Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
WO93/11933PCT/US92/10959
212588~
-- 1 --
PLASTIC RELEASE FILM~WITH TEXTURED
OR NON-PL~NAR SURFACE
The present invention relates to a release film, a
major utility of which is to protect and carry label
stock un~il the label is put into use on an appropriate
surface.
For many years labels have been prepared with an
adhesive applied to one side thereof. In instances
where the adhesive is a pressure sensitive adhesive,
some means had to ~e provided to protect the adhesive
surface in advance of applying the label to the
ultimate surface to be labeled. .A technique has
evolved over the years by which the pressure sensitîve
adhesive is protected by bringing the adhesive surface
into contact with a release layer which has little
tendency to aggressively adhere to the pressure
sensitive adhesive surface. Thus, a second film having
a release surface is brought into con act with the
pressure sensitive surface carried by the label
protecting the pressure sensitive adhesive until the
label is applied to its ultimate surface. It is to be
- understood that the pressure sensitive adhesive can be
applied to the release surface and the label stock
thereafter applied to the adhesive surface. On removal
of the label the pressure sensitive adhesive will
preferentially adhere to the label stock.
Release films can be manufactured separately from the -~
label face stock. The release film is manufactured b~.
applying a commercially available release material ~G
one side of the release film and the combination is
then convolutely wound into a roll stock. Ultimately
this roll stock must be unrolled and slit to a width
dimension suited to a particular label dimension. Next
a pressure sensitive layer is applied over the release
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212~88~ ~ 2 ~
layer and this is mated with the underside of a sheet
of label stock. Alternatively the label stock can have
the pressure sensitive adhesive applied to it's
undersurface which in turn is mated with the release
S label. Following this, label indicia is printed onto
the surface of label and, thereafter, the label is die
cut so that it can be separated from the release
sheet-label stock combination.
During the unwinding of release film roll stock for
re-dimensioning purposes, serious problems can arise.
After the release material is applied as a coating
layer on the substrate and subjected to electron beam
curing and during the convoluted winding of the stock,
a portion of or a fraction of the release material is
transferred to the back side of the release film.
Later when this release roll is unwound to receive
label stock thereon, and subsequently rewound, some
release material or a fraction thereof transfers to the
surface of the label stock prior to the label stock
receiving printed indicia. This transferred release -~
material causes imperfections to occur during the label
printing process. The transferred release material
interferes with printing. This leads to the need to
discard the combination of material at a point when the
product is almost completely ready for use or
marketing.
Furthermore, as a result of rapid unwinding, a high
electrostatic potential develops at the point of
unroll. This electrostatic potential can achieve
dangerous levels which can lead to fire, explosion, or
physical injury. Another problem is that the film will
not always track in an even, unvarying manner as it
moves employed in the manufacture of the product.
This invention seeks to overcome the aforementioned
WO93/11933 212 5 8 8 5 PCT/US92/10959
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difficulties.
In one aspect, the present invention provides a rel~ase
film compri~ing an oriented thermoplastic polymeric
s~bstrate layer having a surface layer comprising an
ethylene-propylene block copolymer on one side thereof
and a release coating on the other side thereof. While
it is not completely understood, it is believed that
the ethylene-propylene block copolymer surface has a
distinctive texture which causes, during unwind of a
roll of said film, a reduced electrostatic potential, ~-
in comparison to a smooth surface and said surface
texture permits even, unvarying transport over rollers
during manufacture and use.
In another aspect, the invention provides a release
film comprising an oriented thermoplastic polymeric ~-
layer having one side thereof a release coating
comprising a silicone-acrylate release material, the
coating including therein a quaternary ammonium salt.
The substrates contemplated herein can be any polymeric
film substrate which can effectively carry a release
coating on one side thereof and an ethylene-propylene
block copolymer surface on the other side thereof.
Preferred substrates include, polyolefin films which
are oriented and preferably biaxially oriented. The
substrate can be a homopolymer, copolymer or a bl nd
thereof. A preferred homopolymer is polypropylene.
Particularly preferred are isotatic polypropylenes
containing at least 80% by weight of isotatic
polypropylene. This substrate layer can be
homopolypropylene having a melting point range from
32lD to 336~F. Commercially available materials of
this description include Exxon 4612 and FINA 3371. It
is to be understood that the substrate can be a single
material or a combination of coextruded substrate
WO93/11933 PCT/US92/lO9Sg
21~5~8~ 4
materials. For example, polypropylenes of different
melt indexes can be employed to yield excellent
handling characteristics. The substrate can be
provided in any thickness which facilitates either
S human or machine handling~ A preferred thickness range
can be from 0.5 mils to 3 mils. The substrate material
can be composed of one or a plurality of layers and may
be transparent or opaque.
The ethylene-propylene block copolymer can have an
ethylene content of less than 20% by weight; for
example, from 2 to 20 and preferably from 3 to 15~, and
a melt flow index from 1 to 100 g~10 minutes, -~
preferably from 3 to 50 g/10 minutes. A preferred --
ethylene-propylene block copolymer is commercially
available as Himont 8523, having a melt flow index of
about 6.0 q/10 minutes. The release film substrate can
be formed for example by coextruding the polypropylene
film of choice with the above identified
ethylene-propylene block copolymer followed by
biaxially orienting the combination 4.3 times in the
machine direction and 8 times in the transverse
direction.
The block copolymer coated substrate is now in
condition to receive a commercial release coating on
the side opposite to the ethylene-propylene block
copolymer. The select~d release coating can be applied
by any convenient technique, for example, by
differential offset gravure coating. Thereafter, if
the proprietary release coating needs to be cured it
can be done so by any prior art technique. A
convenient class of release coatings is described in
U.S. Patent No. 4,678,846 and 4,306,050. In essence,
these release coatings are silicone polymers having
acrylic functional end groups. The material is applied
to the opposite side of the block copolymer coated
WO93/lls33 PCT/US92/10959
212588~
polypropylene film by differential offset gravure
coating and the coating is cured by exposure to
energized electrons at the rate of 2.5 Mrads in a RPC
electron beam processor. It is to be understood than
curing can be accomplished within the range from 1 to
5, preferably from 2 to 3 Mrads.
The release material of the present invention includes
(meth)acrylate ester modified organopolysiloxane
mixtures, comprising essentially equilibrated
organopolysiloxanes with, on the average, more than 25
to fewer than 200 silicone atoms and which additionally
contain 2 to 30 weight percent o~ organopolysiloxanes
with, on the average, 2 to 25 silicone atoms and 2 to
30 weight percent of organopolysiloxanes with, on the
average, 200 to 2,000 silicone atoms.
As used herein, the organopolysiloxane fractions having -~-
more than 25 to less than 200 silicone atoms are
sometimes referred to as the first fraction, those
having 2 to 25 silicone atoms are referred to as the
second fraction, and those having 200 to 2,000 silicone
atoms are referred to as the third fraction.
Especially preferr~d are those (meth) acrylate ester
modified organopolysiloxane mixtures which contain,
besides the e~sentially equilibrated organopolysiloxane
with, on the average, more than 25 to fewer than 200
silicone atoms, 5 to 20 weight percent of
organopolysiloxanes with, on the average, 5 to 25
siltcone atoms and 5 to 20 weight percent of
organopolysiloxanes with, on the average, 200 to ~ 70
silicone atoms.
The organopolysiloxanes contained in the
organpolysiloxane mixtures preferably correspond to the
WO93/11933 PCT/US92/10959
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8 3 ~
formula:
Ra- Si - Qb
I
4-(a+b)
.
in which R is an alkyl radical with 1 to 4 carbon
atoms, preferably, the methyl radical. R may, however, -
also be a vinyl or phenyl radical. Moreover, the R
radical may also represent different moieties in the
molecule, so that some R radicals represent methyl
radicals and the other R radicals may, for example,
represent a vinyl or a phenyl radical. Preferably, at
least 90% of the R radicals are alkyl radicals,
especially methyl radicals.
Q is an organic radical which contains the acrylate
or methacrylate ester groups. Preferably, the acrylate
or methacrylate ester radical is linked to the silicone
atom through an sioc bridge. The acrylate or
methacrylate radical may moreover be derived from
pentaerythritol triacrylate, pentaerythritol
trimethacrylate, dipentaerythritol pentaacrylate,
dipentaerythritol pentamethacrylate,
ditrimethylolpropane triacrylate, ditrimethylolpropane
trimethacrylate, ditrimethylolethane triacrylate,
ditrimethylolethane trimethacrylate, trimethylolpropane
di(meth)acrylate, trimethylolethane di~meth)acrylate,
glycerin di(meth)acrylate, hydroxyethyl acrylate,
hydroxpropyl acrylate and neopentyl glycol
monoacrylate.
The acrylate or methacrylate ester radical may,
however, also be linked through an SiC bridge with the
organopolysiloxane. a has a value of 1.0 to 2.2; b has
a value of 0.001 to 1.6. The fractions of different
WO93/11933 PCT/US92/10959
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average molecule weight contained in the inventive
acrylate or methacrylate ester modified ;~
organopolysiloxane mixtures may differ in respect to
the R and Q radicals and the a and b subscripts.
Organosilicone species in the above referenced
silicone acrylate release coatings are believed to
migrate from the coating to adjacent contacting
surfaces. The cause of this migration may be
nonfunctionalized silicone remaining in the release
coating. These migratable species are not bound or
fixed in the cured coating and thus will migrate to
adjacent contacting surfaces. I~ has been found that
by including a quaternary ammonium salt in the silicone
acrylate material prior to applying it to the release
substrate that by s~me reaction the migratable mat~rial -~
is either prevented from migrating or converted to a
material which has no adverse effect on label printing. -~
What is known is that the inclusion of the quaternary
ammonium salt solves this expensive problem. The
silicone acrylate release coating normally is applied
to the substrate in a quantity of from about 0~2-l.2
grams/l000 in2, preferably about 0.7 g/l000 in2.
The quaternary ammonium salt can be added to the
silicone acrylate release coating material in a -~
proportion of from 0.2-8 wt %. The substrate can be
from l.8 to about 2.2 mils thick. Examples of ~
quaternary ammonium salts include the following:
o Dimethylaminoethyl methacrylate dimethyl sulfate
("Madquat Q-5" by Norsolac, Inc.)
.
o (3-Lauramidopropyl)trimethyl ammonium methyl
sulfate
("~yastat LS" by American Cynamid)
WO93/11933 PCT/US92/10959
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o Stearamidopropyl-dimethyl-2-hydroxyethyl ammonium
nitrate
~"Cyastat S~" by American Cynamid)
o N,N-bis(2-hydroxyethyl)-N-(3-dodecycloxy-2-
hydroxypropyl)methyl ammonium methyl sulfate ~
("Cyastat 609" by American Cynamid) ~`
o Stearamidopropyl-dimethyl-2-hydroxyethyl ammonium
dihydrogen-phosphate
("Cyastat SP" by American Cynamid)
o Trialkylalkyletherammonium salts (e.g. Emers~at
6660-A from Henkel Corp.)
Examples of the release film in accordance with the
present invention in comparison with a prior art
release film is shown below. The release compositions
were coated onto a 2.0 mil biaxially oriented
polypropylene and cured by conventional electron beam
radiation technique. The release coating was a
silicone-acrylate identified as RC450 from Th.
Goldschmidt of Essen, Germany, to which was added 2,4
and 8% by weight of trialkylalkyletherammonium salt.
The release force (grams/inch) was measured using a
TESA4154 tape and a TLMI release force tester. The
film-was convolutely wound and so held for a period of
l week at 125F., so that the magnitude of release
material transfer to the back side of the film could
be measured. The film was then unrolled and the rating
of ink wetting was mea~ured using a #8800 Berol magic
marker. Rating l = high silicone migration, causing a
severe ink wetting problem; rating lO = no silicone
migration, i.e., no ink wetting problem. The results
WO93~1933 PCT/US92~10959
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2125885 - 9 ~
are shown in the table below.
TABLE -;~
Cured Coating Degree of Ink ~-~
Sample No. Formulation Release Force Wettin~ `
.
(a) Release coating 37 g/in Rating 1 ~--
(b) (a)+2% additive 32 g/in Rating 8
(c) (a)+4% additive 27 g/in Rating 8
(d) (a)+8% additive 28 g/in Rating 8
The above data shows the outstanding decrease in the ~-~
amount of transferred or migrated release material to ~-
the back side of the release film. The data also shows
that the quaternary ammonium salt modified
silicone-acrylate release material decreased the
release force to a moderate extent, thus maintaining
its release effectiveness.
The silicone-acrylate coated release liner is then
convolutely wound into a roll which is approximately
from 60 to 80 inches in width. For test purposes the
roll stock of the present invention was unrolled at
speeds from 300 to 1500 feet per minute, simulating
the unroll speed for purposes of slîtting the roll
stock to form lower dimension rolls. During this
unrolling no dangerous electrostatic discharge levels
were noted. In addition, the film tracked in an even,
unvarying manner.
