US2062442A - Method for making paper - Google Patents

Description

Dec. 1, 1936. J. CAMPBELL 2 METHOD FOR MAKING PAPER Filed May 7, 1954 INVENTOR ATTORNEY Patented Dec. 1, 1936 UNITED STATES PATENT OFFICE} METHOD FOR MAKING PAPER Application May 7, 1934, Serial No. 724,236

4 Claims.

My invention relates to the manufacture of paper and more particularly to a new and improved method of, and apparatus for, producing a paper containing an alkali or alkaline earth filler free from. foam marks, possessing satisfactory opacity, brightness and formation.

Heretofore in the manufacture of alkali or alkaline earth filled paper, alum or other acidic material capable of functioning both as a mordant to set the color in the paper and to flocculate the alkali or alkaline earth filler or mixtures thereof, has been added to the beater or stock mixing apparatus containing the pulp and other desired ingredients making up the furnish. The addition of such material has been found to produce excessive foaming as the furnish is fed onto the wire or other web forming mechanism of the paper machine. The occurrence of such foaming not only impairs the paper formation but also produces foam marks on the finished paper. The foam is apparently due to the fact that the gases formed as a result of the chemical reaction between the filler and the acid setting material is occluded or held in suspension in the large mass of stock in the beater or mixing tank but becomes liberated when the stock flows on the wire in a wide, comparatively thin stream of relatively low consistency.

Accordingly, the primary object of my invention is to provide a method for the incorporation into a furnish containing alkali or alkaline earth fillers or mixture of the same, as for example, calcium carbonate, of a solution of an acidic setting material, as for example, alum or magnesium chloride and the like in such a manner that the pH value of the solution does not become 7.0 or lower, but at all times remains alkaline, that is a number greater than 7.0, Whereby excessive foaming is avoided and whereby the resultant paper is smooth and free from foam marks or other defects which normally result from excessive foaming of the stock.

Another object of my present invention is to provide a new and improved method for the manufacture of an alkali or alkaline earth, or mixture of the same, filled paper, which substances are normally reactive with acidic material, wherein the acid mordanting and setting material is added to a paper furnish containing said filler in such a manner that the pH value of the filler always remains on the alkaline side, that is, above 7.0 even in localized areas in the furnish whereby foaming of the stock is avoided.

These and other objects of my invention will become more apparent from a study of the folcomp-anying drawing in which my improved method and apparatus is schematically illustrated wherein the portion of a paper machine with which my invention is associated is schematically set forth.

In the drawing, l0 represents the usual beater chest or stock mixing device, and the stock is drawn therefrom through the conduit H into a Jordan l2. The stock passes from the Jordan through a conduit l3 and into a machine chest It. From there it passes through conduit l5 into a second Jordan l6. From this Jordan a conduit l'i leads the stock into a head or flow box I8. Other arrangements and systems may be utilized in practicing my invention, and'it is to be appreciated that the foregoing is simply a preferred and existing arrangement.

The head or flow box is provided with the usual apron l9, and slice 20 to regulate the amount of stock flowing out over the apron. The usual Fourdrinier wire 2| passes over the breast roll 22 and the web is formed on the wire in the usual manner. The white water draining from the wire and containing the unretained filler in suslowing description and with reference to the acpension and in solution together with other solids such as pulp in suspension are collected in a wire pit or other collecting device 23. Part of this white water is thereafter clarified and passed back into the system in one manner or another,

the remaining portion being brought back to the machine for re-use.

The apparatus comprising. the preferred form of my invention is henceforth described. A conduit 24 leads from the wire pit or other collecting device 23 to return at least a portion of the white Water containing filler in suspension and/ or solution and other solid matter to the system. A pump, as illustrated a vertical plunger pump 25,

is associated with the conduit 24 to return this portion of the white water and elevates the same above the J ordans and beater chest. The conduit is bent upon itself and the white water is passed downwardly into an auxiliary chest 26 wherein an ingot or ingots of alum are placed. The stream,

of white water containing particles of alkali or alkaline earth filler, in the particular instance calcium carbonate, and other solids, strikes against the ingots of alum, and due to the formation of calcium sulphate by the interaction of they calcium carbonate and alum, a thin filmor skin of this substance is formed on the surface of the alum ingots, thereby causing the gradual wearing away of the ingots. This action prevents toomuch of the alum from going into solution. The

alum in the solution of the white water containing the calcium carbonate in solution fiocculates' the latter. In operation it occasionally happens that portions of the ingots of alum chip off, but inasmuch as these cannot enter into the system no harmful eifects occur.

The hydrogen ion concentration in the solution in the auxiliary chest is sufiiciently low as to maintain the solution substantially neutral or at most but slightly acid, but contains suflicient ions to set the color in the furnish and to cause a sufiicient additional flocculation of the carbonate filler in the furnish to obtain the desired retention of the filler in the finished paper. This solution is preferably added to the furnish through a conduit 28 tapped into the conduit ll between the beater l0 and Jordan I2.

The solution containing alum, as above described, is thus added to the furnish at a uniform,

rate, and at a point in the system where it is most likely to come into close association with all of the furnish and is immediately thoroughly dispersed through the furnish by the rapid mixing action of the Jordan. I have found that when such a solution is added to furnishes containing acid reactive fillers in a fine stream of relatively low concentration that the fiocculating action between the solution and the filler will be sumcient to obtain the proper retention of the latter in the sheet and the amount of gas generated by such action is not sufficient to cause foaming. According to prior practices it has been found that when alum is added to certain furnishes in a fine, relatively concentrated stream directed into a large, relatively slow moving mass of furnish, immediately at the point of combination there will be a relatively rapid reaction between the alum and other chemicals such as carbonates. This reaction results in the release of a large amount of carbon dioxide gas, calcium sulphate, aluminum hydroxide and other solid reaction products. Due to the density and mass of the furnish the carbon dioxide gas does not escape until the furnish passes onto the wire of the machine and makes its appearance as foam, causing foam marks in the finished paper. By means of my improved method, however, the furnish and alum solution is intimately and evenly mixed and the hydrogen in concentration is sufliciently low to maintain a pH value on the alkaline side at all points through the mix. According to my invention the amount of carbon dioxide gas liberated is not greater than that amount sumcient to combine with the normal calcium carbonate filler to form an acid carbonate. In other words all of the gas formed is absorbed by the filler whereby foaming is prevented as the furnish passes onto the wire of the machine.

Instead of using blocks or ingots of alum I can also allow a stream of dilute alum solution to fiow into the auxiliary chest, and by providing the chest with suitable mixing mechanism, can obtain the same results as when alum in ingot or block form is used.

It can be appreciated that the alum and the remainder of the furnish is thoroughly mixed in the space of a relatively few seconds and thereafter will be in close association for a relatively long period of time; for instance, several hours in the machine chest. The furnish in the machine chest is usually circulated by very slowly moving paddles or other means andduring this circulation reaction as desired may take place. It was ordinarv practice heretofore to add alum and other chemicals to the pulp in the heater, or possibly one of the chests, and it was found that before the slowly circulating pulp in these mechanisms was thoroughly mixed with the alum solution there had taken place a too violent reaction in certain areas and no reaction in other areas. This is avoided by my process.

An advantage which is immediately apparent is that a sample of the entire uniform mass may be obtained immediately as the furnish emerges from the Jordan, and the control man does not need to wait several hours until he feels that the mixture is uniform. Thus in a relatively short period of time an analysis may be made and the amount of alum solution may be instantly. controlled by limiting the amount of white water pumped back over the alum ingots. This is very important since the amount of alum must be empirically determined for each grade of paper being made, and either too much or too little alum can do immense harm since the amount of alum controls to a large extent the retention of filler, the setting of the color and the qualities of the paper, such as opacity, brightness, two-sidedness and other properties. In all prior systems of which I am aware the control of alum was necessarily delayed several hours until a thorough mixture could be sampled, and as a result of such delay there might be as much as two or three tons of inferior paper made by the machine before such defects could be uniformly and thoroughly corrected.

It will be appreciated by those skilled in the art that my invention is not limited to the use of calcium carbonate as a filler nor to alum as the acid setting solution. Any of the alkali or alkaline earth fillers may be employed as well as any of the acid reactive mordanting compounds.

Other apparatus may be utilized and I do not intend to be limited except by the scope of the following claims:

What I claim is:

1. The method of adding alum to a furnish containing acid reactive filler comprising passing Water over an ingot of alum and adding the resulting solution to the furnish before it passes into the Jordan and while it is passing through a relatively constricted conduit.

2. In the method of making paper, the steps of passing white water containing alkaline filler in suspension over ingots of alum and incorporating the resulting solution into the furnish between the beater and the Jordan.

3. In the manufacture of filled paper, the steps of passing a stream of white Water containing calcium carbonate in suspension over a block of alum whereby suspended matter is fiocculated and the pH value of the mixture is maintained at approximately '7, adding such mixture in a stream to a furnish containing calcium carbonate after said furnish has been subjected to a beating action.

4. In the manufacture of paper containing calcium carbonate as a filler, the steps of treating white water containing calcium carbonate in suspension with alum until the pH value of said solution is maintained at a figure sufliciently neutral to prevent a formation of free carbon dioxide gas, the carbon dioxide gas being formed entering into combination with the calcium carbonate to form calcium bicarbonate, adding such solution in a stream to a furnish containing calcium carbonate.

JOHN CAMPBELL.

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