U.S. patent application number 11/222210 was filed with the patent office on 2006-02-16 for release liner for pressure sensitive adhesives.
This patent application is currently assigned to 3M Innovative Properties Company. Invention is credited to Eugene G. Hennen.
Application Number | 20060035020 11/222210 |
Document ID | / |
Family ID | 25458585 |
Filed Date | 2006-02-16 |
United States Patent
Application |
20060035020 |
Kind Code |
A1 |
Hennen; Eugene G. |
February 16, 2006 |
Release liner for pressure sensitive adhesives
Abstract
A release liner for use with a pressure sensitive adhesive. The
release liner includes a film of a thermoplastic elastomeric
olefin.
Inventors: |
Hennen; Eugene G.; (Lake
Elmo, MN) |
Correspondence
Address: |
3M INNOVATIVE PROPERTIES COMPANY
PO BOX 33427
ST. PAUL
MN
55133-3427
US
|
Assignee: |
3M Innovative Properties
Company
|
Family ID: |
25458585 |
Appl. No.: |
11/222210 |
Filed: |
September 8, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
08929863 |
Sep 15, 1997 |
6982107 |
|
|
11222210 |
Sep 8, 2005 |
|
|
|
Current U.S.
Class: |
427/207.1 ;
264/130; 264/171.11; 264/230 |
Current CPC
Class: |
C09J 2415/006 20130101;
C09J 2483/005 20130101; C08L 23/12 20130101; Y10T 428/14 20150115;
Y10T 428/1471 20150115; Y10T 428/1452 20150115; C09J 2423/005
20130101; Y10T 428/1476 20150115; C09J 2423/006 20130101; C09J 7/40
20180101; C08L 23/16 20130101; Y10T 428/31667 20150401 |
Class at
Publication: |
427/207.1 ;
264/230; 264/171.11; 264/130 |
International
Class: |
B05D 5/10 20060101
B05D005/10; B27B 17/00 20060101 B27B017/00 |
Claims
1. A method for making a release liner for use with a
pressure-sensitive adhesive applied to a substrate during a heating
and cooling cycle comprising: (a) extruding a film comprising a
selected material that exhibits thermal expansion and contraction
properties similar to those exhibited by the substrate; and (b)
providing at least one release surface on the film for release of
the film from the adhesive.
2. The method of claim 1 wherein the substrate comprises
thermoplastic elastomeric olefin (TEO).
3. The method of claim 1 wherein the selected material comprises
thermoplastic elastomeric olefin (TEO).
4. The method of claim 1 wherein the selected material comprises
polyethylene.
5. The method of claim 1 wherein the material is selected by
comparing the coefficients of thermal expansion and contraction of
candidate materials with the coefficients of thermal expansion and
contraction of the substrate.
6. The method of claim 1 wherein the release surface is provided by
coating a release material onto a surface of the film.
7. The method of claim 6 wherein the release material comprises
silicone.
8. The method of claim 6 wherein the release material comprises
polyethylene.
9. A method for using a release liner comprising: (a) applying a
pressure-sensitive adhesive adhered to a release liner to a
substrate; (b) heating said substrate having the pressure-sensitive
adhesive and release liner adhered thereto; and (c) cooling said
substrate having the pressure-sensitive adhesive and release liner
adhered thereto; such that the release liner does not significantly
buckle or substantially shrink away from the pressure-sensitive
adhesive.
Description
[0001] This application is a divisional of U.S. Ser. No. 08/929863,
filed Sep. 15, 1997, now allowed, the disclosure of which is herein
incorporated by reference.
FIELD OF THE INVENTION
[0002] This invention relates to a release liner for pressure
sensitive adhesive articles.
BACKGROUND OF THE INVENTION
[0003] Currently, many pressure-sensitive adhesive tapes and other
pressure-sensitive adhesive-coated articles have a release liner
applied to the adhesive during or following manufacture. For
example, the release liner can serve as a carrier for a pressure
sensitive adhesive transfer tape or a double-coated tape, both of
which are tacky on both sides of the tape. The adhesive tape on a
release liner is typically supplied on a convolutely wound roll,
and then unwound and laminated to an article or substrate. The
release liner is typically left in place while the article is
converted, packaged, and shipped to ultimate users, and in many
instances is left in place until the article is bonded to and
adhered to another substrate with the pressure-sensitive adhesive.
Release liners are used for one or more of a number of purposes,
including, for example, preventing contamination of the adhesive
layer, facilitating handling of the adhesive-coated article (e.g.,
by providing support thereto as well as covering the adhesive),
identifying the articles to which they are applied, etc.
[0004] The type of adhesive is typically matched to the type of
release liner. For example, state-of-the-art release liners for
acrylic pressure-sensitive tapes are polyethylene or polypropylene
films. These films have been successfully used for acrylic
pressure-sensitive adhesives for many years because they do not
require a separate coating (e.g. silicones) to provide a release
surface. Silicone-coated polyester release liners are also
well-known in the art.
[0005] Conventional polyolefin-based or polyester release liners
that function well at ambient temperatures are, however, often
unsuitable for use in manufacturing processes that involve heating
and cooling a substrate after application of an adhesive tape but
before removal of the release liner. For example, during the
painting process, painted thermoplastic automobile parts are
typically exposed to temperatures of about 250.degree. F. or higher
for extended periods of time to cure the paint and then cooled. It
is often desirable to apply an adhesive tape with a release liner
to an unpainted substrate, paint the substrate and cure the paint
at high temperature, then remove the release liner after cooling.
Polyethylene release liners, however, cannot withstand high
temperatures used in paint curing ovens and can melt, shrink or
buckle during procedures that involve heating and cooling.
Silicone-coated polyester liners can withstand high temperatures,
but are also unsuitable for applications that involve thermal
cycling because they do not expand and contract at the same rate as
thermoplastic polyolefin substrates when heated and cooled, and the
polyester liners tend to pull away from the ends of the adhesive
tape upon heating or buckle upon subsequent cooling.
[0006] What is needed in the industry is a release liner for
pressure sensitive adhesives, particularly for acrylic foam tapes,
that is suitable for use in manufacturing applications that involve
heating and cooling of a substrate.
SUMMARY OF THE INVENTION
[0007] The present invention provides a release liner for pressure
sensitive adhesives articles such as single- or double-sided tapes,
films, labels, and the like. The release liner of the present
invention comprises a thermoplastic elastomeric olefin (TEO). TEO
imparts thermal stability to the liner so that it is not likely to
significantly decompose or melt when exposed to elevated
temperatures during manufacturing and processing of a typical
substrate to which it is applied. The use of TEO in the release
liner also decreases the likelihood that the liner will shrink away
significantly from the adhesive upon heating, or significantly
buckle upon cooling. The release liner of the present invention is
thus especially suitable for, although not limited to, use in
manufacturing processes conducted at elevated temperatures,
particularly those that involve heating to temperatures, such as
exposure to temperatures of about 90.degree. C. to about
150.degree. C. for periods of up to one-half hour or one hour or
more, followed by cooling to room temperature (i.e., about
20.degree. C. to about 25.degree. C.).
[0008] Preferably the release liner is a film, i.e. a sheet
material, having at least one release surface comprising a release
material such as a silicone, polyethylene, fluorocarbon, or
polypropylene. The release surface can be provided as an integral
part of the release liner, or, alternatively, in the form of a
separate release layer or coating. The release surface imparts to
the release liner the surface adhesion and release characteristics
desired in view of the adhesive to which the liner is to be
applied. It also functions to create a coherent surface to which
the pressure-sensitive adhesive can be laminated.
[0009] A preferred embodiment of the release liner comprises (i) a
TEO core and (ii) a release layer or coating comprising a release
material comprising a polyethylene, polypropylene, fluorocarbon, or
silicone. The release layer or coating provides the release surface
that contacts the adhesive. The TEO core may be composed
exclusively of a TEO, or may be a blend of TEO and one or more
other materials such as polyethylene.
[0010] In another preferred embodiment, the release liner comprises
a mixture, preferably a blend, of TEO and at least one other
material, preferably a release material such as polyethylene or
silicone, in proportions so as to provide the release surface as an
integral part of the release liner; a separate release coating or
layer is not included.
[0011] The present release liner is preferably tear-resistant. It
preferably exhibits a low release value from acrylate-based
adhesives, as described below, and has high cross web strength. A
nick or tear in the release liner of the present invention
typically will not propagate like a tear in a polyethlyene or
polypropylene liner. When present, the release coating further
reduces stress on the release liner during removal from the
adhesive.
[0012] Also provided by the invention is a method for making a
release liner for use with an adhesive applied to a substrate
during a heating and cooling cycle. The method involves fashioning
a release liner from a material that exhibits thermal expansion and
contraction properties similar to those observed for the intended
substrate. For example, the coefficients of thermal expansion and
contraction of the substrate can be measured, and an extrudable
material exhibiting similar thermal coefficients can be selected or
fabricated. A film comprising the selected material is extruded,
and at least one release surface is provided on the film for
release of the film from the adhesive. The extruded film is
thermally stable under the manufacturing or processing conditions
(e.g., a thermal cycle involving exposure to an elevated
temperature for a defined period of time) to which the intended
substrate (after application of the adhesive with liner) will be
subjected. Preferably, the intended substrate comprises a TEO, and
the release liner is also formulated from a TEO, preferably an
extrusion grade of the same TEO. In a particularly preferred
embodiment of the method of the invention, the intended substrate
is an automobile body part comprising TEO.
[0013] The present invention further provides a method for using a
release liner during heating and cooling of an intended substrate.
A release liner is adhered to a pressure sensitive adhesive, then
applied to a substrate. The substrate is exposed to elevated
temperatures for a period of time, then returned to room
temperature. The release liner does not significantly buckle or
substantially shrink away from the pressure-sensitive adhesive
during the heating or cooling processes, and preferably remains
coextensive with the pressure-sensitive adhesive after being
returned to room temperature.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0014] Preferred release liners of the invention take the form of a
film (i.e., a sheet material) comprising a thermoplastic
elastomeric olefin (TEO). As used herein, the terms release liner,
liner, release film and release sheet are interchangeable.
Thermoplastic elastomeric olefins (TEOs), also referred to in the
art as thermoplastic polyolefins (TPOs), are a class of materials
which are both thermoplastic and elastic in nature. TEO is
typically a blend of a rubbery material, such as, for example, an
ethylene propylene rubber (such as ethylene-propylene monomer [EPM]
or ethylene-propylene-diene-monomer [EPDM]), a nitrile rubber, or a
styrene butadiene rubber, with a thermoplastic (such as
polypropylene, polyethylene, or polyvinyl chloride), and is often
compounded with a variety of additives and fillers, such as carbon
black, plasticizers, antidegradants, fillers, and the like. TEO is
commercially available typically as a blend of polypropylene and
EPDM. Alternatively, the TEO can be formed by copolymerizing a
thermoplastic, for example polypropylene, with a rubbery material,
such as ethylene-propylene rubber. The rubbery material can be
either vulcanized or not vulcanized.
[0015] The relative proportion of thermoplastic, preferably
polypropylene, to rubbery material in a TEO can range from about
15% by weight thermoplastic to about 85% thermoplastic, and about
85% rubbery material to about 15% rubbery material, respectively.
The higher the amount of thermoplastic, the more brittle and the
more like a thermoplastic the TEO is. A higher amount of rubbery
material will make the TEO closer to rubber in characteristics.
TEOs are formulated to produce the desired end-use characteristics.
Accordingly, the various TEOs useful for liners in the practice of
the invention are selected so as to provide the release liner with
expansion and contraction characteristics that match or approximate
those of the substrate, preferably a TEO substrate, to which it
will be adhered.
[0016] Preferably, the TEO used in the release liner comprises from
about 30% to about 70% by weight thermoplastic, and about 70% to
about 30% rubbery material. More preferably, the TEO comprises from
about 40% to about 60% by weight thermoplastic, and about 60% to
about 40% by weight rubbery material. Particularly preferred
because of its commercial availability is a TEO comprising
polypropylene and ethylene propylene rubber. The preferred ranges
of thermoplastic to rubbery material are particularly suitable for
liners used to protect pressure-sensitive adhesive tapes on TEO
substrates such as those used in many current automotive body side
moldings.
[0017] In addition to providing the release liner with increased
stability at elevated temperatures and an improved ability to
expand and contract upon heating and contract in concert with its
intended substrate, TEO as a component of the liner can also impart
tear resistance without the use of a woven (fiber) or nonwoven
reinforcing layer. This is advantageous because the use of other
layers can limit the amount of elasticity and flexibility of the
liner, and thereby limit the uses of the pressure-sensitive
adhesive article.
[0018] TEOs useful in the practice of the invention include
commercially available TEOs such as those available under the
DEXFLEX trade name from D & S Plastics Intl. (Auburn Hills,
Mich.), those under the ALCRYN trade name available from DuPont Co.
(Wilmington, Del.), those under the MULT-FLEX trade name available
from Multibase (Copley, Ohio), and those under the POLYTROPE TPP
trade name available from A. Schulman (Akron, Ohio). The grade of
TEO is selected for the type of processing that will be used to
make the release liner, and is preferably an extrusion grade, such
as Dexflex SB-814 available from D & S Plastics Intl.
Commercially available TEOs may include other additives such
fillers, processing aids, plasticizers, and the like.
[0019] The release liner of the invention can be made by processes
that are commercially known, and available. These processes include
blown film extrusion or coextrusion for films having multiple
layers and sheet extrusion or coextrusion. The films can be made in
thicknesses of about 0.0005 inch to about 0.010 inch, and
preferably in thicknesses of about 0.001 inch to about 0.008 inch.
Generally, thinner films are desired for cost considerations, but
it may be necessary to use thicker films to obtain certain
properties such as tear resistance, tensile strength, and the
like.
[0020] Various additives may be blended into the TEO resin prior to
extrusion, or they may be added directly to the extruder. The
additives are included in typical amounts for the purpose for which
they are intended, and include fillers, colorants (e.g., dyes or
pigments), slip agents, anti-blocking agents, processing aids, and
the like.
[0021] Anti-blocking agents are particularly useful for outer
layers of polyethylene to prevent sticking or blocking between
layers of polyethylene when the extruded film is wound onto a roll.
Useful materials include diatomaceous earth either by itself, or
preferably in a low density polyethylene binder. Antiblocking
agents are typically included in amounts of from about 1% to about
20% by weight of the polyethylene resin, and preferably in amounts
of from about 3% to about 8%.
[0022] Polyethylenes are useful as processing aids to enhance the
extrusion and film flatness of TEO resins. They can optionally be
blended with the TEO to affect the release characteristics of the
film. Any type of polyethylene may be used, and low density
polyethylene and linear low density polyethylene are preferred. The
polyethylenes can be used in amounts from about 1% to 99% by
weight, and is preferably used in amounts of about 15% or
greater.
[0023] Colorants (e.g., dyes or pigments) are useful as additives
and are typically used in amounts of about 0.1% to about 5% by
weight of the film composition, and preferably from about 0.3% to
about 3%.
[0024] In one embodiment of the release liner of the invention, the
TEO is provided in a film core (referred to herein as a TEO film
core or simply TEO core) to which a release coating or layer is or
can be applied. The TEO core can be exclusively TEO (including,
optionally, additives, fillers, and the like), or, alternatively,
can be a mixture or blend of TEO and one or more other polymers
such as polyethylene. In this embodiment, it is not necessary that
the polymer with which the TEO is blended to form the TEO core be
effective to impart the desired release properties to the film
(although it may be), because the release surface is provided by
the release coating or layer. Preferably, the TEO core comprises
from about 5% by weight to about 100% by weight TEO, and more
preferably from about 10% to about 100% TEO. The selection of the
relative amounts of TEO and other polymer is determined by the end
properties needed for the release liner, e.g., tensile strength,
tear resistance, etc. The release coating (described in more detail
below) is or can be applied to one or both sides of the TEO film
core, depending upon the intended use and the release
characteristics desired. Typically, the release coating for this
embodiment is in the form of a layer that constitutes about 7% to
about 15% of the total thickness of the release liner. Where the
adhesive is present on a substrate, the TEO core and the release
coating are substantially co-extensive throughout at least that
portion of the liner which is contacted to the adhesive-coated
portion of the substrate.
[0025] In a second embodiment, the release liner of the invention
further comprises a release material such as a polyethylene,
polypropylene, fluorocarbon or silicone, in such proportion so as
to provide the release surface as an integral part of the release
liner. This is preferably achieved by mixing, preferably by
blending, a TEO with at least one other material selected to impart
the desired release properties to the TEO blend when formed into a
film; commercially available TEO typically does not itself provide
a suitable release because it adheres too strongly to the adhesive.
However, a TEO can be formulated, e.g., by varying the amount of
thermoplastic such as polyethylene or polypropylene, so as to
provide an integral release surface without the need for blending
with another release material. In this embodiment of the invention,
inclusion of a separate surface release coating or layer is
optional.
[0026] Suitable materials with which TEO can be mixed to integrate
the desired release properties into the release liner of the second
embodiment include polymers such as polyolefins, preferably
polyethylenes and polypropylenes, and copolymers of ethylene such
as ethylene vinyl acetate. Preferably, the TEO is mixed with
polyethylene. For a release liner of the second embodiment that is
particularly useful with acrylic adhesives, a polyethylene is
blended with TEO in relative amounts of about 95% to about 50% by
weight polyethylene and about 5% to about 50% by weight TEO, more
preferably about 90% to about 60% by weight polyethylene and 10% to
40% by weight TEO. The preferred blends of TEO and polyethylene
provide acceptable release properties from acrylic adhesives
without a separate release coating. As the percentage of TEO
increases, and the percentage of polyethylene decreases, the
pressure-sensitive adhesive adheres more tightly to the liner and
removal of the liner becomes more difficult. This is particularly
true if the adhesive and liner are heated at an elevated
temperature because heat tends to promote an increase in adhesion
of pressure-sensitive adhesives to liners.
[0027] Useful polyethylenes for both the first and second
embodiments include high density polyethylenes having a typical
density around 0.96 g/cc (grams/cubic centimeter), medium density
polyethylenes having a typical density of about 0.93 g/cc to about
0.94 g/cc, low density polyethylenes having densities of about 0.90
g/cc to about 0.92 g/cc, linear low density polyethylenes, and very
low density polyethylenes having densities below about 0.90 g/cc.
In general, the higher the density, the higher the release force
needed to remove the liner from a pressure-sensitive adhesive.
Lower density polyethylenes provide lower release values. The
selection of the material depends upon the desired release
properties. Polyethylenes of different densities can be blended
together, or they can be blended with ethylene co-polymers to
provide the desired properties. For example, a blend of high
density polyethylene with a low density polyethylene can be used to
make a medium density polyethylene having intermediate release
values between high and low density polyethylenes.
[0028] Another useful polyethylene for use in the TEO mixtures of
both the first and second embodiments is a very low density
polyethylene formed as a copolymer of ethylene and an alpha olefin
having from about 3 to about 10 carbon atoms using a metallocene
polymerization catalyst. Suitable alpha-olefins include butene-1,
hexene-1, octene-1, and combinations thereof. The copolymers have a
density of less than about 0.90 g/cc, preferably less than about
0.89 g/cc, and more preferably, less than about 0.88 g/cc. The
copolymers also have a narrow molecular weight distribution as
defined by having a polydispersity of about 1 to about 4, and
preferably about 1.5 to about 3.5. The polydispersity is defined as
the ratio of the weight average molecular weight to the number
average molecular weight. Additionally, the copolymers can be
characterized by a composition distribution breadth index (referred
to hereinafter as "CDBI"). The CDBI is defined as the weight
percent of the copolymer molecule having a co-monomer content
within 50 percent (i.e., .+-.50%) of the median total molar
co-monomer content. The CDBI and the method for its determination
is described in U.S. Pat. No. 5,206,075, incorporated herein by
reference. The CDBI of suitable copolymers is preferably greater
than 70% and more preferably greater than 80%. Suitable copolymers
are commercially available from Exxon Chemical Co. under the EXACT
tradename and from Dow Chemical Co. under the ENGAGE trade
name.
[0029] Release coatings or layers applied to the TEO film core in
the first embodiment preferably include a release material
comprising a polyolefin, more preferably polyethylene or
polypropylene, that imparts the desired release characteristics to
the liner. Other release materials that can be used as coatings or
outer layers with the first embodiment of the release liner include
silicones, e.g., polysiloxanes, epoxy silicones, as well as
perfluoroethers, fluorocarbons, polyurethanes, and the like.
Release materials are known and are described in various sources
including patent literature. For example, epoxy silicones are
disclosed in U.S. Pat. No. 4,822,687 (Kessel et al.), U.S. Pat. No.
5,217,805 (Kessel et al.), U.S. Pat. No. 5,576,356 (Kessel et al.),
U.S. Pat. No. 5,332,797 (Kessel, et al.); perfluoropolyethers are
disclosed in U.S. Pat. No. 4,830, 910 (Larson), fluorocarbons in a
polymer matrix are disclosed in U.S. Pat. No. 5,110,667 (Galick et
al.) and various types of silicones are described in U.S. Pat. No.
2,588,367 (Dennett), U.S. Pat. No. 3,960,810 (Chandra et al.), U.S.
Pat. No. 4,162,356 (Grenoble), U.S. Pat. No. 4,306,050 (Koerner et
al.); British Patent No. 1,375,792 (Colquhoun et al.), and German
Patent No. 2,736,499 (Hockemeyer), each of which is incorporated
herein by reference. Commercially available release materials are
available from various suppliers such as General Electric Co.
(Albany, N.Y.), Dow Corning under to SYL-OFF tradename, (Midland,
Mich.), Wacher Chemie (Germany), and Th. Goldschmidt AC (Germany).
Coatings are commercially available from Akrosil (Menasha, Wis.),
and Daubert (Willowbrook, Ill.).
[0030] Release materials can be applied to the TEO core as solvent
or water-based coatings, solventless coatings, hot melt coatings,
or they can be co-extruded with the TEO core using conventional
processes. Solvent and water-based coatings are typically applied
to the TEO core by processes such as roll coating, knife coating,
curtain coating, gravure coating, wound rod coating, and the like.
The solvent or water is then removed by drying in an oven, and the
coating is optionally cured in the oven. Solventless coatings
include 100% solids compositions such as silicones or epoxy
silicones which are coated onto the TEO by the same types of
processes used for solvent coating, and then cured by exposure to
ultraviolet light. Optional steps include priming the TEO before
coating or surface modification of the TEO such as with corona
treatment. Hot melt coatings such as polyethylenes or
perfluoroethers are 100% solids coatings which are heated and then
applied through a die or with a heated knife. Hot melt coatings are
preferably applied by co-extruding the release material with the
TEO core in blown film or sheet extruder for ease of coating and
for process efficiency.
[0031] The TEO core can be coated on one or both sides to provide a
release liner of the first embodiment. The amount of release force,
e.g., the force required to remove the liner from the adhesive, can
range from almost zero to about 60 ounces per inch width (oz/in).
When the release force is on the higher end of the range, i.e.,
above about 50 oz/in, it is difficult to start removal of the liner
as well as to continue removal of the liner once a part of the
liner has been removed from the adhesive. With high removal forces,
the liner can tear or the adhesive may be pulled away from the
intended substrate causing distortion or wrinkling of the adhesive
and adversely affecting the adhesive holding power. The lower end
of the removal force range, e.g., less than about 5 oz/in is
typically known as the "premium release" and these values are
usually obtained with silicone coatings. At times, premium release
may not be desired if the liner releases too easily and pops off of
the adhesive to expose the adhesive to dirt and other
contamination. Release values of about 15 to about 45 oz/in are
suitable for most applications so that the liner adheres well
enough to the adhesive to avoid popping off while remaining easily
removable.
[0032] The release surface of the release liner of the invention
thus preferably exhibits a release value of less about 60 oz./inch,
more preferably less than about 45 oz./inch, most preferably less
than about 30 oz./inch, as measured in the Release Force Test
Method described below. Where the release material comprises a
silicone, the release value of the release surface of the liner is
preferably less than about 10 oz./inch, more preferably less than
about 5 oz/inch.
[0033] When both sides are coated, the coatings on each side may be
the same or they may be different to provide a differential
release. For differential release, the release liner will have a
higher release force on one side than the other. For example, one
side of a release liner may be coated with a silicone release
material having a release force from a pressure sensitive adhesive
of 10 ounces/inch (oz/in) and the other side may have a silicone
release material having a release force of 20 oz/in. This ensures
that the adhesive will adhere more tightly to one side of the liner
than the other so that when a roll of tape is unwound, the adhesive
consistently stays on the same side of the release liner.
[0034] The liner of the invention is useful for any type of
pressure-sensitive adhesive used in the industry. This includes
pressure-sensitive adhesives based on acrylate or acrylics,
polyesters, silicones, block copolymers, ethylene vinyl acetate,
and the like. The selection of the release surface will depend upon
the type of pressure-sensitive adhesive to which it is adhered. For
example, release surfaces of polyethylene, polypropylene,
perfluoroethers, and silicone are useful with acrylate
pressure-sensitive adhesives, and perfluoroethers are useful for
silicone pressure-sensitive adhesives.
[0035] Useful pressure sensitive adhesives in the practice of this
invention include acrylic adhesives, natural rubber adhesives,
tackified block copolymer adhesives, polyvinyl acetate adhesives,
ethylene vinyl acetate adhesives, silicone adhesives, polyurethane
adhesives, thermosettable pressure-sensitive adhesives such as
epoxy acrylate or epoxy polyester pressure-sensitive adhesives, and
the like. These types of pressure-sensitive adhesives are known in
the art and are described in the Handbook of Pressure Sensitive
Adhesive Technology, Satas (Donatas), 1989, 2.sup.nd edition, Van
Nostrand Reinhold, as well as the patent literature. The pressure
sensitive adhesives may also include additives such as
cross-linking agents, fillers, gases, blowing agents, glass or
polymeric microspheres, silica, calcium carbonate fibers,
surfactants, and the like. The additives are included in amounts
sufficient to effect the desired properties.
[0036] The release liner of the invention is preferably used with a
heat-stable, pressure-sensitive, adhesive. Heat stable,
pressure-sensitive adhesives include acrylate pressure-sensitive
adhesives such as, for example those described in Re 24906
(Ulrich), U.S. Pat. No. 4,181,752 (Martens et al.), U.S. Pat. No.
4,818,610 (Zimmerman et al.) and silicone pressure-sensitive
adhesives. The adhesives can be prepared by any of the known
methods including emulsion polymerization, solvent polymerization,
e-beam polymerization, ultraviolet light polymerization, and the
like. Typically, acrylate adhesives are homopolymers and copolymers
of monofunctional unsaturated acrylic or methacrylic acid ester
monomers of non-tertiary alcohols having from about 1 to about 20
carbon atoms, and preferably from about 4 to about 12 carbon atoms.
A co-monomer may optionally be included to improve the cohesive
strength of the adhesive. Such reinforcing co-monomers useful in
making the copolymers typically have a higher homopolymer glass
transition temperature than the glass transition temperature of the
acrylic acid ester homopolymer.
[0037] Suitable acrylic acid ester monomers include 2-ethylhexyl
acrylate, isooctyl acrylate, isononyl acrylate, n-butyl acrylate,
decyl acrylate, dodecyl acrylate, octadecyl acrylate, and mixtures
thereof. Preferred monomers include isooctyl acrylate, n-butyl
acrylate, and mixtures thereof.
[0038] Useful reinforcing co-monomers include acrylic acid,
methacrylic acid, itaconic acid, acrylamide, substituted
acrylamides, N-vinyl pyrrolidone, N-vinyl caprolactam, isobornyl
acrylate, and cyclohexyl acrylate. Preferred co-monomers include
acrylic acid, N-vinyl caprolactam, and isobornyl acrylate.
[0039] In a typical process to make pressure sensitive adhesive
transfer tapes, an adhesive composition is coated onto a release
liner. The adhesive is then cured to form a gelled film on the
liner, and the release liner with the adhesive is rolled up into a
large roll. Alternatively, the adhesive may be coated and cured on
one liner, and then transferred onto a different liner before
converting. The adhesive coated sheet is then converted into narrow
rolls by slitting the large roll and winding the narrow width tape
onto cores for customer use. The liners of the invention can also
be used with foam tapes such as 5605 and 5344 Acrylic Foam Tapes
available from Minnesota Mining & Manufacturing Co. (St. Paul,
Minn.), as well as double coated tapes.
[0040] The release liner of the invention is preferably thermally
stable (i.e., stable to heat), that is, it retains structural
integrity insofar as it will not melt or decompose significantly at
elevated temperatures used in the manufacturing or processing of an
intended substrate. A preferred release liner retains structural
integrity when exposed to temperatures of about 90.degree. C., more
preferably about 120.degree. C., most preferably about 150.degree.
C., for a period of about 20 minutes, more preferably for a period
of about one-half hour, most preferably for a period of about one
hour.
[0041] The release liner of the invention preferably exhibits
substantially no shrinking or buckling when brought to room
temperature after being exposed to an elevated temperature for an
extended period of time. A preferred liner exhibits substantially
no shrinking or buckling when brought to room temperature (i.e.,
about 20-25.degree. C.) after being exposed to a temperature of
about 90.degree. C., more preferably about 120.degree. C., most
preferably about 150.degree. C., for a period of about one-half
hour, more preferably about one hour. Shrinking and buckling can be
avoided by selecting a release liner having thermal expansion and
contraction coefficients substantially similar to those of the
intended substrate. The coefficients of thermal expansion and
contraction of the release liner are preferably within at 10% of
the thermal expansion and contraction coefficients of the intended
substrate or article to which an adhesive film comprising the liner
is applied.
[0042] Although preferred embodiments of the release liner of the
invention are thermally stable, tear-resistant, and/or exhibit
substantially no shrinking or buckling when brought to room
temperature after being exposed to an elevated temperature for an
extended period of time, it is to be understood that the present
invention is not to be unnecessarily limited. Accordingly, any
release liner for use with a pressure sensitive adhesive, which
release liner comprises a TEO, is within the scope of the present
invention.
[0043] The following non-limiting examples further illustrate the
present invention. Unless otherwise indicated, the following test
procedures were used in the examples. The particular materials and
amounts thereof recited in these examples, as well as other
conditions and details, are to be interpreted to apply broadly in
the art and should not be construed to unduly restrict or limit the
invention in any way.
Test Methods
Release Force
[0044] Samples are prepared by laminating the release side or
surface of the liner to the adhesive side of a pressure-sensitive
adhesive tape (5344 Acrylic Foam Tape Minnesota Mining &
Manufacturing Co., St. Paul, Minn.) using a hand roller to
eliminate air pockets. The other side of the tape is protected with
a standard polyethylene release liner. Strips measuring 2.54 cm
wide by 17.8 cm long are cut and then aged for 3 days at room
temperature (about 20-25.degree. C.) and tested, or aged at
70.degree. C. for 7 days and tested. To test, the standard
polyethylene liner is removed and the adhesive tape is laminated to
the bed of an IMASS Adhesion Tester (Imass Inc. Hingham, Mass.).
The liner is then pulled away from the adhesive at a 180 degree
angle and a speed of 30 cm/minute. The force required to remove the
liner is reported in ounces/inch (oz/in).
Tear Resistance
[0045] A 5.08 cm by 15.24 cm sample of the liner is cut with the
5.08 cm dimension being the minor axis and the 15.24 dimension
being the major axis. The major axis is the test direction (downweb
or crossweb). A 1.9 cm notch is cut from one edge at the middle of
the minor axis and parallel to the major axis of the sample. The
sample is placed in an INSTRON Tensile Tester (Instron Corp,
Canton, Mass.) having a 2.54 cm jaw separation such that the notch
is positioned in line with the jaws. The jaws are separated at a
speed of 19.7 cm per minute and the average force required to tear
the sample is recorded. Samples are run in both the downweb
direction and the crossweb direction. The test results are recorded
in pounds.
Expansion and Contraction on a TEO Substrate
[0046] The substrate used in this example is an injection molded
thermoplastic polyolefin (DEXFLEX 777, D & S Plastics Intl.,
Auburn Hills, Mich.) body side molding obtained from Lexamar (Boyne
City, Mich.). The molding is about 4 feet in length. The release
liner is laminated to an adhesive tape (5344 Acrylic Foam Tape),
and a 32 inch long strip of adhesive tape with the release liner is
applied to the molding. The molding is then heated at 149.degree.
C. for 30 minutes, and then cooled to room temperature. The liner
is examined for wrinkling or buckling, and whether or not the liner
has shrunk and left exposed adhesive at the ends of the tape.
EXAMPLE 1
[0047] A film was prepared by extruding a blend of 85 parts of TEO
(thermoplastic elastomeric olefin) and 15 parts of LLDPE (linear
low density polyethylene), and about 1 part of a red pigment
(PM4532 available from Techmer, Clinton, Tenn.) to a thickness of
0.153 mm thick using a blown film extruder. The TEO was a
thermoplastic polyolefin having fillers and constituting a 50/50
blend of polypropylene and EPDM (ethylene propylene diene monomer).
It was obtained as DEXFLEX SB-814 from D&S Plastics Intl. (now
Solvay Engineered Plastics, Auburn Hills, Mich.). The LLDPE was a
linear low density polyethylene available as ESCORENE LD117.85 from
Exxon Chemical Co. (Houston, Tex.). The blown film extruder was run
to achieve sufficiently high melt flow temperatures to provide a
uniform flat film. Extruder temperatures ranged from about
177.degree. C. to about 205.degree. C. The film was then coated on
each side with ultraviolet cured silicone compositions available
from Akrosil to make a release liner. Specifically, one side of the
composite was coated with H2C (Akrosil), which has a low release
value, and the other side was coated with H3B (Akrosil), which has
a higher release value. The release liner was tested for release
force on the H3B side. The release force after 3 days at room
temperature (about 20-25.degree. C.) was 0.96 oz/inch, and after 7
days at 70.degree. C., the release force was 2.3 oz/inch. The liner
was tested for expansion and contraction on a TEO substrate as
described in the Test Methods above. It did not exhibit any visible
shrinkage or wrinkling.
EXAMPLE 2
[0048] A 0.153 mm thick film composite was prepared by coextruding
0.127 mm of TEO (DEXFLEX SB-814) having about 1% red pigment
(PM4532) as a core, 0.013 mm of LDPE (low density polyethylene) on
one surface of the TEO, and 0.013 mm of MDPE (medium density
polyethylene) on the other surface of the TEO, on a blown film
extruder. The low density polyethylene had a density of 0.92 g/cc
and was obtained under the tradename PETROTHENE NA353 from Quantum
Chemical Corp (Cincinnati, Ohio). The medium density polyethylene
had a density of about 0.93 g/cc and was a blend of 33 parts by
weight LDPE (PETROTHENE NA353) and 67 parts high density
polyethylene having a density of 0.96 g/cc. It was obtained under
the tradename PETROTHENE LT6180 from Quantum Chemical Corp. The
medium and low density polyethylenes provided differential release
surfaces for an acrylate pressure-sensitive adhesive. The release
liner was tested for tear strength. The liner had a machine
direction tear strength of 0.5 pounds and a cross direction tear
strength of 4.9 pounds. The liner was tested for expansion and
contraction on a TEO substrate as described in the Test Methods
above. It did not exhibit any visible shrinkage or wrinkling.
EXAMPLES 3-6
[0049] A release liner was prepared by blending TEO (DEXFLEX
SB-814), with varying amounts of a low density polyethylene as
shown in Table 1, and forming a 0.153 mm thick film using a blown
film extruder. The TEO was colored with a carbon black pigment. The
polyethylene was DOWLEX 2045 which is a linear low density
polyethylene having a density of 0.92 g/cc and a narrow molecular
weight distribution. The liners were tested for release force as
described above except that the samples were aged in an oven at
121.degree. C. for 30 minutes and cooled to room temperature before
testing. The release values are shown in Table 1. The data show
that in the preferred ranges of TEO and polyethylene (Examples 5
and 6), acceptable release values (i.e., under about 40 oz/inch)
are obtained. All of the liners were tested for expansion and
contraction on a TEO substrate using the Test Method described
above. None of them exhibited any visible shrinkage or wrinkling.
TABLE-US-00001 TABLE 1 TEO/LDPE Blends Example Parts TEO Parts LDPE
Release Force oz/in 3 80 20 55.4 4 60 40 65.2 5 20 80 39.4 6 10 90
29.1
[0050] The complete disclosure of all patents, patent documents,
and publications cited herein are incorporated by reference. The
foregoing detailed description and examples have been given for
clarity of understanding only. No unnecessary limitations are to be
understood therefrom. The invention is not limited to the exact
details shown and described, for variations obvious to one skilled
in the art will be included within the invention defined by the
claims.
* * * * *