JP3000086B2 - Inkjet recording ink - Google Patents

Description

The present invention relates to a novel ink for inkjet recording,
More specifically, the present invention relates to an ink useful for a printing method for recording an output from a word processor, a computer, a measuring instrument, and the like, particularly an ink jet recording method.

[Prior Art] The ink jet recording method has been widely used because it is noiseless, plain paper can be used as a recording medium, and printing speed is high. The pressure-on-demand method has been often used in the ink jet recording that has been proposed so far, and recently, a head that employs means for applying heat to the ink in the liquid chamber to discharge the ink has been adopted. Has been put to practical use because it is relatively easy to manufacture.

Some of the inks used in the method of ejecting a solid ink at room temperature while heating it to a liquid state are introduced. (1) A compound that is solid at room temperature and melts by heating, such as didodecyl sebacate, is used as a vehicle. (USP 3653932), (2) a solid ink at room temperature in which a recording material is melted or dispersed in a specific medium (JP-A-55-54368), and (3) a hot-melt ink containing natural wax (JP-A-58-1983). No. 108271), (4) Inks containing alcohols, ketones or acids having higher alkyl groups
JP-A-61-83268), and (5) an ink containing a thermosetting resin having a high hydroxylation (JP-A-62-48774). By using such ink,
Electrophotographic paper, typewriter paper, high quality paper, medium quality paper,
A clear image can be formed in a single color or a multicolor color on almost any recording medium such as a bond paper, a film, a cloth, and a plate.

In addition, these are excellent characteristics that cannot be obtained with a liquid ink such as a water-based ink that has been conventionally used in the above-described ink jet recording method.

However, in all of these conventional solid inks, since the face wash is dissolved or dispersed in a specific medium, the ratio of the medium is increased, and bleeding from the specific medium is observed. In addition, a pigment such as carbon black is used to form a black recorded image, or a black forming unit is used by mixing a plurality of types of dyes.
Not only is there a problem in imparting reliability, but also in the case of a dye-mixed type, it is difficult to obtain a pure black tone.

[Problems to be Solved by the Invention] The present invention is free from inconvenience as in the prior art,
There are ink jet recording inks that provide a stable clear image with a desired color tone over a long period of time.

[Means for Solving the Problems] The ink jet recording ink of the present invention is a coloring material thermoplastic resin comprising an electron-donating color-forming organic compound comprising a leuco dye and an electron-accepting color-developing organic compound, and a plasticizer. And is solid at normal temperature, is heated and melted, flies, and is solidified on a recording medium.

The present inventors have replaced the conventional ink with an electron-donating color developing organic compound, an electron-accepting color developing organic compound, which has not been considered in the field of the ink jet recording method, as an ink for ink jet recording. I confirmed that it can be used. The present invention has been made by this.

 Hereinafter, the present invention will be described in more detail.

The ink of the present invention comprises an electron-donating color-forming organic compound (for convenience, sometimes referred to as “A compound”) and an electron-accepting color-developing organic compound (for convenience, sometimes referred to as “B compound”). Contains. Here, a heat-sensitive compound (sometimes referred to as “C compound” for convenience) may be added as necessary. These compounds A, B and C are all solid at room temperature, but need to have a melting point suitable for the melting temperature during recording. Therefore, in practice, a room temperature solid ink having a necessary and appropriate melting temperature utilizing eutectic is prepared.

That is, the present invention can obtain a pure black tone with a single dye from a coloring material composed of an electron-donating color-forming organic compound and an electron-accepting color-developing organic compound. It is intended to provide a room-temperature solid ink that can be easily formed in multiple colors by changing the type, and can be maintained on a general-purpose recording member (recording medium) and has a stable discharge state with a clear color and is melted at the time of ejection. is there.

(1) The electron-donating color-forming organic compound is generally a leuco compound which is a dye precursor, and has a skeleton represented by the following formula (I) in black coloration. The melting point can be reduced by changing each substituent. In the formula (I), R ³ represents —H, —CH ₃ , —OCH ₃ ,
Although -Cl, etc., here illustrate specific compounds from No.1 to No.11 as -CH _3.

In addition, there are many black-coloring leuco compounds used in the field of pressure- and heat-sensitive recording. There are a number of chromogenic leuco compounds that provide freely selectable color species, and representative leuco compounds among them are as follows (No. 12).
To No. 18).

The following color-forming leuco compounds (No. 19 and No. 20) exhibiting infrared absorption that can be optically read by LD light can be exemplified.

(2) The electron-accepting color-developing compound has a function of supplying a proton to the color-forming leuco compound (A compound) to form a colored body, and specifically, is a compound having a phenolic hydroxyl group. , Monophenols and polyphenols, and it is possible to impart a melting point that can be selected by introducing a substituent such as an alkyl group, an aryl group, an acyl group, an alkoxycarbonyl group, or a halogen.

 The following are representative examples.

In addition, there are many electron-accepting color developing compounds used in the field of pressure- and heat-sensitive recording.

Other non-phenolic color developing compounds include aliphatic / aromatic carboxylic acid sulfone compounds, thiourea compounds, thiocyanate compounds, triazole compounds, and phosphate ester compounds.

(3) The heat-sensitizing compound (C compound) lowers the melting start temperature of the dye precursor system composed of the color-forming leuco compound (A compound) and the electron-accepting color developing compound (B compound) by eutectic melting. It is required to have a function of improving compatibility and lowering the melt viscosity (melting acceleration function), and to promote the formation of dyes for use in various states from liquids to crystals and solids depending on the type of substituent.

In this case, too, a large number of compounds can be applied depending on the kind of the substituent, and some typical examples are shown below.

In addition, many heat-sensitive sensitizing compounds used in the field of pressure- and heat-sensitive recording can be used.

As described above, it is essential that the ink of the present invention contains the A compound and the B compound, but good results can be obtained by coexisting the C compound with these compounds. In addition, in the ink of the present invention, adhesive strength, cohesive strength,
PVC-vinyl acetate copolymer to further improve the practical performance according to the purpose of imparting environmental resistance such as heat resistance and cold resistance,
A thermoplastic polymer such as a polyester-based polymer can be appropriately selected and added.

Further, in order to impart initial tackiness during melting and residual tackiness during solidification, a tackifier such as terpene resin, butyral resin, petroleum resin, esterified rosin or hydrogenated rosin can be appropriately selected and added. .

Further, a small amount of a natural wax or a synthetic wax, or a plasticizer such as phthalic acid or phosphoric acid esters can be appropriately added for the purpose of improving the heat fluidity and the leakage to the recording member (recording medium). .

Furthermore, due to the properties of the coloring composition of the present invention, a fixed melting time is maintained, so that strict temperature control is performed to prevent overheating, deterioration due to light, oxygen, ozone, or deterioration of the function due to mold generation, etc. Amines,
It is effective to appropriately select and add also an antioxidant stabilizer and a fungicide containing sulfur and phosphorus.

The ink (colorable composition) of the present invention is applicable to conventionally proposed ink jet recording methods. An example of a typical method is a pulse-on-demand method in which a pulse voltage according to an image is applied to a piezoelectric element such as PZT, and pressure is applied to ink in an ink chamber to push out ink from a nozzle. As a typical example of the method, there is an electrostatic suction method in which a pulse voltage according to an image is applied to an electrode to induce a charge in the ink to suck the ink from a nozzle toward a recording paper. Specific examples of these ink jet systems are described in, for example, Journal of the Institute of Television Engineers of Japan 37 (7) 540 (1983). Among these conventional ink jet recording methods, in the method of continuously forming ink droplets and collecting and reusing the ink such as a method of controlling the charge amount, the ink according to the present invention which becomes solid or has a high viscosity at room temperature When the ink is used, it is necessary to keep the ink at a low viscosity by heating in the ink collecting section. Therefore, the ink of the present invention is more preferably used for a drop-on-demand type recording apparatus.

FIG. 1 schematically shows a particularly desirable ink jet recording apparatus using the ink of the present invention. Here, reference numeral 6 denotes a print head, and ink is heated at an appropriate temperature (for example, about 90 ° C.) by a heater (not shown) in the head.
° C). A pressure is applied to the ink filled in the head in accordance with an image signal by a piezoelectric element (not shown), and the liquefied ink flies in the direction of the platen 12 to print on the recording paper supplied on the platen. . The recording paper 1 includes a paper feed roller 3 and a paper
It is supplied onto the platen by guides 4 and 5, and rollers 9 and 1
0, the sheet is conveyed to the discharge tray 16 by the separation claw 11. The print head 6 is scanned so as to reciprocate on guide shafts 7 and 8. In addition, an infrared lamp 13 is preferably provided inside the platen 12, and the platen is, for example, about 65 to
Heated to 70 ° C. 14 is a sensor for detecting the temperature of the platen, and 15 is a controller for feeding back the detected temperature and changing the output of the lamp so that the temperature of the platen becomes constant.

Although a means for heating the platen is not always necessary, if the surface of the platen is heated, when the ink flying in the direction of the platen reaches the heated recording paper, a part of the ink is discharged inside the recording medium. In this case, the toner is fixed in such a manner that it has penetrated to some extent, so that good fixing is performed.

Example Next, an example will be described. Here, both% and parts are based on weight.

Example 1 Electron-donating color-forming organic compound (No. 9 compound) 1.5% Electron-accepting color developing compound (No. 32 compound) 1.5% Wax (dipalmityl phosphate) 92.0% Polymer (vinegar) (B-PVC copolymer) 5.0% Heat-sensitive compound (No. 44 compound) 20.0% 100 parts of these mixtures were dissolved in 350 parts of THF and mixed well with stirring. The obtained solution was added to about 0.5 μm Teflon
After filtration using a filter, THF was distilled off to obtain a test ink.

This ink was filled in the ink jet recording apparatus shown in FIG. 1 to record an image. In this recording, the ink in the head was heated to about 90 ° C., and the platen was heated to about 65 to 70 ° C. The maximum frequency for printing is 4KHz
The printing was performed under the conditions that the printing density was 8 dots / mm, the droplet diameter was about 100 μm, the droplet speed was about 4 m / sec, and the distance between the nozzle and the printing surface was about 1 mm.

Under the above conditions, commercial high quality paper, bond paper, medium quality paper, OH
When printing was performed on the P sheet, a clear image was obtained with high density in pure black on any recording medium. The obtained image was stored for 3 months at 30 ° C.
No changes were observed in the images. In addition, a continuous operation for 1000 hours and a suspension test for 2 months were performed with the above-mentioned apparatus. In each test, stable ejection characteristics were obtained, and a clear image unchanged from the initial one was obtained. .

Comparative Example 1 An ink having the following formulation was prepared in the same manner as in Example 1 in place of the ink formulation in Example 1, then filled in the same device, and printed in the same manner.

Beeswax 35.0% Candelilla wax 62.0% Oil black 3.0% The obtained image was as clear as the image of Example 1, and the image did not change upon storage.
After printing was stopped for a month, it was impossible to print without discharging ink from the nozzles.

Example 2 Electron-donating color-forming organic compound (No. 12 compound) 2.0% Electron-accepting color-developing compound (No. 27 compound) 2.0% Polymer (saturated polyester resin) 9.0% Heat-sensitizing compound (No. 87.0% 100 parts of these mixtures were dissolved in 200 parts of THF to prepare an ink in the same manner as in Example 1, and printing was performed in the same manner as in Example 1. As a result, a clear yellow image was obtained. Was.

Example 3 Electron-donating color-forming organic compound (No. 14 compound) 2.0% Electron-accepting color-developing compound (No. 29 compound) 2.0% Wax (myristyl acid phosphate) 71.0% Polymer 5.0% (vinyl chloride) -Vinyl acetate-phosphate ester copolymer,
Denka Vinyl # 1000P, manufactured by Denki Kagaku Kogyo Co., Ltd. 100 parts of a mixture composed of 20.0% of a heat-sensitized compound (No. 43 compound) was dissolved in 350 parts of THF to prepare an ink in the same manner as in Example 1. When printing was performed in the same manner, a clear orange-red image was obtained.

Example 4 Electron-donating color-forming organic compound (compound of No. 17) 1.5% Electron-accepting color-developing compound (compound of No. 31) 1.5% Heat-sensitizing compound (compound of No. 41) 17.0% 100 parts of a mixture consisting of 80.0% of the sensitizing compound (No. 48 compound) was dissolved in 200 parts of THF to prepare an ink in the same manner as in Example 1, and printing was performed in the same manner as in Example 1. Image was obtained.

Example 5 Electron-donating color-forming organic compound (No. 8 compound) 1.0% Electron-donating color-forming organic compound (No. 19 compound) 2.0% Electron-accepting color developing compound (No. 33 compound) 100% of a mixture of 3.5% heat-sensitizing compound (No. 40 compound) and 93.5% was dissolved in 150 parts of THF to prepare an ink in the same manner as in Example 1, and printing was performed in the same manner as in Example 1. As a result, a black image was obtained, and optical reading with LD light (semiconductor laser light) of 780 nm was possible.

[Effect of the Invention] According to the use of the ink for ink jet recording of the present invention, a stable ejection state can be maintained, and since the ink itself is a solid at room temperature having a necessary appropriate melting temperature utilizing eutectic, handling is also easy. Easy.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a recording apparatus particularly useful when the ink of the present invention is used for ink jet recording. 1 ... Recording paper, 6 ... Print head 12 ... Platen roller, 12 ... Infrared lamp

Continuation of the front page (56) References JP-A-2-51570 (JP, A) JP-A-62-295973 (JP, A) JP-A-47-22734 (JP, A) JP-A-58-183770 (JP) , A) JP-A-46-3564 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C09D 11/00-11/20

Claims (2)

(57) [Claims] 1. A colorant thermoplastic resin comprising an electron-donating color-forming organic compound comprising a leuco dye and an electron-accepting color-developing organic compound, and a plasticizer. An ink jet recording ink characterized in that it flies over and is solidified on a recording medium. 2. A coloring material comprising an electron-donating color-forming organic compound comprising a leuco dye and a color-sensitive material comprising an electron-accepting color-developing organic compound, which contains a heat-sensitizing compound which promotes solvent and color development. The ink for inkjet recording according to claim 1, wherein