Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
,~ W092/20754 PC~/~S92/01')74
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Field of Invention
The present invention relates to epoxide-based
adhesives, particularly adhesives whose hond ~trength is
i~?~ ~ enhanced through photopolymerization. The invention
also relates to transparent overlays with such adhesive
which can be applied to documents to deter tampering.
Backqround
Pressure-sensitive adhesives ("PSAs")
exhibiting tackiness at room temperature have been made
in a variety of compositions. Such adhesives offer
advantages of easy application, with successful bonding
typically being achieved upon application of limited
~;~ pressure, e.g., hand pressure. In many cases, such
adhesives tend to exhibit reduced bond strength when
subjected to elevated temperatures or organic solvents.
Although the bond strength of
pressure-sensitive adhesives is acceptable for many
; applications, in some instances, an adhesive that
provides useful room temperature tackiness as well as
resistance to adhesive failure under elevated
temperatures or upon exposure to organic solvents is
desired.
, one technique sometimes used to improve the
performance, e.g., increase the shear strength and peel
resistance, o~ certain pressure-sensitive adhesives at
elevated temperatures or in the presence of organic
solvents is to further crosslink the adhesive after its
application to a substrate. Such crosslinking can be
induced photochemically or thermally, or via chemical
reaction, e.g., 8uch as with moisture or encapsulated
~ 35 reactants. It has been observed, however, that in some
; instances crosslinking a pressure-sensitive adhesive
results in a reduction in adhesiveness. For example,
U.S. Patent No. 4,286,047 (Bennett et al.) discloses a
- normally tacky, pressure-sensitive adhesive having an
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epoxy equivalent value of about 400 to about 900 which
is susceptible to ultraviolet-induced detackification.
U.S. Patent No. 4,690,957 (Fujioka et al.);
x Chemical Patents Index, Basic Abstracts ~ournal, Section
Ch, r~eek 8519, 3 July 1985, Derwent Publications Ltd.,
GB, Class A, AN 85-113545/19 & JP A 60 055 069
(Mitsubishi Electric Corp.), 29 March 1985; and Chemical
Patents Index, Basic Abstracts Journal, Section Ch, Week
8518, 26 June 1985, Derwent Publications Ltd., London,
GB, Class A, AN 85-107731/18 ~ JP A 60 051 717
(Mitsubishi Electric Corp.), 23 March 1985 disclose
ultraviolet radiation-c~rable resin compositions which
each comprise:
a) 100 parts by weight of an epoxy resin
having two or more oxirane groups in each molecule
thereof;
b) 0.5 to 20 parts by weight of a phenoxy
resin having a molecular weight of from 10,000 to
60,000;
c) 0.5 to 20 parts by weight of a polyol; and
d) O.S to 10 parts by weight of a photo-
initiator.
U.S. Patent No. 4,2S6,828 (Smith) discloses
photocopolymerizable compositions which contain
epoxides, organic material with hydroxyl functionality,
and a photosensitive aromatic sulfonium or iodonium salt
of a halogen-containing complex ion.
U.S. Patent Nos. 4,173,476 and 4,231,951 (~oth
Smith et al.) disclose photopolymerizable epoxide
compositions containing triarylsulfonium complex salts
~` as photoinitiators.
U.S. Patent No. 4,218,531 (Carlson) discloses
photopolymerizable compositions containing epoxides, `-
aromatic sulfonium complex salts, and a material
containing at least one non-aromatic carbon-carbon
ethylenic unsaturation. The reference teaches that such
compositions can be cured without generation of
offensive odors.
i' :` 2 1 ~ ,~ 2 ~ 0
U.S. Patent No. 4,593,051 (Koleske) disclose~
photocopolymerizable compositions comprising an epoxide,
organic compound having two or more active hydrogens per
molecule, and photoinitiator.
Summary of Invention
The present invention provides a normally
tacky, pressure-sensitive adhesive which, upon exposure
to ultraviolet radiation, undergoes crosslinking to
result in increased bond strength and bond durability.
Bonds made with the adhesive compositions provided
herein typically exhibit resistance to failure, e.g.,
shear release, peel release, or cohesive failure, under
elevated temperatures (e.g., about 100C) and/or
exposure to organic solvents. Furthermore, the
compositions provided herein exhibit high transparency
to visible light both before and a~ter being cured.
Coupled with the bond strength characteristics mentioned
above, this makes adhesive compositions of the invention
well suited for use on tamper-resistant overlays for
documents.
In brief summary, the novel adhesives provided
comprise, and if desired may consist essentially of,
epoxide resin, polymeric film former, photoinitiator,
and polyol. Adhesives of the invention contain between
about 20 and about 80 parts by weight of film former per
100 parts by weight of epoxide component, between about
l and about 10 parts by weight of photoinitiator per 100
parts by weight of epoxide component, and between about
30 2 and about 20 parts by weight of polyol per 100 parts
- ~ ` by weight of epoxide component. Adhesives of the
invention may also optionally contain one or more of the
following: reactive diluent, solvent, toughening agent,
and other additive.
Adhesives of the present invention typically
exhibit an initial tackiness sufficient to provide an
initial peel strength of about 0.28 kilograms/centimeter-
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~ W092/20754 PCT/US92/l)1~ ~
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bisphenol A ("DGEHBA"), and bisphenol F ~'IDGEBFI');
cycloaliphatic epoxides; epoxide cre~ol novolac re~ins;
epoxide phenol novolac resins; and the like. Such
epoxide resins may be used singly or in combinations of
two or more.
. DGEBA resins are commonly available, e.g., from
Shell Chemical Company, Dow Chemical Company, and Ciba
Geigy Company. Typically, low molecular weight DGEBA
resins with an epoxy equivalent weight of below about
280 are preferred. DGEBA resins with epoxy equivalent
weights substantially above that range, e.g., above
about 300 or more, typically tend to be more solid in
character and less liquid in character at room
temperature, thereby reducing the desired tackiness of
the composition.
i Illustrative examples of cycloaliphatic epoxide
resins useful herein include those having an average of
two or more epoxide groups per molecule. The preferred
cycloaliphatic epoxide is 3,4-epoxide cyclohexylmethyl
-3,4-epoxidecyclohexane carboxylate, e.g., available
commercially as EPOXIDE ERL 4221 from Union Carbide
Company. Readily available, this is a fast reacting,
low viscosity resin. Bis~(3,4-epoxidecyclo-hexylmethyl)
adipate is an illustrative example of a cycloaliphatic
epoxide resin which is useful herein.
Phenol-novolac and cresol-novolac epoxide
resins are multifunctional resins derived from
epichlorohydrin and polynuclear phenolia or cresol
novolac. They are typically characterized by low
amounts of ionic and hydrolyzable chlorine impurities
and high chemical and thermal resistance. Illustrative
examples of commercially available supplies thereof
include Ciba-Geigy's EPN and ECN Epoxide Resin series.
Adhesive compositions o~ the present invention
may contain one or more of the epoxide resins described
above. Preferably, the room temperature viscosity of
the epoxide resin mixture is between about 1,000 and
about 30,000 centipoise, preferably between about 3,000
and about ~0,000 centipoise. Adhesive compositions made
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width (25 ounces/inch-width) when laminated to a
stainless steel panel and rolled once with a ~ 0
kilogram (4.5 pound) roller. Prior to being cured, the
adhesives provide a low bond strength, i.e., an overlap
shear strength of less than about 7.0
kilograms/centimeter2 (100 pounds/inch2) when laminated
between chromic acid etched aluminum panels. Upon full
cure of the adhesive with ultraviolet radiation
activation, sometimes in conjunction with heat, a bond
strength sufficient to provide an overlap shear strength
of about 141 kilograms/centimeter2 (2000 pounds/inch2)
on chromic acid etched aluminum may be achieved.
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Detailed Description of Illustrative Embodiments
Epoxide resins which may be used herein
include those containing two or more epoxide groups
having the formula:
/ \
-Cl I ,
and which are liquid at room temperature. The polymeric
film formers discussed below are typically relatively
non-tacky. In order to impart desired room temperature
tacky, pressure-sensitive characteristics to the overall
composition, the epoxide resin is preferably a liquid at
room temperature. Illustrative examples of useful
epoxide resins include diglycidyl ethers of various
phenol8, e.g., bisphenol A ("DGEBA"), hydrogenated
W092t207s4 PC~/US92/01974
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with epoxide resins having viscosities which are too
high may tend to exhibit undesirably low tack, whereas
those made with epoxide resins having visco~it~e~ which
are too low may tend to be subject to resin migration
and phase separation.
c- The polymeric film former is a pol~meric
material having a molecular weight which is higher than
that of the epoxide resin component. The film former
should be compatible with the epoxide resin, i.e., they
should not undergo phase separation such as during
storage of the resultant adhesive composition or of an
article comprising same. Polymeric materials which can
form a tough film at room temperature are preferred.
The film former preferably has a weight average
molecular weight between about lO,O00 and about 30,000.
~dhesive compositions made with film formers having
molecular weights which are too low tend to provide
poorer peel strength prior to photopolymerization.
Adhesive compositions made with film formers having
molecular weights which are too high may be harder to
make as the film former is typically more difficult to
handle, to dissolve, etc., and may be too viscous.
Illustrative examples of polymeric film formers
which are useful herein include polyacrylates,
polymethacrylates, phenoxy resins, polysulfones, and
polyether sulfones.
The proportion of film former incorporated in
adhesives of the invention will depend in part upon the
nature o~ the epoxide component, the particular film
former, and the degree of room temperature tackiness
desired. Typically, adhesives of the invention will
contain between about 15 and about lO0, preferably
between about 20 and about B0, and most preferably
between about 40 and about 60, parts by weight of film
former per lO0 parts by weight of epoxide component.
Adhesive compositions of the invention
typically contain a polyol component to increase the
initial tackiness, post cure flexibility, and open time
of the adhesive composition. Illustrative examples of
WO 92/20754 ~cr/Us92/0l974
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poly~ls which are useful in adhesive compositions o~ the
invention include the ~ollowing: polyether polyol,
polyester polyol, polycaprolactone polyol. The
aforementioned U.S. Patent Nos. 4,256,82~ and 4,593,051
disclose pol~ols which are useful in photopolymerizable
epoxide compositions. ,
Adhesive compositions of the invention
typically contain between about 2 and about 20 parts,
preferably between about 3 and about 15 parts, and more
lo preferably between about 4 and about lo parts, by weight
of polyol per loo parts by weight of epoxide component.
Adhesive compositions containing too much polyol tend to
undergo ultraviolet curing more slowly and, once cured,
exhibit lower peel strengths. Adhesive compositions
containing too little polyol may not cure completely,
even with thermal post treatment.
Many photoinitiators known for use in
photopolymerizable epoxide compositions may be used in
adhesive compositions of the invention. Illustrative
examples are disclosed in the aforementioned U.S. Patent
Nos. 4,231,951 and 4,256,828 and U.S. Patent No.
4,058,401 (Crivello). Preferred photoinitiators include
triaryl sulfonium salts and diaryl iodonium complex
salts. These photoinitiators are typically thermally
stable and readily available commercially and exhibit
good ultraviolet reactivity.
Adhesive compositions of the invention
typically contain between about 1 and about 10,
preferably between about 1.5 and about 6, and more
preferably between about 2 and about 4, parts by weight
of photoinitiator per 100 parts by weight of epoxide
component. Use of excessive amounts of photoinitiator
may act as a screen, thereby impairing the desired
photopolymerization of the adhesive. Also, large
residual amounts of unused initiator may tend to impair
the bonding characteristics of the cured adhesive.
If desired, adhesive compositions of the
invention may also contain one or more of such additives
as metal particles, metal-coated particles, coloring
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agents, processing aids, adhesion promoters, wett~ng
agents, and coupling agents.
Metal particles and metal-coated particles can
be incorporated to render the adhesive composition
conductive including anisotropically conductive if
desired. Illustrative examples include nickel particles
between about 6 and about 25 microns in diameter which
can be randomly dispersed in the composition.
The adhesive composition may be substantially
clear and colorless or may be colored by use of such
coloring agents as dyes and pigments. It will be
understood, however, that coloring agents may tend to
increase the opacity of the adhesive composition so as
to affect the photocuring properties thereof,
particularly when the adhesive is used in thick layers.
Accordingly, coloring agents used herein should be
selected and used in such quantities as will not
undesirably inhibit the photocuring properties of the
adhesive composition.
Adhesive compositions o~ the invention may
contain processing aids and modifiers, e.g., rheology
controlling agents such as fumed silica. Illustrative
examples of adhesion promoters and coupling agents
include silanes and titanates. Fluorochemical and other
surface energy controlling agents may be used. The
various components used in compositions of the invention
are preferably compatible with each other such that the
cured adhesive is substantially transparent, thereby
permitting the composition to be used in overlays, e.g.,
over information on documents.
Adhesives of the invention may be supplied in
film form, e.g., between release liners as a transfer
tape, to be laminated to a substrate.
Photopolymerization of the composition may be performed
after the various elements are assembled, e.g., by
exposure to ultraviolet radiation through a substrate
which is sufficiently transparent to such wavelengths,
or the adhesive may be exposed prior to assembly. Under
typical conditions, e.g., temperature of about 25C,
WO92/20754 PCT/~IS92/0~974
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relative humidity of about 60 percent, and W exposure
of about 0.1 Joule/centimeter2, adhesive compositions o~
the invention typically exhibit an open time of about 1
to 2 minutes. --
Adhesive compositions of the invention can be
used to bond substrates that previously known thermally ,
cured epoxide adhesives bonded, simultaneously providing
the advantages discussed herein. Subsequent to curing
by ultraviolet radiation, adhesives of the invention may
optionally be heated, i.e., thermally postcured or
thermal post treatment, to enhance the structural bond
strength of the bond. Typically, such treatment
involves heating the adhesive to a temperature of about
100C to about 120C for several minutes.
In some instances, adhesives of the invention
can be used to make transparent overlays for making
documents more tamper-resistant. One typical embodiment
of such overlays compriseæ a protective cover sheet such
as disclosed in U.S. Patent No. 3,170,183 (Sevelin et
al.), incorporated herein by reference, with a layer of
the adhesive provided herein on the back side. In an
inexpensive embodiment, the cover sheet may simply be
single or multi-ply polymer film, e.g., polyester, which
is typically preferably flexible and abrasion resistant.
Exa~p~e~
The invention will be further explained by the
~ollowing illustrative examples which are intended to be
nonlimiting. Unless otherwise indicated, all amounts
are expressed in parts by weight.
Unless otherwise indicated, the following test
method wa5 uged.
Ovçrlap Shear Strength
Overlap Shear Strength of indicated adhesives
was determined using aluminum panels having an overlap
^ region of about 1.0 inch by about 0.5 inch (2.5 by 1.3
centimeters). The aluminum panels were conditioned in
chromic acid at a temperature of about 65C to about
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70C for about 15 minutes and then rinsQd with tap
water. The panels were then allowed to dry at room
temperature for about 30 minutes and then at about 60C
to about 65C for 30 minutes. The sub~ect adhesive wa~
applied to a test panel at a thickne~s o~ about 1 to
. about 2 mils (25 to 50 microns), activated with
ultraviolet radiation as indicated, and then the ~econd
panel laminated thereto. Unless otherwise indicated,
the bond was then thermally postcured at about 110C to
lo about 115C ~or 20 minutes.
Examples 1-4
Adhesives were made using the following
components:
15 Notation Explanation
EPON 828 DGEBA resin from Shell Chemical
Company;
DER 684-EK40 Phenoxy resin in MEK, 40 percent by .
volume, from Dow Chemical company;
20 UCAR PKHH Solid phenoxy resin from Union Carbide
Company;
TASHFA Triarylsulfonium he~xafluorantimonate;
NIAX PPG 4025 Polypropylene glycol from Union Carbide
Company;
25 BTA-IIIF Plastic toughening agent from Rohm and
Haas Company;
CABOSIL M-5 Fumed silica, surface area 200 ~ 25
meters2/gram, from Cabot
Corporation;
CABOSIL N70-TS Fumed silica, surface area 100 + 20
meters2/gram, from Cabot
Corpor~tion;
MEK Methyl ethyl ketone, reagent grade;
Ni-CP Nickel-coated particles, 10 micron
average diameter.
The composition in each Example was as fol~ows:
Component Example
_ l _ _2 3 4
EPON 828 35.0 35.0 35.0 30.0
- .
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DER 684-EK40 21.0 0.0 24.0 36.0
UCAR P~H 0. 0 9 . O
TASHFA 1.70 1.70 0.73 0.75
NIAX PPG 4025 1.50 1.50 1.70 2.0
BTA-IIIF 4.0 0.0 0.0 0.0
CABOSIL M-5 1.3 1.3 0.0 0.0
CABOSIL N70-TS 0~0 0.0 1.25 1.3
MEK 2.0 15.0 0.0 4.0
Ni-CP 0.0 0.0 2.5 0.0
In Examples 1 and 2, the adhesive compositions
were cured with 6 seconds exposure to a 100 watt W -A
mercury bulb providing a W input of about 0.2
Joules/centimeter2 at room temperature. In Examples 3
~. .1
and 4, the adhesive compositions were cured with a 200
Watts/inch (79 Watts/centimeter) electrodeless mercury
lamp in a W processor. The exposure was measured with
a W-A radiometer to be about 0.050 Joules/centimeter2.
The joints were thermally postcured under slight
compression pressure using small binder clips. In each
sample, the adhesive composition was substantially
transparent before and after cure.
The Overlap Shear Strength of the adhesive in
each Example in kilograms/centimeter2 (in pounds/inch2)
was as follows:
Example_1 _ _2 _ ___ _4 _
Overlap Shear211 120 127 127
(3000) (1700~ (1800) (1800)
Example 5
Adhesive of the same composition as in Example
~ ~ 3 was placed in a thickness of between about 1.5 and
about 2 A 0~ mils (37 and 50 microns) onto two substrates:
(1) a gold-plated circuit board and (2) a glass slide.
The adhesive was activated with exposure to a 200
Watts/inch (79 Watts/centimeter) mercury lamp with total
energy output of about 0.050 Joules/centimeter2. A
flexible printed circuit was laminated to the adhesive
under about 30 kilograms/centimeter2 pressure at about
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110C for 10 seconds. The laminates were postcllred at
110C for 20 minutes.
The resistance,between the flexible printed
circuit leads and gold circuit board was 0.2 ohms or
less. The resistance between the adjacent leads o~ the
printed circuit was greater than 20 mega ohms, the
maximum value of the ohm meter used. This demonstrates
the highly anisotropic conductivity properties which may
be obtained with adhesives of the invention.
Example 6
An adhesive was made with the following
components:
Amount Components
1549.3 EPONEX DRH 1510, DGEHBA epoxide resin from
Shell Chemical Company;
31.-2 DER 684-EK40;
1.7 NIAX PPG 4025;
2.9 TASHFA;
2014.0 MEK;
0.9 CABOSIL M-5.
The adhesive was coated with a knife coater
onto the bottom side of 3M CONFIRM Brand Retroreflective
Security Laminate from which the commercially-shipped
adhesive had been removed to provide a dry thickness
between about 1 and about 2 mils (25 to 50 micrometers).
After evaporation of the MEX solvent, several samples of
the laminate were cut from the sheet and applied to a
document.
Each sample was exposed through the security
laminate using a 100 Watt WA mercury bulb placed at
between about 3 and about 5 inches (between about 7.6
and about 12.7 centimeters) from the document to cure
the adhesive. Irradiation for between about 0.5 and
about 3 minutes provided substantially equivalent
performance. The text on the doc~ment was easily
readable through the overlay in each sample.
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Different samples were treated with high
temperature, low temperature, water immersion, high
humidity, and immersion in organic solvents. Even after
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treat~e~ 6 Qersion for the indicated periods, none
of the samples could be removed from the document
without so severely damaging the document or the overlay
as to render them unusable. Samples were exposed to the
indicated conditions or immersed in the indicated
solvents for the indicated period shown in Table I.
Unless otherwise indicated, test was performed at room
temperature of about 23C.
Table I
Condition Duration
Exposure to 150C 30 minutes
Exposure to -300C 30 minutes
Immersion in water at 23C 30 days
Exposure to lO0 percent 30 days
relative humidity at 60C
" , .
. Immersion in Heptane 24 hours
Immersion in Turpentine 24 hours
Immersion in Acetonitrile l hour*
Immersion in Toluene 1 hour*
Immersion in Methanol 1 hour*
Immersion in Isopropanol 1 hour*
Immersion in Acetone 1 minute*
Immersion in Dimethyl formamide 1 minute*
Immersion in Ethyl acetate l minute*
Immersion in Chloroform 1 minute*
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* Substrate was destroyed when tested for longer
durations. Adhesive not observed to have
degraded. , .
~ Various modifications and alterations of this
: invention will become apparent to those skilled in the
art without departing from the scope and spirit of this
invention.
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