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United States Patent Office Patented Feb. 10, 1948 2,435,566 UNITED STATES PATENT OFFICE 2.435.566 ' PEROXIDE BLEACHING 0F GROUND woon Daniel 0. Adams and George B. Hughey, ton, Va... assignors to West Virginia PulpCoving and Paper Company, New York, N. Y., a corporation of Delaware No Drawing. Application" October 16, 1944, Serial No. 558.951 ' 3 Claims. (01. 8-—104) Our invention relates to the bleaching of 2 ground wood, more especially groundloak and Example I other ground woods such as chestnut, chestnut A 14.8 gram sample of red oak ground wood in oak, maple, etc., which contain substantial the form of a slurry or 5% oven dried (0. D.) amounts of tannin compounds and other natural color bodies. consistency was extracted for one hour at 77° F. In recent with an NaOH solution at a. concentration oi.’ 1 years much study has been given to gram per liter. At the end of one hour the'pulp ' the bleaching of ground wood. Usually and espe was thickened and thoroughly washed. The ex cially for the manufacture of newsprint, ground tracted pulp was then treated with a quantity wood is not bleached. However, the desirable 10 of sodium peroxide equal to 3.5% of the weight printing characteristics of paper containing a of the unbleached pulp on a dry basis, 1. e., .525 large proportion of ground wood have led'to pro gram. The pulp was in the form of a slurry oi’ posals for its use in high grades of paper such 5% consistency at a temperature of 92° F. The as magazine, book paper and the like. In many . initial DH was 11.3. At the end of 220 minutes instances a base ground wood sheet or one con 15 the peroxide was exhausted and 100 milliliters taining a substantial proportion of ground wood of a solution containing 5% S02 were added. Aft is coated with a suitable coating composition. er 20 minutes the pulp was thickened in a ?lter However, to be successful the ground wood must and washed. The brightness of the resulting pulp have a reasonably good color of substantial per was 59.20 determined by the General Electric manence. otherwise only a slight proportion of it 20 re?ection meter. A similar test keeping condi may be used in the furnish; or ii.’ used in sub tions the same save that the caustic extraction stantial proportion in the base sheet an undesir was omitted resulted in a brightness reading of ably heavy coat must be given it inorder to have 55.4% whereby the gain in brightness due'to the a ?nal product of acceptable brightness. caustic extraction was 5.20%. ~ One method currently proposed is the use of‘ 25 certain peroxides under alkaline conditions, e. g., Example II hydrogen peroxide, sodium perborate, sodium per oxide. of which sodium peroxide is usually recom Essentially the same example was carried out mended as being the cheapest and easiest to as above except that in the peroxide bath there was added sodium silicate equal to 4% of the handle. However, in‘ applying known methods of 30 peroxide bleaching to ground woods rich in tan unbleached pulp, or .6 gram, and su?‘lcient mag nin compounds it has not been possible to achieve nesium sulfate to make the concentration in the the same or comparable brightness of the bleached ?nal mixture equal to 100 parts per million. The pulp as is obtained with ‘long ?bered ground pulp during this treatment was in a slurry having woods, as for example spruce. We have discov 5% O. D. consistency and maintained at a tem ered that an improvement of several points on perature of 90*’ F. The initial pH of the mixture the General‘ Electric Brightness Scale may be was 11.7. ' The peroxide was exhausted at the had by subjecting the ground wood rich in tan end of 350 minutes. 100 milliliters 01' 5% solu nin to a preliminary caustic extraction which is tion of sulfur dioxide were added and after 20 minutes the pulp was ?ltered and washed. The then followed by the peroxide bleach, this im 40 provement step being carried out with minimum brightness of the resulting pulp was 61.8 as deter expense in handling and materials and with no mined by the General Electric re?ection meter. additional degradation of the ?ber. Our explana In the caustic extraction step temperature has tion of the action of the extracting agent is that not been found to be critical. At 65° F. substan it removes color bodies and other substances 45 tially the same results were obtained as at 140° which make it impracticable to obtain a bright F. The amount of caustic in the extraction step ness equal to that of bleached spruce ground wood. of 2% based upon the dry weight of the, pulp may After the peroxide bleach is Lad the brightness be increased somewhat, but thus far no bene ?cial results have been had when the quantity of may be further increased by the use oi.’ an after caustic exceeded 16% bleach. as for example sulfurous acid in any oi.’ 50 based upon the dry weight _ its several available forms, i. e., bisul?tes and of the pulp. In carrying out the peroxide bleach, others yielding sul?te ion in effective quantities. brightening occurred at all pH’s above 8 or 9 Our invention will be best understood by ref and improved substantially as the pH increased. erence to the following detailed examples illus It will be noted that in theexamples given the trative thereof. ' highest pH was 11.7. This is not believed to be 65 'the limit. The amount of-sul?te added in the 2,485,586 4 stantially more than sixteen per cent. ‘based upon after bleach stage is also not critical, although the dry weight of the pulp, and then subjecting the brightness falls off when less than 5% of the ground wood to the bleaching action of an SO: based on the unbleached pulp is used. The alkaline solution containing an alkali metal per reaction is rapid and not over 5 minutes is re oxide. quired for completion. 3. The method of peroxide bleaching of ground As indicated in Example II, sodium .silicate and oak wood to yield a ground wood of a bright magnesium sulfate may be added to the above ness at least equal to that which obtains by the if desired. In some cases, however, no marked peroxide bleaching of ground spruce wood, which improvement resulted from their use. 10 comprises ?rst extractingtherefromthe tannin In lieu of caustic soda other soluble hydromrl and color bodies soluble in dilute aqueouscaustic ion yielding alkalis especially those having an alkali solution at temperatures under the boil alkali metal cation may be used. Examples are ing point thereof, then subjecting the extracted trisodium phosphate, sodium sul?de, sodium sul ground wood to the bleaching action of an alka ?te, sodium silicate, etc., as well as the corre line solution containing an alkali metal peroxide. sponding salts of the alkai metals or ammonia. 15. DANIEL O. ~ADAMS. We claim: ' GEORGE B. HUGHEY. 1. The method of peroxide bleaching of ground wood of the type rich in tannin and color bodies REFERENCES CITED to yield a ground wood of a brightness at least equal to that which obtains by the peroxide 20 The following references are of record in the bleaching of ground spruce wood, which comprises ?le of this patent: ' ?rst extracting therefrom the tannin and color UNITED STATES PATENTS bodies soluble in dilute aqueous caustic alkali so lution at temperatures under the boiling point Number Name Date the extracted ground 25 2,187,016 Craig -_ ___________ .... Jan. 16, 1940 ‘thereof, then subjecting 1,539,433 Schorger -____......-- May 26, 1925 wood to the bleaching action of an alkaline so lution containing an alkali metal peroxide. 1,052,675 Loomis .......... ..- Feb. 11, 1913 2. The method of peroxide bleaching of ground 200,085 Patrick -.._.._..-..-........ Feb. 5, 1878 wood of the type rich in tannin and color bodies 1,843,467 Traquair _________ _- Feb. 2, 1932 to yield a ground wood of a brightnessat least 30 223,670 Farrell __________ .... Jan. 20, 1880 equal to that which obtains by the peroxide 263,797 Mitscherlich ...... .. Sept. 5, 1882 bleaching of ground spruce wood, which com FOREIGN PATENTS prises ?rst extracting therefrom the tannin and Number Country _ Date color bodies soluble in dilute aqueous caustic al 35 101,475 Great Britain -_,_-_- Oct. 11, 1917 kali solution at temperatures under the boiling 298,333 Great Britain .... -- Oct. 11, 1928 point thereof, by treating same with a dilute.so-' 296,547 Great Britain .... __ Sept. 6, 1928 lution of sodium hydroxide in quantity not sub .
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