US006982107B1
`
`(12) United States Patent
`Hennen
`
`(10) Patent N0.:
`(45) Date of Patent:
`
`US 6,982,107 B1
`Jan. 3, 2006
`
`(54) RELEASE LINER FOR PRESSURE
`SENSITIVE ADHESIVES
`
`(75)
`
`Inventor: Eugene G_ Hennen’ Lake Elmo’ MN
`(US)
`
`5,589,434 A * 12/1996 Takahara et al. .......... .. 503/227
`5,663,116 A *
`9/1997 Kamimura et al.
`....... .. 503/227
`5,691,022 A
`11/1997 Knauf
`
`428/532
`..
`5,700,571 A * 12/1997 Logue et al.
`.............. .. 428/418
`5,728,469 A *
`3/1998 Mann et al.
`5,840,783 A * 11/1998 Momchilovich et al.
`522/412
`
`(73) Assigneez 3M Innovative Properties Company’
`St. Paul, MN (US)
`
`....... .. 428/195
`5,972,480 A * 10/1999 Yoshikawa et al.
`FOREIGN PATENT DOCUMENTS
`
`( * ) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`use 154(b) by 925 days
`
`(21) APP1- N04 03/929,363
`
`(22)
`
`Filed:
`
`Sep. 15, 1997
`
`JP
`JP
`W0
`wo
`
`02175776
`XP 002087319
`WO 93/11933
`wo 94/16885
`
`7/1990
`12/1993
`6/1993
`8/1994
`
`OTHER PUBLICATIONS
`
`Handbook ofPressare SensitiveAa'hesive Technology, Satas
`g]§§n6a82(1)s), 1989, 2nd edition, Van Nostrand Reinhold, pp.
`<41-hernloplastic
`E1aSt0InerS:a Handbook
`of Plastics
`Elastomers and Composites 3,“ Edition: CharlesA Harper)
`Ed‘; MCGMWOHHL New York; Chapter 5, pp. 5.15.44
`(1996).
`J.A. Brydson in Plastics Materials, 6”“ Edition; Butterworth
`H'
`:OfdEld'
`.251252291292
`ememann
`X or ’
`Hg an ’ pp
`’
`’
`’
`’
`856-858 (1995).
`Polymer Technology Dictionary, 15‘ Edition; T. Whelan,
`Consultant; Chapman & Hall: London; pp. 125, 126, 378,
`438-443 (1994).
`D&S Plastics Int’l, Technical Data Sheets (DEXFLEX E-
`1501 and DEXFLEX SB814).
`
`* cited by examiner
`
`Primary Examiner—Harold Pyon
`Assistant Examiner—Alicia Chevalier
`
`(74) Attorney, Agent, or Firm—Lisa P. Fulton
`
`(57)
`
`ABSTRACT
`
`A release liner for use with a pressure sensitive adhesive.
`The release liner includes a film of a thermoplastic elasto-
`meric olefin.
`
`51 Claims, N0 Drawings
`
`(51)
`
`Int Cl
`B373 37/00
`U.S. C].
`. . . . . . . . . . . . . . . . . ..
`
`(2006.01)
`
`428/418; 428/446; 428/451
`(58) Field of Classification Search ............. .. 428/40.1,
`428/413, 41.7, 41.8, 446, 451
`See application file for Complete Search history:
`References Cited
`U.S. PATENT DOCUMENTS
`
`(56)
`
`..................... .. 260/13
`3/1952 Dennett
`12/1960 Ulrich . . . . . . . . . . . .
`. . . . .. 206/59
`6/1976 Chandra et al.
`260/46.5
`7/1979 Grenoble . . . . .
`. . . . .. 528/31
`1/1980 Martens et al.
`427/54.1
`.
`12/1981 Koerner et al.
`. . . . . .. 528/26
`. . . . .
`7/1982 Shibano et al.
`............. .. 428/40
`4/1989 Zimmerman et al.
`..... .. 428/345
`4/1989 Kessel et al.
`428/447
`5/1989 Larson ......... ..
`428/336
`5/1992 Galick et al.
`428/202
`12/1992 Johnson et al.
`428/40
`.
`1/1993 Johnson et al.
`............. .. 428/40
`4/1993 Hodgson, Jr.
`............. .. 428/216
`6/1993 Kessel et al.
`............. .. 428/352
`6/1993 Epple et al.
`............... .. 528/27
`7/1994 Kessel et al.
`11/1996 Leir et al. ................... .. 522/31
`
`
`
`2,588,367 A
`RE24,906 E
`3,960,810 A
`4,162,356 A
`4,181,752 A
`4,306,050 A
`4,339,485 A
`4,818,610 A
`4,822,687 A
`4,830,910 A
`5,110,667 A
`5,167,995 A
`5,178,924 A
`5,206,075 A
`5,217,805 A
`5,221,394 A
`5,332,797 A
`5,576,356 A
`
`Page 1 of 10
`
`BOREALIS EXHIBIT 1058
`
`Page 1 of 10
`
`BOREALIS EXHIBIT 1058
`
`

`
`1
`RELEASE LINER FOR PRESSURE
`SENSITIVE ADHESIVES
`
`FIELD OF THE INVENTION
`
`US 6,982,107 B1
`
`2
`SUMMARY OF THE INVENTION
`
`This invention relates to a release liner for pressure
`sensitive adhesive articles.
`
`BACKGROUND OF THE INVENTION
`
`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, pack-
`aged, 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.
`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 polypro-
`pylene 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.
`
`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° 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. Sili-
`cone-coated polyester liners can withstand high tempera-
`tures, 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.
`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.
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`Page 2 of 10
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`The present invention provides a release liner for pressure
`sensitive adhesive 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 adhe-
`sive 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° C. to about 150° C. for periods
`of up to one-half hour or one hour or more, followed by
`cooling to room temperature (i.e., about 20° C. to about 25°
`C.).
`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.
`
`Apreferred embodiment of the release liner comprises
`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 pro-
`vides 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.
`In another preferred embodiment, the release liner com-
`prises a mixture, preferably a blend, of TEO and at least one
`other material, preferably a release material such as poly-
`ethylene 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.
`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.
`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 process-
`
`Page 2 of 10
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`

`
`US 6,982,107 B1
`
`3
`
`ing 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 adhe-
`sive 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 auto-
`mobile body part comprising TEO.
`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.
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`DETAILED DESCRIPTION OF PREFERRED
`EMBODIMENTS
`
`Preferred release liners of the invention take the form of
`
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`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 interchange-
`able. 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 polypropy-
`lene, 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 vul-
`canized or not vulcanized.
`
`thermoplastic, preferably
`The relative proportion of
`polypropylene, to rubbery material in a TEO can range from
`about 15% by weight thermoplastic to about 85% thermo-
`plastic, 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 thermo-
`plastic the TEO is. Ahigher 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.
`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 com-
`mercial availability is a TEO comprising polypropylene and
`ethylene propylene rubber. The preferred ranges of thermo-
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`4
`plastic 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.
`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.
`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.
`
`The release liner of the invention can be made by pro-
`cesses that are commercially known, and available. These
`processes include blown film extrusion or coextrusion for
`films having multiple layers and sheet extrusion or coextru-
`sion. 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.
`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 pur-
`pose for which they are intended, and include fillers, colo-
`rants (e.g., dyes or pigments), slip agents, anti-blocking
`agents, processing aids, and the like.
`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 poly-
`ethylene 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%.
`Polyethylenes are useful as processing aids to enhance the
`extrusion and film flatness of TEO resins. They can option-
`ally be blended with the TEO to affect the release charac-
`teristics of the film. Any type of polyethylene may be used,
`and low density polyethylene and linear low density poly-
`ethylene 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.
`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%.
`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
`
`Page 3 of 10
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`Page 3 of 10
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`

`
`US 6,982,107 B1
`
`5
`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. When the adhesive is
`
`present on a substrate, the TEO core and the release coating
`are substantially co-extensive throughout at least that por-
`tion of the liner which is contacted to the adhesive-coated
`
`portion of the substrate.
`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, prefer-
`ably 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 inven-
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`tion, inclusion of a separate surface release coating or layer
`is optional.
`Suitable materials with which TEO can be mixed to
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`
`integrate the desired release properties into the release liner
`of the second embodiment include polymers such as poly-
`olefins, 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 per-
`centage 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.
`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 polyethyl-
`enes having densities of about 0.90 g/cc to about 0.92 g/cc,
`
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`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 adhe-
`sive. Lower density polyethylenes provide lower release
`values. The selection of the material depends upon the
`desired release properties. Polyethylenes of different densi-
`ties 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.
`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 copoly-
`mers 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 distribu-
`tion 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 con-
`tent. 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.
`
`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 characteris-
`tics 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, polyure-
`thanes, 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.); perfiuoropolyethers are disclosed
`in U.S. Pat. No. 4,830,910 (Larson), fiuorocarbons 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 trade-
`name, (Midland, Mich.), Wacher Chemie (Germany), and
`
`Page 4 of 10
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`Page 4 of 10
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`US 6,982,107 B1
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`7
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`Th. Goldschmidt AC (Germany). Coatings are commercially
`available from Akrosil (Menasha, Wis.), and Daubert (Wil-
`lowbrook, Ill.).
`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 coat-
`ings are typically applied to the TEO core by processes such
`as roll coating, knife coating, curtain coating, gravure coat-
`ing, 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 sili-
`cones 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.
`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 remov-
`able.
`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.
`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.
`
`10
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`15
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`20
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`25
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`30
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`35
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`40
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`45
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`50
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`55
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`60
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`65
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`8
`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 sur-
`faces of polyethylene, polypropylene, perfluoroethers, and
`silicone are useful with acrylate pressure-sensitive adhe-
`sives, and perfluoroethers are useful for silicone pressure-
`sensitive adhesives.
`
`Useful pressure sensitive adhesives in the practice of this
`invention include acrylic adhesives, natural rubber adhe-
`sives,
`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 poly-
`ester 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'” edition, Van Nos-
`trand 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.
`The release liner of the invention is preferably used with
`a heat-stable, pressure-sensitive, adhesive. Heat stable, pres-
`sure-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 adhe-
`sives 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 rein-
`forcing co-monomers useful
`in making the copolymers
`typically have a higher homopolymer glass transition tem-
`perature than the glass transition temperature of the acrylic
`acid ester homopolymer.
`Suitable acrylic acid ester monomers include 2-ethylhexyl
`acrylate, isooctyl acrylate, isononyl acrylate, n-butyl acry-
`late, decyl acrylate, dodecyl acrylate, octadecyl acrylate, and
`mixtures thereof. Preferred monomers include isooctyl acry-
`late, n-butyl acrylate, and mixtures thereof. Useful reinforc-
`ing 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.
`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 transfer