Note: Descriptions are shown in the official language in which they were submitted.
wlnts4clbo~o~doc/dlp 211~ 2 3 0
--25--
~
hBSTRACr
A thermopla&tic p~lyolefin film havinç~ one or bot~
curfaces of ~he film partially fluor~na~ed to
O s~s~ntially increas~ cling and de::raase biock is
provids~. Æ partially fluorinated thermoplastic
s~retch f ilm of ethylenef acPtate haYing increa~ed cling
- and d~c~oas~d b~ock ~ ~ also provided.
,
~: :
_ .
A~ENDED SHEET
wo g3,24559 ~ 3 0 PCr/US93/05273
FLOURINE TREATMENT OF POLYOLEFIN FILMS
Cross Reference to Related Applications
This Application is a continuation-in-part of USSN
893,282, filed June 4, 1992.
Field of the Invention
The present invention relates generally to
thermoplastic films and, more particularly, to
partially fluorinated thermoplastic films especially
well suited for use in various applications.
Background of the Invention
One type of polyolefin film, stretch/cling films,
is useful in a wide variety of fields including ~he
bundling and packaging of food and other goods. One
application of particular relevance to the present
invention is in the b~ndling of goods for shipping and
storage such as the bundling of large rolls of carpet~
:fabric or the like for shipping. An important subset
o~ these:bundling applications is in the c~ntainment ~;
: and unitizing of pallet loads. In such applications,
it is desirable that the film have cliny properties to
:: prevent unraveling of the film from the pallet. The
~ tension in the stretched film may also cause the film 5
: ~ : to be more susceptible to punctures and tears. It is
~also desirable for polyolefin films, as a whole, to.~.
ihave good stretch, tensile, puncture resistance and
~eax resistance properties. Thermal stability o~ the
: ~ various film components is important for the recycling
of edge trim and film scrap generated in the various
~ilm produc~ion processes.
:~
To impart cling properties to, or improve the
cling properties sf, a particular f ilm, a number of
- 2-~23~ ~
~93/24~59 PCT/USg3/~273
2 --
well-known tackifying additives have been utilized.
Common tackifying additives include polybutenes,
terpene resins, alkali metal stearates and hydrogenated
rosins and rosin esters. The use of t~ckifying
additives, however, may not be desirable. These
additives have a tendency to accumulate on the stretch
wrapping apparatus often requiring additional periodic
cleaning and maintenance. They also can migrate into
the bundled or unitized articles resulting in damage to
such articles, as well as migrating throughout a film,
even a multilayer film, causing tackiness on both
~ides. In palletizing operations, this may cause the
film on adjacent pallets to cling together resulting in
tear, puncture or other damage to the wrap and
jeopardizing the integrlty of the unitized load.
For this reason, it is desirable for stretch/cling
type film to have slip or "anti-cling" properties on
its "outer" side to prevent this interpallet cling.
Slip is defined in terms of coefficient of friction.
In other words, it is desirable that the "outer" side
of the ilm have a low coefficient of friction in
contact with another object, particularly another like
film. As with cling, slip can be imparted to the film
or improved through the use of various well-known slip,
anti-cling and/or antiblock additives including
silicas, silicates, diatomaceous earth and various
lubricants. -~
In addition to conventional anti-cling additives,
film cling properties can be altered by exposure to a
corona disch~rge. The reactivity of discharge
particles can alter the surface chemistry of the film
and consequently its physical characteristics. The
effeck of such exposure can be observed by changes in
film surface energy.
W~93/2455~ 2 1 ~ ~ 2 3 0 PCT/~93~5273
Mo~a recently, the use of multilayer films has
gained popularity. With a multilayer film, one can
o~tain a stretch/cling wrap having cling properties on
one side and slip properties on the other side. (See
S for example, UOS. Patent 4,518,654~.
Other multilayer films comprising layers of the
various aforementioned stretch/cling materials are
disclosed in U.S. Patents 3,508,944, 3,817,821,
40022,646, 4,082,877, 4,147,827, 4,18g,~20, 4,194~039,
4,303,710, ~,399,180, 4,364,981, 4,418,114, 4,425,268,
-4,436,788, 4,504,434, 4,588,650 and 4,671,987; U.K.
Patent Application 2,123,747; French Patent 2,031,801:
and European Pa~ent ~pplication No. 0,198,~91. These
multilayer films are generally produced by one of a
number of well-known ~oextrusion processes also
di-~closed in the aforementioned references.
Many of the multilayer films, however, still
suffer fro~ shortcomings possessed by their indi~idua'.
layers. For insta~ce, most still require the use of
tackifying additives to impart cling properties to the
ilm. Others do not possess desired slip properties,
particularly when in a highly stretched sta~e. Still
25~ others do not possess a desirable combina ion of
: stretch, tensile, tear resistance, puncture resistance
:~ and thermal stability properties.
It is known to treat various polymer surfaces by
flu~rination. Materials like polytetrafluorethylene
(PTFE) have been used extensively and haYe ~ery low
polar sur~ace energies~ As an al~ernative to
fluorinated polymers like PTFE which are relatively
expensive, localized fluorination at the polymer
surface has been used to reduce cost.
2ll~.2~a
W093t24~s9 P~T/US~3/OS273
U. S. Patent 3,740,325 to Maulon discloses a
material and process for making a surface fluorinated
material. The treated material is said to have greater
water resistance, corrosion and soil resistance and be
more like PTFE.
U. S. Patent 3,647,613 to Scotland discloses a
surfa~e fluorinated high density polyethylene used for
making containers suitable for storing hydrocarbons.
The HDPE surface containing a concentration of 0.01 to
30 micrograms of fluorine per square centimeter was
said t~ improve Permeabilitv characteristics to
gasoline. -
U~ S. Patent 4,880,675 discloses plastic ~-
containers comprising a polyethylene inner layer
coextruded with a polypropylene outer layer wherein the
inner layer is treated with a reactive fluorine source~
Such treatment is said prevent the absorption of flavor
or aroma compounds by the container lining.
UO S. Patent 4,743,419 to Bierschenk discloses an
on-line method for co~tinuous fluorination of a polymer
film while the film is being extruded.
25~
U. S. Patents 4,264,7SO and 4,~04,256 to Anand et
al. disclose a process for making fluorinated low
energy polymer surfaces by exposure ts ions or radicals
of fluorinated species in a cold plasma and polymers
having;a substantially completely fluorinated surface
o~ low surface energy which is substantially ~xygen
free.
.~
Sur~ace fluorination of high density and low
densi~y polye~hylene films between 40 degrees C ~nd lOO
degrees C is described by Volkmann et al. in
Makromolecular Chemie, Macromolecular Symposium, Vol.
W093/24559 2 1 1 S 2 ~ O PCT/US93/~5273
25, pp. 243-248 (198~). The reaction is said to be
diffusion controlled with the degree of fluorination
increased by greater F2 concentration in the
fluorinating gas mixture.
Processes for surface fluorinating polymer films
have been observed to introduce oxygen into the surface
as a rea~-tion byproduct when reaction times are smaller
than those required to achieve complete surface
fluorination. Anand et al. attributes this fact to a
post-reaction with atmospheric oxygen or oxygen
.impurities possibly due to radicals trapped in the
subsurface or some unreacted bonds on the surface. At
any rate, this phenomenon is n~t generally o~served
; 15 following c~mplete surface fluorination.
The presence of oxygen following a partial
fluorinatic-- of a polymer surface increases surface
; ~ energy, particularly the polar component, making the
surface more adherent. Milker and Koch, "Surface
Pretreatment of Polymer webs by Means of Fluorine'l; and
Milker and Koch, "Fluorine Makes Plastics Flexible";
describe a fluorination process for producing polymer
fi~ms said to ha~ good adhesion properties. The
process is said to alter the surface on a more or less
~ permanent basis so that the polar character of the
; ~ material is increased.
Summary~__f the Invention
The present invention resides in part in the -~
discovery that the properties of a polyolefin film are
~ surprisingly enhanced following partial fluorination of
one or both exterior surfaces o~ the film. Broadly the
~5 treatment comprises exposing one or both surfaces o~
the film to a dilute mixture of a fluorination species
in a carrier gas for a time period less than that
21~'.2~
W~93/24~5~ - PCT~US93/05~73
required to achieve complete surface fluorination and
subsequently exposing the partially fluorinated film -:
surface to oxygen.
In one embodiment, the present invention provides
a thermoplastic film having excellent cling properties,
even without the use of a tackifying additive. In
fact, it is desired with the present invention to omit
the use of such tackifying additives, in one
embodiment, such that a cling layer is essentially free
of tackifier.
..
This invention further provides films with
enhanced wettability, printability and/or inkability. ~-
~:
The present invention further provides a
multilayer stretch/cling film having excellent cling
~;~ properties on one side and excellent slip properties on
: ~an opposite side, even in a highly stretched state.
:~
Still further, the present invention provides a
multilayer stretch/cling film whîch, as a whole,
: :
possesses desirable stretch, tensile strength, puncture .
resistance, tear resistance and thermal stability
properties.
Finally, the present-invention provides a process
for producing such polyolefin films.
:~ :
Detail;ed Description of Preferred_ mbodiments
.
- One or both surfaces of the coextruded layers of a
film are partially fluorinated to enhance properties.
The fluorination reaction catalyzes an oxygenation by-
reaction upon exposure to air. The surface to be
treated is exposed to a suitable source of reactive
fluorine, such as~ for example, fluorine-con~aining
.
'~
W093/2~559 2 1 1 ~` 2 3 ~ PCT/US93/~5~73
plasmas, fluorine-containing gas m~xtures, fluorine
dissolved in solvents, UV activated fluorine gas
mixtures, and the like. For example, any of the
e~uipment and methodology for fluorination described in
Volkman or Milker and Xoch can be used. A preferred
fluorination method is direct fluorination using a gas
mixture of molecular fluorine in an inert carrier gas.
Processes for fluorinating one or both sides of
film material in either batch or continuous operations
are known. In a continuous process, the film i5
introduced into a reaction chamber generally having
special locks at either end so that the film may be
continuously passed through the chamber without
permitting gas to escape. The locks typically have a
low pr~ssure seal pro~ided by a vacuum pump. Fluorine
is metered from compressed cylinders generally
pressurized with the diluent gas to achieve higher fill
pressure. Gas exiting the reaction chamber is
cc spressed, combined with makeup gas and recycled ~o
maintain a steady gas flowrate through the reactor. An
absorber may be used to remove HF byproduct gas from
the recycle stream. Very pure nitrogen is provided as
flu:~h and diluent gas. Waste fluorine can be catalyzed
to hydrogen fluorlde then absorbed by an absorbent such
as calcium hydroxide.
.
The duration of the exposure to F2 and air
required to obtain the desired enhancement of
properties such as cling, slip, printability, ink
retention and wetability depends on the con tions o:
exposure, the film composition and properties, F~
con~entration, etc. It is important that the
~luorinatio~ reaction is not permitted to go to
completion, i.e~ to replace a majority of the available
hydrogen atoms attached to the carbon backbone.
Fluorinati~n is substantially complete if a majority of
., . ., . ,,, ., .. . , ... , . , . . , .. ., . , ... ,~ .. .. . . .. . . .. . .. ... .. ..... . .
21 1 ~2c~
W0~3/24~59 PCT/US93/05273
the available surface hydrogen atoms are substituted
for fluorine atoms so that there is relatively little
further fluorination upon further continued fluorine
exposure. Partial fluorination is indicated by a
dispersive surface energy less than the corresponding
polar surface energy, in contrast to a surface energy
higher than the polar surface energy when complete
surface fluorination is achieved.
In general, F2 exposure times of from 1 to 30
minutes are suitable. Subsequent oxygenation of the
film surface is generally instantaneous upon exposure
to air, although exposure to oxygen can be extended to
ensure complete oxygenation without adversely affecting
the desirable film properties.
The amount of F2 needed to enhance properties is
relatively minor. Cling and block are improved in some
instances with a fluorine:carbon surface stoichiometry,
as low as 0.001, as determined by X-ray photoelectron
spectroscopy (XPS). However, if the fluorine:carbon
surface stoichîometry is too high, the surface may not
become activated for reaction to oxygen, a low polarity
surface is produced and cling is adversely affec~ed.
The fluorine:carbon surface stoichiometry is preferably
in the range of from about O. 001 to about 3.0, more
preferably about O. 01 to about 1.0, more preferably
from about 0.01 to about 0.15. The amount of oxygen
bonds f ormed by the activated surface depends on
30 surface F/C stoichiometry and the substrate material.
For polyethylene, a suitable O/C stoichiometry is about
10 % or greater. The extent of surfa~e activation for
any given substrate material ( as represented by
subsequent O/C ratio) is beliaved to undergo a maximum
35 at a specific degree of surface fluorination ( i . e. F/C
ratio) .
W~93J24~59 2 ~ l ~ 2 3 a PCT/VS93/05273
While not wishing to be bound by any particular
theory, fluorination is thought to proceed by a radical
mechanism by the abstraction of hydrogens. To the
extent that some radicals produced do not react during
the fluorination, subsequent reactivity with oxygen
occurs. Oxygenation increases the polar surface energy
which is a measure of hydrophilicity. The radicals can
also react with carbons on neighboring chains producing
a degree of surface crosslinking. Crosslinking reduces
any tendency for interfacial diffusion (i. ~.
blocking).
..
Thermol21ast_c Stretch/Clinq Films
Thermoplastic films produced in accordance with
the present invention have excellent cling properties
on the cling layer and slip properties on the non-cling
la~er. In a preferred embodiment, the use of
tackifying additives can be avoided because of the
excellent cling properties of the cling layer polymer
against a partially fluorinated non-cli~g surface. The
treatm~nt while enhancing the cling property of the
stretch/cling film does not, however, substantially
increase the tendency to block, and generally a
substantial decrease in the block is found. The non
cling layer is preferably treated, however either side
may be treated~ The present thermoplastic films, as a
whole, additionally have desirable stretch, tensile,
puncture resistance and tear resistance properties.
Further, the thermoplastic materials used for the cling
: and non-cling layer have excellent thermal stability,
and edge trim scra~ _an be processed without
signifirant loss of film performance. This combination
of properties makes the thermoplastic films o~ the
35 present invention especially well suited for use as ~;
stretch/cling wraps.
2~1 J23~
W~3/~45~9 PCT/US93/05273
:. .
The thermoplastic film preferrably comprises a
cling layer and a non-cling layer, wherein one or both
of the exterior surfaces is partially fluorinated. The
cling layer comprises a polymer of two or more
monomers, wherein a first monomer comprises ethylene
and a second monomer comprises an acrylate. Acrylate,
in the singular, refers to both a single acrylate and
combinations of different acrylates. These polymers
will generally be referred to as ethylene-acrylate ~or
EA) polymPrs.
Acrylates useful in the present invention are those of
~he general formula:
:
R
~5
:
CH2 = C - COOR'
wherein R is selected from hydrogen or a hydrocarbon
group having from l to 22 carbon atoms, preferably an
~lkyl, aryl, aromatic, olefin or the like hydrocarbon
group and wherein R' is selected from the same or
ifferent of these hydrocarbon groups.
Pre~erred acrylates comprise those wherein R is
~5 selected from hydrogen or an alkyl group and wherein R'
is the same or different of such alkyl group. Specific
examples of preferred acrylates include methyl
acrylate, ethyl acrylate, propyl acrylate, n-butyl
acrylate, 2-ethylhexyl acrylate, decyl acrylate,
octadecyl acrylate, methyl methacrylate, ethyl
methacrylate, n-butyl methacrylate and the like. Of
these, methyl acxylate is particularly preferred.
.~ .
In the preferred embodiment, the EA polymer
compri~es an acrylate content of between about ~% to
about 40~, more pre~erably between about 10% to about
35%, most preferably between about 20% to about 30%,
W~93/245~9 2 1 1 ~ 2 3 0 ~CT/US93/0~73
and especially between about 24% to abou~ 2~% by weight
based upon the weight of the EA polymer. The ~A
polymer may have a wide range of melt indexes (MI),
generally between about 0.1 to ab~out 30 d~/min, more
preferably betwe~-~ about 1 to about 10 dg/min ~ASTM D-
123B, Condition -
The EA polymer may also comprise one or more freP
rad ally polymerizable termonomers. Sui-able examples
inc-ude, but are not limited to, vinyl esters, acrylic
acids ~i.e. methacrylic and ethacrylic acid), other
acrylates, carbon monoxide and the like. These
additional termonomer~ will generally be present in
smal~ amounts, usually less than a total of about 10%
7 5 by weight based upon the weig~ of the EA polymer.
Optionally~ tackifying additive may be added to
the EA pol~ r during the polymerization reaction or
subsequently blended in to improve the cling properties
20 ~ of the film. A wide variety of tackifying additives
are well known in the art including, for example,
polybu~enes, atactic polypropylenes, terpene resins,
hydro~enated rosins, rosin esters and other like
hydrocarbon tackifying resins. It should be noted,
however, that the aforedescribed ~A polymers produce
films of sufficient cling so as to not req~ire the use
o~ a tackifying additive. The use of tackifying
additives i5 contemplated by this invention but is not
necessarily preferred. In a preferred embodiment, the -~
EA polymer is essentially free of a tackifying !
~dditive.
.
The cling layer preferably comprises between about
5% to about 95%, more preferably between about 5% to
about 35%, most preferably between about 10% to about
20% o~ the combined thickness of the cling and non- ;
cling layers.
2~2~
W~93~245~9 P~T/US93/05273
The second layer of the multilayer stretch film
comprises a non-cling layer opposite the cling layer.
The non-cling layer comprises any suitable polyolefin
or combina~ion of polyolefins such as polyethylene,
polypropylene, copolymers of ethylene and propylene,
and polymers obtained from ethylene and/or propylene
copolymerized with minor amounts of other olefins,
particularly C4-C12 olefins. Particularly preferred
are medium density polyethylene (MDPE), polypropylene
and linear low density polyethylene (LLDPE), i.e., a
copolymer of ethylene with up to about 20~ by weight
C4-C10 olefin(s~. Especially preferred olefin
comonomers include l-butene, l-hexene, 1-octene and 4
methyl pentene-l.
Suitable MDPEs include those having a density in
the range of from about 0.92 to about 0.95 g/cc and a
wide ranging MI, generally up to about 30 dg/min
preferahly between about 0.5 to about 10 dg/min.
~ : :
Suitable LLVPEs include those having a density
greater than about O.9oO g/cc more preferably in the
range of from about 0.900 to about 0.940 g/cc. The
2~ LLDPEs may also have a wide ranging MI, generally up to
about 30 dg/min, preferably between about 0.5 to about
10 dg/min.
Suitable polypropylene is normally solid and
30 i50tactic, i.e., greater than 90% hot heptane
insolubles, having wide ranging melt flow rates of from
about 0.1 to about 300 dg/min. As is known, such
polypropylene is normally crystalline with a density
range of from about 0.89 to about 0.91 g/cc for
i~otactic polypropylene. Employing polypropylene in
~he non-cling layer has the additional advantage of
imparting a~rasion resistance thereto.
s
win/94clbO90.doc/dlp 2 ~ I $ 2 3 0
.
- 13 -
T~e n~n-cling l~yer pre~'era~ y co~prises between
abou~ 5% to ~bc~ut 95%, more prefe:rably betwe~n abou~
~5% to about ~%, ~os~ preferably betweerl abs:~u~ 80% ~o
5 about 909~ o~ the combined thicknes~; o~ the clingJnon-
cling layers .
~ ttable,_Prln ble, Inkabl~ Film:~ .
Alternate embodim~nts of the inven~ion provid~ .:
~ttabl~, printable and~or inkable polyol~fix- films.
- 5he ingle or multilay~r f ilm~e ae de~cribe~ ab~r~
or other polyole~in ~ilms such ac homo or co-
poly~thyl~ne, homo ~r co-polypropylenQ, ~thylene, vinyl
aceta~ and th~ like may be partially fluor~nat@d to
enhance wet~ability, pr~ntability and~or ink ret~ntion. -
Wetting is the idea that maximum ir~ter~cial
adhesiYe ~ond st~en~th ~6 achie~ed when the adhes~ve ~.
cc~m~; into contact with the a~herent and the
intermolecular force~: acro6s tha in~er~ac~ ar~ ~
maxi~niz~d. The partially fluorinat~d film~ o~ thi~ :~
ntlon have increa~ed wettabil~ty when ctampared to
~5 t~e non-fluorinated films. Wettabil:i~y i-~ measured
u ing etandard tr~t solutions w~ll known in th~ a~t :~
D2578-94). AST~ D2578-94 iY, h~r~2by incor~orat~d
by r~ronce. Wettability i~ ~lsc~ c:om~only ~ported in
t~ o~ pol~r sur~ace energy which i m~asured by t~e
3 0 geo3llatric m~n e~uation as shown for exalRpl~ on pag~
143 o ~ ne~ Inter~ace an~ ~d~, I)e~er Pub.
lg82. In ess~nc~ partially ~luorinat~d ~
bec::ome~ ~or~ rQceptive to ink~, dy2~;, pigffl~n~t~;
a~QciY4~, t2~ r8~ hot mcl1 adh~iYe~ and t~he like
yidding s~ong~ ~nds. ~h~ w~3tt~bility o:e ~e
part~ al ly ~luorlnated ~ iB
AMENDED SHEET
, . . .
W093/24559 2 1 1 3 2 3 v PCT/US93/0~273
substantially improved when compared to the non
flourinated films. In preferred embodiments the
partially flourinated films will have a polar surface
energy of at least about 10 dynes/cm, preferrably at
5 least about 15 dynes/cm, even more preferrably at least
about 20 dynes~cm, even more preferrably at least about
30 dynes/cm.
Thus, this invention contemplates partially
10 flourinated films with adhesive compositions coated
thereon ~or use in many applications such as tapes and
labels. Suitable adhesives include hot melt
compositions, pressure sensitive adhesive
composistions, contact adhesive compositions and the
15 like. Examples include EVA based hot melts,
polyurethanes and polyacrylates.
This invention also contemplates films partially
flourinated without adhesives used in a variety of
20 applications such as packages, bags, containers and the
` like.
Likewise, the partially flourinated films are also
~ore receptive to inks, dyes and other printing or
25 coloring agents known to those of ordinary skill in the
art including Fuchsine (CI 42510), Calcocid Greens (CI
44090), titanium dioxide, colloidal carbon, graphite,
ceramics, clays, phosphor particles, metal particles s
and the like.
These agents may be applied by any of several
methods known in the art, for example the pigment may
be combined with a resin such as nitrocellulose or a
polyamide and a solvent such as ethylacrylate or n
35 propyl alchohol to form a printing liquid that îs then
applied to a substrate. Rotogra~ure and Flurography
are examples.
~ ~ ,' ,' ! " . - .,
W09~/24559 2 1 1 ~ 2 3 ~ PCT/US93/05273
- 15 - -~
The various films may also include one or more
intermediate layers between the layers for any one of a
number of well-known purposes such as, for example, to
providP structural support, to modify the overall
physical properties balance of the film, to utilize the
recycle trim and scrap or to provide a barrier layer to
oxygen or other gases. As just indicated, this
intermediate layer may comprise the recycle trim and
scrap, or may comprise any other suitable polymer. The
intermediate layer(s), however, while preferred, is
~optional and should not be considered a limitation on
the present invention.
The film layers of the present invention may, if
desired, also include one or more other well-known
;~ additives such as antioxidants, ultraviolet absorbers,
antistatic agents, release agents, pigments, colorants
or the like.
2V
Additionally, normal trim and scrap from the film
production process, or from suitably recovered and
reprocessed films can be recycled into layers,
:~ preferably the core structural layer of a three-layer
film.
The EA polymers prefered for use in stretch cling
films may be produced by any one of a number of well- ;
known processes such as, for example, those described
in U. S. Patent No. 3,350,372, which is incorporated by
reference for all purposes as if fully set ~orth.
Generally ethylene and any comonomers such as an
acrylate to make an EA copolymer and, if desired,
another monomer(s) are metered into, for example, a
hîgh pressure autoclave reactor along with any one of a
number of well-known free radical polymerization :
initiators (catalysts) suitable for produclng EA
Wog3/24~sg 2 1 ~ ~ 2 ~ ~ PCT/~S93/~5273
- 16 -
polymers. Particularly preferred catalysts include
organic peroxides such as, for example, lauroyl
peroxide, di-tert butyl pero:xide, tert butyl peroxide
and various azo compounds. ~Typically, the catalyst
will be dissolved in a suitable organic liquid such as
benzene, mineral oil or the like. Ordinarily the
catalyst is used at a level of between about 50 to
about 20,000 ppm, more preferably between about 100 to
about 250 ppm based upon the weight of the monomers.
MDPE, LLDPE and polypropylene may be made by well
known Ziegler catalyst processes including gas phase,
slurry, solution, and the like and are readily
available commercially.
In preparing the thermoplastic films of the
present invention, any one of a number of well-known
extrusion or coextrusion (in the case of multilayer
films) techniques as disclosed in the previously
2Q incorporated references may ~e utilized. As preferred
exampl s, any of the blown or chill roll cast processes
-~ as disclosed and described in those references i5
suitable for use in producing thermoplastic films in
accordance with the present invention.
As previously mentioned, the thermoplastic films
of the present invention have properties making them
especially well suited for use as strPtch/cling films,
however this use should not be considered a limitation
on the present invention. For example, these films can
be made into other forms, such as a tape, by any one of
a number o~ well-known cutting, slitting and/or
rewinding operations. Physical properties including~
but not limited to, tensile strength, tear strength and
elongation can be adjusted over wide ranges by altering
the resin types and specifications as appropriate to
W093/245~9 2 1 ~ 8 ~ 3 ~ P~T/~S93/05~73
- 17 -
meet the requirements to a given wrapping, bundling or
taping application.
For bundlingl packaging and unitizing
applications, the thermoplastic film of the present
invention is stretch-wrapped by any one of a number of
well-known procedures (such as those disclosed in the
aforementioned incorporated references) around an
article or a plurality of articles preferably so that
the cling layer faces inside (towards the article) and
the non~cling layer faces outside (away from the
article). Typical of articles suitable for bundling,
packaging and unitizing with the present thermoplastic
film include, but are not limited to, various
foodstuffs ~canned or fresh), rolls of carpet, liquid
containers and various like goods normally
containerized and/or palletized for shipping, storage
and/or display.
.~
The foregoing more general discussion of this
invention will be further exemplified by the following
specific examples offered by way of illustration and
not limitation of the above-described invention.
'~
25 Examples ~
- ,-.
In the following examples, I/0 cling is reported
as the force in grams required to partially peel apart
two strips of film. A first film strip is ~ttached to --
a 30 degrees inclined plane - th the outside (O)
surface (non-cling) facing ~ ird. A second 1" X 8"
strip is placed on top of t~. irst strip with the ~`
inside (I) surface (cling) f~cing downward. Pressure is
applied to the second strip to cause the two strips to
st1c~ together. If an evaluation of cling under
stretched condi~ions is desired, hoth film strips are
prestretched and allowed to relax before testing. The
211~23SJ
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- 18 -
end of the second strip at the base of the inclined
plane is attached, by clip and string, to an apparatus
which can exert a strain at a constant rate ~Instron
1130~, The two strips are then pulled apart at a
crosshead speed of 10 cm/min until the aforementioned
string is parallel with the base of the inclined plane.
The force at this point is reported as cling.
Block is reported as the 180 degree peel strength
of the outside surface (non-cling~ of a first film
specimen press~d with 200 psi at 154 degrees F (1.378
~MPa at 103.3 degrees C) against the inside surface
~cling) of a second film specimen for a specified
length of time.
~- The block, cling or slip of multicompositional,
multilayer films, refers to properties the film has
when in physical contact with itself such as on a roll
or a wrapped pallet. Such properties are generally
ref~renced by noting the location of the surfaces or
layers in contact (i.e. inside/outside (I/O)).
Examples 1-2 and Com~arative~Examples ~-6
: ~
A MDPE film was made from a resin having a melt
index of 2 and a density of 0.9Z g/cc produced in a gas
phase reactor. The film was fluorinated using two
different degrees of fluorination~ One film had high
fluorine concentration at the surface and the other a
low fluorine concentration. Film surface stoichiometry
for O/C and F/C as determined by x-ray spectroscopy
(XPS) is given in Table I.
Fluorination was conducted by a commercial
; 35 ~luorination service which is believed to have used a
con~entional batch apparatus wherein the film substrate
was exposed to a gas mixture of molecular fluorine in a
WO 93/?4~59 2 1~ ~ 2 3 ~ PCT/US93/05273
-- 19 -- :
pure nitrogen carrier gas for a set period of time in a
reactor vessel. The fluorinated films were handled
normally in air prior to physical testing.
To illustrate the effect of fluorine treatment on
blocking tendency, film interfaces were prepared by
pressing together a cling layer surface comprising a 24
EMA film and a non-cling layer surface comprising the
fluorinated MDPE described above. The pressing
conditions were 200 psi pressure and 158 degrees F
tempera~ure (1.378 MPa and 105.5 degrees C~ for a set
-period of time. The blocking tendency was gauged by
the peel for-e required to separate the films. As seen
in Table II, interfaces made with both the low and high
fluorinated MDPE required very little peel force
compared to the film interface lacking a fluorinated
surface. Furthermore, the low fluorinated film
interface was almost as resistant to blocking as the
high fluorinated film interface.
,
~ . .
: .
h ~ J
W~93~24~9 PC~/US93/05273
- 20 -
TABLE I
SURFACE STOICHIOMETRY
iWULE SU~fACE sualAcE SlOlCHlC~ETI~ ~F~U E~
t I ~DPE ¦ 0.17 1 0.02t ¦ lD. 1 1 3~,8
Ce~ 07E I 0.~1 1 o.n~ I ~.3 1 0.1
1 0
TABLE II
BLOCXING TEST RESU~TS
__
E~4PLE SIL~ I~TEIltACE PIIESS II~E PEEL ~CE
~-tn)~ ~ lb~
~; ~ _ClI~C L_l~ ~101-CII~IC U~E~ __
~: ~ ~Ult7RE~TED E~A Esa~l~ 1 ~0 ¦ 0.0~
~ . ~
t~. 2UNt'llEATE9 ~ Cc~. ~A~I~ 0.01
.. ; . ,....... . _
Cc~p. 3U~REAl~ED ~U WlREl~ED ~PE 30 0.25
_ __ ~
Cony~. ~,U~ E~.lED t~U UdT~EAlED ~lDPE 5 0.2)'
:: 2~i ~2~, S SU)
_ , _ __ _
Sa~p, SU~ EAtl) ~1 UlllIEA~ED I~PE ~/O 0.~7
: ~ . t2~ S ~A)
_ _ _~ ~
CIVP S ~-~A~ ~ U~ 1 2C O 5
30l -~
a-200 psi/158F press conditions (1.378 MPa and 105.5
degrees C)
Example 3 and Comparative Exam~les 7-8
Zero % stretch cling was measured for film
interfaces prepared similarly to Examples 1-2 and
Compara~ive Examples 1-6. The results were compared to
a similar film wherein the interface surface was not
win/9~clbO9t).dlocfdlp 2118 2 3 ~
-- 21 --
fluor~nat~d. As seen in Table III, the fil~ interac~
(l:xample 3 ) ha~ring the low f}uorine ~reatad surface
5 showed enhanced cling. The film inter~ac~ (Comp.
Example 7~ having the high fluorine treated sur~c~ had
~ery 1 ittle clang, a expected .
'rABLB III
CLING TEST RESULTS
__
IW~4 ~I.q Cl~ t ~ ~tl
. __ _ ,~
_ tLItt~ ~ ~ .
3 WT~AlE~ E~ll~ ~ 3~a ¦ 2
_. ~# StU~ _
.~b r wr~A~ ~ . ~ ¦
~ ~ ~ ~ ~ I_
~ ~ ~ D _ _~N~
,
:.
.;
~ ,
._
~ .,
. .
AMENDED SHE~
.
