US3019157A

US3019157A - Web-forming fibrous suspensions of improved freeness

Info

Publication number: US3019157A
Application number: US765320A
Authority: US
Inventors: Jr Walter F Reynolds; Norman T Woodberry
Original assignee: American Cyanamid Co
Current assignee: Wyeth Holdings LLC
Priority date: 1958-10-06
Filing date: 1958-10-06
Publication date: 1962-01-30
Anticipated expiration: 1979-01-30
Also published as: FR1238588A; DE1264942B; DE1264942C2; GB873560A

Description

United States Patent ()fiice 3,019,157 WEB-FORMING FIBROUS SUSPENSIONS OF IMPROVED FREENESS Walter F. Reynolds, Jr., and Norman T. Woodberry, Stamford, Conn., assignors to American Cyanarnid Company, New York, N.Y., a corporation of Maine No Drawing. Filed Oct. 6, 1958, Ser. No. 765,320 16 Claims. (Cl. 162-168) The present invention relates to the manufacture of paper, cardboard, hardboard, building board and similar waterlaid cellulosic webs (hereinafter for brevity termed paper) by a process wherein papermaking pulp is treated with an anionic vinyl polymer of ultrahigh molecular weight to increase its freeness when the pulp is sheeted upon a papermaking wire screen.

The above-mentioned cellulose products are and have long been manufactured by a process which comprises agitating or beating cellulose fibers in water until the fibers have developed a hydrated and frayed surface, flowing the fibers upon a continuously moving wire screen to form a waterlaid web, allowing the free water in the web to drain therethrough, and removing substantially all of the rest of the water by the use of suction followed by drying rolls. One of the limiting factors of papermaking machines is the rate at which the free Water drains through the web, and in the past numerous attempts have been made to increase this rate.

It has long been known that paper pulp is chiefly composed of two types of fibrous materials, one being long cellulose fibers, and the other being the fines (i.e., the particles which pass through a screen having 100 wires to the inch and which are predominantly composed of cell-wall fragments). It has likewise long been known that the fines are the principal components of the pulp which seriously retard the passage of free water through the waterlaid web. Up to the present it has not been found possible to treat the pulp prior to sheeting so as to substantially increase the freeness of the pulp without at the same time seriously decreasing the tensile strength of the paper.

The discovery has now been made that a substantial improvement in the manufacture of paper can be effected by forming on the fibers and fines of the papermaking pulp a hydrous alumina complex of an ultra-high molecular weight water-soluble anionic linear carbon chain polymer substantially composed of carbamoylalkylene and carboxyalkylene linkages, as more particularly hereinafter specified. We have found that in preferred embodiments the presence of the hydrous alumina-polymer complex on the fibers during sheeting results in the formation of a Web through which water drains at a substantially increased rate permitting a major increase in papermaking machine production ratios, without more than negligibly adversely affecting the quality of the paper produced.

A preferred embodiment of the invention is illustrated by the following flow-diagram:

Form aqueous suspension of cellulose papermakmg fibers Add between 0.5% and. 5% (based on dry weight of fibers) of alum thereby decreasing pH below 5 Add alkali to raise pH by 0.1 pH unit but not above pH 8 Patented Jan. 30, 1962 Add 0.000175 to 0.1% (on dry Weight of fibers) of anionic carbamoylalkylenecarboxyalkylene polymer having a molecular weight 5,000,000

Sheet Dry tion is not known and we do not wish to be bound by any theory. Comparative laboratory experiments based on the preparation of a series of pulps containing increasing amounts of the hydrous alumina-polymer complex have shown that the effect of the complex is to cause selective agglomeration of the fines, i.e., agglomeration or coalescence of the fines without corresponding agglomeration or coalescence of the large cellulose fibers. These conclusions are based on the observation that the hydrous alumina-polymer complex, when present in amounts called for by the present invention, causes a major improvement in the rate at which free water drains through the wet web during the papermaking operation without objectionably changing the formation of the sheets obtained. The process thus has substantially no adverse effect upon the dry tensile strength of the sheet.

The process of the invention has following additional advantages:

1) The process is very effective. In preferred embodiments we have found it possible to increase machine speeds by more than 20%. Since papermaking machines are customarily run at the maximum speed of which they are capable in any instance, the present invention permits a substantial increase in machine output.

(2) The process is economical. To date we have not found it necessary to use more than about 0.1% of polymer, based on the dry weight of the fibers, and usually far less is required.

(3) The process is simple. It may be incorporated in most cconventional papermaking processes and does not require unusual control. It may be used in conjunction with existing white-water systems and in connection with currently used commercial pulps.

Formation of the hydrous alumina-polymer complex on the fibers and fines may be accomplished in a variety of ways. In the manufacture of raw paper such as news print, towelling, facial tissues, and coating rawstock, it is generally most convenient to form the hydrous alumina by addition of alum to the papermaking fibrous suspension followed by alkali, the polymer being added subsequently, just prior to the sheeting step. The function of the alkali is to form alumina floc, hereinafter sometimes also termed hydrous alumina. This hydrous alumina must be formed prior to addition of the polymer, but the caustic may be added with or in advance of the alum.

Alternatively still, the alum and alkali may be added first, after which the pulp may be washed with water to remove all free ions and unadsorbed hydrous alumina. The polymer is then added just before the sheeting step, as described. This procedure yields a paper containing no free polyvalent metal or sulfate ions and is thus of particular value to the photographic industry. The procedure is of theoretical interest as it shows that the results obtained stem from formation of the hydrous aluminapolymer. complex directly on the. surface of the fibers.

Further, any water-soluble hydrolyzable aluminum salt may be used in place of alum, and for this purpose aluminum chloride, aluminum bromide, aluminum nitrate and aluminum benzoate are suitable.

In the manufacture of rosin sized paper, according to a preferred embodiment of the present invention, the rosin size followed by alum is preferably added as is customary at the beater or similar location in the papermaking system, after which the polymer is added immediately prior to sheeting. The rosin size acts as an alkali but the supplementary addition of caustic alkali is sometimes advantageous, particularly where the amount of rosin size added is small. The amount of alum added should preferably be sufiicient to decrease the pH of the suspension below 5, set the size when added, and yield sufficient alumina hydrate for formation of the complex in effective amount.

The agglomerates of fines which are formed upon addition of the polymer are weak physically, and hence the pulp is best sheeted immediately thereafter without 11nnecessary agitation.

The action of the polymer in causing selective agglomeration of the fines is practically instantaneous. The polymer is therefore generally best added as a dilute solution across the width of the headbox. Where the headbox is closed, the polymer is best added immediately upstream therefrom, for example at the headbox screens, so that in either event the polymer is uniformly distributed in the fibrous suspension without need for agitation.

After treatment as described above, the pulp is processed in customary manner. It will be found, however, that the speed of the machine can be substantially increased.

Viewed from the point of view of the treated suspension it will be seen from the foregoing that the present invention provides a fibrous suspension comprising cellulose fibers and cellulose cell-wall fines uniformly carrying the aforementioned hydrous alumina-polymer complex, the amount of the complex being sufficient to increase the freeness of the suspension but insufficient to decrease substantially the dry tensile strength which paper made from the fibrous suspension would otherwise possess, i.e., would possess in the absence of the complex.

The pulp may be wholly composed of natural fibers or may contain a minor proportion of fibrillated synthetic fibers and in addition may contain minor conventional amounts of supplementary materials commonly used in papermaking such as pigments, dyes and fillers.

The amount of alum (or other equivalent salt) needed by the process of the present invention is at least about 1%, calculated as Al (SO .14H O based on the dry weight of the fibers, and considerably more, up to about 5%, can be used without harm. We prefer to have about 2% to 3% present, as this amount is sufiicient to form an adequate amount of hydrous alumina floc, and avoids the danger of forming too little.

The minimum amount of alkali needed is small. In general, an effective amount of hydrous alumina is formed when the amount of alkali (or rosin size) added is sufficient to decrease the acidity of the alum-treated suspension by 0.1 pH unit and preferably by 0.5 pH unit. Best results are generally obtained when the amount of alkali added is sufiicient to increase the pH to 5.5-6.5. Good results are still obtained even when the pH is increased into the alkaline range, at least up to about pH 8.

The amount of polymer added in any one instance according to the present invention depends on a number of variables of which the composition of the polymer itself, its molecular weight, the particular pulp or pulp mixture used (and proportion of fines therein) are perhaps the most important. At one extreme, at least sufiicient polymer is added to increase the speed at which free water drains through the web. At the other extreme, the amount of polymer added is insufficient to decrease substantially the dry tensile strength of the paper.

In general, more polymer is needed to produce a given increase in machine speed when the proportion of carboxyl groups is outside the preferred range and when the molecular weight is low as compared with high. Moreover, pulps which are high in fines and pulps which are highly hydrated are particularly responsive to the polymer complex and less polymer is needed in the case of such pulps than is required in the case of less highly beaten and hydrated pulps. As a result, the optimum amount of polymer to be added in any one instance is generally most conveniently determined by actual trial, employing the methods illustrated in the examples below as guides.

The polymer employed in the process of the present invention is substantially composed of carbamoylalkylene and carboxyalkylene i l-( (o 0 OH)- linkages containing not more than 4 carbon atoms each having a molecular weight in excess of 5 million determined from its intrinsic viscosity by modified Staudinger shear varies between 600 and 1500 reciprocal seconds at the solids concentrations used. The values obtained are plotted to infinite dilution, which gives the intrinsic viscosity of the polymer in deciliters per gram.

The molecular weight is calculated from modified Staudinger formula wherein M is the weight average molecular weight, and is the intrinsic viscosity determined as shown above.

Suitable polymers may be prepared by partially hydrolyzing a polyacrylamide of ultra-high molecular weight or by copolymerizing acrylamide and acrylic acid in suitable ratio to suitable molecular weight.

The polymerization reaction is advantageously performed by polymerizing a suitable monomer or mixture of monomers in the presence of particular classes of redox catalyst systems. These are mixtures of water-soluble tertiary amines with oxidizing agents such as the watersoluble persulfates, for example an alkali metal or ammonium persulfate, or with peroxides such as hydrogen peroxide and the like and, as a second class, mixtures of water-soluble bromates such as an alkali metal bromate with water-soluble sulfite reducing agents such as sodium sulfite or sodium bisulfite. When these catalyst systems are used it is possible to obtain polymers within the molecular weight ranges discussed herein by controlling the polymerization temperature and the molar ratios of the two ingredients of the redox catalyst system.

When the tertiary amine-chemical oxidant'redox system is used, polyacrylamides having molecular weights of 10-11 million and higher are obtained by employing a substantial molar excess of tertiary amine over the persulfate or peroxide, and in most cases quantities of from 2 to about 6 mols of tertiary amine for each mol of persulfate or peroxide, and in most cases quantities of from 2 to about 6 'mols of tertiary amine for each mol of persulfate or peroxide should be used. Polymers having molecular weights from about 6 to 10-11 million are also obtainable with molar ratios of the catalyst ingredients within this range when polymerization temperatures in excess of about 30 C. are used, particularly when the weight ratio of the catalyst system to the acrylamide monomer in solution is increased. When the second type of 'redox system is used the preferred new polyacrylamides having molecular weights of at least 10-11 million are produced by operating at temperatures below 20 C. and preferably below 10 C. with a system containing from about 0.1 to 0.8 mol of the sulfite for each mol of the bromate. The intrinsic viscosity of the polymer decreases as the molar ratio of the sulfite to the bromate approaches 1:1, and also as the weight ratio of bromate to acrylamide monomer is increased. A molecular weight of 5 million is about the least that makes the present invention economically worth while, and much better results without offsetting difficulties are obtained from polymers having a molecular weight in excess of 10 million, and particularly in the range of -25 million, which are therefore preferred. The polymers larger than about 25 million molecular weight yield still better results, but because of their high viscosity even at great dilutions are not as convenient to use and thus fall outside of the preferred range.

The polymeric linkages specified above result from the presence of combined acrylamide, methacrylamide, acrylic acid, methacrylic acid, etc. The polymers may contain minor amounts of other active linkages, for example those derived from maleamide, maleimide, maleamic acid and maleic acid. The polymers may further contain minor amounts of inert (diluent) linkages, for example those derived from acrylonitrile, vinyl acetate (which on hydrolysis subsequent to polymerization yields alcoholic groups), styrene and the lower acrylate and methacrylate esters. It is within the scope of the invention to employ mixtures of polymers of the above description.

The invention will be further illustrated by reference to the examples. These examples constitute embodiments of the invention and are not to be regarded as limitations thereon.

Example 1 The following illustrates the preparation of an ultrahigh molecular weight linear carbon chain polymer suitable for use in the process of the present invention by homopolymerizing acrylamide followed by hydrolysis of a portion of the amide groups.

Distilled water was freed from oxygen by boiling for 15 minutes under a blanket of nitrogen and cooled to C. (also under nitrogen). A solution was made by dissolving 70 parts by weight (1 mol) of acrylamide in 630 parts of this water and charged into a jacketed reactor having a bottom inlet for the injection of nitrogen. Ammonium persulfate and 3,3',3"-nitrilotrispropionamide were added in amounts of 0.04% and 0.16%, respectively, on the weight of the acrylamide and mixed by vigorous injection of nitrogen. Active polymerization began withma few minutes and was continued under a nitrogen blanket for about 8 hours when it was about 98% complete.

During the reaction the temperature was maintained at 20 C. by admission of cooling fluid into the jacket.

The material was dissolved in 6,400 parts of hot water containing 2 parts /go mol) of sodium hydroxide causing hydrolysis of about 5% of the carbamoyl linkages. The product was thus composed of carbamoylethylene and carboxyethylene linkages having the respective theoretical formulae of and -CH CH(CO0H)-. It had an intrinsic viscosity of 18 dl./gm. and hence a calculated molecular weight of about 10.5 million.

6 Example 2 The following illustrates the preparation of a similar ultra-high molecular weight polymer by direct copolymerization of acrylamide and acrylic acid.

A 10% by weight solution of a :5 molar ratio acrylamidezacrylic acid mixture was prepared. in distilled oxygen-free water containing sufiicient of a 120.3 molar ratio sodium bromate:s0dium sulfite mixture to provide 0.02% by weight of sodium bromate based on the Weight of the monomer mixture. The mixture was reacted by the method of Example 1 at 0-5 C. to about 98% completion. During the reaction a small proportion of the amide groups present underwent hydrolysis to carboxyl groups.

The intrinsic viscosity of the polymer as determined by the method of Example 1 was 20 dL/grn. and the calculated molecular weight Was therefore 12.5 million.

Example 3 The following illustrates the effect of the principal steps of the process of the present invention upon the freeness of pulp.

Groundwood pulp having a Canadian standard freeness of 132 ml. (TAPPI standard T-227-m50), a pH of 5.5 and a consistency of 0.3% was divided into portions which were treated as shown in the table below. The alum was added as a 10% aqueous solution in amount equal to 2% of the dry weight of the fibers (sufficient to decrease the pH to 4.6), the alkali (sodium hydroxide) was added as a 10% aqueous solution in amount sufficient to increase the pH to 6.0, and the resin as a 0.1% aqueous solution in amount equal to 0.0125% of the dry weight of the fibres. The aliquots were gently stirred for a few minutes after each treatment. Freeness was determined after each addition to show the effect of each of the steps.

The treated samples were made into paper at basis weight of 45 lb. per 25" x 40/500 ream and the dry tensile strength of the sheets determined by the TAPPI method. Results were as follows. Values shown in parentheses are the results obtained from control pulps, as shown in the footnotes.

1 Millions, calculated from intrinsic viscosity.

2 N o polymer added. Value is freeness of untreated groundwood pulp. Alum only. No polymer or alkali added.

Alum and alkali only. N o polymer added.

This table shows that the addition of polymer (without alum or alkali) caused the freeness of the pulp to decrease; that the addition of alum and polymer (without alkali) also caused the freeness to decrease; but that the addition of alum and alkali, followed by addition of polymer, caused a major improvement in freeness.

Example 4 The following illustrates the effect of variations in the amount of alum, alkali and polymer on the freeness of a commercially important pulp (bleached northern kraft p p)- The pulp had a Canadian standard freenss of 135, a pH of 5.6, and a consistency of 0.3%. It was divided into aliquots which were treated as shown in the table below according to the procedure of Example 3. Results were as follows.

. Alum Added Alkali Percent Canadian Run No. Added Polymer Freeness,

to pH Added Ml. Percent pH Control A T 135 1 0.5 5.0 6. 0.025 165 2... 1.0 4. 7 6.0 0.025 480 3 2. 0 4. 2 6. 0 0. 025 490 3.0 4. 1 6.0 0. 025 510 5.0 6.0 0.025 500 2.0 4. 2 4. 0.025 380 2. 0 4. 2 5.0 0.025 350 2.0 4.2 5.5 0.025 440 2. 0 4. 2 6. 0 0. 025 475 2. 0 4. 2 6. 5 0. 025 495 2. 0 4. 1 4. 4 None 200 2.0 4. 1 4.1 0.025 150 2. 0 4.1 4. 4 0.025 360 2. 0 4.1 5. 0 0. 025 390 2. 0 4.1 7.0 0.025 540 2.0 4.1 8. 0 0.025 410 2. 0 4. 1 6. 0 None 190 2.0 4. 1 6.0 0.00125 220 2. 0 4. 1 6. 0 0.0025 250 2. 0 4.1 6. 0 0.0083 370 2. 0 4. 1 6. 0 0. 0167 450 2.0 4.1 6. 0 0.025 500 2. 0 4. 1 6. 0 0. 042 540 2.0 4. 1 6.0 0.05 545 2. 0 4. 1 6. 0 0. 1 550 The results when plotted on coordinate paper to form a series of graphs show that in general between about 1% and 5% of alum should be added based on the dry weight of the fibers, and that suificient alkali should be added to increase the pH by at least about 0.1 pH unit up to about pH 8, that 0.05% or 0.1% of resin based on the dry weight of the fibers is about the maximum effective amount.

The results further show that the range in which the alum is most economically added is 1%-3% of the dry weight of the fibers, that no more alkali need be added than is necessary to increase the pH to about 6 or 7, and that most eflicient utilization of the polymer (in terms of increased freeness) results when the polymer is added in amount between about 0.001% and 0.01% of the dry weight of the fibers.

Example 5 The following shows that the process of the present invention does not cause substantial harm to the paper produced.

The pulp used was a northern bleached kraft pulp beaten to a Canadian standard frecness of 225 ml. at 0.3% consistency. Two portions were withdrawn. One sample was treated with 1.5% of gum rosin size, 2% alum and 0.0 125% of the polymer of Example 1, based on the dry weight of the fibers. The resulting pulp had a pH of 5.5.

The second portion was treated in the same way except that addition of the polymer was omitted and instead the pH of the example was adjusted to 5.5 with hydrochloric acid. The freeness values of the two pulps were determined and the pulps were made into paper according to standard laboratory procedure and subjected to standard tests with the following results.

Pulp Treatment Physical Property 1.5% rosin 1.5% rosin size, 2.0% sire, alum (no 2.0% alum, polymer) 0.0125% polymer Pulp:

Freeness, Canadian Standard, ml 225 375 Paper:

Basis weight, lbs 46. 2 47.2 Caliper, mils 3. 9 3.8 Specific gravity (apparent) 0. 655 0.685 Opacity, Bausch 8r Lomb tester. 73.9 73.7 Tensile strength, lb./i uch 22. 3 22. 2 Mullen, p.s.i 32 31 Fold, M.I.T 81 84 Internal bonding strength, it.-lb 0. 123 0. 142 Sizing (modified BKY ink test) seconds," 106 131 The results show that the principal properties Were unchanged by the polymer treatment except sizing, which was improved.

We claim:

1. A process of manufacturing paper which comprises uniformly forming on the cellulose fibers and cell-wall fines of a papermaking aqueous cellulose fibrous suspension a hydrous alumina complex of a water-soluble anionic linear carbon chain polymer having a molecular weight in excess of 5 million as calculated from intrinsic viscosity by modified Standinger equation, substantially composed of carbamoylalkylene and carboxyalkylene linkages containing not more than 4 carbon atoms each, the number of said carboxyalkylene linkages being between about 2% and 20% of the total number of carbamoylalkylene and carboxyalkylene linkages, sheeting said suspension on a papermaking screen to form a waterlaid web, draining free water from said web, and drying said web to form paper, the amount of said complex being suhicient to increase the rate at which free water drains through said web and being insuificient to decrease substantially the dry tensile strength of said paper.

2. A process according to claim 1 wherein the fibrous suspension is groundwood.

3. A process according to claim 1 wherein the fibrous suspension is glassine stock.

4. A process according to claim 1 wherein the molecular weight of the polymer is in excess of 10 million.

5. A process of manufacturing paper which comprises forming an aqueous suspension of cellulose papermaking fibers, adding thereto between about 0.5% and 5% of a watersoluble aluminum metal salt based on the dry weight of fibers, thereby decreasing the pH of the suspension below 5, adding sufficient of a watersoluble alkali to decrease the acidity of the suspension by at least 0.1 of a pH unit but insufficient to raise the pH of the suspension above about 8, adding between about 0.0001% and 0.1% based on the dry weight of the fibers of a water-soluble anionic linear carbon chain polymer having a molecular weight in excess of 5 million substantially composed of carbamoylalkylene and carboxyalkylene linkages containing not more than 4 carbon atoms each, the number of carboxyalkylene linkages being between about 2% and 15 of the total number of carbamoylakylene and carboxyalkylene linkages, sheeting said suspension on a papermaking screen to form a waterlaid web, draining free water from said web, and drying said web to form paper.

6. A process according to claim 5 wherein the watersoluble aluminum salt is papermakers alum.

7. A process according to claim 5 wherein the amount of alum added is between 1% and 3% of the dry weight of the fibers.

8. A process according to claim 5 wherein the amount of alkali added is insufficient to raise the pH of the suspension above 7.

9. A process according to claim 5 wherein the weight of added polymer is between 0.001% and 0.01% of the dry weight of the fibers.

10. A process according to claim 5 wherein the anionic polymer is added to the suspension of papermaking fibers immediately ahead of the sheeting screen.

11. A process of manufacturing rosin sized paper which comprises forming an aqueous suspension of cellulose paper making fibers, adding thereto alum in excess of that needed to set the rosin size to be added, adding rosin size in amount at least sufiicient to size the fibers and increase the pH of the suspension by at least 0.5 pH unit, adding between about 0.0001% and 0.01%, based on the dry weight of the fibers, of a water-soluble anionic linear carbon chain polymer having a molecular weight in excess of 10 million substantially composed of carbamoylalkylene and carboxyalkylene linkage containing not more than 4 carbon atoms each, the number of carboxyalkylene linkages being between about 2% and 15% of the total number of carbamoylalkylene and carboxyalkylene linkages,

sheeting said suspension on a papermaking screen to form a waterlaid web, draining fresh water from said web, and drying said web to form paper.

12. A process according to claim 11 wherein the pH of the suspension on addition of the polymer is between 5.5 and 6.5.

13. A papermaking aqueous fibrous suspension comprising cellulose fibers and cellulose cell-wall fines uniformly carrying a hydrous alumina complex of a watersoluble anionic linear carbon chain polymer having a molecular weight in excess of 5 million as calculated from intrinsic viscosity by modified Staud-inger equation, substantially composed of carbamoylalkylene and carboxyalkylene linkages containing not more than 4 carbon atoms each, the number of said carboxyalkylene linkages being between about 2% and 20% of the total number of carbamoylalkylene and carboxyalkylene linkages, the amount of said complex being sufiicient to increase the ireeness of said suspension but insuflicient to decrease substantially the dry tensile strength which paper made therefrom would otherwise possess.

14. A suspension according to claim 13 wherein the of the weight of References Cited in the file of this patent UNITED STATES PATENTS 2,729,560 House et a1. Jan. 3, 1956 2,761,856 Suen et a1 Sept. 4, 1956 2,767,089 Refrew Oct. 16, 1956 2,820,777 Suen et al Jan. 21, 1958 2,831,841 Jones Apr. 22, 1958 2,884,058 Schuller et a1 Apr. 28, 1959 2,889,299 Ritson June 2, 1959 2,930,106 Wrotnowski Mar. 29, 1960 OTHER REFERENCES Casey: Pulp and Paper, vol. I (1952), Interscience Publishers Inc., N.Y., pp. 377, 596, 597.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,019, 157 January 30, 1962 Walter F. Reynolds, Jr, et a1.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 2, line 48, for "cconventional" read conventional column 4, lines 73 to 75, strike out "and in most cases quantities of from 2 to about 6 mols of tertiary amine for each mol of persulfate or peroxide"; column 6, line 73, for "freenss." read freeness ,column 7, second table, last column, opposite "Internal bonding strength, ft.lb." for "O. 142" read O. 124 column 8, line 72, for "linkage read linkages column 10, line 5, for "fibruous" read fibrous Signed and sealed this 27th day of November 1962.

(SEAL) Attest: OHNSON ERNEST in n; DAVID L. LADD .xxxxxxx 7 Attesting Officer Commissioner of Patents

Claims

5. A PROCESS OF MANUFACTURING PAPER WHICH COMPRISES FORMING AN AQUEOUS SUSPENSION OF CELLULOSE PAPERMAKING FIBERS, ADDING THERETO BETWEEN ABOUT 0.5% AND 5% OF A WATER-SOLUBLE ALUMINUM METAL SALT BASED ON THE DRY WEIGHT OF FIBERS, THEREBY DECREASING THE PH OF THE SUSPENSION BELOW 5, ADDING SUFFICIENT OF A WATER-SOLUBLE ALKALI TO DECREASE THE ACIDITY OF THE SUSPENSION BY AT LEAST 0.1 OF A PH UNIT BUT INSUFFICIENT TO RAISE THE PH OF THE SUSPENSION ABOVE ABOUT 8, ADDING BETWEEN ABOUT 0.0001% AND 0.1% BASED ON THE DRY WEIGHT OF THE FIBERS OF A WATER-SOLUBLE ANIONIC LINEAR CARBON CHAIN POLYMER HAVING A MOLECULAR WEIGHT IN EXCESS OF 5 MILLION SUBSTANTIALLY COMPOSED OF CARBAMOYLALKYLENE AND CARBOXYALKYLENE LINKAGES CONTAINING NOT MORE THAN 4 CARBON ATOMS EACH, THE NUMBER OF CARBOXYALKYLENE LINKAGES BEING BETWEEN ABOUT 2% AND 15% OF THE TOTAL NUMBER OF CARBAMOYLAKYLENE AND CARBOXYALKYLENE LINKAGES, SHEETING SAID SUSPENSION ON A PAPERMAKING SCREEN TO FORM A WATERLAID WEB, DRAINING FREE WATER FROM SAID WEB, AND DRYING SAID WEB TO FORM PAPER.