Polyester laminate containing biaxially oriented polypropylene film and method of making the same.

PCT WORLD INTELLECTUAL PROPERTY OROANIZATION * Intematímrsl Burean -

INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATTON TREATY (PCT)

<td>(51) Internattanal Patent Claaatflratlan 6: B29C 55/02, B32B 27/32, 27/36</td><td>To the</td><td colspan="2">(11) International Publicatton Number: WO 96/40485 (43) International Publlcation Date: 19 December 1996 (19.12.96)</td>

<td colspan="3">(21) International Application Number: PCT / US96 / 0942O (22) International Flltag Date: 7 June 1996 (07.06.96) (30) Priorlty Date: 08 / 483,687 7 June 1995 (07.06.95) US (60) Parcnt Application or Grant (63) Xelated by Continuadon US 08 / 483,687 (OP) Flled on 7 June 1993 (07.06.95) (71) Appllcant (for all designated States except US): QPF, INC. [US / US); 601 Eait Lalce Street, Strcamwood, IL 60107 (US). (72) Inventor; and (75) Inventon / Applicaiits (for US onfy): DAVIS, Alan, M. [US / US]; 630 Fairfield Orive, Bamngton, IL 60010 (US). LAWRENCE. John [US / US]; 302 Hickoty Lañe, Sehaumburg, IL 60193 (US). ΜΕΗΤΛ, Deepak [IN / US]; 228 Cortea Court, Naperville, IL 60563 (US). (74) Agent: ZELLER, lames, P .; Manhall, O'Toole, Gentein, Murray &amp; Borun, 6300 Sears Tower, 233 S. Wacker Drive, Chicago, IL 60606-6402 (US).</td><td>(81) Designated States: AL, AM. AT, AU, AZ, BB, BG, BR, BY, CA, CH, CN, CZ, DE, DK, EE, ES, Π, GB, GE, HU, IS, JP. KE, KG, KP, KR, KZ. LK, LR, LS, LT, LU. LV. MD, MG, MK, MN, MW, MX, NO, NZ, PL, PT, RO, RU, SD. SE, SG, SL SK, TJ, TM. TO, TT, UA UG, US, UZ, VN, ARIPO patent (KE, LS, MW, SD, SZ, UG), Burasian patent (AM, AZ, BY, KG, KZ, MD, RU, TJ, TM) , European patent (AT. BE, CH, DE, DK, ES. FL FR, GB, GR, ΙΕ, ΓΓ, LU, MC, NL, PT, SE), OAPI patent (BF, BJ, CF. CG, O, CM, GA, GN, ML, MR, NE, SN, TD, TG). Publiihed With International search report. With amended claims.</td>

<td colspan="4">(54) Title: POLYESTER LAMINATE CONTAINING BIAXIALLY ORIENTED POLYPROPYLENE FILM AND METHOD OF MARINO THE SAME (57) Abetract Polyester-containing multilayer biaxiaUy-oriented polypropylene Sima are provlded. According to tbe lnverttion, a two- or three-layer polyester-containing cap layer is kindness to a manoaxiaUy oriented polypropylene core, followed by orientation of tbe resulting compoalte in a dircction tnnsvene to the directlon of orientation of the core layer. At leatt one tie layer ia interpoaed between the core and the polyeater. Advantageoualy, the polyeater contatos lilicone fluid aa a proceaaing ald.</td>

-1 POLYESTER LAMINATE CONTAINING FILM OF

POLYPROPYLENE BIAXIALLY ORIENTED AND

METHOD FOR DOING THE SAME

BACKGROUND OF THE INVENTION Field of the Invention

The invention relates to multi-layer polyolefin film structures, and methods of making the same, and more particularly, the invention relates to a biaxially oriented polypropylene film incorporating at least one layer of polyester. Description of Related Technique

Bi-axially oriented polypropylene (BOPP) films are widely used in packaging because they have good rigidity, strength, optical properties (low haze and high gloss), and moisture barrier properties. Users of packaging films, particularly users of biaxially oriented polypropylene films, are continually · seeking structures with improved impresability, metallization properties, and gas barrier. Due to their olefinic nature, biaxially oriented polypropylene constructions have low surface energy and require treatment (crown, flame, etc.) in order to be printed or metallized. Polyester is known to have a

-2high surface energy and that has excellent printing and metallization attributes. Additionally, polyester, in both transparent and metallized structures, offers improved gas barrier performance to biaxially oriented polypropylene films. This is especially true in the case of metallized polyester films, which are in order of magnitude or lower in the oxygen transmission rate.

Although there has been a need for biaxially oriented polypropylene films incorporating polyester layers, in previous attempts problems have been encountered in obtaining acceptable processability and optical characteristics, adequate interfold adhesion, and other properties to produce biaxially oriented polypropylene structures containing polyester. . For example, the

United States Patent No. 5,324,467 describes a process for the preparation of a multilayer oriented laminate film, having at least three layers, including polypropylene, a bonding layer, and copolyester. Films are formed by combining the layers in the molten state, either in coextrusion, or in separate extrusions that are put together outside the die, and then subsequently cooling the film, uniaxially or biaxially orienting it, and heat setting it to enclose the properties. A major problem in

-3Structure production, in accordance with this method in commercial scale equipment, is the strong tendency of polyester to adhere to the heated metal rolls of the machine's steering orientation section. This makes it difficult to achieve good optical properties, free of visual defects, and can also decrease other properties such as the sealing initiation temperature.

United States Patent No. 4,874,656 describes a multilayer laminate having high mechanical strength and impermeability to gases and vapors. In the structures described, a polyester layer is bonded to a polypropylene layer after the polypropylene is biaxially oriented, the polyester layer is quite thick (i.e. 12-24 microns), and the structure includes a sheet metal layer metal and a layer of polyethylene. Although it is possible to bond a polyester layer to a biaxially oriented polypropylene layer after biaxial orientation, this method is impractical for incorporating thin polyester layers.

The United States of America Patent

No. 4,924,525 also describes a structure where a polyester laminate adheres to a biaxially oriented polypropylene film after the polypropylene is biaxially oriented, preventing the use of polyester layers in the final structure.

-4 COMPENDITION OF THE INVENTION

It is an object of the invention to overcome one or more of the problems described above.

Accordingly, the invention provides a biaxially oriented polypropylene film, incorporating a polyester layer, and a method of making the same.

The inventive multilayer film is prepared by the steps of forming a polypropylene core, orienting the core in a first direction, providing on at least one side thereof, a multilayer outer film (cover layer) comprising at least one polyester layer , and at least one bonding layer interposed between the polyester layer and the core, and orienting the resulting multilayer film in a second direction transverse to the first direction.

Conveniently, the polyester layer contains enough silicone fluid to provide substantially uniform elongation characteristics.

The invention also provides a white or colored biaxially oriented polypropylene film incorporating a polyester layer that is prepared by adding inorganic minerals, pigments, or dyes to the polypropylene core.

For those skilled in the art it will be obvious 25 more objectives and advantages of the invention, by a review of the

The following detailed description is taken in conjunction with the appended claims.

DETAILED DESCRIPTION OF THE INVENTION

The invention addresses different concerns of the prior art by providing a structure that places polyester in the outer layer of the film, thereby taking advantage of the improved impresability and metallization attributes of polyesters, also eliminates the difficulty of contacting the polyester on the heated rolls of the machine's steering guide and, in addition, provides thin layers of polyester, that allow an economic value structure to be produced. A further benefit of the invention is that a wide range of polyester products, including amorphous homopolymer grades, can be included in the inventive film structures. This allows the designer a wide selection when making films with optical properties, printability and metallization attributes, as well as improved stiffness and heat resistance.

The films of the present invention provide an excellent barrier against flavors and aromas. Furthermore, since the polyester layer of the inventive film is formed from a high molecular weight extruded polymer, there is no problem with loss of flavor and aroma barrier due to breakage or abrasion. Furthermore, the

-6 biaxially oriented polypropylene films with an outer polyester layer can be quickly printed or metallized, or adhesive coated on the polyester surface. In addition, the opposite film surface can be metallized to the polyester side, leaving the polyester layer available for other modifications.

Generally, the inventive polyester-containing biaxially oriented polypropylene film includes a core and a multi-layer outer film (cover layer), or film adhered to at least one core surface. The biaxially oriented polypropylene multilayer film of the invention is prepared using inter-stretch or lamination coating techniques.

The biaxially oriented polypropylene core comprises a polypropylene layer and, in one embodiment, also comprises a tie layer, as described below.

The cover layer is applied to one or both surfaces of the monoaxially oriented core layer. The cover layer comprises a layer of a polyester resin, and at least one bonding layer comprising a polyolefin adhesive. The polyolefin adhesive bonding layer is placed between the polyester layer and the core.

Additionally, the polyester layer contains a

-7 Sufficient amount of silicone fluid, as a processing aid, to provide substantially uniform elongation characteristics to the polyester layer.

In a preferred embodiment, the cover layer contains a second bonding layer comprising a polypropylene copolymer or terpolymer or linear ethylene polymer, interposed between the polyolefin adhesive bonding layer and the core. In a variation of this embodiment, the polypropylene copolymer or terpolymer link layer forms part of the core, and is positioned adjacent to the polyolefin adhesive link layer in the final structure. This tie layer can be oriented with the polypropylene core layer.

The biaxially oriented polypropylene multilayer film of the invention is prepared by the steps of forming and orienting the core in a first direction, providing the cover layer to at least one side of the monoaxially oriented core, to form a multilayer film, and then orienting the resulting multilayer film in a second direction transverse (and preferably perpendicular) to the first direction, to provide a biaxially oriented multilayer film.

The biaxially oriented multilayer film can then be subjected to a heat setting treatment, to allow the film to crystallize. In a modality

-8 preferred, an outer surface of the polyester layer is metallized.

The invention is described in more detail below.

Core Structure

As stated above, the core may be a polypropylene monolayer, or it may comprise a multilayer structure that includes a core layer of a polypropylene with a bonding layer on one or both sides of the core.

The term polypropylene, as used herein with reference to the core, generically denotes a semi-crystalline polymer, with a majority of polymerized propylene, and specifically includes isotactic homopolymers of propylene, copolymers of propylene with up to 25 weight percent ethylene or butene , propylene terpolymers with ethylene and butene, and mixtures thereof.

Preferred polypropylenes are those that are selected from propylene homopolymers and propylene copolymers, with less than three weight percent comonomer, such as ethylene or butene. Casting flow rates of 1 to 15 dg / minute, and preferably 1.5 to 6 dg / minute, as measured in accordance with ASTM D1238-90b, Condition 230 / 2.16 (formerly Condition F), are suitable for film leaf or blown.

-9 The thickness of the core layer is limited only as dictated by the limitations of the oriented polypropylene splicing process, and will typically range from about 12 microns to about 50 microns.

The core may optionally include a bonding layer comprising a polypropylene copolymer or terpolymer or a linear ethylene polymer, coextruded with the polypropylene core layer. While the polypropylene core may be a homopolymer, the co-extruded bonding layer comprises a copolymer of propylene with up to 25 percent by weight of ethylene or butene, mixtures thereof, or a linear ethylene polymer, such as low linear polyethylene density (LLDPE). The thickness of the total core structure is limited only by the limitations of the stretching process, as described above, and is therefore typically from about 12 microns to about 50 microns thick. The thickness of an individual coextruded bond layer is typically from about 0.5 microns to about 2 microns thick.

An important class of biaxially oriented polypropylene films are white, pigmented films that are used in packaging applications. For example, confectionery is often packaged with white biaxially oriented polypropylene films, because the films provide a barrier against light,

-1010 to avoid premature deterioration initiated by ultraviolet light, and white films present a clean, attractive surface.

For white film versions made in accordance with the invention, the structure of the transparent film core is modified by the addition of incompatible inorganic minerals. An especially important mineral is titanium dioxide, TiO₂, the most commonly used white pigment. The typical TiO concentration range₂ in the nucleus it is from one percent by weight to 15 percent by weight. Thicker films require less TiO₂ to achieve the same whiteness. For inventive films, the preferred concentration range is four percent by weight to 10 percent by weight.

Other minerals that can be used are aluminum oxide, calcium sulfate, calcium carbonate, magnesium carbonate, sodium silicate, mica, clay, talc, and the like, ranging from two percent by weight to 25 percent in core weight. The action of these minerals is to cause the formation of cavities or holes in the film. These cavities contribute to making the film more opaque due to the multiple light scattering. The concentration of the minerals and their particle sizes help determine the hole structure and many properties of the film.

Other additives can be used, such as

-1111 antioxidants, lubricants, surfactants, antistatics, slip agents, antiblocking agents, nucleating agents, coupling agents, and coated minerals. Similarly, adding pigments and dyes (inorganic and organic) to the core or encapsulating coextruded layers of the white versions can yield colors other than white.

The addition of the minerals can be accomplished by using a separate mineral feed stream within the extruder that produces the molten polypropylene core layer, or by initially mixing a dry mixture of the mineral and polypropylene, and then extruding the mixture. , or through a master batch concentrate. The masterbatch concentrates of the minerals in the separately add these concentrates to the core extruder feed with the polypropylene.

In one embodiment, the white film core structure comprises three co-extruded layers. The central layer containing the minerals (typically 10 microns to 50 microns thick) is encapsulated by two coextruded outer polyolefin layers. These encapsulating layers typically 0.5 microns to 5 microns thick, provide continuous nonporous layers. In one way, these encapsulating layers can contain TiO₂ to increase power

-1212 bleach. In another version, these encapsulating layers may contain TiO₂ and cavity-forming minerals such as CaCO₃, for example, while the middle layer is TiO-free₂ or other minerals.

Cover Film

The cover layer comprises a three-layer or three-layer film, including an outer polyester layer, and a first bonding layer comprising a grafted or polar olefin polymer adhesive. Preferably, the cover layer also includes a second tie layer comprising a propylene copolymer with up to 25 weight percent ethylene or butene, a propylene terpolymer, ethylene, adhesive, mixtures thereof, or a polymer of linear ethylene, such as linear low-density polyethylene.

The polyester layer comprises a crystalline copolyester, a crystallizable amorphous polyester homopolymer, or a crystallizable amorphous copolyester. (The terms crystalline and amorphous describe the solid state structure of the polyester as supplied by the vendor, and prior to orientation.)

By the term copolyester is meant that polyester is the reaction product of at least one polyol and a carboxylic acid, there being a total of at least three monomers selected from the

-1313 polyols and acids. Homopolymer polyesters are understood to include a single polyol and a single acid moiety.

The polyester layer contains, as a processing aid, a sufficient concentration of a silicone fluid (i.e., a dimethyl polysiloxane or equivalent), preferably of a high molecular weight (eg, having a viscosity in the range of 300,000 cps to approximately 2,000,000 cps, most preferably approximately 1,000,000 cps, as measured by the Brookfield viscometer), in an amount sufficient to provide uniform polyester elongation characteristics. Typically, a polyester layer intended for subsequent metallization will contain from about 1,000 ppm to about 3,000 ppm of silicone fluid, preferably from about 1,000 ppm to about 2,000 ppm (based on the weight of the polyester) in the polyester layer. Polyesters that are not intended for metallization may contain higher concentrations (eg, up to about one percent by weight) of silicone fluid, if desired. (Silicone fluid concentrations greater than about one percent by weight lead to an intermittent, non-stable state extrusion.)

Baysilone M 1,000,000 silicone fluid is the

-1414 preferred silicone fluid.

The silicone fluid can be added to the polyester by intensive mixing with polyester resin pills, in order to coat the pills, followed by drying of the coated pills, and extrusion. A Henschel mixer is suitable for preparing silicone fluid coated pills.

The polyolefin adhesive bond layer adhered to the polyester layer comprises an ethylene copolymer with an ester, such as an ethylene / vinyl acetate copolymer, an ethylene / methyl acrylate copolymer, an ethylene / acrylate copolymer. n-butyl, an ethylene / ethyl acrylate copolymer, or ethylene methacrylic acid (EMAA), for example. Alternatively, the first bonding layer may comprise a grafted polyolefin adhesive, such as a polyethylene or polypropylene backbone grafted with at least one ethylenically unsaturated carboxylic acid, an anhydride, or other derivative, as known in the art. .

In a preferred embodiment, the cover layer also comprises a second tie layer comprising a propylene copolymer or terpolymer or a linear ethylene polymer such as linear low-density polyethylene, as described above. In this embodiment, the grafted ethylene / ester or polyolefin copolymer adhesive is

-1515 interposes between the second bonding layer and the polyester layer.

The respective thicknesses of the polyester layer, the first tie layer, and the second tie layer, can vary within wide ranges, and are substantially independent of each other. Typical approximate thicknesses for the polyester layer, the first tie layer, and the second tie layer in the final film are as follows:

Polyester layer: 0.75 to 2.5 microns

First bond layer: 1.0 to 2.5 microns

Second bond layer: 0.25 to 1.5 microns

Preferably, the total thickness of the cover layer is in the range of about 2.0 microns to about 6.5 microns in the final film.

The cover layer can be formed by any suitable process, including blown or cast film co-extrusion, as desired.

Although no additional additives are required for the polyester layer, suitable antiblock agents such as zeolites can be conveniently used. Other silicates, clays, talcs, and silicas are suitable antiblock agents, and antiblock agents are generally used in a concentration of about 500 to about 10,000 ppm (preferably about 500 to about 1,500 ppm) based on the weight of the polyester.

-1616

Other additives, particularly stabilizers, can be used to protect the cover layer from degradation during processing, or to impart other desired attributes to the final film.

Preparation of Multilayer Polypropylene Film

Biaxially Oriented

The polyester-containing shell layer is added to the core by coating or lamination by stretch. (In Rice et al., U.S. Patent No. 5,156,904, the disclosure of which is incorporated herein by reference, coating or lamination processes are disclosed by interest stretching). In this method, the core is formed by extruding and casting the polypropylene core, orienting the core in a first (machine) direction, forming the outer films containing polyester, providing the cover layer on one or both sides of the oriented core , to produce a monoaxially oriented multilayer film, and orienting the resulting multilayer film in a second transverse (and preferably perpendicular) direction to the first direction.

In practice, a monolayer core or a coextruded laminate of the core polypropylene, and a linear • copolymer or terpolymer bonding layer of propylene or polyethylene, can be cast onto a roll held at a

-1717 temperature in the range of, for example, 10 ° C to 100 ° C, reheat on rolls heated to a temperature (for example, 100 ° C to 204 ° C) high enough to soften the polymer (s) (s) in the core, but still below the melting point of the propylene polymer therein, and then orient in the machine direction. After subsequent addition of the cover layer (s), the resulting film is reheated to a temperature preferably higher than the softening point of the outer film layers (eg 73 ° C) , and somehow below the melting point of the core polypropylene (eg 150 ° C to 165 ° C), and the film is oriented in a second direction transverse (and preferably perpendicular) to the machine direction.

A cover layer can be applied to one or both sides of the core. Similarly, the core may contain a bonding layer of propylene polymer or terpolymer or linear ethylene polymer, on one or both sides of the polypropylene core. The biaxially oriented polypropylene multilayer structure can be, but need not be symmetrical; for example, a two-layer cover film may be placed on one side of the core, with a three-layer cover film on the other.

The following non-limiting examples illustrate the practice and benefits of the invention.

-1818

EXAMPLES

All the films described in the following examples were produced in a sequential orientation process. In this process the core layer was extruded and formed into a sheet, prior to orientation in the machine direction. The core layer was then oriented approximately 500 percent. The cover layers were adhered to the core layer and the resulting multilayer film was fed to a tender oven, where the film was cross-oriented approximately 900 percent, heat set, cooled, and wound onto a roll . The initial thickness of the core layer in all examples was approximately 810 microns. The thickness after orientation in the machine direction was 162 microns. The evaluated cover layers varied in thickness from 20 to 35 microns. The thickness of the final multilayer films ranged from about 20 to 30 microns. The output rate of the examples ranged from 113 kilograms / hour to 183 kilograms / hour. The core layers were produced using one or two grades of commercially available isotactic homopolymer polypropylene resin - Fina 3275 or Exxon 4152. Other film grade polypropylene resins are suitable for use as the core layer in the described experiments. Example 4 describes the representative process conditions that were used to produce the

-1919 movies in all examples.

Sample Evaluation Methodology

Many films made in accordance with the invention were evaluated to see the key attributes listed below. Since an intended use of the films is for packaging, either alone or in laminations, the films must exhibit good appearance, sealability, and integrity. In addition, economic considerations indicate that films are processed quickly with ample processability and low waste.

Visual Criteria

All transparent films were evaluated for their haze and optical defects. Haze was measured in accordance with ASTM D-1003.

Evaluation Comments

Fog &lt;2, minimal optical defects Fog &lt;3, minimal optical defects Fog &lt;5, some optical defects

Excellent

Good

Regular

Deficient

Fog&gt; 5

Sealing Strength of Polyester Layer

All transparent (i.e. non-metallized) films were evaluated for seal strength by cutting 2.54-centimeter-wide strips and sealing the polyester surface to itself at three temperatures, i.e. 110 ° C , 125 ° C, and 145 ° C, in a heat sealer

-2020

Brugge München, NDS type, using a residence time of 0.5 seconds and 0.5 psi of applied pressure. The seals were pulled on an Instron 4201 test machine. The maximum value was noted and the failure mode determined by visual inspection. An acceptable seal is considered to have a minimum maximum force of 75 grams / inch. Destruction denotes a failure mode at the sealing interface or excessive deformation of the film. Delamination denotes a failure mode between the layers of the film (for example, the bond / polyester interface, or the bond / core interface). Evaluation Comments

Excellent initiation of sealing at lowest temperature, failure mode destruction

Good initiation of sealing below 125 ° C, failure mode destruction

Regular Initiation of sealing at 110 ° C, failure mode

Delamination

Poor Unacceptable stamps

Interlaminal Adhesion Before Metallization

This property was evaluated by heating sealing films together, as described above, and noting the failure mode at different temperatures. The test was conducted on samples of transparent film process on interlaminal adhesion.

-2121

<td>Evaluation</td><td>Comments</td>

<td>Excellent</td><td>100 percent DESTRUCTION stamps on all</td>

<td>Good</td><td>the temperatures Failure mode predominates DESTRUCTION</td>

<td>Regular</td><td>DESTRUCTION failure mode in some cases</td>

<td>Deficient</td><td>SLIDE 100 percent Metal Bond</td>

This property was evaluated by applying five 20.32 centimeter strips of Scotch brand 610 tape (from 3M) to the metallized surface in both the machine and cross direction, pressing the strips firmly to the film, and then quickly pulling tape at a 90 ° angle to the substrate. The failure mode (metal delamination or delamination at a polymer / polymer interface) was denoted as the percentage of metal removed from the surface. The samples were then valued.

<td>Evaluation</td><td>Comments</td>

<td>Excellent</td><td>0-10 percent metal delamination</td>

<td>Good</td><td>10-50 percent metal delamination</td>

<td>Deficient</td><td>metal delamination of&gt; 50 percent and / or any sign of delamination in a polymer / polymer interface Process 1 way &lt;í</td>

This is a broad category that includes aspects for the preparation of the cover layer, the adhesion of the

-2222 cover layer to combined film layer, and subsequent operations.

core, the elongation of the processing through

Evaluation

Cnmon ta τ-ί nc

Excellent

Good

Regular

Wide process window, strong adhesion, fast elongation, good winding characteristics, good conversion properties Narrower process window, good adhesion, good elongation, winding and conversion characteristics

Narrow process window, adhesion elongation under conditions (some elongation bands adequate, optimal conversion properties evident), adequate

Difficult to process, inconsistent adhesion, non-uniform elongation characteristics. In the table titled Summary of Results after the descriptions of the examples, the evaluations of the films are presented.

Example 1 - Combining Monolayer Outer Film to

Laminated Treated Propylene Homopolymer

Deficient

Interestiramiento

In this example, a monolayer core of an isotactic polypropylene homopolymer was extruded onto a roll

-2323 pour / cool, subsequently heat conditioned, oriented 500 percent in the machine direction and then surface treated using a flame treatment technique. A monolayer outer film produced using an amorphous copolyester was subsequently adhered to a treated surface of the polypropylene homopolymer. The resulting structure was reheated, oriented approximately 900 percent crosswise, cooled, and wound onto a roll.

The film produced in this manner exhibited acceptable optical properties although some unevenness in stretch was noted in the copolymer. Interlaminal adhesion to copolyester of polypropylene was very low (&lt;50 grams / inch). The film was not subjected to other processes (i.e. metallization) due to low interlaminal adhesion.

Example 2 - Combining a Two-Layer Cover Layer With a Propylene Homopolymer by Inter-lamination Lamination

In this example, a monolayer core of an isotactic polypropylene homopolymer was extruded onto a cast / cooled roll, subsequently heat conditioned, and then oriented 500 percent in the machine direction. A series of two-layer cover films produced was subsequently adhered using a copolymer of

-2410 amorphous polyester and various link layer resins to propylene homopolymer. The resulting structures were reheated, oriented approximately 900 percent crosswise, wound and wound onto a roll. The resulting clear films were tested, prior to metallization, to verify their visual appearance, sealing strength, and interlaminal adhesion. Each of the examples was then metallized to an optical density of 2.1 using aluminum in a vacuum deposition chamber. Metallized samples were evaluated to verify sealing strength (on the non-metallic side) and metal adhesion.

Structure 2A) Layer of

Polyester:

Layer of

Link:

Structure 2B) Layer of

Polyester:

Layer of

Link:

90% Selar PT 8307 from DuPont

9% Eastman Kodabond 13162

1% C0047

100% Admer AT776

90% Selar PT 8307 from DuPont

9% Eastman Kodabond 13162

1% C0047

100% Quantum EVA UE 635 (Ethylene vinyl acetate copolymer)

-2525

Structure 2C)

Layer of

Polyester:

90% Selar PT 8307 from DuPont

9% Eastman Kodabond 13162

1% C0047

100% Bynel 446 and 774 layer of

DuPont

Link: (Maleic Anhydride Graft Ethylene Vinyl Acetate Copolymer)

These films were an improvement on the films produced in Example 1. They exhibited acceptable sealing strength and interlaminal adhesion. The film produced in this way did not stretch evenly and was difficult to process. The two-layer cover film was very brittle and had poor tear strength. This resulted in difficulty in adhering the uncovered layer to the core layer and in an excessive occurrence of tissue breakdown during cross-orientation.

Structure 2B exhibited lower sealing strength and interlaminal adhesion than either Structure 2A or 2C. The low melting point of the ethylene vinyl acetate (AEV) bond layer led to relatively easy delamination with the polyester layer either during sealing or the result of metallization.

-2626

These tests optimized the layer thickness for a two-layer cover film. A copolyester layer in excess of 22 microns thick was not evenly elongated. A copolyester layer less than 6 microns thick did not produce good low temperature seals. These phenomena of thickness were also true for the bond layer. A bond layer in excess of 22 microns thick was not evenly elongated. A bonding layer less than 8 microns thick had poor crease adhesion and did not evenly stretch the copolyester.

Example 3 - Adding a Processing Aid to Improve the Stretch of the Polyester Layer

In this example, a monolayer core of an isotactic polypropylene homopolymer was extruded onto a cast / cooled roll, subsequently heat conditioned, and then oriented 500 percent in the machine direction. To each surface of the core layer, one of five cover layer constructions was adhered by inter-stretch lamination. In each case the resulting structure was reheated, oriented approximately 900 percent crosswise, cooled, and wound onto a roll. Clear films were tested, prior to metallization, to verify visual appearance, sealing strength, and interlaminal adhesion. Each of the samples was then metallized to an optical density of 2.1

-2727 using aluminum in a vacuum deposition chamber. Metallized samples were evaluated to verify sealing strength (on the non-metallized side) and metal adhesion. The five structures used in this example are described below.

Structure 3A)

Structure 3B)

Layer of

Polyester

Layer of

Link:

Polyester layer

Layer of

Link:

DuPont 89% Selar PT 8307 (Amorphous Copolyester)

DuPont 10% Selar PR 4234 (hardened copolyester)

1% C0047 Glide / Antiblock Masterbatch Ethylene Methyl Acrylate Copolymer Blend (70% Chevron 2205, 30% Chevron EMAC + 2305)

DuPont 93% Selar PT 8307 (amorphous copolyester)

6% Eastman Kodabond 13162 (PETG copolymer ^

1% C0047 MB

Ethylene Methyl Acrylate Copolymer (70% Chevron 2205, 30%

-2828

Structure 3C)

Polyester layer

Layer of

Link:

3D structure)

Structure 3E)

Polyester layer

Layer of

Link:

Polyester layer

Chevron EMAC + 2305)

DuPont 93% Selar PT 8307 (amorphous copolyester)

6% Eastman Kodabond 13162 (PETG copolymer)

1% C0047 MB

3000 ppm silicone fluid Ethylene Methyl Acrylate Copolymer (70% Chevron 2205, 30%

Chevron EMAC + 2305)

DuPont Seal PT 8307 (Amorphous Copolyester)

1% C0047 MB

3000 ppm silicone fluid

Ethylene Methyl Acrylate Copolymer (70% Chevron 2205, 30%

Chevron EMAC + 2305)

DuPont Seal PT 8307 (Amorphous Copolyester)

3000 ppm Baysilone M

-2929

1,000,000 silicone fluid

Copolymer layer

Binding: Ethylene Methyl Acrylate (70% Chevron 2205, 30%

Chevron EMAC + 2305)

In each case, the total thickness of the cover layer was approximately 23 microns, including 15 microns of the polyester layer and 10 microns of the bond layer.

Structure 3A exhibited excessive haze and poor luster (poor visuals) and only regular sealing force due to the presence of the hardened copolyester.

Structure 3B was difficult to process due to brittleness which resulted in uneven elongation and tissue breakdown. This resulted in only visuals, sealing strength, and regular interlayer adhesion, due to inconsistency across the tissue.

Structure 3C exhibited improved processability compared to Structure 3B, which resulted in more uniform properties.

Structure 3D processed similarly to Structure 3C without the use of PETG copolymer, which improved the processability of Selar PT 8307 in the absence of other additives.

Structure 3E again processed so

-3030 similar to Structure 3C but had the best visuals and good processability.

In all cases, the adhesion of the bonding layer to the core was reduced after metallization, resulting in graduated downward performance.

Example 4 - Combining a Two- and Three Cover Layer

Layers with a Propylene Homopolymer Core

In this example, a monolayer of isotactic polypropylene homopolymer with a melting strength of 254 ° C was extruded into a casting roll set at a temperature of 36 ° C to form the core layer. The initial thickness of the core layer was approximately 810 microns. The surface of the core layer opposite the casting roll was then contacted against a cooling roll with a surface temperature of 72 ° C. The core layer film was then conditioned by heating to 121 ° C by contacting a series of heated rolls and subsequently oriented in the machine direction 500 percent through a pair of rolls heated to 141 ° C. The monoaxially oriented core layer, 162 microns thick, was then contacted on each surface to temper the roll setting at a temperature of 141 ° C. At that point in the process, the cover layer structures, each approximately 23 microns thick, thermally adhered to the

-3131 core. This experiment evaluated three different shell layer structures, each of which was applied to the surface of the core layer to make a symmetrical structure. The 208 micron thick multilayer film structures were then inserted into an endless chain mechanism (being supported by a series of clamps) and placed in an oven. After reconditioning the multilayer film at 121 ° C, the structure was cross-oriented 900 percent and subsequently cooled to about 80 ° C and wound onto a roll. The final thickness of each sample was approximately 23 microns. The process output rate was approximately 400 pounds / hour (182 kilograms / liter). The line speed in the extrusion and casting section was 26 meters / minute while after machine orientation, the line speed increased to 113 / meters / minute.

Transparent films were tested, prior to metallization, to verify visual appearance *; sealing strength, and interlaminal adhesion. Each of the samples was then metallized to an optical density of 2.1 using aluminum in a vacuum deposition chamber. Metallized samples were evaluated to verify sealing strength (on the non-metallized side) and metal adhesion.

Structure 4A) Layer of

-3232

<td>Polyester:</td><td>90% Selar PT 8307 from DuPont</td>

<td>Layer of Link:</td><td>9% Eastman Kodabond 13162 1% C0047 100% Quantum EVA UE 635</td>

<td>Structure 4B) Layer of</td><td></td>

<td>Polyester:</td><td>90% Selar PT 8307 from DuPont</td>

<td>Layer of</td><td>9% Eastman Kodabond 13162 1% C0047 Bynel 446 and 774 mix of</td>

<td>Link:</td><td>DuPont</td>

<td>Structure 4C) Layer of</td><td></td>

<td>Polyester:</td><td>100% Selar PT 8307 de</td>

<td>the. Cap</td><td>DuPont 1500 ppm Baysilone M 1,000,000 fluid silicone Quantum EMA EMTR002</td>

<td>Link:</td><td> •</td>

<td>2a. Cap</td><td>Random Copolymer</td>

<td>Link:</td><td>Polypropylene</td>

<td>Structure 4C, the</td><td>(Exxon 9122, PD 9263, PT 9524, PT 9513, Fine CR6671BB, 6571) which incorporates a structure</td>

-3333 three-layer cover film exhibited the best properties of any of the films produced. It quickly processed through a wide range of processing conditions and produced a film with excellent visual properties, excellent sealing strength, and superior interlaminal adhesion both before and after metallization. The three layer outer film was evenly stretched, processed quickly, was not brittle, and had good tear strength.

Structure 4C exhibited the best interlaminal adhesion, both before and after metallization. While most of the two-layer structures exhibited a reduction in interlaminal adhesion after metallization, the interlaminal adhesion of the three-layer outer film was unchanged.

Additionally, these tests were useful in optimizing the layer thickness for a three layer cover film. A copolyester layer in excess of 23 microns thick was not evenly elongated. A co-polyester layer less than six microns thick did not produce good low temperature seals. These phenomena in thickness were true for the bond layers. A first bond layer in excess of 8 microns thick was not evenly elongated. A bond layer less than 4 microns thick had poor crease adhesion and did not stretch the copolyester

-3434 evenly. A second bond layer in excess of 6 microns was not elongated evenly. A bonding layer less than 4 microns thick had poor crease adhesion and did not stretch the copolyester evenly.

Finally, these tests were useful in optimizing the level of process aid required in the polyester layer. A level below 1000 ppm did not give good stretching properties. A level in excess of 3000 ppm reduced the sealing properties and did not give good metal adhesion.

Example 5 - Combining Two Three-Layer Films With One. Polypropylene Homopolymer By Lamination By

Interestiramiento

In this example, a monolayer core of an isotactic polypropylene homopolymer was extruded onto a cast / cooled roll, subsequently heat conditioned, and then oriented 500 percent in the machine direction. Two three-layer shell layers were adhered to each core layer surface by roll lamination. In each case the resulting structure was reheated, oriented approximately 900 percent crosswise, cooled, and wound onto a roll. Clear films were tested, prior to metallization, to verify visual appearance, sealing strength, and interlaminal adhesion. Then it metallized

-3535 each of the samples at an optical density of 2.1 using aluminum in a vacuum deposition chamber. Metallized samples were evaluated to verify sealing strength (on the non-metallized side) and metal adhesion.

One of the three layer cover films was produced using an amorphous copolyester and subsequently adhering it to the polypropylene homopolymer. This layer had excellent low temperature sealing properties. A second three layer outer film was produced with a blend of a crystallizable amorphous copolyester and amorphous copolyester or a crystallizable amorphous homopolymer and amorphous copolyester. This layer produced an excellent base for metallization.

Structure 5A)

Cap

External

Mix of Selar PT

DuPont 8307/8111

1500 ppm Baysilone M 1,000,000 silicone fluid ·

<td>the. Cap</td><td>Quantum EMA, EMTR002</td>

<td>Link:</td><td></td>

<td>2a. Cap</td><td>Random copolymer</td>

<td>Link:</td><td>polypropylene</td>

(Exxon 9122, PD 9273,

PT 9524, PT 9513, Fine

-3610

CR6671BB, 6571)

Structure 5B)

Cap

External:

Mix of Selar PT

DuPont 8307/7001 la. Cap

Quantum EMA, EMTR002 Link:

2a. Cap

Link:

Polypropylene Random Copolymer (Exxon 9122, PD 9273, PT 9524, PT 9513, Fina

CR6671BB, 6571)

Films produced in this way resolved many of the concerns that were noted with the previous structures. The multilayer biaxially oriented polypropylene films were stretched evenly and were not proven to be difficult to process. The three-layer outer films were not brittle and had good tear resistance.

The observations of the useful layer thickness and the silicone fluid concentration averages were identical to those of Example 4.

-37 Summary of Results

<img file="MX9701002A_D0001.tif" />

LT)

ΙΠ

-3838

In each of Examples 6-8 white films were prepared by the inventive method wherein the core layer was oriented to a degree of 500 percent in the machine direction, followed by application of the outer layers to the core and the orientation of the resulting three-layer films to a degree of 900 percent in the cross direction.

Example 6 - White Film

A three layer white film with a total gauge of 26 microns was prepared. The core (22 microns) contained 8.4 weight percent CaCo₃, as a cavity forming agent with four weight percent TiO₂ for bleaching and 87.6 percent by weight of a 2 MFR homopolymer polypropylene. An outer layer (a myria) was an ethylene propylene random copolymer sealing layer made from a 6 weight MFR resin with 6.5 weight percent ethylene. The other outer layer used the same three-layer cover film as described in Structure 4C, above. The film had an optical density of 0.4 and a pleasant white appearance.

Example 7 - White Film

The film of Example 7 had the same core structure as the film of Example 6 with CaCO₃ and uncle₂ and a 22 micron caliber. On each side of the core were co-extruded layers of three sheets of the same polypropylene

-3939 2 MFR homopolymer used in the core, but without minerals. On one side of this three-layer core was the three-layer cover film described in Structure 4C. The film in Example 7 had an optical density of 0.18 and a somewhat pearly, pleasant white appearance. When the film was vacuum metallized with aluminum on the surface of the film opposite the polyester side, the optical density increased to 1.6. Therefore, the white film had a shiny aluminized surface.

Example 8 - White Film

In this example, a white film was made as in Example 7 except that after orienting the core (including encapsulated layers) in one direction, a thick EVA cover layer was provided on one side of the core. The resulting multilayer film was then oriented in a second direction transverse to the first.

The final caliber of the film was 41 microns. The thickness of the EVA layer was approximately 11 microns. This thickness of the EVA layer was used to improve the sealing strength at lower applied temperatures. The film of Example 8 was cut into 25 micron wide strips. The EVA surfaces of two strips were then heat sealed to each other at temperatures in the range of 230 ° F (110 ° C) to 270 ° F (132.22 ° C). The process was repeated at different temperatures (0.5 seconds of applied heat and 20 psi of pressure). In the same way,

-4040 The ethylene propylene copolymer seal layers of Example 6 were heat sealed to themselves. The structures of Example 8 with the thick EVA layer initiated the sealing at lower temperatures and gave about twice the sealing strength to the ethylene propylene copolymer layers.

From the foregoing detailed description it will be apparent to those skilled in the art that the invention provides useful biaxially oriented polypropylene film compounds containing cover films using amorphous or crystalline copolyesters or amorphous homopolymer polyesters. For some applications, composite films containing three-layer polyester outer layers are preferred because they offer superior processability, inter-fold adhesion, and characteristic appearance.

The use of silicone fluid as a processing aid in the polyester layer improves the elongation capacity and uniformity of the layer and eliminates the need to mix additional amorphous copolyester as a processing aid. The biaxially oriented polypropylene multilayer films of the invention retain the excellent surface energy characteristic of polyesters, thereby providing an excellent surface for metallization. Pretreatment of the polyester layer is not necessary to achieve excellent adhesion of

-4141 metal.

Furthermore, films can be printed and laminated using conventional methods.

Biaxially oriented polypropylene films using copolyester have excellent optical characteristics and can be sealed.

The above detailed description is given for clarity and understanding only, and no unnecessary limitations should be understood thereto, as modifications within the scope of the invention will be apparent to those skilled in the art.