US3077430A - Paper containing acrylamide copolymer - Google Patents

Description

3,fi77,d3fi Patented Feb. 12, 1963 line 3,077,4536 PAPER CfiNTAlNlNG ACRYLAMHDE CGPULYl/illlt dewell T. Moore, Stamford, Conn, assignor to American Cyanamitl Company, New York, Niki, a corporation of Maine No Drawing. Filed Sept. 25, 1959, Ser. No. 842,212 8 Claims. (Cl. 162-168) The present invention relates to paper of improved dry strengths resulting from a content of a diallylmelamineacrylamide copolymer. The invention includes such paper containing rosin size, dyes, fillers, etc., together with the papermaking processes involved.

The term paper" as used herein includes cardboard, hardboard, tissue and all other waterlaid webs in substantial part composed of waterlaid cellulose fibers.

N,N-diallylmelamine (hereinafter termed diallylmelamine) is a relatively new chemical compound which heretofore has found no utility in dry strength paper manufacture. It is insoluble in water, and does not homopolymerize.

The discoveries have now been made that paper composed of waterlaid cellulose fibers carrying a small adsorbed amount of a normally water-soluble dlallylmelamine-acrylamide copolymer possesses improved dry strength as compared with paper containing none of the copolymer. I have further found that such paper processes improved wet strength when the copolymer contains thermoset methylol groups, and that the presence of the copolymer on rosin sized fibers improves the Water resistance imparted by the size.

The invention is based on my discovery that watersoluble diallylmelarnine copolymers are suificiently strongly cationic to be absorbed in large amounts from aqueous solution by cellulose fibers suspended therein, and that when the fibers carrying the copolymer are sheeted to form a web and the web is dried, the copolymer tends to bond locally or spot weld the fibers together, thereby increasing the dry strength of the sheet.

In preferred instances the invention has increased dry tensile strength values by more than 25%, and when a methylol diallylmelamine-acrylamide copolymer has been employed, wet tensile strength values have been obtained comparable to those possessed by commercial wet strength papers. Finally, the presence of the copolymer has nearly doubled the efiectiveness of rosin size when present, as measured by standard laboratory sizing tests.

The paper of the present invention is prepared by f rming an aqueous suspension of cellulose papermaking fibers, adding thereto a small amount of a cationic watersoluble diallylmelamine-acrylamide copolymcr, sheeting the fibers to form a waterlaid web, and drying the web.

The process is applicable to any of the common furnishes. Groundwood, unbleached and bleached kraft and hardwood pulps have been found to benefit from the treatment. The copolymer is advantageously added to the fibrous suspension as a dilute aqueous solution immediately before the suspension is sheeted, for example at the fan pump. The copolymer is rapidly and substantively adsorbed from solution by the fibers.

However, in the manufacture of rosin sized paper advantage is taken of the cationic nature of the polymer. Preferably, the copolymer is added to the fibrous suspension first, and is substantively adsorbed. The fibers are then rosin sized in an ordinary manner. Evidently the absorbed polymer assists deposition of the rosin size, and beneficially affects the amount and orientation of the copolymer deposited. The copolymer has no effect as a size, and the water resistance possessed by rosin sized paper containing diallylmelamine-acrylamide copolymer is greatly superior to the water resistance of resin sized paper containing none of the copolymer.

An important advantage of the use of the diallylmelamine-acrylamide copolymer in conjunction with rosin size is that it permits formation of paper having normal dry tensile strength. Rosin sized paper is ordinarily weaker than corresponding unsized paper.

A further advantage of the invention is that it permits the manufacture of rosin sized paper having an alkaline pH. Rosin sized paper ordinarily has an acid pH (about 4.5) and is therefore subject to acid tendering on aging. The paper of the present invention likewise may contain acid-sensitive pigments such as ultramarine.

The copolymer may be added along or in conjunction with cationic wet strength agents and cationic sizes. The process tolerates the addition of numerous materials which have been added to the beater, and thus it desired, pigments such as clay, titanium dioxide, blanc fixe and calcium carbonate may be incorporated prior to sheeting.

Paper according to the present invention is made by forming an aqueous suspension of cellulose papermaking fibers, adding thereto a small amount of a cationic Water soluble diallylmelamine-acrylamide copolymer as strengthening agent, sheeting the fibers to form a waterlaid web, and drying the web. The copolymer is rapidly and substantively adsorbed by the fibers.

A flow sheet of the invention in one preferred embodiment is as follows:

MM Form aqueous suspension of cellulose papermalcing fibers Add alum as complexing agent Sheet suspension to form a web Dry the web Paper of improved dry strength is obtained both fr m acid and alkaline pulps. Paper of somewhat better dry strength results when alum is added as complexing agent. The optimum amount is most easily found by laboratory trial; generally enough alum to increase the pH f the suspension to 4.5-5.0 after addition of the copolymer is enough.

Paper of improved wet and dry strength is obtained by employing a cationic water-soluble thermosetting methylol diallylmelamine-acrylamide copolyrner in the process described above, and sheeting the fibers at an acid pH to facilitate subsequent thermosetting of the copolymer.

Rosin sized paper is manufactured according to the present invention by adding a small amount of a cationic water-soluble diallylmelaminc-acrylamide copolymer as strengthening agent to a cellulose fiber suspension, rosinsizing the fibers by adding rosin size and alum, sheeting so /vane Jr the fibers to form a web, and drying the web. In preferred instances the copolymer acts to counteract the nor mal weakening etlect imparted by the size and to increase the water-resistance and ink-resistance which the sheet would otherwise possess. Moreover, the suspension may be sheeted at an alkaline pH to produce alkaline paper.

The process tolerates the addition of such materials as have heretofore been added to paperrnaking pulps, and thus it is within the scope of the present invention to add clay filler, titanium dioxide, calcium carbonate and ultramarine pigments, and dyes to the pulp before sheeting.

The copolymer of the present invention is substantially composed of vinyl units (hereinafter termed the diallylmelamine and acrylamide components), having the theoretical formulae:

I NH2 and or methylol derivatives thereof, the acrylarnide component being present in preponderant amounts, i.e., more than 50% by weight. If desired, the copolymer may be exclusively composed of the units illustrated above, in which event the paper containing the polymer will have substantially improved dry strength but low wet strength, so that the paper can be easily repulped without need for special mechanical or chemical treatment.

The copolyrner may contain methylol substituents formed by reacting some or all of the NH groups shown above with formaldehyde. Advantageously, the number i such groups present should be sufiicient to render the polymer thermosetting. The minimum effective proportion for this purpose may be determined by heating the polymer briefly at 190 F. at a pH below 5 Conversion of the copolymer to water-insoluble form shows that sufficient methylol groups are present to render the copolymer thermosetting.

The copolymer may contain minor amounts of units other than those described above. Thus the copolymer may contain a minor amount of combined styrene, in which event the polymer will impart sizing in addition to dry strength. Moreover, the polymer may contain hydrophilic cationic groups for example those introduced by chlorornethylstyrene quaternized with a water-soluble tertiary amine. The amount of such supplementary units should be insufficient to cancel the cationic, water-soluble character of the copolyrncr.

it is of particular interest that the copolymer may and often advantageously will contain carboxylic groups such as are introduced by a combined content of acrylic acid, or by hydrolysis of some of the amide units present, the proportion of such carboxylic acid groups (which are anionic), however, being insufficient to change the essentially cationic character of the polymer as a whole. Polymers of this type (hereinafter termed diallymelamiue acrylarnide-acrylic acid copolymers) form a complex with alum, and paper composed of cellulose fibers bonded together by this complex possesses better dry strength than would otherwise be the case.

Paper composed of fibers carrying normally watersoluble cationic copolymers prepared from dimethallylmelamine and acrylamide are within the scope of the invention.

The invention will be more particularly illustrated by the examples. These examples represent preferred embodiments of the invention and are not to be construed as limitations thereon.

Example 1 The following illustrates the dry strength possessed by i aper according to the present invention composed of cellulose fibers bonded together by varying amounts of diallylrnelamine-acrylamide copolymers containing no methylol groups.

An unbleached southern kraft pulp was diluted to a consistency of 0.6%. A diallylmelamine-acrylamide copolymer (as a 5% aqueous solution) was then added in amounts shown below, alkali added to adjust the pH of the suspension to 7.0, and the-suspension was sheeted to yield sheets having a dry basis weight of 10-0 1b. (25 x 40"/500 ream). The wet sheets were dried at 240 C. 'for 1 minute, and their dry and wet tensile strengths determined by standard laboratory methods.

None of the sheets had a wet tensile strength in excess of 3.8 lb. per inch and could be repulped by ordinary beater processing.

The copolymers used were prepared as follows. Diallylmelamine and acrylamide monomers were mixed in the ratio shown in the table below, 0.15% based on the weight of the mixture of thiornalic acid added thereto, and one part by weight of the mixture dissolved in 9 parts by weight of water at C. acidified to pH 2 with hydrochloric acid. The mixture was reacted at 7080 C. with slow addition of an aqueous solution containing 1% based on the weight of the monomers of (NH S 0 as initiator. The reactions were stopped by cooling and neutralization when the solutions were evidently near gelation.

Results were as follows:

Copolymor Dry Tensile Run No.

DAM :AM Percent Pulp Found, Percent Ratio 1 Added 9 pH 3 1b./in. Incr.

1 Initial (before polymerization).

2 Based on dry weight of fibers.

2 After addition of copolymer.

4 Corrected to 100 lb. basis weight.

The dry strength values obtained can be increased by 2-5 lb. by adding sufllcient alum after addition of the copolymer to decrease the pH of the suspension to 4.5, or by adding an equal amount at the outset.

Example 2 The following illustrates the dry and wet tensile strength possessed by paper containing a thermoset methylol diallylmelamine-acrylarnide copolymer.

A diallylmelamine-acrylamide copolyrner was prepared by heating 50 gm. each of diallylmelamine and acrylarnide and 0.5 gm. of benzoyl peroxide in 400 gm. of dioxane in a flask equipped with agitator, reflux condenser and electric heating mantle. At 88 C. cooling was applied to maintain the reaction at 90 C. When the exotherm subsided, the flask was maintained at C. for 90 minutes. The polymer was filtered oft and washed with dioxane. By analysis the ratio of components in the copolymer was found to be 28.91711, showing that the diallylrnelamine reacted more slowly than the acrylamide.

The copolymer was methylolated by stirring 5.0 gm. of the copolymer into a mixture of 16 gm. of 37% aqueous methanol-free formaldehyde and 224 ml. of water,

heating rapidly to 80 (3., adding 5 ml. of 28% acetic acid, cooling to 20 C. and diluting with water to 1% solids.

A series of paper sheets was prepared by the method of Example 1 except that bleached northern kraft pulp was used, 2% of alum based on the dry weight of the fibers was added after addition of the copolymer giving the pump a pH of 4.7, and the pulp was sheeted at a calculated basis weight of 48.5 lb. (25" x 40/500 ream).

A second series of sheets was prepared in similar manner except that the pulp was adjusted to the various pH values shown in the table before sheenng.

Results were as follows:

Copolymer Dry Tensile Per- Wet Run. No. cent Pulp Ten- DAM AM Percent Alum pI-I Found, Persil Ratio 1 Added 2 Added lb./i.n.= cent 1b./in

Incr.

1 By analysis of eopolymer. 1 Based on dry weight of fibers. Corrected to 48.5 lb. basis weight.

Example 3 The following illustrates the effectiveness of small amounts of diallylmelamine-acrylamide copolymer in increasing the water and ink resistance imparted by rosin size.

A series of handsheets was prepared by the general method of Example 1 employing bleached northern kraft pulp. To one aliquot was added 1% of alum, to another aliquot was added wood rosin size and alum, and to the third was added diallylmelamine-acrylarnide copolymer solution, wood rosin size and alum, in amounts shown in the table below.

The aliquots were then formed into handsheets which were tested by the method of Example 1. Results were as follows:

1 Percentages based on dry weight of fibers.

The above data shows that paper produced by the use of 0.5% copolymer and 0.6% rosin size in comibnation possesses much better resistance to penetration by water and ink than paper produced by rosin size and alum alone, while being about 19% stronger.

Example 4 The following illustrates the dry strength and sizing properties possessed by rosin sized paper of the present invention made at acid and alkali pH values.

The procedure of Example 3 was repeated using a bleached sulfite pulp and copolymers formed by copo1ymerization of diallyl-melamine and acrylamide in 5:95, :90 and 20:80 weight ratios.

Results were as follows. The first three runs were controls.

Pulp Treatment 1 Sizing Results Run No. Poiy- Rosin Dry 11-30 In}:

mer, Size, Alum, pH Tensile, Resist. Resist. percent percent percent lb./in. Currier, BKY,

Sec. Sec.

Diallylmelamine :acrylarnide ratio 5:

Diallylmelamine:acrylamide ratio 10:90

Diallylmelamine :aerylamide ratio 20 80 X Percentages based on dry weight of the fibers.

I claim:

1. Paper of improved wet and dry strength composed of cellulose fibers locally bonded together by a small adsorbed amount of a thermoset cationic, normally watersoluble thermosetting methylol diallylmelamineacrylamide copolymer.

2. Paper of improved dry strength composed of celluose fibers locally bonded together by a small adsorbed amount of a complex of alum with a cationic, normally water-soluble diallylmelamine-acrylamide-acrylic acid copolymer.

3. Sized paper of improved dry strength composed of resin sized cellulose fibers locally bonded together by a small adsorbed amount of a cationic, normally water soluble diallylmelamine-acrylamide copolymer.

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

5. Process for manufacturing paper of improved dry strength, which comprises forming an aqueous suspension of cellulose papermaking fibers, adding a small amount of a cationic, water-soluble diallylmelamine-acrylamide acrylic acid copolymer as strengthening agent thereby adsorbing said copolymer on said fibers, adding alum as complexing agent for said copolymer, sheeting said fibers to form a waterlaid web, and drying said web.

6. Process of manufacturing paper of improved wet and dry strength, which comprises forming an aqueous suspension of cellulose papermaking fibers, adding thereto a small amount of a cationic, water-soluble thermosetting methylol diallylmelamine-acrylamide copolymer as strengthening agent thereby adsorbing said copolymer on said fiber, sheeting said fibers at a pH to form a waterlaid web, and drying said web at a temperature between C. and 250 C. until said copolymer has thermoset.

7. Process of manufacturing rosin size-d paper of improved dry strength, which comprises forming an aqueous suspension of cellulose papermaking fibers, adding thereto a small amount of a cationic, water-soluble diallylmelamine-acrylamide copolymer as strengthening agent thereby adsorbing said copolymer on said fibers, rosinsizing the fibers carrying said copolymer, sheeting said fibers to form a waterlaid web, and drying said web.

8. A process according to claim 7 wherein the fibers are sheeted at an alkaline pH.

(References on following page) References 651%: in the file of this patent UNITED STATES PATENTS House et a1. Ian. 3, 1956 5 8 Lundberg et a1. July 30, 1957 Wrotnowski Mar. 29, 1960 Stilbert et a1 Feb. 21, 1961 FOREIGN PATENTS Canada Sept. 25, '1951 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,077,430 February 12, 1963 Sewell T. Moore corrected below.

Column 4 line 28, for "80% C, read 80 C., column 5, line 63, for "comibnation" read combination Signed and sealed this 11th day of February 1964c (SEAL) Attest:

' EDWIN Lo. REYNOLDS ERNEST W SWIDER Attesting Officer Ac ti ng Commissioner of Patents

Claims (1)

1. 5. PROCESS FOR MANUFACTURING PAPER OF IMPROVED DRY STRENGTH, WHICH COMPRISES FORMING AN AQUEOUS SUSPENSION OF CELLULOSIC PAPERMAKING FIBERS, ADDING A SMALL AMOUNT OF A CATIONIC, WATER-SOLUBLE DIALLYLMELAMINE-ACRYLAMIDE ACRYLIC ACID COPOLYMER AS STRENGTHENING AGENT THEREBY ADSORBING SAID COPOLYMER ON SAID FIBERS, ADDING ALUM AS COMPLEXING AGENT FOR SAID COPOLYMER, SHEET SAID FIBERS TO FORM A WATERLAID WEB, AND DRYING SAID WEB.