JP7709740B2 - Liquid for maintaining ink application device, and method for maintaining ink application device - Google Patents

Description

The present invention relates to a liquid for preserving an ink application device and a method for preserving an ink application device.

In recent years, for example, ink applicators have become more precise as the quality of printed matter improves. In more precise ink applicators, the risk of failure is increasing due to foreign matter, such as aggregates generated in the ink, entering the ink flow path. In order to maintain the cleanliness of the ink flow path in such ink applicators, ink applicator maintenance liquid is used. By performing maintenance such as cleaning the ink flow path using ink applicator maintenance liquid, it becomes possible to use the ink applicator in a normal state. As disclosed in Patent Documents 1 to 4, components of ink applicator maintenance liquid include polymerizable monomers, aromatic solvents, aliphatic hydrocarbon solvents, ester solvents, etc.

JP 2016-191062 A JP 2006-160894 A JP 2013-194123 A JP 2000-044993 A

The ink applicator maintenance liquid contains low-viscosity components to ensure fluidity in the ink flow path, which can improve the cleanability of the ink flow path, for example. However, ink applicator maintenance liquid that ensures fluidity can be highly aggressive to rubber components used in the ink flow path, which can reduce the performance of the rubber components. This reduction in the performance of the rubber components can, for example, lead to a reduction in the sealing ability of the ink flow path.

In order to solve the above problems, one aspect of the present invention provides an ink applicator maintenance liquid for use in maintaining an ink applicator, the liquid comprising:
The composition contains at least one compound selected from the compounds represented by the following general formulas (1) and (2).

R ¹ -(CO) _x -(OR ³ ) _n -O-(CO) _x -R ² ...(1)
R ¹ OCO-R ⁴ -COOR ¹ ...(2)
In general formulas (1) and (2), R ¹ represents a hydrocarbon group having 7 to 11 carbon atoms, R ² represents a hydrogen atom or a hydrocarbon group having 7 to 11 carbon atoms, R ³ represents a hydrocarbon group having 3 to 6 carbon atoms, R ⁴ represents a hydrocarbon group having 2 to 4 carbon atoms, n represents an integer of 1 to 3, and x represents an integer of 0 or 1.

The present invention has the effect of suppressing deterioration in the performance of the rubber material used in the ink flow path even when fluidity in the ink flow path is ensured.

The following describes an embodiment of the ink applicator preservation liquid and the ink applicator preservation method. Note that hereinafter, the ink applicator preservation liquid may be simply referred to as the "preservation liquid."

<Applications of ink coating equipment maintenance liquid>
The ink applicator maintenance liquid is used for the purpose of maintaining the ink applicator. The maintenance liquid is used for the purpose of cleaning the ink flow path, maintaining the constancy of the ink flow path, etc. The maintenance liquid may be circulated through the ink flow path in the ink applicator and its associated equipment, or may be filled in the ink flow path for a certain period of time.

The ink applicator has an ink flow path including an ink storage section, an ink coating section, an ink discharge section, a connection section connecting the coating section and the storage section, and a connection section connecting the coating section and the discharge section. The ink storage section may be disposed outside the ink applicator. The ink storage section may have a connection section that is connected to the discharge section without going through the coating section. The ink discharge section may be disposed outside the ink applicator. The ink applicator preservation liquid may be used to clean the storage section disposed outside the ink applicator and the connection section that connects the storage section and the ink applicator. The ink applicator preservation liquid may be used to clean the discharge section disposed outside the ink applicator and the connection section that connects the discharge section and the ink applicator.

Examples of components that make up the ink flow path include supply pipes, supply pipe connection members, ink cartridges, ink reservoir tanks, waste liquid receivers, waste liquid storage tanks, connection members to the tanks, valve sealants, tube pumps (peristaltic pumps), diaphragm pumps, print heads, printing plate cylinders, ink rollers, printing blankets, ink chambers, anilox rollers, etc.

The member constituting the ink flow path includes a rubber member. The type of rubber member is not particularly limited. For example, the rubber member may be at least a part of the member constituting the ink flow path. The rubber member may be a sealing member constituting the ink flow path. For example, the sealing member may be a gasket, a packing, an O-ring, etc. The rubber member may be an inner layer or an outer layer of the member constituting the ink flow path.

The rubber of the rubber member is a material that has rubber elasticity or rubber-like elasticity at room temperature, and is specified, for example, in JIS 6200 (2008), JIS 6200 (2019), etc. In more detail, rubber refers to a material that can be modified or is already in a state where it is essentially insoluble (swellable) in boiling solvents, such as benzene, methyl ethyl ketone, or an ethanol/toluene azeotrope. When modified and free of diluents, rubber shrinks to less than 1.5 times its original length within one minute even when stretched to twice its length at room temperature (18°C to 29°C) and held as is for one minute before relaxing. In addition, rubber has the property that, in the modified rubber state, it cannot be easily remolded into a permanent shape even when heated and pressured.

Examples of rubber include natural rubber, isoprene rubber, chloroprene rubber, isobutylene isoprene rubber, nitrile butadiene rubber (nitrile rubber), ethylene propylene rubber, ethylene propylene diene rubber, styrene butadiene rubber, chlorosulfonated ethylene rubber, urethane rubber, polyester urethane rubber, polyether urethane rubber, silicone rubber, fluororubber, tetrafluoroethylene propylene rubber, and perfluoro rubber.

Examples of ink application methods for ink application devices include inkjet, offset, roll coater, flexography, gravure, silk screen, pad, spray coating, etc. The ink application device preservation liquid of this embodiment can be suitably used for ink application devices using the inkjet method.

<Ingredients of ink application device maintenance liquid>
The ink applicator maintenance liquid contains at least one compound selected from the compounds represented by the following general formulas (1) and (2). The ink applicator maintenance liquid preferably further contains at least one compound selected from the compounds represented by the following general formulas (3) and (4). The ink applicator maintenance liquid preferably further contains a stabilizer.

<Compounds represented by general formulas (1) to (4)>
The compounds represented by the general formulas (1) and (2) are cleaning components. A maintenance liquid containing the cleaning component is filled into an ink flow path. By discharging the maintenance liquid filled into the ink flow path from the ink flow path, ink components, aggregates of ink components, volatile matter present in the ink flow path, etc. can be removed from the ink flow path.

R ¹ -(CO) _x -(OR ³ ) _n -O-(CO) _x -R ² ...(1)
R ¹ OCO-R ⁴ -COOR ¹ ...(2)
In general formulas (1) and (2), R ¹ represents a hydrocarbon group having 7 to 11 carbon atoms. This hydrocarbon group may be any of a linear, branched, and cyclic hydrocarbon group. The carbon number of R ¹ is preferably 8 to 11, and more preferably 8 to 10. When the carbon number of R ¹ is 7 or more, it is possible to suppress the attacking property against rubber members. When the carbon number of R ¹ is 11 or less, it is possible to increase the fluidity of the conservation liquid. From the viewpoint of further suppressing the attacking property against rubber members, it is preferable that R ¹ does not contain an unsaturated bond.

In general formula (1), R ² represents a hydrogen atom or a hydrocarbon group having 7 to 11 carbon atoms. This hydrocarbon group may be any of a linear, branched, and cyclic hydrocarbon group. The carbon number of R ² is preferably 8 to 10, and more preferably 8 or 9. When the carbon number of R ² is 7 or more, the attacking property against rubber members can be suppressed. When the carbon number of R ² is 11 or less, the fluidity of the conservation liquid can be increased. From the viewpoint of further suppressing the attacking property against rubber members, it is preferable that ^{R 2} does not contain an unsaturated bond.

In the general formula (1), R ³ represents a hydrocarbon group having 3 to 6 carbon atoms. When R ³ has 3 or more carbon atoms, the stability of the conservation liquid when mixed with the ink can be improved. Specifically, even if the conservation liquid is mixed with the ink at an arbitrary ratio in the ink flow path and left to stand, the occurrence of turbidity due to gelation of the mixed liquid or the generation of foreign matter can be suppressed. This improves the cleanliness of the ink flow path, thereby improving the constancy of the ink application device. When R ³ has 6 or less carbon atoms, the fluidity of the conservation liquid can be increased. From the viewpoint of further reducing the aggressiveness against rubber members, the hydrocarbon group of ^{R 3} preferably does not contain an unsaturated bond, and more preferably is a straight-chain or branched type not containing an unsaturated bond.

In the general formula (2), ^R4 represents a hydrocarbon group having 2 to 4 carbon atoms. This hydrocarbon group is preferably linear or branched. From the viewpoint of further suppressing attacking rubber members, ^R4 preferably does not contain an unsaturated bond.

In general formula (1), n represents an integer of 1 to 3. In this case, the fluidity of the preservation liquid can be increased. In general formula (1), x represents an integer of 0 or 1. In this case, the fluidity of the preservation liquid can be increased.

The compound represented by the general formula (1) may be used alone or in combination of two or more. The compound represented by the general formula (2) may be used alone or in combination of two or more.
Examples of the compounds represented by general formulas (1) and (2) include propylene glycol mono-2-ethylhexyl ether, dipropylene glycol mono-2-ethylhexyl ether, propylene glycol mono-2-ethylhexanoate, 3-(2-ethylhexyloxy)propionic acid, bis(2-ethylhexyl) succinate, diisononyl succinate, diisodecyl succinate, bis(2-ethylhexyl) glutarate, diisononyl glutarate, diisodecyl glutarate, diheptyl adipate, bis(2-ethylhexyl) adipate, diisononyl adipate, and diisodecyl adipate.

The content of the compounds represented by general formulas (1) and (2) in the conservation liquid is preferably 30% by mass or more, more preferably 32.5% by mass or more, and even more preferably 35% by mass or more. By increasing the content of the compounds represented by general formulas (1) and (2) in the conservation liquid, it is possible to further suppress the aggressiveness against rubber members. There is no particular upper limit on the content of the compounds represented by general formulas (1) and (2) in the conservation liquid.

The compounds represented by the general formulas (3) and (4) are also cleaning components, similar to the compounds represented by the general formulas (1) and (2). When the compounds represented by the general formulas (3) and (4) are the first cleaning component, the compounds represented by the general formulas (3) and (4) are the second cleaning component.

R ⁶ -(OR ⁵ ) _m -OR ⁷ ...(3)
R ⁷ -(CO) _y -(OR ⁵ ) _p -OCOR ⁶ ...(4)
In general formulas (3) and (4), R ⁵ represents a hydrocarbon group having 3 to 6 carbon atoms. This hydrocarbon group may be any of a linear, branched, and cyclic hydrocarbon group. When R ⁵ has 3 or more carbon atoms, the occurrence of turbidity due to gelation or the occurrence of foreign matter in a mixed liquid mixed with ink can be suppressed. This can improve cleanability. When R ⁵ has 6 or less carbon atoms, the fluidity of the conservation liquid can be improved. From the viewpoint of further suppressing aggressiveness against rubber members, it is preferable that R ⁵ does not contain an unsaturated bond.

In general formulas (3) and (4), R ⁶ represents a hydrocarbon group having 1 to 6 carbon atoms. This hydrocarbon group may be any of a linear, branched, and cyclic hydrocarbon group. When the carbon number of R ⁶ is 1 or more, the attacking property against rubber members can be further suppressed. When the carbon number of R ⁶ is 6 or less, the fluidity of the conservation liquid can be increased. From the viewpoint of further suppressing the attacking property against rubber members, it is preferable that R ⁶ does not contain an unsaturated bond.

In general formulas (3) and (4), R ⁷ represents a hydrogen atom or a hydrocarbon group having 1 to 6 carbon atoms. This hydrocarbon group may be any of a linear, branched, and cyclic hydrocarbon group. When the carbon number of R ⁷ is 1 or more, the attacking property against rubber members can be further suppressed. When the carbon number of R ⁷ is 6 or less, the fluidity of the conservation liquid can be increased. From the viewpoint of further suppressing the attacking property against rubber members, it is preferable that R ⁷ does not contain an unsaturated bond.

In general formula (3), m represents an integer of 2 or 3. In this case, the fluidity of the preservation liquid can be increased while suppressing volatility. In general formula (4), p represents an integer of 1 or 2. In this case, the fluidity of the preservation liquid can be increased. In general formula (4), y represents an integer of 0 or 1. In this case, the fluidity of the preservation liquid can be increased while suppressing volatility.

The compound represented by the general formula (3) may be used alone or in combination of two or more. The compound represented by the general formula (4) may be used alone or in combination of two or more.
Examples of the compounds represented by the general formulas (3) and (4) include dipropylene glycol monomethyl ether, dipropylene glycol dimethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol diethyl ether, tripropylene glycol monomethyl ether, dipropylene glycol monopropyl ether, dipropylene glycol mono-n-butyl ether, dipropylene glycol methyl ether acetate, propylene glycol diacetate, dipropylene glycol methyl-n-butyl ether-3-methoxy-3-methyl-1-butyl acetate, 1,4-butanediol diacetate, 1,3-butylene glycol diacetate, and 1,6-hexanediol diacetate.

The total content of the compounds represented by general formulas (3) and (4) in the conservation liquid is preferably 70% by mass or less, more preferably less than 70% by mass, even more preferably 69% by mass or less, and most preferably 60% by mass or less.

The total content of the compounds represented by general formulas (1) to (4) in the conservation liquid is preferably 65% by mass or more, more preferably 68% by mass or more, and even more preferably 70% by mass or more. By increasing the total content of the compounds represented by general formulas (1) to (4) in the conservation liquid, it is possible to further reduce the aggressiveness against rubber members.

The conservation liquid may contain ethylene glycol ether-based solvents and diethylene glycol ether-based solvents as compounds other than those represented by the above general formulas (1) to (4). However, from the viewpoint of increasing the stability of the conservation liquid when mixed with the ink, the content of ethylene glycol ether-based solvents and diethylene glycol ether-based solvents in the conservation liquid is, for example, preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 1% by mass or less. It is most preferable that the conservation liquid does not contain ethylene glycol ether-based solvents and diethylene glycol ether-based solvents.

Examples of ethylene glycol ether-based solvents and diethylene glycol ether-based solvents include ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether, ethylene glycol monoethyl ether acetate, diethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, ethylene glycol monobutyl ether acetate, diethylene glycol monoisobutyl ether, diethylene glycol monoisobutyl ether, ethylene glycol monohexyl ether, diethylene glycol monohexyl ether, ethylene glycol monophenyl ether, diethylene glycol monophenyl ether, ethylene glycol monobenzyl ether, and diethylene glycol monobenzyl ether.

<Stabilizer>
The components in the conservation liquid and the ink components in the ink flow path may be deteriorated by, for example, active energy rays (e.g., ultraviolet rays) contained in lighting, outdoor light, etc., and heat applied during storage or use of the conservation liquid. More specifically, the components in the conservation liquid and the ink components in the ink flow path may undergo deterioration reactions such as oxidation, solidification, thickening, and discoloration due to active energy rays and heat. Such deterioration reactions lead to a decrease in the cleanliness of the ink flow path, so it is preferable for the conservation liquid to contain a stabilizer that suppresses the deterioration reactions.

As the stabilizer, a compound that suppresses the above-mentioned deterioration reaction, for example, a compound having an antioxidant function, a polymerization inhibitor function, etc., can be used. From the viewpoint of efficiently suppressing the above-mentioned deterioration reaction, it is preferable that the stabilizer contains at least one type selected from a compound containing a (meth)acrylate group and a phenothiazine-based compound.

Compounds containing a (meth)acrylate group have a mechanism within the molecule that suppresses deterioration reactions such as oxidation-reduction reactions and polymerization reactions of ink components. (Meth)acrylate refers to acrylate or methacrylate. Examples of compounds containing a (meth)acrylate group include hindered amines containing a (meth)acrylate group, hindered phenols containing a (meth)acrylate group, compounds containing a phenyl (meth)acrylate group represented by the following general formula (5), glyceryl propoxy tri(meth)acrylate, and bisphenol A diglycidyl di(meth)acrylate.

In general formula (5), R ⁸ represents a hydrogen atom or a methyl group, and R ⁹ to R ¹⁸ each independently represent a hydrogen atom, a hydroxy group, a hydrocarbon group having 1 to 16 carbon atoms, an alcohol group having a hydrocarbon group having 1 to 16 carbon atoms, an ether group consisting of an alcohol having a hydrocarbon group having 1 to 4 carbon atoms and an alcohol having a hydrocarbon group having 1 to 14 carbon atoms, or an ester group consisting of a carboxylic acid having a hydrocarbon group having 1 to 4 carbon atoms and an alcohol having a hydrocarbon group having 1 to 14 carbon atoms. The alcohol group refers to a hydrocarbon group having one or more hydroxyl groups.

More specific examples of compounds containing a (meth)acrylate group include 2-tert-butyl-6-(3-tert-butyl-2-hydroxy-5-methylbenzyl)-4-methylphenyl acrylate, 2-[1-(2-hydroxy-3,5-di-tert-pentylphenyl)ethyl]-4,6-di-tert-pentaphenyl acrylate, tetramethylpiperidyl methacrylate, and pentamethylpiperidyl methacrylate.

The compound containing a (meth)acrylate group may be used alone or in combination of two or more.
The content of the compound containing a (meth)acrylate group in the conservation liquid is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, and even more preferably 0.1% by mass or more. By increasing the content of the compound containing a (meth)acrylate group in the conservation liquid, the stability of the mixed liquid can be easily ensured even when the conservation liquid and the ink are mixed during operation shutdown.

The content of the compound containing a (meth)acrylate group in the preservation liquid is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 2.5% by mass or less. By reducing the content of the compound containing a (meth)acrylate group in the preservation liquid, the curing property of the ink is less likely to be inhibited even if the preservation liquid is mixed into the ink during operation.

Examples of phenothiazine compounds include phenothiazine, 2-methoxyphenothiazine, 2-cyanophenothiazine, bis(α-methylbenzyl)phenothiazine, 3,7-dioctylphenothiazine, and bis(α,α-dimethylbenzyl)phenothiazine.

The phenothiazine compound may be used alone or in combination of two or more kinds.
The content of the phenothiazine-based compound in the conservation liquid is preferably 0.001% by mass or more, more preferably 0.005% by mass or more, and even more preferably 0.01% by mass or more. By increasing the content of the phenothiazine-based compound in the conservation liquid, the stability of the mixture can be easily ensured even if a mixture of the conservation liquid and the ink is present in the ink flow path during operation shutdown.

The content of phenothiazine-based compounds in the preservation liquid is preferably 1% by mass or less, more preferably 0.8% by mass or less, and even more preferably 0.5% by mass or less. By reducing the content of phenothiazine-based compounds in the preservation liquid, the curing property of the ink is less likely to be inhibited even if the preservation liquid is mixed into the ink during operation.

Examples of stabilizers other than the above-mentioned compounds containing (meth)acrylate groups and phenothiazine-based compounds include hindered phenol-based compounds that do not have a (meth)acrylate group, nitrosamine-based compounds, hindered amine-based compounds that do not have a (meth)acrylate group, and phosphorus-based compounds.

<Ingredients other than those listed above>
The preservation liquid may contain, for example, a cyclic carbonate, a polybasic acid ester, an acylglycerol, a polymerizable compound, and the like.

Examples of cyclic carbonates include ethylene carbonate, propylene carbonate, and butylene carbonate. Examples of polybasic acid esters include dimethyl glutarate, diethyl glutarate, dimethyl succinate, diethyl succinate, dimethyl adipate, diethyl adipate, diisopropyl adipate, diethyl sebacate, and tributyl acetyl citrate. Examples of acylglycerols include triacetin and tripropionin. Examples of polymerizable compounds include (meth)acrylate compounds, vinyl ether compounds, and oxetane compounds.

The preservation liquid may contain water and a surface tension adjuster as necessary. The surface tension adjuster is a compound that can adjust the surface tension of the preservation liquid to a predetermined range. Examples of surface tension adjusters include ionic surfactants, nonionic surfactants, and modified silicone oils.

Examples of anionic surfactants of ionic surfactants include fatty acid salts, alkyl sulfate ester salts, benzenesulfonates, naphthalenesulfonates, sulfosuccinate ester salts, polyoxyethylene sulfate ester salts, and phosphate ester salts.

Examples of fatty acid salts include sodium stearate, potassium oleate, and partially hydrogenated sodium tallow fatty acid.
Examples of alkyl sulfate salts include sodium dodecyl sulfate, tri(2-hydroxyethyl)ammonium dodecyl sulfate, and sodium octadecyl sulfate.

Examples of benzenesulfonates include sodium nonylbenzenesulfonate, sodium dodecylbenzenesulfonate, sodium octadecylbenzenesulfonate, and sodium dodecyldiphenyletherdisulfonate.

Examples of naphthalenesulfonates include sodium dodecylnaphthalenesulfonate and naphthalenesulfonic acid-formaldehyde condensates.
Examples of sulfosuccinate salts include sodium didodecyl sulfosuccinate and sodium dioctadecyl sulfosuccinate.

Examples of polyoxyethylene sulfate ester salts include sodium polyoxyethylene dodecyl ether sulfate, tri(2-hydroxyethyl)ammonium polyoxyethylene dodecyl ether sulfate, sodium polyoxyethylene octadecyl ether sulfate, and sodium polyoxyethylene dodecyl phenyl ether sulfate.

Phosphate ester salts include, for example, potassium dodecyl phosphate and sodium octadecyl phosphate.
Examples of cationic surfactants of ionic surfactants include quaternary ammonium salts, such as alkylamine salts such as octadecyl ammonium acetate, coconut oil amine acetate, dodecyl trimethyl ammonium chloride, octadecyl trimethyl ammonium chloride, dioctadecyl dimethyl ammonium chloride, and dodecyl benzyl dimethyl ammonium chloride.

Examples of zwitterionic surfactants of ionic surfactants include alkyl betaines and amine oxides. Examples of alkyl betaines include dodecyl betaine and octadecyl betaine. Examples of amine oxides include dodecyl dimethyl amine oxide.

Examples of nonionic surfactants include polyoxyethylene alkyl ethers, polyoxyethylene phenyl ethers, sorbitan fatty acid esters, sorbitol fatty acid esters, and glycerin fatty acid esters.

Examples of polyoxyethylene alkyl ethers include polyoxyethylene dodecyl ether, polyoxyethylene hexadecyl ether, polyoxyethylene octadecyl ether, and polyoxyethylene (9-octadecenyl) ether.

Examples of the polyoxyethylene phenyl ethers include polyoxyethylene octylphenyl ether and polyoxyethylene nonylphenyl ether.
Examples of sorbitan fatty acid esters include sorbitan dodecanoate, sorbitan hexadecanoate, sorbitan octadecanoate, sorbitan (9-octadecenoate) ester, sorbitan (9-octadecenoate) triester, polyoxyethylene sorbitan dodecanoate, polyoxyethylene sorbitan hexadecanoate, polyoxyethylene sorbitan octadecanoate, polyoxyethylene sorbitan octadecanoate triester, polyoxyethylene sorbitan (9-octadecenoate) ester, and polyoxyethylene sorbitan (9-octadecenoate) triester.

As the sorbitol fatty acid esters, for example, polyoxyethylene sorbitol (9-octadecenoic acid) tetraester can be mentioned.
Examples of glycerin fatty acid esters include glycerin octadecanoic acid ester and glycerin (9-octadecenoic acid) ester.

Examples of modified silicone oils include polyether-modified silicone oil, methylstyrene-modified silicone oil, olefin-modified silicone oil, alcohol-modified silicone oil, and alkyl-modified silicone oil.

The preservation liquid may contain a dispersant as necessary. The dispersant is a component that suppresses aggregation of particulate components such as coloring components and fillers that are dispersed in the ink when the ink and the preservation liquid are mixed. Examples of dispersants include polymeric dispersants and low molecular weight dispersants.

<Viscosity of conservation liquid>
The viscosity of the conservation liquid is preferably 30 mPa·s or less at 25° C., more preferably 20 mPa·s or less, and even more preferably 15 mPa·s or less. By keeping the viscosity of the conservation liquid low, for example, it becomes possible to easily supply the conservation liquid to the ink flow path. In addition, by keeping the viscosity of the conservation liquid low, for example, it becomes possible to improve the mixability with the ink. The lower limit of the viscosity of the conservation liquid is not particularly limited, but is, for example, 0.5 mPa·s or more at 25° C.

<Preparation of maintenance liquid and maintenance method for ink application device>
The preservation liquid containing a plurality of compounds is prepared by mixing using a mixer as necessary. The preservation liquid may be used after degassing. By using the degassed preservation liquid, it is possible to dissolve the air bubbles present in the ink flow path into the preservation liquid. This makes it possible to easily remove the air bubbles mixed into the ink flow path. The degree of degassing of the preservation liquid can be controlled using the amount of dissolved oxygen. The amount of dissolved oxygen in the preservation liquid is preferably 9.0 mg/L or less, more preferably 6.0 mg/L or less, and even more preferably 4.0 mg/L or less. In addition, it is preferable that the preservation liquid is filtered from the viewpoint of reducing the risk of contamination by foreign matter. The preparation method of the preservation liquid preferably includes at least one of a filtration step and a degassing step. The filtration step and the degassing step can be performed according to a conventional method. The filtration step and the degassing step can also be performed by utilizing the ink flow path. That is, for example, by using a filtration device and a degassing device equipped in the ink flow path, the filtration step and the degassing step of the preservation liquid can be performed when the preservation liquid is used. When the ink application method of the ink application device is an ink jet method, it is preferable to carry out a filtering step and a deaeration step of the conservation liquid.

Methods for maintaining the ink application device include a method for cleaning the inside of the ink flow path using a preservation liquid, and a method for maintaining the constancy of the ink flow path using a preservation liquid. A method for cleaning the inside of the ink flow path using a preservation liquid includes a method for removing ink components and foreign matter by manually or automatically supplying the preservation liquid to the ink flow path and discharging it from the ink flow path. Such a cleaning process may be repeated multiple times. Also, the preservation liquid may be circulated within the ink flow path.

A method of using a conservation liquid to maintain the constancy of the ink flow path is to fill the ink flow path with the conservation liquid. Filling the ink flow path with conservation liquid when the ink application device is manufactured can, for example, prevent air bubbles from entering the ink flow path. Furthermore, filling the ink flow path with conservation liquid when the ink application device is stopped temporarily or for a long period of time after operation of the ink application device can prevent solidification or aggregation due to drying or reaction of ink residue, and prevent air bubbles from entering the ink flow path.

After the preservation liquid is discharged from the ink flow path, the preservation liquid adhering to the coating section of the ink coating device may be removed. Methods for removing the preservation liquid include, for example, wiping or absorbing with fibers or porous materials, scraping with a wiping blade, and removal with an air blower.

The preservation liquid has good compatibility with components such as (meth)acrylate compounds used in the active energy ray curable composition. For this reason, it is preferable to use it in an ink application device using the active energy ray curable composition. Examples of uses of the active energy ray curable composition include uses for coloring to express characters, photographs, illustrations, figures, or symbols. Uses of the active energy ray curable composition may be uses other than those for coloring, such as overcoat agents, undercoat agents, spot coating agents, adhesives, and primers. The ink referred to in this specification also includes compositions used for uses other than those for coloring.

<Actions and Effects of the Present Embodiment>
Next, the operation and effects of this embodiment will be described.
(1) An ink applicator maintenance liquid used for the purpose of maintaining an ink applicator contains at least one compound selected from the compounds represented by the above general formulas (1) and (2). This configuration exhibits the effect of suppressing deterioration in the performance of rubber members used in the ink flow path even when fluidity in the ink flow path is ensured. By ensuring fluidity in the ink flow path, the maintenance liquid can easily flow through the ink flow path, and therefore, for example, it becomes possible to easily discharge the maintenance liquid from the ink flow path. This makes it possible to efficiently discharge foreign matter and air bubbles in the ink flow path. In addition, since deterioration in the performance of the rubber members used in the ink flow path can be suppressed, deterioration in the sealing property of the ink flow path can be suppressed and components in the rubber members can be suppressed from flowing out. Therefore, the ink applicator maintenance liquid can be suitably used for cleaning the ink flow path and maintaining the constancy of the ink flow path.

The compounds represented by the above general formulas (1) and (2) have long-chain hydrocarbon groups at their ends, which is believed to prevent penetration between the rubber molecular chains due to steric hindrance. This is believed to prevent swelling of rubber components, decomposition of rubber components, or leakage of components from rubber components.

(2) The total content of the compounds represented by general formulas (1) and (2) in the conservation liquid is preferably 30% by mass or more. In this case, it is possible to further suppress the attack on rubber members.

(3) It is preferable that the preservation liquid further contains at least one compound selected from the compounds represented by the above general formulas (3) and (4). In this case, for example, it is possible to keep the viscosity of the preservation liquid low, so that the fluidity of the preservation liquid can be easily ensured.

(4) The total content of the compounds represented by the above general formulas (1) to (4) in the conservation liquid is preferably 65% by mass or more. In this case, it is possible to further suppress the attack on rubber members.

(5) The total content of the compounds represented by the general formulas (3) and (4) in the conservation liquid is preferably 70% by mass or less. In this case, by ensuring the content of the compounds represented by the general formulas (1) and (2), it is possible to further suppress the aggressiveness against rubber members.

(6) The viscosity of the conservation liquid at 25°C is preferably 30 mPa·s or less. In this case, for example, it becomes possible to easily supply the conservation liquid to the ink flow path. In addition, by keeping the viscosity of the conservation liquid low, it is possible to improve the mixability with the ink, which, for example, improves the cleaning properties of the ink flow path.

(7) It is preferable that the preservation liquid does not contain ethylene glycol ether-based solvents and diethylene glycol ether-based solvents. In this case, for example, it is possible to increase the stability when the preservation liquid and the ink are mixed. In particular, when the ink is an active energy ray-curable composition, it is preferable that the ink does not contain ethylene glycol ether-based solvents and diethylene glycol ether-based solvents.

(8) It is preferable that the preservation liquid further contains a stabilizer containing a compound having at least one of the functions of anti-oxidation and polymerization inhibition. In this case, it is possible to suppress the deterioration reaction of the components in the preservation liquid and the ink components in the ink flow path. This makes it possible to suppress the deterioration of the cleanliness of the ink flow path. It is further preferable that the stabilizer contains at least one type selected from a compound containing a (meth)acrylate group and a phenothiazine-based compound.

(9) The ink application method of the ink application device is preferably an inkjet method. The above-mentioned preservation liquid can be suitably used for preserving more precise ink flow paths such as those in the inkjet method.

(10) The amount of dissolved oxygen in the preservation liquid is preferably 9.0 mg/L or less. In this case, it is possible to dissolve air bubbles present in the ink flow path into the preservation liquid. This makes it possible to easily remove air bubbles that have become mixed into the ink flow path.

Next, examples and comparative examples will be described. The following examples 1, 4, and 9 are reference examples shown as references for the invention according to the claims.
(Examples 1 to 16 and Comparative Examples 1 to 5)
In Examples 1 to 16 and Comparative Examples 1 to 5, the raw materials were placed in a container so as to have the compositions shown in Tables 1 to 3, and the mixture was stirred at room temperature until no solid matter remained. The mixture was then filtered using a glass fiber filter (manufactured by Advantec Toyo Co., Ltd., product name: GS-25) to prepare a preservation solution.

The viscosity of the prepared conservation liquid and the conservation liquid-test ink mixture described below was measured at a measurement temperature of 25° C. using a viscometer (manufactured by Toki Sangyo Co., Ltd., product name: RE85L).
In Table 1, the units of the numerical values showing the compositions are mass %. The abbreviations in Table 1 are as follows.

"Compound A11" is a compound represented by general formula (2), and is bis(2-ethylhexyl) adipate (manufactured by J-Plus, trade name: DOA).
"Compound A12" is a compound represented by general formula (2), and is diisodecyl adipate (manufactured by J-Plus, trade name: DIDA).

"Compound A13" is a compound represented by general formula (1) and is propylene glycol-mono-2-ethylhexanoate (manufactured by Yokkaichi Chemical Co., Ltd., product name: Wigenol EHP-01).

"Compound A21" is a compound represented by general formula (3) and is dipropylene glycol monopropyl ether (manufactured by Nippon Nyukazai Co., Ltd., product name: propyl propylene diglycol).

"Compound A22" is a compound represented by general formula (4), and is 1,6-hexanediol diacetate (manufactured by Daicel Corporation, trade name: 1,6-HDDA).
"Compound A3" is a compound other than the compounds represented by the above general formulas (1) to (4), and is a mixture of dimethyl succinate, dimethyl glutarate, and dimethyl adipate (manufactured by Taoka Chemical Co., Ltd., product name: No. 23 Ester).

"Compound A4" is a compound other than the compounds represented by the above general formulas (1) to (4), and is acetyl tributyl citrate (manufactured by J-Plus Co., Ltd., trade name: ATBC).
"Compound A5" is a compound other than the compounds represented by the above general formulas (1) to (4), and is ethylene glycol monohexyl ether (manufactured by Nippon Nyukazai Co., Ltd., trade name: hexyl glycol).

"Compound A6" is a compound other than the compounds represented by the above general formulas (1) to (4), and is ethylene glycol monobenzyl ether (manufactured by Nippon Nyukazai Co., Ltd., product name: benzyl glycol).

"Compound A7" is a compound other than the compounds represented by the above general formulas (1) to (4), and is diethylene glycol monobutyl ether (manufactured by Nippon Nyukazai Co., Ltd., product name: butyl diglycol).

"Compound B11" is a compound containing a (meth)acrylate group, and is tetramethyl piperidinyl methacrylate (manufactured by Showa Denko Materials, product name: FA-712HM).

"Compound B12" is a compound containing a (meth)acrylate group, and is a mixture of glyceryl propoxy triacrylate and bisphenol A diglycidyl diacrylate (manufactured by RAHN, product name: GENORAD16).

"Compound B13" is a compound containing a (meth)acrylate group, and is 2-tert-butyl-6-(3-tert-butyl-2-hydroxy-5-methylbenzyl)-4-methylphenyl acrylate (manufactured by Sumitomo Chemical Co., Ltd., product name: Sumilizer GM(F)).

"Compound B21" is a phenothiazine-based compound, phenothiazine (manufactured by Seiko Chemical Co., Ltd.).
(Evaluation of the suitability of rubber components)
An O-ring (manufactured by Air Water Mach, thickness: 1.9 mm, inner diameter: 8.8 mm) was prepared as a rubber member to be used for the evaluation. The materials for the O-ring were the following five types of materials 1 to 5 specified in JIS B2401-1 (2012).

Material 1: NBR-70-1 (nitrile rubber, product name: N7-438)
Material 2: NBR-70-2 (nitrile rubber, product name: N7-995)
Material 3: EPDM-70 (ethylene propylene rubber, product name: E7-512)
Material 4: VMQ-70 (silicone rubber, product name: S7-947)
Material 5: FKM-70 (fluororubber, product name: F7-135)
The O-rings made of the above materials 1 to 5 were subjected to a storage test as follows.

First, the mass of each O-ring before storage was measured to the unit of mg using a precision balance. The mass of each O-ring before storage was set to m0 [mg].
Next, each O-ring was placed separately in a 20 mL brown bottle, and 5 g of the preservation liquid of Example 1 was poured into each brown bottle. After sealing each brown bottle, it was stored at a temperature of 60° C. for 4 weeks.

After storage, the O-rings were removed from the brown bottles, and the preservative liquid adhering to the surface of each O-ring was wiped off. Each O-ring was left at room temperature for one day, and then the mass of each O-ring was measured again. The mass of each O-ring after storage is defined as mi [mg].

The mass change rate of each O-ring before and after the storage test was calculated according to the following formula.
Mass change rate [%] = (mi [mg] - m0 [mg]) / m0 [mg] x 100
The rubber component suitability was evaluated based on the calculated mass change rate according to the following evaluation criteria.

When the mass change rate was within the range of 0.0% or more and 10.0% or less: the attacking effect on rubber components was very low, and the compatibility with rubber components was excellent (○○).
When the mass change rate was 10.1% or more and 20.0% or less: the attacking effect on rubber members was low, and the compatibility with rubber members was evaluated as good (◯).

When the mass change rate was within the range of -3.0% or more and less than 0.0%, it was evaluated as being somewhat aggressive to rubber parts and somewhat poor in compatibility with rubber parts (Δ-).
When the mass change rate was within the range of 20.1% or more and 30.0% or less: the attacking power to rubber parts was somewhat high, and the compatibility with rubber parts was somewhat poor (Δ+).

When the mass change rate was −3.1% or less, it was evaluated as being highly aggressive to rubber members and poor in compatibility with rubber members (×−).
When the mass change rate was 30.1% or more, it was evaluated as being highly aggressive to rubber parts and poor in compatibility with rubber parts (×+).

The conservation fluids of Examples 2 to 16 and Comparative Examples 1 to 5 were also evaluated for suitability for rubber members in the same manner as the conservation fluid of Example 1. The evaluation results of suitability for rubber members are shown in Tables 2 to 4.
(Evaluation of Mixing Stability with Ink)
Samples for evaluating mixing stability were prepared by mixing the conservation liquid of Example 1 and the test ink at a predetermined mass ratio. Seven types of samples, Samples 1 to 7, were prepared with different mass ratios.

Sample 1: Mass of conservation liquid/mass of test ink=1/99
Sample 2: Mass of conservation liquid/mass of test ink=5/95
Sample 3: Mass of conservation liquid/mass of test ink=20/80
Sample 4: Mass of conservation liquid/mass of test ink=50/50
Sample 5: Mass of conservation liquid/mass of test ink=80/20
Sample 6: Mass of conservation liquid/mass of test ink=95/5
Sample 7: Mass of conservation liquid/mass of test ink=99/1
The test inks were prepared by placing the raw materials in a container so as to have the composition shown in Table 1, stirring in a water bath at 40 to 50°C until no solid matter remained, and then filtering using a glass fiber filter paper (manufactured by Advantec Toyo Co., Ltd., product name: GS-25).

The raw materials (product names) of the test inks in Table 1 are as follows.
"VEEA" is 2-(2-vinyloxyethoxy)ethyl acrylate (manufactured by Nippon Shokubai Co., Ltd., trade name: VEEA).

"SR9087" is phenoxy polyethylene glycol acrylate (manufactured by Sartomer Corporation, trade name: SR9087).
"SR508" is dipropylene glycol diacrylate (manufactured by Sartomer Corporation, trade name: SR508NS).

"OMNIRAD TPO" is 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide (manufactured by IGM Resins).
"OMNIRAD 184" is 1-hydroxycyclohexyl phenyl ketone (manufactured by IGM Resins).

"ITX" is 2-isopropylthioxanthone (manufactured by DKSH Japan, trade name: Lunacure 2-ITX).
"VARIPLUS AP" is a ketone aldehyde condensation resin (manufactured by EVONIK Industries AG, product name: VARIPLUS AP).

"TEGO GLIDE 440" is a polyether-modified siloxane copolymer (manufactured by EVONIK Industries AG, product name: TEGO GLIDE 440).

"Irganox 1010" is pentaerythritol tetrakis (3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) (manufactured by BASF, product name: Irganox 1010).

The above samples 1 to 7 were degassed using a vacuum degassing device until the amount of dissolved oxygen was 2.0±0.1 ppm. The amount of dissolved oxygen in each sample was measured using an oxygen sensor (a diaphragm-type galvanic cell-type oxygen sensor, manufactured by Iijima Electronics Co., Ltd., product name: B-506). Each degassed sample was filled into a sealed container from which the air had been removed in advance.

Each sample was stored for 4 weeks in an atmosphere at 60°C. The viscosity change rate was calculated from the viscosity of each sample measured beforehand and the viscosity of each sample after 4 weeks of storage according to the following formula. The viscosity of each sample measured beforehand is V0 [mPa·s], and the viscosity of each sample after storage is Vi [mPa·s].

Viscosity change rate [%] = Vi [mPa·s] / V0 [mPa·s] × 100
The mixed stability with the ink was evaluated based on the calculated viscosity change rate and the appearance of the sample after storage according to the following evaluation criteria.

For all samples 1 to 7, if the viscosity change rate is within the range of ±10.0%, and no abnormal appearance such as cloudiness of the liquid due to the generation of foreign matter, generation of foreign matter such as sol-like substances, or gelation is observed in any of the samples, the sample is evaluated as having excellent mixing stability with the ink (○○).

In all of the samples 1 to 7, the above-mentioned abnormalities in appearance were not observed, but in at least one sample, the viscosity change rate was within the range of 10.1% or more and 20.0% or less, or -20.0% or more and -10.1% or less: the mixing stability with the ink was evaluated as good (○).

None of the above appearance abnormalities were observed in samples 1 to 7, but if the viscosity change rate in at least one sample was 20.1% or more or -20.1% or less, it was evaluated as having poor mixing stability with ink (△).

When the above-mentioned abnormal appearance was observed in at least one of Samples 1 to 7, the sample was evaluated as having very poor mixing stability with ink (x).
The maintenance liquids of Examples 2 to 16 and Comparative Examples 1 to 5 were also evaluated for mixing stability with ink in the same manner as the maintenance liquid of Example 1. The evaluation results of mixing stability with ink are shown in Tables 2 to 4.

As shown in Tables 2 and 3, the viscosity of the conservation liquid in each Example at 25° C. is kept low, and it is therefore possible to ensure the fluidity in the ink flow path.

It can also be seen that the conservation liquids of the respective Examples give excellent or good evaluation results with respect to the suitability of the rubber members of Materials 1 to 5 above.
It is also apparent that in Examples 1 to 15, excellent results were obtained with respect to mixing stability with the ink.

As shown in Table 4, the conservation liquid of each comparative example was evaluated as being somewhat poor or poor in terms of suitability for at least one of the rubber members of Materials 1 to 5.
<Additional Notes>
The technical ideas that can be understood from the above-described embodiment and modified examples will be described.

(Appendix 1) An ink applicator maintenance liquid used for maintaining an ink applicator, comprising:
A liquid for maintaining an ink application device, comprising at least one compound selected from the compounds represented by the above general formulas (1) and (2).

(Appendix 2) The ink applicator preservation liquid described in (Appendix 1) has a total content of the compounds represented by the general formulas (1) and (2) in the ink applicator preservation liquid of 30 mass% or more.

(Appendix 3) A liquid for preserving an ink application device according to (Appendix 1) or (Appendix 2), further comprising at least one compound selected from the compounds represented by the above general formulas (3) and (4).

(Appendix 4) The ink applicator preservation liquid described in (Appendix 3) has a total content of the compounds represented by the general formulas (1) to (4) in the ink applicator preservation liquid of 65 mass% or more.

(Appendix 5) The ink applicator preservation liquid described in (Appendix 3) or (Appendix 4), in which the total content of the compounds represented by the general formulas (3) and (4) in the ink applicator preservation liquid is 70 mass% or less.

(Appendix 6) An ink application device maintenance liquid according to any one of (Appendix 1) to (Appendix 5), having a viscosity at 25°C of 30 mPa·s or less.
(Appendix 7) An ink application device maintenance liquid according to any one of (Appendix 1) to (Appendix 6), which does not contain an ethylene glycol ether solvent or a diethylene glycol ether solvent.

(Appendix 8) An ink application device preservation liquid according to any one of (Appendix 1) to (Appendix 7), further comprising a stabilizer containing a compound having at least one of an antioxidant function and a polymerization inhibitor function.

(Appendix 9) The ink application device preservation liquid described in (Appendix 8) contains at least one stabilizer selected from a compound containing a (meth)acrylate group and a phenothiazine-based compound.

(Appendix 10) The ink applicator preservation liquid according to any one of (Appendix 1) to (Appendix 9), wherein the ink applicator has an ink-jet system.
(Appendix 11) An ink applicator maintenance liquid according to any one of (Appendix 1) to (Appendix 10), wherein the amount of dissolved oxygen in the ink applicator maintenance liquid is 9.0 mg/L or less.

(Appendix 12) A method for maintaining an ink application device, comprising maintaining the ink application device using the ink application device maintenance liquid described in any one of (Appendix 1) to (Appendix 11) above.

Claims (11)

1. An ink applicator maintenance liquid used for maintaining an ink applicator of an ink jet system, comprising:
at least one first compound selected from 3- (2-ethylhexyloxy)propionic acid, bis(2-ethylhexyl) succinate, diisononyl succinate, diisodecyl succinate, bis(2-ethylhexyl) glutarate, diisononyl glutarate, diisodecyl glutarate, diheptyl adipate, bis(2-ethylhexyl) adipate, diisononyl adipate, and diisodecyl adipate;
and at least one second compound selected from dipropylene glycol monomethyl ether, dipropylene glycol dimethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol diethyl ether, tripropylene glycol monomethyl ether, dipropylene glycol monopropyl ether, and dipropylene glycol mono-n-butyl ether;
The ink applicator maintenance liquid has a total content of the first compound in the ink applicator maintenance liquid of 30 mass% or more, and a total content of the first compound and the second compound in the ink applicator maintenance liquid of 65 mass% or more . 2. The ink applicator maintenance fluid according to claim 1 , which is free of water. The ink applicator maintenance liquid according to claim 1 or 2, wherein the total content of the second compound in the ink applicator maintenance liquid is 70 mass % or less. The ink application device preservation liquid according to claim 1 or 2, which has a viscosity of 30 mPa·s or less at 25°C. The ink application device preservation liquid according to claim 1 or 2, which does not contain ethylene glycol ether-based solvents and diethylene glycol ether-based solvents. The ink application device preservation liquid according to claim 1 or 2, further comprising a stabilizer containing a compound having at least one of an antioxidant function and a polymerization inhibitor function. The ink applicator maintenance liquid according to claim 6 , wherein the stabilizer comprises at least one selected from the group consisting of a compound containing a (meth)acrylate group and a phenothiazine-based compound. The ink applicator preservation liquid according to claim 1 or 2, wherein the amount of dissolved oxygen in the ink applicator preservation liquid is 4.0 mg/L or less. The ink jet ink applicator is used in an ink flow path of the ink jet ink applicator,
The ink applicator preservation liquid according to claim 1 or 2, wherein the ink flow path has a rubber member. A method for maintaining an ink application device, comprising maintaining the ink application device of the inkjet type using the ink application device maintenance liquid according to claim 1 or 2. The method for maintaining an ink applicator according to claim 10 , further comprising a deaeration step for reducing an amount of dissolved oxygen in the ink applicator maintenance liquid.