US 2872313 A
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U ited States harem All PULPING OF PAPER BROKE. CONTAINING. WET-STRENGTH RESINS Ronald R; House, Darien, and Yun Ju, Stamford,C'o'nn., assignors to American Cyanamid Company, New York, N. Y., a corporation of Maine No Drawing. Application September. 8, 1955 Serial No. 533,259.
3 Claims. (Cl. 921.4)
This invention relates to the pulping of wet-strength pa'per broke. More particularly, the invention relates to. the pulping of broke carrying high molecular weight material or resin as agent imparting wet strength, so as to form a pulp which can be sheeted either alone or in admixture with fresh pulp to yieldlgood quality paper.
In all paper mills a certain amount of the product is lost as trim or broke, andevery efiort is made to repulp this paper thereby eliminating waste. Paper carrying rosin size, Wax size, starch, clay,gums and similar additives can be charged directly intothe beater and reduced to a pulp without difiiculty by the normal actionthereof, although a short alkali soak is sometimes found helpful. Wet-strength webs (i. e.,- webs composed of cellulose fibers bonded together by an absorbed content of'wet strength resin) are not alfectedby this treatmerit to more than a negligibleextent,and up tothe'" present pulping of these webs has been deemed to require in combination an elevated temperature, an acid pH, and intensive mechanical disintegration assistedby steam jets. The method and apparatus therefor are respectively disclosed in U. S. Patents Nos. 2,394,273 to Thomas and 2,423,097 to Goehler et al.; see also the article by J. C. Barthel in the March- 21', 1955, issue of t the Paper Trade Journal and thevarticleby Trout'in.
TAPPI 34, 539 (1951).
The discovery has now been made that the pulping.
of wet-strength broke is greatly facilitated by 'conta'cting the broke with a diluteaqueous solution of an oxidizing salt and maintaining the broke in contact therewith until the fiber-resin-fiber bonds therein have substantially loosened, that is, loosened to the point where the broke can be pulped in conventional pulping equipment such as a beater, hydropulper, refiner or dynapulper. have found that in the great majority of instances soaking thebr-okefor less than anhour in a preferrednsalt solution loosens the fiber-resin-iiber bonds so extensively that the broke need not be subjected to the'steamejet disintegrationreferred to above andcan be added directly to the mechanical pulper, and that in :oth'erdnstances the bonds. are loosened to such anextent that much milder mechanical disintegration is 'sumcient as compared to the disintegration that would otherwise be necessary.
The process is useful in connectionwith .brokecon taining any adsorbed wet strength resin.
The invention does not depend upon any particular times, temperatures concentrations, or pHvalues. Good results have been obtained with oxidizing salt' concemv trations of A% to 5%, contact times of from a minute or less to an hour or two, and temperatures varying from room temperature to the boil."
According to one'method for employing the present invention broke, trim, or other scrap is charged directly,
to a dilute aqueous solution of an oxidizing salt in a tank and allowed to soak in the solution until the fiber resin-fiber bonds have substantially loosened. Stirring is helpfulbut not necessary, and no pH adjustment is generally required. When the desired loosening has occurred the solution is drained off, after which the paper is ready for pulping.
Preferably at the beginning of the soak a substantial excess of oxidizing salt is present so' as to avoid undue prolongation of the treatment. The pH of the oxidizing salt solution ordinarily need not be adjusted and satisfactory bond loosening takes place with minimal harm to the fibers With solution having pH values between-about 7 and 10. A wetting agent may be added and is sometimes helpful particularly in connection with oily or waxy broke and a hot oxidizing salt solution is used. Temperatures .between F. and F. are suitable.v The precise amount of oxidizing salt which should be added in each instance varies because of the difference in effectiveness of particular salts in loosening the fiber-resin-fiber bonds and the strength of the bonds resulting principally from the amount and kind of wet strength-resin present. Hence the optimum kind, amount and concentration of oxidizing agent in the solution are best predetermined by laboratory trial, using the procedures shown in the examples below as guides. Termination of the treatment occurs when the fiberresin-fiber-bonds have loosened to such an extent that the broke can be disintegrated in ordinary papermaking equipment at hand.
The principal commercially available oxidizing agents have been tested, including sodium hypochloride (NaClO),- sodium chlorite (NaClO sodium chlorate (NaClO potassium chlorate (KClO), calcium hypochlorite [Ca(ClO) ammonium persulfate and hence the water-soluble metal hypochlorites are preferred.
Example 1 The effectiveness of a number of colorless oxidizing salts as pulping agents for several representative wetstrength papers is illustrated by the following. All tests were run :at room temperature without pH adjustment and the solutions were not agitated. In each instance 100 cc. of solution Was employed containing the percentage of oxidizing salt shown in the table and paper strips weighing about 0.5 gm. were employed as the test samples.
The strips were tested by cautiously pulling the sheets with the fingers in the same manner that cloth is tested for tendering, and the decrease in fiber-resin bonding was rated on a uniform scale according to which 0 designates practically no loss of strength (equivalent to no loss in bonding), 3 designates practically complete loss of wet strength, and l and 2 designate proportionate intermediate values.
on this scale, Wet strength paper having a terminal bond strength rating between 2 and 3 can be pulped in a commercial beater .without need for steam-jet treatment, and a rating of 1-2 represents a very material loosening ofthe bonds.
The paper employed had been prepared in the labora tory in uniform manner by forming a beaten suspension of commercial unbleached northern kraft fibers at about 0.6% consistency, adding 3% of the wet strength resin shown in the table followed by 2% of alum (weights tory handsheet machine at a basis weight between 45,
and 50 lbs. per 25" x 40"/500 ream, pressing the sheets between blotters, and drying the sheets at a temperature between 240 and 260 F. for a time between 2 and minutes to give the initial wet strength shown in the table.
The ethylenimine resin was prepared by homopolymerizing ethylenimine to the high viscosity necessary for wet strength purposes. The resin was essentially a high molecular weight polyalkylenepolyamine.
The Hofmann resin was a linear carbon chain polymer every other chain carbon atom of which carried an amino group. The resin was prepared in accordance with Example 4 of copending application Serial No. 363,394, filed June 22, 1953, by myself et al.
The Epi-TETA resin was prepared by the condensation of 0.6 mol of epichlorhydrin with 0.2 mol of triethylenetetramine, as shown in Example 1 of U. S. Patent No. 2,595,936.
The IBPA-DCE resin was made by refluxing 131.2 gm. of 3,3-iminobispropylamine, 87.5 gm. of 1,2-dichlorethane, and 50 cc. of water for two hours. The resin was essentially a straight chain polyazoalkane probably containing a few six-membered rings resulting from condensation of dichlo-rethane with the polymeric NHCH CH -NH linkages formed by reaction of 3,3-iminobispropylamine with 1,2-dichlorethane.
.Results are as follows:
4 of Example 1 in dilute sodium hypochlorite solution at room temperature and pH 10 with following results:
Paper Strength After NaOlO Strength 1 2 10 15 30 Min Min. Min. Min. Min.
1 For explanation of ratings see Ex. 1.
These results show that a paper which is very resistant to alkali is quickly made ready for pulping when treated according to the present invention.
Example 3 The efiect of heat is illustrated by the following.
The procedure of Example 2 was repeated except that the concentration of the sodium hypochlorite was decreased to 0.25 and the temperature increased to 65 C. A pulping value of 1-2 was obtained in 10 minutes and a value between 2-3 and 3 in 30 minutes, showing that moderate temperature greatly accelerates the loosening of the bonds by the oxidizing salt.
Example 4 The procedure of Example 1 was repeated using paper prepared by addition of 3% (dry fiber basis) of the melamine-formaldehyde acid colloid of U. S. Patent No. 2,345,543 to slush stock followed by 1% alum. The paper was dried at 240 F. for 2 minutes and had wet. strength of 10 lb./ in.
The paper was soaked in 0.25% sodium hypochlorite solution at 65 C. for 30 minutes. The paper had a NaClO Test Paper 5% NaClOz 5% Ca(ClO)2 5% (NH4)S2Q3 5% 211113802 Wet Strength pH WS Resin 1 1a Ethylen'unlne. 4. 5 5. 3 1b d0 9. 0 6. 9 4. 5' 5. 6
Epi-TETRA 4. 5 4. 0 3b do 9.0 4.9 4a IBPA-DCE 4. 5 5.2 4b do 9. 0 6. 8
1 For description of resins see text above.
3 Wet strength, lb./in. (adjusted to lb. basis weight).
The results show that in every case rapid and extensive pulping rating of 1 at 30 minutes and a rating of 2-3 at loosening of its fiber-resin-fiber bonds was effected, the speed of loosening depending principally on the variables shown in the table.
Example 2 The pulping of paper containing a phenol-resorcinolformaldehyde-bisulfite wet-strength resin is illustrated by the following. This resin was selected as it is generally considered to give outstandingly permanent wet strength at alkaline pH.
The resin corresponded to the resin of Example 3 of Canadian Patent No. 473,753 and was prepared by refluxing a reaction mixture comprising 131.6 parts of phenol, 9.5 parts of sodium metabisulfite, 66 parts of resorcinol and a total of 243.4 parts of 37% formaldehyde to a Gardner-Holdt viscosity of H under conditions set forth in the patent.
Wet strength paper containing the resin was made according to Example 1. The paper was heated for 2 minutes at 240 F. and had a wet strength of 7.5 lbs/in.
We claim: 1. A process for the pulping of paper broke compose of cellulose fibers bonded together by an adsorbed content of at least one wet-strength resin which comprises: slurrying said broke with a dilute aqueous solution of an inorganic oxidizing salt thereby loosening the fiber-resinfiber bonds in said broke, and then subjecting the broke to mechanical pulping.
2. A process according to claim 1 wherein the oxidizing salt is a water-soluble colorless metal hypochlorite.
3. A process according to claim 1 wherein the oxidizing salt solution is hot.
References Cited in the file of this patent UNITED STATES PATENTS 1,576,994 Plumstead Mar. 16, 1926 (Other references on following page) 5 6 UNITED STATES PATENTS 265,055 Great Britain Feb. 3, 1927 Wells Mar. 5, 1935 Fennel Oct. 10, 1950 OTHER REFERENCES Driessen Dec. 25, 1951 y: Pulp and Paper, vol. 1, page 602 (1952), Hill June 9, 1953 E cience Publishers, Inc., New York.
FOREIGN PATENTS Germany Nov. 10, 1915