Note: Descriptions are shown in the official language in which they were submitted.
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Lignocellulosic materials with lignocellulosic fibers in the outer layers and
expanded plastics
particles present in the core
Description
The present invention relates to lignocellulosic materials having a core and
two outer layers, the
core comprising expanded plastics particles and the outer layers comprising
lignocellulosic fi-
bers.
CH-A-370 229 discloses compression moldings which possess both light weight
and compres-
sive strength and which consist of wood chips or wood fibers, a binder, and a
porous, foamable
or partly foamable, plastic that serves as filler.
A disadvantage of these compression moldings is that they do not have plastics-
free outer lay-
ers, meaning that customary coating technologies (e.g., lining with furniture
foil or short-cycle
coating with melamine films) lead to poor results.
DE-U-20 2007 017 713 discloses weight-reduced chipboard panels through
combination of
wood chips and evenly distributed foamed polystyrene beads in the middle ply
of the panel.
A disadvantage of these materials is that the flexural strength, the screw
pullout resistance and
the surface quality are not sufficient for all applications.
WO-A-2008/046890 discloses lightweight, single-ply and multi-ply wood based
materials which
comprise wood particles, a filler of polystyrene and/or styrene copolymer
having a bulk density
of 10 to 100 kg/m3, and binder. The filler is advantageously evenly
distributed within the wood
based material. The wood based materials are produced from wood veneers, from
wood chips
or from wood fibers, more particularly from wood chips and and wood fibers.
A disadvantage of these materials is that an improvement in the properties for
a given panel
density is achievable only with an increase in the amount of glue and/or the
amount of polymer
and hence with an increase in the costs.
It was an object of the present invention, therefore, to remedy the
disadvantages recited above,
and more particularly to provide lightweight lignocellulosic materials having
improved flexural
strengths, improved screw pullout values and/or good surface properties, these
materials con-
tinuing to possess good processing properties, like conventional high-density
wood based mate-
rials.
Found accordingly have been new and improved lignocellulosic materials having
a core and two
outer layers and comprising or, preferably, consisting of, in the core
A) 30% to 98% by weight of lignocellulose particles;
B) 1 % to 25% by weight of expanded plastics particles having a bulk
density in the range
from 10 to 150 kg/m3,
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C) 1% to 50% by weight of one or more binders selected from the group
consisting of phe-
noplast resin, aminoplast resin, and organic isocyanate having at least two
isocyanate
groups, and
D) 0% to 30% by weight of additives
and in the outer layers
E) 70% to 99% by weight of lignocellulose fibres,
F) 1% to 30% by weight of one or more binders selected from the group
consisting of phe-
noplast resin, aminoplast resin, and organic isocyanate having at least two
isocyanate
groups, and
G) 0% to 30% by weight of additives.
The statement of the percent by weight of components A, B, C, D, E, F and G
relates to the dry
weight of the component in question as a proportion of the overall dry weight.
The sum total of
the percent by weight figures for components A, B, C and D is 100% by weight.
The sum total of
components E, F and G likewise makes 100% by weight. In addition, not only the
outer layers
but also the core comprise water, which is not taken into account in the
weight figures. The wa-
ter may originate from the residual moisture present in the lignocellulose
particles, from the
binder, from additionally added water, for dilution of the binders or for
moistening of the outer
layers, for example, or from the additives, such as aqueous curing agent
solutions or aqueous
paraffin emulsions, for example, or else from the expanded plastics particles
when they are
foamed, for example, using steam. The water content of the core and of the
outer layers can be
up to 20% by weight, i.e., 0% to 20% by weight, preferably 2% to 15% by
weight, more prefera-
bly 4% to 10% by weight, based on 100% by weight overall dry weight. The ratio
of the overall
dry mass of the core to the overall dry mass of the outer layers is generally
100:1 and 0.25:1,
preferably 10:1 to 0.5:1, more preferably 6:1 to 0.75:1, more particularly 4:1
to 1:1.
The lignocellulosic materials (lignocellulose materials) of the invention can
be produced as fol-
lows:
The components for the core and the components for the outer layers are mixed
generally sep-
arately from one another.
For the core, the lignocellulose particles A may be mixed with the components
B, C and D
and/or with the component constituents comprised therein (i.e., two or more
constituents, such
as substances or compounds, for example, from the group of one component) in
any desired
order. Components A, B, C an D may in each case be composed of one, two (Al,
A2 or Bl, B2,
or Cl, C2 or D1, D2) or a plurality of component constituents (Al, A2, A3,...,
or Bl, B2, B3,... ,
Cl, C2, C3,..., or D1, D2, 03,...).
Where the components consist of a plurality of component constituents, these
component con-
stituents may be added either as a mixture or separately from one another. In
the case of sepa-
rate addition, these component constituents may be added directly after one
another or else at
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3
different points in time not following directly on from one another. In the
event, for example, that
component C is composed of two constituents Cl and C2, this means that C2 is
added immedi-
ately after Cl or Cl is added immediately after C2, or that one or more other
components or
component constituents, component B for example, are added between the
addition of Cl and
C2. It is also possible for components and/or component constituents to be
premixed with other
components or component constituents before being added. For example, an
additive constitu-
ent D1 may be added to the binder C or to the binder constituent Cl before
this mixture is then
added to the actual mixture.
.. Preferably, first of all, the expanded plastics particles B are added to
the lignocellulose particles
A, and this mixture is thereafter admixed with a binder C or with two or more
binder constituents
Cl, C2, etc. Where two or more binder constituents are used, they are
preferably added sepa-
rately from one another. The additives D are preferably partially mixed with
the binder C or with
a binder constituent (i.e., a plurality of constituents, such as substances or
compounds, for ex-
ample, from the group of the component) and then added.
For the outer layers, the lignocellulose fibers E are mixed with the
components F and G and/or
with the component constituents present therein (i.e., a plurality of
constituents, such as sub-
stances or compounds, for example, from the group of one component) in any
desired order.
For the two outer layers it is possible to use either the same mixture or two
different mixtures,
preferably the same mixture.
Where the components consist of a plurality of component constituents, these
constituents can
be added either as a mixture or separately from one another. In that case,
these component
.. constituents can be added directly after one another or else at different
points in time not follow-
ing directly on from one another. The additives G are preferably partially
mixed with the binder F
or a binder constituent and then added.
The resulting mixtures A, B, C, D and E, F, G are layered one on top another
and compressed
by a customary process, at elevated temperature, to give a lignocellulosic
molding. For this pur-
pose, a mat is produced on a support, said mat being composed of these
mixtures in the order
E, F, G/A, B, C, DIE, F, G ("sandwich construction"). This mat is compressed
customarily at
temperatures from 80 to 300 C, preferably 120 to 280 C, more preferably 150 to
250 C, and at
pressures from 1 to 50 bar, preferably 3 to 40 bar, more preferably 5 to 30
bar, to form mold-
ings. In one preferred embodiment, the mat is subjected to cold precompaction
ahead of this
hotpressing. Compression may take place by any of the methods known to the
skilled person
(see examples in "Taschenbuch der Spanplatten Technik", H.-J. Deppe, K. Ernst,
4th edn.,
2000, DRW ¨ Verlag Weinbrenner, Leinfelden Echterdingen, pages 232 to 254, and
"MDF- Mit-
teldichte Faserplatten" H.-J. Deppe, K. Ernst, 1996, DRW- Verlag Weinbrenner,
Leinfelden-
Echterdingen, pages 93 to 104). These methods use discontinuous pressing
techniques, on
single-stage or multistage presses, for example, or continuous pressing
techniques, on double-
belt presses, for example.
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The lignocellulose materials of the invention generally have an average
density of 300 to
600 kg/m3, preferably 350 to 590 kg/m3, more preferably 400 to 570 kg/m3, more
particularly
450 to 550 kg/m3.
The lignocellulose particles of component A are present in the lignocellulosic
materials of the
core in amounts from 30% to 98% by weight, preferably 50% to 95% by weight,
more preferably
70% to 90% by weight, and their base material may be any desired wood variety
or mixtures
thereof, examples being spruce, beech, pine, larch, lime, poplar, eucalyptus,
ash, chestnut and
fir wood or mixtures thereof, preferably spruce, beech or mixtures thereof,
more particularly
spruce, and may comprise, for example, wood parts such as wood laths, wood
strips, wood
chips, wood fibers, wood dust or mixtures thereof, preferably wood chips, wood
fibers, wood
dust and mixtures thereof, more preferably wood chips, wood fibers or mixtures
thereof ¨ of the
kind used for producing chipboard, MDF (medium-density fiberboard) and HDF
(high-density
fiberboard) panels. The lignocellulose particles may also come from woody
plants such as flax,
hemp, cereals or other annual plants, preferably from flax or hemp. Particular
preference is giv-
en to using wood chips of the kind used for producing chipboard. If mixtures
of different lignocel-
lulose particles are used, for example mixtures of wood chips and wood fibers,
or of wood chips
and wood dust, then the proportion of wood chips is preferably at least 75% by
weight, i.e., 75%
to 100% by weight, more preferably at least 90% by weight, i.e., 90% to 100%
by weight. The
average density of component A is generally 0.4 to 0.85 g/cm3, preferably 0.4
to 0.75 g/cm3,
more particularly 0.4 to 0.6 g/cm3.
Starting materials for lignocellulose particles are customarily lumber from
forestry thinning, for-
est residuals, residual industrial lumber and used lumber, and also plants
containing wood fiber.
Processing to the desired lignocellulosic particles, wood particles such as
wood chips or wood
fibers for example, may take place in accordance with known methods (e.g., M.
Dunky, P.
Niemz, Holzwerkstoffe und Leime, pages 91 to 156, Springer Verlag Heidelberg,
2002).
Within the lignocellulosic materials of the outer layer, the lignocellulose
fibres of component E
are present in amounts of from 70% to 99% by weight, preferably 75% to 97% by
weight, more
preferably 80% to 95% by weight consisting of at least 75% by weight, i.e.,
75% to 100% by
weight, of lignocellulose fibers, preferably at least 85% by weight, i.e., 85%
to 100% by weight,
more preferably at least 95% by weight, i.e., 95% to 100% by weight. Most
preferably, exclu-
sively, i.e., 100% by weight of, lignocellulose fibers are used. Raw materials
used may be
woods from all of the wood varieties or woody plants listed under component A.
Following me-
chanical comminution, the fibers can be produced by grinding operations, after
a hydrothermal
pretreatment, for example. Fiberizing processes are known from Dunky, Niemz,
Holzwerkstoffe
und Leime, Technologie und Einflussfaktoren, Springer, 2002, pages 135 to 148,
for example.
The average density of component E is generally 0.3 to 0.85 g/cm3, preferably
0.35 to
0.8 g/cm3, more particularly 0.4 to 0.75 g/cm3.
Component A may comprise the customary small amounts of water, from 0% to 10%
by weight,
preferably 0.5% to 8% by weight, more preferably 1% to 5% by weight (in a
customary low
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range of fluctuation of 0% to 0.5% by weight, preferably 0% to 0.4% by weight,
more preferably
0% to 0.3% by weight). This quantity figure is based on 100% by weight of
absolutely dry wood
substance, and describes the water content of component A after the drying (by
customary
methods known to the skilled person) immediately prior to mixing with the
first component or
5 with the first component constituent or with the first mixture selected
from B, C and D.
In one preferred embodiment, component E may comprise small amounts of water
from 0% to
10% by weight, preferably 0.5% to 8% by weight, more preferably 1% to 5% by
weight (in a cus-
tomary low range of fluctuation of 0% to 0.5% by weight, preferably 0% to 0.5%
by weight, more
preferably 0% to 0.3% by weight). This quantity figure is based on 100% by
weight of absolutely
dry wood substance, and describes the water content of component E after the
drying (by cus-
tomary methods known to the skilled person) immediately prior to mixing with
the first compo-
nent or component constituent or mixture selected from F and G.
In another preferred embodiment, component E may comprise water at from 30% to
200% by
weight, preferably 40% to 150% by weight, more preferably 50% to 120% by
weight (in a range
of fluctuation of 0% to 20% by weight, preferably 0% to 10% by weight, more
preferably 0% to
5% by weight). This quantity figure is based on 100% by weight of absolutely
dry wood sub-
stance, and describes the water content of component E immediately prior to
mixing with the
first component or with the first component constituent or with the first
mixture selected from F
and G. In this embodiment, following the addition of a part of all of the
components and/or com-
ponent constituents, drying takes place according to methods known to the
skilled person; pref-
erably, this drying takes place after the addition of all of the components.
Suitable expanded plastics particles (component B) include expanded plastics
particles, prefer-
ably expanded thermoplastics particles, having a bulk density from 10 to 150
kg/m3, preferably
to 130 kg/m3, more preferably 35 to 110 kg/m3, more particularly 40 to 100
kg/m3 (deter-
mined by weighing a defined volume filled with the bulk material).
30 Expanded plastics particles B are used generally in the form of spheres
or beads having an av-
erage diameter of 0.01 to 50 mm, preferably 0.25 to 10 mm, more preferably 0.4
to 8.5 mm,
more particularly 0.4 to 7 mm. In one preferred embodiment the spheres have a
small surface
area per unit volume, in the form of a spherical or elliptical particle, for
example, and advanta-
geously are closed-cell spheres. The open-cell proportion according to DIN ISO
4590 is gener-
ally not more than 30%, i.e., 0% to 30%, preferably 1% to 25%, more preferably
5% to 15%.
Suitable polymers on which the expandable or expanded plastics particles are
based are gen-
erally all known polymers or mixtures thereof, preferably thermoplastic
polymers or mixtures
thereof, which can be foamed. Examples of highly suitable such polymers
include polyketones,
polysulfones, polyoxymethylene, PVC (rigid and flexible), polycarbonates,
polyisocyanurates,
polycarbodiimides, polyacrylimides and polymethacrylimides, polyamides,
polyurethanes, ami-
noplast resins and phenolic resins, styrene homopolymers (also referred to
below as "polysty-
rene" or "styrene polymer"), styrene copolymers, C2-Cio olefin homopolymers,
C2-010 olefin co-
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polymers, and polyesters. For producing the stated olefin polymers it is
preferred to use the
1-alkenes, examples being ethylene, propylene, 1-butene, 1-hexene and 1-
octene.
The polymers, preferably the thermoplastics, may additionally be admixed with
the customary
additives forming a basis for the expandable or expanded plastics particles
B), examples being
UV stabilizers, antioxidants, coating materials, hydrophobing agents,
nucleators, plasticizers,
flame retardants, soluble and insoluble, organic and/or inorganic dyes,
pigments, and ather-
manous particles, such as carbon black, graphite or aluminum powder, together
or spatially
separate, as adjuvants.
Component B may customarily be obtained as follows:
Suitable polymers, using an expansion-capable medium (also called "blowing
agent") or com-
prising an expansion-capable medium, can be expanded by exposure to microwave
energy,
thermal energy, hot air, preferably steam, and/or to a change in pressure
(this expansion often
also being referred to as "foaming") (Kuntstoff Handbuch 1996, volume 4,
"Polystyrol" , Hanser
1996, pages 640 to 673 or US-A-5,112,875). In the course of this procedure,
generally, the
blowing agent expands, the particles increase in size, and cell structures are
formed. This ex-
panding can be carried out in customary foaming apparatus, often referred to
as "prefoamers".
Such prefoamers may be installed permanently or else may be portable.
Expanding can be car-
ried out in one or more stages. In the one-stage process, in general, the
expandable plastics
particles are expanded directly to the desired final size. In the multistage
process, in general,
the expandable plastics particles are first expanded to an intermediate size
and then, in one or
more further stages, are expanded via a corresponding number of intermediate
sizes to the de-
sired final size. The compact plastics particles identified above, also
referred to herein as "ex-
pandable plastics particles", generally have no cell structures, in contrast
to the expanded plas-
tics particles. The expanded plastics particles generally have a low residual
blowing agent con-
tent, of 0% to 5% by weight, preferably 0.5% to 4% by weight, more preferably
1% to 3% by
weight, based on the overall mass of plastic and blowing agent. The expanded
plastics particles
obtained in this way can be placed in interim storage or used further without
other intermediate
steps for producing component B of the invention.
The expandable plastics particles can be expanded using all of the blowing
agents known to the
skilled person, examples being aliphatic C3 to C10 hydrocarbons, such as
propane, n-butane,
isobutane, n-pentane, isopentane, neopentane, cyclopentane and/or hexane and
isomers
thereof, alcohols, ketones, esters, ethers or halogenated hydrocarbons,
preferably n-pentane,
isopentane, neopentane and cyclopentane, more preferably a commercial pentane
isomer mix-
ture of n-pentane and isopentane.
The amount of blowing agent in the expandable plastics particles is generally
in the range from
0.01% to 7% by weight, preferably 0.01% to 4% by weight, more preferably 0.1%
to 4% by
weight, based in each case on the expandable plastics particles containing
blowing agent.
7
One preferred embodiment uses styrene homopolymer (also called simply
"polystyrene" herein),
styrene copolymer or mixtures thereof as the sole plastic in component B.
Polystyrene and/or styrene copolymer of this kind may be prepared by any of
the polymerization
techniques known to the skilled person; see, for example, Ullmann's
Encyclopedia, Sixth Edition,
2000 Electronic Release or Kunststoff-Handbuch 1996, volume 4 "Polystyrol'',
pages 567 to 598.
The expandable polystyrene and/or styrene copolymer is generally prepared in a
conventional
way by suspension polymerization or by means of extrusion processes.
In the case of the suspension polymerization, styrene, optionally with
addition of further
cornonomers, can be polymerized in aqueous suspension in the presence of a
customary
suspension stabilizer by means of radical-forming catalysts. The blowing agent
and any other
customary adjuvants may be included in the initial charge for the
polymerization or else added to
the batch in the course of the polymerization or after the polymerization has
ended. The resultant
beadlike, expandable styrene polymers impregnated with blowing agent, after
the end of the
polymerization, can be separated from the aqueous phase, washed, dried and
screened.
In the case of the extrusion process, the blowing agent can be mixed into the
polymer via an
extruder, for example, conveyed through a die plate and pelletized under
pressure to form
particles or strands.
The preferred or particularly preferred expandable styrene polymers or
expandable styrene
copolymers described above have a relatively low blowing agent content. Such
polymers are also
referred to as "low in blowing agent". A highly suitable process for producing
expandable
polystyrene or expandable styrene copolymer low in blowing agent is described
in US-A-
5,112,875.
As described, it is also possible to use styrene copolymers. Advantageously,
these styrene
copolymers contain at least 50% by weight, i.e., 50% to 100% by weight,
preferably at least 80%
by weight, i.e., 80% to 100% by weight, of copolymerized styrene, based on the
mass of the
plastic (without blowing agent). Examples of comonomers contemplated include a-
methylstyrene,
ring-halogenated styrenes, acrylonitrile, esters of acrylic or methacrylic
acid with alcohols having
1 to 8 C atoms, N-vinylcarbazole, maleic acid, maleic anhydride,
(meth)acrylamides and/or vinyl
acetate.
The polystyrene and/or styrene copolymer may advantageously include a small
amount of a
copolymerized chain-branching agent, in other words a compound having more
than one double
bond, preferably two double bonds, such as divinylbenzene, butadiene and/or
butanediol
diacrylate. The branching agent is used generally in amounts from 0.0005 to
0.5 morY0, based on
styrene. Mixtures of different styrene (co)polymers can be used as well.
Highly suitable styrene
homopolymers or styrene copolymers are crystal-clear polystyrene (GPPS), high-
impact poly-
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styrene (HIPS), anionically polymerized polystyrene or high-impact polystyrene
(A-IPS), sty-
rene-a-methylstyrene copolymers, acrylonitrile-butadiene-styrene polymers
(ABS), styrene-
acrylonitrile (SAN), acrylonitrile-styrene-acrylic ester (ASA), methyl
acrylate-butadiene-styrene
(M BS), methyl methacrylate-acrylonitrile-butadiene-styrene (MABS) polymers or
mixtures there-
of, or used with polyphenylene ether (PPE).
Preference is given to using plastics particles, more preferably styrene
polymers or styrene co-
polymers, more particularly styrene homopolymers, having a molecular weight in
the range from
70 000 to 400 000 g/mol, more preferably 190 000 to 400 000 g/mol, very
preferably 210 000 to
400 000 g/mol.
These expanded polystyrene particles or expanded styrene copolymer particles
may be used,
with or without further measures for blowing agent reduction, for producing
the lignocellulosic
substance.
The expandable polystyrene or expandable styrene copolymer or the expanded
polystyrene or
expanded styrene copolymer customarily has an antistatic coating.
The expanded plastics particles B are generally in an unmelted state even
after compression to
.. form the lignocellulose material, this meaning that the plastics particles
B have generally not
penetrated or impregnated the lignocellulose particles, but instead are
distributed between the
lignocellulose particles. The plastics particles B can customarily be
separated from the lignocel-
lulose by physical methods, as for example after the comminuting of the
lignocellulose material.
The overall amount of the expanded plastics particles B, based on the overall
dry mass of the
core, is generally in the range from 1% to 25% by weight, preferably 3% to 20%
by weight, more
preferably 5% to 15% by weight.
It has emerged as being advantageous to match the dimensions of the above-
described ex-
panded plastics particles B to the lignocellulose particles, preferably wood
particles A), or vice
.. versa.
This matching is expressed below by the relationship of the respective d'
values (from the Ros-
in-Rammler-Sperling-Bennet function) of the lignocellulose particles,
preferably wood particles
A, and of the expanded plastics particles B.
The Rosin-Rammler-Sperling-Bennet function is described in DIN 66145, for
example.
The d' values are determined by conducting sieve analyses first of all for
determining the parti-
cle size distribution of the expanded plastics particles B and lignocellulose
particles, preferably
wood particles, A, in analogy to DIN 66165, Parts 1 and 2.
The values from the sieve analysis are then inserted into the Rosin-Rammler-
Sperling-Bennet
function, and d' is calculated.
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The Rosin-Rammler-Sperling-Bennet function is:
R = 100*exp(-(d/d')n))
The definitions of the parameters are as follows:
R residue (% by weight) remaining on the respective sieve tray
d particle size
d' particle size at 36.8% by weight of residue
n width of the particle size distribution
Highly suitable lignocellulose particles A, preferably wood particles, have a
d' value according to
Rosin-Rammler-Sperling-Bennet (definition and determination of the d' value as
described
above) in the range from 0.1 to 5, preferably 0.3 to 3, and more preferably
0.5 to 2.75.
Highly suitable lignocellulose materials are obtained when the d' values
according to Rosin-
Rammler-Sperling-Bennet of the lignocellulose particles, preferably wood
particles A and for the
particles of the expanded plastics particles B are subject to the following
relationship:
d' of the particles A 2.5 x d' of the particles B, preferably
d' of the particles A 2.0 x d' of the particles B, more preferably
d' of the particles A 1.5 x d' of the particles B, very preferably
d' of the particles A d' of the particles B.
The overall amount of the binder C, based on the overall mass of the core, is
in the range from
1% to 50% by weight, preferably 2% to 15% by weight, more preferably 3% to 10%
by weight.
The overall amount of the binder F, based on the overall dry mass of the outer
layer(s), is in the
range from 1% to 30% by weight, preferably 2% to 20% by weight, more
preferably 3% to 15%
by weight.
The binders of component C and of component F may be selected from the group
consisting of
phenoplast resin, aminoplast resin, and organic isocyanate having at least two
isocyanate
groups, using identical or different binders or binder mixtures of components
C and F, prefera-
bly different binders, with particular preference phenoplast and aminoplast in
both cases. The
weight figure in the case of phenoplast or aminoplast resins relates to the
solids content of the
corresponding component (determined by evaporating the water at 120 C over the
course of 2
hours in accordance with Gunter Zeppenfeld, Dirk Grunwald, Klebstoffe in der
Holz- und MO-
belindustrie, 2nd edition, DRW-Verlag, page 268), while in relation to the
isocyanate, more par-
ticularly the PMDI (polymeric diphenylmethane diisocyanate), it relates to the
isocyanate com-
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ponent per se, in other words, for example, without solvent or emulsifying
medium.
The term "phenoplast" refers to synthetic resins or modified products obtained
by condensation
of phenol with aldehydes. Besides unsubstituted phenol, derivatives of phenol
are used for the
5 manufacture of phenoplast resins. These include cresols, xylenols and
other alkylphenols (for
example p-tert-butylphenol, p-tert-octylphenol and p-tert-nonylphenol),
arylphenols (for example
phenylphenol and naphthols) and divalent phenols (such as resorcinol and
bisphenol A). The
most important aldehyde component is formaldehyde, which is used in variaous
forms, including
aqueous solution and solid paraformaldehyde, and also as compounds which give
rise to for-
10 maldehyde. Other aldehydes (for example acetaldehyde, acrolein,
benzaldehyde and furfural)
are employed to a more limited extend, as also are ketones. Phenoplast resins
can be modified
by chemical reaction of the methylol or the phenolic hydroxyl groups and/or by
phyisical disper-
sion in the modifying agent (EN ISO 10082).
Prefered phenoplast resins are phenol aldehyde resins, most preferably phenol-
formaldehyde
resins. Phenol-formaldehyde resins (also called PF resins) are known from, for
example, Kun-
ststoff-Handbuch, 2nd edition, Hanser 1988, volume 10, "Duroplaste", pages 12
to 40.
As aminoplast resin it is possible to use all aminoplast resins known to the
skilled person, pref-
erably those known for the production of wood based materials. Resins of this
kind and also
their preparation are described in, for example, Ullmanns Enzyklopadie der
technischen
Chemie, 4th, revised and expanded edition, Verlag Chemie, 1973, pages 403 to
424 "Amino-
plaste", and Ullmann's Encyclopedia of Industrial Chemistry, vol. A2, VCH
Verlagsgesellschaft,
1985, pages 115 to 141 "Amino Resins", and also in M. Dunky, P. Niemz,
Holzwerkstoffe und
Leime, Springer 2002, pages 251 to 259 (UF resins) and pages 303 to 313 (MUF
and UF with a
small amount of melamine). Generally speaking, they are polycondensation
products of com-
pounds having at least one ¨ optionally substituted partially with organic
radicals ¨ amino group
or carbamide group (the carbamide group is also called carboxamide group),
preferably car-
bamide group, preferably urea or melamine, and an aldehyde, preferably
formaldehyde. Pre-
ferred polycondensation products are urea-formaldehyde resins (UF resins),
melamine-
formaldehyde resins (MF resins) or melamine-containing urea-formaldehyde
resins (MUF res-
ins), more preferably urea-formaldehyde resins, examples being Kaurit glue
products from
BASF SE.
Particularly preferred polycondensation products are those in which the molar
ratio of aldehyde
to the ¨ optionally substituted partially with organic radicals ¨ amino group
and/or carbamide
group is in the range from 0.3:1 to 1:1, preferably 0.3:1 to 0.6:1, more
preferably 0.3:1 to 0.55:1,
very preferably 0.3:1 to 0.5:1. Where the aminoplasts are used in combination
with isocyanates,
the molar ratio of aldehyde to the ¨ optionally substituted partially with
organic radicals ¨ amino
group and/or carbamide group is in the range from 0.3:1 to 1:1, preferably
0.3:1 to 0.6:1, more
preferably 0.3:1 to 0.45:1, very preferably 0.3:1 to 0.4:1.
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The stated aminoplast resins are used customarily in liquid form, customarily
as a 25% to 90%
by weight strength solution, preferably a 50% to 70% by weight strength
solution, preferably in
aqueous solution, but may also be used in solid form.
The solids content of the liquid aqueous aminoplast resin can be determined in
accordance with
Gunter Zeppenfeld, Dirk Grunwald, Klebstoffe in der Holz- und MObelindustrie,
2nd edition,
DRW-Verlag, page 268.
The constituents of the binder C and of the binder F can be used per se alone
¨ that is, for ex-
ample, aminoplast resin or organic isocyanate or PF resin as sole constituent
of binder C or of
binder F. In addition, however, the resin constituents of binder C and of
binder F may also be
used as a combination of two or more constituents of the binder C and/or of
the binder F; these
combinations preferably comprise an aminoplast resin and/or phenoplast resin.
In one preferred embodiment a combination of aminoplast and isocyanate can be
used as bind-
er C. In this case, the total amount of the aminoplast resin in the binder C,
based on the overall
dry mass of the core, is in the range from 1% to 45% by weight, preferably 4%
to 14% by
weight, more preferably 6% to 9% by weight. The overall amount of the organic
isocyanate,
preferably of the oligomeric isocyanate having 2 to 10, preferably 2 to 8
monomer units and on
average at least one isocyanate group per monomer unit, more preferably PM Dl,
in the bind-
er C, based on the overall dry mass of the core, is in the range from 0.05% to
5% by weight,
preferably 0.1% to 3.5% by weight, more preferably 0.5% to 1.5% by weight.
Components D and G may each independently of one another comprise different or
identical,
preferably identical curing agents that are known to the skilled person, or
mixtures thereof.
These components are customarily used if the binder C and/or F comprises
aminoplasts or
phenoplast resins. These curing agents are preferably added to the binder C
and/or F, in the
range, for example, from 0.01% to 10% by weight, preferably 0.05% to 5% by
weight, more
preferably 0.1% to 3% by weight, based on the overall amount of aminoplast
resin or pheno-
plast resin.
Curing agents for the aminoplast resin component or for the phenoplast resin
component are
understood herein to encompass all chemical compounds of any molecular weight
that acceler-
ate or bring about the polycondensation of aminoplast resin or phenoplast
resin. One highly
suitable group of curing agents for aminoplast resin or phenol-formaldehyde
resin are organic
acids, inorganic acids, acidic salts of organic acids, and acidic salts of
inorganic acids, or acid-
forming salts such as ammonium salts or acidic salts of organic amines. The
components of this
group can of course also be used in mixtures. Examples are ammonium sulfate or
ammonium
nitrate or organic or inorganic acids, as for example sulfuric acid, formic
acid or acid-
regenerating substances, such as aluminum chloride, aluminum sulfate or
mixtures thereof.
One preferred group of curing agents for aminoplast resin or phenoplast resin
are organic or
inorganic acids such as nitric acid, sulfuric acid, formic acid, acetic acid,
and polymers with acid
groups, such as homopolymers or copolymers of acrylic acid or methacrylic acid
or maleic acid.
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Phenoplast resins, preferably phenol-formaldehyde resins can also be cured
alkylenically. It is
preferred to use carbonates or hydroxides such as potassium carbonate and
sodium hydroxide.
Further examples of curing agents for aminoplast resins are known from M.
Dunky, P. Niemz,
Holzwerkstoffe und Leime, Springer 2002, pages 265 to 269, and further
examples of curing
agents for phenoplast resins, preferably phenol-formaldehyde resins are known
from M. Dunky,
P. Niemz, Holzwerkstoffe und Leime, Springer 2002, pages 341 to 352.
The lignocellulose materials of the invention may comprise further,
commercially customary
additives and additives known to the skilled person, as component D and as
component G, in-
dependently of one another identical or different, preferably identical
additives, in amounts from
0% to 10% by weight, preferably 0.5% to 5% by weight, more preferably 1% to 3%
by weight,
examples being hydrophobizing agents such as paraffin emulsions, antifungal
agents, formal-
dehyde scavengers, such as urea or polyamines, for example, and flame
retardants.
The thickness of the lignocellulose materials of the invention with expanded
plastics particles in
the core and with lignocellulosic fibers in the outer layers varies with the
field of application and
is situated in general in the range from 0.5 to 100 mm, preferably in the
range from 10 to
40 mm, more particularly 15 to 20 mm.
In a preferred embodiment of the invention, the expandable plastics particles
B are present in
nonuniform distribution in the core. This means that the weight ratio X of
expanded plastics par-
ticles B to lignocellulose particles A in the outer regions of the core
("exterior") is different from
the weight ratio Y of expanded plastic particles B to lignocellulose particles
A in the inner region
of the core ("interior"), in other words is greater or lesser in the outer
regions of the core ("exte-
rior") than in the inner region of the core ("interior"). The inner region of
the core is generally
separated from the two outer regions of the core by faces extending parallel
to the panel plane.
The inner region of the core is understood to be the region which comprises
20% to 80% by
weight, preferably 30% to 70% by weight, more preferably 40% to 60% by weight,
more particu-
larly 45% to 55% by weight, very preferably 50% by weight of the overall dry
mass of the core
and is situated between the two outer regions. The two outer regions may have
the same mass,
in other words in each case 25% by weight, or approximately the same mass,
i.e.,
25.01:24.99% to 25.99:24.01% by weight, preferably 25.01:24.99% to 25.8:24.2%,
more prefer-
ably 25.01:24.99% to 25.6:24.4%, more particularly 25.01:24.99% to 25.4:24.6%,
or a different
mass, based on the overall dry mass of the core, i.e., 26:24% to 40:10% by
weight, preferably
26:24% to 30:20% by weight, more preferably 26:24% to 27:23% by weight, more
particularly
26:24% to 26.5:23.5% by weight. The sum total of the inner region and of the
two outer regions
of the core makes up 100% by weight. To determine the weight ratio X of
expanded plastics
particles B to lignocellulose particles A in the outer regions of the core,
all expanded plastics
particles B and all lignocellulose particles A which are comprised in the two
outer regions are
used. In this case, the ratio X', which describes the ratio of plastics
particles B to lignocellulose
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particles A in one of the two outer regions, can be different from or the same
as the ratio X"
which describes the ratio in the other of the two outer regions.
In the material of the invention, the ratio Z between the weight ratio X of
expanded plastics par-
ticles to lignocellulose particles in the outer regions of the core
("exterior") and the weight ratio Y
of expanded plastics particles to lignocellulose particles in the inner region
of the core ("interior")
is 1.05:1 to 1000:1, preferably 1.1:1 to 500:1, more preferably 1.2:1 to
200:1. In a further pre-
ferred embodiment, this ratio Z is 0.001:1 to 0.95:1, preferably 0.002:1 to
0.9:1, more preferably
0.005:1 to 0.8:1.
The nonuniform distribution of the plastics particles B in the core may be
generated as follows:
A plurality of mixtures of components A, B, C and D can be produced,
containing different mass
ratios of components A and B. These mixtures can be scattered in succession.
In this case,
there ought generally to be only slight mixing, or none, of the mixtures with
different mass ratios
of components A and B. As a result, a nonuniform distribution of the expanded
plastics particles
in the core of the lignocellulose material can be achieved. In this context,
both the wood parti-
cles A and the plastics particles B can be separated beforehand into different
fractions, by
screening, for example. Each of the mixtures may comprise different fractions
of the wood parti-
cles A and/or of the plastics particles B.
In another embodiment, the nonuniform distribution of the plastics particles B
in the core may be
accomplished by separative scattering. In this case, scattering takes place
using a means which
ensures that the spheres accumulate either in the outer regions or in the
inner regions of the
core, depending on the size and/or on the weight. This can be accomplished,
for example, by
scattering the mixture A, B, C, D using a screening system. In one preferred
embodiment, this
system is equipped with screens of different hole sizes which are arranged
mirror-symmetrically.
With particular preference, a support bearing the material for the lower outer
layer is conveyed
beneath a scattering means in which a screen system is disposed in such a way
that at the be-
ginning of the scattering means (in production direction) there are screens
with a small hole
size, with the hole size of the screens increasing inwardly toward the middle
of the scattering
station, and decreasing again at the end of the station. The disposition of
the screens means
that small lignocellulose particles enter into the outer regions of the core,
those close to the out-
er layer, and large lignocellulose particles enter the inner region of the
core. At the same time,
small plastics particles enter the outer regions of the core, those close to
the outer layer, and
large plastics particles enter the inner region of the core. Depending on the
size distribution of
the lignocellulose particles and of the plastics particles, this produces
different mass ratios of
lignocellulose particles A to plastics particles B. Scattering stations of
this kind are described in
EP-B-1140447 and DE-C-19716130.
For example, the lignocellulose particle scattering station may comprise two
metering silos each
housing a plurality of back-scraping rakes. The bulk material, composed of
different large parti-
cles A and of components B, C and D ("core mixture"), can be supplied to the
metering silos
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(e.g., from above). Disposed on the underside of each of the metering silos
may be a bottom
belt which runs over two deflecting rollers and which, in each case together
with a discharge
roll, forms a discharge unit for the core mixture. Beneath each of the
discharge rolls there may
be a continuous scraper belt which is guided over two deflecting rollers and
whose lower tower
can be guided in each case over screen devices with different hole sizes, thus
forming different
sections of the screen devices. Together with the scraper belts, the screen
devices form frac-
tionating means by which the lignocellulosic particles A and the plastics
particles B of the core
mixture can be fractionated according to their sizes. The sections of the
screen devices may be
disposed in such a way that the fine lignocellulose particles A and/or
plastics particles B are
each scattered, in those regions of the scattering station that lie externally
in the transport direc-
tion of the web, onto the lower outer layer, while the coarse lignocellulose
particles A and/or
plastics particles B are scattered, via the internal regions of the
fractionating means, onto the
outer layer (see in detail EP-B-1140447).
According to another advantageous embodiment of the invention, at least a part
of the appor-
tioning sections in each case comprises an abrasive element which bears
against the surface of
the screen means and, when the apportioning sections are moved, is guided
abradingly over
the surface of the screen means. An abrasive element bearing under gentle
pressure against
the surface of the screen means for each apportioning section or at least some
of the apportion-
ing sections further strengthens the cleaning effect which comes about when
the apportioning
sections are moved over the surface of the screen means. At the same time, the
abrasive ele-
ments reinforce the force component that acts on the particles in a direction
perpendicular to the
screen surface, thereby producing an increase in the throughput. The transport
means is pref-
erably designed as a scraper belt, more particularly as a continuous scraper
belt. In this way,
particularly simple and inexpensive configuration of the transport means is
possible. Here, ad-
vantageously, the scraper belt is formed previously for the particles at least
over a subregion in
a direction perpendicular to the surface of the screen means, thereby allowing
the particles to
be tipped from the metering silo via its feed unit through the scraper belt
and onto the screen
means. This does away with the need for any complicated configuration of the
feed unit. Ac-
cording to a further advantageous embodiment of the invention, the scraper
belt comprises
drivers, more particularly platelike drivers, which are provided preferably at
regular intervals on
a continuous support element in chain or belt form. In this case, the support
element may be
mounted in each case centrally on the drivers. It is also possible, however,
for a plurality of sup-
port elements, more particularly two chain or belt support elements, to be
provided, each fas-
tened in the region of the lateral outside edges of the drivers. This
increases the stability of a
scraper belt designed in accordance with the invention. Preferably, the
drivers are fastened de-
tachably on the support element or support elements, and/or are of air-
impervious design. This
ensures that, on the one hand, the drivers used can be optimally tailored to
the screen means
employed, and on the other hand that worn drivers can be replaced by new ones.
According to
another advantageous embodiment of the invention, the abrasive elements are
formed in each
case by a section of the drivers. In this way, the design of the means of the
invention can be
particularly cost-effective, since no separate components are needed for the
abrasive elements.
In particular, at least in their sections forming the abrasive elements, the
drivers are of flexible
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design, being made from hard rubber, for example. This allows the abrasive
elements to con-
form to the surface of the screen means, thereby ensuring, even in the event
of a certain irregu-
larity in the screen surface, that the abrasive elements bear on the surface
of the screen means
with a certain pressure over their entire width and also over their entire
range of movement.
5 .. According to another preferred embodiment of the invention, the drivers
are of abrasion-
resistant design, at least in their sections forming the abrasive elements,
and more particularly
possess an abrasion-resistant coating, such as a Teflon coating, for example.
The sections of
the drivers that form the abrasive elements may be designed either in one
piece with the drivers
or else as separate components. Where the abrasive elements are designed as
separate corn-
10 ponents, they are preferably mounted detachably on the drivers, so that
they can be replaced in
the event of wear. According to another advantageous embodiment of the
invention, the drivers,
at least in their sections forming the abrasive elements, are formed from
water-repellent nonad-
hering material. This prevents the particles wetted with binder remaining
stuck to the drivers,
which could limit the pickup capacity of the apportioning sections. According
to a further pre-
15 .. ferred embodiment of the invention, the screen means comprises screen
zones, more particu-
larly two screen zones, with different screen openings. In this way, particles
of different size are
fractionated by the screen zones with different-sized screen openings. In this
context, in particu-
lar, the screen zones are arranged one after another along the direction of
movement of the
apportioning sections that are movable over the surface of the screen means,
and preferably
the screen openings of the screen zone/zones situated in the direction of
movement of the ap-
portioning sections are larger than the screen openings of the screen
zone/screen zones situat-
ed counter to the direction of movement. This ensures that, as they pass over
the screen sur-
face, the particles with small diameter pass first through the screen means,
while in the next
screen zone, lastly, the next-larger particles pass through the screen.
Depending on the number
of screen zones and on the size of the screen openings, therefore, the desired
fractioning of the
particles is achieved. These fractionated particles may either be tipped, in
accordance with the
screen zones, into different collecting means for the different particle
sizes, or, for example, may
be tipped onto a moving conveyor belt which is disposed beneath the screen
means and on
which, in this way, a web with different distributions of particle sizes over
its thickness can be
produced.
According to a further advantageous embodiment of the invention, the
continuous scraper belt
is guided via two deflection rolls, and so a lower belt section runs directly
on the surface of the
screen means, and an upper belt section runs at a particular distance from the
surface of the
screen means, more particularly in each case substantially parallel to the
surface of the screen
means. In this way, a particularly compact design is possible for a means of
the invention. Pref-
erably in this case, at least at one end of the scraper belt, more
particularly in the region of the
deflection rolls, there is a pickup means provided for picking up expelled
particles. These parti-
cles may be alien bodies present in the bulk material, such as screws or
nails, for example; al-
ternatively, they may be aggregations or particles which exceed a maximum
permissible size,
and which are expelled and taken away in order that even the largest screen
openings of the
screen means cannot become clogged. According to another preferred embodiment
of the in-
vention, at least in regions between the upper and lower belt sections, an
intermediate base is
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provided, and the drivers bear, with their ends opposed to the sections
forming the abrasive
elements, against the intermediate base, meaning that, when the apportioning
sections are
moved, these ends are guided abradingly over the intermediate base. With this
embodiment,
bulk material applied from the metering silo via its feed unit initially to
the intermediate base can
be brought in a defined way to a particular position between the deflection
rollers. In this case,
according to one preferred embodiment, the intermediate base may extend from
one deflection
roller in the direction of movement of the upper belt section toward the
opposite, other deflection
roller; between this other deflection roller and the end of the intermediate
base that faces this
other deflection roller, a region is formed which is pervious for the
particles in a direction per-
.. pendicular to the surface of the screen means. Particularly when this
region is formed from fur-
ther screen means possessing relatively large screen openings, it is possible
here for there to
be a preliminary deposition of alien bodies or particles having a size which
is above the size of
these screen openings. Only those particles that pass through the further
screen means fall
onto the underlying screen means, over which they are moved by means of the
transport
.. means. According to another preferred embodiment of the invention, there
are two scraper belts
situated one after the other in the longitudinal direction, and the scraper
belts are in particular
arranged mirror-symmetrically to one another. In this case, advantageously, a
distribution
means, more particularly in the form of a shuttle distributor, is positioned
downstream of the
feed unit of the metering silo, and can be used to supply the particles taken
from the metering
silo through the feed unit to the two scraper belts, more particularly in
alternation. By means of
this design it is possible, starting from one metering silo, to distribute
particles to two different
scraper belts. Especially when the two scraper belts can be driven in opposing
directions, and
so the two upper belt sections can be moved in a mutually divergent way, and,
between the
upper and the lower belt sections, in a manner already described, an
intermediate base is pro-
vided, it is possible for the particles applied via the distribution means to
the respective interme-
diate bases to be transported to the ends of the scraper belts that are
situated in opposite direc-
tions, where they are applied in each case to the screen means disposed
beneath the scraper
belts. Given appropriate sizing of the screen openings of these screen means,
particularly when
the size of the screen openings increases in the direction of movement of the
lower belt sec-
tions, the material for the core can be formed on a moving conveyor belt
disposed beneath the
screen means, and on which the lower outer layer has already been scattered,
the formation of
the core material being such that the fine lignocellulose particles A and/or
plastics particles B
are accumulated in the outer layers of the core, and the coarse lignocellulose
particles A and/or
plastics particles B are accumulated in the inner layer of the core. Instead
of a distribution
means, it is also possible, for example, for there to be two metering silos by
which the two
scraper belts are charged with particles. In all embodiments, the screen means
and/or the fur-
ther screen means is preferably designed as an oscillating screen or as a
vibrating shaker
screen. In this case, the bulk material fed to the screen means is loosened
further, meaning that
fine particles and, subsequently, medium-sized particles at a distance from
the screen pass
more quickly toward the screen openings and through them (see in detail DE-C-
197 16 130).
Another preferred embodiment is the use of a roller scattering system with
specially profiled
rolls (roll screen). In this case as well, preferably, a symmetrical
construction is selected, mean-
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ing that small lignocellulose particles A and/or small plastics particles B
enter the outer regions
of the core, those close to the outer layer, and large lignocellulose
particles A and/or large plas-
tics particles B enter the inner region of the core. One particularly
preferred embodiment is the
use of one or more ClassiFormerTm devices. Suitability is possessed, for
example, by the Classi-
former CC from Dieffenbacher, which has a symmetrical construction.
Alternatively it is possible
to use two Classiformers C, arranged opposite and one after the other.
Lignocellulose materials, as for example wood based materials, are an
inexpensive and re-
source-protecting alternative to solid wood, and have become very important
particularly in fur-
niture construction, for laminate floors and as construction materials.
Customarily serving as
starting materials are wood particles of different thicknesses, examples being
wood chips or
wood fibers from a variety of woods. Such wood particles are customarily
compressed with nat-
ural and/or synthetic binders and optionally with addition of further
additives to form wood based
materials in panel or strand forms.
Lightweight wood based materials are very important for the following reasons:
Lightweight wood based materials lead to greater ease of handling of the
products by the end
customers, as for example when packing, transporting, unpacking or
constructing the furniture.
Lightweight wood based materials result in lower costs for transport and
packaging, and it is
also possible to save on materials costs when producing lightweight wood based
materials.
Lightweight wood based materials may, as when used in means of transport, for
example, result
in a lower energy consumption by those means of transport. Furthermore, using
lightweight
wood based materials, it is possible to carry out more cost-effective
production of, for example,
materials-intensive decorative parts, relatively thick worktops and side
panels in kitchens.
There are numerous applications, as for example in the bathroom or kitchen
furniture segment
or in interior outfitting, where lightweight and economic lignocellulosic
materials having im-
proved mechanical properties, as for example improved flexural strengths and
screw removal
values, are sought after. Moreover, such materials are to have an extremely
good surface quali-
ty, in order to allow application of coatings, for example a paint or varnish
finish, having good
properties.
Examples
1. Production of the expanded polymer particles
The expandable polystyrene Polystyrol Kaurit Light 200 from BASF SE served as
starting ma-
terial. The polystyrene particles were treated with steam and foamed to a bulk
density of 50 g/I
in a batch prefoamer. The expanded polymer particles obtained in this way
(component B) were
stored at room temperature in an air-permeable cloth sack for 7 days before
further use.
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2. Production of the wood materials
Three different mixtures of the starting materials were produced for each wood
material board.
Mixture 1: Components E, F, G for the covering layers
Mixture 2: Components A, B, C, D for the outer region of the core
Mixture 3: Components A, B, C, D for the inner region of the core
Component B is omitted for comparative example 1, i.e. the mixtures 2 and 3
then comprise
only the components A, C and D. For comparative example 2 and example 3
according to the
invention, mixtures 2 and 3 are identical. In comparative examples 1 and 2,
mixture 1 comprises
wood shavings as component E, in all other examples wood fibers.
The mixtures were each produced in a laboratory mixer, with the solid
constituents being intro-
duced first and mixed. The liquid constituents were premixed in a vessel and
then sprayed on.
For mixture 1, fine covering layer spruce shavings having a moisture content
of 5.9% or wood
fibers having a moisture content of 2.8% were used (component E).
For mixtures 2 and 3, middle layer shavings composed of shavings having a
moisture content of
3.2% were used (component A).
Kaurit glue 347 having a solids content of 67% from BASF SE was used as
binder (compo-
nents C and F). For mixture 1, 40 parts by weight of water and 1 part by
weight of 52% strength
ammonium nitrate solution (in each case based on 100 parts by weight of Kaurit
glue 347) were
added to the glue before application to the solid constituents of the mixture.
For mixtures 2 and
3, 4 parts by weight of 52% strength ammonium nitrate solution (based on 100
parts by weight
of Kaurit glue 347) were added to the glue before application to the solid
constituents of the mix-
tures.
For the covering layers (mixture 1), the amount of glue mix is set so that a
glue addition of 10%
is obtained, i.e. 10 parts by weight of glue (based on solids) per 100 parts
by weight of E (based
on solids).
For the core (both for the outer region ¨ mixture 2 ¨ and for the inner region
of the core ¨ mix-
ture 3), the amount of glue mix is set so that a glue addition of 8.0% is
obtained, i.e. 8.0 parts
by weight of glue (based on solids) per 100 parts by weight of the mixture of
A and B (based on
solids).
The mixtures were subsequently placed on top of one another in layers in a 30
x 30 cm mold so
as to obtain a wood material mat having a symmetrical structure made up of 5
layers (se-
quence: mixture 1, mixture 2, mixture 3, mixture 2, mixture 1). The amounts
were selected so
that the weight ratio of the layers (based on dry matter) was in each case
15.5:20.5:28:20.5:15.5.
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In all examples comprising component B, the mass ratio of the total amount of
component B
comprised in the inner three layers to the total amount of component A
comprised in the inner
three layers is the same (based on solids).
The total weight of the wood material mat was selected so that the desired
density is obtained
at a prescribed thickness of 18.5 mm at the end of the pressing process.
The wood material mat was then precompacted cold and pressed in a hot press. A
thickness of
16 mm was set here. The pressing temperature was in each case 210 C and the
pressing time
was 210s.
3. Examination of the wood materials
3.1 Density
The determination of the density was carried out 24 hours after production in
accordance with
EN 1058.
3.2 Transverse tensile strength
The determination of the transverse tensile strength was carried out in
accordance with EN 319.
3.3 Flexural strength and E modulus in bending
The determination of the flexural strength and the E modulus in bending was
carried out in ac-
cordance with DIN EN 310.
3.4 Screw pullout resistance
The determination of the screw pullout resistance was carried out in
accordance with DIN EN
320. Only the screw pullout resistances for the surfaces were measured.
3.5 Lift-off strength
The determination of the lift-off strength as a measure of the surface quality
was carried out in
accordance with DIN EN 311.
PF 72979
Examples
0
Examples 1 and 2: Comparative examples using shavings in the covering layer
(with and without expanded polymer particles in the core) t..)
=
-,
Examples 3 to 7: Examples according to the invention
c,.)
,
=
,z
5
t.)
c.,
Example Component Ratio X Ratio Y Ratio Z Density
Transverse Flexural Screw Lift-off
E ("exterior") ("interior") (= X:Y)
tensile strength pullout res. strength
strength
[kg/m3] [N/mm2]
[N/mm2] [N] [N/mm2]
1 Shavings a) a) - 502 0.44
6.5 590 0.6
2 Shavings 0.075 0.075 1 506 0.57
8.4 680 0.8
3 Fibers 0.075 0.075 1 495 0.59
12.2 770 0.8 P
2
4 Fibers 0.083 0.063 1.32 495 0.59
12.5 790 1.0
2
5 Fibers 0.102 0.036 2.83 503 0.57
13.1 820 1.0
6 Fibers 0.064 0.092 0.70 500 0.63
12.0 760 0.9 .
.."
7 Fibers 0.036 0.136 0.26 493 0.68
12.3 770 0.8 .,
a) this comparative example does not comprise any expanded polymer particles
I'd
n
-i
m
1-:
t.,
=
-,
t.,
--
-.1
c.,
00
