suspension supplied through line 44 and valve 45 -, through lines 51-54.

A flushing device 41 (equivalent to pre-integration device 25 of Figure 1) produces water jets for flushing the web and the flushed water is collected by n box 125, fed to a fifth separation tank 145 through line 135 having a controllable valve. Tank 145 is also provided with sprayer 155 fed through line 55, liquid outlet 165 for water, driven by pump 185, and gas outlet 175, which connects to a second vacuum fan 43 h combined line 177 and then to exhaust 179. Underpressure in the tanks ing the withdrawal of aqueous residue from the suction boxes to the separation tanks is secured by vacuum fans or pumps 42 and 43. Connecting lines 83 and 84 provided with control valves t gas outlets 173 and 174 of tion tanks 143 and 144, respectively, with the second vacuum fan 43, so as to allow the more downstream separation tanks 143 and 144 to be evacuated by fan 43 instead of, or in addition to, fan 42. The liquid lines 161-165 convey the deaerated aqueous residue to the pulper 4, by means of pumps 181-185, in which the constituents of the three-phase suspension are mixed in the appropriate s.

[0059] The Figures only serve to illustrate an embodiment of the ion and do not limit the claimed ion in any way. The same applies to the Examples below.

EXAMPLES AND TEST METHODS Test methods used for determining properties and parameters of the nonwoven material as described herein will now be ned in more detail. Also a test method for measuring air content of the three-phase foam-forming suspension is presented.

Furthermore, some examples illustrate advantages of using the method as defined in the appended claims and the product provided by such method are presented below.

P6058078PCT 20160901 Test method - ess The thickness of a sheet al as described herein can be determined by a test method following the ples of the Standard Test Method for Nonwoven Thickness according to EDANA, WSP 120.6.R4 (12). An apparatus in accordance with the standard is available from IM TEKNIK AB, Sweden, the apparatus having a Micrometer available from Mitutoyo Corp, Japan (model ID U-1025). The sheet of material to be measured is cut into a piece of 0 mm and conditioned (23°C, 50 % RH, =4 hours). The measurement should be performed at the same conditions. During measurement the sheet is placed beneath the pressure foot which is then d. The thickness value for the sheet is then read after the pressure value is stabilised. The measurement is made by a precision eter, wherein a distance created by a sample between a fixed reference plate and a parallel pressure foot is measured. The measuring area of the pressure foot is 5x5 cm. The pressure applied is 0.5 kPa during the measurement. Five measurements could be performed on different areas of the cut piece to determine the thickness as an average of the five measurements.

Test method – Air content Equipment A spiral connected to an inlet for foam, air or water and a corresponding outlet, the spiral having volume of 2 l. The spiral is placed on a scale/balance.

Calibration Calibration is done by emptying the spiral by blowing ssed air through it and zero setting value of the scale when it is empty, i.e. only filled with air, which is balanced to the calibrated value of zero (0), i.e. 0 vol.% liquid present in the spiral. The spiral is then filled with water and the weight of this water is determined, which gives the calibrated value of 100, i.e. 100 vol.% of liquid present in the spiral.

Measurement

[0065] An emptied spiral is filled with the sion/foam to be tested and weighed and the weight is linearly correlated to the calibrated 0 and 100 end values representing the volume percentage of liquid present in the spiral. Thus, the measured value ponds to the percentage of liquid part of the foam. The air content is then calculated as the remaining percentage up to sum up to 100 percentage. e 1 An absorbent sheet material of nonwoven that may be used as a wipe such as an industrial cleaning cloth was produced by laying a web of polypropylene filaments on a running conveyor fabric and then applying on the polymer web a pulp dispersion containing about 0.5 wt.% of a 88:12 weight ratio of wood pulp and polyester staple fibres. The staple fibres contained a e of 1.7 dtex fibres with two different lengths, namely 50 wt.% of the fibres having a length 6 mm and 50 wt.% of the fibres having a length 18 mm. The dispersion further included about 0.03 wt.% of a non-ionic surfactant (ethoxylated fatty alcohol) by foam forming in a head box, introducing a total of about 30 vol.% of air (on total foam volume). For the foam ion loop, an installation as P6058078PCT 20160901 diagrammatically ed in Figure 2 was used, involving multiple separation units for deaerating the spent foaming sion. The air content of the aqueous suspension leaving the deaeration unit was about 10% by volume. The foam cycle in the loop was about 3000 kg/min per m width of formed web; the width of the freshly wet-laid web was about 1.4 m. The weight proportion of the polypropylene filaments was 25 wt.% on dry weight basis of the end product. The amounts were chosen so as to arrive at a basis weight of the end product of 55 g/m2. The combined fibre web was then ted to hydroentanglement using multiple water jets at increasing pressures of 40- 100 bar providing a total energy supply at the hydroentangling step of about 180 kWh/ton as measured and calculated as described in CA 841938, pp. 11-12 and subsequently dried. The speed of wind-up of the dried sheet of 1.3 m width was 225 m/min.

P6058078PCT 20160901

Claims (20)

Claims 1.

1. A s of producing a nonwoven sheet material of natural and/or man-made fibres, comprising: a) providing a three-phase (gas-liquid-solid) suspension ning water, natural and/or man-made fibres, a surfactant, and 20-50 vol.% of air, b) depositing the sion onto a moving carrier sieve to produce a fibrous web on the carrier, c) removing aqueous residue of the sion through the carrier sieve, e) recycling the aqueous residue to step a), and before step e), subjecting the aqueous residue to a step d) of phase separation, in which the aqueous residue is conveyed through one or more phase separation tanks in an ially horizontal direction while ing a depressurised ace above the aqueous e, the phase-separation resulting in reducing the air content of the aqueous residue to below 20 vol.%.

2. The process according to claim 1, wherein conveying the aqueous residue h the one or more separation tanks comprises breaking the foam.

3. The process according to claim 1 or 2, wherein the aqueous residue is removed through the carrier by means of two or more suction boxes, the suction boxes being arranged consecutively along the direction of movement of the carrier, the residue collected in each suction box being conveyed to a distinct phase separation tank.

4. The process according to any one of claims 1-3, wherein, after step c), steps b) and c) are repeated as steps b’) and c’), respectively, and aqueous e from step c’) is ted to step d), wherein it is conveyed through one or more phase separation tanks.

5. The process according to claim 4, wherein the one or more phase separation tanks through which the aqueous e from step c’) is conveyed are distinct from the one or more phase separation tanks through which aqueous e from step c) is conveyed.

6. The process according to any one of claims 1-5, wherein, in a step f), the fibrous web produced is subsequently subjected to pre-integration by ng with water, spent flushing water being removed through the carrier.

7. The process according to claim 6, wherein removed flushing water is conveyed through a further phase separation tank and then fed to step a).

8. The process according to claim 6, wherein removed flushing water is used for spraying water through the headspace of the one or more phase separation tanks of step d) and sprayed water is collected in the aqueous residue. P6058078PCT 20160901

9. The process according to any one of the preceding claims, which further ses, after step b) or after optional step f): g) optionally transferring the fibrous web from said moving carrier sieve, being a first moving carrier sieve, to a second moving carrier sieve, said second moving carrier sieve having a porosity which is smaller than the porosity of said first moving carrier sieve, h) hydroentangling the fibrous web on said second moving carrier, i) drying the hydroentangled sheet and optionally imprinting, conditioning, ioning and/or packaging the dried sheet to produce a ready-for-use sheet material.

10. The process according to any one of the preceding claims, wherein the suspension contains n 0.01 and 0.2 wt.% of surfactant.

11. The process according to any one of the preceding claims, wherein the surfactant is a nonionic surfactant.

12. The process according to any one of the preceding claims, wherein the fibrous material in the suspension comprises short fibres of between 1 and 25 mm length, and includes at least 25 wt.% of cellulosic pulp having fibre lengths of between 1 and 5 mm.

13. The process according to any one of the preceding claims, wherein the phase suspension contains between 20 and 45 vol.% of air.

14. The process according to any one of the preceding claims, n the three-phase suspension is deposited in step b) at a rate of between 2100 and 6000 l/min per m width of produced fibrous web.

15. The process according to any one of the ing claims, wherein prior to step b), a polymer web is deposited, which r web contains at least 50 wt.% of synthetic filaments, and the combined web resulting from the deposition of the pulp-containing suspension onto the polymer web ns between 15 and 45 wt.% of the synthetic filaments on dry matter basis of the combined web.

16. An apparatus for ing and ing aqueous residues sing: (1) one or more dewatering units, a dewatering unit comprising: 1a. a suction box capable of withdrawing a residual fluid of an aqueous suspension deposited on a carrier sieve through said carrier sieve; 1b. a phase separation tank having a lower section and an upper section, the lower section forming a liquid flow passage and being in fluid tion with said suction box at one side and being in fluid connection with a liquid withdrawal system at an opposite side, the upper section g a headspace and having a gas outlet, P6058078PCT 20160901 (2) one or more exhausters, an exhauster being connected to one or more of the gas outlets of the headspace, and being capable of withdrawing gas from the phase separation tank.

17. The apparatus according to claim 16, wherein the number of dewatering units is 3-5.

18. The apparatus according to claim 17 or 17, wherein the phase separation tank comprises a spray liquid inlet and a spraying device ted to the spray liquid inlet, the spraying device being arranged for spraying liquid in the headspace of the tank.

19. The apparatus according to any one of claims 16-18, further comprising a modified dewatering unit, in which a suction box is capable of withdrawing flushing water from a flushing , and further sing a r exhauster, which is connected to the gas exit line of the modified dewatering unit.

20. The tus according to claim 19, wherein the further exhauster is not connected to at least one of the gas exit lines of the plurality of dewatering units. WO 41355