Anionic preflocculation of fillers used in papermaking
A method of preparing a stable dispersion of flocculated filler particles for use in papermaking processes comprises use of an anionic first flocculating agent to an aqueous dispersion of filler particles, followed by addition of a second anionic flocculating agent to the dispersion and further optional shearing of the resultant filler flocs to the desired particle size resulting in shear resistant filler flocs with a defined and controllable size distribution.
1. A method of preparing a stable dispersion of flocculated filler particles having a specific particle size distribution for use in papermaking processes comprising:
a) adding a first flocculating agent to an aqueous dispersion of filler particles, the dispersion in an amount sufficient to mix uniformly in the dispersion without causing significant flocculation of the filler particles the first flocculating agent being anionic and having an RSV of at least 3 dL/g;
b) adding a second flocculating agent to the dispersion in an amount sufficient to initiate flocculation of the filler particles in the presence of the first flocculating agent wherein the second flocculating agent is anionic;
c) shearing the flocculated dispersion to provide a dispersion of filler flocs having the desired particle size; and
d) causing or allowing flocculation of the filler particles prior to adding them to a paper stock and wherein no paper stock is present during the flocculation.
2. The method of claim 1 , wherein the filler flocs have a median particle size of 10-100 μm.
3. The method of claim 1 , wherein the filler is selected from the group consisting of calcium carbonate, kaolin clay, talc, titanium dioxide, alumina trihydrate, barium sulfate and magnesium hydroxide.
4. The method of claim 1 , wherein the first flocculating agent is selected from the group consisting of partially hydrolyzed acrylamide and copolymers of acrylamide and sodium acrylate.
5. The method of claim 1 , wherein the first flocculating agent is a copolymer of acrylamide and sodium acrylate having an anionic charge of 5-75 mole percent and an RSV of at least 15 dL/g.
6. The method of claim 1 , wherein the filler particles are selected from the group consisting of precipitated calcium carbonate, ground calcium carbonate and kaolin clay, and mixtures thereof.
7. The method of claim 1 , wherein the filler flocs have a median particle size of 10-70 μm.
8. The method of claim 1 , further comprising adding one or more microparticles to the flocculated dispersion after addition of the second flocculating agent.
9. A method of making paper products from pulp comprising:
forming an aqueous cellulosic papermaking furnish,
adding an aqueous dispersion of filler flocs prepared according to the method of claim 1 to the furnish,
draining the furnish to form a sheet, and
drying the sheet.
10. The method of claim 1 , wherein the first flocculating agent comprises an anionic charge of greater than 50 mole % up to about 75 mole %.
11. The method of claim 1 , wherein the first flocculating agent comprises an anionic charge of about 75 mole %.
12. The method of claim 1 , wherein the filler flocs have a median particle size between 10 μm and less than 50 μm.
13. The method of claim 1 , wherein the filler flocs have a median particle size of about 10 μm.