Note: Descriptions are shown in the official language in which they were submitted.
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TWO-PART MOISTURE CURABLE POLYURETHANE ADHESIVE
This application relates to a two-part polyurethane based adhesive useful in
bonding porous and nonporous materials. The adhesive is especially useful in
bonding glass
into window frames, for example, windshields into automobiles.
Polyurethane adhesive compositions typically comprise at least one urethane
prepolymer. Adhesives useful for bonding to nonporous substrates, such as
glass, to metal, are
well known (see U.S. Patents 4,374,237 and 4,687,533). When glass is installed
in automobiles
on a production line, a one-part moisture curable polyurethane adhesive is
preferably used, as
the equipment needed forthe application of such an adhesive in an automobile
assembly plant
is less expensive than the equipment needed to apply a two-part adhesive. One-
part
polyurethane adhesives are disclosed in U.S. Patents 4,374,237 and 4,687,533.
In the automotive aftermarket replacement industry, glass is often bound into
automobiles through the use of two-part moisture curable polyurethane
adhesives. Two-part
Polyurethane adhesives are used because they offer rapid initial cure,
allowing for rapid drive-
away times. Two-part polyurethane adhesives are well-known; see, for example,
U.S.
Patent 4,835,01 Z and DE 4,210,277. Despite the relatively rapid drive-away
times afforded by
two-part polyurethane adhesives, the market demands faster curing adhesives
which allow
even faster drive-away times, for instance, 60 minutes from application and
more preferably 30
minutes from application. If the adhesive cures too rapidly, then the window
installer loses the
necessary time to install and properly place the glass into the frame before
the adhesive
becomes too intractable to work with. Working time is defined as the period
from application
of adhesive until the adhesive becomes too intractable to work with, and is
preferably 10 to 12
minutes.
Future regulations in the U.S. will require dual airbags in vehicles. During
crashes,
the airbags inflate and exert additional pressure on the windshield. Federal
Transportation
Agency regulations require that windshields remain in place at crashes of up
to 30 mph (48
KPH). This requires adhesives which have enhanced strength at the drive-away
time. To meet
such a standard, the lap shear strengths of the adhesive should be preferably
150 psi (1033 kPa)
at the designated drive-away time as determined according to ASTM D-3163.
Therefore, what is needed is a two-part polyurethane adhesive which
facilitates
faster drive-away time, which meets the strength requirements defined above
and which still
provides for a reasonable working time to facilitate proper placement of glass
in window
frames.
The invention is a two-part adhesive comprising as a first part:
A. a polyurethane prepolymer having reactive isocyanate moieties;
and a second part
B. a curative composition comprising
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i) a polyurea, comprising the reaction product of a polyamine and
a polyisocyanate, dispersed in a polyether polyol-based
polyurethane prepolymer having reactive hydroxyl moieties, and
optionally, a plasticizer;
ii) a compound having at least one oxazolidine moiety capable of
reacting with an isocyanate under curing conditions; and
iii) a catalyst capable of catalyzing the reaction of isocyanate and
hydroxyl moieties in the presence of moisture.
In another embodiment, the invention is a process for binding two substrates
together which comprises:
i) contacting a portion of part A with a portion of part B of the adhesive
composition described hereinbefore;
ii) applying the mixture of part A and part B to a first substrate; and
iii) contacting a second substrate with the mixture of part A and part B
previously applied to the first substrate under conditions such that the
mixture cures and binds the first substrate to the second substrate.
The adhesive of this invention provides reasonable drive-away times for
replacement glass it binds into automobiles. Such drive-away times are
preferably 60 minutes
and more preferably 30 minutes from application of the adhesive. The adhesive
of the
invention also provides reasonable working times, 10 to 12 minutes.
Additionally, the lap shear
strengths of the adhesive atthe drive-away time is preferably 150 psi (1033
kPa) and more
preferably 250 psi (1723 kPa) according to ASTM D-31&3.
Suitable isocyanate-containing urethane prepolymers for use in part A include
any compound having an average isocyanate functionality of at least 0.7 and a
molecular
weight of at least 2000. Preferably, the average isocyanate functionality of
the prepolymer is
at least 0.7, more preferably at least 0.9 and even more preferably 1.2 or
greater. Preferably,
the isocyanate functionality of the prepolymer is 2.0 or less and more
preferably 1.4 or less.
Preferably, the molecular weight of the prepolymer is at least 2500 and more
preferably at
least 3000; and is preferably no greater than 20,000, more preferably no
greater than 15,000
and most preferably no greater than 10,000. The prepolymer may be prepared by
any suitable
method, such as by reacting an isocyanate-reactive compound containing at
least two
isocyanate-reactive groups with an excess over stoichiometry of a
polyisocyanate under
reaction conditions sufficient to form the corresponding prepolymer.
Preferable polyisocyanates for use in preparing the prepolymer include any
aliphatic, cycloaliphatic, arylaliphatic, heterocyclic or aromatic
polyisocyanate, or mixture
thereof, with an average isocyanate functionality of at least 2.0 and an
equivalent weight of at
least 80. Preferably, the isocyanate functionality of the polyisocyanate is at
least 2.0, more
preferably at least 2.2, and is more preferably at least 2.3; and is
preferably no greater than 4.0,
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more preferably no greater than 3.5, and is most preferably no greater than
3Ø Higher
functionalities may also be used, but may cause excessive crosslinking, and
result in an adhesive
which is too viscous to handle and apply easily, and can cause the cured
adhesive to be too
brittle. Preferably, the equivalent weight of the polyisocyanate is at least
100, more preferably
at least 110, and is more preferably at least 120; and is preferably no
greater than 300, more
preferably no greater than 250, and is most preferably no greater than 200.
Examples of such polyisocyanates include ethylene diisocyanate,
1,4-tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate, 1,12-dodecane
diisocyanate, cyclobutane-1,3-diisocyanate, cyclohexane-1,3- and 1,4-
diisocyanate and
mixtures of these isomers; 1-isocyanato-3,3,5-trimethyl-5-isocyanato methyl
cyclohexane (see,
for example, German Auslegeschrift No. 1,202,785); 2,4- and 2,6-
hexahydrotolylene
diisocyanate and mixtures of these isomers, hexahydro-1,3- and/or 1,4-
phenylene diisocyanate,
perhydro-2,5'- and/or 4,4'-diphenyl methane diisocyanate,1,3- and 1,4-
phenylene
diisocyanate, 2,4- and 2,6-tolylene diisocyanate and mixtures of these
isomers, diphenyl
methane-2,4'- and/or4,4'-diisocyanate, naphthylene-1,5-diisocyanate, tripheny)
methane-
-4,4',4"-triisocyanate, polyphenyl polymethylene polyisocyanates of the type
obtained by
condensing aniline with formaldehyde, followed by phosgenation and such as
described, for
example, in British Patents 874,430 and 848,671, perchlorinated aryl
polyisocyanates of the
type described in German Auslegeschrift 1,157,601, polyisocyanates containing
carbodiimide
groups of the type described in German Patent 1,092,007, diisocyanates of the
type described in
U.S. Patent 3,492,330, polyisocyanates containing allophanate groups of the
type described, for
example, in British Patent 994,890, in Belgian Patent 761,626 and in published
Dutch Patent
Application No. 7,102,524, polyisocyanates containing isocyanurate groups of
the type
described in German Patents 1,022,789; 1,222,067 and 1,027,394 and in German
Offenlegungsschrift 1,929,034 and 2,004,048, polyisocyanates containing
urethane groups of
the type described, for example, in Belgian Patent 752,261 or in U.S. Patent
3,394,164,
polyisocyanates containing acrylated urea groups as described in German Patent
1,230,778,
polyisocyanates containing biuret groups of the type described, for example,
in German Patent
1,101,392, in British Patent 889,050 and in French Patent 7,017,514,
polyisocyanates obtained
bY telomerization reactions of the type described, for example, in Belgian
Patent 723,640,
polyisocyanates containing ester groups of the type described, for example, in
British Patents
965,474 and 1,072,956, in U.S. Patent 3,567,763 and in German Patent 1,231,688
and reaction
products of the aforementioned isocyanates with acetals as described in German
Patent 1,072,385. Preferably, the polyisocyanate is an aromatic or
cycloaliphatic polyisocyanate
such as dipheny!methane-4,4'-diisocyanate, isophorone diisocyanate,
tetramethylxylene
diisocyanate, and is most preferably dipheny!methane-4,4'-diisocyanate.
The term "isocyanate-reactive compound" as used herein includes any organic
compound having on average at (east two, and preferably no more than four,
isocyanate-
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reactive moieties, such as a compound containing an active hydrogen moiety or
an imino-
functional compound. For the purposes of this invention, an active hydrogen
moiety refers to a
moiety containing a hydrogen atom which, because of its position in the
molecule, displays
significant activity according to the Zerewitnoff test described by Wohler in
the Journal of the
American Chemical Society, Vol. 49, p. 3181 (1927). Illustrative of such
active hydrogen
moieties are-COOH,-OH,-NHZ,-NH-,-CONHZ,-SH,and-CONH-. Typicalactivehydrogen-
containing compounds include polyols, polyamines, polymercaptans and
polyacids. Suitable
imino-functional compounds are those which have at least one terminal imino
group per
molecule, such as are described, for example, in U.S. Patent 4,910,279.
Preferably, the
isocyanate-reactive compound is a polyol, and is more preferably a polyether
poiyol.
Suitable polyols useful in the preparation of the prepolymers useful in part A
include polyether polyols, polyester polyols, poly(alkylene carbonate)polyols,
hydroxyl-contain-
ing polythioethers, polymer polyols, and mixtures thereof. Polyether polyols
are well-known in
the art and include polyoxyethylene, poiyoxypropylene, polyoxybutylene, and
polytetra-
methylene ether diols and triols which are prepared by reacting an
unsubstituted or halogen-
or aromatic-substituted alkylene oxide with an initiator compound containing
two or more
active hydrogen groups such as water, ammonia, a polyalcohol, or an amine.
Such methods are
described in U.S. Patents 4,269,945; 4,218,543; and 4,374,210. In general,
polyether polyols
may be prepared by polymerizing alkylene oxides in the presence of an active
hydrogen-
containing initiator compound. Most preferred, however, are ethylene oxide-
capped polyols
prepared by reacting glycerine with propylene oxide, followed by reacting with
ethylene oxide.
Preferable alkylene oxides include ethylene oxide, propylene oxide, butylene
oxides, styrene oxide, epichlorohydrin, epibromohydrin, and mixtures thereof.
Preferable
initiator compounds include water, ethylene glycol, propylene glycol,
butanediol, hexanediol,
glycerin, trimethylol propane, pentaerythritol, hexanetriol, sorbitol,
sucrose, hydroquinone,
resorcinol, catechol, bisphenols, novolac resins, phosphoric acid, amines, and
mixtures thereof.
Polyester polyols are also well known in the art and may be prepared by
reacting
a polycarboxylic acid or anhydride thereof with a polyhydric alcohol. Examples
of preferable
polycarboxylic acids include succinic acid, adipic acid, suberic acid, azelaic
acid, sebacic acid,
phthalic acid, isophthalic acid, malefic acid, trimellitic acid, phthalic acid
anhydride,
tetrahydrophthalic acid anhydride, hexahydrophthalic acid anhydride,
tetrachlorophthalic acid
anhydride, endomethylene tetrahydrophthalic acid anhydride, malefic acid
anhydride, glutaric
acid anhydride, fumaric acid, and mixtures thereof. Examples of preferable
polyhydric alcohols
include ethylene glycols, propane diols, butane diols, 1,6-hexanediol, 1,8-
octanediol,
neopentylglycol, glycerol, trimethylol propane, pentaerythritol, quinitol,
mannitol, sorbitol,
methyl glycoside, diethylene glycol, triethylene glycol, tetraethylene glycol,
polyethylene
glycols, polypropylene glycols, and mixtures thereof.
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Preferable polymer polyols include dispersions of polymers of vinyl monomers
in a
continuous polyol phase, particularly dispersions of styrene/acrylonitrile
copolymers. Also
useful are the so-called polyisocyanate polyaddition (PIPA) polyols
(dispersions of polyurea-
polyurethane particles in a polyol) and the polyurea dispersions in polyols
(PHD polyols).
Copolymer polyols of the vinyl type are described in U.S. Patents 4,390,645,
4,463,107,
4,148,840 and 4,574,137.
Preferably, the isocyanate-reactive compound has a functionality of at least
1.5,
more preferably at least 1.8 and most preferably at least 2.0; and is
preferably no greater than
4.0, more preferably no greater than 3.5 and most preferably no greater than
3Ø Preferably,
the equivalent weight of the isocyanate-reactive compound is at least 200,
more preferably at
least 500 and most preferably at least 1000; and is preferably no greater than
3500, more
preferably no greater than 3000 and most preferably no greater than 2500.
The isocyanate-containing prepolymer may be prepared by any suitable method,
such as bulk polymerization and solution polymerization. The reaction to
prepare the
prepolymer is carried out under anhydrous conditions, preferably under an
inert atmosphere
such as a nitrogen blanket, to prevent crosslinking of the isocyanate groups
by atmospheric
moisture. The reaction is preferably carried out at a temperature between
0°C and 150°C,
preferably between 25°C and 80°C, until the residual isocyanate
content determined by
titration of a sample is very close to the desired theoretical value. The
isocyanate content in the
prepolymers is preferably in the range of 1.0 percent to 15 percent, more
preferably in the
range of 1.5 percent to 10.0 percent, even more preferably in the range of 1.5
percent to 5.0
percent and most preferably in the range of 1.8 percent to 3.0 percent.
The isocyanate-containing urethane prepolymers are present in part A in an
amount sufficient such that, when mixed with part B, the resulting adhesive
cures to
sufficiently bond substrates together. Preferably, the lap shear strengths of
bonds so formed is
150 psi (1033 kPa) or greater and is achieved after 60 minutes and more
preferably after 30
minutes. Preferably, the isocyanate-containing polyurethane prepolymers of
part A are
present in an amount of 55 parts by weight of part A or greater, and more
preferably 65 parts
by weight of part A or greater. Preferably, the isocyanate-containing
polyurethane
prepolymers of part A are present in an amount of 85 parts by weight of part A
or less, more
preferably 83 parts by weight of part A or less and even more preferably 75
parts by weight or
less. Part A of the adhesive of the invention may be formulated with fillers
and additives
known in the prior art for use in elastomeric compositions. By the addition of
such materials,
physical properties such as viscosity flow rates can be modified. However, to
prevent
premature hydrolysis of the moisture-sensitive groups of the polyurethane
prepolymer, fillers
should be thoroughly dried before admixture therewith.
Optional components for part A of the adhesive of the invention include
reinforcing fillers. Such reinforcing fillers increase the ultimate strength
of the adhesive and
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may improve the thixotropic properties. Such fillers are well known to those
skilled in the art
and include carbon black, titanium dioxide, calcium carbonate, surface treated
silicas, titanium
oxide, fumed silica and talc. Preferred reinforcing fillers comprise carbon
black. In one
embodiment, more than one reinforcing filler may be used, of which one is
carbon black and in
such embodiment, a sufficient amount of carbon black is used to provide the
desired black
color to part A. The reinforcing fillers are used in sufficient amount to
increase the strength of
the adhesive and to provide thixotropic properties to part A. Preferably, the
reinforcing filler is
present in an amount of 1 part by weight of part A or greater, more preferably
15 parts by
weight of part A or greater and most preferably 17 parts by weight of part A
or greater.
Preferably, the reinforcing filler is present in an amount of 40 parts by
weight of part A or less,
more preferably 25 parts by weight of part A or less and most preferably 23
parts by weight of
part A or less.
Among optional materials in part A of the adhesive formulation are clays.
Preferred clays useful in the invention include kaolin, surface treated
kaolin, calcined kaolin,
aluminum silicates and surface treated anhydrous aluminum silicates. The clays
can be used in
any form which facilitates formulation of a pumpable adhesive. Preferably, the
clay is in the
form of pulverized powder, spray dried beads and finely ground particles.
Clays may be used in
an amount of 0 parts by weight of part A or greater, more preferably 1 part by
weight of part A
or greater and even more preferably 6 parts by weight of part A or greater.
Preferably, the
clays are used in an amount of 20 parts by weight or less of part A and more
preferably 10 parts
by weight or less.
Part A of the adhesive composition of the invention may further comprise a
catalyst known for promoting the cure of polyurethanes in the presence of
moisture.
Preferable catalysts include metal salts such as tin carboxylates, organo
silicon titanates, alkyl
Z5 titanates, bismuth carboxylates, and dimorpholinodiethyl ether or alkyl
substituted
dimorpholinodiethyl ethers. Among preferred catalysts are bismuth octoate,
dimorpholinodiethyl ether and (di-(2-(3,5-dimethylmorpholino)ethyl)) ether.
Such catalysts,
when employed, are preferably employed in an amount based on the weight of
part A of 0.1
parts by weight or greater, more preferably 0.2 parts by weight or greater and
most preferably
0.4 parts by weight or greater. Such catalysts are preferably employed in an
amount, based on
the weight of part A, of 5 parts by weight or less, more preferably 1.75 parts
by weight or less,
even more preferably 1 part by weight or less and most preferably 0.6 parts by
weight or less.
Part A of the adhesive composition of this invention may further comprise
plasticizers so as to modify the rheological properties to a desired
consistency. Such materials
should be free of water, inert to isocyanate groups and compatible with a
polymer. Suitable
plasticizers are well-known in the art and preferable plasticizers include
alkyl phthalates such
as dioctylphthalate or dibutylphthalate, partially hydrogenated terpene
commercially available
as "HB-40", trioctyl phosphate, epoxy plasticizers, toluene-sulfamide,
chloroparaffins, adipic
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acid esters, castor oil, toluene and alkyl naphthalenes. The amount of
plasticizer in part A is
that amount which gives the desired theological properties of part A.
Preferably, plasticizers
are used in part A in an amount of 0 parts by weight or greater based on the
weight of part A,
more preferably 10 parts by weight or greater, even more preferably 30 parts
by weight or
greater, and most preferably 35 parts by weight or greater. The plasticizer is
preferably used in
an amount of 40 parts by weight or less based on the total amount of part A
and more
preferably 35 parts by weight or less.
Part A of the adhesive of this invention may further comprise stabilizers
which
function to protect the adhesive composition from moisture, thereby inhibiting
advancement
and preventing premature crosslinking of the isocyanates in the adhesive
formulation.
Included among such stabilizers are diethylmalonate and alkylphenol alkylates.
Such stabilizers
are preferably used in an amount of 0.1 parts by weight or greater based on
the total weight of
part A, preferably 0.5 parts by weight or greater and more preferably 0.8
parts by weight or
greater. Such stabilizers are used in an amount of 5.0 parts by weight or less
based on the
weight of part A, more preferably 2.0 parts by weight or less and most
preferably 1.4 parts by
weight or less.
Other components commonly used in adhesive compositions may be used in part
A of the adhesive composition of this invention. Such materials are well known
to those skilled
in the art and may include ultraviolet stabilizers and antioxidants.
ZO As used herein, all parts by weight relative to the components of part A
are based
on 100 total parts by weight of part A.
Part A of the adhesive composition of this invention may be formulated by
blending the components together using means well known in the art. Generally,
the
components are blended in a suitable mixer, such as a Hockmeier mixer. Such
blending is
preferably conducted in an inert atmosphere in the absence of oxygen and
atmospheric
moisture to prevent premature reaction. It may be advantageous to add any
plasticizers to the
reaction mixture for preparing the isocyanate-containing prepolymer so that
such mixture may
be easily mixed and handled. Alternatively, the plasticizers can be added
during blending of all
the components in part A. Once part A is formulated, it is packaged in a
suitable container such
that it is protected from atmospheric moisture and oxygen. Contact with
atmospheric moisture
and oxygen could result in premature crosslinking of the polyurethane
prepolymer containing
isocyanate groups.
Optionally, part A of the adhesives of the invention may further comprise a
thixotrope. Such thixotropes are well known to those skilled in the art and
include alumina,
limestone, talc, zinc oxides, sulfur oxides, calcium carbonate, perlite, slate
flour, salt (NaCI) and
cyclodextrin. The thixotrope may be added to part A of the adhesive of the
invention in a
sufficient amount to give the desired theological properties. Preferably, the
thixotrope is
present in an amount of 0 parts by weight or greater based on the weight of
part A, preferably
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1 part by weight or greater. Preferably, the optional thixotrope is present in
an amount of 10
parts by weight or less based on the weight of part A and more preferably 2
parts by weight or
less.
The second part of the adhesive composition of the invention, referred to
herein
as part B, is a curative composition which comprises a polyurea, comprising
the reaction
product of a polyamine and a polyisocyanate, dispersed in a polyurethane
prepolymer having
reactive hydroxyl moieties (hereinafter hydroxyl-containing prepolymer) which
is derived from
1 or more polyether polyols and 1 or more polyisocyanates, wherein such
dispersion optionally
contains plasticizers. The polyurea preferably does not react with hydroxyl
moieties. The
Polyurea is prepared by the reaction of a polyamine, preferably a diamine,
with a
polyisocyanate, preferably a diisocyanate. The polyurea and polyamine are
mixed and undergo
immediate reaction at room temperature. Thereafter, the polyurea is contacted
with 1 or more
polyether polyols or hydroxyl-containing polyurethane prepolymers, preferably
under high
shear conditions, to disperse the polyurea into the polyether polyol or
hydroxyl-containing
prepolymer. Preferably, the isocyanate used to prepare the polyurea is a
cycloaliphatic or
aliphatic polyisocyanate, as the use of cycloaliphatic and aliphatic
isocyanates facilitate
handling and stability of the polyurea. Preferably, the isocyanate is a
diisocyanate. Preferably
the polyurea has a urea functionality of 8 percent or greater, more preferably
10 percent or
greater and most preferably 15 percent or greater. Preferably, the polyurea
has a functionality
of 40 percent or less and more preferably 20 percent or less. Functionality as
used herein with
respect to the polyurea refers to weight percent of urea groups present in the
polyurea, based
on weight. The polyurea is contained in part B to provide hard segments in the
finely cured
adhesive. The polyurea further affords rapid viscosity build-up and cure of
the adhesive.
Preferably, the polyurea is a solid to enhance the stability of part B.
Preferably, the polyurea is
initially dispersed in a polyether polyol and the hydroxyl-containing
polyurethane prepolymer
is prepared in situ thereafter.
Preferably, the polyether polyol in which the polyurea is dispersed is a triol
and
more preferably a polyoxyalkylene-based triol. Preferably, such
polyoxyalkylene oxide triol
comprises a polyoxypropylene chain with a polyoxyethylene end cap. Such
materials are well
known in the art and initiators and alkylene oxides which may be used in the
preparation of
the triol are described hereinbefore. A particularly preferred polyether trio)
is a 1,2,3-propane
triol initiated polyoxypropylene with a polyoxyethylene end cap. Preferably,
such triol has
molecular weight of 2000 or greater and more preferably 4500 or greater.
Preferably, such
triol has molecular weight of 8000 or less and more preferably 6000 or less.
Below 2000
molecular weight, the viscosity of the dispersion is too low and above 8000
molecular weight, it
may be too difficult to disperse the polyurea in the triol.
The hydroxyl-containing prepolymer may be prepared by reacting the dispersion
of polyurea in polyether triol with a diol and a polyisocyanate under
conditions such that a
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polyurethane prepolymer is prepared and the polyurea does not participate in
the reaction in a
significant way. The polyether diol is preferably a polyoxyalkylene-based
polyether. Such
polyethers are described hereinbefore in the description of part A of the
adhesive composition.
More preferably, such diols are polyoxypropylene polyoxyethylene diols.
Preferably, such
polyoxyethylene polyoxypropylene diols contain 30 percent by weight or greater
ethylene
oxide groups and more preferably 60 percent by weight or greater ethylene
oxide groups.
Preferably, such diols contain 100 percent by weight or less of ethylene oxide
moieties, more
preferably 70 parts by weight or less of ethylene oxide moieties. Care must be
taken above
70 weight percent ethylene oxide moieties, as the diol becomes very reactive.
Under such
conditions, low catalyst amounts and lower temperatures may be necessary to
retain control
over the reaction. Preferably, the diol used has a molecular weight of 250 or
greater, as below
250, the viscosity of the material may be too low, more preferably the diol
has a molecular
weight of 2000 or greater. Preferably, the diol has a molecular weight of 4000
or less, as above
4000, the viscosity may be too high, and more preferably the molecular weight
is 3000 or less.
The polyisocyanate used in the advancement is any polyisocyanate useful in
preparing a polyurethane prepolymer. Such materials are described hereinbefore
in reference
to the description of part A of the adhesive of this invention. The relative
ratio of hydroxyl
groups to isocyanate groups should be such that the resulting prepolymer has
no free
isocyanate groups, as such isocyanate group will react with the polyurea
prematurely.
Preferably, the ratio of isocyanate groups to hydroxyl groups is such that a
reasonable
advancement occurs. Preferably, the equivalent ratio of the isocyanate groups
to the hydroxyl
groups is 0.1:1 or greater and more preferably 0.2:1 or greater. The
equivalent ratio should
not be so high so as to prevent complete reaction of the isocyanate moieties.
Preferably, the
equivalent ratio of isocyanate groups to the hydroxyl groups is 0.95:1 or
less, even more
preferably 0.8:1.0 or less and most preferably 0.7:1.0 or less.
Preferably, aliphatic isocyanates are used as handling of the material is
easier and
the isocyanates are less reactive, thereby allowing greater control of the
reaction.
The reactions to prepare the hydroxyl-containing prepolymer may be carried out
in the presence of urethane catalysts. Examples of such catalysts include the
stannous salts of
carboxylic acids, such as stannous octoate, stannous oleate, stannous acetate,
and stannous
laureate; dialkyltin dicarboxylates, such as dibutyltin dilaureate and
dibutyltin diacetate;
tertiary amines and tin mercaptides. Preferably, the reaction to prepare the
prepolymer is
catalyzed by stannous octoate. The amount of catalyst employed is generally
between 0.005
and 5 percent by weight of the mixture catalyzed, depending on the nature of
the isocyanate.
The prepolymer is preferably prepared by contacting the polyurea dispersed in
a
triol and the diol in the absence of catalyst and heating the mixture to
48°C or greater, more
preferably 50°C or greater. The mixture is heated to a temperature of
56°C or less, more
preferably 52°C or less. The polyisocyanate is then added to the
mixture and the mixture is
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subjected to mixing so as to evenly disperse the polyisocyanate in the
reaction mixture.
Thereafter, the polyurethane catalyst is added. After addition of the
catalyst, an exotherm
generally results. Preferably, the peak temperature of the exotherm is
58°C or greater and
more preferably 60°C or greater. Preferably, the peak temperature of
the exotherm is 70°C or
less, more preferably 58°C or less. Thereafter, plasticizer may be
added after the exotherm
recedes, that is, the temperature drops, to dilute the reactants and quench
the reaction. The
reaction should be run such that all free isocyanate moieties are reacted with
hydroxyl
moieties. The reaction should be performed in the absence of atmospheric
moisture.
The resulting prepolymer must have free hydroxyl moieties which are capable of
reacting with the free isocyanate moieties of the isocyanate-containing
prepolymer of part A.
The hydroxyl number of the resulting polymer is preferably 5 or greater and
more preferably 25
or greater. Preferably, the hydroxyl number of the resulting prepolymer is 60
or less and more
preferably 40 or less. The resulting prepolymer with polyurea dispersed
therein must be
handleable and, therefore, preferably has a viscosity of 25,000 centipoise or
greater and more
preferably 30,000 centipoise or greater. The hydroxyl-containing prepolymer
having poiyurea
dispersed therein preferably has a viscosity of 45,000 centipoise or less and
more preferably
40,000 centipoise or less. The hydroxyl-containing prepolymer preferably has a
molecular
weight of 9000 or greater, more preferably 15,000 or greater and preferably
has a molecular
weight of 22,000 or less, more preferably 18,000 or less.
The polyurea is present in the hydroxyl-containing polyurethane prepolymer
dispersion in an amount of 8 parts by weight of the dispersion or greater,
more preferably 15
parts by weight or greater and most preferably 20 parts by weight or greater.
Such polyurea is
present in the dispersion in an amount of 50 parts by weight or less based on
the weight of the
dispersion, more preferably 40 parts by weight or less and most preferably 30
parts by weight
or less. The hydroxyl-containing prepolymer is present in the dispersion in an
amount of 50
parts by weight or more based on the dispersion, more preferably 60 parts by
weight or more
and most preferably 70 parts by weight or more. The hydroxyl-containing
prepolymer is
present in the dispersion in an amount based on the weight of the dispersion
of 85 parts by
weight or less, even more preferably 75 parts by weight or less. The
plasticizer present in the
dispersion is present in an amount of 0 parts by weight of the dispersion or
more preferably
20 parts or greater and most preferably 30 parts by weight or greater. The
plasticizer is present
in the dispersion in an amount of 40 parts by weight or less based on the
weight of the
dispersion, and most preferably 35 parts by weight or less. Parts by weight of
the dispersion
relates to a dispersion having 100 total parts. The polyurea dispersion in
hydroxyl-containing
prepolymer is present in part B in an amount of 30 parts by weight or greater
based on the
weight of part B and more preferably 65 parts by weight or greater. The
dispersion is present
in part B in an amount of 90 parts by weight or less based on the total weight
of part B and
more preferably 70 parts by weight or less.
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The curative composition of part B further comprises a latent crosslinking
material containing at least one oxazolidine meiety. Such material is present
to function as a
crosslinker during the final cure of the adhesive. Examples of such latent
crosslinking materials
include those described in U.S. Patents4,396,681; 3,743,626; 4,118,376;
4,192,937; and
5,235,062. In one embodiment, such latent crosslinkers comprise
bisoxazolidines which are the
reaction product of a diisocyanate with a hydroxy alkyl-substituted
oxazolidine such as an N-
hydroxyethyl oxazolidine. The preferred isocyanates are cycloaliphatic and
aliphatic
isocyanates such as hexamethylene diisocyanate. A preferred oxazolidine-
containing
compound is commercially available from Mobay as Hardener OZ which is carbamic
acid, 1,6-
hexanediyl bis-, bis(2-(2-(1-methylethyl)-3-oxazolidinyl)ethyl) ester.
The oxazolidine-containing compound is present in a sufficient amount to
enhance the crosslinking of the polyurethane during curing. If too much is
present, there is
insufficient work time and if too little is present, the open time is too
long. If the open time is
too long, the drive-away time is too long. Preferably, the latent crosslinker
is used in an
amount of 0.01 parts or greater based on part B, more preferably 0.02 parts by
weight or
greater and most preferably 0.04 parts by weight or greater. Preferably, the
latent crosslinker
is present in an amount of 0.1 parts by weight or less, more preferably 0.06
parts by weight or
less.
The curative composition of part B further comprises a catalyst useful in
polyurethane reactions. Such catalysts are well known in the art and include
metal salts such as
tin carboxylates, organo silicon titanates, alkyl titanates and bismuth
carboxylates. A preferred
catalyst is bismuth octoate. Such catalyst is preferably used in an amount of
0.1 parts or greater
based on the weight of part B and more preferably 0.2 parts by weight or
greater. Such catalyst
is preferably used in an amount of 1 part by weight based on the weight of
part B or less and
more preferably 0.6 parts by weight or less.
The curative composition of part B may further comprise a plasticizer. The
plasticizers which may be used and the amounts of such plasticizers which may
be used are
described with respect to part A. The plasticizer may be added all or in part
during the
preparation of the polyurea dispersed in hydroxyl-containing polyurethane
prepolymer or may
be added during formulation of part B of the adhesive of this invention.
Part B may further comprise a reinforcing filler and/or clay as described
hereinbefore with respect to part A. Additionally, B may further comprise
antioxidants and UV
stabilizers as described hereinbefore.
As used herein, all parts by weight relative to part B are based on 100 total
parts
bY weight of part B.
The curative composition of part B may be prepared by contacting the
ingredients
under conditions such as to blend the material. Such contacting can occur in
the standard
mixers under conditions well known to those skilled in the art. The curative
composition of
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part B is preferably prepared and stored in a moisture-free environment so as
to prevent
premature curing.
The adhesive composition of the invention is used to bind porous and nonporous
substrates together. The two parts of the composition are kept separate until
j ust before use.
Just prior to application, the two parts are contacted and mixed. Thereafter,
the mixed
adhesive composition is applied to a substrate and the adhesive on the first
substrate is
thereafter contacted with a second substrate. The ratio of part A to part B
should be sufficient
to allow curing of the adhesive to give the desired drive-away time and lap
shear strengths as
defined hereinbefore. Preferably, the ratio of isocyanate from part A to
hydroxyl groups from
part B is 0.5:1 or greater and more preferably 0.65:1 or greater. Preferably,
the ratio of
isocyanate groups contained in part A to hydroxyl groups in part B is 0.95:1
or less and more
preferably 0.9:1 or less. Preferably, the two parts of the adhesive are
formulated such that,
during mixing, the volume of part A to part B side is equal. Although this is
not necessary, it
greatly simplifies application of the adhesive to substrates. In preferred
embodiments, the
surfaces to which the adhesive is applied is cleaned and primed prior to
application; see, for
example, U.S. Patents 4,525,511; 3,707,521 and 3,779,794. Generally, the
adhesives of the
invention are applied at ambient temperature in the presence of atmospheric
moisture.
Exposure to atmospheric moisture is sufficient to result in curing of the
adhesive. Curing can be
accelerated by the addition of additional water or by applying heat to the
curing adhesive by
means of convection heat or microwave heating. Preferably, the adhesive of the
invention is
formulated to provide a working time of 6 minutes or greater, more preferably
10 minutes or
greater. Preferably, the working time is 15 minutes or less and more
preferably 12 minutes or
less.
Viscosities as described herein are determined according to the following
procedure: measured using the Brookfield Viscometer, Model RVT, at standard
conditions of
72°F (22°C) and 50 percent relative humidity. The viscometer is
calibrated using silicone oils of
known viscosities, which vary between 5000 cps to 50,000 cps. A set of RV
spindles that attach
to the viscometer are used for the calibration. All measurements are done
using the No. 5
spindle at a speed of 1 revolution per second for 5 minutes until the
viscometer equilibrates.
The viscosity corresponding to the equilibrium reading is then calculated
using the calibration.
Molecular weights as described herein are weight average molecular weights
which are
determined using the Waters Model 590 Gel Permeation Chromatograph. This unit
is
connected to a multiwavelength detector and a differential refractometer to
measure the
elution volume. A column of styrogel is used for the size exclusion and it can
determine
molecular weights from 250 to 50,000. The molecular weight of the prepolymer
is then
determined by measuring the elution volume through this column using
tetrahydrofuran as
the eluting solvent. The molecular weight is then calculated from a
calibration curve of
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molecular weight versus elution volume obtained from a polystyrene
polyethylene glycol
column.
In reference to polyurethane prepolymers, functionality is determined
according
to the following formula,
moles diol-NCO adduct x diol-NCO functionality + moles triol-NCO adduct x
triol-
NCO functionality + moles excess polyisocyanate monomer x its functionality
moles diol-NCO adduct + moles triol-NCO adduct + moles excess polyisocyanate
monomer
wherein moles excess polyisocyanate monomer are calculated according to the
following formula,
moles of isocyanate - (2x moles of diol + 3x moles of triol)
and the moles of isocyanate, diol and triol are based on the amount of each in
the
starting formulation.
Functionality of the raw materials is generally disclosed by the raw material
supplier. It can be determined empirically by means of titrating the polyol or
isocyanate to
determine the average number of functional groups per molecule. One skilled in
the art knows
how to determine the functionality based on data developed by titration.
The following examples are provided to illustrate the invention, but are not
intended to limit the scope thereof. All parts and percentages are by weight
unless otherwise
indicated.
Preparation of Isocyanate Functional Prepolymer
A polyether polyurethane prepolymer with low degree of branching was
prepared by mixing 363.68 g of a polyoxypropylene diol having an average
molecular weight
of 2000 commercially available under the trade name "PPG 2025" with 527.04 g
of a
Polyoxypropylene triol having an average molecular weight of 4500 and
commercially
available under the trade name "Poly G 85-36." Mixing was carried out in a
reactor by heating
the mixture to 55°C. 160.6 g of diphenylmethane-4,4'-diisocyanate and
0.17 g of stannous
octoate was added to the mixture. The whole mixture was then reacted for one
hour. Finally,
525.44 g of a plasticizing agent, diallyl phthalate, was added to the mixture
and the mixing
continued for one hour. The resultant prepolymer is referred to herein as
isocyanate functional
prepolymer 1.
Preparation of Part A of Adhesive Composition
Three adhesive compositions useful as Part A were prepared using a portion of
the isocyanate functional prepolymer of Example 1. The prepolymer was placed
in a planetary
mixer and degassed for 20 minutes. Carbon black and, in some embodiments, clay
were added
to the mixer, and the mixture was mixed for 20 minutes under vacuum.
Dimorpholinodiethyl
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ether (DMDEE) was added as a catalyst to the mixture and mixed for another 20
minutes and
packaged in tubes. The components of each composition are compiled in Table 1.
Table I
Components of Adhesive Compositions Part A
A-1 A-2 A-3 '
Isocyanate functional 540.32 270.16 568
Prepolymer 1, g
Carbon Black (g) 213 136.65 ~ 229.6
Clay tg) 60 -- --
DMDEE (g) 1.9 0.95 2.4
BØ1 (g) __ __ 0.4
~~ Bismuth Octoate.
Preparation of Hydroxyl Functional Prepolymer
Hydroxyl functional polyurea dispersed polyether polyurethane prepolymers
were synthesized by contacting a polyoxyalkylate diol and a polyurea dispersed
polyoxyalkylate triol. These mixtures were stirred and heated to 55°C
and diphenylmethane-
4,4'-diisocyanate and stannous octoate were added and mixed for 30 minutes.
Plasticizing
agent, dialkyl phthalate, was added and the mixtures stirred for another 30
minutes. The
resultant prepolymers were viscous materials with zero free isocyanate
functionalities. The
components used to prepare each hydroxyl functional prepolymer are compiled in
Table II.
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Table II
Components For Hydrozyl Functional Prepolymers Used In Part B
OH OH OH
Prepolymer-1 Prepolymer-25 Prepolymer-3
Polyozyalkylate 660.251 5123 463.21
diol (g)
Polyurea dispersed 607.952 10242 --
Polyozyalkylate
triol {g)
Polyo~yalkylate -- -- 615.524
triol (g)
Diphenylmethane 77.7 64 41.28
4,4'-diisocyanate
Stannous Octoate 1.2 0.16 0.32
(g)
Plasticizer {g) 404.25 -- 479.68
1. Available under the trade name "Poly G55-56" from Olin Chemicals having
an average molecular weight of 2000.
2. Polyurea dispersed polyoxyalkylate triol available underthe trade name
"Dermophen 1920".
3. Polyoxyalkylate diol having an average molecular weight of 1000 g available
from The Dow Chemical Company under the trade name "Voranol 5287".
4. Polyoxyalkylate triol having an average molecular weight of 2000 available
from Olin Chemicals under the trade name "Poly G85-36".
5. The prepolymer was stirred for 30 minutes after addition of catalyst and
then packaged.
Preparation of Adhesive Composition Part B
Part B curative compositions were prepared using the hydroxyl functional
prepolymers mixed with latent polyamino alcohol based on urethane
bisoxazolidine
commercially available under the trade name "Hardener OZ" as a crosslinking
agent for
10 minutes under vacuum. Bismuth octoate was then added to these mixtures
which were
stirred for another 15 minutes. Carbon black and clay were added to these
mixtures and mixed
for 20 minutes under vacuum. The mixtures were further mixed for another 20
minutes, after
which they were packaged in tubes. The components of each composition made are
compiled
i~ Table III.
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Table III - Composition of Part of Adhesive
B
Compositions
Part B Adhesive B-1 B-2 B-3 B-4 B-5
Composition
OH Prepolymer 1 2 2 2 3 '
Amount of OH 270 280 560 336 581.84
Prepolymer (g)
Bisozazolidine 0.325 0.19 0.12 0.14 --
(g)
Bismuth Octoate 0.6 0.19 0.39 0.23 2.16
Carbon Black 60 96 192 115.2 192
Clay 60 -- -- -- --
Testing of Adhesives
Parts A-1 and B-1 were inserted into separate compartments of a high-speed
mixing electric gun with the appropriate dynamic mixing heads. The material in
both tubes
were extruded at high speeds at a 1:1 ratio on a volume basis using this gun
and the cure rate
for this adhesive was 140 psi (964 kPa) within an hour, determined by a quick
adhesion test
described below.
ZO For determining cure rate, a 1 x 1 /4' (z.54 cm x 0.62 cm) thick bead is
extruded on
a primed glass plate. A metal plate, which is also primed, is then placed on
top of the extruded
bead. The assembly is allowed to cure at 72°F (22°C) and 50
percent relative humidity for 60
minutes. The plates are then separated by pulling the two plates perpendicular
to the plane of
the bead one hour after assembly. The curing rate is recorded as the force
required to separate
the plates in psi.
Adhesive compositions were contacted and tested as described above at 30, 60
and 90 minutes from bonding. The components and results are compiled in Table
IV.
35
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Table
IV
Part A A-1 A-3 A-3 A-3 A-2
Part B B-1 B-2 B-3 B-4 B-5
X Bismuth Octoate 0.15 0.05 0.05 0.05 0.27
% Hardener OZ 0.08 0.05 0.015 0.03 0
Working time 12 17 15 8 7
(minutes)
si in 30 minutes 27.5 34 68 75 ~ 19.18
~kpa) (189) (234) (469) (517) (132)
1o psi in 60 minutes 166 82 129 125 74.98
(kPa) (1144) (565) (889) (861) (517)
si in 120 minutes 373 185 175 216 113.77
(kpa) (2570) (1275) (1205) (1488) (784)
The last formulation used conventional triol and is comparative.
25
35
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