CA1276537C - Tinted heat-shrinkable multilayer films comprising vinylidene chloride-vinyl chloride copolymer - Google Patents

Abstract

TINTED HEAT-SHRINKABLE MULTILAYER FILMS
COMPRISING A VINYLIDENE CHLORODE-VINYL
CHLORIDE COPOLYMER
Abstract of the Invention A transparent heat shrinkable, multilayer film comprising:
(a) at least one layer comprising a vinylidene chloride-vinyl chloride copolymer; and (b) at least one layer comprising a thermoplastic polymer; and (c) a sufficient amount of a dioxazine violet pigment to provide a film which retains an aesthetically acceptable violet appearance despite exposure to elevated temperatures and/or irradiation.

Description

æ 7~f3~

TINTED HEAT-SHRlNKABLF MULTILAYER FILMS -~:
COMPRISIN~ A VT~yLIDENE CHLORIDE ~INYL

Field of_the In_ nt~on This inYention relates to tinted, transparen~, hea~shrinkable, multilayer films suitable for use in packa~ing primal and sub-prl~al meat cuts, wherein said film co~prises at least one layer comprising a vinyl~dene chlor~de-vinyl chloride copolymer. Th~s invention also relates to bags produced from said films.
Background of the Invention Films used in meat packaging applicat~ons are generally multilayer ~omposit~ons having at least one layer capable of providing the film with good oxygen barrier properties. Frequently, the barrier layer of khese films comprises a vinylidene chloride - vinyl chlor~de copolymer, commonly ~ signated as polyvinylidene chloride or PYDC.
Although PVDC layers generally prov~de films with relatively low rates of gas transmission~ over a period of time PYDC copolymers tend to degrade, forming de~radation products which include chromophores. The presence of chromophores accounts for the yel 1 ow t~ nt often sbserved i n PYDC-containing films.
A pronounced yel 1 ow ti nt i s general ly unacceptable in films ~sed to package meat products9 part~cularly fresh red ~eat cuts. Films so tin~ed tend to impart a yellow appearance to meat fat which customers frequently associate with undesirable product aging or spoilage.

D-1~,031 ~ ~7 ~ xposure to eleva~ed temperatures and/or irradiation gener~lly accelerates the rate of PVDC
degradation, thereby accelerating the rate of chromophore production and ~ntenslfying the degree of film yellowing. HoweYer, irraldia~ion of PYDC~containing films often improves properties such as the puncture resistance, tens~le strength and toughness thereof. Accordingly~ in the production of PYDC-containing films for ~eat packaging applica~ions, manufacturers must frequently welgh the undesirabillty of film discoloration against the property benefits obtained by irradiation.
Additionally, undesir~ble film yellowing may result from polymeric resins reaching degradation induring temperatures during film extrusion. When th~s occurs it is common practice to stop produc~ion to remove the yellowed res~n from a syste~. Thus, in terms of system shut-down time and raw materi al loss, this type of thermally induced PVDC
degrad~tion can have an economically disadvantageous impact on film production.
Prior to this invention, several a~tempts were made to produce a PVDC-containing fil~ sultable for me~t packaging applica~ions by the incorporation of one or ~ore accep~ahle p~gments into same. That is, only certain film colors are considered aes~hetically ~ccep~able in mea~ packaging with PYDC-containing filrns. These attempts resulted in films where~n discoloration was either ineffectively masked or wherein the pigmented ~llms took on ~n undesirahle ~in~ following irradiation and/or eleva~ed tempera~ure exposure. Masking has been D-1~,031 ~ ~'7~37 found to he particularly difficul~ since throughout the period of film storage the color being masked Is continuously intensifying.
Accordingly, it is an object of this invention to prov;de a transparenl: heat-shrinkable, vinylidene chloride-vinyl chloride copolymer-containin~ film which has an aesthe~ically accep~able appearance for packaging fresh and processed meats. ~t ~ a further ohject of this invention to provide a transparent heat shrinkable, vinylidene chloride-vinyl chloride copolymer-containing film which upon exposure ~o elevated tempera ure and/or irr~d~ation retains an aesthetically acceptable appearanre for meat packaging applicatîon~, preferably, over extended storage periods.
Definitions For purposes of defining this invention the following definitions shall apply:
Hunter Color Scales - L, a and b - The amount of one of three stimuli, each rep~esenting different dimensions sf the Hun~er Opponent-Colors System, which in co~bination define a color for Standard Observer CIE 1931 ~2-).
Hunter a-Yalue - A value on the Hunter red-green chromaticity sc~le which provides a measure of specimen redness when positive and specimen greenness when nega~ive.
~ unter b-Yal ue - A value on the Hunter yellow-blue chromatic~ty scale which provides a measure of specimen yellowness when positive ~nd specimen blueness when nega~ive.

D-15,031 ~.~'7~3~

Hunter L-Yalue - A value on ~he Hunter ~hite-black chro~aticity scale of 0 to 1007 Whereih zero represen~s black and 100 represents whlte, which provides a measure of specimen lightness.
Tristimulus Test - Th~ following test procedure:
A Tristimulus colori~eter manufactured by Hunter Associates Laboratory, Inc. of Reston9 Virginia, designated as Model D25A-9, operating under the Test Conditions hereinafter defined, ls calibrated against a Wh~e Standard having a ~unter a value of -0.9, a Hunter b value of -1~7 and a Hunter L value of 91.31. The calibrated instrument ~s thereafter used to obtain the Hunter a, b and L
~alues of a single ~hickness of a transparen~ film specimen measured against a white tile background, ~herein said white tile barkground has ~un~er a, b and L values of -0.75, ~1.29, and 91.S8 respectively. The procedure is repeated five times at different specimen locations wi~h the values reported being an average of the five measurements obtai ned.
Test Condit~ons: .
A 45 angle of illumination to the speci~en normal; a 0 vi ewi ng angl e ts the normal; a su~tended sour~e aperture angle o~ 75; a subtended receptive aper~ure angle of 11-; an aperture diameter of 2 inches (51 mm~; type DZA low voltage halogen lamp; spectral l~gh~ being excluded from the viewed ligh~; and the spectral response being adjusted for average daylight designated as CIE
Illuminate C.

D-15,031 ~.Z~53 Yisible Yellowing - A eolor within the ~_ .,.
visible li~ht spectrum ch2rscterized by a wavelength range of from about 560 ~o about 590 nanometers.
Summary of ~he Invent~on In one embodiment the instant ~nvention comprlses a transparent heat shrinkable, multllayer film comprising:
(a) at least one layer comprising a vinylidene chloride-vinyl chloride copolymer, (b) at least one layer compri s~ ng a thermoplastic polymer; and ~ c) a suffic~en~ amoun~ of a dioxazine violet pigment to prov~de the film wi~h a violet tint after having heen sub~ected ~o a ~emperature of 120F for a period of 3 days, and preferably for a period of 7 days. As used herein, "violet t~nt"
means a color within the visible light spectrum which is charac~erized by a wavelength range of from about 380 to about 440 nanometers. In a preferred embodiment, ~he violet tint is described by a Hunter L-Value within a range of from about 80 to about 90 a ~unter a-Yalue within a range of from about +Q.25 to about ~6, and a Hunter b-Yalue within a range of from about -0.25 to about -7, as per the Tristimulus Test.
In another embodiment this inven~ion relates ~o a ~ransparent heat shrinkable, multilayer film comprislng:
(a) at leas~ one irradiated layer comprising a Yinylidene chloride-vinyl chloride copolymer;

D-15,031 ~.2~6 (b) a~ least one layer comprising a thermopl~stic polymer; and (c~ ~ sufficient amount of a dioxazine violet pigment to provide ~he f11m wlth a violet tint, wherein said t~nt ~s preferably described by a ~unter L-Value with;n a range of from about 80 ~o about 90, a Hunter a-Value within a range of from about ~0.25 to about ~6, and a Hunter b-Value within a range of from about -0.2S to about ~7 as per the Tristimulus Test.
In a further embodiment this invention comprises a transparent, heat shrinkable mul~ilayer film comprising.
(a) at least one layer comprisSng a vinylidene chloride-vinyl chloride copolymer, said layer(s) being visually perceived as having a yellow tint ~bsent pigmentation thereof;
(b~ at least one layer comprising a thermopl asti o polymer; and (c) a cufficient amount of a dioxazine violet pigment to provide the ~ilm wi~h a Hun~er L-Value within a range of from about 80 to about 90, a ~un~er a-Yalue within a range of from abou~ +0.25 to about ~6, and a Hunter b-Yalue within a range of from about -0.25 l;o about -7 as per the Tri stimul us Tes t .
Brief ~escription of The Drawin~ - Figune 1 is a graphic representation of cotor development in irrad1ated films after various s~orage periods.

D-15,031 ~ J~ ~3 Detailed Descrip~ion of the Invention , It has been found that unlike other pigments knownt.
to the inventors which produce colored films which are acceptable to ~he meat indus~ry, but which are not effective in masking a yellow color~ a d~oxazine violet pigment may be incorporated ~nto a mult~layer film having a vinyl~dene chloride-~inyl chlor~de copolymer-containing layer to effectiYely mask the yellow color of vi nyl i dene chlor~de-vinyl chloride copolymer derived chromophores. Additionally, it has been found tha~ a film p~gmented wfth a dioxazine violet generally retains ~ts violet tint even after exposure to elevated temper~ure and/or ~rradiation, and that a f~lm so p~gmented typically retains a v~olet tint over an extended storage period, often for periods in excess of l year at 70F. This is a remarkable disco~ery in view of the fact that the yel 1 ow col or of the PVDC layer continues to intensify as the film ages. Films having tints described by Hunter-Values within the previously defined ranges are found to be particularly well su~ted ~or meat packaging applications.
In contrast, b~sed on our present knowledge we believe that multilayer films con~aining other violet pigments which are not dioxazine compounds will not re~ain the vjolet tint after exposure to radiation and/or elevated ~emperatures. For example, Viole~ l9 (color Index No. 46500) is a quinacridone chemical class compound which will cause an irradia~ed PVDC-con~ain1ng multilayer film to acquire ~n orange red cast, ~h~ch is an unacceptable color for the packaging of primal and D-15,031 ~ 2 7653~7 subprimal meat cuts.
. The violet pigments suitable for USQ here~n are included among the class of dioxazine compounds more particularly described in U.S. Pa~ent ~os.
2tO16,013; 2,02~,09~; 2,082,344; 2,115,508;

2,244,294; 2,91R,465; 2,95/lD37E3; ~,oog,913;

3,065,229; 3,130,195; and 3,3107~56. Included among such p;gments are compounds oF the formula:

R~R Formula I

herein X is selected from the group consisting of hydroaen, halogen radicals, alkyl radicals and aryl radicals, and R is a substituted or unsubstituted aroma~ic or heterocyclic radi . al bound by two adjacent c~rbon al:oms.
Among the above descri bed Formula I
compounds are compositions wherein X is selected frcm the group consisting of hydrogen, chlorine and bromine, and 2 is selected from the group consisting of phenyl, naphthyl 9 anthryl~ phenanthryl, carbazolyl, tibenzofuryl, dibenzothienyl, fluoryl, and xanthyl radicals.
It is well accepted in the art that pigments ident~fied as having the structure previously defined by Formula I will exhibit D - 1 5 , 0 31 7~37 variations in color depending upon the precise chemi cal i denti ~y thereof . Those pi gments of ~:
i nterest herein are violet dioxazines which when used in sufficien~ quanti~y impart a viol t tint to PYDC-contai ni ng filmsO
Carbazole dioxazine violets of the formula:

~$~D Fcrmula 11 R' t:l wherein R' is selected from the group consisting of hydrogen, alkyl radicals and benzyl radicals, are found to be particularly well suited to the practice of this invention, with c~rbazole dioxazines of the formula:

Cl C2H5 Formula III
b~o~
~ 2H5 rl being especially desirable.

D - 1 5 , 03 1 ~1.2~i3~

10 ~

Carbazole dioxazlne violets may be prepared by a ~wo-step reac~ion, wherein an amino ethyl carbazole is first condensed with chlor7nal in ~
high-boiling solvent and the resulting conden~ation product is thereafter reacted ~ith d ring closing agent (e.gO benzene sulfonyl) to produce a crude product which may be subjected to one or more refining processes to produce a pigment of desired purity. Various methods for produc~ng c~rbazole dioxazine violet pigments are described ~n U.S.
Patent ~os. 2,857,400 and ~,022,299.
The heat shr~nkable multilayer films of the presen~ invention are charac~erized as having at least one layer compri 5i ng a vinylidene chloride-vinyl chloride copolymer. Yinyl1dene chl ori de-vinyl chloride copolymers suitable for use here~n typically contain a minimum of about 65 weight percent vinylidene chloride9 and preferably contain from about 70 to about 95 weight percent of vinylidene chloride, based on the weigh~ of the copolymer. At vinylidene chloride concentrations less than 65~ by weight, vinylidene chloride-vinyl chloride copolym~rs generally exhibit unsatisfactory oxygen barrier properties, whereas, at concen~rations in excess of 95~ the copoly~er is generally not extrudable. The remainder of the copolymer is preferably vinyl chlor~de, but it ~ay include acrylonitrile, an acryla~e ester such as methyl methacrylate, and ~he like. In order to aid in extrus10n, the copolymer may fur~her co~prlse a plastic~2er in an amoun~ not ~n excess of 5 weight percent, but preferably less than 4 weight percent, D-15,031 3~

based on the weight of ~he copolymer. Plastic~zers suttable for use herein include compositions such as dibutyl sebacate and epox~dized soybean oil.
The fllms of this invention have one or more additional thermoplastic layers comprising film grade polymers which ~nclude ethylene-vinyl ~ce~ate copolymers; polyethylene; polypropylene;
polybutylene; linear and/or branched copolymers of ethylene and C3 to C18 alpha-olefins; ionomers;
and mixtures thereof. The combination of layer structure and components should be selected ~n such a manner so as to provide a transparent heat shrinkable film suitable for meat packaging applications.
In one embodiment, the film of this invention has at least two layers, one of said layers comprising a vinylidiene chloride-vinyl chloride copolymer and another of said layers comprislng a thermoplast~c polymer such as, ~or example, an ethylene vinyl acetate copolymer. ~ilnls comprising a firs~ outer 7ayer comprising a thermopldstic polymer, for example an ethylene-vinyl acetate copolymer; a core layer comprising a vinylidPne chloride^vinyl chloride copolymer; and a second outer layer comprising a thermoplastic polymer, for example an ethylene-vinyl acetate copolymer~ are also suitable for use herein.
I n a pre~erred embodi ment, the ethylene-vinyl acetate copolymers of this invention include compositions selected from the group consi sti ng of ~ a ) an ethyl ene-vinyl acetate copolymer having a melt index of from about 0.1 to D - 1 5 , 03 1 ~1.2~S3~

about 1.0 decigram per minute and a vinyl acetate content of from about 9 to about 18 weight percent, and preferably from ~bout 10 to about 15 weight Dercent, based on the weight of s~aid ethylene-vinyl acetate copolymer, and (b) a blend of t~o ethylene-vinyl acetate copolymers, wherein one of said ethylene-~inyl acetate copolymers has a melt index of from about 0.1 to about 1.0 dec~gram per minu~e and a vinyl aceta~e content of from abou~ 10 to about lB weight percent, based on the weight of said copolymer, and the other e~hylene-vinyl acetate copolymer has a melt ~ndex of from about 0.1 ~o about 1.0 dec~gram per minute and a vinyl ace~a~e content of from about 2 to about 10 weight percent,.
based on the weight of said copolymer, where~n said blend has a total vinyl acetate content of from about 9 to about 18 weight percen~, and preferably from about 10 to about lS weight percent, based on the combined weight of sald ethylene-vinyl acetate copolymers.
The films of this inYention generally have thicknesses ranging from about 1~75 to about 3.0 mils, with film thickness depend~ng in part upon the particular layer structure. At thicknesses in excess of 3.0 mils, clipping problems may be encountered ~n bags produced therefrom, whereas at thicknesses less ~han 1.75 mils, the film may have undesirably low puncture resistance. Typically, the PVDC layers of the su~ject fll~s haYe thicknesses ranging from about 0.25 to about 0.45 mil.
The tinted fll~s of ~his invention ~ay be produced by the ~ncorporation of dioxazine v~slet D-15jO31 ~ Z'7~i~3~7 _ 13 -pig~ent into one or more film l~yers. For ease and ~onveni ence in film manufa~turing, ~t is generallyr preferred that the pigment be used in the form of a resi n concentrate. Resln concentrates may be prepared using any su~able m~thod for dispersing solid materials in polymers, for lexample by extrusion or milling. In general, polymers sui~able for use in resin concentrates are those polymers which are compatible with the fil~ layer into which the pigment ~s introduced. By compat~ble it is meant that the polymer is at least dispersible in the film layer into which it is incorporated. In general, a resin coneentrate may cont~in p~gment in an amount of up to about 1 percPnt by weight, based on the total weight of the pigment and res~n components thereof, and typically contains pigment ln an amount of from about 0.5 to about 1 percent by weight, based on the total weight of ~he pigment and resin components thereof.
Pigment may he incorporated into a film by combining a resin concentrate with the feed ma~erial of one or more Film layers by any sui~able mixing method. The amount of resin concentrate incorpora~ed into a given film layer is variable and depends upon factors which include the number of layers into wh1ch p~gment ~ill be inc~rporated, the polyvinylid~ne chloride content of the film, 2nd the degree of thermal and/or radiation exposure s~id polyv~nylidene chloride is subjec~ed to. ~esirably, a film should contain sufficient ~igment to provide a film wh~ch, despite exposure of a PYDC layer thereof to rad~ation levels in excess of about D-15,031 ~.~ 76~ ~3 ~

megarad, and more particularly to dosage levels between about 3 and about 5 megarads, reta1ns an t aes~hetically acceptable violet tint, preferably for storage periods in excess of 200 days a~
temperatures of about 70F and mos~ preferably for storage periods in excess of 300 days at tempera~ures of about 70~F.
Preferably~ PYDD containing multilayer films sui~able for use in meat packaging applica~ions are produced by the incorporation therein of dioxazine Yiolet pigment ~n an amount of from about 0.01 to about 0.04 percent by weight, based on the total weight of the vinylidene chloride-vinyl chlsr~de copolymer present In same.
At pigment concentrations less than about 0.01 percent by weight, based on the we~ght of the vinylidene chlorlde-vinyl chloride copolymer, film yellowing may be inadequately masked, whereas, at plgment concentrations in excess cf about 0.04 percent by weight, based on the ~eight sf the vi nyl i dene chloride-vinyl chloride copolymer, the violet tint imparted ~o a film ~ay be so ~ntense as to alter the natural color of mea~ products packaged therein.
Following incorpora~ion of pigment into the feed material of one or more layers, said feed material ~ay he extruded by known techniques to produce a tubular or flat multilayer extrudate which is thereafter biaxlally stretched ~o produce a hea~
shrinkable f~lm. For exampl e, feed material forming the various film layers may be co-extruded through a cireular die to produce a ~ultil ayer prlmary tube D-15,031 ~'7~37 which ~s thereaf~er biaxially stretched by means of the "double bubble" technique disclosed in U.S.
Patent No. 3,5S5,604 to Pahlke. Alternatively, the feed material forming the various f;lm layers ~ay be slot cast to produce a multilayer film which is thereafter biaxially stretched by tentering techniques. Followinq.biaxial stretching, the mul ti 1 ayer f I 1 m may be irradiated to a des~red dosage level such as by passing same through an electron beam i rradi ati on unit.
In another aspect of this ~nYention, bags suitable for the shrink packaging of primal and sub-primal meat cuts are prov~ded from the afore-descr~bed multilayer films. The bags may be produced from the multilayer films of this inYention by heat sealing. For instance, if the films of ~his invention are produced ~n the form of tubul~r fil~, bags can be produced therefrom by heat sealing one end of a length of ~he tubular f~lm or by sealing both ends of the tube and then slitting one edge to form the bag mouth. If the films of this invention are made in the form of flat sheets, bags can be formed ~herefrom by heat sealing ~hree edges of two superimposed sheets of film. When carrying out the heat sealing opera~ion, the surfaces which are heat sealed to each other ~o form seams are the said firs~ outer layers of the films of the invention.
Thus, for exampl e 9 when forming a bag by heat sealing one edge of a length of tubular film, the inner surface of the tube, i.e. 9 the surface which will be heat sealed to i~self, will be ~he said first outer layer of the f~lm.

D-15,031 ~6~3~J~' 6 ~

The fol 1 owi ng exampl es are i ntended to illus~rate, but ln no way limit the present t in~ention.
Example_I
Biaxially stretched three-layer films were prepared by a "double bubble" process similar ~o ~ha~ disclosed in U.3~ Patent No. 3,4~,044, by co-extruding the poly~eric materials fcrming the various film layers through a mult.ilayer die to produce a primary tube which was l:hereaf~er biaxially stretched to produce a heat shrinkable film. The stretched f~lms ~ere thereafter irradiated ~o a dosage level of about 3 megarads, wound i nto webs, and ma~ ntai ned at a tempera~ure of 1 20F to simul ate storage periods of up to about 250 days a~ 70F. At ~ar~ous time ~ntervals the films were compared to a set of color standards and given a nu~erical rating. Film colors were ra~ed on a scale of 1 to 3 wherein 1 represented a slight yellow tint, 2 represented a moderate yellow tint and 3 represented a relatively dark yellow tint which was deemed unaccept~ble for meat packaging applications, The change in film color over time is graphically illus~rated in Figure 1 wherein ~he color data ~or ~lms 1 ~ 2 ~ha~e bee~ combined.
The film designated herein as film 1 had an inner layer of ethylene-vi~yl acetate copolymer having a melt index of about 0.25 decigram per minu~e and a vinyl aoetate content of about 12 percent by weight, based on the weight of the copolymer; a core layer of vinylidene chloride-~inyl ~.~t~S3~-~J

chloride copolymer containing about 85 weight percent vinylidene chloride and abou~ 15 weigh~ ~:
percent vinyl chloride, based on the we~ght vf the copolymer; and an outer layer comprising a blend of ~a) about 75 weight percent ~f ethylene-v~nyl acetate eopolymer having a vinyl acetate conten~ of about 12 weight percent, based on the weight of the copolymer and a melt ~ndex of about 0.35 decigram per minute, and (b) about 25 weight percent of ethylene-vinyl acetate copolymer having a vinyl acetate content of about 4.5 weight percent, based on the weight of the copolymer and a melt index of about 0.25 decigram per minute. F~lm 1 had a total thickness of 2.4 mils.
The film designated here~n as film 2 had the same composition as film 1, except that the ou~er layer comprised an ethylene-vinyl acetate copolymer having a vinyl acetate eontent of about 15 wei ght percent, based on the wei ght of the copolymer and a mel t i ndex of about 0. 5 decigram per minute, Film 2 had a total thickness of 2.4 mil s.
~.
Biaxially oriented three-layer films having the compositions descrlbed in T~ble I were prepared by the "double-bubble" process disclosed in U.S.
Patent No. 3,456,044. In producing the fil~s, ~he polymeric materials forming the various film layers were firs~ co-extruded through a mul~ilayer die to produce a primary tube; the primary tube was thereafter bi~xially stretched to produce a secondary tube which was then irradia~ed ~o a dosage D-15,a31 level of about 3 megarads. Follow~ng ~rradiation, the films desi~nated as film nos. 3 and 4 were wound into webs and malnta~ned at a temperature of 1209F
for a period o~ four days to simulate a storage period of 100 to 120 days at 70F; the films designated as film nos. S t~ 8 were wound into webs and maintained at a temperature of 120~F for a period of three days to simulate a s.torage period of 75 to 90 days at 70F.
As used in Table I, the following designations are as herein defined:
Red concentrate - A resin concentrate available ~rom Amerchem, Inc~ under the product designation "Red 3083~E4".
Blue concentrate - ~ resin conrentra~e available from Americhem, Inc. under the product designation "Blue 7176-El".
Red-Blue concentrate - a resin concentrate containing three parts by welght of blue to one p~rt by weight of red, o~ the previously described red and blue concentrates.
Following irradi~tion, ~he fil~ designated as film 3 had a yellow t;nt which wa. ~ntenslfled by accelerated aging. Film ~o. 25 had a blue color which turned ~o green upon irradiation and, since the green color was unaccept~ble, no aceelerated aging at 120F was undertaken. Films No. 26 and 27 both had a dark reddi sh brown ti nt upon manufacture and, because this color was unaccep~able to begin with, no irradiation was undertaken since the i rradi ation would only create a darker unacceptable color. Followin~ irradiation, films 4 D-15,031 s3~.

~hrough 8 al 1 had an undesirabl e greeni sh gray cast which was intensified by accelerated aging. None ~f the pi gment combi nati ons of Exarnpl e I I were successful in masking the film yellowing which took pl ace duri ng i rradi ati on and accel erated ag~ ng .

D-l 5 ,031 . " ' ' '' `` , 7~

TABLE I
~ayer Composit~onl_ _ Film Firs~ Core 3 Second 4 Mo.Outer Layer~ ~3~ Outer La~er EYA PYDC 99.9% EVA
0.1~ ~lue concentrate 26 EVA PVDC 99.75~ EVA
0.2~X Red concentrate 27 EVA PVDC 99.5X EYA
0.5~ Red concentrate 3.7~ Blue concentrate 1.25~ Red concentrate EYA PYDC 91.5~ E~A
3.5~ Blue concentrate 5.0~ Red concentrate 3.0~ Blue concentrate 6.0X Red concentrate 7 EVA PVDC 94.0~ EVA
4.0~ Red concentrate 2.0~ Red-Blue concentrate 8 YA PYDO 92.0g EYA
4.0~ Red concentrate 4.0g Red-Blue cDncentrate ~1) The films produced ~n accordance w~th Example II had a total th~ckness of 2040 mil s; with the first ou~er layer haYing a ~h~ckness of 1 42 mils, the core layer having a thickness of 0.34 mil D and the second outer layer having a thickness of 0.64 mil.
(2 ) The EVA copolymer used to produce the first outer 1 ayer of Example II films had a vinyl acetate content of 11 percent by weight, based on the total weight of the copolymer, and a mel~ index of 0.25.

D~15,031 (3) The PVD~ copolymer u~ed to produce the core layer of Example II films had a vinyl chloride conten~-of 15 percent by weight, based on the total we1ght of the copolymer.
(4) The EVA copolymer used to produce the second outer layer of Example II films ha~ a vinyl acetate content of 10.5 percent by weight, based on ~he ~otal weight of the copolymer, and a mel~ index of 0.35.

Example III
Multilayer films were made in accordance with the procedure of Example II, except that following ~rradiation the films were maintained at a temperature of 120F ~or a period of one week to simulate an aging per~od of 175 to 210 days at 70~F. The composition of the various films tested is provided in Table II along with a description of film color following irradiation and accelerated aging. The colors designated as rose violet, d~ep rose v~oletJ pale violet, medium viole~, and deep violet were all deemed aesthetically acceptable for meat packaging applications. That is, samples containing at least 2.5 wt.~ Yiolet 23 concentrate in the second outer layer of EYA effectively masked the yellow color of ~he irradiated PYDC-containing films, while samples containing 2.0 wt.~ Violet 23 ~oncentrate in this layer did no~ provide acceptable masking of the yellow color. It ~s to be noted that 2.5 wt.~ of Violet 23 concen~ra~e in the second outer layer of EYA corresponds to the preferred lower limit of plyment which was defined hereinabove as being 0.01 percent by weight of Violet 23 pigmen~
in the multilayer film, based upon the total wei~h~
of PYDC copolymer contained ln the film.

D-15,031 .

~7~

- 2~ -Yiolet 23 concentrate9 as desi~nated in Table II, is a resin concentrate contain~ng 0.5 percent by wei3ht, based on the total weight of the EYA and pigment components thereo~F, of a carbazole dioxazine pigment ~dentified as Violet 23, available from American Hoechst under the produc~ designa~on HOSTAPERM Violet RL Special 74-4007, and 99.5 percent by weight based on the total weight of the EYA and pigment components thereof, of an EVA
copolymer.
The EYA and PYDC resins used to form the i`irst outer layers, second outer layers and core layers of the f~lms of thls Example are as described in Exampl e I 1.
The data presented ~n T~ble II shows that, when used in sufficient concentration, the pigment designated as Violet 23 provided an ~rradiated PVDC-containing film with an aesthetically acceptable tint over an extended period of time.

D-15,031 ;3~

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~7 EXAI~PLE IY
....
Bi axi al ly ori ented pl gmented and unpigmented ~hree layer ~lms having first outer layers comprising an ethyl ene vi nyl ace~ate ccpolymer having a v~nyl ~cetate content of 11 wei ght percent, based on the weight of the copolymer, and a melt index of 0.25 decigrams per m7nute; core layers comprising a vinyl~diene chloride-vinyl chloride copoly~er having a vinyl chlor~de content of 16 weight percent, based on the weight of the copolymer; and second outer layers comprising a blend of ~a~ 75 weight percent ethylene vinyl acetate copolymer havirg a v~nyl acetate content of 12 weight percent,based on the weight of the copolymer7 and a melt index of 0.35 decigra~s per minute and (b) 25 weight percent e~hylene vinyl aeet~te copolymer hav~ng a v~nyl ~cetate content ~f 4 wei ght percent, based on the weight of the copolymer, and a melt index of 0.25 declgrams per minu~e, were prepared by the "double-l)ubble" process di scl osed i n U . S. Paten~ No. 3 ,456 ,Q44 . The fi 1 ms are more parti çul arly described ~n Table III.
Violet 23 concentrate referred to ~n Table III ~s as defined ln Exa~ple III.
The fi lms were produeed by co-extrudi ng the polymeric ma~er~als forming the var~ous film layers through a multilayer die ~o produce a primary tube which was then biaxially stre~ched to produce an oriented film. Therea~ter, a f~rst group of films was maintained a~ a temperature of 120~F for a period of 3 days withou~ ~ur~her ~reatment. A
second group of f~lms was ~rradiated to a dosage D-15,031 ~7~i3~J
; 2~ -level of 3 megarads following orien~ati~n and was thereafter maintained at a ~emperature o~ l~O-F fo~r a period of 3 days.
. Hunter a, b and L-Yalues obtained as per the Tristimulus Test herein defined, as well as color data for each group of films, are reported in Table IY~ The data presented in Table IV shows that following accelerated aging, both irradiated and non-irradiated films pigmented with Violet 23 retained an ae~thetically acceptable violet tint.
The data also shows that a given quantity of Yiolet 23 effectively masks PVDC degradation regardless of whether it is ~ncorporated ~nto one or more film layers.

TABLE III

Film Co~positionstl) Fil~
~lo Outer Layer 1 Core Laver Outer Layer 2 21 EVA (1.45) PVDC ~0.30) 97.0% EVA (0.65) 3.0X Violet 23 concentrate 22 EYA (1.85) PVDC (0.35) 97.0P EVA ~0.80 3.0~ Viole~ 23 concentrate 23 EVA (1.45) 96.2X PVDC ~0.30) EYA (0.65) 3.8~ Yiolet 23 concentrate 24 g9.3X EYA 11.45) 99.0~ PVDC (0.30) 99.3~ EVA (0.65) 0.7~ Yiolet 23 l.OX Violet 23 0.7~ Violet 23 concentra~e concentrate concentra~e (1) Layer thicknesses, in units of mils appear ~n parenthesis following layer designaticns.
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Claims (14)

1. A transparent, heat shrinkable multilayer film comprising:
(a) at least one layer comprising a vinylidene chloride-vinyl chloride copolymer;
(b) at least one layer comprising a thermoplastic polymer; and (c) a sufficient amount of a dioxazine violet pigment to provide the film with a violet tint after said film is maintained at a temperature of 120°F for a period of 3 days.

2. A transparent, heat shrinkable multilayer film in accordance with claim 1 wherein said vinylidene chloride-vinyl chloride copolymer layer has been irradiated to a dosage level of at least about one megarad.

3. A transparent, heat shrinkable multi-layer film comprising:
(a) at least one layer comprising a vinylidene chloride-vinyl chloride copolymer said layer being visually perceived as yellow absent pigmentation thereof;
(b) at least one layer comprising a thermoplastic polymer; and (c) a sufficient amount of a dioxazine violet pigment to provide the film with a Hunter L-Value within a range of from about 80 to about 90, a Hunter a-Value within a range of from about +0.25 to about +6, and a Hunter b-Value within a range of from about -0.25 to about -7, as per the Tristimulus Test.
D-15,031

4. A transparent, heat shrinkable multilayer film comprising:
(a) at least one irradiated layer comprising a vinylidene chloride-vinyl chloride copolymer; and (b) at least one layer comprising a thermoplastic polymer; and (c) sufficient amount of a dioxazine violet pigment to provide the film with a Hunter L-Value in a range of from about 80 to about 90, a Hunter a-Value in a range of from about +0.25 to about +6, and a Hunter b-Value in a range of from about -0.25 to about -7, as per the Tristimulus Test.

5. A transparent, heat shrinkable multilayer film in accordance with claims 1, 3 or 4 wherein said dioxazine violet pigment is a carbazole dioxazine violet of the formula

6. A transparent, heat shrinkable multilayer film in accordance with claims 3 or 4 wherein said vinylidene chloride-vinyl chloride copolymer layer has been irradiated to a dosage level between about 3 megardas and about 5 megarads.

7. A transparent, heat shrinkable multilayer film in accordance with claim 1 wherein said pigment is present in said film an amount of from about 0.01 to about 0.04 percent by weight based on the total weight of vinylidene chloride-vinyl chloride copolymer present therein.

8. A transparent, heat shrinkable multilayer film in accordance with claims 1, 3 or 4 wherein said vinylidene chloride-vinyl chloride copolymer has a vinylidene chloride content of from about 70 to about 95 weight percent, based on the weight of the copolymer.

9. A transparent, heat shrinkable multilayer film in accordance with claims 1, 3 or 4 wherein said thermoplastic polymer comprises an ethylene-vinyl, acetate copolymer.

10. A transparent, heat shrinkable multilayer film in accordance with claim 1 wherein said violet tint is described by a Hunter L-Value within a range of from about 80 to about 90, a Hunter a-Value within a range of from about +0.25 to about +6, and a Hunter b-Value within a range of from about -0.25 to about -7, as per the Tristimulus Test.

11. A transparent, heat shrinkable multilayer film which comprises:
(a) a layer comprising a vinylidene chloride-vinyl chloride copolymer irradiate to a dosage level of at least about 1 megarad;

(b) at least one layer comprising a thermoplastic polymer; and (c) from about 0.01 to about 0.04 percent by weight, based on the total weight of the vinylidene chloride-vinyl chloride copolymer, of a carbazole dioxazine pigment.

12. A transparent, heat shrinkable multilayer film in accordance with claim therein the carbazole dioxazine pigment is of the formula:

and the vinylidene chloride-vinyl chloride copolymer layer has been irradiated to a dosage level between about a megarads and about 5 megarads.

13. A transparent, heat shrinkable multilayer film in accordance with claim 4 wherein said film retains a Hunter L-Value within a range of from about 80 to about 90, a Hunter a-Value within a range of from about +0.25 to about +6, and a Hunter b-Value within a range of from about -0.25 to about -7 after being maintained at a temperature of 120°F
for a period of 3 days.

14. A bag for use in meat packaging applications formed from the film of claims 1, 4 or 11.