JPH0114948B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an aqueous inkjet recording ink. More specifically, the present invention relates to an improved water-based jet recording ink that can be used for a long time without clogging the nozzle of a jet printer, and can provide recorded matter with good light resistance. By the way, the basic printing principles of known inkjet recording methods include electrostatic attraction type, intermittent ejection type using pulse pressure, and continuous ejection using continuous pressure of several atmospheres, from the viewpoint of the method of ejecting ink droplets from the nozzle. There are methods such as types. In addition, from the viewpoint of how to control ink droplets, there are charge deflection type, electric field deflection type, and non-charge type (on-demand type). In practice, it appears that various combinations of the above-mentioned ejection methods and ink droplet control methods have been proposed and implemented as recording methods each having its own features.
However, the appropriate physical properties (viscosity, surface tension, etc.) and electrical properties of the ink differ depending on the method and the shape of the nozzle used. Therefore, in any inkjet method, ink must be continuously and stably ejected as uniform ink droplets from fine nozzles. Therefore, the basic problem to be solved in inkjet printers is to completely prevent clogging of the nozzle portion and ensure continuous and stable generation of ink particles over a long period of time. Another important point is that stable ink particles can be created again after a temporary pause. Naturally, fine nozzles can become clogged even by the adhesion of even a small amount of solvent-insoluble solids. Furthermore, even if a solid object adheres to a part of the nozzle, the ink ejection direction changes. Therefore, in order to eject ink particles continuously and stably, not only must the viscosity and surface tension of the ink composition be appropriate, but also the solvent-insoluble solids in the ink composition must be completely removed. It is necessary to remove it. It is also necessary to completely prevent the generation of solvent-insoluble solids over time. By the way, when coloring a water-based inkjet recording ink, it is usually possible to remove or prevent the generation of solvent-insoluble solids by using a water-soluble dye. However, in systems using water-soluble dyes, it is easier to meet the basic requirements of the inkjet method, such as preventing the generation of solvent-insoluble solids, but on the other hand, the light resistance of the recorded material is insufficient. There is a drawback that arises. To be more specific, recorded characters may disappear or become difficult to read after a certain period of time, and especially in the case of color images, there may be discoloration of the image due to differences in the light fastness of the mixed dyes. occurred often. In other words, the water-soluble dyes used in conventional water-based jet ink compositions have insufficient light fastness, cause nozzle clogging, and meet various conditions necessary for jet inks such as continuous jetting properties, as well as problems with printing materials. In view of the types of colors, hues, etc. required at the time, there were naturally limitations on the types that could be used. Therefore, one of the inventors of the present invention previously proposed an ink composition containing a water-soluble ultraviolet absorber in order to improve the various drawbacks and limiting conditions mentioned above. (Japanese Patent Publication No. 56-18151) However, the requirements for light resistance in this type of market are becoming more severe. In addition, the solvent is mainly a ketone organic solvent,
A soluble ionizable salt as a conductivity imparting agent is added to an inkjet recording ink whose main components are a solvent-soluble dye and a solvent-soluble synthetic resin such as vinyl chloride copolymer or vinyl acetate copolymer. Ink compositions are known. (Japanese Unexamined Patent Publication No. 52-96106) However, since this ink composition uses an organic ketone solvent with a hydrogen bonding force of moderate or lower, it imparts conductivity, which is not normally necessary in water-based ink compositions. agent is essential. In addition, in the ink composition, the solvent-soluble dye is expected to have the effect of improving light resistance due to its compatibility with the synthetic resin, but the ionizable components in the composition are particularly sensitive to alkali metals and alkaline earth metals. In the case of salt, since it has almost no compatibility with synthetic resins, it can hardly be expected to improve the light resistance of dyes. In addition, it is generally known that the light resistance of a dyed product (an inkjet recorded product in the present invention) is closely influenced (interacted) by various conditions such as the substrate, coexisting substances, and environmental conditions. As sufficient research results have not yet been obtained regarding these various problems in photobleaching, it is still difficult to construct a unified theoretical system. For example, regarding substrates, well-known unique problems in interaction with substrates include the high light fastness of cationic dyed acrylic fibers and the low light fastness of nylon dyed yellow vat dyes. etc. are known. However, there is no knowledge of this kind regarding inkjet recorded matter. Therefore, in order to obtain a jet ink composition with excellent light resistance, the present inventors conducted various studies on substances that improve light resistance by coexisting with dyes, and as a result, arrived at the present invention. Therefore, it is an object of the present invention to further improve the light resistance of recorded materials, to avoid clogging of nozzles, which conventionally has been unavoidable in inkjet systems, and to provide a water-soluble ink composition for use in aqueous jet ink compositions. The present invention provides a new aqueous inkjet recording ink aimed at expanding the types of dyes. This objective was unexpectedly solved by a specific water-soluble quencher. That is, the present invention provides an aqueous inkjet recording ink containing a water-soluble dye, a wetting agent, and water as its main components, which further includes potassium iodide, potassium bromide, potassium chloride, potassium thiocyanate, cobalt sulfate, copper sulfate, and potassium sulfate. The present invention relates to an inkjet recording ink characterized by containing at least one water-soluble quenching substance selected from iron, nickel sulfate, and nickel oxalate. In the present invention, the above-mentioned quenching substance, that is, a substance that deactivates the fluorescence of an excited substance by interaction [Kyoritsu Shuppan Co., Ltd., Chemistry Encyclopedia No. 4, No.
[Page 769] at least one compound selected from potassium iodide, potassium bromide, potassium chloride, potassium thiocyanate, cobalt sulfate, copper sulfate, ferrous sulfate, nickel sulfate, and nickel oxalate is used. . Among these, at least one of potassium iodide, potassium bromide, copper sulfate, cobalt sulfate, and potassium thiocyanate is particularly preferably used. The quenching substance is preferably present in an amount of 0.1 in an ink composition based on a water-soluble dye, a wetting agent, and water.
It is contained in a range of 5% by weight. Naturally, if the amount of the quenching substance used is too small, the effect of improving light resistance cannot be obtained. On the other hand, if the amount is too large, the color rendering properties tend to deteriorate and the nozzle gets clogged with precipitates, so it is also not preferable. On the other hand, as the water-soluble dye used in the aqueous inkjet recording ink of the present invention, any dye having good solubility in water can be used. however,
The advantage of the present invention is that a stronger addition effect appears in dyes with weak light resistance. Specific examples of the water-soluble dyes include CIDirect Blue236, CIDirect Blue203, CIDirect
Direct Blue202, CIDirect Blue15, CIAcid
Blue7, CIAcid Blue9, CIDirect Blue199,
CIAcid Yellow1, CIDirect Red227, CI
Direct Red225, CIAcid Red87, CIAcid
Red92, CIAcid Red52, CIAcid Red94, CI
Examples include Acid Red289, CIDirect Black51, etc. Further, in the present invention, a wetting agent that is liquid at room temperature is used. Specific examples of the humectant include polyhydric alcohols such as diethylene glycol, triethylene glycol, polyethylene glycol #300, glycerin, propylene glycol, etc.
Alkyl ethers of polyhydric alcohols and their acetate esters, such as ethylene glycol monomethyl ether, diethylene glycol, monobutyl ether, ethylene glycol monomethyl ether acetate, tripropylene glycol methyl ether, etc.Hydroxyalkyl formamides, such as those in which the carbon atom of the alkyl group Hydroxyalkylformamides ranging from 1 to 4:
Alternatively, N-vinyl-2-pyrrolidone oligomer synthesized by the method described in JP-A-50-102407, etc. may be used. These humectants can be used alone or in combination. The inkjet recording ink of the present invention includes:
For example, make the following combination. Water-soluble dye 0.1~
15% by weight, 5-40% by weight of wetting agent, 0.1-5% by weight of the water-soluble quenching substance, remainder water. Note that the aqueous inkjet recording ink of the present invention as described above has a viscosity of 1.2 to 30 centipoise, from the practical viewpoint of use in an inkjet system.
Preferably, the non-volatile content is in the range of about 50% by weight or less. Furthermore, although the PH etc. of the ink can be varied over a wide range, precipitation may occur depending on the type and PH of the quenching substance, so it is preferable to adjust the ink as appropriate. For example, it is preferable to use copper sulfate after adjusting the pH to about 4 or lower, or to 10.5 or higher with an ammonia solution. The aqueous ink jet recording ink of the present invention may further contain a water-soluble solvent, such as dioxane, acetone, diacetone alcohol, alkyl alcohol having 1 to 3 carbon atoms, dimethylformamide, dimethyl sulfoxide, N
-Methyl-2-pyrrolidone and the like may be used alone or in combination of two or more. If necessary, as a surface tension adjuster,
Cationic surfactants, such as sodium alkyl sulfate; anionic surfactants, such as alkylpyridium sulfates; nonionic surfactants, such as polyoxyethylene alkyl ether; or amphoteric surfactants. You may. Furthermore, if necessary, viscosity modifiers such as hydroxypropyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, polyvinyl alcohol; sodium dehydroacetate, 1,2-
Amine salt of benzisothiazolin-3-one, 6
A small amount of a fungicide or preservative such as -acetoxy-2,4-dimethyl-m-dioxane may also be added. Further, oxygen absorbers such as sodium sulfite and sodium hydrogen sulfite can also be used together. The aqueous inkjet recording ink of the present invention thus obtained completely satisfies the requirements and performance of the inkjet system, such as prevention of nozzle clogging. Moreover, the light resistance of the recorded material can be significantly improved. In addition, it is possible to expand the so-called range of selection by using various water-soluble dyes. As a result of the above, its industrial effects are immeasurable. Hereinafter, the present invention will be specifically explained with reference to Examples. However, there is no intention to limit it to these specific examples. Examples 1 to 13 Ink raw materials were stirred and mixed for 0.5 hours or more at various ratios as shown in Table 1, and each raw material was dissolved in water. The mixture was then pressure-filtered through a 1.2μ membrane filter manufactured by Millipore Co., Ltd. to obtain an aqueous jet ink composition. These aqueous jet ink compositions were then continuously recorded using an on-demand inkjet printer, and the recording state after 100 hours was determined.
The continuous ejection stability was determined based on the print quality of the recorded matter. Regarding light resistance, after irradiating the recorded matter for a predetermined time using a xenon fade meter (manufactured by Suga Test Instruments Co., Ltd.) (irradiation energy 464 joules/cm ² hr), a reflection densitometer (RD915, manufactured by Masbeth) was used. The degree of fading was compared using the ratio of optical density to the initial value (100). The results obtained are shown in Table 1. Comparative Examples 1 to 4 Water-based jet ink compositions were prepared from the compositions shown in Table 1, which were conventionally thought to have good light resistance, in the same manner as in the above examples. The resulting composition was tested for continuous jet stability and light resistance in the same manner as in the Examples.

[Table] Judgment criteria:
Light resistance ◎: 90% or more, ○: 80-89% △: 50-70
%, ×: 40% or less Continuous jetting stability ○: No nozzle clogging As is clear from the results shown in Table 1 above, the jet ink composition of the present invention achieves good continuous jetting without any loss of jetting characteristics in the inkjet method. It has stability, and the light resistance of recorded matter is also extremely excellent.

Claims (1)

[Scope of Claims] 1. An aqueous inkjet recording ink containing a water-soluble dye, a wetting agent, and water as main components, further comprising potassium iodide, potassium bromide, potassium chloride, potassium thiocyanate, cobalt sulfate, copper sulfate, and sulfuric acid. An inkjet recording ink characterized by containing at least one water-soluble quenching substance selected from ferrous iron, nickel sulfate, and nickel oxalate. 2. The inkjet recording ink according to claim 1, wherein the quenching substance is contained in the inkjet recording ink in an amount of 0.1 to 5% by weight.