U.S. patent application number 13/035205 was filed with the patent office on 2011-06-23 for release liner.
Invention is credited to Daniel Berg.
Application Number | 20110152459 13/035205 |
Document ID | / |
Family ID | 43617262 |
Filed Date | 2011-06-23 |
United States Patent
Application |
20110152459 |
Kind Code |
A1 |
Berg; Daniel |
June 23, 2011 |
Release Liner
Abstract
The present invention is a release liner including a film formed
of a thermoplastic polymer and a non-migratory silicone additive.
The additive is formed with a siloxane polymer that can be added
directly to the thermoplastic polymer prior to compounding the
thermoplastic polymer into an extrudable release liner film. The
additive provides the desired release properties to the film, and
due to bonds formed between the siloxane polymer and a binding
component added to the siloxane polymer during formation of the
additive, as well as the high molecular weight of the siloxane
polymer, is non-migratory.
Inventors: |
Berg; Daniel; (Elm Grove,
WI) |
Family ID: |
43617262 |
Appl. No.: |
13/035205 |
Filed: |
February 25, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12138757 |
Jun 13, 2008 |
7897666 |
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13035205 |
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60944200 |
Jun 15, 2007 |
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Current U.S.
Class: |
525/106 ;
525/474 |
Current CPC
Class: |
C08K 9/06 20130101 |
Class at
Publication: |
525/106 ;
525/474 |
International
Class: |
C08L 83/07 20060101
C08L083/07; C08L 23/12 20060101 C08L023/12 |
Claims
1. A non-migratory additive for a release liner, the additive
consisting essentially of: a) polydiorganosiloxane compound; b) a
binding agent bound to the polydiorganosiloxane compound by
hydrogen and covalent bonds formed during the formation of the
additive; and c) optionally one or more additional ingredients
selected from the group consisting of fillers, cure agents,
lubricants, ultraviolet light stabilizers, antioxidants, catalyst
stabilizers, flame retardants, antiblock agents, and combinations
thereof.
2. The additive of claim 1, wherein the binding agent is selected
from the group consisting of: fumed silica, a silicone resin
including at least one non-functionalized hydroxyl group, an acid
containing at least one non-functionalized hydroxyl group and
combinations thereof.
3. The additive of claim 1, wherein the binding agent is an organic
or an inorganic acid having at least one non-functionalized
hydroxyl group.
4. The additive of claim 1, wherein the binding agent is an
inorganic acid having at least one non-functionalized hydroxyl
group, that is not boric acid.
5. The additive of claim 1, wherein the binding agent is an MQ
resin.
6. The additive of claim 1, wherein the polydiorganosiloxane
compound has a molecular weight of at least 60,000 amu.
7. The additive of claim 7, wherein the polydiorganosiloxane
compound has a molecular weight of between about 75,000 amu and
2,000,000 amu.
8. The additive of claim 1, wherein the polydiorganosiloxane
compound has a viscosity of at least 50 Pas.
9. The additive of claim 9, wherein the polydiorganosiloxane
compound has a viscosity of at least 60 Pas.
10. The additive of claim 1, wherein the polydiorganosiloxane
compound has at least one side chain selected from the group
consisting of: C1-C60 alkyl groups, aromatic rings, hydrogen,
hydroxyl groups, vinyl groups and phenyl groups.
11. A release liner composition comprising: a) approximately 100
parts by weight of a thermoplastic polymer; b) 0.01-20 parts by
weight of a non-migratory additive consisting essentially of a
polydiorganosiloxane compound and a binding agent bound to the
polydiorganosiloxane compound by hydrogen bonds formed during the
formation of the additive; and c) optionally 0.001 to 120 parts of
other known process aids such as fillers, pigments, process aids,
stabilizers and melt flow modifiers.
12. The release liner composition of claim 11, wherein the binding
agent is selected from the group consisting of: fumed silica, a
silicone resin including at least one non-functionalized hydroxyl
group, an acid containing at least one non-functionalized hydroxyl
group and combinations thereof.
13. The additive of claim 1, wherein the binding agent is an
organic or an inorganic acid having at least one non-functionalized
hydroxyl group.
14. The additive of claim 1, wherein the binding agent is an
inorganic acid having at least one non-functionalized hydroxyl
group, that is not boric acid.
15. A method for forming a release liner comprising the steps of:
a) providing a thermoplastic polymer, a non-migratory additive
consisting essentially of a polydiorganosiloxane compound and a
binding agent bound to the polydiorganosiloxane compound by
hydrogen and covalent bonds formed during the formation of the
additive, and optionally other known process aids such as fillers,
pigments, process aids, stabilizers and melt flow modifiers; b)
compounding the thermoplastic polymer, the non-migratory additive,
and optionally other known process aids into a release liner
composition; and c) extruding the release liner composition into a
liner film.
16. A method for forming a release liner additive comprising the
steps of: a) providing a polydiorganosiloxane compound, a binding a
binding agent bound to the polydiorganosiloxane compound by
hydrogen and covalent bonds formed during the formation of the
additive, and optionally other known process aids such as fillers,
pigments, process aids, stabilizers and melt flow modifiers; b)
compounding the polydiorganosiloxane compound, the binding
component and optionally the other known process aids into an
additive composition.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority as a continuation of U.S.
Non-Provisional application Ser. No. 12/138,757, filed on Jun. 13,
2008, now U.S. Pat. No. 7,897,666, which claims priority from U.S.
Provisional Patent Application Ser. No. 60/944,200, filed on Jun.
15, 2007, which are each incorporated by reference herein in their
entirety.
FIELD OF THE INVENTION
[0002] The present invention relates to release liners, and more
specifically to a release liner formed with a non-migratory, ultra
high molecular weight silicone component.
BACKGROUND OF THE INVENTION
[0003] Release liners are films or papers used for the release from
adhesives, adhesive laminate constructions, or mastics in
industrial operations. The term release liner is also used for
films and papers that are used to cover and subsequently release
from various objects, materials or parts, such as in molding
operations or when handing certain types of materials. However,
even though they are viable for this particular application, these
types of release liners are used quite differently from those
liners used in covering adhesives. Consequently, release liners
used to cover various parts and objects, as opposed to adhesives,
have very different performance criteria, which are generally much
less stringent than those criteria applicable to liners used to
cover adhesives. For example, many of the release liners used to
cover various parts and objects are not sensitive to migration or
adhesive release levels, as the liners do not contact an adhesive
on the part or object to which they are secured.
[0004] With respect to those release liners used to cover and
protect adhesives, "release level" and "release profile" are
collective terms used to describe the behavior of the adhesive and
release liner assessed by a number of test criteria used in
measuring the tension needed to pull an adhesive away from the
release liner. Most release liners must have some tension or
adherence to the adhesive against which they are applied to keep
the liner in position over the adhesive, and yet should be able to
be pulled off of the adhesive at the correct speed and force to
function properly. The release tension profile for a release liner
is a very complex phenomenon.
[0005] For liners that are to be used in adhesive constructions,
the release liner industry commonly uses silicone release coatings
applied over polymeric film substrates to generate liner stock.
Polyethylene terepthalate, polyethylene and polypropylene are
common polymer film substrates for these liners, preferred grades
of which are commonly known in the art. To coat these polymeric
films with the silicone coating, the polymeric film must normally
be corona-treated or ozone treated after it has been formed in an
extrusion process to facilitate the bonding of the silicone coating
to the substrate. The polymeric film is then coated with the
silicone composition and cured in a suitable manner before it can
be used as a release liner in a laminate assembly. Common curing
methods include subjecting the silicone coating to infrared
radiation, electron beam radiation, UV radiation or heated forced
air to produce a dry stable silicone coated surface that will
function to control the release of adhesives.
[0006] In addition to the silicone coating and curing steps being
highly capital cost intensive with high operation and maintenance
costs, one significant issue with the process of forming release
liners in this manner is that the step of coating and subsequently
curing the silicone composition onto the polymeric film introduces
a wide array of variables that can detrimentally affect the proper
adhesion and the correct release levels of the final film. More
particularly, the release liner must be formed with the polymeric
substrate and silicone coating to have a good subsequent release,
i.e., the adhesive covered by the liner must have good adhesive
strength after the laminate including the adhesive has been aged
and released from the liner. A common problem that arises in the
use of liners including the silicone coating applied in this manner
is the migration of loose silicone fluid, usually in the form of
uncured silicone polymer or residual oils and process fluids, from
the liner onto the adhesive. As a result of this migration, the
re-adhesion of the adhesive to an object other than the liner is
significantly reduced.
[0007] The prior art includes a number of examples of silicone
materials compounded into thermoplastic resins that produce a
variety of properties. For example, U.S. Pat. Nos. 5,708,084 and
5,708,085 teach polyolefin compositions which can be extruded at
relatively high rates to provide extrudate having increased
hydrophobicity, said compositions comprising (A) 100 parts by
weight of a thermoplastic resin; (B) 1 to 5 parts by weight of an
interactive diorganopolysiloxane process aid, said
diorganopolysiloxane having a number average molecular weight of at
least 10,000. However, in these references, the description
includes discussion of how the siloxane migrates to the surface of
the plastic material, creating the desirable properties for the
composition disclosed ion those references, which is directly
opposite to the requirements for a release liner to be utilized on
adhesives.
[0008] In addition, U.S. Pat. No. 6,080,489 discloses such a
composition that exhibits surprisingly improved properties, such as
having reduced coefficient of friction, consistent coefficient of
friction over time, increased hydrophobicity and improved abrasion
resistance. The composition includes (A) 100 parts by weight of a
thermoplastic resin; (B) at least 0.5 parts by weight of a siloxane
blend having both a high molecular weight (Mw) siloxane and a low
Mw siloxane, where the high Mw siloxane has a viscosity greater
then the low Mw siloxane. The blend of siloxanes disclosed provides
the increased beneficial characteristics for the resulting products
formed from the material. However, as with the previous references,
other than the variation of the composition of the siloxane blend,
there is nothing disclosed in the composition that effectively
prevents the siloxanes from migrating to the surface of the
product.
[0009] As a result, with the compositions disclosed in these
references, migration of the composition may still occur because
there is nothing to tether it into the polymer matrix. For this
reason, the silicone additive concentrates disclosed in these
references are not suitable for and have not found widespread use
in commercial release liner films.
[0010] In U.S. Pat. No. 7,105,233, this reference teaches the use
of organo-modified siloxanes for use as a surface modifier additive
for polyolefin films which can be employed as a release liner.
However, this composition also suffers from potential migration of
the siloxane to the surface of the film because the siloxane is
only embedded into the composition through the use of mechanical
shearing forces prior to an extrusion process, and is not
intertwined or otherwise bound in any manner into the system. Thus,
the siloxane additive can migrate and subsequently interfere with
re-adhesion of an adhesive. Additionally, the siloxanes of this
invention contain Si--O--C bonds which are susceptible to
hydrolytic degradation, further reducing adhesive performance
stability over time.
[0011] As a result, each of these alternative silicone additive
compounds has certain problems associated with it, for example,
difficulties in adequately locking or binding the particular
silicone compound in the polymer forming the liner, the costs of
the particular additive compound and the chemical complexity of the
compounds and the consequent potential interactions, i.e.,
migration, of the compound and other components of the release
liner or the adhesive to which the liner and silicone compound are
applied.
[0012] Other prior art examples include EP-A 254 050, which
describes the production of a release liner by extruded application
of a release agent comprising a organopolysiloxane compound that
has been reacted with hydrocarbon compounds, and WO 91/15538 that
describes release films comprising a base polymer and additive
formed with a hard segment polymer to determine the compatibility
with the base polymer, and a soft segment polymer which can be a
polydiorganosiloxane polymer. However, neither of the materials
disclosed in these references are capable of producing a
commercially effective release liner.
[0013] Therefore, it is desirable to develop a siloxane additive
for use in the formation of a release liner that does not migrate
from the release liner onto the adhesive to detrimentally affect
the release properties and the adhesion properties of the adhesive
over which the release liner is applied. It is also desirable to
develop a silicone-based additive having these benefits that is
also economically feasible and easy to produce.
SUMMARY OF THE INVENTION
[0014] According to one aspect of the present invention, a
migration-resistant additive is provided for use in release liner
compositions, the additive including a polydiorganosiloxane and a
binding agent capable of hydrogen bonding with
polydiorganosiloxanes. More particularly, the additive is comprised
of a high molecular weight diorganopolysiloxane having a viscosity
of greater than 50 Pas and capable of hydrogen bonding with a
binding agent or component having a number of hydroxyl groups
thereon that is added to the diorganopolysiloxane polymer during
the formation of the additive.
[0015] According to another aspect of the present invention, the
additive is used to form release liner compositions having: (A) a
thermoplastic polymer and (B) the migration resistant additive
including a polydiorganosiloxane and a binding agent capable of
hydrogen bonding with polydiorganosiloxanes. More particularly, the
present invention relates to a composition comprising: (A) 100
parts by weight of a thermoplastic resin; and (B) at least 0.1 part
by weight of a non-migratory silicone additive that preferably
takes form of a high molecular weight diorganopolysiloxane having a
viscosity of greater than 50 Pas and a binding agent or component
having a number of hydroxyl groups thereon that added to and
capable of hydrogen bonding with the diorganopolysiloxane polymer
during the formation of the additive. When added to the primary
polymer or resin, the hydroxyl groups on the binding agent can also
form hydrogen bonds with the polymer or resin, thereby bonding the
additive in position with regard to the polymer or resin, and
preventing any migration of the additive with regard to the polymer
or resin.
[0016] According to still another aspect of the present invention,
the migration-resistant additive composition provides a method of
producing a thermoplastic composition having improved release and
enhanced demolding capabilities. More specifically, the
non-migratory silicone additive is used as a process additive that
is incorporated into the polymer to be used as the primary
component of the release liner. The non-migratory silicone additive
is compounded into the polymer in a manner that, as a result of the
chain length and morphology of the additive, enables the additive
to intertwine with the primary component polymer matrix, preventing
any migration of the additive from the polymer. Further, the form
of the migration-resistant additive enables the additive to be
added to directly to the polymer melt, which can then be mixed and
extruded directly into a release film or liner.
[0017] According to another aspect of the present invention, the
use of the migration-resistant additive as a process additive
during the process for forming the film to be used as the release
liner eliminates the requirement for a separate step in as in prior
art processes where a silicone release layer is applied to, and
subsequently treated on the surface of the extruded film layer.
[0018] According to still another aspect of the present invention,
the migration-resistant additive and the release liner formed with
the additive are each formed from easy to prepare or commercially
available components, thereby improving the commercial economic
viability of the release liner.
[0019] Other aspects, features and advantages of the present
invention will be made apparent from the following detailed
description.
DETAILED DESCRIPTION OF THE INVENTION
[0020] The present invention is, in part, a release liner formed as
a mixture of a suitable thermoplastic polymer film (A) and a
migration-resistant, or non-migratory siloxane polymer additive
(B). The additive is formed of a polydiorganosiloxane and a binding
agent capable of hydrogen bonding with the polydiorganosiloxanes.
More preferably, the additive is comprised of a high molecular
weight diorganopolysiloxane having a viscosity of greater than 50
Pas and a binding agent or component having a number of hydroxyl
groups thereon that is capable of hydrogen bonding with and added
to the diorganopolysiloxane polymer during the formation of the
additive.
[0021] In the additive compositions of the present invention, the
binding agent bonds with the siloxane polymer in part due to the
bonding of the siloxane polymer to the binding component via
hydrogen bonding during the formation of the additive composition.
The phenomenon and mechanisms associated with hydrogen bonding of
various types of polydiorganosiloxanes are well described in the
art. These bonds are very strong and dynamic and render the
siloxane polymer tethered or bound to the binding component when
admixed with one another. In addition, when the additive formed
with the siloxane polymer and the binding agent are added to the
polymeric film selected for the release liner, the additive has
increased chain entanglement with the film. This maintains the
additive stationary within the film, rendering the additive
non-migratory within the polymer forming the film.
[0022] Concerning those thermoplastic resins that can constitute
the component (A) of the invention are preferably polyolefins, but
can be other thermoplastic resins and plastomers as well, such as
nylons, polyesters, polystyrenes, polyurethanes and acrylic resins,
among others. As used herein, the term "thermoplastic resin" is
meant to include those polymers which soften when exposed to heat
and then return to original condition when cooled to room
temperature. In the case where the thermoplastic resin is a
polyolefin, it may be selected from homopolymers of olefins as well
as interpolymers of one or more olefins with each other and/or up
to about 40 mole percent of one or more monomers which are
copolymerizable with the olefins. Component (A) may also be a blend
of two or more of the above mentioned homopolymers or
interpolymers.
[0023] Preferably, the thermoplastic polymer or resin (A) has a
density of about 0.850 to 1.400 g/cc, more preferably 0.875 to
0.960 g/cc, and weight average molecular weight of about 40,000 to
about 200,000. The thermoplastic resin (A) may be made by any
methods known in the art, such as using Ziegler Natta type
catalysts and metalocence based catalysts i.e. single site
catalysts, or may be produced by a condensation type
polymerization. The above polymers are well known in the art and
further description thereof is considered unnecessary.
[0024] The siloxane polymer or blends thereof utilized in the
additive (B), in addition to being capable of hydrogen bonding with
the binding agent and optionally forming a limited amount of
covalent bonds with the binding agent, preferably takes form of a
high molecular weight diorganopolysiloxane. More preferably, the
diorganopolysiloxane has a viscosity of greater than 50 Pas.
Additionally, the diorganopolysiloxane has an average molecular
weight (Mw) of at least about 60,000 atomic mass units (amu), and
more preferably between about 75,000 amu to about 2,000,000 amu. In
addition, the siloxane polymer can have a number of side chains
attached to the main polymeric chain. The groups or radicals that
can form these side chains on the siloxane backbone can include,
for example, C1-C60 alkyl groups, aromatic rings, hydrogen,
hydroxyl groups, vinyl groups and phenyl groups, among others.
[0025] The siloxane polymer molecule used to form the additive is
selected to be a large molecule. In addition to the bonding
interaction between the siloxane polymer and the biding agent, the
size of the siloxane polymer aids in fixing the additive to the
thermoplastic film component, thereby helping to prevent the
migration of the siloxane polymer. In particular, the large
siloxane polymer molecule can physically wrap around and become
entangled with the polymeric film component.
[0026] The additive composition of the present invention
additionally contains a binding agent. The binding agent is any
material capable of forming hydrogen bonds with the siloxane
polymer to bind the siloxane polymer and the binding agent to form
the additive. Additionally, because of potential reactivity of the
functional groups associated with hydrogen bonding, the binding
agent can form covalent bonds with the siloxane polymer under
certain circumstances, further enhancing the bonding between the
siloxane polymer and the binding agent.
[0027] The binding component can take various forms, including a
solid particle mentioned above, e.g., silica, a suitable resin
material, such as a siloxane based MQ resin, a metal
hydroxyl-containing molecule, or an inorganic or organic acid
having multiple hydroxyl groups thereon, such as boric acid or
phosphoric acid, among others, so long as the binding agent is able
to form a sufficiently strong hydrogen bond with the siloxane
polymer to provide the non-migratory function to the additive. In
particular, the binding component possesses surface hydroxyl
functional groups to induce hydrogen bonding with the side chain
groups disposed on the backbone of the siloxane component. In
another embodiment, the binding agent is selected from group
consisting of an inorganic or organic acid having multiple hydroxyl
groups thereon which is not boric acid, such as phosphoric acid, MQ
siloxane resin and fumed silica.
[0028] In addition, it may be necessary to employ other process or
treating aids commonly known in the art of silicone preparations,
to improve mixing and processing of the siloxane and binding
components to form the additive. One example of such a process aid
is a short chain di-hydroxy endblocked polydimethyl siloxane. Yet
another known process aid that can be added to the mixture of the
components for the additive of the present invention is a silane.
Other process aids may be shorter chain diorganopolysiloxanes
containing dimethyl, methyl phenyl and methyl vinyl siloxane
segments. These process aids are used to assist in the formation of
the additive of the present invention, but do not directly effect
the final release liner produced from this invention.
[0029] The release liner compositions of the present invention are
prepared by thoroughly dispersing at least 0.1 part by weight of
siloxane additive composition (B) in 100 parts by weight of
thermoplastic polymer (A). Higher amounts of the additive component
(B) of between about 0.1 part to 50 parts can be used to form a
masterbatch or concentrate of the composition for further
processing. For finished release liners formed using the
composition having the thermoplastic polymer (A) and the additive
(B), it is preferred that about 0.1 to less than 10 parts by weight
of component (B) are used for each 100 parts by weight of component
(A).
[0030] For use with the thermoplastic polymer (A), the additive (B)
can be formed as a fluid or as a solid, e.g., small particles,
granules or pellets, that can be added directly to the
thermoplastic polymer (A) during processing of the release liner
composition. Further, the dispersion of the additive (B) into the
thermoplastic resin (A) may be accomplished by any of the
traditional means for mixing additives into thermoplastic resins at
elevated temperature. For example, the two components (A) and (B)
may be blended in a twin-screw extruder, a Banbury mixer, a
two-roll mill or a single-screw extruder, either with or without a
mixing head. The equipment used to mix these components is thus not
critical as long as a uniform dispersion of (B) in (A) is attained.
Preferably, the dispersed particle size is no larger than about 40
micrometers.
[0031] In addition to the above components (A) and (B), the release
liner compositions of the present invention may also contain one or
more of the following components: fillers, cure agents, lubricants,
ultraviolet light stabilizers, antioxidants, catalyst stabilizers,
flame retardants and other process aids commonly employed in the
modification of polyolefins. Moreover, up to 5% by weight of their
total composition of the present invention could be an antiblock
agent, and flame retardants can added to the total composition.
Specific non-limiting examples of the above additional ingredients
include the following substances: diatomaceous earth,
octadecyl-3-(3,5-di-5-butyl 4-hydroxyphenyl)propionate,
bis(2-hydroxyethyl) tallowamine, calcium stearate,
N,N-bis(2,2,6,6-tetramethyl-4-piperidinyl)-1,6-hexanediamine
polymer with 2,4,6-trichloro-1,3,5-trizaine and
2,4,6-trichloro-1,3,5-trizaine and 2,4,4-trimethyl 1,2-pentanamine,
dimethyl succinate polymer with
2,2,6,6-tetramethyl-1-piperridineethano-1,2,2-thiobis)-4-tert-octylphenol-
ato]n-butylamine nickel, tris(2,4-di-tert-butylphenyl)phoshite,
bis(2,4-di-t-butylphenyl) pentaerythritol diphosphite,
trisnonylphenylphospite, polyethylene glycol, Erucamide, titanium
dioxide, titanium dioxide, alumina, hydrated alumina, talc,
2-hydroxy-4-n-octyloxy-benzophenone, silicone dioxide, zinc oxide,
zinc sulfide, and zinc stearate.
[0032] When the thermoplastic resin (A) and additive (B) are
compounded into the film used to form the release liner, the
additive (B) self-assembles into microscopic cells/domains within
the film. These domains are very non-adhering to adhesives over
which the release liners formed by the film will be positioned. In
particular, the chain entanglement and binding properties of the
components of the additive (B) will prevent the individual
molecules of the additive (B) from adhering to the adhesive upon
removal of the release liner including the additive (B), and thus
will not negatively affect the subsequent adhesion of the adhesive
to another substrate.
[0033] One embodiment of the composition for the non-migratory
siloxane additive is the combination of a high molecular weight
silicone gum, such as Shin-Etsu KE76 BS, sold by Shin Etsu Chemical
Co. of Tokyo, Japan, in an amount of around 100 parts by weight,
with a binding agent, such as Aerosil 200 fumed silica, sold by
Degussa of Frankfurt, Germany, in an amount of 30 parts by weight,
and optionally an appropriate part by weight of a process aid, such
as Dow Corning CD 4-2737 hydroxy terminated dimethylsiloxane
process aid sold by Dow Corning of Midland, Mich. The addition of a
silicone additive with a silicone or siloxane polymer of this high
molecular weight provides the polymer film used as the release
liner with a component that functions to provide the desired
release level to a release liner formed of the polymer and
additive. Further, the ultra high molecular weight and long chain
length of the non-migratory silicone additive enables the additive
to become entangled with the polymer, such that the additive cannot
migrate out of the polymer.
[0034] Another embodiment of the inventive composition is the
combination of a thermoplastic film grade resin and up to 15% of
the commercially available additive Genioplast P sold by Wacker
Chemical. The Genioplast P is a mixture of high molecular weight
polydiorganosiloxane and silica with other process additive that
unlike other commercially available silica and polydiorganosiloxane
compounds is induced and allowed to hydrogen bond. Surprisingly,
when dispersed into a thermoplastic polymer melt, the Genioplast P
hydrogen bonding mechanism is not disrupted and the silica and
siloxane complex remains in tact and remains non-migratory in
nature. This surprising property allows the combination of a film
grade thermoplastic resin and the Genioplast P useful as a release
liner.
[0035] In a particularly preferred embodiment, the composition of a
release liner formed with the novel non-migratory additive
includes: a) 100 parts by weight of a polymer capable of producing
filmic release tapes and liners such as polyethylene terepthalate
(PET), polypropylene (PP), or polyethylene (PE), among others; b)
between 0.1 to less than 10 parts by weight of the non-migratory
additive; and c) optionally 0.001 to 120 parts of other known
polymer film additives such as fillers, pigments, process aids,
stabilizers and melt flow modifiers. These components are admixed
with one another in a suitable manner to arrive at a composition
that can be extruded into a film, which can be directly employed as
a release liner, i.e., that is ready for use as a release liner or
tape as it is extruded. Yet another embodiment of this invention is
the use of a mixture of siloxanes of various molecular weights and
organo-functionalities in conjunction with a binding component or
agent, or a blend of agents.
[0036] In the method of the present invention for forming the
release liner including the non-migratory additive, the method
enables the production of economically viable film release liner by
the simple addition of a non-migratory additive to the polymer for
the film. This method eliminates the need for silicone coating and
curing stations, as required by prior art release liner formation
methods, dramatically reducing the costs and capital required to
produce these liners and tape backings. It also reduces the number
of variables that contribute to a release profile for the liner.
This is due to the fact that the chemistry of the non-migratory
additive is very simple and predictable, such that the subsequent
adhesion and ageing profiles of the liners so formed are easier to
control. This results in commercially viable liner constructions
that can be used in, but not limited to, traditional applications
such as tapes, merchant release liner films for adhesive labels,
co-extruded poly coated papers, hot melt adhesive backing, roofing
shingle tape and packaging tapes, among other applications.
[0037] Additionally, this method of production for the liner
including the bound, non-migratory silicone additive can be used in
forming a single or multiple layer extruded film. In the embodiment
of a multilayer film, the addition of the silicone additive to the
outside layers of a co-extruded layered film allows for a reduction
of the use of the silicone additive, while also allowing for
printing on the opposite side of the film from the silicone
additive containing layer.
Experimental
[0038] The following experimental examples are provided for
reference and are not intended to limit the application of the
inventive composition.
[0039] Additive A is a commercially available alkyl-modified
siloxane used in high temperature release and lubricant
applications that does not include the binding agent(s) utilized in
the non-migratory additives of the present invention.
[0040] Additive B is Genioplast P, which is an ultra high molecular
weight silicone additive comprised of a combination of 100 parts
methyl vinyl functional polydiorganosiloxane with up to 200 parts
fumed silica and up to 20 parts of boric acid.
[0041] Additive C is an non-migratory ultra high molecular weight
silicone additive compound produced with Shin-Etsu KE76 BS hydroxyl
terminated polydimethyl siloxane gum, sold by Shin Etsu Chemical
Co. of Tokyo, Japan, in an amount of around 100 parts by weight,
with a binding agent, Aerosil 200 fumed silica, sold by Degussa of
Frankfurt, Germany, in an amount of 30 parts by weight, and an
appropriate part by weight of a process aid, Dow Corning CD 4-2737
hydroxy terminated dimethylsiloxane process aid sold by Dow Corning
of Midland, Mich.
[0042] These compounded materials were produced with a 0.65
MI/0.904 Density Homo-polymer Polypropylene using a Haake Torque
Rheometer with 20:1 L/D Bradender twin screw counter rotating
extruder with 4 temperature segments at an rpm ranging from 30 to
50 and a temperature profile of between 375 degrees Fahrenheit and
475 degrees Fahrenheit.
[0043] Films of a polypropylene homopolymer with a density of 0.904
g/cc and MFI of 0.65 were produced with and without the additives
A-C using a 25:1 L/D Brabender single screw with a blown film die.
The extruded blown film was collected on a vertical blown film
tower. During extrusion the torque values were measured at 30 rpm
to observe any process aid attributes resulting from the increased
lubricity. The results in Table 1 show that the inventive compounds
process well and in fact lower torque on the extruder which is
desirable. The control was the polymer with no additive
present.
TABLE-US-00001 TABLE 1 % Additive Additive Torque 1 0.0% Control
30.00 2 5.0% Additive B 12.00 3 2.0% Additive A 9.60
[0044] Static coefficient of friction (COF) can be a proxy
measurement to determine the presence of the additive on the
surface of a film. Reduction of COF indicates the relative amount
of silicone additive available to promote release. The static COF
measurements were performed film on film with an increasing angle
arm device. The test specimens were formed of the same
polypropylene material used in the prior testing, and were
approximately 1''.times.4'' are attached to the aluminum lever arm
and a 150 g steel block with a face dimension of 1'.times.2''. The
arm raises until the block begins to move. The angle of the arm is
measured when the blocks slides and in converted to COF by the
calculating the tangent of the angle. The dynamic surface tension
was directly measured. However, visual observations were made on
the amount of pressure required to keep the "slide" of the block
going. The results disclosed in Table 2 demonstrate that the
additives formed according to the present invention (B and C) can
reduce the COF as much or more than additive (A) currently used for
this purpose.
TABLE-US-00002 TABLE 2 % Additive Additive COF 1 0.0% Control 0.42
2 4.0% Additive A 0.29 3 5.0% Additive B 0.27 4 5.0% Additive C
0.28
[0045] Demolding was evaluated by placing compounded pellets of the
polypropylene thermoplastic material both including and omitting
the additives A-C into aluminum mold dishes and heated for 2 hours
at 210 C. so the pellets melted and coalesced. The molds were
cooled to room temperature and the molded puck was removed from the
mold. The difficulty of removal was given a scale from 1 to 10
where 1 is given when the puck falls out of the mold with no force
and 10 being fused to the mold and destruction of the puck would be
necessary. The scale in between is the approximate force required
to separate the puck from the mold. The clarity of the puck was
observed as well. The control material in highly translucent and
that was given a 1 rating and 2 indicates an significant increase
in haze and 3 is opaque. These results are provided in Table 3.
[0046] It can be seen that the use of the additives have a dramatic
impact on demolding over the control. The tethered additives B and
C performed as well as the un-tethered siloxane A and much better
than the control containing no additive. The clarity is reduced
however.
TABLE-US-00003 TABLE 3 Adhesion Clarity Release Additive Rating
Rating 1 Control 9.5 1 2 5% Additive A 3.5 1 3 1% Additive B 2 3 4
10% Additive C 3.5 2
[0047] Adhesive properties or release was measured by testing the
blown polypropylene films produced without the additives A-C under
TLMI 180 peel test procedures using TESA tape 7475 pulled at 300
inches per minute. The tape laminated samples were conditioned at
140 F for 20 hours before peeling.
[0048] For subsequent adhesion, the Finat 11 test procedure was run
which applies an unused piece of TESA tape and a piece of tape that
has been in touch with the substrate for the 20 hr oven test as in
the peel test. The tapes are allowed to dwell on a clean steel
plate for twenty minutes and pulled at 12 inches per minute at a
180 degree angle. The result is divided by the control result to
get the % subsequent adhesion.
[0049] Table 4 demonstrates that these additives do have an
adhesive release profile and can act as a melt additive release
agent to produce ready to use release liner films. The control was
welded to the tape and could not be removed. The most surprising
observation was the high percentage subsequent adhesion. This
demonstrates that the additive is non-migratory even under harsh
heated storage conditions. Additive A, which again does not include
the binding agent of the additives of the present invention, is not
tethered in the manner as this invention and shows migration to the
adhesive interface and low subsequent adhesion. The commercially
viable subsequent adhesion level is above 90%.
TABLE-US-00004 TABLE 4 % 300 ipm % Subseq. Additive Additive
Release Adhesion 1 0.0% Control Welded Welded 2 5.0% Additive C
375.00 94 3 5.0% Additive B 612.00 100 4 4.0% Additive A 161.00
78
[0050] While embodiments of the invention have been illustrated and
described, it is not intended that these embodiments illustrate and
describe all possible forms of the invention. Rather, the words
used in the specification are words of description rather than
limitation, and it is understood that various changes may be made
without departing from the spirit and scope of the invention. More
specifically, various other alternatives are contemplated is being
within the scope of the following claims particularly pointing out
and distinctly claiming the subject matter regarded as the
invention.
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