FLAT-BOTTOM BAG MADE WITH RECYCLED POLYETHYLENE

Abstract

In some embodiments, a flat-bottom pouch (SUP) is prepared using a polyethylene structure with a first and a second band. The bands are laminated together to form the polyethylene structure used to prepare the SUP. One band contains a layer of recycled polyethylene (r.PE). In some cases, the use of r.PE has been observed to reduce the effectiveness of the sealing layer of the overall structure. In some embodiments, the SUP described herein has a two-layer sealing system to mitigate this problem.

Description

FLAT-BOTTOM BAG MADE WITH RECYCLED POLYETHYLENE Field of Invention This description refers to a laminated structure prepared by laminating a first polyethylene strip to a second polyethylene strip. This laminated structure is suitable, for example, for making a stand-up pouch (SUP). The SUP is made from recycled polyethylene and is recyclable. Background of the Invention Flat-bottom pouch (SUP) packaging is widely used commercially for consumer goods. These pouches are appealing to consumers and, when properly designed, make very efficient use of a minimal amount of polymer material to prepare the packaging. SUP packaging was first produced over 30 years ago. An initial design used a laminated material of one layer of polyethylene terephthalate (PET) and one layer of polyethylene (PE). This type of design is still used commercially with a typical structure that has a thin layer (approximately 0.0127 mm (0.5 mils) or 0.12 mm thick) of PET and a thicker layer (approximately 0.0762 mm (3 mils) or 0.75 mm) of PE. Ref. 331066 One problem with this SUP design is that the bags are difficult to recycle due to the different construction materials. It is already known how to prepare a recyclable SUP made solely from polyethylene (or at least 95% PE, since many recycling facilities can recycle a coextruded or laminated film containing at least 95% PE as pure PE material). For example, US Patent Application Publication No. 2016 / 0229,157 (from NOVA Chemicals) describes a SUP containing at least 95% PE by weight and is therefore recyclable. Another requirement is the use of recycled polyethylene (r.PE) in new bags. It has been observed that including r.PE in a SUP can reduce the effectiveness of the sealing layer in the film structure used to prepare the SUP. It has now been discovered that a two-layer sealing system mitigates this problem and provides improved sealing effectiveness. Brief Description of the Invention This document describes laminated structures made of polymeric materials, the laminated structure including: A) an outer band that includes: Al) a first layer A comprising a pRcznn / zznz / E / YiAi composition of HDPE, and A. 2) a second layer A comprising polyethylene selected from LLDPE, MDPE, and HDPE; B) an inner band that includes: Bl) a first layer B that is in contact with the outer band, wherein the first layer B includes polyethylene selected from LLDPE and MDPE, B.2) a second layer B that includes recycled polyethylene, and B.3) a sealing structure that includes: B.3.1) a sealing surface layer including a polyethylene sealant, and B.3.2) a layer adjacent to the sealing surface layer that includes a polyethylene having a density that is a) greater than the density of the polyethylene sealant and b) less than the density of the central layer that is in contact with the layer adjacent to the sealing surface layer; and wherein I) the outer band is laminated to the inner band, and II) HDPE, MDPE, LLDPE, recycled polyethylene and polyethylene sealant collectively make up at least 95% by weight of the polymeric materials used to prepare the laminated structure. This document describes laminated structures made of polymeric materials, the laminated structure including: pRcznn / zznz / E / YiAi A) an outer band that includes: A) a first layer A that includes an HDPE composition, A. 2) a second layer A comprising polyethylene selected from LLDPE, MDPE, and HDPE, and A. 3) a third layer A comprising polyethylene selected from LLDPE, MDPE, and HDPE; B) an inner band that includes: Bl) a first layer B that is in contact with the outer band, wherein the first layer B includes polyethylene selected from HDPE, LLDPE and MDPE, B.2) a second layer B that includes recycled polyethylene, and B.3) a sealing structure that includes: B.3.1) a sealing surface layer including a polyethylene sealant, and B.3.2) a layer adjacent to the sealing surface layer that includes a polyethylene having a density that is a) greater than the density of the polyethylene sealant and b) less than the density of the central layer that is in contact with the layer adjacent to the sealing surface layer; and wherein I) each of the outer and inner bands optionally comprises at least one additional layer of polyethylene between Al and A.3 and Bl and B.3, pRcznn / zznz / E / YiAi II) the outer band is laminated to the inner band, and III) HDPE, MDPE, LLDPE, recycled polyethylene and polyethylene sealant collectively make up at least 95% by weight of the polymeric materials used to prepare the laminated structure. Brief Description of the Figures Figures 1 and 2 illustrate the properties of the stamps prepared using different internal bands. Detailed Description of the Invention In one configuration, the polymeric material used to manufacture the SUP includes different types of polyethylene. In another configuration, the polymeric material used to manufacture the SUP consists essentially of different types of polyethylene; that is, the only polymeric material used to manufacture the SUP in this configuration is polyethylene. The term polyethylene refers to polymers that contain ethylene and may contain an optional comonomer. Suitable examples of polyethylene include: 1) High-density polyethylene (HDPE) - a homopolymer or copolymer of polyethylene that has a density of approximately 0.95 to approximately 0.97 g / cc; 2) Medium-density polyethylene (MDPE) - a polyethylene copolymer having a density of approximately 0.93 to approximately 0.95 g / cc; 3) Linear low-density polyethylene (LLDPE) - a polyethylene copolymer having a density of approximately 0.915 to approximately 0.93 g / cc; and 4) a polyethylene sealant: a polyethylene material that is suitable for the preparation of a thermoformed seal or, for example, a polyethylene selected from 1) a polyethylene copolymer having a density of approximately 0.88 to 0.915 g / cc (VLDPE); and 2) a high-pressure low-density (LD) polyethylene - a polyethylene homopolymer prepared with a free radical initiator in a high-pressure process, having a density of approximately 0.91 to approximately 0.93 g / cc. In some embodiments, only the outer band comprises a layer of HDPE. In another embodiment, both the inner and outer bands of the laminated structure include HDPE in at least one layer. The HDPE layers provide stiffness / hardness to the SUP. In one embodiment, these HDPE layers are separated by at least one layer of lower-density polyethylene (such as LLDPE), and this lower-density polyethylene provides impact and puncture resistance. Furthermore, by separating the layers of rigid HDPE, the overall stiffness and torsional strength of the SUP are improved compared to a structure containing an equivalent amount / thickness of HDPE in a single layer—in a manner that could be referred to as an I-beam effect (by analogy with the steel I-beams that are widely used in building construction). The adjacent layer is in contact with the sealing surface layer on one side and, on the other side of the material adjacent to the layer, is in contact with a core layer. The material adjacent to the layer includes a polyethylene composition that has a density greater than the density of the sealing surface layer but less than the density of the core layer with which it is also in contact. In one embodiment, the polyethylene composition is a mixture of polyethylenes; in another embodiment, it includes only one type of polyethylene. In embodiments where the inner and outer bands optionally comprise at least one additional polyethylene layer between A1 and A.3 and B1 and B.3, the additional layers include polyethylene compositions comprising HDPE, MDPE, LLDPE, or combinations thereof. In these additional embodiments, these layers consist of HDPE, MDPE, LLDPE, or combinations thereof. In these additional embodiments, these layers include recycled polyethylene. Those skilled in the art will appreciate that when preparing a multi-layer blown film on a multi-layer line, each layer can be produced by a single line, or a layer can result from multiple consecutive lines producing layers of identical composition in successive layers. As an example, a five-layer line could produce a structure of compositions A / B / C / D / E, producing a 5-layer film. Alternatively, the same five-layer line could be used to create a 5-layer film of composition A / A / B / C / C, effectively producing a three-layer film. In some forms, the laminated structure of this description is suitable for the preparation of a flat bottom bag (SUP). SUP packaging is well known. Typically, it is prepared from a roll material (i.e., a film - or a laminated structure as described in this document) using a variety of well-known techniques and machines. SUPs are manufactured in many sizes and are typically used to package consumer goods in small quantities (e.g., from approximately 0.635 mm (25 thousandths of an inch) to 2 liters). The contents of SUP packages are typically described as flowable—the term flowable being proposed to encompass particulate solids (such as candy, nuts, and breakfast cereals); liquids (e.g., beverages); and pastes / emulsions / purees (such as yogurt and baby food). In one embodiment, the SUP is designed to allow the contents of the opened package to flow easily from (and / or be consumed directly from) the SUP. For example, the top of the SUP may be fitted with an integral straw (for beverages) or a spout for pastes, emulsions, purees, and the like. Such designs are well known and an example is described in Canadian Patent Application Serial No. 2,612,940 (Rogers). In some models, the SUP typically opens at the top of the packaging. The SUP can be opened with a tear strip; or an accessory (or cap) that allows the packaging to be resealed; or other caps / closures, etc., known to those skilled in the technique. In one mode, the laminated structure is printed on the interface between the two bands - that is, either on the inner surface of the first band or on the outer surface of the second band. Detailed descriptions are provided below of various first (outer) band configurations; various second (inner) band configurations; various adhesive configurations; and various printing configurations. In one embodiment, the first (outer) band forms the outer wall of the laminated structure. In one mode, the laminated structure is printed on the interface between the first band and the second band pRcznn / zznz / E / viAi (internal). Because the print is viewed through the outer band, in some formats, low haze values ​​on the outer band may be desirable. Additionally, in some formats, high gloss may be desirable, as many consumers perceive a high-gloss finish as an indication of high quality. Furthermore, in some modalities, it is desirable that the outer layer provides hardness / rigidity to the laminated structure so that a SUP made from the laminated structure is self-supporting. Therefore, a balance of good optical properties and hardness may be desired for the outer web. HDPE is known to provide the desired hardness, but it is also known to have poor optical properties. Consequently, in one embodiment, a very thin layer of HDPE is used as a surface layer in the outer web, along with a layer of lower-density polyethylene. Additional descriptions of these modalities are provided below. Multi-layer outer band, or A band In general, using a thick, single-layer HDPE film to form the outer band of a SUP could provide a structure with adequate rigidity. However, a thick HDPE layer can have poor optical properties. This could be resolved by printing on the outer (surface) side of the outer band to create an opaque SUP. However, this design might not be very resistant to wear and tear, as the print can be easily scratched and damaged during shipping and handling. In one embodiment, the structure described in this document mitigates these problems by providing a coextruded multi-layer film for the outer band in which at least one layer (layer A1) is prepared from HDPE and at least one layer (layer A.2) is prepared from a lower density polyethylene (such as LLDPE, LD, or VLDPE). In one modality, HDPE is also characterized by having a melting index, I2, of 0.1 to 10 (or, for example, 0.3 to 3) grams / 10 minutes. In one embodiment, the first layer A is an HDPE composition that includes a nucleating agent. In one modality, LLDPE is also characterized by having a melting index, I2, of 0.1 to 5 (or, for example, 0.3 to 3) grams / 10 minutes. In one embodiment, LLDPE is further characterized by being prepared using a single-site catalyst (such as a metallocene catalyst) and by having a molecular weight distribution, Mw / Mn (i.e., weighted average molecular weight divided by numerical average molecular weight) of approximately 2 to approximately 4. This type of pAcznn / zznz / E / YiAi LLDPE is typically referred to as sLLDPE. In one embodiment, very low-density polyethylene (VLDPE) is a copolymer of ethylene that has a density of approximately 0.88 to 0.915 g / cc and a melt index, I2, of approximately 0.5 to 10 g / cc. All of the materials described above are well known and commercially available. Lower-density polyethylene can improve the optics of the multilayer web. In one embodiment, the multilayer structure is a three-layer coextruded film of the A / B / A type, where A is an LLDPE (e.g., a single-site catalyzed LLDPE) and B is an HDPE composition. This type of film provides excellent optical properties—to the point where, in some embodiments, some of these films have been observed to have better optical properties than a single-layer film made from the same LLDPE. In another embodiment, the LLDPE used in band A is mixed with a smaller amount (0.2 to 10% by weight) of an LD polyethylene having a melt index, I2, of 0.2 to 5, or, for example, 0.2 to 0.8. Certain LLDPE blends, and LLDPE and LD blends, have been observed to have superior optical properties and greater hardness compared to LLDPE alone (particularly when the LLDPE is an sLLDPE). In some modalities, it has been observed that the use of an LD resin that has a melting index of approximately 0.2 to 0.8 grams / 10 minutes will be effective for this purpose (and experts in the technique commonly refer to this type of LD resin as fractional melt LD). In another modality, the LLDPE used in band A is mixed with a smaller amount (0.2 to 10% by weight) of an HDPE resin and a nucleating agent. The term nucleating agent, as used herein, is proposed to convey to those skilled in the art its conventional meaning of preparing nucleated polyolefin compositions, primarily an additive that changes the crystallization behavior of a polymer as the polymer melt cools. Examples of conventional nucleating agents that are commercially available and widely used as polypropylene additives are sorbital dibenzylidene esters (such as products sold under the trademark MILLAD® 3988 by Milliken Chemical and IRGACLEAR® by Giba Specialty Chemicals). In some embodiments, the nucleating agents must be well dispersed in the polyethylene. In some embodiments, the amount of nucleating agent used is comparatively small—from 200 to 10,000 parts per million by weight (based on the weight of the polyethylene)—so those skilled in the art will appreciate that some care must be taken to ensure that the nucleating agent is well dispersed. In some embodiments, the nucleating agent is added in finely divided form (less than 50 microns, or, for example, less than 10 microns) to the polyethylene to facilitate mixing. Examples of nucleating agents that may be suitable for use include the cyclic organic structures described in U.S. Patent No. 5,981,636 (and salts thereof, such as disodium bicyclo[2.2.1]heptene dicarboxylate); saturated versions of the structures described in U.S. Patent No. 5,981,636 (as described in U.S. Patent No. 6,465,551; Zhao et al., Milliken); salts of certain cyclic dicarboxylic acids having a hexahydrophthalic acid (or HHPA) structure as described in U.S. Patent No. 6,599,971 (Dotson et al., Milliken); Phosphate esters, such as those described in U.S. Patent No. 5,342,868 and those sold under the trade names NA-11 and NA-21 by Asahi Denka Kogyo, and metallic salts of glycerol (or, for example, zinc glycerolate). The calcium salt of 1,2-cyclohexanedicarboxylic acid, the calcium salt (no.(CAS Registry No. 491589-22-1), typically provides good results for the nucleation of pRcznn / zznz / E / YiAi of HDPE. The nucleating agents described above could be described as organic (in that they contain carbon and hydrogen atoms) to distinguish them from inorganic additives such as talc and zinc oxide. Talc and zinc oxide are commonly added to polyethylene (to provide antiblocking and acid scavenging, respectively) and provide some limited nucleation functionality. The organic nucleating agents described above may be better (but more expensive) than inorganic nucleating agents. In one embodiment, the amount of organic nucleating agent is 200 to 2000 parts per million (based on the total weight of the polyethylene in the layer containing the nucleating agent). In some forms, these LLDPE / HDPE / nucleating agent blends have also been found to provide superior optical properties and a higher modulus (greater hardness) than 100% LLDPE. In another embodiment, the outer band is a three-layer coextruded film of the A / B / A type, where A is HDPE and B is a lower-density polyethylene, for example, the LLDPE compositions described above (including LLDPE compositions that are blends with LD compositions and LLDPE that are blends with HD and a nucleating agent). These films provide good rigidity. B. Inner band - (with recycled polyethylene); also band B; also sealing band The inner band forms the interior of a SUP that is prepared from the laminated structure. Bl) a first layer B that is in contact with the outer band, wherein the first layer B includes polyethylene selected from HDPE, LLDPE and MDPE, B.2) a second layer B that includes recycled polyethylene, and B.3) a sealing structure that includes: B.3.1) a sealing surface layer including a polyethylene sealant, and B.3.2) a layer adjacent to the sealing surface layer that includes a polyethylene having a density that is a) greater than the density of the polyethylene sealant; and b) less than the density of the central layer that is in contact with the layer adjacent to the sealing surface layer. Bl Surface layer of the interface A surface layer of the inner belt is prepared from a polyethylene composition that has a lower density than HDPE to provide a layer with improved impact and tear resistance properties compared to layers prepared from HDPE. In one embodiment, this layer is made predominantly of LLDPE (including sLLDPE) that has a melting index of pRcznn / zznz / E / YiAi 0.3 to 3 grams for 10 minutes. The layer can also be prepared using a larger amount of LLDPE (or sLLDPE) and a smaller amount of LD (e.g., a fractional melt LD, as described above) or the LLDPE + HDPE + nucleating agent mixture as described above. In another modality, this surface layer can be prepared with MDPE (or a mixture of MDPE with a smaller amount of another polyethylene, such as the mixtures with LD, and the mixtures with HDPE and the nucleating agent described above). In one form, this surface layer is printed. Accordingly, this description includes incorporating any of the well-known film modifications that facilitate the printing process. For example, the surface layer may undergo corona arc treatment to improve ink adhesion. Alternatively, the surface layer may contain an opacifying agent (such as talc, titanium oxide, or zinc oxide) to enhance the appearance of the printed surface. B.2 A central layer that includes recycled polyethylene (r.PE) The inner band includes at least one layer containing r.PE. The inner band includes a central layer containing r.PE. In one embodiment, the central layer consists essentially of r.PE (i.e., the entire polymer used in this layer is r.PE). There are many sources and types of recycled polyethylene that are useful for the various applications described in this document. As used here, the term recycled polyethylene (or r.PE) refers to recycled polyethylene regardless of its source. In one example, recycled polyethylene is any polyethylene that has been exposed to at least one heating process—that is, that has been melted, molded, or extruded at least once. In one instance, r.PE can be post-industrial recycled (PIR) material, which generally refers to polyethylene that has been used in a manufacturing process but has not been sold to an end consumer (such PIR polyethylene is commonly produced as scrap, offcuts, or unspecified parts in a manufacturing process—it is recovered for reuse either in the same process or, alternatively, it may be sold to other manufacturers / converters for use in a different process). In one form, r.PE is post-consumer recycled polyethylene (or PCR). PCR is recovered from waste streams and cleaned before reuse. In one specific modality, PCR is prepared from recycled liquid containers (e.g., milk or juice). The r.PE can have a density of 0.910 to 0.97 g / cc pRcznn / zznz / E / YiAi and a melting index, I2, of 0.2 to 20. In one form, r.PE has a density of 0.93 to 0.95 g / cc and a melting index, I2, of 0.2 to 10. In other modalities, the density is from 0.910 to 0.930, or from 0.930 to 0.950, or from 0.950 to 0.960. B.3 Sealant structure: sealing layer (B.3.1) and adjacent or following layer (B.3.2) The inner band has two outer layers, or surface layers, primarily the interface surface layer (layer B1, above) and the inner surface layer, also referred to in this document as the sealing layer (B.3.1). The sealing layer is prepared from a polyethylene sealant—that is, a type of polyethylene that readily melts and forms seals when subjected to sealing conditions. Those skilled in the art will recognize that two types of polyethylene are preferred for use as sealants, primarily: polyethylene copolymers having a density of approximately 0.88 to 0.915 g / cc; and LD polyethylene (as described above). In some applications, lower-density polyethylene copolymers are preferred. As a general rule, the cost of these lower-density polyethylenes increases with decreasing density, so the optimal polyethylene sealant resin will typically be the highest-density polyethylene that provides satisfactory sealing strength. A polyethylene sealant with a density of approximately 0.900 to 0.914 g / cc will provide satisfactory results for many applications. Other examples of polyethylene sealants include ethylene-vinyl acetate (EVA) and ionomers (e.g., copolymers of ethylene and an acid comonomer, with the resulting acid comonomer being neutralized, e.g., by means of sodium, zinc, or lithium; ionomers are commercially available under the registered trademark SURLYN®). The use of EVA and / or ionomers is less preferred because they can cause difficulties when the SUP is recycled (however, as noted above, many recycling facilities will accept a SUP containing up to 5% EVA or ionomer for recycling). B.3.2 Next layer adjacent to It has been observed that the use of recycled PE in the inner band has reduced the effectiveness of the sealing layer (compared to an inner band made with virgin HDPE instead of recycled PE). The reasons for this are not fully understood. However, it has been observed that the use of a selected polyethylene in the layer that is in contact with (or adjacent to) the sealing layer improves seal performance. For the sake of clarity: the sealing layer (described above) is a surface layer used to seal the SUP, and the layer adjacent to it is a core layer that is adjacent to / in contact with the sealing layer and is also in contact with another core layer. In one embodiment, the layer adjacent to it has a density of 0.917 to 0.921 g / cc. In some embodiments, the sealing layer B.3.2 (the one adjacent to the layer) may include recycled polyethylene alone or blended with virgin polyethylene.In these modalities, the density of the selected polyethylene, the recycled polyethylene, or the mixture of the two, meets the relative densities, allowing the layer adjacent to the sealing surface layer to have a polyethylene that has a density that is a) greater than the density of the polyethylene sealant; and b) less than the density of the central layer that is in contact with the layer adjacent to the sealing surface layer. In one embodiment, the rLLDPE has a density of 0.927 g / cm3 and is mixed with a VLDPE that has a density of 0.914 g / cm3. In one embodiment, the rLLDPE has a density of 0.928 g / cm3 and is mixed with a VLDPE that has a density of 0.912 g / cm3. B.5 HDPE In one embodiment, the inner band also includes at least one layer prepared from a pRcznn / zznz / E / YiAi composition of HDPE, which optionally includes a nucleating agent. In one embodiment, the second layer B includes an HDPE composition that includes a nucleating agent. HDPE is a common commercial item. Most commercially available HDPE is prepared from a catalyst containing at least one metal (e.g., chromium or a group IV transition metal such as Ti, Zr, or Hf). HDPE manufactured from a Cr catalyst typically contains some long-chain branching (LCB). HDPE manufactured from a Group IV metal generally contains less LCB than HDPE manufactured from a Cr catalyst. As used in this document, the term HDPE refers to a polyethylene (or a composition of the polyethylene blend, as the context requires) that has a density of approximately 0.95 to 0.97 grams per cubic centimeter (g / cc). In one embodiment, the melt index (I2) of HDPE is approximately 0.2 to 10 grams per 10 minutes. In one embodiment, HDPE is supplied as a blend composition that includes two HDPEs with melt values ​​that are separated by at least ten. Further details of this HDPE blend composition are provided below. Composition of the HDPE mixture Mixture components Component a) of the mixture Component (a) of the polyethylene composition blend used in this embodiment includes an HDPE with a comparatively high melt index. As used herein, the term melt index is proposed to refer to the value obtained per ASTM D 1238 (when carried out at 190°C, using a weight of 2.16 kg). This term is also referred to herein as I² (expressed as grams of polyethylene that flow during the 10-minute test period, or grams / 10 minutes). As those skilled in the art will recognize, the melt index, I², is generally inversely proportional to the molecular weight. In one embodiment, component (a) of the blend has a comparatively high melt index (or, as stated alternatively, a comparatively low molecular weight) compared to component (b) of the blend. The absolute value of I2 for component a) of the mixture in these mixtures is generally greater than 5 grams / 10 minutes. However, the relative value of I2 for component a) of the mixture is more important and should generally be at least 10 times higher than the value of I2 for component b) of the mixture [whose I2 value for component b) of the mixture is referred to in this document as I2']. Therefore, for illustrative purposes: if the I2' value of component b) of the mixture is 1 gram / 10 minutes, then the I2 value of component a) of the mixture is, for example, at least 10 grams / 10 minutes. In one embodiment, component a) of the mixture may be further characterized by: i) having a density of 0.95 to 0.97 g / cc; and ii) being present in an amount of 5 to 60% by weight of the total HDPE mixture composition (with component b) of the mixture forming the remainder of the total composition), in amounts of 10 to 40% by weight, or, for example, 20 to 40% by weight. The use of more than one high-density polyethylene to form component a) of the mixture is permitted. The molecular weight distribution is determined by dividing the weighted average molecular weight (Mw) by the numerical average molecular weight (Mn), where Mw and Mn are determined by gel permeation chromatography, according to ASTM D 6474-99. The Mw / Mn of component a) is, for example, 2 to 20, or, for example, 2 to 4. Although not intended to be limited by theory, it is believed that a low Mw / Mn value (2 to 4) for component a) may improve the crystallization rate and overall barrier performance of blown films and web structures prepared according to this description. Component b) of the mixture Component b) of the mixture is also a high-density polyethylene having a density of 0.95 to 0.97 g / cc (e.g., 0.955 to 0.968 g / cc). The melting index of component b) of the mixture is also determined using ASTM D 1238 at 190 °C with a 2.16 kg load. The melting index value for component b) of the mixture (referred to herein as I2') is lower than that of component a) of the mixture, indicating that component b) of the mixture has a comparatively higher molecular weight. The absolute value of I2' is, for example, 0.1 to 2 grams / 10 minutes. The molecular weight (Mw / Mn) distribution of component b) is not critical for success, although an Mw / Mn of 2 to 4 is an example for component b). Finally, the ratio of the melting index of component b) divided by the melting index of component a) is, for example, greater than 10 / 1. Component b) of the mixture may also contain more than one HDPE resin. General composition of the HDPE mixture The overall composition of the high-density blend is formed by mixing blend component a) with blend component b). In one embodiment, this overall HDPE blend has a melt index (ASTM D 1238, measured at 190 °C with a 2.16 kg load) of 0.5 to 10 grams / 10 minutes (e.g., 0.8 to 8 grams / 10 minutes). The blends can be made by any mixing process, such as: 1) physical mixing of the particulate resin; 2) co-feeding of different HDPE resins to a common extruder; 3) melt mixing (in any conventional polymer mixing apparatus); 4) solution mixing; or 5) a polymerization process employing 2 or more reactors. A suitable HDPE blend composition can be prepared by molten blending the following two blend components in an extruder: 10 to 30% by weight of component a): where component a) is an HDPE resin having a melt index, I2, of 15 to 30 grams / 10 minutes and a density of 0.95 to 0.97 g / cc, with 90 to 70% by weight of component b): where component b) is an HDPE resin having a melt index, I2, of 0.8 to 2 grams / 10 minutes and a density of 0.95 to 0.97 g / cc. An example of a commercially available HDPE resin suitable for component a) is sold under the trade name SCLAIR® 79F, which is an HDPE resin prepared by homopolymerization of ethylene with a conventional Ziegler-Natta catalyst. It has a typical melt index of 18 grams / 10 minutes, a typical density of 0.963 g / cc, and a typical molecular weight distribution of approximately 2.7. Examples of commercially available pAcznn / zznz / E / YiAi HDPE resins that are suitable for component b) of the mixture include (with typical melt index and density values ​​shown in parentheses): SCLAIR® 19G (melt index = 1.2 grams / 10 minutes, density = 0.962 g / cc); MARFLEX® 9659 (available from Chevron Phillips, melt index = 1 gram / 10 minutes, density = 0.962 g / cc); and ALATHON® L 5885 (available from Equistar, melt index = 0.9 grams / 10 minutes, density = 0.958 g / cc). In some embodiments, the HDPE blend composition is prepared by a solution polymerization process using two reactors operating under different polymerization conditions. This provides a relatively uniform blend of the HDPE blend components. An example of this process is described in U.S. Patent No. 7,737,220 (Swabey et al.). In one formulation, the HDPE composition is prepared using only ethylene homopolymers. This type of composition is suitable if it is desired to optimize (maximize) the barrier properties of the structure. In another approach, HDPE compositions can be prepared using copolymers, as this will allow for some improvement in physical properties, such as impact resistance. In yet another approach, a smaller quantity (less than 30% by weight) of a lower-density polyethylene can be mixed into the HDPE composition (as this can again improve impact resistance). In one embodiment, the HDPE blend composition described above is combined with an organic nucleating agent (as previously described) in an amount of approximately 300 to 3000 parts per million by weight, based on the weight of the HDPE blend composition. The calcium salt (previously described) of 12-cyclohexanedicarboxylic acid, the calcium salt (CAS 491589-221), is suitable. In some embodiments, the use of an HDPE composition prepared with a group IV transition metal (e.g., Ti) is preferred when the HDPE composition contains a nucleating agent. It has been observed that this type of nucleated core layer provides outstanding barrier properties (i.e., reduced transmission of water, gas, and grease), which is desirable for many packaging applications. In some modalities, it has been observed that the presence of the nucleating agent improves the modulus of the HDPE layer (compared to a non-nucleated layer of equivalent thickness). The use of a nucleated HDPE blend composition of the type described above provides a barrier to oxygen and water transmission. The performance of this barrier layer is adequate for many products. However, those skilled in the art will recognize that improved barrier performance can be achieved through the use of certain barrier polymers, such as ethylene-vinyl alcohol (EVOH), ionomers, and polyamides. The use of large quantities of such non-polyethylene barrier resins can make it very difficult to recycle films, structures, and SUPs manufactured with a combination of polyethylene and non-polyethylene materials. However, it is still possible to recycle such structures if the quantities (less than 10% by weight, especially less than 5% by weight) of the non-polyethylene materials are low. Those skilled in the technique will also recognize that, in some modalities, the use of certain barrier resins other than polyethylene may require the use of a bonding layer to allow adhesion between the non-polyethylene barrier layer and the remaining polyethylene layers. Printing process As previously mentioned, in some applications, the laminated structure described here is printed at the interface between the two webs. Suitable processes include the well-known rotogravure and flexographic printing techniques, which typically use nitrocellulose or water-based inks. pRcznn / zznz / E / YiAi The outer band (described above) forms the exterior of the SUP, and the inner band forms the interior of the SUP. Those skilled in the art commonly refer to the outer band as the printed band and the inner band as the sealing band. Lamination / manufacturing process One step in the manufacture of the laminated structure requires laminating the first strip to the second strip. Many commercially available techniques exist for this lamination step, including the use of a liquid adhesive (which may be solvent-based, solvent-free, or water-based); a hot melt adhesive; and thermal bonding. The SUP packs described above are laminated. Those skilled in the art will understand that a similar SUP could be produced by coextrusion (using the same materials in the same layers as the laminated SUP). However, laminated SUP can be printed on the web interface (whereas coextruded SUP is printed on a surface layer) – consequently, the print quality (and scratch resistance) of laminated SUP is superior. In one configuration, the inner band B has a total thickness equal to the thickness of band A. In other configurations, band B can be from approximately twice that of outer band A to 5 times that of outer band A. In one form, the total thickness of the inner band is 0.0330 to 0.1524 mm (1.3 to 6.0 thousandths of an inch), 0.0457 to 0.0660 mm (1.8 to 2.6 thousandths of an inch), or, for example, 0.0508 to 0.0635 mm (2.0 to 2.5 thousandths of an inch). In one configuration, the thickness of the first layer is up to 10–20% (of the total thickness of the three layers); the second layer is 40–70%; the third layer is 10–15%; the fourth layer is 10–20%; and the fifth layer is 10–20%. However, someone skilled in the art would recognize that, with equipment capable of up to nine layers, further division of the structure can be achieved as more layers become available. It should be noted that the first and second layers could be further divided into multiple layers by adding a component to modify the sealing strip's properties beyond those directly related to sealing. Such properties could include a moisture barrier or the desire to increase the PCR content of the overall sealing strip. The maximum number of total layers will be limited by the number of layers possible in a single extrusion unit (known as a coextrusion blown film line).Furthermore, an expert in the technique might recognize that each extrusion unit capable of manufacturing, for example, nine layers, can nevertheless be used to manufacture films composed of fewer layers. In another embodiment, the inner band also includes a barrier layer, where the barrier layer is located between the first B layer and the second B layer. In some embodiments, the barrier layer includes EVOH, with the additional condition that the total weight of the barrier layer is less than 5% by weight, based on the combined weight of EVOH and the total weight of polyethylene used in the entire structure. In another embodiment, two bonding layers are included, such that a first bonding layer is located on one side of the barrier layer and a second bonding layer is located on the other side of the barrier layer. In other forms, the outer band A may have a thickness of approximately 0.0254 (1 thousandth of an inch) to approximately 0.0355 mm (1.4 thousandths of an inch) and the inner band may have a thickness of approximately 0.0508 (2) to approximately 0.0768 mm (3 thousandths of an inch). In another embodiment, the outer band includes an outer surface layer made of HDPE (having a thickness of, for example, approximately 0.0203 mm (0.8 mils)) and an LLDPE layer having a thickness of, for example, approximately 0.0101 mm (0.4 mils). In this embodiment, the inner layer may be an A / B / C structure, wherein layer A is made of LLDPE (having a thickness of, for example, approximately 0.0101 mm (0.4 mils)); Layer B is made of nucleated HDPE (which has a thickness of, for example, approximately 0.0381 mm (1.5 thousandths of an inch)) and layer C is a sealing resin (such as VLDPE) which has a thickness of, for example, approximately 0.0076 mm (0.3 thousandths of an inch). Those skilled in the technique will recognize that the thickness described above can be easily modified to change the physical properties of the SUP. For example, the thickness of the HDPE layers can be increased (if a stiffer SUP is desired) or the thickness of the LLDPE layer(s) can be increased to improve impact resistance. The total thickness of the laminated structure (i.e., the outer and inner bands) ranges from approximately 0.0762 mm (3 mils) to approximately 0.1016 mm (4 mils) in one modality. The SUP is then prepared from the laminated structure using techniques and machinery known to those skilled in the art. In one modality, the laminated structure is sealed using heat seals to form the SUP. In another modality, the seals can be formed using ultrasonic sealing. Examples The following briefly describes the test procedures for characterizing SUP packaging. pRcznn / zznz / E / YiAi 1. Melting index: I2, was determined in accordance with ASTM D1238. [Note: I2 measurements were performed on a 2.16 kg weight at 190 °C]. Test results were reported in units of grams / 10 minutes or, alternatively, decigrams / minute (dg / min). 2. Density was determined using the displacement method in accordance with ASTM D792. 3. The brightness was determined by ASTM D2457. 4. Turbidity was determined by ASTM D1003. List of materials The following polyethylenes were used in the examples. pRcznn / zznz / E / YiAi Resin Type Melt Index (g / 10 min) Density (g / cc) Comonomer Band 1. ZN-1 1 0.958 none printed 2. ZN-2 0.8 0.934 hexene both 3. ZN-3 0.55 0.934 octene seal 4. DCT-1 1 0.914 octene sealer 5. DCT-2 4 0.912 octene sealer 6. SSC-1 .nuc 1.2 0.967 none sealer 7. rLLDPE 1.5 0.928 octene sealer 8. rHDPE-1 0.6 0.962 blended sealer 9. rHDPE-2 0.6 0.960 blended sealer The prefix ZN indicates that the polyethylene was prepared using a Ziegler Naphtha catalyst system. The prefix SSC indicates that the polyethylene was prepared using a single-site catalyst system. The term - (nuc) indicates that the resin contains a nucleating agent (target point of 1200 parts per million by weight of a commercially available nucleating agent sold under the trade name HYPERFORM® 20E by Milliken Chemicals). External band Four blown films were prepared as candidates for the outer band of the flat-bottom bag. The films were prepared on a conventional blown film line. The total thickness of all films was 0.059 mm (2.35 mils). Films 1.1 and 1.4 were made from a single resin. Films 1.2, 1.3, and 1.5 were multilayer structures containing HDPE and either MDPE or LLDPE. The hardness values ​​in the transverse (TD) and machine (MD) directions (expressed in q / cm) for each of these films are shown in Table 1. The thickness of the ZN-1 layer in the multilayer films was 0.0292 mm (1.15 mils). The sealing tests were completed by pressing two film strips together (sealing layer to sealing layer) for a fixed period of time at a set pressure and temperature. The temperature was varied to determine a minimum sealing temperature required to provide a minimum / specified sealing strength (reported as the sealing start temperatures). The sealing temperatures were increased until the sealing strength began to decrease (due to polymer melting / failure). The results are plotted in the figures. Seal strength is determined using an instrument that separates the seal and records the force required to do so. Test methods for determining some seal characteristics are provided below. Sealing resistance The seal strength test was performed on an instrument designed for this purpose and sold under the trade name INTSTRUME™ 5 - Head Universal Tester. The test was generally conducted according to the instrument manufacturer's recommended procedures. Hot stickiness Hot tack is a measure of a seal's ability to withstand load before it cools completely; this ability is important for seal packing and form filling. The test was conducted using an instrument designed for this purpose and sold under the name J&B Hot Tack Tester. In general, the tests were carried out according to the procedures recommended by the instrument manufacturer. The specific conditions are summarized below. Continued: Sealing pressure: 0.27 N / mm² Sealing time: 0.5 s Cooling time: 0.5 s Gripper separation speed: 200 mm / sec Peel compensation: 5 mm Sample width: 25 mm Sample length: 8 mm pRcznn / zznz / E / YiAi Table 2 Printed comic strip movies STRUCTURE 1.1 ZN-1 1.2 ZN-l / SSC-2 1.3 ZN-l / ZN-2 1.4 ZN-2 1.5 ZN-l(nuc) / ZN-2 Table 3 shows an internal (comparative) band that has a single sealing layer. Table 3 (Comparative) Resin Layer Quantity 1 ZN-3 30% 2 SSC-1 nuc / rHDPE-1 40% 3 DCT-1 30% Table 4 shows an inventive inner band with a two-layer sealing system (layers 3 and 4). Layer 4 is the sealing layer (a surface layer) and layer 3 is the layer adjacent to it. Table 4 Internal band structure (Inventive) Resin Layer Quantity 1 ZN-2 20% 2 rHDPE-1 55% 3 DCT-l / rLLDPE 10% 4 DCT-1 15% Table 5 shows another four-layer film suitable for the inner band (again, layer 4 is the sealing layer and layer 3 is the layer adjacent to it). Table 5 Inner band structure Resin Layer Quantity 1 ZN-2 20% 2 rHDPE-1 55% 3 DCT-l / rLLDPE 10% 4 DCT-1 15% Table 6 shows a five-layer film suitable for the inner band. Layer 5 is the sealing layer and layer 4 is the layer adjacent to it. Table 6 Internal band Resin Layer Quantity 1 ZN-2 5% 2 rLLDPE / rHDPE-2 15% 3 rHDPE-1 55% 4 DCT-l / rLLDPE 10% 5 DCT-1 15% Tables 7-9 show examples of the seven-layer films for the inner band. Layer 7 is the sealing layer, and layer 6 is the layer adjacent to it. Table 7 Resin Layer Quantity 1 ZN-2 5% 2 rLLDPE / rHDPE-2 15% 3 SSC-1 .nuc 5% 4 rHDPE-1 45% 5 SSC-1 .nuc 5% 6 DCT-l / rLLDPE 10% 7 DCT-1 15% Table 8 Resin Layer Quantity 1 ZN-2 5% 2 rLLDPE / rHDPE-2 15% 3 SSC-1 .nuc 7.5% 4 rHDPE-1 40% 5 SSC-1 .nuc 7.5% 6 DCT-l / rLLDPE 10% 7 DCT-1 15% Table 9 Resin Layer Quantity 1 ZN-2 5% 2 rLLDPE / rHDPE-2 15% 3 SSC-1 .nuc 7.5% 4 rHDPE-1 40% 5 SSC-1 .nuc 7.5% 6 DCT-l / rLLDPE / DCT-2 10% 7 DCT-1 15% The structure shown in Table 8 has a very good balance of sealing and hot tack properties, optical properties, and stiffness. It is possible to improve the optical properties (reduce turbidity) by replacing SSC-1 with ZN-1, but this comes at the cost of reduced stiffness and MVTR. The structure shown in Table 9 has a very good balance of sealing and hot tack properties, optical properties, and stiffness. It is possible to improve the optical properties (reduce turbidity) by replacing SSC-1 with ZN-1, but this comes at the cost of reduced stiffness and MVTR. Figure 1 graphically shows the improvement of the pRcznn / zznz / E / viAi cold sealing profile. Table 10 Sealing characteristics of sealing strips Hot tack start temperature °C Maximum hot tack strength (N) Seal start temperature °C Maximum seal strength (N) Table 3 83.2 7.0 101.9 30.7 Table 4 82.6 6.1 105.6 31.5 Table 8 78.4 8.5 98.0 38.0 Table 9 82.8 7.5 98.6 36.8 Finished laminated structure The finished laminated structure is prepared by laminating the first (outer) strip to the second (inner) strip. Table 10 provides representative data for two completed structures. Industrial applicability A flat-bottom bag (SUP) made of polyethylene incorporates a sealing structure that improves the manufacturing and use of the SUP. The SUP is useful for packaging a wide variety of consumer goods. It is hereby stated that, as of this date, the best method known to the applicant for putting the aforementioned invention into practice is the one that is clear from the present description of the invention.

Claims

1. A laminated structure made of polymeric materials, characterized in that it comprises: A) an outer band comprising: A.1) a first layer A comprising an HDPE composition, and A.2) a second layer A comprising polyethylene selected from LLDPE, MDPE, and HDPE; B) an inner band comprising: B.1) a first layer B in contact with the outer band, wherein the first layer B comprises polyethylene selected from LLDPE and MDPE, B.2) a second layer B comprising recycled polyethylene, and B.3) a sealing structure comprising: B.3.1) a sealing surface layer comprising a polyethylene sealant, and B.3.2) a layer adjacent to the sealing surface layer comprising a polyethylene having a density that is a) greater than the density of the polyethylene sealant; and b) less than the density of the central layer that is in contact with the layer adjacent to the sealing surface layer; and pAcznn / zznz / E / YiAi wherein I) the outer band is laminated to the inner band, and II) the HDPE, MDPE, LLDPE, recycled polyethylene and the polyethylene sealant collectively form at least 95% by weight of the polymeric materials used to prepare the laminated structure.

2. A laminated structure made of polymeric materials, characterized in that it comprises: A) an outer band comprising: A) a first layer A comprising a composition of HDPE, and A. 2) a second layer A comprising polyethylene selected from LLDPE, MDPE, and HDPE, A. 3) a third layer A comprising polyethylene selected from LLDPE, MDPE, and HDPE; B) an inner band comprising: B1) a first layer B in contact with the outer band, wherein the first layer B comprises polyethylene selected from HDPE, LLDPE, and MDPE, B. 2) a second layer B comprising recycled polyethylene, and B. 3) a sealing structure comprising: B.

3. 1) a sealing surface layer comprising a polyethylene sealant, and pRcznn / zznz / E / YiAi B. 3.2) a layer adjacent to the sealing surface layer that includes a polyethylene having a density that is a) greater than the density of the polyethylene sealant; and b) less than the density of the central layer that is in contact with the layer adjacent to the sealing surface layer; and wherein I) each of the outer and inner bands optionally comprises at least one additional layer of polyethylene between A1 and A.3 and B1 and B.3, II) the outer band is laminated to the inner band, and III) the HDPE, MDPE, LLDPE, recycled polyethylene and polyethylene sealant collectively constitute at least 95% by weight of the polymeric materials used to prepare the laminated structure.

3. The structure in accordance with any of the preceding claims, characterized in that the layer adjacent to the sealing surface layer has a density of 0.917 to 0.921 g / cc and the polyethylene sealant has a density of 0.88 to 0.915 g / cc.

4. The structure in accordance with any of the preceding claims, characterized in that the polyethylene sealant has a density of 0.900 to 0.914 g / cc.

5. The structure in accordance with any of the preceding claims, characterized in that the inner band further comprises an additional layer between B1 and B.3 comprising HDPE that optionally contains a nucleating agent.

6. The structure in accordance with any of the preceding claims, characterized in that the second layer B comprises HDPE that contains a nucleating agent.

7. The structure in accordance with any of the preceding claims 2-6, characterized in that the inner band further comprises an additional layer between Al and A.3 comprising HDPE that optionally contains a nucleating agent.

8. The structure according to any of the preceding claims, characterized in that the inner band further comprises a barrier layer, wherein the barrier layer is located between the first layer B and the second layer B.

9. The structure in accordance with any of the preceding claims, characterized in that the inner band further comprises at least one layer comprising recycled polyethylene.

10. The structure in accordance with any of the preceding claims, characterized in that the inner band further comprises at least one layer comprising a mixture of HDPE, MDPE, or LLDPE with recycled polyethylene.

11. The structure according to claim 10, characterized in that the barrier layer comprises EVOH, with the additional condition that the total weight pRcznn / zznz / E / YiAi of the barrier layer is less than 5% by weight, based on the combined weight of EVOH and the total weight of the polyethylene used in the structure.

12. The structure according to any of the preceding claims, characterized in that a first bonding layer is located on one side of the barrier layer and a second bonding layer is located on the other side of the barrier layer.

13. A flat-bottomed bag, characterized in that it is prepared from the structure in accordance with any of the preceding claims.