Image forming apparatus and image forming method

Abstract

To provide an image forming device suppressing waving of a recording medium and establishing compatibility between image density and image dryness.SOLUTION: An image forming device includes: black ink containing water, an organic solvent, carbon black, and a resin A and a resin B; a black ink applying means for applying the black ink to a recording medium; an irradiation means for irradiating the recording medium to which the black ink is applied with visible light or ultraviolet light having the wavelength of 700 nm or shorter. When a glass transition point of the resin A is defined as TgA, a glass transition point of the resin B is defined as TgB, and an image surface temperature after the irradiation means performs irradiation to the recording medium is defined as Ti, a relationship of TgA<Ti<TgB is satisfied.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus and an image forming method. [Background technology]

[0002] Inkjet recording is a method of recording in which ink droplets are ejected from extremely fine nozzles directly onto a recording medium, causing the ink droplets to adhere to the recording medium, thereby obtaining characters or images.

[0003] In recent years, image forming methods using inkjet recording have become widespread in industrial applications. In particular, high-speed printing has become possible due to improvements in inkjet technology. Therefore, in order to accommodate inkjet recording for high-speed printing, an image forming method using ink with high color development, high gloss, and excellent drying and fixing properties is desired.

[0004] Water-based inks, which use water as the main ingredient, are widely used because they are safe and inexpensive. In high-speed printing, heat drying is generally used to quickly dry the water and solvents in the ink, but when the image dries, the print medium (recording medium) loses moisture, causing the print medium to ripple (also known as paper waviness). In particular, with cut sheets, unlike roll paper, the tension applied to the print medium during print drying is small, making paper waviness a common problem.

[0005] Furthermore, when a black ink containing a carbon black pigment is printed and then dried by heating, the carbon black is exposed on the surface of the image, which causes a problem of reduced image density and glossiness. For this reason, Patent Document 1 discloses a technique for printing black using mainly the black ink when using plain paper, and printing composite black using mainly inks other than the black ink when using glossy paper or matte paper.

[0006] Patent documents 2 to 4 disclose a technique of using a three-color composite black of cyan, magenta, and yellow instead of black ink for special papers such as glossy paper, semi-glossy paper, and matte paper. Furthermore, for example, Patent document 5 discloses a technique of improving glossiness by applying clear ink onto an image. Summary of the Invention [Problem to be solved by the invention]

[0007] The method of preparing different types of ink for each type of paper in Patent Document 1 and the method of applying clear ink onto the image in Patent Document 5 require a large number of ink tanks and heads, and the subsystem for maintaining and recovering the heads also becomes large. This causes the problem of high costs, and is still insufficient in suppressing waviness in the print medium and achieving both drying properties and image density. In addition, when a three-color composite black of cyan, magenta, and yellow is used without using black ink as in Patent Documents 2 to 4, the achromatic color gamut tends to be colored because black is expressed without using black ink. In addition, the cost is high because the three colors are mixed to express the black gradation.

[0008] SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to provide an image forming apparatus capable of suppressing waviness of a recording medium and achieving both image density and image drying properties. [Means for solving the problem]

[0009] In order to solve the above problems, the image forming apparatus of the present invention has a black ink containing water, an organic solvent, carbon black, and resins A and B, a black ink applying unit that applies the black ink to a recording medium, and an irradiation unit that irradiates the recording medium to which the black ink has been applied with visible light or ultraviolet light having a wavelength of 700 nm or less, and the glass transition point of the resin A is set to Tg A The glass transition temperature of the resin B is Tg BThe irradiation means irradiates the recording medium. Immediately after The image surface temperature is T i When Tg A <T i <Tg B The present invention is characterized in that: Effect of the Invention

[0010] According to the present invention, it is possible to provide an image forming apparatus capable of suppressing waviness of a recording medium and achieving both image density and image drying property. [Brief description of the drawings]

[0011] [Figure 1] 1 is a perspective view of an image forming apparatus according to a first embodiment; [Diagram 2] FIG. [Diagram 3] FIG. 11 is an explanatory side view of an image forming apparatus according to a second embodiment. [Figure 4] FIG. 11 is a plan view illustrating a main part of an image forming apparatus according to a second embodiment. [Diagram 5] FIG. 11 is an explanatory plan view of a head according to a second embodiment. [Figure 6] FIG. 13 is an overall explanatory diagram of an image forming apparatus according to a third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The image forming apparatus and the image forming method according to the present invention will be described below with reference to the drawings. Note that the present invention is not limited to the following embodiments, and may be modified, added, modified, deleted, or otherwise altered within the scope of what a person skilled in the art can conceive, and any embodiment is within the scope of the present invention as long as it achieves the functions and effects of the present invention.

[0013] In general, when an image is dried by heating at a temperature equal to or higher than the minimum film-forming temperature, the resin contained in the ink forms a film, and an image with good fixability can be obtained. In the case of color inks containing pigments other than carbon black, when a resin film is formed by heating and drying, the image surface becomes smooth and the image density is improved.

[0014] On the other hand, in the case of black ink containing carbon black, when a resin film is formed by heating and drying, the carbon black is exposed on the surface, which increases the surface roughness and reduces the image density. Therefore, if the glass transition temperature (Tg) of the resin contained in the ink is low, the minimum film-forming temperature is also low and the thermal energy required to form the resin film is small, but the black image density after drying is low. Conversely, if the Tg of the resin in the ink is high, the black image density is high, but the thermal energy required to form the resin film is large.

[0015] In this case, if the image is dried at a high temperature, the resin rapidly forms a film, which increases surface roughness and tends to reduce image density, but drying at a low temperature can suppress the decrease in image density. Therefore, it is believed that by controlling the drying time for a long period of time at a low temperature for black ink containing both low and high Tg resins, it is possible to obtain an image with low drying energy and high image density.

[0016] It has been found that if a method of drying by heating and drying through irradiation with energy rays is used as the drying method at this time, it is possible to prevent the image temperature from rising too high, which would otherwise cause a decrease in the image density of the black ink. In addition, when an image is irradiated with ultraviolet or visible light as a heat drying method, the coloring material contained in the ink absorbs these rays and generates heat, so that only the printed parts are heated and the water and solvent in the ink evaporates. Since the non-printed parts are not heated, the recording medium is not unnecessarily heated and water evaporation is suppressed, which has been found to be effective in preventing paper waving (also called recording medium waviness). In particular, water-based inks that contain 50% or more water in the ink have a high drying rate but are prone to paper waving, so the use of ultraviolet or visible light is very effective.

[0017] Based on these findings, the present inventors have completed the image forming apparatus of the present invention. The image forming apparatus of the present invention comprises a black ink containing water, an organic solvent, carbon black, and resins A and B, a black ink applying means for applying the black ink to a recording medium, and an irradiation means for irradiating the recording medium to which the black ink has been applied with visible light or ultraviolet light having a wavelength of 700 nm or less, and the glass transition point of the resin A is set to Tg A The glass transition temperature of the resin B is Tg B and the image surface temperature after the irradiation means irradiates the recording medium is T i When Tg A <T i <Tg B This makes it possible to suppress waviness of the recording medium and to achieve both image density and image drying property.

[0018] The image forming method of the present invention includes a black ink applying step of applying a black ink containing water, an organic solvent, carbon black, and resins A and B to a recording medium, and an irradiation step of irradiating the recording medium to which the black ink has been applied with visible light or ultraviolet light having a wavelength of 700 nm or less, and the glass transition point of the resin A is raised to Tg A The glass transition temperature of the resin B is Tg B and the image surface temperature after the recording medium is irradiated in the irradiation step is T i When Tg A <T i <Tg B The present invention is characterized in that:

[0019] The image forming apparatus of the present invention may further comprise a color ink containing water, an organic solvent, a coloring material, and a resin C, and a color ink applying unit for applying the color ink to the recording medium. In this case, the glass transition temperature of the resin C is Tg C When Tg C <Ti It is preferable that the above condition is satisfied. This can improve the drying property of the color ink. Similarly, the image forming method of the present invention may have a color ink applying step.

[0020] <Ink> The ink used in the present invention will now be described. The black ink used in the present invention contains water, an organic solvent, carbon black, resin A, and resin B. The color ink used in the present invention contains water, an organic solvent, a coloring material, and resin C.

[0021] In the ink used in the present invention, the carbon black and coloring material are preferably in the form of a pigment dispersion, and other components may be further contained. In the following, unless otherwise specified, the term "ink" refers to both black ink and color ink.

[0022] -Carbon black- Examples of the carbon black (CI Pigment Black 7) contained in the black ink include furnace black, lamp black, acetylene black, and channel black.

[0023] The carbon black content in the black ink is preferably from 2% by mass to 10% by mass, and more preferably from 4% by mass to 7% by mass.

[0024] -Coloring materials- The coloring material contained in the color ink is not particularly limited, and pigments and dyes can be used. The pigment may be an inorganic pigment or an organic pigment. These may be used alone or in combination of two or more. Mixed crystals may also be used.

[0025] Examples of pigments that can be used include black pigments, yellow pigments, magenta pigments, cyan pigments, white pigments, green pigments, orange pigments, glossy pigments such as gold and silver pigments, and metallic pigments. As inorganic pigments, titanium oxide, iron oxide, calcium carbonate, barium sulfate, aluminum hydroxide, barium yellow, cadmium red, chrome yellow, etc. can be used. As organic pigments, azo pigments, polycyclic pigments (e.g., phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, indigo pigments, thioindigo pigments, isoindolinone pigments, quinophthalone pigments, etc.), dye chelates (e.g., basic dye chelates, acid dye chelates, etc.), nitro pigments, nitroso pigments, aniline black, etc. can be used. Among these pigments, those having good affinity with the solvent are preferably used. In addition, resin hollow particles and inorganic hollow particles can also be used.

[0026] Specific examples of pigments for black include metals such as copper, iron (CI Pigment Black 11) and titanium oxide, and organic pigments such as aniline black (CI Pigment Black 1).

[0027] In addition, for color, CI 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, CI Pigment Yellow Range 5, 13, 16, 17, 36, 43, 51, CI 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 Carmine 6B), 60:1, 63:1, 63:2, 64:1, 81, 83, 88 , 101 (red oxide), 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, CI Pigment Violet 1 (Rhodamine Lake), 3, 5:1, 16, 19, 23, 38; CI Pigment Blue 1, 2, 15 (Phthalocyanine Blue), 15:1, 15:2, 15:3, 15:4 (Phthalocyanine Blue), 16, 17:1, 56, 60, 63; CI Pigment Green 1, 4, 7, 8, 10, 17, 18, 36, etc.

[0028] The dye is not particularly limited, and acid dyes, direct dyes, reactive dyes, and basic dyes can be used. One type of dye may be used alone, or two or more types may be used in combination. Examples of the dyes include CI Acid Yellow 17, 23, 42, 44, 79, 142, CI Acid Red 52, 80, 82, 249, 254, 289, CI Acid Blue 9, 45, 249, CI Acid Black 1, 2, 24, 94, CI Food Black 1, 2, CI Direct Yellow 1, 12, 24, 33, 50, 55, 58, 86, 132, 142, 144. ,173, CI Direct Red 1, 4, 9, 80, 81, 225, 227, CI Direct Blue 1, 2, 15, 71, 86, 87, 98, 165, 199, 202, CI Directed Black 19, 38, 51, 71, 154, 168, 171, 195, CI Reactive Red 14, 32, 55, 79, 249, and CI Reactive Black 3, 4, 35.

[0029] The content of the coloring material in the ink is preferably from 0.1% to 15% by mass, and more preferably from 1% to 10% by mass, from the viewpoints of improving image density, good fixing property and ejection stability.

[0030] Methods for dispersing a pigment to obtain an ink include a method of introducing a hydrophilic functional group into the pigment to make it a self-dispersing pigment, a method of dispersing the pigment by coating the surface of the pigment with a resin, and a method of dispersing the pigment using a dispersant.

[0031] As a method for introducing a hydrophilic functional group into a pigment to make it a self-dispersing pigment, for example, a method in which a functional group such as a sulfone group or a carboxyl group is added to a pigment (e.g., carbon) to make it dispersible in water can be mentioned.

[0032] As a method for dispersing a pigment by coating its surface with a resin, there is a method in which the pigment is encapsulated in a microcapsule to make it dispersible in water. This can be called a resin-coated pigment. In this case, it is not necessary for all of the pigments blended in the ink to be coated with a resin, and uncoated or partially coated pigments may be dispersed in the ink as long as the effect of the present invention is not impaired.

[0033] Examples of the method for dispersing using a dispersant include a method for dispersing using a known low molecular weight dispersant or a polymeric dispersant, typified by a surfactant. As the dispersant, for example, anionic surfactants, cationic surfactants, amphoteric surfactants, nonionic surfactants, etc. can be used depending on the pigment. RT-100 (nonionic surfactant) manufactured by Takemoto Oil Co., Ltd. and sodium naphthalenesulfonate formalin condensate can also be suitably used as dispersants. The dispersants may be used alone or in combination of two or more.

[0034] It is possible to obtain ink by mixing a pigment with materials such as water or an organic solvent, or it is also possible to manufacture ink by mixing a pigment with other materials such as water and a dispersant to prepare a pigment dispersion, and then mixing the resulting mixture with materials such as water or an organic solvent. The pigment dispersion is obtained by mixing and dispersing water, a pigment, a pigment dispersant, and other components as required, and adjusting the particle size. Dispersion is preferably performed using a dispersing machine. The particle size of the pigment in the pigment dispersion is not particularly limited, but the maximum frequency in terms of the maximum number is preferably 20 nm or more and 500 nm or less, more preferably 20 nm or more and 150 nm or less, in order to improve the dispersion stability of the pigment and the image quality such as ejection stability and image density. The particle size of the pigment can be measured using a particle size analyzer (Nanotrac Wave-UT151, manufactured by Microtrac Bell Co., Ltd.).

[0035] The content of the pigment in the pigment dispersion is not particularly limited and can be appropriately selected depending on the purpose. From the viewpoints of obtaining good ejection stability and increasing image density, the content of the pigment is preferably from 2.0% by mass to 8.0% by mass, and more preferably from 3.5% by mass to 7.0% by mass. It is preferable that the pigment dispersion is degassed, if necessary, by filtering coarse particles using a filter, a centrifugal separator, or the like.

[0036] -Organic solvents- The organic solvent used in the present invention is not particularly limited, and any water-soluble organic solvent can be used. Examples of the organic solvent include polyhydric alcohols, ethers such as polyhydric alcohol alkyl ethers and polyhydric alcohol aryl ethers, nitrogen-containing heterocyclic compounds, amides, amines, and sulfur-containing compounds.

[0037] Specific examples of the water-soluble organic solvent include ethylene glycol, diethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 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, and the like. polyhydric alcohols such as 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-1,3-pentanediol, and petriol, ethylene glycol monoethyl ether, and ethylene glycol monobutyl ether. polyhydric alcohol alkyl ethers such as diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, tetraethylene glycol monomethyl ether, and propylene glycol monoethyl ether; polyhydric alcohol aryl ethers such as ethylene glycol monophenyl ether and ethylene glycol monobenzyl ether; nitrogen-containing heterocyclic compounds such as 2-pyrrolidone, N-methyl-2-pyrrolidone, N-hydroxyethyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, ε-caprolactam, and γ-butyrolactone; amides such as formamide, N-methylformamide, N,N-dimethylformamide, 3-methoxy-N,N-dimethylpropionamide, and 3-butoxy-N,N-dimethylpropionamide; amines such as monoethanolamine, diethanolamine, and triethylamine; sulfur-containing compounds such as dimethyl sulfoxide, sulfolane, and thiodiethanol; propylene carbonate, and ethylene carbonate. It is preferable to use an organic solvent having a boiling point of 250° C. or less, since this not only functions as a wetting agent but also provides good drying properties.

[0038] Polyol compounds having 8 or more carbon atoms and glycol ether compounds are also suitably used. Specific examples of polyol compounds 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 alkyl ethers 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; and polyhydric alcohol aryl ethers such as ethylene glycol monophenyl ether and ethylene glycol monobenzyl ether.

[0039] When a resin is used, it is preferable that the solvent contains an amide solvent, 3-ethyl-3-hydroxymethyloxetane, and propylene glycol monomethyl ether. Examples of the amide solvent include 3-methoxy-N,N-dimethylpropionamide, 3-ethoxy-N,N-dimethylpropionamide, and 3-butoxy-N,N-dimethylpropionamide. These may be used alone or in combination of two or more. Among these, amide solvents such as 3-methoxy-N,N-dimethylpropionamide and 3-butoxy-N,N-dimethylpropionamide are more preferred from the viewpoints of promoting film-forming properties of the resin and improving abrasion resistance.

[0040] The boiling point of the organic solvent is preferably 180°C or higher and 300°C or lower. When the boiling point of the organic solvent is 180°C or higher, the evaporation rate during drying can be appropriately adjusted. In addition, the sufficient leveling property reduces the unevenness of the image surface, improving the gloss. When the boiling point of the organic solvent is 300°C or lower, the drying property of the ink can be improved.

[0041] The content of the organic solvent in the ink is not particularly limited and can be appropriately selected depending on the purpose. From the viewpoints of the drying property and ejection reliability of the ink, however, the content is preferably from 10% by mass to 60% by mass, and more preferably from 20% by mass to 60% by mass.

[0042] The content of the amide solvent is preferably from 0.05% by mass to 10% by mass, and more preferably from 0.1% by mass to 5% by mass, based on the total amount of the ink.

[0043] It is preferable that the ink contains diethylene glycol and triethylene glycol, since this improves the ejection stability during continuous image formation, and the ink has a high vapor pressure even at high temperatures and therefore has good drying properties. The content of diethylene glycol and triethylene glycol is preferably 1% by mass or more and 10% by mass or less, more preferably 3% by mass or more and 6% by mass or less, based on the total amount of the ink. When the content is 1% by mass or less, the ejection stability can be improved. When the content is 10% by mass or less, the amount of organic solvent remaining in the image area on the recording medium is small, so that plasticization of the resin can be suppressed and fixability can be maintained, and therefore image transfer to a heated roller can be suppressed.

[0044] -resin- The type of resin contained in the ink is not particularly limited and can be appropriately selected depending on the purpose. Examples of the resin include urethane resin, polyester resin, acrylic resin, vinyl acetate resin, styrene resin, butadiene resin, styrene-butadiene resin, vinyl chloride resin, acrylic styrene resin, and acrylic silicone resin.

[0045] Among these, it is preferable to use a styrene-acrylic resin, and it is preferable that both resin A and resin B are styrene-acrylic resins. It is also preferable that resin C contained in the color ink is a styrene-acrylic resin.

[0046] Resin particles made of these resins may be used. The resin particles may be dispersed in water as a dispersion medium to form a resin emulsion, and then mixed with materials such as coloring materials and organic solvents to obtain an ink. The resin particles may be appropriately synthesized or may be commercially available. These may be used alone or in combination of two or more types of resin particles.

[0047] Among the above resin particles, acrylic resin particles are widely used because they have excellent ejection stability and are inexpensive.

[0048] Examples of acrylic resin particles include acrylic silicone resin particles and styrene acrylic resin particles. These may be used alone or in combination of two or more. Among these, styrene acrylic resin particles are preferred from the viewpoints of abrasion resistance and drying property, since they are less likely to absorb the solvent in the ink.

[0049] Styrene acrylic resin particles can be made, for example, by emulsion polymerization, dispersion polymerization, suspension polymerization, milling or solution / bulk polymerization followed by post-emulsification, and the like. As the styrene-acrylic resin particles, commercially available products may be used as appropriate. Examples of commercially available styrene acrylic resin particles include trade names: J-352, J-390, J-450, J-511, J-734, J-741, J-775, J-840, J-7100, J-7600, HPD-71, HRC-1645, JDX-5050, PDX-6102B (all manufactured by BASF), and trade name: UC-3900 (manufactured by Toagosei Co., Ltd.).

[0050] The volume average particle diameter of the resin particles is not particularly limited and can be appropriately selected depending on the purpose. From the viewpoint of obtaining good fixing property and high image hardness, it is preferably 10 nm or more and 1,000 nm or less, more preferably 10 nm or more and 200 nm or less, and particularly preferably 10 nm or more and 100 nm or less. The volume average particle size can be measured, for example, using a particle size analyzer (Nanotrac Wave-UT151, manufactured by Microtrac-Bell Co., Ltd.).

[0051] The resin content in the ink is preferably 2.0% by mass or more and 12% by mass or less. By being 2.0% by mass or more, the fixability is improved, and by being 12% by mass or less, the ejection stability and storage stability of the ink are not impaired. More preferably, it is 3.0% by mass or more and 8.0% by mass or less.

[0052] The black ink in this embodiment may contain resins other than resin A and resin B, but preferably contains only resin A and resin B. When resins other than resin A and resin B are contained, the content of the other resins in the ink is preferably 2% by mass or less, and more preferably 1% by mass or less.

[0053] The color ink in this embodiment may contain a resin other than resin C, but preferably contains only resin C. When a resin other than resin C is contained, the content of the other resin in the ink is preferably 2% by mass or less, and more preferably 1% by mass or less.

[0054] Resin A and resin B contained in the black ink have Tg A <T i <Tg B It is preferable to select a resin that satisfies the following: T i <Tg A ,Tg B In the case of Tg, good drying properties cannot be obtained. A ,Tg B <T i In the case of , not only is good drying property not obtained, but good image density is also not obtained.

[0055] The glass transition temperature Tg of the resin is preferably 20° C. or higher and 150° C. or lower. AThe temperature is preferably 20° C. or higher and 50° C. or lower. When the temperature is 20° C. or higher, the storage stability of the ink is good. When the temperature is 20° C. or higher and 50° C. or lower, the image film can be formed suitably by drying, and thus the drying property is improved.

[0056] In addition, the glass transition point Tg of resin B B The temperature is preferably 80° C. or higher and 150° C. or lower. When the temperature is 80° C. or higher, the image density of the black ink is improved, and when the temperature is 150° C. or lower, the drying property is improved.

[0057] The Tg A is 20° C. or more and 50° C. or less, B is 80°C or more and 150°C or less, i It is more preferable that the temperature is more than 50° C. and less than 80° C. In this case, the image density and drying property can be further improved.

[0058] In color inks containing pigments other than carbon black, the Tg of the resin is preferably 20° C. or more and 80° C. or less. In this case, the image can be suitably formed into a film by drying, improving the image density and improving the drying properties. C <T i From the viewpoints of image density and drying property, the Tg of the resin C that satisfies the above relationship is preferably 20° C. or more and 80° C. or less.

[0059] The glass transition point referred to in this specification can be measured in accordance with the method described in JIS K7121, for example, using a differential scanning calorimetry (DSC) device (device name: Thermo plus EVO2 / DSC manufactured by Rigaku) ​​at a measurement temperature of 30°C to 300°C and a heating rate of 2.5°C per minute.

[0060] When analyzing from the ink, 5 g of ink is dried at 50°C for 10 hours, and the peak measured in accordance with the method described in JIS K7121 using, for example, a differential scanning calorimetry (DSC) device (device name: Thermo plus EVO2 / DSC manufactured by Rigaku) ​​at a measurement temperature of 30°C to 300°C with a heating rate of 2.5°C per minute is regarded as the Tg of the resin.

[0061] - Lubricant - The ink preferably contains a lubricant. By containing a lubricant in the ink, it is possible to improve the abrasion resistance. Furthermore, by using a lubricant in combination with a resin, it is possible to improve the glossiness. The lubricant is not particularly limited and can be appropriately selected depending on the purpose. For example, wax is included.

[0062] The wax may, for example, be polyethylene wax. As the polyethylene wax, commercially available products may be used as appropriate. There are no particular limitations on the commercially available polyethylene wax, and it can be appropriately selected depending on the purpose, and examples thereof include polyethylene wax (product name: AQUA PETRO DP2502C, manufactured by Toyo ADL Co., Ltd.) and polyethylene wax (product name: AQUA PETRO DP2401, manufactured by Toyo ADL Co., Ltd.) etc. These may be used alone or in combination of two or more kinds.

[0063] The content of the lubricant is preferably 0.05% by mass or more and 2% by mass or less, more preferably 0.05% by mass or more and 0.5% by mass or less, even more preferably 0.05% by mass or more and 0.45% by mass or less, and particularly preferably 0.15% by mass or more and 0.45% by mass or less, based on the total amount of the ink. When the content is 0.05% by mass or more and 2% by mass or less, it is possible to improve the abrasion resistance and gloss. When the content is 0.05% by mass or more and 0.45% by mass or less, it is possible to improve the storage stability and ejection stability of the ink.

[0064] The particle size of the solid content in the ink is not particularly limited and can be appropriately selected depending on the purpose, but in terms of improving image quality such as ejection stability and image density, the maximum frequency in terms of maximum number is preferably 20 nm or more and 1000 nm or less, more preferably 20 nm or more and 150 nm or less. The solid content includes resin particles, pigment particles, etc. The particle size can be measured using a particle size analyzer (Nanotrac Wave-UT151, manufactured by Microtrac Bell Co., Ltd.).

[0065] -water- The water content in the ink is not particularly limited and can be appropriately selected depending on the purpose. From the viewpoint of the drying property and ejection reliability of the ink, however, it is preferably from 10% to 90% by mass, and more preferably from 20% to 70% by mass.

[0066] The water is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include purified water, ion-exchanged water, ultrafiltered water, reverse osmosis water, distilled water, and other pure water, ultrapure water, etc. These may be used alone or in combination of two or more kinds.

[0067] -Additives- If necessary, surfactants, antifoaming agents, antiseptics, antifungals, rust inhibitors, pH adjusters, etc. may be added to the ink.

[0068] --Surfactant-- As the surfactant, any of silicone-based surfactants, fluorine-based surfactants, amphoteric surfactants, nonionic surfactants, and anionic surfactants can be used. Silicone surfactants are not particularly limited and can be appropriately selected according to purpose.Among them, those that do not decompose even at high pH are preferred, such as side chain modified polydimethylsiloxane, both end modified polydimethylsiloxane, one end modified polydimethylsiloxane, side chain both end modified polydimethylsiloxane, etc., and those having polyoxyethylene group or polyoxyethylene polyoxypropylene group as modified group are particularly preferred because they show good properties as aqueous surfactants.In addition, polyether modified silicone surfactants can also be used as the silicone surfactant, such as a compound in which a polyalkylene oxide structure is introduced into the Si part side chain of dimethylsiloxane.

[0069] As the fluorosurfactant, for example, perfluoroalkyl sulfonic acid compounds, perfluoroalkyl carboxylic acid compounds, perfluoroalkyl phosphate compounds, perfluoroalkyl ethylene oxide adducts, and polyoxyalkylene ether polymer compounds having perfluoroalkyl ether groups on the side chain are particularly preferred because they have low foaming properties. As the perfluoroalkyl sulfonic acid compounds, for example, perfluoroalkyl sulfonic acid, perfluoroalkyl sulfonate, etc. are included. As the perfluoroalkyl carboxylic acid compounds, for example, perfluoroalkyl carboxylic acid, perfluoroalkyl carboxylate, etc. are included. As the polyoxyalkylene ether polymer compounds having perfluoroalkyl ether groups on the side chain, for example, sulfate ester salts of polyoxyalkylene ether polymers having perfluoroalkyl ether groups on the side chains, salts of polyoxyalkylene ether polymers having perfluoroalkyl ether groups on the side chains, etc. are included. As counter ions of the salts in these fluorosurfactants, Li, Na, K, NH4, NH3CH2CH2OH, NH2(CH2CH2OH)2, NH(CH2CH2OH)3, etc. are included.

[0070] Examples of amphoteric surfactants include lauryl aminopropionate, lauryl dimethyl betaine, stearyl dimethyl betaine, and lauryl dihydroxyethyl betaine.

[0071] Examples of nonionic surfactants include polyoxyethylene alkylphenyl ethers, polyoxyethylene alkyl esters, polyoxyethylene alkylamines, polyoxyethylene alkylamides, polyoxyethylene propylene block polymers, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, and ethylene oxide adducts of acetylene alcohol.

[0072] Examples of the anionic surfactant include polyoxyethylene alkyl ether acetates, dodecylbenzene sulfonates, laurates, and salts of polyoxyethylene alkyl ether sulfates. These may be used alone or in combination of two or more.

[0073] The silicone surfactant is not particularly limited and can be appropriately selected depending on the purpose. Examples of the silicone surfactant include side-chain modified polydimethylsiloxane, both-end modified polydimethylsiloxane, one-end modified polydimethylsiloxane, and both-end side-chain modified polydimethylsiloxane. Polyether-modified silicone surfactants having a polyoxyethylene group or a polyoxyethylene polyoxypropylene group as a modifying group are particularly preferred because they exhibit good properties as an aqueous surfactant.

[0074] Such surfactants may be appropriately synthesized or commercially available products, such as those available from BYK-Chemie Co., Ltd., Shin-Etsu Chemical Co., Ltd., Dow Corning Toray Silicone Co., Ltd., Nippon Emulsion Co., Ltd., and Kyoeisha Chemical Co., Ltd.

[0075] The polyether-modified silicone surfactant is not particularly limited and can be appropriately selected depending on the purpose. For example, it can be a surfactant represented by the general formula (S-1) in which a polyalkylene oxide structure is introduced into the Si part side chain of dimethylpolysiloxane.

[0076] [ka]

[0077] (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.) As the polyether-modified silicone surfactant, commercially available products can be used, such as KF-618, KF-642, KF-643 (Shin-Etsu Chemical Co., Ltd.), EMALEX-SS-5602, SS-1906EX (Nihon Emulsion Co., Ltd.), FZ-2105, FZ-2118, FZ-2154, FZ-2161, FZ-2162, FZ-2163, FZ-2164 (Dow Corning Toray Silicone Co., Ltd.), BYK-33, BYK-387 (BYK-Chemie Co., Ltd.), TSF4440, TSF4452, TSF4453 (Toshiba Silicon Co., Ltd.), and the like.

[0078] The fluorine-based surfactant is preferably a compound having 2 to 16 fluorine-substituted carbon atoms, and more preferably a compound having 4 to 16 fluorine-substituted carbon atoms. Examples of fluorine-based surfactants include perfluoroalkyl phosphate compounds, perfluoroalkyl ethylene oxide adducts, and polyoxyalkylene ether polymer compounds having perfluoroalkyl ether groups in side chains, etc. Among these, polyoxyalkylene ether polymer compounds having perfluoroalkyl ether groups in side chains are preferred because they have low foaming properties, and fluorine-based surfactants represented by general formula (F-1) and general formula (F-2) are particularly preferred.

[0079] [ka]

[0080] In the compound represented by the above 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.

[0081] [General formula (F-2)] C n F 2n+1- CH2CH(OH)CH2-O-(CH2CH2O) a -Y

[0082] In the compound represented by the above general formula (F-2), Y is H or C m F 2m+1 m is an integer from 1 to 6, or CH2CH(OH)CH2-C m F 2m+1 m is an integer between 4 and 6, or C p H 2p+1 where p is an integer from 1 to 19. n is an integer from 1 to 6. a is an integer from 4 to 14.

[0083] As the fluorine-based surfactant, commercially available products may be used. Examples of such commercially available products 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.); Fullard FC-93, FC-95, FC-98, FC-129, FC-135, FC-170C, FC-430, and FC-431 (all manufactured by Sumitomo 3M Limited); Megafa F-470, F-1405, F-474 (all manufactured by Dainippon Ink & Chemicals, Inc.); 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 Chemours); 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 OMNOVA Co., Ltd.), Unidyne DSN-403N (manufactured by Daikin Industries, Ltd.), and the like. Among these, FS-3100, FS-34, FS-300 manufactured by Chemours Co., Ltd., FT-110, FT-250, FT-251, FT-400S, FT-150, FT-400SW manufactured by NEOS Co., Ltd., Polyfox PF-151N manufactured by OMNOVA Co., Ltd., and Unidyne DSN-403N manufactured by Daikin Industries, Ltd. are particularly preferred from the viewpoint of excellent print quality, particularly color development, penetration into paper, wettability, and uniform dyeing.

[0084] The content of the surfactant in the ink is not particularly limited and can be appropriately selected depending on the purpose. From the viewpoints of excellent wettability and ejection stability and improved image quality, the content is preferably from 0.001% by mass to 5% by mass, and more preferably from 0.05% by mass to 5% by mass.

[0085] --Antifoaming agent-- 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, silicone-based defoaming agents are preferred because of their excellent foam breaking effect.

[0086] --Preservative and fungicidal agent-- The antiseptic and antifungal agent is not particularly limited, and examples thereof include 1,2-benzisothiazolin-3-one.

[0087] --Rust inhibitor-- The rust inhibitor is not particularly limited, and examples thereof include acid sulfite and sodium thiosulfate.

[0088] --pH adjuster-- There are no particular limitations on the pH adjuster, so long as it is capable of adjusting the pH to 7 or higher, and examples of the pH adjuster include amines such as diethanolamine and triethanolamine.

[0089] -Total solids content- The total solid content of the resin, lubricant, pigment, etc. contained in the ink is preferably 7.0% by mass or more and 14.0% by mass or less. If it is 7.0% by mass or more, the scratch resistance is improved, and if it is 14.0% by mass or less, the ejection stability and storage stability of the ink are good.

[0090] -Ink properties- The physical properties of the ink are not particularly limited and can be appropriately selected depending on the purpose. For example, it is preferable that the viscosity, surface tension, pH, etc. are within the following ranges. The viscosity of the ink at 25°C is preferably from 5 mPa·s to 30 mPa·s, more preferably from 5 mPa·s to 25 mPa·s, in order to improve print density and character quality and to obtain good ejection properties. Here, the viscosity can be measured using, for example, a rotational viscometer (RE-80L manufactured by Toki Sangyo Co., Ltd.). The measurement conditions are 25°C, a standard cone rotor (1°34' x 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., in order to ensure that the ink is appropriately leveled on the recording medium and the drying time of the ink is shortened. The pH of the ink is preferably from 7 to 12, and more preferably from 8 to 11, from the viewpoint of preventing corrosion of metal members that come into contact with the ink.

[0091] <Recording Media> The recording medium used for recording is not particularly limited, but examples thereof include plain paper, glossy paper, special paper, cloth, film, OHP sheets, general-purpose printing paper, and the like.

[0092] <Uses of the image forming apparatus, means provided in the image forming apparatus, and steps included in the image forming method> In the present invention, the image forming apparatus and image forming method refer to an apparatus capable of ejecting ink, various treatment liquids, etc. onto a recording medium, and a method of recording using the apparatus. The recording medium refers to an object onto which ink or various treatment liquids can be attached even temporarily. This image forming apparatus can include not only a head portion that ejects ink, but also means related to feeding, conveying, and discharging a recording medium, and other devices called pre-processing devices and post-processing devices. The image forming apparatus and the image forming method have a heating unit (drying unit) used in a heating step (drying step). The heating unit includes, for example, a unit for heating the print surface or the back surface of a recording medium.

[0093] In addition, the image forming apparatus and image forming method are not limited to those that visualize meaningful images such as characters and figures with ink. For example, they also include those that form patterns such as geometric designs and those that create three-dimensional images. Furthermore, this image forming device includes not only desktop types, but also wide-width image forming devices capable of printing on A0-sized recording media, and continuous-feed printers that can use continuous paper wound into a roll as a recording medium.

[0094] In the present invention, the terms image formation, recording, printing, printing, etc. are all synonymous. Recording medium, media, and printed material are all synonymous.

[0095] Each step in the image forming method of the present invention can be carried out by using each means described here.

[0096] -Ink application means- The ink applying means may be, for example, a liquid ejection head (also called a head or ejection head) having a plurality of nozzle rows for ejecting liquid. An inkjet head may be used as the liquid ejection head. The ink applying means may be, for example, a black ink applying means or a color ink applying means, and the number and arrangement of the ink applying means may be changed as appropriate. Also included are both serial type devices in which the liquid ejection head is moved and line type devices in which the liquid ejection head is not moved.

[0097] -Heating means- The heating means is also called drying means, and examples of the heating means include non-contact heating means and contact heating means. In this embodiment, the non-contact heating means has an irradiation means for irradiating the recording medium with visible light or ultraviolet light having a wavelength of 700 nm or less. As the irradiation means, an ultraviolet light irradiation device or a visible light lamp can be used. For example, UV-LED or LED can be used. The wavelength indicates the peak wavelength. The irradiation means irradiates the recording medium with visible light or ultraviolet light after ink has been applied to the recording medium by the black ink application means or the color ink application means.

[0098] As described above, in this embodiment, the image surface temperature after the irradiation unit irradiates the recording medium is defined as T i (T image (also referred to as θ) the following relationship is satisfied: Tg A <T i <Tg B This makes it possible to prevent unnecessary heating of the carbon black and waviness caused by evaporation of moisture from the recording medium.

[0099] To satisfy such a relationship, for example, it can be controlled by appropriately selecting the types of resin A and resin B. Other examples include a method of changing the heating time such as the irradiation time, a method of changing the conveying speed of the recording medium, a method of changing the wavelength or irradiation intensity of visible light or ultraviolet light, and a method of changing the heating time or heating temperature of a heating means other than the irradiation means.

[0100] Said T i is preferably greater than 50°C and less than 80°C. i When the temperature is higher than 50° C., the drying property is improved, and when the temperature is lower than 80° C., the image density is improved.

[0101] Image surface temperature T i As a method for measuring, for example, a non-contact infrared temperature sensor can be placed near the downstream of the irradiation means, i.e., downstream of the irradiation means and near the position where the irradiation ends (which may be called the drying exit, etc.).

[0102] The contact heating means is not particularly limited, and examples thereof include a heated roller and a heated drum. When a roller or drum is used, the recording medium can be heated by wrapping it around the roller or drum. Heating by the contact heating means can be performed before, during, or after printing.

[0103] The surface temperature of the roller or drum is the image surface temperature T i In this case, waviness due to evaporation of water from the recording medium can be further suppressed.

[0104] The heating time after the ink is applied can be changed as appropriate, but is preferably 0.5 seconds or more, and more preferably 0.5 to 2 seconds. By drying, the resin forms a film, which changes the surface roughness and allows the image glossiness to be controlled, so by setting the heating time to 0.5 seconds or more, the solvent in the image can be sufficiently dried, and the scratch resistance can be improved.

[0105] <First embodiment of image forming apparatus> An image forming apparatus according to a first embodiment will be described with reference to FIGS. Fig. 1 is a perspective view of the apparatus, and Fig. 2 is a perspective view of the main tank. An image forming apparatus 400, which is an example of a recording apparatus, is a serial type image forming apparatus.

[0106] A mechanism section 420 is provided inside an exterior 401 of the image forming apparatus 400. Each ink storage section 411 of the main tanks 410 (410k, 410c, 410m, 410y) for each color of black (K), cyan (C), magenta (M), and yellow (Y) is formed of a packaging material such as an aluminum laminate film. The ink storage section 411 is stored in a storage container case 414 made of, for example, plastic. Thus, the main tanks 410 are used as ink cartridges for each color.

[0107] On the other hand, a cartridge holder 404 is provided at the back side of the opening when the cover 401c of the apparatus body is opened. A main tank 410 is detachably attached to the cartridge holder 404. As a result, each ink outlet 413 of the main tank 410 communicates with an ejection head 434 for each color via a supply tube 436 for each color, and ink can be ejected from the ejection head 434 to a recording medium.

[0108] In this embodiment, the display / input unit 120 may be used to display and input settings.

[0109] Second embodiment of image forming apparatus An image forming apparatus according to a second embodiment will be described with reference to Fig. 3 to Fig. 5. Fig. 3 is a side view of the image forming apparatus, Fig. 4 is a plan view of the main parts of the image forming apparatus, and Fig. 5 is a plan view of the head.

[0110] This image forming device is a serial type inkjet recording device and includes a printing section (image forming section) 101 that prints on a recording medium (hereinafter referred to as "medium") 2 as a printing material, a transport section 102 that transports the medium 2, a roll storage section 103 that stores the medium 2, and a roll winding section 104 that winds up the medium 2.

[0111] This device uses a roll body 1 in which a medium 2 is wound in a roll shape. The roll body 1 is stored in a roll storage section 103, and a pair of transport rollers 31 pulls out the medium 2 from the roll body 1 and delivers it.

[0112] 4, the printing unit 101, which serves as both an example of a black ink applying means and an example of a color ink applying means, is equipped with a liquid ejection head (hereinafter also referred to as a "head") 11 having a plurality of nozzle rows that eject liquid, as a liquid ejection means, mounted on a carriage 12. The carriage 12 is held by a guide member 13 so as to be reciprocatable in the main scanning direction (the direction perpendicular to the paper surface in FIG. 3).

[0113] Here, as shown in FIG. 5, the head 11 has multiple nozzle rows Na to Ne in which multiple (m) nozzles n1 to nm that eject liquid are arranged, and is mounted on a carriage 12 with the nozzle arrangement direction aligned with the medium transport direction (sub-scanning direction).

[0114] The nozzle rows Na to Nc of the head 11 include, for example, color ink nozzle rows used to eject color inks such as black (K), yellow (Y), magenta (M), and cyan (C). The nozzle row Nd of the head 11 includes, for example, a transparent ink nozzle row used to eject transparent ink. The nozzle row Ne of the head 11 includes, for example, a pretreatment liquid nozzle row used to eject pretreatment liquid. Note that, although one head has five nozzle rows Na to Ne in this example, a configuration having a plurality of nozzle rows in a plurality of heads is also possible.

[0115] The transport unit 102 has a transport roller 21 and an opposing roller 22, which are transport means, disposed upstream of the printing unit 101 in the medium transport direction (arrow A direction: sub-scanning direction), and transports the medium 2 between them. Also, a platen member 25 that guides the medium 2 is disposed opposite the printing unit 101.

[0116] The roll winding section 104 includes a winding roll 41 that winds up the medium 2 .

[0117] A pre-heater 51, a print heater 52, and a post-heater 53, which are examples of heating means, are arranged along the transport direction of the medium 2.

[0118] The pre-heater 51 is a heater that heats the medium 2 before the printing area by the printing unit 101. The print heater 52 is a heater that heats the medium 2 in the printing area by the printing unit 101. The post-heater 53 is a heater that heats the medium 2 after printing by the printing unit 101. The pre-heater 51, print heater 52, and post-heater 53 can be electric heaters using ceramics or nichrome wire, or the like.

[0119] Further, an irradiation device 54 that irradiates energy rays such as ultraviolet rays and visible light rays onto the medium 2 is provided downstream of the post heater 53. By irradiating the printing surface with energy rays by the irradiation device 54, the pigment in the ink generates heat and can be dried.

[0120] <Third embodiment of image forming apparatus> An image forming apparatus according to a third embodiment will be described with reference to Fig. 6. Fig. 6 is a diagram illustrating the overall configuration of the image forming apparatus.

[0121] A printing apparatus 1000 (an image forming apparatus according to this embodiment) comprises a paper feed section 100, an image forming section 200, a drying section 300, a reversing section 500 for double-sided printing, and a paper ejection section 600.

[0122] Paper P is conveyed one by one from a paper feed tray 110 of a paper feed section 100 by a feeder 140, temporarily stopped by a pair of registration rollers 130, and then fed to an image forming section 200 at a predetermined timing.

[0123] In the image forming section 200, the paper P is transported to the paper carrying drum 210 via a receiving cylinder 201, and an image is formed on the paper P by the inkjet head 220 on this paper carrying drum 210. At that time, the color of the inkjet head 220 used for image formation is switched depending on the printing mode selected by the operator. The operator can select one of three printing modes, for example, monochrome mode, full color mode, and full color + white mode, depending on the image to be printed.

[0124] When the monochrome mode is selected, only the inkjet head 220K is used for image formation, and the inkjet heads 220C, 220M, 220Y, and 220W remain protected by their caps even during printing operations. When the full-color mode is selected, the inkjet heads 220K, 220C, 220M, and 220Y are used for image formation, and the inkjet head 220W remains protected by its cap even during printing operations. When the full-color + white mode is selected, all of the inkjet heads 220K, 220C, 220M, 220Y, and 220W are used for image formation.

[0125] Thereafter, the paper is transported to the drying device 300 via the delivery drum 202 . In the drying section 300, the paper P is transported on a drying transport belt 302, and a UV light irradiation device 301 irradiates the paper P with UV light, thereby drying the printed image.

[0126] In the case of single-sided printing, the paper P passes through the inversion section 500 and is discharged to the paper discharge tray 610 of the paper discharge section 600. In the case of double-sided printing, the paper P is transported to the inversion roller 520 via the transport roller 510 by a branching claw (not shown). Here, the paper P stops once, then switches back and is transported in the opposite direction. After switching back, the paper P passes through the transport rollers 530, 540, and 550 of the double-sided path, and rejoins the pair of registration rollers 130 of the paper feed section, where image formation on the back side begins. EXAMPLES

[0127] The present invention will be described in more detail below by way of examples, but the present invention is not limited to these examples.

[0128] (Examples 1 to 12, Comparative Examples 1 to 6) <Preparation of black pigment dispersion> 20 g of carbon black (Degussa FW100), 20 mmol of the compound of the following structural formula (1), and 200 mL of ion-exchanged water were mixed in a Silverson mixer (6,000 rpm) at room temperature (25°C) to obtain a slurry. When the pH of the obtained slurry was higher than 4, 20 mmol of nitric acid was added. After 30 minutes, sodium nitrite (20 mmol) dissolved in a small amount of ion-exchanged high-purity water was slowly added to the above mixture. The mixture was then heated to 60°C with stirring and reacted for 1 hour. A modified pigment was produced in which the compound of the following structural formula (1) was added to carbon black. Next, the pH was adjusted to 10 with an aqueous NaOH solution, and a modified pigment dispersion was obtained after 30 minutes. A dispersion containing a pigment bonded to at least one geminal bisphosphonic acid group or geminal bisphosphonic acid sodium salt was subjected to ultrafiltration using a dialysis membrane using high purity ion-exchange water, and then ultrasonic dispersion was performed to prepare a [black pigment dispersion] (pigment solid content: 15% by mass).

[0129] [ka]

[0130] <Preparation of styrene acrylic resin emulsion> In a reaction vessel equipped with a stirrer, reflux condenser, dropping device, and thermometer, 900g of ion-exchanged water and 1g of sodium lauryl sulfate were charged, and the temperature was raised to 70°C while stirring and replacing with nitrogen. The internal temperature was kept at 70°C, and 4g of potassium persulfate was added as a polymerization initiator and dissolved. An emulsion was prepared by adding a total of 1000g of compounds corresponding to the monomers listed in the table to 450g of ion-exchanged water and 3g of sodium lauryl sulfate in the ratios listed in Table 1 under stirring, and the emulsion was continuously dropped into the reaction solution over 4 hours. After the dropwise addition, the emulsion was aged for 3 hours. The obtained aqueous emulsion was cooled to room temperature, and then ion-exchanged water and an aqueous sodium hydroxide solution were added to adjust the solid content to 30% by mass and the pH to 8, to obtain [styrene acrylic resin emulsion 1].

[0131] [Styrene-acrylic resin emulsions 2 to 7] were obtained in the same manner as [Styrene-acrylic resin emulsion 1], except that they were produced according to the formulation (monomer weight ratio) shown in Table 1.

[0132] [Table 1]

[0133] <Preparation of Polyurethane Resin Emulsion> Into an autoclave reactor equipped with a stirrer and a jacket, 500g of amorphous polycarbonate diol (Duranol T5651, manufactured by Asahi Kasei Chemicals) with a number average molecular weight (Mn) of 500, 45.8g of dimethylolpropionic acid, 358g of isophorone diisocyanate (IPDI), 29.4g of triethylamine, and 650g of acetone were charged while introducing nitrogen. Then, the mixture was heated to 80°C and a urethane reaction was carried out over 5 hours to produce a prepolymer. The system was returned to 40°C and then maintained at that temperature. After checking the NCO% present in the system, water was slowly added, and the mixture was heated and stirred for 30 minutes, after which an extender (isophoronediamine (IPDA)) was added and the mixture was heated and stirred for 3 to 6 hours. Finally, the organic solvent was removed to obtain a polyurethane resin emulsion with a solid content concentration of 31% by mass. The volume average particle size of the polyurethane resin in the obtained polyurethane resin emulsion was 106 nm, and the glass transition temperature was -22.02°C.

[0134] <Ink preparation example> The components were mixed and stirred according to the formulations shown in Tables 2 and 3, and then filtered through a polypropylene filter (product name: Profile Star, manufactured by Nippon Pall Corporation, average pore size: 1.5 μm) to prepare each of the inks shown in Tables 2 and 3. The silicone surfactant was a polyether-modified siloxane copolymer manufactured by Evonik under the product name: TEGO WET270.

[0135] The product names and manufacturer names for the ingredients in the table are as follows: 3-Methoxy-3-ethyl-1-propanol: manufactured by Tokyo Chemical Industry Co., Ltd. 3-Methyl-1,3-butanediol: Tokyo Chemical Industry Co., Ltd. 1,3-Butanediol: Tokyo Chemical Industry Co., Ltd. 2-Propyl-1,3-pentanediol: manufactured by Tokyo Chemical Industry Co., Ltd.

[0136] In the table, the "water content" is the value obtained by subtracting the solid content of the coloring material and resin from the total amount of ink, then subtracting the amount of surfactant, and then subtracting the total amount of organic solvent.

[0137] <Evaluation and Measurement> <<Image formation>> The image forming apparatus of FIG. 6 was equipped with cut-sheet paper (product name: Lumi Art Gloss, manufactured by Stora Enso, basis weight: 130 g / m) as a recording medium. 2 , paper width: 521 mm) and printed a black image with a recording resolution of 1,200 dpi x 1,200 dpi. Next, the recording medium was irradiated with light from a UV-LED lamp (device name: Semray UV 4003, manufactured by Heraeus) as an irradiation means (irradiation device) under the conditions in the table below. In Comparative Example 5, IR (infrared irradiation means) was used, and in Comparative Example 6, hot air means was used.

[0138] When forming an image, the temperature and time were controlled by adjusting the irradiation intensity of the irradiation device and the conveying speed of the recording medium. Image surface temperature T i The measurement was performed by installing a non-contact infrared temperature sensor downstream of the irradiation means, infrared irradiation means, and hot air means (drying outlet) and measuring the image surface temperature immediately after drying.

[0139] The surface temperatures of the pre-heater, print heater, and post-heater are the image surface temperature T i The following was made:

[0140] <<Image density>> Ink deposition amount on recording medium: 0.9μL / cm 2 The image density of the image formed in the above step was measured using an image densitometer (X-Rite eXact manufactured by X-Rite Corporation). The image density was evaluated according to the following evaluation criteria. ⊚, ◯, and △ are acceptable.

[0141] [Evaluation Criteria] ◎: Image density is 2.5 or more ○: Image density is 2.3 or more and less than 2.5 △: Image density is 2.0 or more and less than 2.3 ×: Image density is less than 2.0

[0142] <<Drying>> The image area formed on the recording medium was rubbed with a crock meter 3 minutes after printing, and the image was visually inspected to determine whether scraping had occurred. Above a certain drying energy, the image would no longer scrape off. The drying energy required to prevent scraping was measured. The drying energy was calculated as the product of the amount of light irradiated by the irradiation device and the irradiation time. Drying performance was evaluated according to the following evaluation criteria. ◎, ◯, and △ are acceptable.

[0143] [Evaluation Criteria] ◎: Drying energy required is 1500mJ / cm 2 is less than ○: Energy required is 1500mJ / cm 2 More than 2000mJ / cm 2 is less than △: Energy required is 2000mJ / cm 2 More than 2500mJ / cm 2 is ×: Energy required is 2500mJ / cm 2 That's all.

[0144] <<Paper waviness>> The recording medium (printed matter) on which the image was formed was visually observed and evaluated. The paper waviness was evaluated according to the following evaluation criteria. ⊚, ◯, and △ are acceptable.

[0145] [Evaluation Criteria] ◎: No curling or waviness is observed on the printed matter. ○: The print is slightly wavy, but there is almost no curl. △: Wavy wrinkles appear all over the print, and curls can be seen at the edges. ×: The print curls and has wavy wrinkles all over.

[0146] The results are also shown in the table below. In the table, the drying method mainly describes the irradiation means, infrared irradiation means, and hot air means.

[0147] [Table 2]

[0148] [Table 3]

[0149] From the above results, it is possible to irradiate visible light or ultraviolet light with a wavelength of 700 nm or less and obtain a TgA <T i <Tg B It can be seen that by satisfying the above, an image having a high image density, good drying properties, and good paper waviness can be formed.

[0150] (Example 13 and Example 14) Next, in the same manner as for the black ink of the above example, the components were mixed and stirred according to the formulation shown in Table 4 below, and then filtered through a polypropylene filter (product name: Profile Star, manufactured by Nippon Pall Corporation, average pore size: 1.5 μm) to prepare each of the ink sets shown in Table 4. Next, an image was formed in the following manner, and the image density was evaluated. Drying property and paper waviness were evaluated in the same manner as in the above-mentioned examples.

[0151] <Image formation> The image forming apparatus of FIG. 6 was equipped with cut-sheet paper (product name: Lumi Art Gloss, manufactured by Stora Enso, basis weight: 130 g / m) as a recording medium. 2 A mixed image of four colors (black, cyan, magenta, and yellow) was printed at a recording resolution of 1,200 dpi x 1,200 dpi. At this time, either high gloss printing mode or low gloss printing mode was selected, and in high gloss printing mode the inks were ejected in the order of black, cyan, magenta, and yellow, and in low gloss printing mode the inks were ejected in the order of yellow, magenta, cyan, and black. Next, the recording medium was irradiated with light from a UV-LED lamp (device name: Semray UV 4003, manufactured by Heraeus) under the conditions in the table below. In addition, the winding device, the irradiation intensity of the irradiation device, the conveying speed of the recording medium, and the image surface temperature T i The measurement, preheater, etc. were the same as in the above embodiment.

[0152] <Image density> Ink deposition amount on recording medium: 0.9μL / cm 2The image density of the image formed in the above step was measured using an image densitometer (X-Rite eXact manufactured by X-Rite Corporation). The image density was evaluated according to the following evaluation criteria. ⊚, ◯, and △ are acceptable.

[0153] [Black Evaluation Criteria] ◎: Image density is 2.5 or more ○: Image density is 2.3 or more and less than 2.5 △: Image density is 2.0 or more and less than 2.3 ×: Image density is less than 2.0

[0154] [Cyan Evaluation Criteria] ◎: Image density is 2.5 or more ○: Image density is 2.3 or more and less than 2.5 △: Image density is 2.0 or more and less than 2.3 ×: Image density is less than 2.0

[0155] [Magenta Evaluation Criteria] ◎: Image density is 2.3 or more ○: Image density is 2.2 or more and less than 2.3 △: Image density is 2.0 or more and less than 2.2 ×: Image density is less than 2.0

[0156] [Yellow evaluation criteria] ◎: Image density is 1.4 or more ○: Image density is 1.3 or more and less than 1.4 △: Image density is 1.2 or more and less than 1.3 ×: Image density is less than 1.2

[0157] The results are also shown in the table below.

[0158] [Table 4]

[0159] From the above results, even when color ink is used, the Tg C <T i It can be seen that by satisfying the above, an image having a high image density, good drying properties, and good paper waviness can be formed. [Explanation of symbols]

[0160] 2 Recording media 11 Liquid ejection head 12 Carriage 13 Guide member 21 Transport roller 22 Counter roller 25 Platen member 31 Transport roller pair 41 Rolls 51 Preheater 52 Print heater 53 Post Heater 54 Irradiation device 101 Printing Department 102 Conveyor 103 Roll storage section 104 Roll winding section 120 Display input means 400 Image forming device 401 Exterior of image forming device 401c Device body cover 404 Cartridge Holder 410 Main Tank 410k, 410c, 410m, 410y Main tanks for black (K), cyan (C), magenta (M), and yellow (Y) 411 Ink storage unit 413 Ink outlet 414 Storage container case 420 Mechanism Department 434 Discharge Head 436 Supply Tube [Prior art documents] [Patent documents]

[0161] [Patent Document 1] JP 2002-327138 A [Patent Document 2] JP 2006-140655 A [Patent Document 3] JP 2004-82709 A [Patent Document 4] JP 2000-225719 A [Patent Document 5] JP 2016-196177 A

Claims

1. a black ink containing water, an organic solvent, carbon black, and a resin A and a resin B; a black ink applying means for applying the black ink to a recording medium; an irradiation means for irradiating the recording medium onto which the black ink has been applied with visible light or ultraviolet light having a wavelength of 700 nm or less, The glass transition temperature of the resin A is Tg Ａ The glass transition point of the resin B is Tg Ｂ and the image surface temperature immediately after the irradiation means irradiates the recording medium is T ｉ When Tg Ａ <T ｉ <Tg Ｂ An image forming apparatus comprising:

2. 2. The image forming apparatus according to claim 1, wherein the resin A and the resin B are styrene-acrylic resins.

3. The Tg Ａ is 20° C. or more and 50° C. or less, The Tg Ｂ is 80°C or more and 150°C or less, Said T ｉ 3. The image forming apparatus according to claim 1, wherein the temperature is higher than 50° C. and lower than 80° C.

4. a color ink containing water, an organic solvent, a color material, and a resin C; a color ink applying means for applying the color ink to the recording medium, The glass transition temperature of the resin C is Tg Ｃ When Tg Ｃ <T ｉ 4. The image forming apparatus according to claim 1, wherein the above-mentioned condition is satisfied.

5. a black ink application step of applying a black ink containing water, an organic solvent, carbon black, a resin A, and a resin B to a recording medium; an irradiation step of irradiating the recording medium to which the black ink has been applied with visible light or ultraviolet light having a wavelength of 700 nm or less, The glass transition temperature of the resin A is Tg Ａ The glass transition point of the resin B is Tg Ｂ The surface temperature of the image immediately after the recording medium is irradiated in the irradiation step is T ｉ When Tg Ａ <T ｉ <Tg Ｂ An image forming method, comprising the steps of:

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