SE521591C2 - Method of preparing a particle having coating of interacting polymers and paper or nonwoven product containing the particles - Google Patents

Abstract

Method of producing a particle or group of particles having a coating of at least two, preferably at least three, outside each other located thin layers of interacting polymers, at which the particle or group of particles is treated in consecutive steps with solutions of the interacting polymers. Excess of the previous polymer is removed between each treatment step alternatively the respective polymer is added only in such an amount in each step that substantially all polymer is absorbed to the particle surface. It is also referred to a paper- or nonwoven product containing fibers and/or fillers containing particles or groups of particles of the mentioned kind.

Description

This means that there is a great need for new ways of treating fibers or other particles contained in the paper, such as filler particles, in the wet end of the paper machine. Treatment with a similar process as glue press may also be of interest if the quality of the paper produced thereby increases in a satisfactory manner, so that the above-mentioned disadvantages become less significant.

It is known to build up thin multilayers of electroactive polymers on an electrostatically charged substrate for use in optics, such as sensors, friction reduction, etc. This is described in Niin Solid Films, 210/211 (1992) 831-835 and in Thin Solid Films, 244 (1994) 806-809. The substrate is then dipped alternately in dilute solutions of a polycation or a polyanion with intermediate rinsing to remove residues of the previous polyion which are not bound to the substrate. The thickness of each deposited layer amounts to 5-20Å as described. There is no indication that the substrate being treated could be fibers.

US 5,338,407 describes a method for improving the dry strength properties of paper, adding to the stock an anionic carboxymethyl guar or carboxymethylhydroxyethyl guar and a cationic guar. These two components are added either in admixture or separately. However, there is no indication that the treatment takes place under such conditions that a double layer is built up on the fibers with one component in one layer and the other component in the other.

U.S. Patents 5,507,914 and 5,185,062, among others, describe methods for improving the dewatering properties and retention of paper by adding anionic and cationic polymers to the pulp. There is also no indication here that the treatment takes place under such conditions that a double or multilayer is built up on the pulp fibers with the anionic component in one layer and the cationic component in the other layer.

The object and main features of the invention The object of the present invention is to provide particles or groups of particles, in particular fibers and / or filler particles, in which the construction of the particle surface is controlled in a controlled manner and given the desired properties. This has been achieved in that the particle or particle group has a coating of at least two, preferably at least three, superimposed thin layers of polymers, which interact with each other by electrostatic forces, dispersion forces, hydrogen bonding or other type of interacting requirements.

The particles or particle groups can be of any type, but primarily refers to fibers such as cellulose fibers, regenerated fibers or different types of synthetic fibers, as well as filler particles.

The interacting polymers are preferably alternating cationic and anionic polyelectrolytes, but they can also be so-called zwitterions.

The thickness of each of said thin layers preferably amounts to between 3 and 10Å, preferably between 7 and 20Å.

The invention further relates to a paper or nonwoven product, which contains fibers and / or filler particles as above.

It further relates to a method of producing a particle or particle group of the above kind, treating the particle or particle group in consecutive steps with solutions of the interacting polymers, and wherein the treatment time for each step is sufficient for a thin layer of desired thickness to be formed.

Description of drawings Fig. 1 shows in the form of a bar graph the tensile strength index of sheets made of cellulose fibers with different numbers of applied polymer layers.

Fig. 2 shows in the form of a bar graph the tensile strength index on paper containing different amounts of filler particles treated according to the invention.

Fig. 3 shows a tensile index opacity diagram for paper containing different amounts of filler particles treated according to the invention.

DESCRIPTION OF THE INVENTION According to the present invention, particles or particle groups, e.g. cationic and anionic polyelectrolytes are used as interacting polymers, the technique described among other things in the above-mentioned articles from Thin Solid Films with the difference that according to the invention it is fibrers or other particles or groups thereof which constitute the substrate.

The particles are treated in consecutive steps with solutions of the interacting polymers, the treatment time for each step being sufficient to form a layer of desired molecular thickness of desired thickness, preferably in the order of 5-100 Å. The interaction between the particles can be constituted by electrostatic forces, the polymers being constituted by alternating cationic and anionic polyelectrolytes, or by the interaction between nonionic polymers by means of, for example, dispersion forces or hydrogen bonds. Examples of this type of interaction between nonionic polymers are adsorption of polyethylene oxide on unbleached cellulose fibers and complex formation between polyethylene oxide and polyacrylic acid.

In the case where the interacting polymers consist of alternating cationic and anionic polyelectrolytes, for particles or groups of particles having an anionic surface, as is the case, for example, with cellulose fibers, the first layer is a cationic polyelectrolyte, and vice versa. Any excess polyelectrolyte can be removed between usual treatment steps, for example by rinsing with water. Alternatively, only such an amount of the respective polymer is added in each step that all the polymer is adsorbed to the particle surface.

The method is based on electrostatic attraction between oppositely charged polyelectrolytes to build up the desired multilayers. By treating fi brema in successive steps with a solution containing polyions of opposite charge and allowing these to spontaneously adsorb to the particle surface, multilayers of the specified type are formed. In principle, all types of polyelectrolytes can be used.

By such treatment of particles or particle groups, such as fibers, it is possible to make new types of surface modifications on them. For example, by treating fibers with successive layers of hydrophobic, charged polyelectrolytes, it would be possible to develop, for example, new types of hydrophobicization chemicals for hydrophobicizing paper. It is also conceivable to build up "intelligent" surface layers on fibers, which change properties with temperature, pH, salt content, etc. These changes could, for example, be based on fundamental knowledge of modern theories of interaction between polymers and surfactants.

Additional applications are ion-exchanging fibers where "membranes" with ion-exchanging properties are built up on the surface, wet strength agents where the polymers added are reactive with both fibers and each other to give permanent bonds between the fibers and the production of high-swelling surface layers where the chemicals that are added form swollen gel structures on the fiber surface for use in absorbent hygiene products. Another possible application is new types of fibers for printing paper, where the polyiners that are adsorbed change color when they are exposed to an electric, magnetic or electromagnetic field. Such types of polymers are already available today.

The fibers that can be treated with the method according to the invention can be of any kind, both natural and synthetic fibers. Above all, however, it refers to cellulose fibers. However, it is also conceivable to treat synthetic fibers, for example to give them a more hydro-surface. Groups of fibers or particles can also be treated according to the method.

Example 1 The following example shows the increase in tensile strength of sheets made in a dynamic sheet former. The pulp used was bleached SWK (softwood sulphate pulp) which was dissolved in accordance with SCAN-C 18:65, diluted to 3 g / l and the pH adjusted to 8. PVAm (polyvinylamine), a cationic polymer, was added in excess and allowed to react after which the excess polymer was washed away from the fiber suspension with the aid of water.

Then CMC (carboxymethylcellulose), an anionic polymer, was added in excess and after 10 minutes, non-adsorbed polymer was removed by washing. Addition of PVAm and CMC was repeated in fl your steps. After each addition of CMC, the so-called dynamic sheet former was used to produce sheets with a basis weight of 80 g / m 2. The sheets were tested for tensile strength according to SCAN-P 67:93. The results are reported in Table 1 below and clearly show an improvement in tensile strength index with the number of applied polymer layers. 521 591 6 Table I Polymer layer (P = PVAm, C = CMC) Tensile strength index (kNm / kg) No polymer 39.0 P 53.6 PC 56.6 PCPC V 69A PCPCPC 75.8 The results are also illustrated in Figs. 1 in the drawings.

Example 2 This example used papermaking fillers treated with multilayer adsorption of the same polymers as in Example 1 above, i.e. polyvinylamine and carboxymethylcellulose. Paper sheets of 80 g / mz were manufactured in a dynamic sheet former. The sheets were tested for ash content, tensile index and opacity.

The results are shown in Table 2 below. With the ash content of the ash contents treated as above, which is added to the paper.

Polymer layer Ash content (%) Tensile strength index Opacity (%) (P = PVAm, C = CMC) (kNm / kg) No polymer 0.0 47, 78.8 No polymer 20.6 19.7 87.1 P 7.5 38 .3 82.9 P 14.3 30.5 86.7 P 21.7 23.8 89.5 PCP 7.5 37.9 83.5 PCP 13.9 31.7 87.8 PCP 24.3 26 .6 90.7 PCPCP 9.0 40.0 84.7 PCPCP 18.0 35.9 87.0 PCPCP 28.0 30.0 91.0 The results are also illustrated in Figs. 2 and 3. Fig. 2 shows here the effect on the strength of paper containing different amounts of filler particles treated according to 521 cm -1 in the invention. Fig. 3 shows the effect on paper opacity when using different amounts of filler particles treated according to Example 2 above.

Claims (9)

10 15 20 25 30 521 591: r: ä 'Patent claim A method of preparing a particle or groups of particles having a coating of at least two, preferably at least three, interacting polymers, the particles or groups of particles being treated in consecutive steps with solutions of the interacting polymers, characterized in that excess of the preceding polymer is removed between each treatment step or alternatively that the respective polymer is added only in such an amount in each step that substantially all of the polymer is adsorbed to the particle surface. Method according to claim 1, characterized in that the particle is a fi ber. Method according to claim 2, characterized in that fi bem is a cellulose fi ber. A method according to claim 2, characterized in that fi bem is a synthetic or regenerated fiber. Method according to claim 1, characterized in that the particle is a filler particle or other particle type included in papermaking. Method according to one or more of the preceding claims, characterized by 20; The interacting polymers are alternating cationic and anionic polyelectrolytes or ampholytes. Method according to one or more of the preceding claims, characterized in that each of said thin layers has a thickness between 3 and 100 Å. Method according to one or more of the preceding claims, characterized in that each of said thin layers has a thickness between 7 and 20 Å. Paper or nonwoven product, characterized in that it contains sheets, filler particles or other particles according to one or more of claims 1-8.