Ink for recycling, packaging material for recycling, and method for recycling packaging material for recycling

Abstract

To provide an ink for recycling which enables regeneration of a colorless resin and is resistant to discoloration during the processing step of a packaging material, a packaging material for recycling using the ink, and a method for recycling the packaging material for recycling.SOLUTION: The present invention provides a recycling ink to be used in a packaging material for recycling. The recycling ink contains: a dye (A) which has a thermal decomposition temperature or sublimation temperature of 150°C or more and 270°C or less, and is resistant to discoloration at 25°C or more and 120°C or less.SELECTED DRAWING: None

Description

[Technical field]

[0001] SUMMARY OF THE DISCLOSURE The present invention relates to a method for recycling ink, a method for recycling packaging material, and a method for recycling the packaging material. [Background technology]

[0002] From the viewpoints of environmental protection and effective use of resources, various studies are being conducted on the recycling of plastic products. In recent years, there has been a particularly high demand for material recycling in order to realize a recycling-oriented society.

[0003] Although plastic film packaging materials (hereinafter referred to as film packaging materials) contain base materials such as recyclable plastic films, they are often incinerated as waste or disposed of unused in landfills, etc. Even if the plastic film is separated and recovered from the film packaging material, it is difficult to sufficiently remove the printing ink, so that colored plastic materials are usually recovered. Therefore, after recycling, they become gray to black plastic films mixed with various colors, and their applications are limited, such as containers and hangers. Since these are originally colored black or gray, new designs, etc. cannot be added.

[0004] In order to be able to freely express colors even after recycling, it is necessary to separate and recover colorless plastic film, and various methods have been considered. For example, Patent Document 1 discloses a method of embedding recycling information in the body of a PET bottle and separating the bottles based on the information. Patent Document 2 discloses a method of deinking the bottles to easily and thoroughly remove printing ink in a process of separating and recovering plastic films from film packaging materials. Patent Document 3 discloses a recycling method using a colored layer that contains a coloring material that is irreversibly decolorized by thermal stimulation. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2020 / 186234 [Patent Document 2] Patent No. 2022-182777 [Patent Document 3] International Publication No. 2023 / 085225 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the method disclosed in Patent Document 1 aims at the separate collection of the PET bottle body, and forms unevenness directly on the PET bottle body by laser marking to provide information regarding recycling. In order to form unevenness by laser marking, the substrate needs to have a certain thickness, as in the case of a PET bottle. Therefore, it is difficult to apply the disclosed method to film packaging materials that are thinner than PET bottles. In particular, in order to realize material recycling of film packaging materials, not only is it necessary to simply separate and collect the film packaging materials from waste, but it is also necessary to have a technology that can remove unnecessary components such as printing ink from the collected film packaging materials (deinking) and separate and collect only recyclable materials such as plastic films.

[0007] Furthermore, the method disclosed in Patent Document 2 includes a deinking step, which tends to make the process complicated and increase costs. Furthermore, the method disclosed in Patent Document 3 has a problem in that the heat resistance of the coloring material is poor, and the color fades even in the temperature range of the process of forming the packaging material, for example, heat sealing.

[0008] Therefore, an object of the present invention is to provide a recycled ink that can regenerate colorless resin and does not fade during the processing stage of the packaging material, a recycled packaging material using said ink, and a recycling method for the recycled packaging material. [Means for solving the problem]

[0009] The inventors conducted extensive research into how to regenerate the film into a colorless film through material recycling, and discovered that the above-mentioned problems could be solved by using a coloring material that loses its color when heated to a certain temperature or above during the recycling process, thereby completing the present invention.

[0010] That is, the present invention provides A recycled ink for use on recycled packaging materials, comprising: The present invention relates to a recyclable ink containing a dye (A) whose thermal decomposition temperature or sublimation temperature is 150°C or higher and 270°C or lower, and which does not fade at temperatures between 25°C and 120°C.

[0011] The present invention also relates to the above-mentioned recycling ink, wherein the dye (A) contains at least one dye selected from the group consisting of triphenylmethane, cyanine, squarylium, azo, and xanthene.

[0012] The present invention also relates to a packaging material having a film substrate and a printed layer formed from the recycled ink.

[0013] The present invention also relates to a recyclable packaging material having a film substrate, a printed layer formed from the recyclable ink, and a sealant.

[0014] The present invention also relates to the above-mentioned recycling packaging material, wherein the film substrate and the sealant contain the same resin.

[0015] The present invention also relates to the above-mentioned recyclable packaging material, wherein the film substrate and the sealant contain an olefin.

[0016] The present invention also relates to a method for recycling a packaging material for recycling, which includes a step of heating and decolorizing a packaging material for recycling having a printed layer containing a dye (A) whose thermal decomposition temperature or sublimation temperature is 150°C or higher and 270°C or lower and which does not decolorize at 25°C or higher and 120°C or lower. Effect of the Invention

[0017] According to an embodiment of the present invention, it is possible to provide a recycled ink that can regenerate colorless resin and does not fade during the processing stage of the packaging material, a recycled packaging material using the ink, and a recycling method for the recycled packaging material. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Hereinafter, embodiments of the present invention will be described. However, the present invention is not limited to the embodiments described below and includes various embodiments.

[0019] The ink for recycling of the present invention is intended to be used for packaging materials for recycling, and contains a dye (A) whose thermal decomposition temperature or sublimation temperature is 150° C. or higher and 270° C. or lower, and which does not fade at temperatures between 25° C. and 120° C. Therefore, by heating the packaging material so that the dye (A) is thermally decomposed or sublimated, the color can be erased and the material can be recycled into a colorless plastic film or the like. In this specification, the thermal decomposition temperature is defined as the temperature at which a weight loss of 5% occurs as measured by a thermogravimetric differential thermal analyzer (TG-DTA) or the like. In addition, since the heat treatment such as heat sealing performed in the process of forming the packaging material is generally at about 120°C, it is possible to prevent the color of the printed layer from disappearing during these treatments.

[0020] (Dye (A)) The dye (A) having a thermal decomposition temperature or sublimation temperature of 150° C. or more and 270° C. or less and not decolorizing at a temperature of 25° C. or more and 120° C. or less is not particularly limited, but is preferably a dye selected from the group consisting of triphenylmethane, cyanine, squarylium, azo, and xanthene. Examples of triphenylmethane dyes include Basic Blue 7, Acid Violet 49, Acid Green 5, Acid Green 16, Acid Green 50, and Basic Green 1; examples of cyanines include Basic Yellow 11, Basic Yellow 13, Basic Red 12, and Solvent Red 41; examples of azo dyes include Basic Red 76; and examples of xanthene dyes include Basic Violet 10. Also included are dyes having the following structures: (Dye A-1) Yellow cyanine dye [ka] (Dye A-2) Cyanine blue dye [ka] (Dye A-3) Cyanine violet dye [ka] (Dye A-4) Cyanine red dye [ka] (Dye A-5) Squarylium-based green dye [ka] (Dye A-6) Azo red dye [ka]

[0021] The thermal decomposition temperature or sublimation temperature is preferably 160°C to 260°C, more preferably 170°C to 250°C, and even more preferably 180°C to 240°C, from the viewpoint of the recycling temperature of the packaging material.

[0022] The dye (A) is preferably the main component of the colorant contained in the ink, and is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more of the colorant. The content of the dye (A) is preferably 1 to 50% by mass, more preferably 3 to 30% by mass, of the total mass of the ink.

[0023] (binder resin) The ink for recycling of the present invention preferably contains a binder resin. Examples of the binder resin include acrylic resin, polyester resin, polyurethane resin, polyamide resin, acrylic urethane resin, and acrylic polyester resin, and polyurethane resin is particularly preferred.

[0024] The polyurethane resin preferably has an acid value of 15 to 70 mgKOH / g. In another embodiment, the polyurethane resin preferably has an acid value of 15 to 70 mgKOH / g and a hydroxyl value of 1 to 35 mgKOH / g.

[0025] The acid value is the amount of acid in 1 g of resin calculated by titrating the acid with an alkali, converted into mg of potassium hydroxide. The hydroxyl value is the amount of hydroxyl in 1 g of resin calculated by esterifying or acetylating the hydroxyl in the resin and back titrating the remaining acid with an alkali, converted into mg of potassium hydroxide. Both the acid value and the hydroxyl value are values ​​measured according to JIS K0070. From the viewpoint of lamination suitability, the polyurethane resin preferably has an acid value of 20 to 50 mg KOH / g, more preferably an acid value of 25 to 40 mg KOH / g. In addition, the hydroxyl value is preferably 10 to 30 mg KOH / g, more preferably a hydroxyl value of 15 to 27 mg KOH / g.

[0026] The molecular weight distribution (Mw / Mn) of the polyurethane resin is preferably 6 or less. Mw represents the weight average molecular weight, and Mn represents the number average molecular weight. When Mw / Mn is 6 or less, the influence caused by excess high molecular weight components, unreacted components, side reaction components, and other low molecular weight components can be avoided, and drying properties and lamination suitability are improved. The molecular weight distribution is preferably 5 or less, and more preferably 4 or less. The molecular weight distribution is preferably 1.5 or more, and more preferably 1.2 or more. Mw, Mn, and Mw / Mn are values ​​calculated using polystyrene equivalent values ​​that can be determined by gel permeation chromatography (GPC). If the molecular weight distribution is within the applicable range and the acid value is within the above range, the drying property, substrate adhesion, retort resistance, etc. are further improved.

[0027] In order to obtain a molecular weight distribution (Mw / Mn) within the above range, the ratio of urethane synthesis raw materials / organic solvent (solid content ratio), the dropping speed of reactive raw materials such as polyisocyanate, and further the stirring speed during the reaction and the uniformity of the reaction liquid can be appropriately set in the polyurethane resin synthesis, thereby making it possible to obtain a molecular weight distribution within the range. When a chain extension reaction is further carried out, it is particularly preferable to balance the dropping / contact speed and stirring speed of the polyamine and urethane prepolymer described below, and further to control the temperature range during chain extension to a certain range, from the viewpoint of obtaining a molecular weight distribution within a predetermined range.

[0028] In addition, it is preferable to set the charging ratio of the reaction raw materials to an appropriate ratio from the viewpoint of obtaining a molecular weight distribution in a predetermined range. Examples of the charging ratio include the NCO / OH ratio, which is the ratio of the hydroxyl groups of the polyol and hydroxy acid, and the isocyanate groups of the polyisocyanate. Examples of the charging ratio include the amino group / NCO ratio, which is the ratio of the amino group of the polyamine and the isocyanate group of the urethane prepolymer. In order to control the molecular weight distribution, it is preferable to use a polymerization terminator (also called a reaction terminator) for the purpose of preventing excessive polymerization reaction. Examples of the polymerization terminator include monoalcohols and monoamines.

[0029] The weight average molecular weight (Mw) of the polyurethane resin is preferably 10,000 to 100,000, more preferably 15,000 to 70,000, and even more preferably 15,000 to 50,000. When Mw is within the above range, blocking resistance, working efficiency in the ink printing process, printability, etc. are improved.

[0030] The polyurethane resin may have an amine value. When the polyurethane resin has an amine value, the amine value is preferably 0.1 to 20 mgKOH / g, more preferably 1 to 10 mgKOH / g. When the amine value is within the above range, the adhesion to the substrate is good. The amine value is the number of mg of potassium hydroxide equivalent to the amount of hydrochloric acid required to neutralize the amino groups contained in 1 g of resin. The amine value can be measured by the following method in accordance with JIS K0070 (1992). First, accurately weigh out 0.5 to 2 g of sample (sample solid content: Sg). Add 50 mL of a mixed solution of methanol / methyl ethyl ketone = 60 / 40 (mass ratio) to the accurately weighed sample to dissolve it. Add bromophenol blue as an indicator to the resulting solution, and titrate the resulting solution with 0.2 mol / L ethanolic hydrochloric acid solution (titer: f). The point at which the color of the solution changes from green to yellow is set as the endpoint, and the titration volume (A mL) at this point can be used to calculate the amine value using the following formula. Amine value = (A x f x 0.2 x 56.108) / S [mgKOH / g]

[0031] The polyurethane resin is not limited by its production method, but it is preferable to use, for example, a polyurethane resin obtained by reacting a polyisocyanate, a polyol, and a hydroxy acid. It is also more preferable to use a polyurethane resin obtained by reacting a urethane prepolymer obtained by reacting a polyisocyanate, a polyol, and a hydroxy acid with a polyamine (called a chain extension reaction). In either case, the polyurethane resin can be given an acid value by using a hydroxy acid.

[0032] (Polyisocyanate) The polyisocyanate used in the polyurethane resin is preferably a diisocyanate and / or a triisocyanate, and aromatic, aliphatic or alicyclic diisocyanates can be suitably used. For example, 1,5-naphthylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 4,4'-diphenyldimethylmethane diisocyanate, 4,4'-dibenzyl isocyanate, dimethyldiphenylmethane diisocyanate, tetramethyldiphenylmethane diisocyanate, 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, m-xylylene diisocyanate, p-xylylene diisocyanate, o-xylylene diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate and other aromatic diisocyanates, Tetramethylene diisocyanate, hexamethylene diisocyanate, isopropylene diisocyanate, methylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate and other aliphatic diisocyanates, Preferred examples of the diisocyanate include cyclohexane-1,4-diisocyanate, hydrogenated xylylene diisocyanate, isophorone diisocyanate, lysine diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, 1,3-bis(isocyanatomethyl)cyclohexane, methylcyclohexane diisocyanate, m-tetramethylxylylene diisocyanate, and other alicyclic diisocyanates such as dimer diisocyanate in which the carboxyl group of a dimer acid is converted to an isocyanate group. These may be used alone or in combination of two or more.

[0033] Among the above, it is preferable to use at least one selected from isophorone diisocyanate, 4,4'-diphenylmethane diisocyanate, xylylene diisocyanate, hydrogenated xylylene diisocyanate, tolylene diisocyanate, hexamethylene diisocyanate, and dicyclohexylmethane-4,4'-diisocyanate in terms of reactivity, etc. It is also preferable that these diisocyanates are triisocyanates that are trimers and have an isocyanurate structure.

[0034] (Polyol) The polyurethane resin has a structural unit derived from a polyol. The polyol is not particularly limited, and is preferably, for example, polyether polyol, polyester polyol, or polycarbonate polyol. The polyol is a general term for a compound having at least two hydroxyl groups in one molecule, but does not include the hydroxy acid described below. Further, as the polyol, other dimer diol, hydrogenated dimer diol, castor oil modified polyol, etc. may be used. The polyurethane resin preferably has at least one type of structural unit selected from a polyether structural unit, a polyester structural unit, and a polycarbonate structural unit, and more preferably contains a structural unit derived from a polyester polyol. The polyurethane resin preferably contains 10 to 75 mass % of structural units derived from polyol, more preferably 15 to 70 mass %, and further preferably 20 to 65 mass %, of the total mass of the polyurethane resin.

[0035] The polyol is preferably used in such a manner that the polyester polyol-derived structural unit is contained in an amount of 5% by mass or more of the total mass of the polyol-derived structural units. In one embodiment, based on the total mass of the polyol-derived structural units, the content of the polyester polyol-derived structural units is preferably 10% by mass or more, more preferably 30% by mass or more, and even more preferably 40% by mass or more.

[0036] The number average molecular weight of the polyol is preferably 500 to 10,000. The number average molecular weight used for the polyol here is calculated from the hydroxyl value. The hydroxyl value is a value measured according to JIS K0070. When the number average molecular weight of the polyol is 10,000 or less, the blocking resistance to plastic films is excellent. When the number average molecular weight of the polyol is 500 or more, the flexibility of the polyurethane resin coating is excellent and the adhesion to plastic films is excellent. For these reasons, the number average molecular weight of the polyol may more preferably be 1,000 to 5,000.

[0037] (Polyester polyol) Suitable examples of polyester polyols include polyester polyols made of a condensate of a dibasic acid and a diol, and polyester polyols made of a polylactone polyol, which is a ring-opening polymer of a cyclic ester compound. Polyester diols are preferred. Suitable examples of the dibasic acid include adipic acid, phthalic anhydride, isophthalic acid, terephthalic acid, maleic acid, fumaric acid, succinic acid, oxalic acid, malonic acid, pimelic acid, azelaic acid, sebacic acid, suberic acid, glutaric acid, 1,4-cyclohexyldicarboxylic acid, dimer acid, and hydrogenated dimer acid, among which adipic acid and succinic acid are preferred.

[0038] Suitable examples of the diol include ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,3-butanediol, 1,6-hexanediol, 1,8-octanediol, 1,9-nonanediol, neopentyl glycol, 3-methyl-1,5-pentanediol, 2-methyl-1,3-propanediol, 3,3,5-trimethylpentanediol, 2,4-diethyl-1,5-pentanediol, 1,12-octadecanediol, 1,2-alkanediol, 1,3-alkanediol, 1-monoglyceride, 2-monoglyceride, 1-monoglycerin ether, 2-monoglycerin ether, dimer diol, and hydrogenated dimer diol.

[0039] The polyester polyol can be used alone or in a mixture of two or more kinds. Furthermore, a polyol having three or more hydroxyl groups and a polycarboxylic acid having three or more carboxyl groups can be used in combination as raw materials for the polyester polyol. Suitable examples of the cyclic ester compound include α-acetolactone, β-propiolactone, γ-butyrolactone, δ-valerolactone, and ε-caprolactone.

[0040] The binder resin is preferably contained in an amount of 0.5 to 50 mass % in terms of solid content, more preferably 5 to 30 mass %, based on the total mass of the ink. By being in the above range, the viscosity of the ink becomes appropriate, and printing suitability such as halftone dot reproducibility becomes good when the ink is applied to a film substrate using any printing method.

[0041] (Other inks) In addition to the recycling ink of the present invention, clear ink may be used as a colorless ink when printing on the same film substrate. The clear ink refers to an ink or printed layer that is approximately opaque or colorless and transparent, and does not exclude slight coloring caused by binder resins, extender pigments, additives, etc. The solid content of the clear ink is preferably 5 to 50 mass %, more preferably 10 to 40 mass %, of the total mass of the ink. Furthermore, the binder resin is preferably contained in an amount of 0.5 to 50 mass %, more preferably 5 to 30 mass %, of the total mass of the ink. By being in the above range, the viscosity of the clear ink becomes appropriate, and when the ink is applied to a film substrate using any printing method, the printing suitability such as halftone dot reproducibility becomes good. Note that the "solid content" refers to the total mass % of non-volatile components.

[0042] (Extender pigment) The clear ink preferably contains an extender pigment. Examples of the extender pigment include silica, barium sulfate, kaolin, clay, calcium carbonate, magnesium carbonate, and metal oxides such as zinc oxide and zirconium oxide. These are used to improve fluidity, film strength, and optical properties. Among them, silica is preferably used, and it is preferable that the extender pigment is hydrophilic. The average particle size of the extender pigment is preferably 0.5 to 10 μm, and more preferably 1 to 8 μm. The extender pigment is preferably contained in an amount of 0.5 to 40% by mass, and more preferably 1 to 30% by mass, based on the total mass of the ink. This is because the blocking property of the clear ink layer is improved, and the wettability of the pattern ink is improved when the pattern ink is overprinted.

[0043] (Ink manufacturing) The ink for recycling of the present invention can be produced by dissolving and / or dispersing the binder resin, the colorant containing the dye (A), the extender pigment, etc. in an organic solvent. For example, a colorant, a binder resin such as a polyurethane resin, a vinyl chloride-vinyl acetate copolymer resin, silica particles, and an organic solvent as required are dispersed in advance, and the colorant composition is mixed with a polyurethane resin, an organic solvent as required, other resins, additives, and the like to produce an organic solvent-based ink. The organic solvent may be a mixed solution of a plurality of organic solvents. The viscosity and color of the organic solvent-based ink can be adjusted by appropriately adjusting the size of the grinding media of the dispersing machine, the filling rate of the grinding media, the dispersion processing time, the discharge speed of the pigment dispersion, the viscosity of the pigment dispersion, and the like. As the dispersing machine, a commonly used one, such as a roller mill, a ball mill, a pebble mill, an attritor, or a sand mill, can be used. It is preferable to produce the ink using a sand mill.

[0044] The viscosity of the ink is preferably in the range of 20 to 500 mPa·s, and more preferably 30 to 300 mPa·s. When the viscosity of the ink is adjusted to be within the above range, appropriate printability can be easily obtained in the printing process. The viscosity of the ink can be adjusted by the amount of the polyurethane resin and other binder resins, the amount of the organic solvent, and further the dispersion conditions of the pigment.

[0045] (Formation of printing layer) The printing layer can be formed, for example, by printing on a substrate using a printing ink and then removing the volatile components. The printing method is preferably a gravure printing method or a flexographic printing method, and, for example, the ink is diluted with a diluting solvent to a viscosity and concentration suitable for gravure printing, and is supplied to each printing unit alone or in a mixture and applied. The printing layer can then be obtained by fixing the coating by drying in an oven or the like.

[0046] <Packaging materials> Generally, packaging materials have a multi-layer structure to meet different required performance for each application. For example, there are packaging materials having a film substrate and a printed layer formed from the ink for recycling of the present invention, and packaging materials having a film substrate, a printed layer formed from the ink for recycling of the present invention, and a sealant in this order. The packaging material may further have an adhesive layer between the printed layer and the sealant. (Film substrate) The film substrate may be, for example, a plastic film of a thermoplastic resin or a thermosetting resin, preferably a film of a thermoplastic resin, such as polyolefin, polyester, polyamide, polystyrene, vinyl chloride resin, vinyl acetate resin, ABS resin, acrylic resin, acetal resin, polycarbonate resin, or cellulose-based plastic.

[0047] More specifically, polyester resin films such as polyethylene terephthalate, polyethylene naphthalate (PEN), polylactic acid (PLA), etc., polyolefin resin films such as polyethylene (PE), polypropylene (PP), etc., polystyrene resin films, polyamide resin films such as nylon 6, poly-p-xylylene adipamide (MXD6 nylon), etc., polycarbonate resin films, polyacrylonitrile resin films, polyimide resin films, laminates thereof (for example, nylon 6 / MXD6 / nylon 6, nylon 6 / ethylene-vinyl alcohol copolymer / nylon 6), or mixtures thereof, etc. are used. Among them, those having mechanical strength and dimensional stability are preferable. The thickness of the film substrate is preferably 5 μm or more and 200 μm or less, more preferably 10 μm or more and 100 μm or less, and further preferably 10 μm or more and 50 μm or less.

[0048] Examples of the sealant include plastic films of polyethylene such as low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE) and high-density polyethylene (HDPE), acid-modified polyethylene, polypropylene (PP), acid-modified polypropylene, copolymerized polypropylene, ethylene-vinyl acetate copolymer, ethylene-(meth)acrylic acid ester copolymer, ethylene-(meth)acrylic acid copolymer, ionomer and other polyolefin resins. Among these, linear low-density polyethylene and unstretched polypropylene are particularly preferred from the viewpoint of heat sealability. The thickness of the sealant is not particularly limited, but is preferably in the range of 10 to 200 μm, more preferably 15 to 150 μm, in consideration of processability into packaging materials, heat sealability, etc. Also, by providing unevenness with a height difference of 5 to 20 μm, it is possible to impart slipperiness to the sealant and tearability of packaging materials.

[0049] The method for laminating the sealant is not particularly limited, and examples thereof include a method of laminating a removable adhesive layer and a sealant by heat (thermal lamination, dry lamination) described below, and a method of melting the sealant, extruding it onto the adhesive layer, and cooling and solidifying it to laminate (extrusion lamination method).

[0050] It is preferable that the film substrate and the sealant contain the same resin, so that they are compatible when melted and can be recycled as a high-quality resin. In particular, it is preferable that the film substrate and the sealant are made of olefin.

[0051] <How to recycle packaging materials> In material recycling, used film packaging materials are typically heated to over 250°C, where they are melted and integrated to regenerate new plastic film. The recycling method of the present invention includes a step of heating and decolorizing a packaging material for recycling having a printed layer containing a dye (A) whose thermal decomposition temperature or sublimation temperature is 150°C or higher and 270°C or lower and which does not decolorize at 25°C or higher and 120°C or lower. This makes it possible to produce colorless recycled plastic without the de-inking process, which differs from the case when conventional highly heat-resistant organic pigments are used, and it can also be used in consumer products, which are in high demand and require the addition of new designs.

[0052] The heating temperature in the recycling step is not particularly limited as long as the dye (A) is decolorized by thermal decomposition or sublimation, but is preferably a temperature equal to or higher than the thermal decomposition or sublimation temperature of the dye (A). Here, "a temperature equal to or higher than the thermal decomposition or sublimation temperature of the dye (A)" means a temperature equal to or higher than either the thermal decomposition or sublimation temperature, and is preferably 3°C or higher, more preferably 5°C or higher.

[0053] A specific recycling method preferably includes a heating and melting kneading step of heating and melting the packaging material to form a resin composition, an extrusion step of extruding the resulting resin composition, and a cooling step of cooling the extruded resin composition to form a recycled plastic. The shape of the recycled plastic is not particularly limited, and examples include rod-like, particulate, cubic, rectangular, and amorphous. The decolorizing step is preferably included in the heating and melting step.

[0054] From the viewpoint of handling, it is preferable to include a crushing step of crushing the packaging material before the heating and melting kneading step. Also, from the viewpoint of removing foreign matter such as dust and dirt, it is preferable to include a cleaning step of cleaning the plastic laminate before the heating and melting kneading step. Furthermore, from the viewpoint of removing moisture, it is preferable to include a dehydration and drying step of dehydrating and drying the packaging material before the heating and melting kneading step. In addition, it is preferable to add an additive in the heating and melting kneading step. Also, from the viewpoint of removing foreign matter, it is preferable to provide a foreign matter separation device at the discharge section of the extrusion device. Furthermore, from the viewpoint of handling of the recycled plastic, it is preferable to include a pelletizing step of shredding the extruded resin composition after or simultaneously with the cooling step.

[0055] The heat melting temperature can be appropriately selected depending on the thermal decomposition temperature or sublimation temperature of the dye (A), but is preferably 160° C. to 260° C., more preferably 170° C. to 250° C., and even more preferably 180° C. to 240° C. When it is within the above range, both uniformity and low thermal history of the recycled plastic can be achieved, resulting in good results in immediate film foreign matter, immediate film discoloration, aged film foreign matter, and aged film discoloration.

[0056] Molded products can be obtained by molding the recycled plastic obtained by the present invention. The molding method is not particularly limited, and examples include injection molding, extrusion molding, blow molding, and compression molding. Molded products can be used for various purposes such as home appliances, stationery, automobile parts, toys, sports goods, medical supplies, and building and construction materials.

[0057] For example, the recycled polyethylene obtained can be heated and melted, extruded using a slit-shaped device called a T-die, molded into a film, and then cooled and solidified with a cooling roll to obtain a polyethylene film. The heat-melting temperature is preferably 100 to 210°C. The thickness of the film molded body is preferably 10 to 300 μm. EXAMPLES

[0058] The present invention will be described in more detail below, but is not limited to these examples as long as it does not deviate from the technical concept of the present invention. In the following, "parts by mass" will be simply written as "parts" and "% by mass" will be simply written as "%".

[0059] <Preparation of binder resin solution 1> 100 parts of polyester polyol having a number average molecular weight of 2,000, which is a condensation product of 3-methyl-1,5-pentanediol and sebacic acid, 1 part of 1,4-butanediol, 28.5 parts of isophorone diisocyanate, and 32.1 parts of ethyl acetate were mixed and reacted under a nitrogen atmosphere at 90°C for 5 hours to obtain a urethane prepolymer with a terminal isocyanate. Next, 11.0 parts of isophoronediamine, 1.0 parts of N-(2-aminoethyl)ethanolamine, 1.0 parts of dibutylamine, and 298.1 parts of mixed solvent 1 (ethyl acetate / isopropanol=70 / 30 (mass ratio)) were stirred and mixed, and the obtained urethane prepolymer with terminal isocyanate was gradually added at 40° C. The mixture was reacted at 80° C. for 1 hour to obtain a solution of urethane resin PU1 with a solid content of 30 mass%, an amine value of 6.5 mg KOH / g, a hydroxyl value of 3.8 mg KOH / g, and a weight average molecular weight of 50,000.

[0060] <Manufacturing recycled ink> (Manufacturing of recycled ink (P-1)) The mixture of the following components was stirred and mixed until homogeneous to prepare a recycle ink (P-1). Basic Blue 7 Part 1 Binder resin solution 1 45 parts 4 parts isopropyl alcohol

[0061] (Manufacture of recycled inks (P-2) to (P-18)) As shown in Table 1, recycling inks (P-2) to (P-18) were prepared in the same manner as the recycling ink (P-1).

[0062] [Table 1]

[0063] (Manufacturing of ink (PP-1)) A mixture of the following composition was stirred and mixed to a uniform consistency, and then dispersed for 5 hours in an Eiger mill (Eiger Japan "Mini Model M-250 MKII") using zirconia beads with a diameter of 0.5 mm. Pigment Blue 15:3 1 part Binder resin solution 1 4 parts 4 parts isopropyl alcohol The following raw materials were added to the obtained dispersion and mixed homogeneously to prepare ink (PP-1). Binder resin solution 1 15 parts

[0064] (Manufacture of Inks (PP-2) to (PP-3)) As shown in Table 1, inks (PP-2) to (PP-3) were prepared in the same manner as ink (PP-1).

[0065] [Table 2]

[0066] (Manufacturing of ink (PP-4)) A temperature-sensitive ink (Metamocolor (registered trademark) manufactured by Pilot Ink Co., Ltd.) was used as ink (PP-4). The temperature-sensitive ink contains (a) 1.25 parts of 3-(4-diethylamino-2-ethoxyphenyl)-3-(1-ethyl-2-methylindol-3-yl)-4-azaphthalide as an electron-donating color-developing organic compound, (b) 5 parts of 4,4'-(2-methyl-propylidene)bisphenol as an electron-accepting compound, (c) 35 parts of a thermochromic microcapsule pigment (blue at 42°C or less, colorless at 45°C or more) in which a reversible thermochromic composition consisting of 25 parts of stearyl alcohol and 25 parts of stearyl myristate as compounds that cause an electron donor / acceptor reaction between the components (a) and (b) in a specific temperature range is encapsulated (blue at 42°C or less, colorless at 45°C or more), and 20 parts of an acrylic resin.

[0067] <Measurement of the temperature at which the dye decomposes or sublimates> The thermal decomposition or sublimation temperatures of the dyes used in the resulting inks (P-1) to (P-15) and (PP-1) to (PP-4) were measured by TG-DTA, and the following evaluations were made. A: 150℃ or more and 270℃ or less B: 271℃ or higher C: Below 149℃

[0068] The results are shown in Table 3. Specifically, the dyes used in the examples had a thermal decomposition temperature but did not have a sublimation temperature. The thermal decomposition temperatures of Basic Blue 7, Basic Red 12, and Basic Yellow 13 were 220°C, 250°C, and 240°C, respectively.

[0069] [Table 3]

[0070] <Production and evaluation of packaging materials> Example 1 The recycled ink (P-1) was diluted with isopropyl alcohol to a viscosity of 16 seconds in a Zahn cup #3, and then the diluted recycled ink was printed on the corona-treated surface of a uniaxially oriented polyethylene (MDOPE) film (thickness 25 μm) that had been corona-treated on one side using a gravure printing machine equipped with a gravure plate with a plate depth of 60 μm at a printing speed of 50 m / min and an in-line oven temperature of 60°C to produce a packaging material (XF-1). The obtained film (XF-1) was subjected to a heat resistance test by heat sealing. The heat sealing conditions are as follows. Equipment: Heat seal tester manufactured by Tester Sangyo Co., Ltd. Seal width: 10mm from the folded part Heater temperature: 120℃ Sealing pressure: 2kg / cm 2 Sealing time: 1 second

[0071] The chromaticity (L*, a*, b*) of the heat-sealed portion of (XF-1) was measured before and after the treatment, the color difference (ΔE*ab) was calculated, and the following evaluation was performed. The evaluation results are shown in Table 4. Color difference (ΔE*ab) less than 5: ◯ (no change) Color difference (ΔE*ab) is 5 or more but less than 10: △ (slight change) Color difference (ΔE*ab) is 10 or more: × (obvious change)

[0072] The obtained film (XF-1) was passed through a twin-screw extruder at 250° C. for 5 minutes and molded into a recycled film having a thickness of 25 μm. The chromaticity (L*, a*, b*) of the obtained recycled film and the uncoated MDOPE film were measured, and the color difference (ΔE*ab) between the two films was calculated and the following evaluation was made. The evaluation results are shown in Table 4. Color difference (ΔE*ab) less than 5: 〇 (almost colorless) Color difference (ΔE*ab) is 5 or more but less than 10: △ (slightly colored) Color difference (ΔE*ab) is 10 or more: × (obviously colored)

[0073] (Examples 2 to 22, Comparative Examples 1 to 7) As shown in Table 4, (XF-2) to (XF-22) and (XXF-1) to XXF-7) were prepared and evaluated in the same manner as in Example 1. The evaluation results are shown in Table 4.

[0074] [Table 4]

[0075] <Preparation and evaluation of laminated packaging materials> (Manufacture of uninked packaging material T) A polyether-based reactive urethane adhesive (Toyo-Morton "TM-340V / CAT-29B") was applied to the corona-treated surface of a uniaxially oriented polyethylene (MDOPE) film (thickness 25 μm) that had been corona-treated on one side using a dry laminator equipped with a gravure plate with a plate depth of 40 μm to form an adhesive layer, and a low-density polyethylene (LDPE) film (thickness 60 μm) was laminated onto the adhesive layer as a sealant. The laminate film produced was stored at 40°C for one day to obtain uninked packaging material T, which was laminated in the order of film substrate / adhesive layer / sealant.

[0076] (Example 23) A polyether-based reactive urethane adhesive ("TM-340V / CAT-29B" manufactured by Toyo-Morton) was applied to the printed layer of the packaging material (XF-1) obtained in Example 1 using a dry laminator equipped with a gravure plate with a plate depth of 40 μm to form an adhesive layer, and a low-density polyethylene (LDPE) film (thickness 60 μm) was laminated onto the adhesive layer as a sealant. The produced laminate film was stored at 40° C. for 1 day to obtain a packaging material (YF-1) laminated in the order of film substrate / printed layer / adhesive layer / sealant. The obtained packaging material (YF-1) was passed through a twin-screw extruder at 250°C for 5 minutes and molded into a recycled film with a thickness of 25 µm. The chromaticity (L*, a*, b*) of the obtained recycled film and the uncoated packaging material T was measured, and the color difference (ΔE*ab) between the two films was calculated and the following evaluation was performed. The results are shown in Table 5. Color difference (ΔE*ab) less than 5: 〇 (almost colorless) Color difference (ΔE*ab) is 5 or more but less than 10: △ (slightly colored) Color difference (ΔE*ab) is 10 or more: × (obviously colored)

[0077] Next, the obtained packaging material (YF-1) was passed through a twin-screw extruder at 250° C. for 5 minutes to be molded into a recycled film having a thickness of 160 μm. The haze of this film was measured, and the transparency was evaluated as follows. The results are shown in Table 5. Haze value less than 15: Good Haze value is 15 or more and less than 50: △ (practical range) Haze value over 50: × (poor)

[0078] (Examples 24 to 44, Comparative Examples 8 to 14) As shown in Table 5, (YF-2) to (YF-22) and (YYF-2) to (YYF-7) were prepared and evaluated in the same manner as in Example 23. The evaluation results are shown in Table 5.

[0079] [Table 5]

Claims

1. A recycled ink for use on recycled packaging materials, comprising: A recyclable ink containing a dye (A) having a thermal decomposition temperature or sublimation temperature of 150°C or higher and 270°C or lower, and which does not fade at a temperature of 25°C or higher and 120°C or lower.

2. 2. The recycling ink of claim 1, wherein the dye (A) comprises at least one selected from the group consisting of triphenylmethane, cyanine, squarylium, azo, and xanthene.

3. A packaging material having a film substrate and a printed layer formed from the recycled ink according to claim 1 or 2.

4. 3. A recyclable packaging material comprising a film substrate, a printed layer formed from the recyclable ink according to claim 1 or 2, and a sealant.

5. 5. The recyclable packaging material of claim 4, wherein the film substrate and the sealant comprise the same resin.

6. 5. The recyclable packaging material of claim 4, wherein the film substrate and sealant comprise an olefin.

7. A method for recycling a packaging material for recycling, comprising a step of heating and decolorizing a packaging material for recycling having a printed layer containing a dye (A) whose thermal decomposition temperature or sublimation temperature is 150°C or higher and 270°C or lower and which does not decolorize at 25°C or higher and 120°C or lower.

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