Highly filled sheets and method of preparation thereof

• US 4,225,383 A
• Filed: 12/14/1978
• Issued: 09/30/1980
• Est. Priority Date: 02/02/1978
• Status: Expired due to Term

• Current Assignee: Chemtech II LP (Dow, Inc.)
• Original Assignee: The Dow Chemical Company (Dow, Inc.)
• Inventors: McReynolds, Kent B.
• Primary Examiner(s): Bashore, S. Leon
• Assistant Examiner(s): Chin, Peter
• Application Number:
  US05/969,749
• Time in Patent Office: 656 Days
• Field of Search: 162/168 R, 162/169, 162/181 R, 162/183, 162/146, 162/145, 162/157 R, 162/156, 260/42.17, 260/42.55, 260/42.18, 260/42.32
• US Class Current: 162/156
• CPC Class Codes: D21H 17/35 Polyalkenes, e.g. polystyrene
• CPC Class Codes: D21H 17/43 Carboxyl groups or derivatives thereof
• CPC Class Codes: D21H 17/67 Water-insoluble compounds, e.g. fillers, pigments
• CPC Class Codes: D21H 17/675 Oxides, hydroxides or carbonates
• CPC Class Codes: D21H 23/765 Addition of all compounds to the pulp

Abstract

A sheet which is a composite of (A) from about 1 percent to about 30 percent of a water-dispersible fiber such as wood fiber, (B) from about 2 percent to about 30 percent of a film-forming, water-insoluble, organic polymer such as a copolymer of styrene and butadiene and (C) from about 60 percent to about 95 percent of a finely-divided, substantially water-insoluble, non-fibrous, inorganic filler such as magnesium hydroxide is prepared by steps comprising:

(I) providing an aqueous dispersion of the fiber;

(II) mixing therewith (A) the inorganic filler and (B) the organic polymer in the form of an ionically stabilized latex;

(III) colloidally destabilizing the resulting mixture to form a fibrous agglomerate in aqueous suspension;

(IV) distributing and draining the aqueous dispersion on a porous substrate such as a wire to form a wet web; and

(V) drying the web.

Claims

1. A method for preparing a sheet comprising:

(I) providing an aqueous dispersion of from about 1 percent to about 30 percent of a water-dispersible fiber;

(II) mixing therewith (A) from about 60 percent to about 95 percent of a finely-divided, substantially water-insoluble, non-fibrous, inorganic filler and (B) from about 2 percent to about 30 percent of a binder containing a film-forming, water-insoluble, organic polymer in the form of an ionically stabilized latex having not greater than 0.7 milliequivalent of bound charge per gram of polymer in the latex;

(III) colloidally destabilizing the resulting mixture to form a fibrous agglomerate in aqueous suspension having the characteristics that at a concentration of 100 grams of solids in 13,500 milliliters, the suspension will drain in a time of from about 4 seconds to about 120 seconds in a 10-inch by 12-inch Williams Standard Sheet Mould having a 2-inch outlet and a 30-inch water leg and fitted with a 100-mesh, stainless steel screen having a wire diameter of 0.0045 inch to provide in one pass at least 85 percent retention of solids which contain at least 60 percent by weight of filler;

(IV) distributing and draining the aqueous suspension on a porous support to form a wet web; and

(V) drying the web;

said ionically stabilized latex being devoid of sufficient non-ionic stabilization to interfere with formation of the fibrous agglomerate;

said percentages being on a dry weight basis, calculated on the total dry weight.

2. The method of claim 1 in which the aqueous dispersion of fiber has a consistency of from about 0.1 percent to about 6 percent.

3. The method of claim 1 in which the aqueous dispersion of fiber has a consistency of from about 0.5 percent to about 3 percent.

4. The method of claim 1 in which the latex is anionic.

5. The method of claim 1 in which the latex is cationic.

6. The method of claim 1 in which the fiber is cellulosic.

7. The method of claim 6 in which the aqueous dispersion of fiber has a Canadian Standard Freeness at 0.3 percent consistency of from about 300 milliliters to about 700 milliliters.

8. The method of claim 1 which has the additional step of wet pressing the web.

9. The method of claim 1 in which the amount of the fiber is from about 5 percent to about 15 percent.

10. The method of claim 1 in which the amount of latex is from about 5 percent to about 15 percent.

11. The method of claim 1 in which the amount of filler is from about 70 percent to about 90 percent.

12. The method of claim 1 in which the latex contains copolymerized styrene and butadiene.

13. The method of claim 1 in which the latex contains a copolymer of an ethylenically unsaturated carboxylic acid.

14. The method of claim 1 in which the drain time is from about 15 seconds to about 60 seconds.

15. The method of claim 1 in which the drain time is from about 30 seconds to about 45 seconds.

16. The method of claim 1 in which the destabilizing step is carried out by mixing with the product of steps (I) and (II) a sufficient amount of water-soluble or water-dispersible, ionic compound or polymer having a charge opposite in sign to that of the ionic stabilization of the latex.

17. The method of claim 1 in which the filler is magnesium hydroxide.

18. The method of claim 1 in which the fiber includes a polyester fiber.

19. The method of claim 1 in which the fiber includes fibrillated polyethylene.

20. The method of claim 1 in which the fiber includes glass fibers.

21. The method of claim 1 in which the latex is a blend of at least two different latex compositions.

22. The method of claim 21 in which at least one of the latexes contains a copolymer of an ethylenically unsaturated carboxylic acid.

23. The method of claim 1 which is asbestos-free.

24. The method of claim 1 in which the organic polymer has a bound charge of from about 0.03 to about 0.4 milliequivalent per gram of polymer in the latex.