Note: Descriptions are shown in the official language in which they were submitted.
212236~
Z 423pct /tc 13.04.1994
GLUNZ AG
59063 Hamm, Caldenhofer Weg 159
Method for the production-of particle- or fiberboard
The invention relates to a method for the production of
particle- or fiberboard, in which lignocellulose containing
particles or fibers are glued with an NC0-groups con$aining
binder, formed in the shape of a mat, and pressed to form the
particle- or fiberboard under the influence of heat.
It is known from the AT-PS 270 189 to produce particle- and
fiberboard using a binder containing NC0-groups as reactive
groups. In this an isocyanate is brought upon lignocellulose
containing particles or fibers. From the particles resp. fibers
a mat is then formed, which is hot-pressed to the particle- or
fiberboard under the influence of heat. A particle- or
fiberboard bonded with a binder having NCO-groups has the
advantage of excellent moisture resistance and no emission of
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formaldehyde from the binder. It prooves to be disadvantageous,
though, that binders containing NCO-groups have a smaller
bonding effect as compared to other binders, which additionally
has to be activated by relatively high temperatures and long
pressing times during the hot-pressing of the particle- or
fiberboard. Correspondingly, the cost of a high binder content
in the end product and a small throughput of the hot presses, as
well as a relatively high amount of rejects are noticed
negatively in the production of particle- or fiberboard using a
binder containing NCO-groups. It must be noted that increasing
the pressing temperatures, in order to reach the temperature
needed to harden the binder inside the mat faster, is limited by
the fact that rapidly evaporating substances, especially water
vapor, durinq the hot-pressing adversely affect the ~uality of
the particle- resp. fiberboard.
It is therefore the object of the invention to further develop
a method of the type described above, so that stable particle-
or fiberboards are obtainable with a smaller amount of binder
and/or that the pressing times can be reduced and/or that the
pressing temperatures may be reduced.
In the production of amino plastic resin bonded~particle- and
fiberboard it is known to apply various catalysts, especially
acids, in order to accelerate the hardening of the amino plastic
resin. For instance, it is known from the DE-OS 27 45 809 to use
sulfide waste lye with a pH-value of 4.0 in a solid fraction of
approximately 10 percent by weight of the amino plastic resin.
So far no catalysts are applied in the production of particle-
and fiberboard using a binder containing NCO-groups. This is
surprising in view of the long time for which this method is
known. The reason is probably that it is feared that a possible
catalyst would lead to difficulties in connection with the open
storage time of the glued particles resp. fibers between the
glueing and the hot-pressing. A hardening of the binder in this
open storage time, which lasts typically between 15 and 30
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minutes, reduces its glueing effect. This is considerable
especially for the relatively small glueing effect of a binder
containing NCO-groups.
In performing the polyurethane reaktion for the production of
polyurethane foam material from polyol and isocyanate the use of
catalysts is well known. According to the technical manual
"Bayer-Polyurethanes", edition 1.79 tertiary amines and organic
tin compounds are used as activators for the polyurethane
reaction. In this, tertiary amines with NCO-reactive groups are
advantageous insofar as tbese are chemically integrated into the
polyurethane foam material after performing the polyurethane
reaction and therefore deactivated.
The use of catalysts which are used in performing the
polyurethane reaction in the production of polyurethane foam
materials for the production of particle- or fiberboard using a
binder containing NCO-groups seems fundamentally impossible to
someone skilled in the art. It should be noted that the
polyurethane reaction is a fast reaction, which in the
production of polyurethane foam materials sets in immediately
upon the mixing of the polyol with the isocyanate in the
presence of the catalyst, even at low temperatures. It is to be
feared that the use of a binder containing NCO-groups with the
addition of a catalyst that accelerates polyurethane reactions
would make the pressing of the glued particles or fibers into a
stable particle- or fiberboard impossible after only minutes of
open storage time, since the glueing effect of the binder would
have been largely, if not fully, reduced, i. e. used up.
In the production of particle- or fiberboard tertiary amines are
not known as catalysts which accelerate the hardening of the
binder during the hot-pressing.
The US-PS 4 772 442 discloses a method of the type described
above for the production of particle- or fiberboard using a
binder containing NCO-groups, in which a fatty substance is used
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as a separation aid of the hot-pressed particle- or fiberboaxd
from the surface of the press. In one embodiment the separation
aid is applied as an aqueous solution, to which triethanolamine
is added as an emulsifying agent. There is no mention of a
catalytic effect of the triethanolamine concerning the binder in
the US-PS 4 772 442.
From the De-OS 34 38 735 a binder additive for the production of
amino plastic resin bonded particle- and fiberboards is known.
The binder additive is supposed to improve the flame resistivity
of the particle- or fiberboard, without impairing its stability.
Constituents of the binder additive apart from boric acid are
for instance a water soluble amine or polyamine as well as a
further water soluble compound with at least one organically
bound hydroxyl group or a liquid alcohol. Isocyanate may also be
added to the binder consisting mainly of amino plastic resin as
a binder constituent containing NCO-groups. A catalytic effect
of the amines or polyamines as such on the hardening of the
binder is not seen in the DE-OS 34 38 735 by someone skilled in
the art. It does especially not disclose an immediate bonding of
the amines with binders containing NCO-groups, insofar as these
are used solely as binders.
For these reasons it is surprising that the object of the
invention is solved by adding a catalyst that accelerates
polyurethane reactions to the binder which contains NCO-groups.
Contrary to all expectations a variety of known catalysts that
accelerate the polyurethane reaction in the production of
polyurethane foam materials are suitable as an additive to the
binder containing NCO-groups as reactive groups used in the
production of particle- and fiberboard. Especially the
preservation of the glueing effect during the open storage time
of the glued particles or fibers, which was so far seen as
critical, is found to be unproblematic. Open storage times of up
to 30 minutes and more show no noticable influence on the
efficiency of the binder, to which the catalyst has been added,
during the hot-pressing, when the catalyst has been chosen
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carefully from the commercially available additives which
accelerate a polyurethane reaction. At the same time the
pressing times may be reduced by as much as 30 % without a
degradation in quality. To the contrary, even an improvement of
the mechanical properties of the particle- resp. fiberboard is
observed. This is due to the fact that the catalyst causes the
formation of urethane bonds between the lignocellulose
containing particles resp. fibers and the binder that contains
NCO-groups during the hot-pressing of the glued particles resp.
fibers, while the fraction of binder internal polycarbamide
bonds is correspondingly reduced. Alternatively or parallel to
the reduction of the process time a reduction of the process
temperature of up to approximately 30 K is possible. ~his leads
to a significantly reduced fraction of rejects due to water
vapor damage.
It is understood that not all catalysts accelerating a
polyurethane reaction are equally well suited as an additive to
the binder in the production of particle- or fiberboard usin~ a
binder that contains NCO-groups. In principle all ~nown types of
catalysts that accelerate polyurethane reactions can be used,
though. Taking into consideration the embodiments of the method
for the production of particle- or fiberboards described
hereinafter an especially well suited catalyst can be chosen
without problems.
The binder may be brought onto the particles or fibers in an
aqueous suspension or emulsion, where the catalyst is dissolved
in the water. A water soluble catalyst has the advantage that it
is evenly distributable in the binder. Smaller amounts of the
usually expensive catalyst are then sufficient, than when the
catalyst is insoluble in water and must be dispersed in the
water. The application of the NCO-groups containing binder onto
the particles resp. fibers in the form of an aqueous suspension
is a common ~ethod in the production of particle- and
fiberboard. Likewise, the use of suspensions resp. emulsions
based on toluol is common. Here, the catalyst would accordingly
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be added to the binder by way of the toluol.
The catalyst may have a hydroxyl group. The hydroxyl group of
the catalyst is, among other things, an indication of the water
solubility of the catalyst.
The catalyst may be chemically integrated in the particle- or
fiberboard during the pressing. A catalyst tightly bound after
the hot-pressing is chemically deactivated. This is of special
importance, since polyurethane reactions accelerating catalysts
all have strongly irritating or even toxic properties in an
unbonded state. These irritating or even toxic properties of the
catalyst do not matter after the chemical integration in the
particle- or fiberboard, though.
The catalyst may be a tertiary amine. Amines are the best known
group of polyurethane reaction accelerating catalysts. In the
production of particle- and fiberboard using a NCO-groups
containing binder especially tertiary amines are found to be
advantageous. These are tightly bonded in the compounds created
during the hot-pressing of the glued particles or fibers and
therefore chemically deactivated, when the have a NCO-reactive
group. Secondary and primary amines are bonded in the NCO-groups
containing binder by NH/NCO-reactions.
For the realization of the invention ether- or aliphatic amines
seem to be especially well suited.
Should in some instances problems occur with common,
commercially available catalysts for a polyurethane reaction
with respect to the open storage time in the production of
particle- or fiberboards when using a NCO-groups containing
binder, these may be overcome by using a blocked catalyst, that
is activatable by heat. These catalysts, too, are per se known
to accelerate a polyurethane reaction to someone skilled in the
art.
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A blocked catalyst that is activatable by heat is easily
obtainable by masking the catalyst with an acid. With a suitably
chosen acid the reaction product disintegrates at a temperature
that lies above the temperature characteristic for the opsn
storage time, but in the lower region of temperatures attained
during the hot-pressing of the particles resp. fibers.
The catalyst may be applied in a concentration of 0.001 to 2.0
percent by weight, especially 0.005 to 0.5 percent by weight,
relative to the NCO-groups containing binder. The low fractions
of polyurethane reaction accelerating catalyst which are
sufficient to provide the desired effect clearly show that, even
though the catalyst is possibly chemically integrated in the
reaction product, it is a genuine catalyst in the classical
sense and not an actual reaction partner. It is furthermore
required that the concentration of the catalyst be small, so
that the production of particle- and fiberboard using the
catalyst has commercial advantages. It would not make sense if
the attainable reduction in the process time of approximately 30
% resp. the reduction of the process temperature by 30 K resp.
the saving of binder would be equaled or surpassed by
expenditures for the catalyst.
The NCO-groups containing binder may be a polyisocyanate,
especially polymer 4,4'-methylendiisocyanate (PMDI). The PMDI
used at this time in the production of particle- or fiberboard
as a NCO-groups containing binder is suited for the production
of particle- and fiberboard using a polyurethane reactions
accelerating catalyst, without the need of compositional
changes.
The invention is further explained with the aid of a preferred
embodiment.
In a standard production plant for the production of particle-
board using a NCO-groups containing binder a commercially
available polyurethane reactions accelerating catalyst was added
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to the binder. The binder, a polymer 4,4'methylendiisocyanate
(PMDI) was used in an aqueous solution. The ratio of binder to
water was 1:1. The binder was a commercially available,
unmodified polyisocyanate (Desmodur 1520 A, Bayer Leverkusen
AG). The polyurethane reactions accelerating catalyst was a
water-soluble, tertiary amine (Texacat-DPA, Texaco-Chemical
Deutschland GmbH) and was added to the water fraction of the
binder emulsion in concentration corresponding to 0.5 percent by
weight of the PNDI fraction of the emulsion. The particles were
glued with the thus enriched emulsion in the usual way.
Following the forming of a mat from the particles and the
pressing to a particle-board under the influence of heat, the
quality of the resulting particle-boards was examined as a
function of the pressing time. Even when remaining approximately
25 % below the usual pressing time, no deteriation of the
quality was observed. Instead, an improvement of the mechanical
qualities of the particle-board was observed, even when
remaining significantly below the usual pressing time.
Concerning the open storage times, no significant reduction of
the binding effect oP the binder was found for times up to 30
minutes. This coveres the whole span of common open storage
times. All in all, it is found that the new method for the
production of particle- or fiberboards using a NC0-groups
containing binder and a polyurethane reactions accelerating
catalyst can be implemented on existing production plants,
yielding an increased output of up to one third at the same
level of quality. The financial expenditure for the catalyst is
small compared to the advantages attainable. -
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