JP2002265827A - Thermal-printing ink composition for ink jet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermal-printing ink composition for an ink jet recorded in a decolored state, having a sufficient color density when colored, having a high coloring speed and a high decoloring speed, and excellent in printing stability. SOLUTION: The ink composition for ink jet thermal printing comprises a coloring agent consisting of a reversible heat sensitive material, a wetting agent and a solvent or dispersant, and after an image is printed with the ink composition on a recording sheet having a color developing agent applied on it, the recording sheet is heated at a specified temperature to color or discolor the printed image. The reversible heat-sensitive material is a dye of the general formula I (wherein, n is an integer of 1 to 4), and the content of coloring agent in the ink composition is 1-5 wt.%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink composition for ink-jet thermal recording, and more particularly to a reversible ink-jet thermal recording ink composition capable of recording in a decolored state and developing color only when necessary. .

[0002]

2. Description of the Related Art In recent years, with the development of the information society, recording devices such as copiers, printers, and faxes have been commercialized.
Recording paper is used as a medium for transmitting and storing information. For example, Japanese Patent Application Laid-Open No.
Japanese Patent Application Laid-Open No. 255120 discloses an ink jet recording apparatus of an ink jet print recording system.

[0003] Further, there is an increasing need to create and store confidential documents as one of the document management in a company. Documents visualized by the above recording device must be stored and stored in terms of confidentiality.
There is not enough management method. It would be ideal if a document created by a personal computer or word processor was not stored as it was, but was recorded in a decolored state to make it impossible to read the document and to make it develop color only when necessary.

[0004]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above circumstances, and performs recording in a decolored state, and has a sufficient color density at the time of color development. It is an object of the present invention to provide an ink composition for ink-jet thermal recording that is fast and has good ink jetting stability.

[0005]

The ink composition for ink jet thermal recording of the present invention is an ink composition comprising a colorant comprising a reversible thermosensitive material, a wetting agent, and a solvent or a dispersion medium. By heating the recording sheet after printing on the recording sheet coated with the colorant with the ink composition to a predetermined temperature, a printed image develops or loses color.

In the present invention, a specific dye as described below is used as a reversible thermosensitive material constituting a colorant, and an ink composition containing the dye is coated with a developer made of a reversible thermosensitive material with a resin. By printing on the recorded recording sheet and changing the heating temperature, coloring and decoloring of the printed image are performed.

The ink composition for ink-jet thermal recording of the present invention is initially colorless when printed by an ink-jet printer. As a heating means for coloring and decoloring these characters and images (printed images), a heating roller, an infrared lamp, a hot plate, a hot air heater, or the like is used, and the heating is performed at a temperature equal to or higher than the melting point of the dye in the ink composition. It is preferable that the heating rate is extremely high.

In order to develop or erase a printed image, the printed image is heated to a predetermined temperature. As the heating temperature for color development, a temperature higher than the melting point of the dye in the ink or the color developer applied to the recording sheet is required, and the heating temperature for decoloring is a unique temperature determined by the color developer.

The dye in the ink composition after printing with an ink jet printer dissolves with the developer heated above the melting point on the recording sheet to form a color. When cooled to room temperature as it is, the dye and the developer are combined and solidified to maintain a color-developed state.

In order to erase the colored characters or images, the molecules start to move by heat by reheating to a temperature lower than the melting point of the dye or the developer, and the developer crystallizes and separates from the dye. Then, the color is erased.

When heated to a temperature higher than the melting point of the dye and the developer from the decolored state, the color develops again, and the color is heated again to a temperature lower than the melting point, whereby the color development and decoloration can be repeated.

Therefore, the use of the reversible ink composition for ink-jet thermal recording of the present invention makes it possible to colorless a document which is valued for confidentiality, and only the sender or receiver of the document or image can recolor the document. It is possible to see.

The first necessary property of the ink composition for reversible ink jet thermal recording is that the ink has a sufficient coloring density. The ability to dissolve or disperse a dye or a developer satisfying the coloring density in the ink.

The second necessary property is that the color development speed by heating after printing and the color erasing speed by reheating are high, and the reversible thermosensitive material of the present invention satisfies these conditions.

The third necessary characteristic is the stability of ink ejection, and the ink ejection direction does not bend and the ejection direction is always constant. As a wetting agent or a solubilizing agent in which the colorant dye is well dissolved or well dispersed, an optimum one must be used.

The components of the ink composition for reversible ink jet thermal recording include a dye constituting a colorant, a wetting agent, a viscosity adjusting agent, a surface tension adjusting agent, a preservative, and the like.

As the coloring agent in the ink composition, various dyes such as direct dyes, acid dyes, basic dyes, reactive dyes and disperse dyes have been used. In the ink composition for thermal recording, a dye which is a reversible thermosensitive material is used. Depending on the development of dyes, recording / erasing of color print images is also possible.

The ink jet thermal recording ink composition of the present invention has a wetting agent and a viscosity adjusting agent in addition to the dye as a coloring agent. The wetting agent is used even when the ink is dried at the nozzles of the print head. In addition, the solidification of the ink must be prevented, and the ink must always contain moisture due to its hygroscopicity, and the solubility and dispersibility of the dye must not be reduced. The viscosity adjusting agent is used to optimize the viscosity of the ink in the state of the particles, and the type and amount of the viscosity adjusting agent must be appropriate. It is preferable that the wetting agent also has a dissolving agent for the colorant.

As the aqueous wetting agent or viscosity modifier used in the ink, there are ethylene glycols. Examples of the ethylene glycols include ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol # 100, polyethylene glycol # 200, polyethylene glycol # 300, and polyethylene glycol # 400.

These ethylene glycols prevent solidification of the ink even for long-term storage, and do not cause clogging of the print head. Further, the present invention provides an ink composition for ink-jet thermal recording having stable ink characteristics without changing the physical properties of the ink or deteriorating the ink.

Similarly, as a non-aqueous wetting agent or viscosity adjusting agent, it must be liquid in use. If a solidifying material is used, the ejection of the ink is stopped, and the nozzle is clogged when the ink dries.

In order to solve this problem, the present inventor has developed an ink containing a colorant dissolving agent which enhances the solubility and dispersibility of the colorant and does not cause clogging, and has been described above. The present invention has been accomplished by solving the problem of obtaining an ink composition having the characteristics of an ink for use.

The ink composition for ink-jet thermal recording of the present invention is filled in an ink supply section or an ink flow path of an ink-jet printer, and the components in the ink do not precipitate even when left for a long period of time. The ink can be supplied to the unit without difficulty, and the ink droplets can be ejected without distortion, so that the ink ejection characteristics are good.

In addition, since the dye or developer as a colorant has high solubility, the nozzle is not clogged even when it is filled in a print head of an ink jet printer and left for a long period of 6 months or more. In addition, the ink ejection direction is very stable.

The nozzle diameter is wide depending on the type of print head used in the ink jet printer. For example, the nozzle diameter can be changed to 50 to several hundreds μm. However, when the nozzle diameter in this range is used, no clogging of the nozzle is caused. .

The dye and the developer in the ink composition used in the present invention are represented by the following structural formulas (I) to (VII).
It is a compound of I).

[0027]

Embedded image (In the formula, n is an integer of 1 to 4.)

[0028]

Embedded image (In the formula, n is an integer of 1 to 4.)

[0029]

Embedded image (In the formula, n is an integer of 1 to 4.)

[0030]

Embedded image (In the formula, n is an integer of 1 to 4.)

[0031]

Embedded image (Where X is Cl, Br or I, and n is an integer of 1 to 4.)

[0032]

Embedded image (Where X is Cl, Br or I, and n is an integer of 1 to 4.)

[0033]

Embedded image (Where X is Cl, Br or I, and n is an integer of 1 to 4.)

[0034]

Embedded image (Where X is Cl, Br or I, and n is an integer of 1 to 4.)

Specifically, the following compounds can be mentioned.

[0036]

Embedded image

[0037]

Embedded image

FIG. 1 to FIG. 4 are explanatory views of the color development and decoloration states using the heating means. FIG. 1 shows a printing state on plain paper by an ink jet, and the characters and images after printing are colorless and cannot be read.

FIG. 2 shows a state of color development by heating the heating roller after printing. By heating the printing surface to a temperature equal to or higher than the melting point of the dye or the developer, characters and images are colored and visualized.

FIG. 3 shows a decolored state due to the heating of the heating roller after color development, in which the colored color of characters and images disappears by reheating to a temperature lower than the melting point of the dye or developer,
Return to a colorless state.

FIG. 4 shows the state of color development by irradiation of an infrared lamp after printing. By irradiating the printing surface with a temperature higher than the melting point of the dye or the developer and heating it, characters and images are colored and visualized. .

When the color is reheated by irradiating an infrared lamp to lower the melting point of the dye and the developer after the color is formed, the color of the characters and images disappears, and the color returns to a colorless state. The recording sheet for recording characters and images may be paper coated with a developer or a plastic sheet. It suffices if the dye in the ink and the developer on the recording sheet such as a recording paper or a plastic sheet dissolve and form a color to form a clear character or image.

[0043]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described specifically based on embodiments, but the present invention is not limited to these embodiments.

Example 1 Ink Composition 1 (Component): (Weight Content) Dye: 3.0% by Weight

[0045]

Embedded image

Wetting agent, dissolving agent: triethylene glycol 13.0% by weight Solvent: ion exchange water 84.0% by weight

The above-described ink composition for thermal recording is printed by an inkjet printer on a recording paper coated with the following developer with a water-soluble resin PVA. At this time, the printing surface is colorless. Developer applied to recording paper:

[0048]

Embedded image

Next, the dye printed on the recording paper and the color developer applied to the recording paper are heated to 200 ° C. by a heating roller, whereby the printed portion develops color. The developed image is again erased by heating to 130 ° C.

Example 2 Ink Composition 2 (Component): (Weight Content) Dye: 3.5% by Weight

[0051]

Embedded image

Wetting agent, dissolving agent: diethylene glycol 14.0% by weight Solvent: ion-exchanged water 82.5% by weight

The ink composition for thermal ink-jet recording of the above-mentioned components was prepared by an ink-jet printer in Example 1.
Is printed on recording paper coated with the developer (a). At this time, the printing surface is colorless.

Next, by heating the dye and developer of the ink on the recording paper to 200 ° C. with a heating roller, the printed portion develops color. The developed image is again erased by heating to 130 ° C.

Example 3 Ink Composition 3 (Component): (Weight Content) Dye: 3.0% by Weight

[0056]

Embedded image

Wetting agent, dissolving agent: ethylene glycol 13.5% by weight Solvent: ion-exchanged water 83.5% by weight

The ink composition for ink-jet thermal recording of the above-mentioned components was prepared by an ink-jet printer in Example 1.
Is printed on recording paper coated with the developer (a). At this time, the printing surface is colorless.

Next, the printed portion is colored by heating the dye and developer of the ink on the recording paper to 200 ° C. with a heating roller. The developed image is again erased by heating to 130 ° C.

Example 4 Ink Composition 4 (Component) (Weight Content) Dye: 3.5% by Weight

[0061]

Embedded image

Wetting agent, dissolving agent: ethylene glycol 13.0% by weight Solvent: ion-exchanged water 83.5% by weight

The ink composition for ink-jet thermal recording of the above-mentioned components was prepared by an ink-jet printer in Example 1.
Is printed on recording paper coated with the developer (a). At this time, the printing surface is colorless.

Next, the printed portion is colored by heating the dye and developer of the ink on the recording paper to 200 ° C. with a heating roller. The developed image is again erased by heating to 130 ° C.

[0065]

According to the present invention, an ink-jet printing method is provided in which an ink composition containing a colorant made of a reversible heat-sensitive material is used to print on a recording sheet coated with a color developer and heat to perform color development and decoloration. The confidential document can be temporarily erased by the thermal recording method. Moreover, the ink composition for ink-jet thermal recording of the present invention has a sufficient color density at the time of color development, a high color development speed and a high color erasure speed, good ink ejection stability, and good color repetition of color development and erasure. Can respond to.

Further, in the present invention, by using a reversible heat-sensitive material having a specific structural formula (I) to (VIII) as a coloring agent in the ink composition, a developer is applied with the ink composition. Inkjet thermal recording, which prints on a printed recording sheet and heats it to develop and erase colors, can temporarily erase confidential documents with clear characters and images, and more effectively repeats coloring and erasing. Can be done

In the present invention, by setting the content of the colorant in the ink composition to 1 to 5% by weight, printing is performed on a recording sheet coated with a color developer using the ink composition, and the color is formed by heating. By virtue of the ink-jet thermal recording method of clearing and erasing, clear characters and images can be recorded more effectively, and can be temporarily erased, and moreover, repetition of coloring and erasing can be performed more favorably.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a printing state using an ink composition of the present invention.

FIG. 2 is an explanatory diagram showing a color development state by heating a heating roller after printing using the ink composition of the present invention.

FIG. 3 is an explanatory diagram showing a decolored state by heating a heating roller after printing using the ink composition of the present invention.

FIG. 4 is an explanatory diagram showing a color development state by irradiation of an infrared lamp after printing using the ink composition of the present invention.

Claims (10)

[Claims] 1. An ink composition comprising a colorant comprising a reversible thermosensitive material, a wetting agent, and a solvent or a dispersion medium, which is printed on a recording sheet coated with a developer with the ink composition. A printed image that develops or loses color by heating the recording sheet to a predetermined temperature. 2. The ink composition for ink-jet thermal recording according to claim 1, wherein the reversible thermosensitive material constituting the colorant is a compound represented by the following structural formula (I). Embedded image (In the formula, n is an integer of 1 to 4.) 3. The ink composition for ink-jet thermal recording according to claim 1, wherein the reversible thermosensitive material constituting the colorant is a compound represented by the following structural formula (II). Embedded image (In the formula, n is an integer of 1 to 4.) 4. The reversible thermosensitive material constituting the colorant is a compound represented by the following structural formula (III).
3. The ink composition for ink-jet thermal recording according to item 1. Embedded image (In the formula, n is an integer of 1 to 4.) 5. The ink composition for thermal ink jet recording according to claim 1, wherein the reversible thermosensitive material constituting the colorant is a compound represented by the following structural formula (IV). Embedded image (In the formula, n is an integer of 1 to 4.) 6. The ink composition for ink-jet thermal recording according to claim 1, wherein the reversible thermosensitive material constituting the colorant is a compound represented by the following structural formula (V). Embedded image (Where X is Cl, Br or I, and n is an integer of 1 to 4.) 7. The ink composition for thermal ink jet recording according to claim 1, wherein the reversible thermosensitive material constituting the colorant is a compound represented by the following structural formula (VI). Embedded image (Where X is Cl, Br or I, and n is an integer of 1 to 4.) 8. The reversible thermosensitive material constituting the colorant is a compound represented by the following structural formula (VII).
3. The ink composition for ink-jet thermal recording according to item 1. Embedded image (In the formula, X is Cl, Br or I, and n is an integer of 1 to 4.) 9. The reversible thermosensitive material constituting the colorant is a compound represented by the following structural formula (VIII).
3. The ink composition for ink-jet thermal recording according to item 1. Embedded image (Where X is Cl, Br or I, and n is an integer of 1 to 4.) 10. The ink composition having a colorant content of 1
The ink composition for ink-jet thermal recording according to any one of claims 1 to 9, wherein the amount is from 5 to 5% by weight.