WO1998049226A1

WO1998049226A1 - Polymeric film including microspheres

Info

Publication number: WO1998049226A1
Application number: PCT/US1998/008328
Authority: WO
Inventors: Kimberly Ann Mudar
Original assignee: Cryovac, Inc.
Priority date: 1997-04-25
Filing date: 1998-04-24
Publication date: 1998-11-05
Also published as: AU7159298A; AR012502A1

Abstract

A thermoplastic packaging film includes a carrier layer containing up to about 1.0 weight percent of spherical alkali aluminosilicate ceramic particles having a refractive index of about 1.52. The carrier layer preferably is a heat sealable layer which includes a polymer having mer units derived from ethylene. The refractive index of the overall film, and particularly that of the carrier layer, preferably is in the range of about 1.50 to about 1.54.

Description

POLYMERIC FILM INCLUDING MICROSPHERES

BACKGROUND INFORMATION

1. Field of the Invention This invention relates to thermoplastic packaging films, more particularly to extruded, multilayer, heat shrinkable films with excellent machinability and optical properties.

2. Background of the Invention

Thermoplastic films, especially those including polyolefinic materials, have been used to package goods that can be damaged by the ambient environment and that can benefit from an aesthetically pleasing appearance (e.g., perishable food products). Optical properties contribute to the aesthetic consumer appeal of products packaged in such films.

One optical property of significant importance is haze, which is a measure of light scattering. Films with high haze reduce the contrast of packaged objects when such objects are viewed through such films. Therefore, films with as little haze as possible are preferred. Nevertheless, films with good optical properties also must possess a low coefficient of friction (COF) to be able to be manufactured at economically feasible speeds and to exhibit the ease of use demanded by end users. To reduce the COF of a given film, one or more antiblocking agents commonly are incorporated into packaging films.

Providing films that possess both a low COF and desired optics has continued to present a challenge for quite some time. Widely used antiblocking agents such as aluminum silicates and diatomaceous earths, which have proven effective in reducing the COF of films in which they are incorporated, also tend to deleteriously affect the optical properties of those same films. Films containing such antiblocking agents generally have an increased haze. This characteristic is believed to result from the difference between the refractive indices of the antiblocking agent and the film or, perhaps, the antiblocking agent and the polymeric film layer in which the antiblocking agent has been incorporated (i.e., the carrier layer). Such antiblocking agents also tend to build up on the surfaces of manufacturing and processing equipment and often must be dried prior to incorporation into the polymer(s) from which the film is made. Over the past several years, a new type of antiblocking agent has begun to gain wider acceptance. These relatively new antiblocking agents, often called microspheres, are substantially spherical aluminosilicate ceramic particles that can be solid or hollow and can be obtained in a variety of diameters. Films incorporating such microspheres as antiblocking agents have exhibited improved COFs.

Such microspheres generally appear gray to the unaided eye and have a refractive index of about 1.55. Because refractive index is an inherent physical property, i.e., a property determined by the chemical nature of the material, it does not vary with size. Thus, regardless of the diameter of the gray microsphere used, the refractive index of that microsphere has been somewhere close to 1.55.

The refractive indices of polyolefins widely used in packaging films generally is significantly lower than 1.55. For example, most polypropylenes have a refractive index in the range of about 1.47-1.50 and most low density polyethylenes have a refractive index in the range of about 1.51-1.52. High density polyethylene, which is not as commonly used in transparent packaging films, has a refractive index of about 1.54.

Copolymers that include mer units derived from propylene or ethylene can have refractive indices either higher or lower than the ranges just given, depending on the nature of the comonomer(s) used. For instance, commercially available ethylene/vinyl acetate copolymers generally have refractive indices in the range of about 1.47-1.50. Of significant utility would be a thermoplastic packaging film with the improved

COF provided by gray microspheres but with optical properties better than those previously obtained.

SUMMARY OF THE INVENTION Briefly, the present invention provides a thermoplastic packaging film that includes a heat sealable layer and up to about 1.0 weight percent of essentially spherical alkali aluminosilicate ceramic particles disposed in a carrier layer. The heat sealable layer includes a polymer that includes mer units derived from ethylene. The ceramic particles have a refractive index of about 1.52, and the film has an overall refractive index of at least about 1.50. The carrier layer can be the heat sealable layer.

In another aspect, the present invention provides a thermoplastic packaging film that includes a heat sealable layer and up to about 1.0 weight percent of essentially spherical alkali aluminosilicate ceramic particles disposed in a carrier layer. The heat sealable layer includes a polymer that includes mer units derived from ethylene. The ceramic particles have a refractive index of about 1.52, and the carrier layer has an overall refractive index of at least about 1.50. The carrier layer can be the heat sealable layer.

Films of the present invention exhibit excellent COFs while simultaneously maintaining good optical properties. Specifically, the refractive index of the antiblocking agent used to lower the COF of the film is substantially similar to those of the overall film and/or the layer in which the antiblocking agent is incorporated. Packaging films in which perishable goods can be aesthetically presented thus are described.

The following definitions apply hereinthroughout unless a contrary intention is expressly indicated:

"(meth)acrylic acid" includes both acrylic acid and/or methacrylic acid; "(meth)acrylate" includes both acrylate and methacrylate;

"ionomer" means a metal salt of an ethylene/(meth)acrylic acid copolymer;

"polymer" means the product of a polymerization reaction, and is inclusive of homopolymers, copolymers, terpolymers, tetrapolymers, etc.;

"copolymer" means a polymer formed by the polymerization reaction of at least two different monomers and is inclusive of random copolymers, block copolymers, graft copolymers, etc.;

"differing", when used to describe the relative nature of two or more polymers or copolymers, means differences in any one or more chemical or physical attributes including, but not limited to, chemical composition, comonomer composition, relative distribution of comonomer mer units, relative percentages of comonomers, molecular weight, molecular weight distribution, melt flow, and density;

"package" means one or more packaging materials (e.g., a film) configured around a product;

"film" is used in its most generic sense to include all plastic web materials, although those having a thickness of 0.25 mm or less are most preferred;

"inner layer" (or "internal layer") means any layer of a multilayer film having both of its principal surfaces directly adhered to other layers of the film; "outer layer" means any layer of a film having one or none its principal surfaces directly adhered to another layer of the film;

"inside layer" means an outer layer of a multilayer film packaging a product which is closest to the product, relative to the other layers of the multilayer film; "outside layer" or "skin layer" means that layer of a multilayer film packaging a product which is farthest from the product relative to the other layers of the multilayer film;

"between", when used in conjunction with a subject layer and two or more object layers, means both direct adherence of the subject layer to the two other layers it is between, as well as including a lack of direct adherence to either or both of the two other layers the subject layer is between, i.e., one or more additional layers can be imposed between the subject layer and one or more of the layers the subject layer is between;

"seal layer", "sealing layer", "heat seal layer", and "sealant layer" mean

(a) with respect to lap-type seals, one or more outer film layer(s) (in general, up to the outer 75 +m (3 mils) of a film can be involved in the sealing of the film to itself or another layer) involved in the sealing of the film to itself, another film layer of the same or another film, and/or another article which is not a film, or

(b) with respect to fin-type seals, an inside film layer of a package, as well as supporting layers within 75 +m (3 mils) of the inside surface of the innermost layer, involved in the sealing of the film to itself; "seal" means a bonding of a first region of a film surface to a second region of a film surface created by heating (e.g., by means of a heated bar, hot air, infrared radiation, ultrasonic sealing, etc.) the regions to at least their respective seal initiation temperatures;

"barrier", when used in conjunction with films and/or film layers, means an ability to exclude one or more gases (e.g., O₂); "core layer" means an inner layer which has a primary function other than serving as an adhesive or compatibilizing agent for adhering two other layers to one another (e.g., providing a desired level of strength or modulus);

"abuse layer" (or "puncture resistant layer") means a layer, normally an outer layer that is resistant to abrasion, puncture, and other potential causes of reduction of package integrity, as well as potential causes of reduction of package appearance quality;

"tie layer" means an inner film layer having the primary purpose of providing interlayer adhesion to adjacent layers that otherwise do not adhere to one another; "bulk layer" means any layer which has the purpose of increasing the abuse resistance, toughness, modulus, etc., of a multilayer film and generally comprises polymers that are inexpensive relative to other polymers in the film which provide some specific purpose unrelated to abuse resistance, modulus, etc.; "carrier layer" means a layer which contains one or more adjuvants;

"lamination" and "laminate" (or "laminated film") mean the process, and resulting product, of the bonding of two or more film layers or other materials and include coextrusion as well as adhesive bonding; "adhere" means, (a) when used in connection with two or more films, to bond the films to one another using a heat seal or other means such as, for example, a layer of adhesive between the films, or

(b) when used in connection with film layers, to bond a subject film layer to an object film layer, without a tie layer, adhesive, or other layer therebetween; "total free shrink" means the percent dimensional change in a 10 cm x 10 cm specimen of film, when shrunk at 85°C (185°F), with the quantitative deteirnination being carried out according to ASTM D 2732, as set forth in the 1990 Annual Book of ASTM Standards, vol. 08.02, 368-371, the entire disclosure of which is incorporated herein by reference; "machine direction" means along the length of a film, i.e., in the direction of the film as it is formed during extrusion and/or coating; and

"transverse direction" means across a film, i.e., the direction that is perpendicular to the machine direction.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Films of the present invention include heat sealable layer and a layer that includes up to about 1.0 percent by weight alkali aluminosilicate ceramic particles that have a refractive index of about 1.52. The carrier layer and/or the overall film preferably has a refractive index of at least about 1.50, more preferably a refractive index of about 1.50 to about 1.54, most preferably a refractive index of about 1.52 (i.e., as close as possible to the ceramic particles. Also, the heat sealable layer preferably is the carrier layer. All the layers and polymeric components of a given film combine to provide an overall refractive index. For example, many packaging films presently in use include one or more layers that include polyolefinic materials and, as described previously, such materials generally have refractive indices in the range of from about 1.46 to about 1.54. Alkali aluminosilicate ceramic particles that have a refractive index of about 1.52 have been found to be excellent antiblocking agents in polyolefin-containing films, particularly those that have a polyethylene-containing heat sealable layer and an overall refractive index of at least about 1.50. Further, the carrier layer preferably has a refractive index that approximates that of the ceramic particles. Thus, the carrier layer preferably has a refractive index of at least about 1.50, more preferably from about 1.50 to about 1.54. Where such a carrier layer is an external layer, the reduction in haze is especially noticeable. Most preferably, the carrier layer is the heat sealable layer.

The heat sealable layer of the film of the present invention includes one or more polymers having mer units derived from ethylene. Although ethylene homopolymer can be used, copolymers are preferred. Exemplary copolymers include those that comprise mer units derived from one or more of propylene, C -C₂o ι-»-olefins, vinyl acetate, (meth)acrylic acid, and Cι-C o esters of (meth)acrylic acid. Ionomers also can be useful. Preferred copolymers are ethylene/V→-olefin copolymers.

The relatively recent advent of single site-type catalysts (e.g., metallocenes) necessitates further definitional clarification when discussing ethylene homo- and copolymers. Heterogeneous polymers are those having relatively wide variation in molecular weight and composition distribution. Polymers prepared with, for example, conventional Ziegler Natta catalysts are heterogeneous. Such polymers can be used in a variety of layers of the film of the present invention, including the heat sealable layer. On the other hand, homogeneous polymers have relatively narrow molecular weight and composition distribution. Homogeneous polymers differ structurally from heterogeneous polymers in that they exhibit a relatively even sequencing of comonomers within a chain, a mirroring of sequence distribution in all chains, and a similarity of chain lengths, i.e., a narrower molecular weight distribution. Homogeneous polymers typically are prepared using metallocene or other single site-type catalysts. Homogeneous polymers also can be used in a variety of layers of the film of the present invention, including the heat sealable layer. The term "ethylene/i→-olefin copolymer" as used herein refers both to heterogeneous materials such as low density polyethylene (LDPE), medium density polyethylene (MDPE), linear low density polyethylene (LLDPE), and very low and ultra low density polyethylene (VLDPE and ULDPE), as well as to homogeneous materials which, in general, are prepared by the copolymerization of ethylene and one or more -»-olefins. Preferably, the comonomer is a C -C₂o ι→-olefin, more preferably, a C -Cι₂ r→-olefin, still more preferably, a C -C₈ ι→- olefin. Particularly preferred i-→-olefins include 1-butene, 1-hexene, 1-octene, and mixtures thereof. In general, from about 80 to 99 weight percent ethylene and from 1 to 20 weight percent →-olefin, preferably from about 85 to 95 weight percent ethylene and from 5 to 15 weight percent π→-olefin, a copolymerized in the presence of a single site catalyst. Examples of commercially available homogeneous materials include the metallocene catalyzed ExactO resins (Exxon Chemical Co.; Baytown, Texas), substantially linear AffinityD and Engaged resins (Dow Chemical Co.; Midland, Michigan), and TafmeiO linear resins (Mitsui Petrochemical Corp.; Japan) Homogeneous ethylene/i→-olefin copolymers can be characterized by one or more methods known to those of skill in the art, such as molecular weight distribution (M_w M_n), composition distribution breadth index (CDBI), narrow melting point range, and single melt point behavior. The molecular weight distribution, also known as polydispersity, can be determined by, for example, gel permeation chromatography. Homogeneous ethylene/ →- olefin copolymers to be used in a layer of the film of the present invention preferably have an M_w/M_n of less than 2.7; more preferably from about 1.9 to 2.5; still more preferably, from about 1.9 to 2.3.

The CDBI of homogeneous ethyleneΛ→-olefin copolymers generally is greater than about 70 percent. CDBI is defined as the weight percent of copolymer molecules having a comonomer content within 50% (i.e., D 50%) of the median total molar comonomer content. CDBI can be determined by temperature rising elution fractionation as described by, for example, Wild et. al., J. Poly. Sci. -Poly. Phys. Ed, vol. 20, 441 (1982). Linear polyethylene, which does not contain a comonomer, is defined to have a CDBI of 100%. CDBI determination clearly distinguishes homogeneous copolymers (CDBI values generally above 70%) from presently available VLDPEs (CDBI values generally less than 55%). Homogeneous ethylene/V→-olefin copolymers also typically exhibit an essentially single melting point with a peak melting point (T_m), as determined by differential scanning calorimetry (DSC), of from about 60° to 105°C, more precisely a DSC peak T_m of from about 80° to 100°C. As used herein, the phrase "essentially single melting point" means that at least about 80% (by weight) of the material corresponds to a single T_m at a temperature within the range of from about 60°C to 105°C, and essentially no substantial fraction of the material has a peak melting point in excess of about 115°C as determined by DSC analysis (e.g., on a Perkin ElmerG System 7 Thermal Analysis System). The presence of higher melting peaks has been found to be detrimental to film properties such as haze and seal initiation temperature.

Homogeneous ethylene/h→-olefin copolymers inherently are more tacky, less dense, etc., than corresponding heterogeneous ethylene/r→-olefin copolymers. Because of these characteristics, they generally require the presence of more antiblocking agent than do corresponding heterogeneous ethylene/i→-olefin copolymers. Thus, the efficacy of ceramic microspheres relative to commonly antiblocking agents (discussed infra) provides a special advantage where homogeneous ethylene/i→-olefin copolymers are the carrier layer. In such circumstances, far lower loading levels (of antiblocking agent) than normally are necessary can be used.

In addition to providing excellent heat sealability, ethylene-containing copolymers advantageously have refractive indices in the vicinity of those of the aforedescribed ceramic particles. Where the heat sealable layer is also the carrier layer, the refractive index of the heat sealable layer must be at least about 1.50, preferably from about 1.50 to about 1.54. Such similarity in refractive indices between the heat sealable layer and the antiblocking agent reduces undesirable haze. Alkali aluminosilicate ceramic particles useful as antiblocking agents in accordance with the present invention have refractive indices of about 1.52. Such particles are available in a variety of sizes and size distributions. Generally, the median particle size is no greater than about 10 +m. Preferably, the median particle size is from about 2.0 to about 8.0 +m. More preferably, the median particle size is about 3.0 to about 5.5 +m. Preferred alkali aluminosilicate ceramic particles are ZeeosphereO microspheres (Zeelan Industries, Inc.; St. Paul, Minnesota). These particular microspheres are believed to be hollow, although that particular characteristic is not believed to be critical to their efficacy.

Regardless of source, the ceramic particles can constitute up to about 1.0% (by wt.) of the carrier layer. Preferably, however, they constitute no more than about 1.0% (by wt.) of the film. A preferred loading range is from about 0.25 weight percent to about 0.75 weight percent. Most preferably, the ceramic microspheres are present in an amount of at least about 0.35 weight percent.

The amount of particles included in the carrier layer can depend on the desired COF and haze values for the film and the size of the particles employed. Specifically, where the ceramic particles have a mean diameter of up to about 5.5 +m (such as, for example, W-210 Zeeosphere™ microspheres, which are reported to have a median diameter of about 3.5 +m), they preferably are present in an amount of at least 0.35 weight percent. However, where the ceramic particles have a mean diameter of more than about 5.5 +m (such as, for example, W-410 Zeeosphere™ microspheres which are reported to have a median diameter of about 4.5 to about 5.0 +m), at least about 0.25 weight percent particles can provide the desired balance of COF and haze properties.

Because such small amounts of microspheres can produce a relatively large reduction in the COF of a film into which they are incorporated, deleterious build up can be lessened substantially. In general, build up is accumulation of film additives on one or more suraces of packaging equipment caused by repeated friction between the surface(s) and the film, particularly when the packaging equipment is being run at high speeds. Build up often presents a significant problem during a packaging operation because it tends to slough off of the equipment surface(s) into and/or onto the packages being formed. At a minimum, this results in unsightly packages, and, in the case of food packages, can result in food law concerns.

Film additives that can contribute to build up include antiblocking agents, antifoggants, antistats such as surfactants, and slip agents such as waxes. Build up composed primarily of typical antiblocking agents (e.g., aluminum silicates and diatomaceous earths) normally is abrasive and can tear the film being produced or processed. Equipment surfaces can be cleaned often to avoid package failure caused by build up. However, repeated cleaning can result in a significant amount of down time for many packaging operations.

Although there is no formal test methodology available for measuring build up, it often is measured in grams of build up per 5,000 feet (1524 m) of film run in a packaging operation.

Although the packaging film of the present invention can have just a single layer (i.e., a layer derived from the blend described above), at least two layers are preferred. Where more than one layer is desired, the film can have any number of layers and any total thickness as long as the film provides the desired properties for the particular packaging operation in which the film is to be used (e.g., barrier properties, free shrink, shrink tension, optics, modulus, seal strength, etc.). Preferably, the film has a total of from 1 to 20 layers, more preferably from 2 to 12 layers, most preferably from 3 to 10 layers. Preferably, each of the layers of such a multilayer film has a refractive index of at least about 1.46. Thermoplastic films are employed in a variety of food and non-food packaging applications. The physical properties required of a film for any given end use application often determine the composition of the film and/or the compositions of the various layers of the film. Where a variety of properties are required, a variety of layers containing differing polymeric components can be, and usually are, employed. For example, where gas barrier properties are desired, a layer including, for example, ethylene/vinyl alcohol copolymer (EVOH), vinylidene chloride copolymer, or one or more of certain polyamides (e.g., nylons) can be included in the multilayer film structure. If the barrier employed is one which is known to be sensitive to moisture, such as EVOH, and the application requires exposure of the film to moisture, then one or more moisture barrier layers also can be included. If the film is likely to be subjected to abuse during handling and/or transport, an abuse layer can be provided (either as an inner or outer layer). One or two sealable layers can be provided to allow for sealing of the film to itself or another packaging article during the formation of a package. One or more core layers also can be provided, and films with at least one core layer are preferred for many applications.

Often, blends of polymers are used to optimize the properties provided by a single layer or to provide a single layer with multiple properties. Depending on the number and type of layers present, the packaging film of the present invention can be used for a wide variety of purposes, For example, it can be used to produce bags for packaging fresh red meat, smoked and processed meat, pork, cheese, poultry, and the like, as described in, for example, U.S. Patent Nos. 3,741,253 (Brax et al.), 3,891,008 (D'Entremont), 4,048,428 (Baird), and 4,284,458 (Schirmer). Also, it can be used as a shrink film in packaging applications for packaging food and non-food items such as are described in, for example, U.S. Patent Nos. 4,551,380 and 4,643,943 (both to Schoenberg).

The packaging film of the present invention can have oxygen, moisture, or odor barrier functionality, as described in, for example, U.S. Patent Nos. 4,064,296

(Bornstein et al.), 4,724,185 (Shah), 4,839,235 (Shah), and 5,004,647 (Shah). The film can be used as or in connection with a patch (as disclosed in, for example, U.S. Patent Nos. 4,755,403 and 4,770,731 (both to Ferguson)). Also, the film can be irradiated, oriented, annealed, and/or heat set. Additionally, the film of the present invention can be laminated, adhesively adhered, extrusion coated, or extrusion laminated onto a substrate to form a laminate. Lamination can be accomplished by joining layers with adhesives, joining with heat and pressure, and even spread coating and extrusion coating.

Where a barrier layer is included, the packaging film of the present invention can be used in applications in which the product(s) being packaged preferably is to be protected from one or more detrimental materials (e.g., atmospheric O₂). More particularly, the material of the present invention can take the form of stretch film, film suitable for vertical or horizontal form-fill-and-seal end use, lidstock film, film suitable for vacuum skin packaging, film suitable for use as a barrier bag, film suitable for use as a patch bag, film suitable for use in case ready packaging, film suitable for use in a thermoformed container (particularly in a film used as a liner in a thermoformed tray, such as a polystyrene tray), aroma odor barrier film, film suitable for use in cook-in end use applications (especially heat shrinkable bags, heat shrinkable and non-heat shrinkable casings, and containers thermoformed from non-heat shrinkable films and sheets), and medical film. Those of ordinary skill in the art can envision other packaging applications in which the film of the present invention can be used; these too are within the scope of the present invention. The film of the present invention can be manufactured by a variety of processes known in the art. The particular process chosen normally will depend on the ultimate end use for the material. For example, where the material is to be used as a shrink film, various blown bubble manufacturing techniques can be employed. Various film blowing, free film extrusion, extrusion coating processes, etc., can be envisioned by one of ordinary skill of the art.

The film of the present invention can be irradiated to induce crosslinking. In the irradiation process, the film is subjected to an energetic radiation treatment, such as corona discharge (see, e.g., U.S. Patent Nos. 4,120,716 and 4,879,430), plasma, flame, ultraviolet, X-ray, gamma ray, beta ray, and high energy electron treatment, which induces crosslinking between molecules of the irradiated material. The proper dosage level can be determined by standard dosimetry methods known to those of ordinary skill in the art, and the precise amount of radiation to be used of course depends on the particular structure and its end use. Preferably, the film is irradiated at a level of from about 0.5 to about 15 megarads (MR), more preferably about 1 to about 12 MR. Further details on the irradiation of polymeric films can be found in, for example, U.S. Patent No. 4,064,296 (Bornstein et al.).

The film of the present invention preferably is oriented, more preferably biaxially oriented. Preferably, the film is both biaxially oriented and heat shrinkable. A film that is oriented has been elongated, generally at an elevated temperature (i.e., the orientation temperature), then set or locked in the elongated configuration by cooling. This combination of elongation at elevated temperature followed by cooling causes an alignment of the polymer chains to a more parallel configuration, thereby dramatically altering the mechanical properties of the film. When an unrestrained, unannealed, oriented film subsequently is heated to its orientation temperature, the film shrinks almost to its original, i.e., pre-elongation, dimensions. Such a film is said to be heat shrinkable.

Often, the term orientation ratio (i.e., the product of the extent to which a film is oriented in several directions, usually two directions perpendicular to one another) is used when describing the degree of orientation of a given film. Orientation in the machine direction is referred to as "drawing", whereas orientation in the transverse direction is referred to as "stretching". For films extruded through an annular die, stretching is obtained by blowing the film to produce a bubble. For such films, drawing is obtained by passing the film through two sets of powered nip rolls, with the downstream set having a higher surface speed than the upstream set, with the resulting draw ratio being the surface speed of the downstream set of nip rolls divided by the surface speed of the upstream set of nip rolls.

Objects and advantages of this invention are further illustrated by the following examples which exemplify films according to the present invention. The particular materials and amounts thereof, as well as other conditions and details, recited in these examples should not be used to unduly limit this invention.

EXAMPLES

The following resins were used in the production of a variety of multilayer films in accordance with the present invention, as set forth below.

EAO- 1 : Dowlex™ 2045 heterogeneous ethylene/octene copolymer having a density of 0.920 g/cm³ and a melt index of 1.0 (Dow Chemical Co.).

EAO-2: Dowlex™ 2037 heterogeneous ethylene/octene copolymer having a density of 0.935 g/cm³ and a melt index of 2.5 (Dow Chemical Co.). EAO-3 : Attane™ 4202 heterogeneous ethylene/octene copolymer having a density of 0.913 g/cm³ and a melt index of 3.3 (Dow Chemical Co.).

EPC: PD9302 ethylene/propylene copolymer having 3.3% (by wt.) of ethylene and a density of 0.895 g/cm³ (Exxon Chemical Co.).

PP: PD4062 polypropylene having a density of 0.900 g/cm³ and a melt index of 3.3 (Exxon Chemical Co.).

EVA: PE 1335 ethylene/vinyl acetate having 3.5% by weight vinyl acetate (Rexene Products Inc.; Odessa, Texas).

PB: 0300PB polybutylene having a density of 0.915 g/cm³ (Shell Chemical

Co.; Houston, TX). SURF-1 : Atmos™ 300K Special surfactant containing 88% mono- and diglycerides and 12% propylene glycol (Witco Corp.; Melrose Park, Illinois).

SURF-2: Atmos™ 695K surfactant (Witco Corp.) SURF-3 Pationic™ 907 distilled monoglyceride surfactant, 97% minimum monoglycerides (Patco Div of American Ingredients, Kansas City, Missouri)

CLAY Kaopolite™ SF anhydrous aluminum silicate (Kaopolite Inc )

WAX A blend of erucamide, ethylene bis-stearamide, and, optionally, behenamide waxes

W-410 W-410 Zeeosphere™ white alkali aluminosilicate ceramic microspheres having a hardness of 6 on the Mohs scale and a median particle size of 7 4 +m

W-210 W-210 Zeeosphere™ white alkali aluminosilicate ceramic microspheres having a hardness of 6 on the Mohs scale and a median particle size of approximately 4 5 - 5 0 +m

To evaluate the films described below, a variety of tests were employed These can be summarized as follows

Haze A measure of the amount of light scattered by a film specimen It is responsible for reducing the contrast of objects viewed through the specimen It is measured according to the method set forth in ASTM D-1003

Coefficient of Friction (COF The ratio of frictional force to the force acting perpendicular to two surfaces in contact With respect to films, friction is the resisting force that arises when the surface of one film specimen slides over an adjacent surface of either that or another film specimen Static COF is related to the force required to begin movement of the surfaces relative to each other

Kinetic COF is related to the force required to sustain this movement Both are measured according to the method set forth in ASTM D-1894

Build up The accumulation of film additives on packaging equipment surfaces It is reported herein in g/5,000 feet (1524 m) of film run

Examples 1-3 A palindromic five layer film having the structure skin/tie/core/tie/skin was coextruded The core layer was a barrier layer, the tie layers were modified polymers, and the skin layers were a blend of 48 87% (by wt ) EAO-1, 24 44% (by wt ) EAO-2, 24.44 (by wt.) EVA, 1.5% (by wt.) SURF-1, and 0.75% (by wt.) W-410. The film was oriented out of hot air at about 1 16° to about 119°C. The oriented film had a total thickness of about 25 +m, and the thicknesses of the individual layers were in an approximate ratio of 2/2/1/2/2.

A film similar to that just described, except that its skin layers were made from blends of different composition, also was prepared. The outer skin layer was made from a blend of 48.87% (by wt.) EAO-1, 24.44% (by wt.) EAO-2, 24.44% (by wt.) EVA, 1.5% (by wt.) SURF-1, and 0.75% (by wt.) W-410. The inner skin layer was made from a blend of 47% (by wt.) EAO-1, 23.5% (by wt.) EAO-2, 23.5% (by wt.) EVA, 4% (by wt.) SURF-1, and 2% (by wt.) CLAY.

A film similar to the first described film, except that its skin layers were made from a blend of 47% (by wt.) EAO-1, 23.5% (by wt.) EAO-2, 23.5% (by wt.) EVA, 4% (by wt.) SURF-1, and 2% (by wt.) CLAY, also was prepared. Because neither skin layer contained an alkali aluminosilicate ceramic particle, this film was for comparative purposes only.

These films (designated 1-3, respectively) were tested for haze and static COF, as described above. The results are set forth in Table I below. (The comparative film was tested twice, and both sets of numbers are reported.)

Table I

The data of Table I show that the films of the present invention (i.e., Examples 1 and 2) both demonstrate an improved static COF over the comparative film (i.e., Example 3). The haze of the first film was quite low while the second film had only an acceptable haze, probably because it contained an antiblocking agent other than that taught in the present invention. Examples 4-6

Additional five layer films, similar to those described in Examples 1-3 above but with different skin layer compositions, were prepared. The skin layer compositions (with all percentages being by weight) were as follows:

4 -- 47.75% EAO-2, 47.75% EAO-3, 4% SURF-1, 0.5% W-210

5 -- 49.87% EAO-2, 49.87% EAO-3, 4% SURF-1, 0.25% W-210

6 ~ 47% EAO-2, 47% EAO-3, 4% SURF-1, 2% CLAY

Because the film of Example 6 did not use white microspheres as antiblocking agent, it is a comparative.

These films were tested for haze and static COF, as described above. The results are set forth in Table II below.

Table II

The data of Table II show that significantly less ceramic microsphere-type antiblocking agent can be used to produce static COF results that are similar to those obtained with higher amounts of a standard antiblocking agent (c.f Examples 4 and 6). Additionally, as the amount of ceramic microspheres is decreased, static COF increases while haze decreases (c.f. Examples 4 and 5). This latter observation indicates that optimization between the two properties is possible through very simple experimentation.

Examples 7-8 Additional five layer films, similar to those described in Examples 1-3 above but with different skin layer compositions, were prepared. The skin layer compositions (with all percentages being by weight) were as follows: 7 -- 47.5% EAO-2, 47.5% EAO-3, 4% SURF-1, 1% W-210

8 - 47% EAO-2, 47% E AO-3 , 4% SURF- 1 , 2% CLAY

Because the film of Example 8 did not use white microspheres as antiblocking agent, it is a comparative.

These films were tested for haze and static COF, as described above. The results are set forth in Table III below.

Table III

The data of Table III again show that significantly less ceramic microsphere-type antiblocking agent can be used to produce static COF results that are better than those obtained with higher amounts of a standard antiblocking agent. Additionally, as the amount of ceramic microspheres increases to around 1 weight percent, the haze of the film becomes a greater concern.

Examples 9-11 Three palindromic three layer films having the structure skin/core/skin were coextruded. The core layer was DowlexD 2045 ethylene/octene copolymer (Dow Chemical Co.) and the skin layers for the various films were blends of those materials listed below (with all percentages being by weight):

9 -- 72.5% EPC, 15% PB, 1 1.575% PP, 0.437% WAX, 0.437% W-210

10 - 72.5% EPC, 15% PB, 11.6% PP, 0.5% WAX, 0.4% W-410

11 - 72.5% EPC, 15% PB, 11.35% PP, 0.65% WAX, 0.5% CLAY

Because the film of Example 11 did not use white microspheres as antiblocking agent, it is a comparative.

The films were oriented out of hot air at about 116° to about 119°C. The oriented films had total thicknesses of about 15 +m, and the thicknesses of the individual layers were in an approximate ratio of 1/2/1. These films were tested for haze and static COF, as described above. In a trial packaging run, the films were evaluated for build up as well. The results are set forth in Table IV below.

Table IV

The data of Table IV show that films with ceramic microspheres result in far less build up during processing than do films with traditional antiblocking agents, even though the haze and COF properties of the films are similar. (Compare Examples 9 and 10 with Example 11). Also, a comparison of Examples 9 and 10 show that films with similar weight amounts of W-210 and W-410 Zeeosphere™ microspheres in a heat sealable layer can exhibit widely different properties.

Examples 12-14 Additional five layer films, similar to those described in Examples 1-3 above but with different skin layer compositions, were prepared. The skin layer compositions (with all percentages being by weight) were as follows:

12 -- 48.75% EAO-1, 24.375% EAO-2, 24.375% EAO-3, 1.0% SURF-2, 1.0% SURF-3, 0.5% W-210

13 48.75% EAO-2, 48.75% EAO-3, 1.0% SURF-2, 1.0% SURF-3, 0.5% W-210

14 .. 47⁰/0 _EA0.1 23.5% EAO-2, 23.5% EVA, 4% SURF- 1 , 2% CLAY

Because the film of Example 14 did not use white microspheres as antiblocking agent, it is a comparative.

The films were oriented out of hot air at about 116° to about 119°C. The oriented film had a total thickness of about 19 +m, and the thicknesses of the individual layers were in an approximate ratio of 2/2/1/2/2. These films were tested for haze and static COF, as described above. The results are set forth in Table V below.

Table V

(For comparative Example 14, one standard deviation for haze was 0.4 and for COF was 0.05.)

The data of Table V show that significantly improved haze can be obtained when substantially lower amounts of ceramic microspheres are used as the antiblocking agent.

Various modifications and alterations that do not depart from the scope and spirit of this invention will become apparent to those skilled in the art. This invention is not to be unduly limited to the illustrative embodiments set forth herein.

Claims

WHAT IS CLAIMED:

1. A thermoplastic packaging film comprising: a) a heat sealable layer comprising a polymer comprising mer units derived from ethylene, and b) disposed in a carrier layer, up to about 1.0 weight percent of essentially spherical alkali aluminosilicate ceramic particles having a refractive index of about 1.52, said film having an overall refractive index of at least about 1.50.

2. The film of claim 1 wherein said carrier layer is said heat sealable layer.

3. The film of claim 1 wherein said particles appear white to the unaided eye.

4. The film of claim 1 wherein said film is heat shrinkable.

5. The film of claim 1 wherein said overall refractive index is about 1.50 to about 1.54.

6. The film of claim 1 wherein said particles have a median diameter of up to about 3.5 +m.

7. The film of claim 6 wherein said particles are present in an amount of at least about 0.35 weight percent.

8. The film of claim 1 wherein said particles have a median diameter greater than about 3.5 +m.

9. The film of claim 8 wherein said particles are present in an amount of at least about 0.25 weight percent.

10. The film of claim 1 wherein said polymer further comprises mer units derived from one or more of propylene, vinyl acetate, (meth)acrylic acid, Cι-C₂o esters of (meth)acrylic acid, and C -C₂₀ r→-olefins.

11. A thermoplastic packaging film comprising: a) a heat sealable layer comprising a polymer comprising mer units derived from ethylene, and b) disposed in a carrier layer, up to about 1.0 weight percent of essentially spherical alkali aluminosilicate ceramic particles having a refractive index of about 1.52, said carrier layer having an overall refractive index of at least about 1.50.

12. The film of claim 1 1 wherein said carrier layer is said heat sealable layer.

13. The film of claim 1 1 wherein said particles appear white to the unaided eye.

14. The film of claim 11 wherein said film is heat shrinkable.

15. The film of claim 1 1 wherein said overall refractive index of said carrier layer is about 1.50 to about 1.54.

16. The film of claim 11 wherein said particles have a median diameter of up to about 5.5 +m.

17. The film of claim 16 wherein said particles are present in an amount of at least about 0.35 weight percent.

18. The film of claim 1 1 wherein said particles have a median diameter of greater than about 3.5 +m.

19. The film of claim 18 wherein said particles are present in an amount of at least about 0.25 weight percent.

20. The film of claim 1 1 wherein said polymer further comprises mer units derived from one or more of propylene, vinyl acetate, (meth)acrylic acid, Cι-C₂o esters of (meth)acrylic acid, and C₄-C₂₀ i→-olefins. AMENDED CLAIMS

[received by the International Bureau on 7 September 1998 (07.09.98); original claims 3-6, 8, 10, 13-16, 18 and 20 amended; remaining claims unchanged (2 pages)]

2. The film of claim 1 wherein said carrier layer is said heat sealable layer.

3. The film of any of claims 1 to 2 wherein said particles appear white to the unaided eye.

4. The film of any of claims 1 to 3 wherein said film is heat shrinkable.

5. The film of any of claims 1 to 4 wherein said overall refractive index is about 1.50 to about 1.54.

6. The film of any of claims 1 to 5 wherein said particles have a median diameter of up to about 3.5 μm.

8. The film of any of claims 1 to 5 wherein said particles have a median diameter greater than about 3.5 μm.

10. The film of any of claims 1 to 9 wherein said polymer further comprises mer units derived from one or more of propylene, vinyl acetate, (meth)acrylic acid, - C₂o esters of (meth)acrylic acid, and C -C₂n α-olefins.

12. The film of claim 11 wherein said carrier layer is said heat sealable layer.

13. The film of claim any of claims 11 to 12 wherein said particles appear white to the unaided eye.

14. The film of any of claims 11 to 13 wherein said film is heat shrinkable.

15. The film of any of claims 11 to 14 wherein said overall refractive index of said carrier layer is about 1.50 to about 1.54.

16. The film of any of claims 11 to 15 wherein said particles have a median diameter of up to about 5.5 μm.

18. The film of any of claims 11 to 15 wherein said particles have a median diameter of greater than about 3.5 μm.

20. The film of any of claims 11 to 19 wherein said polymer further comprises mer units derived from one or more of propylene, vinyl acetate, (meth)acrylic acid, O- C₂o esters of (meth)acrylic acid, and C -C₂o α-olefins.