JP2024066537A - Method for separating and recovering plastic base material - Google Patents

Abstract

To provide a method for separating and recovering a laminate suitable for plastic recycling, which has an excellent detachment property of a coating layer such as a printing layer and an adhesive layer, and further suppresses redeposition of a detached coating layer component by suppressing curling of a base material even under a condition where the amount of a laminate is large during detachment treatment.SOLUTION: There is provided a method for separating and recovering a plastic base material, comprising the steps of: detaching a coating layer by bringing the laminate having a plastic base material and at least one coating layer selected from the group consisting of a primer layer, a printing layer, and an adhesive layer into contact with a detaching liquid to detach the coating layer; and recovering the detached plastic base material, which is a method for separating and recovering a laminate in which a content of the laminate is 0.5 mass% or more based on the total mass of the detaching liquid.SELECTED DRAWING: None

Description

The present invention relates to a method for separating and recovering a plastic substrate from a laminate having at least a plastic substrate layer and a coating layer.

In recent years, packaging made from plastic film, plastic bottles, and other plastic products have been discarded and dumped into the ocean as garbage, causing environmental pollution. These plastic products break down in seawater and turn into submicron-sized fragments (microplastics), which float in the seawater. When these microplastics are ingested by marine organisms such as fish, they become concentrated in the organisms' bodies, and there are concerns that they may affect the health of seabirds and humans that consume these marine organisms as food.

Examples of the above-mentioned plastic products include food packaging packages with a multi-layer structure that uses plastic film. In such food packaging packages, various plastic substrates such as polyester substrates, nylon substrates (NY), polypropylene substrates (PP), and polyethylene substrates (PE) are used as the film substrate. These film substrates are printed with printing ink, and are then bonded to other film substrates or heat-melting resin substrates via adhesives, etc., before being cut and heat-sealed to form packages. However, such food packaging packages with a multi-layer structure contain multiple different materials that are not compatible with each other, which creates the problem that they cannot be recycled as materials in their current state.

Regarding material recycling of such multi-layered packaging materials, for example, Patent Documents 1 and 2 disclose a technology for removing not only the surface-printed structure but also the printed layer from a multi-layered laminate by treating a laminate having a release layer containing a polyurethane resin having a predetermined acid value with an alkaline aqueous solution. Patent Document 3 discloses a technology for removing the adhesive layer from a multi-layered laminate by treating a laminate having a polyester polyol-based adhesive having a predetermined acid value with an alkaline aqueous solution.

JP 2020-090627 A JP 2021-098294 A JP 2020-084130 A

However, in the detachment process described in Patent Documents 1 to 3, it was found that if the amount of the laminate treated with the alkaline aqueous solution is increased in order to improve the processing efficiency, collisions between the substrates increase, the substrate curls around the coating layer, and the detachability decreases, which is a new problem. This was particularly noticeable in the case of a substrate made of an olefin resin. In addition, since the coating layer component in the processing liquid also increases, the coating layer after detachment is more likely to reattach to the substrate. Furthermore, if the stirring speed is increased to improve the detachability, the detached coating layer is finely dispersed and easily reattaches to the plastic substrate, which is a problem. Here, "reattachment" refers to the fact that the detached layer, such as the printed layer or adhesive layer, which has been detached from the substrate is finely dispersed by stirring and reattaches to the substrate, which causes coloring of the substrate to be recovered and deterioration of the properties of the recycled material. That is, the molding material (hereinafter also referred to as the recycled material or recycled substrate) obtained by recycling the plastic substrate to which the printed layer has been reattached as described above causes deterioration in appearance and physical properties due to coloring.
When the substrate curls, not only does it become difficult to remove the coating layer, but it also entangles the dispersed material from the detached coating layer, which cannot be removed in the washing process, causing a deterioration in the properties of the recycled material.

The object of the present invention is therefore to provide a method for separating and recovering a laminate suitable for plastic recycling, which has excellent releasability of coating layers such as printed layers and adhesive layers by suppressing curling of the substrate even under conditions where a large amount of the laminate is being removed, and furthermore, which suppresses reattachment of the detached coating layer components. Furthermore, the object of the present invention is to provide a method for producing a high-quality molding material obtained by hot molding the recovered plastic substrate.

As a result of extensive research, the inventors have found an effective means for suppressing curling. That is, the present invention is a method for separating and recovering a plastic substrate, comprising the steps of contacting a plastic substrate and a laminate having a coating layer with a release liquid to release the coating layer, and recovering the released plastic substrate,
The content of the laminate is 0.5% by mass or more based on the total mass of the desorption liquid,
The present invention relates to a method for separating and recovering a laminate, in which, after the detachment step, the proportion of plastic substrates in a state in which the substrate is wound around the end of the substrate one or more times is less than 50 mass % of the total plastic substrates after the detachment step.

The present invention also provides a method for separating and recovering a plastic substrate, the method comprising the steps of contacting a plastic substrate and a laminate having a coating layer with a release liquid to release the coating layer, and recovering the released plastic substrate,
The content of the laminate is 0.5% by mass or more based on the total mass of the desorption liquid,
This relates to a separation and recovery method in which, when the volumes of 5 g of the laminate (A) before the desorption step and 5 g of the plastic substrate (B) after the desorption step are measured using a 5.0×10 ^{−4 m3} measuring cylinder (inner diameter 5 cm), the volume of (B) is at least 1 time and less than 4 times the volume of (A).

The present invention also provides a method for separating and recovering a plastic substrate, the method comprising the steps of contacting a plastic substrate and a laminate having a coating layer with a release liquid to release the coating layer, and recovering the released plastic substrate,
The content of the laminate is 0.5% by mass or more based on the total mass of the desorption liquid,
the eluate contains a compound having an HLB value greater than 0 and less than 20 and water;
The present invention relates to a separation and recovery method in which the long side of the laminate immediately before detachment is 1 mm to 3 cm, and this method is characterized in that 50% or more by weight of the entire laminate is made up of laminates having a length of 1 mm to 3 cm.

The present invention also relates to the above separation and recovery method, in which the elution liquid contains a surfactant and water.

The present invention also relates to the above separation and recovery method, in which the coating layer includes a printed layer, and the content of the printed layer is 0.01% by mass or more relative to the total mass of the elution liquid.

In addition, the present invention further includes a step of cutting the laminate before contacting the laminate with the release liquid,
This relates to the above separation and recovery method, wherein 50 mass % or more of the laminate after the cutting step has a long side of 3 cm or less.

The present invention also relates to the above separation and recovery method, in which at least one of the coating layers contains a compound having an acidic group.

The present invention also relates to the above separation and recovery method in which the plastic substrate is an olefin substrate.

The present invention also relates to a method for producing molding materials, which comprises melt-kneading the plastic substrates recovered by the above-mentioned separation and recovery method.

The present invention also relates to a method for producing a molded body, which comprises hot molding the molding material obtained by the above-mentioned manufacturing method.

The present invention provides a method for separating and recovering a plastic substrate from a laminate suitable for plastic recycling, which is excellent in the releasability of coating layers such as printed layers and adhesive layers by suppressing curling of the substrate under conditions where the amount of printed layer during the removal process is large, and further suppresses reattachment of detached coating layer components. Furthermore, it provides a method for producing a high-quality molding material obtained by hot molding the recovered plastic substrate.

The following describes in detail the embodiments of the present invention. However, the following description of the embodiments and requirements is merely an example of the embodiments of the present invention, and the present invention is not limited to these contents as long as it does not exceed the gist of the present invention.

In a method for separating and recovering a plastic substrate from a plastic substrate and a laminate having a coating layer, if the amount of the laminate relative to the release liquid is increased to improve processing efficiency, the amount of the coating layer relative to the release liquid also increases, resulting in poor release properties and making the coating layer components more likely to reattach to the substrate after release. Furthermore, under stirring conditions, the frequency of collisions of the laminate increases, resulting in a problem that the laminate and the plastic substrate after release tend to curl. In addition, since stirring causes countless wrinkles in the substrate, the volume of the substrate after the release step is generally larger than that before the release step, but there was also a tendency for the volume of the substrate to increase even further as the plastic substrate curls after release.

The inventors have found that by detaching the plastic substrate such that the proportion of curled plastic substrates after the detachment step is less than 50 mass% of the total plastic substrates after the detachment step under conditions where the amount of laminate relative to the detachment liquid is large, it is possible to effectively suppress reattachment while maintaining the excellent detachability of the coating layer. This is believed to be due to the appropriate control of the polarity and interfacial free energy of the substrate surface.

In order to reduce the proportion of curled plastic substrates after the above-mentioned desorption step to less than 50% by mass, the following measures can be taken: selecting the conditions during the desorption test, such as temperature, adding a surfactant to the desorption liquid, and reducing the size of the laminate; however, the present invention is not limited to these measures, and it is preferable to combine each measure appropriately. Each measure will be described in detail later.

<Separation and recovery method>
The method for separating and recovering a laminate of the present invention includes a step of contacting a plastic substrate and a laminate having a coating layer in contact with the plastic substrate with a release liquid to remove the coating layer and separate and recover the plastic substrate, wherein the content of the laminate is 0.5 mass% or more relative to the total mass of the release liquid, the proportion of the plastic substrates curled after the release step is less than 50 mass% relative to the total plastic substrates after the release step, and/or the volume ratio before and after the release step is 1 time or more and less than 4 times.

<Step of removing coating layer (also referred to as removal step)>
The separation and recovery method of the present invention includes a step of contacting a plastic substrate and a laminate having a coating layer in contact with the plastic substrate with a release liquid to release the coating layer. Hereinafter, the coating layer released from the substrate by the release liquid is also referred to as a release layer.

In the present invention, "detachment" refers to the detachment of the substrate from the laminate as a result of the detachment layer being dissolved or swelled by the detachment liquid and peeling off, and includes both cases where the detachment layer dissolves and detaches from the substrate, and where the detachment layer does not dissolve but peels off due to neutralization, swelling, etc., and detaches from the substrate.

Since the present invention aims to obtain the plastic substrate after detachment as a recycled substrate or regenerated substrate, an embodiment in which as much of the detachment layer, etc., is removed from the plastic substrate is preferable. Specifically, it is preferable that at least 50% by mass or more of the detachment layer, out of 100% by mass, has been detached. More preferably, 60% by mass or more, even more preferably 80% by mass or more, and particularly preferably 90% by mass or more has been detached. This does not necessarily mean that the coating layer peels off from the interface with the substrate.

<Curling of plastic substrate>
In the present invention, the state in which the end of the plastic substrate is rolled up one or more times is referred to as "curl". The rolled portion may be the entire substrate or a part of the substrate. When the substrate is bent in a U-shape or folded in a V-shape, it does not appear to be rolled up one or more times.
If the laminate is curled before detachment, it becomes difficult to detach the coating layer and separate the plastic substrate. Also, if the plastic substrate is curled after detachment, the dispersion of the coating layer after detachment is caught in the curl, which makes it difficult to remove by washing after the detachment step, leading to deterioration of the properties of the recycled material.

In the present invention, the proportion of curled plastic substrates after the detachment step is preferably less than 50% by mass, more preferably less than 30% by mass, even more preferably less than 20% by mass, and particularly preferably less than 10% by mass, based on the total amount of curled plastic substrates after the detachment step. As described above, when the proportion of curled plastic substrates is less than 50% by mass, the detachability of the coating layer is improved and the tendency of the detached coating layer components to become entrapped and reattach is suppressed, resulting in a high-performance recycled material.

In the present invention, it has been observed that the plastic substrate tends to curl when the amount of the laminate treated with the release liquid is increased. Since it is not possible to unequivocally describe a method for preventing curling, the invention is specified by the curled state or the volume ratio before and after the release step, but curling is particularly unlikely when the release liquid contains water and a compound with an HLB value greater than 0 and less than 20, and when the long side of the laminate just before release is 1 mm to 3 cm and 50% by weight or more of the entire laminate is 1 mm to 3 cm.

[The long side]
The long side of the laminate refers to the long side of a rectangle circumscribing the laminate when viewed from the surface side of the laminate, the rectangle being set to have the smallest area.
Since the long side of a typical laminate exceeds 3 cm, a step of cutting the laminate so that the long side is 3 cm or less is required before the detachment step. It is preferable that 50% by weight or more of the laminate as a whole has a long side of 3 cm or less after cutting. Moreover, it is preferable that the laminate has a long side of 1 mm or more after cutting in terms of ease of recovering the substrate.

<Volume ratio before and after desorption process>
The degree of curling of the laminate can also be determined by measuring the volume of the crushed laminate (A) before the detachment step and the volume of the plastic substrate (B) after the detachment step per 5 g of ^each sample using a 5.0 × 10 ^-4 m3 measuring cylinder (inner diameter 5 cm) and calculating the volume ratio (B)/(A) before and after the detachment step.
In the desorption step, the laminate is stirred, so that the substrate is wrinkled in countless ways. In general, the volume of the substrate after the desorption step is larger than that before the desorption step. If the amount of the laminate relative to the desorption liquid is increased to improve the processing efficiency, the frequency of collision of the laminate increases, and the substrate curls by rolling up the ends in an attempt to reduce the interfacial free energy, thereby reducing the surface area with the desorption liquid. The substrate curls, and the volume of the substrate further increases. As described above, when the substrate curls, it promotes a decrease in detachability and reattachment, causing a decrease in the properties of the recycled material. Therefore, the lower the volume ratio before and after the desorption step, the more preferable it is. The volume ratio before and after the desorption step is preferably 1 to 4 times, more preferably 3 times or less, and even more preferably 2 times or less.

<Release solution>
The release liquid may be any liquid capable of swelling and dissolving the coating layer, and may be appropriately selected in consideration of the ease of release of the coating layer described below. Examples of such release liquid include water, a basic aqueous solution, and an acidic aqueous solution. From the viewpoint of the environment and maintaining the properties of the recycled material using the recovered plastic substrate, an aqueous solution is preferable. The release liquid preferably contains 50% by mass or more of water, more preferably 70% by mass or more, and even more preferably 80% by mass or more.
These release liquids may be heated. The temperature of the release liquid when the laminate is immersed is preferably in the range of 25 to 120° C., more preferably 30 to 100° C., and particularly preferably 50 to 80° C. A higher release temperature is preferable from the viewpoint of release properties, and a lower release temperature is preferable from the viewpoint of suppression of substrate curling and suppression of re-adhesion.

From the viewpoint of releasing the urethane adhesive layer that is typically used in packaging materials, the release liquid is more preferably a basic aqueous solution containing a basic compound.

The immersion time in the desorption liquid is preferably in the range of 1 minute to 24 hours, more preferably 1 minute to 12 hours, even more preferably 1 minute to 6 hours, and even more preferably 1 minute to 1 hour.

In order to improve the desorption efficiency, it is preferable to stir, vibrate, circulate, or the like the desorption liquid.
The rotation speed of the stirring blade is preferably 80 to 5000 rpm, and more preferably 80 to 4000 rpm.

[Compounds with HLB values greater than 0 and less than 20]
The release liquid preferably contains a compound having an HLB value of more than 0 and less than 20. In particular, when the release liquid contains a surfactant as described below, a substrate that does not curl tends to be obtained.

[Surfactant]
The release liquid preferably contains water and a surfactant. The surfactant mainly plays a role in improving the release property of the coating layer. This is thought to be because the action of the surfactant makes it easier for the release liquid to penetrate into coating layers such as the primer layer, the printing layer, and the adhesive layer, and promotes the release property. In addition, when the amount of the laminate relative to the release liquid is increased in the separation and recovery, the laminate and the separated substrate tend to curl with the released ink particles and the like wrapped around them, and even if the laminate and the separated substrate are immersed in the release liquid, it is difficult to cleanly remove the ink particles and the like wrapped around the curl. However, when the release liquid contains a surfactant, the surfactant is adsorbed on the laminate and the separated substrate surface, suppressing curling. As a result, the release property is improved and reattachment can be suppressed.
Furthermore, when the release liquid contains a surfactant, it is possible to release a coating layer in contact with a plastic substrate even in the absence of a release layer.

The HLB value is an index value relating to the affinity of a surfactant for water and oil, and is calculated by dividing the HLB value into two equal parts, with a substance having no hydrophilic groups having an HLB value of 0 and a substance having only hydrophilic groups having an HLB value of 20. The concept of HLB was proposed by William Griffin of the Atlas Powder Company in 1949, and several methods for determining the HLB value by calculation have been proposed, but in the present invention, the HLB value can be calculated from the following formula using the Griffin method.
Formula) HLB = 20 x [(molecular weight of hydrophilic group contained in surfactant) / (molecular weight of surfactant)]
Examples of the hydrophilic group contained in the surfactant include a hydroxyl group and an ethyleneoxy group.

The HLB value of the surfactant in the present invention is preferably 7 or more. With an HLB value of 7 or more, excellent release properties and anti-reattachment properties are exhibited. The HLB value of the surfactant is preferably 8 or more, more preferably 10 or more. The HLB value of the surfactant is preferably 20 or less, more preferably 19 or less, and even more preferably 17 or less. An HLB value of 20 or less is preferable because it has excellent defoaming properties.

The type of surfactant may be, for example, nonionic, anionic, cationic, or amphoteric, and the type and amount of the surfactant may be appropriately selected according to the required properties. From the viewpoint of releasing property and foaming property, the surfactant is preferably at least one selected from the group consisting of anionic surfactants and nonionic surfactants.
Moreover, the surfactant preferably has a structure to which alkylene oxide (hereinafter, also referred to as AO) is added, because this improves the releasing property and the preventing property of reattachment.

(Nonionic surfactant)
The nonionic surfactant is not particularly limited, but is preferably an alkylene oxide adduct in which an alkylene oxide is added. More preferably, it is a compound obtained by adding an alkylene oxide to an alcohol having active hydrogen, a compound obtained by adding an alkylene oxide to an amine, or a compound obtained by adding an alkylene oxide to a fatty acid. The addition may be either random addition or block addition. The number of carbon atoms of the alkylene oxide is preferably 2 to 4.
The nonionic surfactant is preferably an alcohol-based nonionic surfactant in which an alkylene oxide having 2 to 4 carbon atoms is added to an alcohol.

[Alcohol-based nonionic surfactant]
Examples of alcohol-based nonionic surfactants include alkylene oxide adducts of primary or secondary alcohols having a total of 8 to 24 carbon atoms, and alkylene oxide adducts of alkylphenols having a total of 8 to 12 carbon atoms. The primary or secondary alcohols having a total of 8 to 24 carbon atoms may be either saturated or unsaturated.
Examples of the primary or secondary alcohol having a total of 8 to 24 carbon atoms include lauryl alcohol, stearyl alcohol, oleyl alcohol, dodecyl alcohol, arachidyl alcohol, behenyl alcohol, lignoceryl alcohol, and myristyl alcohol.
Examples of the alkylene oxide to be added to the alcohol include ethylene oxide, propylene oxide, and butylene oxide, and it is preferable that ethylene oxide is essential. The number of moles of the alkylene oxide to be added is preferably 1 to 100 moles, more preferably 2 to 50 moles, per mole of the alcohol or alkylphenol. The above range is preferable because it has excellent elimination properties.

[Fatty acid-based nonionic surfactant]
The fatty acid-based nonionic surfactant is not particularly limited in structure, and examples thereof include alkylene oxide adducts of higher fatty acids having a total of 10 to 24 carbon atoms, fats and oils consisting of esters of the above-mentioned saturated or unsaturated higher fatty acids having a total of 10 to 24 carbon atoms and glycerin, and further alkylene oxide adducts of mixtures of the above-mentioned fats and oils and polyhydric alcohols having a carbon number of 2 to 10. The above-mentioned higher fatty acids having a total of 10 to 24 carbon atoms may be either saturated or unsaturated.
Examples of the higher fatty acids having a total of 10 to 24 carbon atoms include saturated higher fatty acids such as lauric acid, myristic acid, palmitic acid, stearic acid, arachic acid, and behenic acid; and unsaturated higher fatty acids such as palmitoleic acid, oleic acid, elaidic acid, linoleic acid, linolenic acid, erucic acid, and ricinoleic acid. Examples of the dihydric to decahydric polyhydric alcohols include ethylene glycol, propylene glycol, glycerin, polyglycerin, sorbitol, sorbitan, and sucrose. The type and number of moles of alkylene oxide added are the same as those described in the section on [Alcohol-based nonionic surfactants] above.

[Amine-based nonionic surfactant]
Examples of the amine-based nonionic surfactant include AO adducts of saturated or unsaturated primary or secondary amines having a total carbon number of 8 to 36. Examples of the amine include 2-ethylhexylamine, di-2-ethylhexylamine, laurylamine, dilaurylamine, tetradecylamine, ditetradecylamine, hexadecylamine, dihexadecylamine, stearylamine, distearylamine, oleylamine, dioleylamine, etc. The type and number of moles of AO added are the same as above.

(Anionic Surfactant)
The anionic surfactant is preferably a non-soap surfactant, and examples thereof include sulfonic acid-based anionic surfactants, sulfate ester-based anionic surfactants, carboxylate-based anionic surfactants, and phosphate ester-based anionic surfactants.

[Sulfonic acid-based anionic surfactant]
Examples of the sulfonic acid anionic surfactant include alkylsulfonic acid, alkylbenzenesulfonic acid, alkylnaphthalenesulfonic acid, alkyldiphenyletherdisulfonic acid, alkylmethyltaurine, sulfosuccinic acid diester, alkylene oxide adduct of sulfonic acid, and salts thereof.Specific examples include hexanesulfonic acid, octanesulfonic acid, decanesulfonic acid, dodecanesulfonic acid, toluenesulfonic acid, cumenesulfonic acid, octylbenzenesulfonic acid, dodecylbenzenesulfonic acid, dinitrobenzenesulfonic acid, and lauryldodecylphenyletherdisulfonic acid.

[Sulfate ester-based anionic surfactants]
Examples of the sulfate anionic surfactant include sulfate (alkyl ether sulfate), alkylene oxide adduct of sulfate, and salts thereof. Specific examples include lauryl sulfate, myristyl sulfate, and polyoxyethylene lauryl ether sulfate.

[Carboxylic acid type anionic surfactant]
Examples of the carboxylic acid-based anionic surfactant include alkyl carboxylic acids, alkyl benzene carboxylic acids, alkylene oxide adducts of carboxylic acids, and salts thereof. Specific examples of the surfactant that can be used include lauric acid, myristic acid, palmitic acid, stearic acid, polyoxyethylene lauryl ether acetic acid, and polyoxyethylene tridecyl ether acetic acid.

[Phosphate ester-based anionic surfactant]
Examples of the phosphate anionic surfactant include phosphate (alkyl ether phosphate), alkylene oxide adduct of phosphate, and salts thereof.Specific examples include octyl phosphate, lauryl phosphate, tridecyl phosphate, myristyl phosphate, cetyl phosphate, stearyl phosphate, polyoxyethylene octyl ether phosphate, polyoxyethylene lauryl ether phosphate, etc.

The anionic surfactant preferably has an alkyl group having 2 to 24 carbon atoms or an alkenyl group having 2 to 24 carbon atoms, and more preferably has an alkyl group having 8 to 18 carbon atoms. The alkyl group or the alkenyl group may be linear or branched.
In addition, when the anionic surfactant is an alkylene oxide adduct, examples of the alkylene oxide include ethylene oxide, propylene oxide, and butylene oxide, with ethylene oxide being preferred. The number of moles of alkylene oxide added is preferably 1 to 12 moles, more preferably 1 to 8 moles, per mole of alcohol or alkylphenol. The above range is preferred because of excellent releasability.

Examples of the salt constituting the anionic surfactant include metal salts such as sodium, potassium, magnesium, calcium, etc. These salts may be used alone or in combination of two or more.
Among these, from the viewpoint of releasability and anti-reattachment properties, preferred anionic surfactants are sulfonate type and phosphate type, and more preferred are alkyl sulfonate, polyoxyalkylene alkyl ether sulfonate, polyoxyalkylene alkyl ether phosphate, etc.

(Cationic Surfactant)
Examples of cationic surfactants include alkylamine salts and quaternary ammonium salts. Specific examples of usable surfactants include stearylamine acetate, trimethyl coconut ammonium chloride, trimethyl beef tallow ammonium chloride, dimethyldioleyl ammonium chloride, methyl oleyl diethanol chloride, tetramethyl ammonium chloride, lauryl pyridinium chloride, lauryl pyridinium bromide, lauryl pyridinium disulfate, cetyl pyridinium bromide, 4-alkyl mercaptopyridine, poly(vinylpyridine)-dodecyl bromide, and dodecylbenzyl triethyl ammonium chloride.

(Amphoteric surfactant)
Examples of amphoteric surfactants include lauryl dimethylaminoacetate betaine, 2-alkyl-N-carboxymethyl-N-hydroxyethyl imidazolinium betaine, coconut oil fatty acid amidopropyl dimethylaminoacetate betaine, polyoctyl polyaminoethyl glycine, and imidazoline derivatives.

These surfactants may be used alone or in combination of two or more. The content of the surfactant in the release liquid is preferably in the range of 0.001 to 10 mass%, more preferably in the range of 0.005 to 7 mass%, even more preferably in the range of 0.03 to 5 mass%, and even more preferably in the range of 0.05 to 3 mass%, based on the mass of the release liquid. A content of 0.001 mass% or more is preferable because it suppresses curling of the substrate, provides excellent release properties, and also suppresses reattachment of the released coating layer components, while a content of 10 mass% or less is preferable from the viewpoint of defoaming properties.

[Antifoaming agent]
In the present invention, it is also preferable that the release liquid further contains an antifoaming agent. By using the antifoaming agent in combination with the above-mentioned surfactant, good antifoaming properties can be exhibited without reducing the release property and the reattachment prevention property, and foaming caused by the surfactant can be suppressed. Examples of the antifoaming agent include silicone-based compounds and non-silicone-based compounds.

(Silicone-based compounds)
Examples of the silicone-based compound include emulsion type, self-emulsifying type, oil type, oil compound type, and solvent type.
The emulsion type is a silicone-based defoaming agent in which a silicone oil compound is emulsified with an activator to form an O/W type (oil in water type) emulsion. Examples of such an antifoaming agent include "KM-89" and "KM-98" manufactured by Shin-Etsu Chemical Co., Ltd., "FC2913" and "SILFOAMSE47" manufactured by Wacker Asahi Kasei Silicone Co., Ltd., and "BYK-015" and "BYK-1640" manufactured by BYK Japan Co., Ltd.
The self-emulsifying type is a silicone-based defoaming agent containing 100% active ingredients that becomes an emulsion state when diluted and mixed with water. Examples of the self-emulsifying type include "KS-540" and "X-50-1176" manufactured by Shin-Etsu Chemical Co., Ltd., and "SILFOAM SD670" and "SILFOAM SD850" manufactured by Wacker Asahi Kasei Silicones.
The oil type is a 100% silicone oil defoamer that does not contain solvents or additives, and examples thereof include "KM-89" and "KM-98" manufactured by Shin-Etsu Chemical Co., Ltd., "AK350" and "AK12500" manufactured by Wacker Asahi Kasei Silicone Co., Ltd., and "BYK-1770" manufactured by BYK Japan Co., Ltd.
The oil compound type is a silicone-based defoaming agent in which silica particles are blended with silicone oil. Examples of such defoaming agents include "KM-89" and "KM-98" manufactured by Shin-Etsu Chemical Co., Ltd., "SILFOAM SC370" and "PULPSIL22274VP" manufactured by Wacker Asahi Kasei Silicone Co., Ltd., and "BYK-017" and "BYK-018" manufactured by BYK Japan Co., Ltd.
Solvent-type defoamers are silicone-based defoamers in which silicone oil is dissolved in a solvent, and examples thereof include "KM-89" and "KM-98" manufactured by Shin-Etsu Chemical Co., Ltd., and "BYK-019" and "BYK-025" manufactured by BYK Japan.

(Non-silicone compounds)
Examples of the non-silicone compounds include fatty acid ester compounds, urea resin compounds, paraffin compounds, polyoxyalkylene glycol compounds, acrylic ester copolymers, ester polymers, ether polymers, amide polymers, emulsion types of mineral oils, polysiloxane adducts, fluorine compounds, vinyl polymers, acetylene alcohol, acrylic polymers, special vinyl polymers, ethylene glycol, and higher alcohols (such as octyl alcohol and cyclohexanol).

One type of defoaming agent may be used alone, or two or more types may be used in combination. The content of the defoaming agent in the release liquid is preferably in the range of 0.0001 to 5 mass%, more preferably in the range of 0.001 to 4.5 mass%, even more preferably in the range of 0.01 to 4 mass%, still more preferably in the range of 0.02 to 3.5 mass%, and particularly preferably in the range of 0.03 to 3 mass%, based on the mass of the release liquid. If it is 0.0001 mass% or more, the defoaming properties are excellent, and if it is 5 mass% or less, the release properties and anti-reattachment properties are excellent.

The above-mentioned defoaming agent is preferably at least one selected from the group consisting of emulsion-type silicone compounds, self-emulsifying silicone compounds, and non-silicone compounds, from the viewpoints that it has good alkali resistance and is unlikely to reduce the releasability or anti-reattachment properties when combined with the above-mentioned surfactant.

[Basic Compounds]
As described above, the release liquid used in the present invention is preferably a basic aqueous solution containing a basic compound from the viewpoint of releasing a urethane adhesive layer that is commonly used in packaging materials.
The basic compound is not particularly limited, and for example, sodium hydroxide (NaOH), potassium hydroxide (KOH), calcium hydroxide (Ca(OH) ₂ ), ammonia, barium hydroxide (Ba(OH) ₂ ), and sodium carbonate (Na ₂ CO ₃ ) are preferably used. More preferably, it is at least one selected from the group consisting of sodium hydroxide and potassium hydroxide.
The content of the basic compound in the basic aqueous solution is preferably in the range of 0.1 to 20 mass%, more preferably 0.3 to 15 mass%, and even more preferably 0.5 to 10 mass%, based on the mass of the basic aqueous solution. Within the above range, the basic aqueous solution can retain sufficient basicity to dissolve or swell the detachment layer described below and detach the plastic substrate.

The release liquid penetrates the edge of the laminate, comes into contact with the release layer, and dissolves or swells it, separating the plastic substrate from the release layer. Therefore, in order to efficiently proceed with the release process, it is preferable that the laminate is cut or crushed so that the release layer is exposed on the cross section when it is immersed in the release liquid. In such a case, the substrate layer can be released in a shorter time.

<Content of the laminate before removal (also referred to as processing amount)>
The content of the laminate when the laminate is separated in the release liquid is 0.5% by mass or more, preferably 0.5% by mass or more and 10% by mass or less, more preferably 1% by mass or more and 8% by mass or less, even more preferably 1.5% by mass or more and 7% by mass or less, and even more preferably 2% by mass or more and 6% by mass or less, based on the total mass of the release liquid. If it is 0.1% by mass or more, it is preferable from the viewpoint of processing efficiency. If it is 10% by mass or less, it is preferable from the viewpoint of release property and anti-reattachment property.

<Process for separating and recovering plastic substrates>
After the detachment step, the separated plastic substrate is collected. As a collection method, a known means can be applied by utilizing the difference in physical properties between the plastic substrate after detachment and the coating layer pieces after detachment. For example, a floating and sinking means using specific gravity or a centrifugal separation means can be applied. In addition, when the size of the plastic substrate after detachment and the size of the coating layer after detachment are different, a means of sorting using a net can be applied.
After separation and recovery, the recovered plastic substrate can be, for example, washed with water and dried to form a recycled substrate. The recycled substrate can be, for example, melt-kneaded to form pellets or heated to form a molded product.

<Laminate>
The laminate used in the present invention comprises a plastic substrate and a coating layer. The coating layer may be, for example, at least one coating layer selected from the group consisting of a primer layer, a printing layer, and an adhesive layer. The layer in contact with the plastic substrate is detached by the above-mentioned release liquid, which allows the plastic substrate to be recovered and recycled. In the present invention, in order to improve the release property, it is preferable to provide a primer layer in contact with the plastic substrate layer and having high affinity with the release liquid.

<Printed layer>
In the present invention, the printed layer may be provided in contact with the plastic substrate, or in the case where the laminate has a primer layer, the printed layer may be provided in contact with the primer layer. The printed layer is a layer that forms an arbitrary printed pattern for the purpose of decoration, imparting an aesthetic feel, displaying the contents, expiration date, manufacturer or seller, etc., and includes a solid printed layer. The printed layer may be formed of a single layer or multiple layers.
When the printed layer contains a water-soluble resin or a compound having an acidic group, which will be described later, it also functions as a release layer.
The printing ink used to form the printed layer can be produced by dissolving and/or dispersing at least a colorant, a dispersant, and a binder resin in a solvent, and may contain other components as necessary.

The content of the printed layer when the laminate is separated in the release liquid is 0.01% by mass or more, preferably 0.05% by mass or more and 1% by mass or less, and more preferably 0.1% by mass or more and 0.5% by mass or less, based on the total mass of the release liquid. A content of 0.01% by mass or more is preferable from the viewpoint of processing efficiency. A content of 1% by mass or less is preferable from the viewpoint of preventing reattachment.

[Coloring agent]
The printing layer may be colored or colorless, and contains a known colorant used in printing inks and paints. Such colorants are not particularly limited, and may include inorganic pigments, organic pigments, dyes, metal powders that impart metallic luster, near-infrared absorbing materials, and ultraviolet absorbing materials.
Examples of inorganic pigments include color pigments such as titanium oxide, red iron oxide, Prussian blue, ultramarine blue, carbon black, and graphite; and extender pigments such as calcium carbonate, kaolin, clay, barium sulfate, aluminum hydroxide, and talc.
As the organic pigment, a soluble azo pigment, an insoluble azo pigment, an azo lake pigment, a condensed azo pigment, a copper phthalocyanine pigment, a condensed polycyclic pigment, etc. are suitably used.
However, the pigment is not limited to these, and any pigment listed by its generic name in the Color Index can be used as appropriate. Among them, when the release solution is a basic aqueous solution, a pigment that is not eluted in the basic aqueous solution and has alkali resistance is preferred. Preventing the elution of the pigment makes it easy to reuse the basic aqueous solution.
The alkali resistance of a pigment is generally estimated based on the skeleton or structure of the pigment, and examples of alkali-resistant pigments include inorganic pigments, C.I. Pigment Blue 15, and C.I. Pigment Yellow 83.
When the pigment is titanium oxide, the content of titanium oxide in the printed layer is preferably 20 to 80% by mass, more preferably 30 to 75% by mass. When the pigment is an inorganic pigment other than titanium oxide, an extender pigment, or an organic pigment, the content of each of these pigments in the printed layer is preferably 0.5 to 60% by mass, more preferably 10 to 50% by mass.

[Dispersant]
The printing layer contains a pigment derivative and/or a resin-type dispersant as a dispersant for the colorant, which improves the release property. Furthermore, the dispersion stability and stability over time of the ink are improved. These may be used alone, but it is preferable to use them in combination, as this further improves the dispersion stability and stability over time.

(Pigment derivatives)
Pigment derivatives are compounds in which a substituent has been introduced into the pigment skeleton. In printing ink, the pigment skeleton of the pigment derivative is adsorbed onto the pigment surface in the printing ink, and the substituent portion of the pigment derivative is oriented toward the solvent in the printing ink, thereby dispersing the pigment in the printing ink.
As the pigment derivative, for example, a pigment having a functional group such as a carboxyl group, a sulfonic acid group, a carbonyl group, a sulfonyl group, etc. added to the skeleton of a phthalocyanine-based, azo-based, anthraquinone-based, quinacridone-based, etc. pigment, and a salt thereof can be preferably used. These can be used alone or in combination.

Commercially available pigment derivatives that can be preferably used include Solsperse 5000, Solsperse 12000 (manufactured by Lubrizol Japan), BYK-SYNERGIST 2100, BYK-SYNERGIST 2105 (manufactured by BYK-Chemie Japan), Efka 6745, Efka 6750 (manufactured by BASF), etc. These can be used alone or in combination.

It is preferable that the pigment derivative exhibits the same or a similar color as the pigment in the ink. For example, when added to black ink or cyan ink, a phthalocyanine pigment derivative can be preferably used as the pigment derivative.

The total amount of pigment derivatives is preferably 0.01 to 10% by mass, more preferably 0.05 to 6% by mass, and even more preferably 0.1 to 4% by mass, relative to the total colorant. If it is 0.01% by mass or more, the dispersion stability of the printing ink is good, and the releasability is also improved. Furthermore, if it is 0.01 to 10% by mass, it contributes to improving the releasability and suppressing reattachment, and can be regenerated into a high-quality recycled molding material.

(Resin-type dispersant)
Resin-type dispersants have an affinity site for the pigment composition having the property of adsorbing to the pigment composition, and a site compatible with the pigment composition carrier, and act to stabilize the dispersion in the pigment composition carrier by adsorbing to the pigment composition. Specific examples of resin-type dispersants include polyurethane, polyacrylate and other polycarboxylate esters, unsaturated polyamides, polycarboxylic acids, polycarboxylate (partial) amine salts, polycarboxylate ammonium salts, polycarboxylate alkylamine salts, polysiloxanes, long-chain polyaminoamide phosphates, hydroxyl-containing polycarboxylate esters, and modified products thereof, oil-based dispersants such as amides formed by the reaction of poly(lower alkylene imines) with polyesters having free carboxyl groups, and salts thereof, (meth)acrylic acid-styrene copolymers, (meth)acrylic acid-(meth)acrylic acid ester copolymers, styrene-maleic acid copolymers, polyvinyl alcohols, and water-soluble resins and water-soluble polymer compounds such as polyvinylpyrrolidone, polyesters, modified polyacrylates, ethylene oxide/propylene oxide adducts, and phosphate esters, which can be used alone or in a mixture of two or more, but are not necessarily limited to these.

The total amount of resin-type dispersant is preferably 0.01 to 30% by mass, more preferably 0.05 to 20% by mass, and even more preferably 0.1 to 10% by mass, relative to the total colorant. If it is 0.01% by mass or more, the dispersion stability of the printing ink will be good, and the release properties will also be improved. Furthermore, if it is 30% by mass or less, the water resistance of the printed layer will be good.

[Binder resin]
As the binder resin of the printing layer, for example, a nitrocellulose-based, cellulose acetate propionate or other fiber material, a chlorinated polypropylene-based, vinyl chloride-vinyl acetate copolymer-based, polyester-based, acrylic-based, urethane resin-based and acrylic urethane-based, polyamide-based, polybutyral-based, cyclized rubber-based, chlorinated rubber-based, or a binder using them in combination as appropriate can be used. When the printing layer contains a water-soluble resin or a compound having an acidic group, which will be described later, the printing layer also functions as a release layer. These resins may be used alone or in combination of two or more.

[Primer layer]
The laminate used in the present invention may have a primer layer. When the laminate has a primer layer, the primer layer is preferably disposed in contact with the plastic substrate, formed from a primer composition having a water-soluble resin or a compound having an acidic group, and serves to release the plastic substrate by dissolution, peeling, or the like with a release liquid.

(Water-soluble resin)
The water-soluble resin may be any resin that swells or dissolves in water and can be removed from the plastic substrate. The water may be heated to a temperature of about 25 to 100° C. This allows the primer layer to be removed by water (including warm water).
Such resins can be selected from known resins as long as they do not impair water solubility, and examples thereof include water-soluble polyester resins, water-soluble polyamide resins, water-soluble polyimide resins, water-soluble acrylic resins, water-soluble polyurethane resins, water-soluble polyallylamine resins, water-soluble phenolic resins, water-soluble epoxy resins, water-soluble phenoxy resins, water-soluble urea resins, water-soluble melamine resins, polyvinyl alcohol resins, and modified products of these resins. These can be used alone or in combination of two or more. Among them, polyvinyl alcohol (PVA) resins are preferably used from the viewpoints of availability and release properties.
When the water-soluble resin has film-forming properties, the water-soluble resin may be used as the binder resin constituting the primer layer.

As the polyvinyl alcohol resin, in addition to unmodified polyvinyl alcohol, modified polyvinyl alcohol obtained by copolymerizing various monomers during the production of vinyl ester resin and saponifying the copolymer, or various post-modified polyvinyl alcohols obtained by introducing various functional groups into unmodified polyvinyl alcohol by post-modification may be used. In addition, modified polyvinyl alcohols may be further post-modified. These modifications may be performed within a range that does not impair the water solubility of the polyvinyl alcohol resin.
These resins may be used alone or in combination of two or more.

Preferred examples of polyvinyl alcohol resins include resins containing structural units with primary hydroxyl groups in the side chains, and ethylene-modified polyvinyl alcohol resins. Among these, polyvinyl alcohol resins containing structural units with primary hydroxyl groups in the side chains are preferred, as they have excellent melt moldability and water solubility. The number of primary hydroxyl groups in these structural units is usually 1 to 5, preferably 1 to 2, and more preferably 1. It is also preferable for them to have secondary hydroxyl groups in addition to the primary hydroxyl groups.

The saponification degree of the polyvinyl alcohol resin used in the present invention (measured according to JIS K 6726) is usually 60 to 100 mol%. The preferred range of the saponification degree varies depending on the modified species. For example, in the case of an unmodified polyvinyl alcohol resin, it is usually 60 to 99.9 mol%, preferably 70 to 99.0 mol%, more preferably 75 to 98.5%. The saponification degree of the modified polyvinyl alcohol resin containing a side chain 1,2-diol structural unit is usually 60 to 99.9 mol%, preferably 65 to 99.8 mol%, more preferably 70 to 99.5 mol%. If the saponification degree is too low, the water solubility tends to decrease. The saponification degree of the ethylene-modified polyvinyl alcohol resin modified with a small amount of ethylene is usually 60 mol% or more, preferably 70 to 99.5 mol%, particularly preferably 75 to 99.0 mol%.
The saponification degree within the above range is preferable because it provides excellent water solubility and good releasability, and is also preferable because it provides excellent coatability when forming a primer layer.

The average degree of polymerization of the polyvinyl alcohol resin (measured in accordance with JIS K 6726) is usually 100 to 3,000, preferably 150 to 2,000, more preferably 180 to 1,000, and particularly preferably 200 to 800.

(Compound having an acidic group)
The compound having an acidic group may be a resin having an acidic group or a low molecular weight compound having an acidic group, which allows the primer layer to be removed by the above-mentioned basic aqueous solution.

Examples of the resin having an acidic group include a cellulose resin, a urethane resin, a polyamide resin, a vinyl chloride/vinyl acetate copolymer, a ketone resin, a polyester resin, and a (meth)acrylic resin. Examples of the acidic group include a carboxy group, a phosphoric acid group, a sulfo group, a sulfino group, and the like, or an ester or salt thereof.
Furthermore, as the resin having an acidic group, a rosin-modified resin having an acid value, such as maleic rosin or fumaric rosin, can be used.
In addition, examples of resins having an acidic group that can be used include radical copolymers such as styrene-(meth)acrylic resins, styrene-maleic acid (anhydride) resins, and terpene-maleic acid (anhydride) resins, which are obtained by copolymerizing polymerizable monomers having an acidic group, such as polymerizable monomers having a carboxy group, such as itaconic acid, maleic acid, fumaric acid, and cinnamic acid; polymerizable monomers which are acid anhydrides, such as itaconic acid anhydride and maleic acid anhydride; polymerizable monomers having a sulfonic acid group, such as sulfonated styrene; and polymerizable monomers having a sulfonamide group, such as vinylbenzenesulfonamide; and acid-modified polyolefin resins.
These may be used alone or in combination of two or more.

The low molecular weight compound having an acidic group refers to a compound that does not have a molecular weight distribution and has a molecular weight of 1,000 or less. Examples of such compounds include saturated fatty acids such as lauric acid, myristic acid, palmitic acid, margaric acid, and stearic acid; unsaturated fatty acids such as oleic acid, linoleic acid, linolenic acid, arachidonic acid, eicosapentaenoic acid, docosahexaenoic acid, and sorbic acid; hydroxy acids such as lactic acid, malic acid, and citric acid; aromatic carboxylic acids such as benzoic acid, phthalic acid, isophthalic acid, terephthalic acid, salicylic acid, gallic acid, mellitic acid, and cinnamic acid; dicarboxylic acids such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, fumaric acid, and maleic acid; tricarboxylic acids such as aconitic acid; oxocarboxylic acids such as pyruvic acid and oxaloacetic acid; carboxylic acid derivatives such as amino acids and nitrocarboxylic acids; and acid anhydrides such as trimellitic anhydride and pyromellitic anhydride.
The low molecular weight compound having an acidic group can be used in combination with the above-mentioned resin having an acidic group or a known binder resin constituting a known primer layer to form a primer layer.

From the viewpoint of recoating suitability, the primer layer preferably contains a compound having an acidic group. Also, from the viewpoint of printability, the primer layer preferably contains a urethane resin having an acidic group, an acrylic resin having an acidic group, or a rosin-modified resin. The primer layer may contain one of these resins alone or two or more of them in combination.

[Urethane resin having acidic groups]
The urethane resin having an acidic group is not particularly limited, and examples thereof include a urethane resin obtained by reacting a polyol having an acidic group with a polyisocyanate, a resin obtained by reacting a polyol with a polyisocyanate and modifying with an acid the hydroxyl groups in the urethane resin obtained by reacting a polyol with a polyisocyanate, and a resin obtained by reacting an amino group in a urethane urea resin obtained by reacting a polyamine with an isocyanate group in a urethane resin obtained by reacting a polyol with a polyisocyanate.
In addition, as the urethane resin having an acidic group, a resin obtained by reacting a polyol containing a hydroxy acid with a polyisocyanate may be used. By using a hydroxy acid as the polyol, it is possible to impart an acid value derived from a carboxy group to the urethane resin, and it is possible to improve the releasability. In addition, when the urethane resin having an acidic group has an isocyanate group, a part of the isocyanate group may be reacted with a polyamine to introduce a urea bond to form a urethane urea.

Polyol
Polyol is a general term for a compound having at least two hydroxyl groups in one molecule. The number average molecular weight of the polyol is preferably 500 to 10,000, more preferably 1,000 to 5,000. The number average molecular weight is calculated from the hydroxyl value of the polyol, and the hydroxyl value refers to a value measured according to JIS K 0070. When the number average molecular weight of the polyol is 500 or more, the flexibility of the primer layer is excellent and the adhesion to the plastic substrate is improved. When the number average molecular weight is 10,000 or less, the blocking resistance to the plastic substrate is excellent.

The polyol is not particularly limited, and more preferably, at least one polyol selected from the group consisting of polyester polyol, polyether polyol, and polycarbonate polyol is used. The polyol may further include other dimer diol, hydrogenated dimer diol, castor oil modified polyol, etc.
That is, the urethane resin preferably contains a structural unit derived from at least one polyol selected from the group consisting of polyester polyol, polyether polyol, and polycarbonate polyol. Since the ester bond site of the polyester polyol is hydrolyzed by alkali to improve the releasability, the urethane resin more preferably contains a structural unit derived from a polyester polyol.
The content of the polyol-derived structural units is preferably 10 to 75% by mass, more preferably 15 to 70% by mass, and even more preferably 20 to 65% by mass, based on the total amount of the urethane resin. The content of the polyester polyol-derived structural units is preferably 5% by mass or more, more preferably 30% by mass or more, even more preferably 60% by mass or more, and particularly preferably 80% by mass or more, based on the total amount of the polyol-derived structural units.

Hydroxy acids
The polyol may contain a hydroxy acid. The hydroxy acid refers to a compound having both a hydroxyl group, which is an active hydrogen group, and an acidic functional group in one molecule. The acidic functional group refers to a functional group that can be neutralized with potassium hydroxide when measuring the acid value, and specific examples thereof include a carboxy group and a sulfonic acid group, and a carboxy group is preferred. As such a hydroxy acid, for example, a dimethylolalkanoic acid such as 2,2-dimethylolpropionic acid, 2,2-dimethylolbutanoic acid, or 2,2-dimethylolvaleric acid is preferably used.

<Polyisocyanate>
The polyisocyanate is not particularly limited and can be selected from conventionally known polyisocyanates. It preferably contains a diisocyanate or triisocyanate, and more preferably contains an aromatic, aliphatic or alicyclic diisocyanate. These may be used alone or in combination of two or more kinds.

Polyamines
The polyamine for forming the urethane urea is not particularly limited, and is preferably a diamine compound. In addition, a diamine having a hydroxyl group may be used because it can introduce a hydroxyl group into the urethane resin.

The acid value of the urethane resin having acidic groups is preferably 15 mgKOH/g or more, more preferably 15 to 70 mgKOH/g, and even more preferably 20 to 50 mgKOH/g. If it is 15 mgKOH/g or more, it is preferable because the release property by the release liquid is good, and if it is 70 mgKOH/g or less, it is preferable because the adhesion to the substrate and the retort resistance are good. The hydroxyl value of the urethane resin is preferably 1 to 35 mgKOH/g, and more preferably 10 to 30 mgKOH/g. If it is 1 mgKOH/g or more, it is preferable because the release property by the release liquid is good, and if it is 35 mgKOH/g or less, it is preferable because the adhesion to the substrate is good.

The weight average molecular weight of the urethane resin having an acidic group is preferably 10,000 to 100,000, more preferably 15,000 to 70,000, and even more preferably 15,000 to 50,000. The molecular weight distribution (Mw/Mn) of the urethane resin is preferably 6 or less. Mw represents the weight average molecular weight, and Mn represents the number average molecular weight. When the molecular weight distribution is 6 or less, the release property, drying property of the primer composition, and retort resistance are excellent. In addition, the smaller the molecular weight distribution, that is, the sharper the molecular weight distribution, the more uniform the dissolution and peeling action by the release liquid occurs, and the release property of the plastic substrate is improved. The molecular weight distribution is more preferably 5 or less, and even more preferably 4 or less. In addition, the molecular weight distribution is preferably 1.5 or more, and more preferably 1.2 or more.
In the present invention, Mw, Mn and molecular weight distribution (Mw/Mn) are values calculated as polystyrene by gel permeation chromatography (GPC).

The urethane resin having an acidic group may have an amine value. When the urethane resin has an amine value, the amine value is preferably 0.1 to 20 mgKOH/g, and more preferably 1 to 10 mgKOH/g. If it is within the above range, the adhesion to the substrate is excellent.

The number of urethane bonds in the polyurethane resin having an acidic group is preferably 1 to 3 mmol/g, more preferably 1.5 to 2 mmol/g. The number of urea bonds is preferably 0 to 3 mmol/g, more preferably 0.2 to 1 mmol/g. The total number of urethane bonds and urea bonds is preferably 1 to 6 mmol/g, more preferably 1.7 to 3 mmol/g.
By setting the number of urethane bonds and the number of urea bonds within the corresponding ranges, releasability and adhesion to substrates are improved.

[Acrylic resin having acidic group]
Examples of acrylic resins having an acidic group include polymers obtained by polymerizing a monomer containing a (meth)acrylic monomer having an acidic group, such as (meth)acrylic acid or maleic acid; and resins obtained by polymerizing a monomer containing a (meth)acrylic monomer having a hydroxyl group or a glycidyl group, and then modifying the functional group to introduce a carboxyl group (e.g., maleic anhydride modified resin).
The acid value of the acrylic resin having an acidic group is preferably 50 mgKOH/g or more, and more preferably 100 mgKOH/g or more.

[Rosin-modified resin]
Rosin-modified resins are resins prepared using rosin as one of the raw materials. Rosin contains a mixture of resin acids such as abietic acid, palustric acid, isopimaric acid, and levopimaric acid, and these resin acids contain hydrophilic and chemically active carboxyl groups, some of which have conjugated double bonds. Therefore, various rosin-modified resins are prepared by combining polyhydric alcohols and polybasic acids and polycondensing them, adding resol, which is a condensate of phenol, to the benzene ring contained in the rosin skeleton, or by carrying out a Diels-Alder reaction with maleic anhydride or maleic acid, which are dienophiles, to add maleic acid or maleic anhydride skeletons. Various types of such rosin-modified resins are commercially available, and it is also possible to obtain and use them.

Examples of rosin-modified resins include maleated rosin, fumarated rosin, rosin-modified maleic acid resin, rosin-modified fumaric acid resin, rosin-modified phenolic resin, rosin-modified alkyd resin, and rosin-modified polyester resin. In the present invention, any rosin-modified resin may be used, but among these, those containing in their structure at least one moiety derived from maleic acid, maleic anhydride, fumaric acid, and fumaric anhydride are preferably used. A resin "containing in its structure at least one moiety selected from the group consisting of maleic acid, maleic anhydride, fumaric acid, and fumaric anhydride" is prepared using at least one selected from the group consisting of maleic acid, maleic anhydride, fumaric acid, and fumaric anhydride as part of the raw material, and for example, refers to rosin-modified maleic acid resin or rosin-modified fumaric acid resin obtained by condensation polymerization of maleic acid or fumaric acid as part of a polybasic acid, maleic rosin or fumaric rosin having a structure in which maleic acid, maleic anhydride, fumaric acid, or fumaric anhydride is added as a dienophile by Diels-Alder reaction, or resins in which other chemical species are further polymerized using the functional groups contained in these.

The acid value of the rosin-modified resin is preferably 10 to 400 mg KOH/g, and more preferably 100 to 300 mg KOH/g.

(Other ingredients)
The primer layer may contain a resin other than the water-soluble resin or the compound having an acidic group.
Examples of such resins include cellulose resins, polyamide resins, vinyl chloride resins such as vinyl chloride-vinyl acetate copolymer resins or vinyl chloride-acrylic copolymer resins, ethylene-vinyl acetate copolymer resins, vinyl acetate resins, acrylic resins, styrene resins, dammar resins, styrene-acrylic copolymer resins, polyester resins, alkyd resins, terpene resins, phenol-modified terpene resins, ketone resins, cyclized rubbers, chlorinated rubbers, butyral, polyacetal resins, petroleum resins, and modified resins thereof. These resins may be used alone or in combination of two or more.
Among them, the primer layer preferably contains at least one resin selected from the group consisting of cellulose resin, vinyl chloride resin, rosin resin, and acrylic resin, and more preferably contains vinyl chloride resin or acrylic resin.
The mass ratio of the urethane resin having an acidic group to the other resin (urethane resin having an acidic group:other resin) is preferably 95:5 to 50:50. This range is preferable because, when the printed layer is peeled off together with the primer layer in a basic aqueous solution, the printed layer is peeled off in a thin film state, making it easy to recover.

The primer layer may contain a body pigment. Examples of the body pigment include silica, barium sulfate, kaolin, clay, calcium carbonate, magnesium carbonate, zinc oxide, zirconium oxide, and other metal oxides. Among these, silica is preferred, and hydrophilic silica is more preferred.
The average particle size of the extender pigment is preferably 0.5 to 10 μm, more preferably 1 to 8 μm. The content of the extender pigment in the primer layer is preferably 0.5 to 10 mass %, more preferably 1 to 5 mass %. When the average particle size and the content of the extender pigment are within the above ranges, the wettability of the printing layer is improved, and image quality is improved.

The primer layer may be a layer in which the above-mentioned urethane resin having an acidic group is crosslinked with a curing agent. By introducing a crosslinked structure into the primer layer, the penetration and bleeding of the printing layer formed on the primer layer is suppressed, and excellent image quality can be achieved.
The curing agent may be, for example, a polyisocyanate. The polyisocyanate is not particularly limited and may be selected from conventionally known polyisocyanates, for example, an aliphatic polyisocyanate or an aromatic aliphatic polyisocyanate. These may be used alone or in combination of two or more kinds.

The primer layer may further contain known additives. Examples of known additives include dispersants, wetting agents, adhesion aids, leveling agents, defoamers, antistatic agents, viscosity modifiers, metal chelates, trapping agents, antiblocking agents, wax components other than those mentioned above, and silane coupling agents.

The thickness of the primer layer is preferably in the range of 0.5 to 3.0 μm, more preferably 0.6 to 2.0 μm, and even more preferably 0.8 to 1.5 μm, and can be formed using known methods.

[Adhesive layer]
The laminate of the present invention may have an adhesive layer. When the laminate has an adhesive layer, the adhesive layer is preferably disposed in contact with the plastic substrate, contains a compound having an acidic group, and plays a role in releasing the plastic substrate by dissolving or peeling with a release liquid. When the adhesive layer contains a resin having an acidic group or a low molecular weight compound having an acidic group, the adhesive layer can be released using the above-mentioned basic aqueous solution.
For the compound having an acidic group, the resin having an acidic group, and the low molecular weight compound having an acidic group, the description of (Compound having an acidic group) in the above section [Primer layer] can be cited.
The method for forming the adhesive layer is not limited, and the adhesive layer can be formed by using a known method.

From the viewpoint of releasability, the adhesive layer may be a cured product of an adhesive containing a polyester polyol having an acidic group and at least one polyisocyanate selected from the group consisting of an aliphatic polyisocyanate and an araliphatic polyisocyanate. The cured product corresponds to a resin having an acidic group.
The adhesive layer may also be a cured product of an adhesive containing a polyester polyol, at least one polyisocyanate selected from the group consisting of aliphatic polyisocyanates and araliphatic polyisocyanates, and a low molecular weight compound having an acidic group.

(Polyester polyol)
The polyester polyol may have an acidic group, and may be appropriately selected from known polyester polyols.By including such a polyester polyol, when a basic aqueous solution is used as the release liquid, the release property is improved by having an ester bond with high affinity with a basic compound, which is preferable.The polyester polyol may be used alone or in combination of two or more kinds.

The polyester polyol is not particularly limited, but polyester polyols obtained by reacting a carboxyl group component with a hydroxyl group component; and polyester polyols obtained by ring-opening polymerization of lactones such as polycaprolactone, polyvalerolactone, and poly(β-methyl-γ-valerolactone) are preferably used.
Examples of the carboxyl group component include dibasic acids such as terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid, phthalic anhydride, adipic acid, azelaic acid, sebacic acid, succinic acid, glutaric acid, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, maleic anhydride, and itaconic anhydride, or dialkyl esters thereof, or mixtures thereof.
Examples of the hydroxyl group component include diols such as ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, triethylene glycol, butylene glycol, neopentyl glycol, trimethylolpropane, glycerin, 1,6-hexanediol, 1,4-butanediol, 1,4-cyclohexanedimethanol, 3-methyl-1,5-pentanediol, 3,3'-dimethylolheptane, 1,9-nonanediol, polyoxyethylene glycol, polyoxypropylene glycol, polytetramethylene ether glycol, polyether polyol, polycarbonate polyol, polyolefin polyol, acrylic polyol, polyurethane polyol, and mixtures thereof.
The above carboxyl group components and hydroxyl group components may be used in combination of two or more kinds.

The polyester polyol may be a polyester urethane polyol obtained by reacting a hydroxyl group in a polyol with a polyisocyanate. The polyester polyol has a urethane bond, and thus exhibits excellent heat resistance and adhesiveness.
Examples of the polyisocyanate include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, xylylene diisocyanate, diphenylmethane diisocyanate, isophorone diisocyanate, 1,5-naphthalene diisocyanate, hexamethylene diisocyanate, and hydrogenated diphenylmethane diisocyanate.

The polyester polyol may be an acid anhydride-modified product obtained by reacting an acid anhydride with a hydroxyl group in the polyol, thereby introducing a carboxyl group, which is an acidic group, into the polyester polyol.
Examples of the acid anhydride include pyromellitic anhydride, mellitic anhydride, trimellitic anhydride, and trimellitic ester anhydride. Examples of the trimellitic ester anhydride include ethylene glycol bisanhydrotrimellitate and propylene glycol bisanhydrotrimellitate.

The acid value of the polyester polyol is preferably 5.0 mgKOH/g or more, more preferably 10.0 mgKOH/g or more. The acid value of the polyester polyol is preferably 100 mgKOH/g or less, more preferably 80 mgKOH/g or less. When the acid value of the polyester polyol is in the above range, when the polyester polyol is contacted with a release liquid that is a basic aqueous solution, the basic aqueous solution penetrates and decomposes the polyester polyol, thereby exhibiting better release properties.
When the adhesive contains a plurality of polyester polyols, the acid value of the entire polyester polyols can be determined from the acid value of each polyester polyol and its mass ratio.

The number average molecular weight (Mn) of the polyester polyol is preferably 3,000 to 25,000, more preferably 5,000 to 20,000, and particularly preferably 7,000 to 15,000. If the number average molecular weight of the polyester polyol is 3,000 or more, not only the coatability but also sufficient retort resistance can be exhibited, and if it is 20,000 or less, not only the coatability but also the release property is improved, so this is preferable.

In order to satisfy various physical properties required for the packaging material, the polyester polyol component may contain a combination of multiple polyester polyol components. For example, the polyester polyol may contain a polyester polyol having a number average molecular weight of 5,000 to 20,000, and may further contain a polyester polyol having a number average molecular weight of less than 3,000 in order to improve adhesion to the substrate.
The content of the polyester polyol having a number average molecular weight of less than 3,000 is preferably 0 to 30% by mass, more preferably 0 to 20% by mass, based on the total mass of the polyester polyol. When the content is 30% by mass or less, retort resistance can be maintained.

(Other polyols)
The adhesive constituting the adhesive layer may contain a polyol other than the polyester polyol. The polyol that may be contained other than the polyester polyol is not particularly limited, and examples thereof include polycarbonate polyol, polycaprolactone polyol, polyether polyol, polyolefin polyol, acrylic polyol, silicone polyol, castor oil-based polyol, and fluorine-based polyol.

(Polyisocyanate)
The polyisocyanate to be combined with the above-mentioned polyester polyol to form the adhesive layer is preferably at least one selected from the group consisting of known aliphatic polyisocyanates and araliphatic polyisocyanates.

Examples of the aliphatic polyisocyanate include acyclic aliphatic diisocyanates such as trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, 1,2-propylene diisocyanate, and 1,2-butylene diisocyanate; alicyclic diisocyanates such as 1,4-cyclohexane diisocyanate, 1,3-cyclohexane diisocyanate, and 3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate (hereinafter, referred to as isophorone diisocyanate); and polyisocyanates such as allophanate type, nurate type, biuret type, and adduct type derivatives derived from the above diisocyanates, or complexes thereof.
The derivative is preferably a nurate type or an adduct type, more preferably an adduct type. As the aliphatic polyisocyanate, a polyisocyanate derived from hexamethylene diisocyanate (hereinafter also referred to as HDI) is preferred, which is easy to ensure a balance between releasability and laminate properties.

Examples of aromatic aliphatic polyisocyanates include aromatic aliphatic diisocyanates such as 1,3- or 1,4-xylylene diisocyanate or mixtures thereof, ω,ω'-diisocyanato-1,4-diethylbenzene, 1,3- or 1,4-bis(1-isocyanato-1-methylethyl)benzene or mixtures thereof; and polyisocyanates derived from the above aromatic aliphatic diisocyanates, such as allophanate type, nurate type, biuret type, and adduct type derivatives, or complexes thereof.

(Other polyisocyanates)
The adhesive may contain polyisocyanates other than the aliphatic polyisocyanates and aromatic aliphatic polyisocyanates, as long as the effects of the present invention are not impaired. Examples of such polyisocyanates include aromatic diisocyanates such as toluene diisocyanate and diphenylmethane diisocyanate; and polyisocyanates such as derivatives of the above diisocyanates or complexes thereof.

The polyol and polyisocyanate may be mixed in such a ratio that the molar ratio (NCO/OH) of the isocyanate groups of the polyisocyanate to the hydroxyl groups of the polyol is 0.3 to 10.0. Preferably, the molar ratio is 0.3 to 7.0, and more preferably, 0.5 to 5.0.

(Other ingredients)
The adhesive layer may contain, in addition to a silane coupling agent, a phosphorus oxygen acid or a derivative thereof, a leveling agent, an antifoaming agent, and a reaction accelerator, inorganic fillers (e.g., silica, alumina, mica, talc, aluminum flakes, glass flakes), layered inorganic compounds, stabilizers (e.g., antioxidants, heat stabilizers, ultraviolet absorbers, hydrolysis inhibitors), rust inhibitors, thickeners, plasticizers, antistatic agents, lubricants, antiblocking agents, colorants, fillers, crystal nucleating agents, catalysts for adjusting the curing reaction, and the like.

<Plastic substrate layer>
Examples of the plastic substrate include polyolefin resin, polyester resin, polyamide resin, polystyrene resin, vinyl chloride resin, vinyl acetate resin, ABS resin, acrylic resin, acetal resin, polycarbonate resin, polyvinyl alcohol resin, and cellulose-based plastics.

From the viewpoint of reuse as a recycled substrate, the plastic substrate is preferably a polyolefin substrate containing a polyolefin resin. Examples of substrates containing such polyolefin resin include plastic substrates such as polyethylene (PE) and biaxially oriented polypropylene (OPP), as well as sealant substrates such as low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), high-density polyethylene (HDPE), acid-modified polyethylene, non-oriented polypropylene (CPP), acid-modified polypropylene, and copolymer polypropylene.
The plastic substrate may be a gas barrier substrate that has been subjected to a gas barrier treatment.

The thickness of the plastic substrate layer is not particularly limited and may be appropriately selected depending on the application. It is preferably 5 to 200 μm, more preferably 10 to 150 μm. The thinner the thickness, the easier the substrate curls and the more difficult it is to remove. Examples of gas barrier substrates include aluminum foil, plastic substrates having a metal vapor deposition layer such as aluminum, and a metal oxide vapor deposition layer such as silica or alumina. For economical reasons, the thickness of the aluminum foil is often in the range of 3 to 50 μm. Furthermore, the aluminum foil, aluminum vapor deposition layer, and alumina vapor deposition layer dissolve in a basic aqueous solution and are removed, so they function as a removal layer and can separate adjacent polyolefin resins.

Examples of the laminate structure of the present invention are given below, but the laminate structure is not limited thereto. In the following structures, the "substrate layer" does not have to be a single layer, and may be a laminate in which multiple substrates are laminated.
・Plastic substrate layer/printed layer ・Plastic substrate layer/primer layer/printed layer ・Plastic substrate layer/printed layer/adhesive layer/plastic substrate layer ・Plastic substrate layer/primer layer/printed layer/adhesive layer/plastic substrate layer ・Substrate layer/printed layer/adhesive layer/plastic substrate layer ・Plastic substrate layer/primer layer/printed layer/adhesive layer/vapor deposition layer/plastic substrate layer

<Method of manufacturing plastic substrate>
The above-mentioned separation and recovery method can be used to produce a plastic substrate. The plastic substrate may be a substrate that has been fragmented by crushing, cutting, pulverization, etc. The method for producing a plastic substrate includes, for example, preparing a laminate having at least a plastic substrate layer and a coating layer, and recovering the plastic substrate by the above-mentioned separation and recovery method.

<Method of manufacturing molding material>
A molding material can be produced by melt-kneading the plastic substrate recovered by the above-mentioned separation and recovery method. The method for producing a molding material of the present invention preferably includes the following steps 1 to 3. Alternatively, the above-mentioned method for separating and recovering a laminate or the method for producing a plastic substrate may include at least the following step 1, and the method for producing a molding material may include at least the following step 3. When the molding material includes a master batch, it may further include the following step 4.
(Step 1) A step of crushing the laminate and immersing it in a release liquid to remove the plastic substrate from the laminate, or a step of crushing the laminate and immersing it in a release liquid to remove the coating layer from the laminate. (Step 2) A step of recovering the plastic substrate obtained in step 1 and washing it with water. (Step 3) A step of melt-kneading the plastic substrate obtained in step 2 to obtain a recycled resin. (Step 4) A step of mixing a master batch with the recycled resin obtained in step 3 to obtain a molding material.

The method for crushing the laminate in step 1 is not particularly limited, and examples thereof include methods using a jaw crusher, impact crusher, cutter mill, stamp mill, ring mill, roller mill, jet mill, and hammer mill.
Step 2 may further include a drying step, if necessary. By step 2, a recovered plastic substrate (also called a recycled substrate or a recycled plastic substrate) can be obtained.

The melt-kneading method in step 3 refers to adding various additives such as antioxidants as necessary, mixing using a Henschel mixer, tumbler, disperser, etc., and then mixing and dispersing using a batch type kneader such as a kneader, roll mill, super mixer, Henschel mixer, Schuggie mixer, vertical granulator, high-speed mixer, Furmatrix, ball mill, steel mill, sand mill, vibration mill, attritor, or Banbury mixer, a twin-screw extruder, a single-screw extruder, or a rotor-type twin-screw kneader. This results in a recycled resin, which is a resin composition. The shape of the recycled resin is not particularly limited and may be in the form of pellets, powder, granules, or beads. It is preferable to use a twin-screw extruder for the melt-kneading step.

[Master Badge]
The molding material of the present invention may further contain a masterbatch. The masterbatch is not particularly limited as long as it is compatible with the recycled resin, and generally, a mixture of a thermoplastic resin such as a polyethylene resin or a polypropylene resin and a colorant can be used. The thermoplastic resin contained in the masterbatch may be used alone or in combination of two or more kinds.
The master batch in the present invention may contain, within the scope not impairing the effects of the present invention, a metallic soap of an alkali metal, an alkaline earth metal, or zinc, hydrotalcite, a nonionic surfactant, a cationic surfactant, an anionic surfactant, an amphoteric surfactant, an antistatic agent, a flame retardant such as a halogen-based, phosphorus-based, or metal oxide, a lubricant such as ethylene bis alkyl amide, an antioxidant, an ultraviolet absorber, or a filler.

<Molded body>
The molding material obtained by the above-mentioned production method can be heated and molded to obtain a molded article. The heating and molding method is not particularly limited, and examples thereof include injection molding, extrusion molding, blow molding, and compression molding.
Molding materials produced using the plastic substrates recovered by the separation and recovery method of the present invention are of high quality because the printed layer is detached and reattachment of the detached components is suppressed, and they can be used in a variety of fields, such as home appliances, stationery, automobile parts, toys, sporting goods, medical materials, and building and construction materials.

The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. Note that parts and percentages in the present invention represent parts by mass and percentages by mass unless otherwise noted.

<Molecular weight and molecular weight distribution>
The weight average molecular weight (Mw), number average molecular weight (Mn) and molecular weight distribution (Mw/Mn) were measured by gel permeation chromatography (GPC) and calculated as molecular weights using polystyrene as a standard substance. The measurement conditions are shown below.
GPC device: Showa Denko Shodex GPC-104
Columns: The following columns were used in series connection:
Showa Denko Shodex LF-404 x 2 Showa Denko Shodex LF-G x 2
Detector: RI (differential refractometer)
Measurement conditions: column temperature 40°C
Eluent: tetrahydrofuran Flow rate: 0.3 mL/min

<Acid value>
The acid value was measured according to the method described in JIS K 0070 (1992).

<Production of primer composition and resin for printing ink>
[Synthesis Example 1-1] (Polyurethane Resin P1)
In a reactor equipped with a reflux condenser, a dropping funnel, a gas inlet tube, a stirrer, and a thermometer, while introducing nitrogen gas, 152.2 parts of PPA (a polyester polyol composed of a polycondensate of propylene glycol and adipic acid and having a number average molecular weight of 2,000), 15.2 parts of PPG (a polyether polyol composed of polypropylene glycol and having a number average molecular weight of 2,000), 13.6 parts of BD (1,4-butanediol), 99.8 parts of IPDI (isophorone diisocyanate), and 200 parts of NPAC (normal propyl acetate) were charged and reacted at 90° C. for 5 hours to obtain a urethane prepolymer solution having an isocyanate group at the end.
Next, a mixture of 19.2 parts of AEA (2-(2-aminoethylamino)ethanol) and 350 parts of IPA (isopropyl alcohol) was added dropwise at room temperature over 60 minutes, and then reacted at 70° C. for 3 hours to obtain a polyurethane resin solution.
NPAC was added to the resulting polyurethane resin solution to adjust the solid content, thereby obtaining a solution of polyurethane resin P1 having a solid content concentration of 30%, a weight average molecular weight of 27,000, Mw/Mn=3.1 and an acid value of 0.0 mgKOH/g.

[Synthesis Example 1-2] (Polyurethane Resin P2)
In a reactor equipped with a reflux condenser, a dropping funnel, a gas inlet tube, a stirrer, and a thermometer, 135.7 parts of PPA, 13.6 parts of PPG, 28.3 parts of DMPA (2,2-dimethylolpropanoic acid), 105.7 parts of IPDI, and 200 parts of NPAC were charged while introducing nitrogen gas, and the mixture was reacted at 90°C for 5 hours to obtain a urethane prepolymer solution having an isocyanate group at its end.
Next, a mixture of 16.7 parts of AEA and 350 parts of IPA was added dropwise at room temperature over 60 minutes, and the mixture was allowed to react at 70° C. for 3 hours to obtain a polyurethane resin solution.
NPAC was added to the resulting polyurethane resin solution to adjust the solid content, thereby obtaining a solution of polyurethane resin P2 having a solid content concentration of 30%, a weight average molecular weight of 30,000, Mw/Mn=3.0 and an acid value of 39.3 mgKOH/g.

<Production of primer layer-forming composition>
[Production Example 1-1] (Primer composition S1)
87 parts of polyurethane resin P2 solution, 5 parts of EA, 5 parts of IPA, and 3 parts of silica particles (P-73 manufactured by Mizusawa Chemical Industries, Ltd.: hydrophilic silica particles having an average particle size of 3.8 μm) were mixed and stirred using a disper to obtain primer composition S1.

<Production of printing ink>
[Production Example 2-1] (Printing ink R1)
Indigo pigment P.B.15 (C.I.Pigment Blue 15) 10 parts, BYK-SYNERGIST2100 (manufactured by BYK Japan) 0.2 parts, DISPER BYK-142 (manufactured by BYK Japan) 0.5 parts, polyurethane resin P1 solution 24.3 parts, PVC solution (vinyl chloride-vinyl acetate copolymer resin solution (Nissin Chemical Solvine TAO, solid content 30%, EA solution)) 5 parts, EA 10 parts, IPA 10 parts were mixed and stirred, and dispersion treatment was performed for 20 minutes using a sand mill as a bead mill. Then, polyurethane resin P1 solution 20 parts, EA 10 parts, IPA 10 parts were mixed and stirred to obtain printing ink R1.

[Production Example 2-2] (Printing ink R2)
10 parts of indigo pigment P.B.15, 0.2 parts of BYK-SYNERGIST2100, 0.5 parts of DISPER BYK-142, 24.3 parts of polyurethane resin P2 solution, 5 parts of PVC solution, 10 parts of EA, and 10 parts of IPA were mixed and stirred, and dispersed for 20 minutes using a sand mill as a bead mill. After that, 20 parts of polyurethane resin P2 solution, 10 parts of EA, and 10 parts of IPA were mixed and stirred to obtain printing ink R2.

<Production of polyol used in adhesive>
[Synthesis Example 2-1] (Polyester polyol B1)
In a reaction vessel equipped with a stirrer, a thermometer, a reflux condenser, a dropping tank and a nitrogen gas inlet tube, 124 parts of ethylene glycol, 212 parts of neopentyl glycol, 368 parts of 1,6-hexanediol, 645 parts of isophthalic acid, 36 parts of adipic acid and 265 parts of sebacic acid were charged, and the temperature was raised to 250°C while stirring under a nitrogen stream to carry out an esterification reaction. After a predetermined amount of water was distilled and the reaction was continued until the acid value was 5 or less, the pressure was gradually reduced and a deglycolization reaction was carried out at 1 mmHg or less for 5 hours to obtain a polyester polyol. Thereafter, 35 parts of isophorone diisocyanate was gradually added, and the reaction was carried out at 150°C for about 2 hours to obtain a polyester polyurethane polyol. 12.0 parts of ethylene glycol bis-anhydrotrimellitate was added to 100 parts of this polyester polyurethane polyol and reacted at 180°C for about 2 hours, and then diluted with ethyl acetate until the solid concentration reached 50%, thereby obtaining a solution of partially acid-modified polyester polyol B1 having a number average molecular weight of 9,000 and an acid value of 30.3 mgKOH/g.

[Synthesis Example 2-2] (Polyester polyol B2)
A reaction vessel equipped with a stirrer, a thermometer, a reflux condenser, a dropping tank and a nitrogen gas inlet tube was charged with 58 parts of ethylene glycol, 412 parts of diethylene glycol, 343 parts of neopentyl glycol, 517 parts of isophthalic acid and 393 parts of adipic acid, and the mixture was heated to 250 ° C. while stirring under a nitrogen stream to carry out an esterification reaction. After a predetermined amount of water was distilled and the reaction was continued until the acid value was 5 or less, the pressure was gradually reduced and the deglycolization reaction was carried out at 1 mmHg or less for 5 hours to obtain a polyester polyol. 4.0 parts of trimellitic anhydride were added to 100 parts of this polyester polyol, and the mixture was reacted at 180 ° C. for about 2 hours, and then diluted with ethyl acetate until the solid content concentration was 50%, to obtain a solution of partially acid-modified polyester polyol B2 with a number average molecular weight of 2,000 and an acid value of 23.5 mg KOH / g.

<Preparation of Polyisocyanate>
[Preparation Example 1] (Polyisocyanate C1)
Coronate 2785 (biuret type polyisocyanate derived from hexamethylene diisocyanate, manufactured by Tosoh Corporation) was diluted with ethyl acetate to adjust the solid concentration to 50% and NCO% to 9.6%, to obtain a solution of polyisocyanate C1.

<Manufacture of adhesive>
[Production Example 3-1] (Adhesive D1)
90 parts of the polyester polyol B1 solution, 10 parts of the polyester polyol B2 solution, and 8 parts of the polyisocyanate C1 solution were mixed, and EA was added to prepare an adhesive solution with a solids concentration of 30%.

<Production of Laminate>
The method for producing the laminate will be described below. The primer composition and the printing ink were each diluted with a mixed solvent of EA/IPA (mass ratio 70/30) to a viscosity of 15 seconds (25° C., Zahn cup #3 (manufactured by Rigo Co., Ltd.) before use. The thickness of the primer layer and the printing layer were each adjusted to about 1.5 μm.

[Production Example 4-1] (Laminate L1)
The diluted primer composition S1 and the printing ink R1 were printed in that order onto an OPP (corona-treated stretched polypropylene film, thickness 20 μm) using a gravure printing machine equipped with a gravure plate with a plate depth of 30 μm, and then dried at 50° C. to obtain a laminate having a configuration of OPP/S1/R1.
Next, adhesive D1 was applied and dried using a dry laminator onto the printed layer of the obtained laminate so that the film thickness after drying would be approximately 3 μm, and then the adhesive D1 was laminated with CPP (unstretched polypropylene film, thickness 30 μm) to obtain a laminate L1 having a configuration of base layer (OPP)/primer layer (S1)/printed layer (R1)/adhesive layer (D1)/base layer (CPP).

[Production Example 4-2] (Laminate L2)
Adhesive D1 was applied to OPP using a dry laminator so that the film thickness after drying would be approximately 3 μm, and then dried. The OPP was then bonded to CPP to obtain a laminate L2 having a structure of base layer (OPP)/adhesive layer (D1)/base layer (CPP).

[Manufacturing Example 4-3] (Laminate L3)
The diluted primer composition S1 and printing ink R1 were printed in that order onto the OPP using a gravure printing machine equipped with a gravure plate with a plate depth of 30 μm, and then dried at 50° C. to obtain a laminate L3 having a structure of base layer (OPP)/primer layer (S1)/printing layer (R1).

[Manufacturing Example 4-4] (Laminate L4)
The diluted printing ink R1 was printed onto the OPP using a gravure printing machine equipped with a gravure plate with a plate depth of 30 μm, and dried at 50° C. to obtain a laminate L4 having a structure of base layer (OPP)/printed layer (R1).

[Manufacturing Example 4-5] (Laminate L5)
The diluted printing ink R2 was printed onto the OPP using a gravure printing machine equipped with a gravure plate with a plate depth of 30 μm, and dried at 50° C. to obtain a laminate L5 having a structure of base layer (OPP)/printed layer (R2).

[Production Example 4-6] (Laminate L6)
The diluted printing ink R1 was printed onto PET (polyethylene terephthalate film, thickness 12 μm) using a gravure printing machine equipped with a gravure plate with a plate depth of 30 μm, and dried at 50° C. to obtain a laminate L6 having a structure of base layer (PET)/printing layer (R1).

The abbreviations in Table 1 are as follows.
OPP: Corona-treated oriented polypropylene film, thickness 20 μm
CPP: Unstretched polypropylene film, thickness 30 μm
PET: polyethylene terephthalate film, thickness 12 μm

<Production of eluent>
[Production Example 5-1] (eluent A1)
2 parts of sodium hydroxide and 98 parts of water were mixed and stirred with a disperser to obtain a elution liquid A1.

[Production Examples 5-2 to 5] (Elimination Solutions A2 to A5)
Elimination solutions A2 to A5 were obtained in the same manner as in Production Example 5-1, except that in addition to sodium hydroxide and water, polyoxyethylene lauryl ether (HLB; 13.6) as a nonionic surfactant, polyoxyethylene alkyl ether phosphate (HLB; 12) as an anionic surfactant, and BYK-1650 (manufactured by BYK Japan, silicone-based emulsion-type defoamer, solids concentration 27.5%) as an antifoaming agent were blended according to the blending compositions shown in Table 2.

<Separation and Recovery of Laminate>
[Example 1]
500 g of the release solution A3 and 25 g of a sample cut from the laminate L1 to a size of 1.5 cm x 0.5 cm were placed in a 1000 mL stainless steel beaker and stirred at 60° C. and 2000 rpm. The separation and recovery state of the laminate was evaluated as follows.

[Examples 2 to 16, Comparative Examples 1 to 5]
In addition, the state of separation and recovery of the laminate was evaluated in the same manner as in Example 1, except that the material, crushing size, amount of the laminate and the printed layer relative to the desorption liquid, and temperature were changed to those shown in Table 3. Note that 0.2 g of the laminate in Comparative Example 1 corresponds to 100 samples cut out of the laminate L1 to a size of 1 cm x 1 cm.
The results are shown in Table 3. The amounts of the laminate, printed layer, and film relative to the release liquid were calculated assuming the densities of the primer layer, printed layer, and adhesive layer to be 1 g/cm ³ , the densities of the OPP substrate and CPP substrate to be 0.91 g/cm ³ , and the density of the PET substrate to be 1.38 g/cm ³ .

<Evaluation of Laminate>
(Substrate Separation)
For the laminates with adhesive layers, the substrates were sampled 20 minutes, 40 minutes, and 1 hour after the start of stirring, and were washed with water and dried. Thirty substrates were randomly selected from the obtained substrates, and the thickness of the substrates was measured. From the thickness of the substrates, it was determined whether the laminate was separated between the adhesive layers, and the evaluation was performed according to the following criteria.
A (Excellent): All 30 pieces separated 20 minutes after the start of stirring.
B (Good): All 30 sheets separated 40 minutes after the start of stirring.
C (Fair): All 30 pieces separated 1 hour after the start of stirring.
D (unacceptable): One hour after the start of stirring, unseparated substrate remains.

(Removability of printed layer)
For the laminate having a primer layer and/or a printed layer on a plastic substrate, the substrate was sampled 20 minutes, 40 minutes, and 1 hour after the start of stirring, and then washed with water and dried. From the obtained substrate, 10 substrates 1 after separation were sampled, and the removal area rate of the printed layer was visually confirmed and evaluated according to the following criteria. This evaluation was performed on substrates with substrate separability ratings of A to C.
A (excellent): 90% or more of the printed layer peels off from the substrate 20 minutes after the start of stirring.
B (good): 90% or more of the printed layer peels off from the substrate 40 minutes after the start of stirring.
C (passable): 90% or more of the printed layer peels off from the substrate 1 hour after stirring begins.
D (unacceptable): Peeling of the printed layer on the substrate is less than 90% one hour after the start of stirring.

(Removability of adhesive)
For the laminates with adhesive layers, the substrates were sampled 20 minutes, 40 minutes, and 1 hour after the start of stirring, and then washed with water and dried. From the obtained substrates, 10 substrates 2 after separation were sampled, and the presence or absence of an absorption peak of the adhesive was confirmed using FT-IR for a total of 20 locations, two locations on the front and back of each substrate 2, and evaluated according to the following criteria. This evaluation was performed on substrates that were rated A to C for substrate separability.
A (Excellent): 20 minutes after the start of stirring, no absorption peak of the adhesive was observed in 18 or more of 20 locations on the substrate.
B (Good): 40 minutes after the start of stirring, no absorption peak of the adhesive was observed in 18 or more of 20 locations on the substrate.
C (Acceptable): One hour after stirring was started, no absorption peak of the adhesive was observed in 18 or more of 20 locations on the substrate.
D (unacceptable): One hour after stirring was started, adhesive absorption peaks were observed in 3 or more of 20 locations on the substrate.

(Reattachment of printed layer)
Two hours after the start of stirring, the substrate was collected, washed with water, and dried. From the obtained substrates, 10 substrates 1 were sampled, and the obtained 10 substrates were spread out and stacked, and the color values L ^* _x , a ^* _x , and b ^* _x were measured using a spectrophotometer (X-rite eXact, manufactured by X-rite Corporation).
On the other hand, when it was confirmed that 90% or more of the printed layer had detached from the substrate, the detached substrate was recovered in the same manner, and 10 substrates were spread out and stacked, and the color values L ^* _y , a ^* _y , and b ^* _y were measured.
The color difference ΔE immediately after detachment and after the end of the test was calculated using the following formula, and the reattachment was evaluated according to the following criteria. Note that this evaluation was carried out for samples that were rated A to C in terms of substrate separation ability.
(Formula) ΔE = ((L ^* _x - L ^* _y ) ² + (a ^* _x - a ^* _y ) ² + (b ^* _x - b ^* _y ) ² ) ^1/2
A (Excellent): ΔE is less than 3 B (Good): ΔE is 3 or more and less than 10 C (Acceptable): ΔE is 10 or more and less than 20 D (Unacceptable): Other than A to C

(Reattachability of adhesive layer)
Two hours after the start of stirring, the detached substrate was collected, washed with water, and dried. From the obtained substrates, 10 substrates 2 after separation were sampled, and the presence or absence of an absorption peak of the adhesive was confirmed using FT-IR for a total of 20 locations, two locations on the front and back of each substrate. This evaluation was performed on substrates rated A to C for substrate separation.
A (Excellent): Adhesive absorption peaks were confirmed in less than three locations.
B (good): The number of locations where an absorption peak of the adhesive was confirmed was 3 or more and less than 5.
C (Acceptable): The number of locations where the absorption peak of the adhesive was confirmed was 5 or more but less than 7.
D (Unacceptable): Adhesive absorption peaks were confirmed in 7 or more locations.

(Processing Efficiency)
Two hours after the start of stirring, the substrate was recovered, washed with water, and dried. The weight of the recovered substrate was then measured to determine its amount relative to the charged eluent, and the weight was evaluated according to the following criteria.
A (Excellent): The amount of recovered substrate relative to the amount of the charged eluent is 3% by mass or more. B (Good): The amount of recovered substrate relative to the amount of the charged eluent is 1% by mass or more and less than 3% by mass. C (Acceptable): The amount of recovered substrate relative to the amount of the charged eluent is 0.4% by mass or more and less than 1% by mass. D (Unacceptable): The amount of recovered substrate relative to the amount of the charged eluent is less than 0.4% by mass.

(Curl of Recycled Substrate)
After 2 hours from the start of stirring, the substrate was collected, washed with water, and dried. 1 g of the obtained substrate was sampled, and the substrates in a state where the substrate was curled up one or more times from the end of the substrate (hereinafter also referred to as "curl") were separated and weighed, and the ratio of the curled substrates to the total plastic substrates after detachment was calculated and evaluated according to the following criteria. In addition, 0.1 g of Comparative Example 1 was sampled and evaluated in the same manner.
A (Excellent): Less than 10% by weight of the substrate is curled. B (Good): 10% to less than 30% by weight of the substrate is curled. C (Acceptable): 30% to less than 50% by weight of the substrate is curled. D (Unacceptable): 50% or more by weight of the substrate is curled.

(Fluff volume ratio before and after desorption)
Two hours after the start of stirring, the substrate was collected, washed with water, and dried. 5 g of the obtained substrate was sampled, and the volume (A) was measured using a 5.0×10 ^{−4 m3} measuring cylinder (inner diameter 5 cm). 5 g of a crushed sample of the laminate was also sampled before the detachment test, and the volume (B) was similarly measured. The volume ratio of the volume (B) to the volume (A) was determined, and evaluated according to the following criteria. 2 g of Examples 3, 15, and 16, and 0.1 g of Comparative Example 1 were sampled, and evaluated in the same manner.
A (Excellent): Volume (B) is less than twice the volume (A). B (Good): Volume (B) is between twice and three times the volume (A). C (Acceptable): Volume (B) is between three and four times the volume (A). D (Unacceptable): Volume (B) is more than four times the volume (A).

(Manufacturing of recycled film and evaluation of recycled material haze)
Two hours after the start of stirring, the plastic substrate was recovered, washed with water, and dried. The recovered substrate was then extruded at 200°C using a single-screw extruder and pelletized to obtain pellets of recycled resin. The recycled resin was extruded at 200°C using a T-die film molding machine to produce a recycled film with a thickness of 50 μm.
The haze of the recycled film was measured using a haze meter (SH7000, manufactured by Nippon Denshi Kogyo Co., Ltd.) and evaluated according to the following criteria.
A (Excellent): Haze is 20% or less. B (Good): Haze is 20% or more but less than 40%. C (Fair): Haze is 40% or more but less than 60%. D (Fail): Haze is 60% or more.

Comparative Example 1, which is the current example, has a small treatment amount, and therefore the treatment efficiency is extremely low. Example 12 and Comparative Example 2 are examples in which no surfactant is used, and the degree of curling is suppressed when the treatment amount is about 10 times the current amount, but when it is 100 times or more the current amount, significant curling is observed. Examples 14 and 15 and Comparative Examples 3 and 4 are examples in which the long side of the crushing size is 3 cm or more, and the degree of curling is suppressed when the treatment amount is about 10 times the current amount, but when it is 50 times or more the current amount, significant curling is observed. Example 16 and Comparative Example 5 are examples in which the treatment temperature is high, and the degree of curling is suppressed when the treatment amount is about 10 times the current amount, but when it is 100 times or more the current amount, significant curling is observed.
The above evaluation results show that the separation and recovery method of the present invention makes it possible to easily detach the coating layer from the laminate even when a large amount of the laminate is being processed, and thus makes it possible to obtain a high-quality plastic substrate with little reattachment of the coating layer, and further to obtain a high-quality molding material with little coloration.

The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. In the present invention, parts and percentages are by mass unless otherwise noted. Example 13 is a reference example.

Claims (8)

A method for separating and recovering a plastic substrate, comprising: a step of contacting a plastic substrate and a laminate having a coating layer with a release liquid to release the coating layer; and a step of recovering the released plastic substrate,
The content of the laminate is 0.5% by mass or more based on the total mass of the desorption liquid,
A method for separating and recovering a laminate, in which after the detachment step, the proportion of plastic substrates in a state in which the substrate is wrapped around the end of the substrate one or more times is less than 50 mass% of all plastic substrates after the detachment step. A method for separating and recovering a plastic substrate, comprising: a step of contacting a plastic substrate and a laminate having a coating layer with a release liquid to release the coating layer; and a step of recovering the released plastic substrate,
The content of the laminate is 0.5% by mass or more based on the total mass of the desorption liquid,
A separation and recovery method in which, when the volumes of 5 g of the laminate (A) before the desorption step and 5 g of the plastic substrate (B) after the desorption step are each measured using a 5.0 x ^{10-4 m3} measuring cylinder (inner diameter 5 cm), the volume of (B) is at least 1 time and less than 4 times the volume of (A). A method for separating and recovering a plastic substrate, comprising: a step of contacting a plastic substrate and a laminate having a coating layer with a release liquid to release the coating layer; and a step of recovering the released plastic substrate,
The content of the laminate is 0.5% by mass or more based on the total mass of the desorption liquid,
the eluate contains a compound having an HLB value greater than 0 and less than 20 and water;
A method for separating and recovering, in which the long side of the laminate immediately before detachment is 1 mm to 3 cm accounts for 50% by weight or more of the entire laminate. The separation and recovery method according to any one of claims 1 to 3, wherein the elution liquid contains a surfactant and water. The separation and recovery method according to any one of claims 1 to 3, wherein the coating layer includes a printed layer, and the content of the printed layer is 0.01 mass% or more relative to the total mass of the elution liquid. The method further includes a step of cutting the laminate before contacting the laminate with the release liquid,
The separation and recovery method according to any one of claims 1 to 3, wherein 50 mass% or more of the laminate after the cutting step has a long side of 3 cm or less. The method for separating and recovering a laminate according to any one of claims 1 to 3, wherein at least one of the coating layers contains a compound having an acidic group. The method for separating and recovering a laminate according to any one of claims 1 to 3, wherein the plastic substrate is an olefin substrate.