US2173167A - Paper and method of making the same - Google Patents

Description

Patented Sept. 19, 1939 UNITED STATES PATENT CFFICE PAPER- AND METHOD OF MAKING THE SAME I Rexi'ord William Hovey, Bronxville, N. Y., assignor to Oxford Paper Company, a corporation of Maine No Drawing.

Application June 26, 1937,

.Serial No. 150,539

7 Claims.

, whole or in part from groundwood pulp insofar as its fibrous content is concerned.

The principal object of the invention is to improve the qualities of that type of paper, particularly its color and brightness.

Groundwood pulp is used in making paper chiefly because of its cheapness and because it makes possible a light weight sheet of high opacity. It has the disadvantage, however, of imparting to the finished sheet a poor printing surface as well as a yellowish or brownish color which has been characterized as off-shade or dull. The more groundwood used in the furnish the darker will be the color of the sheet and the poorer its grade. However, the brightness of airdried fibrous furnish mixtures composed of chemical pulps and groundwood is not, as might be expected, directly proportional to the percentage of groundwood in the funiish. Actually the brightness of a chemical pulpgroundwood mixture is much lower than one would calculate. In other words, the brightness of suchamixture is not an additive property of the mixture. Actual tests have shown that adding a small percentage of groundwood to a bright chemical pulp, such as bleached sulphite pulp, lowersthe brightness of the mixture greatly and into a brightness range very little greater than that of the groundwood itself. For instance, adding lessthan 25% of groundwood to bleached sulphite pulp having a brightness of approximately 8'7 lowers its brightness to" less than 70. its the percentage of groundwood is increased above 25% the loss of brightness of the mixture is much more gradual.

The brightness range of chemical pulp-ground- .wood furnishes, is therefore quite limited for any practical groundwood usage, say 20% or overs It will thus be seen that even the. bettergrades of groundwood paper. containing a substantial amount of very bright chemical pulp, and a relatively small percentage of grou'ndwood-while somewhat brighter than the poorer grades containing more groundwoodare still dull and of low brightness. Consequently they have been classified up to this time as poor grades of paper,

when compared with papers containing no.

groundwood, and therefore they are used only in publications of the lower class. It is apparent from the foregoing that groundwood has a much greater covering and tinctorial power than chemical pulps. No doubt this covering and tinctorial power of .groundwood also accounts for the fact that even when a clay filler is used with groundwood paper the clay is incapable of im proving the brightness of the paper sufliciently to take the paper out of its poor grade classification.

Not only is groundwood pulp unsatisfactory for use in the better grades of paper because of its original dark color, but also because it discolors or darkens still more when the web is subjected to the heat of the usual driers of the paper making machine. Bleached chemicalpulps can be produced which do not discolor appreciably when heat dried, but it is impracticable to produce groundwood pulp which will not be discolored by the heat of the driers.

In accordance with my .invention .1 improve the qualities of groundwood paper, particularly its color and brightness and printability by the use of an alkaline filler, such as calcium carbonate, which possesses high brightness and great tinctorial power and which may be produced in very fine particle size thus giving it high covering power, the use of such filler being in excess of a certain unexpected minimum amount hereinafter specified. This minimum amount, which I have ascertained to be quite different from what one would suppose, as hereinafter explained, has been found to be necessary to completely offset or counteract the discoloration of the groundwood due to heat drying, it being only the filler in excess of that minimum amount that serves to increase the brightness of the Paper above the original brightness level of the unheated (or airdried) fibrous furnish.

' In making groundwood paper pitch troubles are often encountered due to the pitchy' constituents of the wood. These separate out and often agglomerate and then deposit in the heaters, stufi lines, chests, Jordans, on the machine wire and on the dandy and wet press rolls and other places. Even if pitch troubles do not develop they are l atent and may be easily and unexpectedly brought on by some slight departure from standproved by the use of alkaline fillers, such as calcium carbonate.

It is well recognized that the use of hard water, or the presence of excessive amounts of lime salts in chemical pulps augments pitch troubles and it might be expected from this that the use of an alkaline filler in groundwood paper is wholly impracticable. However, I have discovered that this is not the case as actual use of the invention has shown that an alkaline filler does not always augment pitch troubles.

If the discoloration of the groundwood pulp due to the heat drying is to be oflset so that'the dried sheet is at least as bright as a corresponding air dried groundwood sheet containing no filler, a certainamount of carbonate filler must be added to the furnish to accomplish this, and more than this amount must be used to enhance the brightness of the sheet beyond this point. I have discovered that the amount of carbonate filler which is required to ofiset the heat discoloration of the groundwood and'to enhance the brightness of the sheet beyond this point is quite difierent from the amount that one would be led to expect from the great brightness, covering power and tinctorial powers of this type of filler.

' I have ascertained that when carbonate filler is employed with groundwood pulp the alkalinity of the filler causes an additional discoloration of the groundwood and with any given type of groundwood a certain minimum quantity ;of the solid carbonate particles must be present to 0!!- set this additional alkaline discoloration. Therefore, the amount of carbonate filler, that will Just supply this minimum quantity of solid particles, has no brightening eilect at all. It is only the quantity of carbonate filler over and above this amount that becomes eflective in enhancing the brightness. Actual tests have shown that as the quantity of carbonate filler is increased by small amounts from zero, the brightness of the sheet is first lowered until a maximum discoloration is produced. Thereafter additional amounts of carbonate filler will start to increase the brightness from the minimum level so that eventually a point is reached where the brightness of the finished sheet is again at the starting point, in other words, just equal to the brightness of a corresponding groundwood sheet that contained no carbonate filler. This is the minimum amount of carbonate filler that is required to just oflfset the discoloration due solely to the alkalinity of the filler. The maximum amount of discoloration, and the percentage of carbonate filler which will produce the maximum discoloration, vary to some extent with difierent types of groundwood. Likewise, the minimum amount of carbonate filler that is required to just offset the discoloration due solely to the alkalinity of the filler varies withdiflerent types of groundwood. The tests showed that approximately 3% to 9% of carbonate filler is required, depending upon the type of groundwood used, before the discoloration duesolely to the alkalinity of the 'fiiler is oflfset. Additional amounts of carbonate filler have the effect of brightening the sheet beyond this point and eventually a point is reached where theamount of carbonate filler is Just sufiicient to offset the discoloration of the groundwood due to heat drying. 'With some types of groundwood tested it was found that the amount of carbonate filler required to ac-' complish this was as high as 20%. The least amount of carbonate filler required by any of the groundwood samples tested was 10%. The average for all of the types of groundwood tested was approximately 14%. These results show that in every case the amount of carbonate filler that should be used to offset the heat discoloration of the groundwood and to enhance the brightness of the sheet beyond this point is in excess of 10%. The percentage figures referred to are based on the total weight of the finished sheet.

It will be understood that the invention is not limited to the use of any particular amount of carbonate filler in excess of 10%. By using a sufficient amount of carbonate filler in excess of 10% it is possible to make paper from a furnish containing a large percentage of groundwood that is equally as bright as an average grade of clay filled book or publication paper made from bleached soda and sulfite pulp. While the invention is concerned with the manufacture of paper that is ordinarily known as groundwood paper, it is not limited to the use of all groundwood pulp, as chemical pulps, either bleached or unbleached, may also be, used with the groundwood if desired. In fact, it is customary to use a certain percentage of chemical pulps in the manufacture of most of the paper known as groundwood paper.

It has been found by actual tests that the above mentioned minimum of 10% of carbonate filler holds true even when the groundwood comprises as low as 20%.of the fibrous furnish and the remainder of the'fibrous furnish comprises commercial sulfite and soda pulp. These tests, conducted with furnishes containing various chemical pulps, and in which groundwood formed various percentages, showed that the minimum amount of carbonate filler required to ofi-set both alkali and heat discoloration was about 10% when the groundwood constituted a practicable percentage of the furnish, i. e., 20% or over. It is apparent that the high covering and tinctorial power of groundwood as compared to chemical .pulp, which seems to cause the great loss in brightness of a chemical pulp-groundwood mixture, evenwhen a small percentage of groundwood is used, as pointed'out above, is partly responsible for the large amount of carbonate filler that is required to accomplish my purpose, even though the percentageQoflgrqundwood in the furnish is relativelylow, .[Thus'the minimum amount of carbonate filler; which. the paper should contain to off-setthe alkali'and heatldiscoloration of the groundwood and to enhance the brightness of thepaperjbeyond this point is in excess of 10%" for mixed chemical pulp groundwood furnishes containing a practicable amount of groundwood, and also for furnishes containing all groundwood.

It is known in the paper industry that when dyestuffs are used for tinting papers which containa high percentage of groundwood, the resulting shade is not pleasing to the eye. However, I have discovered by experimentation that groundwood papers can be tinted with dyestuffs to a very pleasing shade if alkaline fillers, such as calcium carbonate, are incorporated with the paper in amounts exceeding 10% ofthe paper weight. There are dyestufls, such as pigment dyestufis, on the market which are effective at pH values of about 7.0 and which are, therefore, well suited for the manufacture of papers containing groundwood and alkaline fillers.

Paper made in accordance with my invention may be either sized or unsized. The size may berosin size, paraflin emulsion or any other suitable sizing material. All of the ingredients may be added to the beater or at any other suitable point, or any ingredient may be added wherever desired. Satisfactory unsized high grade publication paper has been made in accordance with the invention from a furnish which includes as its principal ingredients, unbleached groundwood pulp, bleached sulfite pulp. bleached soda pulp, calcium carbonate filler, alum and in some instances starch. Substantially the same furnish with the addition of size may be used to produce a satisfactory sized high grade publication paper. If the alkaline filler used has suflicient alkalinity to impart to freshly boiled distilled water a pH as high'as 9 or 10, it may be desirable to pretreat it prior to its addition to the furnish with alum or other acidic material to reduce its pH to around 7.5. While I do not believe this to be essential, so far as pitch troubles are concerned, it may eliminate other troubles that sometimes arise when-the furnish is too alkaline.

Unsized high grade book and magazine paper having the desired properties may be made from the illustrative furnish shown in the. following table:

Materials added at the beater: Pounds Bleached sulfite pulp .400 Bleached soda pulp 575 Unbleached groundwood 500 Broke 200 Alkaline filler, preferably calcium carbonate 700 Alum I a 20 Materials added to mix proportionately and continuously at the Jordan outlet. Alum 30 Sized-high grade book and magazine paper may be made from the following illustrative furnish:

Materials added proportionately and continuously at Jordan inlet. Alkaline filler, preferably calcium carbonate..- 700 Materials added proportionately v and continuously at Jordan outlet. Alum 45 High grade newsprint may be made from the following illustrative furnish:

Materials added at the beater: Pounds Unbleached sulfite pulp 400 Unbleached groundwood 1000 Broke 300 Alkaline filler, preferably calcium carbonate 700 Alum 20 Materials added to mix proportionately and continuously at the Jordan outlet.

Alum

The weights appearing in the above furnishes are on the air dry basis. It will be noted that in the first two tables the groundwood pulp constitutes substantially 30% of the fibrous furnish, and the alkaline filler constitutes substantially 30% of the combined fibrous and filler furnish, calculated on the air dry basis. In the third table the percentage of alkaline filler remains substanexpensive and I prefer not to use them in cases where it is desired to keep down the cost of production of the paper. It has been found that an inexpensive paper fulfilling the objects of the invention can be made without the use of these or any of the other relatively expensive materials.

While the above furnishes indicate the use of unbleached groundwood, bleached groundwood may be used if so desired.

The brightness of the paper will depend in part upon the percentage of groundwood used in the furnish, but no matter how much groundwood is used the paper' filled with alkaline filler in accordance with my invention will be very much improved in this and other respects over groundwood papers heretofore made in which the same amount of groundwood has been used. In fact even when my paper contains a large percentage of groundwood it may be made brighter than groundwood papers heretofore made which contained a smaller percentage of groundwood. The book and magazine paper made in accordance with the above illustrative furnishes will be as bright as the average grade clay filled publication paper made from chemical pulp.

Light weight papers of high opacity may be made by my method because both groundwood and the alkaline filler are good opacity increasing ingredients. Moreover, the substance that produces the discoloration due to alkalinity and heat drying remains in the paper and also serves as an opacity increasing agent and adds its own opacity effect to that produced by the presence of the groundwood and the solid filler particles. Thus the brightening of the sheet is accomplished, not bychemically ,altering the groundwood or the discoloring substance formed by the alkalinity and heat drying. Such an action would remove or chemically alter the discoloring substance and chemically restore the groundwood to its originalcolo r. In my method the brightening effect of the carbonate filler is more of a mechanical one as the discoloring substance formed in the paper due to'alkalinity and heat drying is permittedto remain in the paper without alteration to increase its opacity, as above stated, and the solid particles of carbonate mechanically cover up or obscure the discoloring substance and the original dull or dark color of the groundwood. A light weight paper made in accordance with the invention has greater opacity than the same weight paper made from sulfite and soda pulp containing either clay or calcium carbonate as a filler, and likewise has greater opacity than a ground wood paper filled with clay.

' Rapid.modern printing and costly distribution conditions have created a demand for an econ0mical printing paper, such as newsprint, book and magazine paper possessing high color, brightness, high opacity, smooth surface and .rapidprintability (ink receptivity). Paper made by my method satisfies all of these requirements. The high opacity which is obtained by the conjoint terial. fade less rapidly than the cheaper grades, and it use of groundwood and alkaline filler makes possible the use of lighter weight sheets which will materially reduce distribution costs. A smooth filled surface is obtained by the use of alkaline filler and it also imparts rapid ink receptivity.

It is well recognized that most groundwood papers fade rapidly, particularly so if they possess acidity from the use of alum or other acidic ma- The better grades of groundwood paper is therefore possible, by employing a more expensive groundwood, to produce paper which has fairly good permanence but this is at the sacrifice of low cost. Paper made in accordance with my invention is neutral or slightly alkaline and as a consequence fades less rapidly than the usual groundwood papers employing the same grade of groundwood, and other materials. The invention makes it possible to utilize an inexpensive grade of groundwood and yet produce a paper which will not fade rapidly. It has been proposed to make a neutral unsized groundwood paper which does not fade rapidly by omitting alum from the furnish but the omission of alum from a furnish containing groundwood accentuates the possibility of pitch troubles and other machine operation difllculties. My invention makes possible an unsized groundwood paper which does not fade rapidly and yet it is not necessary to omit alum from the furnish. On the contrary, alum may be used for its advantages in helping to eliminate pitch troubles and other machine operation difilculties because the desired non-acid character of the paper is brought about by the use of the alkaline filler. Moreover, the expedient of omitting alum to obtain a neutral groundwood paper which will not fade rapidly obviously cannot be resorted to in making a sized groundwood paper where alum is essential to precipitate the size. Inasmuch as my process permits the use of alum without producing an acidic paper the invention makes pos- L sible a sized groundwood paper which will not fade rapidly and in the manufacture of which the alum may be used for its usual function of precipitating the size and for its additional advantage of helping to eliminate pitch troubles and other machine operation difiiculties. I am aware of the proposal to make neutral sized paper by employing sodium aluminate to supply a portion of the alumina necessary for rosin sizing, and at the same time effect neutralization of alum-acidity. The useof sodium aluminate for this purpose, however, entails added expense, and further, the presence of an alkaline filler accomplishes the same end in that it causes complete hydrolysis of alum producing the desired alumina and likewise' neutralizes the alum-acidity.

The termalkaline filler as used herein is intended to include those fillers which impart a pH greater than 7 to freshly boiled distilled water.

I prefer to use calcium carbonate as the filler because of its small expense, it being available at many mills in the form of a by-product of the soda recovery process.

By the term "furnish" is meant a blended mix ture of paper making ingredients completed either in the beater or at a point before web formation.

As I make use of substantial amounts of two inexpensive ingredients, i. e., groundwood pulp, and calcium carbonate, considerable economy is effected. I

The'better grade of paper made in accordance with my invention, notwithstanding the fact that it is primarily a groundwood paper, and notwithstanding its small cost of production, has such properties as to enable it to rank with papers that are used in high grade publications. This makes it possible for publishers who have been using an expensive, high grade paper to substitute for it my groundwood paper and thereby effect a considerable saving without sacrificing the good appearance and other characteristics of their publications. It should be understood, however, that the invention is not limited to the production of groundwood paper which is capable of competing with the high grade book and publication papers, becauseall groundwood papers down to the lowest grade newsprint can be greatly improved in appearance, printability, and other properties by the use of the invention. This makes it possible for publishers of newspapers and the lower class publications, who use groundwood paper, to greatly improve the appearance and other qualities of their publications at less expense, or very little, if any, increase in expense.

I claim:

1: Groundwood paper made from a furnish containing groundwood pulp as part of the fibrous constituents and alkaline carbonate filler, the major portion of the balance of the fibrous constituents of the furnish consisting of at least one pulp of the papermaking group consisting of sulfite pulp and soda pulp, the groundwood being present 'in the paper to the extent of at least 20% of the fibrous constituents of the paper and said alkaline carbonate filler being present in the paper in excess of 10% of the weight of the paper, the brightness of the paper being enhanced by the presence of the alkaline carbonate filler.

2. Groundwood paper made from a furnish containing groundwood pulp as part of the fibrous constituents and alkaline carbonate filler, the major portion of the balance of the fibrous constituents of the furnish consisting of sulfite pulp and soda pulp, the groundwood being present in the paper to the extent of at least 20% of the fibrous constituents of the paper, and said alkaline carbonate filler being present in the paper in excess of 10% of the weight of the paper, the brightness of the paper being engfnced by the presence of the alkaline carbonate ler. 3. Groundwood paper in accordance with gllaim 1 in which the filler is calcium carbonate ler. 4. Groundwood paper in accordance with claim 2 in which the filler is calcium carbonate 5. The method of making groundwood paper whose brightness has been enhanced by alkaline carbonate filler, which comprises preparing a furnish containing groundwood pulp as part of the fibrous constituents and alkaline carbonate filler, the major portion of the balance of the fibrous constituents of the furnish consisting of at least one pulp of the papermaking group consisting of sulfite pulp and-soda pulp; the groundwood pulp being added in an amount such that it will constitute at least 20% of the fibrous constituents of the paper, and the alkaline carbonate filler being added in an amount such that the paper will contain in excess of 10% of the alkaline carbonate filler based on the weight of the paper, and thereafter forming a mixture into a paper web.

6. The method of making groundwood paper whose brightness has been enhanced by alkaline carbonate filler, which comprises preparing a furnish containing groundwood pulp as part of the fibrous constituents and alkaline carbonate filler, the major portion of the balance of the fibrous constituents of the furnish consisting of sulfite pulp and soda pulp, the groundwood pulp being added in an amount such that it will constitute at least 20% of the fibrous constituents of the paper, and the alkaline carbonate filler being added in an amount such that the paper will contain in excess of 10% of the alkaline carbonate flller based on the weight of the paper, and thereafter forming the mixture into a-paper web.

7. The method of making groundwocd paper filler which comprises bringing into association alkaline filler and groundwood pulp and making paper therefrom, the' groundwood pulp constituting substantially 30% of the fibrous furnish calculated on the air-dry basis and the alkaline filler constituting substantially 30% of the combined,flb1f0us and'filler furnish calculated on the air-dry basis.