KR100479335B1 - Multilayer polyamide film structures - Google Patents

Abstract

The coextruded film comprises one inner core layer of a polyamide homopolymer or copolymer, and on each side of the polyamide core, at least one of a polyolefin homopolymer or copolymer and an unsaturated carboxylic acid and / or anhydride thereof. It has an outer layer of the formulation of the adhesive composition comprising a polyolefin having a functional moiety. Coextruded films are typically made by blown film technology. Such structures are suitable for use as release and barrier films for sheet forming and other reinforced plastic applications.

Description

Multilayer Polyamide Film Structure {MULTILAYER POLYAMIDE FILM STRUCTURES}

The present invention relates to a multilayer film structure. More specifically, the invention relates to one inner core layer of a polyamide homopolymer or copolymer and, on each side of the polyamide core, an olefin containing homopolymer or copolymer and an unsaturated carboxylic acid and / or anhydride thereof. A coextruded blown film having an outer skin layer comprising a blend of an adhesive composition comprising a polyolefin having at least one functional moiety of. Such structures are suitable for use as release and barrier films for sheet molding composition applications.

There is a significant need in various industries for manufacturing structural parts that are strong, permanent and lightweight. There is a particular need in the automotive and aerospace industries to manufacture such strong, lightweight structural parts for energy efficient vehicles, airplanes and related equipment. These applications require sufficient durability and strong enough plastic to replace the most commonly used metal structure support members present in such vehicles.

The reinforced plastic part should have similar weight and component strength as the metal component with reduced weight. Structural composites were made from sheet forming compounds (SMC) that quickly match-die formed. Typically SMC consists of a mixture of unsaturated polyesters, crosslinkable polymer resins, chopped fiber reinforcements and other additives. Composites are generally prepared by attaching chopped fibers onto a layer of fluid resin supported on a transfer film to form a matrix. Generally, it can be formed into large rolls by passing through a series of kneading and compacting rolls. After a few days of standing time, the polyester is partially cured and the viscosity is increased to a suitable concentration. The SMC is then used to make a molded article by cutting one SMC from a roll, peeling off the carrier film and then placing the SMC in a heated mold for molding and complete curing.

There is a similar reinforced plastic material that is processed in a slightly different manner than the SMC composition as is known in the art. These include thick molding compounds (TMC) and bulk molding compounds (BMC). As used below, for convenience the term "SMC" is intended to include such other materials.

Carrier films have been formed of polyethylene and polyolefins. While such films have good release from SMC materials, they are inherently weak and require the use of relatively thick films to support the SMC materials during the process. The weakness of such films increases the breakage of similar carrier films, leading to downtime and downtime in the manufacturing process. Importantly, such polyethylene films are very permeable to styrenic monomers, which are present in SMC compositions as crosslinking agents for polyester resins. These polyethylene films not only release styrene monomer into the atmosphere during manufacture, but also release significant amounts during stable storage of the SMC structure.

The release of styrene monomer into the production environment increases marked toxicity and environmental hazards. To solve this problem, one conventional technique has been to form a film, which is a sandwich (styrene vapor barrier) of a polyamide core covered with a polyethylene layer on each side. However, one problem with this structure is that the polyamides and polyolefins do not adhere sufficiently to each other, which obviously reduces the strength of the film.

One film, which has had significant commercial success, is formed from a combination of low crystalline polyolefins and polyamides. Such films are described, for example, in US Pat. No. 4,444,829, which is incorporated herein by reference. This film, sold by Allied Signals, has very good release, good styrene barrier and high strength. However, this film is relatively expensive compared to the film of polyethylene. Many polyamides are also hygroscopic in high moisture conditions so that the film can have reduced strength.

Efforts have also been made to improve the coextruded polyamide / polyolefin films described above. One technique is to put a tie adhesive layer on both sides between the polyamide layer and the polyolefin layers. Although these films have good release properties and styrene barrier properties, these five layers of structure complicate manufacturing and increase costs.

Thus, there is a clear need for films that can be reliably released from SMC compounds and block any significant styrene monomer permeation while at the same time having high structural strength in all environments. It is therefore an object of the present invention to provide films that can release from SMC compounds, prevent significant styrene monomer permeation and are useful for the production of very high strength SMCs.

Summary of the Invention

The present invention consists of at least one polyamide layer and a polyolefin layer attached to both sides of the polyamide layer, the polyolefin layer comprising a blend of at least one olefin containing polymer and an adhesive, the adhesive being an unsaturated carboxylic acid or A multilayer film is provided comprising at least one polyolefin having at least one functional moiety thereof.

In addition, the present invention

a) coextruding a molten polyamide layer and a molten polyolefin layer attached to each of both sides of the polyamide layer through a coextrusion die, wherein the polyolefin layer comprises a blend of at least one olefin containing polymer and an adhesive, The adhesive comprises at least one polyolefin having at least one functional moiety of an unsaturated carboxylic acid or anhydride thereof; And

b) blowing the gas through a jet concentric with the first and second circular dies to form bubbles for expanding the polyamide layer and the polyolefin layer;

It also provides a method for producing a multilayer film.

The invention consists of at least one polyamide layer and a polyolefin layer attached to both sides of the polyamide layer, the polyamide layer comprising at least one nylon 6 and nylon 6,6; The polyolefin layer comprises a blend of at least one olefin containing polymer and an adhesive, the adhesive further providing a multilayer film suitable for use as a carrier web for reinforced plastics comprising maleic anhydride modified ethylene α-olefin copolymer.

An adhesive tie comprising a core of polyamide and a polyolefin having at least one functional moiety of an olefin containing homopolymer or copolymer and an unsaturated carboxylic acid and / or carboxylic anhydride on each face of the core of the polyamide. A multilayered multipolymer release / barrier film is obtained that consists of an outer layer comprising a blend of compositions. This film has excellent strength, release from the SMC compound and blockage of styrene monomer channels. The polyamide core and the outer polyolefin compound film have proper adhesion to each other so that a tie adhesive layer is unnecessary in the middle. As a result, a carrier film with low cost, high strength, excellent release properties and excellent styrene permeability is obtained.

In the practice of the present invention, a multilayered film consisting of a polyamide layer and a polyolefin skin layer attached to each of both sides of the polyamide layer is produced. The polyolefin layer comprises a blend of at least one olefin containing polymer and an adhesive. The adhesive comprises at least one polyolefin having at least one functional moiety of unsaturated carboxylic acid or anhydride thereof.

The polyamide layer may comprise a polyamide homopolymer, a copolymer or a combination thereof. Suitable polyamides for use in the present invention include aliphatic polyamides or aliphatic / aromatic polyamides. As used herein, "aliphatic polyamide" is a polyamide characterized by the presence of repeating carbonamide groups as components of the polymer chain separated from each other by at least two aliphatic carbon atoms. Examples of these polyamides or combinations thereof are those having repeating monomer units represented by the following general formula:

Wherein R and R ¹ are the same or different and are alkylene groups of at least about two carbon atoms, preferably alkylene groups having from about 2 to about 12 carbon atoms. As used herein, "aliphatic / aromatic polyamides" are characterized by the presence of repeating carbonamide groups as components of the polymer chain, wherein the carbonyl moiety is separated by an aliphatic moiety having at least two carbon atoms and nitrogen The groups are separated by aromatic moieties. Examples of aliphatic / aromatic polyamides are those having repeating units of the formula:

Wherein R ² and R ³ are different and are alkylene groups having at least 2 carbon atoms, preferably 2 to about 12 carbon atoms, or arylene, preferably substituted or unsubstituted phenylene, alkylenephenylene or Dialkylenephenylene, the aliphatic moiety has from 1 to about 7 carbon atoms and the permissible substituent is alkyl, alkoxy or halo, provided that when R ² is arylene, R ³ is alkylene and R ² is alkylene , R ³ is arylene or dialkylenephenylene.

Examples of suitable aliphatic polyamides include poly (hexamethylene adipamide) (nylon 6,6), poly (hexamethylene sebaamide) (nylon 6,10), poly (heptamethylene pimelamide) (nylon 7,7) , Poly (octamethylene subberamide) (nylon 8,8), poly (hexamethylene azelamide) (nylon 6,9), poly (nonmethylene azelamide) (nylon 9,9), poly (decamethylene azelamide Polyamides formed by the reaction of diamines and diacids such as (Nylon 10,9). Examples of useful aliphatic polyamides are those formed by the polymerization of amino acids and derivatives thereof, such as lactams. Useful polyamides include poly (4-aminobutyric acid) (nylon 4), poly (6-aminohexanoic acid) (nylon 6, also known as poly (caprolactam)), poly (7-aminoheptanoic acid) ( Nylon 7), poly (8-aminooctanoic acid) (nylon 8), poly (9-aminononanoic acid) (nylon 9), poly (10-aminodecanoic acid) (nylon 10), poly (11-aminoundecanoic acid (Nylon 11), poly (12-aminododecanoic acid) (nylon 12), etc. are mentioned. Combinations of two or more aliphatic polyamides may also be used.

Copolymers formed from repeating units of such reinforced aliphatic polyamides can be used to prepare polyamide layers. Such aliphatic polyamide copolymers include caprolactam / hexamethylene adipamide copolymer (nylon 6 / 6,6), hexamethylene adipamide / caprolactam copolymer (nylon 6,6 / 6), trimethylene Adipamide / hexamethylene azelamide copolymer (nylon trimethyl 6,2 / 6,2), hexamethylene adiamide / hexamethylene azelamide / caprolactam copolymer (nylon 6,6 / 6,9 / 6) Although these etc. are mentioned, it is not limited to this.

Preferred polyamides for use in the practice of the present invention are poly (caprolactam) and poly (hexamethylene adipamide), with poly (caprolactam) being most preferred.

Aliphatic polyamides used in the practice of the present invention may be obtained from commercial sources or may be prepared according to known manufacturing techniques. For example, poly (caprolactam) is available from Allied Signals Inc. in Morristown, NJ under the trade name CAPRON ^R. The number average molecular weight of the polyamide can be very wide. Aliphatic polyamides typically have a "film forming molecular weight" meaning high enough to form free standing films but low enough to melt the blend into the film. Such number average molecular weights are known to those skilled in the art of film formation and are typically at least about 5,000 as measured by the formic acid viscosity (FAV) method (ASTM D-789). In this method, a solution of 11 g of aliphatic polyamide in 100 ml of 90% formic acid at 25 ° C. is used. In a preferred embodiment of the invention, the number average molecular weight of the aliphatic polyamide is in the range of about 5,000 to about 100,000, and in particularly preferred embodiments it is in the range of about 10,000 to about 60,000. Most preferably, the number average molecular weight of the aliphatic polyamide is about 20,000 to about 40,000.

Examples of aliphatic / aromatic polyamides include poly (hexamethylene isophthalamide), poly (2,2,2-trimethyl hexamethylene terephthalamide), poly (m-xylylene adiamide) (MXD6), poly (p Xylylene adipamide), poly (hexamethylene terephthalamide), poly (dodecamethylene terephthalamide) and the like. Combinations of two or more aliphatic / aromatic polyamides can also be used. Most preferred aliphatic / aromatic polyamides are poly (m-xylylene adiamide).

Aliphatic / aromatic polyamides may be prepared by known manufacturing techniques or may be obtained from commercial sources. The number average molecular weight of aliphatic / aromatic polyamides can be very wide. Typically, aliphatic / aromatic polyamides have a "film forming molecular weight" meaning high enough to form a free standing film but low enough to melt the blend into a film. Such number average molecular weights are known to those skilled in the art of film formation and are typically at least about 5,000 as measured by the formic acid viscosity method described above. In a preferred embodiment of the invention, the number average molecular weight of the aliphatic / aromatic polyamide is in the range of about 5,000 to about 100,000, and in particularly preferred embodiments it is in the range of about 10,000 to about 60,000. Most preferably, the number average molecular weight of the aliphatic / aromatic polyamide is from about 20,000 to about 40,000.

A polyolefin layer is attached to each of the two sides of the polyamide layer. The polyolefin layer comprises a blend of at least one olefin containing polymer and an adhesive or tie composition. The adhesive comprises at least one polyolefin having at least one functional moiety of unsaturated carboxylic acid or anhydride thereof.

Polyolefins used in the present invention include polymers of alpha-olefin monomers having about 2 to about 6 carbon atoms and include homopolymers, copolymers (including graft copolymers) and terpolymers of alpha-olefins. Examples of homopolymers include ultra low density (ULDPE), low density (LDPE), linear low density (LLDPE), medium density (MDPE), or high density polyethylene (HDPE); Polypropylene; Polybutylene; Polybutene-1; Poly-3-methylbutene-1; Poly-pentene-1; Poly-4-methylpentene-1; Polyisobutylene; And polyhexene.

Polyolefins, such as polyethylene, are usually distinguished on the basis of the density obtained from the number of branched chains per 1,000 carbon atoms in the polyethylene backbone in the molecular structure. Typically the branch is a C ₃ -C ₈ olefin, which is preferably butene, hexene or octene. For example, HDPE has a relatively low number of short branched chains (less than 20 per 1,000 carbon atoms) that are relatively high density, ie, in the range of about 0.94 gm / cc to about 0.97 gm / cc. LLDPE has a shorter branched chain in the range of 20 to 60 per 1,000 carbon atoms with a density of about 0.91 to about 0.93 gm / cc. LDPE with a density of about 0.91 to about 0.93 gm / cc has long branched chains (20-40 per 1,000 carbon atoms) instead of short branched chains in LLDPE and HDPE. ULDPE has a higher branching concentration than LLDPE and HDPE, that is, in the range of about 80 to about 250 per 1,000 carbon atoms and a density of about 0.88 to 0.91 gm / cc. Examples of copolymers and terpolymers include ethylene-propylene copolymers; Ethylene-butene copolymers; ethylene-pentene copolymers; Ethylene-hexene copolymers; And copolymers and terpolymers of alpha-olefins with other olefins such as ethylene-propylene-diene copolymers (EPDM). The term polyolefin as used herein also includes copolymers with acrylonitrilebutadiene-styrene (ABS) polymers, vinyl acetate, acrylates, methacrylates, and the like. Preferred polyolefins are prepared from alpha-olefins, most preferably ethylene polymers, copolymers and terpolymers. The polyolefin can be obtained by any known method. The polyolefin may have a weight average molecular weight of about 1,000 to about 1,000,000, preferably about 10,000 to about 500,000. Preferred polyolefins are polyethylene, polypropylene, polybutylene and copolymers, and combinations thereof. Most preferred polyolefin is polyethylene.

According to the present invention, suitable adhesives include modified polyolefin compositions comprising polyolefins having at least one functional moiety of unsaturated polycarboxylic acids and anhydrides thereof. The polyolefin may be those listed above. Unsaturated carboxylic acid and its anhydride include maleic acid and its anhydride, fumaric acid and its anhydride, crotonic acid and its anhydride, citraconic acid and its anhydride, itaconic acid and its anhydride and the like. Of these, maleic anhydride is most preferred. Modified polyolefins suitable for use in the present invention are described in US Pat. Nos. 3,481,910; 3,480,580; And the compositions described in US Pat. Nos. 4,612,155 and 4,751,270. Most preferred adhesives are maleic anhydride modified ethylene α-olefin copolymers known as linear ultra low density polyethylene. Preferred modified polyolefin compositions comprise from about 0.001% to about 10% by weight functional moieties based on the total weight of the modified polyolefin. More preferably the functional moiety comprises about 0.005 to about 5 weight percent, most preferably about 0.01 to about 2 weight percent. The modified polyolefin composition may contain up to about 40 weight percent of the alkyl esters and thermoplastic elastomers described in US Pat. No. 5,139,878. The most preferred adhesive is Flexomer 1373 from Union Carbide, which is a 10% maleic anhydride modified copolymer of ethylene and butene.

The weight percentage of the adhesive in the polyolefin layer is from about 3% to about 80%, preferably from about 3% to about 25%, more preferably from about 5% to about 15%, most preferably based on the weight of the polyolefin layer composition. Preferably in the range of about 5% to about 10%. The remainder is an olefin containing polymer except for any of the adhesives described below, which may be present in the polyolefin layer.

Each layer of the multilayer film structure may contain additives conventionally used for such films. Examples of such additives are pigments, dyes, slip additives, fillers, nucleating agents, plasticizers, lubricants, barrier agents, stabilizers and antioxidants, thermal stabilizers and ultraviolet light stabilizers. They may be present in amounts up to about 10% by weight of the layer.

The multilayer film of the present invention can be produced by conventional methods useful for producing multilayer films including coextrusion and extrusion lamination techniques. In the most preferred method, the film is formed by coextrusion. A molten plasticized stream of polyamide and polyolefin layer material is fed to the coextrusion die. In the die, the layers are paralleled and combined and then removed from the die as a single multilayer film of polymeric material. Suitable coextrusion techniques are described in more detail in US Pat. Nos. 5,139,878 and 4,677,017 except that the coextrusion in the present invention is performed at about 460 ° F (238 ° C) to about 510 ° F (266 ° C). . Coextrusion techniques include the use of multi-manifold dies such as standard dies, circular dies, as well as the use of multi-manifold dies and feed blockers used to form multilayer cast films to form flat cast films and cast sheets. Preferably the multilayered film is made by blown film coextrusion. The film is formed of what is known in the art as a blown film device comprising a multi-manifold circular die head with concentric circular holes. The multilayer film is formed by coextrusion of a molten polyamide layer through a circular die and a molten polyolefin layer on each side of the polyamide layer through an additional circular die concentric with the first circular die. Gas, usually air, is then blown through a jet concentric with the circular die to form a polyamide layer and a polyolefin layer which are bubble expanded. Bubbles are then self-destructive in a pair of attached multilayer films with two edges attached. Typically a pair of attached multilayer films are separated from at least one edge and separated into a pair of multilayer films before rolling up.

An unexpected advantage of the present invention is that the modified polyolefin improves the bubble stability of the blown film resulting in unexpectedly improved adhesion of the polyolefin film to the polyamide film. In particular, maleic anhydride modified ethylene α-olefins, when added to polyethylene unmodified in an amount of about 5% to about 10% polyethylene by weight, produce a composition having a special adhesion of nylon 6 to a film, and Low melt index helps to maintain bubble stability imparted by unmodified polyethylene. This is important in multi-layer blown film manufacturing processes, especially for thin polyolefin skins that enclose a heavy core of nylon.

The advantage of the coextruded film is to form the multilayer film in one process step by combining the molten layers of each film layer of the polyamide and polyolefin blend into a single film structure. Preferably, the multilayers form bonds that cannot be separated from each other. As used herein, the term “inseparable bond” means a bond strength of at least about 700 g / inch as measured by testing a film according to the methods described in ASTM D-3359-90 and F88-85.

In order to produce a multilayer film by a coextrusion process, the components used to form the individual films need to be compatible with the film extrusion process. In this respect the term "commercially available" means that the film-forming composition used to form the film has sufficiently similar meltability to allow coextrusion. Meltities of interest include, for example, melting point, melt flow index, apparent viscosity as well as melt stability. It is important that this compatibility exists to ensure the production of multilayer films having a relatively uniform thickness and good stability across the width of the film produced. As is known in the art, film-forming compositions that are not sufficiently compatible to be useful in coextrusion processes often produce films with poor interfacial lamination, poor physical properties as well as poor apparent appearance. One skilled in the art can readily consider the above compatibility to select a polymer having the desired physical properties and determine the optimal combination of relevant properties of adjacent layers without undue experimentation. Using an extrusion process, the components used to form the multilayer film can be used within a relatively close temperature range to extrude through conventional dies. In a preferred embodiment, the polyamide has a formic acid viscosity FAV of about 120 to about 250 by ASTM D-789 and the polyolefin layer has a melt index unit (MI) of about .5 to about 3 as measured by ASTM D-1238. When having a melt index of), the film may be commercially available. That is, the polyamide and polyolefin layers will flow uniformly in the coextruder.

Alternatively, the multilayer film of the present invention can be produced by lamination so that the multilayer film structure is formed from a prefabricated film fleece by methods known in the art. The basic methods used in film lamination techniques are melting, wet combining and thermal reactivation. Melting, a laminating method, consists of a polymer in which two or more film fliers, thermally and pressure laminated, easily form an interfacial bond. Wet combinations and thermal reactivation are useful for laminating films that are incompatible with adhesive materials. Typically, lamination is done by positioning the individual layers of the film of the present invention with each other under conditions of heat and pressure sufficient to combine the layers into a single film. Typically the polyolefin and polyamide layers position each other and the combination passes through the nip of a pair of heated lamination rollers by techniques known in the art as described in US Pat. No. 3,355,347. Lamination heating is performed at a temperature in the range of about 75 ° C. to about 175 ° C. at a pressure ranging from about 5 psig (0.034 MPa) to about 100 psig (0.69 MPa) for about 5 seconds to about 5 minutes, preferably about 30 seconds to about 1 minute. I can do it.

Multilayer films consisting of three or more layered structures can be stretched or oriented in any desired direction using methods known to those skilled in the art. Examples of such methods include those described in US Pat. No. 4,510,301. Optionally, the film is in a direction consistent with the direction of movement of the film withdrawn from the film forming apparatus, referred to in the art in the "machine direction", or a direction perpendicular to the machine direction, referred to in the art in the "crosswise direction". And uniaxially, or biaxially in both machine and transverse directions. The films of the present invention have sufficient dimensional stability to be stretched by about 1.5 times, preferably at least 3 times, more preferably from 3 times to about 10 times in the machine direction or in the transverse direction or both. Typically for use in the present invention, the oriented film formed from the composition of the present invention is preferably prepared at a draw ratio of about 1.5: 1 to about 6: 1, preferably at a draw ratio of about 3: 1 to about 4: 1. do. As used herein, the term "stretch ratio" refers to an increase in the dimension in the stretching direction. Thus, films having a draw ratio of 2: 1 are doubled in length during the stretching process. Generally, the film is drawn by passing through a series of preheating and heating rolls. The heated film is moved through a set of downstream nip rolls at a faster speed than the nip rolls introducing the film in the upstream position. The rate change is compensated for by stretching to the film.

Each layer of the multilayer film structure may have a different thickness, but the overall thickness of the multilayer structure is from about 0.3 mil (7.6 μm) to about 5.0 mil (127.0 μm), preferably from about 0.5 mil (12.7 μm) to about 1.5 mil The range of (37.5 micrometers) is preferable. In a preferred embodiment, the core comprises from about 50% to about 90%, preferably from about 70% to about 80% of the total film thickness and each outer layer is from about 5% to about 25% of the total film thickness, preferably About 10% to about 15%. It is understood that such thicknesses are desirable to easily provide a flexible film, and that other film thicknesses can be made to meet specific needs and fall within the scope of the present invention.

It has been found that the films produced according to the present invention have low cost, good strength, release from SMC compounds and blockage of styrene monomer channels. The polyamide core and outer polyolefin blend film have adequate adhesion to each other so that an intermediate tie glue layer is unnecessary. The polyolefin layer also provides good moisture barrier properties, preventing moisture from passing through the polyamide layer.

The following non-limiting examples are used to illustrate the invention.

Example 1

The two extruder systems consist of two 3.2 cm (1 1/4 ") Killion single screw extruders, one with L / D = 24/1 and the other with L / D = 30/1. Poly (epsiloncaprol) Lactam) (nylon 6, formic acid viscosity = 135, manufactured by Allied Signal) L / D = 30 with an extrusion profile set at 232 ° C., 254 ° C. and 260 ° C. for heating zones 1-3 and 260 ° C. for adapters. Feed to an extruder of 1. The melt temperature was measured at 257 ° C. The poly (ethylene) blend comprising the unmodified polyethylene and the modified polyethylene whose composition is listed below was 238 ° C., 252 for heating zones 1-4. Extruded in an extruder with L / D = 24/1 with an extrusion profile set at 260 ° C., 257 ° C. and 260 ° C. and an adapter for 260 ° C. Melt temperature was measured at 260 ° C. Coextrusion film maintained at 260 ° C. After passing the die, the extrudate is cast on a roll maintained at 38 ° C. and then Cast on a chill roll set at 35 ° C. The resulting film had a thickness of 25 μm The unmodified poly (ethylene) material used in the poly (ethylene) blend was as follows:

LDPE ³ : low density PE-density = 0.919, melt index = 0.65, 602AS, manufactured by Westlake Chemical.

LLDPE ⁴ : Linear low density PE-density = 0.920, melt index = 1, Escorene LL-3001, manufactured by Exxon Chemical Company.

MDPE ⁵ : medium density PE-density = 0.941, melt index = 4, Dowlex 2027A, manufactured by Dow Chemical Company.

HDPE ⁶ : High Density PE-Density = 0.954, Melt Index = 6, Paxon A55-060, manufactured by Exxon.

The modified poly (ethylene) material used in the poly (ethylene) blend was as follows:

Maleic anhydride (MA) modified ethylene-butene copolymer: density = 0.903, melt index = 3, Vicat softening temperature (ASTM D-1525): 53 ° C., Flexomer DEFA-1373, manufactured by Union Carbide Chemicals.

MA Modified LLDPE: Density = 0.92, Melt Index = 2, Vicat Softening Temperature (ASTM D-1525): 86 ° C., Admer NF500, manufactured by Mitsui Petrochemicals.

MA Modified HDPE: Density = 0.95, Melt Index = 1.3, Melt Temperature = 136 ° C, Bynel 4003, manufactured by Dupont.

Ethylene-methacrylate acid ionomer: density = 0.96, melt index = 1, cation: Zn, Vicat softening temperature (ASTM D-1525): 71 ° C, Surlyn 9721, manufactured by DuPont.

Selected maleic anhydride modified polyethylene was pelletized at a different rate than the selected unmodified polyethylene. The resin blend was extruded and then cast into a film as two outer skin layers with nylon 6 cores. The skin layer is about 10% on each side of the overall thickness. Nylon 6 core is about 80% of the total thickness. The film was then subjected to an adhesion test with Scorch 610 tape. Scotch 610 tape, 2.54 cm (1 inch) wide, was applied to both sides of the film. Next, it peeled off the film. If the adhesion between the nylon 6 core and the poly (ethylene) blend is weak, ie less than 700 gm / in, the layers can be separated. If the amount of modified poly (ethylene) is large, the adhesion becomes stronger. Below the critical level of modified poly (ethylene) in unmodified poly (ethylene), the film cannot be separated. Table 1 shows the percentage of modified poly (ethylene) in unmodified poly (ethylene) in three layers of coextruded films containing PEskin and nylon 6 cores providing inseparable bond strength.

Percentage of modified polyethylene in the unmodified polyethylene of the 3-layer coextruded film to inseparable bond strength LDPE ³ LLDPE ⁴ MDPE ⁵ HDPE ⁶ MA ¹ modified ethylene α-olefin copolymer ² 10% 10% 15% 20% MA Modified LLDPE ⁴ 40% 50% 60% 80% MA Modified HDPE ⁶ 80% 80% 80% 70% Ethylene-Methacrylic Acid Ionomer ⁷ 60% 60% 50% 30% Note: 1. MA: maleic anhydride 2. Ethylene α-olefin copolymer: known as linear ultra low density polyethylene 3. LDPE: low density polyethylene 4. LLDPE: linear low density polyethylene 5. MDPE: medium density polyethylene 6. HDPE: high density Polyethylene 7. Ethylene-methacrylic acid ionomer: known as Surlyn ^R from DuPont

Example 2 (Comparative)

Commercially blown film coextrusion apparatuses are used to produce three-layer, symmetrical films consisting of two polyolefins, the polyamide of the core layer and the skin (outer) layer. A production rate of 300-500 lbs per hour was achieved. The film gauge was 1-1.5 mils. The melting temperature for the polyolefin layer is from 380 ° F. to 395 ° F .; Melting temperatures for the polyamides were between 460 ° F and 500 ° F.

The composition of the skin layer was 25% LLDPE, 25% HDPE, 50% Admer NF 500 (Mitsui).

The composition of the core layer was 100% nylon 6.

Layer distribution: 20% skin / 60% core / 20% skin.

Film gauge: 1.6mil.

Film adhesion was poor. The layers can be easily separated into a tape to aid peeling using a Scotch # 610 tape.

Example 3 (Comparative)

Example 2 was repeated with the following skin and core compositions:

Composition of the skin layer: 85% LLDPE, 15% Surlyn ionomer.

Composition of the core layer: 100% nylon 6.

Layer distribution: 15% skin / 70% core / 15% skin.

Film gauge: 1.0mil.

Film adhesion was poor. The layers can be separated without the use of tape.

Example 4

Example 2 was repeated with the following skin and core compositions:

Composition of skin layer: 90% high pressure LDPE, 10% maleated polyethylene (DEFA 1373)

Composition of the core layer: 100% nylon 6.

Layer distribution: 11.5% skin / 77% core / 11.5% skin.

Film gauge: 1.1mil.

Film adhesion was excellent. The layers cannot be separated by a tape to aid peeling.

It can be seen from the above that the present invention provides a film having excellent adhesion.

Claims (23)

At least one polyamide layer; And It consists of two polyolefin layers attached to both sides of this polyamide layer, each polyolefin layer independently comprising a combination of linear low density polyethylene and an adhesive, wherein the adhesive comprises maleic anhydride modified linear low density polyethylene. A multilayer film characterized by the above-mentioned. The multilayer film of claim 1 wherein the polyamide layer comprises a polyamide homopolymer, a copolymer or a combination thereof. The multilayer film of claim 1 wherein the polyamide layer comprises a polyamide selected from the group consisting of having repeating monomer units represented by the general formula: Wherein R and R ¹ are the same or different and an alkylene group of at least about two carbon atoms, an aliphatic / aromatic polyamide, has a repeating unit of the formula: Wherein R ² and R ³ are different and are an alkylene group or arylene having at least two carbon atoms, and the aliphatic moiety has 1 to 7 carbon atoms and the permissible substituent is alkyl, alkoxy or halo, provided that R ² is When arylene, R ³ is alkylene and when R ² is alkylene, R ³ is arylene or dialkylenephenylene. 2. The polyamide layer according to claim 1, wherein the polyamide layer is poly (hexamethylene adipamide), poly (hexamethylene sebaamide), poly (heptamethylene pimelamide), poly (octamethylene subvertamide), poly (hexamethylene azel Amide), poly (nonamethylene azelamide), poly (decamethylene azelamide), poly (4-aminobutyric acid), poly (6-aminohexanoic acid), poly (7-aminoheptanoic acid), poly (8-amino Octanoic acid), poly (9-aminononanoic acid), poly (10-aminodecanoic acid), poly (11-aminoundecanoic acid), poly (12-aminododecanoic acid), caprolactam / hexamethylene adipamide Copolymer, Hexamethylene Adipamide / Caprolactam Copolymer, Trimethylene Adipamide / Hexmethylene Azelamide Copolymer, Hexamethylene Adipamide / Hexmethylene Azelamide / Caprolactam Copolymer, Poly (Caprolactam ), Poly (hexamethylene adipamide), poly (hexamethylene iso Phthalamide), poly (2,2,2-trimethyl hexamethylene terephthalamide), poly (m-xylylene adipamide), poly (p-xylylene adipamide), poly (hexamethylene terephthalamide) And a polyamide selected from the group consisting of poly (dodecamethylene terephthalamide) and mixtures thereof. The multilayer film of claim 1, wherein the average molecular weight of the polyamide is in the range of about 5,000 to about 100,000. The multilayer film of claim 1, wherein the olefin containing polymer comprises at least one component selected from the group consisting of alpha-olefin homopolymers, copolymers and terpolymers. The polymer of claim 1 wherein the olefin containing polymer is ultra low density, low density, linear low density, medium density or high density polyethylene, polypropylene, polybutylene, polybutene-1, poly-3-methylbutene-1, poly-pentene- 1, poly-4-methylpentene-1, polyisobutylene, polyhexene, ethylene-propylene copolymers; Ethylene-butene copolymers; ethylene-pentene copolymers; Ethylene-hexene copolymers; Ethylene-propylene-diene copolymers, acrylonitrilebutadiene-styrene polymers; A multilayer film comprising at least one component selected from the group consisting of copolymers of olefins with vinyl acetate, acrylates and methacrylates and mixtures thereof. The multilayer film of claim 1, wherein the olefin containing polymer has an average molecular weight of about 1,000 to about 1,000,000. The multilayer film of claim 1 wherein the adhesive is a maleic anhydride modified ethylene α-olefin copolymer comprising from about 0.001 to about 10 weight percent maleic anhydride moiety based on the total weight of the adhesive. The multilayer film of claim 1 wherein the adhesive is a maleic anhydride modified ethylene-butene copolymer comprising from about 0.001 to about 10 weight percent maleic anhydride moiety based on the total weight of the adhesive. The multilayer film of claim 1, wherein the amount of adhesive in the polyolefin layer is in the range of about 5% to about 15% based on the weight of the polyolefin layer composition. The method of claim 1, wherein the olefin containing polymer comprises unmodified polyethylene; The adhesive is a maleic anhydride modified ethylene α-olefin copolymer comprising from about 0.001 to about 10 weight percent maleic anhydride portion based on the total weight of the adhesive; The adhesive is present in the polyolefin layer in an amount from about 5% to about 10% polyethylene; And the polyamide layer comprises nylon 6. The multilayer film of claim 1 wherein the polyamide and polyolefin layers form inseparable bonds with each other having a bond strength of at least about 700 g / inch. The multilayer film according to claim 1, which extends uniaxially or biaxially. In the manufacturing method of the multilayer film, a) coextruding a molten polyamide layer and a molten polyolefin layer attached to each of both sides of the polyamide layer through a coextrusion die, wherein the polyolefin layer comprises a blend of at least one olefin containing polymer and an adhesive, The adhesive comprises at least one polyolefin having at least one functional moiety of an unsaturated carboxylic acid or anhydride thereof; b) blowing the gas through a jet concentric with the first and second circular dies to form bubbles for expanding the polyamide layer and the polyolefin layer; And c) forming a film having a thickness of about 38 micrometers or less Method for producing a multilayer film, characterized in that consisting of. The method of claim 15, d) the bubbles are uniformly broken to form a pair of attached multilayer films having two edges attached thereto; And e) cutting a pair of attached multilayer film at at least one edge And then further comprising. 17. The method of claim 16, wherein the pair of attached multilayer films are cut at each two edges to separate the pair of multilayer films. 16. The method of claim 15, wherein the polyamide layer comprises a polyamide homopolymer, a copolymer or a combination thereof. 16. The method of claim 15, wherein the olefin containing polymer comprises at least one component selected from the group consisting of alpha-olefin homopolymers, copolymers or terpolymers. 16. The unsaturated carboxyl of claim 15 wherein the adhesive is selected from the group consisting of maleic acid, maleic anhydride, fumaric acid, fumaric anhydride, crotonic acid, crotonic anhydride, citraconic acid, citraconic anhydride, itaconic acid and itaconic anhydride A polyolefin homopolymer, copolymer or terpolymer modified with an acid or anhydride thereof. 16. The method of claim 15, wherein the adhesive is a maleic anhydride modified ethylene α-olefin copolymer comprising from about 0.001 to about 10 weight percent maleic anhydride moiety based on the total weight of the adhesive. The polymer of claim 15 wherein the olefin containing polymer comprises unmodified polyethylene; The adhesive is a maleic anhydride modified ethylene α-olefin copolymer comprising from about 0.001 to about 10 weight percent maleic anhydride portion based on the total weight of the adhesive; The adhesive is present in the polyolefin layer in an amount from about 5% to about 10% polyethylene; And the polyamide layer comprises nylon 6. The multilayer film of claim 1 wherein the film is suitable for use as a carrier web for reinforced plastics, wherein the polyamide layer comprises at least one nylon 6 and nylon 6,6.