CA2130192C

CA2130192C - Elastic articles having improved unload power and a process for their production

Info

Publication number: CA2130192C
Application number: CA002130192A
Authority: CA
Inventors: Aspy K. Mehta
Original assignee: Exxon Chemical Patents Inc
Current assignee: ExxonMobil Chemical Patents Inc
Priority date: 1992-02-19
Filing date: 1993-02-17
Publication date: 1998-02-24
Anticipated expiration: 2013-02-17
Also published as: EP0629151B1; EP0629151A1; US5241031A; CA2130192A1; DE69306765D1; DE69306765T2; JPH07503913A; WO1993016863A1

Abstract

Disclosed is a process for producing an elastic film of improved unload power which comprises producing a precursor film comprising an elastomer of ethylene copolymerized with a C3 to C20 alpha-olefin comonomer and/or a C3 to C20 polyene comonomer, the elastomer having a density of from 0.855 g/cm3 to 0.900 g/cm3, a melt index of from 0.2 to 1000 dg/min, a molecular weight distribution in the range of about 1.5 to 30, and a Composition Distribution Breadth Index (CDBI) of at least 45 percent; orienting the film to a draw ratio in the range of from 2:1 to 20:1; and annealing the oriented film at a temperature between the softening point and melting point of the elastomer. Further disclosed is an elastic film oriented to a draw ratio of from 2:1 to 20:1 and comprising a copolymer of ethylene polymerized with at least one comonomer selected from the group consisting of C3 to C20 alpha-olefins and C3 to C20 polyenes, the copolymer having a density in the range of 0.855 to 0.900 g/cm3, a melt index in the range of 0.2 to 100, with a composition distribution index of at least 45 percent.

Description

Wo93/t6863 ~ PCI/US93/01413 ~ 13019~

ELASTIC ARTICLES HAVING IMPROVED UNLOAD POWER AND A
PROCESS FOR 1~1~;1~ PRODUCTION
.

FIELD OF T~E INVENTION

The present invention relates to elastic articles and a method for their production. More particularly this invention relates to ethylene-based plastomerarticles having improved unload power and a process for their production. Even more particularly this invention relates to a plastomer precursor which, by a post 10 polymerization process of orienting and annealing, is made into an article having improved unload power.

BACKGROUND OF T~E ~NVENT~ON

Elastomeric polymers are utilized in a wide variety of applications for which non-elastic polymers are totally unsuited. For example, in articles of clothing, such elastomeric polymers are utilized as neck, wrist, waist, ankle and head bands. As the garrnent is worn, the elastic polymer band must have enough "unload power" to hold it in place. When the garment is not worn, it is generally desirable that the elastic polymer band have a low "residual set" so that the elastic polymer band of the garment returns essentially to its original shape. In addition, the elastic polymer band must also demonstrate a high degree of repeatability as the gallllen~
is worn over a long period of time. In terrns of garment applications, these constraints dictate which of those elastomeric polymer compositions now known can be fabricated into article forms which can be placed into applications in garments.
"Unload power" is an important elastic tensile property in elastics applications, particularly for garment applications. For example, in diaper applications, the unload power of an elastomeric article provides an indication of the retractive force which holds the elastomeric article which is part of the diaper Ieg of the garment against the infant's body. Tn all elastomeric materials, the unload power is lower than the load power (the force required to extend the strip). This difference shows up as a hysterisis (i.e. the force to extend is different than the force to hold in place) and is larger for synthetic elastomers than in the case of a natural rubber. "Residual set" refers to the change between the length of an elastomeric material before and after its extension to a certain length for a certain time for a certain number of cycles. Residual set may be for example, the percent change in length of a film after extension of the film to 200 percent of its initial s length through 5 cycles. Each cycle would consist of e~en~ing the film to 200 percent of its initial length, holding the film extended for a time period, rele~cing the e~tending force, and allowing the film to return for a time period.
Typical elastic materials utilized for clothing applications include polyureth~nçs, ethylene-propylene rubbers (EP or EPR), inclu~ing ethylene-o propylene-diene terpolymers (EPDM), and natural rubbers.
Polyurethanes have the desired unload power, residual set and repeatability for use in most garment applications. However, polyurethanes have a relatively high specific gravity,-which results in a lower yield of polyurethane articles hence a higher cost as compared to cotnparable lower specific gravity polymers.
Furthermore, where the garment is to be used once and quickly discarded, such aswith surgical ga~ c,lls or disposable diapers, polyurethanes as an element thereof are overenv;.-ee. ed for the desired use of that ga.llle..t and thus overly expensive.
For garrnent applications, conventional EPs and EPDMs have very poor intrinsic physical properties and for such applications generally must be blended with a 20 plastic material such as low density polyethylene, linear low density polyethylene or ethylene vinyl acetate copolymers. Ideally, for suitability in such ga,lllent applications an EP and/or EPDM which does not need such blending has been desired.
For polyurethanes, EPs and EPDMs, to get an "accordion" shape or 2s "gather" forrnation, such as around the leg opening of a disposable diaper, it has been necess~. y to expose that portion of the overall garment article to heat tocause shrinkage of the elastomeric article of the garment. Conventionally, used elastic materials require a relatively high shrinkage temperature. In addition, many of them require pre-stretching for good gather formation. Exposing the garment 30 article to such a relatively high temperature may be detrimental to the overall ptopel lies of the garment. Further, the commonly used elastic tnaterials generally have to be melt glued to achieve bonding to the garment, such as to a polyolefinlayer in the garment. Controlled heat bonding to .such a polyolefin substrate, if possible would be advanta_eous.

wo 93/16863 ~ g 2 PCr/US93tO1413 A need exists for an elastic article that can be economically utilized in disposable garment applications. There also exists a need for use in garment applications an elastic article with a relatively low shrinkage te,l"~e,~ture.
Additionallyt there exists a need for an elastic article that can be heat bonded/sealed s to polyolefins.
A need still exists for elastic articles of optimum quality for particular uses.It is still a desire of the art to provide elastic articles having high quality characteristics composed of ethylene based plastomers.
Accordingly, the present invention relates to elastic materials having o improved unload powers, wherein the elastic materials comprise ethylene based elastomers and plastomers made from metallocene catalysts. Such elastic materials having improved unload powers are produced by subjecting a precursor elastic film to orienting and annealing.

5 SUMMARY OF T~E INVENTlON
.

Acco, ding to one embodiment of the present invention there is provided a process for producing an elastic film of improved unload power which comprises providing a precursor film that is oriented and anne~led. Prer~ably~ the film 20 COl"~" ises a copolymer of ethylene polymerized with at least one comonomer selected from the group concistinlJ of C3 to C20 alpha-olefins and C3 to C20 polyenes, wherein the copolymer has a density in the range of about 0.855 g/cm3 to about 0.900 g/cm3, a melt index in the range of about 0.2 to about lOOO, with a Composition Distribution Breadth Index (CDBI) at least about 45 percent. The 25 orientation of the film is to a draw ratio in the range of about 2: l to about 20: l .
The anne~ling is conducted at a temperature between the film softening point andmelting point. The co~"bil1alion of orientation and annealing provides the opponunity for novel property profiles. Significant variation in the property profile can be achieved by controlling the amount of orientation and ~nnP~1inv adopted 30 during the fabrication.
According to another embodiment of the present invention there is provided an elastic film orientated to a draw ratio in the range of 2:1 to 20:1 and comprising a copolymer of ethylene polymerized with at least one comonomer selected from the group consisting of C3 to C20 alpha-olefins and C3 to C20 polyenes, wherein the copolymer has a density in the range of 0.~55 g/cm3 to 0 900 g/cm3, a melt index in the range of 0.5 to about 1000, with a CDBI of at least about 45 percent Preferably, the elastomer utilized in the present invention is a plastomer that s is an ethylene based polymer which may be made using a transition metal metallocene catalyst. The plastomer having a prefe-ied density range between 0.88 to 0.900 g/cm3.
In another embodiment, the elastic film of the invention is bonded or sealed to polyolefins.
BRIEF DESCRlPT~ON OF T~E DRAWlNGS

FIG. 1 is a sci-em~tic of the present invention showing the precursor film being made by the slit film extrusion process (also lerelled to as ribbon yarn extrusion process), wherein the melted polymer is extruded through a die to formthe precursor film. Also shown are the orienting and ~nnealing appa~lus for lS making an elastic film having improved unload power.
FIG. 2 is a s~ern~tic of the present invention showing the precursor film being made by the blown film process, wherein the melted pol,vmer is blown into a tube and air cooled to form the precursor film. Also shown are the orienting and~nnP~ling app~allls for making an elastic film having improved unload power.
FIG. 3 illustrates the hysterisis testing procedure used for det~ the unload power and residual set.
FIG. 4 plots the unload power at various extensions up to 100 percent for elastic sample Nos. 1, 2, 5 and 7.
FIG. 5 is a graph ofthe solubility distribution and composition ~3i~ ion 2s of a copolymer (X) having a narrow solubility disllibulion composition disllibulion and composition distribution and copolymer (Y) having a broad solubility distribution composition di~l-ibulion and composition distribution.
FIG. 6 is a graph illustrating the co.lelalion between dissolution temperature and composition used to convert the temperature scale to a composition scale.
FIG. 7 is a graph illustrating the method for calcul~ting CDBI.

DETAILED DESCR~PTION OF T}~E INVENTION

.,~

s The present invention provides a fabncation method for increasing the unload power of an elastic material. According to ASTM definitions relating to mbber, elastic materials are considered those materials which rapidly return to apploxi-"ately their initial dimensions and shape after sub~ deformation by a s ~veak stress and release of the stress. In the present invention, elastic materials are considered those which when stretched to twice their original length (2X) at room temperature (18 to 29~C) and held at 2X for one minute, will retract to less than l 5X within one minute after the deforming force is released.
The present invention relates to elastic film having improved unload power 0 produced by orienting and ~nn.o~ling a precursor elastic film. The precursor film is first formed by any suitable method. Once formed, the precursor film is then subjected to a co---bi~,alion of orienting and ~nne~ling to improve its unload power.
The precursor elastic film which is to be further processed to improve its unload power according to the method of the present invention may be produced by any suitable method. Methods of making film are disc~lcced by J. H Briston and L.L.
Katan in Plastic Films~ (2nd ed. 1983). Com~nonly known methods of producing film which may be utilized in the present invention include casting (extrusion and solvent), calen-lering and extrusion methods, such as blow extrusion or slit die extrusion.
The present invention is suitable for improving the unload power of thin elastic articles. Such thin elastic articles are cG,,ul~only known as ribbon, tape, film, strip, etc. The di~,ence between these particular terms is generally dimensional.
For example, tape is generally thought of as being na~lu~h than film. In the present invention, the terms "ribbon", "tape", "film" and "strip" are generally 2s interchangeable, with the present invention suitable for application to thin elastic articles and not ~iinten~ionally limited. Regardless of the method of producing the precursor film, once the precursor film has been produced, it must be further processed to improve unload power of the film. This is accompli~ed by a combination of orienting and ~nne~lin~ the precursor film.
Orientation of non-elastic films such as polypropylene, polystyrene, nylon and polyethylene terephth~l~te to improve clarity, impact ~llel~glh and, particularly in the case of polypropylene, its barrier properties is well known in the art.
However, while it is not known to orient and anneal elastic materials, the methods utilized on non-elastic film are generally suitable for use with in the present process .~

WO 93/16863 ~ 1 3 0 1 9 2 PCI /US93/01413 - . : 6 -for orienting elastic film.
The orienting and annealing of the film may be carried out monoaxially in the machine direction or the transverse direction or in both directions (biaxially) either simultaneously or sequentially using conventional equipment and processess following cooling of the precursor film. Blown films are prefere,.lially stretched in machine direction or in both directions whereas cast films are preferably stretched in the machine direction. Generally, for orientation in the machine direction, the precursor film is passed around two rollers driven at di~renl surface speeds andfinally to a take up roller. The second driven roller which is closest to the take up o roll is driven faster than the first driven roller. As a consequence the film is stretched between the driven rollers. Conventional "godet" stands as are well known in the art may also be utilized.
Film orientation may also be carried out in a tentering device with or .
without machine direction orientation to impart transverse direction orientation in 5 the film. The film is gripped by the edges for processing through the tentering device. For most final applications, the precursor film is monoaxially oriented in the m~clline direction.
The morphology of the plastomer derived tapes can be viewed as a matrix of amorphous material interspersed with crystallites. For orienting it is generally 20 necess~ry that the film be heated to between its softening point and its melting point. This heating is necessary to allow extension or orientation to be inducedinto the film. Since the temperature is between the film softening point and melting point, the smaller imperfect crystallites will melt, whereas larger more perfectcrystallites of the plastomer will remain. The molecules in the amorphous matrix25 become oriented or extended depending on the draw ratio and other material and fabrication parameters.
For ~nne~lin-J the temperature is still between the film softening point and melting point. The annealing step is necessary to anneal or perfect the crystallites that survived the orienting step and to relax out stresses. This ~nne~ling aids in 30 ",~int~in;ng the orientation or extension induced in the orienting step. The ~nn~lin~ temperature is preferably less than the orienting temperature.
Generally once the film leaves the annealing step, ambient cooling is sufficient. In most cases, the film from the annealing step is then spooled in awinding unit.

wO 93/l6863 PCI/US93/01413 ~ 130192 Suitable film making/orientinglannealing processes are shown in FIGs. 1 and 2 ~iccllcsed below. A commercially available orientation line includes the Killion ribbon yarn line (model serial number 3874).
FIG. I shows a schematic of a slit film extrusion process. The elastic s pellets are fed into hopper 10 of extruder 12. In extruder 12 the elastic pellets are heated to above their melting point and extruded through die 15 into film 3. Film 3 is subsequently cooled by quenching in water bath 19. Slitter 22 is an optional station that slits film 3 into two or more narrower tape sections 5. Orientation and anne~ling takes place utilizing first godet stand 25, second godet stand 28, third o godet stand 30, orienting oven 26 and annealing oven 29. Tape 5 is subsequently wound into spools in winding unit 33. In the orienting and annealing ovens, the material is generally heated to a temperature above the softening point but less that its melting point.
FIG. 2 shows a schematic of a blown film extrusion process. The elastic pellets are fed into hopper 10 of extruder 12. In extruder 12 the elastic pellets are heated to above their melting point and extruded through die 15 into tube shapedfilm 3. Film 3 is subsequently air cooled in blown-film tower lB. Slitter 22 is an optional station that slits film 3 into two or more narrower tape sections 5.
Orientation and anne~ling takes place utili7ing first godet stand 25, second godet stand 28, third godet stand 30, orienting oven 26 and ~nnP~ling oven 29. Tape 5 is subsequently wound into spools in winding unit 33.
In the process of the present invention, the draw ratio to which the film is oriented may be any ratio that will improve the unload power of the film to desired levels. In both FIGs. 1 and 2, Vl, V2 and V3 repl ese"t the film travel speed at2s various points as indic~ted. The draw ratio is the ratio of V2 to Vl. Generally, the draw ratio ofthe drawn film could be at least 2:1, preferably at least 4:1 and most preferably at least 6:1. The upper limit on the draw ratio is generally limited by the properties of the elastic material utilized and the desired end properties of the drawn film. Generally, the draw ratio will not exceed 20:1, preferably the draw ratio will not exceed 10:1 and most preferably the draw ratio will not exceed 6:1.
Generally, V3 is such that the film orientation can be maintained during the annealing step. This means that V3 is generally at or near V2.
In the present invention, the type of elastomer utilized will depend upon economics and the properties desired in the final end product. Generally the wo 93/16863 PCr/US93/01413 ~130192 elastomer can be any of the group consisting of plastomer, styrene-hutadiene copolymer, polychloroprene (neoprene), nitrile rubber, butyl rubber, polysulfiderubber (Thiokol), cis-1,4-polyisoprene, ethylene-propylene co and terpolymers (EPR and EPDM rubber), silicone rubber and polyurethane rubber. Preferably, the s elastomer utilized in the present invention refer generally to a class of ethylene based polymers having a density of less than 0.900 g/cm3 (down to 0.855 g/cm3) at a molecular weight, Mw greater than 20,000 (200 MI and lower). Within the density ranges of elastomers above, the preferred ethylene based polymers are plastomers. Plastomers for the purposes of this patent application have an ethylene o crystallinity between plastics linear low density and very low density polyethylenes) and ethylenelalpha-olefin elastomers and generally have a density of less than 0.900 g/cm' down to 0.88 glcm~.
The plastomer utilized in the present invention is selected from the group of polymers consisting of ethylene polymerized with at least one comonomer selected1S from the group cons;sling of C3 to C20 alpha-olefins and C3 to C20 polyenes.Plastomer utilized in the present invention are selected from the group of polymers concisting of ethylene polymerized with at least one comonomer selected from thegroup consisting of C3 to C20 alpha-olefins. The types of monomers selected in the plastomer utilized in the present invention will depend upon economics and the desired end use of the resultant fabricated material. The polyene utilized in the present invention generally has in the range of 3 to 20 carbon atoms, preferably, the polyene has in the range of 4 to 15 carbon atoms. The polyene is preferably a diene, that generally has in the range of 3 to 20 carbon atoms. Preferably, the diene utilized in the present invention is a straight chain, branched chain or cyclic 2s hydrocarbon diene preferably having from 4 to 20 carbon atoms, and more preferably from 4 to 15 carbon atoms, and most preferably in the range of 6 to 15 carbon atoms. Most preferably, the diene is a non-conjugated diene. Examples of suitable dienes are straight chain acyclic dienes such as: 1,3-butadiene, 1,4-hexadiene and 1,6-octadiene; branched chain acyclic dienes such as: 5-methyl-1,4-hexadiene, 3,7-dimethyl-1,6-octadiene, 3,7-dimethyl-1,7-octadiene and mixed isomers of dihydro myricene and dihydroocinene; single ring alicyclic dienes such as: 1,3-cyclopentadiene, 1,4-cylcohexadiene, 1,5-cyclooctadiene and 1,5-cyclododecadiene; and multi-ring alicyclic fused and bridged ring dienes such as:
tetrahydroindene, methvl tetrahydroindene, dicylcopentadiene. bicyclo-(2,2,1)-~130192 ~

hepta-2-5-diene; alkenyl, alkylidene, cycloalkenyl and cycloalkylidene norbornenes such as 5-methylene-2-norbornene (MNB), 5-propenyl-2-norbornene, 5-isopropylidene-2-norbornene, 5-(4-cyclopentenyl)-2-norbomene, 5-cyclohexylidene-2-norbornene, 5-vinyl-2-norbornene and norbornene. Particularly s preferred dienes are 1,4-hexadiene, 5-ethylidene-2-norbornene, 5-vinyllidene-2-norbornene, 5-methylene-2-norbornene and dicyclopentadiene. The especially preferred dienes are 5-ethylidene-2-norbornene and 1,4-hexadiene.
Generally, the alpha-olefins suitable for use in the present invention contain in the ran_e of 3 to 20 carbon atoms, more preferably, of 3 to 16 carbon atoms o and, most preferably 3 to 8 carbon atoms. Illustrative non-limiting examples of such alpha-olefins are propylene~ I-butene, l-pentene, l-hexene, l-octene and 1-dodecene and the like.
Preferably, the plastomers utilized in the material of the present invention are either ethylene/alpha-olefin copolymers or ethylene/alpha-olefin/diene terpolymers. Illustrative non-limiting examples of suitable copolymers are thosesuch as ethylene/butene-l~ ethylene/hexene-l, ethylene/octene-l, and ethylene/propylene copolymers. Suitable examples of terpolymers include ethylene/propylene/1,4-hexadiene and ethylene/butene-1/1,4-heY~t~iene.
The plastomers suitable in the present invention with desired monomer levels can be prepared by polymerization of the suitable monomers in the presence of supported or unsupported catalyst systems. Preferably the catalyst system utilized is a metallocene catalyst system.
The precise monomer content of the plastomers utilized in the present invention will depend upon economics and the desired applications of the result~nt materials. Typically the plastomers utilized in the present invention, will generally comprise in the range of 65 mole percent to 93 mole percent ethylene (based on the total moles of monomer). Preferably, the plastomers have a minimum of 68 mole percent, most preferably, 73 mole percent ethylene, a maximum of 91, most preferably, 88 mole percent ethylene.
The plastomers utilized in the present invention for example can have an ethylene crystallinity less that 35 percent. Preferably, the ethylene crystallinity is less than 20 percent.
The elastomers utilized in the present invention have a density in the range of 0.855 ~cm3 to 0.900 g/cm3 . Preferably, the elastomers have a density of 0.860 wO 93/16863 ~ 1 ~ U 1 ~d 2 PCr/US93/01413 g/cm3, and more preferably 0.865 ~/cm3. Preferably the elastomers have a densitvof 0.890 g/cm3, and more preferably 0.88 g/cm3 . Most preferably in this presentinvention is the density ranPe of between 0.860 g/cm3 to 0.88 g/cm3. Densities were measured using standard accepted procedures, except that they were s additionally conditioned by holding them for 48 hours at ambient temperature (23~
C), prior to density measurement.
The melt index (MI) of the plastomers utilized in the present invention is such that the plastomer can be extruded into the desired end product. In addition, the MI must be such that the plastomer will have sufficient drawability as desired.
o Generally the melt index is in the range of 0.2 dg/min to 1000 dg/min, preferably the MI is in the range of 0.5 dg/min to 50 dg/min, and most preferably in the range of 1 dg/min to 5 dg/min. MI as measured herein was determined according to ASTM D-1238 (190/2.16). High load MI was determined according to ASTM D-1238 (190/21.6).
The plastomers utilized in the present invention have a molecular weight distribution such that the polymer will have the desired drawability and be processable into the desired end product. The ratio of MW/Mn is generally in therange of 1.5 to 30. The maximum ratio is preferably 10 and most preferably 4.
The minimum ratio is preferably 1.8, most preferably 2Ø
The composition distribution breadth index (CDBI) of the plastomers utilized in the present invention is generally 45 percent or higher. Preferably, the CDBI is 80 percent or higher. Most preferably, the CDBI is 60 percent or higher,and ever more preferably, 70 percent or higher. As used herein, the CDBI is defined as the weight percent of the copolymer molecules having a comonomer 2s content within 50 percent (i.e. + 50%) of the median total molar comonomer - content. The CDBI of linear polyethylene, which does not contain a comonomer, is defined to be 100%.
The CDBI is determined via the technique of_emperature Bising Elution Fractionation (TREF). CDBI determination clearly distinguishes, for example, theplastomers utilized in this invention (narrow composition distribution as assessed by CDBI values of 45% or higher) from products traditionally utilized in prior art (broad composition distribution as assessed by CDBI values generally less than 45%). Composition distribution (CD), composition distribution breadth index (CDBI) were determined by techniques known in the art, such as temperature WO 93/16863 PCr/US93/01413 ~ 13U1~2 1, .

rising elution fractionation as described, for example, in U.S. Patent 5,008,201, or in Wild et al., J. Polymer Sci. Poly. Phvs. Ed.. volume 20, page 441 (1982), both of which are hereby fully incorporated herein by reference. Solubility Distribution is measured using a column of length 164 cm and 1.8 cm inner diameter is packed s with non-porous glass beads (20-30 mesh) and immersed in a temperature programmable oil bath. The bath is stirred very vigorously to minimi7e temperature gradient within the bath, and the bath te~pe~ture is measured using a platinum recist~nce thermometer. About 1.6 g of polymer is placed in a sample preparationchamber and repeatedly ev~c~l~ted and filled with nitrogen to remove oxygen fromo the system. A metered volume of tetrachlorethylene solvent is then purnped into the sample preparation chamber, where it is stirred and heated under 3 atmospheres pressure at 140~C to obtain a polymer solution of about 1 percent concentration. A metered volume of this solution, 100 cc is then pumped into thepacked column thermostated at a high temperature, 120~C.
The polymer solution in the column is subsequently cryst~lli7ed by cooling the column to 0~C at a cooling rate of~20~C/min. The column temperature is then t~ ed at this te,l,pe,alure for 25 min. at 0~C. The elution stage is then begun by pumping pure solvent, preheated to the temperature of the oil bath, through the column at a flow rate of 27 cc/min. Fffluent from the column passes through a heated line to an IR detector which is used to measure the absorbance of the effluent stream. The absorbance of the polymer carbon-hydrogen stretching bands at about 2960 cm~ 1 serves as a continuous measure of the relative weight percent concentration of polymer in the effluent. Af'~er passing through the infrared detector the te."pe, a~l~re of the effluent is reduced to about 1 1 0~C, and the2s pressure is reduced to atmospheric pressure before passing the effluent stream into an automatic fraction collector. Fractions are collected in 3~C intervals. In the elution stage pure tetrachlorethylene solvent is pumped through the column at 0~C
at 27 cc/min. for 25 min. This flushes polymer that has not cryst~lli7ed during the cooling stage out of the column so that the percent of uncrystallized polymer (i.e.
the percent of polymer soluble at 0~C can be determined from the infrared trace. The temperature is then programmed upward at a rate of 1.0~C/min. to 120~C. A
solubility distribution curve, i.e. a plot of weight fraction of polymer solubilized as a function of temperature, is thus obtained.
The procedure for calculating the Solubility Distribution Breadth Index wo 93/16863 PCI/US93/01413 ~130~2 (SDBI) is set forth below.
Solubility distributions of two ethylene interpolymers are shown in FIG. 5.
Here, for illustration purposes only, Sample X has a narrow solubility distribution and elutes over a narrow temperature range compared to Sample Y, which has a s broad solubility distribution A solubility distribution breadth index (SDBI) is used as a measure of the breadth of the solubility distribution curve. Let w(T) be the weight fraction of polymer eluting (dissolving) at temperature T. The average dissolution temperature, T ave is given by 120 l~o TaVe= IT )~(T)dT, where ¦i~(T)dT= 1.
O O

SDBI is calculated using the relation:

1S SDBI(~C)= [¦(T TaVe)4W(T)dT]II4 SDBI is thus analogous to the standard deviation of the solubility distribution curve, but it involves the fourth power rather than the second power to T - TaVe) 20 Thus, for example, the narrow solubility distribution Sample X and the broad solubility distribution Sample Y in Figure 5 have SDBI values equal to 14.6~C and 29.4~C, rcspcc~ ely. The prefe..ed values of SDBI are less than 23~C and more plere,led less than 20~C and even more preferred less than 16~C.
The composition distribution (CD) of a crystalline interpolymer is 2s determined as follows. The composition and number average molecular weight, Mn7 of fractions collected in various narrow temperature intervals for several poly(ethylene-co-butene)'s was determined by C13 N~ and size exclusion chromatography, respectively. Fi_ure 6 is a plot of mole percent comonomer vs.
elution temperature for fractions having Mn ~ 1~,000. The curve drawn through 30 the data points is used to correlate composition with elution temperature fortemperatures greater than 0~C. The correlation between elution temperature and composition becomes less accurate as the Mn of a fraction decreases below 15,000 Such errors can be elimin~ted by direct measurement ofthe composition of effluent fractions by C13 NMR. Alternatively, the elution temperature-composition calibration for high molecular weight fractions given in Figure 6 may s be corrected based on the Mn Of effluent fractions and an experiment~lly established correlation between Mn and elution te.~.pe.~lu.e that applies for Mn <
15,000. However, it is assumed that such low molecular weight molecules are present to a negligible e~ctent and that any errors caused are negligible. A
correlation curve such as the one in FIG. 6 is applicable to any ~o-csenti~lly random o poly(ethvlene-co~-olefin) provided, however, that the a-olefin is not propylene.
The temperature scale of a solubility distribution plot can thus be transformed to a composition scale, yielding a weight fraction of polymer versuscomposition curve. As seen from the composition scale in Figure 6, Sample X
contains molecules sp~nning a narrow composition range, whereas Sample Y
15 contains molecules sp~nninSJ a wide composition range. Thus, Sample X has a narrow composition distribution whereas Sample Y has a broad composition distribution.
~ qu~ e measure of the breadth of the composition distribution is provided by the CDBI. CDBI is defined to be the percent of polymer whose 20 composition is within 50% of the median comonomer composition. It is c~lc~ ted from the composition distribution curve and the norm~li7f~l cllm~ tive integral of the~omposition distributior~ curve, as illustrated in Figure î. The median ~ composition, Cmed, corresponds to the composition at the point where the c .m~ tive integral equals 0.5. The di~1~nce between the values ofthe 25 cum--l~tive integral at compositions 0.5 Cmed and 1.5 Cmed (71 - 29, or 42%, in this example) is the CDBI of the copolymer. CDBI values fall between zero and one, with large values indicating narrow CD and low values in-]i~l;.~, broad CD.Thus, now le~,ling back to Figure 5, the narrow and broad CD copol,vmers have CDBrs equal to 95.5% and 42%, respectively. It is difficult to measure the CD
30 and CDBI of copolymers having very low comonomer content with high accuracy so the CDBI of polyethylenes with densities greater than 0.94 g/cc is defined to be equal to 100%
Unless otherwise indicated, terms such as "comonomer content", "average comonomer content" and the like refer to the bulk comonomer content of the " '.~3 ~~.3~ lg~ ;

indicated interpolymer blend, blend component or fraction on a molar basis.
The benefits to the discovery of the subject invention that accrue from the structural features of plastomers alluded to above (vis-a-vis molecular weight distribution, composition distribution, molecular weight, comonomer type and s amount) are elucid~ted as follows. The narrow molecular weight distribution provides high strength and good draw down. The narrow composition distribution (high CDBI value) provides low tackiness and a low melting temperature/melting range (for heat shrinkage and "gather" formation at relatively low temperatures).
The comonomer incorporation level in plastomers affords low specific gravity foro hiPh end product yields (e.g., yards/lb of polymer). Yet, plastomers have modest levels of ethylene crystallinity (around 20%) which give rise to orientability and strength in the fabricated elastic articles. Control of the molecular weight allows control of orientation and elasticity. Finally, plastomers are hydrocarbon-based and so chemically quite inert.
~ 15 The plastomers useful in the present invention may be produced by any suitable method that will yield a polymer having the required ~)rope, lies, that when fabricated into an elastic article by the method of the present invention, will have suitable residual set and unload power properties. An illustrative non-limiting example of a particularly suitable method of making the plastomer useful in the 20 present invention utilizes a class of highly active olefin catalysts described earlier as transition metal metallocenes, which are well known especially in the preparation of polyethylene and copolyethylene-alpha-olefins. There are a number of structural variables which affect the ultimate properties of the plastomer. Two of the mostimportant are composition distribution (CD) and molecular weight distribution.
2s Composition distribution refers to the distribution of comonomer between copolymer molecules. This feature relates directly to polymer cryst~lli7~bility,optical properties, toughness and many other important use characteristics.
Molecular weight distribution plays a significant role in melt processability as well as the level and balance of physical properties achievable. Also important is the 3~ molecular weight (MW) of the polymer, which determines the level of melt viscosity and the ultimately desired physical properties of the polymer. The type and amount of comonomer also affects the physical properties and crystallizability of the copolymer.
The plastomers utilized in the present invention may be made by any wo 93/16863 PCI/US93/01413 ~t30192 suitable process which allows for the proper control of the above mentioned structural features (MW, MWD, CD, comonomer type and amount) to yield the desired polymer with the desired elastics properties. One suitable method is through the use of a class of highly active olefin catalysts known as transition metal s metallocenes.
Metallocenes are well known especially in the preparation of polyethylene and copolyethylene-alpha-olefins. These catalysts, particularly those based on group IV transition metals, zirconium, titanium and hafnium, show extremely highactivity in ethylene polymerization. The metallocene catalysts are also highly o flexible in that, by manipulation of catalyst composition and reaction conditions, they can be made to provide polyolefins with controllable molecular weights fromas low as about 200 (useful in applications such as lube oil additives) to about 1 million or higher, as for example in ultra high molecular weight linear polyethylene.
At the same time, the molecular weight distribution of the polymers can be controlled from extremely narrow (as in a polydispersity, MWlMn~ of about 2), tobroad (as in a polydispersity of 8 or above).
"Metallocene" catalysts for the purposes of this application are herein defined to contain one or more cyclopent~dienyl or other pi-bonded moiety.
Cyclopentadienylide catalyst systems using a metallocene complex in conjunction with an alumoxane or reaction product thereof are suitable for pl epa. ing the polymer utilized in the invention. The metallocene catalyst, for example may be represented by the general formula (Cp)mMRnR'p wherein a Cp is a substituted or unsubstituted cyclopentadienyl ring; M is a Group IV,V, VI transition metal; R and R' are independently selected halogen, hydrocarbyl group, or hydrocarboxyl groups having 1-20 carbon atoms; m = 1-3, n = 0-3, p = 0-3, and the sum of m + n + p equals the oxidation state of M. Various forms of the catalyst system of the metallocene type may be used for polymerization to prepare the polymer components of the present invention including those of the homogenous or the heterogeneous, supported catalyst type wherein the catalyst and alumoxane cocatalyst are together supported or reacted together onto an inert support for polymerization by gas-phase, high pressure, slurry, or solution polymerization.
The use of metallocene catalysts for the polymerization of ethylene is US-A-4,937,299 and EP-A-0 129 368 published July 26~ 1989, US-A-4,808,561, US-A-4,814,310. and US-A-4~937-299. Specific methods for making ethylene/alpha-- 16- 2 ~ 30 1 92 - olefin copolymers, and ethylene/alpha-olefin/diene terpolymers are taught in US-A-4,871,705. The alumoxane may be prepared with water for example in the form of a hydrated ferrous sulfate. Other cocatalysts may be used w th metallocenes, such as trialkylalum num compounds; or ionizing ionic activators or compounds such as, s tri (n-butyl) ammonium tetra(pentaflurophenyl) boron, which ionize the neutralmetallocene compound. Such ionizing compounds may contain an active proton, or some other cation associated with (but not coordinated or only loosely coordinated to) the l~...~i.l;..~ ion ofthe ionizing ionic compound. Such compounds are described in EP-A-0 277 003 and EP-A-0 277 004 both published August 3, 1988.
0 Further, the metallocene catalyst col"ponent can be monocyclopentadienyl heteroatom co.~1;.i~.;.,~ co~ ou.ld, which is activated, for example, by either an alumoxane or an ionic activator to form an active polym~ri7~tion catalyst system to produce polymers useful in this present invention as is shown for example by W092/00333 published January 9, 1992, US-A-5,096,867 and 5,055,438, EP-A-0 420 436 and WO91/04257. The catalyst systems described above may be optionally prepolym~ri7~d or used in conjunction with an additive COlllpOllellt to enhance catalytic productivity. Utili_ing a metallocene catalyst, the polymers of the present invention can be produced in accordance with any suitable polymerization process, including a slurry polym~ri7~tion, gasphase polymerization and high ~le.,~ule polym~ri7~tion process.
Utilizing a transition metal metallocene catalyst, the p!~.lo~ rs useful in the present invention can be produced in accor~ance with any suitable pol-yl~leli~lion process, including a slurry polymerization, gas phase poly-l-e~ ion, and high 2s pressure polymerization process.
The p!~tomer of the present invention may be fabricated into any form that is suitable for the use to which it will serve.

REFERENT~AL EXAI~PLES
In order to provide a better underst~n~lin~ of the present invention including representative advantages thereof, the following lerele--lial examples are offered as related to actual tests perforrned in the practice of this invention, and illustrate the suprising and unexpected elastic properties of this present invention - - -WO 93/16863 i ~ ~ PCr/US93/01413 ~130~92 and are not intended as a limitation on the scope of the invention Preparation of Ethylene/alpha-olefin Plastomer (2.8MI, 0.88D, hexene-l comonomer) PROCESS SUMMARY

R~ Comon. C~ A~g. Tot. Wet Tot.Tot. Cat.
TEMP. (Lb) Press. C2 C2 Prod Cat.Cocat. E~.
Target (C6) TargeV R~in ~Lb) "~ (mg)(Lb) (Lb/
Actu~l Actual R~te (Lb) Lb (~F) (Psi) (Lblmin) Cat) 131/r35.5+3 201 60/60+2 0.15 60 150 35.4 7 19.15 * 10wt% solution in toluene o The catalyst system for polymerizing this ethylene copolymer comprised bis(n-butylcyclopentadienyl) zirconium dichloride as catalyst and a 10 wt%
methylalumoxane in toluene solution as cocatalyst.
The pol~"~e~ization was conducted in a batch mode using a diluent phase polymerization process. A 150 gallon pilot plant reactor was used to carry out the polymerization. Prior to charging the reactants the reactor vessel was rinsed with triethyl aluminum and purged with nitrogen. Isopentane diluent was then fed to the reactor via a mol-sieve bed to remove moisture. Next the required weights of hexene-l comonomer and cocatalyst solution (10 wt% MAO in toluene) were charged. The reactor contents were heated to reaction temperature. At thermal e~uilibrium, ethylene was slowly fed to the reactor until the pressure set point was reached.
Reaction was initiated by controlled addition of catalyst (3 x 10 mg charges). This was followed by addition, as needed, to build and sustain a controllable reaction. Reaction rate was monitored by noting reactor temperature~s and heat removal rates from the water heat exchanger. The reaction was killed a~er 60 Ibs of ethylene had been fed to the reactor. Product recovery began by slowly venting the reactor to 5 psi, followed by adding water and, with a nitrogen purge to flare, heating the mixture to 1 65~F to flash remove the isopentane and wo 93~16863 - PCr/US93/01413 30~g2 unreacted comonomer. The product was recovered from the reactor, compounded with Irganox-1076 stabilizer and melt extruded to screen out contaminants and pelletize the material.
The produce was analyzed to have a Melt Index of 2.8, density of 0.88 s g/cm3 and a Melt Index Ratio (I2 1 .6/I2 16) of 23 . It will be recognized by persons skilled in the art that products with different Melt Indices and Densities to the above product can be obtained by adjusting the process conditions. Additionally,the composition of the product can be altered, depending on the choice of alpha-olefin comonomer.

Table 1 shows the description of the samples utilized in this example.
Numbers 1 and 2 are the same plastomer sample made according to example 1 above. Number 1 was fabricated to a draw ratio of 5:1 according to the method ofthe present invention, whereas Number 2 was produced in a traditional cast film operation and was not subject to the co-.lbh-ation of orientation and ~nne~ling as was Number 1. Numbers 3, 4 and 6 have appreciable levels of ethylene crystallinity and do not show good elastic response and extensibility by the fabrication of this method. Numbers 5, 6 and 7 are commercially available materials. Number 5 was obtained in 2 mil strip form, whereas Number 7 was obtained in 2 mil film form.
Elastic sample No. 1 and non-elastic sample Nos. 3, 4 and 6 were fabricated into oriented tapes or ribbons, using a Killion ribbon yarn line (Model 2s Serial No. 3874). This apparatus can be represented by the schematic of FIG. 1 except that a slitter was not utilized.
Table 2 provides a dimensional characterization of the fabricated strip samples used in the evaluation.
The hysterisis testing procedure used is shown in FIG. 3. The method is based on a procedure described by DuPont in its brochure on its polyether urethane elastic product, T-722A. The testin~ was conducted on an Instron Model No.
1122. Twelve inch len~ths of the sample film strip to be tested were held by theInstron jaws and extended 100% using a cross-head speed of 500 mrn/min.
Following the extension, the cross head was retracted, also at 500 mmlmin, back to WO 93/16863 PCr/US93/01413 ~130192 ,9 the ori_inal position. This cycling was conducted six times. The force versus extension curves were plotted (chart speed also 500 mm/min) as is shown in FIG.
3. Key pieces of information that are extracted from these plots are maximum force reached at the end of each extension (Ib force), residual set at the end of five s cycles (cm, %) and the unload powers measured during the fifth cycle retraction at various elongations (Ib force). Generally five lengths were tested for each sample, with mean values over these samples developed.
FIG. 4 plots the unload power at various extensions up to 100 percent for elastic sample Nos. l, 2, 5 and 7. Sample Nos. 3, 4 and 6 were too crystalline o (non-elastic) and did not have sufficient extensibility to survive the repeated cycling to 100 percent. As seen in FIG. 4, the unload power is very dependent on the particular fabrication approach. The same polymer (plastomer of Example 1 ) can be made to show di~renl unload power values, depending on fabrication technique. The fabrication process of this invention which includes the 15 co,.-bination of orientation and annealing, provided a much higher value of unload power than was obtained using a traditional extrusion casting fabrication technique.
Table 4 shows a summary of the hysterisis testing on cycling to 100%
extension. The set after 5 cycles appears comparable for the 4 samples, ranging from 15 to 20 percent, per the testing procedure followed. The high unload power20 and the favorable low set value provided by sample No. 1 (plastomer ribbon), demonstrate the utility of the fabrication process of this invention to provide suitable elastic end products.
Table 3 shows shrinkage measurements at elevated temperatures (i.e.
shrinkage of original lengths) on the 4 samples that survived cycling to lO0 percent 25 extension. The fabrication process of this invention provides high shrinkage at lower teml)elalures7 which is an advantage in certain elastic applications (compare values for plastomer ribbon versus plastomer cast film strip).
Table 5 quantifies the force at break values and the ultimate elongation values during tensile testing of the tape/film on an Instron Model 1122 with cross 30 head speed of 500 mm/min.

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(Cycling to 0~/, xtension) (Cycling to I~C% ~xtension)(Cyclin~ to 00'~/O Extension)(Cycling to 100% Extension, LB LB LB LB
At 10%Elong 0.0000 00000 00000 00000 At 20% Elong 0.0050 0.0068 0.0360 0.0084 A~ 30% Elong 0.0750 0.0358 0.0940 0.0268 At 40% Elong 0.1713 0.0610 0.1474 0.0429 At 50% Elong 0.2788 0.0886 0.1954 0.0569 At 60% Elong 0.4125 0.1172 0.2480 0.0729 At 70% Elong 0.5975 0.1486 0.3030 0 0915 ()n~o Elo~ 0.8913 0.t876 0.3826 0.1131 At 90% Elong 1.4313 0.2340 0.5000 0.1395 At 100% Elong 2.8762 5,3780 0 8384 OriL~inal Length30.6175 30.8200 30.9300 30.9500 Set After S Cycles6.1125 5,3780 4.4950 5.1200 (CM) -~
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Claims

- 26 -I Claim:

1. An elastic film having been orientated to a draw ratio in the range of about 2:1 to about 20:1, said film comprising a copolymer of ethylene polymerized with at least one comonomer selected from the group consisting of C3to C20 alpha-olefins and C3 to C20 polyenes utilizing a metallocene catalyst, said copolymer having a density in the range of 0.855 g/cm3 to less than 0.900 g/cm3, a melt index in the range of 0.2 to 1000, a Composition Distribution Breadth Index of 45 percent or higher and a molecular weight distribution in the range of about 1.5 to 30.

2. The elastic film of claim 1 wherein the copolymer has a density from 0.88 to less than 0.900 g/cm3.

3. The elastic film of any one of the preceding claims wherein the copolymer has a melt index less than 100.

4. The elastic film of any one of the preceding wherein the elastic film is produced by slit-die extrusion.

5. The elastic film of any one of the preceding wherein the elastic film is produced by blown film extrusion.

6. The elastic film of any one of the preceding wherein the alpha-olefin is selected from the group consisting of propylene, 1-butene, 1-pentene, 1-hexene, 1-octene and 1-dodecene.

7. The elastic film of any one of preceding claims wherein the copolymer has a density in the range from 0.860 g/cm3 to 0.890 g/cm3, a melt index from 0.5 to 50, a molecular weight distribution from 1.8 to 10, and a Composition Distribution Breadth Index of at least 60 percent.

8. The elastic film of any one of the preceding claims wherein the polyene is a diene selected from the group consisting of straight chain dienes, branched chain dienes and cyclic hydrocarbon dienes.

9. The elastic film of any one of the preceding claims wherein the diene is selected from the group consisting of 1,3-butadiene, 1,4-hexadiene, 1, 6-octadiene, 5 -methyl- 1,4-hexadiene, 3,7-dimethyl- 1,6-octadiene, 3,7-dimethyl- 1, 7-octadiene, mixed isomers of dihydro myricene and dihydroocinene, 1, 3-cyclopentadiene, 1,4-cylcohexadiene, 1,5-cyclooctadiene and 1, 5-cyclododecadiene, tetrahydroindene, methyl tetrahydroindene, dicylcopentadiene, bicyclo-(2,2,1)-hepta-2-5-diene, 5-methylene-2-norbornene (MNB), 5-propenyl-2-norbornene, 5-isopropylidene-2-norbornene, 5-(4-cyclopentenyl)-2-norbornene, 5-cyclohexylidene-2-norbornene, 5-vinyl-2-norbornene and norbornene.

10. The elastic film of any one of the preceding claims wherein the copolymer comprises in the range of 65 mole percent to 93 mole percent ethylene (based on the total moles of monomer).

11. The elastic film of any one of the preceding claims wherein the copolymer comprises in the range of 73 mole percent to 88 mole percent ethylene (based on the total moles of monomer).

12. The elastic film of any one of the preceding claims wherein the coploymer has an ethylene crystallinity less than 20 percent.

13. The elastic film of any one of the preceding claims wherein the elastic film is bonded or sealed to polyolefins.

14. A product made with the elastic film of any one of the preceding claims.