U.S. patent application number 11/228370 was filed with the patent office on 2009-07-02 for pressure sensitive adhesive suitable for aircraft exterior applications.
Invention is credited to Bruce K. Keough, Larry K. Olli, Diane C. Rawlings.
Application Number | 20090169794 11/228370 |
Document ID | / |
Family ID | 40688672 |
Filed Date | 2009-07-02 |
United States Patent
Application |
20090169794 |
Kind Code |
A1 |
Rawlings; Diane C. ; et
al. |
July 2, 2009 |
PRESSURE SENSITIVE ADHESIVE SUITABLE FOR AIRCRAFT EXTERIOR
APPLICATIONS
Abstract
A pressure sensitive adhesive (PSA) suitable for aircraft
exterior applications formed by reacting a cross-linker with an
un-crosslinked adhesive can resist many aircraft fluids and can
maintain a bond to a protective barrier film of an applique at low
and high temperatures. An exemplary PSA includes at least a first
release liner and a crosslinked adhesive releasably bonded thereto.
The crosslinked adhesive suitably is formed by reacting a
polyisocyanate crosslinker with an un-crosslinked acrylic adhesive.
The PSA can exhibit a peel strength between around 2-8 psi at
temperatures between around 180-250 degrees Fahrenheit. In an
exemplary method to provide a PSA, an un-crosslinked acrylic
adhesive, a solvent, and a polyisocyanate crosslinker are mixed
together. The mixture is reacted on a release liner. A portion of
the solvent is driven off, and the polyisocyanate crosslinker is
reacted with itself and with reactive groups remaining on the
un-crosslinked acrylic adhesive.
Inventors: |
Rawlings; Diane C.;
(Bellevue, WA) ; Olli; Larry K.; (Seattle, WA)
; Keough; Bruce K.; (Kent, WA) |
Correspondence
Address: |
Boeing (TLG);c/o Toler Law Group
8500 Bluffstone Cove, Suite A201
Austin
TX
78759
US
|
Family ID: |
40688672 |
Appl. No.: |
11/228370 |
Filed: |
September 17, 2005 |
Current U.S.
Class: |
428/41.8 ;
156/289; 427/208.4; 428/355EN |
Current CPC
Class: |
C08K 5/0025 20130101;
Y10T 428/2852 20150115; Y10T 428/2878 20150115; C09J 2301/408
20200801; Y10T 428/14 20150115; C09J 2433/00 20130101; C08K 5/29
20130101; Y10T 428/1476 20150115; C09J 7/10 20180101 |
Class at
Publication: |
428/41.8 ;
428/355.EN; 427/208.4; 156/289 |
International
Class: |
C09J 133/02 20060101
C09J133/02; B32B 7/12 20060101 B32B007/12; B05D 5/10 20060101
B05D005/10; B32B 37/12 20060101 B32B037/12 |
Claims
1. A pressure sensitive adhesive comprising: at least a first
release liner; and a crosslinked adhesive releasably bonded to the
first release liner, the crosslinked adhesive being formed by
reacting a polyisocyanate crosslinker with an un-crosslinked
acrylic adhesive in a mixture including at least ninety-two percent
by weight of the un-crosslinked acrylic adhesive, wherein the
crosslinked adhesive exhibits a peel strength in a range between
around 2 pounds per square inch and around 8 pounds per square inch
at temperatures in a range between around 180 degrees Fahrenheit
and around 250 degrees Fahrenheit.
2. The pressure sensitive adhesive of claim 1, further comprising a
second release liner, the crosslinked adhesive further being
releasably bonded to the second release liner.
3. The pressure sensitive adhesive of claim 1, wherein the
polyisocyanate crosslinker includes an aliphatic polyisocyanate
crosslinker.
4. (canceled)
5. An applique comprising: a barrier film; and a pressure sensitive
adhesive disposed on the barrier film, the pressure sensitive
adhesive including a crosslinked adhesive disposed on a release
liner, the crosslinked adhesive being formed by reacting a
polyisocyanate crosslinker with all un-crosslinked acrylic adhesive
in a mixture including at least ninety-two percent by weight of the
un-crosslinked acrylic adhesive, wherein the crosslinked adhesive
exhibits a peel strength in a range between around 2 pounds per
square inch and around 8 pounds per square inch at temperatures in
a range between around 180 degrees Fahrenheit and around 250
degrees Fahrenheit.
6. The applique of claim 5, wherein the polyisocyanate crosslinker
includes an aliphatic polyisocyanate crosslinker.
7. (canceled)
8. The applique of claim 5, wherein the barrier film includes a
polymer film.
9. A method of providing a pressure sensitive adhesive, the method
comprising: mixing together a mixture of an un-crosslinked acrylic
adhesive, a solvent, and a polyisocyanate crosslinker; reacting the
mixture for a first predetermined time period; coating the reacted
mixture on at least a first release liner; driving off a portion of
the solvent; and reacting the polyisocyanate crosslinker with the
un-crosslinked acrylic adhesive.
10. The method of claim 9, wherein the mixture includes around 92
percent to around 99 percent by weight of the un-crosslinked
acrylic adhesive, around 0 percent to around 2 percent by weight of
the solvent, and around 1 percent to around 6 percent by weight of
the polyisocyanate crosslinker.
11. The method of claim 9, wherein mixing together imparts to the
mixture a first viscosity.
12. The method of claim 11, wherein: before expiration of the first
predetermined time period, reacting the mixture imparts to the
mixture a second viscosity that is greater than the first
viscosity; and at expiration of the first predetermined time
period, reacting the mixture imparts to the mixture a third
viscosity that is greater than the first viscosity but less than
the second viscosity.
13. The method of claim 9, further comprising coating the at least
first release liner with silicone before coating the reacted
mixture on the at least first release liner.
14. The method of claim 9, wherein coating the reacted mixture
includes covering the mixture with a second release liner.
15. The method of claim 14, further comprising coating the second
release liner with silicone before covering the mixture with the
second release liner.
16. The method of claim 9, wherein driving off a portion of the
solvent includes heating in an environment at a first predetermined
temperature the reacted mixture for a second predetermined time
period.
17. The method of claim 16, wherein the first predetermined
temperature is in a range between around 120 degrees Fahrenheit and
around 130 degrees Fahrenheit and the second predetermined time
period is in a range between around 2 minutes and around 3
minutes.
18. The method of claim 16, wherein driving off a portion of the
solvent further includes heating in an environment at a second
predetermined temperature the reacted mixture for a third
predetermined time period.
19. The method of claim 18, wherein the second predetermined
temperature is in a range between around 150 degrees Fahrenheit and
around 200 degrees Fahrenheit, and the third predetermined time
period is in a range between around 2 minutes and around 3
minutes.
20. The method of claim 9, wherein driving off a portion of the
solvent drives off the solvent such that a remaining amount of the
solvent is less than around 1 percent by weight.
21. The method of claim 18, wherein reacting the crosslinker with
the un-crosslinked adhesive includes heating in an environment at a
third predetermined temperature the reacted mixture for a fourth
predetermined time period.
22. The method of claim 21, wherein the third predetermined
temperature is in a range between around 320 degrees Fahrenheit and
around 350 degrees Fahrenheit, and the fourth predetermined time
period is in a range between around 2 minutes and around 3
minutes.
23. The method of claim 9, wherein the polyisocyanate crosslinker
includes an aliphatic polyisocyanate crosslinker.
24. A pressure sensitive adhesive made according to a process
comprising: mixing together a mixture of an un-crosslinked acrylic
adhesive, a solvent, and a polyisocyanate crosslinker, the mixture
including at least ninety-two percent by weight of the
un-crosslinked acrylic adhesive; reacting the mixture for a first
predetermined time period; coating the reacted mixture on at least
a first release liner; driving off a portion of the solvent; and
reacting the polyisocyanate crosslinker with the un-crosslinked
acrylic adhesive, wherein a resultant crosslinked adhesive exhibits
a peel strength in a range between around 2 pounds per square inch
and around 8 pounds per square inch at temperatures in a range
between around 180 degrees Fahrenheit and around 250 degrees
Fahrenheit.
25. The pressure sensitive adhesive of claim 24, further comprising
a second release liner, the crosslinked adhesive further being
releasably bonded to the second release liner.
26. The pressure sensitive adhesive of claim 24, wherein the
polyisocyanate crosslinker includes an aliphatic polyisocyanate
crosslinker.
27. (canceled)
Description
BACKGROUND
[0001] Replacing paint on aircraft exterior surfaces with
applique's is desirable for a variety of reasons, including weight
reduction, elimination of hazardous materials associated with
painting and paint stripping, maintenance cost savings, and
lightning strike protection. Appliques also allow incorporation of
drag-reducing riblets and hydrophobia/anti-ice materials and
textures.
[0002] Appliques typically include three components: (i) a
protective barrier film; (ii) a pressure sensitive adhesive (PSA);
and (iii) a release liner. Typical material requirements for
appliques used on aircraft include: a temperature range from around
-65 degrees Fahrenheit up to around 230 degrees Fahrenheit; fluid
resistance to a wide range of substances such as jet fuel,
hydraulic fluid, aircraft wash fluids, de-icing fluids, lube oil,
and the like; exposure to environmental conditions such as
ultraviolet (UV) radiation, hot condensing humidity, salt spray,
rain erosion, wind erosion, and the like; and easy removal and
repair.
[0003] The PSA plays an important role in an applique's ability to
withstand such conditions. In addition, and unlike paint systems,
ability to maintain bond of an applique to an aircraft skin may
affect flight safety considerations. For example, it must be
demonstrated that an applique will not peel in flight as a large
section or "gore"--even if peeling initiates due to impact or other
damage.
[0004] Current PSAs used for aircraft exterior applications
generally are acrylic polymer-based adhesives, and can have good
moisture resistance and relatively high bond strengths. While some
current PSAs are resistant to some aircraft fluids, few PSAs are
currently available that can resist all aircraft fluids, can
withstand extended exposure to high humidity, and can maintain
adhesion over a wide range of temperatures. For example, many
acrylic PSAs tend to lose peel adhesion to the protective barrier
film at temperatures above 150 degrees Fahrenheit.
[0005] A current PSA available from the 3M Company maintains
adhesion values over a temperature range of -65 degrees Fahrenheit
to 230 degrees Fahrenheit or higher while resisting aircraft fluids
such as jet fuel. However, this PSA is unavailable as a transfer
film adhesive (which is the form used in several current
appliques). Moreover, cost of this PSA precludes its use as a
commercially-viable PSA for commercial aircraft use.
[0006] Currently known PSAs with acceptable resistance to aircraft
fluids typically lose the bond interface to the protective barrier
film as the PSA and the barrier film go through their glass
transition temperatures. In such a case, in the event of a fracture
at the interface the PSA will remain adhered to the underlying
substrate but the barrier film will peel off the PSA. In addition,
the PSAs fail cohesively on peeling at a low peel strength at high
temperatures, such as temperatures greater than 200 degrees
Fahrenheit.
[0007] The foregoing examples of related art and limitations
associated therewith are intended to be illustrative and not
exclusive. Other limitations of the related art will become
apparent to those of skill in the art upon a reading of the
specification and a study of the drawings.
SUMMARY
[0008] The following embodiments and aspects thereof are described
and illustrated in conjunction with products and methods which are
meant to be exemplary and illustrative, not limiting in scope. In
various embodiments, one or more of the problems described above in
the Background have been reduced or eliminated, while other
embodiments are directed to other improvements.
[0009] Embodiments provide a pressure sensitive adhesive (PSA)
suitable for aircraft exterior applications. By reacting a
cross-linker with an un-crosslinked adhesive, a resultant PSA can
resist many aircraft fluids and can maintain a bond to a protective
barrier film of an applique at low and high temperatures.
[0010] An exemplary pressure sensitive adhesive includes a release
liner and a crosslinked adhesive releasably bonded to the release
liner. The crosslinked adhesive suitably is formed by reacting a
polyisocyanate crosslinker with an un-crosslinked acrylic adhesive.
In one presently preferred embodiment, the crosslinker is an
aliphatic polyisocyanate crosslinker. However, the crosslinker need
not be aliphatic.
[0011] According to an aspect, the pressure sensitive adhesive can
exhibit improved high-temperature peel strength over current PSAs.
For example, the pressure sensitive adhesive can exhibit a peel
strength between a minimum peel strength of around 2 pounds per
square inch (psi) and a maximum peel strength of around 8 psi at
temperatures between around 180 degrees Fahrenheit and around 250
degrees Fahrenheit.
[0012] According to another embodiment, an exemplary method
provides a pressure sensitive adhesive. An un-crosslinked acrylic
adhesive, a solvent, and a polyisocyanate crosslinker are mixed
together. The mixture is reacted on a release liner. A portion of
the solvent is driven off, and the polyisocyanate crosslinker is
reacted with itself and with reactive groups remaining on the
un-crosslinked acrylic adhesive.
[0013] In addition to the exemplary embodiments and aspects
described above, further embodiments and aspects will become
apparent by reference to the drawings and by study of the following
detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] Exemplary embodiments are illustrated in referenced figures
of the drawings. It is intended that the embodiments and figures
disclosed herein are to be considered illustrative rather than
restrictive.
[0015] FIG. 1 is a side view of an exemplary pressure sensitive
adhesive;
[0016] FIG. 2 is a side view of the pressure sensitive adhesive of
FIG. 1 incorporated in an applique that is applied to a substrate;
and
[0017] FIG. 3 is a flowchart of an exemplary method of providing a
pressure sensitive adhesive.
DETAILED DESCRIPTION
[0018] Referring to FIG. 1 and by way of overview, an exemplary
pressure sensitive adhesive (PSA) 10 is suitable for aircraft
exterior applications. By reacting a cross-linker with an
un-crosslinked adhesive, the resultant PSA 10 can resist many
aircraft fluids and can maintain a bond to a protective barrier
film (not shown in FIG. 1) of an applique (not shown in FIG. 1) at
low and high temperatures. Given by way of non-limiting example,
the exemplary PSA 10 includes release liners 12 and a crosslinked
adhesive 14 releasably bonded to the release liners 12. The
crosslinked adhesive 14 suitably is formed by reacting a
polyisocyanate crosslinker, such as without limitation an aliphatic
polyisocyanate crosslinker, with an un-crosslinked acrylic
adhesive. Advantageously and as a result, the PSA 10 can exhibit
improved high-temperature peel strength over current PSAs. Details
of the PSA 10 and a method of making the PSA 10 will now be set
forth below.
[0019] The PSA 10 includes release liners 12. While two of the
release liners 12 are shown, in one embodiment only one release
liner 12 is provided (and the resultant PSA 10 is self-wound) if
that liner and the release are stable at the processing
temperatures (discussed below) for the PSA. In another embodiment,
the adhesive could be cast directly onto the applique film (thereby
entailing use of no release liners) if it is heat stable enough. In
one presently preferred embodiment, two of the release liners 12
are provided such that one release liner 12 stays on when the other
release liner 12 is peeled off. The release liners 12 are
releasably bonded at a surface 16 to the crosslinked adhesive 14
such that the release liners 12 can be cleanly removed from the
crosslinked adhesive 14 without tearing or otherwise damaging the
release liners 12 or the crosslinked adhesive 14. The release
liners 12 suitably each are pieces of film, such as without
limitation polyester, polyethylene, or coated paper. The film
typically is provided as a roll product. The release liners 12 are
each coated at the surface 16 with a thin coating of a non-stick
substance, such as without limitation silicone, polyethylene, or
fluorochemicals. Thickness of the release liners 12 suitably is in
a range between around 1-6 mils depending on the composition and
stiffness of the release liners 12. For example, polyester liners
are often around 1-2 mils thick and paper liners may be between
around 3-6 mils thick. The release liners 12 desirably have a
uniform thickness so the PSA 10 can be uniform in thickness. The
release liners 12 are selected such that they are able to withstand
the processing temperatures, discussed below, of the PSA 10.
Alternately and at higher cost, the PSA 10 may be processed on one
liner and then switched to another liner. An important feature of
the release liners 12 is differential release. Regardless of
whether the PSA 10 is coated on one release liner 12 or two release
liners 12, the tight release is significantly weaker that the PSA
10 or film product itself so that the release liner 12 will peel
off when it is desired to use an applique without creating shock
lines or other distortion of the PSA 10. It is also helpful to have
some stiffness in the release liner 12 so that it peels uniformly
without kinking.
[0020] The crosslinked adhesive 14 suitably is formed by reacting a
polyisocyanate crosslinker, such as without limitation an aliphatic
polyisocyanate crosslinker, with an un-crosslinked acrylic
adhesive. The un-crosslinked acrylic adhesive preferably exhibits
resistance to several aircraft solvents, jet fuel, lube oil, water,
and the like. At high temperatures (on the order of around 180-200
degrees Fahrenheit), the un-crosslinked acrylic adhesive also
preferably exhibits a minimum peel strength of around 2 pounds per
square inch (psi) and a maximum peel strength of around 8 psi. The
un-crosslinked acrylic adhesive suitably is any of a number of
commercially-available acrylic adhesives. Given by way of
non-limiting example, a suitable un-crosslinked acrylic adhesive
includes Gelva Multipolymer Solution.TM. (GMS) 3051, available from
Cytec Surface Specialties. The following explanation will be noted
regarding use herein of the terminology "un-crosslinked adhesive".
It is initially noted that polymers that comprise PSAs could be
considered as "crosslinked" because that is how PSA polymers are
formed. However, embodiments set forth herein provide additional
crosslinking between the isocyanate (that is, the polyisocyanate
crosslinker) and the PSA polymer (that is, the "un-crosslinked
acrylic adhesive") and also to the isocyanate itself (isocyanates
will crosslink with themselves in the presence of any water).
[0021] The crosslinker suitably is an aliphatic isocyanate
(hexamethylene diisocyanate (HDI) trimer). The crosslinker is used
as a hardener for the un-crosslinked acrylic adhesive. The
aliphatic isocyanate crosslinker has three functional isocyanate
(--N.dbd.C.dbd.O) groups on a ring structure of medium-short carbon
chains. A suitable aliphatic isocyanate crosslinker is
Desmodur.RTM. N3300 available from Bayer AG. The aliphatic
isocyanate crosslinker suitably has an NCO content of around
21.8+0.3 percent; a viscosity at 23 degrees Centigrade of around
3,000+750 mPas; and monomeric HDI of less than around 0.15 percent.
The aliphatic isocyanate crosslinker may be supplied in
solvent-free form. The crosslinker need not be an aliphatic
isocyanate crosslinker, and other crosslinkers may be used as
desired for a particular application. For example, the crosslinker
may be an aromatic isocyanate or an epoxy. As a further example,
the crosslinker may be a blocked isocyanate that unblocks at
temperatures used for processing the adhesive, such as Bayer
bl3175.
[0022] As a result of reacting the aliphatic isocyanate crosslinker
with the un-crosslinked acrylic adhesive, the resultant crosslinked
adhesive 14 has an increased crosslink density compared to the
un-crosslinked acrylic adhesive. Advantageously, this increased
crosslink density of the crosslinked adhesive 14 makes the PSA 10
well-suited for use in an applique for an aircraft exterior. This
is because the increased crosslink density results in increased
high-temperature cohesive strength and peel strength of the
crosslinked adhesive 14 compared to the un-crosslinked acrylic
adhesive.
[0023] Referring additionally to FIG. 2, the crosslinked adhesive
14 provided with the PSA 10 is used in an exemplary applique 18.
The applique 18 suitably is any applique that is used as a paint
replacement system. For example, the applique 18 may be a transfer
film applique used as a paint replacement system for aircraft. An
exemplary applique in which the crosslinked adhesive 14 may be used
is described in U.S. patent application Ser. No. 10/941,429 for
"Applique" by Diane C. Rawlings and Bruce K. Keough and assigned to
The Boeing Company, the entire contents of which are incorporated
by reference. In general terms, the applique 18 includes a barrier
film 20, such as without limitation a polymer film. If two release
liners 12 (FIG. 1) are provided, then one of the release liners 12
is removed from the crosslinked adhesive 14. The barrier film 20 is
disposed on the crosslinked adhesive 14. The remaining release
liner 12 (FIG. 1) is removed from the crosslinked adhesive 14, and
the crosslinked adhesive 14 is bonded to a substrate 22, such as
without limitation a skin of an aircraft.
[0024] While the applique 18 may be used as a paint replacement
system on any surface as desired, the applique 18 (that is, any
applique that uses the crosslinked adhesive 14) is especially
well-suited for use on an aircraft skin. This is because the
crosslinked adhesive 14 has a minimum peel strength with the
barrier film 20 of around 2 psi and a maximum peel strength of
around 8 psi at higher temperatures--from around 180 degrees
Fahrenheit up to around 250 degrees Fahrenheit--than temperatures
that are achievable with current PSAs.
[0025] An exemplary method of providing the PSA 10 will now be
described. Referring now to FIGS. 1 and 3, a method 100 begins at a
block 102. At a block 104, the un-crosslinked acrylic adhesive, a
solvent, and the alophatic isocyanate crosslinker are mixed. The
solvent reduces the viscosity of the aliphatic isocyanate
crosslinker so the mixture does not cure into a substance that can
not be poured. The un-crosslinked acrylic adhesive and the
aliphatic isocyanate crosslinker have been described above. The
solvent suitably is any solvent that is compatible with the
uncrosslinked acrylic adhesive and the aliphatic isocyanate
crosslinker. Given by way of nonlimiting example, suitable solvents
include esters, ketones and aromatic hydrocarbons such as ethyl
acetate, butyl acetate, methoxpropylacetate, acetone, methyl ethyl
ketone, methyl isobutyl ketone, cyclohexanone, toluene, xylene,
solvent naptha 100, and mixtures thereof. In one presently
preferred embodiment, ethyl acetate is used as the solvent.
[0026] The mixture includes around 92 percent to around 99 percent
by weight of the un-crosslinked acrylic adhesive, around 0 percent
to around 2 percent by weight of the solvent, and around 1 percent
to around 6 percent by weight of the aliphatic polyisocyanate
crosslinker. In one presently preferred embodiment, the mixture
includes around 96.74 percent by weight of the un-crosslinked
acrylic adhesive, around 1.63 percent by weight of the solvent, and
around 1.63 percent by weight of the aliphatic polyisocyanate
crosslinker. The mixture is mixed for around 20 minutes or so. The
viscosity of the mixture increases during mixing such that the
mixture gels within around 20 minutes or so of mixing.
[0027] At a block 106 the mixture is reacted. The time period that
the mixture is reacted suitably is around 24 hours or so. At the
end of the reaction time period, the mixture can be poured. While
the mixture reacts, the viscosity increases from the viscosity of
the mixture at the end of mixing at the block 104. During the
reaction, the viscosity of the mixture increases to a maximum value
such that the mixture is gelatinous and can not be poured. As the
reaction continues past this point, the viscosity of the mixture
decreases. By the end of the reaction time period, the viscosity of
the mixture has decreased to a viscosity that is less than the
maximum viscosity exhibited during the reaction but greater than
the viscosity at the beginning of the reaction at the block 106. At
the end of the reaction time period, the viscosity of the mixture
is such that the mixture can be poured and coated using
conventional coating equipment.
[0028] At a block 108, the surface 16 of one of the release liners
12 is coated with a non-stick substance such as silicone and the
reacted mixture is coated thereon. If two release liners 12 are
provided, then the surface 16 of the other release liner 12 is
coated with the non-stick substance and is placed on top of the
reacted mixture. The non-stick substance is applied to the surface
16 to make the release liner(s) 12 and the crosslinked adhesive 14
releasably (as opposed to permanently) bonded to each other.
[0029] At a block 110 a portion of the solvent is driven off. The
reacted mixture is heated at desired times at desired temperatures
until the remaining solvent is less than around 1 percent by
weight. As will be understood by the description that follows, the
block 110 and a subsequent processing block are preferably
performed in a multiple zone oven. As will also be understood from
an explanation of subsequent processing, it may be desirable to
reduce line speed of the multiple zone oven to speeds that are
slower than line speeds that may typically be encountered in
commercial off-the-shelf ovens. The release liner(s) 12 (suitably
in roll form) with the reacted mixture coated thereon are fed into
a first stage of an oven that has a temperature suitably between
around 120-130 degrees Fahrenheit and preferably around 125 degrees
Fahrenheit for a time period between around 2-3 minutes. This
time-at-temperature combination is based on a typical oven stage of
around 25 feet or so in length with a line speed of around 10 feet
per minute or so. Again, it will be understood that this line speed
may be lower than typical line speeds of current commercial
off-the-shelf ovens.
[0030] In one present embodiment, driving off the solvent at the
block 110 continues. The reacted mixture enters a second stage of
an oven that has a temperature suitably between around 150-200
degrees Fahrenheit and preferably around 200 degrees Fahrenheit for
a time period between around 2-3 minutes. This time-at-temperature
combination is based on a typical oven stage of around 25 feet or
so in length with a line speed of around 10 feet per minute or so.
At the end of heating in the second stage of the oven, the
remaining solvent has been reduced to less than around 1 percent by
weight. However, any time-at-temperature combination may be
effected to drive off the solvent as desired for a particular
application. For example, a higher line speed may be used in a
commercial off-the-shelf oven in combination with a higher oven
temperature in order to drive off the solvent. Further, the solvent
may be driven off in fewer than two stages or more than two stages
as desired for a particular application and as determined by
constraints, such as line speed, of available ovens.
[0031] At a block 112 the crosslinker is reacted with the
un-crosslinked acrylic adhesive. The reacted mixture (with the
solvent driven off) enters a third stage of an oven that has a
temperature suitably between around 320-350 degrees Fahrenheit and
preferably around 350 degrees Fahrenheit for a time period between
around 2-3 minutes. This time-at-temperature combination is based
on a typical oven stage of around 25 feet or so in length with a
line speed of around 10 feet per minute or so. In general, the
longer the time-at-temperature and the higher the temperature, the
more the increase in crosslink density and the more solvent driven
off.
[0032] It may be possible to use higher temperatures at higher line
speeds, depending on material properties of the release liner(s)
12. Time-at-temperature variations may be determined according to
reaction rate relationships to temperature (that is in general,
reaction rate doubles for every temperature increase of 10 degrees
Centigrade). For example, if desired the block 112 could be
performed in an oven stage with a line speed of around 40 feet per
minute at around 390 degrees Fahrenheit for a time of around 2-3
minutes. As another example, the block 112 could be performed in an
oven stage with a line speed of around 50 feet per minute (industry
typical line speed) at around 400 degrees Fahrenheit for a time of
around 2-3 minutes. However, some release liners, such as those
made of polyester, may tend to distort at temperatures greater than
350 degrees Fahrenheit.
[0033] While a number of exemplary embodiments and aspects have
been illustrated and discussed above, those of skill in the art
will recognize certain modifications, permutations, additions, and
sub-combinations thereof. It is therefore intended that the
following appended claims and claims hereafter introduced are
interpreted to include all such modifications, permutations,
additions, and sub-combinations as are within their true spirit and
scope.
* * * * *