WO2011149886A1

WO2011149886A1 - Heat-sealable polyolefin-based film comprising olefin block copolymer

Info

Publication number: WO2011149886A1
Application number: PCT/US2011/037669
Authority: WO
Inventors: Mark S. Heard; Rajen M. Patel
Original assignee: Dow Global Technologies LLC
Current assignee: Dow Global Technologies LLC
Priority date: 2010-05-28
Filing date: 2011-05-24
Publication date: 2011-12-01
Anticipated expiration: 2012-11-28
Also published as: WO2011149886A8

Abstract

Freezer-to-microwave bags or pouches are made from a heat-sealable film comprising: A) A sealant layer comprising a blend of a random copolymer polypropylene (RCPP) and an olefin block copolymer (OBC), the OBC having a density of 0.885 g/cc or less and a melt index (I2) of 5 or less; and B) A core layer comprising a blend of a propylene homopolymer (hPP) and an olefin block copolymer (OBC), the OBC having a density of 0.885 g/cc or less and a melt index (I2) of 5 or less. The bags and pouches exhibit very good low temperature toughness without sacrificing the heat resistance necessary for microwave heating.

Description

HEAT-SEALABLE POLYOLEFIN-BASED

FILM COMPRISING OLEFIN BLOCK COPOLYMER

FIELD OF THE INVENTION

[0001] This invention relates to polyolefin films. In one aspect the invention relates to heat-sealable polyolefin-based films while in another aspect, the invention relates to heat- sealable polyolefin-based films comprising an olefin block copolymer. In yet another aspect the invention relates to such films in freezer-to-microwave applications.

BACKGROUND OF THE INVENTION

[0002] Films for freezer-to-microwave applications require high heat resistance to stand up to temperatures generated in microwave ovens. Typically, random copolymer polypropylene (RCPP) sealant layers and homopolymer polypropylene (hPP) core layers are used to provide the required sealability and heat resistance. The problem with typical polypropylene (PP) resins (RCPP, hPP, impact copolymer (ICP) or other) is that they have poor low temperature impact resistance. As a result, frozen food pouches made from PP-rich (e.g., greater than 50 weight percent (wt%) PP) films exhibit brittle failure if dropped after storage in a freezer.

[0003] Heat sealable film for use in freezer-to-microwave applications with improved impact resistance is desired. The film should have adequate low temperature toughness, e.g., when formed into a pouch, filled and stored at -5 °C, the film should not exhibit brittle failure when the pouch is dropped. The film should also have adequate heat resistance to withstand microwaving, e.g., when formed into a pouch, the film should withstand the heat generated from microwaving and steam cooking frozen vegetables and foods containing protein and fat. In addition, the film should have sufficient bubble stability such that excessive wrinkles are not formed during film fabrication when collapsing the blown film bubble.

SUMMARY OF THE INVENTION

[0004] In one embodiment the invention is a heat-sealable film comprising

A. A sealant layer comprising a blend of a random copolymer polypropylene and an olefin block copolymer (OBC), the OBC having a density of 0.885 g/cc or less and a melt index (I₂) of 5 or less; and B. A core layer comprising a blend of a propylene homopolymer and an olefin block copolymer (OBC), the OBC having a density of 0.885 g/cc or less and a melt index (I₂) of 5 or less.

In one embodiment the OBC is present in both the sealant and core layers in an amount of 30 wt% or less. In one embodiment the invention is a bag or pouch made from the film. In one embodiment the invention is a freezer-to-microwave bag or pouch made from the film. The bags and pouches of this invention exhibit very good low temperature toughness without sacrificing the heat resistance necessary for microwave heating. The OBC also contributes to the melt strength of the RCPP and hPP resins for reduced or wrinkle-free film fabrication.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Definitions

[0005] Unless stated to the contrary, implicit from the context, or customary in the art, all parts and percents are based on weight and all test methods are current as of the filing date of this disclosure. For purposes of United States patent practice, the contents of any referenced patent, patent application or publication are incorporated by reference in their entirety (or its equivalent US version is so incorporated by reference) especially with respect to the disclosure of synthetic techniques, definitions (to the extent not inconsistent with any definitions specifically provided in this disclosure), and general knowledge in the art.

[0006] The numerical ranges in this disclosure are approximate, and thus may include values outside of the range unless otherwise indicated. Numerical ranges include all values from and including the lower and the upper values, in increments of one unit, provided that there is a separation of at least two units between any lower value and any higher value. As an example, if a compositional, physical or other property, such as, for example, molecular weight, viscosity, melt index, etc., is from 100 to 1 ,000, then all individual values, such as 100, 101, 102, etc., and sub ranges, such as 100 to 144, 155 to 170, 197 to 200, etc., are expressly enumerated. For ranges containing values which are less than one or containing fractional numbers greater than one (e.g., 1.1 , 1.5, etc.), one unit is considered to be 0.0001 , 0.001, 0.01 or 0.1 , as appropriate. For ranges containing single digit numbers less than ten (e.g., 1 to 5), one unit is typically considered to be 0.1. These are only examples of what is specifically intended, and all possible combinations of numerical values between the lowest value and the highest value enumerated, are to be considered to be expressly stated in this disclosure. Numerical ranges are provided within this disclosure for, among other things, the component amounts of the inventive blends and compositions and the various process parameters.

[0007] "Composition", "formulation" and like terms means a mixture or blend of two or more components. In the context of the inventive compositions of this invention, the mixture or blend of materials include a polyolefin and an olefin block copolymer.

[0008] "Blend," "polymer blend" and like terms mean a composition of two or more polymers. Such a blend may or may not be miscible. Such a blend may or may not be phase separated. Such a blend may or may not contain one or more domain configurations, as determined from transmission electron spectroscopy, light scattering, x-ray scattering, and any other method known in the art. Such blends include both mechanical blends made by admixing two or more of the components together in any mechanical manner, e.g., stirring, tumbling, folding, etc., and in-situ or in-reactor blends made by forming and/or mixing the blend components together during the polymerization process in which the polymer components are made.

[0009] Polymer" means a polymeric compound prepared by polymerizing monomers, whether of the same or a different type. The generic term polymer thus embraces the term homopolymer, usually employed to refer to polymers prepared from only one type of monomer, and the term interpolymer as defined below.

[0010] "Interpolymer" means a polymer prepared by the polymerization of at least two different types of monomers. This generic term includes copolymers, usually employed to refer to polymers prepared from two different types of monomers, and polymers prepared from more than two different types of monomers, e.g., terpolymers, tetrapolymers, etc.

[0011] "Olefin-based polymer", "polyolefin" and like terms mean a polymer containing, in polymerized form, a majority weight percent of an olefin, for example ethylene or propylene, based on the total weight of the polymer. Non-limiting examples of olefin-based polymers include ethylene-based polymers and propylene-based polymers.

[0012] "Homopolymer polypropylene (hPP)" and like terms includes not only polymers made exclusively from units derived from propylene, but also polymers made from units derived from propylene and a minor amount, e.g., typically less than 1 , more typically less than 0.75, wt% of units derived from another olefin monomer, most typically ethylene. These propylene polymers containing minor amounts of units derived from one or more other olefins are commonly known as mini-random propylene copolymers.

Random Copolymer Polypropylene

[0013] Random copolymer polypropylene (RCPP) is a polypropylene copolymer containing a small (e.g., 1-6 wt%) amount of ethylene or an alpha-olefin, typically ethylene. The RCPP used in the practice of this invention is distinct from both the hPP and other olefin polymers. It is distinct from hPP because it comprises 1 or more weight percent units derived from other olefin monomers, and it is distinct from other olefin polymers, e.g., narrow polydispersity plastomers and elastomers, because it has at least one of a melting point (as determined by differential scanning calorimetry (DSC)) of 120°C or more, or is made from a multi-site catalyst such as a Ziegler-Natta catalyst, or has a molecular weight distribution (MWD, aka polydispersity) of at least 3.5. For purposes of this invention, the RCPP typically has a melt index (I₂, 230°C/2.16 kg) typically less than 20, more typically less than 10 and even more typically less than 3, g/10 minutes as measured by ASTM D1238.

[0014] The presence of the comonomer in the copolymer changes the crystallinity, and thus the physical properties, of the polypropylene. In comparison with polypropylene homopolymer (hPP), RCPP exhibits improved optical properties, improved impact resistance, increased flexibility and a decreased melting point. RCPP is used in many applications, typically those that require improved clarity and/or impact resistance (as compared to hPP). For example, the properties of RCPP make it attractive for use in the manufacture of food containers for refrigerator and freezer use.

[0015] Propylene random copolymers are produced by the simultaneous polymerization of propylene and ethylene and/or an a-olefin in the same reactors used to produce homopolymer polypropylene. These copolymers are commercially available and include DOW Polypropylene 6D20, 6D43 and 6D83K all available from The Dow Chemical Company.

Polypropylene Homopolymer

[0016] The polypropylene homopolymer used in the practice of this invention typically has a melt index (I₂, 230°C/2.16 kg) typically less than 20, more typically less than 10 and even more typically less than 3, g/10 min as measured by ASTM D1238. These copolymers are commercially available and include DOW Polypropylene 5D49, 5D98, 5E16S and 5E89 all available from The Dow Chemical Company.

Olefin Block Interpolymer

[0017] "Olefin block interpolymer", "olefin block copolymer", "multi-block interpolymer", "segmented interpolymer", "OBC" and like terms refer to a polymer comprising two or more chemically distinct regions or segments (referred to as "blocks") preferably joined in a linear manner, that is, a polymer comprising chemically differentiated units which are joined end-to-end with respect to polymerized ethylenic functionality, rather than in pendent or grafted fashion. In a preferred embodiment, the blocks differ in the amount or type of incorporated comonomer, density, amount of crystallinity, crystallite size attributable to a polymer of such composition, type or degree of tacticity (isotactic or syndiotactic), regio-regularity or regio-irregularity, amount of branching (including long chain branching or hyper- branching), homogeneity or any other chemical or physical property. Compared to block interpolymers of the prior art, including interpolymers produced by sequential monomer addition, fluxional catalysts, or anionic polymerization techniques, the multi-block interpolymers used in the practice of this invention are characterized by unique distributions of both polymer polydispersity (PDI or Mw/Mn or MWD), block length distribution, and/or block number distribution, due, in a preferred embodiment, to the effect of the shuttling agent(s) in combination with multiple catalysts used in their preparation. More specifically, when produced in a continuous process, the polymers desirably possess PDI from 1.7 to 3.5, preferably from 1.8 to 3, more preferably from 1.8 to 2.5, and most preferably from 1.8 to 2.2. When produced in a batch or semi- batch process, the polymers desirably possess PDI from 1.0 to 3.5, preferably from 1.3 to 3, more preferably from 1.4 to 2.5, and most preferably from 1.4 to 2.

[0018] The term "ethylene multi-block interpolymer" means a multi-block interpolymer comprising ethylene and one or more interpolymerizable comonomers, in which ethylene comprises a plurality of the polymerized monomer units of at least one block or segment in the polymer, preferably at least 90, more preferably at least 95 and most preferably at least 98, mole percent of the block. Based on total polymer weight, the ethylene multi-block interpolymers used in the practice of the present invention preferably have an ethylene content from 25 to 97, more preferably from 40 to 96, even more preferably from 55 to 95 and most preferably from 65 to 85, percent.

[0019] Because the respective distinguishable segments or blocks formed from two of more monomers are joined into single polymer chains, the polymer cannot be completely fractionated using standard selective extraction techniques. For example, polymers containing regions that are relatively crystalline (high density segments) and regions that are relatively amorphous (lower density segments) cannot be selectively extracted or fractionated using differing solvents. In a preferred embodiment the quantity of extractable polymer using either a dialkyl ether or an alkane- solvent is less than 10, preferably less than 7, more preferably less than 5 and most preferably less than 2, percent of the total polymer weight.

[0020] In addition, the multi-block interpolymers used in the practice of the invention desirably possess a PDI fitting a Schutz-Flory distribution rather than a Poisson distribution. The use of the polymerization process described in WO 2005/090427 and USP 7,608,668 results in a product having both a polydisperse block distribution as well as a polydisperse distribution of block sizes. This results in the formation of polymer products having improved and distinguishable physical properties. The theoretical benefits of a polydisperse block distribution have been previously modeled and discussed in Potemkin, Physical Review E (1998) 57 (6), pp. 6902-6912, and Dobrynin, J. Chem.Phvs. (1997) 107 (21), pp 9234-9238.

[0021] In a further embodiment, the polymers of the invention, especially those made in a continuous, solution polymerization reactor, possess a most probable distribution of block, lengths. In one embodiment of this invention, the ethylene multi-block interpolymers are defined as having:

(a) Mw/Mn from about 1.7 to about 3.5, at least one melting point, Tm, in degrees Celsius, and a density, d, in grams/cubic centimeter, where in the numerical values of Tm and d correspond to the relationship

Tm > -2002.9 + 4538.5(d) - 2422.2(d)², or

(b) Mw/Mn from about 1.7 to about 3.5, and is characterized by a heat of fusion, ΔΗ in J/g, and a delta quantity, ΔΤ, in degrees Celsius defined as the temperature difference between the tallest DSC peak and the tallest CRYSTAF peak, wherein the numerical values of ΔΤ and ΔΗ have the following relationships: ΔΤ > -0.1299 (ΔΗ) + 62.81 for ΔΗ greater than zero and up to 130 J/g

ΔΤ > 48C for ΔΗ greater than 130 J/g

wherein the CRYSTAF peak is determined using at least 5 percent of the cumulative polymer, and if less than 5 percent of the polymer has an identifiable CRYSTAF peak, then the CRYSTAF temperature is 30C; or

(c) Elastic recovery, Re, in percent at 300 percent strain and 1 cycle measured with a compression-molded film of the ethylene/a-olefin interpolymer, and has a density, d, in grams/cubic centimeter, wherein the numerical values of Re and d satisfy the following relationship when ethylene/cc-olefin interpolymer is substantially free of crosslinked phase:

Re > 1481 - 1629(d); or

(d) Has a molecular weight fraction which elutes between 40C and 130C when fractionated using TREF, characterized in that the fraction has a molar comonomer content of at least 5 percent higher than that of a comparable random ethylene interpolymer fraction eluting between the same temperatures, wherein said comparable random ethylene interpolymer has the same comonomer(s) and has a melt index, density and molar comonomer content (based on the whole polymer) within 10 percent of that of the efhylene/oc-olefin interpolymer; or

(e) Has a storage modulus at 25 °C, G'(25C), and a storage modulus at 100 °C, G'(100 °C), wherein the ratio of G'(25 °C) to G'(100 °C) is in the range of 1 : 1 to 9: 1.

[0022] The ethylene/oc-olefin interpolymer may also have:

(a) Molecular fraction which elutes between 40 °C and 130 °C when fractionated using TREF, characterized in that the fraction has a block index of at least 0.5 and up to 1 and a molecular weight distribution, Mw/Mn, greater than 1.3; or

(b) Average block index greater than zero and up to 1.0 and a molecular weight distribution, Mw/Mn greater than 1.3.

[0023] Suitable monomers for use in preparing the ethylene multi-block interpolymers used in the practice of this present invention include ethylene and one or more addition polymerizable monomers other than ethylene. Examples of suitable comonomers include straight-chain or branched a-olefins of 3 to 30, preferably 3 to 20, carbon atoms, such as propylene, 1-butene, 1-pentene, 3-methyl-l-butene, 1-hexene, 4-methyl-l-pentene, 3-methyl- 1-pentene, 1-octene, 1-decene, 1-dodecene, 1 -tetradecene, 1 -hexadecene, 1- octadecene and 1-eicosene; cyclo-olefins of 3 to 30, preferably 3 to 20, carbon atoms, such as cyclopentene, cycloheptene, norbornene, 5-methyl-2-norbornene, tetracyclododecene, and 2-methyl- l,4,5,8-dimethano-l ,2,3,4,4a,5,8,8a-octahydronaphthalene; di-and polyolefins, such as butadiene, isoprene, 4-methyl-l ,3-pentadiene, 1,3-pentadiene, 1,4-pentadiene, 1 ,5-hexadiene, 1 ,4-hexadiene, 1 ,3-hexadiene, 1 ,3-octadiene, 1 ,4-octadiene, 1 ,5-octadiene, 1 ,6-octadiene, 1 ,7-octadiene, ethylidenenorbornene, vinyl norbornene, dicyclopentadiene, 7-methyl-l ,6- octadiene, 4-ethylidene-8-methyl-l ,7-nonadiene, and 5,9-dimethyl-l ,4,8-decatriene; and 3-phenylpropene, 4-phenylpropene, 1 ,2-difluoroethylene, tetrafluoroethylene, and 3,3,3- trifluoro- 1 -propene.

[0024] Other ethylene multi-block interpolymers that can be used in the practice of this invention are elastomeric interpolymers of ethylene, a C3_-20 a-olefin, especially propylene, and, optionally, one or more diene monomers. Preferred a-olefins for use in this embodiment of the present invention are designated by the formula CH₂=CHR*, where R* is a linear or branched alkyl group of froml to 12 carbon atoms. Examples of suitable oc-olefins include, but are not limited to, propylene, isobutylene, 1 - butene, 1 -pentene, 1 -hexene, 4- methyl- 1-pentene, and 1-octene. One particularly preferred a-olefin is propylene. The propylene based polymers are generally referred to in the art as EP or EPDM polymers. Suitable dienes for use in preparing such polymers, especially multi-block EPDM type- polymers include conjugated or non-conjugated, straight or branched chain-, cyclic- or polycyclic dienes containing from 4 to 20 carbon atoms. Preferred dienes include 1 ,4-pentadiene, 1 ,4-hexadiene, 5-ethylidene-2-norbornene, dicyclopentadiene, cyclohexadiene, and 5-butylidene-2-norbornene. One particularly preferred diene is 5-ethylidene-2-norbornene.

[0025] Because the diene containing polymers contain alternating segments or blocks containing greater or lesser quantities of the diene (including none) and a-olefin (including none), the total quantity of diene and a-olefin may be reduced without loss of subsequent polymer properties. That is, because the diene and a-olefin monomers are preferentially incorporated into one type of block of the polymer rather than uniformly or randomly throughout the polymer, they are more efficiently utilized and subsequently the crosslink density of the polymer can be better controlled. Such crosslinkable elastomers and the cured products have advantaged properties, including higher tensile strength and better elastic recovery.

[0026] The ethylene multi-block interpolymers useful in the practice of this invention have a density of less than 0.885, preferably less than 0.88 and more preferably less than 0.875, g/cm³. The ethylene multi-block interpolymers typically have a density greater than 0.85, and more preferably greater than 0.855, g/cm³. Density is measured by the procedure of ASTM D792. Low density ethylene multi -block interpolymers are generally characterized as amorphous, flexible and having good optical properties, e.g., high transmission of visible and UV-light and low haze.

[0027] The ethylene multi-block interpolymers useful in the practice of this invention have a melt index (I₂) of less than 10, preferably less than 5 and more preferably less than 1 , g/10 min. Melt index is measured by the procedure of ASTM D1238 (190 °C, 2.16 kg).

[0028] The ethylene multi-block interpolymers useful in the practice of this invention have a 2% secant modulus of less than about 150, preferably less than about 140, more preferably less than about 120 and even more preferably less than about 100, mPa as measured by the procedure of ASTM D-882-02. The ethylene multi-block interpolymers typically have a 2% secant modulus of greater than zero, but the lower the modulus, the better the interpolymer is adapted for use in this invention. The secant modulus is the slope of a line from the origin of a stress-strain diagram and intersecting the curve at a point of interest, and it is used to describe the stiffness of a material in the inelastic region of the diagram. Low modulus ethylene multi-block interpolymers are particularly well adapted for use in this invention because they provide stability under stress, e.g., less prone to crack upon stress or shrinkage.

[0029] The ethylene multi-block interpolymers useful in the practice of this invention typically have a melting point of less than about 125. The melting point is measured by the differential scanning calorimetry (DSC) method described in WO 2005/090427 (US2006/0199930). Ethylene multi-block interpolymers with a low melting point often exhibit desirable flexibility and thermoplasticity properties useful in the fabrication of the modules of this invention. [0030] The ethylene multi-block interpolymers used in the practice of this invention, and their preparation and use, are more fully described in USP 7,579,408, 7,355,089, 7,524,91 1 , 7,514,517, 7,582,716 and 7,504,347.

Film

[0031] The films of this invention comprise a sealant layer and a core layer. Typically, the film comprises a core layer sandwiched between two sealant layers, and typically at least one sealant layer comprises an external layer, i.e., a layer with one facial surface open to the environment, of the film. The film can comprise additional layers, e.g., one or more gas barrier layers, and if present, these additional layers are typically located between the sealant and core layers. The thickness of the film and the thickness of the individual layers of the film can vary as desired. Typically, the total thickness of the film, i.e., all layers combined, is less than 10, more typically less than 5 and even more typically less than 3, mils.

[0032] The sealant layer, or at least one of the sealant layers if the film comprises two or more sealant layers, comprises a blend of RCPP and OCB. Typically, the amount of OCB present in the sealant layer does not exceed 40, preferably it does not exceed 35 and more preferably it does not exceed 30, wt%. The minimum amount of OCB in the sealant layer is typically at least 5, more typically at least 10 and even more typically at least 15, wt%.

[0033] The core layer, or at least one of the core layers if the film comprises two or more core layers, comprises a blend of hPP and OCB. Typically, the amount of OCB present in the core layer does not exceed 40, preferably it does not exceed 35 and more preferably it does not exceed 30, wt%. The minimum amount of OCB in the core layer is typically at least 5, more typically at least 10 and even more typically at least 15, wt%.

[0034] Each layer of the film can comprise one or more additional polymers to provide additional improvements in properties to the layer and/or film including, but not limited to, processability, modulus, compressive strength, hardness, toughness and aesthetics of the final fabricated article. Examples of the "additional polymers" include, but are not limited to, polypropylene plastomers and/or elastomers with a melting point (as determined by DSC) of less than 120°C, or made from a single-site catalyst such as a metallocene or constrained geometry catalyst, or has a molecular weight distribution (MWD) of less than 3.5; high density polyethylene (HDPE); medium density polyethylene (MDPE); low density polyethylene (LDPE) and linear low density polyethylene (LLDPE). If an additional polymer is present, typically it is present in an amount of less than 40, more typically less than 35 and even more typically less than 30, wt% based on the total weight of the blend from which the layer is made.

[0035] Various additives and fillers may be incorporated into the blends from which the layers are made. These materials include, without limitation, stability control agents, nucleating agents, inorganic fillers, conductive fillers, pigments, colorants, antioxidants, acid scavengers, ultraviolet absorbers or stabilizers, flame retardants, processing aids, extrusion aids, anti-static agents, cling additives (for example, polyisobutylene), and anti-block additives. Examples of antioxidants are hindered phenols (such as, for example, IRGANOX™. 1010) and phosphites (for example, IRGAFOS™. 168) both trademarks of, and commercially available from, Ciba Geigy Corporation.

[0036] The additives and fillers are advantageously employed in functionally equivalent amounts known to those skilled in the art. For example, the amount of antioxidant employed is that amount which prevents the polymer components from undergoing oxidation at the temperatures and environment employed during storage and ultimate use of the articles made from the blends. Such amount of antioxidants is usually in the range of from 0.01 to 10, preferably from 0.02 to 5, more preferably from 0.03 to 2, wt% based upon the weight of the polymer blend. Similarly, the amounts of any of the other enumerated additives are the functionally equivalent amounts. For fillers, the amounts used can be and often are far in excess of the amounts used for such additives as antioxidants, UV stabilizers or absorbers, etc. The amount of filler used, if any, can range from less than 1 weight percent to 50 or more weight percent. The actual amount of filler employed will depend upon, among other things, the other components of the film, the film construction, the end use of the film, the cost of the filler, and the like.

[0037] The manner in which the film is fabricated is not important to this invention. Any fabrication technique can be used including co-extrusion, extrusion/lamination, casting/lamination and the like. In one embodiment, the film consists of two external sealant layers and a single core layer, each layer is made using a blown film process, and then the individual layers are laminated to one another with or without the use of an adhesive.

[0038] In one embodiment the film is fabricated into a bag or pouch for frozen food packaging. The bags are formed from the films using any convenient method, and filled with food also using any convenient method. The packaged food is then stored under freezing conditions. At the time the food is ready for preparation for consumption, the bag can be moved directly from a freezer to a microwave for heating without an intermediate thawing.

[0039] Although the invention has been described with certain detail through the preceding embodiments, this detail is for the primary purpose of illustration. Many variations and modifications can be made by one skilled in the art without departing from the spirit and scope of the invention as described in the following claims.

Claims

What is claimed is:

1. A heat-sealable film comprising:

A. A sealant layer comprising a blend of a random copolymer polypropylene (RCPP) and an olefin block copolymer (OBC), the OBC having a density of 0.885 g/cc or less and a melt index (I₂) of 5 or less; and

B. A core layer comprising a blend of a propylene homopolymer (hPP) and an olefin block copolymer (OBC), the OBC having a density of 0.885 g/cc or less and a melt index (I₂) of 5 or less.

2. The film of Claim 1 comprising the core layer sandwiched between two sealant layers.

3. The film of Claim 1 in which the amount of OBC in each of the layers is less than 30 weight percent.

4. The film of Claim 1 in which the RCPP and hPP each has an MFR of less than lO g/lO min.

5. The film of Claim 1 in which the OBC is an ethyl ene/a-olefin multi-block copolymer.

6. The film of Claim 5 in which the OBC has (a) a molecular fraction that elutes between about 40°C and about 130°C when fractionated using temperature rising effluent fractionation (TREF), characterized in that the fraction has a block index of at least 0.5 and up to 1 and a molecular weight distribution (PDI, Mw/Mn, MWD) greater than 1.3, or (b) an average block index greater than zero and up to 1.0 and an MWD greater than 1.3.

7. The film of Claim 5 in which the OBC has at least one of the following properties: (i) a molecular weight distribution of greater than 1.3, (ii) a density of less than 0.90 g/cc, (iii) a 2% secant modulus of less than 150 MegaPascal (MPa) as measured by ASTM D-882-02, (iv) a melt point of less than 125°C, (v) an a-olefin content of at least 10 and less than 80 wt% based on the weight of the interpolymer, (vi) a Tg of less than -35°C, and (vii) a melt index (MI) of less than 100 grams per 10 minutes (g/10 min).

8. The film of Claim 1 with a total thickness of less than 10 mils.

9. A pouch made from the film of Claim 1.

10. The pouch of Claim 9 containing frozen food.