PL-23~ , S
The pre8ent inventlon relates to relatlvely thin thermoplastic ii~ms which can be produced economically and efiiciently at relatively high production rates, and methods for produ d ng these films.
'rPlastic" rilms are ubiquitous in todag' 8 world.
While lt would be imposs1ble to li~t al~ the many uses for these thermoplastic rilm~, they can be said to range between a large number Or applications in whlch the iilm ls a pack-~ging element for other products and an equally large number Or u-es wherein the rilm i8 an element Or the product lt3elf~
For instance~ the latter category includes a variety of health care applications wherein the "plastic" iilm is em-ploged as the backlng or protective layer in a aisposable dlaper, sanitar~ napkin, surglcal dresslng, or the like.
Typically, iilms useful ~or these purposes are ex-truded at high speeds from melts of msterials such as poly-eth~lene~ polyethylene terephthalate, polyvlnyl chloride and s~milar polgoleiins, polyesters, and vinyls. All these materials posses~ relati~ely sharp melting points and are considered heat seaLable under cortaln conditioQs. However, th y are relativelg nonelastlc and generally exhlbit a high rubber modulus. Thus, they do not possess the elasticitg and conformability o~ a natural rubber film. These plastic riIms also are well known ior their "plastic" feeling, i.e., they are generally smooth and slippery and oftentimes rela-tively stiff at any thickness above 1 mil or so. Rubber films, on the other hand~ are quite flexible and may possess .
1091415 . PL-237 a high coe~ficient o~ ~rlction~ Howe~er, rubber films are not thermoplastic in the sense that they do not posses~ a ~harp meltlng point, and are not heat sealable or capable of belng heat shaped if desired.
Furthermore~ there iJ no known method of extrud-ing thin natural rubber rilms at high speeds. Instead, rubber ~ilm must be cast rrom dlsperslons of rubber parti-cles ln a techniqus limited to produclng very.th~n rllms at low 3peeds~ As a re~ult, natural rubber fllms are extremely e~pen8i~e a8 compared to plastlc iilms I ha~e produced a thin eL~stic and thermop1astic rilm whlch possosses the advantages of both "plastfc" fl1ms and rubber rilms wlthout the dlsadvanta6es of either,. and which can be produced economically at production speéds comparablo to those attainable in the manuracture of con~en-tional thermoplastlc iilms.
My nlm is h~ghly thermoplastic and unllke rubber ~n ~hat it possesses a re}atively sharp meltlng polnt and is capable being heat shaped, and is a.dapted to iorm permanent heat seal8 to ~ub8trate8 8uch a~ paper and boxboQrd at relatively low heat seillng peak temperatures~ generally not abo~e about 350F., in no more than 4 seconds oi clamplng tlme, as described more fully her.einarter. At the same tlme the film of my lnvention possesses the best properties of rubber in that it is highly elastic and has :25 a relatively low rubber modulus~ i.e., it exhibits an elastic recovery ~rom 50 percent stretch of at least about 75 percent, pre-rerably ~t least about 90 percent,. and a 50 percent rubber moduluæ
of not above about 2,000, preferably not above about l,000, pounds .
- 1091415 ` PI,-237 per square inch at 50 percent elongation. The ~ilm may be de~igned to have, and normally does possess, relatlvely htgh friction propertie~ which make it nonslippery. It also is very fle~ible, extensible and 30ft and normally ex-hiblts a Gurley stl~fne~8 of not aboYe about one at a th~c~-ness o~ one miL and an elongation to brea~ oi at leaQt about 300 percent, preferably at least about 400 percent, ln at least one dlrection~ FinaIly, and very lmportantly, the pro-duct o~ my invention can be produced in the form of a thin ~0 ~llm economically at hlgh speeds wlthout sacrlricing product characteri~tlcs.
The ~ilm oi my inventton is selr-supportin6 and thin, i.e.~ not abo~e about 10 mils, preferably not above about 5 , mil8, ln thicknes8, and it can be produced economically at ; 15 thtc~ne~ses o~L mll and~below. It is ~ormed ~rom an elasto-meric and thermcplastlc film ~or~ing composltlon which com-prises an eli8tomeric component and a resin component. The elastomerlc component conslsts essentially o~ linear or radlal A-B-A block copolymers or mixtures of these linear or radial A-B-A block copolymers with ~imple A-8 block copolymers. In the8e block copolymers the A-blocks are derived from styrene or styrene hom~o6ues and the B-blocks are derl~ed ~rom con~u-gated dienes or lower a1kenes~ The resln component consist3 essentially oi low molecular weight reslns having a number average molecular weight not above about 3,000 and which are adapted to assoclate principally with the thermoplastic A-blocks of the said block copolymers.
According to a further broad aspect of the present invention, there is provided a self-supporting elastic and thermoplastic film not above about 10 mils in thickness and being extruded and hot drawn from an elastomeric and thermo-plastic film forming composition which comprises an elasto-meric component and a resin component, said elastomeric com-ponent consisting essentially of linear or radial A-B-A block copolymers or mixtures of said A-B-A copolymers with A-B block copolymers, said A-blocks being derived from styrene or sty-rene homologues and said B-blocks being derived from conju-gated dienes or lower alkenes, said A-blocks having a mole-cular weight of at least 6,000: said resin component consist-ing essentially of low molecular weight resins being adapted to associate principally with the thermopLastic A-blocks of ~aid block copolymers and having a number average molecular weight not above 3,000 said compo~ition comprising at least about 85 parts of the low molecular weight A-block associating resins per one hundred parts by weight of the elastomeric com-ponent: said film possessing: (1) an elastic recovery from 50 percent stretch of at least about 75 percent, (2) a rubber ~odulus of not above about 2,00 pounds per square inch at 50 percent elongation, and ~3) a Gurley stiffness at a thickne~s of 1 mil of not above about 1.
, - 4a -1~141S
I have di9covered that I can produce a thin elas-tic and thermoplastic ~ilm possessing uni~orm product charac-teri~tlc~ economically at high speed~ by extruding it rrom melt of the above described film rorming compo~ition which contalns at least about-ô5 parts, pre~erably at least about 100 and not abo~e about 200 parts, of the low molecular wei~ht A-bloc~ associating reslns per one hundred parts by weight Or the elastomeric component. Normally thl3 proportion of the reJln component wlth respect to the elastomerlc component of the c~mpositlon ls surrlcient to assure that the plasticity o~
the composition is relati~ely low and does not change materiall~
when it 15 wor~ed at an elevated temperature approximating the temperature of extrusion.
In thi~ connection, the pr~cess o~ my lnvention com-prisee reedlng into an extruder an elast~merlc and thermoplas-tlc ~ilm forming composition compri~ing an elasto~eric compo-nent and a resin ccmponen~ o~ the type5 descrlbed hereinbefore.
This composltion exhibits a Brabender tor~ue change o~ not above about 200 meter-grams, preferably not above about 100 ~eter-grams, when worked in & Type REE 6 (Range l,000 _ 5,000 meter-grams) Plastograph mQnufactured~by C. W~ Brabender at 75 ~.p.m. and 220~C. for 45 minutes followlng an inltial 5 minute mixing period. This is a much more severe te~t than would be encountered in actual extrusion. For instance, ~ z5 while extruslon may take place at about the same temperature, ; the extrudate normally is worked for less than 5 minute~ at an r.p.m. ranging from 75 to 150. However, the more severe working in the ~rabender Plastograph is appropriate for - establishing a standard because a more measurable (larger) increment may be used to control a lesser deviation in actual _5_ ` 10914~5 practice. The maximum torque change of 200, preferably 100, meter-gram~ in 45 minutes of working in the Plastograph is an indication of relatively stable processing characteristics and consistent properties, as will be explained more fully herein-after. Processing stability is of particular importance and essential for product consistency in the extrusion of the thin elastic and thermoplastic films of this invention.
Then the composition is thoroughly mixed and melted in the extruder, passed through an elongated extrusion die, drawn while hot to reduce the thickness of the extrudate and cooled to produce an elastic and thermoplastic film having a thickness not above about 10 mils. The importance of hot drawing a similar extrudate is explained in United States Letters Patent No. 3,783,072. In the hot drawing process of this invention it is highly important to maximize the stability of the film forming composition as measured by minimizing the Brabender tor~ue change a~ described hereinbefore, because changes in the stability of the composition are magnified by the hot drawing step and thus may result in defects and other variations in product consistency.
According to a further broad aspect of the present invention, there is provided a process of extruding thin, self-supporting, elastic and thermoplastic film which comprises feeding into an extruder an elastomeric and thermoplastic film forming composition comprising an elastomeric component and a resin component, said elastomeric component consisting essen-tially of linear or radial A-B-A block copolymers or mixtures of said A-B-A copolymers with A-B block copolymers, said A-blocks being derived from styrene or styrene homologues and said B-blocks being derived from conjugated dienes or lower alkenes, said A-blocks having a molecular weight of at least 6,000, said resin component consisting essentially of low : ~) ,~ ~.
". ~ 415 molecular weight resins being adapted to associate princi-pally with the thermoplastic A~blocks of said block copoly-mers and having a number average molecular weight not above about 3,000, the proportion of said resin component with res-pect to said elastomeric component being sufficient to assure that the composition exhibits a Brabender torque change in 45 minutes at 220C. of not above about 200 meter-grams, thor-oughly mixing and melting said composition in the extruder, : passing the melted compo3ition through an elongated extrusion die, and drawing the extruded composition while hot away : from the die to reduce its thickness and then cooling it to produce an elastic and thermoplastic film having a thickness not above about 10 mils.
As indicated hereinbefore, the film forming compo-~ition of this invention comprises an elastomeric component and a resin component, and the elastomeric component consists essent1ally of linear or radial A-B-A block copolymers or mixtures of these A-B-A block copolymers with simple A-B block copolymers. However, the proportion of A-B block copolymers in the mixture of A-B-A and A-B block copolymers should not exceed about 75 percent by weight and lower percentages nor-mally would be used.
- 6a -~) Pr,-237 1~91415 The A-B-A b~ock copolymers'of this in~ention are oi the type which conslsts of A-blocks ~end blocks) deri~ed, l.e., polymerized or copolymerized, from styrene or styrene homo'Logues;'and B-blocks (center blocks) derived ~rom conJu-gated dlenes, ~uch as lsoprene or butadiene, or from lower al~enes~ such as ethylene snd butylene. Small proportions of , . .
other monomors al80 may enter into the block copoLymers them-sel~es~ The lndl~ldual A-block~ ha~e a number averago molecu-Lar weight o~ at loast about 6,ooo, prererably ln the range Or 10 . about 8,ooo -'30,000, and the A-blocks constltute about 5-50 percent, prererabL~ about L0-30 percent, by weight o~ the block copolymer. The number a~erage molecular weight o~ the B-blocks for linear A-B-A block copolymer~ preierably i3 ln the range of about 45~000 - 180,000 and that oi the llnear copolymer~. ltsel~,.
1 15 pre~or~bly 1~ in the range Or about 75,000 - 200,000. The nwm-! ber a~erage molecul~r wei pt Or the radlal A-B-A block copolymers pre~erably'is in the range Or about 125,000 - 400,000. m e ; ~ deslgnation A-3-A includes what are sometlmes called A-3-C
: I ~ block copolymers wherein the end blocks are''dlfierent irom~one another but both are deri~ed irom styrene or styrene homologues.
Thi8 applle~ both to lineQr and radial block copolymers. The term "llnear block copolymer" (or copolymers) includes branched A-B-A copolymers as well as unbranched A-B-A copolymers.
The radlal A-B-A polymers useful in this invention ~25 are of the type described in United States Letters Patent No.
~ 3,281,383 and conform to the following general formula:
:~ (A-B-)nX, wherein A is a thermoplastic block polymerized from . ~ styrene or styrene homologues, B is an elastomeric block derived _7_ .,"
lGX91 ~ 1 S
rrom con~ugated dienes or lower alkenes, as indicated above, X is an organlc or inorganlc connectlng molecule, with a ~unctlonality of 2-4 as described in Patent No. 3,281,383 or possibly wlth a higher ~unctionallty as described in the article entitled "New Rubber is Backed by Star~" appearing on page 35 of the June 11, 1975 issue of Chemical Week. "n'r then is a number correspondlng to the functionality o~ X.
~he A-B block copo~ymers of this in~ention are o~
tho type descrlbed ln Unlted States ~etters Patent Nos. 3,519,585 ~10 and 3,787,531 and comprlse A and ~-blocks derived from the mono-mers described hereinbe~ore in connectlon with the A-B-A copoly-mers.
The elastomeric component of the fllm ~orming com-posltion o~ this ln~entlon may include small amounts of othor mor- conventional elastomers but these should not exceed about .
25 percent by welght o~ the elastomeric component. These other olastomers may tnclude, hlghly broken down natural rub~ers and butadlene-styrene random copolymer rubbers, synthetlc poly-lsoprene, chloroprene rubbers, nitrile rubbers, butyl rubbers~
and the llke. Potentially elastomeric liquid polymers also may be employed a8 addltl~es but normally in lower proportions not abo~e about 10 percent by weight of the elastomerlc component.
The resin component o~ this inventlon consists es-sentially of low molecular weight resins which are adapted to associate principally wlth, and are principally compatlble with, the thermoplastic A-blocks of the said block copolymers.
These lnclude low molecular welght resins based on polyalpha-~ . .~ ,.. ...
1~3i415 Pl-237 methylstyrene, polystyrene, polyvinyl toluene and similar aromatic resln~, a~ well as copolymers thereof, coumarone lndene and related cyclic compounds. Prererred re81ns for th~s purpose pos3ess a-number average molecular weight not above aboùt 3,000 although higher molecular weight reslns in the low molecular weight range al~o ~ay be employed.
Smal~ propcrtion~r l.e.~ not abc~e about 25 percent Or the elastomerlc component, oi various other resins, which (ii tac~ i~ desired) may include conventional tac~ifying resins ~10 such as hydrocarbon reslns, ros~n, hydrogenated rosln, ~os~n e8ters, polyterpene resins~ and the like, also may be em-ployed ln the resin component of the ~ilm forming composition of this inventlon~
The ~ilm rormlng composition also may contaln rela-tl~ely small proportlons Or various other materials such as antioxidsnts, heat stabilize~s and ultra~iolet adsorbers, re-lease a3ents~ extender~ ~illers and the like. Typical anti-oxidants are 2,5 ditertiary amyl hydroquinone and titertiary butyl cresol~ Simila~Ly~ conventional heat stabilizers such as the zinc salts of alkyl dithiocarbamates may be uqed.
Lecithin i8 one release material which has been round to be particularly suitable in minor amounts in thls type of ex-trudable particulate ml~ture. However, waxes and various other release agents or 81ip agents also may be added in this manner. Relatively small proportions, in the neighborhood of 25 parts by weight o~ the elastomeric component, o~ ~arious ex^
tenders such as higher molecular weight polystyrenes, nonreac-tive phenol-formaldehyde resins~ linear polyester resinq, poly-ethylene, p~lypropylene, etc., also may be included in the fiLm forming composition of this invention. Similarly, the particulate mixture of thi~ invention may include relatively _g_ ... . . ..
5 ~~Z37 ~lL proportlons, s~y 25~parts by weight o~ the elastomeric .~ component, of r~llors and plgments such as zinc oxide, alumi-num hydrate, clay, calclum carbonate, titanlum dloxide, carbon b~ack and others. Many Or these fillers and p~gments also may be used in pow~ered ~orm as parting agents to be mixed with ; thermoplastic elastomer particles to prevent these particles from agglomerating prior to blending wlth reqin particles ana ~ ~ other materials.
:, In order to achieve a Brabender tor~ue change Or not above about 200, pre~erably not above about ~00, meter-~rams undor tho condltlons speciiied herelnbefore with the above-de~cribod type Or low molecular wei pt resins of this.invention, : It is~ prererred that the ~lIm ~orm~ng composition comprise at les8t about 85 parts.,. pre~erably about 100 Fart~ 0~ the afore-15~ sald low molecular.welght resin per one hundred parts by wei pt Or the olastomeric component Or the composition. In general the bloc~ copolymers o~ thi~ lnvention behave in one o~ two ways whe.n : . . . . .
workod at 220C. in the ab.sence of re~ln. T.hey either cross-link and `thicken, or break down and decrease in viscos~ty. For ln-1 .
stance, copo~ymers based on butadlene B-blocks wllI cross-link and thicken wheroas those based on isoprene B-blocks will break .
~down and~lose.viscosity. A typical.styrene-butadiene-styrene : (S-B-S) block copolymer of the type used ln thls ln~entlon glves ~: an lnereased torque readlng or Brabender torque increase of about Z5~ 600 meter-grams when worked for 45 minutes a~ described, whereas ;~1 a typlcal styrene-lsoprene-styrene (S-I-S) block copolymer glves a Brabender torque decrease o~ slightly over 300 meter-~rams.
Whe modlfied with the resln component of thls lnventlon, nelther the torque lncrease of the S-B-S block copolymer or the decrease . .
:30 Or the S-I-S block copolymer normally will exceed about 100 meter-grams, thereby assuring processing stabillty and product consist-; ency.
,. --10--. .
' lW~415 - PL-237 In the process of this invention the iilm iorming -campositlon i8 ~ed into the extruder where it is mlxed, melted and thoroughly blended at ele~ated temperatures which may be in the neighborhood of 325 - 4250F Then the resulting me~t 18 passed through an elongated ~xtrusion die and preferably drawn while hot to reduce the thickness 0~ the e~trudate. For instance, the extrudate mag be re-duced to a twentleth o~ its or~ginal th~ckness or less to produce a rll~ of less than 1 mil in thickness. On the other hand when the resultlng film ls to be in the neighbor-hocd o~ 10 mils thlck~ the orlginal thickness of the extru-date may be ~ess than twice that of the fllm~- The still hot drawn ril~ preferabl~ is cooled or quenched by running it through a cooling water bath or by passln6 it over a chllled cooling roll or by some other means deslgned to bring the temperature Or the film''well below its 30ftenlng temperature.
Howe~er, ~the iilm mag be laminated wlth some other materlal or treated while hot and before it is completely cooled.
For instance, the hot rilm may be shaped by embos~lng or by treating it ln accordance with the process of United States Letters Patent ~o. 3,632,269 to produ¢e a permanen~ly 3haped elastic and thenmoplastic 3heet material which pre~ents a discontinuous p~anar surface. This surface may be reticular, or ~ay include a grooved embossing pattern o~ protru~ions and depressions, or it may co~prise any other permanently shaped discontinuous planar configuration. The hot film may be laminated with fibrous or adsorbent substrates, such as paper, woodpulp, nonwo~en fabrics, etc., or even with .. .
-11 - . . ' . , . .
.. . .
_ m91415 ,' !
wo~en or knitted fabricR, or lt may be laminated w~th ~ilm~
or ~oils of other ~aterials. .Slmiiarly, after lts forma-tion the film may be heat sealed to any o~ these substrates by conventional heat sealing technlq~es.
: 5 The iil~ o~ thi~ in~ention has a multitude of ap- plications bu~ it will have particular uttlity where the combination of rubbery elasticlty and thermopl3sticity are de~ired! As indicated above, the unlque thermopla~ticity .Or this film ma~es lt possible to permanently shape the ~ilm or heat ~esl it to a substrate while retaining its other unique properties~ including it~ high elasticity, ~lexibility, ~oft hand and.high ~rlction properties.
Other and rurther ad~antages o~ the ~ilm and pro-ce~s Or this in~entlon wlll be apparent to one skilled ln the art from the following descriptlon, examples and clalms.
The rollowing examples are gi~en only by way of lllustratlon and are not intended to llmlt the ~cope of the in~entlon In any way. Table A.gi~es the ~ilm forming composl-. tlon ~or Examples I-VII.together wi$h their Brabender tor~ue change characterlstlcs and the phy~ical characteris~ics of the re~ulting extruded rl1ms. In the examples, all propor-tions are expressed in parts per one hundred parts b~ welght Or the total elastomeric component unless otherwlse indicated .
and Brabender torque change is expressed in meter-gra~s change after 45 minutes working ln the manner described herein-~ before.
,,~ ~ . .
. -12-.~ , . . .
lor91 415- ~L-23T
Film-thickness iq expre~3ed ln ~119, or thousand~
Or an inch, tens~le strength 1Q pounds per square lnch to brea~ the n lm as measured on an Instron tenslle tester with an inltial Jaw separation of one inch at a ~peed of twelve lnches per minute, and elongation i~ the percentage whlch the rilm must be stretched in a 6i~en dlrection to brea~ it, l.e., strotched dimenslon at broak minus normal dlm~nsion, over normal dlmension in that direction, times a hundred.
In all casc~ the desi6natlon "M.D~" means "machine direction"
lengthwl9e ln the dlrectlon o~ processing and "C.D." means "cro~s diroctlon. n ELB8tic recovery ls percentage Or immQdiate recovery ~n length a~ter bcing stretched ~i~t~ (50) percent Or origlnal length and thcn relea~ed to allow rrce return. It ls a ~unc-tlon Or the amount o~ stretch rocovered over tho amount o~
stretch. The a~ount o~ stretch equals the length when stretched minus the original length and the amount Or stretch recovered equals thc length when stretched minus the length a~ter rocovery.
. ~ . . . .
~ Rubber modulu~ 13 tenslle stress ln pounds per s~uare inch of ;~20; ~lnltial cro88 8ection mea9ured at one halr inch extension per inc Or length or 50 percent elongation. This ls called 50 per-cent rubber modulus.
... . .
GurLey stlrrness ls measured as an opposite or ln-v~rse measure of ~lexiblllty with a standard Gurley ~tiffness 25~ tester using l.0 by 1.5 inch samples wlth 1/4 lnch o~ s~mple ; in the ~aw and 1/4 lnch overlapplng the blade. The mea~ured Gurley stifrness then ls con~erted to stiffness at a thlckness one mil by dividing the measured stl~fness by the cube of ;:
the measured thickness in mil9. The coef~ic$ent oi slid-lng fr~ction 18 measured by drawing the ~ilm samples hori-zontally over a chrome plated s~ooth metal panel with a 500 gram we~gh~ on top Or the fllm~ ~hls is done in a ~LMI ad-5 he~ion tester at a p~lling speed o~ 12 inches per minute.
Heat sealabllity is measured by clamping each~llm sample in an open sandwich with a sheet of standard ~iber-board test m~teria~ between the ~aws of an Erich Internationa~
Corporatlon ~ag Sealer at 42 p.~.i. alr pre sure. The ~iber-bo~rd is Standard Reference ~aterlal 1810 speciiied in UnitedStates Department of Commerce Standard ~or Tape Adheslon Testing Wo. 16 (M:L-B-131E~ Class 2). One of the ~aws is heated and the other is unheated~ The boxboard ls pl&~ed in contact with the heated ~aw and the ~llm in contact wtth the unheated ~aw. ~oth ~aws are cooled to ambient temporature by air ~ets prior to clamplng. When the test material i3 in posltion between the ~aws, the bottom Jaw is heated by an electri~ heater to seal the fllm to the boxboard by heat trans-ferre* through the board. The heatlng time perlod required to heat the lower ~aw to the minimum ~eak temperature necessary to permanQntly heat seal the ~ilm to the boxboard, using a clsmpfng period of 4 seconds, then is measured. The minlmum peak permanent heat seallng temperature corresponding to the time recorded, then is obtalned by reference to a time-tempera-ture calibration cur~e ~or the instrument obtained by measuring te~peratures at the bonding surface of the boxboard. The minimum peak temperature referred to is that reached at the time the electric heater is deenergized at the end of the heat-ing time period.
lOgl415 ~1 o o ~ o u~ 8 ~D o ~ o N O
1-1 U~ I N O t~ . ~ 0 I ~ 2 N --I 01 ~ O N N 0~ I
I O 1~ ~ N O O 0~ ~ O O O
O N --~ ' O ~I N It O ~ N 0 O N 1~ ~ I
N ~ N 11~ ~` o 1~-- ~ ~' U~ --I
~ ~1 8 o ~. ~ ~ 8 ~ 0 ~
0 u ~ o ~ ~ 3 N _~ O N N V~ I
o 8 ~ o o o ~i ~ N N
~1 . . . .
~ls rl N
11~ 0 N; N C
~ 5 ~ 5 ~ R
C:l ~0 . ~ E ~ ) C C C ~ ~
C . O O O O `O ~
~; o N O~ O N ~ ~. O X C
C ~ g ~0 ~ ~ ~ ~ ~ 0 o ~ g C C ' C ~ 0 ~ O
Y t~ 0 '~ NE~ ~ ~ P C~
, O U~ O U~
~ N c~, lQ~141S
- P~-237 It will be 8een that the ~llms o~ all of the above examples are quite ela~tlc, i.e., possess an ela~tic recovery a~ter 50 perc~nt elongation of about 80 percent or more and generally well ab~e 90 percent. In iact, all the ~ilms of ; the examples hR~e an ela~tlc reco~ery of over 90 percent ex-*
cept ~or those formulated with the PIccotex polyalphamethyl-styrene-~lnyl toluene resins Furthermore~ all the r~lms pos8esJ a low rubber modulus, i.e., below about 2,000 lb~./ln.
at 50 percent elongation and all but one have a modulus at 50%
L0 olongation oi not abo~e about 1,000 lbs./ln.2.
The PS1~8 ot the example~ are not partlcul6rly orionted a8 evidenced ~rom the ten8ile 8trength readlngs ln the machlne and cross-directlons and ~enerally possess a hlgh elongation, i.e., at least about 500 percent ln both direction~.
L5 ~n.Pact, there are only two readlngs below 500 percent and the~ are weLl abo~e 300 perce~t.
The rilms are highly ~lexlble, exhibitlng ~urley sti~ness readings as low as 0.05 mg./ln.2/mil and no higher than 0.75 mg./ln.2/~il. They also are not sllppery, i.e., they po~sess a dynamic coeificient of ~rlctlon well above 0.5, more specirically between l and 3. The maxlmum permanent heat se~ling temperature determlned as de~cribed hereinbefore rangos between 150F. and 2800F., well below 350F.
Finally, all fllms when worked ln a Brabender plasto-t. ~
graph ~or 45 mlnutes as descrlbed herelnbePore, show a Bra-bender torque change loss o~ no more than 150 meter-grams and all but two of the Pilms show a Brabender torque change o~
not abo~e 100 meter-grams.
*Regi~tered Trademark PL-237:
~n the rore~oing examples Kraton* 1107 copolymer ls a thermoplastlc elasto~eric A-B-A (styrene-isoprene-styrene) block copolymer Or this lnventlon ofrered by the Shell Chemical Company, whereln the styrene content (that .o~ the A-blocks) is about 12-15 percent, clo~er to 15 per-cent by weight Or the block copolymer, and the polymer possesse~ a solutlon vlqcôslty oi about 2,000 centipolses at 25 percent ~olid~ ln toluene at roo~ temperature t~sing a Brook~ield Vlscometer wlth a No. 4 splndle at 60 r.p.m.), and a number avora~e moloculsr weight o~ about 110,000 -125,000.. Eraton 1102 copolymer 19 another A-2-A block copolym~r o~rered by Shell but this ~9 a styrene-butadiene-styrene copolymer wherein the ~tyrene blocks const~tute about 30 perc~nt o~ the copolgmer.. The number average mole-c~lar weight o~ Kraton 1102 copol~mer also is about 125,000.
Salpreno 420 copoly~er is a radial styrene-lsoprene-~; styrene block copal~mer o~ the type descxibed hereinbefore ; which has a number a~erage molecular weight of 240,000 and a styrene content oi about 15 percent.
. !20 Cumar 509 LX.resin is a solld coumarone indene re-: sin oifered by the Ne~llle Chemical Co., and having a soften-ing point of abo~t 145C. Amoco 18-210 and 18-290 resin~ are ~olld polyalphamethylstyrenes of~ered by Amoco*Chemical Co., with so~tening points of about 210F. (99C.) and 290F. (143C.) ~25~ respectlvely. Plccotex*100 and 120 reslns are polyalphamethyl-styrehe vinyl toluene copolymers of~ered by Hercules Chem1cal Go., with meltlng points of 100C. and 120C., respectl~ely.
' : -17-: *Regi~tered Trademark ..~
~ 1415 PL-237 ~ aving now described t~e invention in speci~lc detail and exempl~led the manner in which it m~y be carried lnto practice, it will be readlly apparsnt to those skilled in the art that innumerable variations, applications, modi-~ications, and extenslon~ of the ba~ic principle~ involved ~-y b~ ~-d- wlthcuO dep-re~ng rrO~ leJ 91rle or ~cop-.
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