CA2417184C - Moisture barrier film - Google Patents
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Abstract
A multiple layer film useful in moisture barrier packaging applications has at least one layer comprising a blend of propylene polymer or copolymer, and a hydrocarbon resin; and two additional layers comprising a propylene polymer or copolymer, ethylene alpha olefin copolymer, ionomer, polybutene, or blends thereof. A core layer of ethylene vinyl alcohol copolymer or other oxygen barrier material, or high density polyethylene, can be included in some embodiments. A
preferred embodiment of the multi-layer film exhibits excellent moisture barrier and optical properties, and shrink properties as well if the film has been oriented. High oxygen barrier is also a feature in embodiments including EVOH or other oxygen barrier materials.
preferred embodiment of the multi-layer film exhibits excellent moisture barrier and optical properties, and shrink properties as well if the film has been oriented. High oxygen barrier is also a feature in embodiments including EVOH or other oxygen barrier materials.
Description
MOISTURE BARRIER FILM
This application is a divisional application of copending application 2,106,258,. filed September 15, 1993.
FIELD OF THE INVENTION
This invention relates to thermoplastic films for packaging; and more particularly, this invention relates to a mufti-layer film having high moisture barrier characteristics.
BACKGROUND OF THE INVENTION
Thermoplastic film, and in particular polyolefin materials, have been used for some time in connection with packaging of various articles including food products which require protection from the environment, an attractive appearance, and resistance to abuse during tee~ storage and distribution cycle. Suitable optical properties are also desirable in order to provide far inspection of the packaged product after packaging, in the distribution chain, and ultimately at point of sale. Optical properties such as high gloss, high clarity, and low haze characteristics contribute to an aesthetically attractive packaging material and packaged product to enhance the consumer appeal of the product.
Various polymeric materials have been used to provide lower moisture permeability in order to reduce the transmission of moisture through the packaging film and thereby extend the shelf life of products such as food, medical, electronic, and other items which are sensitive to moisture gain or loss. For some products, maintenance of a high moisture content is desirable, and the film ideally minimizes loss of moisture from the package to the environment. For other products, maintenance of a low moisture content is desirable, and the film ideally minimizes gain of moisture from the environment through the packaging material.
It is also often desirable to include in a packaging film a shrink feature, i.e. the propensity of the film upon exposure to heat to shrink or, if restrained, create shrink tension within the packaging film. This property is imparted to the film by orientation of the film during its manufacture. Typically, the manufactured film is heated to its orientation temperature and stretched in either a longitudinal (machine) or transverse direction (i.e. monoaxial orientation), or both directions (i.e.
biaxial orientation), in varying degrees to impart a certain degree of shrinkability in the film upon subsequent heating.
When biaxial orientation is done, it ca.n be simultaneous or sequential; that is, the orientation can be done in each of the directions in turn, or else both the longitudinal and transverse orientation can be done at the same time. Any suitable technique, such as blown bubble or tenterframing, can be used to achieve orientation of the film. After being so stretched, the film is rapidly cooled to provide this latent shrinkability to the resulting film. One advantage of shrinkable film is the tight, smooth appearance of the wrapped product that results, providing an aesthetic package as well as protecting the packaged product from environmental abuse. Various food and non-food items may be and have been packaged in shrinkable films.
It is sometimes also desirable to orient a packaging film and thereafter heat set the film by bringing the film to a temperature near its orientation temperature.
This produces a film with substantially less shrinkability, while retaining much of the advantages of orientation, including improved tensile strength, modulus and optical properties.
Of interest are U.S. Patent Nos. 4,921,749 (Bossaert et al); 5,085,943 (Crighton et al); 5,091,237 (Schloegel et al); 5,128,183 (Buzio); and 5,212,009 (Peiffer et al) disclosing the use of hydrocarbon resins.
SUMMARY OF THE INVENTION
The present invention provides a thermoplastic multilayer film characterized by good moisture barrier properties. Further, the present invention provides a thermoplastic multilayer film having an aesthetic appearance with good clarity, and other desirable optical properties.
The present invention also provides a thin thermoplastic multilayer film having toughness and abrasion resistance.
The present invention also provides a thermoplastic multilayer film which may be totally coextruded, oriented, and have good moisture barrier and, in some cases, both moisture barrier and oxygen barrier properties.
The present invention relates to a thermoplastic mufti-layer film comprising a core layer comprising a blend of propylene polymer or copolymer, or ethylene alpha olefin copolymer, and a hydrocarbon resin; and two outer layers comprising a propylene polymer or copolymer, ethylene alpha olefin copolymer, polybutene, or blends thereof.
In another aspect, the present invention relates to a thermoplastic mufti-layer film comprising a core layer comprising a blend of propylene polymer or copolymer, and a hydrocarbon resin; two intermediate layers, on opposite surfaces of the core layer, comprising propylene polymer or copolymer, or a polymeric adhesive; and two outer layers comprising a propylene polymer or copolymer, ethylene alpha olefin copolymer, ionomer, polybutene, or blends thereof.
The present invention also relates to a thermoplastic multi-layer film comprising a core layer comprising an ethylene alpha olefin copolymer, ethylene propylene copolymer, rubber modified ethylene 3a propylene copolymer, or ethyene propylene butene terpolymer; two intermediate layers, on opposite surfaces of the core layer, comprising a blend'of propylene polymer or copolymer, and a hydrocarbon resin; and two outer layers comprising a propylene polymer or copolymer, ethylene alpha olefin copolymer, ianomer, polybutene, or blends thereof.
A film with oxygen barrier as well as moisture barrier properties comprises a core layer comprising an oxygen barrier material; two intermediate layers, on opposite surfaces of the core layer,. comprising a polymeric adhesive; two outer layers comprising a blend of propylene polymer or copolymer, or polybutene, and a hydrocarbon resin; and a polymeric sealant layer adhered to at least one of the outer layers.
An alternative film with at least seven layers comprises a core layer comprising high density polyethylene; two intermediate layers, on opposite surfaces of the core layer, comprising a polymeric adhesive, ethylene vinyl acetate copolymer, or ethylene alpha olefin copolymer;
two outer layers comprising a blend of propylene polymer or copolymer, and a hydrocarbon resin; and two outermost layers comprising propylene polymer or copolymer, polybutene, or blends thereof.
Another alternative is a film comprising a core layer comprising an oxygen barrier material; two intermediate layers, on apposite surfaces of the core layer, comprising polyamide; two tie layers, each disposed on a respective polyamide layer, comprising a polymeric adhesive, ethylene alpha olefin copolymer, or ethylene vinyl acetate copolymer;
two moisture barrier layers, adhered to respective adhesive layers, comprising a blend of propylene polymer or copolymer, and a hydrocarbon resin; and two outermost. layers comprising a propylene polymer, propylene copolymer, ethylene alpha olefin copolymer, or polybutene.
In another aspect of the invention, a method of making a thermoplastic multilayer film comprises the steps of coextruding an interior layer of a blend of propylene polymer or copolymer, and a hydrocarbon resin, and two outer layers comprising a propylene polymer or copolymer, ethylene alpha olefin copolymer, polybutene, or blends 7/930727.1 TXTt~Q 4 thereof; cooling the coextruded multi-layer film; and collapsing the cooled film.
In one aspect, the invention of the parent application provides a thermoplastic mufti-layer film, comprising: (a) a core layer comprising a blend of propylene polymer or copolymer, and a hydrocarbon resin; and (b) two outer layers comprising a polymeric material selected from the group consisting of: i) ethylene alpha olefin copolymer, ii) polybutene, and iii) blends thereof.
In a further aspect, the invention of the parent application provides a thermoplastic mufti-layer film comprising: (a) a core layer comprising a blend of propylene polymer or copolymer, and a hydrocarbon resin; (b) two intermediate layers, on opposite surfaces of the core layer, comprising propylene polyrrler or copolymer, or polymeric adhesive; and (c) two outer layers comprising a polymeric material selected from the group consisting of: i) ethylene alpha olefin copolymer, ii) ionomer, iii) polybutene, and iv) blends thereof.
2~ In one aspect, the invention i.n this divisional application provides a thermoplastic heat shrinkable, multi-layer film, comprising: (a) a core layer comprising a material selected from the group consisting of: i) ethylene alpha olefin copolymer, ii) ethylene propylene copolymer, iii) rubber modified EPC, and iv) ethylene propylene butene terpolymer; (b) two intermediate layers, on opposite surfaces of the core layer, comprising a. blend of propylene polymer or copolymer, and a hydrocarbon resin; and (c) two outer layers comprising a polymeric material selected from the group consisting of: i) propylene polymer, ii) propylene copolymer, iii) ethylene alpha olefin copolymer, iv) ionomer, v) polybutene, and vi) blends thereof; wherein the film exhibits a free shrink, at 240°F, of at least 10% in the longitudinal direction, and at least 15o in the transverse direction.
In a further aspect, the invention in this divisional application provides a thermoplastic mufti-layer film, comprising: (a) a core layer comprising high density polyethylene; (b) two intermediate layers, on opposite surfaces of the core layer, comprising a polymeric material selected from the group consisting of: i) polymeric adhesive; ii) ethylene vinyl acetate copolymer; and iii) ethylene alpha olefin copolymer; (<:) two outer layers comprising a blend of propylene polymer or copolymer, and a hydrocarbon resin; and (d) two outermost layers comprising propylene polymer or copolymer, polybutene, or blends thereof .
DEFINITIONS
"Hydrocarbon resin" (''HC" herein) and the like as used herein means resins made by the polymerization of monomers composed of carbon and hydrogen only.
Thermoplastic resins of low molecular weight made from relatively impure monomers derived from coal-tar fractions, petroleum distillates, etc. are also included. A discussion of HC resins can be found e.g. in U.S. Patent Nos. 4,921,749 (Bossaert et al); 5,091,237 (Schloegel et al); and 5,128,183 (Buzio) .
"Ethylene alpha olefin copolymer" (EAO) is used here to include such materials as linear low density polyethylene (LLDPE); very low and ultra low density polyethylene (VLDPE and ULDPE); and metallocene catalyzed polymers such as those supplied by Exxon. Tafmer (tm) 5a ' 64536-829D
materials supplied by Mitsui are also included. These materials generally include copolymers of ethylene with one or more comonomers selected from C4 to C1o alpha olefins such as butene-l, hexene-l, octene-1, etc. in which the molecules of the copolymers comprise long chains with relatively few side chain branches or cross-linked structures. This molecular structure is to be contrasted with conventional low or medium density polyethylenes which are more highly branched than their respective counterparts. '°LLDPE" as defined here has a density in the range of from about 0.916 grams per cubic centimeter to about 0.940 grams per cubic centimeter. Generally, "EAO" as used here includes both homogeneous and heterogeneous polymers.
"Intermediate layer" and the like is used herein to define a layer in a multi-layer film enclosed on both sides by other layers, i.e. disposed between other layers of the film.
The term "oriented" and the like is used herein to define a polymeric material in which the molecules have been aligned in the 5b longitudinal and/or transverse direction by a process such as a tenter frame or blown bubble process.
"Propylene polymer" and the like is used here t:o mean polymerized propylene in its homopolymer form, and "propylene copolymers°' means copolymers such as ethyene propylene copolymer, where generally small amounts of a comonomer such as ethylene are included in the copolymer.
Terpolymers axe also included.
"Polymeric adhesive" and the like here means polymeric materials, of any suitable composition, which can be used to create or enhance interlaminar bonds in multilayer thermoplastic films. Polyolefins are preferred, especially those which have been mod~.fied, e.g. by carboxylic acid ar acid anhydride in a graft copolymer.
"Rubber modif ied EPC°' and the like here means an EPC which has been modified by the inclusion of other moieties in the polymer structure.
Such material may provide improved elasticity or other properties.
An example is believed to be Himont KS - 052 P, or those available from Rexene (E1 Paso).
"Ethylene propylene butene terpolymer" and the like is used here to mean a terpolymer incorporating these three comonomers in various percentages. An example is KT - 021 from Himont, or those available from Sumitomo.
"Core layer" as used herein means an intermediate layer of a multilayer film, and the central layer where the film has an odd number of layers.
BRIEF DESCRIPTION OF THE DRAWINGS
Further details are given below with reference to the drawing figures wherein Figure 1 is a schematic cross section of a preferred 7/930727.1 TXTMBQ 6 embodiment of a multi-layer moisture barrier film of the invention, and Figures 2 and 3 are alternative embodiments of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring specifically to the drawings, in Figure 1, a schematic cross section of a preferred embodiment of the multi-layer moisture barrier film of the invention is shown. The multi-layer film 10 has the generalized structure o~° A/B/A where A is an outer layer, and B is a core layer comprising a moisture barrier material.
Core layer 12 preferably comprises a blend of a propylene polymer or copolymer, and a hydrocarbon resin, this blend shown as a spotted/striped layer. A typical example of a propylene homopolymer is Exxon PD 4062 E7*, or those available from Fina, or Himont PD 064*. A preferred propylene copolymer is ethylene propylene Copolymer sold under the designation Fina 8473*
or Fina 8473X*. This material has an ethylene content of about 40. A preferred hydrocarbon resin is Regalrez 1128* or 1139* from Hercules. The HC resin preferably comprises between about 30o and 50% by weight of the blend.
Outer layers 14 and 16 are preferably ethylene propylene copolymer (EPC), polypropylene (PP), or blends thereof. If only polypropylene resin is used, the film can be difficult to use for packaging applications involving heat sealing. Therefore, it is preferable to use EPC alone, or the blend of the two materials.
Commercial resin examples are those discussed above for core layer 12. An alternative polypropylene for the outer layers 14 and 16 *Trade-mark 7 is Himont PD 064. These blend layers may include from 0-100s EPC
and 1000-0°~ PP, although preferably the blend layers include between about 96s and 85s EPC and between about 4o and 15s PP;
even more preferably, the blend layer. includes about 92o EPC and 8s PP. EAO and polybutene can also be used in the outer layers.
7a In Figure 2, a schematic cross section of another embodiment of the mufti-layer. moisture barrier film of the invention is generally~~shown.
The mufti-layer film has the structure of A/B/C/B/A where A is an outer layer, B is:..an intermediate adhesive layer, and C is a core layer comprising.a moisture barrier material.
The core layer preferably comprises a blend of a propylene polymer or copolymer, and.'a hydrocarbon resin. Suitable materials are those described above for core layer 12 of f~.lm 1~.
The outer layers are preferably the materials discussed above for outer layers 14 and 16 of film 10. The outer layers also preferably include an HC such as described for core layer 12 of film 1~.
The intermediate layers preferably comprise a propylene polymer or copolymer, or blends thereof, optionally blended with hydrocarbon resin.
An alternative A/B/C/B/A structure is also within the scope of this invention, and specifically shown by the position of the moisture barrier layers in the film of Fig.2.
In this alternative, core layer 24 preferably comprises an ethylene alpha olefin copolymer,, more preferably a linear EAO" Very low density polyethylene (VLDPE), and linear low density polyethyene (LhDPE) are preferred. A suitable LLI3PE is Dowlex 20457M The core layer 24 can also comprise EPC, a rubber modified EPC, or an ethylene terpolymer, especially an ethylene propylene butane terpolymer such as KT 021 P from Himont.
Outer layers 20 and 28 are preferably the materials discussed above for outer layers 14 and 16 of film lC~.
Intermediate layers 22 and 26 preferably comprise a blend of a propylene polymer or copolymer, and a hydrocarbon resin. Suitable materials are those described above for core layer 12 of film 10. An alternative material for layers 22 and 26 is Exxon 6042, which is believed to be a blend of polypropylene and hydrocarbon resin.
In Figure 3, a schematic cross section of another embodiment of the mufti-layer moisture barrier film of the invention is shown. The mufti-layer film 30 has the generalized structure of A/B/C/D/C/B/A where A is an outer layer, B is a moisture barrier layer, C is an intermediate adhesive layer, and D is a core layer comprising an oxygen barrier material.
Core layer 38 preferably comprises an oxygen barrier material such as ethylene vinyl alcohol copolymer, vinylidene chloride copolymer, polyester, or polyamide.
Outer layers 32 and 44 are preferably the materials discussed above for outer layers 14 and 16 of film 10.
Intermediate layers 36 and 40 preferably comprise a propylene polymer or copolymer, such as Exxon PD 4062 E7. Alternative materials are polymeric adhesives, especially carboxylic acid or malefic anhydride-modified polyolefins and more preferably polypropylene-based carboxylic acid or malefic anhydride-modified adhesives. Conventional lamination or other suitable methods may sometimes be necessary, depending on the nature of the respective layers, to ensure adequate interlaminar bond strength.
Moisture barrier layers 34 and 42 preferably comprise a blend of a propylene polymer or copolymer, and a hydrocarbon resin. Suitable materials are those described above for core layer 12 of film 10. An alternative material for layers 34 and 42 is Exxon 6042.
An alternative film with at least seven layers comprises a core layer 38 comprising high density polyethylene; two intermediate layers 36 and 40, on opposite respective surfaces of the core layer, comprising a polymeric adhesive, ethylene vinyl acetate copolymer, or ethylene alpha olefin copolymer; two moisture barrier layers 34 and 42 comprising 7/930727.1 TXTMBQ 9 a blend of propylene polymer or copolymer and a hydrocarbon resin; and two outermost layers 32 and 44 comprising propylene polymer or copolymer.
A multilayer film. of four or six Layers, and/or possessing both moisture barrier and oxygen barrier properties, can also be made in accordance with the present invention. In such alternative constructions, a blend of HC resin with propylene polymer or copolymer can be present in any of the layers of the multilayer film.
The core, intermediate, and moisture barrier layers of such a film can be like that of film 30. A sealant layer is coextruded with, or extrusion coated, extrusion laminated, or adhesive laminated, by means and methods well known in the art, to one of the moisture barrier layers. The sealant layer, which can be disposed on one or both outer surfaces of the film structure, preferably comprises an ethylene alpha olefin copolymer, more preferably a linear E;AO. Very low density polyethylene (VLDPE), and linear low density polyethyene (LLDPE) are preferred. A suitable T~T-nPE is Dowlex. 2045. The sealant layer can also comprise EPC, a rubber modified EPC, an ethylene propylene butane terpolymer such as KT 021 P from Himont, an ethylene vinyl acetate copolymer, an ethylene alkyl acrylate copolymer" an ethylene acrylic or methacrylic acid copolymer, or an ionomer.
The films of the present invention can be made by coextrusion, extrusion coating, extrusion laminating, and conventional adhesive lamination techniques well known in the art, using annular or slot die extrusion equipment as appropriate.
The beneficial low moisture transmission rates (high moisture barrier) and other properties associated with exemplary films of the present invention are demonstrated in the Tables.
The resins used in these examples are identified in Table 1, and the films made from these resins are identified in Tables 2 through 8.
7/930727.1 TXTMBQ ~ 10 Physical properties of these films are itemized. in the remaining Tables. Values given are typically average values obtained from four replicate measurements; values for MVTR are average obtained from three samples.
The terms and abbreviations In the Tables have the following meaning:
"PP" = polypropylene.
"EPC" = ethylene propylene copolymer.
"EAO" = ethylene alpha olefin copolymer.
"EPB" = ethylene propylene butane terpolymer.
"EVOH" = ethylene vinyl alcohol copolymer.
"ADH" - polymeric adhesive; ABH 1 is an ethylene butane - based adhesive from Du Pont; ADH 2 is an EPC-based adhesive from Mitsui.
"AB" = antiblock.
"MO" = mineral oil.
"Tensile°° = tensile at break and 73° f, in PSI (ASTM D
882-81).
"PSI" = pounds per square inch (ASTM 882-81).
"IJnshrunk" - a film sample or samples that were not shrunk by exposure to heat at the time of testing for the stated property.
"Shrunk" = a film sample or samples that were shrunk by exposure to heat at the time of testing for the stated property.
"I°D°' = longitudinal orientation direction.
7/930727.1 TXTMBQ 11 "TD'° = transverse orientation direction.
"Modulus" = madulus of elasticity (ASTM 882-81) in PSI at 73°F.
"Haze" = haze {ASTM D 1003-61 {reapproved 1977)) in per cent.
"Clarity°' - total light transmission (ASTM D 1003 Method A) in percent.
"Gloss°' - gloss measured at 45° angle to film surface (ASTM D
2457-70 (reapproved 1977)).
'°MVTR 1" = moisture ( water ) vapor transmission rate ( ASTM F 372 ) in grams/24 hours, I00 square inches at 100 relative humidity and 100°F.
"MVTR 2" = moisture (water) vapor transmission rate (ASTM F 372) in grams/24 hours, 100 square inches at 90o relative humidity and 100°F.
''OTR" = oxygen transmission rate (ASTM D 3985-81) in cc at standard temperature and pressure~ in 24 hours, per square meter, at one atmosphere, at Oo relative humidity.
"Tear°' = tear propagation in grams at 73°F (ASTM D 1938-79).
"Film Thickness" = the average thickness {gauge) of the film samples in mils (_ .001 inches).
"Tensile'° = tensile strength at break (ASTM D 882-~81) in psi.
"Elongation°° = elongation at break {ASTM D 882-81) in percent.
"Ball Burst°' - ball burst impact in centimeters-kilograms at 73°F
(ASTM D 3'420-80).
7/930727.1 TXTMBQ 12 ~~gI~, ~~p,~ SUPPLIER
pp 1 Profax PD-064 Himont pp 2* [see footnote]
PP 3 PD 4062 Exxon PP 4** Eseorene PD 6042 Exxon [see footnote]
EPC 1. Fina 8473 or Fin.a Fina 8473 X
EPC 2***
[see footnote) EPC 3 PD 9302 Exxon EPB 1 KT-021 Hitr~ont HC Regalrez 1128 Hercules HC Escorez 5340 Exxon HC Regalrez 1139 Hercules EAO 1 Dowlex 2045.03 Dow EAO 2 Dowlex 2045.04 Dow ADH 1 Bynel CXA 4104 Du Pont 7/930727.1 TXTMBQ 13 ADH 2 Adorer Qf 551 A P~itsui EVOH 1 EVAL SC H-103 Evalca EVOH 2 EYAL hC F-Igl A Evalca EVOH 3 EVAL LC H~103 Evalca MO 1 Kaydol witco *PP 2 is a masterbatch blend of PP 1 with about 4%, by weight ~f the blend, of a silica=couta.~ning anti-~blocki~ig ag~:nt, abcut 5% by .vreight of amide waxes, and about 1% of a Iubr~.cating agent. The amide waxes and lubricating agent.are well known in the art as slip agents.
** PP 4 is Escorene PD 60421; believed to be a blend of polypropylene and hydrocarbon resin.
***EPC 2 is a blend of EPC 1 blended with about 1:5%, by weight of the blend, of an antiblock agent, and 0.50, by weight of the blend, of a mineral oil.
TABLE 2 ( CONTROL ) Initial efforts to make a moisture barrier material involved the use of homopolymer polypropylene in a core layer, with sealant. layers of propylene copolymer on both surfaces of the core layer. The object was to maximize thickness of the core layer to minimize the moisture vapor transmission rate (MVTR), while still maintaining adequate free shrink and sealabil.ity properties of the film. The MVTR did not prove adequate for at least some moisture barrier packaging applications. An example of this film .is given below:
EXAMPLE FILM STRUCTURE
1. 92% EPC 1 + 8% PP 2/ PP 1 /92% EPC 1 + 8% PP 2 The generalized structure of the film of Example 1 was A/B/A.
Relative layer thickness ratios:
A = 1.0; B = 2.0; A = 1Ø
The films of Table 3 were made in an effort to make a moisture barrier material with lower MVTR. This was achieved using hydrocarbon resin blended with homopolymer polypropylene. It was found that these formulations had much lower moisture vapor transmission rate (MVTR) than those of Table 2. However, they could not be oriented much over 4.5 X 4.5 racking (orientation) ratio because of equipment limitations. On other equipment, e.g. a modified bubble process or tenterframing, higher orientation (racking) rates can be achieved. They also could not be made into heavier gauge films because of relatively poor tear properties. Examples of these films are given below:
EXAMPLE FILM STRUCTURE
2 . 90% f 92 % EPC 1 + 8 % PP 21 + lOgA HC 1 84.5% PP 3 + 15% HC 1 + 0.5% MO 1 90 % 92% EPC 1 + 8 % PP 2 ] + 10 % HC 1 The generalized structure of the i=ilm of Example 2 was A/B/C/B/A.
Relative layer thickness ratios:
2.5 : 0.8 : 3.7 : 0.6 ; 2.4.
3 . 92 % EPC 1 + 8 % PP 2 / PP 4 / 92 % EPC 1 + 8 % PP 2 The generalized structure of the filet of Example 3 was A/B/A.
Relative layer thickness ratios;
1 ; 2 : 1 4 . 92 % EPC 1 + 8 % PP 2 / PP 4 / 92 % EPC 1 + 8 % PP 2 The generalized structure of the film of Example 4 was A/B/A.
Relative layer thickness ratios:
1 : 3 : 1.
7/930727.1 TXTMBQ 16 Alternative films of Table 4 were made in which, in effect, the core layer of the films of Table 3 (i.e. the layer ccantaining the hydrocarbon resin) were °'split'° into two substrate (intermediate) layers.
A "new"
core layer of e.g. LLDPE or EPC is introduced. The practical effect of this is to improve tear properties of the film, related to tape creasing during the orientation process, so that it can be oriented at e.g. 6 x 6 ratio. The film was in fact oriented at 4 x 4.5 because of the equipment limitations discussed for the Examples of Table 3. Examples of these films are given below:
EXAMPLE FILM STRUCTURE
This application is a divisional application of copending application 2,106,258,. filed September 15, 1993.
FIELD OF THE INVENTION
This invention relates to thermoplastic films for packaging; and more particularly, this invention relates to a mufti-layer film having high moisture barrier characteristics.
BACKGROUND OF THE INVENTION
Thermoplastic film, and in particular polyolefin materials, have been used for some time in connection with packaging of various articles including food products which require protection from the environment, an attractive appearance, and resistance to abuse during tee~ storage and distribution cycle. Suitable optical properties are also desirable in order to provide far inspection of the packaged product after packaging, in the distribution chain, and ultimately at point of sale. Optical properties such as high gloss, high clarity, and low haze characteristics contribute to an aesthetically attractive packaging material and packaged product to enhance the consumer appeal of the product.
Various polymeric materials have been used to provide lower moisture permeability in order to reduce the transmission of moisture through the packaging film and thereby extend the shelf life of products such as food, medical, electronic, and other items which are sensitive to moisture gain or loss. For some products, maintenance of a high moisture content is desirable, and the film ideally minimizes loss of moisture from the package to the environment. For other products, maintenance of a low moisture content is desirable, and the film ideally minimizes gain of moisture from the environment through the packaging material.
It is also often desirable to include in a packaging film a shrink feature, i.e. the propensity of the film upon exposure to heat to shrink or, if restrained, create shrink tension within the packaging film. This property is imparted to the film by orientation of the film during its manufacture. Typically, the manufactured film is heated to its orientation temperature and stretched in either a longitudinal (machine) or transverse direction (i.e. monoaxial orientation), or both directions (i.e.
biaxial orientation), in varying degrees to impart a certain degree of shrinkability in the film upon subsequent heating.
When biaxial orientation is done, it ca.n be simultaneous or sequential; that is, the orientation can be done in each of the directions in turn, or else both the longitudinal and transverse orientation can be done at the same time. Any suitable technique, such as blown bubble or tenterframing, can be used to achieve orientation of the film. After being so stretched, the film is rapidly cooled to provide this latent shrinkability to the resulting film. One advantage of shrinkable film is the tight, smooth appearance of the wrapped product that results, providing an aesthetic package as well as protecting the packaged product from environmental abuse. Various food and non-food items may be and have been packaged in shrinkable films.
It is sometimes also desirable to orient a packaging film and thereafter heat set the film by bringing the film to a temperature near its orientation temperature.
This produces a film with substantially less shrinkability, while retaining much of the advantages of orientation, including improved tensile strength, modulus and optical properties.
Of interest are U.S. Patent Nos. 4,921,749 (Bossaert et al); 5,085,943 (Crighton et al); 5,091,237 (Schloegel et al); 5,128,183 (Buzio); and 5,212,009 (Peiffer et al) disclosing the use of hydrocarbon resins.
SUMMARY OF THE INVENTION
The present invention provides a thermoplastic multilayer film characterized by good moisture barrier properties. Further, the present invention provides a thermoplastic multilayer film having an aesthetic appearance with good clarity, and other desirable optical properties.
The present invention also provides a thin thermoplastic multilayer film having toughness and abrasion resistance.
The present invention also provides a thermoplastic multilayer film which may be totally coextruded, oriented, and have good moisture barrier and, in some cases, both moisture barrier and oxygen barrier properties.
The present invention relates to a thermoplastic mufti-layer film comprising a core layer comprising a blend of propylene polymer or copolymer, or ethylene alpha olefin copolymer, and a hydrocarbon resin; and two outer layers comprising a propylene polymer or copolymer, ethylene alpha olefin copolymer, polybutene, or blends thereof.
In another aspect, the present invention relates to a thermoplastic mufti-layer film comprising a core layer comprising a blend of propylene polymer or copolymer, and a hydrocarbon resin; two intermediate layers, on opposite surfaces of the core layer, comprising propylene polymer or copolymer, or a polymeric adhesive; and two outer layers comprising a propylene polymer or copolymer, ethylene alpha olefin copolymer, ionomer, polybutene, or blends thereof.
The present invention also relates to a thermoplastic multi-layer film comprising a core layer comprising an ethylene alpha olefin copolymer, ethylene propylene copolymer, rubber modified ethylene 3a propylene copolymer, or ethyene propylene butene terpolymer; two intermediate layers, on opposite surfaces of the core layer, comprising a blend'of propylene polymer or copolymer, and a hydrocarbon resin; and two outer layers comprising a propylene polymer or copolymer, ethylene alpha olefin copolymer, ianomer, polybutene, or blends thereof.
A film with oxygen barrier as well as moisture barrier properties comprises a core layer comprising an oxygen barrier material; two intermediate layers, on opposite surfaces of the core layer,. comprising a polymeric adhesive; two outer layers comprising a blend of propylene polymer or copolymer, or polybutene, and a hydrocarbon resin; and a polymeric sealant layer adhered to at least one of the outer layers.
An alternative film with at least seven layers comprises a core layer comprising high density polyethylene; two intermediate layers, on opposite surfaces of the core layer, comprising a polymeric adhesive, ethylene vinyl acetate copolymer, or ethylene alpha olefin copolymer;
two outer layers comprising a blend of propylene polymer or copolymer, and a hydrocarbon resin; and two outermost layers comprising propylene polymer or copolymer, polybutene, or blends thereof.
Another alternative is a film comprising a core layer comprising an oxygen barrier material; two intermediate layers, on apposite surfaces of the core layer, comprising polyamide; two tie layers, each disposed on a respective polyamide layer, comprising a polymeric adhesive, ethylene alpha olefin copolymer, or ethylene vinyl acetate copolymer;
two moisture barrier layers, adhered to respective adhesive layers, comprising a blend of propylene polymer or copolymer, and a hydrocarbon resin; and two outermost. layers comprising a propylene polymer, propylene copolymer, ethylene alpha olefin copolymer, or polybutene.
In another aspect of the invention, a method of making a thermoplastic multilayer film comprises the steps of coextruding an interior layer of a blend of propylene polymer or copolymer, and a hydrocarbon resin, and two outer layers comprising a propylene polymer or copolymer, ethylene alpha olefin copolymer, polybutene, or blends 7/930727.1 TXTt~Q 4 thereof; cooling the coextruded multi-layer film; and collapsing the cooled film.
In one aspect, the invention of the parent application provides a thermoplastic mufti-layer film, comprising: (a) a core layer comprising a blend of propylene polymer or copolymer, and a hydrocarbon resin; and (b) two outer layers comprising a polymeric material selected from the group consisting of: i) ethylene alpha olefin copolymer, ii) polybutene, and iii) blends thereof.
In a further aspect, the invention of the parent application provides a thermoplastic mufti-layer film comprising: (a) a core layer comprising a blend of propylene polymer or copolymer, and a hydrocarbon resin; (b) two intermediate layers, on opposite surfaces of the core layer, comprising propylene polyrrler or copolymer, or polymeric adhesive; and (c) two outer layers comprising a polymeric material selected from the group consisting of: i) ethylene alpha olefin copolymer, ii) ionomer, iii) polybutene, and iv) blends thereof.
2~ In one aspect, the invention i.n this divisional application provides a thermoplastic heat shrinkable, multi-layer film, comprising: (a) a core layer comprising a material selected from the group consisting of: i) ethylene alpha olefin copolymer, ii) ethylene propylene copolymer, iii) rubber modified EPC, and iv) ethylene propylene butene terpolymer; (b) two intermediate layers, on opposite surfaces of the core layer, comprising a. blend of propylene polymer or copolymer, and a hydrocarbon resin; and (c) two outer layers comprising a polymeric material selected from the group consisting of: i) propylene polymer, ii) propylene copolymer, iii) ethylene alpha olefin copolymer, iv) ionomer, v) polybutene, and vi) blends thereof; wherein the film exhibits a free shrink, at 240°F, of at least 10% in the longitudinal direction, and at least 15o in the transverse direction.
In a further aspect, the invention in this divisional application provides a thermoplastic mufti-layer film, comprising: (a) a core layer comprising high density polyethylene; (b) two intermediate layers, on opposite surfaces of the core layer, comprising a polymeric material selected from the group consisting of: i) polymeric adhesive; ii) ethylene vinyl acetate copolymer; and iii) ethylene alpha olefin copolymer; (<:) two outer layers comprising a blend of propylene polymer or copolymer, and a hydrocarbon resin; and (d) two outermost layers comprising propylene polymer or copolymer, polybutene, or blends thereof .
DEFINITIONS
"Hydrocarbon resin" (''HC" herein) and the like as used herein means resins made by the polymerization of monomers composed of carbon and hydrogen only.
Thermoplastic resins of low molecular weight made from relatively impure monomers derived from coal-tar fractions, petroleum distillates, etc. are also included. A discussion of HC resins can be found e.g. in U.S. Patent Nos. 4,921,749 (Bossaert et al); 5,091,237 (Schloegel et al); and 5,128,183 (Buzio) .
"Ethylene alpha olefin copolymer" (EAO) is used here to include such materials as linear low density polyethylene (LLDPE); very low and ultra low density polyethylene (VLDPE and ULDPE); and metallocene catalyzed polymers such as those supplied by Exxon. Tafmer (tm) 5a ' 64536-829D
materials supplied by Mitsui are also included. These materials generally include copolymers of ethylene with one or more comonomers selected from C4 to C1o alpha olefins such as butene-l, hexene-l, octene-1, etc. in which the molecules of the copolymers comprise long chains with relatively few side chain branches or cross-linked structures. This molecular structure is to be contrasted with conventional low or medium density polyethylenes which are more highly branched than their respective counterparts. '°LLDPE" as defined here has a density in the range of from about 0.916 grams per cubic centimeter to about 0.940 grams per cubic centimeter. Generally, "EAO" as used here includes both homogeneous and heterogeneous polymers.
"Intermediate layer" and the like is used herein to define a layer in a multi-layer film enclosed on both sides by other layers, i.e. disposed between other layers of the film.
The term "oriented" and the like is used herein to define a polymeric material in which the molecules have been aligned in the 5b longitudinal and/or transverse direction by a process such as a tenter frame or blown bubble process.
"Propylene polymer" and the like is used here t:o mean polymerized propylene in its homopolymer form, and "propylene copolymers°' means copolymers such as ethyene propylene copolymer, where generally small amounts of a comonomer such as ethylene are included in the copolymer.
Terpolymers axe also included.
"Polymeric adhesive" and the like here means polymeric materials, of any suitable composition, which can be used to create or enhance interlaminar bonds in multilayer thermoplastic films. Polyolefins are preferred, especially those which have been mod~.fied, e.g. by carboxylic acid ar acid anhydride in a graft copolymer.
"Rubber modif ied EPC°' and the like here means an EPC which has been modified by the inclusion of other moieties in the polymer structure.
Such material may provide improved elasticity or other properties.
An example is believed to be Himont KS - 052 P, or those available from Rexene (E1 Paso).
"Ethylene propylene butene terpolymer" and the like is used here to mean a terpolymer incorporating these three comonomers in various percentages. An example is KT - 021 from Himont, or those available from Sumitomo.
"Core layer" as used herein means an intermediate layer of a multilayer film, and the central layer where the film has an odd number of layers.
BRIEF DESCRIPTION OF THE DRAWINGS
Further details are given below with reference to the drawing figures wherein Figure 1 is a schematic cross section of a preferred 7/930727.1 TXTMBQ 6 embodiment of a multi-layer moisture barrier film of the invention, and Figures 2 and 3 are alternative embodiments of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring specifically to the drawings, in Figure 1, a schematic cross section of a preferred embodiment of the multi-layer moisture barrier film of the invention is shown. The multi-layer film 10 has the generalized structure o~° A/B/A where A is an outer layer, and B is a core layer comprising a moisture barrier material.
Core layer 12 preferably comprises a blend of a propylene polymer or copolymer, and a hydrocarbon resin, this blend shown as a spotted/striped layer. A typical example of a propylene homopolymer is Exxon PD 4062 E7*, or those available from Fina, or Himont PD 064*. A preferred propylene copolymer is ethylene propylene Copolymer sold under the designation Fina 8473*
or Fina 8473X*. This material has an ethylene content of about 40. A preferred hydrocarbon resin is Regalrez 1128* or 1139* from Hercules. The HC resin preferably comprises between about 30o and 50% by weight of the blend.
Outer layers 14 and 16 are preferably ethylene propylene copolymer (EPC), polypropylene (PP), or blends thereof. If only polypropylene resin is used, the film can be difficult to use for packaging applications involving heat sealing. Therefore, it is preferable to use EPC alone, or the blend of the two materials.
Commercial resin examples are those discussed above for core layer 12. An alternative polypropylene for the outer layers 14 and 16 *Trade-mark 7 is Himont PD 064. These blend layers may include from 0-100s EPC
and 1000-0°~ PP, although preferably the blend layers include between about 96s and 85s EPC and between about 4o and 15s PP;
even more preferably, the blend layer. includes about 92o EPC and 8s PP. EAO and polybutene can also be used in the outer layers.
7a In Figure 2, a schematic cross section of another embodiment of the mufti-layer. moisture barrier film of the invention is generally~~shown.
The mufti-layer film has the structure of A/B/C/B/A where A is an outer layer, B is:..an intermediate adhesive layer, and C is a core layer comprising.a moisture barrier material.
The core layer preferably comprises a blend of a propylene polymer or copolymer, and.'a hydrocarbon resin. Suitable materials are those described above for core layer 12 of f~.lm 1~.
The outer layers are preferably the materials discussed above for outer layers 14 and 16 of film 10. The outer layers also preferably include an HC such as described for core layer 12 of film 1~.
The intermediate layers preferably comprise a propylene polymer or copolymer, or blends thereof, optionally blended with hydrocarbon resin.
An alternative A/B/C/B/A structure is also within the scope of this invention, and specifically shown by the position of the moisture barrier layers in the film of Fig.2.
In this alternative, core layer 24 preferably comprises an ethylene alpha olefin copolymer,, more preferably a linear EAO" Very low density polyethylene (VLDPE), and linear low density polyethyene (LhDPE) are preferred. A suitable LLI3PE is Dowlex 20457M The core layer 24 can also comprise EPC, a rubber modified EPC, or an ethylene terpolymer, especially an ethylene propylene butane terpolymer such as KT 021 P from Himont.
Outer layers 20 and 28 are preferably the materials discussed above for outer layers 14 and 16 of film lC~.
Intermediate layers 22 and 26 preferably comprise a blend of a propylene polymer or copolymer, and a hydrocarbon resin. Suitable materials are those described above for core layer 12 of film 10. An alternative material for layers 22 and 26 is Exxon 6042, which is believed to be a blend of polypropylene and hydrocarbon resin.
In Figure 3, a schematic cross section of another embodiment of the mufti-layer moisture barrier film of the invention is shown. The mufti-layer film 30 has the generalized structure of A/B/C/D/C/B/A where A is an outer layer, B is a moisture barrier layer, C is an intermediate adhesive layer, and D is a core layer comprising an oxygen barrier material.
Core layer 38 preferably comprises an oxygen barrier material such as ethylene vinyl alcohol copolymer, vinylidene chloride copolymer, polyester, or polyamide.
Outer layers 32 and 44 are preferably the materials discussed above for outer layers 14 and 16 of film 10.
Intermediate layers 36 and 40 preferably comprise a propylene polymer or copolymer, such as Exxon PD 4062 E7. Alternative materials are polymeric adhesives, especially carboxylic acid or malefic anhydride-modified polyolefins and more preferably polypropylene-based carboxylic acid or malefic anhydride-modified adhesives. Conventional lamination or other suitable methods may sometimes be necessary, depending on the nature of the respective layers, to ensure adequate interlaminar bond strength.
Moisture barrier layers 34 and 42 preferably comprise a blend of a propylene polymer or copolymer, and a hydrocarbon resin. Suitable materials are those described above for core layer 12 of film 10. An alternative material for layers 34 and 42 is Exxon 6042.
An alternative film with at least seven layers comprises a core layer 38 comprising high density polyethylene; two intermediate layers 36 and 40, on opposite respective surfaces of the core layer, comprising a polymeric adhesive, ethylene vinyl acetate copolymer, or ethylene alpha olefin copolymer; two moisture barrier layers 34 and 42 comprising 7/930727.1 TXTMBQ 9 a blend of propylene polymer or copolymer and a hydrocarbon resin; and two outermost layers 32 and 44 comprising propylene polymer or copolymer.
A multilayer film. of four or six Layers, and/or possessing both moisture barrier and oxygen barrier properties, can also be made in accordance with the present invention. In such alternative constructions, a blend of HC resin with propylene polymer or copolymer can be present in any of the layers of the multilayer film.
The core, intermediate, and moisture barrier layers of such a film can be like that of film 30. A sealant layer is coextruded with, or extrusion coated, extrusion laminated, or adhesive laminated, by means and methods well known in the art, to one of the moisture barrier layers. The sealant layer, which can be disposed on one or both outer surfaces of the film structure, preferably comprises an ethylene alpha olefin copolymer, more preferably a linear E;AO. Very low density polyethylene (VLDPE), and linear low density polyethyene (LLDPE) are preferred. A suitable T~T-nPE is Dowlex. 2045. The sealant layer can also comprise EPC, a rubber modified EPC, an ethylene propylene butane terpolymer such as KT 021 P from Himont, an ethylene vinyl acetate copolymer, an ethylene alkyl acrylate copolymer" an ethylene acrylic or methacrylic acid copolymer, or an ionomer.
The films of the present invention can be made by coextrusion, extrusion coating, extrusion laminating, and conventional adhesive lamination techniques well known in the art, using annular or slot die extrusion equipment as appropriate.
The beneficial low moisture transmission rates (high moisture barrier) and other properties associated with exemplary films of the present invention are demonstrated in the Tables.
The resins used in these examples are identified in Table 1, and the films made from these resins are identified in Tables 2 through 8.
7/930727.1 TXTMBQ ~ 10 Physical properties of these films are itemized. in the remaining Tables. Values given are typically average values obtained from four replicate measurements; values for MVTR are average obtained from three samples.
The terms and abbreviations In the Tables have the following meaning:
"PP" = polypropylene.
"EPC" = ethylene propylene copolymer.
"EAO" = ethylene alpha olefin copolymer.
"EPB" = ethylene propylene butane terpolymer.
"EVOH" = ethylene vinyl alcohol copolymer.
"ADH" - polymeric adhesive; ABH 1 is an ethylene butane - based adhesive from Du Pont; ADH 2 is an EPC-based adhesive from Mitsui.
"AB" = antiblock.
"MO" = mineral oil.
"Tensile°° = tensile at break and 73° f, in PSI (ASTM D
882-81).
"PSI" = pounds per square inch (ASTM 882-81).
"IJnshrunk" - a film sample or samples that were not shrunk by exposure to heat at the time of testing for the stated property.
"Shrunk" = a film sample or samples that were shrunk by exposure to heat at the time of testing for the stated property.
"I°D°' = longitudinal orientation direction.
7/930727.1 TXTMBQ 11 "TD'° = transverse orientation direction.
"Modulus" = madulus of elasticity (ASTM 882-81) in PSI at 73°F.
"Haze" = haze {ASTM D 1003-61 {reapproved 1977)) in per cent.
"Clarity°' - total light transmission (ASTM D 1003 Method A) in percent.
"Gloss°' - gloss measured at 45° angle to film surface (ASTM D
2457-70 (reapproved 1977)).
'°MVTR 1" = moisture ( water ) vapor transmission rate ( ASTM F 372 ) in grams/24 hours, I00 square inches at 100 relative humidity and 100°F.
"MVTR 2" = moisture (water) vapor transmission rate (ASTM F 372) in grams/24 hours, 100 square inches at 90o relative humidity and 100°F.
''OTR" = oxygen transmission rate (ASTM D 3985-81) in cc at standard temperature and pressure~ in 24 hours, per square meter, at one atmosphere, at Oo relative humidity.
"Tear°' = tear propagation in grams at 73°F (ASTM D 1938-79).
"Film Thickness" = the average thickness {gauge) of the film samples in mils (_ .001 inches).
"Tensile'° = tensile strength at break (ASTM D 882-~81) in psi.
"Elongation°° = elongation at break {ASTM D 882-81) in percent.
"Ball Burst°' - ball burst impact in centimeters-kilograms at 73°F
(ASTM D 3'420-80).
7/930727.1 TXTMBQ 12 ~~gI~, ~~p,~ SUPPLIER
pp 1 Profax PD-064 Himont pp 2* [see footnote]
PP 3 PD 4062 Exxon PP 4** Eseorene PD 6042 Exxon [see footnote]
EPC 1. Fina 8473 or Fin.a Fina 8473 X
EPC 2***
[see footnote) EPC 3 PD 9302 Exxon EPB 1 KT-021 Hitr~ont HC Regalrez 1128 Hercules HC Escorez 5340 Exxon HC Regalrez 1139 Hercules EAO 1 Dowlex 2045.03 Dow EAO 2 Dowlex 2045.04 Dow ADH 1 Bynel CXA 4104 Du Pont 7/930727.1 TXTMBQ 13 ADH 2 Adorer Qf 551 A P~itsui EVOH 1 EVAL SC H-103 Evalca EVOH 2 EYAL hC F-Igl A Evalca EVOH 3 EVAL LC H~103 Evalca MO 1 Kaydol witco *PP 2 is a masterbatch blend of PP 1 with about 4%, by weight ~f the blend, of a silica=couta.~ning anti-~blocki~ig ag~:nt, abcut 5% by .vreight of amide waxes, and about 1% of a Iubr~.cating agent. The amide waxes and lubricating agent.are well known in the art as slip agents.
** PP 4 is Escorene PD 60421; believed to be a blend of polypropylene and hydrocarbon resin.
***EPC 2 is a blend of EPC 1 blended with about 1:5%, by weight of the blend, of an antiblock agent, and 0.50, by weight of the blend, of a mineral oil.
TABLE 2 ( CONTROL ) Initial efforts to make a moisture barrier material involved the use of homopolymer polypropylene in a core layer, with sealant. layers of propylene copolymer on both surfaces of the core layer. The object was to maximize thickness of the core layer to minimize the moisture vapor transmission rate (MVTR), while still maintaining adequate free shrink and sealabil.ity properties of the film. The MVTR did not prove adequate for at least some moisture barrier packaging applications. An example of this film .is given below:
EXAMPLE FILM STRUCTURE
1. 92% EPC 1 + 8% PP 2/ PP 1 /92% EPC 1 + 8% PP 2 The generalized structure of the film of Example 1 was A/B/A.
Relative layer thickness ratios:
A = 1.0; B = 2.0; A = 1Ø
The films of Table 3 were made in an effort to make a moisture barrier material with lower MVTR. This was achieved using hydrocarbon resin blended with homopolymer polypropylene. It was found that these formulations had much lower moisture vapor transmission rate (MVTR) than those of Table 2. However, they could not be oriented much over 4.5 X 4.5 racking (orientation) ratio because of equipment limitations. On other equipment, e.g. a modified bubble process or tenterframing, higher orientation (racking) rates can be achieved. They also could not be made into heavier gauge films because of relatively poor tear properties. Examples of these films are given below:
EXAMPLE FILM STRUCTURE
2 . 90% f 92 % EPC 1 + 8 % PP 21 + lOgA HC 1 84.5% PP 3 + 15% HC 1 + 0.5% MO 1 90 % 92% EPC 1 + 8 % PP 2 ] + 10 % HC 1 The generalized structure of the i=ilm of Example 2 was A/B/C/B/A.
Relative layer thickness ratios:
2.5 : 0.8 : 3.7 : 0.6 ; 2.4.
3 . 92 % EPC 1 + 8 % PP 2 / PP 4 / 92 % EPC 1 + 8 % PP 2 The generalized structure of the filet of Example 3 was A/B/A.
Relative layer thickness ratios;
1 ; 2 : 1 4 . 92 % EPC 1 + 8 % PP 2 / PP 4 / 92 % EPC 1 + 8 % PP 2 The generalized structure of the film of Example 4 was A/B/A.
Relative layer thickness ratios:
1 : 3 : 1.
7/930727.1 TXTMBQ 16 Alternative films of Table 4 were made in which, in effect, the core layer of the films of Table 3 (i.e. the layer ccantaining the hydrocarbon resin) were °'split'° into two substrate (intermediate) layers.
A "new"
core layer of e.g. LLDPE or EPC is introduced. The practical effect of this is to improve tear properties of the film, related to tape creasing during the orientation process, so that it can be oriented at e.g. 6 x 6 ratio. The film was in fact oriented at 4 x 4.5 because of the equipment limitations discussed for the Examples of Table 3. Examples of these films are given below:
EXAMPLE FILM STRUCTURE
5. 92 a EPC. 1 + 8% PP 2 / PP 4 / EAO 1 / PP 4 / 92 o EPC 1 + $~ PP 2 The generalized structure of the film of Example 5 was A/B/C/B/A.
Relative layer thickness ratios:
1.5 : 3 : 1 : 3 : 1.5.
Relative layer thickness ratios:
1.5 : 3 : 1 : 3 : 1.5.
6. 92% EPC 1 + g p PP 2 / PP 4 / EPC 1 / PP 4 / 92% EPC 1 + 8 o PP 2 The generalized structure of the film of Example 6 was A/B/C/B/A.
Relative layer thickness ratios:
1.5 : 3 : 1 : 3 : 1.5 7/930727.1 TXTMBQ 17 The inventor took the basic constructions of Table 4, and oriented them at generally higher racking ratios of 6 x ~. The result was a film showing improvements in ~i.a. lower) MVTR. Examples of these films are given below:
EXAMPLE FILM STRUCTURE
7 . 92 % EPC 1 + 8 % PP 2 / PP 4 / EAO 1 / PP ~ / 92% EPC 1 + 8% PP 2 The generalized structure of the fi7ln of Example' 7 was A/B/C/B/A. This film was like that of Example 5, but with both MD and TD racking ratios of about 6 x ~ in tYae longitudinal and transverse directions respectively.
Relative layer thickness ratios:
1.5 : 3 : 1 : 3 : 1.5.
Relative layer thickness ratios:
1.5 : 3 : 1 : 3 : 1.5 7/930727.1 TXTMBQ 17 The inventor took the basic constructions of Table 4, and oriented them at generally higher racking ratios of 6 x ~. The result was a film showing improvements in ~i.a. lower) MVTR. Examples of these films are given below:
EXAMPLE FILM STRUCTURE
7 . 92 % EPC 1 + 8 % PP 2 / PP 4 / EAO 1 / PP ~ / 92% EPC 1 + 8% PP 2 The generalized structure of the fi7ln of Example' 7 was A/B/C/B/A. This film was like that of Example 5, but with both MD and TD racking ratios of about 6 x ~ in tYae longitudinal and transverse directions respectively.
Relative layer thickness ratios:
1.5 : 3 : 1 : 3 : 1.5.
8. 92 % EPC 1 + 8 % PP 2 / FP 4 / E.~O 1 / PP 4 /° 92% EPC 1 + 8 % PP 2 The generalized structure of the film of Example 8 was A/B/C/B/A. This film was like that of Example 7, but oriented at a higher temperature compared to Example 7.
Relative layer thickness ratios:
1.5 : 3 : 1 : 3 : 1.5 9. 92 % EPC 1 + 8 % PP 2 / PP 4 / EA~J 2 / PP 4 / 9 2% EPC 1 + 8% PP 2 7/930727.1 TXTMBQ 18 The generalized structure of the film of Example 9 was A/B/C/B/A.
Relative layer th5.ckness ratios:
1.5 : 3 : 1 : 3 : 1.5.
. 92 % EPC 1 + 8% PP 2 / PP 4 / EPB 1 / PF 4 / 92 % EPC 1 + 8 % PP 2 The generalized structure of the film of Example 10 was A/B/c/B/A.
Relative layer thickness ratios:
1.5 : 3 : 1 : 3 : 1.5.
11. 92 % EPC 1 + 8 % PP 2 70 % PP 3 + 30 % HC 2 70 % PP 3 + 30% HC 2 92 % EPC 1 + 8 % PP 2 The generalized structure of the film of Example 11 was A/B/C/B/A.
Relative layer thickness ratios:
1.5 : 3 : 1 : 3 : 1:5.
12 . 90 % EPC 1 + 10 % PP 2 / PP 4 / EPC 1 / PP 4 / 90 % EPC 1 + 10 % PP 2 The generalized structure of the film of Example 12 was A/B/C/B/A.
7/930727.1 TXTMBQ 19 Relative layer thickness ratios:
1.5 : 3 : 1 : 3 : 1.5.
13 . 90% EPC 1 + 10% PP 2 / PP 4 / EPC 1 / PP 4 / 90% EPC 1 + 10 % PP 2 The generalized structure of the film of Example 13 was A/BJC/B/A. This film was like that of Example 12, but lower racking ratios of 4.5 x 4.5 to produce a film of 132 gauge thickness.
Relative layer thickness ratios:
1.5 :- 3 : 1 : 3 : 1.5.
14. 90% EPC 1 + 10% PP 2 / PP 4 / EPC 1 / PP 4 / g0% EPC 1 + 10% PP 2 The generalized structure of the film of Example 14 was A/B/C/B/A. This film was like that of Example 13, but with slightly higher racking ratios (4.5 x 5.0) and a final film thickness of 155 gauge.
Relative layer thickness ratios:
1.5 : 3 : 1 : 3 : 1.5.
15. 87.5% EPC 3 + 12.5% PP 2 EPC: 3 87.5% EPC 3 + 12.5% PP 2 The generalized structure of the film of Example 15 was A/B/C/B/A.
7/930727.1 TXTMBQ 20 Relative layer thickness ratios:
1.5 : 3 : 1 : 3 : 1.5.
16. 84% EPC 3 + 16% PP 2 84 % EPC 3 + 16 % PP 2 The generalized structure of the film of Example 16 was A/B/c/B/A.
Relative layer thickness ratios:
1.5 : 3 : 1 : 3 : 1.5.
17 . 86 % EPC 3 + 14 % PP 2 86 % EPC 3 + 14 % PP 2 The generalized structure of the film of Example 17 was A/B/C/B/A.
Relative layer thickness ratios:
1.5 : 3 : 1 : 3 : 1.5.
The inventor made a seven layer film (Example 18;8 as a control, and then made two moisture/oxygen barrier seven-layer films (Examples 19 and 20~ with good results. Examples of these films are given below:
7/930727.1 TXTMBQ 21 EXAMPLE FILM STRUCTURE
18. 92% EPC 1 + 8% PP 2 92% EPC 1 + 8% PP 2 The generalized structure of the film of Example 38 was A/B/C/D/C/B/A.
Relative layer thickness ratios:
1 : 2.5 : 1 : 1 : 1 : 2.5. . 1 19 . 92 % EPC 1 + 8 % PP 2 92 % EPC 1 + 8 % PP 2 The generalized structure of the film of Example 19 was A/B/C/D/C/B/A.
Relative layer thickness ratios:
1.5 : 2 : 1 : 1 : 1 : 2 : 1.5 7/930727.1 TXTMBQ 22 20. 92% EPC 1 + 8% PP 2 PP° 4 92 % EPC 1 + 8 % PP 2 The generalized structure of the film of Example 20 was A/B/C/D/C/B/A.
Relative layer thickness ratios:
1.5 : 2 : 1 : 1 : 1 : 2 : 1.5 Two alternative films of seven layers have the structure:
21. 92 % EPC 1 + 8 % PP 2 92 % EPC 1 + 8 % PP 2 The generalized structure of the film of Example 21 is A/B/C/D/C/B/A.
Relative layer thickness ratios:
1 : 2.5 : 1 : 1 : 1 : 2.5 .: 1 7/930727.1 TXTMBQ 23 22 . 92 o EPC 1 + 8 a pp 2 92~ EPC 1 + 8o PP 2 The generalized structure of the film of Example 22 is AeB/~iD/~/B/A.
Relative layer thickness ratios:
1 : 2.5 : 1 : 1 : 1 : 2.5 : 1 Twa additional alternative films of five layers were made, and are compared in Table 13 with the film of Example 17. These two additional films have the following structures:
23. 86% EPC 3 + 14% PP 2 85 o EPC 3 + 15 o HC 3 86% EPC 3 + 14o PP 2 The generalized structure of the film of Example 23 is A/B/C/B/A.
Relative layer thickness ratios:
1.5 : 3 : 1 : 3 : 1.5 7/930727.1 TXTNiBQ 24 24. 86% I85% EPC 3 + 15% HC 31 + 14% PP 2 85% EPC 3 + 15% HC 3 85% EPC 3 + 15% HC 3 The generalized structure of the film of Example 24 is A/B/C/B/C.
Relative layer thickness ratios:
1.5 : 3 : 1 : 3 : 1.5 7/930727.1 TXTMBQ ' 25 Example 1 Example 2 Example 3 Example 4 (control) Modulus LD 239,480 279,920 316,030 336,820 TD 214,690 260,240 298,930 316,820 Free Shrink/Shrink Tension at 200F:
TD 12/388 14/381 17/5:?8 17/504 at 220F:
TD 18/432 19,/383 24/540 25/548 at 240F:
at 260F:
7/930727.1 TXTMBQ 26 Haze Unshrunk 1.2 1.7 1.3 1.3 Shrunk 1.6 2.3 3.2 2.1 Clarity Unshrunk 81 8? 87 8g Shrunk 80 84 83 87 Gloss Film Thickness !,mils) (related to MVTR data given below) Unshrunk Actual 0.96 0.80 0.77 0.75 Unshrunk 0.60 0.67 0.60 0.55 Corrected for '75 gauge 0.77 0.71 0.62 0.55 7/930727.1 TXTMBQ 27 Unshrunk-0.49 0.55 0.48 0.45 Corrected for 75 gauge 0.63 0.59 0.49 0.45 7/930727.1 TXTMBQ 28 Example 7 Example 8 Example 9 Example 10 Modulus LD 271,200 299,200 ------- -------TD 292,100 337,900 ------_ _______ at 220F:
at 240F:
at 260F:
Lp __ __ 27 28 Haze Unshrunk --- --- 1.7 1.8 Clarityy tlnshrunk -- __ 82 84 7/930727.1 TXTMBQ 29 GLOSS
Film Thickness (mils) related to MVTR data given below) Unshrunk 0.86 0.76 0.86 0.77 Shrunk 1.00 0.97 ---- ----Unshrunk 0.51 0.56 ____ -___ Shrunk 0.41 0.46 ---- ----Corrected for 75 gauge Unshrunk 0.58 0.57 ---- ----Shrunk 0.55 0.59 ---- ----7/930727.1 TXTMBQ ~ 30 Unshrunk 0.45 0.47 0.42 0.43 Shrunk 0.35 0.38 ---- ---Corrected for 75 gauge Unshrunk 0.52 0.48 0.48 0.44 Shrunk 0.47 0.49 ---- _-__ Tear (grams) LD -- --- 8.6 5.0 TD -- °- 8.4 6.1 7/930727.1 TXTMBQ 31 Example 11 Example 12 Ex~am~le 13 Example 14 Modulus LD 345,750 352,880 322,950 320,470 TD 374,990 392,020 334,660 319,420 Free Shrink at 240F:
LD 20~ 17 18 14 daze Unshrunk 48.5 1.3 3.3 5.3 Clarity Unshrunk Gloss 7/930727.1 TXTMBQ 32 Film Thickness (mils) (related to MVTR data given below}
Unshrunk 0.85 0.81 1.40 1.60 Unshrunk 0.36 0.36 0.23 0.19 Corrected for ~75 Gauge 0.41 0.39 0.43 0.41 Tear (grams) LD -- -- 8.6 5.0 TD -- -- 8.4 6.1 7/930727.1 TXTMBQ 33 Example 19 Exazrtple 20 Modulus LD 300,890 307,3$0 TD 315,460 291,480 Free Shrink/Shrink Tension at 220F:
at 240F:
at 260F:
at 280F:
at 300F:
7/930727.1 TXTMBQ 34 ilaZe Unshrurlk 1.6 1.8 Clarity Unshrunk 76 76 Gloss Film Thickness (mils) (related to M'ITR data given below) Unshrunk 1.09 1.12 IrIVTR 2 Non-shrunk 0.35 0.33 Corrected for 75 gauge 0.51 0.49 Tear 7/930727.1 TXTMBQ , 35 Tensile LD 19,415 20,407 TD 19;296 16,990 Elonqatian 3.0 4.5 7/930727.1 TXTMBQ 36 Example 17 Example 23 Example 24 ~lodulus LD 398,000 420,000 437,000 TD 442,000 473,000 488,000 at 220°F:
at 240F:
at 260F:
at 280F:
at 30bF:
7/930727.1 TXTMBQ 37 Haze Unshrunk 1.8 2.0 1.2 Clarity Unshrunk 82 81 82 Gloss Film Thickness (mils) (related to MVTR data given below) Unshrunk 0.89 0.91 0.82 Unshrunk 0.33 0.36 0.33 Corrected for 75 gauge 0.39 0.44 0.36 Tear 7/930727.1 TXTNlBQ 38 Tensile LD 28,000 31,000 28,000 TD 29,000 33,000 29,000 Elongation 7/930727.1 TXTMDQ 39 In a typical working example of making the film of the present invention:
An ethylene propylene copolymer (Fins 8473) containing about 4% by weight ethylene, was blended with the polypropylene .in a blend ratio of about 92% by weight EPC and 8% by weight PP. (The PP percentage includes the additives discussed above).
The EPC/PP blend was then blended with a hydrocarbon resin (Regalrez 1128 from Hercules) in a blend ratio of about 90% by weight EPC/PP and 10% by weight HC.
A second blend was also prepared, in a blend ratio of about 84.5% by weight PP (Exxon PD 4062 E7), 15% by weight HC (Regalrez 1128), and 0.5%
white mineral oil (Kaydol from Y~itco Chemical).
A circular coextrusion die was fed with three extruders to prepare a five layer shrink film. One extruder was used to feed the blend of EPC
or polypropylene, and HC, as a melt to the e~aru~ion die to form the outer layers. Another extruder fed a polypropylene (Exxon PD 4062 E7) to the extrusion die to provide the intermediate layers in the mufti-layer film. The third extruder provided the second blend of PP
and HC to the extrusion die.
The extruded tape was rapidly cooled to room temperature and collapsed by pinch rolls. The tape was subsequently heated to an orientation temperature. Using a bubble technique will known in the art, internal air pressure stretched the tape to about 4.5 times its unstretched dimensions in the longitudinal (machine) direction and about 4.0 times its unstretched dimensions in the transverse direction to form a bubble which provided biaxial orientation to the resulting film. The bubble was then rapidly cooled by chilled air in order to maintain the oriented state of the film. Finally, the bubble was collapsed and the expanded film gathered on a take-up roll. After orientation, the total wall thickness of the film was about one mil with 50% of the structure being the blend of ethylene propylene copolymers.- and polypropylene; 150 7/930727.1 TXTMBQ . 40 of the structure being the intermediate layers~ and the remainder or 35%
of the structure being the core layer.
It will be clear to one skilled in the art that the degree of stretching may be varied to obtain the desired degree of film gauge or thickness and to regulate the desired amount of shrink tension, free shrink, and other shrink properties of the final film, depending on the packaging application. Preferred stretching or racking ratios are between about 3.0 and 8.0 in both the machine and transverse directions.
The mufti-layer film of the present invention is preferably not irradiated. However, the sealant material, if extrusion laminated, extrusion coated, or conventionally laminated to the substrate moisture barrier film, can itself be irradiated or electronically or chemically crosslinked prior to lamination. Irradiation may be accomplishe~3 by means well known in the art.
The blend ratios of the EPC and PP may be varied according to desired properties or end-use of the mufti-layer film. For example, increasing the polypropylene in the blend wi7.1 add stiffness to the film, but also increase the sealing temperature of the film.
Conversely, increasing the EPC in the blend tends to lower the shrink temperature of the oriented film, or to increase shrink at the same temperature, and also lowers the sealing temperature of the film. A
preferred blend includes between about 4 a and 15 o PP and between about 96% and 85% EPC.
The multilayer film of the present invention is preferably oriented either monoaxially or biaxially, and preferably used as a shrink film.
Optionally, the oriented film may be further processed by reheating the film to a temperature near its orientation temperature, i.e. either somewhat below, at, or somewhat about its orientation temperature, to heat set the film. This future processing step has the advantage of substantially retaining many of the favorable physical characteristics of an oriented film, such as higher tensile strength; modulus and 7/930727.1 TXTMBQ 41 improved optical properties, while providing a substantial shrink-free film in applications where a shrink feature is undesirable.
The film of the present invention can utilize hydrocarbon resin in at least one or more, or even all the layers of the film, as long as the HC resin in any given layer is compatible from a process and performance point of view with the resin with which it is blended.
Films in accordance with this invention are preferably oriented, and preferably heat shrinkable. Preferred films exhibit a free shrink at 240° F of at least 10a (LD) and 15% (TD), more preferably at least 15%
(LD) and 22% (TD).
Obvious modifications to the invention as described may be made by one skilled in the art without departing from the spirit and scope of the claims as presented below.
7/930727.1 TXTMBQ 42
Relative layer thickness ratios:
1.5 : 3 : 1 : 3 : 1.5 9. 92 % EPC 1 + 8 % PP 2 / PP 4 / EA~J 2 / PP 4 / 9 2% EPC 1 + 8% PP 2 7/930727.1 TXTMBQ 18 The generalized structure of the film of Example 9 was A/B/C/B/A.
Relative layer th5.ckness ratios:
1.5 : 3 : 1 : 3 : 1.5.
. 92 % EPC 1 + 8% PP 2 / PP 4 / EPB 1 / PF 4 / 92 % EPC 1 + 8 % PP 2 The generalized structure of the film of Example 10 was A/B/c/B/A.
Relative layer thickness ratios:
1.5 : 3 : 1 : 3 : 1.5.
11. 92 % EPC 1 + 8 % PP 2 70 % PP 3 + 30 % HC 2 70 % PP 3 + 30% HC 2 92 % EPC 1 + 8 % PP 2 The generalized structure of the film of Example 11 was A/B/C/B/A.
Relative layer thickness ratios:
1.5 : 3 : 1 : 3 : 1:5.
12 . 90 % EPC 1 + 10 % PP 2 / PP 4 / EPC 1 / PP 4 / 90 % EPC 1 + 10 % PP 2 The generalized structure of the film of Example 12 was A/B/C/B/A.
7/930727.1 TXTMBQ 19 Relative layer thickness ratios:
1.5 : 3 : 1 : 3 : 1.5.
13 . 90% EPC 1 + 10% PP 2 / PP 4 / EPC 1 / PP 4 / 90% EPC 1 + 10 % PP 2 The generalized structure of the film of Example 13 was A/BJC/B/A. This film was like that of Example 12, but lower racking ratios of 4.5 x 4.5 to produce a film of 132 gauge thickness.
Relative layer thickness ratios:
1.5 :- 3 : 1 : 3 : 1.5.
14. 90% EPC 1 + 10% PP 2 / PP 4 / EPC 1 / PP 4 / g0% EPC 1 + 10% PP 2 The generalized structure of the film of Example 14 was A/B/C/B/A. This film was like that of Example 13, but with slightly higher racking ratios (4.5 x 5.0) and a final film thickness of 155 gauge.
Relative layer thickness ratios:
1.5 : 3 : 1 : 3 : 1.5.
15. 87.5% EPC 3 + 12.5% PP 2 EPC: 3 87.5% EPC 3 + 12.5% PP 2 The generalized structure of the film of Example 15 was A/B/C/B/A.
7/930727.1 TXTMBQ 20 Relative layer thickness ratios:
1.5 : 3 : 1 : 3 : 1.5.
16. 84% EPC 3 + 16% PP 2 84 % EPC 3 + 16 % PP 2 The generalized structure of the film of Example 16 was A/B/c/B/A.
Relative layer thickness ratios:
1.5 : 3 : 1 : 3 : 1.5.
17 . 86 % EPC 3 + 14 % PP 2 86 % EPC 3 + 14 % PP 2 The generalized structure of the film of Example 17 was A/B/C/B/A.
Relative layer thickness ratios:
1.5 : 3 : 1 : 3 : 1.5.
The inventor made a seven layer film (Example 18;8 as a control, and then made two moisture/oxygen barrier seven-layer films (Examples 19 and 20~ with good results. Examples of these films are given below:
7/930727.1 TXTMBQ 21 EXAMPLE FILM STRUCTURE
18. 92% EPC 1 + 8% PP 2 92% EPC 1 + 8% PP 2 The generalized structure of the film of Example 38 was A/B/C/D/C/B/A.
Relative layer thickness ratios:
1 : 2.5 : 1 : 1 : 1 : 2.5. . 1 19 . 92 % EPC 1 + 8 % PP 2 92 % EPC 1 + 8 % PP 2 The generalized structure of the film of Example 19 was A/B/C/D/C/B/A.
Relative layer thickness ratios:
1.5 : 2 : 1 : 1 : 1 : 2 : 1.5 7/930727.1 TXTMBQ 22 20. 92% EPC 1 + 8% PP 2 PP° 4 92 % EPC 1 + 8 % PP 2 The generalized structure of the film of Example 20 was A/B/C/D/C/B/A.
Relative layer thickness ratios:
1.5 : 2 : 1 : 1 : 1 : 2 : 1.5 Two alternative films of seven layers have the structure:
21. 92 % EPC 1 + 8 % PP 2 92 % EPC 1 + 8 % PP 2 The generalized structure of the film of Example 21 is A/B/C/D/C/B/A.
Relative layer thickness ratios:
1 : 2.5 : 1 : 1 : 1 : 2.5 .: 1 7/930727.1 TXTMBQ 23 22 . 92 o EPC 1 + 8 a pp 2 92~ EPC 1 + 8o PP 2 The generalized structure of the film of Example 22 is AeB/~iD/~/B/A.
Relative layer thickness ratios:
1 : 2.5 : 1 : 1 : 1 : 2.5 : 1 Twa additional alternative films of five layers were made, and are compared in Table 13 with the film of Example 17. These two additional films have the following structures:
23. 86% EPC 3 + 14% PP 2 85 o EPC 3 + 15 o HC 3 86% EPC 3 + 14o PP 2 The generalized structure of the film of Example 23 is A/B/C/B/A.
Relative layer thickness ratios:
1.5 : 3 : 1 : 3 : 1.5 7/930727.1 TXTNiBQ 24 24. 86% I85% EPC 3 + 15% HC 31 + 14% PP 2 85% EPC 3 + 15% HC 3 85% EPC 3 + 15% HC 3 The generalized structure of the film of Example 24 is A/B/C/B/C.
Relative layer thickness ratios:
1.5 : 3 : 1 : 3 : 1.5 7/930727.1 TXTMBQ ' 25 Example 1 Example 2 Example 3 Example 4 (control) Modulus LD 239,480 279,920 316,030 336,820 TD 214,690 260,240 298,930 316,820 Free Shrink/Shrink Tension at 200F:
TD 12/388 14/381 17/5:?8 17/504 at 220F:
TD 18/432 19,/383 24/540 25/548 at 240F:
at 260F:
7/930727.1 TXTMBQ 26 Haze Unshrunk 1.2 1.7 1.3 1.3 Shrunk 1.6 2.3 3.2 2.1 Clarity Unshrunk 81 8? 87 8g Shrunk 80 84 83 87 Gloss Film Thickness !,mils) (related to MVTR data given below) Unshrunk Actual 0.96 0.80 0.77 0.75 Unshrunk 0.60 0.67 0.60 0.55 Corrected for '75 gauge 0.77 0.71 0.62 0.55 7/930727.1 TXTMBQ 27 Unshrunk-0.49 0.55 0.48 0.45 Corrected for 75 gauge 0.63 0.59 0.49 0.45 7/930727.1 TXTMBQ 28 Example 7 Example 8 Example 9 Example 10 Modulus LD 271,200 299,200 ------- -------TD 292,100 337,900 ------_ _______ at 220F:
at 240F:
at 260F:
Lp __ __ 27 28 Haze Unshrunk --- --- 1.7 1.8 Clarityy tlnshrunk -- __ 82 84 7/930727.1 TXTMBQ 29 GLOSS
Film Thickness (mils) related to MVTR data given below) Unshrunk 0.86 0.76 0.86 0.77 Shrunk 1.00 0.97 ---- ----Unshrunk 0.51 0.56 ____ -___ Shrunk 0.41 0.46 ---- ----Corrected for 75 gauge Unshrunk 0.58 0.57 ---- ----Shrunk 0.55 0.59 ---- ----7/930727.1 TXTMBQ ~ 30 Unshrunk 0.45 0.47 0.42 0.43 Shrunk 0.35 0.38 ---- ---Corrected for 75 gauge Unshrunk 0.52 0.48 0.48 0.44 Shrunk 0.47 0.49 ---- _-__ Tear (grams) LD -- --- 8.6 5.0 TD -- °- 8.4 6.1 7/930727.1 TXTMBQ 31 Example 11 Example 12 Ex~am~le 13 Example 14 Modulus LD 345,750 352,880 322,950 320,470 TD 374,990 392,020 334,660 319,420 Free Shrink at 240F:
LD 20~ 17 18 14 daze Unshrunk 48.5 1.3 3.3 5.3 Clarity Unshrunk Gloss 7/930727.1 TXTMBQ 32 Film Thickness (mils) (related to MVTR data given below}
Unshrunk 0.85 0.81 1.40 1.60 Unshrunk 0.36 0.36 0.23 0.19 Corrected for ~75 Gauge 0.41 0.39 0.43 0.41 Tear (grams) LD -- -- 8.6 5.0 TD -- -- 8.4 6.1 7/930727.1 TXTMBQ 33 Example 19 Exazrtple 20 Modulus LD 300,890 307,3$0 TD 315,460 291,480 Free Shrink/Shrink Tension at 220F:
at 240F:
at 260F:
at 280F:
at 300F:
7/930727.1 TXTMBQ 34 ilaZe Unshrurlk 1.6 1.8 Clarity Unshrunk 76 76 Gloss Film Thickness (mils) (related to M'ITR data given below) Unshrunk 1.09 1.12 IrIVTR 2 Non-shrunk 0.35 0.33 Corrected for 75 gauge 0.51 0.49 Tear 7/930727.1 TXTMBQ , 35 Tensile LD 19,415 20,407 TD 19;296 16,990 Elonqatian 3.0 4.5 7/930727.1 TXTMBQ 36 Example 17 Example 23 Example 24 ~lodulus LD 398,000 420,000 437,000 TD 442,000 473,000 488,000 at 220°F:
at 240F:
at 260F:
at 280F:
at 30bF:
7/930727.1 TXTMBQ 37 Haze Unshrunk 1.8 2.0 1.2 Clarity Unshrunk 82 81 82 Gloss Film Thickness (mils) (related to MVTR data given below) Unshrunk 0.89 0.91 0.82 Unshrunk 0.33 0.36 0.33 Corrected for 75 gauge 0.39 0.44 0.36 Tear 7/930727.1 TXTNlBQ 38 Tensile LD 28,000 31,000 28,000 TD 29,000 33,000 29,000 Elongation 7/930727.1 TXTMDQ 39 In a typical working example of making the film of the present invention:
An ethylene propylene copolymer (Fins 8473) containing about 4% by weight ethylene, was blended with the polypropylene .in a blend ratio of about 92% by weight EPC and 8% by weight PP. (The PP percentage includes the additives discussed above).
The EPC/PP blend was then blended with a hydrocarbon resin (Regalrez 1128 from Hercules) in a blend ratio of about 90% by weight EPC/PP and 10% by weight HC.
A second blend was also prepared, in a blend ratio of about 84.5% by weight PP (Exxon PD 4062 E7), 15% by weight HC (Regalrez 1128), and 0.5%
white mineral oil (Kaydol from Y~itco Chemical).
A circular coextrusion die was fed with three extruders to prepare a five layer shrink film. One extruder was used to feed the blend of EPC
or polypropylene, and HC, as a melt to the e~aru~ion die to form the outer layers. Another extruder fed a polypropylene (Exxon PD 4062 E7) to the extrusion die to provide the intermediate layers in the mufti-layer film. The third extruder provided the second blend of PP
and HC to the extrusion die.
The extruded tape was rapidly cooled to room temperature and collapsed by pinch rolls. The tape was subsequently heated to an orientation temperature. Using a bubble technique will known in the art, internal air pressure stretched the tape to about 4.5 times its unstretched dimensions in the longitudinal (machine) direction and about 4.0 times its unstretched dimensions in the transverse direction to form a bubble which provided biaxial orientation to the resulting film. The bubble was then rapidly cooled by chilled air in order to maintain the oriented state of the film. Finally, the bubble was collapsed and the expanded film gathered on a take-up roll. After orientation, the total wall thickness of the film was about one mil with 50% of the structure being the blend of ethylene propylene copolymers.- and polypropylene; 150 7/930727.1 TXTMBQ . 40 of the structure being the intermediate layers~ and the remainder or 35%
of the structure being the core layer.
It will be clear to one skilled in the art that the degree of stretching may be varied to obtain the desired degree of film gauge or thickness and to regulate the desired amount of shrink tension, free shrink, and other shrink properties of the final film, depending on the packaging application. Preferred stretching or racking ratios are between about 3.0 and 8.0 in both the machine and transverse directions.
The mufti-layer film of the present invention is preferably not irradiated. However, the sealant material, if extrusion laminated, extrusion coated, or conventionally laminated to the substrate moisture barrier film, can itself be irradiated or electronically or chemically crosslinked prior to lamination. Irradiation may be accomplishe~3 by means well known in the art.
The blend ratios of the EPC and PP may be varied according to desired properties or end-use of the mufti-layer film. For example, increasing the polypropylene in the blend wi7.1 add stiffness to the film, but also increase the sealing temperature of the film.
Conversely, increasing the EPC in the blend tends to lower the shrink temperature of the oriented film, or to increase shrink at the same temperature, and also lowers the sealing temperature of the film. A
preferred blend includes between about 4 a and 15 o PP and between about 96% and 85% EPC.
The multilayer film of the present invention is preferably oriented either monoaxially or biaxially, and preferably used as a shrink film.
Optionally, the oriented film may be further processed by reheating the film to a temperature near its orientation temperature, i.e. either somewhat below, at, or somewhat about its orientation temperature, to heat set the film. This future processing step has the advantage of substantially retaining many of the favorable physical characteristics of an oriented film, such as higher tensile strength; modulus and 7/930727.1 TXTMBQ 41 improved optical properties, while providing a substantial shrink-free film in applications where a shrink feature is undesirable.
The film of the present invention can utilize hydrocarbon resin in at least one or more, or even all the layers of the film, as long as the HC resin in any given layer is compatible from a process and performance point of view with the resin with which it is blended.
Films in accordance with this invention are preferably oriented, and preferably heat shrinkable. Preferred films exhibit a free shrink at 240° F of at least 10a (LD) and 15% (TD), more preferably at least 15%
(LD) and 22% (TD).
Obvious modifications to the invention as described may be made by one skilled in the art without departing from the spirit and scope of the claims as presented below.
7/930727.1 TXTMBQ 42
Claims (3)
1. A thermoplastic heat shrinkable, multi-layer film, comprising:
(a) a core layer comprising a material selected from the group consisting of:
i) ethylene alpha olefin copolymer, ii) ethylene propylene copolymer, iii) rubber modified EPC, and iv) ethylene propylene butene terpolymer;
(b) two intermediate layers, on opposite surfaces of the core layer, comprising a blend of propylene polymer or copolymer, and a hydrocarbon resin; and (c) two outer layers comprising a polymeric material selected from the group consisting of:
i) propylene polymer, ii) propylene copolymer, iii) ethylene alpha olefin copolymer, iv) ionomer, v) polybutene, and vi) blends thereof;
wherein the film exhibits a free shrink, at 240°F, of at least 10% in the longitudinal direction, and at least 15% in the transverse direction.
(a) a core layer comprising a material selected from the group consisting of:
i) ethylene alpha olefin copolymer, ii) ethylene propylene copolymer, iii) rubber modified EPC, and iv) ethylene propylene butene terpolymer;
(b) two intermediate layers, on opposite surfaces of the core layer, comprising a blend of propylene polymer or copolymer, and a hydrocarbon resin; and (c) two outer layers comprising a polymeric material selected from the group consisting of:
i) propylene polymer, ii) propylene copolymer, iii) ethylene alpha olefin copolymer, iv) ionomer, v) polybutene, and vi) blends thereof;
wherein the film exhibits a free shrink, at 240°F, of at least 10% in the longitudinal direction, and at least 15% in the transverse direction.
2. A thermoplastic multi-layer film, comprising:
(a) a core layer comprising high density polyethylene;
(b) two intermediate layers, on opposite surfaces of the core layer, comprising a polymeric material selected from the group consisting of:
i) polymeric adhesive;
ii) ethylene vinyl acetate copolymer; and iii) ethylene alpha olefin copolymer;
(c) two outer layers comprising a blend of propylene polymer or copolymer, and a hydrocarbon resin; and (d) two outermost layers comprising propylene polymer or copolymer, polybutene, or blends thereof.
(a) a core layer comprising high density polyethylene;
(b) two intermediate layers, on opposite surfaces of the core layer, comprising a polymeric material selected from the group consisting of:
i) polymeric adhesive;
ii) ethylene vinyl acetate copolymer; and iii) ethylene alpha olefin copolymer;
(c) two outer layers comprising a blend of propylene polymer or copolymer, and a hydrocarbon resin; and (d) two outermost layers comprising propylene polymer or copolymer, polybutene, or blends thereof.
3. The film of claim 2, which is oriented and heat shrinkable.
Applications Claiming Priority (5)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US94724492A | 1992-09-18 | 1992-09-18 | |
| US07/947,244 | 1992-09-18 | ||
| US08/116,798 | 1993-09-10 | ||
| US08/116,798 US5482771A (en) | 1992-09-18 | 1993-09-10 | Moisutre barrier film |
| CA 2106258 CA2106258C (en) | 1992-09-18 | 1993-09-15 | Moisture barrier film |
Related Parent Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2106258 Division CA2106258C (en) | 1992-09-18 | 1993-09-15 | Moisture barrier film |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2417184A1 CA2417184A1 (en) | 1994-03-19 |
| CA2417184C true CA2417184C (en) | 2003-12-09 |
Family
ID=27169591
Family Applications (3)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002417182A Expired - Fee Related CA2417182C (en) | 1992-09-18 | 1993-09-15 | Moisture barrier film |
| CA002417179A Expired - Fee Related CA2417179C (en) | 1992-09-18 | 1993-09-15 | Moisture barrier film |
| CA002417184A Expired - Fee Related CA2417184C (en) | 1992-09-18 | 1993-09-15 | Moisture barrier film |
Family Applications Before (2)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002417182A Expired - Fee Related CA2417182C (en) | 1992-09-18 | 1993-09-15 | Moisture barrier film |
| CA002417179A Expired - Fee Related CA2417179C (en) | 1992-09-18 | 1993-09-15 | Moisture barrier film |
Country Status (1)
| Country | Link |
|---|---|
| CA (3) | CA2417182C (en) |
-
1993
- 1993-09-15 CA CA002417182A patent/CA2417182C/en not_active Expired - Fee Related
- 1993-09-15 CA CA002417179A patent/CA2417179C/en not_active Expired - Fee Related
- 1993-09-15 CA CA002417184A patent/CA2417184C/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| CA2417179A1 (en) | 1994-03-19 |
| CA2417184A1 (en) | 1994-03-19 |
| CA2417182C (en) | 2003-12-02 |
| CA2417182A1 (en) | 1994-03-19 |
| CA2417179C (en) | 2003-11-04 |
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