Ink composition for inkjet recording, and image formation apparatus

Abstract

To provide an ink composition for inkjet recording that is excellent in fixability to a non-permeable recording medium.SOLUTION: An ink composition for inkjet recording includes: a microcapsule coloring material which includes a coloring material within a resin coat, and exhibits thermochromic property; a dispersion liquid including an aqueous urethane resin and water; and at least one wetting agent selected from the group consisting of glycerin, ethylene glycol, and propylene glycol, wherein a ratio of the aqueous urethane resin occupied in the ink composition is in a range of 5 to 20 mass%, a ratio of the wetting agent occupied in the ink composition is in a range of 5 to 30 mass%, and the ink composition is styrene-free.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] An embodiment of the present invention relates to an ink composition for ink jet recording and an image forming apparatus. [Background technology]

[0002] Inkjet image forming devices perform printing by ejecting ink from the nozzles of an inkjet head and depositing the ink on a recording medium. In addition to paper, non-permeable recording media such as plastic film are used as the recording medium. When a non-permeable recording medium is used as the recording medium, the ink does not permeate the recording medium and remains on the surface of the recording medium, so the ink forms a film and is fixed on the recording medium.

[0003] On the other hand, as an inkjet recording ink, a thermochromic ink containing a pigment that exhibits reversible thermochromicity is known. As such a thermochromic pigment, one containing a reversible thermochromic composition consisting of an electron donating organic color-forming compound, an electron accepting compound, and a reaction medium that reversibly causes an electron donating / receiving reaction between the electron donating organic color-forming compound and the electron accepting compound in a specific temperature range is known. Such a thermochromic pigment can have the form of a microcapsule in which the reversible thermochromic composition is encapsulated in a resin coating. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2020-63320 A Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide an ink composition for ink jet recording that has excellent fixability to non-permeable recording media. [Means for solving the problem]

[0006] According to the first embodiment, A microcapsule color material in which a color material is encapsulated in a resin coating and exhibits thermochromic properties; A dispersion containing an aqueous urethane resin and water; At least one humectant selected from the group consisting of glycerin, ethylene glycol, and propylene glycol; An ink composition for ink jet recording comprising: the proportion of the aqueous urethane resin in the ink composition is within a range of 5 to 20% by mass, the ratio of the humectant in the ink composition is within a range of 5 to 30 mass %, Styrene-free An ink jet recording ink composition is provided.

[0007] According to the second embodiment, A container containing the ink composition according to the first embodiment; an inkjet head that receives the ink composition from the container and ejects the ink composition toward a recording medium; An image forming apparatus comprising: [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram illustrating an example of an image forming apparatus according to an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] 1. Ink composition for ink-jet recording The present inventors have newly discovered a problem that when particles containing a styrene-acrylic resin are blended as a fixing agent in an ink for inkjet recording, the storage stability of the ink (dispersion stability of the microcapsule pigment) decreases due to the presence of residual styrene monomer, and the ejection properties of the ink decrease. The present inventors have solved this problem by preparing a styrene-free ink using a specific fixing agent.

[0010] That is, the ink composition for ink jet recording according to the embodiment is A microcapsule color material in which a color material is encapsulated in a resin coating and exhibits thermochromic properties; A dispersion containing an aqueous urethane resin and water; At least one humectant selected from the group consisting of glycerin, ethylene glycol, and propylene glycol; Including, the proportion of the aqueous urethane resin in the ink composition is within a range of 5 to 20% by mass, the ratio of the humectant in the ink composition is within a range of 5 to 30 mass %, It is styrene-free.

[0011] In the following description, it will first be described that the ink composition for inkjet recording is styrene-free, and then each component of the ink composition for inkjet recording will be described. In the following description, the ink composition for inkjet recording will also be referred to as the "ink composition" or "ink."

[0012] As described above, the ink composition according to the embodiment is styrene-free. The term "styrene-free" means that the ink composition does not substantially contain styrene. For example, the term "styrene-free" means that the styrene concentration in the ink composition is below the detection limit, for example, 1000 ppm or less. Note that the term "styrene-free" does not exclude cases where a trace amount of styrene is inevitably mixed in.

[0013] The styrene-free ink composition has excellent storage stability. Specifically, the viscosity of the styrene-free ink composition is unlikely to increase after storage. More specifically, the styrene-free ink composition has a viscosity of preferably 45 mPa·s or less, more preferably 30 mPa·s or less, and even more preferably 20 mPa·s or less after storage at 45°C for two weeks. The viscosity of the ink composition after storage at 45°C for two weeks is not particularly limited, but is, for example, 1.0 mPa·s or more. That is, the styrene-free ink composition has a viscosity of preferably 1.0 to 45 mPa·s, more preferably 1.0 to 30 mPa·s, and even more preferably 1.0 to 20 mPa·s after storage at 45°C for two weeks. In addition, for a styrene-free ink composition, the percentage ratio of the viscosity V1 of the ink composition after storage at 45°C for two weeks to the viscosity (initial viscosity) V2 of the ink composition immediately after preparation (i.e., the percentage ratio V1 / V2) is preferably 250% or less, more preferably 200% or less, and even more preferably 150% or less. The percentage ratio V1 / V2 is not particularly limited, but is, for example, 100% or more. That is, the percentage ratio V1 / V2 is preferably 100 to 250%, more preferably 100 to 200%, and even more preferably 100 to 150%. When the viscosity or percentage ratio V1 / V2 of the ink composition after storage is within the above range, such an ink composition can be said to be styrene-free.

[0014] The above viscosity refers to the viscosity value measured using a cone-plate type rotational viscometer according to the method specified in JIS Z8803:2011 "Method of measuring viscosity of liquids". As the cone-plate type rotational viscometer, for example, an E-type viscometer TV-100 manufactured by Toki Sangyo Co., Ltd. can be used. Specifically, the viscosity in this specification refers to the viscosity value measured using a cone-plate type rotational viscometer with a 0.8° cone angle under conditions of a temperature of 25°C and a rotation speed of 20 rpm. Therefore, the viscosity described in this specification represents the viscosity at 25°C.

[0015] The ink composition according to the embodiment is styrene-free and therefore has excellent storage stability. Therefore, the ink composition according to the embodiment does not need to contain a colorant dispersant. However, this does not exclude the ink composition according to the embodiment from containing a colorant dispersant.

[0016] Next, each component of the ink composition for ink jet recording will be described.

[0017] <Microcapsule color material> The microcapsule color material is a microcapsule in which a color material is encapsulated by a resin coating. The microcapsule color material exhibits thermochromism. As the microcapsule color material, a known microcapsule pigment exhibiting thermochromism can be preferably used. The microcapsule pigment may be an irreversible type that cannot re-develop the original color after discoloration, or a reversible type that can repeatedly change color and re-develop color. For example, as the microcapsule pigment, a known microcapsule pigment exhibiting thermodecolorization can be used. In this case, the microcapsule pigment may be an irreversible type that cannot re-develop the color after discoloration, or a reversible type that can repeatedly discolor and develop color.

[0018] According to one example, a microcapsule pigment exhibiting thermal decolorization uses a thermochromic composition containing (a) a color former, (b) a color developer, and (c) a decolorizer as encapsulants. 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 representative color former is a leuco dye. The (b) color developer can be a compound that receives 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 in a specific temperature range. Such microcapsule pigments containing the components (a) to (c) are reversible and are known.

[0019] Therefore, known components can be used for each of the components (a) to (c), and the blending ratio of the components (a) to (c) can be appropriately determined.

[0020] Furthermore, various additives such as antioxidants, ultraviolet absorbers, infrared absorbers, dissolution aids, and preservatives and antifungals can be added to the microencapsulated pigment as long as their functions are not adversely affected.

[0021] Microencapsulated pigments are advantageous in that they are chemically and physically stable, and therefore can maintain the same composition and provide the same effects under various conditions of use.

[0022] Microencapsulation can be carried out by a known method. Examples of materials for the capsule wall include epoxy resin, urea resin, urethane resin, isocyanate resin, etc. Furthermore, a secondary resin film can be provided on the surface of the microcapsule depending on the purpose to impart durability or modify the surface properties.

[0023] The microcapsule pigment preferably has a mass ratio of encapsulation / wall film of 7 / 1 to 1 / 1. By keeping the wall film ratio within this range, it is possible to prevent a decrease in color density and clarity during color development. The microcapsule pigment more preferably has a mass ratio of encapsulation / wall film of 6 / 1 to 1 / 1.

[0024] The microencapsulated pigment has an average particle size of, for example, 300 to 5000 nm, preferably 300 to 4000 nm, and more preferably 500 to 3000 nm. If the particle size is smaller, the color development tends to decrease. If the particle size is larger, the dispersibility in the ink and the inkjet dischargeability tend to decrease.

[0025] In this specification, the average particle size of the microencapsulated pigment is the average particle size (median size) of particles equivalent to an equal volume sphere. The optimum measurement can be performed using a laser diffraction / scattering type particle size distribution analyzer SALD7000 manufactured by Shimadzu Corporation, which is a laser diffraction / scattering type particle size distribution analyzer calibrated by a direct measurement method.

[0026] Examples of the direct measurement methods include the image analysis method, in which the area (two-dimensional) of each particle is measured from an image taken with a microscope to determine the equivalent diameter, and the Coulter method (electrical sensing zone method), in which a constant current is passed through a tiny hole (aperture) in a detector using a Coulter counter, and the equivalent diameter is measured from the change in impedance that occurs when a particle passes through the hole.Calibration of the laser measurement method is performed based on the values ​​obtained by these methods.

[0027] The average particle size can be measured by image analysis, for example, by using Mountech's image analysis type particle size distribution measurement software "MacView" to determine the particle region, calculating the projected area equivalent circle diameter (Heywood diameter) from the area of ​​the particle region, and measuring the average particle size of particles equivalent to a sphere of equal volume using this value.

[0028] Measurement of the average particle size using the Coulter method is applicable when the particle size of all or most of the particles exceeds 0.2 μm, and can be measured using, for example, a particle size distribution analyzer "Multisizer 4e" manufactured by Beckman Coulter.

[0029] The microcapsule color material may be blended 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, based on the total amount of the ink.

[0030] <Dispersion containing water-based urethane resin and water> The aqueous urethane resin may be dispersed in water in the form of particles, or in the form of a liquid. That is, a dispersion containing an aqueous urethane resin and water may be a suspension in which aqueous urethane resin particles are dispersed in water, or an emulsion in which the aqueous urethane resin is solubilized in water. The "aqueous" in "aqueous urethane resin" does not mean water-soluble, but means hydrophilic.

[0031] The dispersion is preferably composed of a dispersoid entirely made of an aqueous urethane resin and water as a dispersion medium. That is, the dispersion is preferably an aqueous dispersion of an aqueous urethane resin. More specifically, the dispersion is preferably a suspension in which particles made only of an aqueous urethane resin are dispersed in water, or an emulsion in which only an aqueous urethane resin is solubilized in water.

[0032] The aqueous urethane resin may be cationic or anionic. The aqueous urethane resin is, for example, cationic. For example, when the microcapsule color material is cationic, the cationic aqueous urethane resin is less likely to react with the cationic microcapsule color material and has excellent dispersibility, so it is preferable to use the cationic aqueous urethane resin.

[0033] The aqueous urethane resin may be any of polyester-based urethane resin, polycarbonate-based urethane resin, and polyether-based urethane resin. For example, when a polyester film such as a polyethylene terephthalate film is used as the recording medium, it is preferable to use a polyester-based urethane resin from the viewpoint of ink fixation.

[0034] As the aqueous urethane resin, for example, those sold by Taisei Fine Chemical Co., Ltd. under the name of "urethane dispersion", such as WBR-2122C, WBR-2101, WBR-3004, WBR-016U, etc. can be used. WBR-2122C is an aqueous dispersion of a cationic polyester-based urethane resin. WBR-2101 is an aqueous dispersion of an anionic polycarbonate-based urethane resin. WBR-3004 is an aqueous dispersion of an anionic polyether-based urethane resin. WBR-016U is an aqueous dispersion of an anionic polyether-based urethane resin.

[0035] The aqueous urethane resin acts as a fixing agent. When the recording medium is non-permeable, the aqueous urethane resin enables the formation of a print layer with excellent fixing properties on the recording medium. The aqueous urethane resin also improves the abrasion resistance of the print layer.

[0036] The aqueous urethane resin (solid content) can be blended in an amount of, for example, 5 to 20% by mass, and preferably 8 to 15% by mass, based on the total amount of the ink.

[0037] As described above, when a commercially available product is used as the aqueous urethane resin, the aqueous urethane resin exists as a dispersed phase of a dispersion liquid in which the continuous phase is water until it is mixed with the microcapsule coloring material. The ink composition can be obtained, for example, by mixing the aqueous dispersion liquid of the aqueous urethane resin with other components such as the microcapsule coloring material and water. Ion-exchanged water or pure water can be used as the water added when preparing the ink composition.

[0038] The ink composition can contain water in a proportion of, for example, 40 to 90% by mass, and preferably 50 to 80% by mass. Here, the amount of water refers to the total amount of water contained in the aqueous dispersion of the aqueous urethane resin and water added when preparing the ink composition.

[0039] <Wetting agent> The humectant is at least one selected from the group consisting of glycerin, ethylene glycol, and propylene glycol. The humectant preferably contains glycerin. That is, it is preferable to use glycerin alone as the humectant, or to use glycerin in combination with propylene glycol and / or ethylene glycol. It is further preferable to use glycerin and ethylene glycol in combination as the humectant, or to use glycerin, ethylene glycol, and propylene glycol in combination as the humectant.

[0040] The humectant may be blended in an amount of, for example, 5 to 30% by mass, preferably 6 to 25% by mass, and more preferably 9 to 20% by mass, based on the total amount of the ink. When two or more humectants are used in combination, the amount of the humectant refers to the total amount.

[0041] <Additional ingredients> In addition to the above components, the ink composition may further contain additives, such as general-purpose auxiliaries such as a colorant dispersant, a discharge stabilizer, a viscosity adjuster, a preservative, a moisturizer, a wetting agent, and a defoaming agent.

[0042] As described above, the ink composition according to the embodiment is styrene-free, and therefore has excellent storage stability (dispersion stability of the microcapsule colorant), and does not need to contain a colorant dispersant. That is, according to one example, the ink composition does not contain a colorant dispersant. Alternatively, the ink composition according to the embodiment may contain a colorant dispersant. That is, according to another example, the ink composition contains a colorant dispersant in addition to the above components. In this case, the ink composition can further improve the storage stability of the ink. As the colorant dispersant, for example, a polyether phosphate ester known in the art to be usable as a colorant dispersant can be used. The colorant dispersant can be blended in an amount of, for example, 0.1 to 3 mass%, preferably 0.1 to 2.5 mass%, and more preferably 0.1 to 2 mass% relative to the total amount of the ink.

[0043] <pH of ink composition> The ink composition preferably has a pH of 6 to 8. When the pH of the ink composition is within this range, hydrolysis of the aqueous urethane resin is unlikely to occur, and a printed layer with excellent fixability can be formed.

[0044] <Effects> The ink composition according to the embodiment is styrene-free, contains an aqueous urethane resin as a fixing agent, and further contains at least one humectant selected from the group consisting of glycerin, ethylene glycol, and propylene glycol. Such an ink composition can achieve excellent fixing properties to non-permeable recording media.

[0045] 2. Image forming equipment The ink composition described above can be used in an ink jet type image forming apparatus. A container containing the ink composition described in the section "1. Ink composition for ink-jet recording" With The ink composition is supplied from the container, and the ink composition is ejected toward a recording medium. Inkjet head and It is equipped with:

[0046] An example of an ink jet type image forming apparatus will be described below with reference to FIG. 1 includes a housing provided with a paper discharge tray 118. In the housing, cassettes 100 and 101, paper feed rollers 102 and 103, pairs of conveying rollers 104 and 105, a pair of registration rollers 106, a conveying belt 107, a fan 110, a negative pressure chamber 111, pairs of conveying rollers 112, 113 and 114, inkjet heads 115C, 115M, 115Y and 115Bk, ink cartridges 116C, 116M, 116Y and 116Bk, tubes 117C, 117M, 117Y and 117Bk, and a heater 120 are provided.

[0047] The cassettes 100 and 101 contain recording media F of different sizes. The recording media F are, for example, non-permeable recording media. The non-permeable recording media refer to recording media on which, when an ink layer is formed on the surface, the ink does not permeate into the recording medium and remains on the surface of the recording medium. Examples of non-permeable recording media include plastic films. Examples of plastic films include polyethylene terephthalate films and polyvinyl chloride films. Alternatively, the non-permeable recording media may be a base material such as paper coated with plastic, a base material such as paper with a plastic film bonded thereto, or paper manufactured using synthetic resins such as polyolefin resins and polystyrene resins as the main raw material.

[0048] A paper feed roller 102 or 103 takes out a recording medium F corresponding to the size of the selected recording medium from a cassette 100 or 101, and conveys it to pairs of conveying rollers 104 and 105 and a pair of registration rollers .

[0049] The conveyor belt 107 is given tension by a drive roller 108 and two driven rollers 109. Holes are provided at predetermined intervals on the surface of the conveyor belt 107. A negative pressure chamber 111 connected to a fan 110 is provided on the inside of the conveyor belt 107 in order to attract the recording medium F to the conveyor belt 107. Pairs of conveyor rollers 112, 113, and 114 are provided downstream of the conveyor belt 107 in the conveying direction.

[0050] Above the conveyor belt 107, four rows of inkjet heads are arranged, which eject ink according to image data onto the recording medium F. From upstream, the rows are 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.

[0051] The inkjet heads 115C, 115M, 115Y, and 115Bk are provided 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, which contain the corresponding inks. These cartridges 116C, 116M, 116Y, and 116Bk are connected to the inkjet heads 115C, 115M, 115Y, and 115Bk by tubes 117C, 117M, 117Y, and 117Bk, respectively.

[0052] The ink composition contained in at least one of the ink cartridges 116C, 116M, 116Y, and 116Bk is the ink composition according to the embodiment. Here, as an example, it is assumed that the ink compositions contained in the ink cartridges 116C, 116M, 116Y, and 116Bk are all the ink compositions according to the embodiment.

[0053] Furthermore, above the conveyor belt 107, a heater 120 is installed so as to be located downstream of the four rows of inkjet heads. The heater 120 heats the print layer formed on the recording medium F to promote drying of the ink. This causes the print layer to become a film and be fixed on the recording medium F. The heating temperature of the heater 120 is preferably lower than the color change temperature of the microcapsule color material that exhibits thermochromicity. The heater 120 can be installed at any position on the conveyor path from the conveyor belt 107 to the paper discharge tray 118 as long as it is installed downstream of the four rows of inkjet heads. Alternatively, the heater 120 may be omitted, or a blower may be installed instead of the heater 120.

[0054] 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, and 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.

[0055] Under the control of the image processing means, the paper feed roller 102 or 103 takes out recording media F of the selected size one by one from the cassette 100 or 101, and conveys them to the conveying roller pairs 104 and 105 and the registration roller pair 106. The registration roller pair 106 corrects the skew of the recording media F and conveys the recording media F at a predetermined timing.

[0056] The negative pressure chamber 111 sucks in air through holes in the conveyor belt 107. Therefore, the recording medium F, while being adsorbed to the conveyor belt 107, is conveyed successively to positions below the inkjet heads 115C, 115M, 115Y and 115Bk as the conveyor belt 107 moves.

[0057] Under the control of the image processing means, the inkjet heads 115C, 115M, 115Y and 115Bk eject ink in synchronization with the timing of the transport of the recording medium F. In this way, color print layers are formed at desired positions on the recording medium F.

[0058] Thereafter, the recording medium F is transported to a position below the heater 120, which heats the printed layer formed on the recording medium F. This causes the printed layer to become a coating and be fixed onto the recording medium F. Heating by the heater 120 can increase the adhesion of the printed layer to the recording medium F, particularly when the recording medium F is non-permeable.

[0059] Thereafter, the pairs of conveying rollers 112, 113, and 114 eject the recording medium F on which the image has been formed onto an ejection tray 118.

[0060] 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, this image forming apparatus can form a printed image with excellent fixability on a non-permeable recording medium. Therefore, this image forming apparatus can form a printed image with excellent abrasion resistance. EXAMPLES

[0061] [1] Preparation of thermally erasable ink <Example 1: Thermally erasable ink 1> As the coloring material, a microcapsule pigment (average particle size: 600 nm) in which a thermally decolorable composition (reversible thermochromic composition) is encapsulated by a resin coating was used. As the water-based urethane resin, WBR-2122C manufactured by Taisei Fine Chemical Co., Ltd. was used. WBR-2122C is a water dispersion of a cationic polyester-based urethane resin. 5 parts by weight of coloring material, 5 parts by weight of aqueous urethane resin (solid content), 10 parts by weight of glycerin and 5 parts by weight of ethylene glycol as wetting agents, 1 part by weight of Surfynol (registered trademark) 465 manufactured by Nissin Chemical Industry Co., Ltd. as a discharge stabilizer, 0.2 parts by weight of Proxel (registered trademark) XL-2 manufactured by Arcsada Japan Co., Ltd. as a preservative, and pure water were mixed to a total of 100 parts by weight. The resulting mixture was stirred using a stirrer and then filtered. As a result, thermally decolorable ink 1 was obtained.

[0062] <Example 2: Thermally erasable ink 2> As shown in the table below, except that the amount of water-based urethane resin added (solid content) was changed to 12 parts by mass, thermally erasable ink 2 was prepared in the same manner as thermally erasable ink 1. Pure water was added so that the total amount of ink was 100 parts by mass. In the preparation of subsequent thermally erasable inks, pure water was added so that the total amount of ink was 100 parts by mass.

[0063] <Example 3: Thermally erasable ink 3> Thermo-decolorizable ink 3 was prepared in the same manner as thermo-decolorizable ink 1, except that the amount of the aqueous urethane resin added (solid content) was changed to 20 parts by mass as shown in the table below.

[0064] <Example 4: Thermally erasable ink 4> As shown in the table below, thermally decolorizable ink 4 was prepared in the same manner as thermally decolorizable ink 1, except that 10 parts by mass of glycerin and 5 parts by mass of propylene glycol were used as the humectants.

[0065] <Example 5: Thermally erasable ink 5> Thermally erasable ink 5 was prepared in the same manner as thermally erasable ink 1, except that the amount of aqueous urethane resin added (solid content) was changed to 12 parts by mass, and 10 parts by mass of glycerin and 5 parts by mass of propylene glycol were used as humectants, as shown in the table below.

[0066] <Example 6: Thermally erasable ink 6> Thermally erasable ink 6 was prepared in the same manner as thermally erasable ink 1, except that the amount of aqueous urethane resin added (solid content) was changed to 20 parts by mass, and 10 parts by mass of glycerin and 5 parts by mass of propylene glycol were used as humectants, as shown in the table below.

[0067] <Example 7: Thermally erasable ink 7> Thermo-decolorizable ink 7 was prepared in the same manner as thermo-decolorizable ink 1, except that the amount of the aqueous urethane resin added (solid content) was changed to 22 parts by mass as shown in the table below.

[0068] <Example 8: Thermally erasable ink 8> Thermo-decolorizable ink 8 was prepared in the same manner as thermo-decolorizable ink 1, except that the amount of the aqueous urethane resin added (solid content) was changed to 3 parts by mass as shown in the table below.

[0069] <Example 9: Thermally erasable ink 9> Thermally erasable ink 9 was prepared in the same manner as thermally erasable ink 1, except that the amount of aqueous urethane resin added (solid content) was changed to 12 parts by mass, and 10 parts by mass of glycerin, 10 parts by mass of ethylene glycol, and 10 parts by mass of propylene glycol were used as humectants, as shown in the table below.

[0070] <Example 10: Thermally erasable ink 10> As shown in the table below, thermally erasable ink 10 was prepared in the same manner as thermally erasable ink 1, except that the amount of aqueous urethane resin added (solid content) was changed to 12 parts by mass and 5 parts by mass of glycerin was used as a humectant.

[0071] <Example 11: Thermally erasable ink 11> As shown in the table below, thermally erasable ink 11 was prepared in the same manner as thermally erasable ink 1, except that the amount of aqueous urethane resin added (solid content) was changed to 12 parts by mass and 4 parts by mass of glycerin was used as a humectant.

[0072] <Example 12: Thermally erasable ink 12> Thermally erasable ink 12 was prepared in the same manner as thermally erasable ink 1, except that the amount of aqueous urethane resin added (solid content) was changed to 12 parts by mass, and 10 parts by mass of glycerin, 11 parts by mass of ethylene glycol, and 11 parts by mass of propylene glycol were used as humectants, as shown in the table below.

[0073] <Example 13: Thermally erasable ink 13> As shown in the table below, thermally decolorable ink 13 was prepared in the same manner as thermally decolorable ink 1, except that WBR-016U manufactured by Taisei Fine Chemical Co., Ltd. was used as the aqueous urethane resin in an amount of 12 parts by mass (solid content). WBR-016U is an aqueous dispersion of an anionic polyether urethane resin.

[0074] <Example 14: Thermally erasable ink 14> As shown in the table below, thermally decolorable ink 14 was prepared in the same manner as thermally decolorable ink 1, except that WBR-3004 manufactured by Taisei Fine Chemical Co., Ltd. was used as the aqueous urethane resin in an amount of 12 parts by mass (solid content). WBR-3004 is an aqueous dispersion of an anionic polyether urethane resin.

[0075] <Example 15: Thermally erasable ink 15> As shown in the table below, the thermally erasable ink 15 was prepared in the same manner as the thermally erasable ink 1, except that WBR-2101 manufactured by Taisei Fine Chemical Co., Ltd. was used as the aqueous urethane resin in an amount of 12 parts by mass (solid content). WBR-2101 is an aqueous dispersion of an anionic polycarbonate-based urethane resin.

[0076] <Example 16: Thermally erasable ink 16> As shown in the table below, thermally erasable ink 16 was prepared in the same manner as thermally erasable ink 1, except that 12 parts by mass (solid content) of WBR-016U manufactured by Taisei Fine Chemical Co., Ltd. was used as the aqueous urethane resin, and 5 parts by mass of ethylene glycol was used as the wetting agent.

[0077] <Example 17: Thermally erasable ink 17> As shown in the table below, thermally erasable ink 17 was prepared in the same manner as thermally erasable ink 1, except that 12 parts by mass (solid content) of WBR-016U manufactured by Taisei Fine Chemical Co., Ltd. was used as the aqueous urethane resin, and 30 parts by mass of ethylene glycol was used as the wetting agent.

[0078] <Example 18: Thermally erasable ink 18> As shown in the table below, thermally erasable ink 18 was prepared in the same manner as thermally erasable ink 1, except that 12 parts by mass (solid content) of WBR-016U manufactured by Taisei Fine Chemical Co., Ltd. was used as the aqueous urethane resin, and 5 parts by mass of propylene glycol was used as the wetting agent.

[0079] <Example 19: Thermally erasable ink 19> As shown in the table below, thermally erasable ink 19 was prepared in the same manner as thermally erasable ink 1, except that 12 parts by mass (solid content) of WBR-016U manufactured by Taisei Fine Chemical Co., Ltd. was used as the aqueous urethane resin, and 30 parts by mass of propylene glycol was used as the wetting agent.

[0080] <Example 20: Thermally erasable ink 20> As shown in the table below, the amount of water-based urethane resin added (solid content) was changed to 12 parts by mass, and 0.15 parts by mass of a colorant dispersant was added as an additional component, but other than that, a thermally discolorable ink 20 was prepared in the same manner as the thermally discolorable ink 1. A polyether phosphate ester (Phosphanol RS-710 manufactured by Toho Chemical Industry Co., Ltd.) was used as the colorant dispersant.

[0081] [2] Evaluation method <Evaluation of fixation> Using the prepared ink, a printed layer was formed on a recording medium by an inkjet image forming device. A polyethylene terephthalate film (PET film) and a polyvinyl chloride film (PVC film) were used as the recording medium. The printed layer was fixed onto the recording medium by heating.

[0082] Fixation was evaluated by a friction fastness test. Specifically, a white cotton cloth was attached to the tip of the friction element of a friction fastness tester, and the print layer on the recording medium was rubbed by moving the friction element back and forth five times under a constant load and speed. The image density before and after rubbing was measured, and the ink fixation rate was calculated using the following formula. Ink fixation rate [%] = (image density after rubbing / image density before rubbing) x 100

[0083] The fixing property was evaluated according to the following evaluation criteria. A: Ink fixation rate 95% or more B: Ink fixation rate: 90% to less than 95% C: Ink fixation rate less than 90%.

[0084] <Evaluation of storage stability; visual evaluation> The prepared ink was placed in a glass sample bottle, the bottle was sealed, and the bottle was stored for 60 days in a thermostatic chamber set at 50° C. After that, the presence or absence of precipitate was visually confirmed.

[0085] The storage stability was evaluated according to the following criteria. A: No precipitate was formed. B: A small amount of precipitate was formed. C: A large amount of precipitate was deposited.

[0086] <Evaluation of maintainability> The ink thus prepared was used to perform printing using an inkjet image forming apparatus. After that, the apparatus was left for 24 hours under a temperature condition of 25° C. After 24 hours, printing was performed again and the ejection properties of the inkjet head were examined.

[0087] The discharge property after 24 hours (i.e., maintainability) was evaluated according to the following evaluation criteria. A: Stable ejection was possible without a cleaning operation (i.e., an operation to forcibly eject ink) B: The ejection was unstable after 24 hours, but stable ejection became possible after cleaning. C: The ejection was unstable after 24 hours, and stable ejection was not possible even after a cleaning operation.

[0088] [3] Evaluation results The composition of the thermally erasable ink and the evaluation results are shown in the table below.

[0089] [Table 1]

[0090] [Table 2]

[0091] [Table 3]

[0092] The values ​​in the table represent the mass percentage of each component in the ink. None of the thermally erasable inks prepared contained styrene. Specifically, the styrene concentration of all the thermally erasable inks was below the detection limit, specifically 1000 ppm or less. In addition, the pH of all the thermally erasable inks prepared was within the range of 6 to 8.

[0093] The thermally erasable inks 1 to 6, 9, 10, and 13 to 20 obtained good results in all evaluations of fixation, storage stability, and maintenance (see Examples 1 to 6, 9, 10, and 13 to 20).

[0094] On the other hand, the thermally erasable inks 7, 8, 11 and 12 did not show good results in at least one of the evaluations of fixation, storage stability and maintenance (see Examples 7, 8, 11 and 12). From the results of Examples 7 and 8, it can be seen that when the amount of water-based urethane resin is small, fixation decreases, and when the amount of water-based urethane resin is large, storage stability and maintenance decrease. Also, from the results of Examples 11 and 12, it can be seen that when the amount of wetting agent is small, maintenance decreases, and when the amount of wetting agent is large, fixation decreases.

[0095] [4] Effect of styrene on the storage stability of ink Styrene-free thermally erasable ink and styrene-containing thermally erasable ink were prepared, and the storage stability of the ink was evaluated by viscosity measurement.

[0096] Styrene-free thermally erasable inks were prepared in the same manner as described in the above Examples 1 to 20. The prepared inks are referred to as styrene-free thermally erasable inks 1 to 20. On the other hand, styrene-containing thermally erasable inks were prepared in the same manner as described in the above Example 1, except that an aqueous dispersion of core-shell particles having a core made of acrylic resin and a shell made of urethane resin (WEM-200U manufactured by Taisei Fine Chemical Co., Ltd.) was used instead of the aqueous urethane resin.

[0097] The styrene-free thermally erasable inks 1 to 20 had styrene concentrations below the detection limit, specifically below 1000 ppm. On the other hand, the thermally erasable inks containing styrene contained styrene as a residual monomer component of the acrylic resin that constitutes the core part of the core-shell particles, and had styrene concentrations exceeding 1000 ppm.

[0098] The prepared thermally erasable ink was stored in a thermostatic chamber set at 45°C for two weeks. The viscosity of the thermally erasable ink was then measured using a cone-plate type rotational viscometer in accordance with the method specified in JIS Z8803:2011 "Method of measuring viscosity of liquids." The cone-plate type rotational viscometer used was a Toki Sangyo E-type viscometer TV-100. The viscosity was measured using a 0.8° cone angle at a temperature of 25°C and a rotation speed of 20 rpm.

[0099] It was visually confirmed that no precipitate was formed in the styrene-free thermally erasable inks 1 to 20 after storage. On the other hand, it was visually confirmed that precipitate was formed in the thermally erasable inks containing styrene after storage. For this reason, the viscosity of the styrene-free thermally erasable inks 1 to 20 after storage was measured, while the viscosity of the thermally erasable inks containing styrene after storage was not measured. The viscosity measurement results (i.e., the viscosity after storage V1, the viscosity immediately after preparation V2, and the percentage ratio V1 / V2) are shown in the table above. The styrene-free thermally erasable inks had a low viscosity of approximately 20 mPa·s or less even after storage. In addition, the percentage ratio V1 / V2 of the styrene-free thermally erasable inks was 250% or less, and the increase in viscosity after storage was suppressed. From these results, it can be seen that the styrene-free inks are less likely to increase in viscosity after storage and exhibit excellent storage stability (dispersion stability of microcapsule pigments).

[0100] Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and spirit of the invention, and are included in the scope of the invention and its equivalents described in the claims. [Explanation of symbols]

[0101] 100...cassette, 101...cassette, 102...paper supply roller, 103...paper supply roller, 104...pair of transport rollers, 105...pair of transport rollers, 106...pair of registration rollers, 107...transport belt, 110...fan, 111...negative pressure chamber, 112...pair of transport rollers, 113...pair of transport rollers, 114...pair of transport rollers, 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...paper output tray, 120...heater, F...recording medium.

Claims

1. A microcapsule color material in which a color material is encapsulated in a resin coating and exhibits thermochromic properties; A dispersion containing an aqueous urethane resin and water; At least one humectant selected from the group consisting of glycerin, ethylene glycol, and propylene glycol; An ink composition for ink jet recording comprising: the proportion of the aqueous urethane resin in the ink composition is within a range of 5 to 20% by mass, the ratio of the wetting agent in the ink composition is within a range of 5 to 30 mass %, Styrene-free An ink composition for ink-jet recording.

2. The ink composition according to claim 1 , wherein the aqueous urethane resin is a cationic type.

3. The ink composition according to claim 1, wherein the ink composition has a pH of 6 to 8.

4. 2. 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 that receives the ink composition from the container and ejects the ink composition toward a recording medium; An image forming apparatus comprising:

Images