Method for separating silicone coating from plastic film

Abstract

The invention relates to a method for separating a silicone coating from a plastic film, comprising: a step of crushing a material made of a plastic sheet containing a silicone coating; at least one removal step of the silicone coating, the at least one removal step comprising at least one ultrasonic activation with an immersed sonar probe; at least one step of washing the material made of plastic with a chemical agent, wherein the silicone residue dispersed on the surface is eliminated by using an immersed sonar probe; washing with water at room temperature; a step of drying the material; wherein a liquid generated in at least one of the removal step and the washing step enters a water treatment step in which separation between clear water and a sludge containing the silicone is performed.

Description

Technical Field

[0001] The present invention relates to a method for separating silicone coatings from plastic films. This method allows for more efficient recycling of each component. The present invention belongs to the field of plastics recycling technology and, in particular, relates to a method for recycling coated polyester plastic films and the like.

[0002] A recycling technology is described, which consists of separating the silicone coating from the plastic film material in an aqueous medium and by activation using ultrasound. Furthermore, the recycling of the water used in the process is disclosed, by separating the silicone from the clean water itself in the form of a slurry and introducing the clean water back into the system. Background Art

[0003] Manufacturing PET with a silicone coating offers significant advantages over other typical materials used to date, such as paper. The incorporation of silicone as a coating improves the physical properties of the film itself, imparting greater consistency and strength, as well as tear resistance and high non-stick properties. Furthermore, it offers strong resistance to ultraviolet (UV) radiation and low water permeability.

[0004] For this reason, it is widely used in different industrial fields, including: manufacturing pressure-sensitive adhesives as carrier films or release media, such as materials in digital mobile phones, electronic screens, automotive applications, household appliances, glass manufacturing, printing, medicine and other surface protection. Usually, the silicone used as coating can have various types, such as oil-type silicones (between 10Da and 100Da), resins (between 100-500Da) and rubbers (between 500Da and 2000Da). The most commonly used plastic support for silicone coatings is mainly polyester film (PET).

[0005] During the manufacturing process of silicone coated films, "waste" or "scrap" is generated which must be treated for optimal recycling. The same is true for plastic materials when used for design purposes.

[0006] Without prior silicone removal, recycling this material results in low-quality plastic material for low-value-added applications. A sustainable solution is needed to remove these coatings to obtain silicone-free PET and thus increase its recycling rate.

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

[0008] Application US2002 / 0000239A1 describes a process for removing silicone residues from ceramic or metal electronic surfaces, preferably using a nonionic surfactant and an organic solvent. The use of a solvent requires the implementation of an infrastructure for the safe storage of the solvent used, which increases the cost of the facility itself. Furthermore, it is necessary to ensure that the resulting waste is disposed of in a manner that does not disrupt the ecosystem.

[0009] It's also possible to find technologies describing the removal of ink from single-layer and multilayer materials in aqueous media, in which the use of ultrasound has been incorporated to improve process efficiency. Patents CN108501255A, CN113752430A, and JPS59189946A describe the use of ultrasound in a washing step to recycle plastic materials. Furthermore, CN110774485A and WO2022044941A1 are also noteworthy, first describing the treatment of previously ground laminated plastics with an aqueous solution to remove ink printed on the surface. After washing and drying steps in water using ultrasound, the resulting plastic sheets are free of ink.

[0010] Regarding ink removal, tests posted on YouTube by Brio Ultrasonics found that paint coatings could be removed from various surfaces, and that using ultrasonic waves, using an ultrasonic bath device in a water medium could facilitate this separation / removal process.

[0011] In this context, the previously cited CN110774485A discloses, on the one hand, a method for cleaning and recycling hard plastic waste, based on a stage of surface washing of the material to remove small particles or dust adhering to the plastic surface (using ultrasonic bath technology), and a second stage for removing fatty compounds by high-pressure cleaning. This document does not address the problem of separating the plastic from the silicone coating, nor does it propose the possibility of purifying and recycling the water used in the washing stage.

[0012] On the other hand, JPH0663942 discloses a method for removing resin from plastic surfaces, specifically polycarbonate resin from optical discs, where these plastic surfaces also contain an aluminum reflective layer. This method is based on the use of an ultrasonic bath. This document does not address silicones and does not describe the possibility of recovering the protective coating. It also does not address the possibility of purifying and recycling the water used in the process.

[0013] In the case of a combination of these last two prior arts by experts in the field, the problem of separating the silicone coating from the plastic surface cannot be solved, since with these techniques the silicone does not degrade and therefore cannot be separated and recovered; and in addition, the problem of treating the water used in the process also needs to be solved.

[0014] These methods known in the prior art do not disclose how to separate the silicone coating from the plastic surface, nor how to recover the plastic material and silicone separately. Similarly, there is no mention of methods for recovering and recycling the aqueous solution used during sample processing, nor is there any mention of the possibility of recycling and reusing the recovered aqueous solution. Therefore, the problem of how to increase the recycling rate of silicone-coated plastic films remains to be effectively solved.

[0015] Applicants are not aware of any solution that solves these problems as effectively as claimed in the present invention. Summary of the Invention

[0016] The invention relates to a method for separating a silicone coating from a plastic film, according to the claims. Different embodiments thereof solve the problems existing in the prior art.

[0017] Given the vast quantities of plastic produced worldwide and the need to find a useful second life for them, removing the coatings deposited on these materials is essential. In this sense, a process has been developed that makes it possible to separate silicone coatings from membrane materials, thereby improving the quality of the material itself and adding value to the recycled product.

[0018] The method for separating silicone-coated plastic materials involves various steps, including pretreatment, grinding, and the use of ultrasound in an aqueous medium to separate the silicone coating. Depending on the purity of the material being recovered, incorporating ultrasound into the system can significantly shorten process residence times and also reduce the use of cleaning agents. This reduces foam formation, thereby reducing or even eliminating the use of defoamers. This reduces the high costs associated with the consumption of defoamers and the costs associated with water treatment.

[0019] The method includes an environmentally sustainable system that recycles the water used in the process. This technology allows for water treatment, recycling clean water back into the system, and recovering the released silicone as a slurry, which can then be processed for other industrial applications. Therefore, the present invention offers the advantage of separating and purifying water used in previous steps of the overall process, thereby reducing the amount of water required.

[0020] Furthermore, as shown in patent US9751899B2, by separating the silicone from the solution, the silicone can be recovered and reused in other applications, thereby greatly reducing the waste generated in the process to a minimum.

[0021] The method developed by the present invention can be used both for recycled products (which have been used for the purpose for which they were produced) and for materials produced during the manufacturing process of the plastic coating which have to be "discarded", "scrapped" or cut up.

[0022] In this context, the present invention has developed an innovative technology that uses ultrasound as a water-based activation method to remove silicone coatings from plastic film materials. The silicone can be of the following types: gaseous (less than 10 Da); oil (between 10 Da and 100 Da); resin (between 100-500 Da) and / or rubber (between 500 Da and 2000 Da). This method is particularly suitable for resins.

[0023] Specifically, the method for separating a silicone coating from a plastic film comprises:

[0024] a step of fragmentation of a material made of plastic sheets containing a silicone coating; at least one step of removal of said silicone coating from the plastic in one or more tanks containing an aqueous solution at 20-100° C. and under mechanical stirring, said step comprising at least one ultrasonic activation for at least 10 minutes using an immersion sonar probe at a frequency between 15 and 100 kHz, and at least one separation of the silicone solids;

[0025] at least one washing step of the material made of plastic with a chemical agent, in which silicone residues dispersed on the surface are eliminated by using an immersion sonar probe at frequencies and amplitudes similar to those of the previous step;

[0026] A rinse step with room temperature water; and

[0027] drying step;

[0028] wherein the liquid produced in the step of removing the silicone coating and / or the step of washing with a chemical agent is subjected to a water treatment, in which separation is performed between clean water and a sludge containing the silicone, and the silicone is recovered; and

[0029] In the water treatment, clean water can be recycled back to the previous steps.

[0030] In a possible embodiment of the invention, the liquid produced in the rinsing step can also be subjected to a water treatment in which a separation of clean water is performed; and in which the clean water can be recycled back to any removal, washing or rinsing step.

[0031] The ultrasonic waves generated by the submerged sonar probe are emitted at 15-100 kHz, preferably between 15-25 kHz, with a specific contribution to the solution of 3-200 J / ml. The amplitude is 12-42 microns. In this sense, compared to other technologies known in the prior art, the present invention is based on the use of a submerged sonar probe to generate ultrasonic waves that produce focused, imploding (cavitation) microbubbles for ultrasonic cleaning, rather than the prior art use of an ultrasonic bath that generates ultrasonic waves from the reactor wall toward the center. In the present invention, the use of a submerged sonar probe is essential, and the use of an ultrasonic bath for the process is not possible.

[0032] The drying step may include mechanical drying and hot air drying.

[0033] Further variants are described in the independent claims and below.

[0034] Taking into account the previously indicated, the system used to develop the above method comprises:

[0035] a toothed roll crusher (un trituradador de cuchillas), which may comprise movable and fixed blades, and a series of screens for particle size classification;

[0036] at least one tank containing an aqueous solution at a temperature of 20-100° C.; the at least one tank comprising a blade or propeller stirrer and an immersion sonar probe;

[0037] at least one sink;

[0038] Drying equipment having a centrifuge or other mechanical separation system and a hot air drying system or the like; and

[0039] At least one water treatment apparatus or tank containing means for separating silicone sludge and recovering recyclable water.

[0040] Finally, it must be considered that throughout the description and claims, the term "comprises" and its variations are not intended to exclude or restrict other technical features or additional elements. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] To supplement the description that will be given below and to help better understand the characteristics of the invention, according to a preferred practical embodiment of the invention, the accompanying drawings are included as an integral part of said description, in which the following are depicted in an illustrative and non-limiting manner:

[0042] Figure 1 : Figures of exemplary embodiments of the described methods and of the apparatus involved therein. DETAILED DESCRIPTION

[0043] Several embodiments of the present invention will be briefly described below as illustrative and non-limiting examples thereof.

[0044] The method of this embodiment is based on a material consisting of a plastic sheet containing a silicone coating. The input material can be a polyester film (PET), polyethylene (PE), polypropylene (PP) or polyamide (PLA). If this material comes from waste, it may arrive on the mandrel. In this case, the preliminary step (0) is to remove the plastic from the mandrel and remove unsuitable materials or foreign matter (for example, using a magnet to remove ferromagnetic materials, or by washing to remove dust and other similar contaminants). Otherwise, move directly to the first stage, corresponding to the grinding or crushing step (1). Similarly, if the material has already been reduced in size, the first stage can be eliminated.

[0045] The crushing step (1) of the example is carried out with a toothed roll crusher to obtain a ground material with a size of 2-10 cm, preferably 4-6 cm. The toothed roll crusher has movable and fixed blades and a series of screens for screening the particle size.

[0046] The next step is to remove the silicone coating (2) or to clean it in order to recover the remaining material, usually PET plastic. The removal of the coating (2) takes place in one or more tanks containing an aqueous solution at a temperature of 20-100°C, and comprises at least one ultrasonic activation with an immersion sonar probe at a frequency of between 15-25 kHz for at least 10 minutes, and at least one separation of the silicone solids. In an embodiment of the present invention, a first ultrasonic activation with an immersion sonar probe at a frequency of between 15-25 kHz for at least 10 minutes, and a first separation of the silicone solids, is followed by a second first ultrasonic activation with an immersion sonar probe at a frequency of between 15-25 kHz for at least 10 minutes, and a second separation of the silicone solids.

[0047] In the chemical washing tank, mechanical stirring is performed using a blade or propeller stirrer, and ultrasonic activation is performed using an immersion sonar probe. This chemical washing step is based on an aqueous solution containing a surfactant at a concentration of between 0.1 g / l and 50 g / l, preferably 0.1-2 g / l, to improve process economy and reduce defoamer consumption, although it is possible to achieve an efficiency of over 80%. The agent can be a surfactant, each of which has a quaternary ammonium salt structure, an ether structure, an aromatic sulfonate structure, and / or an alkyl chain structure composed of carbon chains formed from C4-C24. The pH depends on the type of material, with a preferred range of 1-5 or 8-14. For example, the defoamer can be a mixture of polydimethylsiloxane and other silicone derivatives.

[0048] The plastic material is washed with chemical agents (3) and then rinsed (4) and dried (5) in relevant steps.

[0049] The liquid generated from the tank of the silicone coating removal step (2) and / or the washing step (3) is diverted to the water treatment (6) step to recover the silicone in the slurry (7).

[0050] The material is washed (3) in water with a chemical agent to remove any silicone residues and / or trace residues that may be present on the surface, and by way of example, a sonar probe may be applied at a frequency and amplitude similar to that of the previous step. In the water treatment step (6), the washing water is preferably conveyed to a water treatment tank or device. Washing (3) can be carried out in the same tank as that used to clean or remove the coating (2).

[0051] The washing step (3) is repeated several times in one or more successive tanks until the plastic film is completely clean. Drying (4) is then carried out, initially in a drying apparatus with a centrifuge or other mechanical separation system, and then by hot air drying or similar drying. This allows obtaining a reusable material with a low moisture content. For example, it can be melted for granulation.

[0052] It will be understood that water at room temperature refers to clear water at a temperature preferably between 20°C and 25°C.

[0053] In addition, in this embodiment, the liquid produced in the flushing (4) is subjected to a water treatment step (6) and clean water is separated therefrom.

[0054] The water treatment (6) step separates clean water (95-99% purity) from the silicone-containing slurry. The clean water can be recycled or, depending on the needs of the system, can be sent to tanks for washing (3), coating removal (2), or rinsing (4). This recycling has the advantage of optimizing water consumption. In addition, the water treatment equipment or tank contains a device for separating the silicone slurry or sludge by evaporation-condensation or by other techniques such as membrane filtration, evaporation, decantation (without flocculation), decantation in the case of flocculation, or a combination of these techniques to recover recyclable water.

[0055] The slurry is conveyed to recover the silicone (7), which can be carried out in several ways, for example by converting it into alkoxysilane as described in US Pat. No. 9,751,899 B2.

[0056] It is believed that the present invention is applicable to the following working conditions: such as at a temperature of 40-100°C, in the coating removal step (2), the plastic concentration is 1-200 g / l, and the surfactant is included in a concentration between 0.1 g / l and 50 g / l, and the hydraulic retention time (HRT) is 10-60 minutes.

[0057] In this way, a test was carried out in which 2874 kg of plastic material to be treated was processed and 2526 kg of clean plastic material was produced, with a total loss of 348 kg of plastic and silicone sludge, wherein it was possible to dry a total of 268 kg of plastic and obtain 80 kg of silicone sludge that was subsequently processed. As a result, a silicone removal rate of 82% was achieved.

Claims

1. A method for separating a silicone coating from a plastic film, the method comprising: A crushing step (1) of a material made of a plastic sheet containing a silicone coating; at least one step (2) of removing the silicone coating from the plastic is carried out in one or more tanks containing an aqueous solution at 20-100° C. and under mechanical stirring, this step comprising at least one ultrasonic activation for at least 10 minutes at a frequency between 15 and 100 kHz using an immersion sonar probe, and at least one separation of the silicone solids; at least one washing step (3) of the material made of plastic with a chemical agent, wherein silicone residues dispersed on the surface are eliminated by using an immersion sonar probe at a frequency similar to that of the previous step; a rinsing step (4) with room temperature water; and a drying step (5) of the material; The liquid generated in at least one of the removal step (2) and the washing step (3) with a chemical agent enters a water treatment step (5) where separation is performed between clean water and sludge containing the silicone, and then enters a silicone recovery step (6).

2. The method for separating a silicone coating from a plastic film according to claim 1, characterized in that In the washing step (3) with a chemical agent, the concentration of the surfactant in the aqueous solution is between 2 g / l and 50 g / l.

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

4. The method for separating a silicone coating from a plastic film according to claim 1, characterized in that In the washing step (3) with a chemical reagent, the proportion of the surfactant in the aqueous solution is 0.1-2 g / l.

5. The method for separating a silicone coating from a plastic film according to claim 1, characterized in that The drying step (5) comprises mechanical drying and hot air flow drying.

6. The method for separating a silicone coating from a plastic film according to claim 1, characterized in that The method comprises a preliminary step (0) of removing unsuitable material.

7. The method for separating a silicone coating from a plastic film according to claim 1, characterized in that The size of the material in the coating (2) removal trough is 2-10 cm.

8. The method for separating a silicone coating from a plastic film according to claim 1, wherein the clean water separated from the water treatment step (6) is recycled back to the removal step (2) of the silicone coating.

9. The method for separating a silicone coating from a plastic film according to claim 1, wherein the clean water separated from the water treatment step (6) is recycled back to the washing step (3) with the chemical agent.

10. The method for separating a silicone coating from a plastic film according to claim 1, wherein the liquid produced in the rinsing step (4) enters the water treatment step (5), in which separation of the clean water is performed and then the clean water is recycled back to any of the removal step (2), the washing step (3) or the rinsing step (4).

11. A system for separating a silicone coating from a plastic film, said system being used for carrying out the method according to any one of claims 1 to 10, characterized in that: The system comprises: Toothed roller crusher (un trituradador de cuchillas); at least one tank containing an aqueous solution at a temperature of 20-100° C.; the at least one tank comprising a blade or propeller stirrer and an immersion sonar probe; at least one sink; Drying equipment, the drying equipment having a mechanical separation system and hot air drying; as well as At least one water treatment apparatus or tank containing means for separating silicone sludge and recovering recyclable water.

12. The system of claim 11, wherein the toothed roll crusher comprises movable blades and fixed blades, 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. The system of claim 11, wherein the water treatment apparatus or drum comprises means for separating the silicone sludge by evaporation.

15. The system of claim 11, wherein the water treatment apparatus or tank comprises a recirculating water recovery device such as membrane filtration, evaporation, decantation, decantation under flocculation, or a combination of these technologies.

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