US3019156A - Wet strength paper containing polyamide - Google Patents

Description

United States Patent Ofitice 3,019,156 Patented Jan. 30, 1962 3,019,156 WET STRENGTH PAPER CONTAINING POLYAMIDE Lennart A. Luudberg, Stamford, Conn., and Lucius H. Wilson, Valdosta, Ga., assignors to American Cyanamid Company, New York, N.Y., a corporation of Maine No Drawing. Filed Apr. 29, 1957, ser No. 655,488 8 Claims. (Cl. 162-468) The present invention relates to Wet-strength paper. More particularly, the invention relates to wet-strength paper cbntaining a normally water-soluble cationic linear methylenebisacrylamide-alkylene-polyamine condensate as agent imparting wet strength. The invention includes the papermaking processes involved.

In the past the manufacture of Wet-strength paper has been successfully performed on a large scale by the addition of Water-soluble cationic resinous condensates to aqueous slurries of papermaking fibers. The condensates are substantively adsorbed by the fibers while in aqueous suspension and bond or spot Weld the fibers together when sheeted and dried.

In the past, effective adsorption of the bonding agent has generally required that the cellulose pulp be acid during adsorption of the resin, and development of satisfactory wet strength has generally required that the agent have a substantial content of formaldehyde which acts as cross-linking agent when the fibers are sheeted and dried.

The present invention provides a new papermaking process which may be carried out at an alkaline pH, and provides a new form of wet-strength paper which need not contain any formaldehyde at all.

The discovery has now been made that the normally water-soluble cationic methylenebisacrylamide-polyamine condensates are particularly advantageous 'as Wet-strength agents in the manufacture of paper. In the first place, the condensates are adsorbed by cellulose fibers in aqueous suspensions not only at normally acid pH values but at alkaline pH values as Well. In numerous instances we have been successful in making Wet-strength paper at pH values as high as 9.0, thus demonstrating that the acid corrosion problem can be eliminated. In the second place, the agents need contain no formaldehyde or inorganic anionic material so that they are particularly suitable for the manufacture of photographic and electrical paper. Thirdly, the condensates are non-thermosetting unless otherwise desired. As a result, the paper need not be heated at any particular temperature for development of substantial Wet strength. Finally, the condensates are readily converted to three-dimensional thermosetting form, for example, by reaction with formaldehyde, as a result of which paper of still better wet strength can be prepared on the alkaline side.

The paper of the present invention is thus composed of a Waterlaid Web of cellulose fibers bonded together by a small but effective adsorbed amount of a normally watersoluble cationic linear methylenebisacrylamide-polyfunctional amine condensate. If desired, the condensate in its normal form may be thermosetting resulting from a combined content of formaldehyde. The paper may have an alkaline pH.

Broadly, paper is manufactured according to the present invention by forming a dilute aqueous suspension of papermaking cellulose fibers, adding thereto a small but effective amount of a water-soluble cationic methylene bisacrylamide-polyfunctional amine condensate as wetstrength agent thereby adsorbing said condensate on said fibers, sheeting the fibers to form a waterlaid web, and drying the web. The pulp may have an acid or alkaline pH during the operation. Where the condensate has been pre-reacted with formaldehyde to render it thermosetting, drying at F.-260 F. for /2 to 5-10 minutes is generally about sufiicient to develop the maximum strengthening properties of the resin.

More in detail the paper of the present invention is manufactured by forming an aqueous slurry of beaten (i.e., hydrated) cellulose fibers at a normal consistency between about 0.5 and 5%. There is then added an appropriate amount of the wet-strength condensate with circulation of the pulp for a few minutes to allow uniform adsorption to occur. The pulp is then sheeted and dried in normal fashion.

In the process the pH of the pulp during addition of the condensate may be any desired value within the normal limits of about pH 4 and pH 10 and there is no necessity to change the pH of the pulp after addition of the resin, although, if desired this may be done. Better wet strength is generally obtained when the pH of the pulp during the adsorption step is on the alkaline side. If desired, the fibers may be sized by addition of rosin size and alum preferably added prior to the Wet-strength agent, in which case to prevent desorption of the size the pH of the pulp should not be made alkaline thereafter.

It is further within the scope of the invention to add fillers, opacifiers or colorants to the slurry prior to sheet formation. The present invention permits materials of these types such as Ultramarine, calcium carbonate and magnesium carbonate (Raffold) to be added.

The amount of condensate added in any one instance is determined chiefly by the amount of wet strength which it is desired the paper should possess. A noticeable improvement results from the addition of at least 0.1% of the resin based on the dry weight of the fibers. The wet strength imparted tends to level off When more than about 5% by weight of the agent is added. In practice, we prefer to add between about /2 and 3 of the agent based on the dry weight of the fiber as in this range substantial wet strength is imparted with about maximum efiiciency in the utilization of the agent. The condensate is rapidly adsorbed, generally in less than 15 minutes.

The condensates may be prepared by reacting methylenebisacrylamide or equivalent material with a watersoluble alkylenediamine or polyalkylenepolyamine so as to form a linear condensate. In general, sufiicient of the alkylenediamine or polyalkylenepolyamine should be used so that the methylenebisacrylamide reacts preferentially with the terminal primary amino groups thereof thereby favoring formation of linear chains. There may thus be used between about 0.5 mol to 2.0 mol of the methylenebisacrylamide per mol of 'alkylenepolyamine or polyalkylenepolyamine and this ratio is constant whether or not the polyamine is a simple alkylenediamine such as ethylenediamine, trimethylenediamine, etc., or triethylenetetramine, tetraethylenepentamine, 3,3'-iminobispropylamine or the condensation products of the foregoing amines with small amounts of alkylenedichlorides or epichlorohydrin so as to build up largely essentially strait chain polyamines. The alkylene groups referred to contain not in excess of six carbon atoms.

As methylene-bisacrylamide, there may be used methylenebisacrylamide itself and water-soluble substantially non-ionic derivatives thereof including methylenebismethacrylamide and N,N-dimethylmethylenebisacrylarnide. condensate imparting best wet strength are gener- 'ally made by reacting the polyamine and methylenebisacrylamide in substantially equirnolecular ratio, followed by addition of a chain stopper as the point of gelation is neared. This procedure constitutes a simple means for developing a condensate which is substantially linear and water-soluble though of large molecular size.

The polymer syrups obtained are normally alkaline and the polymer therein may be converted to thermosetting form by reaction with formaldehyde. Generally between about to 1 mol of formaldehyde is added per aldehyde-reactive nitrogen atom present, which is sufiicient to cause extensive cross-linking when the polymer is thermocured on the fibers.

The reaction between the methylenebisacrylamide and the polyamine proceeds rapidly at moderate temperatures and may be terminated by adding a secondary alkyl amine when molecular growth has proceeded to the point short of gelation where the condensate is sufiiciently cationic, the secondary amine acting as chain stopper. The point at which the condensate exhibits cationic properties may be determined by the well-known electrophoresis method and in practice occurs when the reaction mass has become quite viscous. The chain stopper is added at such point as to permit production of a highly viscous reaction product which, however, is water-soluble. Alternatively, the reaction may be halted by the addition of a large amount of water with rapid cooling. When less than about 0.85 mol of methylenebisacrylamide is used per mol of polyalkylenepolyamine or alkylenepolyamine, cross-linking does not occur and a chain stopper need not be used.

The invention does not primarily depend upon the particular raw materials employed or the ratio in which they are reacted. A number of condensation products of the type described which are suitable for the practice of the present invention are disclosed in application Serial No. 623,555, filed on November 21, 1956, by L. A. Lundberg, now Patent No. 2,934,528.

The invention will be more particularly described by the examples which follow. These examples illustrate embodiments of the invention and are not to be construed as limitations thereon.

Example 1 The following illustrates the preparation of a watersoluble cationic 1:1 molar ratio methylenebisacrylarnidealkylene-polyamine condensate employing ethylenediamine as the polyamine and diethylamine as the chain stopper.

In a round-bottomed flask equipped with thermometer, reflux condenser and stirrer were placed 30.8 gm. of methylenebisacrylamide (0.2 mol), 12.4 gm. of ethylenediamine (0.2 mol) and 63.8 gm. of water. The mixture was heated slowly to 70 C. and held for several minutes at this temperature until the syrup became very viscous. There was then added 3.7 gm. of diethylamine (0.05 mol) and heating continued for half an hour on a steam bath to a maximum temperature of 84 C. The product was a clear essentially linear water-white syrup which remained stable on standing.

The condensate was tested by adding 3.0% to a 0.6% aqueous dispersion of bleached kraft pulp (resin solids based on the dry weight of the fibers), adjusting the pH of the suspension to 9.0 with sodium hydroxide, allowing the suspension to stand with gentle agitation for minutes during which adsorption of the condensate occurred on the fibers. The pulp was sheeted on a Nash handsheetmachine. The sheets were pressed between blotters and dried for 2 minutes at 240 F. on a Noble and Wood handsheet dryer. Additional sheets were made in the same way and given an extra cure by hanging for 10 minutes in an oven at 260 C.

The first set of sheets had a wet strength of 4.6 lb./ in. and the second set (with extra cure) had a wet strength of 5.2 lb./ in. The basis weight of the sheets was 47.9 lb. per 25" x 40/500 ream.

Example 2 The procedure of Example 1 was repeated except that 29.6 gm. (0.2 mol) of triethylenetetramine was used in place of the ethylenediamine, the amount of water was decreased to 61.4 gm. and the amount of diethylamine increased to 7.3 gm. (0.1 mol).

The first three reagents were mixed and heated at 50 C. for seven minutes, after which the diethylamine was added. A similar condensate resutled, which was tested in accordance with Example 1. The paper was tested in similar manner yielding wet-strength values of 4.6 lb. and 4.8 lb./in. at a basis weight of 49.9 lb.

Example 3 The procedure of Example 2 was repeated except that the amount of Water initially added was increased to 184 gm. and the mixture heated for 10 minutes at 50 C. at which point the syrup became very viscous. No chain stopper was employed and instead 365 gm. of water at 50 C. was added and the mixture allowed to cool.

The syrup was tested in the same manner as the foregoing syrup and gave wet strength values of 4.7 lb. and 5.0 lb. at a basis weight of 49.4 lb. under conditions of regular and extra cure respectively.

Example 4 In the foregoing examples the condensate was .nonthermosetting.

The following illustrates the preparation of a thermoseting condensate and the effect of slow drying on the strength of the wet-strength bond developed. The procedure for the preparation of the condensate of Example 2 was repeated, after which 32.7 gm. (0.4 mol) of 37% aqueous formalin solution was added 10 minutes after the diethylamine had been run in. The formaldehyde was reacted with the condensate over 15 minutes at elevated temperature rendering the condensate thermosetting and the solution cooled. The condensate was tested according to the method of Example 1. The paper had a wet strength of 5.3 lb. at a basis weight of 48.6 lb.

Example 5 The procedure of Example 2 was repeated using 26.2 gm. (0.2 mol) of 3,3-iminobispropylamine in place of the triethylenetetramine. The wet strength of the paper was 5.5 lb./in. at 49.3 lb. basis weight.

We claim:

1. Wet-strength paper composed of waterlaid interfelted cellulose fibers bonded together by a small but effective adsorbed content of a normally water-soluble cationic linear methylenebisacrylamide-alkylenepolyamine condensate as agent imparting said wet strength.

2. Paper according to claim 1 wherein the condensate is a normally thermosetting methylenebisacrylamide-alkylenepolyamine-formaldehyde condensate in thermoset form.

3. Paper according to claim 1 having an alkaline pH.

4. Paper according to claim 1 wherein the alkylenepolyamine is ethylenediamine.

5. Paper according to claim 1 wherein the alkylenepolyamine is 3,3-iminobispropylamine.

6. A process of manufacturing paper of improved wet strength which comprises forming a dilute aqueous suspension of papermaking cellulose fibers, adding thereto an effective amount of an aqueous solution of a cationic watersoluble methylenebisacrylamide-alkylenepolyamine condensate as wet-strength agent, whereby said condensate is adsorbed by said fibers, sheeting the fibers to form a Waterlaid web, and drying said web.

7. A process according to claim 6 wherein the suspension is alkaline during and subsequent to adsorption of the condensate.

8. A process according to claim 6 wherein the condensate is a thermosetting cationic methylenebisacrylamidealkylenepolyamine-formaldehyde condensate and the Web is heated at a temperature between about 180 and 260 F. for /2 to 5 minutes to dry the web and thermoset the condensate thereon.

References Cited in the file of this patent UNITED STATES PATENTS Kleiner et al June 30, 1953 Jen Nov. 6, 1956 Lundberg et a1 June 4, 1957 Lundberg et a1 July 30, 1957 Aycock et a1 Apr. 22, 1958

Claims (1)

1. 6. A PROCESS OF MANUFACTURING PAPER OF IMPROVED WET STRENGTH WHICH COMPRISES FORMING A DILUTE AQUEOUS SUSPENSION OF PAPERMAKING CELLOUSE FIBERS, ADDING THERETO AN EFFECTIVE AMOUNT OF AN AQUEOUS SOLUTION OF A CATIONIC WATER-SOLUBLE METHYLENSBISACRYLAMIDE-ALKYLENEPOLYAMINE CONDENSATE AS WET-STRENGTH AGENT, WHEREBY SAID CONDENSATE IS ADSORBED BY SAID FIBERS, SHEETING THE FIBERS TO FORM A WATERLAID WEB, AND DRYING SAID WEB.