Note: Descriptions are shown in the official language in which they were submitted.
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The Use of Modified Starch Products as Retention Agents
in the Production of Paper
The invention relates to the use of starch or
starch derivatives, which have been modified with polyelec-
trolytes based on dialkylaminoalkyl(meth)acrylamides and
pulped in the presence of inorganic additives, as retention
agents for pigments, mineral fillers, and fibrous fines in
paper manufacturing.
Pigments and fillers are added as essential paper
components in the production of the paper pulp dispersion
and bound using retention aids during sheet forming. Ac-
cording to the statements in Wochenblatt fur Papierfabrika-
tionen 5 (1991), pp. 149-154, for example, cationic bulk
starches are extensively used as colloidal auxiliary agents
to improve the retention, draining and strength of the
paper where, in particular, by using cationic starch ethers
according to Ullmann, 4th edn., 1979, Vol. 17, p. 581, the
retention of pigments and fines is improved.
The retentive effect of starch ethers is limited,
however, and therefore, high molecular weight, cationic
polyelectrolytes having higher charge density are also used
as retention agents. For example, these high molecular
weight polyelectrolytes are copolymers of acrylamide and
esters of (meth)acrylic acid with di(C1-C2)alkylamino-
(Cz-C6)alkylalcohols or copolymers of acrylamide and amides
of (meth) acrylic acid with di (C1-CZ) alkylamino (Cz-C6) alkyl-
amines, each of which is present in protonated or qua-
ternized form. Retention agents based on such a,(3-
unsaturated N-substituted carboxylic acid amides have been
described in EP-A-0,038,573.
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According to WO 86/00100, a process for the produc-
tion of paper is known wherein, in order to improve the re-
tention, the paper pulp is added with colloidal binders ob-
tained on the basis of silicic acid modified with aluminum
silicate on the surface thereof and cationic or amphoteric
carbohydrates, preferably such as starch or amylopectin.
EP-A-0,703,314 and WO 97/04168 suggest the use of
special cationic amylopectin starches to improve the reten-
tion, optionally using colloidal silicic acid, anionic
polyacrylamides or bentonite.
Furthermore, microparticle systems are known as re-
tention agents from Wochenblatt fur Papierfabrikationen 20,
1994, pp. 785-790, where a paper pulp dispersion initially
is pretreated using cationic starch or cationic polyacryl-
amides, flocculated and dispersed, and subsequently
reflocculated prior to sheet forming, using silica
microparticle systems or by adding bentonite or aluminum
salts. The mufti-stage processing mode leads to improved
retention values.
Furthermore, a process for the production of paper
has been described in EP-B-0,227,465 wherein, using complex
partial steps, the pulp and separately, the mineral filler
as well are initially treated with a synthetic polyelectro-
lyte of same charge each time and subsequently, the treated
filler is subjected to a treatment using a polymer poly-
electrolyte of opposite charge.
Likewise, a mufti-stage process for improving the
retention is known from US-A-5,126,014, wherein the paper
pulp, prior to an optional mufti-stage shear treatment, is
added with calcium carbonate as filler, cationic starch, a
cationic coagulant, and an anionic flocculant and, follow-
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ing at least one shear treatment stage, bentonite or col-
loidal silicic acid are added thereto.
Also, the modification of starch products using
cationic polyelectrolytes is known from prior art.
A process for the production of cationic starch is
known from EP-A-0,803,512, according to which the starch in
dry state is roasted with cationic polymers at temperatures
of from 60 to 200°C for a period of from 10 minutes to 5
hours, to be used as paper strengthening agent.
Furthermore, the modification of starch using
ionic, particularly cationic polyelectrolytes has been de-
scribed in EP-B-0,282,761, WO 96/05373 and WO 96/13525. To
this end, according to EP-B-0,282,761, cationic polymers of
diallyldimethylammonium chloride, N-vinylamine or N-vinyl-
imidazoline are heated with native potato starch or one
already pulped, while according to WO 96/05373, cationic
polymers are reacted with preferably anionic starch, and
according to WO 96/13525, preferably hydrolyzed, cationic
polymers of N-vinylformamide, polyethyleneimines or poly-
alkylamines are reacted with starches of any type. These
reaction products, as is the case, with starches modified
with copolymers of (meth)acrylamide and dialkylaminoalkyl-
(meth)acrylamide, are only recommended as dry strengthening
agents for paper manufacturing.
More and more waste paper and wood pulp dispersions
are being processed in paper manufacturing and therefore,
the level of fines such as cellulose short fibers and min-
eral fillers in the paper pulp dispersions is increasing.
Furthermore, and as a general rule, the level of inorganic
fillers and pigments has to be increased further in order
to obtain a paper of an appearance accepted on the market .
It is well-known, however, that the strength of paper is
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adversely affected with increasing levels of fines and, in
particular, of mineral fillers and pigments. Thus, for ex-
ample, it is evident from the publication by K. Ritter and
H. Forkel, "Papierfaserstofftechnik" Symposium 1997, 21, p.
4, that the tear resistance of paper as a measure for the
strength thereof decreases with increasing ash content in
the paper, which is regarded as a measure for the content
of mineral fillers and pigments in the paper.
It was therefore the object of the present inven-
tion to improve the retention of pigments, fillers and
fines in well-known paper manufacturing, preferably using
waste paper, with no additional processing steps, i.e.,
without the partial steps mentioned above, and without ad-
versely affecting the mechanical strength of the paper.
According to the invention, this is accomplished by
using modified starch as retention agent for pigments, in-
organic fillers and fines in paper manufacturing, said
modified starch being obtained by pulping starch, starch
derivatives and/or degradation products thereof in aqueous
solution and in the presence of at least one cationic poly-
mer constituted of at least 20 wt.-o of polymerized dial-
kylaminoalkyl(meth)acrylic acid amide moieties present in
protonated, preferably quaternized form, and with addition
of at least one particulate additive based on an inorganic
mineral substance prior to, during, or after pulping.
Native starches, such as potato starch, wheat
starch, cereal flour, corn starch, tapioca starch, sago
starch, as well as starches having an increased hydrolysis
content, rice starch, pea starch and/or mixtures thereof,
starch degradation products, particularly dextrins or oxi-
dized starches such as dialdehyde starch, starch deriva-
tives like chemically modified starches, particularly ani-
onic starches such as carboxystarch and starch degraded by
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persulfate, anionic starch esters such as starch phosphoric
acid mono- or diesters, starch acetates and starch cit-
rates, anionic starch ethers such as carboxymethylstarch,
carboxymethyl-2-hydroxyethylstarch, or carboxymethyl-3-hy-
droxypropylstarch, or cationic starch derivatives such as
N-containing starch ethers, particularly starches having
primary or secondary amino or imino groups, and tertiary
amino groups positively charged by protonation with acids,
and quaternized ammonium groups are employed as starch com-
ponent.
Native starches such as potato starch, wheat
starch, corn starch, rice starch, pea starch, and/or mix-
tures thereof, as well as anionic starches and/or cationic
N-containing starch ethers are preferably used.
Homo- or copolymers of dialkylaminoalkyl(meth)-
acrylic acid amides are preferably used as cationic
polymers, including at least 20 wt.-o of polymerized amide
moieties of (meth)acrylic acid and/or acrylic acid and
preferably di (C1-CZ) alkylamino (Cz-C6) alkylamines, each one
being present in protonated or quaternized form. Their
production has been reported in EP-A-0,013,416 or in EP-A-
0,113,038, for example, the corresponding disclosure of
these publications hereby being incorporated by reference.
Preferably, these polymerized moieties are derived
from protonated or quaternized N-dialkyl-substituted
(meth)acrylic acid amides such as dimethylaminoethylacryl-
amide or -methacrylamide, dimethylaminopropylacrylamide or
-methacrylamide, diethylaminopropylacrylamide or -meth-
acrylamide, diethylaminoethylacrylamide or -methacrylamide,
diethylaminomethylacrylamide or -methacrylamide, as well as
N',N'-dimethylamino-2,2-dimethylpropylacrylamide or -meth-
acrylamide or mixtures thereof, reacted with well-known
quaternizing agents. For example, dimethyl sulfate, diethyl
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sulfate, methyl chloride, ethyl chloride, preferably di-
methyl sulfate or methyl chloride are possible as qua-
ternizing agents.
The polyelectrolytes may include additional moie-
ties of unsaturated monomers, e.g. diallyldimethylammonium
chloride. These monomers incorporated by polymerization may
also be water-soluble, non-ionogenic monomers such as
acrylamide, methacrylamide, N-(C1-Cz)-alkylated (meth)-
acrylamides, N-vinylamide, vinylformamide, N-vinylacet-
amide, N-vinyl-N-methylacetamide, N-vinylpyrrolidone. In
addition, suitable water-soluble monomers are N-methylol-
acrylamide, N-methylolmethacrylamide, as well as N-meth-
ylol(meth)acrylamides partially or completely etherified
with monohydric C1-C9 alcohols .
Likewise, the copolymers may include limited
amounts, preferably up to 10 wt.-o, of sparingly water-
soluble and/or water-insoluble monoethylenically unsatu-
rated monomers such as (meth)acrylic acid alkyl esters and
vinyl acetate, as long as the solubility of the copolymers
in water is retained.
The polymer products to be used according to the
invention preferably have a molecular weight m.w. (g/mol)
in a range of from 1.0 x 105 to 40 x 106, more preferably in
a range of from 2.0 x 106 to 15 x 106, with 5.0 x 106 to
15 x 106 being particularly preferred.
The viscosity was determined using a to polymer so-
lution in loo NaCl solution on a Brookfield RVT viscometer,
spindle 1-3/10 r.p.m. at 20°C, indicating >10 mPa~s for the
polymers being used.
Clay, preferably swellable, silicic acid, prefera-
bly silicic acid sol and/or polysilicates modified with
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aluminum, polyorthosilicic acid, polyorthosilicic acid
modified with aluminum, bentonite, titanium dioxide, or
talc are possible as particulate additives based on
inorganic mineral substances, i.e., which may also consist
thereof. These materials preferably are present as micro-
particles or microgels. It is particularly preferred to use
bentonite, talc, titanium dioxide, or silicic acid sol.
The reaction of the starch component with the cati-
onic homo- or copolymers of preferably protonated or qua-
ternized dialkylaminoalkyl(meth)acrylic acid amides can be
effected in aqueous dispersion and in batchwise fashion in
a reaction vessel, or in a continuous-flow process, e.g. in
a jet boiler under heat exposure at temperatures of from 70
to 130°C, preferably 90-100°C, with addition of the inor-
ganic additive and optionally under pressure, thus pulping
the starch component. The reaction conditions and suitable
apparatus-related conditions are in accordance with the
statements in Wochenblatt fur Papier 4, 1991, pp. 127-130,
the disclosure of which is hereby incorporated by refer-
ence.
The addition of additives based on inorganic min-
eral substances in amounts of from,0.l to 15 wt.-o, pref-
erably from 3 to 15 wt.-o, more preferably from 5 to
13 wt.-%, relative to the modified starch component, in the
production of these modified starch components prior to
starch pulping or during starch pulping, preferably prior
to the modifying reaction and pulping with the cationic
homo- or copolymer, provides a retention agent having im-
proved effectiveness as to the retention capacity for fill-
ers and fines.
The aqueous dispersion of the starch component em-
ployed in the modification and not pulped yet preferably
has a content of from 0.5 to 20 wt.-%, more preferably from
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0.5 to 10 wt.-o, and highly preferably from 2.0 to 10 wt.-o
of starch component. The aqueous solution of the polyelec-
trolyte used in the modification has a content of from 0.1
to 2.0 wt.-%, preferably from 0.1 to 0.5 wt.-o, and highly
preferably from 0.1 to 0.3 wt.-o of cationic homo- or co-
polymers. In said modification, the weight ratio of starch
component to cationic polyelectrolyte ranges from 4:1 to
25:1, preferably from 10:1 to 25:1, and more preferably
from 14:1 to 20:1.
The modified starch products, together with the in-
organic additives, preferably in the form of an aqueous so-
lution, can be used as retention agents in the production
of all paper grades and cardboards. Preferably, they are
suited for use in the production of paper based on sulfite
or sulfate cellulose in bleached or non-bleached condition;
such a fibrous material may consist of up to 100 wt.-o of
wood pulp and/or waste paper, and for this reason alone has
a high level of mineral fillers, pigments and fibrous
fines.
According to the invention, the retention agent of
the invention is added to the aqueous paper pulp dispersion
in an amount of from 0.1 to 10 wt.-o solids, preferably
from 0.5 to 5 wt.-%, and more preferably from 1.0 to
3 wt.-o, relative to the dry mass or paper pulp mass, up-
stream from the stock inlet of the paper machine, and pref-
erably as an aqueous solution with stirring. The addition
is made to the aqueous dispersion which may already contain
calcium carbonate, kaolin, aluminum silicate and oxide
hydrate, satin white, talc, gypsum, barite, calcium sili-
cate, lithopone, and kieselguhr as fillers, as well as syn-
thetic, organic fillers from the recycling material, or has
been added therewith.
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Advantageously, the retention agent of the inven-
tion is added to the pulp dispersion in the machine chest,
upstream from the vertical separator, and upstream or down-
stream from the stock flow pump, prior to sheet forming.
Using the retention agent of the invention based on
modified starch and inorganic additives, excellent reten-
tion of the fillers is achieved and surprisingly, despite
increased filler and thus, ash content of the paper, a de-
terioration of the strength values is avoided. In particu-
lar, this is the case when using paper pulp dispersions
containing percentages of waste paper or wood material such
as wood pulp and thermomechanical pulp (TMP) or consisting
thereof.
It has also been determined that the use of the re-
tention agent according to the invention does not interfere
with the effect of optical brighteners added to improve the
whiteness of the paper pulp.
The invention will be illustrated in more detail
with reference to the following Examples.
Examples 1 to 4:
A In a heatable vessel, 250 g of an aqueous 4.0 wt.-o
dispersion of native potato starch, product name C*Gel
30002, Co. Cerestar Holding B.V., was mixed with 250 g
of a 0.25 wt.-o solution of a water-soluble cationic
polymer with stirring, added with varying amounts of
bentonite, respectively with addition of talc, and
heated at a temperature of from 95 to 100°C. No mineral
substance was added in Comparative Example 1. The mix-
ture was maintained in said temperature range for 15 to
20 minutes, then cooled, and used as retention agent.
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Copolymers of trimethylammoniumpropylacrylamide chlo-
ride and acrylamide having a quaternized monomer per-
centage of 70 wt.-o were used as water-soluble cationic
polymers.
B A 4.0 wt.-o pulp suspension made of 100 wt.-o waste pa-
per was diluted with water to a content of 1 wt.-o and
added with stirring with the retention agent produced
according to A. The retention agent was added in an
amount of 2.125 wt.-o, relative to the dry content of
the pulp suspension.
C Using the pulp suspension obtained according to B, test
sheets having a gram weight of about 100 g/cm' were pro-
duced in a laboratory using the Rapid-Kothen process in
accordance with DIN 54358 on a sheet forming apparatus
model 20-12 MC from the Haage company. The sheets were
dried and stored overnight under normal conditions at
23°C and 50o relative humidity.
After weighing the papers, gram weight, ash content
according to DIN 54373 and bursting pressure according to
DIN 63141 were determined.
The overall retention indicates the ratio of the
amount of dry material employed in paper manufacturing to
the amount of material remaining in the final paper. This
can be determined by weighing the respective amounts of ma-
terial.
The ash retention indicates the ratio of the ash
content of the amount of (dry) material employed in paper
manufacturing to the ash content of the final paper. This
is determined by determining the respective ash content.
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The retention of fines indicates the ratio of the
fines content in the amount of (dry) material employed in
paper manufacturing to the fines content in the final pa-
per.
Using a Britt Dynamic drainage jar, the respective
amounts of fines are determined as follows:
An aqueous paper pulp suspension including 0.5 g of dry pa-
per material, from which suspension the paper is produced
(StWG), is diluted to about 1 wt.-% using tap water. This
suspension is stirred at 750 r.p.m. for some seconds and
then drained with stirring. The residue is added with an-
other 500 ml of water, stirred, and drained. The process is
repeated 4-5 times until the filtrate is completely clear,
i.e., no fine fibers can be washed out anymore. The residue
on the screen is placed on a tared filter and determined
gravimetrically (drying at 110°C).
Calculation of fines content: Fines content = 100 - amount of coarse material
(%)
The amount of coarse material corresponds to the amount of
fibers present on the filter.
Amount of coarse material in g
Fines content = 100 -
0.5 g x 1 wt.-
The corresponding values from Comparative Example 1
and Examples 1 to 4 are given in Table 1.
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Table 1
Comparative Example Ash content Overall retentionBursting pressure
1/
Exam les 1 to 4 wt.-% wt.-% kPa
Mod. starch with 93.3 89.1 95
no min-
eral substance added
Mod. starch 9.7 95.3 90.7 104
Bentonite 0.3
Mod. starch 9.5 95.2 92.1 106
Bentonite 0.5
Mod. starch 9.0 97.6 96.7 92
Bentonite 1.0
Mod. starch 9.0 95.3 94.0 -
Talc 1.0
Comparative Example 2
The procedures A, B and C of Examples 1 to 4 were
the same, but the cationic polymer specified in A of Exam-
ples 1 to 4 was tested as such as retention aid in sheet
forming.
The corresponding values are given in Table 2.
Table 2
Comparative Cationic Ash contentOverall retentionBursting pressure
ratio
Example in copolymer(wt.-%) (wt.-%) (kPa)
wt.-
2* 70 0 44.8 60
* With no starch component
