U.S. patent application number 15/757877 was filed with the patent office on 2018-11-22 for one-component toughened epoxy adhesives with improved adhesion to oily surfaces and high wash-off resistance.
The applicant listed for this patent is Dow Global Technologies LLC. Invention is credited to Jeannine Flueckiger, Andreas Lutz, Daniel Schneider.
Application Number | 20180334596 15/757877 |
Document ID | / |
Family ID | 58239875 |
Filed Date | 2018-11-22 |
United States Patent
Application |
20180334596 |
Kind Code |
A1 |
Lutz; Andreas ; et
al. |
November 22, 2018 |
ONE-COMPONENT TOUGHENED EPOXY ADHESIVES WITH IMPROVED ADHESION TO
OILY SURFACES AND HIGH WASH-OFF RESISTANCE
Abstract
Epoxy adhesives include a latent curing agent, a reactive
toughener having capped isocyanate groups, and certain urea
compounds. The toughener is made by chain extending and capping a
mixture of isocyanate-terminated prepolymers. The prepolymers
include an isocyanate-terminated polyether and an
isocyanate-terminated diene polymer. The adhesives have excellent
wash-off resistance and excellent ability to adhere to oily
substrates.
Inventors: |
Lutz; Andreas; (Galgenen,
CH) ; Schneider; Daniel; (Waedenswil, CH) ;
Flueckiger; Jeannine; (Freienbach, CH) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Dow Global Technologies LLC |
Midland |
MI |
US |
|
|
Family ID: |
58239875 |
Appl. No.: |
15/757877 |
Filed: |
September 6, 2016 |
PCT Filed: |
September 6, 2016 |
PCT NO: |
PCT/US16/50341 |
371 Date: |
March 6, 2018 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
62216395 |
Sep 10, 2015 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61B 5/6882 20130101;
C08G 18/3215 20130101; C08G 18/675 20130101; C09J 163/00 20130101;
C08G 18/12 20130101; A61N 1/0551 20130101; C08G 59/686 20130101;
C08G 18/6204 20130101; C08G 18/698 20130101; A61B 5/0492 20130101;
C08L 75/08 20130101; C08G 18/73 20130101; C09J 163/04 20130101;
A61N 1/0558 20130101; C01B 32/182 20170801; C08G 65/33348 20130101;
A61B 5/04888 20130101; A61B 2562/125 20130101; C08G 18/755
20130101; C08G 18/8067 20130101; C08G 59/4021 20130101; C08G 18/24
20130101; C08G 18/4854 20130101; C08G 18/10 20130101; A61B 5/04001
20130101; A61B 5/6877 20130101; C08G 18/10 20130101; C08G 18/2825
20130101; C08G 18/12 20130101; C08G 18/282 20130101; C09J 163/00
20130101; C08L 75/08 20130101 |
International
Class: |
C09J 163/04 20060101
C09J163/04; C09J 163/00 20060101 C09J163/00; C08G 18/10 20060101
C08G018/10; C08G 18/62 20060101 C08G018/62; C08G 18/24 20060101
C08G018/24; C08G 18/75 20060101 C08G018/75; C08G 18/32 20060101
C08G018/32; C08G 59/40 20060101 C08G059/40; C08G 65/333 20060101
C08G065/333 |
Claims
1. A one-component epoxy adhesive comprising in admixture: A) at
least 25 weight percent, based on the weight of the adhesive, of
one or more non-rubber-modified epoxy resins; B) 5 to 45 weight
percent, based on the weight of the composition, of a reactive
elastomeric toughener having capped isocyanate groups, which
reactive elastomeric toughener includes a chain-extended and then
isocyanate-capped mixture of i) a 1000 to 10,000 number average
molecular weight isocyanate-terminated polyether and ii) a 1000 to
10,000 number average molecular weight isocyanate-terminated diene
polymer; C) one or more latent epoxy curing agents in an amount
sufficient to cure the adhesive; and D) 0.1 to 5 weight percent,
based on the weight of the adhesive, of at least one urea compound
having one or more urea groups and a molecular weight per urea
group of up to 250, the adhesive being devoid of an aminophenol
curing accelerator.
2. The one-component epoxy adhesive of claim 1 wherein the urea
compound is polyurea corresponding to a reaction product of an
aromatic polyisocyanate with a dialkyl amine.
3. The one-component epoxy adhesive of claim 2 wherein the urea
compound corresponds to a reaction product of an aliphatic
polyisocyanate with a dialkyl amine.
4. The one-component epoxy adhesive of claim 3 wherein the urea
compound is isophorone bis(dimethyl urea).
5. The one-component epoxy adhesive of claim 2 wherein the urea
compound is one or more of 2,4'- and/or 4,4'-methylene bis(phenyl
dimethyl urea) and 2,4- and/or 2,6-toluene bis(dimethyl urea).
6. The one-component epoxy adhesive of claim 1 wherein the latent
epoxy curing agent includes dicyanamide.
7. The one-component epoxy adhesive of claim 1 wherein the
toughener is made in a process that includes the steps of
chain-extending the mixture of the isocyanate-terminated polyether
and the isocyanate-terminated diene polymer and then capping the
remaining isocyanate groups of the chain-extended material.
8. The one-component epoxy adhesive of claim 1 wherein the
isocyanate groups of the isocyanate-terminated polyether and the
isocyanate-terminated diene polymer are aliphatic isocyanate
groups.
9. The one-component epoxy adhesive of claim 1 wherein the capped
isocyanate groups of the toughener are capped with a monophenol or
an aminophenol.
10. A method comprising forming a layer of the adhesive of claim 1
at a bondline between two substrates to form an assembly, and then
curing adhesive layer at the bondline to form an adhesive bond
between the two substrates.
11. A method for adhering a first oily substrate to a second
substrate, comprising 1) forming a layer of the adhesive of any of
claims 1 through 9 at a bondline between the first oily substrate
and the second substrate to form an assembly that includes the
first and second substrates each in contact with the adhesive
composition at the bondline; then 2) degreasing the assembly to
remove oil from the first oily substrate; and then 3) heating the
degreased assembly to an elevated temperature to cure the
adhesive.
12. The method of claim 11 which further comprises the steps of:
1-A): after step 1) and before step 2), fastening the assembly
using mechanical means, by spot-curing one or more portions of the
adhesive composition, or both, to maintain the substrates and
adhesive in a fixed position relative to each other, wherein at
least a portion of the adhesive remains uncured; and 2-A): after
step 2) and before step 3), contacting the fastened assembly with a
heat-curable coating to form a coated and fastened assembly.
13. The method of claim 12 wherein the heat-curable coating is
cured in step 3).
14. The method of claim 12, wherein the degreasing step 2) is
performed at a temperature of at least 50.degree. C.
15. A reactive elastomeric toughener having capped isocyanate
groups, which reactive elastomeric toughener includes a
chain-extended and then isocyanate-capped mixture of i) a 1000 to
10,000 number average molecular weight isocyanate-terminated
polyether and ii) a second isocyanate-terminated prepolymer which
is a reaction product of an organic polyisocyanate with a 1000 to
10,000 number average molecular weight isocyanate-terminated
polymer or copolymer of butadiene.
16. An epoxy adhesive containing at least one epoxy resin and the
reactive toughener of claim 15.
17. A method comprising forming a layer of the adhesive of claim 16
at a bondline between two substrates to form an assembly, and then
curing adhesive layer at the bondline to form an adhesive bond
between the two substrates.
Description
[0001] This invention relates to one-component epoxy adhesives that
contain an elastomeric toughener.
[0002] Toughened one-component epoxy adhesives are used extensively
in the automotive and other industries for metal-metal bonding as
well as bonding metals to other materials. These adhesives often
contain "tougheners" that help the cured adhesive resist failure.
The tougheners have blocked isocyanate groups that, 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, WO 2007/003650, WO2012/091842, 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 1 498 441A, 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.
[0003] In many metal bonding applications, where one or both
substrates are metals, the metal substrate to be bonded is
contaminated with an oily material. The oil is often a lubricant or
an anti-corrosion fluid. Anti-corrosion fluids are often applied to
metal sheet by their manufacturers, to prevent surface corrosion
from occurring until such later time as the metal is fabricated
into some specific part or product, and/or until a protective
coating is applied. Lubricants are commonly applied to metals when
they are fabricated, such as by cutting, molding or stamping. The
lubricants reduce wear on the metals and the tooling. There is a
recent trend towards using higher viscosity oils for these
purposes.
[0004] In specific manufacturing settings, this oil often remains
on the metal at the time the adhesive is applied. When vehicle
bodies are assembled, for example, it is often convenient to
partially or fully assemble the vehicle body before removing the
oil from the individual metal parts. This way, the partially or
fully assembled body can be washed or "degreased" at once, rather
than degreasing the separate components individually.
[0005] The presence of the oil creates two distinct problems.
[0006] The first problem has to do with the ability of the adhesive
to adhere strongly to the substrate. The presence of an oily
material on the substrate surface creates a physical barrier
separating the adhesive and metal. If the adhesive is to adhere
strongly to the metal, it is necessary that the adhesive overcome
this barrier. This means the adhesive must be able to penetrate the
oil while the adhesive is in an uncured or at most partially cured
state, in effect removing the physical barrier between adhesive and
substrate. This becomes more difficult as the viscosity of the oil
increases. Current toughened epoxy adhesives often do not penetrate
the oil as well as is needed.
[0007] The second problem arises in manufacturing processes in
which the degreasing step is performed after the adhesive is
applied but before it is cured. In such a case, the adhesive must
withstand the degreasing process without being washed off. Wash-off
resistance therefore, is an important attribute of adhesives that
are used in these kinds of manufacturing processes. The problem
becomes more difficult as the industry trends towards using higher
viscosity oils. Higher viscosity oils often require higher
degreasing temperatures. At these higher temperatures, the adhesive
becomes more susceptible to being washed away.
[0008] Thus, a desirable toughened adhesive has the ability to bond
to oily surfaces and in addition is resistant to being washed off.
Such an adhesive must also perform adequately in terms of bond
strength and impact resistance.
[0009] This invention is in one aspect a one-component epoxy
adhesive comprising in admixture:
A) at least 25 weight percent, based on the weight of the adhesive,
of one or more non-rubber-modified epoxy resins; B) 5 to 45 weight
percent, based on the weight of the composition, of a reactive
elastomeric toughener having capped isocyanate groups, which
reactive elastomeric toughener includes a chain-extended and then
isocyanate-capped mixture of i) a 1000 to 10,000 number average
molecular weight isocyanate-terminated polyether and ii) a 1000 to
10,000 number average molecular weight isocyanate-terminated diene
polymer; C) one or more latent epoxy curing agents in an amount
sufficient to cure the adhesive; and D) 0.1 to 3 weight percent,
based on the weight of the adhesive, of at least one urea compound
having one or more urea groups and a molecular weight per urea
group of up to 250, the adhesive being devoid of an aminophenol
curing accelerator.
[0010] Applicants have found that through the simultaneous
selection of the specific toughener and the urea compound, an
adhesive is produced that adheres very well to oily substrates. In
addition, the adhesive has good wash-off resistance and cures to
form an adhesive bond that has good lap shear strength and impact
peel resistance.
[0011] The benefits of the invention are not obtained when the
toughener is present without the urea compound, or when the urea
compound is present together with various other tougheners. The
selection of both together appears to be necessary.
[0012] The invention is also a method comprising forming a layer of
the adhesive of the invention at a bondline between two substrates
to form an assembly, and then curing the adhesive layer at the
bondline to form an adhesive bond between the two substrates. At
least one and preferably both of the members may be metals.
[0013] In a specific embodiment, the invention is a method for
adhering a first oily substrate to a second substrate,
comprising
[0014] 1) forming a layer of the adhesive of any of claims 1-9 at a
bondline between the first oily substrate and the second substrate
to form an assembly that includes the first and second substrates
each in contact with the adhesive composition at the bondline;
then
[0015] 2) degreasing the assembly to remove oil from the first oily
substrate; and then
[0016] 3) heating the degreased assembly to an elevated temperature
to cure the adhesive.
[0017] Such a method may further comprise steps of
[0018] 1-A): after step 1) and before step 2), fastening the
assembly using mechanical means, by spot-curing one or more
portions of the adhesive composition, or both, to maintain the
substrates and adhesive in a fixed position relative to each other,
wherein at least a portion of the adhesive remains uncured; and
[0019] 2-A): after step 2) and before step 3), contacting the
fastened assembly with a heat-curable coating to form a coated and
fastened assembly. In this process, the coating and the adhesive
are cured in step 3).
[0020] The invention is also reactive elastomeric toughener having
capped isocyanate groups, which reactive elastomeric toughener
includes a chain-extended and then isocyanate-capped mixture of i)
a 1000 to 10,000 number average molecular weight
isocyanate-terminated polyether and ii) a 1000 to 10,000 number
average molecular weight isocyanate-terminated diene polymer.
[0021] The invention is in still another aspect an epoxy adhesive
containing
A) at least 25 weight percent, based on the weight of the adhesive,
of one or more non-rubber-modified epoxy resins; B) 5 to 45 weight
percent, based on the weight of the composition, of a reactive
elastomeric toughener having capped isocyanate groups, which
reactive elastomeric toughener includes a chain-extended and then
isocyanate-capped mixture of i) a 1000 to 10,000 number average
molecular weight isocyanate-terminated polyether and ii) a 1000 to
10,000 number average molecular weight isocyanate-terminated diene
polymer; C) one or more latent epoxy curing agents in an amount
sufficient to cure the adhesive; and D) 0.1 to 5 weight percent,
based on the weight of the adhesive, of at least one urea compound
having one or more urea groups and a molecular weight per urea
group of up to 250, the adhesive being devoid of an aminophenol
curing accelerator.
[0022] FIG. 1A is a photograph of separated oily metal substrates
with applied adhesive of the invention, which demonstrates
excellent performance on the tack test described below.
[0023] FIG. 1B is a photograph of separated oily metal substrates
with applied adhesive, which demonstrates adequate performance on
the tack test described below.
[0024] FIG. 1C is a photograph of separated oily metal substrates
with applied adhesive, which demonstrates poor performance on the
tack test described below.
[0025] Suitable epoxy resins include 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 1.8 epoxide groups per molecule. The epoxy
resin(s) are not rubber-modified, meaning that, prior to curing the
adhesive, the epoxy resins are not chemically bonded to a
rubber.
[0026] Suitable epoxy resins include 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
such as the diglycidyl ethers of C.sub.2-24 alkylene 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; cycloaliphatic epoxy
resins, and any combination of any two or more thereof.
[0027] Suitable epoxy resins include diglycidyl ethers of bisphenol
A resins such as are sold by The Dow Chemical Company 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.
[0028] Suitable epoxy novolac resins that are commercially
available include those sold as D.E.N..RTM. 354, D.E.N..RTM. 431,
D.E.N..RTM. 438 and D.E.N..RTM. 439 from The Dow Chemical
Company.
[0029] Suitable cycloaliphatic epoxy resins include those described
in U.S. Pat. No. 3,686,359, incorporated herein by reference.
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.
[0030] 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.
[0031] The epoxy resin preferably is one or more diglycidyl ethers
of a polyhydric phenol or a mixture thereof with up to 10 percent
by weight of another type of epoxy resin. The most preferred epoxy
resins are diglycidyl ethers of bisphenol-A and diglycidyl ethers
of bisphenol-F. These can have average epoxy equivalent weights of
from about 170 to 600 or more, preferably from 225 to 400.
[0032] An especially preferred 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 epoxy
resins.
[0033] The epoxy resin preferably will constitute at least about 25
weight percent of the adhesive, more preferably at least about 30
weight percent, and still more preferably at least about 40 weight
percent. The epoxy resin may constitute up to about 75 weight
percent of the adhesive, more preferably up to about 60 weight
percent.
[0034] In some embodiments, the adhesive composition contains 30 to
60, preferably 40 to 60, weight percent of a diglycidyl ether of
bisphenol A that has an epoxy equivalent weight of up to 225, and 0
to 10%, preferably 2 to 6 weight percent, of a diglycidyl ether of
bisphenol A that has an epoxy equivalent weight of 400 or greater,
preferably 400 to 1500. Such an adhesive composition optionally
contains 0.5 to 10 weight percent of a different epoxy resin such
as an epoxy novolac resin or an epoxy cresol novolac resin.
[0035] The toughener is an elastomeric material that has terminal
capped isocyanate groups. It is made in a process that includes the
steps of chain-extending a mixture of isocyanate-terminated
compounds and then capping the remaining isocyanate groups of the
chain-extended material.
[0036] The isocyanate-terminated compounds include i) at least one
1000 to 10,000 number average molecular weight
isocyanate-terminated polyether and ii) at least one 1000 to 10,000
number average molecular weight isocyanate-terminated diene
polymer.
[0037] The polyether portion of the isocyanate-terminated polyether
may be a polymer of one or more of tetrahydrofuran (tetramethylene
oxide), 1,2-butylene oxide, 2,3-butylene oxide, 1,2-propylene oxide
and ethylene oxide, with polymers or copolymers of at least 70
weight percent, based on the total weight of the polymer or
copolymer, of tetrahydrofuran, 1,2-butylene oxide, 2,3-butylene
oxide and 1,2-propylene oxide being preferred. Polymers of at least
80 weight percent tetrahydrofuran, based on the total weight of the
polymer or copolymer are especially preferred.
[0038] The isocyanate-terminated polyether is conveniently prepared
by the reaction of an amine- or hydroxyl-terminated polyether with
a polyisocyanate, at a ratio of at least 1.5 equivalents,
preferably 1.8 to 2.5 equivalents or 1.9 to 2.2 equivalents, of
polyisocyanate per equivalent of amine- and/or hydroxyl groups on
the starting polyether. The starting polyether preferably has 2 to
3, more preferably 2, amine and or hydroxyl groups per molecule.
The polyisocyanate preferably has 2 isocyanate groups per molecule.
The isocyanate-terminated polyether preferably has 2 to 3, more
preferably 2, isocyanate groups per molecule. The starting
polyether preferably has a number average molecular weight of 900
to 800, more preferably 1500 to 6000 or 1500 to 4000. The
polyisocyanate preferably has a molecular weight of up to 300.
[0039] The isocyanate-terminated diene polymer is conveniently
prepared by the reaction of an amine- or hydroxyl-terminated diene
polymer with a polyisocyanate, at a ratio of at least 1.5
equivalents, preferably 1.8 to 2.5 equivalents or 1.9 to 2.2
equivalents, of polyisocyanate per equivalent of amine- and/or
hydroxyl groups on the starting diene polymer.
[0040] The starting diene polymer preferably has a glass transition
temperature, prior to reaction with the polyisocyanate, of no
greater than -20.degree. C. and preferably no greater than
-40.degree. C. The diene polymer is a liquid homopolymer or
copolymer of a conjugated diene, especially a diene/nitrile
copolymer. The conjugated diene 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.
[0041] The starting diene polymer preferably has 2 to 3, more
preferably 2, amine and/or hydroxyl groups per molecule. The
polyisocyanate preferably has 2 isocyanate groups per molecule. The
isocyanate-terminated diene polymer preferably has 2 to 3, more
preferably 2, isocyanate groups per molecule. The starting diene
polymer preferably has a number average molecular weight of 900 to
800, more preferably 1500 to 6000 and still more preferably 2000 to
3000. The polyisocyanate preferably has a molecular weight of up to
300.
[0042] The isocyanate-terminated polyether and
isocyanate-terminated diene polymer can have aromatic isocyanate
groups, but the isocyanate groups are preferably aliphatic. When
the isocyanate-terminated polymers are made in the process
described above, 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.
[0043] The isocyanate-terminated polyether and
isocyanate-terminated diene polymer may be made separately and then
blended. Alternatively, they are made simultaneously by blending an
amine- or hydroxyl-terminated polyether and an amine- or
hydroxyl-terminated diene polymer, each as described above, and
reacting the blended materials with a polyisocyanate to form the
mixture of isocyanate-terminated species directly.
[0044] The weight ratio of isocyanate-terminated polyether and
isocyanate-terminated diene polymer may be, for example, about 5:95
to 95:5. A preferred weight ratio is about 50:50 to 95:5 and a more
preferred ratio is about 70:30 to 90:10.
[0045] The reaction to form the isocyanate-terminated polymers can
be performed by combining the materials in the stated ratios and
heating to 60 to 120.degree. C., optionally in the presence of a
catalyst for the reaction of isocyanate groups with the
isocyanate-reactive groups of the polyether or diene polymer. The
reaction is continued until the isocyanate content is reduced to a
constant value, or to a target value, or until the amine- and or
hydroxyl groups of the starting polyether or diene polymer are
consumed.
[0046] If desired, branching can be introduced into the
isocyanate-terminated polyether and/or isocyanate-terminated diene
polymer. When they are made a process such as described before,
this can be done by adding branching agent into the reaction
between the polymeric starting materials and the polyisocyanate.
The branching agent, for purposes of this invention, is a polyol or
polyamine compound 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 the starting polymer
(i.e., the amine- or hydroxyl-terminated polyether or diene
polymer). 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 number average
molecular weight of up to 599, especially up to 500.
[0047] The mixture of isocyanate-terminated polyether and
isocyanate-terminated diene polymer is chain extended to produce a
chain extended, isocyanate-terminated prepolymer. Chain extenders
include 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.
[0048] The chain extension reaction is performed in the same
general manner as the prepolymer-forming reaction. Enough of the
prepolymers are 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. 1.5
to 4 or more, preferably 1.75 to 3 and more preferably 1.8 to 2.5
equivalents of isocyanate groups may be provided per equivalent of
isocyanate-reactive groups contributed by the chain extender during
the chain extension reaction.
[0049] The chain extension reaction is performed by combining the
mixture of isocyanate-terminated polyether and
isocyanate-terminated diene polymer with the chain extender, and
subjecting the mixture to conditions under which the
isocyanate-reactive groups of the chain extender react isocyanate
groups of the isocyanate-terminated materials to form the
chain-extended prepolymer.
[0050] The chain-extended prepolymer will be a mixture of
materials. It will consist mainly of isocyanate-terminated polymers
that correspond to two or more of the starting
isocyanate-terminated polymers coupled together by residue(s) of
the chain extender. A portion of the prepolymer molecules will have
two or more polyether chains, corresponding to the polyether chains
of the isocyanate-terminated polyether. A portion of the prepolymer
molecules will have one or more polyether chains, corresponding to
the polyether chains of the isocyanate-terminated polyether, and
one or more diene polymer chains, corresponding to the diene
polymer chains of the isocyanate-terminated diene polymer. There
may be prepolymer molecules that having two more diene polymer
chains, corresponding to the diene polymer chains of the
isocyanate-terminated diene polymer. The chain-extended prepolymer
may contain small quantities of unreacted starting materials,
and/or of reaction products of one molecule of chain extender with
only one molecule of isocyanate-terminated polyether or
isocyanate-terminated diene polymer.
[0051] Conditions for the chain-extension reaction are generally as
described with respect to the reaction of the amine- or
hydroxyl-terminated polymer with the polyisocyanate.
[0052] The isocyanate groups of the chain-extended prepolymer are
then capped by reaction with a capping group. Various types of
capping groups are suitable including those described in U.S. Pat.
No. 5,202,390, U.S. Pat. No. 5,278,257, U.S. Pat. No. 7,615,595, US
Published Patent Application Nos. 2005-0070634, 2005-0209401,
2006-0276601 and 2010-0019539, WO 2006/128722, WO 2005/118734 and
WO 2005/0070634, all incorporated herein by reference. Among the
useful capping agents are:
[0053] a) Aliphatic, aromatic, cycloaliphatic, araliphatic and/or
heteroaromatic monoamines that have one primary or secondary amino
group. Examples of such capping compounds include monoalkyl amines
such as methyl amine, ethyl amine, isopropyl amine, sec-butylamine,
t-butyl amine; dialkyl amines such as dimethylamine, diethylamine,
diisopropylamine, di-sec-butylamine, dihexylamine and dioctyl
amine; cyclohexylamine or dicyclohexylamine wherein the cyclohexyl
groups are optionally substituted with one or more alkyl groups;
benzylamine and diphenylamine wherein the phenyl groups are
optionally substituted with one or more alkyl groups; morpholine;
N-alkylpiperadines and imidazols having an amine hydrogen atom.
[0054] b) phenolic compounds, including monophenols, polyphenols
and aminophenols. Examples of monophenols include phenol, alkyl
phenols that contain one or more alkyl groups that each may contain
from 1 to 30 carbon atoms, naphthol, a halogenated phenol,
cardanol, or naphthol. Suitable polyphenols contain two or more,
preferably two, phenolic hydroxyl groups per molecule and 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 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 aminonaphthols, and the like.
Among the phenolic compounds, the monophenols and aminophenols are
generally preferred.
[0055] c) Benzyl alcohol, which may be substituted with one or more
alkyl groups on the aromatic ring;
[0056] d) Hydroxy-functional acrylate or methacrylate compounds
such as 2-hydroxyethylacrylate, 2-hydroxypropylacrylate,
4-hydroxybutylacrylate, 2-hydroxy-butylacrylate,
2-aminopropylacrylate, 2-hydroxyethylmethacrylate,
2-hydroxypropyl-methacrylate, 4-hydroxybutylmethacrylate and
2-hydroxybutylmethacrylate;
[0057] e) thiol compounds such as alkylthiols having 2 to 30,
preferably 6 to 16, carbon atoms in the alkyl group, including
dodecanethiol;
[0058] f) alkyl amide compounds having at least one amine hydrogen
such as acetamide and N-alkylacetamide; and
[0059] g) a ketoxime.
[0060] The monophenol and aminophenol capping agents are generally
preferable. In some embodiments, at least 90%, preferably at least
95%, more preferably at least 98%, up to 100% of the isocyanate
groups of the prepolymer are capped with capping agents of one or
more of these types. In such embodiments any remaining uncapped
isocyanate groups may be capped with another type of capping
agent.
[0061] The capping reaction can be performed under the general
conditions described already, i.e., by combining the materials in
the stated ratios and allowing them to react at room temperature or
an elevated temperature such as 60 to 120.degree. C., optionally in
the presence of a catalyst for the reaction of isocyanate groups
with the isocyanate-reactive groups of the capping agent. The
reaction is continued until the isocyanate content is reduced to a
constant value, which is preferably less than 0.1% by weight. Fewer
than 3%, preferably fewer than 1%, of the isocyanate groups may
remain uncapped.
[0062] The resulting toughener suitably has a number average
molecular weight of at least 3000, preferably at least 4,000, to
about 35,000, preferably to about 20,000 and more preferably to
about 15,000, as measured by GPC, taking into account only those
peaks that represent molecular weights of 1000 or more.
[0063] The polydispersity (ratio of weight average molecular weight
to number average molecular weight) of the toughener 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.
[0064] The toughener should constitute at least 5 weight percent of
the adhesive composition. The amount of toughener may be 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.
[0065] The adhesive also contains a latent curing agent. A curing
agent is consider to be "latent" for purposes of this invention if
the adhesive, including components A)-D) as set forth above,
exhibits a curing temperature of at least 60.degree. C. The curing
temperature preferably is at least 80.degree. C., and may be at
least 100.degree. C. or at least 140.degree. C. It may be as high
as, for example, 180.degree. C. The "curing temperature" refers to
the lowest temperature at which the structural adhesive achieves at
least 30% of its lap shear strength (DIN ISO 1465) at full cure
within 2 hours. The lap shear strength at "full cure" is measured
on a sample that has been cured for 30 minutes at 180.degree. C.,
which conditions represent "full cure" conditions.
[0066] Suitable latent curing agents include materials such as
boron trichloride/amine and boron trifluoride/amine complexes,
melamine, diallylmelamine, guanamines such as dicyandiamide, methyl
guanidine, dimethyl guanidine, trimethyl guanidine, tetramethyl
guanidine, methylisobiguanidine, dimethylisobiguanidine,
tetramethylisbiguandidine, heptamethylisobiguanidine,
hexamethylisobiguanidine, 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. Dicyandiamide is a particularly preferred
curing agent.
[0067] The latent curing agent is used in an amount sufficient to
cure the adhesive. 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
adhesive, more preferably at least about 2.5 weight percent and
even more preferably at least 3.0 weight percent thereof. The
curing agent preferably constitutes up to about 15 weight percent
of the adhesive composition, more preferably up to about 10 weight
percent, and most preferably up to about 8 weight percent.
[0068] The adhesive contains 0.1 to 5, preferably 0.25 to 3, weight
percent of at least one urea compound having one or more urea
groups and a molecular weight per urea group of up to 250. The urea
compound(s) may have the structure:
##STR00001##
wherein n is 1 or more, R is an unsubstituted or unsubstituted
alkyl, cycloalkyl and/or aromatic radical, R.sup.1 is hydrogen,
unsubstituted alkyl, substituted alkyl, phenyl or substituted
phenyl, and each R.sup.2 is independently alkyl, substituted alkyl,
phenyl or substituted phenyl. R may be the residue, after removal
of isocyanate groups, from a mono- or polyisocyanate compound. R
may contain, for example, up to 20 carbon atoms, preferably up to
15 carbon atoms. Preferably, R, each R.sup.2 and R.sup.1 (if not
hydrogen) are bonded to the adjacent nitrogen atom through an
aliphatic carbon atom. n is preferably 1 to 4, more preferably 1, 2
or 3, and most preferably 2.
[0069] Examples of aromatic ureas include
3-phenyl-1,1-dimethylurea, 3-(p-chlorophenyl)-1,1-dimethylurea,
3-(3,4-dichlorophenyl)-1,1-dimethyl urea.
[0070] Other aromatic ureas include those corresponding to reaction
products of an aromatic polyisocyanate with a dialkyl amine.
Examples include 2,4'- and/or 4,4'-methylene bis(phenyl dimethyl
urea) and 2,4- and/or 2,6-toluene bis(dimethyl urea).
[0071] Examples of aliphatic ureas include tetraalkyl urea
compounds in which the alkyl groups each independently have 1 to
12, preferably 1 to 2 carbon atoms, such as tetramethylurea and
tetraethylurea.
[0072] A preferred type of aliphatic urea corresponds to a reaction
product of an aliphatic (including cycloaliphatic) isocyanate with
a dialkyl amine. Examples include isophorone bis(dimethyl urea),
cyclohexane bis (dimethyl urea), hexane-1,6-bis(dimethyl urea),
4,4'-methylene bis(cyclohexane dimethyl urea), and the like. A
commercially available isophorone bis(dimethylurea) product is
Omicure.TM. U-35, available from Emerald Performance Materials.
[0073] In addition to improving adhesion to oily substrates (when
used in conjunction with the toughener described herein) the urea
compound also is believed to function as a curing accelerator,
i.e., a catalyst for the curing reaction between the epoxy resin
and hardener. Accordingly, it is not necessary to include a
separate curing accelerator or catalyst in the adhesive composition
of the invention.
[0074] However, if an additional curing accelerator is desired, it
is preferably encapsulated or otherwise a latent type that becomes
active only upon exposure to elevated temperatures. Examples of
these include tert-acryl- or alkylene amines like
benzyldimethylamine, piperidine or derivatives thereof,
C.sub.1-C.sub.12 alkylene imidazole or N-arylimidazoles such as
2-ethyl-2-methylimidazol, or N-butylimidazol or 6-caprolactam. Such
an additional accelerator, if present at all, may be present in an
amount of 0.01 to 4 weight percent of the adhesive.
[0075] At least one type of curing accelerator, aminophenol
compounds, has been found to contribute to poorer performance even
when the urea compound is present. Therefore, the adhesive of the
composition is devoid of aminophenol compounds.
[0076] The adhesive of the invention may contain various other,
optional ingredients, in addition to those described above.
[0077] The adhesive may contain one or more mineral fillers. 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 suitable
mineral fillers 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 Dualite.TM., and those sold by Akzo Nobel
under the trade designation Expancel.TM..
[0078] All or part of the mineral filler may be in the form of
fibers having a diameter of 1 to 50 .mu.m (D50, as measured by
microscopy) and an aspect ratio of 6 to 20. The diameter of the
fibers may be 2 to 20 .mu.m or 2 to 10 .mu.m, and the aspect ratio
may be 8 to 20 or 8 to 16. The diameter of the fiber is taken as
that of a circle having the same cross-sectional area as the fiber.
The aspect ratio of the fibers may be 6 or more, such as 6 to 25, 6
to 20, 8 to 20 or 8 to 15.
[0079] Alternatively, all or part of the mineral filler may be in
the form of low aspect ratio particles having an aspect ratio of 5
or less and a longest dimension of up to 100 .mu.m, preferably up
to 25 .mu.m.
[0080] The mineral filler(s) may constitute, for example, 1 to 40%
of the total weight of the adhesive composition. In some
embodiments, it constitutes at least 5% or at least 7.5% of the
weight of the adhesive composition, and may constitute up to 25%,
up to 20% or up to 15% of the weight thereof.
[0081] The adhesive may contain up to 10% by weight, preferably 1
to 6% by weight of fumed silica.
[0082] The adhesive may include a rubber component that does not
include capped isocyanate groups, which is a separate material from
the toughener described above. Such a rubber component is optional
and can be omitted. One advantage of this invention is that
excellent properties can be obtained even when the adhesive is
devoid of such a component.
[0083] The optional rubber component may be, for example, a liquid
rubber, preferably having two or more epoxide-reactive groups, such
as amino or preferably carboxyl groups. 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, as measured by differential scanning
calorimetry. Such a liquid rubber component may be entirely or
partially reacted with an epoxy resin to form a rubber-modified
epoxy resin that has epoxy groups.
[0084] Such a 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. The liquid 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. 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.
[0085] Other suitable rubbery materials include amine-terminated
polyethers, fatty acids (which may be dimerized or oligomerized),
and elastomeric polyester.
[0086] Another type of rubber that may be present in the adhesive
composition is a core-shell rubber. 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. 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, or may
be a silicone rubber. 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. Examples of useful core-shell rubbers include those
described in EP 1 632 533 A1 and 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.
[0087] The total rubber content of the adhesive of the invention
can range from as little as 0 weight percent to as high as 30
weight percent, based on the total weight of the adhesive. If a
rubber is present at all, a preferred rubber content is up to 20
weight percent, up to 15 weight percent or up to 5 weight percent.
No portion of the elastomeric toughener is considered in
calculating total rubber content.
[0088] In specific embodiments, the adhesive of the invention has a
total rubber content of no more than 5%, preferably no more than
1%, and more preferably no more than 0.5% by weight. The adhesive
may have a rubber content of zero.
[0089] A monomeric or oligomeric, addition polymerizable,
ethylenically unsaturated material is optionally present in the
adhesive composition. 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 adhesive
composition 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 adhesive through selective
polymerization of the ethylenic unsaturation.
[0090] The adhesive composition 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.
[0091] The foregoing adhesive composition is formed into a layer at
a bondline between two substrates to form an assembly, and the
adhesive layer is cured at the bondline to form an adhesive bond
between the two substrates.
[0092] The adhesive can be applied to the substrates by any
convenient technique. It can be applied cold or be applied warm if
desired. It can be applied manually and/or robotically, using for
example, a caulking gun, other extrusion apparatus, or jet spraying
methods. Once the adhesive composition is applied to the surface of
at least one of the substrates, the substrates are contacted such
that the adhesive is located at a bondline between the
substrates.
[0093] After application, the adhesive is cured by heating it to at
or above its curing temperature. Generally, this temperature is at
least 60.degree. C., and is preferably 80.degree. C. or above, more
preferably 140.degree. C. or above. Preferably, the temperature is
180.degree. C. or less.
[0094] 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.
[0095] The invention has particular benefits when one or both of
substrates have an oily material on a surface to which the adhesive
is applied. By "oily material", it is meant an electrostatically
neutral, hydrophobic material that has a melting temperature of
40.degree. C. or lower and a viscosity of at least 5 centistokes (5
mm.sup.2/s) at 40.degree. C. as measured by ASTM D445. The
viscosity may be, for example, at least 8 centistokes, at least 20
centistokes or at least 50 centistokes to as much as 500
centistokes, as much as 250 centistokes or as much as 125
centistokes at that temperature. By "hydrophobic", it is meant the
material is soluble in water to the extent of no more than 2 parts
by weight per 100 parts by weight water at 23.degree. C. The oily
material may include, for example, a petroleum product, a plant or
animal oil or fat, and/or a synthetic oil such as various types of
synthetic ester lubricants. Examples of oily materials include for
example, lubricating oils such as sewing machine oils, stamping
oils, motor oils, soldering pastes, gear lubricants, die
lubricants, trim press lubricants, and aviation oils, axle and
transmission oils, compressor oils, electrical oils, gear oils,
hydraulic fluids, process oils, slideway oils and turbine oils.
Such oils include those sold, for example, by Fuchs Lubricants UK
PLC, International Chemical Company, Philadelphia, Pa., USA,
Chemtool Inc., Rockland, Ill., USA, and Lamson Oil Co., Rockland,
Ill., USA, among many others. A specific example is Anticorit.TM.
PL3802-35 from Fuchs Lubricants UK. The oily material may contain
various types of contaminants. The amount of oil on the surface of
the substrate to which the adhesive is applied may be, for example
0.1 to 10 g/m.sup.2, 0.25 to 5 g/m.sup.2, or 0.5 to 2.5
g/m.sup.2.
[0096] The excellent wash-off resistance of adhesive of the
invention is particularly beneficial when one or both of the
substrates is coated at the time the adhesive is applied to the
substrate with an oil having a viscosity of at least 50 mm.sup.2/s
at 40.degree. C. In some manufacturing processes, the oil coating
is removed in a washing step (commonly referred to as "degreasing")
that takes place after the adhesive is applied and before it is
cured. When higher viscosity oils are present, the washing
temperature is often increased to 40.degree. C. or more, or
50.degree. C. or more, to facilitate removal of the oil. These
higher washing temperatures require the adhesive to be highly
resistant to washing off, so it is not removed with the oil;
therefore the wash-off resistance of the inventive adhesive is of
particular value in cases in which a step of washing off
(degreasing) an oil coating is performed at a temperature of at
least 40.degree. C. or at least 50.degree. C. after the adhesive is
applied but before it has been cured.
[0097] 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, which are frequently contaminated
with an oil as described above. 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.
[0098] 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 adhesive to the frame components (which may be coated
with an oil as described above), then apply the coating, and cure
the adhesive at the same time the coating is baked and cured.
Between the steps of applying the adhesive and applying the
coating, the assembly may be fastened together to maintain the
substrates and adhesive in a fixed position relative to each other,
until the curing step is performed. Mechanical means can be used as
a fastening device. These include, for example, temporary
mechanical means such as various types of clamps, bands and the
like, which can be removed once the curing step is completed. The
mechanical fastening means can be permanent, such as, for example,
various types of welds, rivets, screws, and/or crimping methods.
Alternatively or in addition, the fastening can be done by
spot-curing one or more specific portions of the adhesive
composition to form one or more localized adhesive bonds between
the substrates while leaving the remainder of the adhesive uncured
until a final curing step is performed after the coating is
applied.
[0099] 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. All
molecular weights are number averages unless otherwise
indicated.
[0100] In the following examples:
[0101] Epoxy Resin A is a liquid diglycidyl ether of bisphenol A,
having an epoxy equivalent weight of about 187.
[0102] Epoxy Resin B is a mixture of solid and liquid diglycidyl
ethers of bisphenol A. The mixture has an epoxy equivalent weight
of about 240.
[0103] Epoxy Resin C is an epoxy novolac resin having an epoxy
equivalent weight of about 179.
[0104] Epoxy Resin D is an epoxy-functional diluent.
[0105] Toughener A is an elastomeric toughener containing blocked
isocyanate groups. It is prepared by mixing 54.79 parts of a 2000
molecular weight polytetrahydrofuran and 13.67 parts of a 2800
molecular weight, hydroxyl-terminated polybutadiene polymer at
120.degree. C., cooling the mixture to 60.degree. C., adding 15.09
parts of isophorone diisocyanate and a tin urethane catalyst and
heating the resulting reaction mixture to 85.degree. C. for 45
minutes under nitrogen. Then, 5.74 parts of o,o'-diallylbisphenol A
are added, and the mixture is stirred for 120 minutes under vacuum
in a 100.degree. C. bath. 10.65 parts of cardanol are then added
and the mixture is stirred for another 240 minutes under vacuum in
a 105.degree. C. bath.
[0106] Toughener B is an elastomeric toughener containing blocked
isocyanate groups. It is prepared by mixing 57.58 parts of a 2000
molecular weight polytetrahydrofuran and 14.39 parts of a 2800
molecular weight hydroxyl-terminated polybutadiene polymer at
120.degree. C., cooling the mixture to 60.degree. C., adding 11.54
parts of hexamethylene diisocyanate and a tin urethane catalyst and
heating the resulting reaction mixture to 85.degree. C. for 45
minutes under nitrogen. Then, 5.74 parts of o,o'-diallylbisphenol A
are added, and the mixture is stirred for 120 minutes under vacuum
in a 100.degree. C. bath. 10.58 parts of cardanol are added and the
mixture is stirred for 240 minutes under vacuum in a 105.degree. C.
bath.
[0107] Toughener C is an elastomeric toughener having capped
isocyanate groups sold as Struktol.TM. 3604 by Struktol Company of
America.
[0108] The Core-Shell Rubber is a dispersion of core-shell rubber
particles in an epoxy resin, sold as Kane Ace MX 156 by Kaneka
Corporation.
[0109] Urea A is a 4,4'-methylene bis (phenyl dimethyl urea),
commercially available as Omicure U-52 from Emerald Performance
Products.
[0110] Urea B is isophorone bis(dimethylurea), commercially
available as Omicure U-35 from Emerald Performance Products.
[0111] Urea C is tetramethylurea.
[0112] EP796 is tris(2,4,6-dimethylaminomethyl)phenol in a
poly(vinylphenol) matrix.
Examples 1 and 2 and Comparative Samples A and B
[0113] Adhesive Examples 1 and 2 and Comparative Samples A and B
are prepared by blending ingredients as indicated in Table 1:
TABLE-US-00001 TABLE 1 Parts By Weight Comp. Comp. Component Ex. 1
Ex.2 Samp. A Samp. B Epoxy Resin A 28.44 28.44 28.44 34 Epoxy Resin
B 17 17 17 14.19 Epoxy Resin C 3 3 3 0 Toughener A 19.0 19.0 19.0
19.0 3-glycidyloxypropyltriethoxysilane 0.61 0.61 0.61 0.61
Surfactant 0.28 0.28 0.28 0.28 Colorant 0.35 0.35 0.35 0.35
Dicyanamide 5.17 5.17 5.15 5.22 Urea A 0 0.7 0.5 0 Urea B 0.7 0 0 0
EP796 0 0 0.3 0.7 Hydrophobic Fumed Silica 7.0 7.0 7.0 7.2 Calcium
Carbonate 10 10 10 10 Calcium Oxide 6.5 6.5 6.5 6.0 Talc 0.2 0.2
0.2 0.2 Glass Microspheres 1.75 1.75 1.75 2.25
[0114] Test samples for tensile strength, elongation and elastic
modulus measurements are made by curing a portion of each sample
for 30 minutes at 180.degree. C. Test specimens are cut from the
cured samples and evaluated according to DIN EN ISO 527-1.
[0115] Impact peel testing is performed for each adhesive sample.
The test coupons for the impact peel testing are 90 mm.times.20 mm
with a bonded area of 30.times.20 mm. The adhesive sample is then
applied to the bond area of a 1.2 mm-thick HC420LAD+Z100 hot dipped
zinc coated steel coupon. A 1.2 mm-thick HC340LAD+ZE 50-50
electrolytically zinc coated coupon is placed into contact with the
adhesive, and the assembly squeezed under a weight of about 10 kg
to prepare each test specimen, with spacers present to maintain an
adhesive layer thickness of 0.2 mm. The assembled test specimens
are cured at 180.degree. C. for 30 minutes. The impact peel testing
is performed in accordance with the ISO 11343 wedge impact method.
Testing is performed at an operating speed of 2 m/sec with samples
at a temperature of 23.degree. C.
[0116] Lap shear specimens are made using coupons of the same
materials. The specimens are made by sprinkling glass beads (0.2 mm
diameter) onto one of the coupons, applying the adhesive sample,
and then positioning the second coupon on top of the adhesive. The
bonded area in each case is 25.times.10 mm, and the adhesive layer
thickness is controlled by the glass beads to 0.2 mm. The test
specimens are cured for 30 minutes at 180.degree. C. and evaluated
for lap shear strength in accordance with DIN ISO 1465. Testing is
performed at 23.degree. C. and a test speed of 10 mm/minute.
Viscosity and yield stress are measured on a Bohlin CS-50
rheometer, C/P 20, up/down 0.1-20 s.sup.-1, with data evaluated
according to the Casson model.
[0117] A tack test is performed to evaluate the ability of each
adhesive to penetrate an oily coating. Two 40.times.125 mm metal
coupons are coated with about 1.8 g/m.sup.2 of a petroleum-based
stamping oil that has a kinematic viscosity of 60 centistokes at
40.degree. C. (Anticorit PL3802-395 from Fuchs Lubricants). Each
adhesive samples is blended with 2 weight percent 0.2 mm glass
beads to act as spacers. The adhesive is applied over the surface
of one of the coupons. The other coupon is laid on top of the
adhesive, and the assembly squeezed under an applied weight of
about 10 kg. After 30 minutes at room temperature, the coupons are
manually separated, and inspected for the distribution of the
adhesive between the coupons. The desired result is that the
adhesive is distributed evenly between the coupons after they are
separated, as this indicates a good ability for the adhesive to
penetrate through the oil layer.
[0118] The distribution of the adhesive on the separated coupons is
rated as "excellent", "adequate" or "poor". An "excellent" rating
means the adhesive is distributed essentially between the separated
coupons, with few if any areas where the adhesive has been pulled
away from either coupon. A sample of an "excellent rating" is shown
in FIG. 1A. An "adequate" rating means that although there is some
adhesive on each of the separated coupons, there are significant
areas (10 to 60% of the total contact area of the adhesive with the
coupon) from at least one of the coupons where the adhesive has
become pulled away. A sample of an "adequate" rating is shown in
FIG. 1B. A "poor" rating means that the adhesive is pulled away
from at least one of the coupons at more than 60% of the surface
area to which it is applied. A sample of a "poor" rating is shown
in FIG. 1C.
[0119] Wash-off testing is performed by applying an adhesive bead
to a 200.times.40 mm metal panel. A smaller (150.times.20 mm) panel
is placed on top of the adhesive bead, and five punch rivets are
set along the length of the assembly at a regular distance of 27
mm. During the riveting process, a portion of the adhesive is
squeezed out from under the smaller panel and becomes exposed.
Triplicate samples are produced with each adhesive. The samples are
vertically mounted to a stirrer and rack assembly. The rack
assembly is immersed in 60.degree. C. water and rotated at 140 rpm
for three minutes. The test samples are oriented on the stirred and
rack assembly so they move edge-on through the water as the stirred
rotates. The samples are then removed from the water, and the
exposed portion of the adhesive is examined visually.
[0120] Wash-off is indicated by the deformation of the exposed area
of the adhesive layer, particularly at the edges where it tends to
become separated from the surface of the larger metal coupon. If no
material deformation occurs, the sample is accorded an "excellent"
rating. Samples with only minor deformation of the adhesive are
rated as "good". Samples in which the edges of the exposed adhesive
layer are ruptured and have begun to wash onto the exposed surface
of the smaller panel are rated "fair". A "poor" rating indicates
substantial wash-off, with significant loss of material and/or
washing of significant portions of the adhesive onto the exposed
surface of the smaller panel.
[0121] Results of the various testing are as indicated in Table
2.
TABLE-US-00002 TABLE 2 Designation Comp. Comp. Ex. 1 Ex. 2 Samp. A
Samp. B Accelerator Urea A/EP EP Urea B Urea A 796 796 Property
Elastic Modulus, MPa 1800 2020 N.D. 1940 Tensile Strength, MPa 33
34 N.D. 33 Elongation at Break, % 3.6 3.8 N.D. 3.4 Impact Peel
Str., N/mm 25 27 N.D. 26.0 Lap Shear Str., MPa 33 31.4 32.2 32.9
Yield stress, 45.degree. C., Pa 880 950 675 600 Viscosity,
45.degree. C., Pa s 77 77 89 67 Tack Test Rating Excellent
Excellent Poor Poor Wash-off Test Rating Excellent Excellent Fair
Fair
[0122] Examples 1 and 2 both exhibit excellent results on the tack
and wash off tests. Comparative Sample A is made from essentially
the same formulation as Examples 1 and 2, except part of the urea
is replaced with an aminophenol. Despite the presence of both the
urea and the chain-extended toughener, the tack test rating falls
to poor, indicating an inability of this adhesive to penetrate
through an oily coating on the substrate. Comparative Sample B is a
slightly different formulation that when cured exhibits adhesive
and mechanical properties very similar to those of Examples 1 and
2. However, Comparative Sample B contains the aminophenol
accelerator and no urea. Its wash-off rating is only fair and the
tack test rating is poor.
[0123] These examples demonstrate the very substantial effect of
the selection of curing accelerator on the ability of the adhesive
to penetrate an oily coating and to resist wash-off. These results
are particularly surprising in view of the very small quantity of
accelerator in the formulations; the curing accelerator constitutes
less than 1% of each of these formulations.
Examples 3-5 and Comparative Samples C and D
[0124] Adhesive Examples 3 through 5 and Comparative Samples C and
D are prepared by blending ingredients as indicated in Table 3:
TABLE-US-00003 TABLE 3 Parts By Weight Comp. Comp. Component Ex. 3
Ex.4 Ex. 5 Samp. C Samp. D Epoxy Resin A 30.03 30.03 28.30 28.41
33.88 Epoxy Resin B 18 18 20 15 15 Epoxy Resin C 3 3 3 0 0
Toughener B 17 17 17 20 19 Toughener C 0 0 0 5 0
3-glycidyloxypropyl- 0.61 0.61 0.61 0.61 0.61 triethoxysilane
Surfactant 0.28 0.28 0.28 0.28 0.28 Colorant 0.35 0.35 0.4 0.35
0.35 Dicyanamide 4.83 4.83 4.81 5.00 5.33 Urea A 0.7 0.35 0 0 0
Urea B 0 0.35 0.7 0 0 EP796 0 0 0 0.7 0.7 Hydrophobic Fumed Silica
6.5 6.5 6.2 6.4 6.4 Calcium Carbonate 10 10 10 10 10 Calcium Oxide
6.5 6.5 6.5 6.0 6.0 Talc 0.2 0.2 0.2 0.2 0.2 Glass Microspheres 2 2
2 2.25 2.25
[0125] These adhesives are evaluated as described in the preceding
example. Results are as indicated in Table 4:
TABLE-US-00004 TABLE 4 Designation Comp. Comp. Ex. 3 Ex.4 Ex. 5
Samp. C Samp. D Accelerator Urea A Urea A Urea B Urea B EP 796 EP
796 Property Elastic Modulus, MPa 1780 1810 1870 1580 1840 Tensile
Strength, MPa 31 33 33 28 33 Elongation at Break, % 4.2 4.6 4.4 4.2
3.9 Impact Peel Str., N/mm 27 25 25 33 27 Lap Shear Str., MPa 32.3
30.4 33.7 29.2 31.2 Yield stress, 45.degree. C., Pa 681 706 763 607
675 Viscosity, 45.degree. C., Pa s 88 84 72 113 89 Tack Test Rating
Excellent Excellent Excellent Poor Poor Wash-off Test Rating
Excellent Excellent Excellent Fair Fair
[0126] The data in Table 4 again shows the large and unexpected
effect of curing agent on tack test rating. The aminophenol has a
large adverse affect, whereas the urea curing agents produce
adhesives that perform excellently on the tack test. Other
properties are largely unchanged across this set of adhesives.
Examples 6-8
[0127] Adhesive Examples 6 through 8 are prepared by blending
ingredients as indicated in Table 5:
TABLE-US-00005 TABLE 5 Parts By Weight Component Ex. 6 Ex. 7 Ex. 8
Epoxy Resin A 24.62 30.03 22.56 Epoxy Resin B 24 18 27 Epoxy Resin
C 3 3 3 Toughener A 17 17 17 3-glycidyloxypropyl- 0.61 0.61 0.61
triethoxysilane Surfactant 0.28 0.28 0.28 Colorant 0.35 0.35 0.35
Dicyanamide 4.74 4.83 4.75 Urea A 0.35 0.7 0.5 Urea B 0.35 0 0
Tetramethylurea 0 0 1.0 Hydrophobic Fumed Silica 6.0 6.5 7.5
Calcium Carbonate 10 10 10 Calcium Oxide 6.5 6.5 6.5 Talc 0.2 0.2
0.2 Glass Microspheres 2 2 1.75
[0128] These adhesives are evaluated as described in the preceding
example. Results are as indicated in Table 6:
TABLE-US-00006 TABLE 6 Designation Ex. 6 Ex. 7 Ex. 8 Accelerator
Urea A Urea A Urea B Urea A TMU Property Elastic Modulus, MPa 1950
2050 1980 Tensile Strength, MPa 36 35 36 Elongation at Break, % 4.3
3.9 3.8 Impact Peel Str., N/mm 24 24 27 Lap Shear Str., MPa 34.2
31.8 34.7 Yield stress, 45.degree. C., Pa 630 725 877 Viscosity,
45.degree. C., Pa s 81 72 67 Tack Test Rating Excellent Excellent
Adequate Wash-off Test Rating Excellent Excellent Good
[0129] As before, the selection of the chain-extended toughener in
conjunction with urea accelerators leads to adequate or better
results in the tack test and good or better results in the wash-off
test, when no aminophenol is present. Ex. 8 demonstrates that the
substitution of tetramethyl urea (TMU) for a part of Urea A leads
to some loss in tack test and wash-off resistance, although the
performance of that sample is till considered to be generally
good.
Comparative Samples E and F
[0130] Comparative Samples E and F are prepared by blending
ingredients as indicated in Table 7. Toughener C is an amine-capped
toughener prepared according to Example 2 of U.S. Pat. No.
8,404,787. Toughener D is a bis-phenol A capped toughener described
as Toughener B in WO 2005/007766. Neither Toughener C nor Toughener
D is chain extended, and neither is formed from an
isocyanate-terminated butadiene polymer.
TABLE-US-00007 TABLE 7 Parts By Weight Comp. Comp. Component Sample
E Sample F Epoxy Resin A 19.0 0 Epoxy Resin B 30 48.8 Epoxy Resin C
3 3 Toughener C 0 17 Toughener D 17 0
3-glycidyloxypropyltriethoxysilane 0.61 0.61 Surfactant 0.28 0.28
Colorant 0.35 0.35 Dicyanamide 4.6 4.6 Urea B 0.7 0.7 Hydrophobic
Fumed Silica 6.0 6.0 Calcium Carbonate 10 10 Calcium Oxide 6.5 6.5
Talc 0.2 0.2 Glass Microspheres 2 2
[0131] These adhesives are evaluated as described in the preceding
example. Results are as indicated in Table 8:
TABLE-US-00008 TABLE 8 Designation Comp. Comp. Sample E Sample F
Property Elastic Modulus, MPa 2110 1930 Tensile Strength, MPa 38 34
Elongation at Break, % 3.7 3.8 Lap Shear Str., MPa 36 34 Yield
stress, 45.degree. C., Pa 613 557 Viscosity, 45.degree. C., Pa s 96
78 Tack Test Rating Poor Poor Wash-off Test Rating Poor Poor
[0132] The tack test and wash-off results demonstrate the need for
the simultaneous selection of toughener and curing accelerator.
Although these samples are cured with a urea curing accelerator,
and contain no aminophenol, they nonetheless perform poorly on the
tack and wash-off tests. These poorer results are attributed to the
selection of the different tougheners. The selection of toughener
has a particularly large impact on wash-off test results.
* * * * *