EP1241296A2 - Process for stabilizing brightness of lignin-containing fibrous material, a composition for stabilizing the brightness thereof and thus stabilized fibrous material - Google Patents

Abstract

(Cyclo)aliphatic thiols with other hydrophilic groups, unsaturated thiols, and thiols or di- and poly-sulfides with hetero-atoms are used to prevent light-induced yellowing in lignin-containing fibre materials. Thioglycerol, dithiothreitol mercaptoacetic acid and 2- or 3-mercaptopropionic acid are not included. A method for stabilizing the degree of whiteness of lignin-containing fibre materials (LFM) against light-induced yellowing by the use of thio compounds (I) as stabilizers, in which (I) comprise: (i) thiols with aliphatic or cycloaliphatic thiol group(s) and other hydrophilic group(s) selected from -OH, -NH2, -NHR<1>, -NR<1>R<2>, -COOH, -SO3H, -PO3H2 or salts of these acids and bases; (ii) thiols with (cyclo)aliphatic thiol group(s) and C=C double bond(s); (iii) thiols with thiol group(s) attached to a hetero atom; and (iv) di- or poly-sulfides with hetero atom(s) attached to the di- or poly-sulfide groups. R<1>, R<2> = 1-4C alkyl, 2-4C hydroxyalkyl (e.g. hydroxyethyl or dihydroxypropyl), 2-4C alkanoyl or hydroxyalkanoyl. Independent claims are also included for: (1) lignin-containing LFM with a stabilized degree of whiteness, especially paper and cardboard from mechanically-produced (thermo-mechanically or chemo-thermo-mechanically) wood pulp or high-yield pulp, containing (I) in the fibre material itself or in a layer formed by impregnation, sizing or coating; (2) compositions containing (I) in an aqueous, organic or aqueous-organic liquid or paste-like medium which can be applied by spraying or coating; and (3) UV absorbers for stabilizing the degree of whiteness of LFM, comprising compounds of formula HO-Ar-CH=C(R<3>)-CO-R<4>. R<3> = H, 1-12C alkanoyl (especially acetyl, propionyl or n-butanoyl) or 1-12C alkoxycarbonyl (especially -COOCH3 or -COOC2H5); R<4> = 1-12C alkyl, especially methyl, ethyl, n-propyl, iso-propyl or n-butyl; Ar = phenylene or naphthylene, with OH in the ortho or para position to the C=C group and optionally substituted with alkyl (preferably methyl, ethyl, n- or iso-propyl, n-, sec.- or tert.-butyl), alkoxy (preferably methoxy or ethoxy), phenyl, p-(o-)-hydroxy-phenyl, benzoyl, -COOH or -SO3H

Description

The invention relates to a method for Whiteness stabilization with lignin content Fibrous materials, especially paper and cardboard mechanically produced fibrous materials, especially wood pulp, against light-induced yellowing. The process includes the Use of a sulfur-containing whiteness stabilizer. The The invention is also directed to the invention available whiteness-stabilized lignin-containing Fibrous materials as well as on a Stabilizer composition.

The low whiteness stability of lignin-containing high-yield fiber materials, like using mechanical produced fibrous materials, in particular thus thermomechanically (TMP), chemo-thermomechanical (CTMP) or through Stone grinding of wood (SGW) fiber materials is a serious obstacle, such High yield fiber materials obtained, in particular Wood materials, for the production of highly refined paper and Use cardboard products. Especially bleached Wood and cellulose containing lignin are highly susceptible for light-induced yellowing.

About causes and prevention of light-induced Yellowing of pulp is reported by J. S. Gratzl in "Das Paper "39/10 A (1985), pages V16 to V23. To increase of whiteness and improvement of light resistance of Cellulose, especially lignin-rich high yield Pulp, reductive measures, such as a Treatment of the pulp with sodium boranate or the Use a combination of formaldehyde with a Dithionite salt or addition of tin (II) salts. The inclination for yellowing can also be achieved by using a UV filter, for example a 2-hydroxybenzophenone or 2-Hydroxybenztriazols can be effectively reduced.

As part of mechanistic studies by Dian Yan Lee et al. (Holzforschung 45 (1991) suppl. Pages 15 to 20) it was found that 1-thioglycerin, both in the Mechanical bleaching and whiteness stabilization produced fiber is effective to some extent. A disadvantage of thioglycerol is its low molecular weight and hence its unpleasant smell, that of a practical one Application opposes. C. Heitner ("Pulp Bleaching Principles and Practice ", C. W. Dence, D. W. Reeve, eds., TAPPI PRESS, Atlanta, 1996, pages 183 to 211) gives one Overview of the state of the art in yellowing lignin-containing fibers. The use is reported of phosphites, UV absorbers, and radical scavengers, such as Ascorbic acid, thiols and thioethers. It is in the WO 99/05108 found that in this document substances mentioned are still insufficient and practical applicable solution to reduce light-induced Represent yellowing.

According to a further study on light and heat-induced yellowing of fibrous materials (M. Beyer, Ch. Bäurich and K. Fischer in "Das Papier", Issue 10A (1995), Pages V8 to V14) let the yellowing through targeted application of a combination of ascorbic acid with a compound containing a thiol group counteract. This will further improve achieved that on a containing the combination mentioned A pigment coat is applied to paper. This document it is not possible to determine which structure the thiol to have effective resistance to yellowing cause.

According to US Pat. No. 5,942,567, the yellowing of Casting resins through the use of a combination of one phenolic antioxidant and a non-aromatic Reduce thiol compound. The thiols are around alkyl mercaptans, such as in particular hexyl mercaptan, Dithioglycol and 3-mercaptopropyltriethoxysilane, which all e are unpleasant to smell. A note on the use such a combination as a whiteness stabilizer for Lignin-containing fibrous materials, such as paper, can be do not take from this document.

U.S. Patent 6,059,927 teaches a method of Whiteness stabilization of mechanically produced bleached Pulps. To do this, add a to the mass of the wood pulp Combination of an aqueous formaldehyde solution with a Carbonate used; a further increase in Resistance to yellowing is achieved by using a Polyethylene glycol bisthiols causes, where as Thiol compound exclusively polyethylene glycol bisthiolactate and called polyethylene glycol bisthioglycolate become. The amount of these thiols is in the range of 2 to 6 wt .-%, based on the wood pulp. Disadvantageous This method is the high amount used in the above Bisthiols. There is no reference to this document remove what these bisthioles in the absence of Formaldehyde and carbonate for whiteness stabilization can be used.

Studies by B. J. W. Cole at al. (Journal of Wood Chemistry and Technology, 20 (1), 1-17 (2000)) on Bleaching and photostabilizing high-yield fibers show that ethylene glycol bismercaptoacetate (= Ethylene glycol dithioglycolate) a bleaching and has a stabilizing effect, whereas pentaerythritol tetrathioglycolate is ineffective in bleaching and in the examined System only leads to a slight discoloration.

Effective whiteness stabilization of TMP and CTMP fibers, or papers made from it according to WO 99/05108 through the use of derivatives of 1-oxyl-2,2,6,6-tetramethylpiperidin-4-ol and selected Hydroxylamine salts causes. Through the additional effort of coadditives, such as UV absorbers, antioxidants, Nitrons, fluorescent brighteners and sulphurous ones Stabilizers, the effect is increased. Both sulfur-containing stabilizers, which only in combination with an N-oxide or hydroxylamine light stabilizer Used, they are connections with a thiol or thioether group. The following are named Thiols, which are predominantly odorous compounds: thioglycerin, Dithiothreitol, 2,2'-oxydiethanethiol, 2- (2'-methoxyethoxy) ethanethiol, Thioglycolic acid, 2- and 3-mercaptopropionic acid and their Na salts, diesters of the above Mercaptocarboxylic acid with ethylene glycol and polyethylene glycol and trimethylolpropane tri (3-mercaptopropionate).

The object of the present invention is another Process for stabilizing whiteness of lignin Fibrous materials against light-induced yellowing as well as available paper and cardboard with improved To show resistance to yellowing. According to another Task should be to be used according to the invention Whiteness stabilizers should be as odorless as possible and alone, but especially in combination with others known whiteness stabilizers or coadditives the lowest possible total concentration of additives show high effectiveness. Another task is aimed on providing one or more Composition containing whiteness stabilizers, their Use in the bulk of the fiber or in an agent for impregnation or coating, such as sizing or a so-called dash, the fibrous material to a high degree of whiteness stabilization.

These tasks, as well as further tasks, as they result from the further description, are solved by the invention defined in the claims. According to the invention, a whiteness stabilizer from the series of (i) thiols, which has at least one aliphatically or cycloaliphatically bound thiol group and additionally at least one further hydrophilic group from the series -OH, -NH ₂ , -NHR ¹ , -NR ¹ R ² , where R ¹ and R ^{2 are} C ₁ - to C ₄ -alkyl or C ₂ to C ₄ -hydroxyalkyl, such as hydroxethyl and dihydroxypropyl, C ₂ - to C ₄ -alkanoyl- or - Hydroxyalkanoyl, or together represent cycloalkyl, have -COOH, -SO ₃ H and -PO ₃ H ₂ and salts of the acid and base function, (ii) thiols which have at least one aliphatically or cycloaliphatically bound thiol group and additionally have at least one CC double bond (iii) thiols which have at least one thiol group bonded to a heteroaromatic, and (iV) di- and polysulfides with at least one heteroaromatic bonded to the di / polysulfide group, where thioglyceri n, dithiothreitol mercaptoacetic acid, 2- and 3-mercaptopropionic acid, and their salts are excluded as whiteness stabilizers.

Under the term "lignin-containing fibrous materials" all materials are understood which are essential Contain a component containing a lignin fiber. at the fibrous materials are in particular Lignin-containing wood materials, however, are also lignin-containing ones Pulp accessible to the process of the invention. A Stabilization of the degree of whiteness and thus prevention of Yellowing is especially so-called high-yield wood pulp, which are thermomechanical (TMP) or chemothermomechanical (CTMP) or by stone grinding (SGW) be obtained of technical importance. Both mentioned raw materials are inexpensive Raw materials, which with sufficient whiteness stabilization, sowhol in medium quality papers as well high quality paper and cardboard use can find. The method according to the invention is suitable also in a special way to stabilize the whiteness of bleached wood pulp, which without stabilization in tend to yellowing in a special way.

According to the yellowing resistance lignin-containing fibrous materials as well as those made from them Increase materials and thus stabilize the whiteness, when a thiol compound according to the invention is effective Quantity in the manufacture of the fibrous material is used. The amount used depends on the desired degree of stabilization and depending on whether and in what extent other whiteness stabilizers and / or Co-additives in the manufacture of the fibrous material be used. The amount used is usually present Thio compound according to the invention in the range from 0.01 to 5 % By weight, preferably 0.1 to 3% by weight and particularly preferably 0.5 to 2 wt .-%, each based on the dry fiber.

In the whiteness stabilizers according to the invention from Group (i) are thiols, which are at least an aliphatic or cycloaliphatic bond Thiol group and additionally at least one demanding have hydrophilic group. Such thiols can have different structures, such as:

Mercapto alcohols of the general formula (HS) _m X (OH) _n , wherein X is an optionally alkyl-substituted cycloaliphate, a linear or branched hydrocarbon radical having 4 to 20 C atoms, in particular 5 to 8 C atoms, and m and n for a whole Number from 1 to 5. Examples are di-, tri- and tetrathiopentites and hexites.

Mercapto alcohols of the general formula (HS) _m Y (OH) _n , in which Y represents a cycloaliphatic, linear or branched hydrocarbon radical with a total of one radical interrupted by a -O-, -S-, -NH or N-alkyl bridge 4 to 20 carbon atoms and m and n have the abovementioned meaning. Examples are reaction products of polyhydric alcohols with ethylene sulfide or a mercaptoalkyl halide, with at least one hydroxyl group remaining on the hydrocarbon radical.

Mercapto alcohols of the general formula (HS (CH ₂ ) _p -COO) _m Z (OH) _n ,, in which Z has the meaning of X or Y or represents a polymeric hydrocarbon chain, m and n has the aforementioned meaning or in the case of a polymeric skeleton can also far exceed the values mentioned and p stands for 1 or 2, where the mercapto group can be bonded internally or terminally. It is preferably an ester of a polyhydric alcohol, such as ethylene glycol, di-, tri- and 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 mercaptoacetic acid (= thioglycolic acid) - and 3-mercaptopropionic acid, mono- and dimercaptosuccinic acid. The polyhydric alcohol can also be partially esterified with a mercaptocarboxylic acid other than the aforementioned. The polymeric alcohols which are esterified with a mercaptocarboxylic acid are, for example, an oligosaccharide or polysaccharide, such as starch, or polyvinyl alcohol.

Particularly suitable mercapto alcohols of the aforementioned Kind are the di- or triester of pentaerythritol with Mercaptoacetic acid or 1 or 2-mercaptopropionic acid, in particular pentaerytritol trithiol glycolate, and the Di-, tri- or tetraester of a pentitol or hexitol, especially sorbitol tetrathioglycolate. It was found, that such compounds have a much better effect have as a whiteness stabilizer similar to previously known structured connections, but not free ones Have more hydroxyl group.

Mercaptoamines, which act as a hydrophilic group (s) as a hydrophilic group (s) on a linear, cycloaliphatic or branched, carbon skeleton, which can be interrupted once or several times by -O-, -S-, -NH- or N-alkyl, also have a stabilizing effect Contain NH ₂ -, NHR ¹ - or NR ¹ R ² group, where R ¹ and R ^{2 may be the} same or different and stand for a lower alkyl group, such as methyl, ethyl, propyl, hydroxyethyl, hydroxypropyl or dihydroxypropyl or be connected to one another can. Examples are N-mercaptoethyl-diethylenetriamine and N-mercatoethyldiethanolamine, and salts of these amines.

Thiols with an acid function as a hydrophilic group exemplary mercapto-succinic acid, Dimercaptosuccinic acid, mercaptopropanesulfonic acid, Mercaptoethylaminomethanphosphonsäure. Are also effective Salts, especially alkali salts, of the acid mentioned.

A particularly preferred group of thiols from the group (i) Mercaptoamino acids, such as in particular cysteine, are N-acylated Mercaptoamino acids such as acetylcysteine and diund Oligopeptides with at least one amino acid containing mercapto groups. A particularly good one Whiteness stabilizer, which is also completely odorless and is particularly effective with costabilitors, that is Tripeptide glutathione (γ-glutamylcysteine glycine).

It has been found that the anti-yellowing effect of mercapto compounds by additionally at least one olefinic CC double bond is increased (group (ii)). These are preferably compounds which have a Have ally structure. Examples are esters of Allyl alcohol or cinnamon alcohol with a mercaptocarboxylic acid with 2 to 4 carbon atoms, such as thioglycolic acid, thiolactic acid and mercaptosuccinic acid.

Surprisingly, thiols which contain at least one mercapto group on a heteroaromatic have proven to be effective yellowing inhibitors (group (iii)). The heteroaromatics are 5- and 6-membered heteroaromatics, optionally with a fused other aromatic or heteroaromatic ring system. They have one, two or three heteroatoms from the O, S and N series, rings with two or three heteroatoms being preferred, such as from the series s-triazine, thiadiazole, thiazole, diazole. In addition to at least one mercapto group, such heteroaromatics optionally also contain one or two amino or alkylated amino groups, alkyl mercapto or alkoxy groups. Monomercapto-diamino-s-triazines and dimercapto-amino-triazine are particularly preferred, it being possible for amino groups to be substituted by one or two C ₁ -C ₃ -alkyl groups or allyl groups or to be part of a five- or six-membered ring. Examples are: 2-mercapto-4-allylamino-6-diethylamino-s-triazine, 2,4-dimercapto-6-allylamino-s-triazine and 2-mercapto-4-ethylamino-6-morpholino-s-triazine. Finally, trimercapto-s-triazine, in particular in the form of a mono-, di- and trialkali salt, also stabilizes the whiteness. The mercaptotriazine compounds can be obtained in a manner known per se by stepwise reaction of cyanuric chloride with one or two amines and sodium hydrogen sulfide.

Whiteness stabilizers of group (iv) contain one or multiple di- or polysulfide groups on one Heteroaromatics of the type already mentioned or between two heteroaromatics. Be among the polysulfide groups also understood tri- and tetrasulfides. The second function of a polysulfide can be replaced by hydrogen or alkali metal, or be saturated by oligomerization.

Examples are 2,4-di-polysulfido-6-diethylamino-s-triazine, bis-2-methylamino-1,3,4-thiadiazin-5-yl-disulfide and bis- [2,4-di (dialkylamino) - triazin-6-yl] tetrasulfide. The preparation of the polysulfidotriazine takes place, for. B. by reacting 2-diethylamino-4,6-dimercapto-s-triazine with S ₂ Cl ₂ in petroleum ether; the thiadiazinyl disulfide can be obtained by oxidation of the methylamino-mercapto-1,3,4-thiadiazole with H ₂ O ₂ , and the said tetrasulfide by reaction of the corresponding bis (dialkylamino) triazinylmercapto compound with S ₂ Cl ₂ .

The effect to be used according to the invention Whiteness stabilizers with one or more thiol groups or di- / polysulfide groups can be through the Use of known whiteness stabilizers or Increase costabilizers. This is about Substances from the series of light stabilizers, in particular those from the series of sterically hindered nitroxides and Hydroxylamines and salts thereof (= HALS stabilizers), UV absorbers, Antioxidants, fluorescent brighteners, Radical scavengers, metal deactivators, phosphites, aromatic sulfides and other reducing agents than Thiols.

The HALS light stabilizers are Compounds as exemplified in WO 99/05108 and U.S. Patents 5,496,875 and 6,080,864. Suitable compounds are e.g. 1-oxyl-2,2,6,6-tetramethyl-4-hydroxypiperidine; 1-hydroxy-2,2,6,6-tetramethyl-4-hydroxypiperidinium chloride or generic carboxylic acid salt such as tetra (1-hydroxy-2,2,6,6-tetramethyl-4-hydroxypiperidinium) ethylenediaminetetraacetate; 1-oxyl-2,2,6,6-tetramethyl-4-alkyloxypiperidin; Octadecyl-2,2,6,6-tetramethyl-4-piperidinylcarbonat. The amount used such stabilizers are conveniently located in Range from 0.01 to 2% by weight. combinations Thiols according to the invention, in particular those from the Group (i), such as polyvalent mercaptocarboxylic acid esters Alcohols, amino acids containing thiol groups or Oligopeptides, with HALS light stabilizers lead to whiteness stabilization to a synergistic effect, so the total amount of stabilizers is reduced or the effectiveness by means of a small addition of a HALS stabilizer, such as 0.02 to 0.2% by weight can be increased.

worin bedeuten:

R¹: H, (C₁-C₁₂)-Alkanoyl, insbesondere Acetyl, Propionyl, n-Butanoyl; (C₁-C₁₂)Alkoxycarbonyl, insbesondere -COOCH₃, -COOC₂H₅,

R²: (C₁-C₁₂)-Alkyl, linear oder verzweigt, insbesondere Methyl, Ethyl, n-Propyl, n-Butyl, i-Propyl

Ar-OH: Hydroxysubstituierter Arylrest, wobei mindestens eine Hydroxylgruppe in ortho- oder para-Stellung des an der olefinischen Doppelbindung gebundenen Aromaten gebunden ist, zusätzlich weitere Substituenten, wie Alkyl, insbesondere Methyl, Ethyl, Propyl, n-Butyl, i-Propyl, sek-Butyl, tert.-Butyl, Alkoxy, insbesondere Methoxy und Ethoxy, Phenyl, p(o)-Hydroxyphenyl, Benzoyl, -COOH und SO₃H am Aromaten gebunden sein können und wobei Ar für den Benzol- oder Naphthalinring steht.

The UV absorbers are known substances from the series of benzotriazoles and benzophenones, such as 3-tert-butyl-4-hydroxy-5- (2H-benzotriazol-2-yl) hydrocinnamic acid and 2- (2- hydroxy-3,5-di-tert-butylphenyl) -2H-benzotriazole; 2,4-dihydroxybenzophenone and 2,2-dihydroxy-4,4-dimethoxy-5,5-disulfobenzophenone di-Na salt. Another class of UV absorbers which, in the absence of whiteness stabilizers according to the invention, are suitable for whiteness stabilization of lignin-containing fibrous materials are substances with the structural element of the general formula:

in which mean:

R ¹ : H, (C ₁ -C ₁₂ ) alkanoyl, especially acetyl, propionyl, n-butanoyl; (C ₁ -C ₁₂ ) alkoxycarbonyl, in particular -COOCH ₃ , -COOC ₂ H ₅ ,

R ² : (C ₁ -C ₁₂ ) alkyl, linear or branched, in particular methyl, ethyl, n-propyl, n-butyl, i-propyl

Ar-OH: Hydroxy-substituted aryl radical, where at least one hydroxyl group is bonded in the ortho or para position 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, sec-butyl, tert-butyl, alkoxy, in particular methoxy and ethoxy, phenyl, p (o) -hydroxyphenyl, benzoyl, -COOH and SO ₃ H can be bound to the aromatic and where Ar stands for the benzene or naphthalene ring.

3-Methoxy-4-hydroxybenzylidene malonic acid esters are particularly suitable and 3- (3-methoxy-4-hydroxybenzylidenpentane-2,4-dione.

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

Phosphites and phosphonites, especially sterically hindered Compounds such as tris (2,4-di-tert-butylphenyl) phosphite, support the degree of whiteness stabilization as Peroxide and radical scavengers work.

Various hydrazine derivatives, such as isophthaloyl dihydrazide and N, N-bis (salicyloyl) hydrazine are metal deactivators effective. Another class are complexing agents from the Series of citrates, gluconates, keto acids, Aminocarboxylic acids such as EDTA, DTPA and phosphonates such as Hydroxyethane diphosphonate (HEDP).

The fluorescent brighteners are in particular to known substances from the series 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, Polyvinyl pyrrolidone and polytetrahydrofuran are suitable Costabilatoren.

One or more are particularly preferred thiols or di- / polysulfides according to the invention in combination with a HALS light stabilizer or other radical scavenger and a UV absorber from the series of benzotriazoles or Benzophenone and optionally additionally or alternatively an antioxidant, especially a sterically hindered one Phenol, used because it has a synergistic effect comes into its own. Examples of particularly effective ones Combinations are: glutathione or sorbitol tetrathioglycolate, 2,2,6,6-tetramethyl-4-hydroxypiperidine N-oxide or a derivative thereof and 2- (2-hydroxyphenyl) benzotriazole.

One or more to be used according to the invention Whiteness stabilizers of the thiol or di / polysulfide series or a combination of these compounds with one or more costabilizers from the range of The aforementioned substance classes can be in different places the manufacturing process of the fibrous material for Get involved. It is possible the one or the Whiteness stabilizers and costabilizers individually or in Form of a composition of the mass of the pulp, the e.g. is in the form of a pulp. The addition is e.g. before, during or after an eventual carried out bleaching stage or during dewatering of the fibrous material possible.

An alternative and most preferred Embodiment is the whiteness stabilizer or one contained composition in the form of a solution or Suspension on the at least partially drained Fiber material sprayed on. This spraying process then close at the paper and Carton making known sizing and / or Coating levels.

According to a further preferred alternative, the whiteness stabilizer to be used according to the invention or a composition containing it is added to the medium used for sizing or coating the paper or cardboard and applied to the fiber material with it.
It has been found that a substantial increase in the yellowing-inhibiting effect of the whiteness stabilizers to be used according to the invention and the composition containing them is achieved by applying a pigment-containing, in particular titanium dioxide-containing coating after the whiteness stabilizer has been applied, for example by impregnation or together with the application of glue. According to a particularly preferred embodiment, the whiteness stabilizer (s) and optionally costabilizer (s) are applied to the fibrous material together with titanium dioxide and possibly other components of a size or coating and processed in a manner known per se to form the finished paper or cardboard.

Another object of the invention is a whiteness-stabilized lignin-containing fibrous material, especially paper and cardboard made from mechanically produced Wood pulp or high-yield pulp, which are bleached or can be unbleached, which is a whiteness stabilizer from the series of the thiols to be used according to the invention, Contains di- or polysulfides of groups (i) to (iv). Here, the whiteness stabilizer can both Mass as well as in a sizing or coating or in a surface layer of the impregnation Fibrous material are.

According to a particularly preferred embodiment of the whiteness-stabilized lignin-containing fibrous material according to the invention, it contains a coating - this can be sizing or a coating with a coating color which contains titanium dioxide. A TiO ₂ content in the range from 0.1 to 5% by weight, based on the dried coating, leads to a significant increase in the resistance to yellowing.

As in the description of the method according to the invention has been detailed, except for one or several whiteness stabilizers according to the invention also other known whiteness stabilizers and / or Costabilizers in the bulk of the fibrous material or contained in a sizing or coating on this his.

Another object of the invention is directed to a Composition, which at least one of the Whiteness stabilizers to be used according to the invention the group (i) to (iv) in an aqueous, organic or aqueous-organic sprayable or coatable contains liquid or pasty medium. Preferably the composition contains one or more of the above described preferred stabilizers. According to one contains particularly preferred embodiments Composition additionally one or more others Whiteness stabilizers / costabilizers from the range of Radical scavengers, such as HALS light stabilizers, antioxidants, UV absorbers, reductants, fluorescent brighteners, Metal deactivators, phosphites and aromatic sulfides. According to a particularly preferred embodiment, contains the composition the combination of one whiteness stabilizer according to the invention, a HALS light stabilizer and / or a UV absorber and / or a Antioxidant. Examples of such compositions are previously mentioned. The expediently contains the Composition of at least one of the invention Whiteness stabilizer, a HALS light stabilizer and a UV absorber in a weight ratio of 1 to (0.02 to 0.5) to (0.2 to 2), especially 1 to (0.05 to 0.2) to (0.5 to 2). With a preferred composition is a coating color for coating a Fiber material. One particularly preferably contains such coating color in addition to usual basic ingredients a combination of for whiteness stabilization at least one whiteness stabilizer according to the invention, at least one UV absorber and at least one Radical scavengers.

Particularly preferred compositions contain, besides at least one whiteness stabilizer according to the invention additionally titanium dioxide. Compositions for Sizing or a final stroke can be used additionally contain usual sizing components or Binders and other inorganic pigments, Additives and dispersing agents.

The invention brings a multitude to the professional world other highly effective whiteness stabilizers for Prevention of yellowing containing lignin Fibrous materials, such as paper and cardboard in particular made available. Let the whiteness stabilizers alone, but preferably in combination with known whiteness stabilizers and / or costabilizers apply, whereby synergistic effects are achieved. A The yellowing resistance is further increased by the additional use of titanium dioxide in the sizing or in one stroke. The objects according to the invention make it possible to produce mechanically produced fibers Manufacture high quality paper and cardboard, since the risk of light-induced yellowing from the Use of whiteness stabilizers according to the invention is decisive is reduced.

The invention is illustrated by the following examples clarified.

Examples

1. Einzelsubstanzen Die in Tabelle 1 angegebenen Substanzen wurden in Form einer Lösung auf das Papier aufgetragen. Die Auftragsmenge betrug 1 Masse-% auf den Zellstoff berechnet. Nach dem Trocknen wurde bestrahlt. Bestrahlungsdauer 10h im Xenontestgerät, Stufe 2. Bestimmt wurde der Weißgrad (WG) (%) in Zeitabhängigkeit; hieraus ergibt sich der Weißgradverlust als Differenz (= dWG) des Weißgrades vor (=WG₀) und nach (WG_10h) der Bestrahlung oder als relativer Weißgradabfall dWG·100/WG₀.. Nummer Stabilisator WG₀(%) vor Bestrahlung WG₁₀ (%) nach 10h WG₀ - WG₁₀ VB 1 kein 86 55 31 B 1 2-Diallylamino-4-(3'-Methoxypropyl)amino-6-mercapto-1,3,5-triazin 88 67 21 B 2 2-N-piperidino-4-Ethylamino-6-mercapto-1,3,5-trazin 87 65 22 B 3 2,2'-Bis-(5-Methylamino-1,3,4-thiadiazolyl)disulfid 81 61 20 VB 2 2,2,6,6-Tetramethyl-4-hydroxypiperidin-N-oxid
(ist gefärbt!) 78 56 22 B 4 Sorbitoltetrathioglycolat 83 58 25 B 5 Pentaerythritoltriatiolglykolat 83 58 25 VB 3 Pentaerythrittetrathioglykolat 86 54 32 Die Beispiele 1 bis 5 zeigen die gute Wirkung erfindungsgemäßer Thiole. Die Wirkung ist gleich oder besser als jene des HALS-Stabilisators des Vergleichsbeispiels VB 2. Der Vergleich des Beispiels 5 mit Vergleichsbeispiel VB 3 zeigt den unerwarteten Einfluss der zusätzlichen Hydroxylgruppe.

2. Kombinationen Untersucht wurden Kombinationen aus einem erfindungsgemäßen Weißgradstabilisator(WGS) gemäß der Tabelle 2a und b (1 Gew.-%), dem HALS-Lichtstabilisator (Radikalfänger = RF) 2,2,6,6-Tetramethyl-4-hydroxypiperidin-N-oxid (0,1 Gew.-%) und dem UV-Absorber (UV) 2-(2-Hydroxyphenyl)-benzotriazol (1 Gew.-%). Die Anwendung und Testung erfolgten analog wie unter 1 beschrieben. In Tabelle 2 b ist der relative Weißgradabfall (%) nach 10 h bzw. 20 h Bestrahlung angegeben Nummer Kombination WG₀ (%) vor Bestrahlung WG₁₀ (%) nach 10h WG₀ - WG₁₀ VB 1 ohne WGS, RF und UV 86 55 31 VB 4 Ohne WGS;
mit RF und UV 87 68 19 B 6 Sorbitol-tetrakisthioglykolat und RF und UV 87 75 12 Nummer Kombination (WG_t-WG₀) · 100 / WG₀ nach 10 h (%) nach 20 h (%) VB 1 ohne WGS, RF und UV 33 42 VB 4 ohne WGS, mit RF und UV 22 31 B 6 Sorbitol-tetrakisthioglycolat mit RF und UV 14 22 B 7 Cinnamyl-mercaptoglykolat mit UV und RF 19 26,5

3. Kombinationen und TiO₂ im Strich Untersucht wurden Kombinationen, enthalten erfindugsgemäße Weißgradstabilisatoren (WGS) den unter 2. genannten UV-Absorber (UV) und Radikalfänger (RF). Einsatzmenge, soweit vorhanden, wie zuvor 1 % WSG, 0,1 %RF, 1 % UV, jeweils bezogen auf den Faserstoff). Nach dem Auftragen der jeweiligen Stabilisatorzusammensetzung und Trocknung wurde ein TiO₂-enthaltender Strich aufgetragen.Zusammensetzung der Streichfarbe: 5 Teile anorganisches Pigment davon 4 Teile Calciumcarbonat, 0,9 Teile Kaolin, 0,1 Teile Titandioxid, 3,5 Teile Bindemittel, 3,5 Teile Wasser, Dispergierhilfsmittel. Strichdicke 12 g/m².Die Ergebnisse folgen aus der Tabelle 3 a: Stabilisatorfreies Vergleichsbeispiel VB 5 stabilisatorfreies Papier wurde nur mit der angegebenen Streichfarbe gestrichen. Stabilisatorfreies Papier. Das Papier gemäß Beispiel 8 enthielt unter dem Strich eine Imprägnierung mit Glutathion (1 Gew.-%, bezogen auf Farbstoff), jenes des Beispiels 9 zusätzlich RF 0,1 Gew.-% und UV (1 Gew.-%). Der Vergleich zeigt die Wirkungssteigerung beim Wechsel vom strichfreien, nicht stabilisierten System (VB 1) zum System mit einem TiO₂haltigen Strich (VB 5), zum System mit Glutathion unter einem TiO₂-haltigen Strich (B 8) und schließlich einen TiO₂-haltigen Strich auf einem Papier mit einer Glutathion, RF und UV enthaltenden Imprägnierung. Nummer Stabilisator; Strich WG₀ (%) WG₁₀ (%) nach 10h WG₀ - WG₁₀ (%) VB 1 kein Stabilisator, kein TiO₂ 86 55 31 VB 5 kein Stabilisator, aber Strich mit TiO₂ 88 68 20 B 8 Glutathion + Strich mit TiO₂ 85 72 13 B 9 Glutathion und RF und UV und Strich mit TiO₂ 85 80 5 Die Beispiele B 10 und B 11 in Tabelle 3 bverdeutlichen den Einfluss von TiO₂ im Strich. Die Strichzusammensetzung enthielt in B 10 kein TiO₂ aber 1 Teil Kaolin, in Beispiel 11 0,7 Teile Kaolin und 0,3 Teile TiO₂; die übrigen Bestandteile entsprachen der zuvor beschriebenen Strichzusammensetzung. Nummer Stabilisator; Strich WG₀(%) WG₁₀ (%) nach 10h WG₀ - WG₁₀ (%) B 10 Pentaerythrit-tris-thioglykolat und RF und UV und Strich ohne TiO₂ 83,5 77,5 6 B 11 Pentaerythrit-tris-thioglykolat und RF und UV und Strich mit TiO₂ 86,5 82,5 4 Die Beispiel 10 und 11 verdeutlichen den Einfluss von TiO₂ im Strich.

A TCF-bleached Aspen-CTMP pulp with 86% whiteness was used as the paper base

1. Individual substances The substances listed in Table 1 were applied to the paper in the form of a solution. The amount applied was 1% by mass calculated on the pulp. After drying, it was irradiated. Irradiation time 10h in the xenon test device, level 2. The whiteness (WG) (%) was determined as a function of time; this results in the loss of whiteness as the difference (= dWG) between the whiteness before (= WG ₀ ) and after (WG _10h ) the irradiation or as a relative drop in whiteness dWG · 100 / WG ₀ .. number stabilizer WG ₀ (%) before irradiation Flat share ₁₀ (%) after 10h WG ₀ - WG ₁₀ VB 1 no 86 55 31 B 1 2-diallylamino-4- (3'-methoxypropyl) amino-6-mercapto-1,3,5- triazine 88 67 21 B 2 2-N-piperidino-4-ethylamino-6-mercapto-1,3,5- trazine 87 65 22 B 3 2,2'-bis (5-methylamino-1,3,4-thiadiazolyl) disulfide 81 61 20 VB 2 2,2,6,6-tetramethyl-4-hydroxypiperidine N-oxide
(is colored!) 78 56 22 B 4 Sorbitoltetrathioglycolat 83 58 25 B 5 Pentaerythritoltriatiolglykolat 83 58 25 VB 3 pentaerythritol tetrathioglycolate 86 54 32 Examples 1 to 5 show the good effect of thiols according to the invention. The effect is the same or better than that of the HALS stabilizer of comparative example VB 2. The comparison of example 5 with comparative example VB 3 shows the unexpected influence of the additional hydroxyl group.

2. Combinations Combinations of an inventive whiteness stabilizer (WGS) according to Tables 2a and b (1% by weight), the HALS light stabilizer (radical scavenger = RF), 2,2,6,6-tetramethyl-4-hydroxypiperidine N-oxide (0.1% by weight) and the UV absorber (UV) 2- (2-hydroxyphenyl) benzotriazole (1% by weight). The application and testing was carried out analogously to that described under 1. Table 2 b shows the relative drop in whiteness (%) after 10 h and 20 h irradiation number combination WG ₀ (%) before irradiation Flat share ₁₀ (%) after 10h WG ₀ - WG ₁₀ VB 1 without WGS, RF and UV 86 55 31 VB 4 Without WGS;
with RF and UV 87 68 19 B 6 Sorbitol tetrakisthioglycolate and RF and UV 87 75 12 number combination (WG _t -WG ₀ ) 100 / WG ₀ after 10 h (%) after 20 h (%) VB 1 without WGS, RF and UV 33 42 VB 4 without WGS, with RF and UV 22 31 B 6 Sorbitol tetrakisthioglycolate with RF and UV 14 22 B 7 Cinnamyl mercaptoglycolate with UV and RF 19 26.5

3. Combinations and TiO ₂ in the Stroke Combinations were investigated which contain whiteness stabilizers (WGS) according to the invention, the UV absorber (UV) and radical scavenger (RF) mentioned under 2. Amount used, if available, as before 1% WSG, 0.1% RF, 1% UV, each based on the fiber). After the application of the respective stabilizer composition and drying, a coating containing TiO _{2 was} applied. 5 parts water, dispersing agent. Line thickness 12 g / m ^2. The results follow from Table 3 a: Stabilizer-free comparative example VB 5 stabilizer-free paper was only coated with the specified coating color. Stabilizer-free paper. The paper according to Example 8 contained an impregnation with glutathione (1% by weight, based on dye), that of Example 9 additionally had RF 0.1% by weight and UV (1% by weight). The comparison shows the increase in effectiveness when changing from the line-free, non-stabilized system (VB 1) to the system with a TiO _2- containing line (VB 5), to the system with glutathione under a TiO _2- containing line (B 8) and finally a TiO ₂ -stroke on a paper with an impregnation containing glutathione, RF and UV. number Stabilizer; stroke Flat share ₀ (%) Flat share ₁₀ (%) after 10h Apartment ₀ - Apartment ₁₀ (%) VB 1 no stabilizer, no TiO ₂ 86 55 31 VB 5 no stabilizer, but streak with TiO ₂ 88 68 20 B 8 Glutathione + line with TiO ₂ 85 72 13 B 9 Glutathione and RF and UV and streak with TiO ₂ 85 80 5 Examples B 10 and B 11 in Table 3 illustrate the influence of TiO ₂ in the line. The coating composition contained no TiO ₂ in B 10 but 1 part kaolin, in example 11 0.7 parts kaolin and 0.3 parts TiO ₂ ; the remaining components corresponded to the line composition described above. number Stabilizer; stroke Flat share ₀ (%) Flat share ₁₀ (%) after 10h Apartment ₀ - Apartment ₁₀ (%) B 10 Pentaerythritol tris thioglycolate and RF and UV and line without TiO ₂ 83.5 77.5 6 B 11 Pentaerythritol tris thioglycolate and RF and UV and line with TiO ₂ 86.5 82.5 4 Examples 10 and 11 illustrate the influence of TiO ₂ in the line.

Claims (23)

A process was found for stabilizing the whiteness of lignin-containing fibrous materials, against light-induced yellowing, comprising the use of a thio compound as a whiteness stabilizer in an amount effective to increase the resistance to yellowing in the production of the fibrous material,
characterized in that as a whiteness stabilizer a compound from the series of (i) thiols which have at least one aliphatically or cycloaliphatically bound thiol group and additionally at least one further hydrophilic group from the series -OH, -NH ₂ , -NHR ¹ , -NR ¹ R ² , where R ¹ and R ^{2 are} C ₁ - to C ₄ -alkyl or C ₂ to C ₄ -hydroxyalkyl, such as hydroxethyl and dihydroxypropyl, C ₂ - to C ₄ -alkanoyl or -hydroxyalkanoyl, or together represent cycloalkyl, -COOH, -SO ₃ H and -PO ₃ H ₂ as well as salts of acid and base function, (ii) thiols which have at least one aliphatically or cycloaliphatically bound thiol group and additionally have at least one CC double bond (iii) thiols which have at least one thiol group bonded to a heteroaromatic, and (IV) di- and polysulfides with at least one heteroaromatic bonded to the di- / polysulfide group uses, with thioglycerol, dithiothreitol mercaptoacetic acid, 2- and 3-mercaptopropionic acid, and their salts are excluded as whiteness stabilizer. Method according to claim 1,
characterized in that the whiteness of materials from essentially mechanically, thermomechanically or chemothermomechanically produced lignin-containing unbleached or bleached fibrous materials, in particular paper or cardboard made from wood pulp, is stabilized. The method of claim 1 or 2,
characterized in that the whiteness stabilizer or a composition containing it is added to the bulk of the fibrous materials or a size or coating color composition to be applied to a fibrous material or a solution or suspension of a composition containing the whiteness stabilizer is sprayed onto the uncoated fibrous material. Method according to claims 1 to 3,
characterized in that , in addition to at least one whiteness stabilizer according to the invention, one or more other whiteness stabilizers and / or one or more costabilizers from the range of UV absorbers, antioxidants, metal deactivators, radical scavengers, fluorescent brighteners, phosphites, reducing agents and aromatic sulfides, in particular containing a combination uses a UV absorber and a radical scavenger. Method according to one of claims 1 to 4,
characterized in that a fibrous material equipped with a whiteness stabilizer according to the invention in the mass, in a surface coating or by means of impregnation is coated with a coating color containing titanium dioxide or a non-finished fibrous material is coated with a coating color containing an inventive whiteness stabilizer and titanium dioxide. Method according to one of claims 1 to 5,
characterized in that the whiteness stabilizer of group (i) is an ester of a polyhydric alcohol from the series consisting of ethylene glycol, di-, tri- and 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 and water-soluble polymeric alcohols , such as in particular polyvinyl alcohol, with a mercaptocarboxylic acid from the series mercaptoacetic acid (= thioglycolic acid), 2- and 3-mercaptopropionic acid, mono- and dimercaptosuccinic acid, wherein at least one hydroxyl group of the polyhydric alcohol is unesterified. Method according to claim 6,
characterized in that a di- or triester of pentaerythritol with mercaptoacetic acid or 1 or 2-mercaptopropionic acid, in particular pentaerythritol trithiol glycol, or a di-, tri- or tetraester of a pentite or hexitol, in particular sorbitol tetrathiogycolate, is used as a whiteness stabilizer. Method according to one of claims 1 to 5,
characterized in that the whiteness stabilizer of group (ii) used is an ester of an alcohol with an allyl structural element, in particular allyl alcohol and cinnamon alcohol, with a mercaptocarboxylic acid having 2 to 4 carbon atoms, preferably cinnamon alcohol thioglycolate. Method according to one of claims 1 to 5,
characterized in that the whiteness stabilizer of group (iii) is a mercapto-s-triazine, mercapto-triazole, mercapto-diazole, mercapto-1,3,4-thiadiazole compound, in particular 2-mercapto-4,6 -diamino-s-trazin, where the amino groups may be the same or different alkyl, cycloalkyl or allyl substituted. Method according to one of claims 1 to 5,
characterized in that the whiteness stabilizer of group (iv) is a compound from the series 2-amino-4,6-bis-polysulfidostiazine, bis-4,6-diamino-s-triazin-2-yl-tetrasulfide or bis- 5-amino-1,3,4-triadiazol-2-yl-di-and tetrasulfide, where the amino groups can each be alkyl, cycloalkyl or allyl substituted. Method according to one of claims 1 to 5,
characterized in that the whiteness stabilizer of group (i) of claim 1 is an amino acid containing thiol groups, especially cysteine, a thiol group-containing N-acylated amino acid, especially N-acetylcysteine, or a thiol group-containing oligopeptide, especially glutathione. Whiteness-stabilized lignin-containing fibrous material, in particular paper and cardboard made from mechanically produced (thermomechanical, chemothermomechanical) wood pulp or high-yield pulp, characterized by the presence of a whiteness stabilizer of thiols, di- and polysulfides according to groups (i) to (iv) of claim 1 in the mass of Fiber material or / and in a layer produced by impregnation, sizing or by means of a coating color. Whiteness-stabilized lignin-containing fibrous material according to claim 12,
characterized in that the fibrous material is a bleached wood pulp or high-yield pulp. Whiteness-stabilized lignin-containing fibrous material, according to claim 12 or 13
characterized in that it has a coating of a titanium dioxide containing sizing or coating color. Whiteness-stabilized lignin-containing fibrous material according to one of claims 12 to 14,
characterized in that it in the mass / or in and produced by impregnating and / or coating layer additionally one or more other whiteness stabilizers and / or costabilizers from the group of radical scavengers, such as HALS light stabilizers (= h indered a mine l ight s tabilizer), UV absorbers, fluorescent brighteners, antioxidants, metal deactivators, reducing agents, phosphites and other aromatic sulfides. Composition containing whiteness stabilizer, characterized in that it contains at least one whiteness stabilizer according to the invention as claimed in claim 1 and preferably as claimed in one of claims 6 to 11 in an aqueous, organic or aqueous-organic sprayable or coatable liquid or pasty medium. A composition according to claim 16,
characterized in that it additionally contains one or more other whiteness stabilizers and / or costabilizers from the radical scavenger series, such as HALS light stabilizers, antioxidants, UV absorbers, reductants, fluorescent brighteners, metal deactivators, phosphites and aromatic sulfides. A composition according to claim 16 or 17,
characterized in that, in addition to a whiteness stabilizer according to the invention, a HALS light stabilizer, in particular 2,2,6,6 tetramethyl-4-hydroxypiperidine-N-oxide, and / or a UV absorber, in particular a 2-hydroxyaryl-benzotriazole, a hydroxybenzophenone or a Contains 2-substituted 3- (hydroxyaryl) acrylic acid ester, and / or an antioxidant from the series of sterically hindered phenols. A composition according to claim 18,
characterized in that it contains a whiteness stabilizer according to the invention, a HALS light stabilizer and a UV absorber in a weight ratio of 1 to (0.02 to 0.5) to (0.2 to 2), in particular 1 to (0.05 to 0.2) to (0.5 to 2). Composition according to one of Claims 16 to 19,
characterized in that it contains a dispersant and / or an organic binder or sizing agent and / or titanium dioxide. Composition according to one of Claims 16 to 20,
characterized in that it is a coating color for coating a fiber material. UV absorber for use to stabilize the whiteness of lignin-containing fiber materials,
characterized by a structural element of the general formula

in which mean:

R ¹ :

H, (C ₁ -C ₁₂ ) alkanoyl, especially acetyl, propionyl, n-butanoyl; (C ₁ -C ₁₂ ) alkoxycarbonyl, in particular -COOCH ₃ , -COOC ₂ H ₅ ,

R ² :

(C ₁ -C ₁₂ ) alkyl, linear or branched, especially methyl, ethyl, n-propyl, n-butyl, i-propyl

Ar-OH:

Hydroxy-substituted aryl radical, where at least one hydroxyl group is bonded in the ortho or para position 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, sec-butyl, tert-butyl, alkoxy, especially methoxy and ethoxy, phenyl, p (o) -hydroxyphenyl, benzoyl, -COOH and SO ₃ H can be bound to the aromatic and where Ar stands for the benzene or naphthalene ring.

UV absorber for use in whiteness stabilization of lignin-containing fibrous materials according to claim 22,
characterized in that it is 3-methoxy-4-hydroxybenzylidenmalonsäuredialkylester, where alkyl is methyl or ethyl.