Note: Descriptions are shown in the official language in which they were submitted.
CA 02340641 2001-02-12
WO 00/12819 PCT/EP99/05999
Manufacture of Paper
This invention relates to the production of paper which is strengthened by
starch. Various processes for making paper, and for making paper strengthened
by
starch, are described in, for instance, W095/33096, which is incorporated
herein by
reference.
Processes which are currently of particular interest in paper making comprise
providing a cellufosic thin stock suspension, flocculating this suspension,
shearing the
flocculated suspension, reflocculating the sheared suspension by adding an
aqueous
reflocculating composition, draining the suspension through a wire to form a
wet
sheet, and drying the sheet. The flocculation is generally caused by the use
of a
natural or synthetic polymeric retention aid and the reflocculation is
generally caused
by the use of an aqueous suspension of bentonite or other anionic
microparticulate
material.
It is known to include starch in the final sheet so as to improve the
strength.
One conventional treatment comprises applying a solution of substantially
fully
cooked starch to the sheet before final drying. It is also known to apply
partially or
wholly uncooked starch in this position and to cook it during the drying. It
is also
known to include substantially uncooked starch in the aqueous suspension
before
drainage, for instance as a result of being added with the polymeric retention
aid or
with the aqueous reflocculating composition. The substantially uncooked starch
may
have been slightly cooked so as to facilitate its final cooking, but most or
all of the
cooking is conducted during the drying stage thereby converting the
substantially
uncooked starch to substantially fully cooked starch in the final sheet.
In the invention, substantially fully cooked starch is added to the suspension
after the suspension has been flocculated, and preferably after the
flocculated
suspension has been sheared. Preferably the aqueous reflocculating composition
comprises the substantially fully cooked starch.
The aqueous reflocculating composition preferably comprises an aqueous
dispersion of anionic microparticulate material. The substantially fully
cooked starch
may be precooked to its substantially fully cooked state and then the cooked
starch
and the anionic microparticulate material may be blended to form the final
dispersion
containing both. For instance the starch may be cooked and then mixed with an
CA 02340641 2001-02-12
WO 00/12819 PCT/EP99/05999
2
aqueous dispersion of the microparticulate material.
Preferably, however, the reflocculating composition is made by mixing
substantially uncooked starch with an aqueous dispersion of the
microparticulate
material and cooking the starch in that dispersion. If necessary or desirable,
the
resultant dispersion may then be diluted with water. It seems that cooking the
starch
in the presence of the microparticulate material generates a particularly
desirable
structure within the reflocculating composition.
Preferred anionic particulate materials are swelling clays such as silica,
colloidal silicic acid and colloidal silicas, polysilicate and polysilicic
acid microgels and
aluminium modified versions of these, and organic microparticles, for instance
all as
described in W095133096.
Another reflocculating composition that can be used is an aqueous solution of
a polymer which is generally counterionic to the polymeric retention aid which
was
used for causing the initial flocculation of the cellulosic thin stock
suspension, and in
particular it can be a material as described in W098129604.
The starch must be fully cooked prior to drainage, and preferably prior to
addition to the aqueous celiulosic thin stock suspension, by which we mean
that the
starch granules must have burst and become substantially fully gelatinised.
Naturally
it is usually necessary to maintain the starch under some degree of agitation
during
cooking, as is conventional.
Preferably substantially no uncooked starch is included in the suspension
which is drained, and thus it is not necessary to rely on cooking of the
starch during
drying of the sheet.
The starches which can be used can be any of the conventional starches such
as cationic, anionic or amphoteric starches and can be derived from, for
instance,
com. wheat, potato or tapioca or may be recovered starch.
In another embodiment of the invention, the aqueous reflocculating
composition can contain. as its essential component, merely cooked starch
which is
sufFciently counterionic to the sheared cellulosic flocs for it to act as a
reflocculating
composition. In practice the cooked starch which best meets this requirement
is
usually amphoteric cooked starch.
CA 02340641 2001-02-12
WO 00/12819 PCT/EP99/05999
3
Accordingly, the invention also provides a novel paper making process in
which the reflocculation of the sheared suspension is achieved merely by
adding
cooked amphoteric or other suitable starch, without the customary anionic
microparticulate material. Such processes give satisfactory retention and
drainage
properties despite the absence of the microparticulate material.
All the processes of the invention give improved strength, for instance as
indicated by the burst strength.
The amount of starch which is to be added will be selected having regard to
the degree of strength that is required and having regard to the other
components in
the suspension. Generally it is at least 0.5 and usually at least 1 % by
weight and can
be as much as 10 or 15% by weight, based on the dry weight of the cellulosic
thin
stock.
The polymeric retention aid which is used can be cationic starch but is
generally a synthetic polymer. The synthetic polymer can comprise a
combination of
!ow and high molecular weight polymers, as is known, but generally the final
polymeric retention aid which is added is a synthetic polymer having intrinsic
viscosity
at least 4dl/g. The synthetic polymer can be non-ionic, anionic or cationic,
but is
usually cationic. Preferably the retention aid is a synthetic cationic polymer
of
intrinsic viscosity of at least 4dl/g. Typically the cationic polymers may be
copolymers of acrylamide with for instance diallyl dimethyl ammonium chloride
or
dialkylaminoalkyl (meth) -acrylate or -acrylamide polymers (usually as acid
addition or
quaternary ammonium salt). Suitable materials are described in, for instance
W095133096 and in the documents to which it refers.
Similarly, reference should be made to those documents for a description of
suitable cellulosic materials and process steps.
The process can be used to generate any weight of paper, including paper
board, and so may be low weight or high weight. The invention is of particular
value
in relatively low weight materials since it is in these materials that it can
be difficult to
achieve adequate cooking of uncooked starch during the drying stage. Thus, for
instance, the invention is of particular value in the production of sheets of
below 150
grams per square metre. but it can also be applied to higher weight sheets and
boards.
CA 02340641 2001-02-12
WO 00/12819 PCT/EP99/05999
4
Chelating agent may be incorporated in the reflocculating composition andlor
in the aqueous phase in which the starch is to be cooked, if the water is
hard.
The following examples illustrate the invention.
CA 02340641 2001-02-12
WO 00/12819 PCTlEP99/05999
5
Example 1
110 grams per square metre hand sheet was prepared by flocculating cellulosic
thin
stock with higher molecular weight water soluble cationic polymer derived from
acrylamide and cationic monomer in conventional manner followed by shearing
followed by the addition of an aqueous reflocculating composition.
The burst strength (in KPA) depended on the reflocculating composition.
In one series of experiments, the reflocculating composition consisted of an
aqueous dispersion of bentonite alone or with anionic potato starch. The burst
strength when the bentonite was used alone was 299KPA. The burst strength when
the anionic potato starch was cooked in the bentonite dispersion was 352 and
the
burst strength when the anionic starch was cooked and added after the shearing
but
before the bentonite was 322.
Example 2
Example 1 was repeated and varying the reflocculating composition. When
bentonite
was added alone the burst strength was 169. The burst strength when precooked
anionic starch was included in the bentonite dispersion was 281. The burst
strength
when the anionic starch was cooked in the bentonite was 350. The burst
strength
when the anionic starch was precooked and added after the shearing, but in the
absence of any bentonite during the process, was 308.
When amphoteric starch was included and cooked in the bentonite, the burst
strength was 271. When amphoteric starch was cooked and added after the
shearing
stage but without the addition of bentonite then or subsequently good
retention was
obtained and the burst strength was 379. In this series of experiments the
amount of
starch was 7% based on fibre.
Example 3
Free drainage test was carried out on a packaging grade paper furnish derived
from
waste using a copolymer of acryiamide with dimethylaminoethyl acrylate, methyl
chloride quaternary ammonium salt of intrinsic viscosity in excess of 12d1/g
as the
retention aid and either bentonite or cooked starch as the reflocculating
composition.
For each dose the free drainage was measured in secands for 100m1. 200mi anti
CA 02340641 2001-02-12
WO 00/12819 PCT/EP99/05999
6
300m1 drained respectively and shown in Table 1.
Table 1
Treatment Dose (ppm) Seconds for Seconds for Seconds for
1 OOmI 200m1 300m1
Retention 300 5 ' 2g 7g
Aid
Bentonite 3000
Retention 500 5 23
Aid
Bentonite 3000
Retention 500 3 15 42
Aid
Cooked Starch30000
Retention 500 3 15 37
Aid
Cooked Starch40000
Retention 500 2.5 12 31
Aid
Cooked Starch60000
As can be seen the tests using cooked starch in place of bentonite gave faster
free
drainage.
Examale 4
Britt dynamic retention tests were carried out on a packaging grade paper
furnish
derived from waste using a copolymer of acrylamide with dimethyiaminoethyl
acrylate,
methyl chloride quaternary ammonium salt of intrinsic viscosity in excess of
12dllg as
the retention aid and either bentonite or cooked starch as the reflocculating
composition. The solids content in the water drained and the retention were
measured
for each test and shown in Table 2.
CA 02340641 2001-02-12
WO 00/12819 PCT/EP99/05999
7
Table 2
Treatment Dose (ppm) Back water solids Retention
%
Retention Aid 500 0.240 79.6
Bentonite 3~0
Retention Aid 500 0.198 83.8
Cooked Starch 40000
As can be seen from the results the test with cooked starch shows improved
retention.
Example 5
Example 3 was repeated except using a newsprint stock derived from 70% deinked
waste and 30% mechanical pulp. The results are shown in table 3.
Table 3
Treatment Dose (ppm) Seconds for Seconds for Seconds for
1 OOmI 200m1 300m1
Retention 1000 11 45 -
Aid
Bentonite 3000
Retention 1000 5 23 60
Aid
Cooked Starch40000
The test using cooked starch showed improved drainage times.
Example 6
Example 4 was repeated except using a newsprint stock derived from 70% deinked
waste and 30% mechanical pulp. The results are shown in table 4
CA 02340641 2001-02-12
WO 00/12$19 PCT/EP99/05999
8
Table 4
Treatment Dosee (ppm)Back water solidsRetention ~
%
Retention Aid 1000 0.38 68.6
Bentonite 3000
Retention Aid 1000 0.27 77.7
Cooked Starch 40000
Higher retention was achieved using cooked starch in place of bentonite.
Example 7
The process of Example 1 was repeated using a 0.7% brown millstock and using
750
grams per tonne of a copolymer of acrylamide with dimethylaminoethyl acrylate,
methyl chloride quaternary ammonium salt of intrinsic viscosity in excess of
12dllg as
the retention aid. Five series of experiments were conducted using as the sole
reflocculating composition an anionic cooked starch, three types of amphoteric
cooked starch and an unmod~ed cooked potato starch at various doses. The burst
strength of the paper sheets formed were measured and the results are shown in
Table 5.
Table 5
Cooked Starch RetlocculatingCorrected
Composition Burst
Strengths
(Kpa)
for
various
starch
dosages
(Kg/tonne)
5 10 20 30 40
anionic Aniofax AP25 228.6 256.8 260.41 280.6 279.5
amphoteric CATO 245 259.2 284.1 273.9 308.4 316.0
amphoteric CATO 247 255.0 253.9 263.0 289.3 320.5
arnphoteric CATO 255 257.8 266.7 294.7 314.4 346.7
Unmodified Potato Starch 239.7 243.8 260.6 269.1 271.2
~ i
As a comparison the process was repeated using bentonite in place of cooked
starch.
The burst sttrengths are shown in Table 6.
CA 02340641 2001-02-12
WO 00/12819 PCT/EP99/05999
Table 6
Corrected
Burst
Strengths
(Kpa)
for
various
starch
dosages
(Kg/tonne)
0.5 1 2 3 4
bentonite 207 210 208 205 200
As can be seen the burst strength of the paper was greatly improved when using
cooked starch as the refloccuiating composition.
