Note: Descriptions are shown in the official language in which they were submitted.
1 325090
64536-568D
This applicatisn is a divisional application of - -:
Canadian Patent Application Serial No. 502,615 filed on ~:
February 25, 1986. ~:
,~.
-: .
FIELD OF THE INVENTION ~ .
Thi~ i~vention relates to thermopla~tlc packagin~ fllms and
r-cept-cle~ such as pouches, ~J8, ant caslngs made tberefro~ In partic~
ul-r, ~hi~ lDveDtlon relates to plastlc fil3~ and ~ags which are heat
~brlDk~bl- aDd hav~ i~provet shrink, tear, barrler a~t puncture reslstance
prop-rtle~
, "~ ... ..
~ACKGROUND O~ TH~ INVENTION ~ `
Shr~nkabl~ thermopla~tlc fllms having a gas barrier have found ~ -
Y-ny u~eful applic-tloD~ in packaglng of meats, cheeses, poultry, ~od
~u~erou~ other food aDt ~o~-food -products. There is alway~ the search -~
lor i~prove~eDt ln thesc fil~s to make the~ have better barrle~ proper-
tl~-, better ~bu~e resistance, bettcr tear resl~tance, lmproved clarity,
snd ea der ~ ndl~ag.- Ona fll~ of thl- type 1~ a multi-layer fll~ having
~y~ of polyethylcn~/s~n/polyethyleD- ~hlch 1~ di~elosed in U S
Patent No 3,821,182 whlch issuet on June 28, i974 to Wllliam G Baird,
.
401/B50409/2/1
,~ .
~ ','`
.. . 1 3.2`5.... 0 9 ~
Jr. ee. al. The shrlnk and abuse resistance of such a film 18 1mproved by
lrratiatiog the film to cros8-link the polyethylene layers prior to
heating and orienting the fllm by the trapped bubble technique.
Another film laminate that has been quite successful 18 that
dlsclosed in U.S. Patent No. 3,741,253 which is6ued on June 26, 1973 to
Harri J. Brax et. al. Di~clo8ed in this patent is a multi-ply laminate
which has a first layer of cross-llnked ethylene-vinyl acetate copolymer
directly ~oined to a middle layer of a copolymer of vinylldene chloride
which is ~oined to another ethylene-vinyl acetate copolymer layer. The
ethylene-yinyl acetate copolymer (hereinafter EVA) layer has lmproved
properties over the previously used polyethylene and, i4 the extruslon
coatlng method used to produce the multi-layer fllm according to the Brax
et. al. patent, the substrate EVA layer is preferably cros6-linked by
irratiatiOD before the saran layer i8 extru~ion coated thereon thus
avolding lrradlation of the saran layer. Saran (vinylidene chloride
copolymer) tends to discolor under high energy irradiation.
An alternate and successful ~ulti-layer film where a hydrGlyzed
ethylene-vin~l acetate copolymer is used as a barrier layer instead of
saran i~ discloset in U.S. Patent No. 4,064,296 which issued on
December 29, 1977, to Norman D. Bornstein et. al. A heat shrinkable
multi-layer film i~ formet by coextruding the hydrolyzed ethylene-vlnyl
acetate copoly er (someti~es abbreviated "~EVA" or called ethylene-vinyl
alcohol and -abbre~iated "EVAL" or "EVO~".) Since EVOH does not suffer
fro~ the effects of radiatio~ a coextruded product such as EVA/EVOH/EVA
can readily be cross-linked by irradiation before orientation.
~ nother way of improving the perfor~ance of packaging films has
been to blend various polymers. In U.S. Patent No. 3,090,770 which 1s6ued
401/850409/2/2
: - ...... , ., ,:.:, -~.,: - -. . , . . ., .- ,.:. . - . ,. -. ,, .. :: -:. :- .. .... .-. .. ., : -
on May 21, 1973 to Razmlc S- Gre~orian, the blending of cross-llnked
polyethylene with non-cross-~inket polyethylene i8 di~closet to improve
the clarlty of a film. Such blend6 were accompli6hed by using dlfferlng
proportions of hlgh, low and medium denslty polyethylene. This Patent
also ti6closet a cro~8-llnked polyethylene; and, U.S. Patent 3,118,866~
which issued on January 28, 1964 to the same inventor, is dlrected to an
ethylene composltlon and the process of cross-llnklng by chemlcal means.
The olefln polymers and copolymers have been partlcularly attractive
because of low cost, availabillty, and wlte range of satisfactory charac-
terlstlcs for packaglng fllms.
Recently, the medium and low denslty l~Dear polyethylenes have
become commercially avallable and have begun to be used ln a number of
pac~aging appllcatlons. One of the early patents in thls fleld is U.S.
- . . .
Patent No. 4,076,698 which lssued on February 28, 1978 to Arthur Wlllia~
Anterson and dlscloses an interpolymer composed of ethylene and mono-
alpha-olefinlc hydrocarbons conta~ning flve to ten carbon atoms per
~oleculc ant the proportion o~ the mono-oleflnic hytrocarbon belng 3 to 7
percent of the welght of the lnterpolymer with a melt index from 0.3 to 20
and a tenslty of 0.93 to 0.94. Llnear polymers of thls type are charac-
terlzet by actually belng an lDterpolymer-or copolymer with another olefin
ant havlng a relatlvely straight ~olecular chaln, that 16, having a chaln
wlth no slde branches or llmlted slte branching. Low density versions of
this type of fllm where denslty 18 in the range of O.g20 to 0.926 are
produced by a low pressure process as opposed to ths high pressure process
which produces a branched, low denslty polyethylene. Linear low denslty
polyethylene~ abbrevlated herei~after as "LLDPE", has found many applica-
tlons and uses as exempllflet by U.S. Patent No. 4,364,981 whlch lssued on
" ~,
401/850409/2/3 ~
. ~
;, , . . , .... .. . . , .. , .... ~ . - , .. , , . . . , - .. . -:
7 3~
,ecember 21, 1982 to Jerome T. Horner and tiscloses an EVA/LLDPE/EVA
structure a8 does al80 U-S- Patent No. 4,399,180 which lssued on August
16, 1983 to Wllliam F- Brlggs et. al. In U.S. Patent No. 4,457,960 a
multi-layer structure is disclosed of EVA/Saran/EVA-LLDPE-blent.
Still another polymeric material hag mo~e recently entered the
market having different propertles from the copolymers which comprlse the
LLDPE cla6s of materials. The~e copolymers are known as very low density
polyethylene ~hereinafter abbrevlated "VLDPE") and whereas conventional
polyethylenes and LLDPEs have densltie~ as low as 0.912, the VLDPE' 8
currently on the market have densltles below 0.910, speciflcally, 0.900 to
0.906, and lt is thought that densltles as low as 0.860 will be
forthcoming. European Patent Application No. 120,503 ~Union Carbide) has
been published dlscloslng a method of maklng VLDPE. In "Plastics
Technology" msgazine for Septembes 1984 at page 113, a news item eDtitled
"Introduclng Very Low Density PE" briefly describet some of VLDPE's
propertles and ~tated that lt's what the manufacturer "Calls an entirely
new class of polyethylene, consistlng of llnear copolymers that can be
produced at tensitles down to 0.89 or lower. What makes them special i8
an unique comblnst~on of properties in between those of standard PE's and
polyoleflDlc rubbers". In the October 1984 ls6ue of "Plastics Technology"
at page 13 another artlcle appeared entitled "New Kind of Polyethjlene
Combines nexlblllty, Toughness, Heat Resi~tance". This article lists a
number of the properties of VLDPE and compares them with EVA and states
that uses for thi~ material is for squeeze tubes, bottles, hoses, tubing,
drum liners and film. VLDPE is also listed as having potential a8 an
adtitive. It is expected to be used as a blending resin in high density
polyethylene, polypropylene, EVA, and some EPR's, wlth all of which VLDPE
is compatlble.
401/85~409/2/4
. - . - . ... . . . . .. . .
1 325D90
Accortlng to the article, the first two commercially available grade6 are
from Unlon Carbide and are de6ignated "DFDA-1l37 NT7", which has a narrow
moleculsr weight dl8trlbution, higher toughness, clarity, ant glos6 and
FDA clearance for food contact. The other secin 18 DFDA-1138 whlch 18
almed partlcularly at film, has a broad molecular weight dlstrlbutlon, and
18 cuperlor in processablllty. On page 15 in the ~ame article, lt is
stated that "the new reslns have been in~ectlon molded, extruded, blow
molded, and thermoformed on standard equipment". It is noted that blown
fllm can be extruded on systems deslgned either for conventionsl LDPE or
for LLDPE. ~owever, the company generally reco ends LLDPE-type scre~
de6igns in higher torque capabllity, especially with narrow-MWD grades.
The artlcle observes that the enlarged dle gaps requlred by LLDPE are not
requlred for VLDPE and that conventlonal blown fllm dle gaps of 30-40 mil
have proven satlsfactory at blow up ratios of 2-3:1. For blown fllm,
DFDA-1137 and 1138 are sald to extrude much like Z-~I LLDPE or 0.5~
LDPF. An artlcle slmilar to the one ln "Plastics Technology" appeared ln
the October 1984 lssue of "Plastlcs World" at page 86.
In the abo~e mentloned European Patent Applicatlon publlcatlon
No. 120,503, publlshed October 3, 1984, a process for preparing very low
denslty ethylene polymers ln a fluldlzed bet is described. These ethylene
polymers are classlfled as ha~ing a density of less than 0.9l rams per
cublc centlmeter and havlng a melt flow lntex whlch is preferably from 0.2
to 4.0-
Now, returnlng to the speclfic application of polymers to~ackaglng fllm and-receptacles made therefrom, a very successful and
useful fllm ls made accordlng to the process shown ln U.S. Patent No.
3,~41,253 mentioned above. A heat shrinkable bag can be made from ~uch
40ll850409~2/~
.. ~ . ,~ - . , - . -,, : , . .,, . , . . : . . . .. . .
1 3i~ '9`:~
fllm which has wite appllcatlon, partlcularly for meat, poultry, ant dairy
products. In fact, heat shrinkable polymeric fllms have gained rather
~lde spread acceptance for packaglng meat, particularly fre~h meat and
processed meat. Bags made from the hea~t ghrlnkable film are supplled to a
meat packer being sealet at one end with the other end open and ready to
receive a meat product. After the cut of meat is placed in the bag, the
bag will normally be evacuated and the open end of the bag closed by heat
sealing or by applying a metal clip. This process is advantageously
c~rried out within'a vscuum chamber where the evacuatlon and application
of the clip or heat seal ls done automatically. After the ba8 i8 removed
from the chamber lt iB heat shrunk by applying heat which process can be ~-'-
performet by i ersing the filled bag into a hot water bath or conveying
it through a hot air tunnel.
In the usual distribution chain, a whole primal or subprimal i~
packaged ~ithln shrink bags of this type. The meat within the bag will --
travel from a central ~laughter house ~here it hss been packaged to a
retall supermsrket where the bag wlll ~e opened and the meat will be cut
for re~all portions. Thu~, the bags of thi~'type must fiatlsfy a number of
requirements whlch are lmposet by both the slaughter house or pa~king
house and by the bag user. Furthermore, often the bag i8 placed in the
show ca~e at the retail supermsrket for special promotions when a whole
loin, for example, l~ to be sold to the consumer for his U8~. Ae thi~
poi~t, it i8 tesirabl~ to have an attractive package whereby there has
been relatlvely complete 6hrinkage of the bag around the product 50 that
the bag is not wrinkled and the blood and ~uices are not trapped in the
folds of the ~rinkle~. Accordingly, it is one ob~ect of the present
invention to provide a film sod receptacle made therefrom which has
lmproved shrink characteristics over ba~s used in the past. ~' -
4~1/850409/2~6 -
. . :......... . .. . -, . .. : , : . . .
~ 32~
:
Another lmportant characteristlc of a ba8 i8 the capablllty of
the bag to physically survive the proce~s of be$ng fllled, evacuated,
sealet, closed, he-t ~hrunk, boxed, shlpped about the country, unloaded,
ant stored at the retail supermarket. Thi8 type of abuse rules out many
polymeric films. Accordingly, it is another ob~ect of the present
lnvention to provlde a new comblnat~on of polymerlc fllms whlch wlll
withstand the abuRe of pack~ng, shlpplng, ant storlng.
Anotber feature requiret by bags uset for the foregoing tescribed
applicatlon is that the bag must also be strong enough to survive the
handllng involvet in moving packaged meat which may welgh 100 pounds or
more or large chunks of cheese welghing 60 lbs. or more. In particular,
when the chunk of ueat or cube of cheese i8 pushet into the bag its bottom
seal must withstand the force of the meat or cheese as it hits the seal.
Al~o, in bags that are made by folding a sheet wlth the fold as the
bottom of the ~ag and by ~ealing the side~, seal strength i8 quite an
important factor. Accordingly, lt is stlll another ob~ect of the present
invention to provide a bag which has improved seal streDgth over
prevlously avallabie bag~.
It l~ also vcry desirable for the bag to serve as a barrler
agalnst oxygen from the surroundlng atmosphere whlch will detrimentally
affect the fresh meat protuct. Accortlngly, $t i8 yet another ob~ect of
the present invention to provlde a flexible fll~ product which will
~alntaln during its packagi~g life tlme an effective barrier to gases and
oxygen, in particular.
One of the more common hazards $n packaging ant distrlbuting
products in flexlble packaglng materials is the hazart of the materlal
recelvlng a puncture whlch will release the vacuu~ inside the bag ant
allcw oxygen to enter. Anyehing from the appllcation of the clip to the
4011850409/2/7
: .
,
~ 32;~i~9~ :
pre~ence of a bone ln the meat can c8~8e a puncture. Accordiogly, it 16
an important ob~ect of the pre6ent lnvention to provide ~ fllm whlch has
- 6uperior puncture resistance.
SUMMARY OF THE INVENTION
It ha~ been found that the above mentioned ob~ects are achieved
by the present invention which, in one aspect, is a multi-layer,
thermoplastlc barrier film includin& a layer compris$ng very low density
polyeth~lene (VLDPE) having a density of 0. io6 grsms per cubic centl-
~eter or lower; a barrier layer comprising a material selected from the
group consisting of: (1) copolymers of vinylldene chloride and (2)
hydrolized ethylene-~inyl acetate copolymers; and a thermoplastic
polymeric layer, said layer being on the side of the barrier layer oppo-
s$te that of the layer comprising very low density polyethylene. The
thermoplastic poly~eric layer may advantageously compri6e a material
~elected fro~ the group consi~ting of: (a) ethylene. polymer~ and
copoly~ers and (b) blend~ of polymers and copolymers.selected from group
- (a). A pasticularly advantageous thermoplastic polymeric layer i8 one
whlch comprises ethylene-vlnyl acetate copolymers or a very low density
polyethylene. An unexpected result which .the.multilayer fllm of the
invention glves 18 that while VLDP~ has a high melting point, e.g.,
244-F, it can.be oriented out of.hot.water, l.e.r below the.boiling point
sf ~aeer and hence it will be shrinkable below the boillng polnt. Such
propertle~ greatly enhance its usefulness in psckaglng appllcatlons.
I~ another- aspect. the fil~ of the present in~ention i8 a
multl-layer thermoplastlc barrler fllm includlng a layer comprlslng a very
lo~ denslty polyethylene; and a layer comprising a polymeric barrier
401/850409/2/8
,-:`: . ::~ ; :- :- . , , .: ,,: :
1 32 5 3~
64536-568
material. Advantageously, the very low density polyethylene
material may be cross-linked. A preferable method of cross-
linking is to cross-link by irradiation although the material may
be cross-linked by chemical means. Also, in certain instances
where the barrier material is hydrolyzed ethylene-vinyl acetate
copolymer, it may be advantageous to cross-link the barrier
material.
In still another aspect, the present invention is a
seamless tubular film made from any one of the multi-layer film
combinations set forth above by a tubular or annular extrusion or
coextrusion process.
In yet another aspect, the invention is a bag or pouch
made from the film of the invention.
In a further aspect, the invention is a process for
- making a multi-layer, thermoplastic barrier film having a layer of
very low density polyethylene by orienting it below 100C (212F) -~
according to the process step~ described hereinafter. A feature
of this aspect of the invention is that the very low density
polyethylene layer of the multi-layer film may be cross-linked.
Accordingly, the invention herein comprises a multi~
layer, thermoplastic barrier film comprising: (a) a layer ~-
comprising very low density polyethylene havinq a density of less
than 0.910 gms/cc; ~b) a barrier layer comprising a material
selected from the group consisting of: (1) copolymers or
vinylidene chloride and (2) hydrolyzed ethylene-vinyl acetate ;
- copolymers; (c) a thermoplastic polymeric layer, said layer being ~
on the side of the barrier layer opposite to that of layer (a); ;
g '' '
- 1 32509~
64536-568
said multi-layer film being oriented and heat shrinkable at a
temperature below 100C (212F).
The invention also comprises a multi-layer thermoplastic
barrier film comprising: (a) a layer comprising cross-linked very
low density polyethylene having a density of less than 0.910 -
gms/cc; (b) a layer comprising a polymeric barrier material; (c) a
thermoplastic polymeric layer, said layer being on the side of the
barrier layer opposite that of layer (a).
DEFINITIONS :
The term "polyethylene" (PE) as used herein refers to a
family of resins obtained by polymerizing the gas ethylene, C2H4.
By varying the catalysts and methods of polymerization, properties
such as density, melt index, cry~tallinity, degree of branching
and cross-linking, molecular weight and molecular weight
distribution can be regulated over wide ranges. Polyethylenes
having densities ranging from about 0.915 to 0.925 are called "low
density polyethylenesn. Those having densities from about 0.926
to about 0.940 are called "medium den~ity polyethylenes", and
those
9a
` ~ 3250~0
having densitles above about 0.940 are callet "high den~lty polyethyl-
enes". (See "Wh~ttington'g Dlctlonary of Pla6tlcg, 1978). Molecule6 ln
conventional low denglty polyethylene are branched and linket in random
fa6hlon, those ln the hlgher den~ity polyethylene6 are llnket in longer
chalns with fewer 61de branches. Conventlonal low density PE i~ ~ometlmes
called branched low denslty PE.
The term "llnear low density polyethylene ~LLDPE)" a~ used herein
refers to copolymer6 of ethylene wlth one or more co-monomers selected
from C4 to Cio alpha oleflns such as butene-l, octene-l, hexene-l,
pentene-l, etc. in whlch the molecules thereof comprlse long chalns wlth
fe~ branche~ or cross-linked structures. Thi6 copolymer i~ sometlmes
called "lo~ pressure", low denslty polyethylene thereby referring to the
polymerizatlon process which produces ie. Preferably, the den~ity ~hould
be malntalned between 0.916 and 0.925.
The term "very low density polyethylene" as used hereln means
llDear PE copol~mers havlng a denslty of less than O.9lO gm/cc and as low
aa 0.ô60 or even lover. .
The ten~ "ethylene-vinyl acetate copoly~er" (EVA) as used hérein
.
refer~ to a copolymer formed from ethylene and vlnyl acetate monomers
~herein the ethylene units are present in a ma~or amount and the vinyl-
acetate units are present in a minor amount.
An "orlented" or "heat ~hrinkable" material ls defined herein ~8
a material which, when h~ated to an appropriate temperature absve room
temperature-(to, for example 96C) will have a frse shrink of 5Z or
greater in at lea~ one linear direction.
4Dl/850409/2/lO
.: : : . .: . : -
1 3250qo
64536-568
DETAILED DESCRIPTION
A preferred method of making the film of the present
invention is that according to the process outlined and described
in U.S. Patent No. 3,741,253 (Brax et. al.). In this process the
first or substrate layer of the film is extruded through a conven-
tional tubular extruder whose die is modified to handle very low
density polyethylene resin to form a tubular tape or film. The
preferred resin is "DFDA-1137 NT7" from Union Carbide Corporation
which has a density of approximately 0.906 grams per cubic centi-
meter, a melt index of 0.721 grams/l0 minutes, a melting point of
244~F, anc is a butene based copolymer. The extrudate has a dia-
meter of about 3 1/2 inches with a wall thickness of 19 to 20 mils
as it leaves the die. After leaving the die the substrate i9
cooled and flattened. At this point it may be sent through an
irradiation vault where it will be irradiated by high energy elec-
trons to a dosage of preferably about 4.5 MR. Depending on the
characteristics desired, this dosage can vary from 2 to 20 MR.
After leaving the irradiation vault the substrate i8 again inflat-
ed and sent through a first tubular extrusion coating die where it
receives a coating of about 3.5 mils of vinylidene chloride
copolymer. After receiving the coating of vinylidene chloride
copolymer the still inflated and now double-walled film passes
through a second tubular extrusion coating die where it receives a
layer of about 5.0 mils of ethylene vinyl acetate copolymer which
has a vinyl acetate content of about 5%. After receiving the
final coating, the film i~ cooled, collap~ed and rolled up. It is
` 1 325090
64536-568
now a three layer tubular tape having a wall thickness of approxi-
mately 27.5 mils. This tape is subsequently unrolled, fed through
a bath of hot water held at 205 to 210F, preferably close to
210F, and as it leaves the hot .
- lla - `~
.. . .
. . ~ - , -
1 3~50'~0
... .
water lt i~ lnflated and blown into thln tublng where its wall thlckne6s
will be 2.4 mlls. Thls 16 the trapped bubble technlque whlch 18 well
known in the art. The fllm 18 rapldly coolet to set the orlentatlon and
then rollet up for further processlng.
It i8 qulte fiurprlslng that the VLDPE havlng a melt temperature
of 244F can be oriented at 205F, particularly, when the VLDPE 18 the
substrate of i- barrler fllm. Normally, an olefin based poly~er
would be expected to orient at not more than 10F to 15F below its
melting polnt. For exa~ple, in the above mentioned U.S.P. 3,741,253 the
EV~ h~s a melt polnt of sbout 205F and iA oriented at about 190F.
Slnce films shrink at or near orientation temperature, this means that
packages mate from fllm according to the invention can be shrunk in hot
water baths.
One further processing step can be taken to make end ~eal bag~ by
transversely sealiDg and ~evering acros~ the seamless tubular film as it
is laid flat to make indivldual bags. Side sealed bags may be made by
~lltting the se~less tubular f$1m along one of its edges after which it
1~ transversely sealed ant severed into bags. The ~ide seals are the
sealiDg and ~everiDg seams aDd the bottom of the bag is the unsllt edge
of the fil~. -Other bag and pouch making methods known ln the art may be
readily adapted to making receptacle~ from the multi-layer film of the
present i~vention.
The substrate film of ~ery low density p,olyethylene may be
extruded as a monolayer substrate or coextruded as a multi-layer substrate
and then irradiated depenting upon the desired char-cteristic~ of the
final fllm. Furthermore, adtltlonal layers may be extrusion coated upon
the lnflated substrate 80 that fllms havlng 4, 5, and 6 or more layers ~ay
result.
401/850409/2/12
~ ~ .
1 3250qO
~ n alternate method of manufacturing a fllm accordiog to the
present invention i~ to employ the method dlsclosed ln U.S. Patent No.
4,379,117 whereln the extruder6 feed to a common coextruslon die whereln
the inner layer 18 VLDPE polymer, the center layer 18 a ~inylltene chlo-
rlde copolymer and the outer layer wlll be an ethylene vlnyl acetate
copolymer. Thl8 fllm can be blown lnto a tube lmmedlately upon leavlng
the coextruslon dle. If lt is desired to irradlate all three layers of
film, lt is preferable to use EVOH in place of the vinylidene chlorlde
copolymer layer as vinylldene chloride copolymers do not react well to
radlatlon tendlng to turn an undesirable brow~lsh color. Agaln, the fllm
18 not limlted to three layers and will preferably be extruded ln the form
of an uDstretchet tape after whlch it 18 lrradlated and then oriented by
the ~ame type trapped bubblè technique as descrlbed above and ~hown and
descrlbed U.S. Patent ~o. 4,379,117.
Returnlng no~ the process of U.S. Patent No. 3,741,253, three
runs were made whlch de Dstrate the lmproved a~d unexpected results of
u~ing a YLDPE layer iD conJuDctlon wlth a vlnylidene chlorlde copolymer
(PYDC) layer to ma~e an improved barrier fllm and receptacle.
In the control ssmple a film accorting to U.S. Patent No.
3,471,253-wa~ produced~ l~e single_substrate 1ayer 8s disclosed in that
patent is, ln the control sample actually two layers, l.e., the two layers
to the left of t~e PVDC_film were coextruded_~nt irradiatet pFlor to
receivlng ~ coating of PVDC aDd followed by a coating of EVA. The layer
constructlon with the thickness i~ mils of each layer ls as follow~:
Conerol: EVA/EV~/PVDCtEYA
14.5/3.0/3.5/6.5
401/850409/2113
1~
- : . . .. ~ - . .: .. .. .. . . . . , . . ; ........ .
.: ~ . . : . . .. ~. . ... . . .. .. . .
:.: . -. . .- : - ~ -- ~ - , -
1 325090
The two EVA layers to the left were lrradistet to a do~age of 4.5
MR and represent the sub6trate. The tape was oriented from a hot water
bath at 210-F and stretched to a wall thickDess of 2.4 mll6 by the trapped
bubble technique.
EXAMPL~ 1
The thicker 6ubstrate layer (14.5 mils) was DFDA-1137 NT7, a
VLDPE res~n fro~ Union Carbide. The process Dset was the 6ame as for the
coDtrol sample and the layer construction was as follow6 having the same
thicknesses as the control 6a~ple:
VIDPE/EVA/PYDC/EVA
t~is extruslon coating process, the EVA layer interposed
between the VLDPE surface or 6kin layer and the PVDC layer is ~o placed
to pro~ote adhesion between the layers snd to lessen any tendency of the
film to delaminate as VLDPE does not adhere to PVDC as well as does EYA.
- . . ,'' ' ''
EXAMPLE 2
The secoDd example ~as run in the same ~aDner as the first
~xample and-the control sample excepe that both outer layers of the film
~ere VLDPE DXFP-1137 resln. This;structure was as follows: -
VLDPE/EVA/PVDC/VLDPF ' :-
The tapes produced ln Examples i and 2 were oriented $n the same ~ -
manner a~ the eontrol sa~ple. The physical properties of the film6 are
set forth ln Table I below.
401/85040912/14
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TABLE I
Para~eter Control Example I Exsmple 2 Te~t Procedure
Ten~ile Strength (PSI)
Longitutlnal 8,490 8,430 11,300 ASTM D882-81
Transver~e 10,920 10,750 11,090
Elongation at Break
(Percentage) 206 277 314 ASTM D882-81
Tear Propagation at
?3F (Grams)
Longitutinal 22.75 480 258.75 ASTM D1938-79
Transverse 21.0 240 265.5
Free Shrlnk at l90-F
(Percent)
Longltudinal 37 33 38 ASTM D2732-70
Transverse 51 48 47
Shrlnk Tenslon at
195~ (PSI)
Longltudinal 248 183 234 ASTM D2838-81
Transverse - 303 342 385
Ball Burst I3pact
at 73-F (CM~KG) 12.5 20.6 28.1 ASTM D3420-80
Optical Properties
at 73-~
Haze (Percent) 2.8 4.1 8.7 ASTM D1003-61 -
Water Vapor Transmisslo~
at 100-~ :
Grams/24 hours, lOb sq. ASTM F 372
in. 100~ R~ 0.76 0.49 0.48
(Gauge-mils) (2.21) (2.48) (2.38)
Oxygen Trans2i~slon at
73-~
CC (STP/24 ~ours, sq. ~-
~eter, ATM~ 39.2 31.3 26.4 ASTM D3985-81
(Gauge-mil~) - (2.42) (2.38)(2-37)
The e~amples show a slgnificant and unexpected improvement in
ball burst ~trengt~ which i~ direcsly related to the puncture resistance
and 18 a highly-desirsble property~ln a film which wlll be used to package
401/85~40912J15
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1 325090
a wlde variety of irregular article~, particularly those whicb may contaln
bones and wlll be subJected to a variety of abuslve condltlons.
Another u~expected and beneflclal result is the fact that there
wa8 8 reduction in the oxygen ~ransmi6~ion ra~e 80 that the film of
Examples l and 2 demonstrated improved barrier properties. Normally, one
would not expect the substitution of a lower density material (VLDPE) for
a blgher density one (EVA) to result in a better barrier, partlcularly,
siDce the polyethylenes, in general, have poor oxygen barrler properties
as compared to saran, EVOH, nylon, etc.
The same result occurred with water vapor transmis6ion ln that
lt was lowered by the 6ub6titutlon of the lower density VLDPE layerfi for
tbe hlgher density EVA layers.
Furthermore, both films containing VIDPE layer~ ~howed i~proved
elongatlon before breakage too~ place thus lndicating the film wlll stand
more abuse before rupturing or tearing.
And, as stated above, a very surprising and unexpectet re~ult
was that the VLDPE, having a melt point of 244F, could be oriented out
of a hot water bath somc 40-F below lts melt point.
Bss-d on the ~ork tone above, three layer fllms c~mprising the
follo~iDg ~tructures can-be made. The particular four layer structures
mate a~o~e in the control and in Examples-l and 2 were-made fro~ a four
e~trùder configuration using an--EV~-layer- between-the VLDPE-and-PVDC to ~:
promote layer-to-ls~er adhesion. Thus, all samples were run on the same
equlpment. $he followlng-examples can be ~ade based on this work.
EYample j:--VLDPE/PVDC/EVA
(InsideOutsite tube wall)
tube wall)
-~,.
401185040912116
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64536-568
Example 4: EVA/PVDC/VLDPE
(Inside (Outside tube wall)
tube wall)
Example 5: VLDPE/EVA/PVDC/VLDPE
(In3ide) (Outside)
In this structure it i8 preferred that the inside VLDPE
and EVA layers be irradiated before the PVDC and outer VLDPE
layer~ are coated thereon.
Example 6: VLDPE/Adhesive/PVDC/Adhesive/VLDPE
(Inside) (Out~ide)
This structure is preferred for maximum delamination
protection. The adhesive can be an EVA of 10% or greater vinyl -~
acetate content, a Plexar* brand adhesive from Chemplex Company of -~
Rolling Meadow~, Illinois, or a CXA brand adh0sive from duPont
Corporation of Wilmington, Delaware. The inside VLDPE and adhe-
sive layers are preferably coextruded a~ a tube, cooled, flattened
and irradiated while the remaining three layers are sequentially
extru~ion coated onto the substrate after it has been irradiated
and inflated.
Example 7: By coextruding according to the process of the above
mentioned USP 3,821,182, a preferred structure as follows may be
obtained: ~-
*Trade-marX
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64536-568D
VLDPE/Adhesive/HEVA/Adhesive/YLDPE, where the
adhesives are selected as in Example 6 and the
entire structure may be irradiated and oriented.
. .
~hile the present lnvention has been te~cribed with reference
to tubular coextruslon and stretching by ehe trapped bubble
technique other method~ of manufacture are available 6uch as
coextruding the multilayer fll~ through a slot die and then
stretchlng the fllm by u~e of tenter frames In adtltlon, ln
certain applicatio~ blend~ of VLDPE, LLDPE and/or EVA may be
u~et to achleve desired prope~tles.
Numerous layer combinatlon~ will become evident to tho~e
skilled ln th- art upon readlDg thla dl~closure. The scope of
~he invention i- ll lt-d only by the followiDg claims~
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