JPH0348950B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a liquid composition generally referred to as an ink (hereinafter referred to as an ink) and the use of the ink for recording on a recording material such as paper or resin film by an inkjet method. The present invention relates to an inkjet recording method. (Prior art) The inkjet recording method includes various ink ejection methods (for example, an electrostatic suction method, a method that applies mechanical vibration or displacement to the ink using a piezoelectric element, a method that heats the ink, and uses the pressure generated at that time. method is known), ink droplet
A part or all of them are attached to a recording material such as paper to perform recording. As inks used in such inkjet recording methods, inks in which various water-soluble dyes or pigments are dissolved or dispersed in water or a liquid medium consisting of water and a water-soluble organic solvent are known and used. There is. (Problems to be Solved by the Invention) It is natural that conventional inks such as those mentioned above are required to have various performances, but the most required performance is when recording is performed using ink. The stability of the liquid means that there will be no clogging or sedimentation in the nozzle, orifice or pen tip of the recording device when recording is interrupted or no recording is performed for a long period of time. This problem is particularly important in inkjet systems that use thermal energy because foreign matter tends to deposit on the surface of the heat generating head due to temperature changes. However, in the case of conventional inks, several additives are required to satisfy various conditions such as ink ejection conditions, long-term storage stability, image clarity and density during recording, surface tension, and electrical properties. In addition, the dyes used also contain various impurities, which can clog the nozzles and orifices of the inkjet device, form deposits on the surface of the heating head, and cause sedimentation during long-term storage. There are various problems such as the occurrence of objects,
Despite the various excellent characteristics of the inkjet recording system, this is one of the reasons why it has not become widespread. Therefore, the main object of the present invention is to solve the above-mentioned drawbacks of the prior art, to avoid clogging of nozzles, orifices, etc. even during use and long-term storage, despite high dye concentrations, and in particular to avoid clogging of nozzles, orifices, etc. An object of the present invention is to provide an inkjet recording method for recording on a recording material such as paper or resin film using the ink and the inkjet ink, which has excellent stability and does not cause sedimentation in the heat generating head of an inkjet device using the inkjet device. . As a result of intensive research to achieve the above object, the present inventor has found that commercially available dyes contain many impurities (e.g., various organic and inorganic substances such as dispersants and leveling agents) in addition to dyes. Since these impurities mainly cause the problems mentioned above, we have studied the various effects of these impurities and found that they can clog nozzles and orifices, form sediments during ink storage, and especially when using thermal energy. The main cause of foreign matter depositing on the heating head in the inkjet method is the iron contained in the ink, and by using ink that does not contain iron, the above-mentioned problems of the conventional technology can be solved. The present invention has been completed based on the discovery that the problem can be solved. (Means for Solving the Problems) That is, the present invention provides an ink containing a water-soluble dye used in an inkjet recording method in which thermal energy is applied to the ink and the ink is ejected as droplets. Reduce the iron content to 4ppm
An ink characterized by the following adjustments, and an inkjet recording method in which thermal energy is applied to the ink via a heat-generating head, and the ink is ejected as droplets from fine holes to record on a recording material. , the ink includes a water-soluble dye,
In addition, the iron content contained in the ink is reduced to 4ppm.
This is an inkjet recording method characterized by the following adjustments. To explain the present invention in more detail, the basic components of the ink used in the present invention are already known, and the dyes include water-soluble dyes such as direct dyes, acid dyes, basic dyes, and reactive dyes. Examples of inks that are particularly suitable as inkjet recording method inks and meet the required performance such as clarity, water solubility, stability, and light resistance include CI Direct Black 17, 19, 32, 51,
71, 108, 146; CI Direct Blue 6, 22,
25, 71, 86, 90, 106, 199; CI Direct Red, 1, 4, 17, 28, 83; CI Direct Erotic
12, 24, 26, 86, 98, 142; CI Direct Orange 34, 39, 44, 46, 60; CI Direct Violet 47, 48; CI Direct Brown 109; CI
Direct Green 59; CI Assisted Black 2, 7, 24, 26, 31, 52, 63, 112, 118; CI Assisted Blue 9, 22, 40, 59, 93, 102, 104,
113, 117, 120, 167, 229, 234; CI Assured Red 1, 6, 32, 37, 51, 52, 80, 85, 87, 92,
94, 115, 180, 256, 317, 315; CI Assisted Yellow 11, 17, 23, 25, 29, 42, 61, 71; CI Assisted Orange 7, 19; CI Assisted Yellow
49; CI basic black 2; CI basic blue 1, 3, 5, 7, 9, 24, 25, 26, 28,
29; CI basic credentials 1, 2, 9, 12, 13,
14, 37; CI Basic Violet 7, 14,
27; Examples include CI Food Black 1 and 2.
The above dye examples are particularly preferred for inks applicable to the recording method of the present invention, but the present invention is not limited to these dyes. Such water-soluble dyes are generally used in a proportion of about 0.1 to 20% by weight in conventional inks, but in the present invention, based on the findings of the present invention, they are used within the above range. Of course, it also shows better liquid stability than conventional ink compositions even when used in a higher amount than conventional ink compositions.
Moreover, it does not produce sediment. The solvent used in the ink used in the present invention is water or a mixed solvent of water and a water-soluble organic solvent, and particularly preferred is a mixed solvent of water and a water-soluble organic solvent. It contains a polyhydric alcohol that has an anti-drying effect. Further, as water, it is preferable to use deionized water rather than ordinary water containing various ions. Examples of water-soluble organic solvents used in combination with water include methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, tert-butyl alcohol, and isobutyl alcohol. Alkyl alcohols with 1 to 4 carbon atoms; amides such as dimethylformamide and dimethylacetamide; ketone or keto alcohols such as acetone and diacetone alcohol; ethers such as tetrahydrofuran and dioxane; polyalkylene glycols such as polyethylene glycol and polypropylene glycol Class; ethylene glycol, propylene glycol, butylene glycol, triethylene glycol, 1,2,6-
Alkylene glycols in which the alkylene group contains 2 to 6 carbon atoms, such as hexanetriol, thiodiglycol, hexylene glycol, diethylene glycol; glycerin; ethylene glycol methyl (or ethyl) ether, diethylene glycol methyl (or ethyl) ether, triethylene glycol; Ethylene glycol monomethyl (or ethyl)
Lower alkyl ethers of polyhydric alcohols such as ether; N-methyl-2-pyrrolidone, 1,3-
Examples include dimethyl-2-imidazolidinone. Among these many water-soluble organic solvents, polyhydric alcohols such as diethylene glycol and lower alkyl ethers of polyhydric alcohols such as triethylene glycol monomethyl (or ethyl) ether are preferred. The content of the water-soluble organic solvent in the ink is generally 0 to 95% by weight, preferably 10 to 80% by weight, more preferably 10 to 80% by weight based on the total weight of the ink.
It ranges from 20 to 50% by weight. The water content at this time depends on the type of solvent component mentioned above,
Generally 10 to 100% by weight, preferably 10 to 70% by weight, more preferably 20 to 70% by weight based on the total weight of the ink, depending on the composition and desired properties of the ink. It is considered to be within the range of %. The basic components of the ink used in the present invention are as described above, but the main feature of the present invention is that the iron content contained in the ink is 4 ppm or less. The inventor of the present invention conducted intensive research on the stability of ink and found that since the dyes used in conventional inks were originally manufactured for dyeing textiles, various additives such as surfactants were used. It contains a large number of impurities, including leveling agents, sodium chloride, sodium sulfate, and alkaline earth metal salts, and it is known that these impurities cause various problems in inkjet recording and writing instruments. The inventor of the present invention also diligently removed these impurities to obtain a highly pure dye and made an ink with it, which solved the problem to a considerable extent, but the inkjet method, especially the thermal energy In the inkjet method used,
It was not always possible to sufficiently prevent foreign matter from being deposited on the heat head. As a result of further detailed research, the present inventor discovered that iron in ink is the main cause of deposits on the surface of a thermal head, leading to the present invention. The method for adjusting the iron content in the ink will be specifically explained below. That is, first, sodium sulfate is added to an aqueous dye solution of a desired concentration to salt out the dye. Next, the deposited precipitate is collected by filtration, washed with a saturated pure aqueous solution of sodium sulfate, and then dried. After dissolving a predetermined amount of the obtained dry solid in a water-soluble organic solvent, the aqueous solution is filtered to obtain a filtrate.
The water-soluble organic solvent in this case may be any solvent as long as it is a poor solvent for sodium sulfate and a good solvent for the dye, and the solvent can be selected arbitrarily to the one that is most suitable for the structure of the dye to be treated. I can do it. Usually, alcohols, glycols, and glycol ethers can be preferably used. Next, a predetermined amount of water is added to the obtained filtrate, stirred, and then passed through a cation exchange resin layer. The solution treated with the cation exchange resin is left to stand for 7 to 10 days after appropriate pH adjustment, and then filtered. Thereafter, additives are added as needed and stirred to prepare the ink. Then, the iron content in the ink is measured using an atomic absorption spectrophotometer to confirm whether it is 4 ppm or less, and then the ink is used. In the treatment procedure described above, the first salting-out treatment is mainly aimed at removing sodium chloride, which is a typical impurity often contained in ordinary commercially available dyes, and the next treatment with a water-soluble organic agent is ,
This is carried out to remove impurities in the dye, including both the sodium sulfate originally contained therein and the sodium sulfate added in large amounts during the salting-out treatment. The subsequent treatment with a cation exchange resin and the standing treatment represent one method for reducing the iron content in the ink, which is the object of the present invention. Removal of ionized iron and standing treatment are effective in removing colloidal iron. Although one method for adjusting the iron content in the ink composition has been described above, the adjustment method is not limited to this method, and methods that can remove ionized iron or colloidal iron compounds, etc. All of them can be used effectively. Examples include an aeration method, a coagulation-sedimentation method using a flocculant, a filtration method, a lime softening method, and an electrolytic method. The source of iron contamination as an impurity is thought to be the water used for things other than dyes, but iron contamination can be avoided by using treated water such as distilled water, ion exchange water, or a combination of these as water for ink. be able to. The biggest source of iron contamination is the dyes used;
In particular, when the dye used is a commercially available product, its content is often very large, and analysis examples show that some dye powders contain up to several thousand ppm. Above, we mainly explained the removal of iron contained in ink, but in reality, along with the removal of iron,
Removal of various inorganic salts such as common salt and sodium sulfate,
Alternatively, it is common to also remove calcium and the like. The basic composition of the ink of the present invention and used in the present invention is as described above, but various other conventionally known dispersants, surfactants, viscosity modifiers, surface tension modifiers, etc. may be added as necessary. I can do it. For example, viscosity modifiers such as polyvinyl alcohol, celluloses, and water-soluble resins; various cationic, anionic, or nonionic surfactants; surface tension modifiers such as diethanolamine and triethanolamines; PH modifiers using buffers; Examples include fungicides and the like. Further, when preparing an ink for use in an inkjet recording method in which the recording liquid is charged, a resistivity adjuster such as inorganic salts such as lithium chloride, ammonium chloride, and sodium chloride is added. When applied to an inkjet method that ejects ink through the action of thermal energy, the thermal properties (e.g., specific heat, coefficient of thermal expansion, thermal conductivity, etc.) may be adjusted. . The inks of the present invention and used in the present invention obtained as described above have sufficiently solved the problems of the prior art, and have excellent recording properties (signal response, droplet formation stability, ejection stability, long-term continuous recording performance, ink ejection stability after long periods of non-operation), storage stability,
It is well-balanced in terms of fixability to recording materials, light fastness of recorded images, weather resistance, etc., and is useful as an ink for various types of inkjet recording. It is suitable as an ink for an inkjet recording system that uses thermal energy, which is most disliked, and can provide excellent recording. (Example) Next, the present invention will be further explained by giving examples. Note that "%" or "%" in the text is based on weight. Example 1 "Preparation of Ink" A 10% aqueous solution of a commercially available dye; "Special Black 7984" (manufactured by Bayer) was prepared, and then sodium sulfate was added to the aqueous solution and stirred to salt out the dye. The precipitate was collected by filtration, washed with a saturated pure aqueous solution of sodium sulfate, and dried. A predetermined amount of the dry solid was weighed so that the dye concentration in the resulting ink was 3%, and mixed with ethylene glycol and N-methyl-2-pyrrolidone in a ratio of 3:1.
Dissolved in the mixture. Next, this aqueous solution was filtered under pressure using a Teflon filter with an average pore size of 1 micron, and 60 parts of water was added to 40 parts of the filtrate and stirred to prepare an ink. Next, the ink was passed through a layer of cation exchange resin "C-464" manufactured by Sumitomo Chemical Co., Ltd. Thereafter, the effluent was adjusted to pH 9.8 with a 0.1N aqueous sodium hydroxide solution, and left in a plastic container for 10 days. The mixture was filtered under pressure again using a 1 micron Teflon filter to obtain the ink of the present invention. The iron content in this ink was measured using an atomic absorption spectrophotometer and was found to be 3.8 ppm. Using this ink, an on-demand type multi-head (discharge orifice diameter 35 microns, heating resistor, resistance value,
When the following T1 to T5 were investigated using a recording device with a drive voltage of 150 ohms, a drive voltage of 30 volts, and a frequency of 2 KHz, good results were obtained in all cases. (T1) Long-term stability: Even after the ink is sealed in a plastic film bag and stored at -30℃ and 60℃ for 6 months, no precipitation of insoluble matter is observed, and there is no change in the physical properties or color tone of the liquid. Ta. (T2) Ejection stability: Continuous ejection was performed for 24 hours in an atmosphere of room temperature, 5°C, and 40°C, and stable high-quality recording was possible from beginning to end under all conditions. (T3) Discharge responsiveness: Investigated discharging for 2 seconds and discharging after standing for 2 months, but in both cases, there was no clogging at the orifice tip, and recording was stable and uniform. (T4) Quality of recorded images: The images recorded on the recording materials listed in Table 1 below were high in density and clear. After 6 months of exposure to room light, the rate of decrease in concentration was less than 1%. (T5) Fixability on various recording materials: After 15 seconds of printing on the recording materials listed in Table 1 below, the presence or absence of image shift/bleeding was determined by rubbing the printed area with a finger, and there was no image shift/bleeding. It showed excellent fixing properties. Examples 2 to 5 Inks were prepared using the commercially available dyes shown in Table 2 below in the same manner as in Example 1, and T1 to T5 were examined in the same manner as in Example 1 for each ink. All of these showed excellent results similar to Example 1. Example 6 The ink of Example 2 was used as the yellow ink, the ink of Example 3 was used as the magenta ink, the ink of Example 4 was used as the cyan ink, and the ink of Example 5 was used as the black ink in Examples 2 to 5. A full-color photograph was reproduced using an inkjet recording device similar to that used in the original. The resulting image had extremely clear colors and good color reproduction. Comparative Example The dye “Special Black” shown in Example 1
A 10% aqueous solution of ``7984'' was prepared, and then sodium sulfate was added to the aqueous solution and stirred to salt out the dye. Next, the precipitate was collected by filtration, washed with a pure aqueous solution of sodium sulfate, and dried. A predetermined amount of the dry solid was weighed out so that the dye concentration in the resulting ink would be 3%, and dissolved in a 3:1 mixture of ethylene glycol and N-methyl-2-pyrrolidone. Next, this solution was mixed with an average pore size of 1
It was filtered under pressure using a micron Teflon filter, and 60% water was added to 40% of the filtrate and stirred to prepare a sample ink. The iron content in this ink was measured using an atomic absorption spectrophotometer and was found to be 6.1 ppm. When this ink was examined at T1 to T5 in the same manner as in Example 1, precipitation of insoluble matter was observed in the ink after one month of ink storage. Furthermore, in (T2), ink often failed to be ejected, forcing us to change the drive voltage (increase the voltage). When the surface of the heating head was observed under a microscope, a brown precipitate was observed to be attached. In (T3), it was observed that the orifice became clogged and the ink ejection became unstable after being left for one month. Furthermore, regarding this dye, we created an ink that was treated by adding only a treatment with a cation exchange resin to the above-mentioned treatment process, and an ink that was similarly treated by adding only a standing treatment to the above-mentioned treatment process. When the iron content was measured, the value was 4.8 ppm for the former and 5.1 ppm for the latter. Similarly, when testing T1 to T5 with respect to these, an improvement was recognized compared to one in which these additional processes were not performed at all, but the performance could not be said to be sufficient from a practical standpoint.

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Claims (1)

[Scope of Claims] 1. A liquid composition containing a water-soluble dye used in an inkjet recording method in which a liquid composition is ejected as droplets by applying thermal energy, the composition containing iron. A liquid composition characterized in that the amount is adjusted to 4 ppm or less. 2. In an inkjet recording method in which thermal energy is applied to a liquid composition via a heat-generating head and the liquid composition is ejected as droplets from micropores to record on a recording material, the liquid composition is water-soluble. The composition contains a dye and the iron content contained in the composition.
An inkjet recording method characterized by being adjusted to 4ppm or less.