JP2013072057A - Water-in-oil (w/o) type emulsion ink for inkjet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a water-in-oil (W/O) type emulsion ink for inkjet printing which is excellent in storage stability at high temperature.SOLUTION: A water phase containing a water-soluble dye is dispersed in an oil phase containing a water-insoluble polar solvent having α value of 9 or more by use of a polygylceryl fatty acid ester including oleic acid or isostearic acid as a fatty acid moiety and having HLB of 7-14 as an emulsifier. The mixing amount of the emulsifier is 25-70 pts.wt. relative to 100 pts.wt. of the whole aqueous phase, and the concentration of the water-soluble dye in the water phase is 1/2 or more of the maximum solubility of the die. The water-insoluble polar solvent with α value of 9 or more is an ester-based solvent or an alcohol-based solvent, and the content is preferably 15-35 mass% of the total amount of the ink in the former case, and 5-15 mass% in the latter case. The emulsion ink is preferably composed of 40-99 mass% oil phase and 60-1 mass% water phase.

Description

  The present invention relates to a water-in-oil (W / O) emulsion ink for inkjet which is suitable for use in inkjet printing and has excellent storage stability at high temperatures.

  Ink-jet printing is characterized by non-contact printing by ejecting ink droplets from fine nozzles, and each company is developing ink-jet ink with the aim of miniaturizing ink droplets, speeding up printed materials, and increasing the size. Is going.

  As an ink used in ink jet printing (referred to as “ink jet ink” in the present specification), an aqueous dye / pigment ink using a dye and / or pigment as a colorant is generally used for personal and office use. The water-based dye / pigment ink has a high printing density due to the high water absorption of paper fibers, and the amount of show-through, which is the printing density viewed from the back side of the printed matter, is reduced. On the other hand, since the paper is dried in a state where pressure is applied when paper is made, when water adheres, hydrogen bonds between paper fibers are cut and paper curl is generated. This paper curl is conspicuous when a cut sheet is used, and affects the positional accuracy of the ink droplets and the paper conveyance. In particular, in order to aim at high-speed printing, it was necessary to eliminate paper curl.

  A technique for eliminating paper curl includes reducing or eliminating the amount of water in the ink. Therefore, if oil-based ink is used, paper curl does not occur and it is suitable for high-speed printing.

  Business printers that employ a line head type ink jet method are attracting attention because they have a fixed head and are capable of mass printing at high speed and are inexpensive. This inkjet printer for high-speed printing usually uses an oil-based pigment ink that uses a pigment as a colorant, but it is obtained because the ink penetrates the back of the printed material when printed compared to other types of printers. The printed matter has a low print density and a lot of showthrough.

  One solution to this problem is to emulsify water in an oil-based ink to make a water-in-oil (W / O) emulsion ink. This emulsion ink has an effect that the printing density is high and the back-through is reduced as compared with the oil-based dye / pigment ink. In a water-in-oil (W / O) emulsion ink, if a colorant is blended in the oil phase (outer phase), the bleeding becomes severe. Therefore, it is preferable to blend the colorant in the water phase (inner phase). In this case, as a coloring material used in the aqueous phase, it is desirable to use a dye from the viewpoints of ink storage stability and ejection properties.

  Several proposals have been made regarding water-in-oil (W / O) emulsion inks that use a dye as a colorant in the aqueous phase (see, for example, Patent Documents 1 and 2). It has been confirmed that the inks proposed in these patent documents have good storage stability at 50 ° C. for one month. However, in the case of transporting ink by ship, since the ink is required to have a performance that does not change even after storage at 70 ° C. for one month, the storage temperature was raised to 70 ° C. and a storage test was conducted. Separation / precipitation of the aqueous phase and precipitation of the dye occurred, and there was a problem that the storage stability at high temperature was insufficient.

JP-A-4-170475 JP-A-4-183762

  The present inventors include a polyglycerin fatty acid containing a colorant in an oil phase, an organic value of an emulsifier of 600 to 1700, an inorganic value of 600 to 1300, and a fatty acid portion of oleic acid or isostearic acid. Developed a water-in-oil (W / O) emulsion ink that exhibits good storage stability without the separation and settling of an aqueous phase even after storage at 70 ° C for 1 month by using an ester. Patent application doing. However, even in this ink, when a dye was blended in the aqueous phase in order to suppress bleeding, a foreign matter derived from the dye was generated during storage at 70 ° C., and the storage stability was tended to deteriorate.

  Accordingly, an object of the present invention is to provide a water-in-oil (W / O) emulsion ink suitable for ink jet printing which is excellent in storage stability and does not generate foreign matters during storage at high temperatures.

  As a result of intensive research under the above-mentioned objectives, the present inventors have used a specific amount of a specific polyglycerin fatty acid ester as an emulsifier for a water-in-oil (W / O) emulsion ink, and set the colorant concentration in the aqueous phase. By maintaining a predetermined range and containing a predetermined water-insoluble polar solvent in the oil phase, a water-in-oil (W / O) emulsion ink having excellent discharge performance and storage stability can be obtained. As a result, the present invention has been completed.

That is, according to the present invention, in a water-in-oil (W / O) emulsion ink for inkjet, wherein a water phase containing a water-soluble dye is dispersed in an oil phase using a polyglycerol fatty acid ester as an emulsifier, the oil The phase contains a water-insoluble polar solvent having an α value of 9 or more, and the polyglycerin fatty acid ester has a fatty acid portion of oleic acid or isostearic acid and an HLB of 7 to 14, and its blending amount Is 25 to 70 parts by weight when the total amount of the aqueous phase is 100 parts by weight, and the concentration of the water-soluble dye in the aqueous phase is ½ or more of the maximum dissolution concentration of the water-soluble dye in water. A water-in-oil (W / O) emulsion ink for inkjet is provided.
Here, in the present invention, “water-soluble” of the water-soluble dye means a dye having a maximum solubility in water at 20 ° C. of 1.0 wt% or more. In addition, “water-insoluble” of a water-insoluble polar solvent means an organic solvent having a maximum solubility in water at 20 ° C. of less than 1.0 wt%.

It is considered that the generation of foreign matters during storage at high temperatures is suppressed by the following mechanism.
(1) The water particles of the water-in-oil (W / O) emulsion ink evaporate in the vicinity of the gas-liquid interface, and the dye is deposited. Is formed.
(2) The film grows with time and increases in thickness, and further grows, so that the film is broken and the fragments settle in the ink.
(3) Coarse water particles aggregated and coalesced around the settled fragments and the deposited dye gather, and the fragments grow to form foreign matters.
Therefore, in order to prevent the generation of foreign substances, it is effective to suppress the film formation due to the micelle formation of the dye. Therefore, in the present invention, a predetermined water-insoluble polar solvent is used and the emulsifier itself is used as an oil. By making it easy to dissolve in the phase, it is considered that adsorption of the emulsifier to the above-described dye is suppressed, and as a result, generation of foreign matters can be suppressed.

  According to the present invention, a specific polyglycerin fatty acid ester is used as an emulsifier for forming a water-in-oil (W / O) emulsion, the oil phase contains a predetermined organic solvent, and a dye is added to the water phase. Since a predetermined amount is blended, a water-in-oil (W / O) emulsion ink for inkjet having excellent storage stability at high temperatures can be obtained.

Hereinafter, the present invention will be described in more detail.
The water-in-oil (W / O) emulsion ink of the present invention is obtained by mixing an oil phase and an aqueous phase and dispersing the aqueous phase as fine particles in the oil phase.

  The oil phase is mainly composed of an organic solvent, a colorant, and an emulsifier, but may contain other components as necessary.

  As the organic solvent, a water-insoluble polar solvent having an α value of 9 or more is used. Specific examples of the structure include ester, alcohol, fatty acid and ether. These may be used alone or in combination of two or more. Here, the reason why the polar solvent is limited to water-insoluble is that, in the case of the water-soluble polar solvent, the aqueous phase is separated in the ink and the storage stability is lowered.

The α value is represented by an arctangent function of (inorganic value) / (organic value) as derived from the following equation.
tan α = (inorganic value) / (organic value)
α = tan ⁻¹ {(inorganic value) / (organic value)}
And there exists the following relationship between HLB mentioned later and this alpha value.
HLB = 10 · tan α = 10 × {(inorganic value) / (organic value)}

  The “organic value” and “inorganic value” are based on the concept used in the “Organic Conceptual Diagram” proposed by Satoshi Fujita, and the organic compound is derived from the covalent bond chain in its carbon region. Is divided into two factors, “organic” and “inorganic” due to electrostatic effects existing in substituents (functional groups), each of which is quantified, and is determined from the structure of each compound. Value. Matters relating to the “Organic Conceptual Diagram” are described in detail in the book “Systematic Organic Qualitative Analysis (mixture)” by Kaoru Fujita, Kazama Shobo (1974) and the like.

  Examples of the ester solvent include higher fatty acid esters having 5 or more, preferably 9 or more, and more preferably 12 to 32 carbon atoms in one molecule. For example, isodecyl isononanoate, isotridecyl isononanoate, and isononanoic acid. Isononyl, methyl laurate, isopropyl laurate, hexyl laurate, isopropyl myristate, isopropyl palmitate, isooctyl palmitate, hexyl palmitate, isostearyl palmitate, isooctyl isopalmitate, methyl oleate, ethyl oleate, oleic acid Isopropyl, butyl oleate, hexyl oleate, methyl linoleate, isobutyl linoleate, ethyl linoleate, butyl stearate, hexyl stearate, isooctyl stearate, Isopropyl stearate, 2-octyldodecyl pivalate, soybean oil methyl, soybean oil isobutyl, tall oil methyl, tall oil isobutyl, diisopropyl adipate, diisopropyl sebacate, diethyl sebacate, propylene glycol monocaprate, propylene glycol dicaprate, Examples include trimethylolpropane tri-2-ethylhexanoate, glyceryl tri-2-ethylhexanoate, and pentaerythritol tetra-2-ethylhexanoate.

  Examples of the alcohol solvent include aliphatic higher alcohols having 12 or more carbon atoms in one molecule. Specifically, higher alcohols such as isomyristyl alcohol, isopalmityl alcohol, isostearyl alcohol, and oleyl alcohol. Examples include alcohol.

  Examples of the fatty acid solvent include fatty acids having 4 or more, preferably 9 to 22 carbon atoms in one molecule, such as isononanoic acid, isomyristic acid, hexadecanoic acid, isopalmitic acid, oleic acid, and isostearic acid. Is mentioned.

  Examples of ether solvents include glycol ethers such as diethyl glycol monobutyl ether, ethylene glycol monobutyl ether, propylene glycol monobutyl ether, propylene glycol dibutyl ether, and acetates of glycol ethers.

  When an ester solvent is used as the water-insoluble polar solvent having an α value of 9 or more, the blending ratio is preferably 15 to 35 parts by weight with respect to 100 parts by weight of the total amount of ink. When a higher alcohol solvent is used, the blending ratio is preferably 3 to 15 parts by weight with respect to 100 parts by weight of the whole ink.

  As the organic solvent, in addition to the water-insoluble polar solvent having an α value of 9 or more, a water-insoluble polar solvent or non-polar solvent having an α value of less than 9 can be used. Specific examples of the former include ester solvents such as 2-hexyldecyl stearate and trimethylolpropane triisostearate. These can be used alone or in combination of two or more.

  As non-polar solvents, petroleum hydrocarbon solvents such as naphthenic, paraffinic, and isoparaffinic solvents can be used. Specifically, aliphatic saturated hydrocarbons such as dodecane, “Isoper, Exol” manufactured by ExxonMobil ( All of them are trade names), “AF Solvent” (trade name) manufactured by JX Nippon Oil & Energy Corporation, “Sansen, Thumper” (all trade names) manufactured by Sun Oil Co., Ltd., and the like. These can be used alone or in combination of two or more.

  As the colorant, any of dyes and pigments can be used. They can be used alone or in combination.

  The pigment is not particularly limited, and may be any organic pigment or inorganic pigment that is commonly used in the technical field of printing. Specifically, carbon black, cadmium red, chrome yellow, cadmium yellow, chromium oxide, pyridian, titanium cobalt green, ultramarine blue, Prussian blue, cobalt blue, azo pigment, phthalocyanine pigment, quinacridone pigment, isoindo Rinone pigments, dioxazine pigments, selenium pigments, perylene pigments, thioindigo pigments, quinophthalone pigments, metal complex pigments and the like can be suitably used. These pigments may be used alone or in combination of two or more.

  The colorant is preferably contained in the range of 0.01 to 20% by mass with respect to the total amount of ink.

  As the emulsifier, a polyglycerin fatty acid ester whose fatty acid part is oleic acid or isostearic acid and whose HLB is 7 to 14 is used. Here, the polyglycerol fatty acid ester refers to an esterified product of polyglycerol and a fatty acid. When the polyglycerin fatty acid ester does not satisfy the requirements of the present invention, the discharge performance and the storage stability are inferior. It is preferable that the fatty acid portion is isostearic acid because both the discharge performance and the storage stability can be improved to a high degree.

  In the polyglycerol fatty acid ester, the degree of polymerization of glycerol is preferably 4 to 10, and more preferably 6 to 10. Moreover, it is preferable that several (for example, 1 to 3) of the higher fatty acids per molecule of the polyglycerin are added by ester bonds. The organic value of the polyglycerin fatty acid ester is preferably 550 to 2300, and the inorganic value is preferably 600 to 2500. The more preferable organic value of the polyglycerin fatty acid ester is 600 to 1700, and the more preferable inorganic value is 600 to 1300. When the organic value is larger than 2300 or when the inorganic value is larger than 2500, the viscosity of the ink becomes high. Specific examples of preferred polyglycerin fatty acid esters include tetraglyceryl monooleate, hexaglyceryl monooleate, decaglyceryl trioleate, tetraglyceryl monoisostearate, hexaglyceryl monoisostearate, decaglyceryl diisostearate and the like.

  The amount of the emulsifier used in the present invention is preferably 25 to 70 parts by weight when the total aqueous phase (the total of water and water-soluble dye) is 100 parts by weight. If it is used in this range, the separation and coalescence of the aqueous phase at high temperature can be suppressed, but if it is less than 25 parts by weight, it is not preferable because the separation and coalescence of the aqueous phase occurs during storage at high temperature. If it exceeds the parts by weight, the viscosity of the ink increases and foreign matter tends to be generated during storage at high temperatures, resulting in a decrease in ejection performance.

  The oil phase can be prepared by, for example, supplying all components into a known disperser such as a bead mill in a batch or divided and dispersing the mixture, and if desired, passing it through a known filter such as a membrane filter. For example, after preparing a mixed liquid in which a part of the solvent and the whole amount of the pigment and the pigment dispersant are uniformly mixed and dispersing with a disperser, the remaining components are added to the dispersion and a filter is added. It can be prepared by passing through.

  The aqueous phase is mainly composed of a water-soluble dye and water, but may contain other components as necessary.

  The water-soluble dye is not particularly limited, and among basic dyes, acid dyes, direct dyes, soluble vat dyes, acid mordant dyes, mordant dyes, reactive dyes, vat dyes, sulfur dyes, and the like, water-soluble dyes and reduction dyes. It is possible to use a dye that has been rendered water-soluble by such means. Specifically, examples of water-soluble dyes include azo dyes, rhodamine dyes, methine dyes, azomethine dyes, xanthene dyes, quinone dyes, phthalocyanine dyes, triphenylmethane dyes, diphenylmethane dyes, and methylene blue. Any one of these dyes may be used alone, or two or more of these dyes may be used in combination.

  The water phase is obtained by dissolving a water-soluble dye in water, and if necessary, a metal salt, an electrolyte, a moisturizer, a water-soluble polymer, an oil-in-water (O / W) resin emulsion, an antifungal agent, an antiseptic, pH It is composed by dissolving a conditioner, an antifreezing agent and the like.

  Ion exchange water is used as water. The water content in the aqueous phase is preferably 2 to 30% by mass of the total ink. When the content is less than 2% by mass, the ink surface concentration is the same as that of oil-based ink. When the content is more than 30% by mass, the viscosity is increased and the ejection performance is lowered.

  The water-soluble dye is not particularly limited as long as it is soluble in water, and examples thereof include azo series, anthraquinone series, and azine series.

  The water-soluble dye is blended so that its concentration becomes 1/2 or more of the maximum dissolution concentration of the water-soluble dye in water. When the water-soluble dye concentration is less than this, no foreign matter is generated, but the print density decreases due to the low density.

  It is preferable to further add a dissolution aid to the aqueous phase. In this case, since the dye is infiltrated and adsorbed on the paper fiber in a state dissolved to the molecular state, the coloring of the dye is improved. As the dissolution aid, an amine surfactant is preferable. Examples of the amine surfactant include polyalkylene oxide adducts of organic amines such as ethylene oxide (EO) or propylene oxide (alkylamine, alkenylamine, alkylhydroxylamine, alkenylhydroxylamine, oxyalkylamine, oxyalkenylamine, etc.) PO) adducts. Of these, ethylene oxide (EO) or propylene oxide (PO) adducts of alkylamines are preferred. As such amine-based surfactants, those commercially available as Solsperse 20000, Solsperse 27000, Solsperse 46000 (all trade names) manufactured by Nippon Lubrizol Co., Ltd., and TAMNO-15 (trade names) manufactured by Nikko Chemicals Co., Ltd. can be used. . The blending amount of the dissolution aid is preferably 0.1 to 10% by mass, more preferably 0.3 to 8% by mass with respect to the total amount of ink.

  Further, it is preferable to add glycerin or diglycerin to the aqueous phase in order to reduce the ink viscosity and improve the dischargeability. The blending amount of glycerin or diglycerin is preferably 10 to 70% by mass and more preferably 20 to 65% by mass with respect to the entire aqueous phase. When the amount is less than 10% by mass, it is difficult to obtain the effect of reducing the viscosity. When the amount is more than 70% by mass, the ejection stability and the storage stability may be deteriorated.

  The water-in-oil (W / O) emulsion ink for inkjet according to the present invention can be produced by mixing and emulsifying the above oil phase and water phase. The aqueous phase and the oil phase may be prepared separately in advance, and then the aqueous phase solution may be added to the oil phase solution to emulsify, or the components constituting the oil phase may be added to the aqueous phase collectively or individually. Thereafter, it may be emulsified. A known emulsifier such as a disper mixer or a homomixer can be used for the production.

  The particle size of the aqueous phase in the oil phase after emulsification is preferably 80 to 500 nm. If it is smaller than 80 nm, the surface density of the printed matter is lowered, or the color of the dye is deteriorated. When the thickness is larger than 500 nm, the discharge property in the ink jet is deteriorated.

  The inkjet ink of this invention is mix | blended so that it may become 40-99 mass% of oil phases, and 60-1 mass% of water phases. When the ratio of the water phase exceeds 60% by mass, it becomes difficult to form a water-in-oil (W / O) emulsion. When the ratio of the aqueous phase is less than 1% by mass, the print density may be lowered or the printout may be exposed. In general, since the ink viscosity tends to increase as the ratio of the aqueous phase increases, the blending ratio of both phases is preferably 50 to 98% by mass of the oil phase and 50 to 2% by mass of the aqueous phase, and 55 to 97 of the oil phase. The mass% and the water phase 45-3 mass% are more preferable.

  The viscosity at 23 ° C. of the water-in-oil (W / O) emulsion ink of the present invention thus obtained is preferably set in the range of 3 to 100 mP · s, and in the range of 5 to 30 mPa · s. It is more preferable to set to 10 to 20 mPa · s. The viscosity of the ink can be adjusted by adjusting the type and amount of components of the oil phase and the amount of the aqueous phase. In general, the smaller the amount of aqueous phase and / or the amount of emulsifier, the lower the viscosity of the ink, but the lower the storage stability of the emulsion.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to this Example.

Examples 1-14, Comparative Examples 1-9
A pigment dispersion was obtained by mixing the pigment and dispersant in the blending amounts shown in Table 1 or 2 with a part of the solvent shown in the same table and dispersing the pigment with a rocking mill (manufactured by Seiwa Giken). The pigment dispersion was diluted with the remaining solvent, and then the surfactant was dissolved therein to obtain an oil phase. To this oil phase, ion-exchanged water or a mixture of ion-exchanged water and an additive was added dropwise with stirring at 5000 rpm using a high-speed homogenizer “Viscotron” (trade name: manufactured by Microtech Nichion), and then 5 at 20000 rpm. A water-in-oil (W / O) emulsion ink was prepared by stirring for a minute. In addition, the compounding quantity of each component in Table 1 and Table 2 is shown by the mass part.

The inkjet inks obtained in the above examples and comparative examples were evaluated by the following methods. These evaluation results are shown in Tables 1 and 2. The maximum dye concentration in these tables was determined by the following method.
An excess amount of the dye was added to 10 g of water, stirred for 3 hours at 25 ° C., then allowed to stand overnight at a constant temperature of 25 ° C., the undissolved dye was removed by filtration, and the dye was saturated. An aqueous solution was prepared. 1 g of this saturated aqueous solution was dried in an oven at 100 ° C., the mass of the remaining residue (solid content) was measured, and the result was defined as the maximum solubility of the dye at 25 ° C.

(1) Storage stability In the unstable water-in-oil (W / O) emulsion ink, the water content of the ink upper layer decreases with time. Storage stability was evaluated by measuring the amount of water in the upper layer of the ink and comparing it with the amount of water prepared. A water-in-oil (W / O) emulsion ink was placed in a 10 ml screw vial and allowed to stand in a thermostatic bath at 70 ° C. for 2 weeks and 4 weeks, and then the water content of the ink upper layer was measured. The ink was sampled from the top of the container, and the moisture content was measured using a Karl Fischer moisture measuring device (701 type, manufactured by Metrohm Shibata Co., Ltd.).
Ink upper layer water remaining rate (%):
{Water amount of ink upper layer after storage (mass%) / water content of preparation (mass%)} x 100
The stability was evaluated based on the following criteria using the water residual ratio expressed as described above as an index.
○: Ink upper layer water residual ratio is 70% or more (A, B)
X: Ink upper layer water residual ratio is less than 70% (C, D, E)
In the above evaluation criteria, A is 90% or more, B is 70% or more and less than 90%, C is 30% or more and less than 70%, D is 20% or more and less than 30%, and E is 20%. %, And in the results of Tables 1 and 2, in addition to the results of ◯ and ×, the evaluations of A to E are shown in parentheses.

(2) Existence of foreign matter The ink in the screw vial is No. After naturally filtering with 5 paper, the presence or absence of foreign matter on the paper was visually observed and judged based on the following criteria.
○: There is no clogging of the filtrate, and no foreign matter is found on the paper. ×: There is a clogging of the filtrate, or there is a foreign matter on the paper.

(3) Evaluation Method of Printed Surface Density (Color Development) A solid image was printed on plain paper (ideal mat IJ (W), produced by Riso Kagaku Kogyo Co., Ltd.) using ORPHIS HC5500. The printed surface density was evaluated by measuring the OD value on the surface of the solid image using an OD meter (RD920, manufactured by Macbeth Co.).

In addition, the symbol of the raw material of Table 1-Table 3 is as follows.
Decaglyceryl diisostearate: Decaglyn 2-ISV (trade name) manufactured by Nikko Chemicals
Decaglyceryl trioleate: Decaglyn 3-OV (trade name) manufactured by Nikko Chemicals
Tetraglyceryl monoisostearate: Sakamoto Pharmaceutical Co., Ltd. IS-401P (trade name)
AF Solvent No. 6: JX Nippon Oil & Energy, petroleum hydrocarbon solvent, AF-6 (trade name)
Hexyl laurate: Nikko Chemicals, LAH (trade name)
Diethyl sebacate: manufactured by Nikko Chemicals, DES-SP (trade name)
Propylene glycol dicaprate: Nikko Chemicals, PPD (trade name)
Glyceryl tri-2-ethylhexanoate (= triethylhexanoin): TRIFAT S-308 (trade name) manufactured by Nikko Chemicals
Tetra-2-ethylhexanoic acid pentaerythritol: Nikko Chemicals, PENTALAN-408 (trade name)
2-hexyldecyl stearate: Nikko Chemicals, ICS-R (trade name)
Trimethylolpropane triisostearate: TRIALAN-318H (trade name) manufactured by Nikko Chemicals
Isomyristyl alcohol: Fine Oxocol 140-N (trade name) manufactured by Nissan Chemical Industries, Ltd.
Water-soluble dyes: Nippon Kayaku Co., Ltd., KST Black J-BL Liquid (trade name)

  From the results of Table 1, Examples 1 to 14 satisfy all the requirements of the present invention for the organic solvent in the oil phase, the polyglycerin fatty acid ester as the emulsifier, and the water-soluble dye concentration in the aqueous phase. It can be seen that film formation, separation of aqueous phase and occurrence of coalescence can be suppressed, and no foreign matter is generated even after storage for 4 weeks under a high temperature condition of 70 ° C., and the storage stability at high temperature is excellent.

In contrast, the results shown in Table 2 show the following.
Since Comparative Example 1 did not contain a non-water-soluble polar solvent in the oil phase but contained only a non-polar solvent, the generation of foreign matters was observed, and the storage stability at high temperatures was poor.
In Comparative Examples 2 and 3, since the content of the emulsifier is less than the predetermined range, no foreign matter is generated in Comparative Example 2, but separation of the aqueous phase is observed. In Comparative Example 3, foreign matter is generated. In both cases, the storage stability at high temperatures is inferior.
In Comparative Example 4, since the concentration of the water-soluble dye in the aqueous phase was less than the predetermined range of the present invention, the generation of foreign matter was not observed, but the printing density was lowered.
In Comparative Examples 5 and 6, since the α value of the polar solvent contained in the oil phase is less than 9, separation of the aqueous phase, coalescence, and generation of foreign matters are observed, and the storage stability at high temperatures is poor.
In Comparative Example 7, the water-soluble dye concentration in the aqueous phase was increased to the maximum solubility of the dye, but the oil phase did not contain a water-insoluble polar solvent having an α value of 9 or more. No foreign matter was observed until storage for 2 weeks, but foreign matter was observed after storage for 4 weeks, and the long-term storage stability at high temperatures was poor.
In Comparative Example 8, the fatty acid portion of the polyglycerol fatty acid ester used as an emulsifier did not satisfy the requirements of the present invention, and no foreign matter was generated after storage at 70 ° C. for 4 weeks, but separation and coalescence of the aqueous phase were observed. Therefore, the storage stability at high temperatures is poor.
Comparative Example 9 uses polyoxyethylene nonylphenyl ether as an emulsifier, does not use the polyglycerin fatty acid ester of the present invention, and does not generate foreign matter even after storage at 70 ° C. for 4 weeks. Since the unity was recognized, the storage stability at high temperatures is poor.

  Since the water-in-oil (W / O) emulsion ink for inkjet of the present invention is excellent in ejection performance and storage stability, it is used as an ink for business printers employing the line head type inkjet system, particularly in the field of inkjet printing. Available.

Claims (7)

In a water-in-oil (W / O) emulsion ink for inkjet, in which an aqueous phase containing a water-soluble dye is dispersed in an oil phase using a polyglycerin fatty acid ester as an emulsifier,
The oil phase contains a water-insoluble polar solvent having an α value of 9 or more,
The polyglycerin fatty acid ester has a fatty acid portion of oleic acid or isostearic acid and an HLB of 7 to 14, and its blending amount is 25 to 70 parts by weight when the entire aqueous phase is 100 parts by weight.
A water-in-oil (W / O) emulsion ink for inkjet, wherein the concentration of the water-soluble dye in the aqueous phase is ½ or more of the maximum dissolution concentration of the water-soluble dye in water. 2. The water-in-oil (W / O) emulsion ink for inkjet according to claim 1, wherein the polyglycerol fatty acid ester has a glycerol polymerization degree of 4 to 10. 3. The water-in-oil (W / O) emulsion ink for inkjet according to claim 1, wherein 1 to 3 fatty acids are added per molecule of the polyglycerin fatty acid ester. The water-in-oil (W / O) emulsion ink for inkjet according to claim 1, wherein the organic value of the polyglycerin fatty acid ester is 550 to 2300 and the inorganic value is 600 to 2500.   The water-in-oil (W / O) emulsion ink for ink-jet recording according to any one of claims 1 to 4, wherein the water-insoluble polar solvent having an α value of 9 or more is an ester-based and / or alcohol-based solvent.   6. When the ester solvent is used for the water-insoluble polar solvent having an α value of 9 or more, the blending amount is 15 to 35 parts by weight with respect to 100 parts by weight of the total amount of the ink. 6. The water-in-oil (W / O) emulsion ink for inkjet described.   6. When the alcohol solvent is used for the water-insoluble polar solvent having an α value of 9 or more, the blending amount is 3 to 15 parts by weight with respect to 100 parts by weight of the total amount of the ink. 6. The water-in-oil (W / O) emulsion ink for inkjet described.