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

Abstract

Lignin-containing fibrous materials, in particular paper and card, are treated with whiteness stabilizers for the purpose of reducing light-induced yellowing. The whiteness stabilizer are (i) thiols with at least one additional hydrophilic group from the series consisting of OH, NH 2 , NHR 1 m NR 1 R 2 , COOH, SO 3 H and PO 3 H 2 and an amino acid/peptide structure (ii) thiols with a CC double bond (iii) or heteroaromatic thiols and (iv), heteroaromatic disulfides or polysulfides. HALS light stabilizers and/or UV stabilizers are advantageously additionally employed. The stability is increased further by a TiO 2 -containing coat on the fibrous material. Stabilzer compositions and fibrous material stabilized according to the invention, containing a whiteness stabilizer of group (i) to (iv) are also disclosed.

We claim:  
     
         1 . A process for stabilizing the whiteness of a lignin-containing fibrous material against light-induced yellowing, comprising contacting said fibrous material with a thio compound as a whiteness stabilizer in an active amount for increasing the resistance to yellowing during the production of the fibrous material, said thio compound being selected from the group consisting of 
 (i) a thiol which has at least one aliphatically or cycloaliphatically bonded thiol group and additionally at least one further hydrophilic group selected from the group consisting of —OH, —NH 2 , —NHR 1 , —NR 1 R 2 , wherein R 1  and R 2  represent C 1 - to C 4 -alkyl or C 2  to C 4 -hydroxyalkyl, C 2 - to C 4 -alkanoyl- or -hydroxyalkanoyl, or together represent cycloalkyl, or —COOH, —SO 3 H and —PO 3 H 2  and salts of the acid and base function,    (ii) a thiol which contains at least one aliphatically or cycloaliphatically bonded thiol group and additionally at least one CC double bond,    (iii) a thiol which contains at least one thiol group bonded to a heteroaromatic, and    (iv) a di- and polysulfide with at least one heteroaromatic bonded to the di-/polysulfide group,    with the proviso that thioglycerol, dithiothreitol mercaptoacetic acid, 2- and 3-mercaptopropionic acid, and salts thereof are excluded as the whiteness stabilizer.    
     
     
         2 . The process according to  claim 1 , wherein the fibrous material is selected from the group consisting of substantially mechanically, thermomechanically or chemo-thermomechanically produced lignin-containing unbleached and bleached fibrous substances and mixtures thereof.  
     
     
         3 . The process according to  claim 2  wherein the fibrous material is paper or card from wood pulp.  
     
     
         4 . The process according to  claim 1  further comprising adding said whiteness stabilizer to pulp of the fibrous material or to a size or brush-on color composition to be applied to a fibrous material, or a solution or suspension of a composition comprising the whiteness stabilizer is sprayed on to non-coated fibrous material.  
     
     
         5 . The process according to  claim 2  further comprising adding said whiteness stabilizer to pulp of the fibrous material or to a size or brush-on color composition to be applied to a fibrous material, or a solution or suspension of a composition comprising the whiteness stabilizer is sprayed on to non-coated fibrous material.  
     
     
         6 . Process according to  claim 1  further comprising adding to the fibrous material in addition to said thiol compound whiteness stabilizer or co-stabilizer selected from the group consisting of UV absorber, antioxidant, a metal deactivator, agent which trap free radicals, fluorescent brightener, phosphite, reducing agent and aromatic sulfide.  
     
     
         7 . Process according to  claim 2  further comprising adding to the fibrous material in addition to said thiol compound whiteness stabilizer or co-stabilizer selected from the group consisting of UV absorber, antioxidant, a metal deactivator, agent which trap free radicals, fluorescent brightener, phosphite, reducing agent and aromatic sulfide.  
     
     
         8 . Process according to  claim 4  further comprising adding to the fibrous material in addition to said thiol compound whiteness stabilizer or co-stabilizer selected from the group consisting of UV absorber, antioxidant, a metal deactivator, agent which trap free radicals, fluorescent brightener, phosphite, reducing agent and aromatic sulfide.  
     
     
         9 . The process according to  claim 1  wherein a fibrous material treated with a whiteness stabilizer in the pulp, in a surface coating or by means of impregnation is coated with a brush-on color comprising titanium dioxide, or a non-treated fibrous material is coated with a brush-on color comprising a whiteness stabilizer and titanium dioxide.  
     
     
         10 . The process according to  claim 2  wherein a fibrous material treated with a whiteness stabilizer in the pulp, in a surface coating or by means of impregnation is coated with a brush-on color comprising titanium dioxide, or a non-treated fibrous material is coated with a brush-on color comprising a whiteness stabilizer and titanium dioxide.  
     
     
         11 . The process according to  claim 4  wherein a fibrous material treated with a whiteness stabilizer in the pulp, in a surface coating or by means of impregnation is coated with a brush-on color comprising titanium dioxide, or a non-treated fibrous material is coated with a brush-on color comprising a whiteness stabilizer and titanium dioxide.  
     
     
         12 . The process according to  claim 6  wherein a fibrous material treated with a whiteness stabilizer in the pulp, in a surface coating or by means of impregnation is coated with a brush-on color comprising titanium dioxide, or a non-treated fibrous material is coated with a brush-on color comprising a whiteness stabilizer and titanium dioxide.  
     
     
         13 . The process according to  claim 1  wherein said thiol (i) is an ester of a polyhydric alcohol selected from the group 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, with a mercaptocarboxylic acid selected from the group consisting of mercaptoacetic acid (=thioglycollic acid), 2- and 3-mercaptopropionic acid, mono- and dimercaptosuccinic acid, wherein at least one hydroxyl group of the polyhydric alcohol is non-esterified.  
     
     
         14 . The process according to  claim 2  wherein said thiol (i) is an ester of a polyhydric alcohol selected from the group 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, with a mercaptocarboxylic acid selected from the group consisting of mercaptoacetic acid (=thioglycollic acid), 2- and 3-mercaptopropionic acid, mono- and dimercaptosuccinic acid, wherein at least one hydroxyl group of the polyhydric alcohol is non-esterified.  
     
     
         15 . The process according to  claim 4  wherein said thiol (i) is an ester of a polyhydric alcohol selected from the group 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, with a mercaptocarboxylic acid selected from the group consisting of mercaptoacetic acid (=thioglycollic acid), 2- and 3-mercaptopropionic acid, mono- and dimercaptosuccinic acid, wherein at least one hydroxyl group of the polyhydric alcohol is non-esterified.  
     
     
         16 . The process according to  claim 6  wherein said thiol (i) is an ester of a polyhydric alcohol selected from the group 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, with a mercaptocarboxylic acid selected from the group consisting of mercaptoacetic acid (=thioglycollic acid), 2- and 3-mercaptopropionic acid, mono- and dimercaptosuccinic acid, wherein at least one hydroxyl group of the polyhydric alcohol is non-esterified.  
     
     
         17 . The process according to  claim 9  wherein said thiol (i) is an ester of a polyhydric alcohol selected from the group 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, with a mercaptocarboxylic acid selected from the group consisting of mercaptoacetic acid (=thioglycollic acid), 2- and 3-mercaptopropionic acid, mono- and dimercaptosuccinic acid, wherein at least one hydroxyl group of the polyhydric alcohol is non-esterified.  
     
     
         18 . The process according to  claim 6 , wherein said ester is a di- or triester of pentaerythritol with mercaptoacetic acid or 1 or 2-mercaptopropionic acid, or a di-, tri- or tetraester of a pentitol or hexitol.  
     
     
         19 . The process according to  claim 18  wherein the ester is selected from the group consisting of pentaerythritol trithiolglycollate said sorbitol tetrathioglycollate.  
     
     
         20 . The process according to  claim 1  wherein said thiol compound is an ester of an alcohol with an allyl structural element, with a mercaptocarboxylic acid having 2 to 4 C atoms.  
     
     
         21 . The process according to  claim 20  wherein said ester is cinnamyl alcohol thioglycollate.  
     
     
         22 . The process according to  claim 1  wherein the compound is a mercapto-s-triazine, mercapto-triazole, mercapto-diazole, mercapto-1,3,4-thiadiazole compound, 2-mercapto-4,6-diamino-s-trazine, wherein the amino groups can be substituted by alkyl, cycloalkyl or alkyl.  
     
     
         23 . The process according to  claim 1  wherein the thiol compound is a compound selected from the group consisting of 2-amino-4,6-bis polysulfido-s-triazine, bis-4,6-diamino-s-triazin-2-yl tetrasulfide, bis-5-amino-1,3,4-triadiazol-2-yl di- and tetrasulfide, wherein the amino groups can in each case be alkyl-, cycloalkyl- or allyl-substituted.  
     
     
         24 . The process according to  claim 1  wherein the thiol an amino acid containing thiol groups, an N-acylated amino acid containing thiol groups, or an oligopeptide containing thiol groups.  
     
     
         25 . The process according to  claim 24  wherein the compound is selected from the group consisting of cysterine, N-acetylcysterine and glutathione.  
     
     
         26 . Whiteness-stabilized lignin-containing fibrous material, of mechanically produced, thermomechanically, chemo-thermomechanically wood pulp or high-yield cellulose, containing a whiteness stabilizer selected from the group consisting of the thiols, di- and polysulfides according to groups (i) to (iv) of  claim 1  in at least one of the pulp of the fibrous material and in a layer produced by impregnation, sizing or by a brush-on color.  
     
     
         27 . Whiteness-stabilized lignin-containing fibrous material according to  claim 26 , wherein the fibrous substance is a bleached wood pulp or high-yield cellulose.  
     
     
         28 . Whiteness-stabilized lignin-containing fibrous material according to  claim 26  which has a coating of a size or coating color comprising titanium dioxide.  
     
     
         29 . Whiteness-stabilized lignin-containing fibrous material according to  claim 27  which has a coating of a size or coating color comprising titanium dioxide.  
     
     
         30 . Whiteness-stabilized lignin-containing fibrous material according to  claim 26  further comprising in the pulp and/or in a layer produced by impregnation and/or coating, one or more other whiteness stabilizers and/or co-stabilizers selected from the group consisting of agents which trap free radicals, UV absorbers fluorescent brighteners, antioxidants, metal deactivators, reducing agents, phosphites and other aromatic sulfides.  
     
     
         31 . A composition comprising a whiteness stabilizer, characterized by a content of at least one whiteness stabilizer according to  claim 1 , in an aqueous, organic or aqueous-organic liquid or paste-like medium which can be used for spraying or coating.  
     
     
         32 . A composition comprising a whiteness stabilizer, characterized by a content of at least one whiteness stabilizer according to  claim 13 , in an aqueous, organic or aqueous-organic liquid or paste-like medium which can be used for spraying or coating.  
     
     
         33 . Composition according to  claim 31 , further comprising one or more other whiteness stabilizers and/or co-stabilizers selected from the group consisting of agents which trap free radicals, antioxidants, UV absorbers, reducing agents, fluorescent brighteners, metal deactivators, phosphites and aromatic sulfides.  
     
     
         34 . Composition according to  claim 31  further comprising a HALS light stabilizer, and/or an antioxidant from the series consisting of sterically hindered phenols.  
     
     
         35 . The composition according to  claim 34  containing 2,2,6,6 tetramethyl-4-hydroxypiperidine N-oxide, and/or a 2-hydroxyaryl-benzotriazole a hydroxybenzophenone or a 2-substituted 3-(hydroxyaryl)acrylic acid ester.  
     
     
         36 . Composition according to  claim 34  additionally comprising 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).  
     
     
         37 . Composition according to  claim 31  characterized in that it comprises a dispersing agent and/or an organic binder or sizing agent and/or titanium dioxide.  
     
     
         38 . Composition according to  claim 31  characterized in that it is a brush-on color for coating a fibrous material.  
     
     
         39 . UV absorbers for use for stabilizing the whiteness of lignin-containing fibrous materials, characterized by a structural element of the formula  
       
         
           
           
               
               
           
         
       
       wherein: 
 R 1 : denotes H, (C 1 -C 12 )-alkanoyl, in particular acetyl, propionyl, n-butanoyl; (C 1 -C 12 ) alkoxycarbonyl, in particular —COOCH 3 , —COOC 2 H 5 ,  
 R 2 : denotes (C 1 -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 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 bonded to the aromatic, and wherein Ar represents the benzene or naphthalene ring.  
 
     
     
         40 . UV absorbers for use for stabilizing the whiteness of lignin-containing fibrous substances according to  claim 39  characterized in that it is a 3-methoxy-4-hydroxybenzylidene-malonic acid dialkyl ester, wherein alkyl represents methyl or ethyl.