Method for manufacturing a multilayer flexible packaging material that can be peeled off by underwater treatment.

Abstract

The present invention relates to a method for producing a multilayer flexible packaging material that is selectively peeled off by treatment with water. a) A step of preparing a polar polymer layer and a non-polar polymer layer, b) A step of coating at least one of the layers, i.e., a layer intended to be selectively recycled, with a polyvinyl alcohol (ethylene vinyl alcohol) copolymer that can be partially crosslinked with a water-dispersible polyisocyanate. c)b) This step includes bonding the coating layer obtained in step b) with a 2K polyurethane adhesive.

Description

[Technical Field]

[0001] The present invention relates to a method for producing a multilayer flexible packaging material that is selectively peeled off by water treatment. [Background technology]

[0002] prior art Recycling flexible food packaging is an important process for reducing the environmental impact of the materials and promoting a circular economy. Flexible food packaging is often made of composite materials such as laminated plastics and aluminum, which can make recycling difficult. However, various technologies are available to separate these materials and recover recyclable components such as aluminum and plastic. The recycling process for flexible food packaging typically involves separating and washing the materials. The materials are then repurposed into new products such as shopping bags, irrigation pipes, and new food packaging. It should be noted that recycling flexible food packaging is not the only solution to reduce environmental impact. The use of more sustainable alternative materials, such as biodegradable and compostable materials, should also be considered.

[0003] Consumers should also be educated about the importance of proper recycling and disposal of flexible food packaging in order to increase collection rates and reduce environmental impact. Composite plastic flexible packaging is used in a wide range of products, including food, beverages, and personal care products. However, due to the nature of the composite materials, it often contains different types of plastics, aluminum, and other components, making recycling difficult. Therefore, recycling such packaging is a major challenge, but it is necessary to reduce the environmental impact resulting from its manufacture and disposal. Various recycling technologies exist that can be used for such packaging, including aluminum recovery, plastic separation, and conversion into new products such as urban paving and decorative items.

[0004] Even with structures made from a single material, such as multilayer polypropylene or polyethylene, the presence of additional components like inks, adhesives, and various additives results in a material that is not transparent, very often dark in color, and contaminated with inks, adhesives, and other substances, thus limiting its recyclability. Therefore, numerous attempts have been made to separate and regenerate the original material using chemical or mechanical methods.

[0005] Chemical recycling, which converts polymers into oligomers and monomers through thermal decomposition or other processes, yields good results but has the drawback of using levels of energy that significantly impact carbon dioxide emissions. Conversely, mechanical recycling presents problems with contamination from inks, adhesives, and additives. The resulting granules have poor color and contain contaminants, making them unsuitable for reuse in the production of virgin raw materials.

[0006] EP1973733B1 describes a structure for multilayer laminate packaging characterized by resistance to heat treatment. WO2023 / 277861A1 describes a recyclable film comprising a first film and a second film laminated to the first film. The first film includes a first polypropylene layer, a second polypropylene layer, and an ethylene-vinyl alcohol (EVOH) layer between the first and second polypropylene layers. The ethylene-vinyl alcohol layer enhances the barrier effect against oxygen and ultraviolet light. Methods for recycling multilayer structures are described in EP3725485.

[0007] WO2022 / 037891A1 relates to a recyclable multilayer packaging single material comprising multiple polypropylene-containing layers, wherein at least one of the polypropylene-containing layers is bonded to two adjacent layers by different adhesives. EP3885095A1 describes a method for recycling multi-material laminates using a mixture of water and essential oils to improve the sustainability of the recycling process. [Overview of the project]

[0008] Description of the Invention The present invention aims to solve the problem of separating and recycling the components of multilayer materials used in flexible packaging in order to facilitate their reuse. This problem was solved by a method for producing a multilayer flexible packaging material, which involves coating at least one of two polymer layers having different polarities with a polyvinyl alcohol ethylene-vinyl alcohol copolymer, and then bonding them together with a suitable polyurethane adhesive.

[0009] Therefore, in its first embodiment, the object of the present invention is a method for producing a multilayer flexible packaging material that is selectively peeled off by treatment with water, a) A step of preparing a polar polymer layer and a non-polar polymer layer, b) A step of coating at least one of the layers with a polyvinyl alcohol ethylene-vinyl alcohol copolymer, c)b) includes a step of bonding the coating layer obtained in step b) with a 2K polyurethane adhesive. The material obtained by the method according to the present invention can be selectively exfoliated by separating the individual layers of the structure by treating it in hot water (60-95°C) with the help of a nonionic surfactant and / or in the presence of an alkali.

[0010] A selective exfoliation process constitutes a further objective of the present invention. In this way, containers made from the material obtained from the process according to the present invention are collected after use and sent to a delamination device, where the individual materials can be separated by sedimentation due to differences in density. Once separated, the granular portion derived from the coated plastic film is completely clean and can be processed in conventional plastic recycling equipment. [Modes for carrying out the invention]

[0011] The polar polymer layer is typically polyester, polyethylene terephthalate, or polylactic acid. The non-polar polymer layer is typically selected from polypropylene (biaxially oriented, amorphous, or extruded), low-density polyethylene, or high-density polyethylene. Polyvinyl chloride (PVC) and oriented polyamides can also be used. The thickness of the two layers is usually in the range of 10 to 1000 nm. Polyethylene terephthalate is preferred as the polymer for the polar layer, and extruded polypropylene is preferred as the polymer for the non-polar layer.

[0012] The polyvinyl alcohol ethylene-vinyl alcohol copolymer (PVOH / EVOH) used for coating preferably has a degree of hydrolysis greater than 98% (mol), as measured according to standard EN ISO 3681. In one or both polar and nonpolar coating steps, the copolymer is dissolved in water in the presence of C2-C6 coalescent alcohol at a concentration ranging from 5.0 to 20% by weight. The copolymer solution typically has a viscosity in the range of 3000 to 5000 mPa.s, as measured with a Brookfield viscometer (4% solids content) at 23°C.

[0013] A hydrophilic modified polyisocyanate with an NCO content of 15% - 23%, a viscosity of less than 3500 mPa·s, a free monomer content of less than 1.0%, and a weight percentage in the range of 0.1 - 5.0% can be dispersed in a copolymer solution. As a result, the copolymer is partially cross-linked, and as a result, the tack of the adhesive increases, and the structural stability in a wet environment is improved. The ethylene-vinyl alcohol copolymer coating can be partially cross-linked with a water-dispersible polyisocyanate (0.10 - 5.0% by weight).

[0014] The 2K NCO-terminated polyurethane adhesive is solventless or solvent-based. The solventless or solvent-based -NCO component has a viscosity in the range of 100 - 14000 mPa·s at 23°C, and the NCO content is 4.0 - 32.0% on a molar basis. The solventless or solvent-based -OH curing agent component has a viscosity in the range of 10 - 8000 mPa·s at 23°C and an OH value of 30 - 1000 mgKOH / g.

[0015] There are two steps for coating with a laminator. 1) Coating with an aqueous solution of PVOH / EVOH, 20 - 35 m / min, blowing temperature 65 - 90°C, dry film 1.0 - 4.0 g / m 2 , curing time 4 - 14 days at 15 - 70°C. Both the polar film 1 and the non-polar plastic film 2 can be coated. To improve the structural stability, a water-dispersible polyisocyanate can be dispersed in the aqueous solution at a concentration of 0.1 - 5.0% based on the solid content of the aqueous solution. 2) Using a mixture with a preferred ratio of 100(NCO) / 50(OH), bond two films under the following conditions. 50 - 400 m / min, for the solvent of the self-supporting adhesive film, blowing furnace air 45 - 60°C, dry film 2.0 - 8.0 g / m 2 , in-drum curing 4 - 10 days at 20 - 70°C.

Brief Description of the Drawings

[0016] [Figure 1]Figure 1 shows the scheme of the multilayer structure obtained by the method according to the present invention. Reference numeral 1 denotes a polar film, reference numeral 2 denotes a non-polar film, reference numeral 3 denotes a coating layer made of an ethylene-vinyl alcohol copolymer, and reference numerals 3 and 4 denote polyurethane adhesive layers. [Figure 2] Figure 2 shows the components of the structure after peeling and recycling treatment.

Example

[0017] The present invention will be described in more detail with the following examples. Example 1: Combination of polyethylene terephthalate (PET) and cast polypropylene (CPP). A 10% aqueous solution of PVOH / EVOH is applied to a PET plastic film (1) with a thickness of 10 - 15 μm, and a dry film of 0.5 - 2.0 g / m 2 is coated. The coated roll film can be stored at 25 - 60°C for 6 - 8 days for curing. After the above process, the coated film can be adhered to another plastic film (2) made of CPP with a thickness of 20 - 30 μm using a 2K polyurethane adhesive system of 4.0 - 8.0 g / m 2 . NCO component: 8000 - 10000 mPa·s at 23°C, solvent-free, 10 - 12 wt% NCO. -OH component: 3500 - 6500 mPa·s at 23°C, solvent-free, OH value 190 - 215 mgKOH / g. After a curing time of 4 - 10 days at 40 - 60°C under pressure of the laminate film roll, the measured adhesion strength is surprisingly high, and the two films do not seem to peel off. The cut and pulverized material is immersed in hot water (80 - 90°C) for 20 - 40 minutes in a basic solution of 7 < pH < 10, with or without a surfactant of up to 0.5%. When this material is washed with pure water, the two plastics can be separated by floating. The coated PET film flakes (1) become clean and deposit on the base, while the remaining (2) float on the surface still contaminated with the adhesive. Even after heat treatment at 220°C for 1 hour, the film flakes (1) remain clean and transparent. There is no yellowing or browning as in the case of the plastic flakes obtained from Film 2, so there are no signs of organic residues contaminating the plastic pieces with the adhesive. The material can be easily reused.

[0018] Example 2: Combination of polyethylene terephthalate (PET) and cast polypropylene (CPP). A 10% aqueous solution of PVOH / EVOH is applied to a CPP plastic film (2) with a thickness of 75 - 85 μm, covering a dry film of 0.5 - 2.0 g / m 2 of. The coated roll film can be stored at 25 - 60°C for 6 - 8 days for curing. After the above process, the coated film can be adhered to another plastic film (1) made of PET with a thickness in the range of 10 - 15 μm using a 2K polyurethane adhesive system of 4.0 - 8.0 g / m 2 . NCO component: 8000 - 10000 mPa·s at 23°C, solvent-free, NCO 10 - 12 wt%. -OH component: 3500 - 6500 mPa·s at 23°C, solvent-free, OH value 190 - 215 mgKOH / g. After a curing time of 4 - 10 days at 40 - 60°C under pressure of the laminated film roll, the measured adhesion strength is surprisingly high and the two films seem inseparable. The cut and crushed material is immersed in hot water (80 - 90°C) for 40 - 60 minutes in a basic solution with 7 < pH < 10, with or without the presence of a surfactant not exceeding 0.5 wt%. When this material is washed with pure water, the two plastics can be separated by floating. The flakes derived from the PET film (1) deposit on the bottom surface, and the other flakes (2) remain floating on the surface and become completely clean. Even after heat treatment at 220 °C for 1 hour, the thin flakes of the film (2) remain clean and transparent. The plastic flakes are not contaminated with adhesive residues. The materials can be easily reused. This example shows the selectivity of the peeling process.

[0019] Example 3: Manufacture of a pouch with a hot-seal structure composed of polyethylene terephthalate (PET) and cast polypropylene (CPP). A 10% aqueous solution of PVOH / EVOH is applied to a PET plastic film (1) with a thickness of 10 - 15 μm, and a dry film of 0.5 - 2.0 g / m 2 is coated. The coated roll film can be stored at 25 - 60 °C for 6 - 8 days for curing. After this step, the coated film can be adhered to another plastic film (2) made of CPP with a thickness of 10 - 40 μm using a 2K polyurethane adhesive system, 4 - 8 g / m 2 . NCO component: 8000 - 10000 mPa·s at 23 °C, solvent-free, 10 - 12 wt% NCO. -OH component: 3500 - 6500 mPa·s at 23 °C, solvent-free, OH value 190 - 215 mgKOH / g. After a curing time of 4 - 10 days at 40 - 60 °C under pressure of the laminated film roll, the measured adhesion strength is surprisingly high, and the two films seem inseparable. The sheet thus obtained is packaged by a hot-sealing process at 150 °C and folded into a pouch. The sealed part is cut and separated from the metal residues. After cutting and pulverizing, only the sealed part is immersed in hot water (80 - 90 °C) for 20 - 40 minutes in a basic solution with 7 < pH < 10, with or without a surfactant of up to 0.5 wt%. When this material is washed with pure water, the two plastics can be separated by floating. The thin flakes of the coated PET film (1) become clean and deposit on the base, and the remaining (2) floats on the surface contaminated with the adhesive. Even after heat treatment at 220°C for 1 hour, the film flakes (1) remain clean and transparent. Like the plastic flakes obtained from Film 2, no yellowing or browning occurs, and there are no signs of organic residues contaminating the plastic pieces with the adhesive. This material can be easily reused even in the case of hot sealing.

[0020] Comparative Example 4: Combination of biaxially oriented polypropylene (BoPP) and cast polypropylene (CPP). A 10% aqueous solution of PVOH / EVOH is applied to a CPP plastic film (2) with a thickness of 15 - 25 μm, and a dry film of 0.5 - 2.0 g / m2 is coated. The coated roll film can be stored at 25 - 60°C for 6 - 8 days for curing. After this step, the coated film is adhered to another plastic film (2) made of BoPP with a thickness of 二十 - 30 μm using a 2K polyurethane adhesive system, 4.0 - 8.0 g / m 2 、. NCO component: 8000 - 10000 mPa.s at 23°C, solvent-free, 10 - 12 wt% NCO. -OH component: 3500 - 6500 mPa.s at 23°C, solvent-free, OH value 190 - 215 mgKOH / g. Under pressure of the laminated film roll, after a curing time of 4 - ten days at 40 - 60°C, the measured adhesion strength is surprisingly high, and the two films seem not to be peeled off. The cut and crushed material is immersed in hot water (80 - 90°C) for 20 - 40 minutes in a basic solution with 7 < pH < 10, with or without the presence of up to 0.5 wt% surfactant. When washed with pure water, the two plastics cannot be separated by floating. No peeling occurs at all. As shown in Table 1, there is no density separation of various substances, and the COD of water is the same before and after treatment.

[0021]

Table 1

[0022] Example 5: Combination of polyethylene terephthalate (PET) and biaxially oriented polypropylene (BoPP). Partial cross-linked coating. A 0.5% aqueous solution of water-dispersible polyisocyanate having the following properties is dispersed in a 10% aqueous solution of PVOH / EVOH. - NCO content 15~23% - Viscosity 3500mPa.s or less - Free monomer content less than 1.0% A 10% aqueous solution of PVOH / EVOH is applied to a PET plastic film (1) with a thickness of 10-15 μm, and 0.5-2.0 g / m² is added. 2 Cover with a drying film. The coated roll film can be stored at 25-60°C for 6-8 days for curing. After the above process, the coated film is bonded with a 2K polyurethane adhesive system, 4.0-8.0 g / m². 2 , can be used to bond to another plastic film (2) made of BoPP with a thickness in the range of 20-30μ. NCO content: 8000-10000 mPa.s at 23°C, solvent-free, NCO 10-12% by weight. -OH component: 3500-6500 mPa.s at 23℃, solvent-free, OH value 190-215 mg KOH / g. When adhesive film rolls are cured under pressure at a temperature of 40-60°C for 4-10 days, the adhesive strength is measured and found to be twice as high as when water-dispersible polyisocyanate is not used. The cut and crushed material, without surfactants, 6.5

Claims

1. A method for producing a multilayer flexible packaging material that is selectively peeled off by treatment with water, a) A step of preparing a polar polymer layer and a non-polar polymer layer, b) A step of coating at least one of the layers with a polyvinyl alcohol / ethylene vinyl alcohol copolymer, A manufacturing method characterized by comprising the step of bonding the coated layer obtained in step b) with a 2K polyurethane adhesive.

2. The manufacturing method according to claim 1, wherein the coating of the ethylene-vinyl alcohol copolymer is partially crosslinked with a water-dispersible polyisocyanate (0.10 to 5.0% by weight).

3. The manufacturing method according to claim 1, wherein the polar polymer layer is a layer selected from polyethylene terephthalate or polylactic acid.

4. The manufacturing method according to any one of claims 1 to 3, wherein the nonpolar polymer layer is a layer selected from polypropylene (biaxially oriented, amorphous, or extruded) and low-density or high-density polyethylene.

5. The manufacturing method according to claim 4, wherein the nonpolar polymer layer comprises cast polypropylene.

6. The method for producing the polyvinyl alcohol / ethylene vinyl alcohol copolymer having a degree of hydrolysis of more than 98% (mol), according to any one of claims 1 to 5.

7. The manufacturing method according to any one of claims 1 to 6, wherein the nonpolar layer is coated with a polyvinyl alcohol / ethylene vinyl alcohol copolymer.

8. The manufacturing method according to any one of claims 1 to 6, wherein the polar layer is coated with a polyvinyl alcohol / ethylene vinyl alcohol copolymer.

9. The manufacturing method according to any one of claims 1 to 6, wherein both the polar layer and the non-polar layer are coated with a polyvinyl alcohol / ethylene vinyl alcohol copolymer.

10. b) The manufacturing method according to any one of claims 1 to 9, wherein the coating step is carried out by coating a layer with an aqueous solution of polyvinyl alcohol / ethylene vinyl alcohol copolymer in the presence of C2-C6 coalescent alcohol at a concentration in the range of 5.0 to 20% by weight.

11. An aqueous solution of an ethylene-vinyl alcohol copolymer is partially crosslinked by the addition of 0.10 to 5.0% of a water-dispersible polyisocyanate, wherein the polyisocyanate is - NCO content is 15% to 23%. - Viscosity measured at 23°C with a Brookfield viscometer is less than 3500 mPa·s. - A manufacturing method according to any one of claims 1 to 10, wherein the free monomer content is less than 1.0%.

12. The manufacturing method according to any one of claims 1 to 11, wherein the NCO-terminated 2K polyurethane adhesive may be solvent-free or solvent-based.

13. The manufacturing method according to claim 12, wherein the adhesive comprises a -NCO component having a viscosity in the range of 100 to 14,000 mPa·s at 23°C and an NCO content of 4.0 to 32.0% on a molar basis, and an -OH curing agent component having a viscosity in the range of 10 to 8,000 mPa·s at 23°C and an OH value of 30 to 1,000 mgKOH / g.

14. A multilayer flexible packaging material obtained by the manufacturing method described in any one of claims 1 to 13.

Images