WO2015028275A1

WO2015028275A1 - Inclined wire former, method for the production of a wet-laid nonwoven web by means of an inclined-wire former and nonwoven web

Info

Publication number: WO2015028275A1
Application number: PCT/EP2014/067002
Authority: WO
Inventors: Thomas Weigert; Kai PÖHLER
Original assignee: Voith Patent Gmbh; TRüTZSCHLER GMBH & CO. KG
Priority date: 2013-08-26
Filing date: 2014-08-07
Publication date: 2015-03-05

Abstract

An inclined wire former for a wire part of a machine for producing a fibrous web, in particular a nonwoven web, comprises a forming fabric (6), which in the wire running direction runs at least in parts at an oblique angle with respect to the horizontal, at least one multilayer headbox (1) having several sections (2) being provided in the oblique section of the forming fabric (6) through which sections (2) a plurality of fibrous suspensions can be applied simultaneously to the forming fabric (6) to produce fiber layers (4). The plurality of sections (2) are provided with flexible segments (3) which are particularly mobile relative to each other.

Description

Schrägsiebformer, process for producing a wet-laid nonwoven web by means of a Schrägsiebformers and nonwoven web

The invention is based on a Schrägsiebformer for producing a wet-laid nonwoven web according to the preamble of claim 1, a method for producing a wet-laid nonwoven web according to the preamble of claim 9 and a nonwoven web produced in accordance with the preamble of claim 13. Nonwovens are in many today various embodiments for a large number of applications in the paper and textile industry for the production of various consumer products in use. Examples include nonwovens for the clothing industry or moist wipes in the cosmetics industry. Such nonwoven fabrics are formed according to the prior art by means of different methods and devices, as described by way of example in WO 2007/018980 A2. The cited publication discloses an apparatus for forming a nonwoven product comprising a former suitable for receiving a raw material and for forming the product, and a shoe calender which takes over and further processes the nonwoven product.

Multi-ply products are usually made by a combination of different types of web forming in different sequential stages. As an example, EP 0 992 338 A2 is cited, from which a three-layer water-strengthened web with a sandwich structure emerges. There are long synthetic fibers on the top and bottom layers and other fibers, such as short cellulosic fibers, a mixture of short cellulose and short synthetic or other natural fibers in the middle layer. The synthetic fibers (synthetic fibers) in the outer layers have a length in the range of 40 to 100 mm and the cellulose fiber in the middle layer a length of 1 to 8 mm. The optional short synthetic or optional other natural fibers can range in length from 1 to 27 mm and the cellulose fibers are selected from wood pulp and cotton.

When hydroentangling the nonwoven layers, synthetic fibers with a length of more than 40 mm usually have to be used in order to achieve a sufficient strength of the nonwoven layers during hydroentanglement. Alternatively, a binder may be added. However, both aspects have in common that the fibers are not biodegradable, which is a problem especially in so-called "flushable" products such as moist wipes and similar hygiene products.

Today's methods for producing multilayer products are expensive, since the individual layers usually have to be produced separately, brought together and then solidified. Synthetic fibers are also considerably more expensive than, for example, cellulose fibers.

It is accordingly an object of the invention to provide a method in which several layers of web can be formed simultaneously, which manages without synthetic fibers and additives such as binder so that the ecological aspects - Flushability and biodegradability - account is taken and also the economic demands lower production costs met.

The object is achieved with respect to the Schrägsiebformers by the characterizing features of claim 1, in terms of the method by the characterizing features of claim 9 and with respect to the nonwoven web by the characterizing features of claim 13 respectively in combination with the generic features.

According to the invention, it is provided that the oblique wire former has an at least sectionally inclined forming fabric, in the oblique stretch of which at least one multilayer headbox with several sections is provided, through which several pulp suspensions simultaneously for the production of fiber layers are applied to the forming fabric, wherein the plurality of sections with flexible, in particular relatively movable, lamellae are provided, and wherein the fibers of the plurality of pulp suspensions of synthetic fibers, which are made of natural materials and / or consist of natural fibers.

In a further embodiment, the lamellae can be adjusted relative to each other, whereby a thickness of the pulp layers is variable. In this case, the slats are preferably rigid.

This makes it possible to process the fiber suspensions at least partially or wholly from natural fibers which have short fiber lengths, since the individual layers of the fibrous web are deposited wet on each other and form bonds which stabilize the fibrous web even in the absence of synthetic long fibers.

The method is characterized in that, after the preparation of several fiber suspensions, a simultaneous feeding of the several sections of the multilayer headbox takes place, wherein each of the sections is fed with one of the fiber suspension. The layered application of the fiber suspensions in layers from the headbox sections to the forming screen aids in the formation of a high quality nonwoven web that is successively dewatered. As the fibers for the plurality of pulp suspensions, synthetic fibers made of natural materials and / or natural fibers are used.

The nonwoven web according to the invention is produced in several layers and the fibers contained therein have a length of less than 25 mm, in particular less than 20 mm, preferably less than 15 mm, which are selected alone or in combination, for example: Wood pulp, BSKP (bleached long fiber pulp) , BHKP (bleached short fiber pulp), manila hemp, cotton, china grass, ramie, lyocell, viscose,. The fibers mentioned are natural fibers, such as For example, wood pulp, NBKP, LBKP, Manila hemp, cotton, Chinese grass, ramie or synthetic fibers made of natural materials, such as lyocell, viscose, which can be used in a cost effective manner for high quality end products. The synthetic fibers made of natural materials are also referred to as artificial fibers, in contrast to synthetic fibers, also called synthetic fibers, which consist of plastic materials.

The nonwoven web may be made of two, three or more layers. Since the fiber lengths of a nonwoven web made of synthetic fibers, which are made of natural materials and / or natural fibers, not exactly a length with a certain value, but a frequency distribution subject, the specified length ranges are defined so that 80%, preferably 90% and in particular 95% of the fibers are in the stated length ranges. For a nonwoven web with synthetic fibers made of natural materials and / or natural fibers of less than 25 mm in length, in particular less than 20 mm, preferably less than 15 mm, 80%, preferably 90% and in particular 95% % of the fibers have a length of less than 25 mm, in particular less than 20 mm, preferably less than 15 mm.

Further advantageous aspects of the invention will become apparent from the dependent claims.

According to advantageous embodiments, it may be provided that the thickness of the pulp layers is the same or different. This makes it easy to adapt to the demands placed on the final product.

Advantageously, for the same purpose, the plurality of fiber suspensions may be different in their solids content and / or in their composition of matter. For example, in a three-ply nonwoven web, the outer plys may contain by weight more natural fibers than synthetic fibers. With a suitable division they can 75% to 85% natural fibers and 25% to 15% synthetic fibers contain. In the middle layer, the ratio may contain 50% to 70% natural fibers and 50% to 30% synthetic fibers. The layer distribution, that is the thickness and / or the weight per unit area of the individual layers, is preferably the same for all layers.

In a second practical case, the ply split may be such that the thickness and / or basis weight of the outer plys is 20% each and the inner ply is 60% of the total nonwoven web. The outer layers contain by weight the same amount of natural fibers as synthetic fibers and the middle layer more natural fibers than synthetic fibers, for example, 85% to 95% natural fibers and 15% to 5% synthetic fibers.

Which layer distribution and which fiber compositions are selected in the individual layers depends on the application of the dissolvable nonwoven. By weight, more natural fibers in the outer layers results in a faster dissolution of the web and vice versa results in a, in particular temporarily, better strength of the web.

The solids content is preferably 0.01 to 0.1%.

According to an advantageous aspect of the invention, the sheet formation of the nonwoven web in aqueous suspension takes place with formation of hydrogen bonds, which stabilizes the nonwoven web in itself and makes it more durable.

This can be further enhanced by the fact that the fiber suspensions are mixed with means for increasing the internal hydrogen bonds.

Preferably, the pulp suspensions may contain alone or in combination: groundwood, BSKP, BHKP, manila hemp, cotton, china grass, ramie, lyocell, viscose. Due to the inventive design of the Schrägsiebformers it is possible to use fibers of length less than 25 mm, in particular less than 20 mm, preferably less than 15 mm, in the pulp suspensions. In one possible case of practice, the lamellae associated with the sections may be adjusted relative to one another to adjust the thickness of the layers of the fibrous web.

Preferably, as a further method step after the dewatering of the fibrous web, a hydroentanglement of the fibrous web can be provided.

The invention will be described in more detail below with reference to the drawings without loss of generality. In the figures: FIG. 1 shows a highly schematic side view of a skew wire former designed according to the invention. FIG.

A fibrous web is commonly produced by a machine for producing a fibrous web, as described in outline below. First, a fiber suspension is provided, the so-called substance, which in addition to water contains a certain content of solids, which in turn consists of fibers and of aggregates. According to a possible embodiment, the fibrous web is formed on a forming fabric using a headbox or former by applying the fiber suspension to the forming fabric. The Formiersieb is permeable to liquids and gases, which is why the water present in the fiber suspension by gravity (wire, Schrägsiebformer), by dewatering devices such as suction boxes or by introducing the suspension between two forming fabrics and subsequent dewatering under pressure from the fibrous web are removed and thereby both the fibrous web formed and the dry content of the fibrous web can be raised. After sheet formation and primary dewatering, the fibrous web is usually subjected to further moisture reduction in one or more presses and then in a variably designed dryer section until finally the roll-up of the finished fibrous web takes place. Thereafter, further processing steps such as slitting, brushing, calendering, etc., depending on the quality of the fibrous web.

According to the invention, the formation of a fibrous web in the form of a nonwoven web for the application of nonwoven products for the clothing and sanitary paper industry is considered. Nonwovens are used in particular in the area of so-called flushable wipes, ie for moist hygiene papers and similar cosmetic articles which are rinsed down after use. It is easy to see that there is a high demand in this area for environmentally friendly materials and their customer-friendly processing. Resource conservation and biodegradability are playing an increasingly important role in the production of such hygiene articles.

A limiting factor has hitherto been the fact that the fibers which are biodegradable, although they allow high-quality and cost-effectively producible products in terms of texture, softness, bulk, etc., but the breadth of use is limited by short fiber lengths. Synthetic fibers are easily manufactured in lengths over 40 mm, while natural or synthetic fibers based on natural raw materials seldom show fiber lengths over 25 mm. Accordingly, the durability and thus the applicability to the end customer is often unsatisfactory.

A remedy here should create multi-layer products, in which several layers produced separately from each other and joined together to improve the durability and applicability. However, this is expensive and therefore expensive.

According to the invention, a nonwoven web or fibrous web is now based on exclusively natural fibers and / or synthetic fibers of natural materials using a multilayer headbox. Such a multilayer headbox allows the application of differently composed fiber suspensions in one step on a forming fabric, which is designed and oriented so that the individual layers of the fibrous web successively applied successively and first dehydrated in this order. The layers of the fibrous web lie directly against each other and thus enter into connections within each layer as well as between the layers, which enable the use of short and shortest fibers and nevertheless the production of a very durable and high-quality product.

The headbox 1 for low solids content (0.01 to 0.1% solids content), which is shown very schematically in FIG. 1, is designed according to the invention for an inclined wire former. The principle of a headbox 1 for low solids content is known per se and therefore need not be explained in more detail here. The headbox 1, in the exemplary embodiment, three sections 2, which are each fed separately with material. The sections 2 are adjoined by optionally adjustable lamellae 3, which can be used to vary the layer thickness of individual layers 4 of the nonwoven web 5, which are applied to a forming fabric 6. The fins 3 are preferably flexible. As a result, the speed of the pulp suspension between the slats can be kept the same. This prevents mixing of the pulp suspension of the individual layers 4 after the slats and before dewatering. Furthermore, the slats 3 separate the respective streams. This can ensure that the individual layers 4 are drained one after the other and do not mix before dewatering. In the example shown, the slats 3 are the same length. However, they can also be designed with different lengths, for example, the pulp suspension in the individual layers 4 before the merging of the layers sequentially at least partially separated from each other to drain. This can improve the ply purity in the finished nonwoven web. For this purpose can be provided be that the Formiersieb facing blade 3 is shorter than the other blades. 3

In principle, however, there is a better connection of the individual layers with one another according to the invention (also known as the gap strength), than with the alternatively mentioned separate production methods of the individual layers.

The preferably structured forming fabric 6 can be woven or have a surface with further elevations produced, for example, by printing.

As can be seen from FIG. 1, when the fiber suspension of all portions of the fibrous web 5 simultaneously flows out, a first portion firstly reaches the forming fabric 6 to form a first layer 4.1 and is thus first dewatered. A second layer 4.2 follows directly thereafter and resting on the first layer 4.1, and then on this and on this resting in the embodiment, a third layer 4.3.

In Fig. 1 is further symbolically below the forming fabric 6, the fibrous web 5 leaving water shown. Not shown are other installations such as suction boxes or other drainage measures, which should support the removal of the water from the suspension.

The lamellae in Fig. 1 are movably mounted, so that the thickness of the layers 4.1, 4.2, 4.3 of the fibrous web 5 is adjustable. The division of the individual layers 4 may be different. It is conceivable to have a uniform distribution (in each case 33% per layer 4) or even gradations (eg 20%, 60%, 20% divided among the different layers 4). Furthermore, it is also possible to mix various of the fibers specified below in the individual layers 4. The illustrated, exemplary three-layer embodiment of the headbox 1 eliminates the disadvantages of the prior art, since previously known the individual layers 4 had to be made separately and presented here the solution Production in only one process step and an initial bond between the layers allows.

The fabric for the fibrous web 5 can be prepared with variable proportions of natural and synthetic fibers. 100% natural fibers are possible as well as 100% synthetic fibers based on natural materials, as well as any mixing ratio. Natural fibers may be present alone or in a mixture: groundwood, BSKP, BHKP, Manila hemp, cotton or Chinese grass, ramie or similar. Synthetic fibers made from natural materials may be used alone or in mixture: viscose or lyocell. Typical fiber lengths for natural fibers are 1 to 3 mm, for synthetic fibers commonly less than 25 mm, in particular less than 20 mm, or even less than 15 mm.

The distribution of the individual fibers can vary and vary depending on the requirements of the product. More natural fibers in layers 4.1 and 4.3 promote flushability. More Lyocell fibers in layers 4.1 and 4.3 increase the strength. In principle, a maximum possible use of natural fibers is to be preferred in order to reduce production costs. The use of natural fibers in an aqueous suspension forms an initial wet strength during hydrogen bonding production, which improves the running stability of the process without having to resort to chemical or other binders. However, the fabric may be suitably treated to increase the active surface area and enhance the tendency to internal hydrogen bonds.

Foliation in an aqueous suspension allows the use of fibers shorter than 10 mm, in particular shorter than 5 mm and even shorter than 1 mm. Shorter fibers increase the structural softness of the final product. Downstream of the headbox 1 according to the invention may be provided not shown, substantially known Wasserervernadelungsstrecke to reinforce the structure of the fibrous web 5. For basis weights of the fibrous web 5, which are in particular about 40 to about 90 g / m ^2, the fibrous web can be further dewatered in a press 5 Langnip the Schrägsiebformer 1 below. The nip length here is longer than 250 mm, preferably longer than 300 mm and in particular longer than 500 mm. In a further embodiment, the fibrous web 5 can be further dewatered to the inclined wire former 1, in a belt press forming a long-nip press. The fibrous web 5 can preferably be guided on the Formiersieb 6, in a looping over a suction roll. In the wrapping area of the suction roll, a vacuum can be applied. If the forming fabric 6 is a structured sieve configured as a structure imparting the fibrous web 5, then the structure of the fibrous web 5 is prevented from being displaced in the further course of the process. In the looping area, dewatering in a long-nip press is continued by a combination of pressure and air flow and if possible heat, either individually or in combination with one another. In the long-nip press, the pressure is generated by expressing the fibrous web in a long nip between a plurality of string-forming fabrics, such as forming fabrics, structured sieves, press felts or press belts. All fabrics are permeable to air and / or steam flow. The air flow can be between 100 and 300 m ³ / (min m ² ), preferably at 210 m ³ / (min m ² ). The air flow has ambient temperature. When heat is applied, this should be for hot air at temperatures between 50 ° and 250 °, typically 200 °, with steam of up to 2 kg of steam per kg of dry product, preferably 0.5 kg of steam per kg of dry product. In a preferred case, the string package which is laid, for example, around a suction roll or a curved suction surface, for forming a long nip, consists of a felt, a sieve, which is preferably a structured sieve, and a tensioned band. The fibrous web 5 is located between the felt and the screen, wherein the felt between the paper web and the suction roll or the curved suction surface is arranged. To the suction roll or to the vacuum is preferably applied from 0.25 to 0.6 bar, preferably 0.45 bar. The diameter of the suction roll, or twice the radius of the curved suction surface is between 500 and 1400 mm, preferably between 750 and 1200 mm. The wrap angle is between 90 ° and 180 °, preferably 100 ° to 120 °. The resulting dewatering pressure field can be increased by applying a tensile stress of more than 20 kN / m, preferably more than 30 kN / m, in particular more than 40 kN / m, to the tensioned band.

A typical string package that wraps around the suction roll could be a permeable ribbon, a textured forming mesh 6, followed by the fibrous web 5 and a felt (seen in the direction of air flow).

During the pressing operation in the elongated nip, the fibrous web 5 is protected by the structured forming fabric 6, so that bulk, that is the specific volume, and structure are maintained. The increase in the dry content of the fibrous web compared to the Saugkastenentwässerung according to the prior art is at least 10% or more. This leads to an increase in production capacity, reduces energy consumption and avoids the installation of additional drying components.

Since the drainage takes place on a felt, the moisture cross profile will be much more uniform than when dewatering with a suction box. The felt also supports the reduction of fiber loss rate. After dewatering, the fibrous web is transferred to a heated drying unit, preferably a TAD (through air drying) drying cylinder. The proposed concept can be operated with or without hydroentanglement. Additional hydroentanglement and perforation patterns can be created by high pressure water jets that improve the structural and surface properties of the fibrous web 5 as well as the fiber bond.

Claims

claims

1 .Schrägsiebformer for a wire section for a machine for producing a nonwoven web, comprising a Formiersieb (6) extending in the wire direction, at least in sections at an angle oblique to the horizontal, wherein in the oblique stretch section of the Formiersiebs (6) at least one multilayer headbox (1) is provided with a plurality of sections (2) through which a plurality of pulp suspensions for producing pulp layers (4) can be applied to the forming fabric (6) at the same time, characterized in that the plurality of sections (2) are provided with flexible lamellae (3) which are movable relative to each other ) and wherein the fibers of the plurality of pulp suspensions of synthetic fibers, which are made of natural materials and / or consist of natural fibers.

2. Schrägsiebformer according to claim 1, characterized in that the

Thickness of the fiber layers (4) is the same or different.

3. Schrägsiebformer according to claim 1 or 2, characterized in that the plurality of fiber suspensions are different in their solids content and / or in their composition of matter.

4. Schrägsiebformer according to any one of the preceding claims, characterized in that the solids content is 0.01 to 0.1%.

5. Schrägsiebformer according to claim 4, characterized in that the

Sheet formation of the fibrous web (5) is carried out in aqueous suspension to form hydrogen bonds.

6. Schrägsiebformer according to claim 4 or 5, characterized in that the fiber suspensions are added with means for increasing the internal hydrogen bonds.

7. Schrägsiebformer according to any one of the preceding claims, characterized in that the pulp suspensions contained alone or in combination: groundwood, BSKP, BHKP, Manila hemp, cotton, Chinese grass, ramie, lyocell, viscose.

8. Schrägsiebformer according to any one of the preceding claims, characterized in that the length of the fibers in the pulp suspensions or in the nonwoven web is less than 25 mm, in particular less than 20 mm, preferably less than 15 mm.

9. A method for producing a wet-laid nonwoven web using a Schrägsiebformers, in particular according to one of the preceding claims, characterized in that the method comprises the following steps: i) preparation of several fiber suspensions, ii) simultaneous feeding of the plurality of sections (2) of a multilayer Headbox (1), wherein each of the sections (2) is fed with one of the fiber suspension; iii) layering the fiber suspensions in layers (4) from the headbox sections (2) onto a forming fabric (6) to form a fibrous web (5); iv) successively dewatering the fibrous web (5) through the forming fabric (6), and using as fibers for the plurality of fibrous suspensions synthetic fibers made from natural materials and / or natural fibers.

10. The method according to claim 9, characterized in that are used as fibers for producing the nonwoven web fibers having a length of less than 25 mm, in particular less than 20 mm, preferably less than 15 mm.

1 1. A method according to claim 9 or 10, characterized in that the

Adjustment of the thickness of the layers (4) of the fibrous web (5) with the sections (2) associated with laminations (3) are adjusted relative to each other.

12. The method according to any one of claims 9 to 1 1, characterized in that as a further method step v) after the dewatering of the fibrous web (5) a water jet solidification of the fibrous web (5) is provided.

13. Nonwoven web produced by means of a method according to any one of claims 9 to 12, characterized in that the nonwoven web is made in multiple layers and contains fibers in a length of less than 25 mm, in particular less than 20 mm, preferably less than 15 mm, the alone or in combination are selected from: groundwood, BSKP, BHKP, Manila hemp, cotton, Chinese grass, ramie, lyocell, viscose.

14. Machine with a Schrägsiebformer according to one of claims 1

to 8, characterized in that the Schrägsiebformer a

Langnip is subordinated.

15. Machine according to claim 14, characterized in that the

Langnip is designed as a belt press.