Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
2 0 ~ 9 0 ~ ~ o. z . 0050/40658
Cationic urea-formaldehyde_condensates preparation
thereof and use thereof in ~he paper industry
The present invention relates to cationic urea-
formaldehyde condensates, to a process for pr~paring
them, and to their use as strength enhancers in paper-
making.
It is known that urea-formaldehyde condensation
products are u~ed a~ wet strength enhancers in
papermaking. Cationically modified urea-formaldehyde
condensates which are preparable by condensing urea and
formaldehyde in the presence of amines or polyamines are
likewise used as wet strength enhancers in papermaking.
Compar~d with unmodified urea-formaldehyde condensates
they show improved effectiveness. It is also pos~ible to
use condensation products of melamine, urea and
formaldehyde for enhancing the wet strength of paper.
EP-B-0 123 196 discloses a process for preparing
water-soluble cationic urea-formaldehyde resins wherein
urea and formaldehyde are condensed in a molar ratio of
from 1:1.5 to 1:3 in the presence of polyamines by first
(a) precondensing at pH 8-14, then acidifying and (b)
condensing at pH 1-5 till the onset of gelling, (c)
adding from 0.3 to 1.5 mol of formaldehyde per mole of
urea used, (d) postcondensing and then neutralizing the
resin solution. The polyamines used here per mole of urea
in the end product comprise from 5 to 50 g of poly-
ethyleneLmine containing from 20 to 15,000 ethyleneimine
units in copolymerized form. The water-soluble cationic
urea-formaldehyde resins thus obtainable are used as
auxiliaries in papermaking for enhancing the dry and wet
strength of paper. When paper webs which contain these
resins as strength enhancers are dried, an undesirable
release of formaldehyde is observed. The release of
formaldehyde during the drying of paper finished with the
urea-formaldehyde resins mentioned at the beginning as
wet strength enhancers is, however, still greater by far
than with the condensation products of EP-B-0 123 196.
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It is an object of the present invention to
provide urea-formaldehyde condensates which, when used as
wet strength enhancers for paper, do not release as much
formaldehyde in the drying of the paper as the conden-
sates based on urea and formaldehyde hitherto used for
this purpose.
We have found that this object is achieved by
cationic urea-formaldehyde condensates obtainable by
a) reacting urea with at least one alkanolamine in a
molar ratio of from 1:1 to 6:1 at from 130 to 180C
with elimination of ammonia,
b) methylolating the reaction product of stage (a) with
formaldehyde in an aqueous medium at a basic pH,
c) condenslng the methylolation product in an aqueous
medium at pH 0-6 with formation of a water-soluble
cationic urea-formaldehyde condensate until the
onset of gelling, and
d) terminating the condensation reaction by adjusting
the pH to 6.2-8 and optionally diluting the reaction
mixture with water.
Modification of the cationic urea-formaldehyde
condensates is achieved by carrying out the methylolation
of stage (b) in the presence of from 0.5 to 5 mol, based
on 1 mol of alkanolamine in stage (a), of urea, ethylene-
urea, melamine, dicyandiamide or mixtures thereof. The
cationic urea-formaldehyde condensates thus obtainable
are used as strength enhancers in papermaking. When paper
containing these condensates as strength enhancers is
dried, less formaldehyde is released compared with known
strength enhancers based on modified or unmodified urea-
formaldehyde conden~ates.
The cationic urea-formaldehyde condensates of the
present invention are prepared in a multistage reaction.
In stage (a) first urea is reacted with at least one
alkanolamine in a molar ratio of from 1:1 to 6:1, pre-
ferably from 3:1 to 4:1, at from 130 to 180C, preferably
at from 140 to 160C, with elimination of ammonia. Any
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common alkanolamine can be used, eg. ethanolamine,
diethanolamine, triethanolamine, diethylethanolamine,
n-propanolamine, isopropanolamine, diisopropanolamine,
di-n-propanolamine, triisopropanolamine, tri-n-propanol-
5amine, aminoethoxyethanol, dimethylethanolamine, diethyl-
ethanolamine (sic) and dLmethylaminoethoxyethanol. The
alkanolamines can be used either alone or mixed with one
another. Particular preference is given to the use of
triethanolamine. The condensation reaction takes place
10with elimination of ammonia from the urea used, forming
carbamts (sic). The reaction also produces an increase in
the viscosity of the reaction mixture. The condensation
is for example carried on until at 150C the reaction
mixture has a viscosity of at least 300 mPas. Preferably,
15the reaction is carried on until the viscosities of the
reaction mixtures, always determined at 150C, are from
300 to 3000 mPas. The reaction product thus obtainable
can be isolated in the form of a powder or dissolved in
water.
20Process stage (b) is a methylolation of the
reaction products of stage (a). The methylolation is
preferably carried out with formaldehyde in an aqueous
solution at a basic pH. The concentration of the aqueous
solution in terms of reaction products from (a) and
25formaldehyde is from 10 to 80, preferably from 40 to 60,
% by weight. The pH of these aqueous solutions is
ad~usted for the methylolation to values of from 7.5 to
14, preferably from B to 11. The methylolation itself is
effected with the addition of formaldehyde, which can be
30passed into the solution of the reaction product (a)
either in the form of an aqueous solution, as paraformal-
dehyde or else as a gas. Preference is given to using
formaldehyde in the industrially customary aqueous
solution having a concentration of from 37 to ~0~ by
35 weight.
The methylolation can be carried out in the
presence of modifiers, such as urea, ethyleneurea,
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melamine, dicyandiamide and/or propyleneurea. The modi-
fiers can be added to the aqueous solution of the reac-
tion product obtained in stage (a) in the form of an
aqueous solution or else as a powder. The modifiers are
used in an amount of from 0.5 to 5 mol, based on 1 mol of
the alkanolamine incorporated as condensed units in stage
(a). The methylolation in process stage (b3 is
customarily carried out at from 50 to 90C. The methyl-
olation, which may also be termed a precondensation,
takes from about 10 minutes to 2 hours, depending on the
temperature. It is followed by the condensation in
process stage (c).
To condense the methylolated products of process
stage (b), the pH of the aqueous solution is adjusted to
0-6, preferably l-S. This can be done not only with
mineral acids but also with organic acids, for example
sulfuric acid, phosphoric acid, hydrochloric acid, formic
acid, acetic acid, propionic acid, p-toluenesulfonic
acid, benzenesulfonic acid, amidosulfuric acid and
chloroacetic acid. It is of course also possible to use
mixtures of various acids. The condensation in process
stage (c) is carried out at from 60 to 100C, preferably
at from 70 to 90C. Water-soluble cationic urea-formal-
dehyde condensates are formed. It is preferably carried
on until gelling is evident from the fact that the
stirrer vortex disappears, even at high speeds, and
instead the reaction product climbs up the stirrer. The
condensation reaction takes from 15 minutes to 3 hours,
depending on the temperature and the pH, high tempera-
tures producing short reaction times and high pH values
producing long condensation times.
As soon as the methylolation products being
condensed are observed to undergo gelling, the condensa-
tion reaction is terminated in reaction stage (d) by
ad~usting the pH to 6.2-8, preferably 6.5-7.5. To neutra-
lize the reaction mixture to values within the stated pH
range, use is made for example of sodium hydroxide
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solution, potassium hydroxide solution, ammonia, amines,
sodium carbonate, potassium carbonate, sodium bicarbonate
or mixtures of two or more bases. Preference is given to
using sodium hydroxide solution. The reaction mixture may
be diluted with water before the condensation is ter-
minated or else not until after a base has been added for
the purpose of ad~usting the pH. This produces aqueous
solutions having a concentration of from 5 to 50% by
weight in respect of cationic urea-formaldehyde conden-
sates. Preferably, the concentration of the condensates
is ad~usted in such a way that the aqueous solutions are
from 8 to 40% strength by weight. It is of course also
possible to isolate the cationic urea-formaldehyde resins
from the aqueous solutions in solid form by evaporating
the water aftex the conden~ation reaction has been
terminated.
The cationic urea-formaldehyde condensates thus
obtainable are preferably used in the form of the aqueous
solution as strength enhancer in papermaking. This
purpose requires amounts of from 0.1 to 10% by weight of
the condensates, based on the dry paper fiber. The
cationic urea-formaldehyde condensates of the present
invention can be used in the making of any known paper,
cardboard or paperboard grade, for example writing,
printing and packaging papers. The papers can be made
from a plurality of different fiber materials, for
example from sulfite or sulfate pulp in the bleached or
unbleached state, groundwood, waste paper, thermomechani-
cal pulp (TMP) and chemothermomechanical pulp (CTMP).
The cationic condensates may either be added to
the paper stock prior to sheet formation or be applied to
the surface of a sheet of paper, for example in the size
press. After drying, the papers obtained will in all
cases have improved strength values. Preferably, the
cationic urea-formaldehyde condensates are added to the
paper stock suspension in amounts of from 0.5 to 5% by
weight, based on dry paper stock. The pH of the
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suspension is within the range from 4.0 to 10, preferably
from 6.0 to 8.5. The cationic condensates can be used not
only in the making of lightweight coating (LWC) paper but
also for paperboard or cardboard. The basis weight i~
within the range from 30 to 200, preferably from 35 to
150, g/m2 in the case of paper, and may be up to 600 g/m2
in the case of cardboard.
In the examples which follow, parts and per-
centages are by weight.
EXAMPLE 1
15 parts of triethanolamine and 27 parts of urea
are heated with stirring under nitrogen to 160C and left
at that temperature until 6.5 parts of ammonia have been
eliminated. The reaction mixture is then cooled down to
100C, and 17 parts of water are added.
The aqueous solution is then admixed with 42
parts of 40~ strength aqueous formaldehyde solution and
10 parts of urea and methylolated at 60C for 30 minutes.
Then sufficient formic acid is added to bring the reac-
tion mixture to pH 5.0, and the reaction mixture is
heated to 80C and condensed at that temperature until
the stirrer vortex originally present has disappeared.
100 parts of water are then added, followed by sufficient
sodium hydroxide solution until the reaction mixture pH
is 7Ø An aqueous solution of a cationic urea formal-
dehyde condensate with a solid~ content of about 30% is
obtained. The aqueous solution of the condensate is
infinitely thinnable with water.
Comparative Example 1 in accordance with EP-B-0 123 196
565 parts (7.5 mol) of formaldehyde in the form
of a 40~ strength aqueous solution, 220 parts (3.7 mol)
of urea and 190 part~ of water were mixed with S0 part~
of a 50% strength aqueous solution of a polyethyleneimine
containing 35 copolymerized ethyleneimine units, and the
mixture was heated to 70C with stirring. After the
mixture had been stirred at that temperature for 30
minutes, it was adjusted to pH 4.3 with formic acid. At
2 ~ .3
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that pH and 70C the reaction mixture was condensed until
the onset of gelling was observed. The condensation time
was 2 hours. Following this main condensation, a mixture
of 151 parts (2.0 mol) of formaldehyde in the form of a
50% strength aqueous solution, 4 parts of ethylene-
diamine, 30 parts of water and 50 parts of methanol was
added, and the resulting mixture was adjusted to pH 5.8
with 20~ strength aqueous sodium carbonate solution. The
reaction mixture was post-condensed at 70C for 1 hour
and then adjusted to pH 6.2. An aqueous solution of a
polyethyleneimine-modified urea-formaldehyde condensate
having a solids content of about 35% was obtained.
Comparative resin 2
As directed in Example 1 of DE-C-2 241 713, a
stirred vessel was charged with 3.2 mol of 25~ strength
formaldehyde per mole of melamine and then with the
melamine, and the contents were heated at a uniform rate
to 70C in the course of 30 minutes, during which a clear
solution formed at pH 6-7.
After stirring at that temperature for one hour,
6.8 mol of 22% strength formaldehyde were added with
effective cooling. A temperature of 30C was reached
after about 40 min. 0.09 mol of concentrated salt solu-
tion and 0.25 mol of 89% phosphoric acid were added at
that temperature, and the resin solution was diluted with
52 mol of water.
EXAMPLE 2
URe of the cationic condensate of Example 1 as
strength enhancer for paper.
An experimental papermaking machine having an
operating width of 65 cm was used to produce paper having
a basis weight of 70 g/m2 from 50% bleached pine sulfite
pulp and 50~ bleached beech sulfite pulp at a speed of
60 m/min. The pH of the stock suspension was ad~usted to
4.5 with 2~ aluminum sulfate (calculated on dry fiber)
and sulfuric acid. The freeness was 30 Schopper-Riegler
(SR). This model stock was used to test the
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effectiveness of the cationic condensate of Example 1 and
of the comparative resins 1 and 2. In each case the
strength enhancer was added to the thick stock.
The paper thus produced was subjected to measure-
ments of the dry breaking length in accordance withDIN 53 112 Sheet 1 and of the wet breaking length in
accordance with DIN 53 112 Sheet 2. The values reported
in the Table are averages from the longitudinal and
transverse direction of the paper relative to the paper
machine.
Moreover, the amount of formaldehyde released by
the paper web was determined in the first suction hood
of the first dryer group(I) and the second dryer group
(II) of the experimental paper machine.
First, the above-described model stock was used
to produce a paper by dispensing with the addition of a
wet strength enhancer. Then the cationic condensate of
Example 1 and thereafter the comparative resins 1 and 2
were each used as strength enhancer. The quantities added
and the results obtained therewith are shown in the
~able.
2~9~3~
9 - O . Z . O0S0/40658
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