JP2007169370A - Ink set - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ink set usable for inkjet printing methods ejecting heated state ink from a head, wherein color fluctuation in printing is little. <P>SOLUTION: The ink set of ink and used in inkjet printing method is provided, in which method ink liquid at normal temperatures is heated to have viscosity of ≥5 mPa s but <10 mPa s to be ejected from a head of a piezo system, and, wherein, each ink is obtained by dispersing a pigment in a mixture solvent of at least water and a water-soluble organic solvent and values of temperature coefficient β of each ink and of temperature dependence formula 1 of the ink viscosity are so uniform as within a range of ±5% arithmetic mean of each ink used for the ink set. Wherein, formula 1 is η=α×exp(β/T), in which formula, η is viscosity (mPa s), T is an absolute temperature (K), α is a constant and β is a temperature coefficient. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an ink set used for ink jet recording, and more particularly to an ink set suitable for an ink jet recording method characterized in that the ink is ejected from a piezo head in a heated state.

  An ink jet image printing method is a method in which fine droplets of ink are ejected from an ink jet recording head and attached to a target recording medium for printing. The ink jet method is advantageous in that its mechanism is relatively simple, inexpensive, and can form a high-definition and high-quality image.

  Inks used in the ink jet method include water-based inks, oil-based inks, solvent inks, and the like depending on the type of liquid medium contained therein. The ink is liquid at room temperature, but there is also ink such as hot melt ink that performs discharge recording by melting a wax type ink that is solid at room temperature to be in a liquid state. In addition, UV inks containing components that are cured by ultraviolet rays are also on the market.

  Thus, the presence of various inks is a proof that inkjet is used in various printing applications, and the applications are still expanding. Under such circumstances, there is a need for a printer system that ejects ink with high viscosity as the ink functions.

  As a method for ejecting ink having such a high viscosity, a method in which the head is heated to reduce the viscosity of the ink and ejected is disclosed (for example, see Patent Document 1).

  Furthermore, an ink jet recording method and an ink jet ink in which ink is heated and ejected are described (for example, see Patent Documents 2 to 4).

  As a method for heating the ink, a method in which a heater is incorporated in the head and a temperature sensor is incorporated in or outside the head to perform feedback temperature control is generally used. In practice, it is difficult to control the temperature, and the temperature will be in the range of about ± 5 ° C.

  On the other hand, the viscosity of the ink sensitively affects the temperature, and also affects the amount of ejected droplets and the ejection speed. Therefore, when the ink temperature changes, the ink discharge amount changes through the ink viscosity change, and the recording density changes.

  In a printer using a plurality of inks such as a color printer, when the ink discharge amount between the inks changes, the hue of the printed matter appears, and the influence on the human eye is greater than the density change of the same hue.

In the ink jet recording method and ink jet printer in which ink is ejected by heating, it is necessary to consider the change in the ink viscosity due to the temperature change, particularly the difference in the viscosity change between the inks. This is not mentioned in ink jet printers.
JP 2003-136756 A JP 2003-21663 A JP 2004-339489 A JP 2004-351443 A

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an ink set used in an ink jet recording method in which ink is ejected from a head in a heated state, with little color variation during recording. There is.

  The above object of the present invention can be achieved by the following configuration.

  1. In an ink set of ink used in an ink jet recording method in which ink that is liquid at normal temperature is heated and ejected from a piezo-type head with a viscosity of 5 mPa seconds or more and less than 10 mPa seconds, each ink contains at least water and a water-soluble organic solvent The temperature coefficient β of each ink of Equation 1 in the temperature dependence of the ink viscosity expressed below is the average of the arithmetic average of each ink used in the ink set. An ink set characterized by being in the range of 5%.

Formula 1 η = α · exp (β / T)
(In the formula, η represents viscosity (mPa seconds), T represents absolute temperature (K), α represents a constant, and β represents a temperature coefficient.)

  According to the present invention, it is possible to provide an ink set used in an ink jet recording method in which ink is ejected from a head in a heated state with little color variation during recording.

  Hereinafter, the best mode for carrying out the present invention will be described in detail.

  In the present invention, the heating temperature of the ink is 30 ° C. or higher and lower than 100 ° C., preferably 40 ° C. or higher and 90 ° C. or lower.

  Further, the ink can be heated in the ink head, in the case of heating in the middle of the ink supply path, or in the case of heating the whole from the ink cartridge. However, the heating method in the ink head is preferable because the heating range is small and the amount of energy to be applied is small.

  In addition, although the effect of the present invention can be obtained by heating the ink by any method, a method of heating using a heater is preferable. Moreover, it is preferable not only to heat, but also to control the temperature by feeding back the temperature measured by the temperature sensor.

  The head used in the present invention is a piezo head. Piezo heads are superior in terms of ejection stability at high temperatures in thermal ink ejection systems than in thermal systems. However, compared to the thermal method, the piezo method has a great influence on the appropriate amount of liquid to fly and the flying speed, and control of the ink viscosity is very important for stable recording. In order to control the ink viscosity, a method of precisely controlling the heating temperature of the ink can be considered, but since the piezo drive itself for ejection becomes the heat source, the channel that is driven and the channel that is not driven There was a problem that the temperature control could not substantially catch up because of the high temperature of several kHz to several tens of kHz.

  In the ink set of the present invention, the value of the temperature coefficient β of each ink is adjusted to be within a range of ± 5% of the arithmetic average of the ink set, thereby suppressing print color fluctuation due to temperature fluctuation.

  A method for adjusting the temperature dependence of the ink viscosity is shown below as a specific example. The temperature dependence of the ink viscosity can be expressed by Equation 1.

  In Equation 1, α and β are values inherent to the substance, and β is related to the temperature dependence of the viscosity. This constant is an intermediate value in the case of a mixture. For water-soluble organic solvents used in water-based inkjet inks, there is almost no literature data on temperature dependence of viscosity. For example, the following methods can be used to determine constants α and β from the results. It is.

  Using a rheometer with a 1 ° cone plate, MCR-300 (manufactured by Perphysica Corporation), the viscosity (mPa second) at a shear rate of 0.001 (1 / sec) is measured while changing the temperature.

The obtained data can be plotted by taking the reciprocal of absolute temperature on the horizontal axis and the viscosity on the vertical axis, and fitting with the above approximate expression to obtain the values of α and β. Fitting error is shown by R ^2. Table 1 summarizes the measurement results for several solvents.

  Of course, the value of α varies depending on the solvent, so the value of temperature coefficient β also varies. Further, as can be seen from the table, there is no correlation between α and β between the solvents, and α that affects the absolute value of the ink viscosity and β that affects the temperature dependence can be independently adjusted by selecting the solvent.

  As a method for making the temperature dependence of the ink viscosity uniform in the ink set, it can be considered that the solvent composition is the same, but the content of the pigment in the ink differs depending on the color depending on the color. In addition, the temperature dependency varies depending on the type of pigment, and the temperature dependency of the viscosity cannot be made uniform between ink sets simply by making the solvent composition the same.

  Ink with a large amount of pigment tends to decrease the value of temperature coefficient. In this case, the temperature coefficient can be adjusted by increasing the content of the solvent having a high temperature coefficient.

  The viscosity of the ink set of the present invention is 10 mPa seconds or more and less than 50 mPa seconds at 25 ° C. With an ink of 50 mPa seconds or more, even if the ink temperature is 90 ° C., the viscosity does not decrease to a region where the emission property is sufficiently stable.

  Moreover, the viscosity in the heated state at the time of emission is 5 mPa seconds or more and less than 10 mPa seconds. When emitted at 10 mPa seconds or more, there are many satellites, and when printing is performed, fine dust is generated around the dots, which is undesirable because the printed matter lacks fineness.

  The ink of the present invention may be any ink as long as it is an aqueous pigment ink containing at least water, a water-soluble organic solvent, and a pigment.

  Hereinafter, the ink composition of the present invention will be described in detail.

  As the pigment that can be used in the ink of the present invention, conventionally known pigments can be used without particular limitation, and any of water-dispersible pigments, solvent-dispersible pigments and the like can be used. For example, organic pigments such as insoluble pigments and lake pigments. And inorganic pigments, such as carbon black, can be used preferably. This pigment is present in a dispersed state in the ink, and the dispersion method may be any of self-dispersion, dispersion using a surfactant, polymer dispersion, and microcapsule dispersion. Dispersion is particularly preferred from the standpoint of fixability.

  The insoluble pigment is not particularly limited. Dioxazine, thiazole, phthalocyanine, diketopyrrolopyrrole and the like are preferable.

  Specific pigments that can be preferably used include the following pigments.

  Examples of the magenta or red pigment include C.I. I. Pigment red 2, C.I. I. Pigment red 3, C.I. I. Pigment red 5, C.I. I. Pigment red 6, C.I. I. Pigment red 7, C.I. I. Pigment red 15, C.I. I. Pigment red 16, C.I. I. Pigment red 48: 1, C.I. I. Pigment red 53: 1, C.I. I. Pigment red 57: 1, C.I. I. Pigment red 122, C.I. I. Pigment red 123, C.I. I. Pigment red 139, C.I. I. Pigment red 144, C.I. I. Pigment red 149, C.I. I. Pigment red 166, C.I. I. Pigment red 177, C.I. I. Pigment red 178, C.I. I. Pigment red 202, C.I. I. Pigment red 222, C.I. I. Pigment violet 19 and the like.

  Examples of the pigment for orange or yellow include C.I. I. Pigment orange 31, C.I. I. Pigment orange 43, C.I. I. Pigment yellow 12, C.I. I. Pigment yellow 13, C.I. I. Pigment yellow 14, C.I. I. Pigment yellow 15, C.I. I. Pigment yellow 15: 3, C.I. I. Pigment yellow 17, C.I. I. Pigment yellow 74, C.I. I. Pigment yellow 93, C.I. I. Pigment yellow 128, C.I. I. Pigment yellow 94, C.I. I. And CI Pigment Yellow 138.

  Examples of the pigment for green or cyan include C.I. I. Pigment blue 15, C.I. I. Pigment blue 15: 2, C.I. I. Pigment blue 15: 3, C.I. I. Pigment blue 16, C.I. I. Pigment blue 60, C.I. I. And CI Pigment Green 7.

  Examples of black pigments include C.I. I. Pigment black 1, C.I. I. Pigment black 6, C.I. I. Pigment black 7 and the like.

  The average particle size in the dispersed state of the pigment contained in the inkjet ink produced by the production method of the present invention is preferably 50 nm or more and less than 200 nm. When the average particle size of the pigment dispersion is less than 50 nm or 200 nm or more, the stability of the pigment dispersion tends to deteriorate, and the storage stability of the ink tends to deteriorate.

  The particle size of the pigment dispersion can be determined by a commercially available particle size measuring instrument using a dynamic light scattering method, an electrophoresis method, or the like. Accurate and often used.

  The pigment used in the ink of the present invention is preferably used after being dispersed by a disperser together with a dispersant and other additives necessary for various desired purposes. As the disperser, a conventionally known ball mill, sand mill, line mill, high-pressure homogenizer, or the like can be used. In particular, the particle size distribution of the ink produced by dispersion with a sand mill is sharp and preferable. The material of the beads used for sand mill dispersion is preferably zirconia or zircon from the viewpoint of contamination of bead fragments and ionic components. Furthermore, the bead diameter is preferably 0.3 mm to 3 mm.

  In the ink of the present invention, it is preferable to use a polymer dispersant in the dispersion.

  The polymer dispersant referred to in the present invention has a polymer component having a molecular weight of 5000 or more and 200000 or less. The polymer dispersant is selected from styrene, styrene derivatives, vinyl naphthalene derivatives, acrylic acid, acrylic acid derivatives, maleic acid, maleic acid derivatives, itaconic acid, itaconic acid derivatives, fumaric acid and fumaric acid derivatives. Examples thereof include a block copolymer comprising at least one kind of monomer, a random copolymer and salts thereof, polyoxyalkylene, and polyoxyalkylene alkyl ether.

  In the case of an acidic polymer dispersant, it is preferably added after neutralization with a neutralizing base. Here, the neutralizing base is not particularly limited, but is preferably an organic base such as ammonia, monoethanolamine, diethanolamine, triethanolamine, or morpholine.

  Moreover, in this invention, it is preferable that the addition amount of a polymer dispersing agent is 10-100 mass% with respect to a pigment.

  Examples of the water-soluble organic solvent preferably used as the solvent used in the ink of the present invention include alcohols (for example, methanol, ethanol, propanol, isopropanol, butanol, isobutanol, secondary butanol, tertiary butanol, pen) (Tanol, hexanol, cyclohexanol, benzyl alcohol, etc.), polyhydric alcohols (for example, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, butylene glycol, hexanediol, pentanediol, Glycerin, hexanetriol, thiodiglycol, 1,3-propanediol, 1,4-butanediol, 1,5 Pentanediol, 1,2-pentanediol, 1,2-hexanediol, 1,2,6-hexanetriol, etc., polyhydric alcohol alkyl ethers, amines (eg, ethanolamine, diethanolamine, triethanolamine, N -Methyldiethanolamine, N-ethyldiethanolamine, morpholine, N-ethylmorpholine, ethylenediamine, diethylenediamine, triethylenetetramine, tetraethylenepentamine, polyethyleneimine, pentamethyldiethylenetriamine, tetramethylpropylenediamine, etc.), amides (for example, formamide N, N-dimethylformamide, N, N-dimethylacetamide, etc.), heterocycles (for example, 2-pyrrolidone, N-methyl-2-pyrrolidone, cyclohexylpi Pyrrolidone, 2-oxazolidone, etc.), sulfoxides (e.g., dimethyl sulfoxide), sulfones (e.g., sulfolane), urea, acetonitrile, and acetone.

  Furthermore, in the ink of the present invention, the SP value of the most water-soluble organic solvent among the water-soluble organic solvents is 16.5 or more and less than 24.6, and the SP value is 16.5 or more and less than 24.6. It is preferable that the content of the water-soluble organic solvent is 30% by mass or more of the total ink mass. With this solvent composition, it is possible to prevent the occurrence of curling when recording on plain paper.

The solvent solubility parameter (SP value) in the present invention is a value represented by the square root of the molecular cohesive energy. F. Fedors, Polymer Engineering Science, 14, p147 (1974). The unit is (MPa) ^1/2 and refers to the value at 25 ° C.

  Hereinafter, examples of water-soluble organic solvents having an SP value of 16.5 or more and less than 24.6 are shown together with the SP value. Needless to say, the present invention is not limited to this.

Ethylene glycol monomethyl ether (SP value: 24.5)
Ethylene glycol monoethyl ether (23.5)
Ethylene glycol monobutyl ether (22.1)
Ethylene glycol monoisopropyl ether (22.3)
Diethylene glycol monomethyl ether (23.0)
Diethylene glycol monoethyl ether (22.4)
Diethylene glycol monobutyl ether (21.5)
Diethylene glycol diethyl ether (16.8)
Triethylene glycol monomethyl ether (22.1)
Triethylene glycol monoethyl ether (21.7)
Triethylene glycol monobutyl ether (21.1)
Propylene glycol monomethyl ether (23.0)
Propylene glycol monophenyl ether (24.2)
Dipropylene glycol monomethyl ether (21.3)
Tripropylene glycol monomethyl ether (20.4)
1,3-dimethyl-2-imidazolidinone (21.8)
In the ink of the present invention, in addition to the above description, if necessary, the output stability, print head and ink cartridge compatibility, storage stability, image storage stability, and other various performance improvement objectives are known. Various additives such as polysaccharides, viscosity modifiers, specific resistance regulators, film forming agents, ultraviolet absorbers, antioxidants, anti-fading agents, antifungal agents, rust preventives, etc. may be appropriately selected and used. For example, oil droplet fine particles such as liquid paraffin, dioctyl phthalate, tricresyl phosphate, silicon oil, ultraviolet absorbers described in JP-A-57-74193, 57-87988, and 62-261476, As described in Kaisho 57-74192, 57-87989, 60-72785, 61-146591, JP-A-1-95091 and 3-13376, etc. Anti-fading agents, fluorescent whitening agents described in JP-A Nos. 59-42993, 59-52689, 62-280069, 61-242871, and JP-A-4-219266 Can be mentioned.

  The ink used in the recording method of the present invention is preferably degassed.

  Ink deaeration may be performed by any method, but a deaeration method using a hollow fiber deaeration module is preferable from the viewpoint of deaeration efficiency and ejection reliability. Furthermore, the degassing method using the external reflux type hollow fiber degassing module has a small pressure loss when degassing the pigment ink, and the dispersion stability is not deteriorated due to the high differential pressure before and after the degassing. preferable. As such an external reflux type hollow fiber deaeration module, a commercially available one can be used, and examples thereof include Dainippon Ink & Chemicals, Inc. SEPAREL EF-002A-P and SEPARELEF-004P.

  Various resins are used as the material of the hollow fiber, and in particular, poly-4 methylpentene 1 resin or polytetrafluoroethylene resin has a large amount of ink and its deaeration performance is less likely to deteriorate during processing. It is preferable because the ink component and the dispersant are less likely to adhere to the outer surface of the hollow fiber and the ink components are less likely to change.

  In the present invention, the degree of deaeration is measured by the dissolved oxygen concentration. Examples of the method for measuring the dissolved oxygen concentration include the Ostwald method (see Experimental Chemistry Course 1, Basic Operation [I], page 241, 1975, Maruzen), the method of measuring by the mass spectrum method, the galvanic cell type, It can be measured using a simple oxygen concentration meter such as a polarographic type or a colorimetric analysis method. The dissolved oxygen concentration can also be easily measured using a commercially available dissolved oxygen concentration meter (DO-30A type manufactured by Toa Denpa Kogyo Co., Ltd.).

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto.

(Preparation of dispersion)
The pigment, aqueous solvent, and polymer dispersant were weighed according to the following dispersion formulation, and ion exchange water was added to make 100 parts as a whole. After premixing with a dissolver, 340 g of 1.5 mm zirconia beads were added. Each dispersion was prepared by dispersing with a filled bead mill (Mini Cer, manufactured by Ashizawa Finetech).

<Yellow dispersion>
Yellow pigment: Paliotol Yellow D-0960 (manufactured by BASF)
20 parts Floren TG-760W (manufactured by Kyoeisha Chemical Co., Ltd.) (as solid content) 6 parts tripropylene glycol monomethyl ether 20 parts <Magenta dispersion>
Magenta pigment: Fastgen Super Magenta RG
(Dainippon Ink Co., Ltd.) 20 parts Jonkrill 501 (as solid content) 8 parts Tripropylene glycol monomethyl ether 15 parts <Cyan dispersion>
Cyan pigment: Heliogen Blau D-7086 (BASF)
15 parts BYK191 (produced by Big Chemie) (as solids) 6 parts tripropylene glycol monomethyl ether 20 parts [Preparation of ink]
Thereafter, each material was weighed and mixed according to the following ink formulation, and filtered with a # 1000 mesh metal mesh filter to obtain inks 1-8.

<Ink 1>
Yellow dispersion 30 parts Tripropylene glycol monomethyl ether 65 parts Ion exchange water 5 parts <Ink 2>
Magenta dispersion 25 parts Tripropylene glycol monomethyl ether 60 parts Propylene glycol 5 parts Ion exchange water 10 parts <Ink 3>
Cyan dispersion 20 parts triethylene glycol monomethyl ether 40 parts diethylene glycol monomethyl ether 25 parts ion exchange water 15 parts <Ink 4>
Cyan dispersion 20 parts Tripropylene glycol 20 parts Triethylene glycol monomethyl ether 40 parts Ion-exchanged water 20 parts <Ink 5>
Yellow dispersion 30 parts Tripropylene glycol 50 parts Diethylene glycol monomethyl ether 10 parts Ion exchange water 10 parts <Ink 6>
Magenta dispersion 25 parts Tripropylene glycol 45 parts Triethylene glycol monobutyl ether 15 parts Ion-exchanged water 15 parts <Ink 7>
Cyan dispersion 20 parts Tripropylene glycol 45 parts Triethylene glycol monobutyl ether 15 parts Ion-exchanged water 20 parts <Ink 8>
Cyan dispersion 20 parts Tetraethylene glycol 40 parts Propylene carbonate 30 parts Ion-exchanged water 10 parts [Deaeration treatment]
Degassing treatment for inks 1 to 8 using an external circulation hollow fiber degassing module: Dainippon Ink & Chemicals, Inc. SEPAREL EF-002A until the dissolved oxygen concentration is less than 0.5 ppm (25 ° C.). went.

[Print sample]
A printer using a piezo-type inkjet head with 256 nozzles having the same structure as the head with a heater described in Japanese Patent Application Laid-Open No. 2003-136756 was filled with ink in the combinations shown in Table 2. Next, as shown in FIG. 1, ten continuous images each having an area ratio of 60% were printed with yellow, magenta, and cyan inks on the shaded portion of A4 size photo glossy paper (manufactured by Epson).

[Evaluation of print sample]
The obtained print samples were evaluated for the first and tenth solid images. In addition, the Lab value of the printed part was measured and compared. ΔE = (ΔL ² + Δa ² + Δb ² ) ^0.5
◎ ΔE between the first sheet and the tenth sheet is less than 3 ○ ΔE between the first sheet and the tenth sheet is less than 5 Δ: ΔE between the first sheet and the tenth sheet is XX which is less than 10: ΔE between the first sheet and the tenth sheet is 10 or more XX: ΔE in the first and last portions in the first sheet is 5 or more.

[Curl evaluation]
Solid images with 60% area ratio of yellow, magenta, and cyan inks on almost the entire surface of A4-sized plain paper (manufactured by Konica Minolta Business Technologies; NR-A80) under the same conditions as printing on photo glossy paper Printed.

Next, the printed plain paper was left in a flat place with the printed surface facing up in an environment of 23 ° C. and 55% RH for one day, and the state of the paper was observed.
A: Almost flat, even at the most floating part at the four corners, the lifting height is less than 5 mm. O: The lifting height at the most floating part at the four corners is 5 mm or more and less than 10 mm. Δ: Most floating at the four corners. The height of the lifted portion is 10 mm or more and less than 20 mm. X: The height of the lift of the most floating portion at the four corners is 20 mm or more and less than 50 mm. XX: The height of the floating of the most floating portion at the four corners Is rounded into a cylindrical shape of 50 mm or more, and measurement is impossible. Table 3 shows the obtained results.

  As can be seen from Table 3, ink set 1 and ink set 4 whose temperature coefficient β exceeds ± 5% of the arithmetic average of the ink set, significant color fluctuations occur between prints or within one print. On the other hand, in the ink set 2 and the ink set 3 in which the value of the temperature coefficient β is equal to ± 5% of the arithmetic average of the ink set, ΔE is also less than 3, and the color variation is the human eye. It turns out that it is in the range which is not understood.

  Further, it can be seen that the ink set 2 does not cause the curling of plain paper.

It is a figure which shows the printing part of evaluation.

Claims (1)

In an ink set of ink used in an ink jet recording method in which ink that is liquid at normal temperature is heated and ejected from a piezo-type head with a viscosity of 5 mPa seconds or more and less than 10 mPa seconds, each ink contains at least water and a water-soluble organic solvent The temperature coefficient β of each ink of Equation 1 in the temperature dependence of the ink viscosity expressed below is the average of the arithmetic average of each ink used in the ink set. An ink set characterized by being in the range of 5%.
Formula 1 η = α · exp (β / T)
(In the formula, η represents viscosity (mPa seconds), T represents absolute temperature (K), α represents a constant, and β represents a temperature coefficient.)

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