U.S. patent application number 14/379767 was filed with the patent office on 2016-01-21 for photobase generators as latent ionic crosslinkers for acrylic pressure-sensitive adhesives.
The applicant listed for this patent is 3M INNOVATIVE PROPERTIES COMPANY. Invention is credited to Mary M. Caruso, Jason D. Clapper, Ann R. Fornof, Babu N. Gaddam, Larry R. Krepski, Hae-Seung Lee, Serkan Yurt.
Application Number | 20160017073 14/379767 |
Document ID | / |
Family ID | 47754991 |
Filed Date | 2016-01-21 |
United States Patent
Application |
20160017073 |
Kind Code |
A1 |
Fornof; Ann R. ; et
al. |
January 21, 2016 |
PHOTOBASE GENERATORS AS LATENT IONIC CROSSLINKERS FOR ACRYLIC
PRESSURE-SENSITIVE ADHESIVES
Abstract
The present disclosure provides an ionically crosslinkable
composition comprising a (meth)acrylate copolymer component having
pendant acid functional groups and pendant photobase functional
groups. On exposure to light, the pendant photobase group
photolyzes to provide a pendant amine group, that ionically
crosslinks the copolymer.
Inventors: |
Fornof; Ann R.; (St. Paul,
MN) ; Gaddam; Babu N.; (Woodbury, MN) ; Lee;
Hae-Seung; (Woodbury, MN) ; Clapper; Jason D.;
(Lino Lakes, MN) ; Krepski; Larry R.; (White Bear
Lake, MN) ; Caruso; Mary M.; (Maplewood, MN) ;
Yurt; Serkan; (Woodbury, MN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
3M INNOVATIVE PROPERTIES COMPANY |
Saint Paul |
MN |
US |
|
|
Family ID: |
47754991 |
Appl. No.: |
14/379767 |
Filed: |
February 8, 2013 |
PCT Filed: |
February 8, 2013 |
PCT NO: |
PCT/US2013/025268 |
371 Date: |
August 20, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61604584 |
Feb 29, 2012 |
|
|
|
Current U.S.
Class: |
524/555 ;
526/311 |
Current CPC
Class: |
C09J 7/385 20180101;
C08F 220/1808 20200201; C08F 220/1808 20200201; C08F 222/10
20130101; C09J 133/14 20130101; C08F 220/343 20200201; C08F 220/06
20130101; C08F 220/343 20200201; C08F 220/06 20130101 |
International
Class: |
C08F 222/10 20060101
C08F222/10; C09J 7/02 20060101 C09J007/02; C09J 133/14 20060101
C09J133/14 |
Claims
1. An ionically crosslinkable composition comprising a
(meth)acrylate copolymer component having pendant acid-functional
groups and pendant photobase generator groups, which on exposure to
light, the pendant photobase groups fragment or photolyze to
provide pendant amine groups to form ionic crosslinks with the
acid-functional groups, wherein (meth)acrylate copolymer component
comprises: i. 45 to 99 parts by weight of an (meth)acrylic acid
ester of non-tertiary alcohol; ii. 0.5 to 15 parts by weight of an
acid functional ethylenically unsaturated monomer; iii. 0.5 to 15
parts by weight of ethylenically unsaturated monomer having
photobase generator groups; iv. 0 to 10 parts by weight of a
non-acid functional, ethylenically unsaturated polar monomer; v. 0
to 5 parts vinyl monomer; and vi. 0 to 5 parts of a multifunctional
(meth)acrylate; based on 100 parts by weight total monomer.
2. The ionically crosslinkable composition of claim 1, wherein the
pendant photobase generator is an oxime ester, a benzyl carbamate,
a benzoin carbamate, an O-carbamoylhydroxyamine, an
O-carbamoyloxime, an aromatic sulfonamide, an N-arylformamide, or
an 4-(ortho-nitrophenyl)dihydropyridine.
3. (canceled)
4. (canceled)
5. The ionically crosslinkable composition of claim 1 wherein the
(meth)acrylate copolymer component having pendant photobase
generator groups comprises monomer units derived from monomers of
the formula ##STR00010## wherein R.sup.1 is a photolabile group
which may be photolyzed to an amine; R.sup.2 is H or a
C.sub.1-C.sub.4 alkyl group; R.sup.3 is a divalent alkylene or
arylene; X is --O-- or --NR.sup.2--, R.sup.4 is H or
C.sub.1-C.sub.4 alkyl.
6. The ionically crosslinkable composition of claim 5 wherein
R.sup.1 is an oxime ester, a benzyl carbamate, a benzoin carbamate,
an O-carbamoylhydroxyamine, an O-carbamoyloxime, an aromatic
sulfonamide, an N-arylformamide, or an
4-(ortho-nitrophenyl)dihydropyridine.
7. The ionically crosslinkable composition of claim 1, wherein the
pendant said photobase generator group is an o-nitrobenzyl
carbamate of an amine.
8. The ionically crosslinkable composition of claim 1 having zero
weight percent of multifunctional (meth)acrylate monomer units.
9. The ionically crosslinkable composition of claim 1 comprising 5
to 10 parts by weight, of photobase monomer units.
10. The ionically crosslinkable composition of claim 1 wherein the
(meth)acrylate copolymer of is of the formula
.about.[M.sup.ester].sub.a[M.sup.acid].sub.b[M.sup.PBG].sub.c[M.sup.polar-
].sub.d[M.sup.multi].sub.e.about., where [M.sup.ester] represents
(meth)acrylate monomer units, [M.sup.acid] represent acid
functional monomer units. [M.sup.PBG] represents photobase monomer
units, [M.sup.polar], represent non-acid polar monomer units,
[M.sup.multi] represent multifunctional (meth)acrylate monomer
units, subscript a is 45 to 99 parts by weight, subscript b is 0.5
to 15 parts by weight, subscript c is 0.5 to 15 parts by weight,
subscript d is 0 to 15 parts by weight, subscript e is 0 to 5 parts
by weight, and the sum of a to e is 100 parts by weight.
11. The ionically crosslinkable composition of claim 1 wherein the
(meth)acrylate copolymer is prepared by free radical polymerization
of acid-functional monomer units, amine photobase functional
monomer units, (meth)acrylate monomer units, optional non-acid
functional, polar monomer units, optional vinyl monomer units and
optional multifunctional (meth)acrylate monomer units.
12. The ionically crosslinkable composition of claim 11 wherein the
free radical polymerization is initiated by a thermal or
photoinitiator.
13. The ionically crosslinkable composition of claim 12 wherein the
free radical polymerization is initiated by a photoinitiator having
an absorbance spectrum distinct from those frequencies that would
trigger the photobase generator group.
14. The ionically crosslinkable composition of claim 1 wherein the
(meth)acrylate copolymer, when photolyzed, is of the formula:
.about.[M.sup.ester].sub.a[M.sup.acid].sub.b[M.sup.AMINE].sub.c[M.sup.pol-
ar].sub.d[M.sup.multi].sub.e.about., where [M.sup.ester] represents
(meth)acrylate monomer units, [M.sup.acid] represent acid
functional monomer units, [M.sup.AMINE] are monomer units having a
pendant amine group, [M.sup.polar] represents non-acid polar
monomer units, [M.sup.multi] represent multifunctional
(meth)acrylate monomer units, subscript a is 45 to 99 parts by
weight, subscript b is 0.5 to 15 parts by weight, subscript c* is
0.5 to 15 parts by weight, subscript d is 0 to 15 parts by weight,
subscript e is 0 to 5 parts by weight, and the sum of a to e is 100
parts by weight.
15. (canceled)
16. An adhesive article comprising the ionically crosslinkable
adhesive composition of claim 1 on a backing.
17. The ionically crosslinkable composition of claim 1, wherein the
photobase generator monomer units having photobase generator groups
are derived from ortho-nitrobenzyl carbamates of the formula:
##STR00011## where R.sup.9 is hydrogen or alkyl, R.sup.4 is H or
C.sub.1-C.sub.4 alkyl; X.sup.2 is --O-- or --S--; R.sup.6 is
polyvalent alkyl or aryl, and y is at least 1.
18. The ionically crosslinkable composition of claim 14, wherein
the monomer units having pendant amine groups liberated by
photolysis of the formula: ##STR00012## R.sup.2 is H or a
C.sub.1-C.sub.4 alkyl group; R.sup.3 is a (hetero)hydrocarbyl
group; X is --O-- or --NR.sup.2--, and R.sup.4 is H or
C.sub.1-C.sub.4 alkyl, and subscript x is 0.5 to 15 parts by weight
based on 100 parts of total monomer in the copolymer.
Description
[0001] This invention relates to (meth)acrylate copolymer
compositions that may be photoactivated by actinic radiation to
ionically crosslink such copolymers. The pressure-sensitive
adhesives and tape articles prepared therefrom are characterized by
exhibiting an overall balance of adhesive and cohesive
characteristics and exceptional load bearing capabilities.
BACKGROUND INFORMATION
[0002] Pressure-sensitive tapes are virtually ubiquitous in the
home and workplace. In its simplest configuration, a
pressure-sensitive tape comprises an adhesive and a backing, and
the overall construction is tacky at the use temperature and
adheres to a variety of substrates using only moderate pressure to
form the bond. In this fashion, pressure-sensitive tapes constitute
a complete, self-contained bonding system.
[0003] According to the Pressure-Sensitive Tape Council,
pressure-sensitive adhesives (PSAs) are known to possess properties
including the following: (1) aggressive and permanent tack, (2)
adherence with no more than finger pressure, (3) sufficient ability
to hold onto an adherend, and (4) sufficient cohesive strength to
be removed cleanly from the adherend. Materials that have been
found to function well as PSAs include polymers designed and
formulated to exhibit the requisite viscoelastic properties
resulting in a desired balance of tack, peel adhesion, and shear
holding power. PSAs are characterized by being normally tacky at
room temperature (e.g., 20.degree. C.). PSAs do not embrace
compositions merely because they are sticky or adhere to a
surface.
[0004] These requirements are assessed generally by means of tests
which are designed to individually measure tack, adhesion (peel
strength), and cohesion (shear holding power), as noted in A. V.
Pocius in Adhesion and Adhesives Technology: An Introduction,
2.sup.nd Ed., Hanser Gardner Publication, Cincinnati, Ohio, 2002.
These measurements taken together constitute the balance of
properties often used to characterize a PSA.
[0005] With broadened use of pressure-sensitive tapes over the
years, performance requirements have become more demanding. Shear
holding capability, for example, which originally was intended for
applications supporting modest loads at room temperature, has now
increased substantially for many applications in terms of operating
temperature and load. So-called high performance pressure-sensitive
tapes are those capable of supporting loads at elevated
temperatures for 10,000 minutes. Increased shear holding capability
has generally been accomplished by crosslinking the PSA, although
considerable care must be exercised so that high levels of tack and
adhesion are retained in order to retain the aforementioned balance
of properties.
[0006] 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
corrosive or toxic by-products; generation of undesirable color;
requirement of a separate photoactive compound to initiate the
crosslinking reaction; and high sensitivity to oxygen.
SUMMARY
[0007] The present disclosure provides an ionically crosslinkable
composition comprising:
a (meth)acrylate copolymer component having pendant acid functional
groups and pendant photobase functional groups. On exposure to
light, the pendant photobase group fragments or photolyzes to
provide a pendant amine group, that ionically crosslinks the
copolymer. The adhesive composition may be used in the construction
of adhesive articles, such as single and double coated adhesive
tapes, and in affixing substrates together.
[0008] The pressure-sensitive adhesives of this disclosure provide
the desired balance of tack, peel adhesion, and shear holding
power, and further conform to the Dahlquist criteria; i.e. the
modulus of the adhesive at the application temperature, typically
room temperature, is less than 3.times.10.sup.6 dynes/cm at a
frequency of 1 Hz.
[0009] "Alkyl" means a linear or branched, cyclic or acylic,
saturated monovalent hydrocarbon having from one to about 28,
preferably one to 12, carbon atoms, e.g., methyl, ethyl, 1-propyl,
2-propyl, pentyl, and the like.
[0010] "Alkylene" means a linear saturated divalent hydrocarbon
having from one to about twelve carbon atoms or a branched
saturated divalent hydrocarbon radical having from three to about
twelve carbon atoms, e.g., methylene, ethylene, propylene,
2-methylpropylene, pentylene, hexylene, and the like.
[0011] "heteroalkyl" includes both straight-chained, branched, and
cyclic alkyl groups with one or more heteroatoms independently
selected from S, O, and N with both unsubstituted and substituted
alkyl groups. Unless otherwise indicated, the heteroalkyl groups
typically contain from 1 to 20 carbon atoms. "Heteroalkyl" is a
subset of "hydrocarbyl containing one or more S, N, O, P, or Si
atoms" described below. Examples of "heteroalkyl" as used herein
include, but are not limited to, methoxy, ethoxy, propoxy,
3,6-dioxaheptyl, 3-(trimethylsilyl)-propyl, 4-dimethylaminobutyl,
and the like. Unless otherwise noted, heteroalkyl groups may be
mono- or polyvalent, i.e. monovalent heteroalkyl or polyvalent
heteroalkylene.
[0012] "aryl" is an aromatic group containing 6-18 ring atoms and
can contain optional fused rings, which may be saturated,
unsaturated, or aromatic. Examples of an aryl groups include
phenyl, naphthyl, biphenyl, phenanthryl, and anthracyl. Heteroaryl
is aryl containing 1-3 heteroatoms such as nitrogen, oxygen, or
sulfur and can contain fused rings. Some examples of heteroaryl
groups are pyridyl, furanyl, pyrrolyl, thienyl, thiazolyl,
oxazolyl, imidazolyl, indolyl, benzofuranyl, and benzthiazolyl.
Unless otherwise noted, aryl and heteroaryl groups may be mono- or
polyvalent, i.e. monovalent aryl or polyvalent arylene.
[0013] "(hetero)hydrocarbyl" is inclusive of hydrocarbyl alkyl and
aryl groups, and heterohydrocarbyl heteroalkyl and heteroaryl
groups, the later comprising one or more catenary oxygen
heteroatoms such as ether or amino groups. Heterohydrocarbyl may
optionally contain one or more catenary (in-chain) functional
groups including ester, amide, urea, urethane, and carbonate
functional groups. Unless otherwise indicated, the non-polymeric
(hetero)hydrocarbyl groups typically contain from 1 to 60 carbon
atoms. Some examples of such heterohydrocarbyls as used herein
include, but are not limited to, methoxy, ethoxy, propoxy,
4-diphenylaminobutyl, 2-(2'-phenoxyethoxy)ethyl, 3,6-dioxaheptyl,
3,6-dioxahexyl-6-phenyl, in addition to those described for
"alkyl", "heteroalkyl", "aryl", and "heteroaryl" supra.
DETAILED DESCRIPTION
[0014] The present disclosure provides an ionically crosslinkable
composition comprising:
a (meth)acrylate copolymer component having pendant acid functional
groups and pendant amine photobase functional groups.
[0015] In one embodiment, the acid-functional copolymer may
comprise a copolymer of interpolymerized monomer units including
acid-functional monomer units, amine photobase functional monomer
units, (meth)acrylate monomer units, optional non-acid functional,
polar monomer units, optional vinyl monomer units and optional
multifunctional (meth)acrylate monomer units. More particularly,
the acid-functional (meth)acrylate copolymer may comprise: [0016]
1) 45 to 99 parts by weight, preferably 85 to 99 parts by weight,
of an (meth)acrylic acid ester monomer units; [0017] 2) 0.5 to 15
parts by weight, preferably 5 to 10 parts by weight, of an acid
functional monomer units; [0018] 3) 0.5 to 15 parts by weight of
photobase generator monomer units; [0019] 4) 0 to 15 parts by
weight of a second, non-acid functional, polar monomer units;
[0020] 5) 0 to 15 parts vinyl monomer units, and [0021] 6) 0 to 5
parts by weight of multifunctional (meth)acrylate monomer units,
where the sum of the monomer units is 100 parts by weight.
[0022] The (meth)acrylate ester monomer useful in preparing the
acid functional (meth)acrylate adhesive copolymer is a monomeric
(meth)acrylic ester of a non-tertiary alcohol, which alcohol
contains from 1 to 14 carbon atoms and preferably an average of
from 4 to 12 carbon atoms.
[0023] Examples of monomers suitable for use as the (meth)acrylate
ester monomer 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, citronellol, dihydrocitronellol, and the like. In
some embodiments, the preferred (meth)acrylate ester monomer is the
ester of (meth)acrylic acid with butyl alcohol or isooctyl alcohol,
or a combination thereof, although combinations of two or more
different (meth)acrylate ester monomers are suitable. In some
embodiments, the preferred (meth)acrylate ester monomer is the
ester of (meth)acrylic acid with an alcohol derived from a
renewable sources, such as 2-octanol, citronellol,
dihydrocitronellol.
[0024] The adhesive copolymer generally comprises 45 to 99,
preferably 85 to 99 parts by weight of an (meth)acrylic acid ester
monomer units, and most preferably 90 to 95 parts by weight.
[0025] In some embodiments it is desirable for the (meth)acrylic
acid ester monomer component to include a high T.sub.g monomer. By
high T.sub.g monomer it is meant the homopolymer of such monomers
have a T.sub.g of at least 25.degree. C., and preferably at least
50.degree. C. Examples of suitable high T.sub.g monomers useful in
the present invention include, but are not limited to, 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, benzyl methacrylate, 3,3,5
trimethylcyclohexyl acrylate, cyclohexyl acrylate, N-octyl
acrylamide, and propyl methacrylate or combinations.
[0026] When high T.sub.g monomers are included, the (meth)acrylate
ester component may include up to 30 parts by weight, preferably up
to 20 parts by weight of the (meth)acrylate ester monomer
component. The T.sub.g of the resulting copolymer may be estimated
by the Fox equation, as is known in the art.
[0027] In some embodiments the (meth)acrylic acid ester monomer
component may comprise (meth)acrylate ester of 2-alkyl alkanols
wherein the molar carbon number average of said 2-alkyl alkanols is
12 to 32. The Guerbet alcohol Guerbet alkanol-derived (meth)acrylic
monomers have the ability to form (co)polymers with unique and
improved properties over comparable, commonly used PSA acrylate
(co)polymers. These properties include a very low T.sub.g, a low
solubility parameter for acrylic polymers, and a low storage
modulus creating a very conformable elastomer. This combination of
properties provides PSAs with enhanced adhesion to low surface
energy substrates as compared to current acrylic PSA compositions.
When Guerbet monomers are included, the (meth)acrylate ester
component may include up to 30 parts by weight, preferably up to 20
parts by weight of the (meth)acrylate ester monomer component. Such
Guerbet (meth)acrylate esters are described in Applicant's
copending U.S. 2011-0237725 (Lewandowski et al.) and is
incorporated herein by reference.
[0028] The copolymer further comprises an acid functional monomer,
where the acid functional group may be an acid per se, such as a
carboxylic acid, or a portion may be a 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.
[0029] Due to their availability, acid functional monomers of the
acid functional copolymer 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. The acid functional monomer is
generally used in amounts of 0.5 to 15 parts by weight, preferably
5 to 10 parts by weight, based on 100 parts total monomer in the
adhesive copolymer.
[0030] The polar monomers useful in preparing the copolymer are
both somewhat oil soluble and water soluble. As used herein the
term "polar monomers" are exclusive of acid functional
monomers.
[0031] 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 polar monomer may be present in
amounts of 0 to 15 parts by weight, preferably 0.1 to 10 parts by
weight, most preferably 0.5 to 5 parts by weight, based on 100
parts by weight (meth)acrylate ester monomer.
[0032] 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 15 parts by weight, and when present, preferably 1 to 5
parts by weight, based on 100 parts by weight total monomer in the
adhesive copolymer.
[0033] In order to increase cohesive strength of the coated
adhesive composition, a multifunctional (meth)acrylate may be
incorporated into the blend of polymerizable monomers. 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. The amount and
identity of multifunctional (meth)acrylate is tailored depending
upon application of the adhesive composition. Typically, the
multifunctional (meth)acrylate is present in amounts less than 5
parts based on total dry weight of adhesive copolymer. More
specifically, the multifunctional (meth)acrylate may be present in
amounts from 0.01 to 5 parts, preferably 0.05 to 1 parts, based on
100 parts total monomers of the copolymer.
[0034] The crosslinkable composition further comprises
interpolymerized monomer units having pendant photobase generator
groups that, on exposure to radiation, provides an amine. The use
of the photobase generator (PBG) groups overcomes a problem in the
art by controlling the rate of crosslinking. It has been found that
acid-functional (meth)acrylate copolymer can be ionically
crosslinked by amines. However, due to its high reactivity, the
crosslinking reactions are very fast and uncontrollable; mixing
acid-functional (meth)acrylate copolymer and amines results in
instant gelation. The use of a photobase generator (PBG) can create
free amines upon UV irradiation. When a copolymer containing amine
photobase generator monomer units is formulated with
acid-functional (meth)acrylate copolymer, the mixture is very
stable and easy to process (e.g., coating) without any gelation. UV
irradiation of this formulation can generate free pendant amines
which can form ionic crosslinks by reacting with acid-functional
monomer units of the (meth)acrylate copolymer.
[0035] The photobase generator groups are not specifically limited
so long as the groups generate a pendant amine group directly or
indirectly with light irradiation. Photobase generators useful in
the present invention are any polymerizable monomers which liberate
amines upon exposure to light, typically at a wavelength of about
270 to 420 nanometers, however other wavelengths may be suitable.
The photobase generator includes groups that include an oxime
ester, a benzyl carbamate, a benzoin carbamate, an
O-carbamoylhydroxyamines, an O-carbamoyloximes, an aromatic
sulfonamide, an N-arylformamide, or an
4-(ortho-nitrophenyl)dihydropyridine.
[0036] The acid-functional (meth)acrylate copolymer component
further comprises monomer units having pendant amine photobase
generator units. The (meth)acrylate copolymer having pendant amine
photobase generators include interpolymerized units of monomers of
the general formulae:
##STR00001##
wherein R.sup.1 comprises a photolabile group that on exposure to
light provides an amine group; R.sup.2 is H or a C.sub.1-C.sub.4
alkyl group; R.sup.3 is a (hetero)hydrocarbyl group, including
divalent alkylene or arylene;
X is --O-- or --NR.sup.2--, and
[0037] R.sup.4 is H or C.sub.1-C.sub.4 alkyl.
[0038] The adhesive copolymer comprises 0.5 to 15 parts by weight,
preferably 5 to 10 parts by weight, of photobase generator monomer
units.
[0039] It will be understood that the formula represents a
photobase generator monomer unit wherein the polymerized monomer
units having a pendant amine liberated by photolysis of the
formula:
##STR00002##
R.sup.1 comprises a photolabile group that on exposure to light
provides an amine group; R.sup.2 is H or a C.sub.1-C.sub.4 alkyl
group; R.sup.3 is a (hetero)hydrocarbyl group, including divalent
alkylene or arylene;
X is --O-- or --NR.sup.2--, and
[0040] R.sup.4 is H or C.sub.1-C.sub.4 alkyl, and subscript x is
the weight fraction of the monomer unit in the copolymer, i.e. 0.5
to 15 parts by weight based on 100 parts of total monomer in the
copolymer.
[0041] Useful ortho-nitrobenzyl carbamates include compounds of the
formula:
##STR00003##
where R.sup.9 is hydrogen or alkyl, R.sup.4 is H or C.sub.1-C.sub.4
alkyl;
X.sup.2 is --O-- or --S--;
[0042] R.sup.6 is polyvalent alkyl or aryl, and y is at least 1. It
will be understood that the penyl group may be further substituted
by one or more lower alkyl and/or alkoxy groups.
[0043] More specifically, suitable O-carbamoylhydroxylamines
include compounds of the formula
##STR00004##
where R.sup.7 and R.sup.8 are independently alkyl or aryl, R.sup.9
is hydrogen or alkyl, R.sup.4 is H or C.sub.1-C.sub.4 alkyl;
R.sup.6 is polyvalent alkyl or aryl, and y is at least 1.
[0044] Suitable O-carbamoyloximes include compounds of the
formula:
##STR00005##
where R.sup.7 and R.sup.8 are independently alkyl or aryl, R.sup.9
is hydrogen or alkyl, R.sup.4 is H or C.sub.1-C.sub.4 alkyl;
R.sup.6 is polyvalent alkyl or aryl, and y is at least 1.
[0045] Suitable sulfonamides include compounds of the formula
##STR00006##
where Ar is an aryl group, R.sup.9 is hydrogen or alkyl, R.sup.4 is
H or C.sub.1-C.sub.4 alkyl; R.sup.6 is polyvalent alkyl or aryl,
and y is at least 1.
[0046] Other amides also will be suitable, for example formanilide
and other aryl substituted amides. In the above described formulas,
aryl is typically phenyl. As referred to in the above formulas, an
alkyl group may be of a straight chain or branched configuration,
or comprise a cyclic structure, and typically contains from 1 to 15
carbon atoms, more typically from 1 to 6 carbon atoms. An alkyl
group is suitably either unsubstituted or substituted at one or
more available positions. The substituents may be, for example,
halo, aryl, or alkyl. Similarly, an aryl group also may be
unsubstituted or substituted at one or more available positions by,
for example, halo, aryl or alkyl.
[0047] The polymerizable photobase generators may be prepared by
the reaction of a polymerizable ethylenically-unsaturated compound
having a reactive isocyanate functional group with a photolabile
compound having co-reactive amine or hydroxyl functional group. For
example, the polymerizable photobase generators may be prepared by
the reaction between a polymerizable ethylenically-unsaturated
isocyanate functional compound with a photolabile compound having a
reactive isocyanate reactive functionality. The isocyanate
co-reactive functionality of the photolabile compound may comprise
an alcohol or amine functional group.
[0048] Preferred isocyanate-functional monomers include
isocyanatoalkyl esters of ethylenically unsaturated carboxylic
acids such as 2-isocyanatoethyl methacrylate and 2-isocyanatoethyl
acrylate; acryloyl isocyanates such as methacryloyl isocyanate, and
other ethylenically-unsaturated isocyanate functional monomers such
as those described in U.S. Pat. No. 5,130,347 (Mitra). Of these
isocyanate functional monomers, 2-isocyanatoethyl methacrylate
(IEM) is preferred due to its availability. It will be apparent to
one skilled in the art that many pairs of electrophilic and
nucleophilic functional groups may be used in the preparation of
the polymerizable photobase monomers.
[0049] Suitable benzyl carbamates can be prepared by the reaction
of a isocyanate-functional (meth)acrylate (such as
isocyanatoalkyl(meth)acrylate) with a suitable benzyl alcohol in
the presence of a suitable catalyst. Thus
o-nitrobenzylcarbamate(meth)acrylate photobase monomers may be
prepared by the reaction of 2-nitrobenzyl alcohol with as
isocyanatoalkyl(meth)acrylate, neat or in a suitable solvent,
typically with heating, and in the presence of a suitable catalyst.
Suitable solvents include ether and tetrahydrofuran.
Photoactivation of this base generator provides a copolymer having
a pendant alkyl amine group.
[0050] Photobase generators are further described in M. Shirai et
al. Photochemical Reactions of Quatemary Ammonium Dithiocarbamates
as Photobase Generators and Their Use in The Photoinitiated Thermal
Crosslinking of Poly(gycidylmethacrylate), Journal of Polymer
Science, Part A: Polymer Chemistry, vol. 39, pp. 1329-1341 (2001)
and M. Shirai et al., "Photoacid and photobase generators:
chemistry and applications to polymeric materials", Progress in
Polymer Science, vol. 21, pp. 1-45, XP-002299394, 1996. For further
information on the preparation of photobase generator compounds see
J. Cameron et al., J. Am. Chem. Soc., vol. 113, no. 11, 4303-4313
(1991); J. Cameron et al., J. Polym. Mater. Sci. Eng., 64, 55
(1991); and J. Cameron, et al., J. Org. Chem., 55, 5919-5922
(1990), all of which are incorporated herein by reference for their
teaching of preparation of photobase generator compoundss. See also
U.S. Pat. No. 5,650,261 (Winkel), incorporated herein by reference
for its teaching of photobase generators and the preparation
thereof.
[0051] The use of a photobase generator may produce residue
products from the photochemical production of base. Upon exposure
to actinic radiation, the photobase generators will photolyze
yielding a pendant amine-functional copolymer and a residue
compound. For example, monomer unit having a pendant benzyl
carbamate of an amine will photolyze to yield the pendant amine
group and a phenyl ketone as the "residue of a photobase
generator". Oxime esters, O-carbamoylhydroxyamines,
O-carbamoyloximes, and benzoin carbamates will yield ketones as
residues. Benzyl carbamates will yield benzyl alcohols as residues.
Ortho-nitrobenzyl carbamates will yield ortho-nitrosobenzaldehyde
as a residue. Aromatic sulfonamides will yield the aromatic
hydrocarbon moiety that was originally bonded to the sulfonyl group
as a residue. Such residues are present in small amounts and do not
normally interfere with the desired adhesive properties of the
resulting copolymer. The residues may be detected by conventional
analytical techniques, such as infrared, ultraviolet and NMR
spectroscopy, gas or liquid chromatography, mass spectroscopy, or a
combination of such techniques. Thus, the present invention may
comprise cured (meth)acrylate adhesive copolymer and detectable
amounts of residues from a photobase generator.
[0052] In each embodiment, the (meth)acrylate copolymer components
may be prepared by exposing the component monomers to energy in the
presence of an initiator, such as a thermal or photoinitiator. The
polymerizations may be conducted in the presence of, or preferably
in the absence of, suitable solvents such as ethyl acetate, toluene
and tetrahydrofuran which are unreactive with the functional groups
of the component (meth)acrylate co polymer(s).
[0053] The composition may be polymerized with either a thermal
initiator or photoinitiator. Any conventional free radical
initiator may be used to generate the initial radical. Examples of
suitable thermal initiators include peroxides such as benzoyl
peroxide, dibenzoyl peroxide, dilauryl peroxide, cyclohexane
peroxide, methyl ethyl ketone peroxide, hydroperoxides, e.g.,
tert-butyl hydroperoxide and cumene hydroperoxide, dicyclohexyl
peroxydicarbonate, 2,2,-azo-bis(isobutyronitrile), and t-butyl
perbenzoate. Examples of commercially available thermal initiators
include initiators available from DuPont Specialty Chemical
(Wilmington, Del.) under the VAZO trade designation including
VAZO.TM. 67 (2,2'-azo-bis(2-methybutyronitrile)) VAZO.TM. 64
(2,2'-azo-bis(isobutyronitrile)) and VAZO.TM. 52
(2,2'-azo-bis(2,2-dimethyvaleronitrile)), and Lucidol.TM. 70 from
Elf Atochem North America, Philadelphia, Pa.
[0054] Useful photoinitiators include benzoin ethers such as
benzoin methyl ether and benzoin isopropyl ether; substituted
acetophenones such as 2,2-dimethoxyacetophenone, available as
Irgacure.TM. 651 photoinitiator (Ciba Specialty Chemicals), or as
Esacure.TM. KB-1 photoinitiator (Sartomer Co.; West Chester, Pa.),
and dimethoxyhydroxyacetophenone; 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.
[0055] It will be understood that useful photoiniators include
those having an absorbance spectrum distinct and separate from
those frequencies that would trigger the photobase generator group.
Should the absorbance spectra of the photoinitiator and the
photobase generator group overlap, initiation of monomer
polymerization would concurrently initiate photolysis of the
photobase generator group, leading to premature gellation. As a
useful illustration, a nitrobenzyl photobase generator group
absorbs and photolyzes in the range of 260-345 nm. One may select a
photoinitiator having an absorbance maximum outside this range,
such as Irgacure.TM. 819 having an absorbance range of 350-450.
Different combinations of photobase generator groups and
photoinitiators may be used.
[0056] These thermal and photoinitiators can be employed in
concentrations ranging from about 0.0001 to about 3.0 pbw,
preferably from about 0.001 to about 1.0 pbw, and more preferably
from about 0.005 to about 0.5 pbw, per 100 pbw of the monomers.
[0057] Solventless polymerization methods, such as the continuous
free radical polymerization method described in U.S. Pat. Nos.
4,619,979 and 4,843,134 (Kotnour et al.); the essentially adiabatic
polymerization methods using a batch reactor described in U.S. Pat.
No. 5,637,646 (Ellis); and, the methods described for polymerizing
packaged pre-adhesive compositions described in U.S. Pat. No.
5,804,610 (Hamer et al.) may also be utilized to prepare the
polymers.
[0058] The resulting copolymers have the general structure
.about.[M.sup.ester].sub.a[M.sup.acid].sub.b[M.sup.PBG].sub.c[M.sup.polar-
].sub.d[M.sup.multi].sub.e.about., where [M.sup.ester] represents
(meth)acrylate monomer units, [M.sup.acid] represent acid
functional monomer units. [M.sup.PBG] represents photobase monomer
units, [M.sup.polar], represent non-acid polar monomer units,
[M.sup.multi] represent multifunctional (meth)acrylate monomer
units, and the subscripts a to e represent the parts by weight of
the respective monomer units in the adhesive copolymer, as
previously described. The copolymer may be a block or random
copolymer.
[0059] On exposure to light of a sufficient wavelength, the
photobases generator group of the above copolymer photolyzes to
provide a pendant amine. That is, all or a portion of the M.sup.PBG
interpolymerized monomer units photolyze to M.sup.AMINE monomer
units, providing a copolymer of the general formula
.about.[M.sup.ester].sub.a[M.sup.acid].sub.b[M.sup.AMINE].sub.e[M.sup.po-
lar].sub.d[M.sup.multi].sub.e.about.,
where [M.sup.AMINE] are the interpolymerized monomer units having a
pendant amine group, and the subscript "c*" represents the parts by
weight of the monomer unit in the adhesive copolymer. It will be
appreciated that subscript c* will be equal to or less than
subscript c. The pendant amine group can ionically crosslink the
copolymer by acid-base reaction with the pendant acid groups.
[0060] The curable composition may also be prepared by a syrup
polymerization technique. "Syrup polymer composition" refers to a
solution of a solute polymer in one or more solvent monomers, the
composition having a viscosity of from 500 to 10,000 cPs at
22.degree. C. Here, a monomer mixture consisting of the
(meth)acrylate monomer, the acid functional monomer, optionally the
polar monomer and vinyl monomer, but lacking the photobase
generator monomer are combined and partially polymerized using a
thermal- or photoinitiator. The resulting syrup polymer, comprising
a (meth)acrylate solute copolymer and unreacted solvent monomers,
is then combined with the photobase generator monomer and
photoinitiator. Subsequent treatment with UV radiation will
simultaneously polymerize the solvent monomers (including the
photobase monomer) and photolyze the photobase generator group to
yield a pendant amine. Alternatively, the photoinitiator and
photobase generator groups may be chosen to have non-overlapping
absorbances so that the photoinitiator may be initiated at a first
frequency to polymerize the solvent monomers, and the photobase
generator subsequently photolyzed at a second frequency.
[0061] The pressure sensitive adhesives may also contain one or
more conventional additives. Preferred additives include
tackifiers, plasticizers, dyes, antioxidants, and UV stabilizers.
Such additives can be used if they do not affect the superior
properties of the pressure sensitive adhesives.
[0062] If tackifiers are used, then up to about 100 parts by
weight, preferably less than 75% by weight, and more preferably
less than 50% by weight based on 100 parts by weight total adhesive
polymer would be suitable. In some embodiments no tackifiers may be
used. Suitable tackifiers for use with (meth)acrylate polymer
dispersions include rosin acids, rosin esters, such as glycerol
esters of rosin and pentaerythritol esters of rosin, terpene
phenolic resins, hydrocarbon resins including hydrogenated
hydrocarbon resins, and cumarone indene resins. The type and amount
of tackifier can affect properties such as contactability, bonding
range, bond strength, heat resistance and specific adhesion.
[0063] The adhesive composition of the present invention may
contain a plasticizer, if desired. The plasticizer softens the
adhesive, and as a result, the substrate is more easily wetted by
the adhesive. Further, the use of a plasticizer may improve the
adhesive properties, including peel and shear. The plasticizer may
be hydrophobic oils, hydrophilic or a combination thereof. The
plasticizer can be added in an amount ranging from about 0.1 to
about 20 weight percent of the adhesive composition and preferably
from about 0.5 to about 10 weight percent.
[0064] Useful plasticizers are compatible with the acrylic pressure
sensitive adhesive, such that once the plasticizer is mixed into
the acrylic pressure sensitive adhesive, the plasticizer does not
phase separate from the pressure sensitive adhesive. By "phase
separation" or "phase separate," it is meant that by differential
scanning calorimetry (DSC) no detectable thermal transition, such
as a melting or glass transition temperature can be found for the
pure plasticizer in the plasticized adhesive composition. Some
migration of the plasticizer from or throughout the plasticized
adhesive can be tolerated, such as minor separation due to
composition equilibrium or temperature influences, but the
plasticizer does not migrate to the extent that phase separation
occurs between the adhesive and the plasticizing agent. Plasticizer
compatibility with the adhesive can also be dependent upon the
chemical nature of the plasticizer and the monomeric content of the
adhesive.
[0065] For non-aqueous compositions oil soluble species such as
phthalates (e.g. dioctyl adipate, and bis 2-ethylhexyl adipate),
citrates (e.g. trihexyl citrate and trioctyl citrate), adipates
(e.g. dioctyl phthalate, and bis 2-ethylhexyl phthalate) and
maleates (e.g. dibutyl maleate).
[0066] Adhesive articles may be prepared by coating the adhesive or
pre-adhesive composition on a suitable support, such as a flexible
backing Examples of materials that can be included in the flexible
backing include polyolefins such as polyethylene, polypropylene
(including isotactic polypropylene), polystyrene, polyester,
polyvinyl alcohol, poly(ethylene terephthalate), poly(butylene
terephthalate), poly(caprolactam), poly(vinylidene fluoride),
polylactides, cellulose acetate, and ethyl cellulose and the like.
Commercially available backing materials useful in the invention
include kraft paper (available from Monadnock Paper, Inc.);
cellophane (available from Flexel Corp.); spun-bond poly(ethylene)
and poly(propylene), such as Tyvek.TM. and Typar.TM. (available
from DuPont, Inc.); and porous films obtained from poly(ethylene)
and poly(propylene), such as Teslin.TM. (available from PPG
Industries, Inc.), and Cellguard.TM. (available from
Hoechst-Celanese).
[0067] 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.
[0068] The above-described compositions are 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. 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.
EXAMPLES
Test Methods
Peel Adhesion Test
[0069] A test sample was prepared by placing a 0.5 (12.2 cm) inch
wide by 7 inch (178 cm) long adhesive tape on a 100 cm by 250 cm
glass plate, which had been cleaned by wiping with isopropanol. The
tape was rolled down onto the panel with two passes of a 2 kg
roller. The test was conducted on a slip/peel tester (Instrumentors
Inc.; Strongsville, Ohio) with the tape removed from the plate at a
peel angle of 180.degree. at a rate of 12 inches per minute (0.305
m/min) for a total of 10 seconds. The force required to remove the
tape was measured in ounces per 0.5 inch. Measurements for two tape
samples were averaged and values were converted to N/dm.
Shear Strength Test
Room Temperature Shear
[0070] A test sample was prepared by placing a 0.5 inch by 2 inch
strip of adhesive coated tape on the edge of a stainless steel
panel, that had been cleaned with isopropanol, so that the tape
overlapped the panel by 0.5 inch by 1 inch, leaving a 1 inch by 0.5
inch portion of the tape free of the panel. The tape was rolled
down onto the panel using two passes of a 2 kg roller. A 1000 gram
weight was attached to the free end of the tape and the sample was
hung vertically until failure occurred; that is the weight fell
from the plate, or the test was terminated at 10,000 minutes. The
time to failure was recorded. Tests were run in triplicate and the
average time to failure or 10,000 minutes, if no failure, was
reported.
High Temperature Shear
[0071] Test samples were prepared in the same manner as for the
room temperature shear test except that a 500 gram weight was
attached to the tape and samples were hung vertically in an oven
set at 70.degree. C. until failure or the test was terminated.
Preparation of 2-({[(2-nitrobenzyl)oxy]carbonyl}amino)ethyl
2-methylacrylate (NBMA)
[0072] A monomer was prepared by adding 14.4 g 2-nitrobenzyl
alcohol (Alfa Aesar, Ward Hill, Mass.), 14.6 g isocyanatoethyl
methacrylate (Aldrich, Milwaukee, Wis.), and 1 drop of dibutyltin
dilaurate (Alfa Aesar, Ward Hill, Mass.) to a 4-ounce jar. The jar
was sealed and placed in a 70.degree. C. oven for 2 hours. The
resulting reaction mixture was analyzed by infrared spectroscopy
(Nexus 670 FT-IR E.S.P.; Thermo Nicolet Corporation; Madison, Wis.)
which showed no absorbance at 2250 cm.sup.-1, indicating
substantially no remaining isocyanate functionality. The reaction
mixture was cooled and 40 mL of toluene were added to it. The jar
was then capped and refrigerated overnight. The next day, the white
crystals that had separated were filtered off and dried to produce
26.9 g of NBMA. NMR and IR spectral analyses confirmed the
structure of the product.
Example 1
[0073] A monomer mixture was prepared by adding 83.0 g of ethyl
acetate to an 8 oz (236.5 mL) amber bottle followed by adding 38.65
g of isooctyl acrylate (IOA), 2.93 g of acrylic acid (AA--Alfa
Aesar, Ward Hill, Mass.), 2.20 g of NBMA, and 43.6 mg of initiator
(Vazo 67 (2,2'-Azobis(2-methylbutyronitrile); Dupont; Wilmington,
Del.). The monomer mixture was purged with nitrogen for 10 minutes
then placed in a launder-o-meter (Atlas, Inc.; Athens, Ga.) and run
for 2 days at 60.degree. C. to produce an adhesive polymer
composition.
Example 2
[0074] An adhesive polymer composition was prepared as in Example 1
except the composition was prepared with 81.25 g of ethyl acetate,
40.27 g of IOA, 3.03 g AA, 0.45 g of NBMA, and 43.75 mg of
initiator (Vazo 67).
Examples 3-8
[0075] Pressure sensitive adhesive tapes were prepared by knife
coating the compositions of Examples 1 and 2, as shown in Table 1,
onto a primed polyester film (Hostaphan.TM.3SAB polyester film;
Mitsubishi Polyester Film, Inc.; Greer, S.C.), and drying the
coated film in an oven set at 100.degree. C. The dried coating
thickness of the adhesive was about 25 to 50 micrometers. The
adhesives were then crosslinked by exposing the adhesive to UV
radiation from a Fusion UV lamp (Fusion UV Systems INC.;
Gaithersburg, Md.) having a Quartz UV H bulb at different energy
levels shown in Table 1. The tapes were measured for 180.degree.
Peel Adhesion and Shear Strength. Results are shown in Table 1.
TABLE-US-00001 TABLE 1 Adhesive UV Total Energy Shear Strength
(min) 180.degree. Peel Ex Composition (mJ/cm.sup.2) (RT)
(70.degree. C.) (N/dm) 3 Example 1 200 117 10 60 4 Example 1 400
2159 10000 53 5 Example 1 600 10000 10000 48 6 Example 1 No UV cure
28 1 78 7 Example 2 600 10000 10000 34 8 Example 2 No UV cure 34 3
40
Example 9
[0076] A composition was prepared by mixing 110 g IOA, 8.1 g AA,
1.2 g NBMA, 0.24 g photoinitiator
(Irgacure.TM.819--Bis(2,4,6-trimethylbenzoyl)-phenylphosphineoxide;
Ciba Specialty Chemicals; Tarrytown, N.Y.) and 0.18 g iso-octyl
thioglycolate (Aldrich; Milwaukee, Wis.).
[0077] Rectangular pieces of 0.065 mm thick clear polyethylene
vinyl acetate film (VA-24, Flint Hills Resources; Wichita, Kans.)
were heat sealed on 3 edges to form pouches weighing about 1.4 g
each. Each pouch was filled with about 28 grams of the composition
and carefully heat sealed on the fourth edge, taking care to avoid
trapping air bubbles. The pouches were then immersed in a constant
temperature water bath at 17.degree. C. and irradiated with lamps
with emitting intensity visible blue light (Sylvania Super Blue
F40T12-430 nm) for seven minutes on each side to polymerize the
composition and form a pressure sensitive adhesive.
Examples 10-13
[0078] The adhesive of Example 7 in pouches was compounded with two
tackifiying resins in the amounts shown in Table 2. The tackifying
resins were Foral 85E (Eastman Co.; Kingsport, Tenn.) and Escorez
2520 (ExxonMobile Co.; Houston, Tex.). The pouches of adhesive were
mixed in a high temperature compounder (Half Size Mixer; C.W.
Brabender Instruments, Inc.; Hackensack, N.J.) for 5 minutes at a
temperature setting of 145.degree. C. and 100 revolutions per
minute. Tackifying resins, if added, were added to the adhesive
melt in the compounder and allowed to mix for an additional 10
minutes. The mixing chamber was then cooled to 100.degree. C. and
the rotation of the mixing paddles was reversed to expel and
collect blended adhesive material.
[0079] The adhesive mass was cooled and approximately 1.5 grams of
the compounded material was placed between a primed polyester film
(Hostaphan.TM.3SAB polyester film; Mitsubishi Polyester Film, Inc.;
Greer, S.C.) and a silicone treated polyester film (Silphan S36;
Siliconature SPA; Godega di Sant'Urbano, Italy). This construction
was placed between the plates of a heated press (Carver, Inc.;
Wabash, Ind.) with plate temperatures set at 100.degree. C. and
compressed until the adhesive mass was approximately 0.08
millimeters thick to form a pressure sensitive adhesive coated
film. The pressed film was cooled and the release liner was
removed. Some of the adhesive samples were exposed a Fusion UV lamp
(Fusion UV Systems INC.; Gaithersburg, Md.) having a Quartz UV H
bulb. The adhesive coated films were cut into appropriate tape
widths and lengths for testing and tested for Shear Strength and
Peel Adhesion. Results are shown in Table 2.
TABLE-US-00002 TABLE 2 Foral Escorez UV Total Static Shear Adhesive
85E 2520 Energy @70.degree. C. 180.degree. Peel Ex (g) (g) (g)
(mJ/cm.sup.2) (min) (N/dm) 10 30 0 0 1200 10000 25 11 20 8.7 1.1
1200 10000 51 12 20 8.7 1.1 1500 10000 48 13 30 0 0 No UV cure 13
53
[0080] This disclosure provides the following illustrative
embodiments: [0081] 1. An ionically crosslinkable composition
comprising a (meth)acrylate copolymer component having pendant
acid-functional groups and pendant photobase generator groups.
[0082] 2. The ionically crosslinkable composition of embodiment 1,
wherein the pendant photobase generator is an oxime ester, a benzyl
carbamate, a benzoin carbamate, an O-carbamoylhydroxyamine, an
O-carbamoyloxime, an aromatic sulfonamide, an N-arylformamide, or
an 4-(ortho-nitrophenyl)dihydropyridine. [0083] 3. The ionically
crosslinkable composition of any of the previous embodiments,
wherein the acid-functional (meth)acrylate copolymer component
comprises: [0084] i. 45 to 99 parts by weight of an (meth)acrylic
acid ester of non-tertiary alcohol; [0085] ii. 0.5 to 15 parts by
weight of an acid functional ethylenically unsaturated monomer;
[0086] iii. 0.5 to 15 parts by weight of ethylenically unsaturated
monomer having photobase generator groups; [0087] iv. 0 to 10 parts
by weight of a non-acid functional, ethylenically unsaturated polar
monomer; [0088] v. 0 to 5 parts vinyl monomer; and [0089] vi. 0 to
5 parts of a multifunctional (meth)acrylate; [0090] based on 100
parts by weight total monomer. [0091] 4. The ionically
crosslinkable composition of any of the previous embodiments,
wherein on exposure to UV irradiation, the photobase generator
groups photolytically cleave to yield pendent amine groups that
ionically crosslink with the acid-functional groups. [0092] 5. The
ionically crosslinkable composition of any of the previous
embodiments wherein the (meth)acrylate copolymer component having
pendant photobase generator groups comprises monomer units derived
from monomers of the formula
[0092] ##STR00007## [0093] wherein [0094] R.sup.1 is a photolabile
group which may be photolyzed to an amine; [0095] R.sup.2 is H or a
C.sub.1-C.sub.4 alkyl group; [0096] R.sup.3 is a divalent alkylene
or arylene; [0097] X is --O-- or --NR.sup.2--, [0098] R.sup.4 is H
or C.sub.1-C.sub.4 alkyl. [0099] 6. The ionically crosslinkable
composition of embodiment 5 wherein R.sup.1 is an oxime ester, a
benzyl carbamate, a benzoin carbamate, an O-carbamoylhydroxyamine,
an O-carbamoyloxime, an aromatic sulfonamide, an N-arylformamide,
or an 4-(ortho-nitrophenyl)dihydropyridine. [0100] 7. The ionically
crosslinkable composition of any of the previous embodiments,
wherein the pendant said photobase generator group is an
o-nitrobenzyl carbamate of an amine. [0101] 8. The ionically
crosslinkable composition of any of the previous embodiments having
zero weight percent of multifunctional (meth)acrylate monomer
units. [0102] 9. The ionically crosslinkable composition of any of
the previous embodiments comprising 5 to 10 parts by weight, of
photobase monomer units. [0103] 10. The (meth)acrylate copolymer of
any of the previous embodiments of the formula
[0103]
.about.[M.sup.ester].sub.a[M.sup.acid].sub.b[M.sup.PBG].sub.c[M.s-
up.polar].sub.d[M.sup.multi].sub.e.about., where [0104]
[M.sup.ester] represents (meth)acrylate monomer units, [M.sup.acid]
represent acid functional monomer units. [M.sup.PBG] represents
photobase monomer units [M.sup.polar], represent non-acid polar
monomer units, [M.sup.multi] represent multifunctional
(meth)acrylate monomer units, and the subscripts a to e represent
the parts by weight of the respective monomer units in the adhesive
copolymer. [0105] 11. The copolymer of any of the previous
embodiments prepared by free radical polymerization of
acid-functional monomer units, amine photobase functional monomer
units, (meth)acrylate monomer units, optional non-acid functional,
polar monomer units, optional vinyl monomer units and optional
multifunctional (meth)acrylate monomer units. [0106] 12. The
copolymer of embodiment 11 wherein the free radical polymerization
is initiated by a thermal or photoinitiator. [0107] 13. The
copolymer of embodiment 12 wherein the free radical polymerization
is initiated by a photoinitiator having an absorbance spectrum
distinct from those frequencies that would trigger the photobase
generator group. [0108] 14. The photolyzed (meth)acrylate copolymer
of any of the previous embodiments of the formula:
[0108]
.about.[M.sup.ester].sub.a[M.sup.acid].sub.b[M.sup.AMINE].sub.c[M-
.sup.polar].sub.d[M.sup.multi].sub.e.about., where [0109]
[M.sup.ester] represents (meth)acrylate monomer units, [M.sup.acid]
represent acid functional monomer units, [M.sup.AMINE] are monomer
units having a pendant amine group [M.sup.polar], represents
non-acid polar monomer units, [M.sup.multi] represent
multifunctional (meth)acrylate monomer units, and the subscripts a,
b, c*, d and e represent the parts by weight of the respective
monomer units in the adhesive copolymer. [0110] 15. An ionically
crosslinked (meth)acrylate copolymer comprising a copolymer of the
formula:
[0110]
.about.[M.sup.ester].sub.a[M.sup.acid].sub.b[M.sup.AMINE].sub.c[M-
.sup.polar].sub.d[M.sup.multi].sub.e.about., where [0111]
[M.sup.ester] represents (meth)acrylate monomer units, [M.sup.acid]
represent acid functional monomer units, [M.sup.AMINE] are monomer
units having a pendant amine group [M.sup.polar], represents
non-acid polar monomer units, [M.sup.multi] represent
multifunctional (meth)acrylate monomer units, and the subscripts a,
b, c*, d and e represent the parts by weight of the respective
monomer units in the adhesive copolymer, and [0112] the residue of
a photobase generator group. [0113] 16. An adhesive article
comprising the ionically crosslinked adhesive composition of any of
the previous embodiments on a backing [0114] 17. The copolymer of
any of the previous embodiments, wherein the photobase generator
monomer units are ortho-nitrobenzyl carbamates of the formula:
[0114] ##STR00008## [0115] where [0116] R.sup.9 is hydrogen or
alkyl, [0117] R.sup.4 is H or C.sub.1-C.sub.4 alkyl; [0118] X.sup.2
is --O-- or --S--; [0119] R.sup.6 is polyvalent alkyl or aryl, and
y is at least 1. [0120] 18. The copolymer of embodiment 4, wherein
the monomer units having pendant amine groups liberated by
photolysis of the formula:
[0120] ##STR00009## [0121] R.sup.1 comprises a photolabile group
that on exposure to light provides an amine group; [0122] R.sup.2
is H or a C.sub.1-C.sub.4 alkyl group; [0123] R.sup.3 is a
(hetero)hydrocarbyl group, including divalent alkylene or arylene;
[0124] X is --O-- or --NR.sup.2--, and [0125] R.sup.4 is H or
C.sub.1-C.sub.4 alkyl, and subscript x is the weight fraction of
the monomer unit in the copolymer.
* * * * *