Inkjet recording ink composition and image forming apparatus

Abstract

To provide an ink composition for inkjet recording that achieves superior dischargeability even after remaining unused for an extended time.SOLUTION: An ink composition for inkjet recording according to an embodiment contains water, a microcapsule colorant with a colorant enclosed in a resin coating, polyether phosphoester as a dispersant, and cellulose nanofibers with an average fiber length of 400-1000 nm. The content of the cellulose nanofibers is 1.5-12 pts.mass relative to 100 pts.mass of the microcapsule colorant.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] Embodiments of the present invention relate to an ink composition for inkjet recording and an image forming apparatus.

Background Art

[0002] An inkjet type image forming apparatus ejects ink from nozzles of an inkjet head and attaches it to a recording medium to perform printing. It is known that when an inkjet type image forming apparatus remains unused for a long period of time, the nozzles of the inkjet head become clogged with ink.

[0003] On the other hand, as an ink for inkjet recording, a thermochromic ink containing a pigment that exhibits reversible thermochromism is known. Such a thermochromic pigment includes a reversible thermochromic composition composed of an electron-donating color-forming organic compound, an electron-accepting compound, and a reaction medium that reversibly causes an electron transfer reaction between the electron-donating color-forming organic compound and the electron-accepting compound in a specific temperature range. Such a thermochromic pigment can have a form of microcapsules in which the reversible thermochromic composition is encapsulated by a resin coating.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The problem to be solved by the present invention is to provide an ink composition for inkjet recording that can achieve excellent ejection performance even after the inkjet type image forming apparatus has remained unused for a long period of time.

Means for Solving the Problems

[0006] According to the first embodiment, Water and, Microcapsule colorants in which colorants are encapsulated by a resin coating, Polyether phosphate ester as a dispersant, Cellulose nanofibers having an average fiber length of 400-1000 nm and Includes, An inkjet recording ink composition is provided, which contains the cellulose nanofibers in an amount of 1.5 to 12 parts by mass per 100 parts by mass of the microcapsule colorant.

[0007] According to the second embodiment, A container containing the ink composition according to the first embodiment, An inkjet head is supplied with the ink composition from the container and ejects the ink composition toward a recording medium. An image forming apparatus is provided that includes the following. [Brief explanation of the drawing]

[0008] [Figure 1] A schematic diagram showing an example of an image forming apparatus according to an embodiment. [Modes for carrying out the invention]

[0009] In inkjet image forming apparatuses, ink ejection performance deteriorates if they remain unused for extended periods. In particular, the inventors focused on the problem that inks containing microcapsule pigments are prone to clogging when left unused in an inkjet image forming apparatus for extended periods. The inventors discovered that this problem can be solved by combining ink containing microcapsule pigments with a specific type of dispersant and cellulose nanofibers of a predetermined fiber length, and thus completed the present invention.

[0010] 1. Ink composition for inkjet recording The inkjet recording ink composition according to this embodiment is Water and, Microcapsule colorants in which colorants are encapsulated by a resin coating, Polyether phosphate ester as a dispersant, Cellulose nanofibers having an average fiber length of 400-1000 nm and Includes, The cellulose nanofiber is contained in an amount of 1.5 to 12 parts by mass per 100 parts by mass of the microcapsule colorant.

[0011] The following describes each component of the inkjet recording ink composition. In the following description, the inkjet recording ink composition will also be referred to as "ink composition" or "ink."

[0012] <Water> For the "water," deionized water or pure water can be used. The water can be added in an amount of, for example, 40 to 90% by mass, preferably 50 to 80% by mass, relative to the total amount of ink.

[0013] <Microcapsule colorants> Microcapsule colorants are microcapsules in which a colorant is encapsulated by a resin coating. Microcapsule colorants preferably exhibit thermal color change properties. Preferably, known microcapsule pigments that exhibit thermal color change properties can be used as microcapsule colorants. Microcapsule pigments may be of an irreversible type that cannot revert to its original color after color change, or they may be of a reversible type that can repeatedly change color and re-color. For example, known microcapsule pigments that exhibit thermal decolorization properties can be used as microcapsule pigments. In this case, microcapsule pigments may be of an irreversible type that cannot revert to its original color after decolorization, or they may be of a reversible type that can repeatedly decolorize and re-color.

[0014] According to one example, a microcapsule pigment exhibiting thermochromism uses, as an inclusion, a thermochromic composition containing (a) a color-forming compound, (b) a developer, and (c) a decolorizing agent. (a) The color-forming compound is a component that determines color and can be a compound that donates electrons to the developer and develops color. A typical color-forming compound is a leuco dye. (b) The developer can be a compound that receives electrons from the color-forming compound and functions as a developer for the color-forming compound. (c) The decolorizing agent (color change temperature adjuster) can be a compound that reversibly causes an electron transfer reaction between the color-forming compound and the developer in a specific temperature range. The microcapsule pigment containing the components (a) to (c) is a reversible type and is well-known.

[0015] Therefore, for the components (a) to (c), known components can be used respectively. Also, the blending ratios of the components (a) to (c) can be determined as appropriate.

[0016] Furthermore, various additives such as antioxidants, ultraviolet absorbers, infrared absorbers, solubilizing agents, antiseptic and antifungal agents can be added to the microcapsule pigment as long as they do not affect its function.

[0017] The microcapsule pigment is chemically and physically stable, and thus is excellent in that it can be maintained in the same composition and exhibit the same effects under various usage conditions.

[0018] Microencapsulation can be carried out by known methods. Examples of the material for the capsule wall membrane 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.

[0019] The microcapsule pigment preferably has an inclusion / wall film ratio of 7 / 1 to 1 / 1 (mass ratio). By having the ratio of the wall film within this 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).

[0020] 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.

[0021] In this specification, 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 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.

[0022] 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 detection 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 particles pass through the hole. The calibration of the laser measurement method is performed based on the values obtained by these methods.

[0023] The measurement of the average particle diameter by the image analysis method can be performed, for example, by using the image analysis type particle size distribution measurement software "MacView" manufactured by Mounttech to determine the area of the particles, calculating the equivalent diameter of the projected area circle (Heywood diameter) from the area of the particle area, and measuring it as the average particle diameter of particles equivalent to equal-volume spheres based on that value.

[0024] The Coulter method for measuring average particle size is applicable when the particle size of all or most particles exceeds 0.2 μm, and can be measured using, for example, the Beckman Coulter Multisizer 4e particle size distribution analyzer.

[0025] The microcapsule colorant can be added in an amount of, for example, 3 to 30% by mass, preferably 3 to 20% by mass, and more preferably 5 to 15% by mass, relative to the total amount of ink.

[0026] <Polyether phosphate esters as dispersants> Polyether phosphate esters used as dispersants are phosphate esters of polyethers, and are compounds having multiple phosphate ester groups in a single molecule.

[0027] Polyether phosphate esters function as dispersants in inks, and the mechanism is thought to be as follows: The phosphate ester groups of polyether phosphate esters act as adsorption functional groups to other substances such as microcapsule pigments. Specifically, by having multiple phosphate ester groups in a single molecule, they adsorb to other compounds at multiple locations, forming a network that extends throughout the entire ink composition. When the amount is small relative to the adsorbed substance, such as microcapsule pigments, it exhibits viscosity by binding the pigments together. On the other hand, when the amount is large relative to the adsorbed substance, it exhibits functions such as stabilization due to steric hindrance (dispersant) and delaying the development of viscosity (leveling agent).

[0028] As the polyether phosphate ester, any polyether phosphate ester known to be usable as a dispersant in the art can be used. Commercially available polyether phosphate esters can also be used, for example, Disparon 3500 (manufactured by Kusumoto Chemical Co., Ltd.), Disparon DA-375 (manufactured by Kusumoto Chemical Co., Ltd.), Disparon DA-325 (manufactured by Kusumoto Chemical Co., Ltd.), Disparon AQ-320 (manufactured by Kusumoto Chemical Co., Ltd.), Disparon AQ-330 (manufactured by Kusumoto Chemical Co., Ltd.), HIPLAAD_ED-152 (manufactured by Kusumoto Chemical Co., Ltd.), HIPLAAD_ED-153 (manufactured by Kusumoto Chemical Co., Ltd.), HIPLAAD_ED-154 (manufactured by Kusumoto Chemical Co., Ltd.), HIPLAAD_ED-118 (manufactured by Kusumoto Chemical Co., Ltd.), and HIPLAAD_ED-174. Examples include (manufactured by Kusumoto Chemical Co., Ltd.), HIPLAAD_ED-251 (manufactured by Kusumoto Chemical Co., Ltd.), Prysurf A215C (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), Neoscore CM57 (manufactured by Toho Chemical Industry Co., Ltd.), Adekacol TS (manufactured by ADEKA), Adekacol CS (manufactured by ADEKA), DISPERBYK-180 (manufactured by Bic Chemie Co., Ltd.), Phosphanol RA-600 (manufactured by Toho Chemical Industry Co., Ltd.), Phosphanol ML-240 (manufactured by Toho Chemical Industry Co., Ltd.), Phosphanol RS-610 (manufactured by Toho Chemical Industry Co., Ltd.), and Phosphanol RS-710 (manufactured by Toho Chemical Industry Co., Ltd.).

[0029] In addition to being an excellent dispersant, polyether phosphate esters are also superior in that they do not easily penetrate microcapsule colorants and are less likely to enter the microcapsules and cause dissolution or precipitation of the encapsulated substances.

[0030] Polyether phosphate ester can be added to the ink in an amount of, for example, 1 to 30 parts by mass, preferably 2 to 26 parts by mass, and more preferably 3 to 25 parts by mass, per 100 parts by mass of microcapsule colorant.

[0031] <Cellulose nanofiber> Cellulose nanofibers are materials obtained by breaking down (defibrillating) plant fibers such as wood fibers (pulp) to the nanoscale. Cellulose nanofibers have an average fiber length of 400 to 1000 nm. Preferably, cellulose nanofibers have an average fiber length of 500 to 900 nm, and more preferably 600 to 800 nm.

[0032] The average fiber length of cellulose nanofibers refers to the number-average fiber length. The number-average fiber length can be determined as follows: The fiber length is measured from atomic force microscope images (3000 nm × 3000 nm) of cellulose nanofibers fixed on mica sections, and the number-average fiber length is calculated from the measurement results of 150 or more fibers (e.g., 150 fibers). Fiber length is measured using the image analysis software WinROOF (manufactured by Mitani Corporation) in the range of 100 nm to 2000 nm.

[0033] If the average fiber length of cellulose nanofibers is too long, it is thought that they may clog the nozzles when ejecting ink in an inkjet image forming machine, or that the viscosity may increase, making ejection difficult. If the average fiber length of cellulose nanofibers is too short, it is thought that they may not intertwine well with the microcapsule colorants.

[0034] Cellulose nanofibers with an average fiber length of 400-1000 nm offer the following advantages: They possess high transparency and do not hinder the color development of colorants. They also have high dispersibility in ink and do not obstruct ink ejection from the inkjet head nozzles. Furthermore, they do not clog the nozzles or narrow passages within the inkjet head. In addition, their viscosity can be kept at a level suitable for ejection by inkjet image forming machines.

[0035] Cellulose nanofibers have an average fiber diameter of, for example, 1 to 10 nm, preferably 2 to 5 nm. The average fiber diameter refers to the number-average fiber diameter. The number-average fiber diameter can be measured in the same way as the number-average fiber length. Cellulose nanofibers also have an aspect ratio (i.e., the ratio of average fiber length to average fiber diameter) of, for example, 100 to 400, preferably 110 to 350. Thus, when cellulose nanofibers have relatively fine fibers and a relatively large aspect ratio, the above-mentioned effect of cellulose nanofibers on dischargeability can be further enhanced.

[0036] While cellulose nanofibers are not particularly limited as long as they have an average fiber length of 400 to 1000 nm, for example, TEMPO-oxidized cellulose nanofibers and phosphate-esterified cellulose nanofibers can be used. TEMPO-oxidized cellulose nanofibers are obtained by reacting wood fibers with a TEMPO (2,2,6,6-tetramethylpiperidine 1-oxyl) catalyst to convert the primary hydroxyl groups of cellulose into carboxyl groups, and then mechanically defibrating them. TEMPO-oxidized cellulose nanofibers are available from Nippon Paper Industries.

[0037] Only when cellulose nanofibers are incorporated into the ink in combination with polyether phosphate ester as a dispersant can such ink exhibit excellent ejection properties even after prolonged periods of non-use in an inkjet image forming apparatus. This is thought to be due to the following reason: When cellulose nanofibers are used in combination with polyether phosphate ester as a dispersant, the polyether phosphate ester intertwines with the microcapsule pigment and also intertwines with the network between the cellulose nanofibers, thus stably maintaining the microcapsule pigment. As a result, when the ink at the nozzle tip dries out during non-use of the inkjet image forming apparatus, the cellulose nanofibers, together with the dispersant, form a film on the ink at the nozzle tip, preventing the ink inside the nozzle from drying out.

[0038] Cellulose nanofibers can be incorporated into the ink in an amount of, for example, 1.5 to 12 parts by mass, preferably 2 to 11 parts by mass, and more preferably 2 to 10 parts by mass, per 100 parts by mass of microcapsule colorant.

[0039] <Additional ingredients> In addition to the above components, the ink may further contain additives. For example, it may further contain general-purpose auxiliary agents such as dispersants, stabilizers, viscosity modifiers, preservatives, humectants, wetting agents, and defoamers.

[0040] <Effects> The ink composition according to the embodiment contains cellulose nanofibers having an average fiber length of 400 to 1000 nm in combination with a polyether phosphate ester as a dispersant. As a result, the ink composition according to the embodiment can achieve excellent ejection performance even after being unused for a long period of time in an inkjet image forming apparatus.

[0041] 2. Image forming apparatus The ink composition described above can be used in an inkjet image forming apparatus. That is, an inkjet image forming apparatus can be used in an inkjet image forming apparatus. A container containing the ink composition described in section "1. Inkjet recording ink composition", An inkjet head is supplied with the ink composition from the container and ejects the ink composition toward a recording medium. It is equipped with.

[0042] Below, an example of an inkjet image forming apparatus will be described with reference to Figure 1. The image forming apparatus shown in Figure 1 includes a housing equipped with a paper output tray 118. Inside the housing are cassettes 100 and 101, paper feed rollers 102 and 103, transport roller pairs 104 and 105, registration roller pair 106, transport belt 107, fan 110, negative pressure chamber 111, transport roller pairs 112, 113 and 114, inkjet heads 115C, 115M, 115Y and 115Bk, ink cartridges 116C, 116M, 116Y and 116Bk, and tubes 117C, 117M, 117Y and 117Bk.

[0043] Cassettes 100 and 101 contain recording media P of different sizes. Paper feed rollers 102 or 103 take the recording media P corresponding to the selected size from cassette 100 or 101 and transport it to transport roller pairs 104 and 105 and registration roller pair 106.

[0044] 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 110 is installed to attract the recording medium P to the conveyor belt 107. Downstream of the conveyor belt 107 in the conveying direction, conveyor roller pairs 112, 113, and 114 are installed. A heater can be installed in the conveying path from the conveyor belt 107 to the output tray 118 to heat the printed layer formed on the recording medium P.

[0045] Above the conveyor belt 107, four rows of inkjet heads are arranged, each ejecting ink onto the recording medium P according to the image data. From upstream, the order is: inkjet head 115C ejecting cyan (C) ink, inkjet head 115M ejecting magenta (M) ink, inkjet head 115Y ejecting yellow (Y) ink, and inkjet head 115Bk ejecting black (Bk) ink.

[0046] Each inkjet head 115C, 115M, 115Y, and 115Bk is equipped with a cyan (C) ink cartridge 116C, a magenta (M) ink cartridge 116M, a yellow (Y) ink cartridge 116Y, and a black (Bk) ink cartridge 116Bk, each containing the corresponding ink. These cartridges 116C, 116M, 116Y, and 116Bk are connected to the inkjet heads 115C, 115M, 115Y, and 115Bk, respectively, by tubes 117C, 117M, 117Y, and 117Bk.

[0047] The ink composition contained in at least one of the ink cartridges 116C, 116M, 116Y, and 116Bk is an ink composition according to the embodiment. Here, as an example, the ink compositions contained in ink cartridges 116C, 116M, 116Y, and 116Bk are all ink compositions according to the embodiment.

[0048] Next, the image forming operation of this image forming apparatus will be described. First, an image processing means (not shown) starts image processing for recording, generates an image signal corresponding to the image data, and also generates control signals to control the operation of various rollers and the negative pressure chamber 111.

[0049] The paper feed roller 102 or 103, under the control of the image processing means, takes out one recording medium P of the selected size at a time from the cassette 100 or 101 and transports it to the transport roller pair 104 and 105 and the registration roller pair 106. The registration roller pair 106 corrects the skew of the recording medium P and transports the recording medium P at a predetermined timing.

[0050] The negative pressure chamber 111 draws in air through the holes in the conveyor belt 107. Consequently, the recording medium P, while held in place by the conveyor belt 107, is sequentially transported to positions below the inkjet heads 115C, 115M, 115Y, and 115Bk as the conveyor belt 107 moves.

[0051] The inkjet heads 115C, 115M, 115Y, and 115Bk eject ink in synchronization with the timing of the transport of the recording medium P, under the control of the image processing means. As a result, a color image is formed at the desired position on the recording medium P.

[0052] Subsequently, the transport roller pairs 112, 113, and 114 discharge the recording medium P on which the image has been formed to the output tray 118. If a heater is installed in the transport path from the transport belt 107 to the output tray 118, the printed layer formed on the recording medium P may be heated by the heater. Heating with a heater can improve the adhesion of the printed layer to the recording medium P, especially when the recording medium P is non-permeable.

[0053] As described above, in this image forming apparatus, the ink compositions contained in the ink cartridges 116C, 116M, 116Y, and 116Bk are all ink compositions according to the embodiment. Therefore, even after a long period of disuse, this image forming apparatus is less prone to ink clogging in the nozzles of the inkjet head and can exhibit excellent ejection performance. Consequently, even if this image forming apparatus has not been used for a long period after printing, it can start ejecting ink from the beginning without performing maintenance operations such as head cleaning to clear ink clogging. This image forming apparatus has the advantage of requiring less maintenance to clear ink clogging. [Examples]

[0054] [1] Production of cellulose nanofibers (CNF) [CNF production example 1] 5 g of bleached, unbeaten pulp derived from coniferous trees was mixed with 0.5 mmol of TEMPO catalyst (Sigma Aldrich) and 7.35 mmol of sodium bromide. Deionized water was added to make up 500 mL, and the mixture was stirred until uniformly dispersed. Then, 2.3 mmol of sodium hypochlorite was added to initiate the oxidation reaction. During the reaction, the pH of the system was maintained between 10.0 and 10.5 with a 0.5 N sodium hydroxide aqueous solution. After neutralizing the reaction solution with hydrochloric acid until neutral, the resulting solution was filtered through a glass filter and thoroughly washed with water to obtain oxidized pulp.

[0055] The above pulp was dispersed in ion-exchanged water to prepare an oxidized pulp slurry adjusted to a concentration of 3% (w / v). The slurry was then beaten (preliminary defibration treatment) using a Startlab RMH type (manufactured by AIMEX Co., Ltd.). The pulp slurry, which had undergone the preliminary defibration treatment described above, was diluted to a concentration of 1% (w / v), and then subjected to defibration treatment at a processing pressure of 150 MPa using an ultra-high pressure wet atomization device, NanoVeta (Yoshida Machinery Industry Co., Ltd.). This yielded a cellulose nanofiber dispersion.

[0056] Furthermore, after degassing the obtained cellulose nanofiber dispersion using an ultrasonic device, the resulting cellulose dispersion was observed using an atomic force microscope (AFM), and the number-average fiber length was found to be 800 nm. We will name this cellulose nanofiber "Type III".

[0057] [CNF production example 2] A cellulose nanofiber dispersion was produced using the same method as in CNF Production Example 1, except that the processing pressure of the ultra-high pressure wet atomization device NanoVeta was changed to 100 MPa. After degassing the obtained cellulose nanofiber dispersion using an ultrasonic device, the resulting cellulose dispersion was observed using an atomic force microscope (AFM), and the number-average fiber length was found to be 1100 nm. We will name this cellulose nanofiber "Type IV".

[0058] [2] Preparation of thermochromic ink <Example 1A: Thermochromic ink 1A> As a colorant, microcapsule pigments (average particle size: 600 nm) containing a heat-decolorizing composition (reversible heat-changeable composition) encapsulated in a resin coating were used. Three parts by mass of the colorant, 28 parts by mass of glycerin, 0.09 parts by mass of polyether phosphate ester (Phosphanol RS-710 manufactured by Toho Chemical Industry Co., Ltd.) as a dispersant, 1 part by mass of Surfinol® 465 manufactured by Nisshin Chemical Industry Co., Ltd. as a discharge stabilizer, 0.2 parts by mass of Proxel® XL-2 manufactured by Arcsarda Japan Co., Ltd. as a preservative, and 67.61 parts by mass of pure water were mixed and stirred using a stirrer. Then, 0.1 parts by mass of cellulose nanofiber was added, stirred using a homogenizer, and then filtered. This yielded heat-decolorizing ink 1A.

[0059] The cellulose nanofibers used were TEMPO-oxidized cellulose nanofibers (manufactured by Nippon Paper Industries Co., Ltd.), with a number-average fiber length of 600 nm, a number-average fiber diameter of 3-4 nm, and an aspect ratio of 150-200. Hereafter, these cellulose nanofibers will be referred to as "Type I".

[0060] <Example 1B~1E: Thermochromic ink 1B~1E> Except for changing the amount of dispersant added as shown in the table below, the thermochromic inks 1B to 1E were prepared in the same manner as thermochromic ink 1A. Pure water was added so that the total volume of ink was 100 parts by mass. Similarly, in the preparation of subsequent thermochromic inks, pure water was added so that the total volume of ink was 100 parts by mass.

[0061] <Example 2A~2D: Thermochromic ink 2A~2D> Except for changing the amount of cellulose nanofiber added, as shown in the table below, the thermochromic inks 2A to 2D were prepared using the same method as thermochromic ink 1A.

[0062] <Example 3A~3G: Thermochromic ink 3A~3G> Except for changing the amount of cellulose nanofiber added, as shown in the table below, the thermochromic inks 3A to 3G were prepared using the same method as thermochromic ink 1A.

[0063] <Example 4A: Thermochromic ink 4A> Except for changing the type of cellulose nanofiber from Type I to Type III (number-average fiber length: 800 nm), the thermochromic ink 4A was prepared using the same method as thermochromic ink 1A. <Example 4B~4E: Thermochromic ink 4B~4E> Except for changing the amount of dispersant added as shown in the table below, the thermochromic inks 4B to 4E were prepared using the same method as thermochromic ink 4A.

[0064] <Example 5A~5D: Thermochromic ink 5A~5D> Except for changing the amount of cellulose nanofiber added, as shown in the table below, the thermochromic inks 5A to 5D were prepared using the same method as thermochromic ink 4A.

[0065] <Example 6A~6E: Thermochromic ink 6A~6E> As shown in the table below, the thermochromic inks 6A to 6E were prepared using the same method as thermochromic ink 1A, except that a dispersant was not added and the amount of cellulose nanofiber added was changed.

[0066] <Example 7A~7F: Thermochromic ink 7A~7F> As shown in the table below, the thermochromic inks 7A to 7F were prepared using the same method as thermochromic ink 1A, except that the type and amount of cellulose nanofiber added were changed. The cellulose nanofiber used was TEMPO-oxidized cellulose nanofiber (manufactured by Nippon Paper Industries Co., Ltd.), with a number-average fiber length of 300 nm, a number-average fiber diameter of 3 to 4 nm, and an aspect ratio of 75 to 100. Hereafter, this cellulose nanofiber will be referred to as "Type II".

[0067] <Example 8A~8F: Thermochromic ink 8A~8F> Except for the absence of a dispersant, as shown in the table below, the thermochromic inks 8A to 8F were prepared using the same method as thermochromic inks 7A to 7F.

[0068] <Example 9A~9C: Thermochromic ink 9A~9C> Except for changing the amount of cellulose nanofiber added, as shown in the table below, the thermochromic inks 9A to 9C were prepared using the same method as thermochromic ink 1A.

[0069] <Example 10A~10D: Thermochromic ink 10A~10D> As shown in the table below, the thermochromic inks 10A to 10D were prepared using the same method as thermochromic ink 1A, except that the type of cellulose nanofiber was changed from type I to type II and the amount of dispersant added was changed.

[0070] <Example 11A~11C: Heat-decolorizing ink 11A~11C> As shown in the table below, the thermochromic inks 11A to 11C were prepared using the same method as thermochromic ink 1A, except that the type of cellulose nanofiber was changed from Type I to Type II and the amount of cellulose nanofiber added was changed.

[0071] <Example 12A: Thermochromic ink 12A> As shown in the table below, thermochromic ink 12A was prepared using the same method as thermochromic ink 1A, except that the type of cellulose nanofiber was changed from type I to type III and no dispersant was added.

[0072] <Example 13A~13C: Heat-decolorizing ink 13A~13C> As shown in the table below, the thermochromic inks 13A to 13C were prepared using the same method as thermochromic ink 1A, except that the type of cellulose nanofiber was changed from Type I to Type III and the amount of cellulose nanofiber added was changed.

[0073] <Example 14A~14B: Thermochromic ink 14A~14B> Using polyvinylpyrrolidone as a dispersant, thermochromic inks 14A to 14B were prepared using the same method with the compositions listed in the table below.

[0074] <Example 15A~15F: Thermochromic ink 15A~15F> As shown in the table below, the thermochromic inks 15A to 15F were prepared using the same method as thermochromic ink 1A, except that the type of cellulose nanofiber was changed from Type I to Type IV (number-average fiber length: 1100 nm) and the amount of cellulose nanofiber added was changed.

[0075] <Example 16A~16F: Thermochromic ink 16A~16F> Except for the absence of a dispersant, as shown in the table below, the thermochromic inks 16A to 16F were prepared using the same method as thermochromic inks 15A to 15F.

[0076] <Examples 17A-17D: Thermochromic inks 17A-17D> As shown in the table below, the thermochromic inks 17A to 17D were prepared using the same method as thermochromic ink 1A, except that the type of cellulose nanofiber was changed from type I to type IV and the amount of dispersant added was changed.

[0077] <Example 18A~18C: Thermochromic ink 18A~18C> As shown in the table below, the thermochromic inks 18A to 18C were prepared using the same method as thermochromic ink 1A, except that the type of cellulose nanofiber was changed from type I to type IV and the amount of cellulose nanofiber added was changed.

[0078] [3] Evaluation method <Evaluation of variance> The prepared inks were visually inspected to check for color aggregation and gelation. 50g of ink that showed no color aggregation or gelation was filtered. The variance was evaluated using the following criteria. A: We were able to filter the entire 50g of ink. B: It was not possible to filter out the entire 50g of ink. C: Aggregation of colorants or gelation of the ink was observed.

[0079] <Evaluation of discharge after 24 hours> The prepared ink was filtered, and then ejection tests were conducted using an inkjet image forming apparatus. Specifically, after refreshing the nozzle (i.e., forcibly ejecting all the ink from the tube from the ink cartridge to the inkjet head), the apparatus was left at room temperature (approximately 25°C) for 24 hours. After 24 hours, the ink was ejected, and the ejection performance was evaluated according to the following criteria. A: Discharge was possible from all nozzles. B: Dispensing was possible with more than half of the nozzles (however, dispensing was not possible with some nozzles). C: Dispensing was possible with less than half of the nozzles. D: Discharge failed from all nozzles. -: The evaluation of discharge performance could not be performed because the evaluation results for dispersion were unsatisfactory.

[0080] [4] Results The ink composition and evaluation results are shown in the table below.

[0081] [Table 1]

[0082] [Table 2]

[0083] [Table 3]

[0084] [Table 4]

[0085] [Table 5]

[0086] [Table 6]

[0087] [Table 7]

[0088] [Table 8]

[0089] [Table 9]

[0090] [Table 10]

[0091] [Table 11]

[0092] The values ​​in the table represent the mass percentage of each component in the ink. In the table above, cellulose nanofiber is abbreviated as "CNF". Also, in the table above, polyether phosphate ester is abbreviated as "P" and polyvinylpyrrolidone as "PVP".

[0093] <Example 1A~1E: Thermochromic ink 1A~1E> The heat-decolorizing inks 1A to 1E showed good results in all evaluations of dispersibility and ejection performance after 24 hours. These results indicate that good results can be obtained by incorporating cellulose nanofibers with an average fiber length of 600 nm into the ink, and by incorporating polyether phosphate ester as a dispersant in an amount of 2 to 26% by mass relative to the colorant.

[0094] <Example 2A~2D: Thermochromic ink 2A~2D> The heat-decolorizing inks 2A to 2D showed good results in all evaluations of dispersibility and ejection performance after 24 hours. These results indicate that good results can be obtained by incorporating cellulose nanofibers with an average fiber length of 600 nm into the ink at a concentration of 2 to 10% by mass relative to the colorant, and by incorporating polyether phosphate ester as a dispersant into the ink.

[0095] <Example 3A~3G: Thermochromic ink 3A~3G> The heat-decolorizing inks 3A and 3B showed good results in all evaluations of dispersibility and ejectability after 24 hours. On the other hand, the heat-decolorizing inks 3C, 3D, 3F, and 3G could not be evaluated for ejectability due to pigment aggregation or ink gelation. Furthermore, heat-decolorizing ink 3E could not be ejected after 24 hours in an inkjet image forming apparatus. These results indicate that in order to achieve good ink ejectability after 24 hours, cellulose nanofibers must be incorporated into the ink in an amount greater than 1.3% by mass but less than 13.3% by mass relative to the pigment.

[0096] <Example 4A~4E: Thermochromic ink 4A~4E> The heat-decolorizing inks 4A to 4E showed good results in all evaluations of dispersibility and ejection performance after 24 hours. These results indicate that good results can be obtained by incorporating cellulose nanofibers with an average fiber length of 800 nm into the ink, and by incorporating polyether phosphate ester as a dispersant in an amount of 2 to 26% by mass relative to the colorant.

[0097] <Example 5A~5D: Thermochromic ink 5A~5D> The heat-decolorizing inks 5A to 5D showed good results in all evaluations of dispersibility and ejection performance after 24 hours. These results indicate that good results can be obtained by incorporating cellulose nanofibers with an average fiber length of 800 nm into the ink at a concentration of 2 to 10% by mass relative to the colorant, and by incorporating polyether phosphate ester as a dispersant into the ink.

[0098] <Example 6A~6E: Thermochromic ink 6A~6E> The heat-decolorizing inks 6A and 6C could not be ejected after 24 hours in an inkjet image forming apparatus. Furthermore, the ejection performance of the heat-decolorizing inks 6B, 6D, and 6E could not be evaluated due to pigment aggregation or ink gelation. These results indicate that incorporating polyether phosphate ester as a dispersant into the ink is essential to achieve good ink ejection performance after 24 hours.

[0099] <Example 7A~7F: Thermochromic ink 7A~7F> The ejection performance of the heat-decolorizing ink 7A could not be evaluated due to the aggregation of the colorant. Furthermore, the heat-decolorizing inks 7B to 7F could not be ejected after 24 hours in an inkjet image forming apparatus. These results indicate that, in order to achieve good ink ejection performance after 24 hours, it is necessary to incorporate cellulose nanofibers with an average fiber length longer than 300 nm into the ink.

[0100] <Example 8A~8F: Thermochromic ink 8A~8F> The heat-decolorizing inks 8A-8F could not be ejected after 24 hours in an inkjet image forming apparatus. These results indicate that in order to achieve good ink ejection after 24 hours, it is necessary to incorporate polyether phosphate ester as a dispersant into the ink and to incorporate cellulose nanofibers with an average fiber length of longer than 300 nm into the ink.

[0101] <Example 9A~9C: Thermochromic ink 9A~9C> The heat-decolorizing ink 9A could not be ejected after 24 hours in an inkjet image forming apparatus. Furthermore, the ejection performance of heat-decolorizing inks 9B and 9C could not be evaluated due to pigment aggregation or ink gelation. These results indicate that, in order to achieve good ink ejection performance after 24 hours, cellulose nanofibers must be incorporated into the ink in an amount greater than 1% by mass but less than 14% by mass relative to the pigment.

[0102] <Example 10A~10D: Thermochromic ink 10A~10D> The heat-decolorizing inks 10A to 10D could not be ejected after 24 hours in an inkjet image forming apparatus. These results indicate that in order to achieve good ink ejection after 24 hours, it is necessary to incorporate cellulose nanofibers with an average fiber length longer than 300 nm into the ink.

[0103] <Example 11A~11C: Heat-decolorizing ink 11A~11C> The heat-decolorizing inks 11A to 11C could not be ejected after 24 hours in an inkjet image forming apparatus. These results indicate that in order to achieve good ink ejection after 24 hours, it is necessary to incorporate cellulose nanofibers with an average fiber length longer than 300 nm into the ink.

[0104] <Example 12A: Thermochromic ink 12A> The heat-decolorizing ink 12A could not be ejected after 24 hours in an inkjet image forming apparatus. This result indicates that the inclusion of polyether phosphate ester as a dispersant in the ink is essential to achieve good ink ejection performance after 24 hours.

[0105] <Example 13A~13C: Heat-decolorizing ink 13A~13C> The heat-decolorizing ink 13A could not be ejected after 24 hours in an inkjet image forming apparatus. Furthermore, the ejection performance of heat-decolorizing inks 13B and 13C could not be evaluated due to pigment aggregation or ink gelation. These results indicate that, in order to achieve good ink ejection performance after 24 hours, cellulose nanofibers must be incorporated into the ink in an amount greater than 1% by mass but less than 14% by mass relative to the pigment.

[0106] <Example 14A~14B: Thermochromic ink 14A~14B> In the heat-decolorizing inks 14A and 14B, dispersants other than polyether phosphate ester were incorporated into the ink. These inks did not exhibit good dispersibility even when cellulose nanofibers were incorporated. These results indicate that, in order to achieve good ink dispersibility, it is necessary to use cellulose nanofibers in combination with polyether phosphate ester as a dispersant.

[0107] <Example 15A~15F: Thermochromic ink 15A~15F> The heat-decolorizing inks 15A, 15D-15F could not be evaluated for ejection performance due to pigment aggregation or ink gelation. Furthermore, heat-decolorizing inks 15B-15C could not be ejected from some nozzles of the inkjet image forming apparatus after 24 hours due to poor dispersibility. These results indicate that, in order to achieve good ink dispersibility, it is necessary to incorporate cellulose nanofibers with an average fiber length shorter than 1100 nm into the ink.

[0108] <Example 16A~16F: Thermochromic ink 16A~16F> The heat-decolorizing inks 16A to 16C could not be ejected after 24 hours in an inkjet image forming apparatus due to poor dispersibility. Furthermore, the ejection performance of the heat-decolorizing inks 16D to 16F could not be evaluated due to gelation. These results indicate that, in order to achieve good ink dispersibility, it is necessary to incorporate polyether phosphate ester as a dispersant into the ink, and to incorporate cellulose nanofibers with an average fiber length shorter than 1100 nm into the ink.

[0109] <Examples 17A-17D: Thermochromic inks 17A-17D> The heat-decolorizing inks 17A-17D had poor dispersibility and could not be ejected from some nozzles of the inkjet image forming apparatus after 24 hours. These results indicate that, in order to achieve good ink dispersibility, it is necessary to incorporate cellulose nanofibers with an average fiber length shorter than 1100 nm into the ink.

[0110] <Example 18A~18C: Thermochromic ink 18A~18C> The heat-decolorizing inks 18A-18C had poor dispersibility and could not be ejected from some nozzles of the inkjet image forming apparatus after 24 hours. These results indicate that, in order to achieve good ink dispersibility, it is necessary to incorporate cellulose nanofibers with an average fiber length shorter than 1100 nm into the ink.

[0111] While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be carried out in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents. [Explanation of symbols]

[0112] 100...Cassette, 101...Cassette, 102...Paper feed roller, 103...Paper feed roller, 104...Conveyor roller pair, 105...Conveyor roller pair, 106...Register roller pair, 107...Conveyor belt, 110...Fan, 111...Negative pressure chamber, 112...Conveyor roller pair, 113...Conveyor roller pair, 114...Conveyor roller pair, 115Bk...Inkjet head, 115C...Inkjet head, 115M...Inkjet head, 115Y...Inkjet head, 116Bk...Ink cartridge, 116C...Ink cartridge, 116M...Ink cartridge, 116Y...Ink cartridge, 117Bk...Tube, 117C...Tube, 117M...Tube, 117Y...Tube, 118...Output tray, P...Recording medium.

Claims

1. Water and, Microcapsule colorants in which colorants are encapsulated by a resin coating, Polyether phosphate ester as a dispersant, Cellulose nanofibers having an average fiber length of 400-1000 nm and Includes, An inkjet recording ink composition comprising the cellulose nanofiber in an amount of 1.5 to 12 parts by mass per 100 parts by mass of the microcapsule colorant.

2. The ink composition according to claim 1, wherein the microcapsule colorant exhibits thermal discoloration.

3. The ink composition according to claim 1, wherein the polyether phosphate ester is contained in an amount of 1 to 30 parts by mass per 100 parts by mass of the microcapsule colorant.

4. The ink composition according to claim 1, wherein the microcapsule colorant has an average particle size of 300 to 5000 nm.

5. A container containing the ink composition according to any one of claims 1 to 4, An inkjet head is supplied with the ink composition from the container and ejects the ink composition toward a recording medium. An image forming apparatus equipped with [a specific feature].

Images