JP6627527B2 - Oil-based inkjet ink composition and image forming method - Google Patents

Description

  The present invention relates to an oil-based inkjet ink composition and an image forming method.

  As an inkjet ink (hereinafter, also referred to as “ink”) used for recording using an inkjet recording method, development of an oil-based inkjet ink composition using diethylene glycol diethyl ether or the like as a main solvent has been advanced.

  By the way, since diethylene glycol diethyl ether has a hygroscopic property, when this oil-based ink is used for a long time, foreign matter derived from the pigment is deposited in the ink, and the deposited foreign matter may clog the filter provided in the ink supply path. As a result, ink ejection failure may occur. Therefore, for example, Patent Documents 1 and 2 disclose techniques for reducing the generation of foreign substances by adjusting the content of components contained in ink.

WO 2009/63656 pamphlet JP 2010-150314 A

However, recently, the inventors have found that a small amount of water infiltrates from the outside by penetrating the tube used for the ink supply path, and that potassium and sulfate (SO ₄₎ It was discovered that ^2- ) was dissolved, and then precipitated as K ₂ SO ₄ or the like insoluble in the solvent used for the ink, and the filter was clogged. The above technique does not disclose the control of the amount of potassium and sulfate to suppress the generation of foreign substances. Further, the solvent described in Patent Document 2 is an acetate-based solvent, which has low hygroscopicity and does not cause any problem with respect to foreign matter, but has a strong odor of printed matter and may have poor print color density.

  Therefore, according to some aspects of the present invention, by solving at least a part of the above-described problems, it is possible to suppress the generation of a foreign substance derived from a potassium compound, and to prevent the occurrence of ink ejection failure. An object of the present invention is to provide an oil-based inkjet ink composition having excellent stability and reduced odor, and an image forming method.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following aspects or application examples.

[Application Example 1]
One embodiment of the oil-based inkjet ink composition according to the present invention,
It contains a compound A represented by the following general formula (1) and a pigment as a solvent, and has a sulfate group content of 80 ppm or less.
R ^1- (O-C _n H _2n ) _m -OR ² (1)
(In the general formula (1), R ¹ and R ² are an alkyl group having 1 to 4 carbon atoms, which may be the same or different, m is an integer of 1 to 7, and n is 1 to 3 Represents an integer.)

According to the aspect of Application Example 1, by containing the compound A and setting the sulfate content to 80 ppm or less, even when moisture permeates from the outside air into the ink supply path, the potassium compound is less likely to precipitate. Accordingly, it is possible to provide an oil-based inkjet ink composition which does not cause ink ejection failure, has excellent ejection stability, and has reduced odor.

[Application Example 2]
In the above application example,
The potassium content can be up to 120 ppm.

[Application Example 3]
In the above application example,
The sulfate content may be 5 ppm or more and 80 ppm or less.

[Application Example 4]
In the above application example,
The potassium content can be from 5 ppm to 120 ppm.

[Application Example 5]
In the above application example,
As a solvent, compound B represented by the following general formula (2) can be further contained.
^{_{R 3 - (O-C n}} H 2n) m -OH ··· (2)
(In the general formula (2), R ³ is an alkyl group having 2 to 7 carbon atoms, m is an integer of 1 to 7, and n represents an integer of 1 to ^3. )

[Application Example 6]
In the above application example,
The content of the compound B can be 2% by mass or more and 20% by mass or less.

[Application Example 7]
In the above application example,
The pigment may be carbon black.

[Application Example 8]
One embodiment of the image forming method according to the present invention includes:
An image forming method for forming an image by discharging droplets of the oil-based inkjet ink composition according to the application example,
The discharge of the droplet is performed using an ink jet recording apparatus in which at least one of an ink flow path portion and an ink storage portion that is in contact with ink has a resinous member.

  According to the aspect of Application Example 8, by using the oil-based inkjet ink composition according to the application example, even when moisture permeates from the outside air into the ink supply path, the potassium compound is less likely to be precipitated, and the ink ejection is performed. It is possible to provide an image forming method that does not cause a defect, has excellent ejection stability, and has reduced odor.

[Application Example 9]
In the above application example,
The inkjet recording apparatus may have a head including a filter that transmits particles having a major axis of 15 μm or less.

FIG. 2 is a diagram schematically illustrating a configuration of an inkjet recording apparatus that can be used in the embodiment.

  Hereinafter, some embodiments of the present invention will be described. The embodiment described below describes an example of the present invention. The present invention is not limited to the following embodiments at all, and includes various modifications to be made without departing from the spirit of the present invention. Note that not all of the configurations described below are essential configurations of the present invention.

  In the present invention, the `` oil-based inkjet ink composition '' refers to a solvent-based inkjet ink composition used in an inkjet recording method, and includes an organic solvent as a main solvent, and an ink that does not use water as a main solvent. is there. Preferably, the content of water in the ink is 3% by mass or less, more preferably 1% by mass or less, even more preferably less than 0.05% by mass, and still more preferably less than 0.01% by mass. It is more preferably less than 0.005% by mass, and most preferably less than 0.001% by mass. Alternatively, the ink composition may be substantially free of water. “Substantially not contained” means not intentionally contained.

1.1. Oil-based inkjet ink composition The oil-based inkjet ink composition according to one embodiment of the present invention contains a compound A represented by the following general formula (1) and a pigment as a solvent, and has a sulfate content of 80 ppm or less. It is characterized by the following.
R ^1- (O-C _n H _2n ) _m -OR ² (1)
(In the general formula (1), R ¹ and R ² are an alkyl group having 1 to 4 carbon atoms, which may be the same or different, m is an integer of 1 to 7, and n is 1 to 3 Represents an integer.)
It is characterized by the following. Hereinafter, the components contained in the oil-based inkjet ink composition according to the present embodiment will be described in detail.

  The oil-based inkjet ink composition used in the present embodiment uses the solvent represented by the general formula (1) and has a sulfate group content of 80 ppm or less, so that moisture permeation from the outside air into the ink supply path is prevented. Even if there is, it is possible to suppress the generation of foreign matters derived from the potassium compound, and it is possible to obtain an oil-based inkjet ink composition that does not cause ink ejection failure, has excellent ejection stability, and has reduced odor. Hereinafter, components contained in the oil-based ink used in the present embodiment and components that may be contained will be described in detail.

1.1.1. Compound A represented by general formula (1) (first solvent)
In the oil-based inkjet ink composition, a compound represented by the above general formula (1) is contained as a main solvent (first solvent), and in the above general formula (1), “the carbon number in R ¹ and R ² is 1 to 1”. The “alkyl group of 4” may be a linear or branched alkyl group, and specifically, may be a methyl group, an ethyl group, an n-propyl group, an iso-propyl group, an n-butyl group, a sec. -Butyl group and tert-butyl group. Examples of the “C _n H _2n (alkylene) group” in which _n represents an integer of 1 to 3 include a methylene group, an ethylene group, an n-propylene group, and an isopropylene group.

  The compound represented by the general formula (1) is a glycol ether such as an alkylene glycol diether and is excellent in drying property on a recording medium. The glycol ethers can be used alone or as a mixture of two or more.

Examples of the alkylene glycol diether include ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol ethyl methyl ether, diethylene glycol dibutyl ether, diethylene glycol butyl methyl ether, triethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and triethylene glycol dimethyl ether. Ethylene glycol diethyl ether, triethylene glycol dibutyl ether, triethylene glycol butyl methyl ether, tetraethylene glycol dimethyl ether, tetraethylene glycol diethyl ether, tetraethylene glycol dibutyl ether, pentaethylene glycol Dimethyl ether, pentaethylene glycol diethyl ether, pentaethylene glycol dibutyl ether, hexaethylene glycol dimethyl ether, hexaethylene glycol diethyl ether, hexaethylene glycol dibutyl ether, heptaethylene glycol dimethyl ether, heptaethylene glycol diethyl ether, heptaethylene glycol dibutyl ether, propylene glycol Examples thereof include dimethyl ether, propylene glycol diethyl ether, dipropylene glycol dimethyl ether, and dipropylene glycol diethyl ether.

  The lower limit of the content of the compound A represented by the general formula (1) contained in the oil-based inkjet ink composition is preferably 30% by mass or more based on the total mass (100% by mass) of the oil-based ink. , 40% by mass or more, and even more preferably 50% by mass or more. The upper limit is preferably 95% by mass or less, more preferably 90% by mass or less, even more preferably 85% by mass or less, and still more preferably 80% by mass or less, It is particularly preferred that the content be 75% by mass or less. When the content is 30% by mass or more, the wet spreadability of the droplet is improved, and a good image having excellent smoothness can be formed. Further, when the content is 95% by mass or less, the image is prevented from being stained due to generation of mist.

  In the oil-based inkjet ink composition used in the present embodiment, the compound A represented by the general formula (1) is used as a main solvent, and further, the sulfate group content is adjusted to 80 ppm or less, thereby deriving from the potassium compound. An oil-based inkjet ink composition that can suppress generation of foreign matter that does not occur, does not cause ink ejection failure, has excellent ejection stability, and has reduced odor.

1.1.2. Compound B (second solvent) represented by general formula (2)
In the present embodiment, the oil-based inkjet ink composition has a second solvent represented by the following general formula (2) in addition to the solvent represented by the general formula (1) as a main solvent (first solvent). It is preferable to include a solvent that is the compound represented.
^{_{R 3 - (O-C n}} H 2n) m -OH ··· (2)
(In the general formula (2), R ³ is an alkyl group having 2 to 7 carbon atoms, m is an integer of 1 to 7, and n represents an integer of 1 to ^3. )

  By including a solvent that is a compound represented by the general formula (2) as the second solvent, the moisture absorption rate and the drying property of the oil-based inkjet ink composition according to the present embodiment are adjusted, and the wet-spreading property and the mist Reduction and the like are possible. In addition, by including a solvent that is a compound represented by the above general formula (2), it is possible to reduce the generation of foreign matter.

Here, the “alkyl group having 2 to 7 carbon atoms” in R ³ can be a linear or branched alkyl group, for example, an ethyl group, an n-propyl group, an iso-propyl group, Examples thereof include an n-butyl group, a sec-butyl group, a tert-butyl, a pentyl group, a hexyl group and a heptyl group. Examples of the “C _n H _2n (alkylene) group” in which _n represents an integer of 1 to 3 include a methylene group, an ethylene group, an n-propylene group, and an isopropylene group.

Specific examples of the solvent that is the compound represented by the general formula (2) include alkylene glycol monoethers, and these compounds can be used alone or in combination of two or more.

  Examples of the alkylene glycol monoether include, for example, ethylene glycol monoethyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, ethylene glycol monophenyl ether, ethylene glycol monoheptyl ether, diethylene glycol monoethyl ether, and diethylene glycol. Monobutyl ether, diethylene glycol monohexyl ether, diethylene glycol monobenzyl ether, diethylene glycol monoheptyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, tetraethylene glycol monoethyl ether, tetraethylene glycol monobutyl ether Tetraethylene glycol monomethyl heptyl ether pentaethylene glycol monoethyl ether, pentaethylene glycol monobutyl ether, hexaethylene glycol monobutyl ether, epta ethylene glycol monobutyl ether, propylene glycol monoethyl ether, dipropylene glycol monoethyl ether and the like.

  The content of the solvent as the compound B represented by the general formula (2) with respect to the total amount of the oil-based inkjet ink composition (the total amount when a plurality of types are used) is preferably from 2% by mass to 20% by mass. Or less, more preferably 3% by mass or more and 15% by mass or less, particularly preferably 5% by mass or more and 10% by mass or less.

1.1.3. Cyclic ester The oil-based inkjet ink composition according to this embodiment may contain a cyclic ester (lactone) as a solvent. Since the oil-based ink contains a cyclic ester, a part of the recording surface of the recording medium (for example, a recording surface containing a vinyl chloride resin) can be dissolved to allow the oil-based ink to penetrate into the recording medium. By penetrating the ink into the recording medium in this manner, the rub resistance (friction fastness) of the image recorded on the recording medium can be improved. That is, since the cyclic ester has a high affinity with the vinyl chloride resin, the components of the oil-based inkjet ink composition are easily infiltrated (easily bite) on the recording surface. As a result of the cyclic ester having such an action, it is considered that an oil-based ink containing the cyclic ester can form an image having excellent abrasion resistance even under severe conditions.

  An ester is a compound having a structure in which a hydroxyl group and a carboxyl group are dehydrated and condensed in one molecule having a hydroxyl group and a carboxyl group. Further, the cyclic ester has a structure in which a heterocyclic ring containing two or more carbon atoms and one oxygen atom, and a carbonyl group is arranged adjacent to an oxygen atom forming the heterocyclic ring, It is a compound generically called.

  Among the cyclic esters, those having a simple structure include, for example, β-propiolactone, β-butyrolactone, γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone. be able to. The number of heterocyclic ring members of the cyclic ester is not particularly limited. Further, for example, an arbitrary side chain may be bonded to the heterocyclic ring members. The cyclic ester may be used alone or as a mixture of two or more.

From the viewpoint of further increasing the abrasion resistance of an image formed by the oil-based inkjet ink composition according to the embodiment, among the cyclic esters exemplified above, a cyclic ester having 3 to 7 membered rings is preferable, and a 5-membered ring ester is preferable. It is more preferable to use a cyclic ester having a ring or a six-membered ring, and in any case, it is more preferable not to have a side chain. Specific examples of such a cyclic ester include β-butyrolactone, γ-butyrolactone, and γ-valerolactone. In addition, since such a cyclic ester has a particularly high affinity for polyvinyl chloride, when it is attached to a recording medium containing polyvinyl chloride, it is possible to obtain a remarkable effect of increasing the abrasion resistance. it can.

  The content of the oil-based inkjet ink composition relative to the total amount (when a plurality of types are used, the total amount is 5% by mass or more and 50% by mass or less, preferably 7% by mass or more when a cyclic ester is blended). It is at most 30% by mass, more preferably at least 10% by mass and at most 20% by mass.

1.1.4. Other Solvents In the oil-based inkjet ink composition according to the present embodiment, the following compounds can be used as a solvent in addition to the compounds represented by the general formulas (1) and (2) and the cyclic esters. .

  Examples of such a solvent include alcohols (eg, methyl alcohol, ethyl alcohol, propyl alcohol, butyl alcohol, isopropyl alcohol, and fluorinated alcohol), ketones (eg, acetone, methyl ethyl ketone, cyclohexanone), and carboxylic esters (eg, acetic acid). Methyl, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, etc.), ethers (diethyl ether, dipropyl ether, tetrahydrofuran, dioxane, etc.), polyhydric alcohols (ethylene glycol, diethylene glycol, triethylene glycol) , Polyethylene glycol, polypropylene glycol, propylene glycol, butylene glycol, 1,2,6-hexanetriol, thioglycol, hexylene Call, glycerin, trimethylol ethane, trimethylol propane, etc.) and the like.

  When the oil-based ink contains (polyhydric) alcohols or the like, the total content is determined by improving the wet-spreading property and the permeability on the recording medium to reduce shading unevenness, storage stability and ejection reliability. From the viewpoint of ensuring the property, the content is preferably 0.05% by mass or more and 30% by mass or less, more preferably 0.1% by mass or more and 20% by mass or less based on the total mass of the oil-based ink. When the content of the (polyhydric) alcohol is within the above range, the wettability, penetrability, and drying property of the ink become good, and an image having good print density (color developability) may be obtained. . In addition, when the content of the (polyhydric) alcohol is within the above range, the viscosity of the ink can be made appropriate, and the occurrence of nozzle clogging or the like can be reduced in some cases.

  In addition, amines may be blended in the oil-based ink. For example, triethanolamine, tripropanolamine, tributanolamine, N, N-dimethyl-2-aminoethanol, N, N-diethyl-2-aminoethanol And one or more of them can be used. When the amines are contained, the total content is preferably from 0.05% by mass to 5% by mass, and more preferably from 0.1% by mass to 3% by mass, based on the total mass of the oil-based inkjet ink composition. It is more preferred that:

  Examples of the solvent include higher fatty acid esters such as methyl laurate, isopropyl hexadecanoate (isopropyl palmitate), isopropyl myristate, methyl oleate, and ethyl oleate; and dicarboxylic acids (carbons) of aliphatic hydrocarbons having 2 to 8 carbon atoms. A dibasic acid diester obtained by diesterifying a number excluding carbon of a carboxyl group with an alkyl group having 1 to 5 carbon atoms, and a monocarboxylic acid of an aliphatic hydrocarbon having 6 to 10 carbon atoms (the number of carbon atoms of the carboxyl group is Alkylamides (N, N-dimethyldecaneamide, etc.) obtained by amidating carbon (excluding carbon) (substituents substituting an amide nitrogen atom are each independently a hydrogen atom or an alkyl group having 1 to 4 carbon atoms) And the like.

  One or more of the other solvents exemplified here can be added to the oil-based ink in an appropriate amount.

  Next, components that are dispersed or dissolved in the above-mentioned solvent in the oil-based inkjet ink composition used in the present embodiment will be described.

1.1.5. Pigment The oil-based inkjet ink composition used in the present embodiment contains a pigment as a coloring material. The present invention is particularly advantageous because pigments tend to cause the generation of foreign substances due to moisture absorption. As the pigment, pigments such as inorganic pigments and organic pigments may be used, and one kind may be used alone, or two or more kinds may be used in combination.

  As the organic pigment, for example, azo pigments (for example, azo lake, insoluble azo pigment, condensed azo pigment, chelate azo pigment, etc.), polycyclic pigments (phthalocyanine pigment, perylene and perylene pigment, anthraquinone pigment, quinacridone pigment, dioxane pigment, Thioindigo pigments, isoindolinone pigments, quinophthaloni pigments, etc., dye lakes (eg, basic dye lakes, acid dye lakes, etc.), nitro pigments, nitroso pigments, aniline black, daylight fluorescent pigments and the like. In addition, examples of the inorganic pigment include carbon black, titanium dioxide, silica, and alumina.

  The content of the pigment can be appropriately set as desired and is not particularly limited, but is usually 0.1% by mass or more and 10% by mass or less based on the total mass of the oil-based inkjet ink composition. It is preferably from 0.5% by mass to 8% by mass, more preferably from 1% by mass to 6% by mass. When the content of the pigment is in the above range, the coloring property is excellent, and the image formed by this ink composition has good weather resistance.

  In addition, since the pigment contains a sulfate group that causes a potassium compound as a foreign substance, the foreign substance is easily precipitated. Therefore, it is preferable to use the pigment to be used after removing the sulfate group by performing a purification operation as appropriate. Above all, carbon black may contain a sulfate group in the process of its production, and it is preferable to remove the sulfate group by performing an appropriate purification operation when used.

  The pigment can be purified by a known pigment purification method. For example, as a method for purifying carbon black, an aqueous dispersion of carbon black is brought into contact with various water-soluble chelating agents to elute metal components contained in carbon black, as described in JP-A-2005-113091. After being transferred to the liquid phase by being captured by the chelating agent, a method of solid-liquid separation, as described in JP-A-2005-220320, after strongly stirring the carbon black aqueous dispersion, filtration and the like As a method for separation, a method of washing and eluting with an aqueous solution of an inorganic acid as described in JP-A-58-222157.

  By refining the above pigment, the content of sulfate groups in the oil-based inkjet ink composition is reduced to 80 ppm or less. In order to further suppress precipitation of the potassium compound as a foreign substance, the upper limit of the sulfate content in the oil-based inkjet ink composition is preferably 70 ppm or less, more preferably 60 ppm or less, and 50 ppm or less. It is more preferred that: When it is in this range, precipitation of a potassium compound is suppressed even when potassium is contained in the oil-based ink. The lower limit of the sulfate content in the oil-based ink is preferably 3 ppm or more, more preferably 4 ppm or more, and even more preferably 5 ppm or more. The lower the content of sulfate group in the oil-based ink, the better. However, if the content is too low, mist may be generated and adhere to the nozzle surface, and the recorded image may be stained.

  The above-mentioned sulfate content can be measured, for example, by a known ion chromatography method.

1.1.6. Dispersant The oil-based inkjet ink composition used in the present embodiment may contain a pigment dispersant in order to disperse the pigment. As the dispersant, any dispersant used in ordinary oil-based inks, particularly, oil-based ink for inkjet recording can be used. As the dispersant, it is preferable to use a dispersant that works effectively when the solubility parameter of the organic solvent is 8 to 11. Commercially available products can be used as such a dispersant, and specific examples thereof include, for example, Hinoact KF1-M, T-6000, T-7000, T-8000, T-8350P, and T-8000E (any of them). Polyesters such as Takefu Fine Chemical Co., Ltd.), Solsperse 20000, 24000, 32,000, 32,500, 33500, 34000, 35200, 37500, 39000 (all manufactured by LUBRIZOL), Disperbyk-161, 162, 163, 164. 166, 180, 190, 191, 192, 2091, 2095 (all manufactured by Big Chemie Japan), Floren DOPA-17, 22, 33, G-700 (all manufactured by Kyoeisha Chemical Co., Ltd.), Azispar PB821, PB71 (All manufactured by Ajinomoto Co., Inc.), LP4010, LP4050, LP4055, POLYMER400,401,402,403,450,451,453 (all manufactured by EFKA Chemicals Co., Ltd.), and the like.

  The content when the pigment dispersant is used can be appropriately selected according to the pigment to be contained, but is preferably 5 parts by mass or more and 200 parts by mass with respect to 100 parts by mass of the pigment in the oil-based ink. Or less, more preferably 30 to 120 parts by mass.

1.1.7. Fixing Resin The oil-based ink used in the present embodiment may contain a fixing resin for fixing the above-described pigment to a recording medium.

  As the fixing resin, acrylic resin, styrene acrylic resin, rosin modified resin, phenol resin, terpene resin, polyester resin, polyamide resin, epoxy resin, vinyl acetate resin, vinyl chloride resin, fibrous resin such as cellulose acetate butyrate, vinyl And a toluene-α-methylstyrene copolymer resin. Among them, at least one resin selected from the group consisting of an acrylic resin and a vinyl chloride resin is preferable, and a vinyl chloride resin is more preferable. By containing these fixing resins, the fixability to a recording medium can be improved, and the abrasion resistance is also improved.

  The solid content of the fixing resin in the oil-based inkjet ink composition used in the present embodiment is preferably 0.05% by mass or more and 15% by mass or less, more preferably 0.1% by mass or more and 10% by mass or less. Preferably it is 1 to 5 mass%. When the content of the fixing resin is in the above range, excellent fixability to a recording medium can be obtained.

<Acrylic resin>
Examples of the acrylic resin include poly (meth) acrylic acid, poly (meth) methyl acrylate, poly (meth) acrylate, (meth) acrylate- (meth) acrylate copolymer resin, and styrene- (meth) acrylate. ) (Meth) acrylic monomers such as acrylic copolymer resins, ethylene- (meth) acrylic acid copolymer resins, ethylene alkyl (meth) acrylate resins, ethylene- (meth) acrylate copolymer resins, and others And a copolymer resin with the above monomer. These can be used alone or in combination.

  Commercially available products may be used as the acrylic resin, such as Acrypet MF (trade name, manufactured by Mitsubishi Rayon Co., acrylic resin), Sumipex LG (trade name, manufactured by Sumitomo Chemical Co., acrylic resin), Paraloid B series (Trade name, manufactured by Rohm and Haas, acrylic resin), Parapet G-1000P (trade name, manufactured by Kuraray, acrylic resin) and the like. In the present invention, “(meth) acrylic acid” means both acrylic acid and methacrylic acid, and “(meth) acrylate” means both acrylate and methacrylate.

<Vinyl chloride resin>
Examples of the vinyl chloride resin include, for example, copolymers of vinyl chloride, vinyl acetate, vinylidene chloride, acrylic acid, maleic acid, and other monomers such as vinyl alcohol. A copolymer containing a structural unit derived therefrom (hereinafter also referred to as a “vinyl chloride vinyl acetate copolymer”) is preferable, and a vinyl chloride vinyl acetate copolymer having a glass transition temperature of 60 to 80 ° C. is more preferable.

  The vinyl chloride-vinyl acetate copolymer can be obtained by a conventional method, for example, by suspension polymerization. Specifically, water, a dispersant, and a polymerization initiator are charged into a polymerization vessel, and after deaeration, vinyl chloride and vinyl acetate are injected to perform suspension polymerization, or a part of vinyl chloride and vinyl acetate are injected. To start the reaction, and the suspension polymerization can be carried out while the remaining vinyl chloride is injected during the reaction.

  The vinyl chloride-vinyl acetate copolymer preferably contains 70 to 90% by mass of vinyl chloride units. When the content is in the above range, the compound is stably dissolved in the oil-based inkjet ink composition, and thus has excellent long-term storage stability. Furthermore, it is possible to obtain excellent ejection stability and excellent fixability to a recording medium.

  Further, the vinyl chloride-vinyl acetate copolymer may have other structural units together with a vinyl chloride unit and a vinyl acetate unit, if necessary, such as a carboxylic acid unit, a vinyl alcohol unit, and a hydroxyalkyl acrylate unit. Particularly, a vinyl alcohol unit is preferable. It can be obtained by using a monomer corresponding to each unit described above. Specific examples of the monomer that gives a carboxylic acid unit include, for example, maleic acid, itaconic acid, maleic anhydride, itaconic anhydride, acrylic acid, and methacrylic acid. Specific examples of the monomer giving the hydroxyalkyl acrylate unit include, for example, hydroxyethyl (meth) acrylate, hydroxyethyl vinyl ether, and the like. The content of these monomers is not limited as long as the effects of the present invention are not impaired. For example, copolymerization can be performed within a range of 15% by mass or less based on the total amount of the monomers.

  Commercially available polyvinyl chloride vinegar copolymers may be used, for example, Solvain CN, Solvain CNL, Solvain C5R, Solvain TA5R, Solvain CL, Solvain CLL (all manufactured by Nissin Chemical Industry Co., Ltd.) And Kanevinyl HM515 (manufactured by Kaneka Corporation).

  The average degree of polymerization of these resins is not particularly limited, but is preferably from 150 to 1100, and more preferably from 200 to 750. When the average degree of polymerization of these resins is in the above range, the resins are stably dissolved in the oil-based inkjet ink composition used in the present embodiment, and thus have excellent long-term storage stability. Furthermore, it is possible to obtain excellent ejection stability and excellent fixability to a recording medium. The average degree of polymerization of these resins is calculated from the specific viscosity measured, and can be determined according to the average degree of polymerization calculation method described in “JIS K6720-2”.

  The number average molecular weight of these resins is not particularly limited, but is preferably 10,000 to 50,000, more preferably 12,000 to 42,000. The number average molecular weight can be measured by GPC, and can be obtained as a relative value in terms of polystyrene.

1.1.8. Surfactant The oil-based inkjet ink composition used in the present embodiment includes a silicone-based surfactant, a fluorine-based surfactant, or a nonionic surfactant from the viewpoint of reducing surface tension and improving wettability with a recording medium. A polyoxyethylene derivative which is a surfactant may be added.

  As the silicon-based surfactant, it is preferable to use polyester-modified silicon or polyether-modified silicon. Specific examples include BYK-315, 315N, 347, 348, BYK-UV3500, 3510, 3530, and 3570 (all manufactured by BYK Japan KK).

  As the fluorine-based surfactant, it is preferable to use a fluorine-modified polymer. Specific examples include BYK-340 (manufactured by BYK Japan KK), Surflon S-211, S-131, S-132, and S-141. , S-144, S-145 (manufactured by Asahi Glass Co., Ltd.), Futuregent 100, 150, 251 (manufactured by Neos Co., Ltd.), Megafax F477 (manufactured by DIC Corporation), FC-170C, FC-430, Florard FC4430 (manufactured by Sumitomo 3M Limited); FSO, FSO-100, FSN, FSN-100, FS-300 (manufactured by Dupont); FT-250, 251 (manufactured by Neos Corporation), and the like.

  In addition, it is preferable to use an acetylene glycol-based surfactant as the polyoxyethylene derivative. As specific examples, Surfynol 82, 104, 465, 485, TG (all manufactured by Air Products Japan), Olfin STG, E1010 (all manufactured by Nissin Chemical Co., Ltd.), Nissan Nonion A-10R, A-13R (All manufactured by NOF Corporation), Floren TG-740W, D-90 (manufactured by Kyoeisha Chemical Co., Ltd.), Neugen CX-100 (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) and the like.

  The content of the surfactant in the oil-based inkjet ink composition used in the present embodiment is preferably 0.05% by mass or more and 3% by mass or less, more preferably 0.1% by mass or more and 2% by mass or less, and still more preferably. Is from 0.5% by mass to 1% by mass.

1.1.9. Other Components If necessary, the oil-based inkjet ink composition used in the present embodiment may include a pH adjuster, a chelating agent such as ethylenediaminetetraacetate (EDTA), a preservative, a fungicide, and a rust preventive. For example, a substance for imparting predetermined performance can be added.

  In addition, it is preferable that the potassium content in the oil-based inkjet ink composition used in the present embodiment is 120 ppm or less. Here, the amount of potassium in the oil-based inkjet ink composition can be measured, for example, by elemental analysis using an ICP-OES device (dielectric-coupled plasma emission spectrometer).

In the present specification, “potassium content” means potassium metal content in terms of metal. Further, in the present specification, potassium contained in an oil-based inkjet ink composition refers to one that can react with a sulfate group, for example, ionic potassium such as potassium ion or potassium salt, and potassium present in a pigment compound. It does not include potassium that cannot react with sulfate groups, such as potassium existing in inorganic substances such as potassium and potassium silicate.

  The content of potassium in the oil-based ink is preferably as low as possible because the presence of the sulfate group in the oil-based ink causes a potassium compound as a foreign substance to precipitate. The upper limit of the potassium content in the oil-based ink is more preferably 100 ppm or less, more preferably 80 ppm or less, and particularly preferably 70 ppm or less. Further, the lower limit of the potassium content in the oil-based ink is preferably 3 ppm or more, more preferably 4 ppm or more, and even more preferably 5 ppm or more. As described above, when a certain amount of potassium is contained in the oil-based ink, the conductivity of the ink is increased, and the ink droplets are less likely to be charged. As a result, the adhesion of mist to the nozzle surface is reduced.

1.1.10. Method for Preparing Oil-Based Inkjet Ink Composition The oil-based inkjet ink composition used in the present embodiment is obtained by mixing the above-described components in an arbitrary order and removing impurities by filtering or the like as necessary. As a method of mixing the components, a method of sequentially adding materials to a container equipped with a stirring device such as a mechanical stirrer or a magnetic stirrer and stirring and mixing the materials is preferably used. As a filtration method, centrifugal filtration, filter filtration, or the like can be performed as necessary.

1.1.11. Physical Properties of Oil-Based Inkjet Ink Composition The oil-based inkjet ink composition used in the present embodiment has a surface tension at 20 ° C. of 20 mN / m or more and 50 mN from the viewpoint of a balance between recording quality and reliability as an ink for inkjet recording. / M, more preferably from 25 mN / m to 40 mN / m. The surface tension was measured by using an automatic surface tensiometer CBVP-Z (manufactured by Kyowa Interface Science Co., Ltd.) to confirm the surface tension when the platinum plate was wetted with the ink at 20 ° C. can do.

  From the same viewpoint, the viscosity of the oil-based inkjet ink composition at 20 ° C. is preferably from 2 mPa · s to 15 mPa · s, more preferably from 2 mPa · s to 10 mPa · s. The viscosity was measured by using a viscoelasticity tester MCR-300 (manufactured by Pysica), increasing the Shear Rate to 10 to 1000 in an environment of 20 ° C., and reading the viscosity at the time of Shear Rate 200. Can be measured.

1.1.12. Uses and Effects The oil-based inkjet ink composition according to the embodiment is a solvent ink containing a solvent that is the compound A represented by the general formula (1), and is used for recording on a film medium such as a vinyl chloride recording medium. Since the image quality at the time of the display is excellent, it is particularly suitable for sign applications to be exhibited outdoors. The vinyl chloride recording medium is not particularly limited as long as it contains a vinyl chloride resin. Examples of the recording medium containing a vinyl chloride resin include a hard or soft vinyl chloride film or sheet.

  In addition, the oil-based inkjet ink composition according to the present embodiment has a high hygroscopic property because the solvent which is the compound represented by the general formula (1) is the main solvent, and the tube used in the ink supply path. There is a tendency that a small amount of water penetrating from the outside and penetrating from the outside causes a potassium compound derived from a component derived from the pigment to precipitate and clog the filter. However, by using the solvent represented by the general formula (1) and having a sulfate group content of 80 ppm or less, it is possible to suppress the generation of a foreign substance derived from a potassium compound even when a pigment is contained. This makes it possible to obtain an oil-based inkjet ink composition which does not cause ink ejection failure, has excellent ejection stability, and has reduced odor.

1.2. Image Forming Method An image forming method according to an embodiment of the present invention is an image forming method of forming an image by discharging droplets of the oil-based inkjet ink composition, wherein the discharging of the droplets is performed by ink. It is characterized in that at least one of the ink flow path portion and the ink storage portion that is in contact is performed using an ink jet recording apparatus having a resinous member. Thereby, a recorded matter having an image formed on the recording medium is obtained, and even when moisture permeates from the outside air into the ink supply path, the potassium compound is less likely to precipitate, and ink ejection failure does not occur. It is possible to provide an image forming method with excellent ejection stability and reduced odor.

  In the image forming method according to the present embodiment, the step of forming an image may be performed on a recording medium heated to 30 ° C. or more and 60 ° C. or less. By attaching the above-described ink composition onto the recording medium heated in this manner, the drying property of the ink can be improved.

  Further, the image forming method according to the present embodiment may include post-heating (after-heating) for further heating the recording medium after the step of forming an image. By further providing a post-heating step, the drying property of the ink can be further improved.

  As an ink jet recording apparatus that can include the above-described steps, any apparatus that discharges the above-described ink composition as droplets from fine nozzles of a recording head and adheres the droplets to a recording medium can be used. Can be. Hereinafter, an ink jet printer having a mechanism capable of heating a recording medium will be described as an example of an ink jet recording apparatus that can be used in the present embodiment.

  FIG. 1 is a perspective view illustrating a configuration of an inkjet recording apparatus (hereinafter, referred to as a “printer”) that can be used in the present embodiment. The printer 1 shown in FIG. 1 is a so-called serial printer. The serial printer refers to a printer in which a recording head is mounted on a carriage that moves in a predetermined direction, and the recording head moves along with the movement of the carriage to discharge droplets onto a recording medium.

  As shown in FIG. 1, the printer 1 has a carriage 4 on which a recording head 2 is mounted and an ink cartridge (ink storage unit) 3 is detachably mounted, and a recording medium P disposed below the recording head 2 and transported. Platen 5 to be heated, a heating mechanism 6 for heating the recording medium, a carriage moving mechanism 7 for moving the carriage 4 in the medium width direction of the recording medium P, and a medium feeding mechanism for conveying the recording medium P in the medium feeding direction. And 8. Further, the printer 1 has a control device CONT for controlling the operation of the entire printer 1. The medium width direction is the main scanning direction (head scanning direction). The medium feeding direction is a sub-scanning direction (a direction orthogonal to the main scanning direction).

  The recording head 2 includes a nozzle plate (not shown) having a plurality of nozzle holes on a surface facing the recording medium P to which ink is to be attached. The plurality of nozzle holes are arranged in a row, thereby forming a nozzle surface on the nozzle plate surface.

  The ink cartridge 3 that supplies ink to the recording head 2 includes four independent cartridges. Each of the four cartridges is filled with the above-described oil-based ink. Although the number of cartridges is four in the example of FIG. 1, the number of cartridges is not limited thereto, and a desired number of cartridges can be mounted.

Further, the ink cartridge 3 is not limited to the one mounted on the carriage 4 as shown in FIG. 1. Instead, for example, the ink cartridge 3 is mounted on the housing side of the printer 1 and an ink supply tube (not shown) is mounted. ) May be supplied to the recording head 2.

  It is preferable that the ink cartridge 3, which is a storage section for storing ink, is formed of a resin member such as plastic or an aluminum laminate material that does not transmit gas. Since the ink cartridge 3 is formed of a member having no gas permeability such as a resinous member, moisture absorption of the oil-based inkjet ink composition according to the present embodiment and generation of foreign substances due to aggregation of pigment-derived components are suppressed. Has long-term storage stability. Accordingly, it is possible to provide an image forming method which does not cause ink ejection failure, has excellent ejection stability, and has reduced odor.

  An ink flow path portion (for example, an ink supply path provided in the recording head 2 or the above-described ink supply tube) in contact with ink from the ink cartridge 3 to a nozzle hole for discharging ink is usually made of resin. It is preferable that the member be made of a member or a metal member such as SUS. When a resinous material such as Teflon (registered trademark) is used as a tube as the resinous material used for the ink flow path, it is preferable because it is easy to dispose and has a high degree of freedom such as being usable for a movable part. . In particular, when the ink flow path is movable (for example, when the ink cartridge 3 is mounted on the housing side of the printer 1 and supplied to the recording head 2 via an ink supply tube). It is preferable to use a resinous member. However, when a resinous member is used for the ink flow path, the permeation of gas or moisture may not be completely prevented, and the permeation of moisture may occur in this member. In that case, by combining with the oil-based inkjet ink composition according to the present embodiment, even when there is moisture permeation from the outside air into the ink supply path, the potassium compound is less likely to be precipitated, and ink ejection failure does not occur. It is possible to provide an image forming method with excellent ejection stability and reduced odor.

  Here, a filter (not shown) for removing foreign matter and bubbles mixed in the ink is arranged in the ink supply flow path provided in the recording head 2. The material of the filter is not limited as long as it has the strength and corrosion resistance required for ink filtration, and stainless steels such as SUS316 and SUS316L, which have a low iron content, are preferable. As the type of weaving, a nonwoven fabric type can be used, in addition to a plain weave, a twill weave, a plain tatami weave, a twill tatami weave, or the like, in which a foreign matter collecting portion has a regular weave. In the present embodiment, the filter is processed into a filter having a micron-order mesh structure by, for example, weaving a fine stainless steel wire such as stainless steel (SUS) into a twill tatami pattern.

  The size of the filter mesh is not particularly limited as long as the foreign matter collecting ability can be improved while suppressing an increase in pressure loss as much as possible. For example, a filter through which particles having a major axis of 15 μm or less are preferably transmitted. . That is, the mesh size of the filter preferably has an opening of 15 μm or less. "Open" means the maximum particle size of the particles passing through the filter. Here, the particle diameter can be obtained, for example, by measurement using a flow-type particle image analyzer FPIA-3000 (manufactured by Sysmex Corporation). Examples of such a filter include a twill tatami woven metal filter (average wire diameter: 0.02 to 0.07 μm) having a mesh of 1200 mesh or more, and commercially available products include, for example, a twill manufactured by Manabe Industry Co., Ltd. Among the wire nets for the folding filter, a filter of 1200 mesh to 2600 mesh is exemplified.

  The carriage 4 is mounted in a state of being supported by a guide rod 9 which is a support member provided in the main scanning direction. The carriage 4 is moved in the main scanning direction along a guide rod 9 by a carriage moving mechanism 7. In the example of FIG. 1, the carriage 4 moves in the main scanning direction. However, the present invention is not limited to this. The carriage 4 may move in the sub-scanning direction in addition to the movement in the main scanning direction. .

The installation position of the heating mechanism 6 is not particularly limited as long as it is provided at a position where the recording medium P can be heated. In the example of FIG. 1, the heating mechanism 6 is installed on the platen 5 at a position facing the head 2. As described above, if the heating mechanism 6 is installed at a position facing the head 2, the position where the droplets adhere to the recording medium P can be reliably heated, so that the droplets adhered to the recording medium P can be efficiently dried. it can.

  The heating mechanism 6 includes, for example, a print heater mechanism for heating the recording medium P by contacting it with a heat source, a mechanism for irradiating infrared rays or microwaves (electromagnetic waves having a maximum wavelength of about 2,450 MHz), or hot air. A dryer mechanism for spraying or the like can be used.

  The heating of the recording medium P by the heating mechanism 6 is performed before or when the droplets discharged from the nozzle holes (not shown) adhere to the recording medium P. In this way, the droplets attached to the recording medium P can be quickly dried. Control of various heating conditions (for example, timing of heating, heating temperature, heating time, and the like) is performed by the control unit CONT.

  The heating of the recording medium P by the heating mechanism 6 is performed such that the recording medium P maintains a temperature range of 35 ° C. or more and 50 ° C. or less from the viewpoint of improving the drying property of the ink and preventing deformation of the recording medium. preferable. Here, the temperature for heating the recording medium means the temperature of the surface of the recording surface of the recording medium during heating.

  The printer 1 may further include a second heating mechanism (not shown) in addition to the heating mechanism 6. By providing the printer 1 with the second heating mechanism, the heating process can be performed by the printer 1. The second heating mechanism is installed downstream of the heating mechanism 6 in the transport direction of the recording medium P. The second heating mechanism heats the recording medium P after heating the recording medium P by the heating mechanism 6, that is, after the droplets discharged from the nozzle holes (not shown) adhere to the recording medium P. Is what you do. Thereby, the drying property of the droplets of the ink composition adhered to the recording medium P can be further improved. As the second heating mechanism, any of the mechanisms described in the heating mechanism 6 (for example, a dryer mechanism or the like) can be used.

  The linear encoder 10 detects the position of the carriage 4 in the main scanning direction with a signal. The detected signal is transmitted to the control device CONT as position information. The control device CONT recognizes the scanning position of the recording head 2 based on the position information from the linear encoder 10, and controls the recording operation (ejection operation) by the recording head 2. Further, the control device CONT is configured to variably control the moving speed of the carriage 4.

The recording medium P is not particularly limited, but according to the image forming method according to the present embodiment, the glossiness and the like of the recorded image are improved even when a low-absorbing recording medium is used. Here, the "low absorptive recording medium" refers to water absorption of up to 30msec1 ^{/ 2} from the contact start in Bristow (Bristow) method of 10 mL / ^{m 2} or less is a recording medium at least a recording surface This property What is necessary is just to have. According to this definition, the “low-absorbing recording medium” in the present invention includes a non-absorbing recording medium that does not absorb water at all. The Bristow method is the most widespread method for measuring the amount of liquid absorbed in a short time, and is also adopted by the Japan Pulp and Paper Technology Association (JAPAN TAPPI). Details of the test method are described in the standard No. of “JAPAN TAPPI Paper and Pulp Test Method 2000 Edition”. 51 "Paper and paperboard-Liquid absorbency test method-Bristow method".

Specific examples of the low-absorbing recording medium include a sheet, a film, and a fiber product containing a low-absorbing material. Further, the low-absorbing recording medium includes a layer containing a low-absorbing material (hereinafter, referred to as a “low-absorbing layer”) on the surface of a substrate (for example, paper, fiber, leather, plastic, glass, ceramics, metal, etc.). ). The low-absorbing material is not particularly limited, and examples thereof include an olefin resin, an ester resin, a urethane resin, an acrylic resin, and a vinyl chloride resin.

  Among these, as the low-absorbing recording medium, those having a recording surface containing a vinyl chloride resin can be preferably used. The above-described non-aqueous ink composition contains a carbonate-based solvent, and this compound dissolves a recording surface containing a vinyl chloride-based resin, so that the ink composition can penetrate into a recording medium. As a result, the abrasion resistance of images and characters recorded on the recording surface containing the vinyl chloride resin can be further improved. Specific examples of the vinyl chloride resin include polyvinyl chloride, vinyl chloride-ethylene copolymer, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl ether copolymer, vinyl chloride-vinylidene chloride copolymer, and vinyl chloride. -Maleic acid ester copolymer, vinyl chloride- (meth) acrylic acid copolymer, vinyl chloride- (meth) acrylic acid ester copolymer, vinyl chloride-urethane copolymer and the like. In addition, there are no particular restrictions on various properties such as the thickness, shape, color, softening temperature, and hardness of the low-absorbent recording medium.

  The image forming method according to the present embodiment is an image forming method for forming an image by discharging droplets of the oil-based inkjet ink composition, wherein the discharging of the droplets is performed by an ink flow path portion that comes into contact with ink or By using an ink jet recording apparatus in which at least one of the ink containing sections has a resinous member, even when moisture permeates from the outside air into the ink supply path, the potassium compound is less likely to precipitate, resulting in poor ink ejection. This makes it possible to provide an image forming method which does not cause odor, has excellent ejection stability, and has reduced odor.

2. Examples Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited to only these Examples. In the Examples and Comparative Examples, “parts” and “%” are based on mass unless otherwise specified.

2.1. Preparation of Ink Composition Only the amount of the organic solvent corresponding to the concentration shown in Table 1 was put in a container, and the mixture was stirred for each ink to obtain a mixed solvent. Part of the obtained mixed solvent was separated, and the pigment dispersant and the following 2.2. A pigment dispersion was obtained by adding a predetermined amount of a pigment purified by the refining operation described above, preliminarily dispersing using a homogenizer, and performing a dispersion treatment with a bead mill filled with zirconia beads having a diameter of 0.3 mm. . Then, the resin was added to a part of the mixed solvent, and the mixture was stirred to obtain a completely dissolved resin solution. In the above pigment dispersant, the remainder of the mixed solvent, the surfactant and the above resin solution were mixed, stirred for 1 hour, and then filtered using a 5 μm PTFE membrane filter. An ink composition of a comparative example was obtained.

Among the components used in Table 1, the components described by trade names or abbreviations are as follows.
-Carbon black: trade name "SPECIAL BLACK4", manufactured by Degussa Co., Ltd.-Pigment Blue: Pigment Blue 15: 3
-Solvain C5R: trade name, manufactured by Nissin Chemical Co., Ltd., vinyl chloride-vinyl acetate copolymer-SS39000: trade name "Solsperse 39000", manufactured by Lubrizol Japan Ltd., pigment dispersant-Futagent 251: trade name, trade name Neos, fluorinated surfactant

2.2. Purification of Pigment The pigment used in each of Examples and Comparative Examples shown in Table 1 was subjected to a purification operation. The pigment used in Example 1 was a pigment purified by the following basic purification operation. The pigments used in Examples 2 and after and in Comparative Examples were obtained by changing the degree of purification by increasing or decreasing the amount of ultrapure water in the basic purification operation.
<Basic purification operation>
The pigment (20 parts by mass) and ultrapure water (80 parts by mass) were mixed, preliminarily stirred, and then mixed with an ultrasonic homogenizer for 30 minutes to prepare a slurry. Thereafter, the obtained slurry was centrifuged with a centrifugal separator (10000 rpm, 30 minutes), carbon black was separated from the slurry, and the supernatant solution was discarded to obtain wet carbon black. Further, drying was performed at 150 ° C. for 120 minutes in a nitrogen gas, and water was removed to produce a purified carbon black.

2.3. Measurement of the amount of sulfate groups For each of the prepared ink compositions, equal amounts of ink and pure water were put into a separating funnel, shaken well, and allowed to stand, and the liquid in the aqueous layer was taken out. The removed liquid was filtered through a membrane filter to remove aggregates, and used as an analytical sample. The amount of sulfate in the ink composition was measured for this analysis sample by an anion analysis system using an ion chromatograph (ICS-1500 type) manufactured by Dionex. The column used was IonPacAG12A / IonPacAS12A, the mobile phase was a sodium hydrogencarbonate solution (1.7 mmol / L), the flow rate was 1.5 mL / min, and the electrical conductivity detector was used as the detector.

2.4. Measurement of Potassium Content and Sodium Content Each of the prepared ink compositions was subjected to dry decomposition (including acid melting), and then heated and dissolved with dilute acid to obtain a fixed volume. The amounts of potassium and sodium in the test solution were measured by ICP emission spectroscopy (ICP-AES method) using 720-ES (manufactured by Agilent Technologies).

2.4. Evaluation test 2.4.1. Foreign matter evaluation 10% of ultra-pure water was added to 10 cc of the prepared ink composition, left for 5 days in a room temperature release system, stirred, filtered with a # 2300 mesh metal filter, and captured on the filter surface. The crystalline foreign matter was observed and evaluated according to the following criteria.
(Evaluation criteria)
×: Crystalline foreign matter was visually observed on the filter surface, and more than 1% of the filter surface area was covered with the foreign matter.
Δ: Crystalline foreign matter was visually observed on the filter surface, and 1% or less of the filter surface area was covered with the foreign matter.
：: No crystalline foreign matter was visually observed on the filter surface, and the increase in filter weight after drying was 1 mg or more.
A: No crystalline foreign matter was visually observed on the filter surface, and the increase in filter weight after drying was less than 1 mg.

2.4.2. Discharge stability evaluation 1
A 2600 mesh twill tatami woven metal filter (wire diameter 0.03 mm, long diameter 4.9 μm)
A filter that passes particles of m or less. ), And using an ink jet printer (MJ-8000C modified from Seiko Epson Corporation) having an ink tube made of Teflon (registered trademark), each of the ink compositions shown in Table 1 was converted to 200 μm polyvinyl chloride. Printing was performed on a sheet (Vucal 900, manufactured by Lintec Corporation), and the ink ejection stability was evaluated by the following measurement method. Printing of a high-duty image pattern of 10 mg / inch ² was performed for two consecutive days, then paused, and after 180 days, the same image was printed again. The total amount of ink used is 100 ml. Thereafter, the recoverability of missing dots after cleaning from the printed sample was visually observed, and the occurrence of unrecoverable dot missing after cleaning was evaluated according to the following criteria.
(Evaluation criteria)
Good: Missing dots are recovered by cleaning.
×: No recovery is performed even after cleaning.

2.4.3. Discharge stability evaluation 2
Discharge Stability In the actual machine evaluation 1, the Teflon (registered trademark) ink tube portion was changed to a SUS tube, and the plastic member was removed from the liquid contact portion of the printer. Other evaluations were performed in the same manner as in the evaluation of discharge stability 1.

2.4.4. Mist Actual Machine Evaluation After the completion of the ejection stability actual machine evaluation 1, the head was removed and the amount of ink mist adhering to the nozzle surface was visually observed, and evaluated according to the following criteria.
(Evaluation criteria)
Δ: Mist adhered to more than 50% of the nozzle surface.
：: Mist adhered to more than 30% and 50% or less of the nozzle surface.
A: Mist is attached to more than 10% and 30% or less of the nozzle surface.
A: The mist adhesion amount on the nozzle surface is 10% or less.

2.4.5. Example Using Acetate-Based Solvent In all Examples and Comparative Examples, evaluation was performed in the same manner except that Compound A was replaced with “dipropylene glycol monomethyl ether acetate”.

2.5. Evaluation Results First, in Comparative Example 3 containing no pigment, the amounts of potassium and sulfate were below the detection limit, and no foreign matter was generated, but mist was generated. Further, in Comparative Examples 1 and 2 in which the sulfate content was more than 80 ppm, foreign matter was generated. In particular, in Comparative Example 2 in which the sulfate content and the potassium content were large, the result was that the ejection stability was poor. In contrast, in Examples in which the sulfate content was 80 ppm or less, the generation of foreign matter was suppressed in each case. Compared with the case where no compound B was added, when the potassium content was 5 ppm or more and 120 ppm or less, no crystalline foreign matter was visually observed on the filter surface, but the potassium content was 120 ppm. In Example 13 which was super, crystalline foreign matter was visually observed on the filter surface. In addition, from the results of Examples 3 and 8, when the sulfate group content and the potassium content were low, mist adhered to the nozzle surface.

  Further, in the example in which the monoalkyl ether was added as the compound B, the generation of foreign matter and mist adhesion were further suppressed. However, when the content of the monoalkyl ether was as high as 20 parts by mass, the effect of suppressing mist adhesion was improved. However, the effect of suppressing the generation of foreign matter was not different from the example in which the addition was not performed. Further, as shown in Example 7, even when Na was present in a large amount, there was no effect on the generation of foreign matters and the adhesion of mist. Furthermore, from Example 10, good results were obtained also in examples using other pigments as the pigment.

In “2.4.5. Example using acetate-based solvent”, in each of the examples,
The evaluation results of foreign matter and mist adhesion were ◎, and the evaluation results of discharge stability evaluation 1 and 2 were ○. However, the ink composition using dipropylene glycol monomethyl ether acetate as a main solvent has a generally stronger odor than the ink composition of the present invention using compound A, and also has a printing sample on the first day of the actual stability evaluation 1 of ejection stability. Was inferior in color density. As described above, the ink composition using the acetate-based solvent has low hygroscopicity and does not cause any problem with respect to generation of foreign matter and mist adhesion, but has a problem of odor.

  As described above, by using the oil-based inkjet ink composition included in the scope of the present invention, it is possible to suppress the generation of a foreign substance derived from a potassium compound, without causing ink ejection failure, and improving ejection stability. It was revealed that an oil-based inkjet ink composition and an image forming method with excellent and reduced odor could be obtained. Further, mist adhesion was suppressed by reducing the amount of potassium. Further, by adding a monoalkyl ether as the compound B, the effect of suppressing generation of foreign matter and mist adhesion was improved.

  The present invention is not limited to the embodiments described above, and various modifications are possible. For example, the invention includes configurations substantially the same as the configurations described in the embodiments (for example, a configuration having the same function, method, and result, or a configuration having the same object and effect). The invention also includes a configuration in which a non-essential part of the configuration described in the embodiment is replaced. Further, the invention includes a configuration having the same operation and effect as the configuration described in the embodiment, or a configuration capable of achieving the same object. Further, the invention includes a configuration obtained by adding a known technique to the configuration described in the embodiment.

  DESCRIPTION OF SYMBOLS 1 ... Printer, 2 ... Recording head, 3 ... Ink cartridge, 4 ... Carriage, 5 ... Platen, 6 ... Heating mechanism, 7 ... Carriage moving mechanism, 8 ... Medium feeding mechanism, 9 ... Guide lot, 10 ... Linear encoder, P ... Recording medium, CONT ... Control device

Claims (9)

An oil-based inkjet ink composition comprising a compound A represented by the following general formula (1) and a pigment as a solvent, and having a sulfate content of 80 ppm or less.
R ^1- (O-C _n H _2n ) _m -OR ² (1)
(In the general formula (1), R ¹ and R ² are an alkyl group having 1 to 4 carbon atoms, which may be the same or different, m is an integer of 1 to 7, and n is 1 to 3 Represents an integer.)   The oil-based inkjet ink composition according to claim 1, wherein the potassium content is 120 ppm or less.   The oil-based inkjet ink composition according to claim 1, wherein the sulfate group content is 5 ppm or more and 80 ppm or less. The potassium content is 5 ppm or more and 120 ppm or less;
The oil-based inkjet ink composition according to any one of claims 1 to 3. The oil-based inkjet ink composition according to any one of claims 1 to 4, further comprising a compound B represented by the following general formula (2) as a solvent.
_{^{R 3 - (O-C n}} H 2n) m -OH ··· (2)
(In the general formula (2), R ³ is an alkyl group having 2 to 7 carbon atoms, m is an integer of 1 to 7, and n represents an integer of 1 to ^3. )   The oil-based inkjet ink composition according to claim 5, wherein the content of the compound B is 2% by mass or more and 20% by mass or less.   The oil-based inkjet ink composition according to any one of claims 1 to 6, wherein the pigment is carbon black. An image forming method for forming an image by discharging droplets of the oil-based inkjet ink composition according to any one of claims 1 to 7.
An image forming method, wherein the ejection of the droplets is performed using an ink jet recording apparatus in which at least one of an ink flow path portion and an ink storage portion in contact with ink has a resinous member.   The image forming method according to claim 8, wherein the inkjet recording apparatus includes a head having a filter that transmits particles having a major axis of 15 μm or less.

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