Note: Descriptions are shown in the official language in which they were submitted.
ACC-21 ~ 1 6 ~8
1 BACKGROUND OF THE INVENTION
2 Ethylene vinyl alcohol ~EVOH) copolymers are recognized to
3 have considerable value in packaging films, and especialiy those
4 intended or use with foods and other products that require
protection against oxygen. This is, of course, b~cause of the
6 excellent oxygen barrier properties of EVOH copolymer films,
which are exhibited even in sections as thin as about 0.l mil or
8 less. Despite this, the EVOH resins suffer from a number of
9 drawbacks.
In particular, films made from EVOH tend to lack toughness
11 and to be relatively brittle, particularly in the thin sections
1~ in which they are most economically used. Moreover, of the films
13 1 with which they are desirably and most practically combined, the
14 I EVOH copolymers exhibit good adhesion only to those made of
¦ nylon, thus necessitating the utilization of supplemental
lfi ¦ adhesives when other resins are to be joined thereto. The EVOH
17 I copolymers are also quite expensive.
18 ¦ On the other hand, it is also well recogni~ed that films of
19 ¦ high molecular weight, relatively high melting point polyamides
¦ exhibit outstanding levels of toughness and tensile strength,
21 ¦ while at the same time offering good adhesion to a variety of
22 ¦ resinous substrates or coatings; however, nylon is not an
23 ¦ effective oxygen barrier polymer, for certain applications.
24 ¦ Consequently, separate layers of EVOH copolymers and polyamides
1 are presently employed in composite film structures, so as to
~6 ¦ obtain a desirable comhination of the properties that are
27 ¦ afforded by each.
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. I ~
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1 ¦ Although it is entirely feasihle to produce composite films
2 ¦ of the foregoing nature by coextrusion or by extrusion ccating,
3 ¦ it is found to be rather difficult to achieve the measure of
4 ¦ control necessary to produce uniform layers of the components,
¦ optimal adhesion, and a desirable balance of properties.
6 Moreover, property variations are not readily made, as is
7 desirable in many instances to tailor the film to use for
8 ¦ specific applications.
9 ¦ It is believed that attemp~s have been made in the past to
l produce blends of polyamide resins (as well as other polymers)
11 ¦ with ethylene vinyl alcohol copolymers, in an endeavor to provide
12 extended compositions from which sing]e-layer films exhibiting
13 ¦ desirable properties might be produced. However, as far as is
14 ¦ known such attempts have been unsuccessful, due primarily to
¦ compatibility problems and the difficulty of extruding the
1~ ¦ blended resins, while preserving the desirable properties of the
17 ¦ components. In particular regard to the film~fcrming polyamide
18 ¦ resins, those which exhibit the desired properties are
19 ¦ processable only at temperatures that are considerably above the
processing temperatures of the EVOH resins. Consequently, it has
21 ¦ not heretofore been possible to extrude a blend of the two
22 ¦ ingredients without intolerable degradation ~essentially gel
23 l formation) of the copolymer. Moreover, it would be anticipated
24 that, in any such blend, the excellent oxygen barrier
¦ characteristics of the EVOH copolymer would be significantly
26 l compromised, due to the presence of the polyamide resin, and
27 ¦ that, conversely, the inherent physical or structural properties ¦
~8 ¦ of the polyamide would be diminished in direct proportion to the
amount oi EVOH copolymer inc~ud l~
ACC-21
1 Accordingly, it is a primary object of the present
invention to provide a novel blend of a film-forming polyamide
3 resin and an EVOEI copolymer, which blend is processable at
4 temperatures below those at which any substantial deyradation of
the EVOH copolymer will be encountered, to produce a film having
6 a desirable balance of oxygen barrier and structural properties.
7 It is also an object of the invention to provide such a
8 blend which is adapted to be coextruded with a second resin, to
9 ¦ produce a composite film in which adhesion between the layers is
¦ at a desirable level.
11 ¦ Another object of the invention is to provide a novel
12 ¦ process by which films having relatively high levels of strength
13 ¦ and toughness, and excellent oxygen barrier chsracteristics, can
14 ¦ be produced with relative facility and good economy, which
¦ process may entail the coextrusion with a second, distinct resin.
16 ¦ A further object of the invention is to provide novel
17 ¦ products produced by the methods of the invention.
18 ¦ SUMMARY OF THE INVENTION
19 ¦ It has now been found that certain of the foregoing and
¦ related objects of the invention are readily attained in a
21 ¦ synthetic resin blend comprising a polyamide resin, an EVOH
~2 ¦ copolymer, and a plasticizer for the polyamide resin. In
~3 ¦ accordance therewith, about 90 to 20 weight percent of a
24 ¦ film-forming polyamide resin, having a molecular weight of about
¦ 20,000 to 30,000, and a melting point temperature of about 415
2~ ¦ degrees to 440 degrees Fahrenheit, is intimately admixed with
27 l about 10 to 80 weight percent of an EVOH copolymer, having a
28 ¦ molecular weight of about 15,000 to 30,000 and a melting point
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ACC-21
1 temperature of about 325 degrees to 375 degrees Fahrenheit. The
2 plasticizer is incorporated with the polyamide resin and the EVOH
3 copolymer in an amount of about 2 to 25 percent, based upon the
4 1 weight of the polyamide resin, and it will be effective to lower
the pro~essing temperature of the latter to a value approximating
6 that of the copolymer, and below the temperature at which any
7 substantial degradation would occur therein.
8 In preferred embodiments, the amount of the film-forming
9 ~ polyamide will be about 75 to 25 percent, and conversely, the
¦ amount of the EVOH copolymer will be about 25 to 75 percent, with
11 the plasticizer being included in an amount of about 5 to 15
12 percent, again based upon the weight of polyamide present. The
13 plasticizer will normally be of such a composition, and used in
14 such a concentration, as to permit processing of the blend at a
l temperature of about 400 degrees to 480 degrees (and preferably
16 l about 430 degrees to 450 degrees) Fahrenheit, and generally the
17 ¦ plasticizer will be compounded with the film-forming polyamide
18 resin prior to admixture with the ethylene vinyl alcohol
19 ¦ copolymer. The plasticizer may be of either monomeric or
2n polymeric nature, and suitable classes of compounds include long
21 chain fatty acid amides, aromatic sulfonamides and polyamides
2~ ¦ having a molecular weigh~ of 5,000 to 25,000 and a melting point
23 1 temperature below about 400 degrees Fahrenheit; specific
24 preferred plasticizers are lauramide, o,p-toluenesulfonamide,
N-ethyl~o,p-toluene-sulfonamide, and polyamides of 7,000 to
2~ l0,000 molecular weight.
27 Other objects of the invention are provided by a novel
28 method of making a film, wherein a blend of the foregoing
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ACC-21 l
1 ¦ composition is initially produced, preferably by pre-compounding
2 ¦ the plasticizer and the film-forming polyamide resin. The blend
3 ¦ is heated to the processing temperature, and is then forced
4 ¦ through the die of an extruder to convert it to a molten film,
¦ after which the film is cooled to solidify it a~d to permit
6 recovery of the ultimate product. Generally, the processing
7 I temperature will be in excess of 400 degrees Fahrenheit, and
8 I preferably it will be in the range of 430 degrees to 480 degrees
9 ¦ Fahrenheit.
¦ In the practice of the method, a ~econd resin, different in
11 composition from the blend, may be combined therewith in the die,
12 to produce a laminar structure comprised of layers of the two
1~ I components. The laminar structure will then .~e forced through
14 ¦ the die to convert it to a film comprised of layers of the
¦ copolymer and of the second resin.
16 ¦ DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
17 ¦ EVOH copolymers that are suitable for use herein will
l8 ¦ generally contain at least about 55, and as much as 80, weight
19 ¦ percent of vinyl alcohol in the molecule; the preferred
¦ copolymers will contain about 60 to 75 weight percent of the
21 ¦ vlnyl alcohol moiety. The remainder of the molecule will consist
2~ ¦ essentially of ethylene; however, because such products are
~3 ¦ produced by hydrolysis of ethylene vinyl acetate copolymers, some
2~ ¦ residual vinyl acetate will usually be present in the resin.
~5 ¦ Normally, there will be less than about 3 weight percent of vinyl
2~ l acetate, and preferab]y i~ will be present at a level below 1.5 !
27 ¦ percent. The RVOH copolymers will typically have molecular
~8 weig s in the range of about 20,000 to 30,000, corresponding
~-
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ACC-21 l
1 ¦ roughly to melt indices of about g to 1.5; the melt index values
2 ¦ for these resins are determined in accordance with ASTM Test
3 ¦ D~1238, Procedure E or L, using a weight of 2160 grams and a
4 ¦ temperature of either 190 degrees or 230 degrees Centigrade, as
¦ appropriate. Typically, the copolymers will have'densities of
6 about 1.1 to 1.2, and their melting points will normally range
7 ¦ from about 325 degrees to 375 degrees Fahrenheit; suitable
8 ¦ temperatures for processing them will be about 400 degrees to 480
9 ¦ degrees (and preferably about 430 degrees to 450 degrees)
¦ Fahrenheit. While the degradation temperature of EVOH is
11 ¦ generally regarded to be about 450 degrees, it should he
12 ¦ appreciated that this is not inconsistent, due to the residence
13 ¦ time factor and its effect upon degradation. Specific EVOH
14 ¦ resins that are suitable for use are available from Kuraray and
¦ from Nippon Gohsei, both of Japan, the products of the f`ormer
16 ¦ company being designated EP-E and EP-F, and those of the latter
17 ¦ company being designated GL-D and GL-E.
18 ¦ Insofar as the nylon utilized for blending with the EVOH
19 ¦ copolymer i~ concerned, virtually any high molecular weight,
¦ relatively high melting film-forming polyamide resin may be
21 ¦ utilized. Thus, while the polycondensation resins such as nylon
22 ¦ 66 may be employed to advantage, for most purposes the addition
23 polymer nylon 6 will be preferred as a practical matter. To be
24 ¦ suitable for use, the nylon will generally have a molecular
¦ weight in the range of 20,000 to 30,000, and a melting point
26 l temperature of about 415 degrees to 440 degrees Fahrenheit~ with
27 ¦ a melting point temperature of about 430 degrees being optimal in ¦
28 ~ many ses. Such polyamide resins are nor~ally processed at
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ACC-21 l
1 temperatures of about 510 degrees to 540 degrees, thus giving
~ rise to the fundamental difficulty which has heretofore precluded
3 the successful formulation of extrudable blends of nylon with
4 EVOH copolymersO
¦ The compositions of the present invention arle, on the other
~ hand, processable at temperatures that are sufficiently low that
7 ~ degradation of the EVOH resin is avoided, and this result is
8 I achieved by the incorporation into the composition of an agent
9 I that serves as an effective plasticizer for the film-forming
¦ nylon. While some of the agents utilized may not previously have
11 ~ been regarded as plasticizers, in the present blends they do
12 I appear to perform that function. In other words, the
13 ¦ plasticizing agents are capable of intermolecular hydrogen
14 ¦ bonding within the polyamide resin, to effectively lower the
¦ temperature at which it can be processed. As a result,
lG ¦ film-forming nylons that normally process at a temperature of
I about 510 degrees to 540 degrees Fahrenheit become processable at
18 ¦ temperatures that are considerably lower and that are, in fact,
19 ¦ within a range of temperatures at which the EVOH copolymer is
~0 ¦ also processable and not subject to significant degradation.
21 ¦ More particularly, the plasticized film-forming polyamide resins
22 ¦ are processable with the EVVH resins at temperatures of about 400
23 ¦ degrees to 480 degrees Fahrenheit, with preferred temperatures
24 ¦ being about 430 degrees to 450 degrees.
¦ The amount of plasticizer utilized may vary between fairly
26 ¦ wide limits, and as little as 2 percent or as much as 25 percent,
27 ¦ based upon the weight of the polyamide resin, may be employed.
28 For satisfa tory resalts, however, it will often be necessary to
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1 I use a concentration of plasticizer in excess of 2 percent, and
~ ¦ therefore 5 weight percent will usually represent a preferred
3 lower li;nit. Conversely, amounts of plasticizer in excess of
4 I about 15 weight percent will frequently produce little added
¦ benefit, and therefore that concentration represents a preerred
6 ¦ upper limit in most instances. The amount utilized in any given
7 I case will, of course, depend upon a number of factors, including
8 ¦ the composition of the polyamide film-forming resin and of the
9 ¦ specific plasticizer employed, the actual processing temperatures
¦ involved, etc.
Insofar as specific plasticizers are concerned, the
12 preferred agents fall within three main categories, namely the
13 ¦ long chain fatty acid amides (i.e., those containing 16 to 18
14 I carbon atoms in the chain), the aromatic sulfonamides, and the
¦ polyamides which exhibit a melting point temperature of less than
16 ¦ about 400 degrees Fahrenheit. Within those categories, the most
17 desirable plasticizers are lauramide, o,p-toluenesulfonamide,
18 N-ethyl-o,p-toluenesulfonamide (the two sulfonamides of course
19 being mixtures of the ortho and para isomers), and polyamides
such as nylon 6,36, nylon 11 and nylon 12 having molecular
Yl weights of about 7,000 ~o 10,000~ Other suitable specific
2~ products that can be used as the plasticizing agent include nylon
23 11 and 12 of about 25,000 molecular weight and melting at
24 temperatures of about 370 degrees and 350 degrees ~ahrenheit,
respectively, 2,2,4-trimethyl-1,3-pentane-diol, cumylphenyl-
benzoate, and a product offered commercially py Paul and Stein
27 Brothers of New York, New York under the ~ STYSOLAK AW,¦
~8 referred to as a polyethylene oxide. Based upon the foregoing
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ACC-21
¦ it is believed ~hat other suitable plasticizing agents for use in
~ ¦ the compositions of the present invention will occur 'co those
3 ¦ ski]led in the art. For example, it should be mentioned that the
4 ¦ two aromatic sulfonamide compounds specified above are
commer~ al~y available from the ~lonsanto Chemical Company under
I 7'~0 ~c;r~
¦ the~4~t~ s SANTICIZER 9 and 8, respectively; other similar
7 ¦ compounds sold under the same brand designation may also function
8 ¦ desirably in the instant blends.
9 ¦ In producing the blends of the invention, it will generally
¦ be desirable to premix the plasticizer with the film-forming
11 ¦ polyamide, so as to ensure that the plasticizer will be mos~
1~ effective in producing the desired result. This may best be done
13 ¦ in a compounding extruder or the like, depending to some extent
l4 l upon the physical state (i.e., whether it is a solid or a li~uid~
¦ of the additive. It will generally be most advantageous to
1~ ¦ produce pellets of the plasticized polyamide, which can then be
17 ¦ admixed with pellets of the ~VOH copolymer, such as in a ribbon
1~ ¦ blender, prior to introduction into the extruder which is to be
lQ ¦ used for conversion to the film.
~0 ¦ S~ch conversion may be effected in any suitable manner,
21 ¦ such as by cast or blown film extrusion. As indicated
22 ¦ previously, the compositions of the invention may also be
23 ¦ coextruded by such techniques with resins of different
24 ¦ composition for various purposes, such as to enhance certain
¦ properties or to provide properties that are not possessed by the
2~ ¦ blend film itself. For example, to provide a packaging material
~7 ¦ capable of heat sealing at relatively low temperatures, it may be I
28 I desirable to provide a layer of an ionomer resin (i.e., DuPont
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SURLYN ta trademark)) on one side of the film. I-t migh-t be
emphasized a-t this point tha-t, due to the presence of nylon in
-the blend, i-t may be possible to achieve adequa-te adhesion bet-
ween the blend layer and the SURLYN (a trademark) layer withou-t
the utilization of any added adhesive; the same is not generally
-true of :Eilms made of EVOH copolymer, per se. Moreover, even in
those ins-tances in which an adhesive layer is utilized, still
the blends of the inven-tion offer considerable advantage, in
-that -the level of adhesion is enchanced considerably.
As taugh-t in United States Ratent Nos. 4,233,367, to
Ticknor and Rein, 4,239,826, to Knott and Wang, and 4,254,169 to
Schroeder (all of which are of common assignment herewith) a
number of suitable extrudable adhesives are available on the
market, typical of which are the products sold by Chemplex
Company under the trademark PLEXAR, and described in United
States Patent Nos. 4,087,587 and 4,087,588, and the resins sold by U.S.
Industrial Chemicals Company, di-vision of National Distillers and Chemical
Corp. under the trademark S-2037 and S-2038, which are described in United
Patent No. 4,239,826. Other suitable adhesives are available from Norchem 20 Company under the trademark No. 2910, and from DuPont as under the trade-
mark CXA 3101. In all ins-tances, it is believed -that such ad-
hesives may be categorized as either an anhydride modified poly-
olefin or a partially hydrolyzed ethylene vinyl acetate copoly-
mer.
As suggested above, the ratio of EVOH copolymer to
polyamide film-forming resin in the blends will, of course, have
a very significant effect upon the na-ture of -the film produced.
: Thus, the higher the proportion of EVOH copolymer present in the
composition, the greater will be its oxygen barrier capabilities.
Tensile, tear and impact strength (as well as adhesive
properties) will generally be increased in accordance with the
amount of nylon present, and the cost of the blend will be
reduced commensurately. From the standpoint of oxygen barrier
properties, little improvement in the ability of nylon itself to
serve that function is realized until the concentration of EVOH
copolymer in the composition reaches about 20 percent; therefore,
that represents a practical lower limit upon the amount of the
copolymer to be included. On the other hand, the structural
properties of ethylene vinyl alcohol resin are not substantially
improved unless at least about 10 weight percent (based upon the
total composition) of the film-forming nylon is blended
therewith; hence, that will usually represent a practical lower
limit upon the amount of nylon to be used. However, it should be
appreciated that the incorporation of nylon in virtually any
concentration may be of some benefit, if for no reason other than
as a cost-saving measure.
A surprising aspect of the invention resides in the
fact that as much as 30 weight percent of the plasticized nylon
may be included in the blend without reducing the oxygen barrier
properties of the EVOH resin significantly, and this has
generally been found to hold true regardless of the nature of the
plasticizing agent utilized. More particularly, the
unadulterated EVOH resins will normally transmit oxygen at a rate
less than one cubic centimeter-mil, per square meter of surface
area, during a period of 24 hours under conditions of zero
relative humidity and 73 degrees Fahrenheit. The blends of the
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~CC-21 1 ~191~'~8
1 ¦ invention containing as much as 30 percent of film forming
¦ polyamide are capable of oxygen barrier performance at rates not
3 ¦ in excess of the same value. Perhaps it should be mentioned that
4 ¦ oxygen transmission at the indicated rate is regarded to
¦ characterize an excellent oxygen barrier film, and generally the
6 ¦ apparatus utilized for the determination (e.g., a MoCon oxygen
7 analyæer) will not therefore be designed to measure lower values.
8 ¦ Exemplary of the efficacy of the present invention are the
9 1 following specific Examples:
¦ EXAMPLE ONE
ll ¦ Nylon 6, having a molecular weight of about 25,000 and a
12 melting point temperature of about 430 degre~s Fahrenheit, is
13 ¦ compounded at about 430 degrees to 440 degrees Fahrenheit with
14 l either lauramide or nylon 12 (having a molecular weight of about
¦ 25,000, and a melting point temperature of about 347 degrees
lG l Fahrenheit) to produce preblends containing 95 percent by weight
17 1 of the nylon 6, and 5 percent of the plasticizer. Pellets of the
18 l foregoing preblend.s and of EVOH copolvmer (Kuraray EP-F) are then
1~ ¦ admixed in a ribbon blender, in proportions to provide 25:75;
¦ 50:50 and 25:75 blends of each of the two lngredients (i.e., the
21 ¦ preblend and the EVOH). These are then converted into films by
22 ¦ forcing them through an extruder having a one-inch screw and
~3 ~ fitted with a die head having 14" wide die lips, and onto a
~4 chill roll, from which the Eilms are recovered for testing; the
¦ films are of different thicknesses, varying from about l to 3
26 l mils. Each film is tested for tensile strength and percent
27 1 elongation ~both Instron, at break - ASTM D-882), tear strength
28 l (constant radius - ASTM D 1922) total energy impact strength
. ~ ~ A ~k~
~ 6~
ACC-21
1 (dar~ - ASTM D-20O19~06) and for oxygen transmission (MoCon
2 oxygen analyzer - 24 hours at zero relative humidity and 73
3 degrees Fahrenheit); films of the nylon preblends and of the EVOH
4 copolymer ~re subjected to the same tests, for comparison
purposes.
6 As a result, it is found that in all instances the
7 elongation and tear strength (in both the machine and also the
8 cross machine directions) of the films produced from the blends
9 ¦ of the invention are superior (and in some instances dramatically
so) than those made from the straight EVOH copolymer. Similarly,
11 the machine direction and cross machine direction tensile
12 strengths of the blend films are better (and again, in some cases
13 l~ dramatically so~ than the EVOH films, as are their impact
1~ ¦ strengthsO However, it is to be noted that the film made from
¦ the 75:25 EVOH:nylon blend plasticized with nylon 1~ evidences
16 somewhat diminished tensile ancl impact strength values, from
17 I which it can be hypothesized that, although the polymeric
1~ ¦ plasticizers enable blending and processing with the EVOH
19 ¦ copolymers (thereby offering economic benefits), they do not
¦ necessarily enhance structural properties.
21 ¦ Insofar as oxygen barrier performance is concerned, in all
~2 ¦ instances the blend films exhibit better properties than do the
23 plasticized nylon films, per se, and the results appear to be
24 independent of the particular plasticizer employed. Moreover,
'25 the decrease in oxygen transmission seems to be a non-linear
26 function, in that the improvement in barrier capability occurs at ¦
27 a rate that is disproportionately greater than the increase in
~8 EVOH concentration would predict. Finally, at concentrations of
119~
ACC-21
1 25 percent EVOH the oxygen barrier capability of the blend films
is virtually indistinguishable from that of the unmodified EVOH
3 films, e~idencing a value of less than one cubic centimeter-mil
4 per square meter, under the conditions previously set forth.
EX_MP.LE TWO
6 ¦ Films are produced from blends having the same composition
7 ¦ as those described in connection with Example One above, with the
8 exception that different plasticizing agents are substituted for
9 ¦ the lauramide or nylon 12 materials employed therein.
l Specifically, such b]ends are made using SANTICIZER 8 (N-ethyl-
11 l o,p-toluenesulfonamide), 2,2,4-trimethyl-1,3~pentanediol, nylon
12 l 11 (molecular weight 25,000), nylon 11 (molecular weight 7,000),
13 l nylon 6,36 ~molecular weight 10,000), STYSCLAC AW, and
14 ¦ cumylphenylbenzoate. In all instances, the films exhibit
¦ properties similar to those described above, performance being
1~ ¦ generally in decreasing order of benefit, as listed.
17 ¦ EXAMPLE THREE
18 ¦ Again, films are made as described in Example One, but
1~ l utilizing in place of the EP-F copolymer the EVOH resins sold
~0 I under the designations EP-E, GL-D, and GL-E (each of which is
21 ¦ further identified hereinabove), and a 50:50 mixture of the GL-D
22 ¦ and GL-E resins. In addition, lauramide is utilized at a
23 ¦ concentration of 10 percent in all instances, and nylon 66 is
24 ¦ substituted for the nylon 6 of the foregoing Examp]e. Results
¦ comparable to those indicated therein are realized.
2~ ¦ EXAMPLE ~O~R
27 ~ A preblend of nylon 6 containing 25 percent, based upon the ¦
28 weigh thereof, ~E SANTICIZEI (o,p-toluenesulfonamide) is
,
~cc~ 1L916q~8
1 ¦ compounded and formed into pellets, which are mixed with pellets
2 ~ of EP-F resin to produce a 60:40 EVOH:nylon mixture. The mixture
3 ¦ is heated to a temperature of about 430 degrees Fahrenheit, and
4 the melt is forced through the combining head of an extruder,
into which a quantity of fused PLEXAR 3 (ethylene vinyl acetate
6 ¦ based adhesive) is also introduced for coextrusion with the blend
7 ¦ onto a chill roll. The resultant composite film is recovered and
8 ¦ tested for peel-strength~ and it is found that the level of
9 ¦ adhesion between the layers is appoximately two foot pounds per
inch of width of the strip utilized in the test. This can be
11 contrasted with the results achieved wherein the same PLEXAR is
12 ¦ coextruded under comparable conditions with the same, but
13 ¦ nylon-free, EVOH copolymer, a peel strength of only about one
14 ¦ foot pound per inch being exhibited by the resultant film.
Thus, it can be seen that the present invention provides a
1~ novel blend of a film-forming polyamide resin and an EVOH
17 copolymer, which blend is processable at temperatures below those
18 at which any substantial degradation of the ~VOH copolymer will
19 be encountered, to produce a film having a desirable balance of
oxygen barrier and structural properties. The blend is well
21 suited for coextrusion with a second resin, to produce a
2~ composite film in which adhesion between the layers is at a
23 desirable level. The films can be produced with relative
24 facility and good economy, and the invention also provides novel
~5 processes for producing such films, and novel films produced
27 thereby.
~8
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