Storage stable solutions of optical brighteners
The instant invention relates to storage stable solutions of optical brighteners based on certain salt forms of anilino-substituted bistriazinyl derivatives of 4,4′-diaminostilbene-2,2′-disulphonic acid and of organic acids which do not need extra solubilizing additives.
1. An aqueous solution consisting essentially of 15 to 35% by weight of a compound of formula (1)
wherein
R is hydrogen or a methyl radical,
M + is Li + , Na + , or K + ,
n is less than or equal to 1.5, and
of 0.1 to 2.0% by weight of an organic acid selected from the group consisting of citric acid, glycolic acid, acetic acid and formic acid.
2. An aqueous solution according to claim 1 , consisting essentially of 15 to 35% by weight of a compound of formula (1) and wherein
R is hydrogen or a methyl radical,
M + is Na + , and
n is less than or equal to 1.5, and of 0.1 to 2% by weight of citric acid.
3. An aqueous solution according to claim 2 , wherein
R is hydrogen,
M + is Na + , and
n is less than or equal to 1.5.
4. An aqueous solution according to claim 2 , wherein
R is hydrogen,
M + is Na + , and
n is less than or equal to 1.2.
5. An aqueous solution according to claim 1 , further comprising one or more carriers, antifreezes, defoamers, solubilizing aids, preservatives, complexing agents or organic by-products.
6. A process for preparing an aqueous solution, wherein the aqueous solution comprises 10 to 40% by weight of a compound of formula (1)
wherein
R is hydrogen or a methyl radical,
M + is Li + , Na + , or K + ,
n is less than or equal to 1.5, and of 0.05 to 5% by weight of an organic acid selected from the group consisting of citric acid, glycolic acid, acetic acid and formic acid, comprising the step of converting a compound of formula (2)
wherein
R is defined as above,
in the form of an aqueous solution to a mixed salt form (1) in which at least 25% of the M + ions associated with the sulphonate groups have been replaced by (CH 3 ) 2 NH + CH 2 CH 2 OH ions, by treatment with 2-dimethylaminoethanol and an organic acid.
7. An optical brightener for textiles, paper, board and non-wovens comprising an aqueous solution as claimed in claim 1 .
8. An aqueous suspension of pulp comprising an aqueous solution as claimed in claim 1 .
9. A process for whitening of paper comprising the steps of
providing a pulp suspension,
adding 0.01 to 2% by weight based on dry fibre of an aqueous solution
wherein the aqueous solution consists essentially of 15 to 35% by weight of a compound of formula (1)
wherein
R is hydrogen or a methyl radical,
M is Li + , Na + , or K + ,
n is less than or equal to 1.5, and
0.1 to 2% by weight of an organic acid selected from the group consisting of citric acid, glycolic acid, acetic acid and formic acid,
producing a paper sheet from the pulp suspension,
pressing and drying the paper sheet.
10. A process for whitening of paper comprising the steps of
preparing an aqueous coating composition by mixing together chalk or other white pigments, one or more dispersing agents, a primary latex binder and optionally a secondary binder, and optionally other additives,
adding 0.01 to 3% by weight based on dry pigment of an aqueous solution
wherein the aqueous solution consists essentially of 15 to 35% by weight of a compound of formula (1)
wherein
R is hydrogen or a methyl radical,
M + is Li + , Na + , or K + ,
n is less than or equal to 1.5, and
of 0.1 to 2% by weight of an organic acid selected from the group consisting of citric acid, glycolic acid, acetic acid and formic acid,
applying the coating composition to a paper sheet to form a coated paper sheet, and
drying the coated paper sheet.
11. An aqueous solution according to claim 1 , which is free from solubilising auxiliaries.
12. An aqueous solution according to claim 1 , which is stable to storage at 4° C. for at least two weeks either in the absence or presence of crystal seeds.
13. An aqueous solution according to claim 1 , wherein the organic acid comprises citric acid.
14. An aqueous solution according to claim 1 , wherein the organic acid comprises glycolic acid.
15. An aqueous solution according to claim 1 , wherein the organic acid comprises acetic acid.
16. An aqueous solution according to claim 1 , wherein the organic acid comprises formic acid.