JP4196930B2 - Fluorescent aqueous ink for ink jet recording and cartridge containing the ink - Google Patents

Description

The present invention relates to a fluorescent aqueous ink for ink-jet recording having a high fluorescence intensity and the fluorescence intensity does not decrease over time. The present invention also relates to an ink cartridge containing the fluorescent aqueous ink for ink jet recording.

The ink jet recording method is a recording method in which ink is ejected from nozzles, slits, porous films, etc., and recording is performed on paper, cloth, films, and the like. As a method for ejecting ink, for example, an electrostatic attraction method for ejecting using electrostatic attraction force, a drop-on-demand method for applying mechanical vibration or displacement to ink using a piezoelectric element, and heating the ink There is known a thermal ink jet method or the like that generates bubbles by using the pressure generated at this time. Recording is performed by forming ink droplets by these ink ejection methods and attaching some or all of these to a recording material.

The development of inks that can be applied in various fields using such an ink jet recording system is progressing. In particular, fluorescent inks containing fluorescent dyes absorb light of a specific wavelength (excitation light) and emit light having a wavelength longer than that of excitation light (fluorescence). Attempts have been made to apply such a method to record information on a recording medium and to read information by emitting fluorescence by irradiating ultraviolet rays as excitation light. Further, for example, Patent Document 1 discloses a water-resistant water-based fluorescent ink for imprinting a postage-based postal indicia.

However, when printing on paper using a fluorescent aqueous ink containing a fluorescent dye, there is a problem in that the fluorescence intensity decreases after a few days even if a high fluorescence intensity is obtained immediately after printing.

JP-A-9-291246

The present invention has been made to solve such problems, and an object of the present invention is to provide a fluorescent water-based ink for ink-jet recording which has high fluorescence intensity and does not decrease with time.

In accordance with the present invention, C.I. I. Acid Red 52; and glycol; and the distance between hydroxyl groups of the glycol is C.I. I. The distance between atoms directly bonded to the carbon atom at the 3rd position of the xanthene skeleton of Acid Red 52 and the atom directly bonded to the carbon atom at the 6th position of the xanthene skeleton is approximately equal to or longer than the above-mentioned C.I. I. Der molar ratio of 100 or more of the glycol to acid red 52 is, for inkjet recording fluorescence aqueous ink wherein the glycol is triethylene glycol is provided. Positions such as the 3rd, 6th and 9th positions of the xanthene skeleton are specified according to a nomenclature established by the International Union of Pure and Applied Chemistry (IUPAC).

In the present invention, an ink cartridge containing the fluorescent aqueous ink for ink jet recording is also provided. The ink cartridge includes a container having an arbitrary shape for containing ink. The ink cartridge may be mounted on the ink jet head or may be attached in the main body case of the ink jet recording apparatus. In the latter case, ink is supplied from the ink cartridge to the inkjet head via a flexible tube or the like.

According to the present invention, it is possible to provide a fluorescent aqueous ink for ink-jet recording which has high fluorescence intensity and does not decrease with time.

The fluorescent aqueous ink for inkjet recording of the present invention contains a fluorescent dye having a xanthene skeleton and glycol. A fluorescent dye having a xanthene skeleton has particularly high fluorescence intensity among fluorescent dyes, and a fluorescent ink having high fluorescence intensity can be obtained even with a small content. A chemical formula representing a fluorescent dye having a xanthene skeleton is represented by the following formula (1). In addition, the number attached | subjected to the carbon atom in following formula (1) shows the position number of the carbon atom designated by the nomenclature which an international pure and applied chemical alliance (IUPAC) establishes. In this specification, all the position numbers of carbon atoms are designated according to the nomenclature defined by the International Union of Pure and Applied Chemistry (IUPAC).

In formula (1), R ¹ may be the same or different, and two R ² may be the same or different. R ⁴ and R ⁵ may be the same or different, and in the case of an alkyl group, it is an alkyl group having 1 to 5, preferably 1 to 2 carbon atoms.

The fluorescent dye used in the fluorescent water-based ink for inkjet recording of the present invention comprises a substituent bonded to the 9th carbon atom of the xanthene skeleton and a portion other than the substituent bonded to the 9th carbon atom (xanthene skeleton and xanthene skeleton). The difference of the hydrophilicity index logP from that including a substituent bonded to the skeleton is 2.6 or more. If it is less than 2.6, the fluorescence intensity of the resulting fluorescent water-based ink for ink-jet recording decreases with time, which is not preferable.

As an example of the fluorescent dye having the xanthene skeleton, C.I. I. The chemical formula of Basic Red 1 is represented by the following formula (3) as C.I. I. The chemical formula of Basic Violet 10 is shown. C. I. In Basic Red 1, and the 9-position substituents attached to a carbon atom of a xanthene skeleton _{COO (C 2 H 5) -C} 6 H 4 - to radicals, C. I. In the basic violet 10, the substituent bonded to the carbon atom at the 9-position of the xanthene skeleton is a COOH—C ₆ H ₄ — group.

In the present specification, the hydrophilicity index logP means a partition coefficient of octanol and water, and can be obtained by the following formula (4).

In formula (4), Σ _i represents the sum of the inorganic values, and Σ _o represents the sum of the organic values. One carbon atom has an organic value of 20, one hydrogen atom has an inorganic value of 100, and for other substituents, an organic value and an inorganic value are determined for each substituent. ing. The part other than the substituents bonded to the 9th carbon atom of the xanthene skeleton and the logP of the substituent bonded to the 9th carbon atom of the xanthene skeleton of the fluorescent dye having the main xanthene skeleton calculated by the above formula (4) Table 1 shows the log P.

As the glycol used in the fluorescent water-based ink for ink jet recording of the present invention, those having a hydroxyl group distance that is substantially equal to or longer than the distance between the 3- and 6-position bonded atoms of the xanthene skeleton of the fluorescent dye are used. Here, “substantially equivalent” means that the distance between the two hydroxyl groups of the glycol is in the range of 80% to 120% with respect to the distance between the 3- and 6-bond atoms in the xanthene skeleton. If it is less than 80%, it is considered that glycol cannot be coordinated to the xanthene skeleton in a bridge form as described below. The distance between the hydroxyl groups of the glycol is preferably 500% (5 times) or less of the distance between the 3- and 6-position bonded atoms of the xanthene skeleton of the fluorescent dye. If it exceeds 500%, the glycol cannot be bridged and coordinated with the atom directly bonded to the carbon atom at the 3-position of the xanthene skeleton and the atom directly bonded to the carbon atom at the 6-position, as described below. The binding strength between the fluorescent dye and glycol may be insufficient, and the fluorescence intensity after printing may decrease over time. As said range, More preferably, it is 90 to 200%, More preferably, it is 90 to 150%. Further, when the glycol is polyethylene glycol, it becomes insoluble in the ink solvent when the distance between the hydroxyl groups exceeds 500% of the distance between the 3- and 6-position bonding atoms of the xanthene skeleton.

In the present specification, in the fluorescent dye, the interatomic distance between the atom directly bonded to the 3-position carbon atom of the xanthene skeleton and the atom directly bonded to the 6-position carbon atom of the xanthene skeleton (the 3-position of the xanthene skeleton). The distance between the atoms bonded to the 6th position of the fluorescent dye and the center of the atoms directly bonded to the carbon atom at the 6th position of the xanthene skeleton. Specifically, for example, C.I. represented by the above formula (2). I. In Basic Red 1, the distance between the center of the nitrogen atom bonded to the carbon atom at the 3rd position and the center of the nitrogen atom bonded to the carbon atom at the 6th position is represented by C.I. I. In the basic violet 10, it means the distance between the center of the nitrogen atom bonded to the third carbon atom and the center of the nitrogen atom bonded to the sixth carbon atom.

Further, “distance between hydroxyl groups of glycol” means the distance between the center of oxygen atom of one hydroxyl group of glycol and the center of oxygen atom of the other hydroxyl group, and specifically, for example, the following formula (5 ) Or the distance between the oxygen atom centers of the hydroxyl groups at both ends of the polypropylene glycol represented by the following formula (6). Such interatomic distance can be calculated using software such as Chem3D manufactured by Fujitsu Limited. The interatomic distance in the compounds described in the present specification is expressed as the distance when the molecular structure of the compound is drawn using Chem3D manufactured by Fujitsu Limited and then the minimization energy (minimization of energy) is performed.

Table 2 shows the distance between the 3- and 6-position bonded atoms of the xanthene skeleton of the fluorescent dye having the main xanthene skeleton, and Table 3 shows the distance between the hydroxyl groups of the main glycols.

In Table 3, since polyethylene glycol # 200 and polypropylene glycol # 400 have distribution in molecular weight, average values are shown.

The present inventors have found that a fluorescent aqueous ink for ink-jet recording can be obtained by using a fluorescent dye and glycol that satisfy the above-mentioned requirements in combination with high fluorescence intensity and the fluorescence intensity does not decrease with time even after printing. The headline and the present invention were completed. Although this principle has not been fully elucidated, the present inventor believes that it is based on the following theory.

In general, dissolving a substance in a solvent means that the solvent molecules are solvated in the substance. That is, the fact that the dye is dissolved in the water-based ink means that the dye molecule is solvated by water molecules and other solvent molecules. At this time, the portion where the water molecule and other solvent molecules are solvated and the degree of solvation are determined by the structure of the dye. The same applies to fluorescent dyes having a xanthene skeleton.

According to the knowledge of the present inventors, the fluorescent dye having a xanthene skeleton has the effect of enhancing the fluorescence intensity of glycol, glycol ether, pyrrolidone, etc. on the atoms directly bonded to the 3rd and 6th carbon atoms of the xanthene skeleton. It has been found that the fluorescence intensity is enhanced by the coordination of the molecules it has. Therefore, in order to obtain a high fluorescence intensity, it is important that a specific solvent molecule having an action of enhancing the fluorescence intensity is effectively coordinated at a specific position of the fluorescent dye molecule. However, when a fluorescent dye having a xanthene skeleton is dissolved in water under normal conditions, many water molecules are preferentially coordinated with the fluorescent dye molecule, and solvent molecules that have an action of enhancing fluorescence intensity are fluorescent. It becomes difficult to coordinate with the dye molecule, and it is difficult to obtain a fluorescent action enhancing effect.

On the other hand, if a difference in hydrophilicity is provided in the molecular structure of the fluorescent dye having a xanthene skeleton, a specific solvent molecule having an action of enhancing the fluorescence intensity is effectively arranged at a specific position of the fluorescent dye molecule. It is thought that it can rank. For example, in the fluorescent dye having a xanthene skeleton, the hydrophilicity of the substituent bonded to the 9th carbon atom of the xanthene skeleton is higher than the portion other than the substituent bonded to the 9th carbon atom. Water molecules preferentially coordinate to the side of the substituent bonded to the carbon atom of the carbon atom, on the other hand, other than the substituent bonded to the carbon atom at the 9th position, particularly to the 3rd and 6th position carbon atoms of the xanthene skeleton. It is considered that a solvent molecule having an action of enhancing fluorescence intensity is preferentially coordinated to a portion containing atoms directly bonded, and high fluorescence intensity can be obtained.

On the other hand, even when a specific solvent molecule having an action of enhancing fluorescence intensity is coordinated to a specific position of the xanthene skeleton, the specific solvent molecule having an action of enhancing fluorescence intensity is easily separated after printing. If so, the fluorescence intensity decreases with time after printing. Among the specific solvent molecules having the action of enhancing fluorescence intensity such as glycol, glycol ether, pyrrolidone, etc., glycol ether is highly hydrophobic because one or both ends of the molecule are ether groups, and immediately on the paper surface. Osmose | permeates in the thickness direction and fiber direction of paper, and will isolate | separate from fluorescent dye. In addition, since pyrrolidone has a high vapor pressure, it is separated from the fluorescent dye by evaporation over time. On the other hand, since glycol has higher hydrophilicity than glycol ether, the penetration rate into paper is relatively slow and the vapor pressure is low. Therefore, glycol is effective for decreasing the fluorescence intensity with time. In addition, glycol is advantageous in relation to the structure of the fluorescent dye as described above for the following reasons. Since glycol has a hydroxyl group at the terminal, it is easily coordinated in a bridge-like manner to a portion containing atoms directly bonded to the 3rd and 6th carbon atoms of the xanthene skeleton of the fluorescent dye. This bridge-like coordination is thought to increase the fluorescence intensity of the fluorescent dye as a result of further increasing the electron density of the xanthene skeleton by linking with the electron resonance structure of the xanthene skeleton. On the other hand, when the solvent is a glycol ether, it has a hydrophilic group and a hydrophobic group, so that it is coordinated to a portion containing atoms directly bonded to the 3rd and 6th carbon atoms of the xanthene skeleton as described above. It is difficult to increase the fluorescence intensity as in the case of glycol. Pyrrolidone is also unlikely to form a bridge like glycol, so it is considered that the fluorescence intensity does not increase as in the case of glycol.

Furthermore, when the distance between the hydroxyl groups of the glycol is equal to or greater than the distance between the 3- and 6-position bonding atoms of the xanthene skeleton of the fluorescent dye, the glycol is bonded directly to the 3-position carbon atom of the xanthene skeleton and 6 It can be bridged and coordinated to an atom directly bonded to the carbon atom at the position, and the bond between the fluorescent dye and the glycol becomes strong. Accordingly, since glycol is difficult to separate from the fluorescent dye even after printing, it is possible to suppress a decrease in fluorescence intensity with time. From the above, if a fluorescent dye that meets the above requirements and a glycol are used in combination, the glycol binds preferentially to the effective position of the fluorescent dye with a strong intensity, so that the fluorescence intensity decreases with time even after printing. It is considered that a fluorescent water-based ink for inkjet recording is obtained.

The preferable lower limit of the content of the fluorescent dye in the fluorescent aqueous ink for ink jet recording of the present invention is 0.1% by weight, and the preferable upper limit is 2% by weight. If it is less than 0.1% by weight, sufficient fluorescence intensity may not be obtained. If it exceeds 2% by weight, the energy absorbed by the fluorescent dye is converted into light by the interaction of the atomically excited fluorescent dye. There may be a concentration quenching phenomenon in which the fluorescence intensity decreases instead of transitioning to a non-radiation process that does not radiate, resulting in a decrease in fluorescence intensity.

The preferred lower limit of the glycol content in the fluorescent aqueous ink for ink jet recording of the present invention is 10% by weight, and the preferred upper limit is 45% by weight. If the amount is less than 10% by weight, the effect of preventing a sufficient decrease in fluorescence intensity with time may not be obtained. If the amount exceeds 45% by weight, the ink becomes highly viscous, which may adversely affect the ejection stability of the ink. is there.

The fluorescent water-based ink for ink-jet recording of the present invention contains water. As the water, water having a small content of cationic ions and anionic ions such as ion-exchanged water and distilled water is preferably used instead of ordinary water. The water content is preferably 10% by weight and the preferred upper limit is 90% by weight, although it depends on the desired ink characteristics and the type and composition of the fluorescent dye and glycol used. If it is less than 10% by weight, the ratio of components other than water will inevitably increase, and ink will bleed or increase in viscosity when printed on paper, making it difficult to introduce ink into the nozzle. There is. If it exceeds 90% by weight, the ink viscosity after the volatile component has evaporated may become too high and non-ejection may occur. A more preferred lower limit is 15% by weight, and a more preferred upper limit is 80% by weight.

The basic configuration of the fluorescent water-based ink for ink-jet recording of the present invention is as described above. For the purpose of improving ejection stability, compatibility with head and ink cartridge materials, storage stability, image storage stability, and other various performances. In response to the above, further various conventionally known wetting agents, penetrants, surfactants, viscosity modifiers, surface tension regulators, pH regulators, metal rust inhibitors, specific resistance regulators, film formers, ultraviolet absorbers, You may contain antioxidant, discoloration prevention agent, antiseptic | preservative antifungal agent, etc.

For example, for the purpose of preventing ink drying, lower alcohols such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, tert-butyl alcohol; dimethylformamide, dimethylacetamide, etc. Amides; Ketones such as acetone and diacetone alcohol or keto alcohols; Ethers such as tetrahydrofuran and dioxane; Alkylene glycols such as thioglycol and hexylene glycol; Glycerin; Water-soluble organic substances such as 1,3-dimethyl-2-imidazolidinone A solvent may be contained. Of these, glycerin is preferred. When the ink contains water and glycerin, it is desirable that the weight of water, glycol, and glycerin in the ink is such that GC ≦ GO <W is established when the weights of W, GO, and GC are respectively expressed. .

Also, for the purpose of increasing the drying speed on paper after printing, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, triethylene glycol monomethyl Ether, triethylene glycol monoethyl ether, triethylene glycol monopropyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol mono Propyl ether, G Propylene glycol monomethyl ether, tripropylene glycol monoethyl ether, may contain glycol ethers such as tripropylene glycol monopropyl ether.

Furthermore, for the purpose of adjusting the viscosity of the ink, it may contain polyvinyl alcohol, cellulose, water-soluble resin, and the like. These may be used alone or in combination of two or more.

In the case of applying the fluorescent water-based ink for ink jet recording of the present invention to an ink jet method in which it is ejected by the action of thermal energy, thermal physical properties such as specific heat, thermal expansion coefficient, and thermal conductivity may be adjusted.

Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples.
<Example 1, Reference Examples 1 and 2>
The fluorescent dyes and glycols shown in Table 4, water and glycerin as a wetting agent were prepared with the compositions shown in Table 4. After stirring the prepared ink material, it filtered with the 0.2 micrometer membrane filter, and the ink of Example 1 and the reference examples 1 and 2 was prepared. Table 4 shows the difference in hydrophilicity index logP between the substituent bonded to the 9th carbon atom of the xanthene skeleton of the fluorescent dye used and the portion other than the substituent bonded to the 9th carbon atom. The difference in the log P of the fluorescent dye used in each ink of the example is 2.6 or more. Table 4 shows the distance between the 3-6 position atoms of the xanthene skeleton of the fluorescent dye used and the distance between hydroxyl groups of the glycol used. The distance between the hydroxyl groups of the glycol used in each ink of the examples is longer than the distance between the 3- and 6-position bonded atoms of the xanthene skeleton of the fluorescent dye. Further, in Table 4, the amount of glycol with respect to the fluorescent dye is expressed as a molar ratio.
<Comparative Examples 1-3>
The fluorescent dyes and glycols shown in Table 4, water and glycerin as a wetting agent were prepared with the compositions shown in Table 4. After stirring the prepared ink material, it filtered with the 0.2 micrometer membrane filter, and prepared the ink of Comparative Examples 1-3. The difference in the log P of the fluorescent dyes used in the inks of Comparative Example 1 and Comparative Example 2 is less than 2.6. Further, the distance between hydroxyl groups of glycols used in the inks of Comparative Examples 2 and 3 is shorter than 80% of the distance between the 3- and 6-bond atoms of the xanthene skeleton of the fluorescent dye (for example, in Comparative Example 3). The distance between the hydroxyl groups of diethylene glycol was about 75% of the distance between the 3- and 6-bonded atoms of the xanthene skeleton of the fluorescent dye). In Table 4, the number of moles of glycol used per mole of fluorescent dye is shown as a molar ratio.
<Evaluation>
The inks prepared in Example 1, Reference Examples 1 and 2, and Comparative Examples 1 to 3 were recorded on plain paper (XEROX, XEROX 4200) using an inkjet printer (manufactured by Brother Industries, Ltd., MFC-5100J). Using the spectroscopic photometer (F-4500, manufactured by Hitachi High-Technologies Corporation) after recording for 3 days at the normal temperature and normal pressure after printing, using the spectroscopic fluorometer (F-4500), the peak intensity was measured. This was made into fluorescence intensity. The wavelength of the excitation light source at the time of fluorescence intensity measurement was 254 nm, and the fluorescence measurement wavelength was 600 nm. The fluorescence intensity was evaluated according to the following criteria. Evaluation was performed according to the following criteria from the fluorescence intensity on the day of printing and 3 days after printing. The results are shown in Table 4.
A: The fluorescence intensity after 3 days of printing is 100% or more compared to the fluorescence intensity on the printing day B: The fluorescence intensity after 3 days of printing is 80% or more and less than 100% compared to the fluorescence intensity of the printing day C: On the printing day The fluorescence intensity after 3 days of printing is less than 80% compared to the fluorescence intensity.

As can be seen from Table 4, the fluorescence intensity of all of the inks of the comparative examples is reduced by 20% or more, but the fluorescence intensity of all of the inks of the examples is increased.

In the ink prepared in Example 1, the ink composition, particularly C.I. I. Samples 1 to 4 were prepared by changing the amount of triethylene glycol used in Acid Red 52 to various values (molar ratios) as shown in Table 5. The fluorescence intensity of each prepared sample was measured and evaluated in the same manner as in Example 1. The results are shown in Table 5. Further, for the ink of Example 1 and Samples 1 to 4, C.I. I. The relationship between the molar ratio of triethylene glycol to acid red 52 and the fluorescence intensity is shown in the graph of FIG. In FIG. 1, the results of Reference Examples 1 and 2 are also displayed. From this graph, C.I. I. It can be seen that when the molar ratio of triethylene glycol to acid red 52 exceeds 100, the fluorescence intensity is maintained even after 3 days of printing. On the other hand, when the added amount of triethylene glycol is small, the fluorescence intensity does not increase so much. This is probably because triethylene glycol has a low probability of interacting with the dye as described above (coordinating in a bridge form), or the interaction is hindered by other substances.

It is a graph which shows the relationship between the molar ratio of the glycol with respect to the fluorescent dye used by the Example and the comparative example, and fluorescence intensity ratio.

Claims (5)

C. I. Acid Red 52;
Including glycols;
The distance between hydroxyl groups of the glycol is the C.I. I. The distance between atoms directly bonded to the carbon atom at the 3rd position of the xanthene skeleton of Acid Red 52 and the atom directly bonded to the carbon atom at the 6th position of the xanthene skeleton is approximately equal to or longer than the interatomic distance.
C. above. I. The molar ratio of the glycol to Acid Red 52 is Ri der 100 or more,
The fluorescent aqueous ink for inkjet recording , wherein the glycol is triethylene glycol . C. above. I. Jet recording fluorescence aqueous ink according to claim 1 Symbol placement content of less than 2 wt% 0.1 wt% or more of Acid Red 52. The fluorescent water-based ink for ink-jet recording according to claim 1 or 2, wherein the content of triethylene glycol is 10 wt% or more and less than 45 wt%. Further comprising water and glycerol, in the ink, water, each by weight of triethylene glycol and glycerin, W, GO, when expressed in GC, any claim 1-3 for GC ≦ GO <W is satisfied 2. A fluorescent water-based ink for ink-jet recording. An ink cartridge containing the ink jet recording fluorescence aqueous ink according to any one of claims 1-4.

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