Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
WO 96/23105 2~ ~ 1~ 37 PCT/FI96/00051
A method for increasing the hydrophobicity of printing
papers and a hydrophobe composition for the method
The present invention relates to a method of improving
the hydrophobicity of printing papers by means of inter-
nal sizing of the paper. The invention also concerns a
hydrophobe composition for performing of the method. A
particular object of the invention is to improve the hyd-
rophobicity of paper by means of using a ketene dimer
compound as a hydrophobic sizing agent. The purpose of
improving the hydrophobicity is to impart the paper web a
degree of sizing that makes the paper compatible with
ink-jet printing.
The resistance properties of paper to wetting and penet-
ration are conventionally enhanced in papermaking by
means of internal sizing, where during the paper making
process compounds are added into the paper pulp which
increase the hydrophobicity of the paper fibers.
Printing papers, which are chiefly used as office paper
in various types of copiers, printers and printing
machines, are expected to exhibit high brightness among
other properties, as well as acceptable permanence in
archive document use. The brightness and archiving perma-
nence properties can be affected through the type of fil-
ler used for the paper. One filler compatible with the
above-described requirements is precipitated calcium car-
bonate (PCC). However, a problem is involved in the use
of this filler, because it requires a neutral or alkaline
environment for a proper functioning. Such a process con-
dition excludes the use of conventional hydrophobic si-
zing of paper by means of the rosin-alum system. As known
in the art, this drawback is overcome by the use of hyd-
rophobic sizes based on ketene dimer compounds such as
alkyl, alkenyl, aryl and alkaryl ketene dimer sizes.
Such sizes are, however, hampered by other problems par-
WO 96/23105 220 1~ 3_7 PCT/F196/00051
2
ticularly in paper grades intended for office printing
use that have to be compatible with different printer
types. Namely, besides a application in ink-jet printing,
the same paper grade should do as copier paper, laser
printing paper, etc. When optimized for the above-men-
tioned ink-jet use, the base paper must be sized with
such great amounts of ketene dimer combination sizes that
ultimately the size causes problems in the alternative
printer types. In practice, the degree of sizing may
amount to, e.g., 0.1 - 0.2 % of fiber dry weight in the
web.
Over time, ketene dimer compounds have been found proble-
matic as a sizing agent due to their migration tendency
in the finished paper. Owing to such migration, the con-
tent of the ketene dimer compound is enriched in the
outer layers of the sheet. Migration is made possible by
the fact that the curing reactions of ketene dimer com-
pounds are so slow that the added agents lose their mig-
ration capability not earlier than after a few days from
the finishing of the sheet.
A disadvantageous effect of ketene dimer compound enrich-
ment is easier slippage of the sheet surface, i.e.,
decrease of surface frictional resistance. Reduced fric-
tion is harmful particularly in printing and copier paper
grades, because the lowered threshold of slippage causes
paper handling problems in printing or copying machines
whose paper transfer elements fail to provide their in-
tended function on slippery paper grades.
Also the above-mentioned filler, namely, the precipitated
calcium carbonate causes indirectly easier slippage of
the sheet. This is because this filler has been found to
disturb the hydrophobic sizing process, whereby greater
amounts of size must be used per unit weight of fiber in
comparison to the use of another type of filler.
WO 96/23105 220 13 37 PCT/FI96/00051
3
On the other hand, it has been found that ketene dimer
based sizing fails to bond completely on the fiber during
sheet formation, whereby a fraction of the sizing agent
remains circulating in the system and of this fraction a
portion bonds later on the fiber. When circulating in the
system, the sizing compound is subjected to the hydroly-
zing effect of water resulting in a partial decomposition
of the sizing compound into corresponding ketones. Also a
fraction of the size retained in the base web will remain
unbonded to the fiber, whereby the size may undergo hyd-
rolyzation by the moisture contained in the web. These
phenomena are harmful particularly in copier use, where
the sheet is subjected to heating in the copying machine,
whereby the decomposition of unbonded size and its migra-
tion, along with the moisture released from the sheet, to
the surface of the sheet are accelerated. Resultingly,
the machine parts of the copier may become contaminated
and the copying result deteriorated. To eliminate these
risks, determination of residual ketone content in paper
grades intended for copier use has been instigated.
According to the present invention, an essential improve-
ment has now been achieved to overcome the above-
described problem by virtue of performing hydrophobic
sizing using a sizing dispersion in which the amount of
water-soluble colloidal polymer is at least 100 % of the
amount of the hydrophobic sizing compound.
Herein, it has firstly been noted that ketene dimer com-
pound used as the hydrophobic sizing agent is better bon-
ded to the fiber, and, secondly, that the precipitated
calcium carbonate used as the filler has no essential
disturbing effect on the sizing process. Owing to the
latter fact, less is needed, whereby said smaller amount
of the hydrophobic sizing agent can be retained close to
the fiber in an improved manner until the curing of the
hydrophobic sizing agent has proceeded to a level pre-
CA 02201337 2008-04-15
4
venting migration. Additionally, it was found that the invention
offered improved ink penetration properties with respect to the
water penetration. This effect is of extremely high importance to
the quality of ink-jet printing that is becoming ever more widely
used.
Preferably, the content of hydrophobic sizing agent is approx. 1-15
% by weight, advantageously 6-15 % by weight.
The invention has furthermore been found applicable in cases where
the ketene dimer compound employed as a hydrophobic sizing agent in
the sizing of paper is complemented with other conventional
hydrophobic sizing agents such as alkenyl succinic anhydride (ASA)
and/or rosin. In one embodiment, aluminum sulphate is also present
at 2-15% by weight of the colloidal polymer.
Preferably, the content of ASA is 20-70 %, advantageously 30-50 %,
by weight of the ketene dimer. Preferably, the content of rosin is
approx. 20-50 % by weight of the ketene dimer.
The invention is next explained with the help of the following
examples elucidating the function of the invention in its different
embodiments.
Example 1
A pilot-scale test run was carried out, in which internal sizing was
performed for a finepaper grade with added precipitated calcium
carbonate (PCC) as the filler. The filler (tradename Albacar LO) was
used at 22 % level by fiber dry weight. The fiber in the base web
was 75 % birch fiber beaten to 23 SR freeness and the fiber slurry
was adjusted to pH 7. The rest, 25 %, of the fiber was pine fiber
equally beaten to 23 SR freeness and fiber slurry also adjusted to
pH 7. Internal sizing of the paper web was performed using Raisamyl
135 starch at 5 kg/ton pulp addition rate. The basis weight of the
produced paper web was 80 g/m2. The paper machine was run at
60 m/min resulting in a production rate of 4.08 kg/min. The
retention agent used in the process was BMA 590 (colloidal sodium
silicate) at an addition rate of 300 g/ton pulp. The paper web was
also surface sized using Raisamyl 406 LO starch at 6 % solids
addition level. The hydrophobic compound used as a sizing agent was
alkyl ketene dimer (AKD).
WO 96/23105 2-20 1~ 3-7 PCT/FI96/00051
The test runs were performed using the different formula-
tions of hydrophobic size listed below for internal siz-
ing:
5 1. Conventional AKD sizing with Raisafob 940, in
which the amount of starch protective colloid addi-
tion was not more than 20 % by weight of sizing
agent.
2. AKD sizing, amount of starch protective colloid
addition 50 % by weight of sizing agent.
3. AKD sizing, amount of starch protective colloid
addition 100 % by weight of sizing agent.
4. AKD sizing, amount of starch protective colloid
addition 150 % by weight of sizing agent.
5. AKD sizing, amount of starch protective colloid
addition 200 % by weight of sizing agent.
6. AKD sizing, amount of starch protective colloid
addition 250 % by weight of sizing agent.
7. AKD sizing, amount of starch protective colloid
addition 300 % by weight of sizing agent.
8. AKD sizing, amount of protective colloid addi-
tion using PEI (polyimin KK)* in an amount of 200 %
by weight of sizing agent.
Notes: *) polyethylene imine
The tests were run using two levels of sizing agent, na-
mely, adding the sizing agent (AKD) at 0.1 % and 0.2 %
levels by fiber dry weight.
The starch used as the protective colloid component was
Raisamyl 150 which is a degraded special starch grade.
The degree of sizing in the manufactured papers were tes-
ted by measuring the water absorbance of the paper sheets
in the Cobb60 test from the sheet surface, while the ink
penetration of the sheets was measured using the Schroder
test. Also the brightness of test sheets was measured.
WO 96/23105 2~ ~ 1~ 37- PCT/F196/00051 ~
6
The test runs gave the following results:
Test no./ Cobb, test Schr6der test Brightness
[g/m2] (100-->90%, s)
Amount of size 0.1 % 0.2 % 0.1 % 0.2 % [%]
1 78.2 28.3 0 10 92.7
2 76.3 28.1 1 11 92.6
3 41.5 26.6 2 15 92.7
4 29.3 20.2 5 135 92.8
5 25.0 18.4 18 248 93.0
6 24.8 18..3 20 253 92.9
7 24.7 18.2 21 255 93.0
8 28.8 18.1 21, 262 91.1
From the above results it can be seen that, at an additi-
on rate of the sizing agent of 0.1 % by fiber dry weight,
a sufficient addition rate of the protective colloid com-
ponent is at approx. 200 % level by hydrophobic sizing
agent solids weight, whereby this combination provides
such a Cobb6o value of less than 25 g/m2 that conventional-
ly is considered to represent a sufficient level of si-
zing. For the larger, 0.2 wt.%, addition rate of the si-
zing agent, the corresponding water repellency value is
attained using an addition rate of the protective colloid
component as low as 100 % of the hydrophobic sizing agent
solids weight. Also polyethylene imine (PEI) was found
(test run no. 8) to act as a protective colloid component
at the same addition rate (200 %), however, with the pe-
nalty that paper brightness is adversely affected parti-
cularly in grades manufactured using optical brighteners.
The ink penetration property of the paper web is improved
significantly up to 200 % addition rate of the protective
colloid component, whereafter this property at higher =
addition rates stays approximately at the same level as
when using PEI.
WO 96/23105 220 13 3. 7 PCT/FI96/00051
7
Example 2
A production-scale test run was performed on a finepaper
machine by making paper at 78 g/m2 basis weight. The paper
was manufactured using pulp comprised in 60/40 ratio of
birch to pine fiber. The amount of filler added to the
base web was at 22 % level by fiber dry weight, whereby
70 % of the filler was precipitated calcium carbonate
(PCC, Albacar LO) and 30 % of ground CaCO3. The retention
system was formed by corn starch and an anionic component
(Compozil).
The AKD sizing was applied using two different formula-
tions:
1. Raisafob 940, conventional AKD sizing, amount of pro-
tective colloid component not more than 20 % of sizing
material dry weight.
2. Raisafob 500, AKD sizing using starch as the protec-
tive colloid component with an amount increased to 200 ~
of size dry weight. The starch added as the protective
colloid component was Raisamyl 150 EH.
The test runs were carried out using AKD sizing at 0.12 %
level by fiber dry weight. Tests were performed in mul-
tiple series using both of-the above sizing formulations
in identical conditions to eliminate random error from
the results. The test data is listed in the table below:
220 13 37
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WO 96/23105 ~ t~ O 1 3 3 7 PCT/FI96/00051
9 ~
Example 3
A production-scale test run was carried out in which the
following sizing formulations were compared:
= 1. Raisafob 940 AKD sizing, amount of starch protec-
tive colloid addition not more than
20 % by weight of sizing agent.
2. Raisafob 500 AKD sizing, amount of starch protec-
tive colloid addition 200 % by weight
of sizing agent.
The paper made herein was a office paper grade intended
for multipurpose use. The production target values for
the paper grade were set as follows: residual ketone con-
tent less than 0.4 mg/g (for copier use), black density
greater than 1.2 in B/W printing on ink-jet printers and
combination black density greater than 0.75 in multicolor
printing.
Test run conditions:
Paper grade: Office paper (multipurpose)
Basis weight: 80 g/m2
Base web composition: 70% birch fiber at 23 SR
freeness
70% pine fiber at 23 SR freeness
Filler: Precipitated calcium carbonate (PCC)
Retentionsystem: Two-component formulation (po-
lymer + bentonite)
Surface sizing: Raisamyl 408 starch + 1.5 kg
styrene acrylate polymer/ton
pulp solids
Paper machine speed: 980 m/min
AKD addition rate: 1 kg AKD/ton pulp solids, or
alternatively, 1.4 kg AKD/ton
pulp solids
WO 96/23105 220 13 37 PCT/FI96/00051
Test results:
Sizing Addition Cobb,, Ink penetra- Residual Black density, Black density,
agent rate tion HST 80 ketone B/W printing, comp. color
[kg/ton] [g/mq [%, s] [mg/g] felt side printing, felt side
5 RF940 1 25 80 0.41 1.02 0.64
RF940 1.4 23 153 0.68 1.22 0.82
RF500 1.4 21 238 0.27 1.38 0.90
As is evident from the above results, the sizing proper-
10 ties are clearly improved by the use of RF 500. Addi-
tionally, the residual ketone content remains below the
set target value. Also the density target values set for
ink-jet printing are exceeded. By contrast, using the
RF 940 sizing formulation with a low protective colloid
content it is not possible to meet the upper limit set
for the residual ketone content. Hence, the paper made in
this process is not suited for the intended copier use.
If the size addition rate is reduced to a level of
1 kg/ton pulp solids, the RF 940 sizing formulation may
marginally meet the level set for the maximum allowable
residual ketone content, however, with the penalty of not
meeting required ink penetration criteria.
The invention has further been found suitable for use in
such paper sizing applications in which a fraction of the
hydrophobic sizing agent is composed, besides of AKD,
additionally of another sizing agent suited for improve-
ment of water repellency such as alkenyl succinic anhyd-
ride (ASA). However, as ASA sizing formulations do not
offer hydrophobic properties as effective as those of AKD
sizing formulations, they must be used in larger amounts
to achieve comparable ink-jet printability qualities. Due
to the staining problems caused by the required large
addition rates of ASA sizing in papermaking, this sizing
approach appears less favored. However, because the use
of an ASA sizing formulation in the present application
WO 96/23105 220 13 37 PCT/FI96/00051
11
would give a low residual ketone content in the finished
sized paper, which is a definite benefit when using the
paper in copiers. The well-known problematic properties
of this sizing agent require that the sizing furnish be
prepared in the immediate vicinity of the papermaking
process. In the following example, the behavior of this
sizing formulation type is described.
Example 4
A production-scale test run was carried out to compare
the behavior of the following sizing formulations:
1. Raisafob 500 AKD sizing, amount of starch protec-
tive colloid addition 200 % by weight
of the ketene dimer.
2. Raisafob MF ASA sizing, dispersed in bulk sizing
starch Raisamyl 135 in an ASA/starch
ratio of 1:2.
3. Raisafob 500 AKD sizing plus Raisafob MF,
+ Raisafob MF added separately.
4. New sizing AKD/Raisafob 500 type sizing
formulation dispersion + ASA dis-
persed therein in AKD/ASA ratio of
50/50:
The paper made herein was a office paper grade intended
for multipurpose use. The production target values for
the paper grade were set as follows: ketene content less
than 0.4 mg/g (for copier use), black density greater
than 1.2 in B/W printing on ink-jet printers and combina-
tion black density greater than 0.75 in multicolor print-
ing.
WO 96/23105 220 13 3 7 PCT/FI96/00051
12
Test run conditions:
Paper grade: Office paper (multipurpose)
Basis weight: 80 g/m2
Base web composition:
70 % birch fiber at 23 SR freeness
30 % pine fiber at 23 SR freeness
Filler: Precipitated calcium carbonate (PCC)
at 20 % level by fiber dry weight
Retention system: Two-component formulation (polymer +
bentonite)
Surface sizing: Raisamyl 408 starch + 1.5 kg styrene
acrylate polymer/ton pulp solids
Paper machine speed:
980 m/min
AKD addition rate: 1.4 kg/ton pulp solids (as AKD, com-
bined with Raisafob RF500)
ASA addition rate: 1.4 kg/ton pulp solids (combined with
Raisafob MF)
AKD/ASA addition rate:
0.7 kg + 0.7 kg/ton pulp solids (com-
bined with Raisafob RF500 and
Raisafob MF, respectively, using sep-
arate additions)
New sizing formulation:
0.7 kg + 0.7 kg/ton pulp solids (ASA
dispersed in Raisafob RF500)
WO 96/23105 2,20 13 37 PCT/F196/00051
13
Test results:
Sizing Addition Cobb6o Ink penetra- Residual Black density, Black density,
agent rate tion HST 80 ketone B/W printing, comp. color
[kg/ton] [g/ml [ Xo,s] [mg/g] felt side printing, felt side
RF500 1.4 22 24 0.29 1.32 1.06
RF MF 1.4 23 122 0 1.14 0.58
RF500 0.7+0.7 22 173 0.15 1.18 0.78
+RF
MF
New 0.7+07 21 208 0.15 1.21 0.86
formula-
tion
As is evident from the above results, the requirements
set for the compatibility of the manufactured paper with
ink-jet printability are not met using ASA sizing alone.
Admittedly, the paper exhibits,zero residual ketone con-
tent. The novel type of combination sizing formulation is
capable of meeting the requirements set for both copier
and ink-jet printing use. The results also show the ef-
fect of the hydrolysis of ASA on the sizing efficiency
when the ASA is dispersed in warm starch used as the in-
ternal size and then added separately. With regard to
ink-jet printing, also herein the novel sizing formulati-
on gives better density values than those achieved using
ASA alone.
In a similar fashion as combining with ASA sizing, the
AKD dispersion based on Raisafob 500 may be combined with
rosin sizing. In general, rosin imparts good friction
properties and does not make the paper slippery as typi-
cally is the case using AKD sizing alone. This improve-
ment is described in the example below.
Example 5
In this example a pilot-scale paper machine was employed
WO 96/23105 220 13 3 7 PCT/F796/00051
14
to compare the water repellency of a paper web achievable
by three different sizing formulations: first, using con-
ventional AKD sizing (Raisafob 940), second, using AKD
combined a protective colloid component formed by Raisa-
myl 150 EH in an amount of 200 % of sizing agent dry
weight, and third, testing the effect according to the
present invention of the protective colloid component
(Raisamyl 150 EH, 200 % by sizing agent dry weight) com-
bined with AKD plus rosin used as a hydrophobic sizing
agent. The dry weight ratio of AKD to rosin was 50/50.
The base web was formed from a pulp comprising 75 % of
birch fiber at 23 SR freeness and 25 % of pine fiber at
23 SR freeness. Bulk sizing of the paper web was perfor-
med using Raisamyl 125 at 0.5 % addition level by fiber
dry weight. The retention system was formed by a two-com-
ponent system in which Percol 162 was added at 0.02 %
level and bentonite at 0.2 % level by fiber dry weight.
The paper web was surface sized using Raisamyl 408 SP,
which was added at 5 % level by fiber dry weight. The
amount of filler added to the base web was kaolin at 20 %
level by fiber dry weight. The pulp slurry pH was in the
range 6.9 - 7Ø The sheets produced were measured for
water absorbance in the Cobb60 test on both the felt and
wire sides of the sheet. Similarly, the static and kine-
tic coefficients of friction were determined. Also the
addition rate of surface sizing was monitored. The test
results are given in the table below.
Sizing Raisafob 940 AKD+ AKD+rosin+
formulation Raisamyl 150 EH Raisamyl 150 EH
Addition rate 0.12 0.12 0.20
Cobb,, felt side 18.6 18.3 28.1
Cobb6D, wire side 20.1 20.2 31.9
Static coeff. of 0.395 0.428 0.465
friction
WO 96/23105 220 13 37 PCTlF196/00051
Kinetic coeff. of 0.222 0.229 0.355
friction
Surface size addi- 1.9 1/min 1.81/mi.n 1.41/min
tion rate
5
As is evident from the above results, the best sizing
properties are achieved using the AKD sizing dispersion
containing Raisamyl 150 EH starch as the protective col-
loid component. Also the friction properties of the sheet
10 are improved over a sheet sized using a conventional AKD
sizing formulation (Raisafob 940). The results also indi-
cate that a sizing dispersion having the AKD/rosin com-
bination as the sizing agent in the protective colloid
also performs excellently particularly in terms of its
15 friction values, which refer to minimal migration tenden-
cy of the sizing agent in spite of the slightly increased
size addition rate over that used in the comparative test
runs. Admittedly, the sizing efficiency in terms of water
repellency herein remains lower than that achieved in the
comparative test runs.
. - -,
