Water-based OP varnish and water-based flexographic ink

Abstract

To provide a water-based overprint (OP) varnish for a shrink label which is excellent in adhesion, wet friction resistance, and antiblocking property and can form a coating in which whitening during heating and shrinking is suppressed can be formed on various substrates to be printed.SOLUTION: A water-based OP varnish for shrink labels containing a binder resin, water, and a water-soluble organic solvent, wherein the binder resin satisfies the following requirement (1). [Requirement (1)]: a content of a constitutional unit derived from a methacrylic monomer is 90 mass% or more, (i) an A-B diblock copolymer having an A chain and a B chain, or (ii) a B-A-B triblock copolymer having an A chain, and a B chain and containing a group represented by the following formula (1) in the A chain. [0110](R represents an alkylene group having 2 to 18 carbon atoms, etc., X and Y represent O or NH, and "*" represents the bonding position in the A chain).SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to an aqueous OP varnish and an aqueous flexographic ink for shrink labels.

Background Art

[0002] In recent years, as means for packaging beverages, cosmetics, daily necessities, etc., packaging means such as paper containers, steel cans, aluminum cans, glass containers, and plastic containers have been utilized while taking advantage of their respective characteristics. In order for consumers to easily distinguish a company's own products from similar products of other companies, many improvements have been made to such packaging means not only in terms of color tone and display method but also in terms of shape and the like.

[0003] Shrink labels are widely used as means for packaging various articles of various shapes (Patent Document 1). A shrink label is obtained by disposing a tubular heat-shrinkable plastic film printed with a desired image or the like on the surface of a container or the like and then heat-shrinking it for attachment and packaging. As the heat-shrinkable plastic film, shrinkable polyvinyl chloride, shrinkable polystyrene, shrinkable polyethylene terephthalate, shrinkable polypropylene, and the like are used.

[0004] For printing shrink labels, inks containing solvents and binder resins suitable for the characteristics of various films are used. For example, inks containing an organic solvent and a binder resin obtained by using an acrylic resin and nitrocellulose in combination have been proposed for shrinkable polyvinyl chloride, shrinkable polystyrene, and shrinkable polyethylene phthalate (Patent Document 2). Further, for shrinkable polypropylene, an ink containing toluene and chlorinated polypropylene as a binder resin is used.

[0005] In recent years, the development of environmentally friendly products has been required, and among them, water-based inks have attracted attention. There is also a demand for water-based inks used for printing on resin film substrates, and many studies have been conducted on the transition from oil-based gravure inks to water-based flexo inks (Patent Documents 3 and 4).

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0007] Since water-based inks substantially do not contain volatile organic solvents, the burden on the environment is small, but there are often problems with the abrasion resistance (wet abrasion resistance) of the formed coating film in a wet state. In practical use, when shrink labels are transported in a wet state, problems such as the ink coating film being easily peeled off may occur.

[0008] Also, when the glass transition temperature (Tg) of the overprint (OP) varnish for shrink labels or the binder resin contained in the ink is relatively high, the transparency of the coating film may be impaired during the heat shrinkage of the shrink label, and whitening may easily occur. Such whitening is often suppressed by using a binder resin with a relatively low glass transition temperature. However, when using a binder resin with a relatively low glass transition temperature, the blocking resistance of the coating film decreases, and problems such as the coating films sticking to each other are likely to occur.

[0009] The present invention has been made in view of the problems of such prior art, and the object thereof is to provide an aqueous overprint (OP) varnish for shrink labels that is excellent in adhesion, wet rub resistance, and blocking resistance, and can form a coating film with suppressed whitening during heat shrinkage on various substrates to be printed.

[0010] Another object of the present invention is to provide an aqueous flexographic ink for shrink labels that can form a coating film excellent in adhesion, wet rub resistance, and blocking resistance on various substrates to be printed. [Means for Solving the Problems]

[0011] That is, according to the present invention, the following aqueous OP varnish is provided. [1] An aqueous OP varnish for shrink labels containing a binder resin, water, and a water-soluble organic solvent, wherein the binder resin satisfies the following requirements (1) to (5).

[0012] [Requirement (1)]: An (i) A-B diblock copolymer having an A chain and a B chain, or (ii) a B-A-B triblock copolymer having an A chain and a B chain and containing a group represented by the following general formula (1) in the A chain, wherein the content of structural units derived from methacrylic acid-based monomers is 90% by mass or more.

[0013] TIFF0007714483000001.tif38170 (In the general formula (1), R represents a linear, branched, or cyclic alkylene group having 2 to 18 carbon atoms, or a di-, tri-, or tetraalkylene (having 2 to 4 carbon atoms) glycol group, X and Y each independently represent O or NH, and "*" represents the bonding position in the A chain)

[0014] [Requirement (2)]: The A chain has an acid value of 20 mgKOH / g or less, a glass transition temperature of 30°C or less, a number average molecular weight of 15,000 to 35,000, and a molecular weight distribution (weight average molecular weight / number average molecular weight) of 1.6 or less. [Requirement (3)]: The B chain contains a structural unit derived from methacrylic acid, has an acid value of 50 to 200 mgKOH / g, and a number average molecular weight of 1,000 to 15,000. [Requirement (4)]: It has a glass transition temperature of 40°C or lower, a number average molecular weight of 20,000 to 50,000, and a molecular weight distribution of 1.6 or less. [Requirement (5)]: At least a part of the carboxy groups is neutralized with at least one alkaline substance selected from the group consisting of ammonia, dimethylaminoethanol, and aminomethylpropanol to form self-emulsified emulsion particles having a number average particle diameter of 50 to 500 nm.

[0015] [2] The A chain does not contain a structural unit derived from a methacrylate having an acidic group, and contains a structural unit derived from at least one monomer selected from the monomer group (i) consisting of benzyl methacrylate, cyclohexyl methacrylate, isobornyl methacrylate, t-butylcyclohexyl methacrylate, tetrahydrofurfuryl methacrylate, and methyl methacrylate, and a structural unit derived from at least one monomer selected from the monomer group (ii) consisting of 2-ethylhexyl methacrylate, lauryl methacrylate, tetradecyl methacrylate, stearyl methacrylate, and behenyl methacrylate. The B chain contains a structural unit derived from methacrylic acid, a structural unit derived from at least one monomer selected from the monomer group (i), and a structural unit derived from at least one monomer selected from the monomer group (ii). The aqueous OP varnish according to [1] above. [3] The carboxy groups of at least one polymer having a carboxy group selected from the group consisting of polyethylene, polypropylene, poly-α-olefin, silicone, and copolymers thereof are neutralized with an alkaline substance and self-emulsified to form emulsion particles, and the aqueous OP varnish according to [1] or [2] above further contains the emulsion particles as a wax component.

[0016] Further, according to the present invention, there is provided an aqueous flexographic ink as shown below. [4] An aqueous flexographic ink for shrink labels, containing the aqueous OP varnish according to any one of [1] to [3], a pigment, and a pigment dispersant for dispersing the pigment. [5] The aqueous flexographic ink according to [4], wherein the content of the pigment is 1 to 60% by mass, the content of the water is 20 to 80% by mass, the content of the water-soluble organic solvent is 30% by mass or less, the content of the pigment dispersant is 0.5 to 10% by mass, and the content of the binder resin is 10 to 30% by mass.

Advantages of the Invention

[0017] According to the present invention, it is possible to provide an aqueous OP varnish for shrink labels that is excellent in adhesion, wet rub resistance, and blocking resistance, and can form a coating film with suppressed whitening during heat shrinkage on various substrates to be printed.

[0018] Further, according to the present invention, it is possible to provide an aqueous flexographic ink for shrink labels that can form a coating film excellent in adhesion, wet rub resistance, and blocking resistance on various substrates to be printed.

Embodiments for Carrying Out the Invention

[0019] <Aqueous OP Varnish> One embodiment of the aqueous OP varnish for shrink labels of the present invention contains a binder resin, water, and a water-soluble organic solvent. And the binder resin satisfies the following requirements (1) to (5). Hereinafter, the details of the aqueous OP varnish of this embodiment will be described.

[0020] [Requirement (1)]: An (i) A-B diblock copolymer having A and B chains, or (ii) a B-A-B triblock copolymer having A and B chains and containing a group represented by the following general formula (1) in the A chain, wherein the content of the structural unit derived from the methacrylic acid-based monomer is 90% by mass or more.

[0021] TIFF0007714483000002.tif38170(In the general formula (1), R represents a linear, branched, or cyclic alkylene group having 2 to 18 carbon atoms, or a di-, tri-, or tetraalkylene (2 to 4 carbon atoms) glycol group, X and Y each independently represent O or NH, and "*" indicates the bonding position in the A chain.)

[0022] [Requirement (2)]: The A chain has an acid value of 20 mgKOH / g or less, a glass transition temperature of 30 °C or less, a number average molecular weight of 15,000 to 35,000, and a molecular weight distribution (weight average molecular weight / number average molecular weight) of 1.6 or less.

[0023] [Requirement (3)]: The B chain contains a structural unit derived from methacrylic acid, has an acid value of 50 to 200 mgKOH / g, and a number average molecular weight of 1,000 to 15,000.

[0024] [Requirement (4)]: It has a glass transition temperature of 40 °C or less, a number average molecular weight of 20,000 to 50,000, and a molecular weight distribution of 1.6 or less.

[0025] [Requirement (5)]: At least some of the carboxy groups are neutralized with at least one alkaline substance selected from the group consisting of ammonia, dimethylaminoethanol, and aminomethylpropanol to form self-emulsified emulsion particles having a number average particle diameter of 50 to 500 nm.

[0026] (Binder resin) The binder resin is the main component of the film (coating film) formed by coating and drying the aqueous OP varnish, and is a polymer component that can exhibit effects such as adhesion to a substrate such as a plastic film, abrasion resistance, water resistance, chemical resistance, solvent resistance, and surface protection. The binder resin forms emulsion particles in a state of being dispersed in an aqueous medium by neutralizing at least a part of the carboxy groups in an A-B diblock copolymer or a B-A-B triblock copolymer with an alkaline substance and self-emulsifying. The A chain in the A-B diblock copolymer and the B-A-B triblock copolymer (hereinafter, collectively simply referred to as "block copolymer") is a water-insoluble polymer chain, and is a polymer chain that can exhibit properties such as adhesion to a substrate such as a plastic film, flexibility, and abrasion resistance. On the other hand, the B chain in the block copolymer is a polymer chain having a carboxy group. By neutralizing and ionizing this carboxy group, the B chain is water-affinitive and dissolves. That is, the B chain is a polymer chain having a function of dispersing and emulsifying the block copolymer in an aqueous medium. In addition, since the B chain has a carboxy group, it also contributes to improving the adhesion to a substrate such as a plastic film. The content of the binder resin in the aqueous OP varnish is preferably 10 to 50% by mass, more preferably 20 to 45% by mass, based on the whole of the aqueous OP varnish.

[0027] The aqueous OP varnish of the present embodiment may further contain an aqueous resin other than the above binder resin, if necessary. Examples of the aqueous resin other than the binder resin include aqueous polyurethane resin, aqueous polyester resin, aqueous acrylic resin, aqueous styrene-acrylic resin, aqueous styrene-maleic anhydride resin, aqueous cellulose-based resin, and aqueous vinyl chloride copolymer resin.

[0028] [A-B diblock copolymer and B-A-B triblock copolymer] The binder resin is (i) an A-B diblock copolymer having an A chain and a B chain, or (ii) a B-A-B triblock copolymer having an A chain and a B chain and containing a group represented by the general formula (1) in the A chain. The content of the structural unit derived from the methacrylic acid-based monomer in the block copolymer is 90% by mass or more, preferably 95% by mass or more, and more preferably 98% by mass or more.

[0029] The polystyrene-reduced number average molecular weight (Mn) of the binder resin (block copolymer) measured by gel permeation chromatography (GPC) is 20,000 to 50,000, preferably 25,000 to 45,000. By setting the number average molecular weight within the above range, good adhesion to a substrate such as a plastic film can be achieved, and a coating film excellent in wet rub resistance can be formed. If the number average molecular weight of the binder resin is less than 20,000, the physical properties of the formed coating film cannot be sufficiently improved. On the other hand, a block copolymer having a number average molecular weight exceeding 50,000 may have problems such as requiring an excessive time for polymerization and an excessively high viscosity of the resin solution.

[0030] The molecular weight distribution (weight average molecular weight (Mw) / number average molecular weight (Mn)) of the binder resin (hereinafter also referred to as "PDI") is 1.6 or less, preferably 1.5 or less. When the molecular weight distribution of the binder resin exceeds 1.6, it becomes difficult to form a coating film excellent in adhesion to a substrate such as a plastic film.

[0031] The glass transition temperature (Tg) of the binder resin is 40°C or lower, preferably 30°C or lower. By setting the glass transition temperature to 40°C or lower, the softness of the binder resin is improved, and a coating film excellent in properties such as wet rub resistance, adhesion, film-forming property, and followability to the film during heat shrinkage can be formed. The glass transition temperature (Tg) may be either a value measured using a differential thermal analyzer or the like (actual measured value) or a value calculated from the Tg of the homopolymer (theoretical value). However, the glass transition temperature (Tg) in this specification is a value (theoretical value) calculated from the Tg of the homopolymer. For example, in the case of a polymer (copolymer) obtained by copolymerizing x types of monomers, assuming the mass (g) of each monomer as "W1, W2, ··· Wx" and the Tg (°C) of the homopolymer of each monomer as "T1, T2, ··· Tx", the Tg (T (°C)) of this copolymer can be calculated from the following formula (A). 1 / T = W1 / (T1 + 273) + W2 / (T2 + 273) + ··· Wx / (Tx + 273) ···(A)

[0032] As the value of the Tg of the homopolymer, the value described in "Polymer Handbook 4th Edition" may be used, or alternatively, the values in various other documents may be used. In this specification, the value described in "Polymer Handbook 4th Edition" is used.

[0033] [A chain] The A chain is a polymer chain (polymer block) that forms a water-insoluble film (coating film) with durability. Therefore, the structural units constituting the A chain are preferably structural units derived from monomers with high hydrophobicity. Specifically, the A chain preferably contains a structural unit derived from at least one monomer selected from the monomer group (i) consisting of benzyl methacrylate, cyclohexyl methacrylate, isobornyl methacrylate, t-butylcyclohexyl methacrylate, tetrahydrofurfuryl methacrylate, and methyl methacrylate, and a structural unit derived from at least one monomer selected from the monomer group (ii) consisting of 2-ethylhexyl methacrylate, lauryl methacrylate, tetradecyl methacrylate, stearyl methacrylate, and behenyl methacrylate.

[0034] The glass transition temperature (Tg) of the A chain is 30 °C or lower, preferably 20 °C or lower. The monomers included in the above-mentioned monomer group (ii) all have long-chain alkyl groups and tend to lower the Tg. Therefore, it is preferable that the content of the structural unit derived from the monomer of the monomer group (ii) in the A chain is higher than the content of the structural unit derived from the monomer of the monomer group (i). However, if the A chain is composed only of the structural unit derived from the monomer of the monomer group (ii), the binder resin may become too soft and the blocking resistance may decrease slightly. Therefore, by including the structural unit derived from the monomer of the monomer group (i), which tends to increase the Tg, in the A chain, the Tg of the binder resin can be adjusted and the blocking resistance can be further improved.

[0035] The A chain may contain a structural unit derived from a methacrylate having an acidic group such as methacrylic acid. However, the content of the structural unit derived from the methacrylate having an acidic group in the A chain is preferably such that the A chain does not dissolve in water when neutralized. The acid value of the A chain is 20 mgKOH / g or less, preferably 10 mgKOH / g or less, more preferably 0 mgKOH / g. That is, it is preferable that the A chain substantially does not contain a structural unit derived from a methacrylate having an acidic group.

[0036] The A chain may further contain a structural unit derived from a methacrylic acid monomer other than the monomers of monomer group (i) and the monomers of monomer group (ii) (other methacrylic acid monomers). Examples of other methacrylic acid monomers include monofunctional methacrylates having substituents such as ethyl, propyl, butyl, hexyl, octyl, decyl, methoxyethyl, butoxyethyl, phenoxyethyl, nonylphenoxyethyl, isobornyl, dicyclopentanyl, dicyclopentenyl, dicyclopentenyloxyethyl, glycidyl, 2-hydroxyethyl, 2-hydroxypropyl, 4-hydroxybutyl, dimethylaminoethyl, diethylaminoethyl, polyethylene glycol, polypropylene glycol, polyethylene glycol monomethyl ether, polypropylene glycol monomethyl ether, poly-ε-caprolactone, and polydimethylsiloxane.

[0037] The number average molecular weight (Mn) in terms of polystyrene of the A chain measured by GPC is 15,000 to 35,000, preferably 17,000 to 30,000. By setting the number average molecular weight of the A chain within the above range, a coating film excellent in performance such as adhesion and wet rub resistance can be formed. If the number average molecular weight of the A chain is less than 15,000, the adhesion of the formed coating film to a substrate such as a plastic film becomes insufficient. On the other hand, an A chain with a number average molecular weight exceeding 35,000 requires an excessive amount of time for polymerization and may have too large a particle size of the formed particles.

[0038] The molecular weight distribution (PDI) of the A chain is 1.6 or less, preferably 1.5 or less. When the molecular weight distribution of the A chain exceeds 1.6, it becomes difficult to form a coating film with excellent adhesion to a substrate such as a plastic film.

[0039] When the binder resin is a B-A-B triblock copolymer, the A chain constituting the B-A-B triblock copolymer contains a group represented by the following general formula (1). The group represented by the following general formula (1) is, for example, a group (residue) derived from a polymerization initiator compound used when producing a B-A-B triblock copolymer by living radical polymerization described later. That is, by subjecting a methacrylic monomer to living radical polymerization using a specific polymerization initiator, the group represented by the following general formula (1) can be introduced into the main chain of the A chain. The group represented by the following general formula (1) is a group having an ester bond with a tertiary carbon atom and is difficult to hydrolyze. Therefore, the group represented by the following general formula (1) is a group that is difficult to hydrolyze even under high pH conditions containing an alkali and can exist relatively stably. Therefore, a B-A-B triblock copolymer having an A chain containing the group represented by the following general formula (1) in the main chain is a binder resin excellent in durability such as long-term storage stability.

[0040] TIFF0007714483000003.tif38170(In the general formula (1), R represents a linear, branched, or cyclic alkylene group having 2 to 18 carbon atoms, or a di-, tri-, or tetraalkylene (2 to 4 carbon atoms) glycol group, X and Y each independently represent O or NH, and "*" represents the bonding position in the A chain)

[0041] Examples of the group represented by R in the general formula (1) include an ethylene group, a propylene group, a methylethylene group, a butylene group, a hexylene group, a cyclohexylene group, a hexyler dimethylene group, a phenyldimethylene group, a decamethylene group, an octamethylene group, a diethylene glycol group, a triethylene glycol group, a tetraethylene glycol group, a dipropylene glycol group, a tripropylene glycol group, a tetrapropylene glycol group, a ditetramethylene glycol group, and the like. In the general formula (1), R is preferably an ethylene group, a propylene group, or a tetramethylene group. In the general formula (1), X and Y are both preferably "O".

[0042] For example, when producing a B-A-B triblock copolymer by living radical polymerization described later using a polymerization initiation compound having a group represented by the general formula (1), polymer chains extend from both ends of the group represented by the general formula (1) (the "*" part in the general formula (1)). The molecular weights of the two polymers extending from both ends may be the same or different.

[0043] [B chain] The B chain is a polymer chain (polymer block) containing structural units derived from methacrylic acid. That is, a carboxy group derived from methacrylic acid is present in the B chain, and when this carboxy group is neutralized with an alkaline substance and ionized, the B chain becomes hydrophilic and dissolves in water. In an aqueous medium, the water-insoluble A chain is granulated, and the B chain dissolved in water stabilizes the granulated A chain. Thereby, the binder resin can be emulsified and dispersed in the aqueous medium. Also, since the B chain dissolves in water, it has the property (redissolubility) of redissolving the block copolymer in water even when dried. Furthermore, since the carboxy group forms a hydrogen bond or the like with a base material such as a plastic film, a coating film excellent in adhesion can be formed.

[0044] The acid value of the B chain is 50 to 200 mgKOH / g, preferably 60 to 150 mgKOH / g. When the acid value of the B chain is less than 50 mgKOH / g, the B chain does not dissolve in water, making it difficult to disperse and emulsify the binder resin in the aqueous medium. On the other hand, when the acid value of the B chain exceeds 200 mgKOH / g, the hydrophilicity of the B chain is too high, easily deteriorating the properties such as water resistance and chemical resistance of the coating film, and the viscosity during polymerization may become excessively high, making it difficult to form a block structure.

[0045] The B chain preferably contains a structural unit derived from methacrylic acid, a structural unit derived from at least one monomer selected from the aforementioned monomer group (i), and a structural unit derived from at least one monomer selected from the aforementioned monomer group (ii). The B chain may further contain a structural unit derived from a methacrylic acid-based monomer other than the monomers of monomer group (i) and the monomers of monomer group (ii) (the aforementioned "other methacrylic acid-based monomers").

[0046] The number average molecular weight (Mn) in terms of polystyrene of the B chain measured by GPC is from 1,000 to 15,000, preferably from 2,000 to 10,000. When the number average molecular weight of the B chain is less than 1,000, the water-soluble B chain is too short, the dispersibility and emulsifying property of the granulated A chain decrease, and the overall particle size may increase. On the other hand, when the number average molecular weight of the B chain exceeds 15,000, the hydrophilicity becomes too high, the water resistance of the formed coating film decreases, and the viscosity of the aqueous OP varnish may become excessively high.

[0047] [Method for producing block copolymer] The block copolymer can be synthesized by a conventionally known method. Among them, living polymerization methods such as living anionic polymerization method, living cationic polymerization method, and living radical polymerization method are preferred, and the living radical polymerization method is particularly preferred from the viewpoints of conditions, materials, and equipment. Examples of the living radical polymerization method include atom transfer radical polymerization method (ATRP method), reversible addition-fragmentation chain transfer polymerization method (RAFT method), nitroxide method (NMP method), organotellurium method (TERP method), reversible transfer catalyzed polymerization method (RTCP method), and reversible catalyst-mediated polymerization method (RCMP method). Among them, the RTCP method and RCMP method using an organic compound as a catalyst and an organic iodide as a polymerization initiation compound are preferred. These methods use relatively safe commercially available compounds, do not use heavy metals or special compounds, and are advantageous in terms of cost and purification. Furthermore, by making the growth end tertiary iodine, an accurate block structure can be easily formed with general equipment.

[0048] The polymerization can be either thermal polymerization or photopolymerization, and an azo radical generator, a peroxide radical generator, a photosensitizer, etc. may be added to the polymerization reaction system. The polymerization form may be any of solvent-free, solution polymerization, and emulsion polymerization, and solution polymerization is preferred. When producing a polymer emulsion by dispersing the obtained block copolymer in an aqueous medium, it is preferable to use the same organic solvent as the water-soluble organic solvent used in the aqueous medium during solution polymerization, because the reaction solution after the polymerization reaction can be used as it is.

[0049] When producing an A-B diblock copolymer, either the A chain or the B chain may be polymerized first. However, if the B chain is polymerized first, methacrylic acid may remain in the polymerization system. In this case, a structural unit derived from methacrylic acid may be introduced into the A chain to be polymerized later, so it is preferable to polymerize the A chain first and then polymerize the B chain.

[0050] The method for producing a B-A-B triblock copolymer preferably has a polymerization step of using an iodine-containing organic compound represented by the following general formula (2) as a polymerization initiation compound (polymerization initiator). In the presence of the iodine-containing organic compound (polymerization initiation compound) represented by the following general formula (2), living radical polymerization is carried out in an organic solvent in the order of the A chain and the B chain to obtain a B-A-B triblock copolymer. Similar to the case of producing an A-B diblock copolymer, the RTCP method or the RCMP method using an organic compound as a catalyst and an organic iodide as a polymerization initiation compound is preferred.

[0051] TIFF0007714483000004.tif33170(In the general formula (2), R represents a linear, branched, or cyclic alkylene group having 2 to 18 carbon atoms, or a di-, tri-, or tetraalkylene (having 2 to 4 carbon atoms) glycol group, and X and Y each independently represent O or NH)

[0052] R, X, and Y in general formula (2) have the same meanings as R, X, and Y in general formula (1). The organic compound represented by general formula (2) can be synthesized by a conventionally known method. For example, a diol, amino alcohol, and diamine having a group represented by R (hereinafter also collectively referred to as "diol etc.") are prepared. The prepared diol etc. is reacted with bromoisobutyric acid bromide to obtain a dibromo compound. Thereafter, the obtained dibromo compound is reacted with a compound such as sodium iodide for halogen exchange to obtain an organic compound represented by general formula (2). Further, the above diol etc. is reacted with methacrylic acid chloride or methacrylic anhydride, or transesterified with methyl methacrylate to methacrylate the hydroxyl group or amino group. Thereafter, by adding hydrogen iodide, a compound represented by general formula (2) can be obtained.

[0053] [Polymer emulsion] The binder resin (block copolymer) is self-emulsified with at least a part of the carboxy groups neutralized with an alkaline substance, and forms emulsion particles in an aqueous medium containing water and a water-soluble organic solvent. The number average particle diameter of the emulsion particles is 50 to 500 nm, preferably 70 to 350 nm. When the number average particle diameter of the emulsion is less than 50 nm, the viscosity of the aqueous OP varnish becomes excessively high and the hydrophilicity becomes high, so the physical properties of the formed coating film deteriorate. On the other hand, when the number average particle diameter of the emulsion exceeds 500 nm, foreign substances such as so-called "bumps" are likely to be formed in the formed coating film. The number average particle diameter of the emulsion particles is a value measured and calculated by a dynamic light scattering type particle size distribution measuring device.

[0054] The alkaline substance that neutralizes the carboxy group in the block copolymer is at least one selected from the group consisting of ammonia, dimethylaminoethanol, and aminomethylpropanol. The amount of the alkaline substance is preferably an amount that neutralizes a part or all of the acidic groups such as the carboxy group in the block copolymer.

[0055] Methods for neutralizing, emulsifying, and dispersing block copolymers are conventionally well-known. For example, after synthesizing a block copolymer by solution polymerization, alkaline water can be added while stirring the polymerization solution for dispersion and emulsification. Further, after polymerization, the block copolymer taken out by methods such as (i) drying; (ii) precipitating in a poor solvent; or (iii) neutralizing and dissolving in water and then adding an acid to precipitate, etc., may be emulsified and dispersed in water while being neutralized, and may be heated as necessary.

[0056] (Water) The aqueous OP varnish of this embodiment contains water as an essential component. As the water, it is preferable to use ion-exchanged water, distilled water, purified water, etc. The content of water in the aqueous OP varnish is preferably 30 to 70% by mass based on the total amount of the aqueous OP varnish.

[0057] (Water-soluble organic solvent) The aqueous OP varnish of this embodiment contains a water-soluble organic solvent. As the water-soluble organic solvent, it is preferable to use one having good wettability with respect to the plastic film which is the base material (substrate to be printed). Furthermore, it is preferable to use a water-soluble organic solvent that can function as a leveling agent on the surface of the base material and can also function as a film-forming aid for improving the film-forming property of the binder resin.

[0058] Examples of water-soluble organic solvents include alcohol solvents such as methanol, ethanol, and isopropanol; ketone solvents such as acetone; alkylene glycol solvents such as ethylene glycol, diethylene glycol, propylene glycol, and dipropylene glycol; alkylene glycol monoalkyl ether solvents such as ethylene glycol methyl ether, diethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monopropyl ether, dipropylene glycol monomethyl ether, and tripropylene glycol monomethyl ether; glycerin solvents such as glycerin, diglycerin, and ethylene oxide adducts of glycerin; amide solvents such as 2-pyrrolidone, N-methylpyrrolidone, 3-methoxy-N,N-dimethylpropionamide, and 3-butoxy-N,N-dimethylpropionamide; urea solvents such as tetramethylurea and dimethylimidazolidinone; carbonate solvents such as ethylene carbonate and dimethyl carbonate; and the like.

[0059] The content of the water-soluble organic solvent in the aqueous OP varnish is preferably 1 to 30% by mass, more preferably 3 to 20% by mass, based on the total amount of the aqueous OP varnish. If the content of the water-soluble organic solvent is less than 1% by mass, the leveling property may decrease and the physical properties of the coating film (adhesion, wet rub resistance) may slightly decrease. On the other hand, if the content of the water-soluble organic solvent exceeds 30% by mass, poor drying of the coating film may easily occur, and the physical properties of the coating film (adhesion, wet rub resistance, blocking resistance) may slightly decrease.

[0060] (Wax component) The aqueous OP varnish of this embodiment preferably further contains a wax component. By further containing the wax component, the wet rub resistance of the formed coating film can be further improved.

[0061] As the wax component, it is preferable to use emulsion particles formed by neutralizing the carboxy group of at least one polymer having a carboxy group selected from the group consisting of polyethylene, polypropylene, poly α-olefin, silicone, and copolymers thereof with an alkaline substance and self-emulsifying. The average particle diameter of the emulsion measured by the Coulter counter method is preferably 0.5 to 10 μm, and more preferably 2 to 8 μm. Specific examples of the wax component include, under the following trade names, Chemiparle W100, W200, W300, W308, W310, W400, W410, W500, W700, W800 (above, manufactured by Mitsui Chemicals, Inc.), etc. The content of the wax component in the aqueous OP varnish is preferably 1 to 7% by mass based on the total amount of the aqueous OP varnish.

[0062] (Additive) The aqueous OP varnish of the present embodiment can further contain various additives as required. Examples of the additives include organic solvents other than the aforementioned water-soluble organic solvents, leveling agents, surface tension adjusters, pH adjusters, rheology adjusters, ultraviolet absorbers, light stabilizers, antioxidants, curing agents, dyes, fillers, thickeners, defoamers, fungicides, antistatic agents, metal fine particles, magnetic powders, and the like.

[0063] (Water-based flexographic ink) One embodiment of the water-based flexographic ink for shrink labels of the present invention contains the aforementioned aqueous OP varnish, a pigment, and a pigment dispersant for dispersing the pigment. That is, the water-based flexographic ink of the present embodiment contains the aforementioned binder resin, water, a water-soluble organic solvent, a pigment, and a pigment dispersant. The content of the binder resin in the water-based flexographic ink is preferably 10 to 30% by mass based on the total amount of the ink. The content of water in the water-based flexographic ink is preferably 20 to 80% by mass based on the total amount of the ink. Also, the content of the water-soluble organic solvent in the water-based flexographic ink is preferably 30% by mass or less based on the total amount of the ink.

[0064] (Pigment) Examples of the pigments include conventionally known organic pigments and inorganic pigments used in common inks, paints, recording materials, etc. Examples of the organic pigments include colored pigments such as phthalocyanine-based, azo-based, azomethine azo-based, azomethine-based, anthraquinone-based, perinone·perylene-based, indigo·thioindigo-based, dioxazine-based, quinacridone-based, isoindoline-based, isoindolinone-based, diketopyrrolopyrrole-based, quinophthalone-based, and indanthrene-based pigments; and carbon black pigments such as furnace black, lamp black, acetylene black, and channel black. Examples of the inorganic pigments include titanium oxide, zinc oxide, zinc sulfide, barium sulfate, silica, aluminum, calcium carbonate, chromium oxide, red iron oxide, mica, etc.

[0065] The content of the pigment in the aqueous flexographic ink is preferably 1 to 60% by mass based on the total amount of the aqueous flexographic ink. When an organic pigment is used as the pigment, the content of the organic pigment in the aqueous flexographic ink is preferably 1 to 35% by mass based on the total amount of the aqueous flexographic ink. When an inorganic pigment such as titanium oxide or barium sulfate is used as the pigment, the content of the inorganic pigment in the aqueous flexographic ink is preferably 10 to 60% by mass based on the total amount of the aqueous flexographic ink.

[0066] (Pigment dispersant) The pigment dispersant is a component for dispersing the pigment in the ink. The pigment dispersant may be any dispersant that can stably disperse the pigment and is not particularly limited. Among them, from the viewpoints of excellent pigment adsorption ability and dispersion stability, it is preferable to use a pigment dispersant in a state where a vinyl-based polymer having an acid value of 50 to 250 mgKOH / g is neutralized with an alkaline substance and is finely dispersed or dissolved.

[0067] The vinyl-based polymer preferably has acidic groups such as carboxy groups, sulfonic acid groups, and phosphoric acid groups. By neutralizing acidic groups such as carboxy groups with an alkaline substance, the vinyl-based polymer can be made hydrophilic to water and can be finely dispersed or dissolved in the ink.

[0068] Vinyl polymers having an acidic group usually have structural units derived from monomers having an acidic group. Examples of monomers having an acidic group include (meth)acrylic acid, maleic (anhydride), itaconic (anhydride), styrenecarboxylic acid, monomers obtained by monoesterifying (meth)acrylate monomers having a hydroxyl group with a carboxylic anhydride, dibasic acid, or polycarboxylic acid, vinylsulfonic acid, acrylamidomethylpropyne sulfonic acid, vinylphosphoric acid, methacryloyloxyethylphosphoric acid, and the like.

[0069] Vinyl polymers have structural units derived from vinyl monomers. Examples of vinyl monomers include aromatic vinyl monomers such as styrene, vinyltoluene, and vinylnaphthalene; acrylic acid monomers such as butyl acrylate and 2-ethylhexyl acrylate; the aforementioned "other methacrylic acid monomers"; vinyl ester monomers such as vinyl acetate; heterocyclic vinyl monomers such as vinylpyridine and vinylimidazole; and the like.

[0070] Examples of vinyl polymers include styrene-acrylic acid copolymers, styrene-maleic acid copolymers, styrene-ethyl acrylate-acrylic acid copolymers, styrene-acrylic acid-ethoxyethyl acrylate copolymers, styrene-methacrylic acid copolymers, styrene-methacrylic acid-2-hydroxyethyl methacrylate copolymers, benzyl methacrylate-methacrylic acid copolymers, styrene-methacrylic acid-dimethylaminoethyl methacrylate-butyl acrylate copolymers, styrene-maleic acid-polyethylene glycol propylene glycol monobutyl ether monoamine amidated copolymers, styrene-methyl methacrylate-2-ethylhexyl methacrylate-methacrylic acid copolymers, and the like.

[0071] Examples of commercially available pigment dispersants include those sold under the following trade names: Dispex AA 4030, 4040, 4140, CX 4230, 4231, 4234, 4240, 4320, Ultra FA 4404, 4416, 4425, 4431, 4437, 4480, 4483, Ultra PA 4550, 4560, Ultra PX 4575, 4585 (manufactured by BASF); DYSPERBYK 180, 184, 185, 187, 190, 191, 192, 193, 194N, 199, 2010, 2012, 2013, 2015, 2055, 2060, 2061, 2081, 2096 (manufactured by BYK-Chemie); TEGO Dispers 715W, 740W, 741W, 750W, 755W, 757W, 760W, 761W, 765W (manufactured by EVONIK); and so on.

[0072] The content of the pigment dispersant in the aqueous flexographic ink is preferably 0.5 to 10% by mass based on the total amount of the ink. Also, the amount of the pigment dispersant is preferably 5 to 60 parts by mass with respect to 100 parts by mass of the pigment. When the amount of the pigment dispersant with respect to 100 parts by mass of the pigment is less than 5 parts by mass, the dispersion stability of the pigment tends to decrease, and the dispersion stability and storage stability of the aqueous flexographic ink may decrease. On the other hand, when the amount of the pigment dispersant with respect to 100 parts by mass of the pigment exceeds 60 parts by mass, the viscosity of the aqueous flexographic ink may increase excessively, the storage stability may decrease, and it may affect the properties such as water resistance, chemical resistance, and adhesion of the formed coating film.

[0073] (Manufacture of Aqueous Flexographic Ink) The aqueous flexographic ink of this embodiment can be manufactured according to a conventionally known method. Hereinafter, a series of procedures for the manufacturing method of the aqueous flexographic ink will be exemplified. First, a pigment, a pigment dispersant, water, and a water-soluble organic solvent are mixed to obtain a mixture. Next, the obtained mixture is subjected to a dispersion treatment using a bead mill, a pearl mill, a sand mill, a ball mill, a roll mill, an attritor, or the like. Thereafter, a binder resin and various additives are added, and if necessary, diluted with water and a water-soluble organic solvent to obtain the target aqueous flexographic ink.

[0074] (Printed substrate) Both the aqueous OP varnish and the aqueous flexo ink of this embodiment are suitable as OP varnishes and flexo inks for shrink labels. As the substrate (printed substrate) that constitutes the shrink label, a plastic film that shrinks by heat treatment can be used. Among them, it is preferable to use a heat-shrinkable plastic film having high mechanical strength and chemical strength and good printability. Examples of such heat-shrinkable plastic films include stretched polyester films, shrinkable polyvinyl chloride films, shrinkable polystyrene films, shrinkable polyethylene terephthalate films, shrinkable polypropylene films, and the like. The surface (printing surface) of the plastic film may be untreated, or may be subjected to surface treatments such as plasma treatment, corona treatment, radiation treatment, and silane coupling treatment. The plastic film may have a single-layer structure or a multilayer structure. Furthermore, the plastic film may be subjected to aluminum vapor deposition or transparent vapor deposition.

[0075] (Hardener) When printing with the aqueous flexo ink of this embodiment, it is preferable to add a hardener to the ink. By adding a hardener, a coating film with further improved physical properties such as adhesion and wet rub resistance can be formed. As the hardener, it is preferable to use a crosslinking agent for aqueous inks such as polyisocyanate-based, oxazoline-based, carbodiimide-based, and epoxy-based.

[0076] It is preferable to add 0.1 to 8 parts by mass of a curing agent to 100 parts by mass of the aqueous flexographic ink, and it is more preferable to add 0.5 to 5 parts by mass of the curing agent. When the addition amount of the curing agent is less than 0.1 part by mass with respect to 100 parts by mass of the aqueous flexographic ink, the crosslinking reaction does not proceed sufficiently, and the physical properties of the formed coating film do not improve much. On the other hand, when the addition amount of the curing agent exceeds 8 parts by mass with respect to 100 parts by mass of the aqueous flexographic ink, the viscosity of the aqueous flexographic ink may increase significantly during printing, and the blocking resistance of the formed coating film may slightly decrease.

[0077] Commercially available products of the curing agent include, under the following trade names, Duranate WB40-100, WB40-80D, WT20-100, WT30-100, WL70-100, WE50-100 (above, manufactured by Asahi Kasei Corporation); Epocross K-2010E, K-2020E, K-2030E, WS-300, WS-500, WS-700 (above, manufactured by Nippon Shokubai Co., Ltd.); Carbodilite V-02, V-02-L2, SV-02, V-04, V-10, E-02, E-05 (above, manufactured by Nisshinbo Chemical Inc.); Denacol EX-612, EX-614, EX-614B, EX-622, EX-313, EX-314, EX-421, EX-521, EX-321, EX-321L, EX-411 (above, manufactured by Nagase ChemteX Corporation); etc.

Examples

[0078] Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited to these examples. In addition, "parts" and "%" in the examples and comparative examples are based on mass unless otherwise specified.

[0079] <Production of Binder Resin (Polymer Emulsion)> (Synthesis Example 1) Into a reaction vessel, 335.9 parts of diethylene glycol monobutyl ether (BDG), 0.8 part of iodine, 2.8 parts of 2,2-azobis(4-methoxy-2,4-dimethylvaleronitrile) (trade name "V-70", manufactured by Fuji Film Wako Pure Chemical Industries, Ltd.) (V-70), 0.1 part of diphenylmethane (DPM), 45.5 parts of benzyl methacrylate (BzMA), and 128.9 parts of 2-ethylhexyl methacrylate (EHMA) were added. While bubbling nitrogen, the mixture was stirred and polymerized at 45°C for 4 hours to synthesize a polymer (A chain). The solid content measured by sampling a part of the reaction solution was 28.4%, and the polymerization conversion rate calculated based on the solid content was 82.0%. The number average molecular weight (Mn) in terms of polystyrene of the A chain measured by GPC using tetrahydrofuran (THF) as the developing solvent was 18,000, and the dispersity (PDI = weight average molecular weight (Mw) / number average molecular weight (Mn)) was 1.37.

[0080] After the temperature of the obtained polymer solution of the A chain was lowered to 40°C, 2.8 parts of V-70, 12.9 parts of methacrylic acid (MAA), 29.9 parts of BzMA, and 51.2 parts of EHMA were added. Polymerization was carried out at 40°C for 4 hours to form a B chain, and an A-B diblock copolymer was obtained. The acid value (theoretical acid value) of the B chain was 89.4 mgKOH / g. The theoretical acid value of the B chain was calculated according to the following procedure.

[0081] First, the amount (parts) of MAA per 1 part of the B chain is calculated according to the following formula. 12.9 / (12.9 + 29.9 + 51.2) = 0.137 (parts)

[0082] Next, using the molecular weight of MAA "86.1" and the molecular weight of KOH "56.1", the theoretical acid value (mgKOH / g) of the B chain can be calculated according to the following formula. (0.137 / 86.1)×56.1×1,000 = 89.4 (mgKOH / g)

[0083] The solid content measured by sampling a part of the reaction solution was 44.6%, and the polymerization conversion rate was about 100%. The Mn of the obtained A-B diblock copolymer was 28,000, and the PDI was 1.38. The acid value (measured acid value) of the A-B diblock copolymer calculated by titration with an ethanolic 0.1N potassium hydroxide solution was 31.3 mgKOH / g.

[0084] Under room temperature conditions, 10 parts of 28% aqueous ammonia and 397 parts of ion-exchanged water were added and neutralized to obtain polymer emulsion D-1. The solid content of polymer emulsion D-1 was 26.5%. The number average particle diameter of the emulsion particles measured using a dynamic light scattering particle size distribution measuring device (particle size analyzer, trade name "nanoSAQRA", manufactured by Otsuka Electronics Co., Ltd.) was 77.7 nm.

[0085] (Synthesis Examples 2 to 5, Comparative Synthesis Examples 1 and 2) Polymer emulsions D-2 to D-5, H-1 and H-2 were obtained in the same manner as in Synthesis Example 1 described above, except that the formulations shown in Tables 1 and 2 were used. The meanings of the abbreviations in Tables 1 and 2 are shown below. ·MFG: Propylene glycol monomethyl ether ·PFG: Propylene glycol monopropyl ether ·IPA: 2-Propanol ·CHMA: Cyclohexyl methacrylate ·StMA: Stearyl methacrylate ·LMA: Lauryl methacrylate ·IBXMA: Isobornyl methacrylate ·MMA: Methyl methacrylate ·HEMA: 2-Hydroxyethyl methacrylate ·DMAE: Dimethylaminoethanol ·AMP: Aminomethylpropanol

[0086] TIFF0007714483000005.tif172170

[0087] TIFF0007714483000006.tif203170

[0088] (Synthesis Example 6) Into a reaction vessel, 344.4 parts of BDG, 2.3 parts of ethylene glycol bis(2-iodoisobutyrate) (EBIB), 3.1 parts of V-70, 0.3 part of N-iodosuccinimide (NIS), 46.2 parts of BzMA, and 173.4 parts of EHMA were charged. While bubbling nitrogen, the mixture was stirred and polymerized at 40 °C for 4 hours to synthesize a polymer (A chain). The solid content measured by sampling a part of the reaction solution was 34.4%, and the polymerization conversion rate was 87.0%. The Mn in terms of polystyrene of the A chain was 21,000, and the PDI was 1.44.

[0089] 1.4 parts of V-70, 13.2 parts of MAA, 31.0 parts of BzMA, and 10.9 parts of EHMA were added. Polymerization was carried out at 40 °C for 4 hours to form a B chain, and a B-A-B triblock copolymer was obtained. The acid value (theoretical acid value) of the B chain was 156.2 mgKOH / g. The solid content measured by sampling a part of the reaction solution was 43.9%, and the polymerization conversion rate was about 100%. The Mn of the obtained B-A-B triblock copolymer was 26,000, and the PDI was 1.48. The acid value (measured acid value) of the B-A-B triblock copolymer was 31.3 mgKOH / g. Under room temperature conditions, a mixture of 10.2 parts of 28% aqueous ammonia and 407.0 parts of ion-exchanged water was added for neutralization to obtain a polymer emulsion T-1. The solid content of the polymer emulsion T-1 was 26.1%, and the number average particle diameter of the emulsion particles was 63.6 nm.

[0090] (Synthesis Examples 7 to 10, Comparative Synthesis Examples 3 and 4) Polymer emulsions T-2 to T-5, H-3, and H-4 were obtained in the same manner as in the aforementioned Synthesis Example 6, except that the formulations shown in Tables 3 and 4 were used.

[0091] TIFF0007714483000007.tif185170

[0092] TIFF0007714483000008.tif205170

[0093] <Manufacture of Aqueous OP Varnish> (Example 1) 270 parts of polymer emulsion D-1, 22.5 parts of water, 6 parts of polyethylene wax dispersion (trade name "Chemipar W500", manufactured by Mitsui Chemicals, Inc.), 0.6 part of antifoaming agent (trade name "Tegoformex 805N", manufactured by Evonik Industries AG), 0.3 part of surfactant (trade name "Tego Wet 500", manufactured by Evonik Industries AG), and 0.6 part of thickener (trade name "SN Thickener 623N", manufactured by San Nopco Ltd.) were mixed. Using a disper, the mixture was stirred well to obtain aqueous OP varnish NS-1.

[0094] (Examples 2 to 10, Comparative Examples 1 to 4) Except for using polymer emulsions of the types shown in Table 5, aqueous OP varnishes NS-2 to NS-10 and HNS-1 to HNS-4 were obtained in the same manner as in Example 1 described above.

[0095] <Manufacture of Shrink Label (1)> As the substrate to be printed (substrate film), a heat-shrinkable plastic film (trade name "HST", manufactured by Gunze, Ltd.) in which a polystyrene film and a polyethylene terephthalate film were laminated was prepared, and the surface thereof was subjected to corona treatment. An aqueous color ink (trade name "Hydric FCF series", manufactured by Dainichi Seika Kogyo Co., Ltd.) was diluted with tap water so that the viscosity at 25 °C measured with a Zahn cup #4 (manufactured by Rika Co., Ltd.) was 14 seconds to prepare a coating color ink. A flexo hand puller equipped with an anilox roll (cell volume 4.5 cm 3 / m 2 ) was used as an applicator, and the prepared coating color ink was applied onto the substrate film to form a color ink layer.

[0096] After adding 5 parts of an epoxy curing agent (trade name "Denacol EX-612", manufactured by Nagase ChemteX Corporation) to 100 parts of aqueous OP varnish, the mixture was diluted with tap water so that the viscosity at 25 °C measured with a Zahn cup #4 (manufactured by Rika Co., Ltd.) was 15 seconds to prepare a coating OP varnish. An anilox roll (cell volume 8.5 cm3 / m 2 A flexo hand proofer equipped with 2 was used as an applicator, and a coating OP varnish prepared on a color ink layer formed on a base film was applied. Subsequently, it was dried at 25 °C for 48 hours to form a coating film, and a test coated article (shrink label) was obtained.

[0097] <Evaluation of Aqueous OP Varnish> (Adhesion) After thoroughly drying the shrink label using a dryer, cellophane tape (product name "Cellotape (registered trademark)", manufactured by Nichiban Co., Ltd.) was firmly pressed against the solid part of the coating film (image) and then peeled off. Then, the peeling condition of the coating film was visually observed, and the adhesion of the coating film was evaluated according to the evaluation criteria shown below. The results are shown in Table 5. ◎: The coating film did not peel off at all. ○: The coating film peeled off slightly. △: The area of the peeled coating film was smaller than the area of the coating film that remained without peeling. ×: The area of the peeled coating film was larger than the area of the coating film that remained without peeling.

[0098] (Blocking Resistance) An untreated base film and a shrink label were laminated, and left in a constant temperature bath at 40 °C for 24 hours under a load of 7 kg / cm 2 . Then, the peeling resistance when peeling the untreated film and the shrink label, and the appearance of the coating film of the shrink label were confirmed, and the blocking resistance of the coating film was evaluated according to the evaluation criteria shown below. The results are shown in Table 5. Among the evaluation criteria shown below, "◎" and "〇" were set as the acceptable levels (pass). ◎: There was no transfer of the coating film to the untreated surface, and there was no peeling resistance. 〇: There was almost no transfer of the coating film to the untreated surface, and a slight peeling resistance was felt. △: Slight transfer of the coating film to the untreated surface was observed, and a slight peeling resistance was felt. △×: Transfer of the coating film to the untreated surface was observed, and a peeling resistance was felt. ×: Severe transfer of the coating film to the untreated surface was observed, and strong peeling resistance was felt.

[0099] (Wet rub resistance) Using a Kagaku-shinbun type friction fastness tester (trade name "RT-300", manufactured by Dai-eki Kagaku Co., Ltd.), the coating film surface of the shrink label was rubbed 100 times under a load of 200 g with a white cloth moistened with water. The state of the coating film after 100 rubs was visually observed, and the wet rub resistance of the coating film was evaluated according to the evaluation criteria shown below. The results are shown in Table 5. ◎: The coating film did not peel off at all. ○: The coating film peeled off slightly. △: The area of the peeled coating film was smaller than the area of the coating film that remained unpeeled. ×: The area of the peeled coating film was larger than the area of the coating film that remained unpeeled.

[0100] (Shrink whitening) Except for not forming the color ink layer, a test specimen (shrink label) of the coating OP varnish alone was produced in the same manner as described above for "Manufacture of Shrink Labels". The produced shrink label was immersed in hot water at 85°C for 5 seconds to obtain a shrink film shrunk by 50%. Using an integrating sphere type haze meter, the haze value (ratio (%)) of the diffused light transmission amount to the total light transmission amount of the shrink film was measured, and the shrink whitening of the coating film was evaluated according to the evaluation criteria shown below. The results are shown in Table 5. ○: The haze value was less than 30. △: The haze value was 30 or more and less than 40. ×: The haze value was 40 or more.

[0101] TIFF0007714483000009.tif116170

[0102] <Manufacture of Aqueous Flexo White Ink> (Example 11) 40 parts of titanium oxide (trade name "R-960", manufactured by DuPont), a white pigment, 7.5 parts of water, and 2 parts of a pigment dispersant (trade name "DYSPERBYK 190", manufactured by BYK Chemie) were mixed to obtain a mixture. After kneading and dispersing the mixture obtained using a bead mill, 45 parts of polymer emulsion D-1, 5 parts of a polyethylene wax dispersion (trade name "ChemPearl W500", manufactured by Mitsui Chemicals), 0.2 part of an antifoaming agent (trade name "Tego Foamex 805N", manufactured by Evonik), 0.1 part of a surfactant (trade name "Tego Wet 500", manufactured by Evonik), and 0.2 part of a thickener (trade name "SN Thickener 623N", manufactured by San Nopco) were added, and the mixture was sufficiently stirred to obtain aqueous flexo white ink F-1.

[0103] (Examples 12 to 20, Comparative Examples 5 to 8) Except for using polymer emulsions of the types shown in Table 6, aqueous flexo white inks F-2 to F-10 and HF-1 to HF-4 were obtained in the same manner as in Example 1 described above.

[0104] <Manufacture of Shrink Labels (2)> As a substrate to be printed (substrate film), a heat-shrinkable plastic film (trade name "HST", manufactured by Gunze) in which a polystyrene film and a polyethylene terephthalate film were laminated was prepared with its surface corona-treated. An aqueous color ink (trade name "Hydric FCF Series", manufactured by Dainichi Seika Kogyo Co., Ltd.) was diluted with tap water so that the viscosity at 25°C measured with a Zahn cup #4 (manufactured by Rheonics Co., Ltd.) was 14 seconds to prepare a coating color ink. An anilox roll (cell volume 4.5 cm 3 / m 2 ) was used as an applicator with a flexo hand puller equipped, and the prepared coating color ink was applied onto the substrate film to form a color ink layer.

[0105] After adding 5 parts of an epoxy curing agent (trade name "Denacol EX-612", manufactured by Nagase ChemteX Corporation) to 100 parts of an aqueous flexo white ink, it was diluted with tap water so that the viscosity at 25 °C measured with a Zahn cup #4 (manufactured by Rika Kogyo Co., Ltd.) would be 15 seconds, and an aqueous flexo white ink for coating was prepared. Anilox roll (cell volume 13 cm 3 / m 2 ) equipped flexo hand proofing machine was used as an applicator, and the prepared aqueous flexo white ink for coating was applied onto the color ink layer formed on the base film. Then, it was dried at 25 °C for 48 hours to form a coating film, and a test coated article (shrink label) was obtained.

[0106] <Evaluation of Aqueous Flexo White Ink> In the same manner as in the above-mentioned "Evaluation of Aqueous OP Varnish", "adhesion", "blocking resistance", and "wet rub resistance" were evaluated. The results are shown in Table 6.

[0107] (Storage Stability) The aqueous flexo white ink was stored at 40 °C for 1 week, and the change in viscosity over time was measured, and the storage stability was evaluated according to the following evaluation criteria. The viscosity of the ink was measured using a Zahn cup (No. 4). The results are shown in Table 6. ◎: The viscosity change was less than ±10%. ○: The viscosity change was ±10% or more and less than ±15%. △: The viscosity change was ±15% or more and less than ±20%. ×: The viscosity change was ±20% or more.

[0108] TIFF0007714483000010.tif119170

Industrial Applicability

[0109] Both the aqueous OP varnish and the aqueous flexo ink of the present invention are useful as an OP varnish and an ink for shrink labels.

Claims

1. containing a binder resin, water, and a water-soluble organic solvent, wherein the binder resin is an aqueous OP varnish for a shrink label that satisfies the following requirements (1) to (5). [Requirement (1)]: The content of the structural unit derived from the methacrylic acid-based monomer is 90% by mass or more, and (ii) it is a B-A-B triblock copolymer having an A chain and a B chain and containing a group represented by the following general formula (1) in the A chain. (In the general formula (1), R represents a linear, branched, or cyclic alkylene group having 2 to 18 carbon atoms, or a di-, tri-, or tetraalkylene (having 2 to 4 carbon atoms) glycol group, X and Y independently represent O or NH, and "*" represents the bonding position in the A chain) [Requirement (2)]: The A chain has an acid value of 20 mgKOH / g or less, a glass transition temperature of 30°C or less, a number average molecular weight of 15,000 to 35,000, and a molecular weight distribution (weight average molecular weight / number average molecular weight) of 1.6 or less. [Requirement (3)]: The B chain contains a structural unit derived from methacrylic acid, has an acid value of 50 to 200 mgKOH / g, and a number average molecular weight of 1,000 to 15,000. [Requirement (4)]: It has a glass transition temperature of 40°C or less, a number average molecular weight of 20,000 to 50,000, and a molecular weight distribution of 1.6 or less. [Requirement (5)]: At least a part of the carboxy groups is neutralized with at least one alkaline substance selected from the group consisting of ammonia, dimethylaminoethanol, and aminomethylpropanol to self-emulsify, and emulsion particles having a number average particle diameter of 50 to 500 nm are formed.

2. The A chain does not contain a structural unit derived from a methacrylate having an acidic group, and contains a structural unit derived from at least one monomer selected from the monomer group (i) consisting of benzyl methacrylate, cyclohexyl methacrylate, isobornyl methacrylate, t-butylcyclohexyl methacrylate, tetrahydrofurfuryl methacrylate, and methyl methacrylate, and a structural unit derived from at least one monomer selected from the monomer group (ii) consisting of 2-ethylhexyl methacrylate, lauryl methacrylate, tetradecyl methacrylate, stearyl methacrylate, and behenyl methacrylate. The aqueous OP varnish according to claim 1, wherein the B chain contains a structural unit derived from methacrylic acid, a structural unit derived from at least one monomer selected from the monomer group (i), and a structural unit derived from at least one monomer selected from the monomer group (ii).

3. The aqueous OP varnish according to claim 1 or 2, further containing emulsion particles formed by neutralizing the carboxy group of at least one polymer having a carboxy group selected from the group consisting of polyethylene, polypropylene, poly-α-olefin, silicone, and copolymers thereof with an alkaline substance and self-emulsifying, as a wax component.

4. An aqueous flexographic ink for shrink labels, containing the aqueous OP varnish according to any one of claims 1 to 3, a pigment, and a pigment dispersant for dispersing the pigment.

5. The content of the pigment is 1 to 60% by mass, The content of the water is 20 to 80% by mass, The content of the water-soluble organic solvent is 30% by mass or less, The content of the pigment dispersant is 0.5 to 10% by mass, The aqueous flexographic ink according to claim 4, wherein the content of the binder resin is 10 to 30% by mass.

Images