JP4837901B2 - Oil-based inkjet ink - Google Patents

Description

  The present invention relates to an oil-based inkjet ink that is excellent in pigment dispersion stability and ejection stability from an inkjet head nozzle.

  The ink jet recording method is a method in which high-fluidity ink jet ink is ejected as ink particles from fine head nozzles, and an image is recorded on a printing medium placed opposite to the nozzles. Since it is possible, it has spread rapidly in recent years. As an ink used in such an ink jet recording method, a so-called water-based dye ink in which a dye is dissolved in water is frequently used. However, the water-based dye ink has poor weather resistance and water resistance, and depending on the type of paper. Had problems such as ink bleeding.

  In order to solve the above problems, various so-called oil-based pigment inks in which a pigment is finely dispersed in a water-insoluble solvent have been proposed (see, for example, Patent Document 1). However, the oil-based pigment ink is obtained by finely dispersing a pigment that is solid particles in a low-viscosity solvent, so that it is difficult to ensure the dispersion stability of the pigment, and when pigment aggregation occurs. However, there is a problem that clogging occurs in the head nozzle, and as a result, stable ink discharge performance cannot be obtained.

  In addition, an emulsion-type ink containing both water and a water-insoluble solvent and having either water or a water-insoluble solvent as a discontinuous phase has been proposed (see Patent Document 2). It is difficult to maintain the stability of the nozzle, and there is a problem that stable ejection from the nozzle cannot be obtained.

JP 2003-261808 A JP-A-6-25574

  Accordingly, an object of the present invention is to provide an oil-based inkjet ink (hereinafter referred to as oil-based ink) excellent in pigment dispersion stability and ejection stability from an inkjet head nozzle.

As a result of intensive studies based on the above object, the present inventors have made an oil-based ink excellent in pigment dispersion stability and ejection stability from an inkjet head nozzle by incorporating a small amount of water in the oil-based ink. As a result, the present invention was completed.
That is, according to the present invention, an oil-based inkjet ink comprising a pigment, a pigment dispersant, a water-insoluble organic solvent and water, the water-insoluble organic solvent is contained in an amount of 60% by weight or more of the total amount of the ink, There is provided an oil-based inkjet ink characterized in that the water content based on the Karl Fischer method is in the range of 0.2% by weight or more of the total amount of ink and not more than the solubility in ink.

  According to the present invention, when preparing an oil-based ink by dispersing a pigment in a water-insoluble organic solvent, a minute amount of water is added, and the water content in the oil-based ink finally obtained is adjusted. Although it is unknown, an oil-based inkjet ink having excellent pigment dispersion stability and excellent ejection stability without causing clogging due to aggregation of the pigment in the inkjet head nozzle can be obtained. In addition, the oil-based ink of the present invention is configured as a single continuous phase in the liquid phase and is not in the form of an emulsion, so that there is no problem of ink ejection failure due to destabilization of the emulsion such as an emulsion type ink.

  Hereinafter, the present invention will be described in more detail with reference to embodiments of the oil-based inkjet ink of the present invention.

  The water-insoluble organic solvent used in the present invention is not particularly limited, and conventionally known solvents such as hydrocarbon solvents, ester solvents, alcohol solvents, higher fatty acid solvents and the like can be used. These may be used alone or in combination of two or more. When using 2 or more types mixed, it is necessary for a liquid mixture to form a single continuous phase.

  Examples of the hydrocarbon solvent include aliphatic hydrocarbon solvents, alicyclic hydrocarbon solvents, aromatic hydrocarbon solvents, and the like. As the aliphatic hydrocarbon solvent and alicyclic hydrocarbon solvent, “Nippon Oil Co., Ltd.“ Tclean N-16, Tclean N-20, Tclean N-22, No. 0 Solvent L, No. 0 Solvent M, No. 0 Solvent ” "H, AF-4, AF-5, AF-6, AF-7" (all trade names), "Nisseki Isosol, Naphthezol" (all trade names) manufactured by Nippon Petrochemicals, "Exxon Mobil" IsoparG, IsoparH, IsoparL, IsoparM, ExxolD40, ExxolD80, ExxolD100, ExxolD140, ExxolD140 "(all trade names).

  As ester solvents, methyl laurate, isopropyl laurate, isopropyl myristate, isopropyl palmitate, isostearyl palmitate, methyl oleate, ethyl oleate, isopropyl oleate, butyl oleate, methyl linoleate, isobutyl linoleate, Ethyl linoleate, isopropyl isostearate, soybean oil methyl, soybean oil isobutyl, tall oil methyl, tall oil isobutyl, diisopropyl adipate, diisopropyl sebacate, diethyl sebacate, propylene glycol monocaprate, trimethylolpropane tri-2-ethylhexanoate And glyceryl tri-2-ethylhexanoate.

  Examples of the alcohol solvent include isomyristyl alcohol, isopalmityl alcohol, isostearyl alcohol, oleyl alcohol and the like.

  Examples of the higher fatty acid solvent include isononanoic acid, isomyristic acid, isopalmitic acid, oleic acid, and isostearic acid.

  In the present invention, among the above water-insoluble organic solvents, an ester solvent, an alcohol solvent, or a mixed solvent thereof is preferably used as a main component from the viewpoint of dispersion stability of the pigment.

  In the present invention, the addition amount of the water-insoluble organic solvent is 60% by weight or more, preferably 70 to 98% by weight of the total amount of the ink.

  In addition to the water-insoluble organic solvent, the oil-based ink of the present invention can be added with a water-soluble organic solvent as long as it is compatible with this and forms a single continuous liquid phase. The water-soluble organic solvent is not particularly limited, and conventionally known solvents such as lower alcohols can be used.

The pigment used in the present invention is not particularly limited, and conventionally known inorganic pigments and organic pigments can be used. Examples of inorganic pigments include titanium oxide, bengara, cobalt blue, ultramarine blue, bitumen, carbon black, calcium carbonate, kaolin, clay, barium sulfate, talc, and silica. Examples of the organic pigment include insoluble azo pigments, azo lake pigments, condensed azo pigments, condensed polycyclic pigments, and copper phthalocyanine pigments. These pigments may be used alone or in appropriate combination. Of these, an azo lake pigment is preferably used alone from the viewpoint of improving the ink ejection stability.
The added amount of the pigment is preferably 0.5 to 20% by weight based on the total amount of the ink.

  The pigment dispersant is not particularly limited as long as the colorant to be used is stably dispersed in the solvent, but among them, it is preferable to use a polymer dispersant.

  Specifically, “Solsperse 5000 (phthalocyanine ammonium salt type), 13940 (polyesteramine type), 17000, 18000 (aliphatic amine type), 22000, 24000, 28000” (all trade names) manufactured by Nippon Lubrizol Corporation; “Efka 400, 401, 402, 403, 450, 451, 453 (modified polyacrylate), 46, 47, 48, 49, 4010, 4050, 4055 (modified polyurethane)” manufactured by Efka CHEMICALS (all trade names); “Demol P, EP”, “Poise 520, 521, 530”, “Homogenol L-18 (polycarboxylic acid type polymer surfactant)” (all trade names) manufactured by Kao Corporation; “Disparon KS” manufactured by Enomoto Kasei Co., Ltd. -860, KS-873N4 (polymer polyester Salt) ”(all trade names);“ Discall 202, 206, OA-202, OA-600 (multi-chain polymer nonionic) ”(all trade names) manufactured by Daiichi Kogyo Seiyaku Co., Ltd. It is done.

The oil-based ink of the present invention is adjusted so that the water content is in the range of 0.2% by weight or more of the total amount of ink and not more than the solubility in the ink, preferably 0.2 to 2% by weight, more preferably 0.3 to 1%. It is adjusted to be in the range of 5% by weight. As a result, an oil-based ink that forms a continuous phase of the liquid phase and exhibits excellent pigment dispersion stability and ejection stability from the inkjet head nozzle can be obtained.
This amount of water can be usually adjusted by adding water when preparing the oil-based ink by mixing the above components. However, each component such as an organic solvent, a pigment dispersant, and a pigment may also contain a trace amount of water due to its moisture retention. In addition, the moisture of each component may fluctuate due to moisture absorption and desorption in the ink manufacturing process (for example, raw material preparation process and pigment dispersion process). In addition, the water content of the oil-based ink also varies depending on moisture absorption / release during preparation. For this reason, the sum of the water content of each component before mixing and the amount of added water at the time of ink preparation does not necessarily match the water content of the finally obtained oil-based ink. Therefore, the amount of water to be added varies depending on the type and moisture retention of the organic solvent used, the environmental conditions at the time of pigment dispersion, the storage conditions of each component, etc., but usually 0.1 to 3 wt. %. In the present invention, the water content means a value measured based on the Karl Fischer method.

  The oil-based ink of the present invention can be prepared by dispersing a pigment in a liquid component such as the organic solvent, the pigment dispersant, and water. As a preparation method, the pigment may be dispersed by adding the total amount of the pigment, the pigment dispersant and the organic solvent and the predetermined amount of water to a known disperser such as a bead mill, and the pigment dispersant and A pigment dispersion prepared by dispersing the entire amount of the pigment while adding the predetermined amount of water to a part of the organic solvent may be prepared in advance, and the remaining organic solvent may be further mixed therewith.

  The oil-based ink of the present invention thus obtained needs to be in a state where the pigment (solid phase) is dispersed in a single continuous liquid phase. This is because the water content in the ink falls within the above range. This can be achieved by adjusting. In order to confirm that the liquid phase of the oil-based ink forms a single continuous phase, it is determined by observing the appearance of the liquid phase obtained by mixing all components other than the pigment, especially transparency. it can. If the appearance of the liquid phase is transparent and the interface between the components of the liquid phase is not confirmed, it is determined that the liquid phase forms a single continuous phase.

  The oil-based ink of the present invention is suitable for use in a commercial inkjet printer. In order to obtain a stable discharge property from the head of the printer, it is preferable to prepare the ink so that the viscosity at 23 ° C. is 5 to 30 mPa · s. Such viscosity adjustment can be performed by appropriately selecting the type and amount of the water-insoluble organic solvent and other components.

  The oil-based ink according to the present invention does not affect the dispersion stability of the pigment or the ejection stability of the ink, and is within the range that is completely compatible with the liquid phase of the ink. Various additives such as an agent can be added.

  Hereinafter, the present invention will be described in more detail with reference to preferred examples of the oil-based inkjet ink of the present invention, but the present invention is not limited to these examples.

[Raw materials used]
(1) Pigment Brilliant Carmine 6B (trade name 6B320, manufactured by Dainippon Ink & Chemicals, Inc.)
Permanent Red 2B (trade name R-3118, manufactured by Dainippon Ink & Chemicals, Inc.)
(2) Pigment dispersant Solsperse 28000 (trade name, manufactured by Nippon Lubrizol Corporation)
(3) Ester solvent Soybean oil isobutyl (4) Alcohol solvent Isostearyl alcohol (5) Petroleum hydrocarbon solvent AF-5 (trade name, manufactured by Nippon Oil Corporation)
(6) Distilled water (7) Antioxidant Dibutylhydroxytoluene

Examples 1-4 and Comparative Examples 1-3
Each of the above raw materials was dispersed with a bead mill at a blending ratio shown in Table 1 to prepare a pigment dispersion (component A). Thereafter, this pigment dispersion was dispersed in various solvents shown in Table 2 at the blending ratio shown in Table 2, and the obtained dispersion was filtered through a 3.0 μm membrane filter. 3 oil-based ink was obtained. Each ink was evaluated as follows. The results are shown in Table 2.

(1) Viscosity Using a rheometer (trade name Rheostress RS300) manufactured by Hake, the viscosity at 23 ° C. and stress 10 Pa of the oil-based ink prepared by the above method was measured immediately after the ink was prepared.

(2) Water content in oil-based ink The water content in the oil-based ink prepared by the above method was measured by the Karl Fischer method. For measurement, a 701 type Titrino moisture meter manufactured by Metrohm was used.

(3) Appearance of mixed liquid phase in oil-based ink Except for removing the pigment, after preparing a mixed liquid of component A with the blending ratio shown in Table 1, this mixed liquid of component A was changed to the organic solvent shown in Table 2. Mixing was performed at the blending ratio shown in the table. The obtained mixed liquid was put into a transparent glass bottle, and the appearance of the mixed liquid in the bottle was visually observed and evaluated as follows. The results are shown in Table 2.
○: Transparent and interface between liquid components cannot be confirmed (single continuous liquid phase)
X: Low transparency or interface between liquid components can be confirmed (liquid phase is discontinuous)

(4) Dispersion stability of pigment The oil-based ink obtained by the above method was put in a glass bottle, sealed, and stored in an environment at 60 ° C. for 10 days, and then the viscosity was measured in the same manner as in the above (1). It was compared with the viscosity value measured immediately after preparation. The results are shown in Table 2.
○: When the viscosity change is less than 3% ×: When the viscosity change is 3% or more

(5) Ink ejection stability The oil-based ink after storage in (4) above is introduced into a piezo-piezo type line head, and the ink is ejected continuously for 1 hour from 318 nozzles arranged in a line. The number of nozzles that stopped discharging ink was measured. This operation was repeated 10 times, and the average number of nozzles that no longer ejected ink per time (1 hour) was determined and evaluated as follows. The results are shown in Table 2.
A: The average value is 0.0 to less than 0.3. O: The average value is 0.3 to less than 1.0. X: The average value is 1.0 or more.

From the results of Table 2, in the case of Examples 1 to 4 belonging to the present invention, since the water content in the ink is 0.2% by weight or more, the liquid phase forms a single continuous phase, and the pigment dispersion It was confirmed that it was excellent in stability and ejection stability. In Examples 2 to 4 where the water content is 0.3% by weight or more, the ejection stability is particularly excellent.
On the other hand, in the case of Comparative Example 1, since the water content in the ink is less than the range of the present invention, the liquid phase forms a single continuous phase, but the dispersion stability of the pigment and the ejection stability of the ink. Inferior to In the case of Comparative Example 2, since the amount of water in the ink was larger than the range of the present invention, the dispersion stability of the pigment and the ejection stability of the ink were inferior, and the liquid phase was discontinuous. In the case of Comparative Example 3, a water-insoluble organic solvent (mainly an alcohol solvent) is used. However, since the amount of water in the ink is larger than the range of the present invention, the dispersion stability of the pigment and the ejection stability of the ink are inferior. At the same time, the liquid phase was discontinuous.

Claims (5)

An oil-based inkjet ink comprising a pigment, a pigment dispersant, a water-insoluble organic solvent and water, the water-insoluble organic solvent containing 60% by weight or more of the total amount of the ink;
The water-insoluble organic solvent consists of an ester solvent, an alcohol solvent and a hydrocarbon solvent,
The ester solvent is lauric acid ester, myristic acid ester, palmitic acid ester, oleic acid ester, linoleic acid ester, isostearic acid ester, soybean oil ester, tall oil ester, adipic acid ester, sebacic acid ester, propylene glycol monocaprate At least one selected from the group consisting of trimethylolpropane tri-2-ethylhexanoate, and glyceryl tri-2-ethylhexanoate,
The alcohol solvent is at least one selected from the group consisting of isomyristyl alcohol, isopalmityl alcohol, isostearyl alcohol, and oleyl alcohol;
An oil-based inkjet ink characterized in that the water content based on the Karl Fischer method is in the range of 0.2% by weight or more of the total amount of ink and not more than the solubility in ink. The oil-based inkjet ink according to claim 1, wherein the pigment is an azo lake pigment. The oil-based inkjet ink according to claim 1 or 2, wherein the water content is 0.2 to 2% by weight of the total amount of the ink. An oil-based inkjet ink comprising a pigment, a pigment dispersant, a water-insoluble organic solvent and water, wherein the water-insoluble organic solvent contains 60% by weight or more of the total amount of the ink, It consists of ester solvent, alcohol solvent and hydrocarbon solvent, and the ester solvent is lauric acid ester, myristic acid ester, palmitic acid ester, oleic acid ester, linoleic acid ester, isostearic acid ester, soybean oil ester, tall oil ester, adipine And at least one selected from the group consisting of acid ester, sebacic acid ester, propylene glycol monocaprate, trimethylolpropane tri-2-ethylhexanoate, and glyceryl tri-2-ethylhexanoate, and the alcohol solvent is isomyristyl alcohol , Isopal Chill alcohol, isostearyl alcohol, and is at least one selected from the group consisting of oleyl alcohol, water content based on the Karl Fischer method, it is adjusted to the following ranges solubility 0.2% by weight or more ink in the ink total amount An ink jet printing method, wherein the oil-based ink jet ink is discharged from an ink jet head nozzle to perform printing. The ink-jet printing method according to claim 4, wherein the water content is 0.2 to 2% by weight of the total amount of ink.