Note: Descriptions are shown in the official language in which they were submitted.
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The present invention comprises chemical pulps
having improved strength, drainability and beatability,
and a process of making said pulp.
In the production of lignocellulose-based sheet
structures from a suspension of fibres and water, the
fibre is first treated mechanically in the wet state.
This operation, the beating operation, is one of
the most important unit operations of paper technology.
By different beating methods, it is possible to obtain
different quality characteristics in the sheet, and
it is possible to change the usefulness of diferent
fibre raw materials.
However, the mechanical treatment principles for
achieving different product characteristics are extreme-
ly uncertain, and primarily the basic mechanisms of
the beating process are unknown, for which reason beat-
ing may be said to be effected more or less by ancient
tradition.
The fibre material has a complex morphological
structure~ and the changes which occur in the beating
zone are heterogeneous, which makes it difficult to
give a more detailed description thereof. Traditionally,
the beating effect is divided into
- fibre length shortening
- fines production
- delamination
- external fibrillation
- swelling
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- dislocations
- reduced degree of polymerization~
As a result of these beating effects~ the tensile
strength of the fibre in the wet state is increased,
whereas the modulus of elasticity is decreased. Beaten
and dried fibres have higher values of ~oth tensile
strength and modulus of elasticity than unbeaten fibres.
The greatest change in the characteris~ics of the
paper occurs in the initial beating phase. Usually,
an increase in density, elongation at break and in all
strength characteristics, with the exception of the
tearing strength, is obtained; whereas opacity, permea-
bility to air and dimensional hygrostability are re-
duced.
An analysis of the effect of the beating operation,
and the cause therefor, on the finished paper~ is render-
ed difficult by the insufficient knowledge of the origin
of the paper qualities. Generallyg it may be said that
the fine material formed and the softening (which implies
increased swelling) of the fibre are highly importantO
The swelling of the cellulose fibre may be regardPd
on the basis of the physical chemistry for gels, and
it will be seen how different parameters~ such as pH,
temperature, salt content etc. affect the swelling con-
dition of the fibre as well as the swelling level of
the fine fibre fraction.
27 Traditionally, the beating efficiency is increased
by modifying the construction of the beating element
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and the concentration of the cellulose material in the
beating apparatus. Moreover, also changes in tempera-
ture and pH and the addition of different chemicals
have been tried to achieve a desired increase in beat-
ing efficiency in connection with the papermaking pro-
cess, i.e. in the further treatment of the pulp as first
dried.
A mechanical modification of the beating element
has given no incontestable results. However, a develop-
ment towards hiqher strength characteristics in beated
lignocellulose materials after treatment in present day
beating equipment can be seen. Regarding the change
in the chemical conditions during beating~ no major
effects have been observed as compared with what is
obtained by conventional papermaking technology.
The present invention has for its objec~ to provide
a chemical pulp having improved strength, drainability
and beatability
A further object of the invention is to provide
a process of making a chemical pulp having improved
strengthJ drainability and beatability.
These and other objects are achieved in that the
wooden raw material after cooking is mixed with an aqueous
solution of one or more low~molecular salts Preferably,
0.1-10% by weight of salt, based upon the dry pulp,
are incorporated.
27 The basic idea of the present invention is that
a low-molecular salt shall be present during drying,
at least in the initial phase thereofu
It is known that the swelled fibre "collapses"
when pulp is dried, i.e. the gel structure disappears.
A subsequent addition of water in the manufacture of
paper does not cause the fibre to revert to its original
state, i.e. this process is at least partly irreversible.
One explanation why the swelled fibre "collapses" upon
drying is that, when the water is removed, ~he cellulose
chains will come so close to one another that hydrogen
bonds are established between these chains. In this
manner, the cavities in the gel structure of the pulp
will disappear. The subsequent addition of water during
the continued treatment of the pulp is unable to break
the hydrogen bonds, and an irreversible '~collapse" has
~hus occurred.
Surprisingly~ it has now been found that it is
possible to interfere with the formation of hydrogen
bonds by adding water-soluble low-molecular salts to
the pulp already after the production9 but prior to
the drying thereof~ These salts penetrate into the ca-
vities of the gel structure and form therein steric
hindrances preventing the cellulose chains from getting
close to one another, whereby the formation of hydrogen
bonds is substantially eliminated
By substantially preventing~ in the manner described
abovet the irreversible "collapse" of the fibre gel
27 structure, the fibres can again swell when water is
added and~ on the whole, revert to the state befor~
the drying.
In this manner, improved strength, dralnability
and beatability of the treated pulp as compared with
untreated pulp are obtained.
For carrying t~le process according to the present
invention into effect, the undried, bleached or unbleach-
ed chemical pulp is mixed with an aqueous solution of
suitable low-molecular salts. After this addition, the
pulp is dried in conventional manner, for instance by
using a flash drier, by the supply of heat through ra-
diation or convection (for instance by means of a fan
drier for pulp) or by means of heated surfaces to which,
if desired, a pressure has been applied ~for instance
a cylinder drier for pulp).
Suitable salts for adding to the pulp are low-mole-
cular water soluble salts. It is important that the
molecular si~e of these salts be sufficiently small
to enable the salts to penetrate into the gel structure
and to be deposited therein while forming a steric hin-
drance.
Furthermore~ it is important that the added salt
does not form ions detrimental to the subsequent use
of the pulp. Thus~ it will be appreciated thatl when
the pulp is again suspended in water after drying~ a
large part of these deposited salts will be redissolved,
and consequently a salt forming chlorine ions is not
always suitable because chlorine ions are frequently
27 undesired in the subsequent treatment. Since the final
use of the pulp often is not known to the pulp producer,
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it is preferred to use a salt which is used in other
contexts in the production of pulp and paper. Examples
of suitable salts are sodium sulphate and sodium thio-
sulphate which are chemicals commonly used by the pulp
industry. Also organic salts may be us~d, provided that
their molecules are sufficiently small for penetration
into the cavities of the ~el structure
Very small amounts of the active component are
required to obtain the desired effects~ Generally, some
tenths of a per cent~ based upon the dry weight of the
pulp will suffice, but up to about 10~ by weight may
be used~
An alternative method of imparting the desired
characteristics to the pulp is to admix to untreated
pulp, in suitable proportions, a pulp treated in the
above mentioned manner so that the entire pulp mixture
will have the desired characteristics.
The following Examples of embodiments of the present
invention must not be taken to restrict the scope of
the invention as defined by the appended claims.
EXAMPLES
The tests accounted for in the Examples were made
in accordance with the SCAN Test methods puklished and
recommended by the Central Laboratories of the Cellulose
Industries in Denmark, Finland, Norway and 5weden:
The following SCAN methods have been used:
27 SCAN:C lg Drainage resistance of pulp according
to the Schopper-Riegler method.
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SCAN:C 24 seating of pulp in a PFI ~Paper Research
Institute) mill.
SCAN:C 25 Laboratory beating in Valley beater
SCAN:C 26 Manufacture of laboratory sheets for physical
testing.
SCAN:C 27R Light scatter coefficient.
SCAN:C 28 Determination of the physical characteris~
tics of laboratory sheets.
SCAN:C 24 Bursting strength.
SCAN-C 11 Tearing strength of paper and board.
SCAN:P 16 Tensile strength and elongation.
EXAMPLE 1
Sodium sulphate (Na2so4) was dissolved in water
to a suitable concentration~ in which solution an un~
dri~d and bleached softwood sulphate pulp having an
initial water content of about 80~ was dispersed to
a final pulp concentration of 5~. After some minutes,
the pulp was dewatered by draining and pressing to a
dry solids content of about 35%. After air drying at
about 60C, the pulp was beaten in a Valley beater where
the pH was adjusted to 5 after slashing with NaOH or
H2SO~. The concentration of sodium sulphate in the dried
pulp was calculated on the basis of the dry solids con~
tents of the initial pulpl the concentration of the
dispersion~ and the pressed pulp. The reference used
was a sample which had been dispersed in water without
27 the addition of salt and which otherwise had been subject
ed to the same treatment as aboveO
The following comparison values between the reference
and samples having different contents of sodium sulphate
were obtained:
Tensile index, kNm/kq
Beating time, min. 10 20
Ref. 61 83 92~5
Sample 3~ Na2SO~ 72.5 92 100.~
Sample 6~ " 74~5 94.5102.5
Sample 10~ " 75.0 93.0104.5
EXAMPLE 2
The procedure according to Example 1 was repeated,
but at a drying temperature of 90-95C and with 5% of
sodium sulphate in the dried sample. The following re-
sults were obtained:
Tensile index~ kNm/kg
Beating time, min~ 10 20 30
Ref. 58 79~5 89
Sample 67 89.5 99.5
EXAMPLE 3
The procedure according to Example 1 was repeated,
but beating was effected in a PFI millO The sodium sul-
phate concentrations in the dried pulp were those stated
27 in the Table.
The following results were obtained upon comparison
with the same drainage, 30SR:
Na2S04, %
0 3 6 10
Number of beating revs 4600 4200 3800 3500
Tensile index, kNmjkg 94100 105 107
The following results were obtained upon comparison
with the same tensile index, 85 kNm/kg
l\la2S04 ~ g6
0 3 6 10
Number of beating revs 3200 2400 20001700
EXP~PLE 4
The procedure according to Example 1 was repeated,
but the pulp was an undried and unbleached softwood
sulphate pulp. The concentration of sodium sulphate
in the dried pulp is stated in the Table~ The following
results were obtained:
Te~sile index~ kNm/kg
Beating time, min.10 20 30
Ref.
Sample 0.5~ Na2S04 44.5 64~5 77~0
Sample 2.5% " 47 66~5 79.5
EXAMPLE 5
lhe procedure according to Example 1 was repeated,
but the salt was sodium chloride. The following results
were obtained:
Tensile index, kNm/kg
Beating time, min. 10 20 30
Ref. ~1 83.5 9205
Sample 5~ NaCl-~2 89.5 102.0
EXAMPLE 6
The procedure according to Example 1 was repeated,
but the salt was sodium thiosulphate. The following
results were obtained:
Tensile index, kNm/kg
Bea~ing time, min. 10 20 30
Ref. 59.0 82.S 92~5
Sample 3~ Na2S20367.089.5 9700
Sample 6~ " 74.0 95.5 106.5
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EXAMPLE~: 7
The procedure according to Example 1 was repeated,
but the pulp was undried and unbleached sulphate pulp
to which sodium thiosulphate had been added. The fol-
lowing results were obtainedO
Tensile index, kNm~kg
Beating timeO min. 10 20
Ref. 36.5 5~.u 69.0
Sample 1~ Na2S203 42.5 62.~ 77~0
Sample 2.5% " 47.0 66.0 81.5
EXAMPLE 8
The procedure according to Example 1 was repeated,
but the additives were monoethanol amine ~MEA), diethanol
amine (DEA) and triethanol amine (TEA), respectively.
The following results were obtained:
Tensile index~ kNm/kg
Beating tim~ min.10 20 30
Ref. 57.5 80.U 92.0
Sample 3% MEA 69.0 90.0 100.5
Sample 3~ DEA 70.0 89.5 9805
Sample 1.5% TEA ~ 84.~ 98.5
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E~AMPLE g
The procedure according to Example 1 was r2peated,
but the pulp was unbleached sulphate pulp and the additive
consisted of urea. The following results were obtained:
Tensile index, kNm/kg
Beating time9 min. 10 20 30
Ref. 36.5 56.0 69.~
Sample 2.5% urea 42.5 62 5 78.5
EXAMPLE 10
The procedure according to Example 1 was repeated,
but with the difference tha~ the starting material was
a dried and bleached sulphate pulp. No significant diffe
rences between the reference and a 3%, 6% and 10%, respec-
tively, addition of Na2SO4 were observed.
EXAMPLE 11
An undried and unbeaten bleached sulphate pulp
was dried in conventional manner on a papermaking machine
on a pilot scale. The wet web was sprayed wi~h a solution
of chemicals ~see the Table) ahead of the pre~s sectionc
The final amount of chemicals added to the clried pulp
was estimated by extraction with hot water~ In the case
of ammonium carbonate which is gasified upon drying
of the pulp, the amount added was calculated on the
basis of the concentration and flow of the other chemi-
cals through the spray pipe. The pulp thus dried was
~ispersed in a pulper and beaten, whereupon paper was
.
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produced on a pilot scale, all in accordance with known
technique. During the paper production, only chemicals were
added to control the pH to 6 (NaOH and H2SO4, respective-
ly). The pH adjustment was carried out already in the pul-
per. The results are shown in the Table below. To minimize
the effect of the variation in the interrelation of the
longitudinal/transverse strengths~ the Table indicates
ngthlongitudinalX tenSile strength~t
All strengths have been evaluated at one and the same
beating operation~ The reference used was a pulp which
upon drying had been sprayed with water~ but which other-
wise had been subjected to the same treatment.
Sample Tensile index, kNm/kq
RefO
0.7 % (NH4)2SO4 68.5
l.U ~ (NH4)2CO3 68.0
1.0 % Na2SO4 68.5
2-0 ~ Na254 73-~
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