Film with substrate layer containing antiblocking agent

A film includes a first outer layer comprising a polymeric material; a second outer layer including a polymeric material; and a substrate layer disposed between the first and second outer layers. The substrate layer includes a polymer and an antiblocking agent. Additional internal layers can be included, some or all of which can include a polymer and an antiblocking agent.

FIELD OF THE INVENTION
 The present invention relates generally to multilayer films, and
 particularly to packaging films. The present invention also relates to
 packages, especially packages having one or more seals, as well as
 packaged products.
 BACKGROUND OF THE INVENTION
 For some time it has been known to provide a packaging film which contains
 antiblocking agents, such as particulate silica, in one or both outside
 layers of the film. These antiblocking agents offer two advantages. First,
 they help to prevent the film from sticking or blocking to itself when the
 film is rolled up on itself during the manufacture of the film. Second,
 the antiblock offers a beneficial "roller bearing" effect when the film is
 run across metal parts in typical commercial packaging equipment. An
 example of such equipment is a Doboy.TM. horizontal form/fill/seal
 machine.
 Fatty acid amides, sometimes referred to as slip agents, are often also
 included in the film, in order to provide the film with a desirable
 film-to-film coefficient of friction, so that packaged products slide
 freely when in contact with one another. This is desired in order to
 facilitate alignment of packaged products for the bulk packaging thereof,
 for example in boxes, as well as providing a desired low film-to-equipment
 coefficient of friction.
 Unfortunately, antiblock particulates on the surface of the film, as well
 as fatty acid amides, are believed to often slough off of the film and
 accumulate on the metal parts of food packaging machines. This undesirable
 build up on the metal surfaces sometimes results in scratching of the
 film. In extreme cases, tearing of the film occurs, rendering it unfit for
 its commercial purpose. The metal parts must be cleaned. This of course
 interrupts the continuous operation of the equipment, thereby increasing
 cost of production.
 Abrasion of machine parts can also result from the use of films containing
 antiblocking agents in the surface layer, akin to the use of sandpaper on
 a metal surface.
 In addition, the possibility exists for sluffing off of the antiblocking
 agent into the product being packaged in the film.
 It is thus desirable to reduce or eliminate the presence of antiblocking
 agent on the surface of the film, while still providing the benefits
 offered by such agents.
 SUMMARY OF THE INVENTION
 As a first aspect, the present invention relates to a multilayer film
 comprising a first outer layer comprising a polymeric material; a second
 outer layer comprising a polymeric material; and a substrate layer,
 disposed between the first and second outer layers, comprising a polymeric
 material and an antiblocking agent.
 As a second aspect, the present invention relates to a multilayer film
 comprising a first outer layer comprising a polymeric material; a second
 outer layer comprising a polymeric material; a core layer, disposed
 between the first and second outer layers, comprising a polymeric
 material; and a first substrate layer, disposed between the core layer and
 the first outer layer, comprising a polymeric material and an antiblocking
 agent.
 Optionally, one or more additional substrate or internal layers can be
 included in the film structure of the invention.

DETAILED DESCRIPTION OF THE INVENTION
 As used herein, the term "film" is used in a generic sense to include a
 web, film, sheet, laminate, or the like, whether coextruded, extrusion
 laminated, extrusion coated, conventionally laminated, or otherwise
 produced by any other process.
 As used herein, "antiblocking agent" refers to an additive that is
 incorporated into a film to prevent the surface of a film from sticking to
 itself or other surfaces. These are organic or inorganic materials that,
 when included in a layer of a film, affect the final film surface
 topography on at least one outside surface of the film. It has been
 discovered that antiblocking agents can be incorporated in the substrate
 layer of a multilayer film, yet still create protrusions or roughness on
 at least one of the outer surfaces of the film. This occurs because of the
 presence of the antiblocking agent, which results in a deformation of the
 adjacent outer layer, causing the polymer of the outer layer to be
 displaced in portions of the outer layer near the antiblocking material.
 It is believed that in accordance with the invention, a majority of the
 individual antiblocking agent particles or units will be encapsulated
 within the polymer of the substrate and adjacent layers of the film. Thus,
 these particles or units will typically not break the outer surfaces of
 the film. It is theorized that these particles or units are "shrouded" by
 the surrounding polymers, and therefore less likely to slough off or
 dislodge from the film during a commercial packaging process. Yet, because
 of the roughness described above, achieved by the spatial impact of the
 presence of the antiblocking agent, the benefits traditionally associated
 with the use of antiblocking agents are substantially retained.
 As used herein, the phrases "seal layer", "sealing layer", "heat seal
 layer", "sealant layer", and the like, refer to an outer film layer, or
 layers, 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.
 Sealing can be performed by many means, such as using a hot wire, hot
 knife, heated bar, hot air, infrared radiation, ultrasonic sealing, etc.
 As used herein, the term "oriented" refers to a polymer-containing material
 which has been stretched at an elevated temperature (the orientation
 temperature), followed by being "set" in the stretched configuration by
 cooling the material while substantially retaining the stretched
 dimensions. Upon subsequently heating unrestrained, unannealed, oriented
 polymer-containing material to its orientation temperature, heat shrinkage
 is produced.
 As used herein, the term "monomer" refers to a relatively simple compound,
 usually containing carbon and of low molecular weight, which can react to
 form a polymer by combining with itself or with other similar molecules or
 compounds.
 As used herein, the term "comonomer" refers to a monomer which is
 copolymerized with at least one different monomer in a copolymerization
 reaction, the result of which is a copolymer.
 As used herein, the term "polymer" refers to the product of a
 polymerization reaction, and is inclusive of homopolymers, copolymers,
 terpolymers, etc. In general, the layers of a film can consist essentially
 of a single polymer, or can have still additional polymers together
 therewith, i.e., blended therewith.
 As used herein, the term "homopolymer" is used with reference to a polymer
 resulting from the polymerization of a single monomer, i.e., a polymer
 consisting essentially of a single type of repeating unit.
 As used herein, the term "copolymer" refers to polymers formed by the
 polymerization reaction of at least two different monomers. For example,
 the term "copolymer" includes the copolymerization reaction product of
 ethylene and an alpha-olefin, such as 1-hexene. However, the term
 "copolymer" is also inclusive of, for example, the copolymerization of a
 mixture of ethylene, propylene, 1-hexene, and 1-octene.
 As used herein, the term "polymerization" is inclusive of
 homopolymerizations, copolymerizations, terpolymerizations, etc., and
 includes all types of copolymerizations such as random, graft, block, etc.
 As used herein, the term "copolymerization" refers to the simultaneous
 polymerization of two or more monomers.
 As used herein, a copolymer identified in terms of a plurality of monomers,
 e.g., "propylene/ethylene copolymer", refers to a copolymer in which
 either monomer may copolymerize in a higher weight or molar percent than
 the other monomer or monomers.
 As used herein, copolymers are identified, i.e., named, in terms of the
 monomers from which the copolymers are produced. For example, the phrase
 "propylene/ethylene copolymer" refers to a copolymer produced by the
 copolymerization of both propylene and ethylene, with or without
 additional comonomer(s).
 As used herein, terminology employing a "/" with respect to the chemical
 identity of a copolymer (e.g., "an ethylene/alpha-olefin copolymer"),
 identifies the comonomers which are copolymerized to produce the
 copolymer. As used herein, "ethylene alpha-olefin copolymer" is the
 equivalent of "ethylene/alpha-olefin copolymer."
 As used herein, the phrase "heterogeneous polymer" refers to polymerization
 reaction products of relatively wide variation in molecular weight and
 relatively wide variation in composition distribution, i.e., typical
 polymers prepared, for example, using conventional Ziegler-Natta
 catalysts. Heterogeneous polymers are useful in various layers of the film
 used in the present invention. Although there are a few exceptions (such
 as TAFMER.TM. linear homogeneous ethylene/alpha-olefin copolymers produced
 by Mitsui Petrochemical Corporation, using Ziegler-Natta catalysts),
 heterogeneous polymers typically contain a relatively wide variety of
 chain lengths and comonomer percentages.
 As used herein, the phrase "heterogeneous catalyst" refers to a catalyst
 suitable for use in the polymerization of heterogeneous polymers, as
 defined above. Heterogeneous catalysts are comprised of several kinds of
 active sites which differ in Lewis acidity and steric environment.
 Ziegler-Natta catalysts are heterogeneous catalysts. Examples of
 Ziegler-Natta heterogeneous systems include metal halides activated by an
 organometallic co-catalyst, such as titanium chloride, optionally
 containing magnesium chloride, complexed to trialkyl aluminum, as is
 disclosed in patents such as U.S. Pat. No. 4,302,565, to GOEKE, et. al.,
 and U.S. Pat. No. 4,302,566, to KAROL, et. al., both of which are hereby
 incorporated, in their entireties, by reference thereto.
 As used herein, the phrase "homogeneous polymer" refers to polymerization
 reaction products of relatively narrow molecular weight distribution and
 relatively narrow composition distribution. Homogeneous polymers are
 useful in various layers of the multilayer film used in the present
 invention. Homogeneous polymers are structurally different from
 heterogeneous polymers, in that homogeneous polymers exhibit a relatively
 even sequencing of comonomers within a chain, a mirroring of sequence
 distribution in all chains, and a similarity of length of all chains,
 i.e., a narrower molecular weight distribution. Furthermore, homogeneous
 polymers are typically prepared using metallocene, or other single-site
 type catalysts, rather than using Ziegler Natta catalysts.
 More particularly, homogeneous ethylene/alpha-olefin copolymers may be
 characterized by one or more methods known to those of skill in the art,
 such as molecular weight distribution (M.sub.w /M.sub.n), composition
 distribution breadth index (CDBI), and narrow melting point range and
 single melt point behavior. The molecular weight distribution (M.sub.w
 /M.sub.n), also known as polydispersity, may be determined by gel
 permeation chromatography. The homogeneous ethylene/alpha-olefin
 copolymers useful in this invention generally have (M.sub.w /M.sub.n) of
 less than 2.7; preferably from about 1.9 to 2.5; more preferably, from
 about 1.9 to 2.3. The composition distribution breadth index (CDBI) of
 such homogeneous ethylene/alpha-olefin copolymers will generally be
 greater than about 70 percent. The CDBI is defined as the weight percent
 of the copolymer molecules having a comonomer content within 50 percent
 (i.e., plus or minus 50%) of the median total molar comonomer content. The
 CDBI of linear polyethylene, which does not contain a comonomer, is
 defined to be 100%. The Composition Distribution Breadth Index (CDBI) is
 determined via the technique of Temperature Rising Elution Fractionation
 (TREF). CDBI determination clearly distinguishes the homogeneous
 copolymers used in the present invention (narrow composition distribution
 as assessed by CDBI values generally above 70%) from VLDPEs available
 commercially which generally have a broad composition distribution as
 assessed by CDBI values generally less than 55%. The CDBI of a copolymer
 is readily calculated from data obtained from techniques known in the art,
 such as, for example, TREF as described, for example, in Wild et. al., J.
 Poly. Sci. Poly. Phys. Ed., Vol. 20, p.441 (1982). Preferably, the
 homogeneous ethylene/alpha-olefin copolymers have a CDBI greater than
 about 70%, i.e., a CDBI of from about 70% to 99%. In general, the
 homogeneous ethylene/alpha-olefin copolymers in the multilayer films of
 the present invention also exhibit a relatively narrow melting point
 range, in comparison with "heterogeneous copolymers", i.e., polymers
 having a CDBI of less than 55%.
 A homogeneous ethylene/alpha-olefin copolymer can, in general, be prepared
 by the copolymerization of ethylene and any one or more alpha-olefin.
 Preferably, the alpha-olefin is a C.sub.3 -C.sub.20 alpha-monoolefin, more
 preferably, a C.sub.4 -C.sub.12 alpha-monoolefin, still more preferably, a
 C.sub.4 -C.sub.8 alpha-monoolefin. Still more preferably, the alpha-olefin
 comprises at least one member selected from the group consisting of
 butene-1, hexene-1, and octene-1, i.e., 1-butene, 1-hexene, and 1-octene,
 respectively. Most preferably, the alpha-olefin comprises octene-1, and/or
 a blend of hexene-1 and butene-1.
 Processes for preparing and using homogeneous polymers are disclosed in
 U.S. Pat. No. 5,206,075, U.S. Pat. No. 5,241,031, and PCT International
 Application WO 93/03093, each of which is hereby incorporated by reference
 thereto, in its entirety. Further details regarding the production and use
 of homogeneous ethylene/alpha-olefin copolymers are disclosed in PCT
 International Publication Number WO 90/03414, and PCT International
 Publication Number WO 93/03093, both of which designate Exxon Chemical
 Patents, Inc. as the Applicant, and both of which are hereby incorporated
 by reference thereto, in their respective entireties.
 Still another genus of homogeneous ethylene/alpha-olefin copolymers is
 disclosed in U.S. Pat. No. 5,272,236, to LAI, et. al., and U.S. Pat. No.
 5,278,272, to LAI, et. al., both of which are hereby incorporated by
 reference thereto, in their respective entireties.
 As used herein, the phrase "homogeneous catalyst" refers to a catalyst
 suitable for use in the polymerization of homogeneous polymers, as defined
 above. Homogeneous catalysts are also referred to as "single site
 catalysts", due to the fact that such catalysts typically have only one
 type of catalytic site, which is believed to be the basis for the
 homogeneity of the polymers resulting from the polymerization.
 As used herein, the term "polyolefin" refers to any polymerized olefin,
 which can be linear, branched, cyclic, aliphatic, aromatic, substituted,
 or unsubstituted. More specifically, included in the term polyolefin are
 homopolymers of olefin, copolymers of olefin, copolymers of an olefin and
 a non-olefinic comonomer copolymerizable with the olefin, such as vinyl
 monomers, styrenic monomers, modified polymers thereof, and the like.
 Specific examples include polyethylene homopolymer, polypropylene
 homopolymer, polybutene, ethylene/alpha-olefin copolymer,
 propylene/alpha-olefin copolymer, butene/alpha-olefin copolymer,
 ethylene/vinyl acetate copolymer, ethylene/ethyl acrylate copolymer,
 ethylene/butyl acrylate copolymer, ethylene/methyl acrylate copolymer,
 ethylene/acrylic acid copolymer, ethylene/methacrylic acid copolymer,
 modified polyolefin resin, ionomer resin, polymethylpentene,
 olefin/styrene copolymers, etc. Modified polyolefin resin is inclusive of
 modified polymer prepared by copolymerizing the homopolymer of the olefin
 or copolymer thereof with an unsaturated carboxylic acid, e.g., maleic
 acid, fumaric acid or the like, or a derivative thereof such as the
 anhydride, ester or metal salt or the like. It could also be obtained by
 incorporating into the olefin homopolymer or copolymer, an unsaturated
 carboxylic acid, e.g., maleic acid, fumaric acid or the like, or a
 derivative thereof such as the anhydride, ester or metal salt or the like.
 As used herein, terms identifying polymers, such as "polyamide",
 "polyester", "polyurethane", etc. are inclusive of not only polymers
 comprising repeating units derived from monomers known to polymerize to
 form a polymer of the named type, but are also inclusive of comonomers,
 derivatives, etc. which can copolymerize with monomers known to polymerize
 to produce the named polymer. For example, the term "polyamide"
 encompasses both polymers comprising repeating units derived from
 monomers, such as caprolactam, which polymerize to form a polyamide, as
 well as copolymers derived from the copolymerization of caprolactam with a
 comonomer which when polymerized alone does not result in the formation of
 a polyamide. Furthermore, terms identifying polymers are also inclusive of
 mixtures, blends, etc. of such polymers with other polymers of a different
 type. More preferably, however, the polyolefin is the polymerization
 product of one or more unsubstituted olefins, the polyamide is the
 polymerization product of one or more unsubstituted amides, etc.
 As used herein, the phrase "ethylene alpha-olefin copolymer", and
 "ethylene/alpha-olefin copolymer", refer to such heterogeneous materials
 as linear low density polyethylene (LLDPE), and very low and ultra low
 density polyethylene (VLDPE and ULDPE); and homogeneous polymers such as
 metallocene-catalyzed EXACT.TM. linear homogeneous ethylene/alpha olefin
 copolymer resins obtainable from the Exxon Chemical Company, of Baytown,
 Tex., and TAFMER.TM. linear homogeneous ethylene/alpha-olefin copolymer
 resins obtainable from the Mitsui Petrochemical Corporation. All these
 materials generally include copolymers of ethylene with one or more
 comonomers selected from C.sub.4 to C.sub.10 alpha-olefin such as butene-1
 (i.e., 1-butene), hexene-1, octene-1, etc. in which the molecules of the
 copolymers comprise long chains with relatively few side chain branches or
 cross-linked structures. This molecular structure is to be contrasted with
 conventional low or medium density polyethylenes which are more highly
 branched than their respective counterparts. The heterogeneous
 ethylene/alpha-olefin commonly known as LLDPE has a density usually in the
 range of from about 0.91 grams per cubic centimeter to about 0.94 grams
 per cubic centimeter. Other ethylene/alpha-olefin copolymers, such as the
 long chain branched homogeneous ethylene/alpha-olefin copolymers available
 from The Dow Chemical Company, known as AFFINITY.TM. resins, are also
 included as another type of homogeneous ethylene/alpha-olefin copolymer
 useful in the present invention.
 In general, the ethylene/alpha-olefin copolymer comprises a copolymer
 resulting from the copolymerization of from about 80 to 99 weight percent
 ethylene and from 1 to 20 weight percent alpha-olefin. Preferably, the
 ethylene/alpha-olefin copolymer comprises a copolymer resulting from the
 copolymerization of from about 85 to 95 weight percent ethylene and from 5
 to 15 weight percent alpha-olefin.
 As used herein, the phrase "substrate layer" refers to any layer, of a
 multilayer film, having both of its principal surfaces directly adhered to
 another layer of the film. Preferably, the term "substrate layer" refers
 to a layer adjacent an outer layer.
 As used herein, the phrase "outer layer" refers to any film layer of film
 having less than two of its principal surfaces directly adhered to another
 layer of the film. In multilayer films, there are two outer layers, each
 of which has a principal surface adhered to only one other layer of the
 multilayer film.
 As used herein, the phrase "internal layer" refers to a substrate layer.
 As used herein, the term "extrusion" is used with reference to the process
 of forming continuous shapes by forcing a molten plastic material through
 a die, followed by cooling or chemical hardening. Immediately prior to
 extrusion through the die, the relatively high-viscosity polymeric
 material is fed into a rotating screw of variable pitch, i.e., an
 extruder, which forces the polymeric material through the die.
 As used herein, the term "coextrusion" refers to the process of extruding
 two or more materials through a single die with two or more orifices
 arranged so that the extrudates merge and weld together into a laminar
 structure before chilling, i.e., quenching. Coextrusion can be employed in
 film blowing, free film extrusion, and extrusion coating processes.
 As used herein, the phrase "machine direction", herein abbreviated "MD",
 refers to a direction "along the length" of the film, i.e., in the
 direction of the film as the film is formed during extrusion and/or
 coating.
 As used herein, the phrase "transverse direction", herein abbreviated "TD",
 refers to a direction across the film, perpendicular to the machine
 direction.
 As used herein, the phrase "free shrink" refers to the percent dimensional
 change in a 10 cm.times.10 cm specimen of film, when shrunk at 200.degree.
 F., with the quantitative determination being carried out according to
 ASTM D 2732, as set forth in the 1990 Annual Book of ASTM Standards, Vol.
 08.02, pp.368-371, which is hereby incorporated, in its entirety, by
 reference thereto. The film according to the present invention preferably
 has a "total free shrink at 200.degree. F.", i.e., the sum of the free
 shrink in the machine direction, at 200.degree. F., and the free shrink in
 the transverse direction, at 200.degree. F., of from about 10 to 80
 percent; more preferably, from about 15 to 70 percent; still more
 preferably, from about 20 to 60 percent, such as 25 to 40 percent. Unless
 specified otherwise, the phrase "free shrink", as used herein, refers to
 total free shrink.
 In the film according to the present invention, the outer film layers
 preferably comprise polyolefin. Preferably, the polyolefin comprises at
 least one member selected from the group consisting of polyethylene and
 polypropylene. Preferably, the polyethylene comprises at least one member
 selected from the group consisting of linear low density polyethylene
 (LLDPE), very low density polyethylene (VLDPE), linear medium density
 polyethylene (LMDPE), high density polyethylene (HDPE), ethylene/vinyl
 acetate copolymer (EVA), ethylene/butyl acrylate copolymer (EBA), and
 homogeneous ethylene/alpha-olefin copolymer. Preferably, the polypropylene
 comprises at least one member selected from the group consisting of
 propylene homopolymer, propylene/ethylene random copolymer,
 propylene/butene copolymer, and propylene/ethylene/butene terpolymer.
 Preferably, the propylene/ethylene random copolymer comprises ethylene mer
 in an amount of from about 0.5 to 30 weight percent, based on the weight
 of the propylene/ethylene random copolymer; more preferably, ethylene mer
 in an amount of from about 0.5 to 10 percent, and still more preferably,
 from about 2 to 6 weight percent. The polypropylene may comprise
 syndiotactic polypropylene.
 Although conventional heterogeneous polymers are disclosed in the examples,
 below, the outer layers may instead, or additionally, comprise homogeneous
 polymer, such as homogeneous ethylene/alpha-olefin copolymer.
 A particularly preferred outer layer comprises propylene/ethylene
 copolymer, polybutylene, and homopolymer polypropylene. Another
 particularly preferred outer layer comprises propylene/ethylene random
 copolymer and polypropylene homopolymer. The outer layer may further
 comprise butylene homopolymer, i.e., in addition to one or more of the
 polyolefins described above.
 Another preferred outer layer comprises a blend of linear low density
 polyethylene and ethylene/vinyl acetate copolymer. Linear medium density
 polyethylene can also be included.
 The inner layer(s) of the film preferably comprises ethylene-based polymer,
 more preferably ethylene/alpha-olefin copolymer, including both
 heterogeneous ethylene/alpha-olefin copolymer and homogeneous
 ethylene/alpha-olefin copolymer. Linear low density polyethylene (LLDPE)
 is a preferred heterogeneous ethylene/alpha-olefin copolymer for use in
 the core layer.
 The antiblocking agent may comprise mineral-based antiblocking agent and/or
 synthetic-based antiblocking agent. Mineral-based antiblocking agents
 include both silica-based agents (e.g., diatomaceous earth, quartz, and
 silica sand), as well as others such as kaolin, talc, feldspar, and
 calcium carbonate. Synthetic-based antiblocking agents include synthetic
 silica antiblocking agents, for example gel-type synthetic silica, and
 precipitated-type synthetic silica.
 Preferably, the antiblocking agent comprises at least one member selected
 from the group consisting of silica, silicate, and glass, and preferably
 the antiblocking agent is in the form of approximately spherical
 particles. However, particles of irregular shape, and angular particles,
 can be used. Preferably, the antiblocking agent comprises at least one
 member selected from the group consisting of aluminum silicate (clay),
 silica (silicon dioxide), sodium calcium alumino silicate, magnesium
 silicate (talc), and calcium silicate; more preferably, at least one
 member selected from the group consisting of aluminum silicate, silica,
 sodium calcium alumino silicate, and magnesium silicate; still more
 preferably, at least one member selected from the group consisting of
 aluminum silicate, silica, and sodium calcium alumino silicate; yet still
 more preferably, at least one member selected from the group consisting of
 aluminum silicate and silica; and yet still more preferably, aluminum
 silicate. Preferred antiblocking agents are W-410 and JC-30. These
 materials are described herein.
 The antiblocking agent can comprise an organic material such as crosslinked
 or uncrosslinked organic materials. Examples include polyester, EVOH
 (ethylene/vinyl alcohol copolymer), nylon 6, nylon 6,6, syndiotactic
 polystyrene, engineering resins, liquid crystalline polymers, and aromatic
 nylons. Selecting the appropriate antiblocking agent depends at least in
 part on the nature of the layer in which the antiblocking agent is
 present. The Vicat softening point of the organic antiblocking agent
 should be sufficiently higher than that of the host polymer such that the
 organic antiblocking agent functions as an antiblocking agent as described
 herein.
 In accordance with the present invention, antiblocking agents have an
 average particle size (diameter) of from about 0.1 to 10 microns, such as
 1 to 8 microns, and 2 to 6 micrometer, and are preferably present at a
 level of from 0.1 to 6 weight percent, such as 0.2 to 4 wt. %, and 0.3 to
 3 wt. %, based on the weight of the substrate layer.
 An organosiloxane, i.e., silicone oil, can optionally be included in or on
 one or more layers of the films of the present invention. The
 organosiloxane preferably comprises at least one member selected from the
 group consisting of polydimethylsiloxane, polymethylphenylsiloxane,
 olefin-modified silicone, polyether (e.g., polyethylene glycol,
 polypropylene glycol)-modified silicone, olefin/polyether-modified
 silicone, epoxy-modified silicone, amino-modified silicone,
 alcohol-modified silicon, etc. Among these, polydimethylsiloxane is
 preferred.
 The organosiloxane is preferably present in the substrate layer in an
 amount of from about 0.1 to 1.0 weight percent based on the weight of the
 substrate layer, more preferably in an amount of from about 0.1 to 0.5
 weight percent, still more preferably 0.16 to 0.5 weight percent, and yet
 still more preferably in an amount of 0.18 to 0.5 weight percent.
 Optionally, one or more of the outer layers and/or substrate layer(s)
 includes fatty amide, preferably in an amount of from about 0.1 to 1
 percent, based on the weight of the layer; more preferably, from about 0.2
 to 0.6 percent; still more preferably, from about 0.2 to 0.4 percent.
 Preferably, the fatty amide comprises at least one member selected from
 the group consisting of primary fatty amide, secondary fatty amide,
 tertiary fatty amide, fatty alkanolamide, and fatty bisamide. More
 specifically, the fatty amide preferably comprises at least one member
 selected from the group consisting of erucamide, stearamide, oleamide,
 behenamide, and ethylene bisstearamide.
 Fatty amides are described in detail in Arthur L. McKenna, "Fatty Amides"
 (1992, Witco Chemical Corporation), which is hereby incorporated by
 reference thereto, in its entirety.
 Although the film preferably has a film-to-film coefficient of friction of
 from about 0.1 to 0.9, more preferably the film has a film-to-film
 coefficient of friction of from about 0.1 to 0.7, still more preferably,
 from about 0.1 to 0.5, and yet still more preferably, from about 0.1 to
 0.3.
 The film has a total thickness of preferably less than about 20 mils, more
 preferably the film has a total thickness of from about 0.2 to 10 mils,
 still more preferably from about 0.3 to 4 mils, and yet still more
 preferably, from about 0.4 to 2 mils, such as 0.5 to 1 mil.
 The measurement of optical properties of plastic films used in packaging,
 including the measurement of total transmission, haze, clarity, and gloss,
 is discussed in detail in Pike, LeRoy, "Optical Properties of Packaging
 Materials", Journal of Plastic film & sheeting, Vol. 9, No. 3, pp. 173-180
 (July 1993), which is hereby incorporated by reference thereto, in its
 entirety.
 The measurement of all angles of reflected or transmitted light from a
 sample is called goniophotometry. A Gardner Goniophotometer is capable of
 determining total transmission, i.e., measuring light striking at any and
 all angles, and the reflection or transmission of this light from any
 angle.
 The film clarity can be measured using the method of ASTM D 1746, as set
 forth in the 1990 Annual Book of ASTM Standards, Vol. 08.02, pp.76-78,
 which is hereby incorporated, in its entirety, by reference thereto. Haze
 can be measured using the method of ASTM D 1003, as is discussed below.
 Gloss can be measured using the method of ASTM D 2457, as set forth in the
 1990 Annual Book of ASTM Standards, Vol. 08.02, pp.266-269, which is
 hereby incorporated, in its entirety, by reference thereto.
 Clarity refers to the optical distinctness with which an object can be seen
 when viewed through the sheet. Clarity may be thought of as the
 distinctness with which an object appears when viewed through a film.
 Clarity may also be described as the quality of image formation through a
 sheet, and depends upon the linearity of the passage of light rays through
 the material. Small deflections of the light, caused by the scattering
 centers of the material, bring about a deterioration of the image, i.e., a
 decrease in clarity, these deflections being much smaller than those
 registered in haze measurements.
 Although the film of the present invention preferably has a clarity of from
 about 20 percent to 100 percent, more preferably the film has a clarity of
 from about 40 to 100 percent, still more preferably from about 60 to 100
 percent, and still more preferably, from 80 to 100 percent. Some of the
 multilayer films of the present invention are preferably irradiated to
 induce crosslinking. In the irradiation process, the film is subjected to
 an energetic radiation treatment, such as corona discharge, plasma, flame,
 ultraviolet, X-ray, gamma ray, beta ray, and high energy electron
 treatment, which induce cross-linking between molecules of the irradiated
 material. The irradiation of polymeric films is disclosed in U.S. Pat. No.
 4,064,296, to BORNSTEIN, et. al., which is hereby incorporated in its
 entirety, by reference thereto. BORNSTEIN, et. al. discloses the use of
 ionizing radiation for crosslinking the polymer present in the film.
 To produce crosslinking, a suitable radiation dosage of high energy
 electrons, preferably using an electron accelerator, with a dosage level
 being determined by standard dosimetry methods. Other accelerators such as
 a Van de Graaff generator or resonating transformer may be used. The
 radiation is not limited to electrons from an accelerator since any
 ionizing radiation may be used. The ionizing radiation can be used to
 crosslink the polymers in the film. Preferably, the film is irradiated at
 a level of from 2-15 MR, more preferably 2-10 MR. As can be seen from the
 descriptions of preferred films for use in the present invention, the most
 preferred amount of radiation is dependent upon the film composition,
 thickness, etc., and its end use.
 The antiblocking agent can be used in a substrate layer or layers, and
 optionally in one or more other layers of a wide variety of film and sheet
 materials. More specifically, the antiblocking agent can be used in any
 one or more of the substrate layers of films disclosed in: U.S. Pat. No.
 4,532,189, issued Jul. 30, 1985 to W. B. Mueller; U.S. Pat. No. 4,551,380
 issued Nov. 5, 1985 to J. H. Schoenberg; U.S. Pat. No. 4,724,185 issued
 Feb. 9, 1988 to G. P. Shah; U.S. Pat. No. 4,755,419 issued Jul. 5, 1988 to
 G. P. Shah; U.S. Pat. No. 5,023,143 issued Jun. 11, 1991 to M. Nelson;
 U.S. Pat. No. 5,298,302, issued Mar. 29, 1994 to P. R. Boice; and U.S.
 Pat. No. 5,482,771, issued Jan. 9, 1996 to G. P. Shah. Each of these
 patents is hereby incorporated by reference thereto, in its entirety.
 In addition to the above listed patents, the present invention is
 especially useful in symmetrical three-layer films, and symmetrical
 five-layer films, each having propylene-based outer layers and at least
 one ethylene-based inner layer. Films which can beneficially use the
 invention include barrier films as well as non-barrier films, irradiated
 as well as non-irradiated films, symmetrical and non-symmetrical films,
 films containing adhesive layers, and films containing one or more
 interior functional layers.
 FIG. 1 illustrates a cross-sectional view of a preferred, oriented
 three-layer film 10. First layer 12 is an outer film layer which can serve
 as a sealing layer, and either an abuse layer or a product contact layer.
 Second layer 14 is a substrate film layer which can serve as a bulk layer.
 Third layer 16 is also an outer layer, and can also serves as a sealing
 layer as well as an abuse layer or a product contact layer. In the
 preferred film illustrated in FIG. 1, first layer 12 and third layer 16
 are of substantially identical chemical composition and substantially
 identical thickness, so that multilayer film 10 has a substantially
 symmetrical cross-section. Outer layers 12 and 16 each comprise a
 polymeric material, and substrate layer 14 comprises a polymeric material
 and an antiblocking agent 17.
 FIG. 2 shows a film 20 like that of FIG. 1, but including five layers. The
 antiblocking agent 27 is present in two substrate layers 24 and 28,
 flanked respectively by the central core layer 26 and outer layers 22 and
 30.
 FIG. 3 shows an unoriented five layer film 32; FIG. 4 shows the same film
 after orientation, and similar to the film of FIG. 2. A preferred method
 for making the film of the present invention is as set forth in U.S. Pat.
 Nos. 4,532,189, and 5,298,302, both patents incorporated by reference
 herein in their entirety. Individual resin components or blends which are
 to form each layer are fed to extruders. Inside the extruders, the polymer
 beads are forwarded, melted, and degassed, following which the resulting
 bubble-free melt is forwarded into a die head, and extruded through an
 annular die, resulting in a tape, in the form of a tubing, the tape
 preferably having a thickness of about 5 to 50 mils. The tape is then
 rapidly cooled to room temperature (optionally by water spray from a
 cooling ring) and thereafter collapsed by pinch rolls. Although the tape
 can be irradiated, the tape is preferably not irradiated because
 polypropylene, a preferred polymer for use in the film, degrades with
 radiation. However, in the event that the film comprises only polymers
 which do not degrade upon irradiation, it may be preferred to irradiate
 the tape. The tape is then heated to a preferred orientation temperature
 by using a radiant heating means (e.g., infrared radiation) and/or
 conductive heating means (e.g., superheated steam) and/or convective
 heating means (e.g., heated air). A preferred orientation temperature is
 from about 75.degree. C. to 175.degree. C., more preferably from about
 90.degree. C. to 160.degree. C. After reaching the desired orientation
 temperature, the heated tape is directed through pinch rolls, following
 which the heated tape is inflated, resulting in a trapped bubble. Using
 this bubble technique, which is well known to those of skill in the art,
 internal air pressure stretches the heated tape in an amount of from about
 1.5.times. to 8.times. in the transverse direction (preferably from about
 3.times. to 7.times.). Simultaneously, roller speed differential, i.e.,
 between the first and second set of pinch rolls, simultaneously draws the
 heated tape in an amount of from about 1.5.times. to 8.times. in the
 machine direction (preferably from about 3.times. to 7.times.). In this
 manner, a biaxially oriented film 20 is formed. The biaxially oriented
 film is then rapidly cooled using chilled air, in order to maintain the
 degree of biaxial orientation. Finally, the biaxially oriented film is
 wound onto a take-up roll.
 EXAMPLES
 The invention is illustrated by the following examples, which are provided
 for the purpose of representation, and are not to be construed as limiting
 the scope of the invention. Unless stated otherwise, all percentages
 disclosed herein are based on weight.
 The following resins were employed in the Examples set forth below.
 PEC: Escorene.TM. PD 9302 propylene/ethylene random copolymer having 3.3%
 by weight of ethylene, obtained from the Exxon Chemical Americas, of
 Houston, Tex.
 PB: Duraflex 0 300 .TM. polybutylene homopolymer having a density of 0.915
 g/cc, obtained from the Shell Chemical Company, of Hahnville, La.
 PP: PD 4062E-7 .TM. polypropylene homopolymer having a density of 0.90
 g/cc, also obtained from the Exxon Chemical Americas.
 PBR1 Cefor.TM. DS4D31 propylene/butene random copolymer with 8% butene from
 Shell.
 PBR2 Cefor.TM. DS4D05 propylene/butene random copolymer with 14% butene
 from Shell.
 PEB1: KT-221P.TM. propylene/ethylene/butene random copolymer from Montel
 Polyolefins USA.
 PEB2: KT-021P.TM. propylene/ethylene/butene random copolymer from Montel
 Polyolefins USA.
 AB1: Zeeospheres W-410.TM. ceramic microspheres, used as antiblocking agent
 with spherical shape and average size (diameter) of 4 micrometers from
 Zeelan Industries.
 AB2 Silton JC-30.TM. metal silicate particles, used as antiblocking agent
 with average size (diameter) of 3 micrometers, distributed by
 International Resources, Inc.
 AB3 Syloblock S200.TM., used as antiblocking agent with average size
 (diameter) of 2 micrometers, from W. R. Grace.
 AB4 Zeeospheres W-610.TM. ceramic microspheres, used as antiblocking agent
 with spherical shape and average size (diameter) of 6 micrometers.
 AB5 Silton JC-50.TM. metal silicate particles, used as antiblocking agent
 with average size (diameter) of 5 micrometers.
 ABB: KAOPOLITE SFO SPECIAL .TM. blend of kaolin silica having an average
 particle size of 0.7 microns with approximately 4% by weight of fatty acid
 amides, obtained from Kaopolite, Inc., of Union, N.J.
 SO: SF 18-350 .TM. polydimethylsiloxane (i.e., silicone oil), obtained from
 the General Electric Company of Waterford, N.Y.
 FA1: KEMAMIDE W-40 .TM. N-N'-ethylene-bis-stearamide (a fatty amide), also
 obtained from the Witco Corp.
 FA2: KEMAMIDE E Ultra .TM. fatty amide of erucic acid, obtained from the
 Witco Corp., Humko Chemical Division, of Charlotte, N.C.
 FA3: KEMAMIDE B .TM. fatty amide of behenic acid, obtained from the Witco
 Corp., Humko Chemical Division, of Charlotte, N.C.
 MO: KAYDOL .TM. white mineral oil, also supplied by Witco Corp.
 LLDPE: DOWLEX 2045.03 .TM. linear low density polyethylene, a heterogeneous
 ethylene/octene copolymer having a density of 0.920 g/cc and a melt index
 of 1.1, obtained from The Dow Chemical Company, of Midland, Mich.
 PE1: Dowlex.TM. 2045.04 LLDPE, an ethylene/1-octene copolymer with a
 density of 0.920 gm/cc and an octene-1 comonomer content of 6.5%.
 PE2: Dowlex.TM. 2037 LMDPE, an ethylene/1-octene copolymer with a density
 of 0.935 gm/cc. and an octene-1 comonomer content of 2.5%.
 EV1: PE 1335 ethylene/vinyl acetate copolymer with 3.3% vinyl acetate
 monomer, from Rexene.
 MBC=masterbatch of approximately 90% by weight of PP, approximately 4% by
 weight of ABB, and approximately 6% by weight of a blend of fatty acid
 amides. ("MB" means masterbatch.)
 For each of the examples and comparative examples, the film was coextruded.
 The film was made with silicone oil (i.e., polydimethylsiloxane) sprayed
 onto the inside surface of the tape, immediately after extrusion.
 Following extrusion and cooling, the film structure was oriented 5.times.
 in the machine direction, and 5.times. in the transverse direction, using
 a hot air trapped bubble method. The final oriented film had a thickness
 of about 0.6 mils.
 Comparative Example 1
 A film having the following structure and percent layer thicknesses was
 extruded:

72.5% PEC + 15% PB + 12.5% MB [94.6% PP + 2.0% FA1
 + 3.4% FA2]
 80% PEC + 15% PB + 5% MB [90% PP + 10% AB5]
 LLDPE
 80% PEC + 15% PB + 5% MB [90% PP + 10% AB5]
 72.5% PEC + 15% PB + 12.5% MBC
 Comparative Example 2
 A monolayer film having the following structure was extruded: 90% PEB1+10%
 MB [94% PEB2+4% kaolin clay+0.5% erucamide+0.5% behemamide+1% oleamide].
 Example 4
 A film having the same structure as that of Example 2, but with percent
 layer thicknesses of 5/15/60/15/5, was extruded.
 Example 5
 A film having the same structure as that of Example 3 was made, but which
 was extruded (see below) such that the layer having the formulation:
EQU 72.5% PEC+15%PB+12.5%MB[94.6%PP+2.0%FA1+3.4%FA2]
 formed the inside surface of the tubular film (on which a silicone was
 sprayed during extrusion). Contrast this with the film of Example 3, in
 which the layer having the formulation:
EQU 72.5%PEC+15%PB+12.5%MBC
 formed the inside surface of the tubular film (on which a silicone was
 sprayed during extrusion).
 Comparative Example 3
 A commercially available monolayer film, Vanguard F-100.TM. from Okura, is
 believed to be a monolayer polyolefinic film.
 Comparative Example 4
 A film like that of Comparative Example 1 was made.
 Comparative Example 5
 A film having the following A/B/C structure and percent layer thicknesses
 (25/50/25) was extruded:

50% PE1 + 25% PE2 + 25% MB [95% EV1 + 5% slip and antiblock
 agents]
 PE1
 50% PE1 + 25% PE2 + 25% MB [95% EV1 + 5% slip and antiblock
 agents]
 Example 8
 A film like that of Comparative Example 6 is made, but which includes in
 the core layer (i.e. the central layer of the film) an antiblocking agent.
 Example 9
 A film like that of Comparative Example 7 is made, but which includes in
 the core layer (i.e. the central layer of the film) an antiblocking agent.
 TABLE 1
 Build-up (in grams)
 Example Roll 1 Roll 2 Average
 Comp. 1 0.0349 0.0342 0.0346
 1 0.0034 0.0041 0.0038
 2 0.0002 0.0020 0.0011
 3 0.0044 0.0079 0.0062
 Comp. 2 0.0126 0.0038 0.0110
 4 0.0037 0.0037 0.0037
 5 0.0029 0.0025 0.0027
 Comp. 3 0.0014 0.0051 0.0033
 Comp. 4 0.0257 0.0431 0.0344
 Comp. 5 0.0198 0.0251 0.0225
 6 0.0017 0.0015 0.0016
 7 0.0006 0.0010 0.0008
 Comp. 6 0.0295 -- 0.0295
 Comp. 7 0.0465 -- 0.0465
 TEST METHODOLOGY
 In a series of in-house tests, a roll of film of each example was unwound,
 and the film passed over a steel bar. Film tension was maintained to keep
 the film in contact with the bar. The entire roll was used for each test,
 approximately 8000 ft for 60 gauge film. The buildup (i.e. aggregation of
 material on the steel bar) was collected and weighed in grams as reported
 in the Table above. Usually two rolls of each formulation were run to
 improve sampling average and to make the comparisons more meaningful. The
 ideal situation requires that control rolls be used each time film samples
 are evaluated to eliminate any bias which may result from changes in
 atmospheric conditions and/or test equipment setup parameters.
 Although the present invention has been described in connection with the
 preferred embodiments, it is to be understood that modifications and
 variations may be utilized without departing from the principles and scope
 of the invention.
 An fatty acid amide can optionally be present in any of the film layers of
 films of the present invention, and/or on an outside surface layer of the
 film. A polyorganosiloxane can optionally be present in any of the film
 layers of films of the present invention, and/or on an outside surface
 layer of the film. A mineral oil can optionally be present in any of the
 film layers of films of the present invention, and/or on an outside
 surface layer of the film. An antistatic agent can optionally be present
 in any of the film layers of films of the present invention, and/or on an
 outside surface layer of the film. An antifogging agent can optionally be
 present in any of the film layers of films of the present invention,
 and/or on an outside surface layer of the film.