Patent Description:
In recent years, plastics have been used in a very wide variety of applications such as containers and packaging bags, and many of them are composed of completely different types of films, inorganic substances such as aluminum, inks and the like for functional reasons. In particular, printed matters in which inks or the like are used are indispensable in information transmission to general consumers and product distribution management for containers and packaging bags, and are printed or print-processed on the surface of containers or the like.

Plastics are partially separated and collected, and are recycled and used as secondary products because of plastics being less likely to decompose in nature, and for resource saving, economic efficiency and the like. However, when plastic products on which printing or the like has been performed are mixed at the time of recycling, the entire recycled products are colored or partially colored. Thus, such plastic products cannot be reused in many cases because coloring of recycled products significantly lowers the commercial value. Physically fatal defects may be also caused. Such plastic products on which printing or the like has been performed are currently discarded without being collected (for reuse).

In view of the current state where plastic films, plastic containers and the like on which printing or the like has been performed are rarely reused, and are mostly discarded, a method for removing printed matters from plastic products has been conventionally studied from the viewpoint of recycling plastics on which printing has been performed (for example, <CIT>). <CIT> relates to a method for producing a thermoplastic resin composition to be used as a material of a soluble material for three-dimensional molding that is usable as a support member. <CIT> relates to blends of water-dispersible polyesters or polyamides and carboxylic acids and their use in ink and coating compositions. <CIT> relates to antimicrobial toner particles comprising a sulfonated polyester resin comprising a metal ion, and a metal ion dispersed therein and thereon <CIT> relates to a method for detaching and removing the ink layer from the heat shrinkable label having the alkaline water desorptive ink layer. <CIT> relates to an article having a peelable layer to form the printing such as letters and patterns directly thereon or via another layer provided thereon.

The present invention is a method for removing a printing layer comprising: a printing layer removing step of treating a printed matter with neutral water at <NUM> or more to remove the water-soluble printing layer, wherein the printed matter comprises a water-soluble printing layer containing a water-soluble resin for printing including a monomer unit A having a sulfonate group; and a monomer unit B having no hydrophilic group, wherein a percentage of the monomer unit A based on a total of all monomer units is <NUM> to <NUM> mol% as defined in the claims.

In the technique described in <CIT> above, an alkaline aqueous solution is used to remove an ink layer. An alkaline aqueous solution has a high risk for the human body, and needs to be handled with care. In addition, when printed matters are immersed in an alkaline aqueous solution, substrates are eroded by the alkali, and recycling may become impossible.

One idea to solve the above-mentioned problems is an ink containing a water-soluble material that can be dissolved in neutral water such as polyvinyl alcohol. However, conventional water-soluble materials have poor water resistance, and thus, when conventional water-soluble materials are used in printed matters that are often placed in an environment with relatively high humidity (for example, household detergent containers or the like), the printing layer may be peeled off due to humidity in the environment.

The present disclosure provides a water-soluble resin for printing capable of realizing a printed matter from which a printing layer can be safely and efficiently removed with neutral water and which is excellent in water resistance.

The present disclosure is a water-soluble resin for printing including a monomer unit A having a sulfonate group; and a monomer unit B having no hydrophilic group, wherein a percentage of the monomer unit A based on a total of all monomer units is <NUM> to <NUM> mol%.

According to the present disclosure, a water-soluble resin for printing capable of realizing a printed matter from which a printing layer can be safely and efficiently removed with neutral water and which is excellent in water resistance can be provided.

One embodiment according to the present disclosure is explained below.

The water-soluble resin for printing of the present embodiment includes a monomer unit A having a sulfonate group; and a monomer unit B having no hydrophilic group other than the hydrophilic group that constitutes the polymerization related to the production of the resin (hereinafter, also simply referred to as a hydrophilic group), and a percentage of the monomer unit A based on a total of all monomer units is <NUM> to <NUM> mol%. According to the water-soluble resin for printing of the present embodiment, a printed matter from which a printing layer can be safely and efficiently removed with neutral water and which is excellent in water resistance can be realized. In the present specification, the term "water-soluble" means that a resin dissolves in <NUM> of neutral water at <NUM> in an amount of <NUM> or more.

From the viewpoint of safely and efficiently removing a printing layer with neutral water, the resin composition preferably dissolves in neutral water at <NUM> in an amount of <NUM>% by mass or more, more preferably dissolves in neutral water at <NUM> in an amount of <NUM>% by mass or more, and still more preferably dissolves in neutral water at <NUM> in an amount of <NUM>% by mass or more.

Examples of the neutral water include water and an aqueous solution having a pH of <NUM> to <NUM>. Specific examples of the neutral water include deionized water, pure water, tap water, and industrial water, and deionized water or tap water is preferable from the viewpoint of availability. The neutral water can contain other components such as a water-soluble organic solvent and a surfactant. Examples of the water-soluble organic solvent include lower alcohols such as methanol, ethanol, and <NUM>-propanol, glycol ethers such as propylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol mono-tertiary butyl ether, and diethylene glycol monobutyl ether, and ketones such as acetone and methyl ethyl ketone. Examples of the surfactant include anionic surfactants such as an alkyl sulphate ester salt, an alkyl ether sulphate ester salt, an olefin sulfonate, and an alkyl ether carboxylate; cationic surfactants such as alkyltrimethylammonium salt; and nonionic surfactants such as polyoxyethylene alkyl ether and alkyl glycoside.

Examples of the water-soluble resin include a water-soluble polyester resin, a water-soluble polyamide resin, a water-soluble polyimide resin, a water-soluble acrylic resin, a water-soluble polyurethane resin, a water-soluble polyallylamine resin, a water-soluble phenol resin, a water-soluble epoxy resin, a water-soluble phenoxy resin, a water-soluble urea resin, a water-soluble melamine resin, a polyvinyl alcohol resin, and modified products of these resins. These can be used singly or in combination of two or more types thereof. Among them, from the viewpoint of exhibiting the effects of the present invention, at least one selected from the group consisting of a water-soluble polyester resin, a water-soluble polyamide resin, and a water-soluble acrylic resin are preferable, and a water-soluble polyester resin is more preferable.

The monomer unit A has a sulfonate group. The monomer from which the monomer unit A is derived is referred to as a monomer A.

Though the monomer unit A is not particularly limited as long as the monomer unit A is a monomer unit having a sulfonate group, a dicarboxylic acid monomer unit having a sulfonate group (hereinafter, also referred to as a dicarboxylic acid monomer unit A) is preferable from the viewpoint of achieving removal of a printing layer with neutral water and the viewpoint of improving the water resistance of a printed matter.

The monomer A is preferably at least one selected from the group consisting of carboxylic acids having a sulfonate group, amines, and amino acids, and more preferably carboxylic acids having a sulfonate group from the viewpoint of achieving removal of a printing layer with neutral water, the viewpoint of improving the water resistance of a printed matter, and the viewpoint of ease of polymerization reaction during production of the water-soluble resin. Among the carboxylic acids, at least one selected from the group consisting of aromatic carboxylic acids having a sulfonate group are more preferable, and at least one selected from the group consisting of sulfonate group-containing aromatic dicarboxylic acids are more preferable from the same viewpoint. Among them, at least one selected from the group consisting of sulfophthalic acids and sulfonaphthalenedicarboxylic acid are preferable, at least one selected from the group consisting of sulfophthalic acids are still more preferable, at least one selected from the group consisting of sulfoisophthalic acids and sulfoterephthalic acids are still more preferable, and <NUM>-sulfoisophthalic acid is further preferable from the same viewpoint.

The sulfonate group is preferably a sulfonate group represented by -SO<NUM>M<NUM> (M<NUM> represents a counterion of a sulfonic acid group that constitutes the sulfonate group, and from the viewpoint of achieving removal of a printing layer with neutral water, M<NUM> is preferably at least one selected from the group consisting of a metal ion and an ammonium ion, more preferably at least one selected from the group consisting of a metal ion, still more preferably at least one selected from the group consisting of an alkali metal ion and an alkaline earth metal ion, still more preferably at least one selected from the group consisting of an alkali metal ion, still more preferably at least one selected from the group consisting of a sodium ion and a potassium ion, and still more preferably a sodium ion. ) from the viewpoint of achieving removal of a printing layer with neutral water and the viewpoint of ease of polymerization reaction during production of the water-soluble resin.

The content of the sulfonate group in the water-soluble resin is preferably <NUM> mmol/g or more, more preferably <NUM> mmol/g or more, and still more preferably <NUM> mmol/g or more from the viewpoint of achieving removal of a printing layer with neutral water, and is preferably <NUM> mmol/g or less, more preferably <NUM> mmol/g or less, and still more preferably <NUM> mmol/g or less from the viewpoint of improving the water resistance of a printed matter. The content of the sulfonate group in the water-soluble resin is preferably <NUM> to <NUM> mmol/g, more preferably <NUM> to <NUM> mmol/g, and still more preferably <NUM> to <NUM> mmol/g from the viewpoint of achieving removal of a printing layer with neutral water and the viewpoint of improving the water resistance of a printed matter.

The percentage of the monomer unit A based on a total of all monomer units of the water-soluble resin is <NUM> mol% or more, preferably <NUM> mol% or more, more preferably <NUM> mol% or more, and still more preferably <NUM> mol% or more from the viewpoint of achieving removal of a printing layer with neutral water, and is <NUM> mol% or less, preferably <NUM> mol% or less, and more preferably <NUM> mol% or less from the viewpoint of improving the water resistance of a printed matter. The percentage of the monomer unit A based on a total of all monomer units of the water-soluble resin is <NUM> to <NUM> mol%, preferably <NUM> to <NUM> mol%, more preferably <NUM> to <NUM> mol%, and still more preferably <NUM> to <NUM> mol% from the viewpoint of achieving removal of a printing layer with neutral water and the viewpoint of improving the water resistance of a printed matter.

The monomer unit B has no hydrophilic group. The monomer from which the monomer unit B is derived is referred to as a monomer B. Though the monomer unit B is not particularly limited as long as the monomer unit B is a monomer unit having no hydrophilic group, a dicarboxylic acid monomer unit having no hydrophilic group (hereinafter, also referred to as a dicarboxylic acid monomer unit B) is preferable from the viewpoint of achieving removal of a printing layer with neutral water and the viewpoint of improving the water resistance of a printed matter.

The hydrophilic group is not particularly limited as long as the hydrophilic group exhibits hydrophilicity. Examples of the hydrophilic group include a primary amino group, a secondary amino group, a tertiary amino group, a quaternary ammonium group, an oxyalkylene group, a hydroxyl group, a carboxyl group, a carboxyl group, a phosphoric acid group, a phosphate group, a sulfonic acid group, and a sulfonate group.

The dicarboxylic acid from which the dicarboxylic acid monomer unit B is derived (hereinafter, also referred to as a dicarboxylic acid monomer B) is more preferably at least one selected from the group consisting of an aromatic dicarboxylic acid having no hydrophilic group and an aliphatic dicarboxylic acid having no hydrophilic group, and more preferably at least one selected from the group consisting of an aromatic dicarboxylic acid having no hydrophilic group from the viewpoint of achieving removal of a printing layer with neutral water, the viewpoint of improving the water resistance of a printed matter, and the viewpoint of ease of polymerization reaction during production of the water-soluble resin.

The percentage of a total of the aromatic dicarboxylic acid based on a total of the dicarboxylic acid monomer B is preferably <NUM> mol% or more, more preferably <NUM> mol% or more, and still more preferably <NUM> mol% or more from the viewpoint of achieving removal of the printing layer with neutral water.

The percentage of a total of the aromatic dicarboxylic acid based on a total of the monomer B is preferably <NUM> mol% or less, more preferably <NUM> mol% or less, and still more preferably <NUM> mol% or less from the viewpoint of improving the water resistance of the printing layer.

Examples of the aromatic dicarboxylic acid having no hydrophilic group include at least one selected from the group consisting of terephthalic acid, isophthalic acid, <NUM>,<NUM>-furandicarboxylic acid, and <NUM>,<NUM>-naphthalenedicarboxylic acid. Among them, at least one selected from the group consisting of terephthalic acid, isophthalic acid, and <NUM>,<NUM>-naphthalenedicarboxylic acid are preferable from the viewpoint of achieving removal of a printing layer with neutral water and the viewpoint of improving the water resistance of a printed matter.

Examples of the aliphatic dicarboxylic acid having no hydrophilic group include at least one selected from the group consisting of malonic acid, succinic acid, glutaric acid, adipic acid, <NUM>,<NUM>-cyclohexanedicarboxylic acid, and <NUM>,<NUM>-adamantanedicarboxylic acid. Among them, at least one selected from the group consisting of adipic acid and <NUM>,<NUM>-cyclohexanedicarboxylic acid are preferable from the viewpoint of achieving removal of a printing layer with neutral water and the viewpoint of improving the water resistance of a printed matter.

The percentage of the amount of substance of the monomer unit B based on a total of the amount of substance of all monomer units in the water-soluble resin is preferably <NUM> mol% or more, more preferably <NUM> mol% or more, and still more preferably <NUM> mol% or more from the viewpoint of improving the water resistance of a printed matter, and is preferably <NUM> mol% or less, more preferably <NUM> mol% or less, and still more preferably <NUM> mol% or less from the viewpoint of achieving removal of a printing layer with neutral water. The percentage of the amount of substance of the monomer unit B based on a total of the amount of substance of all monomer units in the water-soluble resin is preferably <NUM> to <NUM> mol%, more preferably <NUM> to <NUM> mol%, and still more preferably <NUM> to <NUM> mol% from the viewpoint of improving the water resistance of a printed matter and the viewpoint of achieving removal of a printing layer with neutral water.

The molar ratio of the monomer unit A to the monomer unit B in the water-soluble resin (the monomer unit A/the monomer unit B) is preferably <NUM>/<NUM> or more, more preferably <NUM>/<NUM> or more, still more preferably <NUM>/<NUM> or more, and still more preferably <NUM>/<NUM> or more from the viewpoint of achieving removal of a printing layer with neutral water and the viewpoint of improving the water resistance of a printed matter, and preferably <NUM>/<NUM> or less, more preferably <NUM>/<NUM> or less, still more preferably <NUM>/<NUM> or less, still more preferably <NUM>/<NUM> or less, and still more preferably <NUM>/<NUM> or less from the same viewpoint.

The weight average molecular weight of the water-soluble resin is preferably <NUM> or more, more preferably <NUM> or more, and still more preferably <NUM> or more from the viewpoint of improving the water resistance of a printing layer, and is preferably <NUM>,<NUM> or less, more preferably <NUM>,<NUM> or less, still more preferably <NUM>,<NUM> or less, and still more preferably <NUM>,<NUM> or less from the viewpoint of achieving removal of a printing layer with neutral water. In the present specification, the weight average molecular weight is measured by the method described in Examples.

When the water-soluble resin is a water-soluble polyester resin, the water-soluble resin includes a diol monomer unit C other than the monomer unit A and the monomer unit B. The diol from which the diol monomer unit C is derived is also referred to as a diol C.

As the diol C, an aliphatic diol, an aromatic diol and the like can be used, and an aliphatic diol is preferable from the viewpoint of availability of raw materials of the water-soluble polyester resin.

The carbon number of the diol C is preferably <NUM> or more from the viewpoint of achieving removal of a printing layer with neutral water and the viewpoint of improving the water resistance of a printed matter, and is preferably <NUM> or less, more preferably <NUM> or less, still more preferably <NUM> or less, and still more preferably <NUM> or less from the same viewpoint.

Examples of the aliphatic diol include at least one selected from the group consisting of a chain diol and a cyclic diol, and a chain diol is preferable from the viewpoint of availability of raw materials and a cyclic diol is preferable from the viewpoint of achieving removal of a printing layer with neutral water.

The percentage of a total of the cyclic diol based on a total of the diol C is preferably <NUM> mol% or more, more preferably <NUM> mol% or more, and still more preferably <NUM> mol% or more from the viewpoint of achieving removal of a printing layer with neutral water, and is preferably <NUM> mol% or less, more preferably <NUM> mol% or less, and still more preferably <NUM> mol% or less from the viewpoint of availability of raw materials.

The carbon number of the chain diol is preferably <NUM> or more from the viewpoint of improving the water resistance of a printing layer, and is preferably <NUM> or less, still more preferably <NUM> or less, and still more preferably <NUM> or less from the viewpoint of achieving removal of the printing layer with neutral water.

The chain diol is preferably at least one selected from the group consisting of ethylene glycol, <NUM>,<NUM>-propanediol, <NUM>,<NUM>-propanediol, <NUM>,<NUM>-butanediol, <NUM>,<NUM>-butanediol, <NUM>,<NUM>-butanediol, neopentyl glycol, <NUM>,<NUM>-pentanediol, <NUM>,<NUM>-hexanediol, diethylene glycol, triethylene glycol, polyethylene glycol, dipropylene glycol, and polypyrene glycol, more preferably at least one selected from the group consisting of ethylene glycol, <NUM>,<NUM>-propanediol, <NUM>,<NUM>-propanediol, and triethylene glycol, and still more preferably at least one selected from the group consisting of ethylene glycol, <NUM>,<NUM>-propanediol, and triethylene glycol from the viewpoint of achieving removal of a printing layer with neutral water and the viewpoint of improving the water resistance of a printed matter.

The carbon number of the cyclic diol is preferably <NUM> or more, more preferably <NUM> or more, still more preferably <NUM> or more from the viewpoint of improving the water resistance of a printing layer, and is preferably <NUM> or less, still more preferably <NUM> or less, still more preferably <NUM> or less, still more preferably <NUM> or less, and still more preferably <NUM> or less from the viewpoint of improving the water resistance of a printing layer.

The cyclic diol is preferably at least one selected from the group consisting of <NUM>,<NUM>-cyclohexanedimethanol, hydrogenated bisphenol A, isosorbide, bisphenoxyethanolfluorene, bisphenol fluorene, biscresoxyethanolfluorene, and biscresol fluorene, and more preferably one or two selected from the group consisting of <NUM>,<NUM>-cyclohexanedimethanol and isosorbide from the viewpoint of achieving removal of a printing layer with neutral water and the viewpoint of improving the water resistance of a printed matter.

The water-soluble polyester resin can have monomer units other than the dicarboxylic acid monomer unit A, the dicarboxylic acid monomer unit B, and the diol monomer unit C as long as the effects of the present embodiment are not impaired.

The method for producing the water-soluble polyester resin is not particularly limited, and a conventionally known method for producing a polyester resin can be applied.

The water-soluble resin for printing can be a water-soluble resin composition for printing containing other components.

The content of the water-soluble resin in the water-soluble resin composition for printing is preferably <NUM>% by mass or more, more preferably <NUM>% by mass or more, more preferably <NUM>% by mass or more, and still more preferably <NUM>% by mass or more, and is preferably <NUM>% by mass or less, more preferably <NUM>% by mass, and still more preferably <NUM>% by mass or less from the viewpoint of achieving removal of a printing layer with neutral water and the viewpoint of improving the water resistance of a printed matter.

The water-soluble resin composition can contain a salt other than the water-soluble resin (component β). The component β is preferably an organic salt compound represented by the following General Formula (<NUM>) from the viewpoint of achieving removal of a printing layer with neutral water and the viewpoint of improving the water resistance and heat resistance of a printed matter.

(In the General Formula (<NUM>), R<NUM> represents a hydrocarbon group optionally having a substituent and having <NUM> to <NUM> carbon atoms, n represents a number of <NUM> or <NUM>, Xn+ represents a sodium ion, a potassium ion, a lithium ion, an ammonium ion, or a phosphonium ion when n is <NUM>, and Xn+ represents a magnesium ion, a calcium ion, a barium ion, or a zinc ion when n is <NUM>.

In the General Formula (<NUM>), R<NUM> represents a hydrocarbon group optionally having a substituent and having <NUM> to <NUM> carbon atoms including the carbon atoms of the substituent from the viewpoint of achieving removal of a printing layer with neutral water and the viewpoint of improving heat resistance. The hydrocarbon group can be any of an aliphatic hydrocarbon group, an alicyclic hydrocarbon group, and an aromatic hydrocarbon group. When the hydrocarbon group is an aromatic hydrocarbon group, the carbon number of the hydrocarbon group is preferably <NUM> or more, more preferably <NUM> or more, still more preferably <NUM> or more, and preferably <NUM> or less, and more preferably <NUM> or less from the viewpoint of achieving removal of a printing layer with neutral water and the viewpoint of improving heat resistance.

As the substituent, a substituent containing at least one selected from the group consisting of a carbon atom, an oxygen atom, a nitrogen atom, a sulfur atom, a phosphorus atom, a silicon atom, and a halogen atom is preferable, among them, a hydrocarbon group having <NUM> to <NUM> carbon atoms or an alkyl halide group having <NUM> to <NUM> carbon atoms is preferable, a hydrocarbon group having <NUM> to <NUM> carbon atoms is more preferable, and a hydrocarbon group having <NUM> to <NUM> carbon atoms is still more preferable from the viewpoint of achieving removal of a printing layer with neutral water and the viewpoint of improving heat resistance.

In the General Formula (<NUM>), Xn+ represents a sodium ion, a potassium ion, a lithium ion, an ammonium ion, a phosphonium ion, a magnesium ion, a calcium ion, a barium ion, a zinc ion, or a phosphonium ion, is preferably a sodium ion, a potassium ion, a lithium ion, an ammonium ion, or a phosphonium ion, and is still more preferably a phosphonium ion from the viewpoint of achieving removal of a printing layer with neutral water and the viewpoint of improving heat resistance. Among phosphonium ions, a tetraalkylphosphonium ion is preferable, and a tetrabutylphosphonium ion is more preferable from the viewpoint of achieving removal of a printing layer with neutral water and the viewpoint of improving heat resistance.

In the General Formula (<NUM>), n is preferably <NUM> from the viewpoint of achieving removal of a printing layer with neutral water and the viewpoint of improving heat resistance.

The content of the organic salt compound in the water-soluble resin composition is preferably <NUM>% by mass or more, more preferably <NUM>% by mass or more, and still more preferably <NUM>% by mass or more from the viewpoint of achieving removal of a printing layer with neutral water, and is preferably <NUM>% by mass or less, more preferably <NUM>% by mass or less, and still more preferably <NUM>% by mass or less from the viewpoint of achieving removal of a printing layer with neutral water.

For the content of the organic salt compound in the water-soluble resin composition, a ratio of the amount of substance (mol) of the alkyl sulfonic acid ion (R<NUM>-SO<NUM>-) of the organic salt compound to a total of the amount of substance (mol) of the hydrophilic group and the amount of substance (mol) of the sulfonate group of the water-soluble resin (amount of substance of alkyl sulfonic acid ion of the organic salt compound/total of amount of substance of hydrophilic group and amount of substance of sulfonate group of the water-soluble resin) is preferably <NUM> or more, more preferably <NUM> or more, still more preferably <NUM> or more, and still more preferably <NUM> or more from the viewpoint of achieving removal of a printing layer with neutral water, and is preferably <NUM> or less, more preferably <NUM> or less, and still more preferably <NUM> or less from the viewpoint of achieving removal of a printing layer with neutral water.

The water-soluble resin composition can contain a compatibilizer from the viewpoint of improving adhesiveness to a substrate and a printing layer. Examples of the compatibilizer include Bondfast (registered trademark) 7B and Bondfast <NUM> (manufactured by Sumitomo Chemical Co. ); Rotador (registered trademark) AX8840 (manufactured by Arkema Inc. ); JONCRYL (registered trademark) ADR4370S, JONCRYL ADR4368CS, JONCRYL ADR4368F, and JONCRYL ADR4300S (manufactured by BASF SE); and ARUFON (registered trademark) UG4035, ARUFON UG4040, and ARUFON UG4070 (manufactured by Toagosei Co. Examples of the reactive compatibilizer having an acid anhydride group include UMEX (registered trademark) <NUM> (manufactured by SANYO CHEMICAL INDUSTRIES, LTD. ); ADMER (registered trademark) (manufactured by Mitsui Chemicals, Inc. ); MODIPER (registered trademark) A8200 (manufactured by NOF CORPORATION); OREVAC (registered trademark) (manufactured by Arkema Inc. ); FG1901 and FG1924 (manufactured by KRATON CORPORATION); and Tuftec (registered trademark) M1911, Tuftec M1913, and Tuftec M1943 (manufactured by Asahi Kasei Chemicals Corporation). Examples of the reactive compatibilizer having an isocyanate group include CARBODILITE LA-<NUM> (registered trademark) manufactured by Nisshinbo Chemical Inc.

The content of the component γ relative to <NUM> parts by mass of the component α of the water-soluble resin composition is preferably <NUM> part by mass or more, more preferably <NUM> parts by mass or more, and still more preferably <NUM> parts by mass or more from the viewpoint of improving the water resistance of a printing layer, and is preferably <NUM> parts by mass or less, and more preferably <NUM> parts by mass or less from the same viewpoint.

The water-soluble resin composition can contain other components as long as the effects of the present invention are not impaired. Examples of the other components include resins other than the component α, plasticizers such as benzoic acid polyalkylene glycol diester, fillers such as calcium carbonate, magnesium carbonate, glass spheres, graphite, carbon black, carbon fiber, glass fiber, talc, wollastonite, mica, alumina, silica, kaolin, whisker, and silicon carbide, and elastomers.

In addition, if necessary, known substances such as an ultraviolet absorber, an antioxidant, a silicon additive, a fluorine additive, an antistatic agent, a silane coupling agent, an adhesion aid, a rheology control agent, an antifogging agent, a colorant, a crosslinking agent, a pH adjustor, a film forming agent, a leveling agent, a thickener, a water repellent agent, and an antifoaming agent can be appropriately added.

Examples of the elastomers include an acrylic elastomer, an olefin elastomer, a styrene elastomer, a polyester elastomer, a urethane elastomer, a polyamide elastomer, and a silicone elastomer. Among these, at least one selected from the group consisting of an acrylic elastomer and a styrene elastomer are preferable, and an acrylic elastomer is more preferable. The styrene elastomer is preferably at least one selected from the group consisting of a styrene-butadiene copolymer and a styrene-butadiene-ethylene copolymer. The acrylic elastomer is preferably a methacrylic acid-alkyl acrylate copolymer. Examples of commercially available products of the elastomer include KURARITY (registered trademark) LA2250, KURARITY LA2140, and KURARITY LA4285 (manufactured by KURARAY CO. Examples of the olefin elastomer include Kraton (registered trademark) ERS polymer (manufactured by Kraton Corporation); Kraton A polymer and Kraton G polymer (manufactured by Kraton Corporation); "Tuftec H" series and "Tuftec P" series (manufactured by Asahi Kasei Chemicals Corporation); and SEPTON (registered trademark) and HYBRAR (registered trademark) (KURARAY PLASTICS CO.

The content of the elastomer of the water-soluble resin composition relative to <NUM> parts by mass of the component α is preferably <NUM> parts by mass or more, more preferably <NUM> part by mass or more, and still more preferably <NUM> parts by mass or more from the viewpoint of improving the water resistance of a printing layer, and is preferably <NUM> parts by mass or less, more preferably <NUM> parts by mass or less, still more preferably <NUM> parts by mass or less, and still more preferably <NUM> parts by mass or less from the same viewpoint.

When the water-soluble resin for printing or the water-soluble resin composition for printing is contained in a printing layer, solubility in neutral water can be imparted to the printing layer. That is, the water-soluble resin for printing and the water-soluble resin composition for printing can be used as a solubility imparting agent for imparting solubility in neutral water to a printing layer. When the water-soluble resin for printing and the water-soluble resin composition for printing are used as a vehicle for printing, solubility in neutral water can be imparted to a printing layer. By using the water-soluble resin for printing or the water-soluble resin composition for printing in a printing primer, a printed matter from which a printing layer can be safely and efficiently removed with neutral water and which is excellent in water resistance can be realized.

The method for producing a printed matter according to the first embodiment not encompassed by the wording of the claims includes a water-soluble printing layer forming step of forming a water-soluble printing layer containing the water-soluble resin for printing on a substrate. The printed matter includes a water-soluble printing layer containing the water-soluble resin for printing.

The water-soluble printing layer forming step is a step of forming a water-soluble printing layer containing the water-soluble resin for printing on a substrate.

The substrate is not particularly limited as long as printing can be performed on the substrate. The component of the substrate on which printing is performed is also not particularly limited, and examples thereof include a resin substrate, a metal substrate, a glass substrate, a paper substrate, a wood substrate, and a fibrous substrate. Further, examples of the resin substrate include synthetic resins such as nylon resins such as nylon <NUM>, nylon <NUM>, nylon <NUM>, nylon <NUM>, and nylon <NUM>, polyester resins such as polyethylene terephthalate (PET), polytrimethylene terephthalate (PTT), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), polybutylene naphthalate (PBN), polylactic acid (PLA), and polyhydroxyalkanoate (PHA), polyolefin resins such as polyethylene (PE), polypropylene (PP), and acrylonitrile butadiene styrene (ABS), acryl resins, vinyl chloride resins, polycarbonate resins, polystyrene resins, and ethylene-vinyl alcohol copolymer resins.

The printing method used in the water-soluble printing layer forming step is not particularly limited, and for example, an inkjet printing method, a letterpress printing method, an intaglio printing method, a flat plate printing method, a stencil printing method can be used.

The ink used for printing in the water-soluble printing layer forming step is an ink suitable for the printing method used in the printing layer forming step, and is not particularly limited as long as the water-soluble resin for printing is contained. The ink used for printing in the water-soluble printing layer forming step can be one obtained by adding the water-soluble resin for printing to a known ink, or one obtained by adding a pigment or other additives to a vehicle for a printing ink containing the water-soluble resin for printing.

The vehicle for a printing ink contains the water-soluble resin for printing, a water-soluble organic solvent, a surfactant, and water.

The water-soluble organic solvent can be a liquid or a solid at normal temperature (<NUM>). In the present specification, the water-soluble organic solvent refers to an organic solvent having an amount of dissolution of <NUM> or more when the organic solvent is dissolved in <NUM> of water at <NUM>.

The total amount of the water-soluble organic solvent in the vehicle for a printing ink is preferably <NUM>% by mass or more, more preferably <NUM>% by mass or more, and still more preferably <NUM>% by mass or more from the viewpoint of improving the leveling property, and is <NUM>% by mass or less, preferably <NUM>% by mass or less, and more preferably <NUM>% by mass or less from the viewpoint of reducing the environmental load.

The boiling point of the water-soluble organic solvent can be less than <NUM>. Examples of the water-soluble organic solvent having a boiling point of less than <NUM> include monohydric alcohols such as ethanol, <NUM>-propanol, and <NUM>-propanol, and among these, <NUM>-propanol is preferable.

The content of the water-soluble organic solvent having a boiling point of less than <NUM> in the vehicle for a printing ink is preferably <NUM>% by mass or more, more preferably <NUM>% by mass or more, and still more preferably <NUM>% by mass or more from the viewpoint of improving the leveling property, and is preferably <NUM>% by mass or less, more preferably <NUM>% by mass or less, and still more preferably <NUM>% by mass or less from the viewpoint of improving the leveling property.

The water-soluble organic solvent can contain a glycol ether having a boiling point of <NUM> or more and <NUM> or less from the viewpoint of improving the leveling property.

The molecular weight of the glycol ether is preferably <NUM> or more, more preferably <NUM> or more, and still more preferably <NUM> or more, and is preferably <NUM> or less, more preferably <NUM> or less, and still more preferably <NUM> or less.

The boiling point of the glycol ether is preferably <NUM> or more, more preferably <NUM> or more, and still more preferably <NUM> or more, and is preferably <NUM> or less, more preferably <NUM> or less, and still more preferably <NUM> or less from the viewpoint of improving the leveling property. The boiling point represents a normal boiling point (boiling point under normal atmospheric pressure). When two or more types of glycol ethers are used, the boiling point of the glycol ethers is a weighted average efficiency weighted by the content (% by mass) of each glycol ether.

Examples of the glycol ether include alkylene glycol monoalkyl ether and alkylene glycol dialkyl ether.

The carbon number of the alkyl group of the glycol ether is preferably <NUM> or more, and more preferably <NUM> or more, and is preferably <NUM> or less, and more preferably <NUM> or less. The alkyl group is preferably a branched chain.

The alkylene glycol monoalkyl ether is preferably at least one selected from alkylene glycol monoalkyl ether and an alkylene glycol dialkyl ether, more preferably alkylene glycol monoalkyl ether, and still more preferably diethylene glycol monoisobutyl ether from the viewpoint of improving the drying property and the leveling property.

The content of the glycol ether in the vehicle for a printing ink is <NUM>% by mass or more, preferably <NUM>% by mass or more, and more preferably <NUM>% by mass or more from the viewpoint of improving the leveling property, and is <NUM>% by mass or less, preferably <NUM>% by mass or less, and more preferably <NUM>% by mass or less from the viewpoint of improving the leveling property.

The mass ratio of the glycol ether to the total amount of the water-soluble organic solvent in the vehicle for a printing ink [glycol ether/total amount of water-soluble organic solvent] is preferably <NUM>/<NUM> to <NUM>/<NUM>, more preferably <NUM>/<NUM> to <NUM>/<NUM>, and still more preferably <NUM>/<NUM>.

The surfactant is preferably at least one selected from an anionic surfactant, a nonionic surfactant other than acetylene glycol surfactants, and an amphoteric surfactant, and two or more of these can be used in combination.

Among them, a nonionic surfactant is preferable from the viewpoint of further improving the leveling property. Examples of the nonionic surfactant include an alcohol surfactant and a silicone surfactant, and two or more of these can be used in combination. A silicone surfactant is preferable from the viewpoint of wettability to a printing substrate.

Examples of the silicone surfactant include dimethylpolysiloxane, polyether-modified silicone, amino-modified silicone, carboxy-modified silicone, methylphenylpolysiloxane, fatty acid-modified silicone, alcohol-modified silicone, aliphatic alcohol-modified silicone, epoxy-modified silicone, fluorine-modified silicone, cyclic silicone, and alkyl-modified silicone. Among them, polyether-modified silicone is preferable from the viewpoint of wettability to a printing substrate, and PEG-<NUM> methyl ether dimethicone is still more preferable.

The surfactant preferably contains an acetylene glycol surfactant. As the acetylene glycol surfactant, an acetylene glycol having <NUM> or more and <NUM> or less carbon atoms and an ethylene adduct of the acetylene glycol are preferable, and an acetylene glycol having <NUM> or more and <NUM> or less carbon atoms is more preferable from the viewpoint of improving the leveling property. The carbon number of the acetylene glycol is preferably <NUM> or more, and more preferably <NUM> or more, and is preferably <NUM> or less, more preferably <NUM> or less, and still more preferably <NUM> or less. Specific examples thereof include at least one acetylene glycols selected from <NUM>,<NUM>,<NUM>,<NUM>-tetramethyl-<NUM>-decine-<NUM>,<NUM>-diol, <NUM>,<NUM>-dimethyl-<NUM>-octyne-<NUM>,<NUM>-diol, and <NUM>,<NUM>-dimethyl-<NUM>-hexyne-<NUM>,<NUM>-diol, and ethylene oxide adducts of the acetylene glycols from the viewpoint of improving the leveling property. Among them, <NUM>,<NUM>,<NUM>,<NUM>-tetramethyl-<NUM>-decine-<NUM>,<NUM>-diol is preferable.

The content of water of the vehicle for a printing ink is preferably <NUM>% by mass or more, more preferably <NUM>% by mass or more, and still more preferably <NUM>% by mass or more from the viewpoint of improving the leveling property while reducing volatile organic compounds, and is preferably <NUM>% by mass or less, more preferably <NUM>% by mass or less, and still more preferably <NUM>% by mass or less from the viewpoint of improving the leveling property while keeping a good drying property. When any other components other than the water-soluble organic solvent, the surfactant, and water are contained in the vehicle for a printing ink, a part of the content of water can be replaced with the content of any other components.

The ink contains the water-soluble resin for printing and a pigment.

The type of the pigment can be an inorganic pigment or an organic pigment.

Examples of the inorganic pigment include carbon black and metal oxides, and carbon black is preferable for black inks. Examples of the carbon black include furnace black, thermal lamp black, acetylene black, and channel black. Examples of the pigment for white inks include metal oxides such as titanium dioxide, zinc oxide, silica, alumina, and magnesium oxide. These inorganic pigments can be surface-treated with a known hydrophobizing agent such as a titanium coupling agent, a silane coupling agent, and a higher fatty acid metal salt.

Examples of the organic pigment include an azo pigment, a diazo pigment, a phthalocyanine pigment, a quinacridone pigment, an isoindolinone pigment, a dioxazine pigment, a perylene pigment, a perinone pigment, a thioindigo pigment, an anthraquinone pigment, and a quinophthalone pigment.

The hue of the pigment is not particularly limited, and any chromatic color pigments such as yellow, magenta, cyan, red, blue, orange, and green can be used in chromatic color inks.

The content of the pigment in the ink is preferably <NUM>% by mass or more, more preferably <NUM>% by mass or more, still more preferably <NUM>% by mass or more, and is preferably <NUM>% by mass or less, more preferably <NUM>% by mass or less, and still more preferably <NUM>% by mass or less from the viewpoint of print density.

The pigment can be contained in the ink as pigment-containing polymer particles by being dispersed in polymer particles.

The polymer that constitutes the pigment-containing polymer particles is not particularly limited as long as the polymer is a polymer used for an ink. When the polymer is a polymer other than the water-soluble resin for printing (hereinafter, also referred to as a polymer a), both a water-soluble polymer and a water-insoluble polymer can be preferably used as the polymer a. However, a water-insoluble polymer is more preferable.

The water-insoluble polymer refers to a polymer having an amount of dissolution of less than <NUM> when the polymer is dried at <NUM> for <NUM> hours to reach a constant weight, and is dissolved in <NUM> of water at <NUM>, and the amount of dissolution is preferably less than <NUM> and more preferably less than <NUM>. In the case of an anionic polymer, the amount of dissolution is an amount of dissolution when the anionic group of the polymer is neutralized by <NUM>% with sodium hydroxide.

Examples of the polymer include polyester, polyurethane, and a vinyl polymer, and a vinyl polymer obtained by addition polymerization of a vinyl monomer such as a vinyl compound, a vinylidene compound, and a vinylene compound is preferable from the viewpoint of dispersion stability of a pigment.

As the vinyl polymer, one that contains a constitutional unit derived from an ionic monomer (a-<NUM>) (hereinafter also referred to as "component (a-<NUM>)") is preferable, and a water-soluble vinyl polymer obtained by copolymerizing a monomer mixture A containing an ionic monomer (a-<NUM>) and a nonionic monomer (a-<NUM>) (hereinafter also referred to as "component (a-<NUM>)")(hereinafter, also simply referred to as "monomer mixture A") is more preferable. The water-soluble vinyl polymer has a constitutional unit derived from the component (a-<NUM>) and a constitutional unit derived from the component (a-<NUM>).

The weight average molecular weight of the polymer a is preferably <NUM>,<NUM> or more, more preferably <NUM>,<NUM> or more, and still more preferably <NUM>,<NUM> or more, and is preferably <NUM>,<NUM> or less, more preferably <NUM>,<NUM> or less, still more preferably <NUM>,<NUM> or less, and still more preferably <NUM>,<NUM> or less from the viewpoint of improving the dispersion stability of the pigment particles dispersed with the polymer in the ink and the viewpoint of improving the fixing strength of the ink to the printing substrate.

Examples of the ionic monomer include an anionic monomer and a cationic monomer, and an anionic monomer is preferable.

Examples of the anionic monomer include a carboxylic acid monomer, a sulfonic acid monomer, and a phosphoric acid monomer, and a carboxylic acid monomer is preferable, and acrylic acid is more preferable.

Examples of the nonionic monomer include a styrene monomer and a hydroxyalkyl (meth)acrylate; polyalkylene glycol (meth)acrylate; alkoxy polyalkylene glycol (meth)acrylate; and phenoxy(ethylene glycol-propylene glycol copolymer) (n = <NUM> to <NUM>, ethylene glycol therein : n = <NUM> to <NUM>) (meth)acrylate, and a styrene monomer is preferable.

As the styrene monomer, styrene, <NUM>-methylstyrene, α-methylstyrene, vinyltoluene, and divinylbenzene are preferable, and styrene is more preferable.

The content of the polymer a in the ink is preferably <NUM>% by mass or more, more preferably <NUM>% by mass or more, and still more preferably <NUM>% by mass or more, and is preferably <NUM>% by mass or less, more preferably <NUM>% by mass or less, still more preferably <NUM>% by mass or less, and still more preferably <NUM>% by mass or less from the viewpoint of fixability.

The mass ratio of the polymer a to the pigment [polymer a/pigment] is preferably <NUM>/<NUM> to <NUM>/<NUM>, more preferably <NUM>/<NUM> to <NUM>/<NUM>, still more preferably <NUM>/<NUM> to <NUM>/<NUM>, and still more preferably <NUM>/<NUM> to <NUM>/<NUM> from the viewpoint of improving ink stability.

The content of the pigment-containing polymer particles in the ink is preferably <NUM>% by mass or more, more preferably <NUM>% by mass or more, and still more preferably <NUM>% by mass or more, and is preferably <NUM>% by mass or less, more preferably <NUM>% by mass or less, still more preferably <NUM>% by mass or less, and still more preferably <NUM>% by mass or less from the viewpoint of printing density and fixability.

The pigment-containing polymer particles can be produced by the method described in Production Example II, paragraph <NUM>, <CIT>.

The ink can contain, as an optional component, various additives such as a pH adjuster, a viscosity modifier, an antifoaming agent, an antiseptic agent, and a rust inhibitor depending on the application.

The method for removing a printing layer of the first embodiment includes a printing layer removing step of treating the printed matter with neutral water at <NUM> or more to remove the water-soluble printing layer as defined in the claims.

The temperature of the neutral water for treating the printed matter in the printing layer removing step is preferably <NUM> or more, more preferably <NUM> or more, still more preferably <NUM> or more, and still more preferably <NUM> or more from the viewpoint of efficiently removing the printing layer. The temperature is preferably <NUM> or less, more preferably <NUM> or less, and still more preferably <NUM> or less from the viewpoint of the upper limit of the water temperature and the ease of temperature control in the recycling step.

The method for treating the printed matter with neutral water at <NUM> or more is not particularly limited, and examples thereof include immersion cleaning, electrolytic cleaning, spray cleaning, scrub cleaning, ultrasonic cleaning, and steam cleaning. The printed matter can be treated with the neutral water after being subjected to a treatment such as cutting.

A substrate from which the printing layer has been removed can be obtained by the method for removing a printing layer.

The method for producing a printed matter of the second embodiment not encompassed by the wording of the claims includes a water-soluble printing primer layer forming step of forming a water-soluble printing primer layer containing the water-soluble resin for printing on a substrate; and a printing layer forming step of forming a printing layer on the water-soluble printing primer layer. The printed matter includes, in sequence, the substrate; the water-soluble printing primer layer containing the water-soluble resin for printing; and the printing layer.

The water-soluble printing primer layer forming step is a step of forming a water-soluble printing primer layer containing the water-soluble resin for a printing primer on a substrate.

The substrate that can be used in the present embodiment is the same as the substrate that can be used in the first embodiment.

The method for forming the water-soluble printing primer layer on the substrate is not particularly limited, and examples thereof include a method of preparing an application liquid containing the water-soluble resin for a printing primer or the water-soluble resin composition for a printing primer, applying the application liquid by a conventional application method such as a gravure method, a letterpress (flexo) method, an offset method, a roll coater method (transfer method), a spray method, a brush coating method, a bar coater method, an inkjet method, a screen method, a die coating method, a spin coating method, a dip method, a meyer bar method, and an air knife method, and then drying the application liquid.

The concentration of the water-soluble resin in the application liquid is preferably <NUM>% by mass or more, more preferably <NUM>% by mass or more, and still more preferably <NUM>% by mass or more, and preferably <NUM>% by mass or less, more preferably <NUM>% by mass or less, and still more preferably <NUM>% by mass or less from the viewpoint of improving the efficiency of application and the uniformity of the printing primer layer.

The solvent used for preparing the application liquid is not particularly limited as long as the solvent is a solvent that can be used as a solvent.

The method for drying the application liquid applied onto the substrate is not particularly limited, and a conventional drying method can be applied.

The thickness of the water-soluble printing primer layer formed on the substrate after drying is preferably <NUM> or more, more preferably <NUM> or more, and still more preferably <NUM> or more from the viewpoint of preventing the ink or the like related to the printing layer formed on the water-soluble printing primer layer from passing through the water-soluble printing primer layer and adhering to the substrate and the viewpoint of cost reduction, and is preferably <NUM> or less, more preferably <NUM> or less, still more preferably <NUM> or less, and still more preferably <NUM> or less from the viewpoint of flexibility of the primer layer, improvement of productivity, and cost reduction.

The printing layer forming step is a step of forming a printing layer on the water-soluble printing primer layer. The printing method used in the printing layer forming step is not particularly limited, and for example, an inkjet printing method, an electrophotographic printing method, a laser printing method, a letterpress printing method, an intaglio printing method, a flat plate printing method, and a stencil printing method can be used.

The ink used for printing is not particularly limited, and examples thereof include an ink suitable for the printing method used in the printing layer forming step. The ink used in the printing layer forming step can contain the water-soluble resin for printing, but does not necessarily need to contain the water-soluble resin for printing.

The formation of the water-soluble printing primer layer and the formation of the printing layer can be performed continuously (in-line), or the formation of the detachment layer and the printing can be performed separately.

The method for removing a printing layer of the second embodiment is the same as the method for removing a printing layer of the first embodiment except that the water-soluble printing primer layer and the printing layer are removed.

By the method for removing a printing layer, a substrate from which the water-soluble printing primer layer and the printing layer have been removed can be obtained.

The printing primer of the present embodiment can be used as a printing primer for a label of a container and the like of a household detergent and the like that are often placed under a high humidity environment.

The pressure is expressed in an absolute pressure. "Normal pressure" refers to <NUM> kPa.

A method for synthesizing water-soluble resin compositions <NUM> to <NUM> and an acrylic-styrene copolymer composition is described below. The percentage of the monomer unit A based on a total of all monomer units of the water-soluble resin, the weight average molecular weight of the water-soluble resin or the acrylic-styrene copolymer composition, and the content of the water-soluble resin or the acrylic-styrene copolymer composition in the composition calculated from the amount of raw materials added are shown in Table <NUM>.

Into a <NUM> stainless steel separable flask (with a K tube, a stirrer, a nitrogen inlet tube), <NUM> of dimethyl <NUM>,<NUM>-naphthalenedicarboxylate (manufactured by Tokyo Chemical Industry Co. , first class), <NUM> of dimethyl sodium <NUM>-sulfoisophthalate (manufactured by FUJIFILM Wako Pure Chemical Corporation), <NUM> of ethylene glycol (manufactured by FUJIFILM Wako Pure Chemical Corporation, highest quality), <NUM> of titanium tetrabutoxide (manufactured by Tokyo Chemical Industry Co. , first class), and <NUM> of sodium acetate (manufactured by FUJIFILM Wako Pure Chemical Corporation, highest quality) were charged, the temperature of the surface of a mantle heater was raised from <NUM> to <NUM> over <NUM> hour with the mantle heater with stirring under normal pressure and a nitrogen atmosphere, and the mixture was stirred for <NUM> hours at the temperature to perform a transesterification reaction. Then, <NUM> of tetrabutylphosphonium dodecylbenzenesulfonate (manufactured by TAKEMOTO OIL & FAT Co. , ELECUT S-<NUM>) was added thereto, and the resulting mixture was stirred for <NUM> minutes. Then, the temperature of the surface of the heater was raised from <NUM> to <NUM> over <NUM> minutes, and at the same time, the pressure was reduced from normal pressure to <NUM> kPa to perform a reaction for <NUM> hours under the conditions. Then, a reaction was performed while stirring at <NUM> Pa for <NUM> minutes, then nitrogen was introduced into the stainless steel separable flask, and the pressure was returned to normal pressure. The temperature of the surface of the heater was raised from <NUM> to <NUM> at normal pressure over <NUM> minutes, then a reaction was performed with stirring at <NUM> Pa for <NUM> minutes, and then, a reaction was performed with stirring while gradually increasing the degree of pressure reduction from <NUM> Pa to <NUM> Pa over <NUM> minutes. Finally, nitrogen was introduced into the stainless steel separable flask, and the pressure was returned to normal pressure to obtain a water-soluble resin composition <NUM> containing a water-soluble polyester resin <NUM>.

A water-soluble resin composition <NUM> containing a water-soluble polyester resin <NUM> was obtained by performing the same procedures as in the synthesis of the water-soluble resin composition <NUM> except that, after the temperature of the surface of the heater was maintained at <NUM> and the mixture was stirred for <NUM> hours to perform a transesterification reaction, the procedure of adding tetrabutylphosphonium dodecylbenzenesulfonate and stirring the resulting mixture for <NUM> minutes was not performed.

Into a <NUM> stainless steel separable flask (with a K tube, a stirrer, a nitrogen inlet tube), <NUM> of dimethyl <NUM>,<NUM>-naphthalenedicarboxylate (manufactured by Tokyo Chemical Industry Co. ), <NUM> of dimethyl sodium <NUM>-sulfoisophthalate (manufactured by SANYO CHEMICAL INDUSTRIES, LTD. ), <NUM> of <NUM>,<NUM>-propanediol (manufactured by Tokyo Chemical Industry Co. ), <NUM> of titanium tetrabutoxide (manufactured by Tokyo Chemical Industry Co. ), and <NUM> of sodium acetate (manufactured by FUJIFILM Wako Pure Chemical Corporation) were charged, the temperature of the surface of a mantle heater was raised from <NUM> to <NUM> over <NUM> minutes with stirring with the mantle heater under normal pressure and a nitrogen atmosphere, and the mixture was stirred at the temperature for <NUM> hours to perform a transesterification reaction. Then, the pressure was reduced from normal pressure to <NUM> kPa to perform a reaction for <NUM> hour, and then the pressure was reduced from <NUM> to <NUM> kPa to perform a reaction for <NUM> hours. Finally, nitrogen was introduced into the stainless steel separable flask, and the pressure was returned to normal pressure to obtain a water-soluble resin composition <NUM> containing a water-soluble polyester resin <NUM>.

Into a <NUM> stainless steel separable flask (with a K tube, a stirrer, a nitrogen inlet tube), <NUM> of dimethyl terephthalate (manufactured by Tokyo Chemical Industry Co. ), <NUM> of dimethyl sodium <NUM>-sulfoisophthalate (manufactured by SANYO CHEMICAL INDUSTRIES, LTD. ), <NUM> of <NUM>,<NUM>-cyclohexanedimethanol (manufactured by FUJIFILM Wako Pure Chemical Corporation, cis-trans mixture), <NUM> of <NUM>,<NUM>-propanediol (manufactured by Tokyo Chemical Industry Co. ), <NUM> of titanium tetrabutoxide (manufactured by Tokyo Chemical Industry Co. ), and <NUM> of sodium acetate (manufactured by FUJIFILM Wako Pure Chemical Corporation) were charged, the temperature of the surface of a mantle heater was raised from <NUM> to <NUM> over <NUM> minutes with the mantle heater with stirring under normal pressure and a nitrogen atmosphere, and the mixture was stirred for <NUM> hours at the temperature to perform a transesterification reaction. Then, the temperature of the surface of the heater was raised from <NUM> to <NUM> over <NUM> minutes, and at the same time, the pressure was reduced from normal pressure to <NUM> kPa to perform a reaction for <NUM> hours under the conditions. Then, the pressure was further reduced to <NUM> kPa while maintaining the temperature at <NUM> to perform a reaction for <NUM> hours, finally, nitrogen was introduced into the stainless steel separable flask, and the pressure was returned to normal pressure to obtain a water-soluble resin composition <NUM> containing a water-soluble polyester resin <NUM>.

Into a <NUM> stainless steel separable flask (with a K tube, a stirrer, a nitrogen inlet tube), <NUM> of dimethyl terephthalate (manufactured by Tokyo Chemical Industry Co. ), <NUM> of dimethyl isophthalate (manufactured by Tokyo Chemical Industry Co. ), <NUM> of dimethyl sodium <NUM>-sulfoisophthalate (manufactured by SANYO CHEMICAL INDUSTRIES, LTD. ), <NUM> of <NUM>,<NUM>-cyclohexanedimethanol (manufactured by FUJIFILM Wako Pure Chemical Corporation, cis-trans mixture), <NUM> of <NUM>,<NUM>-propanediol (manufactured by Tokyo Chemical Industry Co. ), <NUM> of titanium tetrabutoxide (manufactured by Tokyo Chemical Industry Co. ), and <NUM> of sodium acetate (manufactured by FUJIFILM Wako Pure Chemical Corporation) were charged, the temperature of the surface of a mantle heater was raised from <NUM> to <NUM> over <NUM> minutes with the mantle heater with stirring under normal pressure and a nitrogen atmosphere, and the mixture was stirred for <NUM> hours at the temperature to perform a transesterification reaction. Then, the temperature of the surface of the heater was raised from <NUM> to <NUM> over <NUM> minutes, and at the same time, the pressure was reduced from normal pressure to <NUM> kPa to perform a reaction for <NUM> hours under the conditions. Then, the pressure was further reduced to <NUM> kPa while maintaining the temperature at <NUM> to perform a reaction for <NUM> hours, finally, nitrogen was introduced into the stainless steel separable flask, and the pressure was returned to normal pressure to obtain a water-soluble resin composition <NUM> containing a water-soluble polyester resin <NUM>.

Into a <NUM> stainless steel separable flask (with a K tube, a stirrer, a nitrogen inlet tube), <NUM> of dimethyl terephthalate (manufactured by Tokyo Chemical Industry Co. ), <NUM> of dimethyl isophthalate (manufactured by Tokyo Chemical Industry Co. ), <NUM> of dimethyl sodium <NUM>-sulfoisophthalate (manufactured by SANYO CHEMICAL INDUSTRIES, LTD. ), <NUM> of <NUM>,<NUM>-cyclohexanedimethanol (manufactured by FUJIFILM Wako Pure Chemical Corporation, cis-trans mixture), <NUM> of <NUM>,<NUM>-propanediol (manufactured by Tokyo Chemical Industry Co. ), <NUM> of titanium tetrabutoxide (manufactured by Tokyo Chemical Industry Co. ), and <NUM> of sodium acetate (manufactured by FUJIFILM Wako Pure Chemical Corporation) were charged, the temperature of the surface of a mantle heater was raised from <NUM> to <NUM> over <NUM> minutes with the mantle heater with stirring under normal pressure and a nitrogen atmosphere, and the mixture was stirred for <NUM> hours at the temperature to perform a transesterification reaction. Then, the temperature of the surface of the heater was raised from <NUM> to <NUM> over <NUM> minutes. Then, the pressure was reduced from normal pressure to <NUM> kPa over <NUM> minutes to perform a reaction for <NUM> hours under the conditions, and finally the pressure was returned to normal pressure to obtain a water-soluble resin composition <NUM> containing a water-soluble polyester resin <NUM>.

Into a <NUM> stainless steel separable flask (with a K tube, a stirrer, a nitrogen inlet tube), <NUM> of dimethyl terephthalate (manufactured by Tokyo Chemical Industry Co. ), <NUM> of dimethyl sodium <NUM>-sulfoisophthalate (manufactured by SANYO CHEMICAL INDUSTRIES, LTD. ), <NUM> of <NUM>,<NUM>-cyclohexanedimethanol (manufactured by FUJIFILM Wako Pure Chemical Corporation, cis-trans mixture), <NUM> of <NUM>,<NUM>-propanediol (manufactured by Tokyo Chemical Industry Co. ), <NUM> of tetrabutylphosphonium dodecylbenzenesulfonate (manufactured by TAKEMOTO OIL & FAT Co. , ELECUT S-<NUM>), <NUM> of titanium tetrabutoxide (manufactured by Tokyo Chemical Industry Co. ), and <NUM> of sodium acetate (manufactured by FUJIFILM Wako Pure Chemical Corporation) were charged, the temperature of the surface of a mantle heater was raised from <NUM> to <NUM> over <NUM> minutes with the mantle heater with stirring under normal pressure and a nitrogen atmosphere, and the mixture was stirred for <NUM> hours at the temperature to perform a transesterification reaction. Then, the temperature of the surface of the heater was raised from <NUM> to <NUM> over <NUM> minutes, and at the same time, the pressure was reduced from normal pressure to <NUM> kPa to perform a reaction for <NUM> hours under the conditions. Finally, nitrogen was introduced into the stainless steel separable flask, and the pressure was returned to normal pressure to obtain a water-soluble resin composition <NUM> containing a water-soluble polyester resin <NUM>.

Into a <NUM> stainless steel separable flask (with a K tube, a stirrer, a nitrogen inlet tube), <NUM> of dimethyl terephthalate (manufactured by Tokyo Chemical Industry Co. ), <NUM> of dimethyl sodium <NUM>-sulfoisophthalate (manufactured by SANYO CHEMICAL INDUSTRIES, LTD. ), <NUM> of <NUM>,<NUM>-cyclohexanedimethanol (manufactured by FUJIFILM Wako Pure Chemical Corporation, cis-trans mixture), <NUM> of <NUM>,<NUM>-propanediol (manufactured by Tokyo Chemical Industry Co. ), <NUM> of triethylene glycol (manufactured by Tokyo Chemical Industry Co. ), <NUM> of tetrabutylphosphonium dodecylbenzenesulfonate (manufactured by TAKEMOTO OIL & FAT Co. , ELECUT S-<NUM>), <NUM> of titanium tetrabutoxide (manufactured by Tokyo Chemical Industry Co. ), and <NUM> of sodium acetate (manufactured by FUJIFILM Wako Pure Chemical Corporation) were charged, the temperature of the surface of a mantle heater was raised from <NUM> to <NUM> over <NUM> minutes with the mantle heater with stirring under normal pressure and a nitrogen atmosphere, and the mixture was stirred for <NUM> hours at the temperature to perform a transesterification reaction. Then, the temperature of the surface of the heater was raised from <NUM> to <NUM> over <NUM> minutes, and at the same time, the pressure was reduced from normal pressure to <NUM> kPa to perform a reaction for <NUM> hours under the conditions. Finally, nitrogen was introduced into the stainless steel separable flask, and the pressure was returned to normal pressure to obtain a water-soluble resin composition <NUM> containing a water-soluble polyester resin <NUM>.

Into a <NUM> stainless steel separable flask (with a K tube, a stirrer, a nitrogen inlet tube), <NUM> of dimethyl terephthalate (manufactured by Tokyo Chemical Industry Co. ), <NUM> of dimethyl sodium <NUM>-sulfoisophthalate (manufactured by SANYO CHEMICAL INDUSTRIES, LTD. ), <NUM> of <NUM>,<NUM>-cyclohexanedimethanol (manufactured by FUJIFILM Wako Pure Chemical Corporation, cis-trans mixture), <NUM> of <NUM>,<NUM>-propanediol (manufactured by Tokyo Chemical Industry Co. ), <NUM> of isosorbide (manufactured by Tokyo Chemical Industry Co. ), <NUM> of tetrabutylphosphonium dodecylbenzenesulfonate (manufactured by TAKEMOTO OIL & FAT Co. , ELECUT S-<NUM>), <NUM> of titanium tetrabutoxide (manufactured by Tokyo Chemical Industry Co. ), and <NUM> of sodium acetate (manufactured by FUJIFILM Wako Pure Chemical Corporation) were charged, the temperature of the surface of a mantle heater was raised from <NUM> to <NUM> over <NUM> minutes with the mantle heater with stirring under normal pressure and a nitrogen atmosphere, and the mixture was stirred for <NUM> hours at the temperature to perform a transesterification reaction. Then, the temperature of the surface of the heater was raised from <NUM> to <NUM> over <NUM> minutes, and at the same time, the pressure was reduced from normal pressure to <NUM> kPa to perform a reaction for <NUM> hours under the conditions. Then, the pressure was reduced from <NUM> to <NUM> kPa to perform a reaction for <NUM> hour, and then the pressure was reduced from <NUM> to <NUM> kPa to perform a reaction for <NUM> hours. Finally, nitrogen was introduced into the stainless steel separable flask, and the pressure was returned to normal pressure to obtain a water-soluble resin composition <NUM> containing a water-soluble polyester resin <NUM>.

Into a <NUM> stainless steel separable flask (with a K tube, a stirrer, a nitrogen inlet tube), <NUM> of dimethyl terephthalate (manufactured by Tokyo Chemical Industry Co. ), <NUM> of dimethyl sodium <NUM>-sulfoisophthalate (manufactured by SANYO CHEMICAL INDUSTRIES, LTD. ), <NUM> of <NUM>,<NUM>-cyclohexanedimethanol (manufactured by FUJIFILM Wako Pure Chemical Corporation, cis-trans mixture), <NUM> of <NUM>,<NUM>-propanediol (manufactured by Tokyo Chemical Industry Co. ), <NUM> of isosorbide (manufactured by Tokyo Chemical Industry Co. ), <NUM> of tetrabutylphosphonium dodecylbenzenesulfonate (manufactured by TAKEMOTO OIL & FAT Co. , ELECUT S-<NUM>), <NUM> of titanium tetrabutoxide (manufactured by Tokyo Chemical Industry Co. ), and <NUM> of sodium acetate (manufactured by FUJIFILM Wako Pure Chemical Corporation) were charged, the temperature of the surface of a mantle heater was raised from <NUM> to <NUM> over <NUM> minutes with the mantle heater with stirring under normal pressure and a nitrogen atmosphere, and the mixture was stirred for <NUM> hours at the temperature to perform a transesterification reaction. Then, the temperature of the surface of the heater was raised from <NUM> to <NUM> over <NUM> minutes, the mixture was stirred for <NUM> minutes, then the pressure was reduced from normal pressure to <NUM> kPa to perform a reaction for <NUM> hours under the conditions. Finally, nitrogen was introduced into the stainless steel separable flask, and the pressure was returned to normal pressure to obtain a water-soluble resin composition <NUM> containing a water-soluble polyester resin <NUM>.

Into a <NUM> stainless steel separable flask (with a K tube, a stirrer, a nitrogen inlet tube), <NUM> of dimethyl terephthalate (manufactured by Tokyo Chemical Industry Co. ), <NUM> of dimethyl <NUM>,<NUM>-cyclohexanedicarboxylate (manufactured by FUJIFILM Wako Pure Chemical Corporation, cis-trans mixture), <NUM> of dimethyl sodium <NUM>-sulfoisophthalate (manufactured by SANYO CHEMICAL INDUSTRIES, LTD. ), <NUM> of <NUM>,<NUM>-cyclohexanedimethanol (manufactured by FUJIFILM Wako Pure Chemical Corporation, cis-trans mixture), <NUM> of <NUM>,<NUM>-propanediol (manufactured by Tokyo Chemical Industry Co. ), <NUM> of tetrabutylphosphonium dodecylbenzenesulfonate (manufactured by TAKEMOTO OIL & FAT Co. , ELECUT S-<NUM>), <NUM> of titanium tetrabutoxide (manufactured by Tokyo Chemical Industry Co. ), and <NUM> of sodium acetate (manufactured by FUJIFILM Wako Pure Chemical Corporation) were charged, the temperature of the surface of a mantle heater was raised from <NUM> to <NUM> over <NUM> minutes with the mantle heater with stirring under normal pressure and a nitrogen atmosphere, and the mixture was stirred for <NUM> hours at the temperature to perform a transesterification reaction. Then, the temperature of the surface of the heater was raised from <NUM> to <NUM> over <NUM> minutes, and at the same time, the pressure was reduced from normal pressure to <NUM> kPa to perform a reaction for <NUM> hours under the conditions. Then, the pressure was further reduced to <NUM> kPa while maintaining the temperature at <NUM> to perform a reaction for <NUM> hours, finally, nitrogen was introduced into the stainless steel separable flask, and the pressure was returned to normal pressure to obtain a water-soluble resin composition <NUM> containing a water-soluble polyester resin <NUM>.

Into a <NUM> stainless steel separable flask (with a K tube, a stirrer, a nitrogen inlet tube), <NUM> of dimethyl terephthalate (manufactured by Tokyo Chemical Industry Co. ), <NUM> of dimethyl adipate (manufactured by Tokyo Chemical Industry Co. ), <NUM> of dimethyl sodium <NUM>-sulfoisophthalate (manufactured by SANYO CHEMICAL INDUSTRIES, LTD. ), <NUM> of <NUM>,<NUM>-cyclohexanedimethanol (manufactured by FUJIFILM Wako Pure Chemical Corporation, cis-trans mixture), <NUM> of <NUM>,<NUM>-propanediol (manufactured by Tokyo Chemical Industry Co. ), <NUM> of tetrabutylphosphonium dodecylbenzenesulfonate (manufactured by TAKEMOTO OIL & FAT Co. , ELECUT S-<NUM>), <NUM> of titanium tetrabutoxide (manufactured by Tokyo Chemical Industry Co. ), and <NUM> of sodium acetate (manufactured by FUJIFILM Wako Pure Chemical Corporation) were charged, the temperature of the surface of a mantle heater was raised from <NUM> to <NUM> over <NUM> minutes with the mantle heater with stirring under normal pressure and a nitrogen atmosphere, and the mixture was stirred for <NUM> hours at the temperature to perform a transesterification reaction. Then, the temperature of the surface of the heater was raised from <NUM> to <NUM> over <NUM> minutes, and at the same time, the pressure was reduced from normal pressure to <NUM> kPa to perform a reaction for <NUM> hours under the conditions. Then, the pressure was further reduced to <NUM> kPa while maintaining the temperature at <NUM> to perform a reaction for <NUM> hours, finally, nitrogen was introduced into the stainless steel separable flask, and the pressure was returned to normal pressure to obtain a water-soluble resin composition <NUM> containing a water-soluble polyester resin <NUM>.

The same synthesis as the synthesis of the water-soluble resin composition <NUM> was performed except that into a <NUM> stainless steel separable flask (with a K tube, a stirrer, a nitrogen inlet tube), in addition to <NUM> of dimethyl terephthalate (manufactured by Tokyo Chemical Industry Co. ), <NUM> of dimethyl isophthalate (manufactured by Tokyo Chemical Industry Co. ), <NUM> of dimethyl sodium <NUM>-sulfoisophthalate (manufactured by SANYO CHEMICAL INDUSTRIES, LTD. ), <NUM> of <NUM>,<NUM>-cyclohexanedimethanol (manufactured by FUJIFILM Wako Pure Chemical Corporation, cis-trans mixture), <NUM> of <NUM>,<NUM>-propanediol (manufactured by Tokyo Chemical Industry Co. ), <NUM> of titanium tetrabutoxide (manufactured by Tokyo Chemical Industry Co. ), and <NUM> of sodium acetate (manufactured by FUJIFILM Wako Pure Chemical Corporation), <NUM> of tetrabutylphosphonium dodecylbenzenesulfonate (manufactured by TAKEMOTO OIL & FAT Co. , ELECUT S-<NUM>) was charged to obtain a water-soluble resin composition <NUM> containing a water-soluble polyester resin <NUM>.

Into a <NUM> stainless steel separable flask (with a K tube, a stirrer, a nitrogen inlet tube), <NUM> of dimethyl <NUM>,<NUM>-naphthalenedicarboxylate (manufactured by Tokyo Chemical Industry Co. , first class), <NUM> of dimethyl sodium <NUM>-sulfoisophthalate (manufactured by FUJIFILM Wako Pure Chemical Corporation), <NUM> of ethylene glycol (manufactured by FUJIFILM Wako Pure Chemical Corporation, highest quality), <NUM> of titanium tetrabutoxide (manufactured by Tokyo Chemical Industry Co. , first class), and <NUM> of sodium acetate (manufactured by FUJIFILM Wako Pure Chemical Corporation, highest quality) were charged, the temperature of the surface of a mantle heater was raised from <NUM> to <NUM> over <NUM> hour with the mantle heater with stirring under normal pressure and a nitrogen atmosphere, and the mixture was stirred for <NUM> hours at the temperature to perform a transesterification reaction. Then, <NUM> of tetrabutylphosphonium dodecylbenzenesulfonate (manufactured by TAKEMOTO OIL & FAT Co. , ELECUT S-<NUM>) was added thereto, and the resulting mixture was stirred for <NUM> minutes. Then, the temperature of the surface of the heater was raised from <NUM> to <NUM> over <NUM> minutes, and at the same time, the pressure was reduced from normal pressure to <NUM> kPa to perform a reaction for <NUM> hour and a half under the conditions. Then, a reaction was performed while stirring at <NUM> Pa for <NUM> minutes, then nitrogen was introduced into the stainless steel separable flask, and the pressure was returned to normal pressure. The temperature of the surface of the heater was raised from <NUM> to <NUM> at normal pressure over <NUM> minutes, then a reaction was performed with stirring at <NUM> Pa for <NUM> minutes, and then, a reaction was performed with stirring while gradually increasing the degree of pressure reduction from <NUM> Pa to <NUM> Pa over <NUM> minutes. Finally, nitrogen was introduced into the stainless steel separable flask, and the pressure was returned to normal pressure to obtain a water-soluble resin composition <NUM> containing a water-soluble polyester resin <NUM>.

Into a <NUM> stainless steel separable flask (with a K tube, a stirrer, a nitrogen inlet tube), <NUM> of dimethyl <NUM>,<NUM>-naphthalenedicarboxylate (manufactured by Tokyo Chemical Industry Co. , first class), <NUM> of dimethyl terephthalate (manufactured by Tokyo Chemical Industry Co. , first class), <NUM> of dimethyl sodium <NUM>-sulfoisophthalate (manufactured by FUJIFILM Wako Pure Chemical Corporation), <NUM> of ethylene glycol (manufactured by FUJIFILM Wako Pure Chemical Corporation, highest quality), <NUM> of magnesium acetate (manufactured by FUJIFILM Wako Pure Chemical Corporation) were charged, the temperature of the surface of a mantle heater was raised from <NUM> to <NUM> over <NUM> minutes with the mantle heater with stirring under normal pressure and a nitrogen atmosphere, and the mixture was stirred for <NUM> hours at the temperature to perform a transesterification reaction. Then, <NUM> of antimony trioxide (manufactured by FUJIFILM Wako Pure Chemical Corporation), <NUM> of triethyl phosphate (manufactured by FUJIFILM Wako Pure Chemical Corporation), and <NUM> of silica gel were added, and the temperature of the surface of the heater was raised from <NUM> to <NUM> over <NUM> minutes, and at the same time, the pressure was reduced from normal pressure to <NUM> to <NUM> Pa to perform a reaction for <NUM> hours under the conditions. Finally, nitrogen was introduced into the stainless steel separable flask, and the pressure was returned to normal pressure to obtain a water-soluble resin composition <NUM> containing a water-soluble polyester resin <NUM>.

Into a reaction vessel, <NUM> parts by mass of styrene (manufactured by FUJIFILM Wako Pure Chemical Corporation), <NUM> parts by mass of acrylic acid (manufactured by FUJIFILM Wako Pure Chemical Corporation), <NUM> parts by mass of ethyl acetate (manufactured by FUJIFILM Wako Pure Chemical Corporation), <NUM> parts by mass of isopropyl alcohol (manufactured by FUJIFILM Wako Pure Chemical Corporation), and <NUM> parts by mass of azobisisobutyronitrile (manufactured by FUJIFILM Wako Pure Chemical Corporation) were added, mixed, and polymerized at <NUM> for <NUM> hours under a nitrogen gas atmosphere to obtain an acrylic-styrene copolymer composition containing an acrylic-styrene copolymer. The percentage of the amount of substance of the monomer unit A based on a total of the amount of substance of all monomer units in the copolymer was calculated from the amount of the raw materials added.

A sample was dissolved in a mixed solvent of deuterated chloroform and deuterated trifluoroacetic acid, and an amount of substance A obtained by dividing an integral value A of a peak derived from a benzene ring in a monomer unit (monomer unit A) derived from dimethyl sodium <NUM>-sulfoisophthalate by the number of protons corresponding to the benzene ring in the monomer unit A and an amount of substance B obtained by dividing an integral value B of a peak derived from a benzene ring in a monomer unit (monomer unit B) derived from dimethyl terephthalate, dimethyl isophthalate, or both of them by the number of protons corresponding to the benzene ring in the monomer unit B were calculated by proton NMR measurement using NMR MR400 manufactured by Agilent. The value obtained by dividing the amount of substance A by <NUM> times the sum of the amount of substance A and the amount of substance B, expressed in percentage (<NUM> × amount of substance A/(<NUM> × (amount of substance A + amount of substance B)), was defined as the percentage of the amount of substance of the monomer unit A based on a total of the amount of substance of all monomer units in the water-soluble polyester resin.

However, when the monomer unit B is a monomer unit derived from cyclohexane or adipic acid, the percentage of the amount of substance of the monomer unit (monomer unit A) derived from dimethyl sodium <NUM>-sulfoisophthalate based on a total of the amount of substance of all monomer units in the water-soluble polyester resin was determined by the following method.

A sample was dissolved in a mixed solvent of deuterated chloroform and deuterated trifluoroacetic acid, and an amount of substance A obtained by dividing an integral value A of a peak derived from a benzene ring in a monomer unit (monomer unit A) derived from dimethyl sodium <NUM>-sulfoisophthalate by the number of protons corresponding to the benzene ring in the monomer unit A, an amount of substance B obtained by dividing an integral value B of a peak derived from a benzene ring in a monomer unit (monomer unit B) derived from dimethyl terephthalate, dimethyl isophthalate, or both of them by the number of protons corresponding to the benzene ring in the monomer unit B, and an amount of substance C obtained by dividing an integral value C of a peak corresponding to carbonyl α-position in monomer unit (monomer unit C) derived from aliphatic dimethyl carboxylate by the number of protons corresponding to vicinity of ester in the monomer unit C were calculated by proton NMR measurement using NMR MR400 manufactured by Agilent. The value obtained by dividing the amount of substance A by <NUM> times the sum of the amount of substance A, the amount of substance B, and the amount of substance C expressed in percentage (<NUM> × amount of substance A/(<NUM> × (amount of substance A + amount of substance B + amount of substance C)), was defined as the percentage of the amount of substance of the monomer unit A based on a total of the amount of substance of all monomer units in the water-soluble polyester resin.

A calibration curve was prepared from standard polystyrene or standard polymethyl methacrylate using a gel permeation chromatograph (GPC) method under the following conditions to determine the weight average molecular weight (Mw).

A sample sandwiched between polyimide films was placed on a hot plate heated to <NUM>, and a spatula was pressed from above to prepare a sheet having a thickness of about <NUM>. A sample (<NUM> to <NUM>) was cut out from the sheet with scissors, precisely weighed, and sealed in an aluminum pan, the temperature was raised from <NUM> to <NUM> at <NUM>/min, and then the sample was cooled at a set temperature of <NUM> using a DSC apparatus (DSC <NUM> manufactured by Seiko Instruments Inc. The glass transition temperature (°C) of each resin composition was determined from the DSC curve obtained by raising the temperature again to <NUM> at <NUM>/min.

Aqueous solutions of <NUM>% by mass of the water-soluble resin compositions described in Tables <NUM> and <NUM> and <NUM>% by mass of deionized water were applied onto substrate films described in Tables <NUM> and <NUM> using a bar coater, and dried by heating at <NUM> for <NUM> minutes to form a printing primer layer. Further, on the printing primer layer, printing was performed with a tabletop gravure printing machine (manufactured by Matsuo Sangyo Co. , K-printing proofer) using an oil gravure ink (PANNECO AM manufactured by TOYO INK CO. ) whose viscosity is adjusted to <NUM> seconds with a diluent (PN <NUM> solvent manufactured by TOYO INK CO. ) using a Zahn cup #<NUM> to prepare a sample. The water-soluble resin composition <NUM> in Tables <NUM> and <NUM> is polyvinyl alcohol (PVA-<NUM> manufactured by KURARAY CO.

Samples were prepared in the same procedure as in Example <NUM> except that aqueous solutions of <NUM>% by mass of the water-soluble resin composition described in Tables <NUM> and <NUM> and <NUM>% by mass of deionized water were used.

The substrates described in Tables <NUM> and <NUM> are as follows.

Each of the prepared samples was immersed in tap water at a temperature described in Table <NUM>, and the detachment state of the printing primer layer having a printed matter was observed while stirring. When the printed matter spontaneously dropped from the substrate film almost completely within <NUM> minutes, the time (minutes) was described.

Each of the prepared samples was immersed in <NUM> of tap water at a temperature described in Table <NUM> and stirred for <NUM> minutes, and then each sample was dried with hot air at <NUM> for <NUM> hour. The removal percentage of the printed matter was measured from the area ratio of the printed matter obtained by measuring the areas of the printed matter before immersion in tap water and after drying. For the measurement of the area of the printed matter, an image was captured using a scanner function in which the image quality was set to <NUM> dpi using a digital full-color multifunction printer MP C5504 manufactured by Ricoh Co. , and the area of the printed matter was measured using an image obtained by binarizing the scanned image with the threshold value set to <NUM> using an image processing software "WinRoof" manufactured by MITANI CORPORATION. The removal percentage was calculated using the following formula.

Each sample was immersed in tap water at <NUM> for <NUM> hours, and then the presence or absence of lifting of the detachment layer having the printed matter on the surface of the substrate film and the tendency of detachment due to scratching with a spatula were observed. The results were evaluated by the following indices.

The evaluation results are shown in Tables <NUM> and <NUM>.

The water-soluble resin composition <NUM> synthesized above (<NUM>) was weighed and dissolved in <NUM> of deionized water heated to <NUM>, <NUM> of the pigment aqueous dispersion and <NUM> of a thickener (ADEKA NOL UH-<NUM> manufactured by ADEKA CORPORATION) were added to the obtained aqueous solution, and the mixture was stirred at <NUM> rpm. A mixed solution obtained by adding <NUM> of a <NUM>% by mass solution of <NUM>,<NUM>,<NUM>,<NUM>-tetramethyl-<NUM>-decine-<NUM>,<NUM>-diol in propylene glycol (Surfynol <NUM> PG-<NUM> manufactured by Air Products & Chemicals Inc. ) and <NUM> of PEG-<NUM> methyl ether dimethicone (KF-<NUM> manufactured by Shin-Etsu Chemical Co. ) to <NUM> of diethylene glycol monoisobutyl ether (manufactured by FUJIFILM Wako Pure Chemical Corporation) was further added thereto, and the mixture was stirred at room temperature for <NUM> minutes and then filtered with a stainless steel wire mesh (<NUM> mesh) to obtain an ink composition <NUM>.

The water-soluble resin composition <NUM> synthesized above (<NUM>) was weighed and dissolved in <NUM> of deionized water heated to <NUM>, and <NUM> of <NUM>-propanol (manufactured by FUJIFILM Wako Pure Chemical Corporation) was added to the obtained aqueous solution to prepare a diluent. The diluent prepared above (<NUM>) was added to <NUM> of a commercially available aqueous gravure ink, and the mixture was stirred at room temperature for <NUM> minutes and then filtered with a stainless steel wire mesh to obtain an ink composition <NUM>.

An ink composition <NUM> was obtained in the same manner as in the method for preparing an ink composition <NUM> except that <NUM>-propanol was not added.

Using each ink composition described in Table <NUM>, gravure printing was performed on a corona-treated surface of a PET film (manufactured by FUTAMURA CHEMICAL CO. , biaxial oriented polyethylene terephthalate film). The printing was performed by solid printing at a printing density of <NUM>% with an attached electronic engraving plate (line number: <NUM> lines/inch, plate depth: <NUM>) using a tabletop gravure printing machine (manufactured by Matsuo Sangyo Co. , K-printing proofer).

Each of the prepared samples was immersed in tap water at a temperature described in Table <NUM>, and the detachment state of the printed matter having a printed matter was observed while stirring. When the printed matter spontaneously dropped from the substrate film almost completely within <NUM> minutes, the time (minutes) was described.

Claim 1:
A method for removing a printing layer, comprising:
a printing layer removing step of treating a printed matter with neutral water at <NUM> or more to remove the water-soluble printing layer,
Wherein the printed matter comprises a water-soluble printing layer containing a water-soluble resin for printing, comprising:
a monomer unit A having a sulfonate group; and
a monomer unit B having no hydrophilic group,
wherein a percentage of the monomer unit A based on a total of all monomer units is <NUM> to <NUM> mol%.