Heat-resistant heat-sealing film

Abstract

A multilayer film is disclosed. The multilayer film may include a core layer and a heat seal layer, wherein the heat seal layer includes a polypropylene copolymer and a polyethylene copolymer. The polypropylene copolymer of the heat seal layer has specific properties, such as ethylene content and iCCD elution curve, to facilitate the desired properties of the film. The multilayer film can form an effective heat seal even when in contact with heated contents. The multilayer film may be formed as a pouch, where the pouch is adapted to carry hot or heated contents.

Description

TECHNICAL FIELD

[0001] The embodiments described herein relate generally to multilayer films, and more specifically, to multilayer films suitable for use in heat-sealed packaging. BACKGROUND

[0002] Heat-sealable bags made from multilayer films are a common form of packaging. The multilayer film can include a core polymer layer that provides the desired strength and other film properties, and includes a heat-seal layer. The multilayer film can also include other layers, such as a barrier layer, a tie layer, a print layer, or a metal foil layer. The multilayer film can be folded and sealed to form a bag that is open at one end and closed on the other sides and other ends. Contents can be added to the bag through the open end, at which time the open end is pinched, causing the heat-seal layers on the two sides of the pinch to contact each other and heat to seal the open end.

[0003] Many factors can affect the strength of a heat seal, including the length and width of the seal, the temperature and pressure used to form the seal, the time the temperature and pressure are maintained, and the contents of the heat-seal layer. Package converters often desire to run packaging lines quickly, and therefore often select heat-seal layers that allow a strong seal to be formed using only a short cycle of pressure, heating, and cooling.

[0004] Many heat-sealable bags contain hot contents, such as hot food or even hot bitumen. The heated contents prevent the heat seal from cooling after it is formed, and can significantly reduce the strength of the seal.

[0005] Accordingly, there is a need for multilayer films that include polymer combinations that can be used in heat-seal layers and that can form strong heat seals even when in contact with heated contents. SUMMARY

[0006] A first aspect of the present invention is a multilayer film. The multilayer film according to the embodiments disclosed herein comprises at least: (A) a core layer comprising a polyolefin polymer and (B) a heat-seal layer, wherein the heat-seal layer comprises: a. 30 wt% to 80 wt% of a polypropylene copolymer having: i) a total ethylene content (Et) of 5 wt% to 30 wt%, based on the total weight of the polypropylene copolymer; and ii) a density of 0.80 g / cc to 0.95 g / cc; and iii) a melt index of no more than 5 dg / min at 230 °C; and iv) an iCCD profile, wherein at least 10 wt% of the polypropylene copolymer elutes from 25 °C to 35 °C and no more than 30 wt% of the polypropylene copolymer elutes between 35 °C and 100 °C in an iCCD elution test from 25 °C to 150 °C; and b. 20 wt% to 70 wt% of a polyethylene copolymer having a density of 0.895 g / cc to 0.925 g / cc and a melt index of less than 3 dg / min at 190 °C.

[0007] Also disclosed is a bag comprising the multilayer film according to the embodiments.

[0008] Also disclosed is a method of packaging a heated material. The method according to the embodiments disclosed herein comprises the steps of a. placing a material having a temperature of at least 90°C in an open ended bag from the second aspect of the invention, and b. heat sealing the open end of the bag to completely close the bag.

[0009] The multilayer film of the invention can form strong heat seals even when in contact with heated contents of up to 140°C or higher. BRIEF DESCRIPTION OF DRAWINGS

[0010] Figure 1 Results of iCCD analysis performed on the three polypropylene resins used in the working examples are shown. DETAILED DESCRIPTION

[0011] The present invention relates to a multilayer film comprising at least a core layer and a heat seal layer. In some embodiments, the multilayer film comprises at least 3 layers or at least 4 layers or at least 5 layers. In some embodiments, the multilayer film comprises at most 20 layers or at most 15 layers or at most 10 layers or at most 9 layers or at most 8 layers or at most 7 layers. The multilayer film can comprise at least a core layer having a polyolefin polymer and a heat seal layer, wherein the heat seal layer comprises a polypropylene copolymer and a polyethylene copolymer.

[0012] One of the layers in the multilayer film is a core layer comprising a polyolefin polymer. The polyolefin polymer includes polyethylene or polypropylene or a blend of polyethylene and polypropylene.

[0013] As used herein, “polyethylene” or “ethylene-based polymer” means a polymer comprising greater than 50 mole percent of units derived from ethylene monomer. This includes homopolymers or copolymers (meaning units derived from two or more comonomers) based on ethylene. Common forms of ethylene-based polymers known in the art include, but are not limited to: low density polyethylene (LDPE); linear low density polyethylene (LLDPE); ultra low density polyethylene (ULDPE); very low density polyethylene (VLDPE); single-site catalyzed linear low density polyethylene, including both linear and substantially linear low density resins (m-LLDPE); medium density polyethylene (MDPE); and high density polyethylene (HDPE).

[0014] Polyethylene grades commonly used in multilayer films include:

[0015] • high density polyethylene (HDPE) having a density of 0.94 g / cc to 0.98 g / cc;

[0016] • linear low density polyethylene (LLDPE) having a density of 0.915 g / cc to 0.94 g / cc;

[0017] • low density polyethylene (LDPE) having a density of 0.90 g / cm3to 0.93 g / cm3; and / or

[0018] • very low density polyethylene (VLDPE) having a density of 0.88 g / cc to 0.915 g / cc.

[0019] Polypropylene grades commonly used in multilayer films include:

[0020] • polypropylene homopolymer;

[0021] • polypropylene random copolymer; and

[0022] • polypropylene block copolymer.

[0023] Certain polypropylene copolymers, referred to as "impact copolymers," can have a rubber content that imparts higher impact resistance. In some embodiments, the impact copolymers include block copolymers of propylene and ethylene containing blocks with low ethylene content and blocks with high ethylene content. In some embodiments, the impact copolymers include polypropylene random copolymers and / or polypropylene polymer blends.

[0024] In some embodiments, "polyethylene" is a copolymer comprising repeat units derived from ethylene and repeat units derived from other 1-alkenes, such as 1-butene, 1-hexene, and / or 1-octene. (By "majority" is meant more than 50% by weight, unless otherwise indicated.) Likewise, polypropylene (PP) random and block copolymers can comprise repeat units derived from propylene and repeat units derived from ethylene. Altering the selection and ratio of monomers, catalysts, and reaction conditions used to make the polyolefins can yield a wide range of different polyolefin grades with different properties, such as density, melt viscosity, and physical strength.

[0025] In some embodiments, the core layer can include a polymer to achieve desired physical properties of the film, such as tensile strength and modulus, dart impact strength, tear strength, temperature resistance, and melt strength. In some embodiments, the core layer includes HDPE. In some embodiments, the core layer includes LLDPE. In some embodiments, the core layer includes a polyethylene having a density of 0.895 g / cc to 0.930 g / cc and a melt index of less than 3 dg / min at 190°C. In some embodiments, the core layer includes VLDPE. In some embodiments, the core layer includes a polyethylene having a density of at least 0.890 g / cc or at least 0.895 g / cc or at least 0.900 g / cc or at least 0.905 g / cc or at least 0.907 g / cc or at least 0.910 g / cc. In some embodiments, the core layer includes a polyethylene having a density of at most 0.930 g / cc or at most 0.925 g / cc or at most 0.922 g / cc or at most 0.920 g / cc.

[0026] In some embodiments, the core layer includes a polyethylene having a melt index (I2) of no more than 5 dg / min or no more than 4 dg / min or no more than 3 dg / min or no more than 2 dg / min or no more than 1 dg / min or no more than 0.8 dg / min or no more than 0.6 dg / min or no more than 0.4 dg / min at 190°C. In some embodiments, the core layer includes a polyethylene having a melt index (I2) of at least 0.01 dg / min or at least 0.05 dg / min or at least 0.1 dg / min at 190°C.

[0027] In some embodiments, the core layer includes a polypropylene homopolymer. In some embodiments, the core layer includes a polypropylene random copolymer. In some embodiments, the core layer includes a polypropylene block copolymer. In some embodiments, the polypropylene in the core layer has a density of at least 0.890 g / cc or at least 0.895 g / cc or at least 0.900 g / cc. In some embodiments, the polypropylene in the core layer has a density of at most 0.92 g / cc or at most 0.91 g / cc or at most 0.905 g / cc. In some embodiments, the polypropylene in the core layer has a melt index (I2) of at most 6 dg / min or at most 4 dg / min or at most 3 dg / min at 230°C. In some embodiments, the polypropylene in the core layer has a melt index (I2) of at least 0.5 dg / min or at least 1 dg / min or at least 2 dg / min at 230°C.

[0028] In some embodiments, the core layer comprises a blend of two or more polyolefin polymers, such as at least 2 polyethylene polymers or at least 2 polypropylene polymers or at least one polyethylene blended with at least one polypropylene (PP) polymer. Examples of common polymer blends include blends of polyolefins, such as blending high density polyethylene (HDPE) or linear low density polyethylene (LLDPE) with low density polyethylene (LDPE) or with polyethylene elastomers. Some polypropylenes are not compatible with polyethylene and can require a compatibilizer. On the other hand, some polypropylenes effectively blend with polyethylene and do not require a compatibilizer. For example, polypropylene block copolymers comprising polyethylene blocks are more likely to effectively blend with polyethylene, especially lower density polyethylene with relatively high levels of comonomer.

[0029] In some embodiments, the core layer comprises a blend of polyethylene with a polypropylene copolymer having the same properties as the polypropylene copolymer used in the heat seal layer.

[0030] In some embodiments, the core layer comprises at least 10 wt% or at least 15 wt% or at least 20 wt% or at least 25 wt% or at least 30 wt% or at least 35 wt% or at least 40 wt% or at least 42 wt% or at least 45 wt% of the polypropylene copolymer. In some embodiments, the core layer comprises at most 65 wt% or at most 60 wt% or at most 55 wt% or at most 50 wt% or at most 48 wt% or at most 45 wt% of the polypropylene copolymer, based on the total weight of the core layer. In some embodiments, the core layer comprises at least 35 wt% or at least 40 wt% or at least 45 wt% or at least 50 wt% or at least 52 wt% or at least 55 wt% of the polyethylene. In some embodiments, the core layer comprises 100 wt% or at most 90 wt% or at most 85 wt% or at most 80 wt% or at most 75 wt% or at most 70 wt% or at most 65 wt% or at most 60 wt% or at most 55 wt% of the polyethylene, based on the total weight of the core layer.

[0031] The multilayer film has two outer surfaces opposite each other, and the polymer layer on each side of the film is referred to as a face layer. In the film of the present invention, one face layer is the heat seal layer. In a two-layer film, the other face layer is the core layer. In a three or more layer film, the other face layer can be the core layer or another polymer layer.

[0032] The heat seal layer can comprise a. from 30 wt% to 80 wt% of a polypropylene copolymer, based on the total weight of the heat seal layer, that: i. comprises from 5 wt% to 30 wt% of repeat units derived from ethylene; and i. has a density from 0.80 g / cc to 0.95 g / cc; and ii. has a melt index of no more than 5 dg / min at 230°C; and iii. elutes at least 10 wt% of the PP copolymer from 25°C to 35°C and no more than 30 wt% of the PP copolymer elutes between 35°C and 100°C in an iCCD elution test from 25°C to 150°C; and b. from 20 wt% to 70 wt% of a polyethylene copolymer having a density from 0.895 g / cc to 0.925 g / cc and a melt index of less than 3 dg / min at 190°C. The iCCD elution test is conducted by the test method described below.

[0033] In some embodiments, the polypropylene copolymer has a density of at least 0.85 g / cc or at least 0.88 g / cc or at least 0.89 g / cc or at least 0.895 g / cc or at least 0.90 g / cc. In some embodiments, the polypropylene copolymer has a density of at most 0.92 g / cc or at most 0.91 g / cc or at most 0.905 g / cc.

[0034] In some embodiments, the polypropylene copolymer in the heat seal layer has a melt index (I2) of at most 4 dg / min or at most 3 dg / min at 230°C. In some embodiments, the polypropylene copolymer has a melt index (I2) of at least 0.5 dg / min or at least 1 dg / min or at least 2 dg / min at 230°C.

[0035] The polypropylene copolymer can be characterized based on the total ethylene content (Et), which is the average weight percent of repeat units derived from ethylene, based on the total weight of the polypropylene copolymer. In some embodiments, the polypropylene copolymer has a total ethylene content (Et) of at least 8 wt% or at least 10 wt% or at least 12 wt%. In some embodiments, the polypropylene copolymer has a total ethylene content (Et) of at most 28 wt% or at most 25 wt% or at most 20 wt%. In some embodiments, the polypropylene copolymer comprises at most 92 wt% or at most 90 wt% or at most 88 wt% of repeat units derived from propylene. In some embodiments, the polypropylene copolymer comprises at least 72 wt% or at least 75 wt% or at least 80 wt% of repeat units derived from propylene. In some embodiments, the polypropylene copolymer comprises at most 10 wt% or at most 5 wt% or at most 2 wt% or at most 1 wt% or 0 wt% of repeat units derived from monomers other than propylene and ethylene, based on the total weight of the polypropylene copolymer.

[0036] In some embodiments, the polypropylene copolymer in the heat seal layer is a random copolymer. In some embodiments, the polypropylene copolymer in the heat seal layer is an impact copolymer that includes a component of crystalline polypropylene homopolymer or polypropylene copolymer, referred to as the crystalline phase, and a component of amorphous ethylene-propylene random copolymer, referred to as the rubber phase. The crystalline phase can have a low ethylene content, while the rubber phase has a higher ethylene content than the crystalline phase. In some embodiments, the impact polypropylene copolymer is a block copolymer in which segments of the crystalline phase polymer and segments of the rubber phase polymer are bound to one another.

[0037] PCT Patent Application WO 2017 / 040127 Al by Cong et al. (March 9, 2017) describes an improved method of measuring the comonomer content and distribution of polyolefins (iCCD) adapted from temperature rising elution fractionation (TREF). The test method describes the specific implementation of the iCCD analysis. In the iCCD analysis, the polymer can be fractionated into a low temperature (from 25°C to 35°C) eluting fraction, a medium temperature (from more than 35°C to 105°C) eluting fraction, and a high temperature (more than 105°C) eluting fraction.

[0038] In the iCCD analysis as described in the test method, the polypropylene copolymer for the heat seal layer has at least 10 wt% of the polymer recovered in the low temperature fraction. In some embodiments, the low temperature fraction is at least 12 wt% or at least 14 wt% or at least 15 wt%. In some embodiments, the low temperature fraction is at most 30 wt% or at most 25 wt% or at most 20 wt% or at most 18 wt% or at most 16 wt%.

[0039] In the iCCD analysis as described in the test method, the polypropylene copolymer for the heat seal layer has at most 30 wt% of the polymer recovered in the medium temperature fraction. In some embodiments, the medium temperature fraction is at most 25 wt% or at most 20 wt% or at most 18 wt% or at most 16 wt% or at most 15 wt%. In some embodiments, the medium temperature fraction is at least 5 wt% or at least 8 wt% or at least 10 wt% or at least 12 wt% or at least 14 wt%.

[0040] In some embodiments, the polypropylene copolymer in the heat seal layer has a tensile yield strength of at least 18 MPa or at least 20 MPa or at least 22 MPa or at least 24 MPa. In some embodiments, the polypropylene copolymer has a tensile yield strength of at most 40 MPa or at most 30 MPa or at most 28 MPa or at most 26 MPa.

[0041] Suitable polypropylene copolymers for the heat seal layer are commercially available, as previously described. Other materials can be prepared by known methods.

[0042] In some embodiments, the polyethylene copolymer in the heat seal layer can have a density of 0.895 g / cc to 0.925 g / cc. In some embodiments, the polyethylene copolymer has a density of at least 0.900 g / cc or at least 0.905 g / cc or at least 0.907 g / cc or at least 0.910 g / cc. In some embodiments, the polyethylene copolymer has a density of at most 0.922 g / cc or at most 0.920 g / cc or at most 0.915 g / cc or at most 0.912 g / cc or at most 0.910 g / cc.

[0043] The polyethylene copolymer in the heat seal layer can have a melt index (I2) of less than 3 dg / min at 190 °C. In some embodiments, the polyethylene copolymer has a melt index (I2) of at most 2 dg / min or at most 1.5 dg / min or at most 1 dg / min or at most 0.9 dg / min at 190 °C. In some embodiments, the polyethylene copolymer has a melt index (I2) of at least 0.1 dg / min or at least 0.3 dg / min or at least 0.5 dg / min or at least 0.7 dg / min or at least 0.8 dg / min at 190 °C.

[0044] In some embodiments, the polyethylene copolymer in the heat seal layer can have a melt temperature of at least 85 °C or at least 90 °C or at least 95 °C or at least 100 °C or at least 102 °C or at least 104 °C or at least 106 °C. In some embodiments, the polyethylene copolymer in the heat seal layer can have a melt temperature of at most 125 °C or at most 120 °C or at most 115 °C or at most 110 °C or at most 108 °C or at most 106 °C.

[0045] In some embodiments, the comonomer in the polyethylene copolymer in the heat seal layer comprises 4 to 10 carbon atoms. In some embodiments, the comonomer includes butene. In some embodiments, the comonomer comprises or consists essentially of hexene. In some embodiments, the comonomer comprises or consists essentially of octene. (“Consists essentially of’ means that the concentration of any other monomer is low enough that the other monomer does not materially change the properties of the resulting polymer.)

[0046] In some embodiments, the polyethylene copolymer in the heat seal layer comprises at least 2 wt% or at least 5 wt% or at least 10 wt% repeat units derived from the comonomer. In some embodiments, the polyethylene copolymer in the heat seal layer comprises at most 35 wt% or at most 30 wt% or at most 25 wt% repeat units derived from the comonomer. The units not derived from the comonomer are derived from ethylene.

[0047] In some embodiments, the polyethylene copolymer in the heat seal layer comprises a blend of 2 or more polyethylene copolymers that individually and / or collectively satisfy the limitations and / or embodiments previously described.

[0048] Suitable polyethylene copolymers for the heat seal layer are commercially available. Other materials can be prepared by known methods.

[0049] The heat seal layer can comprise 30 wt% to 80 wt% of the polypropylene copolymer. In some embodiments, the heat seal layer comprises at least 33 wt% or at least 36 wt% or at least 39 wt% or at least 40 wt% of the polypropylene copolymer. In some embodiments, the heat seal layer comprises at most 75 wt% or at most 70 wt% or at most 60 wt% or at most 50 wt% or at most 45 wt% or at most 40 wt% of the polypropylene copolymer.

[0050] The heat seal layer can comprise 20 wt% to 70 wt% of the polyethylene copolymer. In some embodiments, the heat seal layer comprises at least 25 wt% or at least 30 wt% or at least 40 wt% or at least 50 wt% or at least 55 wt% or at least 60 wt% of the polyethylene copolymer. In some embodiments, the heat seal layer comprises at most 67 wt% or at most 64 wt% or at most 61 wt% or at most 60 wt% of the polyethylene copolymer.

[0051] In some embodiments, the heat seal layer comprises at most 30 wt% of other polymers in addition to the polypropylene copolymer and the polyethylene copolymer, or at most 20 wt% or at most 10 wt% or at most 5 wt% or at most 2 wt% or 0 wt% of other polymers. Examples of other polymers used in the heat seal layer can include ethylene-vinyl acetate copolymers.

[0052] In some embodiments, the polypropylene and polyethylene copolymers in the heat seal layer are compatible with each other, meaning that they form a uniform blend without a compatibilizer. In some embodiments, the heat seal layer further comprises a compatibilizer, as previously discussed. Examples of suitable compatibilizers can be available under the INTUNE ™ The trademarks are commercially available.

[0053] In some embodiments, the heat seal layer is at least 5 microns thick or at least 10 microns or at least 15 microns thick or at least 20 microns thick, at least 50 microns thick, at least 100 microns thick, at least 150 microns thick, at least 200 microns thick. In some embodiments, the heat seal layer is at most 300 microns thick or 250 microns thick or 200 microns thick or at most 150 microns or at most 120 microns thick or at most 100 microns thick or at most 80 microns thick. For example, in some embodiments, the heat seal layer is 15 to 100 microns thick or 20 to 80 microns thick. In some embodiments, the heat seal layer is 80 to 300 microns thick or 100 to 200 microns thick.

[0054] The thickness of the core layer can vary. In some embodiments, the core layer is at least 50 microns thick or at least 60 microns thick or at least 70 microns thick. In some embodiments, the core layer is at most 300 microns thick or at most 250 microns thick or at most 200 microns thick or at most 150 microns thick.

[0055] In some embodiments, the core layer is thicker than the heat seal layer. In some embodiments, the thickness of the core layer is at least 100% or at least 110% or at least 125% or at least 150% or at least 175% or at least 190% of the thickness of the heat seal layer. In some embodiments, the thickness of the core layer is at most 1000% or at most 800% or at most 500% or at most 400% or at most 300% of the thickness of the heat seal layer.

[0056] In some embodiments, the multi-layer film contains only a core layer and a heat seal layer. In some embodiments, the multi-layer film contains at least 3 layers or at least 4 layers or at least 5 layers. In some embodiments, the multi-layer film contains at most 20 layers or at most 15 layers or at most 10 layers or at most 9 layers or at most 8 layers or at most 7 layers.

[0057] In some embodiments, the other layers contain polyolefins, as previously described. In some embodiments, all or substantially all of the polymers in the multi-layer film are polyolefins, as previously described. By "substantially all" is meant that the amount of non-polyolefin polymers is small enough that the non-polyolefin polymers do not materially alter the properties of the film.

[0058] In some embodiments, the other layers contain non-polyolefin polymers. Common non-polyolefin polymers used in multi-layer films include polyethylene terephthalate (PET) (such as Mylar), polystyrene (PS and high impact polystyrene HIPS), polyvinyl chloride (PVC), polyvinylidene chloride (PVDC), polyamide (PA) (including nylon), ethylene vinyl alcohol (EVOH), ethylene-vinyl acetate (EVA).

[0059] In some embodiments, the multilayer film includes a barrier layer to reduce the flow of water, air, or flavor components through the multilayer film. Common barrier layers include EVOH, polyamide, or PVDC.

[0060] In some embodiments, a "tie layer" can be added between two layers that have poor adhesion to each other to prevent delamination of these layers. Tie layers typically include a polymer or polymer blend that has good adhesion to both of the layers adjacent to the tie layer. Suitable tie layer polymers are known and commercially available. Examples of suitable tie layers for polyolefins are sold under the INTUNE ™ and VERSIFY ™ brand names. Examples of suitable tie layer polymers for adhering polyolefins to non-polyolefin polymers are sold under the AMPLIFY ™ and BYNEL ™ brand names.

[0061] In some embodiments, the face layer opposite the heat seal layer is a print layer that includes a polymer that provides a good appearance and provides a good print surface. Examples of polymers used in print layers include polyethylene and polypropylene and blends thereof.

[0062] In some embodiments, the face layer opposite the heat seal layer is a second heat seal layer. The second heat seal layer can independently have content as described for the first heat seal layer. Alternatively, the second heat seal layer can include other polymers, such as ethylene-vinyl acetate copolymer.

[0063] In some embodiments, the core layer and the heat seal layer are directly adhered to each other. In some embodiments, the core layer and the heat seal layer are joined together by a tie layer. In some embodiments, one or more other layers are interposed between the core layer and the heat seal layer. For example, the multilayer film can include a barrier layer between the core layer and the heat seal layer, and optionally one or more tie layers to adhere the barrier layer to the core layer and / or the heat seal layer.

[0064] In some embodiments, the polymers in one or more layers of the multilayer film can include additives. Examples of common additives include antistatic agents, color enhancers, dyes, lubricants, fillers, pigments, primary antioxidants, secondary antioxidants, processing aids, UV stabilizers, nucleating agents, slip agents such as erucamide, antiblocking agents such as talc, and combinations thereof. In some embodiments, the additives comprise no more than 5 wt%, or no more than 4 wt%, or no more than 3 wt%, or no more than 2 wt%, or no more than 1 wt% of any polymer, based on the total weight of such polymer. In some embodiments, the additives comprise substantially 0 wt% of the polymer composition. In some embodiments, the layers that will form the interior surface of the pouch include only additives approved by the applicable regulatory agency for food contact.

[0065] The multilayer film of the present application can be made by conventional co-extrusion methods, such as a cast film or blown film process. In an example of a co-extrusion process, different polymer compositions intended for different layers of the multilayer film are softened (and optionally blended) in separate extruders and discharged to a multi-layer extrusion die that extrudes each polymer composition into one or more layers in the multilayer film. In an example of a cast film process, a flat die extrudes the multilayer film onto a rotating drum that can pull the film and stretch the film in the machine direction to uniaxially orient it. In an example of a blown film process, an annular die extrudes a tube of the multilayer film that is pulled by a bubble to stretch the film in the machine and transverse directions and biaxially orient the film. The tubular film can then be slit to form one or more flat films. Suitable co-extrusion processes for multilayer films are well known.

[0066] In some embodiments, such as when a cast film process is used, the multilayer film is uniaxially oriented. In some embodiments, such as when a blown film process is used, the multilayer film is biaxially oriented.

[0067] The thickness of the film can vary depending on its intended use and properties. In some embodiments, the multilayer film is at least 90 micrometers thick or at least 110 micrometers or at least 130 micrometers. In some embodiments, the multilayer film is at most 350 micrometers thick or at most 300 micrometers thick or at most 250 micrometers or at most 200 micrometers.

[0068] In some embodiments, the multilayer film has an MD tensile strength of at least 25 MPa or at least 30 MPa or at least 35 MPa. There is no maximum desired tensile strength, but in some cases a tensile strength higher than 100 MPa can be unnecessary.

[0069] In some embodiments, the multilayer film has a 2% secant modulus of at least 250 MPa or at least 300 MPa or at least 350 MPa. There is no maximum desired 2% secant modulus, but in some cases a 2% secant modulus higher than 1000 MPa can be unnecessary.

[0070] In some embodiments, the multilayer film has a dart drop impact strength of at least 400 g or at least 450 g or at least 500 g. There is no maximum desired dart drop impact strength, but in some cases a tensile strength higher than 1000 g can be unnecessary.

[0071] In some embodiments, the multilayer film has an MD Elmendorf tear strength of at least 400 g or at least 450 g or at least 500 g. In some embodiments, the multilayer film has an MD Elmendorf tear strength of at most 1200 g.

[0072] In some embodiments, the multilayer film provides a seal strength of at least 40 N / 25 mm or at least 45 N / 25 mm or at least 50 N / 25 mm or at least 55 N / 25 mm or at least 58 N / 25 mm or at least 60 N / 25 mm when tested at a seal temperature of 170°C according to the test method. There is no maximum desired seal strength, but in some cases a seal strength higher than 120 N / 25 mm can be unnecessary.

[0073] In some embodiments, the multilayer film has at most 20 or at most 15 or at most 10 or at most 8 or at most 6 or at most 4 pinholes after 5400 cycles of Gelbo flex fatigue testing. In certain embodiments, the multilayer film has no pinholes or at least 1 pinhole or at least 2 pinholes.

[0074] In some embodiments, the multilayer film is formed into an open pouch, such as by:

[0075] • folding the film along the length (machine direction) dimension to form a tube, with the heat seal layers at the edges of the film contacting each other;

[0076] • heat pressing the edges of the film together to seal the film tube closed;

[0077] • heat pressing the tube together along the cross direction of the length (machine direction) dimension to close one end of the tube and form a pouch that is open at one end and closed at the other end; and

[0078] • cutting the tube below the cross direction heat seal to separate the pouch from the rest of the tube, or partially perforating or otherwise weakening the tube below the cross direction heat seal so that the pouch can be torn from the tube later.

[0079] In some embodiments, the pouch is filled in-line as it is formed, and sealed closed by a second cross direction heat seal at the open end of the pouch. For example, the film can be used in a conventional form, fill, and seal process. Alternatively, in some embodiments, the pouch can be recycled and stored in an open-ended empty pouch state for filling and heat sealing at a different time. Alternatively, in some embodiments, the tube can be partially perforated or otherwise weakened below the cross direction heat seal, and then wound up to provide a tubular roll from which the pouches can be torn off later; tearing off one pouch provides an open end for the next pouch on the roll.

[0080] In some embodiments, the pouch of the present invention comprises a tube of multilayer film that is sealed at one end and open at the other end. In such embodiments, the heat seal layers can be on the inside of the pouch, so that the pouch can be sealed by pinching the opposite sides at the open end of the pouch together across the opening and heating them to seal them together. However, other more complex embodiments are possible.

[0081] In the method of the present application, the contents are placed in the bag and the open end is heat sealed.

[0082] Pouches made using a multi-layer film can be particularly useful when the contents are placed in the pouch while hot and the pouch is heat sealed before the hot contents can cool. In some embodiments, the contents of the pouch are at a temperature of at least 90°C or at least 100°C or at least 110°C or at least 120°C or at least 130°C or at least 140°C when the pouch is sealed. In some embodiments, the contents of the pouch are at a temperature of at most 150°C or at most 145°C or at most 140°C when the pouch is sealed.

[0083] In some embodiments, the multi-layer film provides a heat seal strength of at least 40 N / 25 mm or at least 45 N / 25 mm or at least 50 N / 25 mm when in contact with hot contents having a temperature of up to 140°C. There is no maximum desired seal strength, but in some cases a seal strength higher than 120 N / 25 mm can be unnecessary.

[0084] Test Methods

[0085] The following test methods were used in this application:

[0086]

[0087]

[0088] iCCD analysis The iCCD method is described in PCT Publication WO 2017 / 040127 Al (Aug. 24, 2016) by Cong et al. The test uses a PolymerChar Crystallization Elution Fractionation (CEF) instrument equipped with an IR-5 detector (PolymerChar) and a two-angle light scattering detector Model 2040 (Precision Detectors, now Agilent Technologies). The CEF instrument is equipped with an autosampler with N2purge capability.

[0089] The iCCD column is packed with gold-plated nickel particles (Bright 7GNM8-NiS, Nippon Chemical Industrial Co.) in a 15 cm (length) x ¼" (ID) stainless steel tube. The column is packed and conditioned using the slurry method described in the above-mentioned patent by Cong et al. The final pressure of the trichlorobenzene slurry pack is 150 bar.

[0090] Column temperature calibration is performed using a mixture of the following:

[0091] • Solvent: o-Dichlorobenzene (ODCB, 99% anhydrous grade or technical grade);

[0092] • Reference material: linear homopolymer polyethylene (with zero comonomer content, melt index (I2) of 1.0 dg / min, polydispersity (Mw / Mn) of about 2.6) at a concentration of 1.0 mg / ml; and

[0093] • Reference material: eicosane (2 mg / ml).

[0094] The iCCD temperature calibration was performed in four steps:

[0095] a. Calculate the delay volume, which is defined as the temperature shift after the measured peak elution temperature of eicosane minus 30.0 °C;

[0096] b. Subtract the temperature shift of the elution temperature from the iCCD raw temperature data. This temperature shift is a function of experimental conditions such as elution temperature, elution flow rate, etc.;

[0097] c. Create a linear calibration line that converts the elution temperature in the range of 30.0 °C and 140.0 °C such that the linear homopolymer polyethylene reference has a peak temperature at 101.0 °C and eicosane has a peak temperature at 30.0 °C;

[0098] d. Linearly extrapolate elution temperatures below 30.0 °C for the soluble fraction measured isothermally at 30 °C by using a elution heating rate of 3 °C / min as described in column 12, lines 1-3 of U.S. Patent 9,688,795 B2) of Cerk et al. Figure 1

[0099] To prepare the samples, the polymer to be measured was mixed with ODCB in the autosampler at 4 mg / ml (unless otherwise indicated) and shaken at 158 °C for 1 hour. A 200 μΐ aliquot of the sample was injected. The crystallization temperature profile was from 110 °C to 30 °C at 3 °C / min, a thermal equilibration at 30 °C for 2 minutes (including the soluble fraction elution time set to 2 minutes), an elution from 30 °C to 145 °C at 3 °C / min. The flow rate during crystallization was 0.0 ml / min. The flow rate during elution was 0.50 ml / min. The data were collected at a rate of one data point per second.

[0100] According to the Rayleigh-Gans-Debys approximation (described in Striegel and Yau, "Modern Size-Exclusion Liquid Chromatography", 2ndEdition, John Wiley & Sons, 2001, pp. 230-231), the intrinsic viscosity of a polymer is given by the following equation: Modern Size Exclusion Liquid Chromatogram ​, pages 242 and 263), the molecular weight of the polymer and the molecular weight of the polymer fractions are determined directly from the light scattering detector (90 degree angle) and the concentration detector (IR-5). The integration window is set to integrate the entire chromatogram for elution temperatures ranging from 23.0 °C to 120 °C (temperature calibration specified above). The molecular weight calculations and calibration are performed in the GPCOne ™ software.

[0101] The molecular weight (Mw) is calculated from the iCCD includes the following steps:

[0102] • The inter-detector offset is measured. This offset is defined as the geometric volume offset between the light scattering detector relative to the concentration detector. It is calculated as the difference in elution volume (mL) of the polymer peak between the concentration detector and the light scattering chromatogram. The inter-detector offset is converted to a temperature offset by using the elution thermal rate and the elution flow rate.

[0103] • The MW detector constant is calculated by using a HDPE sample with a known weight average molecular weight in the range of 100,000 g / mol to 140,000 g / mol and the area ratio of the LS and concentration integrated signals. A linear high density polyethylene (with zero comonomer content, melt index (I2) of 1.0, and a polydispersity Mw / Mn of approximately 2.6 by conventional gel permeation chromatography) is used. The same experimental conditions as the normal iCCD method described above are used, except for the following parameters: crystallization at 10 °C / min from 140 °C to 137 °C, thermal equilibration at 137 °C for 1 minute as the soluble fraction elution time, soluble fraction (SF) time of 7 minutes, elution at 3 °C / min from 137 °C to 142 °C.

[0104] • The flow rate during crystallization is 0.0 ml / min.

[0105] • The flow rate during elution is 0.80 ml / min.

[0106] • The sample concentration is 1.0 mg / ml.

[0107] • Prior to integration, each LS data point in the LS chromatogram is shifted to correct for the inter-detector offset. The LS and concentration chromatograms are integrated against the baseline for the entire elution temperature range of step (1).

[0108] • The Mw of the polymer is calculated by using the ratio of the integrated light scattering detector (90 degree angle) to the concentration detector and using the MW detector constant.

[0109] The iCCD elution profile is displayed as "dW f / dT versus elution temperature", where dW f / dT is the weight fraction (W) of the polymer eluting at temperature T.f ). Calculate the weight percentage (w%) of the elution fraction from 25°C to 35°C using the following formula. 25-35 ) and the weight percentage (w%) of the elution fraction from 35°C to 100°C. 35-100 ).

[0110]

[0111]

[0112] Seal strength test A bag with an internal dimension of 15cm wide × 20cm high was produced by sealing two layers of film together on three sides, leaving one side opening for filling. Sealing was performed using a Lako SL-2 digital heat sealer. Sealing conditions were: temperature: 200℃; pressure: 6.8psi; seal width: 1mm; residence time: 0.5s. The bag was allowed to cool to room temperature before use.

[0113] Heating and equilibration of silicone oil at 140°C.

[0114] Place the empty bag in a 1L container and pour hot oil at 140°C into the bag. Immediately seal the bag and test it using a J&B 4000 HotTack tester with the following settings: Sample width: 25mm; Sealing strip width: 5mm; Sealing pressure: 0.275MPa; Sealing time: 0.5s; Cooling time: 24h; Peeling speed: 500mm / min.

[0115] Example

[0116] The examples used the polymers shown in Table 1. Samples of each polypropylene resin were analyzed by iCCD as described in the test methods. The results are shown in... Figure 1 And in Table 1.

[0117]

[0118] Under the conditions shown in Table 2, the polymers in Table 1 were extruded into 3-layer films on a blown film extrusion line.

[0119]

[0120] The content of each membrane is shown in Table 3. The membrane thickness, dart impact strength, tear resistance, hot fill seal strength, and pinholes were tested, and the results are shown in Table 3.

[0121]

[0122]

[0123] Aspect 1. A multilayer film comprising at least: (A) a core layer comprising a polyolefin polymer and (B) a heat seal layer, wherein the heat seal layer comprises: a. 30 wt% to 80 wt% of a polypropylene copolymer having: i. a total ethylene content (Et) of 5 wt% to 30 wt%, based on the total weight of the polypropylene copolymer; and ii. a density of 0.80 g / cc to 0.95 g / cc; and iii. a melt index of no more than 5 dg / min at 230 °C; and iv. an iCCD profile in which at least 10 wt% of the polypropylene copolymer elutes from 25 °C to 35 °C and no more than 30 wt% of the polypropylene copolymer elutes between 35 °C and 100 °C in an iCCD elution test from 25 °C to 150 °C; and b. 20 wt% to 70 wt% of a polyethylene copolymer having a density of 0.895 g / cc to 0.925 g / cc and a melt index of less than 3 dg / min at 190 °C.

[0124] Aspect 2. The multilayer film of aspect 1, wherein the core layer comprises a polyethylene having a density of 0.895 g / cc to 0.930 g / cc and a melt index of less than 3 dg / min at 190 °C.

[0125] Aspect 3. The multilayer film of aspect 1 or aspect 2, wherein the polypropylene copolymer of the heat seal layer has: a. a total ethylene content (Et) of 8 wt% to 20 wt%, based on the total weight of the polypropylene copolymer; and b. a density of 0.895 g / cc to 0.910 g / cc; and c. a melt index (I2) of 1 dg / min to 3 dg / min at 230 °C.

[0126] Aspect 4. The multilayer film of aspects 1 to 3, wherein the core layer comprises 25 wt% to 65 wt% of the polypropylene copolymer and 35 wt% to 75 wt% of a polyethylene having a density of 0.895 g / cc to 0.930 g / cc and a melt index of less than 3 dg / min at 190 °C.

[0127] Aspect 5. The multilayer film of aspects 1 to 4, wherein the core layer and the heat seal layer comprise a polyethylene having a density of 0.905 g / cc to 0.922 g / cc and a melt index of 0.1 dg / min to 1.0 dg / min at 190 °C.

[0128] Aspect 6. The multilayer film of aspects 1-5, wherein the polypropylene copolymer has an iCCD elution profile in which 12 wt% to 18 wt% of the polypropylene copolymer elutes at temperatures from 25 °C to 35 °C in an iCCD elution test from 25 °C to 150 °C.

[0129] Aspect 7. The multilayer film of aspects 1-6, wherein the polypropylene copolymer has an iCCD elution profile in which 10 wt% to 20 wt% of the polypropylene copolymer elutes at temperatures between 35 °C and 100 °C in an iCCD elution test from 25 °C to 150 °C.

[0130] Aspect 8. The multilayer film of aspects 1-7, wherein the polypropylene copolymer in the heat seal layer is an impact copolymer.

[0131] Aspect 9. The multilayer film of aspects 1-8, wherein the polypropylene copolymer in the heat seal layer is an impact copolymer, and wherein: a. 12 wt% to 18 wt% of the polypropylene copolymer elutes at temperatures between 25 °C and 35 °C in an iCCD elution test from 25 °C to 150 °C; and b. 10 wt% to 20 wt% of the polypropylene copolymer elutes at temperatures between 35 °C and 100 °C in an iCCD elution test from 25 °C to 150 °C.

[0132] Aspect 10. The multilayer film of aspects 1-9, wherein the heat seal layer comprises 35 wt% to 50 wt% of the polypropylene copolymer.

[0133] Aspect 11. The multilayer film of aspects 1-10, wherein the core layer comprises 25 wt% to 65 wt% of a polypropylene copolymer and 35 wt% to 75 wt% of a polyethylene as described in aspect 3, the polyethylene having a density of 0.895 g / cc to 0.930 g / cc and a melt index of less than 3 dg / min at 190 °C.

[0134] Aspect 12. The multilayer film of aspects 1-11, wherein the core layer and the heat seal layer comprise a polyethylene having a density of 0.905 g / cc to 0.922 g / cc and a melt index of 0.1 dg / min to 1.0 dg / min at 190 °C.

[0135] Aspect 13. The multilayer film according to Aspect 1, wherein the heat seal layer comprises: a. 35 wt% to 50 wt% of the polypropylene copolymer, wherein: i. the total ethylene content (Et) of the polypropylene copolymer is 8 wt% to 20 wt%, based on the total weight of the polypropylene copolymer; and ii. the density of the polypropylene copolymer is 0.895 g / cc to 0.910 g / cc; and iii. the melt index (I2) of the polypropylene copolymer at 230 °C is 1 dg / min to 3 dg / min; iv. 12 wt% to 18 wt% of the polypropylene copolymer elutes at a temperature between 25 °C and 35 °C in an iCCD elution test from 25 °C to 150 °C; and v. 10 wt% to 20 wt% of the polypropylene copolymer elutes at a temperature between 35 °C and 100 °C in an iCCD elution test from 25 °C to 150 °C; and b. 50 wt% to 65 wt% of the polyethylene copolymer having a density of 0.900 g / cc to 0.912 g / cc and a melt index of 0.5 dg / min to 1.5 dg / min.

[0136] Aspect 14. A bag comprising the multilayer film according to any one of Aspects 1 to 13.

[0137] Aspect 15. A method of packaging a heated material, the method comprising the steps of: a. placing a material having a temperature of at least 90 °C in an open-ended bag according to Aspect 14, and b. heat sealing the open end of the bag to completely enclose the bag.

Claims

1. A multilayer film, the multilayer film comprising at least: (A) a core layer comprising a polyolefin polymer and (B) a heat-sealing layer, wherein the heat-sealing layer comprises: a) 30% to 80% by weight of a polypropylene copolymer, said polypropylene copolymer having: i) a total ethylene content (Et) of 5% to 30% by weight, based on the total weight of the polypropylene copolymer; and ii) a density of 0.80 g / cc to 0.95 g / cc; and iii) A melt index not exceeding 5 dg / min at 230°C; and iv) iCCD curves, wherein in an iCCD elution test from 25°C to 150°C, at least 10% by weight of the polypropylene copolymer is eluted from 25°C to 35°C, and no more than 30% by weight of the polypropylene copolymer is eluted between 35°C and 100°C; and b) 20% to 70% by weight of a polyethylene copolymer having a density of 0.895 g / cc to 0.925 g / cc and a melt index of less than 3 dg / min at 190°C.

2. The multilayer film according to claim 1, wherein the core layer comprises polyethylene having a density of 0.895 g / cc to 0.930 g / cc and a melt index of less than 3 dg / min at 190°C.

3. The multilayer film according to any preceding claim, wherein the polypropylene copolymer of the heat-sealable layer has: a) A total ethylene content (Et) of 8% to 20% by weight, based on the total weight of the polypropylene copolymer; and b) Densities ranging from 0.895 g / cc to 0.910 g / cc; and c) Melt index (I2) at 230°C, ranging from 1 dg / min to 3 dg / min.

4. The multilayer film according to any of the preceding claims, wherein the core layer comprises 25% to 65% by weight of the polypropylene copolymer and 35% to 75% by weight of polyethylene, the polyethylene having a density of 0.895 g / cc to 0.930 g / cc and a melt index of less than 3 dg / min at 190°C.

5. The multilayer film according to any of the preceding claims, wherein the core layer and the heat-sealing layer comprise polyethylene having a density of 0.905 g / cc to 0.922 g / cc and a melt index of 0.1 dg / min to 1.0 dg / min at 190°C.

6. The multilayer membrane according to any of the preceding claims, wherein the polypropylene copolymer has an iCCD elution profile, wherein in an iCCD elution test at 25°C to 150°C, 12% to 18% by weight of the polypropylene copolymer is eluted at a temperature of 25°C to 35°C.

7. The multilayer membrane according to any of the preceding claims, wherein the polypropylene copolymer has an iCCD elution profile, wherein in an iCCD elution test at 25°C to 150°C, 10% to 20% by weight of the polypropylene copolymer is eluted at a temperature between 35°C and 100°C.

8. The multilayer film according to any of the preceding claims, wherein the polypropylene copolymer in the heat-sealing layer is an impact copolymer.

9. The multilayer film according to any preceding claim, wherein the polypropylene copolymer in the heat-sealing layer is an impact copolymer and wherein: a) In iCCD elution tests from 25°C to 150°C, 12% to 18% by weight of the polypropylene copolymer were eluted at temperatures between 25°C and 35°C; and b) In iCCD elution tests from 25°C to 150°C, 10% to 20% by weight of the polypropylene copolymer were eluted at temperatures between 35°C and 100°C.

10. The multilayer film according to any of the preceding claims, wherein the heat-sealing layer comprises 35% to 50% by weight of the polypropylene copolymer.

11. The multilayer film according to any of the preceding claims, wherein the core layer comprises 25% to 65% by weight of a polypropylene copolymer and 35% to 75% by weight of polyethylene as described in claim 3, said polyethylene having a density of 0.895 g / cc to 0.930 g / cc and a melt index of less than 3 dg / min at 190°C.

12. The multilayer film of claim 11, wherein the core layer and the heat-sealing layer comprise polyethylene having a density of 0.905 g / cc to 0.922 g / cc and a melt index of 0.1 dg / min to 1.0 dg / min at 190°C.

13. The multilayer film according to claim 1, wherein the heat-sealing layer comprises: a) 35% to 50% by weight of the polypropylene copolymer, wherein: i) Based on the total weight of the polypropylene copolymer, the total ethylene content (Et) of the polypropylene copolymer is from 8% to 20% by weight; and ii) The density of the polypropylene copolymer is from 0.895 g / cc to 0.910 g / cc; and iii) The melt index (I2) of the polypropylene copolymer at 230°C is 1 dg / min to 3 dg / min; iv) In iCCD elution tests from 25°C to 150°C, 12% to 18% by weight of the polypropylene copolymer were eluted at temperatures between 25°C and 35°C; and v) In iCCD elution tests from 25°C to 150°C, 10% to 20% by weight of the polypropylene copolymer were eluted at temperatures between 35°C and 100°C; and b) 50% to 65% by weight of the polyethylene copolymer, the polyethylene copolymer having a density of 0.900 g / cc to 0.912 g / cc and a melt index of 0.5 dg / min to 1.5 dg / min.

14. A bag comprising a multilayer film according to any one of claims 1 to 13.

15. A method for packaging heated materials, the method comprising the following steps: a) Placing the material at a temperature of at least 90°C in a bag with one open end as described in claim 14, and b) Heat seal the open end of the bag to completely close the bag.

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