US0087.09611B2
`
`(12) United States Patent
`Haley
`
`(10) Patent No.:
`(45) Date of Patent:
`
`US 8,709,611 B2
`Apr. 29, 2014
`
`(54) MULTILAYER FILMS HAVING REDUCED
`CURLING
`
`(75) Inventor: Jeffrey C. Haley, Cincinnati, OH (US)
`(73) Assignee: Fightar Chemicals, LP, Houston, TX
`
`(*) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 204 days.
`
`(21) Appl. No.: 12/802,523
`
`(22) Filed:
`
`Jun. 8, 2010
`
`(65)
`
`Prior Publication Data
`US 2011 FO3OO391 A1
`Dec. 8, 2011
`(51) Int. Cl.
`B32B 27/08
`(2006.01)
`B32B 27/00
`(2006.01)
`B32B 27/30
`(2006.01)
`B32B 27/32
`(2006.01)
`B29C 65/00
`(2006.01)
`(52) U.S. Cl.
`USPC ..................... 428/516; 428/4744; 428/476.9;
`428/522; 428/523: 156/60
`(58) Field of Classification Search
`None
`See application file for complete search history.
`
`(56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`4/2004 Botros
`6,716,928 B2
`7,569,630 B2 * 8/2009 Ma et al. ....................... 524,221
`2004/OO38055 A1
`2/2004 Hawighorst
`2008/0227900 A1* 9, 2008 Borke et al. .................. 524,388
`2009/00291.82 A1
`1/2009 Aubee et al. ............... 428,476.9
`OTHER PUBLICATIONS
`Barry A. Morris, DuPont, Wilmington, Delaware, “Reducing Curlin
`Multilayer Blown Film. Part I: Experimental Results, Model Devel
`opment and Strategies.” Presented at 2001 TAPPI Polymers, Lami
`nations and Coatings Conference, Aug. 27-30, 2001.
`Barry A. Morris, DuPont, Wilmington, Delaware, “Reducing Curlin
`Multilayer Blown Film. Part II: Application of Predictive Modeling
`to a Barrier Cereal Liner Film.” Presented at 2001 TAPPI Polymers,
`Laminations and Coatings Conference, Aug. 27-30, 2001.
`PCT International Search Report and the Written Opinion—Mailed
`Nov. 21, 2011 for Corresponding PCT/IB2011/00 1680.
`* cited by examiner
`
`Primary Examiner — Sheeba Ahmed
`
`(57)
`ABSTRACT
`Disclosed is a multilayer film. The multilayer film has the
`general structure of A/B/A/C or B/A/B/C, wherein A is a
`nucleated high density polyethylene (HDPE) layer. B is a
`single or multilayer structure, and C is a seal layer. Adding a
`nucleating agent to HDPE improves the water vapor barrier
`property of the HDPE layer and the multilayer film, but it also
`causes the multilayer film to curl in the conventional multi
`layer film structures. The invention provides a multilayer
`film, which includes at least one layer of nucleated HDPE,
`with reduced or eliminated curling while retaining high water
`vapor barrier.
`
`4,906,172 A *
`6,306,996 B1
`
`3, 1990 Stewart ...................... 425, 1744
`10, 2001 Cecchin et al.
`
`15 Claims, No Drawings
`
`EPL LIMITED EX1006
`U.S. Patent No. 10,889,093
`
`0001
`
`

`

`1.
`MULTILAYER FILMS HAVING REDUCED
`CURLING
`
`US 8,709,611 B2
`
`FIELD OF THE INVENTION
`
`The invention relates to a multilayer film. More particu
`larly, the invention relates to a multilayer film that possesses
`good water vapor barrier property and reduced curling.
`
`BACKGROUND OF THE INVENTION
`
`10
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`15
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`Polyethylene is widely used to prepare food packaging
`films and bags such as cereal liners and cake mix bags, gro
`cery bags, stretch-wraps, shrink-wraps, garbage can liners,
`and shipping bags. Some applications, such as food packag
`ing films and bags, require films to have sufficient water vapor
`and oxygen barrier properties to preserve the contents. The
`packaging films usually have a multilayer structure. Depend
`ing on the intended application, the number, type, and
`arrangement of layers employed will vary. Ethylene-vinyl
`alcohol (EVOH) copolymers and polyamides (nylons) are
`often used as barrier layers. Polyethylene is often used as one
`or more layers.
`High density polyethylene (HDPE) is often used as a layer
`in the multilayer films because of its high strength and modu
`25
`lus. HDPE can be nucleated. Nucleated HDPE has improved
`water vapor barrier property. Thus when nucleated HDPE is
`used as a layer in a multilayer film, it provides the film not
`only with physical strength but also with increased barrier to
`water vapor. One problem associated with the use of nucle
`ated HDPE in a multilayer film is that nucleated HDPE causes
`the multilayer films to curl to a greater extent. The curling
`brings inconvenience to the film manufacturers and consum
`ers. Therefore, there is a need to reduce or eliminate the
`curling of multilayer film caused by the use of nucleated
`HDPE.
`
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`SUMMARY OF THE INVENTION
`
`45
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`The invention relates to a multilayer film. By “film. I mean
`40
`to include both films (which are normally referred to those
`having a thickness less than or equal to 10 mils) and sheets
`(which are normally referred to those having a thickness
`greater than 10 mils). The multilayer film of the invention has
`the general structure of A/B/A/C or B/A/B/C, wherein A is a
`nucleated high density polyethylene (HDPE) layer, B is a
`single or multilayer structure, and C is a seal layer. Preferably
`the seal layer C is selected from the group consisting of linear
`low density polyethylenes (LLDPE), low density polyethyl
`enes (LDPE), ethylene-vinyl acetate copolymers (EVA),
`polyolefin ionomers, the like, and mixtures thereof. Adding a
`nucleating agent to HDPE improves the water vapor barrier
`property of the HDPE layer and the multilayer film thereby.
`However, nucleated HDPE causes the multilayer film to curl
`to a greater extent in the conventional multilayer film struc
`tures. The invention provides a multilayer film, which
`includes at least one layer of nucleated HDPE, with reduced
`or eliminated curling while retaining high water vapor barrier.
`
`50
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`55
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`DETAILED DESCRIPTION OF THE INVENTION
`
`60
`
`The invention is a multilayer film. The multilayer film has
`the general structure of A/B/A/C or B/A/B/C, wherein A is a
`nucleated high density polyethylene (HDPE) layer, B is a
`single or multilayer structure, and C is a seal layer. By “nucle
`ated HDPE, I mean that the HDPE contains a nucleating
`agent. Unless specified as “nucleated HDPE in this appli
`
`65
`
`2
`cation, the term HDPE refers only to those which do not
`contain nucleating agents. By 'seal layer.' I mean the layer of
`the multilayer film which softens at lower temperature than
`the rest layers of the film structure, so that the film can be heat
`sealed. Seal layer may directly contact with the goods, such as
`meat or vegetables, protected by the multilayer film.
`Suitable nucleated HDPE comprises a nucleating agent
`and an HDPE resin. Suitable HDPE for making the nucleated
`HDPE includes ethylene homopolymers and copolymers of
`ethylene and C-olefins. Suitable O.-olefins include 1-butene,
`1-hexene, and 1-octene, the like, and mixtures thereof. Pref
`erably, the C-olefin content in the nucleated HDPE is less than
`2 wt %. The nucleated HDPE has a density preferably within
`the range of 0.940 to 0.970 g/cm, and more preferably within
`the range of 0.945 to 0.965 g/cm. The nucleated HDPE has
`a melt index MI preferably within the range of 0.001 to 100
`dg/min, and more preferably within the range of 0.05 to 50
`dg/min. Density is measured according to ASTM D1505; and
`MI is measured according to ASTM D 1238 at 190° C. and
`2.16 kg. Unless specifically mentioned, all density and MI in
`this application are measured according to these ASTM meth
`ods.
`The nucleated HDPE can be multimodal. By “multimo
`dal. I mean that the nucleated HDPE comprises at least two
`components, one of which has a relatively low molecular
`weight, and the other which has a relatively high molecular
`weight. Many HDPE resins are commercially available; for
`instance L5885 and M6020 HDPE are resins from Equistar
`Chemicals, LP. They can be readily nucleated by a nucleating
`agent.
`Suitable nucleating agents for making the nucleated HDPE
`include those known to the industry. Preferably, the nucleat
`ing agents are selected from the group consisting of glycerol
`alkoxide salts, hexahydrophthalic acid salts, the like, and
`mixtures thereof. The salts include ammonium and metal
`salts. Preferably, the glycerol alkoxide salt is selected from
`the group consisting of Zinc, magnesium, and calcium glyc
`erolates and mixtures thereof. More preferably, the glycerol
`alkoxide salt is a zinc glycerolate. Preferably, the hexahydro
`phthalic acid salt is selected from the group consisting of zinc,
`magnesium, and calcium hexahydrophthalates, the like, and
`mixtures thereof. More preferably, the hexahydrophthalic
`acid salt is calcium hexahydrophthalate. Many glycerol
`alkoxide salts and hexahydrophthalic acid salts are commer
`cially available. For instance, Zinc glycerolate is available
`from Ciba Specialty Chemicals as Irgastab(R) 287. Calcium
`hexahydrophthalate is available from Milliken Company as
`Hyperform(RHPN-20E. The amount of nucleating agent used
`in the nucleated HDPE varies depending on many factors
`such as the nucleating agent type, the properties of the HDPE,
`and the targeted improvement of the barrier properties. In
`general, the nucleating agent is used in an amount within the
`range of 0.01 to 1 wt % of the HDPE. Preferably, the amount
`of the nucleating agent is within the range of 0.05 to 0.5 wt %
`of the HDPE.
`The seal layer C is preferably selected from the group
`consisting of linear low density polyethylene (LLDPE), low
`density polyethylene (LDPE), ethylene-vinyl acetate copoly
`mers (EVA), polyolefin ionomers, the like, and mixtures
`thereof. Suitable LLDPE resins include copolymers of ethyl
`ene and C-olefins. Suitable C-olefins include 1-butene, 1-hex
`ene, and 1-octene, the like, and mixtures thereof. The C-olefin
`content in the LLPDE is preferably within the range of 5 to 15
`wt %. The LLDPE has a density preferably within the range of
`0.865 to 0.935 g/cm, and more preferably within the range
`0.905 to 0.935 g/cm. The LLDPE has a melt index MI
`preferably within the range of 0.5 to 50 dg/min, and more
`
`0002
`
`

`

`US 8,709,611 B2
`
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`3
`preferably within the range of 1 to 15 dg/min. Many LLDPE
`resins are commercially available; for instance GS707
`LLDPE and GA501 are from Equistar Chemicals, LP.
`Suitable LDPE for use in the invention include those
`known to the industry. LDPE is usually made by free radical
`polymerization under high pressure. There are two basic pro
`cesses for the manufacture of LDPE: autoclave and tubular.
`Both autoclave LDPE and tubular LDPE are Suitable for use
`in the invention. The LDPE has a density preferably within
`the range of 0.915 to 0.935 g/cm, and more preferably within
`the range of 0.918 to 0.932 g/cm. The LDPE has a melt index
`MI preferably within the range of 0.1 to 100 dg/min, and
`more preferably within the range of 0.5 to 50 dg/min. Many
`LDPE resins are commercially available and suitable for use
`as a seal layer. An example of suitable LDPE resin is Petroth
`ene NA860 from Equistar Chemicals, LP. Ethylene-vinyl
`acetate copolymers (EVA) are made by the free radical copo
`lymerization of ethylene and vinyl acetate. Suitable EVA
`comprises preferably from 2 to 30 wt % of vinyl acetate, and
`more preferably from 5 to 18 wt % of vinyl acetate. The
`suitable EVA has a melt index MI preferably within the range
`of 2 to 500 dg/min. Many EVA resins are commercially
`available; for instance, EVA UE624 is a product of Equistar
`Chemicals, LP. Suitable polyolefin ionomers include ammo
`25
`nium and metal salts of olefin-acrylic acid and olefin-meth
`acrylic acid copolymers. Examples are sodium, Zinc, and
`magnesium salts of ethylene-acrylic acid copolymers and
`ethylene-methacrylic acid copolymers. Many polyolefin
`ionomers are commercially available; for instance, the Sur
`lyn Rionomers is from Du Pont Chemical Company.
`Layer B can be a single layer or a multilayer structure.
`When B is a single layer, it is preferably a polyolefin layer.
`Suitable polyolefin for use as a Blayer in the multilayer film
`of the invention is preferably selected from the group consist
`ing of polyethylene, polypropylene, and poly 1-butene. Suit
`able polyethylene include the above-discussed HDPE,
`LLDPE, and LDPE, the like, and mixtures. Suitable polypro
`pylene includes amorphous polypropylene, semi-crystalline
`polypropylene, the like, and mixtures thereof. Preferably, the
`semi-crystalline polypropylene is selected from the group
`consisting of propylene homopolymers, copolymers of pro
`pylene with at least one other C to Co C-olefin, the like, and
`mixtures thereof. Copolymers of propylene include random
`copolymers and impact copolymers. Preferred C-olefins for
`Such copolymers include ethylene, 1-butene, 1-pentene,
`1-hexene, methyl-1-butenes, methyl-1-pentenes, 1-octene,
`1-decene, the like, and mixtures thereof. “Semi-crystalline.”
`as used herein, means that the crystallinity is greater than or
`equal to 40%, preferably greater than or equal to 55%, and
`more preferably greater than or equal to 80%. Preferably, the
`semi-crystalline polypropylene has a melt flow rate (as deter
`mined by ASTM D-1238-01 at a temperature of 230° C. and
`at a load of 2.16 kg) within the range of 0.001 to 500 dg/min.
`Preferably, the semi-crystalline polypropylene has a density
`within the range of 0.897 to 0.925 g/cm and a weight average
`molecular weight (Mw) within the range of 85,000 to 900,
`000. Suitable poly 1-butene includes homopolymers of
`1-butene, copolymers of 1-butene with at least one other C to
`Co C-olefin, the like, and mixtures thereof. Preferred C-ole
`fins for Such copolymers include ethylene, propylene, 1-pen
`tene, 1-hexene, methyl-1-butenes, methyl-1-pentenes,
`1-octene, 1-decene, the like, and mixtures thereof. The poly 1
`butene has a melt index preferably within the range of 0.01 to
`1000 dg/min, more preferably within the range of 0.1 to 750
`dg/min. Methods for producing poly 1-butene are known. For
`instance, see U.S. Pat. No. 6,306,996; the teachings of this
`
`55
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`50
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`65
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`4
`patent are herein incorporated by reference. Polyethylene is a
`preferred polyolefin for use as a B layer. HDPE and LLDPE
`are particularly preferred.
`When Blayer is a multilayer structure, B preferably has a
`structure of tie layer/barrier layer/tie layer and the multilayer
`film preferably has a structure of A/B/NC. Tie layer is also
`called tie layer adhesive or adhesive layer. Preferably the tie
`layer resin comprises a maleated polyolefin. It comprises
`preferably from 0.5 to 25 wt %, preferably 5 to 20 wt %, and
`more preferably 5 to 15 wt %, of a maleated polyolefin.
`Suitable maleated polyolefin for use as a tie layer in the
`invention include maleated polyethylene, maleated polypro
`pylene, and maleated poly 1-butene. Methods for maleating
`polyolefin are known. For instance, U.S. Pat. No. 6,716,928,
`the teachings of which are incorporated herein by reference,
`teaches maleating a propylene impact copolymer. Suitable
`polyethylene, polypropylene, and poly 1-butene for making
`the maleated polyolefin include those discussed above. Pref
`erably, the maleated polyolefin is a maleated HDPE. The
`maleated polyolefin contains preferably from 0.1 to 10 wt %,
`more preferably from 0.5 to 5 wt %, and most preferably from
`1 to 2.5 wt %, of grafted maleic anhydride. Preferably the tie
`layer resin comprises an elastomer. Suitable elastomers
`include olefin-based elastomers and conjugated diene-based
`elastomers. By “olefin elastomer.' I mean any olefin poly
`mers or copolymers which have elastomeric characteristics.
`Suitable polyolefin elastomers include ethylene-propylene
`rubber, ethylene-acrylate rubber, ethylene-1-butene rubber,
`ethylene-propylene-diene rubber (EPDM), polyethylene
`plastomers, elastoplastic polypropylene or impact polypro
`pylene, the like, and mixtures thereof. Preferably the poly
`olefinelastomers are selected from the group consisting of
`ethylene-propylene rubber, ethylene-1-butene rubber,
`EPDM, the like, and mixtures thereof. Ethylene-propylene
`rubber is particularly preferred. By "conjugated diene-based
`elastomer.' I mean any conjugated diene-containing poly
`mers and copolymers which have a glass transition tempera
`ture (T) below room temperature (25° C.). In other words,
`the conjugated diene-containing polymers and copolymers
`are in elastomeric or rubber state at room temperature.
`Examples of conjugated diene-based elastomers include
`polybutadiene, polyisoprene, butadiene-vinyl aromatic ran
`dom and block copolymers, isoprene-vinyl aromatic random
`and block copolymers, hydrogenated butadiene-vinyl aro
`matic block copolymers, hydrogenated isoprene-vinyl aro
`matic block copolymers, the like, and mixtures thereof. Pref
`erably, the conjugated diene-based elastomers are selected
`from the group consisting ofbutadiene-styrene block copoly
`mers, isoprene-styrene block copolymers, hydrogenated
`butadiene-styrene block copolymers, hydrogenated isoprene
`styrene block copolymers, the like, and mixture thereof. More
`preferably, the conjugated diene-based elastomers are
`selected from the group consisting of styrene-butadiene-sty
`rene triblock copolymers (SBS), styrene-isoprene-styrene tri
`block copolymers (SIS), the like, and mixtures thereof. SBS
`is particularly preferred. The tie layer resin comprises pref
`erably from 15 to 65 wt %, more preferably from 25 to 55 wt
`%, and most preferably from 25 to 45 wt %, of the elastomer.
`The tie layer resin preferably comprises a base resin in an
`amount within the range of 35 to 95 wt % of the tie layer resin.
`LLDPE is a preferred based resin for the tie layer. Suitable
`LLDPE includes those which are discussed above.
`Suitable barrier layer includes any polymers which provide
`water vapor or oxygen barrier properties. Suitable barrier
`layer is preferably selected from the group consisting of eth
`ylene-vinyl alcohol copolymers (EVOH), polyamides (ny
`lons), the like, and mixture thereof. Suitable polyamides
`
`0003
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`

`

`US 8,709,611 B2
`
`6
`With these two dimensions, the radius of curvature, r, is
`calculated numerically using the equation
`
`5
`include nylon 6, nylon 6.6, nylon 12, nylon 6.12, nylon 6.66,
`the like, and mixtures thereof. EVOH is made by saponifica
`tion/hydrolysis of EVA. Suitable EVOH contains preferably
`from 30 to 50 molar % of vinyl alcohol.
`The multilayer film of the invention can be made by a
`variety of processes. It can be made by co-extrusion, coating,
`and other laminating processes. The film can be made by
`casting or blown film processes. Blown film processes
`include high-stalk and in-pocket processes. In a high-stalk
`process, the extrudate exits the annular opening in the die in
`the form of a tubular “stalk’ that is inflated a distance (usually
`the length of the stalk) from the extrusion die. For an in
`pocket blown process, the tube is inflated as the tube exits the
`extrusion die. After the tube is flattened and cooled, it can be
`slit to form a film.
`The invention includes a method for reducing or eliminat
`ing the curling of a multilayer film having the general struc
`ture of A/B/C. The method comprises adding a layer to the
`multilayer film to form a new film structure of A/B/NC or
`B/A/B/C. Layers A, B, and C are discussed above.
`The multilayer thin film of the invention has many uses. It
`is particularly useful for food packaging films and bags where
`low curling and low water vapor permeation rate are required,
`including cereal liners and cake mix bags.
`The following examples merely illustrate the invention.
`Those skilled in the art will recognize many variations that are
`within the spirit of the invention and scope of the claims.
`Comparative Example 1
`
`A three-layer film, A/B/C, is produced using a blown film
`line capable of producing films with up to seven layers. The
`film is produced at a rate of 2001b/hr, using a 0.095 inch thick
`die gap, a frost line height of 15 inches, and a blow up ratio of
`2.5:1. The film is 0.002 inch thick. Resins A and C are the
`outer layers of the film and Resin B is the center layer of the
`film. Resin A is a nucleated HDPE. The HDPE is an ethylene
`homopolymer having a density of 0.960 g/cm and a melt
`index MI of 2.0 dg/min. Resin A contains 500 ppm of a
`nucleating agent (Hyperform(R) HPN-20E is from Milliken
`and Company). The nucleating agent is used to improve the
`water vapor barrier properties of the film. Resin B is an HDPE
`copolymer with a density of 0.947 g/cm and MI of 1.1
`dg/min. Resin C is an LDPE with a density of 0.920 g/cm and
`a MI of 1.0 dg/min. The percentage of the total film taken by
`each layer in the A/B/C film structure is 35%/50%/15%.
`Film curling is characterized by cutting a 2 inchx2 inch
`“X” into each film, where the two cuts of the X are perpen
`dicular. Each cut is oriented with a 45 degree angle to both the
`machine and transverse directions. The two cuts produce four
`triangles, which are then free to curl. The X is oriented so that
`two of the triangles curl only in the machine direction of the
`film, and two of the triangles curled only in the transverse
`direction. The films are mounted onto a rigid Substrate and
`allowed to curl for 20 hours. After 20 hours, the direction of
`curl (either towards or away from the side of the film with
`resin C) is noted, and the radii of curvature of the curl in both
`the machine and transverse directions are measured. A larger
`radius of curvature in this measurement indicates less curl.
`When films curl by an amount that is more than 90 degrees,
`the radius of curvature is measured directly. When films curl
`less than 90 degrees, it is difficult to measure the radius
`directly. In these cases, the radius of curvature is determined
`by measuring the distance, 1, from the base of the triangle to
`its free point and the distance, w, from the base of the triangle
`to the projection of the free point into the plane of the film.
`
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`The curl direction and radius of curvature in the machine
`(MD) and transverse (TD) directions of this film are tabulated
`in Table 1. Comparative Example 1 shows a very large ten
`dency to curl, as indicated by its very small radius of curvature
`in both of the machine and transverse directions. This film
`curls towards the C layer direction. Water vapor transmission
`rate is measured at 100% relative humidity following the
`method of ASTM F1249. The 1% secant modulus in the
`machine direction is measured following the method of
`ASTM E111. Water vapor transmission rate and modulus are
`tabulated in Table 1.
`
`Example 2
`
`A four-layer film is produced using the same film equip
`ment and processing conditions as used in Comparative
`Example 1. This film has the same total thickness as the film
`in Comparative Example 1 (0.002 in). Identical resins A, B
`and C are used to produce this film structure. The four layer
`structure is arranged as an A/B/NC film, where the percentage
`of the total film in each layer is 7%/50%/28%/15%. The total
`fraction of the film taken up by the combined Alayers is 35%,
`which is identical to the A fraction in Comparative Example
`1. Curl testing is performed on Example 2 in a manner iden
`tical to the test used on Comparative Example 1, and the
`results are presented in Table 1. Example 2 curls away from
`the C layer direction (the direction opposite of the curl direc
`tion of Comparative example 1). Example 2 curls less than
`Comparative Example 1, as indicated by the much higher
`radii of curvature. Water vapor transmission rate is measured
`at 100% relative humidity following the method of ASTM
`F1249. The 1% secant modulus in the machine direction is
`measured following the method of ASTM E111. Water vapor
`transmission rate and modulus are tabulated in Table 1. The
`water vaportransmission rate and modulus are essentially the
`same as Comparative Example 1.
`Example 3
`
`A four-layer film is produced using the same film equip
`ment and processing conditions as used in Comparative
`Example 1. This film has the same thickness as the film in
`Comparative Example 1 (0.002 in). Identical resins A, B and
`C are used to produce this film structure. The four-layer
`structure is arranged as an A/B/A/C film, where the percent
`age of the total film in each layer was 15%/50%/20%/15%.
`The total fraction of the film taken up by the combined A
`layers is 35%, which is identical to the A fraction in Com
`parative Example 1. Curl testing is performed on Example 3
`in a manner identical to the test used on Comparative
`Example 1, and the results are presented in Table 1. Example
`3 curls toward the C layer direction (the same direction as the
`curl direction of Comparative Example 1, and the opposite
`direction as the curl direction in Example 2). Example 3 curls
`less than Comparative Example 1, as indicated by the much
`higher radii of curvature. Water vapor transmission rate is
`measured at 100% relative humidity following the method of
`ASTM F1249. The 1% secant modulus in the machine direc
`tion was measured following the method of ASTM E111.
`
`0004
`
`

`

`7
`Water vapor transmission rate and modulus are tabulated in
`Table 1. The water vapor transmission rate and modulus are
`essentially the same as Comparative Example 1.
`Comparative Example 4
`
`A three-layer film is produced using the same film equip
`ment and processing conditions as used in Comparative
`Example 1. This film has the same thickness as Comparative
`Example 1 (0.002 in). Resins B and C are the same materials
`that are used in Comparative Example 1. Resin A is an HDPE
`homopolymer with a density of 0.960 g/cm and a MI of 1.1
`dg/min. Resin A contains 500 ppm of a nucleating agent
`(Hyperform R) HPN-20E is from Milliken and Company)
`used to improve the water vapor barrier properties of the film.
`The three-layer film structure is arranged as a B/A/C film
`structure, where percentage of the total film taken by each
`layer is 35%/50%/15%. Curl testing is performed on Com
`parative Example 4 in a manner identical to the test used on
`Comparative Example 1, and the results are presented in
`Table 1. Comparative Example 4 curls away from the C layer
`direction. Water vapor transmission rates are measured at
`100% relative humidity following the method of ASTM
`F1249. The 1% secant modulus in the machine direction is
`measured following the method of ASTM E111. Water vapor
`transmission rate and modulus are tabulated in Table 1.
`
`10
`
`15
`
`25
`
`Example 5
`
`30
`
`35
`
`40
`
`A four-layer film is produced using the same film equip
`ment and processing conditions as used in Comparative
`Example 4. This film has the same thickness as the film in
`Comparative Example 4 (0.002 in). Identical resins A, B and
`C are used to produce this film structure. The four-layer
`structure is arranged as a B/A/B/C film, where the percentage
`of the total film in each layer was 20%/50%/15%/15%. The
`total fraction of the film taken up by the combined Blayers is
`35%, which is identical to the B fraction in Comparative
`Example 4. Curl testing is performed on Example 5 in a
`manner identical to the test used on Comparative Example 1,
`and the results are presented in Table 1. Example 5 curls
`toward the C layer direction (the direction opposite of the curl
`direction of Comparative example 4). Example 5 curls less
`than Comparative Example 4, as indicated by the higher radii
`of curvature. Water vapor transmission rate is measured at
`45
`100% relative humidity following the method of ASTM
`F1249. The 1% secant modulus in the machine direction is
`measured following the method of ASTM E111. Water vapor
`transmission rate and modulus are tabulated in Table 1. The
`water vapor transmission rate and modulus are essentially the
`same as Comparative Example 4.
`Example 6
`
`50
`
`A four-layer film is produced using the same film equip
`ment and processing conditions as used in Comparative
`Example 4. This film has the same thickness as the film in
`Comparative Example 4 (0.002 in). Identical resins A, B and
`C are used to produce this film structure. The four-layer
`structure is arranged as a B/NB/C film, where the percentage
`of the total film in each layer was 25%/50%/10%/15%. The
`total fraction of the film taken up by the combined Blayers is
`35%, which is identical to the B fraction in Comparative
`Example 4. Curl testing is performed on Example 6 in a
`manner identical to the test used on Comparative Example 1,
`and the results are presented in Table 1. Example 6 essentially
`does not curl at all. Water vaportransmission rate is measured
`
`55
`
`60
`
`65
`
`US 8,709,611 B2
`
`8
`at 100% relative humidity following the method of ASTM
`F1249. The 1% secant modulus in the machine direction is
`measured following the method of ASTM E111. Water vapor
`transmission rate and modulus are tabulated in Table 1. The
`water vaportransmission rate and modulus are essentially the
`same as Comparative Example 4.
`
`TABLE 1
`
`RESULTS SUMMARY
`
`Ex. No.
`
`1% Secant
`MD Curvature TD Curvature WVTR
`Radius, mm Radius, mm g/m/day Modulus, kpsi
`
`C1
`2
`3
`C4
`5
`6
`
`3
`10
`14
`7
`9
`No Curl
`
`5
`12
`34
`2O
`25
`No Curl
`
`2.0
`2.0
`2.1
`2.0
`2.0
`2.0
`
`114
`114
`116
`117
`117
`119
`
`I claim:
`1. A multilayer film having a general structure of A/B/A/C
`or B/A/B/C, wherein A is a nucleated high density polyeth
`ylene (HDPE) layer, B is a single or multilayer structure, and
`C is a seal layer
`wherein the nucleated HDPE comprises an HDPE and a
`nucleating agent selected from the group consisting of
`glycerol alkoxide salts, hexahydrophthalic acid salts,
`and mixtures thereof
`wherein when the multilayer film has the structure A/B/A/
`C, A is present in a total amount equal to about 35 wt.%.
`based upon the total weight of the multilayer film, and
`wherein when the multilayer film has the structure B/A/
`B/C, B is present in a total amount equal to about 35 wt.
`%, based upon the total weight of the multilayer film.
`2. The multilayer film of claim 1, wherein C is selected
`from the group consisting of linear low density polyethylene
`(LLDPE), low density polyethylene (LDPE), ethylene-vinyl
`acetate copolymers (EVA), polyolefin ionomers, and mix
`tures thereof.
`3. The multilayer film of claim 1, wherein B is a single
`HDPE layer or LLDPE layer.
`4. The multilayer film of claim 1, having the general struc
`ture of A/B/A/C.
`5. The multilayer film of claim 4, wherein B is a multilayer
`structure of tie layer/barrier layer/tie layer.
`6. The multilayer film of claim 5, wherein the barrier layer
`is an ethylene-vinyl alcohol copolymer layer or a polyamide
`layer.
`7. The multilayer film of claim 5, wherein the tie layer
`comprises a maleated polyolefin.
`8. A method for reducing or eliminating the curling of a
`multilayer film having a general structure of A/B/C or B/A/C,
`said method comprising adding a layer to the multilayer film
`to form a new film structure of A/B/A/C or B/A/B/C; wherein
`A is a nucleated high density polyethylene (HDPE) layer, Bis
`a single or multilayer structure, and C is a seal layer
`wherein the nucleated HDPE comprises an HDPE and a
`nucleating agent selected from the group consisting of
`glycerol alkoxide salts, hexahydrophthalic acid salts,
`and mixtures thereof
`wherein when the multilayer film has the structure A/B/A/
`C, A is present in a total amount equal to about 35 wt.%.
`based upon the total weight of the multilayer film, and
`wherein when the multilayer film has the structure B/A/B/
`C, B is present in a total amount equal to about 35 wt.%.
`based upon the total weight of the multilayer film.
`
`0005
`
`

`

`US 8,709,611 B2
`
`10
`
`9
`9. The method of claim 8, wherein C is selected from the
`group consisting of LLDPE, LDPE, EVA, polyolefin iono
`mers, and mixtures thereof.
`10. The method of claim 8, wherein B is a single HDPE
`layer or LLDPE layer.
`11. The method of claim 10, wherein the new film structure
`is A/B/A/C.
`12. The method of claim 11, wherein B is a multilayer
`structure of tie layer/barrier layer/tie layer.
`13. The method of claim 12, wherein the barrier layer is an
`ethylene-Vinyl alcohol copolymer layer or a polyamide layer.
`14. The method of claim 12, wherein the tie layer com
`prises a maleated polyolefin.
`15. An article which comprises the multilayer film of claim
`
`1.
`
`10
`
`15
`
`0006
`
`