Note: Descriptions are shown in the official language in which they were submitted.
1 338075 Mo3202
LeA 26,007
PROCESS FOR THE PREPARATION OF COMPRESSION MOLDED MATERIALS
BACKGROUND OF THE INVENTION
This invention relates to a process for the production
of compression molded materials using polyisocyanate binders or
mixtures of polyisocyanates and other binders together with
polyether or polyester polyols and mixtures thereof and alkylene
carbonates.
Compression molded materials, such as chipboard,
composite board, or other such molded products, are con-
ventionally produced bv hot pressing inorganic or organic rawmaterials, such as a mass of wood shavings, wood fibers, or other
material containing lignocellulose, with various glues or
binders. The woodworking industry, which is the largest
manufacturer of compression molded materials, still uses what has
generally been regarded as the most important binders, including,
for example, aqueous dispersions or solutions of urea-form-
aldehyde ("aminoplast") or phenol-formaldehyde ("phenoplast")
resins.
The use of polyisocyanates or polyisocyanate solutions
instead of i-onmaldehyde l~ased resins as ~inders for pressboard is also
known (German Offenlegungsschriften 1,271,984, 1,492,507,
1,653,177, and 2,109,686). Polyisocyanates, which have been
increasingly used industrially as binders since 1973, improve the
stability and moisture rPQ~ rP and increase the mechanical
strength of the products. In addition, polyisocyanate binders
have extensive process technology advantages, as disclosed in
German Offenlegungsschrift 2,109,686.
The large scale industrial production of materials
bonded with polyisocyanates, especially materials containing
lignocellulose such as wood chipboard, has, however, been
hindered at least in part because, in contrast to materials which
are bonded with aminoplast resins, chips blended wi~h poly-
isocyanates have no intrinsic tackiness (i.e., no capacity for
adhesiveness) at room temperature. Even precomæression at room temperature
- I 338075
,
("cold pressing") of materials blended wi~h polyisocyanates,
but which are still moist, will not yield preforms that are
sufficiently stable and self-supporting for the purposes of many
production plants. As a result, the universal application of
5 polyisocyanates for the production of compression molded
materials is made very difficult.
The molded chips or shavings that are spread over
belts, press plates, and the like are transferred to other belts,
plates, rolls, or the like on their way to the hot press. These
10 preforms are then discharged from them or the supports are pulled
out from under them. In order to enable this process to be
carried out without destroying the preforms of chips and without
damaging their outer zones, the preforms are subjected to a cold
precol~pression. This precompression is also
15 intended to bond the surface chips together so that as the hot
press plates are brought together the air escaping between the
preforms and the plates will not carry away any chips (i.e., so
that no cavities will form on the surfaces due to the escape of
air). Prepresses operating continuously and in cycles
20 are available to subject the chips to specific pressures of up to
40 bar for from 10 to 60 seconds.
One object of the present invention is development of a
process which eliminates the disadvantage of the lack of cold
tack of chips blended with polyisocyanate binders while at
25 the same time not sacrificing the easy pourability of the bonded
chips, a characteristic necessary for spreading chips easily
into the required shapes of the preforms. The process according
to the invention solves this problem in a manner which is
surprisingly simple for one skilled in the art.
SUMMARY OF THE INVENTION
This invention relates to a process for the preparation
of compression molded materials comprising compressing substrates
with binders based on polyisocyanates, wherein said binders
comprise
(a) polyisocyanates,
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(b) compounds containing at least two
isocyanate reactive hydrogen atoms, and
(c) aklylene carbonates, and
(d) optionally, other additives.
DETAILED DESCRIPTION OF THE INVENTION
In the preferred embodiments according to
the invention, the various constituents can have the
following compositions and properties:
(i) the binder can contain from about 10 to
about 250 parts by weight (preferably from 20 to 80
parts by weight), based on 100 parts by weight of
polyisocyanate, of the compounds (b) and (c) with the
weight ratio of component (b) to component (c) being
in the range of from about 0.5:1.0 to about 10.0:1.0;
(ii) the alkylene carbonate can be propylene
carbonate;
(iii) the compounds containing at least two
isocyanate reactive hydrogen atoms are polyethers or
polyesters having a molecular weight range of from
about 400 to about 10,000 and containing hydroxyl
groups;
; (iv) the binder can contain aromatic
polyisocyanates;
(v) the aromatic polyisocyanates can be
mixtures of diphenylmethane diisocyanates and
polyphenyl-polymethylene polyisocyanates obtainable by
aniline-formaldehyde condensation followed by
phosgenation; and
(vi) the binder can additionally contain
aqueous condensation products of urea, melamine,
phenol, and tannin or any mixtures thereof with
formaldehyde and/or sulfite waste liquors.
I
I
1 338075
Cold tack of chips blended with the above
binders, for example, chips of raw materials
containing lignocellulose, is achieved using the
process of this invention. The advantages afforded by
the polyisocyanates as binders for compression molded
materials may, therefore, also be applied to
production lines in which cold tack of the chips is
essential for the preforms. The possibility of
reducing the time required for compression in the hot
press is of particular economical advantage. The
capacity for cold tack of chips blended with the
binders according to the invention provides further
advantages. Damage in the surface zones of preforms
of scattered chips is reduced or prevented; the
reduction in losses due to damage at the edges
enhances economical utilization of the unfinished
boards. The advantages of the process of this
invention also makes the process attractive for
installations in which cold tack of the chip preforms
is not absolutely essential.
Thus, a particular advantage of the process
of the invention arising from the cold tack
characteristic is that the composition or mixture of
substrates and the binder of the invention can be
compressed to form a preform without the application
of heat.
In a particular embodiment of the process of
the invention, the substrate and the binder are mixed,
the resultant mixture is compressed, without the
application of heat, to form a preform, and the
preform is molded under heat and pressure.
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The combination of polyols with
polyisocyanates as binders (German
Offenlegungsschriften 2,538,999 and 2,403,656) and the
addition of alkylene carbonates (e.g., propylene
carbonate) to polyisocyanate (U.S. Patent 4,359,507i
J. Elast. Plast., 16, 206-228 (1984) have been fully
described. Such binders, however, cannot be
economically used unless the liquids are applied to
the chips as a very fine spray. For highly viscous
polyols, application is achieved by using a colloidal
solution of the polyol component in a liquid medium,
such as water (German Offenlegungsschrift 2,538,999).
Alkylene carbonates (e.g., propylene carbonate),
because of their low viscosity, may be used as such or
together with the polyisocyanate. The behaviour of
blended chips using these known methods, however, does
not differ from the behaviour of chips blended only
with pure polyisocyanate binders. ~oreover, the
addition of compounds containing hydroxyl groups leads
to the rapid formation of the corresponding
polyurethanes. Thus, satisfactory use of these
methods under the conditions customarily used in the
woodworking industry (i.e., storage of the blended raw
material for up to 60 minutes, in part at elevated
temperatures) would not be expected.
It must, therefore, be considered all the
more surprising to one skilled in the art to find that
the addition of polyols and alkylene carbonate to
polyisocyanate binders (or mixtures of polyisocyanates
with other binders) in quantities of from about 10 to
about 250 parts by weight (preferably 20 to 80
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parts by weight), based on 100 parts by weight of polyisocyanate,
results in cold tack of such blended raw materials
with retention of good pourability.
The polyol and alkylene carbonate are added in
5 proportions ranging from about 0.5:1.0 to about 10.0:1.0 parts by
weight (preferably from 1.0:1.0 to 3.0:1.0 parts by weight). In
contrast to raw materials which have been blended using poly-
isocyanates alone, the ble~d raw materials according to the
invention retain their cold tack in storage.
10 Furthermore, the addition of the polyols and alkylene carbonates
according to the invention allows a reduction, often a
considerable reduction, of time needed for compressing the
materials in the hot press, depending on the temperature of the
press, without loss of the physical and mechanical properties of
15 the boards obtained as end products.
Suitable alkylene carbonates include liquid cyclic
alkylene carbonates (i.e., cyclic alkylene esters of carboxylic
acids), preferably propylene carbonate and butylene carbonate.
Suitable polyisocyanates used according to the
20 invention include aliphatic, cycloaliphatic, araliphatic,
aromatic, and heterocyclic polyisocyanates, such as described by
W. Siefken in Justus Liebigs Annalen der Chemie, 562, pages 75 to
136, for example, those corresponding to the following formula:
Q(NCO)n
wherein
Q is an aliphatic hydrocarbon group containing about 2 to
about 18 (preferably 6 to 10) carbon atoms; a
cycloaliphatic hydrocarbon group containing about 4 to
about 15 (preferably 5 to lO) carbon atoms; an aromatic
hydrocarbon group containing about 6 to about 15
(preferably 6 to 13) carbon atoms; or an araliphatic
hydrocarbon group containing about 8 to about 15
(preferably 8 to 13) carbon atoms; and
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n is 2 to 4 (preferably 2).
Examples of such polyisocyanates include 1,4-tetramethylene diiso-
cyanate, 1,6-hexamethylene diisocyanate, 1,12-dodecane diisocyanate,
cyclobutane-1,3-diisocyanate, cyclohexane-1,3- and -1,4-diisocyanate and
S any mixtures of these isomers, 1-iso-cyanato-3,3,5-trimethyl-5-isocya-
natomethylcyclohexane (German Auslegeschrift 1,202,785, U.S. Patent
3,401,190), 2,4- and 2,5-hexahydrotolylene diisocyanate and any mixtures
of these isomers, hexahydro-1,3- and/or-1,4-phenylene diisocyanate,
perhydro 2,4'- and/or 1,4-phenylene diisocyanate, 2,4- and 2,6-tolylene
10 diisocyanate and any mixtures of these isomers, diphenyl-methane-2,4'-
and/or-4,4'-diisocyanate, and naphthylene-1,5-diisocyanate.
Other suitable polyisocyanates include triphenylmethane-
4,4',4"-triisocyanate; polyphenyl-polymethylene polyisocyanates
obtainable by aniline-formaldehyde condensation followed by
15 phosgenation as described, for example, in United Kingdom Patents
874,430 and 848,671, issued 1961 and 1960 (respectively); m- and p-
isocyanatophenylsulphonyl isocyanates according to U.S. Patent
3,454,606; perchlorinated aryl polyisocyanates as described, for example,
in German Auslegeschrift 1,157,601 (U.S. Patent 3,277,138);
20 polyisocyanates containing carbodiimide groups as described in German
Patentschrift 1,092,007 (U.S. Patent 3,152,162) and in Gerrnan
Offenlegungssch,irlen 2,504,400, 2,537,685, and 2,552,350; norbomane
diisocyanates according to U.S. Patent 3,492,330; polyisocyanates
containing allophanate groups as described, for example, in United
25 Kingdom Patent 994,890 issued 1965, Belgian Patent 761,626, and
Netherlands Patent 7,102,524; polyisocyanates containing isocyanurate
groups as described, for example, in U.S. Patent 3,001,973, German
Patentschriften 1,022,789, 1,222,067, and 1,027,394, and in German
Offenlegungsschriften 1,929,034 and 2,004,048; polyisocyanates
30 containing urethane groups as described, for example, in Belgian Patent
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752,261 or U.S. Patents 3,394,164 and 3,644,457; polyisocyanates
containing acylated urea groups acoording to German Patententschrift
1,230,778; polyisocyanates containing biuret groups as described, for
example, in U.S. Patents 3,124,605, 3,201,372, and 3,124,605 and UK
Patent 889,050 issued 1962; polyisocyanates containing ester groups as
described, for example in UK Patent 965,474, issued 1964, U.S. Patent
3,567,763, and German Patentschrift 1,231,688; reaction products of the
above-mentioned isocyanates with acetals according to German
Patentschrift 1,072,385; and polyisocyanates containing polymeric faKy
acid esters according to U.S. Patent 3,455,883.
Isocyanate-group-containing distillation residues from
commercial production of isocyanates may also be used, optionally
dissolved in one or more of the above mentioned polyisocyanates. Any
mixtures of the above mentioned polyisocyanates may also be used.
Aromatic polyisocyanates are preferred. Particularly
preferred are commercially available polyisocyanates, for example, 2,4-
and 2,6-tolylene diisocyanate and any mixtures of these isomers ("TDI");
polyphenyl-polymethylene polyisocyanates, which may be prepared by
aniline-formaldehyde condensation followed by phosgenation ("crude
MDI"), and polyisocyanates containing carbodiimide groups, urethane
groups, allophanate groups, isocyanurate groups, urea groups, or biuret
groups ("modified polyisocyanates"), especially those modified poly-
isocyanates derived from 2,4- and/or 2,6-tolylene diisocyanates or from
4,4'- and/or 2,4'-diphenylmethane diisocyanate.
The compounds containing at least two isocyanate reactive
hydrogen atoms and generally having a molecular weight of from 400 to
10,000 are preferably compounds containing hydroxyl groups, especially
compounds containing from 2 to 8 hydroxyl groups, and especially those
with molecular weights of from about 1000 to about 8000 (preferably from
1500 to 4000).
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The preferred compounds include polyesters or polyethers
containing at least 2 (generally from 2 to 8 and preferably from
2 to 4) hydroxyl groups, such as those known in the art for the
production of both homogeneous and cellular polyurethanes.
Suitable hydroxyl-containing polyesters include, for
example, reaction products of polyhydric (preferably dihydric)
alcohols, optionally together with trihydric alcohols, and
polybasic (preferably dibasic) carboxylic acids. Instead of the
free polycarboxylic acids, corresponding polycarboxylic acid
10 anhydrides or corresponding polycarboxylic acid esters of lower
alcohols or mixtures thereof may he used for the preparation of
the polyesters used according to the invention. Suitable
polycarboxylic acids include aliphatic, cycloaliphatic, aromatic,
and heterocyclic polycarboxylic acids and may he substituted, for
15 example, with halogen atoms, and/or may be unsa~urated.
Examples of carboxylic acids and derivatives thereof
that are suitable for preparation of hydroxyl-containing
polyesters include succinic acid, adipic acid, suberic acid,
azelaic acid, sebacic acid, phthalic acid, isophthalic acid,
20 trimellitic acid, phthalic acid anhydride, tetrahydrophthalic
acid anhydride, hexahydrophthalic acid anhydride, tetra-
chlorophthalic acid anhydride, endomethylene tetrahydrophthalic
acid anhydride, glutaric acid anhydride, maleic acid, maleic acid
anhydride, fumaric acid, dimerized and trimerized unsaturated
25 fatty acids optionally mixed with monomeric unsaturated fatty
acids such as oleic acid, dimethylterephthalate, and terephthalic
acid bisglycol ester.
Examples of polyhydric alcohols that are suitable for
preparation of hydroxyl-containing polyesters include ethylene
30 glycol, 1,2- and 1,3-propanediol, 1,4- and 2,3-butanediol,
1,6-hexanediol, 1,8-octanediol, neopentyl glycol, 1,4-bis-
(hydroxymethyl)cyclohexane, 2-methyl-1,3-propanediol, glycerol,
trimethylol propane, 1,2,6-hexanetriol, 1,2,4-butanetriol,
trimethylol ethane, pentaerythritol, quinitol, mannitol and
35 sorbitol, formitol, 1,4,3,6-dianhydrosorbitol, methyl glycoside,
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diethylene glycol, triethylene glycol, tetraethylene glycol and
higher polyethylene glycols, dipropylene glycol and higher
polypropylene glycols, and dibutylene glycol and higher
polybutylene glycols. The polyesters may contain a proportion of
5 carboxyl end groups. Polyesters of lactones, such as -capro-
lactone, or of hydroxycarboxylic acids, such as hydroxycaproic
acid, may also be used.
Suitable polyethers containing at least 2 (generally 2
to 8 and preferably 2 or 3~ hydroxyl groups include known types
10 that may be prepared, for example, by the polymerization of
epoxides, such as ethylene oxide, propylene oxide, butylene
oxide, styrene oxide, or epichlorohydrin, or polymerization of
tetrahydrofuran. Such polymerizations may be carried out using
only the monomers, for example, in the presence of Lewis-
15 catalysts such as BF3. The polymerization may also be carriedout by chemical addition of the epoxides (preferably ethylene
oxide and propylene oxide, optionally as mixtures or
successively) to starting components containing reactive hydrogen
atoms, such as water, alcohols, ammonia or amines, including, for
20 example, ethylene glycol, 1,3- or 1,2-propanediol, trimethylol
propane, glycerol, sorbitol, 4,4'-dihydroxydiphenylpropane,
aniline, ethanolamine, or ethylene diamine. It is often
preferred to use polyethers in which the OH groups are
predominantly (up to about 90~ by weight thereof, based on all
25 the OH groups present in the polyether) primary OH groups.
Also suitable are sucrose polyesters (for example, DE-B
1,176,358 and 1,064,938), and polyethers started on formitol or
formose (DE-A 2,639,083). Polybutadienes containing OH groups
are also suitable. Mixtures of polyesters and polyethers may, of
30 course, also be used.
Compounds in the molecular weight range of from 32 to
399 containing at least two isocyanate reactive hydrogen atoms
may also be used as a component in the process of the invention.
Suitable such compounds are compounds containing hydroxyl groups,
35 amino groups, thiol groups, carboxyl groups, or a combination
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1 338075
thereof (preferably hydroxyl groups and/or amino groups), and are
used as chain extenders or crosslinking agents. Such compounds
generally contain from about 2 to about 8 (preferably 2 to 4)
isocyanate reactive hydrogen atoms. These compounds may also be
5 used as mixtures of different such compounds in the molecular
weight range of from 32 to 399 containing at least two isocyanate
reactive hydrogen atoms. Examples of such compounds are fully
described, for example, in German Offenlegungsschrift 3,430,285,
on pages 19 to 23.
Optional components in the process of the invention
include auxiliary agents, for example, known catalysts and
surface active additives such as emulsifiers and stabilizers.
Suitable catalysts include tertiary amines such as
triethylamine, tributylamine, N-methylmorpholine, N-ethyl-
15 morpholine, N,N,N',N'-tetramethylethylene diamine, penta-
methyldiethylene triamine, and higher homologues (German
Offenlegungsschriften 2,624,527 and 2,624,528), 1,4-diaza-
bicyclo[2.2.2]octane, N-methyl-N'-(dimethylaminoethyl)piperazine,
bis(dimethylaminoalkyl)piperazines (German Offenlegungsschrift
20 2,636,787), N,N-dimethylbenzylamine, N,N-dimethylcyclohexylamine,
N,N-diethylbenzylamine, bis(N,N-diethylaminoethyl~ adipate,
N,N,N',N'-tetramethyl-1,3-butanediamine, N,N-dimethyl- ~phenyl-
ethylamine, 1,2-dimethylimidazole, 2-methylimidazole, monocyclic
and bicyclic amidines (German Offenlegungsschrift 1,720,633),
25 bis(dialkylamino)alkyl ethers (U.S. Patent 3,330,782, German
Auslegeschrift 030,558, and German Offenlegungsschriften
1,804,361 and 2,618,2LO), and tertiary amines containing amide
groups (preferably formamide groups) according to German
Offenlegungsschrift 2,523,633 and 2,732,292. The catalysts used
30 may also be the known Mannich bases of secondary amines (such as
dimethylamine) and aTdehydes (preferably formaldehyde) or ketones
(such as acetone) and phenols.
Suitable catalysts also include certain tertiary amines
containing isocyanate reactive hydrogen atoms. Examples of such
35 catalysts include triethanolamine, triisopropanolamine, N-methyl-
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diethanolamine, N-ethyl-diethanolamine, N,N-dimethylethanolamine,
their reaction products with alkylene oxides (such as propylene
oxide and/or ethylene oxide) and secondary-tertiary amines
according to German Offenlegungsschrift 2,732,292.
Sila-amines containing carbon-silicon bonds may also be
used as catalysts, for example, those described in German
Patentschrift 1,229,290 (corresponding to U.S. Patent 3,620,984).
Examples of suitable sila-amines include 2,2,4-trimethyl-2-
silamorpholine and 1,3-dimethylaminomethyl tetramethyldisiloxane.
Suitable catalysts also include nitrogen-containing
bases, such as tetraalkylammonium hydroxides; alkali metal
hydroxides, such as sodium hydroxide; alkali metal phenolates,
such as sodium phenolate; and alkali metal alcoholates, such as
sodium methoxide. Hexahydrotriazines (German Offenlegungsschrift
15 1,709,043~ and tertiary amines containing amide groups
(preferably formamide groups) (German Offenlegungsschriften
2,523,633 and 2,732,292) may also be used as catalysts. Known
Mannich bases of secondary amines (such as dimethylamine) and
aldehydes (preferably formaldehyde~ or ketones (such as acetone)
20 and phenols may also be used as catalysts.
Other suitable catalysts include organic metal
compounds, especially organic tin compounds. Suitable organic
tin compounds include those containing sulfur, such as di-n-octyl
tin mercaptide (German Auslegeschrift 1,769,367 and U.S. Patent
25 3,645,927), and, preferably, tin(II) salts of carboxylic acids,
such as tin(II) acetate, tin(II) octoate, tin(II~ ethylhexoate,
and tin(II) laurate, as well as tin (IV)compounds, such as
dibutyl tin dilaurate.
Any of the above-mentioned catalysts may, of course, be
30 used as mixtures.
Further representatives of catalysts to be used
according to the invention and details concerning their mode of
action are described in Kunststoff Handbuch, Volume VII,
published by Vieweg and Hochtlen, Carl Hanser Verlag, Munich
35 1966, e.g., on pages 96 to 102.
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~ The catalysts are generally used in a quantity ranging
from about 0.001 to about 10~ by weight, based on the quantity of
polyisocyanate.
Suitable surface active additives include emulsifiers
5 and foam stabilizers. Suitable emulsifiers include, for example,
the sodium salts of ricinoleic sulfonates and salts of fatty
acids with amines, for example, oleic acid diethylamine or
stearic acid diethanolamine. Other suitable surface active
additives include alkali metal or ammonium salts of sulfonic
10 acids (such as dodecylbenzenesulfonic acid or dinaphthyl-
methanedisulfonic acid), of fatty acids (such as ricinoleic
acid), or of polymeric fatty acids.
Suitable substrates used in the process of the
invention include lignocellulose-containing raw materials that
15 can be bonded with the binders according to the invention.
Examples of suitable lignocellulose-containing materials include
wood, woodbark, cork, bagasse,straw, flax, bamboo, esparto, rice
husks, and sisal and coconut fibers. Other suitable substrates
for compression molding include other organic raw materials (for
20 example, all kinds of plastic waste) and inorganic raw materials
(for example, expanded mica or silicate balls). The substrate
may be used in the form of granulates, shavings or chips, fibers,
spheres, or powder and may have a moisture content of, for
example, from about O to about 35% by weight (preferably from 4
25 to 20~ by weight).
It is possible, but less preferred, to apply the
components of the binder combination (polyisocyanate, polyether
polyol or polyester polyol, and alkylene carbonate) separately to
the material which is to be bonded. It is preferable to use the
30 polyether or polyester polyol and the alkylene carbonate as a
mixture with the polyisocyanate as binder.
In the process of the invention, the binder is added to
the organic and/or inorganic material to be bonded in a quantity
of about 0.5 to about 20~ by weight (preferably 2 to 12~ by
35 weight), based on the total weight of the end product. The
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resultant material is compressed to form boards or three
dimensionally shaped molded products, generally under heat and
pressure (for example, about 70 to about 250C and about 1 to
about 150 bar).
Multilayered boards or molded parts may be produced in
analogous manner from veneers, paper, or woven fabrics by
treating the layers with the binder as described above and
subsequently pressing them, generally at elevated temperature and
elevated pressure. Temperatures of from about 100 to about 250C
10 are preferred, with 130 to 200C being most preferred. The
initial compression pressure is preferably in the range of from
about 5 to about 150 bar, although the pressure in most cases
drops towards 0 bar during the compression process.
The binders used according to the invention may also be
15 used in combination with aqueous solutions of condensation
products of formaldehyde and urea and/or me~ ine and~r phenol, which are
the binders most commonly used in the woodworking industry. In
addition, the binders may be combined with less commonly used
binders and impregnating agents, for example, those based on
20 polyvinyl acetate or other synthetic resin lattices, sulfide
waste liquors, or tannin. When using a mixture of the binders
according to the invention with these additional binders, the
proportions used are from about 1:20 to about 20:1 (preferably
from 1:5 to 5:1). The polyisocyanate mixtures and the additional
25 binders may be used separately or as a mixture.
The following examples further illustrate details for
the process of this invention. The invention, which is set forth
in the foregoing disclosure, is not to be limited either in
spirit or scope by these examples. Those skilled in the art will
30 readily understand that known variations of the conditions of the
following procedures can be used. Unless otherwise noted, all
temperatures are degrees Celsius and all percentages are
percentages by weight.
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-
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The following polyols are used as starting components
in the Examples:
Polyether Polyol I prepared from l,2-propanediol and propylene
5 oxide and having an OH number of 284 and a viscosity of 75 mPas
at 25C.
Polyether Polyol II prepared from 1,2-propanediol, propylene
oxide, and ethylene oxide and having an OH number of 185 and a
viscosity of 130 mPas at 25C.
10 Polyether Polyol III prepared from ethylene diamine and propylene
oxide and having an OH number of 60 and a viscosity of 660 mPas
at 25C.
Example 1
Face 1 ayer industrial chips (moisture content u = 15.0%
15 by weight oven-dried ("o.d.") wood) (2800 9) and core layer
chips (u = 10.0% o.d.) (6400 9) were each sprayed with 5% by
weight o.d. of a binder consisting of a mixture of 70~ by weight
crude diphenylmethane-4,4'diisocyanate having an isocyanate
content of 30~ by weight, 10% by weight polyether polyol I, 10%
20 by weight polyether polyol II, and 10% by weight of propylene
carbonate. This material was spread out to form three-layered
board preforms and at selected time intervals was compressed both
cold and hot under pressure.
Example 2
Boards were prepared as in Example 1 except that the
binder was composed of a mixture of 70~ by weight crude
diphenylmethane-4,4'diisocyanate having an isocyanate content of
30% by weight, 20% by weight polyether polyol III, and 10% by
weight propylene carbonate. The isocyanate and the polyol/
30 alkylene carbonate mixture were sprayed separately on the chips.
Compression molding was performed as in Example 1.
Example 3
Face layer industrial chips (u = 12.0% o.d.) (4200 9)
were sprayed with 13% by weight o.d. of a binder consisting of a
35 mixture of 80% by weight crude diphenylmethane-4,4'-diisocyanate
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having an isocyanate content of 30~ by weight, 12% by weight
polyether polyol II, and 8% by weight propylene carbonate. The
chips were spread out to form single-layered board preforms and
compression molded as in Example 1.
5 Example 4
Boards were prepared as in Example 3 except that one
half of the binder was a mixture of 70% by weight crude
diphenylmethane-4,4'-diisocyanate having an isocyanate content
30% by weight, 20% by weight polyether polyol I, and 10% by
10 weight polypropylene carbonate and the second half of the binder
was a commercial E1 urea-formaldehyde resin. Three percent by
weight o.d. of each half portion of binder was sprayed on the
chips. Compression molding was performed as in Example 1.
All board preforms which ~er~ prepressed at room temperature
according to Examples 1 to 4 e ~hibited cold ~ac~
in contrast to chips which have been treated with
polyisocyanate alone. Under hot pressing conditions, samples
prepared according to the invention also have advantages over the
comparison samples under identical experimental conditions. Test
20 results are shown in the following Table.
TABLE
Example Gross Density Transverse Tensile 1)
of Boa3ds Strength (~Pa)
(kg/m ) V20 V100
Comparison experiment 680 0.94 0.27
using 5~ by weight o.d.
Desmodur ~ PU 1520 A
1 680 1.13 0.33
2 680 1.09 0.34
3 850 0.82
4 650 0.84
o.d. = calculated percent by weight based on absolutely dry, oven
dried wood
Trans-~erse tensile strength V 20 and V 100 tested according to German
Standard DIN 68763 (flat pressed particle boards for building)
1 338075
EXAMPLE 5
The following binders were used in Example 5.
Binder I: a prepolymer comprising 70 parts by weight of crude
diphenylmethane-4,4'-diisocyanate having an isocyanate content
of 30% by weight and a viscosity of 300 mPa.s at 25-C, and a
mixture of 10 parts by weight of polyether polyol I and 10
parts by weight of polyether polyol II. V~scosity of about
52,000 mPa.s/25-C.
Binder II: the prepolymer of binder I containing 10 parts by
weight of propylene carbonate. Viscosity of about 9300 mPa.s/
25-C.
Binder III: an in-situ mixture of 70 parts by weight of crude
diphenylmethane-4,4'-diisocyanate having an isocyanate content
of 30% by weight and a viscosity of 300 mPa.s at 25-C, 10 parts
by weight of polyether polyol I, 10 parts by weight of
polyether polyol II, and 10 parts by weight of propylene
carbonate (corresponds to binder used ln Example 1, and
illustrative of the invention).
:
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1 338075
A batch of face layer industrial chips (moisture
content u=14.0% by weight oven dried wood) (3950 9) was sprayed
with binder II or binder III in amounts of 10.4% by weight o.d.
(quantity of binder based on prepolymer of diphenylmethane-
4,4'-diisocyanate/polyol). The chips were spread out to form
single-layer board preforms and were compressed at specific
intervals in the cold state, after which the cold tack was
determined.
Binder I, the prepolymer, was not usable due to its
lo high viscosity (about 52,000 mPa.s/2~-C after 14 days).
Binder II, the prepolymer diluted with 10 parts by
weight of propylene carbonate, has a viscosity of about 9300
mPa.s/25-C, which is still too high. Binder II can only be
applied with great difflculty using high pressure spraying and
is therefore not practical for indus~rial use. Upon exposure to
atmospheric moisture, Binder II very quickly forms a skln on
its surface and it has a tendency to foam.
Binder II and Binder III display almost the same
degree of cold tack when the chlps are blended therewith and
compressed in the cold state.
Binder III has the advantages of being easy to handle
and use, and economical to produce as the production costs
associated with prepolymerization are dispensed with. ~he
customer needs only to use one type of diphenyl-4,4'-dliso-
cyanate, to which polyether polyol and propylene carbonate can
if necessary be added in the required quantities, depending on
the type of applications involved.
; 30
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