Image forming apparatus

Abstract

To provide a thermochromic UV-curable ink that has excels at color changing function and can achieve high discharge stability in inkjet recording, and an inkjet image formation device for the ink.SOLUTION: An image formation device according to an embodiment includes: an inkjet head which discharges an ink composition to a recording medium, forming an ink layer on the recording medium, wherein the ink composition includes a thermochromic pigment, water, a water-soluble or water-dispersible polymerizable compound, a water-soluble crosslinker, and a water-soluble photopolymerization initiator, a dryer for drying the ink layer, and an irradiator for irradiating the dried ink layer with ultraviolet rays.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] Embodiments of the present invention relate to an image forming apparatus in the position .

Background Art

[0002] Inks containing a thermochromic pigment and an ultraviolet curable resin (hereinafter also referred to as thermochromic ultraviolet curable inks) are known. Such inks exhibit thermochromism and have the property of curing with ultraviolet light.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The problem to be solved by the present invention is heat discoloring ultraviolet curable to provide an inkjet type image forming apparatus for ink.

Means for Solving the Problems

[0005] According to an embodiment, an ink composition containing a thermochromic pigment, water, a water-soluble or water-dispersible polymerizable compound, a water-soluble crosslinking agent, and a water-soluble photopolymerization initiator is ejected onto a recording medium to form an ink layer on the recording medium, and an image forming apparatus is provided, which includes an inkjet head, a drying device for drying the ink layer, and an irradiation device for irradiating ultraviolet light onto the dried ink layer.

Brief Description of the Drawings

[0006]

Figure 1

Modes for Carrying Out the Invention

[0007] 1. Image forming apparatus The image forming apparatus according to the embodiment includes an inkjet head that discharges an ink composition onto a recording medium to form an ink layer on the recording medium, a drying device that dries the ink layer, and an irradiation device that irradiates ultraviolet rays onto the dried ink layer. In this image forming apparatus, the ink composition contains a pigment that exhibits thermochromism, water, a water-soluble or water-dispersible polymerizable compound, a water-soluble crosslinking agent, and a water-soluble photopolymerization initiator.

[0008] An example of the image forming apparatus according to the embodiment will be described with reference to the drawings. FIG. 1 is a schematic diagram showing an example of the image forming apparatus according to the embodiment.

[0009] The inkjet printer 100 shown in FIG. 1 includes a housing provided with a paper discharge tray 120. Inside the housing, a cassette 101a and 101b, a paper feed roller 102 and 103, a pair of conveyance rollers 104 and 105, a pair of registration rollers 106, a conveyance belt 107, a drive roller 108, a driven roller 109, a fan 121, a negative pressure chamber 111, a pair of conveyance rollers 112, 113 and 114, an inkjet head 115, an ink cartridge 116, a tube 117, a drying device 118, an ultraviolet irradiation device 119, and a control device 122 are installed.

[0010] The cassettes 101a and 101b accommodate recording media F of different sizes. The recording medium F is, for example, a non-absorbent recording medium. A non-absorbent recording medium refers to a recording medium that does not absorb ink. An example of a non-absorbent recording medium is a plastic film. Alternatively, the non-absorbent recording medium may be one in which a plastic is coated on a base material such as paper, one in which a plastic film is adhered to a base material such as paper, or one in which a metal is vapor-deposited on the surface of a plastic film. The paper feed roller 102 or 103 takes out the recording medium F corresponding to the selected size of the recording medium from the cassette 101a or 101b and conveys it to the pair of conveyance rollers 104 and 105 and the pair of registration rollers 106.

[0011] The conveyor belt 107 is tensioned by a drive roller 108 and two driven rollers 109. Holes are provided at predetermined intervals on the surface of the conveyor belt 107. Inside the conveyor belt 107, a negative pressure chamber 111 connected to a fan 121 is installed to adsorb the recording medium F to the conveyor belt 107. Downstream in the conveying direction of the conveyor belt 107, conveying roller pairs 112, 113, and 114 are installed.

[0012] The inkjet head 115 is installed above the conveyor belt 107. The inkjet head 115 discharges thermochromic ultraviolet curable ink onto the recording medium F according to image data. The control device 122 includes a CPU, ROM, RAM, etc., and performs image processing control, drive control of each roller, discharge control of the inkjet head 115, and control of the drying device 118 and the ultraviolet irradiation device 119.

[0013] The ink cartridge 116 is installed above the inkjet head 115. The ink cartridge 116 stores thermochromic ultraviolet curable ink. The ink cartridge 116 is connected to the inkjet head 115 by a tube 117. [[ID=!1]]

[0014] The thermochromic ultraviolet curable ink is water-based ink. An example of the thermochromic ultraviolet curable ink is thermo-decolorable ultraviolet curable ink. Details of the thermochromic ultraviolet curable ink will be described later. Also, in the following description, the thermochromic ultraviolet curable ink is simply referred to as ink.

[0015] The inkjet printer 100 is provided with one inkjet head so as to be able to form a monochromatic image, but may be provided with a plurality of inkjet heads so as to be able to form a color image.

[0016] The drying device 118 is installed downstream of the inkjet head 115. The drying device 118 dries the ink ejected onto the recording medium F. The drying device 118 may be a heater or a blower that blows air. Alternatively, the drying device 118 may include a heater and a blower and blow heated air.

[0017] The ultraviolet irradiation device 119 is installed downstream of the drying device 118. The ultraviolet irradiation device 119 irradiates the ink from which moisture has been removed with ultraviolet light. This hardens the ink and fixes it on the recording medium F.

[0018] The inkjet printer 100 includes an inkjet head 115 and a medium holding mechanism that faces the inkjet head 115 and holds the recording medium F. The medium holding mechanism also functions as a recording paper moving mechanism that moves the recording medium F. The medium holding mechanism includes a conveyor belt 107, a drive roller 108, a driven roller 109, a negative pressure chamber 111, and a fan 121.

[0019] The image forming operation of this inkjet printer 100 will now be described. First, the control device 122 starts image processing for recording, generates an image signal corresponding to the image data, and generates control signals for controlling the operations of the various rollers, the negative pressure chamber 111, and the like.

[0020] Under the control of the control device 122, the paper feed roller 102 or 103 takes out recording media F of the selected size one by one from the cassette 101a or 101b and transports them to the pairs of transport rollers 104 and 105 and the pair of registration rollers 106. The pair of registration rollers 106 corrects the skew of the recording media F and transports the recording media F at a predetermined timing.

[0021] The negative pressure chamber 111 sucks air through the holes of the conveyor belt 107. Therefore, the recording medium F is adsorbed to the conveyor belt 107 and is conveyed to the position below the inkjet head 115 as the conveyor belt 107 moves.

[0022] The inkjet head 115 discharges thermochromic ultraviolet curable ink in synchronization with the timing at which the recording medium F is conveyed under the control of the control device 122. Thereby, an ink layer is formed at a desired position on the recording medium F.

[0023] Thereafter, the drying device 118 dries the ink layer on the recording medium F in synchronization with the timing at which the recording medium F is conveyed under the control of the control device 122. Thereby, moisture is removed from the ink layer on the recording medium F.

[0024] Thereafter, the ultraviolet irradiation device 119 irradiates the dried ink layer with ultraviolet rays in synchronization with the timing at which the recording medium F is conveyed under the control of the control device 122. Thereby, the ink layer is fixed on the recording medium F. In this way, when the ink is cured after drying the ink layer to remove moisture, sufficient curing can be achieved.

[0025] After the ink is fixed, the pair of conveying rollers 112, 113, and 114 discharge the recording medium F to the paper discharge tray 120.

[0026] As shown in FIG. 1, the inkjet head 115 and the drying device 118 are arranged close to each other. Also, the drying device 118 and the ultraviolet irradiation device 119 are arranged close to each other. Therefore, before the inkjet head 115 finishes the operation of discharging ink to the recording medium F, the drying device 118 starts the drying operation of drying the ink on the recording medium F, and the ultraviolet irradiation device 119 starts the irradiation operation of irradiating the ink on the recording medium F with ultraviolet rays. In this way, before all the ink ejection operations onto a single recording medium F are completed, the ink on the recording medium F is promptly dried and then promptly fixed. By doing so, it is possible to prevent the ejected ink from spreading on the recording medium F and form a high-definition image. In particular, when a non-absorbent medium is used as the recording medium F, if the operations from ink ejection to fixing are promptly completed, it is possible to prevent the ink before fixing from being rubbed on the recording medium F.

[0027] Note that the inkjet printer 100 may be configured such that the inkjet head 115 and the drying device 118 are arranged separately, and the drying device 118 starts the drying operation after all the ink ejection operations onto a single recording medium F are completed. Similarly, the inkjet printer 100 may be configured such that the drying device 118 and the ultraviolet irradiation device 119 are arranged separately, and the ultraviolet irradiation device 119 starts the irradiation operation after all the drying operations of the ink on a single recording medium F are completed.

[0028] 2. Ink Hereinafter, the ink composition used in the above-described image forming apparatus will be described. As described above, the ink composition is a water-based thermochromic ultraviolet curable ink, which exhibits thermochromism and has the property of curing with ultraviolet light. The ink composition contains a thermochromic pigment, water, a water-soluble or water-dispersible polymerizable compound, a water-soluble crosslinking agent, and a water-soluble photoinitiator.

[0029] Each component of the ink composition, namely, the "thermochromic pigment", "water", "water-soluble or water-dispersible polymerizable compound", "water-soluble crosslinking agent", and "water-soluble photoinitiator", will be described in order. In the following description, the ink composition is simply referred to as ink.

[0030] The "thermochromic pigment" may be a known thermochromic pigment particle. The color pigment particle may be an irreversible type that cannot regain its original color after discoloration, or a reversible type that can repeatedly change color and regain color. For example, the pigment may be a known thermochromic pigment particle. In this case, the color pigment particle may be an irreversible type that cannot regain its color after discoloration, or a reversible type that can repeatedly fade and recolor.

[0031] The color pigment particles are preferably microencapsulated pigments. Microencapsulated pigments are chemically and physically stable, and are therefore advantageous in that they maintain the same composition and can provide the same effects under various conditions of use.

[0032] According to one example, a microencapsulated pigment exhibiting thermal decolorization contains, as encapsulated components, (a) a color former, (b) a color developer, and (c) a decolorizer. The (a) color former is a component that determines color and can be a compound that donates electrons to the color developer to develop color. A typical color former is a leuco dye. The (b) color developer can be a compound that accepts electrons from the color former and functions as a color developer for the color former. The (c) decolorizer (color change temperature regulator) can be a compound that reversibly causes an electron transfer reaction between the color former and the color developer within a specific temperature range. Microencapsulated pigments containing the components (a) to (c) are reversible and are well known.

[0033] Therefore, known components can be used for the components (a) to (c), and the blending ratios of the components (a) to (c) can be determined appropriately.

[0034] Furthermore, various additives such as antioxidants, ultraviolet absorbers, infrared absorbers, dissolution aids, antiseptics and antifungals can be added to the microencapsulated pigments as long as they do not affect their functions.

[0035] Microencapsulation can be carried out by known methods. Examples of the material for the diaphragm of the capsule include epoxy resin, urea resin, urethane resin, isocyanate resin, etc. Furthermore, a secondary resin film can be provided on the surface of the microcapsule according to the purpose to impart durability or modify the surface characteristics.

[0036] The microcapsule pigment preferably has a range of inclusion / wall film = 7 / 1 to 1 / 1 (mass ratio). By having the ratio of the wall film within the range, it is possible to prevent a decrease in color density and sharpness during color development. More preferably, the microcapsule pigment is within the range of inclusion / wall film = 6 / 1 to 1 / 1 (mass ratio).

[0037] The microcapsule pigment has an average particle diameter of, for example, 300 to 5000 nm, preferably 300 to 4000 nm, more preferably 500 to 3000 nm. When the particle diameter becomes smaller, the color development tendency tends to decrease. When the particle diameter becomes larger, the dispersibility in the ink and the inkjet ejection property tend to deteriorate.

[0038] As the average particle diameter of the microcapsule pigment, the average particle diameter (median diameter) of particles equivalent to equal-volume spheres is used. For the most optimal measurement, it can be measured using a laser diffraction type particle size distribution measuring device SALD7000 manufactured by Shimadzu Corporation, a laser diffraction / scattering type particle size distribution measuring device calibrated by a direct measurement method.

[0039] Examples of the above direct measurement method include the image analysis method, in which calibration is performed by measuring the area (two-dimensional) of individual particles from an image taken with a microscope to measure the equivalent diameter, and the Coulter method (electrical sensing zone method), in which a constant current is passed through a minute hole (aperture) of a detector using a Coulter counter, and the equivalent diameter is measured from the change in impedance that occurs when the particle passes through the hole. The calibration of the laser measurement method is performed based on the values obtained by these methods.

[0040] Measurement of the average particle size by the image analysis method can be performed, for example, by using the image analysis type particle size distribution measurement software "MacView" manufactured by Mountech Co., Ltd. to determine the region of the particles, calculating the equivalent diameter of the projected area circle (Heywood diameter) from the area of the particle region, and measuring it as the average particle size of the particles equivalent to an equal volume sphere based on that value.

[0041] Measurement of the average particle size by the Coulter method is applicable when the particle size of all particles or most particles exceeds 0.2 μm, and it can be measured, for example, by using the particle size distribution measurement device "Multisizer 4e" manufactured by Beckman Coulter, Inc.

[0042] The colored pigment particles can be blended in an amount of, for example, 3 to 30% by mass, preferably 3 to 20% by mass, more preferably 5 to 15% by mass, based on the total amount of the ink.

[0043] As the "water", ion-exchanged water or pure water can be used. Water can be blended in an amount of, for example, 40 to 90% by mass, preferably 50 to 85% by mass, more preferably 60 to 80% by mass, based on the total amount of the ink.

[0044] The "water-soluble or water-dispersible polymerizable compound" is preferably a water-soluble polymerizable compound, more preferably a water-soluble methacrylamide monomer, and even more preferably a water-soluble monofunctional methacrylamide monomer. The methacrylamide monomer refers to a monomer having a methacrylamide group. The monofunctional methacrylamide monomer refers to a monomer having one methacrylamide group. Examples of the "water-soluble or water-dispersible polymerizable compound" include 4-[(3-methacrylamidopropyl)dimethylammonio]butane-1-sulfonic acid, urethane acrylate, methoxyethyl acrylate, isobutyl (meth)acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, and the like.

[0045] The polymerizable compound can be blended in an amount of, for example, 5 to 30% by mass, preferably 10 to 30% by mass, more preferably 10 to 20% by mass, based on the total amount of the ink.

[0046] The "water-soluble crosslinking agent" is preferably a water-soluble acrylamide monomer, and is a water-soluble polyfunctional acrylamide monomer. The acrylamide monomer refers to a monomer having an acrylamide group. The polyfunctional acrylamide monomer refers to a monomer having multiple (e.g., 2 to 4) acrylamide groups in one molecule. Examples of the "water-soluble crosslinking agent" include N-[tris(3-acrylamidopropoxymethyl)methyl]acrylamide and N,N'-methylenebisacrylamide.

[0047] The water-soluble crosslinking agent can be blended in an amount of, for example, 2 to 15% by mass, preferably 5 to 15% by mass, and more preferably 5 to 10% by mass, based on the total amount of the ink.

[0048] The "water-soluble photopolymerization initiator" may be a known water-soluble photopolymerization initiator, such as the water-soluble photopolymerization initiator disclosed in International Publication No. 2017-145484. An example of the "water-soluble photopolymerization initiator" is FOM-03011 (FUJIFILM Wako Pure Chemical Industries, Ltd.).

[0049] The water-soluble photopolymerization initiator can be blended in an amount of, for example, 0.2 to 2% by mass, preferably 0.5 to 2% by mass, and more preferably 0.5 to 1% by mass, based on the total amount of the ink.

[0050] In addition to the above components, the ink composition may further contain additives, such as general-purpose auxiliaries such as dispersants, stabilizers, viscosity adjusters, preservatives, humectants, wetting agents, and antifoaming agents.

[0051] An example of the composition of the ink composition is shown below. [composition] Thermochromic microcapsule pigment: 10.0% by mass 4-[(3-methacrylamidopropyl)dimethylammonio]butane-1-sulfonic acid: 15.0% by mass N-[Tris(3-acrylamidopropoxymethyl)methyl]acrylamide: 7.5% by mass Water-soluble photopolymerization initiator: 0.8% by mass Dispersant: 0.6% by mass Preservative: 0.02% by mass Ion-exchanged water: balance (66.08% by mass

[0052] [Preparation method] First, 60 parts by mass of water is added to 10.0 parts by mass of microcapsule pigment showing thermochromism. Then, 15.0 parts by mass of 4-[(3-methacrylamidopropyl)dimethylammonio]butane-1-sulfonic acid, 7.5 parts by mass of N-[tris(3-acrylamidopropoxymethyl)methyl]acrylamide, 0.8 parts by mass of water-soluble photopolymerization initiator, 0.6 parts by mass of polyoxyethylene derivative ammonium salt as a dispersant, 0.02 parts by mass of 1,2-benzisothiazolin-3-one as a preservative, and 6.08 parts by mass of water as the balance are added to prepare a total of 100.0 parts by mass of a mixture. The mixture is stirred to obtain an ultraviolet-curable ink in which the microcapsule pigment showing thermochromism is dispersed.

[0053] 3. Effects Inks of the type cured by ultraviolet rays are generally organic solvent-based inks mainly composed of ultraviolet-curable resins, rather than water-based inks. Therefore, when a pigment showing thermochromism is incorporated into such an ultraviolet-curable ink, the pigment showing thermochromism may come into contact with the organic solvent and impair the color-changing function. In addition, organic solvent-based ultraviolet-curable inks have a high viscosity at room temperature. Therefore, when such an ultraviolet-curable ink is ejected with an inkjet printer, it is necessary to heat the ink to lower the viscosity.

[0054] On the other hand, described above Since the thermochromic ultraviolet-curable ink is a water-based ink, the pigment showing thermochromism can be stably retained in the ink while maintaining the color-changing function. Also, described aboveSince the ink is water-based, it has a lower viscosity compared to conventional ultraviolet curable inks based on organic solvents. Therefore, described above the ink can be ejected by an inkjet printer without heating.

[0055] Thus, described above the ink is excellent in color change function and can achieve high ejection stability in inkjet recording. Also, described above since the ink has high ejection stability, excellent printability can be achieved. In addition, described above since the ink is ultraviolet curable, excellent fixing property can be achieved.

[0056] Also, the inkjet type image forming apparatus according to the embodiment ejects the thermochromic ultraviolet curable ink having the above effects onto a recording medium to form an ink layer, then dries the ink layer, and further fixes it by ultraviolet irradiation. Therefore, the image forming apparatus according to the embodiment can described above exhibit the same effects as the ink. That is, the image forming apparatus according to the embodiment can achieve high ejection stability, excellent printability, and excellent fixing property. Also, the fixed image can exhibit an excellent color change function. Further, the image apparatus according to the embodiment has the advantage of not requiring a heating operation during ink ejection.

[0057] Although some embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are included in the invention described in the claims and its equivalent scope.

Description of Reference Numerals

[0058] 100... Inkjet printer, 101a, 101b... Cassettes, 102, 103... Paper feed rollers, 104, 105... Pair of conveying rollers, 106... Pair of resist rollers, 107... Conveyor belt, 108... Driving roller, 109... Driven roller, 111... Negative pressure chamber, 112, 113, 114... Pair of conveying rollers, 115... Inkjet head, 116... Ink cartridge, 117... Tube, 118... Drying device, 119... Ultraviolet irradiation device, 120... Paper discharge tray, 121... Fan, 122... Control device, F... Recording medium

Claims

1. An inkjet head that discharges an ink composition containing a heat-discoloring pigment, water, a water-soluble or water-dispersible polymerizable compound, a water-soluble crosslinking agent, and a water-soluble photopolymerization initiator onto a recording medium to form an ink layer on the recording medium, a drying device that dries the ink layer, and an irradiation device that irradiates ultraviolet rays onto the dried ink layer An image forming apparatus comprising:

2. The image forming apparatus according to claim 1, wherein before the inkjet head finishes discharging the ink composition onto the recording medium, the drying device starts a drying operation for drying the ink layer, and the irradiation device starts an irradiation operation for irradiating the ultraviolet rays onto the ink layer.

3. The image forming apparatus according to claim 1 or 2, wherein the recording medium is a non-absorbent recording medium.

4. The image forming apparatus according to any one of claims 1 to 3, wherein the pigment is a microcapsule pigment.

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