AU779547B2

AU779547B2 - Process for stabilizing the whiteness of lignin-containing fibrous materials, stabilizer composition and fibrous materials stabilized with this

Info

Publication number: AU779547B2
Application number: AU26117/02A
Authority: AU
Inventors: Christian Baurich; Mario Beyer; Klaus Fischer; Harald Jakob; Helmut Koch; Karsten Krasselt; Hans Ulrich Suss
Original assignee: Degussa GmbH
Current assignee: Evonik Operations GmbH
Priority date: 2001-03-14
Filing date: 2002-03-14
Publication date: 2005-01-27
Anticipated expiration: 2022-03-14
Also published as: US20020174491A1; CA2376543A1; NZ517679A; NO20021248L; NO20021248D0; DE10112101A1; EP1241296A2; EP1241296A3; AU2611702A

Description

S&FRef: 587354

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

Name and Address of Applicant: Actual Inventor(s): Address for Service: Degussa AG Benningsenplatz 1 D-40474 Dusseldorf Germany Klaus Fischer, Mario Beyer, Helmut Koch, Karsten Krasselt, Christian Baurich, Harald Jakob, Hans Ulrich Suss Spruson Ferguson St Martins Tower,Level 31 Market Street Sydney NSW 2000 (CCN 3710000177) Process for Stabilizing the Whiteness of Lignincontaining Fibrous Materials, Stabilizer Composition and Fibrous Materials Stabilized with This Invention Title: The following statement is a full description of this invention, including the best method of performing it known to me/us:- 5845c 010019 BL AL 1 1 Process for stabilizing the whiteness of lignin-containing fibrous materials, stabilizer composition and fibrous materials stabilized with this Description The invention relates to a process for stabilizing the whiteness of lignin-containing fibrous materials, in particular paper and cardboard of mechanically produced fibrous materials, in particular wood pulp, against lightinduced yellowing. The process comprises the use of a sulfur-containing whiteness stabilizer. The invention furthermore relates to whiteness-stabilized lignincontaining fibrous materials obtainable according to the invention and to a stabilizer composition.

SThe low stability to whiteness of lignin-containing high- 15 yield fibrous materials such as are obtainable using mechanically produced fibrous substances, that is to say in particular fibrous substances produced thermomechanically (TMP), chemo-thermomechanically (CTMP) or by stone-grinding of wood (SGW), is a serious obstacle to employing high- 20 yield fibrous substances obtained in this way, in particular wood pulps, for the production of high-finish paper and card products. Bleached lignin-containing wood pulps and celluloses in particular are highly susceptible to light-induced yellowing.

The causes and prevention of light-induced yellowing of celluloses are reported by J. S. Gratzl in "Das Papier" 39/10 A (1985), pages V16 to V23. For increasing the whiteness and improving the light stability of celluloses, in particular lignin-rich high-yield celluloses, reductive measure are suitable, such as treatment of the cellulose with sodium boranate or the use of a combination of formaldehyde with a dithionite salt or addition of tin(II) salts. The tendency towards yellowing can furthermore be 010019 BL AL 1 2 reduced effectively by using a UV filter, for example a 2hydroxybenzophenone or 2-hydroxybenzotriazole.

In the context of mechanistic studies by Dian Yan Lee et al. (Holzforschung 45 (1991) suppl. pages 15 to 20), it was found that 1-thioglycerol is active to a certain extent in both the bleaching and the stabilization of the whiteness of mechanically produced fibrous substances. A disadvantage of thioglycerol is its low molecular weight and therefore also its unpleasant smell, which impedes use in practice.

C. Heitner ("Pulp Bleaching-Principles and Practice", C. W.

Dence, D. W. Reeve, eds., TAPPI PRESS, Atlanta, 1996, pages 183 to 211) gives an overview of the prior art on yellowing of lignin-containing fibrous substances. The use of phosphites, UV absorbers and agents which trap free 15 radicals, such as ascorbic acid, thiols and thioethers, is reported. It is stated in WO 99/05108 that the substances mentioned in this document are still not an adequate and practically applicable solution for avoiding light-induced yellowing.

According to another study of light- and heat-induced yellowing of fibrous substances Beyer, Ch. Baurich and K. Fischer in "Das Papier", volume 10A (1995), pages V8 to :o V14) yellowing can be counteracted by targeted application of a combination of ascorbic acid with a compound containing a thiol group. A further improvement is achieved by applying a pigmented coat to a paper comprising the combination mentioned. This document does not reveal what structure the thiol must have to effect effective resistance to yellowing.

According to US Patent 5,942,567, yellowing of casting resins can be reduced by using a combination of a phenolic antioxidant and a non-aromatic thiol compound. The thiols are alkylmercaptans, such as, in particular, hexylmercaptan, dithioglycol and 3mercaptopropyltriethoxysilane, all of which are an odour 010019 BL AL 1 3 nuisance. No reference to the use of such a combination as a whiteness stabilizer for lignin-containing fibrous materials, such as paper, is to be found in this document.

The doctrine of US Patent 6,059,927 is a process for stabilizing the whiteness of mechanically produced bleached wood pulps. For this, a combination of an aqueous formaldehyde solution with a carbonate is employed in the wood pulp substance; a further increase in the resistance to yellowing is effected by using a polyethylene glycol bisthiol, polyethylene glycol bisthiolactate and polyethylene glycol bisthioglycollate being mentioned exclusively as the thiol compound. The amount of these thiols employed is in the range from 2 to 6 based on the wood pulp. The high amount of the said bisthiols 15 employed is a disadvantage of this process. No indication that these bisthiols can be employed in the absence of formaldehyde and carbonate for stabilizing whiteness can be found in this document.

Studies by B. J. W. Cole at al. (Journal of Wood Chemistry and Technology, 20 1 17 (2000)) on the bleaching and photostabilization of high-yield fibrous substances show that ethylene glycol bismercaptoacetate (=ethylene glycol dithioglycollate) has a bleaching and stabilizing action, while pentaerythritol tetrathioglycollate has no bleaching action and leads to only a slight decolorization in the system investigated.

Effective stabilization of the whiteness of TMP and CTMP fibrous substances or papers produced therefrom is effected according to WO 99/05108 by the use of derivatives of 1oxyl-2,2,6,6-tetramethylpiperidin-4-ol and selected hydroxylamine salts. The action is increased by additional use of co-additives, such as UV absorbers, antioxidants, nitrones, fluorescent brighteners and sulfur-containing stabilizers. The sulfur-containing stabilizers, which are employed only in combination with an N-oxide or hydroxylamine light stabilizer, are compounds with a thiol or thioether group. The following thiols, which are predominantly compounds presenting an odour nuisance, are mentioned: thioglycerol, dithiothreitol, 2,2'-oxydiethanethiol, 2-(2'-methoxyethoxy)-ethanethiol, thioglycollic acid, 2- and 3mercaptopropionic acid and Na salts thereof, diesters of the mercaptocarboxylic acid mentioned with ethylene glycol and polyethylene glycol and trimethylolpropane tri(3-mercaptopropionate).

The object of the present invention is to provide a further process for stabilizing the whiteness of lignin-containing fibrous materials against light-induced yellowing and paper and card with improved resistance to yellowing, which are obtainable by this process. According to another object the whiteness stabilizers to be used according to the invention should have the lowest possible smell and show a high activity by themselves, but in particular in combination with other known whiteness stabilizers or co-additives at the lowest possible total concentration of additives.

A further object is aimed at providing a composition comprising one or more whiteness stabilizers, the use of which in the pulp of the fibrous substance or in a composition for impregnating or coating, such as a size or a so-called coat, the fibrous material leads to a high stabilization of the whiteness.

These objects and further objects such as emerge from the further description are achieved by the invention defined in the claims. According to the invention, there is provided a process for stabilising the whiteness of lignin-containing fibrous materials against light-induced yellowing, comprising the use of a thio compound as a whiteness stabiliser in an active amount for increasing the resistance to yellowing during the production of the fibrous material, wherein a thiol compound from the series consisting of ester of a polyhydric alcohol having a cycloaliphatic, linear or branched hydrocarbon radical with 4 to 20 C-atoms, which radical can be interrupted once or several times by a NH- or -N(alkyl) -bridge, with a mercaptocarboxylic acid, wherein at least one hydroxyl group of the polyhydric alcohol is non-esterified; mercaptoamines containing on a linear, cycloaliphatically or branched carbon skeleton, which can be interrupted once or several times by -NH- or N-alkyl, at least one

NH

2

NHR

1 or NR 1

R

2 group, wherein R' and R 2 may be identical or different and may represent a lower alkyl group, hydroxyethyl, hydroxypropyl or dihydroxypropyl with one another or may be 30 bonded together; mercaptoamino acid; (ii) thiols which contain at least one aliphatically or cycloaliphatically bonded thiol group and additionally at least one CC double bond, (iii) thiols which contain at least one thiol group bonded to a heteroaromatic, and [IADAUBJBXX)o4224.doc: KOB (iv) di- and polysulfides with at least one heteroaromatic bonded to the di- or polysulfide group, is employed as the whiteness stabiliser, wherein thioglycerol, dithiothreitol mercaptoacetic acid, 2- and 3-mercaptopropionic acid, and salts thereof are excluded as the whiteness stabiliser.

The term "lignin-containing fibrous materials" is understood as meaning all materials which comprise a lignin-containing fibrous substance as the essential constituent. The fibrous substances are, in particular, lignin-containing wood pulps, but lignin-containing celluloses are also acceptable to the process according to the invention. Stabilization of the whiteness and therefore prevention of yellowing is of industrial importance in particular in so-called high-yield wood pulps which are to obtained thermomechanically (TMP) or chemo-thermomechanically (CTMP) or by stone-grinding (SGW). The raw materials mentioned are inexpensive raw materials which, if the whiteness stabilization is adequate, can be employed both in papers of medium quality and in high-quality papers and cards. The process according to the invention is also particularly suitable for stabilizing the whiteness of bleached wood pulps, which tend to yellow in particular without stabilization.

The resistance to yellowing of lignin-containing fibrous substances and the materials produced therefrom can be increased and the whiteness thus stabilized if a thiol compound according to the invention [I:\DAYLIB\UBXX042l24doc:KOB 010019 BL AL 1 6 is employed in an active amount during the production of the fibrous material. The amount employed depends on the desired degree of stabilization and on whether and to what extent further whiteness stabilizers and/or co-additives are employed in the production of the fibrous material. The amount of thio compound according to the invention employed is conventionally in the range from 0.01 to 5 wt.%, preferably 0.1 to 3 wt.% and particularly preferably 0.5 to 2 in each case based on the dry fibrous substance.

The whiteness stabilizers according to the invention from group are thiols which have at least one aliphatically or cycloaliphatically bonded thiol group and additionally at least one hydrophilic group according to the claims.

Such thiols can have various structures, such as, for 15 example: Mercaptoalcohols of the general formula (HS)mX(OH)n, wherein X represents an optionally alkyl-substituted cycloaliphatic, a linear or branched hydrocarbon radical having 4 to 20 C atoms, in particular 5 to 8 C atoms,and m and n represent an integer from 1 to 5. Examples are di-, tri- and tetrathiopentitols and -hexitols.

Mercaptoalcohols of the general formula (HS)mY(OH)n, wherein Y represents a linear or branched hydrocarbon radical which is interrupted once or several times by a -NH-or N-alkyl bridge and has 4 to 20 C atoms in total and m and n have the abovementioned meaning. Examples are reaction products of polyhydric alcohols with ethylene sulfide or a mercaptoalkyl halide, at least one hydroxyl group remaining on the hydrocarbon radical.

Mercaptoalcohols of the general formula

(HS(CH

2 )p-COO)mZ(OH)n, wherein Z has the meaning of X or Y or represents a polymeric hydrocarbon chain, m and n have the abovementioned meaning or in the case of a polymeric matrix can also far go beyond the values mentioned and p 010019 BL AL 1 7 represents 1 or 2, wherein the mercapto group can be bonded internally or terminally. These are preferably an ester of a polyhydric alcohol, such as ethylene glycol, di-, triand polyethylene glycol, propane-1,2 and -1,3-diol, butane- 1,4-diol, hexane-1,2,6-triol, trimethylolethane (TME),trimethylolpropane (TMP), erythritol, pentaerythritol (penta), di-TME, di-TMP, di-penta, sugar alcohols, sugar acids and lactones thereof with a mercaptocarboxylic acid from the series consisting of mercaptoacetic acid thioglycollic acid), 2- and 3-mercaptopropionic acid, monoand dimercaptosuccinic acid. The polyhydric alcohol can also be partly esterified with a mercaptocarboxylic acid other than those mentioned above. The polymeric alcohols esterified with a mercaptocarboxylic acid are, for example, 15 an oligo- or polysaccharide, such as starch, or polyvinyl alcohol.

Particularly suitable mercaptoalcohols of the abovementioned type are the di- or triester of pentaerythritol with mercaptoacetic acid or 1 or 2- 20 mercaptopropionic acid, in particular pentaerytritol [sic] trithiolglycollate, and the di-, tri- or tetraester of a pentitol or hexitol, in particular sorbitol tetrathioglycollate. It has been found that such compounds have a considerably better action as a whiteness stabilizer 25 than the compounds which are already known and have a similar structure but no longer contain a free hydroxyl group.

Mercaptoamines which contain, as hydrophilic group(s), at least one NH 2

NHR

I or NRR 2 group, wherein R 1 and R 2 can be identical or different and can represent a lower alkyl group, such as methyl, ethyl, propyl, hydroxyethyl, hydroxypropyl or dihydroxypropyl, or can be bonded togehter, on a linear, cycloaliphatic or branched carbon skeleton, which can be interrupted once or several times by -NH- or N-alkyl, also have a stabilizing action.

010019 BL AL 1 8 Examples are N-mercaptoethyl-diethylenetriamine and Nmercatpoethyl-diethanolamine, and salts of these amines.

Thiols with an acid function as the hydrophilic group are, for example, mercaptosuccinic acid, dimercaptosuccinic acid, mercaptopropanesulfonic acid, mercaptethylaminomethanephosphonic acid. Salts, in particular alkali metal salts, of the acids mentioned are also active.

A particularly preferred group of thiols of group are mercaptoamino acids, such as, in particular, cysteine, Nacylated mercaptoamino acids, such as acetylcysteine, and di- and oligopeptides with at least one amino acid containing mercapto groups. A particularly good whiteness stabilizer, which moreover is completely odour-free and is 15 highly active especially with co-stabilizers, is the tripeptide glutathione (y-glutamylcysteineglycine).

It has been found that the yellowing-inhibiting action of S" mercapto compounds is increased by additionally at least ~one olefinic CC double bond (group These are preferably compounds which have an allyl structure.

Examples are esters of allyl alcohol or cinnamyl alcohol with a mercaptocarboxylic acid having 2 to 4 C atoms, such as thioglycollic acid, thiolactic acid and mercaptosuccinic acid.

Surprisingly, thiols which contain at least one mercapto group on a heteroaromatic have proved to be an active yellowing inhibitor (group(iii)). The heteroaromatics are and 6-membered heteroaromatics with optionally another fused-on aromatic or heteroaromatic ring system. They contain one, two or three heteroatoms from the series consisting of O, S and N, rings with two or three heteroatoms being preferred, such as from the series consisting of s-triazine, thiadiazole, thiazole, diazole.

Such heteroaromatics optionally contain, in addition to at 010019 BL AL 1 9 least one mercapto group, one or two amino or alkylated amino groups, alkylmercapto or alkoxy groups. They are particularly preferably monomercapto-diamino-s-triazines and dimercapto-amino-s-triazine, it being possible for amino groups to be substituted by one or two Ci- to C 3 alkyl groups or allyl groups or to be part of a five- or six-membered ring. Examples are: 2-mercapto-4-allylamino-6diethylamino-s-triazine, 2,4-dimercapto-6-allylamino-striazine and 2-mercapto-4-ethylamino-6-morpholino-striazine. Finally, trimercapto-s-triazine, in particular in the form of a mono-, di- and tri-alkali metal salt, also has a whiteness-stabilizing action. The mercaptotriazine compounds can be obtained in a manner known per se by stepwise reaction of cyanuric chloride with one or two S 15 amines and sodium hydrogen sulfide.

Whiteness stabilizers of group (iv) contain one or more dior polysulfide groupings on a heteroaromatic of the type already mentioned above or between two heteroaromatics.

Polysulfide groups are also understood as meaning tri- and S 20 tetrasulfides. The second function of a polysulfide can be saturated by hydrogen or an alkali metal, or by oligomerzation.

Examples are 2,4-di-polysulfido-6-diethylamino-s-triazine, i bis-2-methylamino-l,3,4-thiadiazin-5-yl disulfide and bis-[2,4-di(dialkylamino)-triazin-6-yl] tetrasulfide. The polysulfidotriazine is prepared e.g. by reaction of 2diethylamino-4,6-dimercapto-2-triazine with S 2 C1 2 in petroleum ether; thiadiazinyl disulfide is obtainable by an oxidation of methylamino-mercapto-1,3,4-thiadiazole with

H

2 0 2 and the tetrasulfide mentioned can be obtained by reaction of the corresponding bis(dialkylamino)triazinylmercapto compound with S 2 C1 2 010019 BL AL 1 The action of whiteness stabilizers to be used according to the invention which have one or more thiol groups or di- /polysulfide groups can be increased by the co-use of known whiteness stabilizers or co-stabilizers. These are substances from the series consisting of light stabilizers, in particular those from the series consisting of sterically hindered nitroxides and hydroxylamines and salts thereof HALS stabilizers), UV absorbers, antioxidants, fluorescent brighteners, agents which trap free radicals, metal deactivators, phosphites, aromatic sulfides and reducing agents other than thiols.

The HALS light stabilizers are compounds such as are mentioned by way of example in WO 99/05108 and US Patents 5,496,875 and 6,080,864. Suitable compounds are e.g. 1oxyl-2,2,6,6-tetramethyl-4-hydroxypiperidine; 1-hydroxy- 2,2,6,6-tetramethyl-4-hydroxypiperidinium chloride or a *.carboxylic acid salt according to this type, such as tetra(l-hydroxy-2,2,6,6-tetramethyl-4-hydroxypiperidinium) ethylenediaminetetraacetate; 1-oxyl-2,2,6,6-tetramethyl-4- 20 alkyloxypiperidine; octadecyl-2,2,6,6-tetramethyl-4piperidinyl carbonate. The amount of such stabilizers o* employed is expediently in the range from 0.01 to 2 wt.%.

Combinations of thiols according to the invention, in e particular those from group such as mercaptocarboxylic 25 acid esters of polyhydric alcohols, amino acids or oligopeptides containing thiol groups, with HALS light stabilizers lead to a synergistic effect in respect of the whiteness stabilization, so that the total amount of stabilizers can be reduced, or the activity can be increased noticeably by means of a small addition of a HALS stabilizer, such as 0.02 to 0.2 wt.%.

The UV absorbers are known substances from the series consisting of benzotriazoles and benzophenones, such as 3tert-butyl-4-hydroxy-5-(2H-benzotriazol-2-yl)-hydrocinnamic acid and 2-(2-hydroxy-3,5-di-tert-butylphenyl)-2H- 010019 BL AL 1 11 benzotriazole; 2,4-dihydroxybenzophenone and 2,2-dihydroxy- 4,4-dimethoxy-5,5-disulfobenzophenone di-Na salt. A further class of UV absorbers which are suitable for stabilizing the whiteness of lignin-containing fibrous substances in the absence of whiteness stabilizers according to the invention comprises substances with the structural element of the general formula: HO-Ar =0 H O=0

R

2 10 wherein:

R

1 denotes H, (C 1

-C

12 )-alkanoyl, in particular acetyl, propionyl, n-butanoyl; (Ci-C 12 )alkoxycarbonyl, in particular

-COOCH

3

-COOC

2

H

5 R2: denotes (Ci-C 12 )-alkyl, linear or branched, in particular methyl, ethyl, n-propyl, n-butyl, i-propyl Ar-OH: denotes hydroxy-substituted aryl radical, wherein at least one hydroxyl group is bonded in the ortho- or paraposition of the aromatic bonded to the olefinic double bond, in addition further substituents, such as alkyl, in particular methyl, ethyl, propyl, n-butyl, i-propyl, secbutyl, tert-butyl, alkoxy, in particular methoxy and ethoxy, phenyl, p(o)-hydroxyphenyl, benzoyl, -COOH and S0 3 H, can be bonded to the aromatic, and wherein Ar represents the benzene or naphthalene ring.

010019 BL AL 1 12 3-Methoxy-4-hydroxybenzylidene-malonic acid esters and 3- (3-methoxy-4-hydroxybenzylidene-pentane- 2 ,4-dione are particularly suitable.

The antioxidants are usually sterically hindered phenols, such as 2,6-di.-tert- butyl-4-methylphenol, hydroxylated thiodiphenyl ethers, triazines, such as 2,4bis(octylmercapto)-6-(3,5-di-tert-butyl-4-hydroxyanilino- 1,3,5-triazine.

Phosphites and phosphonites, in particular sterically hindered compounds, such as tris(2,4-di-tert-butylphenyl) phosphite, assist the whiteness stabilization, since they act as agents which trap peroxides and free radicals.

Various hydrazine derivatives, such as isophthaloyl 15 dihydrazide and N,N-bis(salicyloyl)hydrazine, are active as metal deactivators. A further class comprises complexing agents from the series consisting of citrates, gluconates, keto acids, aminocarboxylic acids, such as EDTA, DTPA and phosphonates, such as hydroxyethane-diphosphonate

(HEDP).

20 The fluorescent brighteners are, in particular, known substances from the series consisting of stilbene derivatives, such as 4,4'-(diphenyl)-stilbene and 4,4'-bis- (triazinylamino)-stilbene-2,2'-disulfonic acid.

Polymeric inhibitors, such as polyethylene glycol, polyvinylpyrrolidone and polytetrahydrofuran, are also suitable co-stabilizers.

One or more thiols or di-/polysulfides according to the invention in combination with a HALS light stabilizer or other agents which trap free radicals and a UV absorber from the series consisting of benzotriazoles or benzophenones and optionally additionally or alternatively an antioxidant, in particular a sterically hindered phenol, 010019 BL AL 1 13 are particularly preferably employed, since a synergistic is fully effective here. Examples of particularly active combinations are: glutathione or sorbitol tetrathioglycollate, 2,2,6,6-tetramethyl-4hydroxypiperidine N-oxide or a derivative thereof and 2-(2hydoxyphenyl)-benzotriazole.

One or more whiteness stabilizers to be used according to the invention from the series consisting of thiols or di- /polysulfides or a combination of these compound(s) with one or more co-stabilizers from the series consisting of the abovementioned substance classes can be employed at various points in the production process of the fibrous material. It is possible to add the whiteness stabilizer or stabilizers and co-stabilizers individually or in the form of a composition to the mass of the fibrous substance, which is present e.g. in the form of a pulp. The addition is possible e.g. before, during or after a bleaching stage which is optionally carried out, or during the dewatering of the fibrous material.

o In an alternative and usually preferred embodiment, the whiteness stabilizer or a composition comprising it is sprayed in the form of a solution or suspension on to the fibrous material, which has been at least partly dewatered.

This spraying process is then followed by the sizing and/or i 25 coating stages known in paper and card production.

According to another preferred alternative, the whiteness stabilizer to be used according to the invention or a composition comprising it is introduced into the medium used for sizing or coating the paper or card and applied to the fibrous material with this.

It has been found that a considerable intensification of the yellowing-inhibiting effect of the whiteness stabilizers to be used according to the invention and composition comprising such can be achieved by applying a pigment-containing coat, in particular containing titanium 010019 BL AL 1 14 dioxide, after application of the whiteness stabilizer, for example by impregnation or together with the size application. According to a particularly preferred embodiment, the whiteness stabilizer or stabilizers and optionally co-stabilizers are applied to the fibrous material together with titanium dioxide and optionally other constituents of a size or coating and the material is processed to the finished paper or card in a manner known per se.

The invention also provides a whiteness-stabilized lignincontaining fibrous material, in particular paper and card of mechanically produced wood pulp or high-yield cellulose, which can be bleached or unbleached, which comprises a whiteness stabilizer from the series consisting of the 15 thiols, di or polysulfides of groups to (iv) to be used according to the invention. The whiteness stabilizer here can be either in the pulp or in a size or coating or in a surface layer of the fibrous material produced by impregnation.

S 20 According to a particularly preferred embodiment of the whiteness-stabilized lignin-containing fibrous material according to the invention, this comprises a coating which can be the size or a coating with a brush-on colour which comprises titanium dioxide. A TiO 2 content in the 25 range from 0.1 to 5 based on the dried coating, leads to a significant increase in the resistance to yellowing.

As has been explained in detail in the description of the process according to the invention, in addition to one or more whiteness stabilizers according to the invention, the pulp of the fibrous material or a size or coating on this can also comprise other known whiteness stabilizers and/or co-stabilizers.

The invention also provides a composition which comprises at least one of the whiteness stabilizers to be used 010019 BL AL 1 according to the invention from group to (iv) in an aqueous, organic or aqueous-organic liquid or paste-like medium which can be used for spraying or coating. The composition preferably comprises one or more of the preferred stabilizers described above. According to a particularly preferred embodiment, the composition additionally comprises one or more other whiteness stabilizers co-stabilizers from the series consisting of agents which trap free radicals, such as HALS light stabilizers, antioxidants, UV absorbers, reducing agents, fluorescent brighteners, metal deactivators, phosphites and aromatic sulfides. According to a particularly preferred embodiment, the composition comprises the combination of a whiteness stabilizer according to the invention, a HALS ee 15 light stabilizer and/or a UV absorber and/or an I antioxidant. Examples of such compositions have already been mentioned above. The composition expediently comprises at least one whiteness stabilizer according to the invention, a HALS light stabilizer and a UV absober [sic] in a weight ratio of 1 to (0.02 to 0.5) to (0.2 to in particular 1 to (0.05 to 0.2) to (0.5 to A preferred composition is a brush-on colour for coating a fibrous material. For the purpose of stabilization of the dagree of whiteness such a brush-on colour particularly preferably comprises, in addition to conventional base constituents, a combination of at least one whiteness stabilizer according to the invention, at least one UV absorber and at least one agent which traps free radicals.

Particularly preferred compositions additionally comprise titanium dioxide, in addition to at least one whiteness stabilizer according to the invention. Compositions which are used for sizing purposes or a final coat additionally comprise conventional sizing components or binders and 010019 BL AL 1 16 further inorganic pigments, additives and dispersing auxiliaries.

Experts are provided by a large number of further highly active whiteness stabilizers for prevention of yellowing of lignin-containing fibrous materials, such as, in particular, paper and card, by the invention. The whiteness stabilizers can be used by themselves, but preferably in combination with known whiteness stabilizers and/or costabilizers, synergistic effects being achieved. A further increase in the resistance to yellowing is effected by the additional use of titanium dioxide in the size or in a coat. The subject matter according to the invention allows mechanically produced fibrous substances to be employed for the production of high-quality papers and cards, since the S 15 risk of light-induced yellowing is reduced decisively by :the use of whiteness stabilizers according to the invention.

The invention is illustrated with the aid of the following examples Examples In each case a TCF-bleached aspen CTMP cellulose with a whiteness of 86 was used as the paper base I. Individual substances The substances shown in table 1 were applied to the paper in the form of a solution. The amount applied was 1 by weight, calculated with respect to the cellulose.

After drying, irradiation was carried out. Irradiation time 10h in a xenon test apparatus, level 2. The whiteness as a function of time was determined; the loss in whiteness results from this as the difference dW) between the whiteness before and after (Wloh)the irradiation or as the relative drop in 010019 BL AL 1 whiteness dW*100/Wo..

Table 1 Number Stabilizer W 0 before W 10

W

irradiation after 10h W 10 CE 1 none 86 55 31 E 1 2-diallylamino-4-(3'- 88 67 21 Methoxypropyl) amino- 6-mercapto-1, triazine E 2 2-N-piperidino-4- 87 65 22 Ethylamino-6mercapto-1, trazine E 3 2,2'-bis-(5- 81 61 methy2lamino-1, 3, 4thiadiazolyl) disulf ide CE 2 2,2,6,6-tetramethyl- 78 56 22 4 -hydroxypiperidine N -oxide (is coloured!) E 4 sorbitol 83 58 tetrathioglycollate E 5 pentaerythritol 83 58 triatiolglycollate [sic] CE 3 pentaerythritol 86 54 32 tetra-thioglycollate Examples 1 to 5 show the good action of thiols according to the invention. The action is the same or better than that of the HALS stabilizer of comparison example CE 2.

Comparison of example 5 with comparison example CE 3 shows the unexpected influence of the additional 0 hydroxyl group.

010019 BL AL 1 2. Combinations Combinations of a whiteness stabilizer (WS) according to the invention according to table 2a and b (1 the HALS light stabilizer (agent which traps free radicals FRT) 2,2,6,6-tetramethyl-4-hydroxypiperidine N-oxide (0.1 and the UV absorber (UV) 2-(2-hydroxyphenyl)benzotriazole (1 were investigated. The use and testing were carried out analogously to those described under 1. The relative decrease in whiteness after irradiation for 10 h and 20 h is shown in table 2 b.

Table 2a Number Combination W before W 1 o Wo irradiation after 10h W 1 o CE 1 no WS, FRT and UV 86 55 31 CE 4 no WS; 87 68 19 with FRT and UV E 6 sorbitol tetrakis- 87 75 12 thioglycollate and FRT and UV 010019 BL AL 1 r Table 2b Number Combination (Wt-Wo) 100 Wo after 10 h after 20 h CE 1 no WS, FRT and UV 33 42 CE 4 no WS, with FRT and 22 31

UV

E 6 sorbitol tetrakis- 14 22 thioglycollate with FRT and UV E 7 cinnamyl mercapto- 19 26.5 glycollate with UV and FRT 3. Combinations and TiO 2 in a coat Combinations comprising whiteness stabilizers (WS) according to the invention the UV (UV) absorber mentioned under 2. and an agent which traps free radicals (FRT) were investigated. The amount employed, where present, as before 1 WSG [sic], 0.1 %FRT, 1 UV, in each cased based on the fibrous substance). After application of the particular stabilizer composition and drying, a TiO 2 -containing coat was applied.

Composition of the brush-on colour: 5 parts of inorganic pigment, of which 4 parts of calcium carbonate, 0.9 part of kaolin, 0.1 part of titanium dioxide, 3.5 parts of binder, 3.5 parts of water, dispersing auxiliary. Coat thickness 12 g/m 2 The results follow from table 3 a: Stabilizer-free comparison example CE stabilizer-free paper was coated only with the stated brush-on colour. Stabilizer-free paper. The paper 010019 BL AL 1 according to example 8 comprised, under the coat, an impregnation with glutathione (1 based on the dyestuff), and that of example 9 additionally FRT 0.1 wt.% and UV (1 The comparison shows the increase in action on changing from the coat-free, nonstabilized system (CE 1) to the system with a TiO 2 containing coat (CE to the system with glutathione under a TiO 2 -containing coat (E 8) and finally a TiO 2 containing coat on a paper with an impregnation comprising glutathione, FRT and UV.

Table 3 a Number Stabilizer; coat Wo Wo W1o after CE 1 no stabilizer, no 86 55 31 Ti0 2 CE 5 no stabilizer, but 88 68 coat with TiO 2 E 8 glutathione coat 85 72 13 with TiO 2 E 9 glutathione and 85 80 FRT and UV and coat with Ti02 Examples E 10 and E 11 in table 3 illustrate the influence of TiO 2 in the coat. The coat composition in E 10 comprised no TiO 2 by 1 part of kaolin, in example 11 0.7 part of kaolin and 0.3 part of TiO 2 the other constituents corresponded to the coat composition described above.

010019 EL AL 1 Table 3 b Number E 10* E 11* Stabilizer; coat pentaerythritol tristhioglycollate and FRT and UV and coat without TiO 2 pentaerythritol tristhioglycollate and FRT and UV and coat with TiO 2 WO M% W3 0 af ter W1 0

M%

83.5 -77.5~ 6 I -t 86.5 52.5 86.5 82.5 The abovementioned coat composition comprised [sic] E 10 0 part of TiO 2 but 1 part of kaolin; in 5 example 11 the composition 0.7 part of kaolin and 0.3 part of TiO 2 Examples 10 and 11 illustrate the influence of TiO 2 in the coat.

Claims

1. A process for stabilising the whiteness of lignin-containing fibrous materials against light-induced yellowing, comprising the use of a thio compound as a whiteness stabiliser in an active amount for increasing the resistance to yellowing during the production of the fibrous s material, wherein a thiol compound from the series consisting of ester of a polyhydric alcohol having a cycloaliphatic, linear or branched hydrocarbon radical with 4 to 20 C-atoms, which radical can be interrupted once or several times by a NH- or -N(alkyl) -bridge, with a mercaptocarboxylic acid, wherein at least one hydroxyl group of the io polyhydric alcohol is non-esterified; mercaptoamines containing on a linear, cycloaliphatically or branched carbon skeleton, which can be interrupted once or several times by -NH- or N-alkyl, at least one NH 2 NHR 1 or NR 1 R 2 group, wherein R 1 and R 2 may be identical or different and may represent a lower alkyl group, hydroxyethyl, hydroxypropyl or dihydroxypropyl with one another or may be bonded together; mercaptoamino acid; (ii) thiols which contain at least one aliphatically or cycloaliphatically bonded thiol group and additionally at least one CC double bond, (iii) thiols which contain at least one thiol group bonded to a heteroaromatic, and 20 (iv) di- and polysulfides with at least one heteroaromatic bonded to the di- or polysulfide group, is employed as the whiteness stabiliser, wherein thioglycerol, dithiothreitol mercaptoacetic acid, 2- and 3-mercaptopropionic acid, and salts thereof are excluded as the whiteness stabiliser.

2. The process according to claim 1, wherein a di- or triester of pentaerythritol with mercaptoacetic acid or 1- or 2-mercaptopropionic acid, or a di-, tri- or tetra-ester of a pentitol or hexitol, is employed as the whiteness stabiliser.

3. The process according to claim 2, wherein said ester of pentaerythritol is pentaerythritol trithiolglycollate.

4. The process according to claim 2, wherein said ester of a pentitol or hexitol is sorbitol 30 tetrathioglycollate. Process according to claim 1, wherein an ester of an alcohol with an allyl structural element with a mercaptocarboxylic acid having 2 to 4 carbon atoms is used as the whiteness stabiliser of group (ii).

6. The process according to claim 5, wherein said alcohol with an allyl structural element is allyl alcohol or cinnamyl alcohol. [I:\DAYLIB\LIBXXj04224.doc:KOB

7. The process according to claim 5, wherein said ester is cinnamyl alcohol thioglycollate.

8. The process according to claim 1, wherein a mercapto-s-triazine, mercapto-triazole, mercapto-diazole, or mercapto-1,3,4-thiadiazole compound is used as the whiteness stabiliser of group (iii).

9. The process according to claim 8, wherein said mercapto-s-triazine compound is 2-mercapto-4,6-diamino-s-triazine, wherein the amino groups are substituted in an identical or different manner by alkyl, cycloalkyl or allyl. The process according to claim 1, wherein a compound selected from the series io consisting of 2-amino-4,6-bispolysulfido-s-triazine, bis-4,6-diamino-s-triazin-2-yl tetrasulfide, and bis-5-amino-1,3,4-tridiazol-2-yl di-and tetrasulfide, wherein the amino groups in each case are alkyl- ,cycloalkyl-, or allyl-substituted, is used as the whiteness stabiliser of group (iv).

11. The process according to claim 1, wherein an amino acid containing thiol groups, an N-acylated amino acid containing thiol groups, or an oligopeptide containing thiol groups, is employed as the whiteness stabiliser of group

12. The process according to claim 11, wherein said amino acid is cysteine.

13. The process according to claim 11, wherein said N-acylated amino acid is N- acetylcysteine.

14. The process according to claim 11, wherein said oligopeptide is glutathione. 20 15. The process according to claim 1, wherein the whiteness of materials from substantially mechanically, thermomechanically or chemo-thermomechanically produced lignin- containing unbleached or bleached fibrous substances is stabilised.

16. The process according to claim 15, wherein said lignin-containing unbleached or bleached fibrous substance is paper or card from wood pulp.

17. The process according to claim 1, wherein the whiteness stabiliser or a composition comprising it is added to the pulp of the fibrous substances or to a size or brush-on colour composition to be applied to a fibrous material, or a solution or suspension of a composition comprising the whiteness stabiliser is sprayed on to the non-coated fibrous material.

18. The process according to claim 1, wherein in addition to at least one whiteness 30 stabiliser as defined in claim 1, one or more other whiteness stabilisers and/or one or more co- stabilisers from the series consisting of UV absorbers, antioxidants, metal deactivators, agents which trap free radicals, fluorescent brighteners, phosphites, reducing agents and aromatic sulfides, are employed. [I:\DAYLIB\UBXX]04224doc: KOB

19. The process according to claim 18 wherein in addition to at least one whiteness stabiliser a combination comprising a UV absorber and an agent which traps free radicals is employed. The process according to claim 1, wherein a fibrous material treated with a whiteness stabiliser as defined in claim 1 in the pulp, in a surface coating or by means of impregnation, is coated with a brush-on colour comprising titanium dioxide, or a non-treated fibrous material is coated with a brush-on colour comprising a whiteness stabiliser as defined in claim 1 and titanium dioxide.

21. A process for stabilising the whiteness of lignin-containing fibrous materials against to light induced yellowing, substantially as hereinbefore described with reference to any one of the examples but excluding the comparative examples.

22. Whiteness-stabilised lignin-containing fibrous material prepared according to the process of claim 1.

23. Whiteness-stabilised lignin-containing fibrous material, characterised by the presence of a whiteness stabiliser of the thiols, di- and polysulfides according to groups to (iv) of claim 1 in the pulp of the fibrous material and/or in a layer produced by impregnation, sizing or by means of a brush-on colour.

24. The whiteness-stabilised lignin-containing fibrous material according to claim 23, wherein said material is paper or card of mechanically, thermomechanically, or chemo- 20 thermomechanically produced wood pulp or high-yield cellulose.

25. The whiteness-stabilised lignin-containing fibrous material according to claim 23, wherein the fibrous substance is a bleached wood pulp or high-yield cellulose.

26. The whiteness-stabilised lignin-containing fibrous material according to claim 23, wherein said material has a coating of a size or coating colour comprising titanium dioxide.

27. The whiteness-stabilised lignin-containing fibrous material according to claim 23, wherein said material additionally comprises, in the pulp and/or in a layer produced by impregnation and/or coating, one or more other whiteness stabilisers and/or co-stabilisers selected from the series consisting of agents which trap free radicals, UV absorbers, fluorescent brighteners, antioxidants, metal deactivators, reducing agents, phosphites and other aromatic sulfides. S" 30 28. The whiteness-stabilised lignin-containing fibrous material according to claim 27, wherein said agent which traps free radicals is a HALS light stabilisers (Hindered Amine Light Stabiliser).

29. Whiteness-stabilised lignin-containing fibrous material, substantially as hereinbefore described with reference to any one of the examples but excluding the comparative examples. [I:\DAYLIB\LIBXX]04224.doc: KOB A composition comprising a whiteness stabiliser, characterised by a content of at least one whiteness stabiliser as defined in claim 1 in an aqueous, organic or aqueous-organic liquid or paste-like medium which can be used for spraying or coating.

31. The composition according to claim 30, wherein said whiteness stabiliser is as defined in any one of claims 1 to 14.

32. The composition according to claim 30, wherein said composition additionally comprises one or more other whiteness stabilisers and/or co-stabilisers selected from the series consisting of agents which trap free radicals, antioxidants, UV absorbers, reducing agents, fluorescent brighteners, metal deactivators, phosphites and aromatic sulfides.

33. The composition according to claim 32, wherein said other whiteness stabilisers or co- stabilisers are HALS light stabilisers.

34. The composition according to claim 30, wherein in addition to a whiteness stabiliser as defined in claim 1, the composition further comprises a HALS light stabiliser, and/or a UV absorber, and/or an antioxidant selected from the series consisting of sterically hindered phenols.

35. The composition according to claim 34, wherein said HALS light stabiliser is 2,2,6,6- tetramethyl-4-hydroxypiperidine N-oxide.

36. The composition according to claim 34, wherein said UV absorber is selected from a 2-hydroxyaryl-benzotriazole, a hydroxybenzophenone, and a 2-substituted 3-(hydroxy-aryl)acrylic acid ester. 20 37. The composition according to claim 34 wherein said composition comprises a whiteness stabiliser as defined in claim 1, a HALS light stabiliser, and a UV absorber in a weight ratio of 1 to (0.02 to 0.5) to (0.2 to 2).

38. The composition according to claim 37, wherein the ratio of said whiteness stabiliser to HALS light stabiliser to UV absorber is 1 to (0.05 to 0.2) to (0.5 to 2).

39. The composition according to claim 30, wherein said composition comprises a dispersing agent and/or an organic binder or sizing agent and/or titanium dioxide. The composition according to claim 30, wherein said composition is a brush-on colour "for coating a fibrous material.

41. A composition comprising a whiteness stabiliser, substantially as hereinbefore described with reference to any one of the examples but excluding the comparative examples.

42. UV absorbers for use in stabilising the whiteness of lignin-containing fibrous materials, characterised by a structural element of the general formula *l•e [I:\DAYLIB\LIBXX04224 doc:KOB HO-Ar\ /R H C C=O R wherein: R 1 denotes H, (C1.C 1 2)-alkanoyl, or (C1-C1 2 alkoxycarbonyl, R 2 denotes linear or branched (Cl-C12)-alkyl, Ar-OH denotes hydroxy-substituted aryl radical, wherein at least one hydroxyl group is bonded in the ortho- or para-position of the aromatic ring bonded to the olefinic double bond, in addition at least one further substituent selected from alkyl, alkoxy, phenyl, p(o)-hydroxyphenyl, benzoyl, -COOH and SO 3 H can be bonded to the aromatic, and wherein Ar represents a benzene or naphthalene ring. 1o 43. The UV absorber according to claim 42, wherein R 1 is acetyl, propionoyl, or n- butanoyl.

44. The UV absorber according to claim 42, wherein R 1 is -COOCH 3 or -COOC 2 H 5 The UV absorber according to claim 42, wherein R 2 is methyl, ethyl, n-propyl, n-butyl, or i-propyl.

46. The UV absorber according to claim 42, wherein said further alkyl substituent on the aryl radical is selected from methyl, ethyl, propyl, n-butyl, i-propyl, sec-butyl, and tert-butyl.

47. The UV absorber according to claim 42, wherein said further alkoxy substituent on the aryl radical is methoxy or ethoxy. 20 48. UV absorbers for use in stabilising the whiteness of lignin-containing fibrous substances according to claim 42, wherein said UV absorber is a 3-methoxy-4-hydroxybenzylidene- malonic acid dialkyl ester, wherein alkyl represents methyl or ethyl.

49. UV absorbers, substantially as hereinbefore described with reference to any one of the examples but excluding the comparative examples. Dated 2 July, 2003 -Degussa AG Patent Attorneys for the Applicant/Nominated Person SPRUSON FERGUSON •ooo [I\DAYLIB\LIBXX]04224doc:KOB