Note: Descriptions are shown in the official language in which they were submitted.
- ~2395~7
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Production of paper, cardboard and board having high dry
strength, wet strength and alkali resistance
Wet-strength paper is produced in practice by
adding to the paper stock at neutral or slightly alkaline
pi virtually exclusively resins which are prepared by
reacting epichlorohydrin with basic long-chain polyamide-
amine of U.S. Patent Z,926,116). Since the polyamide
chain on which the resins are based undergoes as hydrolytic
cleavage relatively easily, these resins have the disk
advantage of a relatively short shelf life. The alkali resistance of the papers treated with these resins is us-
satisfactory.
U.S. Patent 3,7û0,623 discloses resins which are
prepared by reacting epichlorohydrin with polymers of dip
allylaminesO Such products make it possible to prepare papers having high dry strength, wet strength and alkali
resistance. However, the resins are very expensive and
are therefore not used in industry. The disadvantages of
these resins are that they first have to be activated with
an alkali in the paper factory before they reach optimum
activity, and that they cause pronounced dulling of the
whiteness of the paper treated with them.
It is an object of the present invention to pro-
vise resins which, when added to the paper stock at
neutral or slightly alkaline phi increase the dry
strength, wet strength and alkali resistance of the paper
thus produced. The resins should be capable of being used
directly without activation, and furthermore should not
cause any dulling of the whiteness of the paper.
We have found that this object is achieved, in
accordance with the invention, by a process for the pro-
diction of paper, cardboard and board having high dry
strength, wet strength and alkali resistance, by adding an
aqueous polymer solution to the paper stock and draining
the latter over a screen to form a sheet, if the aqueous
polymer solution used is a product which is obtained by
I
I`
Lowe
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reacting
(1) a homcpolymer of a vinylimidazole of the formula I
R2
CON
R N' t I )
Choctaw
where R1, R2 and R3 are each H or SHEA, and R1 may
5 furthermore be C2Hs, C3H7 or C4Hg, or
to) a water-soluble copolymer of
a) not less than 10X by weight of a vinyl;midazole of the
formula I,
b) not more than 90X by weight of acrylamide and/or moth-
10 acrylamide and, of requ;red,c) not more than 30X by eight of acrylonitrile, moth-
acrylonitrile, vinyl acetate, vinylpyrrolidone, an ethylene-
gaily unsaturated C3-C5-carboxylic acid or one of its
esters,
15 with ep;chlorohydr;n in a ratio of from 0.02 to Z.9 moles
of epichlorohydrin per equivalent of basic nitrogen in the
homopolymer or copolymer.
Homopolymers and copolymers of vinylimidazole are
known. They are obtained by, for example, polymerization
2 of vinylimidazoles of the formula I
R2
CON
R 3 TIC - R 1 ( I )
SCHICK
where R1, R2 and R3 are each H or SHEA and R1 may
furthermore be C2Hs~ C3H7 or C4H9~ in aqueous
solution on the presence of a free-radical polymerization
25 initiator, at from 40 to 100C, preferably from 60 to
100C. Where R1 is colloquial, it can be n-propyl or
isopropyl and where R1 is C4 alkyd, it can be n-butyl,
isobutyl or tert.-butyl.
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For the preparation of copolymers of vinylimida-
zone, not less than 5X by weight of a vinylimidazole of
the formula I is used as component pa), while not more
than 95% by weight of acrylamide and/or methacrylamide are
5 employed as component (b) of the copolymers. polymers
of tax from 15 to 30% by weight of a v;nylimidazoLe of the
formula I, where R1, R2 and R3 are each H, or R2
and R3 are each H and R1 is methyl, or a mixture of
the monomers, and tub) from 85 to 70X by weight of acryl-
10 aside are preferably used as the starting polymer for the preparation of the wet-strength resins.
The copolymers can be modified, for example, in
that they contain, as component (c) in the form of Capella-
merited units, not more than 30Z by weight of acrylo-
15 nitrite, methacrylonitrile, vinyl acetate, vinylpyrroli-
done, an ethylenically unsaturated C3-C5-carbo~ylic acid
or one of its esters. The monomers of component (c) are
employed in an amount such that the resulting copolymers
are still water-soluble. Hence, for example, long-chain
20 esters of ethylenically unsaturated C3-C5-carboxylic
acids are copolymerized in an amount of not more than
about 5X by weight, whereas methyl acrylate or acrylo-
neutral can be present on the copolymers in an amount as
high as 30X by weight. The copolymers can also be mod;-
25 fled by simultaneously using a number of the monomers stated under lo) in the polymerization, ego acrylonitrile
and acrylic acid, acrylonitrile, vinyl acetate and vinyl-
pyrrolidone, or acrylic acid and acrylates.
The homopolymers and copolymers of the vinyl-
30 imidazole have K values of from 30 to 150, preferably from to 120 determined according to H. Fikentscher on 0.1Z
strength polymer solutions in SO strength aqueous sodium
chloride solution at Z0C). They are reacted with opt-
chlorohydrin in an aqueous medium to give resins, from
35 0.02 to 2.9, preferably from 1.0 to 2.5, mules of epichloro-
hydrin being employed per equivalent of basic nitrogen in
the polymer. The resins are preferably prepared by adding opt-
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chlorohydrin to an aqueous solution of the homapolymer or
copolymer of a compound of the formula I and allowing the
mixture to react until epoxide is no longer detectable.
In order to be able to monitor the reaction satisfactorily,
5 the ep;chlorohydrin is added continuously or bushes.
The reaction temperature is from 0 to 100C, preferably
from 20 to 80C, and the reaction time is about 2 - 6
hours. The condensation takes place at pi 5 - 10. In
order to obtain stable resin solutions, the pi of the
aqueous solution is brought to 2 - 4 before or after con-
sensation is complete, this preferably being done using
sulfuric acid or formic acid. The readyrprepared aqueous
resin solutions have a solids content of from 10 to 20X by
weight and a viscosity of from 100 to S,000 maps
(measured in a 10X strength solution according to rook-
field, 20 rum, 20C).
The aqueous resin solutions can be used in paper-
making either directly or, if required, after further
dilution with water they can be diluted with water in
Z0 any ratio). For paper making they are added to the paper
stock before sheet formation, in an amount of from 0.1 to
S, preferably from 0.25 to 1, % by weight, based in each
case on the solids. If from 0.005 to I based in each
case on dry fiber material and 100X strength resin, of the
Z5 aqueous resin solution is added to the paper stock slightly
upstream from the head box, these resins constitute excel-
lent creeping assistants, for example for sanitary papers.
The resin solutions used according to the invent
lion are added to the fiber suspension under the usual
30 conditions for paper making. The resins are effective for
all conventional grades of paper, board and cardboard, for
example in the manufacture of writing paper, printing
paper and packaging paper. The papers or boards and card-
boards may have been manufactured from a large variety of
35 fibrous materials, for example bleached or unbleached
sulfite or sulfate pulp, grounded or waste paper, or a
mixture of the stated types of fiber. The pi of the stock
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suspension us from 4 to 9, preferably from 6 to 8. It is
also possible to apply the resin solution, for example in
a size press, onto the surface of paper which has already
been formed.
In the Examples which follow, parts and percent-
ages are by weight.
The sheets were produced on a Rapid-Kothen labor-
tory sheet former. The dry tear length was determined
according to DIN 53,112, sheet I and the wet tear length
according to DIN 53,112, sheet 2.
The alkali resistance was determined in the same
manner as the wet strength, except that, instead of water,
a 1X strength sodium hydroxide solution was used for
impregnating the paper (5 minutes at 50C).
The whiteness of the paper sheets was determined
with the aid of an Elrefo reflecting photometer, in
accordance with DIN 53,145.
The K value of the polymers was determined accord-
in to H. Fikentscher, Cellulosechemie 13 t1932), 58-64
20 and 71-i4, at 20C in SO strength aqueous sodium chloride
solution; K = k . 103.
Preparation of the resin solutions
Resin 1
a) Preparation of an aqueous solution of a homopolymer
of N-vinylimidazole
500 parts of vinylimidazole and 450 parts of water
were initially taken in a polymerization vessel, and 8
parts of tert.-butyl perethylhexanoate in 40 parts of
methanol were added in the course of 1 hour at 100C,
30 while nitrogen was passed through. When the addition
of the polymerization initiator was complete, the reaction
mixture was polymerized for a further 7 hours at 91C,
and the resulting mixture was then diluted to a solids
content of 30.3% by adding water. A brown, slightly
35 cloudy, very viscous polymer solution was obtained, the K
value of the homopolymer being 86.
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b) Reaction of the homopolymer with epichlorohydrin
878 9 (corresponding to 2.7 equivalents of basic
nitrogen) of a 30.3X strength aqueous solution of the
poly-N-v;nyl;m;dazole obtained as described in a) were
S dotted Thea 1,630 9 of water, 677 9 (7.3 moles) of en;-
chlorohydr;n were added at room temperature, and the mix-
lure was stirred. During thus procedure, the viscosity
of the solution increased slowly. After 30 minutes, 193 9
(2 moles) of sulfuric acid were added, the pi being
brought to 2 as a result. The reaction mixture was heated
to 80C and stirred for 4 hours at this temperature,
2,100 9 of water being added a little at a tome. The
resulting aqueous solution of resin 1 had a solids content
of 17.2X, a pi of 1.7 and a viscosity of 380 maps
Resin 2
a Preparation of an aqueous copolymer solution
250 parts of water were initially taken on a polyp
Morristown vessel, and feeds I and II were added s;multane-
ouzel from two separate feed vessels, on the course of 1
hour, at 90C, while nitrogen was passed through. Feed
I consisted of 150 parts of acrylam;de, 150 parts of
vinylim;dazole and 150 parts of water, whole feed II was
a solution of 3 parts of Z,2'-azobis-(2-am;dinopropane)
d;hydrochlor;de on 47 parts of water. The reaction mix-
25 lure was then polymerized for a further 4 hours at 90C,
and the resulting mixture was brought to a solids content
of 30.3% by adding water. The K value of the copolymer
was 68.
b) Reaction of the copolymer with ep;chlorohydr;n
233 9 (corresponding to 0.4 equivalent of basic
nitrogen) of the 30.3% strength aqueous solution of the
copolymer described in a) were diluted with Z86.5 9 of
water, and 41.6 9 (0.45 mole) of ep;chlorohydrin were
added at room temperature. The reaction mixture was then
35 heated slowly to 75C. After 60 minutes, the v;scos;tyof the reaction mixture had increased substantially. It
was then brought to pi 2 with 44 9 (0.8 mole) of 85X
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strength formic acid, and stirred at 75~C for a further 2
hours, after which the reaction was compute. the reaction
mixture was brought to a solids content of 15% by adding
200 9 of water. The aqueous solution of resin 2 had a
viscosity of 230 maps and a pi of 3Ø
Resin 3
a Preparation of an aqueous copolym~r solution
125 parts of water were initially taken in a
polymerization vessel and heated to 80C Chile being
stirred and while nitrogen was passed through. As soon
as the temperature of 30C had been reached, two differ-
en feeds were introduced continuously into the vessel on
the course of one hour. Feed I consisted of a solution
of 225 parts of acryLamite and 75 parts of N-viny~imida-
zone in Z25 parts of water, while feed II was a solution of 3 parts of Z,2'-azobis-~Z-a~idinopropane) dodder-
chloride in 47 parts of water. When the addition of the
monomers and the initiator was complete, the reaction mix-
lure was polymerized for a further 4 hours at awoke, and
Z0 the resulting mixture was brought to a solids content of
10.1X by adding water. The K value of the copolymer was
84.
b) Reaction of coupler a) with epich~orohydrin
150 9 of water, 16.7 9 ~0.18 mole) of epichloro-
25 hydrin and 9.7 9 Tao mole) of 85% strength formic acid were added to Z97.6 9 corresponding to 0.1 equivalent of
basic nitrogen) of the 10.1X strength aqueous solution of
copolymer a), and the mixture was heated to 75C. React
lion for 4 hours at 75C gave an 8.4% strength aqueous
30 solution of resin 3, the solution having a viscosity of
3,8ûQ maps and a pi of 3.6.
Resin 4
.
a) Preparation of an aqueous copolymer solution
145 parts of water were initially taken in a
35 polymerization vessel and heated to ~0C while being
stirred and while nitrogen was passed through. When the
temperature of the water initially taken had reached 80C,
I 7
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feeds I and II were introduced simultaneously in the
course of one hour. Feed I consisted of a solution of
255 parts of acrylamide and 45 parts of N-vinylimidazole in
255 parts of water, while feed II was a solution of 1.5 9
of 2,2'-azobis-(2-amidinopropane) dihydrochloride in 48.5
parts of water. When the addition of the monomers and the
initiator was complete, the reaction mixture was polyp
merited for a further 4 hours at 80~, and the resulting
mixture was diluted to a solids content of 5X by adding
1û water. The K value of the copolymer was 113.
b) Reaction of copolymer a) with epichlorohydrin
6 9 9 (0.13 mole) of 85% strength formic acid and
11.8 q (û.13 mole) of epichlorohydr;n were added to 894.6 9
(corresponding to 0.08 equivalent of basic nitrogen) of the
5% strength aqueous solution of copolymer a) described
above. The reaction mixture was heated to 80C and
stirred for 5 hours at this temperature. The resulting
aqueous solution of resin 4 had a solids content of 6~0X,
a pi of 3.6 and a viscosity of 600 maps
EXAMPLE 1
100X pine sulfite pulp was converted to a OX
strength stock suspension in water, the pi of the suspend
soon being 7.5 and the degree of freeness 35SR. The
stock suspension was divided into three equal parts, and
each part was processed under the following conditions to
give sheets having a weight per unit area of 80 g/m2:
a) Nothing was added to the stock suspension.
b) 1X, based on the solids, of an aqueous solution of a
commercial neutral wet-strength resin based on a react
lion product of epichlorohydrin with a polyamidoamineobtained from diethylenetriamine and adipic acid was
added to the stock suspension. The neutral wet-strength
resin was prepared as described in Example 1 of U.S.
Patent 2,926,116.
35 c) 1X, based on the solids, of resin 3 described above was
added to the stock suspension.
The dry tear length, the wet tear length, the
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alkali resistance and the whiteness of the three sheets
obtained as described in a), b) and c) were tested. The
results are summarized in Table 1.
TABLE 1
S a) b) c3
Dry tear length (m) 4,450 5,340 5,990
Wet tear length to) 0 1,120 1,190
Paper unaged
Wet tear length (m) 120 1,5Z0 1,450
Paper aged for 5 minutes at
1 1 û C
Alkali resistance 0 725 980
1X strength sodium hydroxide
solution for 5 minutes at 50C
Paper unaged
Alkali resistance 1,0Z0 1,090
1X strength sodium hydroxide
solution for 5 minutes at 50C
Paper aged for 5 minutes at 50C
Whiteness 80 n 5 6 9 O 73 5
Diffuse reflectance (Xj
EXAMPLE 2
100% mixed waste paper was converted to a 0.5X
strength aqueous stock suspension, the pi of the suspend
soon being 7.2 and the degree of freeness 50SR. Theistic suspension was then divided into five equal parts,
and each part was processed under the following conditions
to give sheets having a weight per unit area of 80 g/mZ:
a) no further substances were added to the stock suspension;
30 b) 0.5%, based on dry fiber, of the neutral wet-strength
resin described in Example 1b) was added;
c) 1.0X, based on dry fiber, of the neutral wet-strength
resin described in Example 1b) was added;
d) 0.5%, based on the solids, of resin 4 was added;
35 e) 1.0X, based on the solids, of resin 4 was added.
The dry tear length and the wet tear length of all
paper sheets produced in this manner were measured. The
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results are shown in Table 2.
TABLE Z
Exper;mentDry Wet Wet tear length (m),
tear length tear length aged for 5 minutes
(m) (Al) at 110C
a) 2,420 0 0
b) 2~570 390 590
c) 2,890 5Z0 900
d) 2,750 475 580
e) 3,050 714 910
EXAMPLE 3
A paper consisting of 80% of bleached pine sulfite
pulp and 20% of bleached beech sulfite pulp and having a
weight per unit area of 80 9/m2 was produced, at a speed
of 60 main on an experimental paper machine having a
working width of 75 cm. The pi of the stock suspension
was 7.5, and the degree of freeness was 35SR. Papers
were produced from this stock suspension under the cord;-
lions a) to g) stated below:
a) No substances were added.
b) 0.25% of the neutral wet-strength resin stated on
Example lb) was added.
c) 0.5X of the resin described in b) was added.
do 1.0X of the resin described in b) was added.
e) 0.25X of resin 4 was added.
f) 0.5X of resin 4 was added.
g) 1.0X of resin 4 was added.
The percentages in each case are based on the
solids, to. of the stock suspension and of the resin soul-
lions. The resin solutions described in a) to g) worded to the high density pulp. The wet tear length and
the alkali resistance of the papers produced in this
manner were determined. The values stated are mean values
of measurements along the longitudinal and transverse
directions of the paper with respect to the paper machine.
The following values were obtained:
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TALE 3
Wet tear length Alkali resistance,
(m) 1X strength Noah,
_ 5 mint 50C
a) O O
b) 340 Z40
c) 550 3~0
d) 840 470
e) 405 515
f) 580 735
9) 870 940
