EP1179029A1 - Film with enhanced performance properties - Google Patents

Abstract

Disclosed is a tough and stiff film comprising a blend comprising an alkenyl aromatic polymer and a substantially random interpolymer. The film is particularly suitable for use in applications requiring tough and stiff film, such as a window envelope film or a label. The invention further relates to articles of manufacture comprising such film.

Description

FILM WITH ENHANCED PERFORMANCE PROPERTIES

FIELD OF THE INVENTION

This invention relates to a tough, stiff film, comprising a blend of polymeric materials.

BACKGROUND OF THE INVENTION Blends comprising alkenyl aromatic polymers, for example polystyrene, and alpha-olefin/hindered vinyl or vinylidene interpolymers, for example, ethylene-styrene copolymer, are known in the art. Such blends have been suggested for use in several applications, including films and foams.

WO 95/32095 discloses a heat-shrinkable film comprising an oriented film layer comprising a homogeneous alpha-olef in/vinyl aromatic copolymer. Further proposed is a laminate comprising a foam sheet and a film adhered to the foam sheet which may comprise a polystyrene homopolymer and homogeneous alpha-olefin/vinyl aromatic copolymer.

U.S. Patent No. 5,460,818 describes a compatibilized blend of olefinic polymers and monovinylidene aromatic polymers and an expandable composition comprising such a polymer blend composition and an expanding agent. The disclosed polymer blend composition may comprise (a) an aliphatic alpha-olefin homopolymer or interpolymer, (b) a homopolymer or interpolymer of monovinylidene aromatic monomers, and (c) a substantially random interpolymer comprising an aliphatic alpha-olefin and a vinylidene aromatic monomer.

WO 98/10014 pertains to blends of alpha-olefin/hindered vinylidene monomer interpolymers and vinyl aromatic polymers and foams therefrom. Specifically disclosed are foams comprising a general purpose polystyrene and an ethylene-styrene substantially random copolymer having foam densities ranging from about 40 to about 130 kg/m³. There still is the need for a film structure providing improved performance properties, especially in applications requiring tough and stiff film. Particularly desirable are films exhibiting advantageous mechanical properties in combination with good aesthetics. It is the object of the present invention to provide a film displaying a well balanced combination of performance attributes including high toughness, good stiffness, abrasion resistance, crack resistance, high ultimate elongation and good tear properties in combination with good optical properties. Such properties are required, for example, for films suitable for use as envelope window films, packaging films for window boxes, greeting card overlays and labels. A window envelope is an envelope with one or more openings of any shape, typically rectangular. The opening or openings allow examination of any information, such as a name and an address, printed on a limited area of matter within and are sealed or closed by a window composed of a non-opaque plastic film. Known window films are typically composed of oriented polystyrene, optionally with a small proportion of rubber-reinforced polymer. Typically, a label is affixed to or accompanying an article to furnish identification or other information. For example, a label may be a component of a packaging material, such as a container, which component does not come into contact with the contents of the package. Preferably, a label is printable. A label may have a protective function, for example, with respect to the integrity of the article or the packaging material. Window films and films for use as labels require high stiffness to provide excellent handling and converting in high speed printing operations, envelope manufacturing applications, label manufacturing and end-use application processes. In addition, such films require high surface gloss (for excellent appearance and printability), good tensile strength and toughness properties as well as good scratch or abrasion resistance. It is the object of the present invention to provide a film displaying a well- balanced combination of performance properties such as to render this film particularly suitable for the above-mentioned and related applications, and especially as window film or label.

SUMMARY OF THE INVENTION

The present invention pertains to tough and stiff films, comprising a blend comprising (at least) Component (A) and Component (B). Component (A) is present in an amount of from about 45 percent by weight to about 90 percent by weight, based on the total weight of Components A and B, and Component (B) is present in an amount of from about 10 percent by weight to about 55 percent by weight, based on the total weight of Components A and B. Component (A) is composed of one or more alkenyl aromatic polymers. Component (B) is composed of one or more substantially random interpolymers comprising in polymerized form (i) from about 50 mole percent to 74 mole percent of ethylene and/or one or more alpha-olefin monomers, and ii) from 26 mole percent to about 50 mole percent of one or more vinyl or vinylidene aromatic monomers and/or one or more sterically hindered aliphatic or cycloaliphatic vinyl or vinylidene monomers, and iii) from 0 mole percent to about 20 mole percent of other polymerizable ethylenically unsaturated monomer(s).

The blend components and their ratio are selected to provide films of high stiffness and toughness. The superior stiffness of the films is reflected in modulus (1 percent secant modulus in machine direction) of at least about 85,000 psi. Toughness is reflected in a high tensile toughness and ultimate elongation strength. Further aspects of the invention relate to methods for making the films of the invention and the use of such films.

In another aspect, the present invention provides a window envelope having one or more window openings, the window opening being entirely closed by a non-opaque plastic window, the window being formed of a film according to the present invention. Furthermore, the present invention provides a label for a container, the label being made from a film according to the present invention.

The present invention also provides an article of manufacture comprising the film of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The term "polymeric materials" as used herein refers to polymeric compounds obtainable by polymerizing one or more monomers. The generic terms "polymeric compounds" or "polymer" embrace the term homopolymer, usually employed to refer to polymers prepared from only one monomer, and the term interpolymer as defined hereinafter.

The term "comprising" as used herein means "including". The term "film" as used herein refers to a thin article and includes strips, tapes and ribbons.

The term "multilayer film" as used herein indicates a film consisting of two, three, four, five, six, seven or more layers.

The term foamed film as used herein refers to a monolayer or multilayer structure wherein a layer of the structure is foamed and has a density greater than about 300 kg/m³ and less than the non-foamed polymer. The term "interpolymer" as used herein refers to polymers prepared by the polymerization of at least two monomers. The generic term interpolymer thus embraces the terms copolymer, usually employed to refer to polymers prepared from two different monomers, and polymers prepared from more than two different monomers, such as terpolymers.

As defined herein, the term "substantially random" in the substantially random interpolymer of Component (B) means that the distribution of the monomers of said interpolymer can be described by the Bernoulli statistical model or by a first or second order Markovian statistical model, as described by J. C. Randall in Polymer Sequence Determination. Carbon-13 NMR Method. Academic Press New York, 1977, pp. 71-78.

Preferably, substantially random interpolymers do not contain more than 15 percent of the total amount of vinyl aromatic monomer in blocks of vinyl aromatic monomer of more than 3 units. More preferably, the interpolymer is not characterized by a high degree of either isotacticity or syndiotacticity. This means that in the carbon-13 NMR spectrum of the substantially random interpolymer the peak areas corresponding to the main chain methylene and methine carbons representing either meso diad sequences or racemic diad sequences should not exceed 75 percent of the total peak area of the main chain methylene and methine carbons.

The present invention relates to films comprising blends comprising one or more alkenyl aromatic homopolymers, or copolymers of alkenyl aromatic homopolymers, and/or copolymers of alkenyl aromatic monomers with one or more copolymerizable ethylenically unsaturated comonomers (other than ethylene or linear C₃-C₁₂alpha-olefins) with at least one substantially random interpolymer. The alkenyl aromatic polymer material (Component (A)) may further include minor proportions of non-alkenyl aromatic polymers. The alkenyl aromatic polymer material may be comprised solely of one or more alkenyl aromatic homopolymers, one or more alkenyl aromatic copolymers, a blend of one or more of each of alkenyl aromatic homopolymers and copolymers, or blends of any of the foregoing with a non-alkenyl aromatic polymer. Regardless of composition, the alkenyl aromatic polymer material comprises greater than 50 weight percent and preferably greater than 70 weight percent alkenyl aromatic monomeric units. Most preferably, the alkenyl aromatic polymer material is comprised entirely of alkenyl aromatic monomeric units. Suitable alkenyl aromatic polymers include homopolymers and copolymers derived from alkenyl aromatic compounds such as styrene, alpha-methylstyrene, ethylstyrene, vinyl benzene, vinyl toluene, chlorostyrene, bromostyrene, t-butyl styrene, including all isomers of these compounds. Suitable polymers to be employed as Component (A) also include alkenyl aromatic polymers having a high degree of syndiotactic configuration. A preferred alkenyl aromatic polymer is polystyrene. Minor amounts of monoethylenically unsaturated compounds such as C₂-₆ alkyl acids and esters, ionomeric derivatives, and C^ dienes may be copolymerized with alkenyl aromatic compounds. Examples of copolymerizable compounds include acrylic acid, methacrylic acid, ethacrylic acid, maleic acid, itaconic acid, acrylonitrile, maleic anhydride, methyl acrylate, ethyl acrylate, isobutyl acrylate, n-butyl acrylate, methyl methacrylate, vinyl acetate and butadiene.

General purpose polystyrene is the most preferred alkenyl aromatic polymer material suitable as Component (A) as defined herein. The term "general purpose polystyrene" is defined in the Encyclopedia of Polymer Science and Engineering, Vol. 16, 1989, pages 62-71. Such polystyrene is also referred to as crystal polystyrene or polystyrene homopolymer.

The monoalkenyl aromatic polymers may be suitably modified by rubbers to improve their impact properties. Examples of suitable rubbers are homopolymers of C„-C₆ conjugated dienes, especially butadiene or isoprene; interpolymers of one or more alkenyl aromatic monomers, and one or more C₄-C₆ conjugated dienes; interpolymers of ethylene and propylene or ethylene, propylene and a nonconjugated diene, especially 1 ,6-hexadiene or ethylidene norbornene; homopolymers of C₄-C₆ alkyl acrylates; interpolymers of C₄-C₆ alkyl acrylates and an interpolymerizable comonomer, especially an alkenyl aromatic monomer or a C,-C₄ alkyl methacrylate. Also included are graft polymers of the foregoing rubbery polymers wherein the graft polymer is an alkenyl aromatic polymer. A preferred alkenyl aromatic polymer for use in all of the foregoing rubbery polymers is styrene. A most preferred rubbery polymer is polybutadiene or a styrene/butadiene copolymer.

Impact modified alkenyl aromatic polymers are well known in the art and commercially available.

Suitable polymers to be employed as Component (A) also include alkenyl aromatic polymers having a high degree of syndiotactic configuration. Preferred alkenyl aromatic polymers for use as Component (A) of the present invention include polystyrene, syndiotactic polystyrene, rubber-modified high impact polystyrene, poly (vinyl-toluene), and poly(alpha-methylstyrene).

The substantially random interpolymers of Component(B) as defined herein comprise (i) from about 50 to 74 mole percent of polymer units derived from at least one of ethylene and/or a C₃-C₂₀ alpha (α)-olefin; (ii) from 26 to about 50 mole percent, of polymer units derived from (a) at least one vinyl or vinylidene aromatic monomer, or (b)at least one sterically hindered aliphatic or cycloaliphatic vinyl or vinylidene monomer, or (c) a combination of at least one aromatic vinyl or vinylidene monomer; and (iii) from about 0 to about 20 mole percent of polymer units derived from one or more of ethylenically unsaturated polymerizable monomers other than those derived from (i) and (ii).

Suitable α-olefins include, for example, α-olefins containing from 3 to about 20, preferably from 3 to about 12, more preferably from 3 to about 8 carbon atoms. These α- olefins do not contain an aromatic moiety.

Particularly suitable are ethylene, propylene, butene-1 , 4-methyl-1-pentene, hexene-1 or octene-1 or ethylene in combination with one or more of propylene, butene-1 , 4- methyl-1-pentene, hexene-1 or octene-1.

Polymerizable ethylenically unsaturated monomer(s) include norbornene and C,.₁₀ alkyl or C_{β l0} aryl substituted norbornenes, with an exemplary interpolymer being ethylene/styrene/norbornene.

Suitable vinyl or vinylidene aromatic monomers which can be employed to prepare the substantially random interpolymers include, for example, those represented by the following formula:

AT I (CH₂)_n R¹ - C = C(R²)₂

wherein R¹ is selected from the group of radicals consisting of hydrogen and alkyl radicals containing from 1 to about 4 carbon atoms, preferably hydrogen or methyl; each R² is independently selected from the group of radicals consisting of hydrogen and alkyl radicals containing from 1 to about 4 carbon atoms, preferably hydrogen or methyl; Ar is a phenyl group or a phenyl group substituted with from 1 to 5 substituents selected from halo, C,^- alkyl, and C -haloalkyl; and n has a value from zero to about 4, preferably from zero to 2, most preferably zero. Exemplary vinyl aromatic monomers include styrene, vinyl toluene, α- methylstyrene, t-butyl styrene, chlorostyrene, also including all isomers of these compounds

. Particularly suitable such monomers include styrene and lower alkyl- or halogen-

5 substituted derivatives thereof. Preferred monomers include styrene, α-methylstyrene, the lower alkyl-(C,- C₄) or phenyl-ring substituted derivatives of styrene, such as for example, ortho-, meta-, and para-methylstyrene, the ring halogenated styrenes, para-vinyl toluene or mixtures thereof. The most preferred aromatic vinyl monomer is styrene. o By the term "sterically hindered aliphatic or cycloaliphatic vinyl or vinylidene compounds", it is meant polymerizable vinyl or vinylidene monomers corresponding to the formula:

A¹ I Rⁱ _ C = C(R²)₂

5 wherein A' is a sterically bulky, aliphatic or cycloaliphatic substituent of up to

20 carbons, R¹ is selected from the group of radicals consisting of hydrogen and alkyl radicals containing from 1 to about 4 carbon atoms, preferably hydrogen or methyl; each R² is independently selected from the group of radicals consisting of hydrogen and alkyl radicals containing from 1 to about 4 carbon atoms, preferably hydrogen or methyl; or 0 alternatively R and A' together form a ring system. Preferred aliphatic or cycloaliphatic vinyl or vinylidene compounds are monomers in which one of the carbon atoms bearing ethylenic unsaturation is tertiarily or quatemarily substituted. Examples of such substituents include cyclic aliphatic groups such as cyclohexyl, cyclohexenyl, cyclooctenyl, or ring alkyl or aryl- substituted derivatives thereof, tert-butyl, or norbomyl. Most preferred aliphatic or 5 cycloaliphatic vinyl or vinylidene compounds are the various isomeric vinyl-ring substituted derivatives of cyclohexene and substituted cyclohexenes, and 5-ethylidene-2-norbornene. Especially suitable are 1 -, 3-, and 4-vinylcyclohexene. Simple linear non-branched α-olefins including for example, α-olefins containing from 3 to about 20 carbon atoms such as propylene, butene-1 , 4-methyl-1-pentene, hexene-1 or octene-1 are not examples of o sterically hindered aliphatic or cycloaliphatic vinyl or vinylidene compounds.

One method of preparation of the substantially random interpolymers includes polymerizing a mixture of polymerizable monomers in the presence of one or more metallocene or constrained geometry catalysts in combination with various cocatalysts, as described in EP-A-0,416,815 by James C. Stevens et al. and U.S. Patent No. 5,703,187 by

Francis J. Timmers, both of which are incorporated herein by reference in their entirety.

Preferred operating conditions for such polymerization reactions are pressures from atmospheric up to 3000 atmospheres and temperatures from -30°C to 200°C.

Polymerizations and unreacted monomer removal at temperatures above the autopolymerization temperature of the respective monomers may result in formation of some amounts of homopolymer polymerization products resulting from free radical polymerization. Examples of suitable catalysts and methods for preparing the substantially random interpolymers are disclosed in EP-A-514,828); as well as U.S. Patents: 5,055,438;

5,057,475; 5,096,867; 5,064,802; 5,132,380; 5,189,192; 5,321 ,106; 5,347,024; 5,350,723;

5,374,696; 5,399,635; 5,470,993; 5,703,187; and 5,721 ,185, all of which patents and applications are incorporated herein by reference. The substantially random α-olefin/vinyl aromatic interpolymers can also be prepared by the methods described in JP 07/278230 employing compounds shown by the general formula

Cp l Rl

/

\ /

R3 M

Cp2 R2

wherein Cp¹ and Cp² are cyclopentadienyl groups, indenyl groups, fluorenyl groups, or substituents of these, independently of each other; R and R² are hydrogen atoms, halogen atoms, hydrocarbon groups with carbon numbers of 1 to 12, alkoxyl groups, or aryloxyl groups, independently of each other; m is a group IV metal, preferably Zr or Hf, most preferably Zr; and R³ is an alkylene group or silanediyl group used to crosslink Cp¹ and Cp². The substantially random α-olefin/vinyl aromatic interpolymers can also be prepared by the methods described by John G. Bradfute et al. (W. R. Grace & Co.) in WO 95/32095; by R. B. Pannell (Exxon Chemical Patents, Inc.) in WO 94/00500; and in Plastics Technology, p. 25 (September 1992), all of which are incorporated herein by reference in their entirety. Also suitable are the substantially random interpolymers which comprise at least one α-olefin/vinyl aromatic/vinyl aromatic/α-olefin tetrad disclosed in U.S. Application No. 08/708,869 filed September 4, 1996 and WO 98/09999 both by Francis J. Timmers et al. These interpolymers contain additional signals in their carbon-13 NMR spectra with intensities greater than three times the peak-to-peak noise. These signals appear in the chemical shift ranges of 43.70 to 44.25 ppm and 38.0 to 38.5 ppm. Specifically, major peaks are observed at 44.1 , 43.9, and 38.2 ppm. A proton test NMR experiment indicates that the signals in the chemical shift region 43.70 to 44.25 ppm are methine carbons and the signals in the region 38.0 to 38.5 ppm are methylene carbons. It is believed that these new signals are due to sequences involving two head-to-tail vinyl aromatic monomer insertions preceded and followed by at least one α- olefin insertion, for example, an ethylene/styrene/styrene/ ethylene tetrad wherein the styrene monomer insertions of said tetrads occur exclusively in a 1 ,2 (head to tail) manner. It is understood by one skilled in the art that for such tetrads involving a vinyl aromatic monomer other than styrene and an α-olefin other than ethylene that the ethylene/vinyl aromatic monomer/vinyl aromatic monomer/ethylene tetrad will give rise to similar carbon-13 NMR peaks but with slightly different chemical shifts.

These interpolymers can be prepared by conducting the polymerization at temperatures of from about -30°C to about 250°C in the presence of such catalysts as those represented by the formula

wherein: each Cp is independently, each occurrence, a substituted cyclopentadienyl group π-bound to M; E is carbon or Si; M is a group IV metal, preferably Zr or Hf, most preferably Zr; each R is independently, each occurrence, hydrogen, hydrocarbyl, silahydrocarbyl, or hydrocarbylsilyl, containing up to about 30 preferably from 1 to about 20 more preferably from 1 to about 10 carbon or silicon atoms; each R' is independently, each occurrence, hydrogen, halo, hydrocarbyl, hydrocarbyloxy, silahydrocarbyl, hydrocarbylsilyl containing up to about 30, preferably from 1 to about 20, more preferably from 1 to about 10 carbon or silicon atoms or two R' groups together can be a C..₁₀ hydrocarbyl substituted 1 ,3-butadiene; M is 1 or 2; and optionally, but preferably in the presence of an activating cocatalyst. Particularly, suitable substituted cyclopentadienyl groups include those illustrated by the formula:

wherein each R is independently, each occurrence, hydrogen, hydrocarbyl, silahydrocarbyl, or hydrocarbylsilyl, containing up to about 30, preferably from 1 to about 20, more preferably from 1 to about 10 carbon or silicon atoms or two r groups together form a divalent derivative of such group. Preferably, R independently each occurrence is (including where appropriate all isomers) hydrogen, methyl, ethyl, propyl, butyl, pentyl, hexyl, benzyl, phenyl or silyl or (where appropriate) two such R groups are linked together forming a fused ring system such as indenyl, fluorenyl, tetrahydroindenyl, tetrahydrofluorenyl, or octahydrofluorenyl. Particularly preferred catalysts include, for example, racemic-

(dimethylsilanediyl)-bis-(2-methyl-4-phenylindenyl) zirconium dichloride, racemic- (dimethylsilanediyl)-bis-(2-methyl-4-phenylindenyl) zirconium 1 ,4-diphenyl-1 ,3-butadiene, racemic-(dimethylsilanediyl)-bis-(2-methyl-4-phenylindenyl) zirconium di-C,^ alkyl, racemic- (dimethylsilanediyl)-bis-(2-methyl-4-phenylindenyl) zirconium di-C.^alkoxide, or any combination thereof.

It is also possible to use the following titanium-based constrained geometry catalysts, [N-(1 ,1-dimethylethyl)-1 J-dimethyl-1-[(1 ,2,3,4,5-η)-1 ,5,6,7-tetrahydro-s-indacen- 1-yl]silanaminato(2-)-N]titanium dimethyl; (1-indenyl)(tert-butylamido)dimethylsilane titanium dimethyl; ((3-tert-butyl)(1 ,2,3,4,5-η)-1-indenyl)(tert-butylamido) dimethylsilane titanium dimethyl; and ((3-isopropyl)(1 ,2,3,4,5-η)-1-indenyl)(tert-butyl amido)dimethylsilane titanium dimethyl, or any combination thereof.

Further preparative methods for the interpolymers used in the present invention have been described in the literature. Longo and Grassi (Makromol. Chem.. Volume 191 , pages 2387 to 2396 [1990]) and D'Anniello et al. (Journal of Applied Polymer Science, Volume 58, pages 1701-1706 [1995]) reported the use of a catalytic system based on methylalumoxane (MAO) and cyclopentadienyltitanium trichloride (CpTiCI₃) to prepare an ethylene-styrene copolymer. Xu and Lin (Polymer Preprints. Am. Chem. Soc. Div. Polvm. Chem.) Volume 35, pages 686-687 [1994]) have reported copolymerization using a MgCI TiCi NdCI AI(iBu)₃ catalyst to give random copolymers of styrene and propylene. Lu et al. (Journal of Applied Polymer Science. Volume 53, pages 1453 to 1460 [1994]) have described the copolymerization of ethylene and styrene using a TiCI₄/NdCI-/ MgCI₂/AI(Et)₃ catalyst. Sernetz and Mulhaupt, (Macromol. Chem. Phys.. Vol. 197, pp. 1071-1083, 1997) have described the influence of polymerization conditions on the copolymerization of styrene with ethylene using Me₂Si(Me₄Cp)(n-tert-butyl)TiCI₂/methylaluminoxane Ziegler-Natta catalysts. Copolymers of ethylene and styrene produced by bridged metallocene catalysts have been described by Arai, Toshiaki and Suzuki (Polymer Preprints. Am. Chem. Soc. Div. Polvm. Chem.) Vol. 38, pages 349-350 [1997]) and in U.S. Patent No. 5,652,315, issued to Mitsui Toatsu Chemicals, Inc. The manufacture of α-olefin/vinyl aromatic monomer interpolymers such as propylene/styrene and butene/styrene is as described in U.S. Patent No. 5,244,996, issued to Mitsui Petrochemical Industries Ltd or U.S. Patent No. 5,652,315 also issued to Mitsui Petrochemical Industries Ltd, or as disclosed in DE 197 11 339 A1 to Denki Kagaku Kogyo KK. All the above methods disclosed for preparing the interpolymer component are incorporated herein by reference. Also, although of high isotacticity and therefore not "substantially random", the random copolymers of ethylene and styrene as disclosed in Polymer Preprints Vol. 39, No. 1 , March 1998 by Toru Aria et al. can also be employed as component (B) for the films of the present invention. While preparing the substantially random interpolymer, an amount of atactic vinyl aromatic homopolymer may be formed due to homopolymerization of the vinyl aromatic monomer at elevated temperatures. The presence of vinyl aromatic homopolymer is in general not detrimental for the purposes of the present invention and can be tolerated. The most preferred substantially random interpolymers for use as Component(B) are interpolymers of ethylene and styrene and interpolymers of ethylene, styrene and at least one alpha-olefin containing from 3 to 8 carbon atoms.

Preferably, the substantially random interpolymer comprises in copolymerized form about 70 mole percent or less of ethylene and/or one or more alpha-olefin monomers. A preferred upper limit is about 60 mole percent or less of ethylene and/or one or more alpha-olefin monomers.

Preferably, the substantially random interpolymer comprises about 30 mole percent or more of one or more vinyl or vinylidene aromatic monomers and/or one or more sterically hindered aliphatic or cycloaliphatic vinyl or vinylidene monomers in copolymerized form. A preferred lower limit is about 40 mole percent or more of one or more vinyl or vinylidene aromatic monomers and/or one or more sterically hindered aliphatic or cycloaliphatic vinyl or vinylidene monomers.

The presence of other polymerizable ethylenically unsaturated monomer(s) is optional. Preferably, Component B does not contain such monomer.

The melt index (l₂) according to ASTM D 1238 Procedure A, condition E, generally is from about 0.01 to about 50 g/10 minutes, preferably from about 0.01 to about 20 g/10 minutes, more preferably from about 0.1 to about 7 g/10 minutes, and most preferably from about 0.3 to about 5 g/10 minute. The density of the substantially random interpolymer is generally about 0.930 g/cm³ or more, preferably from about 0.930 to about 1.045 g/cm³, more preferably from about 0.930 to about 1.040 g/cm³, most preferably from about 0.930 to about 1.030 g/cm³. The molecular weight distribution, M-/M-, is generally from about 1.5 to about 20, preferably from about 1.8 to about 10, more preferably from about 2 to about 5. The substantially random interpolymers may be modified by typical grafting, hydrogenation, functionalizing, or other reactions well known to those skilled in the art. The polymers may be readily sulfonated or chlorinated to provide functionalized derivatives according to established techniques. The substantially random interpolymers may also be modified by various chain-extending or crosslinking processes including, but not limited to peroxide-, silane-, sulfur-, radiation-, or azide-based cure systems. A full description of the various crosslinking technologies is described in U.S. Patent No. 5,869,591 and EP-A- 778,852, the entire contents of both of which are herein incorporated by reference. Dual cure systems, which use a combination of heat, moisture cure, and radiation steps, may be effectively employed. For instance, it may be desirable to employ peroxide crosslinking agents in conjunction with silane crosslinking agents, peroxide crosslinking agents in conjunction with radiation, sulfur-containing crosslinking agents in conjunction with silane crosslinking agents. The substantially random interpolymers may also be modified by various crosslinking processes including, but not limited to the incorporation of a diene component as a termonomer in its preparation and subsequent crosslinking by the aforementioned methods and further methods including vulcanization via the vinyl group using sulfur for example as the crosslinking agent. The above-mentioned substantially random interpolymer suitable as component (B) as defined herein is preferably thermoplastic, which means it may be molded or otherwise shaped and reprocessed at temperatures above its melting or softening point.

The blend comprising polymeric materials for use in the present invention is obtainable according to methods known in the art, such as but not limited to, dry blending in a screw extruder, or a Banbury mixer. The dry blended pellets may be directly melt processed into a final solid state article.

Preferred are blends, wherein Component (A) is present in an amount of from about 60 weight percent or more, more preferably in amount of from about 70 weight percent or more. The preferred upper limit for the amount of Component (A) is about 80 weight percent or less. The preferred lower limit for the amount of Component (B) in the blend is about 20 weight percent or more. The preferred upper limit for the amount of Component (B) in the blend is about 40 weight percent or less, more preferably about 30 percent or less.

The film according to the present invention has a thickness of less than about 350 microns (μm), preferably less than about 300 μm and most preferably less than about 250 μm (10 mils).

The film according to the present invention may include one or more additives, for example but not limited to, antioxidants, light stabilizers, processing aids, plasticizers, pigments, fillers, slip additives, antiblock materials, antifog agents, cling agents, tackifiers, blowing agents, nucleators, clarifiers, flame retardant additives.

The film provided herein has little or no free shrink at 90°C. This means that the film has a free shrink, at 90°C, of less than about 20 percent, more preferably of less than about 10 percent. The film of the present invention may be a monolayer or a multilayer film. One or more layers of the film may be oriented or foamed. A multi-layer film of the present invention may contain one, two or more layers comprising a blend as defined herein. Most preferably, the film according to the invention has a thickness of about 0.5 to about 10 mils. Preferably, the present invention pertains to a tough and stiff film, comprising a blend of polymeric materials consisting essentially of Component (A) and Component (B), as described herein. The film of the invention may be printed. Particularly preferred is a film wherein component (A) is composed of one or more polystyrene(s) and component (B) is composed of one or more substantially random ethylene-styrene interpolymer(s). The film of the invention is obtainable according to methods known in the art. The film may be made using a blown or a cast film extrusion process, including co-extrusion and extrusion coating. One or more layers of the film may be expanded, for example with a conventional blowing agent, to make foamed film. One or more films may be laminated to form a multi-layer structure. The films may be (further) oriented after forming via tenter frame, double-bubble or blown film techniques.

In one embodiment, the film of the present invention is an oriented film. The term "orientation" as used herein refers to a process of stretching a hot polymeric article to align the molecular chains in the direction(s) of stretching. When the stretching is applied in one direction, the process is called uniaxial orientation; when the stretching is applied in two (perpendicular) directions, the process is called biaxial orientation. Orientation can be uniaxial or, preferably, biaxial. Orientation may be accomplished according to conventional methods, such as blown film processes, "double-bubble" film processes, cast/tentered film processes or other techniques known in the art to provide orientation. Preferably, the oriented film according to the invention has a modulus (2 percent secant modulus in the machine direction) of more than 150,000 psi (1034 MPa). Preferred oriented films comprise a blend, wherein component (A) is a polystyrene and component (B) is an ethylene-styrene interpolymer. Preferably, Component (A) is present in an amount of more than about 50 to less than about 80, more preferably in amount of about 70 to about 77, most preferably about 75, weight percent, and Component (B) is present in an amount of more than about 20 to less than about 50, more preferably in an amount of 23 to about 30 weight percent, most preferably about 25 weight percent. Preferably, the substantially random ethylene-styrene interpolymer contains from about 60 weight percent to about 75 weight percent, preferably about 70 percent copolymerized styrene. The melt index (condition E) is preferably from about 0.3 to about 5 g/10 minute.

The oriented films of the invention are particularly suitable for use in window envelope and related applications. For window envelope and related applications, high modulus, good cuttability and lower haze are desired properties. The oriented films according to the present invention advantageously combine these properties. The oriented films provided herein are characterized by unexpected changes or improvements in film performance, including toughness, modulus and abrasion resistance. Additionally, optical properties of the blend film of the invention are enhanced compared to conventional rubber modified polystyrene films, especially with respect to gloss (higher) and haze (lower). The films also demonstrate improved dead-fold characteristics as shown by high stress relaxation properties. Furthermore, tear properties are advantageously affected. When blended with a crystalline syndiotactic polystyrene resin (Component (A)) in a ratio described herein ethylene-styrene interpolymer resins provide films with good optical characteristics and unexpected elongation, under suitable biaxial orientation conditions.

In another aspect, the present invention relates to a foamed film. Such film is especially suitable for use as label or in thermoformable articles of manufacture.

To make foamed film structures, either physical or chemical blowing agents may be used to achieve foam densities of more than about 300 kg/m³, preferably more than about 350 kg/m³ and most preferably more than about 400 kg m³. Typically, the foam density is less than about 1000 kg/m³, preferably less than about 950 kg/m³, and most preferably less than 900 kg/m³. The cell sizes of the macrocellular foams will be from about 0.01 to about 5.0 mm, preferably about 0.02 to 2.0 mm, and most preferably 0.02 to about 1.8 mm according to ASTM D3576. The cell sizes of microcellular foams will be less than 0.1 mm. The foams may be open or closed cell, according to ASTM D2856.

A multilayer film of the invention comprising one or more foamed layers comprising a blend comprising Components (A) and (B) as defined herein is obtainable according to methods known in the art, for example, using a co-extrusion process. Preferred are two-layer or three-layer films with one or two surface layers and the foamed layer being the core layer. The surface layer may or may not comprise a blend of polymeric materials consisting essentially of Components (A) and (B) as defined herein. Preferred is a film comprising a foamed layer comprising a blend of Components (A) and (B) as defined herein and one or two non-foamed layers made from Component (A) as described herein, particularly from a polystyrene. In a three-layer structure, preferably, the foamed layer is the core or middle layer.

The label film may be constructed from printed, slit to width, rolls of film with the labels glued to a container, for example a bottle, using conventional adhesives and glues known to the industry. In addition, the films of this invention may be printed, coated with pressure sensitive adhesives, laminated to release papers or films and applied to bottles, containers or other surfaces by conventional pressure sensitive techniques.

Preferred foamed films comprise a blend, wherein Component (A) is a polystyrene and Component (B) is an ethylene-styrene substantially random interpolymer. Preferably, Component (B) is present in an amount of from about 25 to about 35 weight percent.

The bottle may be a glass bottle or a PET bottle. Covering or affixed to a glass bottle, the label may also serve a protective purpose. If the bottle is a PET bottle, the preferred label is a wrap-around label showing more than about 8 g tear in machine direction, and more than about 25 g tear in cross- direction. Elongation of the foamed film according to the invention should be between about 4 to about 5 percent.

The properties of the polymers, blends and films useful for the purpose of the present invention can be determined by the following test procedures. These procedures were used in the Examples.

Melt Index (Ml) is determined according to ASTM D-1238, condition E (190°C, 2J6 kg).

Secant Modulus, ultimate elongation, and ultimate tensile strength are determined according to ASTM-D-882-91.

Haze is determined according to ASTM D-1003.

Gloss is determined according to ASTM D-2457.

Styrene Analysis: Interpolymer or copolymer styrene content and content of atactic polystyrene in the interpolymer of Component (A) can be determined using proton nuclear magnetic resonance (Η-NMR). All proton NMR samples are prepared in 1 ,1 ,2,2- tetrachloroethane-²D (TCE- D). The solutions contain 1.6 -to 3.2 weight percent polymer. Melt index (l₂) is used as a guide for determining sample concentration. Thus when the l₂ is greater than 2 g/10 minutes, 40 mg of interpolymer are used; with an l₂ between 1.5 and 2 g/10 minutes, 30 mg of interpolymer are used; and when the l₂ is less than 1.5 g/10 minutes, 20 mg of interpolymer are used. The interpolymers are weighed directly into 5 mm sample tubes. A 0.75 mL aliquot of TCE-²D is added by syringe and the tube is capped with a tight- fitting polyethylene cap. The samples are heated in a water bath at 85°C to soften the interpolymer. To provide mixing, the capped samples are occasionally brought to reflux using a heat gun. Proton NMR spectra are accumulated on a Varian VXR 300 with the sample probe at

80°C, and referenced to the residual protons of TCE-²D at 5.99 ppm. The delay times are varied between 1 second, and data are collected in triplicate on each sample. The following instrumental conditions are used for analysis of the interpolymer samples: Varian VXR-300, standard ¹H; Sweep Width, 5000 Hz; Acquisition Time, 3.002 seconds; Pulse Width, 8 μseconds; Frequency, 300 MHz; Delay, 1 second; Transients, 16.

The total analysis time per sample is about 10 minutes.

Initially, a 'H NMR spectrum for a sample of polystyrene, STYRON™ 680 (available form The Dow Chemical Company, Midland, Ml) is acquired with a delay time of one second. The protons are "labeled": b, branch; α,alpha; o, ortho; m, meta; p, para, as indicated in the formula below.

Integrals are measured around the protons labeled in the formula; the 'A' designates aPS. Integral A₇, (aromatic, around 7.1 ppm) is believed to be the three ortho/para protons; and integral A₆₆ (aromatic, around 6.6 ppm) the two meta protons. The two aliphatic protons labeled • resonate at 1.5 ppm; and the single proton labeled b is at 1.9 ppm. The aliphatic region is integrated from about 0.8 to 2.5 ppm and is referred to as A_al. The theoretical ratio for A₇₁: A₆₆: A_al is 3:2:3, or 1.5:1 :1.5, and correlates very well with the observed ratios for the STYRON™ 680 sample for several delay times of 1 second. The ratio calculations used to check the integration and verify peak assignments are performed by dividing the appropriate integral by the integral A₆₆ ratio A_r is A-,: / A₆₆. Region A₆₆ is assigned the value of 1. Ratio Al is integral A_al / A₆₆. All spectra collected have the expected 1.5:1 :1.5 integration ratio of (o+p ): m;(α+b). The ratio of aromatic to aliphatic protons is 5 to 3. An aliphatic ratio of 2 to 1 is predicted based on the protons labeled • and b, respectively, in the above formula. This ratio is also observed when the two aliphatic peaks are integrated separately. For the ethylene/styrene interpolymers, the ¹H- NMR spectra using a delay time of one second, have integrals C₇₁, C₆₆, and C_al defined, such that the integration of the peak at 7.1 ppm includes all the aromatic protons of the copolymer as well as the o and p protons of aPS. Likewise, integration of the aliphatic region C_al in the spectrum of the interpolymers included aliphatic protons from both the aPS and the interpolymer with no clear baseline resolved signal from either polymer. The integral of the peak at 6.6 ppm C₆₆ is resolved from the other aromatic signals and it is believed to be due solely to the aPS homopolymer (probably the meta protons). (The peak assignment for atactic polystyrene at 6.6 ppm (integral A₆₆) is made based upon comparison to the authentic sample of STYRON™ 680.) This is a reasonable assumption since, at very low levels of atactic polystyrene, only a very weak signal is observed here. Therefore, the phenyl protons of the copolymer must not contribute to this signal. With this assumption, integral A₆₆ becomes the basis for quantitatively determining the contents of aPS (atactic polystyrene).

10 The following equations are then used to determine the degree of styrene incorporation in the ethylene/styrene interpolymer samples:

(C Phenyl) = C₇₁ + A₇₁ - (1.5 x A

(C Aliphatic) = C_al - 1 5 x A₆₆) s_c = (C Phenyl) /5 ⁵ e_c = (C Aliphatic - (3 x s_c)) /4

E = e_c / (e_c + s_c)

S_c = s_c / (e_ + s_c) and the following equations are used to calculate the mole percent ethylene and styrene in the interpolymers. 0

and

5 wherein s_c and e_c are styrene and ethylene proton fractions in the interpolymer, respectively, and S_c and E are mole fractions of styrene monomer and ethylene monomer in the interpolymer, respectively.

The weight percent of aPS in the interpolymers can be determined using the o following equation:

The total styrene content is also determined by quantitative Fourier Transform Infrared Spectroscopy (FTIR). The following Examples are illustrative of the invention, but are not to be construed as limiting the scope thereof in any manner. The following abbreviations are used in the Examples: PS means polystyrene; ESI means ethylene-styrene substantially random interpolymer; MD means machine direction; CD means cross direction.

Example 1 - Oriented Film Comprising Polystyrene/Ethylene-Styrene Substantially Random

Interpolymer Blend

The polystyrene is STYRON™ 665 available from The Dow Chemical Company. The ESI was obtained as follows: the interpolymer was prepared in a continuously operating loop reactor (36.8 gal, 140 L). The reactor runs liquid full at 475 psig (3,275 kPa) with a residence time of approximately 25 minutes. Raw materials and catalyst/cocatalyst flows were fed. Solvent feed to the reactor was supplied by two different sources. A fresh stream of toluene from a diaphragm pump with rates measured was used to provide flush flow for the reactor seals (20 IbVhour (9.1 kg/hour). Recycle solvent was mixed with uninhibited styrene monomer on the suction side of five diaphragm pumps in parallel. These five pumps supply solvent and styrene to the reactor at 650 psig (4,583 kPa). Fresh styrene flow was measured by flowmeter, and total recycle solvent/styrene flow was measured by a separate flowmeter. Ethylene was supplied to the reactor at 687 psig (4,838 kPa). The ethylene stream was measured by a mass flowmeter. A flowmeter/controlier was used to deliver hydrogen into the ethylene stream at the outlet of the ethylene control valve. The ethylene/hydrogen mixture combines with the solvent/styrene stream at ambient temperature. The temperature of the entire feed stream as it enters the reactor loop was lowered to 2°C by an exchanger with -10°C glycol on the jacket. Preparation of the three catalyst components take place in three separate tanks: fresh solvent and concentrated cataiyst/cocatalyst premix were added and mixed into their respective run tanks and fed into the reactor via variable speed diaphragm pumps. The three component catalyst system enters the reactor loop through an injector and static mixer into the suction side of the twin screw pump. The raw material feed stream was also fed into the reactor loop through an injector and static mixer downstream of the catalyst injection point but upstream of the twin screw pump suction.

Polymerization was stopped with the addition of catalyst kill (water mixed with solvent) into the reactor product line after the flowmeter measuring the solution density. A static mixer in the line provides dispersion of the catalyst kill and additives in the reactor effluent stream. This stream next enters post reactor heaters that provides additional energy for the solvent removal flash. This flash occurs as the effluent exits the post reactor heater and the pressure was dropped from 475 psig (3,275 kPa) down to 450 mmHg (60 kPa) of absolute pressure at the reactor pressure control valve. This flashed polymer enters the first of two hot oil jacketed devolatilizers. The volatiles flashing from the first devolatilizer were condensed with a glycol jacketed exchanger, passed through the suction of a vacuum pump, and were discharged to the solvent and styrene/ethylene separation vessel. Solvent and styrene were removed from the bottom of this vessel as recycle solvent while ethylene exhausted from the top. The ethylene stream was measured with a mass flowmeter. The measurement of vented ethylene plus a calculation of the dissolved gases in the solvent/styrene stream were used to calculate the ethylene conversion. The polymer and remaining solvent separated in the devolatilizer was pumped with a gear pump to a second devolatizer. The second devolatizer was operated at 5 mmHg (0.7 kPa) absolute pressure to flash the remaining solvent. This solvent was condensed in a glycol heat exchanger, pumped through another vacuum pump, and exported to a waste tank for disposal. The dry polymer (less than 1000 ppm total volatiles) was pumped with a gear pump to an underwater pelletizer with a 6-hole die, pelletized, spin-dried, and collected in 1000 pound (454 kg) boxes. The aluminum catalyst component was a commercially available modified methalumoxane Type 3A (MMAO-3A).

The boron cocatalyst type 1 was tris(pentafluorophenyl) borane.

The titanium catalyst was (1 H-cyclopenta[l]phenanthrene-2-yl)dimethyl(t- butylamido)-silanetitanium 1 ,4-diphenylbutadiene). The PS and the ESI were dryblended.

Films C, D, and F were produced using a down-ward blown-orientation process. The die diameter was 2 inches and the melt temperature was about 230°C (line speed of 45 fpm (13.7 m/minute)). The blow-up ratio (circumference of the bubble-shaped film divided by that of the die) was about 12. Film E was a commercial oriented polystyrene window film DWF Clear LD, available from The Dow Chemical Company.

Table I

"Not an example of the present invention.

In sample C, a combination of high gloss and high clarity(low haze), high modulus, high tensile strength and toughness was obtained compared to the conventional polystyrene homopolymer film sample E. Sample D demonstrated the effect of increased levels of ESI above the most preferred levels, resulting in reduced gloss, reduced tensile strength and lower stiffness. Sample F demonstrated the effect of lower styrene content of the ESI material resulting in lower gloss and higher haze. Samples D and F exhibited an unusual, unexpected combination of high toughness, high modulus, high tensile strength and superior optical properties, but were not as good as the most preferred Film C. Scratch-resistance is very important in window film use. The scratch resistance of films C, D and F was tested and compared to film E as reference. In the test, the haze level of each film was measured and recorded. The films were then subjected to a relative motion against a LF Smithe 527 bronze drum under a vacuum of 10 in. Hg to cause scratch on the film. Next, the haze level of each film was again measured and recorded. The extent of scratch on the film was then measured by calculating the change in the measured haze value of each film before and after scratching. A film is considered more scratch resistant when the change in film optical haze due to scratching is less than a film with more haze changes by scratching under the same condition.

Film C, D and F showed significant improvement over film E. The PS/ESI films showed very little abrasion-whitening and haze increase as commonly seen in Clear LD.

Example 2 - Tough and Stiff Foamed Films Made from PS/ESI Blends

A blown film co-extrusion process was used to make a polystyrene-based foam core with two surface layers of unfoamed polystyrene. The foam core was made without ESI resin and with varying amounts of ESI. No ESI was added to the surface layers. The ESI was produced as described in Example 1 above and had a content of copolymer styrene of 69 weight percent and a Ml of 4.6. The polystyrene was Krasten 144 (Kaucuk Corp.; Mw: 260,000; Mn: 104,000; Ml: 6 to 8 g/10 minutes; 1.5 to 2 percent mineral oil). The PS and the ESI were dry blended. The foamed films had a total thickness or gauge of 130 μm + 20 μm.

Table II Foamed Film Properties

The films made with PS/ESI blends were tough and stiff with improved tear and gloss.

Example 3 - Tough and Stiff Films Made from PS/ESI blends

Films were made as described in Table III using a commercial polystyrene resin, STYRON™ 665 available from The Dow Chemical Company, and ESI materials having copolymer styrene contents of 60.6, 67.5 and 71.3 weight percent, respectively.

Table III ESI/Polystyrene Film Blends and Film Properties

Extrusion Parameters (1.25 in. (3.2 cm) Killion Extruder with 3 inch (7.6 cm) blown film Die)

Film Properties

Avg. Thickness (microns) 38 38 38

Optical Properties

As can be seen from the data, higher copolymer styrene contents led to improved gloss, increased modulus, improved tensile strength and increased toughness, indicating a most preferred styrene content in the area of 67 to 72 percent styrene.

Films were fabricated as described in Table IV from dry blends of ESI and polystyrene (STYRON™ 678 available from The Dow Chemical Company) with increasing amounts of polystyrene. Table IV:

Extrusion Parameters (1.25 in. 3.2cm Killion Extruder with 3 inch (7.6 cm) blown film die)

Table V: ESI/Polystyrene Blends and Film Properties

Film Properties

Avg. Thickness (microns) 84 69 76

Optical Properties

From Table V, it can be seen that even low levels of ESI (10 percent) affected tensile elongation and toughness, while higher levels (40 percent) result in improved toughness and tensile elongation while retaining high gloss and stiffness as indicated by 45 degree gloss and 1 percent secant modulus.

Claims

CLAIMS:

I . A tough and stiff film comprising a blend comprising Component (A) and Component (B), wherein Component (A) is present in an amount of from 45 percent to about 90 percent by weight, based on the total weight of components A and B, and Component (B) is present in an amount of from 10 percent by weight to 55 percent by weight, based on the total weight of Components A and B, and wherein Component (A) is composed of one or more alkenyl aromatic polymers and Component (B) is composed of one or more substantially random interpolymers comprising in polymerized form (i) from about 50 mole percent to 74 mole percent of ethylene and/or one or more alpha-olefin monomers, and ii) from 26 mole percent to about 50 mole percent of one or more vinyl or vinylidene aromatic monomers and/or one or more sterically hindered aliphatic or cycloaliphatic vinyl or vinylidene monomers, and iii) from 0 mole percent to about 20 mole percent of other polymerizable ethylenically unsaturated monomer(s).

2. A film according to claim 1 which is a monolayer film.

3. A film according to claim 1 which is a multilayer film.

4. A film according to any of claims 1 to 3 which is an oriented film.

5. A film according to claims 1 to 3 in which at least one layer is a foamed layer.

6. A film according to any of claims 1 to 5, wherein component (A) is a polystyrene.

7. A film according to any of claims 1 to 6, wherein component (B) is an ethylene-styrene substantially random interpolymer.

8. A film according to any of claims 1 to 7 which is a printed film.

9. A window envelope having one or more window openings, the window opening being entirely closed by a non-opaque plastic window patch, the window patch being formed of a film according to claim 1.

10. A label made from a film according to claim 1 .

I I . A film according to claim 4 which has a 2 percent secant modulus in the machine direction of more than 150,000 psi (1034 MPa).

12. A film according to Claim 1 which has a 1 percent secant modulus in the machine direction of more than 85,000 psi (586 MPa).

13. An article of manufacture comprising a film according to Claim 1.