TWI875589B - Method for separating and grouping substrates - Google Patents

Abstract

A method for separating and grouping substrates includes providing a mixture of substrates. The mixture of substrates includes a first substrate and a second substrate that are made of different materials. The first substrate has a first density and the second substrate has a second density, wherein the first density is different from the second density. The method further includes providing a solution that has a third density. At least one of the first density and the second density is different from the third density. The method further includes adding the mixture of substrates into the solution, and the first substrate and the second substrate are separated and positioned at different levels of the solution.

Description

Substrate Sorting Method

The present invention relates to a substrate sorting method, in particular to a substrate sorting method which is fast, safe, low-cost and has high sorting efficiency.

Electronic devices contain a large number of substrates. Traditional methods of disposing of substrates from discarded electronic devices are mainly incineration. However, the incineration method easily causes environmental pollution and cannot be reused. Currently, substrate recycling methods have been developed to reduce environmental pollution, which is in line with the current environmental awareness. Some recycled substrates can also be re-manufactured into other recycled products to increase economic benefits.

The recycling of electronic devices may result in a large number of mixed substrates to be processed. Currently, most methods of sorting mixed substrates take a long time and are less convenient. Taking discarded polarizing plates as an example, the large number of mixed substrates obtained after recycling need to be further sorted and regenerated. Currently, Fourier transform infrared spectrometers (FTIR) are mostly used to identify and classify mixed substrates. Although this method can effectively classify mixed substrates, it is time-consuming and inconvenient. Therefore, although existing substrate sorting methods are generally sufficient to meet their intended purposes, they are not completely satisfactory in all aspects. Researchers continue to seek better substrate sorting methods in all aspects.

Some embodiments of the present disclosure provide a substrate sorting method, comprising: providing a mixed substrate, comprising a first substrate and a second substrate of different materials, wherein the first substrate has a first density, the second substrate has a second density, and the first density is different from the second density; providing a solution, the solution having a third density, wherein at least one of the first density and the second density is different from the third density; and adding the mixed substrate to the solution, so that the first substrate and the second substrate are separated and located at different positions in the solution.

Some embodiments of the present disclosure provide a method for sorting a substrate, comprising: providing the mixed substrate described above, wherein the mixed substrate has a solid weight; providing a container, wherein the container has a bottom area and a height; adding the solution described above into the container; and obtaining a solution volume required for sorting the substrate at a certain sorting rate (e.g., greater than 90%) by the following formula (1): ....Formula (1)

Wherein X is the bottom area of a container containing the aforementioned solution, in cm ² ; Y is the height of the aforementioned container, in cm; Z is the solid weight of the aforementioned mixed substrate, in kg; V is the volume of the aforementioned solution, in L;

The mixed substrate is added into the solution, so that the first substrate and the second substrate are separated and located at different positions in the solution.

Some embodiments of the present disclosure provide a substrate sorting method, comprising: recycling discarded polarizing plates and subjecting them to a treatment process to provide a mixed substrate as described above; providing a solution as described above, and adding the mixed substrate into the solution, separating the first substrate and the second substrate by the difference between the density of the solution and the density of the substrates, and locating them at different positions in the solution.

According to some embodiments, the polarizing plate includes a polarizer and a first protective layer and a second protective layer adhered to opposite sides of the polarizer, and the above-mentioned processing process includes removing iodine from the polarizer and dissolving the polarizer; removing the bonding layer on the first protective layer and the second protective layer; and cleaning the first protective layer and the second protective layer to obtain a clean mixed substrate.

Various implementation methods or examples are presented below to implement different features of the present disclosure, wherein specific elements and their arrangements are described to illustrate the present disclosure, although these are merely examples and should not be used to limit the scope of the present disclosure. For example, when the description mentions that a first element is formed on a second element, it may include an embodiment in which the first element is in direct contact with the second element, and it may also include an embodiment in which other elements are formed between the first element and the second element, wherein the first element and the second element are not in direct contact. In different embodiments and drawings, the same or similar element symbols are used to represent the same or similar elements, but these same or similar element symbol markings are only for the purpose of simply and clearly describing the present disclosure, and do not represent a specific relationship between the different embodiments and/or structures discussed. It is worth noting that the examples are only used to illustrate the technical features of the present disclosure, and are not used to limit the scope of the patent application of the present disclosure. A person with ordinary knowledge in the relevant technical field will be able to make equal modifications and changes based on the following description without departing from the spirit of the present disclosure. Some of the drawings in some embodiments omit some elements to clearly show the technical features of the present disclosure.

In addition, spatially relative terms such as "below", "above", "between" and similar terms may be used to facilitate the description of the relationship between one (or some) elements or features and another (or some) elements or features in the drawings. These spatially relative terms include different orientations of the device in use or operation, as well as the orientations described in the drawings. The device may be rotated to different orientations, and the spatially relative adjectives used therein may also be interpreted accordingly.

Furthermore, the terms "about", "approximately", and "generally" generally mean within +/-20% of a given value, preferably within +/-10%, and more preferably within +/-5%, or within +/-3%, or within +/-2%, or within +/-1%, or within 0.5%. The numerical values given herein are approximate numerical values, that is, in the absence of specific description of "about", "approximately", and "generally", the given numerical values may still imply the meaning of "about", "approximately", and "generally".

Some variations of the embodiments are described below. Although the steps in some of the embodiments described are performed in a particular order, these steps may also be performed in other logical orders. Additional process steps may be performed before, during, and/or after some of the process steps described in the embodiments, and some process steps described in some embodiments may be replaced or deleted by other process steps in the methods of other embodiments. Furthermore, it is understood that other components may be added to the device or system in the embodiments illustrated in the present invention, or some components may be replaced or omitted.

The embodiments of the present disclosure provide a substrate sorting method, which can simply, quickly and safely process the provided mixed substrates (mixture of substrates) through a wet density sorting method, so that each type of substrate is separated in an appropriate sorting solution, which is convenient for picking to complete the substrate sorting. The mixed substrate can be any different type of substrate. For example, the present disclosure can be applied to the recycling process of discarded polarizing plates. After the recycled polarizing plates are subjected to a processing process (for example, to remove iodine, polarizers and residual glue), the related material layers (for example, the protective layers on the upper and lower sides of the polarizers, as described later, which are the substrates of the embodiments) are separated, and then the substrate sorting method of the embodiments can be used to sort and recycle these protective layers. In addition to reducing environmental pollution, the recycled substrate can be re-manufactured into other recycled products.

The following uses polarizing plate recycling as an example to explain the source of mixed substrates and the front-end processing process in the substrate sorting method of some embodiments of the present disclosure.

＜Sources of mixed substrates and front-end processing＞

FIG. 1 is a schematic cross-sectional view of a polarizing plate. The polarizing plate 1 includes a polarizer 102 and a plurality of material layers located on the upper and lower sides of the polarizer 102, such as a first protective layer 104 and a second protective layer 106 that can be attached to opposite surfaces of the polarizer 102 by a bonding layer (not shown). In one embodiment, the first protective layer 104 and the second protective layer 106 may further include other optical film layers, surface protective layers, adhesive layers, and release films (not shown) on the surfaces away from the polarizer 102.

In some embodiments, the polarizer 102 may be a polyvinyl alcohol (PVA) resin film, which may be prepared by saponifying polyvinyl acetate resin. Examples of polyvinyl acetate resins include monomers of vinyl acetate, i.e., polyvinyl acetate, and copolymers of vinyl acetate and other monomers that can be copolymerized with vinyl acetate. Examples of other monomers that can be copolymerized with vinyl acetate include unsaturated carboxylic acids (e.g., acrylic acid, methacrylic acid, ethyl acrylate, n-propyl acrylate, methyl methacrylate), alkenes (e.g., ethylene, propylene, 1-butene, 2-methylpropylene), vinyl ethers (e.g., ethyl vinyl ether, methyl vinyl ether, n-propyl vinyl ether, isopropyl vinyl ether), unsaturated sulfonic acids (e.g., vinyl sulfonic acid, sodium vinyl sulfonate), and the like.

In some embodiments, the material of the first protective layer 104 and the second protective layer 106 can be selected from polymethylmethacrylate (PMMA), triacetyl cellulose (TAC), acrylic resin film, polyaromatic hydroxyl resin film, polyether resin film, cycloolefin resin film (e.g., polybornene resin film), polyethylene terephthalate (PET), polypropylene (PP), cycloolefin polymer (COP), polycarbonate (PC), and a group consisting of any combination thereof.

The adhesive layer may include a water-based adhesive, generally, for example, a polyvinyl alcohol resin or a urethane resin is used as the main component of the water-based adhesive, and in order to improve the adhesiveness, a crosslinking agent or a curing compound such as an isocyanate compound or an epoxy compound may be added to form a composition. In some embodiments, when the main component of the water-based adhesive is a polyvinyl alcohol resin, in addition to partially saponified polyvinyl alcohol and completely saponified polyvinyl alcohol, a modified polyvinyl alcohol resin such as carboxyl-modified polyvinyl alcohol, acetyl-modified polyvinyl alcohol, hydroxymethyl-modified polyvinyl alcohol, and amino-modified polyvinyl alcohol may be used.

In some embodiments, the adhesive layer may be a UV-curable adhesive, and the materials may include, for example: acrylic adhesives, epoxy adhesives, urethane adhesives, polyester adhesives, polyvinyl alcohol adhesives, polyolefin adhesives, modified polyolefin adhesives, polyvinyl alkyl ether adhesives, rubber adhesives, vinyl chloride-vinyl acetate adhesives, SEBS (styrene-ethylene-butylene-styrene copolymer) adhesives, ethylene-styrene copolymers and other ethylene-based adhesives, ethylene-(meth)acrylate methyl copolymers, ethylene-(meth)acrylate ethyl copolymers and other acrylate-based adhesives, etc.

The adhesive layer includes a pressure sensitive adhesive (PSA), a heat sensitive adhesive, a solvent volatile adhesive, and/or an ultraviolet light curable adhesive. In some embodiments, the pressure sensitive adhesive may include natural rubber, synthetic rubber, styrene block copolymer, (meth) acrylic block copolymer, polyvinyl ether, polyolefin, and/or poly (meth) acrylate. In some embodiments, (meth) acrylic acid (or acrylate) refers to both acrylic acid and methacrylic acid. In some embodiments, the pressure sensitive adhesive may include (meth) acrylate, rubber, thermoplastic elastomer, polysilicone, urethane, and combinations thereof. In some embodiments, the pressure-sensitive adhesive is based on a (meth)acrylic pressure-sensitive adhesive or on at least one poly(meth)acrylate.

FIG. 2 is a schematic diagram of the processing process of the waste polarizing plate after recycling according to some embodiments of the present disclosure. In this example, a broken polarizing plate 201 containing polyvinyl alcohol (PVA) polarizers is used as an example for explanation. First, the polarizing plate can be broken into pieces. There is no particular limitation on the size and shape of the broken polarizing plate, so as to facilitate subsequent processing in a container. In some embodiments, the broken pieces of the broken polarizing plate are, for example, in the range of 1 cm ² to 100 cm ² .

Thereafter, as in step 21, water may be used to remove iodine from the broken polarizer 201 and dissolve PVA. In some embodiments, for example, the broken polarizer 201 is immersed in water and kept agitated to remove iodine and dissolve PVA, and to form a first solution 202 containing iodine and PVA. In some embodiments, the first solution 202 may be kept agitated by a stirrer (not shown). It is worth noting that there is no particular limitation on the stirring conditions, and it is possible to stir or not stir, and the first solution 202 may only be kept agitated, as long as the contact area between the water and the broken polarizer 201 can be increased.

In this example, the first solution 202 contains fragments of the protective layer of the polarizer, such as the first protective layer 104 and the second protective layer 106 shown in FIG1 . For simplicity of description, these fragments of the protective layer are referred to as mixed substrates in the following description.

Furthermore, the volume of water used in the above step 21 is sufficient to cover the treated object. In some embodiments, the solid-liquid ratio of the solid weight (in kilograms) of the broken polarizing plate 201 to the volume (in liters) of water is, for example (but not limited to), in the range of 1:10 to 1:200, or other suitable solid-liquid ratio ranges.

Furthermore, the temperature of the water used to remove iodine and dissolve PVA is not particularly limited, and can be room temperature or a high temperature. In some embodiments, the temperature of the water used to remove iodine and dissolve PVA is in the range of 25°C to 100°C, or other suitable temperature ranges. In one example, 90°C water is used to remove iodine and dissolve PVA.

When the polarizing plate has lost its polarization (which can be determined visually or by any other feasible method), the iodine has been removed and the PVA has been dissolved, and the protective layers above and below the PVA (hereinafter referred to as substrates) can be separated, and the mixed substrate 203 can be separated from the first solution 202. For example, the mixed substrate 203 is taken out of the first solution 202. However, at this time, there are still adhesives (such as adhesives and adhesives) remaining on the mixed substrate 203.

Then, as in step 22, the mixed substrate 203 is washed with water to remove the iodine and PVA remaining on the surface of the mixed substrate 203. In one example, the mixed substrate 203 is washed with water and stirred for several minutes at room temperature, and then the mixed substrate 203 is taken out. Adhesives such as adhesives and adhesives still remain on the mixed substrate 204 after washing, which may be referred to as residual adhesives hereinafter.

Then, as in step 23, an alkaline treatment is performed to remove the residual glue on the mixed substrate 204 (e.g., the broken pieces of the first protective layer 104 and the second protective layer 106). For example, the mixed substrate 204 after washing is immersed in the second solution 205, and is continuously heated and left to stand for a period of time to dissolve and remove the residual glue on the mixed substrate 204.

In some embodiments, the second solution 205 is an alkaline solution, and the pH value of the alkaline solution is, for example, in the range of 8 to 14, or other suitable pH value ranges.

Furthermore, the temperature of the second solution 205 for removing the residual glue is not particularly limited, and can be between room temperature and below its boiling point. In some embodiments, the temperature of the second solution 205 is, for example, in the range of 25° C. to 100° C., or other suitable temperature ranges.

Furthermore, the concentration of the second solution 205 for removing residual glue is not particularly limited, but a second solution 205 with a low concentration can be used in consideration of process safety. In some embodiments, the concentration of the second solution 205 is, for example, in the range of 1% to 10%, or other suitable concentration ranges.

Furthermore, in some embodiments, the second solution 205 is a hydroxide solution, a carbonate solution, a bicarbonate solution, or other suitable alkaline solutions. In one example, the second solution 205 is a potassium hydroxide solution.

After standing for a period of time, the mixed substrate 206 can be separated from the second solution 205. For example, the mixed substrate 206 is removed from the second solution 205. However, at this time, the second solution 205 (for example, alkaline solution) still remains on the mixed substrate 206.

Then, as in step 24, the mixed substrate 206 is washed to remove the alkaline solution remaining on the surface of the substrate. In one example, the mixed substrate 206 is washed with water and stirred for several minutes at room temperature, and then the mixed substrate 207 is taken out. After washing, no colloid and alkaline solution remain on the mixed substrate 207, and a clean mixed substrate 207 can be obtained and then recycled. In addition, the embodiment is confirmed by Fourier-transform infrared spectroscopy (FTIR) method that the above treatment method can remove the residual glue on the surface of the substrate.

In this example, the mixed substrate 207 includes, for example, clean fragments of the first protective layer 104 and the second protective layer 106 shown in FIG1 . The clean mixed substrates 207 can be subsequently sorted by the substrate sorting method of the embodiment to facilitate various types of substrate recycling and subsequent re-manufacturing.

In the above embodiment, iodine is first extracted with water to remove the iodine of the polarized light and dissolve the PVA at the same time, and then the residual bonding layer or adhesive layer (such as residual colloid) is removed with alkaline solution. Compared with the previous method of removing iodine with alkaline solution, this example proposes a safer method, which can remove iodine from polarized light and dissolve PVA with water, and the waste liquid generated is also easier to handle. The following also presents some experimental results of the embodiment to illustrate the front-end processing process of the above polarized plate recycling.

In some experiments, water extraction of iodine was performed on different types of polarizers, and the experimental conditions and results are listed in Table 1. Table 1 lists the protective layer materials on the upper and lower sides of the polarizer, and the experiments were conducted using cycloolefin polymer (COP), polymethyl methacrylate (PMMA), triacetate cellulose (TAC), and polyethylene terephthalate (PET) protective layers as examples.

Table 1 Polarizing plate type Polarizer size Solid-liquid ratio temperature Feasibility of iodine extraction Iodine extraction time Substrate separation Embodiment 1 PMMA/COP 0.4cm *4cm 1:20 90℃ V 4 hours Separable Embodiment 2 PET/TAC 0.4cm *4cm 1:20 90℃ V 4 hours Separable Embodiment 3 PET/COP 0.4cm *4cm 1:20 90℃ V 6 hours Separable Embodiment 4 TAC/TAC 0.4cm *4cm 1:20 90℃ V 5 hours Separable

According to the above experiments, as shown in the results of Table 1, different types of polarizers can remove iodine and dissolve PVA through water extraction of iodine, and after removing iodine and dissolving PVA, the substrates on both sides of the polarizer can be separated.

Furthermore, some related experiments have also proposed water extraction of iodine for different polarizing plate sizes and shapes, and the experimental conditions and results are listed in Table 2. The solid-liquid ratio in the experiment refers to the total weight of the solid (g) relative to the liquid volume (ml). For example, if 10g of broken polarizing plate is added to 200ml of water, the solid-liquid ratio is 1:20.

Table 2 Polarizing plate size (cm ² ) Solid-liquid ratio temperature Feasibility of iodine extraction Iodine extraction time Substrate separation Embodiment 1 0.4 *4 1:20 90℃ V 4 hours Separable Embodiment 2 1*1 1:20 90℃ V 5 hours Separable Embodiment 3 2.5*2.5 1:20 90℃ V 8 hours Separable Embodiment 4 5*5 1:20 90℃ V 10 hours Separable Embodiment 5 10*10 1:20 90℃ V 15 hours Separable Embodiment 6 15*15 1:20 90℃ V 20 hours Separable Embodiment 7 25*25 1:20 90℃ V 30 hours Separable Embodiment 8 50*50 1:20 90℃ V 45 hours Separable

According to the above experiments, as shown in the results of Table 2, many polarizing plates of different sizes and shapes can be removed iodine and PVA can be dissolved by water extraction of iodine, and after removing iodine and dissolving PVA, the substrates on both sides of the polarizer can be separated.

Furthermore, some related experiments also proposed to extract iodine from polarizing plates with water at different solid-liquid ratios. The experimental conditions and results are listed in Table 3.

Table 3 Polarizing plate size (cm ² ) Solid-liquid ratio temperature Solid coverage Feasibility of iodine extraction Iodine extraction time Substrate separation Embodiment 1 0.4 *4 1:7.5 90℃ V V 8 hours Separable Embodiment 2 0.4 *4 1:10 90℃ V V 6 hours Separable Embodiment 3 0.4 *4 1:20 90℃ V V 4 hours Separable Embodiment 4 0.4 *4 1:50 90℃ V V 3 hours Separable Embodiment 5 0.4 *4 1:100 90℃ V V 2 hours Separable Embodiment 6 0.4 *4 1:200 90℃ V V 1 hour Separable Comparison Example 1 0.4 *4 1:5 90℃ X V - Inseparable Comparison Example 2 0.4 *4 1:1 90℃ X V -

According to the above experiments, as shown in Table 3, the iodine extraction of polarizing plates can be carried out in a wide range of solid-liquid ratios, such as from 1:7.5 to 1:200. However, if the solid-liquid ratio is too low, such as 1:5 and 1:1 in the comparative example, the solid may be higher than the liquid level, and the iodine extraction of polarizing plates cannot be successfully completed.

Furthermore, some related experiments also proposed to extract iodine from polarizing plates at different temperatures. The experimental conditions and results are listed in Table 4.

Table 4 Polarizing plate size (cm ² ) Solid-liquid ratio temperature Feasibility of iodine extraction Iodine extraction time Substrate separation Embodiment 1 0.4 *4 1:20 25℃ V 12 hours Separable Embodiment 2 0.4 *4 1:20 50℃ V 10 hours Separable Embodiment 3 0.4 *4 1:20 70℃ V 8 hours Separable Embodiment 4 0.4 *4 1:20 90℃ V 4 hours Separable Embodiment 5 0.4 *4 1:20 100℃ V 3.5 hours Separable Comparison Example 1 0.4 *4 1:20 10℃ X - Inseparable Comparison Example 2 0.4 *4 1:20 20℃ X - Inseparable Comparison Example 3 0.4 *4 1:20 110℃ X - Inseparable

According to the above experiments, as shown in Table 4, under the same polarizing plate size and the same solid-liquid ratio, water at room temperature of about 25°C to high temperature of 100°C can complete the extraction of iodine from the polarizing plate. However, too low water temperature, such as 10°C water used in Comparative Example 1 or 20°C water used in Comparative Example 2, does not produce good results in the extraction of iodine from the polarizing plate. Too high water temperature, such as 110°C used in Comparative Example 3, causes the water to boil and evaporate, and the extraction of iodine from the polarizing plate is also not good.

Furthermore, the feasibility of alkaline treatment is also tested in the relevant experiments. Fourier transform infrared spectroscopy (FTIR) can be used to analyze whether there is still an adhesive layer on the substrate before and after the alkaline treatment. In this example, a protective layer with a binder (such as UV glue) connected to the polarizer on one side and an adhesive layer (such as pressure sensitive adhesive (PSA)) on the other side is used as a sample for relevant experiments.

FIG. 3A shows some embodiments of the present disclosure, in which a Fourier transform infrared spectrometer (FTIR) is used to detect a substrate to analyze whether there is an adhesive on the substrate before the alkali treatment, such as a pressure sensitive adhesive (PSA). In the figure, the X-axis is the wave number (cm ^-1 ), and the Y-axis is the transmittance (%) or the absorbance value. After the signal of the functional group region on the Fourier transform infrared spectrum is identified, the fingerprint region signal can be further confirmed for the difference in molecular configuration. The upper signal in FIG. 3A is the signal of the pressure sensitive adhesive on the substrate before the alkali treatment, and the lower signal is the pure pressure sensitive adhesive signal (PSA database). By comparing the two signals, it can be confirmed that there is an adhesive on the substrate before the alkali treatment.

FIG. 3B shows some embodiments of the present disclosure, using a Fourier transform infrared spectrometer (FTIR) to detect the substrate to analyze whether there is a bonding agent, such as UV glue, on the substrate before the alkali treatment. The upper signal in the figure is the UV glue signal on the substrate before the alkali treatment, and the lower signal is the pure UV glue signal. Comparing the two signals can confirm that there is a bonding agent on the substrate before the alkali treatment.

FIG. 3C shows some embodiments of the present disclosure, using a Fourier transform infrared spectrometer (FTIR) to detect the substrate to analyze whether there is an adhesive on the substrate after the alkali treatment. The upper signal in the figure is the signal of the substrate after the alkali treatment, and the lower signal is the signal of the pure substrate. Comparing the two signals, it can be confirmed that there is no adhesive on the substrate after the alkali treatment, and it is a clean substrate.

FIG. 3D shows some embodiments of the present disclosure, using a Fourier transform infrared spectrometer (FTIR) to detect the substrate to analyze whether there is a bonding agent on the substrate after the alkali treatment. The upper signal in the figure is the signal of the substrate after the alkali treatment, and the lower signal is the pure substrate signal. Comparing the two signals, it can be confirmed that there is no bonding agent on the substrate after the alkali treatment, and it is a clean substrate.

Furthermore, some related experiments also proposed to perform alkaline treatment at different temperatures to remove the residual glue on the substrate. The experimental conditions and results are listed in Table 5. These experiments can use Fourier transform infrared spectroscopy (FTIR) to analyze the results to detect whether the colloid on the substrate is completely removed.

Table 5 Alkaline solution type temperature Alkaline treatment feasibility FTIR analysis results Embodiment 1 Potassium Hydroxide 25℃ V Clean substrate Embodiment 2 Potassium Hydroxide 50℃ V Clean substrate Embodiment 3 Potassium Hydroxide 70℃ V Clean substrate Embodiment 4 Potassium Hydroxide 90℃ V Clean substrate Embodiment 5 Potassium Hydroxide 100℃ V Clean substrate Comparison Example 1 Potassium Hydroxide 10℃ X There is still glue residue on the substrate Comparison Example 2 Potassium Hydroxide 20℃ X There is still glue residue on the substrate Comparison Example 3 Potassium Hydroxide 110℃ X There is still glue residue on the substrate

According to the above experiments, as shown in Table 5, the residual glue on the substrate can be removed by alkali treatment with potassium hydroxide solutions of different temperatures (e.g., the second solution 205 shown in step 23 of FIG. 2), and the mixed substrate is immersed in a potassium hydroxide solution of 25°C to 100°C. However, alkaline solutions below room temperature, such as the 10°C potassium hydroxide solution used in Comparative Example 1 or the 20°C potassium hydroxide solution used in Comparative Example 2, have poor glue removal effects. Alkaline solutions with too high temperatures, such as the 110°C potassium hydroxide solution used in Comparative Example 3, have a boiling phenomenon in the liquid, and the glue removal effect is also poor.

Furthermore, some related experiments also proposed using different types of alkaline solutions for alkaline treatment to remove the residual glue on the substrate, and the experimental conditions and results are listed in Table 6. These experiments can use Fourier transform infrared spectroscopy (FTIR) to analyze the results to detect whether the colloid on the substrate is completely removed.

Table 6 Alkaline solution type pH Solid-liquid ratio temperature Alkaline treatment feasibility FTIR analysis results Embodiment 1 Potassium Hydroxide 14 1:20 90℃ V Clean substrate Embodiment 2 Sodium hydroxide 13 1:20 90℃ V Clean substrate Embodiment 3 Calcium hydroxide 12 1:20 90℃ V Clean substrate Embodiment 4 Calcium oxide 12 1:20 90℃ V Clean substrate Embodiment 5 Potassium carbonate 10 1:20 90℃ V Clean substrate Embodiment 6 Sodium carbonate 11 1:20 90℃ V Clean substrate Embodiment 7 Potassium bicarbonate 8 1:20 90℃ V Clean substrate Embodiment 8 Sodium bicarbonate 8 1:20 90℃ V Clean substrate

According to the above experiments, as shown in Table 6, different types of alkaline solutions are used for alkaline treatment. Alkaline solutions are, for example, potassium hydroxide, sodium hydroxide, calcium hydroxide, calcium oxide, potassium carbonate, sodium carbonate, potassium bicarbonate and sodium bicarbonate, and their pH values are, for example, in the range of 8 to 14. These alkaline solutions preferably do not react chemically with the substrate material. The mixed substrate is immersed in these alkaline solutions at high temperature (for example, 90° C.), and the substrate glue residue can be removed.

Furthermore, some related experiments also proposed using different types and concentrations of alkaline solutions for alkaline treatment to remove the residual glue on the substrate. The experimental conditions and results are listed in Table 7. These experiments can use Fourier transform infrared spectroscopy (FTIR) to analyze the results to detect whether the colloid on the substrate is completely removed.

Table 7 Alkaline solution type Solid-liquid ratio Concentration temperature time FTIR analysis Embodiment 1 Potassium Hydroxide 1:20 45% 90℃ 1 hour Clean substrate Embodiment 2 Potassium Hydroxide 1:20 10% 90℃ 2 hours Clean substrate Embodiment 3 Potassium Hydroxide 1:20 5% 90℃ 4 hours Clean substrate Embodiment 4 Potassium Hydroxide 1:20 1% 90℃ 5 hours Clean substrate Embodiment 5 Sodium hydroxide 1:20 45% 90℃ 1 hour Clean substrate Embodiment 6 Sodium hydroxide 1:20 10% 90℃ 2 hours Clean substrate Embodiment 7 Sodium hydroxide 1:20 5% 90℃ 4 hours Clean substrate Embodiment 8 Sodium hydroxide 1:20 1% 90℃ 5 hours Clean substrate

According to the above experiments, as shown in Table 7, alkaline solutions such as potassium hydroxide and sodium hydroxide are used, and the concentrations of the alkaline solutions are 1%, 5%, 10%, and 45%, respectively, to perform alkaline treatment on the mixed substrate. The mixed substrate is immersed in these alkaline solutions at high temperature (e.g., 90°C), and the residual glue on the substrate can be removed. The higher the concentration of the alkaline solution, the shorter the time required for the alkaline solution to remove the glue.

The clean mixed substrate 207 (FIG. 2) obtained as described above, which includes clean fragments of the first protective layer 104 and the second protective layer 106 as shown in FIG. 1, can be sorted by the substrate sorting method of the embodiment described below to recycle different types of substrates, which is beneficial for subsequent product remanufacturing.

＜Base material sorting＞

The embodiments of the present disclosure utilize a wet density separation method to separate mixed substrates in a simple, fast, safe, low-cost, high separation efficiency, and fast separation speed method. FIG. 4 shows a flow chart of a substrate separation method according to some embodiments of the present disclosure. FIG. 5 shows a schematic diagram of a substrate separation according to some embodiments of the present disclosure. Reference may be made to FIG. 4 and FIG. 5 at the same time.

According to some embodiments, referring to step 401 of FIG. 4 , a mixed substrate is provided, which includes a plurality of substrates of different materials and densities. Furthermore, in this example, two substrates are used as an example for illustration. In some embodiments, the density of the substrate is, for example, in the range of about 0.87 to about 1.45, or other density ranges.

According to some embodiments, referring to step 402 of FIG. 4 and step 51 of FIG. 5 , a solution 501 (also referred to as a separation solution) having an appropriate density is prepared according to the mixed substrate to be separated.

Thereafter, referring to step 403 of FIG. 4 and step 52 of FIG. 5 , a proper amount of mixed substrate 510 is added to solution 501 and stirred sufficiently to make the substrate uniformly dispersed.

In some examples, the mixed substrate 510 may include a first substrate 511 and a second substrate 512 of different materials. The first substrate 511 has a first density, the second substrate 512 has a second density, and the first density is different from the second density. The prepared solution 501 has a third density. According to some embodiments, the density of at least one of the first substrate 511 and the second substrate 512 is different from the density of the solution 501.

Afterwards, referring to step 53 of FIG. 5 , the substrate is left to stand for a period of time to wait for the substrates of different densities to be layered in the solution 501. In some embodiments, the substrates with a density less than the sorting solution 501 can float on the upper layer of the solution 501, the substrates with a density greater than the sorting solution 501 can settle on the bottom layer of the solution 501, and the substrates with a density close to the sorting solution 501 can be suspended in the middle layer of the solution 501. The standing time varies depending on the size of the substrate to be sorted and the density difference between the substrate and the solution 501. For example, the greater the density difference between the substrate and the solution 501, the faster it floats or sinks in the solution. However, compared with the traditional substrate sorting method, the wet density sorting method disclosed in the present disclosure can complete the sorting extremely quickly. According to some embodiments, the substrate layering can be completed in the solution by standing for no more than 3 minutes (e.g., 20 seconds to 120 seconds).

In this example, the density of the first substrate 511 is less than the density of the solution 501, and the density of the second substrate 512 is greater than the density of the solution 501. After the mixed substrate 510 is added to the solution 501, the first substrate 511 floats in the solution 501, and the second substrate 512 sinks to the bottom of the solution 501, as shown in step 53 of Figure 5.

Afterwards, referring to step 54 of FIG. 5 , the substrate with a lower density floating on the upper layer of the solution 501 is picked up. For example, in this example, the first substrate 511 with a lower density floating on the upper layer of the solution 501 is picked up, and the first substrate 511 is selected and recycled.

Afterwards, referring to step 55 of FIG. 5 , the substrate with a higher density that settles at the bottom of the solution 501 is picked up to complete the sorting. For example, in this example, the second substrate 512 with a higher density that settles at the bottom of the solution 501 is picked up to complete the sorting and recovery of the second substrate 512.

Of course, the present disclosure is not limited to the above examples. In some other examples, the density of the first substrate 511 may be substantially equal to the density of the solution 501, and the density of the second substrate 512 may be greater than the density of the solution 501. After the mixed substrate 510 is added to the solution 501, the first substrate 511 is suspended in the middle layer of the solution 501, and the second substrate 512 sinks to the bottom of the solution 501, and the subsequent substrate separation can also be achieved. Alternatively, in some other examples, the density of the first substrate 511 may be less than the density of the solution 501, and the density of the second substrate 512 is substantially equal to the density of the solution 501. After the mixed substrate 510 is added to the solution 501, the first substrate 511 may float on the upper layer of the solution 501, and the second substrate 512 may be suspended in the middle layer of the solution 501, and the subsequent substrate separation can also be achieved.

Therefore, according to the above, the first density of the first substrate 511 of the embodiment is less than or equal to the third density of the solution 501, and the second density of the second substrate 512 is greater than or equal to the third density of the solution 501, which can be expressed as first density ≤ third density ≤ second density, and the first density is different from the second density. After the mixed substrate 510 is added to the solution 501, the position of the first substrate 511 in the solution 501 is higher than the position of the second substrate 512 in the solution 501, thereby achieving substrate separation.

Furthermore, when the solution 501 is configured, the maximum density of the solution 501 is the density in the saturated solution state. In some embodiments, when the maximum density of the solution 501 is greater than the first density of the first substrate 511 and the second density of the second substrate 512, the third density of the solution 501 is the average density of the first density and the second density.

If the density of the saturated solution is close to or equal to the average density of the substrate to be sorted, the saturated solution can be directly used as the sorting solution. If the density of the saturated solution is greater than the first density and the second density of the substrate to be sorted, a sorting solution with an average density equal to the sorting substrate can be prepared by a preparation method.

In some embodiments, when the maximum density of the solution 501 (i.e., the density in the saturated solution state) is equal to one of the first density of the first substrate 511 and the second density of the second substrate 512, the saturated solution density can be regarded as the third density. That is, the third density is equal to the first density or the second density that is equal to it.

There is no particular limitation on the preparation method of the separation solution 501 used in the wet density separation method. It can be any salt aqueous solution, as long as it is a uniform solution without sediments under the target density environment. Preferably, the solution 501 does not contain substances that react chemically with the substrate (e.g., the first substrate 511 and the second substrate 512). In some embodiments, the solution 501 is, for example, a salt aqueous solution including sodium chloride, calcium chloride, the like, or a combination thereof.

Furthermore, the volume of the solution 501 used in the above step 52 can cover the treated object. In some embodiments, the solid-liquid ratio of the solid weight (in kilograms) of the mixed substrate 510 to the volume (in liters) of the solution 501 is, for example (but not limited to), in the range of 1:16 to 1:1000, or other suitable solid-liquid ratio ranges.

Although the above examples are illustrated with two substrates, the present disclosure is not limited thereto. The separation method of the embodiment may also be applied to separation of more than two substrates. For example, when three substrates are separated, one of the substrates has a density less than that of the first separation solution and can first float on the upper layer of the solution and be removed, and the remaining two substrates that sink to the lower layer are then separated by the second separation solution.

＜Base material sorting related experiments＞

In some embodiments, the mixed substrate 207 (including the clean fragments of the first protective layer 104 and the second protective layer 106 as shown in FIG. 1 ) obtained by recycling the above-mentioned waste polarizing plate is used as an example of the mixed substrate 510 in the above-mentioned substrate sorting method. The following uses four common substrates COP, PMMA, TAC, and PET as examples and presents some related experiments and results of substrate sorting to illustrate the embodiments. The steps of the experimental substrate sorting method can refer to the above description. Substrate Element Density (g/cm ³ ) COP Cyclo Olefin Polymer 1.01 PMMA Polymethylmethacrylate 1.19 TAC Triacetyl Cellulose 1.3 PET Polyethylene Terephthalate 1.38

The definitions of the terms used in the experiment are as follows:

Solid single processing amount: the weight of substrate input for single sorting.

Sorting time: the time required for substrates of different densities to separate into upper and lower layers in the sorting solution 501 .

Sorting rate: The proportion of the sorted substrate that is actually the substrate after Fourier transform infrared spectroscopy (FTIR) confirmation. If the sorting rate is > 90%, the sorting feasibility is judged to be OK, otherwise it is judged to be NG.

In some experiments, sorting of different types of mixed substrates and different sorting methods were performed, and the results are listed in Table 8.

The wet density separation method of the embodiment can refer to the above description. In addition, other separation methods and their disadvantages in the comparative example in the experiment are briefly described as follows:

The dry specific gravity method is to sort according to the density of the substrate, and the substrate must be dried first. The separation efficiency of the dry specific gravity method is poor and the processing volume is small.

Electrostatic separation uses the different conductivity of various plastics and the electrostatic properties of the electric field acting on the plastics to separate them. However, the substrate must be dried first, and the equipment cost is relatively high.

Optical separation uses optical properties to detect materials to identify different materials, colors or densities, and then sorts the selected materials by compressed air. The disadvantage is that the substrate itself must have color differences, and the equipment cost is high and the sorting rate is low.

The dissolution method uses different solvents to dissolve and separate different types of substrates. The disadvantage is that additional solvents are required, which not only increases the difficulty of waste liquid recycling, but also increases the cost of solvents.

Table 8 Sorting substrate types Sorting method Solid single processing amount (g) Substrate sorting feasibility Sorting time Sorting rate Sorting feasibility Embodiment 1 PMMA/COP Wet density sorting 100g V 35 seconds 95% OK Embodiment 2 PET/TAC 100g V 45 seconds 95% OK Embodiment 3 PET/COP 100g V 20 seconds 97% OK Embodiment 4 PMMA/TAC 100g V 40 seconds 96% OK Embodiment 5 PMMA/PET 100g V 35 seconds 95% OK Embodiment 6 TAC/COP 100g V 35 seconds 95% OK Comparison Example 1 PMMA/COP Dry Gravity Separation 10g V 10 minutes 55% NG Comparison Example 2 PET/TAC 10g V 10 minutes 50% NG Comparison Example 3 PET/COP 10g V 10 minutes 60% NG Comparison Example 4 PMMA/TAC 10g V 10 minutes 50% NG Comparison Example 5 PMMA/PET 10g V 10 minutes 55% NG Comparison Example 6 TAC/COP 10g V 10 minutes 55% NG Comparison Example 7 PMMA/COP Electrostatic separation 10g X(all have static electricity) — — NG Comparative Example 8 PET/TAC 10g — — NG Comparative Example 9 PET/COP 10g — — NG Comparative Example 10 PMMA/TAC 10g — — NG Comparative Example 11 PMMA/PET 10g — — NG Comparative Example 12 TAC/COP 10g — — NG Comparative Example 13 PMMA/COP Optical separation 10g X(all colorless) — — NG Comparative Example 14 PET/TAC 10g — — NG Comparative Example 15 PET/COP 10g — — NG Comparative Example 16 PMMA/TAC 10g — — NG Comparative Example 17 PMMA/PET 10g — — NG Comparative Example 18 TAC/COP 10g — — NG Comparative Example 19 PMMA/COP Dissolution method 10g X(insoluble) — — NG Comparative Example 20 PET/TAC 10g — — NG Comparative Example 21 PET/COP 10g — — NG Comparative Example 22 PMMA/TAC 10g — — NG Comparative Example 23 PMMA/PET 10g — — NG Comparative Example 24 TAC/COP 10g — — NG

According to the above experiments, as shown in Table 8, the substrate separation method of the embodiment has a fast separation speed, and the substrate separation is completed in less than 1 minute, and the single solid processing amount (100g) is larger than the single solid processing amount (10g) of other separation methods. And the substrate separation method of the embodiment can obtain a separation rate of more than 95%.

Furthermore, experiments were conducted on substrates of different sizes and shapes, and the results are listed in Table 9.

Table 9 Substrate size (cm*cm =cm ² ) Solid-liquid ratio Solid single processing amount (g) Substrate sorting feasibility Sorting time Sorting rate Sorting feasibility Embodiment 1 0.4*4 1:40 100g V 30 seconds 95% OK Embodiment 2 1*1 1:40 100g V 40 seconds 97% OK Embodiment 3 5*5 1:40 100g V 60 seconds 98% OK Embodiment 4 10*10 1:40 100g V 120 seconds 99% OK Embodiment 5 15*15 1:40 100g V 145 seconds 99% OK Embodiment 6 25*25 1:40 100g V 200 seconds 99% OK Embodiment 7 50*50 1:40 100g V 350 seconds 99% OK Embodiment 8 100*100 1:40 100g V 400 seconds 99% OK

According to the above experiments, as shown in Table 9, the substrate separation method of the embodiment can process substrates of many different sizes, ranging from substrates with a side length of less than 1 cm to substrates with a side length of up to 100 cm, and can complete substrate separation, and the separation rate exceeds 95%. Furthermore, according to the experiment, the smaller the substrate size, the shorter the time to complete the substrate separation.

Furthermore, the embodiment also deduces the theoretical separation rate of the mixed substrate based on experimental data, and its formula is as follows (1): ....Formula (1)

Where X is the bottom area of the container, in cm ² ;

Y is the height of the container, in cm;

Z is the solid weight of the mixed matrix, in kg;

V is the volume of the solution, in L.

The solid-liquid ratio applicable to the substrate separation method of the embodiment can be any ratio that can cover the processed object, for example (but not limited to) 1:16-1:1000.

The container applicable to the substrate separation method of the embodiment has a bottom area/height ratio that can cover the processed object. In some embodiments, the bottom area/height ratio of the container is, for example (but not limited to), in the range of 23-37.

The shape of the container used in the substrate separation method of the embodiment is not particularly limited and may be any shape.

The theoretical sorting rate formula of the above formula (1) is explained as follows.

About Y/(Y+X/100)

According to the experimental content and results with the container bottom area (X) and container height (Y) as the manipulated variables, the solid weight of the mixed matrix (Z), the volume of the separation solution (V) and other factors remain unchanged as the controlled variables. It is found that the separation rate (strain variable) will be affected by the container bottom area (X) and the container height (Y), among which the container height (Y) has the greatest impact. The item X/100 in the formula is mainly due to the difference in the units of X and Y. In addition, since the value of the container bottom area (X) must be larger than the value of the container height (Y), the value of the container bottom area (X) is reduced to reflect the greater impact of the container height (Y) on the separation rate. Based on the experimental results with the container bottom area (X) and container height (Y) as the manipulated variables, it can be concluded that the sorting rate is proportional to Y/(Y+X/100).

According to experiments, the relationship that the sorting rate is proportional to Y/(Y+X/100) holds true when the container bottom area (X) is, for example, 100 cm ² ~1000000 cm ² , the container height (Y) is, for example, 1 cm ~ 10000 cm, and the container bottom area (X) / container height (Y) is, for example, 23 ~ 37.

About (V-Z)/V

According to the experimental content and results with the mixed matrix solid weight (Z) or the sorting solution volume (V) as the manipulated variables, the factors such as the container bottom area (X) and the container height (Y) are kept constant as the controlled variables, and it is found that the sorting rate (strain variable) is also affected by the solid weight (Z) and the sorting solution volume (V). According to the experimental results, under the premise of the same sorting solution volume (V), if the solid weight (Z) increases, the sorting rate will decrease. On the contrary, under the premise of the same sorting solution volume (V), if the solid weight (Z) decreases, the sorting rate will increase. According to the experimental results, it can be concluded that the sorting rate is proportional to (V-Z)/V.

According to experiments, when the volume of the sorting solution (V) is, for example, 0.1L~10000L, the weight of the mixed substrate solid (Z) is, for example, 0.1kg~10000kg, and the solid-liquid ratio is, for example, 1:16~1:1000, the relationship that the sorting rate is proportional to (V-Z)/V is established.

Furthermore, according to the experimental results, the product of Y/(Y+X/100) and (V-Z)/V is linearly related to the sorting rate, and the coefficient 1.26 is obtained based on this, which is consistent with the actual experimental results. In other words, the coefficient 1.26 and the product of Y/(Y+X/100) and (V-Z)/V (such as formula (1)) can make the sorting rate calculated by the formula consistent with the actual sorting rate results in the experiment.

Furthermore, in the embodiment, multiple sets of experiments were conducted for different solid-liquid ratios and container bottom area height ratios, and the actual sorting rates and theoretical sorting rates (such as formula (1)) of some experiments were listed in Table 10.

Table 10 Solid-liquid ratio (g: ml) Container base area to height ratio Solid single processing amount (g) Sorting time Theoretical sorting rate (%) Actual sorting rate (%) Sorting feasibility Embodiment 1 1:1000 31 5 10 seconds 100% 99% OK Embodiment 2 1:200 31 25 10 seconds 96% 96% OK Embodiment 3 1:40 31 125 30 seconds 94% 92% OK Embodiment 4 1:16 31 312.5 120 seconds 90% 90% OK Embodiment 5 1:40 twenty three 125 30 seconds 100% 100% OK Embodiment 6 1:40 37 125 45 seconds 90% 90% OK Comparison Example 1 1:40 5000 125 45 seconds 2% — NG Comparison Example 2 1:1 31 5000 — — — NG

According to the above experiments, as shown in the results of Table 10, a wide range of solid-liquid ratios can be processed, for example, from 1:16 to 1:1000. In addition, the sorting speed of the substrate sorting method using the embodiment is fast. Even with a high solid content, such as a solid-liquid ratio of 1:16, the substrate stratification is completed in about 2 minutes. However, if the height of the container is too low as in Comparative Example 1 or the amount of solid processed is too much (or the volume is too small) as in Comparative Example 2, it is not conducive to substrate stratification. Furthermore, according to the experimental results, the actual sorting rate of the substrate sorting method using the embodiment is indeed close to the theoretical sorting rate of the above formula (1). Therefore, when the method of the embodiment is used to sort the substrates to be classified, when the sorting rate is to reach a certain percentage (for example, greater than 90%), the volume of solution required to complete the substrate sorting can also be obtained by the above formula (1).

Furthermore, the substrate is sorted using different salt solutions. The density of the sorting solution is set as follows:

Assuming that the density of mixed substrate A = a, the density of mixed substrate B = b, if one of a and b is greater than the maximum density of the sorting solution (i.e. saturated density) (g/cm ³ ), and the other is less than the maximum density of the sorting solution, then the sorting density of the solution is the density of the mixed substrate (a+b)/2. If one of a and b is equal to the maximum density of the sorting solution, then the sorting density is the maximum density of the sorting solution. Some experimental results are listed in Table 11.

Table 11 Salt Type Maximum density of solution Actual sorting density Sorting substrate types (density a/b) Sorting time Sorting rate Sorting feasibility Embodiment 1 Sodium chloride 1.17 1.12 PMMA/COP (1.19/1.01) 30 seconds 95% OK Embodiment 2 Calcium chloride 1.3 1.12 PMMA/COP (1.19/1.01) 40 seconds 94% OK Embodiment 3 Calcium chloride 1.3 1.3 PET/TAC (1.38/1.3) 40 seconds 97% OK Embodiment 4 Sodium chloride 1.17 1.17 PET/COP (1.38/1.01) 50 seconds 98% OK Embodiment 5 Calcium chloride 1.3 1.2 PET/COP (1.38/1.01) 45 seconds 96% OK

According to the above experiments, as shown in the results of Table 11, a solution with a density between the density of the substrate to be sorted can be configured and the substrate sorting method of the embodiment (as shown in the steps of Figures 4 and 5) can be used to quickly complete the substrate sorting.

In summary, the substrate sorting method proposed in the embodiment is to sort the mixed substrate by a wet density sorting method in a simple, fast, safe, low-cost, high-sorting efficiency and fast sorting speed. In the substrate sorting method of the embodiment, the mixed substrate is placed in a sorting solution with an appropriate density, and the substrate with a smaller density can float on the upper layer of the sorting solution, while the substrate with a larger density settles in the lower layer of the sorting solution, thereby achieving the purpose of substrate sorting. The mixed substrate can be any different types of substrates, for example, different protective layers after the recycling of discarded polarizing plates (for example, removing iodine, polarizers and residual glue). The substrate sorting method of the embodiment can be used to sort and recycle these protective layers to reduce environmental pollution. The recycled substrate can also be re-manufactured into other recycled products to achieve environmental protection, carbon reduction, and increase economic benefits.

1: Polarizing plate 102: Polarizer 104: First protective layer 106: Second protective layer 201: Broken polarizing plate 202: First solution 203,204,206,207,510: Mixed substrate 205: Second solution 501: Solution (sorting solution) 511: First substrate 512: Second substrate 21,22,23,24, 401,402,403,51,52,53,54,55: Steps

FIG. 1 is a schematic cross-sectional view of a polarizing plate. FIG. 2 is a schematic diagram of a treatment process of a waste polarizing plate after recycling according to some embodiments of the present disclosure. FIG. 3A is a diagram of some embodiments of the present disclosure, in which a Fourier transform infrared spectrometer (FTIR) is used to detect a substrate to analyze whether an adhesive exists on the substrate before alkaline treatment. FIG. 3B is a diagram of some embodiments of the present disclosure, in which a Fourier transform infrared spectrometer (FTIR) is used to detect a substrate to analyze whether an adhesive exists on the substrate before alkaline treatment. FIG. 3C is a diagram of some embodiments of the present disclosure, in which a Fourier transform infrared spectrometer (FTIR) is used to detect a substrate to analyze whether an adhesive exists on the substrate after alkaline treatment. FIG. 3D shows some embodiments of the present disclosure, where a Fourier transform infrared spectrometer (FTIR) is used to detect the substrate to analyze whether a bonding agent is present on the substrate after the alkali treatment. FIG. 4 shows a flow chart of a substrate sorting method according to some embodiments of the present disclosure. FIG. 5 shows a schematic diagram of substrate sorting according to some embodiments of the present disclosure.

401,402,403: Steps

Claims (19)

A substrate sorting method comprises: providing a mixed substrate, comprising a first substrate and a second substrate of different materials, wherein the first substrate has a first density, the second substrate has a second density, and the first density is different from the second density; providing a solution, the solution has a third density, wherein at least one of the first density and the second density is different from the third density; and adding the mixed substrate to the solution, so that the first substrate and the second substrate are separated and located at different positions in the solution, wherein the first density is less than or equal to the third density, the second density is greater than or equal to the third density, after the mixed substrate is added to the solution, the first substrate floats in the solution, and the second substrate sinks to the bottom of the solution, The first substrate and the second substrate are different materials selected from the group consisting of polymethyl methacrylate, cellulose triacetate, acrylic resin film, polyaromatic hydroxyl resin film, polyether resin film, cycloolefin resin film, polyethylene terephthalate, polypropylene, cycloolefin polymer, polycarbonate, and any combination thereof. A substrate sorting method as claimed in claim 1, wherein the third density is an average density of the first density and the second density. In the substrate sorting method of claim 1, wherein the other of the first density and the second density is the same as the third density, the third density of the solution is the density of the solution in its saturated solution state. A substrate separation method as claimed in claim 1, wherein the solution is an aqueous salt solution, and the aqueous salt solution does not contain a substance that chemically reacts with the substrate. A substrate separation method as claimed in claim 1, wherein the solution comprises sodium chloride, calcium chloride, or a combination thereof. A substrate sorting method as claimed in claim 1, wherein the first density of the first substrate and the second density of the second substrate are both in the range of 0.87 to 1.45. The substrate separation method of claim 1, wherein the ratio of the solid weight of the mixed substrate (in kilograms) to the volume of the solution (in liters) is in the range of 1:16 to 1:1000. The substrate sorting method of claim 1, wherein the sorting rate of the mixed substrate is the following formula (1): ....Formula (1) wherein X is the bottom area of a container containing the solution, in cm ² ; Y is the height of the container, in cm; Z is the solid weight of the mixed matrix, in kg; and V is the volume of the solution, in L. The substrate sorting method of claim 1, wherein the step of providing the mixed substrate further includes: Recycling a waste polarizing plate, wherein the polarizing plate includes a polyvinyl alcohol (PVA) layer and a first protective layer and a second protective layer adhered to opposite sides of the PVA layer; Removing iodine, the PVA layer and the bonding layer to separate the first protective layer and the second protective layer from the PVA layer; and Cleaning the first protective layer and the second protective layer, wherein the first protective layer and the second protective layer are the first substrate and the second substrate of the mixed substrate, respectively. A method for separating substrates, comprising: providing the mixed substrate as described in claim 1, wherein the mixed substrate has a solid weight; providing a container, wherein the container has a bottom area and a height; adding the solution as described in claim 1 into the container; obtaining a solution volume required for separating substrates when the separation rate is greater than 90% by the following formula (1): ....Formula (1) wherein X is the bottom area of the container, in ^cm2 ; Y is the height of the container, in cm; Z is the solid weight of the mixed substrate, in kg; and V is the volume of the solution, in L; and the mixed substrate is added to the solution so that the first substrate and the second substrate are separated and located at different positions in the solution. A substrate sorting method as claimed in claim 10, wherein the bottom area (X) of the container/the height (Y) of the container is 23~37. A substrate sorting method, comprising: Recycling waste polarizing plates and subjecting them to a treatment process to provide the mixed substrate as described in claim 1; Providing the solution as described in claim 1, Adding the mixed substrate to the solution, so that the first substrate and the second substrate are separated and located at different positions in the solution. The substrate sorting method of claim 12, wherein the polarizing plate includes a polarizer and a first protective layer and a second protective layer adhered to opposite sides of the polarizer, and the processing process includes removing the polarizer and the connecting layer to separate the first protective layer and the second protective layer from the polarizer, wherein the first protective layer and the second protective layer are the first substrate and the second substrate, respectively. In the substrate sorting method of claim 13, wherein the polarizer is a PVA layer, the processing process includes: Removing iodine and the PVA layer; Removing the first protective layer and the connecting layer on the second protective layer; and Cleaning the first protective layer and the second protective layer to obtain a clean mixed substrate. The substrate sorting method of claim 14, wherein before removing the iodine and the PVA layer, the treatment process further includes fragmenting the polarizing plate, wherein the step of removing the iodine and the PVA layer includes: Soaking the fragmented polarizing plate in water and maintaining agitation to remove the iodine and dissolve the PVA, and forming a first solution containing iodine and PVA, wherein the first protective layer and the second protective layer are dispersed in the first solution; Separating the first protective layer and the second protective layer from the first solution; and Washing the first protective layer and the second protective layer with water. In the substrate sorting method of claim 15, the temperature of the water for removing iodine and dissolving PVA is in the range of 25°C to 100°C. The substrate separation method of claim 15, wherein the solid-liquid ratio of the solid weight (in kilograms) of the broken polarizing plates to the volume (in liters) of water is in the range of 1:10 to 1:200. The substrate separation method of claim 15, wherein the washed first protective layer and the second protective layer are mixed and immersed in a second solution, and are continuously heated and left to stand for a period of time to remove the bonding layer on the first protective layer and the second protective layer; The first protective layer and the second protective layer are separated from the second solution; and The first protective layer and the second protective layer are washed, wherein the washed first protective layer and the second protective layer are the first substrate and the second substrate of the mixed substrate, respectively. A substrate sorting method as claimed in claim 18, wherein the second solution is an alkaline solution, and the pH value of the alkaline solution is in the range of 8-14, and/or the temperature of the alkaline solution is in the range of 25°C-100°C, and/or the concentration of the alkaline solution is in the range of 1%-10%, and/or the alkaline solution is a hydroxide solution, a carbonate solution, or a bicarbonate solution.

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