Method for cleaning laminate

Abstract

The present invention provides a method which is for cleaning a laminate and in which, even when the laminate includes a coating layer containing a polyamide resin, the coating layer has excellent separability. Provided is a method which is for cleaning a laminate and in which, from a laminate including a plastic substrate layer and a coating layer that is disposed at the outermost surface, the coating layer is separated using a cleaning liquid, said method being characterized by comprising a contact step for bringing the surface of the coating layer into contact with the cleaning liquid, wherein: the coating layer contains a polyamide resin; the cleaning liquid contains an inorganic base, a surfactant, and water; and, in the contact step, the advancing contact angle between the surface of the coating layer and the cleaning liquid is not more than 52.0°, as measured by an expansion method.

Description

Method for cleaning a laminate

[0001] The present invention relates to a method for cleaning a laminate.

[0002] Currently, the amount of waste plastic that is separately collected (recycling rate) is 9% of the plastic produced globally. Among the 91% of waste plastic that is not separately collected, 12% is incinerated, 79% is landfilled, or leaks into the environment (Non-Patent Document 1). One of the reasons for the low recycling rate is the difficulty of the separation and collection system.

[0003] Specifically, in order to recycle plastic, it is necessary to separate and collect waste plastic in which different plastic materials such as polyethylene (PE) and polypropylene (PP) are integrated, by material. However, many plastic products, including laminated films, have different plastic materials adhered to each other, making it difficult to separate and collect them by material. Therefore, there is a strong demand for the construction of a recycling system that can easily separate and collect waste plastic.

[0004] In addition, recycled plastic products are difficult to return to the same products as before recycling from a cost perspective. Moreover, plastic products basically deteriorate every time they are recycled. Therefore, the quality of recycled plastic products inevitably deteriorates.

[0005] In this regard, the reason for the deterioration of the quality of recycled plastic is that ink or pigment is mixed in the plastic as an impurity. In particular, many plastic products are printed on their surfaces, making it difficult to decolorize them in the recycling process. In addition, in addition to the ink layer (printing layer), various coating layers such as a hard coat layer, an adhesive layer, and a peelable primer layer are generally provided on the plastic film constituting the plastic product. However, the components derived from these coating layers can also cause unintended coloring.

[0006] As a result, recycled plastic products are often colored. Such recycled plastic products not only have significantly low commercial value due to the coloring, but also the physical properties can deteriorate starting from impurities. Therefore, a method for producing high-quality recycled plastic products is required.

[0007] For example, Patent Document 1 discloses a method for detaching a detachable ink composition from a printed matter, which is characterized by contacting a printed matter printed using a detachable ink composition containing a predetermined component with an aqueous alkali solution (cleaning liquid).

[0008] Also, Patent Document 2 discloses a method for separating and recovering a laminated film laminated and adhered with a reactive adhesive, which includes a step of immersing the laminated film in an alkali solution (cleaning liquid) while heating and stirring or ultrasonically vibrating the laminated film at 20 to 90°C.

[0009] Science Advances 19 Jul 2017:Vol. 3, no. 7, e1700782

[0010] Japanese Patent Application Laid-Open No. 2001-031899 International Publication No. 2020 / 066652

[0011] By the way, as a coating layer, a coating layer containing a polyamide resin is known, and this is widely used in printed matters (laminates) for surface printing and the like. However, a coating layer containing a polyamide resin is difficult to separate from a plastic material, and the separability of the coating layer was not sufficient with conventional methods.

[0012] Therefore, an object of the present invention is to provide a cleaning method for a laminate that is excellent in the separability of a coating layer even when the laminate includes a coating layer containing a polyamide resin.

[0013] As a result of intensive studies, the present inventors have found that when attempting to separate a coating layer from a laminate having a coating layer containing a polyamide resin, the above problems can be solved when the cleaning liquid and the surface of the coating layer brought into contact with the cleaning liquid are in a relationship where they have a predetermined contact angle, and thus the present invention has been completed. The gist configuration of the present invention for solving the above problems is as follows.

[0014] [1] A method for cleaning a laminate, comprising a plastic substrate layer and a coating layer, the coating layer being disposed on the outermost surface, and separating the coating layer from the laminate using a cleaning liquid, the method comprising a contact step of bringing the surface of the coating layer into contact with the cleaning liquid, the coating layer containing a polyamide resin, the cleaning liquid containing an inorganic base, a surfactant, and water, and at the time of the contact step, the surface of the coating layer and the cleaning liquid being in a relationship where the advancing contact angle measured by the spreading method is 52.0° or less. A method for cleaning a laminate, characterized by the above.

[0015] [2] The method according to [1], wherein the cleaning liquid has a temperature of 50°C or higher.

[0016] [3] The method according to [1] or [2], wherein the surfactant contains an amphoteric surfactant.

[0017] [4] The amphoteric surfactant is represented by the general formula (1a): R １ -R ２ -N ＋ (CH ３ ) ２ CH ２ COO － (1a) [In the general formula (1a), R １ represents a hydrogen atom or a group represented by the formula (2): R ３ C(=O)-NH-, R ２ represents an alkylene group or an alkenylene group, and in the formula (2), R ３ represents a linear or branched alkyl group or a linear or branched alkenyl group.]. The method according to [3], comprising one or more selected from the compounds represented by the above.

[0018] [5] The compound represented by the general formula (1a) is represented by the general formula (1a-1): C ｎ H２ｎ＋１ N ＋ (CH ３ ) ２ CH ２ COO － The method according to [4], wherein the compound is represented by (1a-1) [wherein n represents the average number of moles added].

[0019] [6] The method according to [5], wherein n is 8 or greater in the general formula (1a-1).

[0020] [7] The method according to any one of [1] to [6], comprising: a crushing step of crushing the laminate; an immersion step, which is a contact step of immersing the laminate after the crushing step in the cleaning liquid; and a separation step of separating the coating layer from the laminate by stirring the laminate after the immersion step in the presence of water.

[0021] According to the present invention, it is possible to provide a method for cleaning a laminate that exhibits excellent separation of the coating layer, even when the laminate includes a coating layer containing a polyamide resin.

[0022] The cleaning method for laminates according to the present invention will be described in detail below, based on its embodiments.

[0023] A method for cleaning a laminate according to one embodiment of the present invention (hereinafter sometimes referred to as "the method of this embodiment") is a method for cleaning a laminate comprising a plastic substrate layer and a coating layer, wherein the coating layer is disposed on the outermost surface, and the method comprises a contact step of bringing the surface of the coating layer into contact with the cleaning solution, wherein the coating layer contains a polyamide resin, the cleaning solution contains an inorganic base, a surfactant, and water, and during the contact step, the surface of the coating layer and the cleaning solution are in a relationship where the advancing contact angle measured by the expansion method is 52.0° or less.

[0024] As a result of diligent research by the inventors, it has been found that when separating a coating layer from a laminate using a cleaning solution, if the advancing contact angle between the surface of the coating layer and the cleaning solution, as measured by the expansion method, is 52.0° or less, then excellent separation of the coating layer can be achieved, even if the coating layer contains polyamide resin. This is presumed to be due to improved wettability between the cleaning solution and the surface of the coating layer, thereby improving the separation of the coating layer. Therefore, according to the present invention, it is possible to provide a method for cleaning a laminate that exhibits excellent separation of the coating layer, even when the coating layer contains polyamide resin.

[0025] <Laminate to be processed> In the method of this embodiment, a laminate comprising a plastic substrate layer and a coating layer, wherein the coating layer is disposed on the outermost surface, is used as the object to be processed. In the laminate to be processed, for example, the coating layer is disposed on at least one outermost surface of the laminate.

[0026] (Plastic Substrate Layer) As the plastic constituting the plastic substrate, known resins can be used, such as polyolefin resin, polyamide resin, polyester resin, polyimide resin, polyvinyl chloride resin, and polystyrene resin.

[0027] The polyolefin resin is not particularly limited and includes, for example, polyethylene resins such as low-density polyethylene, high-density polyethylene, and linear low-density polyethylene; polypropylene resins such as OPP (biaxially oriented polypropylene) and CPP (unoriented polypropylene); propylene-ethylene copolymer; ethylene-butene-propylene copolymer; and the like.

[0028] The laminate used in this embodiment preferably comprises a plastic substrate layer (i.e., a polypropylene resin layer) that contains polypropylene resin such as OPP or CPP as the main constituent resin.

[0029] The thickness of the plastic substrate layer is not particularly limited, but is preferably, for example, 5 μm or more, or 10 μm or more, and is also preferably, for example, 500 μm or less, 200 μm or less, 100 μm or less, or 50 μm or less.

[0030] The plastic substrate layer may be a single layer, or it may be a multi-layered layer consisting of the same or different plastic substrate layers.

[0031] (Coating Layer) As described above, the laminate used in this embodiment includes a coating layer. The coating layer is usually formed by applying a coating layer composition (solution) to the surface to be formed. The coating layer is not particularly limited and examples include a printing layer (also called an ink layer), an adhesive layer, a detachable primer layer, a functional coating layer, etc. The laminate may have one of these coating layers alone, or two or more types in combination.

[0032] The coating layer contains a polyamide resin. The polyamide resin is not particularly limited, and known resins can be used. The polyamide resin is preferably a thermoplastic polyamide soluble in organic solvents, and examples include reaction products of an acid component containing a polybasic acid and an amine component containing a polyhydric amine (i.e., polycondensates of polybasic acids and polyhydric amines).

[0033] The polybasic acid is not particularly limited and examples include adipic acid, sebacic acid, azelaic acid, phthalic anhydride, isophthalic acid, suberic acid, glutaric acid, fumaric acid, pimelic acid, oxalic acid, malonic acid, succinic acid, maleic acid, terephthalic acid, 1,4-cyclohexyldicarboxylic acid, trimellitic acid, dimerized polymerized fatty acids (dimer acids), hydrogenated dimerized polymerized fatty acids, trimerized polymerized fatty acids, and hydrogenated trimerized polymerized fatty acids. Fatty acids that make up polymerized fatty acids (dimerized polymerized fatty acids, trimerized polymerized fatty acids) are preferably derived from natural oils such as tall oil, rice bran oil, palm oil, coconut oil, and soybean oil, and those obtained from oleic acid and linoleic acid are preferred. These polybasic acids may be used individually or in combination of two or more.

[0034] The polybasic acid preferably contains dimerized polymerized fatty acids (dimer acids).

[0035] The acidic components mentioned above may further include monobasic fatty acids; such as acetic acid, propionic acid, lauric acid, palmitic acid, benzoic acid, and monocarboxylic acids such as cyclohexanecarboxylic acid.

[0036] The polyhydric amine is not particularly limited and includes, for example, aliphatic polyamines, aromatic aliphatic polyamines, and aromatic polyamines. Examples of aliphatic polyamines include ethylenediamine, propylenediamine, hexamethylenediamine, methylaminopropylamine, and other aliphatic diamines; diethylenetriamine; triethylenetetramine; and alicyclic polyamines such as cyclohexylenediamine and isophoronediamine. Examples of aromatic aliphatic polyamines include xylylenediamine. Examples of aromatic polyamines include phenylenediamine and diaminodiphenylmethane. These polyhydric amines may be used individually or in combination of two or more.

[0037] The polyhydric amine preferably includes aliphatic polyamines and aromatic polyamines.

[0038] The amine component described above preferably further comprises a primary monoamine and / or a secondary monoamine. Examples of primary monoamines include n-butylamine, octylamine, monoethanolamine, and monopropanolamine. Examples of secondary monoamines include diethylamine, diethanolamine, and dipropanolamine.

[0039] The polyamide resin is preferably a polyamide resin derived from rice bran oil, using rice bran fatty acids as a reaction material. Furthermore, when rice bran fatty acids are used as a reaction material, the polyhydric amine preferably contains an aliphatic diamine or an alicyclic polyamine.

[0040] The number-average molecular weight of the polyamide resin is preferably 1,000 to 30,000, and more preferably 1,000 to 20,000, from the viewpoint of maintaining high gloss and blocking resistance of the coating layer (composition for the coating layer). A number-average molecular weight of 1,000 or more provides excellent blocking resistance and heat resistance, while not exceeding 30,000 tends to maintain low-temperature flexibility.

[0041] The acid value of the polyamide resin is not particularly limited, but is preferably 15 mg KOH / g or less. The amine value of the polyamide resin is also not particularly limited, but is preferably 10 mg KOH / g or less.

[0042] The softening point of the polyamide resin is not particularly limited, but is preferably 90 to 150°C, and more preferably 90 to 130°C.

[0043] The polyamide resin content in the coating layer is not particularly limited, but is preferably 25 to 75% by mass, and more preferably 30 to 70% by mass, based on the total amount of solid components in the coating layer.

[0044] The coating layer preferably further contains a cellulose-based resin.

[0045] The cellulose resin is not particularly limited and includes, for example, cellulose ester resins such as cellulose acetate propionate and cellulose acetate butyrate; nitrocellulose (nitrified cotton); hydroxyalkylcellulose, carboxyalkylcellulose, etc. The cellulose ester resin described above preferably has an alkyl group. Examples of the alkyl group include methyl group, ethyl group, propyl group, isopropyl group, butyl group, isobutyl group, pentyl group, hexyl group, etc. The alkyl group may also have substituents. Nitrocellulose (nitrified cotton) is preferably obtained by reacting natural cellulose with nitric acid, and more preferably, three hydroxyl groups in the six-membered ring of the anhydrous glucopyranose group in natural cellulose are substituted with nitrate groups. The nitrogen content of nitrocellulose (nitrified cotton) is preferably 10 to 13% by mass. The average degree of polymerization of nitrocellulose (nitrified cotton) is preferably 30 to 500, and more preferably 45 to 290.

[0046] The weight-average molecular weight of the cellulose resin is preferably 5,000 to 200,000, and more preferably 10,000 to 50,000.

[0047] Preferred cellulose acetate propionate, cellulose acetate butyrate, and nitrocellulose (nitrified cotton) are used as the cellulose-based resin, with nitrocellulose (nitrified cotton) being more preferred. When the coating layer (and the composition for the coating layer) contains nitrocellulose (nitrified cotton) as the cellulose-based resin, the dispersibility of pigments and other elements is improved, which can lead to an improvement in the strength of the coating layer.

[0048] When the coating layer (and the composition for the coating layer) contains a cellulose resin, the content of the cellulose resin in the coating layer is preferably 5 to 25% by mass, and more preferably 7.5 to 20% by mass, based on the total amount of solid components in the coating layer.

[0049] The coating layer may further contain other resins such as urethane resins, acrylic resins, vinyl chloride-vinyl acetate copolymer resins, chlorinated polypropylene resins, ethylene-vinyl acetate copolymer resins, vinyl acetate resins, polyvinyl chloride resins, polyester resins, alkyd resins, rosin resins, rosin-modified maleic acid resins, ketone resins, cycloplastic rubbers, chlorinated rubbers, butyral, and petroleum resins.

[0050] -Printed Layer- The laminate used in this embodiment may include a printed layer as a coating layer. The printed layer is typically a layer containing ink. The printed layer may be a layer on which any picture, pattern, character, and symbol is displayed for the purpose of decoration or aesthetic appeal, or for displaying contents, expiration date, and manufacturer or seller information. Alternatively, the printed layer may be a layer on which no picture, pattern, character, and symbol is displayed (i.e., a layer without gaps, a solid layer).

[0051] The printed layer is formed by printing using, for example, a gravure printer, a flexographic printer, an offset printer, or an inkjet printer. That is, the ink used to form the printed layer may be gravure ink, flexographic ink, offset ink, or inkjet ink.

[0052] The ink may be, for example, an organic solvent-based printing ink, a water-based ink, or an active energy ray-curing ink. The ink contained in the printing layer may be a single type or a combination of two or more types. The printing layer may be a single-color printing layer or a multi-color printing layer.

[0053] -Adhesive Layer- The laminate used in this embodiment may include an adhesive layer as a coating layer. The adhesive constituting the adhesive layer can be any adhesive that can be used in a general-purpose lamination method. Examples of lamination methods include dry lamination and wet lamination using solvent-type laminating adhesives, and non-solvent lamination using solvent-free laminating adhesives.

[0054] Examples of the adhesives mentioned above include vinyl resins, (meth)acrylic resins, polyamide resins, polyester resins, polyether resins, polyurethane resins, epoxy resins, and rubber resins. Such adhesives may be one-component or two-component, and may be curing or non-curing types.

[0055] The adhesive layer is typically formed by applying an adhesive layer composition (solution) to the surface to be bonded and allowing it to dry.

[0056] - Detachable Primer Layer - The laminate used in this embodiment may include a detachable primer layer as a coating layer. In this case, recyclability can be improved, and the quality of recycled plastic can be improved. The detachable primer layer can be easily detached from other layers by treatment with an alkali-containing solution (detachment solution).

[0057] In the laminate, the deleasable primer layer is preferably in contact with the plastic substrate layer. Furthermore, in the laminate, the deleasable primer layer is preferably bonded to and sandwiched between the polyolefin film layer and the coating layers other than the deleasable primer layer (e.g., a printing layer, an adhesive layer, a functional coating layer, etc.). In this case, recyclability can be further improved, and the quality of recycled plastic can be further improved.

[0058] A detachable primer layer is typically formed by applying a detachable primer layer composition (solution) to the surface to be formed and allowing it to dry.

[0059] Furthermore, the desorbable primer layer (and composition for the desorbable primer layer) may contain a resin that forms a film at room temperature. Examples of resins that form a film at room temperature include polyester; polyvinyl chloride; copolymers of vinyl chloride and other unsaturated double-bond-containing monomers; homopolymers of (meth)acrylic acid esters; copolymers of (meth)acrylic acid esters and other unsaturated double-bond-containing monomers; polystyrene; copolymers of styrene monomer and other unsaturated double-bond-containing monomers; ketone-formaldehyde condensates or their hydrogenated products; polyfunctional epoxy resins; polyvinyl acetals; urethane resins; and the like. Examples of polyfunctional epoxy resins include bisphenol A novolac type epoxy resin, bisphenol F novolac type epoxy resin, bisphenol S novolac type epoxy resin, biphenyl type epoxy resin, and naphthalene type epoxy resin. These resins that form a film at room temperature may be used individually or in combination of two or more types.

[0060] In one embodiment, the detachable primer layer preferably contains a urethane resin. Such a detachable primer layer can be formed, for example, using a detachable primer layer composition containing a urethane resin and an aqueous medium.

[0061] Furthermore, urethane resin is a general term for polymer compounds having urethane bonds (-NHCOO-). The above urethane resin can be obtained, for example, by reacting aromatic polyester polyol, polyisocyanate, and, if necessary, chain extenders.

[0062] In another embodiment, the detachable primer layer preferably contains polyvinyl alcohol. Such a detachable primer layer can be formed, for example, using a detachable primer layer composition containing polyvinyl alcohol and an aqueous medium.

[0063] Polyvinyl alcohol is a colorless powder obtained by saponifying polyvinyl acetate. It is also a water-soluble thermoplastic resin and a raw material for the synthetic fiber vinylon.

[0064] Examples of the aqueous medium include water and organic solvents that are miscible with water. The aqueous medium may be used alone or in combination of two or more types. Examples of organic solvents that are miscible with water include alcohols such as methanol, ethanol, n-propanol, and isopropanol; ketones such as acetone and methyl ethyl ketone; polyalkylene glycols such as ethylene glycol, diethylene glycol, and propylene glycol; alkyl ethers of polyalkylene glycols; and N-methyl-2-pyrrolidone.

[0065] - Functional Coating Layer - The laminate used in this embodiment may be provided with a functional coating layer as a coating layer. The functional coating layer may be provided on the laminate for purposes such as hard coating, silicone-based release, IR cut, waterproofing and moisture-proofing, antibacterial properties, UV cut, heat dissipation, photocatalysis, weather resistance, anti-fogging, fingerprint resistance and stain resistance, self-healing, and water and oil repellency. Specifically, examples of functional coating layers include hard coating layers, adhesive layers, release layers, decorative layers, light-shielding layers, ultraviolet shielding layers, antistatic layers, refractive index adjusting layers, and oligomer encapsulation layers. These functional coating layers may be colorless or colored.

[0066] Functional coating layers can be formed by applying various coating agents, such as hard coating agents, self-healing coating agents, anti-fingerprint and anti-fouling coating agents, anti-fogging coating agents, silicone-based release agents, non-silicone-based release agents, waterproof and moisture-proof coating agents, water-repellent and oil-repellent coating agents, photocatalytic coating agents, weather-resistant coating agents, IR-cut coating agents, and other surface modifiers, optical 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, to the surface to be formed. The thickness of these functional coating layers 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.

[0067] The functional coating layer may be a single layer, or it may be a multi-layered layer consisting of the same or different functional coating layers.

[0068] <Cleaning Solution> The cleaning solution contains an inorganic base, a surfactant, and water.

[0069] The inorganic base is not particularly limited and examples include sodium hydroxide and potassium hydroxide. The concentration of the inorganic base in the washing solution is preferably 0.1% to 10% by mass, and more preferably 0.1% to 5% by mass, as a percentage of the total amount of the washing solution.

[0070] The cleaning solution contains a surfactant. The surfactant is not particularly limited and examples include amphoteric surfactants, nonionic surfactants, cationic surfactants, anionic surfactants, etc. These surfactants may be used individually or in combination of two or more.

[0071] The amphoteric surfactant is not particularly limited, and known ones can be used. The amphoteric surfactant has a general formula (1a): R １ -R ２ -N ＋ (CH ３ ) ２ CH ２ COO － (1a) [In general formula (1a), R １is a hydrogen atom or formula (2): R ３ It shows a group represented by C(=O)-NH-, R ２ R represents an alkylene group or an alkenylene group, and in formula (2), ３ It is preferable to include one or more compounds selected from those represented by [ ], where represents a linear or branched alkyl group, or a linear or branched alkenyl group. In this case, the advancing contact angle described later can be made lower, and the separation properties of the coating layer can be further improved.

[0072] R ２ The alkylene group and alkenylene group in the compound may be linear or branched.

[0073] The compound represented by general formula (1a) may be used alone or in combination of two or more types.

[0074] The compound represented by general formula (1a) is general formula (1a-1): C ｎ H ２ｎ＋１ N ＋ (CH ３ ) ２ CH ２ COO － It is preferable that the compound is represented by (1a-1) [wherein n represents the average number of moles added]. In this case, the advancing contact angle described later can be made lower, and the separation performance of the coating layer can be further improved.

[0075] From a similar viewpoint, in general formula (1a-1), n ​​is preferably 8 or greater, more preferably 10 or greater, and particularly preferably 11 or greater.

[0076] The amphoteric surfactant may include a compound having an imidazolinium betaine skeleton.

[0077] Amphoteric surfactants are defined by the general formula (1b): R ４ - (NHC ２ H ４ ) ｎｂ -N(R) ５ ) ２ [In general formula (1b), R ４R represents a linear or branched alkyl group, or a linear or branched alkenyl group, nb represents an integer from 0 to 5, and R ５ This is a hydrogen atom, -CH ２ A group represented by COONa or -CH ２ This indicates a group represented by COOH (however, there are two R groups). ５ They may be the same or different, and there may be at least one R ５ is, -CH ２ It is a group represented by COONa. It may contain one or more compounds selected from those represented by ].

[0078] In general formula (1b), R ４ It is preferably a linear alkyl group, and more preferably has 8 or more carbon atoms, more preferably 10 or more, and particularly preferably 12 or more.

[0079] Amphoteric surfactants have the general formula (1c): R ６ -N ＋ (CH ３ ) ２ O － [In general formula (1c), R ６ This represents a linear or branched alkyl group, or a linear or branched alkenyl group. It may contain one or more compounds selected from those represented by [ ].

[0080] In general formula (1c), R ６ It is preferably a linear alkyl group, and more preferably has 8 or more carbon atoms, more preferably 10 or more, and particularly preferably 12 or more.

[0081] These amphoteric surfactants may be used individually or in combination of two or more.

[0082] Nonionic surfactants are not particularly limited and include, for example, 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, alkyl alkanolamides, acetylene glycols, oxyethylene adducts of acetylene glycols, polyethylene glycol, polypropylene glycol block copolymers, and the like.

[0083] Nonionic surfactants are defined by formula (3): R ７ -O-[CH ２ -CH(X １ )-O] ｎ３ -H (3) [In general formula (3), R ７ X represents a linear or branched alkyl group, a linear or branched alkenyl group, or an octylphenol group. １ It is preferable to include one or more compounds selected from the compounds represented by [ ] (polyoxyalkylene alkyl ethers), where n3 represents a hydrogen atom or a short-chain alkyl group, and n3 represents the average number of moles added.

[0084] R ７ In this material, the linear or branched alkyl group and the linear or branched alkenyl group are preferably linear, and preferably have 10 or more carbon atoms, and preferably 14 or fewer carbon atoms.

[0085] R ７ In this context, an example of an octylphenol group is the octylphenol ethoxylate group.

[0086] These nonionic surfactants may be used individually or in combination of two or more.

[0087] The cationic surfactant is not particularly limited, and known ones can be used. Examples of cationic surfactants include cationic surfactants having a quaternary ammonium skeleton. Specifically, cationic surfactants have the general formula (4): R ８ -N ＋ (R ９ R １０ )-R １１ (4) [In general formula (4), R ８ R represents a linear or branched alkyl group, or a linear or branched alkenyl group. ８ -CH in alkyl and alkenyl groups in ２ - may be substituted with -C(=O)-, -NH-, or -C(=O)-NH-, R ９ and R １０ Each independently represents a hydrogen atom, a linear or branched alkyl group, or a linear or branched alkenyl group, and R １１ R represents a hydrogen atom, a linear or branched alkyl group, a linear or branched alkenyl group, or a phenyl group. １１ -CH in alkyl and alkenyl groups in ３ It may be substituted with a carboxyl group or a phenyl group. It may contain one or more compounds selected from the compounds represented by ].

[0088] There are no particular restrictions on the anionic surfactant; known surfactants can be used.

[0089] The concentration of the surfactant in the cleaning solution is preferably 0.01% to 5% by mass, and more preferably 2% by mass or less, as a percentage of the total amount of the cleaning solution.

[0090] The surfactant in the cleaning solution preferably contains an amphoteric surfactant. In this case, the advancing contact angle, as described later, can be made lower, and the separation of the coating layer is further improved. From a similar viewpoint, it is preferable that the surfactant further contains a nonionic surfactant (i.e., the surfactant contains both an amphoteric surfactant and a nonionic surfactant).

[0091] When the surfactant includes both an amphoteric surfactant and a nonionic surfactant, the mass ratio of the amphoteric surfactant to the nonionic surfactant (mass of amphoteric surfactant:mass of nonionic surfactant) is preferably 1:9 to 9:1, more preferably 2:8 to 8:2, even more preferably 2.5:7.5 to 7.5:2.5, and particularly preferably 3:7 to 7:3.

[0092] When the surfactant includes both amphoteric and nonionic surfactants, the HLB value of the nonionic surfactant is not particularly limited, but is preferably 14.0 or less. In this case, the wettability of the cleaning solution may be further improved, and the separation of the coating layer may be further improved. Here, the HLB value is calculated by the following formula: HLB value = (20 × sum of the formula weights of the hydrophilic parts) / molecular weight

[0093] The cleaning solution may contain appropriate amounts of other components besides those mentioned above, such as organic solvents and defoaming agents.

[0094] Examples of organic solvents include water-soluble alcohols and water-soluble solvents with a flash point of 21°C or higher. Examples of water-soluble alcohols include methanol, ethanol, 1-propyl alcohol, and 2-propyl alcohol. Examples of water-soluble solvents with a flash point of 21°C or higher include diethylene glycol methyl ether, diethylene glycol butyl ether, propylene glycol propyl ether, and 3-methoxy-3-methyl-1-butanol.

[0095] <Contact Step> In the method of this embodiment, the contact step involves bringing the surface of the coating layer in the laminate described above into contact with the cleaning solution. In the contact step, it is sufficient for only a portion of the surface of the coating layer in the laminate to come into contact with the cleaning solution, or the entire surface of the coating layer in the laminate may come into contact with it. Alternatively, in the contact step, the entire surface of the laminate, including the surface of the coating layer, may come into contact with the cleaning solution by immersing the laminate in the cleaning solution.

[0096] The method for bringing the surface of the coating layer in the laminate into contact with the cleaning solution is not particularly limited and includes known methods, such as immersing the laminate in the cleaning solution, applying the cleaning solution to the laminate, spraying the cleaning solution onto the laminate, or passing the cleaning solution through the laminate. The contact step is typically the immersion step described later.

[0097] The temperature of the cleaning solution during the contact process is preferably 50°C or higher. A cleaning solution temperature of 50°C or higher during the contact process allows for a lower forward contact angle, as described later, and further improves the separation of the coated layer. The upper limit of the cleaning solution temperature during the contact process is preferably, for example, a temperature at which the cleaning solution does not boil, and may be 90°C or lower.

[0098] In the contact step, the coating layer can be separated from the laminate. The method of this embodiment preferably includes a step of stirring the laminate in the presence of water after the contact step. This can more actively promote the separation of the coating layer.

[0099] <Advancing Contact Angle> In the contact step of the method of this embodiment, the surface of the coating layer and the cleaning liquid must be in a relationship where the advancing contact angle, measured by the expansion method, is 52.0° or less. By having an advancing contact angle of 52.0° or less during the contact step, excellent separation of the coating layer can be achieved even when the laminate includes a coating layer containing polyamide resin.

[0100] The advance contact angle described above can be calculated by the method described in the examples. The advance contact angle can be adjusted in any way, for example, by appropriately adjusting the type of surfactant contained in the cleaning solution, the temperature of the cleaning solution, or the pH of the cleaning solution.

[0101] A preferred embodiment of the method of this embodiment will be described in detail below. However, the present invention is not limited in any way to this preferred embodiment. In the preferred embodiment, the "laminated body," "plastic substrate layer," "coating layer," and "cleaning liquid" are the same as those described above.

[0102] A preferred embodiment of the method of this embodiment is a method comprising: a crushing step of crushing the laminate; an immersion step, which is a contact step of immersing the laminate after the crushing step in the cleaning solution; and a separation step of separating the coating layer from the laminate by stirring the laminate after the immersion step in the presence of water.

[0103] <Crushing Process> In one preferred embodiment, performing a crushing process can improve the processing efficiency of subsequent processes. The method for crushing the laminate is not particularly limited, and known methods can be used. Crushing of the laminate can be carried out in the presence of water, in which case a known wet crushing pump can be suitably used. Alternatively, crushing of the laminate can be carried out in an air atmosphere where no liquid such as a solvent is present, in which case a known dry crusher can be suitably used. In this case, it is preferable to crush the laminate while cooling the laminate or the dry crusher in order to prevent the plastic substrate layer or coating layer from softening due to frictional heat during crushing and the cross-section of the laminate from fusing together after the crushing process.

[0104] In the crushing process, the laminate can be crushed so that the dimensions in the short side direction and the long side direction are preferably 1 mm to 30 mm, more preferably 1 mm to 20 mm.

[0105] <Immersion Process> In one preferred embodiment, the immersion process corresponds to the contact process described above. In the immersion process, the laminate after the crushing process is immersed in a washing solution. This allows the laminate after the crushing process (i.e., the crushed pieces of the laminate) to swell, and this swelling can further improve the separation properties of the coating layer.

[0106] The immersion step is not mandatory, but it is preferable to include stirring. In this case, the laminate after the crushing step can be swelled more efficiently. The stirring apparatus and conditions are not particularly limited, and known ones can be appropriately adopted. For example, immersion with stirring can be performed by using a container equipped with a motor-driven stirring blade, a container equipped with means for generating ultrasonic waves, or a container equipped with a shaking means as the stirring apparatus.

[0107] In the immersion process, the immersion time is preferably such that the laminate after the crushing process is sufficiently swollen, and specifically, it is preferably 30 minutes or more. Furthermore, from the viewpoint of processing efficiency, the immersion time is preferably 48 hours or less. Also, if the temperature of the washing solution is at room temperature, the laminate after the crushing process can be sufficiently swollen with an immersion time of 24 hours. Furthermore, if the temperature of the washing solution is, for example, 40°C, the laminate after the crushing process can be sufficiently swollen with an immersion time of 16 hours. Furthermore, if the temperature of the washing solution is, for example, 75°C, the laminate after the crushing process can be sufficiently swollen with an immersion time of 120 minutes. In addition, the immersion time can be appropriately adjusted by the combination of whether or not stirring is performed and the immersion temperature as described above.

[0108] <Washing Process> After the immersion process, the laminate (fragmented pieces of the laminate) may have a washing solution containing inorganic bases attached to it. Therefore, in the method of this embodiment, although not particularly limited, it is preferable to perform a washing process after the immersion process to wash the laminate in order to remove the attached inorganic bases. Water can usually be used for washing the laminate in this way.

[0109] <Separation Process> In the separation process, the laminate (crushed pieces of the laminate) after the immersion process or washing process is stirred in the presence of water to separate the coating layer from the laminate. The stirring apparatus and conditions in the separation process are not particularly limited, and known apparatuses and conditions can be appropriately adopted. For example, the laminate can be stirred in the presence of water by using a container equipped with a motor-driven stirring blade, a container equipped with means for generating ultrasonic waves, or a container equipped with a shaking mechanism as the stirring apparatus.

[0110] In the separation process, it is preferable that the water is substantially free of inorganic bases. This helps to suppress the deterioration of the stirring equipment used in the separation process.

[0111] In the separation process, plastic fragments are obtained by separating the coating layer from the laminate (fragmented pieces of the laminate). Therefore, the method of this embodiment allows for the recovery of these plastic fragments in the separation process. The recovery method is not particularly limited and can be any conventional method, such as specific gravity separation in a liquid such as water.

[0112] The present invention will be described in more detail below with reference to examples, but the present invention is not limited in any way to the following examples.

[0113] <Preparation of Polyamide Resin Solution> In a four-necked flask equipped with a stirrer, thermometer, reflux condenser, and nitrogen gas inlet tube, 100 parts by mass of dimer acid (Halidaimer 270S; manufactured by Harima Chemicals Co., Ltd.), 1 part by mass of tall oil fatty acid (Hartol FA-1; manufactured by Harima Chemicals Co., Ltd.), 5 parts by mass of sebaciate, 10 parts by mass of ethylenediamine, 5 parts by mass of hexamethylenediamine, and 0.24 parts by mass of triphenylphosphine were placed. The four-necked flask was then subjected to a nitrogen atmosphere, and the temperature was slowly raised to 200°C while stirring to homogenize under a nitrogen gas flow. Subsequently, dehydration condensation was carried out at 200°C for 5 hours while stirring to obtain a polyamide resin. The polyamide resin had a softening point of 123°C, an amine value of 2 mg KOH / g, an acid value of 8 mg KOH / g, and a number-average molecular weight of 10,000. A polyamide resin solution was obtained by mixing the polyamide resin, isopropyl alcohol, and methylcyclohexane so that the mass ratio (mass of polyamide resin:mass of isopropyl alcohol:mass of methylcyclohexane) was 30:20:40. The solid content of the polyamide resin solution was 30% by mass relative to the total volume of the polyamide resin solution.

[0114] The number-average molecular weight mentioned above was measured using the following equipment and conditions: Equipment: HLC8220 system manufactured by Tosoh Corporation Separation column: Four TSKgelGMHHR-N columns manufactured by Tosoh Corporation Separation column temperature: 40°C Mobile phase: Tetrahydrofuran manufactured by Wako Pure Chemical Industries, Ltd. Flow rate: 1.0 ml / min Sample concentration: 0.4% by mass Sample injection volume: 100 μl Detector: Differential refractometer

[0115] <Preparation of Nitrocellulose Resin Solution> Isopropyl alcohol, ethyl acetate, n-propyl acetate, and methylcyclohexane were mixed in a mass ratio (mass of isopropyl alcohol: mass of ethyl acetate: mass of n-propyl acetate: mass of methylcyclohexane) of 25:25:13:10 to prepare a mixture. 28.6 parts by mass of industrial nitrate cotton L1 / 8 (manufactured by Nobel, nitrocellulose, solid content 70% by mass, viscosity 1.6-2.9% at a solution concentration of 25.0% according to JIS K-6703) were added to 71.4 parts by mass of the prepared mixture and mixed to obtain a nitrocellulose resin solution. The proportion of solids in the nitrocellulose resin solution was 20% by mass relative to the total amount of the nitrocellulose resin solution.

[0116] <Preparation of composition for printing layer (blue)> 40 parts by mass of polyamide resin solution, 15 parts by mass of nitrocellulose resin solution, 10 parts by mass of phthalocyanine-based blue pigment (DIC Corporation, FASTGENBlueLA5380B15:3), 15 parts by mass of isopropyl alcohol, and 30 parts by mass of ethyl acetate were mixed to obtain a composition for the printing layer (blue).

[0117] <Laminate Fabrication> A composition for the printing layer (blue) was applied without gaps onto a plastic film (biaxially oriented polypropylene film, thickness: 20 μm) serving as the plastic substrate layer using a gravure printing press equipped with a gravure plate with a plate depth of 43 μm. Next, the laminate was dried and cured by passing it through a 70°C oven to form a printing layer as a coating layer on the plastic film. In this way, a laminate was obtained having a printing layer (coating layer) on a plastic substrate layer.

[0118] <Preparation of Cleaning Solutions> Cleaning solutions 1 to 21 were prepared by mixing each component to achieve the compositions shown in Table 1 and Tables 1-1 to 1-3. The surfactants in cleaning solutions 1 to 6 consist of component A and component B in the mass ratios shown in Table 1. The surfactants in cleaning solutions 7 to 21 consist of two components selected from component A to component M in the mass ratios shown in Tables 1-1 to 1-3.

[0119]

[0120]

[0121]

[0122]

[0123] *1 Component A: Amhitol 24B (manufactured by Kao Corporation), lauryldimethylaminoacetic acid betaine (compound represented by general formula (1a-1)), amphoteric surfactant *2 Component B: DKS NL Dash 403 (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), polyoxyalkylene alkyl ether, nonionic surfactant, HLB value = 6.5 *3 Component C: DKS NL Dash 408 (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), polyoxyalkylene alkyl ether, nonionic surfactant, HLB value = 12.0 *4 Component D: DKS NL Dash 410 (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), polyoxyalkylene alkyl ether, nonionic surfactant, HLB value = 12.5 *5 Component E: Emulgen 108 (manufactured by Kao Corporation), polyoxyethylene fatty acid ester, nonionic surfactant, HLB value = 12.1 *6 Component F: NIKKOL Component G: NIKKOL BL-21 (Nikko Chemicals), polyoxyethylene alkyl ether, nonionic surfactant, HLB value = 12.3 *7 Component H: Amogen S-H (Daiichi Kogyo Seiyaku Co., Ltd.), alkyldimethylaminoacetic acid betaine (compound represented by general formula (1a-1)), amphoteric surfactant *9 Component I: Amogen CB-H (Daiichi Kogyo Seiyaku Co., Ltd.), coconut oil fatty acid amidopropyl dimethylaminoacetic acid betaine (compound represented by general formula (1a)), amphoteric surfactant *10 Component J: Nissan Anon BDF-R (NOF Corporation), coconut oil fatty acid amidopropyl betaine (compound represented by general formula (1a)), amphoteric surfactant *11 Component K: Nissan Anon BF (manufactured by NOF Corporation), coconut oil alkyl betaine (compound represented by general formula (1a-1)), amphoteric surfactant *12 Component L: Nissan Cation M2-100R (manufactured by NOF Corporation), benzalkonium chloride (compound represented by general formula (4)), cationic surfactant *13 Component M: Nissan Cation F2-50R (manufactured by NOF Corporation), benzalkonium chloride (compound represented by general formula (4)), cationic surfactant

[0124] <Measurement of Forward Contact Angle> The forward contact angle was measured between the laminate (surface of the printed layer) and the cleaning solution at the timing of the immersion process (contact process) described later. The forward contact angle was measured using the expansion method, and a DMo-902 manufactured by Kyowa Interface Science Co., Ltd. was used as the measuring device. The laminate was placed on a base with the side containing the printed layer facing upward. A 4 μL droplet of cleaning solution was formed on the tip of a needle, and the needle was lowered to bring the droplet into contact with the printed layer. Then, the cleaning solution was continuously discharged from the tip of the needle at a discharge rate of 6 μL / s, and the droplet was photographed with a camera 1000 ms (1 second) after the start of discharge. The contact angles at both ends of the photographed droplet were measured, and the average value was taken as the forward contact angle. The forward contact angle was measured while adjusting the temperature of the droplet and laminate to 25°C, 50°C, or 80°C.

[0125] <Crushing Process> The prepared laminate was fed into a dry crusher equipped with a screen with a hole diameter of 10 mm, and crushed so that the pieces were approximately 5-10 mm in the short side direction and 10-20 mm in the long side direction.

[0126] <Immersion Process (Contact Process)> A washing solution was selected from washing solutions 1 to 21 shown in Table 1 and Tables 1-1 to 1-3, and the various conditions of the washing solution, especially the temperature, were adjusted as appropriate. Then, while maintaining the above conditions of the washing solution, the laminated material (crushed pieces of the laminated material) after the crushing process was immersed in the washing solution for 120 minutes while stirring at 500 rpm using a stirrer.

[0127] <Separation Process> A washing and grinding machine "PFS-40" manufactured by Nippon Seam Co., Ltd. (grid mesh size = 5 mmΦ) was used. Using 10 g of the laminate after the immersion process (contact process), the machine was operated at a rotation speed of 600 rpm while supplying water at 15 L / min to separate the coating layer from the laminate.

[0128] <Evaluation of Separability> Photographs were taken of the plastic pieces obtained in the separation process and the laminate after the immersion process using an optical microscope. The print layer adhesion rate was calculated by image processing of the photographs. Using the calculated print layer adhesion rates, the print layer separation rate was calculated from the following formula: Print layer separation rate = (1 - Print layer adhesion rate on the plastic pieces obtained in the separation process / Print layer adhesion rate on the laminate after the immersion process) × 100 Then, an ABC evaluation was performed according to the following criteria. A, B, and C indicate good separation of the print layer (coating layer) in that order. A: Print layer separation rate is 75% or more and 100% or less B: Print layer separation rate is 50% or more and less than 75% C: Print layer separation rate is 0% or more and less than 50% The results are shown in Tables 2 to 7.

[0129]

[0130]

[0131]

[0132]

[0133]

[0134]

[0135] Tables 2 to 7 show that the embodiments according to the present invention exhibit superior separation of the printed layer compared to the comparative examples. This indicates that the cleaning method of the present invention exhibits superior separation of the coating layer even when the laminate comprises a coating layer containing a polyamide resin.

[0136] According to the present invention, it is possible to provide a method for cleaning a laminate that exhibits excellent separation of the coating layer, even when the laminate includes a coating layer containing a polyamide resin.

Claims

1. A method for cleaning a laminate, comprising a plastic substrate layer and a coating layer, wherein the coating layer is disposed on the outermost surface, and the method for separating the coating layer using a cleaning solution, wherein the method comprises a contact step of bringing the surface of the coating layer into contact with the cleaning solution, the coating layer contains a polyamide resin, the cleaning solution contains an inorganic base, a surfactant, and water, and during the contact step, the surface of the coating layer and the cleaning solution are in a relationship where the advancing contact angle measured by the expansion method is 52.0° or less.

2. The method according to claim 1, wherein the cleaning solution has a temperature of 50°C or higher.

3. The method according to claim 1 or 2, wherein the surfactant includes an amphoteric surfactant.

4. The amphoteric surfactant is represented by the general formula (1a): R １ -R ２ -N ＋ (CH ３ ) ２ CH ２ COO － (1a) [In the general formula (1a), R １ represents a hydrogen atom or a group represented by the formula (2): R ３ C(=O)-NH-, R ２ represents an alkylene group or an alkenylene group, and in the formula (2), R ３ represents a linear or branched alkyl group or a linear or branched alkenyl group.]. The method according to claim 3, comprising one or more selected from the compounds represented by the above.

5. The compound represented by the general formula (1a) is: General formula (1a-1): C ｎ H ２ｎ＋１ N ＋ (CH ３ ) ２ CH ２ COO － The method according to claim 4, wherein the compound is represented by (1a-1) [wherein n represents the average number of moles added].

6. The method according to claim 5, wherein n is 8 or greater in the general formula (1a-1).

7. The method according to claim 1, comprising: a crushing step of crushing the laminate; an immersion step, which is a contact step of immersing the laminate after the crushing step in the washing liquid; and a separation step of separating the coating layer from the laminate by stirring the laminate after the immersion step in the presence of water.

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