Note: Descriptions are shown in the official language in which they were submitted.
WO 93~18227 ~ ; ,- PCr/SE93/00205
PROCESS FOR MAKING BOARD
The present invention relates to a process for making
board according to what is commonly referred to as the wet
method. More specifically, the invention concerns an
improved process for making board, by adding the binder at
an early stage of the process. Insulation board, building
board and hardboard, for instance, can be produced by this
process.
When making board according to the wet method, a
stock is prepared from fibres produced from a fibrous raw
material, such as chips and sawdust, by mixing the fibres
with water in several steps. A binder is added to bind the
fibres in the board, whereupon the stock is de~atered and
the fibre pulp is pressed. The binder is added to the
stock and, if water-soluble, is precipitated and fixed to
the fibres by acidification of the stock, e.g. by alum or
acid. The binder may be added at a site where the stock
concentration is about 5-15%, e.g. in the level box,
whereupon precipitation and fixation by acidification take
place where the stock concentration is about 2-3%, e.g. in
the machine chest. Alternatively, both the addition of the
binder and the precipitation thereof on to the fibres may
take place in the machine chest.
This process has the disadvantage that the binder r
when precipitated, deposits not only on the fibres, but
also on the remaining material in the stock. Apart from
useful fibres, the stock contains fibre fragments, i.e.
what is commonly referred to as fines, as well as dissolved
carbohydrate material and, to a certain extent, ligneous
substance in dissolved and colloidal form. Since the water
in the prqcess is at least partly recycled by using, in the
preparation of the stock, the white water from the dewater-
ing step, the contents of these by-products will be com-
paratively high. As a portion of the binder deposits on
these components, this portion will be of no avail to the
fibre matrix. It has thus become necessary to increase the
amount of binder added, which nevertheless has not given
the desired result in certain cases. The dosage of resin is
WO 93/18227 PCI~SE93/00205
, .~
! ~% ~ ; 2
also rëstricted by the fact that dewateriny of the stock 1s
rendered more difficult if the amount of resin ex~eeds a
certain level (about 6-8%). In addition, many board manu-
facturers in Europe have made their processes more or less
closed for environmental reasons (reduced discharge of
COD-consuming materials to recipients). As a result, the
contents of fines and dissolved substances in the white
w~ter have increased even further~ However, the present
invention largely obviates these disadvantages.
One ob;ect of the invention is, therefore, to utilize
the adhesive on the fibre matrix more effectively in the
making of board. Anothex ob~ect of the invention is to
enable dosage of the desired amount of resin on the fibres
without affecting the subsequent dewatering.
As appears from the appended claims, the objects of
the invention are achieved by a process for making board
accordin~ to the wet method, in which a stock is prepared
from fibres produced from a fibr.ous raw material, such as
chips and s~wdust, and a binder is added prior to dewater-
ing and pressin~, the binder being added to the fibres
befoxe the preparation of the stock. It has surprisingly
been found that the binder can be utilized far more effec-
tively if added to the fibres early in the process, before
the supply of water for preparing the stock, resulting in
improved properties of the board. Also, it has become pos-
sible to add very large amounts of binder without adversely
afferting the subsequent process.
In the process according to the invention, conven-
tional equipment is used for making board according to the
wet method. Thus, the wood raw material is conducted, by
preheating with steam, to a defibrator for disintegration.
The resulting fibre pulp is conveyed through a blow line to
chests where the stock is prepared. Fresh water and/or
white water ~s added to the chests, resulting ~n a stock
having a content of ab~ut 5-lS%. This stock is conducted to
a refiner for final ad~ustment of the beating degree. From
the refiner, the stock is conveyed to a machine chest,
where the final dilution w~th water/white water is per-
WO93/18227 ~ ? 1 ~i %~j pcTlsE93/o~2os
formed. At this stage, the stock has a content of about 2-
3%. This stock is conducted to a wet machine to be dewater-
ed, pressed and dried/press-dried (hot press).
In the process according to the invention, the binder
may be added to the fibres at any time before the site
where a substantial amount of water is added for preparing
the stock. The binder is suitably added in the blow line
from the defibrator~ Here, the fibres have a dry solids
content of about 40-60% by weight. This constitutes a
preferred embodtment of the invention. The binder may also
be added to the fibres before the defibrator.
In the inventive process, use is made of such binders
as are predominant in the art. These are curing organic or
inorganic binders, such as phenolic resins, amino resins~
silicates or mixtures thereof. Water-soluble binders are
generally used. When water-soluble resins are employed,
they have to be precipitated and fixed to the fibres,
which is brought about by acidification, e.g. by means of
alum or acid. Preferably, acidification is performed in
connection with the preparation of the stock or prior
thereto, and in that case also prior to the addition of
- the binder. When added in connection with the preparation
of the stock, the precipitating reagent may be added to
the first dilution chest, where the stock concentration is
- 25 ~about 1-15% by weight, usually 5-15% by weight. If acidi-
fication is allowed to take place at a late stage of the
;~ ~ process, e.g. in the machine chest, there is a risk that
some of the water-soluble binder applied to the fibre
matrix is dissolved and instead precipitated on the other
material in the stock, resulting in impaired performance.
Wit~ the present invention, it is also possible to
control~ the penetration of resin into the fibre. As a
result, the properties of the board can be influenced in
different directions, e.g. internal bond strength ana
modulus of rupture versus swelling and water absorption. If
a sparingly soluble or concentrated resin is used, pene-
tration is reduced and the resin is concentrated on the
fibre surfaces. This enhances the possibility of obtaining
WO93/18227 ~ PCT/SE93/00205
tJ
~ 4
active glue joints between the fibres, resulting in higher
strength. In the opposite case, i.e. when diluted and low-
viscosity resins are used~ penetration increases, resulting
in lower swelling and, above all, lower water absorption.
Penetration may also be reduced by adding alum/acid before
the defibrator or before the site where the binder is
added. Thus, the binder will be precipitated directly on
the surface of the acid fibre, and penetration is reduced
to a minimum. Consequently, the present invention enables
several ways of controlling in a given direction the
properties of the end product.
Also, the process according to the invention enables
the addition of very large amounts of binder without ren-
dering dewatering on the wet machine more difficult. The
prior-art process restricts the dosage of the binder to
about 6-8%, requiring at that the aid of certain floccu-
lating chemicals. If the dosage exceeds this level, d~wa-
tering from the wire is impeded to such an extent that
there is a risk of crushing the sheet in the press section.
In the process according to the invention, there are no
dosing problems with contents of from about 0.5% by weight
to about 40% by weight ~based on dry resin on a dry fibre
matrix), suitably up to about 15-20% by weight. Generally,
the binder is used in an amount of about 0.5-10% by weight,
preferably 1-5% by weight.
Making board according to the wet method by the pro-
cess according to the invention does not influence theother process conditions. The binder can be added through
a simple connecting tube on the blow line after the defi-
brator. The amount of binder is ad~usted by a dosing pump.The binder can be precipitated in e.g. a first dilution
chest at a stock concentration of about 10% by means of
alum. Then, the sized stock is allowed to continue in the
process via a refiner, a dilution chest, a machine chest
and a wet machine in conventional manner. Thus, the process
accordin~ to the invention is fairly easy to incorporate in
existing processes.
~ he invention will now be described in more detail
W093/18227 ~ PCT/SE93/00205
with the aid of the following Examples, in which the part
and percentage figures concern parts by weight and per
cent by weight, unless otherwise stated.
Example l
The making of insulation board.
Phenolic resin having a concentration of 40% by weight was
applied by so-called blow-line dosage immediately after the
defibrator through an insert pipe centered in the blow
line. Thus, the phenolic resin was applied to concentrated
hot fibre having a temperature of about 150C (a dry solids
content of about 50% by weight). The resin was dosed by a
suitable dosing pump, and was precipitated and fixed to the
fibre at a high stock concentration (8-10%) immediately
after the cyclone in the first dilution chest.
Precipitation was brought about by the addition of an
alum solution to the diluting water.
The sized fibre (the stock) was then conducted
further in the process via refiners, machine chests and a
wet machine in conventional manner.
The board thickness was ~3 mm.
Dosing Phenolic resin MOR IB Swelling Water abs.
process dosage % MPa MPa 2 h % 2 h %
According
to the
invention 5 6.5 0.26 l.9 12.4
30 Added in ma-
chine chest
typical va- 5 3.0- 0.08- 2.3- 18-30
lues* 3.5 0.12 3.5
35 Standard
board 0 2.7 O.ll 7.0 173
*) An addition of wax forms part of this grade.
W093/18227 PCT/SE93tO020
~ J~ 6
Example 2
Insulation board l6 mm.
The process according to Example l was repeated, the only
s difference being that use was here made of concentrated
phenolic resin of 43% by weight, i.e. having higher vis-
cosity than the resin used in Example l.
Dosing Phenolic resin MOR IB Swelling Water abs.
lO process dosage % MPa MPa 2_h % 2 h %
According
to the
invention 5 4.0 0.16 3.2 15
1~
Added in ma-
ch~ne chest 2 2.2 0.07 3.5 22
*) An addition of wax (2%) forms part of this grade.
It is apparent how the properties can be controlled towards
increased strength by reducing resin penetration, although
with lesser effect on swelling and water absorption.
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