U.S. patent application number 14/515062 was filed with the patent office on 2015-02-05 for adhesives comprising crosslinker with (meth)acrylate group and olefin group and methods.
The applicant listed for this patent is 3M INNOVATIVE PROPERTIES COMPANY. Invention is credited to Corinne E. Lipscomb, Jayshree Seth.
Application Number | 20150037526 14/515062 |
Document ID | / |
Family ID | 50640053 |
Filed Date | 2015-02-05 |
United States Patent
Application |
20150037526 |
Kind Code |
A1 |
Seth; Jayshree ; et
al. |
February 5, 2015 |
ADHESIVES COMPRISING CROSSLINKER WITH (METH)ACRYLATE GROUP AND
OLEFIN GROUP AND METHODS
Abstract
There is provided an article having a release liner and a
pressure sensitive adhesive composition disposed along a major
surface of the release liner, where the pressure sensitive adhesive
composition has at least 50 wt-% of polymerized units derived from
alkyl meth(acrylate) monomer(s); and 0.2 to 15 wt-% of at least one
crosslinking monomers comprising a (meth)acrylate group and a
C.sub.6-C.sub.20 olefin group, the olefin group being optionally
substituted. In another embodiment, an adhesive composition is
described comprising a syrup comprising i) a free-radically
polymerizable solvent monomer; and ii) a solute (meth)acrylic
polymer comprising polymerized units derived from one or more
alkyl(meth)acrylate monomers; wherein the syrup comprises at least
one crosslinking monomer or the (meth)acrylic solute polymer
comprises polymerized units derived from at least one crosslinking
monomer, the crosslinking monomer comprising a (meth)acrylate group
and a C.sub.6-C.sub.20 olefin group, the olefin group being
optionally substituted.
Inventors: |
Seth; Jayshree; (Woodbury,
MN) ; Lipscomb; Corinne E.; (St. Paul, MN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
3M INNOVATIVE PROPERTIES COMPANY |
St. Paul |
MN |
US |
|
|
Family ID: |
50640053 |
Appl. No.: |
14/515062 |
Filed: |
October 15, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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PCT/US2014/033712 |
Apr 11, 2014 |
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14515062 |
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61811982 |
Apr 15, 2013 |
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Current U.S.
Class: |
428/41.3 |
Current CPC
Class: |
Y10T 428/1452 20150115;
C08K 7/28 20130101; C08L 2312/06 20130101; C09J 133/08 20130101;
C09J 7/385 20180101; C09J 2433/00 20130101; B05D 1/42 20130101;
C08K 3/36 20130101; B05D 3/067 20130101; C09J 2301/416
20200801 |
Class at
Publication: |
428/41.3 |
International
Class: |
C09J 7/02 20060101
C09J007/02 |
Claims
1. An article comprising a release liner and a pressure sensitive
adhesive composition disposed on a major surface of the release
liner, wherein the pressure sensitive adhesive comprises at least
50 wt-% of polymerized units derived from alkyl(meth)acrylate
monomer(s); and 0.2 to 15 wt-% of at least one crosslinking monomer
comprising a (meth)acrylate group and a C.sub.6-C.sub.20 olefin
group, the olefin group being straight-chained or branched and
optionally substituted.
2. The article of claim 1 wherein the pressure sensitive adhesive
comprises at least 55, 60, 65, or 70 wt-% of polymerized units
derived from one or more alkyl(meth)acrylate monomer(s).
3. The article of claim 1 wherein the crosslinking monomer has the
formula: ##STR00011## R1 is H or CH.sub.3, L is an optional linking
group; and R2 is an optionally substituted C.sub.6-C.sub.20 olefin
group.
4. The article of claim 3 wherein L comprises one or more alkylene
oxide groups.
5. The article of claim 3 wherein the crosslinking monomer is
selected from the group consisting of citronellyl(meth)acrylate,
geraniol(meth)acrylate, farnesol(meth)acrylate,
undecenyl(meth)acrylate, and oleyl(meth)acrylate.
6. The article of claim 1 wherein the pressure sensitive adhesive
composition comprises at least 50, 55, 60, 65, or 70 wt-% of
polymerized units of alkyl(meth)acrylates comprising 6 to 20 carbon
atoms.
7. The article of claim 1 wherein the pressure sensitive adhesive
comprises a bio-based content of at least 25% of the total carbon
content.
8. The article of claim 1 wherein the pressure sensitive adhesive
comprises polymerized units derived from 2-octyl(meth)acrylate.
9. The article of claim 1 wherein the pressure sensitive adhesive
further comprises filler.
10. The article of claim 9 wherein the filler comprises fumed
silica, glass bubbles, or a combination thereof.
11. The article of claim 1 wherein the pressure sensitive adhesive
composition further comprises a tackifier.
12. The article of claim 1 wherein the pressure sensitive adhesive
composition further comprises polymerized units derived from at
least one monomer selected from acid-functional monomers, non-acid
functional polar monomers, vinyl monomers, and combinations
thereof.
13. The article of claim 1 wherein the pressure sensitive adhesive
further comprises a multifunctional (meth)acrylate crosslinker, a
triazine crosslinker, or a combination thereof.
14. The article of claim 1 wherein the pressure sensitive adhesive
exhibits a 180.degree. degree peel adhesion to stainless steel of
at least 15 N/dm after curing.
15. The article of claim 1 wherein the pressure sensitive adhesive
composition comprises 0 to 1.0 wt-% of polymerized units derived
from acid-functional monomers.
16. The article of claim 1 wherein the pressure sensitive adhesive
composition comprises 0 to 10 wt-% of polymerized units derived
from high Tg monomers.
17. The article of claim 1 wherein the release liner is created by
applying a layer comprising a (meth)acrylate-functional siloxane to
a major surface of a substrate; and irradiating said layer, in a
substantially inert atmosphere comprising no greater than 500 ppm
oxygen, with a short wavelength polychromatic ultraviolet light
source having at least one peak intensity at a wavelength of from
about 160 nanometers to about 240 nanometers to at least partially
cure the layer, optionally wherein the layer is at a curing
temperature greater than 25.degree. C.
18. The article of claim 17 wherein the at least one peak intensity
is at a wavelength between about 170 nanometers to about 220
nanometers.
19. The article of claim 18 wherein the peak intensity is at a
wavelength of about 185 nanometers.
20. The article of claim 17 wherein the short wavelength
polychromatic ultraviolet light source comprises at least one low
pressure mercury vapor lamp, at least one low pressure mercury
amalgam lamp, at least one pulsed Xenon lamp, at least one glow
discharge from a polychromatic plasma emission source, or
combinations thereof.
21. The article of claim 17 wherein the layer consists essentially
of one or more (meth)acrylate-functional siloxane monomers.
22. The article of claim 17 wherein the layer consists essentially
of one or more (meth)acrylate-functional siloxane oligomers.
23. The article of claim 17 wherein the layer consists essentially
of one or more (meth)acrylate-functional polysiloxanes.
24. The article of claim 17 wherein the layer further comprises one
or more copolymerizable materials selected from the group
consisting of monofunctional (meth)acrylate monomers, difunctional
(meth)acrylate monomers, polyfunctional (meth)acrylate monomers
having functionality greater than two, vinyl ester monomers, vinyl
ester oligomers, vinyl ether monomers, and vinyl ether
oligomers.
25. The article of claim 17 wherein the layer further comprises at
least one functional polysiloxane material which does not comprise
a (meth)acrylate functionality.
26. The article of claim 25 wherein the functional polysiloxane
material is selected from at least one a vinyl-functional
polysiloxane, a hydroxy-functional polysiloxane, an
amine-functional polysiloxane, a hydride-functional polysiloxane,
an epoxy-functional polysiloxane, and combinations thereof.
27. The article of claim 17 wherein the layer further comprises at
least one non-functional polysiloxane material.
28. The article of claim 27 wherein the at least one non-functional
polysiloxane material is selected from at least one of a
poly(dialkylsiloxane), a poly(alkylarylsiloxane), a
poly(diarylsiloxane), a poly(dialkyldiarylsiloxane), or a
combination thereof, optionally wherein the non-functional
polysiloxane material comprises from 0.1 wt. % to 95 wt. %,
inclusive, of the at least partially cured layer.
29. The article of claim 17 wherein the layer is substantially free
of an added photoinitiator.
30. The article of claim 17 wherein the layer is substantially free
of an organic solvent.
31. The article of claim 17 wherein the substantially inert
atmosphere comprises no greater than 50 ppm oxygen.
32. The article of claim 17 wherein applying the layer to the
surface of the substrate comprises applying a discontinuous
coating.
33. The article of claim 17 wherein the layer is substantially free
of metal catalyst.
34. An article comprising a release liner and a pressure sensitive
adhesive composition disposed on a major surface of the release
liner, wherein the pressure sensitive adhesive is a UV curable
(meth)acrylic pressure sensitive adhesive that is substantially
free of halogens, and further wherein the release liner comprises a
UV curable release layer on a major surface of a substrate.
35. The article of claim 34 wherein the release layer comprises a
(meth)acrylate-functional siloxane.
36. The article of claim 34 wherein the release liner is derived by
applying a layer comprising a (meth)acrylate-functional siloxane to
a major surface of a substrate; and irradiating said layer, in a
substantially inert atmosphere comprising no greater than 500 ppm
oxygen, with a short wavelength polychromatic ultraviolet light
source having at least one peak intensity at a wavelength of from
about 160 nanometers to about 240 nanometers to at least partially
cure the layer, optionally wherein the layer is at a curing
temperature greater than 25.degree. C.
37. The article of claim 34 wherein the pressure sensitive adhesive
comprises a bio-based content of at least 25% of the total carbon
content.
38. An article comprising a release liner and a pressure sensitive
adhesive composition disposed on a major surface of the release
liner, wherein the pressure sensitive adhesive comprises at least
50 wt-% of polymerized units derived from alkyl(meth)acrylate
monomer(s); and 0.2 to 15 wt-% of at least one crosslinking monomer
comprising a (meth)acrylate group and a C.sub.6-C.sub.20 olefin
group, the olefin group being straight-chained or branched and
optionally substituted, and further wherein the release liner is
derived by applying a layer comprising a (meth)acrylate-functional
siloxane to a major surface of a substrate; and irradiating said
layer, in a substantially inert atmosphere comprising no greater
than 500 ppm oxygen, with a short wavelength polychromatic
ultraviolet light source having at least one peak intensity at a
wavelength of from about 160 nanometers to about 240 nanometers to
at least partially cure the layer, optionally wherein the layer is
at a curing temperature greater than 25.degree. C.
39. The article of claim 38 wherein the pressure sensitive adhesive
comprises a bio-based content of at least 25% of the total carbon
content.
Description
BACKGROUND
[0001] As described in WO 2012/177337, there are two major
crosslinking mechanisms for acrylic adhesives: free-radical
copolymerization of multifunctional ethylenically unsaturated
groups with the other monomers, and covalent or ionic crosslinking
through the functional monomers, such as acrylic acid. Another
method is the use of UV crosslinkers, such as copolymerizable
benzophenones or post-added photocrosslinkers, such as
multifunctional benzophenones and triazines. In the past, a variety
of different materials have been used as crosslinking agents, e.g.,
polyfunctional acrylates, acetophenones, benzophenones, and
triazines. The foregoing crosslinking agents, however, possess
certain drawbacks which include one or more of the following: high
volatility; incompatibility with certain polymer systems;
generation of undesirable color; requirement of a separate
photoactive compound to initiate the crosslinking reaction; and
high sensitivity to oxygen. A particular issue for the electronics
industry and other applications in which PSAs contact a metal
surface is the generation of corrosive by-products and the
generation of undesirable color.
BRIEF DESCRIPTION OF THE DRAWINGS
[0002] The disclosure may be more completely understood in
consideration of the following detailed description of various
embodiments of the disclosure in connection with the accompanying
figures, in which:
[0003] FIG. 1 depicts the tan delta, the ratio of the shear loss
modulus (G'') to the shear storage modulus (G'), as determined by
dynamic mechanical analysis.
[0004] FIG. 2 illustrates an exemplary ultraviolet radiation curing
chamber useful in some exemplary embodiments of the present
disclosure.
[0005] FIG. 3 illustrates an exemplary article including an
ultraviolet radiation cured coating according to some exemplary
embodiments of the present disclosure.
[0006] While the above-identified drawings, which may not be drawn
to scale, set forth various embodiments of the present disclosure,
other embodiments are also contemplated, as noted in the Detailed
Description. In all cases, this disclosure describes the presently
disclosed invention by way of representation of exemplary
embodiments and not by express limitations. It should be understood
that numerous other modifications and embodiments can be devised by
those skilled in the art, which fall within the scope and spirit of
this invention.
SUMMARY
[0007] Thus, industry would find advantage in alternative
crosslinkers that are substantially free of halogens for use in
pressure sensitive adhesives. There is also a need for articles
having these adhesives disposed on a major surface of a release
liner that is substantially free of metal catalyst.
[0008] In one aspect, the present disclosure provides an article
comprising a release liner and a pressure sensitive adhesive
composition disposed on a major surface of the release liner,
wherein the pressure sensitive adhesive comprises at least 50 wt-%
of polymerized units derived from alkyl(meth)acrylate monomer(s);
and 0.2 to 15 wt-% of at least one crosslinking monomer comprising
a (meth)acrylate group and a C.sub.6-C.sub.20 olefin group, the
olefin group being straight-chained or branched and optionally
substituted.
[0009] In some embodiments, the present disclosure provides
articles such as those according to the previously mention aspect
in which the release liner is created by applying a layer
comprising a (meth)acrylate-functional siloxane to a major surface
of a substrate; and irradiating said layer, in a substantially
inert atmosphere comprising no greater than 500 ppm oxygen, with a
short wavelength polychromatic ultraviolet light source having at
least one peak intensity at a wavelength of from about 160
nanometers to about 240 nanometers to at least partially cure the
layer, optionally wherein the layer is at a curing temperature
greater than 25.degree. C.
[0010] In another aspect, the present disclosure provides an
article comprising a release liner and a pressure sensitive
adhesive composition disposed on a major surface of the release
liner, wherein the pressure sensitive adhesive is a UV curable
(meth)acrylic pressure sensitive adhesive that is substantially
free of halogens, and further wherein the release liner comprises a
UV curable release layer on a major surface of a substrate.
[0011] In yet another aspect, the present disclosure provides an
article comprising a release liner and a pressure sensitive
adhesive composition disposed on a major surface of the release
liner, wherein the pressure sensitive adhesive comprises at least
50 wt-% of polymerized units derived from alkyl(meth)acrylate
monomer(s); and 0.2 to 15 wt-% of at least one crosslinking monomer
comprising a (meth)acrylate group and a C.sub.6-C.sub.20 olefin
group, the olefin group being straight-chained or branched and
optionally substituted, and further wherein the release liner is
derived by applying a layer comprising a (meth)acrylate-functional
siloxane to a major surface of a substrate; and irradiating said
layer, in a substantially inert atmosphere comprising no greater
than 500 ppm oxygen, with a short wavelength polychromatic
ultraviolet light source having at least one peak intensity at a
wavelength of from about 160 nanometers to about 240 nanometers to
at least partially cure the layer, optionally wherein the layer is
at a curing temperature greater than 25.degree. C.
DETAILED DESCRIPTION
[0012] The present disclosure describes pressure sensitive
adhesives (PSAs) prepared from crosslinkable (e.g. syrup)
compositions, as well as articles. The crosslinked
pressure-sensitive adhesives provide a suitable balance of tack,
peel adhesion, and shear holding power. Further, the storage
modulus of the pressure sensitive adhesive at the application
temperature, typically room temperature (25.degree. C.), is less
than 3.times.10.sup.5 dynes/cm at a frequency of 1 Hz. In some
embodiments, the adhesive is a pressure sensitive adhesive at an
application temperature that is greater than room temperature. For
example, the application temperature may be 30, 35, 40, 45, 50, 55,
or 65.degree. C. In this embodiment, the storage modulus of the
pressure sensitive adhesive at room temperature (25.degree. C.) is
typically less than 3.times.10.sup.6 dynes/cm at a frequency of 1
Hz. In some embodiments, the storage modulus of the pressure
sensitive adhesive at room temperature (25.degree. C.) is less than
2.times.10.sup.6 dynes/cm or 1.times.10.sup.6 dynes/cm at a
frequency of 1 Hz.
[0013] Words of orientation such as "atop, "on," "covering,"
"uppermost," "overlaying," "underlying" and the like for describing
the location of various layers, refer to the relative position of a
layer with respect to a horizontally-disposed, upwardly-facing
substrate. It is not intended that the substrate, layers or
articles encompassing the substrate and layers, should have any
particular orientation in space during or after manufacture.
[0014] "Layer" refers to any material or combination of materials
on or overlaying a substrate.
[0015] "Overcoat" or "overcoated" describes the position of a layer
with respect to a substrate or another layer of a multi-layer
construction, means that the described layer is atop or overlaying
the substrate or another layer, but not necessarily adjacent to or
contiguous with either the substrate or the other layer.
[0016] The term "separated by" to describe the position of a layer
with respect to another layer and the substrate, or two other
layers, means that the described layer is between, but not
necessarily contiguous with, the other layer(s) and/or
substrate.
[0017] "Syrup composition" refers to a solution of a solute polymer
in one or more solvent monomers, the composition having a viscosity
from 100 to 8,000 cPs at 25.degree. C. The viscosity of the syrup
is greater than the viscosity of the solvent monomer(s).
[0018] "alkyl" refers to straight-chained, branched, and cyclic
alkyl groups and includes both unsubstituted and substituted alkyl
groups. Unless otherwise indicated, the alkyl groups typically
contain from 1 to 20 carbon atoms. Examples of "alkyl" as used
herein include, but are not limited to, methyl, ethyl, n-propyl,
n-butyl, n-pentyl, isobutyl, t-butyl, isopropyl, n-octyl, 2-octyl,
n-heptyl, ethylhexyl, cyclopentyl, cyclohexyl, cycloheptyl,
adamantyl, and norbornyl, and the like. Unless otherwise noted,
alkyl groups may be mono- or polyvalent.
[0019] The term heteroalkyl refers to an alkyl group, as just
defined, having at least one catenary carbon atom (i.e. in-chain)
replaced by a catenary heteroatom such as O, S, or N.
[0020] The term olefin group refers to an unsaturated aliphatic
straight-chained, branched, or cyclic (i.e. unsubstituted)
hydrocarbon group having one or more double bonds. Those containing
one double bond are commonly called alkenyl groups. In some
embodiments, the cyclic olefin group comprises less than 10 or 8
carbon atoms, such as in the case of cyclohexenyl. In some
embodiments, the olefin group may further comprise substituents as
will subsequently be described. The olefin group is typically
monovalent.
[0021] "Renewable resource" refers to a natural resource that can
be replenished within a 100 year time frame. The resource may be
replenished naturally or via agricultural techniques. The renewable
resource is typically a plant (i.e. any of various photosynthetic
organisms that includes all land plants, inclusive of trees),
organisms of Protista such as seaweed and algae, animals, and fish.
They may be naturally occurring, hybrids, or genetically engineered
organisms. Natural resources such as crude oil, coal, and peat
which take longer than 100 years to form are not considered to be
renewable resources.
[0022] "Catenated heteroatom" means an atom other than carbon (for
example, oxygen, nitrogen, or sulfur) that replaces one or more
carbon atoms in a carbon chain (for example, so as to form a
carbon-heteroatom-carbon chain or a
carbon-heteroatom-heteroatom-carbon chain);
[0023] "Cure" means conversion to a crosslinked polymer network
(for example, through catalysis);
[0024] "Fluoro-" (for example, in reference to a group or moiety,
such as in the case of "fluoroalkylene" or "fluoroalkyl" or
"fluorocarbon") or "fluorinated" means only partially fluorinated
such that there is at least one carbon-bonded hydrogen atom;
[0025] "Fluorochemical" means fluorinated or perfluorinated;
[0026] "Heteroorganic" means an organic group or moiety (for
example, an alkyl or alkylene group) containing at least one
heteroatom (preferably, at least one catenated heteroatom);
[0027] "Hydrosilyl" refers to a monovalent moiety or group
comprising a silicon atom directly bonded to a hydrogen atom (for
example, the hydrosilyl moiety can be of formula
--Si(R).sub.3-p(H).sub.p, where p is an integer of 1, 2, or 3 and R
is a hydrolyzable or non-hydrolyzable group (preferably,
non-hydrolyzable) such as alkyl or aryl);
[0028] "Hydroxysilyl" refers to a monovalent moiety or group
comprising a silicon atom directly bonded to a hydroxyl group (for
example, the hydroxysilyl moiety can be of formula
--Si(R).sub.3-p(OH).sub.p where p is an integer of 1, 2, or 3 and R
is a hydrolyzable or non-hydrolyzable group (preferably,
non-hydrolyzable) such as alkyl or aryl);
[0029] "Isocyanato" means a monovalent group or moiety of formula
--NCO;
[0030] "Mercapto" means a monovalent group or moiety of formula
--SH;
[0031] "Oligomer" means a molecule that comprises at least two
repeat units and that has a molecular weight less than its
entanglement molecular weight; such a molecule, unlike a polymer,
exhibits a significant change in properties upon the removal or
addition of a single repeat unit;
[0032] "Oxy" means a divalent group or moiety of formula --O--;
and
[0033] "Perfluoro-" (for example, in reference to a group or
moiety, such as in the case of "perfluoroalkylene" or
"perfluoroalkyl" or "perfluorocarbon") or "perfluorinated" means
completely fluorinated such that, except as may be otherwise
indicated, there are no carbon-bonded hydrogen atoms replaceable
with fluorine.
[0034] "Intensity peak" refers to a local maximum in an emission
spectrum for a UV radiation source when plotted as emission
intensity as a function of emission wavelength. The emission
spectrum may have one or more intensity peaks over the wavelength
range covered by the emission spectrum. Thus, an intensity peak
need not correspond to the maximum emission intensity peak over the
entire wavelength range covered by the emission spectrum.
[0035] "Polychromatic UV radiation," "polychromatic UV light,"
"short wavelength polychromatic UV radiation," and "short
wavelength polychromatic UV light" all refer to ultraviolet
radiation or light having an emission wavelength of 400 nm or less
wherein the emission spectrum includes at least two intensity
peaks, with at least one intensity peak occurring at no greater
than 240 nanometers (nm).
[0036] "Substantially inert atmosphere" refers to an atmosphere
having an oxygen content of no greater than 500 ppm.
[0037] "Substantially free of halogens" refers to a pressure
sensitive adhesive in composition which a substance containing a
halogen atom is not used intentionally as a main component.
[0038] "Substantially free of metal catalyst" refers to a release
composition in which a substance containing a metal catalyst is not
used intentionally as a main component.
[0039] "(Meth)acrylic" or "(meth)acrylic-functional" includes
materials that include one or more ethylenically unsaturated
acrylic- and/or methacrylic-functional groups, e.g.
-AC(O)C(R).dbd.CH.sub.2, preferably wherein A is O, S or NR',
wherein R' is a hydrogen atom or a hydrocarbon group; and R is a
1-4 carbon lower alkyl group, H or F. Herein, "(meth)acryloyl" is
inclusive of (meth)acrylate and (meth)acrylamide. Herein,
"(meth)acrylic" includes both methacrylic and acrylic.
Herein, "(meth)acrylate" includes both methacrylate and
acrylate.
[0040] "Siloxane" includes any chemical compound composed of units
of --O--Si--O-- and having the generalized formula R'.sub.2SiO,
wherein R' is a hydrogen atom or a hydrocarbon group.
[0041] "(Co)polymer" or "(co)polymeric" includes homopolymers and
copolymers, as well as homopolymers or copolymers that may be
formed in a miscible blend, e.g., by coextrusion or by reaction,
including, e.g., transesterification. The term "copolymer" includes
random, block, graft, and star copolymers.
[0042] "Cure" or "curable" refers to a process that causes a
chemical change, e.g., a reaction to solidify a layer or increase
its viscosity.
[0043] "Cured (co)polymer layer" or "cured (co)polymer" includes
both cross-linked and uncross-linked (co)polymers.
[0044] "Cross-linked" (co)polymer refers to a (co)polymer whose
(co)polymer chains are joined together by covalent chemical bonds,
usually via cross-linking molecules or groups, to form a network
(co)polymer. A cross-linked (co)polymer is generally characterized
by insolubility, but may be swellable in the presence of an
appropriate solvent.
[0045] "Unaged peel adhesion" refers to peel adhesion measured
according to the release test described herein on a release surface
maintained at a temperature of no more than 25.degree. C. at no
more than 75% relative humidity for no more than 24 hours before
the measurement. Preferably, the unaged peel adhesion is measured
on a release surface within one hour of preparation of the release
surface.
[0046] "Aged peel adhesion" refers to peel adhesion measured
according to the release test described herein on a release surface
aged for at least seven days at 90.degree. C. and 90% relative
humidity.
[0047] When a group is present more than once in a formula
described herein, each group is "independently" selected unless
specified otherwise.
[0048] The adhesive comprises a (meth)acrylic polymer prepared from
one or more monomers common to acrylic adhesives, such as a
(meth)acrylic ester monomers (also referred to as (meth)acrylate
acid ester monomers and alkyl(meth)acrylate monomers) optionally in
combination with one or more other monomers such as acid-functional
ethylenically unsaturated monomers, non-acid-functional polar
monomers, and vinyl monomers.
[0049] The (meth)acrylic polymer comprises one or more
(meth)acrylate ester monomers derived from a (e.g. non-tertiary)
alcohol containing from 1 to 14 carbon atoms and preferably an
average of from 4 to 12 carbon atoms.
[0050] Examples of monomers include the esters of either acrylic
acid or methacrylic acid with non-tertiary alcohols such as
ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 1-pentanol,
2-pentanol, 3-pentanol, 2-methyl-1-butanol, 3-methyl-1-butanol,
1-hexanol, 2-hexanol, 2-methyl-1-pentanol, 3-methyl-1-pentanol,
2-ethyl-1-butanol, 3,5,5-trimethyl-1-hexanol, 3-heptanol,
1-octanol, 2-octanol, isooctylalcohol, 2-ethyl-1-hexanol,
1-decanol, 2-propylheptanol, 1-dodecanol, 1-tridecanol,
1-tetradecanol, and the like. In some embodiments, a preferred
(meth)acrylate ester monomer is the ester of (meth)acrylic acid
with isooctyl alcohol.
[0051] In some favored embodiments, the monomer is the ester of
(meth)acrylic acid with an alcohol derived from a renewable source.
A suitable technique for determining whether a material is derived
from a renewable resource is through .sup.14C analysis according to
ASTM D6866-10, as described in US2012/0288692. The application of
ASTM D6866-10 to derive a "bio-based content" is built on the same
concepts as radiocarbon dating, but without use of the age
equations. The analysis is performed by deriving a ratio of the
amount of organic radiocarbon (.sup.14C) in an unknown sample to
that of a modern reference standard. The ratio is reported as a
percentage with the units "pMC" (percent modern carbon).
[0052] One suitable monomer derived from a renewable source is
2-octyl(meth)acrylate, as can be prepared by conventional
techniques from 2-octanol and (meth)acryloyl derivatives such as
esters, acids and acyl halides. The 2-octanol may be prepared by
treatment of ricinoleic acid, derived from castor oil, (or ester or
acyl halide thereof) with sodium hydroxide, followed by
distillation from the co-product sebacic acid. Other (meth)acrylate
ester monomers that can be renewable are those derived from ethanol
and 2-methyl butanol. In some embodiments, the (e.g. pressure
sensitive) adhesive composition (e.g. (meth)acrylic polymer and/or
free-radically polymerizable solvent monomer) comprises a bio-based
content of at least 25, 30, 35, 40, 45, or 50 wt-% using ASTM
D6866-10, method B. In other embodiments, the (e.g. pressure
sensitive) adhesive composition comprises a bio-based content of at
least 55, 60, 65, 70, 75, or 80 wt-%. In yet other embodiments, the
(e.g. pressure sensitive) adhesive composition comprises a
bio-based content of at least 85, 90, 95, 96, 97, 99 or 99
wt-%.
[0053] The (e.g. pressure sensitive) adhesive (e.g. (meth)acrylic
polymer and/or solvent monomer) comprises one or more low Tg
(meth)acrylate monomers, having a T.sub.g no greater than
10.degree. C. when reacted to form a homopolymer. In some
embodiments, the low Tg monomers have a T.sub.g no greater than
0.degree. C., no greater than -5.degree. C., or no greater than
-10.degree. C. when reacted to form a homopolymer. The T.sub.g of
these homopolymers is often greater than or equal to -80.degree.
C., greater than or equal to -70.degree. C., greater than or equal
to -60.degree. C., or greater than or equal to -50.degree. C. The
T.sub.g of these homopolymers can be, for example, in the range of
-80.degree. C. to 20.degree. C., -70.degree. C. to 10.degree. C.,
-60.degree. C. to 0.degree. C., or -60.degree. C. to -10.degree.
C.
[0054] The low Tg monomer may have the formula
H.sub.2C.dbd.CR.sup.1C(O)OR.sup.8
wherein R.sup.1 is H or methyl and R.sup.8 is an alkyl with 1 to 22
carbons or a heteroalkyl with 2 to 20 carbons and 1 to 6
heteroatoms selected from oxygen or sulfur. The alkyl or
heteroalkyl group can be linear, branched, cyclic, or a combination
thereof.
[0055] Exemplary low Tg monomers include for example ethyl
acrylate, n-propyl acrylate, n-butyl acrylate, isobutyl acrylate,
t-butyl acrylate, n-pentyl acrylate, isoamyl acrylate, n-hexyl
acrylate, 2-methylbutyl acrylate, 2-ethylhexyl acrylate,
4-methyl-2-pentyl acrylate, n-octyl acrylate, 2-octyl acrylate,
isooctyl acrylate, isononyl acrylate, decyl acrylate, isodecyl
acrylate, lauryl acrylate, isotridecyl acrylate, octadecyl
acrylate, and dodecyl acrylate.
[0056] Low Tg heteroalkyl acrylate monomers include, but are not
limited to, 2-methoxyethyl acrylate and 2-ethoxyethyl acrylate.
[0057] In some embodiments, the (e.g. pressure sensitive) adhesive
(e.g. (meth)acrylic polymer and/or free radically polymerizable
solvent monomer) comprises low Tg monomer(s) having an alkyl group
with 6 to 20 carbon atoms. In some embodiments, the low Tg monomer
has an alkyl group with 7 or 8 carbon atoms. Exemplary monomers
include, but are not limited to, 2-ethylhexyl methacrylate,
isooctyl methacrylate, n-octyl methacrylate, 2-octyl methacrylate,
isodecyl methacrylate, and lauryl methacrylate. Likewise, some
heteroalkyl methacrylates such as 2-ethoxy ethyl methacrylate can
also be used.
[0058] In some embodiments, the (e.g. pressure sensitive) adhesive
(e.g. (meth)acrylic polymer and/or solvent monomer) comprises a
high T.sub.g monomer, having a T.sub.g greater than 10.degree. C.
and typically of at least 15.degree. C., 20.degree. C. or
25.degree. C., and preferably at least 50.degree. C. Suitable high
Tg monomers include, for example, t-butyl acrylate, methyl
methacrylate, ethyl methacrylate, isopropyl methacrylate, n-butyl
methacrylate, isobutyl methacrylate, s-butyl methacrylate, t-butyl
methacrylate, stearyl methacrylate, phenyl methacrylate, cyclohexyl
methacrylate, isobornyl acrylate, isobornyl methacrylate,
norbornyl(meth)acrylate, benzyl methacrylate, 3,3,5
trimethylcyclohexyl acrylate, cyclohexyl acrylate, N-octyl
acrylamide, and propyl methacrylate or combinations.
[0059] In some embodiments, the (meth)acrylic polymer is a
homopolymer. In other embodiments, the (meth)acrylic polymer is a
copolymer. Unless specified otherwise, the term polymer refers to
both a homopolymer and copolymer.
[0060] The T.sub.g of the copolymer may be estimated by use of the
Fox equation, based on the T.sub.gs of the constituent monomers and
the weight percent thereof.
[0061] The alkyl(meth)acrylate monomers are typically present in
the (meth)acrylic polymer in an amount of at least 85, 86, 87, 88,
89, or 90 up to 95, 96, 97, 98, or 99 parts by weight, based on 100
parts by weight of the total monomer or polymerized units. When
high T.sub.g monomers are included in a pressure sensitive
adhesive, the adhesive may include at least 5, 10, 15, 20, to 30
parts by weight of such high Tg monomer(s). When the (e,g. pressure
sensitive) adhesive composition is free of unpolymerized
components, such as tackifier, silica, and glass bubbles, the parts
by weight of the total monomer or polymerized units is
approximately the same as the wt-% present in the total adhesive
composition. However, when the (e.g. pressure sensitive) adhesive
composition comprises such unpolymerized components, the (e.g.
pressure sensitive) adhesive composition can comprises
substantially less alkyl(meth)acrylate monomer(s) and crosslinking
monomer. The (e.g. pressure sensitive) adhesive composition
comprises at least 50 wt-% of polymerized units derived from
alkyl(meth)acrylate monomers. In some embodiments, the pressure
sensitive adhesive composition comprises at least 50, 55, 60, 65,
70, 75, 80, 85, or 90 parts by weight, based on 100 parts by weight
of the total monomer (or wt-% of the total adhesive composition) of
one or more low Tg monomers. For embodied methods wherein the
adhesive is not a pressure sensitive adhesive, the adhesive may
comprise 50, 55, 60, 65, 70, 75, 80, 85, or 90 parts by weight,
based on 100 parts by weight of the total monomer (or wt-% of the
total adhesive composition) of one or more high Tg monomers. The
(meth)acrylic polymer may optionally comprise an acid functional
monomer (a subset of high Tg monomers), where the acid functional
group may be an acid per se, such as a carboxylic acid, or a
portion may be salt thereof, such as an alkali metal carboxylate.
Useful acid functional monomers include, but are not limited to,
those selected from ethylenically unsaturated carboxylic acids,
ethylenically unsaturated sulfonic acids, ethylenically unsaturated
phosphonic acids, and mixtures thereof. Examples of such compounds
include those selected from acrylic acid, methacrylic acid,
itaconic acid, fumaric acid, crotonic acid, citraconic acid, maleic
acid, oleic acid, .beta.-carboxyethyl(meth)acrylate, 2-sulfoethyl
methacrylate, styrene sulfonic acid,
2-acrylamido-2-methylpropanesulfonic acid, vinylphosphonic acid,
and mixtures thereof.
[0062] Due to their availability, acid functional monomers are
generally selected from ethylenically unsaturated carboxylic acids,
i.e. (meth)acrylic acids. When even stronger acids are desired,
acidic monomers include the ethylenically unsaturated sulfonic
acids and ethylenically unsaturated phosphonic acids. In some
embodiments, the acid functional monomer is generally used in
amounts of 0.5 to 15 parts by weight, preferably 0.5 to 10 parts by
weight, based on 100 parts by weight total monomer or polymerized
units. In some embodiments, the (meth)acrylic polymer and/or PSA
comprises less than 1.0, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2,
0.1 or 0 wt-% of polymerized units derived from acid-functional
monomers such as acrylic acid.
[0063] The (meth)acrylic copolymer may optionally comprise other
monomers such as a non-acid-functional polar monomer.
Representative examples of suitable polar monomers include but are
not limited to 2-hydroxyethyl(meth)acrylate; N-vinylpyrrolidone;
N-vinylcaprolactam; acrylamide; mono- or di-N-alkyl substituted
acrylamide; t-butyl acrylamide; dimethylaminoethyl acrylamide;
N-octyl acrylamide; poly(alkoxyalkyl)(meth)acrylates including
2-(2-ethoxyethoxy)ethyl(meth)acrylate, 2-ethoxyethyl(meth)acrylate,
2-methoxyethoxyethyl(meth)acrylate, 2-methoxyethyl methacrylate,
polyethylene glycol mono(meth)acrylates; alkyl vinyl ethers,
including vinyl methyl ether; and mixtures thereof. Preferred polar
monomers include those selected from the group consisting of
2-hydroxyethyl(meth)acrylate and N-vinylpyrrolidinone. The
non-acid-functional polar monomer may be present in amounts of 0 to
10 or 20 parts by weight, or 0.5 to 5 parts by weight, based on 100
parts by weight total monomer. In some embodiments, the
(meth)acrylic polymer and/or PSA comprises less than 1.0, 0.9, 0.8,
0.7, 0.6, 0.5, 0.4, 0.3, 0.2, 0.1 or 0 wt-% of polymerized units
derived from non-acid polar monomers.
[0064] When used, vinyl monomers useful in the (meth)acrylate
polymer include vinyl esters (e.g., vinyl acetate and vinyl
propionate), styrene, substituted styrene (e.g., .alpha.-methyl
styrene), vinyl halide, and mixtures thereof. As used herein vinyl
monomers are exclusive of acid functional monomers, acrylate ester
monomers and polar monomers. Such vinyl monomers are generally used
at 0 to 5 parts by weight, preferably 1 to 5 parts by weight, based
on 100 parts by weight total monomer or polymerized units. In some
embodiments, the (meth)acrylic polymer and/or PSA comprises less
than 1.0, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, 0.1 or 0 wt-% of
polymerized units derived from vinyl monomers.
[0065] In some embodiments, the polymer contains no allyl ether,
vinyl ether or vinyl ester monomer units.
[0066] The adhesive further comprises a crosslinking monomer
comprising a (meth)acrylate group and aC.sub.6-C.sub.20 olefin
group. The olefin group comprises at least one hydrocarbon
unsaturation. In some embodiments, the olefin group comprises
substitutents. The crosslinking monomer may have the formula
##STR00001##
R1 is H or CH.sub.3,
[0067] L is an optional linking group; and R2 is a C.sub.6-C.sub.20
olefin group, the olefin group being optionally substituted.
[0068] For embodiments wherein the crosslinking monomer comprises a
(e.g. divalent) linking group, the linking group (i.e. L) typically
has a molecular weight no greater than 1000 g/mole and in some
embodiments no greater than 500 g/mole, 400 g/mole, 300 g/mole, 200
g/mole, 100 g/mole, or 50 g/mole.
[0069] In some embodiments, the crosslinking monomer comprises a
(meth)acrylate group and an optionally substituted C.sub.6-C.sub.20
olefin group comprising a terminal hydrocarbon unsaturation. In
this embodiment the hydrocarbon unsaturation has the formula:
R.sup.3C.dbd.CR.sup.4R.sup.5
wherein R.sup.4 and R.sup.5 are H and R.sup.3 is H or (e.g.
C.sub.1-C.sub.4) alkyl. Undecenyl(meth)acrylate includes such
terminal unsaturation.
[0070] In other embodiments, the crosslinking monomer comprises a
(meth)acrylate group and an optionally substituted C.sub.6-C.sub.20
olefin group comprising at least one hydrocarbon unsaturation in
the backbone of the optionally substituted C.sub.6-C.sub.20 olefin
group. In this embodiment, the hydrocarbon unsaturation has the
formula:
R.sup.3C.dbd.CR.sup.4R.sup.5
[0071] wherein R.sup.4 and R.sup.5 are independently alkyl and
R.sup.3 is H or (e.g. C.sub.1-C.sub.4) alkyl. In some embodiments,
R.sup.4 and R.sup.5 are each methyl. In this embodiment, R.sup.4 or
R.sup.5 is the terminal alkyl group of the C.sub.6-C.sub.20 olefin
group. Citronellyl(meth)acrylate, geraniol(meth)acrylate and
farnesol(meth)acrylate include a hydrocarbon unsaturation of this
type.
[0072] In some embodiments, the crosslinking monomer comprises a
(meth)acrylate group and an optionally substituted C.sub.6-C.sub.20
olefin group comprising two or more hydrocarbon unsaturations in
the backbone. Some illustrative crosslinking monomers include for
example geraniol(meth)acrylate (e.g.
3,7-dimethylocta-2,6-dienyl]prop-2-enoate) and
farnesol(meth)acrylate (e.g.
3,7,11-trimethyldodeca-2,6,10-trienyl]prop-2-enoate).
[0073] In yet another embodiment of a hydrocarbon unsaturation in
the backbone of the optionally substituted C.sub.6-C.sub.20 olefin
group, R.sup.3 and R.sup.4 are independently H or (e.g.
C.sub.1-C.sub.4) alkyl and R.sup.5 is a terminal alkyl group having
up to 18 carbon atoms. Oleyl(meth)acrylate includes a hydrocarbon
unsaturation of this type.
[0074] In typical embodiments, the substituted C.sub.6-C.sub.20
olefin group does not comprise a carbonyl group. Thus, the
(meth)acrylate group is the only group of the crosslinking monomer
that comprises a carbonyl group. Thus, the crosslinking monomer is
free of other groups that comprise a carbonyl such as an aldehyde,
ketone, carboxylic acid, ester, amide, enone, acryl halide, acid
anhydride, and imide. Hence, the crosslinking monomer comprises or
consists of two types of polymerizable functional groups, i.e. a
single (meth)acrylate group and one or more hydrocarbon
unsaturations.
[0075] The optionally substituted C.sub.6-C.sub.20 olefin group may
be a straight-chain, branched, or cyclic. Further, the hydrocarbon
unsaturation may be at any position.
[0076] When the crosslinking monomer comprises a single hydrocarbon
unsaturation, the unsubstituted C.sub.6-C.sub.20 olefin group may
be characterized as an alkenyl group. In some embodiments, the
alkenyl group has a straight chain. In some embodiments, the
alkenyl group has branched chain, commonly comprising pendent
methyl groups bonded to a straight chain.
[0077] Some illustrative crosslinking monomers comprising an
alkenyl group include citronellyl(meth)acrylate, 3-cyclohexene
methyl(meth)acrylate, undecenyl(meth)acrylate, and oleyl acrylate.
Other C.sub.6-C.sub.20 alkenyl groups include 1-hexenyl, 2-hexenyl,
3-hexenyl, 4-hexenyl, 5-hexenyl, 1-methyl-1-pentenyl,
2-methyl-1-pentenyl, 3-methyl-1-pentenyl, 4-methyl-1-pentenyl,
1-methyl-2-pentenyl, 2-methyl-2-pentenyl, 3-methyl-2-pentenyl,
4-methyl-2-pentenyl, 1-methyl-3-pentenyl, 2-methyl-3-pentenyl,
3-methyl-3-pentenyl, 4-methyl-3-pentenyl, 1-methyl-4-pentenyl,
2-methyl-4-pentenyl, 3-methyl-4-pentenyl, 4-methyl-4-pentenyl;
1,1-dimethyl-2-butenyl; 1,1-dimethyl-3-butenyl;
1,2-dimethyl-1-butenyl; 1,2-dimethyl-2-butenyl;
1,2-dimethyl-3-butenyl; 1,3-dimethyl-1-butenyl;
1,3-dimethyl-2-butenyl; 1,3-dimethyl-3-butenyl;
2,2-dimethyl-3-butenyl; 2,3-dimethyl-1-butenyl;
2,3-dimethyl-2-butenyl; 2,3-dimethyl-3-butenyl;
3,3-dimethyl-1-butenyl; 3,3-dimethyl-2-butenyl;
1,1,2-trimethyl-2-propenyl; and also the isomers of heptenyl,
octenyl, and nonenyl.
[0078] Cyclic alkenyl groups included cyclohexenyl as well as
dicyclopentenyl.
[0079] Provided that the C.sub.6-C.sub.20 olefin group comprises at
least one hydrocarbon unsaturation, the C.sub.6-C.sub.20 olefin
group may optionally comprise substituents. The substituents are
chosen such that the crosslinking monomer comprises at least one
hydrocarbon unsaturation available for crosslinking, as evident by
a measurable and preferably substantial increase in shear
values.
[0080] In some embodiments, the C.sub.6-C.sub.20 olefin group
comprises pendent substituents. For example, when the
C.sub.6-C.sub.20 olefin group comprises two or more hydrocarbon
unsaturations, one or more of the additional hydrocarbon
unsaturations can be reacted to append pendent substituents onto
the C.sub.6-C.sub.20 olefin group backbone.
[0081] In other embodiments, the C.sub.6-C.sub.20 olefin group can
comprise substituents such as a heteroatom (e.g. oxygen) or a (e.g.
divalent) linking group (i.e. "L") between the (meth)acrylate group
and C.sub.6-C.sub.20 olefin group. For example, the starting
alcohol can be chain extended before reacting on the (meth)acrylate
group. In some embodiments, the starting alcohol is chain extended
with one or more alkylene oxide groups, such as ethylene oxide,
propylene oxide, and combinations thereof. One illustrative
crosslinking monomer of this type is the ester of (meth)acrylic
acid of an ethoxylated and/or propoxylated unsaturated fatty
alcohol. Some of such ethoxylated and/or propoxylated unsaturated
fatty alcohols are commercially available as non-ionic surfactants.
Thus, L comprises or consists of alkylene (e.g. ethylene) oxide
repeat units. One illustrative fatty alcohol of this type is
available from Croda as "Brij O2". Such ethoxylated alcohol
comprises a mixture of molecules (wherein n is 1 or 2) having the
general formula
C.sub.18H.sub.35(OCH.sub.2CH.sub.2).sub.nOH.
[0082] The crosslinking monomers can be prepared by reacting the
corresponding alcohol with acryloyl chloride, methylene chloride
and triethylamine, or a combination thereof, such as set forth in
the examples. The crosslinking monomers can also be prepared by
direct esterification with acrylic acid.
[0083] The concentration of crosslinking monomer comprising a
(meth)acrylate group and an optionally substituted C.sub.6-C.sub.20
olefin group is typically at least 0.1, 0.2, 0.3, 0.4 or 0.5 wt-%
and can range up to 10, 11, 12, 13, 14, or 15 wt-% of the (e.g.
pressure sensitive) adhesive composition. However, as the
concentration of such crosslinking monomer increases, the peel
adhesion (180.degree. to stainless steel) can decrease. Thus, in
typically embodiments, the concentration of crosslinking monomer
comprising a (meth)acrylate group and an optionally substituted
C.sub.6-C.sub.20 olefin group is no greater than 9, 8, 7, 6, or 5
wt-% and in some favored embodiments, no greater than 4, 3, 2, or 1
wt-%.
[0084] In some embodiments, the crosslinking monomer comprises a
branched C.sub.6-C.sub.20 having less than 18, or 16, or 14, or 12
carbon atoms, such as in the case of citronellyl acrylate and
geraniol acrylate. In this embodiment, a pressure sensitive
adhesive can be obtained having high shear values (i.e. greater
than 10,000 minutes at 70.degree. C.) in combination with high
adhesion with as little as 0.5 wt-% of such crosslinking monomer.
As the chain length of the branched C.sub.6-C.sub.20 group
increases, the amount of crosslinking monomer needed to provide the
same number of crosslinks increases. For example, in the case of
farnesol acrylate at least 0.7 wt-% or 0.8 wt-% resulted in high
shear values. In the case of cyclic C.sub.6-C.sub.20 olefin groups,
such as in the case of cyclohexane methyl acrylate, at least 2, 3,
4, or 5 wt-% resulted in high shear values. In the case of
crosslinking monomers comprising a straight-chain C.sub.6-C.sub.20
such as in the case of undecenyl acrylate and oleyl acrylate, high
shear values in combination with high adhesion was obtained with
about 1 wt-%. Lower concentrations of undecenyl acrylate and
optionally substituted oleyl acrylate are surmised to also provide
a good balance of properties.
[0085] The (e.g. pressure sensitive) adhesive composition may
comprise a single crosslinking monomer comprising a (meth)acrylate
group and (optionally substituted) C.sub.6-C.sub.20 olefin group or
a combination of two or more of such crosslinking monomers.
Further, the crosslinking monomer may comprise two or more isomers
of the same general structure.
[0086] In favored embodiments, the crosslinked adhesive composition
comprises high shear values to stainless steel or orange peel
drywall, i.e. greater than 10,000 minutes at 70.degree. C., as
determined according to the test methods described in the examples.
The crosslinked pressure sensitive adhesive can exhibit a variety
of peel adhesion values depending on the intended end use. In some
embodiments, the 180.degree. degree peel adhesion to stainless
steel is least 15 N/dm. In other embodiments, the 180.degree.
degree peel adhesion to stainless steel is least 20, 25, 30, 35,
40, 45, 50, 55, 60, 65, 70, or 75 N/dm. The 180.degree. degree peel
adhesion to stainless steel is typically no greater than 150 or 100
N/dm. Such peel adhesive values are also attainable when adhered to
other substrates.
[0087] In some embodiments, such as in the case of optionally
substituted citronellyl(meth)acrylate and oleyl(meth)acrylate, the
crosslinking monomer is a bio-based material. Thus, the use of such
crosslinking monomer is amenable to increasing the total content of
biobased material of the adhesive. Further, since the crosslinking
monomer comprises an olefin group comprising at least 6 carbon
atoms, when the hydrocarbon unsaturation does not crosslink, the
crosslinking monomer can serve the function of a low Tg monomer.
This can be amenable to utilizing higher concentrations of such
crosslinking monomer. Further, the crosslinking monomer does not
form corrosive by-products and has good color stability. In some
embodiments, the b* of the adhesive after exposure to UV or heat,
as described in greater detail in the test method described in the
examples, is less than 1 or 0.9, or 0.8, or 0.7, or 0.6, or 0.5, or
0.4, or 0.3. In some embodiments, the b* of the adhesive after
exposure to UV and heat, as described in greater detail in the test
method described in the examples, is less than 2, or 1.5, or 1, or
0.9, or 0.8, or 0.7, or 0.6, or 0.5, or 0.4, or 0.3.
[0088] The (e.g. pressure sensitive) adhesive may optionally
comprise another crosslinker in addition to the crosslinker having
a (meth)acrylate group and optionally substituted C.sub.6-C.sub.20
olefin group. In some embodiments, the (e.g. pressure sensitive)
adhesive comprises a multifunctional (meth)acrylate.
[0089] Examples of useful multifunctional (meth)acrylate include,
but are not limited to, di(meth)acrylates, tri(meth)acrylates, and
tetra(meth)acrylates, such as 1,6-hexanediol di(meth)acrylate,
poly(ethylene glycol)di(meth)acrylates, polybutadiene
di(meth)acrylate, polyurethane di(meth)acrylates, and propoxylated
glycerin tri(meth)acrylate, and mixtures thereof.
[0090] Generally the multifunctional (meth)acrylate is not part of
the original monomer mixture, but added subsequently after the
formation of the (meth)acrylic polymer. If used, the
multifunctional (meth)acrylate is typically used in an amount of at
least 0.01, 0.02, 0.03, 0.04, or 0.05 up to 1, 2, 3, 4, or 5 parts
by weight, relative to 100 parts by weight of the total monomer
content.
[0091] In some embodiments, the (e.g. pressure sensitive) adhesive
may further comprise a chlorinated triazine crosslinking compound.
The triazine crosslinking agent may have the formula.
##STR00002##
wherein R.sub.1, R.sub.2, R.sub.3 and R.sub.4 of this triazine
crosslinking agent are independently hydrogen or alkoxy group, and
1 to 3 of R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are hydrogen. The
alkoxy groups typically have no greater than 12 carbon atoms. In
favored embodiments, the alkoxy groups are independently methoxy or
ethoxy. One representative species is
2,4,-bis(trichloromethyl)-6-(3,4-bis(methoxy)phenyl)-triazine. Such
triazine crosslinking compounds are further described in U.S. Pat.
No. 4,330,590.
[0092] In some embodiments, the (e.g. pressure sensitive) adhesive
comprises predominantly (greater than 50%, 60%, 70%, 80%, or 90% of
the total crosslinks) or exclusively crosslinks from the
crosslinking monomer that comprises a (meth)acrylate group and an
optionally substituted C.sub.6-C.sub.20 olefin group. In such
embodiment, the (e.g. pressure sensitive) adhesive may be free of
other crosslinking compounds, particularly aziridine crosslinkers,
as well as multifunctional (meth)acrylate crosslinkers, chlorinated
triazine crosslinkers and melamine crosslinkers.
[0093] The (meth)acrylic copolymers and adhesive composition can be
polymerized by various techniques including, but not limited to,
solvent polymerization, dispersion polymerization, solventless bulk
polymerization, and radiation polymerization, including processes
using ultraviolet light, electron beam, and gamma radiation. The
monomer mixture may comprise a polymerization initiator, especially
a thermal initiator or a photoinitiator of a type and in an amount
effective to polymerize the comonomers.
[0094] A typical solution polymerization method is carried out by
adding the monomers, a suitable solvent, and an optional chain
transfer agent to a reaction vessel, adding a free radical
initiator, purging with nitrogen, and maintaining the reaction
vessel at an elevated temperature (e.g. about 40 to 100.degree. C.)
until the reaction is complete, typically in about 1 to 20 hours,
depending upon the batch size and temperature. Examples of typical
solvents include methanol, tetrahydrofuran, ethanol, isopropanol,
acetone, methyl ethyl ketone, methyl acetate, ethyl acetate,
toluene, xylene, and an ethylene glycol alkyl ether. Those solvents
can be used alone or as mixtures thereof.
[0095] Useful initiators include those that, on exposure to heat or
light, generate free-radicals that initiate (co)polymerization of
the monomer mixture. The initiators are typically employed at
concentrations ranging from about 0.0001 to about 3.0 parts by
weight, preferably from about 0.001 to about 1.0 parts by weight,
and more preferably from about 0.005 to about 0.5 parts by weight
of the total monomer or polymerized units.
[0096] Suitable initiators include but are not limited to those
selected from the group consisting of azo compounds such as VAZO 64
(2,2'-azobis(isobutyronitrile)), VAZO 52
(2,2'-azobis(2,4-dimethylpentanenitrile)), and VAZO 67
(2,2'-azobis-(2-methylbutyronitrile)) available from E.I. du Pont
de Nemours Co., peroxides such as benzoyl peroxide and lauroyl
peroxide, and mixtures thereof. The preferred oil-soluble thermal
initiator is (2,2'-azobis-(2-methylbutyronitrile)). When used,
initiators may comprise from about 0.05 to about 1 part by weight,
preferably about 0.1 to about 0.5 part by weight based on 100 parts
by weight of monomer components in the pressure sensitive
adhesive.
[0097] The polymers prepared from solution polymerization have
pendent unsaturated groups that can be crosslinked by a variety of
methods. These include addition of thermal or photo initiators
followed by heat or UV exposure after coating. The polymers may
also be crosslinked by exposure to electron beam or gamma
irradiation.
[0098] One method of preparing (meth)acrylic polymers includes
partially polymerizing monomers to produce a syrup composition
comprising the solute (meth)acrylic polymer and unpolymerized
solvent monomer(s). The unpolymerized solvent monomer(s) typically
comprises the same monomer as utilized to produce the solute
(meth)acrylic polymer. If some of the monomers were consumed during
the polymerization of the (meth)acrylic polymer, the unpolymerized
solvent monomer(s) comprises at least some of the same monomer(s)
as utilized to produce the solute (meth)acrylic polymer. Further,
the same monomer(s) or other monomer(s) can be added to the syrup
once the (meth)acrylic polymer has been formed. Partial
polymerization provides a coatable solution of the (meth)acrylic
solute polymer in one or more free-radically polymerizable solvent
monomers. The partially polymerized composition is then coated on a
suitable substrate and further polymerized.
[0099] In some embodiments, the crosslinking monomer is added to
the monomer(s) utilized to form the (meth)acrylic polymer.
Alternatively or in addition thereto, the crosslinking monomer may
be added to the syrup after the (meth)acrylic polymer has been
formed. The (meth)acrylate group of the crosslinker and other (e.g.
(meth)acrylate) monomers utilized to form the (meth)acrylic polymer
preferentially polymerize forming an acrylic backbone with the
pendent C.sub.6-C.sub.20 olefin group. Without intending to be
bound by theory, it is surmised that at least a portion of the
carbon-carbon double bonds of the pendent C.sub.6-C.sub.20 olefin
group crosslink with each other during radiation curing of the
syrup. Other reaction mechanisms may also occur.
[0100] The syrup method provides advantages over solvent or
solution polymerization methods; the syrup method yielding higher
molecular weight materials. These higher molecular weights increase
the amount of chain entanglements, thus increasing cohesive
strength. Also, the distance between cross-links can be greater
with high molecular syrup polymer, which allows for increased
wet-out onto a surface.
[0101] Polymerization of the (meth)acrylate solvent monomers can be
accomplished by exposing the syrup composition to energy in the
presence of a photoinitiator. Energy activated initiators may be
unnecessary where, for example, ionizing radiation is used to
initiate polymerization. Typically, a photoinitiator can be
employed in a concentration of at least 0.0001 part by weight,
preferably at least 0.001 part by weight, and more preferably at
least 0.005 part by weight, relative to 100 parts by weight of the
syrup.
[0102] A preferred method of preparation of the syrup composition
is photoinitiated free radical polymerization. Advantages of the
photopolymerization method are that 1) heating the monomer solution
is unnecessary and 2) photoinitiation is stopped completely when
the activating light source is turned off. Polymerization to
achieve a coatable viscosity may be conducted such that the
conversion of monomers to polymer is up to about 30%.
Polymerization can be terminated when the desired conversion and
viscosity have been achieved by removing the light source and by
bubbling air (oxygen) into the solution to quench propagating free
radicals. The solute polymer(s) may be prepared conventionally in a
non-monomeric solvent and advanced to high conversion (degree of
polymerization). When solvent (monomeric or non-monomeric) is used,
the solvent may be removed (for example by vacuum distillation)
either before or after formation of the syrup composition. While an
acceptable method, this procedure involving a highly converted
functional polymer is not preferred because an additional solvent
removal step is required, another material may be required (a
non-monomeric solvent), and dissolution of the high molecular
weight, highly converted solute polymer in the monomer mixture may
require a significant period of time.
[0103] The polymerization is preferably conducted in the absence of
solvents such as ethyl acetate, toluene and tetrahydrofuran, which
are non-reactive with the functional groups of the components of
the syrup composition. Solvents influence the rate of incorporation
of different monomers in the polymer chain and generally lead to
lower molecular weights as the polymers gel or precipitate from
solution. Thus, the (e.g. pressure sensitive) adhesive can be free
of unpolymerizable organic solvent.
[0104] Useful photoinitiators include benzoin ethers such as
benzoin methyl ether and benzoin isopropyl ether; substituted
acetophenones such as 2,2-dimethoxy-2-phenylacetophenone
photoinitiator, available the trade name IRGACURE 651 or ESACURE
KB-1 photoinitiator (Sartomer Co., West Chester, Pa.), and
dimethylhydroxyacetophenone; substituted .alpha.-ketols such as
2-methyl-2-hydroxy propiophenone; aromatic sulfonyl chlorides such
as 2-naphthalene-sulfonyl chloride; and photoactive oximes such as
1-phenyl-1,2-propanedione-2-(O-ethoxy-carbonyl)oxime. Particularly
preferred among these are the substituted acetophenones.
[0105] Preferred photoinitiators are photoactive compounds that
undergo a Norrish I cleavage to generate free radicals that can
initiate by addition to the acrylic double bonds. The
photoinitiator can be added to the mixture to be coated after the
polymer has been formed, i.e., photoinitiator can be added to the
syrup composition. Such polymerizable photoinitiators are
described, for example, in U.S. Pat. Nos. 5,902,836 and 5,506,279
(Gaddam et al.).
[0106] Such photoinitiators preferably are present in an amount of
from 0.1 to 1.0 part by weight, relative to 100 parts by weight of
the total syrup content. Accordingly, relatively thick coatings can
be achieved when the extinction coefficient of the photoinitiator
is low.
[0107] The syrup composition and the photoinitiator may be
irradiated with activating UV radiation to polymerize the monomer
component(s). UV light sources can be of two types: 1) relatively
low light intensity sources such as blacklights, which provide
generally 10 mW/cm.sup.2 or less (as measured in accordance with
procedures approved by the United States National Institute of
Standards and Technology as, for example, with a UVIMAP UM 365 L-S
radiometer manufactured by Electronic Instrumentation &
Technology, Inc., in Sterling, Va.) over a wavelength range of 280
to 400 nanometers; and 2) relatively high light intensity sources
such as medium pressure mercury lamps which provide intensities
generally greater than 10 mW/cm.sup.2, preferably 15 to 450
mW/cm.sup.2. Where actinic radiation is used to fully or partially
polymerize the syrup composition, high intensities and short
exposure times are preferred. For example, an intensity of 600
mW/cm.sup.2 and an exposure time of about 1 second may be used
successfully. Intensities can range from 0.1 to 150 mW/cm.sup.2,
preferably from 0.5 to 100 mW/cm.sup.2, and more preferably from
0.5 to 50 mW/cm.sup.2.
[0108] The degree of conversion can be monitored during the
irradiation by measuring the index of refraction of the
polymerizing medium as previously described. Useful coating
viscosities are achieved with conversions (i.e., the percentage of
available monomer polymerized) in the range of up to 30%,
preferably 2% to 20%, more preferably from 5% to 15%, and most
preferably from 7% to 12%. The molecular weight (weight average) of
the solute polymer(s) is typically at least 100,000 or 250,000 and
preferably at least 500,000 g/mole or greater.
[0109] When preparing (meth)acrylic polymers described herein, it
is expedient for the photoinitiated polymerization reactions to
proceed to virtual completion, i.e., depletion of the monomeric
components, at temperatures less than 70.degree. C. (preferably at
50.degree. C. or less) with reaction times less than 24 hours,
preferably less than 12 hours, and more preferably less than 6
hours. These temperature ranges and reaction rates obviate the need
for free radical polymerization inhibitors, which are often added
to acrylic systems to stabilize against undesired, premature
polymerization and gelation. Furthermore, the addition of
inhibitors adds extraneous material that will remain with the
system and inhibit the desired polymerization of the syrup
composition and formation of the crosslinked pressure-sensitive
adhesives. Free radical polymerization inhibitors are often
required at processing temperatures of 70.degree. C. and higher for
reaction periods of more than 6 to 10 hours.
[0110] The pressure-sensitive adhesives may optionally contain one
or more conventional additives. Preferred additives include
tackifiers, plasticizers, dyes, antioxidants, UV stabilizers, and
(e.g. inorganic) fillers such as (e.g. fumed) silica and glass
bubbles.
[0111] In some embodiments, the pressure sensitive adhesive
comprises fumed silica. Fumed silica, also known as pyrogenic
silica, is made from flame pyrolysis of silicon tetrachloride or
from quartz sand vaporized in a 3000.degree. C. electric arc. Fumed
silica consists of microscopic droplets of amorphous silica fused
into (e.g. branched) three-dimensional primary particles that
aggregate into larger particles. Since the aggregates do not
typically break down, the average particle size of fumed silica is
the average particle size of the aggregates. Fumed silica is
commercially available from various global producers including
Evonik, under the trade designation "Aerosil"; Cabot under the
trade designation "Cab-O--Sil", and Wacker Chemie-Dow Corning. The
BET surface area of suitable fumed silica is typically at least 50
m.sup.2/g, or 75 m.sup.2/g, or 100 m.sup.2/g. In some embodiments,
the BET surface area of the fumed silica is no greater than 400
m.sup.2/g, or 350 m.sup.2/g, or 300 m.sup.2/g, or 275 m.sup.2/g, or
250 m.sup.2/g. The fumed silica aggregates preferably comprise
silica having a primary particle size no greater than 20 nm or 15
nm. The aggregate particle size is substantially larger than the
primary particle size and is typically at least 100 nm or
greater.
[0112] The concentration of (e.g. fumed) silica can vary. In some
embodiments, such as for conformable pressure sensitive adhesives,
the adhesive comprises at least 0.5, 1. 0, 1.1, 1.2, 1.3, 1.4, or
1.5 wt-% of (e.g. fumed) silica and in some embodiments no greater
than 5, 4, 3, or 2 wt-%. In other embodiments, the adhesive
comprises at least 5, 6, 7, 8, 9, or 10 wt-% of (e.g. fumed) silica
and typically no greater than 20, 19, 18, 17, 16, or 15 wt-% of
(e.g. fumed) silica.
[0113] In some embodiments, the pressure sensitive adhesive
comprises glass bubbles. Suitable glass bubbles generally have a
density ranging from about 0.125 to about 0.35 g/cc. In some
embodiments, the glass bubbles have a density less than 0.30, 0.25,
or 0.20 g/cc. Glass bubbles generally have a distribution of
particles sizes. In typical embodiments, 90% of the glass bubbles
have a particle size (by volume) of at least 75 microns and no
greater than 115 microns. In some embodiments, 90% of the glass
bubbles have a particle size (by volume) of at least 80, 85, 90, or
95 microns. In some embodiments, the glass bubbles have a crush
strength of at least 250 psi and no greater than 1000, 750, or 500
psi. Glass bubbles are commercially available from various sources
including 3M, St. Paul, Minn.
[0114] The concentration of glass bubbles can vary. In some
embodiments, the adhesive comprises at least 1, 2, 3, 4 or 5 wt-%
of glass bubbles and typically no greater than 20, 15, or 10 wt-%
of glass bubbles.
[0115] The inclusion of glass bubbles can reduce the density of the
adhesive. Another way of reducing the density of the adhesive is by
incorporation of air or other gasses into the adhesive composition.
For example the (e.g. syrup) adhesive composition can be
transferred to a frother as described for examples in U.S. Pat. No.
4,415,615; incorporated herein by reference. While feeding nitrogen
gas into the frother, the frothed syrup can be delivered to the nip
of a roll coater between a pair of transparent, (e.g.
biaxially-oriented polyethylene terephthalate) films. A silicone or
fluorochemical surfactant is included in the froathed syrup.
Various surfactants are known including copolymer surfactants
described in U.S. Pat. No. 6,852,781.
[0116] In some embodiments no tackifier is used. When tackifiers
are used, the concentration can range from 5 or 10 wt-% to 40, 45,
50, 55, or 60 wt-% of the (e.g. cured) adhesive composition.
[0117] Various types of tackifiers include phenol modified terpenes
and rosin esters such as glycerol esters of rosin and
pentaerythritol esters of rosin that are available under the trade
designations "Nuroz", "Nutac" (Newport Industries), "Permalyn",
"Staybelite", "Foral" (Eastman). Also available are hydrocarbon
resin tackifiers that typically come from C5 and C9 monomers by
products of naphtha cracking and are available under the trade
names "Piccotac", "Eastotac", "Regalrez", "Regalite" (Eastman),
"Arkon" (Arakawa), "Norsolene", "Wingtack" (Cray Valley),
"Nevtack", LX (Neville Chemical Co.), "Hikotac", "Hikorez" (Kolon
Chemical), "Novares" (Rutgers Nev.), "Quintone" (Zeon), "Escorez"
(Exxonmobile Chemical), "Nures", and "H-Rez" (Newport Industries).
Of these, glycerol esters of rosin and pentaerythritol esters of
rosin, such as available under the trade designations "Nuroz",
"Nutac", and "Foral" are considered biobased materials.
[0118] Depending on the kinds and amount of components, the
pressure sensitive adhesive can be formulated to have a wide
variety of properties for various end uses.
[0119] In one specific embodiment, the adhesive composition and
thickness is chosen to provide a synergistic combination of
properties. In this embodiment, the adhesive can be characterized
as having any one or combination of attributes including being
conformable, cleanly removable, reusable, reactivatible, and
exhibiting good adhesion to rough surfaces.
[0120] Thus, in some embodiments, the PSA is conformable. The
conformability of an adhesive can be characterized using various
techniques such as dynamic mechanical analysis (as determined by
the test method described in the examples) that can be utilized to
determine that shear loss modulus (G''), the shear storage modulus
(G'), and tan delta, defined as the ratio of the shear loss modulus
(G'') to the shear storage modulus (G'). As used herein
"conformable" refers to the (e.g. first) adhesive exhibiting a tan
delta of at least 0.4 or greater at 25.degree. C. and 1 hertz. In
some embodiments, the (e.g. first) adhesive has tan delta of at
least 0.45, 0.50, 0.55, 0.65, or 0.70 at 25.degree. C. and 1 hefts.
The tan delta at 25.degree. C. and 1 hertz of the (e.g. first)
adhesive is typically no greater than 0.80 or 1.0. In some
embodiments, the tan delta of the (e.g. first) adhesive is no
greater than 1.0 at 1 hertz and temperatures of 40.degree. C.,
60.degree. C., 80.degree. C., 100.degree. C. and 120.degree. C. In
some embodiments, the first adhesive layer has tan delta of at
least 0.4 or greater at 1 hertz and temperatures of 40.degree. C.,
60.degree. C., 80.degree. C., 100.degree. C. and 120.degree. C.
[0121] The PSA and adhesive coated articles can exhibit good
adhesion to both smooth and rough surfaces. Various rough surfaces
are known including for example textured drywall, such as "knock
down" and "orange peel"; cinder block, rough (e.g. Brazilian) tile
and textured cement. Smooth surfaces, such as stainless steel,
glass, and polypropylene have an average surface roughness (Ra) as
can be measured by optical inferometry of less than 100 nanometer;
whereas rough surfaces have an average surface roughness greater
than 1 micron (1000 nanometers), 5 microns, or 10 microns.
[0122] Surfaces with a roughness in excess of 5 or 10 microns can
be measured with stylus profilometry. Standard (untextured) drywall
has an average surface roughness (Ra), of about 10-20 microns and a
maximum peak height (Rt using Veeco's Vison software) of 150 to 200
microns. Orange peel and knockdown drywall have an average surface
roughness (Ra) greater than 20, 25, 30, 35, 40, or 45 microns and a
maximum peak height (Rt) greater than 200, 250, 300, 350, or 400
microns. Orange peel drywall can have an average surface roughness
(Ra) of about 50-75 microns and a maximum peak height (Rt) of
450-650 microns. Knock down drywall can have an average surface
roughness (Ra) greater than 75, 80, or 85 microns, such as ranging
from 90-120 microns and a maximum peak height (Rt) of 650-850
microns. In typical embodiments, Ra is no greater than 200, 175, or
150 microns and Rt is no greater than 1500, 1250, or 1000 microns.
Cinder block and Brazilian tile typically have a similar average
surface roughness (Ra) as orange peel drywall.
[0123] Although many conformable adhesives exhibit good initial
adhesion to a rough surface, the PSA and articles described herein
can exhibit a shear (with a mass of 250 g) to orange peel dry wall
of at least 500 minutes. In some embodiments, the PSA and articles
can exhibit a shear (with a mass of 250 g) to orange peel dry wall
of at least 1000, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000 or
10,000 minutes.
[0124] The PSA and adhesive coated articles can be cleanly
removable from paper. By "cleanly removable from paper" it is meant
that the paper does not tear and the paper does not have any
staining or adhesive residue after removal of the adhesive from the
paper when tested (according to Test Method 3 set forth in the
examples). The 90.degree. peel values to paper (according to Test
Method 3, set forth in the examples) is typically at least 25 and
no greater than 200 or 175 N/dm. In some embodiments, the
90.degree. peel value to paper no greater than 50, 45, or 40
N/dm.
[0125] The PSA and adhesive coated articles can be reusable. By
reusable it is meant that PSA and/or adhesive coated article can
repeatedly be removed and readhered to paper at least 1, 2, 3, 4,
or 5 times. In some embodiments, it can be readhered to paper at
least 5, 10, 15, or 20 times while maintaining at least 80%, 85%,
or 90% of the initial peel adhesion (according to the "Reusability"
test further described in the examples).
[0126] Further, in some embodiments, the adhesive can be
reactivatible, i.e. contaminants can be removed by cleaning the
adhesive layer(s) with soap and water, such as by the test methods
described in WO 96/31564; incorporated herein by reference.
[0127] The adhesives of the present invention may be coated upon a
variety of flexible and inflexible backing materials using
conventional coating techniques to produce adhesive-coated
materials. Flexible substrates are defined herein as any material
which is conventionally utilized as a tape backing or may be of any
other flexible material. Examples include, but are not limited to
plastic films such as polypropylene, polyethylene, polyvinyl
chloride, polyester (polyethylene terephthalate), polycarbonate,
polymethyl(meth)acrylate (PMMA), cellulose acetate, cellulose
triacetate, and ethyl cellulose. Foam backings may be used. In some
embodiments, the backing is comprised of a bio-based material such
as polylactic acid (PLA).
[0128] Backings may also be prepared of fabric such as woven fabric
formed of threads of synthetic or natural materials such as cotton,
nylon, rayon, glass, ceramic materials, and the like or nonwoven
fabric such as air laid webs of natural or synthetic fibers or
blends of these. The backing may also be formed of metal, metalized
polymer films, or ceramic sheet materials may take the form of any
article conventionally known to be utilized with pressure-sensitive
adhesive compositions such as labels, tapes, signs, covers, marking
indicia, and the like.
[0129] Backings can be made from plastics (e.g., polypropylene,
including biaxially oriented polypropylene, vinyl, polyethylene,
polyester such as polyethylene terephthalate), nonwovens (e.g.,
papers, cloths, nonwoven scrims), metal foils, foams (e.g.,
polyacrylic, polyethylene, polyurethane, neoprene), and the like.
Foams are commercially available from various suppliers such as 3M
Co., Voltek, Sekisui, and others. The foam may be formed as a
coextruded sheet with the adhesive on one or both sides of the
foam, or the adhesive may be laminated to it. When the adhesive is
laminated to a foam, it may be desirable to treat the surface to
improve the adhesion of the adhesive to the foam or to any of the
other types of backings. Such treatments are typically selected
based on the nature of the materials of the adhesive and of the
foam or backing and include primers and surface modifications
(e.g., corona treatment, surface abrasion). Suitable primers
include for example those described in EP 372756, U.S. Pat. No.
5,534,391, U.S. Pat. No. 6,893,731, WO2011/068754, and
WO2011/38448.
[0130] In some embodiments, the backing material is a transparent
film having a transmission of visible light of at least 90 percent.
The transparent film may further comprise a graphic. In this
embodiment, the adhesive may also be transparent.
[0131] The above-described compositions can be coated on a
substrate using conventional coating techniques modified as
appropriate to the particular substrate. For example, these
compositions can be applied to a variety of solid substrates by
methods such as roller coating, flow coating, dip coating, spin
coating, spray coating knife coating, and die coating. The
composition may also be coated from the melt. These various methods
of coating allow the compositions to be placed on the substrate at
variable thicknesses thus allowing a wider range of use of the
compositions. Coating thicknesses may vary as previously described.
The syrup composition may be of any desirable concentration for
subsequent coating, but is typically 5 to 20 wt-% polymer solids in
monomer. The desired concentration may be achieved by further
dilution of the coating composition, or by partial drying. Coating
thicknesses may vary from about 25 to 1500 microns (dry thickness).
In typical embodiments, the coating thickness ranges from about 50
to 250 microns. When the multilayer PSA or article is intended to
be bonded to a rough surface, the thickness of the adhesive layer
typically ranges from the average roughness (Ra) to slightly
greater than the maximum peak height (Rt).
[0132] The adhesive can also be provided in the form of a
pressure-sensitive adhesive transfer tape in which at least one
layer of the adhesive is disposed on a release liner for
application to a permanent substrate at a later time. The adhesive
can also be provided as a single coated or double coated tape in
which the adhesive is disposed on a permanent backing.
[0133] For a single-sided tape, the side of the backing surface
opposite that where the adhesive is disposed is typically coated
with a suitable release material. Release materials are known and
include materials such as, for example, silicone, polyethylene,
polycarbamate, polyacrylics, and the like. For double coated tapes,
another layer of adhesive is disposed on the backing surface
opposite that where the adhesive of the invention is disposed. The
other layer of adhesive can be different from the adhesive of the
invention, e.g., a conventional acrylic PSA, or it can be the same
adhesive as the invention, with the same or a different
formulation. Double coated tapes are typically carried on a release
liner. Additional tape constructions include those described in
U.S. Pat. No. 5,602,221 (Bennett et al.), incorporated herein by
reference.
In some embodiments, the pressure sensitive adhesive and a release
layer in the release liner are both UV curable compositions. Any
conventional coating technique can be used to "wet cast" and UV
cure the pressure sensitive adhesive directly onto the UV cured
release layer of the release liner. Optionally the UV cured
pressure sensitive adhesive is "dry laminated" to the LTV cured
release layer of the release liner.
[0134] It is desirable to provide tight side release values of 20
grams/inch or more. It is also desirable to provide a release ratio
(tight side adhesion strength/easy side adhesion release strength)
of 3 or more. A release ratio of 3 or more contributes to the
desired release behavior wherein the adhesive consistently releases
first from the easy side of the liner then subsequently from the
tight side of the liner. It is further desirable to provide both
such characteristics simultaneously.
[0135] Release materials, such as those useful in the presently
disclosed release liners, include UV curable compositions made
using techniques disclosed in US 2013/0059105 (Wright), which is
hereby incorporated by reference. In some embodiments, the present
disclosure describes a method for producing a release liner from an
at least partially cured layer (optionally a fully cured layer),
the method including applying a layer comprising a
(meth)acrylate-functional siloxane to a surface of a substrate, and
irradiating the layer in a substantially inert atmosphere with a
short wavelength polychromatic ultraviolet light source having a
peak intensity at a wavelength of from about 160 (+/-5) nanometers
(nm) to about 240 (+/-5) nm to at least partially cure the layer.
Optionally, the layer is at a curing temperature greater than
25.degree. C.
[0136] Thus, in some exemplary embodiments, the material comprising
the layer may be heated to a temperature greater than 25.degree. C.
during or subsequent to application of the layer to the substrate.
Alternatively, the material comprising the layer may be provided at
a temperature of greater than 25.degree. C., e.g. by heating or
cooling the material comprising the layer before, during, and/or
after application of the layer to the substrate. Preferably, the
layer is at a temperature of at least 50.degree. C., 60.degree. C.
70.degree. C., 80.degree. C., 90.degree. C., 100.degree. C.,
125.degree. C., or even 150.degree. C. Preferably the layer is at a
temperature of no more than 250.degree. C., 225.degree. C.,
200.degree. C., 190.degree. C., 180.degree. C., 170.degree. C.,
160.degree. C., or even 155.degree. C.
[0137] Methods of the present disclosure involve applying a layer
comprising a (meth)acrylate-functional siloxane to a major surface
of a substrate. Generally, the materials comprising the layer may
be oils, fluids, gums, elastomers, or resins, e.g., friable solid
resins. Generally, lower molecular weight, lower viscosity
materials are referred to as fluids or oils, while higher molecular
weight, higher viscosity materials are referred to as gums;
however, there is no sharp distinction between these terms.
Elastomers and resins have even higher molecular weights than gums
and typically do not flow. As used herein, the terms "fluid" and
"oil" refer to materials having a dynamic viscosity at 25.degree.
C. of no greater than 1,000,000 mPasec (e.g., less than 600,000
mPasec), while materials having a dynamic viscosity at 25.degree.
C. of greater than 1,000,000 mPasec (e.g., at least 10,000,000
mPasec) are referred to as "gums."
[0138] In order to obtain the low thicknesses generally desirable
for some silicone coatings, e.g., silicone release materials, it is
often necessary to dilute high molecular weight materials with
solvents in order to coat or otherwise apply them to a substrate.
In some embodiments, it may be preferable to use low molecular
weight silicone oils or fluids, including those having a dynamic
viscosity at 25.degree. C. of no greater than 200,000 mPasec, no
greater than 100,000 mPasec, or even no greater than 50,000
mPasec.
[0139] In some embodiments, it may be useful to use materials
compatible with common solventless coating operations, including,
e.g., those having a kinematic viscosity at 25.degree. C. of no
greater than 50,000 centistokes (cSt), e.g., no greater than 40,000
cSt, or even no greater than 20,000 cSt. In some embodiments, it
may be desirable to use a combination of silicone materials,
wherein at least one of the silicone materials has a kinematic
viscosity at 25.degree. C. of at least 5,000 centistokes (cSt),
e.g., at least 10,000 cSt, or even at least 15,000 cSt. In some
embodiments, it may be desirable to use materials in the layer
having a kinematic viscosity at 25.degree. C. of between 1000 and
50,000 cSt, e.g., between 5,000 and 50,000 cSt, or even between
10,000 and 50,000 cSt.
[0140] In general, depending on the selected material comprising
the layer, including its viscosity, any known coating method may be
used. Exemplary coating methods include roll coating, spray
coating, dip coating, gravure coating, bar coating, vapor coating,
and the like. Once coated, the silicone material is exposed to
short wavelength ultraviolet radiation.
[0141] In accordance with the method of the disclosure, the
(meth)acrylate-functional siloxane may be coated via any of a
variety of conventional coating methods, such as roll coating,
knife coating, or curtain coating. The low viscosity
(co)polymerization mixtures are preferably coated by means
specifically adapted to deliver thin release layers, preferably
through the use of precision roll coaters and electrospray methods
such as those described in U.S. Pat. Nos. 4,748,043 and 5,326,598
(both to Seaver et al.). Higher viscosity mixtures which can be
coated to higher thickness (e.g., up to about 500 .mu.m) can be
provided by selecting higher molecular weight oligomeric starting
materials. Oligomeric or (co)polymeric starting materials can also
be thickened with adjuvants (e.g. thickeners), including but not
limited to particulate fillers such as colloidal silica and the
like, prior to coating.
[0142] In some exemplary embodiments of any of the foregoing, the
layer is applied at a thickness of about 0.1 (+/-0.05) micrometer
(.mu.m) to about 5 (+/-0.1) .mu.m prior to irradiation with the
short wavelength polychromatic light source. In certain exemplary
embodiments, the layer is applied at a thickness of at least about
0.2 (+/-0.05) .mu.m, 0.3 (+/-0.05) .mu.m, 0.4 (+/-0.05) .mu.m, or
even 0.5 (+/-0.05) .mu.m; to about 4 (+/-0.1) .mu.m, 3 (+/-0.1)
.mu.m, 2 (+/-0.1) .mu.m, or even 1 (+/-0.1) .mu.m, prior to
irradiation with the short wavelength polychromatic light
source.
[0143] In other exemplary embodiments, the at least partially cured
layer or even the fully cured layer may have a thickness of 0.1
(+/-0.05) micrometer (.mu.m) to about 5 (+/-0.1) .mu.m. In certain
exemplary embodiments, the at least partially cured layer or even
the fully cured layer has a thickness of at least about 0.2
(+/-0.05) .mu.m, 0.3 (+/-0.05) .mu.m, 0.4 (+/-0.05) .mu.m, or even
0.5 (+/-0.05) .mu.m; to about 4 (+/-0.1) .mu.m, 3 (+/-0.1) .mu.m, 2
(+/-0.1) .mu.m, or even 1 (+/-0.1) .mu.m.
[0144] In any of the foregoing exemplary embodiments, applying the
layer to the surface of the substrate includes applying a
discontinuous coating. In other words, the layer need not cover the
entire major surface of the substrate, and only a portion of the
substrate surface may be covered by the layer. For example, the
layer may be applied to the substrate as a single strip or stripe,
or as a plurality of strips or stripes, as a plurality of dots, or
in any other discernible pattern.
[0145] Exemplary methods of the present disclosure include
UV-radiation curing of the layer, by irradiating the layer, in a
substantially inert atmosphere containing no greater than 500 ppm
oxygen, with radiation (e.g. light) emitted from a short wavelength
polychromatic ultraviolet light source having a peak intensity at a
wavelength of from about 160 (+/-5) nanometers (nm) to about 240
(+/-5) nm, to at least partially cure the layer.
[0146] Substantially inert atmospheres are particularly useful in
embodiments in which the UV-radiation source has radiant output at
wavelengths of less than 200 nm. In such embodiments, oxygen gas
present in the environment may absorb the UV radiation, thereby
substantially preventing the radiation from reaching the target
surface. Thus, in any of the foregoing exemplary embodiments, the
substantially inert atmosphere includes no greater than 500 ppm
oxygen. In some of the foregoing exemplary embodiments, the
substantially inert atmosphere includes no greater than 400 ppm
oxygen, 300 ppm oxygen, 200 ppm oxygen, or even 100 ppm oxygen. In
some of the foregoing exemplary embodiments, the substantially
inert atmosphere includes no greater than 50 ppm oxygen, no greater
than 40 ppm, 30 ppm, 20 ppm, or even 10 ppm oxygen.
[0147] In some exemplary embodiments, the substantially inert
atmosphere may comprise an inert gas such as nitrogen, helium,
argon, or the like. In one embodiment, the methods of the present
disclosure may be carried out in an inert environment including
nitrogen. In embodiments in which an inert gas is used, oxygen
levels in the environment may be as low as 50 ppm, 25 ppm, or even
as low as 10 ppm, and as high as 100 ppm, or even 500 ppm.
[0148] In further exemplary embodiments, the controlled environment
may be operated in a vacuum or a partial vacuum. In some such
embodiments in which vacuum pressures are employed, the pressures
may be as low as 10.sup.-4 torr, 10.sup.-5 torr, or even as low as
10.sup.-6 torr; and be as high as 10.sup.-1 torr, 1 torr, or even
10 torr.
[0149] In further exemplary embodiments, the material comprising
the layer is exposed to short wavelength polychromatic ultraviolet
radiation after applying the layer to the substrate, to at least
partially cure the layer on the substrate. Short wavelength
polychromatic ultraviolet light sources useful in the method of the
present disclosure are those having output in the region from about
160 (+/-5) nm to about 240 (+/-5) nm, inclusive. In some exemplary
embodiments of any of the foregoing, a peak intensity is at a
wavelength between about 170 (+/-5) nm, 180 (+/-5) nm, or even 190
(+/-5) nm; to about 215 (+/-5) nm, 210 (+/-5) nm, 205 (+/-5) nm, or
even 200 (+/-5) nm. In some particular exemplary embodiments, a
peak intensity is at a wavelength of about 185 (+/-2) nm.
[0150] In certain such exemplary embodiments, the short wavelength
polychromatic ultraviolet light source includes at least one low
pressure mercury vapor lamp, at least one low pressure mercury
amalgam lamp, at least one pulsed Xenon lamp, at least one glow
discharge from a polychromatic plasma emission source, or
combinations thereof.
[0151] Suitable plasma emission sources may involve excitation of a
carrier gas (e.g. nitrogen) to generate electrons, ions, radicals,
and photons in the form of a glow discharge. As reported in, for
example, Elsner et al. [Macromol. Mater. Eng., 294, 422-31 (2009)],
a variety of acrylate monomers can be cured in the absence of
photoinitiators using a nitrogen plasma polymerization process in
which a glow discharge (i.e., UV-radiation emission) having peak
intensities near 150 nm, 175 nm, and 220 nm was observed.
[0152] The intensities of incident radiation useful in the
processes of the present disclosure can be from as low as about 1
mW/cm.sup.2 to about 10 W/cm.sup.2, preferably 5 mW/cm.sup.2 to
about 5 W/cm.sup.2, more preferably 10 mW/cm.sup.2 to 1 W/cm.sup.2.
When higher power levels are provided (e.g., greater than about 10
W/cm.sup.2), volatilization of low molecular weight
(meth)acrylate-functional siloxane monomers and oligomers can
result.
[0153] In some exemplary embodiments, it is desirable to select a
short wavelength polychromatic ultraviolet source having an
intensity peak at a wavelength resulting in an absorbance greater
than zero but no greater than about 0.5 (+/-0.05), as determined by
Beer's law for the particular silicone resin being cured and the
thickness. When the absorbance goes above 0.5, a surface layer or
skin may form due to the lack of penetration of the radiation
through the coating thickness resulting in surface absorption and
localized polymerization and cross-linking. Absorbances below 0.3
are acceptable and tend to give more uniform penetration and cure
profiles but are less efficient in terms of radiation capture.
[0154] In certain exemplary embodiments, the absorbance determined
by Beer's law is between 0.3 and 0.5, inclusive, e.g., between 0.4
and 0.5, inclusive, or even between 0.40 and 0.45, inclusive. As
the actual absorbance and the absorbance calculated by Beer's law
increase linearly with thickness, a particular silicone resin may
have the desired absorbance at one thickness, e.g., 1 micrometer,
while the absorbance of the same silicone resin at a greater
thickness, e.g., 10 micrometers, may be too high.
[0155] The layer comprises material that is capable of undergoing
at least a partial cure when exposed to short wavelength
polychromatic ultraviolet radiation. In the presently disclosed
embodiments, the layer comprises at least one
(meth)acrylate-functional siloxane. In some such exemplary
embodiments of any of the foregoing disclosed embodiments, the
release liner layer consists essentially of one or more
(meth)acrylate-functional siloxane monomers. In other such
exemplary embodiments, the layer consists essentially of one or
more (meth)acrylate-functional siloxane oligomers. In certain other
such exemplary embodiments, the layer consists essentially of one
or more (meth)acrylate-functional polysiloxanes.
[0156] The curable materials are applied as a layer on at least a
portion of at least one major surface of a suitable flexible or
rigid substrate or surface or backing, and irradiated using the
prescribed ultraviolet radiation sources. Useful flexible
substrates include, but are not limited to, paper, poly-coated
Kraft paper, supercalendered or glassine Kraft paper, plastic films
such as poly(propylene), biaxially-oriented polypropylene,
poly(ethylene), poly(vinyl chloride), polycarbonate,
poly(tetrafluoroethylene), polyester [e.g., poly(ethylene
terephthalate)], poly(ethylene naphthalate), polyamide film such as
those commercially available under the trade designation "KAPTON"
from DuPont, Wilmington, Del., cellulose acetate, and ethyl
cellulose.
[0157] In addition, suitable substrates for use in the presently
disclosed release liner may be formed of metal, metal foil,
metallized (co)polymeric film, or ceramic sheet material.
Substrates may also take the form of a cloth backing, e.g. a woven
fabric formed of threads of synthetic fibers, or a nonwoven web or
substrate, or combinations of these. One of the advantages of the
use of the short wavelength polychromatic ultraviolet light sources
of the present disclosure is the ability to use such high energy,
low heat sources to (co)polymerize mixtures coated on heat
sensitive substrates. Commonly used longer wavelength ultraviolet
lamps often generate undesirable levels of thermal radiation that
can distort or damage a variety of synthetic or natural flexible
substrates. Suitable rigid substrates include but are not limited
to glass, wood, metals, treated metals (such as those comprising
automobile and marine surfaces), (co)polymeric material and
surfaces, and composite material such as fiber reinforced
plastics.
[0158] In some exemplary embodiments, the substrates may be surface
treated (e.g., corona or flame treatment), coated with, e.g., a
primer or print receptive layer. In certain exemplary embodiments,
multilayer substrates may be used. In certain exemplary
embodiments, the substrate may be smooth or textured, e.g.,
embossed. In some exemplary embodiments, the substrate is embossed
after curing the release material.
[0159] In general, (co)polymerizable (meth)acrylate-functional
siloxanes are useful materials for preparing an at least partially
(or in some embodiments completely) cured layer for a layer
according to the present disclosure. Ethylenically unsaturated free
radically (co)polymerizable siloxanes, including especially the
(meth)acrylate-functional siloxane oligomers and (co)polymers
containing telechelic and/or pendant acrylate or methacrylate
groups, are particularly useful precursor materials for
incorporation in the at least partially cured layers of the present
disclosure. These (meth)acrylate-functional siloxane oligomers can
be prepared by a variety of methods, generally through the reaction
of chloro-, silanol-, aminoalkyl-, epoxyalkyl-, hydroxyalkyl-,
vinyl-, or silicon hydride-functional polysiloxanes with a
corresponding (meth)acrylate-functional capping agent. These
preparations are reviewed in a chapter entitled
"Photo(co)polymerizable Silicone Monomers, Oligomers, and Resins"
by A. F. Jacobine and S. T. Nakos in Radiation Curing Science and
Technology, (Plenum: New York, 1992), pp. 200-214.
[0160] Suitable (co)polymerizable (meth)acrylate-functional
siloxane oligomers include those (meth)acryl-modified polylsiloxane
resins commercially available from, for example, Goldschmidt
Chemical Corporation (Evonik TEGO Chemie GmbH, Essen, Germany)
under the TEGO.TM. RC designation. An example of a blend
recommended for achieving premium (easy) release is a 70:30
(weight/weight, w/w) blend of TEGO RC922 and TEGO RC711.
[0161] Suitable (meth)acrylate-functional polysiloxane resins
include the acrylamido-terminated monofunctional and difunctional
polysiloxane resins described in U.S. Pat. No. 5,091,483 (Mazurek
et al.). These (meth)acrylate-functional polysiloxane resins are
pourable and may be blended for optimized properties such as level
of release, adhesive compatibility, and substrate adhesion.
[0162] In some exemplary embodiments, the (co)polymerizable
precursor composition making up the layer may include essentially
only one or more (co)polymerizable (meth)acrylate-functional
siloxane(s), and is substantially-free of other (co)polymerizable
materials. Thus, in further exemplary embodiments of any of the
foregoing, the layer consists essentially of one or more
(meth)acrylate-functional siloxane monomers. In some such exemplary
embodiments, the layer consists essentially of one or more
(meth)acrylate-functional siloxane oligomers. In other such
exemplary embodiments, the layer consists essentially of one or
more (meth)acrylate-functional polysiloxanes.
[0163] In addition to the (meth)acrylate functional siloxane, the
layer may optionally include one or more (co)polymerizable starting
materials. Suitable (co)polymerizable starting materials may
contain silicon or may not contain silicon.
[0164] Thus, in some exemplary embodiments, the layer further
comprises a non-(meth)acrylate-functional siloxane monomer,
oligomer, or (co)polymer. Such materials can be functional or
non-functional. Examples of non-functional (co)polymerizable
siloxanes include poly(dialkylsiloxanes),
poly(dialkyldiarylsiloxanes), poly(alkylarylsiloxanes), and
poly(diarylsiloxanes), and may be linear, cyclic, or branched.
Examples of functional (but non-(meth)acrylate-functional)
polysiloxanes that may be used include vinyl-functional
polysiloxanes, hydroxy-functional polysiloxanes, amine-functional
polysiloxanes, hydride-functional polysiloxanes, epoxy-functional
polysiloxanes, and combinations thereof.
[0165] In certain exemplary embodiments, the layer further
comprises one or more (co)polymerizable materials selected from the
group consisting of monofunctional (meth)acrylate monomers,
difunctional (meth)acrylate monomers, polyfunctional (meth)acrylate
monomers having functionality greater than two, vinyl ester
monomers, vinyl ester oligomers, vinyl ether monomers, and vinyl
ether oligomers. Suitable vinyl-functional monomers include but are
not limited to acrylic acid and its esters, methacrylic acid and
its esters, vinyl-substituted aromatics, vinyl-substituted
heterocyclics, vinyl esters, vinyl chloride, acrylonitrile,
methacrylonitrile, acrylamide and derivatives thereof,
methacrylamide and derivatives thereof, and other vinyl monomers
(co)polymerizable by free-radical means.
[0166] Monofunctional (meth)acrylate (co)monomers useful in the
methods of the present disclosure include compositions of Formula
1:
[X--].sub.m--Z (1)
wherein X represents H.sub.2C.dbd.C(R.sub.1)C(O)O--, in which
R.sub.1 represents --H or --CH.sub.3, m=1, and Z represents a
monovalent straight chain alkyl, branched alkyl or cycloalkyl group
having from about 1 to about 24 carbon atoms. A class of
particularly suitable monofunctional (co)monomers include
monoethylenically unsaturated monomers having homopolymer glass
transition temperatures (T.sub.g) greater than about 0.degree. C.,
preferably greater than 15.degree. C.
[0167] Examples of suitable monofunctional (meth)acrylate monomers
include but are not limited to those selected from the group
consisting of methyl(meth)acrylate, isooctyl(meth)acrylate,
4-methyl-2-pentyl(meth)acrylate, 2-methylbutyl(meth)acrylate,
isoamyl(meth)acrylate, sec-butyl(meth)acrylate,
n-butyl(meth)acrylate, tert-butyl(meth)acrylate,
isobornyl(meth)acrylate, butyl methacrylate, ethyl(meth)acrylate,
dodecyl(meth)acrylate, octadecyl(meth)acrylate,
cyclohexyl(meth)acrylate and mixtures thereof.
[0168] Particularly suitable monofunctional (meth)acrylate monomers
include those selected from the group consisting of
isooctyl(meth)acrylate, isononyl(meth)acrylate,
isoamyl(meth)acrylate, isodecyl(meth)acrylate,
2-ethylhexyl(meth)acrylate, isobornyl(meth)acrylate,
n-butyl(meth)acrylate, sec-butyl(meth)acrylate, and mixtures
thereof.
[0169] Monofunctional vinyl ester monomers useful in the methods of
the present disclosure include compositions of Formula 1 wherein X
represents H.sub.2C.dbd.CHOC(O)--, m=1, and Z represents a
monovalent straight chain or branched alkyl group having from about
1 to about 24 atoms. Such vinyl ester monomers include but are not
limited to those selected from the group consisting of vinyl
acetate, vinyl 2-ethylhexanoate, vinyl caprate, vinyl laureate,
vinyl pelargonate, vinyl hexanoate, vinyl propionate, vinyl
decanoate, vinyl octanoate, and other monofunctional unsaturated
vinyl esters of linear or branched carboxylic acids comprising 1 to
16 carbon atoms. Preferred vinyl ester monomers include those
selected from the group consisting of vinyl acetate, vinyl
laureate, vinyl caprate, vinyl-2-ethylhexanoate, and mixtures
thereof.
[0170] Other suitable monofunctional (co)monomers include but are
not limited to those selected from the group consisting of acrylic
acid, methacrylic acid, itaconic acid, crotonic acid, maleic acid,
fumaric acid, sulfoethyl methacrylate, N-vinyl pyrrolidone, N-vinyl
caprolactam, acrylamide, t-butyl acrylamide, dimethyl amino ethyl
acrylamide, N-octyl acrylamide, acrylonitrile, mixtures thereof,
and the like. Preferred monomers include those selected from the
group consisting of acrylic acid, N-vinyl pyrrolidone, and mixtures
thereof.
[0171] Free radically (co)polymerizable monofunctional
macromonomers or oligomers (i.e., macromers) of Formula 1, wherein
X is H.sub.2C.dbd.CR.sub.1COO--, R.sub.1 represents --H or
--CH.sub.3, m is 1, and Z is a monovalent (co)polymeric or
oligomeric radical having a degree of (co)polymerization greater
than or equal to 2, and that are substantially free of aromatic,
chloro- and other moieties or substituents that significantly
absorb ultraviolet radiation in the range of about 160 nm to about
240 nm, may also be used in the at least partially cured layers of
the present disclosure.
[0172] Examples of such monofunctional macromonomers or oligomers
include those selected from the group consisting of
(meth)acrylate-terminated poly(methyl methacrylate),
methacrylate-terminated poly(methyl methacrylate),
(meth)acrylate-terminated poly(ethylene oxide),
methacrylate-terminated poly(ethylene oxide),
(meth)acrylate-terminated poly(ethylene glycol),
methacrylate-terminated poly(ethylene glycol), methoxy
poly(ethylene glycol) methacrylate, butoxy poly(ethylene glycol)
methacrylate, and mixtures thereof. These functionalized materials
are preferred because they are easily prepared using well-known
ionic (co)polymerization techniques and are also highly effective
in providing grafted oligomeric and (co)polymeric segments along
free radically (co)polymerized (meth)acrylate (co)polymer
backbones.
[0173] The viscosity of such monofunctional macromonomers or
oligomers useful in practicing the methods of the present
disclosure are generally high enough so that a thickener is not
usually necessary; however; if desired, a thickener or particulate
filler may be advantageously used as an adjuvant, as described
further below.
[0174] Useful difunctional and other polyfunctional
(meth)acrylate-functional free radically (co)polymerizable monomers
include ester derivatives of alkyl diols, triols, tetrols, etc.
(e.g., 1,4-butanediol di(meth)acrylate, 1,6-hexanediol
di(meth)acrylate, trimethylolpropane tri(meth)acrylate, and
pentaerythritol tri(meth)acrylate). Difunctional and polyfunctional
(meth)acrylate and methacrylate monomers described in U.S. Pat. No.
4,379,201 (Heilmann et al.), such as 1,2-ethanediol
di(meth)acrylate, 1,12-dodecanediol di(meth)acrylate,
pentaerythritol tetr(meth)acrylate can also be used in the present
disclosure.
[0175] Difunctional and polyfunctional (meth)acrylates and
methacrylates including (meth)acrylated epoxy oligomers,
(meth)acrylated aliphatic urethane oligomers, (meth)acrylated
polyether oligomers, and (meth)acrylated polyester oligomers, such
as those commercially available from UCB Radcure Inc, Smyrna, Ga.
under the EBECRYL tradename, and those available from Sartomer,
Exton, Pa., may also be employed.
[0176] In further exemplary embodiments, the layer further includes
at least one non-functional polysiloxane material. In some such
further exemplary embodiments, the at least one non-functional
polysiloxane material is selected from a poly(dialkylsiloxane), a
poly(alkylarylsiloxane), a poly(diarylsiloxane), or a
poly(dialkyldiarylsiloxane), optionally wherein the non-functional
polysiloxane material comprises from 0.1 to 95 wt. %, inclusive, of
the layer.
[0177] The non-functional polysiloxane material can be described
generally by the following formula illustrating a siloxane backbone
with a variety of substituents:
##STR00003##
R1 through R4 represent the substituents pendant from the siloxane
backbone. Each R5 may be independently selected and represent the
terminal groups. Subscripts n and m are independently integers, and
at least one of m or n is not zero.
[0178] As used herein, a "nonfunctional polysiloxane material" is
one in which the R1, R2, R3, R4, and R5 groups are nonfunctional
groups. As used herein, "nonfunctional groups" are either alkyl or
aryl groups consisting of carbon, hydrogen, and in some
embodiments, halogen (e.g., fluorine) atoms. In some embodiments,
R1, R2, R3, and R4 are independently selected from the group
consisting of an alkyl group and an aryl group, and R5 is an alkyl
group. In some embodiments, one or more of the alkyl or aryl groups
may contain a halogen substituent, e.g., fluorine. For example, in
some embodiments, one or more of the alkyl groups may be
--CH.sub.2CH.sub.2C.sub.4F.sub.9.
[0179] In certain exemplary embodiments, R5 is a methyl group,
i.e., the nonfunctional polysiloxane material is terminated by
trimethylsiloxy groups. In some embodiments, R1 and R2 are alkyl
groups and n is zero, i.e., the material is a
poly(dialkylsiloxane). In certain embodiments, the alkyl group is a
methyl group, i.e., poly(dimethylsiloxane) ("PDMS"). In other
embodiments, R1 is an alkyl group, R2 is an aryl group, and n is
zero, i.e., the material is a poly(alkylarylsiloxane). In some
particular embodiments, R1 is a methyl group and R2 is a phenyl
group, i.e., the material is poly(methylphenylsiloxane). In other
particular embodiments, R1 and R2 are alkyl groups and R3 and R4
are aryl groups, i.e., the material is a
poly(dialkyldiarylsiloxane). In certain additional embodiments, R1
and R2 are methyl groups, and R3 and R4 are phenyl groups, i.e.,
the material is poly(dimethyldiphenylsiloxane).
[0180] In further exemplary embodiments, the polysiloxane backbone
may be linear. In some alternative exemplary embodiments, the
polysiloxane backbone may be branched. For example, one or more of
the R1, R2, R3, and/or R4 groups may be a linear or branched
siloxane with functional or nonfunctional (e.g., alkyl or aryl,
including halogenated alkyl or aryl) pendant and terminal groups.
In other alternative exemplary embodiments, the polysiloxane
backbone may be cyclic. For example, the silicone material may be
octamethylcyclotetrasiloxane, decamethylcyclo-pentasiloxane, or
dodecamethylcyclohexasiloxane.
[0181] In addition to the foregoing polysiloxanes, various
(polyalkyl)disiloxanes may be advantageously used in the release
liner layer in addition to or in place of at least a portion of the
non-functional polysiloxane material. In some exemplary
embodiments, hexamethyldisiloxane (i.e.
O[Si(CH.sub.3).sub.3].sub.2) may be used advantageously as such a
non-functional (polyalkyl)disiloxane.
[0182] In some exemplary embodiments, the polysiloxane material may
be functional. Generally, functional silicone systems include
specific reactive groups attached to the linear, branched, or
polysiloxane backbone of the starting material. For example, a
linear "functional polysiloxane material" is one in which at least
one of the R-groups of Formula 3 is a functional group:
##STR00004##
[0183] In some such embodiments, a functional polysiloxane material
is one in which at least 2 of the R-groups are functional groups.
Generally, the R-groups of Formula 3 may be independently selected.
In some embodiments, all functional groups are hydroxy groups
and/or alkoxy groups. In certain such exemplary embodiments, the
functional polysiloxane is a silanol terminated polysiloxane, e.g.,
a silanol terminated poly(dimethylsiloxane). In other such
embodiments, the functional silicone is an alkoxy terminated
poly(dimethylsiloxane), e.g., trimethylsiloxy terminated
poly(dimethylsiloxane).
[0184] Other functional groups include those having an unsaturated
carbon-carbon bond such as alkene-containing groups (e.g., vinyl
groups and allyl groups) and alkyne-containing groups.
[0185] In addition to at least one functional R-group, the
remaining R-groups may be nonfunctional groups, e.g., alkyl or aryl
groups, including halogenated (e.g., fluorinated) alky and aryl
groups. In some embodiments, the functionalized polysiloxane
materials may be branched. For example, one or more of the R groups
may be a linear or branched siloxane with functional and/or
non-functional substituents. In some embodiments, the
functionalized polysiloxane materials may be cyclic.
[0186] Although some embodiments of the present disclosure describe
the use of functional silicone materials, the nature of the
functional group is generally not critical to obtaining the desired
cross-linked or cured polysiloxane materials. Although some
reactions may occur through the functional groups, direct
cross-linking between the polysiloxane backbones is often
sufficient to obtain the desired degree of cure.
[0187] Various materials may be advantageously added to the
(co)polymerizable composition used in forming the release liner
layer in order to achieve advantageous effects. Some such adjuvants
include, but are not limited to, the following optional
additives.
[0188] In contrast to most previous methods for curing functional
materials, the methods of the present disclosure do not require the
use of added catalysts or initiators (e.g. photoinitiators). Thus,
advantageously, in some exemplary embodiments, the methods of the
present disclosure do not require the use of an added
photoinitiator. In other words, exemplary methods of the present
disclosure can be used to cure compositions that are "substantially
free" of such catalysts or initiators (e.g., photoinitiators).
[0189] As used herein, a composition is "substantially free of
added catalysts and initiators" if the composition does not include
an "effective amount" of an added catalyst or initiator. As is well
understood, an "effective amount" of a catalyst or initiator
depends on a variety of factors including the type of catalyst or
initiator, the composition of the curable material, and the curing
method (e.g., thermal cure, UV-cure, and the like). In some
embodiments, a particular catalyst or initiator is not present at
an "effective amount" if the amount of catalyst or initiator does
not reduce the cure time of the composition by at least 10%
relative to the cure time for the same composition at the same
curing conditions absent that catalyst or initiator.
[0190] As stated above, the use of added photoinitiators in the
(co)polymerization of (meth)acrylate-functional siloxanes and
oligomers introduces added costs and undesirable residuals and
byproducts to the process. Articles bearing release layers prepared
using the preferred initiator-free method are of particular
significance in medical applications, where photoinitiator-induced
contamination of release layers can lead to skin irritation and
other undesirable reactions. Exclusion of this component can result
in significant direct cost savings, plus elimination of any
expenses involved in qualifying products containing significant
amounts of a photoinitiator.
[0191] In other exemplary embodiments, an optional added
photoinitiator may be advantageously included in the
(co)polymerizable composition. Photoinitiators are particularly
useful when higher (co)polymerization rates or very thin release
layers (or surface cures) are required. When used, photoinitiators
can constitute from as low as about 0.001 to about 5 percent by
weight of a (co)polymerization mixture. These photoinitiators can
be organic, organometallic, or inorganic compounds, but are most
commonly organic in nature. Examples of commonly used organic
photoinitiators include benzoin and its derivatives, benzil ketals,
acetophenone, acetophenone derivatives, benzophenone, and
benzophenone derivatives.
[0192] In contrast to most previous methods for curing functional
materials, the methods of the present disclosure do not require the
use of organic solvents. Thus, in any of the foregoing exemplary
embodiments, the layer may be (is) substantially free of an organic
solvent. In any of the foregoing exemplary embodiments that are
substantially free of organic solvent, the substantially inert
atmosphere preferably includes no greater than 500 ppm oxygen, even
more preferably no greater than 50 ppm oxygen.
[0193] In additional exemplary embodiments of any of the foregoing,
the (co)polymerizable composition may further comprises a
thickener. A thickener may be used in the (co)polymerizable
composition of the present disclosure. A thickener may be used with
monomers, but are generally not necessary with oligomers.
Thickeners can increase the viscosity of the (co)polymerizable
composition. The viscosity needs to be high enough to enable the
(co)polymerizable composition to be coatable. In addition, the
relatively high viscosity may play a role in contributing to the
isolation of the free radicals, thereby improving conversion and
reducing termination. A viscosity in the range of about 400-25,000
centipoise is typically desired.
[0194] Suitable thickeners are those which are soluble in the
(co)polymerizable composition, and generally include oligomeric and
polymeric materials. Such materials can be selected to contribute
various desired properties or characteristics to resultant article.
Examples of suitable polymeric thickening agents include copolymers
of ethylene and vinyl esters or ethers, poly(alkyl acrylates),
poly(alkyl methacrylates), polyesters such as poly(ethylene
maleate), poly(propylene fumarate), poly(propylene phthalate), and
the like.
[0195] Other suitable thickeners are particulate fillers which are
insoluble in the (co)polymerizable composition, including but not
limited to colloidal particulates having a median particle diameter
of less than one micrometer. Suitable inorganic colloidal
particulate fillers that may be used to good advantage as
thickeners and/or adjuvants include commercially available fumed
colloidal silicas such as CAB-.beta.-SILs (Cabot Corp., Billerica,
Mass.) and AER-O-SILs (Evonik North America, Parsippany, N.J.),
colloidal alumina, and the like.
[0196] An exemplary apparatus for using short wavelength
polychromatic ultraviolet radiation to cure a coating on a
substrate is illustrated by FIG. 2. Exemplary substrates 10 each
bearing a layer (e.g., 10A, 10B, 10C, 10D) of a UV-curable
(co)polymerizable composition may be attached at various locations
on the surface 21 of back up roll 20 located in vacuum chamber 30,
as illustrated in FIG. 2. Short wavelength polychromatic
ultraviolet radiation source(s) 40 (e.g., low-pressure short
wavelength polychromatic mercury lamps) may be used to achieve
curing of the layers on the substrates, thereby forming an at least
partially cured layer (optionally a fully cured layer), such as
e.g. a release layer or low adhesion backsize (LAB).
[0197] It will be understood that other apparatus, for example a
continuous roll-to-roll web coater as described in U.S. Pat. No.
6,224,949, may be used in conjunction with one or more short
wavelength polychromatic ultraviolet radiation sources to at least
partially cure a layer of the (co)polymerizable composition on a
substrate, for example, a continuous web or roll of material (e.g.,
a (co)polymeric film).
[0198] In further exemplary embodiments of any of the foregoing,
the at least partially cured layer may be a release layer in a
UV-radiation cured article, such as a liner or an adhesive tape or
film. Optionally, the UV-radiation cured release layer is used as a
surface release layer in a release liner, or as a low adhesion
backsize (LAB) in an adhesive article.
[0199] UV-radiation cured layers prepared according to the methods
of the present disclosure may be used in any of a wide variety of
applications, including, e.g., as release layers, low adhesion
backsize layers, and the like. Various exemplary applications are
illustrated in FIG. 3. Article 100 comprises first substrate 110
and cross-linked silicone layer 120 adhered to first surface 111 of
first substrate 110 forming release liner 210. In some such
exemplary embodiments, the release layer has an unaged peel
adhesion less than about 1.6 Newtons per decimeter. Optionally, the
release layer has an aged peel adhesion less than 50 percent
greater than the unaged peel adhesion.
[0200] Another particularly useful coating derived from the method
of the present disclosure involves the (co)polymerization of a
(meth)acrylated siloxane to form a release layer under a
substantially inert (i.e. oxygen content no greater than 500 ppm)
atmosphere. The use of silicone release layers has been an industry
standard for many years, and is widely employed by liner suppliers
and large, integrated tape manufacturers. Release layers prepared
in this manner may exhibit any desired level of release, including
(1) premium or easy release, (2) moderate or controlled release, or
(3) tight release; premium release requires the least amount of
force.
[0201] Premium release layers (i.e., those release layers having
aged release forces in the range of up to about 1.0 N/dm) are
typically used in release liner applications. Premium release
layers are less useful, however, when coated on the back surface of
pressure-sensitive adhesive tapes, because their low release force
can cause tape roll instability and handling problems. Such a
release layer on the back surface of a pressure-sensitive adhesive
tape construction is often referred to as a "low adhesion
backsize." Release layers having moderate to high levels of aged
release (about 4.0 to about 35 N/dm) are especially useful when
used as low adhesion backsizes.
[0202] In addition, layers containing (meth)acrylated polysiloxanes
for use in the production of release layers may include, as
(co)polymerizable constituents, 100% (meth)acrylated polysiloxanes
or, alternatively may include free radically (co)polymerizable
diluents in addition to the (meth)acrylated polysiloxanes. Such
non-polysiloxane free radically (co)polymerizable diluents can be
used to modify the release properties of the release layers of the
present disclosure and also enhance the coating's mechanical
properties and anchorage to backings or substrates used in
pressure-sensitive adhesive tape or release liner
constructions.
[0203] Depending on the ultimate properties desired in the
(co)polymerized release layers, useful non-polysiloxane free
radically (co)polymerizable diluents include monofunctional,
difunctional and polyfunctional (meth)acrylate vinyl ether, and
vinyl ester monomers and oligomers. Difunctional and polyfunctional
(meth)acrylate and methacrylate monomers such as 1,4-butanediol
di(meth)acrylate, 1,6-hexanediol di(meth)acrylate,
trimethylolpropane di(meth)acrylate, pentaerythritol
tri(meth)acrylate 1,2-ethanediol di(meth)acrylate, 1,12
dodecanediol di(meth)acrylate, trimethylolpropane
tri(meth)acrylate, pentaerythritol tetra(meth)acrylate and
difunctional and polyfunctional (meth)acrylate and methacrylate
oligomers including (meth)acrylated epoxy oligomers,
(meth)acrylated aliphatic urethane oligomers, (meth)acrylated
polyester oligomers, and (meth)acrylated polyethers such as those
commercially available from Cytec Surface Specialties, Woodland
Park, N.J. under the trade designation "EBECRYL", and from
Sartomer, Exton, Pa., may also be advantageously employed.
[0204] The difunctional and polyfunctional (meth)acrylate monomers
and oligomers employed in these release layers can be used at a
concentration of from about 5 to about 95 weight percent,
preferably from about 10 to 90 weight percent, based on the total
weight of the release layer composition. Monofunctional monomers,
such as the (meth)acrylate, vinyl ester and other free radically
co(co)polymerizable monomers listed above, can also be added as
non-polysiloxane free radically (co)polymerizable diluents in the
release layer composition. When used, these monofunctional monomers
may be employed at a concentration of up to about 25 weight percent
based on the total weight of the release layer composition.
Mixtures of monofunctional, difunctional and polyfunctional
non-polysiloxane monomers and oligomers can also be used.
[0205] In another aspect, an adhesive article includes the
foregoing release layer, and an adhesive layer adjacent to the
release layer. Optionally, the adhesive layer includes one or more
adhesive selected from a pressure sensitive adhesive, a hot melt
adhesive, a radiation curable adhesive, a tackified adhesive, a
non-tackified adhesive, a synthetic rubber adhesive, a natural
rubber adhesive, a (meth)acrylic (co)polymer adhesive, and a
polyolefin adhesive. In some embodiments, the adhesive may comprise
a pressure sensitive adhesive, which preferably comprises a
(meth)acrylic (co)polymer.
[0206] Thus, in some exemplary embodiments shown in FIG. 3, in
addition to release liner 210, article 100 further comprises
adhesive 140 releasably adhered to cross-linked silicone layer 120,
forming transfer tape 220. In some embodiments, article 100 further
comprises second substrate 150 adhered to adhesive 140, opposite
cross-linked silicone layer 120.
[0207] In certain exemplary embodiments, the second substrate may
be a release liner, e.g., a release liner similar to release liner
210, and article 100 may be a dual-linered transfer tape. In some
embodiments, the second substrate may be permanently bonded to the
adhesive and adhesive article 100 may be, for example, a tape or
label.
[0208] Although not shown, in some embodiments, substrate 110 may
be coated on both sides with a release material. In general, the
release materials may be independently selected, and may be the
same or different release materials. In some embodiments, both
release materials are prepared according to the methods of the
present disclosure. In some embodiments, self-wound adhesive
articles may be prepared from such two-sided release liners. In
some embodiments, one or more primer layers may be included. For
example, in some embodiments, a primer layer may be located at
surface 111 of substrate 110.
[0209] In various embodiments, the rolls of adhesive coated
substrates of the present disclosure may be rolls of an adhesive
tape that includes a backing layer and an adhesive coating disposed
on a major surface of the backing layer. Common types of adhesive
tapes include masking tape, electrical tape, duct tape, filament
tape, medical tape, transfer tape, and the like.
[0210] The adhesive tape rolls may further include a release
coating, or low adhesion backsize, disposed on a second major
surface. Alternatively, the adhesive tape rolls may include a
release liner (which may have a release coating disposed on a major
surface thereof) in contact with the adhesive coated major surface
of the backing layer. As another example, an adhesive tape roll may
include a release liner comprising a release coating disposed on at
least a portion of each of its major surfaces and an adhesive
coating deposited over one of the release coatings.
[0211] Examples of suitable backing layers include, without
limitation, CELLOPHANE, acetate, fiber, polyester, vinyl,
polyethylene, polypropylene including, e.g., monoaxially oriented
polypropylene and biaxially oriented polypropylene, polycarbonate,
polytetrafluoroethylene, polyvinylfluoroethylene, polyurethane,
polyimide, paper (e.g., Kraft paper), woven webs (e.g., cotton,
polyester, nylon and glass), nonwoven webs, foil (e.g., aluminum,
lead, copper, stainless steel and brass foil tapes) and
combinations thereof.
[0212] The backing layers and release liners, can also include
reinforcing agents including, without limitation, fibers, filaments
(e.g., glass fiber filaments), and saturants (e.g., synthetic
rubber latex saturated paper backings).
[0213] Objects and advantages of this invention are further
illustrated by the following examples. The particular materials and
amounts, as well as other conditions and details, recited in these
examples should not be used to unduly limit this invention.
EXAMPLES
[0214] As used herein, all percentages and parts are by weight.
Amounts of additives, e.g., crosslinkers, photoinitiator,
tackifiers, etc. are expressed in parts per hundred resin (phr) in
which 100 parts of the resin represents the weight of the monomers
that form the polymer backbone, e.g., IOA, 2OA, AA.
Test Methods
Test Method 1: Shear Strength Test 1
[0215] Stainless steel (SS) plates were prepared for testing by
cleaning with methyl ethyl ketone and a clean KIMWIPE tissue
(Kimberly-Clark Corporation, Neenah, Wis.) three times. The
adhesive films described were cut into strips (1.27 cm in width)
and adhered by their adhesive to flat, rigid stainless steel plates
with exactly 2.54 cm length of each adhesive film strip in contact
with the plate to which it was adhered. A weight of 2 kilograms
(4.4 pounds) was over the adhered portion. Each of the resulting
plates with the adhered film strip was equilibrated at room
temperature for 15 minutes. Afterwards, the samples were
transferred to a 70.degree. C. oven, in which a 500 g weight was
hung from the free end of the adhered film strip with the panel
tilted 2.degree. from the vertical to ensure against any peeling
forces. The time (in minutes) at which the weight fell, as a result
of the adhesive film strip releasing from the plate, was recorded.
The test was discontinued at 10,000 minutes if there was no
failure. In the Tables, this is designated as 10,000+ minutes. Two
specimens of each tape (adhesive film strip) were tested and the
shear strength tests were averaged to obtain the reported shear
value in Tables 1-7. In some cases, the samples were prepared and
hung in the same fashion but at room temperature (RT) rather than
70.degree. C. The temperature at which the test was carried out is
indicated in each table.
Test Method 2: 180.degree. Angle Peel Adhesion Test 1
[0216] Peel adhesion was the force required to remove an
adhesive-coated test specimen from a test panel measured at a
specific angle and rate of removal. In the Examples, this force is
expressed in ounces per inch width of coated sheet and the results
are normalized to N/dm. The following procedure was used:
[0217] Peel adhesion strength was measured at a 180.degree. peel
angle using an IMASS SP-200 slip/peel tester (available from IMASS,
Inc., Accord Mass.) at a peel rate of 305 mm/minute (12
inches/minute). Stainless steel (SS) test panels were prepared as
described above. The cleaned panel was allowed to dry at room
temperature. An adhesive coated film was cut into tapes measuring
1.27 cm.times.20 cm (1/2 in..times.8 in.). A test sample was
prepared by rolling the tape down onto a cleaned panel with 2
passes of a 2.0 kg (4.4 lb.) rubber roller. The prepared samples
were dwelled at 23.degree. C./50% RH for 15 minutes before testing.
Four samples were tested for each example. The resulting peel
adhesion was converted from ounces/0.5 inch to ounces/inch (N/dm)
both values being reported in Tables 1-7.
Test Method 3: 90.degree. Angle Peel Adhesion Test 2
[0218] For peel adhesion strength stainless steel (SS) substrates
were cleaned as noted above. Two 1.0 inch (2.54 cm) by 3.0 inch
(7.62 cm) strips of adhesive were laminated to a 0.005 in. (127
micrometers) aluminum foil backing for testing and were adhered to
a stainless steel substrate (cleaned as described above) by rolling
twice in each direction with a 6.8 kg roller onto the tape at 12
inches per minute (305 mm/min). The force required to peel the tape
at an angle of 90.degree. was measured after a 24 hour dwell at
25.degree. C./50% humidity on an Instron (model number 4465,
Instron Corporation, Norwood, Mass.). The measurements for the two
tape samples were in pound-force per inch with a platen speed of 12
inches per minute (about 305 mm/min). The results were averaged and
recorded in Table 8.
Test Method 4: Shear Strength Test 2
[0219] For shear strength a stainless steel (SS) backing was
adhered to a stainless steel (SS) substrate (cleaned as described
above) using a 1.0 inch (2.54 cm) by 0.5 inch (1.27 cm) square for
158.degree. F. (70.degree. C.) temperature shear testing. A weight
of was 1 kg was placed on the sample for 15 minutes. A 500 g load
was attached to the tape sample for testing. Each sample was
suspended until failure and/or test terminated. The time to failure
was recorded. Samples were run in triplicate and averaged for Table
8 below.
Test Method 5--Determination of Yellowing
[0220] Isopropyl alcohol (IPA) was dispensed onto a 2 inch (5.08
cm) by 3 inch (7.62 cm) glass microscopic slide, wiped dry with a
clean KIMWIPE tissue repeated for a total of three washes with IPA
and allowed to air dry. A 2 inch (5.08 cm) by 3 (7.62 cm) inch
strip of adhesive tape with a release liner backing was adhered to
the glass microscopic slide by rolling over the tape twice in each
direction with a hand roller. Samples (with the protecting release
liner removed) were then measured on a CIELAB color scale for b*
using a Ultrascanpro.RTM. spectrophotometer (HunterLab, Reston,
Va.). Samples were measured under four conditions and defined as
follows: [0221] 1. Initial--adhesive measured with no UV or heat
aging. [0222] 2. UV--adhesive exposed to 1.81 J/cm2 of UV A light
from a Fusion H bulb using a Model DRS-120 Fusion processor by
Fusion UV Systems, Inc., Gaithersburg, Md., and measured after 24
hrs of UV exposure. [0223] 3. Heat--adhesive aged at 100.degree. C.
for 1 week in a Despatch LFD Series oven and measured 24 hours
after removal from oven [0224] 4. UV and Heat--combination of UV
(2) followed by Heat (3) Samples were run in triplicate and
averaged results are reported.
Test Method 6: 90.degree. Angle Peel Adhesion Test 3 (Paper
Surface)
[0225] A specimen measuring 1 in. (2.54 cm) wide and more than 3
in. (7.62 cm) long was cut in the machine direction from the test
sample. The liner was removed from one side of the adhesive and it
was placed on an aluminum panel measuring 2 in. by 5 in. (5.1 cm by
12.7 cm). The liner was removed from the other side of adhesive and
placed on a strip of Boise copy paper (available from Packaging
Corporation of America, Lake Forest, Ill., USA) under the trade
designation "X-9" (92 brightness, 24 lb. (90 gsm/12M), 500 sheets,
8.5.times.11 (216 mm by 279 mm)) measuring 1 in. by more than 5 in.
(2.54 cm by more than 12.7 cm) using light finger pressure. The
construction was then rolled once in each direction with a standard
FINAT test roller 4.5 lb (2 kg) at a speed of approximately 12
in./min. (305 mm/min). After applying the strips to the test
panels, the panel samples were allowed to dwell at constant
temperature and humidity (25.degree. C./50% RH) for 10 minutes
before testing. The test panel and strip were placed into a
horizontal support. A jaw separation rate of 305 mm/min. was used.
Test results were measured in grams force/in. and converted to
Newtons/decimeter. The reported peel values are the average of
three 90.degree. angle peel measurements.
[0226] All the examples tested were cleanly removable from the copy
paper unless specified otherwise, meaning that the paper did not
tear and also did not have any staining or residue after removal of
the adhesive.
Test Method 7: Shear Test 3 (Dry Wall)
Preparation of Drywall for Testing
[0227] The substrates employed were standard smooth drywall
obtained from Home Depot (Woodbury, Minn.). Knock-down and
orange-peel drywall was prepared by IUPAT (International Union of
Painters and Allied Trades, 3205 Country Drive, Little Canada,
Minn., USA). The drywall was primed using a paint roller with
Sherwin-Williams Pro-Mar 200. Surfaces were dried for a minimum of
4 hours at ambient conditions before applying next coat of paint.
White paint (Valspar Signature, Hi-def Advanced Color, Eggshell
Interior, #221399, Ultra White/Base A) was applied to primed
drywall using a new paint roller and allowed to dry at ambient
conditions until tackless before applying a second coat of the same
color. The final painted drywall was dried overnight at ambient
conditions and then placed into a 120.degree. C. oven for 1 week.
Samples were removed from oven and cut into desired dimensions
using a draw knife. Samples were dusted off using KIMWIPE tissue,
paper towels, or air (no cleaning with solvents) to remove dust
left over from cutting before use in testing.
[0228] A standard static shear test was performed at elevated
temperature according to Pressure Sensitive Tape Council (Chicago,
Ill.) PSTC-107 (procedure G). The test was performed at 70.degree.
F./50% Relative Humidity. The sample area of adhesive bonded to the
prepared drywall surface was 1 in. (2.54 cm) in the vertical
direction by 1 in. (2.54 cm) in the width direction (rather than
0.5 in. by 0.5 in. (1.27 cm by 1.27 cm) as called for by the
method). Then a 6.8 kg weight was placed on top of the bonded
sample area for 1 minute. After a dwell time of 60 seconds, the
test specimen was hung in the shear stand at desired temperature
and loaded immediately with a 250 g weight. The time to failure for
the adhesive bond was recorded in minutes.
Test Method 8: Dynamic Mechanical Analysis
[0229] Examples 55 and 56 (0.025 in. (625 micrometers) thickness)
were analyzed by Dynamic Mechanical Analysis (DMA) using a
Discovery Hybrid parallel plate rheometer (TA Instruments, New
Castle, Del.) to characterize the physical properties of each
sample as a function of temperature. Rheology samples were prepared
by punching out a section of the PSA with an 8 mm circular die,
removing it from the release liners, centering it between 8 mm
diameter parallel plates of the rheometer, and compressing until
the edges of the sample were uniform with the edges of the top and
bottom plates. The furnace doors that surround the parallel plates
and shafts of the rheometer were shut and the temperature was
equilibrated at 20.degree. C. and held for 1 minute. The
temperature was then ramped from 20.degree. C. to 125 or
130.degree. C. at 3.degree. C./min while the parallel plates were
oscillated at an angular frequency of 1 Hertz and a constant strain
of 5 percent. The results are depicted in FIG. 1.
Test Method 9: 180.degree. Angle Peel Adhesion Test 4 (Liner
Release)
[0230] The 180 degree peel adhesion strength between the release
liner and adhesive was measured for both sides of the liner: the
"wet cast" side, also referred to herein as the "tight side
release" where adhesive was directly cast onto the release liner,
and the "dry laminated", also referred to herein as the "easy side
release where cured adhesive was laminated to the release liner.
Liner release strengths for both sides was measured after aging for
seven days at 23.degree. C. and 50% relative humidity. A 2.54 cm
wide by approximately 20 cm in long sample of the adhesive transfer
tape was cut using a specimen razor cutter. For tight side testing
the sample was applied with its exposed adhesive surface down and
lengthwise onto the platen surface of a peel adhesion tester (Model
SP2000, IMASS Incorporated, Accord; MA). The adhesive transfer tape
was then rolled twice with a 2 kg rubber roller at a rate of 61
cm/minute. The tight side release liner was carefully lifted away
from the adhesive layer adhered to the platen surface, doubled-hack
at an angle of 180 degrees, and secured to the clamp of the peel
adhesion tester. The 180 degree angle release liner peel adhesion
strength was then measured as the liner was peeled from the
adhesive at a rate of 230 cm/min (90 in/min). A minimum of two test
specimens were evaluated with results obtained in grams/inch which
were used to calculate the average release force. All release tests
were carried out at 23.degree. C. and 50% relative humidity (RH).
For easy side testing two samples were applied with the first
attached the platen surface and the second to the outer exposed
(easy side) surface of the release liner covering the first
adhesive layer. The second sample was peeled away from the easy
side release liner.
Test Method 10: 180.degree. Angle Peel Adhesion Test 5 (Adhesive
Strength)
[0231] Both faceside adhesion (i.e., the adhesive strength of the
adhesive surface in contact with the easy side release surface of
the release liner) and backside adhesion (i.e., the adhesive
strength of the adhesive surface in contact with the tight side
release surface of the release liner) were evaluated.
[0232] Stainless steel (SS) plates were prepared for testing by
cleaning with one rinse of acetone followed by three rinses of
heptane and drying. Adhesive transfer tape was used to prepare a
single coated tape having a 0.001 inch (25 micrometer) thick
polyester backing. Two types of tapes were prepared. The first had
the adhesive joined to the backing by the adhesive surface that had
been in contact with the tight side release surface of the release
liner, resulting in an exposed adhesive surface that had been in
contact with the easy side release surface of the release liner.
The second had the adhesive joined to the backing by the adhesive
surface that had been in contact with the easy side release surface
of the release liner, resulting in an exposed adhesive surface that
had been in contact with the tight side release surface of the
release liner. As a result, the first tape sample was evaluated for
faceside adhesive strength and the second tape sample was evaluated
for backside adhesive strength.
[0233] The tape samples were 2.54 cm wide by 20 cm long (1 in. by 8
in.). These were adhered to the stainless steel plates by means of
the exposed adhesive, with 2.54 cm (1 in.) of length in contact
with the plate, and rolled down with two passes in each direction
of a 2 kg rubber roller. The samples were allowed to dwell for 15
minutes at 23.degree. C./50% RH followed by peel adhesion testing
at an angle of 180.degree. at a rate of 30.5 cm/min (12 in./min)
using an IMASS peel tester (described previously). The results were
recorded in ounces/inch (oz/in) and also converted to
Newtons/decimeter (N/dm).
Test Method 11: Overlap Shear Test 4
[0234] Flat, rigid, stainless steel plates were prepared for
testing by cleaning with one rinse of acetone followed by three
rinses of heptane and drying. The adhesives to be tested were cut
into strips measuring 1.27 cm wide and 7.62 cm long, reinforced
with 0.002 in (51 micrometer) aluminum foil and adhered by their
exposed adhesive surface to the stainless steel plates with 2.54 cm
(1 in.) of length and 1.27 cm (0.5 in.) of width of each reinforced
adhesive film strip in contact with the plate. A weight of 2
kilograms (4.4 pounds) was rolled twice over the adhered portion.
Each of the resulting test specimens was equilibrated at room
temperature for 15 minutes. Next, the specimens were transferred to
a 70.degree. C. oven, in which a 1000 gram or 500 gram weight was
hung from the free end of the adhered film strip with the panel
tilted 2.degree. from the vertical. The time (in minutes) at which
the weight fell, as a result of the adhesive film strip releasing
from the plate, was recorded. The test was discontinued at 10,000
minutes if there was no failure and the result recorded as 10,000+
minutes. Two samples of each tape (adhesive film strip) were tested
and the shear strength test results were averaged to obtain the
reported shear values.
Materials
[0235] Material suppliers are listed with the first usage of the
material. If not specified, solvents and reagents can be obtained
from Aldrich. Suppliers are listed in the examples as follows:
Aldrich--Sigma Aldrich, Milwaukee, Wis.
Alfa--Alfa Aesar, Ward Hill, Mass.
BASF--BASF Corporation, Florham Park, N.J.
EMD--EMD Chemicals, Gibbstown, N.J.
Dupont--E. I du Pont de Nemours and Company, Wilmington, Del.
Mitsubishi--Mitsubishi Polyester Film Inc., Greer, S.C.
TCI--TCI, Tokyo, Japan
VWR--VWR International, LLC., Radnor, Pa.
[0236] 2-Octyl Acrylate (2OA)--Prepared according to Preparatory
Example 1 of U.S. Pat. No. 7,385,020 Iso-octyl Acrylate
(IOA)--Obtained from 3M Company (St. Paul, Minn., USA) Acrylic Acid
(AA)--Obtained from BASF Corporation (Florham Park, N.J., USA)
Isobornyl Acrylate (IBXA)--Obtained from San Esters Corporation
(New York, N.Y., USA) Dicyclopentenyl Acrylate (DPA)--Obtained from
Monomer-Polymer Laboratories (Windham, N.H., USA) Irgacure 651
(651)--Obtained from BASF Corporation (Florham Park, N.J., USA)
Irganox 1076 (1076)--Obtained from BASF Corporation (Florham Park,
N.J., USA) Regalrez 6108--Obtained from Eastman Chemical
Corporation (Kingsport, Tenn., USA)
Preparatory Example 1
Citronellyl Acrylate (CiA)
##STR00005##
[0238] A mixture of .beta.-citronellol (300.00 g, 1.92 mol;
Aldrich), hexane (1500 mL), and triethylamine (212.49 g, 2.10 mol;
Aldrich) was cooled in an ice bath. Acryloyl chloride (190.08 g,
2.10 mol; Aldrich) was added dropwise over 5 hours. The mixture was
stirred for 17 hours at room temperature, and then filtered. The
solution was concentrated under vacuum and washed with water. The
solvent was removed under vacuum to provide a crude oil that was
purified by vacuum distillation. A colorless oil (282.83 g of
citronellyl acrylate) was collected at 70-75.degree. C. at 0.30 mm
Hg.
Preparatory Example 2
Geraniol Acrylate (GrA,
[(2E)-3,7-dimethylocta-2,6-dienyl]prop-2-enoate)
##STR00006##
[0240] A 2-liter round bottomed flask fitted with an overhead
stirrer, an addition funnel, and a condenser was charged with
geraniol (195 g, 1.25 mol; Alfa), triethylamine (152 g, 1.50 mol),
and methylene chloride (500 mL; EMD) and then cooled in an ice
bath, and the mixture stirred. A solution of acryloyl chloride (124
g, 1.38 mol;) in methylene chloride (100 mL) was added dropwise
over a 45 minute period. When addition was complete, the ice bath
was removed and the reaction mixture was stirred at room
temperature overnight. The reaction mixture was filtered to remove
the precipitated salts and washed 2 times with 150 mL portions of a
10% solution of hydrochloric acid in water and 2 times with 150 mL
portions of a saturated solution of sodium bicarbonate in water.
The methylene chloride solution was dried over potassium carbonate,
filtered, and the solvent was removed at reduced pressure.
Phenothiazine (50 mg, 0.2 mmol; TCI) was added and the product was
distilled at reduced pressure. Product was collected at a boiling
range of 87 to 92.degree. C. and a pressure range of 0.50 to 0.65
mm. NMR analysis of the distillate confirmed the structure as
geraniol acrylate.
Preparatory Example 3
Farnesol Acrylate (FrA,
[(2E,6E)-3,7,11-trimethyldodeca-2,6,10-trienyl]prop-2-enoate)
##STR00007##
[0242] Farnesol acrylate was prepared as described in Preparatory
Example 2 except the reagents were farnesol (181 g, 0.81 mol;
Alfa), triethylamine (99 g, 0.98 mol), methylene chloride (350 mL),
and acryloyl chloride (81 g, 0.90 mol) in methylene chloride (90
mL). The resulting product was distilled and collected at a boiling
range of 112 to 118.degree. C. and a pressure range of 0.18 to 0.25
mm. NMR analysis of the distillate confirmed the structure as
farnesol acrylate.
Preparatory Example 4
3-Cyclohexene Methyl Acrylate (CMA)
##STR00008##
[0244] A mixture of 3-cyclohexene methanol (95.00 g, 0.85 mol;
Aldrich), methylene chloride (300 mL), and triethylamine (94.11 g,
0.93 mol; EMD) was cooled in an ice bath. Acryloyl chloride (84.17
g, 0.93 mol) was added dropwise over 4 hours. The mixture was
stirred for 17 hours at room temperature, then filtered. The
solution was concentrated under vacuum, then diluted with ethyl
acetate (500 mL; VWR). The solution was washed with saturated
aqueous sodium bicarbonate and brine, then dried over magnesium
sulfate. The solvent was removed under vacuum to provide a crude
oil that was purified by vacuum distillation. A colorless oil
(129.92 g of 3-cyclohexene methyl acrylate) was collected at
62-64.degree. C. at 1.0 mm Hg.
Preparatory Example 5
Undecenyl Acrylate (UDA)
##STR00009##
[0246] Undecenyl alcohol (69.66 g, 0.4090 mol; Alfa), toluene (300
mL), and triethylamine (45.53 g, 0.45 mol) were added to a 1000 mL
3-necked round bottomed flask. The solution was stirred and cooled
to 0.degree. C. in a nitrogen atmosphere. Acryloyl chloride (40.73
g, 0.45 mol) was added dropwise via addition funnel over a period
of 4 hours. The cloudy yellow mixture was then slowly warmed to
room temperature and placed on the rotary evaporator to remove the
toluene. Ethyl acetate (300 mL) was added and the mixture was
filtered through celite, washed with saturated sodium bicarbonate,
and then the solvent was removed under vacuum. The crude yellow oil
was purified by vacuum distillation. A faint yellow oil (55/75 g of
10-undecenyl acrylate) was collected at 90-96.degree. C. @ 0.88 mm
Hg.
Preparatory Example 6
Oleyl Acrylate (OA)
##STR00010##
[0248] A mixture of oleyl alcohol (90.00 g, 0.34 mol; Alfa),
methylene chloride (300 mL), and triethylamine (38.45 g, 0.38 mol)
was cooled in an ice bath. Acryloyl chloride (34.89 g, 0.38 mol)
was added dropwise over 2 hours. The mixture was stirred for 17
hours at room temperature, then filtered. The solution was
concentrated under vacuum. The crude oil was loaded on a column of
silica gel and eluted with hexane. The eluted solution was
collected and concentrated under vacuum to provide a colorless oily
liquid (68.25 g of oleyl acrylate).
Brij 02 Acrylate was prepared according to US2012/0154811.
Examples 1-5 and Comparative Examples C1-C4
[0249] Compositions were prepared by charging a 500 mL jar with 270
g (90 wt. %) 2-octyl acrylate (2OA), 30 g (10 wt. %) of acrylic
acid (AA; BASF), 0.12 g (0.04 phr) of photoinitiator 1
(2,2-dimethoxy-2-phenylacetophenone, Irgacure 651; BASF), and the
amount in phr of one of the monofunctional acrylates (from the
preparatory examples) as shown in Table 1. The monomer mixture was
purged with nitrogen for 10 minutes then exposed to low intensity
UV A light (less than 10 mW/cm.sup.2, referred to as UV A because
the output is primarily between 320 and 390 nm with a peak emission
at around 350 nm which is in the UV A spectral region) until a
coatable syrup (Brookfield viscosity of 100-8000 cP) was formed,
after which an additional 0.48 g (0.16 phr) of photoinitiator 1 was
mixed into the composition.
[0250] The pre-adhesive (i.e. syrup) compositions were then coated
on a release liner at a thickness of about 0.005 inches (127
micrometers) and cured under a nitrogen atmosphere by further
exposure to UVA light from 350 BL light bulbs (40 watt, Osram
Sylvania) as shown in Table 1 for various times to form a pressure
sensitive adhesive (PSA). Total energies were measured using a
Powermap.TM. radiometer equipped with a low intensity sensing head
(available from EIT Inc., Sterling, Va.). The PSA was then
laminated under hand pressure with a small silicone roller to a
primed 0.002 inch (51 micrometer) thick poly(ethylene terepthalate)
backing (trade designation Hostaphan 3SAB PET film; Mitsubishi
Polyester Film, Incorporated, Greer, S.C.) to form a tape for
adhesive testing.
[0251] Comparative Examples C1 and C2 were prepared as described
above except that no crosslinker was added to the prior to the
syruping step. The amounts of 1,6-hexanediol diacrylate (HDDA) was
mixed into the pre-adhesive formulations before coating and
curing.
[0252] Comparative Examples C3 and C4 were prepared as described in
C1 and C2 except that the crosslinker was
2,4,-bis(trichloromethyl)-6-(3,4-dimethoxyphenyl)-triazine
(T1).
[0253] The adhesives were tested for shear adhesion at 70.degree.
C., and 180.degree. angle peel adhesion. Results are shown in Table
1.
TABLE-US-00001 TABLE 1 180.degree. Angle 70.degree. C. Peel
Adhesion Total UV Shear (min) to SS (oz/in, Crosslinker Exposure
(Test N/dm) (Test Ex Material phr (g) mJ/cm.sup.2 Method 1) Method
2) 1 CiA 0.6 1.8 2540 10,000+ 90.3, 98.6 2 CiA 0.8 2.4 2540 10,000+
92.9, 101.6 3 CiA 1.0 3.0 2540 10,000+ 84.9, 92.9 4 GrA 0.6 1.8
1016 10,000+ 91.1, 99.7 5 FrA 0.6 1.8 1016 8264 85.1, 93.1 C1 HDDA
0.1 0.3 1016 3432 41.3, 45.2 C2 HDDA 0.2 0.6 1016 5890 17.2, 18.8
C3 T1 0.1 0.3 593 10,000+ 79.1, 86.2 C4 T1 0.2 0.6 4572 10,000+
74.3, 81.3
Examples 6-10, Comparative Examples C5-C8
[0254] Adhesive compositions and tapes were prepared and tested as
described in Examples 1-5 except that 270 g (90 wt. %) of isooctyl
acrylate (IOA) were used instead of 2OA and the crosslinkers in the
amounts shown in Table 2 were used. Test results are shown in Table
2.
[0255] Adhesives tapes for Comparative Examples C5-C6 were prepared
and tested as described in Comparative Examples C1-C2. Results are
shown in Table 2.
[0256] Adhesives tapes for Comparative Examples C7-C8 were prepared
as described in Comparative Examples C3-C4. Results are shown in
Table 2.
TABLE-US-00002 TABLE 2 180.degree. Angle 70.degree. C. Peel
Adhesion Total UV Shear (min) to SS (oz/in, Crosslinker Exposure
(Test N/dm) (Test Ex Material phr (g) mJ/cm.sup.2 Method 1) Method
2) 6 CiA 1.0 3.0 2535 10,000+ 66.9, 73.2 7 GrA 0.8 2.4 2535 10,000+
65.5, 71.7 8 GrA 1.0 3.0 2535 10,000+ 73.9, 80.8 9 FrA 0.8 2.4 2535
10,000+ 70.3, 77.0 10 FrA 1.0 3.0 2535 10,000+ 66.5, 72.8 C5 HDDA
0.1 0.3 2535 1463 68.9, 75.4 C6 HDDA 0.2 0.6 2535 3481 64.5, 70.6
C7 T1 0.1 0.3 2535 10,000+ 69.5, 76.0 C8 T1 0.2 0.6 2535 10,000+
67.6, 74.0
Examples 11-25
[0257] Adhesive compositions were prepared by charging an 8 ounce
jar with 45 g of IOA, 5 g of AA, 0.02 g of photoinitiator 1 and the
amounts and type of monofunctional acrylates (from preparatory
examples) as shown in Table 3. The monomer mixture was purged with
nitrogen for 5 minutes then exposed to UV A light from a low
intensity black bulb (15 watt, 365 nm peak) until the viscosity
increased and a coatable syrup was prepared.
[0258] An additional 0.08 g (0.16 phr) of the photoinitiator 1 was
mixed into the syrup. The compositions were then knife-coated
between two clear release liners at a 0.005 inch (127 micrometers)
thickness and cured by exposure to UV A light from 350 BL light
bulbs (40 watt, Osram Sylvania) as shown in Table 3. Total UV
exposure was measured with an Uvirad.RTM. Low Energy UV Integrating
Radiometer (EIT, Inc., Sterling, Va.). Tapes were prepared as
described in Examples 1-5, and tested for shear and peel adhesion.
Results are shown in Table 3.
TABLE-US-00003 TABLE 3 180.degree. Angle 70.degree. C. Peel
Adhesion Total UV Shear (min) to SS (oz/in, Crosslinker Exposure
(Test N/dm) (Test Ex Material phr (g) mJ/cm.sup.2 Method 1) Method
2) 11 CiA 2.0 1.0 2189 10,000+ 60.3, 66.0 12 CiA 5.0 2.5 2189
10,000+ 43.1, 47.2 13 CiA 10.0 5.0 2189 10,000+ 27.1, 29.6 14 GrA
2.0 1.0 2189 10,000+ 66.7, 73.0 15 GrA 5.0 2.5 2189 10,000+ 44.2,
48.4 16 GrA 10.0 5.0 2189 10,000+ 23.4, 25.6 17 FrA 2.0 1.0 2189
10,000+ 51.7, 56.6 18 FrA 5.0 2.5 2189 10,000+ 40.7, 44.5 19 FrA
10.0 5.0 2189 10,000+ 26.7, 29.2 20 UDA 1.0 0.5 1712 10,000+ 51.2,
56.0 21 UDA 5.0 2.5 1712 10,000+ 21.7, 23.7 22 CMA 1.0 0.5 1712
1092 75.6, 82.7 23 CMA 5.0 2.5 1712 10,000+ 68.2, 74.6 24 OA 1.0
0.5 1186 10,000+ 74.6, 81.6 25 OA 5.0 2.5 1186 10,000+ 60.0, 65.6
26 Brij O2 A 1.0 0.5 1500 2098 76.1, 83.2 27 Brij O2 A 5.0 2.5 1500
10,000+ 61.4, 67.1
Examples 28-33
[0259] Adhesives and tapes were prepared and tested as described in
Examples 11-27 except that the monofunctional acrylate crosslinker
was not added to the syrup composition, but mixed in prior to
coating and curing. The amounts of crosslinker and test results are
shown in Table 4.
TABLE-US-00004 TABLE 4 180.degree. Angle 70.degree. C. Peel
Adhesion Total UV Shear (min) to SS (oz/in, Crosslinker Exposure
(Test N/dm) (Test Ex Material phr (g) mJ/cm.sup.2 Method 1) Method
2) 28 CiA 1.0 0.5 1422 10,000+ 62.7, 68.6 29 CiA 2.0 1.0 1422
10,000+ 51.2, 56.0 30 GrA 1.0 0.5 1422 10,000+ 69.1, 75.6 31 GrA
2.0 1.0 1422 10,000+ 54.9, 60.1 32 FrA 1.0 0.5 1422 10,000+ 66.0,
72.2 33 FrA 2.0 1.0 1422 10,000+ 52.9, 57.9
Examples 34-39
[0260] Compositions for Examples 34-37 were prepared by charging a
500 mL jar with 467.5 g (93.5 wt. %) of IOA, 32.5 g (6.5 wt. %) of
AA, 0.2 g (0.04 phr) of photoinitiator 2 (trade designation
Irgacure 184; BASF), and the amounts of CiA shown in Table 5. The
monomer mixture was purged with nitrogen for 5-10 minutes then
exposed to low intensity UV A radiation until a coatable syrup was
formed.
[0261] An additional 1.75 g (0.16 phr) of photoinitiator 2 and 50 g
(10 phr) of tackifier (trade designation Foral 85LB, Eastman
Chemical Co., Kingsport, Tenn.) were then mixed into each
composition. The compositions were then coated onto a release liner
at 0.004 inch (101.6 micrometer) thickness and cured under a
nitrogen atmosphere by exposure to UV A light from 350 BL light
bulbs (40 watt, Osram Sylvania) followed by exposure to high
intensity UV C light (greater than 10 mW/cm.sup.2, referred to as
UV C because the output of the bulbs is nearly monochromatic
between 250 and 260 nm in the UV C spectral region) to form a PSA.
Total UV exposure was measured as described for Examples 1-5 and is
shown in Table 5. Tapes were prepared as in Examples 1-5 for
adhesive testing.
[0262] Compositions and tapes for Example 38 were prepared and
tested in the same manner as Example 35 except that 2OA was used
instead of IOA. Test results for all tapes are shown in Table
5.
[0263] Compositions and tapes for Example 39 were prepared and
tested as in Example 35 except the tackifier was trade designation
Regalrez 6108 (Eastman Chemical Co., Kingsport, Tenn.) instead of
trade designation Foral 85LB.
TABLE-US-00005 TABLE 5 180.degree. Angle Total UV 70.degree. C.
Peel Adhesion Exposure Shear (min) to SS (oz/in, Crosslinker
mJ/cm.sup.2 (Test N/dm) (Test Ex Material phr (g) (UVA + UVC)
Method 1) Method 2) 34 CiA 2 10 854 + 276 10,000+ 59.5, 65.1 35 CiA
3 15 854 + 276 10,000+ 49.6, 54.3 36 CiA 5 25 909 + 252 10,000+
25.1, 27.5 37 CiA 10 50 909 + 252 10,000+ 18.0, 19.7 38 CiA 3 15
909 + 252 10,000+ 43.8, 47.9 39 CiA 3 15 880 + 237 10,000+ 45.1,
49.3
Examples 40-42
[0264] Compositions were prepared by charging a 500 mL jar with
420.8 g (93.5 wt %) of IOA, 29.3 (6.5 wt %) g of AA, 0.18 g (0.04
phr) of photoiniator 2 (trade designation Irgacure 184), and the
amounts of CiA shown in Table 6. The monomer mixture was purged
with nitrogen for 5-10 minutes then exposed to low intensity
ultraviolet radiation until a coatable syrup was prepared.
[0265] An additional 1.58 g (0.16 phr) of photoinitiator 2, 45 g
(10 phr) of tackifier (trade designation Foral 85LB), and the
amounts of triazine T2
(2,4,-bis(trichloromethyl)-6-(4-methoxy)phenyl)-triazine) shown in
Table 6 were mixed into the composition. The pre-adhesive (syrup)
formulations were then coated onto a release liner at 0.004 inch
(101.6 micrometer) thickness and cured under a nitrogen atmosphere
by exposure to 883 mJ/cm.sup.2 of UV A light from 350 BL light
bulbs (40 watt, Osram Sylvania). Total UV exposure was measured as
described in Examples 1-5. The PSA was then laminated under hand
pressure with a small silicone roller to a primed poly(ethylene
terepthalate) (Polyester Films, Incorporated, Greer, S.C.) film
backing for adhesive testing.
TABLE-US-00006 TABLE 6 180.degree. Angle 70.degree. C. Peel
Adhesion Shear (min) to SS (oz/in, Crosslinker (CiA/T2) (Test N/dm)
(Test Ex Material phr (g) Method 1) Method 2) 40 CiA and T2
0.8/0.11 3.38/0.51 10,000+ 60.9, 66.6 41 CiA and T2 1.5/0.08
6.75/0.34 10,000+ 54.2, 59.3 42 CiA and T2 2.3/0.04 10.13/0.17
10,000+ 48.5, 53.1
Examples 43-46
[0266] Compositions for Examples 43-45 were prepared by charging a
500 mL jar with 346.9 g (82.6 wt %) of IOA, 3.2 g (0.1 wt %) of AA,
0.14 g (0.04 phr) of photoinitiator1, and the amounts of CiA shown
in Table 7. The monomer mixture was purged with nitrogen for 5-10
minutes then exposed to low intensity ultraviolet radiation to form
a coatable syrup.
[0267] An additional 0.84 g (0.16 phr) of photoinitiator1, 0.26 g
of antioxidant (Irganox 1076), 70 g (17 wt. %) of isobornyl
acrylate (IBXA), and 100.8 g (24 phr) of tackifiers (trade
designation Regalrez 6108) were added. The compositions were mixed
thoroughly by rolling overnight and coated onto release liner at 5
mil (127 micrometer) thickness and cured under a nitrogen
atmosphere by exposure to 827 mJ/cm.sup.2 of UV A light followed by
exposure to 236 mJ/cm.sup.2 UV C light to form a PSA as described
in Examples 34-39. Total UV exposure was measured as described in
Examples 1-5. The PSA was then laminated to a primed poly(ethylene
terepthalate) (Mitsubishi Polyester Films) backing for adhesive
testing. Results are shown in Table 7.
[0268] Compositions and tapes for Example 46 were prepared using
2OA instead of IOA.
TABLE-US-00007 TABLE 7 180.degree. Angle Peel 70.degree. C. Shear
Adhesion to SS Crosslinker (min) (oz/in, N/dm) Ex Material phr (g)
(Test Method 1) (Test Method 2) 43 CiA 3 10.5 19 71.6, 78.3 44 CiA
5 17.5 159 49.0, 53.6 45 CiA 10 35.0 10,000+ 25.8, 28.2 46 CiA 3
10.5 63 71.8, 78.5
Examples 47-48 and Comparative Examples C9-C10
[0269] Example 47 was prepared by charging a 500 mL jar with 306.3
g (87.5 wt. %) IOA, 43.8 g (12.5 wt. %) of AA, 0.14 g (0.04 phr) of
photoinitiator 1, and 2.1 g (0.6 phr) of CiA. The monomer mixture
was purged with nitrogen for 10 minutes then exposed to low
intensity UV A radiation until a coatable syrup was formed, after
which another 0.67 g (0.16 phr) of photoinitiator1 was added. Next,
6.0 g (1.7 phr) of trade designation HDK H15 fumed silica (Wacker
Silicones) were added and the syrup was mixed with a trade
designation Netzsch Model 50 Dispersator. When the fumed silica was
completely dispersed, 28 g (8 phr) of glass bubbles (K15, 3M
Company, St. Paul Minn.) were added and the composition was mixed
thoroughly by rolling overnight.
[0270] The composition was then coated between release liners at a
0.038 inch (965.2 micrometers) thickness and cured by 741
mJ/cm.sup.2 of UV A light from 350 BL light bulbs (40 watt, Osram
Sylvania) to form a PSA. Total UV exposure was measured as
described in examples 1-5.
[0271] A composition and tape Example C9 were prepared as in
Example 47 except that no CiA was added to the syrup composition,
and 0.19 g (0.055 phr) HDDA was added to the syrup before
coating.
[0272] A composition and tape for Example 48 were prepared as in
Example 47 except the composition for the syrup was 315 g (90 wt.
%) of 2OA, 35 g (10 wt %) of AA, 0.14 g (0.04 phr) of
photoinitiator 1, and 3.5 g (1 phr) of CiA.
[0273] A composition and tape for Example C10 were prepared as in
Example C9 except using the composition of Example 48.
[0274] Example 47-48 and C.sub.9-10 were prepared for adhesive
testing and tested as outlined in the test methods 3 and 4.
TABLE-US-00008 TABLE 8 90.degree. Peel Adhe- 70.degree. C. Shear
sion to SS Backbone (min) (lbf-in, kg-cm) Ex Monomer
Crosslinker/phr (Test Method 4) (Test Method 3) 47 IOA CiA/0.6
10,000+ 23.5, 27.1 48 2OA CiA/1 10,000+ 19.2, 22.1 C9 IOA
HDDA/0.055 10,000+ 23.1, 26.6 C10 2OA HDDA/0.055 10,000+ 22.4,
25.8
[0275] Adhesive samples from Examples 3, 35-38, 40-42, and 45, and
C3 were measured for yellowing as described above. Results are
shown in Table 9.
TABLE-US-00009 TABLE 9 Adhesive b* UV Ex Thickness (mil) b* Initial
b* UV b* Heat & Heat 3 5 0.21 0.33 0.36 0.73 35 4 0.22 0.42
0.69 1.29 36 4 0.23 0.30 0.68 1.13 37 4 0.25 0.32 0.63 0.91 38 4
0.23 0.45 0.68 1.11 40 4 0.87 1.28 1.38 2.05 41 4 0.67 0.93 0.98
1.50 42 4 0.44 0.52 0.77 1.11 45 5 0.21 0.32 0.30 0.59 C3 (T1) 5
0.76 1.33 1.14 1.98
Examples 49-52 and C11
[0276] Adhesive composition and tape 49 was made by charging a
glass bottle with 54 g (90 wt. %) 2OA, 6 g (10 wt. %) of AA, 0.6 g
(1 phr) CiA, 0.06 g (0.1 phr) of Vazo 52 (Dupont), and 140 g ethyl
acetate. This mixture was purged with nitrogen gas for 20 minutes,
and the bottle was sealed and placed in a water bath at 52.degree.
C. with shaking for 20 hours. The bottle was then removed, and
sparged with air for 1 minute. 30 g of the final polymer solution
was combined in a jar with 0.17 g (2 phr) of photoinitiator 1 and
rolled to ensure thorough mixing. The composition was then coated
at 0.005 inch (127 micrometers) thickness on a 0.002 inch (51
micrometer) thick Mitsubishi Hostaphan 3SAB PET polyester film, and
dried in an oven at 70.degree. C. for 30 minutes. The dried
adhesive was covered with a release liner and exposed to 982
mJ/cm.sup.2 of UVA light over 10 minutes. Adhesive testing was then
carried out according to test methods 1 and 2 except the shear
strength test was carried out at room temperature rather than
70.degree. C. Results are shown in Table 10.
[0277] Adhesive composition and tape 50 was made and tested in the
same manner as example 46 except that the composition was 90 g (90
wt. %) 2OA, 10 g (10 wt. %) of AA, 2 g (2 phr) CiA, 0.04 g (0.04
phr) isooctyl thioglycolate, 0.1 g (0.1 phr) of Vazo 67 (Dupont),
and 233.3 g ethyl acetate, and the cure was carried out with 762
mJ/cm.sup.2 of UVA light over 10 minutes.
[0278] Adhesive composition 51 was made and tested in exactly the
same way as composition 49 except that no photoinitiator was added.
Adhesive composition 52 was made in exactly the same way as
composition 50 except that no photoinitator was added.
[0279] Adhesive composition and tape C11 was made and tested in the
same fashion as Example 49 except that the composition contained no
CiA, and the cure was carried out with 2011 mJ/cm.sup.2 of UVA
light over 10 minutes.
TABLE-US-00010 TABLE 10 RT Shear 180.degree. Angle (min) Peel
Adhesion Photo- (Modified to SS (oz/in, Crosslinker initator 1 Test
N/dm) (Test Ex Material phr (g) phr g Method 1) Method 2) 49 CiA 1
0.6 2 0.17 5,246 50.3, 55.1 50 CiA 2 2 2 0.17 5,285 58.9, 64.5 51
CiA 1 0.6 0 0 135 54.6, 59.8 52 CiA 2 2 0 0 342 71.4, 78.2 C11 N/A
N/A N/A 2 0.17 880 40.7, 44.6
Examples 53-56
[0280] Examples 53 and 54 were prepared by charging a 500 mL jar
with 350 g (100 wt. %) 2OA, 0.14 g (0.04 phr) of photoinitiator 1,
and a quantity of CiA according to Table 11. The monomer mixture
was purged with nitrogen for 10 minutes then exposed to low
intensity UVA radiation until a coatable syrup was formed, after
which another 0.67 g (0.16 phr) of photoinitiator 1 was added.
Next, 6.0 g (1.7 phr) of HDK H15 fumed silica (Wacker Silicones)
was added and the syrup was mixed with a Netzsch Model 50
Dispersator. When the fumed silica was completely dispersed, 28 g
(8 phr) of glass bubbles (K15, 3M Company, St. Paul Minn.) were
added and the composition was mixed thoroughly by rolling
overnight.
[0281] The composition was then coated at a 0.025 inch (635
micrometers) thickness between a release liner and a primed 0.002
inch (51 micrometer) polyethylene terepthalate (PET) and cured by a
dose of UV A light (shown in Table 11) from 350 BL light bulbs (40
watt, Osram Sylvania) to form a PSA. Total UV exposure was measured
as described in examples 1-5. Adhesive properties were tested
according to test methods 6 and 7 and are shown in Table 11.
[0282] Examples 55 and 56 were made as described above except for
the following 1) the initial composition contained 300 g (100 wt.
%) 2OA, 0.12 g (0.04 phr) of photoinitiator 1, and a quantity of
CiA according to Table 11, 2) 0.57 g (0.16 phr) of photoinitiator
1, 5.1 g (1.7 phr) of HDKH15 fumed silica, and 24 g (8 phr) of
glass bubbles were added after the prepolymer syrup was prepared.
For rheological measurements, the coatable syrup was coated at
0.025 inch (635 micrometer) thickness and cured in the same
manner.
TABLE-US-00011 TABLE 11 70.degree. C. Shear to 90.degree. Angle
Orange Peel Peel Adhesion Dry Wall to Paper (lb-in, Backbone CiA
CiA UV Dose (min.) (Test kg-cm) (Test Ex Monomer (g) (phr)
(mJ/cm.sup.2) Method 7) Method 6) 53 2OA 1.75 0.5 1482 275 4821.3,
5554.6 54 2OA 3.5 1.0 1482 10,000+ 3611.9, 4161.3 55 2OA 4.11 1.37
2664 10,000+ 2677.5, 3084.7 56 2OA 5.49 1.83 2664 8790 2211.9,
2448.3
Examples 57-60
[0283] Adhesive compositions and tapes 57-60 were made and tested
in exactly the same way as examples 11-25. The crosslinkers
employed and adhesive properties are shown in Table 12.
Dicyclopentenyl acrylate (DPA) was obtained from Monomer-Polymer
Laboratories (Windham, N.H., USA). Ethylene glycol dicyclopentenyl
ether acrylate (EGDA) was obtained from Aldrich.
TABLE-US-00012 TABLE 12 180.degree. Peel 70.degree. C. Adhesion to
Total UV Shear (min) SS (oz/in, Crosslinker Exposure (Test N/dm)
(Test Ex Material phr (g) mJ/cm.sup.2 Method 1) Method 2) 57 EGDA
0.5 0.25 2102 1,826 92.2, 100.9 58 EGDA 1.0 0.5 2102 10,000+ 82.1,
89.9 59 DPA 0.5 0.25 1934 2,246 83.3, 91.2 60 DPA 1.0 0.5 1934
10,000+ 85.8, 93.9
TABLE-US-00013 TABLE 13 Low Tg High Tg Monomer Monomer Fumed Glass
(2OA or (AA and/or Crosslinking Tackifier Silica Bubbles Example
IOA) wt-% IBXA) wt-% Monomer wt- % wt-% wt-% wt-% 34 83.2 5.8 CiA -
1.8 8.9 0 0 35 82.5 5.7 CiA - 2.6 8.8 0 0 36 81.0 5.6 CiA - 4.3 8.7
0 0 37 77.7 5.4 CiA - 8.3 8.3 0 0 38 82.5 5.7 CiA - 2.6 8.8 0 0 39
82.5 5.7 CiA - 2.6 8.8 0 0 40 84.0 5.9 CiA/T2 - 0.7/0.1 9.0 0 0 41
83.5 5.8 CiA/T2 - 1.3/0.07 8.9 0 0 42 83.0 5.8 CiA/T2 - 2.0/0.03
8.9 0 0 43 65.2 13.7 CiA - 2.0 18.9 0 0 44 64.3 13.6 CiA - 3.2 18.7
0 0 45 62.3 13.1 CiA - 6.3 18.1 0 0 46 65.2 13.7 CiA - 2.0 18.9 0 0
47 79.1 11.3 CiA - 0.5 0 1.6 7.2 48 81.1 9.0 CiA - 0.9 0 1.5 7.2 53
90.5 0 CiA - 0.5 0 1.6 7.2 54 90.1 0 CiA - 0.9 0 1.5 7.2 55 89.8 0
CiA - 1.2 0 1.5 7.2 56 89.5 0 CiA - 1.6 0 1.5 7.2
Pressure Sensitive Adhesive (PSA) A
[0284] PSA A was made by charging a gallon jar with 1) 1620 g of
2OA, 2) 180 g of AA, 3) 0.72 g (0.04 phr) of 651, and 4) 36 g of
citronellyl acrylate (CiA). The monomer mixture was purged with
nitrogen for 10 minutes then exposed to low intensity ultraviolet
radiation until a coatable syrup was obtained. An additional 2.7 g
(0.15 phr) of 651 was then added. The pre-adhesive formulation were
then coated onto either release liner A or B at 0.002 inches (51
micrometers) thickness and cured under nitrogen by exposure to 366
mJ/cm.sup.2 of UV A light over 43 seconds and 113 mJ/cm.sup.2 of
UVC light over 15 seconds.
Pressure Sensitive Adhesive (PSA) B PSA B was made by charging a
gallon jar with 1) 1620 g of 2OA, 2) 180 g of AA, 3) 0.72 g (0.04
phr) of 651, and 4) 36 g of dicyclopentyl acrylate (DPA). The
monomer mixture was purged with nitrogen for 10 minutes then
exposed to low intensity ultraviolet radiation until a coatable
syrup was obtained. An additional 2.7 g (0.15 phr) of 651 was then
added. The pre-adhesive formulation were then coated onto either
release liner A or B at 0.002 inches (51 micrometers) thickness and
cured under nitrogen by exposure to 366 mJ/cm.sup.2 of UV A light
over 43 seconds and 113 mJ/cm.sup.2 of UVC light over 15
seconds.
Pressure Sensitive Adhesive (PSA) C
[0285] PSA C was made by charging a gallon jar with 1) 1784 g 2OA,
2) 16.2 g of AA, 3) 0.72 g of 651, and 4) 54 g of CiA. The monomer
mixture was purged with nitrogen for 10 minutes then exposed to low
intensity ultraviolet radiation until a coatable syrup was
obtained. An additional 4.3 g (0.24 phr) of 651, 360 g of IBXA,
1.35 g of 1076, and 518.4 g of Regalrez 6108 were then added. The
pre-adhesive formulations were then coated onto release liner A at
0.002 inches (51 micrometers) thickness and cured under nitrogen by
exposure to 884 mJ/cm.sup.2 of UV A light over 3 minutes.
Pressure Sensitive Adhesive (PSA) D
[0286] PSA D was made by charging a gallon jar with 1) 1784 g 2OA,
2) 16.2 g of AA, 3) 0.72 g of 651, and 4) 54 g of DPA. The monomer
mixture was purged with nitrogen for 10 minutes then exposed to low
intensity ultraviolet radiation until a coatable syrup was
obtained. An additional 4.3 g (0.24 phr) of 651, 360 g of IBXA,
1.35 g of 1076, and 518.4 g of Regalrez 6108 were then added. The
pre-adhesive formulations were then coated onto release liner A at
0.002 inches (51 micrometers) thickness and cured under nitrogen by
exposure to 884 mJ/cm.sup.2 of UV A light over 3 minutes.
Release Liner (RL) A
[0287] A 0.002 in. (51 micrometer) thick polyester film having a
silicone acrylate release coating on both sides was prepared using
the process described in Example 61 of US 2013059105.
Release Liner (RL) B
[0288] A 0.004 in. (51 micrometer) thick, 58 pound polycoated Kraft
paper release liner having a silicone acrylate release coating on
both sides was prepared using the process described in Example 61
of US 2013059105.
Examples 61-66
[0289] The various combinations of pressure sensitive adhesives and
release liners shown in Table 14 were evaluated for faceside (FS)
and backside (BS) peel adhesion strengths as describe in Test
Method 10: 180.degree. Angle Peel Adhesion Test 5 (Adhesive
Strength). Construction were also prepared and evaluated for
release liner peel strengths as described in Test Method 9:
180.degree. Angie Peel Adhesion Test 4 (Liner Release). The results
are shown in Table 14. Release values and release ratios were also
observed to remain relatively stable even after aging for 7 days at
70.degree. C., as well as for 7 days at 90% RH and 32.degree. C.
(90.degree. F. In addition, Examples 61-66 all exhibited overlap
shear values of more than 10,000 minutes when evaluated according
to Test Method 11: Overlap Shear Test 4.
TABLE-US-00014 TABLE 14 FS Peel Adhe- BS Peel Adhe- Easy Side Tight
Side Release sion to SS sion to SS Release Release Ratio Ex. PSA RL
(oz/in, N/dm) (oz/in, N/dm) (g/in, g/cm) (g/in, g/cm) (Tight/Easy)
61 A A 34.0, 37.2 39.1, 42.8 6.5, 2.6 28.8, 11.3 4.43 62 B A 45.2,
49.5 41.3, 45.2 5.7, 2.2 24.1, 9.5 4.23 63 A B 41.5, 45.4 39.5,
43.2 8.9, 3.5 58.4, 23.0 6.56 64 B B 48.0, 52.5 40.0, 43.8 7.7, 3.0
50.9, 20.0 6.61 65 C A 37.8, 41.4 40.2, 44.0 9.4, 3.7 32.4, 12.8
3.45 66 D A 36.9, 40.4 48.2, 52.8 6.6, 2.6 26.4, 10.4 4.00
* * * * *