Image forming apparatus and image forming method using the same

Abstract

To provide an image forming device provided with a heating part that can achieve both efficient heating of an image and suppression of a deformation of a recording body.SOLUTION: An image forming device is provided with an image forming unit that forms an image corresponding to image data, on a recording medium. The image forming unit comprises a heating part that heats the image formed on the recording medium. The heating part has a light source that radiates at least infrared rays of light and a wavelength selecting device that selectively attenuates far-infrared rays, of the infrared rays radiated from the light source.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to an image forming apparatus and an image forming method using the same. [Background technology]

[0002] In an image forming apparatus such as an inkjet printer, when an image is formed by directly applying ink containing a coloring material or the like onto a recording medium such as paper or resin using an inkjet head, it is known that the image formed on the recording medium is dried by heating with a light source or the like, and the image is fixed onto the recording medium. In this type of image forming apparatus, from the viewpoint of improving image quality, it is required to quickly dry the image on the recording medium and to suppress deformation of the recording medium, such as curling (warping), caused by heat. For example, JP 2019-162773 A (Patent Document 1) proposes an image forming apparatus (liquid ejection apparatus) in which a filter that passes only infrared rays having a wavelength that resonates with the image on the recording medium (i.e., the ink) is arranged between the IR light source and the recording medium. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2019-162773 A Summary of the Invention [Problem to be solved by the invention]

[0004] According to the above-mentioned Patent Document 1, since only infrared rays having a wavelength that resonates with the image reach the recording medium, it is possible to suppress the temperature rise of the recording medium, and thus to suppress deformation such as curling of the recording medium. However, since the image forming device of Patent Document 1 only infrared rays having a wavelength that resonates with the image reach the recording medium, there is an absolute lack of thermal energy for heating the image, making it difficult to dry the image quickly. Therefore, a technology for quickly drying the image by efficiently heating the image while suppressing deformation of the recording medium has not yet been realized, and its development is eagerly awaited.

[0005] In view of the above-mentioned situation, an object of the present disclosure is to provide an image forming apparatus equipped with a heating section that efficiently heats an image while suppressing deformation such as curling of the recording medium, thereby quickly drying the image, and an image forming method using the same. [Means for solving the problem]

[0006] The present inventors have intensively studied an image forming apparatus capable of achieving the above-mentioned object, and have arrived at the present disclosure. That is, the inventors have focused on the idea of ​​suppressing the temperature rise of the recording medium by attenuating the light of a wavelength that resonates with the recording medium among the light radiated from the light source onto the recording medium, while allowing the light of other wavelengths to reach the recording medium, thereby efficiently utilizing the thermal energy of the light source for drying the image. Specifically, the inventors have found that most of the light of a wavelength that resonates with the recording medium and is absorbed by the recording medium is far infrared, and have come up with the idea of ​​providing an image forming apparatus with a heating unit including a wavelength selection device that selectively attenuates far infrared among the infrared rays that are a part of the light radiated from the light source onto the recording medium, thereby completing the present disclosure.

[0007] That is, according to one aspect of the present disclosure, there is provided an image forming apparatus including an image forming unit that forms an image on a recording medium in accordance with image data, the image forming unit including a heating section that heats the image formed on the recording medium, the heating section including a light source that radiates at least infrared light among light beams, and a wavelength selection device that selectively attenuates far infrared light among the infrared light radiated from the light source.

[0008] It is preferable that the wavelength selection device further selectively attenuates a portion of the mid-infrared radiation among the infrared radiation.

[0009] It is preferable that the wavelength selection device further selectively attenuates mid-infrared light in a wavelength range longer than 2800 nm among the infrared light.

[0010] It is preferable that the wavelength selection device controls the thermal energy of light in a wavelength range of 2800 nm or less radiated onto the recording medium to be at least 20 times the thermal energy of light in a wavelength range longer than 2800 nm radiated onto the recording medium.

[0011] The wavelength selective device preferably includes one or more neutral density filters. The wavelength selection device preferably includes a reflecting mirror.

[0012] The reflecting mirror has a surface that absorbs the far infrared rays radiated from the light source, and the surface is preferably made of ceramics.

[0013] The ceramic is preferably made of aluminum oxide. The reflecting mirror has a surface that absorbs the far infrared rays radiated from the light source, and the surface is preferably anodized.

[0014] The light source preferably has a color temperature of 2400K or higher. According to another aspect of the present disclosure, there is provided an image forming method including a step of forming the image on the recording medium by using the image forming apparatus. Effect of the Invention

[0015] According to the present disclosure, it is possible to provide an image forming apparatus equipped with a heating section that efficiently heats an image while suppressing deformation such as curling of the recording medium, thereby quickly drying the image, and an image forming method using the same. [Brief description of the drawings]

[0016] [Figure 1] FIG. 1 is a graph illustrating the relationship between the wavelength of light (horizontal axis) and the absorptance of light of that wavelength (vertical axis) for a cyan ink and recording medium. [Diagram 2] FIG. 2 is a schematic diagram showing an example of the configuration of an image forming unit provided in the image forming apparatus according to the present embodiment. [Diagram 3] FIG. 3 is a schematic diagram showing an example of the configuration of a heating section provided in the image forming unit. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Hereinafter, an embodiment of the present disclosure (hereinafter also referred to as "the present embodiment") will be described with reference to the drawings. In the drawings used in the following description of the present embodiment, the same reference numerals represent the same or corresponding parts. In addition, in the drawings, the scale is appropriately adjusted to make each component easier to understand, and the scale of each component shown in the drawings does not necessarily match the scale of the actual component. In this specification, an expression in the form of "A~B" means the upper and lower limits of a range (i.e., A or more and B or less), and when no unit is described for A and only a unit is described for B, the unit of A and the unit of B are the same.

[0018] Here, in this specification, "infrared rays" refers to electromagnetic waves having a longer wavelength than the red wavelength of visible light and a shorter wavelength than radio waves, specifically, electromagnetic waves having a wavelength of 0.7 to 1000 μm. The above-mentioned infrared rays are generally classified into "near infrared rays", "mid infrared rays", and "far infrared rays". In this specification, "near infrared rays" refers to electromagnetic waves having a wavelength of 0.7 μm or more and less than 2.5 μm, "mid infrared rays" refers to electromagnetic waves having a wavelength of 2.5 μm or more and less than 4 μm, and "far infrared rays" refers to electromagnetic waves having a wavelength of 4 μm or more and 1000 μm.

[0019] [Image forming device] The image forming apparatus according to the present embodiment is an image forming apparatus including an image forming unit that forms an image on a recording medium according to image data. The image forming unit includes a heating section that heats the image formed on the recording medium. The heating section includes a light source that radiates at least infrared light, and a wavelength selection device that selectively attenuates far infrared light from the infrared light radiated from the light source. The image forming apparatus having such characteristics realizes both efficient heating of the image and suppression of deformation of the recording medium by the heating section, and can therefore quickly dry the image while suppressing deformation of the recording medium.

[0020] The reason why the image forming apparatus according to the present embodiment can quickly dry an image while suppressing deformation of the recording medium is presumed to be as follows. That is, the heating section of the image forming apparatus according to the present embodiment has a light source that radiates at least infrared light among light, and a wavelength selection device that selectively attenuates far infrared light among the infrared light radiated from the light source. Far infrared light includes many light wavelengths that are absorbed by the recording medium by resonating with the recording medium. Therefore, since the heating section has a wavelength selection device that selectively attenuates far infrared light, the light radiated from the light source and having a wavelength that resonates with the recording medium is less likely to reach the recording medium, so that the temperature rise of the recording medium can be suppressed, and thus deformation of the recording medium can be suppressed. On the other hand, since the heating section has the light source and the wavelength selection device, it can allow light of a wavelength other than far infrared light to reach the recording medium, and thus the thermal energy of the light radiated from the light source can be efficiently used to dry the image.

[0021] FIG. 1 is a graph for explaining the relationship between the wavelength of light (horizontal axis) and the absorptance of light at that wavelength (vertical axis) for a cyan ink and recording medium. In FIG. 1, A shows the relationship between the wavelength of light (horizontal axis) and the absorptance of light at that wavelength (vertical axis) in the ink, and B shows the relationship between the wavelength of light (horizontal axis) and the absorptance of light at that wavelength (vertical axis) in a recording medium (specifically, plain paper). According to FIG. 1, A (ink) has a significantly higher absorptance of light on the short wavelength side, such as near infrared rays, than B (recording medium), and B (recording medium) has a higher absorptance of light on the long wavelength side, such as far infrared rays, than A (ink). Therefore, based on FIG. 1, it is presumed that when the heating unit has the light source and wavelength selection device, the temperature rise of the recording medium that absorbs far infrared rays can be suppressed, and the ink absorbs light other than far infrared rays, thereby efficiently drying the image.

[0022] From the above, it is believed that the image forming apparatus according to this embodiment is capable of quickly drying an image while suppressing deformation of the recording medium. The image forming apparatus according to this embodiment will be described in further detail below.

[0023] The image forming apparatus according to the present embodiment is preferably an image forming apparatus implemented as an inkjet printer, for example. Such an image forming apparatus includes the image forming unit, a recording medium feeding unit, a recording medium discharge unit, and a liquid crystal display screen in its housing. The recording medium feeding unit feeds out the recording medium housed in the recording medium feeding unit and conveys the recording medium to the image forming unit in response to a print start job based on a control unit included in the image forming unit. The recording medium discharge unit discharges the recording medium on which the image has been fixed in the image forming unit to the outside of the housing. The liquid crystal display displays information for the user. The liquid crystal display can also accept operations from the user as a touch panel. In the image forming apparatus according to the present embodiment, the recording medium feeding unit, the recording medium discharge unit, the liquid crystal display screen, and other units that are conventionally known can be used.

[0024] [Image forming unit] Next, the image forming unit will be described in detail with reference to FIG. 2. FIG. 2 is a schematic diagram showing an example of the configuration of an image forming unit provided in an image forming apparatus according to this embodiment. Specifically, the image forming unit forms an image on a recording medium by directly applying ink onto the recording medium using an inkjet head in a sheet-fed image forming apparatus. The X direction, Y direction, and Z direction shown in FIG. 2 respectively represent the overall length direction, depth direction (width direction), and height direction of the image forming unit. The recording medium is transported in the X direction (the direction indicated by the arrow C in FIG. 2).

[0025] The image forming unit includes a control unit having a CPU as a print engine in an inkjet printer, for example. The control unit operates each unit of the image forming unit, which will be described later, to perform full-color printing by the CPU executing a given program based on image data input thereto. The control unit may be realized by including one or more dedicated circuits such as ASICs. In addition to the control unit, the image forming unit includes at least a reaction liquid deposition unit 103, an image forming unit 104, and a heating unit 110, which will be described below, as shown in FIG. 2.

[0026] That is, the image forming unit includes a reaction liquid applying section 103 that applies a reaction liquid onto the recording medium 108 to form an image forming area on the recording medium 108, an image forming section 104 that applies ink that reacts with the reaction liquid onto the image forming area according to image data to form an image, and a heating section 110 that heats the ink on the recording medium on which the image has been formed to dry the image formed on the recording medium. The image forming unit further includes a transport section 107 that transports the recording medium 108 in the direction of arrow C. The reaction liquid applying section 103 includes a roller, so that the reaction liquid can be applied onto the recording medium 108 using the roller. The image forming section 104 includes an inkjet recording head, so that the ink can be ejected. The reaction liquid applying section 103, the image forming section 104, and the heating section 110 each have a width in the Y direction that corresponds to the recording medium 108.

[0027] In the image forming unit, each part operates to perform full-color printing under the control of the control unit. First, the transport unit 107 transports the recording medium 108 in the direction of the arrow C. Next, the reaction liquid application unit 103 applies a reaction liquid to the recording medium 108 transported in the direction of the arrow C to form an image forming area on the recording medium 108, and then the image forming unit 104 applies ink to the image forming area according to image data to form an image on the recording medium 108. Thereafter, the recording medium 108 on which the image has been formed is transported in the direction of the arrow C by the transport unit 107 and moves to a position where light radiated from a light source possessed by the heating unit 110 reaches. Finally, the heating unit 110 dries liquid such as ink on the recording medium 108 by radiating light from the light source to the recording medium 108, and the image is dried and fixed on the recording medium 108.

[0028] The main components constituting the image forming unit, that is, the reaction liquid applying section 103, the image forming section 104, the heating section 110 and the transport section 107, will be described in more detail below.

[0029] <Reaction solution application section> The reaction liquid applying unit 103 applies the reaction liquid onto the recording medium 108 in the image forming unit to form an image forming area. In this specification, the term "recording medium" refers to a recording medium used to record an image formed in this type of image forming device, and examples of the recording medium include paper, a film made of resin or metal, a wooden board, cardboard, and cloth. Specific examples of the recording medium include plain paper and OHP (Over Head Projector) film. The recording medium may be a long sheet wound into a roll, or may be a leaf cut to a predetermined size.

[0030] Furthermore, in this specification, the term "image forming area" corresponds to the area where the image is finally formed, and means, so to speak, the area that serves as the base of the image formed with the intention of performing subsequent operations appropriately. Specifically, the "image forming area" is formed by applying a reactive liquid onto the recording medium. Ink is applied to all or part of the image forming area by the image forming unit 104. In this specification, the term "reactive liquid" refers to a liquid containing a component that reacts with the solid content (e.g., pigment, etc.) contained in the ink described below. Furthermore, the reactive liquid "reacts" with the ink (particularly the solid content contained in the ink) means that at least one of the following occurs: the ink aggregates due to the above-mentioned component of the reactive liquid, and the ink becomes highly viscous.

[0031] The reaction liquid applying unit 103 has a reaction liquid container that contains the reaction liquid, and a reaction liquid applying member that applies the reaction liquid contained in the reaction liquid container to the recording medium 108. The reaction liquid applying member may be, for example, a member that can apply the reaction liquid solidly onto the recording medium by using a roller coating method, a bar coating method, a spray coating method, or the like, or a member that can execute a method using an inkjet recording head, etc., as long as it can form an image forming area by applying the reaction liquid to the recording medium. For this reason, for example, a gravure offset roller is suitable as the reaction liquid applying member. Furthermore, an inkjet recording head may be used. However, in order to effectively aggregate or increase the viscosity of the components in the ink by contacting with the ink, it is preferable that the reaction liquid is solidly applied onto the recording medium by the gravure offset roller. In this specification, the "recording head" refers to a device that applies liquid onto the recording medium by having a nozzle portion that has an orifice at one end and incorporates an actuator, an electric circuit portion that drives the actuator, and a liquid supply portion that supplies various liquids to the nozzle portion.

[0032] The amount of reaction liquid applied by the reaction liquid application unit 103 onto the recording medium is not particularly limited, and any amount of liquid permitted by this type of image forming apparatus can be applied onto the recording medium. Furthermore, the reaction liquid application unit 103 can dry the reaction liquid that has formed an image forming area on the recording medium.

[0033] (Reaction solution) The reaction liquid refers to a liquid containing a component that reacts with the solid content (such as a pigment) contained in the ink as described above. The reaction liquid is preferably, for example, an acidic liquid. This allows the reaction with components (such as a resin or pigment) having an anionic group in the ink, thereby flocculating or increasing the viscosity of these. Instead of being acidic, the reaction liquid may contain a polyvalent metal salt or a cationic resin, thereby flocculating or increasing the viscosity of the pigment in the ink or the anionic group in the resin. The reaction liquid preferably does not contain a coloring material (pigment or dye) as described below.

[0034] When the reaction liquid is acidic, the acid used to make the reaction liquid acidic is not particularly limited, but from the viewpoint of reacting with the carboxylic acid group in the ink, it is preferable to use an acid having an acid dissociation constant (pKa) lower than 4.5. Examples of such acids include inorganic acids such as hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, and carbonic acid, organic acids having a carboxyl group, organic acids having a sulfonic group, and organic acids having a phosphoric acid group. Furthermore, when considering the quality of the final form of the recording medium (i.e., yellowing of the printed recording medium, image storage stability, etc.), organic acids are more preferable than inorganic acids as the acid used to make the reaction liquid acidic. Examples of such organic acids include citric acid, isocitric acid, oxalic acid, maleic acid, fumaric acid, malonic acid, succinic acid, glutaric acid, adipic acid, phthalic acid, isophthalic acid, terephthalic acid, 2-pyrrolidone-5-carboxylic acid, benzoic acid, benzoic acid derivatives, salicylic acid, ascorbic acid, malic acid, benzenesulfonic acid, benzenesulfonic acid derivatives, pyruvic acid, and oxaloacetic acid. When the reaction liquid contains an acid, the content (mass %) of the acid is preferably from 1 mass % to 50 mass % based on the mass of the entire reaction liquid.

[0035] When the reaction solution contains a polyvalent metal salt, the polyvalent metal salt may be a salt of a metal having a valence of 2 or more. For example, Ca 2+ , Cu 2+ , Ni 2+ , Mg 2+ , Sr 2+ , B.A. 2+ and Zn 2+ Salts of divalent metals such as Fe 3+ , Cr 3+ , Y 3+ and Al 3+Examples of the salt include salts of trivalent metals such as carbonates, sulfates, nitrates, hydrochlorides, organic acid salts, borates, and phosphates. The reaction solution containing the polyvalent metal salt is preferably adjusted in pH for dissolving the polyvalent metal salt as necessary. Examples of salts preferable as the polyvalent metal salt include calcium nitrate, calcium chloride, aluminum nitrate, and aluminum chloride. When the reaction solution contains a polyvalent metal salt, the content (mass %) of the polyvalent metal salt is preferably 1 mass % or more and 20 mass % or less with respect to the mass of the entire reaction solution.

[0036] When the reaction liquid contains a cationic resin, the cationic resin contained in the reaction liquid is not particularly limited, but it is preferable to use a resin having a quaternary amine, for example, from the viewpoint of the effect per added amount. For example, cationic resins include polyallylamine, polyamine, cationic modified acrylic acid resin, cationic modified (meth)acrylic resin, cationic modified vinyl resin, cationic urethane resin, and copolymers thereof. When the reaction liquid contains a cationic resin, the content (mass%) of the cationic resin is preferably 1% by mass or more and 40% by mass or less, and more preferably 1% by mass or more and 10% by mass or less, based on the mass of the total reaction liquid. Here, when "(meth)acrylic" and "(meth)acrylate" are described in this specification, they respectively mean "both or either of acrylic and methacrylic" and "both or either of acrylate and methacrylate".

[0037] The reaction liquid may contain additives such as solvents and surfactants as necessary, in addition to the above-mentioned components that aggregate the solids in the ink or increase the viscosity. Examples of solvents that can be contained in the reaction liquid include water, glycerin, propylene glycol, dipropylene glycol, tripropylene glycol, tetrapropylene glycol, polypropylene glycol, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, decaglyceryl, 1,4-butanediol, 1,3-butanediol, 1,2,6-hexanetriol, 2-pyrrolidinone, dimethylimidazolidinone, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monobutyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monopropyl ether, triethylene glycol monobutyl ether, tetraethylene glycol monomethyl ether, tetra ... tetraethylene glycol monopropyl ether, tetraethylene glycol monomethyl ether, tetraethylene glycol monoethyl ether, tetraethylene glycol monopropyl ether, tetraethylene glycol monobutyl ether, tetraethylene glycol monoethyl ether, tetraethylene glycol monoethyl ether, tetraethylene glycol monopropyl ether, tetraethylene glycol monoethyl ether, tetraethylene glycol monopropyl ether, tetraethylene glycol monoethyl ether, tetraethylene glycol monopropyl ether, tetraethylene glycol monopropyl ether, tetraethylene glycol monoethyl ether, tetraethylene glycol monopropyl ether, tetraethylene glycol monopropyl ether, tetraethylene glycol monoethyl ether, tetraethylene glycol monopropyl ether, tetraethylene glycol monopropyl ether, tetraethylene glycol monopropyl ether, tetraethylene glycol monopropyl ether, tetraethylene glycol monopropyl ether, Examples of the propylene glycol monoethyl ether include propylene glycol monobutyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monopropyl ether, diethylene glycol monobutyl ether, tripropylene glycol monomethyl ether, tripropylene glycol monoethyl ether, tripropylene glycol monopropyl ether, tripropylene glycol monobutyl ether, tetrapropylene glycol monomethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, triethylene glycol diethyl ether, triethylene glycol dibutyl ether, dipropylene glycol dibutyl ether, tripropylene glycol dibutyl ether, 3-methyl-2,4-pentanediol, diethylene glycol monoethyl ether acetate, 1,2-hexanediol, 1,2-pentanediol, and 1,2-butanediol.

[0038] The above solvent can provide the reaction liquid with physical properties such as viscosity that make it easy to apply the reaction liquid to various recording media. The above solvent is preferably used alone or in combination of two or more of the above-mentioned examples. In particular, it is preferable to include water as a part of the solvent from the viewpoints of coating property, drying property, image quality, safety, etc.

[0039] As the surfactant that can be contained in the reaction liquid, any of cationic, anionic, amphoteric and nonionic surfactants can be used. For example, any of the surfactants that can be contained in the ink described later can be contained in the reaction liquid. The content (mass%) of the surfactant in the reaction liquid is preferably 0.1 mass% or more and 10 mass% or less, and more preferably 2 mass% or more and 8 mass% or less, based on the mass of the total reaction liquid. The reaction liquid can contain other additives for various purposes. For example, polysaccharides, viscosity adjusters, resistivity adjusters, film-forming agents, ultraviolet absorbers, antioxidants, color-fading inhibitors, antifungal agents, rust inhibitors, and the like can be added as necessary. Furthermore, it is also possible to contain oil droplet particles such as liquid paraffin, dioctyl phthalate, tricresyl phosphate, and silicone oil, ultraviolet absorbers, color-fading inhibitors, and fluorescent brighteners in the reaction liquid.

[0040] <Image forming section> The image forming unit 104 forms an image by applying ink that reacts with the reaction liquid onto the imaging area in an image forming unit according to image data. As the image forming unit 104, it is preferable to use an inkjet recording head (hereinafter, a recording head that ejects ink is also referred to as an "inkjet head") and eject ink from the inkjet head to apply it to the recording medium 108. As a method for ejecting ink, various conventionally known methods can be used, such as a method of applying mechanical energy to ink and a method of applying thermal energy to ink.

[0041] The inkjet head is arranged along the Y direction, and the ejection ports for ejecting ink are arranged across the entire width of the recording medium 108. The inkjet head has an ejection port surface on which an ejection port array is formed, and the gap between the ejection port surface and the recording medium 108 facing the ejection port surface can be, for example, about 0.1 to several mm.

[0042] The image forming unit 104 may have a plurality of inkjet heads to apply one or more different colors of ink selected from the group consisting of cyan, magenta, yellow, and black (CMYK) to the recording medium 108. For example, when forming a large number of unit areas that constitute an image using four colors of ink, CMYK, the image forming unit 104 may have four inkjet heads that eject the four colors of ink, CMYK, respectively. These inkjet heads are arranged in a line in the X direction. In addition to the inkjet heads that eject the above four colors of ink, the image forming unit 104 may further have an inkjet head for ejecting a liquid that protects the ink on the recording medium 108. In this specification, the term "ink" may be used to refer to one or more colors of ink collectively. In the following description, the "ink" is described on the premise that the ink is water-based ink, but it may also be oil-based ink as long as the effect of the present disclosure is achieved. In addition, when the ink "reacts" with the reaction liquid, it means that at least one of the following occurs: the ink aggregates due to the components in the reaction liquid (such as polyvalent metal salts) as described above, and the ink becomes highly viscous.

[0043] The amount of ink applied by the image forming unit 104 onto the image forming area is not particularly limited, and any amount of ink allowed in this type of image forming apparatus can be applied onto the image forming area.

[0044] (ink) The inks used are of various colors including cyan, magenta, yellow, and black (CMYK). By using one or more inks of these colors selected from the group consisting of CMYK, a primary color, a multi-color, or a halftone can be formed for each of the many unit areas that make up an image. The inks can contain various components such as coloring materials, resins, aqueous media, surfactants, and other additives. Each component that makes up the ink will be described below.

[0045] i) Coloring material The coloring material contained in the ink may be a pigment or a dye. Any conventionally known pigment may be used as the pigment without any restrictions. For example, water-dispersible pigments, solvent-dispersible pigments, etc. may be used as the pigment. Specifically, organic pigments such as insoluble pigments and lake pigments, and inorganic pigments such as carbon black may be preferably used.

[0046] The insoluble pigment is not particularly limited, but for example, azo, azomethine, methine, diphenylmethane, triphenylmethane, quinacridone, anthraquinone, perylene, indigo, quinophthalone, isoindolinone, isoindoline, azine, oxazine, thiazine, dioxazine, thiazole, phthalocyanine, diketopyrrolopyrrole, etc. can be preferably used. Specifically, the following pigments represented by CI (Color Index) numbers can be preferably used.

[0047] Examples of pigments that can be used for magenta or red include CI Pigment Red 2, CI Pigment Red 3, CI Pigment Red 5, CI Pigment Red 6, CI Pigment Red 7, CI Pigment Red 15, CI Pigment Red 16, CI Pigment Red 48:1, CI Pigment Red 53:1, CI Pigment Red 57:1, CI Pigment Red 122, CI Pigment Red 123, CI Pigment Red 139, CI Pigment Red 144, CI Pigment Red 149, CI Pigment Red 166, CI Pigment Red 177, CI Pigment Red 178, and CI Pigment Red 222.

[0048] Examples of pigments that can be used for orange or yellow include CI Pigment Orange 31, CI Pigment Orange 43, CI Pigment Yellow 12, CI Pigment Yellow 13, CI Pigment Yellow 14, CI Pigment Yellow 15, CI Pigment Yellow 15:3, CI Pigment Yellow 17, CI Pigment Yellow 74, CI Pigment Yellow 93, CI Pigment Yellow 94, CI Pigment Yellow 128, and CI Pigment Yellow 138.

[0049] Examples of pigments that can be used for green or cyan include CI Pigment Blue 15, CI Pigment Blue 15:2, CI Pigment Blue 15:3, CI Pigment Blue 16, CI Pigment Blue 60, and CI Pigment Green 7.

[0050] In addition, when red, green, blue or other intermediate colors are required, the following pigments may be used alone or in combination of two or more: For example, CI Pigment Red 209, CI Pigment Red 224, CI Pigment Red 194, CI Bat Violet 3, CI Pigment Violet 19, CI Pigment Violet 23, CI Pigment Violet 37, CI Pigment Green 36, CI Pigment Blue 15:6, etc. As the black pigment, carbon black or CI Pigment Black 1, CI Pigment Black 6, CI Pigment Black 7, etc. may be used.

[0051] The average particle size of the pigment is preferably 10 nm or more and 200 nm or less, more preferably 10 nm or more and 100 nm or less, and even more preferably 10 nm or more and 50 nm or less. If the average particle size exceeds 200 nm, the dispersion may become unstable. If the average particle size is less than 10 nm, the dispersion may also tend to become unstable, and the storage stability of the ink may decrease. The particle size of the pigment can be measured by a commercially available particle size measuring device using a light scattering method, an electrophoresis method, a laser Doppler method, or the like. Furthermore, the particle size can also be obtained by taking particle images of at least 100 or more pigment particles using a transmission electron microscope, and performing statistical processing of the images using image analysis software such as Image-Pro (manufactured by Media Cybernetics).

[0052] As the dye, it is preferable to use a dye containing a compound having an anionic group, specifically, azo dyes, triphenylmethane dyes, (aza)phthalocyanine dyes, xanthene dyes, anthrapyridone dyes, etc.

[0053] It is preferable to use a pigment rather than a dye as the coloring material contained in the ink. The content (mass %) of the coloring material in the ink is preferably 0.1% by mass or more and 20% by mass or less, and more preferably 0.5% by mass or more and 15% by mass or less, based on the mass of the total ink.

[0054] ii) Resin Examples of the resin contained in the ink include (meth)acrylic, styrene acrylic, acrylonitrile acrylic, vinyl acetate acrylic, polyurethane, polyester, etc. Specifically, the resin contained in the ink is preferably a (meth)acrylic resin or a urethane resin.

[0055] The (meth)acrylic resin is preferably one having a hydrophilic unit and a hydrophobic unit as a constituent unit. Specifically, a resin having a hydrophilic unit derived from (meth)acrylic acid and a hydrophobic unit derived from at least one of a monomer having an aromatic ring and a (meth)acrylic acid ester monomer is preferable. Alternatively, a resin having a hydrophilic unit derived from (meth)acrylic acid and a hydrophobic unit derived from at least one of a monomer of styrene and α-methylstyrene is preferable.

[0056] The hydrophilic unit refers to a unit having a hydrophilic group such as an anionic group. The hydrophilic unit can be formed, for example, by polymerizing a hydrophilic monomer having a hydrophilic group. Specific examples of the hydrophilic monomer having a hydrophilic group include anionic monomers such as acidic monomers having a carboxylic acid group, such as (meth)acrylic acid, itaconic acid, maleic acid, and fumaric acid, and anionic monomers such as anhydrides and salts thereof. Examples of cations constituting the salts of acidic monomers include ions of lithium, sodium, potassium, ammonium, and organic ammonium. The hydrophobic unit refers to a unit not having a hydrophilic group such as an anionic group. Specific examples of the hydrophobic monomer include monomers having an aromatic ring, such as styrene, α-methylstyrene, and benzyl (meth)acrylate, and (meth)acrylic acid ester monomers such as methyl (meth)acrylate, butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate.

[0057] The urethane resin can be obtained, for example, by reacting a polyisocyanate with a polyol, or by reacting a polyisocyanate with a polyol and then adding a chain extender.

[0058] The weight average molecular weight of the resin is preferably 3,000 or more and 30,000 or less, and more preferably 10,000 or more and 20,000 or less. The acid value of the resin is preferably 60 or more and 300 or less. Furthermore, the average particle size of the resin can be measured as the cumulative 50% particle size on a volume basis by using a particle size analyzer (for example, trade name "UPA-EX150", manufactured by Nikkiso Co., Ltd.) by the dynamic light scattering method, and is preferably, for example, 100 nm or more and 500 nm or less.

[0059] The content of the resin in the ink varies depending on the degree of polymerization of the resin, but is preferably 2 to 10% by mass, more preferably 3 to 6% by mass, based on the total mass of the ink. If the content of the resin is too small, it tends to be difficult to achieve the effects of the present disclosure, and if the content of the resin is too large, the ejection properties of the inkjet or the storage stability tends to decrease.

[0060] The resin may be used alone from the above-mentioned examples, or may be used in combination of two or more. Furthermore, the resin may be used as a copolymer, or may be used by dispersing in a solvent in an emulsion state. When dispersing in a solvent in an emulsion state, the average particle size of the resin is preferably 300 nm or less from the viewpoint of not impairing the ejectability by inkjet. When a soluble polymer is used as the resin, its composition and molecular weight should not be particularly limited, but since the ejectability tends to deteriorate as the degree of polymerization of the polymer increases, it is preferable to set the weight average molecular weight to 50,000 or less.

[0061] iii) aqueous medium The ink may contain an aqueous medium. The aqueous medium refers to water or a mixed solvent of water and a water-soluble organic solvent. As the water, deionized water or ion-exchanged water is preferably used. The content of water in the ink is preferably 20% by mass or more and 95% by mass or less with respect to the total mass of the ink. The content of the water-soluble organic solvent in the ink is preferably 3% by mass or more and 50% by mass or less with respect to the total mass of the ink. As the water-soluble organic solvent, any of alcohols, (poly)alkylene glycols, glycol ethers, nitrogen-containing compounds, sulfur-containing compounds, etc. may be used.

[0062] Examples of the water-soluble organic solvent include glycerin, propylene glycol, dipropylene glycol, tripropylene glycol, tetrapropylene glycol, polypropylene glycol, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, decaglyceryl, 1,4-butanediol, 1,3-butanediol, 1,2,6-hexanetriol, 2-pyrrolidinone, dimethylimidazolidinone, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monobutyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monopropyl ether, triethylene glycol monobutyl ether, tetraethylene glycol monomethyl ether, tetraethylene glycol monoethyl ether, ethyl ether, propylene glycol monobutyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monopropyl ether, diethylene glycol monobutyl ether, tripropylene glycol monomethyl ether, tripropylene glycol monoethyl ether, tripropylene glycol monopropyl ether, tripropylene glycol monobutyl ether, tetrapropylene glycol monomethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, triethylene glycol diethyl ether, triethylene glycol dibutyl ether, dipropylene glycol dibutyl ether, tripropylene glycol dibutyl ether, 3-methyl-2,4-pentanediol, diethylene glycol monoethyl ether acetate, 1,2-hexanediol, 1,2-pentanediol, 1,2-butanediol, etc. can be used. The water-soluble organic solvent may be used alone from the above-mentioned types, or two or more types may be used in combination.

[0063] iv) Surfactants The surfactant contained in the ink may be any of cationic, anionic, amphoteric and nonionic. Specific examples of the surfactant should not be particularly limited, but examples of cationic surfactants include aliphatic amine salts, aliphatic quaternary ammonium salts, benzalkonium salts, benzethonium chloride, pyridinium salts, and imidazolinium salts. For example, anionic surfactants include fatty acid soaps, N-acyl-N-methylglycine salts, N-acyl-N-methyl-β-alanine salts, N-acylglutamates, acylated peptides, alkylsulfonates, alkylbenzenesulfonates, alkylnaphthalenesulfonates, dialkylsulfosuccinate salts, alkylsulfoacetates, α-olefinsulfonates, N-acylmethyltaurines, sulfated oils, higher alcohol sulfate salts, secondary higher alcohol sulfate salts, alkyl ether sulfates, secondary higher alcohol ethoxy sulfates, polyoxyethylene alkylphenyl ether sulfates, monoglycerates, fatty acid alkylolamide sulfate salts, alkyl ether phosphate salts, and alkyl phosphate salts.

[0064] For example, amphoteric surfactants include carboxybetaine type, sulfobetaine type, aminocarboxylate, imidazolinium betaine, etc. For example, nonionic surfactants include polyoxyethylene secondary alcohol ether, polyoxyethylene alkylphenyl ether, polyoxyethylene sterol ether, polyoxyethylene lanolin derivative polyoxyethylene polyoxypropylene alkyl ether, polyoxyethylene glycerin fatty acid ester, polyoxyethylene castor oil, hydrogenated castor oil, polyoxyethylene sorbitol fatty acid ester, polyethylene glycol fatty acid ester, fatty acid monoglyceride, polyglycerin fatty acid ester, sorbitan fatty acid ester, propylene glycol fatty acid ester, sucrose fatty acid ester, fatty acid alkanolamide, polyoxyethylene fatty acid amide, polyoxyethylene alkylamine, alkylamine oxide, acetylene glycol, acetylene alcohol, etc.

[0065] From the viewpoint of reducing the surface tension, it is also preferable that some elements in the chemical structure of the surfactant are substituted with fluorine or silicon. The surfactant may be used alone or in combination of two or more of the above-mentioned examples.

[0066] v) Other additives The ink may further contain various known additives for the purpose of improving the ejection property or storage stability of the inkjet head, the compatibility with the print head and the ink cartridge, storage stability, image storage stability, and other performances. For example, the ink may contain polysaccharides, viscosity modifiers, resistivity modifiers, film-forming agents, ultraviolet absorbers, antioxidants, color-fading inhibitors, antifungal agents, and rust inhibitors. The ink may further contain oil droplet particles such as liquid paraffin, dioctyl phthalate, tricresyl phosphate, and silicone oil, ultraviolet absorbers, color-fading inhibitors, and fluorescent brighteners.

[0067] <Heating part> The image forming unit includes a heating section 110 that heats an image formed on the recording medium 108. Specifically, the heating section 110 heats an image (ink) formed on the recording medium 108 in the image forming unit to dry the image, thereby fixing the image on the recording medium 108. The heating section 110 has a light source that radiates at least infrared rays of light, and a wavelength selection device that selectively attenuates far infrared rays of the infrared rays radiated from the light source. The image forming apparatus according to this embodiment realizes both efficient heating of the image on the recording medium 108 and suppression of deformation of the recording medium 108 by the heating section 110, and can therefore quickly dry the image while suppressing deformation of the recording medium 108.

[0068] The heating section will be described in detail below with reference to FIG. 3. FIG. 3 is a schematic diagram showing an example of the configuration of the heating section provided in the image forming unit. In FIG. 3, the heating section 110 has a light source 111 that radiates at least infrared rays, and a wavelength selection device that selectively attenuates far infrared rays from the infrared rays radiated from the light source 111. The wavelength selection device can include either one or two or more neutral density filters 112 and reflectors 113. The wavelength selection device can also include both the neutral density filters 112 and reflectors 113.

[0069] (light source) The type, shape and structure of the light source 111 should not be particularly limited as long as it can radiate at least infrared light among light, but from the viewpoint of versatility, it is preferable that the light source 111 is, for example, an IR light source. The light source 111 may be a halogen lamp. When the light source 111 is an IR light source, a commercially available product can be used. For example, an IR light source with a color temperature of 2400K, an IR light source with a color temperature of 3000K, an IR light source with a color temperature of 3500K, etc. can be used. In other words, it is preferable that the light source 111 has a color temperature of 2400K or more. The light radiated from the light source 111 can also include visible light and ultraviolet light. As a result, even if the far infrared light is attenuated by the wavelength selection device and reaches the recording medium, sufficient heat energy can be applied to the recording medium by light of a wavelength other than the far infrared light, and the image on the recording medium can be dried efficiently.

[0070] The IR light source is preferably 2400K or higher and has a color temperature closer to 2400K, since it is more versatile. On the other hand, the IR light source is preferably 2400K or higher and has a color temperature higher than 2400K, since it is more efficient at using thermal energy. There is no particular upper limit to the color temperature of the IR light source, but it is preferably 3500K or lower from the viewpoint of versatility.

[0071] (Wavelength selection device) The heating unit 110 has a wavelength selection device that selectively attenuates far-infrared rays among the infrared rays radiated from the light source 111 as described above. The type, shape, and structure of the wavelength selection device should not be particularly limited as long as it can selectively attenuate far-infrared rays among the infrared rays, but it is preferable that the wavelength selection device includes, for example, one or more neutral density filters 112. It is also preferable that the wavelength selection device includes a reflector 113. By including one or more neutral density filters 112 and / or a reflector 113 as described above, the wavelength selection device can easily selectively attenuate far-infrared rays among the infrared rays. As described above, the wavelength selection device can also include both one or more neutral density filters 112 and / or a reflector 113.

[0072] When the wavelength selection device includes one or more neutral density filters 112, the far-infrared rays may be selectively attenuated by a single neutral density filter, or the far-infrared rays may be selectively attenuated by combining two or more neutral density filters. As the neutral density filter, for example, a reflective ND filter can be used. When the wavelength selection device includes one or more neutral density filters 112, the neutral density filter 112 is preferably disposed between the light source 111 and the recording medium 108.

[0073] When the wavelength selection device includes the reflecting mirror 113, the reflecting mirror 113 has a reflecting surface 113a as a surface that absorbs far-infrared rays radiated from the light source 111, and the reflecting surface 113a is preferably made of ceramics. Examples of ceramics that constitute the reflecting surface 113a include aluminum oxide. These ceramics have an absorption characteristic of infrared rays, particularly far-infrared rays. In particular, the ceramics that constitute the reflecting surface 113a of the reflecting mirror 113 are more preferably made of aluminum oxide, zirconia, aluminum nitride (AlN) or Si3N4. Furthermore, the reflecting mirror 113 has a reflecting surface 113a as a surface that absorbs far-infrared rays radiated from the light source 111, and the reflecting surface 113a is preferably anodized. When the wavelength selection device includes the reflecting mirror 113, the reflecting surface 113a of the reflecting mirror 113 is preferably disposed in a position facing the recording medium 108 so that the reflected light reaches the recording medium 108. By including the reflecting mirror 113 as described above, the wavelength selection device can easily selectively attenuate far infrared rays from among infrared rays.

[0074] Here, it is preferable that the wavelength selection device further selectively attenuates a part of the mid-infrared rays among the infrared rays. In particular, it is preferable that the wavelength selection device further selectively attenuates the mid-infrared rays in the wavelength range longer than 2800 nm among the infrared rays. The wavelength selection device can further selectively attenuate a part of the mid-infrared rays among the infrared rays by including, for example, one or more neutral density filters 112 and / or a reflecting mirror 113 as described above, and more specifically, it can further selectively attenuate the mid-infrared rays in the wavelength range longer than 2800 nm among the infrared rays. This allows the heating unit 110 to effectively attenuate light in a wavelength range with a higher absorption rate in the recording medium 108 than the image (ink) 109 on the recording medium 108, so that the temperature rise of the recording medium can be further suppressed.

[0075] Furthermore, the wavelength selection device preferably controls the heat energy of the light in the wavelength range of 2800 nm or less radiated onto the recording medium 108 to be 20 times or more the heat energy of the light in the wavelength range longer than 2800 nm radiated onto the recording medium 108. It is even more preferable that the wavelength selection device controls the heat energy of the light in the wavelength range of 2800 nm or less radiated onto the recording medium 108 to be 47 times or more the heat energy of the light in the wavelength range longer than 2800 nm radiated onto the recording medium 108. By such control, both efficient heating of the image (ink) 109 on the recording medium 108 and suppression of deformation of the recording medium 108 can be effectively achieved. Such control can be performed by including, for example, one or two or more neutral density filters 112 and / or reflectors 113 in the wavelength selection device. The upper limit of the above control is not particularly limited, but is preferably 75 times or less from the viewpoint of versatility.

[0076] The thermal energy of the light radiated onto the recording medium 108 can be calculated by multiplying the spectral intensity of the light source 111 by the spectral attenuation rate of the wavelength selection device. Therefore, the thermal energy of light in the wavelength range of 2800 nm or less radiated onto the recording medium 108 can be calculated by multiplying the spectral intensity of light in the wavelength range of 2800 nm or less radiated from the light source 111 by the spectral attenuation rate of the wavelength selection device. The thermal energy of light in the wavelength range longer than 2800 nm radiated onto the recording medium 108 can be calculated by multiplying the spectral intensity of light in the wavelength range longer than 2800 nm radiated from the light source 111 by the spectral attenuation rate of the wavelength selection device.

[0077] (action) Hereinafter, the operation of the heating section 110 of the image forming unit of this embodiment will be described with reference to FIG.

[0078] That is, as shown in Fig. 3, the heating unit 110 has a light source 111 that radiates at least infrared rays, and a wavelength selection device (one or two or more neutral density filters 112 and / or a reflector 113) that selectively attenuates far-infrared rays from the infrared rays radiated from the light source 111. The heating unit 110 first radiates light including infrared rays from the light source 111 in a radial manner. Then, a part or all of the light including infrared rays radiated from the light source 111 passes through one or two or more neutral density filters 112, or is reflected by a reflecting surface 113a of the reflector 113. When the wavelength selection device includes both the neutral density filter 112 and the reflector 113, the light including infrared rays passes through the neutral density filter 112 and is reflected by the reflecting surface 113a of the reflector 113. At this time, at least the far-infrared rays of the infrared rays radiated from the light source 111 are selectively attenuated by being blocked by the neutral density filter 112 or absorbed by the reflecting surface 113a of the reflecting mirror 113. Thereafter, the light including the infrared rays radiated from the light source 111 reaches the recording medium 108 and the image (ink) on the recording medium 108 with at least the far-infrared rays being attenuated. This makes it possible to further suppress an increase in the temperature of the recording medium, and also makes it possible to dry the image on the recording medium by light of a wavelength other than the far-infrared rays.

[0079] In this case, it is preferable that the wavelength selection device further selectively attenuates a part of the mid-infrared rays among the infrared rays, more specifically, it is preferable that the wavelength selection device further selectively attenuates the mid-infrared rays in the wavelength range longer than 2800 nm among the infrared rays. Furthermore, it is preferable that the wavelength selection device controls the thermal energy of the light in the wavelength range of 2800 nm or less radiated onto the recording medium 108 to be 20 times or more the thermal energy of the light in the wavelength range longer than 2800 nm radiated onto the recording medium 108.

[0080] As described above, the image forming apparatus according to this embodiment is provided with the above-mentioned heating section 110 in the image forming unit, thereby realizing both efficient heating of the image on the recording medium 108 and suppression of deformation of the recording medium, thereby making it possible to quickly dry the image while suppressing deformation of the recording medium 108.

[0081] <Transportation section> Conveyance section 107 only needs to be able to transport recording medium 108 in the direction of arrow C, and may include, for example, recording medium pay-out roller 107a and recording medium take-up rollers 107b and 107c, as shown in Fig. 2. The transport speed of recording medium 108 is preferably determined taking into consideration the speed required for each device.

[0082] <Other elements> The image forming unit may include other elements in addition to the above-mentioned reaction liquid application section, image forming section, heating section, and transport section. For example, the image forming unit may include a liquid removal section (not shown) that removes residual liquid remaining on the recording medium on which an image has been formed, and contributes to rapid drying and fixing of the image. In this specification, the term "residual liquid" refers to liquid that includes at least one of a part of the reaction liquid and a part of the ink, and remains as an excess amount without being fixed as an image on the recording medium. For this reason, it is preferable that the liquid removal section is disposed immediately before or immediately after the heating section in the X direction (for example, the direction indicated by the arrow C in FIG. 2), which is the overall length direction of the image forming unit.

[0083] For example, the liquid removing section may include a liquid absorbing member and a pressing member that presses the liquid absorbing member against the image on the recording medium. The shapes of the liquid absorbing member and the pressing member, and the structure thereof, are not particularly limited, but may be, for example, as follows. That is, when the pressing member is cylindrical and the liquid absorbing member is belt-shaped, a structure in which the side surface of the pressing member presses the belt-shaped liquid absorbing member against the recording medium can be exemplified. Furthermore, when the pressing member is cylindrical and has a shape in which the liquid absorbing member is attached to the side surface of the pressing member, a structure in which the pressing member directly presses the liquid absorbing member provided on the side surface against the recording medium can be exemplified. Considering the space inside the image forming apparatus, it is preferable that the liquid absorbing member is belt-shaped. In that case, it is preferable that the liquid removing section includes a tension roller that tensions the belt-shaped liquid absorbing member.

[0084] In addition to the above-mentioned method of bringing a liquid absorbing member into contact with the image, the liquid removing section can also use other methods to remove residual liquid from the recording medium, such as a method of removing residual liquid by heating, a method of removing residual liquid by blowing low humidity air, a method of removing residual liquid by reducing pressure, or a combination of these methods. Furthermore, residual liquid may be removed by the liquid absorbing member and further removed by applying these methods.

[0085] The liquid absorbing member can be made of any known material without any particular limitation, so long as it is a material capable of removing residual liquid on the recording medium. For example, from the viewpoint of efficient removal of residual liquid, a material capable of having a porous structure is preferred, and examples thereof include fiber materials such as cellulose and resin materials such as polyacrylamide resin. A nonwoven fabric or woven fabric can be formed from these fiber materials or resin materials by a known method, thereby forming the liquid absorbing member. Furthermore, it is preferred to subject the surface of the nonwoven fabric or woven fabric to hydrophilic treatment by a method such as sputter etching, irradiation with radiation or H2O ions, or irradiation with excimer (ultraviolet) laser light. In addition, the liquid absorbing member may have a reinforcing member for reinforcing the side surface of the liquid absorbing member, and a joining member such as a tape may be used when the liquid absorbing member is in the form of a belt. It is preferred that the joining member is disposed at a position where it does not come into contact with the image.

[0086] <Action and effect> As described above, the image forming apparatus according to the present embodiment includes the image forming unit described above, and thereby realizes both efficient heating of the image on the recording medium and suppression of deformation of the recording medium. As a result, the image forming apparatus according to the present embodiment can quickly dry the image while suppressing deformation of the recording medium.

[0087] [Image forming method] The image forming method according to the present embodiment includes a step of forming the image on the recording medium by using the image forming apparatus. Specifically, the image forming method according to the present embodiment is preferably an image forming method that uses at least the image forming apparatus to perform the steps of forming an image forming area by applying a reaction liquid on the recording medium (first step), forming an image by applying an ink that reacts with the reaction liquid on the imaging area according to image data (second step), and drying the image formed on the recording medium by heating the image (third step). The image forming method according to the present embodiment realizes both efficient heating of the image on the recording medium and suppression of deformation of the recording medium, thereby allowing the image to be dried quickly while suppressing deformation of the recording medium. Each step included in the image forming method will be described below.

[0088] [1st process] The first step is a step of forming an image forming area by applying a reaction liquid onto a recording body. The first step can be a step of forming an image forming area that is conventionally performed in this type of image forming apparatus. The definitions and details of the terms "recording body", "image forming area" and "reaction liquid" are as described above, so the description will not be repeated.

[0089] [Second process] The second step is a step of forming an image by applying ink that reacts with the reaction liquid onto the imaging area in accordance with image data. The second step can also be an image forming step that has been conventionally performed in this type of image forming apparatus. The definition of the term "ink" and its details are as described above, so the description will not be repeated.

[0090] [3rd step] The third step is a step of drying the image formed on the recording medium by heating the image. Specifically, the third step is performed in a heating section provided in an image forming unit of the image forming apparatus. As described above, the heating section has a light source that radiates at least infrared light out of light, and a wavelength selection device (one or more neutral density filters and / or a reflector) that selectively attenuates far infrared light out of the infrared light radiated from the light source. Details of the "light source" and the "neutral density filter" and "reflector" used in the third step are as described above, and therefore will not be described again.

[0091] In the third step, the heating unit radiates light including infrared rays from the light source, and then passes part or all of the light through one or more neutral density filters serving as a wavelength selection device, or reflects the light on the reflecting surface of a reflecting mirror. At this time, at least the far-infrared rays of the infrared rays radiated from the light source 111 are selectively attenuated by being blocked by the neutral density filter 112, or absorbed by the reflecting surface 113a of the reflecting mirror 113. Then, the light with at least the attenuated far-infrared rays reaches the recording medium and the image (ink) on the recording medium. This makes it possible to efficiently dry the image (ink) on the recording medium, and further suppress the temperature rise of the recording medium.

[0092] In the third step, it is preferable to selectively attenuate a part of the mid-infrared rays of the infrared rays radiated from the light source, and more specifically, it is preferable to selectively attenuate the mid-infrared rays of the infrared rays in a wavelength range longer than 2800 nm.Furthermore, in the third step, it is also preferable to control the thermal energy of the light in a wavelength range of 2800 nm or less radiated onto the recording medium to be 20 times or more the thermal energy of the light in a wavelength range longer than 2800 nm radiated onto the recording medium.

[0093] [Action and Effect] From the above, the image forming method of this embodiment uses the above-mentioned image forming apparatus to achieve both efficient heating of the image on the recording medium and suppression of deformation of the recording medium, thereby making it possible to quickly dry the image while suppressing deformation of the recording medium.

[0094] [Additional Notes] The above description includes the following additional embodiments.

[0095] <Appendix 1> The method includes forming an image on a recording medium by using an image forming apparatus, The steps include forming an imaging area; forming an image by applying ink that reacts with the reaction liquid onto the image forming area in accordance with image data; and drying the image formed on the recording medium by heating the ink on the recording medium on which the image has been formed. the image forming apparatus includes an image forming unit that forms an image on a recording medium according to image data; the image forming unit includes a heating section that heats the image formed on the recording medium, The heating unit includes a light source that radiates at least infrared rays, and a wavelength selection device that selectively attenuates far infrared rays from the infrared rays radiated from the light source, The image forming method, wherein the step of drying the image is performed by the heating section.

[0096] <Appendix 2> The image forming method according to claim 1, wherein the wavelength selection device further selectively attenuates a portion of the mid-infrared light among the infrared light.

[0097] <Appendix 3> The image forming method according to claim 1 or 2, wherein the wavelength selection device further selectively attenuates mid-infrared light in a wavelength range longer than 2800 nm among the infrared light.

[0098] <Appendix 4> The image forming method according to any one of claims 1 to 3, wherein the wavelength selection device controls the thermal energy of light in a wavelength range of 2800 nm or less radiated onto the recording medium to be at least 20 times the thermal energy of light in a wavelength range longer than 2800 nm radiated onto the recording medium.

[0099] <Appendix 5> 5. The method of claim 1, wherein the wavelength selection device comprises one or more neutral density filters.

[0100] <Appendix 6> 6. The image forming method according to claim 1, wherein the wavelength selection device includes a reflecting mirror.

[0101] <Appendix 7> the reflecting mirror has a surface that absorbs the far infrared rays radiated from the light source, 7. The image forming method according to claim 6, wherein the surface is made of ceramic.

[0102] <Appendix 8> 8. The image forming method according to claim 7, wherein the ceramic is made of aluminum oxide.

[0103] <Appendix 9> the reflecting mirror has a surface that absorbs the far infrared rays radiated from the light source, The image forming method according to any one of claims 6 to 8, wherein the surface is anodized.

[0104] <Appendix 10> 10. The image forming method according to any one of claims 1 to 9, wherein the light source has a color temperature of 2400K or more. EXAMPLES

[0105] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these.

[0106] [Example 1] [Preparation of Recording Medium, Reaction Liquid, Ink, Image Forming Apparatus, etc.] Commercially available plain paper (product name: "OK Topcoat+ (A2 73gsm)", manufactured by Oji Paper Co., Ltd.) was prepared as a recording medium.

[0107] Furthermore, a tester machine modified from a commercially available inkjet printer was prepared as an image forming apparatus. The tester machine was equipped with an image forming unit as shown in Fig. 2. That is, the tester machine was equipped with a control unit having a CPU and in which the CPU executes a given program, a reaction liquid application unit having a gravure offset roller, an image forming unit having an inkjet head, and a heating unit that heats an image formed on a recording medium by the image forming unit.

[0108] The heating unit has a configuration as shown in Fig. 3. Specifically, the heating unit has an IR light source (product name: "HYP-8NS", manufactured by HYBEC) with a color temperature of 2400K as a light source that radiates at least infrared light, and a wavelength selection device for selecting wavelengths radiated from the light source. As the wavelength selection device, a light-reducing filter (product name: "ND filter OD2.0 for IR", manufactured by Edmond) that attenuates light with wavelengths of 1800 nm or more was used. One light-reducing filter was used, and this was placed between the light source and the recording medium.

[0109] As the reaction liquid to be applied to the reaction liquid application section of the image forming unit, a liquid having a composition of 5 mass % malonic acid (pKa is 2.83), 5 mass % organic solvent, 4 mass % surfactant, and the remainder ion-exchanged water was prepared.

[0110] As an ink to be applied to the image forming section of the image forming unit, a pigment dispersion liquid having a composition of 40% by mass of pigment dispersion (9% by mass of pigment), 3% by mass of resin, 10% by mass of aqueous organic solvent, 0.5% by mass of surfactant, and the remainder being ion-exchanged water was prepared.

[0111] [Image formation by image forming apparatus] Using the above tester machine, a predetermined image was formed on one recording medium by operating the image forming unit. First, the reaction liquid was applied to the recording medium using the reaction liquid application unit to form an image forming area. Then, the ink that reacts with the reaction liquid was applied to the image forming area according to image data using the image forming unit to form an image. Next, the image on the recording medium was heated by the heating unit (see Figure 2).

[0112] In particular, in the heating section, the light radiated from the light source with a wavelength of 1800 nm or more was attenuated by passing it through the above-mentioned neutral density filter, and this attenuated light was used to heat the recording medium and the image (ink) on the recording medium. In this way, the image was fixed on the recording medium (see Figure 3).

[0113] [Example 2] An IR light source (product name: "HSH-60", manufactured by Fintech) with a color temperature of 3000K was used as the light source, and a dimming filter (a modified version of a commercially available dimming filter) that attenuates light with wavelengths of 2400 nm or more was used as the wavelength selection device. An image formation method was carried out in the same manner as in Example 1, except that the image (ink) on the recording medium was heated.

[0114] [Example 3] An IR light source with a color temperature of 3500K (product name: "NIR126-250-System", manufactured by Adphos) was used as the light source, and a dimming filter (a modified version of a commercially available dimming filter) that attenuates light with a wavelength of 2800 nm or more was used as the wavelength selection device. An image formation method was carried out in the same manner as in Example 1, except that the image (ink) on the recording medium was heated.

[0115] [Example 4] The image forming method was carried out in the same manner as in Example 1, except that a reflector (a modified version of a commercially available reflector) made of ceramics with a surface (reflective surface) that has absorption properties for at least far-infrared rays among infrared rays was used as the wavelength selection device, and the image (ink) on the recording medium was heated. In Example 4, the light with a wavelength of 2800 nm or more is attenuated by the wavelength selection device.

[0116] [Example 5] Except for using an IR light source (product name: "HSH-60", manufactured by Fintech Co., Ltd.) with a color temperature of 3000K as the light source, the image forming method was carried out in the same manner as in Example 4, and the image (ink) on the recording medium was heated. In Example 5, the light with a wavelength of 2800 nm or more is attenuated by the wavelength selection device.

[0117] [Example 6] Except for using an IR light source (product name: "NIR126-250-System", manufactured by Adphos) with a color temperature of 3500K as the light source, the image forming method was carried out in the same manner as in Example 4, and the image (ink) on the recording medium was heated. In Example 6, the light with a wavelength of 2800 nm or more is attenuated by the wavelength selection device.

[0118] [Comparative Example 1] An image forming method was carried out in the same manner as in Example 1, except that no wavelength selection device was provided in the heating section, and the image (ink) on the recording medium was heated.

[0119] [Comparative Example 2] By simulating the image forming apparatus (liquid ejection apparatus) of Patent Document 1, an IR light source (product name: "HYP-8NS", manufactured by HYBEC Corporation) having a color temperature of 2400K was used as the light source, and a heating section was constructed using a dimming filter (a modified version of a commercially available dimming filter) that transmits only light of wavelengths of 300 nm, 600 nm, 650 nm, and 3000 nm as the wavelength selection device. An image forming method was carried out in the same manner as in Example 1, and an image (ink) on a recording medium was heated.

[0120] 〔evaluation〕 <Heat energy utilization rate> For Examples 1 to 6 and Comparative Examples 1 and 2, when the image forming unit of the tester machine was operated, the ratio of light radiated from the light source that reached the recording medium was calculated as the thermal energy utilization rate (unit: %). The higher the value of this thermal energy utilization rate, the more of the thermal energy of the light radiated from the light source can be utilized for drying the image. However, if the thermal energy of the light radiated from the light source cannot be appropriately controlled by the wavelength selection device, it may be difficult to suppress the temperature rise of the recording medium. Note that Comparative Example 1 does not have a wavelength selection device, so the thermal energy utilization rate is 100%.

[0121] <Selection ratio (ink / paper)> For Examples 1 to 6 and Comparative Examples 1 and 2, when the image forming unit of the tester machine was operated, the total amount of heat energy of light absorbed by the image (ink) was calculated as the selection ratio when the total amount of heat energy of light radiated from the light source and absorbed by the recording medium was set to 1. A larger value of this selection ratio means that more of the heat energy of light radiated from the light source can be used to dry the image (ink) and the temperature rise of the recording medium 108 can be suppressed more effectively. Note that the selection ratio was not calculated for Comparative Example 2 because it was impossible to calculate.

[0122] <Control of thermal energy with a wavelength of 2800 nm as the boundary> For Examples 4 to 6 and Comparative Example 1, when the image forming unit of the tester machine was operated, the thermal energy of the light radiated from the light source in the wavelength range of 2800 nm or less that reaches the recording medium was investigated to see how many times the thermal energy of the light radiated from the light source in the wavelength range longer than 2800 nm that reaches the recording medium was controlled. The larger this value is, the more the thermal energy of the light radiated from the light source can be used to dry the image (ink) and the more the temperature rise of the recording medium can be suppressed. The method of calculating the thermal energy of the light that reaches the recording medium is as described above. In Table 2 below, this evaluation is shown as the item "control of thermal energy". For Comparative Example 2, the value related to the control of thermal energy was not calculated because it was impossible to calculate.

[0123] <Evaluation of image fixation> The degree of fixation of the image on the recording medium heated by the heating unit was visually evaluated on the following three scales A to C, using the following index. A: The image was completely dried and extremely well fixed on the recording medium. B: The image was dried within an acceptable range and was well fixed on the recording medium. C: The image did not dry beyond the permissible range, and a part of the image could not be fixed on the recording medium.

[0124] <Evaluation of the degree of deformation of the recording medium> The degree of deformation of the recording medium heated by the heating unit was visually evaluated using the following three indices, A to C. The numerical value used to evaluate the degree of deformation is the distance (mm) of one end of the recording medium from the flat surface, which occurs when one end of the recording medium is in contact with a flat surface and the other end is separated from the flat surface due to warping of the recording medium. A: No deformation (curl) was observed in the recording medium. B: The deformation (curl) of the recording medium was found to be less than 15 mm, which is the allowable value. C: Unacceptable deformation (curl) of 15 mm or more was observed in the recording medium.

[0125] The evaluation results of Examples 1 to 3 are shown in Table 1, and the evaluation results of Examples 4 to 6 are shown in Table 2. Tables 1 and 2 also show the evaluation results of Comparative Examples 1 and 2.

[0126] [Table 1]

[0127] [Table 2]

[0128] <Consideration> According to Tables 1 and 2, Examples 1 to 6 are examples in which far infrared rays from the light radiated from the light source are attenuated by the wavelength selection means, and were excellent in both the <image fixing evaluation> and the <recorded body deformation evaluation>. Specifically, Examples 1 to 6 were excellent in at least one of the <image fixing evaluation> and the <recorded body deformation evaluation> when compared with Comparative Example 1 and Comparative Example 2. In particular, Examples 2, 3, 5, and 6 were even more excellent in both the <image fixing evaluation> and the <recorded body deformation evaluation> due to their high selectivity ratios.

[0129] Each embodiment disclosed herein should be considered as illustrative in all respects and not restrictive. The scope of the present invention is indicated by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims. In addition, the inventions described in the embodiments and each modified example are intended to be implemented, as far as possible, either alone or in combination. [Explanation of symbols]

[0130] 103 reaction liquid application section, 104 image forming section, 107 transport section, 107a recording body feed roller, 107b, 107c recording body take-up rollers, 108 recording body, 109 image (ink), 110 heating section, 111 light source (IR light source), 112 dimming filter, 113 reflecting mirror, 113a reflecting surface (surface).

Claims

1. An image forming apparatus including an image forming unit for forming an image on a recording medium according to image data, the image forming unit includes a heating section that heats the image formed on the recording medium, The heating unit includes a light source that radiates at least infrared light among light beams, and a wavelength selection device that selectively attenuates far infrared light among the infrared light radiated from the light source, The wavelength selection device further attenuates mid-infrared light in a wavelength range longer than 2800 nm among the infrared light, and radiates light in a wavelength range of 2800 nm or less onto the recording medium.

2. 2. The image forming apparatus according to claim 1, wherein the wavelength selection device controls the thermal energy of light in a wavelength range of 2800 nm or less radiated onto the recording medium to be at least 20 times the thermal energy of light in a wavelength range longer than 2800 nm radiated onto the recording medium.

3. 3. The image forming apparatus according to claim 1, wherein the wavelength selection device includes one or more neutral density filters.

4. The image forming apparatus according to claim 1 , wherein the wavelength selection device includes a reflecting mirror.

5. An image forming apparatus having an image forming unit that forms an image on a recording medium according to image data, the image forming unit includes a heating section that heats the image formed on the recording medium, The heating unit includes a light source that radiates at least infrared light among light beams, and a wavelength selection device that selectively attenuates far infrared light among the infrared light radiated from the light source, The wavelength-selective device includes a reflector.

6. the reflecting mirror has a surface that absorbs the far infrared rays radiated from the light source, 6. The image forming apparatus according to claim 4, wherein the surface is made of ceramics.

7. 7. The image forming apparatus according to claim 6, wherein the ceramic is made of aluminum oxide.

8. the reflecting mirror has a surface that absorbs the far infrared rays radiated from the light source, The image forming apparatus according to claim 4 , wherein the surface is anodized.

9. 9. The image forming apparatus according to claim 1, wherein the light source has a color temperature of 2400K or higher.

10. An image forming method comprising a step of forming the image on the recording medium by using an image forming apparatus described in any one of claims 1 to 9.

Images