U.S. patent application number 14/869126 was filed with the patent office on 2016-01-21 for structural epoxy resin adhesives containing chain-extended elastomeric tougheners capped with phenol, polyphenol or aminophenol compounds.
The applicant listed for this patent is Christof Braendli, Andreas Lutz, Irene Maeder, Daniel Schneider. Invention is credited to Christof Braendli, Andreas Lutz, Irene Maeder, Daniel Schneider.
Application Number | 20160017192 14/869126 |
Document ID | / |
Family ID | 45218925 |
Filed Date | 2016-01-21 |
United States Patent
Application |
20160017192 |
Kind Code |
A1 |
Lutz; Andreas ; et
al. |
January 21, 2016 |
STRUCTURAL EPOXY RESIN ADHESIVES CONTAINING CHAIN-EXTENDED
ELASTOMERIC TOUGHENERS CAPPED WITH PHENOL, POLYPHENOL OR
AMINOPHENOL COMPOUNDS
Abstract
Structural adhesives are prepared from a chain extended
elastomeric toughener that contains urethane and/or urea groups,
and have terminal isocyanate groups that are capped with a phenol,
a polyphenol or an aminophenol compound. The adhesives have very
good storage stability and cure to form cured adhesives that have
good lap shear and impact peel strengths.
Inventors: |
Lutz; Andreas; (Galgenen,
CH) ; Schneider; Daniel; (Waedenswil, CH) ;
Braendli; Christof; (Zurich, CH) ; Maeder; Irene;
(Rapperswil, CH) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Lutz; Andreas
Schneider; Daniel
Braendli; Christof
Maeder; Irene |
Galgenen
Waedenswil
Zurich
Rapperswil |
|
CH
CH
CH
CH |
|
|
Family ID: |
45218925 |
Appl. No.: |
14/869126 |
Filed: |
September 29, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13821748 |
Mar 8, 2013 |
9181463 |
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PCT/US2011/062491 |
Nov 30, 2011 |
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14869126 |
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61427192 |
Dec 26, 2010 |
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Current U.S.
Class: |
156/307.1 ;
523/466; 525/107; 525/460 |
Current CPC
Class: |
C09J 5/00 20130101; C08G
18/73 20130101; C08G 18/12 20130101; C08G 18/3215 20130101; C08G
18/3215 20130101; Y10T 156/10 20150115; C08G 18/10 20130101; C09J
155/00 20130101; C08G 18/6677 20130101; C08G 18/10 20130101; C08G
18/4854 20130101; C08K 3/36 20130101; C09J 2463/003 20130101; C09J
163/00 20130101; C08G 18/12 20130101 |
International
Class: |
C09J 163/00 20060101
C09J163/00; C08K 3/36 20060101 C08K003/36 |
Claims
1. A one-part structural adhesive comprising: A) at least one epoxy
resin; B) a reactive elastomeric toughener containing capped
isocyanate groups; and C) one or more epoxy curing agents; wherein
the elastomeric toughener is formed by a) reacting an excess of a
polyisocyanate with a 300-3000 equivalent weight polyol or with a
mixture of a 300-3000 equivalent weight polyol and a branching
agent, to form an isocyanate-terminated prepolymer; b) reacting the
isocyanate-terminated prepolymer with a chain extender to produce a
chain extended, isocyanate-terminated prepolymer, and c) capping at
least 90% of the terminal isocyanate groups of the chain extended,
isocyanate- terminated prepolymer with a capping agent selected
from a monophenol, a polyphenol or an aminophenol.
2. The structural adhesive of claim 1, wherein the 300-3000
equivalent weight polyol is a polyether, a hydroxyl-terminated
polybutadiene or a mixture of a polyether and a hydroxyl-terminated
polybutadiene.
3. The structural adhesive of claim 2, wherein the chain extender
contains two phenolic hydroxyl groups.
4. The structural adhesive of claim 3 wherein the capping agent is
a monophenol.
5. The structural adhesive of claim 3 wherein the capping agent is
a polyphenol.
6. The structural adhesive of claim 3 wherein the capping agent is
an aminophenol.
7. The structural adhesive of claim 2, wherein the epoxy resin
includes at least one diglycidyl ether of a polyhydric phenol.
8. The structural adhesive of claim 2, which contains at least one
epoxide-terminated liquid rubber.
9. The structural adhesive of claim 2, further comprising a latent
catalyst which becomes active only upon exposure to elevated
temperatures.
10. The structural adhesive of claim 9 wherein the latent catalyst
is 2,4,6-tris(dimethylaminomethyl)phenol integrated into a
poly(p-vinylphenol) matrix or 2,4,6-tris(dimethylaminomethyl)phenol
integrated into a novolac resin.
11. The structural adhesive of claim 2 wherein the curing agent
includes one or more of a boron trichloride/amine complex, a boron
trifluoride/amine complex, dicyandiamide, melamine,
diallylmelamine, acetoguanamine and benzoguanamine,
3-amino-1,2,4-triazole, adipic dihydrazide, stearic dihydrazide,
isophthalic dihydrazide, semicarbazide, cyanoacetamide, and
diaminodiphenylsulphones.
12. The structural adhesive of claim 2 further comprising one or
more of calcium carbonate, calcium oxide, talc, carbon black,
textile fibers, glass particles or fibers, aramid pulp, boron
fibers, carbon fibers, a mineral silicate, mica, powdered quartz,
hydrated aluminum oxide, bentonite, wollastonite, kaolin, fumed
silica, silica aerogel, a polyurea compound, a polyamide compound,
or aluminum powder, iron powder or microballoons having an average
particle size of up to 200 microns and density of up to 0.2
g/cc.
13. A method comprising applying the structural adhesive claim 1 to
the surfaces of two members, and curing the structural adhesive to
form an adhesive bond between the two members.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Application Ser. No. 61/427,192 filed Dec. 26, 2010.
[0002] This invention relates to an epoxy-based structural adhesive
containing a chain-extended elastomeric toughener having terminal
isocyanate groups blocked with a phenol, polyphenol or aminophenol
compound.
[0003] Epoxy resin based adhesives are used in many applications.
In the automotive industry, epoxy resin adhesives are used in many
bonding applications, including metal-metal bonding in frame and
other structures in automobiles. Some of these adhesives must
strongly resist failure during vehicle collision situations.
Adhesives of this type are sometimes referred to as "crash durable
adhesives", or "CDAs".
[0004] In order to obtain the good balance of properties that are
needed to meet automotive performance requirements, epoxy adhesives
are often formulated with various rubbers and/or "tougheners". The
tougheners have blocked functional groups which, under the
conditions of the curing reaction, can become de-blocked and react
with an epoxy resin. Tougheners of this type are described, for
example, in U.S. Pat. No. 5,202,390, U.S. Pat. No. 5,278,257, WO
2005/118734, U. S. Published Patent Application No. 2005/0070634,
U. S. Published Patent Application No. 2005/0209401, U. S.
Published Patent Application 2006/0276601, EP-A-0 308 664, EP-A 1
728 825, EP-A 1 896 517, EP-A 1 916 269, EP-A 1 916 270, EP-A 1 916
272 and EP-A-1 916 285.
[0005] Various types of groups have been suggested for blocking the
isocyanate groups of the prepolymer. Among these are various
phenols, polyphenols and aminophenols, as described, for example,
in U.S. Pat. No. 5,278,257 to Mulhaupt. EP-A 1 916 269 describes a
toughener containing both epoxy and phenol blocking groups. Phenol,
polyphenol and aminophenol materials constitute a very suitable
class of capping groups, because cured adhesives made using
tougheners capped with these groups tend to have very good
properties. As described in U. S. Published Patent Application No.
2005/0209401, adhesives containing such tougheners often exhibit,
when cured, very good impact peel strengths at low temperatures. A
problem with tougheners capped with these groups is that the
adhesive composition containing them is not sufficiently
storage-stable. See, e.g., EP 1,498 441 A1 and WO 2007/003650).
These adhesives prematurely begin to advance in molecular weight.
Because of this, the adhesive can thicken or even gel to the point
that it cannot be dispensed properly, does not adhere well to the
substrate or form a strong cured adhesive layer, or otherwise is no
longer usable. Since these adhesives are usually packaged up to
several months before they are ultimately used, a lack of storage
stability represents a very serious practical problem. It is
desirable to provide a one-part adhesive that contains a toughener
capped with phenol, polyphenol or aminophenol groups, which
adhesive has good storage stability and retains good adhesive
properties.
[0006] This invention is a one-part structural adhesive comprising:
[0007] A) at least one epoxy resin; [0008] B) a reactive
elastomeric toughener containing capped isocyanate groups; and
[0009] C) one or more epoxy curing agents; wherein the elastomeric
toughener is formed by [0010] a) reacting an excess of a
polyisocyanate with a 300-3000 equivalent weight polyol or with a
mixture of a 300-3000 equivalent weight polyol and a branching
agent, to form an isocyanate-terminated prepolymer; [0011] b)
reacting the isocyanate-terminated prepolymer with a chain extender
to produce a chain extended, isocyanate-terminated prepolymer, and
[0012] c) capping at least 90% of the terminal isocyanate groups of
the chain extended, isocyanate-terminated prepolymer with a capping
agent selected from a monophenol, a polyphenol or an
aminophenol.
[0013] Surprisingly, the adhesive of the invention is significantly
more storage-stable than an otherwise like adhesive which contains
a phenol, polyphenol or aminophenol toughener that is not chain
extended. The cured adhesive has very good properties, notably good
lap shear and impact peel strength. Lap shear and impact peel
strengths are often, and unexpectedly, significantly higher than
when the toughener is not chain extended.
[0014] The invention is also a method comprising applying the
foregoing structural adhesive to the surfaces of two members, and
curing the structural adhesive to form an adhesive bond between the
two members. At least one and preferably both of the members are
metals.
[0015] The toughener of the invention is elastomeric, contains
urethane and/or urea groups and has terminal isocyanate groups, at
least 90% of which are capped with a phenol, polyphenol or
aminophenol compound.
[0016] Preferably, at least 95% and more preferably at least 98% of
the isocyanate groups on the reactive toughener(s) are capped with
the phenol, polyphenol or aminophenol compound. All of the
isocyanate groups may be capped with the phenol, polyphenol or
aminophenol compound. Up to 10%, preferably not more than 5% and
still more preferably not more than 2% of the isocyanate groups may
be capped with another capping agent. It is preferred that
essentially none (such as 1% or fewer) of those capped isocyanate
groups are capped with an epoxy-functional capping group, (i.e., a
capping group that imparts epoxide functionality to the capped
prepolymer) or a ketoxime capping group. Fewer than 5%, preferably
fewer than 1% of the isocyanate groups may remain uncapped.
[0017] The toughener is made in a process that includes the steps
of forming an isocyanate-terminated prepolymer, chain-extending the
prepolymer and then capping the chain-extended prepolymer.
[0018] The prepolymer is formed by reacting an excess of a
polyisocyanate with a 300-3000 equivalent weight polyol or with a
mixture of a 300-3000 equivalent weight polyol and a branching
agent, to form an isocyanate-terminated prepolymer.
[0019] The 300-3000 equivalent weight polyol is preferably a
polyether polyol or a hydroxyl-terminated butadiene homopolymer or
copolymer. The polyol preferably has 2-3, more preferably 2,
hydroxyl groups per molecule.
[0020] The branching agent, for purposes of this invention, is a
polyol or polyamine compounds having a molecular weight of up to
599, preferably from 50 to 500, and at least three hydroxyl,
primary amino and/or secondary amino groups per molecule. If used
at all, branching agents generally constitute no more than 10%,
preferably no more than 5% and still more preferably no more than
2% of the combined weight of the branching agent and 300-3000
equivalent weight polyol. Examples of branching agents include
polyols such as trimethylolpropane, glycerin, trimethylolethane,
ethylene glycol, diethylene glycol, propylene glycol, dipropylene
glycol, sucrose, sorbitol, pentaerythritol, triethanolamine,
diethanolamine and the like, as well as alkoxylates thereof having
a molecular weight of up to 599, especially up to 500.
[0021] The polyisocyanate may be an aromatic polyisocyanate, but it
is preferably an aliphatic polyisocyanate such as isophorone
diisocyanate, 1,6-hexamethylene diisocyanate, hydrogenated toluene
diisocyanate, hydrogenated methylene diphenylisocyanate
(H.sub.12MDI), and the like.
[0022] An excess of the polyisocyanate compound is used, so that
essentially all of the isocyanate reactive groups of the 300-3000
equivalent weight polyol and branching agent (if any) are consumed
and the resulting prepolymer is terminated in isocyanate groups. It
is generally preferred to combine at least 1.5 equivalents of the
polyisocyanate per equivalent of the isocyanate-reactive materials
(i.e., the 300-3000 molecular weight polyol and the branching
agent, if any), as such a ratio minimizes the formation of
materials that are advanced in molecular weight. More preferably,
from 1.5 to 2.5 equivalents of the polyisocyanate are provided per
equivalent of the isocyanate-reactive materials.
[0023] The prepolymer-forming reaction is performed by mixing the
starting materials and heating them, preferably in the presence of
a catalyst for the reaction of isocyanate groups with hydroxyl
groups. The reaction mixture will typically be from 60 to
120.degree. C., and the reaction is continued until a constant
isocyanate content is obtained, indicating that all of the
isocyanate-reactive groups in the starting materials have been
consumed.
[0024] The resulting prepolymer preferably has an isocyanate
content of from 0.5 to 7% by weight, more preferably from 1 to 6%
by weight and even more preferably from 1.5 to 5% by weight. In
terms of isocyanate equivalent weight, a preferred range is from
700 to 8400, a more preferred range is from 840 to 4200, and an
even more preferred range is from 1050 to 2800. The prepolymer
suitably contains, on average, from about 1.5, preferably from
about 2.0, to about 4, preferably to about 3, and more preferably
to about 2.5 isocyanate groups per molecule.
[0025] The prepolymer is then reacted with a chain extender to
produce a chain extended, isocyanate-terminated prepolymer. Chain
extenders, for purposes of this invention, are polyol or polyamine
compounds having a molecular weight of up to 749, preferably from
50 to 500, and two hydroxyl, primary amino and/or secondary amino
groups per molecule. Examples of suitable chain extenders include
aliphatic diols such as ethylene glycol, diethylene glycol,
triethylene glycol, propylene glycol, dipropylene glycol,
tripropylene glycol, 1,4-butanediol, 1,6-hexane diol,
cyclohexanedimethanol and the like; aliphatic or aromatic diamines
such as ethylene diamine, piperazine, aminoethylpiperazine,
phenylene diamine, diethyltoluenediamine and the like, and
compounds having two phenolic hydroxyl groups such resorcinol,
catechol, hydroquinone, bisphenol, bisphenol A, bisphenol AP
(1,1-bis(4-hydroxylphenyl)-1-phenyl ethane), bisphenol F, bisphenol
K, bisphenol M, tetramethylbiphenol and o,o' -diallyl-bisphenol A,
and the like. Among these, the compounds having two phenolic
hydroxyl groups are preferred.
[0026] The chain extension reaction is performed in the same
general manner as the prepolymer-forming reaction. Enough of the
prepolymer is mixed with the chain extender to provide at least two
equivalents of isocyanate groups per equivalent of
isocyanate-reactive groups contributed by the chain extender. Up to
4 or more, preferably up to 3 and more preferably up to 2.5
equivalents of isocyanate groups may be provided per equivalent of
isocyanate-reactive groups contributed by the chain extender. An
especially preferred amount is from 2 to 2.25 equivalents of
isocyanate groups per equivalent of isocyanate-reactive groups
contributed by the chain extender. As before, the reaction is
preferably performed at an elevated temperature (such as 60 to
120.degree. C.) until a constant isocyanate content is achieved
(indicating that all of the isocyanate-reactive groups have been
consumed).
[0027] The chain-extended prepolymer is terminated with isocyanate
groups. The chain-extended prepolymer will include molecules that
correspond to a coupling of the starting prepolymer with the chain
extender. If more than 2 equivalents of prepolymer are reacted per
equivalent of chain extender, the chain-extended prepolymer will
also contain some quantity of prepolymer molecules that have not
been extended. The chain-extended prepolymer may also contain a
small amount of higher molecular weight reaction products. The
chain-extended prepolymer preferably has an isocyanate content of
from 0.25 to 3% by weight, more preferably from 0.5 to 2.5% by
weight and even more preferably from 0.75 to 2% by weight. In terms
of isocyanate equivalent weight, a preferred range is from 1400 to
17,000, a more preferred range is from 1680 to 8500, and an even
more preferred range is from 2100 to 5700. The chain-extended
prepolymer suitably contains, on average, from about 1.5,
preferably from about 2.0, to about 6, preferably to about 4, more
preferably to about 3 and still more preferably to about 2.5,
isocyanate groups per molecule. An especially preferred prepolymer
contains an average of from 1.9 to 2.2 isocyanate groups per
molecule.
[0028] At least 90% of the isocyanate groups of the chain-extended
prepolymer are then capped by reaction with a monophenol, a
polyphenol or an aminophenol to form the toughener. Examples of
suitable monophenol compounds include, for example, phenol, alkyl
phenols which contain one or more alkyl groups that each may
contain from 1 to 30 carbon atoms, naphthol, or a halogenated
phenol or naphthol. Suitable polyphenols contain two or more,
preferably two, phenolic hydroxyl groups per molecule. Examples of
suitable polyphenols include resorcinol, catechol, hydroquinone,
bisphenol, bisphenol A, bisphenol AP
(1,1-bis(4-hydroxylphenyl)-1-phenyl ethane), bisphenol F, bisphenol
K, bisphenol M, tetramethylbiphenol and o,o' -diallyl-bisphenol A,
as well as halogenated derivatives thereof. Suitable aminophenols
are compounds that contain at least one primary or secondary amino
group and at least one phenolic hydroxyl group. The amino group is
preferably bound to a carbon atom of an aromatic ring. Examples of
suitable aminophenols include 2-aminophenol, 4-aminophenol, various
aminonaphtols, and the like.
[0029] Enough of the phenol, polyphenol or aminophenol compound is
provided to cap at least 90%, preferably at least 95%, more
preferably at least 98%, up to 100% of the isocyanate groups of the
chain extended prepolymer. It is possible to use a mixture of the
phenol, polyphenol or aminophenol compound with up to 10 mol-% of
another capping agent, such as a monoamine, a ketoxime, an
epoxy-functional compound, and the like. However, it is preferred
not to employ such other capping agent.
[0030] The capping reaction can be performed under the general
conditions described already with respect to the prepolymer-forming
and chain-extension reactions, i.e., by combining the materials in
the stated ratios and heating to 60-120.degree. C., optionally in
the presence of a catalyst for the reaction of isocyanate groups
with phenol and/or amino groups, as the case may be. The reaction
is continued until the isocyanate content is reduced to a constant
value, which is preferably less than 0.1% by weight.
[0031] The resulting toughener suitably has a number average
molecular weight from at least 3000, preferably at least 4,000, to
about 35,000, preferably to about 20,000 and more preferably to
about 15,000, measured by GPC, taking into account only those peaks
that represent molecular weights of 1000 or more.
[0032] The polydispersity (ratio of weight average molecular weight
to number average molecular weight) is suitably from about 1 to
about 4, preferably from about 1.5 to 2.5. The toughener suitably
contains, on average, from about 1.5, preferably from about 2.0, to
about 6, preferably to about 4, more preferably to about 3 and
still more preferably to about 2.5, capped isocyanate groups per
molecule. An especially preferred prepolymer contains an average of
from 1.9 to 2.2 capped isocyanate groups per molecule.
[0033] The toughener should constitute at least 5 weight percent of
the adhesive composition. Better results are typically seen when
the amount of toughener is at least 8 weight percent or at least 10
weight percent. The toughener may constitute up to 45 weight
percent thereof, preferably up to 30 weight percent and more
preferably up to 25 weight percent. The amount of toughener that is
needed to provide good properties, particularly good low
temperature properties, in any particular adhesive composition may
depend somewhat on the other components of the composition, and may
depend somewhat on the molecular weight of the toughener.
[0034] The structural adhesive contains at least one epoxy resin.
It is preferred that at least a portion of the epoxy resin is not
rubber-modified, by which it is meant specifically that the epoxy
resin is not chemically bonded to a rubber. A non-rubber-modified
epoxy resin may be added to the structural adhesive as a separate
component, i.e., as something other than a component of a
rubber-modified epoxy resin product or a part of a dispersion of a
core-shell rubber, as described below. In some embodiments of the
invention, a core-shell rubber product is used, which may be
dispersed in some quantity of epoxy resin. Some amount of
non-rubber-modified epoxy resin may be brought into the structural
adhesive in that manner. In other embodiments, a rubber-modified
epoxy resin product used as a component of the structural adhesive
may contain a certain amount of epoxy resin which is not reacted
with the rubber (and thus is not rubber-modified). Some
non-rubber-modified epoxy resin may be brought into the adhesive in
that manner as well.
[0035] A wide range of epoxy resins can be used as a
non-rubber-modified epoxy resin, including those described at
column 2 line 66 to column 4 line 24 of U.S. Pat. No. 4,734,332,
incorporated herein by reference. The epoxy resin should have an
average of at least 2.0 epoxide groups per molecule.
[0036] Suitable epoxy resins include the diglycidyl ethers of
polyhydric phenol compounds such as resorcinol, catechol,
hydroquinone, biphenol, bisphenol A, bisphenol AP
(1,1-bis(4-hydroxylphenyl)-1-phenyl ethane), bisphenol F, bisphenol
K and tetramethylbiphenol; diglycidyl ethers of aliphatic glycols
and polyether glycols such as the diglycidyl ethers of C.sub.2-24
alkylene glycols and poly(ethylene oxide) or poly(propylene oxide)
glycols; polyglycidyl ethers of phenol-formaldehyde novolac resins
(epoxy novolac resins), alkyl substituted phenol-formaldehyde
resins, phenol-hydroxybenzaldehyde resins,
cresol-hydroxybenzaldehyde resins, dicyclopentadiene-phenol resins
and dicyclopentadiene-substituted phenol resins; and any
combination of any two or more thereof.
[0037] Suitable epoxy resins include diglycidyl ethers of bisphenol
A resins such as are sold by Dow Chemical under the designations
D.E.R..RTM. 330, D.E.R..RTM. 331, D.E.R..RTM. 332, D.E.R..RTM. 383,
D.E.R. 661 and D.E.R..RTM. 662 resins.
[0038] Commercially available diglycidyl ethers of polyglycols that
are useful include those sold as D.E.R..RTM. 732 and D.E.R..RTM.
736 by Dow Chemical.
[0039] Epoxy novolac resins can be used. Such resins are available
commercially as D.E.N..RTM. 354, D.E.N..RTM. 431, D.E.N..RTM. 438
and D.E.N..RTM. 439 from Dow Chemical.
[0040] Other suitable non-rubber-modified epoxy resins are
cycloaliphatic epoxides. A cycloaliphatic epoxide includes a
saturated carbon ring having an epoxy oxygen bonded to two vicinal
atoms in the carbon ring, as illustrated by the following structure
III:
##STR00001##
wherein R is an aliphatic, cycloaliphatic and/or aromatic group and
n is a number from 1 to 10, preferably from 2 to 4. When n is 1,
the cycloaliphatic epoxide is a monoepoxide. Di- or polyepoxides
are formed when n is 2 or more. Mixtures of mono-, di- and/or
polyepoxides can be used. Cycloaliphatic epoxy resins as described
in U.S. Patent No. 3,686,359, incorporated herein by reference, may
be used in the present invention. Cycloaliphatic epoxy resins of
particular interest are
(3,4-epoxycyclohexyl-methyl)-3,4-epoxy-cyclohexane carboxylate,
bis-(3,4-epoxycyclohexyl)adipate, vinylcyclohexene monoxide and
mixtures thereof.
[0041] Other suitable epoxy resins include oxazolidone-containing
compounds as described in U.S. Pat. No. 5,112,932. In addition, an
advanced epoxy-isocyanate copolymer such as those sold commercially
as D.E.R. 592 and D.E.R. 6508 (Dow Chemical) can be used.
[0042] The non-rubber-modified epoxy resin preferably is a
bisphenol-type epoxy resin or mixture thereof with up to 10 percent
by weight of another type of epoxy resin. The most preferred epoxy
resins are bisphenol-A based epoxy resins and bisphenol-F based
epoxy resins. These can have average epoxy equivalent weights of
from about 170 to 600 or more, preferably from 225 to 400.
[0043] An especially preferred non-rubber-modified epoxy resin is a
mixture of at least one diglycidyl ether of a polyhydric phenol,
preferably bisphenol-A or bisphenol-F, having an epoxy equivalent
weight of from 170 to 299, especially from 170 to 225, and at least
one second diglycidyl ether of a polyhydric phenol, again
preferably bisphenol-A or bisphenol-F, this one having an epoxy
equivalent weight of at least 300, preferably from 310 to 600. The
proportions of the resins are preferably such that the mixture has
an average epoxy equivalent weight of from 225 to 400. The mixture
optionally may also contain up to 20%, preferably up to 10%, of one
or more other non-rubber-modified epoxy resins.
[0044] A non-rubber-modified epoxy resin preferably will constitute
at least about 25 weight percent of the structural adhesive, more
preferably at least about 30 weight percent, and still more
preferably at least about 35 part weight percent. The
non-rubber-modified epoxy resin may constitute up to about 70
weight percent of the structural adhesive, more preferably up to
about 50 weight percent. These amounts include any
non-rubber-modified epoxy resin that may be brought into the
composition with other components that contain an epoxy resin such
as, for example, a diluent or excess, unreacted reagent.
[0045] The structural adhesive also contains a curing agent. The
curing agent is selected together with any catalysts such that the
adhesive cures rapidly when heated to a temperature of 80.degree.
C. or greater, preferably 140.degree. C. or greater, but cures very
slowly if at all at room temperature (-22.degree. C.) and
temperatures up to at least 50.degree. C. Suitable curing agents
include materials such as boron trichloride/amine and boron
trifluoride/amine complexes, dicyandiamide, melamine,
diallylmelamine, guanamines such as acetoguanamine and
benzoguanamine, aminotriazoles such as 3-amino-1,2,4-triazole,
hydrazides such as adipic dihydrazide, stearic dihydrazide,
isophthalic dihydrazide, semicarbazide, cyanoacetamide, and
aromatic polyamines such as diaminodiphenylsulphones. The use of
dicyandiamide, isophthalic acid dihydrazide, adipic acid
dihydrazide and/or 4,4'-diaminodiphenylsulphone is particularly
preferred.
[0046] The curing agent is used in an amount sufficient to cure the
composition. Typically, enough of the curing agent is provided to
consume at least 80% of the epoxide groups present in the
composition. A large excess over that amount needed to consume all
of the epoxide groups is generally not needed. Preferably, the
curing agent constitutes at least about 1.5 weight percent of the
structural adhesive, more preferably at least about 2.5 weight
percent and even more preferably at least 3.0 weight percent. The
curing agent preferably constitutes up to about 15 weight percent
of the structural adhesive composition, more preferably up to about
10 weight percent, and most preferably up to about 8 weight
percent.
[0047] The structural adhesive will in most cases contain a
catalyst to promote the cure of the adhesive, i.e., the reaction of
epoxy groups with epoxide-reactive groups on the curing agent and
other components of the adhesive. The catalyst is preferably
encapsulated or otherwise a latent type which becomes active only
upon exposure to elevated temperatures. Among preferred epoxy
catalysts are ureas such as p-chlorophenyl-N,N-dimethylurea
(Monuron), 3-phenyl-1,1-dimethylurea (Phenuron),
3,4-dichlorophenyl-N,N-dimethylurea (Diuron),
N-(3-chloro-4-methylphenyfi-N',N'-dimethylurea (Chlortoluron),
tert-acryl- or alkylene amines like benzyldimethylamine,
2,4,6-tris(dimethylaminomethyl)phenol, piperidine or derivatives
thereof, various aliphatic urea compounds such as are described in
EP 1 916 272; C.sub.1-C.sub.12 alkylene imidazole or
N-arylimidazoles, such as 2-ethyl-2-methylimidazol, or
N-butylimidazol and 6-caprolactam. A preferred catalyst is
2,4,6-tris(dimethylaminomethyl)phenol integrated into a
poly(p-vinylphenol) matrix (as described in European patent EP 0
197 892), or 2,4,6-tris(dimethylaminomethyl)phenol integrated into
a novolac resin, including those described in U.S. Pat. No.
4,701,378.
[0048] Preferably, the catalyst is present in an amount of at least
about 0.1 weight percent of the structural adhesive, and more
preferably at least about 0.5 weight percent. Preferably, the
catalyst constitutes up to about 4 weight percent of the structural
adhesive, more preferably up to about 1.5 weight percent, and most
preferably up to about 0.9 weight percent.
[0049] The structural adhesive of the invention may include at
least one liquid rubber-modified epoxy resin. A rubber-modified
epoxy resin for purposes of this invention is a reaction product of
an epoxy resin and at least one liquid rubber that has
epoxide-reactive groups, such as amino or preferably carboxyl
groups. The resulting adduct has reactive epoxide groups which
allow the adduct to react further when the structural adhesive is
cured. It is preferred that at least a portion of the liquid rubber
has a glass transition temperature (T.sub.g) of -40.degree. C. or
lower, especially -50.degree. C. or lower. Preferably, each of the
rubbers (when more than one is used) has a glass transition
temperature of -25.degree. C. or lower. The rubber T.sub.g, may be
as low as -100.degree. C. or even lower.
[0050] The liquid rubber is preferably a homopolymer or copolymer
of a conjugated diene, especially a diene/nitrile copolymer. The
conjugated diene rubber is preferably butadiene or isoprene, with
butadiene being especially preferred. The preferred nitrile monomer
is acrylonitrile. Preferred copolymers are butadiene-acrylonitrile
copolymers. The rubbers preferably contain, in the aggregate, no
more than 30 weight percent polymerized unsaturated nitrile
monomer, and preferably no more than about 26 weight percent
polymerized nitrile monomer.
[0051] The rubber preferably contains from about 1.5, more
preferably from about 1.8, to about 2.5, more preferably to about
2.2, of epoxide-reactive terminal groups per molecule, on average.
Carboxyl-terminated rubbers are preferred. The molecular weight
(M.sub.n) of the rubber is suitably from about 2000 to about 6000,
more preferably from about 3000 to about 5000.
[0052] Suitable carboxyl-functional butadiene and
butadiene/acrylonitrile rubbers are commercially available from
Noveon under the tradenames Hycar.RTM. 2000X162 carboxyl-terminated
butadiene homopolymer, Hycar.RTM. 1300X31, Hycar.RTM. 1300X8,
Hycar.RTM. 1300X13, Hycar.RTM. 1300X9 and Hycar.RTM. 1300X18
carboxyl-terminated butadiene/acrylonitrile copolymers. A suitable
amine-terminated butadiene/acrylonitrile copolymer is sold under
the tradename Hycar.RTM. 1300X21.
[0053] Other suitable rubber materials include amine-terminated
polyethers, fatty acids (which may be dimerized or oligomerized),
and elastomeric polyester.
[0054] The rubber is formed into an epoxy-terminated adduct by
reaction with an excess of an epoxy resin. Enough of the epoxy
resin is provided to react with substantially all of the
epoxide-reactive groups on the rubber and to provide free epoxide
groups on the resulting adduct without significantly advancing the
adduct to form high molecular weight species. A ratio of at least
two equivalents of epoxy resin per equivalent of epoxy-reactive
groups on the rubber is preferred. More preferably, enough of the
epoxy resin is used that the resulting product is a mixture of the
adduct and some free epoxy resin; any such free epoxy resin counts
towards the non-rubber-modified epoxy resin content of the
adhesive. Typically, the rubber and an excess of the polyepoxide
are mixed together with a polymerization catalyst and heated to a
temperature of about 100 to about 250.degree. C. in order to form
the adduct. Suitable catalysts include those described before.
Preferred catalysts for forming the rubber-modified epoxy resin
include phenyl dimethyl urea and triphenyl phosphine.
[0055] A wide variety of epoxy resins can be used to make the
rubber-modified epoxy resin, including any of those described
above. The epoxy resin may be the same or different from that used
to prepare the rubber-modified epoxy resin. Preferred polyepoxides
are liquid or solid glycidyl ethers of a bisphenol such as
bisphenol A or bisphenol F. Halogenated, particularly brominated,
resins can be used to impart flame retardant properties if desired.
Liquid epoxy resins (such as DER.TM. 330 and DER.TM. 331 resins,
which are diglycidyl ethers of bisphenol A available from The Dow
Chemical Company) are especially preferred for ease of
handling.
[0056] The rubber-modified epoxy resin(s), if present at all, may
constitute about 1 weight percent of the structural adhesive or
more, preferably at least about 2 weight percent. The
rubber-modified epoxy resin may constitute up to about 25 weight
percent of the structural adhesive, more preferably up to about 20
weight percent, and even more preferably up to about 15 weight
percent.
[0057] The structural adhesive of the invention may contain one or
more core-shell rubbers. The core-shell rubber is a particulate
material having a rubbery core. The rubbery core preferably has a
T.sub.g of less than -20.degree. C., more preferably less than
-50.degree. C. and even more preferably less than -70.degree. C.
The T.sub.g of the rubbery core may be well below -100.degree. C.
The core-shell rubber also has at least one shell portion that
preferably has a T.sub.g of at least 50.degree. C. By "core", it is
meant an internal portion of the core-shell rubber. The core may
form the center of the core-shell particle, or an internal shell or
domain of the core-shell rubber. A shell is a portion of the
core-shell rubber that is exterior to the rubbery core. The shell
portion (or portions) typically forms the outermost portion of the
core-shell rubber particle. The shell material is preferably
grafted onto the core or is crosslinked or both. The rubbery core
may constitute from 50 to 95%, especially from 60 to 90%, of the
weight of the core-shell rubber particle.
[0058] The core of the core-shell rubber may be a polymer or
copolymer of a conjugated diene such as butadiene, or a lower alkyl
acrylate such as n-butyl-, ethyl-, isobutyl- or
2-ethylhexylacrylate. The core polymer may in addition contain up
to 20% by weight of other copolymerized monounsaturated monomers
such as styrene, vinyl acetate, vinyl chloride, methyl
methacrylate, and the like. The core polymer is optionally
crosslinked The core polymer optionally contains up to 5% of a
copolymerized graft-linking monomer having two or more sites of
unsaturation of unequal reactivity, such as diallyl maleate,
monoallyl fumarate, allyl methacrylate, and the like, at least one
of the reactive sites being non-conjugated.
[0059] The core polymer may also be a silicone rubber. These
materials often have glass transition temperatures below
-100.degree. C. Core-shell rubbers having a silicone rubber core
include those commercially available from Wacker Chemie, Munich,
Germany, under the trade name Genioperl.TM.
[0060] The shell polymer, which is optionally chemically grafted or
crosslinked to the rubber core, is preferably polymerized from at
least one lower alkyl methacrylate such as methyl-, ethyl- or
t-butyl methacrylate. Homopolymers of such methacrylate monomers
can be used. Further, up to 40% by weight of the shell polymer can
be formed from other monovinylidene monomers such as styrene, vinyl
acetate, vinyl chloride, methyl acrylate, ethyl acrylate, butyl
acrylate, and the like. The molecular weight of the grafted shell
polymer is generally between 20,000 and 500,000.
[0061] A preferred type of core-shell rubber has reactive groups in
the shell polymer which can react with an epoxy resin or an epoxy
resin hardener. Glycidyl groups such as are provided by monomers
such as glycidyl methacrylate are suitable.
[0062] A particularly preferred type of core-shell rubber is of the
type described in EP 1 632 533 A1. Core-shell rubber particles as
described in EP 1 632 533 A1 include a crosslinked rubber core, in
most cases being a crosslinked copolymer of butadiene, and a shell
which is preferably a copolymer of styrene, methyl methacrylate,
glycidyl methacrylate and optionally acrylonitrile. The core-shell
rubber is preferably dispersed in a polymer or an epoxy resin, also
as described in EP 1 632 533 A1.
[0063] Preferred core-shell rubbers include those sold by Kaneka
Corporation under the designation Kaneka Kane Ace, including Kaneka
Kane Ace MX 156 and Kaneka Kane Ace MX 120 core-shell rubber
dispersions. The products contain the core-shell rubber particles
pre-dispersed in an epoxy resin, at a concentration of
approximately 25%. The epoxy resin contained in those products will
form all or part of the non-rubber-modified epoxy resin component
of the structural adhesive of the invention.
[0064] The core-shell rubber particles can constitute from 0 to 15
weight percent of the structural adhesive.
[0065] The total rubber content of the structural adhesive of the
invention can range from as little as 0 weight percent to as high
as 30 weight percent. A preferred rubber content for a crash
durable adhesive is from 1 weight percent to as much as 20 weight
percent, preferably from 2 to 15 weight percent and more preferably
from 4 to 15 weight percent.
[0066] Total rubber content is calculated for purposes of this
invention by determining the weight of core-shell rubber (if any),
plus the weight contributed by the liquid rubber portion of any
rubber-modified epoxy resin as may be used. No portion of the
elastomeric toughener is considered in calculating total rubber
content. In each case, the weight of unreacted
(non-rubber-modified) epoxy resins and/or other carriers, diluents,
dispersants or other ingredients that may be contained in a
core-shell rubber product or rubber-modified epoxy resin is not
included. The weight of the shell portion of the core-shell rubber
is counted as part of the total rubber content for purposes of this
invention.
[0067] The structural adhesive of the invention may contain various
other optional components.
[0068] The speed and selectivity of the cure can be enhanced and
adjusted by incorporating a monomeric or oligomeric, addition
polymerizable, ethylenically unsaturated material into the
structural adhesive. This material should have a molecular weight
of less than about 1500. This material may be, for example, an
acrylate or methacrylate compound, an unsaturated polyester, a
vinyl ester resin, or an epoxy adduct of an unsaturated polyester
resin. A free radical initiator can be included in the structural
adhesive as well, in order to provide a source of free radicals to
polymerize this material. The inclusion of an ethylenically
unsaturated material of this type provides the possibility of
effecting a partial cure of the structural adhesive through
selective polymerization of the ethylenic unsaturation.
[0069] At least one filler, rheology modifier and/or pigment is
preferably present in the structural adhesive. These can perform
several functions, such as (1) modifying the rheology of the
adhesive in a desirable way, (2) reducing overall cost per unit
weight, (3) absorbing moisture or oils from the adhesive or from a
substrate to which it is applied, and/or (4) promoting cohesive,
rather than adhesive, failure. Examples of these materials include
calcium carbonate, calcium oxide, talc, carbon black, textile
fibers, glass particles or fibers, aramid pulp, boron fibers,
carbon fibers, mineral silicates, mica, powdered quartz, hydrated
aluminum oxide, bentonite, wollastonite, kaolin, fumed silica,
silica aerogel, polyurea compounds, polyamide compounds or metal
powders such as aluminum powder or iron powder. Another filler of
particular interest is a microballoon having an average particle
size of up to 200 microns and density of up to 0.2 g/cc. The
particle size is preferably about 25 to 150 microns and the density
is preferably from about 0.05 to about 0.15 g/cc. Heat expandable
microballoons which are suitable for reducing density include those
commercially available from Dualite Corporation under the trade
designation DualiteTM, and those sold by Akzo Nobel under the trade
designation Expancel.TM..
[0070] Fillers, pigment and rheology modifiers are preferably are
used in an aggregate amount of about 2 parts per hundred parts of
adhesive composition or greater, more preferably about 5 parts per
hundred parts of adhesive composition or greater. They preferably
are present in an amount of up to about 25 weight percent of the
structural adhesive, more preferably up to about 20 weight percent,
and most preferably up to about 15 weight percent.
[0071] The structural adhesive can further contain other additives
such as dimerized fatty acids, diluents, plasticizers, extenders,
pigments and dyes, fire-retarding agents, thixotropic agents,
expanding agents, flow control agents, adhesion promoters and
antioxidants. Suitable expanding agents include both physical and
chemical type agents. The adhesive may also contain a thermoplastic
powder such as polyvinylbutyral or a polyester polyol, as described
in WO 2005/118734.
[0072] The adhesive composition of the invention is surprisingly
storage-stable. The viscosity of the newly-formulated adhesive
composition is usually somewhat higher than what is seen when the
toughener is not chain extended. However, the adhesive composition
of the invention thereafter builds viscosity at a significantly
slower rate upon storage. The rate of viscosity build is often such
that after several weeks of storage, the viscosity of the adhesive
of this invention is often equal to or even lower than that of the
conventional adhesive that contains the non-chain extended
toughener.
[0073] The amount of time at which the adhesive of the invention
can be aged yet still be usable generally will exceed that of an
otherwise like adhesive that contains a toughener that is not
chain-extended. This advantage is seen despite the known tendency
(as described, for example, in EP 1 498 441 and WO 2007/003650) of
adhesives that contain phenol, polyphenol or aminophenol capped
tougheners to have poor storage stability.
[0074] The adhesive composition can be applied by any convenient
technique. It can be applied cold or be applied warm if desired. It
can be applied by extruding it from a robot into bead form on the
substrate, it can be applied using mechanical application methods
such as a caulking gun, or any other manual application means, and
it can also be applied using jet spraying methods such as a
streaming method or a swirl technique. The swirl technique is
applied using an apparatus well known to one skilled in the art
such as pumps, control systems, dosing gun assemblies, remote
dosing devices and application guns. Preferably, the adhesive is
applied to the substrate using a jet spraying or streaming process.
Generally, the adhesive is applied to one or both substrates. The
substrates are contacted such that the adhesive is located between
the substrates to be bonded together.
[0075] After application, the structural adhesive is cured by
heating to a temperature at which the curing agent initiates cure
of the epoxy resin composition. Generally, this temperature is
about 80.degree. C. or above, preferably about 140.degree. C. or
above. Preferably, the temperature is about 220.degree. C. or less,
and more preferably about 180.degree. C. or less.
[0076] The adhesive of the invention can be used to bond a variety
of substrates together including wood, metal, coated metal,
aluminum, a variety of plastic and filled plastic substrates,
fiberglass and the like. In one preferred embodiment, the adhesive
is used to bond parts of automobiles together or to bond automotive
parts onto automobiles. Such parts can be steel, coated steel,
galvanized steel, aluminum, coated aluminum, plastic and filled
plastic substrates.
[0077] An application of particular interest is bonding of
automotive frame components to each other or to other components.
The frame components are often metals such as cold rolled steel,
galvanized metals, or aluminum. The components that are to be
bonded to the frame components can also be metals as just
described, or can be other metals, plastics, composite materials,
and the like.
[0078] Assembled automotive frame members are usually coated with a
coating material that requires a bake cure. The coating is
typically baked at temperatures that may range from 140.degree. C.
to over 200.degree. C. In such cases, it is often convenient to
apply the structural adhesive to the frame components, then apply
the coating, and cure the adhesive at the same time the coating is
baked and cured.
[0079] The adhesive composition once cured preferably has a Young's
modulus, at 23.degree. C., of about 1000 MPa as measured according
to DIN EN ISO 527-1. Preferably the Young's modulus is about 1200
MPa or greater, more preferably at least 1500 MPa. Preferably, the
cured adhesive demonstrates a tensile strength at 23.degree. C. of
about 20 MPa or greater, more preferably about 25 MPa or greater,
and most preferably about 35 MPa or greater. Preferably, the lap
shear strength of a 1.5 mm thick cured adhesive layer on cold
rolled steel (CRS) and a galvanized coated steed at 23.degree. C.
is about 15 MPa or greater, more preferably about 20 MPa or
greater, and most preferably about 25 MPa or greater measured
according to DIN EN 1465. The impact peel strength at 23.degree. C.
on those substrates is preferably at least 20 N/mm, more preferably
at least 30 N/mm and still more preferably at least 40 N/mm, when
measured according to the ISO 11343 wedge impact method.
[0080] The cured adhesive of the invention demonstrates excellent
adhesive properties (such as lap shear strength and impact peel
strength).
[0081] 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.
EXAMPLE 1 AND COMPARATIVE SAMPLE A
[0082] Toughener 1 is prepared by heating to 60.degree. C., under
nitrogen, 71.5 parts of a 2900 molecular weight
polytetrahydrofuran, and mixing the heated polyol at 60.degree. C.
with 8.3 parts 1,6-hexamethylene diisocyanate. After mixing for 2
minutes, 0.06 parts of dibutyl tindilaurate are added and the
mixture is allowed to react under nitrogen at 85.degree. C. for 45
minutes. The resulting prepolymer has an isocyanate content of
2.6%.
[0083] The prepolymer is then mixed with 3.8 parts of
o,o'-diallylbisphenol A and allowed to react for 40 minutes at
85.degree. C., again under nitrogen, to form a chain-extended
prepolymer having an isocyanate content of 1.2%.
[0084] The chain-extended prepolymer is then mixed with 16.3 parts
of o,o'-diallylbisphenol A under nitrogen. The mixture is allowed
to stir at 85.degree. C. for 25 minutes to cap the remaining
isocyanate groups on the chain-extended prepolymer. The isocyanate
content is reduced to zero.
[0085] The resulting toughener (Toughener 1) is degassed under
vacuum. It has a number average molecular weight (M.sub.n) of
10,200 and a weight average molecular weight (M.sub.w) of
24,000.
[0086] Toughener A is prepared by heating to 60.degree. C., under
nitrogen, 72.8 parts of a 2900 molecular weight
polytetrahydrofuran, and mixing the heated polyol at 60.degree. C.
with 7.6 parts 1,6-hexamethylene diisocyanate. After mixing for 2
minutes, 0.06 parts of dibutyl tindilaurate are added and the
mixture is allowed to react under nitrogen at 85.degree. C. for 45
minutes. The resulting prepolymer has an isocyanate content of
2.0%.
[0087] The prepolymer is then mixed with 19.6 parts of
o,o'-diallylbisphenol A under nitrogen. The mixture is allowed to
stir at 85.degree. C. for 20 minutes to cap the remaining
isocyanate groups on the chain-extended prepolymer. The isocyanate
content is reduced to zero. Toughener A has an M.sub.n of 8700 and
an M.sub.w of 17,500.
[0088] Adhesive Example 1 and Comparative Sample A are prepared by
blending ingredients as indicated in Table 1:
TABLE-US-00001 TABLE 1 Parts By Weight Comp. Component Ex. 1 Sample
A Epoxy resin blend.sup.1 55.6 55.6 Epoxy-terminated rubber.sup.2
13.2 13.2 Toughener 1 14.0 0 Toughener A 0 14.0 Versatic acid
monoepoxy ester.sup.3 1.2 1.2 Fillers/Colorants 5.5 5.5 Fumed
Silica 5.2 5.2 Accelerator.sup.4 1.0 1.0 Dicyandiamide 4.3 4.3
.sup.1A 63:37.0 by weight blend of liquid diglycidyl ethers of
bisphenol A having an epoxy equivalent weight of about 182-187 and
a solid reaction product of epichlorohydrin and bisphenol A having
an epoxy equivalent weight of 475-550. .sup.2An adduct of a
carboxyl-terminated butadiene-acrylonitrile rubber (Hycar .TM.
X13), bisphenol A based epoxy resin and cashew nut oil.
.sup.3Cardura .TM. E10, available from Christ Chemie. .sup.4Tris
(2,4,6-dimethylaminomethyl)phenol in a poly(vinylphenol)
matrix.
[0089] Storage stability is evaluated by storing duplicate samples
of each of Adhesive Example 1 and Comparative Sample A in sealed
containers under nitrogen for various periods of time, at various
temperatures from about 40.degree. C. to 60.degree. C. Viscosity
measurements are made at the start of testing and after storing at
the specified temperatures for the indicated periods of time.
Testing is performed on a Bohlin CS-50 rheometer and a 4.degree./20
mm plate/cone system. The samples are conditioned at 45.degree. C.
for five minutes. While holding the sample at this temperature, the
shear rate is increased from 0.1/second to 20/second over five
minutes, and then decreased back to 0.1/second at the same rate.
Viscosity is measured at a shear rate of 10/second on the up-swing.
Results are as indicated in Table 2.
TABLE-US-00002 TABLE 2 Storage Conditions (Temperature, time)
Initial Final Viscosity, Viscosity, Ratio, Pa s Pa s Final/Initial
% (10/sec) (10/sec) Viscosity Increase** 40.degree. C., 12 weeks
Ex. 1 220 342 1.55 55% Comp. Sample A* 154 451 2.93 193% 50.degree.
C., 6 weeks Ex. 1 220 516 2.35 135% Comp. Sample A* 154 622 4.04
304% 60.degree. C., 3 weeks Ex. 1 220 1355 6.16 516% Comp. Sample
A* 154 1437 9.33 833% *Not an example of the invention.
**Calculated as 100% .times. [(final viscosity - initial
viscosity)/initial viscosity].
[0090] As shown by the data in Table 2, the adhesive of the
invention has a somewhat higher initial viscosity than Comparative
Sample A, but is much more storage stable at each of the
temperatures tested. In all cases, the viscosity of Comparative
Sample A increases at a much faster rate than that of Example 1,
and in all cases reaches a higher absolute value at the end of the
test period. These results indicate that Adhesive Example 1 has a
longer shelf life over a range of temperatures than does
Comparative Sample A, despite having a higher starting
viscosity.
EXAMPLE 2 AND COMPARATIVE SAMPLE B
[0091] Toughener 2 is prepared by heating to 60.degree. C., under
nitrogen, 82.2 parts of a 2900 molecular weight
polytetrahydrofuran, and mixing the heated polyol at 60.degree. C.
with 9.5 parts 1,6-hexamethylene diisocyanate. After mixing for 2
minutes, 0.06 parts of dibutyl tindilaurate are added and the
mixture is allowed to react under nitrogen at 85.degree. C. for 45
minutes. The resulting prepolymer has an isocyanate content of
2.6%.
[0092] The prepolymer is then mixed with 4.4 parts of
o,o'-diallylbisphenol A and allowed to react for 40 minutes at
85.degree. C., again under nitrogen, to form a chain-extended
prepolymer having an isocyanate content of 1.2%.
[0093] The chain-extended prepolymer is then mixed with 3.8 parts
of o-allylphenol under nitrogen. The mixture is allowed to stir at
85.degree. C. for 25 minutes to cap the remaining isocyanate groups
on the chain-extended prepolymer. The isocyanate content is reduced
to zero. The resulting toughener (Toughener 2) is degassed under
vacuum. Toughener 2 has an M.sub.n of 9800 and an M.sub.w of
22,800.
[0094] Toughener B is prepared by heating to 60.degree. C., under
nitrogen, 85.2 parts of a 2900 molecular weight
polytetrahydrofuran, and mixing the heated polyol at 60.degree. C.
with 8.7 parts 1,6-hexamethylene diisocyanate. After mixing for 2
minutes, 0.06 parts of dibutyl tindilaurate are added and the
mixture is allowed to react under nitrogen at 85.degree. C. for 45
minutes. The resulting prepolymer has an isocyanate content of
2.0%.
[0095] The prepolymer is then mixed with 6.1 parts of o-allylphenol
under nitrogen. The mixture is allowed to stir at 85.degree. C. for
20 minutes to cap the remaining isocyanate groups on the
chain-extended prepolymer. The isocyanate content is reduced to
zero. Toughener B has an M.sub.n of 7100 and an M.sub.w of
13,500.
[0096] One-part, heat-activated adhesive formulations are prepared
from each of Toughener 2 and Toughener B. The formulation for
Example 2 is the same as shown in Table 1 for Example 1, except
that Toughener 1 is replaced by an equal amount of Toughener 2.
Comparative Sample B is the same as Comparative Sample A, except
that Toughener A is replaced by an equal amount of Toughener B.
[0097] Storage stability for Example 2 and Comparative Sample B are
evaluated in the same manner described before, with results as
indicated in Table 3.
TABLE-US-00003 TABLE 3 Storage Conditions (Temperature, time)
Initial Final Viscosity, Viscosity, Ratio, Pa s Pa s Final/Initial
% (10/sec) (10/sec) Viscosity Increase** 40.degree. C., 12 weeks
Ex. 2 152 281 1.85 85% Comp. Sample B* 96 213 2.22 122% 50.degree.
C., 6 weeks Ex. 2 152 384 2.53 153% Comp. Sample B* 96 280 2.92
192% 60.degree. C., 3 weeks Ex. 2 152 720 4.74 374% Comp. Sample B*
96 604 6.29 529% *Not an example of the invention. **Calculated as
100% .times. [(final viscosity - initial viscosity)/initial
viscosity].
[0098] At each temperature tested, Example 2 builds viscosity more
slowly than does Comparative Sample B.
EXAMPLE 3 AND COMPARATIVE SAMPLE C
[0099] Toughener 3 is prepared by heating to 60.degree. C., under
nitrogen, 67.6 parts of a 2900 molecular weight
polytetrahydrofuran, and mixing the heated polyol with 0.4
trimethylolpropane until homogeneous. At 60.degree. C., 9.3 parts
of 1,6-hexamethylene diisocyanate are added. After mixing for 2
minutes, 0.06 parts of dibutyl tindilaurate are added and the
mixture is allowed to react under nitrogen at 85.degree. C. for 45
minutes. The resulting prepolymer has an isocyanate content of
3.0%.
[0100] The prepolymer is then mixed with 4.3 parts of
o,o'-diallylbisphenol A and allowed to react for 40 minutes at
85.degree. C., again under nitrogen, to form a chain-extended
prepolymer having an isocyanate content of 1.4%.
[0101] The chain-extended prepolymer is then mixed with 18.4 parts
of o,o'-diallylbisphenol A under nitrogen. The mixture is allowed
to stir at 85.degree. C. for 25 minutes to cap the remaining
isocyanate groups on the chain-extended prepolymer. The isocyanate
content is reduced to zero. The resulting toughener (Toughener 3)
is degassed under vacuum. Toughener 3 has an M.sub.n of 10,900 and
an M.sub.w of 30,750.
[0102] Toughener C is prepared by heating to 60.degree. C., under
nitrogen, 70.9 parts of a 2900 molecular weight
polytetrahydrofuran, and mixing the heated polyol with 0.5 parts of
trimethylolpropane until homogeneous. At 60.degree. C., 8.2 parts
1,6-hexamethylene diisocyanate are added. After mixing for 2
minutes, 0.06 parts of dibutyl tindilaurate are added and the
mixture is allowed to react under nitrogen at 85.degree. C. for 45
minutes. The resulting prepolymer has an isocyanate content of
2.0%.
[0103] The prepolymer is then mixed with 20.3 parts of
o,o'-diallylbisphenol A under nitrogen. The mixture is allowed to
stir at 85.degree. C. for 20 minutes to cap the remaining
isocyanate groups on the chain-extended prepolymer. The isocyanate
content is reduced to zero. Toughener C has an M.sub.n of 9700 and
an M.sub.w of 27,200.
[0104] One-part, heat-activated adhesive formulations are prepared
from each of Toughener 3 and Toughener C. The formulation for
Example 3 is the same as shown in Table 1 for Example 1, except
that Toughener 1 is replaced by an equal amount of Toughener 3.
Comparative Sample C is the same as Comparative Sample A, except
that Toughener A is replaced by an equal amount of Toughener C.
[0105] Storage stability is evaluated for each of these as before,
with results being as indicated in Table 4.
TABLE-US-00004 TABLE 4 Storage Conditions (Temperature, time)
Initial Final Viscosity, Viscosity, Ratio, Pa s Pa s Final/Initial
% (10/sec) (10/sec) Viscosity Increase** 40.degree. C., 24 weeks
Ex. 3 274 1275 4.65 365% Comp. Sample C* 199 1704 8.56 756%
50.degree. C., 8 weeks Ex. 3 274 875 3.19 219% Comp. Sample C* 199
1273 6.40 540% 60.degree. C., 3 weeks Ex. 3 274 1279 4.67 367%
Comp. Sample C* 199 1822 9.16 816% *Not an example of the
invention. **Calculated as 100% .times. [(final viscosity - initial
viscosity)/initial viscosity].
[0106] As shown by the data in Table 4, the adhesive of the
invention has a somewhat higher initial viscosity, but is much more
storage stable at each of the temperatures tested. In all cases,
the viscosity of the Comparative Adhesive increases at a much
faster rate than that of Example 3, and in all cases reaches a
higher absolute value at the end of the test period.
EXAMPLE 4 AND COMPARATIVE SAMPLE D
[0107] Toughener 4 is prepared by heating to 60.degree. C., under
nitrogen, 79.2 parts of a 2900 molecular weight
polytetrahydrofuran, and mixing the heated polyol with 0.5 parts of
trimethylolpropane until homogeneous. At 60.degree. C., 10.9 parts
1,6-hexamethylene diisocyanate are added. After mixing for 2
minutes, 0.06 parts of dibutyl tindilaurate are added and the
mixture is allowed to react under nitrogen at 85.degree. C. for 45
minutes. The resulting prepolymer has an isocyanate content of
3.0%.
[0108] The prepolymer is then mixed with 5.0 parts of
o,o'-diallylbisphenol A and allowed to react for 40 minutes at
85.degree. C., again under nitrogen, to form a chain-extended
prepolymer having an isocyanate content of 3.0%.
[0109] The chain-extended prepolymer is then mixed with 4.4 parts
of o-allylphenol under nitrogen. The mixture is allowed to stir at
85.degree. C. for 25 minutes to cap the remaining isocyanate groups
on the chain-extended prepolymer. The isocyanate content is reduced
to zero. The resulting toughener (Toughener 4) is degassed under
vacuum. Toughener 4 has an M.sub.n of 8700 and an M.sub.w of
27,100.
[0110] Toughener D is prepared by heating to 60.degree. C., under
nitrogen, 83.6 parts of the polytetrahydrofuran, and mixing the
heated polyol with 0.6 parts of trimethylolpropane until
homogeneous. At 60.degree. C., 9.7 parts 1,6-hexamethylene
diisocyanate are added. After mixing for 2 minutes, 0.06 parts of
dibutyl tindilaurate are added and the mixture is allowed to react
under nitrogen at 85.degree. C. for 45 minutes. The resulting
prepolymer has an isocyanate content of 2.0%. The prepolymer is
then mixed with 6.1 parts of o-allylphenol under nitrogen. The
mixture is allowed to stir at 85.degree. C. for 20 minutes to cap
the remaining isocyanate groups on the chain-extended prepolymer.
The isocyanate content is reduced to zero.
[0111] One-part, heat-activated adhesive formulations are prepared
from each of Toughener 4 and Toughener D. The formulation for
Example 4 is the same as shown in Table 1 for Example 1, except
that Toughener 1 is replaced by an equal amount of Toughener 4.
Comparative Sample D is the same as Comparative Sample A, except
that Toughener A is replaced by an equal amount of Toughener D.
Toughener D has an M.sub.n of 7600 and an M.sub.w of 19,700.
[0112] Storage stability is evaluated for each of these as before,
with results being as indicated in Table 5.
TABLE-US-00005 TABLE 5 Storage Conditions (Temperature, time)
Initial Final Viscosity, Viscosity, Ratio, Pa s Pa s Final/Initial
% (10/sec) (10/sec) Viscosity Increase** 40.degree. C., 24 weeks
Ex. 4 188 642 3.41 241% Comp. Sample D* 110 798 7.25 625%
50.degree. C., 12 weeks Ex. 4 188 1424 7.57 657% Comp. Sample D*
110 1690 15.36 1436% 60.degree. C., 4 weeks Ex. 4 188 1540 8.19
719% Comp. Sample D* 110 Gelled NM NM *Not an example of the
invention. **Calculated as 100% .times. [(final viscosity - initial
viscosity)/initial viscosity]. NM--not meaningful, as the aged
adhesive has solidified.
[0113] As shown by the data in Table 6, the adhesive of the
invention has a somewhat higher initial viscosity, but is much more
storage stable at each of the temperatures tested. In all cases,
the viscosity of the Comparative Adhesive D increases at a much
faster rate than that of Example 4, and in all cases reaches a
higher absolute value at the end of the test period.
EXAMPLES 5-7
[0114] Toughener 5 is prepared by heating to 60.degree. C., under
nitrogen, 76.1 parts of a 2000 molecular weight
polytetrahydrofuran, and mixing the heated polyol at 60.degree. C.
with 12.8 parts 1,6-hexamethylene diisocyanate. After mixing for 2
minutes, 0.06 parts of dibutyl tindilaurate are added and the
mixture is allowed to react under nitrogen at 85.degree. C. for 45
minutes. The resulting prepolymer has an isocyanate content of
3.6%.
[0115] The prepolymer is then mixed with 5.9 parts of
o,o'-diallylbisphenol A and allowed to react for 40 minutes at
85.degree. C., again under nitrogen, to form a chain-extended
prepolymer having an isocyanate content of 1.7%.
[0116] The chain-extended prepolymer is then mixed with 5.2 parts
of o-allylphenol under nitrogen. The mixture is allowed to stir at
85.degree. C. for 25 minutes to cap the remaining isocyanate groups
on the chain-extended prepolymer. The isocyanate content is reduced
to zero. The resulting toughener (Toughener 5) is degassed under
vacuum. Toughener 5 has an M.sub.n of 7600 and an M.sub.w of
18,200.
[0117] Toughener 6 is made in the same manner as Toughener 5, using
63.4 parts of the polyol, 10.7 parts of the isocyanate, 0.06 parts
of the catalyst, 4.9 parts of o,o'-diallylbisphenol A in the chain
extension step, and 21.0 parts of o,o'-diallylbisphenol A in the
capping step. Toughener 6 has an M.sub.n of 5900 and an M.sub.w of
13,700.
[0118] Toughener 7 is prepared by heating to 60.degree. C., under
nitrogen, 60.1 parts of a 2000 molecular weight
polytetrahydrofuran, and mixing the heated polyol with 0.4 parts of
trimethylolpropane until homogeneous. At 60.degree. C., 11.6 parts
1,6-hexamethylene diisocyanate are added. After mixing for 2
minutes, 0.06 parts of dibutyl tindilaurate are added and the
mixture is allowed to react under nitrogen at 85.degree. C. for 45
minutes. The resulting prepolymer has an isocyanate content of
4.0%. Toughener 7 has an M.sub.n of 7200 and an M.sub.w of
23,800.
[0119] The prepolymer is then mixed with 5.3 parts of
o,o'-diallylbisphenol A and allowed to react for 40 minutes at
85.degree. C., again under nitrogen, to form a chain-extended
prepolymer having an isocyanate content of 1.9%.
[0120] The chain-extended prepolymer is then mixed with 22.6 parts
of o,o'-diallylbisphenol A under nitrogen. The mixture is allowed
to stir at 85.degree. C. for 25 minutes to cap the remaining
isocyanate groups on the chain-extended prepolymer. The isocyanate
content is reduced to zero. The resulting toughener (Toughener 7)
is degassed under vacuum.
[0121] One-part, heat-activated adhesive formulations are prepared
from each of Toughener 5-7. The formulations for Examples 5-7 are
the same as shown in Table 1 for Example 1, except that Toughener 1
is replaced by an equal amount of Toughener 5-7, respectively.
[0122] Storage stability is evaluated for each of these as before,
with results being as indicated in Table 6.
TABLE-US-00006 TABLE 6 Storage Conditions (Temperature, time)
Initial Final Viscosity, Viscosity, Ratio, Pa s Pa s Final/Initial
% (10/sec) (10/sec) Viscosity Increase** 40.degree. C., 8 weeks Ex.
5 170 250 1.47 47% Ex. 6 173 234 1.35 35% Ex. 7 220 252 1.15 15%
50.degree. C., 6 weeks Ex. 5 170 324 1.91 91% Ex. 6 173 450 2.60
160% Ex. 7 220 532 2.42 142% **Calculated as 100% .times. [(final
viscosity - initial viscosity)/initial viscosity]. NM--not
meaningful, as the aged adhesive has solidified.
[0123] The data in Table 6 shows that the benefit of improved
storage stability is seen across a variety of toughener
compositions.
[0124] Impact peel testing is performed for adhesive Examples 1-7,
and for two commercially available structural adhesive products
(Comparative Adhesives E and F). The substrate is 1.5 mm 1403
steel. The impact peel testing is performed in accordance with ISO
11343 wedge impact method. Testing is performed at an operating
speed of 2 m/sec. Impact peel testing is performed at 23.degree.
C., and strength in N/mm is measured.
[0125] Test coupons for the impact peel testing are 90 mm.times.20
mm with a bonded area of 30.times.20 mm The samples are prepared by
wiping them with acetone. Teflon tape is applied to the coupons to
define the bond area. The structural adhesive is then applied to
the bond area of one coupon and squeezed onto the other coupon to
prepare each test specimen. The adhesive layer is 0.2 mm thick.
Duplicate samples are cured for 30 minutes at 180.degree. C.
[0126] Duplicate test coupons are prepared and are evaluated for
lap shear strength in accordance with DIN ISO 1465. The substrate
is 1.0 mm cold rolled steel grade BCO4. Testing is performed at a
test speed of 10 mm/minute. Testing is performed at 23.degree. C.
Test samples are prepared using each adhesive. The bonded area in
each case is 25.times.10 mm The adhesive layer is 0.2 mm thick.
Duplicate test specimens are cured for 30 minutes at 180.degree.
C.
[0127] The glass transition temperature of a sample of the cured
adhesive is measured by DSC. The glass transition temperature
(T.sub.g) and the results of the impact peel and lap shear testing
are as shown in Table 7.
TABLE-US-00007 TABLE 7 Impact peel Lap shear strength, RT, T.sub.g,
strength, N/mm, .degree. C. MPa energy (J) Ex. 1 90 35.5 56 (21)
Ex. 2 97 30.2 47 (17) Ex. 3 93 36.7 57 (22) Ex. 4 93 32.4 54 (20)
Ex. 5 89 35.5 60 (22) Ex. 6 88 37.6 54 (21) Ex. 7 86 38.2 55 (20)
Comparative 94 32.1 57 (22) Adhesive E Comparative 87 31.5 44 (16)
Adhesive F
[0128] The data in Table 7 indicates that adhesives in accordance
with the invention have, when cured, properties comparable to or
better than the commercially available adhesives. In particular,
lap shear and impact peels strengths are increased significantly in
many cases.
* * * * *