Note: Descriptions are shown in the official language in which they were submitted.
r ~LQ7316~
The instant invention relates to a process for
treating mechanical pulps and/or products prepared therefrom.
Mechanical pulp is a general term used for pulp
types obtained by mechanical defibration of different wood
s~ec~es
~K~ It can be produced by the use of grinding stones or
disk refiners, optionally subsequent to a mild chemical treat-
ment.
As mechanical pulp is relatively inexpensive to
produce compared with cellulose pulps obtained by che~ical
digestion of woo~, such pulps have been widely used as raw
material for the preparation of news print, magazine papers etc
However, as mechanical pulp possesses the undesirable property
that ik undergoes "self sizing" on storage, it has previously
been necessary to store and transport mechanical pulp in a
moist condition, or tc dry the pulp in a special manner, for
instance by the so called "flash drying method". As a conse-
quence of the "self sizing" mechanical wood pulp will after
/ro~oh~ ~c
storage exhibit ~Ybff~e~ properties to a more or lesser de-
gree, dependent on storage time, resin content, storage condi-
tion etc.~ which renders the further treatment difficult when
the pulp is to be further processed.
Due to the "self sizing" mechanical pulp has only
to a minor degree been utilized for absorption purposes, for
ns
instance in napkins~ sanitary pads~-~}b~Gh~7 towels and simi-
lar products. For such purposes has previously been utilized
high ~uality bleached cellulose.
It has been shown that if the resin can be removed
from the mechanical pulp such pulp can advantageously be used
for the above mentioned purposes, such as disclosed in Norwegian
Patent No. 124~193. In accordance with said patent the resin can
- 2 -
` ~733~6Z
be removed from the pulp by extraction with acetone, whereby a
product with good absorption properties is obtained. However,
an industrial extraction process is a complicated and expensive
process requiring large capital investment in extraction appara-
tus, recovering apparatus etc. Acetone extraction of mechanical
pulp has previously been suggested in order to improve the
strength property of the mechanical pulp and in order to facili-
tate the wet defibration in the subsequent production process.
(Brandal & ~indheim, Pulp & Paper Mag. Canada 6~ T 431, 1966).
It has surprisingly been found that it is possible to
treat mechanical pulp in such manner that after agelng it will
retain its original hydrophylic propexty. A mechanical pulp
treated in accordance with the instant invention will after
storage remain hydrophylic and can thus easily be fiberi~ed
during the subsequent process steps. It has further been shown
that such pulp is eminently suitable for absorption purposes,
even if the new process only to a minor degree influences the
resin content of the pulp.
The new process comprises a treatment or impregnation
of the mechanical pulp with a buffer, which buffers in a pH
range of 6-10, preferentially in the range 7-9. Suitable buffers
are alkali metal salts or ammonium salts of for instance phos-
phoric acid, carbonic acid, citric acid and tartaric acid.
The buffer is added to the mechanical pulp, preferentially in the
form of an aqueous solution and in an amount corresponding to at
least 0.2% by weight, based on the dry weight of the pulp, pre-
ferentially 0.5% or more.
Such treatment of the mechanical pulp with an aqueous
solution of the buffer is inexpensive and simple to
.. . . .
r 107 3~
carry out. The addition can be effected in different stages
during the production of the mechanical pulp, depending on the
field of use for the product and the existing equipment. The
addition can for instance take place during the preparation in
the refiner or grinder~ in the white water system of the paper
machine, in the size press or by spraying during or after the
sheet formation, or by injection in the pulp before this optio-
nally is converted to pulp bales. Thus the treatment can be
carried out with the e~isting equipment and can thus be accom-
10 modated to the existing production plants. By means of the new
process one can for instance prepare absorbing materials from
mechanical pulps~ which means substantial savings compared to
the highly refined cellulose products. From resource and environ-
ment point of view the new process represents obvious advan-
15 tageous features.
In the following the invention will be explained by
means of the examples~ showing the effect obtained by the new
treatment.
Different pulp types were treated with the buffer
20 by spraying and submerging the pulp in the buffer solution. The
dry matter of the pulps before submerging or spraying with the
buffer solution were between 25'~o and 90~/0. After treatment the
~c/One
A pulp was dried in a 4~ and flufed (in a Wenneberg-mill).
A part of the thus buffer treated and fluffed pulp was artifi-
25 cially aged at 150C in 1 hour, whereafter the pulp was allowed
to remain at room temperature in 30-60 minutes before the water
absorption o the aged pulp was determined. Water absorption for
non-aged pulp and non-treated pulp were also determined.
The determination of the water absorption rate in
30 these tests were carried out by evenly distributing 10 g air-
~73~6Z
dried, fluffed pulp in a small basket of metal gauze (dimensions
7 cm x 20 cm x 1 cm) which was placed in a container containing
200 ml water. The time taken from the moment the basket was
placed in the container and until the pulp is completely moistened
by the water is a measure for the water absorption rate of the
pulp.
The obtained results are disclosed in the subse-
quent table.
.
~L~739L6Z
~` ~ o ~ ~ o u~ ~ o
~ ~ O ) O OD n a~ O
O ~ U ~ 1~ ~1 Lt~ 0~ t`
. Q ~ tn _
O _
U~
~ s~' ~
,~
a~
CO ~ ~ ' ~ In ~ O ~ U~ O
,. ~ O ~ . ~ ,1 CO ~ ~ ~o ~
mu~ _ ~, co _ ~^_
. t`^ CD~
S~ ~ ~ Q~
~ ~ 4~ R ~ a) Ll 4
O ~i Q a) ~ ~1 o ::~
~ ~ ~ 4J ~1 Q
c: ~ ~ a~ ~a
o a
rl ~n ~, ~o O
~ ~ ~ ~ a
-~ Q ru~ ~1 LJ ~ ~) ~I) ~
~ Ou~ a) (a ~ o o ~a ~, (1) o
~ (U >~ ~ O ~ U ~ Q ~ ~ (a ~ Q
lJ ~1~1 O .~ O l O ~.1 O ~ 5-1 O ~1
z;~ ~ ~ Z ~ Z ,~ o æ ~
U U ~ ~1
Z;~
~i ~ r
4~ U O 03 ~ ~ æ z z æ
~ ~I) Q O ~ 3~I~
m P~ ~ ~ ~ ~ ~ ~ N (~I ~
~IL __ _
. ~ ~U ~ ~ .
~ S~ ~ ~
a) = ~ b~ _ ~ = ~ ~r~ = .'
a) ~ ~ ~ ra .
~ u ~ u u u a
~ ~ .~ ~ .~ .~ ~ ~
r~ ~ ~ ~
~ ~ = ~ _ O _ ~ = ~ ~ S~ _
,_, Ql u O u t) V ~'
PJ 5~ E~ ~ ~ E~ E~
~ 0~ ~ O O O~
.~ ~ ~U ~ ~ ~ ~ ~ ,~UO
4~ = ~ ~ = o ~ ~ = a~ ~ ~ ~ ~ =
O ~ Q~ ~ S rl S rl ,~ Q,
h ~ _ E I Q h R h ta ~) _
O
Z
. ~1 ~ ' ~ ~ n
X _ .
-- 6 -- .
~L~'73~GZ
As apparent from the above disclosed results by
means of the treatment in accordance wlth the invention a sub~
stantial and significant improved water a~sorption rate is ob-
tained compared with non-treated pulp. However, an exception is
represented by the borate buffer~ which apparently has a decreas-
ing effect on the absorption rate for non-aged pulp, however, af-
ter ageing the borate buffer treated pulp shows an improved ab-
sorption rate compared with non-treated pulp.
Further it wiil be apparent that pulps treated with
the di~erent buffers~ with respect to the water absorption rate
hardly is influenced by the artificial ageing~ in that difference
of 1 sec. probably is within the error limit for the testing me-
thods used.
For comparison it can be mentioned that highly
refined cellulose under similar conditions exhibits a water
absorption rate in the order of 5 sec..
The mechanical pulps in accordance with the instant
invention are thus with respect to water absorption rate compar-
able with highly purified cellulose pulps, further as they after
ageing maintain their hydrofilic properties, and consequently are
easily wet defibri~ed in an optional further process, for instance
in a paper mill utilizing mechanical pulp as raw material.
Thus the invention comprises an absorbing agent for
taon~o ~75
use in napkins~ sanitary pads~-LY~3~, towels etc~ which are
characterized in that the mechanical pulp contains a buffer as
disclosed above.
