JP2004263151A - Water-based ink for ink jet recording - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a water-based ink for ink jet recording containing both of the basic dye and the acidic dye, enabling stable jetting without causing clogging by deposition in a head discharge part and enabling recording having high reliability and high accuracy. <P>SOLUTION: The water-based ink for ink jet recording comprises water, the basic dye and the acidic dye having ≤15 Debye dipole moment. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【００１７】
上記酸性染料の含有量は、インク全量に対して０．５〜１０重量％であることが好ましい。０．５重量％未満では、目的とする画像濃度が得られない場合があり、１０重量％を超えると、インク中の水分蒸発後の粘度が高くなりすぎたり析出物を発生させる場合があるからである。より好ましくは１〜５重量％である。
【００１８】
上記水は、一般の水であってもよいが、脱イオン水（純水）を使用することが好ましい。
上記水の配合量は、通常時のインク粘度を正常に保つため、インクの全量に対して４０重量％以上であることが好ましい。
【００１９】
本発明インクジェット記録用水性インクでは、インクジェット記録用水性インクに一般的に使用されている水溶性有機溶剤を添加することが好ましい。
上記水溶性有機溶剤としては、例えば、湿潤剤や浸透剤と呼ばれている物質を使用することができる。
【００２０】
上記湿潤剤は、主としてインクジェットヘッドの先端部において、インク中の水分蒸発による析出発生、インクの乾固を防止する目的で添加される。
上記湿潤剤としては、例えば、ポリアルキレングリコール類；エチレングリコール、ジエチレングリコール、トリエチレングリコール、プロピレングリコール、ブチレングリコール、ジプロピレングリコール、トリプロピレングリコール、ポリエチレングリコール、１，２，６−ヘキサントリオール、チオジグリコール、１，３−ブタンジオール、１，５−ペンタンジオール、ヘキシレングリコール等のアルキレングリコール類；グリセリン；２−ピロリドン、Ｎ−メチル−２−ピロリドン等のピロリドン類等を挙げることができる。これらの湿潤剤は、単独で用いられてもよく、併用してもよい。
【００２１】
上記湿潤剤の含有量は、インク全量に対して５〜５０重量％が好ましい。５重量％未満では、湿潤作用が不充分となり、析出、乾固等の問題が生じることがある。５０重量％を超えると、インクが必要以上に増粘し、吐出不能となったり、記録紙上での乾燥が極端に遅くなる等の問題を生じることがある。より好ましくは１０〜４０重量％である。
【００２２】
上記浸透剤は、記録紙へのインクの浸透速度を速めることにより、紙面上での速乾性を向上させ、浸透に伴うフェザリングを防止する目的で添加される。上記浸透剤としては、低臭気性で蒸気圧の低い多価アルコールモノアルキルエーテルを使用することが好ましい。
上記多価アルコールモノアルキルエーテルとしては特に限定されないが、例えば、ジエチレングリコールモノメチルエーテル、ジエチレングリコールモノブチルエーテル、ジエチレングリコールモノイソブチルエーテル、ジプロピレングリコールモノメチルエーテル、ジプロピレングリコールモノプロピルエーテル、ジプロピレングリコールモノイソプロピルエーテル、ジプロピレングリコールモノブチルエーテル、トリエチレングリコールモノメチルエーテル、トリエチレングリコールモノブチルエーテル、トリプロピレングリコールモノメチルエーテル、トリプロピレングリコールモノブチルエーテル等を挙げることができる。
【００２３】
上記浸透剤の含有量は、インク全量に対して０．２〜２０重量％が好ましい。０．２重量％未満では、インクの記録紙への浸透速度が遅く、乾燥時間、滲みに問題を生じることがある。また、２０重量％を越えると、インクの記録紙への浸透が激しくなり、記録紙の裏までインクが達してしまったり、滲みにも問題を生じることがある。より好ましくは０．５〜１０重量％である。
また、インクの記録紙への浸透、乾燥性を制御する目的で、エタノール、イソプロピルアルコール等の１価アルコールを使用することも可能である。
【００２４】
本発明のインクジェット記録用水性インクの基本構成は以上の通りであるが、その他従来公知の樹脂バインダー、界面活性剤、粘度調整剤、表面張力調整剤、ｐＨ調整剤、染料溶解剤、防腐防カビ剤等を必要に応じて添加することができる。なお、本発明のインクジェット記録用水性インクを、熱エネルギーの作用によってインクを吐出させるタイプのインクジェット方式に適用する場合には、熱的な物性値（例えば比熱、熱膨張係数、熱伝導率等）が調整されていてもよい。
【００２５】
本発明のインクジェット記録用インクは、従来技術の問題点が充分に解決されており、塩基性染料と酸性染料とを混在させる場合であっても、析出によるヘッド吐出部での目詰まりが発生することなく安定した噴射が可能で、高信頼性、高精度の記録が可能となるインクジェット記録用水性インクセットを提供することができる。
【００２６】
【実施例】
以下に実施例を掲げて本発明を更に詳しく説明するが、本発明はこれらの実施例のみに限定されるものではない。
本発明に従ったインク組成を実施例として以下に示す。なお、本実施例では、マゼンタインクについて説明しているが、他色インクでも同様の効果がある。
【００２７】
（実施例１〜４）
塩基性染料として、Ｃ．Ｉ．ベーシックイエロー４０又はＣ．Ｉ．ベーシックレッド１、酸性染料として、双極子モーメントが９．９デバイのＣ．Ｉ．アシッドレッド１４又は双極子モーメントが８．０デバイのＣ．Ｉ．アシッドレッド２７を用い、表２に示した組成のインク材料を混合攪拌後、０．２μｍのメンブランフィルターで濾過を行い、マゼンタインクを調製した。
【００２８】
【表２】

【００２９】
（実施例５〜８）
塩基性染料として、Ｃ．Ｉ．ベーシックバイオレット１０又はＣ．Ｉ．ベーシックバイオレット１１：１、酸性染料として、双極子モーメントが１２．２デバイのＣ．Ｉ．アシッドレッド１８又は双極子モーメントが１０．０デバイのＣ．Ｉ．アシッドレッド８７を用い、表３に示した組成のインク材料を混合攪拌後、０．２μｍのメンブランフィルターで濾過を行い、マゼンタインクを調製した。
【００３０】
【表３】

【００３１】
（比較例１〜４）
塩基性染料として、Ｃ．Ｉ．ベーシックイエロー４０又はＣ．Ｉ．ベーシックレッド１、酸性染料として、双極子モーメントが１５．２デバイのＣ．Ｉ．アシッドレッド１８６又は双極子モーメントが１９．０デバイのＣ．Ｉ．アシッドレッド５２を用い、表４に示した組成のインク材料を混合攪拌後、０．２μｍのメンブランフィルターで濾過を行い、マゼンタインクを調製した。
【００３２】
【表４】

【００３３】
（比較例５〜８）
塩基性染料として、Ｃ．Ｉ．ベーシックバイオレット１０又はＣ．Ｉ．ベーシックバイオレット１１：１、酸性染料として、双極子モーメントが２２．２デバイのＣ．Ｉ．アシッドレッド１又は双極子モーメントが３１．２デバイのＣ．Ｉ．アシッドレッド４２を用い、表５に示した組成のインク材料を混合攪拌後、０．２μｍのメンブランフィルターで濾過を行い、マゼンタインクを調製した。
【００３４】
【表５】

【００３５】
（評価）
実施例１〜８及び比較例１〜８で作製したマゼンタインクについて、析出物の有無の評価及び吐出評価を以下の方法により行った。結果を表６に示した。
【００３６】
（１）析出の有無
実施例１〜８及び比較例１〜８で作製したマゼンタインク５ｇをアズワン社製Ｎｏ．２のガラスビンに入れ、温度６０℃、湿度４０％の恒温恒湿槽内で３日間放置した後、目視及び顕微鏡観察にて析出の有無を確認した。
評価基準は以下の通りである。
○：目視及び顕微鏡観察においても析出は認められなかった。
△：目視では析出は認められなかったが、顕微鏡では析出が認められた。
×：目視において析出が認められた。
【００３７】
（２）吐出評価
ピエゾ素子振動による圧力を与えて液滴を発生させ記録を行うインクジェットプリンタ（ＭＦＣ７４００Ｊ：ブラザー工業製）にてノーマルモード印刷を行い、不吐出がないことを確認した。なお、不吐出が認められた場合には、不吐出が認められなくなるまでメンテナンス（パージ等）を行った。
室温にて上記インクジェットプリンタを３週間放置した後、３回のパージを行って、記録を行い、不吐出の有無を確認した。
評価基準は以下の通りである。
◎：不吐出率が０％であった。
○：不吐出率が１％未満であった。
×：不吐出率が１％以上であった。
なお、（１）析出の有無の評価において、×の評価となったマゼンタインクについては、（２）吐出評価の試験を行わなかった。
【００３８】
【表６】

【００３９】
表６から明らかなように、実施例１〜８で作製したマゼンタインクでは、３日間放置した後も析出が認められず、不吐出も確認できなかった。
一方、比較例１で作製したマゼンタインクでは、目視では、析出が確認できなかったが、吐出評価では、不吐出率が１％以上であった。
また、比較例２〜８で作製したマゼンタインクでは、目視において、析出の発生が確認できた。
【００４０】
以上のことより、塩基性染料と酸性染料とを混在させる場合であっても、双極子モーメントが１５デバイ以下の酸性染料を用いることにより、染料が析出を起こすことなく、鮮やかな色調が得られ高信頼性の記録が可能なマゼンタインクが得られることが確認できた。
【００４１】
【発明の効果】
本発明は、上述の構成よりなるので、塩基性染料と酸性染料とを混在させる場合であっても、析出によるヘッド吐出部での目詰まりが発生することなく安定した噴射が可能で、高信頼性、高精度の記録が可能となるインクジェット記録用水性インクセットを提供することができる。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an aqueous ink for inkjet recording used in an inkjet recording apparatus.
[0002]
[Prior art]
Ink jet recording methods include, for example, an electrostatic suction method, a method of applying mechanical vibration or displacement to ink using a piezoelectric element, or the like, a method of generating bubbles by heating ink, and a method of utilizing pressure at that time. Ink droplets are formed by an ejection method, and a part or all of the ink droplets are attached to a recording material such as paper to perform recording.
Ink jet recording methods have been widely used in recent years because they have no processes such as development and fixing and are easy to colorize. Recently, high-definition and high-speed printing by an ink-jet printer has rapidly progressed, and a color printer capable of printing on plain paper has become mainstream.
[0003]
Under such circumstances, the aqueous ink for inkjet recording used in the inkjet recording method, for example, is capable of stable ejection without causing clogging at the head end of the inkjet printer or in the ink flow path. High performance is required, such as high image quality and color tone, and no fading or discoloration after image formation.
[0004]
In general, a full-color ink jet printer uses an aqueous ink containing an acid dye in many cases from the viewpoint of coloring properties and toxicity to paper. However, there are cases where the vividness is insufficient for some colors, and there is a demand for obtaining a vivid image as drawn with a marker pen. In particular, magenta color has a great effect on human skin color and the like, and such demands are great.
In order to satisfy such a demand, it is preferable to use a basic dye having a vivid color as actually used in a marker pen. However, basic dyes generally have low solubility in water, and when printed on recording paper, a sufficiently high image density may not be obtained. As a means for improving this point and improving the density while maintaining the vividness, a method of mixing a basic dye and an acidic dye has been studied.
[0005]
However, when the basic dye and the acid dye are mixed, a new problem occurs that a precipitate is generated in the aqueous ink. As a factor for generating such a precipitate, the basic dye has a positive charge, and the acidic dye has a negative charge. Was thought to be due to an electrical inquiry between the two.
The degree of precipitation varies depending on the type of dye, the dye concentration, the type and concentration of the solvent, and the like.However, the generation of such precipitates is a major cause of clogging at the head ejection part, and a major obstacle to inkjet printing. It was.
[0006]
[Problems to be solved by the invention]
The present invention has been made in order to solve the above-described problems. Even in an aqueous ink jet recording ink containing both a basic dye and an acid dye, clogging due to deposition occurs in a head discharge portion. An object of the present invention is to provide a water-based ink for ink-jet recording that enables stable ejection without causing any trouble, and enables highly reliable and highly accurate recording.
[0007]
[Means for Solving the Problems]
The present invention is an aqueous ink jet recording ink containing water, a basic dye, and an acid dye having a dipole moment of 15 debyes or less.
Hereinafter, the present invention will be described in detail.
[0008]
The aqueous ink jet recording ink of the present invention contains a basic dye and an acid dye.
[0009]
The basic dye is not particularly limited, and examples thereof include Basic Red 1, 2, 9, 12, 13, 37, 38, 39, 92, C.I. I. Basic Violet 1, 3, 7, 10, 11: 1, 14, C.I. I. Basic Yellow 1, 2, 11, 13, 14, 19, 21, 25, 32, 33, 36, 51, C.I. I. Basic Orange 2, 15, 21, 22, C.I. I. Basic Blue 1, 3, 5, 7, 9, 19, 24, 25, 26, 28, 29, 45, 54, 65, C.I. I. Basic Green 1, 4, C.I. I. Basic Brown 1, 12 and the like can be mentioned.
In addition, each may be used alone, or two or more kinds may be used in combination.
[0010]
The content of the basic dye in the aqueous ink jet recording ink of the present invention is preferably 0.02 to 2% by weight based on the total amount of the ink. If it is less than 0.02% by weight, vividness may be lacking, and if it exceeds 2% by weight, a dye may be precipitated from the viewpoint of solubility. More preferably, it is 0.05 to 1% by weight.
[0011]
The acid dye has a dipole moment of 15 Debye or less.
The present inventors have made intensive studies and found that when mixing a basic dye and an acid dye, the dipole moment of the acid dye is set to 15 debyes or less, thereby preventing clogging due to deposition at the head discharge portion. It has been found that stable jetting is possible without occurrence, and high reliability and high image quality can be obtained, and the present invention has been completed.
The acid dye preferably has a dipole moment of 10 Debye or less.
[0012]
The factors that prevent the generation of precipitates are considered as follows. Basic dyes have a structure in which positive charges take a resonance structure over a wide range of molecules and have low polarity. On the other hand, water has a very high polarity, and a basic dye having a low polarity has low affinity with water, so that it is difficult to dissolve in water and has high hydrophobicity.
On the other hand, acidic dyes have many polar dissociating groups such as sulfonates and carboxylate salts that are completely dissociated in water, and have high hydrophilicity. However, when the polar dissociating group is localized in the molecule, many polar dissociating groups are present, and there are a portion having high hydrophilicity and a portion having high hydrophobicity. In such a case, when the basic dye and the acid dye are mixed, the highly hydrophobic portion of the acid dye interacts with the similarly highly basic dye to dissolve in water. It is considered that the properties are significantly reduced and precipitates are generated.
On the other hand, in the aqueous ink for inkjet recording of the present invention, the polar dissociative group in the molecule is not localized, that is, by using an acid dye having a small dipole moment of the molecule, Since the water molecules are uniformly distributed around the periphery and the water molecules are uniformly coordinated around the acid dye, even if the basic dye tries to combine with the acid dye, these water molecules become steric hindrance and cannot bind, and the precipitate It is considered that the occurrence of the occurrence is prevented.
[0013]
The dipole moment is a value representing the bias of the charge in the molecule. The larger the numerical value, the greater the bias of the charge and the greater the polarity. The dipole moment can be determined by molecular orbital calculation. For example, the molecular orbital calculation software “WinMOPAC3” manufactured by Fujitsu Limited can be used to calculate the dipole moment using the potential function AM1.
[0014]
The acid dye preferably has no resonance structure over a wide range of molecules.
In the case of having such a structure, there is a possibility that a portion having low polarity may be present in the molecule, and a precipitate may be generated in some cases.
[0015]
Acid dyes having a dipole moment of 15 debyes or less include, for example, C.I. I. Acid yellow 17, 23, C.I. I. Acid red 13, 14, 18, 27, 80, 87, 92, C.I. I. Acid violet 49, C.I. I. Acid Blue 45, 74, C.I. I. Acid Black 26 and the like. These acid dyes may be used alone or in combination of two or more for the purpose of adjusting color tone.
Table 1 shows the values of the dipole moments of these acid dyes.
[0016]
[Table 1]

[0017]
The content of the acid dye is preferably 0.5 to 10% by weight based on the total amount of the ink. If the content is less than 0.5% by weight, the desired image density may not be obtained. If the content exceeds 10% by weight, the viscosity of the ink after evaporation of water may become too high or precipitates may be generated. It is. More preferably, it is 1 to 5% by weight.
[0018]
The water may be ordinary water, but it is preferable to use deionized water (pure water).
The amount of the water is preferably 40% by weight or more based on the total amount of the ink in order to maintain the normal viscosity of the ink at normal times.
[0019]
In the aqueous ink for inkjet recording of the invention, it is preferable to add a water-soluble organic solvent generally used for the aqueous ink for inkjet recording.
As the water-soluble organic solvent, for example, a substance called a wetting agent or a penetrant can be used.
[0020]
The wetting agent is added mainly at the tip of the inkjet head for the purpose of preventing precipitation from occurring due to evaporation of water in the ink and drying of the ink.
Examples of the wetting agent include polyalkylene glycols; ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, butylene glycol, dipropylene glycol, tripropylene glycol, polyethylene glycol, 1,2,6-hexanetriol, and thiodiglycol. Examples thereof include alkylene glycols such as glycol, 1,3-butanediol, 1,5-pentanediol, and hexylene glycol; glycerin; and pyrrolidones such as 2-pyrrolidone and N-methyl-2-pyrrolidone. These wetting agents may be used alone or in combination.
[0021]
The content of the wetting agent is preferably 5 to 50% by weight based on the total amount of the ink. If it is less than 5% by weight, the wetting action becomes insufficient, and problems such as precipitation and dryness may occur. If the amount exceeds 50% by weight, the ink may thicken more than necessary, causing problems such as inability to eject ink and extremely slow drying on recording paper. More preferably, it is 10 to 40% by weight.
[0022]
The penetrant is added for the purpose of increasing the speed of penetration of the ink into the recording paper, thereby improving the quick-drying property on the paper surface, and preventing feathering due to penetration. As the penetrant, it is preferable to use a polyhydric alcohol monoalkyl ether having low odor and low vapor pressure.
The above-mentioned polyhydric alcohol monoalkyl ether is not particularly limited. Examples thereof include propylene glycol monobutyl ether, triethylene glycol monomethyl ether, triethylene glycol monobutyl ether, tripropylene glycol monomethyl ether, and tripropylene glycol monobutyl ether.
[0023]
The content of the penetrant is preferably 0.2 to 20% by weight based on the total amount of the ink. If the amount is less than 0.2% by weight, the ink penetrates into the recording paper at a low speed, and may cause problems in drying time and bleeding. On the other hand, if the content exceeds 20% by weight, the penetration of the ink into the recording paper becomes severe, and the ink may reach the back of the recording paper or a problem may occur with bleeding. More preferably, it is 0.5 to 10% by weight.
Further, for the purpose of controlling the penetration of ink into the recording paper and the drying property, it is also possible to use a monohydric alcohol such as ethanol or isopropyl alcohol.
[0024]
The basic constitution of the aqueous ink for ink-jet recording of the present invention is as described above, but other conventionally known resin binders, surfactants, viscosity modifiers, surface tension regulators, pH regulators, dye dissolving agents, antiseptic and mildew Agents and the like can be added as needed. When the water-based ink for ink-jet recording of the present invention is applied to an ink-jet method of a type in which ink is ejected by the action of thermal energy, thermal physical properties (for example, specific heat, thermal expansion coefficient, thermal conductivity, etc.) May be adjusted.
[0025]
The ink-jet recording ink of the present invention has sufficiently solved the problems of the prior art, and even when a basic dye and an acid dye are mixed, clogging at a head ejection portion due to deposition occurs. It is possible to provide a water-based ink set for ink jet recording, which can perform stable ejection without recording, and can perform highly reliable and highly accurate recording.
[0026]
【Example】
Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to only these Examples.
Examples of the ink composition according to the present invention are shown below. In this embodiment, magenta ink is described. However, similar effects can be obtained with other color inks.
[0027]
(Examples 1 to 4)
As basic dyes, C.I. I. Basic Yellow 40 or C.I. I. Basic Red 1, an acidic dye having a dipole moment of 9.9 Debye. I. Acid Red 14 or C.I. having a dipole moment of 8.0 Debye. I. Using Acid Red 27, an ink material having the composition shown in Table 2 was mixed and stirred, and then filtered through a 0.2 μm membrane filter to prepare a magenta ink.
[0028]
[Table 2]

[0029]
(Examples 5 to 8)
As basic dyes, C.I. I. Basic violet 10 or C.I. I. Basic violet 11: 1 as an acid dye, C.I. having a dipole moment of 12.2 Debye. I. Acid Red 18 or C.I. I. Using Acid Red 87, an ink material having the composition shown in Table 3 was mixed and stirred, and then filtered through a 0.2 μm membrane filter to prepare a magenta ink.
[0030]
[Table 3]

[0031]
(Comparative Examples 1-4)
As basic dyes, C.I. I. Basic Yellow 40 or C.I. I. Basic Red 1, an acidic dye having a dipole moment of 15.2 Debye; I. Acid Red 186 or C.I. having a dipole moment of 19.0 Debye. I. Using Acid Red 52, an ink material having the composition shown in Table 4 was mixed and stirred, and then filtered through a 0.2 μm membrane filter to prepare a magenta ink.
[0032]
[Table 4]

[0033]
(Comparative Examples 5 to 8)
As basic dyes, C.I. I. Basic violet 10 or C.I. I. Basic violet 11: 1 as an acid dye, C.I. having a dipole moment of 22.2 Debye. I. Acid Red 1 or C.I. I. Using Acid Red 42, ink materials having the composition shown in Table 5 were mixed and stirred, and then filtered through a 0.2 μm membrane filter to prepare a magenta ink.
[0034]
[Table 5]

[0035]
(Evaluation)
The magenta inks prepared in Examples 1 to 8 and Comparative Examples 1 to 8 were evaluated for the presence or absence of precipitates and the discharge evaluation by the following methods. The results are shown in Table 6.
[0036]
(1) Presence or absence of precipitation 5 g of the magenta ink prepared in Examples 1 to 8 and Comparative Examples 1 to 8 was manufactured by As One Co., Ltd. The glass bottle was placed in the glass bottle No. 2 and left in a thermo-hygrostat at a temperature of 60 ° C. and a humidity of 40% for 3 days.
The evaluation criteria are as follows.
：: No precipitation was observed visually or under a microscope.
Δ: No precipitation was observed visually, but precipitation was observed under a microscope.
×: Precipitation was visually observed.
[0037]
(2) Ejection evaluation Normal mode printing was performed by an ink jet printer (MFC7400J: manufactured by Brother Industries, Ltd.) that performs recording by generating pressure by applying pressure due to piezoelectric element vibration, and it was confirmed that there was no non-ejection. When non-ejection was observed, maintenance (purge, etc.) was performed until no non-ejection was observed.
After the ink jet printer was left at room temperature for three weeks, purging was performed three times, recording was performed, and the presence or absence of non-ejection was confirmed.
The evaluation criteria are as follows.
A: The non-ejection rate was 0%.
：: The non-ejection rate was less than 1%.
X: The non-discharge rate was 1% or more.
In the evaluation of (1) the presence or absence of precipitation, magenta ink evaluated as x was not tested for (2) ejection evaluation.
[0038]
[Table 6]

[0039]
As is clear from Table 6, in the magenta inks prepared in Examples 1 to 8, no precipitation was observed even after being left for 3 days, and no ejection was not confirmed.
On the other hand, in the magenta ink produced in Comparative Example 1, no precipitation was visually observed, but the discharge evaluation showed that the non-discharge rate was 1% or more.
Further, in the magenta inks manufactured in Comparative Examples 2 to 8, the occurrence of precipitation was visually confirmed.
[0040]
From the above, even when a basic dye and an acid dye are mixed, by using an acid dye having a dipole moment of 15 Debyes or less, a vivid color tone can be obtained without causing precipitation of the dye. It was confirmed that a magenta ink capable of highly reliable recording was obtained.
[0041]
【The invention's effect】
Since the present invention has the above-described configuration, even when a basic dye and an acidic dye are mixed, stable ejection can be performed without causing clogging at a head ejection portion due to deposition, and high reliability is achieved. It is possible to provide a water-based ink set for ink-jet recording which enables high-precision recording with high accuracy.

Claims (1)

An aqueous ink jet recording ink comprising water, a basic dye, and an acidic dye having a dipole moment of 15 debyes or less.