Method for Preparing White Paper

Abstract

Object of the invention is the method for preparing white paper which comprises adding to the pulp mass an aqueous formulation comprising a) at least one optical brightener of formula (I) in which the anionic charge on the brightener is balanced by a cationic charge composed of one or more identical or different cations selected from the group consisting of hydrogen, an alkali metal cation, alkaline earth metal, ammonium, ammonium which is mono-, di-, tri- or tetrasubstituted by a C 1 -C 4 linear or branched alkyl radical, ammonium which is mono-, di-, tri- or tetrasubstituted by a C 1 -C 4 linear or branched hydroxyalkyl radical, ammonium which is, di-, tri- or tetrasubstituted by a mixture of C 1 -C 4 linear or branched alkylradical and linear or branched hydroxyalkyl radical or mixtures of said compounds, wherein R 1 and R 1 ′ may be the same or different, and each is hydrogen, C 1 -C 4 linear or branched alkyl, C 2 -C 4 linear or branched hydroxyalkyl, CH 2 CO 2 − , CH 2 CH 2 CONH 2 or CH 2 CH 2 CN, R 2 and R 2 ′ may be the same or different, and each is C 1 -C 4 linear or branched alkyl, C 2 -C 4 linear or branched hydroxyalkyl, CH 2 CO 2 − , CH(CO 2 − )CH 2 CO 2 − , CH(CO 2 − )CH 2 CH 2 CO 2 − , CH 2 CH 2 SO 3 − , CH 2 CH 2 CO 2 − , CH 2 CH(CH 3 )CO 2 − , benzyl, or R 1 and R 2 and/or R 1 ′ and R 2 ′, together with the neighboring nitrogen atom signify a morpholine ring; R 3 signifies hydrogen, —CO 2 − or —SO 3 − and p is 0, 1 or 2, and b) at least one shading dye of formula (II) in which R 4 signifies H, methyl or ethyl, R 5 signifies paramethoxyphenyl, methyl or ethyl, M signifies a cation selected from the group consisting of hydrogen, an alkali metal cation, alkaline earth metal, ammonium, ammonium which is mono-, di-, tri- or tetrasubstituted by a C 1 -C 4 linear or branched alkyl radical, ammonium which is mono-, di-, tri- or tetrasubstituted by a C 1 -C 4 linear or branched hydroxyalkyl radical, ammonium which is, di-, tri- or tetrasubstituted by a mixture of C 1 -C 4 linear or branched alkylradical and linear or branched hydroxyalkyl radical or mixtures of said compounds, c) optionally one or more auxiliaries and d) water.

1 . A method for preparing white paper which comprising the step of adding to the pulp mass an aqueous formulation comprising:
 a) at least one optical brightener of formula (I)   
       
         
           
           
               
               
           
         
         
           the anionic charge on the at least one optical brightener is balanced by a cationic charge including of one or more identical or different cations selected from the group consisting of hydrogen, an alkali metal cation, alkaline earth metal, ammonium, ammonium that is mono-, di-, tri- or tetrasubstituted by a C 1 -C 4  linear or branched alkyl radical, ammonium that is mono-, di-, tri- or tetrasubstituted by a C 1 -C 4  linear or branched hydroxyalkyl radical, ammonium that is di-, tri- or tetrasubstituted by a mixture of C 1 -C 4  linear or branched alkylradical and linear or branched hydroxyalkyl radical and mixtures thereof, and 
         
         b) at least one shading dye of formula (II) 
       
       
         
           
           
               
               
           
         
         c) optionally one or more auxiliaries and 
         d) water. 
       
     
     
         2 . A method according to  claim 1 , wherein in the at least one optical brightener of formula (I) R 3  is —SO 3   −  and p is 1 and the —SO 3   −  group is in the 4-position of the phenyl ring. 
     
     
         3 . The method according to  claim 1 , wherein in the at least one optical brightener formula (I), R 3  is —SO 3   − , p is 2 and the —SO 3   −  groups are in the 2,5-positions of the phenyl ring. 
     
     
         4 . The method according to  claim 1 , wherein in the at least one optical brightener of formula (I), R 3  is —CO 2hu − , p is 1 and the —CO 2   −  group is in the 2 or 4 position of the phenyl ring. 
     
     
         5 . The method according to  claim 1 , wherein in the at least one optical brightener of formula (I) the anionic charge on the at least one optical brightener is balanced by a cationic charge including one or more identical or different cations selected from the group consisting of hydrogen, an alkali metal cation, alkaline earth metal, ammonium that is mono-, di-, tri- or tetrasubstituted by a C 1 -C 4  linear or branched hydroxyalkyl radical, ammonium which that is, di-, tri- or tetrasubstituted by a mixture of C 1 -C 4  linear or branched alkylradical and linear or branched hydroxyalkyl radical and mixtures thereof,
 and   R 1  and R 1 ′ are the same or different, and each is hydrogen, C 1 -C 4  linear or branched alkyl, C 2 -C 4  linear or branched hydroxyalkyl, CH 2 CO 2   − , CH 2 CH 2 CONH 2  or CH 2 CH 2 CN, and   R 2  and R 2 ′ are the same or different, and each is C 1 -C 4  linear or branched alkyl, C 2 -C 4  linear or branched hydroxyalkyl, CH 2 CO 2   − , CH(CO 2 )CH 2 CO 2  or CH 2 CH 2 SO 3   − ,   R 3  is hydrogen, —CO 2   −  or —SO 3   −  and   p is 0, 1 or 2.   
     
     
         6 . The method according to  claim 1 , wherein in the at least one optical brightener of formula (I) the anionic charge on the at least one optical brightener is balanced by a cationic charge including one or more identical or different cations selected from the group consisting of Li + , Na + , K + , Ca 2+ , Mg 2+ , ammonium that is mono-, di-, tri- or tetrasubstituted by a C 1 -C 4  linear or branched hydroxyalkyl radical, ammonium that is, di-, tri- or tetrasubstituted by a mixture of C 1 -C 4  linear or branched alkylradical and linear or branched hydroxyalkyl radical and mixtures thereof,
 R 1  and R 1 ′ are the same or different, and each is hydrogen, methyl, ethyl, propyl, α-methylpropyl, β-methylpropyl, β-hydroxyethyl, β-hydroxypropyl, CH 2 CO 2   − , CH 2 CH 2 CONH 2  or CH 2 CH 2 CN,   R 2  and R 2 ′ are the same or different, and each is methyl, ethyl, propyl, α-methylpropyl, β-methylpropyl, β-hydroxyethyl, β-hydroxypropyl, CH 2 CO 2   − , CH(CO 2   − )CH 2 CO 2   −  or CH 2 CH 2 SO 3   − ,   R 3  is hydrogen, —CO 2   −  or —SO 3   −  and   p is 0, 1 or 2.   
     
     
         7 . The method according to  claim 1 , wherein in the at least one optical brightener of formula (I) the anionic charge on the brightener is balanced by a cationic charge including one or more identical or different cations selected from the group consisting of Na + , K + , triethanolammonium, N-hydroxyethyl-N,N-dimethylammonium, N-hydroxyethyl-N,N-diethylammonium and mixtures thereof,
 R 1  and R 1 ′ are the same or different, and each is hydrogen, ethyl, propyl, β-hydroxyethyl, β-hydroxypropyl, CH 2 CO 2   − , or CH 2 CH 2 CONH 2 ,   R 2  and R 2 ′ are the same or different, and each is ethyl, propyl, β-hydroxyethyl, β-hydroxypropyl, CH 2 CO 2   − , CH(CO 2 )CH 2 CO 2   −  or CH 2 CH 2 SO 3   −  and   R 3  is hydrogen, —CO 2   −  or —SO 3   −  and   p is 0 or 1.   
     
     
         8 . The method according to  claim 1 , wherein the at least one optical brightener of formula (I) is used in an amount from 0.001 to 5% by weight, the % by weight being based on the total weight of dry pulp. 
     
     
         9 . The method according to  claim 1 , wherein in the at least one optical brightener of formula (II)
 R 4  is H, methyl or ethyl,   R 5  is paramethoxyphenyl, methyl or ethyl,   M is a cation selected from the group consisting of hydrogen, an alkali metal cation, alkaline earth metal, ammonium that is mono-, di-, tri- or tetrasubstituted by a C 1 -C 4  linear or branched hydroxyalkyl radical, ammonium that is, di-, tri- or tetrasubstituted by a mixture of C 1 -C 4  linear or branched alkylradical and linear or branched hydroxyalkyl radical and mixtures thereof.   
     
     
         10 . The method according to  claim 1 , wherein in the at least one shading dye of formula (II)
 R 4  is methyl or ethyl,   R 5  is methyl or ethyl,   M is a cation selected from the group consisting of Li + , Na + , K + , ½ Ca 2+ , ½ Mg 2+ , ammonium that is mono-, di-, tri- or tetrasubstituted by a C 1 -C 4  linear or branched hydroxyalkyl radical, ammonium that is di-, tri- or tetrasubstituted by a mixture of C 1 -C 4  linear or branched alkylradical and linear or branched hydroxyalkyl radical and mixtures thereof.   
     
     
         11 . The method according to  claim 1 , wherein in the at least one shading dye of formula (II)
 R 4  is methyl or ethyl,   R 5  is methyl or ethyl,   M is a cation selected from the group consisting of Na + , K + , triethanolammonium, N-hydroxyethyl-N,N-dimethylammonium, N-hydroxyethyl-N,N-diethylammonium and mixtures thereof.   
     
     
         12 . The method according to  claim 1 , wherein the at least one shading dye of formula (II) is used in an amount from 0.0001 to 0.02% by weight, the % by weight being based on the total weight of dry pulp. 
     
     
         13 . The method according to  claim 1 , wherein the aqueous formulation contains one or more auxiliaries selected from the group consisting of antifreezers, dispersing agents, synthetic or natural thickeners, carriers, defoamers, wax emulsions, dyes, inorganic salts, solubilizing aids, preservatives, complexing agents, biocides, cross-linkers, pigments and special resins. 
     
     
         14 . The method according to  claim 1 , wherein the adding step further comprises mixing the at least one optical brightener of formula (I), the at least one shading dye of formula (II) and optionally one or more auxiliaries, wherein the at least one optical brightener, the at least one shading dye and the optional one or more auxiliaries are solids or preformed aqueous solutions. 
     
     
         15 . The method according to  claim 14 , wherein in the aqueous solution, the concentration of compound of formula (I) in water is of from 1 to 50% by weight, the % by weight being based on the total weight of the preformed aqueous solution containing the at least one optical brightener of formula (I). 
     
     
         16 . The method according to  claim 14 , wherein in the aqueous solution, the concentration of the at least one shading dye of formula (II) in water is from 0.001 to 30% by weight, the % by weight being based on the total weight of the preformed aqueous solution containing the the at least one shading dye of formula (II). 
     
     
         17 . The method according to  claim 14 , wherein the pH value of the aqueous formulation is in the range of from 5 to 13. 
     
     
         18 . The method according to  claim 1 , wherein the at least one optical brightener of formula (I) is used in an amount from 0.01 to 3% by weight, the % by weight being based on the total weight of dry pulp. 
     
     
         19 . The method according to  claim 1 , wherein the at least one shading dye of formula (II) is used in an amount from 0.0005 to 0.01% by weight, the % by weight being based on the total weight of dry pulp.