Aqueous slurries of finely divided fillers, their preparation and their use for the production of filler-containing papers
Aqueous slurries of finely divided fillers which are at least partly coated with polymers and which are obtainable by treating aqueous slurries of finely divided fillers with at least one water-soluble amphoteric copolymer whose structures are identified in the specification are used as an additive to the paper stock in the production of filler-containing paper, filler-containing cardboard or filler-containing board by draining of the paper stock.
1. An aqueous slurry of finely divided fillers which are at least partly coated with polymers, comprising an aqueous slurry of finely divided fillers treated with at least one water-soluble amphoteric copolymer comprising as constituent monomer units:
(a) 5 to 70 mol % of N-vinylformamide
(b) 20 to 45 mol % of at least one monoethylenically unsaturated carboxylic acid selected from the group consisting of acrylic acid and methacrylic acid and/or the alkali metal, alkaline earth metal or ammonium salts thereof and
(c) 10 to 50 mol % of vinylamine and/or amidine units of the formula
where X − is an anion.
2. An aqueous slurry as claimed in claim 1 , wherein said slurry contains from 1 to 50% by weight of at least one finely divided filler and wherein the amount of said water-soluble amphoteric copolymer is from 0.05 to 5% by weight, based on filler.
3. An aqueous slurry as claimed in claim 1 , which contains from 10 to 40% by weight of at least one filler.
4. An aqueous slurry as claimed in claim 1 , wherein said water-soluble amphoteric copolymers have a molar mass Mw of at least 10 000.
5. An aqueous slurry as claimed in claim 1 , wherein the degree of hydrolysis of the N-vinylformamide groups incorporated in the form of polymerized units is from 10 to 98%.
6. An aqueous slurry as claimed in claim 1 , wherein said at least one water-soluble amphoteric copolymer comprises as constituent monomer units (a) from 5 to 70 mol % of vinylformamide units, (b) from 20 to 45 mol % of acrylic acid and/or methacrylic acid units and (c) from 10 to 50 mol % of vinylamine units in salt form and amidine units of the formula
7. An aqueous slurry as claimed in claim 1 , wherein said water-soluble amphoteric copolymers carry an excess anionic charge.
8. An aqueous slurry as claimed in claim 1 , wherein said water-soluble amphoteric copolymers carry an excess cationic charge.
9. An aqueous slurry as claimed in claim 1 , wherein said water-soluble amphoteric copolymers have the same amount of cationic and anionic charge.
10. The aqueous slurry of claim 1 wherein said water-soluble amphoteric copolymer further comprises as constituent monomer units,
(c′) other monoethylenically unsaturated monomers which are free of nitrile groups.
11. The aqueous slurry of claim 1 wherein said water-soluble amphoteric copolymer-further comprises as constituent monomer units,
(d) compounds which have at least two ethylenically unsaturated double bonds in the molecule which are at least one compound selected from the group consisting of methylenebisacrylamide, glycol diacrylate, glycol dimethacrylate, glyceryl triacrylate, pentaerythrityl triallyl ether, polyalkylene glycols which are at least diesterified with acrylic acid and/or methacrylic acid, polyols which are at least diesterified with acrylic acid and/or methacrylic acid.
12. The aqueous slurry of claim 11 , wherein said compounds which have at least two ethylenically unsaturated double bonds are a polyol which is at least diesterified with acrylic acid and/or methacrylic acid, wherein said polyol is at least one of pentaerythritol, sorbitol or glucose.
13. The aqueous slurry as claimed in claim 1 wherein said water-soluble amphoteric copolymer further comprises as constituent monomer units
(c′) up to 30 mol % of units of other monoethylenically unsaturated compounds which are free of nitrile groups.
14. A process for the preparation of an aqueous slurry as claimed in claim 1 , wherein from 0.1 to 5% by weight, based on filler, of said amphoteric water-soluble copolymer is added to an aqueous slurry of at least one finely divided filler, or the aqueous slurry of at least one finely divided filler is introduced into an aqueous solution of said water-soluble amphoteric copolymer and the components are mixed in each case.
15. A process as claimed in claim 14 , wherein the electrophoretic mobility of the finely divided filler particles of the aqueous slurry is negative or not more than zero at a pH of 7.
16. The process of claim 14 , wherein said water-soluble amphoteric copolymer further comprises as constituent monomer units,
(c′) other monoethylenically unsaturated monomers which are free of nitrile groups.
17. The process of claim 16 , wherein said water-soluble amphoteric copolymer further comprises as constituent monomer units
(d) compounds which have at least two ethylenically unsaturated double bonds in the molecule which are at least one compound selected from the group consisting of methylenebisacrylamide, glycol diacrylate, glycol dimethacrylate, glyceryl triacrylate, pentaerythrityl triallyl ether, polyalkylene glycol which is at least diesterified with acrylic acid and/or methacrylic acid, a polyol which is at least diesterified with acrylic acid and/or methacrylic acid.
18. The aqueous slurry of claim 17 , wherein said compounds which have at least two ethylenically unsaturated double bonds are a polyol which is at least diesterified with acrylic acid and/or methacrylic acid, wherein said polyol is at least one of pentaerythritol, sorbitol or glucose.
19. A method of filling comprising adding the aqueous slurry as claimed in claim 1 to a paper stock and draining said paper stock,
in the production of a material selected from the group consisting of paper, cardboard and board.