Heat-resistant heat seal film

Abstract

A multilayer film is disclosed. The multilayer film may comprise a core layer and a heat-seal layer, the heat-seal layer comprising a polypropylene copolymer and a polyethylene copolymer. The polypropylene copolymer of the heat-seal layer has certain properties, such as ethylene content and iCCD elution profile, to contribute to 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 can be formed into a bag, which is suitable for carrying hot or heated contents.

Description

Technical Field

[0001] Embodiments described herein generally relate to multilayer films, more specifically, multilayer films suitable for heat-seal packaging.

Background Art

[0002] Heat-sealable bags made from multilayer films are a common form of packaging. Multilayer films can include a core polymer layer that delivers desirable strength and other film properties, and can include a heat-seal layer. Multilayer films can also include other layers such as barrier layers, tie layers, printing layers, or metal foil layers. The multilayer film can be folded and sealed to form a bag with one end open and the other sides and ends closed. Contents can be added to the bag through the open end, the open end is pinched closed, and the heat-seal layers on both pinched sides contact each other and are heated to seal the open end.

[0003] Many factors, including the length and width of the seal, the temperature and pressure used to create the seal, the time the temperature and pressure are maintained, and the contents of the heat-seal layer, can affect the strength of the heat seal. Since packagers often want to run their packaging lines quickly, heat-seal layers are typically selected to form strong seals using only short cycles of pressure, heating, and cooling.

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

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

Summary of the Invention

[0006] A first aspect of the present invention is a multilayer film. A multilayer film according to embodiments disclosed herein comprises at least (A) a core layer containing a polyolefin polymer, and (B) a heat-seal layer comprising a. 30 to 80 weight percent polypropylene copolymer having an iCCD profile in which, i) based on the total weight of the polypropylene copolymer, 5 to 30 weight percent total ethylene content (total ethylene, Et), ii) a density of 0.80 to 0.95 g / cc, and iii) a melt index of 5 dg / min or less at 230°C, and iv) in which, in an iCCD elution test at 25°C to 150°C, at least 10 weight percent polypropylene copolymer elutes at 25°C to 35°C and 30 weight percent polypropylene copolymer or less at 35°C to 100°C, and b. 20 to 70 weight percent polyethylene copolymer having a density of 0.895 to 0.925 g / cc and a melt index of less than 3 dg / min at 190°C.

[0007] A bag containing a multilayer film according to an embodiment is also disclosed.

[0008] A process for packaging heated material is also disclosed. A process according to embodiments disclosed herein includes a. placing material having a temperature of at least 90°C into a bag from a second embodiment of the present invention which is open at one end, and b. heat-sealing the open end of the bag to completely close the bag.

[0009] The multilayer film of the present invention can form a strong heat seal even when in contact with contents heated to over 140°C. [Brief explanation of the drawing]

[0010] [Figure 1] The results of iCCD analysis performed on three polypropylene resins used in the work example are shown. [Modes for carrying out the invention]

[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 three layers, or at least four layers, or at least five 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 may comprise at least a core layer comprising a polyolefin polymer and a heat-seal layer, wherein the heat-seal layer comprises a polypropylene copolymer and a polyethylene copolymer.

[0012] One layer of the multilayer film is a core layer containing a polyolefin polymer. Examples of polyolefin polymers include polyethylene, polypropylene, or a blend of polyethylene and polypropylene.

[0013] As used herein, “polyethylene” or “ethylene polymer” refers to a polymer containing units derived from more than 50 mol% of ethylene monomers. This includes ethylene homopolymers or copolymers (meaning that the units are derived from two or more comonomers). Common forms of ethylene polymers known in the art include low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), ultra-low-density polyethylene (ULDPE), very low-density polyethylene (VLDPE), single-site catalyst linear low-density polyethylene (m-LLDPE) including both linear low-density resins and substantially linear low-density resins, medium-density polyethylene (MDPE), and high-density polyethylene (HDPE).

[0014] Common grades of polyethylene used in multilayer films include the following: ● High-density polyethylene (HDPE) with a density of 0.94 g / cc to 0.98 g / cc, ● Linear low-density polyethylene (LLDPE) with a density of 0.915 g / cc to 0.94 g / cc, ● Low-density polyethylene (LDPE) having a density of 0.90 g / cm³ to 0.93 g / cm³, and / or ● Ultra-low density polyethylene (VLDPE) with a density of 0.88 g / cc to 0.915 g / cc.

[0015] Common grades of polypropylene used in multilayer films include: ● Polypropylene homopolymer, ● Polypropylene random copolymer, and ● Polypropylene block copolymer.

[0016] Certain polypropylene copolymers, referred to as "impact-resistant copolymers," may have a rubber content that imparts higher impact resistance. In some embodiments, the impact-resistant copolymer comprises a block copolymer of propylene and ethylene, which contains blocks with a low ethylene content and blocks with a high ethylene content. In some embodiments, the impact-resistant copolymer comprises a polypropylene random copolymer and / or a polypropylene polymer blend.

[0017] In some embodiments, “polyethylene” is a copolymer comprising repeating units derived from ethylene and repeating units derived from other 1-olefins such as 1-butene, 1-hexene, and / or 1-octene. (Unless otherwise indicated, “primarily” means more than 50 weight percent.) Similarly, polypropylene (PP) random and block copolymers may comprise repeating units derived from propylene and repeating units derived from ethylene. By varying the selection and proportion of monomers, the catalyst used to produce the polyolefin, and the reaction conditions, a wide range of different polyolefin grades with different properties such as density, melt viscosity, and physical strength can be produced.

[0018] In some embodiments, the core layer may contain polymers to achieve desirable physical properties of the film, such as tensile strength and modulus of elasticity, drop dart impact strength, tear strength, temperature resistance, and melt strength. In some embodiments, the core layer contains HDPE. In some embodiments, the core layer contains LLDPE. In some embodiments, the core layer contains polyethylene having a density of 0.895 to 0.930 g / cc and a melt index of less than 3 dg / min at 190°C. In some embodiments, the core layer contains VLDPE. In some embodiments, the core layer contains 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 comprises polyethylene having a density of at most 0.930 g / cc, at most 0.925 g / cc, at most 0.922 g / cc, or at most 0.920 g / cc.

[0019] In some embodiments, the core layer comprises polyethylene having a melt index (I2) of 5 dg / min or less, or 4 dg / min or less, or 3 dg / min or less, or 2 dg / min or less, or 1 dg / min or less, or 0.8 dg / min or less, or 0.6 dg / min or less, or 0.4 dg / min or less at 190°C. In some embodiments, the core layer comprises 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.

[0020] In some embodiments, the core layer comprises a polypropylene homopolymer. In some embodiments, the core layer comprises a polypropylene random copolymer. In some embodiments, the core layer comprises 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.

[0021] In some embodiments, the core layer comprises a blend of two or more polyolefin polymers, such as at least two polyethylene polymers, or at least two 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 blends of high density polyethylene (HDPE) or linear low density polyethylene (LLDPE) with low density polyethylene (LDPE) or polyethylene elastomers. Some polypropylenes are incompatible with polyethylene and may require a compatibilizer. On the other hand, some polypropylenes blend effectively with polyethylene and do not require a compatibilizer. For example, polypropylene block copolymers containing blocks of polyethylene are more likely to blend effectively with polyethylene, particularly low density polyethylene having a relatively high level of comonomer.

[0022] In some embodiments, the core layer comprises a blend of a polypropylene copolymer having the same characteristics as the polypropylene copolymer used in the heat seal layer and polyethylene.

[0023] In some embodiments, the core layer comprises at least 10 weight percent, or at least 15 weight percent, or at least 20 weight percent, or at least 25 weight percent, or at least 30 weight percent, or at least 35 weight percent, or at least 40 weight percent, or at least 42 weight percent, or at least 45 weight percent of a polypropylene copolymer. In some embodiments, the core layer comprises at most 65 weight percent, or at most 60 weight percent, or at most 55 weight percent, or at most 50 weight percent, or at most 48 weight percent, or at most 45 weight percent of a polypropylene copolymer based on the total weight of the core layer. In some embodiments, the core layer comprises at least 35 weight percent, or at least 40 weight percent, or at least 45 weight percent, or at least 50 weight percent, or at least 52 weight percent, or at least 55 weight percent of polyethylene. In some embodiments, the core layer comprises 100 weight percent, or at most 90 weight percent, or at most 85 weight percent, or at most 80 weight percent, or at most 75 weight percent, or at most 70 weight percent, or at most 65 weight percent, or at most 60 weight percent, or at most 55 weight percent of polyethylene based on the total weight of the core layer.

[0024] The multilayer film has two outer surfaces facing each other, and the polymer layers on each surface of the film are called surface layers. In the film of the present invention, one surface layer is a heat-sealing layer. In a two-layer film, the other surface layer is the core layer. In a film of three or more layers, the other surface layer can be the core layer or another polymer layer.

[0025] The heat seal layer may comprise a. 30 to 80 weight percent of a polypropylene copolymer based on the total weight of the heat seal layer, i. containing 5 to 30 weight percent of repeating units derived from ethylene, i. having a density of 0.80 to 0.95 g / cc, ii. having a melt index of 5 dg / min or less at 230°C, and iii. in an iCCD elution test at 25°C to 150°C, at least 10 weight percent of the PP copolymer elutes at 25°C to 35°C, and 30 weight percent or less of the PP copolymer elutes at 35°C to 100°C, and 20 to 70 weight percent of a polyethylene copolymer having a density of 0.895 to 0.925 g / cc and a melt index of less than 3 dg / min at 190°C. The iCCD elution test is performed according to the test method described below.

[0026] 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.

[0027] 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, at least 1 dg / min, or at least 2 dg / min at 230°C.

[0028] Polypropylene copolymers can be characterized based on their total ethylene content (Et), which is the average weight percentage of repeating units derived from ethylene, based on the total weight of the polypropylene copolymer. In some embodiments, the total ethylene content (Et) of the polypropylene copolymer is at least 8 weight percent, or at least 10 weight percent, or at least 12 weight percent. In some embodiments, the total ethylene content (Et) of the polypropylene copolymer is at most 28 weight percent, or at most 25 weight percent, or at most 20 weight percent. In some embodiments, the polypropylene copolymer contains at most 92 weight percent, or at most 90 weight percent, or at most 88 weight percent of repeating units derived from propylene. In some embodiments, the polypropylene copolymer contains at least 72 weight percent, or at least 75 weight percent, or at least 80 weight percent of repeating units derived from propylene. In some embodiments, the polypropylene copolymer includes, based on the total weight of the polypropylene copolymer, at most 10 weight percent, at most 5 weight percent, at most 2 weight percent, at most 1 weight percent, or 0 weight percent repeating units derived from monomers other than propylene and ethylene.

[0029] 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-resistant copolymer comprising a crystalline polypropylene homopolymer or polypropylene copolymer component called a crystalline phase and an amorphous ethylene-propylene random copolymer component called a rubber phase. The crystalline phase may have a low ethylene content, while the rubber phase has a higher ethylene content than the crystalline phase. In some embodiments, the impact-resistant polypropylene copolymer is a block copolymer in which segments of the crystalline phase polymer and segments of the rubber phase polymer are bonded to each other.

[0030] Cong et al.'s PCT patent application WO2017 / 040127A1 (March 9, 2017) describes an improved method to measure comonomer content and distribution (iCCD) for polyolefins, adapted from temperature rising elution fractionation (TREF). The test method describes a specific implementation of iCCD analysis. In iCCD analysis, polymers can be separated into fractions that elute at low temperatures (25°C to 35°C), fractions that elute at medium temperatures (above 35°C to 105°C), and fractions that elute at high temperatures (above 105°C).

[0031] In the iCCD analysis described in the test method, the polypropylene copolymer used in the heat seal layer has at least 10 weight percent of recovered polymer in the low-temperature fraction. In some embodiments, the low-temperature fraction is at least 12 weight percent, or at least 14 weight percent, or at least 15 weight percent. In some embodiments, the low-temperature fraction is at most 30 weight percent, or at most 25 weight percent, or at most 20 weight percent, or at most 18 weight percent, or at most 16 weight percent.

[0032] In the iCCD analysis described in the test method, the polypropylene copolymer used in the heat seal layer has at least 30 weight percent of recovered polymer in the medium-temperature fraction. In some embodiments, the medium-temperature fraction is at most 25 weight percent, or at most 20 weight percent, or at most 18 weight percent, or at most 16 weight percent, or at most 15 weight percent. In some embodiments, the medium-temperature fraction is at least 5 weight percent, or at least 8 weight percent, or at least 10 weight percent, or at least 12 weight percent, or at least 14 weight percent.

[0033] 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.

[0034] Polypropylene copolymers suitable for heat-seal layers are commercially available, as mentioned above. Others can be manufactured by known methods.

[0035] In some embodiments, the polyethylene copolymer in the heat seal layer may have a density of 0.895 to 0.925 g / cc. In some embodiments, the density of the polyethylene copolymer is 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 density of the polyethylene copolymer is 0.922 g / cc, or at most 0.920 g / cc, or at most 0.915, or at most 0.912, or at most 0.910.

[0036] The polyethylene copolymer in the heat-seal layer may have a melt index (I2) of less than 3 dg / min at 190°C. In some embodiments, the melt index (I2) of the polyethylene copolymer at 190°C is at most 2 dg / min, at most 1.5 dg / min, at most 1 dg / min, or at most 0.9 dg / min. In some embodiments, the melt index (I2) of the polyethylene copolymer at 190°C is at least 0.1 dg / min, at least 0.3 dg / min, at least 0.5 dg / min, at least 0.7 dg / min, or at least 0.8 dg / min.

[0037] In some embodiments, the polyethylene copolymer in the heat seal layer may have a melting 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 may have a melting 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.

[0038] In some embodiments, the comonomer in the polyethylene copolymer in the heat seal layer contains 4 to 10 carbon atoms. In some embodiments, the comonomer contains butene. In some embodiments, the comonomer contains hexene or consists essentially of hexene. In some embodiments, the comonomer contains octene or consists essentially of octene. ("Essentially consists of" means that any other monomer is present in a sufficiently low concentration that it does not materially alter the properties of the resulting polymer.)

[0039] In some embodiments, the polyethylene copolymer in the heat seal layer contains repeating units derived from at least 2 weight percent, or at least 5 weight percent, or at least 10 weight percent of comonomers. In some embodiments, the polyethylene copolymer in the heat seal layer contains repeating units derived from at most 35 weight percent, or at most 30 weight percent, or at most 25 weight percent of comonomers. Units not derived from comonomers are derived from ethylene.

[0040] In some embodiments, the polyethylene copolymer in the heat seal layer comprises a blend of two or more polyethylene copolymers that individually and / or collectively satisfy the aforementioned limitations and / or embodiments.

[0041] Polyethylene copolymers suitable for heat-seal layers are commercially available. Others can be manufactured by known methods.

[0042] The heat seal layer may contain 30 to 80 weight percent of polypropylene copolymer. In some embodiments, the heat seal layer contains at least 33 weight percent, or at least 36 weight percent, or at least 39 weight percent, or at least 40 weight percent of polypropylene copolymer. In some embodiments, the heat seal layer contains at most 75 weight percent, or at most 70 weight percent, or at most 60 weight percent, or at most 50 weight percent, or at most 45 weight percent, or at most 40 weight percent of polypropylene copolymer.

[0043] The heat seal layer may contain 20 to 70 weight percent of polyethylene copolymer. In some embodiments, the heat seal layer contains at least 25 weight percent, or at least 30 weight percent, or at least 40 weight percent, or at least 50 weight percent, or at least 55 weight percent, or at least 60 weight percent of polyethylene copolymer. In some embodiments, the heat seal layer contains at most 67 weight percent, or at most 64 weight percent, or at most 61 weight percent, or at most 60 weight percent of polyethylene copolymer.

[0044] In some embodiments, the heat seal layer includes, in addition to the polypropylene copolymer and polyethylene copolymer, at least 30 weight percent of another polymer, or at least 20 weight percent, or at least 10 weight percent, or at least 5 weight percent, or at least 2 weight percent, or 0 weight percent of another polymer. An example of another polymer used in the heat seal layer is ethylene vinyl acetate copolymer.

[0045] In some embodiments, the polypropylene and polyethylene copolymers in the heat-seal layer are compatible with each other, meaning they form a homogeneous blend without a compatibilizer. In some embodiments, the heat-seal layer further includes a compatibilizer, as previously discussed. Examples of suitable compatibilizers are commercially available under the INTUNE® trademark.

[0046] 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, or at least 200 microns thick. In some embodiments, the heat seal layer is at most 300 microns thick, or at least 250 microns thick, or at least 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 at least 20 to 80 microns thick. In some embodiments, the heat seal layer is 80 to 300 microns thick, or at least 100 to 200 microns thick.

[0047] 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.

[0048] 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 percent, or at least 110 percent, or at least 125 percent, or at least 150 percent, or at least 175 percent, or at least 190 percent of the thickness of the heat seal layer. In some embodiments, the thickness of the core layer is at most 1000 percent, or at most 800 percent, or at most 500 percent, or at most 400 percent, or at most 300 percent of the thickness of the heat seal layer.

[0049] In some embodiments, the multilayer film comprises only a core layer and a heat-seal layer. In some embodiments, the multilayer film comprises at least three layers, or at least four layers, or at least five 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.

[0050] In some embodiments, the other layers include polyolefins as described above. In some embodiments, all or essentially all polymers in the multilayer film are polyolefins as described above. "Essentially all" means that the amount of non-polyolefin polymers is so small that they do not materially alter the properties of the film.

[0051] In some embodiments, the other layers include non-polyolefin polymers. Common non-polyolefin polymers used in multilayer 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); and ethylene-vinyl acetate (EVA).

[0052] 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.

[0053] In some embodiments, a “bonding layer” may be added between two layers that do not adhere well to each other to prevent delamination. The bonding layer typically comprises a polymer or polymer blend that has good adhesion to both the bonding layer and the adjacent layers. Suitable bonding layer polymers are known and commercially available. Examples of bonding layers suitable for polyolefins are sold under the trademarks INTUNE® and VERSIFY®. Examples of bonding layer polymers suitable for bonding polyolefins to non-polyolefin polymers are sold under the trademarks AMPLIFY® and BYNEL®.

[0054] In some embodiments, the surface layer opposite the heat-seal layer is a printing layer comprising a polymer that provides a good appearance and a good surface for printing. Examples of polymers used in the printing layer include polyethylene and polypropylene, as well as blends thereof.

[0055] In some embodiments, the surface layer opposite the heat seal layer is a second heat seal layer. The second heat seal layer may independently have the same properties as described for the first heat seal layer. Alternatively, the second heat seal layer may contain other polymers, such as ethylene vinyl acetate copolymer.

[0056] In some embodiments, the core layer and the heat seal layer are directly bonded to each other. In some embodiments, the core layer and the heat seal layer are bonded together by a bonding layer. In some embodiments, one or more other layers are interposed between the core layer and the heat seal layer. For example, a multilayer film may include a barrier layer between the core layer and the heat seal layer, and optionally include one or more bonding layers for bonding the barrier layer to the core layer and / or the heat seal layer.

[0057] In some embodiments, the polymer in one or more layers of the multilayer film may contain additives. Common examples of 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, anti-tack agents such as talc, and combinations thereof. In some embodiments, the additives constitute no more than 5 weight percent, or 4 weight percent, or 3 weight percent, or 2 weight percent, or 1 weight percent of any polymer, based on the total weight of such polymers. In some embodiments, the additives constitute essentially 0 weight percent of the polymer composition. In some embodiments, the layer that will form the inner surface of the bag contains only additives approved for food contact by the applicable regulatory authority.

[0058] The multilayer films of the present invention can be produced by conventional co-extrusion processes such as cast film or blow film processes. 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 into multilayer extrusion dies that extrude each polymer composition as one or more layers of the multilayer film. In an example of a cast film process, a flat die extrudes the multilayer film onto a rotating drum, which stretches the film and elongates it in the machine direction, causing the film to be uniaxially oriented. In an example of a blow film process, an annular die extrudes a tube of multilayer film and stretches it on a bubble, elongating the film in both the machine direction and the transverse direction, causing the film to be biaxially oriented. The tubular film can then be cut into elongated strips to form one or more flat films. Co-extrusion processes suitable for multilayer films are well known.

[0059] 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 blow film process is used, the multilayer film is biaxially oriented.

[0060] The thickness of the film may vary depending on its intended use and properties. In some embodiments, the multilayer film is at least 90 microns thick, or at least 110 microns thick, or at least 130 microns thick. In some embodiments, the multilayer film is at most 350 micrometers thick, or at most 300 micrometers thick, or at most 250 micrometers thick, or at most 200 micrometers thick.

[0061] 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 desirable tensile strength, and in some cases, a tensile strength exceeding 100 MPa may be unnecessary.

[0062] 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 desirable 2% secant modulus, and in some cases, a 2% secant modulus greater than 1000 MPa may be unnecessary.

[0063] In some embodiments, the multilayer film has a drop dart impact strength of at least 400g, or at least 450g, or at least 500g. There is no maximum desirable drop dart impact strength, but in some cases, a tensile strength exceeding 1000g may be unnecessary.

[0064] 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.

[0065] In some embodiments, when tested according to a test method at a sealing temperature of 170°C, the multilayer film provides a sealing 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. There is no maximum desirable sealing strength, but in some cases, a sealing strength greater than 120 N / 25 mm may be unnecessary.

[0066] In some embodiments, after 5400 cycles of Gelboflex testing, the multilayer film has at most 20, at most 15, at most 10, at most 8, at most 6, or at most 4 pinholes. In some embodiments, the multilayer film has no pinholes, or at least one pinhole or at least two pinholes.

[0067] In some embodiments, the multilayer film is formed into an open-type bag as follows: ● The film is folded along its length (machine) and the heat-sealed layers at the edges of the film are brought into contact with each other to form a tube. ● The edges of the film are pressed together with heat to close and seal the film tube. ● While heating, press the tubes together in a transverse direction relative to the length (machine) dimension to form a bag in which one end of the tube is closed, one end is open, and the other end is closed, and ● Cut the tube under the transverse heat seal to separate the bag from the rest of the tube, or partially puncture or weaken the tube under the transverse heat seal so that the bag can be torn off the tube later.

[0068] In some embodiments, bags are filled in a line as they are formed and sealed with a second transverse heat seal at the open end of the bag. For example, a film can be used in a conventional forming, filling, and sealing process. Alternatively, in some embodiments, bags may be collected and stored empty with one end open and filled and heat-sealed at different points in time. Alternatively, in some embodiments, a tube can be partially perforated or weakened under the transverse heat seal and then rolled up to provide a tubular roll from which bags can be torn later, providing an open end for the next bag on the roll by tearing the bag.

[0069] In some embodiments, the bag of the present invention comprises a tube of multilayer film with one end sealed and the other end open. In such embodiments, the heat-seal layer may be on the inside of the bag so that the bag can be sealed by clamping the opposing sides of the open end of the bag together across the open and heating them together to seal them. However, other more complex embodiments are also possible.

[0070] In the process of the present invention, the contents are placed in a bag and the open end is heat-sealed.

[0071] Bags made using multilayer films may be particularly useful when the contents are placed in the bag at a high temperature and the bag is heat-sealed before the high-temperature contents can cool down. In some embodiments, the contents of the bag 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 bag is sealed. In some embodiments, the contents of the bag are at a temperature of at most 150°C, or at most 145°C, or at most 140°C when the bag is sealed.

[0072] In some embodiments, when in contact with high-temperature contents at temperatures up to 140°C, the multilayer 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. There is no maximum desirable sealing strength, but in some cases, a sealing strength greater than 120 N / 25 mm may be unnecessary.

[0073] Test method This application uses the following test method:

[0074] [Table 1]

[0075] iCCD analysis: The iCCD process is described in Cong et al., PCT Publication WO2017 / 040127A1 (August 24, 2016). 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 N2 purging capability.

[0076] The iCCD column is packed with gold-coated nickel particles (Bright 7GNM8-NiS, Nippon Chemical Industrial Co.) in a 15 cm (length) x 1 / 4 inch (inner diameter) stainless steel pipe. The column is packed and prepared using the slurry method described in the patent of Cong et al. above. The final pressure with the trichlorobenzene slurry packing is 150 bar.

[0077] Column temperature calibration is performed using the following mixture: ● Solvent: o-dichlorobenzene (ODCB, 99% anhydrous grade or industrial grade) ● Reference material: Linear homopolymer polyethylene at a concentration of 1.0 mg / mL (with zero comonomer content, melt index (I2) of 1.0 dg / min, and polydispersity (Mw / Mn) of approximately 2.6), and ● Reference material: Eicosan (2 mg / mL).

[0078] iCCD temperature calibration is performed in the following four steps: a. A step of calculating the delayed volume, which is defined as the temperature offset obtained by subtracting 30.0°C from the measured peak elution temperature of eicosane. b. A step of subtracting the temperature offset of the elution temperature from the unedited iCCD temperature data. This temperature offset is a function of experimental conditions such as the elution temperature and elution flow rate. c. A step of creating a linear calibration curve that converts the elution temperature over a range of 30.0°C to 140.0°C such that the linear homopolymer polyethylene reference material has a peak temperature of 101.0°C and eicosane has a peak temperature of 30.0°C. d. For soluble fractions measured isothermally at 30°C, elution temperatures below 30.0°C are linearly extrapolated by using an elution heating rate of 3°C / min, as described in Cerk et al., U.S. Patent No. 9,688,795(B2), column 12, lines 1-3 and Figure 1.

[0079] To prepare the sample, the polymer to be measured is mixed with ODCB at 4 mg / mL in the autosampler (unless otherwise specified) and shaken at 158°C for 1 hour. 200 μl of the sample is injected. The crystallization temperature profile is 110°C to 30°C, 3°C / min, thermal equilibrium is at 30°C for 2 minutes (including the soluble fraction elution time set to 2 minutes), and elution is performed at 30°C to 145°C, 3°C / min. The flow rate during crystallization is 0.0 ml / min. The flow rate during elution is 0.50 mL / min. Data is collected at 1 data point / second.

[0080] By assuming a shape factor of 1 and zero virial coefficients, the molecular weight of the polymer and the polymer fraction are determined directly from the light scattering detector (90-degree angle) and concentration detector (IR-5) according to the Rayleigh-Gans-Debys approximation (Striegel and Yau, Modern Size Exclusion Liquid Chromatogram, Pages 242 and 263). An integration window is set to integrate all chromatograms at an elution temperature in the range of 23.0 to 120°C (temperature calibration is specified above). Molecular weight calculation and calibration are performed using GPCOne® software.

[0081] Calculating molecular weight (Mw) from iCCD involves the following steps: ● Steps to measure the inter-detector offset. The offset is defined as the geometric volume offset between the light scattering detectors relative to the concentration detector. This is calculated as the difference in the 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 elution flow rate. ● The MW detector constant is calculated using HDPE samples with known weight-average molecular weights in the range of 100,000 to 140,000 g / mol, and the area ratio between the LS and the concentration integral signal. Linear high-density polyethylene (with zero comonomer content, a melt index of 1.0 (I2), and a polydispersity Mw / Mn of approximately 2.6 by conventional gel permeation chromatography) is used. The same experimental conditions as the above standard iCCD method are used, except for the following parameters: crystallization from 140°C to 137°C at 10°C / min, thermal equilibrium at 137°C for 1 minute as the soluble fraction elution time, a soluble fraction (SF) time of 7 minutes, and elution from 137°C to 142°C at 3°C / min. ● The flow rate during crystallization is 0.0 mL / min. ● The flow rate during elution is 0.80 mL / min. ● The sample concentration is 1.0 mg / mL. ● Shift each LS data point in the LS chromatogram to correct for the inter-detector offset before integration. Integrate the LS and concentration chromatograms with the baseline subtracted over the entire elution temperature range of step (1). ● The polymer's Mw is calculated using the ratio of the integrated light scattering detector (90-degree angle) to the concentration detector, and by using the MW detector constant.

[0082] The iCCD elution curve is "dW f / dT vs. dissolution temperature is displayed, dW f / dT represents the weight fraction (W) of the polymer that dissolves at temperature T. f ) is the result. Using the following equation, the weight percentage (w%) of the elution fraction from 25°C to 35°C is obtained. 25-35 ), and the weight percentage (w%) of the elution fraction from 35°C to 100°C. 35-100 ) calculate.

[0083]

number

[0084] Sealing Strength Test: A bag with internal dimensions of 15 cm wide x 20 cm high is created by sealing two layers of film together on three sides, leaving one side open for filling. Sealing is performed using a Lako SL-2 Digital Heat Sealer. The sealing conditions are as follows: Temperature: 200°C. Pressure: 6.8 psi. Sealing width: 1 mm. Residence time: 0.5 seconds. The bag is allowed to cool to room temperature before use.

[0085] The silicone oil is heated and equilibrated at 140°C.

[0086] Place an empty bag in a 1L container and pour 140°C hot oil into the bag. Immediately seal the bag and test it using a J&B Model 4000 HotTack tester with the following settings: Sample width: 25 mm. Sealing bar width: 5 mm. Sealing pressure: 0.275 MPa. Sealing time: 0.5 seconds. Cooling time: 24 hours. Peeling speed: 500 mm / min. [Examples]

[0087] The examples use the polymers shown in Table 1. iCCD analysis is performed on each polypropylene resin sample as described in the test method. The results are shown in Figure 1 and Table 1.

[0088] [Table 2]

[0089] Under the conditions shown in Table 2, the polymer from Table 1 is extruded as a three-layer film in a blow film extrusion line.

[0090] [Table 3]

[0091] Table 3 shows the content of each film. The films were tested for thickness, drop dart impact strength, tear resistance, high-temperature filling and sealing strength, and pinholes, and the results are shown in Table 3.

[0092] [Table 4]

[0093] Embodiment 1. A multilayer film comprising at least (A) a core layer containing a polyolefin polymer and (B) a heat-seal layer, wherein the heat-seal layer comprises a. 30 to 80 weight percent polypropylene copolymer, i. a polypropylene copolymer having an iCCD profile in which, based on the total weight of the polypropylene copolymer, at least 10 weight percent polypropylene copolymer is eluted at 25 to 35°C and at 35 to 100°C in an iCCD elution test at 25 to 150°C, at least 10 weight percent polypropylene copolymer is eluted at 25 to 35°C and at 30 weight percent polypropylene copolymer is eluted at 35 to 100°C, and b. a polypropylene copolymer having a density of 0.895 to 0.925 g / cc and a heat-seal layer containing 20 to 70 weight percent polyethylene copolymer having a melt index of less than 3 dg / min at 190°C.

[0094] Embodiment 2. A multilayer film according to Embodiment 1, wherein the core layer comprises polyethylene having a density of 0.895 to 0.930 g / cc and a melt index of less than 3 d g / min at 190°C.

[0095] Embodiment 3. A multilayer film according to Embodiment 1 or Embodiment 2, wherein the polypropylene copolymer in the heat-seal layer has a. a total ethylene content (Et) of 8 to 20 weight percent based on the total weight of the polypropylene copolymer, b. a density of 0.895 to 0.910 g / cc, and c. a melt index (I2) of 1 to 3 d g / min at 230°C.

[0096] Embodiment 4. A multilayer film according to Embodiments 1 to 3, wherein the core layer comprises 25 to 65 weight percent of polypropylene copolymer and 35 to 75 weight percent of polyethylene having a density of 0.895 to 0.930 g / cc and a melt index of less than 3 dg / min at 190°C.

[0097] Embodiment 5. A multilayer film according to Embodiments 1 to 4, wherein the core layer and the heat seal layer contain polyethylene having a density of 0.905 to 0.922 g / cc and a melt index of 0.1 to 1.0 dg / min at 190°C.

[0098] Embodiment 6. A multilayer film according to Embodiments 1 to 5, wherein the polypropylene copolymer has an iCCD elution profile in which 12 to 18 weight percent of the polypropylene copolymer elutes at a temperature of 25 to 35°C in an iCCD elution test at 25°C to 150°C.

[0099] Embodiment 7. A multilayer film according to Embodiments 1 to 6, wherein the polypropylene copolymer has an iCCD elution profile in which 10 to 20 weight percent of the polypropylene copolymer elutes at a temperature of 35 to 100°C in an iCCD elution test at 25°C to 150°C.

[0100] Embodiment 8. A multilayer film according to Embodiments 1 to 7, wherein the polypropylene copolymer in the heat-seal layer is an impact-resistant copolymer.

[0101] Embodiment 9. A multilayer film according to Embodiments 1 to 8, wherein the polypropylene copolymer in the heat-seal layer is an impact-resistant copolymer, and a. in an iCCD elution test at 25°C to 150°C, 12 to 18 weight percent of the polypropylene copolymer elutes at a temperature of 25°C to 35°C, and b. in an iCCD elution test at 25°C to 150°C, 10 to 20 weight percent of the polypropylene copolymer elutes at a temperature of 35°C to 100°C.

[0102] Embodiment 10. A multilayer film according to Embodiments 1 to 9, wherein the heat-seal layer contains 35 to 50 weight percent of polypropylene copolymer.

[0103] Embodiment 11. A multilayer film according to Embodiments 1 to 10, wherein the core layer comprises 25 to 65 weight percent of the polypropylene copolymer described in Embodiment 3, and 35 to 75 weight percent of polyethylene having a density of 0.895 to 0.930 g / cc and a melt index of less than 3 dg / min at 190°C.

[0104] Embodiment 12. A multilayer film according to Embodiments 1 to 11, wherein the core layer and the heat seal layer contain polyethylene having a density of 0.905 to 0.922 g / cc and a melt index of 0.1 to 1.0 dg / min at 190°C.

[0105] Embodiment 13. The heat seal layer is a. 35-50 weight percent polypropylene copolymer, i. the total ethylene content (Et) of the polypropylene copolymer is 8-20 weight percent based on the total weight of the polypropylene copolymer, ii. the density of the polypropylene copolymer is 0.895-0.910 g / cc, iii. the melt index (I2) of the polypropylene copolymer at 230°C is 1-3 dg / min, and iv. iCCD elution test at 25°C-150°C A multilayer film according to Embodiment 1, comprising a polypropylene copolymer in which 12-18 weight percent of the polypropylene copolymer elutes at a temperature of 25°C-35°C in a test, and 10-20 weight percent of the polypropylene copolymer elutes at a temperature of 35°C-100°C in an iCCD elution test at 25°C-150°C, and a polyethylene copolymer in which 50-65 weight percent has a density of 0.900-0.912 g / cc and a melt index of 0.5-1.5 dg / min.

[0106] Embodiment 14. A bag comprising one of the multilayer films described in Embodiments 1 to 13.

[0107] Embodiment 15. A process for packaging heated material, comprising: a. placing material having a temperature of at least 90°C into a bag of Embodiment 14 having one end open; and b. heat-sealing the open end of the bag to completely close the bag.

Claims

1. A multilayer film comprising at least (A) a core layer containing a polyolefin polymer and (B) a heat seal layer, wherein the heat seal layer is a) A polypropylene copolymer in a weight of 30 to 80 percent, i) Based on the total weight of the polypropylene copolymer, the total ethylene content (Et) is 5 to 30 weight percent, and ii) Density of 0.80 to 0.95 g / cc, and iii) Melt index of 5 dg / min or less at 230°C, and iv) A polypropylene copolymer having an iCCD profile in which, in an iCCD elution test at 25°C to 150°C, at least 10% by weight of the polypropylene copolymer is eluted at 25°C to 35°C, and 30% by weight or less of the polypropylene copolymer is eluted at 35°C to 100°C, and b) A multilayer film comprising a heat-seal layer containing 20 to 70 weight percent polyethylene copolymer having a density of 0.895 to 0.925 g / cc and a melt index of less than 3 d g / min at 190°C.

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

3. The polypropylene copolymer of the heat-seal layer a) Based on the total weight of the polypropylene copolymer, the total ethylene content (Et) is 8 to 20 percent by weight, and b) Density of 0.895 to 0.910 g / cc, and c) A multilayer film according to claim 1 or 2, having a melt index (I2) of 1 to 3 dg / min at 230°C.

4. The multilayer film according to any one of claims 1 to 3, wherein the core layer comprises 25 to 65 weight percent of the polypropylene copolymer and 35 to 75 weight percent of polyethylene having a density of 0.895 to 0.930 g / cc and a melt index of less than 3 d g / min at 190°C.

5. The multilayer film according to any one of claims 1 to 4, wherein the core layer and the heat seal layer contain polyethylene having a density of 0.905 to 0.922 g / cc and a melt index of 0.1 to 1.0 dg / min at 190°C.

6. The multilayer film according to any one of claims 1 to 5, wherein the polypropylene copolymer has an iCCD elution profile in which 12 to 18 weight percent of the polypropylene copolymer elutes at a temperature of 25 to 35°C in an iCCD elution test at 25°C to 150°C.

7. The multilayer film according to any one of claims 1 to 6, wherein the polypropylene copolymer has an iCCD elution profile in which 10 to 20 weight percent of the polypropylene copolymer elutes at a temperature of 35 to 100°C in an iCCD elution test at 25°C to 150°C.

8. The multilayer film according to any one of claims 1 to 7, wherein the polypropylene copolymer in the heat-seal layer is an impact-resistant copolymer.

9. The polypropylene copolymer in the heat seal layer is an impact-resistant copolymer. a) In an iCCD elution test at 25°C to 150°C, 12 to 18 weight percent of the polypropylene copolymer eluted at a temperature of 25°C to 35°C. b) A multilayer film according to any one of claims 1 to 8, wherein in an iCCD elution test at 25°C to 150°C, 10 to 20 weight percent of the polypropylene copolymer elutes at a temperature of 35°C to 100°C.

10. The multilayer film according to any one of claims 1 to 9, wherein the heat-seal layer comprises 35 to 50 weight percent of the polypropylene copolymer.

11. A multilayer film according to any one of claims 1 to 10, wherein the core layer comprises 25 to 65 weight percent of the polypropylene copolymer according to claim 3, and 35 to 75 weight percent of polyethylene having a density of 0.895 to 0.930 g / cc and a melt index of less than 3 d g / min at 190°C.

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

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

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

15. A process for packaging heated materials, a) A step of placing a material having a temperature of at least 90°C into a bag according to claim 14, which has one end open, b) A process comprising the step of heat-sealing the open end of the bag to completely close the bag.

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