Process for the Manufacture of Paper and Board

Abstract

The present invention provides a process for the manufacture of paper or board in which the anionic charge at the fibre surface is artificially increased by adding a substantive water soluble anionic compound, providing more sites and enhancing the adsorption of cationic papermaking additives. The preferred anionic compound is a phenolic polymer.

1 . A process for making paper or paper board comprising the steps of:
 adding a water soluble anionic compound (I), which adsorbs on the fibre surface and increases the negative surface charge of the fibre, recorded by means of zeta potential measurements, to an aqueous suspension of cellulosic fibres,   wherein the water soluble anionic compound (1) is a phenolic polymer consisting of recurring units of the formula
   -[P—CH 2 ] n -[Q-CH 2 ] m — 
   wherein   P is an hydroxyl-substituted phenyl ring, wherein the phenyl ring is not further substituted or is substituted with sulphonic acid, sulphonic acid salt, carboxylic acid or carboxylic acid salt groups,   Q is the same as P or an aromatic sulphonic acid or sulphonic acid salt,   m is 1 to 5,   n is 1 to 20;   and   subsequently adding a cationic papermaking additive (2) selected from the group consisting of: a retention aid a drainage aid, a wet strength polymer, a dry strength polymer, a cationic fixative, a softener, a debonder, and a cationic sizing chemical.   
   
   
       2 . A process according to  claim 1 , wherein
 P is selected from the group consisting of: phenol, phenol sulphonic, phenol carboxylic acid, cresol, cresol sulphonic, cresol carboxylic acid, dihydroxy diphenyl sulphone, dihydroxy diphenyl sulphone sulphonic, dihydroxy diphenyl sulphone carboxylic acid, naphthol sulphonic, and naphthol carboxylic acid, and   Q is the same as P or is selected from the group consisting of: naphthalene sulphonic acid, xylene sulphonic acid, cumene sulphonic acid, cresol sulphonic acid and benzene sulphonic acid.   
   
   
       3 . A process according to  claim 1 , wherein the sulphonic or carboxylic acid groups are in the form of sodium, potassium, lithium, ammonium, amino or hydroxyalkylamino salts. 
   
   
       4 . A process according to  claim 1 , wherein the molecular weight of the phenolic polymer is between 2'000 and 30'000 Daltons. 
   
   
       5 . A process according to  claim 1 , wherein the molecular weight of the phenolic polymer is between 10'000 and 30'000 Daltons. 
   
   
       6 . A process according to  claim 1 , wherein the substantive water soluble anionic compound (1) is an anionic direct dyestuff with strong affinity for cellulosic fibres, an optical brightening agent or mixtures thereof. 
   
   
       7 . A process according to  claim 6 , wherein the anionic direct dyestuff is Direct Yellow 11. 
   
   
       8 . A process according to  claim 6 , wherein the optical brightening agent is based on a stilbene sulphonic acid and contains b  2 ,  4 ,  6  or more sulphonic acid groups which may be neutralized with sodium, potassium or lithium hydroxide. 
   
   
       9 . A process according to  claim 1 , wherein the amount of substantive water soluble anionic compound (1), added to the cellulosic fibre suspension prior to any cationic additive (2), is 0.001 to 10% of dry compound, based on the dry weight of cellulosic fibres. 
   
   
       10 . A process according to  claim 9  wherein the amount of substantive water soluble anionic compound (1) is 0.01 to 2% of dry compound. 
   
   
       11 . A process according to  claim 1 , wherein the amount of cationic papermaking additive (2) is 0.01 to 2% of dry compound, based on the dry weight of cellulosic fibres. 
   
   
       12 . A process according to  claim 1 , wherein the cellulosic fibres are derived from bleached, semi-bleached or unbleached wood pulp, deinked pulp or waste paper. 
   
   
       13 . A process according to  claim 1 , wherein the level of conductivity in the aqueous suspension is greater than 1000 micro Siemens. 
   
   
       14 . A process according to  claim 1 , wherein the level of conductivity in the aqueous suspension is greater than 2500 micro Siemens.