Method for cleaning laminates

Abstract

The present invention provides a method for cleaning laminates that offers excellent separation of the coated layer without the need to use a highly basic cleaning solution. [Solution] 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 of the laminate, and the method comprising a contact step of bringing the surface of the coating layer into contact with the cleaning solution, wherein the cleaning solution contains sodium carbonate and / or sodium bicarbonate, 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.

Description

[Technical Field]

[0001] The present invention relates to a method for cleaning laminates. [Background technology]

[0002] Currently, the amount of waste plastic collected separately (recycling rate) worldwide is only 9% of the plastic manufactured. Of the 91% of waste plastic that is not collected separately, 12% is incinerated, and 79% ends up in landfills or is released into the environment (Non-Patent Literature 1). One reason for this persistently low recycling rate is the difficulty of implementing a separate collection system.

[0003] Specifically, in order to recycle plastics, it is necessary to separate and collect waste plastics, which are composed of various plastic materials such as polyethylene (PE) and polypropylene (PP), into individual materials. However, many plastic products, including laminated films, are made by bonding different plastic materials together, making it difficult to separate and collect them individually. Therefore, there is a strong need to develop a recycling system that can easily separate and collect waste plastics.

[0004] Furthermore, from a cost perspective, it is difficult to return recycled plastic products to the same quality as before recycling. Moreover, plastic products inherently degrade with each recycling cycle. Therefore, recycled plastic products inevitably suffer from a decline in quality.

[0005] In this regard, reasons for the decline in the quality of recycled plastics include the mixing of ink or pigments as impurities in the plastics. In particular, since many plastic products are printed on their surfaces, it is difficult to decolorize them in the recycling process. In addition, in plastic films constituting plastic products, 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. However, components derived from these coating layers can also cause unintended coloring.

[0006] As a result of these, recycled plastic products are often colored. Such recycled plastic products not only have significantly low commercial value due to 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] In addition, 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 alkaline solution (cleaning liquid) while heating and stirring the laminated film at 20 to 90°C or vibrating it with ultrasonic waves.

Prior Art Documents

Non-Patent Documents

[0009]

Non-Patent Document 1

Patent Documents

[0010] [Patent Document 1] Japanese Patent Publication No. 2001-031899 [Patent Document 2] International Publication No. 2020 / 066652 [Overview of the project] [Problems that the invention aims to solve]

[0011] Patent documents 1 and 2 describe cleaning solutions used to separate the printed layer from the laminate, which contain strong alkalis such as sodium hydroxide, resulting in highly basic cleaning solutions. When highly basic cleaning solutions are used, the equipment used in the recycling method deteriorates quickly, potentially requiring frequent replacement of the equipment. As a result, the recycling method can become costly. Therefore, it is desirable to minimize the use of highly basic cleaning solutions in recycling methods.

[0012] Therefore, the object of the present invention is to provide a method for cleaning laminates that exhibits excellent separation of the coating layer without using a highly basic cleaning solution. [Means for solving the problem]

[0013] Through diligent research, the inventors discovered that when attempting to separate a coated layer from a laminate using a cleaning solution, the above problem can be solved if the cleaning solution and the surface of the coated layer that comes into contact with the cleaning solution are in a predetermined contact angle relationship, leading to the present invention. The gist of the present invention, which solves the above problems, is as follows.

[0014] [1] A method for cleaning a laminate, comprising a plastic substrate layer and a coating layer, wherein the coating layer is located on the outermost surface of the laminate, and the method for separating the coating layer using a cleaning solution, The method comprises a contact step of bringing the surface of the coating layer into contact with the cleaning liquid, The cleaning solution contains sodium carbonate and / or sodium bicarbonate, a surfactant, and water. During the contact step, the surface of the coating layer and the cleaning liquid have a relationship such that the advancing contact angle measured by the spreading method is 52.0° or less. A method for cleaning a laminate, characterized by this.

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

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

[0017] [4] The amphoteric surfactant is of the general formula (1a): R 1 -R 2 -N + (CH3)2CH2COO - (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-, and R 2 represents an alkylene group or an alkenylene group. 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], including one or more selected from the compounds represented by.

[0018] [5] The compound represented by the general formula (1a) is a compound represented by the general formula (1a-1): C n H 2n+1 N + (CH3)2CH2COO - (1a-1) 〔In the general formula (1a-1), n represents the average number of added moles.〕 The method according to [4], which is a compound represented by.

[0019] [6] In the general formula (1a-1), n is 8 or more, the method according to [5].

[0020] [7] Crushing the laminate, a crushing step, and The aforementioned contact step includes an immersion step in which the laminated material after the crushing step is immersed in the cleaning solution, The method according to any one of [1] to [6], comprising a separation step of separating the coating layer from the laminate by stirring the laminate after the immersion step in the presence of water. [Effects of the Invention]

[0021] According to the present invention, a method for cleaning laminates that exhibits excellent separation of the coating layer without using a highly basic cleaning solution can be provided. [Modes for carrying out the invention]

[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 cleaning solution contains sodium carbonate and / or sodium bicarbonate, 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 the inventors' diligent research, they surprisingly discovered that when separating a coated layer from a laminate using a cleaning solution, the separation of the coated layer is excellent when the advancing contact angle between the surface of the coated layer and the cleaning solution, as measured by the expansion method, is 52.0° or less. This is presumed to be because the wettability between the cleaning solution and the surface of the coated layer is improved, thereby improving the separation of the coated layer. Furthermore, the above-mentioned advancing contact angle relationship can be achieved using a cleaning solution containing sodium carbonate and / or sodium bicarbonate, and such cleaning solutions are typically low in basicity. Therefore, according to the present invention, a method for cleaning laminates that exhibits excellent separation of the coated layer without using a highly basic cleaning solution can be provided.

[0025] <Laminates as the target of processing> 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 base 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 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 include one of these coating layers alone, or two or more in combination.

[0032] The coating layer (printing layer, adhesive layer, detachable primer layer, functional coating layer, etc.) may contain a resin having an acidic group or a low-molecular-weight compound having an acidic group. In addition, the above coating layer may contain a resin that does not have an acidic group, in addition to the resin having an acidic group or a low-molecular-weight compound having an acidic group.

[0033] Examples of resins having acidic groups include rosin-modified maleic acid resins, rosin-modified fumaric acid resins, and polymer resins obtained by copolymerizing polymerizable monomers having acidic groups. Examples of polymerizable monomers having acidic groups include polymerizable monomers having carboxyl groups such as acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, cinnamic acid, or their acid anhydrides, polymerizable monomers having sulfonic acid groups such as sulfonated styrene, and polymerizable monomers having sulfonamide groups such as vinylbenzenesulfonamide. Specific examples of the above polymer resins include (meth)acrylic resins, styrene-(meth)acrylic resins, styrene-(anhydride)maleic acid resins, and terpene-(anhydride)maleic acid resins.

[0034] Examples of low molecular weight compounds containing acidic groups include saturated fatty acids, unsaturated fatty acids, hydroxy acids, aromatic carboxylic acids, dicarboxylic acids, tricarboxylic acids, oxocarboxylic acids, carboxylic acid derivatives, and acid anhydrides.

[0035] Examples of saturated fatty acids include lauric acid, myristic acid, palmitic acid, margaric acid, and stearic acid, while 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, melitic 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 pyruvate and oxaloacetate. Examples of carboxylic acid derivatives include amino acids and nitrocarboxylic acids. Examples of acid anhydrides include trimellitic anhydride and pyromellitic anhydride.

[0036] -Print 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).

[0037] 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.

[0038] 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. Furthermore, the printing layer may be a single-color printing layer or a multi-color printing layer.

[0039] -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.

[0040] 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 types, and may be curing or non-curing types.

[0041] The adhesive layer is typically formed by applying an adhesive layer composition (solution) to the surface to be bonded and allowing it to dry.

[0042] -Desorbing 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).

[0043] In a laminate, the deleasable primer layer is preferably in contact with the plastic substrate layer. Furthermore, it is preferable that the deleasable primer layer in the laminate is bonded to and sandwiched between the plastic substrate layer and other coating layers (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 enhanced.

[0044] 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.

[0045] Furthermore, the detachable primer layer (and composition for the detachable 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 acetal; 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.

[0046] 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.

[0047] Furthermore, urethane resin is a general term for polymer compounds having urethane bonds (-NHCOO-). The above-mentioned urethane resin can be obtained, for example, by reacting an aromatic polyester polyol with a polyisocyanate and, if necessary, a chain extender.

[0048] 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.

[0049] 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.

[0050] 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. 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.

[0051] - Functional coating layer - The laminate used in this embodiment may include 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 resistance, antibacterial properties, UV cut, heat dissipation, photocatalysis, weather resistance, anti-fogging, fingerprint 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.

[0052] 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.

[0053] The functional coating layer may be a layer formed of a metallic material (metal layer). The metal layer may be a metal foil, or a metal vapor-deposited layer formed by the deposition of a metal or metal oxide. Examples of metal foils include foils of metals with excellent malleability such as gold, silver, copper, zinc, iron, lead, tin and their alloys, steel, stainless steel, and aluminum. Examples of metal vapor-deposited layers include layers containing aluminum, aluminum oxide, silica, zinc oxide, etc.

[0054] The functional coating layer may be a single layer or a multilayer consisting of multiple identical or different functional coating layers. For example, the functional coating layer may be a multilayer consisting of a layer formed using the above-mentioned various coating agents and the above-mentioned metal vapor deposition layer. In this case, the layer formed using the above-mentioned various coating agents may be provided in the laminate via a metal vapor deposition layer in contact with the plastic substrate layer.

[0055] <Cleaning solution> The cleaning solution contains sodium carbonate and / or sodium bicarbonate (hereinafter sometimes collectively referred to as "carbonate-based alkaline components"), a surfactant, and water.

[0056] By including sodium carbonate and / or sodium bicarbonate in the cleaning solution, the basicity of the cleaning solution can be reduced. This helps to suppress the deterioration of the equipment used in the cleaning method. The concentration of the carbonate-based alkaline component in the cleaning solution is preferably 0.1% to 10% by mass, and more preferably 0.1% to 5% by mass, as a percentage of the total volume of the cleaning solution.

[0057] 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.

[0058] 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 + (CH3)2CH2COO - (1a) [In general formula (1a), R 1 is a hydrogen atom or formula (2):R 3 The group represented by C(=O)-NH- is shown, 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.

[0059] R 2 The alkylene group and alkenylene group in the compound may be linear or branched.

[0060] The compounds represented by general formula (1a) may be used individually or in combination of two or more.

[0061] Compounds represented by general formula (1a) are those with general formula (1a-1): C n H 2n+1 N + (CH3)2CH2COO - (1a-1) It is preferable that the compound is represented by the general formula (1a-1), where 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.

[0062] 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.

[0063] The amphoteric surfactant may include a compound having an imidazolinium betaine skeleton.

[0064] Amphoteric surfactants have the general formula (1b): R 4 -(NHC2H4) nb -N(R 5 )2 [In general formula (1b), R 4 R 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 R represents a hydrogen atom, a group represented by -CH2COONa, or a group represented by -CH2COOH (however, there are two R groups). 5 They may be the same or different, and at least one R 5 This is a group represented by -CH2COONa. It may also contain one or more compounds selected from those represented by ].

[0065] 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.

[0066] Amphoteric surfactants have the general formula (1c): R6 -N + (CH3)2O - [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 [ ].

[0067] 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.

[0068] These amphoteric surfactants may be used individually or in combination of two or more.

[0069] 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.

[0070] Nonionic surfactants are given by formula (3): R 7 -O-[CH2-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. 1It 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.

[0071] 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.

[0072] R 7 In this context, an example of an octylphenol group is the octylphenol ethoxylate group.

[0073] These nonionic surfactants may be used individually or in combination of two or more.

[0074] 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 The -CH2- in the alkyl and alkenyl groups in R may be substituted with -C(=O)-, -NH-, or -C(=O)-NH-, 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. 11The -CH3 in the alkyl and alkenyl groups in may be substituted with a carboxyl group or a phenyl group. It may also contain one or more compounds selected from those represented by [ ].

[0075] There are no particular restrictions on the anionic surfactant; known surfactants can be used.

[0076] The concentration of the surfactant in the cleaning solution is preferably 0.01% to 5% by mass, and more preferably 2% or less, as a percentage of the total volume of the cleaning solution.

[0077] The surfactant in the cleaning solution preferably contains an amphoteric surfactant. In this case, the advancing contact angle, which will be 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).

[0078] 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.

[0079] When the surfactant includes both an amphoteric surfactant and a nonionic surfactant, 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 using the following formula. HLB value = (20 × sum of formula weights of hydrophilic parts) / molecular weight

[0080] The cleaning solution may also contain appropriate amounts of other components besides those mentioned above, such as organic solvents and defoaming agents.

[0081] 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.

[0082] <Contact process> In the method of this embodiment, the contact step involves bringing the surface of the coating layer in the laminate 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.

[0083] 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 process is typically the immersion process, which will be described later.

[0084] 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.

[0085] During the contact process, the coating layer may 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 layers.

[0086] <Advancing contact angle> In the contact step of the method of this embodiment, the surface of the coating layer and the cleaning solution must be in a relationship where the advancing contact angle, measured by the expansion method, is 52.0° or less. The relationship in which the advancing contact angle during the contact process is 52.0° or less results in excellent separation of the coating layer. Furthermore, the aforementioned relationship in the advancing contact angle can also be achieved using a cleaning solution containing sodium carbonate and / or sodium bicarbonate. Therefore, excellent separation of the coating layer can be achieved without using a highly basic cleaning solution that mainly contains strong alkalis such as sodium hydroxide.

[0087] The aforementioned advancing contact angle can be calculated by the method described in the embodiment. The forward contact angle can be adjusted without particular limitations, for example, by appropriately adjusting the type of surfactant contained in the cleaning solution, the temperature of the cleaning solution, and the pH of the cleaning solution.

[0088] 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.

[0089] A preferred embodiment of the method of this embodiment is: A crushing step for crushing the aforementioned laminate, The aforementioned contact step includes an immersion step in which the laminated material after the crushing step is immersed in the cleaning solution, The method comprises a separation step of separating the coating layer from the laminate by stirring the laminate after the immersion step in the presence of water.

[0090] <Crushing process> In one preferred embodiment, the processing efficiency of subsequent processes can be increased by performing a crushing step. The method for crushing the laminate is not particularly limited, and known methods can be used. The 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, the 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 step.

[0091] 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.

[0092] <Soaking process> In one preferred embodiment, the immersion step corresponds to the contact step described above. In the immersion step, the laminate after the crushing step is immersed in a washing solution. This allows the laminate after the crushing step (i.e., the crushed pieces of the laminate) to swell, and this swelling can further improve the separability of the coating layer.

[0093] 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.

[0094] 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 room temperature, a immersion time of 24 hours is sufficient to sufficiently swell the laminate after the crushing process. Furthermore, if the temperature of the washing solution is, for example, 40°C, a immersion time of 16 hours is sufficient to sufficiently swell the laminate after the crushing process. Furthermore, if the temperature of the washing solution is, for example, 75°C, a immersion time of 120 minutes is sufficient to sufficiently swell the laminate after the crushing process. 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.

[0095] <Washing process> The laminate (crushed pieces of the laminate) after the immersion process may have a cleaning solution containing carbonate-based alkaline components adhering to it. Therefore, in the method of this embodiment, although not particularly limited, it is preferable to perform a cleaning step after the immersion process to clean the laminate in order to remove the adhering carbonate-based alkaline components. Water can usually be used for cleaning the laminate in this way.

[0096] <Separation process> In the separation process, the laminate (or crushed pieces of the laminate) after the immersion 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.

[0097] In the separation process, it is preferable that the water is substantially free of carbonate-based alkaline components. This helps to suppress the deterioration of the stirring equipment used in the separation process.

[0098] 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. [Examples]

[0099] 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.

[0100] <Preparation of cleaning solution> Cleaning solutions 1 to 27 were prepared by mixing each component to achieve the compositions shown in Tables 1 to 5. The surfactants in cleaning solutions 1 to 12 consist of components A and B in the mass ratios shown in Tables 1 and 2. The surfactants in cleaning solutions 13 to 27 consist of two components selected from components A to M in the mass ratios shown in Tables 3 to 5.

[0101] [Table 1]

[0102] [Table 2]

[0103] [Table 3]

[0104] [Table 4]

[0105] [Table 5]

[0106] *1 Ingredient A: Amhitol 24B (manufactured by Kao Corporation), Lauryldimethylaminoacetic acid betaine (compound represented by general formula (1a-1)), amphoteric surfactant *2 Ingredient B: DKS NL Dash 403 (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), polyoxyalkylene alkyl ether, nonionic surfactant, HLB value = 6.5 *3 Ingredient C: DKS NL Dash 408 (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), polyoxyalkylene alkyl ether, nonionic surfactant, HLB value = 12.0 *4 Ingredient D: DKS NL Dash 410 (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), polyoxyalkylene alkyl ether, nonionic surfactant, HLB value = 12.5 *5 Ingredient E: Emulgen 108 (manufactured by Kao Corporation), polyoxyethylene fatty acid ester, nonionic surfactant, HLB value = 12.1 *6 Ingredient F: NIKKOL BL-4.2 (manufactured by Nikko Chemicals Co., Ltd.), polyoxyethylene alkyl ether, nonionic surfactant, HLB value = 12.3 *7 Ingredient G: NIKKOL BL-21 (manufactured by Nikko Chemicals Co., Ltd.), polyoxyethylene alkyl ether, nonionic surfactant, HLB value = 12.2 *8 Ingredient H: Amogen SH (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), alkyldimethylaminoacetic acid betaine, (compound represented by general formula (1a-1)), amphoteric surfactant *9 Ingredient I: Amogen CB-H (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), coconut oil fatty acid amidopropyl dimethylaminoacetic acid betaine (compound represented by general formula (1a)), amphoteric surfactant *10 Ingredient J: Nissan Anon BDF-R (manufactured by NOF Corporation), coconut oil fatty acid amidopropyl betaine (compound represented by general formula (1a)), amphoteric surfactant *11 Ingredient K: Nissan Anon BF (manufactured by NOF Corporation), coconut oil alkyl betaine (compound represented by general formula (1a-1)), amphoteric surfactant *12 Ingredients L: Nissan Cation M2-100R (manufactured by NOF Corporation), benzalkonium chloride (compound represented by general formula (4)), cationic surfactant *13 Ingredient M: Nissan Cation F2-50R (manufactured by NOF Corporation), benzalkonium chloride (compound represented by general formula (4)), cationic surfactant

[0107] <Fabrication of laminates> A gravure ink for surface printing (DIC Graphics, Glossa 507 primary color cyan S2) was applied seamlessly 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. The film was then dried and cured by passing it through a 70°C oven to form a printed layer as a coating layer on the plastic film. In this way, a laminate was obtained, comprising a printed layer (coating layer) on a plastic substrate layer.

[0108] <Measurement of advance contact angle> The advancing contact angle between the laminate (surface of the printed layer) and the cleaning solution was measured at the timing of the immersion process (contact process) described later. The advancing contact angle was measured using the extension 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 upwards. 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 advancing contact angle. The advancing contact angle was measured while adjusting the temperature of the droplet and laminate to 25°C, 50°C, or 80°C.

[0109] <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.

[0110] <Immersion process (contact process)> As the washing solution, washing solutions 1 to 27 shown in Tables 1 to 5 were selected, 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 being stirred at 500 rpm using a stirrer.

[0111] <Separation process> A washing and grinding machine "PFS-40" (grid mesh size = 5mmΦ) manufactured by Nippon Seam Co., Ltd. was used. Using 10g of the laminate after the immersion process (contact process), the machine was operated at a rotation speed of 600rpm while supplying water at 15L / min to separate the coating layer from the laminate.

[0112] <Evaluation of the separation properties of the coating layer> The infrared absorption spectra of the plastic fragments obtained in the separation process and the plastic film used to fabricate the laminate were measured using a Fourier transform infrared spectrophotometer manufactured by Shimadzu Corporation. A difference spectrum was prepared by subtracting the infrared absorption spectrum of the plastic film from the infrared absorption spectrum of the plastic substrate. From the prepared difference spectrum, the main absorption band originating from the coating layer, 1000-1500 cm², was identified. -1 The peak intensity (% (transmittance)) in the vicinity was calculated. Then, an ABC evaluation was performed according to the following criteria. A, B, and C indicate good separation of the coating layer, in that order. A: Peak intensity is 5% or less B: Peak intensity greater than 5% but less than or equal to 10% C: Peak intensity between 10% and 20% The results are shown in Tables 6 to 14.

[0113] [Table 6]

[0114] [Table 7]

[0115] [Table 8]

[0116] [Table 9]

[0117] [Table 10]

[0118] [Table 11]

[0119] [Table 12]

[0120] [Table 13]

[0121] [Table 14]

[0122] Tables 6 to 14 show that the examples according to the present invention exhibit superior separation of the printed layer (coated layer) compared to the comparative examples. This indicates that the cleaning method of the present invention exhibits superior separation of the printed layer (coated layer) even without using a highly basic cleaning solution in the immersion step (contact step). [Industrial applicability]

[0123] According to the present invention, a method for cleaning laminates that exhibits excellent separation of the coating layer without using a highly basic cleaning solution can be provided.

Claims

1. A method for cleaning a laminate, comprising a plastic substrate layer and a coating layer, wherein the coating layer is located on the outermost surface of the laminate, and the method for separating the coating layer using a cleaning solution, The method comprises a contact step of bringing the surface of the coating layer into contact with the cleaning liquid, The cleaning solution contains sodium carbonate and / or sodium bicarbonate, a surfactant, and water. During the aforementioned contact process, the surface of the coating layer and the cleaning solution are in a relationship where the advancing contact angle, as measured by the expansion method, is 52.0° or less. A method for cleaning a laminate, characterized by the features described above.

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 aforementioned amphoteric surfactant has 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

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 － (1a-1) The method according to claim 4, wherein the compound is represented by the general formula (1a-1), where n represents the average number of moles added.

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

7. A crushing step for crushing the aforementioned laminate, The aforementioned contact step includes an immersion step in which the laminated material after the crushing step is immersed in the cleaning solution, The method according to claim 1, comprising 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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