Methods and means for coating paper by film coating

Abstract

This invention relates to the field of paper coating, more in particular to means and methods for providing paper with at least one layer of pigment using film coating to obtain a well printable surface. Provided is a method for preparing coated paper comprising the steps of: a) providing a pigmented wet coating formulation comprising water, 2-20 parts of a binder and 100 parts of pigment, wherein at least 50% of the binder is highly branched starch (HBS) characterized by a molecular weight of between 0.5*10 5 and 1*10 6 Daltons and having a molecular branching degree of at least 6% and which is obtained by treatment of gelatinized starch or starch derivative with a glycogen branching enzyme (EC 2.4.1.18); and wherein at least 70% of the pigment is calcium carbonate; and b) applying the pigmented wet coating formulation to paper by film coating and drying the coated paper.

1 . A method for preparing coated paper comprising the steps of:
 a) providing a pigmented wet coating formulation comprising water, 2-20 parts of a binder and 100 parts of pigment, wherein at least 50% of the binder is highly branched starch (HBS) characterized by a molecular weight of between 0.5*105 and 1*106 Daltons and having a molecular branching degree of at least 6% and which is obtained by treatment of gelatinized starch or starch derivative with a glycogen branching enzyme (EC 2.4.1.18); and wherein at least 70% of the pigment is calcium carbonate; and   b) applying the pigmented wet coating formulation to paper by film coating and drying the coated paper.   
     
     
         2 . The method according to  claim 1 , wherein the HBS has a molecular weight between 0.8*10 5  g/mol to 1.8*10 5  g/mol, preferably between 1*10 5  g/mol and 1.6*10 5  g/mol. 
     
     
         3 . The method according to  claim 1 , wherein the HBS does not contain any residual amylose. 
     
     
         4 . The method according to  claim 1 , wherein at least 70% of the binder is HBS and wherein at least 80% of the pigment is calcium carbonate. 
     
     
         5 . The method according to  claim 1 , wherein said starch or starch derivative is selected from native, unmodified and chemically modified starch derived from non-GMO as well as GMO plant variants. 
     
     
         6 . Method according to  claim 5 , wherein the starch or starch derivative is derived from potato, corn, wheat, tapioca, waxy potato, waxy corn, waxy tapioca, like high amylose potato, high amylose corn, and modified starches including low DE maltodextrins and amylomaltase-treated starch. 
     
     
         7 . The method according to  claim 5 , wherein the starch derivatives are selected from the group consisting of the products of acid or enzymatic hydrolysis of starch and the products of the chemical and physical modifications of starch of any type. 
     
     
         8 . The method according to  claim 7 , wherein starch derivative is cationic starch, oxidized starch or phosphated starch. 
     
     
         9 . The method according to  claim 1 , wherein said glycogen branching enzyme is a thermostable glycogen branching enzyme obtained from a mesophilic or thermophilic organism, preferably glycogen branching enzyme of  Aquifex aeolicus  or  Rhodothermus obamensis.   
     
     
         10 . The method according to  claim 1 , wherein HBS is the sole binder. 
     
     
         11 . The method according to  claim 1 , wherein the pigmented wet coating formulation comprises 100 parts pigment, 2 to 20 parts HBS, 0-10 parts of another modified starch, and 0 to 8 parts styrene-based emulsion polymer binder, and wherein the pigment is calcium carbonate. 
     
     
         12 . The method according to  claim 1 , wherein the solids content of the wet coating formulation is at least 60% by weight, preferably at least 65%, more preferably at least 70% by weight. 
     
     
         13 . The method according to  claim 1 , wherein step b) comprises applying the coating formulation at a speed of at least 1200 m/min in an amount of at least 7 gsm/side by film coating. 
     
     
         14 . A pigmented wet paper coating composition comprising water, 2-20 parts of a binder and 100 parts of pigment, wherein at least 50% of the binder is highly branched starch (HBS) characterized by a molecular weight of between 0.5*10 5  and 1*10 6  Daltons and having a molecular branching degree of at least 6% and which is obtained by treatment of starch or starch derivatives with a glycogen branching enzyme (EC 2.4.1.18); and wherein at least 70% of the pigment is calcium carbonate. 
     
     
         15 . The coating composition according to  claim 14 , having a dry solids content of at least 65% by weight, comprising at least 80% by weight calcium carbonate as its pigment component and a modified starch as binder, the modified starch consisting of said highly branched starch (HBS). 
     
     
         16 . The coating composition according to  claim 14 , wherein said HBS has a molecular weight between 0.8*10 5  g/mol to 1.8*10 5  g/mol, preferably between 1*10 5  g/mol and 1.6*10 5  g/mol. 
     
     
         17 . The coating composition according to  claim 14 , wherein the HBS does not contain any residual amylose, preferably measured. according to the KI/I 2  test. 
     
     
         18 . Coating composition according to  claim 14 , comprising 100 parts pigment, 2 to 20 parts HBS, 0-10 parts of another modified starch, and 0 to 8 parts styrene-based emulsion polymer binder, and wherein the pigment is calcium carbonate. 
     
     
         19 . Coating composition according to  claim 14 , comprising 100 parts pigment, 5 to 20 parts binder in which HBS comprises at least 50%, preferably at least 60%, more preferably 70%, of the total binder and in which said pigment is calcium carbonate. 
     
     
         20 . A coated paper comprising a paper and on the paper an amount of paper coating composition according to  claim 14  from which the water has been reduced or removed. 
     
     
         21 . Coating composition according to  claim 14  for use in film coating of paper or paperboard. 
     
     
         22 . The use of a highly branched starch (HBS) characterized by a molecular weight of between 0.5*10 5  and 1*10 6  Daltons and having a molecular branching degree of at least 6% and which is obtained by treatment of starch or starch derivatives with a glycogen branching enzyme (EC 2.4.1.18) to improve the performance of a film coating process or a film coater apparatus. 
     
     
         23 . Use according to  claim 22 , wherein improving performance comprises reducing misting, reducing water retention, increasing paper surface strength, increasing paper brightness, improving runnability, increasing immobilization speed, or any combination thereof.