Patent Application
20230272236
The present application claims priority to Japanese Patent Application No. 2022-029623 filed Feb. 28, 2022, the contents of which are incorporated herein by reference in their entirety.
A method of improving the storage stability of water-based inks by blending triethanolamine (TEA) as a pH adjuster is known.
According to an aspect of the present disclosure, a water-based ink includes: a pigment; an alkali metal hydrogencarbonate; and water. An amount of the pigment and an amount of the alkali metal hydrogencarbonate satisfy Condition (1): Condition (1): 7.5≤A/B. A is a solid amount of the pigment by mass in the water-based ink relative to a total mass of the water-based ink, and B is the amount of the alkali metal hydrogencarbonate by mass in the water-based ink relative to the total mass of the water-based ink.
According to another aspect of the present disclosure, an inkjet recording method includes ejecting the above-described water-based ink onto a recording medium for recording.
According to a further aspect of the present disclosure, an inkjet recording device includes: an ink storing part; and an ink ejecting part to eject the above-described water-based ink, stored in the ink storing part.
According to a further aspect of the present disclosure, an ink storage container comprising the above-described water-based ink, stored therein.
According to a further aspect of the present disclosure, a printed recording medium includes: a recording medium; and the above-described water-based ink, provided on the recording medium.
A more complete appreciation of the disclosure and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: the FIGURE is a schematic perspective view of an example of an inkjet recording device.
As used herein, the words “a” and “an” and the like carry the meaning of “one or more.” When an amount, concentration, or other value or parameter is given as a range, and/or its description includes a list of upper and lower values, this is to be understood as specifically disclosing all integers and fractions within the given range, and all ranges formed from any pair of any upper and lower values, regardless of whether subranges are separately disclosed. Where a range of numerical values is recited herein, unless otherwise stated, the range is intended to include the endpoints thereof, as well as all integers and fractions within the range. As an example, a stated range of 1-10 fully describes and includes the independent subrange 3.4-7.2 as does the following list of values: 1, 4, 6, 10.
There is demand for increase storage stability, even while reducing the formulation amount of TEA (including not adding TEA), from the standpoint of versatility of the water-based ink composition.
An embodiment of the present disclosure relates to a water-based ink for inkjet recording including: pigment, an alkali metal hydrogencarbonate, and water; and the pigment and the alkali metal hydrogencarbonate satisfy the following condition (1).
7.5≤A/B Condition (1)
A: Formulation amount of pigment solids of the pigment in the total amount of water-based ink for inkjet recording
B: Formulation amount of alkali metal hydrogencarbonate in the total amount of water-based ink for inkjet recording
The water-based ink for inkjet recording of the present disclosure can enhance storage stability even if TEA is not added or if the formulation amount of TEA is reduced, by containing pigment and an alkali metal hydrogencarbonate at a prescribed ratio.
In the present disclosure, the term “mass” may be interpreted as “weight” unless otherwise specified. For example, “mass ratio” may be interpreted as “weight ratio” unless otherwise specified, and “mass %” may be interpreted as “weight %” unless otherwise specified.
The water-based ink for inkjet recording of the present disclosure (hereinafter referred to as “water-based ink” or “ink”) is described below. The water-based ink contains pigments, an alkali metal hydrogencarbonate, and water.
The pigment is not particularly limited, and includes, for example, carbon black, inorganic pigments, organic pigments, and the like. Examples of the carbon black include furnace black, lamp black, acetylene black, channel black, and the like. Examples of inorganic pigments include titanium dioxide, iron oxide inorganic pigments, carbon black inorganic pigments, and the like. Examples of the organic pigments include azo pigments such as azo lakes, insoluble azo pigments, condensed azo pigments, chelated azo pigments; polycyclic pigments such as phthalocyanine pigments, perylene and perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, thioindigo pigments, isoindolinone pigments, quinophthalone pigments, and the like; dye lake pigments such as basic dye-type lake pigments and acid dye-type lake pigments; nitro pigments; nitroso pigments; aniline black daylight fluorescent pigments; and the like. Other pigments can also be used if they can be dispersed in a water-based phase. Specific examples of these pigments include C.I. Pigment Black 1, 6 and 7; C.I. Pigment Yellow 1, 2, 3, 12, 13, 14, 15, 16, 17, 55, 74, 78, 150, 151, 154, 180, 185 and 194; C.I. Pigment Orange 31 and 43; C.I. Pigment Red 2, 3, 5, 6, 7, 12, 15, 16, 48, 48:1, 53:1, 57, 57:1, 112, 122, 123, 139, 144, 146, 149, 150, 166, 168, 175, 176, 177, 178, 184, 185, 190, 202, 209, 221, 222, 224 and 238; C.I. Pigment Violet 19 and 196; C.I. Pigment Blue 1, 2, 3, 15, 15:1, 15:2, 15:3, 15:4, 16, 22 and 60; C.I. Pigment Green 7 and 36; and solid solutions of these pigments, and the like.
The pigment may be a pigment that is dispersed in a solvent by using a resin dispersing agent (also referred to as resin-dispersed pigment). For example, standard polymer dispersing agents and the like (also referred to as resins for pigment dispersion, resin dispersing agents, and the like) may be used as the resin dispersing agent, or they may be prepared in-house. The pigments in the water-based ink of the present disclosure may be encapsulated by polymers. For example, a resin dispersing agent containing at least one of methacrylic acid or acrylic acid as a monomer can be used, including commercially available products for example. The resin dispersing agent may be, for example, block copolymers, graft copolymers, or random copolymers containing two or more monomers selected from the group consisting of hydrophobic monomers such as styrene, styrene derivatives, vinylnaphthalene, vinylnaphthalene derivatives, aliphatic alcohol esters of α,β-ethylenically unsaturated carboxylic acid; acrylic acid; acrylic acid derivatives; maleic acid; maleic acid derivatives; itaconic acid; itaconic acid derivatives; fumaric acid; fumaric acid derivatives; and salts thereof. Commercial products include, for example, “Joncryl (registered trademark) 611”, “Joncryl (registered trademark) 60”, “Joncryl (registered trademark) 586”, “Joncryl (registered trademark) 687”, “Joncryl (registered trademark) 63”, and “Joncryl (registered trademark) HPD296” manufactured by Johnson Polymer Co.; “Disperbyk190” and “Disperbyk191” manufactured by BYK Chemie; “Solsperse 20000” and “Solsperse 27000”, and the like, manufactured by AstraZeneca Corporation; and the like.
The method of dispersing the pigments using the resin for pigment dispersion is, for example, to disperse the pigments using a dispersing device. The dispersing device used for dispersion of the pigments is not limited so long as they are general dispersion machines, such as ball mills, roll mills, sand mills (e.g., high-speed type), and the like.
The pigment may be a self-dispersing pigment. The self-dispersing pigments include those that can be dispersed in water without the use of a dispersing agent, for example, by introducing at least one hydrophilic functional group such as a carbonyl group, hydroxyl group, carboxylic group, sulfo group, phosphate group, or the like, or salts thereof, directly or via other groups into the pigment particles by chemical bonds. The self-dispersing pigments can be those where a pigment is treated by the methods described in Japanese Unexamined Patent Application No. H8-3498 (EP 688836), Japanese PCT Unexamined Patent Application No. 2000-513396 (U.S. Pat. No. 5,837,045), Japanese PCT Unexamined Patent Application No. 2008-524400 (US2006/201380), Japanese PCT Unexamined Patent Application No. 2009-515007 (US2007/100023, US2007/100024), Japanese PCT Unexamined Patent Application No. 2011-515535 (US2009/229489), and the like (the contents of these application are incorporated herein by reference in their entirety). Both inorganic pigments and organic pigments can be used as raw materials for the self-dispersing pigments. Pigments suitable for the above treatment include, for example, carbon blacks such as MA8 and MA100, manufactured by Mitsubishi Chemical Corporation, and the like. The self-dispersing pigments described above may be commercially available, for example. The above commercial products include, for example, CAB-O-JET (registered trademark) 200, CAB-O-JET (registered trademark) 250C, CAB-O-JET (registered trademark) 260M, CAB-O-JET (registered trademark) 270Y, CAB-O-JET (registered trademark) 300, CAB-O-JET (registered trademark) 400, CAB-O-JET (registered trademark) 450C, CAB-O-JET (registered trademark) 465M, CAB-O-JET (registered trademark) 470Y, manufactured by Cabot Corporation; BONJET (registered trademark) BLACK CW-2 and BONJET (registered trademark) BLACK CW-3, manufactured by Orient Chemical Industries Co., LIOJET (registered trademark) WD BLACK 002C, manufactured by Toyo Ink Manufacturing, and the like.
The formulation amount of pigment solids (A) in the total amount of water-based ink is not particularly limited, and can be appropriately determined according to the desired optical density or color saturation, and the like, for example. The formulation amount of the pigment solid (A) portion may be 0.1 mass % to 20 mass %, preferably 1 mass % to 10 mass %, and more preferably 2 mass % to 8 mass %. If the pigment is dispersed in solvent by using a resin disbursing agent, the formulation amount of pigment solids (A) is only the mass of pigment, and the mass of the resin disbursing agent is not included. One type of pigment and resin dispersing agent may be used alone, or a combination of two or more types may be used.
The water-based ink may contain dyes, or the like.
The alkali metal hydrogencarbonate is an alkali metal salt containing a hydrogencarbonate ion, for example, such as at least one of sodium hydrogencarbonate and potassium hydrogencarbonate. The alkali metal hydrogencarbonate is used as a pH adjusting agent.
The formulation amount of alkali metal hydrogencarbonate (B) in the total amount of water-based ink is not particularly limited, and can be appropriately determined according to the desired optical density or color saturation, and the like, for example. The formulation amount (B) may be, for example, 0.05 mass % to 0.8 mass %, preferably 0.1 mass % to 0.8 mass %, and more preferably 0.2 mass % to 0.8 mass %. One type of the alkali metal hydrogencarbonate may be used alone, or two or more types used in combination.
The formulation amount of pigment solids of the pigment in the total amount of water-based ink (A) and the amount of alkali metal hydrogencarbonate in the total amount of water-based ink (B) satisfy the following condition (1).
7.5≤A/B Condition (1)
For the above condition (1), the upper limit of A/B is not particularly limited, and can be appropriate determined by a person of ordinary skill in the art, for example. The upper limit of A/B is, for example, less than 60, or 120 or less, or 300 or less, or the like. The formulation amount of pigment solids of the pigment in the total amount of the water-based ink (A) and the formulation amount of the alkali metal hydrogencarbonate in the total amount of the water-based ink (B) may, for example, satisfy either one of condition (1-1) or condition (1-2).
7.5≤A/B≤120 Condition (1-1)
7.5≤A/B≤60 Condition (1-2)
The water may be ion exchanged water, pure water, or the like. The amount of water to be blended in the total amount of water-based ink (water ratio) is determined in accordance with desired ink characteristics and the like. The water ratio may, for example, be the remainder after the other ingredients. The formulation amount of water may be, for example, 50 mass % to 95 mass %, preferably 55 mass % to 90 mass %, and more preferably 60 mass % to 80 mass %.
The pH (initial pH) of the water-based ink is, for example, less than 9.2. The pH of the water-based ink when stored at 60° C. for one week (pH after storage) is, for example, 7.8 or higher. In other words, the change in pH (pH change) when the water-based ink is stored at 60° C. for one week is, for example, 10% or less. The change in pH may be less than 5%, for example. On the other hand, if the initial pH of the water-based ink is 9.2 or higher, for example, the adhesive in the channel through which the water-based ink passes will deteriorate. Furthermore, a pH after storage of the water-based ink that is less than 7.8, for example, may cause metal corrosion. Therefore, if the change in pH exceeds 10%, there will be problems with adhesion degradation, metal corrosion, and the like. Note that the change in pH can be determined from the following equation (1).
Change in pH=(pH after storage−initial pH)/initial pH (Equation 1)
By formulating the water-based ink so that the pigment and the alkali metal hydrogencarbonate satisfy condition (1), the storage stability can be improved without using TEA or with a reduced formulation amount of TEA. The mechanism for improving the storage stability is hypothesized to be as follows. The reaction between the alkali metal hydrogencarbonate and the water in an aqueous solution increases OH− in the aqueous solution, making the aqueous solution alkaline. Furthermore, the alkali metal hydrogencarbonate dissolves in water to form hydrogencarbonate ions (HCO3−). Furthermore, the hydrogencarbonate ions (HCO3−) will react with water to produce carbonic acid (H3CO3) and hydroxide ions (OH−). The alkali metal hydrogencarbonate is a solid, and does not volatilize but remains in the water-based ink when the water in the water-based ink evaporates, thereby retaining moisture. In other words, adding the alkali metal hydrogencarbonate to the water-based ink provides an anti-caking effect (moisture retention effect), may inhibit drying of water-based ink, and improves storage stability. However, this is only a hypothesis for the mechanism, and the present disclosure is not limited thereto.
The water-based ink may, for example, further contain a surfactant.
The surfactant is not limited and may be appropriately selected in accordance with the purpose, and for example, commercially available products may be used. Specifically, the surfactant may be an acetylene surfactant, or the like, for example.
Commercial acetylene surfactants include: OLFINE (registered trademark) E1004, OLFINE (registered trademark) E1008, and OLFINE (registered trademark) E1010 manufactured by Nissin Chemical Industry; SURFINOL (registered trademark) 440, SURFINOL (registered trademark) 465, and SURFINOL (registered trademark) 485 manufactured by Air Products and Chemicals, Inc.; ACETYLENOL (registered trademark) E40 and ACETYLENOL (registered trademark) E100 manufactured by Kawaken Fine Chemicals Co., and the like.
In addition to or in place of the acetylene surfactant, the water-based ink may contain other surfactants. Examples of other surfactants include nonionic surfactants manufactured by Kao Corporation including the EMULGEN (registered trademark) series, RHEODOL (registered trademark) series, EMASOL (registered trademark) series, EXCEL (registered trademark) series, EMANON (registered trademark) series, AMIET (registered trademark) series, and AMINON (registered trademark) series and the like; nonionic surfactants manufactured by Toho Chemical Industry Co. such as Solvon (registered trademark) series and the like; nonionic surfactants manufactured by Lion Corporation such as DOBANOX (registered trademark) series, LEOCOL (registered trademark) series, LEOX (registered trademark) series, LAOL, LEOCOL (registered trademark) series, LIONOL (registered trademark) series, CADENAX (registered trademark) series, LIONON (registered trademark) series, LEOFAT (registered trademark) series, and the like; anionic surfactants manufactured by Kao Corporation such as the EMAL (registered trademark) series, LATEMUL (registered trademark) series, VENOL (registered trademark) series, NEOPELEX (registered trademark) series, NS SOAP, KS SOAP, OS SOAP, and PELEX (registered trademark) series, and the like; anionic surfactants manufactured by Lion Corporation such as the LIPOLAN (registered trademark) series, LIPON (registered trademark) series, SUNNOL (registered trademark) series, LIPOTAC (registered trademark) TE, ENAGICOL series, LIPAL (registered trademark) series and LOTAT (registered trademark) series, and the like; and cationic surfactants manufactured by DKS Co. such as CATIOGEN (registered trademark) ES-OW and CATIOGEN (registered trademark) ES-L, and the like.
One type of surfactant may be used alone, or a combination of two or more types may be used.
The formulation amount of surfactant in the total amount of water-based ink can be appropriately selected in accordance with the purpose. The formulation amount of the surfactant may be 0.01 to 5 mass %, preferably 0.05 to 5 mass %, and more preferably 0.05 mass % to 3 mass %.
The water-based ink may, for example, further contain a penetrating agent.
The penetrating agent is, for example, at least one of an alkylene diol or a glycol ether compound. Note that the alkylene diols include diols that contain an alkylene diol as a portion of the structure, and the glycol ether compounds contain glycol ether as a portion of the structure. Examples of the alkylene diols include 1,2-hexanediol, 1,2-heptanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 3-methyl-1,3-butanediol, 1,2-pentanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 2-methyl-2,4-pentanediol, and 3-methyl-1,5-pentanediol, and the like. Examples of the glycol ether compounds include ethylene glycol methyl ether, ethylene glycol ethyl ether, ethylene glycol-n-propyl ether, diethylene glycol methyl ether, diethylene glycol ethyl ether, diethylene glycol-n-propyl ether, diethylene glycol-n-butyl ether, diethylene glycol-n-hexyl ether, triethylene glycol methyl ether, triethylene glycol ethyl ether, triethylene glycol-n-propyl ether, triethylene glycol-n-butyl ether, propylene glycol methyl ether, propylene glycol ethyl ether, propylene glycol-n-propyl ether, propylene glycol-n-butyl ether, dipropylene glycol methyl ether, dipropylene glycol ethyl ether, dipropylene glycol-n-propyl ether, dipropylene glycol-n-butyl ether, tripropylene glycol methyl ether, tripropylene glycol ethyl ether, tripropylene glycol-n propyl ether, tripropylene glycol ethyl ether, tripropylene glycol-n-propyl ether, tripropylene glycol-n-butyl ether, and the like.
The water-based ink may contain other penetrating agents in addition to or in place of the at least one alkylene diol or glycol ether compound.
One type of penetrating agent may be used alone or a combination of two or more types may be used.
The formulation amount of the penetrating agent to the total amount of water-based ink is, for example, 1 weight % to 20 weight %, preferably 1 weight % to 15 weight %, and more preferably 1 weight % to 10 weight %.
The water-based ink may, for example, further contain a wetting agent.
The wetting agent is not particularly limited, but examples include lower alcohols such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol and tert-butyl alcohol, and the like; amides such as dimethylformamide, dimethylacetamide, and the like; ketones such as acetone and the like; keto alcohols such as diacetone alcohols and the like; ethers such as tetrahydrofuran, dioxane, and the like; polyethers such as polyalkylene glycol; alkylene glycol; polyhydric alcohols such as glycerin, trimethylolpropane, trimethylolethane and the like; 2-pyrrolidone; N-methyl-2-pyrrolidone; 1,3-dimethyl-2-imidazolidinone; and the like. Examples of the polyalkylene glycol include polyethylene glycol, polypropylene glycol, and the like. Examples of the alkylene glycol include ethylene glycol, propylene glycol, butylene glycol, diethylene glycol, triethylene glycol, dipropylene glycol, tripropylene glycol, thiodiglycol, hexylene glycol, and the like. These wetting agents may be used alone, or in a combination of two or more types. Of these, alkylene glycol, polyhydric alcohols such as glycerin, and the like are preferable.
The amount of the wetting agent in the total amount of the water-based ink may be, for example, 0 mass % to 95 mass %, preferably 5 mass % to 80 mass %, and more preferably 5 mass % to 50 mass %.
The water-based ink may also contain conventionally known additives as needed. The additives include, for example, pH adjusting agents, viscosity adjusting agents, surface tension adjusting agents, anti-mold agents, and the like. Examples of the viscosity adjusting agent include polyvinyl alcohol, cellulose, water-soluble resins, and the like.
The water-based ink may, for example, further contain triethanolamine (TEA) as a pH adjusting agent, or may not substantially contain triethanolamine. From the standpoint of ease of preparation of the water-based ink, it is preferable that the water-based ink be substantially free of triethanolamine. If triethanolamine is included in the water-based ink, the amount should be a sufficiently small amount relative to the formulation amount of the pH adjusting agent (alkali metal hydrogencarbonate) in the total amount of the water-based ink. Specifically, for example, the formulation amount of triethanolamine to the total amount of water-based ink may be 0.1 mass % or less. In addition, the formulation amount of triethanolamine in the total amount of the water-based ink may, for example, be ½ or less, ⅕ or less, or 1/10 or less, than the formulation amount (B) of alkali metal hydrogencarbonate in the total amount of the water-based ink. In general, fewer substances in the water-based ink makes preparation of the water-based ink easier. The water-based ink for inkjet recording does not contain TEA or the formulation amount of TEA can be reduced, and therefore the ease of preparation of the water-based ink can be improved. Furthermore, the water-based ink for inkjet recording of the present disclosure can reduce the amount of TEA to be produced.
Next, the ink storage container of the present disclosure is an ink container that contains water-based ink for inkjet recording, and the water-based ink is the water-based ink for inkjet recording according to the present disclosure. The ink storage container may be a conventionally known container, for example. Examples of ink storage containers include ink cartridges, tanks, pouches, and the like.
Next, the inkjet recording device and inkjet recording method of the present disclosure will be described.
The inkjet recording device of the present disclosure is an inkjet recording device that includes an ink storing part and ink ejecting part, and the ink contained in the ink storing part is ejected by the ink ejecting part. The water-based ink for inkjet recording of the present disclosure is stored in the ink storing part.
The FIGURE illustrates an example configuration of an inkjet recording device of the present disclosure. As illustrated in the drawing, an inkjet recording device 1 includes four ink storing parts (ink cartridge 2), an ink ejecting part (inkjet head) 3, a head unit 4, a carriage 5, a drive unit 6, a platen roller 7, and a purging device 8 as major components.
The four ink cartridges 2 contain four colors of water-based ink, one each of yellow, magenta, cyan and black. For example, at least one of the four water-based inks is the water-based ink of the present disclosure. This example shows a set of four ink cartridges 2, but instead, an integrated ink cartridge may be used, having the interior partitioned to form a water-based yellow ink compartment, a water-based magenta ink compartment, a water-based cyan ink compartment, and a water-based black ink compartment. The main body of the ink cartridge may be a conventionally known cartridge main body, for example.
The inkjet head 3 installed in the head unit 4 records on a recording medium (for example, recording paper) P. The four ink cartridges 2 and the head unit 4 are mounted on the carriage 5. The drive unit 6 moves the carriage 5 back and forth in a straight line direction. The drive unit 6 may be any conventionally known drive unit, for example (see, for example, Japanese Unexamined Patent Application No. 2008-246821 (US2008/241398), the contents of which are incorporated herein in their entirety). The platen roller 7 extends in a reciprocating direction of carriage 5 and is disposed opposite the inkjet head 3.
The inkjet head 3, for example, includes a plurality of layers of thin metal plates. Through holes are formed in each of the thin plates. A plurality of layers of thin plates with through holes form a channel for the water-based ink to pass through. The thin plates, for example, are bonded by an adhesive. Note that some adhesive may deteriorate when the pH of the water-based ink is 9.2 or higher. Some of the metals that form the thin plates can corrode if the pH of the water-based ink is less than 7.8. Therefore, considering the adhesive and thin plates that form the inkjet head 3, the pH of the water-based ink should be, for example, an initial pH of less than 9.2, and the pH of the water-based ink when stored at 60° C. for one week (pH after storage) should be, for example, 7.8 or higher.
The purging device 8 suctions out defective ink containing air bubbles and the like that accumulate inside the inkjet head 3. For example, a conventionally known purging device can be used as the purging device 8 (see, for example, Japanese Unexamined Patent Application No. 2008-246821 (US2008/241398)).
A wiper member 20 is provided on the platen roller 7 side of the purging device 8, adjacent to the purging device 8. The wiper member 20 is formed in the shape of a spatula, and wipes a nozzle forming surface of the inkjet head 3 as the carriage 5 moves. In the FIGURE, a cap 18 covers a plurality of nozzles of the inkjet head 3 when the head has returned to the reset position after recording is finished, in order to prevent the water-based ink from drying out.
In the inkjet recording device 1 of the present example, the four ink cartridges 2 are mounted on one carriage 5 together with the head unit 4. However, the present disclosure is not limited thereto. In the inkjet recording device 1, each of the four ink cartridges 2 may be mounted on a carriage separate from the head unit 4. Each of the four ink cartridges 2 may be arranged and secured in the inkjet recording device 1, rather than being mounted on the carriage 5. In these embodiments, for example, each of the four ink cartridges 2 and the head unit 4 mounted on the carriage 5 are connected by tubing or the like, and the water-based ink is supplied from each of the four ink cartridges 2 to the head unit 4. Furthermore, in these embodiments, four ink bottles in bottle form may be used instead of the four ink cartridges 2. In this case, the ink bottle preferably has an injection port for injecting ink from the outside into the inside.
Inkjet recording using this inkjet recording device 1 is performed, for example, as follows. First, the recording paper P is fed from a paper feeding cassette (not illustrated) provided on the side or below the inkjet recording device 1. The recording paper P is introduced between the inkjet head 3 and the platen roller 7. Prescribed recording is performed on the introduced recording paper P by the water-based ink ejected from the inkjet head 3. After recording, the recording paper P is ejected from the inkjet recording device 1. In the FIGURE, paper feeding and paper ejecting mechanisms for the recording paper P are omitted.
The device illustrated in the FIGURE uses a serial inkjet head, but the present disclosure is not limited thereto. The inkjet recording device may be a line inkjet head or a roller-to-roller device.
Next, the inkjet recording method of the present disclosure is an inkjet recording method that includes a recording step in which water-based ink is ejected onto the recording medium by an inkjet method, and in the recording step, the water-based ink for inkjet recording of the present disclosure is used as the water-based ink. The inkjet recording method of the present disclosure can be performed, for example, using the inkjet recording device of the present disclosure. The recording includes printing, text printing, image printing, and the like.
Next, Examples of the present disclosure will be described along with Comparative Examples. Note that the present disclosure is not limited or restricted by the following Examples and Comparative Examples.
(Preparation of Pigment Dispersion A)
Pure water was added to a mixture of 20 mass % of pigment (carbon black) and 7 mass % of sodium hydroxide neutralized product of styrene-acrylic acid copolymer (acid value of 175 mg KOH/g, molecular weight of 10,000) to achieve a total of 100 mass %, and then the mixture was stirred to obtain a mixture. The mixture was placed in a wet sand mill filled with 0.3 mm diameter zirconia beads and dispersed for 6 hours. Afterwards, the zirconia beads were removed by a separator and filtered through a 3.0 μm pore diameter cellulose acetate filter to obtain pigment dispersion A. The styrene-acrylic acid copolymer is a water-soluble polymer that is generally used as a pigment dispersing agent. Note that in pigment dispersion A, the formulation amount of pigment solids (A) was 15 mass % of the total amount of pigment dispersion A.
(Preparation of pigment dispersion B)
Pure water was added to a mixture of 20 mass % of pigment (C.I. Pigment yellow 74) and 7 mass % of sodium hydroxide neutralized product of styrene-acrylic acid copolymer (acid value of 175 mg KOH/g, molecular weight of 10,000) to achieve a total of 100 mass %, and then the mixture was stirred to obtain a mixture. The mixture was placed in a wet sand mill filled with 0.3 mm diameter zirconia beads and dispersed for 6 hours. Afterwards, the zirconia beads were removed by a separator and filtered through a 3.0 μm pore diameter cellulose acetate filter to obtain pigment dispersion B. In pigment dispersion B, the formulation amount of pigment solids (A) was 15 mass % of the total amount of pigment dispersion B. Note that the sodium hydroxide neutralized product of the styrene-acrylic acid copolymer is a water-soluble polymer that is generally used as a pigment dispersing agent.
The components of the water-based ink composition (Tables 1 to 3), excluding the pigment dispersions A and B, were uniformly mixed to obtain an ink solvent. Next, the ink solvent was added to the pigment dispersions A and B, and mixed until uniform. The resulting mixture was then filtered through a cellulose acetate-type membrane filter (pore diameter 3.00 μm) manufactured by Toyo Roshi Kaisha to obtain water-based ink for inkjet recording of Examples 1 to 18, Comparative Examples 1 to 10, and Reference Example 1, as shown in Tables 1 to 3.
The water-based inks of Examples 1 to 18, Comparative Examples 1 to 10, and Reference Example 1 were subjected to (a) change in pH evaluation and (b) agglomeration evaluation, using the following methods.
(a) Change in pH Evaluation
Each of the water-based inks in the Examples, Comparative Examples, and Reference Example was subjected to a storage test at 60° C. for one week in a thermostatic chamber manufactured by ESPEC Corp., and the pH was measured before and after the storage test. The pH was measured using a tabletop pH meter “F-54” manufactured by HORIBA, Ltd. Next, the change in pH was determined from the pH before and after the storage test using equation (1), and evaluated based on the following evaluation criteria.
—Change in pH evaluation criteria—
A: Initial pH is less than 9.2, the pH after storage is 7.8 or higher, and the change in pH is less than 5%.
B: Initial pH is less than 9.2, the pH after storage is 7.8 or higher, and the change in pH is 5% or higher and 10% or lower.
C: Initial pH 9.2 or higher or the pH after storage is less than 7.8.
D: Initial pH and the pH after storage is not measurable
(b) Agglomeration Evaluation
Similar to the (a) change in pH evaluation, the average particle size of the pigment was measured for each of the water-based inks in the Examples, Comparative Examples, and Reference Example before and after the storage test. The average particle size was measured using a “NICOMP 380ZLS-S” particle sizing instrument (manufactured by Particle Sizing Systems; PSS) at 25° C. The evaluation was then performed according to the following evaluation criteria. Note that if agglomeration occurs, the dispersed pigment particles will gather, and the average particle size of the pigment will increase, and thus it can be determined that the storage stability will be inferior. Therefore, if the results of the agglomeration evaluation are favorable, the water-based ink can be evaluated as having excellent storage stability.
—Agglomeration Evaluation Criteria—A: No change in the average particle size of the pigment before and after storage testing
C: Change in the average particle size of the pigment before and after storage testing
The water-based ink compositions and evaluation results of the water-based inks of Examples 1 to 18, Comparative Examples 1 to 10, and Reference Example 1 are shown in Tables 1 to 3. Table 3 also shows the water-based ink compositions and evaluation results of Example 1 shown in Table 1.
As shown in Table 1, Examples 1 to 18 had evaluation results for the change in pH of “B” or higher, and agglomeration evaluation results of “A” or higher, which is favorable. Of Examples 1 to 7, Examples 1 and 4 to 7, which satisfy condition (1-2), had better change in pH evaluation results than Examples 2 and 3, which have the same conditions except that they do not satisfy condition (1-2). Of Examples 1, 10, and 11, Example 1 had excellent evaluation results for the change in pH, as compared to Examples 10 and 11 where the formulation amount of surfactant or the type of surfactant was different.
On the other hand, Comparative Examples 1 to 8, which did not use the alkali metal hydrogencarbonate, had poor evaluation results for the change in pH. In Comparative Examples 6 and 7, the initial pH and pH after storage could not be measured because of large aggregates of pigment particles. Furthermore, in Comparative Examples 9 and 10 which did not satisfy condition (1), the evaluation results of the agglomeration evaluation were inferior.
As shown in Table 3, Reference Example 1, where only triethanolamine was used as a pH adjusting agent without using the alkali metal hydrogencarbonate, had inferior evaluation results for the change in pH.
As described above, the water-based ink of the present disclosure can both reduce the formulation amount of TEA and improve storage stability. The water-based inks of the present disclosure are widely applicable to inkjet recording on various recording media.
Obviously, numerous modifications and variations of the present invention(s) are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention(s) may be practiced otherwise than as specifically described herein.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2022-029623 | Feb 2022 | JP | national |
