Polyester film recovery method, recovery device, and functional layer remover

Abstract

The present invention aims to provide a polyester film recovery method, recovery device, and functional layer remover that can peel off the functional layer and recover the base film. [Solution] The method for recovering polyester film includes a functional layer removal step (A) in which a laminated polyester film having a functional layer on the surface of the polyester film is washed with a cleaning agent containing (a) an alkalizing agent and (b) a compatibilizer to remove the functional layer, and a recovery step (B) in which the polyester film from which the functional layer has been removed is recovered.

Description

[Technical field]

[0001] The present invention relates to a method for recovering polyester film, a recycled polyester product, an apparatus for recovering polyester film, and a functional layer remover for polyester film. [Background technology]

[0002] Conventionally, waste plastics have been disposed of by landfilling, dumping in the ocean, incineration, etc., but it is becoming increasingly difficult to secure landfill sites, and ocean dumping is an environmental problem because plastics do not decompose. In addition, while waste plastics can be used as heat by incineration, there is the problem that the carbon dioxide emissions contribute to global warming.

[0003] In light of the recent heightening of environmental concerns, there is a need for recycling, such as reusing and regenerating waste plastics, and research and development into this field is being actively carried out. In addition, since most plastics are produced using fossil fuels, there is a need to develop recycling methods in order to make effective use of resources.

[0004] Meanwhile, polyester film, which is a kind of plastic film, is useful as a base film, and is often used as a laminate film having various functional layers laminated on one or both sides. The functional layers include a hard coat layer, a tacky adhesive layer, a decorative layer, a light-shielding layer, a polarizing layer, an ultraviolet-shielding layer, and the like, and a laminate film is used in which a material corresponding to the functional layer is laminated on a polyester film.

[0005] Such laminated films are rarely reused after use, but are instead discarded or incinerated.

[0006] Even if an attempt is made to recycle a laminated film with a functional layer laminated thereon by simply remelting it, the material that constitutes the functional layer will be mixed into the molten polymer, causing an unpleasant odor during extrusion or a decrease in the melt viscosity of the polymer, which can lead to breakage during film production. Even if it were possible to produce a film, degradation of quality due to discoloration of the resulting film or contamination with foreign matter would be unavoidable.

[0007] Furthermore, even if the functional layer is physically removed by scraping it off and then melt extrusion is performed, problems will arise such as the remaining functional layer clogging the filter during the filtration process during extrusion, making it impossible to produce a normal film.

[0008] As a method for recycling laminated films, for example, there is a technology disclosed in Patent Document 1. This technology is a laminated film formed by laminating an easily soluble resin layer and a surface functional layer in this order on at least one side of a base film. With this configuration, after use, the base film is separated and recovered from the laminated film by washing with a solvent that dissolves only the easily soluble resin layer and does not dissolve the base film. The separated and recovered material is remelted, making it possible to regenerate the resin composition that constituted the base film. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] JP 2004-169005 A Summary of the Invention [Problem to be solved by the invention]

[0010] As described above, the method disclosed in Patent Document 1 is based on the premise of a laminated film in which a soluble resin layer and a surface functional layer are laminated in that order on the surface of a base film, and aims to remove the functional layer by dissolving the soluble resin layer. That is, the technique cannot be used for most laminated polyester films that do not have an easily soluble resin layer, and is therefore not versatile. In view of the above circumstances, an object of the present invention is to propose a method for recovering polyester films, which enables peeling off of the functional layer and recovery of the base film, even in the case of a laminated polyester film that does not have a readily soluble resin layer. [Means for solving the problem]

[0011] As a result of intensive research, the present inventors have found that by using a cleaning agent containing an alkalizing agent and a compatibilizing agent, the functional layer can be removed and the polyester film substrate can be efficiently recovered. The present invention has been completed based on this finding. That is, the present invention has the following aspects. (1) A method for recovering a polyester film, comprising: a functional layer removal step (A) of washing a laminated polyester film having a functional layer on the surface of the polyester film with a cleaning agent containing (a) an alkalizing agent and (b) a compatibilizing agent to remove the functional layer; and a recovery step (B) of recovering the polyester film from which the functional layer has been removed. (2) The method for recovering polyester film according to the above (1), wherein the cleaning agent is an aqueous cleaning agent. (3) The method for recovering a polyester film according to the above (1) or (2), wherein the (a) alkalizing agent contains an alkali metal hydroxide. (4) The method for recovering polyester film according to the above (3), wherein the alkali metal hydroxide contains potassium hydroxide. (5) The method for recovering a polyester film according to any one of the above (1) to (4), wherein the cleaning agent further contains (c) a compound having at least one hydroxyl group. (6) The method for recovering a polyester film according to the above (5), wherein the compound (c) having at least one hydroxyl group is an alcohol. (7) The method for recovering polyester film according to (6) above, wherein the alcohol has an acidity constant (pKa) of 8.0 or more and 20.0 or less. (8) The method for recovering a polyester film according to (6) or (7) above, wherein two or more types of the alcohols are used in combination. (9) The method for recovering a polyester film according to any one of (1) to (8) above, wherein the (b) compatibilizer is at least one selected from the group consisting of aromatic sulfonates and hydroxyl group-containing amine compounds. (10) The method for recovering a polyester film according to any one of the above (1) to (9), wherein the temperature of the cleaning agent in the functional layer removing step (A) is 20° C. or higher. (11) A recycled polyester product, at least in part containing, as a raw material, a polyester film recovered by the recovery method according to any one of (1) to (10) above. (12) A polyester film recovery apparatus having a cleaning device, characterized in that in the cleaning device, a laminated polyester film having a functional layer on a surface of the polyester film is washed with a cleaning agent containing (a) an alkalizing agent and (b) a compatibilizing agent, and the polyester film from which the functional layer has been removed is recovered. (13) The polyester film recovery apparatus according to (12) above, further comprising a rinsing device for washing away any cleaning agent adhering to the polyester film from which the functional layer has been removed. (14) The polyester film recovery apparatus according to (13) above, wherein the cleaning agent is a water-based cleaning agent, and the water-based cleaning agent is washed away with water in the rinsing device. (15) The apparatus for recovering a polyester film according to any one of the above (12) to (14), further comprising a drying device for drying the polyester film from which the functional layer has been removed. (16) The polyester film recovery apparatus according to any one of the above (12) to (15), further comprising an unwinding device provided upstream of the cleaning device. (17) The polyester film recovery device according to (16) above, which recovers the polyester film using a roll-to-roll method. (18) The polyester film recovery apparatus according to any one of the above (12) to (15), further comprising a cutting device provided upstream of the cleaning device. (19) A functional layer remover for polyester films, for removing a functional layer from a laminated polyester film having a functional layer on the surface of the polyester film, comprising (a) an alkalizing agent and (b) a compatibilizing agent. (20) The functional layer remover for polyester film according to the above (19), wherein the remover is an aqueous remover. (21) The functional layer remover for polyester film according to the above (19) or (20), wherein the (a) alkalizing agent contains an alkali metal hydroxide. (22) The functional layer remover for polyester film according to the above (21), wherein the alkali metal hydroxide contains potassium hydroxide. (23) The functional layer remover for polyester film according to any one of the above (19) to (22), further comprising (c) a compound having at least one hydroxyl group. (24) The functional layer remover for polyester film according to the above (23), wherein the compound (c) having at least one hydroxyl group is an alcohol. (25) The functional layer remover for polyester film according to the above (24), wherein the alcohol has an acidity constant (pKa) of 8.0 or more and 20.0 or less. (26) The functional layer remover for polyester film according to (24) or (25) above, wherein two or more kinds of the alcohols are used in combination. (27) The functional layer remover for polyester film according to any one of (19) to (26) above, wherein the (b) compatibilizer is at least one selected from the group consisting of aromatic sulfonates and hydroxyl group-containing amine compounds. Effect of the Invention

[0012] According to the recovery method of the present invention, the functional layer can be easily removed from a laminated polyester film having the functional layer, and the base film (polyester film) can be efficiently recovered. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] The method for recovering a laminated polyester film of the present invention includes a functional layer removal step (A) of washing a laminated polyester film having a functional layer on the surface of the polyester film with a cleaning agent containing (a) an alkalizing agent and (b) a compatibilizing agent to remove the functional layer, and a recovery step (B) of recovering the polyester film from which the functional layer has been removed. Here, in the functional layer removal step (A), it is important to use (a) an alkalizing agent and (b) a compatibilizing agent in combination, and by using them in combination, the functional layer on the polyester film can be effectively removed.

[0014] The mechanism by which the combined use of the above-mentioned components (a) and (b) enables the functional layer to be effectively removed is not clear, but is presumed to be as follows.

[0015] In other words, it is presumed that at the interface between the base polyester film and the functional layer, a saponification reaction occurs due to hydroxyl groups ionized from the alkalizing agent, generating (ionizing) carboxylates, which causes the functional layer to swell, peel off, or dissolve. It is believed that the use of the compatibilizer improves the compatibility of the cleaning agent components, facilitating the above reaction, and facilitating peeling of the functional layer.

[0016] <Laminated polyester film> The laminated polyester film in the present invention refers to a film in which a functional layer such as a resin layer is laminated on the surface of a polyester film that is a base film. The polyester film may have a single layer structure or a multilayer structure. In the case of a multilayer structure, it may have a two-layer structure, a three-layer structure, or a four-layer structure or more, and the number of layers is not particularly limited. In addition, the polyester film may be a stretched film such as a biaxially stretched film, or an unstretched film. The polyester constituting the polyester film is not particularly limited, and any polyester available on the market can be appropriately used. Specifically, polyesters obtained by polycondensation of dicarboxylic acids and diols can be mentioned, and the dicarboxylic acid is preferably an aromatic dicarboxylic acid, and the diol is preferably an aliphatic glycol. Examples of the aromatic dicarboxylic acid include terephthalic acid, 2,6-naphthalenedicarboxylic acid, isophthalic acid, phthalic acid, etc. Examples of the aliphatic glycol include ethylene glycol, diethylene glycol, propylene glycol, butylene glycol, 1,4-cyclohexanedimethanol, neopentyl glycol, etc. The polyester may be a homopolyester or a copolymer polyester, and may contain a third component other than the aromatic dicarboxylic acid and the glycol as a copolymer component. Specific examples of polyesters include polyethylene terephthalate, polyethylene-2,6-naphthalate, polybutylene terephthalate, polybutylene-2,6-naphthalate, etc., among which polyethylene terephthalate is preferred. These may also be copolymer polyesters, and for example, polyethylene terephthalate may have dicarboxylic acid units other than terephthalic acid at about 30 mol % or less of the dicarboxylic acid units, and may have diol units other than ethylene glycol at about 30 mol % of the diol units.

[0017] The functional layer is not particularly limited in terms of its constituent components, but is preferably composed of a resin from the viewpoint of removal by the recovery method of the present invention. Examples of the functional layer include a hard coat layer, a tacky adhesive layer, a release layer, a decorative layer, a light-shielding layer, an ultraviolet shielding layer, an easy-adhesion layer (primer layer), an antistatic layer, a refractive index adjustment layer, and an oligomer sealing layer.

[0018] The hard coat layer is a layer provided to impart scratch resistance and the like to the polyester film. The material for forming the hard coat layer is not particularly limited, but examples thereof include monofunctional (meth)acrylates, polyfunctional (meth)acrylates, and cured products of reactive silicon compounds such as tetraethoxysilane.

[0019] The adhesive layer is a layer that is provided for adhesively adhering to other devices, etc., and the material constituting the adhesive layer is not particularly limited, but for example, known adhesive resins such as acrylic, rubber, and silicone-based adhesive resins can be used.

[0020] The release layer is a layer provided to impart releasability to a polyester film, and is, for example, a layer provided on a release film used in forming process paper for green sheets used in the manufacture of ceramic electronic components, and adhesive separators for optical members used in the manufacture of flat panel displays such as polarizing plates and optical filters. There are no particular limitations on the material constituting the release layer, and examples include those containing a cured silicone resin as the main component, modified silicone resins obtained by graft polymerization with urethane resins, epoxy resins, etc., compounds containing long-chain alkyl groups, fluorine compounds, hydrocarbon waxes, etc.

[0021] The decorative layer is a layer provided to impart design, and the material constituting the decorative layer is not particularly limited, but examples thereof include polyurethane resins, vinyl resins, polyamide resins, polyester resins, acrylic resins, polyvinyl acetal resins, etc. Pigments, dyes, etc. are added to these resins to provide decoration.

[0022] The light-shielding layer or ultraviolet light-shielding layer is a layer provided to protect the contents from ultraviolet light, visible light, etc., and the material constituting the light-shielding layer or ultraviolet light-shielding layer is not particularly limited, and examples thereof include various resins described in the decorative layer, inorganic fillers such as calcium carbonate, talc, clay, kaolin, silica, diatomaceous earth, barium sulfate, etc., and organic fillers such as wood flour, pulp powder, cellulose powder, etc.

[0023] The easy-adhesion layer (primer layer) is a layer provided for adhering other layers or films onto the polyester film, and may include, but is not limited to, polyurethane resins, vinyl resins, polyamide resins, polyester resins, acrylic resins, polyvinyl acetal resins, and the like, as well as various crosslinking agents, particles, and the like.

[0024] The antistatic layer is a layer provided to prevent static electricity caused by contact with or peeling off from other materials. Antistatic agents used in the antistatic layer include, but are not limited to, nonionic, cationic, anionic, and amphoteric surfactants, conductive polymers such as polypyrrole, polyaniline, poly(3,4-ethylenedioxythiophene), and poly(4-styrenesulfonate), metal oxide fillers such as SnO2 (Sb-doped), In2O3 (Sn-doped), and ZnO (Al-doped), and carbon compounds such as graphene, carbon black, and carbon nanotubes (CNT). These may be used alone or in combination of two or more. The antistatic layer may be formed from a resin composition containing an antistatic agent. Examples of resins contained in the resin composition include polyester resins, acrylic resins, and urethane resins.

[0025] The refractive index adjusting layer is a layer provided to adjust the refractive index, and the material constituting the refractive index adjusting layer is not particularly limited, but examples thereof include polyester resin, acrylic resin, urethane resin, polycarbonate resin, epoxy resin, alkyd resin, urea resin, fluororesin, metal oxides such as zirconium oxide and titanium oxide, etc. These may be used alone or in combination of two or more.

[0026] The oligomer sealing layer is a layer provided to prevent film whitening and foreign matter after a heating step, and is not particularly limited, and examples of materials constituting the oligomer sealing layer include amine compounds, ionic resins, etc. The oligomer sealing layer may also be a highly crosslinked coating film, etc.

[0027] These functional layers may be a single layer, or two or more types of layers may be laminated. When two or more kinds of layers are laminated, it is preferable that at least one layer is made of a resin.

[0028] <Cleaning agent> The method of the present invention is characterized in that the functional layer removing step (A) involves cleaning with a cleaning agent containing (a) an alkalizing agent and (b) a compatibilizing agent.

[0029] (Alkalinizing agent) The (a) alkalizing agent constituting the cleaning agent of the present invention is a component that makes the cleaning solution alkaline and can also be called an alkaline agent. The alkalizing agent may be an inorganic alkalizing agent or an organic alkalizing agent, but is preferably an inorganic alkalizing agent because it is suitable for combination with the (b) compatibilizing agent described below.

[0030] Examples of the inorganic alkalizing agent include alkali metal hydroxides such as sodium hydroxide, potassium hydroxide, rubidium hydroxide, and cesium hydroxide; alkaline earth metal hydroxides such as calcium hydroxide and barium hydroxide; alkali metal carbonates such as sodium carbonate and potassium carbonate; alkali metal phosphates such as trisodium phosphate, sodium pyrophosphate, sodium tripolyphosphate, sodium tetrapolyphosphate, tripotassium phosphate, potassium pyrophosphate, and potassium tripolyphosphate; alkali metal silicates such as sodium orthosilicate, sodium metasilicate, and potassium silicate; and ammonia.

[0031] Of the inorganic alkalizing agents in the present cleaning agent, alkali metal hydroxides are preferred, sodium hydroxide and potassium hydroxide are more preferred from the viewpoint of availability, and potassium hydroxide is particularly preferred from the viewpoint of cleaning properties.

[0032] The inorganic alkalizing agent in the present cleaning agent may be used alone or in combination of two or more. In particular, it is preferable to use potassium hydroxide and sodium hydroxide in combination from the viewpoints of effect and ease of handling.

[0033] Examples of the organic alkalizing agent include organic amine compounds such as N,N-bis(2-hydroxyethyl)-N-cyclohexylamine, diazabicycloundecene, diazabicyclononene, monomethylamine, dimethylamine, trimethylamine, monoethanolamine, diethanolamine, triethanolamine, morpholine, 2-(dimethylamino)ethanol, 2-(diethylamino)ethanol, 1-amino-2-propanol, and triisopropanolamine. In addition, organic alkalizing agents may include compounds having at least one hydroxyl group, and if the acidity constant (pKa) of the compound is 30 or more, it is treated as an alkalizing agent.

[0034] Of the organic alkalizing agents in the present cleaning agent, monoethanolamine, diethanolamine and triethanolamine are preferred in terms of versatility, monoethanolamine and diethanolamine are more preferred in terms of availability, and monoethanolamine is particularly preferred in terms of cleaning properties.

[0035] The content of the alkalizing agent in the entire cleaning agent is preferably 1 to 20 mass%, more preferably 2 to 15 mass%, and even more preferably 3 to 10 mass%. Within the above range, sufficient effects as a cleaning agent can be obtained.

[0036] (Compatibilizer) In the cleaning agent according to the present invention, the (b) compatibilizer, when used in combination with the (a) component, has the function of promoting the dissolution of the functional layer from the laminated polyester film, and also has the function of solubilizing the (a) component, the (c) component which can be suitably added as described below, and other additives which are added as needed. The (b) compatibilizer is not particularly limited, and any of anionic compatibilizers, cationic compatibilizers, nonionic compatibilizers, and amphoteric compatibilizers can be used. The compatibilizer also includes compounds that correspond to the above-mentioned alkalizing agent. Therefore, in the cleaning agent of the present invention, when the (b) compatibilizer is used in combination with the (a) alkalizing agent, a compatibilizer different from the (a) component is used.

[0037] Examples of anionic compatibilizers include alkylsulfonic acids, alkylbenzenesulfonic acids, alkylcarboxylic acids, aromatic carboxylic acids, alkylnaphthalenesulfonic acids, α-olefinsulfonic acids, dialkylsulfosuccinic acids, α-sulfonated fatty acids, N-methyl-N-oleyltaurine, petroleum sulfonic acids, alkylsulfuric acids, sulfated oils and fats, polyoxyethylene alkyl ether sulfuric acids, polyoxyethylene styrenated phenyl ether sulfuric acids, alkyl phosphoric acids, polyoxyethylene alkyl ether phosphoric acids, polyoxyethylene alkyl phenyl ether phosphoric acids, naphthalenesulfonic acid formaldehyde condensates, and salts thereof.

[0038] Examples of the cationic compatibilizer include quaternary ammonium, tetraalkylammonium, trialkylbenzylammonium, alkylpyridinium, 2-alkyl-1-alkyl-1-hydroxyethylimidazolinium, N,N-dialkylmorpholinium, polyethylene polyamine fatty acid amide, urea condensate of polyethylene polyamine fatty acid amide, quaternary ammonium of urea condensate of polyethylene polyamine fatty acid amide, and salts thereof.

[0039] Examples of the nonionic compatibilizer include polyoxyalkylene ethers such as polyoxyethylene alkyl ethers and polyoxyethylene-polyoxypropylene alkyl ethers; and organic amine compounds such as polyoxyethylene alkylphenyl ethers, polyoxyethylene polystyrylphenyl ethers, polyoxyethylene-polyoxypropylene glycols, polyhydric alcohol fatty acid partial esters, polyoxyethylene polyhydric alcohol fatty acid partial esters, polyoxyethylene fatty acid esters, polyglycerin fatty acid esters, polyoxyethylated castor oil, fatty acid diethanolamides, monomethylamine, dimethylamine, trimethylamine, monoethanolamine, diethanolamine, triethanolamine, morpholine, 2-(dimethylamino)ethanol, 2-(diethylamino)ethanol, 1-amino-2-propanol, triisopropanolamine, polyoxyethylene alkylamines, triethanolamine fatty acid partial esters, and trialkylamine oxides.

[0040] Examples of amphoteric compatibilizers include betaines such as N,N-dimethyl-N-alkyl-N-carboxymethylammonium betaine, N,N,N-trialkyl-N-sulfoalkyleneammonium betaine, N,N-dialkyl-N,N-bispolyoxyethyleneammonium sulfate betaine, and 2-alkyl-1-carboxymethyl-1-hydroxyethylimidazolinium betaine, and aminocarboxylic acids such as N,N-dialkylaminoalkylenecarboxylates.

[0041] Note that the compatibilizer may include (c) a compound having at least one hydroxyl group, which will be described later. However, alkanolamine compounds, alkanolamide compounds, and hydroxy compounds having 12 or more carbon atoms that fall under the following categories are treated as (b) a compatibilizer. Examples of the alkanolamine compound include monoethanolamine, diethanolamine, and triethanolamine, and examples of the alkanolamide compound include monoethanolamide, diethanolamide, and triethanolamide. Examples of hydroxy compounds having 12 or more carbon atoms include polyoxyethylene alkyl ethers, thioethers, polyoxyalkylene glycols, acetylene glycols, esters, and glycosides having 12 or more carbon atoms.

[0042] Among the (b) compatibilizers in the present cleaning agent, aromatic sulfonates and hydroxyl-containing amine compounds are preferred from the viewpoints of compatibility and ease of handling. Specific examples of such compounds include sodium benzenesulfonate, sodium toluenesulfonate, sodium 2,4-dimethylbenzenesulfonate, sodium 2-naphthalenesulfonate, and alkanolamines such as monoethanolamine, diethanolamine, and triethanolamine. Among these, the aromatic sulfonates having high boiling points are more preferred from the viewpoint of increasing the upper limit of the temperature of the cleaning solution. As mentioned above, it is assumed that a compound different from the alkalizing agent (a) is used.

[0043] As a specific example of a combination of the (a) alkalizing agent and the (b) compatibilizer, when an inorganic alkalizing agent is used as the alkalizing agent, at least one of an anionic compatibilizer, a cationic compatibilizer, a nonionic compatibilizer, and an amphoteric compatibilizer may be used as the (b) compatibilizer. Also, when an organic alkalizing agent is used as the (a) alkalizing agent, at least one of an anionic compatibilizer, a cationic compatibilizer, a nonionic compatibilizer other than an organic amine compound, and an amphoteric compatibilizer may be used as the (b) compatibilizer.

[0044] In addition, in the present cleaning agent, it is preferable to use (a) an inorganic alkalizing agent as the alkalizing agent, and (b) at least one kind selected from aromatic sulfonate salts and hydroxyl group-containing amine compounds as the compatibilizing agent. Among them, a combination of at least one inorganic alkalizing agent of sodium hydroxide and potassium hydroxide and an aromatic sulfonate such as sodium 2,4-dimethylbenzenesulfonate is preferred. Also, a combination of at least one inorganic alkalizing agent of sodium hydroxide and potassium hydroxide and at least one hydroxyl group-containing amine compound selected from monoethanolamine, diethanolamine, triethanolamine, morpholine, 2-(dimethylamino)ethanol, 2-(diethylamino)ethanol, 1-amino-2-propanol, and triisopropanolamine is preferred, and among these, a combination of at least one inorganic alkalizing agent selected from sodium hydroxide and potassium hydroxide and at least one hydroxyl group-containing amine compound selected from monoethanolamine and diethanolamine is particularly preferred.

[0045] In order to comprehensively dissolve various additives in the cleaning agent, two or more of the above compatibilizers may be used in combination. The content of the compatibilizer in the cleaning agent is preferably in the range of 1 to 30% by mass. Within this range, sufficient cleaning performance can be obtained. From the above viewpoints, the content of the compatibilizer in the cleaning agent is more preferably in the range of 5 to 25% by mass, and further preferably in the range of 8 to 20% by mass.

[0046] The cleaning agent according to the present invention preferably contains (c) a compound having at least one hydroxyl group.

[0047] (Compounds having at least one hydroxyl group) Examples of the (c) compound having at least one hydroxyl group include alcohols and phenols.

[0048] Examples of the alcohols include monohydric alcohols such as hexafluoro-2-propanol, methyl alcohol, ethyl alcohol, propyl alcohol, butyl alcohol, benzyl alcohol, ethylene glycol monomethyl ether, diethylene glycol monobutyl ether, propylene glycol monomethyl ether, and propylene glycol monoethyl ether; dihydric alcohols such as ethylene glycol, diethylene glycol, and propylene glycol; and polyhydric alcohols such as glycerin.

[0049] Examples of phenols include phenol, xylenol, salicylic acid, picric acid, naphthol, catechol, resorcinol, hydroquinone, pyrogallol, phloroglucinol, dibutylhydroxytoluene, bisphenol A, cresol, estradiol, eugenol, gallic acid, guaiacol, phenolphthalein, serotonin, dopamine, adrenaline, noradrenaline, thymol, tyrosine, and hexahydroxybenzene.

[0050] These may be used alone or in combination of two or more kinds, but it is particularly preferable to use two or more kinds in combination from the viewpoint of enhancing the peeling and cleaning effect.

[0051] Among these, alcohols are preferred from the viewpoint of not impairing the alkalinity of the cleaner and maintaining the cleaning properties.

[0052] From the viewpoint of cleaning properties, the acidity constant (pKa) of the alcohol is preferably in the range of 8.0 or more and 20.0 or less, more preferably 8.0 or more and 18.0 or less, even more preferably 9.0 or more and 16.0 or less, particularly preferably 9.0 or more and 15.6 or less, and most preferably 9.3 or more and 15.4 or less. If the acidity constant (pKa) of the alcohol is within the above range, the alkoxide is generated without impairing the alkalinity of the cleaning agent, improving the cleaning ability of the cleaning agent.

[0053] The acidity constants (pKa) of some alcohols are as follows: hexafluoro-2-propanol (pKa=9.3), benzyl alcohol (pKa=15.4), methanol (pKa=15.5), ethanol (pKa=16.0), 1-propanol (pKa=16.1), 2-propanol (pKa=17.1), 1-butanol (pKa=16.1), tert-butanol (pKa=18.0). From the values ​​of the acidity constants (pKa) of alcohols shown above, it can be said that alcohols with an acidity constant (pKa) of 15.4 or less are alcohols with an acidity constant (pKa) smaller than that of methanol. Moreover, alcohols having an acidity constant (pKa) of 9.3 or more can be said to be alcohols having an acidity constant (pKa) of hexafluoro-2-propanol or more.

[0054] (Preferred embodiment 1 of component (c)) Among the above, from the viewpoint of cleaning ability, hexafluoro-2-propanol, methyl alcohol, ethyl alcohol, propyl alcohol and benzyl alcohol are more preferable. These alcohols have high cleaning ability because protons are easily ionized to generate alkoxides. Among them, hexafluoro-2-propanol, which has high cleaning power, is preferable.

[0055] Furthermore, for the purpose of adjusting the cleaning ability, it is also preferable to use hexafluoro-2-propanol in combination with other alcohols. In the case of combination use, the combination of hexafluoro-2-propanol and methyl alcohol, hexafluoro-2-propanol and ethyl alcohol, and hexafluoro-2-propanol and benzyl alcohol are preferred.

[0056] When hexafluoro-2-propanol and other monohydric alcohols are used as the alcohols, the mass ratio thereof (hexafluoro-2-propanol:other monohydric alcohols) is preferably 1:1 to 1:100, more preferably 1:3 to 1:41, even more preferably 1:4 to 1:20, and particularly preferably 1:5 to 1:10.

[0057] In addition, even when two or more kinds of monohydric alcohols are used in combination, a dihydric alcohol and a polyhydric alcohol may also be used in combination.

[0058] (Preferred embodiment 2 of component (c)) Among the above, benzyl alcohol is preferred from the viewpoints of low volatility and usable temperature range.

[0059] (Preferred embodiment 3 of component (c)) Furthermore, from the viewpoint of enhancing the peeling and cleaning effect, it is preferable to use two or more types in combination, and when two or more types are used in combination, a combination of a hydrophobic monohydric alcohol and a water-soluble monohydric alcohol is preferable from the viewpoint of widely and synergistically exerting the peeling and cleaning effect regardless of the properties of the coating film. The hydrophobic monohydric alcohol refers to a monohydric alcohol that separates into two layers without mixing with water, and the water-soluble monohydric alcohol refers to a monohydric alcohol that mixes with water to form one layer. Among these, it is more preferable to use benzyl alcohol as the hydrophobic monohydric alcohol in combination with one or more selected from hexafluoro-2-propanol, methyl alcohol, ethyl alcohol, and propyl alcohol as the water-soluble monohydric alcohol, and among these, the combination of benzyl alcohol and hexafluoro-2-propanol, and the combination of benzyl alcohol and methyl alcohol are most preferable.

[0060] When two or more types of the alcohols are used in combination, the blending ratio is not particularly limited. From the viewpoint of particularly enhancing the peeling and cleaning effect, the mass ratio of the hydrophobic monohydric alcohol: the water-soluble monohydric alcohol is preferably 1:1 to 20:1, more preferably 1:1 to 10:1, and even more preferably 1.5:1 to 10:1.

[0061] In addition, even when two or more kinds of monohydric alcohols are used in combination, a dihydric alcohol and a polyhydric alcohol may also be used in combination.

[0062] In the cleaning agent, the content of (c) the compound having at least one hydroxyl group is preferably 10 to 99 mass%, more preferably 20 to 98 mass%, and even more preferably 30 to 97 mass%. Within the above range, the amount of (a) the alkalizing agent is appropriate, so that contamination of the polyester film due to precipitation of the alkalizing agent component is suppressed when the polyester film is recovered, and the quality of the recycled polyester film can be maintained.

[0063] The cleaning agent according to the present invention is preferably an aqueous cleaning agent. The aqueous cleaning agent is prepared by dissolving the above-mentioned components (a) to (c) in water and diluting them. The aqueous cleaning agent is relatively safe because it can increase the flash point, and is also advantageous in that water can be used in the rinsing step described below.

[0064] The cleaning agent according to the present invention can contain various additives in addition to the above components (a) to (c). For example, an antioxidant, a rust inhibitor, a pH adjuster, a preservative, a viscosity adjuster, and an antifoaming agent can be added.

[0065] (Antioxidants) The antioxidant is not particularly limited, and an amine-based antioxidant, a phenol-based antioxidant, or the like can be used.

[0066] (rust inhibitor) The rust inhibitor includes inorganic compounds such as chromates, molybdates, and sodium nitrite.

[0067] (pH adjuster) Examples of pH adjusters include lactic acid, carbon dioxide, succinic acid, gluconic acid, citric acid, trisodium citrate, malic acid, phosphoric acid, and the like.

[0068] (Preservatives) Preservatives include parabens, benzoic acid, sodium benzoate, sorbic acid, propionate salts, dehydroacetic acid, sulfur dioxide, and sodium pyrosulfite.

[0069] (Viscosity modifier) Examples of the viscosity modifier include polymer compounds and layered inorganic particles.

[0070] (Antifoaming agent) Examples of the antifoaming agent include fluorine-based compounds, silicone-based compounds, polyether-based compounds, acetylene glycol-based compounds, and chelating agents such as EDTA.

[0071] <Functional layer removal process (A)> The functional layer removal step according to the present invention is a step of removing the functional layer of the laminated film using the cleaning agent. Examples of the removal method include an immersion method in which the film is immersed in a cleaning tank containing the cleaning agent, a coating method in which the cleaning agent in a solution state is applied, and a spraying method in which the cleaning agent in a solution state or a vaporized cleaning agent is sprayed. Among these, the immersion method is preferred from the viewpoint of the permeability of the cleaning agent into the functional layer.

[0072] The temperature of the cleaning agent in the immersion method is preferably room temperature (20°C) or higher. At room temperature (20°C) or higher, the viscosity of the cleaning solution is low and it is easy to penetrate into the functional layer, so good cleaning properties can be obtained. From the above viewpoints, the temperature of the cleaning agent in the immersion method is more preferably 40°C or higher, even more preferably 50°C or higher, and particularly preferably 60°C or higher. The upper limit of the temperature of the cleaning agent is preferably a temperature equal to or lower than the boiling point when the cleaning agent is used in a solution state. In the case of an aqueous cleaning agent, which is a preferred embodiment of the present application, the upper limit is preferably 100° C. or lower, and more preferably 90° C. or lower. In addition, the temperature of the cleaning solution during cleaning is the same as that described above even in the case of a method other than the immersion method. In addition, in the peeling cleaning in the immersion method, microwave irradiation may be performed for the purpose of promoting the hydrolysis reaction.

[0073] The pH of the detergent is preferably 12 or more, more preferably 13 or more, from the viewpoint of cleaning properties.

[0074] It is preferable to adjust the immersion time as follows depending on the type of object to be cleaned.

[0075] When the polyester film having an acrylic adhesive layer as a functional layer is to be cleaned, the cleaning time is preferably 1 second or more and 30 minutes or less. If it is 1 second or more, the cleaning agent can sufficiently penetrate into the functional layer, and cleaning properties can be exhibited. On the other hand, if it is within 30 minutes, the polyester film as the substrate is not excessively dissolved, and the amount of polyester obtained when recovered can be secured. From the above viewpoints, it is more preferable that it is 15 seconds or more and 20 minutes or less, even more preferable that it is 30 seconds or more and 15 minutes or less, and particularly preferable that it is 1 minute or more and 10 minutes or less.

[0076] When the polyester film having an acrylic hard coat layer as a functional layer is to be cleaned, the cleaning time is preferably 1 second or more and 30 minutes or less. If it is 1 second or more, the cleaning agent can sufficiently penetrate into the functional layer, and cleaning properties can be exhibited. On the other hand, if it is within 30 minutes, the polyester film as the substrate is not excessively dissolved, and the amount of polyester obtained when recovered can be secured. From the above viewpoints, it is more preferable that it is 15 seconds or more and 30 minutes or less, even more preferable that it is 30 seconds or more and 25 minutes or less, and particularly preferable that it is 1 minute or more and 20 minutes or less.

[0077] When the polyester film having a silicone release layer as a functional layer is to be cleaned, the cleaning time is preferably 1 second or more and 30 minutes or less. If it is 1 second or more, the cleaning agent can sufficiently penetrate into the functional layer and can exhibit cleaning properties. On the other hand, if it is within 30 minutes, the polyester film as the base material is not excessively dissolved, and the amount of polyester obtained when recovered can be secured. From the above viewpoints, it is more preferable that it is 15 seconds or more and 20 minutes or less, even more preferable that it is 30 seconds or more and 10 minutes or less, and particularly preferable that it is 1 minute or more and 5 minutes or less.

[0078] The specific embodiment of the functional layer removing step depends on the shape of the laminated film that is the waste material. When the waste laminated polyester film is in the form of a roll, it is preferable to install a winding device in front of the cleaning tank containing the cleaning agent, wind the laminated film from the device, introduce it into the cleaning tank and clean it, and then proceed continuously to the next recovery step (B). In addition, in order to efficiently remove the functional layer from the laminated polyester film from the functional layer removal process to the rinsing process described below, equipment equipped with physical means such as a roll brush, ultrasound, micro / nano bubbles, water flow, or compressed cold air may be provided.

[0079] When the laminated polyester film waste is in a lump form, it is preferable to install a cutting device before the cleaning step, cut the laminated polyester film into flakes, and introduce them into the cleaning tank. By cutting into flakes, the contact area between the laminated polyester film and the cleaning agent is increased, making it easier for the cleaning agent to penetrate, and the functional layer can be removed efficiently. In this embodiment, a method is preferred in which the laminated polyester film in flake form is continuously introduced into the cleaning tank using a belt conveyor or the like. By adopting such an embodiment, cleaning can be performed with high productivity. In this embodiment, cleaning can also be performed in a batch manner.

[0080] <Recovery process (B)> After the functional layer removing step (A), the polyester film, which is the base film, is recovered. It is preferable to have a rinsing step and a drying step, which will be described later, before the recovery step. As the recovery method, an appropriate method can be selected depending on the shape of the laminated polyester film, which is the waste material.

[0081] When the laminated polyester film as waste material is in the form of a roll, it can be efficiently recovered by continuously carrying out a roll-to-roll process, appropriately going through a cleaning step, a rinsing step, and a drying step, and then winding it up.

[0082] In the case where the waste laminated polyester film is in a lump form, it is preferable to have a cutting step before the functional layer removing step, as described above. In this embodiment, it is preferable to use a belt conveyer or the like to continuously pass the polyester through a rinsing step and a drying step to recover the polyester in a flake form.

[0083] The polyester film recovered as described above is advantageously pelletized in terms of handling after recovery.

[0084] <Rinse process> In the present invention, it is preferable to have a rinsing step of washing away the cleaning agent after the functional layer removing step (A) and before the recovery step (B). Specifically, this refers to a step of washing away the cleaning agent adhering to the polyester film from which the functional layer has been removed with a rinsing liquid.

[0085] The rinsing liquid is not particularly limited as long as it can wash away the cleaning agent. When using a water-based cleaning agent, which is a preferred embodiment of the present invention, water can be used in the rinsing step.

[0086] The temperature in the rinsing step is preferably around room temperature, specifically, preferably 5 to 50°C, and more preferably 5 to 30°C, from the viewpoint of efficient rinsing.

[0087] Methods for washing off the cleaning agent include a spraying method in which a rinse liquid is sprayed onto the polyester film from which the functional layer has been removed, an immersion method in which the polyester film is immersed in a rinse tank containing a rinse liquid, etc. However, when a cleaning agent that does not need to be washed off is used, the rinsing step can be omitted.

[0088] <Drying process> After the rinsing step, a drying step is preferably performed. The drying step can remove the cleaning agent and / or the rinsing liquid remaining on the polyester film. When the rinsing step is omitted, the drying step is preferably performed after the functional layer removing step (A).

[0089] The conditions for the drying step are not particularly limited, and drying is usually performed for about 1 to 30 minutes at 70 to 150° C. As the drying method, a general method such as heating and drying using an infrared heater or an oven, hot air drying using a hot air dryer, or microwave heating and drying can be used.

[0090] <Recycled polyester products> The polyester film obtained by the recovery method of the present invention can be used as a polyester raw material and can be reused as a so-called recycled polyester product. Specifically, the recovered polyester can be pelletized and stored as pelletized polyester (polyester product). The recovered polyester can also be molded into various polyester products such as polyester films by melt extrusion or the like. In addition, the recovered polyester is preferably pelletized and then molded into various products, because of ease of production.

[0091] The applications of the polyester film are the same as those of ordinary polyester products, for example, it can be used as a polyester film, which is a base film. By forming a functional layer on the base film, it is also possible to reuse it as a laminate film.

[0092] The recycled polyester can be mixed with polyester produced by conventional methods, and a multi-layer film can be made using both recycled polyester and polyester produced by conventional methods.

[0093] Recycled polyester products can be used for a variety of purposes other than films, such as the production of PET bottles, polyester fibers, polyester sheets, and polyester containers.

[0094] The peeled functional layer can also be recovered and reused as necessary.

[0095] <Functional layer remover> According to another aspect of the present invention, there is provided a remover (hereinafter also referred to as "the remover") for removing a functional layer from a laminated polyester film having a functional layer on the surface of a polyester film. The functional layer remover for polyester film according to the present invention is a cleaning agent used in the functional layer removal step (A) in the above-mentioned polyester film recovery method, which is used to remove the functional layer from the polyester film. Specific and preferred aspects of the present remover are the same as those of the above-mentioned cleaning agent, and all of these can be used. The removing agent of the present invention can easily remove the functional layer from the polyester film, and can efficiently recover the polyester film from the laminated polyester film.

[0096] <Polyester film recovery equipment> The polyester film recovery device according to the present invention includes a cleaning device, and recovers the polyester film that has been cleaned by the cleaning device and from which the functional layer has been removed.

[0097] The means for recovering the polyester film is not particularly limited. In the case of a roll, a take-up roll for recovering the polyester film from which the functional layer has been removed may be used. In the case of a lump, the polyester film from which the functional layer has been removed may be transported to a predetermined recovery position by a transport device such as a belt conveyor and recovered.

[0098] The means for unwinding and cutting the polyester film is not particularly limited, but in the case of a roll, it is preferable that the polyester film has an unwinding device, and further, it is preferable that the winding is also performed on a roll, that is, a so-called roll-to-roll method, in which the polyester film can be recovered efficiently. If in chunk form, it is preferred to have a shredding device, which breaks the waste material into flakes, which, as mentioned above, makes the cleaning process more efficient.

[0099] The recovery device preferably has a pelletizing device, and the recovered polyester film is preferably pelletized in the pelletizing device to facilitate handling. In particular, polyester film recovered from lump waste can be made more easily handleable by pelletizing it.

[0100] Additionally, the recovery device preferably includes a rinsing device and a drying device, as described in more detail below.

[0101] (Cleaning Equipment) The cleaning device is a device for cleaning with a cleaning agent containing (a) an alkalizing agent and (b) a compatibilizing agent. A typical example is a cleaning tank filled with the above-mentioned cleaning agent, into which the waste laminated polyester film is introduced and immersed for cleaning. Other examples include a coating device that coats the cleaning agent in a solution state, and a spraying device that forms a mist of the cleaning agent in a solution state or vaporized state, or sprays the mist.

[0102] The cleaning agent is as described above, and is preferably a water-based cleaning agent. By using a water-based cleaning agent, rinsing with water can be performed using a rinsing device described later, which is preferable.

[0103] (Rinse device) The rinsing device is a device for washing away the cleaning agent attached to the polyester film after removing the functional layer with the cleaning agent. Specifically, it can be a spraying device for spraying the rinsing liquid, an immersion device for immersing the polyester film in the rinsing liquid, etc. As described above, by using a water-based cleaning agent as the cleaning agent, water can be used in the rinsing step, which is highly safe and does not require an explosion-proof device, which is also preferable in terms of cost.

[0104] The functional layer that has been peeled off from the polyester film may also be washed away together with the cleaning agent. The water and the material that constituted the functional layer are then separated, and the water can be reused in the rinsing step, and the material that constituted the functional layer can also be reused. The rinsing device may be omitted.

[0105] (drying equipment) The drying device is for drying the polyester film from which the functional layer has been peeled off and the cleaning agent has been washed away, and the drying conditions are as described above. Examples of the drying device include an infrared heater, an oven, a hot air dryer, and a microwave heating dryer. After the drying process in the drying device, the polyester substrate is recovered. Note that, even when the rinsing device is omitted, it is also possible to dry the polyester film from which the functional layer has been peeled off using the drying device. EXAMPLES

[0106] The present invention will now be described in more detail with reference to examples, although the present invention is not limited to the examples described below.

[0107] <Evaluation method> (1) Immersion test The cleaning agent prepared in each Example and Comparative Example was placed in a 30 ml water tank, and the laminated film was immersed in the cleaning agent. The temperature of the cleaning agent, the immersion time, and the sample size are as shown in the table.

[0108] (2) Evaluation of peeling of functional layer (2-1) Visual Inspection (Laminated polyester film having an adhesive layer, and laminated polyester film having a hard coat layer) The immersed laminated film was taken out and the surface was visually observed and evaluated according to the following criteria. ⊚ (very good): The functional layer was dissolved or peeled off, and the polyester film substrate was not significantly damaged, which is particularly preferable from a practical standpoint. ◯ (good): The functional layer is partially dissolved or peeled off, but there is no problem in practical use. Δ (fair): A small part of the functional layer was dissolved or peeled off. × (bad): The functional layer remains, which is problematic in practical use.

[0109] (2-2) X-ray fluorescence analysis (Laminated polyester film with silicone release layer) The surface of the laminated film after cleaning was subjected to a quantitative analysis of the Si element using an X-ray fluorescence analyzer (XRF, "XRF-1800" manufactured by Shimadzu Corporation). The removal rate of the functional layer was measured by setting the amount of Si element on the surface of the laminated polyester film before cleaning to 100% and the amount of Si element on the plain film without the functional layer of the laminated film to 0%. ◎(very good); Removal rate 90~100% ○(good); Removal rate 70~89% ×(bad); Removal rate 0~69%

[0110] (3) Intrinsic viscosity 1 g of polyester was precisely weighed, dissolved in 100 ml of a mixed solvent of phenol / tetrachloroethane = 50 / 50 (mass ratio), and measured at 30°C.

[0111] (Laminated polyester film with functional layer) A laminated polyester film having the following functional layers (I) to (III) was prepared as a sample. (I) Laminated film (laminated polyester film having an acrylic adhesive layer); Commercially available product ("PET75-H120(10) Blue" manufactured by Nichiei Shinka Co., Ltd.), polyethylene terephthalate film thickness: 75 μm, acrylic adhesive layer thickness: 10 μm

[0112] (II) Laminated film (laminated polyester film having an acrylic hard coat layer); A laminated polyester film having an acrylic hard coat layer was obtained by the following procedure. (Preparation of Acrylic Hard Coat Solution) An acrylic hard coat solution was obtained by mixing 24 parts by mass of dipentaerythritol hexaacrylate, 6 parts by mass of 2-hydroxy-3-phenoxypropyl acrylate, 1.5 parts by mass of a photopolymerization initiator (product name: Omnirad 184, manufactured by IGM Resins BV), and 70 parts by mass of toluene. (Preparation of Acrylic Hard Coat Film) The above acrylic hard coat solution was applied onto a polyethylene terephthalate film; a commercially available product ("Diafoil" manufactured by Mitsubishi Chemical Corporation) to a dry film thickness of approximately 9 μm, and cured by exposure to ultraviolet light to obtain a laminated polyester film having an acrylic hard coat layer.

[0113] (III) Laminated film (laminated polyester film having a silicone release layer); commercially available product ("MRF38" manufactured by Mitsubishi Chemical Corporation). Thickness of polyethylene terephthalate film: 38 μm. Limiting viscosity of the polyethylene terephthalate film was 0.67.

[0114] [Example 1] A cleaning agent (pH = 13 or more) was prepared by mixing 5 parts by mass of potassium hydroxide and 5 parts by mass of sodium hydroxide as component (a), 19 parts by mass of monoethanolamine as component (b), 40 parts by mass of benzyl alcohol and 1 part by mass of propylene glycol as component (c), and 30 parts by mass of water as another component. Using the laminated films (I) to (III), cleaning property evaluation was carried out under the conditions shown in Table 1. The results are shown in Table 1. The laminated film (III) was washed at 60°C for 1 minute, and the intrinsic viscosity of the polyester film from which the silicone release layer had been removed was measured. The intrinsic viscosity was 0.67, and there was no change in the intrinsic viscosity of the polyester film before and after washing.

[0115] [Example 2] A cleaning agent (pH = 13 or more) was prepared by mixing 5 parts by mass of potassium hydroxide and 5 parts by mass of sodium hydroxide as component (a), 10 parts by mass of diethanolamine as component (b), 16 parts by mass of benzyl alcohol as component (c), and 64 parts by mass of water as other components. Using the laminated films (I) and (III), cleaning properties were evaluated under the conditions shown in Table 1. The results are shown in Table 1.

[0116] [Example 3] A cleaning agent was prepared by mixing 5 parts by mass of potassium hydroxide as component (a), 17.6 parts by mass of sodium 2,4-dimethylbenzenesulfonate as component (b), 41.3 parts by mass of benzyl alcohol as component (c), and 36.1 parts by mass of water as the other component. Using the laminated film (III), a cleaning property evaluation was carried out under the conditions shown in Table 1. The results are shown in Table 1.

[0117] [Example 4] A cleaning agent was prepared by mixing 5 parts by mass of potassium hydroxide as component (a), 17.6 parts by mass of sodium 2,4-dimethylbenzenesulfonate as component (b), 37.2 parts by mass of benzyl alcohol and 4.1 parts by mass of methanol as component (c), and 36.1 parts by mass of water as the other component. Using the laminated film (III), a cleaning property evaluation was carried out under the conditions shown in Table 1. The results are shown in Table 1.

[0118] [Example 5] A cleaning agent was prepared by mixing 5 parts by mass of potassium hydroxide as component (a), 17.6 parts by mass of sodium 2,4-dimethylbenzenesulfonate as component (b), 31.0 parts by mass of benzyl alcohol and 10.3 parts by mass of methanol as component (c), and 36.1 parts by mass of water as the other component. Using the laminated film (III), a cleaning property evaluation was carried out under the conditions shown in Table 1. The results are shown in Table 1.

[0119] [Example 6] A cleaning agent was prepared by mixing 5 parts by mass of potassium hydroxide as component (a), 17.6 parts by mass of sodium 2,4-dimethylbenzenesulfonate as component (b), 20.7 parts by mass of benzyl alcohol and 20.7 parts by mass of methanol as component (c), and 36.1 parts by mass of water as the other component. Using the laminated film (III), a cleaning property evaluation was carried out under the conditions shown in Table 1. The results are shown in Table 1.

[0120] [Example 7] A cleaning agent was prepared by mixing 5 parts by mass of potassium hydroxide as component (a), 17.6 parts by mass of sodium 2,4-dimethylbenzenesulfonate as component (b), 37.2 parts by mass of benzyl alcohol and 4.1 parts by mass of hexafluoro-2-propanol as component (c), and 36.1 parts by mass of water as the other component. Using the laminated film (III), a cleaning property evaluation was carried out under the conditions shown in Table 1. The results are shown in Table 1.

[0121] [Comparative Example 1] A cleaning agent was prepared by mixing 30 parts by mass of potassium hydroxide as component (a) and 70 parts by mass of water as the other component. Using the laminated films (I) and (III), cleaning performance was evaluated under the conditions shown in Table 1. The results are shown in Table 1.

[0122] [Comparative Example 2] Except for changing the temperature conditions as shown in Table 1, the cleaning performance evaluation was carried out in the same manner as in Comparative Example 1. The results are shown in Table 1.

[0123] As reference examples, a base film (IV) (polyethylene terephthalate film, thickness 52 μm) having no functional layer and a base film (V) (unstretched polypropylene film, thickness 56 μm) were prepared as samples. The sample was immersed in the cleaning agent for 5 minutes, and the thickness was measured using a Mitutoyo Corporation "Thickness Gauge ID-C112X / 1012X" to measure the change in thickness of the substrate. A was given when the thickness change was 3 μm or more, and a B was given when the thickness change was less than 3 μm.

[0124] [Reference example 1] A cleaning test was carried out on the base film (IV) and the base film (V) using a cleaning agent having the same composition as in Example 1 under the conditions shown in Table 1, and the thickness after cleaning was measured. The results are shown in Table 1.

[0125] [Table 1]

[0126] [Reference example 2] In order to confirm the best form of the monohydric alcohol in the cleaning agent, the cleaning conditions were changed to 55° C. and 1 minute of immersion time in Examples 3 to 6, and the cleaning performance was evaluated according to the following criteria. The results are shown in Table 2. As in the above, the cleaning evaluation was performed by quantitatively analyzing the Si element on the surface of the laminated film after cleaning using an X-ray fluorescence analyzer. The removal rate of the functional layer was judged according to the following criteria. ○(good); Removal rate 50~100% △(fair); Removal rate 0~49%

[0127] [Table 2]

[0128] As can be seen from the results shown in Table 1, the method of the present invention made it possible to peel the functional layer from any of the adhesive film, hard coat film, and release film, and to recover the polyester film. Furthermore, the results of Example 1 show that according to the method of the present invention, the intrinsic viscosity (IV) of the polyester film does not decrease before and after the functional layer removal process (cleaning process), and therefore recycled polyester products made from the recovered polyester film are likely to have excellent mechanical properties, etc.

[0129] It is clear that the cleaning agents of Comparative Examples 1 and 2, which contain only component (a) and no component (b), do not exhibit the effects of the present invention.

[0130] From the results of Reference Example 1, it is seen that the surface of the base film (IV) which is a polyester film is partially melted and thinned, whereas the surface of the base film (V) which does not have an ester bond is not melted and is not thinned. In other words, it is considered that the cleaning agent according to the present invention effectively peels off the functional layer by partially dissolving the surface of the polyester film which is the base material.

[0131] Furthermore, from the results of Reference Example 2 (Table 2), it was found that according to the method of the present invention, by using two or more types of alcohols in combination as the compound having at least one hydroxyl group (c), it is possible to peel off the functional layer at a lower temperature and in a shorter time, which is less likely to affect the film. It was also found that an extremely excellent cleaning effect could be obtained by setting the mass ratio of hydrophobic alcohol:water-soluble alcohol to be 1.5:1 to 10:1.

[0132] As described above, according to the present invention, various functional layers can be peeled off with one type of cleaning agent, so that even in a laminated polyester film having multiple different functional layers, all of the functional layers can be peeled off with one liquid. Furthermore, even in the case of a laminated polyester film having a hard coat layer on the front side and an adhesive layer on the back side, for example, the functional layers can be peeled off from both sides in a single cleaning operation, and the polyester film substrate can be recovered.

Claims

1. A method for producing a recycled polyester film, comprising the steps of: washing a laminated polyester film having a functional layer on a surface of the polyester film with a cleaning agent (excluding a morpholine solution having a morpholine concentration of 50% by mass or more) containing (a) an alkalizing agent (excluding a hydroxyl-containing amine compound when the polyester film contains a hydroxyl-containing amine compound as component (b)) and (b) a compatibilizing agent, thereby dissolving a part of the surface of the polyester film and removing the functional layer, the functional layer is a silicone release layer, the (b) compatibilizer is at least one selected from the group consisting of aromatic sulfonates and hydroxyl group-containing amine compounds, A method for producing a recycled polyester film, wherein the removal rate of the functional layer of the polyester film from which the functional layer has been removed is 70% or more.

2. The method for producing a recycled polyester film according to claim 1 , wherein the cleaning agent is a water-based cleaning agent.

3. The method for producing a recycled polyester film according to claim 1 or 2, wherein the (a) alkalizing agent contains an alkali metal hydroxide.

4. The method for producing a recycled polyester film according to any one of claims 1 to 3, wherein the (a) alkalizing agent contains potassium hydroxide.

5. The method for producing a recycled polyester film according to any one of claims 1 to 4, wherein the cleaning agent further contains (c) an alcohol as a compound having at least one hydroxyl group.

6. A method for producing a recycled polyester film as described in claim 5, wherein the alcohols include benzyl alcohol.

7. The method for producing a recycled polyester film according to claim 5 or 6, wherein the alcohol has an acidity constant (pKa) of 8.0 or more and 20.0 or less.

8. The method for producing a recycled polyester film according to any one of claims 5 to 7, wherein two or more types of the alcohols are used in combination.

9. A method for producing a recycled polyester film described in any one of claims 1 to 8, wherein the aromatic sulfonate comprises at least one selected from sodium benzenesulfonate, sodium toluenesulfonate, sodium 2,4-dimethylbenzenesulfonate, and sodium 2-naphthalenesulfonate, and the hydroxyl group-containing amine compound comprises at least one selected from monoethanolamine, diethanolamine, triethanolamine, 2-(dimethylamino)ethanol, 2-(diethylamino)ethanol, 1-amino-2-propanol, and triisopropanolamine.

10. The method for producing a recycled polyester film according to any one of claims 1 to 9, wherein the content of the compatibilizer (b) in the cleaning agent is in the range of 1 to 30 mass%.

11. The method for producing a recycled polyester film according to any one of claims 1 to 10, wherein the temperature of the cleaning agent is 20°C or higher.

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