Method for removing functional layers from plastic film pieces and method for producing recycled plastic pellets

Abstract

A method for removing a functional layer from plastic film pieces, comprising: (A) a step of preparing plastic film pieces having a functional layer and an average size Sp of 5 to 100 mm; and (B) a step of removing the functional layer from the plastic film pieces by a wet crushing process in which the plastic film pieces are crushed in the presence of a liquid while being stirred, wherein in step (B), the average size Sa of the processed film pieces obtained by the wet crushing process is 0.8 times or less the average size Sp of the plastic film pieces.

Description

[Technical Field]

[0001] The present disclosure relates to a method for removing a functional layer from a piece of plastic film and a method for producing recycled plastic pellets. [Background technology]

[0002] Plastic films constituting plastic products are generally provided with functional layers, such as ink layers, hard coat layers, and silicone coating layers, to impart functionality. However, if components derived from these functional layers are mixed into recycled plastic raw materials, they can cause problems such as unintended coloring, the generation of unpleasant odors during the production of recycled plastic pellets, and deterioration of product properties. Therefore, there is a need for a method for recycling plastic products that does not mix these components.

[0003] To address the above-mentioned problems, Patent Document 1 discloses a method for removing ink, which includes the steps of processing the printed film, crushing it, removing the ink from the film, rinsing the film, recovering the cleaning solution, recovering the pigment, and drying the film. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Special Publication No. 2015-520684 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the above-mentioned conventional methods do not necessarily provide sufficient ink removability, and are only intended to remove ink, making it difficult to remove functional layers formed of materials other than ink.

[0006] Therefore, one aspect of the present disclosure aims to provide a method for effectively removing a functional layer from a plastic film piece. Another aspect of the present disclosure aims to provide a method for producing recycled plastic pellets using treated film pieces or processed products thereof recovered through the above method. [Means for solving the problem]

[0007] Some aspects of the present disclosure provide the following [1] to [7].

[0008] [1] 1. A method for removing a functional layer from a piece of plastic film, comprising: (A) preparing a plastic film piece having a functional layer and an average size Sp of 5 to 100 mm; (B) removing the functional layer from the plastic film pieces by a wet crushing process in which the plastic film pieces are crushed in the presence of a liquid while being stirred; The method, wherein in the step (B), the average size Sa of the treated film pieces obtained by the wet crushing treatment is 0.8 times or less the average size Sp of the plastic film pieces.

[0009] [2] the step (B) includes supplying the plastic film pieces and the liquid to a treatment space, performing the wet crushing treatment in the treatment space, and discharging the treated film pieces and the liquid from the treatment space; The method according to [1], wherein the ratio of the volume V2 of the liquid to the volume V1 of the plastic film pieces supplied to the processing space is 0.43 to 99.

[0010] [3] The method according to [1] or [2], further comprising, before the step (B), a step (A') of wetting the plastic film piece with a cleaning liquid.

[0011] [4] The method according to [3], wherein the cleaning solution used in the step (A') contains (a) a surfactant and (b) an inorganic base.

[0012] [5] The method according to any one of [1] to [4], wherein the functional layer is an ink layer.

[0013] [6] The method according to any one of [1] to [4], wherein the functional layer is a functional coating layer containing a silicone resin.

[0014] [7] A method for producing recycled plastic pellets, comprising molding the treated film pieces or treated products thereof recovered through the method according to any one of [1] to [6] into pellets. [Effects of the Invention]

[0015] According to one aspect of the present disclosure, a method for effectively removing a functional layer from a plastic film piece can be provided. Also, according to another aspect of the present disclosure, a method for producing recycled plastic pellets can be provided using treated film pieces or processed products thereof recovered through the above method. DETAILED DESCRIPTION OF THE INVENTION

[0016] Illustrative embodiments of the present disclosure are described below. However, the present disclosure is not limited to the following embodiments. In this specification, a numerical range indicated using "to" indicates a range that includes the numerical values ​​before and after "to" as the minimum and maximum values, respectively. Furthermore, unless specifically stated otherwise, the units of the numerical values ​​before and after "to" are the same. Furthermore, the upper and lower limit values ​​individually stated can be arbitrarily combined. Furthermore, although specific compounds, products, etc. are exemplified below, substances other than those exemplified can also be used as appropriate. Furthermore, in this specification, "(meth)acrylic" means at least one of acrylic and its corresponding methacrylic.

[0017] <Method for removing the functional layer> One embodiment of the present disclosure is a method for removing a functional layer from a plastic film piece (hereinafter simply referred to as "removal method"), which includes the following steps (A) and (B). (A) A step of preparing a plastic film piece having an average size Sp of 5 to 100 mm and having a functional layer (hereinafter also simply referred to as "plastic film piece"). (B) A step of removing the functional layer from the plastic film pieces by a wet crushing process in which the plastic film pieces are crushed in the presence of a liquid while being stirred.

[0018] In the above-described removal method, in step (B), the average size Sa of the processed film pieces obtained by the wet-shredding process is set to 0.8 times or less the average size Sp of the plastic film pieces. That is, in step (B), the wet-shredding process is performed so that the ratio of the average sizes of the film pieces before and after the wet-shredding process (Sa / Sp) is 0.8 or less. The average size Sp is the average value of the sizes of the individual plastic film pieces. The size of an individual plastic film piece refers to the length of the longest line segment within the plane of the plastic film piece. For example, if the plastic film piece is triangular, the size of the longest side; if the plastic film piece is a polygon with four or more sides, the length of the longest diagonal; and if the plastic film piece is circular, the size of the individual plastic film piece is the length of the longest diameter. The average size Sp is determined by randomly selecting 50 plastic film pieces from the entire plastic film fragments and calculating the average value of these.

[0019] In the above removal method, the wet treatment allows the functional layer to be effectively removed from the plastic film piece. The reason for this effect is not clear, but is presumed to be as follows.

[0020] In the wet crushing process, shear forces are applied to the functional layer of the plastic film fragments and the plastic film fragments are agitated. The shear forces and agitation cause the film fragments to rub against each other, and the liquid contacts the functional layer, which is thought to cause the functional layer to separate (peel off) from the plastic film fragments and remove them. Therefore, to improve the removability of the functional layer, it is important to perform the wet crushing process until the film fragments are sufficiently small, thereby increasing the number of times shear forces are applied to the functional layer and the number of times the film fragments rub against each other. In contrast, in the above removal method, the initial average size (Sp) of the plastic film fragments to be treated is 100 mm or less, which is sufficiently small, and the wet crushing process is performed so that the ratio of the average sizes of the film fragments before and after the wet crushing process (Sa / Sp) is 0.8 or less. This increases the number of times shear forces are applied to the functional layer and the number of times the film fragments rub against each other during the wet crushing process, which is thought to improve the removability of the functional layer. Furthermore, in the above removal method, the initial average size Sp of the plastic film pieces to be processed is 5 mm or more, which is sufficiently large. Therefore, even if the above ratio (Sa / Sp) is 0.8 or less, it is considered that the force applied to the functional layer due to the friction between the film pieces during the wet crushing process is sufficiently strong, and this is also presumably one of the reasons why the above effect is obtained.

[0021] From the viewpoint of more effectively removing the functional layer from the plastic film piece, the above-mentioned removal method may further include the following step (A') before step (B). (A') A step of wetting a piece of plastic film with a cleaning solution

[0022] Steps (A), (A') and (B) will be described in detail below.

[0023] (Process:(A)) In step (A), plastic film pieces (plastic film pieces having a functional layer) with an average size Sp of 5 to 100 mm are prepared. These plastic film pieces are obtained, for example, by crushing a plastic film having a functional layer.

[0024] The step (A) may be a step of preparing pre-crushed plastic film pieces, or a step of crushing a plastic film to produce plastic film pieces. In this specification, "crushing" means breaking down a solid (film) into small pieces using a crusher or the like, and terms such as pulverization, crushing, and shredding are also included in "crushing."

[0025] [Plastic film] The plastic film having a functional layer has at least a resin film layer and a functional layer provided on the resin film layer.

[0026] The plastic film is, for example, a plastic film in a non-roll form. The plastic film may be, for example, a plastic film that has become waste (so-called waste plastic film). As the plastic film, films that are generally distributed as packaging materials for food packaging or daily necessities, discarded films having various types of resin film layers, etc. can be used without any particular limitation, and these can also be used in combination. The plastic film can also be cut out from a plastic film in a roll form.

[0027] The plastic film may be either a laminate film having a functional layer on the outermost surface or a laminate film in which the functional layer is provided between multiple resin film layers. When the plastic film is a laminate film having a functional layer on the outermost surface, the removability of the functional layer is improved. Examples of the laminate film having a functional layer on the outermost surface and the laminate film in which the functional layer is provided between multiple resin film layers include front-printed films and back-printed films that are commonly used for food packaging, etc.

[0028] -Resin film layer- Resin film layers can be classified according to their required roles into a base film layer (F1), a sealant layer (F2) that serves as a heat-sealing site when forming a packaging material, and the like.

[0029] Examples of resin films that can be used as the base film layer (F1) include polyolefin films made of low-density polyethylene, high-density polyethylene, linear low-density polyethylene, OPP (biaxially oriented polypropylene), CPP (non-oriented polypropylene), etc.; polyester films made of polyethylene terephthalate (PET), polybutylene terephthalate, etc.; polyamide films made of nylon 6, nylon 6,6, metaxylene adipamide (N-MXD6), etc.; biodegradable films made of polylactic acid, etc.; polyacrylonitrile films, poly(meth)acrylic films, polystyrene films, polycarbonate films, saponified ethylene-vinyl acetate copolymer (EVOH) films, polyvinyl alcohol films, and triacetyl cellulose films. These films may contain pigments. The surfaces of these films may have a vapor-deposited layer formed by vapor-depositing metals such as aluminum and copper, titanium oxide, alumina, silica, etc. The surfaces of these films may be subjected to various surface treatments, such as flame treatment, corona discharge treatment, or chemical treatment using a release primer.

[0030] The resin film that forms the sealant layer (F2) is, for example, a flexible polymer film. Examples of flexible polymer films include polyolefin films such as polyethylene film, polypropylene film, and ethylene-vinyl acetate copolymer film; ionomer resins; EAA resins; EMAA resins; EMA resins; EMMA resins; and biodegradable resins. Examples of resin films that can be used include films known by generic names such as CPP (non-oriented polypropylene) film, VMCPP (aluminum-vapor-deposited non-oriented polypropylene) film, LLDPE (linear low-density polyethylene) film, LDPE (low-density polyethylene) film, HDPE (high-density polyethylene) film, and VMLDPE (aluminum-vapor-deposited non-low-density polyethylene) film. These films may contain pigments. The surfaces of these films may be subjected to various surface treatments, such as flame treatment, corona discharge treatment, or chemical treatment using a release primer.

[0031] From the viewpoint of reuse as a recycled substrate for general consumer use, the resin film layer preferably includes a film (polyolefin film) formed from a polyolefin such as polyethylene or polypropylene, and more preferably includes a polypropylene film. On the other hand, from the viewpoint of reuse as a recycled substrate for industrial use, the resin film layer preferably includes a film (polyolefin film) formed from a polyolefin such as polyethylene or polypropylene, or a film (polyester film) formed from a polyester such as polyethylene terephthalate. The polyolefin may be a stretched film (for example, a uniaxially stretched or biaxially stretched film) or a non-stretched film.

[0032] The thickness of the resin film layer is preferably 5 μm or more and 1000 μm or less, and more preferably 10 μm or more and 500 μm or less.

[0033] -Function layer- The functional layer may be, for example, an ink layer. The ink layer is a layer containing ink and may have the function of displaying any design, pattern, letter, symbol, etc. for the purpose of providing decoration or aesthetic appeal, or displaying the contents, expiration date, manufacturer or seller, etc. The ink layer may also be a solid ink layer that does not have any design, pattern, letter, symbol, etc.

[0034] The ink layer is formed by printing using, for example, a gravure printing machine, a flexographic printing machine, an offset printing machine, an inkjet printing machine, or the like. That is, the ink used to form the ink layer may be an ink for gravure printing (gravure ink), an ink for flexographic printing (flexo ink), an ink for offset printing (offset ink), or an ink for inkjet printing (inkjet ink). Among these, from the viewpoint of ease of removal by the method of this embodiment, it is preferable that the ink forming the ink layer is a gravure ink.

[0035] The ink used to form the ink layer may be, for example, an organic solvent-based printing ink, a water-based ink, or an active energy ray-curable ink. The ink layer may be formed of one type of ink, or may be formed of multiple types of ink. That is, the ink layer may be an ink layer for monochromatic printing, or an ink layer for multicolor printing.

[0036] The ink contains, for example, a binder resin and an organic solvent as main components. The ink may contain a pigment and / or a dye as a colorant. The ink may contain a pigment derivative and / or a resin-type dispersant as a dispersant for the colorant. These materials may be used alone or in combination. The combined use of a pigment derivative and a resin-type dispersant further improves dispersion stability and stability over time.

[0037] The ink may contain a compound having an acidic group from the viewpoint of functional layer removability. The compound having an acidic group can be used without any particular limitation. As the compound having an acidic group, a compound (for example, a resin or a low molecular weight compound) that can be easily mixed with the binder resin and organic solvent, which are the main components of the ink, is preferably used.

[0038] Examples of resins having an acidic group include resins having an acid value such as rosin-modified maleic acid resins and rosin-modified fumaric acid resins, polymerizable monomers having a carboxyl group such as acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, cinnamic acid, or acid anhydrides thereof, polymerizable monomers having a sulfonic acid group such as sulfonated styrene, (meth)acrylic resins copolymerized with polymerizable monomers having an acidic group (for example, polymerizable monomers having a sulfonamide group such as vinylbenzenesulfonamide), radical copolymer resins such as styrene-(meth)acrylic resins, styrene-maleic acid (anhydride) resins, and terpene-maleic acid (anhydride) resins, and acid-modified polyolefin resins. These can be used alone or in combination.

[0039] Examples of low molecular weight compounds having an acidic group include saturated fatty acids, unsaturated fatty acids, hydroxy acids, aromatic carboxylic acids, dicarboxylic acids, tricarboxylic acids, oxocarboxylic acids, carboxylic acid derivatives, acid anhydrides, etc. These can be used alone or in combination.

[0040] Examples of saturated fatty acids include lauric acid, myristic acid, palmitic acid, margaric acid, and stearic acid. Examples of unsaturated fatty acids include oleic acid, linoleic acid, linolenic acid, arachidonic acid, eicosapentaenoic acid, docosahexaenoic acid, and sorbic acid. Examples of hydroxy acids include lactic acid, malic acid, and citric acid. Examples of aromatic carboxylic acids include benzoic acid, phthalic acid, isophthalic acid, terephthalic acid, salicylic acid, gallic acid, mellitic acid, and cinnamic acid. Examples of dicarboxylic acids include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, fumaric acid, and maleic acid. Examples of tricarboxylic acids include aconitic acid. Examples of oxocarboxylic acids include pyruvic acid and oxaloacetic acid. Examples of carboxylic acid derivatives include amino acids and nitrocarboxylic acids. Examples of acid anhydrides include trimellitic anhydride and pyromellitic anhydride. These may be used alone or in combination of two or more.

[0041] The content of the compound having an acidic group may be determined as appropriate within a range that does not impair the printability of the ink, but is preferably in the range of 0.5 to 50 mass % relative to the solid content of the ink, and more preferably in the range of 1.0 to 30 mass %.

[0042] The ink layer may be a single layer or a multi-layer structure. The thickness of the ink layer is preferably 0.1 to 10 μm, more preferably 1 to 5 μm.

[0043] The functional layer may be a layer other than an ink layer, and may be, for example, a functional coating layer formed for the purposes of hard coating, silicone-based release, IR cut, waterproof and moisture-proof, antibacterial, UV cut, heat dissipation, photocatalysis, weather resistance, anti-fogging, fingerprint and stain resistance, self-repair, water and oil repellency, etc. Examples of functional coating layers include a hard coating layer, adhesive layer, release layer, decorative layer, light-shielding layer, ultraviolet-shielding layer, easy-adhesion layer (primer layer), antistatic layer, refractive index adjustment layer, oligomer sealing layer, etc. These functional coating layers may be colorless or colored.

[0044] The functional coating layer can be formed by coating the surface of a resin film layer with a surface modifier, a coating agent used as an electronics material, or the like. Examples of surface modifiers include hard coating agents, self-healing coating agents, fingerprint-resistant and antifouling coating agents, anti-fogging coating agents, silicone-based release agents, non-silicone-based release agents, waterproof and moisture-proof coating agents, water- and oil-repellent coating agents, photocatalytic coating agents, weather-resistant coating agents, and IR-cut coating agents. Examples of various coating agents used as electronic materials include optical pressure-sensitive adhesives, polyimide varnishes, liquid crystal alignment film materials, electromagnetic wave shielding coating agents, fine wiring pastes, antistatic coating agents, high-refractive index coating agents, and optical lens coating agents. The thickness of the functional coating layer formed with these various coating agents is preferably 0.1 μm to 100 μm, more preferably 0.1 μm to 10 μm, and even more preferably 1 μm to 5 μm.

[0045] The functional coating layer may be a metal layer formed from a metal material. The metal layer may be a layer made of metal foil, or may be a metal vapor deposition layer formed by vapor deposition of a metal or metal oxide. Examples of metal foil include foils of metals with excellent ductility, such as gold, silver, copper, zinc, iron, lead, tin, and alloys thereof, steel, stainless steel, and aluminum. Examples of metal vapor deposition layers include layers made of one or more of aluminum, aluminum oxide, silica, zinc oxide, and the like.

[0046] The functional coating layer may be an oxygen absorbing layer, an anchor coating layer, a detachment primer layer (for example, a layer containing a compound having an acidic group as described above) provided to facilitate peeling of the ink layer, etc.

[0047] The functional coating layer may be a single layer or a laminate of different types of layers. For example, the functional coating layer may have a layer formed of one of the various coating agents and the metal vapor deposition layer. In this case, the layer formed of one of the various coating agents may be provided via the metal vapor deposition layer in contact with the resin film layer.

[0048] In the removal method of this embodiment, from the viewpoint of easily obtaining better removability, it is preferable that the functional layer is an ink layer, a functional coating layer containing a silicone resin (for example, a layer formed with a silicone-based release agent), or a functional coating layer containing an acrylic resin (for example, an acrylic hard coating layer). Note that the silicone resin refers to a resin having a polysiloxane (or silsesquioxane) as the main skeleton, and the acrylic resin refers to a resin containing a (meth)acrylic acid ester as a monomer unit.

[0049] The functional layer removed by the removal method of this embodiment is preferably provided in contact with a resin film layer, and more preferably in contact with a polyolefin film. Furthermore, as described above, the functional layer removed by the removal method of this embodiment is preferably provided on the outermost surface of the plastic film (i.e., the outermost layer). The plastic film may have functional layers on the outermost surface and between multiple resin film layers, but the removal method of this embodiment is more suitable for removing functional layers provided on the outermost surface of the plastic film. Therefore, the removal method of this embodiment is preferably a method for removing functional layers provided on the outermost surface of a plastic film.

[0050] The plastic film may further have a layer other than the resin film layer and the functional layer (such as a paper layer made of natural paper or synthetic paper).

[0051] The thickness of the plastic film is preferably 5 μm or more and 200 μm or less, more preferably 10 μm or more and 100 μm or less, and even more preferably 10 μm or more and 50 μm or less.

[0052] [Plastic film piece] The plastic film pieces are crushed pieces of the above-mentioned plastic film. Like the above-mentioned plastic film, the plastic film pieces have at least a resin film layer and a functional layer provided on the resin film layer. The plastic film pieces may be crushed pieces of the above-mentioned plastic film, and may be in a state in which at least a part of the edge or the like of the plastic film pieces is partially peeled off.

[0053] The average size Sp of the plastic film pieces is 5 to 100 mm. Here, from the viewpoint of increasing the recovery rate of the treated film pieces and from the viewpoint of being able to more effectively remove the functional layer, the average size Sp of the plastic film pieces is preferably 7 mm or more, and may be 15 mm or more, 30 mm or more, or 40 mm or more. From the viewpoint of being able to more effectively remove the functional layer, the average size Sp of the plastic film pieces is preferably 80 mm or less, and may be 60 mm or less. From the above viewpoints, the average size Sp of the plastic film pieces is preferably 7 to 80 mm, and may be 15 to 60 mm, 30 to 60 mm, or 40 to 60 mm.

[0054] [Crushing method] The method for crushing the plastic film is not particularly limited and can be performed by a known method. Crushing can be performed under dry conditions (e.g., in an air atmosphere without the presence of liquids such as water or cleaning liquid) or wet conditions (e.g., in liquids such as water or cleaning liquid). In the case of dry conditions, a dry crusher can be used. In the case of wet conditions, a wet crusher can be used, which can crush and pump simultaneously. Crushing under dry conditions avoids intentionally mixing liquid into the next step (step (A') or (B)), making it easier to control the concentration and composition of the liquid used in the next step, and ultimately makes it easier to control the removability of the functional layer. Therefore, crushing under dry conditions is preferable. From this perspective, when crushing under wet conditions, it is preferable to perform a drying process on the plastic film pieces after crushing them and before proceeding to the next step (step (A') or (B)). Crushing may be performed in several steps.

[0055] The dry crusher is not particularly limited, and known techniques for crushing solids or shredding films can be applied, such as jaw crushers, impact crushers, cutter mills, stamp mills, ring mills, roller mills, jet mills, hammer mills, colloid mills, rotary cutters, microcolloiders, mass colloiders, ball mills, power mills, pin mills, airflow crushers (jet mills), shear friction crushers, cutter crushers, impact crushers (hammer mills, ball mills), roll crushers, homogenizers, ultrasonic crushers, etc. To prevent the resin film layer or functional layer from softening due to frictional heat during crushing, which could cause the cross sections of the plastic film pieces to fuse together, it is preferable that crushing be performed while the plastic film or crushing device is cooled.

[0056] The wet crusher is not particularly limited, but may be a wet crusher that can simultaneously crush, disperse, mix, and pump solids in a liquid. Specifically, a crusher having a mechanism for crushing solids in a liquid by shear force and / or friction force is preferred, and a crusher having a mechanism for crushing and pumping plastic films in addition to the above mechanism is more preferred. Examples of such wet crushers include wet crushing pumps, colloid mills, attritors, and beaters.

[0057] The wet crushing pump preferably has a mechanism for crushing the solids using fixed and rotating blades while pumping them in a liquid. A more preferred mechanism is one that performs three-stage crushing using a combination of four components: cutting blades, a crushing impeller, a shroud ring, and a grid.

[0058] When using a wet-type crushing pump having the above-mentioned more preferable mechanism, the plastic film is roughly cut by, for example, the cutting blades of the fixed blades and the edge at the inlet of the crushing impeller of the rotary blades, and then stirred and pumped by the axial-flow crushing impeller, with some of the plastic film hitting the blades of the shroud ring of the fixed blades and being cut. The film that passes through the crushing impeller becomes film fragments, which are further crushed and stirred between the grids, pass through the grids, and are pressurized by the pressure impeller and pumped to the next process. The pumping speed at this time is not particularly limited, but may be, for example, 0.03 m 3 The upper limit of the pumping speed is not particularly limited, and may be set to the standard operating speed of the device (for example, 1.4 m / min). 3 / min). The shape of the grid used in the wet pump of the above mechanism is not particularly limited. The diameter of the grid is related to the size of the plastic film pieces, so it is preferably 5 to 100 mm, and taking into consideration the crushing efficiency and the size of the obtained plastic film pieces, it is more preferably 7 to 80 mm.

[0059] Specific examples of wet fracturing pumps include the KD series from Husqvarna Zenoah, the Suncuta series from Nikuni, the Disintegrator series from Furukawa Industrial Machinery Systems, the Incrusher series and Refiner from Aikawa Iron Works, the Scatter from Sanwa Hydrotech, and the Trigonal from Nippon Coke Company.

[0060] A colloid mill is a machine used to reduce particle size in a dispersion where particles are suspended in a liquid. A colloid mill consists of a rotor-stator combination, where the rotor rotates at high speed relative to the fixed stator. Colloid mills are used to reduce particle size in a liquid by the high level of shear generated by the high speed rotation.

[0061] The crushing section of the colloid mill consists of a toothed, truncated cone-shaped rotor and a stator, and the rotor and stator are tapered so that they narrow as they approach the discharge outlet. The laminated film is crushed by repeatedly applying strong shear, compression, and impact in the ring-shaped gap that narrows as it approaches the discharge outlet.

[0062] Specific colloid mills are not particularly limited as long as they are dispersing machines generally called colloid mills, and examples include the Colloid Mill MK series from IKA, the WCM series from Iwaki, the PUC Colloid Mill series from Mountec, and the Cavitron from Eurotech.

[0063] In the wet crusher, water may be used as the liquid, or a cleaning liquid that can be used in the steps (A') and (B) described below may also be used.

[0064] (Process:(A')) In step (A'), the plastic film piece is wetted with a cleaning solution. Here, "wetting" means bringing the plastic film piece into contact with the cleaning solution and bringing it into a wet state.

[0065] By carrying out step (A'), it is possible to swell each layer (particularly the functional layer) constituting the plastic film, thereby improving the removability of the functional layer in step (B). The effect of step (A') in improving the removability of the functional layer is remarkable when the liquid used in step (B) does not contain a cleaning component (for example, when it is water).

[0066] [Cleaning solution] The cleaning solution is a liquid containing a cleaning component, for example, a cleaning solution containing water and a cleaning component (hereinafter referred to as "aqueous cleaning solution"). When the cleaning solution contains water, the operational stability and environmental stability of step (A') can be improved. The cleaning component can be used alone or in appropriate combination of two or more types. The cleaning component can be selected depending on the type of functional layer, and materials known as functional layer stripping components can also be used.

[0067] The cleaning components include, for example, inorganic bases and surfactants.

[0068] -Inorganic bases- Examples of inorganic bases include sodium hydroxide and potassium hydroxide. The inorganic base may be contained in a concentration of 0.1 to 10% by mass, more preferably 0.1 to 5% by mass, based on the total amount of the cleaning solution (e.g., aqueous cleaning solution). The pH of the cleaning solution containing an inorganic base is preferably 10 or higher, and may be 11 or higher or 12 or higher.

[0069] -Surfactants- The surfactant is not particularly limited, and known surfactants can be used. Examples of surfactants include anionic surfactants, nonionic surfactants, amphoteric surfactants, and cationic surfactants. The surfactants can be used alone or in combination of two or more. The amount of surfactant added is preferably 5% by mass or less, and more preferably 2% by mass or less, based on the total amount of the cleaning solution (e.g., aqueous cleaning solution). The lower limit of the amount of surfactant added is not particularly limited. The amount of surfactant added may be 0% by mass, but when a surfactant is used, it is preferably 0.1% by mass or more.

[0070] In one embodiment, a cleaning liquid containing a nonionic surfactant as a cleaning component is preferably used. Examples of nonionic surfactants include polyoxyalkylene alkyl ethers, polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene fatty acid esters, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene sorbitol fatty acid esters, glycerin fatty acid esters, polyoxyethylene glycerin fatty acid esters, polyglycerin fatty acid esters, sucrose fatty acid esters, polyoxyethylene alkylamines, polyoxyethylene fatty acid amides, fatty acid alkylolamides, alkylalkanolamides, acetylene glycol, oxyethylene adducts of acetylene glycol, and polyethylene glycol / polypropylene glycol block copolymers. Of these, polyoxyethylene nonylphenyl ether, polyoxyethylene octylphenyl ether, polyoxyethylene dodecylphenyl ether, polyoxyethylene alkyl ether, polyoxyethylene fatty acid ester, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, fatty acid alkylolamide, acetylene glycol, oxyethylene adduct of acetylene glycol, and polyethylene glycol polypropylene glycol block copolymer are preferably used.

[0071] In one embodiment, an aqueous cleaning liquid containing 50% by mass or more of water and 0.01% by mass to 5% by mass of a polyoxyalkylene alkyl ether surfactant containing at least one compound represented by the following general formula (1) is preferably used. R 1 -O-[CH2-CH(X 1 )-O]n 1 -H (1)

[0072] In general formula (1), R 1 represents a linear or branched alkyl group, an alkenyl group, or an octylphenol group; n 1 represents the average number of moles added, and X 1represents hydrogen or a short-chain alkyl group, where the short-chain alkyl group means an alkyl group having 1 to 7 carbon atoms.

[0073] R in general formula (1) 1 R is preferably a linear or branched alkyl or alkenyl group having 10 or more carbon atoms. The more carbon atoms there are, exceeding 10, the more easily the functional layer can be removed (especially the ink layer). 1 Suitable specific examples of the alkyl group include a decyl group having 10 carbon atoms, a lauryl group having 12 carbon atoms, a tridecyl group having 13 carbon atoms, a myristyl group having 14 carbon atoms, a cetyl group having 16 carbon atoms, an oleyl group having 18 carbon atoms, and a stearyl group.

[0074] The HLB value of the polyoxyalkylene alkyl ether surfactant containing the compound represented by general formula (1) is not particularly limited. The HLB value may be, for example, 12.5 or more, or less than 12.5. The HLB value here refers to a value that represents the degree of affinity of the surfactant for water and oil (a water-insoluble organic compound), and is defined by the Griffin method (HLB value = 20 × sum of formula weights of hydrophilic moieties / molecular weight).

[0075] As the polyoxyalkylene alkyl ether surfactant, commercially available products can be used, such as the Noigen series, DSK NL-Dash series, and DKS-NL series manufactured by Daiichi Kogyo Seiyaku Co., Ltd., the Nonion series manufactured by NOF Corporation, the Emulgen series manufactured by Kao Corporation, and the Leox series, Leocol series, and Lionol series manufactured by Lion Corporation, among which R in the general formula (1) is 1 The compound containing the group represented by the formula (I) may be used.

[0076] Among polyoxyalkylene alkyl ether surfactants, R in general formula (1) 1Examples of products containing compounds in which the number of carbon atoms in the group represented by the formula (I) is 10 or more and having an HLB value of less than 12.5 include Noigen XL-41, Noigen LF-40X, Noigen TDS-30, Noigen TDS-50, Noigen TDS-70, Noigen TDX-50, Noigen SD-30, Noigen SD-60, DKS NL-15, DKS NL-30, DKS NL-40, DKS NL-50, DKS NL-60, DKS NL-70, Noigen ET-83, Noigen ET-102, DSK NL-Dash400, DSK NL-Dash403, DSK NL-Dash404, and DSK NL-Dash405, all of which are manufactured by Daiichi Kogyo Seiyaku Co., Ltd. NL-Dash408, Noigen LP-55, Noigen LP-70, Noigen ET-65, Noigen ET-95, Noigen ET-115, Noigen ET-69, Noigen ET-89, Noigen ET-109, Noigen ET-129, Noigen ET-149, and NOF Corporation products: Nonion K-204, Persoft NK-60, Nonion P-208, Nonion P-210, Nonion E-202, Nonion E-202S, Nonion E-205, Nonion E-205S, Nonion S-202, Nonion S-207, Nonion EH-204, Nonion ID-203, Nonion HT-505, Nonion HT- Examples of such products include 507, Nonion HT-510, and Nonion HT-512 manufactured by Kao Corporation, and Emulgen 102KG, Emulgen 103, Emulgen 104P, Emulgen 105, Emulgen 106, Emulgen 108, Emulgen 210P, Emulgen 404, Emulgen 408, Emulgen 409PV, Emulgen 705, and Emulgen 707 manufactured by Lion Corporation, and Leox CL-30, Leox CL-40, Leox CL-50, Leox CL-60, Leocal NL-30C, Leocal TD-50, Leocal TD-70, Leocal SC-50, and Leocal SC-70.

[0077] Among polyoxyalkylene alkyl ether surfactants, R in general formula (1) 1is a linear or branched alkyl or alkenyl group having 10 or more carbon atoms and having an HLB value of 12.5 or more, for example, Daiichi Kogyo Seiyaku Co., Ltd.'s products include Noigen XL-61, Noigen XL-6190, Noigen XL-70, Noigen XL-80, Noigen XL-100, Noigen XL-140, Noigen XL-160, XL-400D, Noigen XL-1000, and Noigen LF-6 0X, Noigen LF-80X, Noigen LF-100X, Noigen TDS-80, Noigen TDS-100, Noigen TDS-120, Noigen TDS-200D, Noigen TDS-500F, Noigen TDX-80, Noigen TDX-80D, Noigen TDX-100D, Noigen TDX-120D, Noigen SD-70, Noigen SD-80, Noigen SD-110, Noigen SD-150, DKS NL-80, DKS NL-90, DKS NL-100, DKS NL-110, DKS NL-180, DKS NL-250, DKS NL-450F, DKS NL-600F, Noigen ET-160, Noigen ET-170, Noigen ET-190, DSK Dash410, Noigen LP-80, Noigen LP-100, Noigen LP-180, Noigen ET-135, Noigen ET-165, Noigen ET-159, Noigen ET-189, and NOF Corporation products: Nonion K-220, Nonion K-230, Nonion K-2100W, Persoft NH-90C, Persoft NK-100, Persoft NK-100C, Nonion P-210, Nonion P-213, Nonion E-212, Nonion E-215, Nonion E-230, Nonion S-215, Nonion S-220, Nonion B-250, Nonion ID-20 6. Nonion ID-209, Dispanol TOC, Nonion HT-515, Nonion HT-518, and Kao Corporation products include Emulgen 109P, Emulgen 110, Emulgen 120, Emulgen 123P, Emulgen 130K, Emulgen 147, Emulgen 150, Emulgen 220, Emulgen 320P, Emulgen 350, Emulgen 420, Emulgen 430, Emulgen 709, Emulgen 1108, Emulgen 1118S-70, Emulgen 1135S-70, Emulgen 1150S-60, Emulgen 4085, and Emulgen 2020G-HA.Examples of such products include Emulgen 2025G, and Lion Corporation's products include Rheox CL-90, Rheox CL-230, Rheocal TD-90, Rheocal TD-90D, Rheocal TDA-90-25, Rheocal TDN-90-80, Rheocal TD-120, Rheocal TD-200, Rheocal TDA-400-75, Rheocal SC-80, Rheocal SC-90, Rheocal SC-120, Rheocal SC-150, Rheocal SC-200, Rheocal SC-300, and Rheocal SC-400, and Nikko Chemicals' products include NIKKOL BL-2, NIKKOL BL-4.2, NIKKOL BL-9EX, NIKKOL BL-21, and NIKKOL BL-25.

[0078] Among the compounds represented by general formula (1), R 1 The compound in which is an octylphenol group is preferably octylphenol ethoxylate. Examples of products containing octylphenol ethoxylate include the TRITON (registered trademark) series from Dow Chemical Company, the Igepal CA series from Rhodia, the Nonidet P series from Shell Chemicals, and the Nikkol OP series from Nikko Chemicals.

[0079] In one embodiment, a cleaning solution containing an amphoteric surfactant as a cleaning component is preferably used. The amphoteric surfactant is preferably a betaine-type amphoteric surfactant, and more preferably, for example, an amphoteric surfactant having an alkylcarboxybetaine skeleton or an alkylamidocarboxybetaine skeleton containing at least one compound represented by the following general formula (2a): R 1 -R 2 -N + (CH3)2CH2COO - (2a)

[0080] In general formula (2a), R 1 is hydrogen or C(=O)R 3 -NH-(R 3 represents a linear or branched alkyl or alkenyl group, and R 2represents an alkylene group or an alkenylene group. 1 preferably represents a hydrogen atom.

[0081] The compound represented by general formula (2a) is preferably an amphoteric surfactant having an alkylcarboxybetaine skeleton represented by the following general formula (2a-1). C n H 2n+1 N + (CH3)2CH2COO - (2a-1)

[0082] In the general formula (2a-1), n ​​represents the average number of moles added, and is preferably 8 or more, more preferably 10 or more, and even more preferably 11 or more.

[0083] Specific examples of products corresponding to the amphoteric surfactant containing the compound represented by general formula (2a) include Nissan Anon BDF (registered trademark)-R, Nissan Anon BDF (registered trademark)-SF, Nissan Anon BDC-SF, and Nissan Anon BDL-SF manufactured by NOF Corporation; Amogen CB-H and Amogen HB-C manufactured by Daiichi Kogyo Seiyaku Co., Ltd.; Rekabion B-200 and Rekabion B-300 manufactured by New Japan Chemical Co., Ltd.; and Obazolin CAB-30 and Obazolin ISAB manufactured by Toho Chemical Industry Co., Ltd. Specific examples of amphoteric surfactants containing the compound represented by general formula (2a-1) include Amogene S, Amogene SH, and Amogene K manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.; Amphitol 20BS, Amphitol 24B, and Amphitol 86B manufactured by Kao Corporation; Nissan Anon BF, Nissan Anon BL, and Nissan Anon BL-SF manufactured by NOF Corporation; Rekabion A-100, Rekabion A-200, and Rekabion A-700 manufactured by New Japan Chemical Co., Ltd.; and Obazolin LB and Obazolin LB-SF manufactured by Toho Chemical Co., Ltd.

[0084] As the betaine type amphoteric surfactant, an amphoteric surfactant having an imidazolinium betaine skeleton can also be used.Specific products corresponding to the amphoteric surfactant having an imidazolinium betaine skeleton include, for example, Nissan Anon GLM-R and Nissan Anon GLM-R-LV manufactured by NOF Corporation, and Amphitol 20Y-B manufactured by Kao Corporation.

[0085] The amphoteric surfactant may be a surfactant represented by the following general formula (2b): R 4 -(NHC2H4) nb -N(R 5 )2(2b)

[0086] In general formula (2b), R 4 represents a linear or branched alkyl or alkenyl group, nb represents an integer of 0 to 5, and R 5 represents hydrogen, -CH2COONa or -CH2COOH, but there are two R 5 may be the same or different, and at least one R 5 represents -CH2COONa. In the general formula (2b), R 4 preferably represents a linear alkyl group, and R 4 The number of carbon atoms is preferably 8 or more, more preferably 10 or more, and even more preferably 12 or more.

[0087] Specific examples of amphoteric surfactants containing the compound represented by general formula (2b) include Nissan Anon LG-R and Nissan Anon LA, manufactured by NOF Corporation.

[0088] The amphoteric surfactant may be an amine oxide surfactant represented by the following general formula (2c). R 6 -N + (CH3)2O - (2c)

[0089] In general formula (2c), R 6represents a linear or branched alkyl or alkenyl group. 6 Preferably, R represents a linear alkyl group. 6 The group represented by the formula (I) preferably has 8 or more carbon atoms, more preferably 10 or more carbon atoms, and even more preferably 12 or more carbon atoms.

[0090] Specific examples of amphoteric surfactants containing the compound represented by general formula (2c) include Amogene AOL manufactured by Daiichi Kogyo Seiyaku Co., Ltd. and Amphitol 20N manufactured by Kao Corporation.

[0091] In one embodiment, a cleaning liquid containing a cationic surfactant as a cleaning component is preferably used. The cationic surfactant is preferably a cationic surfactant having a quaternary ammonium skeleton, and more preferably, for example, a cationic surfactant having a quaternary ammonium skeleton containing at least one compound represented by the following general formula (3a): R 1 -N + (R 2 R 3 )-R 4 (3a)

[0092] In general formula (3a), R 1 represents a straight-chain or branched-chain alkyl group or a straight-chain or branched-chain alkenyl group, and -CH2- in the alkyl or alkenyl group may be substituted with -C(=O)-, -NH-, or -C(=O)-NH-. R 2 and R 3 represents a hydrogen atom, a linear or branched alkyl group, or a linear or branched alkenyl group, and -CH2- in the alkyl or alkenyl group may be replaced by -O-. R 4 represents a hydrogen atom, a linear or branched alkyl group, a linear or branched alkenyl group, or a phenyl group, and the terminal —CH3 in the alkyl or alkenyl group may be substituted with a carboxy group or a phenyl group.

[0093] In general formula (3a), R 1is preferably a long-chain alkyl or alkenyl group in order to further enhance the removability of the functional layer (especially the ink layer). 1 is preferably an alkyl or alkenyl group having 8 to 30 carbon atoms, more preferably an alkyl group having 10 to 25 carbon atoms, and even more preferably an alkyl or alkenyl group having 12 to 22 carbon atoms. The alkyl or alkenyl group may be linear or branched, but is preferably linear. 1 is more preferably a straight-chain alkyl group.

[0094] In general formula (3a), R 1 At least one -CH2- in the alkyl group or alkenyl group represented by the formula (I) may be substituted with -C(=O)-, -NH-, or -C(=O)-NH-. Among these, it is preferred that at least one -CH2- in the alkyl group or alkenyl group is substituted with -C(=O)-NH- or -NH-C(=O), and it is preferred that one -CH2- in the alkyl group is substituted with -C(=O)-NH- or -NH-C(=O), and R 1 It is more preferable that the aryl group has an amidopropyl skeleton therein.

[0095] In general formula (3a), R 2 and R 3 is preferably a linear or branched alkyl group or a linear or branched alkenyl group, more preferably a linear or branched alkyl group, even more preferably a linear alkyl group having 1 to 3 carbon atoms, and particularly preferably a methyl group.

[0096] In general formula (3a), R 4 is preferably a linear or branched alkyl group, a linear or branched alkenyl group, or a phenyl group, and more preferably a linear or branched alkyl group. The terminal —CH3 in the alkyl or alkenyl group is preferably substituted with a carboxy group or a phenyl group.

[0097] In general formula (3a), R4 The number of carbon atoms in the alkyl group is preferably 1 to 8, more preferably 1 to 5, even more preferably 1 to 3, and particularly preferably 1 or 2.

[0098] In general formula (3a), R 4 When represents a methyl group, R 2 and R 3 Preferably, R also represents a methyl group, and general formula (3a) represents an alkyltrimethylammonium skeleton. 4 When R represents an ethyl group, the terminal —CH3 in the ethyl group is preferably substituted with a carboxy group or a phenyl group. 4 Preferably, represents —CH—(C(═O)OH or represents a benzyl group.

[0099] The compound represented by general formula (3a) is preferably a cationic surfactant containing a compound with a quaternary ammonium skeleton represented by the following general formula (3a-1). C n H 2n+1 N + (CH3)2R 4 (3a-1)

[0100] In the general formula (3a-1), n ​​represents the average number of moles added, and R 4 is R in general formula (3a) 4 It has the same meaning as R 4 The preferred groups are the same as those in formula (3a).

[0101] In the general formula (3a-1), the average number of moles added represented by n is preferably 8 or more. As the average number of moles added represented by n exceeds 8 and increases, the removability of the functional layer (particularly the ink layer) tends to increase. n H 2n+1Specific examples of the group represented by the formula include an octyl group having 8 carbon atoms, a nonyl group having 9 carbon atoms, a decyl group having 10 carbon atoms, an undecyl group having 11 carbon atoms, a lauryl group having 12 carbon atoms, a tridecyl group having 13 carbon atoms, a myristyl group having 14 carbon atoms, a pentadecyl group having 15 carbon atoms, a cetyl group having 16 carbon atoms, and an oleyl group and a stearyl group having 18 carbon atoms.

[0102] The compound having a quaternary ammonium skeleton is preferably a quaternary ammonium skeleton salt type that forms a salt with a halogen, from the viewpoint of enhancing the removability of the functional layer (especially the ink layer). - , Br - or I - It is more preferable that the compound is a quaternary ammonium skeleton salt type that forms a salt with a halogen atom. Among these, alkyltrimethylammonium halide type, dialkyldimethylammonium halide type, and alkylbenzalkonium halide type compounds are preferred, and alkyltrimethylammonium chloride type, dialkyldimethylammonium chloride type, and alkylbenzalkonium chloride type compounds are more preferred. The quaternary ammonium skeleton salt that forms a salt with the halogen atom promotes hydrolysis of the functional layer (particularly the ink layer) due to the nucleophilic action of the halogen atom, and is therefore thought to contribute to improving the removability of the functional layer (particularly the ink layer).

[0103] Specific products corresponding to the cationic surfactant containing the compound represented by general formula (3a) (including the compound represented by general formula (3a-1)) include, for example, Nissan Cation MA, Nissan Cation SA, Nissan Cation BB, Nissan Cation FB, Nissan Cation PB-300, Nissan Cation ABT2-500, Nissan Cation AB, Nissan Cation AB-600, Nissan Cation VB-M Flake, Nissan Cation VB-F, Nissan Cation 2-DB-500E, Nissan Cation 2-DB-800E, Nissan Cation 2ABT, Nissan Cation 2-OLR, Nissan Cation F2-50R, and Nissan Cation M2-100R manufactured by NOF Corporation; Catiogen TML, Catiogen TMP, Catiogen TMS, Catiogen DDM-PG, Catiogen BC-50, and Catiogen TBB manufactured by Daiichi Kogyo Co., Ltd.; and Coatamine 24P and Coatamine 24P manufactured by Kao Corporation. Examples include Min 86P Concentrate, Cortamin 60W, Cortamin 86W, Sanizol C, and Sanizol B-50. Lion products include Lipoguard C-50, Lipoguard T-28, Lipoguard T-30, Lipoguard T-50, Lipoguard T-800, Lipoguard 16-29, Lipoguard 16-50E, Lipoguard 18-63, Lipoguard 22-80, Lipoguard CB-50, Lipoguard 210-80E, Lipoguard 2C-75, Lipoguard 2HP-75, and Lipoguard 2HP-80. Examples include Guard 2HP flakes, Lipoguard 2HT-75, Lipoguard 2HT flakes, Lipoguard 20-75l, Lipoguard 41-50, TMAC-50, TPAH-40, TBAB-50A, TBAB-100A, TBAH-40, Lipoguard PH-100, BTMAC-50, BTMAC-100A, BTEAC-50, BTEAC-100A, BTBAC-50A, and the like. Examples of products manufactured by Toho Chemical Industry Co., Ltd. include Catinal SPC-20V-S.

[0104] The cationic surfactant preferably contains at least one compound having a primary or secondary alkanolamine skeleton, and more preferably contains at least one compound having a monoalkanolamine skeleton (monoalkanolamine compound).

[0105] As the primary monoalkanolamine, a lower alkanol having 1 to 4 carbon atoms is preferred. Specific examples include monoethanolamine, 2-aminoisobutanol, etc. As the secondary monoalkanolamine, for example, N-methylethanolamine, 2-ethylaminoethanol, isopropanolamine, etc. These monoalkanolamine compounds can be used alone or in appropriate combination of two or more, and can also be used by mixing with water. These monoalkanolamine compounds are preferably in the form of monoalkanolamine salts formed with halogens, and Cl is a preferred example. - It is preferable to form a salt with

[0106] In one embodiment, the cleaning liquid preferably contains an inorganic base and a surfactant, and more preferably is an aqueous cleaning liquid containing water.

[0107] In one embodiment, the cleaning solution may contain, as a cleaning component, an organic solvent such as a water-soluble or water-insoluble alcohol, a water-soluble or water-insoluble glycol ether-based organic solvent, or a water-soluble monoalkanolamine-based organic solvent. The organic solvent may include compounds that fall under the category of surfactants, and such compounds are considered to be included in the cleaning solution as surfactants and organic solvents. When the cleaning solution contains an organic solvent, the cleaning solution does not necessarily need to contain water; however, from the viewpoint of improving the operational stability and environmental stability of step (A'), it is preferable that the cleaning solution contain water.

[0108] - Non-water-soluble alcohols - Examples of water-insoluble alcohols include water-insoluble primary alcohols, which are preferably contained in an amount of 20% by mass or less relative to the amount of water.

[0109] Examples of water-insoluble primary alcohols include butan-1-ol, pentan-1-ol, hexane-1-ol, heptan-1-ol, octan-1-ol, nonan-1-ol, decan-1-ol, undecane-1-ol, dodecane-1-ol, tridecane-1-ol, tetradecane-1-ol, pentadecan-1-ol, hexadecan-1-ol, heptadecane-1-ol, and octadecane-1-ol. 1-ol, nonadecane-1-ol, icosan-1-ol, heneicosan-1-ol, docosan-1-ol, tricosan-1-ol, tetracosan-1-ol, pentacosan-1-ol, hexacosan-1-ol, heptacosan-1-ol, octacosan-1-ol, nonacosan-1-ol, triacontan-1-ol, policosanol, 2-methylpropan-1-ol, benzyl alcohol, etc. Among these, butan-1-ol and benzyl alcohol are preferred.

[0110] -Water-soluble alcohols- Examples of water-soluble alcohols include alcohols specified in the Fire Service Act. Specific examples of water-soluble alcohols include methanol, ethanol, 1-propyl alcohol, and 2-propyl alcohol, and any mixture of these may also be used as industrial alcohols. The water-soluble alcohol is preferably a water-soluble primary alcohol. The water-soluble alcohol is preferably contained in an amount of 20% by mass or more relative to the amount of water.

[0111] -Non-water-soluble glycol ether organic solvent- Examples of water-insoluble glycol ether organic solvents include water-insoluble aromatic glycol ether solvents and water-insoluble ester glycol ether solvents. Examples of water-insoluble aromatic glycol ether solvents include ethylene glycol monophenyl ether (phenoxyethanol), ethylene glycol monobenzyl ether, ethylene glycol dibenzyl ether, diethylene glycol monophenyl ether, diethylene glycol diphenyl ether, and propylene glycol monophenyl ether. Examples of water-insoluble ester glycol ether solvents include ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, ethylene glycol mono-n-butyl ether acetate, diethylene glycol monoethyl ether acetate, propylene glycol monomethyl ether acetate, and dipropylene glycol monomethyl ether acetate. Among these, ethylene glycol monophenyl ether (phenoxyethanol) is preferred. The water-insoluble glycol ether organic solvent is preferably contained in an amount of 20% by mass or less relative to the water.

[0112] -Water-soluble glycol ether organic solvent- Examples of water-soluble glycol ether organic solvents include water-soluble alkylene glycol alkyl ether solvents, which are preferably contained in an amount of 20% by mass or more relative to the amount of water.

[0113] As the water-soluble alkylene glycol alkyl ether solvent, a compound represented by the following general formula (4) (water-soluble alkylene glycol alkyl ether) is preferably used. R 1 -O-[CH2-CH(X)-O] n1 -R 2 (4)

[0114] In general formula (4), R 1 represents an alkyl group having one or more carbon atoms, and R 2represents an alkyl group having one or more carbon atoms or hydrogen, n1 represents an integer of 1 to 3, and X represents hydrogen or a methyl group.

[0115] Examples of compounds represented by general formula (4) include ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dipropyl ether, ethylene glycol methyl ethyl ether, ethylene glycol methyl propyl ether, ethylene glycol ethyl propyl ether, ethylene glycol monobutyl ether, ethylene glycol-tert-butyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monobutyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dipropyl ether, diethylene glycol methyl ethyl ether, diethylene glycol methyl propyl ether, diethylene glycol ethyl propyl ether, triethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, propylene glycol dimethyl ether, propylene glycol diethyl ether, etc. These compounds can be used alone or in appropriate combinations of two or more, and can also be used by mixing with water.

[0116] The content of the compound represented by general formula (4) in the cleaning solution may be 20% by mass or more, and when water is used as the medium, it is preferably 30% by mass or more, and more preferably 40% by mass or more. On the other hand, the upper limit of the content may be 100% by mass, but it is preferable to use water as the medium from the viewpoint of environmental impact and safety.

[0117] Among the compounds represented by general formula (4), the compound represented by the following general formula (5) (water-soluble alkylene glycol monoalkyl ether) is more preferred. R 2 -O-[CH2-CH(X)-O] n2 -H (5)

[0118] In general formula (5), R 2 represents an alkyl group having one or more carbon atoms, n2 represents an integer of 1 to 3, and X represents hydrogen or a methyl group.

[0119] Examples of the compound represented by general formula (5) include ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monobutyl ether, ethylene glycol-tert-butyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monobutyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, and propylene glycol monobutyl ether.

[0120] Furthermore, when the content of water in the aqueous cleaning solution is much more than 50 mass %, the water-soluble alkylene glycol monoalkyl ether represented by R 2It is preferable to use a compound in which n is an alkyl group having 3 or more carbon atoms, n2 is 1 to 3, and X is hydrogen or a methyl group. Examples of such compounds include ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, ethylene glycol tert-butyl ether, diethylene glycol monopropyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, propylene glycol monopropyl ether, and propylene glycol monobutyl ether. These compounds can be used alone or in appropriate combinations of two or more, and can also be used by mixing with water. Among these, diethylene glycol monobutyl ether, ethylene glycol mono-tert-butyl ether, and propylene glycol monopropyl ether are particularly preferred from the viewpoints of environmental friendliness, flammability, and antifoaming properties.

[0121] -Water-soluble monoalkanolamine organic solvent- As the water-soluble alkanolamine organic solvent, primary or secondary monoalkanolamine compounds are preferably used. Examples of primary monoalkanolamine compounds include monoethanolamine, 2-aminoisobutanol, and isopropanolamine. Examples of secondary monoalkanolamine compounds include N-methylethanolamine, 2-ethylaminoethanol, and dimethylaminoethanol. The boiling point of these monoalkanolamine compounds is preferably 150 to 200°C. These monoalkanolamine compounds can be used alone or in appropriate combinations of two or more, and can also be mixed with water for use.

[0122] The water-soluble alkanolamine organic solvent is preferably contained in an amount of 20% by mass or more relative to the water. Primary or secondary monoalkanolamines having a boiling point of 150 to 200°C can be contained in an amount of 10 to 50% by mass relative to the total amount of the cleaning liquid.

[0123] The cleaning component may also be a water-soluble solvent with a flash point of 21° C. or higher. The water-soluble solvent with a flash point of 21° C. or higher is preferably a water-soluble solvent among organic solvents that fall under the second and third petroleum categories defined in the Fire Service Act, and preferred examples include diethylene glycol butyl ether, propylene glycol propyl ether, and 3-methoxy-3-methyl-1-butanol.

[0124] The cleaning solution preferably contains a water-soluble solvent among the above organic solvents. From the viewpoint of improving the removability of the functional layer, the content of the water-soluble solvent is preferably 30% by mass or more, and may be 40% by mass or more, 50% by mass or more, 60% by mass or more, 70% by mass or more, 80% by mass or more, 90% by mass or more, or 95% by mass or more, based on the total amount of the cleaning solution (e.g., aqueous cleaning solution).

[0125] In one embodiment, the cleaning solution preferably contains an inorganic base and an organic solvent, more preferably an inorganic base and a water-soluble solvent. When the cleaning solution contains a water-soluble solvent in addition to the inorganic base, the hydroxide ions generated from the inorganic base are less likely to be hydrated, increasing the nucleophilicity of the hydroxide ions and allowing the functional layer (particularly the ink layer) to be more easily separated (peeled off) from the plastic film piece in a hydrophobic environment.

[0126] Since sodium hydroxide is poorly soluble in organic solvents, it is preferable to use a cationic surfactant in combination with sodium hydroxide and an organic solvent. The cleaning liquid containing sodium hydroxide, an organic solvent, and a cationic surfactant may be, for example, a cleaning liquid containing sodium hydroxide, a cationic surfactant, a water-insoluble aromatic glycol ether solvent, and a water-soluble alcohol or water-soluble alkanolamine solvent.

[0127] Since potassium hydroxide is readily soluble in organic solvents, it is not necessary to use a cationic surfactant in combination with potassium hydroxide. The cleaning solution containing potassium hydroxide and an organic solvent may be, for example, a cleaning solution containing potassium hydroxide and a water-soluble alcohol or an aromatic glycol ether solvent.

[0128] In one embodiment, the cleaning liquid may contain an antifoaming agent. Antifoaming agents are usually used together with water. As the antifoaming agent, a water-soluble organic solvent, a nonionic surfactant having an HLB value in the range of 1 to 3, or the like may be used, or a silicone-based compound may also be used. In terms of high antifoaming ability, silicone-based compounds are preferred, and among them, emulsion-type or self-emulsifying silicone-based compounds are more preferred. These antifoaming agents may be used alone or in combination of two or more types.

[0129] Specific examples of self-emulsifying defoaming agents include X-50-1176, KS-530, and KS-537 manufactured by Shin-Etsu Chemical Co., Ltd. Specific examples of emulsion-type defoaming agents include KM-7750D, KM-7752, and KM-98 manufactured by Shin-Etsu Chemical Co., Ltd., and FS Antifoam 025, FS Antifoam 80, FS Antifoam 92, FS Antifoam 93, DKQ1-1183, and DKQ1-1247 manufactured by Nagase Chemspec Corporation, but are not limited to these.

[0130] The content of the antifoaming agent may be, for example, 0.01 to 5 mass %, 0.02 to 4 mass %, or 0.03 to 3 mass %, based on the total amount of the cleaning liquid (for example, aqueous cleaning liquid).

[0131] [Wet conditions] Methods for wetting a plastic film piece with a cleaning solution include, for example, immersing the plastic film piece in the cleaning solution, applying the cleaning solution to the plastic film piece using a spray, brush, roller, etc., and dripping the cleaning solution onto the plastic film piece.

[0132] When step (A') involves immersing the plastic film pieces in a cleaning solution, the immersion can be performed in a stationary state. However, stirring the cleaning solution and the plastic film pieces simultaneously during immersion allows the plastic film pieces to swell more efficiently. The stirring speed is preferably maintained at a level that minimizes foaming without the addition of an antifoaming agent. The stirring device and stirring method are not particularly limited, and known devices and methods can be used. Usable devices include, for example, devices equipped with a motor equipped with stirring blades that can stir the cleaning solution in a container, devices equipped with an ultrasonic generator, devices capable of shaking the entire container, and wet crushers. Devices that mix the contents using a rotating mechanism, such as a mixing tank with a stirring shaft, a planetary mixer, a Henschel mixer, a continuous kneader, an extruder, a screw feeder, a Ribocone, a Nauta mixer, and a PV mixer, as well as devices that mix the contents by rotating the tank itself, such as a ball mill, a pot mill, an FV dryer, a conical dryer, and a tumbler, can also be used. As the wet crusher, the same crushers as those exemplified in the above step (A) can be used. A known stirring device such as a homodisper can also be used.

[0133] The temperature (liquid temperature) of the cleaning liquid used in step (A') is not particularly limited as long as it can maintain the cleaning liquid in a liquid state, but is preferably 15 to 90°C. From the perspective of reducing CO2 emissions without the need for heating, it is preferable to set the liquid temperature at room temperature (e.g., 15 to 35°C). On the other hand, when prioritizing efficiency as a practical recycling system, a method of shortening the time (wetting time) for contacting the cleaning liquid with the plastic film pieces while heating the cleaning liquid is also preferred. When using an aqueous cleaning liquid in which a surfactant or the like is added to water, it is preferable to adjust the liquid temperature depending on the type of surfactant. The optimal temperature varies depending on the type of surfactant, but is usually preferably 40°C or higher (e.g., 40 to 90°C), and may be 50°C or higher or 60°C or higher.

[0134] The time (wetting time) for which the plastic film pieces are brought into contact with the cleaning solution in step (A') is preferably the time required for the treatment solution to reduce the adhesion between the functional layer and the resin film layer, and is preferably 10 seconds or more (for example, 10 seconds to 48 hours). When step (A') is a step of immersing the plastic film pieces in the cleaning solution, the wetting time (immersion time) can be appropriately adjusted by combining the liquid temperature and agitation. The higher the liquid temperature, the shorter the wetting (immersion time) will be, and the more the plastic film pieces will swell sufficiently.

[0135] In the above step (A'), the type of cleaning liquid can be changed depending on the type of coating agent that forms the functional layer, thereby enabling the functional layer to be removed more effectively.

[0136] For example, when the functional layer is a functional coating layer containing a silicone resin, the use of an alkaline cleaning solution can cause solvolysis of the resin skeleton, thereby promoting separation (peeling) of the functional layer from the plastic film piece. Examples of alkaline cleaning solutions include liquids composed of an alkaline compound, a solvent or dispersion medium that exhibits its alkalinity, a compatibilizer, etc. (for example, a cleaning solution containing the above-mentioned inorganic base, etc.).

[0137] Furthermore, for example, when the functional layer is the above-mentioned metal layer, it is effective to remove the functional layer by utilizing an acid-base reaction between the metal and an acid or alkali. By immersing a plastic film piece in an aqueous solution containing an acid or alkaline substance, not only is the metal layer removed from the side of the metal layer that is not in contact with the resin film layer, but the acid or alkaline substance acts on the interface between the metal layer and the resin film layer, causing the metal layer to separate (peeling off). This reduces the adhesion between the metal layer and the resin film layer, making it possible to more effectively remove the functional layer in step (B). To ensure that the acid or alkaline substance acts efficiently on the interface, it is preferable to use a compound that acts as a phase transfer catalyst, so that the acid or alkaline substance can easily reach the interface via the resin film layer.

[0138] When the functional layer is formed from a non-curable composition, the functional layer can be dissolved in a solvent, and therefore the effect of improving the removability of the functional layer by the above step (A') can be easily obtained.

[0139] (Process:(B)) In step (B), the functional layer is removed from the plastic film pieces by a wet crushing process in which the plastic film pieces are crushed in the presence of a liquid while being stirred (for example, with the plastic film pieces accompanied by a liquid).

[0140] The plastic film pieces are plastic film pieces having an average size Sp of 5 to 100 mm, which are prepared in the above step (A) or obtained through the above step (A').

[0141] The liquid is, for example, water or a cleaning liquid. The cleaning liquid may be a cleaning liquid containing the cleaning components exemplified in step (A'), and preferred examples of the cleaning liquid are the same as the preferred examples of the cleaning liquid shown in step (A'). From the viewpoint of suppressing deterioration of the equipment (corrosion, etc.), the pH of the liquid is preferably 12.0 or less, more preferably 8.0 or less, and even more preferably water. When step (A') is not performed, using a cleaning liquid as the liquid tends to enable better removal of the functional layer.

[0142] Wet crushing can be carried out using known devices and methods. Specific devices include a device equipped with a motor with stirring blades that can stir the cleaning solution in a container, a device equipped with a device that generates ultrasound, a device that can shake the entire container, and the wet crushers exemplified in step (A). Specific examples include the KD series from Husqvarna Zenoah, the Suncutter series from Nikuni, the Disintegrator series from Furukawa Industrial Machinery Systems, the Ink Crusher series and Refiner from Aikawa Iron Works, the Scatter from Sanwa Hydrotech, the Trigonal from Nippon Coke Company, and the alkali cleaning / cleaning deinking equipment and cleaning crusher Scissors Cutter series from Nippon Seam.

[0143] As described above, the wet crushing treatment is carried out so that the ratio (Sa / Sp) of the average size of the film pieces before and after the wet crushing treatment is 0.8 or less. From the viewpoint of more effectively removing the functional layer, the ratio (Sa / Sp) is preferably 0.7 or less, more preferably 0.3 or less, and even more preferably 0.2 or less. From the viewpoint of easily increasing the size of the plastic film after wet crushing and easily increasing the recovery efficiency, the ratio (Sa / Sp) is preferably 0.007 or more, more preferably 0.1 or more. From the above viewpoints, the ratio (Sa / Sp) is preferably 0.007 to 0.8, more preferably 0.1 to 0.3, and even more preferably 0.1 to 0.2. The ratio (Sa / Sp) can be changed by adjusting the size of the plastic film pieces and the conditions of the wet crushing treatment (for example, the clearance and shear rate described below).

[0144] The average size Sa of the processed film pieces obtained by wet crushing may be, for example, 0.3 to 65 mm. From the viewpoint of recoverability, it is preferable that the average size Sa of the processed film pieces is 1 mm or more. The method for measuring the average size Sa of the processed film pieces is the same as the method for measuring the average size of the plastic film pieces described above.

[0145] Step (B) includes, for example, (B-1) supplying plastic film pieces and a liquid to a processing space, (B-2) performing a wet crushing process in the processing space, and (B-3) discharging the processed film pieces and the liquid from the processing space. In step (B-1), the plastic film pieces and the liquid may be supplied to the processing space approximately simultaneously. Specifically, for example, the plastic film pieces may be accompanied by a liquid when being supplied to the processing space. From the viewpoint of more effective removal of the functional layer, it is preferable that the ratio (V2 / V1) of the volume V2 of the liquid to the volume V1 of the plastic film pieces supplied to the processing space be 0.43 to 99. When the ratio (V2 / V1) is 0.43 or more, reattachment of the functional layer separated (peeled) from the plastic film pieces is unlikely to occur. When the ratio (V2 / V1) is 99 or less, separation (peeling) of the functional layer due to friction between the films is likely to proceed. From the viewpoint of more effective removal of the functional layer, the ratio (V2 / V1) is preferably 0.7 or more and 90 or less, and may be 1.5 or more or 10 or more, or 70 or less or 50 or less, or may be 1.5 to 70 or 10 to 50. When steps (B-1) to (B-3) are performed continuously in parallel, the ratio (V2 / V1) may be calculated from the volume of plastic film pieces supplied to the treatment space per unit time and the volume of liquid supplied to the treatment space per unit time. The volume of the plastic film pieces can be calculated by Archimedes' method.

[0146] Step (B) preferably includes a step of passing the plastic film pieces through a clearance of 30 mm or less. This step is carried out, for example, in the processing space described above. In this step, the plastic film pieces are crushed by passing through the clearance while carrying a liquid. The clearance is more preferably 20 mm or less, and even more preferably 10 mm or less. By passing the plastic film pieces through a clearance of 10 mm or less, a high shear force can be applied to the plastic film pieces. Therefore, by setting the clearance to 10 mm or less, it is possible to, for example, scrape off the functional layer from a plastic film on which the functional layer is exposed (such as a front-printed plastic film) or apply shear stress to a plastic film on which the functional layer is provided between multiple films (such as a reverse-printed film), thereby enabling more effective removal of the functional layer.

[0147] When a wet crusher has a crushing mechanism using fixed blades and rotating blades, the clearance can be easily controlled by adjusting the operating conditions. The narrower the clearance, the higher the shear force that can be applied to the plastic film pieces. On the other hand, the narrower the clearance, the more likely it is that the plastic film pieces will clog and the faster the temperature of the liquid (water, cleaning solution, etc.) will rise. Therefore, a clearance of 0.1 mm or more is preferable.

[0148] Methods for providing a clearance of a predetermined size for the plastic film pieces to pass through include, for example, controlling the size gap between the inner wall of the tank of the processing tank in which the plastic film pieces are stirred and the stirring blade to a predetermined size or less, installing a baffle plate at a distance of a predetermined size or less from the tank wall, designing the screen so that the plastic film pieces pass through with holes of a diameter of a predetermined size or less, passing the plastic film pieces between two rolls with a gap of a predetermined size or less, sandwiching the plastic film pieces between a ball mill or the like and causing the media to collide with each other, providing a fixed blade on the outside of the rotating blade like in a homogenizer and controlling the gap between the rotating blade and the fixed blade to a predetermined size or less, and the like.

[0149] In the wet processing step (B), a piece of plastic film is dried for 2000 s. -1 This step may include passing the plastic film piece through a clearance of 30 mm or less. That is, the step (B) may include shearing the plastic film piece at a shear rate of 2000 s -1 The method may include a step of passing the plastic film piece through a clearance of 30 mm or less so that the shear rate is 300 s or less. The higher the shear rate, the greater the effect of scraping off the functional layer from the plastic film piece and the effect of applying shear stress to the plastic film piece. The upper limit of the shear rate is not particularly limited, but may be, for example, 500,000 s -1 It may be.

[0150] The shear rate (D) here is defined, for example, by the following formula: D=v / Δy v: flow velocity (m / s), calculated as v = π × R × (n / 60) π: Pi R: diameter of the rotary blade (m) n: Rotary blade rotation speed (rpm) Δy: Clearance (m), here referring to the gap (m) between the rotary blade and the fixed blade.

[0151] The larger the diameter of the fixed blade of the wet crusher, the higher the flow rate, so the larger the fixed blade size of the wet crusher is, and the narrower the clearance, the higher the shear rate is, so the narrower the clearance is, and the narrower the clearance is, the better.

[0152] The blade design of the fixed blade and rotary blade is preferably such that at least some of the blades are arranged in a radial direction. The blades arranged in a radial direction are preferably inclined at an angle of 2 to 60 degrees, more preferably 5 to 45 degrees, from the radial direction.

[0153] When multiple blades are arranged in parallel on the rotary blade, the blade width of the rotary blade is preferably 0.5 to 5.0 mm, the groove width between the blades is preferably 0.5 to 5.0 mm, and the blade height is preferably 1.0 to 5.0 mm.

[0154] The Froude number (Fr) of stirring in step (B) is preferably 10 or more. The faster the Froude number of stirring, the greater the effect of scraping the ink layer off the plastic film piece and the greater the effect of applying shear stress to the plastic film piece. The upper limit of the Froude number of stirring (Fr) is not particularly limited, but may be, for example, 16.

[0155] The Froude number (Fr) of stirring is defined by the following formula: Fr={(n / 60) 2}×R / g n: Rotary blade rotation speed (rpm) R: diameter of the rotary blade (m) g:Gravity acceleration=9.8(m / s 2 )

[0156] The removal method of the above embodiment may include the following steps (C) to (F) in addition to the above steps (A), (A') and (B). (C) A step of collecting the processed film pieces obtained in step (B). (D) A process for washing the processed film pieces collected in (C). (E) A step of drying the processed film pieces washed in step (D). (F) A step of recovering the liquid used in steps (A), (A') and / or (D).

[0157] In step (C), the treated film pieces are recovered from the mixture of the liquid obtained in step (B) and the treated film pieces. In addition to the treated film pieces, the mixture also contains floating or dissolved components (ink, coating agent, metal, etc.) derived from the adhesive and functional layer that have separated from the plastic film pieces. These components can be removed from the liquid and then separated and recovered. Step (C) can be carried out using known recovery equipment, such as a filter, centrifuge, automatic scraping bar screen, tilting wire screen, or rotating drum screen.

[0158] In step (C), the liquid used in step (B) may be recovered. The recovered liquid may be reused in the same manner as the liquid recovered in step (F) described below.

[0159] In step (D), the recovered processed film pieces may be washed (finish-washed) by stirring them in a rinse solution. This step can remove small pieces of the functional layer remaining on the film surface if the functional layer could not be completely removed in steps (A), (A'), and (B). The rinse solution used in step (D) can be the cleaning solution exemplified as the liquid used in steps (A') and (B). The stirring equipment and stirring method used in step (D) are not particularly limited, and known equipment (e.g., the stirring equipment exemplified in step (A')) and known methods can be used. Known dispersion equipment (e.g., a bead mill) using media such as beads can also be used. Examples of media that can be used include salt, glass beads, and metal beads (e.g., steel beads, zirconia beads, alumina beads). The material of the media can be appropriately selected depending on the properties of the selected rinse solution. The diameter of the media used may be, for example, 0.5 to 20 mm. The residence time in the apparatus in step (D) may be, for example, 1 to 30 minutes.

[0160] In step (E), the treated film pieces washed in step (D) are dried to remove residual moisture. Drying may be performed by one or more methods selected from reduced-pressure heat drying, hot air drying, and pressurized compression drying. As a pretreatment for producing recycled pellets (described below), briquettes may be produced after or during the drying in step (E) using a pressurized compressor such as a Nippon Seam pressurized dehydrator, a Oike Iron Works pellet mill, or an Elcom Stella briquetting machine.

[0161] In step (F), when a liquid is used in step (A) or when steps (A') and / or (D) are performed, the liquid (water, cleaning liquid, rinse liquid, etc.) used in these steps is treated so that it can be reused. Specifically, the liquid is supplied to one or more recycling machines selected from a filter, a centrifuge, and an ultrafilter, and reused after removing solids.

[0162] Although each step in the removal method of the above embodiment is an independent step, they may be performed individually or consecutively.

[0163] The treated film pieces obtained by the removal method described above can be plastic film pieces that do not have a functional layer or have a sufficiently small amount of functional layer attached, and therefore the removal method can be suitably used as a process for producing high-quality recycled plastic raw materials (e.g., recycled plastic pellets).

[0164] The removability of the functional layer in the above-mentioned removal method can be evaluated by the removal rate of the functional layer. When the above-mentioned removal method is a method for removing a functional layer provided on the outermost surface of a plastic film piece, the removal rate of the functional layer can be determined by the following method. First, the outermost surface of the treated film piece obtained by the above removal method (the treated film piece after washing and drying) is photographed with an optical microscope, and the area of ​​the portion where the functional layer is attached (the functional layer attachment area) is calculated by image processing of the photograph. Next, the functional layer removal rate is calculated using the following formula. Functional layer removal rate (%) = (1 - [functional layer adhesion area after cleaning] / [functional layer adhesion area before cleaning]) x 100

[0165] According to the removal method of the above embodiment, the removal rate of the functional layer can be, for example, 50% or more. Furthermore, according to a preferred embodiment of the removal method, the removal rate of the functional layer can be 75% or more or 90% or more.

[0166] For some functional layers (especially functional coating layers), it may be difficult to evaluate their removability visually. However, the removability of the functional layer can be evaluated by quantifying the phenomenon that reflects the spectroscopic properties specific to the material that forms the functional layer, which can be obtained from various spectroscopic analyses such as IR spectrum, Raman spectrum, fluorescent X-ray, NIR, visible light transmittance, haze meter, and spectrophotometer, and comparing the quantitative values.

[0167] <Manufacturing method for recycled plastic pellets> Another embodiment of the present disclosure is a method for producing recycled plastic pellets, which comprises molding treated film pieces recovered through the above-described removal method or a processed product thereof into pellets. Here, the processed product of treated film pieces refers to a product obtained by, for example, subjecting treated film pieces obtained by the removal method of the above-described embodiment to a crushing process, melt-kneading process, or the like.

[0168] The method for forming the treated film pieces or the processed product thereof into pellets is not particularly limited and may be a known method. For example, first, various additives, a masterbatch (generally a mixture of a thermoplastic resin such as a polyethylene resin or a polypropylene resin and a colorant), etc. are added to the treated film pieces or the processed product thereof as needed, and mixed using a Henschel mixer, tumbler, disperser, etc. The resulting mixture is then melt-kneaded using a kneader, roll mill, twin-screw extruder, single-screw extruder, rotor-type twin-screw kneader, etc., and formed into pellets, thereby producing recycled plastic pellets.

[0169] The recycled plastic pellets obtained by the above-mentioned manufacturing method may be free of components (ink, coating agent, etc.) derived from the functional layer of the plastic film material, or may have a sufficiently reduced content of such components. Therefore, by using the above-mentioned recycled plastic pellets as a material, high-quality recycled plastic products can be manufactured. Therefore, the above-mentioned recycled plastic pellets can be used in a variety of fields, such as home appliances, stationery, automotive parts, toys, sporting goods, medical use, and building and construction materials. The recycled plastic product may be, for example, a molded body obtained by hot molding (e.g., injection molding, extrusion molding, blow molding, compression molding, etc.) the above-mentioned recycled plastic pellets. [Example]

[0170] The present disclosure will be described in more detail below using examples and comparative examples, but the present disclosure is not limited to the following examples.

[0171] <Plastic film> In the examples and comparative examples, the following plastic films were used: Film A: Takiron C.I. "Batsugun 5" Film B: "Shinoka" made by Sumika Sekisui Film Film C: Stretched polypropylene (OPP) film having a functional layer (ink layer) prepared in Preparation Example 1 below Film D: A polyester film having a functional layer (acrylic hard coat layer) prepared in Preparation Example 2 below. Film E: A polyester film having a functional layer (silicone coating layer) prepared in Preparation Example 3 below.

[0172] IR analysis of the outermost surfaces of Film A and Film B confirmed that the layer (functional layer) forming the outermost surface contained silicone resin derived from the coating material, based on the peak positions of the absorption spectra. Specifically, the minimum absorption peak derived from the silicone resin was 1099 cm -1 and 1093 cm -1 was detected.

[0173] <Production Example 1> Gravure ink (Glosser 507 Primary Indigo S2, manufactured by DIC Graphics) was applied to an OPP film (30 μm thick) using a proofer to print the ink over the entire surface of the OPP film, forming an ink layer. This resulted in an OPP film (Film C) with an ink layer as a functional layer.

[0174] <Production Example 2> Coating agent 1 (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.

[0175] The above-mentioned Coating Agent 1 was applied to a polyester film ("Lumirror T60" manufactured by Toray Industries, Inc.) so that the dry film thickness was approximately 9 μm. The coating film was then irradiated with ultraviolet light to harden the coating film, forming an acrylic hard coat layer. This resulted in a polyester film (Film D) having an acrylic hard coat layer as a functional layer.

[0176] <Production Example 3> Coating agent 2 was obtained by mixing 100 parts by mass of an addition reaction type silicone resin release agent (manufactured by Shin-Etsu Chemical Co., Ltd. under the trade name "KS-847T"), 1 part by mass of a platinum catalyst (manufactured by Shin-Etsu Chemical Co., Ltd. under the trade name "CAT-PL-50T"), and toluene. The amount of toluene added was adjusted so that the solid content in Coating agent 2 was 1.5% by mass.

[0177] Coating agent 2 was applied to a polyester film ("Lumirror T60" manufactured by Toray Industries, Inc.) by gravure coating to a dry film thickness of approximately 2 μm to form a silicone coating layer, thereby obtaining a polyester film (Film E) having a silicone coating layer as a functional layer.

[0178] <Examples 1 to 111 and Comparative Examples 1 to 5> The above plastic film was treated according to the following steps (A), (A') and (B) to obtain treated film pieces.

[0179] (Process:(A)) The above plastic films (Film A, Film B, Film C, Film D, or Film E) were dry crushed (coarsely crushed) to the following average sizes to produce plastic film pieces (Film pieces A1 to A3, B1, C1, D1, E1). Film piece A1: average size = approx. 50 mm A2 film strip: average size = approx. 18mm A3 film strip: average size = approx. 20mm Film piece B1: average size = approx. 50 mm Film piece C1: average size = approx. 50 mm Film piece D1: average size = approx. 50 mm Film piece E1: average size = approx. 50 mm Film pieces A1 to A3 were made from film A, film piece B1 was made from film B, film piece C1 was made from film C, film piece D1 was made from film D, and film piece E1 was made from film E.

[0180] (Process:(A')) Aqueous solutions containing 2% by mass of sodium hydroxide (immersion solutions S1 to S16) were prepared. The additives shown in Table 1 were blended into immersion solutions S1 to S15 in amounts that would result in 1% by mass based on the total amount of the aqueous solution.

[0181] [Table 1]

[0182] Next, the plastic film pieces obtained in step (A) above were immersed in the immersion liquid at 80°C for 1 hour. The combinations of plastic film pieces and immersion liquids used in each example are shown in Tables 2 to 7. After that, the plastic film pieces were removed from the immersion liquid and rinsed with water. Rinsing was continued until the pH of the water after rinsing was 10 or less.

[0183] (Process:(B)) The plastic film pieces treated in the above step (A') were subjected to a wet crushing treatment using the apparatus and treatment method as shown in the following conditions M1, M2 or M3. [Condition M1] Equipment: Nikuni Sancuta C125H (grid mesh size = 8mmΦ) Treatment method: The above equipment is operated at 50Hz, and 0.05m of water is 3 Plastic film pieces were sequentially fed into the inlet side of the device while the water was flowing at a rate of 1 / min. The amount of plastic film pieces fed (film piece feeding amount) and the ratio of the volume V2 of the water fed to the volume V1 of the plastic film pieces fed (V2 / V1) were adjusted to the values ​​shown in Tables 2 to 4 and Table 7. The fluffy film pieces emerging from the outlet were collected and dried to obtain treated film pieces. [Condition M2] Equipment: Nippon Seam PFS-40 cleaning and crushing machine (grid mesh size = 5mmΦ) Treatment method: The above equipment was operated at a rotation speed of 600 rpm, and films were sequentially added while water was supplied at 15 L / min. The amount of plastic film pieces added (film piece input amount) and the ratio of the volume of water V2 to the volume of plastic film pieces V1 (V2 / V1) were adjusted to the values ​​shown in Tables 2 to 4 and Table 6. The fluffy film emerging from the outlet was collected and dried to obtain treated film pieces. [Condition M3] The conditions were the same as those in M1 above, except that the mesh size of the grid was 30 mmΦ. The amount of plastic film pieces added (film piece input amount) and the ratio of the volume V2 of the water supplied to the volume V1 of the plastic film pieces supplied (V2 / V1) were set to the values ​​shown in Table 5. The fluffy film coming out of the outlet was collected and dried to obtain treated film pieces.

[0184] The recovery rates of the treated film pieces recovered in Examples 1 to 111 and Comparative Examples 1 to 5 were all 95% or higher. The ratios (Sa / Sp) of the average size Sa of the treated film pieces to the average size Sp of the plastic film pieces subjected to step (B) were the values ​​shown in Tables 2 to 7.

[0185] (evaluation) [Examples 1 to 71 and Comparative Examples 1 to 2] In Examples 1 to 71 and Comparative Examples 1 and 2 in which film pieces A1 to A3 or film piece B1 were used, the removability of the functional layer was evaluated by the following method.

[0186] First, in each example, five pieces of the recovered treated film were randomly selected, and the FT-IR spectra of the front and back of the treated film pieces were obtained. From the spectra, the wavenumber at which the minimum absorption peak derived from the silicone resin exists (1099 cm for film pieces A1 to A3) was determined. -1 , and 1093 cm for film piece B1. -1 The transmittance of each film piece was measured, and the average value (average value of five film pieces) was taken as the transmittance of the treated film piece. Using the obtained transmittance and the transmittance of the untreated film piece (film pieces A1 to A3 or B1) previously measured in the same manner, the evaluation index (DC) of the removability of the functional layer (functional coating layer containing silicone resin) was calculated according to the following formula: DC(%)={1-(100-T1) / (100-T0)}×100 T0: Transmittance (%) of the film piece before processing, T1: Transmittance of the processed film piece

[0187] The removability of the functional layer (functional coating layer containing silicone resin) was evaluated according to the following criteria. The higher the evaluation value, the better the removability of the functional layer. The results are shown in Tables 2 to 3 and Table 5. 4: DC is 90 or higher 3: DC value is 50 or greater but less than 90 2: DC value is greater than 10 and less than 50 1: DC value is 10 or less

[0188] [Examples 72 to 103 and Comparative Example 3] In Examples 72 to 103 and Comparative Example 3 in which film piece C1 was used, the removability of the functional layer was evaluated by the following method.

[0189] First, in each example, 50 pieces of processed film were randomly selected from the collected pieces of processed film, and the printed portions of the processed pieces of film were photographed using an optical microscope. The photographs were then processed to calculate the area of ​​the ink-adhered portion (ink-adhered area). The ink removal rate was calculated using the following formula, assuming that ink was adhering to the entire surface of the film piece C1 before processing. Ink removal rate (%) = (1 - ink-adhered area of ​​treated film piece / area of ​​treated film piece) x 100

[0190] The removability of the functional layer (ink layer) was evaluated according to the following criteria. The higher the evaluation value, the better the removability of the functional layer. The results are shown in Tables 4 and 5. 4: Ink removal rate is 95% or more 3: Ink removal rate is between 75% and 95% 2: Ink removal rate is between 50% and 75% 1: Ink removal rate is less than 50%

[0191] [Examples 104 to 111 and Comparative Examples 4 to 5] In Examples 104 to 111 and Comparative Examples 4 and 5 in which film piece D1 or film piece E1 was used, the removability of the functional layer was evaluated by the following method.

[0192] First, in each example, five pieces of film before treatment were randomly selected, and FT-IR spectra were obtained for the front and back of the film (the side coated with the coating agent and the side not coated with the coating agent). The spectra from both sides were compared, and the wavenumber with the largest transmittance difference was determined as the absorption position due to the coating agent. From the above spectrum, the transmittance at the absorption position due to the coating agent was measured, and the average value (average value of the five film pieces) was used as the transmittance of the film piece before treatment. Five pieces of the recovered treated film were also randomly selected, and the average value (average value of the five film pieces) at the absorption position due to the coating agent was calculated in the same manner as above, and this was used as the transmittance of the treated film piece. Using the obtained transmittances of the film pieces before and after treatment, the evaluation index (DC) of the removability of the functional layer was calculated using the following formula. DC(%)={1-(100-T1) / (100-T0)}×100 T0: Transmittance (%) of the film piece before processing, T1: Transmittance of the processed film piece

[0193] The removability of the functional layer (layer formed by a coating agent) was evaluated according to the following criteria. The higher the evaluation value, the better the removability of the functional layer. The results are shown in Tables 6 to 7. 4: DC is 90 or higher 3: DC value is 50 or greater but less than 90 2: DC value is greater than 10 and less than 50 1: DC value is 10 or less

[0194] [Table 2]

[0195] [Table 3]

[0196] [Table 4]

[0197] [Table 5]

[0198]

Table 6

[0199]

Table 7

Claims

1. 1. A method for removing a functional layer from a piece of plastic film, comprising: (A) preparing a plastic film piece having a functional layer and an average size Sp of 40 to 80 mm; (A') wetting the plastic film piece by contacting it with a cleaning solution containing (a) a surfactant and (b) an inorganic base for 10 seconds or more; (B) after the step (A'), removing the functional layer from the plastic film pieces by a wet crushing process in which the plastic film pieces are crushed in the presence of a liquid while being stirred, the step (B) includes supplying the plastic film pieces and water to a treatment space, performing the wet crushing treatment in the treatment space, and discharging the treated film pieces and the liquid from the treatment space; a ratio of a volume V2 of the water to a volume V1 of the plastic film pieces supplied to the processing space is 0.7 to 99; In the step (B), the average size Sa of the treated film pieces obtained by the wet crushing treatment is set to 0.3 times or less the average size Sp of the plastic film pieces.

2. The method of claim 1 , wherein the functional layer is an ink layer.

3. The method according to claim 1 , wherein the functional layer is a functional coating layer containing a silicone resin.

4. A method for producing recycled plastic pellets, comprising molding the treated film pieces or processed products thereof recovered through the method according to any one of claims 1 to 3 into pellets.

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