(12) United States Patent (10) Patent No.: US 8,262,858 B2 Duggirala Et Al

USOO8262858B2

(12) United States Patent (10) Patent No.: US 8,262,858 B2 Duggirala et al. (45) Date of Patent: *Sep. 11, 2012

(54) COMPOSITIONS AND PROCESSES FOR FOREIGN PATENT DOCUMENTS PAPER PRODUCTION EP O899.373 A1 3/1999 FI 104339B A1 12, 1999 (75) Inventors: Prasad Y. Duggirala, Naperville, IL WO WO99,32710 A1 T 1999 (US); Sergey M. Shevchenko, Aurora, W W g35. A. g38 IL (US); Katherine M. Broadus, WO WO 2005 OO1198 A1 1/2005 Aurora, IL (US) WO WO 2005 121442 A1 12/2005 (73) Assignee: Nalco Company, Naperville, IL (US) OTHER PUBLICATIONS (*) Notice: Subject to any disclaimer, the term of this Rocik Thomas, Optical Brighteners in Fine Papers, 1999, TAPPI patent is extended or adjusted under 35 Press, whole document. U.S.C. 154(b) by 0 days Smook, Handbook for Pulp and Paper Technologists, 1992, Angus M YW- y yS. Wilde Publications, 2nd edition, p. 228, 283.* This patent is Subject to a terminal dis- Smook, Handbook for Pulp and Paper Technologists, 1992, Angus claimer. Wilde Publications, 2nd edition, chapter 4.* Calgon Carbon Corporation website, "About UV Oxidation and Dis (21) Appl. No.: 13/074,092 infection.” (downloaded online from www.uvdisinfections.com) 2003 (downloaded online Dec. 3, 2008), whole document. (22) Filed: Mar. 29, 2011 Gullichsen et al., Chemical Pulping 6A, 1999, Faypet Oy, p. A653. Jakara et al., “The Effect of Peracetic Acid in Fine Paper Production.” (65) Prior Publication Data (Abstract) Appita Annual Conference Proceedings (2000), 54th (vol. 1), 169-174. US 2011 FO174455A1 Jul. 21, 2011 Jakara et al., The Use of Peracetic Acid as a Brightening Agent. Related U.S. Application Data systAbstract) Appitappita Ann. GeneralG 1 Conf. Proc. ((1999), ), 53rd (vol. 2),2) (63) Continuation of application No. 1 1/490,738, filed on Jakara et al. "The Use of Peracetic Acid as a Brightening Agent” Jul. 21, 2006, now Pat. No. 7,914,646. Preprint-PAPTAC Annual Meeting, 87th, Montreal, QC, Canada Jan. 30-Feb. 1, 2001. (51) Int. Cl. Millipore Corporation, “What is Ultraviolet Photo-Oxidation” D2 IF II/00 (2006.01) (downloaded online from www.millipore.com), 2008 downloaded D2IC 9/10 (2006.01) online Dec. 3, 2008, whole documen. (52) U.S. Cl...... 162/158; 162/70: 162/162: 8/648 * cited by examiner (58) Field of Classification Search ...... 162/70, 162/158, 162: 8/648, 119 Primary Examiner — Anthony Calandra See application file for complete search history. (74) Attorney, Agent, or Firm — Benjamin E. Carlsen; Andrew D. Sorenson (56) References Cited 57 ABSTRACT U.S. PATENT DOCUMENTS (57) 3.018.287 A 1/1962 Fleck Oxidative compositions and processes that preserve and 3619355 A * 1 1/1971 Silberman ...... 162,135 enhance the brightness and improve color of pulp or paper 4,435,248 A 3, 1984 Arakawa when applied during different stages of the papermaking SS A ck 88: East s al...... 8, 103 process are identified. The oxidative composition and method 5.500151. A 3/1996 g al ...... 510,321 maintains and/or enhances brightness, prevents yellowing, 5,637,193 A * 6/1997 Hassi et al...... 162.78 and enhances the performance of paper products. Used in 6,302,997 B1 * 10/2001 Hurter et al...... 162.65 combination with optical brighteners and/or chelants the oxi 38885 A. 299; Sullis et al. dative agents produce a synergistic effect not previously iden 2004/0050511 A1 3, 2004 Lambert tified in the paper process. 2007.0193707 A1 8/2007 Nguyen 2007/0277947 A1 12/2007 Nguyen 17 Claims, No Drawings US 8,262,858 B2 1. 2 COMPOSITIONS AND PROCESSES FOR ide preparations containing optical brighteners in encapsu PAPER PRODUCTION lated form are disclosed in CA2292107. To date, however, the results have been less than satisfac tory and the economic losses resulting from discoloration and CROSS REFERENCE TO RELATED yellowing present significant ongoing challenges to the APPLICATIONS industry. Accordingly, there remains a need for a successful and practical Solution to loss of brightness and undesirable This is a continuation of application Ser. No. 1 1/490,738, yellowing of pulp and paper. filed Jul. 21, 2006, now U.S. Pat. No. 7,914,646. SUMMARY OF THE INVENTION TECHNICAL FIELD 10 The present invention provides compositions and methods This invention relates to compositions and processes for for improving and stabilizing brightness and enhancing resis improving brightness and optical properties, preventing loss tance to yellowing in the papermaking process. of brightness and for enhancing resistance to thermal yellow In an aspect, this invention is a method of preparing a ing in pulp and paper manufacture. More particularly, this 15 bleached pulp material having enhanced brightness and invention concerns compositions comprising oxidizing enhanced resistance to thermal yellowing comprising: i) pro agents, which either alone or in the presence of optical bright viding bleached pulp material; and ii) contacting the bleached ening agents effectively enhance the brightness and optical pulp material with an effective amount of one or more oxi properties of a paper product as well as increase its thermal dizing agents excluding organic peroxyacids. stability. In another aspect, this invention is a method of making a paper product having enhanced brightness and resistance to BACKGROUND OF THE INVENTION thermal yellowing comprising i) providing bleached pulp; ii) forming an aqueous stock Suspension comprising the Pulps produced by either mechanical or chemical pulping bleached pulp, draining the Stock Suspension to form a sheet; methods possess a color that can range from dark brown to 25 and drying the sheet, whereina) an effective amount of one or creamish depending on the wood type and defibering process more oxidizing agents excluding organic peroxyacids is used. The pulp is bleached to produce white paper products added to the bleached pulp or the stock Suspension, orb) an for a multiplicity of applications. effective amount of one or more oxidizing agents including Bleaching is the removal or alteration of those light-ab organic peroxyacids is added on to the sheet. Sorbing Substances found in unbleached pulp. In the bleach 30 In another aspect, this invention is a method of making a ing of mechanical pulp, the object is to decolorize the pulp paper product having enhanced brightness and resistance to without solubilizing the lignin. Either reducing (e.g. sodium thermal yellowing comprising i) providing bleached pulp; ii) hydrosulfite) or oxidizing (e.g., hydrogen peroxide) bleach forming an aqueous thick stock Suspension comprising the ing agents are usually used. The bleaching is often a multi bleached pulp; iii) adding an effective amount of one or more stage process. The bleaching of chemical pulps is an exten 35 oxidants and one or more optical brighteners to the thick sion of the delignification that started in the digestion stage. stock; iv) diluting the aqueous thick stock Suspension to form The bleaching is often a multistage process, which stages may a thin Stock Suspension; v) draining the thin stock Suspension include chlorine dioxide bleaching, oxygen-alkaline deligni to form a sheet; and vi) drying the sheet. fication, and peroxide bleaching. In another aspect, this invention is a method of preventing Discoloration, mostly ascribed to thermal aging, results in 40 brightness loss and yellowing of a bleached pulp material yellowing and brightness loss in various stages of papermak during storage comprising adding an effective amount of one ing processes employing bleached pulp and in the resultant or more oxidizing agents excluding organic peroxyacids to paper products. The industry invests significantly in chemi the bleached pulp material. cals such as bleaching agents and optical brighteners that In another aspect, this invention is a bleached pulp material improve optical properties of the finished paper or paper 45 which comprises the mixed product of bleached pulp and an products. effective amount of one or more oxidizing agents, wherein For example, post bleaching processes in which pulp is said bleached pulp material has a higher brightness and brought to the desired whiteness using peracids acid are dis enhanced resistance to thermal yellowing, when compared closed in WO OO52258 and WO 9932710. Addition of a with similar pulp not treated with said reducing agents. composition comprising peracetic acid and hydrogen peroX 50 Applicant has also discovered that oxidizing agents in ide to thick stock prior to the addition of optical brightening combination with chelants effectively enhances the bright agents (OBAs) is claimed to reduce the amount of OBA's ness of paper products and further that oxidizing agents used required to achieve a comparable degree of brightness in in combination with optical brighteners enhance the effect of GB2391011. Jukka Jakara et al. The effect of peracetic acid the optical brighteners and improve color Scheme. Accord treatment of bleached kraft pulp in fine paper production, 55 ingly, in additional aspects, this invention is methods of using Preprint-PAPTAC Annual Meeting, 87', Montreal, QC, oxidizing agents in combination with chelants and/or optical Canada Jan. 30-Feb. 1, 2001 (2001) discloses that addition of brighteners to prepare bleached pulp materials having higher peracetic acid to the Stock preparation chests of paper brightness, enhanced resistance to thermal yellowing and machines limits brightness reversion in bleached pulp and improved color schemes. results in significant savings in OBA addition in the paper 60 The oxidizing agent, optical brighteners and chelants may machine. See also, Jukka Jakara et al., The effect of peracetic be used alone or in combination with known additives to acid in fine paper production, Appita Annual Conference enhance the quality of the desired paper product. Proceedings (2000), 54" (Vol. 1), 169-174 and Jukka Jakara et al., The use of peracetic acid as a brightening agent, Appita DETAILED DESCRIPTION OF THE INVENTION Ann. General Conf. Proc. (1999), 53" (Vol. 2), 463-467. 65 Treatment of bleached stock with peroxyacid prior to addition The present invention provides an improved process for of neutral size to the stock is disclosed in F11043398. Perox making paper and paper products exhibiting high optical US 8,262,858 B2 3 4 brightness. Brightness stabilization against thermal yellow containing the group —O-O-, and their metal salts. Such ing, color improvement and brightness enhancement of as peroxymonosulfuric acid (Caro's acid, (HO)SOOOH), bleached pulp and paper product prepared from the bleached peroxydisulfuric acid (HOSOOOSOOH), peroxymono pulp can be achieved by adding one or more oxidizing agents phosphoric acid HPOs, sodium peroxymonocarbonate as defined herein to pulp, paper, paperboard or tissue any Na2CO and peroxydicarbonate Na2CO, and the like. where in the papermaking process. "Peroxyhydrates are inorganic salts containing hydrogen Brightness is a term used to describe the whiteness of pulp peroxide of crystallization, such as Sodium metasilicate per or paper, on a scale from 0% (absolute black) to 100% (rela oxyhydrate Na2SiO.H.O.H2O, and sodium borate peroxy tive to a MgO standard, which has an absolute brightness of hydrate NaBO.H.O.3H2O, and the like. about 96%) by the reflectance of blue light (457 nm) from the 10 “Organic peroxides' are any organic chemicals containing paper. “Thermal brightness loss is a brightness loss in paper a —O—O—group, including organic peroxyacids as defined and pulp under the influence of time, temperature and mois herein, dioxiranes Such as dimethyldioxyrane (CH)2CO ture (non-photochemical brightness loss). "Brightness loss and the like. during storage is thermal brightness loss over time under "Nitrosodisulfonates' are alkali and alkaline earth metal storage conditions. 15 salts of nitrosodisulfonic acid such as potassium nitrosodis Yellowing of a bleached pulp material (brightness rever ulfonate (Fremy's salt) (KSO)NO, and the like. sion) is the loss of brightness of bleached pulp, paper, paper “Hypochlorites”, “chlorites”, “chlorates” and “perchlor board, paper tissue and related materials prepared from the ates', are water-soluble metal salts of hypochlorous HOCl, bleached pulp over a period of time. As used herein, chlorous HOCIO, chloric HOCIO, and perchloric HOCIO, "bleached pulp material' includes bleached pulps as well as acids, respectively, such as Sodium hypochlorite, NaOCl, and paper products prepared from Such pulps. the like. The oxidizing agents described herein are suitable for use “Hypobromites” and “bromites” are water soluble salts of on any bleached pulp material used in papermaking processes hypobromous acid, HOBr, and bromic acid, HBrO, respec and any paper product prepared from the bleached pulp. As tively, including sodium hypobromite, NaOBr, and the like. used herein, "bleached pulp material' means bleached pulp 25 “Chloroamines' and “bromoamines' are ammonium and paper products prepared from the bleached pulp includ derivatives of the formulae NH, Hall, where Halis Clor Br, or ing paper, paperboard, tissue, and the like. alkylamine derivatives NRRHall, where R and R are Oxidizing agents according to this invention include defined above and X and y are independently 1-3. In aqueous chemical Substances capable of transforming functional Solution, chloramines and bromoamines may be present as groups in the bleached pulp material from a lower oxidation 30 the corresponding ammonium salts. category to a higher oxidation category. The benefits of this “Chloroamides' and “bromoamides' are amide derivatives transformation include increased brightness stability in the containing C(O)N(R).HHal, groups where Hal is paper machine and enhanced performance of optical bright defined above, p and q are independently 0-1 and ris 1-2. Such CS. as product compositions formed in a mixture of Sodium Representative oxidizing agents include, but are not lim 35 hypochlorite NaClO and urea HNCONH, or sodium ited to, hydrogen peroxide, organic peroxyacids, organic and hypochlorite NaClO and 5,5-dimethylhydantoin, and the inorganic peroxides (hydroperoxides), Superoxides and per like. oxide-Superoxides, inorganic peroxy acids and salts thereof, “Chlorosulfamides' and “bromosulfamides' are amide peroxyhydrates, water-soluble organic peroxides including derivatives containing -SO2N(R).HHall, where R. Hal, dioxiranes, nitrogen oxide, nitrosodisulfonates, hypochlo 40 p, q and rare defined above. Such as the product composition rites, hypobromites, chlorites, chlorates and perchlorates, formed in a mixture of sodium hypochlorite, NaClO, and bromates, chlorine dioxide, chloroamines, chloroamides, sulfamide, HNSONH, and the like. chlorosulfonamides, bromoamines, bromoamides, bromo Chlorosulfonic acid is a chemical of the formula CISOH. sulfamides, chlorosulfonic acid, chlorine and all of the above Alkyl means a monovalent group derived from a straight in combinations. 45 or branched-chain saturated hydrocarbon by the removal of a As used herein, "hydrogen peroxide” means H2O. single hydrogen atom. The alkyl may be unsubstituted or “Organic peroxyacid means compounds of formula RC Substituted with one or more groups selected from amino, (O)OH and metal salts thereof where R is selected from alkoxy, hydroxy and halogen. Representative alkyl groups alkyl, alkenyl, aryland arylalkyl. Representative organic per include methyl, ethyl, n- and iso-propyl. n-, sec-, iso- and oxyacids include peroxybenzoic acid, CH3C(O)OOH, per 50 tert-butyl, and the like. acetic acid (PAA), CHC(O)OOH, performic acid, HC(O) Alkylene' means a divalent group derived from a straight OOH, perpropionic acid, CHCHC(O)OOH, and the like. or branched chain saturated hydrocarbon by the removal of “Inorganic peroxides' means monobasic (hydroperoxides) two hydrogen atoms, for example methylene, 1.2-ethylene, and dibasic (peroxides) metal derivatives of hydrogen peroX 1,1-ethylene, 1,3-propylene, 2,2-dimethylpropylene, and the ide, H2O, including alkali and alkaline earth metal deriva 55 like. tives such as sodium hydroperoxide (NaOOH), magnesium “Amino” means a group of formula - NYY, where Y peroxide (MgO), and the like. and Y are independently selected from H. alkyl, alkenyl, aryl “Superoxides' means metal derivatives containing the and arylalkyl. Representative amino groups include amino group of O, including alkali and alkaline earth metal deriva (—NH), methylamino, ethylamino, isopropylamino, diethy tives such as Sodium Superoxide (NaO), calcium Superoxide 60 lamino, dimethylamino, methylethylamino, and the like. In (CaO), and the like. aqueous solution, amines may be present as the correspond “Peroxide-superoxides' means mixed alkali metal deriva ing ammonium salts. tives of a formula 2MOMO, where M is an alkali metal, "Aryl means aromatic carbocyclic radicals and heterocy Such as K2O, and the like. clic radicals having about 5 to about 14 ring atoms. The aryl “Inorganic peroxy acids and salts thereof means inorganic 65 may be unsubstituted or Substituted with one or more groups acids containing a —O—O— group, including peroxy selected from amino, alkoxy, hydroxy and halogen. Repre monoacids containing the group —OOH and peroxy diacids sentative aryl include phenyl, naphthyl, phenanthryl, anthra US 8,262,858 B2 5 6 cyl, pyridyl, furyl, pyrrolyl, quinolyl, thienyl, thiazolyl, Sodium dithionite (hydrosulfite) (Na2SO4), magnesium pyrimidyl, indolyl, and the like. dithionite (MgSO), and the like. Arylalkyl means an aryl group attached to the parent “Formamidinesulfinic acid (FAS) means a compound of molecular moiety through an alkylene group. Representative formula H2NC(=NH)SOH and its salts and derivatives arylalkyl groups include benzyl, 2-phenylethyl, and the like. including the sodium salt HNC(=NH)SO-Na. "Halo' and “halogen' mean chlorine, fluorine, bromine Aldehyde bisulfite adducts' means compounds of for and iodine. mula RCH(OH)SOH and metal salts thereof where R is “Salt' means the metal, ammonium, Substituted ammo selected from alkyl, alkenyl, aryl and arylalkyl. Representa nium or phosphonium salt of an inorganic or organic anionic tive aldehydebisulfite adducts include formaldehydebisulfite 10 adduct HOCHSONa, and the like. counterion. Representative metals include Sodium, lithium, "Sulfinamides and ethers of sulfuric acid' means com potassium, calcium, magnesium, and the like. Representative pounds of formula R—S(=O)—R, where R is defined anionic counterions include Sulfite, bisulfate, Sulfoxylate, herein and R is selected from OR and NR-Rs, where R-Rs metabisulfite, thiosulfate, polythionate, hydrosulfite, forma are independently selected from selected from alkyl, alkenyl, midinesulfinate, and the like. 15 aryl and arylalkyl. Representative sulfinamides include eth The oxidizing agent may be used in combination with one ylsulfindimethylamide (CHCHS(O)N(CH)), and the like. or more “activators'. The activators include compositions "Sulfenamides and ethers of sulfenic acid' means com which enhance the effect of the oxidizing agent through pounds of formula R—S-R, where R and R2 are defined catalysis of the oxidation reaction or change in the pH, or above. Representative sulfenamides include ethylsulfendim both. Representative activators include, but are not limited to, ethylamide (CHCHSN(CH)), and the like. phosphoric acid, monosodium phosphate, monosodium Sul "Sulfamides' means compounds of formula R—C fate, monosodium carbonate, TEMPO (2.2.6,6-tetrameth (—S)—NRRs, where R, R and Rs are defined above. Rep ylpiperydidnyoloxyl), 4-hydroxy-TEMPO (4-hydroxy-2.2.6, resentative sulfamides include CHCHC(=S)N(CH), and 6-tetramethylpipery didnyoloxyl), ammonium molybdate, the like. tetraacetylethylenediamine (TAED) and pH-changing 25 “Phosphines' means derivatives of phosphine, PH, nor chemicals affecting oxidation rates Such as acetic acid. “Acti mally organic Substituted phosphines of the formula vated oxidizing agent’ means an oxidizing agent used in RR,RP where Re-Rs are independently selected from H. combination with one or more activators. In some embodi alkyl, alkenyl, aryl, arylalkyland NRRs where R and Rs are ments, the oxidizing agent is activated hydrogen peroxide. defined above. Representative phosphines include (HOCH) In some embodiments, the bleached pulp material may be 30 P(THP), and the like. treated with one or more oxidizing agents and one or more “Phosphites' means derivatives of phosphorous acid reducing agents. “Reducing agents’ refers to chemical sub P(OH), including organic substituted phosphites of the for stances capable of transforming functional groups in the mula (RO)(RO)(RO)P where R-Rs are defined above. bleached pulp material from a higher oxidation category to a Representative phosphites include (CHCHO).P. and the lower oxidation category. The use of reducing agents for 35 like. improving and stabilizing brightness and enhancing resis “Thiophosphites’ means derivatives of phosphorothious tance to yellowing in the papermaking process is described in acid HSP(OH), including organic substituted thiophosphites copending Ser. No. 1 1/397,499, filed Mar. 23, 2006. of formula (RO)(RO)(RS)P where R-Rs are defined Representative reducing agents include Sulfites, bisulfites, above. Representative thiophosphites include (CHCHO) metabisulfites (pyrosulfites), sulfoxylates, thiosulfates, 40 (CHCHS)P and the like. dithionites (hydrosulfites), polythionates, formamidine "Phosphonium salts' means organic Substituted phos sulfinic acid and salts and derivatives thereof, formaldehyde phines of the formula RRRRP"X, where R and Ra-Rs bisulfite adduct and other aldehyde bisulfite adducts, sulfina are as defined above and X is any organic or inorganic anion. mides and ethers of sulfinic acid, sulfenamides and ethers of Representative phosphonium salts include (HOCCHCH.) Sulfenic acid, Sulfamides, phosphines, phosphonium salts, 45 PtHCl (THP), (HOCH) P(SO) (BTHP), and the phosphites, and thiophosphites. like. "Sulfites' means dibasic metal salts of sulfurous acid, Alkenyl' means a monovalent group derived from a HSOs, including dibasic alkali and alkaline earth metal salts straight or branched hydrocarbon containing at least one car such as sodium sulfite (NaSO), calcium sulfite (CaSO), bon-carbon double bond by the removal of a single hydrogen and the like. 50 atom. The alkenyl may be unsubstituted or substituted with “Bisulfites' means monobasic metal salts of sulfurous one or more groups selected from amino, alkoxy, hydroxy and acid, HSOs, including alkali and alkaline earth metal halogen. monobasic salts such as Sodium bisulfite (NaHSO), magne "Alkoxy' means an alkyl group attached to the parent sium bisulfite (Mg(HSO)), and the like. molecular moiety through an oxygen atom. Representative "Sulfoxylates' means salts of sulfoxylic acid, HSO, 55 alkoxy groups include methoxy, ethoxy, propoxy, butoxy, and including zinc sulfoxylate (ZnSO), and the like. the like. Methoxy and ethoxy are preferred. "Metabisulfites (Pyrosulfites) means salts of pyrosulfu In an embodiment, the reducing agent is selected from the rous acid, HSOs, including Sodium metabisulfite group consisting of substituted phosphines, Sulfites, bisulfites (NaSOs), and the like. and metabisulfites. A preferred reducing agent is sodium “Thiosulfates' means salts of thiosulfurous acid, HSO, 60 bisulfate. including potassium thiosulfate (NaSO), and the like. The process of the present invention can be practiced on “Polythionates' means salts of polythionic acid, HSO conventional papermaking equipment. Although papermak (n 2-6), including sodium trithionate (NaSO), salts of ing equipment varies in operation and mechanical design, the dithionic acid, HS2O, such as sodium dithionate NaSO processes by which paper is made on different equipment and the like. 65 contain common stages. Papermaking typically includes a “Dithionites (hydrosulfites) means salts of dithionous pulping stage, bleaching stage, Stock preparation stage, a wet (hydroSulfurous, hyposulfurous) acid, HS2O, including end stage and a dry end stage. US 8,262,858 B2 7 8 In the pulping stage, individual cellulose fibers are liber chlorites, chlorates, bromates, perchlorates, chlorine dioxide, ated from a source of cellulose either by mechanical or chemi chloroamides, chloroamides, chlorosulfamides, bromoam cal action, or both. Representative sources of cellulose ides, bromoamides, bromosulfamides, chlorosulfonic acid, include, but are not limited to, wood and similar “woody' bromosulfonic acid and chlorine. plants, soy, rice, cotton, Straw, flax, abaca, hemp, bagasse, 5 In other embodiments where the oxidizing agents are lignin-containing plants, and the like, as well as original and added prior to sheet formation, the oxidizing agents may be recycled paper, paper tissue and paperboard. Such pulps selected from hydrogen peroxide, activated hydrogen peroX include, but are not limited to, groundwood (GWD), bleached ide, hypochlorites, hypobromites, chloroamines, chloroam groundwood, thermomechanical pulps (TMP), bleached ther ides, chlorosulfamides, bromoamines, bromoamides, bromo momechanical pulps, chemi-thermomechanical pulps 10 Sulfamides, chlorosulfonic acid and bromosulfonic acid. (CTMP), bleached chemi-thermomechanical pulps, deinked In embodiments where the oxidizing agents are added after pulps, kraft pulps, bleached kraft pulps, sulfite pulps, and sheet formation or where the oxidizing agents are added to bleached sulfite pulps. Recycled pulps may or may not be thick stock in combination with optical brighteners, the oxi bleached in the recycling stage, but they are presumed to be dizing agents may be selected from hydrogen peroxide, originally bleached. Any of the pulps described above which 15 organic peroxyacids, inorganic peroxides, Superoxides and have not previously been Subjected to bleaching may be peroxide-superoxides, inorganic peroxyacids and salts bleached as described hereinto provide a bleached pulp mate thereof, peroxyhydrates, water-soluble organic peroxides, rial. nitrosodisulfonates, hypochlorites, hypobromites, chlorites, In an embodiment, the bleached pulp material is selected chlorates, bromates, perchlorates, chlorine dioxide, chloroa from the group consisting of Virgin pulp, recycled pulp, kraft, 20 mides, chloroamides, chlorosulfamides, bromoamines, bro Sulfite pulp, mechanical pulp, any combination of Such pulps, moamides, bromosulfamides, chlorosulfonic acid, bromosul recycled paper, paper tissue, and any paper made from Such fonic acid and chlorine. listed pulps or combinations thereof. In other embodiments where the oxidizing agents are A further advantage of this invention is that it allows for added after sheet formation or where the oxidizing agents are Substituting lower-priced mechanical pulp for higher priced 25 added to thick stock in combination with optical brighteners kraft in printing grade kraft-mechanical paper. Use of the the oxidizing agents may be selected from is selected from chemistry and methods described herein increases the bright hydrogen peroxide, activated hydrogen peroxide, peracetic ness and stability toward yellowing, therefore permitting the acid, hypochlorites, hypobromites, chloroamides, chloroam use of higher amounts of mechanical pulp, with correspond ides, chlorosulfamides, bromoamines, bromoamides, bromo ing reduction in cost, without loss of quality in the resulting 30 Sulfamides, chlorosulfonic acid and bromosulfonic acid. paper product. The oxidants may be pre-formulated or may be formed The pulp is suspended in water in the stock preparation in-situ from mixed components as is known in the art. In-situ stage. Additives Such as brightening agents, dyes, pigments, preparation may be desirable under certain circumstances, for fillers, antimicrobial agents, defoamers, pH control agents example when the desired oxidizing agent is relatively and drainage aids also may be added to the stock at this stage. 35 unstable or is quickly consumed in the system. For example As the term is used in this disclosure, “stock preparation peracetic acid and peracetic acid-hydrogen peroxide mixtures includes such operations as dilution, Screening and cleaning may be formed in situ by mixing hydrogen peroxide and of the stock Suspension that may occur prior to forming of the tetraacetylethylenediamine. Hypobromite can be prepared web. in-situ by mixing sodium bromide and Sodium hypochlorite. The wet end stage of the papermaking process comprises 40 Chloramines may be prepared in-situ by mixing ammonium depositing the stock suspension or pulp slurry on the wire or bromide, urea or dimethylhydantoin and Sodium hypochlo felt of the papermaking machine to form a continuous web of rite. Chlorosulfamates may be prepared in-situ by mixing fibers, draining of the web and consolidation of the web Sodium bromide, Sodium hypochlorite and Sulfamic acid. (pressing”) to form a sheet. Any papermaking machine Applicant has also discovered that oxidizing agents in known in the art is suitable for use with the process of the 45 combination with chelants as described below effectively present invention. Such machines may include cylinder enhance the brightness of a paper product via increased ther machines, fourdrinier machines, twin wire forming mal stability of the pulp and reduction of chromophoric struc machines, tissue machines, and the like, and modifications tures in pulp. thereof. In an embodiment, one or more chelants are added to the In the dry end stage of the papermaking process, the web is 50 bleached pulp or paper product. Suitable chelants according dried and may be subjected to additional processing like size to this embodiment include compounds that are capable of pressing, calendering, spray coating with Surface modifiers, chelating transitional metals that form colored products with printing, cutting, corrugating and the like. In addition to a size pulp constituents and catalyze color-forming reactions in the press and calenderwaterbox, the dried paper can be coated by bleached pulp or paper products. spray coating using a sprayboom. 55 Representative chelants include, but are not limited to, In embodiments where the oxidizing agents are added prior organic phosphonates, phosphates, carboxylic acids, dithio to sheet formation, oxidizing agents other than organic per carbamates, salts of any of the previous members, and any oxyacids are used. When the oxidizing agents are applied combination thereof. after sheet formation or where oxidizing agents are added to “Organic phosphonates' means organic derivatives of thick stock in combination with optical brighteners, oxidizing 60 phosphonic acid, HP(O)(OH), containing a single C P agents including organic peroxyacids are used. bond, such as HEDP (CHC(OH)(P(O)(OH)), 1-hydroxy-1, Accordingly, in embodiments where the oxidizing agents 3-propanediylbis-phosphonic acid ((HO)P(O)CH(OH) are added prior to sheet formation, the oxidizing agents may CHCHP(O)(OH))); preferably containing a single C N be selected from hydrogen peroxide, inorganic peroxides, bond adjacent (vicinal) to the C P bond, such as DTMPA Superoxides and peroxide-Superoxides, inorganic peroxyac- 65 ((HO), P(O)CHNICHCHN(CH2P(O)(OH))), AMP ids and salts thereof, peroxyhydrates, water-soluble organic (N(CHP(O)(OH))), PAPEMP (HO), P(O)CH)NCH peroxides, nitrosodisulfonates, hypochlorites, hypobromites, (CH)CH(OCHCH(CH))N(CH)N(CH2P(O)(OH))), US 8,262,858 B2 9 10 HMDTMP ((HO),P(O)CH)N(CH)N(CHP(O)(OH))), bleached pulp material before or after the oxidizing agents. HEBMP(N(CHP(O)(OH)),CHCH-OH), and the like. Chelants and optical brighteners may be added before, after "Organic phosphates' means organic derivatives of phos or simultaneously with the oxidizing agents or may be for phorous acid, P(O)(OH), containing a single C P bond, mulated with the oxidizing agents for addition to the bleached including triethanolamine tri(phosphate ester) pulp material. (N(CHCHOP(O)(OH))), and the like. The effective amount of oxidizing agent added to the “Carboxylic acids’ means organic compounds containing bleached pulp or paper product is the amount of oxidizing one or more carboxylic group(s), —C(O)OH, preferably ami agent which enhances the brightness and resistance to ther nocarboxylic acids containing a single C-N bond adjacent mal yellowing of the pulp or paper compared to pulp or paper (vicinal) to the C COH bond, such as EDTA ((HOCCH) 10 which is not treated with the oxidizing agents. Methods for NCHCHN(CH-COH)), DTPA ((HOCCH) NCHCHN(CH-COH)CHCHN(CHCOH)), and the determining brightness and resistance to thermal yellowing like and alkaline and alkaline earth metal salts thereof. are described herein. "Dithiocarbamates' include monomeric dithiocarbamates, Typically, about 0.0005 to about 2, preferably about 0.05 to polymeric dithiocarbamates, polydiallylamine dithiocarbam 15 about 0.25 weight percent, based on oven-dried pulp of oxi ates, 2,4,6-trimercapto-1,3,5-triazine, disodium ethylenebis dizing agent is added to the bleached pulp or paper product. dithiocarbamate, disodium dimethyldithiocarbamate, and the As noted above, the oxidizing agent may be used in com like. bination with one or more reducing agents. The reducing In an embodiment, the chelant is selected from the group agent may be added before or after the oxidizing agent. The consisting of diethylene-triamine-pentamethylene phospho effective amount of reducing agent added to the bleached pulp nic acid (DTMPA) and salts thereof, diethylenetriaminepen or paper product is the amount of reducing agent which, in taacetic acid (DTPA) and salts thereof and ethylenediamine combination with the oxidizing agents, enhances the bright tetraacetic acid (EDTA) and salts thereof. ness and resistance to thermal yellowing of the pulp or paper Applicanthas also discovered that oxidizing agents used in compared to pulp or paper which is not treated with the combination with optical brighteners (“OEBAs) enhance the 25 reducing agents. effect of optical brighteners (OBA). The oxidizing agents also Typically, about 0.005 to about 2, preferably about 0.05 to improve the color scheme. This permits reduction of the about 0.25 weight percent, based on oven-dried pulp of reduc amount of OBA's and brighteners such as blue dyes neces ing agent is added to the bleached pulp or paper product. sary to achieve comparable brightness and color. Replacing In a typical application, about 0.001 to about 1, preferably Some of the OBA and dyes with oxidizing agents allows pulp 30 about 0.01 to about 0.1 weight percent of phosphonate, phos and paper manufacturers to reduce production costs and phate or carboxylic acid chelant and/or about 0.002 to about reduce the overall amount of OBA and dyes present, while 0.02 weight percent of dithiocarbamates chelant based on maintaining an acceptable level of brightness in the paper oven-dried pulp is added to the bleached pulp or paper prod product and achieving the target color. In some cases it may uct. be possible to eliminate dyes entirely and maintain color. 35 Optical brighteners are typically added in amounts of about Accordingly, in another embodiment, one or more optical 0.005 to about 2, preferably 0.05 to about 1 weight percent of brighteners (“OEBAs) are added to the bleached pulp or optical brightener based on oven-dried pulp. paper product. The oxidizing agents, reducing agents, chelants and/or "Optical brighteners' are fluorescent dyes or pigments that optical brighteners can be added to bleached pulp or paper at absorb ultraviolet radiation and reemititat a higher frequency 40 any point in the papermaking or tissue making process. Rep in the visible spectrum (blue), thereby effecting a white, resentative addition points include, but are not limited to (a) to bright appearance to the paper sheet when added to the stock the pulp slurry in the latency chest; (b) to the pulp after the furnish. Representative optical brighteners include, but are bleaching stage in a storage, blending or transfer chest; (c) to not limited to azoles, biphenyls, coumarins; furans; ionic pulp after bleaching, washing and dewatering followed by brighteners, including anionic, cationic, and anionic (neutral) 45 cylinder or flash drying; (d) before or after the cleaners; (e) compounds, such as the Eccobrite(R) and Eccowhite(R) com before or after the fan pump to the paper machine headbox: (f) pounds available from Eastern Color & Chemical Co. (Provi to the paper machine white water, (g) to the silo or save all: (h) dence, R.I.), naphthalimides; pyraZenes; Substituted (e.g., in the press section using, for example, a size press, coater or Sulfonated) stilbenes, such as the Leucophor R range of opti spray bar; (ii) in the drying section using, for example, a size cal brighteners available from the Clariant Corporation (Mut 50 press, coater or spray bar, () on the calender using a wafer tenZ, Switzerland), and Tinopal(R) from Ciba Specialty box; and/or (k) on paper in an off-machine coater or size Chemicals (Basel, Switzerland); salts of such compounds press; and/or (1) in the curl control unit. including but not limited to alkali metal salts, alkaline earth The precise location where the oxidizing agents, reducing metal salts, transition metal salts, organic salts and ammo agents, chelants and/or optical brighteners should be added nium salts of Such brightening agents; and combinations of 55 will depend on the specific equipment involved, the exact one or more of the foregoing agents. process conditions being used and the like. In some cases, the In an embodiment, the optical brighteners are selected reducing agents, chelants and/or optical brighteners may be from the group of disulfonated, tetrasulfonated and hexasul added at one or more locations for optimal effectiveness. fonated Tinopal(R) OBAs. Application can be by any means conventionally used in The dosage of oxidizing agents, reducing agents, chelants 60 papermaking processes, including by 'split-feeding and/or optical brighteners is the amount necessary to achieve whereby a portion of the reducing agent, chelant and/or opti the desired brightness and resistance to yellowing of the cal brightener is applied at one point in the papermaking bleached pulp or paper product prepared from the bleached process, for example on pulp or a wet sheet (before the dryers) pulp and can be readily determined by one of skill in the art and the remaining portion is added at a Subsequent point, for based on the characteristics of the reducing agent, chelant or 65 example in the size press. optical brightener, the pulp or paper being treated and the In an embodiment, the oxidizing agents are applied to the method of application. Reducing agents may be added to the bleached pulp material in a thin stock. For purposes of this US 8,262,858 B2 11 12 embodiment, “thin stock’ means a stock solution having a ties to the final paper product and include but are not limited consistency of less than about 5% based on dry solids. to brightening agents, dyes, fillers, sizing agents, starches, In an embodiment, the oxidizing agents are applied to the and adhesives. bleached pulp material in a thick stock, where “thick stock” Control additives are additives incorporated during the means a stock solution having a consistency of about 5 to process of manufacturing the paper so as to improve the about 30% based on dry solids. overall process without significantly affecting the physical In an embodiment, the oxidizing agents are applied to a wet properties of the paper. Control additives include biocides, sheet. retention aids, defoamers, pH control agents, pitch control In an embodiment, the oxidizing agents are applied in the agents, and drainage aids. Paper and paper products made size press. 10 using the process of the present invention may contain one or The activators, chelants and/or optical brighteners can be more functional additives and/or control additives. added to the bleached pulp or paper product before, after or Pigments and dyes impart color to paper. Dyes include simultaneously with the oxidizing agent and with one organic compounds having conjugated double bond systems; another. Any reducing agents should be added before or after aZo compounds; metallic azo compounds; anthraquinones; the oxidizing agent. 15 triaryl compounds, such as triarylmethane; quinoline and In a representative application using reducing agents and related compounds; acidic dyes (anionic organic dyes con optical brighteners, the reducing agents may be added to the taining Sulfonate groups, used with organic rations such as bleached pulp material before or after the optical brighteners, alum); basic dyes (cationic organic dyes containing amine for example in the blend chest or in the thin stock. functional groups); and direct dyes (acid-type dyes having In an alternate application, oxidizing agents optical bright high molecular weights and a specific, direct affinity for cel eners and chelants may be added to the bleached pulp material lulose); as well as combinations of the above-listed suitable in the storage, blending or transfer chest, in a thin Stock or at dye compounds. Pigments are finely divided mineral that can the wet end and in the size press, where the relative dose of be either white or colored. The pigments that are most com optical brighteners added in the wet end is reduced and the monly used in the papermaking industry are clay, calcium relative dose of optical brighteners in the size press is 25 carbonate and titanium dioxide. increased based on the observed higher response of the opti Fillers, are added to paper to increase opacity and bright cal brighteners in the size press when used in combination ness. Fillers include but are not limited to calcium carbonate with oxidizing agents as described herein. A preferred oxi (calcite); precipitated calcium carbonate (PCC); calcium Sul dant for use in the size press is peracetic acid. fate (including the various hydrated forms); calcium alumi Applicant has also discovered that addition of oxidizing 30 nate; Zinc oxides; magnesium silicates, such as talc, titanium agents and optical brighteners to thick stock enhances bright dioxide (TiO). Such as anatase or rutile; clay, or kaolin, ness of the bleached pulp material, improves wet end bright consisting of hydrated SiO, and Al-O; synthetic clay; mica; ness stability and increases fluorescence of the optical bright Vermiculite; inorganic aggregates; perlite; sand; gravel; sand ener (“OEA activation') when compared to oxidant addition stone; glass beads; aerogels, Xerogels; Seagel; fly ash; alu to thick stock followed by OBA addition to thin stock. The 35 mina; microspheres; hollow glass spheres; porous ceramic oxidizing agents may be added to the thick stock before, after spheres; cork; seeds; lightweight polymers; Xonotlite (a crys or simultaneously with the optical brighteners. The oxidizing talline calcium silicate gel); pumice; exfoliated rock, waste agents may also be formulated with the optical brighteners for concrete products; partially hydrated or unhydrated hydraulic addition to the thick stock. A preferred oxidizing agent cement particles; and diatomaceous earth, as well as combi according to this embodiment is peracetic acid. 40 nations of Such compounds. The oxidants may also be formulated with any chelants, Sizing agents are added to the paper during the manufac optical brighteners, and/or activators in a single product for turing process to aid in the development of a resistance to application to the bleached pulp material. A representative penetration of liquids through the paper. Sizing agents can be formulation comprises the oxidizing agent, one or more acti internal sizing agents or external (Surface) sizing agents, and vators and optionally one or more chelants. 45 can be used for hard-sizing, slack-sizing, or both methods of An alternative formulation comprises one or more oxidiz sizing. More specifically, sizing agents include rosin; rosin ing agents and one or more optical brighteners. This formu precipitated with alum (Al(SO4)); abietic acid and abietic lation may be applied to a wet paper sheet as-is or mixed in a acid homologues such as neoabietic acid and levopimaric Surface sizing solution for application to the wet paper sheet. acid; Stearic acid and Stearic acid derivatives; ammonium The formulation may also be applied in the size press. 50 Zirconium carbonate; silicone and silicone-containing com The oxidizing agents, reducing agents, chelants and/or pounds, such as RE-29 available from GE-OSI and SM-8715, optical brighteners may also be used in combination with one available from Dow Corning Corporation (Midland, Mich.); or more partially neutralized polycarboxylic acids, preferably fluorochemicals of the general structure CF (CF).R. polycarboxylic acids such as polyacrylic acid (CHCH wherein R is anionic, cationic or another functional group, (COH)|CHCH(COH), CHCH-COH, where n is about 55 Such as Gortex; alkylketene dimer (AKD). Such as Aquapel 10 to about 50,000. The polycarboxylic acid may be neutral 364, Aquapel (I 752, Heron) 70, Hereon 79, Precise 787, ized to the target pH, (typically 5-6 as discussed below) with Precise 2000, and Precise 3000, all of which are commer alkali Such as Sodium hydroxide. cially available from Hercules, Incorporated (Willmington, The oxidizing agents, reducing agents, chelants and optical Del.); and alkyl succinic anhydride (ASA); emulsions of ASA brighteners and polycarboxylates may be used in addition to 60 or AKD with cationic starch; ASA incorporating alum; other additives conventionally used in papermaking to starch; hydroxymethyl starch; carboxymethylcellulose improve one or more properties of the finished paper product, (CMC); polyvinyl alcohol; methyl cellulose; alginates: assist in the process of manufacturing the paper itself, or both. waxes; wax emulsions; and combinations of Such sizing These additives are generally characterized as either func agents. tional additives or control additives. 65 Starch has many uses in papermaking. For example, it Functional additives are typically those additives that are functions as a retention agent, dry-strength agent and Surface use to improve or impart certain specifically desired proper sizing agent. Starches include but are not limited to amylose; US 8,262,858 B2 13 14 amylopectin; starches containing various amounts of amy Water bath/thermostat accommodating a floating plastic box lose and amylopectin, such as 25% amylose and 75% amy with paper samples 100-ml, application cuvette for the Soak lopectin (corn starch) and 20% amylose and 80% amylopec ing method. tin (potato starch); enzymatically treated Starches; Dry Surface Application Procedure (Surface Sizing, Soaking hydrolyzed starches; heated Starches, also known in the art as Method) “pasted Starches': cationic starches, such as those resulting from the reaction of a starch with a tertiary amine to form a 1. Prepare 8x8-inch hand sheet according to the standard quaternary ammonium salt; anionic starches; ampholytic procedure. The target dry weight is 2.5 g. Pass wet hand starches (containing both cationic and anionic functional sheets through one cycle on the drum dryer. ities); cellulose and cellulose derived compounds; and com 10 2. Cut /sth strip of the sheet (0.31 g). binations of these compounds. 3. In a 50 ml test tube, prepare solutions of pre-cooked starch The method of this invention yields paper products with a (if needed) and reducing agent compound Solutions based bright surface. Moreover, the novel composition further pro on the pre-determined pickup rate and target dose. tects paper from long-term discoloration during regular use. 15 The foregoing may be better understood by reference to the 4. Dip the paper strip into the solution for 10 seconds, let it following examples, which are presented for purposes of drip for 35 seconds and then pass it through the press. illustration and are not intended to limit the scope of the 5. Drum-dry the test sheet and equilibrate at room tempera invention. ture. 6. Measure brightness and yellowness. EXAMPLES Pulp Application Procedure: In these Examples, sufficient 50% aqueous sodium The chemicals were added directly to the pulp (thin stock hydroxide was added to achieve appropriate pH for the agent or thick Stock) and mixed with the pulp in sealed bags. In a or composition being tested. All percentages in these 25 pulp application procedure for OBA enhancement the chemi examples are given on a weight percent dry pulp basis. cals were added directly to the bleached kraft pulp at 20% In these Examples, the following terms shall have the indi consistency, mixed with the pulp in sealed bags and kept at cated meaning. 45-80°C. for 30 min. The pulp was diluted to 5% consistency, Br for ISO brightness R457 (TAPPI 525): Ye for E313 the OBA was added, mixed with the pulp, and the slurry was yellowness; WI for E313 Whiteness; TMP for thermome 30 kept at 50° C. for 20 min. Then the slurry was further diluted chanical pulp: CTMP for chemi-thermomechanical pulp; and hand sheets prepared according to the standard proce RMP for refiner mechanical pulp; OBA for optical bright dure. OBA is added as a commercial product. ener; EDTA for (HOCCH)NCHCHN(CHCO2H), eth 1. Combined Application of an Oxidant and OBA in Surface ylenediaminetetraacetic acid; DTPA for (HOCCH), Sizing Solution. NCHCHN(CH-COH)CHCHN(CHCOH), diethyl 35 enetriaminepentnncetic acid; DTMPA for HOPCHN TABLE 1 CHCHN(CH2POH), diethylene-triamine-pentameth ylene phosphonic acid; PAA for peracetic acid. Softwood kraft, drum-dried handsheets, Surface sizing application in starch (4.4% in paper) Treatment 40 Handsheets were made of bleached pulp and then used in Br gain vs. OBA the experiments, in which the reducing agents were applied Treatment Br Control activation either on a wet sheet (before or after the press) before drum drying or after drum drying (temperature during drum drying: Control 85.5 0.25% Tinopal ABP-A (OBA) 90.2 4.7 45 100° C.). The third option was split-feed application. The O.O375% PAA 86.2 0.7 Surface sizing application was followed by one more round on O.O75% PAA 86.1 O.6 a drum dryer. O.O375% PAA - 0.25% OBA 91.0 5.5 O.8 The load of the tested Agent or Composition solution was O.O75% PAA - 0.25% OBA 91.4 5.9 1.2 determined based on the dry weight of the pulp sample. The 0.12% H2O2 85.8 O.3 Agent or Composition solutions were applied using a rod, as 50 0.12% H-O-, + 0.25% OBA 90.8 5.3 O6 uniformly as possible, as solutions in water. The test sheets 0.041% NaClO 85.6 O.1 were dried using a laboratory drum drier under uniform con 0.041% NaClO + 0.25% OBA 90.7 5.2 O.S ditions (one round). O.S9 OBA 94.2 8.7 The handsheets were made using (a) a Buchner funnel (5g 0.25% NaH2PO + 0.5% OBA 94.8 9.3 O6 o.d. pulp, Ø15 cm, pressed and air-dried) and (b) 55 0.12% H2O, +0.25% 95.5 1O.O 1.3 Noble&Wood handsheet mold (8 in. sq., 60 g/m2). Bright NaH2PO + 0.5% OBA ness was measured using Elrepho and Technidyne instru 0.12% H-O-, + 0.25% 95.1 9.6 1.O mentS. NaHCO3 + 0.5% OBA Test Equipment Laboratory drum drier. 60 “Elrepho3000.” “Technidyne ColorTouch2 (Model ISO)” or We have discovered that optical brighteners can be com another instrument for brightness measurements. bined with oxidant performance enhancers in a Surface sizing Hitachi F-4500 fluorescence spectrometer or another instru Solution. Generally, optical brighteners can react with oxi ment for relative fluorescence intensity measurements. dants. However, we found that the conditions of the surface Micropipette. 65 sizing process are mild enough to prevent this from happen Surface size application kit (pad and size 3-application rod). ing. Different oxidants positively affect performance of opti Constant humidity room (23°C., 50% humidity). cal brighteners. US 8,262,858 B2 15 16 2. Application of Various Oxidants in Thick Stock Pulp (OBA 4. Application of Activated Hydrogen Peroxide is Applied Upon Dilution of the Stock) TABLE 5 TABLE 2 Hardwood kraft, air-dried handshects. Stage I, Softwood kraft, drum-dried handsheets. oxidant application-10% consistency: 60°C., Stage I-10% consistency: 60° C., 1 hr. 3 hr. Stage II, OBA application-4% consistency, Stage II-4% consistency, 60° C. 20 min. 60° C. 20 min (with or without OBA. Tinopal ABP-A). Br gain vs. OBA Br Gain Vs. Oxidant OBA Treatment Br Control activation 10 Control 84.9 0.12% H2O2 O.2 0.374% Tinopal ABP-A (OBA) 96.9 12.0 0.12% H2O + 0.79% 1.7 0.50% Ammonium persulfate 84.8 O.O Tetraacetylethylenediamine 0.50% Ammonium persulfate + 97.2 12.3 O.2 0.12% HO, + 0.5% 1.8 O.374% OBA Monosodium phosphate 0.50% Sodium percarbonate 86.1 1.3 15 0.12% H2O + 0.05% 1.O 0.50% Sodium percarbonate + 98.5 13.6 1.5 Ammonium molybdate O.374% OBA 0.50% Sodium perborate 85.6 O.8 0.50% Sodium perborate + 98.1 13.2 1.2 TABLE 6 O.374% OBA 0.50% Chlororsulfamate 84.5 -0.4 Hardwood kraft, air-dried handsheets. Stage I, 0.50% Chlorosulfamate + 97.3 12.4 O.3 oxidant application-10% consistency: 60°C., O.374% OBA 3 hr. Stage II, OBA application-4% consistency, Control-no incubation 84.4 GO C. 20 min (with or without OBA, Tinopal ABPA). Br Gain Vs. In this example, different oxidants are applied in thick 25 Oxidant OBA stock followed by application of an OBA in a more diluted stock during the papermaking process. Several oxidants show 0.0375% HO, O.S 0.0375% H-O-, + 0.5% 3.1 a synergistic effect with an optical brightener. Monosodium phosphate 3. Synergistic Effect of an Oxidative Pre-Treatment on Opti 0.0375% H-O-, + 0.25% 2.6 cal Brighteners 30 Monosodium phosphate

TABLE 3 TABLE 7 Hardwood kraft, air-dried handsheets. Stage I, oxidant application-10% consistency: 60° C., 3 hr. Hardwood kraft, air-dried handsheets. Stage I, Stage II, OBA application-4% consistency, 60°C., 35 oxidant application-10% consistency: 60°C., 20 min (with or without OBA. Tinopal ABP-A). 3 hr. Stage II, OBA application-4% consistency, 60° C. 20 min (with or without OBA. Tinopal ABP-A). Dosage, Br Gain Oxidant % Actives' wS. OBA Br Gain Vs. Oxidant OBA NaOCl. NaBrisulfamic acid 0.075 4.2 40 1:1-5:2. 0.12% H2O2 O.6 Monochloramine 0.075 2.3 0.12% H2O + 0.50% HPO. 4.0 Sodium 0.075 2.9 0.12% HO, + 0.25% NaHCO, 1.7 hypochlorite/dimethylhydantoin 0.12% H2O + 0.50% NaHCO 4.3 1:1 0.12% H2O + 0.05% Nalco 3.3 Sodium hypochlorite?urea 1.1-1.6 6.7 45 1:1 'Peroxide stabilizer based on DTMPA, available from Nalco Company, Naperville, IL. '% Actives are determined by measuring the total residual chlorine in a dilute sample according to EPA Method 330.5 The data shown in Tables 5-7 illustrate different ways of activating hydrogen peroxide that results in its significantly improved performance in the process. TABLE 4 50 5. Application of Oxidant Compositions in the Thick and Hardwood kraft, air-dried handsheets. Stage I, Thin Stock; Application of Oxidant Compositions in The oxidant application-10% consistency: 60° C., 3 hr. Thick Stock Together with an OBA Stage II, OBA application-4% consistency, 60°C., 20 min (with or without OBA. Tinopal ABP-A). TABLE 8 55 Br gain vs. Hardwood, alkaline pulp, drum-dried handsheets. Dosage, Control Br Gain Stage I, oxidant application-10% consistency: 60°C., Oxidant % Actives' (no OBA) wS. OBA 3 hr. Stage II, OBA application-4% consistency, 60°C., 20 min (with or without OBA. Tinopal ABP-A). NaOCl, NaBrisulfamic acid O.O15 O.8 3.0 1:1-5:2. 60 Br gain vs. Br. Gain vs. NaOClfurea 1:1 O.O15 1.1 2.0 OBA, 4% OBA, 10% Oxidant Consistency Consistency '% Actives are determined by measuring the total residual chlorine in a dilute sample according to EPA Method 330.5 NaOCl NaBrisulfamic acid O.2 1.1 1:1.5:2 (0.0125% actives) The data shown in Tables 3 and 4 show the significant effect 0.09% H-O-, + 0.3% O.S 1.O of different oxidants as OBA activators. Especially interest 65 Monosodium phosphate ing is the documented significant improvement in OBA per formance in absence of actual bleaching with PAA. US 8,262,858 B2 17 18 Table 8 illustrates application of the oxidative chemistry on 2. The method of claim 1 further comprising adding one or pulp of lower (4%) and higher (10%) consistency (hardwood, more chelants to the bleached pulp, the stock Suspension or on 0.35% OBA as product). to the sheet. 3. The method of claim 2 wherein the chelants are selected TABLE 9 from the group consisting of organic phosphonates, phos Hardwood, drum-dried handsheets. phates, carboxylic acids, salts of any of the previous mem bers, and any combination thereof. Br gain vs. Br gain vs. OBA, OBA, the Oxidant 4. The method of claim 2 wherein the optical brighteners O.45% OBA added at 10% are selected from dilsulfonated, tetrasulfonated or hexasul added consistency; 10 fonated stilbene derivatives. together with 0.45% OBA added the Oxidant later at 4% 5. The method of claim 3, wherein the chelant is selected at 10% consistency from the group consisting of diethylene-triamine-pentameth Oxidant consistency (30 min, 60° C.) ylene phosphonic acid (DTMPA) and salts thereof, diethyl 15 enetriaminepentaacetic acid (DTPA) and salts thereof and Pulp #1, alkaline ethylenediaminetetraacetic acid (EDTA) and salts thereof. O.O.19% PAA O.8 0.4 6. The method of claim 1 further comprising adding one or Pulp #2, kraft more reducing agents to the aqueous stock Suspension or onto O.O.19% PAA 1.8 the sheet. O.O38% PAA 2.4 7. The method of claim 6, wherein the reducing agent is O.O75% PAA 2.5 selected from the group consisting of substituted phosphines, sulfites, bisulfites and metabisulfites. Table 9 illustrates performance of the oxidative chemistry 8. The method of claim 1 wherein the oxidizing agents are when OBA and the oxidant are applied together in the thick selected from the group consisting of hydrogen peroxide, stock (10% consistency). For comparison, an example of the 25 organic peroxyacids, inorganic peroxides, Superoxides and lesser gain achieved when the chemistries are applied con peroxide-superoxides, inorganic peroxyacids and salts secutively is given. thereof, peroxyhydrates, water-soluble organic peroxides, While the present invention is described above in connec nitrosodisulfonates, hypochlorites, hypobromites, chlorites, tion with representative or illustrative embodiments, these chlorates, bromates, perchlorates, chlorine dioxide, chloro embodiments are not intended to be exhaustive or limiting of 30 the invention. Rather, the invention is intended to cover all amines, chloroamides, chlorosulfamides, bromoamines, bro alternatives, modifications and equivalents included within moamides, bromosulfamides, chlorosulfonic acid, bromosul its spirit and scope, as defined by the appended claims. fonic acid and chlorine. The invention claimed is: 9. The method of claim 1 wherein the oxidizing agents are 1. A method of enhancing the effectiveness of optical selected from the group consisting of hydrogen peroxide, brighteners in papermaking processes comprising: 35 activated hydrogen peroxide, peracetic acid, hypochlorites, i) providing bleached pulp; ii) forming an aqueous stock Suspension comprising the hypobromites, chloroamines, chloroamides, chlorosulfa bleached pulp; mides, bromoamines, bromoamides, bromosulfamides, chlo iii) draining the stock Suspension to form a sheet; rosulfonic acid, bromosulfonic acid. iv) treating the sheet with an oxidant composition compris 40 10. The method of claim 1 wherein the oxidizing agents ing one or more oxidizing agents at about 0.0005 to and optical brighteners are added onto a wet sheet or added to about 2 weight percent on oven-dried pulp, one or more the bleached pulp material in the size press. optical brighteners, and optionally one or more chelants, 11. The method of claim 10 wherein the oxidizing agents optionally one or more reducing agents, or combinations and optical brighteners are formulated in a surface sizing thereof, 45 Solution comprising starch and added to the bleached pulp and wherein said oxidizing agents are selected from the group consisting of hydrogen peroxide, organic per material in the size press. oxyacids, inorganic peroxides, Superoxides and per 12. The method of claim 1 wherein the oxidizing agent is oxide-superoxides, organic and inorganic peroxyac peracetic acid. ids and salts thereof, peroxyhydrates, water-soluble 13. The method of claim 1 wherein the oxidizing agent is organic peroxides, nitrosodisulfonates, hypochlo 50 hydrogen peroxide. rites, hypobromites, chlorites, chlorates, bromates, 14. The method of claim 2 wherein about 0.05 to about 1 perehlorates, chlorine dioxide, chloroamines, chlo weight percent, based on oven-dried pulp of one or more roamides, chlorosulfamides, bromoamines, bromoa optical brighteners and about 0.05 to about 0.25 weight per mides, bromosulfamides, chlorosulfonic acid, bro cent, based oven dried pulp, of one or more oxidizing agents mosulfonic acid and chlorine and wherein said is added to the bleached pulp, the aqueous stock Suspension or bleached pulp material has a minimum ISO bright onto the sheet. ness of 84.4 and the oxidant composition excludes starch when the oxidant comprises hydrogen peroX 15. The method of claim 1 wherein the optical brighteners ide, organic peroxyacids, inorganic peroxides, Super are added before, after, or simultaneously with the oxidizing oxides and peroxide-Superoxides, organic and inor 60 agents. ganic peroxyacids and salts thereof, peroxyhydrates, 16. The method of claim 1 wherein the optical brighteners and water-soluble organic peroxides; and are formulated with the oxidizing agents. V) drying the sheet, 17. The method of claim 1 wherein said bleached pulp wherein the aqueous stock Suspension comprises a thick material is kraft pulp. stock and a thin stock and the oxidizing agents are added to 65 the thick stock and the optical brighteners are added to the thin stock.