Note: Descriptions are shown in the official language in which they were submitted.
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MOISTURE - ACTIVATED ADHESIVE COMPOSITIONS
FIELD OF THE INVENTION
, The present invention is directed to rapid curing moisture-activated
adhesive compositions and
methods for their production and a process for bonding multiple substrates
using said
~ 5 composition. More specifically, the present invention is directed to
specific moisture-activated
adhesive compositions which are cold curable in the presence of high moisture
content
cellulosic or lignocellulosic substrates.
BACKGROUND OF THE INVENTION
1 o In recent years, the use of "engineered lumber" products by the
construction industry has
become increasingly common - primarily because the availability and cost of
adequate quality
sawn lumber have become increasingly unfavorable. However, the performance of
"engineered lumber" products, which are formed by adhering smaller pieces of
wood together
into a composite material, represents some major challenges to the adhesives
formulator.
1s
Engineered lumber products on the market today, such as finger jointed lumber,
wood I-
beams, and glue-laminated beams (glu-lams), utilize a variety of adhesive
systems, including
phenol - formaldeyhde (PF) based adhesives, polyvinylacetate (PVA) adhesives,
and
isocyanate - based emulsion adhesives. Unfortunately, each of these adhesive
systems has
20 limitations, which compromises the effectiveness of the resultant
engineered lumber
composite.
PF based adhesives require a great deal of heat and time in order to cure, and
are sensitive to
high levels of moisture in the wood. Use of these adhesives systems requires
engineering
25 controls to maintain a low moisture content, and to ensure adequate bonding
occurs within the
composite. The necessity for such costly catalyst and engineering controls
increases
production costs, and limits productivity, which in turn limits the
competitiveness of
engineered lumber in the marketplace. Another major problem associated with
these
adhesives is their "green strength". These adhesives do not produce adequate
bond strength
. 3o immediately - they typically need to "cure" in order to reach their full
potential. This cure
time is a matter of hours, often days - which further adds to production costs
SUBSTITUTE SHEET (RULE 25)
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PVA adhesives have limited strength. To date, they have not proven to be
suitable for use in
structural applications, which require physical properties of a certain
minimum standard. For
example, no commercially available PVA bonded engineered lumber product can
meet the .
ASTM D2259 standard, a frequent requirement for structural lumber
applications. Like the
PF adhesives discussed above - these systems also suffer from the limitations
of slow green
strength development, and a dependency on a great deal of heat and time to
ensure adequate
bond strengths.
Isocyanate-crosslinked latex emulsion adhesives, also have limitations in that
these systems
1o also suffer from the limitations of slow green strength development, and a
dependency on a
great deal of heat to ensure adequate bonding.
Polyisocyanate based adhesive compositions have also been identified for
composite wood
applications. Examples are moisture curable wethane-modified polyisocyanate
adhesives
described in EP-B-723 561 which discloses urethane-modified polyisocyanate
adhesives for
use in plywood panel wood composites. These compositions contain auro ca~a~yuc
~Ywl~~,
designed to increase the reactivity of the polyisocyanate, enabling cure at
ambient
temperatwes in a matter of minutes. However, for engineered lumber products,
the different
processing requirements between panels and lumber becomes extremely important.
As a
2o consequence none of the existing polyisocyanate products, designed for
relatively thin
composite wood panels, exhibits sufficient reactivity to truly be cost-
effective in relatively
thick engineered lumber applications.
It is therefore an object of the present invention to provide an adhesive
composition especially
designed for engineered lumber which impart adequate strength and reactivity
and tack without the need for costly catalyst and processing/engineerning
controls to
overcome inherent problems, such as: maintaining low raw maferial moisture
contents,
providing a great deal of heat and time in order to cure the adhesive, and
protracted "green" ,
strength development.
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These objectives are met by the present adhesive compositions, which
demonstrate excellent
adhesive properties with a prolonged pot life, accelerated cure, particularly
at room
temperatwe. Surprisingly, the compositions according to the present invention
provide equal
performance than those compositions as described in EP 0 723 561. The present
compositions
are activated by the moisture present in the substrate with which they are
being used and thus,
they may be most effectively used with substrates having a relatively high
moistwe content,
even as high as 20% or more. Accordingly, the pxesent compositions are
effectively used with
various types of lignoceliulosic materials and are particularly useful in the
preparation of
engineered lumber products as discussed above.
SUMMARY OF THE INVENTION
The present invention relates to a moisture-activated adhesive composition
comprising the
reaction product of (A) polyisocyanate selected from either (a) a blend of
polymeric MDI and
pure MDI and/or from (b) an isocyanate-terminated prepolymer. (B) an
isocyanate-reactive
t5 component comprising at least one aliphatic tertiary amine group-containing
polyol made by
alkoxylation of amines or aminoalcohols characterized in characterized in that
the total
ethylene oxide content by weight of the total adhesive composition is more
than 2.5%
DETAILED DESCRIPTION OF THE INVENTION
2o According to the present invention, the polyisocyanate component is
selected from either (a) a
blend of polymeric MDI and pure MDI and/or (b) an isocyanate-terminated
prepolymer. In
,~ accordance with the present invention, the blend of polymeric MDI and pwe
MDI have been
found to provide improved penetration into the lignocellulosic substrate and
higher wood
failwe as opposed to glueline failure. A commercially available pure MDI
product suitable for
25 use in the present invention is RubinateTN' 44 available from ICI Americas
Inc. The preferred
blends contain polymeric MDI to pure MDI in ratios of 95:5 to 50:50 and
preferably 60:40 to
80:20.
The isocyanate-terminated prepolymers as used herein, the term "isocyanate-
terminated
3o prepolymer" includes the prepolymer as well as the pseudoprepolymer, i.e.,
a mixture of the
prepoiymer and the polyisocyanate from which the prepolymer is prepared. The
isocyanate-
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PCTIEP00/00034
terminated prepolymer useful in the present compositions should have a free
isocyanate
(NCO) content of from 10 to 29%, preferably 16 to 29%. In general, the
polymeric
polyisocyanate may be prepared by the reaction of an excess of a
polyisocyanate and a polyol,
including aminated polyols or imino/enamines thereof.
Suitable polyols for preparing the isocyanate-terminated prepolymers include:
(a) polyether polyols, thioether polyols and/or hydrocarbon-based polyols
having a
molecular weight of from 1000 to 6000 and an average hydroxyl functionality of
from
1.8 to 4
(b) polyester polyols having a molecular weight of 1000 or more and an average
hydroxyl
functionality of from 1.9 to 4.
Particularly preferred isocyanate-terminated prepolymers useful in the present
invention are
MDI prepolymers, which are the reaction product of an excess of polymeric MDI
and
polyether polyols. The polyether polyols are preferably diols or triols having
hydroxyl values
of 25 to 120. The polyol should have a number average molecular weight in the
range of 1000
to 6000. Such prepolymers should generally have a free-NCO content of more
than 10%,
2o preferably more than 16% and most preferably 16 to 29% Suitable polymers
are those in
which the stoichiometric ratio of isocyanate (NCO) to hydroxyl (OI-~ exceeds
1:1. RubinateTM
M available from ICI Americas is a suitable polymeric MDI composition useful
in the present
invention.
The second component of the present compositions is an isocyanate-reactive
component
characterized in that the total ethylene oxide content by weight of the total
adhesive
composition is more than 2.5%. More preferably, at least 40% of the total
ethylene
oxide content is present as part of the reactant.
3o Reactants suitable for the present invention are reactants comprising at
least one aliphatic
tertiary amine group-containing polyol having an ethylene oxide content of at
least 1%.
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Preferably, the ethylene oxide content of the reactant is from 1 to 90%,
preferably 5 to 60. The
aliphatic tertiary amine group-containing polyol provides and ethylene oxide
content in the
prepolymer of 0.01 to 27%, preferably 0.35 to 12%. Most preferred, the weight
ratio of
ethylene oxide to propylene oxide in the total composition is at least 1 to S,
said propylene
- 5 oxide or ethylene oxide being part of the reactant and/or from an
additional polyol being
present in the total composition.
The aliphatic tertiary amine group-containing polyols are the known
alkoxylation products of
amines or aminoalcohols with at least two active hydrogen atoms with ethylene
oxide and
Io optionally propylene oxide. Suitable initiator molecules include: ammonia,
ethylene diamine,
hexamethylene diamine, methylamine, diaminodiphenyl methane, aniline,
ethanolamine,
diethanolamine, N-methyl diethanolamine, and tetrahydroxyl ethyl
ethylenediamine.
Suitable aliphatic tertiary amine group-containing polyols are those wherein
the initiator
t 5 comprises 1 to 18 and preferably 1 to 6 carbon atoms. Suitable aliphatic
tertiary amine group-
containing polyols have an average molecular weight of about 1500 to 10,000
and preferably
1500 to 6000 and an average OH functionality of 1.8 to 6Ø
Preferred amine group-containing polyols for use in the present invention
includes those
2o prepared from ethylene diamine, triethylene tetramine and triethanolamine.
The present compositions comprise the reactant such as the aliphatic tertiary
amine group-
containing polyol component, in an amount of 1 to 50%, preferably 7 to 30% and
most
preferably 10 to 20% by weight based upon the total amount of isocyanate and
polyol in the
25 composition.
In its most preferred form, the amine group-containing polyol is an ethylene
diamine-based
polyol containing ethylene oxide. Suitable ethylene diamine-based polyols are
those having
an ethylene oxide content of 1 to 90%, preferably 5 to 60%. The ethylene oxide
content refers
3o to the amount of ethylene oxide utilized in the preparation of the polyols
as discussed above.
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During production, the ethylene oxide reacts with the initiator. The polyols
should have a
molecular weight in the range of 1500 to 6000.
Suitable ethylene diamine-based polyols useful in the present compositions
include those of
the following formula:
H(OH4C2)Y(OH6C3)X (C3 H60)X (C2 H40)YH
\
N-CH2-CH2-N
~o / \
H(OH4C2)Y(OH6C3)X (C3 H60)X (C2 H40)YH
wherein x is an integer of 1.0 to 29.0, preferably 4.0 to 20 and most
preferably 4.0 to 14 and y
is an integer of 0.1 to 10.0 and preferably 2.0 to 4Ø Suitable ethylene
diamine-based polyols
t 5 are available commercially, such as the "Synperonic T" series of polyols
available from ICI
Americas Inc.
Preferably, the total ethylene oxide content by weight of the total adhesive
composition is
more than 2.5%. Most preferred, at least 40% of the total ethylene oxide
content is present as
2o part of the reactant. Polypropylene oxide based reactants or additonal
polypropylene oxide
based polyols may be used for the present compositions , preferably whereby
the weight ratio
of ethylene oxide to propylene oxide is at least 1 to 8, said propylene oxide
being part of the
reactant andlor from an additional polyol being present in the total
composition.
25 Preferably, the concentration of nitrogen in the amine group-containing
polyol is
is 0.002 to 0.05 eqN/100g.
The said adhesive composition may be produced in any number of ways such as,
but not -
limited to:
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(i) Sequentially mixing the components at temperatures 25-80oC (with the
proviso
that when using pure MDI it is used above 42oC). Said mixtures are then
allowed
, to react.
(ii) Sequentially mixing and pre-reacting components (a) and (b).
- 5 (iii) Pre-reacting part of the isocyanate component with one of the
isocyanate-reactive
components, then separately pre-reacting the rest of the isocyanate component
with
the other isocyanate-reactive component, and blending the two prepolymers
together.
Catalysts can additionally be incorporated into the present compositions to
further enhance the
cure rate of the compositions. Examples of appropriate catalysts are, e.g.,
tertiary amine
catalysts. Suitable tertiary amine catalysts are available commercially, as
Niax A-4, from
Union Carbide and Thancat DMDEE, from Texaco. Most preferably, the Niax A-4
catalyst is
used in the relatively slower cure systems.
It has been found however, that reactivity can be controlled by the ethylene
oxide in total
composition , so limiting the number of formulations which require the
addition of extra
catalysts.
2o Other additives such as fungicides, tackifiers, UV stabilizers, viscosity
reducers, plasticisers,
fillers and extenders as well as surface tension modifying agents can be added
depending on
the specific application or manufacturing procedure. Furthermore, other
adhesives such as, but
not limited to, UF, PF and PRF can also be incorporated into the formulation.
The adhesive compositions of the present invention have been found to have a
pot life of
approximately three months or more under moisture-free conditions when mixed
prior to
application to a substrate.
The present compositions are also "cold curable", i.e., may be cured at a
temperature of lOoC
3o to room temperature although they can also be hot cured. Thus, the present
compositions may
be caved at temperatures of from lOoC to 250oC. Preferably the present
compositions are
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cured at a temperature of 23oC to 125oC. Generally, most systems will cure at
room
temperature in 10-30 minutes.
The adhesive compositions of the present invention may be used to bond many
different types
of moisture-containing substrates. It is preferred that at least one of the
substrates be selected
from the group consisting of wood, paper, rice hulls, cement, stone, cloth,
grass, corn husks,
bagasse, nut shells, polymeric foam films and sheets, polymeric foams and
fibrous materials.
Preferably, the present composition is used to fabricate multi-substrate
composites or
laminates. Those composites or laminates of particular interest being those
comprising
lignocellulosic or cellulosic materials, such as wood or paper, to prepare
products such as
finger joints, "Glulam" and I- Beams, plywood, wafer board, particleboard,
fiberboard,
chipboard, and oriented wood products, such as "Parallam", available from
McMillan
Bloedell.
As the present adhesive compositions are moisture-activated, it is important
that the substrates
have relatively high moisture contents. Specifically, the substrates should
have moisture
contents of at least 7%. Preferably, the substrates have moisture contents of
10 to 20% by
weight and more preferably 12 to 15% by weight
2o When used to bond multiple substrates together, the present composition is
applied to a
surface of a first substrate. A surface of a second substrate is then
contacted with the surface of
the first substrate containing the present composition. Pressure is then
applied to the contacted
surfaces and the adhesive compositions are allowed to cure. The surface of the
second
substrate against which the first substrate is contacted is generally not
coated with the present
adhesive composition. However, that surface may also be coated prior to
contacting the
substrates.
The present invention is further directed to a process for bonding multiple
substrates
comprising
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(1) applying to a surface of a first substrate the present moisture-activated
adhesive
composition as defined above and contacting the surface of the first substrate
with a
l surface of a second substrate
(2) applying pressure to the contacted surfaces, and
' S (3) curing the adhesive composition.
Additionally, independent of the moisture content, additional water can be
applied to
in the following manner
(a) the first substrate surface prior to the application of the present
composition,
(b) on top of the resin, after application to the first substrate surface
and/or
(c) to the second substrate surface prior to contacting the first, resinated
substrate surface,
or any combinations thereof, to speed up the reaction
15 Such additions of moisture are called "misting". Misting can optionally be
used to increase the
accessibility of water to the reactive isocyanate. Preferably, the application
levels
of water should not exceed 5% of the resin loading.
The present adhesive compositions also provide cold tack immediately after
application to a
2o substrate. This is particularly useful for pre-press operations where
mechanical handling is
often necessary. Cold tack is achieved naturally by the present composition
adhesives,
,. described in this invention. The present compositions may be used as
additives to other resins
and adhesives, which require improved tack properties.
25 The present adhesive compositions may be applied to the surfaces of the
substrates in any
conventional manner. For example, the surface may be coated with the
composition by
spraying, brushing, etc. Suitable means for applying the adhesive compositions
to the surface
of the substrate for a particular application will be evident to one skilled
in the art from the
present disclosure.
- 30
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After the coated substrates are contacted with each other, pressure is applied
thereto. The
pressure should be sufficient to cause the surfaces to adhere to one another.
Generally, the
amount of pressure and the time period for which the pressure is applied are
not limited and
specific pressures and times will be evident to one skilled in the art from
the present
disclosure. However, it has been found preferable that a pressure of
approximately IO to 200
psi (equivalent to 69 to 1380 kPa) be applied for 10 to 20 minutes to cause
appropriate
adhesion for most substrates. Further processing can generally be conducted on
the treated
substrates in less than one hour.
The invention is now illustrated by the following examples, which are not
intended to limit the
scope of the invention.
EXAMPLES
The following adhesive compositions were prepared in accordance with the
present invention.
Example 1
MDI prepolymer 80
2o Polyol 1 20
The MDI prepolymer had an NCO content of 24.9% and was prepared by reacting
Rubinol F-
456 (a polyether diol available from ICI Americas Inc.) with a 69/31 blend of
polymeric MDI
to pure MDI. The polymeric MDI used was RubinateTM M and the pure MDI used was
RubinateTM 44,both available from ICI America Inc. Polyol 1 was "Synperonic T
304" which
is an ethylene diamine-based polyol available from ICI Americas Inc.
Total EO % by weight of the total adhesive composition is 8%.
Comparison example 2a
-
MDI prepolymer 80
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Polyol 2 20
The MDI prepolymer had an NCO content of 24.9% and was prepared by reacting
Rubinol F-
456 (a polyether diol available from ICI Americas Inc.) with a 69/31 blend of
polymeric MDI
S to pure MDI. The polymeric MDI used was RubinateTM M and the pure MDI used
was
RubinateTM 44,both available from ICI Americas Inc. Polyol 2 was "Synperonic T
701 " which
is an ethylene diamine-based polyol available from ICI Americas Inc.
Total EO % by weight of the total adhesive composition is 2.2%.
1 o Example 2b
MDI prepolymer 63.58
Polyol 2 1.91
Polyol 1 8.27
15 Niax A-4 0.64
Calcium Carbonate No.7 25.43
SAG 47 0.07
Same as example 2a with SAG 47 is an antifoam agent available from Union
Carbide. NiaxA-
20 4 is a suitable tertiary amine catalysts available from Union Carbide.
Total EO % by weight of the total adhesive composition is 1.6%.
Example 3
25 MDI prepolymer 84.4
Polyol 1 1 S.OS
DMDEE 0.05
The MDI prepolymer had an NCO content of 25.2% and was prepared by reacting
Rubinol F-
~ 30 456 (a polyether diol available from ICI Americas Inc.) with a
71.2/28.8blend of polymeric
MDI to pure MDI. The polymeric MDI used was RubinateTM M and the pure MDI used
was
f
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RubinateTM 44, both available from ICI Americas Inc. Polyol 1 was "Synperonic
T 304"
which is an ethylene diamine - based polyol available from ICI Americas Inc.
Total EO % by weight of the total adhesive composition is 6%.
s Example 4 . '
MDI prepolymer 80
Polyol 1 20
The MDI prepolymer had an NCO content of 24.9% and was prepared by reacting
Rubinol F-
481 (a polyether diol available from ICI Americas Inc.) with a 69/31 blend of
polymeric MDI
to pure MDI. The polymeric MDI used was RubinateTM M and the pure MDI used was
RubinateTM 44, both available from ICI Americas Inc. Polyol 1 was "Synperonic
T 304"
which is an ethylene diamine - based polyol available from ICI Americas Inc.
1 s Total EO % by weight of the total adhesive composition is 12%.
Example 5
Polymeric MDI 45
20 44 MDI 20
Rubinol F456 15
Synperonic T 304 20
The products were made by sequential addition of the different components. The
final NCO,
2s viscosity and properties are the same as in Example 1.
Total EO % by weight of the total adhesive composition is 8%.
Results
3o Reactivity test measured as the time taken to start foaming when
formulation is .
contacted on a 10% moisture containing aspen wood showed that the formulation
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according to example 1 and 4 is significantly faster than formulation of
example 2 and
equivalent to the formulation of example 3 (formulation with catalyst).
Formulations given in examples 1 and 4, were used to construct single lap
joints using 150 x
~ 5 25 x 3 mm tangentially cut aspen wood. Overlaps were 25 x 25 mm and resin
loadings were
12 mg.m-2. The lap joints were cured at room temperature for 15 minutes and
tested to
failure. Two sets of samples were produced. In the first instance, the resin
was applied to the
wood of moisture content 10%. In the second case, after the application of the
adhesive, an
additional 5% (based on adhesive weight), water content was applied by spray
onto the
adhesive layer. The loads to failure were recorded. The results, listed below,
show a much
higher tensile shear strength and higher percentages of wood failure for the
systems with
added water.
Tensile Strength failure loads in MPa
15 Without mist With mist
Example 1 0.6 3 .5
Example 5 0.6 3.~ ..
i
