Method for recovering plastics

Abstract

To provide a method for recovering plastics, which has a high recovery rate and is capable of recovering plastics with a small residual rate of an ink film.SOLUTION: There is provided a method for recovering plastics, comprising: a process of crushing a plastic product in which an ink film is formed on a surface of a plastic substrate having a specific gravity of 1 g / cm3 or more and to obtain crushed pieces having an average diameter of 1 mm to 10 mm; a process of immersing the crushed pieces in a cleaning solution to obtain ink film fragments and plastic pieces in the cleaning solution; a process of separating the ink film fragments floating in the cleaning solution; and a process of separating the ink film fragments that have settled in the cleaning solution from the plastic pieces that have settled in the cleaning solution to recover the plastic pieces, wherein a surface energy of the ink film is lower than a surface energy of the plastic substrate and lower than a surface tension of the cleaning liquid.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to a method for recovering plastics. [Background technology]

[0002] Conventionally, a method for recording an ink image on a plastic substrate using ink has been known. When a plastic product on which an ink image has been recorded is recycled, the plastic product is crushed, the ink image is peeled off, and the plastic substrate is recovered.

[0003] For example, Patent Document 1 describes a method for recycling a plastic film laminate having at least two layers, in which the laminate is crushed in water or a detergent and simultaneously pressure-fed to reduce the surface roughness of the crushed pieces to 0.7 μm or more. Patent Document 2 describes a method for peeling / removing an ink film, characterized by using an ink cleaner containing a nonionic surfactant and water at a temperature of 25°C or higher to peel and / or remove an ink film from a plastic substrate having the ink film thereon. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2023-32031 [Patent Document 2] International Publication No. 2021 / 230032 Summary of the Invention [Problem to be solved by the invention]

[0005] When recovering plastic from plastic products on which ink images have been recorded, it is sometimes necessary to improve the recovery rate and reduce the rate at which ink films remain on the recovered plastic pieces.

[0006] The present disclosure has been made in consideration of these circumstances, and the problem that one embodiment of the present invention aims to solve is to provide a method for recovering plastics that has a high recovery rate and is capable of recovering plastics with a low rate of residual ink film. [Means for solving the problem]

[0007] The present disclosure includes the following aspects. <1> Specific gravity is 1g / cm 3 a step of crushing the plastic product having an ink film formed on the surface of the plastic substrate to obtain crushed pieces having an average diameter of 1 mm to 10 mm; Immersing the crushed pieces in a cleaning solution to obtain ink film pieces and plastic pieces in the cleaning solution; Separating ink film pieces suspended in the cleaning solution; and a step of separating the ink film pieces that have settled in the cleaning solution from the plastic pieces that have settled in the cleaning solution, and recovering the plastic pieces; The surface energy of the ink film is lower than the surface energy of the plastic substrate and lower than the surface tension of the cleaning liquid. How to recycle plastic. <2> The surface energy of the ink film is 20 mN / m to 25 mN / m. The surface energy of the plastic substrate is 40 mN / m or more, The surface tension of the cleaning liquid is 40 mN / m or more. <1> The method for recovering plastics described in the above. <3> The specific gravity of the ink film is 1.2 g / cm 3 is less than The specific gravity of the plastic substrate is 1.3 g / cm 3 It is super, <1> or <2> The method for recovering plastics described in the above. <4> In the process of separating ink film pieces floating in the cleaning solution, a filter with a mesh size of 20 μm to 100 μm is used. <1> ~ <3> 1. A method for recovering plastics according to any one of the preceding claims. <5> In the process of collecting plastic fragments, a filter with a mesh size of 100 μm to 1000 μm is used. <1> ~ <4> 1. A method for recovering plastics according to any one of the preceding claims. <6> The ink film includes a polymer having an acid group. <1> ~ <5> 1. A method for recovering plastics according to any one of the preceding claims. <7> The ink film contains a polymer including a polyether structure and a polysiloxane structure. <1> ~ <6> 1. A method for recovering plastics according to any one of the preceding claims. [Effects of the Invention]

[0008] According to one embodiment of the present invention, there is provided a method for recovering plastics that has a high recovery rate and is capable of recovering plastics with a low rate of residual ink film. DETAILED DESCRIPTION OF THE INVENTION

[0009] The plastic recovery method of the present disclosure will be described in detail below.

[0010] In this specification, a numerical range indicated using "to" means a range that includes the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In the numerical ranges described in stages in this specification, the upper or lower limit value described in a certain numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. Furthermore, in the numerical ranges described in this specification, the upper or lower limit value described in a certain numerical range may be replaced with a value shown in the examples.

[0011] In this specification, the amount of each component in a composition means the total amount of the multiple substances present in the composition, unless otherwise specified, when multiple substances corresponding to each component are present in the composition. As used herein, a combination of two or more preferred embodiments is a more preferred embodiment. In this specification, the term "process" includes not only an independent process but also a process that cannot be clearly distinguished from other processes, as long as the intended purpose of the process is achieved.

[0012] In this specification, the term "image" refers to a film formed by applying ink in general, and the term "image recording" refers to the formation of an image (that is, a film). Additionally, the concept of "image" in this specification also includes a solid image.

[0013] In this specification, the term "(meth)acrylate" encompasses both acrylate and methacrylate, and the term "(meth)acrylic" encompasses both acrylic and methacrylic.

[0014] As used herein, "plastic pieces" refers to plastic substrates that are smaller in size than the plastic substrates before being crushed. In this specification, the term "ink film pieces" refers to ink films that are smaller in size than the ink films before pulverization.

[0015] The disclosed method for recovering plastics is 3 The method includes the steps of crushing the plastic product having an ink film formed on the surface of the above-mentioned plastic substrate to obtain crushed pieces having an average diameter of 1 mm to 10 mm, immersing the crushed pieces in a cleaning solution to obtain ink film pieces and plastic pieces in the cleaning solution, separating the ink film pieces floating in the cleaning solution, and separating the ink film pieces that have settled in the cleaning solution from the plastic pieces that have settled in the cleaning solution to recover the plastic pieces, wherein the surface energy of the ink film is smaller than the surface energy of the plastic substrate and smaller than the surface tension of the cleaning solution.

[0016] In the plastic recovery method of the present disclosure, first, a plastic product is crushed to obtain crushed pieces having an average diameter of 1 mm to 10 mm. By making the average diameter of the obtained crushed pieces 1 mm to 10 mm, it is possible to recover plastics with a high recovery rate and a low rate of residual ink film. The crushed pieces are separated into ink film pieces and plastic pieces in the cleaning solution. Because the surface energy of the ink film is smaller than the surface energy of the plastic substrate and smaller than the surface tension of the cleaning solution, relatively larger ink film pieces float in the cleaning solution, while relatively smaller ink film pieces and plastic pieces settle in the cleaning solution. By separating the ink film pieces floating in the cleaning solution, the ink film pieces that have settled in the cleaning solution and the plastic pieces that have settled in the cleaning solution remain in the cleaning solution. Then, by separating the ink film pieces that have settled in the cleaning solution and the plastic pieces that have settled in the cleaning solution, it is possible to recover plastic with a high recovery rate and with a low residual ink film rate.

[0017] In contrast, Patent Documents 1 and 2 do not describe separating ink film pieces that have settled in the cleaning solution from plastic pieces that have settled in the cleaning solution.

[0018] Each step in the plastic recovery method of the present disclosure will be described below.

[0019] <Crushing process> The disclosed method for recovering plastics is 3 The method includes a step of crushing the plastic product having an ink film formed on the surface of the plastic base material to obtain crushed pieces having an average diameter of 1 mm to 10 mm (hereinafter also referred to as the "crushing step").

[0020] In the crushing step, the plastic product is crushed. The plastic product to be crushed has an ink film formed on the surface of the plastic substrate. The ink film may be formed on at least a part of the surface of the plastic substrate.

[0021] In the pulverization step, pulverized pieces with an average diameter of 1 mm to 10 mm are obtained. The crushed pieces are crushed pieces of plastic products. When an ink film is formed on a portion of the surface of the plastic substrate, the pulverized pieces include pulverized pieces with an ink film and pulverized pieces without an ink film (i.e., plastic pieces). In the cleaning liquid immersion step described below, the ink film is peeled off from the pulverized pieces with an ink film, and ink film pieces and plastic pieces are obtained.

[0022] The shape of the pulverized pieces is not particularly limited, and may be, for example, scale-like.

[0023] By making the average diameter of the crushed pieces 1 mm or more, the amount of plastic pieces that settle in the cleaning solution increases, improving the recovery rate of plastics. By making the average diameter of the crushed pieces 10 mm or less, the ink film pieces can be easily peeled off from the crushed pieces having the ink film, and plastics with a low rate of remaining ink film can be recovered.

[0024] From the viewpoint of further improving the recovery rate and further reducing the residual rate of the ink film, the average diameter of the pulverized pieces is preferably 1 mm to 20 mm, and more preferably 3 mm to 5 mm.

[0025] The average diameter of the crushed pieces is measured by the following method. Assuming that the crushed pieces are cylindrical, the relationship between the average diameter of the crushed pieces (L), the thickness of the plastic substrate (d), the mass of the crushed pieces (M), and the specific gravity of the plastic substrate (g) is expressed by the following equation. M = π × (L / 2) 2 ×d×g The thickness (d) of the plastic substrate is measured three times before crushing, and the average value is used. The specific gravity (g) of the plastic substrate is 1.38 in the case of polyethylene terephthalate (PET). The mass (M) of the crushed pieces is determined by measuring the mass of 300 crushed pieces and using the average value. L is calculated by substituting M, d, and g into the above formula.

[0026] There are no particular limitations on the method for crushing the plastic products, and the crushing is usually carried out using a known crusher or shredder.

[0027] (Plastic substrate) The shape and components of the plastic substrate are not particularly limited, but the plastic recovery method of the present disclosure is particularly suitable for recycling beverage containers, and the plastic substrate is preferably a plastic molded body for beverage containers. Specifically, the plastic substrate is preferably a PET bottle containing polyethylene terephthalate as a main component.

[0028] The specific gravity of the plastic substrate is 1g / cm 3 or more, 1.3 g / cm 3 More preferably, it is ultra- The specific gravity of the plastic substrate is 1g / cm 3 If this is the case, the plastic pieces will be more likely to settle in the cleaning solution (in other words, the plastic pieces will be less likely to float), thereby improving the recovery rate of plastics. The upper limit of the specific gravity of the plastic substrate is not particularly limited, but is within the range of general-purpose plastics, and is 1.5 g / cm 3 It is preferable that:

[0029] The specific gravity of the plastic substrate is measured using a hydrometer, for example, a submerged displacement density hydrometer (product name "DSG-1, Toyo Seiki Seisakusho Co., Ltd.").

[0030] The thickness of the plastic substrate is not particularly limited, but is, for example, 0.1 mm to 1 mm.

[0031] The surface energy of the plastic substrate is greater than the surface energy of the ink film. From the viewpoint of not impairing the floatability of the ink film, the surface energy of the plastic substrate is preferably 40 mN / m or more, more preferably 42 mN / m or more. Although there are no particular limitations on the upper limit of the surface energy of the plastic substrate, from the viewpoint of improving the releasability of the ink film from the plastic substrate in the washing step, it is preferably 60 mN / m.

[0032] The surface energy of a plastic substrate is measured using the following method. The contact angle between the surface of the plastic substrate, which is the measurement surface, and standard liquids (pure water, diiodomethane, and n-hexadecane) is measured at 25°C. γsv is calculated by solving the following linear equation with three unknowns: d and γsv p and γsv h The sum of these is taken as the surface energy γs. The values ​​of the surface energy dispersion term, polar term, and hydrogen bond term of the above standard liquids are taken from the literature ("Wetting Technology Handbook - Fundamentals, Measurement, Evaluation, and Data - Published by Techno System Co., Ltd., October 2001").

[0033]

number

[0034] γsv d : Surface energy dispersion term of the measurement surface γsv p : Surface energy polarity term of the measurement surface γsv h : Surface energy hydrogen bond term of the measurement surface γLv d : Surface energy dispersion term of standard liquid γLv p : Standard liquid surface energy polar term γLv h : Standard liquid surface energy hydrogen bond term θ: contact angle γL=γLv d +γLvp +γLv h

[0035] (ink film) The ink film formed on the surface of a plastic substrate is a film obtained by, for example, applying ink to the surface of a plastic substrate and curing (or solidifying) it. The method for applying the ink is not particularly limited, but from the viewpoint of recording a fine image on the surface of the plastic substrate, it is preferable to use an inkjet recording method.

[0036] The type of ink is not particularly limited, and may be a water-based ink or an active energy ray curable ink. From the viewpoint of water resistance, the ink is preferably an actinic energy ray-curable ink. That is, the ink film is preferably a film obtained by applying the ink to the surface of a plastic substrate using an inkjet recording method and then curing the ink by irradiating it with actinic energy rays.

[0037] Examples of active energy rays include gamma rays, beta rays, electron beams, ultraviolet rays, and visible light. Of these, ultraviolet rays are preferred as the active energy rays. The ink is preferably an ultraviolet-curable ink.

[0038] There are no particular restrictions on the components contained in the ink, but in the case of an actinic energy ray-curable ink, it is preferable that the ink contains a photopolymerizable compound, and more preferably a photoradical polymerizable compound.

[0039] The type of photoradical polymerizable compound is not particularly limited. As long as the ink contains a photoradical polymerizable compound, the same photoradical polymerization proceeds and an ink film is formed, regardless of the type of the photoradical polymerizable compound.

[0040] From the viewpoint of curability, the photoradical polymerizable compound is preferably a compound having an ethylenically unsaturated group, and more preferably a (meth)acrylate compound.

[0041] The ink may contain only one type of photopolymerizable compound, or two or more types. The number of polymerizable groups that the photopolymerizable compound has is not particularly limited, and may be only one or may be two or more.

[0042] From the viewpoint of reducing residual monomers in the ink film, the proportion of the polyfunctional polymerizable compound in the photopolymerizable compound is preferably 50% by mass or more.

[0043] If the proportion of the polyfunctional polymerizable compound in the photopolymerizable compound is high, the ink film becomes hard and fine pulverized pieces are likely to be generated by pulverization. In the past, it was not possible to separate such fine pulverized fragments, and the fine pulverized fragments were mixed in with the recovered plastic fragments. However, according to the plastic recovery method disclosed herein, even if the ink film is hard and fine pulverized fragments are generated, by carrying out the floating ink film fragment separation step and plastic recovery step described below, it is possible to recover plastic with a low residual ink film rate.

[0044] From the viewpoint of recovering plastics with a low rate of residual ink film, it is preferable that the ink film be easily peeled off from the crushed pieces having the ink film in the cleaning liquid immersion step described below. From the viewpoint of improving the releasability of the ink film from the plastic substrate, the ink film preferably contains a polymer having an acid group.

[0045] Methods for incorporating a polymer having an acid group into the ink film include, for example, a method of incorporating a polymer having an acid group into the ink, and a method of incorporating a photopolymerizable monomer having an acid group into the ink. In the former case, whether the ink is a water-based ink or an actinic energy ray-curable ink, by incorporating a polymer having an acid group into the ink, the ink film can contain the polymer having an acid group. In the latter case, the ink is an actinic ray-curable ink, and the photopolymerizable monomer having an acid group is polymerized by irradiation with actinic ray, so that the ink film contains a polymer having an acid group.

[0046] The ink film may be a single layer or two or more layers, i.e., a single-layer film formed from only one type of ink, or a multi-layer film formed from two or more types of ink. For example, a two-layer ink film is formed by applying a first ink to the surface of a plastic substrate and curing it, and then applying a second ink and curing it.

[0047] From the viewpoint of improving the releasability of the ink film from the plastic substrate, when the ink film has two or more layers, it is preferable that at least one layer contains a polymer having an acid group, and it is more preferable that the layer that is in direct contact with the plastic substrate contains a polymer having an acid group.

[0048] Examples of the acid group in the acid group-containing polymer include a carboxy group, a sulfo group, a phosphonic acid group, a phosphoric acid group, and a sulfonamide group.

[0049] -Photopolymerizable monomers with acid groups- In the present disclosure, a "monomer" refers to a compound having a molecular weight of less than 1000. The molecular weight of a monomer can be calculated based on the type and number of atoms constituting the monomer.

[0050] Examples of polymerizable monomers having a carboxy group include 2-(meth)acryloyloxyethyl succinate, 2-(meth)acryloyloxyethyl phthalate, 2-(meth)acryloyloxyethyl hexahydrophthalate, 2-(meth)acryloyloxypropyl phthalate, 2-(meth)acryloyloxypropyl hexahydrophthalate, 2-carboxyethyl (meth)acrylate, and (meth)acrylic acid.

[0051] Examples of polymerizable monomers having a sulfo group include 2-hydroxy-3-sulfopropyl(meth)acrylate, 2-(meth)acrylamido-2-methylpropanesulfonic acid, 2-sulfoethyl(meth)acrylate, 3-sulfopropyl(meth)acrylate, and 4-styrenesulfonic acid.

[0052] Examples of polymerizable monomers having a phosphoric acid group include 2-phosphonooxyethyl (meth)acrylate and 2-(meth)acryloyloxyethyl acid phosphate.

[0053] Among these, the photopolymerizable monomer having an acid group is preferably a photopolymerizable monomer having a carboxy group from the viewpoints of improving the releasability of the ink film from the plastic substrate, safety, and low viscosity. The content of the photopolymerizable monomer having an acid group is preferably 3% by mass to 30% by mass relative to the total amount of the ink.

[0054] -Polymers with acid groups- In this disclosure, "polymer" means a compound having a weight average molecular weight of 1000 or greater.

[0055] Examples of the polymer having an acid group include a (meth)acrylic copolymer, a polyurethane, a polyvinyl alcohol, a polyvinyl butyral, a polyvinyl formal, a polyamide, a polyester, and an epoxy resin. Among these, the polymer having an acid group is preferably a (meth)acrylic copolymer, a polyurethane, or a polyvinyl butyral.

[0056] In the present disclosure, the (meth)acrylic copolymer refers to a copolymer of (meth)acrylic acid, a (meth)acrylic acid ester (for example, a (meth)acrylic acid alkyl ester, a (meth)acrylic acid aryl ester, a (meth)acrylic acid allyl ester, etc.), a (meth)acrylamide, It refers to a copolymer containing a (meth)acrylic acid derivative, such as a (meth)acrylamide derivative, as a structural unit. Polyurethane is a polymer obtained by the condensation reaction of a polyfunctional isocyanate compound having two or more isocyanate groups with a polyhydric alcohol having two or more hydroxyl groups. Polyvinyl butyral is a polymer obtained by reacting polyvinyl alcohol, obtained by partial or complete saponification of polyvinyl acetate, with butyraldehyde under acidic conditions. Polyvinyl butyral also includes polymers with functional groups introduced into the molecule.

[0057] The (meth)acrylic copolymer preferably contains a structural unit having an acid group. Among these, the acid group is preferably a carboxy group. Examples of the structural unit having a carboxy group include a structural unit derived from (meth)acrylic acid and a structural unit derived from a structural unit represented by the following formula 1:

[0058] [ka]

[0059] In formula 1, R 1 represents a hydrogen atom or a methyl group, and R 2 represents a single bond or an (n+1)-valent linking group. A represents an oxygen atom or -NR 3 - represents R 3 represents a hydrogen atom or a monovalent hydrocarbon group having 1 to 10 carbon atoms. n represents an integer of 1 to 5.

[0060] For preferred embodiments and specific examples of the structural unit represented by Formula 1, as well as preferred embodiments of structural units other than the structural unit represented by Formula 1, reference can be made to Japanese Patent Nos. 4668111 and 5588887.

[0061] In particular, the polymer having an acid group preferably contains a structural unit derived from (meth)acrylic acid and a structural unit derived from a (meth)acrylic acid alkyl ester. The number of carbon atoms in the alkyl group contained in the (meth)acrylic acid alkyl ester is preferably 1 to 10, and more preferably 1 to 6.

[0062] The weight average molecular weight of the polymer having an acid group is preferably 1,000 to 1,000,000, more preferably 5,000 to 500,000, and even more preferably 10,000 to 200,000.

[0063] Furthermore, from the viewpoint of recovering plastics with a low residual ink film, it is preferable that the ink film easily floats in the cleaning liquid after the ink film is peeled off from the crushed pieces having the ink film in the cleaning liquid immersion process described below.

[0064] From the above viewpoint, the ink film preferably contains a polymer having a polyether structure and a polysiloxane structure. When the ink film contains a polymer having a polyether structure and a polysiloxane structure, the ink film has surfactant properties and is more likely to float. In the polymer containing a polyether structure and a polysiloxane structure, the mass ratio of the content of the polysiloxane structure to the content of the polyether structure is preferably 0.5 or more, more preferably 0.6 or more. The upper limit of this mass ratio is, for example, 0.95. By using a polymer having this mass ratio, the surface energy of the ink film can be appropriately controlled.

[0065] Methods for incorporating a polymer having a polyether structure and a polysiloxane structure into an ink film include, for example, a method for incorporating a polymer having a polyether structure and a polysiloxane structure into the ink, and a method for incorporating a photopolymerizable monomer having a polyether structure and a polysiloxane structure into the ink. In the former case, whether the ink is a water-based ink or an actinic energy ray-curable ink, by incorporating a polymer having a polyether structure and a polysiloxane structure into the ink, the ink film can contain the polymer having a polyether structure and a polysiloxane structure. In the latter case, the ink is an actinic ray-curable ink, and the photopolymerizable monomer having a polyether structure and a polysiloxane structure is polymerized by irradiation with actinic ray, so that the ink film contains a polymer having a constitutional unit derived from the photopolymerizable monomer having a polyether structure and a polysiloxane structure.

[0066] When the ink film has two or more layers, it is preferable that at least one layer contains a polymer containing a polyether structure and a polysiloxane structure.

[0067] -Photopolymerizable monomer containing polyether structure and polysiloxane structure- When the ink is an actinic energy ray-curable ink, the photopolymerizable monomer containing a polyether structure and a polysiloxane structure is preferably a compound having a (meth)acryloyl group, a polyether structure, and a polysiloxane structure (hereinafter also referred to as a "specific silicone compound"). When the ink contains a specific silicone compound, the ink film contains a polymer that includes structural units derived from the specific silicone compound.

[0068] The number of (meth)acryloyl groups contained in the specific silicone compound may be only one, or may be two or more. From the viewpoint of separability, the number of (meth)acryloyl groups is preferably 2 or more, and more preferably 3 or more. The upper limit of the number of (meth)acryloyl groups is not particularly limited, but from the viewpoint of ejection property, it is, for example, 5.

[0069] The specific silicone compound is preferably a polyether-modified polydimethylsiloxane having a (meth)acryloyl group. In the polyether-modified polydimethylsiloxane having a (meth)acryloyl group, the position of the polyether chain is not particularly limited, and may be at one end of the main chain, at both ends of the main chain, or as a side chain. The polyether chain is preferably a polyoxyalkylene chain.

[0070] Commercially available specific silicone compounds include, for example, BYK-UV3500, 3505, 3530, 3570, 3575, and 3576 (manufactured by BYK), Tegorad 2100, 2200, 2250, 2300, 2500, 2600, 2700, 2800, 2010, and 2011 (manufactured by Evonik), EBECRYL 350 and 1360 (manufactured by Daicel-Allnex), and KP-410, 411, 412, 413, 414, 415, 416, 418, 420, 422, and 423 (manufactured by Shin-Etsu Silicones).

[0071] From the viewpoint of enhancing the surface activity, the mass ratio of the content of the polysiloxane structure to the content of the polyether structure in the specific silicone compound is preferably 0.5 or more, more preferably 0.6 or more, and the upper limit of this mass ratio is, for example, 0.95.

[0072] The mass ratio of the polysiloxane structure content to the polyether structure content was determined by nuclear magnetic resonance spectroscopy (Nuclear Magnetic Resonance; 1 Calculated by H-NMR.

[0073] The ink used to form the ink film may contain components that are typically contained in known inks, such as colorants, dispersants, resins, polymerization initiators, and polymerization inhibitors.

[0074] When the ink film has two or more layers, the layer in direct contact with the plastic substrate may be a layer formed from a clear ink that does not substantially contain a colorant, and the other layers may be layers formed from colored inks that contain a colorant.

[0075] The surface energy of the ink film is less than the surface energy of the plastic substrate. The surface energy of the ink film is smaller than the surface tension of the cleaning liquid, which will be described later. When the relationship between the surface energy of the ink film, the surface energy of the plastic substrate, and the surface tension of the cleaning liquid satisfies the above-mentioned relationship, the ink film is easily suspended in the cleaning liquid, and as a result, plastics with a low residual ink film can be recovered.

[0076] The surface energy of the plastic substrate is preferably smaller than the surface tension of the cleaning liquid described below. That is, the surface energy of the ink film is preferably smaller than the surface energy of the plastic substrate, and the surface energy of the plastic substrate is preferably smaller than the surface tension of the cleaning liquid. When the relationship between the surface energy of the ink film, the surface energy of the plastic substrate, and the surface tension of the cleaning liquid satisfies the above relationship, the ink film is more likely to float in the cleaning liquid.

[0077] The surface energy of the ink film is not particularly limited, but from the viewpoint of ink ejection properties, it is preferably 20 mN / m or more. Furthermore, from the viewpoint of making it easier for the ink film to float in the cleaning liquid, the surface energy of the ink film is preferably 25 mN / m or less. In other words, the surface energy of the ink film is preferably 20 mN / m to 25 mN / m.

[0078] The surface energy of the ink film is measured in the same manner as the surface energy of the plastic substrate.

[0079] The specific gravity of the ink film is not particularly limited, but from the viewpoint of making it easier for the ink film to float in the cleaning liquid, it is preferably smaller than the specific gravity of the plastic substrate. Specifically, the specific gravity of the ink film is 1.2 g / cm 3 The specific gravity of the plastic substrate is less than 1.3 g / cm 3 Preferably, it is greater than 1000 .mu.m.

[0080] The specific gravity of the ink film is measured using a hydrometer, for example, a submerged displacement density hydrometer (product name "DSG-1, Toyo Seiki Seisakusho Co., Ltd.").

[0081] <Cleaning solution immersion process> The plastic recovery method disclosed herein includes a step of immersing the crushed pieces obtained in the crushing step in a cleaning solution to obtain ink film pieces and plastic pieces in the cleaning solution (hereinafter also referred to as the "cleaning solution immersion step").

[0082] As described above, when an ink film is formed on part of the surface of a plastic substrate, the crushed pieces include crushed pieces with an ink film and crushed pieces without an ink film (i.e., plastic pieces). The cleaning liquid used in the cleaning liquid immersion process is a liquid that can peel off the ink film from the crushed pieces having the ink film, and is a liquid that satisfies the relationship that "the surface energy of the ink film is smaller than the surface tension of the cleaning liquid."

[0083] To facilitate the floating of the ink film in the cleaning liquid, the surface tension of the cleaning liquid is preferably 40 mN / m or more, more preferably 60 mN / m or more. The upper limit of the surface tension of the cleaning liquid is not particularly limited, and is, for example, 75 mN / m.

[0084] The surface tension of the cleaning liquid is measured by a surface tensiometer, for example, an automatic surface tensiometer (product name "DY-300", manufactured by Kyowa Interface Science Co., Ltd.) by the plate method (25°C).

[0085] The cleaning liquid is preferably an alkaline aqueous solution from the viewpoint of removability of the ink film. The pH of the cleaning solution is preferably 8-14, and more preferably 10-13. When the cleaning liquid is an alkaline aqueous solution, examples of the alkaline component include basic metal compounds such as sodium hydroxide and potassium hydroxide; and organic amines such as ammonia and monomethanolamine.

[0086] The concentration of the alkaline component is not particularly limited, but is, for example, 0.1% by mass to 3% by mass relative to the total amount of the cleaning liquid.

[0087] The temperature of the cleaning liquid is preferably 50°C or higher, more preferably 70°C to 95°C, from the viewpoint of facilitating peeling of the ink film. In order to facilitate peeling of the ink film, it is preferable to agitate the cleaning liquid after immersing the crushed pieces in the cleaning liquid. The agitation speed and agitation time are appropriately adjusted.

[0088] In the cleaning solution immersion step, the ink film is peeled off from the crushed pieces with the ink film, yielding ink film pieces and plastic pieces, while the crushed pieces without the ink film remain in the cleaning solution as plastic pieces.

[0089] After the cleaning solution immersion step, it is preferable to stop stirring the cleaning solution and allow it to stand still, from the viewpoint of improving the separation of the ink film pieces. The standing time can be adjusted as appropriate.

[0090] Because the surface energy of the ink film is smaller than the surface tension of the cleaning liquid, relatively large ink film fragments (e.g., ink film fragments with a circle-equivalent diameter of 0.1 mm to 10 mm) float in the cleaning liquid, while relatively small ink film fragments (e.g., ink film fragments with a circle-equivalent diameter of less than 0.1 mm) and plastic fragments settle in the cleaning liquid.

[0091] <Floating ink film fragment separation process> The plastic recovery method of the present disclosure includes a step of separating ink film fragments floating in the cleaning solution (hereinafter also referred to as the "floating ink film fragment separation step").

[0092] As a method for separating the ink film pieces floating in the cleaning liquid, for example, a method using a filter can be mentioned. The filter preferably has an opening size of 20 μm to 100 μm. The material of the filter is not particularly limited, and examples thereof include resin, metal, cloth, and paper.

[0093] Specifically, it is preferable to immerse the filter in the cleaning liquid and scoop up the floating ink film pieces. After the floating ink film fragment separation process, ink film fragments that have settled in the cleaning liquid and plastic fragments that have settled in the cleaning liquid remain in the cleaning liquid.

[0094] <Plastic collection process> The plastic recovery method disclosed herein includes a process of separating ink film fragments that have settled in the cleaning solution from plastic fragments that have settled in the cleaning solution and recovering the plastic fragments (hereinafter also referred to as the "plastic recovery process").

[0095] One method for recovering plastics is to use a filter. The mesh size of the filter is preferably 100 μm to 1000 μm. The ink film particles that settle in the cleaning solution tend to be smaller in size than the plastic particles that settle in the cleaning solution. Therefore, by using a filter with a mesh size of 100 μm to 1000 μm, the ink film fragments that have settled in the cleaning solution can pass through the filter, and as a result, the plastics that have settled in the cleaning solution can be recovered.

[0096] After the plastic recovery process, a cleaning solution is obtained containing ink film fragments that have settled in the cleaning solution. The ink film fragments that have settled in the cleaning solution may be separated for the purpose of reusing the cleaning solution. For example, by using a filter with an opening of 30 μm or less, ink film fragments that have settled in the cleaning solution can be separated. The washing liquid from which the ink film pieces have been separated can be reused to recover plastics. [Example]

[0097] Hereinafter, the present disclosure will be described more specifically with reference to examples, but the present disclosure is not limited to the following examples as long as it does not depart from the gist of the disclosure.

[0098] [Preparation of Cyan Inks 1 to 3 and White Ink 1] In preparing the cyan ink and the white ink, first, a cyan pigment dispersion and a white pigment dispersion were prepared.

[0099] -Preparation of cyan pigment dispersion- Cyan pigment (30 parts by mass), SOLSPERSE32000 (9 parts by mass) as a dispersant, 3MPDDA (60 parts by mass) as a dispersion medium, and UV22 (1 part by mass) as a polymerization inhibitor were placed in a dispersing machine, Motor Mill M50 (manufactured by Eiger), and dispersion treatment was carried out using zirconia beads with a diameter of 0.65 mm at a peripheral speed of 9 m / s for 4 hours to obtain a cyan pigment dispersion.

[0100] -Preparation of white pigment dispersion- White pigment (50 parts by mass), SOLSPERSE41000 (10 parts by mass) as a dispersant, 3MPDDA (39 parts by mass) as a dispersion medium, and UV22 (1 part by mass) as a polymerization inhibitor were charged into a dispersing machine, Motor Mill M50 (manufactured by Eiger), and dispersion treatment was carried out using zirconia beads with a diameter of 0.65 mm at a peripheral speed of 9 m / s for 4 hours to obtain a white pigment dispersion.

[0101] Details of the components contained in the cyan pigment dispersion and the white pigment dispersion are as follows.

[0102] Cyan pigment: CI Pigment Blue 15:4 (product name: Heliogen (registered trademark) Blue D 7110 F, manufactured by DIC Corporation) ) White pigment: TiO2 (product name "KRONOS 2300", manufactured by KRONOS) SOLSPERSE32000: Polyethyleneimine-based dispersant (product name: SOLSPERSE32000, manufactured by Lubrizol) SOLSPERSE41000: Dispersant (product name "SOLSPERSE41000", manufactured by Lubrizol) 3MPDDA: 3-methyl-1,5-pentanediol diacrylate (product name "SR341", manufactured by Sartomer) UV22: A mixture of 2,6-bis(1,1-dimethylethyl)-4-(phenylmethylene)-2,5-cyclohexadiene-1-one and propoxylated glycerin triacrylate (product name "IRGASTAB UV-22," manufactured by BASF)

[0103] Next, the prepared cyan pigment dispersion and white pigment dispersion were mixed with the components shown in Table 1 below so that the content of each component was the content (mass %) shown in Table 1. The mixture was stirred for 20 minutes at 25°C and 5,000 rpm using a mixer (product name "L4R", manufactured by Silverson) to obtain cyan inks 1 to 3 and white ink 1 (shown as "Cyan 1 to Cyan 3, White 1" in Table 1).

[0104] <Polymerizable compound> ·3MPDDA: As above. 4-HBA: 4-hydroxybutyl acrylate (product name "4-HBA", manufactured by Osaka Organic Chemical Industry Ltd.)

[0105] <Polymerization initiator> BAPO: Bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (product name "Omnirad 819", manufactured by IGM Resins BV) Speedcure 7010L: A mixture of 50% by mass of 1,3-di({α-[1-chloro-9-oxo-9H-thioxanthen-4-yl)oxy]acetylpoly[oxy(1-methylethylene)]}oxy)-2,2-bis({α-[1-methylethylene)]}oxymethyl)propane and 50% by mass of trimethylolpropane EO-adduct triacrylate

[0106] <Polymerization inhibitor> UV12: N-nitroso-N-phenylhydroxylamine aluminum salt (product name: FLORSTAB UV-12, manufactured by Kromachem)

[0107] <Specific silicone compounds> The mass ratio M of the content of the polysiloxane structure to the content of the polyether structure is as follows. Tegorad 2010: (meth)acryloyl group-containing silicone surfactant (product name "Tegorad 2010", manufactured by Evonik, mass ratio M: 0.627119) Tegorad 2500: (meth)acryloyl group-containing silicone surfactant (product name "Tegorad 2500", manufactured by Evonik, mass ratio M: 0.937369) Tegorad 2100: (meth)acryloyl group-containing silicone surfactant (product name "Tegorad 2100", manufactured by Evonik, mass ratio M: 0.355208)

[0108] <Acrylic resin> BR113: Product name "Dianal BR113", manufactured by Mitsubishi Chemical Corporation, glass transition temperature 75°C, weight average molecular weight 30,000

[0109] [Table 1]

[0110] [Preparation of clear ink] The following components were mixed: The mixture was stirred for 20 minutes at 25°C and 5000 rpm using a mixer (product name "L4R", manufactured by Silverson) to obtain a clear ink. ·3MPDDA…52.6% by mass ·4-HBA…20% by mass A-SA: 2-acryloyloxyethyl succinic acid (product name: "NK Ester A-SA", manufactured by Shin-Nakamura Chemical Co., Ltd., polymerizable monomer with a carboxyl group) ... 10% by mass ·BAPO…3.8% by mass ·Speedcure7010L …0.2% by mass ·UV12…0.2% by mass ·Tegorad2100…13% by mass ·BR113 …0.2% by mass

[0111] [Creating plastic products with ink films] The plastic substrate was a PET bottle (500 mL PET bottle for carbonated drinks (Fukushima Container Co., Ltd.), specific gravity = 1.38 g / cm 3 Clear ink was applied to the barrel of a PET bottle (product name "CylinderJET," manufactured by Tritec) using an inkjet recording device (product name "KM1800i," manufactured by Konica Minolta). Specifically, the clear ink was applied to an area measuring 7 cm in the longitudinal direction of the PET bottle and 5 cm in the circumferential direction of the PET bottle at a droplet volume of 10.5 pL (picoliter) and a resolution of 600 x 600 dpi (dots per inch), recording a 100% solid image with a thickness of 4 μm to 6 μm. Furthermore, under the same conditions as for the application of the clear ink, cyan ink was applied to the surface to which the clear ink had been applied, recording a 100% solid image with a thickness of 4 μm to 6 μm. After the application of the clear ink and after the application of the cyan ink, respectively, an exposure dose of 10 mJ / cm was used using an LED light source attached to the inkjet recording device. 2 ~100mJ / cm 2 The LED light source used was a UV-LED irradiator (product name "G4B", manufactured by Kyocera Corporation) with a peak wavelength of 385 nm. The PET bottle with the image recorded on it was then placed in an exposure machine. The PET bottle was set horizontally. The exposure machine can rotate the PET bottle. While rotating the entire image recorded on the PET bottle, it was exposed to light using an LED light source. The exposure dose was 50 mJ / cm. 2 ~500mJ / cm 2 The clear ink and the cyan ink were completely cured by irradiation with ultraviolet light at 1000 kJ / cm 2 , to obtain a plastic product. In the image recording, the gap between the PET bottle surface and the inkjet head was adjusted to 0.5 mm to 1 mm, and the ejection voltage was adjusted to adjust the ejected droplet velocity to 7 m / s to 9 m / s.

[0112] <<Example 1>> [Plastic collection] (Crushing process) A plastic product on which an ink film was formed using clear ink and cyan ink 1 was used. Plastic products were crushed using a commercially available small crusher for PET bottles. The mesh size of the crusher was set to 8 mm. When crushed with a mesh size of 8 mm, scaly chips of about 4 mm were obtained.

[0113] (Cleaning solution immersion process) 500 g of scaly chips were stirred in the washing liquid for 15 minutes. After stirring for 15 minutes, the washing solution containing the scaly chips was allowed to stand for 10 minutes. As a cleaning liquid, a 1.5 mass % aqueous solution of sodium hydroxide at 85° C. (cleaning liquid A) was used.

[0114] (Floating ink film fragment separation process) After 10 minutes, ink film fragments that had peeled off from the scaly chips floated on the surface of the cleaning solution containing the scaly chips. The floating ink film fragments were separated and removed using a 75 μm filter (product name: "Precision Polypropylene Mesh," manufactured by AS ONE Corporation).

[0115] (Plastic recovery process) The remaining cleaning solution contained plastic particles and small ink film particles. The plastic pieces were collected using a filter with a mesh size of 500 μm (product name: Polypropylene 31 mesh, manufactured by AXEL).

[0116] After collecting the plastic pieces, the cleaning solution was passed through a filter with a mesh size of 15 μm (product name "Precision Polypropylene Mesh", manufactured by AS ONE Corporation) to separate and remove fine ink film fragments.

[0117] <<Examples 2 to 4>> Plastic pieces were collected in the same manner as in Example 1, except that a plastic product on which an ink film was formed using cyan inks 2 to 4 instead of cyan ink 1 was used.

[0118] <<Example 5, Comparative Example 1>> Plastic pieces were collected in the same manner as in Example 1, except for the following points. In Example 5, the surface of the PET bottle was subjected to a corona treatment once using a corona treatment machine (product name: Corona Oscillator TEC4AX, manufactured by Kasuga Electric Co., Ltd.) at an output of 100 W and a speed of 4 m / min, after which an ink film was formed. In Comparative Example 1, a polyethylene (PE) bottle (wide-mouth) (manufactured by Sanplatec Co., Ltd.) with a specific gravity of 0.91 g / cm was used instead of a PET bottle. 3 ) and an ink film was formed on the surface.

[0119] <<Comparative Example 2>> Plastic pieces were collected in the same manner as in Example 1, except for the following points. In Comparative Example 2, a cleaning solution B was used in which 5% by mass of water contained in the cleaning solution A was replaced with 5% by mass of a silicone surfactant (product name "BYK348" manufactured by BYK).

[0120] <<Comparative Examples 3 and 4>> Plastic pieces were collected in the same manner as in Example 1, except for the following points. In Comparative Example 3, the floating ink film fragment separation step was not performed, and the plastic fragment recovery step was performed after the cleaning liquid immersion step. In Comparative Example 4, after the floating ink film fragment separation step, all solids contained in the washing liquid were recovered.

[0121] <<Comparative Example 5, Example 6, Example 7, Comparative Example 6>> Plastic pieces were collected in the same manner as in Example 1, except for the following points. In Comparative Example 5, Example 6, Example 7, and Comparative Example 6, the mesh size of the pulverizer was changed to 2 mm, 4 mm, 20 mm, and 30 mm, respectively. When crushed with a mesh size of 2 mm, scaly chips of approximately 0.7 mm were obtained. When crushed with a mesh size of 4 mm, scaly chips of about 2 mm were obtained. When crushed with a mesh size of 20 mm, scaly chips of about 10 mm were obtained. When crushed with a mesh size of 30 mm, scaly chips of about 20 mm were obtained.

[0122] [evaluation] (recovery rate) The collected plastic pieces were dried at 40°C for 24 hours. The total mass of the dried plastic pieces was measured and compared with the mass of the plastic substrate to calculate the recovery rate. The recovery rate was calculated using the following formula: Evaluation criteria are as follows: Recovery rate (%) = (total mass of plastic pieces after drying / mass of plastic substrate) x 100 5: Recovery rate is 95% or more. 4: Recovery rate is 90% or more but less than 95%. 3: Recovery rate is 80% or more but less than 90%. 2: Recovery rate is 60% or more but less than 80%. 1: Recovery rate is less than 60%.

[0123] (ink film remaining rate) The collected plastic pieces were dried at 40°C for 24 hours. 100 g of the dried plastic pieces were immersed in 1 kg of hexafluoro-2-propanol (HFIP). Note that the plastic substrate dissolves in HFIP, but the ink film does not dissolve in HFIP. The solution was passed through a filter with 15 μm openings (product name "Precision Polypropylene Mesh", AS ONE Corporation), and the ink film was recovered. The mass of the recovered ink film was measured. The ink film remaining rate was calculated using the following formula: The evaluation criteria were as follows. Ink film remaining rate (%) = (total mass of collected ink film / total mass of plastic pieces after drying) x 100 The total mass of the plastic pieces after drying was 100 g. 5: The remaining ink film is less than 5 ppm. 4: The residual ink film rate is 5 ppm or more and less than 10 ppm. 3: The residual ink film rate is 10 ppm or more and less than 20 ppm. 2: The residual ink film rate is 20 ppm or more and less than 40 ppm. 1: The residual ink film rate is 40 ppm or more.

[0124] (Dischargeability) The ejection properties of cyan ink were evaluated using an inkjet recording device (product name "CylinderJET", manufactured by Tritec) and an inkjet head (product name "KM1800i", manufactured by Konica Minolta). The number of ejection nozzles before image recording was counted using a nozzle check pattern. In addition, after 10 minutes of image recording, the number of ejection nozzles after image recording was counted using a nozzle check pattern. The number of ejection nozzles before image recording and the number of ejection nozzles after image recording were used to calculate the amount of reduction in the number of ejection nozzles. The same test was performed three times, and the ejection properties were evaluated based on the average value N of the amount of reduction in the number of ejection nozzles. The evaluation criteria were as follows: Amount of reduction in number of ejection nozzles = Number of ejection nozzles before image recording - Number of ejection nozzles after image recording 5:N is less than 1. 4:N is greater than or equal to 1 and less than 2. 3:N is greater than or equal to 2 and less than 4. 2:N is 4 or greater and less than 8. 1:N is 8 or more.

[0125] The evaluation results are shown in Tables 2 and 3. In Tables 2 and 3, when the floating ink film fragment separation process and the plastic fragment recovery process were performed, the result was marked with "Y." When the floating ink film fragment separation process and the plastic fragment recovery process were not performed, the result was marked with "N."

[0126] [Table 2] [Table 3]

[0127] In Examples 1 to 7, the specific gravity was 1 g / cm 3The process includes the steps of crushing the plastic products having an ink film formed on the surface of the plastic substrate to obtain crushed pieces with an average diameter of 1 mm to 10 mm, immersing the crushed pieces in a cleaning solution to obtain ink film fragments and plastic fragments in the cleaning solution, separating the ink film fragments floating in the cleaning solution, and separating the ink film fragments that have settled in the cleaning solution from the plastic fragments that have settled in the cleaning solution to recover the plastic fragments.Since the surface energy of the ink film is smaller than the surface energy of the plastic substrate, and the surface energy of the plastic substrate is smaller than the surface tension of the cleaning solution, the recovery rate was high and plastic with a low residual ink film could be recovered. On the other hand, in Comparative Example 1, the specific gravity of the plastic substrate was 1 g / cm 3 The recovery rate was found to be low. In Comparative Example 2, it was found that the surface energy of the ink film was greater than the surface tension of the cleaning liquid, and the ink film remaining rate was high. In Comparative Example 3, the floating ink film fragment separation step was not carried out, and therefore it was found that the ink film remaining rate was high. In Comparative Example 4, the plastic fragment recovery step was not carried out, and it was found that the ink film remaining rate was high. In Comparative Example 5, the average diameter of the pulverized pieces was less than 1 mm, and it was found that the ink film remaining rate was high. In Comparative Example 6, the average diameter of the pulverized pieces was more than 10 mm, and it was found that the ink film remaining rate was high.

Claims

1. Specific gravity is 1 g / cm ３ a step of crushing the plastic product having an ink film formed on the surface of the plastic substrate to obtain crushed pieces having an average diameter of 1 mm to 10 mm; Immersing the crushed pieces in a cleaning solution to obtain ink film pieces and plastic pieces in the cleaning solution; Separating ink film pieces floating in the cleaning liquid; and a step of separating ink film pieces that have settled in the cleaning solution from plastic pieces that have settled in the cleaning solution, and recovering the plastic pieces, the surface energy of the ink film is lower than the surface energy of the plastic substrate and lower than the surface tension of the cleaning liquid; How to recycle plastic.

2. the surface energy of the ink film is 20 mN / m to 25 mN / m; The surface energy of the plastic substrate is 40 mN / m or more, 2. The method for recovering plastics according to claim 1, wherein the surface tension of the cleaning liquid is 40 mN / m or more.

3. The specific gravity of the ink film is 1.2 g / cm ３ is less than The specific gravity of the plastic substrate is 1.3 g / cm ３ The method for recovering plastics according to claim 1 or claim 2, wherein the content of the plastics is greater than 100%.

4. 3. The method for recovering plastics according to claim 1, wherein a filter having a mesh size of 20 μm to 100 μm is used in the step of separating ink film pieces floating in the cleaning liquid.

5. 3. The method for recovering plastics according to claim 1, wherein a filter having a mesh size of 100 μm to 1000 μm is used in the step of recovering the plastic pieces.

6. The method for recovering plastics according to claim 1 or 2, wherein the ink film contains a polymer having an acid group.

7. The method for recovering plastics according to claim 1 or 2, wherein the ink film contains a polymer having a polyether structure and a polysiloxane structure.

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