Method of adsorption of cationic and anionic polymers on the surface of particles and paper or nonwoven products containing such particles

Abstract

The present invention provides a method of producing a particle or group of particles intended for use in making paper- and/or nonwoven products and having a coating of at least two, preferably at least three, thin layers of alternating cationic and anionic polymers located outside each other, in 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. The present invention also relates to a paper- or nonwoven product containing fibers and/or fillers produced according to a method of the invention. The present invention also encompasses paper products containing increased amounts of wet strength agent and tissue paper having improved wet strength.

What is claimed is:  
     
         1 . A method of producing a particle or group of particles for paper or nonwoven products, the particle or group of particles comprising a coating of at least two thin layers of alternating cationic and anionic polymers located outside each other, comprising: 
 treating the particle or group of particles in consecutive steps with solutions of the alternating cationic and anionic polymers wherein the amount of the respective polymer to be added in each step is controlled by charge measurements of each of the polymer solutions or a liquid containing the particle or group of particles and each of the polymer solutions during or after the treatment in each step in order to determine that substantially all polymer is adsorbed to the particle surface in order to produce a particle or group of particles having a coating of at least two thin layers of alternating cationic and anionic polymers.    
     
     
         2 . A method of  claim 1 , further comprising measuring the Z-potential of the particles or groups of particles during and/or after the treatment in each step in order to determine the amount of cationic/anionic polymer adsorbed to the particle surface.  
     
     
         3 . A method of  claim 1 , wherein the particle is a fiber.  
     
     
         4 . A method of  claim 3 , wherein the fiber is a cellulosic fiber.  
     
     
         5 . A method of  claim 3 , wherein the fiber is a synthetic or regenerated fiber.  
     
     
         6 . A method of  claim 1 , wherein the particle is a filler particle, a coating particle, or other type of paper-making particle.  
     
     
         7 . A method of  claim 1 , wherein at least one of the anionic or cationic polymers is a strength additive used in papermaking.  
     
     
         8 . A method of  claim 1 , wherein the process for consecutive absorption of thin layers of interacting polymers on the surface of particles or groups of particles is continuous and wherein the amount of the respective polymer to be added in each step is determined at the starting-up of the process.  
     
     
         9 . A paper or nonwoven product comprising fibers, filler particles, or other particles produced according to the method of  claim 1 .  
     
     
         10 . A paper or nonwoven product comprising at least three thin layers of alternating cationic and anionic polymers located outside each other and at least 1.5% by weight of a wet-strength agent.  
     
     
         11 . A paper or nonwoven product of  claim 10 , wherein the wet-strength agent is a cationic polyelectrolyte.  
     
     
         12 . A tissue paper based on wood pulp cellulose with no admixture of other types of fibers that has a wet tensile index of at least 6.5 Nm/g.  
     
     
         13 . A tissue paper of  claim 12 , wherein said tissue paper contains at least three thin layers of alternating cationic and anionic polymers located outside each other.  
     
     
         14 . A method of  claim 1 , wherein the coating contains at least three thin layers of alternating cationic and anionic polymers.  
     
     
         15 . A method of  claim 7 , wherein the strength additive is a dry-strength and/or a wet-strength agent.  
     
     
         16 . A paper or nonwoven product of  claim 10 , wherein the paper or nonwoven product contains at least 1.7% by weight of a wet-strength agent.  
     
     
         17 . A paper or nonwoven product of  claim 10 , wherein the paper or nonwoven product contains at least 2.0% by weight of a wet-strength agent.  
     
     
         18 . A paper or nonwoven product of  claim 10 , wherein the paper or nonwoven product contains at least 2.2% by weight of a wet-strength agent.  
     
     
         19 . A paper or nonwoven product of  claim 10 , wherein the paper or nonwoven product contains at least 2.5 % by weight of a wet-strength agent.  
     
     
         20 . A paper or nonwoven product of  claim 11 , wherein the cationic polyelectrolyte is polyaminoamideepichlorhydrin (PAE) and/or glyoxylated polyacryl amide (G-PAM).  
     
     
         21 . A tissue paper of  claim 12 , wherein the tissue paper has a wet tensile index of at least 7.0% Nm/g.  
     
     
         22 . A tissue paper of  claim 12 , wherein the tissue paper has a wet tensile index of at least 7.5% Nm/g.