JPH0692550B2 - Ink jet light magenta ink and color ink jet recording method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a recording liquid (hereinafter referred to as an ink) used for inkjet recording, and more specifically, it is excellent even in a light color portion or a mixed color portion in a dark and light ink method. And an ink giving an image having light fastness.

(Prior Art) The inkjet recording method has been attracting attention as one of non-impact technologies that can easily achieve full color. Especially suitable as a recording method for video printers that print out video images and printers that print out hard copies of personal computer graphics (CG) in terms of texture, color reproducibility, and richness of the printer. ing.

Although various methods have been proposed for the inkjet recording method, an inkjet recording method (dark and light ink method) using two or more inks having different dye densities for one or more of each of yellow, magenta, cyan, and black inks has been proposed. ) Has already been proposed by us.

According to the above method, since the highlight ink (light ink) and the dark ink (dark ink) are used, smooth color reproduction is possible over a wide density range from the highlight portion to the dark portion of the image.

(Problems to be Solved by the Invention) However, in the above dark and light ink method, the use of light ink has a great advantage in image formation, but there is a problem in light resistance of an image formed. That is, there is a problem that the light resistance of the image portion using the light ink is slightly lower than that of the image portion using the dark ink.

Generally, in inkjet recording, a water-based ink is used as an ink, that is, a water-soluble dye is often used as a recording agent, and the color tone of the image is excellent, but there are many problems with the light fastness of the image. There was difficulty. In particular, when the dark ink is used at a density of a certain level or higher, even if the dark ink is relatively tough, when it is used as the light ink in a low density region, fading occurs and the image fastness is insufficient.

Thus, the problem of light resistance peculiar to light ink is considered to be due to the aggregate state of dye molecules. That is, the dye molecule in a high-concentration state is a large aggregate in which a large number of molecules are aggregated in the ink, and retains a relatively large molecular association state even when it is recorded on the recording paper.
Therefore, it is considered that it exhibits excellent light resistance. However, when the dye concentration is low, that is, in the case of a light ink, even if an aggregate of molecules is formed, its size is as small as several molecules, so that the aggregate state cannot be sufficiently obtained on the recording paper. It is considered that the material is easily attacked by radical species generated by light, active oxygen (singlet oxygen), etc., and has low light resistance.

Therefore, an object of the present invention is to provide an inkjet ink capable of forming an image having excellent light resistance even with a light ink having a low dye concentration.

Another object of the present invention is to provide an inkjet ink which forms an image having excellent light resistance in a light color portion and a color mixture portion in a dark and light ink method.

(Means for Solving Problems) The above object is achieved by the present invention described below.

That is, the present invention is a light magenta ink applied to color ink jet recording using dark and light inks having different dye densities with respect to the same color ink, wherein a water-soluble magenta dye and β-cyclodextrin are contained in an aqueous medium. Ink-jet light-color magenta ink characterized by having both, and a color ink-jet recording method using dark and light inks each having a different dye concentration for the same color ink, as a light-color ink, a water-soluble dye and β- A color inkjet recording method is characterized in that an ink having both cyclodextrin is used.

(Function) By incorporating β-cyclodextrin into ink, particularly light-colored magenta ink having a relatively low dye concentration, dye molecules are clathrated by β-cyclodextrin, and even after being recorded on a recording paper, light molecules are exposed. The harmful radicals and singlet oxygen generated by the above are less likely to be attacked, and the light resistance of the image is improved.

The mechanism by which β-cyclodextrin added to the ink improves the light resistance of the magenta dye in the ink is not well understood, but it is considered as follows.

That is, when the dye is present in the ink at a concentration capable of forming aggregates (self-association), that is, in the case of dark ink, the coloring part of each dye molecule is protected by the steric hindrance caused by the adjacent molecule during assembly. This makes it practically difficult to attack by harmful radicals (・ OOH, ・ CO) generated by ultraviolet light or visible light and singlet oxygen (energy transfer or electron transfer).

On the other hand, when the dye molecules cannot form an aggregate, or even if several dye molecules are formed, that is, in the case of a light ink, the protection of the coloring part by self-association cannot be expected. It is presumed that the inclusion of the dye with the contact compound protects the color-developed portion and improves the light fastness of the image.

(Preferred Embodiment) Next, the present invention will be described in more detail with reference to a preferred embodiment.

The ink of the present invention comprises, for example, water, a water-soluble dye, a water-soluble organic solvent, a wetting agent, and other additives, and their individual components and blending ratios are all conventionally known inks for inkjet recording. It may be the same as, and is not particularly limited.

The ink of the present invention is obtained by blending β-cyclodextrin at the same time when a light magenta ink is blended from the above individual components. The amount of β-cyclodextrin added to the ink is most preferably in the range of about 1 to 2 mol per mol of the magenta dye in the ink, and if it is significantly less than this range, the effect of improving the light resistance is unsatisfactory. If the amount is sufficiently large, problems such as precipitation in the ink and excessive increase in the viscosity of the ink occur, which is not preferable.

The present invention is particularly effective for light magenta ink,
The light magenta ink referred to in the present invention is a gradation expression power of an ink jet recording head used, for example, one capable of modulating a dot diameter (a Gould method using a piezo element), or a constant dot diameter per pixel. Depending on what changes the number of dots to be printed or the pattern (dither pattern) to be printed (bubble jet method, silonics method),
The dye concentration is about 0.01 to 1 weight, though it depends on the recording paper used. Further, it goes without saying that the dye concentration also changes depending on the magnitude of the molecular extinction coefficient of the dye used. That is, as the light ink, the reflection density of the highlight portion at the time of image formation is set to 0
To 0.5, preferably 0 to 0.3.

In the present invention, individually known dyes for ink are selected to prepare yellow (Y), magenta (M), cyan (C) and, if necessary, black (Bk) inks, and the same color is prepared. With respect to the above, at least one color is useful as a light magenta ink when two or more dark and light inks having different densities are prepared to form a color image.

In such a case, in the conventional method, fading of the light-colored portion and discoloration of the color-mixed portion were fast, and the color image as a whole lacked light resistance. In particular, since the portion containing the magenta dye also has excellent light resistance, a color image having excellent light resistance as a whole image is provided.

Further, regarding the dye, it is effective for any water-soluble dye such as an acid dye and a direct dye used in conventional inks, but a dye such as a magenta dye that easily fades in a light color portion, for example, , CI Acid Red 35, 37 and other magenta dyes are particularly effective.

(Example) Next, an Example is given and this invention is demonstrated further concretely.

Reference example 1 The composition was prepared according to the formulation shown in Table 1 above, and the composition was stirred for about 1 hour and then filtered through a 0.5 μm membrane filter to obtain magenta dark inks A and B and magenta light ink C.
Got

Example 1 The magenta light ink C of Reference Example 1 above was used as the ink of the present invention.

Comparative Example 1 A magenta light ink D of Comparative Example was prepared by excluding β-cyclodextrin in the formulation of Ink C in the ink of Reference Example 1.

Reference Example 2 CI Acid Red 35 was replaced with CI Acid Red 37, the same composition as in Reference Example 1 was used, and magenta dark inks E and F were used.
And magenta light ink G were obtained.

Example 2 The magenta light ink G of Reference Example 2 above was used as the ink of the present invention.

Comparative Example 2 A magenta light ink H of Comparative Example was prepared in which β-cyclodextrin was excluded from the formulation of Ink G in the ink of Reference Example 2.

The inks of Reference Examples 1 and 2, Examples 1 and 2 and Comparative Examples 1 and 2 were subjected to the following tests to compare their performances.

(1) Lightfastness (single color) Inkjet color printer RP-601 (made by Canon)
2cm x 2cm color patch is created using a xenon fade meter Ci-35F (Atlas Electic)
At 100 ° C for 100 hours, and color difference ΔE ^* (L
^* a ^* b ^* color space color difference) is calculated, and ΔE ^* = 0 to 3 is indicated by ○,
ΔE ^* = 7 to 15 was evaluated as x.

The results are shown in Table 2 below.

Example 3 and Comparative Example 3 An inkjet color printer RP-601 (manufactured by Canon Inc.) was used.
A magenta ink of one kind, a cyan ink of two kinds of light and shade, and a black ink were applied to record a portrait including a female face. At this time, for the light magenta ink among the above inks, the inks of Examples 1 and 2 and Comparative Examples 1 and 2 were individually used to produce a total of four prints.

Then, for each print, add a Xenon fade meter Ci
-35F (Atlas Electic) light irradiation (100 hours)
I went.

As a result, the case where no discoloration of the skin color part in the image was observed was evaluated as ◯, and the case where the discoloration was remarkable was evaluated as x.

The results of these evaluations are summarized in Table 2 below.

From the above, by including β-cyclodextrin in a light color (magenta) ink having a relatively low dye concentration,
It was confirmed that discoloration of the image was prevented and the light resistance was improved.

(Effects) By adding β-cyclodextrin to the ink as described above, the light resistance of the image formed from the ink is improved. In particular, in order to express the highlight part and the dark part of the image, in the ink used in the ink jet recording method provided with the corresponding light ink and dark ink, since the light magenta ink contains β-cyclodextrin, The light resistance and the light resistance during color mixing in an image are improved.

Claims (3)

[Claims] 1. A light magenta ink for use in color ink jet recording, wherein dark and light inks having different dye densities are used for the same color ink, wherein a water-soluble magenta dye and β-cyclodextrin are combined in an aqueous medium. A light-colored magenta ink for inkjet, which has. 2. The method according to claim 1, which contains β-cyclodextrin in a ratio of 1 to 2 mol per mol of the dye.
Ink according to item. 3. A color ink jet recording method using dark and light inks having different dye concentrations for inks of the same color, wherein an ink containing a water-soluble dye and β-cyclodextrin in an aqueous medium is used as the light color ink. A color ink jet recording method comprising: