WO1995013329A1

WO1995013329A1 - Multi-phase film and methods relating thereto

Info

Publication number: WO1995013329A1
Application number: PCT/US1994/012892
Authority: WO
Inventors: Yves M. A. Trouilhet; Karlheinz Hausmann; Hans Dieter Flieger
Original assignee: E.I. Du Pont De Nemours And Company
Priority date: 1993-11-10
Filing date: 1994-11-09
Publication date: 1995-05-18
Also published as: AU1052195A

Abstract

The present invention relates generally to low cost, extruded packaging films which are easy-to-open (will easily tear in the film's traverse direction), and in one preferred embodiment, has excellent heat seal, hot tack and adhesion to metal. More specifically, the film compositions of the present invention comprise a first phase (preferably a substantially continuous phase) of a low cost, substantially non-polar base polymer and a second phase (preferably a substantially discontinuous phase) of an adhesive polymer.

Description

TITLE

MULTI-PHASE FILM AND METHODS RELATING THERETO Field of the Invention The present invention relates generally to the low cost, extruded packaging films which are easy-to-open

(will easily tear in the film's traverse direction), and in one preferred embodiment, has excellent heat seal, hot tack and adhesion to metal. More specifically, the film compositions of the present invention comprise a first phase (preferably a substantially continuous phase) of a low cost, substantially non-polar base polymer and a second phase (preferably a substantially discontinuous phase) of an adhesive polymer.

BACKGROUND OF THE INVENTION U.S. 4,183,882 to Weinberg teaches a self-welding shrink film comprising: 1) 30%-95% by weight ethylene homopolymer or copolymer having a melt flow in the range of 0.25 to 5.0; and 2) 5%-70% by weight ethylene copolymer having a melt flow greater than 28. U.S. 4,416,937 to Metzger teaches an adhesive film comprising: 1) about 5%-90% by weight adhesive resin having a melt index of from about 50-70; 2) about 5% to 90% by weight second adhesive resin having a melt index of from about 3-15; and 3) about 5%-70% by weight non- adhesive resin having a melt index from about 3-10.

European patent publication, EP 05 37 080A1 is directed to multilayer films which can be easily torn open in a controlled manner (the film tears easily in the traverse direction of the film) . The publication teaches multilayer films comprising a polyolefin layer and an ionomer layer.

SUMMARY OF THE INVENTION In a first preferred embodiment, the present invention is directed to a film ("film" as used herein, is intended to include sheet, tape, board, or any film-like structure) comprising. a) an adhesive resin consisting essentially of at least one olefinic copolymer having carboxylic acid, anhydride or ester functionality, the adhesive resin defining a melt index less than about 28 and greater than about 5, and a melting point above 25°C; and b) a base resin comprising a substantially non- polar, olefinic polymer having a melt index less than about 5 and a melting point above 25°C; whereby the weight percent of a) based upon the total weight of a) and b) is in the range of about 5% to about 90% , yet more preferably 5% to about 80%.

This first preferred embodiment is particularly useful as a self sealing or self welding film which also has the "easy open" tear properties in the traverse direction.

In a second preferred embodiment, the present invention is directed to a film comprising: a) an adhesive resin consisting essentially of at least one olefinic copolymer having carboxylic acid, anhydride or ester functionality, the adhesive resin defining a melt index less than about 5 and a melting point above about 25°C; and b) a base resin comprising a substantially non- polar, olefinic polymer having a melt index less than about 28 and greater than about 5 and a melting point above about 25°C; whereby the weight percent of a) based upon the total weight of a) and b) is in the range of about 5% to about 90%, yet more preferably, 5% to about 80%.

In this second preferred embodiment, the films generally lack the heat sealing properties of the first preferred embodiment, but nevertheless provide "easy open" tear properties in the traverse direction.

In either preferred embodiment, the preferred adhesive resin is an ionomer, acid copolymer or vinyl ester copolymer, most preferably, ionomer. In the first preferred embodiment, the base resin is substantially concentrated at the core of the film, and the adhesive resin is substantially concentrated at the surfaces of the film. In the second preferred embodiment the base resin is substantially concentrated at the surface of the film, and the adhesive resin is substantially concentrated at the core of the film.

The present invention is also directed to a method for decreasing the traverse tear resistance of a film by incorporating into the film the blend compositions of the present invention. Such films can be monolayer or multilayer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

AND BEST MODE Overview

The present invention relates generally to the blends of:

1. adhesive thermoplastic resin having: a) carboxyl or ester functionality, and b) a melting point above about 25°C, more preferably above about 50°; and

2. relatively non-polar, non-adhesive thermoplastic polyolefin base resin having: a melting point above about 25°C, more preferably about 50°C, wherein the melt index of one of the above resins is less than about 5, and the melt index of the other resin is in the range of less than about 28 and greater than about 5. As used herein, "melt index" numbers are determined according to the procedures of ASTM D-1238 (190°C using a 2.1 kg weight). The present invention further relates to films and laminates made from such blends.

Each of the resin components will be discussed first, and thereafter, combinations of these components will be described. Finally, optional additional ingredients will be discussed and methods of manufacturing the compositions of the present invention will then be described.

Adhesive Component

The adhesive resin component of the polymer blend compositions of the present invention are preferably substantially polar and preferably have a melt index of either:

I. in the range of about 5 to less than about 28 (where the base resin has a melt index of less than about 5) ; or

II. less than about 5 (where the base resin has a melt index in the range of greater than about 5 and less than about 28) .

The compositions according to "I" will generally have a relatively high concentration of adhesive at the surface of the film, and therefore films made from the compositions of I will generally have excellent heat seal, hot tack and adhesion to metal. The compositions of "II" will generally have a relatively high concentration of the base resin at the surface of the film, and therefore will substantially lack the adhesive, hot seal and hot tack properties of I, but nevertheless will have the improved tear properties in the traverse direction, similar to the films of I. "Traverse direction" of the film, as used herein, is intended to mean the direction of the film perpendicular to the direction of the extrusion (which is defined during the original extrusion of the film) . The direction of extrusion is commonly referred to as the "machine" direction (hence, an extruded film is extruded in the machine direction) . Generally speaking, the properties of the film in the machine direction are not identical to the properties in the traverse direction; typically, a film will not readily tear in the traverse direction. However, the film compositions of the present invention can generally be easily torn open in the traverse direction, and this can be particularly advantageous in packaging applications, particularly where very large shapes are packaged. Suitable adhesive resins include random copolymers derived from a major portion of ethylene and a minor proportion of one or more relatively polar monomers such as: 1. ethylenically unsaturated carboxylic acid monomers (e.g., acrylic acid, methacrylic acid, crotonic acid, etc.) or the neutralized metallic salts thereof (e.g., as found in the partially neutralized ethylene/carboxylic acid copolymers which are commonly referred to in the art as ionomers) ;

2. vinyl esters of alkanoic acids (e.g., vinyl acetate, vinyl propinate, vinyl butyrate, etc.);

3. lower alkyl or hydroxyalkyl (e.g., Cl to about C8) esters of the aforementioned ethylenically unsaturated carboxylic acids (e.g., methyl acrylate, ethyl acrylate, hydroxyethyl acrylate, n-butyl acrylate, methyl methacrylate, ethyl methacrylate, etc.); and

4. derivations of the above. Less preferred adhesive resins include graft modified olefin polymers, such as, high density polyethylene/acrylic acid graft copolymers, and ethylene/vinyl acetate copolymers graft modified with ethylenically unsaturated carboxylic acid monomers such as acrylic acid, aleic anhydride, etc.

The most preferred adhesive resins are derived from the addition polymerization of from about 50 to about 85 weight percent ethylene with from about 15 to about 25 weight percent of an ethylenically unsaturated carboxylic acid monomer (especially acrylic or methacrylic acid) or a vinyl ester of an alkanoic acid (especially vinyl acetate or vinyl propionate) .

The adhesive resin component preferably constitutes about 5 to about 90 percent of the total weight of said blends. More preferably, the adhesive resin is present in the range of from about 5 to about 75 weight percent based on the total weight of the blend. Most preferably, the adhesive resin constitutes from about 20 to about 60 weight percent of the blend. The most preferred adhesive components for the blends of the present invention are ionomers. Preferred ionomers are derived from at least: 1. about 10 to about 98 weight parts ethylene (more preferably about 70-98 weight parts ethylene) ; and

2. about 2 to about 90 weight parts acrylic, methacrylic acid, maleic acid, fumaric acid, itaconic acid, or half esters of maleic, fumaric or itaconic acid (more preferably about 2 to about 30 weight parts of the unsaturated acid) wherein the resulting copolymer is wholly or partially neutralized with metal ions selected from groups la, lb, Ha, lib, Ilia, IVa, VIb, and VIII of the Periodic Table of Elements; preferred such metal ions are sodium, potassium, zinc, calcium, magnesium, lithium, aluminum, nickel, and chromium; the most preferred metal ions are sodium or zinc.

The ionomers of the present invention can be prepared by polymerizing ethylene and unsaturated carboxylic acid in the presence of free radical polymerization initiator at elevated temperatures of from about 100° to about 200°C, preferably from about 140° to about 160°C or from about 130° to about 145°C at high pressures, e.g., at least about 140 MPa (20,000 psi) preferably from about 140 MPa (20,000 psi) to about 350 MPa (50,000 psi) followed by neutralization of the carboxylic acid groups of the resultant direct copolymer with metal ions. A suitable polymerization process is discussed in detail in the U.S. Pat. No. 3,264,272, the disclosure of which patent is hereby incorporated by reference.

Base Resin

The preferred base resin is a polyolefin. Preferably, the base resin component has a relatively low density (e.g., from about 0.91 to about 0.93) and most preferably such resin is a non-polar, olefin polymer resin such as, for example, homopolymers of lower alpha -olefins (e.g., homopolymers of ethylene, propylene, etc.), copolymers of a major portion of a lower alpha -olefin (especially ethylene) with a minor portion of higher (e.g., C4-C12) alpha -olefins (e.g., 1-butene, 1-hexene, 1-heptene, 1-octene, etc.), and the like.

The base resin preferably has a melting point of from about 85° to about 120°C with some particularly preferred non-adhesive resin components having melting points of from about 100° to 120°C (especially from 110° to 115°C) .

The base resin is preferably present in the range of from about 5 to about 95 weight percent (more preferably 5-75 wt%), based upon the total weight of the polymer blend. More preferably, however, the base resin component is used in the amount of from about 10 to about 60 weight percent of such polymer blend.

Final Blend Composition

Surprisingly, in the extruded film or sheet application, the blend compositions of the present invention provide adhesion properties which tend to approximate the properties of the adhesive resin by itself, where the melt index of the adhesive is in the range of greater than about 5 and less than about 28 and the melt index of the base resin is less than about 5. Despite the high loading of non-adhesive, base resin, the base resin generally does not dramatically interfere with the adhesive properties of the adhesive resin.

Where the melt index of the adhesive resin is significantly greater than the melt index of the base resin, it is theorized that the difference in polarity and melt index cause the adhesive resin to migrate and concentrate at the surface of the sheet or film. Conversely, the base resin tends to concentrate at the core of the film or sheet. Since the adhesive properties are generally most critical at the surface of the film or sheet, the presence of base resin at the core of the sheet generally is of little consequence to the adhesion, heat sealability, hot tack, etc. of the overall structure.

It is further theorized that (where the melt index of the adhesive resin is substantially greater than the melt index of the base resin) the adhesive material maintains a discrete phase and where high loadings of the base resin are used, the adhesive resin will tend to be a discontinuous phase which concentrates at the surface of the film or sheet and the base resin tends to become a continuous phase which concentrates at the core of the film or sheet. The adhesive resin phase may be separated at the surface by the base resin phase, but generally, sufficient regions of the adhesive material will exist along the surface of the film or the sheet to provide a material with adhesive properties which somewhat approximates a pure adhesive resin material.

In any embodiment of the present invention, the multiphase morphology of the film has been surprisingly found to exhibit improved tear in the traverse direction of the film and to decrease tear in the machine direction. Depending upon the particular application, improved tear in the traverse direction can be particularly advantageous and is quite unusual, compared to many conventional sheets or films comprising only adhesive resin.

In addition to the above-discussed requisite polymer components, the polymer blend compositions of the present invention can further contain other additional polymeric components as well as the usual additional ingredients and additives conventionally employed in the art for various purposes in polymer compositions, films and the like, such as, for example, dyes, pigments, fillers, anti-oxidants, fire-retarding agents, etc. When such optional ingredients are employed, their usage is generally in the content range or loading level typically utilized in the art for such purposes.

The method by which the polymer blend compositions of the present invention are prepared is not particularly critical to the invention and any conventional or non- conventional method and equipment (e.g., conventional extrusion equipment, Brabender mixers, etc.) can, therefore, be employed to admix the required components in the desired proportions. Accordingly, conventional or non-conventional extrusion or coextrusion equipment and processes can be used for obtaining intimate admixture of the individual components of the present polymer blends. The polymer blends can be formulated in a separate extrusion compounding operation prior to the extrusion operation in which the objective film or laminated structures are to be actually made.

Alternatively, the individual components of the subject polymer blends can simply be pre-blended (e.g. in pelletized, granular or powdered form) prior to being fed into the extruder used in the film-forming or extrusion coating operation (or can be individually fed as separate, appropriately metered feed streams to said extruder) , with the desired degree of intimate admixture of said components than being accomplished in said film-forming or extrusion coating extruder rather than in a separate compounding operation.

The polymer blend compositions of the present invention are particularly well-suited for the preparation of free-standing monolayer or multilayered films (e.g., typically having a thickness in the range of from about 0.5 to about 15 mils and oftentimes in the range of from about 1 to 5 mils) for various end uses including usage for lamination to various metallic and non-metallic substrates such as for use as outer coating layers or as intermediate adhesive layers in various laminar objects (e.g., as protective outer coatings for metallic substrates; as outer, heat sealable layers in various cellulosic or synthetic polymer-based packaging materials; as an adhesive layer between the same or different type of non-adhesive substrates, such as, for example, between non-woven nylon fabric and polyurethane foam and the like) as well as usage in extrusion coating operations for the preparation of similar laminar objects.

In the above-noted usage's of the present polymer blends, conventional auxiliary treatments which are typically used, such as, radiation crosslinking, corona discharge surface treatments, etc., of films prepared therewith can optionally be employed to modify particular properties (e.g., elevated temperature flow characteristics, degree of adhesiveness to particular substrates, etc.) which may be of special interest in a given instance.

In one alternative embodiment, the present polymer blends are used as laminatable adhesive monolayer films and thereafter incorporated into one or more layers of a coextruded multiple layer film structures or incorporated with a metal layer or coating.

In the most preferred embodiment, the adhesive resin and base resin are mixed at high shear, preferably at a shear greater than about 100 sec "^ (or inverse seconds), more preferably greater than about 200 sec^~l and most preferably greater than about 300 sec~l. High shear is preferably also by high shear (high speed) extrusion, whereby high shear is accomplished as the resin moves through the die. Such high shear can be accomplished at high die temperatures and fast line speeds. Preferred die temperatures are above about 50°C, more preferably above about 75°C and most preferably above about 100°C. The preferred line speed is preferably at least about 10 meters per minute, more preferably greater than about 15 meters per minute and most preferably at least about 17 meters per minute.

EXAMPLES Materials Ionomer 1: Ethylene/Methacrylic Acid Copolymer Neutralized with Zinc MFI=14

Ionomer 2: Ethylene/Methacrylic Acid Copolymer Neutralized with Sodium MFI=1 PE-1: Exxelor™ 251 Low Density Polyethylene MFI=8

Process

The materials were tumble blended in pellet form and fed into a 30mm laboratory Brabender Plasticoder extruder (PL650.) with a L/D=24 equipped with a laboratory blown film unit Mod 840805. The processing temperature was about 210°C. The "film speed" as used herein, is the pull-off speed of the film take up unit. The final films had a thickness between 60 and 100 micrometers. Analysis

The determination of the Elmendorff tear strength was performed according to ASTM D 1922. In the case where samples showed tear in transverse direction compared to machine direction the ration MD/TD is > 1 and in the behavior of preferred tearing in traverse direction is indicated by "YES" in the column "Easy Tear".

The swelling ratio is defined as: Diameter of filmbubble/diameter of die. The percentages are given weight %. Seal strength was measured by Sentinnel heat seal equipment Model No. 12A8 exercising 0.46 Mpa during 1 second.

TABLE I

Ionomer 1

Ionomer 2

PE-I

MFI Iono/PE (dg/min)

Thickness (microns)

Speed (m/min)

Swell factor

Tear Strength MD N/15mm

Tear Strength TD N/15mm

Ratio MD/TD

Easy Tear

Seal Strength N/15mm

Results

Cl has an inverse viscosity ratio (ionomer outside-PE inside) indicated by measurable seal strength, C2 and C3 have ionomer inside and PE outside. 1 and 2 have same composition as C2 and C3 but provide improved "easy tear" behavior, due to higher pull off speed.

Claims

WHAT IS CLAIMED IS:

1. A film comprising at least one layer, said layer comprising: a) an adhesive thermoplastic resin having: i) carboxyl, anhydride or ester functionality, and ii) a melting point above about 25°C; and b) a non-adhesive thermoplastic polyolefin base resin having a melting point above about 25°C, wherein the melt index of one of the above resins is less than about 5, and the melt index of the other resin is in the range of less than about 28 and greater than about 5, said layer being formed by high shear, high speed extrusion.

2. A film according to Claim 1, wherein the adhesive resin defines a melt index less than about 28 and greater than about 5, and the weight percent of the adhesive resin as a percentage of the total weight of adhesive resin and base resin is in the range of about 5% to about 75%.

3. A film according to Claim 2 wherein the adhesive resin is an ionomer, acid copolymer or vinyl ester copolymer.

4. A film according to Claim 3 wherein the adhesive is derived from a major portion of ethylene and a minor portion of acrylic acid or methacrylic acid.

5. A film according to Claim 2 wherein the weight percent of a) is in the range of about 15%-30%.

6. A film according to Claim 2 wherein the base resin is a polyethylene having a density less than 0.96.

7. A film according to Claim 2 wherein the base resin is a substantially continuous phase and the adhesive resin is a substantially discontinuous phase.

8. A film according to Claim 7 wherein the base resin is substantially concentrated at the core of the film and the adhesive resin is concentrated at the surfaces of the film.

9. A method of decreasing the traverse tear resistance of a film, the improvement comprising: melting an extrudable material comprising an adhesive resin and a base resin and extruding the mixture through a die gap at a rate greater than about 10 meters per minute, wherein: a) the adhesive resin consists essentially of at least one olefinic copolymer having carboxylic acid, anhydride or ester functionality and a melt index less than about 28 and greater than about 5, and a melting point above 25°C; and b) the base resin consists essentially of a substantially non-polar, olefinic polymer having a melt index less than about 5 and a melting point above 25°C; whereby the weight percent of a) based upon the total weight of a) and b) is in the range of about 5 to about 75.