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INK JET INK AND INK JET RECORDING
METHOD
This application is a continuation of International Application No. PCT/JP2005/005309, filed Mar. 16, 2005, which 5 claims the benefit of Japanese Patent Application Nos.
2004- 075391 filed on Mar. 16, 2004, 2004-075392 filed on Mar. 16, 2004, 2004-289652 filed on Oct. 1, 2004 and
2005- 072040 filed on Mar. 14, 2005.
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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to ink jet ink, an ink jet recording method, an ink cartridge, and an ink jet recording 15 apparatus.
2. Related Background Art
An ink jet recording method refers to a method which conducts recording of images and texts by allowing fine 20 droplets of ink to fly according various operational principles to apply them on a recording medium (e.g. paper). The technique has features like high speed, low noise, ease in multicolor printing, high flexibility of recording patterns and no need for development and fixing, and is therefore rapidly 25 spreading to a wide variety of applications. In addition, full color ink jet recording system has been recently developed and this enables formation of multi-color images comparable to those by polychromic printing according to a prepress method or printed images produced by color pho- 30 tography. For printing in small numbers, the technique can produce printed matters at lower costs than usual polychromic or photographic printing. Under such circumstances, in response to the demand for improved recording properties including high speed, high definition and full color of 35 recording, improvement of ink jet recording apparatus and recording method has been attempted. Since image forming apparatuses such as printers to which the ink jet recording system is applied are used in various situations, recording stability is also important and in addition, improved dura- 40 bility of images is a property required for ink.
As recording media used in the ink jet recording method, various items such as plain paper, coated paper, glossy paper, OHP sheet and back print film are marketed, while for general use in offices, low price plain paper is mostly used. 45 However, when plain paper is used as a recording medium, it becomes necessary to decrease or prevent curling phenomenon (warping or curl of paper) which occurs when a large amount of ink is applied on the recording medium, while satisfying the aforementioned properties. This curling 50 phenomenon is mainly attributable to applied moisture. That is, it is known that considerable curling phenomenon occurs when moisture is applied to a large area, or in a greater amount. In the case of ink jet recording conducted on plain paper, reduction or suppression of not only curling phenom- 55 enon during printing but also curling phenomenon after printing caused by drying and evaporation of moisture (curling phenomenon after printing) have become important.
The printed matter (print) obtained according to the ink jet system are used for various purposes, but curled paper 60 cannot be kept flat, causing a lot of troubles such as curling phenomenon when being piled or put in files. In addition, test printing of presentation documents such as slides and OHP sheet is often conducted on inexpensive plain paper and when figures, photographs or background are printed 65 with the secondary color (blue, etc.), paper becomes warped, making it difficult to handle in many cases.
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Some approaches to decrease or prevent curling phenomenon have been proposed so far. For example, ink jet ink containing a solid substance which is soluble in water or an aqueous organic solvent and has four or more hydroxyl groups in a molecular structure is proposed (e.g. see Japanese Patent Application Laid-Open No. H04-332775). In addition, ink containing a saccharide, a sugar alcohol and a specific amide compound as anti-curling agents is proposed (e.g. see Japanese Patent Application Laid-Open No. H06157955, Japanese Patent Laid-Open No. H06-240189, Japanese Patent Application Laid-Open No. H09-165539 and Japanese Patent Application Laid-Open No. H09-176538). Further, ink containing a specific polyhydric alcohol and glycerol in combination is proposed (see e.g. Japanese Patent Application Laid-Open No. H10-130550). Moreover, ink containing a solvent, a polymer binder, a dye mordant, a water-soluble anti-curling compound, a water-soluble desizing compound, a light resistant compound and a defoaming agent is proposed (e.g. see Japanese Patent Application Laid-Open No. 2000-198267).
Curling phenomenon can be suppressed to some extent by incorporating conventional compounds for preventing curling phenomenon, but ink jet recording has been advanced and involves even higher speed, and ejection stability and reliability are important in the process of high speed printing. Accordingly, in addition to ensuring properties such as stability, permeability and viscosity of the ink itself, it is also important to maintain a high level of basic properties of ink for ink jet recording, in particular, ink jet ejection stability, which is more specifically an anti-clogging property at a ejection port (nozzle) of an ink jet recording head, and a start-up characteristic (re-eject ability of ink from a nozzle after temporal suspension (stopping or pausing) of ink ejection), and at the same time to decrease or prevent curling phenomenon.
Accordingly, an object of the present invention is to provide ink jet ink which can decrease or prevent curling phenomenon with ensuring, as required for conventional ink jet ink, a ejection stability after leaving a head and a ejection stability which can prevent initial portions of printing from being unstable or blurred at the beginning of printing (start-up characteristic), an ink jet recording method, an ink cartridge and an ink jet recording apparatus.
In addition, another object of the present invention is to sufficiently decrease or prevent curling phenomenon, thereby making it easier to handle printed matters prepared by using plain paper.
SUMMARY OF THE INVENTION
The above-mentioned objects are achieved by the present invention described below.
That is, the ink jet ink of the present invention comprises at least water, a colorant, a water-soluble organic compound 1 and a water-soluble organic compound 2,
wherein the content X(%) of the water-soluble organic compound 1 is 10 mass % or more based on the total amount of the ink jet ink and the content X(%) of the water-soluble organic compound 1 and the content Y(%) of the watersoluble organic compound 2 based on the total amount of the ink jet ink satisfy the relation of the following formula (I) and formula (II):
0<KY§0.9, (I) X+7gl5% by mass, (II)
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and wherein the water-soluble organic compound 1 is a water-retentive, water-soluble organic compound having a difference between the water retention ability in an environment of a temperature of 23° C. and a humidity of 45% and the water retention ability in an environment of a tempera- 5 ture of 30° C. and a humidity of 80% of 36% or less, and the water-soluble organic compound 2 is a water-soluble organic compound other than the colorant and the watersoluble organic compound 1.
In particular, it is preferable that the content Y(%) of the 10 water-soluble organic compound 2 is Y<15% by mass and the difference between water retention abilities is 40% or more.
Further, another embodiment of the present invention is ink jet ink comprising at least water and a colorant, further 15 comprising a water-soluble organic compound 1-1, a watersoluble organic compound 1-2, and a water-soluble organic compound 2-1, wherein the content Xx(%) of the watersoluble organic compound 1-1 based on the total amount of the ink jet ink, the content X2(%) of the water-soluble 20 organic compound 1-2 based on the total amount of the ink jet ink and the content Yj(%) of the water-soluble organic compound 2-1 based on the total amount of the ink jet ink satisfy the relation of the following formulas (1) to (3):
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0.1S(X2+71)/X1S2.5, (1)
X1+X23kl0% by mass, (2)
X2+7,g3% by mass (3)
2 i j w 30
and wherein the water-soluble organic compound 1-1 is a
water-soluble polyhydric alcohol or water-soluble amide
compound having a difference between the water retention
ability in an environment of a temperature of 23° C. and a
humidity of 45% and the water retention ability in an 35
environment of a temperature of 30° C. and a humidity of
80% of 36% or less, and a molecular weight Mw in the range
of 100 = Mw= 1000, the water-soluble organic compound
1-2 is a water-soluble alkanediol having a difference
between the water retention ability in an environment of a 40
temperature of 23° C. and a humidity of 45% and the water
retention ability in an environment of a temperature of 30°
C. and a humidity of 80% of 36% or less, and a molecular
weight Mw in the range of 100=Mw= 150, the alkanediol
further containing an —OH group at both terminals of a 45
main chain, and the water-soluble organic compound 2-1 is
a water-soluble organic compound other than the colorant,
the water-soluble organic compound 1-1 and the water-
soluble organic compound 1-2.
In particular, it is preferable that the content Yj(%) of the water-soluble organic compound 2-1 is Yx<15% by mass and the difference between water retention abilities is 40% or more.
The ink jet recording method of the present invention 55 comprises applying the above-mentioned ink jet ink to a recording medium by an ink jet head to form an image.
The ink cartridge of the present invention contains the above-mentioned ink jet ink.
The ink jet recording apparatus of the present invention is go equipped with the above-mentioned ink jet ink.
According to the present invention, curling phenomenon can be sufficiently prevented and handling of printed matters of plain paper, in particular, is thus made easier in an ink jet recording method using plain paper. In addition, ink and a 65 recording method using the same which can achieve ejection stability of ink in ink jet recording are provided. Further
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more, ink and a recording method using the same which can achieve excellent image characteristics are provided.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates the results of measurement of water retention ability of water-soluble organic compounds;
FIG. 2 illustrates the difference between water retention abilities in two specific environments;
FIG. 3 is a perspective view illustrating an example of an ink jet recording apparatus;
FIG. 4 is a vertical cross-sectional view of an ink cartridge;
FIG. 5 is a perspective view of a recording unit; and FIG. 6 is a schematic perspective view illustrating an example of an ink jet cartridge having a liquid ejection head.
DESCRIPTION OF THE PREFERRED
EMBODIMENTS
Hereinafter, the present invention is described in more detail referring to preferred embodiments.
[Mechanism of Occurrence of Curling Phenomenon]
The present invention has been made with the aim of preventing curling phenomenon of recording media after applying ink jet ink (hereinafter referred to as "ink") on recording media by an ink jet recording method.
The mechanism of occurrence of curling phenomenon after printing on a recording medium is as follows. Cellulose fiber is formed into paper by a papermaking machine so as to be aligned (substantially forcibly oriented) along the direction of flow of paper. Since cellulose fiber has greatly different degrees of expansion due to moisture in the machine direction and the cross direction, dimensional change which occurs upon application of moisture varies in the short grain and in the long grain. Therefore, when moisture is applied on paper, cellulose fiber in the cross direction of paper is swelled and the length of paper is increased in the direction (mostly the long grain of paper) perpendicular to the flow direction (mostly the short grain of paper) of the papermaking machine when paper is formed. For this reason, when the amount of ink applied, i.e., the amount of moisture applied, is large upon printing, curling phenomenon occurs toward the direction opposite to the plane on which moisture is applied, namely, negative curling phenomenon occurs. However, due to gradual vaporization of moisture which was once absorbed into cellulose fiber, cellulose fiber starts to shrink to allow paper to shrink. According to this, the length of paper becomes shorter than that before moisture is applied. Thus, the paper gradually curls toward the direction of the plane on which moisture is applied, namely, positive curling phenomenon occurs. This seems to occur because moisture applied by printing first enters into hydrogen bond between fibers and as the moisture is transferred due to evaporation or the like, the tension applied at an initial stage is released and printed portions are shrunk. This positive curling phenomenon poses problems when ink jet recording is conducted on recording media such as plain paper.
The inventors of the present invention carried out detail observation of positive curling phenomenon which occurs when printing is conducted by an ink jet recording method. As a result, they have found that the positive curling phenomenon continuously progresses for a long period when ink jet ink is applied on paper unlike the case where moisture is simply applied to paper.
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