JP2022102672A - Label for can - Google Patents

Abstract

To provide a label for a can appropriate for an adhesion onto a can surface while having an electrostatic ink layer by a digital printing machine.SOLUTION: A label for a can is to be laminate-processed onto a can body, and includes a first base material, a primer layer, an electrostatic ink layer, an adhesive layer and a second base material laminated in this order. The adhesive layer includes at least one of: an adhesive composition containing a polyol, a polyisocyanate and an epoxy compound; and a cured product of the adhesive composition.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to labels for cans.

Digital printing using an electrostatic ink composition is used as various packaging materials because it can be used in small lots. For example, in Patent Document 1, a digital printing machine (manufactured by HP, Indigo 20000 label and digital printing machine for packaging) is used on a coated surface on which a primer resin is applied to a first flexible substrate such as a PET film. A technique for obtaining a packaging material by performing electrostatic printing, further applying a cross-linking composition, and then laminating a flexible substrate is disclosed.

Japanese Unexamined Patent Publication No. 2018-530478

However, when a can label is produced using a laminate having a printed surface of an electrostatic ink composition by a digital printing machine and used for manufacturing a can container, the label affixed state on the can container after production is appropriate. It turned out that it may change from the state.

Therefore, the present disclosure provides a can label suitable for sticking to a can surface while having an electrostatic ink layer by a digital printing machine.

In order to achieve the above object, the can label according to one embodiment of the present disclosure is a can label laminated to a can body, and is a first base material, a primer layer, an electrostatic ink layer, and an adhesive. The layers and the second substrate are laminated in this order, and the adhesive layer contains at least one of an adhesive composition containing a polyol, a polyisocyanate and an epoxy compound, and a cured product of the adhesive composition. There is.

According to the above-mentioned label for cans, the curing of the adhesive composition containing the epoxy compound also suppresses the deformation of the label due to heating or the like during the manufacture of the can container. Therefore, a can label suitable for sticking to the can surface can be obtained while having an electrostatic ink layer produced by a digital printing machine.

At least one of the first base material and the second base material may be a polyethylene terephthalate resin film. Labels for cans having a polyethylene terephthalate resin film are excellent in heat resistance and water resistance, and are therefore suitable for labels for cans used in various applications.

The polyol may include an aliphatic polyester polyol, and the epoxy compound may include those having epoxy groups at both ends. Such an adhesive layer has high adhesive strength even in a high temperature environment. Therefore, it is possible to obtain a can label capable of further suppressing deformation of the label due to heating or the like when manufacturing a can container to which the can label is attached.

The epoxy compound may be an embodiment containing a bifunctional alicyclic epoxy compound. Since such an epoxy compound is bifunctional, it increases the number of cross-linking points with the electrostatic ink composition, so that the cross-linking with the electrostatic ink composition is promoted to obtain a strong cross-linking composition. Further, since it is an alicyclic type, it is possible to suppress the reaction with polyisocyanate due to steric hindrance. Therefore, it can be cured stably, and the adhesion at the interface between the adhesive layer and the electrostatic ink layer can be sufficiently excellent.

The polyisocyanate can be an embodiment containing a xylylene diisocyanate derivative. Such polyisocyanates and polyols are excellent in reactivity. As a result, the curability of the adhesive composition is improved, so that deformation of the label attached to the can surface can be suppressed.

According to the present disclosure, there is provided a can label suitable for sticking to a can surface while having an electrostatic ink layer by a digital printing machine.

FIG. 1 is a diagram showing an example of a cross section along a stacking direction (thickness direction) of a can label according to an embodiment. FIG. 2 is a diagram showing an example of a can container to which a can label is attached. FIG. 3 is a diagram showing an example of a cross section of a can container. FIG. 4 is a diagram showing an example of a method for manufacturing a can container.

Hereinafter, embodiments for carrying out the present disclosure will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are designated by the same reference numerals, and duplicate description will be omitted.

[Lab label for cans]
FIG. 1 shows a cross section along a stacking direction (thickness direction) of a can label according to an embodiment. The can label 1 is a label affixed to the surface of a can container. The use of the can container is not particularly limited, and examples thereof include a beverage can in which a beverage is enclosed, a food can in which food, oil and the like are enclosed, an industrial can in which a drug / industrial product or the like is enclosed, and the like.

As shown in FIG. 1, the can label 1 includes a first base film 10 (first base material), a primer layer 40, an adhesive layer 30, and a second base film 20 (second base material). They are stacked in this order. A primer layer 40 is provided on one of the pair of main surfaces of the first base film 10 near the second base film 20.

The first base film 10 and the second base film 20 may be flexible base materials. As the flexible substrate, for example, a film-like thermoplastic polymer can be used. More specifically, as flexible substrates, biaxially oriented polypropylene (BOPP), polyethylene terephthalate (PET), oriented polyamide (OPA), unstretched polypropylene (CPP), linear low density polyethylene (LLDPE), low A film of density polyethylene (LDPE) can be used. As an example, a PET film can be used as the first base film 10 and the second base film 20. As for the second base film 20, a metal foil such as an aluminum foil may be used as the flexible base material. Further, for the second base film 20, a material in which a metal foil such as an aluminum foil and a resin film are combined may be used as the flexible base material.

The thickness of the first base film 10 and the second base film 20 may be 7 to 150 μm, 15 to 90 μm, or 20 to 80 μm. The thickness of the first base film 10 may be larger than the thickness of the second base film 20. From the viewpoint of the heat resistance of the can label 1 and the rigidity of the can label 1, the thickness of the second base film 20 can be 7 μm or more. On the other hand, as the difference in thickness between the first base film 10 and the second base film 20 becomes large, the difference in stress derived from the difference in the thickness of the base film becomes the difference between the first base film 10 and the second base film 20. 2 It is possible to prevent the occurrence of the base film 20 labels and the like.

The primer layer 40 may contain a resin. Examples of the resin include polyvinyl alcohol resin, cellulose resin, polyester, polyamine, polyethyleneimine resin, polyamide resin, polyurethane, polyacrylic polymer hydroxyl group-containing resin, carboxyl group-containing resin, and amine-based polymer. By having the primer layer 40, it is possible to smoothly print the electrostatic ink composition using a digital printing machine. The coating amount of the resin constituting the primer layer 40 may be, for example, 0.01 to 1.5 g / m ² or 0.05 to 1.0 g / m ² .

The can label 1 is provided with an electrostatic ink layer 50 on one of the pair of main surfaces of the primer layer 40, which is closer to the second base film 20. The electrostatic ink layer 50 is composed of an electrostatic ink composition and is provided by electrostatic printing using a digital printing machine. The plurality of electrostatic ink layers 50 in FIG. 1 may have the same composition, or may have different colors by having different compositions from each other. The electrostatic ink layers 50 may be provided so as to be scattered on the primer layer 40, or may be provided so as to cover the entire one surface of the primer layer 40.

The electrostatic ink composition constituting the electrostatic ink layer 50 is an ink composition used for liquid electrophotographic printing, that is, electrostatic printing, and is printed on a base material such as paper and plastic. The electrostatic ink composition may contain a colorant or pigment such as a dye, and a resin. In addition to these, a carrier fluid or a carrier liquid may be included. In addition, it may include a charge director, a charge adjuvant, a surfactant, a viscosity modifier, an emulsifier and other additives.

Colorants include, for example, cyan pigments, magenta pigments, yellow pigments, and black pigments. Examples of the resin include thermoplastic resins such as ethylene acrylic acid copolymer, propylene acrylic acid copolymer, ethylene methacrylic acid copolymer, propylene methacrylic acid copolymer, and ethylene vinyl acetate copolymer.

Examples of the carrier liquid include hydrocarbons, silicone oils, vegetable oils and the like. Hydrocarbons include aliphatic hydrocarbons, branched chain aliphatic hydrocarbons, and aromatic hydrocarbons. The electrostatic ink composition may be substantially free of carrier liquid when printed on a printing substrate (for example, on the first substrate film 10 with the primer layer 40 interposed therebetween). The carrier liquid may be removed, for example, by an electrophoresis process during printing or evaporation. As a result, substantially only the solid content is transferred to the printing substrate.

The charge director has an effect of maintaining a sufficient electrostatic charge on the particles contained in the electrostatic ink composition. Charge directors include, for example, ionic compounds such as fatty acid metal salts, sulfosuccinate metal salts, oxyphosphate metal salts, alkylbenzene sulfonic acid metal salts, aromatic carboxylic acids or aromatic sulfonic acid metal salts. Also mentioned are dual ionic and nonionic compounds such as polyoxyethylated alkylamines, lecithin, polyvinylpyrrolidone, organic acid esters of polyvalent alcohols.

The charge adjuvant has the effect of increasing or stabilizing the charge of the particles contained in the electrostatic ink composition. Examples of the charge adjuvant include barium petronate, calcium petronate, naphthenic acid Co salt, naphthenic acid Ca salt, naphthenic acid Cu salt, naphthenic acid Mn salt, naphthenic acid Ni salt, naphthenic acid Zn salt, naphthenic acid Fe salt, and stear. Examples thereof include acid Ba salt, stearic acid Co salt, stearic acid Pb salt, stearic acid Zn salt, stearic acid Al salt, stearic acid Cu salt, stearic acid Fe salt, and metal carboxylate.

The electrostatic ink composition may include a crosslinked product crosslinked by the components contained in the adhesive layer 30 and / or the primer layer 40. As a result, the strength of the electrostatic ink layer 50 itself and the adhesive strength between the adhesive layer 30, the electrostatic ink layer 50, and the electrostatic ink layer 50 and the primer layer 40 can be sufficiently increased.

The adhesive layer 30 is laminated on the main surface of the primer layer 40 on which the electrostatic ink layer 50 is provided, and is formed so as to cover the electrostatic ink layer 50. That is, when the electrostatic ink layer 50 is formed so as to cover the entire one surface of the primer layer 40, the adhesive layer 30 is the opposite of the main surface of the electrostatic ink layer 50 (the surface in contact with the primer layer 40). It is laminated with respect to the main surface).
As described above, at least one main surface of the electrostatic ink layer 50 (the main surface opposite to the surface in contact with the primer layer 40) is an adhesive surface with the adhesive layer 30.

The adhesive layer 30 may be composed of an adhesive composition, a cured product thereof, or a mixture thereof. The adhesive composition contains a polyol, a polyisocyanate, and an epoxy compound. At least a part of these three components (polyol, polyisocyanate, and epoxy compound) may react with each other to be cured to form a cured product. The adhesive layer 30 containing the above three components and the electrostatic ink layer 50 are in direct contact with each other at the interface thereof. The epoxy compound contained in the adhesive layer 30 and the ink composition contained in the electrostatic ink layer 50 crosslink each other, so that the adhesive strength between the adhesive layer 30 and the electrostatic ink layer 50 is sufficiently high. ..

The polyol has, for example, a number average molecular weight of 400 or more and has two or more hydroxyl groups in one molecule. Polyisocyanates have two or more isocyanate groups in one molecule. Polyols and polyisocyanates react as a main agent and a curing agent, respectively, to produce polyurethane (polyurethane adhesive). The polyol may have a number average molecular weight of, for example, 10,000 or less.

The polyol may contain at least one selected from the group consisting of polyester polyols and polyether polyols. Of these, the polyol may contain a polyester polyol or an aliphatic polyester polyol from the viewpoint of sufficiently increasing the adhesive strength of the adhesive layer 30 in a high temperature environment.

The polyester polyol can be obtained, for example, by a condensation reaction of a polyhydric alcohol with a polybasic acid, an alkyl ester thereof, an acid anhydride thereof, or an acid halide thereof, or a transesterification reaction. Examples of the polyhydric alcohol include low molecular weight diols, low molecular weight triols, low molecular weight polyols having four or more hydroxyl groups, and the like.

Examples of the low molecular weight diol include ethylene glycol, propylene glycol, trimethylene glycol, 1,4-butylene glycol, 1,3-butylene glycol, 1,2-butylene glycol, 1,5-pentanediol and 3-methyl-. 1,5-pentanediol, 2,2-dimethyl-1,3-propanediol, neopentyl glycol, 1,6-hexanediol, 2,2-diethyl-1,3-propanediol, 3,3-dimethylol Examples thereof include heptane, 2-ethyl-2-butyl-1,3-propanediol and the like.

Examples of the low molecular weight triol include glycerin, 2-methyl-2-hydroxymethyl-1,3-propanediol, 2,4-dihydroxy-3-hydroxymethylpentane, 1,2,6-hexanetriol and trimethylolethane. , Trimethylolethane, 2-methyl-2-hydroxymethyl-1,3-propanediol, 2,4-dihydroxy-3- (hydroxymethyl) pentane, and 2,2-bis (hydroxymethyl) -3-butanol. And so on.

Examples of the low molecular weight polyol having four or more hydroxyl groups include tetramethylolmethane, pentaerythritol, dipentaerythritol, D-sorbitol, xylitol, D-mannitol, and D-mannitol.

Examples of the alkyl ester of polybasic acid include methyl ester and ethyl ester of polybasic acid. Examples of the acid anhydride include acid anhydrides derived from polybasic acids. Examples thereof include oxalic anhydride, succinic anhydride, maleic anhydride, phthalic anhydride, 2-alkyl anhydride (12-18 carbon atoms) succinic anhydride, tetrahydrophthalic anhydride, trimellitic anhydride and the like.

Examples of the acid halide include acid halides derived from the above-mentioned polybasic acids. For example, oxalic acid dichloride, adipic acid dichloride, sebatic acid dichloride and the like can be mentioned.

The polyether polyol may be a polyalkylene oxide. For example, it may be obtained by subjecting a low molecular weight polyol as an initiator and subjecting it to an addition reaction with an alkylene oxide such as ethylene oxide and / or propylene oxide. Specific examples include polyethylene glycol, polypropylene glycol, and polyethylene polypropylene glycol (random or block copolymer). Further, for example, polytetramethylene ether glycol obtained by ring-opening polymerization of tetrahydrofuran and the like can be mentioned.

Examples of the polyisocyanate include polyisocyanate monomers, polyisocyanate derivatives, and isocyanate group-terminated prepolymers. The adhesive composition may contain a plurality of types of polyisocyanates that are different from each other. The molar ratio (NCO / OH) of the isocyanate group contained in the polyisocyanate to the hydroxyl group of the polyol may be 0.5 to 10. Such an adhesive composition can form a cured product having high adhesive strength and excellent flexibility.

Examples of the polyisocyanate monomer include aliphatic polyisocyanates, aromatic polyisocyanates, aromatic aliphatic polyisocyanates, and alicyclic polyisocyanates.

Examples of the aliphatic polyisocyanate include trimethylene diisocyanate, 1,2-propylene diisocyanate, butylene diisocyanate (tetramethylene diisocyanate, 1,2-butyrene diisocyanate, 2,3-butylenedi isocyanate, 1,3-butylenedi isocyanate), and 1 , 5-Pentamethylene diisocyanate (PDI), hexamethylene diisocyanate (HDI), 2,4,4-trimethylhexamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, 2,6-diisocyanismethylcapate, etc. Can be mentioned.

Examples of the aromatic aliphatic polyisocyanate include xylylene diisocyanate derivatives. Examples of the xylylene diisocyanate derivative include xylylene diisocyanate (1,3-xylylene diisocyanate or 1,4-xylylene diisocyanate) (XDI) and tetramethylxylylene diisocyanate (1,3-tetramethylxylylene diisocyanate). , Or 1,4-tetramethylxylylene diisocyanate) (TMXDI), ω, ω'-diisocyanate-1,4-diethylbenzene, and a polyol of xylylene diisocyanate obtained by the reaction of xylylene diisocyanate with trimethylolpropane. Examples include denatured substances.

The content of the xylylene diisocyanate derivative with respect to the entire polyisocyanate may be 10% by mass or more, 20% by mass or more, and 30% by mass or more from the viewpoint of improving the reactivity with the main agent (for example, polyol). It may be 40% by mass or more. By setting the content to 30% by mass or more, the reactivity can be further enhanced.

Examples of the alicyclic polyisocyanate include 1,3-cyclopentanediisocyanate, 1,3-cyclopentenediisocyanate, cyclohexanediisocyanate (1,4-cyclohexanediisocyanate, 1,3-cyclohexanediisocyanate), and 3-isosyanatomethyl-3. , 5,5-trimethylcyclohexylisocyanate (isophorone diisocyanate) (IPDI), methylcyclohexanediisocyanate (methyl-2,4-cyclohexanediisocyanate, methyl-2,6-cyclohexanediisocyanate), norbornandiisocyanate (NBDI) and the like. Be done.

Examples of the polyisocyanate derivative include the above-mentioned multimer of polyisocyanate monomer, allophanate modified product, polyol modified product, polyol modified product produced by reaction between the monomer and alcohols, biuret modified product, and urea modified product. , Oxaziazinetrion denatured, carbodiimide denatured, uretdione denatured, uretonimine denatured and the like.

The isocyanate group-terminated prepolymer is a urethane prepolymer having at least two isocyanate groups at the molecular ends. It can be obtained by subjecting a polyol to at least one selected from the group consisting of a polyisocyanate monomer, a polyisocyanate derivative and an isocyanate group-terminated prepolymer by a urethanization reaction. At this time, the molar ratio (NCO / OH) of the isocyanate group contained in the polyisocyanate to the hydroxyl group of the polyol is 0.5 or more, 0.6 or more, 0.8 or more, 1 or more or 1.5 or more. good. The molar ratio (NCO / OH) may be 10 or less, 5 or less, 4 or less, or 3 or less. Examples of the numerical range of the molar ratio (NCO / OH) include 0.5-10, 0.5-5, 0.8-4, and 0.6-3.

The epoxy compound may be a compound having one or more epoxy groups in one molecule. From the viewpoint of further increasing the adhesive strength of the adhesive layer 30 in a high temperature environment, the adhesive layer 30 may have epoxy groups at both ends. Examples of the epoxy compound include a glycisyl ether type epoxy compound, a glycisylamine type epoxy compound, a glycidyl ester type epoxy compound, and an alicyclic epoxy compound (cyclic aliphatic epoxy compound).

The molecular weight of the epoxy compound may be 500 or less, 450 or less, or 400 or less. Such an epoxy compound can be sufficiently penetrated into the electrostatic ink composition constituting the electrostatic ink layer. The lower limit of the molecular weight of the epoxy compound may be, for example, 98.

Examples of the alicyclic epoxy compound include epoxycyclohexylmethyl-epoxycyclohexanecarboxylate and bis (epoxycyclohexyl) adipate.

Examples of the monofunctional alicyclic epoxy compound having one epoxy group in one molecule include 3,4 epoxycyclohexylmethylmethacrylate and 1,2-epoxy-4-vinylcyclohexane. Bifunctional epoxy compounds having two epoxy groups in one molecule include 3', 4'-epoxycyclohexylmethyl-3,4 epoxycyclohexanecarboxylate, bis (3,4-epoxycyclohexylmethyl) adipate, and , 4-Vinylcyclohexene dioxide and the like. Further, as an epoxy compound having one or more epoxy groups in one molecule, 1,2-epoxy-4- of 2,2-bis (hydroxymethyl) -1-butanol represented by the following general formula (I). Examples include (2-oxylanyl) cyclohexane adducts.

In the above general formula (I), n may be an integer of 1 to 4.

The epoxy compound preferably contains a bifunctional alicyclic epoxy compound. By being bifunctional, it is possible to increase the number of cross-linking points with the electrostatic ink composition and the primer resin, promote the curing reaction of the adhesive, and facilitate the curing. Further, since it is an alicyclic type, it is possible to suppress the reaction with polyisocyanate due to steric hindrance. Therefore, the curing is stable, and the adhesion between the electrostatic ink layer 50 and the adhesive layer 30 can be sufficiently excellent.

In the adhesive composition, the content of the epoxy compound with respect to 100 parts by mass of the polyol may be 3 to 25 parts by mass and 6 to 25 parts by mass from the viewpoint of achieving both high adhesive strength and excellent shear suppressing power. It may be 8 to 20 parts by mass. If the content of the epoxy compound is excessive, the excellent shear-suppressing power tends to be impaired. That is, when the adhesive layer 30 is formed, the adhesive surface may shift or the adhesive composition may protrude. If the amount of the epoxy compound is too small, the adhesive strength tends to decrease under high temperature hot water treatment conditions.

In the adhesive composition, the content of polyisocyanate with respect to 100 parts by mass of the polyol may be 10 to 50 parts by mass, and may be 15 to 50 parts by mass, from the viewpoint of sufficiently increasing the sealing strength and the adhesive strength under high temperature hot water treatment conditions. It may be 35 parts by mass, or 20 to 30 parts by mass.

The molar ratio of the epoxy group contained in the epoxy compound to the isocyanate group contained in the polyisocyanate may be 0.5 to 10, may be 1.5 to 9, and may be 2.0 to 6.5. May be good. This makes it possible to maintain a sufficiently high adhesive strength under high temperature hot water treatment conditions.

The adhesive composition constituting the adhesive layer 30 may contain an optional component such as an additive in addition to the above-mentioned components. Additives include, for example, antioxidants, UV absorbers, light stabilizers, fillers, silane coupling agents, epoxy resins, catalysts, coatable improvers, leveling agents, nucleating agents, lubricants, mold release agents, etc. Examples thereof include defoaming agents, plasticizing agents, surfactants, pigments, dyes, organic fine particles, inorganic fine particles, antifungal agents, flame retardants and the like. The adhesive composition may contain a solvent such as an organic solvent.

The adhesive composition constituting the adhesive layer 30 adheres the electrostatic ink layer 50 and the second base film 20. Any layer may be provided between the second base film 20 and the adhesive layer 30. In this case, the adhesive composition adheres the electrostatic ink layer 50 to an arbitrary layer. The adhesive composition forms a urethane bond by reacting with the polyol and polyisocyanate, and exhibits a function as an adhesive. Since the formation of the urethane bond proceeds smoothly even in the coexistence of the epoxy compound, the electrostatic ink layer 50 and the second base film 20 or any layer can be bonded with sufficiently high adhesive strength.

The adhesive composition constituting the adhesive layer 30 may have a function of cross-linking the electrostatic ink composition forming the electrostatic ink layer 50 together with the formation of urethane bonds. Thereby, the adhesive strength between the electrostatic ink layer 50 and the second base film 20 or between the adhesive layer 30 and any layer can be improved.

Even if the ratio of the electrostatic ink in the electrostatic ink layer 50 (ink coverage) becomes high, the content of the epoxy compound contained in the adhesive composition is increased accordingly, so that the electrostatic ink composition is formed. The epoxy compound can be sufficiently permeated into the electrostatic ink layer 50 to be formed. The permeated epoxy compound has an effect of increasing the strength of the electrostatic ink composition (electrostatic ink layer 50) by cross-linking the electrostatic ink composition. Therefore, even if the ink coverage becomes high, the electrostatic ink layer 50 is deformed (for example, wrinkles, along the electrostatic ink layer 50) in the step of attaching the can label 1 to the can container, the subsequent heating step, or the like. It is possible to prevent a part of the can label 1 from floating, etc.).

The adhesive composition can maintain high adhesive strength even after heat treatment, and is also excellent in pot life. Therefore, it is also excellent in workability such as coating and laminating when adhering the electrostatic ink composition and the base material. The adhesive composition contains a polyol and a polyisocyanate forming urethane, and an epoxy compound, and at least a part of these may be a cured product to form an adhesive layer. This can reduce the number of layers constituting the can label 1 as compared with the case where the adhesive layer containing only polyurethane and the epoxy coating layer are separately provided. Therefore, for example, when a laminate to be a label for a can is produced by roll-to-roll, problems such as meandering of the roll after aging and wrinkles due to blocking or the like do not occur. In addition, the aging process after coating can be reduced and the manufacturing efficiency can be improved.

When the electrostatic ink layer 50 and the adhesive layer 30 are in direct contact with each other as in the label 1 for cans, components such as an epoxy compound and / or a polyisocyanate contained in the adhesive composition of the adhesive layer 30 are static. It sufficiently penetrates into the electric ink layer 50. As a result, the electrostatic ink compositions constituting the electrostatic ink layers 50 and 51 can be crosslinked to improve the strength of the electrostatic ink composition (electrostatic ink layer 50) and to improve the adhesive strength between the layers. Can be improved. As shown in FIG. 1, the electrostatic ink layer 50 includes a region not provided on the primer layer 40 (a plain portion without the electrostatic ink layer 50 and not colored by the electrostatic ink). Even in this case, since the epoxy compound is contained in the adhesive layer 30, stickiness can be eliminated. On the other hand, if the epoxy coating layer is provided separately from the adhesive layer 30, when the electrostatic ink layer 50 includes a plain portion, the epoxy compound becomes excessive in the vicinity of the plain portion, and stickiness tends to occur. As described above, even when the can label 1 includes a plain portion on which the electrostatic ink layer 50 is not formed, it is possible to eliminate stickiness while adhering with high adhesive strength.

The thickness of the can label 1 may be, for example, 15 to 200 μm or 18 to 120 μm.

The configuration of the can label 1 can be changed as appropriate. For example, the primer layer 40 may be provided on each of the facing surfaces of the first base film 10 and the second base film 20. Further, between the first base film 10 and the second base film 20, a film layer different from the first base film 10 and the second base film 20 (for example, a resin layer such as a nylon film, an aluminum foil). Etc.) may be provided.

The method for manufacturing the above-mentioned can label 1 will be described below. First, a step of forming a primer layer 40 on one surface of the first base film 10, a step of printing an electrostatic ink composition on the primer layer 40 to form an electrostatic ink layer 50, and an electrostatic ink. It has a step of adhering the layer 50 and one surface of the second base film 20 using an adhesive composition.

The primer layer 40 may be formed by gravure printing on one surface of the first base film 10. The primer layer 40 can be formed by cross-linking a resin raw material with a cross-linking agent. Cross-linking may be performed by irradiation with ionizing radiation such as ultraviolet light, heating, electron beam, and non-ionizing radiation such as microwave radiation. Printing of the electrostatic ink composition can be performed by electrostatic printing using a digital printing machine.

Adhesion of the laminate by the first base film 10, the primer layer 40 and the electrostatic ink layer 50 and the second base film 20 by the adhesive composition can be performed by laminating. Lamination can be performed using any device. The epoxy compound and / or polyisocyanate contained in the adhesive composition permeates the electrostatic ink composition and the primer layer 40 constituting the electrostatic ink layer 50, and together with the components contained in the electrostatic ink composition and the primer layer 40. A cross-linking reaction may be carried out. As a result, the strength of the electrostatic ink layer 50 is improved, and the can label 1 in which the interfaces of the layers are sufficiently bonded can be obtained. At the time of laminating, at least a part of the adhesive composition may be cured to become a cured product. In this way, the can label 1 including the first base film 10, the primer layer 40, the electrostatic ink layer 50, the adhesive layer 30, and the second base film 20 in this order can be manufactured. As an aging treatment for accelerating the curing of the adhesive layer 30, for example, a step of storing the adhesive layer 30 under temperature conditions such as 40 ° C. for several hours to several days may be added.

The can label 1 manufactured in this manner has the configuration and properties as described in the above embodiment. The description of the can label 1 also applies to the description of the above-described embodiment of the manufacturing method.

[Can container with can label attached]
FIG. 2 is a perspective view schematically showing a can container to which the above-mentioned can label is affixed.

The can label 1 is a label affixed to the surface of the can container 100. The use of the can container 100 is not particularly limited, and examples thereof include beverage cans in which beverages are enclosed, food cans in which foods, oils and the like are enclosed, industrial cans in which chemicals / industrial products and the like are enclosed.

The can container 100 includes a body portion 110, a bottom portion 120, and a can lid 200. The body portion 110 is a main body portion of the can container 100 and has a cylindrical shape. By attaching the above-mentioned can label 1 to the body portion 110, for example, characters, symbols, patterns, and the like can be displayed. The bottom portion 120 is provided so as to block one end of the body portion 110. A lid portion 115 for attaching the can lid 200 is formed at an end portion opposite to one end where the bottom portion 120 of the body portion 110 is provided. The can lid 200 fixed to the lid portion 115 may be provided with, for example, a pull tab for opening the can container 100. The can container 100 shown in FIG. 2 is an example of a beverage can, and the shape and the like can be appropriately changed.

The can container 100 is formed by attaching the can label 1 to the can body. As the material of the can body, for example, aluminum and steel can be used, but the material is not limited thereto. Further, the structure of the can body is not limited to, for example, a two-piece can, a three-piece can, a bottle can, or the like. Further, the method for manufacturing the can body is not particularly limited, and is not limited to any of a welded can, a DR (Draw & Redraw Can) can, a DI (Draw & Ironing Method) can, and a TULC (Toyo Ultimate Can).

FIG. 3 is a diagram showing an example of a layer structure in the can container 100 in a state where the can label 1 is attached. As shown in FIG. 3, a can label 1 is attached to the body 90 of the can container 100 via the adhesive layer 80 on the body 110 of the can container 100. When the can label 1 is attached to the can body 90, for example, the label 1 is attached to the can body 90 so that the main surface of the second base film 20 faces the can body 90.

The adhesive layer 80 is composed of, for example, a cured adhesive or a cured semi-cured film. As the adhesive used for the adhesive layer 80, for example, an acrylic resin-based, polyurethane-based, polyester-based, or epoxy resin-based adhesive can be used.

FIG. 4 shows an example of a method for manufacturing the can container 100. The example shown in FIG. 4 is an example of a method in which a can container 100 filled with contents is manufactured by dry molding. Since the can container 100 can be manufactured by various methods as described above, the can container 100 is not limited to the method shown in FIG.

First, dry molding is performed on the metal plate (step S01). In the dry molding step, for example, a coiled metal plate is unwound and stretched (ancholar), and then a polyester resin film such as PET is laminated on one side or both sides of the metal plate. Then, the metal plate after laminating is punched and drawn by a cupping press to obtain a bottomed cylindrical metal material. By further processing this metal material, a can body having a portion corresponding to the body portion 110 and the bottom portion 120 can be obtained.

Next, the can label is adhered to the can body (step S02). The above-mentioned can label 1 is attached so as to cover at least a part of the can body obtained in step S01. At this time, for example, an adhesive or a semi-curable film derived from the adhesive is placed between the sticking surface of the can body to which the can label 1 is attached and the can label 1, and the can label 1 is placed in that state. By adhering, the can label 1 is attached to the can body. The application method can be appropriately adjusted depending on the type of adhesive used.

Next, neck processing is performed on the can body to which the can label is adhered (step S03). By molding one end of the can body by neck processing (necking), the lid portion 115 is formed so that the can lid 200 can be wound when the can lid 200 is attached later. Further, other parts of the can body may be processed at this stage. A known method can be used for neck processing. The neck processing may be performed before the can label is bonded (S02).

Next, the can container is filled with the contents (step S04). After filling the inside of the can body with the contents, the can lid 200 is fixed to the lid portion 115 by, for example, winding, to obtain a can container 100 in a state in which the inside of the can is sealed.

Next, the can container is subjected to pressure heat treatment (step S05). As the pressure heating treatment, for example, a treatment (so-called retort treatment) is performed in which the contents are filled and heated to a state where heat of 100 ° C. or higher is applied. The heating temperature, time, and the like can be changed depending on the contents, but as an example, heating conditions of 105 to 130 ° C. and 30 to 60 minutes can be used. As the pressure heating method, for example, a steam method can be used, but the method is not limited to this. By undergoing the pressure heat treatment, the contents are sterilized and cooked by heating. The can container 100 after the pressure heat treatment can be packed or the like after undergoing various inspections, for example.

[Action]
As described in the above embodiment, the can label 1 according to the present embodiment includes a first base film 10, a primer layer 40, an electrostatic ink layer 50, an adhesive layer 30, and a second base film 20. They are stacked in this order. Further, the adhesive layer 30 contains at least one of an adhesive composition containing a polyol, a polyisocyanate and an epoxy compound, and a cured product of the adhesive composition.

According to the label 1 for cans, the adhesive layer 30 and the electrostatic ink layer are formed by cross-linking the epoxy compound contained in the adhesive layer 30 and the electrostatic ink composition contained in the electrostatic ink layer 50 with each other. Adhesive strength with 50 is increased. Therefore, since the rigidity of the can label 1 is also increased, deformation of the label due to heating or the like during manufacturing of the can container is suppressed. As described above, a can label suitable for sticking to the can surface can be obtained while having an electrostatic ink layer produced by a digital printing machine.

As described above, when manufacturing a can container, a heat treatment is often included in the process, for example, a pressure heat treatment performed after filling the contents. By performing the heat treatment, as described above, the label attached to the can container may be deformed. On the other hand, in the can label 1 described above, the adhesive strength between the adhesive layer 30 and the electrostatic ink layer 50 is sufficiently high due to cross-linking by the epoxy compound contained in the adhesive layer 30. As a result, deformation of the can label during the manufacture of the can container is suppressed.

Further, the electrostatic ink composition produced by a digital printing machine tends to be inferior in heat resistance and strength as compared with other inks. Therefore, by heat-treating a can label having an electrostatic ink layer derived from an electrostatic ink composition, heat-derived deformation occurs in the electrostatic ink layer, and the appearance of the attached can label is May change. On the other hand, in the can label 1 described above, the electrostatic ink composition (electrostatic ink) is formed by cross-linking the epoxy compound contained in the adhesive layer 30 and the electrostatic ink composition contained in the electrostatic ink layer 50. The strength of the layer 50) is increased. As a result, changes in appearance due to deformation of the electrostatic ink layer and the like are suppressed, and it becomes possible to manufacture a can container having an excellent appearance.

At least one of the first base film 10 and the second base film 20 may be a polyethylene terephthalate resin film. Labels for cans having a polyethylene terephthalate resin film are excellent in heat resistance and water resistance, and are therefore suitable for labels for cans used in various applications.

Further, the polyol may contain an aliphatic polyester polyol, and the epoxy compound may include those having epoxy groups at both ends. Such an adhesive layer 30 has high adhesive strength even in a high temperature environment. Therefore, it is possible to sufficiently suppress the generation of gaps in the vicinity of the electrostatic ink layer and the breakage of the electrostatic ink composition during the manufacture or use of the can container after the can label is affixed. can.

The epoxy compound can be an embodiment including a bifunctional alicyclic epoxy compound. Since such an epoxy compound is bifunctional, cross-linking with the electrostatic ink composition is promoted to obtain a strong cross-linking composition. Further, since it is an alicyclic type, it is possible to suppress the reaction with polyisocyanate due to steric hindrance. Therefore, it can be cured stably, and the adhesion at the interface between the adhesive layer and the electrostatic ink layer can be sufficiently excellent.

The polyisocyanate can be an embodiment containing a xylylene diisocyanate derivative. Such polyisocyanates and polyols are excellent in reactivity. As a result, the curability of the adhesive composition is improved, so that deformation of the label attached to the can surface can be suppressed.

Although some embodiments have been described above, the present disclosure is not limited to the above embodiments. For example, the position where the can label is attached is not particularly limited, and may be attached to, for example, the can lid, the bottom, or the like.

The content of the present disclosure will be described in more detail with reference to examples, but the present disclosure is not limited to the following examples.

(Example 1)
[Preparation of laminated body]
A polyethylene terephthalate film (PET film, thickness: 12 μm) was prepared as the first base film. A water-based primer resin (resin containing polyethyleneimine, manufactured by Michelman, trade name: DP050) was applied to one surface of this PET film to form a primer layer. Aqueous polyethyleneimine was applied so that the amount applied was 0.10 to 0.18 g / m ² .

Predetermined printing was performed on the surface of the primer layer using a digital printing machine (manufactured by HP, Indigo 20000 label and digital printing machine for packaging). The ink coverage by one printing was set to 100%. As the electrostatic ink composition, an electrostatic ink composition (HP Indigo electro ink) containing a thermoplastic resin containing a copolymer of ethylene acrylic acid and ethylene methacrylic acid was used. As the colors of the electrostatic ink composition, white (W), yellow (Y), magenta (M), and cyan (C) were used as shown in Table 1. A plurality of samples having different colors and ink coverages of the electrostatic ink composition were prepared. The ink coverage of each color and the total thereof are as shown in Table 1. As shown in Table 1, the total ink coverage was 200 to 500%.

The main agent is an aliphatic polyester polyol (A) (manufactured by Mitsui Chemicals Co., Ltd., trade name: Takelac A626), polyisocyanate (B) (manufactured by Mitsui Chemicals Co., Ltd., trade name: Takenate A50), and 3'as an epoxy compound (C). , 4'-Epoxycyclohexylmethyl-3,4 Epoxycyclohexanecarboxylate and ethyl acetate as a solvent were blended to prepare an adhesive composition having a solid content concentration of 36.5% by mass. The structure of this epoxy compound is as shown in the following formula (1). The mass-based compounding ratio of each component was as shown in Table 1. In the column of [(B) / (A)] × 100 in Table 1, the blending amount (parts by mass) of polyisocyanate with respect to 100 parts by mass of the aliphatic polyester polyol is shown. In the column of [(C) / (A)] × 100 in Table 1, the blending amount (parts by mass) of the epoxy compound with respect to 100 parts by mass of the aliphatic polyester polyol is shown. The column of "epoxy group / isocyanate group" in Table 1 shows the molar ratio of the epoxy group contained in the epoxy compound (C) to the isocyanate group contained in the polyisocyanate (B).

An adhesive composition prepared as described above was applied onto the electrostatic ink layer formed of the electrostatic ink composition using a dry laminating apparatus to form an adhesive layer. The coating amount of the adhesive composition was 4.0 g / m ² .

As the second base film, a base film having an aluminum foil (manufactured by Toyo Aluminum Co., Ltd., thickness: 7 μm), a nylon film and a non-stretched polypropylene film was prepared in this order. Using the above dry laminating apparatus, the second base film was bonded to the adhesive layer so that the adhesive layer and the aluminum foil were in contact with each other to obtain a laminated body. The curing time (aging) was set at 40 ° C. for 2 days. In this way, a laminated film (laminated body) was manufactured. The "laminated body" described in the following examples has a structure that can be used as a can label described in the above embodiment.

[Measurement of adhesive strength (normal temperature)]
The adhesive strength of the prepared laminate was measured according to JIS K 6854-1: 1999. Specifically, the prepared laminate was cut into a width of 15 mm and used as a measurement sample. After peeling the layers at the end of the measurement sample, the peel strength between the layers of the laminated body was measured using a tensile tester under the conditions of an angle of 90 °, a tensile speed of 300 mm / min, and room temperature. This peel strength was defined as the adhesive strength at room temperature (20 ° C.). The measurement results are as shown in Table 1.

(Examples 2 to 6)
A laminate was prepared in the same manner as in Example 1 except that the composition of the adhesive composition was changed as shown in Tables 1 and 2, and the adhesive strength was measured. The measurement results are as shown in Tables 1 and 2.

(Example 7)
The first liquid consisting of an aliphatic polyester polyol (A) (manufactured by Mitsui Chemicals Co., Ltd., trade name: Takelac A626), polyisocyanate (B) (manufactured by Mitsui Chemicals Co., Ltd., trade name: Takenate A50) and an epoxy compound (C). ), And a two-component adhesive contained in a container separately were prepared. The first liquid and the second liquid were mixed to prepare an adhesive composition having the formulation shown in Table 2. A laminate was prepared in the same manner as in Example 1 except that this adhesive composition was used, and the adhesive strength was measured. The measurement results are as shown in Table 2.

(Comparative Example 1)
A laminate was prepared in the same manner as in Example 1 except that the epoxy compound (C) was not blended when the adhesive composition was prepared, and the adhesive strength was measured. The measurement results are as shown in Table 2.

(Comparative Example 2)
An epoxy coating layer was provided by applying the epoxy compound of the formula (1) above the electrostatic ink layer formed by the electrostatic ink composition. The adhesive composition of Comparative Example 1 was applied to the epoxy coating layer. A laminate was prepared in the same manner as in Example 1 except that the above was applied, and the adhesive strength was measured. The coating amount of the epoxy coating layer was set to an amount corresponding to 0.53 parts by mass in the formulation shown in Table 2. The measurement results are as shown in Table 2.

As shown in Tables 1 and 2, the laminates of Examples 1 to 7 using the adhesive layer containing the epoxy compound adhere more than the laminate of Comparative Example 1 using the adhesive layer containing no epoxy or the compound. It was confirmed that the strength was high. In Comparative Example 2, a relatively high adhesive strength was obtained, but it was necessary to increase the number of steps in order to form an epoxy coating layer in addition to the adhesive layer. Curing (aging) of the epoxy coating layer took two days, and the productivity decreased.

In the laminated body of Comparative Example 1, the layers were peeled off near the interface between the electrostatic ink layer and the primer layer. In the laminated body of Comparative Example 2, the electrostatic ink layer was coagulated and broken. On the other hand, in the laminated bodies of Examples 1 to 7, the layers were peeled off at the interface between the electrostatic ink layer and the adhesive layer, and no cohesive failure of the electrostatic ink layer was observed. This suggests that the cohesive force of the electrostatic ink layer is improved. The molar ratio of the isocyanate group contained in the polyisocyanate (B) to the hydroxyl group of the aliphatic polyester polyol (A) in Examples 1 to 7 was in the range of 0.5 to 10.

Next, the adhesive strength and the hot water adhesive strength of the laminates according to Example 5 and Comparative Example 2 after the retort heat treatment were measured. For the measurement, those having a total ink coverage of 500% and those having a total ink coverage of 200% were used. The details of the measurement procedure are as follows.

[Measurement of adhesive strength after retort (120 ° C)]
A three-sided bag was prepared using the laminate, and water was sealed in the three-sided bag. Then, a retort heat treatment (120 ° C. × 30 minutes) was carried out using a retort processing apparatus (manufactured by Hisaka Works). Here, as the retort heat treatment, a steam type pressure heating method was used. After the retort heat treatment, the laminate sample was cut to a width of 15 mm, and the interlayer strength between the ink layer and the layer in contact with the ink layer was measured. The measured peel strength is shown in the column of "120 ° C." in Table 3. Table 3 also shows the adhesive strength at room temperature before the heat treatment.

[Measurement of adhesive strength after retort (130 ° C)]
A three-sided bag was prepared using the laminate, and water was sealed in the three-sided bag. Then, a retort heat treatment (130 ° C. × 30 minutes) was carried out using a retort processing apparatus (manufactured by Hisaka Works). After the retort heat treatment, the laminate sample was cut to a width of 15 mm, and the interlayer strength between the electrostatic ink layer and the layer in contact with the electrostatic ink layer was measured. The measured peel strength is shown in the column of "130 ° C" in Table 3.

[Measurement of hot water adhesion strength]
After peeling the layers at the ends of the laminate cut to a width of 15 mm, the peel strength was measured using a tensile tester in a state of being immersed in hot water at 90 ° C. That is, the peeling angle was free and the tensile speed was 300 mm / min. This peel strength is shown in Table 3 as the hot water adhesion strength.

As shown in Table 3, it was confirmed that the hot water adhesion strength of Example 5 was superior to that of Comparative Example 2.

(Example 8)
[Preparation of adhesive composition and laminate]
A polyethylene terephthalate film (PET film, thickness: 12 μm) was prepared as the first base film. A water-based primer resin (resin containing polyethyleneimine, manufactured by Michelman, trade name: DP050) was applied to one surface of this PET film to form a primer layer. Aqueous polyethyleneimine was applied so that the amount applied was 0.10 to 0.18 g / m ² .

Predetermined printing was performed on the surface of the primer layer using a printing machine manufactured by HP Indigo (trade name: Indigo 2000). As the electrostatic ink composition, an electrostatic ink composition (HP Indigo electro ink) containing a thermoplastic resin containing a copolymer of ethylene acrylic acid and ethylene methacrylic acid was used. As the color of the electrostatic ink composition, white (W), yellow (Y), magenta (M), and cyan (C) were used. As the ink coverage, W200% and C100% + M100% + Y100% + W200% were prepared. In Table 4, the former is referred to as “ink coverage (1)” and the latter is referred to as “ink coverage (2)”. In this way, two types of samples having different ink coverages of the electrostatic ink composition were prepared.

The same adhesive composition as in Example 5 was prepared. The adhesive composition prepared as described above was applied on the electrostatic ink layer formed by the electrostatic ink composition with a handler laminator machine to form an adhesive layer. The coating amount of the adhesive composition was 4.0 g / m ² .

As the second base film, a base film having a nylon film and an unstretched polypropylene film in this order was prepared. The base film was bonded to the adhesive layer so that the adhesive layer and the nylon film were in contact with each other to obtain a laminated body. The curing time (aging) was 40 ° C. × 2 days.

The adhesive strength (normal temperature) and the hot adhesive strength (120 ° C.) of the laminate thus obtained were measured. The method for measuring the adhesive strength (normal temperature) is the same as the method described above. The hot adhesive strength (120 ° C.) is a measurement of the adhesive strength of the laminate produced in accordance with JIS K 6854-1: 1999 under the temperature condition of 120 ° C. in the same manner as the adhesive strength (normal temperature). Is. The measurement results are as shown in Table 4.

(Examples 9 to 12)
When the adhesive composition was prepared, a laminate was prepared in the same manner as in Example 8 except that the blending amount of the polyisocyanate (B) was changed as shown in Table 4. The prepared laminate was evaluated in the same manner as in Example 8. The evaluation results are as shown in Table 4.

(Comparative Example 3)
A laminate was produced in the same manner as in Comparative Example 1 except that the lamination above the electrostatic ink layer formed by the electrostatic ink composition was carried out by a handler laminator machine without using a dry laminating apparatus. The colors and ink coverage of the electrostatic ink composition were as shown in Table 4. The prepared laminate was evaluated in the same manner as in Example 8. The evaluation results are as shown in Table 4.

As shown in Table 4, it was confirmed that in each example, high adhesive strength can be obtained even under high temperature hot water treatment conditions. Further, it was confirmed that the hot adhesive strength (120 ° C.) can be sufficiently increased by adjusting the blending ratio of the polyisocyanate (B) to the aliphatic polyester polyol (A). This indicates that it is possible to maintain a sufficiently high adhesive strength even when a pressure heat treatment is performed in a state of being attached to a can container, such as a can label. On the other hand, in Comparative Example 3 in which the epoxy compound (C) was not used, it was confirmed that the adhesive strength was significantly reduced when exposed to high temperature hot water treatment conditions. In Examples 8 to 12, the molar ratio of the isocyanate group contained in the polyisocyanate (B) to the hydroxyl group contained in the aliphatic polyester polyol (A) was in the range of 0.5 to 10.

(Examples 13 to 17)
Polyester polyol (A1) (Mitsui Chemicals, Inc., Takelac A525), polyisocyanate (B1) (Mitsui Chemicals, Inc., Takenate A52), and 3', 4'-epoxycyclohexylmethyl as the epoxy compound (C). An adhesive composition was prepared by blending -3,4 epoxycyclohexanecarboxylate. The blending ratio was as shown in Table 5. Laminates were prepared and evaluated in the same manner as in Examples 8 to 12, except that such an adhesive composition was used. The evaluation results are as shown in Table 5.

(Comparative Example 4)
An aliphatic polyester polyol (A1) (Mitsui Chemicals, Inc., Takelac A525) and a polyisocyanate (B1) (Mitsui Chemicals, Inc., Takenate A52) were blended as polyols to prepare an adhesive composition. The blending ratio was as shown in Table 5. A laminate was prepared and evaluated in the same manner as in Comparative Example 3 except that such an adhesive composition was used. The evaluation results are as shown in Table 5.

As shown in Table 5, it was confirmed that even when the combination of the aliphatic polyester polyol and the polyisocyanate was changed, high adhesive strength could be obtained in each example. Further, it was confirmed that the hot adhesive strength (120 ° C.) can be sufficiently increased by adjusting the blending ratio of the polyisocyanate (B1) with the aliphatic polyester polyol (A1). On the other hand, in Comparative Example 4 in which the epoxy compound (C) was not used, it was confirmed that the adhesive strength was significantly reduced when exposed to high temperature hot water treatment conditions. In Examples 13 to 17, the molar ratio of the isocyanate group contained in the polyisocyanate (B1) to the hydroxyl group contained in the aliphatic polyester polyol (A1) was in the range of 0.5 to 10.

According to the present disclosure, it is possible to provide a can label suitable for sticking to a can surface while having an electrostatic ink layer by a digital printing machine.

1 ... Can label, 10 ... 1st base film, 20 ... 2nd base film, 30 ... Adhesive layer, 40 ... Primer layer, 50 ... Electrostatic ink layer, 80 ... Adhesive layer, 90 ... Can body, 100 ... Can container.

Claims (5)

A label for cans that is laminated to the can body.
The first base material, the primer layer, the electrostatic ink layer, the adhesive layer, and the second base material are laminated in this order.
The adhesive layer is a can label containing at least one of an adhesive composition containing a polyol, a polyisocyanate and an epoxy compound, and a cured product of the adhesive composition. The label for a can according to claim 1, wherein at least one of the first base material and the second base material is a polyethylene terephthalate resin film. The can label according to claim 1 or 2, wherein the polyol comprises an aliphatic polyester polyol, and the epoxy compound comprises one having an epoxy group at both ends. The can label according to any one of claims 1 to 3, wherein the epoxy compound contains a bifunctional alicyclic epoxy compound. The can label according to any one of claims 1 to 4, wherein the polyisocyanate contains a xylylene diisocyanate derivative.

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