CA1291615C

CA1291615C - Oriented elastomeric film and method of manufacture

Info

Publication number: CA1291615C
Application number: CA000508548A
Authority: CA
Inventors: William John Hodgson, Jr.; Jeffrey Alan Middlesworth
Original assignee: Exxon Chemical Patents Inc
Current assignee: ExxonMobil Chemical Patents Inc
Priority date: 1985-05-08
Filing date: 1986-05-06
Publication date: 1991-11-05
Anticipated expiration: 2008-11-05
Also published as: DE3667259D1; JPH0755537B2; US4714735A; EP0201331A2; JPS6250119A; EP0201331A3; EP0201331B1

Abstract

ABSTRACT OF THE DISCLOSURE

An oriented thermoplastic elastomer comprising an elastomer, EVA, and process oil is prepared by stretch orienting the film at an elevated temperature and annealing the film to freeze in stresses and strains in the film. In one embodiment, the thermoplastic elastomer is provided with a thin coating of a thermoplastic to provide nonblocking.

Description

2 This invention relates generally to the thermoplastic elasto-3 mers and in particular, to the thermoplastic elastomers which have-4 been thermally oriented.
Thermoplastic elastomers possess properties of both thermo-6 plastics and elastomers and have a wide range of applications. In 7 certain applications, a thermoplastic elastomer film is dimensionally 8 stabilized in a stretched condition (wherein stresses and strains in 9 the film have been frozen in) for subsequent use. For example, the stretched thermoplastic elastomer may be applied to a substrate and 11 later heated causing the thermoplastic elastomer to shrink and retain 12 substantial elastic properties. One such use is disclosed in European 13 Patent Application No. 84301717.9 (Publication Number 0ll98l5) wherein 14 the stretched dimensionally stable thermoplastic elastomer is placed on a diaper waistband and reheated causing the thermoplastic elastomer 16 to contract and revert to a heat stable elastic state. The diaper 17 thus, is provided with a flexible and stretchable waistband. A
18 similar application of thermoplastic elastomers is disclosed in 19 European Patent Application No. 84301720.38(Publication Number 0l1~8?7). These publications are cited merely to disclose a possible 21 use of thermoplastic elastomers.
22 In many applications, particularly where the thermoplastic 23 elastomer is secured to a substrate for later contraction by the 24 application of heat, it is important that the thermoplastic elastomer have relatively high shrink force since the substrate resists shrink-26 age. The shrink force is determined by measuring the shrinkage of the 27 film sample against an applied force and is referred to herein as 28 weighted shrink. The weighted shrink properties differ markedly from 29 free shrinkage (no applied weight) and hence is a key property in determining the suitability of a heat shrinkable film on substrates.
31 U.S. Patent 4,303,571, issued to D. S. Jansen et al disclose 32 3 thermoplastic elastomer film comprising 25 to 55 parts by weight of 33 an ethylene-propylene copolymer, 35 to 55 parts by weight of an EVA
34 copolymer and l5 to 25 parts by weight of a liquid hydrocarbon process oil.

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As will be demonstrated in the discussion of the comparative 2 examples contained herein, the elastomeric film made from the composi-3 tion disclosed in U.S. Patent No. 4,303,571 possesses satisfactory 4 shrink properties, but not nearly as good as those possessed by the composition of the present invention, particularly with respect to 6 weighted shrink properties.
7 A problem associated with thermoplastic elastomers is tacki-8 ness which impedes unwinding of the film during processing. This is a 9 particularly serious problem with f;lm compositions containing EVA and 10 processing oil. Moreover, addition of particulate antiblocks are not 1~: particularly effective in thermoplastic elastomers because of the 12 difficulty in dispersing the additives uniformly on the film surface, 13 since the additives tend to concentrate in the elastomer phase.

The present invention provides an improved film composition 16 and process for manufacturing which exhibits excellent shrink force 17 and possesses nonblocking properties.
18 The film composition in one embodiment of the present inven~
19 tion comprises from 10 to 40 weight percent of an olefinic elastomer, 20 not more than 12 weight percent (preferably not more than 10 weight 21 percent) of a normal liquid processing oil, and from 50 to 80 weight 22 percent of a thermoplastic ethylene copolymer, preferably vinyl ace-23 tate copolymer (EVA), all weight percents based on the weight of the 24 three component composition. The film is dimensionally stable in a 25 stretched condition (draw ratio of 1.3:1 to 6:1) and is contractible 2~ to a thermally stable and elastic condition by the application of 27 heat.
28 The method for preparing the thermoplastic elastomer film 29 comprises stretching the film at a temperature below the melting point 30 of the EVA component at a draw ratio between about 1.3:1 and 6:1, 31 annealing the stretched film, and cooling of the film to ambient 32 temperature. The film may be used by securing it to a substrate such 33 as a inelastic thermoplastic or fabric, and heating the film to an 34 elevated temperature whereby the film contracts to a thermally stable 35 length and possesses elastic properties. The composite thus may be 36 expanded by the application of tension which upon release returns to 37 its original shape.

1 In another embodiment of the invention, the film comprises a 2 composite of one layer of a thermoplastic elastomer and-a thin coating 3 of an ethylene polymer or copolymer having a relatively high Melt 4 Index. Upon the subsequent stretch orienting the composite, the - ~
coating becomes even thinner. The thermoplastic elastomer layer is 6 preferably the composition as defined above, particularly if high 7 shrink force is desired in addition to antiblock properties. The 8 coating preferably also contains particulate antiblock additives, thus 9 avoiding the difficult problem of distributing antiblock particles on or near the film surface.
11 The present invention contemplates (l) an improved stretch-12 oriented, dimensionally stable thermoplastic elastomer which is 13 shrinkable upon application of heat, (2) a composite of the thermo-14 plastic elastomer and a substrate wherein the orientation has been released by the application of heat, (3) a method of preparing the 16 oriented thermoplastic elastomer film, (4) a method of manufacturing 17 an elastic composite comprising a thermoplastic elastomer and a sub-18 strate of inelastic material, (5) a thermoplastic elastomer having a 19 thin coating of a nonblocking polymer and (6) a method of preparing a nonblocking thermoplastic elastomer.

22 In describing the present invention, it is necessary to use 23 certain technical terms, some of which are commonly used in the indus-24 try and others of which are defined herein to express a concept, In order to avoid confusion, the following terms used herein 26 shall have the meaning indicated:
27 "Draw ratio" - the ratio of the final stabilized length 28 (after orientation and "snapback") of an oriented film and 29 the initial length of the film before orientation. Draw ratio in unidirectional orientation is also equal to the 31 ratio of the thickness of the stabilized oriented film and 32 the initial unoriented film.
33 "Shrink force" - the force required to prevent shrinkage of 34 an oriented film by application of heat.
"Shrink stress" - the shrink force per unit area (g/cm2).
36 "Annealing" - a heat treatment process for reducing strains 37 and stresses set up in the film during orientation. The 38 process comprises maintaining the film while in stretched ~ . .

~?19~ .5 1 condition at the annealing temperature~ for a period of time, 2 followed by cooling the film to room temperature.
3 I'Thermoplastio elastomer" - frequently called rubbery thermo-4 plastics, are blends of a thermoplastic material and elasto-mer that are processable as a melt, at elevated temperatures, 6 but exhibit properties similar to vulcanized elastomers at 7 room temperature.
8 "Melt Index" (MI) - 9/10 min (ASTM-D 1238; condition E).
9 In its broadest form, the thermoplastic elastomer film compo-sition of the present invention comprises three main components, 11 (1) olefinic elastomer, (2) ethylene copolymer and (3) a hydrocarbon 12 process oil.
13 The concentrations of the three components of the blend are 14 as follows:
Preferred Most 16 Component Concentration Concentration Preferred 17 Olefinic Elastomer10-40 wt X 15-30 wt % 20-3G wt %
18 Ethylene Copolymer50-80 wt % 60-80 wt % 65-75 wt %
19 Process Oil 0-12 wt % 2-lO wt ~ 4-8 wt %
The above concentration range may be combined in any permis-21 slble combination, although the particular combinations shown are pre-22 ferred. For example, a preferred composition comprises 10-40 wt %
23 elastomer, 60-80 wt % ethylene copolymer, and 0-12 wt % process oil.
24 The weiyht concentration of each component is based on the total weight of the three main components.
26 Elastomer Component: The olefinic elastomer component of the 27 composition preferably comprises an ethylene copolymer elastomer, such 28 as a copolymer of ethylene with higher alpha-olefin. Preferred ethy-29 lene elastomer copolymers include EPM (ASTM D-1418-72a ~esignation for an ethylene-propylene elas~omer copolymer) or EPDM (ASTM D-1418--72a 31 designation for an ethylene-propylene d;ene elastomer terpolymer~. I
32 A~so usable are high molecular weight polyisobutylene, butyl rubbers 33 and halogenated butyl rubbers.
34 Preferred ethylene elastomer copolymers for use herein com-prise from 30 to 90 weight percent ethylene, more preferably from 35 36 to 80 weight percent ethylene, and most preferably from 50 to 80 37 weight percent ethylene and have a Mooney viscosity (ML 1~8 at F
38 between 25 and 8G).

~?t~ .5 1 EPDM is a terpolymer of ethylene, a higher alpha-olefin such 2 as propylene, and a nonconjugated diene. In such elastomers, the 3 nonconjugated diolefin may be straight chain, branched chain or cyclic 4 hydrocarbon diolefins having from 6 to 15 carbon atoms.
Of the nonconjugated dienes typically used to prepare these 6 copolymers, preferred are dicyclopentadiene, 1,4-hexadiene, 5-methy-7 lene-2-norbornene and 5-ethylidene-2-norbornenej 5-ethylidene-2-8 norbornene (ENB) and 1,4-hexadiene are particularly preferred diole-9 fins. EPDM elastomers and their method of manufacture are well known to those skilled in the art. Oil extended EPDM elastomers may also be 11 used. Preferred EPDM elastomers contain from 30 to 90 weight percent 12 ethylene and most preferably from 50 to 80 weight percent ethylene, 13 and from 0.6 to 15 weight percent of the nonconjugated diolefin.
14 As mentioned above, the olefinic elastomer useful in this inventlon may also be a polyisobutylene, a copolymer of isobutylene 6 and isoprene (generally known as butyl rubber) or a halogenated co-17 polymer of isobutylene and isoprene (generally known as halogenated 18 butyl rubber, such as chlorinated, brominated and chlorobrominated 19 butyl rubber). Butyl rubber is a vulcanizable rubber copolymer con-taining from 85 to 99.5 percent combined isoolefin having from 4 to 8 21 carbon atoms and from 0.5 to 15 percent combined conjugated diolefin 22 having from 4 to 8 carbon atoms. Such copolymers and their prepara-23 tion are well known, and generally the isoolefin i5 a compound such as 24 isobutylene and the diolefin is a compound such as butadiene or iso-25 prene. Halogenated butyl rubbers are also well known: chlorinated 26 and brominated butyl rubber generally contains from 1.0 to 3.0 weight 2~ percent bromine and from 0.05 to 0.5 weight percent chlorine.
28 Ethylene Copolymer Component: The ethylene copolymers 29 include those of ethylene and alpha-olefins having 3 to 16 carbon atoms such as propylene or l-butene. Also included are copolymers of 31 ethylene with unsaturated esters of a lower carboxylic acid or with an 32 unsaturated carboxylic acid. In particular, copolymers of ethylene 33 with vinyl acetate (EYA), or with acrylic acid (E M ), or methacrylic 34 acid (EMA), are preferred. The ethylene copolymers to be employed generally contain from 50 to 99 weight percent ethylene, most 36 preferably from 60 to 95 weight percent ethylene.

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1 The most preferred ethylene copolymer useful in the present 2 invention is EVA. The EVA may have a vinyl acetate- (VA) content 3 between about 9% and 40~ by weight, with about 15 to 35 weight percent 4 VA being preferred.
VA contents below about 9 wt % do not possess sufficient 6 flex;bility and orientability for purposes o~ the present invention 7 and VA contents above 40 wt % exhibit excessive tackiness. The best 8 balance of orientability and non-tackiness occurs at VA contents 9 between 15 and 35 wt %.
Preferred Melt Index (ASTM-D-1238, Condition E) for EVA is 11 from 1 to 20, with 2 to 10 being most preferred.
12 The ethylene copolymer component normally will determine the 13 operating temperatures of the tentering and annealing operations.
14 These operations may be carried out at temperatures not less than 100F and below (preferably not more than 10F below) the crystalline 16 melting point of the ethylene copolymer component. The annealing step 17 preferably is at + 20F of the orienting temperature. The crystalline 18 melting point of EYA ranges from approximately 105F and 200F, 19 depending on the VA content and MI, with the preferred EVA's having 2~ crystalline melting points between about 130F and 160F. For 21 economics, orienting temperatures of 160F and below are preferred.
22 Process Oil Component: Hydrocarbon oils useful in the 23 present invention function as process aids whose activity is enhanced 24 in the presence of vinyl acetate copolymers, as plasticizers producing low modulus and enhanced elasticity in the solid state and those 26 useful are the normally liquid hydrocarbon processing and extender 27 oils (ASTM D 2226) categorized as aromatic, highly aromatic, naph-28 thenic and paraffinic process oils of a medium viscosity range. Oils 29 sold under the trademarks "Flexon" and "Sunpar" have been found especially useful.
31 Other Additives: The composition may also include a filler 32 material, an antiblock agent, processing aids, stabilizers and other 33 conventional additives.

Resin/Blend Preparation: Preparation of compositions usable 36 in this invention can be achieved in several different ways. The 37 various components may be brought into intimate contact by, for ex-38 ample, dry blending these materials and then passing the overall ~?,~ 6~ S

l composition through a compounding extruder. Alternatively, the com-2 ponents may be fed directly to a mixing device such as~ a compounding 3 extruder, high shear continuous mixer, two roll mill or an internal 4 mixer such as a Banbury mixer. The optional ingredients previously~
described can be added to the composition during this mixing opera-6 tion. Overall, the objective is to obtain a uniform dispersion of all 7 ingredients and this is readily achieved by inducing sufficient shear 8 and heat to cause the plastics component(s) to melt. However, time 9 and temperature of mixing should be control1ed as is normally done by one skilled in the art so as to avoid molecular weight degradation.
1I Film Extrusion: Film from the resin compound may be manufac-1~ tured by conventional tubular extrusion, (blown bubble process) or by 13 cast extrusion, with the latter being preferred. In the cast extru-1~4 sion process, the molten resin is extruded from an elongate die to the form of a web. The web is cast onto a chill roller, which solidifies 1~ the polymer, and finally wound into a roll.
17 The extrusion temperatures, die temperatures, and chill roll 18 temperatures will depend on the composition employed, but generally 19 will be in the following ranges for the compositions of the present invention prepared by cast extrusion:
21 Melt Temperature (F) 350-450 22 Die Temperature (F) 350-450 23 Chill Roll Temperature (F) 70-130 24 The process described above may also include a set of embossing rolls to chill and form the film.
26 Orientation: Orientation of the film may be carried out in 27 the machine direction (MD) or the transverse direction (TD) or both 28 directions (biaxially) using conventional equipment and processes.
29 For orientation in the MD, a polymeric film at an elevated 39 temperature (but below the crystalline melting point of the polymer) 31 is passed ~rom a feed roll of film around two rollers driven at dif-32 ferent surface speeds and finally to a takeup roller. The driven 33 roller closest to the takeup roll is driven faster than the driven 34 roller closest to the feed roll, such that the film is stretched 3~ between the driven rollers. The assembly may include a roller inter-36 mediate the second roller and takeup roller to cool the film. The 37 second roller and the takeup roller may be driven at the same peri-~?t~ S

1 pheral speeds to maintain the film in the stretched condition. If 2 supplementary cooling is not used, the film will cool to ambient 3 temperature on the take up roll.
4 The degree of stretch will depend upon the relative peri- j pheral speeds of $he driven rollers and the distance between the 6 rollers. Stretch rates of 50 to 500 percent~m;nute will be satisfac-7 tory for most MD orientation applications.
8 Preferably, however, film orientation will be carried out in 9 a tenter;ng device to impart TD orientation to the film. The film is cast as described above or is unwound from a film roll and then 11 gripped by the edges for processing through the orientation steps.
12 The film is passed successively through a preheat step, a stretching 13 step at elevated temperatures (e.g. from 100F to a temperature 14 slightly below the crystalline melting po~nt of the ethylene copolymer), an annealing step, and finally a cooling step. (Although 16 cooling may be considered part of the annealing step, for convenience 17 it is described as a separate step herein.) The preheat, orientation, 18 and a portion of the annealing temperature is controlled at an 19 elevated temperature but below the crystalline melting p~int of the polymer. Although not essential, it is preferred that tension be 21 maintained on the film during the annealing and cooling steps to 22 minimize shrinkback. Upon cooling to ambient temperature (i.e., room 23 temperature) or near ambient, the holding force may be released. The 24 film may contract somewhat (snapback) in the TD but will retain substantial portion of its stretched length.
26 The tenter operating conditions can vary within relatively 27 w~de ranges a~d will depend on the several variables including film 28 composition, film thickness, degree of orientation desired, annealing 29 cond;tions, etc. The follow;ng is exemplary of a process for stretch-ing lO0 micron thick film (containing EVA) from 24 inches wide to a 31 f~nal width of about 60 inches, using a tenter manufactured by 3~ Marsha1l and Wil1iams Company of Prov~dence, Rhode Island.

s - g -2 ~ Approximate 3 Step Broad Preferred Typical Time (Sec.
4 Preheat 100-160F 115-140~F 125F 3.0 Stretching100-160F 115-140F 125F 9.0 6 Annealing100-160F 110-150F 120~F 3.0 7 Cooling Ambient Ambient Ambient 6.0 8 As indicated earlier, it is highly desirable to employ an 9 annealing step in the process. Annealing partially relieves the internal stress in the stretched film and dimensionally stabilizes the 11 film for storage. It has been found that by annealing the film at a 12 temperature of + 40F, preferably ~ 20CF of the orientation tempera-13 ture (but slightly below the crystalline melting point of the ethylene 14 copolymer) eliminates undesirable shrinkage during storage. The preferred annealing temperature is between 110F and 130F. Tempera-16 tures which result in excessive stress relieving should be avoided, 17 s~nce substantial frozen in stresses and strains should remain after 18 the process is completed.
19 Annealing can be accomplished by maintaining the film in the stretched condition at the annealing temperature. Preferably, how-21 ever, the annealing and cooling is carried out while permitting the 2~ f;lm to contract slightly, but still under stress. The guide rails of 23 the tenter can be arranged in a converging manner to provide the an-24 nealing and cooling while the film contracts. The controlled shrink-back of from 5 to 30%, preferably between 15 and 25%, of the maximum 26 stretched width has given particu1ar1y good results in e1iminatina 27 storage shrinkage. This annealing and preshrinking removes some of 28 the film stresses and strains so that shrinkage will not occur at 29 storage temperature. However, the annealing and cooling does not remove all the frozen in stress and strain, since upon heating to 31 elevated temperatures above storage temperature the film will shrink.
32 The degree of stretching may vary within wide ranges. Draw 33 ratjos af 1.3:1 to 6:1 are pDssible with 2:1 to 4:1 being preferred 34 for TD tentering. The actual stretching will occur at higher ratios (1:5 to 9:1) to allow for controlled shrinkage and snapback.

' 2 In order to demonstrate the effectiveness of the present 3 invention, particularly in respect of improved shrink force and non-4 blocking properties, a series of experiments were conducted comparing S performance of the film of the present invention with that of the 6 prior art (U.S. Patent No. 4,303,571).
7 Film Samples:
8 Samples having the compositions listed in Table I were 9 prepared by blending the components in the weight concentrations indicated using a Banbury~ mixer. Each composition also included 11 6 wt X ethylene acrylic acid copolymer and filler material (CaC03).
12 The resin blend was cast extruded into 150 micron (approx.) th;ck film 13 using 3" extruder and 30" wide flat die.
14 Properties of the Film:
Each film sample was then tested for orientation/shrinkage 16 properties with an Instron~ (Model 1122) in a temperature controlled 17 chamber. One inch wide strips (cut in the TD) were taken from each 18 sample, marked with lines 4 cm apart and then drawn to 9 cm at 10 19 cm/minute at an elevated temperature (140 and 145F). After orienta-tion, each stretched film was quenched with water and removed from the 21 Instron. Six film strips were drawn for each formulation and the test 22 was run in random order in blocks of nine to eliminate systematic test 23 error, 24 For each formulation, 6 strips were heated in the oven for three minutes at 150F; three strips with a fixed weight and the other 26 three strips freely suspended. The film strips were removed from the 27 oven, allowed to cool ant then measured to determine the % recovery.
28 The % recovery was calculated by the following formula:
29 Percent Recovery = Initlal length*-Final length*~ x 100 Initia engt * - cm 31 * Initial stretched length (cm) after "snapback".
32 ** Final length (cm) after full shrinkage at 150F in oven.
33 Table II presents the results, comparing the three sample 34 average for each formulation of the present invention (Samples A, B
and C) with the three sample average of each formulation of the prior 36 art (Samples D, E and F).
~ 7;c~J e rn ~/r h .5 1 As revealed in Table II, the percent recovery under re- I
2 strained conditions Samples A, B and C was higher than that of Samples 3 D, E, and F. Percent restra;ned recovery for the R, B, C sample group 4 averaged ~6.4%, whereas that of D, E F group averaged 82.3%. The~
shrink force, which is thè force required to keep the film from 6 shrinking can be calculated from these data. As shown in Table II, 7 the shrink force for Samples A, B and C was substantially higher than 8 that for Samp7es D~ E, and F. Samples A and B exhibited particularly 9 improved shrink force.
The higher shrink force of the Samples A, B and C permits use 1l of a thinner gauge film at the same draw ratio as demonstrated by the 12 following experiments.
13 Additional experiments were conducted to demonstrate shrink-14 age as a function of restraining force and shrinkage temperature. Two oriented films having the composltions of Samples A and D were pre-16 pared using a Marshall and Williams Tenter operated under typical 17 conditions described in the Orientation section hereof. Each film 18 thus was processed as follows:
19 Sample A Sample D
Initial Length 22.5 inches 22.5 inches 21 Stretch Length 66 inches 66 inches 22 Controlled Shrinkback 23 Length 60 inches 60 inches 24 Final Stabilized Length SO inches SO inches Film Gauge (Initial)102 m~crons (avg)146 microns (avg) 26 Film Gauge (Final)42 microns (avg)58 microns (avg) 27 Draw Ratio (Initial Film 28 Gauge/Final Film Gauge) 2.42 2.51 Strips (three for each test) of each film sample were taken 31 and subjected to shrinkage in an oven at a controlled temperature 32 (120F or 150F) and at the following restraining forces: O, 12 9, 24 33 9, 36 ~, 48 9 and 60 9. Each strip was permitted to shrink for three 34 minutes. Table III presents the three-strip average for each test.
These data demonstrate that the shrink stress for the composition of 36 the present invention was substantially higher than the composition of 37 the prior art. Moreover, the shrink force for Sample A strips ~?,~16~ ,5 I exhibited substantially hi~her shrink force than the Sample D strips, 2 even though the latter strips were substantially thicker in gauge (and 3 hence larger cross sectional area) than the former strips.
4 It is preferred that the thermoplastic e~astomer film on the present invention have a shrink stress of at least 5,000 g/cm at 6 the orientation temperature, thereby providing sufficient force for 7 its intended purpose. It is also preferred that the shrink force at 8 150F be at least 5,000 g/cm2.
9 It is interesting to note from the Table III data that the shrinkage is generally linear with respect to the ap~lied force. This lI permits calculating the shrink force and shrink stress. Note tha~ the 12 shrink temperature of 150F is higher than the orientation temperature 13 and 120F is lower than that temperature. The higher temperature 1~ results in more shrinkage since more stresses are relieved.
Antiblock Properties 1~ The composition of the present invention also exhibits good 1~ antiblocking properties in comparison to films of the compositions of 18 samples D, E and F.
19 Multi-layers of each film Sample A, B, C, D, E and F compo~i-tions (150 micron thick unoriented) were stored for se~eral weeks.
21 The films were then manually separated and subjectively rated for 22 blocking (i.e., resistance ~o unwinding).
23 Sample Observed Blocking 24 A No blocking B Slight tackiness 26 C No blocking 27i D Fully Blocked 28 E Partial B70cking 29 F Partial Blocking Antiblock property is important in unwinding the film during 31 tentering or during unwinding the oriented film of use. Sticking of 32 the film is undesirable since it slows down the operation or renders 33 the process inoperable.

Another embodiment o~ the present invention is directed 36 specifically at solving blocking associated with thermoplastic elasto-37 mers, particularly those containing process oil and ~or high VA, ethy-38 lene vinyl acetate. These films are tacky by nature and require ,S

1 antiblock agents such as particulate silica. The elastomer present in 2 these blends appears to prevent uniform distri~ution ~f particulate 3 antiblock in the resin with the result that the antiblock does not 4 become uniformly distributed on the film surface. -5 In one aspect of this invention, a thin coating of an ethy-6 lene polymer or copolymer îs provided on one or both sides of the base 7 thermoplastic elastomer (core). The subsequent stretching of the film 8 further reduces the thickness of the coating. The coating thickness 9 ratio (final/initial) is in proportion to the draw ratio. Preferably 10 the coating comprises conventional low density polyethylene (LDPE) 11 having a high Melt Index (in excess of 3.0). Other ethylene polymers 12 and copolymers that may be used as the coating inc1ude linear low 13 density polyethylenes (LLDPE), EVA, etc. These materials should have 14 relatively high Melt Ind,ces (in excess of 3.0, preferably 5.0-30.0) 15 and should be capable of high draw down, making them suitable for 16 coextrusion with the base resin (core layer), and should possess non-17 tacky properties or be treatable to a nontacky condition (e.g.

18 addition of antiblock). Coextrusion is the preferred coating method, 19 but extrusion coating may also be used. r 20 It is essential that the coating be sufficiently thin to 21 avoid interference with the shrink and elastic properties of the 22 thermoplastic elastomer but sufficiently thick to impart antiblock 23 properties to the composite. This latter requirement means that the 24 coating must be capable of carrying uniformly d;stributed therein 25 particulate finely divided antiblock agent.

26 As applied to the core or base resin, the coating will com-27 prise between 2 to lS, preferably 2 to lO weight percent of the com-28 posite and not more than 25 microns thick. Following the orientation, 29 the coating will be reduced to a thickness of not more than 7 microns 30 and as thin as possible. Preferred thickness after orientation is 31 between l and 5 microns.

32 The amount of antiblock in the coating may range from 500 to 33 5,000 ppm, with l,OOO to 4,000 being preferred. The coating may also 34 include slip agents such as erucamide and oleamide.

35 The coating may be applied to only one side of the base resin 36 but preferably is applied to both sides.

s - ~4 -1 It should be noted that the invention comprising the coating 2 embodiment is not restricted to the thermoplastic elastomer composi-3 tion specified in the earlier description of the "Elastomer Component"
4 as the core (although these compositions are the most preferred) but may instead contemplate the use of any thermoplastic elastomer resin 6 composition. The preferred resin composition comprises from lO to 55 7 wt % of the elastomer component, from 35 to 80 wt X of the EVA compo-8 nent, and from 2 to 25 wt % of the processing oil component.

In practice, the process of the present invention may be 11 carried out using an in-line operation wherein the extruder and 12 orientation system (e.g., tenter) are arranged in tandem to form the 13 film by casting or melt embossing followed by film orientation.
14 Alternatively, these operations may be carried out separately.
In a preferred embodiment, the compounded- resin containing 16 the three main ingredients along with the other additives is intro-17 duced into an extruder and extruded into a web from a flat or coat-18 hanger type die and melt embossed through counter rotating chill roll 19 and embossing rolls. The film thickness may vary from 50 to 400 microns before orientation and from lO to 200 microns after 21 orientation. Preferably the film will have a final stabilized thick-22 ness of between lO and lOO microns after orientation and annealing.
23 The film is wound on a take up roll and transferred to tentering 24 equipment or processed in line with the tenter.
The edges of the film are gripped in the tentoring equipment 26 and passed successively through (a) a preheat stage, (b) an expansion 27 stage wherein the film is stretched laterally at an elevated tempera-28 ture, (c) an annealing stage and, finally, (d) a cooling stage where 29 the stretched film is cooled to near ambient temperature. Once the restraining force is released, the film snaps back slightly but 31 retains most of its stretched length. This film is wound on a take up 32 roll, ready for transport or use.
33 The dimensionally stable film may be secured to a flexible 34 substrate and heated causing it to shrink. Shrinkage commences at a few degrees abo~e storage temperature, reaching maximum at some 36 temperature above the orientation temperature.

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i s 1 In the embodiment for the coating of a thermoplastic elasto-2 mer, the operation may be the same as above except tha~ in extrusion 3 of the resin to form the film, a coextrusion die may be used to apply 4 the thin coating on one or both sides of the thermoplastic elastomer-core.
6 In either embodiment, the film produced has excellent shrink 7 force properties and good antiblock properties.

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Claims

1. An oriented film having a blend composition comprising from 10 to 40 weight percent of an olefinic elastomer, not more than 12 weight percent of a normally liquid process oil, and from 50 to 80 weight percent of a thermoplastic ethylene copolymer, said film being stretch oriented in draw ratio of between 1.3:1 and 6:1 and being dimensionally stable, thermally unstable in the stretch oriented con-dition and contractible to a thermally stable and elastic condition by application of heat.

2. A film as defined in claim 1 wherein the thermoplastic ethylene copolymer is selected from EVA, EAA and EMA and wherein the film has been stretch oriented in the transverse direction at a temperature not less than 100°F and not more than 10°F below the crystalline melting point of the copolymer and partially annealed in a stressed condition.

3. A film as defined in claim 2 wherein the ethylene copolymer is EVA.

4. A film as defined in claim 3 wherein the blend composi-tion comprises from 15 to 30 weight percent of an olefinic elastomer selected from EPM and EPDM, from 60 to 80 weight percent of EVA having a vinyl acetate content of 9 to 40 weight percent, and from 2 to 10 weight percent of a normally liquid hydrocarbon process oil, the oil being an aromatic, naphthenic or paraffinic process oil.

5. A film as defined in claim 3 wherein the composition comprises from 20 to 30 weight percent of the olefinic elastomer, from 65 to 75 weight percent of the EVA, and from 4 to 8 weight percent of the processing oil.

6. A film as defined in claim 3 wherein the film has been stretch oriented in the transverse direction at a draw ratio of between 2:1 to 4:1.

7. A film as defined in claim 2 wherein the film has a shrink stress of at least 5,000 g/cm2 at the stretch orientation temperature.

8. A composite comprising (a) a first layer comprising the film defined in claim 1; and (b) a second layer of stretch oriented film adhered to said first layer and comprising a polymer or co-polymer of ethylene having a Melt Index of at least 3.0, said second layer being no thicker than 7 microns in the stretched condition and comprising from 2 to 15 weight percent of the composite.

9. A composite as defined in claim 8 wherein said second layer is coextruded with said first layer.

10. A composite as defined in claim 8 wherein the ethylene polymer or copolymer comprises LDPE having a Melt Index between 5 and 30.

11. A composite as defined in claim 10 wherein the second layer of LDPE is coextruded onto each side of said first layer.

12. An oriented composite comprising (a) a layer of a thermoplastic elastomer film contain-ing from 2 to 25 wt % of a process oil; and (b) a coating of a polymer or copolymer of ethylene coextruded with said first layer and having a Melt Index of between 5 and 30, said coating being less than 7 microns thick in the oriented condition and containing from 500 to 5,000 ppm of a particulate antiblock agent.

13. A process for preparing a heat shrinkable film com-prising (a) extruding a molten blend comprising (i) from 10 to 40 weight percent of an elastomer;
(ii) not more than 10 weight percent of a hydro-carbon oil; and (iii) from 50 to 80 weight percent of a thermo-plastic copolymer of ethylene;
(b) stretch orienting the film in the TD from 1.5 to 9 times its original length at a temperature not less than 100°F and not more than 10°F below the crystalline melting point of the ethylene copolymer;
(c) partially annealing the stretched film; and (d) cooling the film while maintaining stress on the film.

14. A process as defined in claim 13 wherein the ethylene copolymer is selected from EVA, EAA, and EMA.

15. A process as defined in claim 14 wherein the ethylene copolymer is EVA.

16. A process as defined in claim 15 wherein the annealing step is carried out under stress and at a temperature between ? 20°F
of the orienting temperature.

17. A process as defined in claim 16 wherein the annealing and cooling steps are carried out in part by permitting the film to shrink in the TD by no more than 30% of the total stretch distance.

18. A process as defined in claim 13 wherein the stretch orientation stretches the film by between 2 to 4 times its original length in the TD.

19. A process for preparing a heat shrinkable film which comprises (a) stretch orienting a film having a thickness of between 50 and 400 microns and a composition of (i) from 15 to 30 weight percent of an EPM or EPDM
elastomer;
(ii) from 60 to 80 weight percent of an ethylene vinyl acetate copolymer (EVA) having a vinyl acetate content of about 15 to 35 weight percent; and (iii) from 2 to 10 weight percent of a normally liquid hydrocarbon process oil by drawing the film in the transverse direction from 1.5 to 9 times its original length at a temperature of from 100°F to below the crystalline melting point of the EVA;
(b) partially annealing the film at an annealing temperature of ? 40°F of the stretch temperature but less than the crystalline melting point of the EVA while maintaining a stress on the film; and (c) cooling the film to ambient temperature while maintain-ing a stress on the film during at least a portion of the step.

20. The process of claim 19 wherein the annealing step is carried out at a temperature of ? 20°F of the orienting temperature wherein the film is permitted to shrink from its fully stretched length by no more than 30%.

21. A process for manufacturing a heat shrinkable film composite having improved antiblock properties which comprises (a) preparing a film of from 50 to 400 microns thick-ness from a thermoplastic elastomer resin composi-tion comprising an elastomer, a thermoplastic polyolefin and a processing oil;

(b) coextruding with said thermoplastic elastomer film a layer of an ethylene polymer or copolymer to form a composite, said polymer or copolymer having a Melt Index of at least 3.0, and constituting from 2 to 15 wt % of the composite and being no thicker than 25 microns;
(c) stretch orienting the composite at a temperature not less than 100°F and not greater than 10°F below the crystalline melting point of the polyolefin by a draw ratio of between 1.5:1 and 9:1 such that the layer thickness is no greater than 7 microns;
and (d) cooling the stretched composite to form a dimen-sionally stable elastomeric composite which said composite being heat shrinkable at temperatures above the cooling temperatures.

22. The process of claim 13 and comprising the additional step of adhering the dimensionally stable film on to an inelastic substrate and heating the combination to cause said film to shrink drawing the inelastic substrate with it.

23. A composite comprising (a) a layer of flexible substantially inelastic material;
(b) a layer of film as defined in claim 1 secured to the layer of flexible substantially inelastic material whereby application of heat contracts both the film and the layer of flexible, substantially inelastic material.

24. A process for preparing an elasticized composite material which comprises (a) stretch orienting a film having a thickness of between 50 and 400 microns and a composition of (i) from 15 to 30 weight percent of an EPM or EPDM
elastomer;

(ii) from 60 to 80 weight percent of an ethylene vinyl acetate copolymer (EVA) having a vinyl acetate content of about 9 to 40 weight per-cent; and (iii) from 2 to 10 weight percent of a normally liquid hydrocarbon process oil;
by drawing the film in the transverse direction from 1.5 to 9 times its original length at a temperature not less than 100°F and below the crystalline melting point of the EVA;
(b) annealing the film at an annealing temperature of ? 20°F of the orientation temperature while maintaining a stress on the film;
(c) cooling the film to room temperature;
(d) securing a strip of the film to a layer of flexi-ble, substantially inelastic material at longitudi-nally spaced locations along the film to form a composite;
(e) heating the composite to a temperature in excess of 100°F to within ? 20°F of the orienting temperature whereby the film and the layer of flexible, substantially inelastic material contract to an elastic heat stable condition.

25. The process of claim 19 wherein the orienting tempera-ture and annealing temperature are between 100°F and 160°F.

26. The film of claim 3 wherein the EVA has a VA content of between 15 and 35 wt %.