Method for removing ink layers from waste plastic packaging

Abstract

A method for removing an ink layer from a first plastic material to obtain an ink-free first plastic material, the method comprising the steps of: (a) providing a starting material comprising at least a layer of a first plastic material and an ink layer applied to the layer of the first plastic material; (b) contacting the starting material with a metal oxide in solution in the presence of a base to provide a reaction mixture; (c) agitating the reaction mixture under UV light for a suitable time while the ink layer is degraded, wherein the first plastic material remains intact; and (d) recovering the first plastic material from the reaction mixture.

Description

Technical Field

[0001] This invention relates to a method for removing ink layers from waste plastic materials (particularly waste plastic packaging). Background Technology

[0002] Establishing a sustainable circular economy for plastics must be based on replacing virgin plastics with high-quality recycled materials. However, printing inks on packaging plastics and their thermal degradation products can contaminate recycled materials. Replacing commonly used inks is not a viable option because companies are reluctant to use lower-strength inks due to the marketing influence of well-known brand trademarks and colors. Therefore, ink removal (which can be described as "de-inking") is a crucial factor in recycling plastics.

[0003] Crosslinked UV inks are particularly difficult to remove without a specific primer because they are designed to have optimal chemical, mechanical, and thermal resistance. Due to their advantageous properties and energy-efficient processing, the use of UV inks in food packaging is constantly increasing. Therefore, it is highly beneficial to develop a method capable of deinking all types of inks, regardless of their type or specific formulation.

[0004] WO2023091639 describes a method for recycling constituent polymers from multilayer plastic films or mixed plastic waste. This method involves selectively dissolving the polymer in a solvent. Consequently, most of the ink is separated from the dissolved polymer. Alternatively, WO2023091639 describes removing ink from multilayer plastic films or mixed plastic waste by treating them in a solvent containing tetrahydrofuran and N,N-dimethylformamide. This method is carried out at high temperatures above 90°C, resulting in considerable energy consumption. Another disadvantage is the environmental impact of the solvents used to dissolve the different plastics. Summary of the Invention

[0005] The purpose of this invention is to provide a method for removing printing ink from plastic waste materials, which is effective, inexpensive, and can be easily combined with further recycling steps.

[0006] At least one object of the present invention is achieved by the method according to claim 1. A method for removing an ink layer from a first plastic material to obtain an ink-free first plastic material comprises the steps of: (a) providing a raw material comprising at least a layer of the first plastic material and an ink layer applied to the layer of the first plastic material; (b) contacting the raw material with a metal oxide in solution in the presence of an alkali to provide a reaction mixture; (c) stirring the reaction mixture under UV light for an appropriate time while allowing the ink layer to degrade, wherein the first plastic material remains intact; and (d) recovering the first plastic material from the reaction mixture.

[0007] This method effectively removes printing inks from packaging plastics to obtain high-quality recycled material. Even UV-based inks can be decomposed at ambient temperature or slightly elevated temperatures (up to 50°C) and atmospheric pressure (i.e., without pressurizing the reaction mixture). Therefore, the advantage of this method is that it can be carried out effectively below 60°C or even at approximately ambient temperature (20-25°C) and near-normal atmospheric pressure (i.e., approximately 1013.25 mbar). The decomposed ink can then be washed away from the intact plastic material.

[0008] During the deinking step c), due to the reaction environment of alkaline solution, UV light and photocatalyst, the ester bonds in the ink layer are easily broken by alkaline hydrolysis.

[0009] Raw materials can be obtained by crushing plastic waste (especially plastic packaging). Plastic waste can be sorted to obtain a single type of plastic material (such as polypropylene or polyethylene) including a layer of printing ink, or it can be a mixture of such plastics.

[0010] In some embodiments, the first plastic material may be a polyolefin, preferably polypropylene (PP) or polyethylene (PE), such as low-density PE (LDPE) and high-density PE (HDPE), or polyvinyl chloride (PVC) or polystyrene (PS). These plastics do not contain ester bonds, which would otherwise be broken through the reaction.

[0011] In some implementations, the ink layer can be water-based, solvent-based, or UV ink. Water-based inks consist of pigments and resins diluted in water. Solvent-based inks include pigments and resins (binders), which together constitute the solid components of the ink and are diluted using a solvent different from water. UV inks are dried by UV rays. Their major advantages are rapid curing and high levels of adhesion. Such ink layers typically contain ester bonds.

[0012] In some implementations, the appropriate time can be as short as 10 minutes or as long as 5 hours.

[0013] In some embodiments, step c) can be carried out at a temperature between 20°C and 60°C and near-normal atmospheric pressure. Pressure and / or temperature control is not required. The reaction can be carried out under ambient conditions.

[0014] In some embodiments, the metal oxide is selected from the group consisting of: TiO2, V2O5, Cr2O3, CrO3, Mn2O3, FeO, Fe2O3, Fe3O4, Co2O3, NiO, CuO, Cu2O, ZnO, ZrO2, Nb2O5, Mo2O3, RuO, RuO2, RuO4, RhO2, Rh2O3, PdO, Ag2O, Ag2O2, CdO, In2O3, Al2O3, La2O3, CeO2, Ce2O3, HfO2, Ta2O5, WO3, ReO2, ReO3, Re2O3, OsO2, OsO4, IrO2, PtO2, Au2O3, Li2O, Na2O, K2O, MgO, CaO, SrO, BaO, or combinations thereof. In some preferred embodiments of the method of the present invention, the metal oxide is selected from the group consisting of: TiO2, ZnO, ZrO2, Nb2O5, Ta2O5, RuO, Fe2O3, and WO3. Most preferably, the metal oxide is TiO2 or P25.

[0015] In some embodiments, the solution may be a solution containing alcohol and / or water, or the solution may be an aqueous alcohol solution. The alcohol and water may be present in different ratios, for example, alcohol:water from 100:0 to 0:100, or 90:10 to 10:90, or 80:20 to 20:80, or 50:50 to 90:10, preferably 50:50 or 80:20. The alcohol contains 1 to 5 carbon atoms and / or the alcohol is selected from the group consisting of methanol, ethanol, propanol, butanol, pentanol, or combinations thereof. Preferably, the alcohol is ethanol. More preferably, the aqueous alcohol solution is an 80:20 ethanol:water solution. Most preferably, the solution is ethanol or an ethanol:water solution of 90:10 to 10:90.

[0016] In some embodiments of the method of the present invention, the alkali may be selected from those containing NaOH and NaO. t The group consisting of Bu and KOH.

[0017] In some embodiments, alkaline hydrolysis can be carried out at pH 7 to 14, or 8 to 13, or 9 to 12, or 7 to 12, or 7 to 10, or 7 to 9, or 8 to 14, or 8 to 12, or 8 to 10, or 9 to 14, or 9 to 12, or 9 to 10.

[0018] In some embodiments of the method of the present invention, the ratio of plastic polymer to alkali can be 1:1 to 1:20 or 1:1 to 1:10. In preferred embodiments, the ratio of plastic polymer to alkali is 1:20, 1:7.5, 1:1, or 1:3. In other preferred embodiments, the ratio of plastic polymer to alkali is 2:1 to 3:1, preferably 2:1 or 3:1. In some embodiments of the method of the present invention, the ratio of plastic polymer to metal oxide can be 1:0.0375 to 1:0.00125. In preferred embodiments, the ratio of plastic polymer to metal oxide can be 1:0.0375, 1:0.015, 1:0.0075, or 1:0.00125.

[0019] In some embodiments of the method of the present invention, the wavelength of the UV light (ultraviolet light) can be in the range of 100 to 400 nm, preferably in the range of 315 to 400 nm. In other embodiments of the method of the present invention, the light intensity can be in the range of 1 to 150 mW / cm², for example 10 to 150 mW / cm², for example 50 to 150 mW / cm², for example 90 to 150 mW / cm², for example 130 to 145 mW / cm². The light intensity can be approximately 100 mW / cm².

[0020] In some embodiments, the reaction mixture may further comprise a surfactant, preferably a cationic surfactant selected from the group consisting of hexadecyltrimethylammonium bromide (CTAB), hexadecyltrimethylammonium chloride (CTAC), and alkyl dimethyl benzyl ammonium chloride (ADBAC). CTAB is a preferred surfactant.

[0021] In some embodiments, recycling step d) may include washing the first plastic with water, optionally followed by washing with an alcohol (preferably ethanol or methanol). The presence of a surfactant in the reaction mixture can be used to improve the removal of degraded ink molecules from the surface of the first plastic material.

[0022] The inventors have discovered that their previously developed method for depolymerizing PET, as described in WO2020173961, can also be used to effectively remove ink layers from plastic packaging waste containing PP and / or PE. The disclosure of WO2020173961 (particularly the embodiments) is incorporated herein by reference.

[0023] In some embodiments, the method may be implemented in the following cases: the raw material is multilayered, including an additional layer of a second plastic material, wherein the second plastic material is polyethylene terephthalate (PET).

[0024] In some embodiments, during step c), the polyethylene terephthalate (PET) layer is depolymerized into terephthalic acid (TPA) and ethylene glycol (EG).

[0025] Therefore, this method can be used to recycle multilayer waste plastic materials containing PE / PET or PP / PET layers, including ink layers. During the same reaction, the PET layer is degraded / depolymerized, and the ink layer is removed from the remaining and intact PP or PE layer.

[0026] The degradation of plastic materials depends on the type of plastic material used as the starting material. The plastic material layers of PET (such as ID5 in this study) are depolymerized during deinking (sometimes referred to as “delamination”). The deinking or depolymerization reaction targets similar types of bonds, primarily ester bonds, in both the PET and ink layers. Other plastic materials that do not contain these types of bonds (such as PP and PE) are not degraded during the reaction and thus remain intact.

[0027] In some embodiments, terephthalic acid (TPA) and ethylene glycol (EG) can be recovered from the reaction mixture after step c) or d). Recovery of terephthalic acid from the reaction mixture can be carried out by any suitable method, such as:

[0028] - Add water to the reaction mixture until the reaction mixture becomes clear;

[0029] - Separate the reaction mixture into a first solid phase and a first liquid phase;

[0030] - Acidify the first liquid phase (with, for example, concentrated HCl or concentrated H2SO4) until terephthalic acid precipitate is formed;

[0031] - Filter the terephthalic acid precipitate and wash it with water and alcohol (e.g., EtOH).

[0032] In some embodiments, the degraded ink particles can be filtered out from the clarified reaction mixture. Residual ink molecules that cannot be filtered out can be removed using the purification methods described below before acidifying the first liquid phase.

[0033] In some embodiments, separating the reaction mixture into a first solid phase and a first liquid phase may include filtering the reaction mixture. Recovery of ethylene glycol from the reaction mixture can be carried out by any suitable method, such as:

[0034] - Collect the dissolved ethylene glycol in the liquid phase;

[0035] - Distill the liquid phase until ethylene glycol is collected.

[0036] In some embodiments, the method of the present invention may further include recovering metal oxides from the reaction mixture. Recovery of metal oxides from the reaction mixture can be carried out by any suitable method, for example:

[0037] - Add water to the reaction mixture until the reaction mixture becomes clear;

[0038] - Separate the reaction mixture into a first solid phase and a first liquid phase;

[0039] - Separate metal oxides from the first liquid phase (e.g., by filtration).

[0040] Alternatively, metal oxides can be separated by washing terephthalic acid with water and alcohol.

[0041] In some embodiments, the TPA obtained from the depolymerization of the PET layer can be further purified using graphite, activated carbon, and molecular sieves to remove organic and inorganic contaminants, as well as ink molecules (if present). This purification can be performed using the methods described in U.S. Provisional Application No. 63425771, filed with the same applicant as this application, which is incorporated herein by reference in its entirety.

[0042] The purification method may be performed prior to the step of acidifying the first liquid phase during TPA and EG recovery described above, and may include: contacting unpurified terephthalic acid with graphite, activated carbon, and molecular sieves to provide a reaction mixture; stirring the reaction mixture for a first specific time period; filtering the reaction mixture to provide a reaction mixture filtrate; providing graphite, activated carbon, and molecular sieves to the reaction mixture filtrate; stirring the reaction mixture filtrate for a second specific time period; filtering the reaction mixture filtrate to provide a reaction output solution; and precipitating purified terephthalic acid from the reaction output solution.

[0043] By combining this purification method, the following features can be achieved, either alone or in any combination with the aforementioned features:

[0044] - The reaction mixture can be stirred at pH 14.

[0045] - The reaction mixture filtrate can be stirred at pH 7.

[0046] - Graphite, activated carbon, and molecular sieves can be supplied in a 1:6:2 ratio for contact with unpurified terephthalic acid.

[0047] - Graphite, activated carbon, and molecular sieves can be supplied to the reaction mixture filtrate in a 1:6:2 ratio.

[0048] Purified terephthalic acid can be precipitated from the reaction output solution using an acid (preferably hydrochloric acid or sulfuric acid).

[0049] - The first time period can be between 10 and 120 minutes, preferably 30 minutes.

[0050] - The second time period can be between 10 and 120 minutes, preferably 30 minutes.

[0051] - This method can be performed at room temperature.

[0052] - Graphite can include amorphous, crystalline, or flake graphite with a purity of 99% and a particle size range of 5-30 micrometers.

[0053] - Activated carbon may include granular activated carbon having a surface area of ​​500-1500 m2 / g and a particle size of less than 1 mm.

[0054] Molecular sieves can include aluminosilicate crystal molecular sieves, such as zeolite 13X molecular sieve. Zeolite 13X contains an average pore size of 9 angstroms and can absorb molecules with a kinetic diameter of less than 9 angstroms.

[0055] This purification method can be carried out as a batch operation in a reactor vessel, preferably equipped with a stirrer and a plug filter. In some examples, the method described herein can be carried out as a batch operation in multiple reaction vessels configured in series. In some examples, the method described herein can be modified to operate as a continuous process.

[0056] This purification method can reliably output purified terephthalic acid (PTA) with a purity up to 1% higher than that of virgin terephthalic acid after drying, and a whiteness up to 5% brighter.

[0057] The output is typically a metal salt of terephthalic acid (M-PTA, where "M" represents a metal, such as Na* or K* possibly derived from a hydrolysis process) dissolved in water, close to the maximum solubility of M-PTA in solution, which is 7 to 13% by weight. The output can then be subjected to crystallization.

[0058] Tests on deinking methods have shown that even UV-based inks (as well as water-based and solvent-based inks) from different formulations can be decomposed under ambient temperature and pressure, or at slightly elevated temperatures (50°C) and normal pressure. After the deinking process, the decomposed ink can be washed away from the intact plastic material layer.

[0059] Furthermore, this method can also be applied to selectively remove polyethylene terephthalate (PET) layers from multi-layer packaging materials, separating the layers and recovering monomers terephthalic acid (TPA) and ethylene glycol (EG) in addition to the intact plastic layers (e.g., polypropylene (PP) or polyethylene (PE)) after deinking. This is also a crucial step in deinking, as the ink in multi-layer packaging materials is typically located between the layers, making it difficult to access without separation. Attached Figure Description

[0060] The invention will now be described in more detail with reference to the embodiments shown in the accompanying drawings. The drawings show:

[0061] Figure 1 Photos (grayscale) of multilayer raw materials (PE / PET) before and after the deinking process with / without surfactants.

[0062] Figure 2 Photos (grayscale) of the first plastic material of the multilayer raw material (PE / PET) before and after the application of the deinking process.

[0063] Figures 3 to 13 FTIR spectral measurement results for several samples. Detailed Implementation

[0064] Materials and characterization methods. Reagents and solvents were purchased from Sigma-Aldrich, TCI and Carl Roth and were ready for use without further purification.

[0065] Generally, deinking processes are tested using model samples and samples of discarded consumer packaging products. The model samples are packaging materials produced to test ink quality. In the experiments, the deinking performance and, in some cases, the delamination of the samples were investigated.

[0066] Experimental Conditions. Examples of the deinking method are given in Table 1, which shows the type of sample (i.e., raw material) and experimental conditions. In the experiments, i) TiO2 was used as a catalyst, ii) NaOH was used as a base, iii) an 80:20 aqueous alcohol solution of ethanol:water was used as the reaction solution, and iv) the wavelength of UV light was in the range of 100 to 400 nm, preferably in the range of 315 to 400 nm. The pH of the reaction mixture was approximately 14. The “Ink Type” column describes, for example, the basis of the ink applied to a layer of the first plastic material by printing (“Plastic Layer 1” column). The ink can be applied as several layers of different colors (“Ink Layer” column). Sample ID5 has an additional layer of a second plastic material. In this case, the ink is typically located between layers of different plastic materials.

[0067]

[0068] A method for removing an ink layer from a first plastic material to obtain an ink-free first plastic material was performed on the samples. Therefore, as described above, raw materials having the specifications in Table 1 and comprising at least a layer of the first plastic material and an applied ink layer were contacted in solution with a metal oxide in the presence of an alkali to provide a reaction mixture. The reaction mixture was stirred under UV light at ambient conditions (room temperature, atmospheric pressure) or at a high temperature (at atmospheric pressure) of 50°C for an appropriate time (“Conditions” column) to degrade the ink layer. Samples of the first plastic material were recovered and washed at different times during the reaction. In samples ID5-2 and ID5-3, a cationic surfactant was added to the reaction mixture. Good results were obtained using hexadecyltrimethylammonium bromide (CTAB). The results are summarized in Table 2.

[0069]

[0070] Figure 1 Photographs (grayscale) of multilayer raw materials with PE and PET layers (a) and samples ID5 (b), ID5-2 (c) and ID5-3 (d) are shown. Figure 1 a) shows the raw materials before the application of the deinking process. Figure 1 b)-c) show the results in sample ID5 ( Figure 1 b), ID5-2 Figure 1 c) and ID5-3 Figure 1 Under conditions d), the first layer of plastic material (here, PE) after the deinking process. During filming, a foil sheet of the raw material or the complete PE layer after deinking was attached to the surface using transparent tape. Deinking in sample ID5 was only partial. As shown in samples ID5-2 and ID5-3, effective deinking was achieved by adding a surfactant.

[0071] Five samples of discarded consumer packaging products with unknown ink types were tested. The raw material was a multilayer plastic with PE and PET layers and an ink layer in between (Table 3). As described above, the raw material was contacted with a metal oxide in solution in the presence of an alkali and a cationic surfactant (e.g., CTAB) to provide a reaction mixture. The reaction mixture was stirred under UV light at 50°C and normal pressure for an appropriate time (“Conditions” column) to allow the PET layer to separate and depolymerize and the ink layer to degrade. After 120 minutes, the sample containing the first plastic material was recovered and washed. The results are summarized in Table 3.

[0072]

[0073] Figure 2Photographs (grayscale) of samples BID1, BID2, BID3, BID6, and BID7 of multilayer raw materials with PE and PET layers are shown before and after deinking, showing the complete first plastic material (PE) layer. Transparent tape was used to attach the raw materials and the complete PE layer after deinking to the surface during photography. All samples show effective deinking.

[0074] FTIR analysis. FTIR analysis was performed on each sample to detect the presence of ink on the surface of the first plastic material. Figures 3 to 13 The results are shown in Table 4: (a) FTIR spectra of the surface with ink before and after the deinking process; (b) a comparison of the measured FTIR spectra of the first plastic material (PP or PE) surface with the reference spectrum of the pure first plastic material (PP or PE). A summary of the FTIR spectral measurement results is given in Table 4.

[0075]

[0076] In all samples, the first plastic material after deinking exhibited a measurement spectrum that matched well with the reference spectrum based on data retrieved from FTIR software. This demonstrates that deinking was complete even in the presence of PET, and the PET was successfully delaminated.

[0077] In summary, different types of inks (e.g., solvent-based, oil-based, and UV-based) can be removed from plastic surfaces (e.g., PET, PE, or PP). PET delamination / depolymerization and ink removal can be achieved in the same process steps. This is particularly effective for recycling packaging materials composed of different plastic layers (e.g., PET and PE). The PET layers can be degraded into their monomers (terephthalic acid and ethylene glycol) and recycled with good purity and quality. Simultaneously, ink is removed not only from the PET or its monomeric components but also from the intact PE material, which can be reused in virgin quality after washing.

[0078] This method is energy-efficient because it operates under ambient conditions or at normal pressure and temperatures as low as 50°C.

Claims

1. A method for removing an ink layer from a first plastic material to obtain an ink-free first plastic material, the method comprising the steps of: a) Providing raw materials, said raw materials comprising at least a layer of first plastic material and an ink layer applied to the layer of first plastic material; b) In the presence of a base, the raw material is contacted with a metal oxide in solution to provide a reaction mixture; c) Stir the reaction mixture under UV light for an appropriate time while allowing the ink layer to degrade, wherein the first plastic material remains intact; and d) Recover the first plastic material from the reaction mixture.

2. The method according to claim 1, wherein the first plastic material is selected from the group consisting of polyolefins, preferably polypropylene (PP) or polyethylene (PE), such as low-density PE (LDPE) and high-density PE (HDPE), polyvinyl chloride (PVC) or polystyrene (PS).

3. The method according to any one of the preceding claims, wherein the ink layer is a water-based ink, a solvent-based ink, or a UV ink.

4. The method according to any one of the preceding claims, wherein the appropriate time is from 10 minutes to 5 hours.

5. The method according to any one of the preceding claims, wherein step c) is performed at a temperature between 20°C and 60°C and at approximately normal atmospheric pressure.

6. The method according to any one of the preceding claims, wherein the metal oxide is selected from the group consisting of: TiO2, ZnO, ZrO2, Nb2O5, Ta2O5, RuO, Fe2O3, WO3.

7. The method according to any one of the preceding claims, wherein the solution is ethanol or an ethanol:water solution of 90:10 to 10:

90.

8. The method according to any one of the preceding claims, wherein the alkali is selected from those comprising NaOH and NaO. t The group consisting of Bu and KOH.

9. The method according to any one of the preceding claims, wherein the reaction mixture further comprises a surfactant, preferably a cationic surfactant selected from the group consisting of hexadecyltrimethylammonium bromide (CTAB), hexadecyltrimethylammonium chloride (CTAC), and alkyl dimethyl benzyl ammonium chloride (ADBAC).

10. The method according to any one of the preceding claims, wherein the recycling step d) comprises washing the first plastic with water, optionally followed by washing with alcohol, preferably ethanol or methanol.

11. The method according to any one of the preceding claims, wherein the raw material is multilayered, including a layer of a second plastic material, wherein the second plastic material is polyethylene terephthalate (PET).

12. The method of claim 11, wherein during step c), the polyethylene terephthalate (PET) layer is depolymerized into terephthalic acid (TPA) and ethylene glycol (EG).

13. The method of claim 12, wherein after step c) or d), terephthalic acid (TPA) and ethylene glycol (EG) are recovered from the reaction mixture.

14. The method of claim 13, wherein the recovered terephthalic acid (TPA) is purified using graphite, activated carbon, and molecular sieves to remove organic and inorganic contaminants.

15. The method according to any one of the preceding claims, wherein the raw material comprises a first plastic material of one type or a mixture of different types of first plastic materials.

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