DETAILED DESCRIPTION OF THE INVENTION

[0071] In its first embodiment, the film of the invention is a seven-layer structure. The film may have any thickness, and preferably has a thickness of from 2 to 10 mils, most preferably from 2.5 to 7.5 mils.

[0072] The core or central layer 10 is an oxygen barrier layer which contains ethylene vinyl alcohol (“EVOH”) or EVOH copolymer, which is sometimes referred to as saponified ethylene vinyl acetate copolymer. Core layer 10 may have a thickness of between 5 to 20% of the film, preferably about 10%.

[0073] EVOH copolymer is well known in the art of making polymeric film for its favorable properties as an oxygen barrier and gas barrier material. The EVOH used in the layer 10 may comprise up to 44 mole percent ethylene, preferably up to 38 mole percent ethylene. Generally, as the percent ethylene content increases, the gas barrier properties of the EVOH copolymer decrease and its moisture barrier properties increase. However, at higher levels of humidity such as at levels of from 90 to 92% humidity that is common in the packaging of meat, higher ethylene content results in an increase in the moisture barrier properties. In addition, as the ethylene content of the EVOH increases its processablity also improves.

[0074] The invention contemplates any of the various commonly used EVOH resins for layer 10 . Some examples of suitable EVOH resins are LCH101A, manufactured by EVALCA of Lisle, Ill., and ET resin, manufactured by Nippon Gohsei of Japan.

[0075] Disposed in contact with either surface of layer 10 of EVOH, thereby forming a sandwich around the EVOH layer 10 , are layers 11 and 12 of a nylon. Each of layers 11 and 12 may have a thickness of from 5 to 20% of the thickness of the film, preferably about 10%.

[0076] The nylon of layers 11 and 12 may be any of various nylons commonly used in the art of making polymeric films, including nylon 6, nylon 6,6, or nylon 12. However, in a preferred embodiment the nylon comprises an amorphous nylon copolymer that is blended with one or more of various other nylons.

[0077] An amorphous nylon copolymer is a particular type of nylon polymer that differs from crystalline or semicrystalline nylons. Amorphous nylon copolymers are characterized by a lack of crystallinity, which can be shown by the lack of an endotherm crystalline melting point in a Differential Scanning Calorimeter (“DSC”) test ASTM D-3417.

[0078] A lesser degree of crystallinity indicates the ease with which a film can be further fabricated, such as by thermoforming, orienting in the solid state, laminating, or the like. The degree of crystallinity also correlates to the brittleness of the film, and therefore the film's tendency to break or crack when subjected to physical or thermal shock. Physical or thermal shocks generally occur during further converting operations, such as in thermoforming and in the handling involved in fabricating packages, in filling and sealing them, and in shipping the filled and sealed packages in the product distribution system.

[0079] An amorphous nylon copolymer is generally a semicrystalline polymer that is made amorphous by rapid quenching of the melt, thereby preventing the development of a crystalline structure and producing a transparent solid. Alternatively, chemical modifications can be made to the chemical backbone of the polymer in order to significantly reduce or eliminate the ability of the polymer chains to organize in an orderly, crystalline arrangement without need for rapid quenching of the melt.

[0080] It is known in the art of making polymeric films that amorphous nylon copolymers, like other nylons, are ineffective as moisture barrier layers.

[0081] An example of an amorphous nylon copolymer that is suitable for use in the films of the invention is Grivory ® G21, manufactured by EMS-American Grilon, Inc. of Sumter, S.C. Grivory® G21 has a glass transition temperature by the DSC method of approximately 125° C.; a specific gravity of approximately 1.18, as measured by ASTM D792; a moisture absorption after 24 hour immersion of 1.29%, as measured by ASTM D570; and a melt flow index of 90 ml./10 min., as measured by DIN 53735.

[0082] Grivory® G21's physical properties include a tensile strength of 10,400 psi, as measured by ASTM D638; 15% elongation at break, as measured by ASTM D638; a flexural strength of 17,300 psi at ASTM D790; a flexural modulus of 416,000 psi at ASTM D790; an Izod impact strength notched of 1.0 ft.-lb./in., as measured by ASTM D256, and a Shore hardness of 80 D-Scale.

[0083] In a preferred embodiment, the amorphous nylon copolymer of each of layers 11 and 12 is from 5 to 35 weight percent of each layer. The amorphous nylon copolymer of layers 11 and 12 is blended with any of various other nylons. For example, the amorphous nylon copolymer may be blended with nylon 6, nylon 6,6, nylon 6,12, nylon 12, or a partially aromatic polyamide.

[0084] In a preferred embodiment, a nucleating agent is added to the amorphous nylon copolymer, or the amorphous nylon copolymer is blended with a nucleated nylon homopolymer. In a more preferred embodiment, the nucleated homopolymer is a high viscosity nucleated homopolymer, with a viscosity of approximately 120 or above. One such nucleating agent is a high viscosity homopolymer such as 3909 FN, manufactured by Allied Signal Chemical Company.

[0085] Layers 13 and 14 are adhesive layers, which comprise any of the various polymeric adhesives commonly used in the art of making polymeric films. For example, layers 13 and 14 may be anhydride modified polyolefins, such as Bynel® 3930 manufactured by E.I. duPont de Nemours & Co., an EVA-based anhydride modified adhesive, or Plexar®, an LLDPE-based adhesive manufactured by Norchem Chemical Co.

[0086] Layer 13 may have a thickness of from 5 to 20% of the thickness of the film, preferably about 10%. Layer 14 may have a thickness of from 10 to 40% of the thickness of the film, and is preferably about 20%.

[0087] Layer 15 is a nylon outer layer which, like layers 11 and 12 , may comprise an amorphous nylon copolymer, such as Grivory® G21, which is blended with one or more of various other nylons. Layer 15 may have a thickness of from 5 to 20% of the thickness of the film, preferably about 10%. Like layers 11 and 12 , in a preferred embodiment layer 15 comprises from about 5 to 35 percent of the amorphous nylon copolymer that is blended with various other nylons. The layer may include a nucleating agent. Layer 15 is not a moisture barrier.

[0088] In a preferred embodiment, each of nylon layers 11 , 12 and 15 comprise the blend of an amorphous nylon copolymer and a nucleated homopolymer. In a more preferred embodiment, only two of the three layers, most preferably layers 12 and 15 , comprise the blend of an amorphous nylon copolymer and a nucleated nylon homopolymer.

[0089] Layer 15 may further comprise an antiblocking agent, including antiblocking agents which are common in the art of making polymeric films, such as inorganic spheres (especially those derived from a combination of silica and aluminum), talc, diatomaceous earth, silica, calcium carbonate, or other particulate, or combinations of any of these agents. The antiblocking agent serves to roughen the surface of the film, thereby lowering the coefficient of friction between films.

[0090] In a preferred embodiment, layer 15 is a layer in which the antiblocking agent is contained in a nylon carrier composition. One such type of carrier composition is disclosed in commonly owned U.S. Pat. No. 5,109,049, the disclosure of which is incorporated herein by reference. As disclosed in the referenced patent at column 2, line 61 to column 3, line 6, nylon carrier compositions are especially effective when used in forming an outer layer of a multilayer packaging film. In a preferred arrangement, the nylon carrier composition is used in an outer layer and a second outer layer is capable of forming a heat seal.

[0091] In one type of film made with the nylon carrier composition, a polymeric material comprising 20 to 85 percent nylon is combined with 80 to 15 percent of a nylon carrier composition including antiblocking agent. The nylon carrier composition, which may comprise any of various nylons including nylon 6, nylon 6,6 or nylon 6,66, is from 35 to 80 percent antiblocking agent and 65 to 30 percent nylon polymer.

[0092] Alternatively, the film of the nylon carrier composition may be a blend of 95 to 99.5 percent of the nylon polymer and 5 to 0.5 percent of an additive concentrate, in which the additive concentrate includes the antiblocking agent incorporated into a second nylon polymer composition.

[0093] A particular antiblocking agent that is preferred for including in the nylon carrier composition is an antiblock agent manufactured by Zeelan Industries of St. Paul, Minn., under the name “Zeeospheres”. Zeeospheres are inorganic ceramic spheres comprising silica and alumina. For example, zeeospheres are incorporated as the antiblocking agent in the nylon carrier composition Reed Spectrum antiblock no. 1081274.

[0094] Layer 16 is a sealant layer which is capable of forming a heat seal with various other polymeric materials. Heat sealable, as used herein, means sealable or bondable by heat however obtained, for example, by induction or magnetic, ultrasonic, radio frequency, light, laser or other energy sources which cause the materials to bond, fuse or otherwise seal. Such heat sealable materials usually are thermoplastic film forming polymers, are well known in the art, and include ethylene polymers and copolymers, and copolymers of ethylene and an ethylenically unsaturated cononomer selected from the group consisting of carboxylic acids and esters, salts and anhydrides thereof. Layer 16 may comprise any of the various polymers used in a sealant layers, such as LLDPE, including all linear polyethylenes with density up to about 0.95 g/cm, LDPE, EVA, medium density polyethylene (“MDPE”), olefins catalyzed by a single site catalyst, EMA, EMAA, an ionomer, or a blend of any of these polymers, or heat seal coatings. Some examples of the resins that may be used for sealant layer are ULDPE 2256, manufactured by Dow Chemical Company, an octene-based Linear polyethylene, or Dow XU 4909.09.

[0095] Layer 16 may have a thickness of between 15 to 40% of the thickness of the film, and is preferably about 30%.

[0096] Although not depicted in FIG. 1 , the first embodiment may alternatively include an eighth layer disposed in contact with the sixth layer of nylon. The eighth layer comprises an anyhdride modified polyolefin, of the type that is commonly used as a polymeric adhesive. The anhydride modified polyolefin layer may comprise 10 to 20% of the thickness of film.

[0097] FIG. 2 depicts the second embodiment of the films of the invention. In this embodiment, the film does not contain a core layer of EVOH.

[0098] In its second embodiment, the film may have any thickness, and is preferably of a thickness of from 2 to 10 mils, most preferably from 2.5 to 7.5 mils.

[0099] As in the first embodiment, the film has layers 21 and 22 of a nylon, preferably an amorphous nylon copolymer that is blended with a nucleated nylon homopolymer, and more preferably from 5 to 35 percent of an amorphous nylon copolymer. Like layers 11 and 12 in the first embodiment, the amorphous nylon copolymers of layers 21 and 22 are blended with various other nylons. In a preferred embodiment, the amorphous nylon copolymer of layers 21 and 22 is blended with a nucleated nylon homopolymer.

[0100] Disposed between layers 21 and 22 is layer 20 of a polymeric adhesive. Additionally, disposed in contact with layers 21 and 22 are layers 23 and 24 of a polymeric adhesive. Layers 20 , 23 and 24 may be any of various polymeric adhesives commonly used in the art, for example an anhydride grafted polyolefin adhesive.

[0101] Layer 25 comprises a nylon outer layer, which preferably may comprise an amorphous nylon copolymer. Like layers 21 and 22 , in a preferred embodiment layer 25 comprises from about 5 to about 35 percent of the amorphous nylon copolymer. The amorphous nylon copolymer of layer 25 is blended with various other nylons. In a preferred embodiment, the amorphous nylon copolymer is blended with a nucleated nylon homopolymer. The layer may also include an antiblocking agent. Like its counterpart nylon outer layer 15 in the first embodiment, the antiblocking agent of layer 25 may be contained in a nylon carrier composition. Layer 25 is not a moisture barrier.

[0102] In a preferred version of the second embodiment, each of the nylon layers 21 , 22 and 25 comprise a blend of amorphous nylon copolymer and a nucleated homopolymer of nylon 6. In a more preferred embodiment, only two of the layers, most preferably layers 22 and 25 , comprise the blend of an amorphous nylon copolymer and a nucleated nylon homopolymer.

[0103] Layer 26 is a sealant layer which is capable of forming a heat seal with various other polymeric materials. Layer 26 may comprise any of the various polymers used in a sealant layers, such as LLDPE, LDPE, EVA, EMA, EMAA, an ionomer, or a blend of any of these polymers. A preferred sealant for this embodiment is a blend of LLDPE and LDPE.

[0104] In a third embodiment, the film may have any thickness, and is preferably from 2 to 10 mils, most preferably from 2.5 to 7.5 mils.

[0105] In its third embodiment, the film has an oxygen barrier core layer 30 of an EVOH copolymer. The EVOH layer used in layer 30 may comprise up to 44 mole percent ethylene, preferably up to 38 mole percent ethylene.

[0106] Disposed in contact with either surface of layer 30 , thereby forming a sandwich with the EVOH layer in the middle, are layers 31 and 32 of a nylon. Like layers 11 and 12 that form a sandwich about a core EVOH layer in the first embodiment, the nylon of layers 31 and 32 may comprise any of the various nylons commonly used in the art of making polymeric films. In a preferred embodiment, the nylon of layers 31 and 32 is an amorphous nylon copolymer, more preferably from 5 to 35 percent of an amorphous nylon copolymer. The amorphous nylon copolymer is blended with various other nylons such as nylon 6, nylon 6,6, nylon 6,12, nylon 12, or a partially aromatic polyamide.

[0107] Layer 33 , which is disposed in surface-to-surface contact with layer 32 , is an adhesive layer. Like the adhesive layers in both the first and second embodiments of the invention, layer 32 may be any of various commonly used polymeric adhesives including an anhydride modified polyolefin, such as an LLDPE-based anhydride modified polyolefin or an EVA-based anhydride modified polyolefin.

[0108] Layer 34 is a nylon outer layer which, like the nylon outer layers of the first and second embodiments, may comprise an amorphous nylon copolymer. In a preferred embodiment, layer 34 comprises from about 5 to 35 percent of the amorphous nylon copolymer. The amorphous nylon copolymer of layer 34 may be blended with various other nylons. Layer 34 is not a moisture barrier.

[0109] Layer 34 may further comprise an antiblocking agent, including antiblocking agents which are common in the art of making polymeric films. In a preferred embodiment, layer 34 may include the antiblocking agent in a nylon carrier composition.

[0110] Layer 36 , which is disposed in surface-to-surface contact with layer 33 , is an ionomer such as Surlyn®. Layer 37 , which is disposed in surface-to-surface contact with layer 36 , is the sealant layer, which is capable of forming a heat seal with various other polymeric materials. Layer 37 may comprise any of various polymers used in sealant layers, such as LLDPE, LDPE, EVA, EMA, EMAA, an ionomer or a blend of any of these polymers. In a preferred embodiment, layer 37 comprises LLDPE.

[0111] FIG. 4 depicts a fourth embodiment of the films of the invention. In its fourth embodiment the film may have any thickness, and is preferably from 2 to 10 mils, most preferably from 2.5 to 7.5 mils.

[0112] In a fourth embodiment, the film has a core layer 40 of an oxygen barrier EVOH material. The EVOH used in layer 40 may comprise up to 44 mole percent ethylene, preferably up to 38 mole percent ethylene.

[0113] Disposed in contact with either surface of the EVOH layer 40 , so that they form a sandwich around layer 40 , are layers 41 and 42 of a nylon. Like the inner nylon layers of the first, second and third embodiments, the nylon of layers 41 and 42 may be any of various nylons commonly used in the art of making polymeric films. In a preferred embodiment, the layer comprises an amorphous nylon copolymer, and preferably comprises from 5 to 35 weight percent of amorphous nylon copolymer. The amorphous nylon copolymer of layers 41 and 42 may be blended with various other nylons. In a further preferred embodiment layers 41 and 42 of an amorphous nylon copolymer include a nucleating agent.

[0114] Disposed in contact with layers 41 and 42 are layers 43 and 44 of an adhesive. Layers 43 and 44 may be an anhydride modified polyolefin, such as a LLDPE-based anhydride modified polyolefin or an EVA-based anhydride modified polyolefin.

[0115] Layer 45 , which is disposed in surface-to-surface contact with layer 43 of an adhesive, is a non-moisture barrier outer layer. The outer layer may comprise any of the following polymers: medium density polyethylene (“MDPE”), LLDPE, LDPE, EVA, styrene, EMA, EAA, EMAA, an ionomer, or blends of any of these polymers.

[0116] Layer 46 , which is disposed in surface-to-surface contact with layer 44 of an adhesive, is a sealant layer which may comprise any of various polymers used in sealant layers, such as EVA, EMA, EMAA, an ionomer, or blends of any of these polymers.

[0117] FIG. 5 depicts a fifth embodiment of the films in the invention. In its fifth embodiment the film may have any thickness, and is preferably from 2 to 10 mils, most preferably from 2.5 to 7.5 mils.

[0118] In its fifth embodiment, the film has a core layer 50 of an oxygen barrier EVOH material. The EVOH used in layer 50 may comprise up to 44 mole percent ethylene, preferably up to 38 mole percent ethylene.

[0119] Disposed in surface-to-surface contact with either surface of the EVOH layer 50 , so that they form a sandwich around layer 50 , are layers 51 and 52 of a nylon. Like the inner nylon layers of the prior embodiments, the nylon of layers 51 and 52 may be any of various nylons commonly used in the art of making polymeric films. In a preferred embodiment, the layer comprises an amorphous nylon copolymer, and preferably from 5 to 35 weight percent of amorphous nylon copolymer. The amorphous nylon copolymer of layers 51 and 52 may be blended with various other nylons. In a further preferred embodiment layers 51 and 52 of an amorphous nylon copolymer also comprise a nucleating agent.

[0120] Disposed in surface-to-surface contact with layer 51 is layer 53 of an adhesive. Layer 53 may be an anhydride modified polyolefin, such as an LLDPE-based anhydride modified polyolefin or an EVA-based anhydride modified polyolefin.

[0121] Layer 54 , which is disposed in surface-to-surface contact with layer 52 , comprises an anhydride modified polyolefin of the type commonly used as a polymeric adhesive. Layer 54 may be from 10 to 20% of the thickness of the film.

[0122] Layer 55 is disposed in surface-to-surface contact with layer 53 . Layer 55 comprises a bulk polyolefin resin, particularly a low cost resin. Suitable bulk polyolefins include any of the various polyethylenes, EVA, LLDPE, or a regrind of a blend of these or any other polymers. Layer 55 may be from 25 to 40% of the thickness of the film.

[0123] Disposed in surface-to-surface contact with layer 55 is layer 56 of a sealant. Layer 56 is capable of forming a heat seal with various other polymer materials. Layer 56 may comprise any of various polymers used in sealant layers, such as LLDPE, LDPE, EVA, EMA, EMAA, an ionomer or a blend of any of these polymers.

[0124] The films of the invention may be manufactured by any of various methods common in the art of making polymeric films. Preferably, the films of the invention are melt coextruded in a multilayer coextrusion die according to any one of the layer structures of the various embodiments and then formed in the general manner taught by expired U.S. Pat. No. 3,337,663, to Taga, and expired U.S. Pat. No. 3,090,998, to Heisterkamp, both of which are hereby incorporated by reference. The films are coextruded in a tubular form, wherein the first outer layer of the finished film is the inner layer of the tubular form or tube. The tube is then inflated by the admission of air, cooled, collapsed, and wound up to form a finished roll or rolls.

[0125] FIG. 6 depicts a preferred method of manufacturing the films of the invention. A multilayer film according to any of the various embodiments of the invention is coextruded through orifice 72 of die 71 as molten thermoplastic material 75 . The molten thermoplastic material 75 is pulled down through collapsing shield 80 , in the direction of arrows A to B, by nip rollers 73 and 74 . Roller 73 turns upon its axis in a clockwise direction, while roller 74 turns upon its axis in a counter-clockwise direction. Molten thermoplastic material 75 is expanded into a tubular form or “bubble ” by inflation caused by a volume of gas injected through gas outlet 76 . Gas outlet 76 is located in die 72 such that the exhausting air inflates the bubble.

[0126] Air rings 77 are located externally and/or internally of the bubble. As the molten thermoplastic material 75 is inflated into a bubble, the application of air from air rings 77 acts to control the cooling and stabilize the molten thermoplastic material. The air rings 77 can apply air at various temperatures and at a range of velocities. In addition to cooling by air rings 77 , thermoplastic molten material 75 is also cooled by water rings or mandrels 78 , also located both externally and/or internally of the bubble. Like the air rings, the water rings 78 can apply water at various temperatures and at a range of velocities.

[0127] A covering 79 may append from the die to surround the bubble as it exits the die. The length and size of the covering will effect the relative air pressures internally and externally of the bubble.

[0128] The method of making the films of the invention as disclosed above results in thermoplastic multilayer films with improved physical properties over prior art films. These improvements are believed to result from the degree of control over the crystallinity of the polymeric film achieved by this method. The crystallinity is first controlled by the application of air though air rings 77 . The temperature and velocity of the air applied through air rings 77 controls the degree of crystallinity. Subsequently, the rapid cooling caused by the method of water quenching effectively freezes the amount of crystallization achieved during air cooling in the finished polymeric film.

[0129] The water-quenched films of the invention have several improved physical properties over prior art films that are cooled by more conventional methods. For example, the films of the invention have improved clarity and processability.

[0130] While the films of the invention have been described in detail above, the invention is not to be construed as limited thereby. This patent is intended to cover all changes and modifications within the spirit and scope thereof.