JP7031393B2 - Image forming device and image forming method - Google Patents

Description

The present invention relates to an image forming apparatus and an image forming method.

Inkjet printers have been rapidly popularized in recent years as digital signal output devices because they have advantages such as low noise, low running cost, and easy color printing.

As the inkjet ink, a water-based inkjet ink is widely used because it is highly safe for living organisms and the environment. With water-based ink, the water and organic solvent in the ink volatilize when the ink is heated and dried after printing to form an image. In order to improve productivity, it is preferable that the time required for heating and drying is short.

However, the hot air drying method that has been conventionally used has a problem that the drying time of the object to be dried becomes long because it is difficult to perform uniform drying.

In order to deal with such a problem, a drying method of heating by electromagnetic waves such as microwaves and high frequencies has recently been proposed (see, for example, Patent Documents 1 to 4).

However, heating with electromagnetic waves may cause yellowing when heating a substance having high conductivity, for example, black ink used in inkjet, so that there is a problem that the drying strength cannot be increased. There is also a method of expressing black by mixing black with colors such as cyan, magenta, and yellow without using carbon black, but as a result, the total amount of ink increases, which is disadvantageous for drying and the black density does not increase. There's a problem.

An object of the present invention is to provide an image forming apparatus capable of forming an image having a sufficient black density while suppressing yellowing of the image even when dried by electromagnetic waves.

The above problem is solved by the following configuration 1).
1) Ink and
An ink applying means for applying the ink to the recording medium,
It has a heating means for heating the ink applied on the recording medium by electromagnetic waves.
The heating means is a high-frequency dielectric heating means.
The ink contains carbon black, magenta pigment, cyan pigment and yellow pigment as pigments, and further contains urethane resin.
The mass ratio of the pigment (carbon black content / (total content of magenta pigment, cyan pigment and yellow pigment)) is 0.5 or more and 1.0 or less.
An image forming apparatus characterized in that the conductivity at an evaporation rate of 80% of the ink is 0.01 S / m or less .

According to the present invention, it is possible to provide an image forming apparatus capable of forming an image having a sufficient black density while suppressing yellowing of the image even when dried by electromagnetic waves.

It is a side view of the Embodiment of the image forming apparatus of this invention. It is a perspective view of the high frequency dielectric heating apparatus of embodiment of the image forming apparatus of this invention. It is a side view of the high frequency dielectric heating apparatus of embodiment of the image forming apparatus of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. It should be noted that the present invention is not limited to the embodiments shown below, and can be modified within the range conceivable by those skilled in the art, such as other embodiments, additions, modifications, and deletions. However, as long as the action and effect of the present invention are exhibited, it is included in the scope of the present invention.

The image forming apparatus of the present invention includes an ink, an ink applying means for applying the ink to a recording medium, and a heating means for heating the ink applied on the recording medium with an electromagnetic wave. The ink is characterized by containing carbon black, magenta pigment, cyan pigment and yellow pigment.

In recent years, in order to improve the drying property of ink, it has been considered to give a feature to the drying device side, and a drying method using electromagnetic waves such as infrared irradiation, micro-irradiation, and high-frequency dielectric heating has been studied. Black ink containing carbon black is used to form a black image having a good black density, and carbon black has a characteristic of generating heat when irradiated with electromagnetic waves or the like. If electromagnetic waves are used to dry the carbon black, the black image portion may turn yellow due to the heat generated by the carbon black. When electromagnetic waves are used to dry the ink, it is possible to prevent yellowing during drying by lowering the conductivity of the ink by reducing the content of carbon black, but it is possible to avoid a decrease in black density. It becomes a problem that cannot be done.
Therefore, by including magenta (M) pigment, cyan (C) pigment, and yellow (Y) pigment in the black ink containing carbon black, the black image density is improved and yellowing is prevented when the electromagnetic wave is used for drying. The present inventor has found that both of these can be achieved.
Although the detailed mechanism is not known, the black density can be increased by including all the Y, M, and C pigments, and the Y, M, and C pigments have low conductivity, so that the black pigments are among the carbon black pigments. It is speculated that the conductivity may decrease and yellowing may be prevented. That is, it is important that carbon black and other Y, M, and C pigments are dispersed in the black ink. In this case, when the black ink of the present invention is applied onto a recording medium and heated by an electromagnetic wave. However, it is possible to provide an image forming apparatus capable of lowering the conductivity, having a good black density, and preventing yellowing due to the presence of carbon black and other Y, M, and C pigments in a mixed manner.
It is common practice to repeatedly strike Y ink, M ink, and C ink to produce black, but the black density is inferior to that when black ink containing carbon black is used, and the color is also carbon black. It is inferior to the black ink contained. Further, by applying black ink containing carbon black to the recording medium and then applying Y ink, M ink, and C ink, the black density is improved, but the conductivity between the carbon black pigments in the black ink is lowered. Therefore, the problem of yellowing cannot be solved.

From the above, by using carbon black in combination with a magenta pigment, a cyan pigment, and a yellow pigment, the conductivity of the ink is lowered, and it is possible to form an image in which yellowing does not occur even when heated by an electromagnetic wave. Further, by setting these blending amounts in an appropriate range, a sufficient black density can be obtained.
The details will be described below.

<Ink>
Hereinafter, the organic solvent, water, coloring material, resin, additive, etc. used for the ink will be described.

<Organic solvent>
The organic solvent used in the present invention is not particularly limited, and a water-soluble organic solvent can be used. Examples thereof include ethers such as polyhydric alcohols, polyhydric alcohol alkyl ethers and polyhydric alcohol aryl ethers, nitrogen-containing heterocyclic compounds, amides, amines and sulfur-containing compounds.
Specific examples of polyhydric alcohols include, for example, ethylene glycol, diethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, and 1,4-butane. Diol, 2,3-Butanediol, 3-Methyl-1,3-Butanediol, Triethylene Glycol, Polyethylene Glycol, Polypropylene Glycol, 1,2-Pentanediol, 1,3-Pentanediol, 1,4-Pentanediol , 2,4-Pentanediol, 1,5-Pentanediol, 1,2-hexanediol, 1,6-hexanediol, 1,3-hexanediol, 2,5-hexanediol, 1,5-hexanediol, Glycerin, 1,2,6-hexanetriol, 2-ethyl-1,3-hexanediol, ethyl-1,2,4-butanetriol, 1,2,3-butanetriol, 2,2,4-trimethyl- Examples thereof include 1,3-pentanediol and petriol.
Examples of the polyhydric alcohol alkyl ethers include ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, tetraethylene glycol monomethyl ether, and propylene glycol monoethyl ether.
Examples of polyhydric alcohol aryl ethers include ethylene glycol monophenyl ether and ethylene glycol monobenzyl ether.
Examples of the nitrogen-containing heterocyclic compound include 2-pyrrolidone, N-methyl-2-pyrrolidone, N-hydroxyethyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, ε-caprolactam, and γ-butyrolactone. Can be mentioned.
Examples of the amides include formamide, N-methylformamide, N, N-dimethylformamide, 3-methoxy-N, N-dimethylpropionamide, 3-butoxy-N, N-dimethylpropionamide and the like.
Examples of amines include monoethanolamine, diethanolamine, triethylamine and the like.
Examples of sulfur-containing compounds include dimethyl sulfoxide, sulfolane, and thiodiethanol.
Examples of other organic solvents include propylene carbonate and ethylene carbonate.
It is preferable to use an organic solvent having a boiling point of 250 ° C. or lower because it not only functions as a wetting agent but also has good drying properties.

As the organic solvent, a polyol compound having 8 or more carbon atoms and a glycol ether compound are also preferably used. Specific examples of the polyol compound having 8 or more carbon atoms include 2-ethyl-1,3-hexanediol and 2,2,4-trimethyl-1,3-pentanediol.
Specific examples of the glycol ether compound include polyhydric alcohol alkyls such as ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, tetraethylene glycol monomethyl ether, and propylene glycol monoethyl ether. Ethers; Examples thereof include polyhydric alcohol aryl ethers such as ethylene glycol monophenyl ether and ethylene glycol monobenzyl ether.

A polyol compound having 8 or more carbon atoms and a glycol ether compound can improve the permeability of ink when paper is used as a recording medium.

The content of the organic solvent in the ink is not particularly limited and may be appropriately selected depending on the intended purpose, but is preferably 10% by mass or more and 60% by mass or less from the viewpoint of ink drying property and ejection reliability. More preferably, it is 20% by mass or more and 60% by mass or less.

<Water>
The content of water in the ink is not particularly limited and may be appropriately selected depending on the intended purpose, but from the viewpoint of ink drying property and ejection reliability, it is preferably 10% by mass or more and 90% by mass or less, and 20% by mass. % Or more and 60% by mass or less are more preferable.

<Color material>
As the pigment, carbon black, yellow pigment, magenta pigment, and cyan pigment can be used.
As the carbon black, carbon black produced by a known method such as a contact method, a furnace method, or a thermal method can be used.
As a specific example of the pigment, as the yellow pigment, C.I. I. Pigment Yellow 1, 3, 12, 13, 14, 17, 24, 34, 35, 37, 42 (yellow iron oxide), 53, 55, 74, 81, 83, 95, 97, 98, 100, 101, 104 , 108, 109, 110, 117, 120, 138, 150, 153, 155, 180, 185, 213. As magenta pigments, C.I. I. Pigment Red 1, 2, 3, 5, 17, 22, 23, 31, 38, 48: 2, 48: 2 (Permanent Red 2B (Ca)), 48: 3, 48: 4, 49: 1, 52: 2, 53: 1, 57: 1 (Brilliant Calcium 6B), 60: 1, 63: 1, 63: 2, 64: 1, 81, 83, 88, 101 (Bengara), 104, 105, 106, 108 ( Cadmium Red), 112, 114, 122 (Quinacridone Magenta), 123, 146, 149, 166, 168, 170, 172, 177, 178, 179, 184, 185, 190, 193, 202, 207, 208, 209, 213, 219, 224, 254, 264, C.I. I. Pigment Violet 1 (Rhodamine Lake), 3, 5: 1, 16, 19, 23, 38, and Cyan pigments include C.I. I. Pigment Blue 1, 2, 15 (phthalocyanine blue), 15: 1, 15: 2, 15: 3, 15: 4 (phthalocyanine blue), 16, 17: 1, 56, 60, 63, and the like.

Among them, from the viewpoint of lowering the conductivity between carbon black pigments and preventing yellowing, C.I. I. Pigment Yellow 74, C.I. I. Pigment Yellow 138, C.I. I. Pigment Yellow 155, C.I. I. Pigment Yellow 185 is preferable, and the magenta pigment is C.I. I. Pigment Red 122, C.I. I. Pigment Red 202, C.I. I. Pigment Violet 19 is preferable, and Cyan pigment is C.I. I. Pigment Blue 15: 2, C.I. I. Pigment Blue 15: 3, C.I. I. Pigment Blue 15: 4 is preferred.

In order to disperse the pigment to obtain an ink, a method of introducing a hydrophilic functional group into the pigment to obtain a self-dispersing pigment, a method of coating the surface of the pigment with a resin and dispersing it, and a method of dispersing using a dispersant are used. The method, etc. can be mentioned.
As a method of introducing a hydrophilic functional group into a pigment to obtain a self-dispersing pigment, for example, by adding a functional group such as a sulfone group or a carboxyl group to the pigment (for example, carbon black), the pigment can be dispersed in water. The method can be mentioned.
Examples of the method of coating the surface of the pigment with a resin and dispersing the pigment include a method of encapsulating the pigment in microcapsules so that the pigment can be dispersed in water. This can be rephrased as a resin-coated pigment. In this case, it is not necessary that all the pigments blended in the ink are coated with the resin, and the uncoated pigments and the partially coated pigments are dispersed in the ink as long as the effect of the present invention is not impaired. May be.
Examples of the method of dispersing using a dispersant include a method of dispersing using a known low-molecular-weight dispersant and high-molecular-weight dispersant represented by a surfactant.
As the dispersant, for example, an anionic surfactant, a cationic surfactant, an amphoteric surfactant, a nonionic surfactant and the like can be used depending on the pigment.
RT-100 (nonionic surfactant) manufactured by Takemoto Oil & Fat Co., Ltd. and a naphthalene sulfonic acid Na formalin condensate can also be suitably used as a dispersant.
The dispersant may be used alone or in combination of two or more.

The content of the coloring material in the ink is preferably 0.1% by mass or more and 15% by mass or less, more preferably 1% by mass or more and 10% by mass or less, from the viewpoint of improving the image density and good ejection stability. ..
The ink of the present invention contains carbon black, magenta pigments, cyan pigments, and yellow pigments. The lower limit of the content of the carbon black in the ink is preferably 1.0% by mass or more, preferably 2.0% by mass or more, and the upper limit is preferably less than 3.2% by mass, 3.0% by mass. The following are more preferable. In order to improve the black density of the image, it is preferable to contain carbon black in an amount of 1.0% by mass or more. Further, in order to prevent yellowing of the image, the content of carbon black is preferably less than 3.2% by mass, more preferably 3.0% by mass or less.
The ink of the present invention contains a magenta pigment, a cyan pigment, and a yellow pigment in addition to carbon black. The contents of the magenta pigment, the cyan pigment, and the yellow pigment can be arbitrarily included, but the total amount is preferably 0.06% by mass or more, more preferably 2.4% by mass or more, and the upper limit is 5.0. It is preferably mass% or less, and more preferably 4.5 mass% or less. In the present invention, yellowing can be prevented even when the ink contains 0.06% by mass or more of carbon black.
It is preferable to specify the relationship between the total content of magenta pigment, cyan pigment and yellow pigment (hereinafter, may be referred to as YMC pigment) and the content of carbon black, and a certain amount is required to secure the black density. It is preferable to secure the above amount of carbon black. The content of carbon black is preferably less than 3.2% by mass, more preferably 3.0% by mass or less with respect to the total amount of ink, and the total content of magenta pigment, cyan pigment, and yellow pigment in the ink is the ink. It is preferably 0.1% by mass or more and 5% by mass or less with respect to the total amount.
The mass ratio (carbon black content / (YMC pigment content) is preferably 0.4 or more and 5.0 or less, more preferably 0.5 or more and 1.0 or less, more preferably 0.4 or more and 5.0. When it is less than or equal to, the black density is improved, and when it is 0.5 or more and 1.0 or less, yellowing can be prevented more effectively.
In the present invention, it is necessary to include all the YMC pigments, and if one of them is missing, the black density does not improve and the color may become unnatural as black.

Further, from the viewpoint of reducing the conductivity between the carbon black pigments and preventing yellowing, the content of the magenta pigment is preferably 0.02% by mass or more and 2.0% by mass or less with respect to the total amount of the ink, and the cyan pigment is preferable. The content of the yellow pigment is preferably 0.02% by mass or more and 2.0% by mass or less, and the content of the yellow pigment is preferably 0.02% by mass or more and 2.0% by mass or less.

<Pigment dispersion>
It is possible to obtain an ink by mixing a material such as water or an organic solvent with a pigment. It is also possible to produce an ink by mixing a material such as water or an organic solvent with a pigment dispersion obtained by mixing a pigment and other water or a dispersant.
The pigment dispersion is obtained by mixing and dispersing water, a pigment, a pigment dispersant, and other components as necessary, and adjusting the particle size. It is good to use a disperser for dispersion.
The particle size of the pigment in the pigment dispersion is not particularly limited, but the maximum frequency is 20 nm or more in terms of the maximum number because the dispersion stability of the pigment is good and the image quality such as ejection stability and image density is also high. It is preferably 500 nm or less, and more preferably 20 nm or more and 150 nm or less. The particle size of the pigment can be measured using a particle size analyzer (Nanotrack Wave-UT151, manufactured by Microtrac Bell Co., Ltd.).
The content of the pigment in the pigment dispersion is not particularly limited and may be appropriately selected depending on the intended purpose, but is 0.1% by mass from the viewpoint of obtaining good ejection stability and increasing the image density. 50% by mass or more is preferable, and 0.1% by mass or more and 30% by mass or less is more preferable.
It is preferable to degas the pigment dispersion by filtering the coarse particles with a filter, a centrifuge, or the like, if necessary.

<Resin>
The type of resin contained in the ink is not particularly limited and may be appropriately selected depending on the intended purpose. For example, urethane resin, polyester resin, acrylic resin, vinyl acetate resin, styrene resin, butadiene resin, etc. Examples thereof include resins, styrene-butadiene resins, vinyl chloride resins, acrylic styrene resins, and acrylic silicone resins.
Resin particles made of these resins may be used. It is possible to obtain ink by mixing resin particles with a material such as a coloring material or an organic solvent in the state of a resin emulsion in which water is used as a dispersion medium. As the resin particles, those synthesized as appropriate may be used, or commercially available products may be used. Further, these may be used alone or in combination of two or more kinds of resin particles.

The volume average particle size of the resin particles is not particularly limited and may be appropriately selected depending on the intended purpose. However, from the viewpoint of obtaining good fixability and high image hardness, 10 nm or more and 1,000 nm or less are preferable. More than 200 nm is more preferable, and 10 nm or more and 100 nm or less is particularly preferable.
The volume average particle size can be measured using, for example, a particle size analyzer (Nanotrack Wave-UT151, manufactured by Microtrac Bell Co., Ltd.).

The content of the resin is not particularly limited and may be appropriately selected depending on the intended purpose. However, from the viewpoint of fixability and storage stability of the ink, 1% by mass or more and 30% by mass or less with respect to the total amount of the ink. Is preferable, and 5% by mass or more and 20% by mass or less is more preferable.

In the present invention, it is preferable to use an insulating resin as the resin. By containing the insulating resin, the conductivity of the ink can be suitably lowered, and the effect of preventing yellowing is high. As the insulating resin, urethane resin or acrylic resin is more preferable from the viewpoint of further enhancing the effect.

The particle size of the solid content in the ink is not particularly limited and can be appropriately selected depending on the intended purpose. From the viewpoint of improving image quality such as ejection stability and image density, the maximum frequency of the particle size of the solid content in the ink is preferably 20 nm or more and 1000 nm or less in terms of the maximum number, and more preferably 20 nm or more and 150 nm or less. The solid content includes resin particles, pigment particles, and the like. The particle size can be measured using a particle size analyzer (Nanotrack Wave-UT151, manufactured by Microtrac Bell Co., Ltd.).

<Additives>
If necessary, a surfactant, an antifoaming agent, an antiseptic / antifungal agent, a rust preventive agent, a pH adjuster and the like may be added to the ink.

<Surfactant>
As the surfactant, any of a silicone-based surfactant, a fluorine-based surfactant, an amphoteric surfactant, a nonionic surfactant, and an anionic surfactant can be used.
The silicone-based surfactant is not particularly limited and may be appropriately selected depending on the intended purpose. Of these, those that do not decompose even at high pH are preferable. Examples of the silicone-based surfactant include side chain modified polydimethylsiloxane, double-ended modified polydimethylsiloxane, single-ended modified polydimethylsiloxane, and side chain double-ended modified polydimethylsiloxane. Those having a polyoxyethylene group and a polyoxyethylene polyoxypropylene group as the modifying group are particularly preferable because they exhibit good properties as an aqueous surfactant. Further, as the silicone-based surfactant, a polyether-modified silicone-based surfactant can also be used, and examples thereof include compounds in which a polyalkylene oxide structure is introduced into the Si portion side chain of dimethylsiloxane.
Examples of the fluorine-based surfactant include a perfluoroalkyl sulfonic acid compound, a perfluoroalkyl carboxylic acid compound, a perfluoroalkyl phosphate ester compound, a perfluoroalkyl ethylene oxide adduct, and a perfluoroalkyl ether group in the side chain. Polyoxyalkylene ether polymer compounds are particularly preferred because they have low foaming properties. Examples of the perfluoroalkyl sulfonic acid compound include perfluoroalkyl sulfonic acid and perfluoroalkyl sulfonic acid salt. Examples of the perfluoroalkylcarboxylic acid compound include perfluoroalkylcarboxylic acid and perfluoroalkylcarboxylic acid salt. Examples of the polyoxyalkylene ether polymer compound having a perfluoroalkyl ether group in the side chain include a sulfate ester salt of a polyoxyalkylene ether polymer having a perfluoroalkyl ether group in the side chain and a poly having a perfluoroalkyl ether group in the side chain. Examples thereof include salts of oxyalkylene ether polymers. The counter ions of the salts in these fluorine-based surfactants include Li, Na, K, NH ₄ , NH ₃ CH ₂ CH ₂ OH, NH ₂ (CH ₂ CH ₂ OH) ₂ , and NH (CH ₂ CH ₂ OH). ₃ etc. can be mentioned.
Examples of the amphoteric tenside include laurylaminopropionate, lauryl dimethyl betaine, stearyl dimethyl betaine, and lauryl dihydroxyethyl betaine.
Examples of the nonionic surfactant include polyoxyethylene alkyl phenyl ether, polyoxyethylene alkyl ester, polyoxyethylene alkyl amine, polyoxyethylene alkyl amide, polyoxyethylene propylene block polymer, sorbitan fatty acid ester, and polyoxyethylene sorbitan. Examples thereof include a fatty acid ester and an ethylene oxide adduct of acetylene alcohol.
Examples of the anionic surfactant include polyoxyethylene alkyl ether acetate, dodecylbenzene sulfonate, lauryl salt, polyoxyethylene alkyl ether sulfate salt and the like.
These may be used alone or in combination of two or more.

The silicone-based surfactant is not particularly limited and may be appropriately selected depending on the intended purpose. For example, side-chain modified polydimethylsiloxane, double-ended modified polydimethylsiloxane, one-ended modified polydimethylsiloxane, side chain. Examples thereof include both-terminal modified polydimethylsiloxane, and a polyether-modified silicone-based surfactant having a polyoxyethylene group and a polyoxyethylene polyoxypropylene group as modifying groups is particularly preferable because it exhibits good properties as an aqueous surfactant. ..
As such a surfactant, an appropriately synthesized one may be used, or a commercially available product may be used. As commercially available products, for example, they can be obtained from Big Chemie Co., Ltd., Shin-Etsu Chemical Co., Ltd., Toray Dow Corning Silicone Co., Ltd., Nippon Emulsion Co., Ltd., Kyoeisha Chemical Co., Ltd. and the like.
The above-mentioned polyether-modified silicone-based surfactant is not particularly limited and may be appropriately selected depending on the intended purpose. For example, a polyalkylene oxide structure represented by the general formula (S-1) is dimethylpoly. Examples thereof include those introduced into the Si portion side chain of siloxane.

(However, in the general formula (S-1), m, n, a, and b each independently represent an integer, R represents an alkylene group, and R'represents an alkyl group.)
Commercially available products can be used as the above-mentioned polyether-modified silicone-based surfactant, for example, KF-618, KF-642, KF-643 (Shinetsu Chemical Industry Co., Ltd.), EMALEX-SS-5602, SS-. 1906EX (Nippon Emulsion Co., Ltd.), FZ-2105, FZ-2118, FZ-2154, FZ-2161, FZ-2162, FZ-2163, FZ-2164 (Toray Dow Corning Silicone Co., Ltd.), BYK-33, BYK-387 (Big Chemie Co., Ltd.), TSF4440, TSF4452, TSF4453 (Momentive Performance Materials Japan Co., Ltd.) and the like can be mentioned.

As the fluorine-based surfactant, a compound having 2 to 16 carbon atoms substituted with fluorine is preferable, and a compound having 4 to 16 carbon atoms substituted with fluorine is more preferable.
Examples of the fluorine-based surfactant include a perfluoroalkyl phosphate ester compound, a perfluoroalkylethylene oxide adduct, and a polyoxyalkylene ether polymer compound having a perfluoroalkyl ether group in the side chain. Among these, the polyoxyalkylene ether polymer compound having a perfluoroalkyl ether group in the side chain is preferable because it has less foaming property, and is particularly a fluorine-based compound represented by the general formula (F-1) and the general formula (F-2). Surfactants are preferred.

In the compound represented by the general formula (F-1), m is preferably an integer of 0 to 10 and n is preferably an integer of 0 to 40 in order to impart water solubility.

In the compound represented by the above general formula (F-2), Y is H or CmF _{2m + 1} and m is an integer of 1 to 6, or CH ₂ CH (OH) CH ₂ -CmF _{2m + 1} and m is 4 to 6. It is an integer, or CpH _{2p + 1} and p is an integer of 1 to 19. n is an integer of 1 to 6. a is an integer of 4 to 14.
Commercially available products may be used as the above-mentioned fluorine-based surfactant. Examples of this commercially available product include Surflon S-111, S-112, S-113, S-121, S-131, S-132, S-141, and S-145 (all manufactured by Asahi Glass Co., Ltd.); Full Lard FC-93, FC-95, FC-98, FC-129, FC-135, FC-170C, FC-430, FC-431 (all manufactured by Sumitomo 3M Co., Ltd.); Megafuck F-470, F -1405, F-474 (all manufactured by Dainippon Ink and Chemicals Co., Ltd.); Zonyl TBS, FSP, FSA, FSN-100, FSN, FSO-100, FSO, FS-300, UR, Capstone FS-30, FS-31, FS-3100, FS-34, FS-35 (all manufactured by The Chemours Company); FT-110, FT-250, FT-251, FT-400S, FT-150, FT- 400SW (all manufactured by Neos Co., Ltd.), Polyfox PF-136A, PF-156A, PF-151N, PF-154, PF-159 (manufactured by Omniova), Unidyne DSN-403N (manufactured by Daikin Industries Co., Ltd.) Among these, FS-3100, FS-34, FS- of The Chemours Co., Ltd. from the viewpoint of remarkably improving good print quality, especially color development, permeability to paper, wettability, and leveling property. 300, FT-110, FT-250, FT-251, FT-400S, FT-150, FT-400SW manufactured by Neos Co., Ltd., Polyfox PF-151N manufactured by Omninova, and Unidyne DSN-manufactured by Daikin Industries Co., Ltd. 403N is particularly preferable.

The content of the surfactant in the ink is not particularly limited and may be appropriately selected depending on the intended purpose. However, from the viewpoint of excellent wettability and ejection stability and improvement in image quality, 0.001 mass is used. % Or more and 5% by mass or less are preferable, and 0.05% by mass or more and 5% by mass or less are more preferable.

<Defoamer>
The defoaming agent is not particularly limited, and examples thereof include silicone-based defoaming agents, polyether-based defoaming agents, and fatty acid ester-based defoaming agents. These may be used alone or in combination of two or more. Among these, a silicone-based defoaming agent is preferable because it has an excellent defoaming effect.

<Preservatives and fungicides>
The antiseptic and antifungal agent is not particularly limited, and examples thereof include 1,2-benzisothiazolin-3-one and the like.

<Rust inhibitor>
The rust preventive is not particularly limited, and examples thereof include acidic sulfites and sodium thiosulfate.

<pH adjuster>
The pH adjusting agent is not particularly limited as long as the pH can be adjusted to 7 or more, and examples thereof include amines such as diethanolamine and triethanolamine.

The physical characteristics of the ink are not particularly limited and may be appropriately selected depending on the intended purpose. For example, the viscosity, surface tension, pH and the like are preferably in the following ranges.
The viscosity of the ink at 25 ° C. is preferably 5 mPa · s or more and 30 mPa · s or less, preferably 5 mPa · s or more and 25 mPa · s or less, from the viewpoint of improving the print density and character quality and obtaining good ejection properties. More preferred. Here, for the viscosity, for example, a rotary viscometer (RE-80L manufactured by Toki Sangyo Co., Ltd.) can be used. As the measurement conditions, it is possible to measure at 25 ° C. with a standard cone rotor (1 ° 34'× R24), a sample liquid volume of 1.2 mL, a rotation speed of 50 rpm, and 3 minutes.
The surface tension of the ink is preferably 35 mN / m or less, and more preferably 32 mN / m or less at 25 ° C. from the viewpoint that the ink is preferably leveled on the recording medium and the drying time of the ink is shortened.
The pH of the ink is preferably 7 to 12, and more preferably 8 to 11 from the viewpoint of preventing corrosion of the metal member that comes into contact with the liquid.

<Recording medium>
The recording medium used for recording is not particularly limited, and examples thereof include plain paper, glossy paper, special paper, cloth, film, transparency sheet, and general-purpose printing paper.

Further, in the terms of the present invention, image formation, recording, printing, printing, etc. are all synonymous.
Recording media, media, and printed matter are all synonymous.

The ink of the present invention preferably has a conductivity of 0.01 S / m or less when the evaporation rate is 80%.
By satisfying this requirement, it is possible to enhance the effect of the present invention that the conductivity between the carbon black pigments is lowered and an image in which yellowing does not occur even when heated by electromagnetic waves can be formed.
When the evaporation rate is 80%, the ink is heated and evaporated, and the mass after the heating evaporation becomes 20% with respect to the mass of the ink before the heating evaporation.

FIG. 1 is a side view of an embodiment of the image forming apparatus of the present invention.
The image forming apparatus of the present invention shown in FIG. 1 is an inkjet recording apparatus, and includes a carrier 2, an inkjet head 3, a high-frequency dielectric heating apparatus 6a as a heating means for heating by electromagnetic waves, and a recording paper bank 7. Further, 3Y, 3M, 3C, and 3K indicate inks of each color of yellow, magenta, cyan, and black. Generally, a color image is formed by these four colors.

The inkjet head 3 and the high-frequency dielectric heating device 6a are arranged along the direction 100 in which the recording paper 1 is conveyed. Further, a recording paper bank 7 is provided, from which the recording paper 1 is conveyed, and an image is formed on the recording paper 1 by ejecting ink by the inkjet head 3 while being supported by the carrier 2.

In this embodiment, a high-frequency dielectric heating device 6a is used as a heating means for heating by electromagnetic waves. 2 and 3 show a high frequency dielectric heating device 6a. As shown in FIG. 2, the rod-shaped electrode 61 is arranged under the carrier 2. As shown in FIG. 3, the rod-shaped electrode 61 is configured such that adjacent electrodes have different electrodes. A high frequency of, for example, 10 to 80 MHz is applied to the rod-shaped electrode 61. Then, the electric lines of force shown by the dotted lines in FIG. 3 act on the carrier 2, and the ink on the recording paper 1 is heated. The strength of this heating action depends on the material. It is generally known that when a dielectric is placed in a high frequency, heat for Ic, tabδ, and E is generated when the dielectric loss δ (dielectric loss angle), voltage E, and current Ic are used. This tan δ is called a dielectric loss tangent, and the larger this value is, the stronger it is heated, and the smaller this value is, the less likely it is to be heated.

Table 1 shows the values of the dielectric loss tangent tan δ of a general material at a frequency of 1 MHz. As shown in Table 1, water is prominent and has a large tan δ, so that it is easily heated by a high frequency. That is, the water contained in the ink is easily heated by the high frequency. On the other hand, the carrier 2 is made of a very small material having a dielectric loss tangent tan δ of 0.01 or less with respect to a high frequency frequency generated from the high frequency dielectric heating device 6a. For example, polyimide, polypropylene, natural rubber, silicone resin, polycarbonate, polyethylene, Teflon (registered trademark), PFA and the like. Since these materials have a very small dielectric loss tangent tan δ, they are not easily heated by high frequencies.

The operation of the image forming apparatus shown in FIG. 1 will be described.
Ink is supplied to the inkjet head 3 from an ink tank (not shown). The inkjet head 3 ejects small ink droplets to form an image on the recording paper 1. The carrier 2 moves in the direction of the arrow 100 and is conveyed while supporting the recording paper 1.

Further, when the ink passes near the rod-shaped electrode 61 of the high-frequency dielectric heating device 6a, only the water content in the ink is heated and evaporated, so that the ink dries. At this time, the water content in the ink is measured by a water sensor (not shown), and the high-frequency dielectric heating device 6a is used so that the water content in the ink after heating and drying is within the transfer appropriate range according to the obtained measured value. The output and heating time are controlled by control means (not shown). At this time, the output and the heating time of the high-frequency dielectric heating device 6a according to the amount of water in the ink, which is within the appropriate transfer range, are grasped and stored in advance by an experiment.

Instead of measuring the water content in the ink, the amount of ink ejected from the inkjet head 3 may be measured, and the high-frequency dielectric heating device 6a may be controlled according to the amount of the ejected ink. In this case, the output and heating time of the high-frequency dielectric heating device 6a, which is within the appropriate transfer range according to the amount of ink, are grasped and stored in advance by an experiment.

The image forming method of the present invention can be suitably carried out by using the above-mentioned image forming apparatus. That is, an ink applying step of applying an ink containing carbon black, a magenta pigment, a cyan pigment, and a yellow pigment to the recording paper 1 by, for example, an inkjet method, and an ink applied onto the recording paper 1, for example, high frequency dielectric. It has a heating step of heating by a heating device 6a.

In the above description, the form in which the heating means is a high-frequency dielectric heating means has been described as an example, but the present invention is not limited to this, and other known heating means for heating by electromagnetic waves can also be used. For example, a known infrared (IR) irradiation means can be mentioned.

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited to the following Examples. In the example, "part" represents "parts by mass", and "%" represents "% by mass" unless otherwise specified. Further, Examples 2 to 9 are Reference Examples 2 to 9 not included in the present invention.

(Preparation of urethane resin emulsion A)
Polylite OD-X-2420 (polyester polyol manufactured by DIC) 1,500 g, 2,2-dimethylolpropionic acid (DMPA) 220 g, and N in a reaction vessel containing a stirrer, a reflux condenser, and a thermometer. -1,347 g of methylpyrrolidone (NMP) was charged in a nitrogen atmosphere and heated to 60 ° C. to dissolve DMPA.
Next, 1,445 g of 4,4'-dicyclohexylmethane diisocyanate and 2.6 g of dibutyltin dilaurylate (catalyst) were added and heated to 90 ° C., and a urethanization reaction was carried out over 5 hours to obtain an isocyanate-terminated urethane prepolymer. Obtained. The reaction mixture was cooled to 80 ° C., and 4,340 g of triethylamine was added and mixed, and 4,340 g was extracted from the mixture and added to a mixed solution of 5,400 g of water and 15 g of triethylamine under strong stirring.
Next, 1,500 g of ice was added, 626 g of a 35% by mass 2-methyl-1,5-pentanediamine aqueous solution was added, a chain extension reaction was carried out, and the solvent was distilled off so that the solid content concentration became 30% by mass. Then, the obtained resin emulsion was dispersed and treated with a paint conditioner (manufactured by Red Devil, whose speed can be adjusted in the range of 50 to 1,425 rpm), and a polyester-based urethane resin emulsion having a solid content concentration of 40.0% by mass and a Tg of 10 ° C. I got A.
Tg was measured by DSC (Thermo plus EVO2 / DSC manufactured by Rigaku).

<Preparation of acrylic resin emulsion B>
As the acrylic resin emulsion B, Boncoat CF-6140 (manufactured by DIC Corporation, Tg 12 ° C.) was used.

<Preparation of Ethylene Vinyl Acetate Resin Emulsion C>
As the ethylene-vinyl acetate resin emulsion C, S-400HQ (manufactured by Sumika Chemtex Co., Ltd., Tg 0 ° C.) was used.

(Ink preparation)
<Preparation of pigment dispersion>
<< Preparation of Black Pigment Dispersion >>
Tokai Carbon Co., Ltd. carbon black: 100 g of Seast SP (SRF-LS) was added to 3000 mL of a 2.5 N (specified) sodium hypochlorite solution, stirred at a temperature of 60 ° C. and a speed of 300 rpm, and reacted for 10 hours. Oxidation treatment was carried out to obtain a pigment having a carboxylic acid group on the surface of carbon black. This reaction solution was filtered, and the filtered carbon black was neutralized with a sodium hydroxide solution, and ultrafiltration was performed.
Next, ultrafiltration with a dialysis membrane was performed using the pigment dispersion and ion-exchanged water, and ultrasonic dispersion was further performed to concentrate the pigment solid content to 20%. A black pigment dispersion having a volume average particle size of 100 nm. Got

<< Preparation of cyan pigment dispersion >>
In the preparation of the black pigment dispersion, the volume average particle size was 75 nm in the same manner except that the coloring material used was replaced with a copper phthalocyanine pigment (CI Pigment Blue 15: 4, trade name: LX4033) manufactured by Toyo Ink Co., Ltd. A cyan pigment dispersion was obtained.

<< Preparation of Magenta Pigment Dispersion >>
In the preparation of the black pigment dispersion, a magenta pigment dispersion having a volume average particle size of 73 nm was obtained in the same manner except that the coloring material used was replaced with Pigment Red 122 manufactured by Sun Chemical.

<< Preparation of yellow pigment dispersion >>
In the preparation of the black pigment dispersion, a yellow pigment having a volume average particle size of 82 nm is similarly used except that the coloring material used is replaced with a yellow pigment manufactured by Dainichiseika Kogyo Co., Ltd. (Pigment Yellow 74, trade name: Yellow NO.46). A dispersion was obtained.

<Ink preparation method>
Inks 1 to 13 were prepared by mixing and stirring each component according to the formulation (% by mass) as shown in Table 2 and filtering with a 0.2 μm polypropylene filter. As the surfactant, FS-300 (a fluorine-based surfactant manufactured by DuPont) was used.

In Table 2, the content of the pigment dispersion and the content of the emulsions A to C represent the solid content.

The conductivity at an ink evaporation rate of 80% was measured using a digital conductivity meter GM-117S manufactured by Kyoto Electron Corporation. Table 3 shows the measurement results.

(Example 1)
The following evaluations were performed on ink 1 as shown in Table 4.

<Black density>
Using the prepared ink, solid images were formed on plain paper PPC paper 4024 (manufactured by Xerox) and MC glossy paper (manufactured by EPSON), and the black density was measured using an Xrite 938 densitometer. In addition, the case where the black density with respect to plain paper was 1.30 or more was passed, and the case where the image density with respect to glossy paper was 1.80 or more was judged as pass.
From the judgment results of plain paper and glossy paper, the black density was evaluated according to the following criteria.
"Evaluation criteria"
A: Passed both plain paper and glossy paper.
B: Either plain paper or glossy paper passed.
C: Both plain paper and glossy paper failed.

<Evaluation of yellowing of paper after heating>
Similarly, the prepared ink 1 was used to form a solid image on plain paper PPC paper 4024 (manufactured by Xerox) and MC glossy paper (manufactured by EPSON), and the solid image was dried by the drying method shown in Table 4. Chromatic indices a * 2 and b * 2 were measured using an Xrite938 densitometer (measurement conditions: D50 light source, 2 degree field, Status T). The chromatic indices a * 1 and b * 1 of the solid image in the black density evaluation were used, and the saturation difference Δc was calculated for plain paper and glossy paper by the following formula.
[A * and b * are CIE1976L * a * b chromatic indexes of color system]
(Equation 1)
Δc = (Δa ² + Δb ² ) ^(1/2)
* Δa = (a * 2-a * 1), Δb = (b * 2-b * 1)
In addition, the case where Δc for plain paper and glossy paper was 3 or less was judged as acceptable.
From the judgment results of plain paper and glossy paper, the degree of yellowing of the paper after heating was evaluated according to the following criteria.
"Evaluation criteria"
A: Passed both plain paper and glossy paper.
B: Either plain paper or glossy paper passed.
C: Both plain paper and glossy paper failed.

The drying conditions by the drying method are as follows.
High-frequency dielectric: Dielectric heating was performed using an electrode (manufactured by Yamamoto Vinita, 50 cm in length, 20 mm pitch lattice electrode) under drying conditions of 1000 W for 2.5 seconds.
IR: Five seconds after the printing was completed, infrared rays were irradiated for 1 second from 4 cm above the printing surface by an infrared heater. A high-power carbon heater (manufactured by Metro Denki Kogyo Co., Ltd.) was used under the condition of 1,000 ° C. The temperature of the heat source was adjusted by changing the voltage applied to the heater. The heat source temperature was measured using a digital radiation temperature sensor FT-H50K (manufactured by KEYENCE CORPORATION). However, for the high-power carbon heater, the carbon of the heat source is enclosed in a glass tube, so the temperature of the glass tube was measured and the carbon temperature was estimated from it.
Microwave: 5 seconds after printing is completed, ESG-2450S-2A (manufactured by Shimada Rika Kogyo Co., Ltd .; microwave generator) is used to irradiate microwaves (oscillation frequency: 2450 MHz, output: 100 W) for 3 seconds. It was dried.

<Evaluation of dryness>
Similarly, the prepared ink 1 was used to form a solid image on plain paper PPC paper 4024 (manufactured by Xerox) and MC glossy paper (manufactured by EPSON), and the solid image was dried by the drying method shown in Table 4. The filter paper was pressed against the solid portion after drying, and those without ink transfer to the filter paper were judged as acceptable, and those with ink transfer to the filter paper were judged as rejected. From the judgment results of plain paper and glossy paper, the drying property was evaluated according to the following criteria.
"Evaluation criteria"
A: Passed both plain paper and glossy paper.
B: Either plain paper or glossy paper passed.
C: Both plain paper and glossy paper failed.

(Examples 2 to 9)
In Example 1, the evaluation was carried out in the same manner except that the ink and the heating method were changed as shown in Tables 2 and 4.

(Comparative Examples 1 to 5)
In Example 1, the evaluation was carried out in the same manner except that the ink and the heating method were changed as shown in Tables 2 and 5.

Example 1 is a particularly preferred example of the present invention. In these examples, the black density, the degree of yellowing, and the evaluation of dryness were all evaluated as A.

Examples 2 to 9 are preferable examples of the present invention. In these examples, any of the black density, the degree of yellowing, and the evaluation of dryness is evaluated as B, but it can be said that there is no problem in use.

Comparative Examples 1 and 2 are examples in which no cyan pigment, magenta pigment, or yellow pigment is used.
In these examples, when the amount of carbon black is large (Comparative Example 1), yellowing occurs, and when the amount of carbon black is small (Comparative Example 2), there is a problem that the black density is insufficient.

Comparative Examples 3 to 5 are examples in which any of the cyan pigment, the magenta pigment, and the yellow pigment is not used.
In these examples, the solid image was tinted, and as a result, problems occurred in both the black density and the evaluation of yellowing.

1 Recording paper 2 Carrier 3 Inkjet head 6a High frequency dielectric heating device 7 Recording paper bank 61 Rod-shaped electrode

Japanese Unexamined Patent Publication No. 2017-50216 JP-A-2017-119395 Japanese Unexamined Patent Publication No. 2017-165000 Japanese Patent No. 6173020

Claims (4)

With ink
An ink applying means for applying the ink to the recording medium,
It has a heating means for heating the ink applied on the recording medium by electromagnetic waves.
The heating means is a high-frequency dielectric heating means.
The ink contains carbon black, magenta pigment, cyan pigment and yellow pigment as pigments, and further contains urethane resin.
The mass ratio of the pigment (carbon black content / (total content of magenta pigment, cyan pigment and yellow pigment)) is 0.5 or more and 1.0 or less.
An image forming apparatus characterized in that the conductivity at an evaporation rate of 80% of the ink is 0.01 S / m or less . The image forming apparatus according to claim 1 , wherein the content of carbon black in the ink is less than 3.2% by mass with respect to the total amount of the ink. The content of carbon black in the ink is less than 3.2% by mass with respect to the total amount of ink.
The image formation according to claim 1 or 2 , wherein the total content of the magenta pigment, the cyan pigment and the yellow pigment in the ink is 0.1% by mass or more and 5% by mass or less with respect to the total amount of the ink. Device. An ink applying step of applying an ink containing carbon black, magenta pigment, cyan pigment and yellow pigment as pigments and further containing urethane resin to a recording medium,
It has a heating step of heating the ink applied on the recording medium by electromagnetic waves.
In the heating step, heating is performed by a high-frequency dielectric heating means.
The mass ratio of the pigment (carbon black content / (total content of magenta pigment, cyan pigment and yellow pigment)) is 0.5 or more and 1.0 or less.
An image forming method characterized in that the conductivity at an evaporation rate of 80% of the ink is 0.01 S / m or less .

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