Note: Descriptions are shown in the official language in which they were submitted.
- 1 ~3~7~
` `~A process for the production of pa~fer
The present invention relates to a process for the
production of paper utilizing a combination of substances
for improving retention and dewatering. More particularly
, 5 the invention relates to the use of a combination of a
cationic silica based sol and a cationic, organic, poly-
meric retention agent in papermaking.
' It is previously known to use combinations of in- -
i organic silica sols and cationic retention agents in
papermaking. In these cases anionic silica sols have been
I used in combination with cationic polymeric retention
agents, such as for example cationic starch and cationic
, polyacrylamide. Such systems are disclosed for example in
f European patent Nos 41056 and 218674. The effect of
systems comprising an anionic silica sol and a cationic
component is based on the interaction of the two
differently charged substances and it is assumed that
the sol particles with tlleir strong anionic charges to
some degree produce a cross-linking of the polymeric re-
tention agent.
-' Cationic inorganic silica based colloids are per se -
~, known and their use in specific paper making processes is ~-
I also known. Thus the US patents 4309247 and 4366068 dis-
'f close the use of cationic inorganic silica colloids in the
1 25 preparation of filter media based on cellulose fibers. It
y is also known from the Japanese patent publication No. 85-
J 260377 of December 23, 1985 to use cationic colloidal silica -
in ink jet recording paper to improve water resistance of
water soluble dyes and to improve light resistance. In an
example in the Japanese application the preparation of the
ink jet recor~ing paper f~onl a pulp slurry containing talcum,
cationic starch and cationic colloidal-silica is shown.
According to the present invention it has unexpected- ~:
ly been found that a combination of a cationic silica based
35 sol and a cationic, organic, polymeric retention agent can
be used in papermaking and that the combination of the two
components of the same charge gives improved retention and
dewatering. The combination according to the invention
~L
q~ :.-',.
, . . .
~ ~,
,: , , .~ :,. , -, . , .. ~ "-,;, . ., ", . .,, . .. ,i . ,: . ..... .
2~5
~- gives an improved retention of fine fibers and optional
fillers and eases drainage and thereby makes the papermak-
ing process more efficient.
The present invention thus relates to a process for
5 the production of paper by forming and dewatering a suspen-
sion of cellulose containing fibers and optionally fillers
on a wire whereby said formation and dewatering takes place
in the presence of a cationic silica based sol and a
cationic polymeric retention agent selected from the groups
10 cationic guar gum and cationic synthetic polymers.
Silica sols with positively charged particles are, as
stated above, known per se and their preparatlon is dis-
;i closed for example in the US patents 3007878, 3620978 and
ii 3719607. The general methods for preparing cationic silica
¦ 15 sols start from aqueous sols of silica which are reacted
with a basic salt of a polyvalent metal to give the sol
particles a positive surface charge and stabilizers such as
boric acid, alkali metal bases, alkaline earth metal bases,
ammonia etc are often used in the processes. The polyvalent
20 metal salt is usually an aluminum salt, due to availability
- and lower costs, although it is of course also possible to
use basic salts of other polyvalent metals for preparing
! cationic silica based sols, such as chromium, zirconium and
J others. Any basic salt which is water soluble and gives the
f 25 desired positively charged surface can be used and general-
ly the cationic sols are prepared using chlorides, nitrates
or acetates of the metal.
The particles of the cationic sols have a small
average particle size, usually below 100 nm and the size is
30 generally in the range of from 2 nm to 100 nm, more often
in the range of 2 nm to 80 nm. Suitably the particle size
is within the range of from 3 to 20, and preferably from
3.5 to 14 nm. The cationic silica particles will have
positively charged species of the polyvalent metal, prefer-
35 ably of aluminum, on their surfaces and the mole ratio of
aluminum to surface silica can be within the range of from
1:8 to 4:1, suitably within the range of from 1:6 to 4:1
and preferably within the range of from 1:4 to 4:1. Most
;
'.''.' :.
~32~705
~ 3
- preferably the ratio is within the range of 1:2 to 4:1. The
mole ratio of aluminum to surface silica has here been cal-
, culated as in US patent 3,956,171, ie on basis of 8 silicon
atoms per square nm of silica surface whereby the fraction
, 5 of total silica occurring in the surface becomes 8x10-4xA,
where A is the specific surface area of the sol particles
in m2/g. The cationic silica sols used according to the
present invention can be prepared from any anionic silica
sol by reaction with a basic salt of a polyvalent metal
salt as above. They can thus be prepared from commercial
sols of colloidal silica and from silica sols consisting of
polymeric silicic acid prepared by acidification of alkali
metal silicate, for example by mixing mineral acid and
water glass or by using acid ion exchange resins. The
q 15 cationic silica is added to the stock in the form of an
I aqueous sol. The concentration in the cationic sol can be
up to about 50 per cent by weight for sols made from
commercial anionic silica sols and up to about 10 per cent
by weight when made from polysilicic acid. The stability of
20 the last mentioned type of sols is limited and thus con-
centrations about or lower than 5 per cent are suitable.
The stability is generally higher if more aluminum is
i~ present, within the above ratios. From a practical point of
~ view it is anyhow suitable to dilute the sols to a concent-
,f. 25 ration of from 0.05 to 5.0 per cent by weight of the
1 cationic particles, preferably from 0.1 to 2 per cent by
weight, before addition to the stock.
The cationic retention agents which are used in
combination with the cationic silica sols are at papermak-
ing conventional organic, polymeric retention agents, which
have a cationic net charge at the pH at which they are
used, and they are either cationic guar gum or synthetic
cationic polymers. Examples of suitable synthetic cationic
polymers are cationic polyacrylamides, polyethyleneimines
and polyamidoamines. A mixture of two or more cationic
retention agents as above can also be used, and any of
these can also be used in combination with cationic starch.
Synthetic cationic retention agents are preferred, and
4 1324705
particularly cationic polyacrylamide.
The amounts of cationic silica and of cationic
retention agent which are used will of course depend on the
particular stock, presence of fillers and other papermaking
conditions. Usually amounts of from 0.005 to 2.0 per cent
by weight of the cationic silica, as dry, based on dry
~, fibers and optional fillers give good results and the
amounts suitably used are from 0.005 to 1 per cent by
weight. Amounts in the range of from 0.03 to 0.3 per cent
are preferred. The ratio of cationic retention agent to
`~ cationic silica will vary widely depending on for example
the papermaking conditions, the particular cationic polymer
and on other effects desired from this. Usually the weight
~, ratio of cationic retention agent to cationic silica should
';~t 15 be at least 0.01:1 and suitably at least 0.2:1. The upper
limit of the cationic retention agent with lower cation-
~ icity such as guar gum is not critical and can for such
7 cationic polymers be very high, up to a ratio of 100:1, and
higher, and the limit is usually set by economical reasons.
Ratios of cationic retention agent to cationic silica
within the range of 0.2:1 to 20:1 are suitable for most
i, Systems.
~ The two-component system of the present invention can
;,. be used in papermaking from different types of stocks of
'25 papermaking fibers, suitably from stocks containing at
least 50 per cent by weight of cellulose containing fibers.
The components can for example be used as additives to
i stocks from fibers from chemical pulp, such as sulphate and
., sulphite puIp, thermo-mechanical pulp, refiner mechanical
30 pulp or groundwood pulp, from as well hardwood as softwood.
l~ The system of the invention can also advantageously be used
-' for recycled fibers. As mentioned, the stock can also
contain mineral fillers of conventional types, such as eg
kaolin, titanium dioxide, gypsum, chalk and talcum. Par-
35 ticularly good results have been obtained with pulps which
~ are generally considered as difficult and which contain
s fairly high amounts of non-cellulose substances such as
lignin, ie different types of mechanical pulp such as
, -' ;
:- . , :
- 132~705
~, 5
groundwood pulp. The two component system of the invention
is particularly suitable for stocks made up from at least
25 per cent by weight of mechanical pulp and give a much
improved effect in such systems compared with sols of
anionic silica and a cationic retention agent. The terms
paper and papermaking, which are used heréin, do of course
not only include paper anq its production, but also other
cellulose fiber containing sheet or web form products, such
as pulp sheet, board and cardboard and their production.
loThe cationic silica sol and the cationic polymeric
retention agent can be added to the stock separately,
simultaneously or premixed. They can also be added in two
or more increments. It is preferred that the two components
are added separately. It seems that the order of addition
of the sol and the cationic retention agent has some
~i influence on the obtained effect and that when the sols
contain smaller particles a better effect is obtained if
the cationic retention agent is added before the sol of
cationic silica, while for sols of larger particles a
better effect generally is obtained when the cationic
silica is added first and the cationic retention agent is
added subse~uently. The addition of cationic silica and
cationic retention agent according to the invention con-
siderably improves the retention of fines and fillers,
when present, and also considerably improves the dewater-
ing, in comparison with the use of solely the cationic
3~ retention agent. Smaller amounts of cationic polymer can
thus be used for obtaining a desired effect and for expen-
sive cationic polymers, such as polyacrylamide, important
j~ 30 cost-savings can thus be made. Using the system of the
invention the papermaking process can thus be made more
efficient without negative effects on the strength and
- other important properties of the produced paper. The
~ mechanisms contributing to the positive effect of the two
'~ 35 components, which have the same charge, have not been
entirely established, but it is believed-~that the cationic
silica of the sol at least partly neutralizes dissolved
anionic wood substances and that it also improves the
132~705
~- strength of flock, formed from dissolved and solld com-
ponents of the stock by the added cationic retention agent,
` by its capability of penetrating and chargewise neutrallz-
ing the flocks.
e 5 In the present process for production of paper
conventional additives can of course be used in addition to
the two additives according to the invention. Fillers have
been discussed above, and as examples of other additives
can be mentioned sizing agents, rosin based or synthetic
sizing agents, cationic starch, wet strength resins and
aluminum based compounds, such as alum, alumlnate, aluminum
chloride or polyaluminum compounds, can thus be used. The
papermaking process using the present combination of
substances for improved retention and dewatering can be
carried out in a wide pH range, from about 4 to about 9. It
is a special advantage that wood containing papers with
high levels of fines content can be produced at high
retention with the present system without adverse effects
on paper formation.
The invention is further illustrated in the following
examples which, however, are not intended to limit the
same. Parts and per cent relate to parts by weight and per
cent by weight respectively, unless otherwise stated.
Example 1 ' .
The cationic silica sols used in Examples 1 and 2
were prepared as follows. Aluminum chlorohydrate, with the
formula A12(OH)5Cl.2H2O, was heated to 47C under stirring
in a flask equipped with a heating ~acket. When the temp-
erature had been reached anionic silica sols, deionized
with regard to sodium ions, which had been diluted with
deionized water were added for a certain time to allow
reaction with the aluminum chlorohydrate. As a more speci-
fic preparation procedure the following is typical: 408 g
50% A12(OH)5Cl.2H2O solution was warmed to 47C. 657 g of
anionic silica sol containing 15.21% SiO2 were diluted
, with 928 g deionized water. The particles of thls sol had a
size of about 7 nm. The sol was added for 90 minutes at
47C and the obtained cationic sol was then allowed to cool
'' ':~ ' ''
~: "
~~ to room temperature. 1 ~ ~ 4 7 ~ ~
;, In the following tests the dewatering was evaluated
~A with a "Canadian FreenesS Tester" which is the usual method
for characterizing the dewatering or drainage capability
5 according to SCAN-C 21:65.
j The stock system was composed of 60% bleached birch
sulphate pulp and 40% bleached pine sulphate pulp and 30%
of China clay had been added to the system. The chemical
additions are calculated in kg per ton dry stock system
10 (fibre + filler) and the amounts of sols and cationic
polymers are given as dry substance. All chemical additions
were made with a mixing speed of 800 rpm in a Britt Dynamic
Drainage Jar with a blocked outlet for 45 seconds and the
¦ stoc~ systems were then added to the Canadian Freeness
15 Tester. In all tests the sol was added before the polymer.
Different sols were used:
a) Cationic aluminum modified silica sol with a mole ratio
of aluminum to surface silica groups of 1.30:1 and a
particle size of about 7.5 nm.
20 b) Cationic aluminum modified silica sol with a mole ratio
of aluminum to surface silica groups of 2.95:1 and a
particle size of about 7 nm.
} c) Cationic aluminum modified silica sol with a mole ratio
of aluminum to surface silica groups of 3.25:1 and a
~ 25 particle size of about-6 nm.
¦ d) Cationic aluminum modified silica sol with a mole ratio
of aluminum to surface silica groups of 2.40:1 and a
particle size of about 14 nm.
The following cationic polymers were used:
i 30 A) Cationic polyacrylamide, PAM 1, of medium cationicity,
sold by Allied Colloids under the trade mark of PE~OL 292.
B) Polyethyleneimine, PEI, sold by BASF AG under the trade
, mark of POLYMIN.
C) Cationic polyacrylamide, PAM 2, of low cationicity, sold
35 by Allied Colloids under the tra~e mark of P~RCOL 140.
` In the table below the results of the freeness tests
are given in ml CSF. Comparisons with addition of solely
the respective cationic polymers are given. A comparison
B
. -
. .. , ....... .. .,, . - .. . . . , . . .,. .- . ;. , ~. ; ~ ,, ,;. . - .
132~7 0~ `
. was also made with an anionic aluminum modified silica sol
with a particle size of about 5.5 nm.
Sol/amount Cat. polymer/amount stock pH CSF
5 _ kg/ton kg/ton ml
.~ :
a/l.0 PAM1/0.5 4.5 560
;~ a/l.0 PAMl/1.0 4.5 620
a/1.0 PAM1/2.0 4.5 675
'~; 1 0
b/l.0 PAMl/0.5 4.5 540
b/l.o PAMl/l.0 4.5 ,605
b/l.0 PAMl/2.0 4.5 640
~ '.
¦ 15 c/l.0PAMl/0.5 4.5 565
c/l.0PAMl/l.0 4.5 620
c/l.0PAMl/2.0 4.5 660
d/l.0PAMl/0.5 4.5 530
d/l.0PAMl/l.0 4.5 590
d/l.0PAMl/2.0 4.5 640
- PAMl/0.5 4.5 430
7 - PAMl/l.0 4.5 515
- PAMl/2.0 4.5 570
~, -.
Anionic/l.0PAMl/0.5 4.5 305 ~-
Anionlc/l.0PAMl/l.0 4.5 4g5
Anionic/l.0PAMl/2.0 4.5 580
J~ 30
a/1.0PEI/0.6 7.0 430
' a/l.0PEI/l.0 7.0 470
~, a/2.0PEI/2.0 7.0 485
,:
,- 35 - PEI/0.6 7.0 350
- PEI/l.0 7.0 410 -
- PEI/2.0 7.0 435
: ::
~ 1~2~7~5 ~-
~ Sol/amount Cat. polymer/amount stock pH CSF
'~ kg/ton kq/ton ml
a/l.0 PAM2/0.5 4.5 555
a/l.o PA~2/1.0 4.5 625
a/1.o PAM2/2.0 4.5 690
- PAM2/0.5 4.5 410
- PAM2/1.0 4.5 505
- PAM2/2.0 4.5 575
Example 2
In this test the dewatering effect of a system of the
cationic aluminum modified silica sol designated as a) in -
Example 1 and a polyacrylamide, Percol 292, was measured
and a comparison was made with a system of an anionic
aluminum modified sllica sol, with a particle size of about
5.5 nm, and the polyacrylamide. The stock was made up from
groundwood pulp beaten to 130 ml CSF and the pH was ad-
justed to 5 with H2SO4. In the tests with the cationic sol
this was added to the stock before the polyacrylamide,
except in one experiment when the order of dosage was
reversed. In the tests with the anionic sol thls was added
to the stock after the polymer. The added amounts given in
kg/ton are calculated as dry chemicals on dry pulp.
25 Cationic sol Anionic sol Polyacryl- CSF
k~/ton kg/ton ~m ml
~:~ _ - - 130
_ - 0.5 210
- - 1.0 230 ~ ~ -
, ~ 30 - - 2.0 250
,~ - 3 - 0 245
,~ 1.0 - 0.25 290
'~~ 1.0 - 0.5 325
, 1.0 - 0.75 340 -
: 35 1.0 - 1.0 355 `~
1.0 - 2.0 360 :~
1.0 (reversed dosage order) 1.0 270
i
3.0 - 0.25 330 :```
'`'
-
' 10 132~70~
Cationic sol Anionic sol Polyacryl- CSF
kq/ton kq/ton amide kq/ton ml
3.0 - 0.5 375
3.0 - 1.0 425
.0 - 2.0 405
- 1.0 O.S 190
; - 1.0 0.75 230
- 1.0 1.0 255
- 1.0 2.0 280
- 3.0 0.5 190
- 3.0 1.0 240
_ 3.0 2.0 ~ 320
~ 3.0 3.0 360
- 3.0 4.0 350
As evident from the table maximum CSF level is
reached at a much lower addition of polyacrylamide in the
system with the cationic sol, compared with the system
with the anionic sol.
Example 3
Some different cationic silica sols [a), b), c) and
d)] were used in this example.
Sols a) and d) had been prepared according to the
I following: 19.49 g of a 50% solution of polyaluminum
chloride [A12(OH)5Cl.2H2O]x was diluted to 200 g. Into this
2S solution 1000 g of a 1% polysilicic acid were pumped slowly
during 45 minutes at room temperature. The polymeric
silicic acid had been prepared according to the following:
Water glass (Na20.3SiO2) was diluted with water to a SiO2
content of 5 per cent by weight. The aqueous solution was
ion exchanged using ion exchange resin Amberlite IR-120 to
a pH of 2~3. The specific surface area of the obtained acid
polymeric silicic acid was measured by titration according
to the method disclosed by Sears in Analytical Chemistry
28(1956)1981 and was found to be 1450m2/g. This polymeric
silicic acid which was later treated with polyaluminum
chloride consisted of particles of a size of the order of
about 1 nm, to some degree aggregated into chains and
networks. The obtained cationic silica sol had the follow-
: .-
132~7~
11
. lng analysis: 0.39% Al2O3 and 0.84% SiO2 and thus a moleratio of Al to surface silica of about 1:2. Sol a) was made
from a freshly prepared polysilicic acid and sol c) from a
polysilicic acid which had been aged for l day.
Sols b) and d) were prepared as follows: 9.75 g of a
` 50% polyaluminum chloride, [Al2(OH)5Cl.5H2O]x, solution was
diluted to 200 g and 1000 g of a 1% polysilicic acid,
prepared as described above, were added to the solution.
The resulting product had the following analysis: 0.20%
Al2O3 and 0.83% SiO2 and thus a mole ratio Al to surface Si
of about 1:4. Sol b) was made from a freshly prepared
polysilicic acid and sol d) from a polysllicic acid which
3 had been aged for 1 day.
Sols a) to d) were used together with a cationic
polyacrylamide (PAM) sold under the designation Percol 292
by Allied Colloids ln a stock made up from 60% birch
sulphate pulp and 40% pine sulphate pulp. The stock further
contained 30% calcium carbonate and l g/l of Na2SO4.10H2O.
The pH of the stock was 8.5. The polyacrylamide was added
1 20 to the stock before the cationic silica sol, except were
otherwise indicated. The dewatering was evaluated as
disclosed earlier using a Canadian Freeness Tester. The
¦ results are given in the following Table.
¦ 25 PAM Sol;amount CSF
kg/ton kq/ton ml
_ _ 390
0.5 - 475
! b); l 395
', 30 0.5 a); l 595 -~
0.5 b); l 605
0.5 c); l 590
0.5 d); l 600
0.5 b); 1 (reversed 505
dosage order)
A comparison was also made wi ~ anionic aluminum
modified silica sol with a particle size,of about 5.5 nm
and this, in an amount of l kg/ton together with 0.5 kg/ton
--" 132470~
: 12
of PAM gave a CSF of 520.
Example 4
Sols a) and b) of Example 3 and also sols e) and f)
were investigated in combination with cationlc polyacryl-
amide for a stock made up from groundwood pulp. Sol e) had
?,, been prepared according to the following: 27.84 g of a 50% solution of polyaluminum chloride [A12(0H)5Cl.2H20]x was
:,i diluted to 200 g. 1000 g of a 1% polysilicic acid, as in
Example 3, was added to the polyaluminum chloride solution
and the obtained product contained 0.56% Al and 0.83% SiO2
and thus had a mole ratio of Al to surface silica of about
1:1.5. Scl f) had been prepared according to the following:
34.80 g of a 50% polyaluminum chloride, [A12(OH)5C1.5H2O]x,
3 solution was diluted to 200 g and 1000 g of a 1% poly-
silicic acid was added to the solution. The product con-
,~ tained 0.70% A12O3 and 0.83% SiO2 and the mole ratio of Al
to surface Si thus was about 1:1.2.
The groundwood pulp stock contained 2g/1 of -
Na2SO4.10H2O and had a pH of 7Ø The dewatering effect was
investigated as described earlier. In most cases the
cationic polyacrylamide was added to the stock before the -~
addition of the sol, if not reversed dosage order (rdo) has
been indicated. The dosage of the cationic polyacrylamide
was 1.0 kg/ton which had been found to be the optimum
amount for this stock when it was used alone. In the tests
it was noted that the water collected from the freeness
tester was much more clear when combinations of sol and
cationic polyacrylamide were used than when the polyacryl-
amide was used alone and this is an indication of very good
fines retention.
PAM Sol;amount CSF
,~ kq/ton_ kg/ton ml
_ - 120
1.0 - 195
_ b); 1.0 120
1.0 a3; 1.0 400
1.0 a); 1.5 445 -~-
1.0 a); 2.0 485 ~;~
~.-,
24705
13
i
PAMSol;amount CSF
kq/tonkg~ton ml
1.0 a); 2.5 510
1.0 a); 1,0 (rdo) 330
1.0 a); 1.5 (rdo) 345
1.0 a); 2.0 (rdo) 355
1.0 a); 2.5 (rdo) 360
1.0 b); 1.0 420
1.0 b); 1.5 480
1.0 b); 2.0 505
1.0 b); 2.5 530
1.0 e); 1.5 400
1.0 e); 2.0 440
1.0 e); 2.5 435
1.0 f); 1.5 390
1.0 f); 2.0 425
1.0 f); 2.5 435
Example 5
In this example the filler and fines retention was
evaluated in a mill test. The stock was made up from 30% of
chemical pulp, 24% of groundwood pulp and 46% of CaCO3
filler. The concentration of the stock was 0.5% and the pH
was 8.3. The measured fillers and fines content was 76.9%.
A Britt Dynamic Drainage Jar was used to evaluate
retention. The stirrer speed was set to 800 rpm and the
~ wire used was of 200 mesh.
¦~ The cationic sllica sol used was sol a) according to
Example 1 and this was added before the cationic retention
agent. The following cationic retention agents were used in
the different runs:
A) Cationic polyacrylamlde, Percol 292 manufactured by
-~ Allied Colloids~
1~ B) Cationic guar gum.
The results of the tests are shown in the table
.; 35 below. The filler and fines retention (FF ret.) is given in
per cent at different dosages of the respective cationic
polymers. The dosage is calculated as dry polymer on dry
'~ pulp plus flller. The cationic silica sol was used in an
.: ~
1~ 132~71~5
~, amount of 1 kg/ton of dry pulp plus filler. ~omparlsons
were made with addition of solely the $tlonic ~olymer.
i Added cationic Added amount Added solFF ret.
polymer kq/ton _ kg/ton _ %
A 0.25 1 75
A 0.50 1 97
3 A 0.75 1 100
, .
A 0, 25 - 43
. A 0.50 - 61
A 0.75 - . 80
B 2 1 95
B 4 l 95
B 6 l 95 ::
B 2 _ 45
B 4 - 83
B 6 - 90 -~
Example 6
In this example the system of a cationic silica sol
a) according to Example l and cationic polyacrylamide,
was tested in a mill producing magazine paper. The stock
conslsted of 19% sulphate pulp, 37% groundwood pulp, 20% :
l~ thermomechanical pulp and 24% clay, ie a stock with high
amounts of non-cellulosic substances. The pH was 4.45.
Retention was measured with a Britt Dynamic Drainage Jar
and freeness with a Canadlan Freeness Tester.
30 Additions kg/ton Retention % Freeness ml
Sol PAM ----
- 0.25 26.4 llO ~ -~
- 0.50 ~4.6 140 ~
- l.0 57.6 l90 :: ~-
: :
2.0 0.25 41. 7 150 :` -
2.0 0.50 65.0 200 :---.
2.0 l.0 85.6 305 ~
