U.S. patent application number 10/591572 was filed with the patent office on 2007-08-16 for concentrated optical brightener solutions.
Invention is credited to Andrew Clive Jackson.
Application Number | 20070186358 10/591572 |
Document ID | / |
Family ID | 34746007 |
Filed Date | 2007-08-16 |
United States Patent
Application |
20070186358 |
Kind Code |
A1 |
Jackson; Andrew Clive |
August 16, 2007 |
Concentrated optical brightener solutions
Abstract
The instant invention relates to concentrated aqueous solutions
of hexasulphonated stilbene optical brighteners which are
storage-stable in the absence of solubilizing agents like urea. By
removal of salts resulting from the preparation of the optical
brightener one can obtain a concentration of up to 0.350 mol/kg
without losing storage stability. The reduced water content enables
coating compositions which require less drying energy and which
show less water and binder migration into the paper.
Inventors: |
Jackson; Andrew Clive;
(Harrogate, GB) |
Correspondence
Address: |
CLARIANT CORPORATION;INTELLECTUAL PROPERTY DEPARTMENT
4000 MONROE ROAD
CHARLOTTE
NC
28205
US
|
Family ID: |
34746007 |
Appl. No.: |
10/591572 |
Filed: |
February 17, 2005 |
PCT Filed: |
February 17, 2005 |
PCT NO: |
PCT/IB05/00407 |
371 Date: |
September 1, 2006 |
Current U.S.
Class: |
8/648 |
Current CPC
Class: |
D21H 21/30 20130101;
D21H 19/36 20130101; C07D 251/54 20130101; C07D 403/12
20130101 |
Class at
Publication: |
008/648 |
International
Class: |
D06L 3/12 20060101
D06L003/12 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 5, 2004 |
EP |
04005210.2 |
Claims
1. A storage-stable aqueous solution comprising at least one
optical brightener of formula (1) ##STR9## wherein M is hydrogen,
an alkali metal cation, ammonium, or ammonium which is mono-, di-
or trisubstituted by a C.sub.2-C.sub.3-hydroxyalkyl radical, and n
is from 1 to 4, wherein the amount of the at least one optical
brightener is higher than 0.214 mol/kg and no solubilizing agent is
contained in the solution.
2. A storage-stable aqueous solution according to claim 1 wherein M
is hydrogen or a sodium cation, and n is 1 or 2.
3. A storage-stable aqueous solution according to claim 1 wherein
the concentration of the at least one optical brightener is from
0.215 mol/kg to 0.350 mol/kg.
4. A storage-stable aqueous solution according to claim 3 wherein
the concentration of the at least one optical brightener is from
0.250 mol/kg to 0.340 mol/kg.
5. A storage-stable aqueous solution according to claim 1 further
comprising one or more compounds selected from the group consisting
of inorganic salts, carriers, antifreezes, preservatives or
complexing agents.
6. A process for preparing a storage-stable aqueous solution
according to claim 1 comprising the steps of preparing the at least
one optical brightener of formula (1) by reacting a cyanuric halide
with a) a diamine of formula (A) ##STR10## b) an amine of formula
(B) ##STR11## c) an amine of formula (C) ##STR12## to form a
reaction solution, and wherein at least 50% by weight, of the
alkali metal or amine salt generated as a by-product by the
reactions between the diamine of formula a), the amine of formula
b) and the amine of formula c) and the cyanuric halide is removed
from the reaction solution.
7. The process according to claim 6 wherein the removal of the
alkali metal or amine salt is done by ultrafiltration or membrane
filtration of the reaction solution or by isolating the optical
brightener and then redissolving the reaction solution.
8. The process according to claim 7 wherein the removal is done by
membrane filtration.
9. A process for brightening of paper or cellulosic substrate
containing a white pigment comprising the step of adding the
storage stable aqueous solution of the optical brightener according
to claim 1 in a concentration of 0.05 to 0.5% by weight of the
white pigment to the paper or cellulosic substrate during
production thereof.
10. A process according to claim 9 for brightening paper in a
pigmented coating composition after sheet formation comprising the
step of adding to the pigmented coating composition the
storage-stable aqueous solution of claim 1.
11. The process according to claim 6 wherein at least 80% by
weight, of the alkali metal or amine salt generated as a by-product
by the reactions between the diamine of formula a), the amine of
formula b) and the amine of formula c) and the cyanuric halide is
removed from the reaction solution.
12. A paper or cellulosic substrate produced by the process
according to claim 9.
13. A paper or cellulosic substrate produced by the process
according to claim 10.
14. A paper or cellulosic substrate brightened with the
storage-stable aqueous solution according to claim 1.
Description
[0001] The instant invention relates to concentrated aqueous
solutions of hexasulphonated stilbene optical brighteners which are
storage-stable in the absence of solubilizing agents like urea.
Prior Art
[0002] Hexasulphonated stilbene optical brightening agents (OBAs)
are a well-established means of producing coated papers with a high
degree of whiteness. Such optical brighteners are most conveniently
marketed and used in the form of aqueous solutions. Japanese Kokai
62-106965 discloses an optical brightener, or a salt thereof,
##STR1## in which R.sub.1 and R.sub.2 each independently represents
a group selected from ##STR2## and A represents a group selected
from a hydrogen atom, an alkyl group having from 1 to 4 carbon
atoms, which may have a side chain, a hydroxymethyl group, a
hydroxyethyl group, a methylthioethyl group, a benzyl group, a
carboxymethyl group and a carboxyethyl group.
[0003] According to the Kokai, said optical brighteners have a very
high solubility in water and can be commercialized in the form of a
thick solution after removing the sodium chloride produced in the
reaction and concentrating the water content by an appropriate
method. The optical brighteners are claimed to be very effective
for the whitening of paper in a surface treatment.
[0004] Each example of the Kokai describes the preparation of an
optical brightener which is desalinated by ultrafiltration to give
a thick solution. Supposing that in Example 1 the reaction of the
starting compounds gives a 100% yield of said optical brightener
then the maximal concentration in said thick solution would be
0.214 mol/kg (30-32%). Each solution is then rendered
storage-stable by the addition of 10% urea.
[0005] This document therefore teaches that aqueous solutions of
said optical brighteners are unstable at concentrations equal to
0.214 mol/kg (30-32%) without the addition of urea.
[0006] There is however a demand for more concentrated aqueous
solutions of optical brighteners. The concentration of the aqueous
solution is of particular significance when the brightener is
applied in a pigmented coating composition; it is well-known that
papermakers aim to minimise the water-content of the coating
composition in order to minimise drying energy and to minimise
water and binder migration into the base paper. (See, for example,
`The Essential Guide to Aqueous Coating of Paper and Board`, ed. T.
W. R. Dean, PITA, 1997.)
DESCRIPTION OF THE INVENTION
[0007] Surprisingly and in contrast to the teaching of said
Japanese document it has now been found that certain of these
hexasulphonated stilbene OBAs can be prepared in the form of highly
concentrated aqueous solutions that are storage-stable at
concentrations of up to 0.350 mol/kg (about 54% by weight). When
applied to the surface of paper in either a pigmented coating
composition or in the size-press these aqueous solutions provide
superior fluorescent whitening effects.
[0008] An object of the present invention therefore is a
storage-stable aqueous solution comprising an optical brightener of
formula (1) ##STR3## wherein [0009] M is hydrogen, an alkali metal
cation, ammonium, or ammonium which is mono-, di- or trisubstituted
by a C.sub.2-C.sub.3-hydroxyalkyl radical, preferably hydrogen or a
sodium cation, and [0010] n is from 1 to 4, preferably is 1 or 2,
characterized in that the amount of the optical brightener is
higher than 0.214 mol/kg, preferably from 0.215 to 0.350 mol/kg,
more particularly from 0.250 to 0.340 mol/kg, and that no
solubilizing agent is contained in the solution.
[0011] The aqueous solutions of the optical brightener(s) may
optionally contain one or more carriers, antifreezes,
preservatives, complexing agents etc., as well as organic
by-products formed during the preparation of the optical
brightener.
[0012] Carriers are known to give improved whitening
characteristics and may be, e.g., polyethylene glycols, polyvinyl
alcohols or carboxymethylcelluloses.
[0013] Antifreezes may be, e.g., urea, diethylene glycol or
triethylene glycol.
[0014] The compounds of formula (1) are prepared by stepwise
reaction of a cyanuric halide with [0015] a) a diamine of formula
(A) ##STR4## [0016] b) an amine of formula (B) ##STR5## [0017] c)
an amine of formula (C) ##STR6##
[0018] As a cyanuric halide there may be employed the bromide or,
preferably, the chloride.
[0019] Each reaction may be carried out in an aqueous medium, the
cyanuric halide being suspended in water, or in an aqueous/organic
medium, the cyanuric halide being dissolved in a solvent such as
acetone. Each amine may be introduced without dilution, or in the
form of an aqueous solution or suspension. The amines can be
reacted in any order, although it is preferred to react the
aromatic amines first. Each amine may be reacted
stoichiometrically, or in excess. Typically, the aromatic amines
are reacted stoichimetrically, or in slight excess; the aliphatic
amines are generally employed in an excess of 5-30% over
stoichiometry.
[0020] For substitution of the first halogen of the cyanuric
halide, it is preferred to operate at a temperature in the range of
0 to 20.degree. C., and under acidic to neutral pH conditions,
preferably in the pH range of 2 to 7. For substitution of the
second halogen of the cyanuric halide, it is preferred to operate
at a temperature in the range of 20 to 60.degree. C., and under
weakly acidic to weakly alkaline conditions, preferably at a pH in
the range of 4 to 8. For substitution of the third halogen of the
cyanuric halide, it is preferred to operate at a temperature in the
range of 60 to 102.degree. C., and under weakly acidic to alkaline
conditions, preferably at a pH in the range of 7 to 10. The pH may
be controlled by addition of suitable acids or bases as necessary,
preferred acids being e.g., hydrochloric acid, sulphuric acid,
formic acid or acetic acid, preferred bases being e.g., alkali
metal (e.g., lithium, sodium or potassium) hydroxides, carbonates
or bicarbonates, or aliphatic tertiary amines e.g. triethanolamine
or triisopropanolamine.
[0021] A further object of the instant invention is the process for
the preparation of said aqueous solutions wherein the compounds of
formula (1) are prepared as described above and wherein the alkali
metal or amine salt that is generated as a by-product of each
reaction between an amine and a cyanuric halide is removed from the
reaction solution.
[0022] In order to prepare a stable aqueous solution with a
concentration of higher than 0.214 mol/kg (32-33% by weight),
preferably from 0.214 to 0.350 mol/kg, more particularly from 0.250
to 0.340 mol/kg, of a compound of formula (1) without the addition
of solubilizing aids such as ethylene glycol, urea or a mono-, di-
or tri-(2-hydroxyethyl)- or (2-hydroxypropyl)-amine, it is
necessary to remove at least 50%, preferably at least 80 % by
weight, of the alkali metal or amine salt that is generated as a
by-product of each reaction between an amine and a cyanuric halide.
This is preferably done by ultrafiltration or membrane filtration
of the solution formed as described above. Alternatively, the
compound of formula (1) can be isolated by precipitation (e.g. by
the addition of acid) then redissolved.
[0023] A further object of the instant invention is the use of the
instant storage-stable aqueous solutions for brightening of paper
or other cellulosic substrates.
[0024] The concentrated solutions of compounds of formula (1) are
particularly suitable for the brightening of paper after sheet
formation. This may be effected by adding the optical brightener
solution to a pigmented coating composition, or to a sizing
solution or suspension.
[0025] In a preferred aspect to the instant invention, the
concentrated solutions of compounds of formula (1) are applied to
the surface of paper in a pigmented coating composition.
[0026] The coating compositions are essentially aqueous
compositions that contain at least one binder and a white pigment,
in particular an opacifying white pigment, and may additionally
contain further additives such as dispersing agents and
defoamers.
[0027] Although it is possible to produce coating compositions that
are free from white pigments, the best white substrates for
printing are made using opaque coating compositions that contain
10-70% white pigment by weight. Such white pigments are generally
inorganic pigments, e.g., aluminium silicates (kaolin, otherwise
known as china clay), calcium carbonate (chalk), titanium dioxide,
aluminium hydroxide, barium carbonate, barium sulphate, or calcium
sulphate (gypsum).
[0028] The binders may be any of those commonly used in the paper
industry for the production of coating compositions and may consist
of a single binder or of a mixture of primary and secondary
binders. The sole or primary binder is preferably a synthetic
latex, typically a styrene-butadiene, vinyl acetate, styrene
acrylic, vinyl acrylic or ethylene vinyl acetate polymer. The
secondary binder may be, e.g., starch, carboxymethylcellulose,
casein, soy polymers, or polyvinyl alcohol.
[0029] The sole or primary binder is used in an amount typically in
the range 5-25% by weight of white pigment. The secondary binder is
used in an amount typically in the range 0.1-2% by weight of white
pigment; starch however is typically used in the range 5-10% by
weight of white pigment.
[0030] The optical brightener of formula (1) is used in an amount
typically in the range 0.01-1% by weight of white pigment,
preferably in the range 0.05-0.5% by Weight of white pigment.
[0031] The following examples shall explain the instant invention
in more detail. "Parts" means, if not defined differently, "parts
by weight".
PREPARATIVE EXAMPLE 1
[0032] A solution of 21.3 parts aniline-2,5-disulphonic acid and
6.7 parts sodium hydroxide in 30 parts water is added to a stirred
suspension of 15.5 parts cyanuric chloride in 50 parts ice water.
The pH is kept at 6 by the dropwise addition of 30% sodium
hydroxide. The mixture is stirred below 10.degree. C. until primary
aromatic amine groups can no longer be detected by the diazo
reaction. A solution of 14.8 parts
4,4'-diaminostilbene-2,2'-disulphonic acid and 3.2 parts sodium
hydroxide in 20 parts water is then added, the pH is adjusted to
between 6.5 and 7.5 by the addition of 30% sodium hydroxide and the
mixture is stirred at 30.degree. C. until a negative diazo reaction
is obtained. A solution of 12.2 parts L-aspartic acid in 22.9 parts
16% sodium hydoxide is added, and the mixture is heated at reflux
for 6 hours, the pH being kept at 7.5 to 8.5 by the addition of 30%
sodium hydroxide. The aqueous solution so-formed of (2) in the form
of its sodium salt, which is approximately 0.167 mol/kg in
concentration, is desalinated by membrane filtration and
concentrated to 0.330 mol/kg (50% by weight). The resulting
solution, 2.0% in sodium chloride, has a viscosity of 0.23-0.25
Pa.s at 20.degree. C. and shows no signs of precipitation after 2
weeks at 5.degree. C. ##STR7##
PREPARATIVE EXAMPLE 2
[0033] An aqueous solution of (3) in the form of its sodium salt at
a concentration of 0.330 mol/kg (51% by weight) is prepared as
described in Example 1 but using 13.5 parts L-glutamic acid in
place of 12.2 parts L-aspartic acid. The resulting solution, 2.0%
in sodium chloride, has a viscosity of 0.23-0.25 Pa.s at 20.degree.
C. and shows no signs of precipitation after 2 weeks at 5.degree.
C. ##STR8##
APPLICATION EXAMPLE 1
[0034] A coating composition is prepared containing 500 parts chalk
(commercially available under the trade name Hydrocarb 90 from
OMYA), 500 parts clay (commercially available under the trade name
Kaolin SPS from IMERYS), 470 parts water, 6 parts dispersing agent
(a sodium salt of a polyacrylic acid commercially available under
the trade name Polysalz S from BASF), 200 parts latex (an acrylic
ester copolymer commercially available under the trade name Acronal
S320D from BASF) and 30 parts of a 10% solution of carboxymethyl
cellulose (commercially available under the trade name Finnfix 5.0
from Noviant) in water. The solids content is adjusted to 65% by
the addition of water, and the pH is adjusted to 8-9 with sodium
hydroxide.
[0035] The solution of brightener (2) in the form of its sodium
salt, made as described in Preparative Example 1, is added at a
range of concentrations from 0.1 to 0.6% to the stirred coating
composition. The brightened coating composition is then applied to
a commercial 75 gsm neutral-sized white paper base sheet using an
automatic wire-wound bar applicator with a standard speed setting
and a standard load on the bar. The coated paper is then dried for
5 minutes in a hot air flow. The dried paper is allowed to
condition, then measured for CIE Whiteness on a calibrated Elrepho
spectrophotometer. TABLE-US-00001 TABLE 1 CIE Whiteness using OBA
Concentration (%) Brightener of Example 1 0 92.0 0.1 97.9 0.2 102.6
0.3 106.2 0.4 108.4 0.5 110.3 0.6 112.2
[0036] The results are also shown in graphical form in FIG. 1.
* * * * *