Organic solvent-based printing ink with releasability, printed matter and laminate

Abstract

To provide an organic solvent-based printing ink which can desorb ink from a plastic film by an alkali aqueous solution and can suppress re-attachment to the plastic film of a micronized ink piece after desorption, in a laminate having good printing processing suitability and having a surface printing structure and a laminate structure.SOLUTION: Organic solvent-based printing ink is used for forming a desorption layer for desorbing and recycling a base material 1 from a printed matter or a laminate having a base material 1, a desorption layer, and a pattern layer and / or a base material 2 in this order, wherein the organic solvent-based printing ink contains an urethane resin having an acidic group at a terminal.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an organic solvent-based printing ink having releasability, and to a printed matter and a laminate using the same. [Background technology]

[0002] In recent years, packaging, plastic bottles, and other plastic products made from plastic film have been discarded and dumped into the ocean as litter, causing environmental pollution problems. These plastic products break down in seawater, turning into submicron-sized fragments (microplastics), which float in the water. When these plastics are ingested by fish and other marine organisms, they become concentrated in their bodies. This raises concerns about the health of seabirds and humans who consume these marine organisms as food. Furthermore, in the case of laminated packaging, as described below, substances harmful to the human body remain attached to the surface of microplastics due to inks, adhesives, and even coating layers, which is of concern from the perspective of environmental conservation.In order to address this issue, various efforts have been launched to reduce microplastics.

[0003] The plastic products mentioned above primarily include food packaging using plastic substrates. These packages use a variety of plastic substrates, including polyester (PET), nylon (NY), and polypropylene (OPP), as film substrates. These are coated with a design layer using gravure ink, flexographic ink, or other printing inks, and then laminated with a heat-melt resin substrate via an adhesive or the like to form a laminate. The laminate is then cut to an appropriate size and heat-sealed to form a package. Package configurations include those in which the design layer is the outermost layer of the package (called surface printing) and those in which the design layer is present as an intermediate layer between substrates (called laminate or reverse printing). Surface printing refers to a form in which the design layer is not laminated with a substrate or the like, and the design layer is exposed, such as when used on a label.

[0004] Attempts to reduce the amount of microplastics mentioned above include (1) replacing plastic substrates with paper in the above-mentioned packaging, (2) simplifying recycling by limiting the use of plastic substrates to the same type only (called mono-materialization), and (3) recycling plastics after removing impurities.

[0005] In the case of (1) above, using paper as the raw material is promising in terms of safety and recyclability, but it poses problems because its gas barrier properties and water resistance are inferior to those of plastic substrates. While paper coating agents and other materials are being investigated, practical application remains a high hurdle. In the case of (2) above, attempts are being made to recycle the substrate by replacing the plastic substrate with a polyolefin substrate such as polypropylene. However, there is a problem in that the polyolefin substrate does not provide the performance required for applications that require high functionality, such as retort resistance and light blocking. For this reason, technological development is being carried out for the above-mentioned (3) after comprehensively considering recycling efficiency and package performance.

[0006] As for (3) above, attempts have been made to remove the pattern layer (surface-printed ink layer) on the outer surface of a package, which becomes an impurity during the recycling process of plastic substrates, using an alkaline aqueous solution. For example, Patent Document 1 discloses a technology in which an undercoat layer made of an acrylic resin or a styrene-maleic acid resin is provided on a plastic substrate, and the surface-printed layer disposed on the undercoat layer is removed using an alkaline aqueous solution. Furthermore, Patent Document 2 discloses a technology in which an ink containing a urethane resin or an acrylic resin having an acidic group as a binder resin is surface-printed, and the printed layer is then removed using an alkaline aqueous solution. Patent Document 2 discloses a technique for removing ink, which uses a urethane resin having acidic and hydroxyl groups as a binder resin, from a surface-printed print layer and a laminate using an alkaline aqueous solution. However, when removing the ink from the print layer, there is a problem in that the ink film that has peeled off from the substrate reattaches to the substrate, causing the film to become discolored.

[0007] In plastic recycling, improving the quality of recycled products is an extremely important technology when it comes to using recycled plastics again as products such as film and packaging. However, although there are prior documents on techniques for removing ink films, no technology has yet been reported that can prevent the ink particles removed after recycling from re-adhering. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-131484 [Patent Document 2] Japanese Patent Application Publication No. 11-209677 Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention aims to provide an organic solvent-based printing ink that has good printability, meets the performance requirements of packaging materials in surface-printed and laminated configurations, and is capable of removing ink and the like from plastic films using an alkaline aqueous solution, while also making it possible to prevent the removed ink from re-adhering to the printing substrate. [Means for solving the problem]

[0010] As a result of extensive research into the problem, the present inventors have found that the problem can be solved by using the organic solvent-based printing ink described below, and have thus achieved the present invention.

[0011] That is, one embodiment of the present invention is an organic solvent-based printing ink used to form a release layer for recycling by peeling off the substrate 1 from a printed matter or laminate having a substrate 1, a release layer, and a picture layer and / or a substrate 2 in this order, The present invention relates to an organic solvent-based printing ink, wherein the organic solvent-based printing ink contains a urethane resin having an acidic group at the terminal thereof.

[0012] The present invention also relates to the organic solvent-based printing ink, wherein the urethane resin having an acidic group at its terminal has an acid value of 15 to 70 mgKOH / g.

[0013] The present invention also relates to the organic solvent-based printing ink, wherein the acid value derived from the acidic groups at the ends of the urethane resin having acidic groups at the ends is 1 to 50 mgKOH / g.

[0014] The present invention also relates to the organic solvent-based printing ink, wherein the urethane resin having an acidic group at its terminal has a hydroxyl value of 1 to 35 mgKOH / g.

[0015] The present invention also relates to the organic solvent-based printing ink, wherein the acidic group at the end of the urethane resin is derived from an acid anhydride having a ring structure.

[0016] The present invention also relates to the organic solvent-based printing ink, which is a clear ink.

[0017] The present invention also relates to a printed matter having, on a substrate 1, a release layer composed of the above organic solvent-based printing ink.

[0018] The present invention also relates to a laminate having at least a substrate 1, a release layer made of the organic solvent-based printing ink, and a substrate 2.

[0019] The present invention also provides a method for producing a recycled substrate, comprising the step of immersing a printed material in a basic aqueous solution, The printed matter is formed by printing a substrate 1, a release layer formed by the organic solvent-based printing ink, and a picture layer in this order, The method for producing a recycled substrate, wherein the basic aqueous solution contains a basic compound in an amount of 0.5 to 15% by mass of the entire basic aqueous solution, and the temperature of the basic aqueous solution during immersion is from room temperature to 120°C.

[0020] The present invention also provides a method for producing a recycled substrate, comprising the step of immersing a laminate in a basic aqueous solution, the laminate has a release layer formed by the organic solvent-based printing ink between a substrate 1 and a substrate 2, The method relates to a recycled substrate manufacturing method, wherein the basic aqueous solution contains a basic compound in an amount of 0.5 to 15% by mass of the entire basic aqueous solution, and the temperature of the basic aqueous solution during immersion is room temperature to 120°C. [Effects of the Invention]

[0021] By using the organic solvent-based printing ink according to an embodiment of the present invention, it is possible to provide an organic solvent-based printing ink that can remove ink and the like from a plastic film using an alkaline aqueous solution in a laminate having a surface printing configuration and a laminate configuration, and that can prevent the ink film that has been removed from the substrate from re-adhering to the substrate. DETAILED DESCRIPTION OF THE INVENTION

[0022] The following describes in detail the embodiments of the present invention, but the following description of the embodiments or requirements is merely an example of how the present invention can be implemented, and the present invention is not limited to these details as long as it does not deviate from the gist of the present invention.

[0023] In the following description, "organic solvent-based printing ink" may be abbreviated simply as "printing ink" or "ink," but these terms are synonymous. Furthermore, a layer formed from an organic solvent-based printing ink is identical to a "detachment layer capable of being detached from a substrate," and may be referred to simply as a "detachment layer" or "ink layer," but these terms are synonymous. In contrast, a printing ink that is not printed directly on a substrate and does not affect the detachment function is referred to as a "picture ink," and its printed layer is referred to as a "picture ink layer" or "picture layer." However, the picture ink may contain a urethane resin having an acidic group at its terminal, and thus may have the detachment function. Furthermore, a layer that is the same layer but has a portion that is printed directly on the substrate and a portion that is not printed directly on the substrate but is printed via a layer made of a primer (also called a clear ink), as described below, is classified as a "detachment layer."

[0024] A typical embodiment of the present invention is an organic solvent-based printing ink for forming a detachment layer capable of being detached from a substrate, the printing ink being an organic solvent-based printing ink used to peel off a picture layer and / or substrate 2 from a printed matter or laminate having substrate 1, a detachment layer, and a picture layer and / or substrate 2 in this order, thereby forming a detachment layer for recycling substrate 1, and the organic solvent-based printing ink contains a urethane resin having an acidic group at its terminal. The acidic groups at the terminals of urethane resins facilitate the ink layer removal in an alkaline aqueous solution due to the neutralizing interaction with the alkali. The use of acid anhydrides to introduce acidic groups at the terminals makes it possible to prevent the ink components that have been removed from re-adhering to the substrate in the alkaline solution. This effect is further improved when the acid value is between 1 and 50 mg KOH / g.

[0025] However, the organic solvent-based printing ink does not include cases where the acidic component of the urethane resin is neutralized in the ink and the ink has substantially no acid value.

[0026] The term "detachment" as used herein refers to the detachment of the detachment layer from the substrate 1 by neutralization, dissolution, or the like in a basic aqueous solution (alkaline aqueous solution). There are no particular limitations on the basic substance used in the basic aqueous solution, but suitable examples include sodium hydroxide (NaOH), potassium hydroxide (KOH), calcium hydroxide (Ca(OH)2), ammonia, barium hydroxide (Ba(OH)2), and sodium carbonate (Na2CO3). NaOH and / or KOH are preferred. However, the detachment conditions of the present invention are not limited to these. The term "detachment" includes both cases where the detachment layer dissolves and peels off from the substrate, and cases where the detachment layer swells without dissolving and peels off.

[0027] The above-mentioned "re-adhesion" refers to the ink components that have been once detached from the substrate due to dissolution or swelling in a basic aqueous solution (alkaline aqueous solution), and then re-adhere to the substrate.

[0028] The alkaline aqueous solution detaches the release layer from the substrate, but this also includes the case where a design layer, adhesive layer, substrate not in contact with the release layer, etc., which will be described later, are detached together with the release layer.

[0029] The present invention aims to obtain the substrate after detachment as a recycled substrate or regenerated substrate, and a preferred embodiment is one in which as many layers as possible, such as the detachment layer, the design layer, and other layers, are removed from the substrate. Specifically, "having the ability to detach from the substrate" means that, of 100% by mass of the detachment layer, at least 50% by mass or more is detached in the area or thickness direction. It is preferable to use an embodiment in which 60% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more is removed. Furthermore, even if the reattached portion is calculated as not being detached, it is still more preferable that 90% by mass or more is removed.

[0030] The release layer is provided for the purpose of obtaining a recycled substrate. Therefore, in the case of solder resist, color resist, etc., a step of dissolving a part of the layer with an alkaline aqueous solution is included, but the layer cured with active energy rays is intended to leave a certain amount even after the alkaline aqueous solution treatment, and therefore the technical concept is different from that of the release layer in the present invention. Therefore, the release layer in the present invention does not include cases where the release layer is a layer made of a photosensitive resin composition that is not intended for the recovery of recycled substrates, such as solder resist, color resist, etc.

[0031] The mechanism of detachment is thought to be that in a laminate including a detachment layer (for example, in the form of substrate 1 / detachment layer / substrate 2), the alkaline aqueous solution penetrates through the gaps between the substrates and comes into contact with the detachment layer, causing the detachment layer to dissolve or swell and become detached from the substrate. It is preferable to perform the detachment step in a form having a detachment layer on the cross section. Here, even if there are no gaps in the laminate through which the alkaline aqueous solution can penetrate, it is sufficient to cut the laminate in the detachment step and find that the cross section has a detachment layer. On the other hand, in a surface-printed product having a printed layer including a release layer (for example, in an embodiment such as substrate 1 / release layer / pattern layer), the alkaline aqueous solution penetrates the pattern layer and contacts the release layer in addition to the cross section, so release can be performed without any restrictions on the cross section. However, in either the surface-printed product or the laminated product, it is preferable to perform the release treatment by cutting.

[0032] (detachment layer) The release layer in an embodiment of the present invention is formed from an organic solvent-based printing ink, as described below. First, the urethane resin contained as a binder resin in the organic solvent-based printing ink will be described. The binder resin refers to the main resin component for forming the release layer. "Main" means that it accounts for 50% by mass or more of the total amount of resin components that make up the release layer.

[0033] <Urethane resin> In an embodiment of the present invention, the urethane resin is characterized by having acidic groups at its terminals. The acid value derived from the acidic groups at its terminals is preferably 1 to 50 mgKOH / g, more preferably 3 to 40 mgKOH / g, even more preferably 5 to 30 mgKOH / g, and particularly preferably 5 to 20 mgKOH / g. Furthermore, the urethane resin may also have an acid value in its side chains, and the total acid value derived from the side chains and the terminal acidic groups (hereinafter also referred to as the total acid value) is preferably 15 to 70 mgKOH / g, more preferably 20 to 50 mgKOH / g, and even more preferably 25 to 40 mgKOH / g. In a preferred embodiment, the urethane resin further has a hydroxyl value, and the hydroxyl value is preferably 1 to 35 mgKOH / g. 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 groups in 1 g of resin calculated by esterifying or acetylating the hydroxyl groups 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 in accordance with JIS K0070. From the viewpoint of the balance between releasability by an alkaline aqueous solution and retort resistance, the urethane resin preferably has a total acid value of 20 to 50 mgKOH / g, more preferably 25 to 40 mgKOH / g, and more preferably a hydroxyl value of 10 to 30 mgKOH / g, even more preferably 15 to 27 mgKOH / g.

[0034] The weight-average molecular weight (Mw) of the urethane resin is preferably 10,000 to 100,000, more preferably 12,000 to 70,000, and even more preferably 15,000 to 50,000. This is because it improves blocking resistance, work efficiency in the printing process for organic solvent-based printing inks, printability, and the like.

[0035] The urethane resin may have an amine value, and if it does, the amine value is preferably 0.1 to 20 mgKOH / g, and more preferably 1 to 10 mgKOH / g, because this improves the adhesion to the substrate.

[0036] (Urethane resin with terminal acidic groups) The urethane resin includes those having an acidic group at the end. There is no limitation on the method for introducing the acidic group at the end of the urethane resin, and any method can be applied. In one embodiment, the introduction of the terminal acidic group into the urethane resin can be achieved, for example, by preparing a urethane resin having an amino group at the terminal, obtained by reacting a polyisocyanate, a polyol, a polyhydroxy acid, and a polyamine, and then reacting an acid anhydride with the amino group (hereinafter also referred to as modification), thereby imparting an acid value to the terminal of the urethane resin. Note that any known method can be used to introduce the acidic group into the terminal of the urethane resin, and the method is not limited to the above.

[0037] (Urethane resin modified with acid anhydride) The urethane resin modified with an acid anhydride preferably has a structural unit derived from the acid anhydride at the terminal of the urethane resin (a urethane resin modified with an acid anhydride having a ring structure), and the acid anhydride used is not limited, but preferably has an aromatic ring or an alicyclic structure (hereinafter referred to as cyclic).

[0038] (Acid anhydrides having a ring structure) The acid anhydride having a ring structure is preferably an anhydride of a cyclic dicarboxylic acid, specifically phthalic anhydride, trimellitic anhydride, 1,8-naphthalene anhydride, cis-4-cyclohexene-1,2-dicarboxylic anhydride, cis-4-cyclohexane-1,2-dicarboxylic anhydride, pyromellitic anhydride, exo-3,6-epoxy-1,2,3,6-tetrahydrophthalic anhydride, etc. Among them, phthalic anhydride is preferred. However, non-cyclic acid anhydrides such as succinic anhydride, itaconic anhydride, and maleic anhydride may also be used.

[0039] The urethane resin having a terminal amino group and the acid anhydride can be obtained by reacting 0.1 to 1 mole of the acid anhydride, assuming that the equivalent of the amino group is 1. The reaction is carried out in an organic solvent, and there are no particular limitations. As reaction conditions, the temperature is preferably 20 to 80°C, and the time is preferably 30 minutes to 3 hours.

[0040] (Polyisocyanate) The polyisocyanate used in the urethane resin used in the organic solvent-based printing ink of the present invention 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, Suitable examples of such diisocyanates 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 dimer diisocyanate in which the carboxyl groups of dimer acid are converted to isocyanate groups, as well as other alicyclic diisocyanates. These may be used alone or in combination of two or more.

[0041] 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 trimers to form triisocyanates having an isocyanurate structure.

[0042] (Polyol) The urethane resin used in the organic solvent-based printing ink of the present invention has structural units derived from a polyol, and the polyol is not particularly limited, and suitable polyols include, but are not limited to, polyether polyols, polyester polyols, polycarbonate polyols, etc. Polyol is a general term for compounds having at least two hydroxyl groups in one molecule, but does not include polyhydroxy acids, which will be described later.

[0043] Further, other polyols such as dimer diol, hydrogenated dimer diol, castor oil-modified polyol, etc. The urethane resin preferably contains at least one structural unit selected from polyether structural units, polyester structural units, and polycarbonate structural units, and more preferably contains a structural unit derived from a polyester polyol.

[0044] The urethane resin preferably contains 10 to 75 mass % of structural units derived from polyol, more preferably 15 to 70 mass %, and even more preferably 20 to 65 mass %, based on the total mass of the urethane resin.

[0045] The polyol is preferably used in such a manner that the polyester polyol-derived structural units comprise 5% by mass or more of the total mass of the polyol-derived structural units. A content of 30% by mass or more is even more preferred, and a content of 40% by mass or more is even more preferred. Incorporating a polyhydroxy acid (described below) into the urethane resin not only provides alkali-induced releasability, i.e., the ability to remove the release layer and the pattern layer from the plastic substrate using an alkaline aqueous solution, but also further improves releasability by alkaline hydrolysis of the ester bond moieties of the polyester polyol. Therefore, a content of 50% by mass or more is preferred, a content of 70% by mass or more is even more preferred, and a content of 80% by mass or more is even more preferred.

[0046] The number average molecular weight of the polyol is preferably 500 to 10,000. The number average molecular weight used here for the polyol 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 polyol has excellent blocking resistance to plastic films. Furthermore, when the number average molecular weight of the polyol is 500 or more, the urethane resin coating has excellent flexibility and adhesion to plastic films. For these reasons, the number average molecular weight is more preferably 1,000 to 5,000.

[0047] (polyester polyol) Suitable examples of polyester polyols include polyester polyols formed from a condensation product of a dibasic acid and a diol, and polyester polyols formed from polylactone polyols, which are ring-opening polymerization products of cyclic ester compounds. Polyester diols are preferred. Suitable dibasic acids 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, with adipic acid and succinic acid being particularly preferred. 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. The polyester polyols can be used alone or in combination of two or more. Furthermore, a polyol having three or more hydroxyl groups and a polycarboxylic acid having three or more carboxyl groups can also 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.

[0048] The polyester diol also preferably contains a structural unit derived from a polyester, which is a condensation product of a diol having a branched structure and a dibasic acid, because this can improve adhesion to plastic substrates. The diol having a branched structure is preferably a diol having a structure in which at least one hydrogen atom of an alkylene glycol is substituted with an alkyl group. Suitable examples of diols having a branched structure include 1,2-propanediol (propylene glycol), 1,3-butanediol, 2-methyl-1,3-propanediol, neopentyl glycol, 1,4-pentanediol, 3-methyl-1,5-pentanediol, 2,5-hexanediol, 2-methyl-1,4-pentanediol, 2,4-diethyl-1,5-pentanediol, 2-butyl-2-ethyl-1,3-propanediol, 2-methyl-1,8-octanediol, 2,2,4-trimethyl-1,3-pentanediol, and 2,2,4-trimethyl-1,6-hexanediol. Among these, at least one selected from 1,2-propanediol, 3-methyl-1,5-pentanediol, neopentyl glycol, and 2-butyl-2-ethyl-1,3-propanediol is preferred, and the use of polyester polyols containing 1,2-propanediol (propylene glycol) and / or 3-methyl-1,5-pentanediol is even more preferred.

[0049] (Polyhydroxy acid) Polyhydroxy acid refers to a compound having both multiple hydroxyl groups (active hydrogen groups) and an acidic functional group in one molecule. The acidic groups derived from the polyhydroxy acid are located on the side chain of the urethane resin. While there are no particular limitations on the polyhydroxy acid, preferred examples include dimethylolalkanoic acids such as 2,2-dimethylolpropionic acid, 2,2-dimethylolbutanoic acid, and 2,2-dimethylolvaleric acid. These may be used alone or in combination, and the acid value of the urethane resin may be adjusted appropriately to 15 to 70 mgKOH / g. The acid value is measured according to JIS K0070.

[0050] In the above, the acidic functional group refers to a functional group that can be neutralized with potassium hydroxide when measuring the acid value, and specific examples include a carboxyl group and a sulfonic acid group, with a carboxyl group being preferred. Note that, since there is a high probability that the acidic group will remain unreacted with the isocyanate group during the synthesis process of the urethane resin, it allows the urethane resin to maintain its acid value.

[0051] Furthermore, the urethane resin is preferably a urethane resin obtained by reacting a polyisocyanate, a polyol, and a polyhydroxy acid to form a urethane prepolymer having an isocyanate group at its terminal, and then reacting the resulting prepolymer with a polyamine (a chain extension reaction). In this case, urea bonds are generated in addition to urethane bonds. The polyisocyanate, polyol, and polyhydroxy acid used are preferably the same as those described above.

[0052] (Polyamine) The polyamine preferably contains a diamine, and suitable examples of the diamine include, but are not limited to, ethylenediamine, propylenediamine, hexamethylenediamine, isophoronediamine, dicyclohexylmethane-4,4'-diamine, and dimer diamine obtained by converting the carboxyl groups of dimer acid to amino groups. These can be used alone or in combination of two or more. Particularly preferred are diamines having hydroxyl groups, such as 2-hydroxyethylethylenediamine, 2-hydroxyethylpropylenediamine, di-2-hydroxyethylethylenediamine, di-2-hydroxyethylpropylenediamine, 2-hydroxypropylethylenediamine, and di-2-hydroxypropylethylenediamine. By using these, a certain amount of hydroxyl groups remain unreacted in the urethane resin production process, allowing the urethane resin to have a hydroxyl value. Amino acids can also be used for chain extension. An amino acid refers to a compound having both an amino group and an acidic functional group in one molecule, and preferred examples include glutamine, asparagine, lysine, diaminopropionic acid, ornithine, diaminobenzoic acid, and diaminobenzenesulfonic acid. Since there is a high probability that the acidic group will remain unreacted with the isocyanate group during the synthesis of the urethane resin, the acid value can be maintained in the urethane resin.

[0053] (polymerization terminator) A polymerization terminator can also be used in combination with the polyamine. Examples of such a polymerization terminator include dialkylamine compounds such as di-n-dibutylamine, amine compounds having a hydroxyl group, such as monoethanolamine, diethanolamine, butanolamine, 2-amino-2-methyl-1-propanol, tri(hydroxymethyl)aminomethane, 2-amino-2-ethyl-1,3-propanediol, N-di-2-hydroxyethylethylenediamine, N-di-2-hydroxyethylpropylenediamine, and N-di-2-hydroxypropylethylenediamine; Further examples include monoamine amino acid compounds such as glycine, alanine, glutamic acid, taurine, aspartic acid, aminobutyric acid, valine, aminocaproic acid, aminobenzoic acid, aminoisophthalic acid, sulfamic acid, etc. In order to impart a hydroxyl value to the urethane resin, it is preferable to use an amine compound having a hydroxyl group.

[0054] (Synthesis of urethane resin) A method for synthesizing a urethane resin according to an embodiment of the present invention will be described. Urethane resins are produced by reacting polyisocyanate, polyol, and polyhydroxy acid (referred to as a urethane-forming process). The reaction ratio (NCO / OH) of the polyisocyanate, polyol, and polyhydroxy acid is preferably 1.05 to 3.0, more preferably 1.1 to 2.8. The urethane-forming reaction process is preferably carried out at a temperature of 70 to 90°C for 2 to 8 hours, using an organic solvent inert to isocyanate groups as needed, and further using a catalyst if necessary. During this process, polyisocyanate can be added dropwise at an appropriate speed while the polyol and organic solvent are being mixed and stirred. The stirring speed during the reaction is preferably such that the reaction solution is mixed uniformly, and is preferably neither excessively slow nor excessively fast, but is appropriate and uniform.

[0055] When the urethane resin is further subjected to a chain extension reaction with a polyamine as a urethane prepolymer having isocyanate groups at its terminals obtained in the urethane-forming reaction step (referred to as a urea-forming reaction step), it is preferable to appropriately set the solids content of the urethane prepolymer or polyamine before carrying out the reaction, and it is preferable to control the dropping speed at a relatively slow, constant rate. Because the viscosity of the urea-forming reaction step changes significantly as the reaction proceeds, it is preferable to obtain a homogeneous reaction solution, and it is also preferable to set the stirring speed at a relatively high rate. Furthermore, the ratio of isocyanate groups in the urethane prepolymer to amino groups in the polyamine, or amino groups / NCO, is preferably 0.7 to 1.0, and the reaction is preferably carried out at a temperature range of 20 to 60°C for 1 to 8 hours.

[0056] Furthermore, in the urethane resin according to the embodiment of the present invention, the terminal amino groups of the urethane resin obtained in the urea-forming reaction step are reacted with an acid anhydride to modify the terminals with an acid. The reaction is preferably carried out at a temperature of 20 to 80°C for 30 minutes to 3 hours.

[0057] (Combined resin) In embodiments of the present invention, the binder resin may be suitably used in combination with other resins in addition to the urethane resins described above. Examples include, but are not limited to, cellulose-based resins, polyamide resins, vinyl chloride-based resins such as vinyl chloride-vinyl acetate copolymer resins and vinyl chloride-acrylic copolymer resins, rosin-based resins, ethylene-vinyl acetate copolymer resins, vinyl acetate resins, acrylic resins, styrene resins, dammar resins, styrene-maleic acid copolymer resins, styrene-acrylic copolymer resins, polyester resins, alkyd resins, terpene resins, phenol-modified terpene resins, ketone resins, cyclized rubber, chlorinated rubber, butyral, polyacetal resins, petroleum resins, and modified resins thereof. These resins can be used alone or in combination. Among these, at least one resin selected from the group consisting of vinyl chloride-based resins, acrylic resins, cellulose-based resins, styrene-maleic acid copolymer resins, and rosin-based resins is preferred. At least one resin selected from the group consisting of vinyl chloride-based resins, styrene-maleic acid copolymer resins, and rosin-based resins is even more preferred. It is more preferable that the mass ratio of the urethane resin to the co-resin is 95:5 to 50:50, since this makes it easier to recover the detached design layer and the like.

[0058] <Organic solvents> The organic solvent-based printing ink of the present invention contains an organic solvent. While the organic solvent is not limited to the following, known organic solvents can be used, including aromatic organic solvents such as toluene and xylene; ketone-based organic solvents such as methyl ethyl ketone and methyl isobutyl ketone; ester-based organic solvents such as ethyl acetate, n-propyl acetate, isopropyl acetate, and isobutyl acetate; alcohol-based organic solvents such as methanol, ethanol, n-propanol, isopropanol, and n-butanol; and glycol ether-based solvents such as ethylene glycol monopropyl ether and propylene glycol monomethyl ether. Mixtures of these organic solvents are preferred. Among these, organic solvents that do not contain aromatic organic solvents such as toluene and xylene (non-toluene organic solvents) are preferred because they improve the stability over time of gravure inks containing hydrocarbon waxes. Ketone-based organic solvents are even more preferred, and ester-based organic solvents and alcohol-based organic solvents are even more preferred. When ester-based organic solvents and alcohol-based organic solvents are used, a mixed organic solvent containing an ester-based organic solvent:alcohol-based organic solvent ratio of 90:10 to 40:60 by mass is more preferred. The ink may further contain a glycol ether organic solvent in an amount of 5% by mass or less relative to 100% by mass of the ink.

[0059] <Additives> The organic solvent-based printing ink may contain conventionally known additives as appropriate, and in the production of gravure ink, additives such as pigment derivatives, dispersants, wetting agents, adhesion aids, leveling agents, antifoaming agents, antistatic agents, viscosity modifiers, metal chelates, trapping agents, antiblocking agents, wax components other than those mentioned above, isocyanate-based curing agents, and silane coupling agents may be used as needed.

[0060] <Organic solvent-based printing ink> The organic solvent-based printing ink of the present invention includes clear ink and color ink, but does not exclude inks that further contain organic solvents or other inks, etc., within the scope of the present invention.

[0061] <Clear ink (hereinafter also referred to as primer)> The clear ink is printed to form a release layer, which is a primer layer. The term "clear ink" refers to an ink or printed layer that is roughly opaque or colorless and transparent, and does not exclude slight coloring due to binder resins, extender pigments, additives, etc. The clear ink is preferably used as a primer for a design layer, etc. The embodiment of the primer is included in the laminate structure described below. The clear ink preferably has a solids content of 5 to 50% by mass, more preferably 10 to 40% by mass, based on the total mass of the ink. Furthermore, the binder resin content is preferably 0.5 to 50% by mass, more preferably 5 to 30% by mass, based on the total mass of the ink. By keeping the content within the above range, the viscosity of the clear ink becomes appropriate, and when the ink is applied to a plastic film using any printing method, printability such as halftone dot reproducibility is improved. Note that "solids content" refers to the total mass % of non-volatile components.

[0062] (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 these, silica is preferred, and its hydrophilicity is preferable. The average particle size of the extender pigment is preferably 0.5 to 10 μm, and more preferably 1 to 8 μm. The content of the extender pigment in the total ink mass is preferably 0.5 to 10 mass%, and more preferably 1 to 5 mass%. This is because the wettability of the pattern ink is improved when the pattern ink is overprinted.

[0063] <Color ink> Color ink refers to organic solvent-based printing ink containing a colorant, and does not include the clear ink described above. The colorant component is preferably a color dye and / or a color pigment. The solids content of the color ink is preferably 5 to 50% by mass, more preferably 10 to 40% by mass, of the total ink. The colorant content is preferably 1 to 50% by mass, more preferably 3 to 15% by mass, of the total ink, sufficient to ensure the ink's density and coloring strength. The binder resin content is preferably 0.5 to 50% by mass, more preferably 5 to 30% by mass, in terms of solids, of the total ink. The above ranges ensure the color ink has an appropriate viscosity, resulting in good printability, such as halftone dot reproducibility, when applied to plastic film using any printing method. Color inks may also contain supplementary extender pigments, preferably the same as those used for the clear ink described above.

[0064] (color pigments) The colorant is preferably a pigment, and the mass ratio of the binder resin to the color pigment (binder resin / pigment) is preferably 99 / 1 to 10 / 90, and more preferably 80 / 20 to 20 / 80. The color pigment is preferably an organic pigment or an inorganic pigment, and inorganic pigments containing titanium oxide are preferred, while organic pigments made of organic compounds or organometallic complexes are preferred.

[0065] Of the color pigments, organic pigments include, but are not limited to, soluble azo pigments, insoluble azo pigments, azo pigments, phthalocyanine pigments, halogenated phthalocyanine pigments, anthraquinone pigments, anthanthrone pigments, dianthraquinonyl pigments, anthrapyrimidine pigments, perylene pigments, perinone pigments, quinacridone pigments, thioindigo pigments, dioxazine pigments, isoindolinone pigments, quinophthalone pigments, azomethine azo pigments, flavanthrone pigments, diketopyrrolopyrrole pigments, isoindoline pigments, indanthrone pigments, and carbon black pigments. Further examples include carmine 6B, lake red C, permanent red 2B, disazo yellow, pyrazolone orange, carmine FB, cromophtal yellow, cromophtal red, phthalocyanine blue, phthalocyanine green, dioxazine violet, quinacridone magenta, quinacridone red, indanthrone blue, pyrimidine yellow, thioindigo bordeaux, thioindigo magenta, perylene red, perinone orange, isoindolinone yellow, aniline black, diketopyrrolopyrrole red, and daylight fluorescent pigments.

[0066] Among the color pigments, inorganic pigments include white inorganic pigments such as titanium oxide, zinc oxide, zinc sulfide, and chromium oxide. Among the inorganic pigments, titanium oxide is particularly preferred. Titanium oxide exhibits a white color and is preferred in terms of coloring power, hiding power, chemical resistance, and weather resistance. From the viewpoint of printing performance, titanium oxide that has been treated with silica and / or alumina is preferred.

[0067] Among the color pigments, examples of inorganic pigments other than white include aluminum particles, mica, bronze powder, chrome vermilion, yellow lead, cadmium yellow, cadmium red, ultramarine, Prussian blue, red iron oxide, yellow iron oxide, iron black, titanium oxide, and zinc oxide. Aluminum is in the form of a powder or paste, but it is preferably used in the form of a paste from the standpoint of handleability and safety, and may be either a leafing type or a non-leafing type.

[0068] <Manufacture of organic solvent-based printing inks> Organic solvent-based printing inks can be produced by dissolving and / or dispersing a binder resin, an extender pigment, a coloring pigment, etc. in an organic solvent. For example, an organic solvent-based printing ink can be produced by dispersing a pigment, a binder resin such as a urethane resin or vinyl chloride-vinyl acetate copolymer resin, silica particles, and, if necessary, an organic solvent, and then blending the urethane resin, if necessary, the organic solvent, and other resins and additives into the pigment dispersion. The viscosity and color of the organic solvent-based printing ink can be adjusted by appropriately adjusting the size of the grinding media in the disperser, the packing ratio of the grinding media, the dispersion treatment time, the discharge speed of the pigment dispersion, the viscosity of the pigment dispersion, and the like. Commonly used dispersers, such as roller mills, ball mills, pebble mills, attritors, and sand mills, can be used as dispersers. Production using a sand mill is preferred.

[0069] The viscosity of organic solvent-based printing inks is preferably in the range of 20 to 1500 mPa·s, and more preferably 50 to 1000 mPa·s, because this ensures appropriate printability during the printing process. The viscosity of the printing ink can be adjusted by the amount of the urethane resin and other binder resins, the amount of organic solvent, and the pigment dispersion conditions.

[0070] (Picture layer) The design layer is a layer printed on the primer layer and may be formed using a printing ink that does not have the above-mentioned releasability. Specific examples of suitable printing inks include screen ink, gravure ink, flexographic ink, inkjet ink, offset ink, and other printing inks. For example, printing inks described in JP-A-2005-298618, JP-A-2006-299136, JP-A-2009-249388, JP-A-2013-127038, JP-A-2017-19991, JP-A-2006-131844, JP-A-2013-40248, JP-A-2007-231148, and JP-A-2006-257302 can be suitably used. However, the invention is not limited to these. Among these, gravure ink, flexographic ink, and inkjet ink are preferably used, and gravure ink and / or flexographic ink are more preferably used.

[0071] <Printing with organic solvent-based printing ink> Suitable printing methods for organic solvent-based printing inks include screen printing, offset printing, flexographic printing, dry offset printing, gravure printing, and inkjet printing. Of these, gravure printing and flexographic printing are particularly preferred.

[0072] <Gravure printing> (Photogravure version) A gravure plate is a cylindrical metal plate, and recesses for each color are created by engraving, etching, or laser. There are no restrictions on the use of engraving or laser, and they can be set arbitrarily to suit the pattern. Lines per page are appropriately set to 100 to 300 lines per page, and the higher the line per page, the finer the printing. The thickness of the printing layer is preferably 0.1 μm to 100 μm.

[0073] (gravure printing machine) In a gravure printing press, each printing unit is equipped with the gravure plate and doctor blade. There are multiple printing units, and printing units can be set up to handle organic solvent-based printing inks and pattern inks, and each unit has an oven drying unit. Printing is done by rotary printing using a web printing method. The type of plate and doctor blade can be selected appropriately to suit the specifications.

[0074] <Flexographic printing> (flexographic plate) Plates used in flexographic printing include photosensitive resin plates that use UV curing with a UV light source, and elastomer material plates that use direct laser engraving. Regardless of the method used to form the image area of ​​the flexographic plate, plates with a screening line count of 75 lpi or more are used. Any sleeve or cushion tape can be used to attach the plate. (Flexographic printing machine) Flexographic printing machines include CI type multicolor flexographic printing machines and unit type multicolor flexographic printing machines, and ink supply methods include chamber methods and two-roll methods, and any appropriate printing machine can be used.

[0075] <Printed matter and laminates> The form of the printed matter and laminate in the embodiment of the present invention is not limited, but the following forms are preferred. · Base material 1 / Release layer (clear) / Pattern layer Base material 1 / detachment layer (color) / pattern layer Substrate 1 / Removal layer (clear) / Adhesive layer / Substrate 2 Substrate 1 / Removal layer (color) / Adhesive layer / Substrate 2 Base material 1 / Removal layer (clear) / Pattern layer / Adhesive layer / Base material 2 Base material 1 / Removal layer (color) / Pattern layer / Adhesive layer / Base material 2 ·Picture layer / Release layer (clear) / Base material 1 / Adhesive layer / Base material 2 ·Picture layer / Release layer (color) / Base material 1 / Adhesive layer / Base material 2 Base material 1 / Removal layer (clear) / Pattern layer / Removal layer (clear) / Adhesive layer / Base material 2 Base material 1 / Removal layer (color) / Pattern layer / Removal layer (color) / Adhesive layer / Base material 2 In the above, "clear" refers to clear ink, and "color" refers to color ink.

[0076] <Base material 1> Substrates 1 to which organic solvent-based printing inks can be applied include polyethylene, polypropylene and other polyolefin substrates, polycarbonate substrates, polyethylene terephthalate, polylactic acid and other polyester substrates, polystyrene substrates, polystyrene-based resins such as AS resin and ABS resin, polyamide substrates, polyvinyl chloride substrates, various substrates made of polyvinylidene chloride, cellophane substrates, paper substrates, aluminum foil substrates, etc., or film or sheet substrates made of composite materials of these. Among these, polyester substrates and polyamide substrates with high glass transition temperatures are preferably used.

[0077] The substrate may be coated with a metal oxide or the like by vapor deposition on its surface and / or with polyvinyl alcohol, and examples thereof include GL-AE manufactured by Toppan Printing Co., Ltd., in which aluminum oxide is vapor-deposited on the substrate surface, and IB-PET-PXB manufactured by Dai Nippon Printing Co., Ltd. Furthermore, if necessary, a substrate treated with additives such as an antistatic agent or an ultraviolet inhibitor, or a substrate whose surface has been subjected to corona treatment or low-temperature plasma treatment, can also be used.

[0078] <Base material 2> The substrate 2 may be the same as or different from the substrate 1. Preferably, the substrate 2 is a thermoplastic substrate (sometimes called a sealant), and preferred are unstretched polyethylene substrates, unstretched polypropylene substrates, unstretched polyester substrates, etc.

[0079] The thickness of the substrate 2 is not particularly limited, and is preferably from 10 μm to 150 μm, more preferably from 20 μm to 70 μm, taking into consideration processability into packaging containers, heat sealing properties, etc. By providing the substrate 2 with unevenness having a height difference of about several μm, it is possible to impart slipperiness and tearability to the packaging material. The method for laminating the substrate 2 is not particularly limited, and examples include a method in which the printed surface of a laminated film having the substrate 1, a release layer, and a printing layer is bonded to the substrate 2 using a laminating adhesive; a method in which the resin that constitutes the substrate 2 is melted, extruded onto the printing layer, and cooled to solidify; and the like. Other layers such as an adhesive layer and other substrates may be present between the print layer and the substrate 2. Also, there may be a plurality of design layers, adhesive layers and other substrates.

[0080] <Adhesive layer> Bonding substrate 1 and substrate 2 requires a lamination process using an adhesive. Typical examples of lamination include extrusion lamination, dry lamination, and non-solvent lamination. Lamination is a method in which an adhesive layer is applied to one side of a printed material by coating and drying, and then laminated to substrate 2 by pressure bonding. Suitable adhesive layers include, but are not limited to, anchor agent layers, molten resin layers, urethane adhesive layers, and acrylic adhesive layers, and are obtained by melt extrusion, coating, or the like. For example, suitable urethane adhesives include two-component adhesives consisting of a mixture of polyol and isocyanate curing agent, and examples of polyols include polyester-based and polyether-based adhesives.

[0081] (Desorption process) The method for producing a recycled substrate according to an embodiment of the present invention includes a step of immersing a printed material or a laminate in a basic aqueous solution (an alkaline aqueous solution). As a condition for removing a release layer, etc. (a release layer, a design layer, or other layers) according to an embodiment of the present invention, the concentration of the alkaline aqueous solution is preferably 0.5 to 15% by mass, and more preferably 1 to 5% by mass. By keeping the concentration within the above range, the alkaline aqueous solution can maintain sufficient alkalinity for release. In the case of a printed matter, the alkaline aqueous solution penetrates the surface of the printed layer, and in the case of a laminate, the alkaline aqueous solution penetrates from the cross section, contacting the release layer and dissolving it, thereby enabling release. More preferably, the release layer is present on the cross section of the printed matter or laminate, allowing the picture ink layer, substrate, etc. to be released in a shorter time.

[0082] The immersion time in the basic aqueous solution is 1 minute to 12 hours, more preferably 1 minute to 6 hours. The recycled substrate can then be obtained by rinsing with water and drying. The removal rate of the release layer and accompanying pattern layer, adhesive layer, etc. from the substrate 1 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 release layer of the substrate, provided that the release ability of the release layer is uniform in the surface direction (not partially cured, etc.). It is preferable to perform the removal while stirring during immersion. For example, when stirring with a rotating blade of a stirring device, a rate of 80 to 250 rpm is preferred, and a rate of 80 to 200 rpm is even more preferred.

[0083] The temperature of the basic aqueous solution during immersion is preferably room temperature to 120°C, more preferably 25 to 110°C, more preferably 30 to 90°C, and even more preferably 35 to 80°C. The immersion time is 1 minute to 24 hours, more preferably 1 minute to 12 hours. When the plastic substrate (recycled substrate) is then washed with water and dried, the removal rate of the release layer and the accompanying pattern ink layer, adhesive layer, etc. is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more. The alkali concentration of the basic aqueous solution is preferably 0.5 to 15% by mass, more preferably 1.0 to 12% by mass, and even more preferably 1.5 to 10% by mass.

[0084] The amount of alkaline aqueous solution used is preferably 4 to 999 times the mass of the printed matter or laminate. Furthermore, among the alkaline aqueous solutions containing the printed matter or laminate, an embodiment in which the printed matter or laminate is contained in an amount of 0.1 to 20 mass% is preferably used. Furthermore, to improve efficiency, circulating washing, crushing, and stirring of the printed matter or laminate may be performed.

[0085] According to an embodiment of the present invention, a recycled plastic substrate (recycled substrate) can be obtained by removing the release layer from a printed matter or laminate in an alkaline aqueous solution, rinsing the substrate with water, and drying it. The recycled plastic substrate can also be recycled into pellets using an extruder or the like and reused. [Example]

[0086] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. In the present invention, parts and % represent parts by mass and % by mass unless otherwise noted.

[0087] (Molecular weight and molecular weight distribution) The weight average molecular weight (Mw), number average molecular weight (Mn) and molecular weight distribution (Mw / Mn) were measured by GPC (gel permeation chromatography) and calculated as molecular weights converted using polystyrene as a standard substance. GPC equipment: Showa Denko Shodex GPC-104 Columns: The following columns were used in series. Showa Denko Shodex LF-404 (2 pieces) Showa Denko Shodex LF-G Detector: RI (differential refractometer) Measurement conditions: Column temperature 40°C Eluent: tetrahydrofuran Flow rate: 0.3mL / min

[0088] (Acid value and hydroxyl value) In the following, the acid value and hydroxyl value were measured according to the method described in JIS K0070 (1992).

[0089] <Synthesis Example 1> (Synthesis of polyurethane resin P1) A four-neck flask equipped with a stirrer, thermometer, reflux condenser, and nitrogen gas inlet tube was charged with 136.3 parts of PPA (poly(propylene glycol) adipate diol with a number average molecular weight (Mn) of 2000), 13.6 parts of PPG (polypropylene glycol with an Mn of 2000), 25.1 parts of DMPA (2,2-dimethylolpropanoic acid), 3.9 parts of NPG (neopentyl glycol), 88.7 parts of IPDI (isophorone diisocyanate), and 200 parts of NPAC (normal propyl acetate). The mixture was reacted at 90°C for 3 hours under a nitrogen stream to obtain a solution of isocyanate-terminated prepolymer. The resulting prepolymer was then gradually added to a mixture of 16.9 parts of AEA (2-(2-aminoethylamino)ethanol), 0.2 parts of MEA (monoethanolamine), and 350 parts of IPA (isopropyl alcohol) at room temperature, and the mixture was then reacted at 50°C for 1 hour. Next, 11.3 parts of IPDI was added to adjust the amine value to 5.0 mgKOH / g, and then 4.0 parts of phthalic anhydride, equivalent to the amino groups, was added and reacted for 1 hour at 50° C. 150 parts of NPAC was added to the resulting resin solution to adjust the solids content, yielding an oil-based polyurethane resin P1 solution with a solids content of 30%, a mass average molecular weight of 26,000, Mw / Mn=2.8, a total acid value of 40.0 mgKOH / g, a hydroxyl value of 30.8, and a terminal acid value of 5.0 mgKOH / g. The proportion of polyester polyol in the polyol in P1 is 100% by mass.

[0090] Polyurethane resins (P2 to P18) were obtained in the same manner as in Synthesis Example 1, except that the raw materials and charging ratios shown in Table 1 were used. Mw, Mw / Mn, total acid value, hydroxyl value, and properties of terminal functional groups are shown in Table 1. The abbreviations for the raw material compounds shown in Table 1 that were not used in Synthesis Example 1 are as follows: BD: 1,4-butanediol IPDA: Isophoronediamine

[0091] [Comparative Synthesis Example 1] (Polyurethane Resin PP1) A reactor equipped with a reflux condenser, dropping funnel, gas inlet, stirrer, and thermometer was charged with 147.9 parts of PPA, 14.8 parts of PPG, 25.2 parts of DMBA, 96.8 parts of IPDI, and 200 parts of NPAC, and reacted at 90 °C for 3 hours to obtain a resin solution of isocyanate-terminated prepolymer. A mixture of 15.4 parts of AEA and 350 parts of IPA was added dropwise to the resulting isocyanate-terminated prepolymer over 60 minutes at room temperature to carry out a urea reaction, and the reaction was continued for another 3 hours at 70 °C to react the terminal isocyanate groups with IPA. The solids content was further adjusted using 150 parts of NPAC to obtain a polyurethane resin (PP1) solution with a solids content of 30%, a weight average molecular weight of 29,000, Mw / Mn = 3.2, an acid value of 35.1 mg KOH / g, and a hydroxyl value of 27.7 mg KOH / g. The proportion of polyester polyol in the polyol in P15 is 100% by mass.

[0092] [Comparative Synthesis Example 2] (Polyurethane Resin PP2) A polyurethane resin (PP2) was obtained in the same manner as in Comparative Synthesis Example 1, except that the raw materials and charging ratios shown in Table 1 were used. The terminals were blocked with MEA (monoethanolamine), and the terminal functional groups were hydroxyl groups. Mw, Mw / Mn, total acid value, hydroxyl value, and properties of the terminal functional groups are shown in Table 1.

[0093] [Comparative Synthesis Example 3] (Polyurethane Resin PP3) A polyurethane resin (PP3) was obtained by adjusting the amine value to 10.0 mg KOH / g in the same manner as in Comparative Synthesis Example 1, except that the raw materials and charging ratios shown in Table 1 were used. The solid content was then adjusted without terminal acid modification using an acid anhydride, and Mw, Mw / Mn, total acid value, hydroxyl value, and properties of terminal functional groups are shown in Table 1.

[0094] [Example 1] (Preparation of Clear Ink S1) Clear ink S1 was obtained by mixing 87 parts of polyurethane resin P1 solution (solid content 30%), 5 parts of ethyl acetate (EA), 5 parts of IPA, and 3 parts of silica (Mizukasil P-73 hydrophilic silica particles with an average particle size of 3.8 μm, manufactured by Mizusawa Chemical Industries, Ltd.) using a bladed mixer.

[0095] [Examples 2 to 18] (Preparation of clear inks S2 to S18) Clear inks S2 to S18 were obtained in the same manner as in Example 1, except that the raw materials and blending ratios shown in Table 2 were used.

[0096] [Example 19] (Preparation of Color Ink S19) 10 parts of copper phthalocyanine indigo (phthalocyanine LIONOL BLUE FG-7358-G manufactured by Toyocolor Co., Ltd.), 40 parts of polyurethane resin (P2), 3 parts of EA, and 3 parts of IPA were mixed and stirred, and the pigment was dispersed in a sand mill for 20 minutes. After that, 40 parts of urethane resin solution (P2), 2 parts of EA, and 2 parts of IPA were mixed and stirred to obtain indigo color ink (S19). Note that the total value for each component shown in Table 2 is shown.

[0097] (Comparative Examples 1 to 3) (Preparation of Inks SS1 to SS3) Inks SS1 to 3 were obtained in the same manner as in Example 1, except that the raw materials shown in Table 2 were used in the blending ratios shown.

[0098] <Creating printed materials using Clear Ink S1> (Printing configuration A: substrate 1 / release layer / pattern layer) Clear Ink S1 was diluted with an ethyl acetate / IPA mixed solvent (70 / 30 by mass) to a Zahn Cup #3 (manufactured by Rigo Co., Ltd.) for 15 seconds (25°C). Clear Ink S1 and Real NEX 39 Indigo BOS3 (organic solvent-based gravure ink, manufactured by Toyo Ink Co., Ltd.) were then printed in that order onto a corona-treated stretched polypropylene substrate (thickness 20 μm) using a gravure printing press equipped with a gravure plate with a plate depth of 15 μm, and the resulting product was dried at 50°C to obtain a surface-printed product consisting of OPP substrate / release layer (S1) / pattern layer.

[0099] <Preparation of printed matter using each ink obtained in the examples or comparative examples> For each of the inks obtained in the above Examples or Comparative Examples other than Clear Ink S1, printed matter having the same print configuration was produced using the same procedure as for producing printed matter using Clear Ink S1.

[0100] <Preparation of laminate using Clear Ink S1> (Layer structure A: Base material 1 / release layer / pattern layer / adhesive layer / base material 2) Clear Ink S1 was diluted with an EA / IPA mixed solvent (70 / 30 by mass) to a Zahn Cup #3 (manufactured by Rigo Co., Ltd.) for 14 seconds (25°C). Then, Clear Ink S1 and Rio Alpha S R39 Indigo (organic solvent-based gravure ink, manufactured by Toyo Ink Co., Ltd.) were printed in that order onto a corona-treated oriented polypropylene (OPP) film (thickness 20 μm) using a gravure proofing two-color press equipped with a gravure plate with a plate depth of 15 μm. Each unit was dried at 50°C, yielding a printed product having the following order: OPP substrate / release layer (S1) / design layer. Using a dry laminating machine, an adhesive (TM250HV / CAT-RT86L-60 manufactured by Toyo-Morton) was applied to the design layer of this printed material, and it was then laminated with a CPP (unstretched polypropylene film, 30 μm thick) at a line speed of 40 m / min, to obtain a laminated body consisting of OPP substrate / release layer (S1) / design layer / adhesive layer / CPP substrate in that order.

[0101] <Preparation of Laminated Body Using Each Ink Obtained in Examples 2 to 18 or Comparative Examples 1 to 3> Laminates having similar laminate structures were obtained using the inks obtained in Examples 2 to 18 or Comparative Examples 1 to 3 other than Clear Ink S1 in the same manner as above.

[0102] <Releasability evaluation> The printed matter of printing configuration A and the laminated laminate of lamination configuration A prepared in the above examples and comparative examples were cut into 1 cm x 1 cm pieces. 12 g of each sample was stirred at 70°C and 3000 rpm in 400 g of a 2% by mass aqueous solution of sodium hydroxide (NaOH). Ten substrates were sampled at 15 minutes, 30 minutes, 1 hour, and 2 hours after the start of stirring. After washing with water and drying, the removal rate of the printed layer was visually confirmed. A transparent film was recovered from the obtained sample, and the presence or absence of an absorption peak of the adhesive composition was confirmed using FT-IR at five points on the front and back of the film to confirm the removal rate of the adhesive layer. Removal properties were evaluated according to the following criteria. 5 (Excellent): 90% or more of the area of ​​the printed layer and adhesive layer peels off from the substrate in less than 15 minutes. 4 (Good): 90% or more of the area of ​​the printed layer and adhesive layer peels off from the substrate in 15 minutes or more but less than 30 minutes. 3 (Acceptable): 90% or more of the area of ​​the printed layer and adhesive layer peels off from the substrate in 30 to 60 minutes. 2 (Unacceptable): 90% or more of the area of ​​the printing layer and adhesive layer peels off from the substrate within 60 minutes or more but less than 120 minutes. 1 (poor): The printed layer and adhesive layer do not peel off from the substrate even after 120 minutes or more. 3, 4 and 5 are in the range where there are no practical problems.

[0103] <Reattachment evaluation> Three hours after stirring began, the detached substrates were collected, washed with water, and dried. Ten of the resulting substrates were then stacked and the color values ​​L*x, a*x, and b*x were measured using a spectrophotometer (X-rite eXact, manufactured by X-rite). Similarly, ten substrates were stacked and the color values ​​L*y, a*y, and b*y were measured for substrates sampled when 90% of the printing layer and adhesive layer had peeled off in the releasability evaluation. The color difference Δ was calculated using the following formula. ΔE=((L*xL*y)2+(a*xa*y)2+(b*x―b*y)2)1 / 2 The re-adhesion was evaluated according to the following criteria. 5 (Excellent): ΔE is less than 3. 4 (Good): ΔE is 3 or more and less than 20. 3 (Acceptable): ΔE is 20 or more and less than 40. 2 (unacceptable): ΔE is between 40 and 60 1 (poor): ΔE is 60 or more 3, 4 and 5 are in the range where there are no practical problems.

[0104] <Evaluation of substrate adhesion (tape adhesion) in surface-printed materials> For the printed matter of printing configuration A produced in the above examples and comparative examples, cellophane tape (12 mm wide) manufactured by Nichiban Co., Ltd. was applied to the printed layer, and the tape was slowly peeled off, and then suddenly peeled off halfway through, and the degree of peeling of the ink coating was evaluated. 5 (Excellent): The ink film does not peel off at all even when peeled off suddenly. 4 (Good): Less than 25% of the ink coating peels off from the area where it is rapidly peeled off. 3 (Acceptable): The ink coating peels off over an area of ​​25% to less than 75% of the area that is suddenly peeled off. 2 (Not acceptable): When peeled off quickly, 75% or more of the ink film peels off, or when peeled off slowly, only part of the ink film peels off. 1 (poor): The ink film peels off completely from the area that is slowly peeled off. 3, 4 and 5 are in the range where there are no practical problems.

[0105] Example 19 In the above evaluation, a printed matter of print configuration A and a laminated body of layer configuration A were produced in the same manner as above, except that color ink S19 was used and no picture layer was used. The print configuration and layer configuration are shown below. (Printing composition of printed matter) OPP base material / release layer (S19) (Laminated structure of laminated body) The same property evaluations as above were performed using the OPP substrate / release layer (S19) / adhesive layer / CPP substrate, and the results were as follows: tape adhesion rating: 5, release rating for surface-printed material: 4, peeling rating for laminated material: 3, re-adhesion rating for surface-printed material: 4, and re-adhesion rating for laminated material: 4.

[0106] The above evaluation results show that the organic solvent-based printing ink of the present invention has good printability, and in laminates with a surface printing configuration and a laminate configuration, the ink and the like can be removed from the plastic film by an alkaline aqueous solution, and the redeposition of fine ink particles onto the substrate can be suppressed. Furthermore, it has been shown that the organic solvent-based printing ink of the present invention exhibits good substrate adhesion in a surface printing configuration.

[0107] [Table 1]

[0108] [Table 2]

Claims

1. An organic solvent-based printing ink for gravure printing or flexographic printing, used to form a release layer for peeling and recycling a substrate 1 from a printed matter or laminate having a substrate 1, a release layer, and a picture layer and / or a substrate 2 in this order, The organic solvent-based printing ink comprises a urethane resin having an acidic group at its terminal, and the acid value of the urethane resin having an acidic group at its terminal is 15 to 70 mgKOH / g.

2. 2. The organic solvent-based printing ink according to claim 1, wherein the acid value derived from the acidic groups at the terminals of the urethane resin is 1 to 50 mgKOH / g.

3. 3. The organic solvent-based printing ink according to claim 1, wherein the urethane resin having an acidic group at its terminal has a hydroxyl value of 1 to 35 mgKOH / g.

4. 4. The organic solvent-based printing ink according to claim 1, wherein the acidic group at the terminal of the urethane resin is derived from an acid anhydride having a ring structure.

5. 5. The organic solvent-based printing ink according to claim 1, which is a clear ink.

6. A printed matter having a release layer formed on a substrate 1 and composed of the organic solvent-based printing ink according to any one of claims 1 to 5.

7. A laminate comprising at least a substrate 1, a release layer comprising the organic solvent-based printing ink according to any one of claims 1 to 5, and a substrate 2.

8. A method for producing a recycled substrate, comprising the step of immersing a printed material in a basic aqueous solution, The printed matter is formed by printing, in this order, a substrate 1, a release layer formed by the organic solvent-based printing ink according to any one of claims 1 to 5, and a picture layer; The basic aqueous solution contains a basic compound in an amount of 0.5 to 15% by mass based on the total amount of the basic aqueous solution, and the temperature of the basic aqueous solution during immersion is room temperature to 120°C.

9. A method for producing a recycled substrate, comprising the step of immersing a laminate in a basic aqueous solution, The laminate has a release layer formed between a substrate 1 and a substrate 2 using the organic solvent-based printing ink according to any one of claims 1 to 5, The method for producing a recycled substrate, wherein the basic aqueous solution contains a basic compound in an amount of 0.5 to 15% by mass of the entire basic aqueous solution, and the temperature of the basic aqueous solution during immersion is 30 to 120°C.

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