GB2381270A

GB2381270A - Regenerated cellulose fibres treated with metal ions

Info

Publication number: GB2381270A
Application number: GB0125670A
Authority: GB
Inventors: Thomas Jaschinski
Original assignee: SCA Hygiene Products GmbH
Current assignee: Essity Germany GmbH
Priority date: 2001-10-25
Filing date: 2001-10-25
Publication date: 2003-04-30
Anticipated expiration: 2021-10-25
Also published as: DE10239770A1; GB0125670D0; GB2381270B

Abstract

Regenerated cellulose fibres, treated with metal ions, the metal being selected from transition metals of the groups 4 (Ti, Zr, Hf), 5 (V, Nb, Ta), 6 (Cr, Mo, W), 7 (Mn, Tc, Re), 8 (Fe, Ru, Os), 9 (Co, Rh, Ir), 10 (Ni, Pd, Pt), zinc or aluminium, respectively, or combinations thereof, preferably with zirconium or aluminium. The present invention also relates to a planar fibre-based product, in particular paper or non-woven such as tissues, that contain the metal ions-treated regenerated cellulose. This metal ion treatment confers a considerable increase in wet and/or dry strength in the planar fibre-based product. This improvement can be achieved without prior chemical modification of the fibres, <I>e.g.</I> by oxidation.

Description

REGENERATED CELLULOSE FIBRES TREATED WITH METAL IONS AND PRODUCTS MADE THEREFROM DESCRIPTION The present invention relates to regenerated cellulose fibres treated with metal ions and products made there from.

BACKGROUND OF THE INVENTION Regenerated cellulose fibres have been produced for more than 100 years by the viscose and cuprammonium processes, wherein the cellulose chains are dissolved in a derivitized form in a spinning solution, before this solution is extruded from spinnerettes into a regenerated bath.

More recently, the regeneration of cellulose without derivitization in suitable solvents has been explored and attracted much attention. This type of generated cellulose is called"Lyocell". Lyocell is an accepted generic term for fibre composed of cellulose, precipitated from an organic solution in which no substitution of hydroxyl groups takes place and no chemical intermediates are formed. (This name has been accorded by BISFA, the international bureau for the standardization of man-made fibres. By an organic solvent, BISFA means a mixture of an organic chemical in water.) Typically, amine oxides, in particular NMMO, are used as solvent for the production of Lyocell fibres. To name only a few representative examples of patents dealing with this technique, US 4,142, 913; US 4,144, 080; US 4,211, 574; US 4,246, 241; US 4,416, 698; US 5,252, 284; US 5,417, 009; US 4,426, 248; US 4,145, 532 and US 4,196, 282 should be cited.

Regenerated cellulose fibres, in particular Lyocell, are primarily used in the production of textile materials or nonwovens. They are much less frequently used in the production

Pappe, Zellstoff und Holzstoff/vol. 3/Physikalisch- technologische Prüfung der Papierfaserstoffe, pp. 86-87, Springer-Verlag, ISBN 3-540-55896-9).

The initial wet strength originally characterized the strength after sheet formation, and particularly refers to the strength of the initially formed moist paper web at the time of the first free transfer, e. g. from the screen section to a subsequent press section.

More recent prior art defines initial wet strength more broadly than earlier prior art. This definition essentially acts as a parameter for characterizing the strength behaviour of remoistened paper, paper products, tissue paper and tissue products. It is ascertained as the tensile strength of paper soaked over a specific period of time.

In this way, WO 97/36052 and US 5, 760, 212 do indeed define the initial wet strength by means of the normal wet strength determination employed in comparable measuring techniques.

Yet the so-called initial wet strength here corresponds to the wet strength of a sample (test strip) from a test sheet exhibiting a predetermined basis weight and produced under standardized conditions, calculated-after previously soaking the test strip-using a standardized tensile testing device under standardized test conditions.

In addition to the initial wet strength, the aforementioned documents introduce and use the terms"temporary"and "permanent wet strength as further criteria for evaluating the strength of a product after it has been remoistened (wet strength) and hence as criteria for its suitability in everyday practice (for example, the dissolving properties of toilet paper after it has been used in order to avoid clogging up the pipes). The soaking duration and decrease in wet strength over time are used in these documents as criteria to

clogging up. At the same time, toilet paper must not immediately lose its strength properties during use, i. e. whenever it has just briefly come into contact with the moisture from excrement.

To describe the strength properties of paper, the prior art therefore often draws a distinction between a paper's"dry strength","initial wet strength","temporary"and"permanent" wet strength. This also applies to tissue paper and tissue products.

Dry strength is generally determined in a similar manner, in the case of paper usually based on DIN EN ISO 1924-2, Paper and Board, Determination of properties under tensile load.

Part 2: method at a constant rate of elongation, April 1995, (ISO 1924-2: 1994). In the case of tissue paper and tissue products, tests are performed on the basis of DIN EN 12625- 4, Tissue Paper and Tissue Products-Part 4: determination of width-related breaking strength, elongation at break and the tensile energy absorption, January 1999.

The term"initial wet strength"was originally used just to characterize pulps for paper production, such as ground wood pulp, but was later extended to chemical pulp. The initial

wet strength is calculated on a 100 g/m2 test strip produced on the Rapid Köthen device in accordance with German Zellcheming Code of Practice VI/6.

Similarly, the initial wet tensile strength index, initial wet tensile stretch behaviour and initial wet-strength energy absorption index of a wet-pressed laboratory sheet are calculated in accordance with SCAN M 11 and SCAN M 12, with the difference that in these instances, the test strips of the obtained laboratory sheets are tested according to the normal methods of strength testing by means of an electronic tensile testing machine, without needing special-purpose testing equipment (see Werner Franke (editor), Prüfung von Papier,

This is taught, for example, by GB-1,385, 894 that relates to a method of increasing the strength of fibrous cellulosecontaining materials by addition of zirconium compounds.

JP-A-63-211399 teaches the addition of a zirconium compound to a suspension of zirconia fibres and cellulose fibres in the case of wet paper making. The resultant zirconia paper ply is soft and is easy to handle as packaging material.

According to JP-A-6-17399, a zirconium compound (preferably ammonium zirconium carbonate (AZC) ) is added to a pulp suspension in order to reduce the adhesion of accompanying viscous components to the paper machine and to improve its operation, as well as to produce micro projections on the surface of the base paper, thereby improving gravure printing properties without lowering the inter-ply strength.

SU-A-1 268 649 and SU-A-1 268 648 disclose a crosslinking agent based on a water-soluble, hydroxy-containing polymer, e. g. starch or carboxymethylcellulose and a water-soluble zirconium salt which, in combination with polyacrylamide treatment, increases paper's mechanical strength.

Modified techniques for increasing the strength of paper in the wet state are taught in the following applications filed by the Procter & Gamble Company: WO 97/36051, WO 97/36053, WO 97/36037, WO 97/36054 and WO 97/36052. These applications teach the use of aldehyde-containing additives or derivatives in combination with polyhydroxy compounds to generate interfibre bonds increasing the wet strength. The five aforementioned applications express the assumption that the achieved temporary wet strength is attributable to the formation of hemi (acetal) bonds between the hydroxy groups of the cellulose and the generated aldehyde functions, which bestow a higher strength upon the products than pure hydrogen bridges, but which break up relatively quickly upon contact with water.

differentiate between initial, temporary and permanent wet strength.

There are various techniques for increasing the wet strength of paper made from common pulps that have already been in use for some time.

One technique prevents the water from reaching and breaking up the hydrogen bonds, e. g. by applying a water-repellent material to the fibres. The second approach is to provide the paper with additives or reagents that promote the formation of inter-fibre bonds during production itself by addition into the substance.

To increase the wet strength according to the second technique, poly (ethylene imines), polyamide epichlorohydrin resins and urea or melamine formaldehyde condensates are for example used as wet-strength agents. The use of such synthetic resins results in permanent wet strength. On the other hand, however, enhanced wet strength can also be achieved by addition of water-soluble starches or starch derivatives. This effect is nevertheless only temporary and decreases as soon as the starch derivative dissolves. Apart from the aforementioned additives, modified soluble cellulose derivatives are used as wet-strength agents. In this way, for example, the addition of carboxymethyl cellulose is usual as an additive besides the aforementioned polyamide epichlorohydrin resins.

To bond cellulose fibres together according to the second technique, thereby increasing the strength, US-5 873 979 teaches the reaction of the cellulose's hydroxy functions with a C2-C9 dicarboxylic acid.

A similar approach lies in the crosslinking of the hydroxy functions of the cellulose contained in pulp via metal atoms.

Many of the strength-increasing techniques described above require cumbersome process steps. Partially, these techniques also lead to insufficient strength increase.

Thus, it is one object of the present application to provide a regenerated cellulose, in particular Lyocell, which leads to a planar fibre-based product, such as paper or non-woven, showing excellent dry and/or wet strength properties.

It is a further object of the invention to provide a simple and efficient process for the production of this regenerated cellulose.

Further, it is an object of the present invention to provide planar fibre-based products, in particular, paper or nonwoven, comprising a regenerated cellulose and having excellent dry and/or wet strength properties.

SUMMARY OF THE PRESENT INVENTION This object is solved by regenerated cellulose fibres, which were treated with metal ions, the metal being selected from transition metals of the groups 4 (Ti, Zr, Hf), 5 (V, Nb, Ta), 6 (Cr, Mo, W), 7 (Mn, Tc, Re), 8 (Fe, Ru, Os), 9 (Co, Rh, Ir), 10 (Ni, Pd, Pt), zinc or aluminium, respectively, or combinations thereof, preferably with zirconium or aluminium.

The present invention also relates to a planar fibre-based product, in particular paper or non-woven, that contains the metal ions-treated regenerated cellulose.

Surprisingly, it has been found that the present invention leads in a synergetic manner to an increase of wet and/or dry strength, which could not be expected from prior art documents, such as GB-1,385, 894 relating to the treatment of papers with zirconium salts.

More recently, the applicant of the present application found that the wet strength and/or dry strength of paper or nonwoven can be increased by using a cellulosic fibrous material, wherein the C6 hydroxy groups of glucose units within the cellulose chain are oxidized to aldehyde and/or carboxy groups. A similar approach is disclosed in EP 1 077 285 Al and EP 1 077 286 Al. The present applicant has developed this technique further by crosslinking said aldehyde and/or carboxy groups by metal atoms, preferably the zirconium or aluminium, as described in WO 01/34903.

In comparison to numerous patent applications dealing with techniques for improving the strength of paper or non-woven made from common cellulosic materials, in particular pulp, only few examples of applications exist which focus on the strength of webs made from regenerated cellulose.

The already mentioned EP-A-0 574 870 proposes to extrude the amine oxide solution of cellulose through spinning holes having a section which is not circular but shaped, for example "Y-shaped", in order to improve the adhesion of the fibres to each other.

US 6,117, 378 aims at improving the further processing of Lyocell fibres by squeezing water-containing swollen filaments in order to generate flexible twists and other changes of the cross section shape of the filament and fibres.

US 6,042, 890 discloses a process for producing a strengthened fibre assembly wherein the fibre assembly is in contact with an aqueous solution of N-methylmorpholine-N-oxide (NMMO) at elevated temperature under specific conditions and subsequently, washing the fibre assembly.

generic term"Lyocell fibres"will often be used for these fibres. The wording"organic solution"also covers mixtures of organic solvents and water. Preferably, the organic solvent is a tertiary amine-oxide, in particular, N-methylmorpholineN-oxide (NMMO).

Preferably, the Lyocell fibres are thus obtained by a process comprising the steps of a) preparing a cellulose-containing solution in an organic solvent, preferably tertiary amine-oxide, optionally in admixture with water, more preferably NMMO, optionally in admixture with water, from a cellulose-containing raw material, and b) forming fibres by contacting this cellulose-containing solution with a coagulation bath containing a non- solvent for cellulose, in particular, water.

According to the invention, modified Lyocell processes as described in the Section"Background Art"can also be used.

In contrast to native cellulosic materials, such as pulp, the production of Lyocell fibres by the above spinning process leads to continuously formed and typically quite uniform, generally circular or oval cross sections, no crimp, and relatively smooth glossy surfaces. Therefore, they typically show a low inter-fibre adhesion, thus creating a strong need for improvements regarding the dry and/or wet strength properties.

According to the invention, there is no specific limitation regarding the Lyocell fibres which can be used. Further it should be understood that fibres having the same properties, but being sold under a different tradename, such as Tencel fibres produced by Accordis are equally suitable for the invention. Another example for"Lyocell"fibres in the sense of the present invention are fibers produced according to the

This improvement can be achieved without prior modification of the fibres, e. g. by oxidation as taught by WO 01/34903.

DETAILED DESCRIPTION OF THE PRESENT INVENTION REGENERATED CELLULOSE FIBRES TREATED WITH METAL IONS According to the invention, regenerated cellulose fibres treated with metal ions as indicated above are provided.

The wording"regenerated cellulose"fibres is used for fibres containing cellulose as its main component and being precipitated from a solution where the cellulose is present in derivitized or underivitized form.

The regenerated cellulose fibres can stem from a viscose process which is obtained by steeping cellulose in caustic soda to form an alkali cellulose. This is reacted with carbon disulfide to form cellulose xanthate, which is then dissolved in dilute caustic soda solution. After filtration and deaeration the xanthate solution is extruded from submerged spinnerettes into a regenerating bath of sulfuric acid, sodium sulfate, zinc sulfate, and glucose to form continuous filaments. The wording"viscose fibres"also covers modifications of this process.

The regenerated cellulose may also be of cuprammonium type.

In this process, the cellulose solution (in ammoniacal copper oxide solution) is forced through submerged spinnerettes into a solution of caustic soda or diluted sulfuric acid to form the fibres which are then decoppered and washed.

However, it is preferred to use regenerated cellulose fibres composed of cellulose precipitated from an organic solution in which no substitution of hydroxyl groups takes place and no chemical intermediates are formed, in contrast to the aboveindicated viscose and cuprammonium processes. Hereinafter the

treat with zirconium or aluminium ions, ammonium zirconium carbonate (AZC), zirconium acetate or Al2 (SO4) 3 are particularly suitable. The addition of metal ions to regenerated cellulose fibres has a positive influence on the dry strength of the paper or non-woven obtained, which becomes noticeable, e. g. in the form of a higher breaking length. The metal ion treatment of the invention also results in a substantial increase in the breaking length in the case of moist paper or non-woven and leads to an increase in relative wet strength.

The observed increase is much higher than could be expected from known metal ion treatments.

With regard to a homogeneous intermixture, the metalcontaining treatment agent is preferably added in a dissolved form, particularly in a polar solvent. The polar solvent is preferably a protic solvent, more preferably an aqueous solvent. The term"aqueous solution"as used herein shall not exclude that minor amounts of organic solvents are present in water. The treatment agent is preferably used in amounts leading, in the fibres obtained, to a weight ratio of metal (calculated as metal oxide, e. g. Zr02 or A1203/metal treated fibres (oven-dried) ) of 0.01. to 10 wt. %, greater preference being given to 0.01 to 3 wt. %, 0.01 to 2 wt. %, 0.05 to 1.5 wt. %, 0.1 to 1 wt. % in this order. (The term"oven-dried" refers to the determination of the dry content of fibrous material/pulp samples corresponding to DIN EN 20638).

The metal-containing treatment agent can be added at any suitable point during the production of the planar fibre-based product. Generally, it is preferred to add the metalcontaining treatment agent to a slurry, in particular an aqueous slurry of the regenerated fibres before they are further processed to the planar fibre-based product. It is also possible to treat the fibres after formation, e. g. after wet-laying and before drying during (tissue) paper production,

"Alceru"process, which also makes use of NMMO. A description of"Alceru"filaments is found for instance in"Technische Textilien"1994, page 37 ff.

Depending on the type of product (paper, for instance, tissue paper, or non-woven) for which the regenerated cellulose fibres are to be used, the fibre properties are selected in a manner known in the art.

Preferably, the fibres have an average length of 0.01 to 17 mm, in particular 0.5 to 5 mm. The linear density is preferably at least 0.1 dtex, in particular 0.1 to 3.5 dtex, more preferably at least 1.0 dtex, in particular 1.0 to 2.7 dtex.

Non-wovens require preferably an average length of at least 5 mm, in particular 5 to 15 mm.

For the paper production, fibre diameters and lengths as occurring in pulps can be used. Thus, for instance, preferred fibre length ranges from 0.5 to about 6.5 mm. It is also possible to combine shorter fibres (for instance, having an average length of 0.5 to 2 mm with longer fibres having an average length of more than 2 mm to less than 5 mm).

The above-described regenerated cellulose fibres are treated with metal ions.

Without being bound by theory, it is believed that the metal atom results in a covalent crosslinkage of the cellulose hydroxy groups which increases the strength of a product made of the regenerated cellulose, in particular Lyocell.

The treatment agent in use is preferably a water-soluble metal compound, particularly a water-soluble metal salt. More preferably, the metal salt is non-toxic and not coloured in a dry state or as aqueous solution. If the intention is to

PLANAR FIBER-BASED PRODUCT The present invention also relates to planar fiber-based products comprising the metal ions-treated regenerated cellulose according to the invention, preferably in the amount of at least 50 % by weight, in particular at least 80 % by weight, relative to the dry weight of the finished product.

The remaining proportion can, for instance, consist of other synthetic cellulosic materials, natural cellulosic materials, such as cotton linters or pulp fibres.

The wording"planar based-based products"relates to materials made from fibres and having a low thickness in comparison to length and width. They are preferably selected from paper, e. g. tissue paper or non-woven.

The German terms"Vlies"and"Vliesstoffe"are applied to a wide range of products which, in terms of their properties, are located between the groups, paper, paperboard, and cardboard on the one hand and the textile products on the other, and are currently summarized under the term"nonwovens" (see ISO 9092-EN 29092). The invention allows the application of known processes for producing non-wovens, such as what are called air-laid and spun-laid techniques, as well as wet-laid techniques.

Non-wovens may also be called textile-like composite materials, which represent flexible porous fabrics that are not produced by the classic methods of weaving warp and weft or by looping (knitting), but by intertwining and/or by cohesive and/or adhesive bonding of fibres, which may for example be present in the form of endless fibres or prefabricated fibres of a finite length, as synthetic fibres produced in situ or in the form of staple fibres. The nonwovens according to the invention may thus consist of mixtures

or shortly after dry-or wet-laying in the case of non-wovens. Further, the planar product may be produced in a usual manner and then treated in a dry state, for instance by submerging it into a solution of the treatment agent or by spraying the solution onto the product. It is also possible to use common coating techniques, such as applying by doctor blade, in order to treat a wet or dry paper web, in particular a tissue paper web with crosslinking metal ions.

It should be noted that any suitable technique known in the art for applying liquids to a web can be used for treating the planar fibre-based product, be it in a wet or dry state, with metal ions. Thus it is also possible to use printing techniques, which allow applying the metal-containing solution in a specific pattern. By means of printing techniques it is also possible to restrict the treatment to selected areas of the fibre-based planar product. Printing techniques therefore may result in a very efficient and economic use of the metal solution.

The treatment in a wet state may involve the advantage that the metal ions penetrate to a greater extent and thus contribute to the strength properties throughout the thickness of the treated product. The treatment of a dry paper, in particular tissue paper, can be used to focus the strength development on the surface of the treated product.

The metal ions treatment is preferably performed at temperatures of more than 0 to 360 C, particularly 5-99 C. For practical considerations, either room temperature is usually chosen, or the temperature level that is normally set in the production process of the paper or non-woven, whereby it need not be ruled out that the fibrous product is briefly overheated, as is usually the case when treating the surface of the planiform fibrous material product with a stream of hot flue gases.

selects a basis weight of 10 to 40 g/m2 per ply. The total basis weight of multiple-ply tissue products is preferably equal to a maximum of 65 g/m2.) The tensile energy absorption index is arrived at from the tensile energy absorption in which the tensile energy absorption is related to the test sample volume before inspection (length, width, thickness of sample between the clamps before tensile load). Paper and tissue paper also differ in general with regard to the modulus of elasticity that characterizes the stress-strain properties of these planar products as a material parameter.

A tissue's high tensile energy absorption index results from the outer or inner creping. The former is produced by compression of the paper web adhering to a dry cylinder as a result of the action of a crepe doctor or in the latter instance as a result of a difference in speed between two wires ("fabrics"). This causes the still moist, plasticallydeformable paper web to be internally broken up by compression and shearing, thereby rendering it more stretchable under load than an uncreped paper. Most of the functional properties typical of tissue and tissue products result from the high tensile energy absorption index (see DIN EN 12625-4 and DIN EN 12625-5).

One example of papers and paper products is represented by hygiene papers and hygiene products made therefrom, and which are e. g. used in personal grooming and hygiene, the household sector, industry, the institutional field in a wide variety of cleaning processes. They are used to absorb fluids, for decorative purposes, for packaging or even as supporting material, as is common, for example, in medical practices or in hospitals.

Hygiene paper primarily includes all kinds of dry-creped tissue paper, as well as wet-creped paper and cellulose or pulp wadding.

of synthetic fibres in the form of staple fibres and the regenerated cellulose according to the invention.

"Papers"are also planar materials, albeit essentially composed of fibres of a plant origin and formed by drainage of a fibrous-material suspension on a wire or between two continuously revolving wires and by subsequent compression and drainage or drying of the thus produced fibrous mat (cf. DIN 6730, May 1996). The standard restricts the range of mass per unit area (basis weight) for paper to a maximum of 225 g/m2.

The paper can be a packaging paper, a graphic paper or tissue paper. Preferably, the paper is a tissue paper.

Depending on the type of paper, the production process comprises also a sizing and/or smoothing step, along with the typical process steps of sheet formation, pressing, and drying described above.

It should be noted that throughout the description and the claims, depending on the context, the term"paper"or"non- woven"does not only refer to the raw material as obtained from the paper/non-woven machine, but also covers the corresponding further-processed products, since often there is often no strict borderline to distinguish the same. Further,

it should be understood that the term"paper", in particular, "tissue paper"or"non-woven", as used in the claims, extends to the corresponding products, which make use of raw paper, in particular raw tissue paper or raw non-woven.

Based on the underlying compatibility of the production processes (wet laying),"tissue"production is counted among the paper making techniques. The production of tissue is distinguished from paper production by its extremely low basis weight of normally less than 40 g/m2 per ply and its much higher tensile energy absorption index. (In processing inventive fibrous material to tissue paper, one generally

Paper can be formed by placing the fibres, in an oriented or random manner, on one or between two continuously-revolving wires of a paper making machine while simultaneously removing the main quantity of water of dilution until dry-solids contents of usually between 12 and 35 % are obtained.

Drying the formed primary fibrous web occurs in one or more steps by mechanical and thermal means until a final dry-solids content of usually about 93 to 97 %. In the case of tissue making, this stage is followed by the crepe process which crucially influences the properties of the finished tissue product in conventional processes. The conventional dry crepe process involves creping on a usually 4.5 to 6 m diameter drying cylinder, the so-called yankee cylinder, by means of a crepe doctor blade with the aforementioned final dry-solids content of the raw tissue paper (wet creping can be used if lower demands are made of the tissue quality). The creped, finally dry raw tissue paper (raw tissue) is then available for further processing into the paper product or tissue paper product according to the invention.

Instead of the conventional tissue making process described above, the invention gives preference to the use of a modified technique in which an improvement in specific volume is achieved by a special kind of drying within process section b and in this way an improvement in the bulk softness of the thus made tissue paper is achieved. This process, which exists in a variety of subtypes, is termed the TAD (through air drying) technique. It is characterized by the fact that the"primary"fibrous web (like a non-woven) that leaves the sheet making stage is pre-dried to a dry-solids content of about 80% before final contact drying on the yankee cylinder by blowing hot air through the fibrous web. The fibrous web is supported by an air-permeable wire or belt and during its transport is guided over the surface of an air-permeable rotating cylinder drum. Structuring the supporting wire or

The one-ply intermediate products originating from the papermaking machine and made of lightweight paper usually drycreped on a yankee cylinder by means of a crepe doctor are generally described as"tissue paper"or more accurately raw tissue paper. The one-ply raw tissue may be built up of one or a plurality of layers respectively.

All one-ply or multi-ply final products made of raw tissue and tailored to the end user's needs, i. e. fabricated with a wide variety of requirements in mind, are known as"tissue products".

Typical properties of tissue paper include the ready ability to absorb tensile stress energy, their drapability, good textile-like flexibility, properties which are frequently referred to as bulk softness, a high surface softness, a high specific volume with a perceptible thickness, as high a liquid absorbency as possible and, depending on the application, a suitable wet and dry strength as well as an interesting visual appearance of the outer product surface. These properties allow tissue paper to be used, for example, as cleaning wipes (paper wipes, windscreen cleaning wipes, kitchen paper), sanitary products (e. g. toilet paper), paper handkerchiefs, household towels, towels, cosmetic wipes (facials), as serviettes/napkins, bed linens or garments.

If tissue paper is to be made out of the regenerated cellulose according to the invention, the process essentially comprises a) forming that includes the headbox and the wire portion, b) the drying portion (for instance TAD through air drying], or conventional drying on the yankee cylinder) that also usually includes the crepe process essential for tissues, c) as a rule, the monitoring and winding area.

as bringing them together to form larger surrounding packaging or bundles. The individual paper ply webs can also be preembossed and then combined in a roll gap according to the foot-to-foot or nested methods.

EXAMPLES Test methods The following test methods were used to evaluate the regenerated cellulose according to the invention, as compared to regenerated cellulose which corresponds, but which has not been modified by metal ions treatment.

1) Producing the test sheets The test sheets (having a basis weight of approx. 80 g/m2) were made in accordance with the Rapid Köthen method (DIN 54 358-1, February 1981; see also ISO 5269-2: 1980). Before being tested in terms of physical properties e. g. by means of the tensile test, the thus-obtained test sheets were always conditioned for a duration of at least 12 hours in a standard climate at a temperature of (23vil) oc and a relative humidity of (502) % in accordance with DIN EN 20187, Paper, Cardboard and Pulp, a standard climate for pre-treatment and testing and a method of monitoring the climate and pre-treatment of samples, November 1993 (see ISO 187: 1990).

2) Initial wet strength (width-related breaking strength (wet) ) and breaking length (wet) The wet strength according to DIN ISO 3781, Paper and Cardboard, tensile test, determination of the width-related breaking strength after immersion in water, October 1994 (identical to ISO 3781: 1983), is herewith defined as initial wet strength of the fibrous material networks according to the invention, e. g. paper/tissue paper/non-woven.

belt makes it possible to produce any pattern of compressed zones broken up by deformation in the moist state, resulting in increased mean specific volumes and consequently leading to an increase in bulk softness without decisively decreasing the strength of the fibrous web.

Another possible influence on the softness and strength of the raw tissue lies in the production of a layering in which the primary fibrous web to be formed is built up by a specially constructed headbox in the form of physically different layers of fibrous material, these layers being jointly supplied as a pulp strand to the sheet making stage.

When processing the raw fibrous web or raw tissue paper into the final product, the following procedural steps are normally used individually or in combination: cutting to size (longitudinally and/or cross cutting), producing a plurality of plies, producing mechanical ply adhesion, volumetric and structural embossing, chemical ply adhesion, folding, imprinting, perforating, application of lotions, smoothing, stacking, rolling up.

To produce multi-ply tissue paper products, such as handkerchiefs, toilet paper, towels or kitchen paper, an intermediate step preferably occurs with so-called doubling in which the raw tissue in the finished product's desired number of plys is usually gathered on a common multi-ply master roll.

The processing step from the raw tissue that has already been optionally wound up in several plies to the finished tissue product occurs in processing machines which include operations such as repeated smoothing of the tissue, edge embossing, to an extent combined with full area and/or local application of adhesive to produce ply adhesion of the individual plys (raw tissue) to be combined together, as well as longitudinal cut, folding, cross cut, placement and bringing together a plurality of individual tissues and their packaging, as well

Six test strips at a time were measured, the result being indicated as an arithmetic mean.

The breaking length (wet) was calculated from the widthrelated breaking strength in accordance with the following formula (see TAPPI 494-96, Comment 9): RL= 102000 (T/R) where T is the initial wet strength in kN/m and R is the basis weight in g/m2 (in a standard climate) 3) Dry strength (width-related breaking strength (dry) ) and breaking length (dry) The dry strength was determined according to DIN EN ISO 1924- 2, Paper and Cardboard, determination of properties under tensile load. Part 2: Method at a constant rate of elongation, April 1995, (ISO 1924-2 : 1994).

In the case of tissue paper and tissue products, the test is performed in accordance with DIN EN 12625-4, Tissue Paper and Tissue Products-Part 4: Determination of width-related breaking strength, elongation at break and tensile energy absorption, January 1999.

The breaking length (dry) was calculated from the widthrelated breaking strength in accordance with the following formula (see TAPPI 494-96, Comment 9): RL= 102000 (T/R) where T is the tensile strength in kN/m and R is the basis weight in g/m2 (in a standard climate)

When experimentally checking the invention, the tensile test was accordingly performed by means of an electronic tensile test apparatus (Model 1122, Instron Corp. , Canton, Mass. , USA) with a constant rate of elongation of 10 mm/min using a Finch device. The width of the test strips was 15 mm. The strip length was about 180 mm. The free clamping length when using the Finch clamp was about 80 mm. The test strip was secured with both ends in a clamp of the test apparatus. The other end (loop) formed in this way was placed around a pin and treated at 200C with distilled water until complete saturation. The soaking period of the samples before tensile testing was fixed at 30 s. Six test strips at a time were measured, the result being indicated as an arithmetic mean.

To ensure that the wet strength of the samples has fully developed, the samples to be tested were always artificially aged before conducting the tensile test. Aging was effected by heating the samples in an air-circulating drying cabinet to (125 f1) C for a period of 10 min.

A similar approach applies to paper/tissue paper/non-woven products, modified only to the extent that the test strips to be examined were taken from the finished product itself or from the product made thereof and that they do not originate from a laboratory test sheet.

As regards tissue paper and tissue products, DIN ISO 3781 is replaced by DIN EN 12625-5 Tissue Paper and Tissue ProductsPart 5: determination of width-related wet load at break, January 1999. The strip width is then 50 mm, the free clamping length is shortened to about 50 mm, the depth of immersion of the loop formed by the test strip is at least 20 mm. The soaking duration (immersion time) is shortened to 15 s, the rate of elongation is set to a constant (50 2) mm/min, the measurement of the breaking strength is performed on the sample immersed in distilled water.

S. Goldmann GmbH & Co. KG, Bielefeld, Germany) based on the weight of oven-dried fibres (determined according to DIN 20 638) was added to the suspension.

Test sheets having a basis weight of about 80 g/m2 were produced from these zirconium-treated fibres according to the procedure described above, followed by measuring the porosity, the tearing resistance, the dry tensile strength, the elongation, the dry breaking length, the wet tensile strength, the wet breaking length, and the relative tensile strength (wet) according to the above-given test procedures. The results obtained are shown in Table 1.

Comparative Example 1 Example 1 was repeated with the sole difference that no metal ions were added to the fibres. Test sheets were produced in the same manner as indicated above and subjected to the same measurements. The results obtained are shown in Table 1.

Table 1

Sample Poros Tearin Tensil Elonga Break Tensil Break Rel. ity 9 e tion ing e ing tensil resist streng lengt streng lengt e ance ht, h, th, h, streng [ml/m dry [%] dry wet wet th, in] [mN*m/ [N/15m [m] [N/15m [m] Wet m] m] m] [%] Comp. E 5500 150 3, 63 0,81 324 0,06 5,4 1,7 x. 1 Ex. 1 5500 600 13, 49 0,69 1136 0, 67 56,4 5, 0 The above table shows that the present invention allows at least a 3.5 fold increase of dry breaking length to values above 1000 m with fairly small amounts of metal ions. The tearing resistance can be increased to more than 3-fold

4) Relative wet strength The relative wet strength (WS) was calculated as follows:

rel. WS = BSwet/BSdry where BSwet is the width-related breaking strength of the wet sample strip and BSdry is the width-related breaking strength of the dry sample strip, and these values were ascertained in the manner described above.

5) Elongation (in %) The elongation was determined according to EN-12625-4. The elongation represents the ratio of the length of a stretched sample strip at the breaking force to its length before stretching it under controlled conditions.

6) Tearing resistance according to Elmendorff The tearing resistance was determined according to Elmendorff using a test sheet according to the above Item 1 following a process described in DIN 53128.

7) Air permeability (porosity in ml/min) The air permeability was determined according to the Zellcheming Merkblatt V/26/75 ("Bestimmung der Luftdurchlassigkeit nach Bendtsen").

Example 1 30g Tencel"fibres (sold by"Accordis") were suspended in 2 1 deionised water. This fibre suspension was treated over 30 minutes in a disintegrator (produced by"Frank") in order to disintegrate fibre bundles. Then an aqueous solution of 1 wt.-% Bacote 20 (ammonium zirconium carbonate, available from

CLAIMS 1. Regenerated cellulose fibres which were treated with metal ions, said metal being selected from transition metals of any of groups 4-10, aluminium and zinc, and combinations thereof.

2. Regenerated cellulose fibres according to Claim 1, wherein the regenerated cellulose to be treated comprises fibres composed of cellulose, precipitated from an organic solution in which no substitution of hydroxyl groups takes place and no chemical intermediates are formed.

3. Regenerated cellulose fibres according to Claim 1 or 2, wherein the metal is zirconium or aluminium.

4. Regenerated cellulose fibres according to any of Claims 1 to 3, wherein the amount of metal ions (expressed as corresponding metal oxide) is from 0.01 to 10 weight%, based on the regenerated cellulose.

5. Regenerated cellulose fibres according to any of Claims 1 to 4, having a linear density of 0.01 to 3,5 dtex and an average fibre length of 0.01 to 17 mm.

6. Planar fibre-based product comprising the regenerated cellulose according to any of Claims 1 to 5.

7. Fibre-based product according to Claim 6, being selected from a paper or nonwoven.

8. Fibre-based product according to Claim 7, wherein said paper is a tissue paper.

9. A method of producing the regenerated cellulose fibres according to Claims 1-5, comprising the steps of:

values, thus reaching the values above 500 mN-m/m. Further, at least a 10-fold increase of the wet tensile strength to values above 0.5 N/15 mm (tensile strength) or above 50 m (breaking length) is observed. This increase of wet and dry strength properties could not be expected from GB-1, 385,894.

As seen from this document, at a weight percentage of about 1 % zirconium oxide in the treated paper comparable improvements in terms of both dry and wet tensile strength could not be obtained.

In contrast thereto, the inventive treatment with 1 wt.-% ammonium zirconium carbonate (AZC) leads to more than a 3-fold increase in terms of dry strength and more than a 10-fold increase regarding the wet strength.

Claims

Claims: 1. Regenerated cellulose fibres obtainable by treating precipitated regenerated cellulose fibres, without prior modification of the fibres by oxidation, with aluminium or zirconium ions in order to covalently crosslink the cellulose hydroxy groups.
2. Regenerated cellulose fibres according to Claim 1, wherein the regenerated cellulose to be treated comprises fibres composed of cellulose, precipitated from an organic solution in which no substitution of hydroxyl groups takes place and no chemical intermediates are formed.
3. Regenerated cellulose fibres according to Claim 1 or Claim 2, wherein the amount of metal ions (expressed in terms of the corresponding metal oxide) is from 0.01 to 10 weighty, based on the regenerated cellulose.
4. Regenerated cellulose fibres according to any preceding Claim, having a linear density of 0.01 to 3,5 dtex and an average fibre length of 0.01 to 17 mm.
5. Planar fibre-based product comprising regenerated cellulose fibres obtainable by treating precipitated regenerated cellulose fibres, without prior modification of the fibres by oxidation, with aluminium or zirconium ions in order to covalently crosslink the cellulose hydroxy groups.
6. Fibre-based product according to Claim 5, being selected from a paper or nonwoven.
7. Fibre-based product according to Claim 6, wherein said paper is a tissue paper.

<Desc/Clms Page number 27>

(A) providing regenerated cellulose fibres ; and (B) treating the fibres using a metal ions-containing agent, the metal being selected from transition metals of any of groups 4 to 10, zinc and aluminium.

<Desc/Clms Page number 28>

<Desc/Clms Page number 29>
8. A method for producing regenerated cellulose fibres as defined in any of Claims 1-4, comprising treating regenerated cellulose fibres, without prior modification of the fibres by oxidation, with zirconium or aluminium ions in order to covalently crosslink the cellulose hydroxy groups.