CA2118230A1 - Fluorine treatment of polyolefin films - Google Patents

Abstract

A thermoplastic polyolefin film having one or both surfaces of the film partially fluorinated to substantially increase wettability, printability, inkability is provided. A partially fluorinated thermoplastic stretch film of ethylene/acetate having increased cling and decreased block is also provided.

Description

wlnts4clbo~o~doc/dlp 211~ 2 3 0 ~
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 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 .

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.

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 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 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
W093/24~59 P~T/US93/05~73 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 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 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 ~

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~
.

Claims (14)

What is Claimed is:

1. A thermoplastic film comprising:
a cling layer; and a non-cling layer wherein the surface of one of the layers is partially fluorinated.

2. The film of claim 1 wherein the cling layer is a copolymer of ethylene and an acrylate and the non-cling layer is polyethylene or polypropylene.

3. The film of claim 1, wherein the partially fluorinated surface is formed by exposure to fluorine and oxygen.

4. The film of claim 1 or 2 having an adhesive coated on the cling layer, or one or more inks, dyes, pigments or mixtures thereof affixed thereon

5. The film of claims 1, 2, 3 or 4 wherein the non-cling layer is a stretch layer.

6. The film of any of the above claims, wherein the fluorinated surface(s) has a fluorine:carbon surface stoichiometry as determined by x-ray photoelectron spectroscopy of from 0.001 to 3.0, preferably 0.01 to 1Ø

7. The film of any of the above claims further comprising a core layer, preferably a core layer selected from the group consisting of linear low density polyethylene, recycled polyolefins, polypropylene, or a mixture thereof.

8. The thermoplastic film of any of the above claims, at least one layer is selected from the group consisting of high density polyethylene, medium density polyethylene, low density polyethylene, linear low density polyethylene, polypropylene or blends thereof.

9. A process for producing a thermoplastic film having substantially increased cling and/or reduced block comprising:
partially fluorinating a mono, bi or multi layered polyolefin film by exposing one or more surfaces of the polyolefin film to fluorine and oxygen.

10. The process of claim 9 wherein the film comprises at least one layer is selected from the group consisting of high density polyethylene, medium density polyethylene, low density polyethylene, linear low density polyethylene, polypropylene or blends thereof.

11. The process of claim 9 or 10 wherein the film is exposed to oxygen in the form of air.

12. The process of claim 19, 10, or 11 further comprising affixing an ink, dye, pigment or coloring agent to the partially fluorinated film or coating an adhesive composition onto the partially fluorinated film.

13. The process of claim 9, 10, 11, or 12, wherein the fluorinated surface(s) has a fluorine:carbon surface stoichiometry as determined by x-ray photoelectron spectroscopy of from 0.001 to 3Ø

14. The process of claim 13 further comprising coextruding the film with a second polyolefin.