JP7708754B2 - Label, method for removing ink layer from label, and method for manufacturing label - Google Patents

Description

The present disclosure relates to labels, methods for removing ink layers from labels, and methods for manufacturing labels.

In recent years, plastic products such as polyethylene terephthalate (PET) bottles have come into widespread use. From the perspectives of resource conservation and the environment, there is a strong demand for the reuse of plastic products such as PET bottles.

Among plastic products, recycling of PET bottles in particular has already been established. However, although plastic labels with an ink layer printed with product information and the like are sometimes attached to the body of the PET bottle, the labels have not yet been reused.

One of the factors that hinders the reuse of labels is the inability to fully remove the ink layer from the label. If the ink layer cannot be fully removed from the label, the ink may get mixed into the recycled resin that is recycled from the label, making it impossible to produce usable recycled products such as pellets from the recycled resin.

For example, Patent Document 1 describes a plastic label in which a display printing ink layer is formed on a base film via a coating layer that is soluble in an alkaline aqueous solution. In Patent Document 1, the display printing ink layer is alkaline-released by dissolving the coating layer of the plastic label in an alkaline aqueous solution.

JP 2004-240029 A

When labels are actually reused, it is expected that they will be collected as a mixture of labels whose ink layer can be removed by alkali and labels whose ink layer cannot be removed by alkali. When reusing labels, the technology to separate labels whose ink layer can be removed by alkali from labels whose ink layer cannot be removed by alkali has not yet been established.

Even if alkaline removal of the ink layer is performed while there is a mixture of labels whose ink layer can be alkaline removed and labels whose ink layer cannot be alkaline removed, it is necessary to remove the labels whose ink layer cannot be alkaline removed after alkaline removal of the ink layer, so there is a demand for a method of efficiently removing the ink layer.

According to the embodiments disclosed herein, a label can be provided that comprises a substrate, an alkali-soluble coating layer on the substrate, and an ink layer on the coating layer, wherein the coating layer or the ink layer contains a material that emits light when irradiated with energy rays.

According to the embodiment disclosed herein, a method for removing an ink layer from a label can be provided, comprising the steps of: recovering a group of labels including labels that contain a material that emits light when irradiated with energy rays and whose ink layer can be removed by alkaline desorption; irradiating the recovered group of labels with energy rays; separating the labels that have emitted light when irradiated with energy rays; and removing the ink layer from the separated labels by alkaline desorption.

According to the embodiments disclosed herein, a method for producing labels can be provided that includes, as a raw material, a resin derived from labels obtained by the above-mentioned removal method.

According to the embodiments disclosed herein, it is possible to provide a label from which the ink layer can be efficiently removed, a method for removing the ink layer from a label, and a method for manufacturing a label using a resin that contains as a raw material a label from which the ink layer has been removed.

FIG. 2 is a schematic cross-sectional view of a label according to an embodiment. 1A to 1I are diagrams illustrating an example of a flow of a method for removing an ink layer from a label according to an embodiment. 13 is a schematic side view illustrating an example of a process of irradiating the collected label group with energy rays. FIG. FIG. 2 is a schematic cross-sectional view of a label according to Experimental Example 1. FIG. 2 is a schematic side view illustrating a method for evaluating the luminescence of the label in Experimental Example 1. 1 is a schematic cross-sectional view of the labels of Experimental Examples 2 to 4. FIG.

<Label>
Fig. 1 shows a schematic cross-sectional view of a label of an embodiment. As shown in Fig. 1, a label 11 of an embodiment includes a substrate 101, an alkali-soluble coating layer 102 on the substrate 101, and an ink layer 103 on the coating layer 102. The label 11 of an embodiment may be a label having heat shrinkability (shrink label), or may be a label having no heat shrinkability. Furthermore, the label 11 of an embodiment may be a stretch label having self-stretchability, or may be a label having no self-stretchability.

<Base material>
The substrate 101 is a base containing a resin capable of supporting the coating layer 102 and the ink layer 103 .

The resin contained in the substrate 101 may be, for example, a polyester-based resin (polyethylene terephthalate, polyethylene naphthalate, polylactic acid, etc.), a polystyrene-based resin (polystyrene, styrene-butadiene copolymer, etc.), a polyolefin-based resin (polyethylene, polypropylene, etc.), a polyvinyl chloride-based resin, a polyamide-based resin, an aramid-based resin, a polyimide-based resin, a polyphenylene sulfide-based resin, or an acrylic-based resin. The substrate 101 may contain one type of these resins, or may contain two or more types.

As the resin contained in the substrate 101, it is preferable to use a polyester resin, and in particular, it is preferable to use PET. PET is a polyester resin containing terephthalic acid as the main component of the dicarboxylic acid component and ethylene glycol as the main component of the diol component. In addition, PET may contain, as other components, dicarboxylic acids such as isophthalic acid, phthalic acid, adipic acid, sebacic acid, or naphthalenedicarboxylic acid, and may contain diol components such as diethylene glycol, neopentyl glycol, polyalkylene glycol, or 1,4-cyclohexanedimethanol.

The substrate 101 may be, for example, a film having heat shrinkability (shrink film). When the substrate 101 is a shrink film, the processability (conformity to the container) and decorativeness of the label 11 can be improved, and the display area of the label 11 can be further expanded. The substrate 101 may also be, for example, a stretch film having self-stretchability.

The substrate 101 may be a single-layer film consisting of one layer, or may be a multi-layer film consisting of two or more layers. The thickness of the substrate 101 may be, for example, 5 μm to 100 μm, but is not particularly limited.

<Coat layer>
The coating layer 102 is located between the substrate 101 and the ink layer 103, and is a layer containing an alkali-soluble resin.

The coating layer 102 being alkali-soluble means that when a sample having a coating layer 102 measuring 4 cm x 4 cm in length x width formed on a substrate 101 of any size and an ink layer 103 of any kind is provided on the coating layer 102, and the sample is immersed in a 1.5% by mass aqueous sodium hydroxide solution (i.e., 1.5% of the total mass of the sodium hydroxide aqueous solution is sodium hydroxide) at 85°C and stirred at 1500 rpm, 70% or more of the total area of the ink layer 103 will detach from the sample after an immersion time of 15 minutes.

The resin contained in the coating layer 102 may be, for example, a resin having the following (1) to (4):
(1) containing a first resin which is an acrylic acid copolymer resin having a first glass transition temperature T1;
(2) containing a second resin which is an acrylic acid copolymer resin having a second glass transition temperature T2 lower than the above T1;
(3) The apparent acid value of the coating layer 102 is 40 mgKOH/g or more and 150 mgKOH/g or less;
(4) The first resin and the second resin contained in the coating layer 102 account for 50 to 95% by mass in total of the coating layer 102 .

Resins having the above (1) to (4) have good alkali solubility. Therefore, by providing the label 11 with an alkali-soluble coating layer 102 between the substrate 101 and the ink layer 103, the ink layer 103 is also detached from the label 11 as the coating layer 102 is detached from the label 11 by alkali.

In addition to the alkali solubility described above, resins that satisfy the above (1) to (4) also have excellent printability. As a result, the cosmetic properties of the ink layer 103 on the coating layer 102 can be improved.

As shown in (1) and (2) above, the first resin and the second resin are each an acrylic acid copolymer resin. An acrylic acid copolymer resin is a resin that contains acrylic acid and/or methacrylic acid as a main repeating unit and also contains a copolymerizable monomer copolymerizable with acrylic acid and/or methacrylic acid. It is preferable that the total proportion of acrylic acid and/or methacrylic acid and the copolymerizable monomer in the acrylic acid copolymer resin is 60 mol% or more.

Examples of copolymerizable monomers include (meth)acrylic acid alkyl esters (preferably lower alkyl esters of (meth)acrylic acid) such as methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and t-butyl (meth)acrylate; hydroxyl group-containing (meth)acrylates such as hydroxyethyl (meth)acrylate; glycidyl group-containing (meth)acrylates such as glycidyl (meth)acrylate; N,N'-dimethyl (meth)acrylic acid amines; Examples of the copolymerizable monomer include (meth)acrylamides such as N,N'-diethyl(meth)acrylamide, and N,N'-diethyl(meth)acrylamide; amino group-containing (meth)acrylates such as dimethylaminoethyl(meth)acrylate; styrenes such as styrene, vinyl toluene, and α-methylstyrene; vinyl esters such as vinyl acetate and vinyl propionate; vinyl halides such as vinyl chloride; vinyl ethers such as methyl vinyl ether; carboxyl group-containing vinyls such as itaconic acid and maleic anhydride [excluding (meth)acrylic acid]; cyano group-containing vinyls such as acrylonitrile and methacrylonitrile; olefins and dienes such as ethylene and propylene. The copolymerizable monomers can be used alone or in combination of two or more.

Regarding (1) and (2) above, the Tg of each of the first resin and the second resin can be controlled, for example, by adjusting the mass average molecular weight (Mm) of the acrylic acid copolymer resin. For example, by making the Mm of the first resin larger than the Mm of the second resin, the first resin and the second resin can have a relationship of T1>T2. Preferably, the Mm of the first resin is 30,000 or more and 90,000 or less, and the Mm of the second resin is 10,000 or more and less than 30,000.

Regarding (1) and (2) above, T1, which is the Tg of the first resin, is preferably 90°C or higher, more preferably 95°C or higher, and particularly preferably 100°C or higher. The upper limit of T1 can be, for example, about 120°C, from the physical properties of the acrylic acid copolymer resin. T2, which is the Tg of the second resin, is preferably less than 80°C, more preferably 75°C or lower, and particularly preferably 65°C or lower. The lower limit of T2 can be, for example, about 30°C, from the viewpoint of ease of handling. For example, it is preferable that there is a difference between T1 and T2 of 20°C or more, more preferably a difference of 30°C or more, and particularly preferably a difference of 40°C or more. In this case, the deterioration of printability can be more effectively suppressed, and therefore it is possible to particularly improve the cosmetic properties of the ink layer 103.

With regard to (3) above, the apparent acid value of the coating layer 102 means the acid value of a mixed resin consisting of two or more types of resin contained in the coating layer 102. The apparent acid value of the coating layer 102 can be adjusted by controlling the acid values of the first resin and the second resin. The acid values of the first resin and the second resin can be adjusted, for example, by the mixing ratio of (meth)acrylic acid and the copolymerizable monomer.

Regarding (3) above, the apparent acid value of the coating layer 102 is more preferably 50 mgKOH/g or more and 130 mgKOH/g or less, and particularly preferably 55 gKOH/g or more and 125 mgKOH/g or less. In these cases, it is possible to particularly improve the alkali solubility and printability of the coating layer 102.

It is preferable that the acid value of the first resin and the acid value of the second resin are each 40 mgKOH/g or more and 150 mgKOH/g or less. In this case, the apparent acid value of the coating layer 102 can be easily set to 40 mgKOH/g or more and 150 mgKOH/g or less as in (3) above. It is also preferable that the acid value of the first resin is lower than the acid value of the second resin. It is preferable that the acid value of the first resin is less than 60 mgKOH/g. It is also preferable that the acid value of the second resin is 80 mgKOH/g or more.

Regarding (4) above, the first resin and the second resin in the coating layer 102 preferably account for 70% by mass or more and 95% by mass or less of the entire coating layer 102, and more preferably for 80% by mass or more and 95% by mass or less. In these cases, it is possible to particularly improve the alkali solubility and printability of the coating layer 102. In addition, it is preferable that the content ratio of the first resin and the content ratio of the second resin do not differ significantly. From the viewpoint of improving the synergistic effect of containing two types of resin, the first resin and the second resin, it is preferable that the ratio of the content of the first resin to the content of the second resin (the content of the resin with a relatively large content / the content of the resin with a relatively small content) is 3 or less.

The fact that the coating layer 102 contains an alkali-soluble resin can be confirmed, for example, by using various analytical techniques. For example, it can be confirmed that a specific content of acrylic acid copolymer resin is present in the coating layer 102 by nuclear magnetic resonance (NMR), gas chromatography mass spectrometry (GCMS), pyrolysis gas chromatography (pyrolysis GCMS), etc. In addition, the acid value of the coating layer 102 can be confirmed, for example, by titrating the coating layer 102. The titration of the coating layer 102 can be calculated based on the result of dissolving the coating layer 102 in a titration solvent such as a mixed solvent of xylene and dimethylformamide, and performing a potentiometric titration using a potassium hydroxide solution of a predetermined concentration (for example, a 0.1 mol/L potassium hydroxide-ethanol solution). In addition, the fact that the coating layer 102 contains the first resin and the second resin having the above Tg can be confirmed, for example, by subjecting the composition used to form the coating layer described below to a differential scanning calorimetry (DSC) method. The DSC method can be performed using a "DSC6200" manufactured by Seiko Instruments Inc. under the condition of a temperature rise rate of 10° C./min. The Mm of the first resin and the Mm of the second resin can be confirmed, for example, by gel permeation chromatography (GPC).

The first and second resins are preferably methacrylic acid-methyl methacrylic acid copolymers (hereinafter also referred to as "MM copolymers"). In this case, it is possible to significantly improve both the alkali solubility and printability of the coating layer 102. The MM copolymer may be synthesized or may be a commercially available product. Commercially available products suitable for the first resin include "Dianal LR-1941" or "Dianal BR-87" manufactured by Mitsubishi Rayon Co., Ltd. Commercially available products suitable for the second resin include "JONCRYL JDX-C3000" manufactured by BASF Japan Ltd., "ARUFON UC3000" manufactured by Toa Gosei Co., Ltd., or "BR-605" manufactured by Mitsubishi Rayon Co., Ltd. Among them, it is preferable to use a combination of "Dianal LR-1941" and "JONCRYL JDX-C3000" as the first and second resins.

In addition to the first resin and the second resin, the coating layer 102 may contain other components. Preferred other components include cellulose derivatives. When the coating layer 102 contains a cellulose derivative, it is possible to improve the blocking resistance and adhesion of the coating layer 102.

The cellulose derivative contained in the coating layer 102 may be, for example, nitrocellulose, acetylcellulose, carboxymethylcellulose or its salt, methylcellulose, hydroxypropylmethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, cellulose acetate butyrate, or cellulose acetate propionate. It is preferable to use nitrocellulose as the cellulose derivative contained in the coating layer 102. In the coating layer 102, the cellulose derivative may be used alone or in combination of two or more kinds.

The content of the cellulose derivative in the coating layer 102 is preferably 1% by mass or more and 20% by mass or less of the total mass of the coating layer 102, more preferably 5% by mass or more and 15% by mass or less, and particularly preferably 8% by mass or more and 12% by mass or less. In these cases, the blocking resistance and printability of the coating layer 102 can be improved. The cellulose derivative preferably has a degree of polymerization of 35 to 380, more preferably a degree of polymerization of 45 to 290, and particularly preferably a degree of polymerization of 55 to 110. In these cases, it is also possible to improve the blocking resistance and printability of the coating layer 102.

The coating layer 102 may also contain, for example, a vinyl chloride-vinyl acetate copolymer (hereinafter also referred to as "VV copolymer") as a preferred other component. When the coating layer 102 contains a VV copolymer, it is possible to further improve the adhesion between the substrate 101 and the coating layer 102. Therefore, when the coating layer 102 contains an alkali-soluble resin and a VV copolymer, it can function as a base layer with particularly excellent adhesion.

The content of the VV copolymer in the coating layer 102 is preferably 5 to 20 mass% of the total mass of the coating layer 3, more preferably 8 to 18 mass%, and particularly preferably 9 to 12 mass%. In these cases, the adhesion and printability of the coating layer 102 can be improved. The VV copolymer in the coating layer 102 preferably has an Mm of 10,000 to 40,000, and more preferably has an Mm of 15,000 to 35,000. In these cases, the adhesion of the coating layer 102 is significantly improved.

The coating layer 102 may further contain a material that emits light when irradiated with energy rays. This makes it possible to identify and separate the labels 11 of the embodiment having an alkali-soluble coating layer 102 by irradiating the labels 11 with energy rays and causing the coating layer 102 of the labels 11 to emit light.

The energy rays irradiated to the label 11 may be, for example, short-wavelength electromagnetic waves such as X-rays or ultraviolet light, visible light, infrared light, near-infrared light, or microwaves. It is preferable to use ultraviolet light as the energy rays irradiated to the label 11. When ultraviolet light is used as the energy rays irradiated to the label 11, it is easy to cause electronic excitation of the material that emits light when irradiated with the energy rays.

Materials that emit light when irradiated with energy rays can include, for example, fluorescent pigments or phosphorescent pigments.

Fluorescent pigments are pigments that emit light when irradiated with energy rays, but pigments that have phosphorescent properties are excluded from the fluorescent pigments. Examples of fluorescent pigments include organic pigments and inorganic pigments. Examples of organic pigments include fluorescein, coumarin, rhodamine, oxazole, pyrazoline, thiadiazole, spiropyran, pyrenesulfonic acid, benzimidazole, and diaminostilbene. Examples of inorganic pigments include zinc sulfide activated with copper, silver, manganese, etc., zinc silicate activated with manganese, etc., calcium sulfide activated with cadmium, bismuth, etc., strontium sulfide activated with samarium, cerium, etc., and calcium tungstate activated with lead, etc.

More specifically, examples of red fluorescent pigments that can be used include _Y2O2S :Eu, _Y2O3 :Eu, _Y2SiO5 :Eu, _Y3AlO12 :Eu, _Zn3 ( _{PO4 ) 2} : _Mn , _YBO3 :Eu, (Y,Gd) _{BO3 :} Eu, _GdBO3 :Eu, _ScBO3 : _Eu , or _LuBO3 :Eu.

As the blue _fluorescent pigment, for example, _BaMg2Al16O27 :Eu, _Y2SiO5 :Ce, _CaWO4 :Pb, _BaMgAl14O23 :Eu _, or _{the like} can be used.

Examples of green fluorescent pigments that can be _used include _BaMg2Al16O27 :(Eu,Mn), (Ba,Mg _{) Al16O27} : ₍ Eu,Mn), _{Zn2SiO4 :} Mn, _BaAl12O19 :Mn, _SrAl13O19 :Mn, _CaAl12O19 :Mn, _YBO3 : _Tb , _BaMgAl14O23 :Mn, _{LuBO3 :} Tb, _{GdBO3 :} Tb, _{ScBO3 : Tb} , or _{Sr6Si3O3C14 : Eu} .

As the fluorescent pigment, for example, one of the above types may be used alone, or two or more of the above types may be used in combination.

A phosphorescent pigment is a pigment that emits light when irradiated with energy rays and has phosphorescent properties. Examples of phosphorescent pigments that can be used include sulfide-based phosphorescent pigments, oxygen acid salt-based phosphorescent pigments, and alumina oxide-based phosphorescent pigments.

Examples of sulfide-based phosphorescent pigments that can be used include calcium sulfide:bismuth (CaS:Bi), calcium strontium sulfide:bismuth (CaSrS:Bi), zinc sulfide:copper (ZnS:Cu), and zinc sulfide-cadmium:copper (ZnCdS:Cu).

Examples of the oxygen acid salt phosphorescent pigment that can be used include _Zn2SiO4 : _Mn , (Zn,Be) _2SiO4 :Mn, _Ca3 ( _PO4 ) _{2 :} Ce, and _Ca3 ( _PO4 ) ₂ :(Ce,Mn).

Examples of alumina oxide phosphorescent pigments that can be used include aluminum oxide-calcium:europium (CaAl ₂ O ₄ :Eu), aluminum oxide-strontium:europium (SrAl ₂ O ₄ :Eu), and aluminum oxide-barium:europium (BaAl ₂ O ₄ :Eu).

As the phosphorescent pigment, for example, one of the above types may be used alone, or two or more of the above types may be used in combination.

In addition to the above, the coating layer 102 may contain other components for the purpose of improving printability, etc. For example, when the coating layer 102 contains the first resin, the second resin, the VV copolymer, and the cellulose derivative in a predetermined content ratio, the apparent acid value of the coating layer 102 is the sum of the content ratio of each component x the acid value of each resin.

The thickness of the coating layer 102 can be, for example, 0.1 μm or more and 5 μm or less, and preferably 0.3 μm or more and 3 μm or less, but is not particularly limited.

<Ink layer>
The ink layer 103 is located on the coat layer 102 and is a layer containing an ink resin composition. The ink resin composition contained in the ink layer 103 may contain, for example, a pigment, a resin, and an additive. In addition, the ink layer 103 is preferably a design print layer. The design print layer is a layer that contains a pigment and displays a visible pattern or characters, etc.

The ink layer 103 may be provided on the entire surface of the coating layer 102, or may be provided on a part of the coating layer 102. The ink layer 103 may be a single layer or may be multi-layered. The thickness of the ink layer 103 may be, for example, about 0.1 μm or more and 100 μm or less, but is not particularly limited.

The ink layer 103 may further contain a material that emits light when irradiated with energy rays. This makes it possible to identify and separate the label 11 of the embodiment having the alkali-soluble coating layer 102 by irradiating the label 11 with energy rays and causing the ink layer 103 of the label 11 to emit light.

<Other demographics>
The label 11 may further include another layer, such as an overcoat layer, on the ink layer 103. The overcoat layer is a layer for protecting the ink layer 103 from external factors.

<Label manufacturing method>
The label 11 of the embodiment can be manufactured, for example, as follows: First, prepare the substrate 101. The substrate 101 can be prepared, for example, by forming a film by a method such as an extrusion method or a calendar method, and then, if necessary, subjecting the film to a stretching treatment.

Next, the coating layer 102 is formed on one surface of the substrate 101. The coating layer 102 can be formed, for example, by applying a composition containing the resin contained in the coating layer 102 onto one surface of the substrate 101 and then solidifying it.

Next, an ink layer 103 is formed on the surface of the coating layer 102. The ink layer 103 can be formed, for example, by applying an ink resin composition for forming the ink layer 103 onto the surface of the coating layer 102 and then solidifying it.

If the label 11 further comprises another layer, such as an overcoat layer, the other layer can be formed by applying a resin composition for forming the other layer onto the surface of the ink layer 103 and then solidifying it.

<How to remove the ink layer from the label>
2(a) to (i) are diagrams illustrating an example of a flow of a method for removing an ink layer from a label of an embodiment in the case where the label 11 of the embodiment is a shrink label. Hereinafter, the method for removing an ink layer from the label 11 of the embodiment will be described with reference to Figs. 2(a) to (i).

<PET bottle recycling process>
First, as shown in Fig. 2(a), a PET bottle 10 is collected in a collection box 12. Here, a label 11 of the embodiment having an ink layer 103 is attached to the body of the PET bottle 10. In this embodiment, the ink layer 103 is used as a printing layer for product display or the like.

<Compression process>
Next, as shown in FIG. 2( b ), the collected PET bottles 10 with the labels 11 attached are compressed to form labeled bales 20 .

<Collection process>
Next, as shown in FIG. 2( c ), the labeled bale 20 is sent to a recycling plant 30 and accumulated.

<Label collection process>
2D, a label group 50 including the labels 11 of the embodiment and the normal labels 40 is collected. The label group 50 can be collected, for example, as follows.

First, at the recycling plant 30, the label 11 of the embodiment and/or the regular label 40 is removed from the PET bottles 10 in the labeled bale 20, and separated into a label group 50 including the label 11 of the embodiment and the regular label 40 and the PET bottle 10, and the label group 50 including the label 11 of the embodiment and the regular label 40 is collected.

In this embodiment, the normal label 40 is a label in which the coating layer or ink layer is not alkali-soluble and therefore the ink layer cannot be removed by alkali, and which does not contain a material that emits light when irradiated with energy rays.

In addition, the PET bottle 10 from which the label 11 and/or the regular label 40 has been separated is reused in existing PET bottle recycling processes.

<Energy beam irradiation and separation process>
Next, as shown in Fig. 2(e), an energy beam is irradiated onto the collected label group 50. Fig. 3 shows a schematic side view illustrating an example of a process of irradiating an energy beam onto the collected label group 50. Hereinafter, an example of a process of irradiating an energy beam onto the collected label group 50 will be described with reference to Fig. 3.

First, the collected label group 50 is brought into the first dark place 201. Next, the label group 50 is irradiated with energy rays 22 from a light source 21 arranged inside the first dark place 201.

Next, the label group 50 after irradiation with the energy rays 22 is transported out from inside the first dark place 201. Next, the label group 50 transported out from inside the first dark place 201 is transported into the second dark place 202.

At this time, the coating layer 102 of the label 11 of the embodiment after irradiation with the energy rays 22 emits light, so the label 11 of the embodiment appears to glow inside the second dark place 202. On the other hand, the regular label 40 does not contain a material that emits light when irradiated with energy rays, so it does not appear to glow inside the second dark place 202 even if it is irradiated with the energy rays 22.

This makes it possible to separate and collect the label 11 of the embodiment, which appears to glow in the second dark place 202, from the regular label 40, which does not appear to glow in the second dark place 202. The regular label 40, which is collected separately from the label 11 of the embodiment, is reused, for example, in a thermal recycling process.

In this embodiment, the label group 50 is irradiated with the energy beam 22 inside the first dark space 201, but the label group 50 does not necessarily have to be irradiated with the energy beam 22 in a dark space.

<Preheating step>
Next, as shown in Fig. 2(f), the label 11, which is a shrink label, is preheated. There are no particular limitations on the method for preheating the label 11, so long as it is a method that can suppress the amount of shrinkage and curling of the label piece in the alkaline desorption described below. However, it is preferable that the preheating temperature is the same as or higher than the alkaline desorption temperature. From the viewpoint of efficiently removing the ink layer from the label piece in the alkaline desorption described below, it is preferable that the preheating temperature is 5°C or more higher than the alkaline desorption temperature.

Methods for preheating the label 11 include, for example, passing the label 11 through a hot air tunnel 61 or immersing the label 11 in hot water 60 in a hot water tank 62.

However, from the viewpoints of (A) to (D) below, it is preferable to preheat the label 11 by immersing the label 11 in hot water 60 in a hot water tank 62 rather than by passing the label 11 through a hot air tunnel 61.
(A) When hot air is used, the label 11 removed from the PET bottle 10 is blown away by the hot air, making it difficult to control.
(B) The method of immersing in warm water makes it easier to control the temperature.
(C) The warm water immersion method requires a smaller equipment footprint.
(D) The method of immersing in warm water is less likely to cause uneven shrinkage of the label 11 and allows the label 11 to shrink evenly.

For example, when preheating the label 11 by immersing the label 11 in hot water 60 in a hot water tank 62, this can be done by immersing the label 11 in hot water of about 80°C to 90°C for about 10 to 20 seconds.

The preheating temperature means the surface temperature of the label 11 at the time of preheating. Therefore, when the label 11 is preheated by immersing it in hot water 60 in the hot water bath 62, the preheating temperature can be replaced with the temperature of the hot water. Also, when the label 11 is preheated by passing it through the hot air tunnel 61, the preheating temperature can be replaced with the temperature of the hot air.

<Crushing process>
Next, as shown in FIG. 1(g), the preheated label 11 is crushed by a crusher 70 to produce label pieces 71. The method of crushing the preheated label 11 is not particularly limited as long as the size of the label pieces 71 produced after crushing is smaller than the size of the preheated label 11. For example, the preheated label 11 can be crushed to a size (e.g., several cm square) that allows the ink layer 103 to be efficiently removed from the label pieces 71 in the alkali desorption described below. Since the label pieces 71 are obtained by crushing the label 11 of the embodiment, it goes without saying that the layer structure of the label 11 of the embodiment and the layer structure of the label pieces 71 are the same.

<Alkaline removal step>
Next, as shown in FIG. 1(h), the ink layer 103 is removed from the label piece 71 by alkaline desorption. The alkaline desorption can be performed, for example, by immersing the label piece 71 in an alkaline aqueous solution 80 at about 80° C. to 90° C. in a hot alkaline bath 82 for about 30 seconds to 20 minutes and stirring the hot alkaline bath 82. In this case, the label piece 21 can be easily separated into the substrate 101 and the ink coating film 93 in the hot alkaline bath 82. The alkaline desorption can be performed, for example, by immersing the label piece 71 in the above-mentioned alkaline aqueous solution 80 for about 30 seconds to 20 minutes and then washing with water. In this case, the label piece 71 can be easily separated into the substrate 101 and the ink coating film 93 by washing with water (for example, in a water bath). A surfactant may be added to the alkaline aqueous solution 80 for the purpose of further improving the desorption property.

As described above, in this embodiment, the preheating temperature is set to be equal to or higher than the alkali desorption temperature. The alkali desorption temperature means the surface temperature of the label piece 71 at the time of alkali desorption. Therefore, the alkali desorption temperature can be replaced with the temperature of the alkaline aqueous solution 80 in which the label piece 71 is immersed. In terms of efficiently removing the ink layer 103 from the label piece 71 during alkali desorption, it is preferable that the alkali desorption temperature be 65°C or higher. Theoretically, the upper limit of the alkali desorption temperature is 100°C, more preferably, the alkali desorption temperature is 85°C or higher and 95°C or lower, and even more preferably, the alkali desorption temperature is 80°C or higher and 90°C or lower.

After removing the ink layer 103 from the label piece 71, the alkaline aqueous solution 80 may be disposed of as waste liquid, or may be reused as alkaline aqueous solution 80 for alkali removal.

The alkaline aqueous solution 80 is not particularly limited as long as it is capable of removing the ink layer from the label piece 71 by immersing the label piece 71 in it, and is not particularly limited as long as it is an alkaline aqueous solution containing an alkaline substance. As the alkaline aqueous solution 80, for example, an aqueous solution of an alkali metal hydroxide such as sodium hydroxide ( _NaOH ) or potassium hydroxide ( _KOH ), an aqueous solution of an alkali metal carbonate such as sodium carbonate (Na2CO3), an aqueous solution of an alkali metal hydrogen carbonate such as sodium hydrogen carbonate ( _NaHCO3 ), or ammonia water can be used.

The concentration of the alkaline substance in the alkaline aqueous solution 80 can be appropriately selected within a range that does not impair the releasability, operability, or workability of the ink layer 103. The concentration of the alkaline substance in the alkaline aqueous solution 80 is, for example, about 0.1 to 10% by weight, preferably about 0.5 to 5% by weight, and more preferably about 1 to 3% by weight.

<Process for separating the substrate and the ink coating>
Next, as shown in Fig. 1(i), the substrate 101 and the ink coating film 93 are separated. The substrate 101 and the ink coating film can be separated, for example, by collecting the substrate 101 after the ink layer 103 has been removed with a first net 90 having relatively large openings, and collecting the ink coating film 93, which is smaller than the substrate 101, with a second net 92 having relatively small openings. In this manner, the ink layer 103 can be removed from the label 11 of the embodiment. The ink coating film 93 is a film formed by finely dividing the ink layer 103 removed from the substrate 101 during alkali desorption.

The substrate 101 captured by the first net 90 can then be reused as a plastic raw material for the production of plastic products such as pellets. It can also be reused as a shrink label or other label by mixing the substrate 101 into the raw material for a new label. Meanwhile, the ink coating 93 captured by the second net 92 can be reused, for example, in a thermal recycling process.

The method for removing an ink layer from a label in an embodiment includes a step of recovering a label group 50 including labels 11 containing a material that emits light when irradiated with an energy ray 22, a step of irradiating the recovered label group 50 with an energy ray 22, and a step of separating the labels 11 that have emitted light when irradiated with the energy ray 22.

Therefore, according to the method of removing an ink layer from a label of the embodiment, by irradiating the label with energy rays 22 to cause it to emit light, it is possible to establish a technology that makes it possible to distinguish labels 11, whose ink layer 103 can be removed by alkaline desorption, from normal labels 40, whose ink layer 103 cannot be removed by alkaline desorption.

This makes it possible to perform alkaline removal of the ink layer only for labels whose ink layer can be alkaline removed, and eliminates the need to remove labels whose ink layer cannot be alkaline removed after alkaline removal of the ink layer. This makes it possible to efficiently perform alkaline removal of the ink layer from labels whose ink layer can be alkaline removed.

In addition, the method of removing an ink layer from a label in an embodiment includes a step of preheating a label 11 having an ink layer 103, a step of crushing the label 11 after the preheating step to produce label pieces 71, and a step of removing the ink layer 103 from the label pieces 71 by alkali desorption, and the temperature of the preheating can be the same as the temperature of alkali desorption or higher than the temperature of alkali desorption.

In this case, when the label 11 is a shrink label, the ink layer 103 can be removed from the label 11 more efficiently than before.

That is, in the method of removing an ink layer from a label in this embodiment, the label 11 is crushed into label pieces 71 prior to removing the ink layer 103 from the label 11 by alkaline desorption. This is because the ink layer 103 can be efficiently removed from the label 11 by crushing the label 11 into smaller label pieces 71 and performing alkaline desorption in that state.

When shrink label pieces made by crushing shrink labels that have not been preheated are immersed in an alkaline solution, the shrink label pieces will shrink while wrapping around each other and curling in the alkaline solution. It is extremely difficult to remove the ink layer from the curled small pieces of shrink label.

Shrink labels attached to PET bottles etc. are thermally shrunk once when they are attached, but the shrink label still retains the ability to shrink. Therefore, if the temperature of the alkaline aqueous solution is high when the alkali is removed, the shrink label piece will thermally shrink further. On the other hand, if the temperature of the alkaline aqueous solution is low, the ink layer cannot be efficiently removed from the shrink label piece.

Therefore, in the method of removing the ink layer from a label in this embodiment, before the shrink label is crushed into shrink label pieces, the shrink label is preheated at a temperature equal to or higher than the alkali desorption temperature to cause it to thermally shrink in advance. This allows the shape of the shrink label to be, for example, wavy with little curl. If the shrink label is preheated after being crushed, the shrink label pieces will curl overall (roll in a shape) and will be unsuitable for removing the ink layer.

The shrink label that has been preheated to cause it to shrink is then crushed to produce shrink label pieces. Shrink label pieces obtained by crushing a shrink label with a small degree of curl also have a small degree of curl.

The shrink label pieces can then be subjected to alkali desorption at the same or a lower temperature than that used for preheating. In this case, even if the temperature of the aqueous alkaline solution during alkali desorption is high, the ink layer can be removed while suppressing shrinkage of the shrink label pieces during alkali desorption.

For the above reasons, it is believed that the method of removing an ink layer from a label in this embodiment can remove the ink layer from the label 11 more efficiently than conventional methods when the label 11 is a shrink label.

In particular, most shrink labels 11 removed from containers such as PET bottles 10 typically have one side measuring 10 cm or more. Labels 11 of this size are thermally shrunk by preheating, then crushed into pieces several centimeters square, preferably 5 cm square or less, and subjected to alkali desorption at 65°C or higher, preferably 80°C or higher, and more preferably 85°C or higher, thereby significantly improving the efficiency of removing the ink layer 103.

An example of a shrink label 11 suitable for the method of this embodiment is a shrink label that, after being removed from a container such as a PET bottle 10 and immersed in a warm bath at 95°C for 10 seconds, has a shrinkage rate measured in the radial direction (main shrinkage direction) of the container of 30% or more, preferably 40% or more, and more preferably 50% or more.

In the above embodiment of the method for removing an ink layer from a label, the case where the label 11 is a shrink label has been described, but the label 11 used in the embodiment of the method for removing an ink layer from a label does not have to be a shrink label.

In addition, in the above embodiment of the method for removing an ink layer from a label, a case has been described in which a label 11 is used in which the material that emits light when irradiated with energy rays is contained only in the coating layer 102. However, in the embodiment of the method for removing an ink layer from a label, the material that emits light when irradiated with energy rays only needs to be contained in at least one layer constituting the label 11 (for example, only in the coating layer 102, only in the ink layer 103, or both the coating layer 102 and the ink layer 103).

In the above embodiment, when the ink layer 103 is the above-mentioned design printing layer, it is preferable that only the coat layer 102 contains a material that emits light when irradiated with energy rays. If the ink layer 103 is composed of multiple layers (multi-color design printing layers), it becomes complicated to determine how much of the material that emits light when irradiated with energy rays should be included in each layer constituting the ink layer 103, and problems such as the need to change the content of the material that emits light when irradiated with energy rays in each design printing layer may occur. In addition, when the ink layer 103 is composed of multiple layers (multi-color design printing layers), it is preferable to contain a material that emits light when irradiated with energy rays in the ink that constitutes the white layer among the multiple layers constituting the ink layer 103. In this case, it is easy to confirm that the material that emits light when irradiated with energy rays emits light by irradiating the material with energy rays.

In addition, in the above embodiment, when the coating layer 102 contains a material that emits light when irradiated with energy rays, it is preferable that the content of the material that emits light when irradiated with energy rays is 5% by mass or more of the entire coating layer 102.

In addition, in the above embodiment, when the ink layer 103 contains a material that emits light when irradiated with energy rays, it is preferable that the content of the material that emits light when irradiated with energy rays is 5% by mass or more of the entire ink layer 103.

<Label manufacturing method>
The label 11 obtained by the above-mentioned method for removing the ink layer can also be used to produce pellets, etc. By producing a label using the pellets, etc., it is possible to produce a label (recycled label) using the resin derived from the label 11 obtained by the above-mentioned method for removing the ink layer as a raw material.

<Experimental Example 1>
(Creating labels)
In Experimental Example 1, a label 11 (label of Experimental Example 1) was produced having a structure shown in the schematic cross-sectional view of Fig. 4. The label of Experimental Example 1 was produced as follows.

First, a polyethylene terephthalate film (PET film) having a thickness of 20 μm was prepared as the substrate 101. Next, a gravure proofing machine was used to apply a composition for forming the coating layer 102 onto one surface of the PET film, and then the composition was solidified to form the coating layer 102.

The composition for forming the coating layer 102 was prepared by adding 5 parts by mass of phosphorescent ink (NT Hilamic (NF) phosphorescent green) to 100 parts by mass of the composition shown in Table 1 below.

Next, a gravure proofing machine was used to apply an ink resin composition containing Etna crimson as ink onto the coat 102 layer, and then the ink was solidified to form a color layer 103a.

Next, using a gravure proofing machine, an ink resin composition containing white ink (NT Hilamic (NF) 701 white) was applied onto the color layer 103a layer and then solidified to form a white ink layer 103b.

After that, a gravure proofing machine was used to apply a medium onto the white ink layer 103b and then solidified to form an overcoat layer 104, thereby completing the label of experimental example 1.

(Evaluation of luminescence)
The label of Experimental Example 1 was irradiated with ultraviolet light to evaluate the luminescence of the label of Experimental Example 1. Fig. 5 shows a schematic side view illustrating the method for evaluating the luminescence of the label of Experimental Example 1.

As shown in Figure 5, the light emission of the label of Experimental Example 1 was evaluated by irradiating the front surface of the label of Experimental Example 1 with ultraviolet light 22 from light source 21 and evaluating the light emission in a dark place from the front side of label 11, and by irradiating the back surface of the label of Experimental Example 1 with ultraviolet light 22 from light source 21 and evaluating the light emission in a dark place from the back surface side of label 11 (the surface side on which each layer is formed). The light emission of the front and back surfaces of the label of Experimental Example 1 was evaluated based on the following evaluation criteria. The results are shown in Table 2.

(Evaluation Criteria for Luminescence)
A: Strong light emission could be confirmed visually. B: Normal light emission could be confirmed visually. C: Weak light emission could be confirmed visually. D: No light emission could be confirmed visually.

As shown in Table 2, strong light emission from both the front and back sides of the label in Experimental Example 1 was visually confirmed.

<Experimental Example 2>
(Creating labels)
In Experimental Example 2, a label 11a (label of Experimental Example 2) was produced having a configuration shown in the schematic cross-sectional view of Fig. 6. The label of Experimental Example 2 was produced as follows.

First, a 20 μm-thick PET film was prepared as the substrate 101. Next, a gravure proofing machine was used to apply a composition for forming the coating layer 102a onto one surface of the PET film, and then the composition was solidified to form the coating layer 102a.

The composition for forming the coating layer 102 consisted only of the composition shown in Table 1 above, and no phosphorescent ink was added.

Next, an ink resin composition containing Etna crimson was applied as ink onto the coat 102a layer using a gravure proofing machine and then solidified to form a color layer 103a.

Next, using a gravure proofing machine, an ink resin composition containing 100 parts by weight of white ink (NT Hilamic (NF) 701 white) and 5 parts by weight of phosphorescent ink (NT Hilamic (NF) phosphorescent green) was applied onto the color layer 103a layer and then solidified to form a white ink layer 103c.

Then, a gravure proofing machine was used to apply a medium onto the white ink 103c and then solidify it to form an overcoat layer 104. In this way, the label of Experimental Example 2 was produced.

(Evaluation of luminescence)
The label of Experimental Example 2 was irradiated with ultraviolet light in the same manner and under the same conditions as the label of Experimental Example 1, and the luminescence of the label of Experimental Example 2 was evaluated in the same manner and with the same evaluation criteria as the label of Experimental Example 1. The results are shown in Table 3.

As shown in Table 3, for the label of Experimental Example 2, weak luminescence was visually confirmed from the front side, and normal luminescence was visually confirmed from the back side.

<Experimental Example 3>
The label of Experimental Example 3 was produced in the same manner and under the same conditions as the label of Experimental Example 2, except that a white ink layer 103c was formed by applying an ink resin composition containing 100 parts by weight of white ink (NT Hilamic (NF) 701 white) and 10 parts by weight of phosphorescent ink (NT Hilamic (NF) phosphorescent green) onto the color layer 103a layer and then solidifying it.

Then, the label of Experimental Example 3 was irradiated with ultraviolet light in the same manner and under the same conditions as the labels of Experimental Examples 1 and 2, and the luminescence of the label of Experimental Example 3 was evaluated in the same manner and with the same evaluation criteria as the labels of Experimental Examples 1 and 2. The results are shown in Table 4.

As shown in Table 4, in the label of Experimental Example 3, weak light emission could be visually confirmed from the front side, and light emission at a normal level or higher could be visually confirmed from the back side. In particular, as shown in Table 4, when the surface irradiated with ultraviolet light was the back side, strong light emission could be visually confirmed from the back side.

<Experimental Example 4>
The label of Experimental Example 4 was produced in the same manner and under the same conditions as the labels of Experimental Examples 2 and 3, except that a white ink layer 103c was formed by applying an ink resin composition containing 100 parts by weight of white ink (NT Hilamic (NF) 701 white) and 20 parts by weight of phosphorescent ink (NT Hilamic (NF) phosphorescent green) onto the color layer 103a layer and then solidifying it.

Then, the label of Experimental Example 4 was irradiated with ultraviolet light in the same manner and under the same conditions as the labels of Experimental Examples 1 to 3, and the luminescence of the label of Experimental Example 4 was evaluated in the same manner and with the same evaluation criteria as the labels of Experimental Examples 1 to 3. The results are shown in Table 5.

As shown in Table 5, in the label of Experimental Example 4, a normal level of luminescence was visually observed from the front side, but a strong luminescence was visually observed from the back side.

<Evaluation of luminescence from labels in Experimental Examples 1 to 4>
The label of Experimental Example 1, which was produced by incorporating 5 parts by mass of phosphorescent ink in the coating layer 102, was able to confirm strong luminescence from both the front side and the back side, compared to the labels of Experimental Examples 2 to 4, which were produced by incorporating 5 to 20 parts by mass of phosphorescent ink in the white ink layer 103c. This shows that when separating the labels to remove the ink layer by alkali desorption, it is preferable to incorporate the phosphorescent ink in the coating layer between the substrate and the ink layer, rather than incorporating the ink in the ink layer on the coating layer. In addition, when the phosphorescent ink is incorporated in the coating layer, a small amount of the expensive phosphorescent ink can be used, since a strong luminescence can be obtained with a small amount, compared to the case where the phosphorescent ink is incorporated in the ink layer. This is considered to enable the ink layer to be removed from the label more efficiently from the viewpoint of cost.

Although the embodiments and experimental examples have been described above, it has been planned from the outset that the configurations of the above-mentioned embodiments and experimental examples will be appropriately combined.

The embodiments and experimental examples disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present invention is defined by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims.

10 PET bottle, 11, 11a label, 12 collection box, 20 labeled bale, 30 recycling plant, 40 normal label, 50 label group, 60 hot water, 61 hot air tunnel, 62 hot water bath, 70 crusher, 71 label piece, 80 alkaline aqueous solution, 82 hot alkaline bath, 90 first net, 92 second net, 93 ink coating, 101 substrate, 102 coat layer, 103 ink layer, 103a color layer, 103b, 103c white ink layer, 104 overcoat layer, 201 first dark place, 202 second dark place

Claims (7)

A substrate;
an alkali-soluble coating layer on the substrate;
an ink layer on the coating layer;
The coating layer or the ink layer contains a material that emits light when irradiated with an energy ray ,
The label having the alkali-soluble coating layer can be identified and separated by irradiating the label with the energy ray, causing the coating layer or the ink layer to emit light . A substrate;
an alkali-soluble coating layer on the substrate;
an ink layer on the coating layer;
The coating layer or the ink layer contains a material that emits light when irradiated with an energy ray,
The label is capable of being attached to a PET bottle. The label according to claim 1 or 2 , wherein the coating layer contains a material that emits light when irradiated with energy rays. the alkali-soluble coating layer contains a first acrylic acid copolymer resin and a second acrylic acid copolymer resin;
The label according to claim 1 or 2, wherein the coating layer has an apparent acid value of 40 mgKOH/g or more and 150 mgKOH/g or less. a step of recovering a group of labels including labels that contain a material that emits light when irradiated with energy rays and have an ink layer that can be removed by alkaline desorption;
irradiating the collected label group with an energy beam;
a step of separating the labels that have emitted light by irradiating the labels with the energy beam;
removing the ink layer from the separated labels by alkaline desorption. 6. The method for removing an ink layer from a label according to claim 5 , further comprising the step of crushing the separated labels prior to the step of removing by alkaline desorption. A method for producing a label, the method comprising the step of: producing a label using, as a raw material, a resin derived from the label obtained by the removal method according to claim 5 .