GB1596632A

GB1596632A - Filled paper

Info

Publication number: GB1596632A
Application number: GB3155/77A
Authority: GB
Original assignee: Associated Portland Cement Manufacturers Ltd
Current assignee: Associated Portland Cement Manufacturers Ltd
Priority date: 1977-01-26
Filing date: 1977-01-26
Publication date: 1981-08-26
Also published as: IT7847788A0; ZA78491B; DE2803398A1; IE46377B1; FR2378895A1; MX148457A; BE863218A; NO780268L; IE780146L; NL7800825A; FI780214A; RO74134A; IL53882A0; DK30478A; IT1103878B; TR20043A; SE7800904L; IL53882A; FR2378895B1; GR72111B

Description

(54) FILLED PAPER (71) We, THE ASSOCIATED PORTLAND CEMENT MANUFACTURERS LI MITED, a Company organised under the laws of Great Britain, of Portland House, Stag Place, London SW1E 5BJ, England, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to the manufacture of paper containing an acid-reactive filler such as calcium carbonate and sized by the process employing rosin size and papermakers' alum. It is most desirable that this operation should be carried out simply and successfully, in particular because of the economy and free availability of calcium carbonate fillers based on natural minerals, particularly upon chalk. These fillers have other advantages; in particular they confer permanence upon the paper.

Until recently acid-reactive fillers such as calcium carbonate have not been acceptable for papers which are sized by the rosin/alum process. This process requires acid conditions for success and the alkalinity of fillers like calcium carbonate rapidly neutralises added acid or acid generated from the alum by hydrolysis. It is also desirable to use materials like calcium carbonate as a paper coating pigment. The recycled broke derived from paper having such a coating has been a source of difficulty in the sizing of paper made from a stock containing this type of broke. Some mills have found it necessary to dissolve the whole of the calcium carbonate present in the broke in acid while others have employed processes which separated the filler from the pulp by washing. It would evidently be advantageous to avoid these complications.

It is known in the papermaking art that sizing by the rosin/alum process may be achieved under more alkaline conditions if a high free rosin emulsion size is employed than if a rosin soap size is used. It is also known that treatment of calcium carbonate to form flocs in the papermaking stock or before it incorporation into the stock, rather than co-flocs containing both filler and cellulosic fibres, reduces the rate of neutralisation of acid by the calcium carbonate.

Fillers to be incorporated in the paper have generally been added to the pulp in the course of its preparation and supply to the stuff box, sizing material and alum being added subsequently. Retention aids are added later still, for instance after the cleaners, to reduce loss of additives in the course of formation of the paper web.

The present invention provides a papermaking process which includes the steps of supplying a machine headbox with a thick pulp stock treated with rosin size and sufficient alum for fixing the size; continuously conveying the thick pulp stock from the machine headbox to a mixing point where it is diluted with machine backwater; pumping the resultant thin pulp stock to provide a continuous supply of pulp stock to the breast box on a papermaking machine; and incorporating further alum into the thin pulp stock before application of the pulp to the papermaking machine; wherein the thick pulp stock is prepared in the substantial absence of acid-reactive filler, and acid-reactive filler is continuously added to the pulp stock only after the latter has left the machine headbox.

In this manner the paper stock is sized before the acid-reactive filler is added so that the effect of the latter on the sizing process is minimised. The stage at which broke, which may contain recycled calcium carbonate or other pigment from a coating process, is generally added to the pulp is thus effectively separated from the stage at which interference with sizing by such pigment could occur hitherto, and such recycled pigment simply joins that which, preferably in an immediately preceding stage, is added as filler.

Preferably, the further alum is incorporated into the pulp stock after the addition of the acid-reactive filler, which filler is preferably added to the thick pulp stock.

The acid-reactive filler may take any suitable form, the invention being of particular application to the use of chalk whiting. It is advantageous to add the filler in preflocculated form, that is to say as a composition in which the filler is accompanied in aqueous suspension by a flocculant which modifies the condition and in some cases the effective particle size of the filler before the composition is introduced to the paper furnish. Such a preflocculated filler composition has an enhanced ability to flocculate onto the fibre.

The invention is further explained with reference to the accompanying drawings, in which: Figure I is a schematic flow diagram of the relevant part of a conventional papermaking process; and Figure 2 is a schematic flow diagram of the same part of such a process modified according to the invention.

In the Figures there is indicated a papermaking machine 1 which is fed with pulp from a breast box 2 in the usual manner. The pulp has been prepared as thick stock in a preparation stage 30, for instance including a hydropulper, from water 31, paper pulp 32 and filler 41. Rosin size 81 and alum 51 are incorporated in the stock before the latter is supplied to a machine headbox 33 from where it flows as required through conduit 36 to fan pump 6 where the thick stock is diluted to thin stock by admixture of backwater 7. The pump 6 delivers the thin stock through conduit 69 to cleaners 9 from which the stock flows via line 92 to the breast box 2.

In the conventional process illustrated in Figure 1, filler 41 is introduced before the headbox 33, normally before the alum 51. A retention aid 10 is normally added immediately before the breast box 2.

The invention is illustrated in Figure 2. Here the rosin size 82 and sufficient alum 52 to fix the size, are introduced before the headbox 33. (Alternatively, the rosin size and the alum could be added at the headbox 33). To the pulp thick stock, containing the size fixed on the fibre by the alum and flowing through conduit 36, there is continuously added the acid-reactive filler 42, preferably preflocculated whiting, whereby the effect of filler on the sizing is minimised. The thick stock is diluted by admixture of backwater 74 which in the process of the invention advantageously includes broke which may be derived from paper containing acid-reactive coating or loading filler. Such filler is accommodated by the process without difficulty. Further alum 53 is added to the thin stock in line 92 as close to the breast box 2 as possible. Retention aids may be added at this stage if desired, as in Figure 1.

In an embodiment of the invention, an aqueous suspension of cellulosic papermaking fibres, i.e. the pulp, which may already contain filler derived from filler or coated paper broke, is prepared to the thick stock stage at a consistency (oven dry solids content) from 0.25 per cent to 6 per cent by weight. The stock is passed to the machine head box mixed with rosin size, preferably of the high free rosin emulsion type, added in a proportion based on the dry pulp of up to 5.0 per cent, more preferably from 0.15 per cent to 5.0 per cent by weight, and with papermakers' alum, preferably in aqueous solution, in a proportion based on the oven dry pulp of from 0.25 per cent to 10 per cent by weight. The alum serves to adjust the pH of the pulp for sizing, e.g. in the case of "Bumal" rosin sizing ["Bumal is a Registered Trade Markl to about pH 5.5, and to fix the rosin on the fibres. Calcium carbonate filler such as preflocculated aqueous suspension of chalk whiting, is added continuously at a later point in the wet end flow system, to the stock on which the size has become sufficiently fixed. Such addition of filler is preferably made before the stock is continuously mixed with backwater and passed to the cleaners.

The calcium carbonate is generally in the form of an aqueous suspension of individual particles or preferably as a suspension of flocs or agglomerates prepared so as to impart acid resistance to them as described for instance in U. K. Patent Specifications Nos. 1,353,015; 1,425;114; 1,497,280; and 1,527,077.

In the preferred embodiment the second addition of alum is a continuous addition of papermakers' alum in aqueous solution as late as possible in the wet-end stock flow as is consistent with good mixing, i.e. not before the fan pump but close to the breast box, in a proportion by weight based on the oven dry pulp of from 0.25 per cent ot 7.5 per cent.

In this manner the flocculation effect of the alum will compensate for floc breakdown during pulp transport and adjust the pH to 6.5 to 7.5. Retention aids, e.g. polyacrylamides or cationic starches, may be added just before the breast box if desired.

The invention also extends to paper made by the method of the invention.

The following Examples are given for the purpose of illustrating the invention.

Percentages for the rosin and alum additions are by weight of the dry pulp.

Example 1 A ten-hour trial was run on a high-speed printing quality paper machine (using soft water) with the acid rosin sizing system and whiting addition according to the invention in order to assess whether the strength achieved with 16 per cent clay loading could be maintained with 21 per cent whiting loading using this process. The whiting had been preflocculated by means of a starch/alginate combination. The sizing chemical additions were as follows: "Bumal" 0.55 per cent 1st alum 1.4 per cent 2nd alum 1.45 per cent The average whiting loading was 21.8 per cent whilst maintaining strength, and the (British Standard 2644/1955) Cobb water penetration test averaged 20, thus indicating that sizing had been satisfactorily achieved with a higher filler loading.

In this test the "Bumal" size was added at the machine chest, the first alum between the machine chest and the machine headbox. The preflocculated whiting was added before the fan pump and the second amount of alum was added downstream of the cleaners.

Example 2 In a second trial (using hard water) to achieve 7 per cent higher paper loading content without detriment to machine running or paper properties, the "Bumal" was added between the machine chest and the machine chest pump, and the first addition of alum was made between the machine-chest pump and the machine headbox. The preflocculated whiting was added after the machine head box and the second addition of alum was made to the backwater at the mixing pump inlet. A polyacrylamide retention aid (Hydracol 852) was added after the selectifiers during most of the trial.

The sizing chemical additions were as follows: "Bumal" size 0.5 per cent 1st alum 1.5 per cent 2nd alum 1.5 per cent.

The average whiting loading was 22 per cent and the results of the various strength tests (burst, tensile) were as good as the normal specifications of paper containing only 15 per cent loading of the filler. The Cobb water penetration test averaged 18.

WHAT WE CLAIM IS: 1. A papermaking process which includes the steps of supplying a machine headbox with a thick pulp stock treated with rosin size and sufficient alum for fixing the size; continuously conveying the thick pulp stock from the machine headbox to a mixing point where it is diluted with machine backwater; pumping the resultant thin pulp stock to provide a continuous supply of pulp stock to the breast box on a papermaking machine; and incorporating further alum into the thin pulp stock before application of the pulp to the papermaking machine; wherein the thick pulp stock is prepared in the substantial absence of acid-reactive filler, and acid-reactive filler is continuously added to the pulp stock only after the latter has left the machine headbox.

2. A process according to claim 1, wherein the further alum is incorporated into the pulp stock after the addition of acid-reactive filler.

3. A process according to claim 2, wherein the acid-reactive filler is added to the thick pulp stock.

4. A process according to claim 1, 2 or 3, wherein paper broke is added to the pulp stock after the addition of the acid-reactive filler.

5. A process according to any of claims 1 to 4, wherein the acid-reactive filler is added in preflocculated form.

6. A process according to claim 5, wherein the acid-reactive filler comprises calcium carbonate.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. Example 1 A ten-hour trial was run on a high-speed printing quality paper machine (using soft water) with the acid rosin sizing system and whiting addition according to the invention in order to assess whether the strength achieved with 16 per cent clay loading could be maintained with 21 per cent whiting loading using this process. The whiting had been preflocculated by means of a starch/alginate combination. The sizing chemical additions were as follows: "Bumal" 0.55 per cent 1st alum 1.4 per cent 2nd alum 1.45 per cent The average whiting loading was 21.8 per cent whilst maintaining strength, and the (British Standard 2644/1955) Cobb water penetration test averaged 20, thus indicating that sizing had been satisfactorily achieved with a higher filler loading. In this test the "Bumal" size was added at the machine chest, the first alum between the machine chest and the machine headbox. The preflocculated whiting was added before the fan pump and the second amount of alum was added downstream of the cleaners. Example 2 In a second trial (using hard water) to achieve 7 per cent higher paper loading content without detriment to machine running or paper properties, the "Bumal" was added between the machine chest and the machine chest pump, and the first addition of alum was made between the machine-chest pump and the machine headbox. The preflocculated whiting was added after the machine head box and the second addition of alum was made to the backwater at the mixing pump inlet. A polyacrylamide retention aid (Hydracol 852) was added after the selectifiers during most of the trial. The sizing chemical additions were as follows: "Bumal" size 0.5 per cent 1st alum 1.5 per cent 2nd alum 1.5 per cent. The average whiting loading was 22 per cent and the results of the various strength tests (burst, tensile) were as good as the normal specifications of paper containing only 15 per cent loading of the filler. The Cobb water penetration test averaged 18. WHAT WE CLAIM IS:

1. A papermaking process which includes the steps of supplying a machine headbox with a thick pulp stock treated with rosin size and sufficient alum for fixing the size; continuously conveying the thick pulp stock from the machine headbox to a mixing point where it is diluted with machine backwater; pumping the resultant thin pulp stock to provide a continuous supply of pulp stock to the breast box on a papermaking machine; and incorporating further alum into the thin pulp stock before application of the pulp to the papermaking machine; wherein the thick pulp stock is prepared in the substantial absence of acid-reactive filler, and acid-reactive filler is continuously added to the pulp stock only after the latter has left the machine headbox.

7. A papermaking process substantially as hereinbefore described with reference t

Figure 2 of the accompanying drawings.

8. A papermaking process substantially as described in Example 1 or 2.

9. Paper whenever made by a process according to any of claims 1 to 5 and 7.

10. Paper whenever made by a process according to claim 6 or 8.