Method for recovering polyester film and method for producing polyester product

Abstract

To provide a method for efficiently recovering a high-purity polyester film from a polyester film substrate having at least one coating film thereon, with good profitability.SOLUTION: A method for recovering a polyester film from a polyester film substrate including at least one coating film formed on at least a portion of the polyester film includes a step (2) of removing the coating film from the polyester film substrate by contacting at least a surface of the polyester film substrate having the coating film with a solvent, and a concentration of a component derived from terephthalic acid in the solvent wastewater is 0.5 mass% or less.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method for recovering a polyester film from a polyester film substrate having at least one coating film on at least a portion of the polyester film, and a method for producing a polyester product. [Background technology]

[0002] Polyester films are used in a variety of applications due to their excellent mechanical, physical, and chemical properties. Many of these polyester films have coating films with various functions laminated on one or both sides of the surface.

[0003] As the polyester film is used in various applications, the amount of waste and used products generated is also increasing, which leads to the deterioration of the global environment. In order to solve this problem and recycle the polyester film, it is preferable to remove the coating film from the polyester film substrate and reuse it as a polyester film.

[0004] Examples of such techniques include Patent Documents 1 to 3. Patent Document 1 discloses that a polyester-based photographic support having at least one undercoat layer is brought into contact with an alkaline aqueous solution containing sodium hydroxide and / or potassium hydroxide for 5 to 1000 minutes to remove the undercoat layer.

[0005] Patent document 2 discloses a method for removing a functional layer on at least one side of a polyester film, in which the functional layer can be removed in a short period of time by contacting the film with a 20 to 60 mass % alkaline treatment liquid heated to a temperature of 90 to 140°C.

[0006] Furthermore, Patent Document 3 discloses a method for cleaning a release film, which includes a removal step of immersing a release film having a release layer and a polyester film in a decomposition liquid obtained by dissolving an alkaline substance in a mixture of 30% by mass or more of alcohol and water, and then contacting the release film with an organic solvent to remove the release layer from the polyester film. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 8-146560 [Patent Document 2] JP 2020-90094 A [Patent Document 3] JP 2009-291690 A Summary of the Invention [Problem to be solved by the invention]

[0008] However, in the method of Patent Document 1, the contact time between the polyester film substrate and the alkaline treatment liquid is long, which causes significant hydrolysis of the polyester film, whereas in the method of Patent Document 2, the polyester film is brought into contact with a high-temperature, high-concentration alkaline treatment liquid, which causes significant hydrolysis of the polyester film.

[0009] Furthermore, in the method described in Patent Document 3, the polyester film is brought into contact with an alkaline treatment liquid containing alcohol, which causes increased hydrolysis of the polyester film. As the hydrolysis of the polyester film progresses, the mechanical properties are degraded and the amount of recoverable polyester film is also reduced.

[0010] The present invention has been made in consideration of the above, and aims to provide a method for efficiently and profitably recovering a high-purity polyester film from a polyester film substrate having at least one coating film on the polyester film. [Means for solving the problem]

[0011] As a result of investigations aimed at solving the above-mentioned problems, the present inventors have come up with a technique for suppressing hydrolysis of polyester-based films, and have found that such a technique can suppress the elution of polyester-based films into alkaline processing solutions, thereby increasing the amount of polyester-based films that can be recovered and reducing the burden of wastewater treatment of alkaline processing solutions, thereby achieving the desired object, and have completed the present invention.

[0012] In the recovery of polyester-based films, by suppressing hydrolysis of the polyester-based films, the amount of film that can be recovered can be increased, and therefore the polyester-based films can be recovered profitably.

[0013] In addition, by suppressing the elution of the polyester film during recovery of the polyester film, it is possible to prevent a reduction in the wastewater treatment load of the alkaline treatment liquid, and to recover a polyester film with high purity efficiently and profitably.

[0014] The present invention is configured as follows. 1. A method for recovering a polyester film from a polyester film substrate having at least one coating film on at least a part of the polyester film, the method comprising the following step (2): (2) removing the coating film from the polyester-based film substrate by contacting at least the surface of the polyester-based film substrate having the coating film with a solvent, and the concentration of a component derived from terephthalic acid in the solvent wastewater is 0.5 mass% or less; 2. The method according to claim 1, wherein in step (2), the solvent is an alkaline processing liquid. 3. The method according to 1 above, wherein in the step (2), the ratio of the amount of the polyester film substrate treated (g) to the amount of the solvent wastewater (mL) is 0.2 or more. 4. The method according to claim 1, further comprising the following step (1) prior to step (2): (1) A step of contacting at least the surface of the polyester film substrate having the coating film with a surfactant, alcohol, or an aqueous solution in which a surfactant or alcohol is dissolved. 5. The method according to claim 1, further comprising the following step (0) prior to step (2): (0) A step of subjecting the surface of the coating film on the polyester-based film substrate to at least one surface modification treatment selected from corona discharge treatment, plasma treatment, glow discharge treatment, flame treatment, and ultraviolet treatment. 6. A method for producing a polyester product, comprising extruding a polyester film recovered by the method according to any one of 1 to 5 above to produce a polyester product. Effect of the Invention

[0015] According to the polyester film recovery method of the present invention, a coating film can be efficiently removed from a polyester film substrate having at least one coating film on at least a portion of the polyester film, so that a high-purity polyester film can be recovered profitably from used polyester film that would previously have been discarded. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, the present invention will be described in detail based on embodiments. In this specification, unless otherwise specified, the use of "to" indicating a numerical range means that the numerical values ​​before and after it are included as the lower limit and upper limit.

[0017] The method for recovering a polyester-based film of this embodiment (hereinafter also referred to as the method of this embodiment) is a method for recovering a polyester-based film from a polyester-based film substrate including a polyester-based film and at least one coating film provided on at least a portion of the polyester-based film, and includes a step (2) of removing the coating film from the polyester-based film substrate by contacting at least the surface of the polyester-based film substrate having the coating film with a solvent, and in which the concentration of components derived from terephthalic acid in the solvent wastewater is 0.5 mass% or less.

[0018] <Polyester film> The polyester film in the present embodiment is formed by containing a polyester composition. The polyester composition is not particularly limited as long as it contains terephthalic acid, and examples thereof include polyesters obtained by polycondensation of a dicarboxylic acid component and a diol component.

[0019] Examples of the dicarboxylic acid component include various dicarboxylic acid components such as aromatic dicarboxylic acids, linear aliphatic dicarboxylic acids, alicyclic dicarboxylic acids, etc. Specific examples of the dicarboxylic acid component other than terephthalic acid include 2,6-naphthalenedicarboxylic acid, isophthalic acid, and phthalic acid.

[0020] The diol component is preferably an aliphatic glycol, such as ethylene glycol, diethylene glycol, propylene glycol, butylene glycol, 1,4-cyclohexanedimethanol, neopentyl glycol, etc. In addition to diols, polyfunctional alcohols such as trimethylolpropane and pentaerythritol can also be used.

[0021] The polyester film may be a homopolyester film or a copolymer polyester film, and may contain a third component other than the dicarboxylic acid component and the diol component as a copolymer component.

[0022] As the polyester-based film, a polyester-based film mainly composed of polyethylene terephthalate or polyethylene naphthalate is preferably used, more preferably polyethylene terephthalate. These may also be copolymerized polyesters.

[0023] The polyester film may be made of a polyester composition, or the composition may contain additives other than polyester, such as an endblocking agent, an antioxidant, a flame retardant, a fluorescent brightening agent, a matting agent, a plasticizer, or an antifoaming agent.

[0024] The polyester film may be a commercially available product, or when it is produced, it can be produced, for example, by the following method. For example, a polyester film is vacuum dried, fed to an extruder, melted at 260-300°C, extruded into a sheet from a T-shaped die, and wound around a mirror-finished casting drum with a surface temperature of 10-60°C using an electrostatic casting method, and cooled and solidified to produce an unstretched polyester film. The unstretched polyester film is stretched 2.5-5 times in the longitudinal direction between rolls heated to 70-130°C. Then, the film is continuously stretched 2.5-5 times in the width direction in a hot air zone heated to 70-150°C, and then introduced into a heat treatment zone at 190-240°C, where it is heat-treated for 5-40 seconds, and passed through a cooling zone at 100-200°C to complete the crystal orientation, thereby obtaining a polyester film. In addition, during the heat treatment, a relaxation treatment of 0.1-12% may be performed in the width direction or longitudinal direction as necessary.

[0025] In this embodiment, the thickness of the polyester film is not particularly limited, but is preferably 5 μm to 500 μm in consideration of handleability such as strength, rigidity, etc. The thickness of the polyester film is more preferably 10 μm to 200 μm, and particularly preferably 20 μm to 100 μm.

[0026] In this embodiment, the polyester film substrate in the polyester film recovery described later may be in a long shape or in a cut state. In this specification, a long shape means that the length of the long side is about twice or more longer than the length (width) of the short side in a plan view. If the polyester film substrate is long, its length may be about 100 m or more and 10,000 m or less, depending on, for example, the type of device used, and it can be directly recovered without being crushed. Also, as long as it is in a cut state, it is not particularly limited, but it means that the polyester film substrate cut into, for example, 1 mm to 10 mm squares is recovered.

[0027] Since the method of the present embodiment includes a step (2) of contacting at least the surface of the polyester film substrate having the coating film with a solvent, if the polyester film substrates overlap each other, the processability may be reduced. Therefore, from the viewpoint of efficiently removing the coating film from the long polyester film substrate, it is preferable to transport the polyester film substrate wound in a long shape (long polyester film substrate) and contact it with a solvent. More preferably, it is recommended to transport the long polyester film substrate, contact it with the solvent, and then introduce it directly into the next step (washing and drying) described below and wind it up in a roll, that is, to perform a roll-to-roll method.

[0028] The roll-to-roll method is a method of continuous transport of a flexible substrate wound in a roll via multiple guide rolls, where a predetermined treatment is performed during transport and the substrate is wound into a roll again. By treating a long polyester film substrate using the roll-to-roll method, a series of coating film removal steps can be performed continuously in a short time, which is very efficient.

[0029] <Coating film> In the polyester-based film substrate in this embodiment, the polyester-based film has at least one coating film on at least a part thereof. Here, the coating film is a film that can impart various functions to the polyester-based film, such as a release film, an adhesive film, a hard coat film, an easy-adhesion film, and an antistatic film. In the polyester-based film substrate, these coating films may be present on at least one side of the polyester-based film, and may be present on both sides. Furthermore, in the polyester-based film substrate, the coating film may be contained alone, or two or more types may be laminated. In addition, the coating film may have not only a single function but also multiple functions.

[0030] The resin constituting the release film is not particularly limited as long as it is a resin generally used for release films, and examples thereof include silicone resins such as polydimethylsiloxane, amino resins such as melamine resins and urea resins, acrylic resins, epoxy resins, and alkyd resins. These resins may be used alone or in combination of two or more. The release film may contain a release agent such as silicone or wax.

[0031] The resin constituting the adhesive film includes an adhesive that is generally used for adhesive films. The type of the adhesive is not particularly limited, and examples thereof include acrylic adhesives, rubber adhesives, polyurethane adhesives, and silicone adhesives. The adhesive film may further contain a tackifier (tackifier resin).

[0032] The resin constituting the hard coat film is not particularly limited as long as it is a resin generally used for hard coat films, and examples thereof include acrylic resins, urethane resins, epoxy resins, etc. These resins may be used alone or in combination of two or more kinds.

[0033] The resin constituting the easy-adhesion film is not particularly limited as long as it is a resin generally used for easy-adhesion films, and examples thereof include polyester resin, acrylic resin, polycarbonate resin, polyurethane resin, polyvinyl alcohol resin, polyamide resin, polyvinyl acetate resin, etc. These resins may be used alone or in combination of two or more kinds.

[0034] The resin constituting the antistatic film is not particularly limited as long as it is a resin generally used for antistatic films. The antistatic film preferably further contains an antistatic agent. Examples of the antistatic agent include nonionic, cationic, anionic or amphoteric surfactants (conductive polymers such as polypyrrole and polyaniline, metal oxide fillers, carbonaceous materials, etc.). These antistatic agents may be used alone or in combination of two or more.

[0035] The method for forming a coating film on a polyester-based film substrate is not particularly limited, but for example, the coating film can be formed on a polyester-based film using a reverse coating method, a gravure coating method, a rod coating method, a bar coating method, a wire bar coating method, a die coating method, a spray coating method, or the like.

[0036] The thickness of the coating film (when multiple functional films are present, the total thickness of these films) is preferably 0.005 μm or more and 50 μm or less. In order to effectively exert a predetermined function, the thickness is more preferably 0.01 μm or more. On the other hand, if the coating film is too thick, it may take a long time to remove the coating film.

[0037] <Recycling of polyester film> The method of the present embodiment is characterized by including a step (2) of removing the coating film by contacting at least the surface of the polyester-based film substrate having the coating film with a solvent, in which the concentration of components derived from terephthalic acid in wastewater containing the solvent (solvent wastewater) generated by the removal is 0.5 mass% or less.

[0038] In addition, in order to reduce the cost of removing the coating film from the polyester film substrate used in the method of the present embodiment and recovering the polyester film, it is preferable to increase the amount of the polyester film substrate treated with respect to the solvent that is brought into contact with the polyester film substrate in step (2) and reduce the amount of solvent used to remove the coating film. From this perspective, in step (2), the amount of the polyester film substrate treated per 1 mL of solvent is preferably 0.2 g or more, more preferably 0.3 g or more, and even more preferably 0.6 g or more. In step (2), the amount of the polyester film substrate treated per 1 mL of solvent is preferably as large as possible, and the upper limit is not particularly limited, but is, for example, 10 g or less.

[0039] (Dissolution of terephthalic acid-derived components from polyester film by solvents) In step (2), at least the surface of the polyester film substrate having the coating film is brought into contact with the solvent to remove the coating film and recover the polyester film. As a result, the polyester film also comes into contact with the solvent, causing hydrolysis of the polyester film. The hydrolysis of the polyester film causes elution of components derived from terephthalic acid from the polyester film into the solvent. The elution of components derived from terephthalic acid from the polyester film reduces the amount of polyester film recovered from the polyester film substrate. In addition, the high concentration of components derived from terephthalic acid in the solvent wastewater increases the wastewater treatment load when treating the solvent wastewater. For this reason, it is necessary to lower the concentration of components derived from terephthalic acid in the solvent wastewater. The concentration of components derived from terephthalic acid in the solvent wastewater is 0.5% by mass or less, preferably 0.1% by mass or less, and more preferably 0.05% by mass or less.

[0040] In step (2), from the viewpoint of suppressing the solvent cost required for removing the coating film and recovering the polyester film, the amount of the polyester film substrate treated per 1 mL of solvent is preferably 0.2 g or more, more preferably 0.3 g or more, and even more preferably 0.6 g or more. The upper limit of the amount of the treatment is not particularly limited, but from the viewpoint of the deterioration of the treatment effect due to the dissolution of the coating film, the amount of the polyester film substrate treated per 1 mL of solvent is preferably 100 g or less, more preferably 50 g or less, and even more preferably 10 g or less.

[0041] In the method of the present embodiment, in step (2), at least the surface of the polyester film substrate having the coating film is brought into contact with a solvent to remove the coating film and recover the polyester film. Therefore, if the contact time between the polyester film substrate and the solvent is long, hydrolysis of the polyester film progresses, and the concentration of components derived from terephthalic acid in the solvent wastewater increases. From this perspective, it is preferable that the treatment device in the method of the present embodiment is one that can shorten the contact time between the polyester film substrate and the solvent.

[0042] [Step (1) of contacting with a surfactant, an alcohol, or an aqueous solution containing a surfactant or an alcohol] The method of the present embodiment may include a step (1) of contacting at least the coating film-bearing surface of the polyester film substrate with a surfactant, an alcohol, or an aqueous solution of a surfactant or an alcohol, prior to the step (2) of contacting the polyester film substrate with a solvent.

[0043] The surface of the polyester film substrate is hydrophilized by contacting the surface of the polyester film substrate with a surfactant, alcohol, or an aqueous solution of a surfactant or alcohol, and allowing the surfactant or alcohol to penetrate into the coating film of the polyester film substrate. By contacting the surface of the polyester film substrate with a solvent in a pre-hydrophilized state, the penetration of the solvent is promoted, and the coating film can be easily and efficiently removed from the polyester film substrate in a short time. In addition, the elution of components derived from terephthalic acid from the polyester film into the solvent is also suppressed.

[0044] The method of contacting the polyester film substrate with the surfactant, alcohol, or an aqueous solution of the surfactant or alcohol is not particularly limited as long as the surface of the polyester film substrate having at least the coating film can be contacted. For example, the polyester film substrate is immersed in a cleaning tank containing the surfactant, alcohol, or an aqueous solution of the surfactant or alcohol, or the coating method, spraying method, etc. are included. Among these, the immersion method is preferred from the viewpoint of the permeability of the surfactant, alcohol, or an aqueous solution of the surfactant or alcohol into the coating film.

[0045] The alcohol is not particularly limited, and may be a monohydric alcohol or a polyhydric alcohol, and may be a lower alcohol or a higher alcohol.

[0046] Examples of monohydric alcohols include methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol, octanol, nonylnol, decylnol, undecylnol, dodecylnol, methoxyethanol, methoxypropanol, methoxybutanol, methoxyethoxyethanol, ethoxyethanol, ethoxyethoxyethanol, ethoxypropanol, ethoxybutanol, butoxyethanol, butoxypropanol, and butoxybutanol.

[0047] Examples of polyhydric alcohol solvents include ethylene glycol, propylene glycol, diethylene glycol, 1,4-butanediol, glycerin, and polyoxyalkylene polyols.

[0048] Among these, monohydric lower alcohols such as methanol, ethanol, 1-propanol (normal propanol), and 2-propanol (isopropanol) are more preferred, at least one selected from the group consisting of methanol, ethanol, 1-propanol, and 2-propanol is even more preferred, and methanol and ethanol are particularly preferred. The alcohols may be used alone or in combination of two or more.

[0049] The concentration of the alcohol or the aqueous solution in which the alcohol is dissolved is preferably 0.1% by mass to 100% by mass, more preferably 30% by mass to 60% by mass, and further preferably 40% by mass to 50% by mass. If the alcohol concentration is too low, there is a risk that the coating film cannot be sufficiently removed. If the concentration of the alcohol or the aqueous solution in which the alcohol is dissolved is 0.1% by mass or more, a sufficient coating film removal effect can be obtained.

[0050] The temperature of the alcohol or the aqueous solution containing the alcohol may be adjusted depending on the alcohol used, but is preferably 50° C. or less, and more preferably room temperature of 5 to 30° C. If the temperature of the alcohol or the aqueous solution containing the alcohol is too high, the alcohol may boil. If the temperature of the alcohol or the aqueous solution containing the alcohol is 50° C. or less, the alcohol is below the boiling point, and therefore the effect of removing the coating film is promoted.

[0051] The surfactant is not particularly limited, and may be at least one surfactant selected from the group consisting of nonionic surfactants, cationic surfactants, and anionic surfactants. In particular, nonionic surfactants are preferred. The surfactants may be used alone or in combination of two or more.

[0052] Examples of nonionic surfactants include polyoxyethylene alkyl ethers such as polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, polyoxyethylene stearyl ether, and polyoxyethylene oleyl ether; polyoxyethylene alkylphenol ethers such as polyoxyethylene octylphenol ether and polyoxyethylene nonylphenol ether; polyoxyethylene alkylaryl ether; polyoxyethylene fatty acid esters such as polyethylene glycol monolaurate; sorbitan fatty acid esters such as sorbitan monolaurate, sorbitan monopalmitate, sorbitan monostearate, sorbitan tristearate, sorbitan monooleate, and sorbitan trioleate; polyoxyethylene sorbitan fatty acid esters such as polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monopalmitate, polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan tristearate, polyoxyethylene sorbitan moreoleate, and polyoxyethylene sorbitan trioleate; and glycerin fatty acid esters such as stearic acid monoglyceride.

[0053] Examples of the cationic surfactant include alkylpyridinium chloride, alkyltrimethylammonium chloride, dialkyldimethylammonium chloride, and alkyldimethylbenzylammonium chloride.

[0054] Examples of the anionic surfactant include sodium alkyl sulfate, sodium alkylbenzene sulfonate, sodium dialkyl succinate sulfonate, sodium alkyl diphenyl ether disulfonate, sodium polyoxyethylene alkyl ether sulfate, and sodium polyoxyethylene alkyl phenyl ether sulfate.

[0055] The concentration of the surfactant or the aqueous solution in which the surfactant is dissolved is preferably 0.00001% by mass to 100% by mass, more preferably 0.0001% by mass to 100% by mass, further preferably 0.001wt% to 50wt%, and particularly preferably 0.01% by mass to 1% by mass. If the surfactant concentration is too low, the coating film may not be sufficiently removed. If the concentration of the surfactant or the aqueous solution in which the surfactant is dissolved is 0.00001% by mass to 100% by mass, a sufficient coating film removal effect can be obtained, which is preferable.

[0056] The temperature of the surfactant or the aqueous solution in which the surfactant is dissolved may be adjusted depending on the surfactant used, but is preferably 50°C or less, more preferably 40°C or less, and even more preferably 30°C or less. If the temperature of the surfactant or the aqueous solution in which the surfactant is dissolved is 50°C or less, the surfactant can be made highly concentrated, which promotes the removal effect of the coating film. In addition, since nonionic surfactants do not dissolve in water if the temperature is too high, it is preferable to treat them at a temperature below the cloud point of the surfactant.

[0057] The contact time between the polyester film substrate and the surfactant, alcohol, or the aqueous solution in which the surfactant or alcohol is dissolved is preferably within 120 seconds, more preferably 0.001 to 60 seconds, even more preferably 0.001 to 10 seconds, and particularly preferably 0.1 to 10 seconds. If the contact time with the polyester film substrate is too short, there is a risk that the coating film cannot be sufficiently removed, and if the contact time is too long, there is a risk that the device size becomes large, resulting in poor economic efficiency and operability. If the contact time with the polyester film substrate is within 120 seconds, there is good economic efficiency and operability, and the effect of removing the coating film can be enhanced.

[0058] The surfactant, alcohol, or the aqueous solution containing the surfactant or alcohol may contain ultra-fine bubbles as an auxiliary agent to enhance the efficiency of removing the coating film. The alcohol or the aqueous solution containing the alcohol may contain the surfactant, and the surfactant or the aqueous solution containing the surfactant may contain the alcohol.

[0059] Examples of the nonionic surfactant include polyoxyethylene alkyl ethers, polyoxyethylene alkylaryl ethers, polyoxyethylene fatty acid esters, and polyoxyethylene sorbitan fatty acid esters.

[0060] Examples of the cationic surfactant include alkylpyridinium chloride, alkyltrimethylammonium chloride, dialkyldimethylammonium chloride, and alkyldimethylbenzylammonium chloride.

[0061] Examples of the anionic surfactant include sodium alkyl sulfate, sodium alkylbenzene sulfonate, sodium dialkyl succinate sulfonate, sodium alkyl diphenyl ether disulfonate, sodium polyoxyethylene alkyl ether sulfate, and sodium polyoxyethylene alkyl phenyl ether sulfate.

[0062] [Surface modification process (0)] The method of the present embodiment may include a step (0) of performing a surface modification treatment on the surface of the coating film on the polyester film substrate for the purpose of increasing the affinity with a surfactant, alcohol, or an aqueous solution of a surfactant or alcohol, and further the solvent, prior to the step (2) of contacting the polyester film substrate with a solvent.

[0063] The surface modification treatment is not particularly limited, and known methods can be adopted. For example, corona discharge treatment, plasma treatment, glow discharge treatment, flame treatment, ultraviolet treatment, etc. are included. It is preferable to carry out at least one treatment selected from the group consisting of these.

[0064] The surface modification treatment may be carried out before step (2) in which the polyester film substrate is contacted with a solvent. However, in order to increase the affinity with a surfactant, an alcohol, or an aqueous solution in which a surfactant or an alcohol is dissolved, it is more preferable to carry out the surface modification treatment before step (1) in which at least the surface of the polyester film substrate having a coating film is contacted with a surfactant, an alcohol, or an aqueous solution in which a surfactant or an alcohol is dissolved.

[0065] If an analysis of the coating film by X-ray photoelectron spectroscopy after the surface modification treatment shows that the proportion of C-C bonds and C-H bonds has decreased by 0.1% or more, the affinity with a surfactant, alcohol, or an aqueous solution containing a surfactant or alcohol, or an alkaline treatment liquid can be increased.

[0066] For corona discharge treatment, the treatment intensity is 10 to 1000 Wmin / m 2 More than 20 to 200 Wmin / m is preferable. 2 More preferably, 40 to 120 Wmin / m 2 If the treatment intensity is too high, the polyester film tends to be easily damaged, and if the treatment intensity is too low, the alkali treatment time becomes long, and the polyester film tends to be easily damaged. The power density of the corona discharge machine used is preferably 4 to 20 W / cm. 2 If so, the surface treatment can be performed uniformly.

[0067] For UV treatment, the irradiation intensity is 0.5 to 40 mW / cm 2 is preferably 10 to 40 mW / cm 2 More preferably, 15 to 40 mW / cm 2is more preferable. If the irradiation intensity is too high, the polyester film tends to be easily damaged, and if the irradiation intensity is too weak, the alkali treatment time becomes long, and the polyester film tends to be easily damaged. The ultraviolet irradiation time is preferably 3 to 210 seconds, more preferably 30 to 100 seconds, and even more preferably 50 to 70 seconds. If the ultraviolet irradiation time is too long, the size of the device needs to be increased, which increases the manufacturing cost and also tends to cause the polyester film to be easily damaged. If the ultraviolet irradiation time is too short, there is a risk that the coating film cannot be sufficiently removed. In addition, it is preferable to use an electromagnetic wave of invisible light that is shorter than visible light and longer than soft X-rays, with a wavelength of 10 to 400 nm for the ultraviolet light to be irradiated. Examples of sources of ultraviolet light include known lamps such as ultra-high pressure mercury lamps, high pressure mercury lamps, low pressure mercury lamps, carbon arcs, and metal halide lamps, and low pressure mercury lamps are preferred.

[0068] [Step (2) of contacting polyester film substrate with solvent] The method of the present embodiment recovers polyester-based films by including a step (2) of contacting at least the surface of the polyester-based film substrate having the coating film with a solvent. By shortening the time for contacting the polyester-based film substrate with the solvent, the amount of recoverable polyester-based film can be increased and the load of solvent wastewater treatment can be reduced, which is very efficient.

[0069] The solvent used in step (2) of the method of the present embodiment is not particularly limited, but may be an alkaline treatment liquid. The solvent may be used alone or in combination of two or more kinds. In addition, it may contain a surfactant, ultrafine bubbles, alcohol, or the like.

[0070] The solvent treatment may be carried out in one tank or in multiple tanks. When the treatment is carried out in multiple tanks, the types of solvents used may be different or the same.

[0071] When recovering a long polyester film substrate, in order to reduce contact between the polyester film and the solvent, the solvent may be brought into contact only with the surface having the coating film. The method for bringing the solvent into contact only with the surface having the coating film is not particularly limited, but examples thereof include showering.

[0072] The alkaline treatment liquid used in the process of the method of the present embodiment may be a solution in which an alkaline substance is dissolved. The alkaline substance is not particularly limited, but may be, for example, an inorganic alkaline agent such as sodium hydroxide, potassium hydroxide, ammonium hydroxide, lithium hydroxide; sodium silicate, potassium silicate, ammonium silicate; sodium dibasic phosphate, potassium dibasic phosphate, ammonium dibasic phosphate; sodium bicarbonate, potassium bicarbonate, ammonium bicarbonate; sodium carbonate, potassium carbonate, ammonium carbonate; sodium hydrogen carbonate, potassium hydrogen carbonate, ammonium hydrogen carbonate; sodium borate, potassium borate, ammonium borate, etc. Among these, alkali metal hydroxide is preferred, and sodium hydroxide and potassium hydroxide are more preferred. The alkaline substances may be used alone or in combination of two or more.

[0073] The solvent for dissolving the alkaline substance is not particularly limited, but may be, for example, water.

[0074] The concentration of the alkaline substance in the alkaline processing liquid is preferably 0.01% by mass to 10% by mass, more preferably 0.04% by mass to 10% by mass, and even more preferably 1% by mass to 5% by mass. If the concentration of the alkaline substance is too high, the polyester film tends to be easily damaged, and if the concentration is too low, the coating film may not be sufficiently removed. If the content of the alkaline substance is within the above range, the effect of removing the coating film can be obtained and hydrolysis of the polyester film can be suppressed.

[0075] The solvent may contain a surfactant or ultrafine bubbles as an auxiliary agent to prevent reattachment of the removed coating film and to increase the efficiency of removing the coating film. The surfactant is not particularly limited, and examples thereof include nonionic surfactants, cationic surfactants, and anionic surfactants. The surfactants may be used alone or in combination of two or more kinds.

[0076] Examples of the nonionic surfactant include polyoxyethylene alkyl ethers, polyoxyethylene alkylaryl ethers, polyoxyethylene fatty acid esters, and polyoxyethylene sorbitan fatty acid esters.

[0077] Examples of the cationic surfactant include alkylpyridinium chloride, alkyltrimethylammonium chloride, dialkyldimethylammonium chloride, and alkyldimethylbenzylammonium chloride.

[0078] Examples of the anionic surfactant include sodium alkyl sulfate, sodium alkylbenzene sulfonate, sodium dialkyl succinate sulfonate, sodium alkyl diphenyl ether disulfonate, sodium polyoxyethylene alkyl ether sulfate, and sodium polyoxyethylene alkyl phenyl ether sulfate.

[0079] The solvent may contain other additives within the range that does not impair the effects of the present invention. Examples of the additives include antioxidants, pH adjusters, and antifoaming agents.

[0080] The temperature of the solvent is preferably less than 100°C, more preferably 65°C or more and less than 100°C, and even more preferably 65°C or more and 95°C or less. When the temperature of the solvent is 65°C or more, it is preferable because the physicochemical properties of the polyester film are not changed and a high-quality polyester film with few impurities can be obtained without excessive time. In addition, by setting the temperature of the solvent to less than 100°C, it is possible to achieve the reaction at normal pressure, prevent the equipment from becoming large, and suppress the occurrence of hydrolysis of the polyester film due to heating.

[0081] The contact time between the solvent and the polyester film substrate is preferably more than 0 seconds and less than 300 seconds, more preferably more than 0 seconds and 240 seconds or less, even more preferably more than 0 seconds and 180 seconds or less, and particularly preferably more than 0 seconds and 120 seconds or less. If the treatment time is too long, the polyester film is easily hydrolyzed, and the polyester film is dissolved in the alkaline treatment liquid, so that the load when the alkaline treatment liquid is treated as wastewater may be large. The treatment time with the solvent is sufficient so that the coating film can be sufficiently dissolved and swollen, and if the treatment time is too short, the coating film may not be sufficiently removed, so that 1 second or more is more preferable, and 5 seconds or more is even more preferable. If the treatment time with the solvent is within the above range, the effect of removing the coating film can be obtained and damage to the polyester film can be suppressed.

[0082] In step (2) of contacting the polyester film substrate with a solvent, the treatment with the solvent can be appropriately selected depending on the type and thickness of the polyester film or coating film. In order to obtain a high-quality polyester film with few impurities, specifically, for example, it is preferable to contact the long polyester film substrate with an alkaline treatment liquid having a concentration of 0.01% by mass or more and 10% by mass or less heated to a temperature of less than 100°C for more than 0 seconds and less than 300 seconds, and it is more preferable to contact the polyester film substrate with an alkaline treatment liquid having a temperature of 65°C or more and less than 100°C and an alkaline concentration of 0.04% by mass or more and 10% by mass or less for 1 second or more and 180 seconds or less.

[0083] [Step (3) of performing water washing treatment] The method of the present embodiment preferably includes a step (3) of washing the polyester film substrate with water after the step (2) of contacting the polyester film substrate with a solvent. The washing with water is performed to remove a trace amount of the coating film remaining on the polyester film after the step (2) of contacting the polyester film substrate with a solvent, and to remove the solvent remaining on the polyester film after the above treatment.

[0084] The temperature for the water washing treatment in step (3) is not particularly limited, but for example, washing with warm water of about 40° C. to 100° C. will more effectively exhibit the above effects.

[0085] Examples of the method of washing with water include a method of spraying water onto the polyester film from which the coating film has been removed, a method of immersing the polyester film in a water tank, etc. During the water washing treatment, physical washing using a roll brush, microbubbles, water flow, etc. may be performed.

[0086] [Drying treatment] After washing with water, it is preferable to carry out a drying treatment in order to remove water remaining on the polyester film.

[0087] The drying time is preferably 10 seconds or more and 5 minutes or less. When the drying time is 10 seconds or more, the drying is sufficient and blocking can be suppressed. It is more preferably 30 seconds or more. In addition, when the drying time is 5 minutes or less, deformation of the polyester film can be prevented.

[0088] The drying method is not particularly limited, and examples thereof include hot air drying in which hot air is blown onto the substrate, and heat drying in which a non-contact heater is used.

[0089] (multiple processing) The above steps (0) to (3) may be carried out multiple times. By carrying out these treatments multiple times, the polyester film can be treated in a short time without being damaged, such as by a decrease in intrinsic viscosity.

[0090] <Molding of Recycled Polyester Film> The method for producing a polyester product of the present embodiment includes extruding the polyester film recovered by the method of the present embodiment to produce a polyester product.

[0091] Specifically, the recovered polyester film can be pelletized and then molded into various polyester products such as polyester films by melt extrusion or the like.

[0092] The polyester product is not particularly limited, and can be used for ordinary polyester applications, such as polyester films, PET bottles, polyester fibers, polyester sheets, polyester containers, etc. Specifically, it can be used as polyester films, for example.

[0093] The thickness of the polyester film is not particularly limited, but can be set appropriately within the range of 10 to 50 μm. In addition, a coating film can be formed as necessary. Examples of the coating film include a release film, an adhesive film, a hard coat film, an easy-adhesion film, and an antistatic film. In addition, the coating film can be removed from the recovered polyester film, and the polyester film can be recovered again and extrusion-molded to produce a polyester product.

[0094] The polyester products produced from the recycled polyester films are not particularly limited, and can be used for ordinary polyester applications, such as the polyester films, PET bottles, polyester fibers, polyester sheets, and polyester containers described above.

[0095] As described above, the present specification discloses the following configurations. <1> A method for recovering a polyester film from a polyester film substrate having at least one coating film on at least a part of the polyester film, the method comprising the following step (2): (2) removing the coating film from the polyester-based film substrate by contacting at least the surface of the polyester-based film substrate having the coating film with a solvent, and the concentration of a component derived from terephthalic acid in the solvent wastewater is 0.5 mass% or less; <2> In the step (2), the solvent is an alkaline processing liquid. <1> The method according to <3> In the step (2), the ratio of the amount of the polyester film substrate treated (g) to the amount of the solvent wastewater (mL) is 0.2 or more. <1> or <2> The method according to <4> The method includes the following step (1) before the step (2): <1> ~ <3> 2. The method according to claim 1 , (1) A step of contacting at least the surface of the polyester film substrate having the coating film with a surfactant, alcohol, or an aqueous solution in which a surfactant or alcohol is dissolved. <5> The method includes the following step (0) before the step (2): <1> ~ <4> 2. The method according to claim 1 , (0) A step of subjecting the surface of the coating film on the polyester-based film substrate to at least one surface modification treatment selected from corona discharge treatment, plasma treatment, glow discharge treatment, flame treatment, and ultraviolet treatment. <6> <1> ~ <5> 2. A method for producing a polyester product, comprising extruding the polyester film recovered by any one of the methods described above to produce a polyester product. EXAMPLES

[0096] Hereinafter, the embodiment of the present invention will be described in more detail based on examples, but the present invention is not necessarily limited thereto. The usefulness of the coating film removal method according to the present invention can be expressed by the coating film removal ability. In the following, unless otherwise specified, "%" means % by mass, and "parts" means parts by mass.

[0097] (Evaluation of coating film removal) Each characteristic was measured as follows.

[0098] 1. Evaluation of the concentration of components derived from terephthalic acid in the solvent in step (2) The concentration of components derived from terephthalic acid in the solvent was determined from the peak area by liquid chromatography (Model 8500, manufactured by Varian), and evaluated according to the following criteria. "◯" and "Δ" are acceptable, and "×" is unacceptable. [Evaluation Criteria] ○ (Good): Concentration of components derived from terephthalic acid in the solvent is 0.1% by mass or less △ (OK): The concentration of components derived from terephthalic acid in the solvent is more than 0.1% by mass and 0.5% by mass or less. × (Not acceptable): Concentration of components derived from terephthalic acid in the solvent exceeds 0.5% by mass

[0099] 2. Evaluation of the amount of polyester film substrate treated per 1 mL of solvent in step (2) The amount of polyester-based film substrate treated per mL of solvent was evaluated according to the following criteria, where "◯" and "Δ" are pass marks and "×" is fail marks. [Evaluation Criteria] ○ (Good): The amount of polyester film substrate treated is 0.6 g or more per 1 mL of solvent. △ (OK): The amount of polyester film substrate treated is 0.2g or more and less than 0.6g per 1mL of solvent. × (Not acceptable): The amount of polyester film substrate treated is less than 0.2 g per 1 mL of solvent.

[0100] 3. Evaluation of treatability The collected polyester film was cut into small pieces, then molded into a cylindrical shape using a melt press, and the silicon (Si) content was measured using an X-ray fluorescence analyzer (Rigaku Corporation, "Model 3270"). The Si content was quantified using the X-ray fluorescence measurement method, based on a calibration curve of X-ray fluorescence intensity that had been prepared in advance. The processability of each Example or Comparative Example was evaluated based on the obtained Si content according to the following criteria: "A" and "B" are preferable because the coating film was sufficiently removed, and "C" is not preferable because the coating film was not sufficiently removed. [Evaluation Criteria] A: The Si content is below the detection limit (100 ppm by mass). B: Si content is more than 100 mass ppm and less than 500 mass ppm C:Si content is 500 mass ppm or more

[0101] (Preparation of sample film) A laminated polyester film having a release film was prepared as a sample film as follows.

[0102] 1. Preparation of Polyester Film A polyethylene terephthalate film (Toray Industries, Inc.'s "Lumirror" T60, thickness 38 μm, intrinsic viscosity 0.61) was prepared as a polyester film. One side of the film was coated with a 5% toluene solution of a curable silicone resin (containing 100 parts of Toray Dow Corning Silicones Co., Ltd.'s LTC-350B and 0.8 parts of the same company's curing agent SRX-212) using a bar coater, and the film was heated at 100°C in a tunnel oven to produce a release film, which was then wound up.

[0103] 2. Application of ceramic slurry and conductive paste A ceramic slurry having the following composition was uniformly applied to the release layer surface of the release film using a blade coater. This was dried in a tunnel oven at 85°C to form a ceramic layer having a thickness of 20 μm on the release film. Next, a conductive paste having the following composition was screen-printed on the ceramic layer, dried at 80°C for 10 minutes to form an electrode, and then left at 20°C for 1 hour. Ceramic Slurry Composition Ceramic powder (barium titanate): 100 parts Binder (polyvinyl butyral): 10 parts Plasticizer (dioctyl phthalate): 5 parts Solvent (toluene / isopropyl alcohol = 1 / 1 (mass ratio)): 100 parts Conductive paste composition Ni-based powder: 90 parts Organic vehicle: 10 parts Terpineol: 30 parts

[0104] 3. Peeling off of ceramic film and internal electrodes On the release film on which the ceramic layer and electrodes were formed, a 10 cm x 10 cm slit was made only in the coating film on the part on which the ceramic layer and electrodes were formed, and then the ceramic layer and the electrode were sucked with a vacuum suction machine and peeled off from the release film to obtain a long sample film. Note that some of the ceramic layer and the electrode were still attached to the surface of the release layer of the sample film, and could not be peeled off.

[0105] [Example 1] [Surface modification process (0)] The release film side of the sample film was treated with a corona discharge treatment device at a power density of 8 W / cm 2 , Processing intensity 60Wmin / m 2 A corona discharge treatment was carried out.

[0106] [Step (1) of contacting a polyester film substrate with a surfactant, an alcohol, or an aqueous solution containing a surfactant or an alcohol] The corona discharge-treated sample film was immersed for 1 second in an aqueous solution of 0.03 mass % of a nonionic surfactant ("Polyoxyethylene (10) Octylphenyl Ether" manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) at room temperature (25°C).

[0107] [Step (2) of contacting polyester film substrate with solvent] 10 L of a mixed aqueous solution solvent of 3% by mass of sodium hydroxide and 0.03% by mass of a nonionic surfactant ("Polyoxyethylene (10) octylphenyl ether" manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was heated to 80°C. 3 kg of a sample film was then brought into contact with the alkaline processing solution for 60 seconds to remove the release layer, thereby obtaining a recovered polyester film. Using the recovered polyester film and the alkaline processing solution, the above-mentioned "Evaluation of the concentration of terephthalic acid in the solvent", "Evaluation of the amount of polyester film substrate treated per mL of solvent", and "Evaluation of processability" were performed.

[0108] [Washing, drying, pelletizing] The sample film (recovered polyester film) was immersed in a water tank for 45 seconds, and then dried by blowing hot air onto it. The dried sample film was crushed, put into an extruder, melted, and pelletized.

[0109] [Production of polyester film] Pellets obtained from the sample film were dried at 150°C for 3 hours, fed to an extruder, melt-extruded at 285°C, and cast onto an electrostatically charged casting drum at 20°C to obtain an unstretched sheet. This unstretched sheet was stretched 3.1 times in the longitudinal direction using a stretching roll heated to 90°C, then stretched 3.7 times in the transverse direction at 120°C using a tenter-type stretching machine, and then heat-set at 230°C and wound up on a roll.

[0110] [Example 2] A polyester film was produced in the same manner as in Example 1, except that the sample film used was cut into flakes after being subjected to a corona discharge treatment as the surface modification treatment step (0).

[0111] [Examples 3 to 4] A polyester film was prepared in the same manner as in Example 1, except that the temperature of the alkaline treatment liquid in the step (2) of contacting the polyester-based film substrate with the solvent was changed to the conditions shown in Table 1.

[0112] [Example 5] A polyester film was prepared in the same manner as in Example 1, except that the alkaline treatment liquid in the step (2) of contacting the polyester-based film substrate with a solvent was changed to potassium hydroxide shown in Table 1.

[0113] [Examples 6 to 7] A polyester film was prepared in the same manner as in Example 1, except that the concentration of the alkaline treatment liquid in the step (2) of contacting the polyester film substrate with a solvent was changed to the conditions shown in Table 2.

[0114] [Example 8] A polyester film was prepared in the same manner as in Example 1, except that the amount of the sample film was changed to the conditions shown in Table 2.

[0115] [Example 9] A polyester film was produced in the same manner as in Example 1, except that the surface modification treatment step (0) was not carried out.

[0116] [Example 10] A polyester film was produced in the same manner as in Example 1, except that the step (1) of contacting the polyester film with a surfactant, an alcohol, or an aqueous solution containing a surfactant or an alcohol was not carried out.

[0117] [Reference example 1] A polyester film substrate was contacted with an alkaline treatment liquid, washed with water, and dried in the same manner as in Example 1, except that the surface modification treatment step (0) similar to that in Example 1 and the step (1) of contacting the sample film with a surfactant, alcohol, or an aqueous solution containing a surfactant or alcohol were not performed, to prepare a polyester film.

[0118] [Comparative Example 1] The sample film was washed with water and dried in the same manner as in Example 1, without carrying out the surface modification treatment step (0) similar to that in Example 1, and the step (1) of contacting the sample film with a surfactant, alcohol, or an aqueous solution containing a surfactant or alcohol dissolved therein, to prepare a polyester film. In Reference Example 1, the treatment time with the alkaline treatment liquid in step (2) of contacting the polyester film substrate with the solvent was 60 seconds, while in Comparative Example 1, the treatment time with the alkaline treatment liquid was 3,000 seconds.

[0119] [Comparative Example 2] As in Comparative Example 1, the sample film was not subjected to the same surface modification treatment as in Example 1, nor to the step of contacting the sample film with a surfactant, alcohol, or an aqueous solution containing a surfactant or alcohol, but was washed with water and dried in the same manner as in Example 1 to produce a polyester film. In Reference Example 1, the concentration of the alkaline treatment liquid in step (2) of contacting the polyester film substrate with a solvent was 3 mass %, and in Comparative Example 2, the concentration of the alkaline treatment liquid was 30 mass %.

[0120] The evaluation results for Examples 1 to 10, Reference Example 1, and Comparative Examples 1 and 2 are shown in Tables 1 to 4.

[0121] [Table 1]

[0122] [Table 2]

[0123] [Table 3]

[0124] [Table 4]

[0125] As shown in Tables 1 to 4, the method of the present invention makes it possible to cost-effectively and efficiently remove a coating film from a long polyester film substrate having at least one coating film, and to efficiently and effectively recover the polyester film and produce polyester products using the polyester film as part of the raw material.

[0126] In addition, the results of Example 1 showed that by shortening the contact time with the solvent when bringing the solvent into contact with at least the surface of the polyester film substrate having the coating film, it is possible to remove the coating layer while keeping the concentration of terephthalic acid-derived components in the solvent wastewater low.

[0127] In contrast, in Reference Example 1, in which the surface modification treatment step (0) and the step (1) of contacting with a surfactant, alcohol, or an aqueous solution containing a surfactant or alcohol were not performed, the processability was decreased compared to Example 1.

[0128] In Comparative Example 1 and Comparative Example 2, in which step (1) of contacting with a surface modification treatment, a surfactant, an alcohol, or an aqueous solution containing a surfactant or an alcohol was not performed, the concentration of components derived from terephthalic acid in the solvent wastewater in step (2) exceeded 0.5% by mass. In Comparative Example 1, the contact time with the alkaline treatment liquid in step (2) was extended, and in Comparative Example 2, the alkaline treatment liquid in step (2) was made highly concentrated, which enabled removal of the coating film, but increased the concentration of components derived from terephthalic acid in the solvent.

[0129] As described above, according to the method of the present invention, the coating layer can be efficiently removed by contacting the polyester film substrate with the solvent for a short time, and the polyester film can be recovered and polyester products using the polyester film as a part of the raw material can be efficiently manufactured. In addition, since the dissolution of the polyester film into the solvent can be suppressed, the amount of polyester film that can be recovered can be increased, the load of solvent wastewater treatment can be reduced, and the coating film can be efficiently removed, which is extremely useful.

Claims

1. A method for recovering a polyester film from a polyester film substrate having at least one coating film on at least a part of the polyester film, the method comprising the following step (2): (2) A step of removing the coating film from the polyester-based film substrate by contacting at least the surface of the polyester-based film substrate having the coating film with a solvent, and the concentration of a component derived from terephthalic acid in the solvent wastewater is 0.5 mass% or less.

2. The method according to claim 1 , wherein in step (2), the solvent is an alkaline processing liquid.

3. The method according to claim 1 , wherein in the step (2), the ratio of the amount (g) of the polyester film substrate to the amount (mL) of the solvent wastewater is 0.2 or more.

4. The method according to claim 1, further comprising the following step (1) prior to step (2): (1) A step of contacting at least the surface of the polyester film substrate having the coating film with a surfactant, alcohol, or an aqueous solution in which a surfactant or alcohol is dissolved.

5. The method according to claim 1 , further comprising the following step (0) prior to step (2): (0) A step of subjecting the surface of the coating film on the polyester-based film substrate to at least one surface modification treatment selected from corona discharge treatment, plasma treatment, glow discharge treatment, flame treatment, and ultraviolet treatment.

6. A method for producing a polyester product, comprising extruding a polyester film recovered by the method according to any one of claims 1 to 5 to produce a polyester product.

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