How to Separate Silicone Coatings from Plastic Films

Abstract

The present invention relates to a method for separating silicone coatings from plastic films, comprising the steps of: crushing a material formed of a plastic sheet having a silicone coating; at least one removal step to remove the silicone coating, which involves at least one ultrasonic activation using a sonotrode; at least one cleaning step of the plastic material with a chemical agent, in which silicone residues dispersed on the surface are removed by a sonotrode submerged in water; rinsing with water at room temperature; and drying the material, wherein the liquid generated in at least one of the removal and cleaning steps undergoes a water treatment step in which clean water and a silicone-containing sludge are separated.

Description

[Technical Field]

[0001] The present invention relates to a method for separating silicone coatings from plastic films, thereby enabling more efficient recycling of the components. The present invention is in the field of plastic recycling, and in particular to a method for recycling coated polyester plastic films and the like.

[0002] A recycling technology based on the separation of silicone coatings from plastic film materials in an aqueous medium by activation using ultrasound is described. Additionally, recovery of the water used in the process is also disclosed, where the silicone slurry is treated by separating it from the clean water itself, which is then returned to the system. [Background technology]

[0003] The production of PET with a silicone coating offers significant advantages over other typical materials previously used, such as paper. The incorporation of silicone as a coating improves the physical properties of the film itself, giving the material greater toughness and strength, as well as tear resistance and high non-stick properties. It also offers greater resistance to ultraviolet (UV) light and reduced water permeability.

[0004] Therefore, its use as a carrier film or release liner in the manufacture of pressure-sensitive adhesives, digital mobile phones, electronic screens, automotive applications, consumer electronics, glass manufacturing, printing, pharmaceuticals, and other surface protection materials is common in various industrial applications. Silicones commonly used as coatings come in a variety of types, including oil-like (10-100 Da), resin-like (100-500 Da), and rubber-like (500-2000 Da) silicones. The plastic material most commonly used for silicone coating is primarily polyester (PET) film.

[0005] The manufacturing process of silicone coated films generates "waste" or "damaged goods" that must be treated for optimal recycling, as do plastic materials once they are used for their designed purposes.

[0006] Recycling this type of material without first removing the silicone results in a lower-quality plastic material used in lower-value-added applications. Therefore, a sustainable solution to remove these coatings is needed to obtain silicone-free PET and improve its reuse.

[0007] In this sense, patents and / or publications relating to silicone removal from non-plastic surfaces and processes describing the use of ultrasound as an activator in cleaning inks on plastic and non-plastic media can be found in the literature.

[0008] Patent Document 1 describes a process for removing silicone residues from ceramic or metal-electronic surfaces, preferably using a nonionic surfactant and an organic solvent as a reagent. The use of solvents requires the installation of equipment for safely storing the used solvent, which increases the cost of the equipment itself. Furthermore, the generated waste must be disposed of in a way that does not damage the ecosystem.

[0009] It is also possible to find technologies that describe the removal of ink from single-layer / multilayer materials in aqueous media, incorporating the use of ultrasound to increase the efficiency of the process. Patent Documents 2, 3, and 4 describe the recycling of plastic materials using ultrasound in the washing process. Patent Documents 5 and 6 also stand out, which describe the first treatment of pre-shredded laminated plastic with an aqueous solution to remove ink printed on the surface. After a water washing process using ultrasound and drying, a separate plastic sheet free of ink is obtained.

[0010] Regarding ink removal, tests published by BRIO Ultrasonics on YouTube® have been shown to remove paint films from a variety of surfaces, and ultrasound has also been used in aqueous media to facilitate this separation / removal process.

[0011] Patent Document 5, which has been made publicly available, describes a method for cleaning and recycling plastics. This method is based on a surface cleaning process for materials to remove small impurities and fatty compounds adhering to the plastic surface. All of the process is carried out on the surface, and ultrasonic bath technology is used for surface cleaning of dust, paper, etc., while high pressure is used for surface cleaning of fatty compounds without using ultrasound. This document does not describe the separation of plastics from silicone coatings, nor does it suggest the possibility of purifying and recycling the water used in the material cleaning process.

[0012] Similarly, the now publicly known US Pat. No. 6,269,669 describes a method for removing resins from plastic surfaces, in particular polycarbonate resin from compact discs in which an aluminum reflective layer has been added to the polycarbonate, and this methodology employs ultrasonic bath technology. This document does not address silicones and does not describe the possibility of recovering the protective coating, nor does it describe recovering, purifying and recycling the water used in this process.

[0013] Even if an expert in this field were to combine the two immediately preceding prior art techniques, the problem would arise that the silicone is not decomposed and therefore cannot be separated or recovered, and furthermore, there would be no solution to the problem of treating the water used in this process.

[0014] These methods already known in the art do not disclose a method for separating the silicone coating from the plastic surface and recovering the plastic material and the silicone separately.Similarly, these methods do not mention a method for recovering and recycling the aqueous solution used during the sample processing.Therefore, the problem of improving the recycling of plastic films with silicone coatings remains unsolved effectively.

[0015] The applicant is not aware of an effective solution to such a problem as that claimed in the present application. [Prior art documents] [Patent documents]

[0016] [Patent Document 1] US Patent Application Publication No. 2002 / 0000239 [Patent Document 2] Chinese Patent Application Publication No. 108501255 [Patent Document 3] Chinese Patent Application Publication No. 113752430 [Patent Document 4] Japanese Patent Application Publication No. 59-189946 [Patent Document 5] Chinese Patent Application Publication No. 110774485 [Patent Document 6] International Publication No. 2022 / 044941 [Patent Document 7] Japanese Patent Application Publication No. 06-063942 [Patent Document 8] U.S. Patent No. 9,751,899 Summary of the Invention [Problem to be solved by the invention]

[0017] The present invention relates to a method for separating a silicone coating from a plastic film, as claimed in the appended claims, the various embodiments of which solve a problem in the art.

[0018] Considering the large amount of plastics generated worldwide and the need to find useful recycling applications for plastics, there is a great need to remove the coatings deposited on this type of material. In this sense, research and development has been carried out to develop processes that allow the separation of silicone coatings from film materials, improving the quality of the material itself and increasing the added value of the recovered products.

[0019] The method for separating silicone-coated plastic materials involves various steps, such as pretreatment, crushing, and separation of the silicone coating using ultrasound in an aqueous medium. The incorporation of ultrasound into the system significantly reduces process residence times, depending on the purity of the material being recovered, and also allows for the reduction of cleaning chemicals. Foam formation can be reduced, and therefore the use of antifoam agents can be reduced or even avoided. This reduces the high costs associated with the consumption of antifoam agents and the costs associated with water treatment.

[0020] The method involves an environmentally sustainable system that recycles the water used in the process. This technology performs water treatment, recirculates clean water through the system, and recovers the released silicone in the form of a slurry that can be subsequently processed for use in other industrial applications. Thus, the present invention offers the advantage of separating and purifying the water used throughout the process, reducing the amount of water required.

[0021] Furthermore, as shown in Patent Document 8, by separating the silicone from the solution, the silicone can be recovered and reused for other uses, thereby significantly reducing and minimizing waste generated in the process.

[0022] The method developed in this invention can be used not only with recycled products (those that have already served their manufacturing purpose) but also with "waste" or "damaged goods" or off-cuts generated during the production of plastic coatings. [Means for solving the problem]

[0023] In this context, the present invention develops an innovative technology for removing silicone coatings from plastic film materials using ultrasonication as an aqueous-based activation method. Silicones can be gaseous (<10 Da), oily (10-100 Da), resinous (100-500 Da), and / or rubbery (500-2000 Da). Resinous silicones are of particular interest.

[0024] Specifically, the method for separating the silicone coating from the plastic film involves: crushing the material formed of a plastic sheet having a silicone coating; a removal step of removing the silicone coating from the plastic in one or more tanks with an aqueous solution at 20-100°C and mechanical agitation, comprising at least one ultrasonic activation with a sonotrode submerged in water at a frequency of 15-100 kHz for at least 10 minutes and at least one separation of the silicone solids; at least one cleaning step of the plastic material with a chemical agent, in which silicone residues dispersed on the surface are removed by a sonotrode submerged in water, at the same frequency and amplitude as in the previous step; A rinsing process with room temperature water; The drying process and Including, The liquid generated during the removal process and / or chemical cleaning process to remove the silicone coating is subjected to water treatment to separate clean water from silicone-containing sludge and recover the silicone, allowing the clean water to be recycled to one of the previous processes.

[0025] In one possible embodiment of the present invention, the liquid generated in the rinsing step can also be subjected to a water treatment step, in which clean water is separated and can be recycled to either the removal step, the washing step or the rinsing step.

[0026] The ultrasonic waves generated by the sonotrode submerged in water are emitted at a frequency of 15 to 100 kHz, preferably 15 to 25 kHz, with a specific contribution to the solution of 3 to 200 J / mL. The amplitude is 12 to 42 micrometers. In this respect, the present invention, compared to others known in the art, is based essentially on the use of a sonotrode submerged in water to generate and guide ultrasonic waves for carrying out ultrasonic cleaning, instead of the use of an ultrasonic bath, in which bubbles generated by the generation of ultrasonic waves in the solution (cavitation phenomenon) burst when they come into contact with the surface to be treated. In this invention, the use of a sonotrode submerged in water is essential, as it is not possible to carry out the process using an ultrasonic bath.

[0027] The drying process can include mechanical drying and hot air drying.

[0028] Other variants are set out in the dependent claims and are explained below.

[0029] Considering the above, the system used to develop the aforementioned method is a shearing crusher, which may include movable and fixed blades and a series of screens for particle size classification; At least one tank containing an aqueous solution at a temperature of 20 to 100°C, including a blade or propeller agitator and a sonotrode submerged in water; Has chemicals at least one cleaning tank; a rinse tank containing room temperature water; a drying device comprising a centrifuge or other mechanical separation system and a hot air drying system or the like; at least one water treatment device or tank including means for separating silicone sludge and recovering recyclable water; Equipped with.

[0030] Finally, it should be considered that throughout this specification and claims, the terms "comprises," "includes," and their variations are not intended to exclude or limit other technical features or additional elements.

[0031] To supplement the following description and to enable a better understanding of the features of the present invention, according to its preferred and practical embodiments, drawings are attached as an integral part of the following description, in which the following are depicted together with illustrative and non-limiting features: [Brief explanation of the drawings]

[0032] [Figure 1] FIG. 1 illustrates an exemplary embodiment of the described method along with the devices involved therein. DETAILED DESCRIPTION OF THE INVENTION

[0033] Some embodiments of the present invention are briefly described below as illustrative and non-limiting examples thereof.

[0034] The method of this embodiment starts with a material formed of a plastic sheet having a silicone coating. The input material is polyester (PET), polyethylene (PE), polypropylene (PP), or polyamide. (PA)The material can be a film of original origin. If this material comes from waste, it may arrive inserted in a mandrel. In this case, a preliminary step (0) involves removing the plastic from the mandrel and removing any unsuitable or foreign material (for example, using a magnet to remove ferromagnetic materials or cleaning to remove dust and other similar contaminants). If this is not the case, the process goes directly to the first step, which corresponds to the crushing step (1). Similarly, if the material is already small, this first step can be omitted.

[0035] In the embodiment, the crushing step (1) is carried out using a shear crusher to obtain crushed material having a size of 2 to 10 cm, preferably 4 to 6 cm. The shear crusher has a movable blade, a fixed blade, and a series of screens for particle size classification.

[0036] The next step is removal of the silicone coating (2), or washing to recover the remaining material (usually PET plastic). Coating removal (2) is performed in one or more tanks containing an aqueous solution at a temperature of 20-100°C and involves at least one ultrasonic activation at a frequency of 15-25 kHz for at least 10 minutes and at least a first separation of the silicone solids. Specifically, in this embodiment, a first ultrasonic activation at a frequency of 15-25 kHz for at least 10 minutes with a submerged sonotrode and a first separation of the silicone solids is performed, followed by a second ultrasonic activation at a frequency of 15-25 kHz with a submerged sonotrode and a second separation of the silicone solids.

[0037] The chemical tank is mechanically agitated using a blade or propeller agitator, and ultrasonically activated using a submerged sonotrode. The chemical cleaning process can be based on an aqueous solution containing a surfactant at a concentration of 0.1-50 g / L, preferably 0.1-2 g / L. The latter improves process economy and reduces antifoam consumption, but can also achieve efficiencies of over 80%. The chemical can be a surfactant with a quaternary ammonium salt structure, an ether structure, an aromatic sulfonate structure, and / or an alkyl chain structure consisting of a C4-C24 carbon chain. The pH varies depending on the type of material, with preferred ranges being 1-5 or 8-14. For example, the antifoam can be a mixture of a polydimethylsiloxane derivative and other silicones.

[0038] The plastic material is conveyed to a chemical cleaning station (3), followed by a rinsing station (4) and then a drying station (5).

[0039] The liquid generated from the tanks of the silicone coating removal step (2) and / or the washing step (3) is diverted to water treatment (6) with recovery of the silicone in slurry form (7).

[0040] Cleaning of the material with chemicals in water (3) removes silicone residues dispersed on the surface and / or any remaining traces that may be present, for example by applying a sonotrode at the same frequency and amplitude as in the previous step. The cleaning water is preferably conveyed to a tank or device for the water treatment step (6). Cleaning (3) can be carried out in the same tank as the cleaning or removal of the coating (2).

[0041] The washing step (3) is carried out several times in one or several successive tanks until the plastic film is completely washed. Rinse with room temperature water (4). First, drying in a drying device with a centrifuge or other mechanical separation system, then drying with hot air or similar (5)This allows for a reusable material with a reduced moisture content to be obtained, which can then be melted and pelletized, for example.

[0042] Water at room temperature can be understood to refer to clean water preferably at a temperature of 20°C to 25°C.

[0043] Furthermore, in this embodiment, the liquid generated in the rinse (4) is subjected to a water treatment step (6) to separate clean water.

[0044] In the water treatment step (6), clean water (95-99% purity) is separated from the silicone-containing sludge. The clean water is conveyed to the tanks for the washing (3), coating removal (2), and / or rinsing steps (4) as required by the system, thereby optimizing water consumption. Furthermore, the water treatment device or water treatment tank is equipped with a means for separating the silicone sludge by evaporation or by other techniques for recovering recyclable water, such as membrane filtration, evaporation, decantation (without flocculation), decantation with flocculation, or a combination of these techniques.

[0045] The slurry is collected to recover the silicone (7), which can be done in several ways, for example by conversion to alkoxysilanes, as described in US Pat. No. 5,649,399.

[0046] The present invention is believed to be applicable to the following process conditions for coating removal (2): plastic concentration of 1-200 g / L, surfactant concentration of 0.1-50 g / L, temperature of 40-100°C, and hydraulic retention time (HRT) of 10-60 minutes.

[0047] In this regard, a test was carried out and it was found that when 2874 kg of plastic material was received for processing, 2526 kg of clean plastic material was produced, with a total loss of plastic and silicone sludge of 348 kg, of which a total of 268 kg of plastic could be dried and 80 kg of silicone sludge could be obtained for subsequent processing, resulting in a silicone removal rate of 82%.

Claims

1. 1. A method for separating a silicone coating from a plastic film, comprising: (1) a step of crushing a material formed of a plastic sheet having a silicone coating; at least one removal step (2) of removing the silicone coating from the plastic in one or more tanks with an aqueous solution at 20-100°C and mechanical agitation, comprising at least one ultrasonic activation with a sonotrode submerged in water at a frequency of 15-100 kHz for at least 10 minutes and at least one separation of silicone solids; at least one cleaning step (3) of the plastic material with a chemical agent, in which silicone residues dispersed on the surface are removed by a sonotrode submerged in water, at the same frequency and amplitude as in the previous step; A rinsing step (4) with room temperature water; a step (5) of drying the material; Including, The liquid generated in at least one of the removal step (2) and the chemical cleaning step (3) is sent to a water treatment step (5) in which the clean water and the silicone-containing sludge are separated, and then to a silicone recovery step (6). method.

2. 2. The method for separating silicone coatings from plastic films according to claim 1, wherein in the chemical washing step (3), the aqueous solution has a surfactant concentration of 2 to 50 g / L.

3. The method for separating a silicone coating from a plastic film according to claim 2, wherein the surfactant is a surfactant having a quaternary ammonium salt structure, an ether structure, an aromatic sulfonate structure, and / or an alkyl chain structure composed of a carbon chain formed from C4 to C24.

4. 2. The method for separating silicone coatings from plastic films according to claim 1, characterized in that in the chemical washing step (3), the aqueous solution has a surfactant content of 0.1 to 2 g / L.

5. 2. The method for separating silicone coatings from plastic films according to claim 1, characterized in that the drying step (5) includes mechanical drying and hot air drying.

6. 2. A method for separating a silicone coating from a plastic film according to claim 1, characterized in that the method includes a preliminary step (0) of removing undesirable material.

7. 2. The method for separating silicone coatings from plastic films according to claim 1, characterized in that the material in the coating removal (2) tank has a dimension of 2 to 10 cm.

8. 2. The method of claim 1, wherein the clean water separated from the water treatment step (6) is recycled to the removal step (2) for removing the silicone coating.

9. 2. The method for separating silicone coatings from plastic films according to claim 1, wherein the clean water separated from the water treatment step (6) is recycled to the chemical washing step (3).

10. 2. The method for separating silicone coatings from plastic films according to claim 1, characterized in that the liquid generated in the rinsing step (4) is recycled to either the removing step (2), the washing step (3) or the rinsing step (4) via a water treatment step (5) in which the clean water is separated.

11. A system for separating a silicone coating from a plastic film for carrying out the method according to any one of claims 1 to 10, comprising: a shearing crusher; at least one tank containing an aqueous solution at a temperature of 20 to 100°C, comprising a blade or propeller agitator and a sonotrode submerged in water; at least one cleaning tank; a drying device having a mechanical separation system and a hot air drying system; at least one water treatment device or tank including means for separating said silicone sludge and recovering recyclable water; A system comprising:

12. 12. The system of claim 11, wherein the shear-type crusher comprises a moving blade, a fixed blade, and a series of screens for particle size classification.

13. The system of claim 11 , wherein the mechanical separation system of the drying apparatus comprises a centrifuge.

14. 12. The system of claim 11, wherein the water treatment device or water treatment tank comprises means for separating silicone sludge by evaporation.

15. 12. The system of claim 11, wherein the water treatment device or water treatment tank comprises means for recovering recyclable water, such as membrane filtration, evaporation, decantation, decantation with flocculation, or a combination of these techniques.

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