U.S. patent application number 15/056203 was filed with the patent office on 2016-06-23 for urethane-based pressure sensitive adhesives.
The applicant listed for this patent is 3M INNOVATIVE PROPERTIES COMPANY. Invention is credited to James P. DiZio, Audrey A. Sherman, Scott M. Tapio.
Application Number | 20160177149 15/056203 |
Document ID | / |
Family ID | 43085500 |
Filed Date | 2016-06-23 |
United States Patent
Application |
20160177149 |
Kind Code |
A1 |
Sherman; Audrey A. ; et
al. |
June 23, 2016 |
URETHANE-BASED PRESSURE SENSITIVE ADHESIVES
Abstract
Non-silicone, urethane-based adhesives are disclosed which are
prepared by the polymerization of reactive oligomers with the
general formula X-A-B-A-X, where X is an ethylenically unsaturated
group B is a unit free of silicone, and A is a urethane linkage.
The adhesives are optically clear, self wetting and removable.
Adhesive articles, including optical adhesive articles, may be
prepared using the disclosed non-silicone urethane-based
adhesives.
Inventors: |
Sherman; Audrey A.;
(Woodbury, MN) ; Tapio; Scott M.; (Falcon Heights,
MN) ; DiZio; James P.; (St. Paul, MN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
3M INNOVATIVE PROPERTIES COMPANY |
St. Paul |
MN |
US |
|
|
Family ID: |
43085500 |
Appl. No.: |
15/056203 |
Filed: |
February 29, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13320399 |
Jan 12, 2012 |
9296933 |
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PCT/US2010/031689 |
Apr 20, 2010 |
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15056203 |
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61178514 |
May 15, 2009 |
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Current U.S.
Class: |
428/41.8 ;
428/355AC; 428/355N; 522/64; 524/315; 524/377; 524/590 |
Current CPC
Class: |
C08G 71/04 20130101;
C09J 2301/302 20200801; C09J 2203/322 20130101; C09J 2451/00
20130101; Y10T 428/2887 20150115; C08G 2170/40 20130101; C09J 7/22
20180101; C09J 151/08 20130101; C09J 2475/00 20130101; C08G 71/02
20130101; C09J 7/38 20180101; C09J 175/16 20130101; Y10T 428/1476
20150115; C09J 7/0246 20130101; C09J 175/16 20130101 |
International
Class: |
C09J 151/08 20060101
C09J151/08; C09J 7/02 20060101 C09J007/02 |
Claims
1. An adhesive comprising a cured mixture comprising: at least one
X-A-B-A-X reactive oligomer, wherein X comprises an ethylenically
unsaturated group, B comprises a non-silicone segmented unit with a
number average molecular weight of 5,000 grams/mole or greater, and
A comprises a urethane linking group, wherein the X-A-B-A-X
reactive oligomer is the reaction product of a HO--B--OH
hydroxyl-capped prepolymer and an X--Z compound wherein Z is an
isocyanate group and X is an ethylenically unsaturated group linked
to the Z group; and an initiator, wherein the adhesive is a
pressure sensitive adhesive.
2. The adhesive of claim 1, wherein the adhesive is a self-wetting
and removable adhesive.
3. The adhesive of claim 1, wherein cured mixture further comprises
an ethylenically unsaturated material.
4. The adhesive of claim 1, further comprising at least one
additive, wherein the additive comprises a pressure sensitive
adhesive, a plasticizing agent, a tackifying agent or a mixture
thereof.
5. The adhesive of claim 4, comprising 5-60 weight % of added
pressure sensitive adhesive and 5-55 weight % plasticizer.
6. The adhesive of claim 5, wherein the plasticizer comprises
isopropyl myristate or polypropylene glygol.
7. The adhesive of claim 6, wherein the added pressure sensitive
adhesive comprises a (meth)acrylate pressure sensitive
adhesive.
8. The adhesive of claim 7, wherein the added pressure sensitive
adhesive comprises an acid-containing (meth)acrylate pressure
sensitive adhesive.
9. A method of preparing an adhesive comprising: providing a
curable composition comprising: at least one X-A-B-A-X reactive
oligomer, wherein X comprises an ethylenically unsaturated group, B
comprises a non-silicone unit with a number average molecular
weight of 5,000 grams/mole or greater, and A comprises a urethane
linkage; and an initiator; and curing the curable composition to
form a pressure sensitive adhesive.
10. The method of claim 9, wherein the X-A-B-A-X reactive oligomer
is the reaction product of a HO--B--OH hydroxyl-capped prepolymer
and an X--Z compound wherein Z is an isocyanate group and X is an
ethylenically unsaturated group linked to the Z group.
11. The method of claim 9, wherein the adhesive comprises a
self-wetting and removable adhesive.
12. The method of claim 9, wherein the adhesive comprises an
optically clear adhesive.
13. An adhesive article comprising: a pressure sensitive adhesive
comprising: the cured reaction product of at least one X-A-B-A-X
reactive oligomer, wherein X comprises an ethylenically unsaturated
group, B comprises a non-silicone unit with a number average
molecular weight of 5,000 grams/mole or greater, and A comprises a
urethane linking group, wherein the adhesive is self wetting and
removable; and a substrate.
14. The adhesive article of claim 13, wherein the substrate is a
tape backing, a film, a sheet, or a release liner.
15. The adhesive article of claim 14, wherein adhesive is optically
clear.
16. The adhesive article of claim 15, wherein the substrate
comprises a film wherein the film comprises an optically active
film comprising a visible mirror film, a color mirror film, a solar
reflective film, a diffusive film, an infrared reflective film, an
ultraviolet reflective film, a brightness enhancement film, a dual
brightness enhancement film, an absorptive polarizer film, an
optically clear film, a tinted film, a privacy film, a
light-collimating film, or an antireflective film.
17. The adhesive article of claim 13, wherein B comprises an
oxyalkylene group.
18. The adhesive article of claim 13, further comprising a second
substrate, wherein the second substrate comprises a rigid surface,
a flexible surface, a tape backing, a film, a sheet, or a release
liner.
19. The adhesive article of claim 13, wherein the pressure
sensitive adhesive further comprises at least one additive, wherein
the additive comprises a pressure sensitive adhesive, a
plasticizing agent, a tackifying agent or a mixture thereof.
20. The adhesive article of claim 19, comprising 5-60 weight % of
added pressure sensitive adhesive and 5-55 weight %
plasticizer.
21. The adhesive article of claim 19, wherein the plasticizer
comprises isopropyl myristate or polypropylene glygol.
22. The adhesive article of claim 19, wherein the added pressure
sensitive adhesive comprises a (meth)acrylate pressure sensitive
adhesive.
23. The adhesive article of claim 19, wherein the added pressure
sensitive adhesive comprises an acid-containing (meth)acrylate
pressure sensitive adhesive.
Description
FIELD OF THE DISCLOSURE
[0001] The present disclosure relates generally to the field of
adhesives, specifically to the field of pressure sensitive
adhesives that are non-silicone and urethane-based.
BACKGROUND
[0002] Adhesives have been used for a variety of marking, holding,
protecting, sealing and masking purposes. Adhesive tapes generally
comprise a backing, or substrate, and an adhesive. One type of
adhesive, a pressure sensitive adhesive, is particularly useful for
many applications.
[0003] Pressure sensitive adhesives are well known to one of
ordinary skill in the art to possess certain properties at room
temperature 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 pressure
sensitive adhesives are polymers designed and formulated to exhibit
the requisite viscoelastic properties resulting in a desired
balance of tack, peel adhesion, and shear strength. The most
commonly used polymers for preparation of pressure sensitive
adhesives are natural rubber, synthetic rubbers (e.g.,
styrene/butadiene copolymers (SBR) and styrene/isoprene/styrene
(SIS) block copolymers), various (meth)acrylate (e.g., acrylate and
methacrylate) copolymers and silicones. Each of these classes of
materials has advantages and disadvantages.
SUMMARY
[0004] The need remains for adhesives with a range of different
properties. Disclosed herein are urethane-based adhesives
comprising a cured mixture comprising at least one reactive
oligomer with the general formula X-A-B-A-X, wherein X comprises an
ethylenically unsaturated group, B comprises a non-silicone unit
with a number average molecular weight of 5,000 grams/mole or
greater, and A comprises a urethane linking group, wherein the
adhesive is optically clear, self wetting and removable.
[0005] Also disclosed are curable reaction mixtures comprising at
least one X-A-B-A-X reactive oligomer, wherein X comprises an
ethylenically unsaturated group, B comprises a non-silicone unit
with a number average molecular weight of 5,000 grams/mole or
greater, and A comprise a urethane linking group, and an initiator.
In some embodiments, the curable reaction mixture further comprises
additional ethylenically unsaturated material.
[0006] Additionally, methods of preparing adhesives are disclosed,
comprising providing a curable composition comprising at least one
X-A-B-A-X reactive oligomer, wherein X comprises an ethylenically
unsaturated group, B comprises a non-silicone unit with a number
average molecular weight of 5,000 grams/mole or greater, and A
comprises a urethane linkage, and an initiator, and curing the
curable composition.
[0007] Adhesive articles are disclosed comprising a pressure
sensitive adhesive comprising the cured reaction product of at
least one X-A-B-A-X reactive oligomer, wherein X comprises an
ethylenically unsaturated group, B comprises a non-silicone unit
with a number average molecular weight of 5,000 grams/mole or
greater, and A comprises a urethane linking group, wherein the
adhesive is optically clear, self wetting and removable, and a
substrate. A wide range of substrates are suitable for preparing
adhesive articles.
DETAILED DESCRIPTION
[0008] The use of adhesives, especially pressure sensitive
adhesives, in areas such as the medical, electronic and optical
industries is increasing. The requirements of these industries
place additional demands upon the pressure sensitive adhesive
beyond the traditional properties of tack, peel adhesion and shear
strength. New classes of materials are desirable to meet the
increasingly demanding performance requirements for pressure
sensitive adhesives.
[0009] A class of non-silicone urethane-based adhesives,
specifically pressure sensitive adhesives, are disclosed. These
urethane-based adhesives are prepared from curable non-silicone,
urethane-based reactive oligomers. The reactive oligomers contain
free radically polymerizable groups. In some embodiments the
non-silicone urethane-based adhesives contain polyoxyalkylene
(polyether) groups.
[0010] The non-silicone urethane-based adhesives, especially
non-silicone, urethane-based pressure sensitive adhesives, prepared
by the free radical polymerization of non-silicone containing
urethane-based reactive oligomers, have a variety of silicone-like
properties. Among these properties are optical clarity, self
wetting and removability.
[0011] The term "adhesive" as used herein refers to polymeric
compositions useful to adhere together two adherends. Examples of
adhesives are heat activated adhesives and pressure sensitive
adhesives.
[0012] Heat activated adhesives are non-tacky at room temperature
but become tacky and capable of bonding to a substrate at elevated
temperatures. These adhesives usually have a Tg (glass transition
temperature) or melting point (Tm) above room temperature. When the
temperature is elevated above the Tg or Tm, the storage modulus
usually decreases and the adhesive becomes tacky. Typically glass
transition temperature (Tg) is measured using Differentially
Scanning calorimetry (DSC).
[0013] Pressure sensitive adhesive compositions are well known to
those of ordinary skill in the art 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
cleanly removable from the adherend. Materials that have been found
to function well as pressure sensitive adhesives are polymers
designed and formulated to exhibit the requisite viscoelastic
properties resulting in a desired balance of tack, peel adhesion,
and shear holding power. Obtaining the proper balance of properties
is not a simple process.
[0014] The term "non-silicone" as used herein refers to repeat
units, to segmented copolymers or units of segmented copolymers
that are free of silicone units. The terms silicone or siloxane are
used interchangeably and refer to units with dialkyl or diaryl
siloxane (--SiR.sub.2O--) repeating units.
[0015] The term "urethane-based" as used herein refers to
macromolecules that are copolymers or segmented copolymers which
contain at least one urethane linkage. The urethane group has the
general structure (--O--(CO)--NR--) where (CO) defines a carbonyl
group C.dbd.O, and R is hydrogen or an alkyl group.
[0016] The term "segmented copolymer" refers to a copolymer of
linked segments, each segment constitutes primarily a single
structural unit or type of repeating unit. For example, a
polyoxyalkylene segmented copolymer may have the following
structure:
--CH.sub.2CH.sub.2(OCH.sub.2CH.sub.2).sub.nOCH.sub.2CH.sub.2-A-CH.sub.2C-
H.sub.2(OCH.sub.2CH.sub.2).sub.nOCH.sub.2CH.sub.2--
where A is the linkage between the 2 polyoxyalkylene segments, or
it may have the following structure:
--CH.sub.2CH.sub.2(OCH.sub.2CH.sub.2).sub.nOCH.sub.2CH.sub.2-A-B--
where A is the linkage between the polyoxyalkylene segment and the
B segment.
[0017] The term "reactive oligomer" as used herein refers to a
macromolecule which contains terminal free radically polymerizable
groups. "Urethane-based reactive oligomers" are macromolecules
which contain terminal free radical polymerizable groups and at
least one urethane linkage.
[0018] The term "alkyl" refers to a monovalent group that is a
radical of an alkane, which is a saturated hydrocarbon. The alkyl
can be linear, branched, cyclic, or combinations thereof and
typically has 1 to 20 carbon atoms. In some embodiments, the alkyl
group contains 1 to 18, 1 to 12, 1 to 10, 1 to 8, 1 to 6, or 1 to 4
carbon atoms. Examples of alkyl groups include, but are not limited
to, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl,
tert-butyl, n-pentyl, n-hexyl, cyclohexyl, n-heptyl, n-octyl, and
ethylhexyl.
[0019] The term "aryl" refers to a monovalent group that is
aromatic and carbocyclic. The aryl can have one to five rings that
are connected to or fused to the aromatic ring. The other ring
structures can be aromatic, non-aromatic, or combinations thereof.
Examples of aryl groups include, but are not limited to, phenyl,
biphenyl, terphenyl, anthryl, naphthyl, acenaphthyl,
anthraquinonyl, phenanthryl, anthracenyl, pyrenyl, perylenyl, and
fluorenyl.
[0020] The term "alkylene" refers to a divalent group that is a
radical of an alkane. The alkylene can be straight-chained,
branched, cyclic, or combinations thereof. The alkylene often has 1
to 20 carbon atoms. In some embodiments, the alkylene contains 1 to
18, 1 to 12, 1 to 10, 1 to 8, 1 to 6, or 1 to 4 carbon atoms. The
radical centers of the alkylene can be on the same carbon atom
(i.e., an alkylidene) or on different carbon atoms.
[0021] The term "heteroalkylene" refers to a divalent group that
includes at least two alkylene groups connected by a thio, oxy, or
--NR-- where R is alkyl. The heteroalkylene can be linear,
branched, cyclic, substituted with alkyl groups, or combinations
thereof. Some heteroalkylenes are poloxyyalkylenes where the
heteroatom is oxygen such as for example,
--CH.sub.2CH.sub.2(OCH.sub.2CH.sub.2).sub.nOCH.sub.2CH.sub.2--.
[0022] The term "arylene" refers to a divalent group that is
carbocyclic and aromatic. The group has one to five rings that are
connected, fused, or combinations thereof. The other rings can be
aromatic, non-aromatic, or combinations thereof. In some
embodiments, the arylene group has up to 5 rings, up to 4 rings, up
to 3 rings, up to 2 rings, or one aromatic ring. For example, the
arylene group can be phenylene.
[0023] The term "heteroarylene" refers to a divalent group that is
carbocyclic and aromatic and contains heteroatoms such as sulfur,
oxygen, nitrogen or halogens such as fluorine, chlorine, bromine or
iodine.
[0024] The term "aralkylene" refers to a divalent group of formula
--R.sup.a--Ar.sup.a-- where R.sup.a is an alkylene and Ar.sup.a is
an arylene (i.e., an alkylene is bonded to an arylene).
[0025] The term "(meth)acrylate" refers to monomeric acrylic or
methacrylic esters of alcohols. Acrylate and methacrylate monomers
are referred to collectively herein as "(meth)acrylate"
monomers.
[0026] The terms "free radically polymerizable" and "ethylenically
unsaturated" are used interchangeably and refer to a reactive group
which contains a carbon-carbon double bond which is able to be
polymerized via a free radical polymerization mechanism.
[0027] Unless otherwise indicated, "optically clear" refers to an
adhesive or article that has a high light transmittance over at
least a portion of the visible light spectrum (about 400 to about
700 nm), and that exhibits low haze.
[0028] Unless otherwise indicated, "self wetting" refers to an
adhesive which is very soft and conformable and is able to be
applied with very low lamination pressure. Such adhesives exhibit
spontaneous wet out to surfaces.
[0029] Unless otherwise indicated, "removable" refers to an
adhesive that has relatively low initial adhesion (permitting
temporary removability from and repositionability on a substrate
after application), with a building of adhesion over time (to form
a sufficiently strong bond), but remains "removable" i.e. the
adhesion does not build beyond the point where it is permanently
cleanly removable from the substrate.
[0030] Urethane-based adhesives are prepared from curable
non-silicone urethane-based reactive oligomers. The reactive
oligomers contain free radically polymerizable groups. The
non-silicone urethane-based reactive oligomers of this disclosure
have the general structure X-A-B-A-X. In this structure the B unit
is a non-silicone group with a number average molecular weight of
5,000 grams/mole or greater, the A groups are urethane linkages,
and the X groups are ethylenically unsaturated groups.
[0031] The reactive oligomers described by the formula X-A-B-A-X
may be a mixture of reactive oligomers. The mixture of reactive
oligomers may include reactive oligomers which have a functionality
of less than 2. These oligomers can be described by the general
structure X-A-B--Y where X, A, and B are as previously described
and Y is a group that is not free radically polymerizable and may
or may not contain a urethane linkage to the B unit. An example of
a Y group is a hydroxyl (--OH) group which could be the unreacted
remnant from a HO--B--OH precursor. The presence of X-A-B--Y
components along with the X-A-B-A-X components can give a branched
polymer when the mixture is polymerized because the unreactive Y
groups do not become part of polymer backbone.
[0032] This branching, due to the use of monomers that are not
completely difunctional, is a common feature in many polyurethane
adhesives because until recently, purely difunctional diols of high
molecular weight were not available. In the adhesives of the
present disclosure, this branching, when present, does not produce
undesirable properties, but rather may even be desirable. For
example, branching may assist in producing adhesives which have the
desirable silicone-like properties such as self wetting.
[0033] The X-A-B-A-X reactive oligomers may be prepared, for
example, by the reaction of a hydroxyl-functional precursor of
general formula HO--B--OH with 2 equivalents of an
isocyanate-functional precursor of the general formula Z--X, where
the Z group is isocyanate-functional and the X groups are
ethylenically unsaturated groups. The isocyanate functionality of
the Z group reacts with a hydroxyl group of the polyol to form the
urethane linkage.
[0034] A wide variety of HO--B--OH precursors may be used. The
HO--B--OH may be polyol or it may be a hydroxyl-capped prepolymer
such as a polyurethane, polyester, polyamide, or polyurea
prepolymer.
[0035] Examples of useful polyols include, but are not limited to,
polyester polyols (e.g., lactone polyols) and the alkylene oxide
(e.g., ethylene oxide; 1,2-epoxypropane; 1,2-epoxybutane;
2,3-epoxybutane; isobutylene oxide; and epichlorohydrin) adducts
thereof, polyether polyols (e.g., polyoxyalkylene polyols, such as
polypropylene oxide polyols, polyethylene oxide polyols,
polypropylene oxide polyethylene oxide copolymer polyols, and
polyoxytetramethylene polyols; polyoxycycloalkylene polyols;
polythioethers; and alkylene oxide adducts thereof), polyalkylene
polyols, mixtures thereof, and copolymers therefrom.
Polyoxyalkylene polyols are particularly useful.
[0036] When copolymers are used, chemically similar repeating units
may be randomly distributed throughout the copolymer or in the form
of blocks in the copolymer. Similarly, chemically similar repeating
units may be arranged in any suitable order within the copolymer.
For example, oxyalkylene repeating units may be internal or
terminal units within a copolymer. The oxyalkylene repeating units
may be randomly distributed or in the form of blocks within a
copolymer. One example of a copolymer containing oxyalkylene
repeating units is a polyoxyalkylene-capped polyoxyalkylene polyol
(e.g., a polyoxyethylene-capped polyoxypropylene).
[0037] When higher molecular weight polyols (i.e., polyols having
weight average molecular weights of at least about 2,000) are used,
it is often desirable that the polyol component be "highly pure"
(i.e., the polyol approaches its theoretical functionality--e.g.,
2.0 for diols, 3.0 for triols, etc.). These highly pure polyols
generally have a ratio of polyol molecular weight to weight % monol
of at least about 800, typically at least about 1,000, and more
typically at least about 1,500. For example, a 12,000 molecular
weight polyol with 8 weight % monol has such a ratio of 1,500
(i.e., 12,000/8=1,500). Generally it is desirable that the highly
pure polyol contains about 8% by weight monol or less.
[0038] Generally, as the molecular weight of the polyol increases
in this embodiment, a higher proportion of monol may be present in
the polyol. For example, polyols having molecular weights of about
3,000 or less desirably contain less than about 1% by weight of
monols. Polyols having molecular weights of greater than about
3,000 to about 4,000 desirably contain less than about 3% by weight
of monols. Polyols having molecular weights of greater than about
4,000 to about 8,000 desirably contain less than about 6% by weight
of monols. Polyols having molecular weights of greater than about
8,000 to about 12,000 desirably contain less than about 8% by
weight of monols.
[0039] Examples of highly pure polyols include those available from
Lyondell Chemical Company of Houston, Tex., under the trade
designation, ACCLAIM, and certain of those under the trade
designation, ARCOL.
[0040] Where HO--B--OH is a hydroxyl-capped prepolymer, a wide
variety of precursor molecules can be used to produce the desired
HO--B--OH prepolymer. For example, the reaction of polyols with
less than stoichiometric amounts of diisocyanates can produce a
hydroxyl-capped polyurethane prepolymer. Examples of suitable
diisocyanates include, but are not limited to, aromatic
diisocyanates, such as 2,6-toluene diisocyanate, 2,5-toluene
diisocyanate, 2,4-toluene diisocyanate, m-phenylene diisocyanate,
p-phenylene diisocyanate, methylene bis(o-chlorophenyl
diisocyanate), methylenediphenylene-4,4'-diisocyanate,
polycarbodiimide-modified methylenediphenylene diisocyanate,
(4,4'-diisocyanato-3,3',5, 5'-tetraethyl) biphenylmethane,
4,4'-diisocyanato-3,3'-dimethoxybiphenyl, 5-chloro-2,4-toluene
diisocyanate, 1-chloromethyl-2,4-diisocyanato benzene,
aromatic-aliphatic diisocyanates such as m-xylylene diisocyanate,
tetramethyl-m-xylylene diisocyanate, aliphatic diisocyanates, such
as 1,4-diisocyanatobutane, 1,6-diisocyanatohexane,
1,12-diisocyanatododecane, 2-methyl-1,5diisocyanatopentane, and
cycloaliphatic diisocyanates such as
methylene-dicyclohexylene-4,4'-diisocyanate, and
3-isocyanatomethyl-3,5,5-trimethyl-cyclohexyl isocyanate
(isophorone diisocyanate).
[0041] An example of the synthesis of a HO--B--OH prepolymer is
shown in Reaction Scheme 1 (where (CO) represents a carbonyl group
C.dbd.O) below:
HO--R.sup.1--OH+OCN--R.sup.2--NCO.fwdarw.HO--R.sup.1--O--[(CO)N--R.sup.2-
--N(CO)O--R.sup.1--O--].sub.nH Reaction Scheme 1
[0042] where n is one or greater, depending upon the ratio of
polyol to diisocyanate, for example, when the ratio is 2:1, n is 1.
Similar reactions between polyols and dicarboxylic acids or
dianhydrides can give HO--B--OH prepolymers with ester linking
groups.
[0043] To prepare the non-silicone urethane-based reactive
oligomers X-A-B-A-X, typically the HO--B--OH compounds are capped
with an X--Z compound. The Z group of the X--Z compound is an
isocyanate group and the X group is an ethylenically unsaturated
group (i.e. a carbon-carbon double bond) and is linked to the Z
group. The link between the X and Z groups may be a single bond or
it may be a linking group. The linking group may be an alkylene
group, a heteroalkylene group, an arylene group, a heteroarylene
group, an aralkylene group, or a combination thereof.
[0044] Examples of X--Z compounds include a variety of different
isocyanato (meth)acrylates such as isocyanatoethyl methacrylate,
and m-isopropenyl-.alpha.,.alpha.-dimethyl benzyl isocyanate. An
example of the synthesis of a X-A-B-A-X reactive oligomer is shown
in Reaction Scheme 2 below:
HO--B--OH+2OCN--R.sup.3--X.fwdarw.X--R.sup.3--HN(CO)O--B--O(CO)NH--R.sup-
.3--X Reaction Scheme 2
[0045] The B unit in the X-A-B-A-X reactive oligomer is a
non-silicone group that may contain a variety of groups such as
urea groups, amide groups, ether groups, carbonyl groups, ester
groups, alkylene groups, heteroalkylene groups, arylene groups,
heteroarylene groups, aralkylene groups, or combinations thereof.
The B unit may also have a variety of molecular weights, depending
upon the desired properties of the adhesive formed from the
reactive oligomer. Generally, the B unit has a number average
molecular weight of 5,000 grams/mole or greater. In some
embodiments, the B unit is a heteroalkylene group.
[0046] A variety of X-A-B-A-X curable non-silicone urethane-based
reactive oligomers are commercially available. For example, a
urethane acrylate oligomer of weight average molecular weight in
the range of 4,000-7,000 g/mole is commercially available from
Nihon Gosei Kagaku under the trade name "UV-6100B". Also a variety
of urethane oligomers are available from Sartomer Company, Exton,
Pa. under the trade names "CN9018", "CN9002" and "CN9004".
[0047] Non-silicone urethane-based pressure sensitive adhesives may
be prepared by polymerizing X-A-B-A-X reactive oligomers through
the ethylenically unsaturated X groups to form polymers with
adhesive properties. The polymers may contain only X-A-B-A-X
reactive oligomers or they may be copolymers in which additional
monomers or reactive oligomers are incorporated. As used herein,
additional monomers or reactive oligomers are collectively referred
to as ethylenically unsaturated materials.
[0048] Among the additional monomers useful for incorporation are
monomers which contain ethylenically unsaturated groups and are
therefore co-reactive with the reactive oligomers. Examples of such
monomers include (meth)acrylates, (meth)acrylamides, alpha-olefins,
and vinyl compounds such as vinyl acids, acrylonitriles, vinyl
esters, vinyl ethers, styrenes and ethylenically unsaturated
oligomers. In some instances more than one type of additional
monomer may be used.
[0049] Examples of useful (meth)acrylates include alkyl
(meth)acrylates, aromatic (meth)acrylates, and silicone acrylates.
In applications in which it is desirable that the entire adhesive
composition be silicone free, silicone acrylates are generally not
used. Alkyl (meth)acrylate monomers are those in which the alkyl
groups comprise 1 to about 20 carbon atoms (e.g., from 3 to 18
carbon atoms). Suitable acrylate monomers include, for example,
methyl acrylate, ethyl acrylate, n-butyl acrylate, lauryl acrylate,
2-ethylhexyl acrylate, cyclohexyl acrylate, iso-octyl acrylate,
octadecyl acrylate, nonyl acrylate, decyl acrylate, and dodecyl
acrylate. The corresponding methacrylates are useful as well. An
example of an aromatic (meth)acrylate is benzyl acrylate.
[0050] Examples of useful (meth)acrylamides, include acrylamide,
methacrylamide and substituted (meth)acrylamides such as
N,N-dimethyl acrylamide, N,N-dimethyl methacrylamide,
N,N-dimethylaminopropyl methacrylamide, N,N-diethylaminopropyl
methacrylamide. N,N-dimethylaminoethyl acrylamide,
N,N-dimethylaminoethyl methacrylamide, N,N-diethylaminoethyl
acrylamide, and N,N-diethylaminoethyl methacrylamide.
[0051] The alpha-olefins useful as additional monomers generally
include those with 6 or greater carbon atoms. The alpha-olefins
with fewer than 6 carbon atoms tend to be too volatile for
convenient handling under ambient reaction conditions. Suitable
alpha-olefins include, for example, 1-hexene, 1-octene, 1-decene
and the like.
[0052] Examples of useful vinyl compounds include: vinyl acids such
as acrylic acid, itaconic acid, methacrylic acid; acrylonitriles
such as acrylonitrile and methacrylonitrile; vinyl esters such as
vinyl acetate and the vinyl esters of carboxylic acids such as
neodecanoic, neononanoic, neopentanoic, 2-ethylhexanoic, or
propionic acids; vinyl ethers such as alkyl vinyl ethers; and
styrenes such as styrene or vinyl toluene. Other vinyl compounds
that may be useful include N-vinylcaprolactam, vinylidene chloride,
N-vinyl pyrrolidone, N-vinyl formamide, and maleic anhydride. For
some uses, for example electronic applications, it may be desirable
to include vinyl compounds that are free of acidic groups.
[0053] Examples of ethylenically unsaturated oligomers useful for
copolymerization with the urethane-based reactive oligomers
include, for example, ethylenically unsaturated silicone oligomers
such as are describe in the PCT publication number WO 94/20583 and
macromolecular monomers with relatively high glass transition
temperatures as described in U.S. Pat. No. 4,554,324 (Husman et
al.). In applications in which it is desirable that the entire
adhesive composition be silicone free, silicone oligomers are
generally not used.
[0054] The reaction mixture may also, if desired, contain one or
more crosslinking agents. A crosslinking agent is used to build the
molecular weight and the strength of the copolymer. Generally, the
crosslinking agent is one that is copolymerized with the
non-silicone containing urethane-based reactive oligomers and any
optional monomers. The crosslinking agent may produce chemical
crosslinks (e.g., covalent bonds or ionic bonds). Alternatively, it
may produce thermally reversible physical crosslinks that result,
for example, from the formation of reinforcing domains due to phase
separation of hard segments (i.e., those having a Tg higher than
room temperature, generally higher than 70.degree. C.) such as the
styrene macromers of U.S. Pat. No. 4,554,324 (Husman) and/or
acid/base interactions (i.e., those involving functional groups
within the same polymer or between polymers or between a polymer
and an additive) such polymeric ionic crosslinking as described in
WO 99/42536. Suitable crosslinking agents are also disclosed in
U.S. Pat. No. 4,737,559 (Kellen), U.S. Pat. No. 5,506,279 (Babu et
al.), and U.S. Pat. No. 6,083,856 (Joseph et al.). The crosslinking
agent can be a photocrosslinking agent, which, upon exposure to
ultraviolet radiation (e.g., radiation having a wavelength of about
250 nanometers to about 400 nanometers), causes the copolymer to
crosslink.
[0055] Examples of suitable crosslinking agents include, for
example, multifunctional ethylenically unsaturated monomers. Such
monomers include, for example, divinyl aromatics, divinyl ethers,
multifunctional maleimides, multifunctional acrylates and
methacrylates, and the like, and mixtures thereof. Particularly
useful are divinyl aromatics such as divinyl benzene and
multifunctional (meth)acrylates. Multifunctional (meth)acrylates
include tri(meth)acrylates and di(meth)acrylates (that is,
compounds comprising three or two (meth)acrylate groups). Typically
di(meth)acrylate crosslinkers (that is, compounds comprising two
(meth)acrylate groups) are used. Useful tri(meth)acrylates include,
for example, trimethylolpropane tri(meth)acrylate, propoxylated
trimethylolpropane triacrylates, ethoxylated trimethylolpropane
triacrylates, tris(2-hydroxy ethyl)isocyanurate triacrylate, and
pentaerythritol triacrylate. Useful di(meth)acrylates include, for
example, ethylene glycol di(meth)acrylate, diethylene glycol
di(meth)acrylate, triethylene glycol di(meth)acrylate,
tetraethylene glycol di(meth)acrylate, 1,4-butanediol
di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, alkoxylated
1,6-hexanediol diacrylates, tripropylene glycol diacrylate,
dipropylene glycol diacrylate, cyclohexane dimethanol
di(meth)acrylate, alkoxylated cyclohexane dimethanol diacrylates,
ethoxylated bisphenol A di(meth)acrylates, neopentyl glycol
diacrylate, polyethylene glycol di(meth)acrylates, polypropylene
glycol di(meth)acrylates, and urethane di(meth)acrylates.
[0056] The crosslinking agent is used in an effective amount, by
which is meant an amount that is sufficient to cause crosslinking
of the pressure sensitive adhesive to provide adequate cohesive
strength to produce the desired final adhesion properties to the
substrate of interest. Generally, the crosslinking agent is used in
an amount of about 0.1 part to about 10 parts, based on the total
amount of monomers.
[0057] Generally the non-silicone urethane-based adhesives are
pressure sensitive adhesives and have glass transition temperature
(Tg) values of room temperature (approximately 20.degree. C.) or
below. In some embodiments the Tg of the non-silicone
urethane-based adhesives are 0.degree. C. or below, or even
-10.degree. C. or below.
[0058] The non-silicone urethane-based adhesives can be made by
solvent processes, solventless processes (e.g., continuous
solventless processes or polymerization on a surface or in a mold)
or by a combination of these methods.
[0059] Some of the processes suitable for the preparation of the
non-silicone urethane-based adhesives include the free radical
polymerization of non-silicone urethane-based reactive oligomers
with optional ethylenically unsaturated materials in a reactor to
form the non-silicone urethane-based adhesive. The non-silicone
urethane-based adhesive can then be removed from the reaction
vessel. Alternatively, the polymerization can be carried out by
continuously mixing the reactants and depositing the reactants on a
surface (e.g., release liner or substrate) or into a mold and
polymerizing the mixture in place.
[0060] In some embodiments, it has been found convenient to deposit
a mixture of the non-silicone urethane-based reactive oligomer,
additional monomers if desired, and initiator onto a surface,
activate the initiator and cure the adhesive on the surface. The
mixture may or may not contain a solvent. If solvent is used, the
cured adhesive is typically dried to remove the solvent.
[0061] The initiator may be either a thermal initiator or a
photoinitiator. Suitable thermal free radical initiators which may
be utilized include, but are not limited to, those selected from
azo compounds, such as 2,2'-azobis(isobutyronitrile);
hydroperoxides, such as tert-butyl hydroperoxide; and, peroxides,
such as benzoyl peroxide and cyclohexanone peroxide.
Photoinitiators which are useful include, but are not limited to,
those selected from benzoin ethers, such as benzoin methyl ether or
benzoin isopropyl ether; substituted benzoin ethers, such as
anisole methyl ether; substituted acetophenones, such as
2,2-diethoxyacetophenone and 2,2-dimethoxy-2-phenyl acetophenone;
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-(ethoxycarbonyl)oxime or benzophenone
derivatives. Benzophenone derivatives and methods for making them
are well known in the art, and are described in, for example, U.S.
Pat. No. 6,207,727 (Beck et al.). Exemplary benzophenone
derivatives include symmetrical benzophenones (e.g., benzophenone,
4,4'-dimethoxybenzophenone, 4,4'-diphenoxybenzophenone,
4,4'-diphenylbenzophenone, 4,4'-dimethylbenzophenone,
4,4-dichlorobenzophenone); asymmetric benzophenones (e.g.,
chlorobenzophenone, ethylbenzophenone, benzoylbenzophenone,
bromobenzophenone); and free-radically polymerizable benzophenones
(e.g., acryloxyethoxybenzophenone). Benzophenone itself is
inexpensive, and may be preferable if cost is a factor.
Copolymerizable benzophenones may be useful if residual odor or
volatiles are a concern, and may be preferable for those
applications as they become covalently incorporated into the
composition during cure. Examples of useful copolymerizable
photoinitiators are disclosed, for example, in U.S. Pat. No.
6,369,123 (Stark et al.), U.S. Pat. No. 5,407,971 (Everaerts et
al.), and U.S. Pat. No. 4,737,559 (Kellen et al.). The
copolymerizable photocrosslinking agents either generate free
radicals directly or abstract hydrogen abstraction atoms to
generate free radicals. Examples of hydrogen abstraction type
photocrosslinkers include, for example, those based on
benzophenones, acetophenones, anthraquinones, and the like.
Examples of suitable copolymerizable hydrogen abstraction
crosslinking compounds include mono-ethylenically unsaturated
aromatic ketone monomers free of orthoaromatic hydroxyl groups.
Examples of suitable free-radical generating copolymerizable
crosslinking agents include but are not limited to those selected
from the group consisting of 4-acryloxybenzophenone (ABP),
para-acryloxyethoxybenophenone, and
para-N-(methacryloxyethyl)-carbamoylethoxybenophenone. For both
thermal- and radiation-induced polymerizations, the initiator is
present in an amount of about 0.05% to about 5.0% by weight based
upon the total weight of the monomers.
[0062] In addition to the reactants, optional property modifying
additives can be mixed with the reactive oligomers and optional
other monomers provided that they do not interfere with the
polymerization reaction. Typical property modifiers include
tackifying agents (tackifiers) and plasticizing agents
(plasticizers) to modify the adhesive performance of the formed
adhesive composition. If used, the tackifiers and plasticizers are
generally present in amounts ranging from about 5% to about 55% by
weight, about 10 to about 45% by weight or even from about 10% to
about 35% by weight.
[0063] Useful tackifiers and plasticizers are those conventionally
used in the adhesive arts. Examples of suitable tackifying resins
include terpene phenolics, alpha methyl styrene resins, rosin
derived tackifiers, monomeric alcohols, oligomeric alcohols,
oligomeric glycols, and mixtures thereof. Examples of useful
plasticizing resins include terpene phenolics, rosin derived
plasticizers, polyglycols and mixtures thereof. In some embodiments
the plasticizer is isopropyl myristate or a polypropylene
glycol.
[0064] The formed polymer composition may also be blended with
additional pressure sensitive adhesive polymers to modify the
properties of the composition. In some embodiments an acidic
pressure sensitive adhesive, such as an acidic (meth)acrylate
pressure sensitive adhesive, is blended to form an acid-base
interaction with the urethane groups on the non-silicone
urethane-based adhesive copolymer. This acid-base interaction
between the polymers is a Lewis acid-base type interaction. Lewis
acid-base type interactions require that one component be an
electron acceptor (acid) and the other an electron donor (base).
The electron donor provides an unshared pair of electrons and the
electron acceptor furnishes an orbital system that can accommodate
the additional unshared pair of electrons. In this instance acid
groups, typically carboxylic acid groups on the added
(meth)acrylate pressure sensitive adhesive polymer interact with
the unshared electron pairs of the urethane groups.
[0065] Examples of suitable (meth)acrylate pressure sensitive
adhesives include (meth)acrylate copolymers prepared from alkyl
(meth)acrylate monomers and may contain additional monomers such as
vinyl monomers. Examples of such alkyl (meth)acrylate monomers are
those in which the alkyl groups comprise from about 4 carbon atoms
to about 12 carbon atoms and include, but are not limited to,
n-butyl acrylate, 2-ethylhexyl acrylate, isooctyl acrylate,
isononyl acrylate, isodecyl, acrylate, and mixtures thereof.
Optionally, other vinyl monomers and alkyl (meth)acrylate monomers
which, as homopolymers, have a Tg greater than 0.degree. C., such
as methyl acrylate, methyl methacrylate, isobornyl acrylate, vinyl
acetate, styrene, and the like, may be utilized in conjunction with
one or more of the low Tg alkyl (meth)acrylate monomers and
copolymerizable acidic monomers, provided that the Tg of the
resultant (meth)acrylate copolymer is less than about 0.degree.
C.
[0066] When the (meth)acrylate pressure sensitive adhesive is an
acidic copolymer, the acidic (meth)acrylate copolymers typically
are derived from acidic monomers comprising about 2% by weight to
about 30% by weight, or about 2% by weight to about 15% by weight,
of a copolymerizable acidic monomer. Examples of useful acidic
monomers include (meth)acrylic acid, itaconic acid, crotonic acid,
maleic acid, fumaric acid, and the like.
[0067] When used, the added pressure sensitive adhesive may be used
in any suitable amount to achieve the desired properties of the
composition. For example, the added pressure sensitive adhesive may
be added in amounts of from about 5 to about 60 weight % of the
composition.
[0068] In addition, other property modifiers, such as fillers, may
be added if desired, provided that if and when incorporated, such
additives are not detrimental to the properties desired in the
final composition. Fillers, such as fumed silica, fibers (e.g.,
glass, metal, inorganic, or organic fibers), carbon black, glass or
ceramic beads/bubbles, particles (e.g., metal, inorganic, or
organic particles), polyaramids (e.g., those available from DuPont
Chemical Company; Wilmington, Del. under the trade designation,
KEVLAR), and the like which can be added in amounts up to about 30%
by weight. Other additives such as dyes, inert fluids (e.g.,
hydrocarbon oils), pigments, flame retardants, stabilizers,
antioxidants, compatibilizers, antimicrobial agents (e.g., zinc
oxide), electrical conductors, thermal conductors (e.g., aluminum
oxide, boron nitride, aluminum nitride, and nickel particles), and
the like can be blended into these systems in amounts of generally
from about 1 to about 50 percent by total volume of the
composition.
[0069] The adhesives formed by the polymerization of the
non-silicone urethane-based reactive oligomers may be pressure
sensitive adhesives or heat activated adhesives. Generally pressure
sensitive adhesives are formed. These pressure sensitive adhesives
are useful in a wide array of applications.
[0070] The use of reactive oligomers instead of low molecular
weight monomers to generate the pressure sensitive adhesive
polymers results in polymers that are free of volatile unreacted
materials and other low molecular weight impurities after
polymerization. Residual monomers and low molecular weight
impurities may be problematic in certain applications, such as
medical and electronic applications. In medical and electronic
applications, residual monomers and impurities may cause, for
example, undesirable odor or potential contamination of
substrates/articles (e.g., hard disk drives) in which they are in
contact. In addition, the use of reactive oligomers which are free
of silicone is desirable in certain industries, such as the
electronics industry, where silicone contamination is a
concern.
[0071] The adhesive, or the reactive mixture which upon
polymerization forms the adhesive, may be coated onto a surface to
form a wide variety of adhesive articles. For example, the adhesive
can be applied to films or sheeting products (e.g., decorative,
reflective, and graphical), labelstock, tape backings (e.g.,
polymeric films, metal films, paper, creped paper, foams, and the
like), release liners, and the like. The substrate can be any
suitable type of material depending on the desired application.
[0072] The adhesive can be formed into a film or coating by either
continuous or batch processes. An example of a batch process is the
placement of a portion of the adhesive between a substrate to which
the film or coating is to be adhered and a surface capable of
releasing the adhesive film or coating to form a composite
structure. The composite structure can then be compressed at a
sufficient temperature and pressure to form a adhesive coating or
film of a desired thickness after cooling. Alternatively, the
adhesive can be compressed between two release surfaces and cooled
to form an adhesive transfer tape useful in laminating
applications.
[0073] Continuous forming methods include drawing the adhesive out
of a film die and subsequently contacting the drawn adhesive to a
moving plastic web or other suitable substrate. A related
continuous method involves extruding the adhesive and a coextruded
backing material from a film die and cooling the layered product to
form an adhesive tape. Other continuous forming methods involve
directly contacting the adhesive to a rapidly moving plastic web or
other suitable preformed substrate. Using this method, the adhesive
is applied to the moving preformed web using a die having flexible
die lips, such as a rotary rod die. After forming by any of these
continuous methods, the adhesive films or layers can be solidified
by quenching using both direct methods (e.g., chill rolls or water
baths) and indirect methods (e.g., air or gas impingement).
[0074] Adhesives can also be coated using a solvent-based method.
For example, the adhesive can be coated by such methods as knife
coating, roll coating, gravure coating, rod coating, curtain
coating, and air knife coating. The adhesive mixture may also be
printed by known methods such as screen printing or inkjet
printing. The coated solvent-based adhesive is then dried to remove
the solvent. Typically, the coated solvent-based adhesive is
subjected to elevated temperatures, such as those supplied by an
oven, to expedite drying of the adhesive.
[0075] In some embodiments it may be desirable to impart a
microstructured surface to one or both major surfaces of the
adhesive. It may be desirable to have a microstructured surface on
at least one surface of the adhesive to aid air egress during
lamination. If it is desired to have a microstructured surface on
one or both surfaces of the adhesive layer, the adhesive coating or
layer may be placed on a tool or a liner containing
microstructuring. Either the adhesive or the reactive mixture which
upon polymerization forms the adhesive, may be placed on a tool or
a liner. The liner or tool can then be removed to expose an
adhesive layer having a microstructured surface. Upon lamination,
the microstructuring on the surface of the adhesive may disappear
over time as the adhesive wets the surface. This is particularly
desirable where the adhesive is used in an optical construction
where residual microstructuring could interfere with the optical
properties of the optical construction.
[0076] The thickness of the adhesive layer tends to be at least
about 1 micrometer, at least 5 micrometers, at least 10
micrometers, at least 15 micrometers, or at least 20 micrometers.
The thickness is often no greater than about 200 micrometers, no
greater than about 175 micrometers, no greater than about 150
micrometers, or no greater than about 125 micrometers. For example,
the thickness can be 1 to 200 micrometers, 5 to 100 micrometers, 10
to 50 micrometers, 20 to 50 micrometers, or 1 to 15
micrometers.
[0077] The pressure sensitive adhesives are typically optically
clear. Optically clear adhesives may be used to make a wide array
of optical articles. Such articles may include an optical film, a
substrate or both. Such uses include information displays, window
coverings, graphic articles and the like.
[0078] Articles are provided that include an optical film and a
pressure sensitive adhesive layer adjacent to at least one major
surface of the optical film. The articles can further include
another substrate (e.g., permanently or temporarily attached to the
pressure sensitive adhesive layer), another adhesive layer, or a
combination thereof. As used herein, the term "adjacent" can be
used to refer to two layers that are in direct contact or that are
separated by one or more layers. Often, adjacent layers are in
direct contact.
[0079] In some embodiments, the resulting articles can be optical
elements or can be used to prepare optical elements. As used
herein, the term "optical element" refers to an article that has an
optical effect or optical application. The optical elements can be
used, for example, in electronic displays, architectural
applications, transportation applications, projection applications,
photonics applications, and graphics applications. Suitable optical
elements include, but are not limited to, screens or displays,
cathode ray tubes, polarizers, reflectors, and the like.
[0080] Any suitable optical film can be used in the articles. As
used herein, the term "optical film" refers to a film that can be
used to produce an optical effect. The optical films are typically
polymer-containing films that can be a single layer or multiple
layers. The optical films are flexible and can be of any suitable
thickness. The optical films often are at least partially
transmissive, reflective, antireflective, polarizing, optically
clear, or diffusive with respect to some wavelengths of the
electromagnetic spectrum (e.g., wavelengths in the visible
ultraviolet, or infrared regions of the electromagnetic spectrum).
Exemplary optical films include, but are not limited to, visible
mirror films, color mirror films, solar reflective films, infrared
reflective films, ultraviolet reflective films, reflective
polarizer films such as a brightness enhancement films and dual
brightness enhancement films, absorptive polarizer films, optically
clear films, tinted films, privacy films such as light-collimating
films, and antireflective films.
[0081] In some embodiments the optical film has a coating. In
general, coatings are used to enhance the function of the film or
provide additional functionality to the film. Examples of coatings
include, for example, hardcoats, anti-fog coatings, anti-scratch
coatings, privacy coatings or a combination thereof. Coatings such
as hardcoats, anti-fog coatings, and anti-scratch coatings that
provide enhanced durability, are desirable in applications such as,
for example, touch screen sensors, display screens, graphics
applications and the like. Examples of privacy coatings include,
for example, blurry or hazy coatings to give obscured viewing or
louvered films to limit the viewing angle.
[0082] Some optical films have multiple layers such as multiple
layers of polymer-containing materials (e.g., polymers with or
without dyes) or multiple layers of metal-containing material and
polymeric materials. Some optical films have alternating layers of
polymeric material with different indexes of refraction. Other
optical films have alternating polymeric layers and
metal-containing layers. Exemplary optical films are described in
the following patents: U.S. Pat. No. 6,049,419 (Wheatley et al.);
U.S. Pat. No. 5,223,465 (Wheatley et al.); U.S. Pat. No. 5,882,774
(Jonza et al.); U.S. Pat. No. 6,049,419 (Wheatley et al.); U.S.
Pat. No. RE 34,605 (Schrenk et al.); U.S. Pat. No. 5,579,162
(Bjornard et al.), and U.S. Pat. No. 5,360,659 (Arends et al.).
[0083] The substrate included in the article can contain polymeric
materials, glass materials, ceramic materials, metal-containing
materials (e.g., metals or metal oxides), or a combination thereof.
The substrate can include multiple layers of material such as a
support layer, a primer layer, a hard coat layer, a decorative
design, and the like. The substrate can be permanently or
temporarily attached to an adhesive layer. For example, a release
liner can be temporarily attached and then removed for attachment
of the adhesive layer to another substrate.
[0084] The substrate can have a variety of functions such as, for
example, providing flexibility, rigidity, strength or support,
reflectivity, antireflectivity, polarization, or transmissivity
(e.g., selective with respect to different wavelengths). That is,
the substrate can be flexible or rigid; reflective or
non-reflective; visibly clear, colored but transmissive, or opaque
(e.g., not transmissive); and polarizing or non-polarizing.
[0085] Exemplary substrates include, but are not limited to, the
outer surface of an electronic display such as liquid crystal
display or a cathode ray tube, the outer surface of a window or
glazing, the outer surface of an optical component such as a
reflector, polarizer, diffraction grating, mirror, or lens, another
film such as a decorative film or another optical film, or the
like.
[0086] Representative examples of polymeric substrates include
those that contain polycarbonates, polyesters (e.g., polyethylene
terephthalates and polyethylene naphthalates), polyurethanes,
poly(meth)acrylates (e.g., polymethyl methacrylates), polyvinyl
alcohols, polyolefins such as polyethylenes and polypropylenes,
polyvinyl chlorides, polyimides, cellulose triacetates,
acrylonitrile-butadiene-styrene copolymers, and the like.
[0087] In other embodiments, the substrate is a release liner. Any
suitable release liner can be used. Exemplary release liners
include those prepared from paper (e.g., Kraft paper) or polymeric
material (e.g., polyolefins such as polyethylene or polypropylene,
ethylene vinyl acetate, polyurethanes, polyesters such as
polyethylene terephthalate, and the like). At least some release
liners are coated with a layer of a release agent such as a
silicone-containing material or a fluorocarbon-containing material.
Exemplary release liners include, but are not limited to, liners
commercially available from CP Film (Martinsville, Va.) under the
trade designation "T-30" and "T-10" that have a silicone release
coating on polyethylene terephthalate film. The liner can have a
microstructure on its surface that is imparted to the adhesive to
form a microstructure on the surface of the adhesive layer. The
liner can then be removed to expose an adhesive layer having a
microstructured surface.
[0088] The release liner can be removed to adhere the optical film
to another substrate (i.e., removal of the release liner exposes a
surface of an adhesive layer that subsequently can be bonded to
another substrate surface).
[0089] The adhesives are self wetting and removable. The adhesives
exhibit great conformability permitting them to spontaneously wet
out substrates. The surface characteristics also permit the
adhesives to be bonded and removed from the substrate repeatedly
for repositioning or reworking. The strong cohesive strength of the
adhesives gives them structural integrity limiting cold flow and
giving elevated temperature resistance in addition to permanent
removability. In some embodiments the initial removability of an
adhesive coated article bonded to a glass substrate, as measured by
the 90.degree. Peel Adhesion test described in the Examples section
below, is no greater than 2.9 Newtons/decimeter (75 grams per
inch). Upon aging for one week at room temperature the
removability, as measured by the 90.degree. Peel Adhesion test
described in the Examples section below, is no more than 7.7
Newtons/decimeter (200 grams per inch). In other embodiments, the
removability after aging for at least one week at room temperature,
as measured by the 90.degree. Peel Adhesion test described in the
Examples section below, is no more than 15.4 Newtons/decimeter (400
grams per inch), 7.7 Newtons/decimeter (200 grams per inch) or even
3.9 Newtons/decimeter (100 grams per inch).
[0090] Exemplary adhesive articles in which the self wetting and
removability features are especially important include, for
example: large format articles such as graphic articles and
protective films; and information display devices.
[0091] Large-format graphic articles or protective films typically
include a thin polymeric film backed by a pressure sensitive
adhesive. These articles may be difficult to handle and apply onto
a surface of a substrate. The large format article may be applied
onto the surface of a substrate by what is sometimes called a "wet"
application process. The wet application process involves spraying
a liquid, typically a water/surfactant solution, onto the adhesive
side of the large format article, and optionally onto the substrate
surface. The liquid temporarily "detackifies" the pressure
sensitive adhesive so the installer may handle, slide, and
re-position the large format article into a desired position on the
substrate surface. The liquid also allows the installer to pull the
large format article apart if it sticks to itself or prematurely
adheres to the surface of the substrate. Applying a liquid to the
adhesive may also improve the appearance of the installed large
format article by providing a smooth, bubble free appearance with
good adhesion build on the surface of the substrate.
[0092] Examples of a large format protective films include window
films such as solar control films, shatter protection films,
decoration films and the like. In some instances the film may be a
multilayer film such as a multilayer IR film (i.e., an infrared
reflecting film), such as a microlayer film having selective
transmissivity such as an optically clear but infrared reflecting
film as described in U.S. Pat. No. 5,360,659 (Arends et al.).
[0093] While the wet application process has been used successfully
in many instances, it is a time consuming and messy process. A
"dry" application process is generally desirable for installing
large format graphic articles. Adhesives that are self wetting and
removable may be applied with a dry installation process. The
articles are easily attached to a large substrate because they are
self wetting and yet they may be easily removed and repositioned as
needed.
[0094] In other applications, such as information display devices,
the wet application process cannot be used. Examples of information
display devices include devices with a wide range of display area
configurations including liquid crystal displays, plasma displays,
front and rear projection displays, cathode ray tubes and signage.
Such display area configurations can be employed in a variety of
portable and non-portable information display devices including
personal digital assistants, cell phones, touch-sensitive screens,
wrist watches, car navigation systems, global positioning systems,
depth finders, calculators, electronic books, CD or DVD players,
projection television screens, computer monitors, notebook computer
displays, instrument gauges, instrument panel covers, signage such
as graphic displays (including indoor and outdoor graphics, bumper
stickers, etc) reflective sheeting and the like.
[0095] A wide variety of information display devices are in use,
both illuminated devices and non-illuminated devices. Many of these
devices utilize adhesive articles, such as adhesive coated films,
as part of their construction. One adhesive article frequently used
in information display devices is a protective film. Such films are
frequently used on information display devices that are frequently
handled or have exposed viewing surfaces.
[0096] In some embodiments, the adhesives of this disclosure may be
used to attach such films to information display devices because
the adhesives have the properties of optical clarity, self wetting
and removability. The adhesive property of optical clarity permits
the information to be viewed through the adhesive without
interference. The features of self wetting and removability permit
the film to be easily applied to display surface, removed and
reworked if needed during assembly and also removed and replaced
during the working life of the information display device.
EXAMPLES
[0097] These examples are merely for illustrative purposes only and
are not meant to be limiting on the scope of the appended claims.
All parts, percentages, ratios, etc. in the examples and the rest
of the specification are by weight, unless noted otherwise.
Solvents and other reagents used were obtained from Sigma-Aldrich
Chemical Company; Milwaukee, Wis. unless otherwise noted.
TABLE-US-00001 Table of Abbreviations Abbreviation or Trade
Designation Description VDM Vinyl dimethyl azlactone Polyamine-1
Polyoxyalkylene polyamine of approximately 2,000 molecular weight,
commercially available as "JEFFAMINE D-2000" from Huntsman,
Houston, TX. Photoinitiator-1 Photoinitiator "DAROCUR 4265"
commercially. available from Ciba, Hawthorne, NY PET UV-primed
polyester film of polyethylene terephthalate available under the
trade name "Dupont 617" having a thickness of 127 micrometers (5
mils) or 51 micrometers (2 mils) from Dupont Teijin Films,
Richmond, VA. Release Liner Polyester film of 51 micrometer
thickness (2 mils) coated on one side with silicone release agent,
commercially available from CP Film, Martinsville, VA as "T10
Release Liner". UBDA 8K Urea-based diamine of approximately 8,000
molecular weight, prepared as described in Synthesis Example 1.
UBDA 12K Urea-based diamine of approximately 12,000 molecular
weight, prepared as described in Synthesis Example 2. UA-1 Urethane
acrylate, aliphatic urethane oligomer commercially available from
Sartomer Company Inc., Exton PA as "CN9018", with a published Tg =
-56.degree.C. UA-2 Urethane acrylate, commercially available from
Sartomer Company Inc., Exton PA as "CN9004", with a published Tg =
-76.degree. C. UA-3 Urethane acrylate, commercially available from
Sartomer Company Inc., Exton PA as "CN9002", with a published Tg =
-50.0.degree. C. PSA-1 Pressure sensitive adhesive solution, 20%
solids by weight in ethyl acetate, of a copolymer PSA with an
approximate ratio of monomers of 93/7 isoctyl acrylate/acrylic acid
prepared as described in U.S. Pat. RE 24,906 (Ulrich). UA-4
Urethane acrylate, commercially available from Sartomer Company
Inc., Exton PA as "CN972", with a published Tg = -47.degree. C.
UA-5 Urethane acrylate, commercially available from Sartomer
Company Inc., Exton PA as "CN990", with a published Tg =
-37.degree. C. UA-6 Urethane acrylate, commercially available from
Sartomer Company Inc., Exton PA as "CN991", with a published Tg =
+27.degree. C. UA-7 Urethane acrylate, commercially available from
Sartomer Company Inc., Exton PA as "CN929", with a published Tg =
+43.degree. C. TRPGDA Tripropylene glycol diacrylate
Test Methods
90.degree. Peel Adhesion
[0098] Adhesive coatings of 51 micrometers (2 mils) thickness on 51
micrometer (2 mil) thick PET film were cut into 2.54 centimeter by
15 centimeter strips. Each strip was then adhered to a 6.2
centimeter by 23 centimeter clean, solvent washed glass coupon
using a 2-kilogram roller passed once over the strip. The bonded
assembly dwelled at room temperature for about one minute and was
tested for 90.degree. peel adhesion using an IMASS slip/peel tester
with a 90.degree. peel testing assembly (Model SP2000, commercially
available from Instrumentors Inc., Strongsville, Ohio) at a rate of
2.3 meters/minute (90 inches/minute) over a five second data
collection time. Three samples were tested; the reported peel
adhesion value is an average of the peel adhesion value from each
of the three samples. Data was measured in grams/inch width and
converted to Newtons per decimeter (N/dm).
Wet Out Test
[0099] Adhesive coatings of 51 micrometers (2 mils) thickness on
127 micrometer (5 mil) thick PET film were cut into sample squares
of 12.7 by 12.7 centimeters (5 by 5 inches). A 7.6 by 7.6
centimeter (3 by 3 inch) square was marked in the center of the
backside of each sample square. The liner was removed from the
sample square and one corner of the sample square was placed on the
surface of an isopropanol-washed glass coupon. The sample square
was dropped onto the glass surface. The wet out time was measured
using a stopwatch and was started when the wet out front reached
any part of the inner marked square and ended when the inner square
was completely wet out. The wet out time was recorded, and is
reported as the time (in seconds) per area wet out (in square
centimeters).
Titration Method to Determine Molecular Weight
[0100] To determine the molecular weight of a synthesized UBDA, a
measured sample weight (about 4-6 grams) was placed in a jar and
tetrahydrofuran (about 3 times the weight of the sample) was added
with mixing to form a uniform solution. A solution of the indicator
bromophenol blue was added until the color was a deep blue. With
constant stirring, the sample solution was titrated by adding 1.0
Normal HCl (aq) dropwise until a color change from blue to yellow
indicated that the endpoint was reached. The endpoint volume of HCl
titrated was recorded and the molecular weight was calculated.
SYNTHESIS EXAMPLES
Synthesis Example 1
Preparation of UBDA 8K
[0101] A sample of Polyamine-1 (4 moles) was degassed under vacuum
at 100.degree. C. for 1 hour. Freshly ground diphenyl carbonate (3
moles) was added and the mixture stirred to give a uniform mixture.
The mixture was heated to 160.degree. C. for 3 hours under vacuum
to remove phenol byproduct. The resultant product was a urea chain
extended diamine of approximately 8,000 molecular weight (confirmed
by titration, using the method described above).
Synthesis Example 2
Preparation of UBDA 12K
[0102] A sample of Polyamine-1 (6 moles) was reacted with a sample
of diphenyl carbonate (5 moles) using the procedure described in
Synthesis Example 1 above. The resultant product was a urea chain
extended diamine of approximately 12,000 molecular weight
(confirmed by titration, using the method described above).
Comparative Example C1
[0103] To a stirred sample of UBDA 8K (1 mole) was added slowly a
sample of VDM (2 moles) at room temperature. The mixture was
stirred and allowed to react overnight. A sample of
Photoinitiator-1 was added (0.5% by weight). The resultant mixture
was cast between PET and a Release Liner on a knife die and marble
bed hand spread coater to a thickness appropriate for the test to
be run on the sample and cured under low intensity UV exposure
using 40 watt, 350 nanometer bulbs for 10 minutes. Wet out testing
to glass, 90.degree. Peel adhesion to glass (initial and after
aging for 1 week at 70.degree. C.) were carried out using the test
methods described above. The results are presented in Table 1.
Comparative Example C2
[0104] To a stirred sample of UBDA 12K (1 mole) was added slowly a
sample of VDM (2 moles) at room temperature. The mixture was
stirred and allowed to react overnight. A sample of
Photoinitiator-1 was added (0.5% by weight). The resultant mixture
was cast between PET and a Release Liner on a knife die and marble
bed hand spread coater to a thickness appropriate for the test to
be run on the sample and cured under low intensity UV exposure
using 40 watt, 350 nanometer bulbs for 10 minutes. Wet out testing
to glass, 90.degree. Peel adhesion to glass (initial and after
aging for 1 week at 70.degree. C.) were carried out using the test
methods described above. The results are presented in Table 1.
Example 1
[0105] To a stirred sample of UA-1, Photoinitiator-1 was added
(1.0% by weight) and the resultant mixture was cast between PET and
a Release Liner on a knife die and marble bed hand spread coater to
a thickness appropriate for the test to be run on the sample and
cured under high intensity UV exposure using Fusion 600 Watt/in, D
bulbs at 25 feet per minute (7.5 meters per minute) line speed. Wet
out testing to glass, 90.degree. Peel adhesion to glass (initial
and after aging for 1 week at 70.degree. C.) were carried out using
the test methods described above. The results are presented in
Table 1.
Example 2
[0106] To a stirred sample of UA-2, Photoinitiator-1 was added
(1.0% by weight) and the resultant mixture was cast between PET and
a Release Liner on a knife die and marble bed hand spread coater to
a thickness appropriate for the test to be run on the sample and
cured under high intensity UV exposure using Fusion 600 Watt/in, D
bulbs at 25 feet per minute (7.5 meters per minute) line speed. Wet
out testing to glass, 90.degree. Peel adhesion to glass (initial
and after aging for 1 week at 70.degree. C.) were carried out using
the test methods described above. The results are presented in
Table 1.
Example 3
[0107] To a stirred sample of UA-3, Photoinitiator-1 was added
(1.0% by weight) and the resultant mixture was cast between PET and
a Release Liner on a knife die and marble bed hand spread coater to
a thickness appropriate for the test to be run on the sample and
cured under high intensity UV exposure using Fusion 600 Watt/in, D
bulbs at 25 feet per minute (7.5 meters per minute) line speed. Wet
out testing to glass, 90.degree. Peel adhesion to glass (initial
and after aging for 1 week at 70.degree. C.) were carried out using
the test methods described above. The results are presented in
Table 1.
Example 4
[0108] To a stirred sample of UA-1, IPM was added to 20% by weight,
Photoinitiator-1 was added (1.0% by weight) and the resultant
mixture was cast between PET and a Release Liner on a knife die and
marble bed hand spread coater to a thickness appropriate for the
test to be run on the sample and cured under high intensity UV
exposure using Fusion 600 Watt/in, D bulbs at 25 feet per minute
(7.5 meters per minute) line speed. Wet out testing to glass,
90.degree. Peel adhesion to glass (initial and after aging for 1
week at 70.degree. C.) were carried out using the test methods
described above. The results are presented in Table 1.
Example 5
[0109] To a stirred sample of UA-1 (dissolved to in Ethyl Acetate
to 80% solids), IPM was added to 25% by weight of total solids,
TRPGDA was added to 15% by weight total solids, PSA-1 solution was
added to 10% by weight of total solids, Photoinitiator-1 was added
(1.0% by weight of total solids) and the resultant mixture was cast
onto PET and dried for 10 minutes at 70.degree. C. to remove
solvent. A release liner was laminated onto the uncured coating and
the sample was cured under high intensity UV exposure using Fusion
600 Watt/in, D bulbs at 25 feet per minute (7.5 meters per minute)
line speed. Wet out testing to glass, 90.degree. Peel adhesion to
glass (initial and after aging for 1 week at 70.degree. C.) were
carried out using the test methods described above. The results are
presented in Table 1.
Comparative Example C3
[0110] To a stirred sample of UA-4, Photoinitiator-1 was added
(1.0% by weight) and the resultant mixture was cast between PET and
a Release Liner on a knife die and marble bed hand spread coater to
a thickness appropriate for the test to be run on the sample and
cured under high intensity UV exposure using Fusion 600 Watt/in, D
bulbs at 25 feet per minute (7.5 meters per minute) line speed. Wet
out testing to glass, 90.degree. Peel adhesion to glass (initial
and after aging for 1 week at 70.degree. C.) were carried out using
the test methods described above. The results are presented in
Table 1.
Comparative Example C4
[0111] To a stirred sample of UA-5, Photoinitiator-1 was added
(1.0% by weight) and the resultant mixture was cast between PET and
a Release Liner on a knife die and marble bed hand spread coater to
a thickness appropriate for the test to be run on the sample and
cured under high intensity UV exposure using Fusion 600 Watt/in, D
bulbs at 25 feet per minute (7.5 meters per minute) line speed. Wet
out testing to glass, 90.degree. Peel adhesion to glass (initial
and after aging for 1 week at 70.degree. C.) were carried out using
the test methods described above. The results are presented in
Table 1.
Comparative Example C5
[0112] To a stirred sample of UA-6, Photoinitiator-1 was added
(1.0% by weight) and the resultant mixture was cast between PET and
a Release Liner on a knife die and marble bed hand spread coater to
a thickness appropriate for the test to be run on the sample and
cured under high intensity UV exposure using Fusion 600 Watt/in, D
bulbs at 25 feet per minute (7.5 meters per minute) line speed. Wet
out testing to glass, 90.degree. Peel adhesion to glass (initial
and after aging for 1 week at 70.degree. C.) were carried out using
the test methods described above. The results are presented in
Table 1.
Comparative Example C6
[0113] To a stirred sample of UA-7, Photoinitiator-1 was added
(1.0% by weight) and the resultant mixture was cast between PET and
a Release Liner on a knife die and marble bed hand spread coater to
a thickness appropriate for the test to be run on the sample and
cured under high intensity UV exposure using Fusion 600 Watt/in, D
bulbs at 25 feet per minute (7.5 meters per minute) line speed. Wet
out testing to glass, 90.degree. Peel adhesion to glass (initial
and after aging for 1 week at 70.degree. C.) were carried out using
the test methods described above. The results are presented in
Table 1.
TABLE-US-00002 TABLE 1 90.degree. Peel Initial from Glass Wet-out
90.degree. after aging to Peel 1-week glass from 70.degree. C.
Speed Example (N/dm) (N/dm) (sec/cm.sup.2) C1 3.12 6.04 0.55 C2
5.17 12.74 1.39 1 13.90 34.20 0.31 2 0.73 1.16 0.10 3 1.38 2.12
0.16 4 4.13 10.22 0.17 5 2.23 5.40 0.14 C3 0.58 1.30 0.43 C4
<0.38 -- 0.78 C5 <0.38 -- NW C6 <0.38 -- NW NW = No wet
out observed without the application of external pressure.
* * * * *