US2657132A - Manufacturing wet strength paper containing cationic urea-formaldehyde resin - Google Patents

Description

7, 1953 J. H. DANIEL, JR.. El AL 2,657,132

MANUFACTURING WET STRENGTH PAPER CONTAINING CATIONIC UREA-FORMALDEHYDE RESIN Filed March 5, 1947 2 Sheets-Sheet l I I I PETE/V770, PF/PCf/Vf or PIS/N 4005.0

4 I I f 40% k s I k wnarmy/van x Pal/Na: PIA INCH W/OTH g, 3 l 3075 l V 3- R 2 I 20% Q s Q 1 I l my;

/0 20 3o 40 50 so 00 I00 E00 400 J00 700 M50 IN VEN TORS 2 WWW 1953 J. H. DANIEL, JR. ET AL 2, 32

'MANUFACTURING WET STRENGTH PAPER CONTAINING CATIONIC UREA-FORMALDEHYDE RESIN Filed March 5, 1947 2 Sheets-Sheet 2 sou/rm 50c '04" 0 l 2 3 4- 5 6' 7 8 9 O H I? T/Mf l/V Ml/VU7'55 ATTORNEY.

INVENTORSQ P79 E. dab N x7. DAN/2, u/R,

Patented Oct. 27, 1953 MANUFACTURING WET STRENGTH PAPER CONTAINING CATIONIC UREA-FORMAL- RESIN John H. Daniel, Jr., Stamford, Chester-G. Landes, New Canaan, and Tzeng Jiueq Suen, Stamford, Conn assignors to American Cyanamid Company, New York, N. Y., a corporation of Maine Application March 5, 1947, Serial No. 732,648

7 Claims. 1

This invention relates to the manufacture of resinetreated cellulosic fibers and fibrous materials prepared therefrom, and is directed particularly to a method for improving the wet strength 01 felted fibrouseellulosic materials such as paper, board, shaped :paper articles and the like. The invention includes the improved cellulosic fibers and fibrous products themselves as well as methods ofpreparing these products from aqueous suspensions of fibrous cellulosic materials such ,as paper pulp.

It has :been known for some time that the wet tensile strength and the bursting strength of paper can be increased by soaking the formed paper in strong solutions ,of urea-formaldehyde resin, followed by heating the paper to evaporate the water and cure the resin. In some paper mills the urea-formaldehyde resin solution has been applied by spraying the solution onto a moving web of paper, followed by passing the paper over or between heated drying .rolls. However, experience has shown that the impregnation of a formed sheet of paper with a resin solution, followed by curing the resin causes brittleness in the paper with a corresponding reduction in its folding endurance. Moreoventhe evaporation of the additional water introduced with the resin requires a second heating of the paper if it has first been dried, or, if the paper is impregnated While it is still wet, a material reduction in the speed of the drying drums. Despite these objections, however, the so-called tub treatment of preformed paper with relatively concentrated aqueous solutions of synthetic resins is still used in some paper mills for special purposes, and the thermo-setting resins hereinafter described may be applied by this method within the broader scopeof the present invention ifdesired.

In order to ,avoid the difficulties inherent in tub treatment, more recent practice in most paper mills manufacturing wet strength paper has been to apply a melamine-aldehyde resin of a special type, known as colloidal cationic melamine-aldehyde resin. The discovery that this type of resin possesses substantive properties for paper stock, and can be applied to dilute paper pulp suspension in small quantities with a high degree of retention and excellent wet strength in the finished paper, was made jointly with Charles S. Maxwell by one of the present applicants. The details of this method of producing wet strength paper are described in an article in the August 9, 1945, issue of the Paper Trade Journal. Briefly, melamine-formaldehyde resin is dissolved in a water solution of hydrochloric acid or another Z strong acid other than :sulfuric acid to form a solution containing about 0.8 .mol of acid for each mol of melamine and the solution is aged, whereby polymerization takes place and a blue haze develops, indicating the presence of resin particles in the colloidal range. This colloidal solution is added to the water suspension of paper stock in the beater, stock chest, Jordan engine, head box or .at any :other suitable point ahead of the papermaking wire or screen. The stock is then formed into paper by the usual procedure and carried over steam-heated drying rolls which dry thepapenarid cure the resin to a waterinsoluble condition.

It .is a principal object of the present invention to provide papermaking fibers and paper impregnated with a thermosetting urea-formaldehyde resin capable of imparting wet strength thereto, which resin can be applied to the Water suspension of hydrated paperstock in the beater, stock chest, head box -or at any other suitable point ahead of the paper-forming stepas is now done with the colloidal cationic melamine-aldehyde resin described above. Certain practical advantages are obtained by applying urea-f-ormaldehyde resins instead of melamine-formaldehyde resin, notably the problem of broke recovery is greatly simplified when a urea-aldehyde resin is used. Moreover, urea-formaldehyde resins are at present considerably cheaper than are the melamine-aldehyde resins; therefore, the process of the present invention provides a feasible means of producing wet strength paper by the so-oalled beater addition process at a reduced raw material cost.

We have found that the above and other objects are accomplished by applying to fibrous cellulosic material such as paper pulp an uncured thermosetting cationic urea-formaldehyde resin. We have found that the resins of this class are substantive to fibers of .cellulosic material such as paper pulp in aqueous suspension; 1. e., the resin is selectively adsorbed or absorbed by the cellulose fibers from a dilute aqueous solution or dispersion thereof containing these fibers in amounts much greater than those corresponding to the concentration of resin in the solution or to what would be contained in the water normally left in the sheet after forming. The importance of this discovery is evident, for it permits the application to cellulosic fibers of suflicient quantities of a thermosetting urea-formaldehyde resin capable of imparting wet strength while the fibers are in dilute aqueous suspensions of the consistency used in paper mills, which is about 0.145% or, in special processes, at higher consistencies.

The cationic urea-formaldehyde resins which are applied to paper or paper stock by the process of our invention are prepared by condensing a urea-formaldehyde reaction product under acid conditions, and preferably at pH values below 4.0-4.5, in the presence of a cationic nitrogencontaining organic compound that is capable of condensing with the resin. The preferred cationic organic nitrogen compounds which are capable of condensing with dimethylolurea or other ureaformaldehyde reaction products are water-soluble polyfunctional organic nitrogen bases; 1. e., compounds having the ability to copolymerize with urea-formaldehyde under acid conditions. Typica1 examples of such polyfunctional organic bases are the alkylenepolyamines of the formula HzN(C1lI-I2n.HN) 32H in which x is one or more such as ethylenediamine and 1,3-propylenediamine and polyalkylenep'olyamines such as diethylenetriamine, triethylenetetramine, tetraethylenepentamine, the corresponding polypropylenepolyamines and polybutylenepolyamines, also condensation products of alkylenepolyamines (such as the above) with halohydrins such as alpha-dichlorhydrin, epichlorhydrin and the like. monoalkylolamines, dialkylolamines and the like and the water-soluble condensation products thereof with aldehydes such as formaldehyde.

By condensing these and similar polyfunctional cationic organic bases with dimethylol urea and similar primary or substantially monomeric ureaformaldehyde condensation products obtained by condensing urea or thiourea with formaldehyde, preferably under slightly alkaline conditions, with the addition of sufficient acid to reduce the pH to values of about 1.0 to 4.0, and preferablyabout 1.0 to 2.5, measured after the reaction has proceeded for some time, there are obtained cationic urea-formaldehyde resins which are substantive towards hydrated paper stock and can be used in the process of our invention.

It is an important feature of the cationic ureaformaldehyde resins prepared as described above that only relatively small proportions of the polyfunctional organic base need be used to obtain the desired cationic properties. The importance of using only small quantities of the basic material is two-fold; usually the organic bases such as polyalkylenepolyamines are more expensive than corresponding amounts of urea and formaldehyde, also relatively large quantities Would tend to solubilize the thermosetting urea-formaldehyde resin and thus prevent the formation of a water-insoluble bond between the fibrils of the felted paper. In fact, we find that resins containing a larger quantity of organic base than of urea, on a weight basis, possess little or no wet strength-imparting properties. Resins containing a smaller quantity of organic base than of urea, on the other hand, will impart wet strength to paper, and the wet tensile strength increases steadily as the ratio of organic base is decreased to the point where the resin syrups become hydrophobic in character and precipitate upon dilu tion with water. Accordingly, the preferred resins used in practicing the process of the present invention are those which contain about 230% of the organic base, calculated on the weight of urea used, and quantities of 6% to 15% are usually employed.

The cationic urea-formaldehyde resins applied to paper or paper stock by the process of the present invention are preferably prepared by f rst reacting urea with a methylene-yielding substance such as formaldehyde, paraformaldehyde or hexamethylenetetramine in known manner to form a primary urea-formaldehyde condensation product which is usually designated by resin chemists as dimethylol urea. This primary reaction product is preferably formed under neutral or slightly alkaline conditions, the latter being obtained by the addition of a small quantity of basic material such as sodium hydroxide or triethanolamine. A suitable quantity of the polyfunctional organic base is then added as such or after it has first been reacted with formaldehyde and the resin solution is acidified by the addition of hydrochloric acid, nitric acid or other strongly acidic material to reduce the pH to the polymerizing range, which is about 1-4 and preferably l-2. The resin syrup is then further reacted or polymerized, preferably at elevated temperatures on the order of 70"90 C1, in order to bring about a polymerization or copolymerization of the urea-formaldehyde and organic base and thereby produce a cationic resin.

The degree of polymerization of the cationic resin is an important factor. Tests have shown. that much greater wet strength is obtained when the cationic resin is polymerized to a stage wherein a definite increase in its. viscosity has been obtained, and the most efficient resins for wet strength purposes are those having a degree of polymerization corresponding to a viscosity of at least centipoises in a resin syrup of 45% resin solids. Accordingly, we prefer to continue the resin polymerization, by holding the acidified syrups at appropriate temperature ranges as will hereinafter be more definitely explained, until a viscosity on the order of 100 centipoises or higher is obtained. The polymerized resin syrup is then preferably neutralized to a pH on the order of about 6-'7 in order to obtain a product which is stable on storage. Resin syrups prepared by this method are both water-soluble and water-dilutable, and also can be evaporated to dryness and redissolved in water without substantial reduction in their water solubility or utility for the production of wet strength paper.

As has been stated, the cationic urea-formaldehyde resins can be applied to paper or other felted cellulosic products by tub application methods if desired. Thus, for example, preformed and completely or partially dried paper prepared from a chemical pulp such as sulflte, neutral sulfite, rag soda or sulfate or a mechanical pulp such as groundwood or any mixture thereof may be immersed in a 1% to 10% aqueous solution of the resin and impregnated with about 50-100% thereof, based on the weight of the paper. The paper is then heated for about 1-4 minutes at temperatures of 212-300- F. or higher, or for shorter times. at higher temperatures, whereby the paper is dried and the resin is cured to a Water-insoluble condition. The resulting paper has greatly increased wet strength, and therefore this method is well suited for the impregnation of paper towels, absorbent tissue and the like as Well as heavier stock such as wrapping paper, bag paper and the like to impart wet strength characteristics thereto.

The preferred process of the present invention. however, takes advantage of the substantive properties of the cationic urea-formaldehyde resins for hydrated cellulosic fibers. In practicing this process the resin in its uncured and hydrophilic or water-dilutable condition is added to an aqueous suspension of the paper stock, such as any of those enumerated above, in the beater, stock chest. Jordan engine, fan pump. head box or at any other suitable point ahead of the paper making wire or screen followed by forming the treated fibers into a felted product on thewire or cylinder. Ordinarily about 0.5% to 5% or more of the resin solids, based on the dry weight of the paper stock, is added in this manner. The felted product is then heated in the usual manner to dry the paper or boand, thereby curing the resin to its polymerized and waterinsoluble condition and imparting wet strength to the paper.

As is noted above, the thermosetting cationic urea-formaldehyde resins impart substantial wet strength to paper and other products formed of felted cellulosic fibers when suitable amounts are incorporated therein The quantity of resin to be added to the aqueous stock suspension will depend on the degree of dry and wet strength desired in the finished product and on the per cent of resin retained by the paper fibers. Thus, as is shown in Example 1, the addition to the aqueous paper stock suspension of as little as 0.75% produces a Wet strength many times greater than that of the untreated paper. Even smaller quantities on :the order of 0.1%, based on the dry weight of the paper, may be used in some cases. Ordinarily about 0.5-l% to 3% of the resin is introduced into the paper and for special purposes, as much as 840% of resin'may be incorporated therein. The resin not adsorbed by the paper stock may be reused by employing a circulating white water system; i. e. :by using a part or all of the white water from the papermaking machine for preparing further batches of paper pulp suspension.

We have found that the uncured cationic urea-formaldehyde resins contained in paper, whether introduced as a tub size or combined with the cellulosic fibers prior to sheet for1nation by adsorption in aqueous suspension, can be cured under neutral or acid conditions by subjecting the paper to a heat treatment. However, the fastest cure and the best wet strength are obtained by curing the resin under slightly acid conditions, and therefore it is preferable to acidify the paper stock before, during or after the resin addition thereto. In most cases this acidification can be advantageously accomplished by the addition of about 143% of aluminum sulfate (alum) which is frequently used for the purpose of fixing rosin or wax sizes in the paper and therefore entails no added expense. Under these conditions, wet strength is imparted by a cure of 1-2 minutes at 230- 260 F., or for shorter periods at higher temperatures. The degree of wet strength is frequently further increased by longer heating at normal curing or lower temperatures, and this can be obtained for example by storing the finished paper from the drier section in roll whereby the heat of the paper is utilized to cure the resin.

As is noted above, the retention of the cationic resin by the paper fibers and the Wet strength developed in the finished sheet are greatly improved by partially polymerizing the resin. This partial polymerization is accomplished by aciditying the primary urea-formaldehyde condensation product, or dimethylol urea, to pH values below 4.0-4.5, and preferably about 1.0-8.5, and heating the acidified material with the cationic nitrogen-containing organic compound at polymerizing temperatures. Any suitable acid capable of P oducing the low pH desired may be 6 used for the acidification, such as hydrochloric acid, sulfuric acid, nitric acid, and the like.

The polymerization temperatures to be employed are dependent to a certain extent on the ratio of formaldehyde or other methylolyielding substance to urea; with urea resin syrups prepared with up to about 2.5 mols of formaldehyde for each mol of urea any temperature up to about 90 C., or up to the refluxing temperature of the resin syrup may be employed. In syrups prepared from substantially larger quantitles of formaldehyde ii. e., from about 2.5 mole of formaldehyde for each "mol of urea and up) the optimum polymerization temperatures are below 70 0., and are preferably from about C. to about 65 C.

The polymerization of the cationic resin is most readily followed by measuring the viscosity of the resin syrups, and in the following examples this viscosity is expressed in terms of syrups containing about resin solids. However, it

should be understood that the viscosity of these syrups does not change greatly, for a given stage i of polymerization, with a, change in resin solids content from about 35% to about 50%, and therefor the results stated in these examples are equally applicable to syrups polymerized at somewhat lower resin solids content. The improvements obtained with a representative cationic urea-formaldehyde resin as a result of increased polymerization are illustrated in the accompanying drawings, in which:

Fig. 1 is a graph showing the increase in retention of the cationic urea-formaldehyde resin with an increase in viscosity up to about centipoiscs, with a corresponding increase in the wet strength of the paper.

Fig- .2 is a similar graph showing the rapid polymerization of the resin by aging acidified resin solutions of 45% resin solids at elevated temperatures below 65-70 C.

Although the following specific examples may describe in detail certain specific features of the invention, they are given primarily for urposes of illustration and the invention in its broader aspects is not limited thereto.

EXAMPLE 1 A. mixture of 30 grams .5 mol) of urea, 1 grams (1 mol) of 37% aqueous formaldehyde solution and .1 cc. of triethanolamine was heated at 70 C. for 15 minutes, after which 3.8 grams (0.02 mol) of tetraethylenepentamine and 4 cc. of concentrated hydrochloric acid were added. Heatin was then continued at 70 C. for about 1 hour, or until a partially polymerized thermosettin urea-formaldehyde resin having cationic properties was formed. The resulting resin syrup, having a viscosity of about centipoises, was diluted with Water to a 10% solution.

A sample of this resin syrup was further diluted to 1% solids and tested for cationic properties by a modification of the moving boundary method. The dilute resin solution was poured into a test cell having a horizontal portion, elliptical in cross-section, into which platinum electrodes were fused. Between the two electrodes a small plu of ground cotton fibers was suspended in the resin solution. Upon passage of a direct current through the electrodes at 60 volts the cotton plug was observed through a microscope at a level such that any movement of the liquid by electroosmosis is zero, so that movement of the cot.- ton is a measure of its true charge.

The cotton fibers carrying the urea=formaldea hyde-amine resin moved toward the negative electrode (cathode) at a rate of 1.02 cm. per second, thus showing the presence of a positive electrical charge on the resin particles.

Bleached kraft paper pulp was beaten in the usual manner and made into a 0.6% water suspension. Samples were treated with the abovedescribed resin, in some cases with the addition of aluminum sulfate, and made into handsheets which were heated 1 minute at 230 F. to dry the paper and cure the resin. Some of the sheets were given an additional heating of 10 minutes at 260 F. to determine the effect of a more complete cure. The sheets were then tested for dry and wet tensile strength along with a sheet made from the same stool: but containing no resin. In the following table, which shows the results obtained, the per cent of added resin solids and alum is based on the dry weight of the paper pulp; the per cent resin retained is based on the resin added, and the basis weight is the weight in pounds of 500 sheets 25 x 40 inches in size.

Pep Pen Pe1= Tensile strength, lbs./in. Sample cent cent Basis No. resin alum W; weight 7 added added mined I Dry Wet Dry Wet None 48. 7 22. O 0. G 21. 8 O. 6

None 55 51. O 23. O l. 2 23. 2 2. 2

None 55 49. 7 22. 8 1. 6 23. 6 3. 4

None 49 49. 5 24. 2 2. 6 25. 4 6. 2

1 After additional cure.

EXAMPLE 2 A mixture of 271.2 parts by weight of 37% aqueous formaldehyde, preferably methanol-free, and about 3 parts of triethanolamine is charged into a reaction vessel and stirred to a uniform solution. 80 parts by weight of urea are then added and mixed thoroughly. At this point the pH should be within the range of 8.3 to 8.8 and, if necessary, an adjustment is made by adding triethanolamine or formic acid. The mixture is then heated to 70 C. and held at that temperature for 15 minutes. The solution is then cooled to 65 C. and 8 parts by weight of tetraethylenepentamine are added followed by 12 parts of water. After again cooling to 65 C. a mixture of 12 parts by weight of 35% hydrochloric acid and 12 parts of water is added while maintaining the temperature of the batch at 70 C.

The pH of the reaction mixture should be followed at this point. Ten minutes after the acid addition it is usually 2.4 to 2.5 and drops to 1.7 to 1.8 within another 15 minutes. If, at this time, the pH is outside the limits of 1.0 to 2.0 it should be adjusted to a value Within these limits by adding dilute hydrochloric acid or dilute sodium hydroxide.

The temperature of the batch is preferably maintained at 70 C. for one hour after addition of th hydrochloric acid, although a higher temperature and shorter reaction time may be used. It is then reduced, preferably to about 55-60 C., and the viscosity of the resin solution is followed carefully. This reduction in the reaction temperature causes an increase in the viscosity. When a viscosity of 100-200 centipoises or higher has been reached the acid resin is neutralized immediately by adding 18 parts by weight of sodium hydroxide solution. In most cases this will yield a resin having a pH 8 of 6.8-7. Resin syrups prepared by this method are soluble in water at all concentrations and do not become hydrophobic even after several months storage at ordinary atmospheric temperatures (4 to 30 C.), and therefore require no ethanol or other extraneous organic solvents.

EXAMPLE 3 A resin solution prepared as described in Example 2 was used in a commercial mill trial under full-scale operating conditions. The stock was bleached Southern kraft paper pulp beaten to a moderate degree of freeness and treated with 1.25% of its weight of rosin size and sufficient alum (about 2%) to adjust the pH of the stock to 4.9 to 5.0. The concentrated resin solution was diluted with water to 10-20% resin solids and run. to a constant head box and from there through a constant flow meter to the exhaust side of the fan pump, where it was mixed with the stock suspension. The amount of resin added was 1.64% of resin solids, based on the dry weight of the stock. The fourdrinier machine was equipped with 12 drying rolls supplied with steam at 45 pounds gage pressure followed by one yankee supplied with steam at 29 pounds and two after-driers. The machine speed was 650 feet per minute.

Samples of the paper were taken at regular intervals and were tested for wet and dry tensile strength and other physical characteristics. Other samples wer given an additional cure and subjected to the same tests. The test results were as follows:

Sample No 1 2 3 4 5 6 Percent resin in sheet 0.80 0.91 0.70 1. 00 1. l5 1. 70 Basis Wt., 25 x 40500 35. 8 34. 7 35. 8 33. 5 33. 8 42. 3 Tensile, lbs/in. width:

Machine direction, dry. 25. 6 22. 2 22. 8 21. 6 20. 2 22. 8 Machine direction, Wet 6. 0 5. 8 4. 8 4. 8 4. 6 5. 0 Cross direction, d1'y l1. 2 11. 2 10. 2 12. 4 l2. 4 l6. 6 Cross direction, Wei; 2. 8 2. 8 2. 0 3.0 2. 6 4. 6 Mullen, dry 28. 0 27. 5 28. 5 27. 0 27. 0 32. 5 Mullen, wet 11. 5 11.0 9. 5 10.0 10. 5 12.0 Old, MIT 515 495 448 325 405 347 Wet rub 50 51 39 43 48 68 After additional IO-minute cure at 260 F.:

Sample No 1 2 3 4 5 6 Tensile, lbs/in. Width:

Machine direction, dry" 25. 2 24. 6 25. 2 22. 6 20. 0 24. 6 Machine direction, wet 7. 2 6. 8 7. 2 6. 6 5. 6 6. 6 Cross d rection, dry 11.4 11.6 10.8 11.8 13. 4 18.6 Cross direction, wet. 3. 6 3. 6 3.0 3.8 4. 4 5. 2 Mullen, Dry 28. 5 27. 5 30. 0 26. 5 25.0 85. 0 14.0 12. 5 12.0 13. 5 12. 5 l4. (1 537 21' 0 380 470 383 535 68 C8 62 77 74 88 EXAMPLE 4 Another mill trial was made on a fourdrinier machine with the resin of Example 2. A 50- pound bag paper was made from unbleached kraft paper pulp containing 0.34% of its weight of rosin size and sufficient aluminum sulfate to maintain a pH of 4.24.5 in the white water. The Production rate was 8.8 tons per hour at a machine speed of 990 feet per minute, the drying rolls being maintained at 268 F. The resin solution was diluted with water to a concentration of 1 pound resin solids per gallon and introduced. at a uniform rate in an amount equal to 1.67% resin solids, based on the dry weight of the paper stock. Samples of the paper were taken at uniform intervals and tested for wet and dry tensile strength and other physical char- 9 acteristics, and the results were averaged. Other samples were given an extra cure of 10 minutes at 260 F. and were then tested. The results are given the following table:

The retention or the cationic urea-formaldehyde-amine resins by the cellulosic fibers, and the resulting wet strength on heating the formed cellulosie articles to cure the resin, is greatly increased by partially polymerizing the resin. This canbe accomplished by several methods. In urea resin syrups prepared with not more than about 2.5 mols of formaldehyde. or other methylene-yielding substances for each moi of urea the polymerization takes place by continued heating at temperatures of about 70"-90 C. or higher after acidification to a pH value within the range of about 3-6.

Thus, forexample, a resin syrup was prepared by reacting I gram mol of urea. and 2' gram mols of aqueous 37% form-aldehyde containing 2 grams u of triethanolamine at 70" C. for 15 minutes. To this there were added 8 grams (0.0423 mol). of tetraethylenepentamine and a solution of 8 cc. of concentrated hydrochloric acid in 20 cc. of water, and the solution was heated at 70 C. After 5 minutes heating the pH' was 4.1 and a viscosity increase was noticeable. The viscosity increased rapidly upon continued heating at the. same temperature, indicating further Polymerization ofthe resin, until eventually a stiff gel was formed.

In urea-formaldehyde-amine resins prepared by reacting 2.5. tools or more of tormaldehyde or. equivalent quantities of: haraformaldehyde or other methylene-yielding substances for each. H101? of urea there,- is little or no increase in. viscosity after the first 30- minutes or heating under acid conditions at temperatures of W C. or higher. However, the viscosity increase can be continued to the desired range in these resin solutions by lowering the temperature below 70 0.; preferably to about 45-65 C1, and continuingthe reaction at these reduced temperatures. This is shown by the following Four resin syrups were prepared by reacting, in each case, 4 gram mols of urea with 10 gram molsof 37% aqueous formaldehyde containing 8 cc. of triethanolamine and, having a. pH: of 8-5. at 70 C. for M5 minutes. 24 grams of tetraethylenepentamine were then added followed by 28.5 cc. of. concentrated hydrochloric. acid in. 85 cc. of water and, the heating was continued. at 70 C. After" 301 minutes heating the resin. solids content Was about 453%. and the. pH was 1.8 in all the syrups. Heatingwas continued at 70 C. for an additional 30 minutes, at. which time samples were withdrawn, neutralized. by the. addiden of 20%; NaOH solution, and. the. viscosity at 75 25 C. was found to be so oentipoises. The solutions were then treated as follows: Solution A was cooled 1:05.09 C. in. Zminutes and held at this temperature for 8 minutes. Solution B was cooled to 55 C... in 2 minutes and held at this temperature for 10 minutes. Solution C was cooled to 60 G. in 2 minutes and held at this temperature for 12. mmutes. Solution D was maintained at 70 for 12 minuta.

A sample of each solution was. withdrawn every 2 minutes, neutralized with NaOH solution, and tested for viscosity- The results of these tests are shown on Fig. 2 of the drawings. These results. show that the dimethylohirea-amine resins were polymerized in acidified aqueous solutions at temperatures of 60, 55 and 50 C. at constantly increasing rates, but that practically no further polymerization takes place upon continuedheating at 70 C.

The importance of partial polymerization of the resin in the production of wet strength paper is evident from the curves shown on Fig. 1 of the drawings. The data shown on these curves. were obtained by withdrawing portions of the resin solution of Example 2 prior to and during the final polymerization stage at st cc C., immediately neutralizing them and datemanning their viscosity, and then adding them in amounts or 3% resin solids, based on the dry weight oi the fiber, to. 11% aqueous suspensions: oi. krafl; paper pulp. The pulp suspensions were. then madeinto handsheets which were analyzed for resin content and tested for wet strength. The

curves show that: a rap-id increase the resin retensicn with a corresponding increase in wet. strength is obtained as the polymerization of the resin increases to. a stage corresponding to a viscosity of 60-70 centipoises, measured at CL, in a resin solution. Above this stage there is only a. slight increase in retention with continued polymerization and practically no; increase in wet strength.

EXAMPLE 6 Resin No. 1

A solution of 240 grams. t4. mols) of urea in 8.11 grams (10 mols) of aqueous 37% formaldehyde was adjusted to a pH of 8.5 by the addition of 20cc. of a aqueous triethanolamine solution and was then heated at 7044 C. for 30' minutes. Thirty-two grams of dicyandiamide were added and then cc. of 18.4% hydrochloric acid, the.- pH alter. the acidaddition being 2.0,

and heating was; continued at N 25 C. for 55 minutes during which time the. pH rose to 4.0. After cooling and adjusting the pH. to: 3.5. by adding an additional l cc. or hydrochloric. acid the solution. was aged at ac -55 C. for 1.5 hours: and then neutralized by adding sodium hydroxide solution. The viscosity of the resulting guanylurea-modified urea-formaldehyde resin syrup was 225. centi'polses.

50% epichlorhydrin-TEPA aqueous resin solution 12 Water ..d 20. HGl 611.75%) 12 The epiehierhyd'rin resin solution was prepared solution of the tetraethylenepentamine with stirring while maintaining the temperature at about 50 C. followed by continued reaction at the same temperature as described in Example 1 of the copending application of Daniel and Landes, Serial No. 688,334 filed August 3, 1946, now Patent No. 2,595,935, but using equimolecular quantities of epichlorhydrin and tetraethylenepentamine.

The primary urea-formaldehyde resin syrup was prepared and the epichlorhydrin resin solution and hydrochloric acid were added, using the procedure described for Resin No. 1. The pH was 2.8 after adding the hydrochloric acid, and

dropped to 2.0 after heating at '7080 C. for

30 minutes. After raising the pH to 3.3 by adding NaOH the syrup was aged at 55-57 C. for 35 minutes to a viscosity of 250 centipoises and then neutralized with NaOH solution.

Resin No. 3

Grams Urea 250 Formalin, 37% aqueous 811 Diethylenetriamine 24 1;. H01 (18%) 54 The urea was dissolved in the formalin, the pH was adjusted to 8.5 by adding 1.7 cc. of 10% NaOH solution, and the solution heated at 70-75 C. for 30 minutes. It was then cooled to 65 C. and the diethylenetriamine, dissolved in 50 grams of water, was added and the temperature increased to 70 C. The hydrochloric acid was then added (pH after addition being 4.2) and the mix- The viscosity of the resin syrup was 200 centipoises.

Resin No. 4

Grams Urea 180 Formalin, 37% aqueous 608 Diethanolamine 18 I-ICl (17.7%) 3'7 The procedure of Resin No. 3 was followed, the solution being held at 80-85 C. for minutes after adding the diethanolamine and HCl and aged at 5055 C. to a viscosity of 370 centipoises. The neutralized resin syrup was soluble in a mixture of equal parts of water and ethanol.

Resin N0. 5

The quantities and procedure of Resin No. 3 were used, but 52 grams of guanidine hydrochloride were substituted for the diethylenetriamine and 16.4 grams of 18.4% HCl were used to obtain a pH during heating of 1.45. The syrup was aged minutes at -45 degrees to a viscosity of 140 centipoises and neutralized to a pH of '7 with NaOH.

Samples of the above cationic resins were added to beaten kraft paper pulp in amounts of 3% resin solids, based on the dry weight of the paper pulp, and handsheets were made and tested for wet and dry tensile strength as described in Tensile strength, lbs/in. width Percent resin retained Ordinary cure Basis weight Extra cure Resin No.

Dry Wet Dry Wet EXANELE 7 Another important advantage of resin syrups prepared by the method of the present invention is the fact that they can be evaporated to dryness without impairing substantially either their Water solubility or their substantive properties towards hydrated paper stock. Thus, for example, a sample of the tetraethylenepentamine-urea-formaldehyde syrup of Example 2 was evaporated to dryness at room temperature and the resulting white solid was ground. The ground material was redissolved in water and added to an aqueous suspension of beaten kraft paper stock, which was then made into handsheets that were heated in the usual manner to cure the resin. The resulting paper had good wet strength.

Samples of the resin syrup of Example 2 were also spray-dried at a feed rate of 100 cc. per minute in a spray drier equipped with a jacketed nozzle feeding the resin solution to a rotating spray wheel. The temperature conditions were The spray-dried resin was obtained as a fairly dense, dry product, about of which was readily soluble in water. Complete solution was obtained in water containing a small quantity of hydrochloric or other acid, the amount being 'such that a 10% solution of the resin had a pH of 5-6.

These resins were tested for use in the manufacture of wet strength paper by the procedure described in Example 1, using 3% of the resin and 3% of alum, based on the weight of the paper stock, with bleached kraft pulp at a pH of 4.5. The cure was one minute at 230 F.; condition of resin indicates the condition in which the resin was added to the paper pulp suspension. The following test data were obtained:

Tensile P t i I Sample ercen B s.in1

0 ans Y ondition of resin rergstilrd we-fight width I Dry Wet These results show that the spray-dried urea-' formaldehyde-amine resins can be added in the EXAMPLE. 8.

A series of resin syrups was prepared with yarn ing ratios of tetraethylenepentamine to urea, as follows:

Formaldehyde TE 22% solution Resin No. H Mols Urea Grams Grams Mols Grams Mols Resin No. l was prepared by adding the formaldehyde slowly to the tetraethylenepentamme and heating for one hour at 70 C, at a pH of 9.4. In Resin No. 1-a the same procedure was followed, but sufiicient hydrochloric acid was added before heating to lower the pH. to about Resins Nos. 2-6 were prepared by the procedure, described in Example 2; i. e., by first, reacting the urea and formaldehyde under slightly alkaline conditions, then adding the tetraethylenepentamine and suificient hydrochloric acid to give a pH of about 3, continuing the condensation for another 30 minutes and holding for a viscosity of about 125-150 centipoises or higher, and neutralizing with sodium hydroxide.

Handsheets were made from bleached kraft stock using 3% of the above resins, based on the dry weight of the stock. The pH of the stock suspension was adjusted to 4.5 by the addition of alum, except where otherwise noted. The sheets were given an ordinary cure of one minute at 230 F. and some were also given an extra cure of 10 minutes at 260 F., and all were tested for wet and dry tensile strength. The results are given in the following table.

Tensile strength, ]bs./in.

width TEPA Percent Basis Resm N g gg igfi weight Regular cure Extra cure Dry Wet Dry Wet 8 48. 7 20.6 0.6 21. 6 1. 0 49. 8 21. 2 0.6 22.8 0.8 14 47. 2 23. 2 0.6 22.2 1. 4 24 47. 3 21.0 0.8 21. 2 3. 2 37 46. 7 21. 6 l. 8 23. 4 5. 4 45 48. 4 23. 2 3. 2 26. 0 7. 8 26 48. O 22. 8 2. 2 25. 6 7. 6 42 49. 4 24. 0 l. 4 25. 4 6. 8

These results show clearly that the ratio of amine to urea should be maintained below 1:1 and that best results are obtained when it is 0.3:1 or lower; in fact, good results have been obtained with as little as 2 grams of tetraethylenepentamine to 60 grams of urea. The tetraethylenepentamine-formaldehyde condensation roduct itself (Resins Nos. 1 and l-a) produces no increase in wet strength; therefore it is important to use only sufficient of the amine to impart the necessary cationic properties to the urea form aldehyde resin. Experience has shown, however, that the resin syrups become unstable upon dilution to resin solids or less when the quantity or tetraethylenepentamina is lowered to less than. about per cent of the weight or area. used: therefore the preferred quantity is about, 4; to 1.2 grams. for each 60 grams of'urea for the preparation of syrups in which stability after dilution is desired. When the resin syrups are to be used without. prior dilution the amount oi pulyalkyl enepolyamine or other urea. and iormaldehyde reactive amine maybe reduced to aslow as 2--3% or the. weight or the area while retaining. the cationic properties or the resin.

What we claim is:

I. A process for the production or wet strength paper. which comprises adding to an aqueous: suspension of cellulosic paper stock a partially polymerized, hydrophilic cationic. ureaeformal dehyde resin obtained by condensing dimethylol urea and a quantity of an alkylenepolyainine which is about. 6% to: 1.5% of the. weight of the urea in said dimethylol urea at a. pH: below 4.5 and polymerizing the condensation product to a. degree corresponding to a viscosity of at. least centipoises in, a 45 aqueous solution thereof. adsorbing about, 0.1% to 5% of saidresin on said, paper stock, forming the stock so treated into a waterlaid sheet, and heating the. sheet for about 1:4, minutes at 212 F. to 30. F. and hereby iormine, a bond of cured. resin between the fibers ther o 2. A process for the production of wet strength paper which comprises adding to an aqueous suspension of cellulosic paper stock a partially polymerized, hydrophilic cationic urea-formaldehyde resin obtained by condensing dimethylol r urea and a quantity of tetraethylenepentamine which is about 6% to 15% of the weight of the urea in said dimethylol urea at a pH below 4.5 and polymerizing the condensation product to a degree corresponding to a viscosity of at least 100 centipoises in a 45% aqueous solution thereof, adsorbing about 0.1% to 5% of said resin on said paper stock, forming the stock so treated into a waterlaid sheet, and heating the sheet for about 1-4 minutes at 212 F. to 3'00 F. and thereby forming a bond of cured resin between the fibers thereof.

3. A process for the production of wet strength paper which comprises adding to an aqueous suspension of cellulosic paper stock a hydrophilic cationic urea formaldehyde polyfunctional organic nitrogen base resin which is partially polymerized to a degree corresponding to a viscosity of at least 100 centipoises in a 45% aqueous solution thereof, said resin containing a quantity of polyfunctional organic nitrogen base which is within the range of 6% to 15% of the weight of the urea therein, adsorbing about 0.1% to 5% of said resin on said paper stock, forming the stock so treated into a waterlaid sheet, curing said resin to its heat-set and water-insoluble condition by heating it for about 1-4 minutes at 212 F. to 300 F., and thereby forming a bond of cured resin between the fibers of said paper.

4. A process for the production of wet strength paper which comprises adding to an aqueous suspension of cellulosic paper stock a hydrophilic cationic urea formaldehyde polyfunctional organic nitrogen base resin in which the amount of polyfunctional organic nitrogen base is 2-30% of the weight of the urea, adsorbing about 0.1% to 5% of said resin on said paper stock, forming the stock so treated into a waterlaid sheet, and curing said resin to its heat-set and water-insoluble condition by heating said 15 sheet for about 1-4 minutes at 212 F. to 300 F. and thereby forming a bond of cured resin between the fibers of said paper.

5. The process for the production of wet strength paper, which comprises adding to an aqueous suspension of cellulosic paper fiber a hydrophilic, cationic urea-formaldehyde-triethylenetetramine resin in which the triethylenetetramine is 6% to 15% of the weight of the urea, absorbing about 3% based on the fiber of said resin on the fiber, forming the stock so treated into a waterlaid sheet, then heating the sheet for about 100 seconds at 212 F., and thereby forming paper of increased wet strength.

6; A method of producing wet strength paper which comprises applying to the fibers thereof about 0.1% to 5% by weight of a partially polymerized, hydrophilic cationic urea-formaldehyde-polyfunctional organic nitrogen base resin in which the amount of polyfunctional organic nitrogen base is 2-30% of the Weight of the urea and then curing said resin to its heat-set and water-insoluble condition by heating the paper for about 1-4 minutes at 212 F. to 300 F. and thereby forming a bond of cured resin between the fibers of said :paper.

7. A method of producing wet strength paper which comprises applying to the fibers thereof about 0.1% to 5% by weight of a partially polymerized, hydrophilic cationic urea-formalde- 16 hyde-polyfunctional organic nitrogen base resin in which the amount of polyfunctional organic nitrogen base is about 6% to 15% of the weight of the urea and then curing said resin to its heat-set and water-insoluble condition by heating the paper for about 1-4 minutes at 212 F. to 300 F. and thereby forming a bond of cured resin between the fibers of said paper.

JOHN H. DANIEL, JR.

CHESTER G. LANDES.

I'ZENG JIUEQ SUEN.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,009,173 Gams et a1. July 23, 1935 2,197,357 Widmer et al Apr. 16, 1940 2,291,079 Hofferbert July 28, 1942 2,322,887 Schwartz June 29, 1943 2,325,302 Britt July 27, 1943 2,338,602 Schur Jan. 4, 1944 2,345,543 Wohnsiedler et al. Mar. 28, 1944 2,395,825 Hesler Mar. 5, 1946 2,407,376 Maxwell Sept. 10, 1946 OTHER REFERENCES Collins, Paper Ind. and Paper World, June 1943, pp. 263-269.

Maxwell, Pacific Pulp and Paper Ind., Apr. 1943, pp. 6-8.

Claims (1)

1. A PROCESS FOR THE PRODUCTION OF WET STRENGTH PAPER WHICH COMPRISES ADDING TO AN AQUEOUS SUSPENSION OF CELLULOSIC PAPER STOCK A PARTIALLY POLYMERIZED, HYDROPHILIC CATIONIC UREA-FORMALDEHYDE RESIN OBTAINED BY CONDENSING DIMETHYLOL UREA AND A QUANTITY OF AN ALKYLENEPOLYAMINE WHICH IS ABOUT 6% TO 15% OF THE WEIGHT OF THE UREA IN SAID DIMETHYLOL UREA AT A PH BELOW 4.5 AND POLYMERIZING THE CONDENSATION PRODUCT TO A DEGREE CORRESPONDING TO A VISCOSITY OF AT LEAST 100 CENTIPOISES IN A 45% AQUEOUS SOLUTION THERE-

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