JP7694490B2 - Method for recovering polyester support and method for producing polyester product - Google Patents

Description

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

Polyester-based supports have excellent mechanical, physical, and chemical properties and are therefore used in a wide variety of applications for fibers, films, and other molded products. Many of these polyester-based supports have coating films with various functions laminated on one or both sides of the surface.

As the polyester-based supports are used in a variety of applications, the amount of waste and used products generated is also increasing, which leads to the deterioration of the global environment. To solve this problem and recycle the polyester-based supports, it is preferable to remove the coating film from the polyester-based substrate and reuse it as a polyester-based support.

One example of such a technique is Patent Document 1. In Patent Document 1, the coating film on at least one surface of the substrate film is removed by contacting the coating film with a 20 to 60% by mass alkaline treatment liquid heated to a temperature of 90 to 140°C.

JP 2020-90094 A

However, the method described in Patent Document 1 has the problem that the polyester support deteriorates due to contact with a high-temperature, high-concentration alkaline processing solution. In addition, the use of high-temperature, high-concentration alkali also poses the problem of reduced safety and profitability.

The present invention has been made in consideration of the above-mentioned reasons, and its object is to provide a method for safely, profitably, and efficiently recovering a high-purity polyester support from a polyester base material having at least one coating film on a polyester support in a short period of time.

As a result of investigations to solve the above problems, it was found that the desired object can be achieved by contacting the polyester substrate with a surfactant or an aqueous solution containing a surfactant to hydrophilize the surface of the polyester substrate, and then treating the polyester substrate with an alkaline treatment liquid, and thus the present invention was completed. By dividing the process into a first process in which the surface of the polyester substrate is hydrophilized with a surfactant or an aqueous solution containing a surfactant, and a second process in which the surface is treated with an alkaline treatment liquid, the first process and the second process can be performed at different temperatures. By performing the hydrophilization of the surface of the polyester substrate in the first process and the removal of the coating film in the second process under optimal temperature conditions, respectively, it becomes possible to efficiently recover the polyester support in a short time.

The present invention is configured as follows.
(1) A method for recovering a polyester-based support by removing at least one coating film from a polyester-based substrate having at least one coating film on at least a part of the polyester-based support, the method comprising: a first step of contacting at least the surface of the polyester-based substrate having the coating film with a surfactant or an aqueous solution containing a surfactant dissolved therein; and a second step of contacting the polyester-based substrate with an alkaline treatment liquid after the first step.
(2) The method for recovering a polyester support according to (1) above, characterized in that, prior to the first step, at least the surface of the polyester base material having the coating film thereon is subjected to at least one surface modification treatment selected from the group consisting of a corona discharge treatment, a plasma treatment, a glow discharge treatment, a flame treatment, and an ultraviolet treatment.
(3) The method for recovering a polyester support according to (2) above, characterized in that washing with water is carried out after the second step.
(4) The method for recovering a polyester support according to (3) above, wherein in the first step, the surfactant or the aqueous solution in which the surfactant is dissolved is brought into contact for 300 seconds or less.
(5) The method for recovering a polyester support according to (4) above, wherein the surfactant is a nonionic surfactant.
(6) The method for recovering a polyester support according to (5) above, wherein in the second step, the alkaline processing liquid is an alkaline processing liquid having a temperature of less than 100° C. and an alkali concentration of 0.04% by mass or more and 15% by mass or less, and the alkaline processing liquid is brought into contact for 1 second or more and 180 seconds or less.
(7) The method for recovering a polyester support according to (6) above, wherein the polyester support is recovered in a long shape.
(8) A method for producing a polyester product, comprising extruding a polyester support recovered by the method for recovering a polyester support according to any one of (1) to (7) above to produce a polyester product.

According to the present invention, since the coating film can be efficiently removed from a polyester substrate having at least one coating film on at least a portion of the polyester substrate, it is possible to efficiently recover a high-purity polyester substrate in a short time from used polyester substrates that would have been discarded in the past.

The present invention will be described in detail below.
In this specification, the term "to" indicating a range of values is used to mean that the values before and after it are included as the lower and upper limits, unless otherwise specified.

The method for recovering a polyester support of the present invention is a method for recovering a polyester support by removing a coating film from a polyester base material including a polyester support and at least one coating film provided on at least a part of the polyester support, and includes a first step of contacting a surface of the polyester base material having at least the coating film with a surfactant or an aqueous solution in which a surfactant is dissolved, and a second step of contacting the polyester base material with an alkaline treatment liquid after the first step.

<Polyester Support>
The polyester support in the present invention is formed by containing a polyester composition. The polyester composition is not particularly limited, but examples thereof include polyesters obtained by polycondensation of a dicarboxylic acid component and a diol component.

As the dicarboxylic acid component, various dicarboxylic acid components such as aromatic dicarboxylic acids, linear aliphatic dicarboxylic acids, and alicyclic dicarboxylic acids can be used, and examples thereof include terephthalic acid, 2,6-naphthalenedicarboxylic acid, isophthalic acid, and phthalic acid.

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.

The polyester support may be a homopolyester support or a copolymer polyester support. The polyester support may also contain a third component other than the dicarboxylic acid component and the diol component as a copolymer component.

As the polyester-based support, a polyester-based support whose main component is polyethylene terephthalate or polyethylene naphthalate is preferably used. Polyethylene terephthalate is more preferable. These may also be copolymerized polyesters.

The polyester support may be made of a polyester composition, or the composition may contain additives other than polyester. Examples of additives include end-blocking agents, antioxidants, flame retardants, fluorescent brighteners, matting agents, plasticizers, and defoamers.

The polyester support can be prepared by the following method.
For example, a polyester composition 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 support. The unstretched polyester support is stretched 2.5-5 times in the longitudinal direction between rolls heated to 70-130°C. The unstretched polyester support is then 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 heat treatment is performed for 5-40 seconds, and crystal orientation is completed through a cooling zone at 100-200°C to obtain a polyester support. 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.

The thickness of the polyester support is not particularly limited, but considering the strength, rigidity, and other aspects of handling, it is preferably 5 μm or more and 500 μm or less. The thickness of the polyester support is more preferably 10 μm or more and 200 μm or less, and particularly preferably 20 μm or more and 100 μm or less.

In the present invention, in the recovery of polyester-based supports described below, the polyester-based substrate may be in a long shape or in a cut state. If it is in a long shape, the length varies depending on, for example, the type of device used, but it means that it is generally 100 m or more and 10,000 m or less, and it is directly recovered without being crushed. If it is in a cut state, it is not particularly limited, but it means that the polyester-based substrate cut into, for example, 1 mm to 10 mm squares is recovered.

According to the method of the present invention, if the substrate is to be handled in a long shape, the first step of contacting the polyester substrate wound into a roll with a surfactant or an aqueous solution containing the surfactant dissolved therein and the second step of contacting the substrate with an alkaline treatment liquid can be carried out in series, and the coating film can be removed efficiently in a short time. It is preferable to carry out a surface modification treatment of the long polyester substrate described below, contact the substrate with a surfactant or an aqueous solution containing the surfactant dissolved therein, and then contact the substrate with an alkaline treatment liquid, and then introduce the substrate directly into the next step (washing and drying) described below, and wind the substrate into a roll, i.e., a roll-to-roll method is recommended. The roll-to-roll method is a method of continuously transporting a flexible substrate wound into a roll through multiple guide rolls, performing a predetermined treatment during transport, and winding the substrate into a roll again. By carrying out the treatment using the roll-to-roll method, a series of coating film removal steps can be carried out continuously in a short time, which is very efficient.

<Coating film>
The polyester support in the present invention 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 support, such as a release film, an adhesive film, a hard coat film, an easy-adhesion film, and an antistatic film. These coating films may be present on at least one side of the polyester support, and may be present on both sides. Furthermore, the coating film may be present alone, or two or more types may be laminated. Moreover, the coating film may have not only a single function but also multiple functions.

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-based 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 kinds. The release film may also contain a release agent such as silicone or wax.

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

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

The resin constituting the above-mentioned 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.

The resin constituting the antistatic film is not particularly limited as long as it is a resin generally used in antistatic films. It is preferable that the antistatic film 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, and carbon-based substances). These antistatic agents may be used alone or in combination of two or more kinds.

The coating film can be formed on a polyester support by, but not limited to, reverse coating, gravure coating, rod coating, bar coating, wire bar coating, die coating, spray coating, etc.

The thickness of the coating film (if there are multiple functional films, the total thickness of these) is preferably 0.005 μm or more and 50 μm or less. In order to effectively exert the specified function, it is more preferably 0.01 μm or more. On the other hand, if the thickness of the coating film exceeds 50 μm, it may take time to remove the coating film.

Recovery of polyester support
The method for recovering a polyester support of the present invention is characterized by comprising a first step of contacting at least a surface of a polyester base material having a coating film thereon with a surfactant or an aqueous solution containing a surfactant dissolved therein, and a second step of contacting the polyester base material with an alkaline treatment liquid after the first step.

(First step: contacting with a surfactant or an aqueous solution containing a surfactant)
In the first step, a surfactant or an aqueous solution in which the surfactant is dissolved is brought into contact with at least the surface having the coating film of the polyester substrate. The surface of the polyester substrate is hydrophilized by the hydrophobic region of the surfactant facing the polyester substrate or coating film and the hydrophilic region of the surfactant facing the solution side. In the first step, the surface of the polyester substrate is hydrophilized in advance, and then the alkaline treatment liquid is brought into contact with the polyester substrate in the second step described below. This promotes the penetration of the alkaline treatment liquid, and makes it easier to remove the coating film from the polyester substrate efficiently in a short time. A surfactant is a representative example of a compound having both a hydrophilic region and a hydrophobic region, but any compound having both a hydrophilic region and a hydrophobic region can be used.

The method of contacting the surfactant or the aqueous solution in which the surfactant is dissolved is not particularly limited as long as at least the surface of the polyester substrate having the coating film can be brought into contact with the surfactant or the aqueous solution in which the surfactant is dissolved. Examples include a method of immersing the polyester substrate in a cleaning tank containing the surfactant or the aqueous solution in which the surfactant is dissolved, a method of applying the surfactant or the aqueous solution in which the surfactant is dissolved to the polyester substrate, and a method of spraying the surfactant or the aqueous solution in which the surfactant is dissolved to the polyester substrate. Of these, the immersion method is preferred in terms of the permeability of the surfactant or the aqueous solution in which the surfactant is dissolved to the coating film.

The surfactant is not particularly limited, but 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.

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 ethers; 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.

Examples of cationic surfactants include alkylpyridinium chloride, alkyltrimethylammonium chloride, dialkyldimethylammonium chloride, and alkyldimethylbenzylammonium chloride.

Examples of anionic surfactants include sodium alkyl sulfate, sodium alkylbenzene sulfonate, sodium succinate dialkyl ester sulfonate, sodium alkyl diphenyl ether disulfonate, sodium polyoxyethylene alkyl ether sulfate, and sodium polyoxyethylene alkyl phenyl ether sulfate.

The contact time between the polyester substrate and the surfactant or the aqueous solution containing the surfactant is preferably within 300 seconds, more preferably 0.001 to 10 seconds, and even more preferably 0.1 to 10 seconds. If the contact time between the polyester substrate and the surfactant or the aqueous solution containing the surfactant 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 size of the device will become large, resulting in poor economic efficiency and operability. If the contact time between the polyester substrate and the surfactant or the aqueous solution containing the surfactant is within 300 seconds, there is good economic efficiency and operability, and the coating film removal effect can be enhanced.

The concentration of the surfactant or the aqueous solution in which the surfactant is dissolved is preferably 0.00001 wt% to 100 wt%, more preferably 0.0001 wt% to 100 wt%, even more preferably 0.001 wt% to 50 wt%, and particularly preferably 0.01 wt% to 1 wt%. If the surfactant concentration is too low, there is a risk that the coating film will not be sufficiently removed. If the concentration of the surfactant or the aqueous solution in which the surfactant is dissolved is 0.00001 wt% to 100 wt%, a sufficient coating film removal effect can be obtained.

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 lower. If the temperature of the surfactant or the aqueous solution in which the surfactant is dissolved is 50°C or lower, the surfactant can be concentrated to a high level, which promotes the removal of the coating film. Note that non-ionic surfactants will not dissolve in water if the temperature is too high, so it is preferable to treat them at a temperature below the cloud point of the surfactant.

(Surface modification treatment)
For the purpose of increasing the affinity with a surfactant or an aqueous solution containing a surfactant dissolved therein, and further with an alkaline treatment liquid described below, the surface of the coating film may be subjected to a surface modification treatment. The surface modification treatment is not particularly limited, and any known method may be adopted, such as a corona discharge treatment, a plasma treatment, a glow discharge treatment, a flame treatment, an ultraviolet treatment, etc., and it is preferable to carry out at least one treatment selected from the group consisting of these.

The surface modification treatment may be carried out before the second step in which the alkaline treatment liquid is brought into contact, but it is more preferable to carry out the treatment before the first step in order to increase the affinity with the surfactant or the aqueous solution in which the surfactant is dissolved.

If the proportion of C-C bonds and C-H bonds is reduced by 0.1% or more in an analysis using X-ray photoelectron spectroscopy after the surface modification treatment, the effect of increasing affinity with a surfactant or an aqueous solution containing a surfactant dissolved therein, or the alkaline treatment liquid described below can be obtained.

In the case of corona discharge treatment, the treatment intensity is preferably 10 to 1000 Wmin/ ^m2 or more, more preferably 20 to 200 Wmin/ ^m2 , and even more preferably 40 to 120 Wmin/ ^m2 . If the treatment intensity is too high, the polyester support tends to be easily damaged, while if the treatment intensity is too low, the time of the alkali treatment described below becomes long and the polyester support tends to be easily damaged. Furthermore, if the power density of the corona discharge machine used is 4 to 20 W/ ^cm2 , the surface treatment can be performed uniformly.

In the case of ultraviolet treatment, the irradiation intensity is preferably 0.5 to 40 mW/cm ² , more preferably 10 to 40 mW/cm ² , and even more preferably 15 to 40 mW/cm ^2. If the irradiation intensity is too high, the polyester support tends to be easily damaged, and if the irradiation intensity is too weak, the time of the alkali treatment described below becomes long, and the polyester support 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, so the manufacturing cost increases and the polyester support tends 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 10 to 400 nm, that is, invisible light shorter than visible light and longer than soft X-rays. Examples of sources of ultraviolet light that can be used include known lamps such as ultra-high pressure mercury lamps, high pressure mercury lamps, low pressure mercury lamps, carbon arc lamps, and metal halide lamps, with the use of low pressure mercury lamps being preferred.

(Second step: step of contacting with alkaline treatment liquid)
The method for recovering a polyester support of the present invention includes a second step of contacting an alkaline treatment liquid after the first step. By contacting the surface of the polyester base material with a hydrophilic alkaline treatment liquid after the surface of the polyester base material is hydrophilized in the first step, the penetration of the alkaline treatment liquid into the polyester support or coating film is promoted, the coating film is dissolved and swelled, and the bond at the interface between the polyester support and the coating film is weakened, and the coating film that dissolves in the alkaline treatment liquid can be removed from the polyester support in a short period of time.

In the present invention, the treatment with the alkaline treatment liquid may be carried out immediately after the first step or after a desired time interval.

The alkaline treatment liquid used in the present invention can be a solution in which an alkaline substance is dissolved. The alkaline substance is not particularly limited, but examples thereof include inorganic alkaline agents 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 hydroxides are preferred, and sodium hydroxide and potassium hydroxide are more preferred. The above alkaline substances may be used alone or in combination of two or more.

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

The content of the alkaline substance in the alkaline processing liquid is preferably 0.01 to 15% by mass, more preferably 0.04 to 15% by mass, and even more preferably 1 to 10% by mass. If the content of the alkaline substance is too high, the polyester support tends to be easily damaged, and if the content is too low, there is a risk that the coating film cannot 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 damage to the polyester support can be suppressed.

As a method for contacting a polyester substrate with an alkaline treatment liquid, various methods such as immersion, ultrasonic, spray, and vibration methods can be used. The above conditions can be appropriately selected depending on the type and thickness of the polyester substrate and coating film, but in order to obtain a high-quality polyester substrate with few impurities, it is preferable to contact the substrate with an alkaline treatment liquid with a concentration of 0.01 to 15% by mass heated to a temperature of less than 100°C for more than 0 seconds and less than 700 seconds.

The temperature of the alkaline processing liquid is preferably less than 100°C, and more preferably 50 to 95°C. In order to shorten the processing time with the alkaline processing liquid in the second step, it is better to have a high temperature of the alkaline processing liquid, and therefore it is preferable to perform the processing at a temperature equal to or higher than the processing temperature in the first step. Specifically, if the temperature of the alkaline processing liquid is 50°C or higher, the physicochemical properties of the polyester support are not changed, and a high-quality polyester support with few impurities can be obtained without spending excessive time. In addition, since the temperature of the alkaline processing liquid cannot be achieved at normal pressure to exceed 100°C, this leads to an increase in the size of the equipment, and heating causes hydrolysis and dissolution of the polyester support.

The contact time with the alkaline treatment liquid is preferably more than 0 seconds and less than 700 seconds, more preferably more than 0 seconds and less than 600 seconds, even more preferably more than 0 seconds and less than 180 seconds, and particularly preferably more than 0 seconds and less than 120 seconds. If the treatment time is too long, the polyester support tends to be easily damaged, and the polyester support is eluted in the alkaline treatment liquid, which may increase the load when the alkaline treatment liquid is discharged. The treatment time with the alkaline treatment liquid is sufficient so that the coating film can be sufficiently dissolved and swollen. If the treatment time is too short, there is a risk that the coating film cannot be sufficiently removed, so 1 second or more is more preferable, and 5 seconds or more is even more preferable. If the treatment time with the alkaline treatment liquid is within the above range, the effect of removing the coating film can be obtained and damage to the polyester support can be suppressed.

In the present invention, it is more preferable that the treatment with the alkaline treatment liquid in the second step is carried out by contacting the polyester substrate with an alkaline treatment liquid having a temperature of less than 100°C and an alkali concentration of 0.04% by mass to 15% by mass for 1 second to 180 seconds.

The alkaline treatment liquid 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. There are no particular limitations on the surfactant, but for example, a nonionic surfactant, a cationic surfactant, an anionic surfactant, etc. may be used. The surfactant may be used alone or in combination of two or more types.

Examples of nonionic surfactants include polyoxyethylene alkyl ethers, polyoxyethylene alkylaryl ethers, polyoxyethylene fatty acid esters, and polyoxyethylene sorbitan fatty acid esters.

Examples of cationic surfactants include alkylpyridinium chloride, alkyltrimethylammonium chloride, dialkyldimethylammonium chloride, and alkyldimethylbenzylammonium chloride.

Examples of anionic surfactants include sodium alkyl sulfate, sodium alkylbenzene sulfonate, sodium succinate dialkyl ester sulfonate, sodium alkyl diphenyl ether disulfonate, sodium polyoxyethylene alkyl ether sulfate, and sodium polyoxyethylene alkyl phenyl ether sulfate.

The alkaline treatment liquid may contain other additives as long as they do not impair the effects of the present invention. Examples of additives include antioxidants, pH adjusters, and defoamers.

(Washing treatment)
After the second step, it is preferable to carry out a water washing treatment. The washing with water is carried out in order to remove a trace amount of the coating film remaining on the polyester support after the above treatment and to remove the alkaline processing solution remaining on the polyester support after the above treatment.

The temperature of the above water washing process is not particularly limited, but for example, washing with warm water of about 40°C to 100°C will more effectively achieve the above effects.

Methods for washing with water include spraying water onto the polyester support from which the coating film has been removed, and immersing the polyester support in a water tank. During the water washing process, physical washing using a roll brush, microbubbles, water flow, etc. may also be performed.

(Drying treatment)
After washing with water, it is preferable to carry out a drying treatment in order to remove water remaining on the polyester support.

The drying time is preferably 10 seconds or more and 5 minutes or less. If the drying time is less than 10 seconds, the drying may be insufficient and blocking may occur. It is more preferable that the drying time is 30 seconds or more. On the other hand, if the drying time is more than 5 minutes, the polyester support may be deformed.

There are no particular limitations on the drying method, and examples include hot air drying, which involves blowing hot air, and heat drying, which involves heating with a non-contact heater.

(Multiple Processing)
The surface modification step, the first step of contacting the substrate with a surfactant or an aqueous solution containing a surfactant, and the second step of contacting the substrate with an alkaline treatment liquid may be carried out multiple times. By carrying out the treatment multiple times, the polyester support can be treated in a short time without being damaged, such as by a decrease in intrinsic viscosity.

Molding of Recovered Polyester Support
The method for producing a polyester product of the present invention includes extruding the polyester support recovered by the above-mentioned method for recovering a polyester support to produce a polyester product.

Specifically, the recovered polyester support can be pelletized and then molded into various polyester products such as polyester films by melt extrusion or other methods.

The polyester product is not particularly limited, and can be used for ordinary polyester applications, such as producing polyester films, PET bottles, polyester fibers, polyester sheets, and polyester containers. For example, it can be used as a polyester film.

The thickness of the polyester film is not particularly limited, but can usually be set appropriately within the range of 10 to 50 μm. In addition, a coating film can be formed as necessary. Examples 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 support, and the polyester support can be recovered again and extrusion molded to produce a polyester product. The polyester product produced from the recovered polyester support is also not particularly limited, and can be used for normal polyester applications, such as the polyester film, PET bottles, polyester fibers, polyester sheets, and polyester containers described above.

Below, the embodiment of the present invention will be described in more detail based on the 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 in terms of the coating film removal ability. In the following, unless otherwise specified, "%" means "mass %" and "parts" means "mass parts". The properties were measured as follows.

(Evaluation of removal of coating film)
1. Evaluation of processability The recovered polyester support was finely cut, then molded into a cylindrical shape using a melt press, and the silicon (Si) content was measured using a fluorescent X-ray analyzer (Rigaku Corporation, "Model 3270"). Quantitative determination was performed using a fluorescent X-ray measurement method based on a calibration curve of fluorescent X-ray intensity prepared in advance.
The processability of the present invention was evaluated based on the obtained Si content according to the following criteria, where "◎", "◯" and "Δ" are acceptable, and "×" is unacceptable.
[Evaluation Criteria]
◎ (Excellent): The Si content is below the detection limit (100 ppm). ○ (Good): The Si content is more than 100 ppm and less than 300 ppm. △ (Fair): The Si content is 300 ppm or more and less than 500 ppm. × (Unacceptable): The Si content is 500 ppm or more.

2. Evaluation of Damage to Polyester Support 0.1 g of pellets obtained from the recovered polyester support was added to 10 ml of o-chlorophenol and dissolved at 100° C. for 30 minutes, and then the intrinsic viscosity at 25° C. (intrinsic viscosity of the pellets after treatment) was measured using an Ubbelohde viscometer.
Similarly, the intrinsic viscosity at 25° C. (intrinsic viscosity of the pellets before treatment) was measured using pellets obtained from the polyester before laminating the coating film.
The intrinsic viscosity of the treated pellets was compared with that of the pellets before treatment and evaluated according to the following criteria, where "◯" and "Δ" are acceptable and "×" is unacceptable.
[Evaluation Criteria]
○ (Good): The intrinsic viscosity of the pellets after the treatment is reduced by less than 0.005 compared to the intrinsic viscosity of the pellets before the treatment. △ (Fair): The intrinsic viscosity of the pellets after the treatment is reduced by 0.005 or more but less than 0.01 compared to the intrinsic viscosity of the pellets before the treatment. × (Fail): The intrinsic viscosity of the pellets after the treatment is reduced by 0.01 or more compared to the intrinsic viscosity of the pellets before the treatment.

3. Evaluation of Processing Time in Alkaline Processing Liquid The processing time in the alkaline processing liquid used in the second step was evaluated according to the following criteria, where "◎", "◯" and "△" are acceptable, and "×" is unacceptable.
[Evaluation Criteria]
◎ (Excellent): Processing time in an alkaline processing liquid is 120 seconds or less. ○ (Good): Processing time in an alkaline processing liquid is more than 120 seconds and less than 300 seconds. △ (Fair): Processing time in an alkaline processing liquid is 300 seconds or more and less than 700 seconds. × (Unfavorable): Processing time in an alkaline processing liquid is 700 seconds or more.

(Preparation of sample films)
As described below, laminated polyester films A to C each having a release film, an adhesive film and a hard coat film were prepared as sample films.

<Film A: Film having a silicone-based release film>
1. Preparation of polyester-based support having coating film A polyethylene terephthalate film (Toray "Lumirror" T60, thickness 38 μm, intrinsic viscosity 0.61) was prepared as a polyester-based support. One side of the film was coated with a 5% toluene solution of a curable silicone resin (containing 100 parts of LTC-350B from Dow Corning Toray Silicone Co., Ltd. and 0.8 parts of curing agent SRX-212) using a bar coater, and heated at 100° C. in a tunnel oven to prepare a release film, which was then wound up.

2. Coating of ceramic slurry and conductive paste A ceramic slurry having the following composition was uniformly coated on the release layer surface of the above-mentioned release film using a blade coater. This was dried at 85°C in a tunnel oven 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

3. Peeling off of ceramic film and internal electrode On the release film on which the ceramic layer and electrodes were formed, a 10 cm x 10 cm slit was made in the coating film only in the portion where the ceramic layer and electrode 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 film A. Note that some of the ceramic layer and the electrode were still attached to the surface of the release layer of film A and could not be peeled off.

<Film B: Film having acrylic adhesive film>
A polyethylene terephthalate film (Toray "Lumirror", thickness 31 μm, intrinsic viscosity 0.62) was prepared as a polyester support. One side of the film was coated with an acrylic adhesive film to a thickness of 10 μm to prepare Film B having an adhesive film.

<Film C: Film having acrylic hard coat film>
A polyethylene terephthalate film (Toray "Lumirror" T60, thickness 38 μm, intrinsic viscosity 0.61) was prepared as a polyester support. An acrylic hard coat solution having the following composition was uniformly applied to one side of the film using a blade coater to form an acrylic hard coat film with a thickness of 9 μm. The solution was then cured by irradiating with ultraviolet light to produce Film C having an acrylic hard coat film.
Acrylic hard coat solution
Dipentaerythritol hexaacrylate: 95 parts 2-hydroxy-3-phenoxypropyl acrylate: 5 parts Photopolymerization initiator (Irgacure 184, manufactured by BASF Corporation): 4 parts Solvent (methyl ethyl ketone): 100 parts

[Example 1]
(Surface modification treatment)
A film having a silicone-based release film (Film A) was used as a sample film, and the release film side surface of Film A was subjected to corona discharge treatment using a corona discharge treatment device at a power density of 8 W/cm ² and a treatment intensity of 60 Wmin/m ² .

(First step)
The corona discharge-treated sample film was immersed for 1 second in a 0.03 wt % aqueous solution of a nonionic surfactant ("Polyoxyethylene (10) Octylphenyl Ether" manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) at room temperature (25°C).

(Second step)
A mixed aqueous solution of 3 wt% sodium hydroxide and 0.03 wt% nonionic surfactant ("Polyoxyethylene (10) octylphenyl ether" manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was heated to 80°C, and after corona discharge treatment, the sample film that had been brought into contact with the aqueous surfactant solution was immersed in the mixed aqueous solution for 45 seconds and treated to remove the release layer, thereby obtaining a specimen film (recovered polyester-based support). The specimen film was used to carry out the "evaluation of processability" described above.

(Washed, dried, pelletized)
The sample film (recovered polyester support) 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. The pellets obtained were used to perform the above-mentioned "Evaluation of damage to polyester support".

(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 cast drum at 20° C. to obtain an unstretched sheet. This unstretched sheet was stretched 3.1 times in the longitudinal direction by a stretching roll heated to 90° C., then stretched 3.7 times in the transverse direction at 120° C. by a tenter-type stretching machine, and then heat-set at 230° C. and wound up on a roll.

[Example 2]
A polyester film was prepared in the same manner as in Example 1, except that the sample film used was a film having an acrylic adhesive film (film B).

[Example 3]
A polyester film was prepared in the same manner as in Example 1, except that the sample film used was a film having an acrylic hard coat layer (Film C).

[Example 4]
A polyester film was prepared 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 a surface modification treatment.

[Example 5]
A polyester film was prepared in the same manner as in Example 1, except that the surface modification treatment was not carried out.

[Example 6]
A polyester film was prepared in the same manner as in Example 1, except that the surface modification treatment was performed by irradiating the film with ultraviolet light at an irradiation intensity of 30 mW/cm ² for 60 seconds using an ultraviolet irradiator.

[Example 7]
A polyester film was prepared in the same manner as in Example 1, except that a corona discharge treatment was performed on both sides of the film as a surface modification treatment to prevent transfer of the release film to the back surface of the film.

[Example 8]
A polyester film was prepared in the same manner as in Example 1, except that the surfactant used in the first and second steps was an anionic surfactant ("Newcol 290 series" manufactured by Nippon Nyukazai Co., Ltd.).

[Examples 9 to 10]
A polyester film was prepared in the same manner as in Example 1, except that the contact time with the aqueous surfactant solution in the first step was changed to the conditions shown in Table 2.

[Examples 11 to 12]
A polyester film was prepared in the same manner as in Example 1, except that the concentration of the aqueous surfactant solution in the first step was changed to the conditions shown in Table 2.

[Examples 13 to 14]
A polyester film was prepared in the same manner as in Example 1, except that the temperature of the aqueous surfactant solution in the first step was changed to the conditions shown in Table 3.

[Examples 15 to 16]
A polyester film was prepared in the same manner as in Example 1, except that the temperature of the alkaline processing solution in the second step was changed to the conditions shown in Table 3.

[Example 17]
A polyester film was prepared in the same manner as in Example 1, except that the temperature of the aqueous surfactant solution in the first step was changed to the conditions shown in Table 3, which was a temperature equal to or higher than the cloud point (64° C.) of the surfactant.

[Example 18]
A polyester film was prepared in the same manner as in Example 1, except that the concentration of the alkaline processing solution and the contact time in the second step were changed to those shown in Table 3.

[Example 19]
A polyester film was prepared in the same manner as in Example 1, except that the concentration of the alkaline processing solution and the contact time in the second step were changed to those shown in Table 4.

[Examples 20 to 21]
A polyester film was prepared in the same manner as in Example 1, except that the concentration of the alkaline processing solution and the contact time in the second step were changed to those shown in Table 4.

[Example 22]
A polyester film was prepared in the same manner as in Example 1, except that the alkaline treating solution in the second step was changed to potassium hydroxide shown in Table 4.

[Comparative Examples 1 to 2]
The sample film was subjected to the same surface modification treatment as in Example 1, without carrying out the first step, and the second step, and then washed with water and dried in the same manner as in Example 1 to produce a polyester film. In Comparative Example 1, the treatment time in the second step was 45 seconds, and in Comparative Example 2, the treatment time in the second step was 900 seconds.

[Comparative Example 3]
The sample film was subjected to the same surface modification treatment as in Example 1 without carrying out the first step, and the second step, and then washed with water and dried in the same manner as in Example 1 to prepare a polyester film. In Comparative Example 3, the concentration of sodium hydroxide in the second step was set to 25 wt %, and the treatment time was 45 seconds.

[Comparative Example 4]
The sample film was subjected to the same surface modification treatment as in Example 1, without carrying out the second step, and the first step, and then washed with water and dried in the same manner as in Example 1 to prepare a polyester film.

[Comparative Example 5]
A polyester film was produced in the same manner as in Example 1, except that the order was changed so that the first step was carried out after the second step.

The evaluation results for Examples 1 to 22 and Comparative Examples 1 to 5 are shown in Tables 1 to 6 below.

As can be seen from Tables 1 to 6, according to the method of the present invention, it is possible to remove a coating film from a polyester support having at least one coating film, recover the polyester support, and produce a polyester product using the polyester support as a part of a raw material.
Furthermore, from the results of Example 1, it was found that by carrying out the surface modification treatment, the first step of contacting with a surfactant or an aqueous solution containing a surfactant dissolved therein, and the second step of contacting with an alkaline treatment liquid, it was possible to remove the coating layer in a short time without suffering damage such as a decrease in intrinsic viscosity.
In contrast, in Comparative Examples 1, 2, and 3 in which the first step was not carried out, the coating film could not be removed in a short time.

As described above, according to the method of the present invention, by carrying out the first step of contacting the substrate with a surfactant or an aqueous solution in which the surfactant is dissolved, and the second step of contacting the substrate with an alkaline treatment liquid, the coating layer can be removed, and it is possible to recover the polyester support and produce polyester products using the polyester support as part of the raw material. In addition, by carrying out the first and second steps after carrying out the surface modification treatment, it is possible to efficiently remove the coating film in a short time without suffering damage such as a decrease in intrinsic viscosity, which is extremely useful.

Claims (8)

A method for recovering a polyester support by removing a coating film from a polyester base material having at least one coating film on at least a part of the polyester support, the method comprising the steps of:
The method includes a first step of contacting at least the surface of the polyester-based substrate having the coating film thereon with a surfactant or an aqueous solution containing a surfactant dissolved therein, and a second step of contacting the polyester-based substrate with an alkaline treatment liquid after the first step,
A method for recovering a polyester support, comprising : making the surface of the polyester base material hydrophilic in advance in the first step; and then contacting the surface with the alkaline processing liquid in the second step . The method for recovering a polyester support according to claim 1, characterized in that, prior to the first step, at least the surface of the polyester substrate having the coating film thereon is subjected to at least one surface modification treatment selected from the group consisting of corona discharge treatment, plasma treatment, glow discharge treatment, flame treatment, and ultraviolet treatment. The method for recovering polyester-based supports according to claim 2, characterized in that washing with water is carried out after the second step. The method for recovering a polyester support according to claim 3, characterized in that in the first step, the surfactant or an aqueous solution in which the surfactant is dissolved is brought into contact for 300 seconds or less. The method for recovering polyester-based supports according to claim 4, characterized in that the surfactant is a nonionic surfactant. The method for recovering a polyester support according to claim 5, characterized in that in the second step, the alkaline treatment liquid is an alkaline treatment liquid having a temperature of less than 100°C and an alkali concentration of 0.04% by mass to 15% by mass, and the alkaline treatment liquid is brought into contact for 1 second to 180 seconds. The method for recovering a polyester support according to claim 6, characterized in that the polyester support is recovered in a long shape. A method for producing a polyester product, comprising extruding a polyester support recovered by the method for recovering a polyester support according to any one of claims 1 to 7 to produce a polyester product.