Manufacture of paper and paperboard containing wood free pulp

Abstract

The present invention relates to a process of manufacturing paper or paperboard which comprises providing (a) a mechanical pulp and (b) a wood free pulp, combining (a) the mechanical pulp and (b) the wood free pulp to form a mixed pulp comprising no more than 20% by total dry weight of fiber of the mechanical pulp, flowing the mixed pulp as a medium consistency stock and combining the medium consistency stock with dilution water to form a low consistency stock, draining the low consistency stock through a wire or mesh to form a sheet of paper which is dried, in which additional filler and a cationic polymer are added to the mechanical pulp.

Claims

1. A process of manufacturing paper or paperboard, the process comprising: adding a filler and a cationic polymer to a mechanical pulp; combining the mechanical pulp combined with the filler and the cationic polymer and a wood free pulp to form a mixed pulp comprising no more than 20% by total dry weight of fiber of the mechanical pulp; flowing the mixed pulp as a medium consistency stock and combining the medium consistency stock with dilution water to form a low consistency stock; and draining the low consistency stock through a wire or mesh and drying, thereby forming a sheet of paper.

2. The process according to claim 1, wherein an amount of the filler added to the mechanical pulp is from 1% to 20% by dry weight of the mechanical pulp.

3. The process according to claim 1, wherein the filler is also added to the mixed pulp, the medium consistency stock, the low consistency stock, or a combination thereof.

4. The process according to claim 1, wherein the filler is selected from the group consisting of precipitated calcium carbonate, ground calcium carbonate, kaolin and titanium dioxide.

5. The process according to claim 1, wherein an amount of the cationic polymer added to the mechanical pulp is at least 100 g polymer per ton of the dry mechanical pulp.

6. The process according to claim 1, wherein the cationic polymer is a polymer formed from (meth) acrylamide and a cationic monomer.

7. The process according to claim 1, wherein the cationic polymer exhibits an intrinsic viscosity of at least 4 dl/g.

8. The process according to claim 1, wherein the mechanical pulp is a bleached chemical thermo mechanical pulp (BCTMP).

9. The process according to claim 1, wherein the medium consistency stock, the low consistency stock, or both, is treated by adding a retention system.

10. The process according to claim 9, wherein the retention system comprises at least one retention additive comprising at least one cationic polymer.

11. The process according to claim 1, wherein an amount of the cationic polymer added to the mechanical pulp is at least 500 g polymer per ton of the dry mechanical pulp.

Description

EXAMPLES

(1) A synthetic fine paper stock was prepared by combining a wood free pulp (90% by weight of total dry stock) and a bleached chemical thermo mechanical pulp (BCTMP) (10% by weight of total dry stock). The synthetic fine paper stock had a filler content of 20% by total dry weight of stock. Reference to filler means precipitated calcium carbonate (PCC).

(2) The PCC was Omya Syncarb F0474. This precipitated calcium carbonate product has an average particle size diameter of 1.83 μm. In the lab tests the PCC is added at 20% solids. This was diluted in tap water to 20% solids before addition as required.

(3) Wood free pulp 50/50 Hardwood pine: Softwood birch blend beaten to a Schopper Riegler Freeness of 30°.

(4) BCTMP Pulp Supplied from Metso Paper

(5) The wood free pulp and the BCTMP pulp were prepared at 4% consistency and mixed together for 1 minute, stirring at 200 rpm

(6) Reference to extra filler means additional PCC added to either the BCTMP or synthetic fine paper stock.

(7) Cationic Polymer added is Percol PBR20 which is a solid grade cationic polyacrylamide exhibiting an intrinsic viscosity of 10.9 dl/g supplied by BASF. Intrinsic viscosity is determined by the method described above in the description. The Cationic Polymer is dissolved in tap water as a 0.8% by weight solution and further diluted with tap water to 0.1% before addition in the following tests.

(8) 200 ml of water is placed into a 250 ml wide neck bottle. A stirrer is placed into the bottle. The speed of the stirrer should be between 600 and 1000 rev/min. The required amount of dry polymer to give the required concentration (typically 0.2-0.8%) is weighed into a paper weighing boat. The polymer is then slowly sprinkled from the paper boat into the vortex created by stirring such that formation of lumps is avoided (approx. 30 sec). Then the solution is stirred for 30-60 minutes after which time the polymer is ready to use.

(9) Cationic polymer was dosed into the stock using a plastic pipette. When added to thick stock mixed with a stirrer at 200 rpm for 1 minute. When added to thinstock mixed at 500 rpm for 30 seconds.

(10) For clarification since the synthetic fine paper stock contains 10% BCTMP 20% extra filler added to BCTMP is equivalent with the overall dose of 2% extra filler added to the synthetic fine paper stock and 1000 g/tonne Cationic Polymer added to BCTMP is equivalent to the overall dose of 100 g/tonne Cationic Polymer added to the synthetic fine paper stock.

(11) All of the tests also employed 250 g/tonne Cationic Polymer added to the synthetic fine paper stock as a retention aid. This is calculated on the basis of the product as supplied (which is assumed to be substantially the same as active polymer content) on dry weight of stock, which is determined by the method described in the description.

(12) Filler retention results were measured as first past ash retention (FPAR).

(13) First Pass Ash Retention Measurement

(14) 500 mls of stock is placed into a Britt jar Retention tester fitted with a piece of standard Schopper Riegler wire. The stirrer is switched on at 500 rpm and after 10 seconds, polymer solution added as required. After 30 seconds mixing, the tap is opened and the first 25 mls of backwater discarded. The next 100 mls of backwater is collected. The tap is closed, the stirrer switched off and the remaining stock discarded and the apparatus washed clean for the next test

(15) The 100 mls sample is filtered over a pre-weighed and dried ashless filter paper and then dried at 105 degrees C. for 2 hrs. The filter paper is reweighed and the weight of solids in the backwater determined. The filter paper is the placed into a crucible and the crucible placed into a muffle furnace at 550 degrees C. for 3 hours.

(16) The First pass ash Retention is calculated as
100% (wt ash in 100 mls stock−wt ash in 100 mls backwater)/wt. ash in 100 mls of stock

(17) TABLE-US-00001 TABLE 1 Synthetic Fine Paper Cationic Stock Addition Polymer BCTMP Addition Cationic Filler Total in Cationic Polymer Total in final Filler Polymer Filler 20% + 250 (g/t) + FPAR final stock stock No. (%) (g/t) extra (%) extra (g/t) (%) (%) (%) 1 47.8 20 250 2 Extra 100 47.8 20 350 3 Extra 200 49.2 20 450 4 Extra 1 44.6 21 250 5 Extra 10 51.0 21 250 6 Extra Extra 1 52.6 21 350 1000 7 Extra 10 Extra 55.4 21 350 1000 8 Extra Extra 1 59.2 21 450 2000 9 Extra 10 Extra 63.5 21 450 2000 10 Extra 1 Extra 100 52.2 21 350 11 Extra 20 46.3 22 250 12 Extra Extra 2 53.2 22 350 1000 13 Extra 20 Extra 53.4 22 350 1000 14 Extra Extra 2 47.5 22 450 2000 15 Extra 20 Extra 60.3 22 450 2000 16 Extra 2 Extra 100 53.3 22 350 17 Extra 20 Extra 100 47.5 22 350 18 Extra 2 Extra 200 57.7 22 450 19 Extra 20 Extra 200 44.4 22 450

(18) Experiments 1, 2, 3, 4 and 10 show the state of the art, adding extra filler and extra cationic polymer to the low consistency stock.

(19) Experiments 5 and 6 show variations of addition point of filler and polymer, whereas example 7, the novel application of the invention adding both filler and cationic polymer to the mechanical pulp gives the best filler retention result.

(20) At increased cationic polymer levels example 9 of the invention is better than example 8 adding extra cationic polymer in the low consistency stock.

(21) At increased extra filler addition, example 15 of the invention gives a better filler retention result than the state of the art, experiments 16 and 18, and better than other variations of filler and cationic polymer addition.