SK14682002A3 - Method of adsorption of cationic and anionic polymers on the surface of particles and paper or nonwoven product containing such particles - Google Patents

Abstract

Method of producing a particle or group of particles intended for use in paper- and/or nonwovenmaking and having a coating of at least two, preferably at least three, outside each other located thin layers of alternating cationic and anionic polymers, at which the particle or group of particles is treated in consecutive steps with solutions of the alternating cationic and anionic polymers. The amount of the respective polymer to be added in each step is controlled by charge measurements of the treatment solution or a liquid containing the particles or group of particles and the polymer solution, after the treatment in each step in order to determine that substantially all polymer is adsorbed to the particle surface. It is also referred to a paper- or nonwoven product containing fibres and/or fillers produced according to the method. It is further referred to paper products containing increased amounts of wet strength agent and to tissue paper having improved wet strength.

Description

Technical field

The present invention relates to a method for producing a particle or group of particles for use in the manufacture of paper or nonwoven products having at least two, preferably three, thin layers spaced from each other from the outside, from cationic and anionic polymers in which the particle or group of particles is processed in successive steps with solutions of cationic and anionic polymers. It also relates to a paper or nonwoven product comprising such particles or groups of particles. It further relates to paper products having an increased wet strength agent and tissue paper with improved wet strength.

BACKGROUND OF THE INVENTION

The increased use of recycled fibers in papermaking and the use of components with lower binding properties such as mineral fillers causes an increased need for more effective wet and dry strength agents. Traditionally, two different methods have been used to add chemicals that improve strength, i. addition of wet chemicals in paper production or surface treatment with a sizing press. Wet addition is usually more efficient than surface coating based on kg of product used. In order to maintain the wet additions in the paper sheet, the wet step chemicals are almost exclusively cationic, and to reduce their sensitivity to dissolved and colloidal materials and due to the increased electrolyte concentration caused by increased closure of the systems, their cationic charge is usually increased. This in turn leads to a reduced adsorption to the state of saturation of the added chemicals into the fibers, leading to a reduced maximum effect of the added chemicals. This makes it necessary to develop new methods of applying chemicals that improve strength to paper and new chemical systems.

In addition, there is an increased need to improve the opacity of the resulting paper. Since the currently used strength agents negatively contribute to opacity, the need for new methods of increasing paper strength is thereby reinforced.

In this way, sizing presses could be used more intensively, but this would lead to a great reduction in production capacity and production efficiency, since the paper to be dried suddenly depends further on rewetting and insertion of the sizing press.

This causes a great need for new fiber processing pathways and other particles contained in the paper, such as filler particles, in the wet stage of the paper machine.

It is known to build thin multilayers of electroactive polymers on an electrostatically charged substrate for use in optics, e.g. for sensors, friction brakes, etc. This is described, for example, in Thin Solid Films, 210/211 (1992) 831-835 and in Thin Solid Films, 244 (1994) 806-809.

alternately immerse in dilute solutions by rinsing to remove residues of the previous polyion that did not bind to the support. The thickness of each layer described herein is 5 to 20 Anstr. There is no mention that particles such as fillers can reside in the pads.

Here, a polycation pad with processed or particles of fiber

U.S. Pat. No. 5,338,407 discloses a method of improving the dry strength properties of paper by adding anionic carboxymethyl guar or carboxymethylhydroxyethyl guar to the furnishings. The two components are supplied either mixed or separately. There is nothing to suggest that the processing is carried out under conditions such that the double layer is built on fibers with one component in one layer and the other component in the other layer.

US Patents 5,507,914 and 5,185,062 disclose methods for improving the drainage properties and paper retention by adding anionic and cationic polymers to the pulp. There is no mention that processing is carried out under conditions such that the double layer or multilayer has been formed on cellulose fibers with an anionic component in one layer and a cationic component in the other layer.

Double surface treatment of filler particles with anionic or cationic polymers is described in EP-A-0 850 879, WO 95/32335, US-A-4 495 245 and US-A-4 925 530. It is not mentioned that the processing is carried out under controlled conditions such that the double layer or multilayer is formed on cellulose fibers with an anionic component in one layer and a cationic component in the other layer.

International Application PCT / SE99 / 02149 discloses a method as set forth in the introduction, wherein particles or groups of particles having a coating of interactive polymers are produced from at least two, preferably at least three, thin layers spaced from each other from the outside. The particles or groups of particles are treated in successive steps with solutions of interactive polymers, and the respective polymer is added only in an amount at each step such that substantially all of the polymer adsorbs on the surface of the particle. This is accompanied by the removal of an excess of said polymer between each processing step alternately by supplying the respective polymer only in an amount at each step such that substantially all of the polymer adsorbs on the surface of the particles.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method according to the above and which suggests a way to ensure that each polymer for forming a respective layer on the surface of the particles or group of particles is supplied only in an amount at each step that substantially all of the polymer is adsorbed on the particle surface. . This has been accompanied by the fact that the amount of polymer to be delivered at each step is controlled by measuring the electrical charge of the treated solution or liquid containing particles or group of particles and polymer solution, after processing at each step to determine that substantially all the polymer adsorbed on the particle surface.

To determine the amount of cationic / anionic polymer adhered to the particle surface, a 2-potential particle or group of particles can be measured.

The particles or groups of particles may be of an optional type, but fibers, e.g. cellulose fibers, regenerated fibers and various types of synthetic fibers, and filler particles are preferred.

Alternative cationic and anionic polyelectrolytes, which are called amphoteric ions, are preferred as interactive polymers.

According to one embodiment of the invention, the particles are cellulosic fibers suitable for making paper and at least one of the polymers is a strength enhancer such as a wet strength and / or dry strength agent.

The invention also relates to a paper or nonwoven product comprising fibers and / or filler particles produced by the method of the invention described above. The term paper as used herein refers to all types of paper, such as tissue paper, graphic paper, coated cardboard, wiping material, and the like. The nonwoven material is of optional type.

The invention further relates to paper products comprising an increased amount of a wet strength agent and tissue paper having an improved wet strength.

Brief overview of the drawings

Fig. 1 shows the results of measurements of the Z-potential of cellulose fibers treated in successive steps with cationic and anionic polymers in the form of PAE (polyaminoamidepichlorohydrin) and CMC (carboxymethylcellulose).

Fig. 2 shows the result of measurements in the colloidal phase before and after washing the fibers in the experiment of FIG. 1.

Fig. 3 shows the tensile index of 30 gsm sheets of paper made from treated fibers versus the adsorbed amount of PAE.

Fig. 4 shows the Z-potential of the fibers after addition of PAE / CMC / PAE.

Fig 5 shows charge colloidal phase from measurements PCD po uploads PAE / CMC / PAE. Fig 6 shows index tensile strength dry against adsorbed amount PAE. Fig 7 shows index tensile strength wet against

adsorbed amount of PAE.

Fig. 8 shows the relative wet strength versus adsorbed amount of PAE.

DETAILED DESCRIPTION OF THE INVENTION

According to the present invention, particles or groups of particles, e.g. fibers or filler particles, are treated with alternating cationic and anionic polymers to build thin multilayers of interactive polymers on the particle surface.

The particles are treated in successive steps with solutions of alternating cationic and anionic polymers in which the processing time for each step is sufficient to form a layer with the desired molecular thickness. For particles or groups of particles having an anionic surface, such as in the case of cellulose fibers, the first layer must be a cationic polymer, and vice versa. By adding polymers in successive steps, where several layers are formed on the surface of the particles, it is possible to adsorb higher amounts of polymer on the surface of the particles than would be possible by adding them in one mixed step to form only one layer.

The addition is controlled so that substantially no excess amount of the respective polymer is added in each step, while substantially all of the polymer is adsorbed on the particle surface. This is done by measuring the electrical charge of the treating solution or liquid in which the treated particles or group of particles are contained. After adsorption of the allowable amount on the surface of the particle over a period of time, the electrical charge will be close to zero. Charge measurements were performed with current potential measurement, e.g. with a PCD device (Particle Charge Detector).

To determine the amount of cationic / anionic polymer adhered to the particle surface, the Z-potential is measured according to the method described below.

The method according to the invention for producing suitable multilayers is based on the electrostatic attraction between oppositely charged polyelectrolytes. By treating the particles in successive steps with a solution containing counterions of opposite charge, these polyions are absorbed on the surface of the particles, thereby forming multilayers of the intended species. In principle, all types of polyelectrolytes can be used.

According to one embodiment, a method is used to adsorb the strength enhancers in cellulose fibers used in papermaking. Since the cellulose fiber has an anionic surface, the first absorbed polymer will be a cationic polymer. This may be, for example, polyaminoamide-epichlorohydrin (PAE) or glyoxylated polyacrylamide (G-PAM). This layer will form the surface of the fiber that is cationically charged. An anionic polymer e.g. CMC (carboxymethylcellulose). The fiber surface is then changed to anionic again. Then another layer of cationic polymer etc. is added.

By such processing, a higher amount of strength-enhancing additives, e.g. PAE or G-PAM as would be possible with conventional techniques, resulting in improved strength properties of the paper produced.

It is also possible to create new types of surface modifications on particles or groups of particles by means of successive adsorption of thin films of the interactive polymers of the invention. For example, by treating fibers with successive layers of hydrophobic, charged polyelectrolytes, it would be possible to develop new types of hydrophobizing chemical agents for paper hydrophobization. It would also be possible to build intelligent surface layers on fibers that change the properties with temperature, pH, salt content and the like.

Other uses are ion-exchange fibers where membranes with ion-exchange properties on the fiber surface are provided, while fiber-reactive polymers reactive with each other as strength enhancers to provide durable bonding between the fibers and to produce high-swellable surface layers where the added chemical agents form swollen gel structures on the fiber surface for use in adsorbent sanitary articles. Another possible application is new types of printing paper fibers where adsorbed polymers change color when exposed to an electric, magnetic or electromagnetic field. Such polymers are currently available.

The fibers which are treated according to the process of the invention are of the optional type, both natural and synthetic fibers. Cellulose fibers are particularly suitable. However, it would also be possible to process the synthetic fibers, for example to form a more hydrophilic surface.

Groups or clusters of fibers or particles can also be processed by the method of the invention.

Examples of suitable anionic and cationic polyelectrolytes which can be used according to the invention are given below.

Anionic polyelectrolytes: anionic starch with different degrees of substitution, anionic guar, polystyrene sulfonate, carboxylmethylcellulose with different degrees of substitution, anionic galactoglucomannan, polyphosphoric acid, polymethacrylic acid, polyvynilsulfate, alginate, acrylic acid copolymers, acrylamide acrylic acid copolymers.

Cationic polyelectrolyte, cationic guar, cationic polyvinylpyridine and its polyvinylpyrrolidone, chitosan, cationic galactoglucomannan, starch, polyvinylamine,

N-alkyl derivatives, alginate, modified polyacrylamides, polydiallyldialkyl, cationic amidamines, condensation products between dicyanodiamides, formaldehyde and ammonium salt, reaction products between epichlorohydrin, polyepichlorohydrin and ammonium, primary and secondary amine-amine or di-amine-formed amines or polymers , polyethylenimines and polymers formed by the polymerization of dialkylaminoalkylacrylamide monomers.

Example 1

The polymers used during the tests are listed in Table 1 below

Title polymer contractor S. S. * viscosity (MPas) Kenores 1440 Polyaminoamidepichlorohydrin (PAE) EKA Chemicals Parez 631 NC Glyoxylated polyacrylamide (GPAM) Cytec Industries Cekol 50,000 g Carboxymethylcellulose (CMC) Metsä foods fibers 0.78 7200 (2%) horses.) Finnfix BW 04-06 ^: 100-700 (4% horse.)

'N. = degree of substitution

Prior to use, PAE and G-PAM were dissolved in deionized water to 10 g / L. In deionized water, various CMCs were dissolved by dispersion using a hand mixer, to appropriate concentrations of 5 to 10 g / l depending on viscosity.

The pulp used was dried completely bleached TCF, Celeste 85, from SCA Strand. The pulp was milled to 25 ° SR and diluted with drinking water to a concentration of 3 g / l. The pH during the experiments was 7.5 and the conductivity was determined to be 1200 μδ / οιυ using NaCl.

Three, four, five layers of alternating layers of PAE and CMC were formed. Addition of excipients was controlled by Z-potential electric charge measurement and PCD instruments. In some assays, G-PAM was used instead of or together with PAE. The order of addition is shown in Table 2 below.

Table 2

Added (mg / g) An exam PAE CMC PAE CMC PAE G-PAM CMC PAE G-PAM 1 20 20 20 20 20 2 15 7 30 4 15 3 15 4 15 4 15 4. • 30 5 7 2 7 6 7 2 10 7 7 2 15 8 5 1 5 1 5 9 2 7 2 7 10 7 2 7 11 7 2 7 12 7 2 7

Adsorption times for reagents were 10 min.

Preparation of the furnishings

In experiment 1, the amount of PAE and CMC added was in a significant excess, 20 mg / pulp. The pulp was then dewatered, washed with deionized water and re-dewatered between each step to remove excess PAE and CMC. This was repeated until five layers that started and ended with PAE were formed, see Table 2 above.

In experiments 2 to 12, the levels of PAE and CMC were gradually optimized to more realistic levels. Both the third, fourth and fifth layers were formed, see Tab. 2. Reagent addition was carried out without a washing step and was always controlled by charging the charge with the Z-potential of the PCD instruments. Three experiments using G-PAM instead of or together with PAE were performed to evaluate another strength enhancer: wet using a multilayer technique.

Sheet preparation mg / cm ² sheets were created in a dynamic sheet making machine. The leaves were formed by compression and then dried under tension. Two sheets of each sample were formed and then compressed to two different densities at approximately 350 and 450 kg / m ³ . Finally, the leaves were irradiated for 10 minutes at 105 ° C. The tensile stress was then interpolated to a density of 400 kg / m ² . Determination of charge

Determination of fiber charge using a Z-potential instrument

The Z-fiber potential was measured with a flow potential measuring device (Magendans SZ2, from Mutek) [Penniman, JG, Comparison of Pulse Streaming Measurement and Mobility Measurement. , 1992 75 111-115 and Jaycock, M J.: Assumptions Made in Measurement of Zeta-Potenital by Streaming Current / Potential Detectors (Assumptions derived from Potential Measurements with Alternating Current / Potential Flow Detectors) Paper Technology, 1995 36 35- 38.19,20;

Barron, W., et al., Colloids and Surfaces, 1994 88

129-139; Sanders, N.D. and J.H. Schaefer, Comparison of wet-end papermaking chargé-measuring techniques in kraft and groundwood systems (Comparison of charge measurements for wet paper production in kraft paper and wood pulp.) Tappi Journal, 1995 78 142-150.

The potential is measured between two electrodes, one sensing electrode located near the fiber layer that is formed when pressed against the sensor, and the other electrode being a circular electrode located at the bottom of the fiber layer. The conductivity is then measured between the two electrodes and the calculated Z-potential (zeta) ^{1 value is given} . ·,

Determination of colloidal charge using PCD

Mutek's PCD 03 (Particle Charge Detector) measures the difference in voltage caused by the movement of a charged medium, e.g. colloidal substances in white water. High molecular weight polymers and colloidal materials bind to the Teflon surfaces of the instrument. The oscillating piston moves and raises the potential difference that is detected [Jaycock, M.J., Assumption made in the measurement of zetapotencial by streaming current / po.tential. detectors (Assumptions derived from z-potential measurements with AC / potential flow detectors) Paper Technology, 1995 36 35-38; Barron, W., et al. Colloids and Surfaces, 1994 88 129-139 and Sanders, N.D. and J.H. Schaefer, Comparison of wet-end charge-measuring techniques in kraft and groundwood systems (Tappi Journal, 1995 78 142-150, 20-22).

The results are reported as the charge in / equivalents / l, calculated from the amount of reference polymer required for zero charge titration. Colloidal phase charge is measured with PCD.

Expression of tensile strength

Expression of the tensile strength of the sheets was performed according to SCAN standards P44: 81 for wet tensile strength. For wet tensile strength, the test samples were tested according to SCAN P 58:86. The deviation from these standards was that the thickness of the test samples was 15 mm. The wetting time of the samples prior to the tensile strength test was 15 s. Tensile strength results are given as geometric mean values of the longitudinal and transverse directions. CD

- Nm / g.

density

Analysis of sheet strength agents

Total nitrogen content

PAE and G-PAM leaf adsorption was analyzed by measuring total leaf nitrogen. The method is flash-based and is called Dumas Total Nitrogen Analysis and measurements were performed on a Carlo Erba Instrument NA 1500 from CE Termo Quest. The manual was supplied with the instrument.

Ion exclusion chromatography

In some PAE and G-PAM assays, leaf adsorption was analyzed by ion exclusion chromatography.

A 1 g sample of paper was hydrolyzed with 1.0 M NaOH. Hydrolysis was performed at 100 ° C for 24 hours. The PAAE resin was then hydrolyzed to DETA and adipate (see formula below). The solution was neutralized with an ion exchanger and the resulting adipic acid was analyzed by ion exchange chromatography. The wet strength resin was processed and analyzed in the same way to calculate the amount of adipic acid in the respective resin. The result was then used to calculate the amount of PAE resin in the paper.

Ion exclusion chromatography was mainly used to analyze weak inorganic and organic acids. The chromatography column was packed with a stationary phase consisting of sulfonated polystyrene / divinylbenzene deposited on a cation exchanger. Depending on the degree of crosslinking of the polystyrene / divinylbenzene resin, various organic acids could diffuse to a stationary phase to a greater or lesser extent. This mechanism, along with ion exchange, was used to chromatographically separate organic acids from solution.

Suppressed conductivity was used for detection. The equipment used for the analysis is described below:

Columns: 2x Dionex ICE-AS1 columns in series Suppressor: Dionex AMMS-ICE

Detector: Dionex PED (Conductivity Mode)

Eluent: 1.0 mM heptafluorobutyric acid; 0.8 ml / min

The working range for the method was 0.01 to 1% in paper (calculated as dry PAE resin) and the relative standard deviation for the paper sample with 0.3% PAE (dry resin) is 3.8.

Test 1

In Test 1, both PAE and CMC were added in excess according to the order of addition expressed in Table 2. This was done to ensure fiber saturation. During this test, Z-potential and PCD measurements were performed to control polymer adsorption and polymer desorption during the wash step.

Fig. 1 describes the Z-potential of the fibers during Test 1, before and after washing the fibers. As can be seen, the Z-potential is not greatly affected by fiber washing. A small decrease in the Z-potential was observed when washing the PAE-treated fibers and a small increase in the washing of the CMC-treated fibers, which is believed to be due to the desorption of the reagent during the wash step.

Fig. 2 shows the results of colloidal phase charge measurements (PCD measurements) during Test 1, before and after the fiber wash. Fig. 2 shows that when PAE / CMC is added in excess, a large amount of the polymer added remains in the colloidal phase instead of adsorption on the fibers. This excess is removed in the washing step.

Fig. 3 shows the wet tensile index of the leaves relative to the adsorbed amount of PAE. At five layers, the tensile index has stabilized, although PAE adsorption has increased. The explanation for this phenomenon is not clear. However, it is clear that the amount of PAE on the fibers can be increased by the rupturing technique. Using a single addition point, approximately 11 mg / g of PAE can be adsorbed onto the fibers. Using 3 layers

adsorbuj e more than 20 mg / g PAE resulting in tensile strength 50% higher. index Fortress i in strength for drought showed a similar trend as an index strength in strength for wet, but as expected,

the dry strength increase is not as high as the wet strength increase. ¹ _;

Tests 2 to 12

In these assays, different amounts of PAE / CMC were added and the Z-potential and colloidal phase charge were measured. These results of some of these measurements are shown in FIG. 4 and 5. Corresponding images to add in the fourth or fifth layer show the same trends as e.g. increase with PAE addition and decrease with CMC addition.

As shown in FIG. The 5 charge in the colloidal phase moves around zero charge, indicating that adsorption

The PAE / CMC on the fibers is almost complete, i. there is not much reagent left in the aqueous phase. The deviation from the zero charge should preferably not exceed ± 5 με ^ / 1, more preferably + 2 / xeq / l.

In FIG. 6 shows the dry tensile index versus the adsorbed amount of PAE in which e.g. 7 / 27-10-15 means 7 mg / g PAE, 2 mg / g CMC, then 7, 10, 15 mg / g PAE in the third layer. In the tests, the highest dry tensile index was achieved at relatively low adsorbed amounts of PAE. At approximately 5 mg / g, the strength stabilized.

In FIG. 7 shows the wet tensile strength index versus the amount of adsorbed amount of PAE.

Fig. 8 shows the relative wet strength versus adsorbed amount of PAE. Fig. Figures 7 and 8 show that the wet tensile index and relative wet strength are stabilized, but do not appear to fully reach the highest level. As mentioned above, the dry draft index begins to stabilize at a level of 5 mg / g adsorbed amount of PAE. The wet tensile index is stabilized, but at higher levels of PAE adsorbed. A maximum relative wet strength of 40% is achieved.

However, absolute values are also very interesting. Using a multi-layer technique, a wet tensile index of almost 30 Nm / g is achieved. Normal laboratory sheets of 65 g / m ² terminate at approximately 10 Nm / g.

When studying FIG. 6-8 it appears that 3 layers are sufficient to achieve maximum strength in the method used. With three layers almost the highest strength levels could be achieved. However, this may vary for other types of agents and / or other types of particles such as cellulose fibers.

In tests using G-PAM instead of or together with PAE, essentially the same effect as that achieved with PAE was obtained. The wet tensile index was slightly lower when using G-PAM compared to PAE, while in some cases a higher dry strength was obtained. The order of addition using PAE and G-PAM is likely to affect the outcome, e.g. the adsorption of the strength enhancing agent was higher when starting with PAE than G-PAM.

Tests have shown that charge measurements using PCDs and Z-potential measuring instruments provide good control of polymer addition. The multi-layer technique provides an increased amount of agents that adsorb on the fibers, helping to recover e.g. increased strength to a certain level.

In a continuous process, such as paper making, the amount of polymer added is preferably controlled and determined by potential and PCD measurements after each addition of polymer at each step at the start of the process. These amounts were then used in the process. The Z-potential and PCD measurements are preferably performed just behind the headbox during the process. For example, the addition of the first polymer is carried out in the pulper, and the other polymers are then added at various stages of the wet stage of the paper machine.

In the examples above, the addition of strength enhancers to the cellulosic fibers is only described in paper making. However, the invention can be used for the subsequent adsorption of thin films of different types of alternating cationic and anionic polymers on the fiber surface or other types of particles or groups of particles to build thin multilayers of interactive polymers on the particle surface.

By adding polymers in successive steps and forming multiple layers on the particle surface, it is possible that higher amounts of polymer are adsorbed onto the particle surface than is possible by adding them in one step to form only a single layer. With respect to wet strength agents such as PAE and G-PAM, it is possible by the method of the invention to produce paper and nonwoven products containing at least 1.5, preferably at least 1.7, more preferably at least 2.0, and even more preferably at least 2, These values refer to the amount of wet adhesion to the fibers and measured according to the total nitrogen method described above. In some laboratory tests, up to 3.8% of the wet strength enhancing agent adhered to the fibers (Figs. 7 and 8).

most preferably at least 2.5% of a wet strength enhancer

This also means that it is also possible with the method of the invention to produce tissue paper based on cellulose fibers to which no other type of fibers, such as synthetic reinforcing fibers, has been added, the paper having a ductility index of at least 6.5, preferably at least 7, 0 and most preferably at least 7.5 Nm / g. In this regard, the term tissue paper does not include materials that exhibit wet rolling. These values relate to the final tissue paper produced on real paper machines. Fig. 7 shows products made in the laboratory where higher strength values are commonly found. In finished paper products manufactured on actual paper machines and with subsequent processing such as creping, converting, etc. the strength values dropped.

This is shown in the results shown in Table 2. 3 below, which shows strength measurements on two different wet strength tissue paper. Number 1 is a tissue paper used as wipes sold by SCA Hygiene Products AB under the M-Tork brand and having the following composition: 33 wt. CTMP and 67 wt. kraft pulp of softwood.

It contains about 0.7 wt. PAE. Number 2 is paper made from the same pulp type as number 1, wherein the cellulosic fibers were processed in successive steps according to the invention with two PAE layers, one G-PAM layer and two CMC layers. From these results it can be seen that tissue paper no. 2 shows improved strength properties. Further, the papers tested contained a mixture of CTMP and softwood kraft pulp. Even higher values can be expected for papers containing higher amounts or only containing softwood kraft pulp.

Table 3

sample 1 (ref.) 2 (invention) Density g / m ² 24 21 Thickness 2kPa μτα 154 162 Volume 2kPa cm ³ / g 6.4 7.7 Strength. tensile MD, dry N / m 242 438 CD Tensile Strength in drought N / m 223 340 Tensile index ΊMDCD dry Nm / g 10 18 MD expansion% 28 37 CD Expansion% 4.9 4.6 Extensibility λ / MDCD% 11.7 13.1 Work to interrupt MD J / m ² 39 78 Work to interrupt CD J / m ² 7,983 13.63 Work index on interruption MD MDCD J / g 0.7 1.6 Tensile strength MD for wet N / m 102.9 206.8 CD Tensile Strength in wet N / m 60.8 125.8 JMDCD Wet Tensile Index Nm / g 3 8 Relative strength for wet % 34 42

Table 4 shows the results of measurements to determine the amount of PAE strength enhancer in some commercially available woven products and in tissue paper produced according to the invention. Sample A is a tissue paper produced according to the invention corresponding to test sample no. 2 in Table 3.

Sample B is tissue paper manufactured by Fort James and sold under the trade name Lotus Profes. Sample C is tissue paper manufactured by Procter and Gamble and sold under the trade name Bounty. Sample D is tissue paper manufactured by Metsä Särla and sold under the trade name Katrin Cleany.

The amount of PAE in the various tissue papers was measured by the ion exchange chromatography described above and yielded the amount of PAE adsorbed on the fibers. The usual amount of PAE or other wet strength agent added to the furnish is given as a% of wet strength agent solution added to the fiber weight. Wet strength agents are sold as solutions containing 6-25% active ingredient. By the amount of the strength enhancing agent is meant the amount of active ingredient adhered to the fibers. Table 4

sample A (invention) B (ref.) C (ref.) D (ref.) number PAE (% by weight) 2 0.45 1.2 0.7

As can be seen from these results, the paper A produced according to the invention contained significantly higher amounts of PAE than the conventional wet strength products tested.

Claims (8)

PATENT CLAIMS A method for producing a particle or group of particles for use in the manufacture of paper and / or a nonwoven product having a coating of at least two, preferably at least three, thin layers positioned outside each other from alternating cationic and anionic polymers in which the particle or the group of particles is treated in successive steps with alternating cationic and anionic polymer solutions, characterized in that the amount of the respective polymer that is added in each step is controlled by measuring the charge of the treating solution or the liquid containing particles or group of particles and the polymer solution, during and / or after treatment at each step to ensure substantially complete adsorption of the polymer to the particle surface. The method of claim 1, wherein the potential of the particles or groups of particles is measured during and / or after treatment in each step to determine the amount of cationic / anionic polymer adsorbed on the particle surface. The method of the particle is a fiber. 1 or 2, characterized in that: The method of claim 3, wherein the fiber is a cellulose fiber. The method of claim 3, wherein the fiber is a synthetic or regenerated fiber. Method according to claim 1 or 2, characterized in that the particle is a filler particle, a coating particle or another type of particle used in papermaking. Method according to any one of the preceding claims, characterized in that at least one of said polymers is a strength enhancer used in the manufacture of paper, such as a dry and / or wet strength agent. Method according to any one of the preceding claims, characterized in that in a continuous process of subsequent adsorption of thin layers of interactive polymers on the surface of particles or groups of particles, the amount of the respective polymer added in process. each step down on the early 9. Paper or nonwoven product, characterized the because of it comprises fibers, filler particles or a method according to any one of the claims other particles 1 to 8. made 10. Paper or nonwoven product, characterized the because of comprising fibers, filler particles or other particles having at least three thin layers disposed on the outside of each of the alternating cationic and anionic polymers and further comprising at least 1.5, preferably at least 1.7, more preferably at least 2.0 %, even more preferably at least 2.2 and most preferably at least 2.5 wt. increasing agent ,. evnosť '. wet. Paper or nonwoven product according to claim 10, characterized in that the wet strength agent is a cationic polyelectrolyte such as polyaminoamidepichlorohydrin and / or glyoxylated polyacrylamide. 12. Tissue paper based on wood pulp containing no other fiber types, such as synthetic reinforcing fibers, characterized in that it contains three thin layers placed on the outside of each of the alternating cationic and anionic polymers and has a tensile index when wet, at least 6.5, preferably at least 7.0, and more preferably at least 7.5 Nm / g.