US2635045A - Making elastomer containing paper - Google Patents

Description

Patented Apr. 14, 1953 MAKING ELASTOMER CONTAINING PAPER Andrew Loy Moore Bixler, Milford, N. J., and Jacob I. Fisher, Easton, Pa., assignors to Riegel Paper Corporation, New York, N. Y., a corporation of New Jersey No Drawing. Application April 21, 1948, Serial No. 22,498

15 Claims.

This invention relates to improvements in the manufacture of paper having elastomeric materials incorporated therein, and more particularly to the production of a strong, tough and pliable sheet of paper with a high initial tear strength, with a soft, leather-like feel and with good abrasion resistance.

The invention includes an improved method of producing such paper and the improved paper resulting therefrom.

The invention includes an improved method of incorporating elastomeric materials to the extent of about 20% to 50% in a sheet of paper by precip-itating emulsions of elastomeric materials in paper pulp which, instead of having ordinary beater consistencies of around 3 to 5% fiber solids, is diluted to a consistency of around 1% of fiber solids before the addition of the emulsions and the precipitation of the elastomeric materials therefrom; and in which the protective colloid materials are associated with the fibers, rather than with the emulsion, before the emulsion is admixed with the paper pulp and. the elastomeric materials precipitated therefrom.

The invention includes further improvements in the process of making such paper in which the protective colloid materials, and advantageously also part or all of the alum for precipitating the elastomeric materials from the emulsions, are in-.

corporated in the pulp in the beater at ordinary beater consistencies prior to dilution of the pulp to a consistency of around 1 and. the admixture of the emulsions of elastomeric materials therewith.

The invention includes process steps whichare advantageously utilized in combination in producing the improved and superior, tough, pliable sheet of paper with a high initial tear strength.

The process of making paper having elastomeric materials incorporated therein by precipitating rubber latex or synthetic rubber latex or emulsions of elastomeric materials in paper stock is a known process. It is also well known that 2 a strong, tough, pliable sheet of paper may be made.

One of the chief physical properties desired in this type of paper is known and referred to in the paper trade as initial tear or edge tear. The improved process of the present inventionresults in the production of a superior sheet of paper having high initial tear strength as well asa soft, leather-like feel and good abrasion resistance.

Paper pulp or stock at ordinary beater consistencies contains around 3 to 5% of fiber solids in the fiber-water suspension.

While it is possible to obtain fair results by the use of such beater consistencies at the time of precipitation of the elastomeric material from the emulsions, we have discovered that paper with superior physical properties can be made by precipitating the rubber at a stock consistency of about 1 We have found that a consistency of about 1% appears to be an optimum condition for the precipitation. We have found that the maximum physical properties were obtained in the range of from A; of 1% to 1 consistency, with best results at 1%; and that precipitation at materially-higher or lower consistencies than these gave distinctly inferior properties to the paper.

We have also'found that it is important, for best results, to associate the protective colloid materials with the fibers rather than with the emulsion before it is admixed with the fibers. This is contrary to the present procedure and to the commonly accepted teaching of the art that it is the emulsion particles which should be associated with the protective colloid materials before they are admixed with the paper stock. When the present practice is used, and the protective colloid materials areincorp'orated in the emulsion, an apparently uniform precipitation can be obtained without objectionable clotting of the fibers; "but the precipitation of'the elastomeric material, though'it be in the form of a fine flock, Will not be firmly and completely attached to the the ordinary emulsions of this kind, whenpre- 'cip-itated directly with a coagulant such as alum,

tend to come out in the stock as balls or agglomcrates of sticky material, whereas it is desirable that the rubber be precipitated in the form of a fine flock. If the elastomer comes out and forms balls or clots of fibers it is notuniformly distributed on the fibers even though the precipitate be finely divided and evenly distributed. The purpose of incorporating elastomeric materials in paper pulp and of producing paper having elastomeric materials incorporated'thereinis .50 that fibers and a product of inferior physicalproperties is produced. g

The amount oflatex or-elastomeric emulsion used in making thenew paper can be varied to give paper containing from about 20% to about 50%. An amount of about 30% in the paper is advantageous. Above 30% only slight additional strength or toughness is attained, but improved resistance to penetration is obtained,.which is advantageous for certainuses. Below 20% the strength and toughness drop off rapidly. Such an amount of latex or elastomeric emulsion corresponds to from about 25% to about 100% of elastomeric material based on the dry weight of the fibers of the pulp to which the latex or emulsion is added to give paper containing from about to about 50% of elastomeric material.

The improved process of the'present invention will be further illustrated by the following specific example:

Example 1.--100 lbs. of unbleached kraft pulp were beaten to 700 cc. freeness Canadian) in an ordinary paper mill beater. This was done at ordinary paper-making consistency. (3 :to "5%) The stock was then emptied to a chest and diluted to 1% consistency and the'following chemicals were added as colloid protectives: 1 lb. oxalic acid dissolved in 2 gallons of water; 1 lb. sodium hydroxide dissolved in 2% gallons of water;

2 lbs. sodium silicate syrup (special brand) dis- I solved in 2 /2 gallons of .water; .75 lb. alpha protein dissolved in cc.s of ammonium hydroxide in 2V2 gallons of water; '7 .2 lbs.of ammonium hydroxide (28.9%). These chemicals were thoroughly mixed with the fiber water suspension and then the elastomeric emulsion was added. In this case 1 54 lbs. of 27.8% solids synthetic (acrylonitrile-butadiene) rubber latex were used.

After the rubber emulsion was thoroughly mixed, alum was added to coagulate the rubber. The alum was added as a 2% solution andabout 13 lbs. was necessary for complete coagulation. The preferred method was to add it in steps of 2 lbs. at a time, allowing 5 minutes between additions. Thorough mixing was obtained after and during addition. As soon as the precipitation was complete, the stock was ready to run on the paper machine.

In the above example the pulp was diluted from ordinary paper making consistencyto about 1% consistency before the incorporation of the protective-colloids therein. We have found, however, that the protective colloid materials can advantageously be added to the stock in the beater at ordinary beater consistencies (e. g., around 3 to 5%) and that the dilution to 1% consistency can then be made and followed by the addition of the emulsion and precipitation by alum. This procedure is more advantageous for mill operation, while the paper produced is nevertheless paper of the desired improved physical properties.

As an illustration of the improved im'tial tear strength of the paper obtained when the latex or elastomeric emulsion was precipitated at a consistency of 1%, according to the above example, we give below the results obtained with such .5 precipitates in comparison with theresults obtained when the latex or elastomeric emulsion was precipitated at 4% consistency.

It is evident from the above data that the initial tear is very much superior when the latex or elastomeric emulsion is precipitated in the paper pulp at 1% consistency than it is at 4% consistency.

The theory and exact mechanism of the efiect of consistency on the precipitation of elastomerio materials from emulsions in paper stock, as above illustrated, and the reason for the improved results obtained at the optimum consistency of around 1'%, is not yet clearly understood; but the marked improvement in results has been demonstrated. Microscopic studies of the fibers indioate'that .at the :optimum consistency of about 1 1% the precipitated elastomeric particles are evenly distributed and firmly attached to the fibers. Elastomeric materials precipitated materially outside of the optimum consistency range show under the microscope more spotty distribution and poor adhesion to the fibers. At the optimum consistency the water in the slurry becomes completely clear, indicating that the elastomeric material has been finely attached to the fibers; whilemateriallyoutside the optimum consistency range the water of the slurry tends to remain turbid, apparently because the elasto meric precipitate is not completely attached to the'fibers, in which case the retention of the elast-omeric precipitate in the sheet is dependent to a considerable degree on the filtering action as thensheet is being formed. In the optimum range, where the elastomeric material is firmly held by the fibers, apparently by some physical phenomenon, the retention of the elastomeric particles is much more positive than that obtained by simple filtering action.

While we do not desire to limit ourselves by any theoretical explanation of the mechanism or mechanics of the precipitation process, we have been led to believe that when the consistencies are materially below of 1%, the emulsion solids will precipitate mostly or to a considerable extent in the water; while with consistencies of about 1% we are led to believe that the area of total fiber exposed will be such as to allow the emulsion solids to cover each fiber evenly and that when this condition exists each individual fiber adds to the final strength of the sheet. As the consistencies rise above the optimum we are led to believe that the precipitated rubber present does not get on the fibers evenly and coats only part of the fiber surface present, e. g., around l0 to with resulting lowering of the strength of the sheet formed. It may be that the optimum consistency of about 1% issuch that the fibers are so spaced apart as to promote uniform and efiective precipitation of the emulsion solids on .or in such Basis Initial Tear Hand Precipitating Weight Gauge in Tensile, Percent Factor Tear consistency 3,000 Inches p. s. i. Stretch (Tensile X Evaluasq. ft. Stretch) tion 1.0% 162 16. 5/1, 000 2, 15. 4 33, 000 .Good. 4.0% 21/1, 000 1, 474 6.0 8, 850 P001.

intimate contact with the fibers as to give a resulting stock with thefibers so oriented therein and so intimately coated with the fine precipitated elastomer particles as to give the improved properties which we'have observed are obtained in such cases.

The process describedin the above example requires effective and thorough agitation during 75 precipitation and a slow or stepwise addition of the alum.. While the improved paper of high initial tear strength can be produced in this way, we have foundthat the process can be further improved and simplified and paper of the desired superior properties obtained by adding both the protective colloid materials and the alum for partial precipitation to the beater while the stock isat beater consistency of around 3 to 5%. The amount of alum thus added is advantageously about one-half to four-fifths of the alum required for precipitation. This alum is added to the beater after the addition of the protective colloid materials and after these have been well mixed with the stock. This alum can be added as a solution all at one step. We refer to this as the pre-alum addition.

After the pre-alum is well mixed and distribbodiment of the process the alum can be added dry and need not be dissolved in water before the addition to the protected stock. And we have found that this modified process is in certain respects a more simplified process and one better adapted to practical mill scale operation, and is uted throughout the stock, the protected stock is I dumped from the beater to a chest and diluted to 1 consistency and the emulsion is then added and allowed to mix for about 15 minutes. pending on the quantity of the pre-alum used, the elastomeric material is more or less precipitated during this mixing period. An advantageous method of procedure is to add suiiicient pre-alum to precipitate about 80 to 90% of the emulsion solids. The remaining 10 to is then precipitated by further addition of alum added slowly as a 1 solution.

The process carried out with the addition of both the protective colloid materials and the prealum to the beater before dilution is illustrated by the following example:

Example 2.-100 lbs. of unbleached kraft pulp were beaten to 700 cc. freeness (Canadian) in an ordinary paper mill beater at 4% consistency. The following chemicals were thenadded: 1 lb. oxalic acid in 2 gallons of water; 1 lb. sodium hydroxide in 2 gallons of water; 2 lbs. sodium silicate syrup (special brand) in 2 gallons of water; .75 lb. alpha protein dissolved in cc.s of ammonium hydroxide in 2% gallons of water; 7.2 lbs. of ammonium hydroxide (28-29%); and 10 lbs. alum dissolved in sufiicient water to make a 10% solution. After 10 minutes mixing, the

stock was dropped from the beater to a chest and diluted to 1% consistency, then 154 lbs. of 27.8% solids synthetic rubber latex were added. After 15'minutes mixing, 3 lbs. of alum were added slowly but continuously as'a 1% solution. This completely precipitated the rubber latex and the stock was run over the paper machine, giving paper with superior physical properties.

Where alum is added following the addition of the emulsion of elastomericmaterials, as in the processes above described and illustrated'by the foregoing examples, it is important to insure rapid and thorough agitation. While this prob lem is minimized by the addition of most'of the" alum prior to the addition of the emulsion, it is still necessary'to have rapid and thorough agitation "during the addition of the small final portion of alum, after the addition of the emulsion, to complete the precipitation. In the practical carrying out of the process, theagitating'equipment provided in chests may not produce sufficiently rapid and thorough agitation, since the normal operation of paper mill chests does not require such agitation. The provision of supple'-.

mental equipment to produce suchagitation involves added expense and more power for its operation than the usual lower speed equipment.

We have found, however, that our improved process can be carried out advantageously to proagitating our preferred and more practical and advantageous process.

In this improved process, in which all of the alum is added for complete precipitation of the emulsion, prior to dilution and addition of the emulsion, it is important that the quantity of alum required be determined by preliminary test, particularly as the necessary quantity of alum is somewhat flexible and varies with other factors which influence it. Thus the time, the temperature, and the degree of agitation allhave infiuence on the quantity of alum required, all other factors being constant. This necessary quantity can be readily predetermined by test, using the pH of the stock as a measure of the amount of alum'req'uired, under the combination of other conditions existing, and maintaining the pH within narrow limits in carrying out the process.

The range of pH in which most satisfactory results have been obtained in both laboratory and commercial runs has been from about 5.0 to about 6.5, although this range does not appear to be a limiting range. We have further found that when the necessary quantity of alum has been predetermined by test, and the' corresponding pH determined, it is important to control the pH within approximate 0.2.

The rate of precipitation, and the time required for complete precipitation, when all of the alum is added before dilution and before the addition of the rubber latex, are important for best results. tends to cause the rubber to come out in large particles which are not firmly attached to the fibers so that a sheet of inferior strength is produced. Too slow a rate of precipitation tends for a shorter or longer time. The rate of precipitation is also effected by other factors, such as the temperature, the degree or rate of agitation, the kind of protective colloid material used, and the quantity of protective colloid material used. However, these variables, while varying in different plants and under different conditions, will or dinarily be more or less standardized so that a preliminary test, under such standardized conditions, will enable the amount of alum required, and the corresponding pH of the stock (1%), to be predetermined so that the rate of precipitation can be controlled byfcontrollin'g the pH of the stock, within rather narrow limits when the amountof alum and the'c'orresponding pH have beenso predetermined. The effect on the rate of precipitation by'any of :the other factors can be A too rapid rate of precipitationetep nseiediee rnm to beadded' to-determine the properrate of pre. cipitation For example, under one condition of agitation and temperature, a pilot 5.4 may correspond to the. quantity of alum required to give, the proper rateof precipitation; while at anothercondition of agitation and temperature. the same or proper rate 'of precipitation may. be. achieved at a pH of 6.2

he l aeiiir t lunInui I asset w en. to predetermine: the necessary quantity of alum with the emulsion before it is added-to the paper,- are. shown by theiollowing data, which illustratev .the improved initialtear strength obtained when all the protective .colloid materials, were added to the;fiber slurry incomparison with the resultsobtainedwhen only half of the protective colloid materials were added to the latex or elastomer emulsionbefore it was admixed with the fiber slurry. All the other chemicals were added to the pulp as in the examples. In both cases the stock consistency was 1 Treatment nd Tear Evaluation Initial Tea Factor (Tensile X Stretch) Basis Wt.

93% q Percent Gauge in A Tensile,

' Stretch Inches p. s. 1.

All 1protectives added to fiber urry Half of 'protectivcs' added to latex Good.

Fair.-

sistency. The following chemicals were then added: 3 pounds of oxalic acid as 16 solution in water; 3-pounds sodiumhydroxide dry flake; 18 pounds sodium silicate syrup, (special brand) as received; 2%,poundS-alpha; protein dissolved in 75 co, ammonium-,hydroxidedn 1'7 pounds of water; (28-29%.NH3); and-64.-5-pounds of alum, dry ground. Fiveminutesimixing time was allowed between each addition.- Ten minutes was allowed following the addition of the alum for complete solution and; mixing. Th stock was then diluted to 1% consistency anddropped;to achestwith- 648pounds of ;20%- solid ssynthetic rubber latex. The latexwas poureddown the drop line as the stock was going down; This gives rapid and, thorough mixinglof the latexwith the completely buffered stock Theprecipitation was completedin 20 minutes ,from; the-timeof addition of the rubber. The-pI-Iof the bufiered stock at 1% con sistency just betore; the ,latexwas added was 5.2.

he. paper produce finl cord w th: b v e a plewasi eeef om bi etion b epart les of 7 rubber and had:the;snperior.;physical properties, I

especially high initial or edge ,teanshown -by -E xamples l and 2. The -following data are repre-. sentative 1 of paper. made; in accord; with Ex pleB;

added thereto, as, pqmpared med heai rot qtireemai ais are-r ined.

20.5 pounds of ammonium hydroxidev The i r v d esa ie'ntt ineqtb w he roc in -whichthe protective ,colloidrr aterial are add ed to the fiber ,suspensiombefore. the .emulsion is an t ults 0 l.

The states aballatex Had-s the as..

examples to produce paper containing about 30%- of rubber was a latex of synthetic. rubber of the butadiene acrylonitriletype known to the trade as Hycaror Xylos rubber. Such a synthetic rubber latex givesa. resulting sheet of 7 paper with high initial tear. The type of rubber latex to be used in carrying out the process of the invention, as well'as the amount,,can, however, be variedandwill depend on the various properties desired in the finished sheet. Synthetic rubber latex of the type indicated is also advantageous where greaseproofness or oilproofness is required such as for gaskets. Other types of dispersions with elastomeric properties canbe used; such as butadiene-styrene, neoprene, polyvinyl chloride, vinyl copolymers, nylon, and natural rubber, depending onthe particular properties desired in the composite. paperelastomer sheet. Improved elastomeric properties-maybeobtained ;by the addition of suitableplasticizers "with-the resin, if so desired.

The examples given have referred to unbleached kraft pulp. Our invention is not, however, limited to this pulp. Otherpulpssuitable for paper making are included. Some such pulps are-the various wood pulps (sulfite, krait, soda, semichemical, groundwood, etc), rag pulp, rope pulp, jute pulp, etc. pulps are included. The exact choice of pulp and whether or not it is bleached will depend-on the properties desired .to fulfill thefinal use re-.

quirements of thepaper;

Variations can be made in theprocess from the formulas and procedures of the above examples, which are intended to be illustrative but not limiting; Thus, for example, other colloid ma-.

terials than alpha protein-can be usedsuch as, for exampl e,- hemoglobin, casein, starch, sodium alginate, etc., and these may be used in conjunction with or as substitutes for the alpha protein.

This invention includes inits scope various modificationswell known among paper makers and which modification might add desired propertieS-for various special uses. Examples ofsuch well known-modifications that might be useful are-sizing for water resistance with'rosin, synthetic resin or wax, application of materials to produce wet strength;coloring,-filling, calendering, embossing,.etc.;

It i usbe seent at he re ent v t o p ov es i prpvedrroq see r. e pr duction ofa superior, tough, pliable paper sheet with high initial tearstrength, It'will; alsobe seen that ei r nt oniecludes P oc ss steps and f a r s Bleached or unbleached which can advantageously be used in combination with each other. It will further be seen that the improved process of the invention results in the production of a new and superior sheet of paper which is strong, tough and pliable and which is characterized by high initial tear strength, a soft, leather-like feel and good abrasion resistance.

We claim:

1. In the method of making a tough, pliable sheet of paper with a high initial tearstrength, having about to 50% of elastomeric materials incorporated therein, the step which comprises precipitating by the action of a dilute solution of alum the elastomeric material onto the fibers of a slurry of fiber and water containing an emulsion of elastcmeric material and a protective colloid material, while said slurry has a fiber consistency of about 1%.

2. The process according to claim 1 in which the protective colloid material is added to the fiber water slurry prior to the addition thereto of the emulsion of the elastomeric material.

3. The method according to claim 2 in which the precipitation of the emulsion in the slurry is effected by the stepwise addition of an alum solution containing about 2% of alum solids.

4. The method according to claim 2 in which a portion of the alum necessary is incorporated in the fiber Water slurry following the addition of the protective colloid materials and prior to the addition of the emulsion of elastomeric material, the remainder of the alum necessary for precipitation being added following the addition of the emulsion of the elastomeric material, this last portion of the alum being added in dilute solution of about 2% solids concentration and in a stepwise manner.

5. The method according to claim 2 in which about four-fifths of the alum necessary is incorporated in the fiber water slurry followin the addition of the protective colloid materials and prior to the addition of the emulsion of elastomeric material, the remaining one-fifth of the alum necessary for precipitation being added following the addition of the emulsion of the elastorneric material, this last portion of the alum being added in dilute solution of about 2% solids concentration and in a stepwise manner.

6. The method according to claim 2 in which all of the alum necessary for precipitation is incorporated in the fiber water slurry following the addition of the protective colloid materials and prior to the addition of the emulsion of the elastomeric material.

7. The method according to claim 2 in which 'all of the alum necessary for precipitation is incorporated in the fiber water slurry following the addition of the protective. colloid materials and prior to the addition of the emulsion of the elastomeric material, and in which a pH of from about 5.0 to 6.5 is maintained in the slurry when the emulsion of elastomeric material is added.

8. Ijhe method according to claim 2 in which all of the alum necessary for precipitation is incorporated in the fiber water slurry following the addition of the protective colloid materials and prior to the addition of the emulsion of the elastomeric material, and in which the quantity of alum incorporated in the fiber water slurry is such as to effect precipitation of the elastomeric material from the emulsion in from 15 to '45 10 minutes after the addition of the emulsion to the completely buffered fiber water slurry.

9. In the method of making a tough, pliable sheet of paper with a high initial tear strength having about 20% to 50% of elastomeric materials incorporated therein, the steps which comprise adding protective colloid materials to a prepared paper stock at normal beater consistency (about 3-5%), diluting the stock to about 1% consistency, adding an emulsion of the elastomeric material to the diluted stock and precipitating the emulsion in the slurry while it is at said diluted consistency by the action of a dilute solution of alum.

10. The method according to claim. 9 in which at least part of the alum is added to the stockbefore dilution and before the addition of the emulsion of elastomeric material.

11. The method according to claim 9 in which all of the alum necessary for precipitation is incorporated in the fiber water slurry at normal beater consistency, and the slurry is subsequently diluted to about 1% consistency before addition of the elastomeric material.

12. In the method of making a tough, pliable sheet of paper with a high initial tear strength having about 20% to 50% of elastomeric materials incorporated therein, the steps which comprise preparing a paper stock of from about 3 to 5% consistency, adding protective colloid materials thereto, subsequently adding alum thereto, diluting the stock to a slurry of fiber and water having a fiber consistency of about 1%, adding the emulsion of elastomeric material to said slurry and precipitating the emulsion therein while it is at said dilute consistency by the action of a dilute solution of alum.

13. The method according to claim 12 in which alum is also added to the diluted slurry.

14. The method according to claim 12 in which from one-half to four-fifths of the alum required for precipitation is added prior to the addition of the emulsion and in which a solution of about 2% alum is gradually added after the addition of the emulsion to complete the precipitation.

15. The method according to claim 12 in which I all of the alum necessary for precipitation is incorporated in the fiber water slurry at normal beater consistency, and the slurry is subsequently diluted to about 1% consistency before addition of the elastomeric material.

ANDREW LOY MOORE BIXLER. JACOB I. FISHER.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,773,201 Rose Aug. 19, 1930 1,799,217 De Cew Apr. 7, 1931 2,041,968 Schur May 26, 1936 2,215,553 Johnson Sept. 24, 1940 2,330,084 Scott Sept. 21, 1943 2,474,801 Owen June 28, 1949 FOREIGN PATENTS Number Country Date 375,845 Great Britain June 30, 1932 402,982 Great Britain Dec. 14, 1933 OTHER REFERENCES India Rubber World, Feb. 1, 1923, page 283.

Claims (1)

1. IN THE METHOD OF MAKING A TOUGH, PLIABLE SHEET OF PAPER WITH HIGH INITIAL TEAT STRENGHT, HAVING ABOUT 20% TO 50% OF ELASTOMERIC MATERIALS INCORPORATED THEREIN, THE STEP WHICH COMPRISES PRECIPITATING BY THE ACTION OF A DILUTE SOLUTION OF ALUM THE ELASTOMERIC MATERIAL ONTO THE FIBERS OF A SLURRY OF FIBER AND WATER CONTAINING AN EMULSION OF ELASTOMERIC MATERIAL AND A PROTECTIVE COLLOID MATERIAL, WHILE SAID SLURRY HAS A FIBER CONSISTENCY OF ABOUT 1%.