JPH0729445B2 - Image forming method - Google Patents

Description

TECHNICAL FIELD The present invention relates to an image forming method using an inkjet method.

[Prior art]

Conventionally, a so-called ink jet method in which ink droplets are ejected to form dots as a means for forming characters or images on a recording medium (for example, a printing paper), a thermal method using a thermal paper that develops heat, or a heat-melting method is used. There is a thermal transfer method that uses an ink ribbon, and each method is individually devised to change the shade of the printing state and perform multicolor printing. However, in the inkjet method, in order to change the shade and to perform multi-color printing, the nozzle diameter must be reduced and the dot density must be increased to increase the device complexity, clogging, and printing. There were various problems such as slow speed. On the other hand, in order to achieve the light and shade change by the thermal method, it is necessary to increase the dot density, finely control the driving voltage and driving current of the thermal head and the heat pulse width thereof, as in the ink jet method described above. The thermal paper became very delicate, and the equipment became complicated, leading to lower reliability and higher costs. Further, both types have a drawback that they cannot cope with the change in shading in the state of multicolor printing.

〔Purpose〕

The present invention has been made in view of the above-mentioned prior art, and an object of the present invention is to obtain a high-quality image without requiring miniaturization of the nozzle diameter and reduction of the image forming speed, which is simple and inexpensive. And an image forming method capable of facilitating ink drying on a recording medium and faithfully and easily reproducing grayscale changes and multicolor recording corresponding to image information while forming an image. Is.

〔Constitution〕

The present invention provides a first step of forming an image by applying a colored ink to a recording medium by an inkjet method, and heating the image with the colored ink according to image information to change the density of the image, The second object is to achieve the above object by an image forming method characterized in that it has a second step of promoting the drying.

〔Example〕

The present invention will be described in detail below with reference to the embodiments shown in the drawings.

1 and 2 show an embodiment of a dot printer suitable for carrying out the image forming method of the present invention. In these drawings, reference numeral 1 (1A, 1B) is attached to a frame 2. The platen 3 is a carriage that is slidably guided in the left-right direction by the guide members 4 and 5, and a ceramic substrate 6 is provided on the front end side (platen side) of the carriage 3 and The pressure contact surface has a structure in which a plurality of heating elements 7 are arranged. Also,
A storage portion 9 for storing ink 8 which is supplied from an ink supply source (not shown) in the carriage 3 and whose concentration changes due to a temperature difference, a nozzle portion 10 for ejecting the stored ink 8, A piezoelectric conversion element which is arranged around the nozzle portion 10 and contracts the nozzle portion 10 to form an ink droplet.
11 is built in. The nozzle part
As is apparent from FIG. 2, 10 is provided so as to be located below the ceramic substrate 6 having a plurality of heating elements 7. Also, although not apparent from the figure, the heat generation adjacent to the heating elements 7 The pitch with the body 7 and the pitch between the nozzle portion 10 and the adjacent nozzle portion 10 are the same.

Next, the operation of the dot printer having the above configuration will be described.

When the recording medium 12 is fed to a predetermined position by a paper feeding means (not shown), that is, a position facing the nozzle portion 10, the carriage 3 starts to move by a carriage moving means (not shown). Then, an electric signal is input to the piezoelectric conversion element 11 from a control circuit (not shown), and the piezoelectric conversion element 11 sequentially contracts and relaxes in response to the electric signal.

As a result, ink droplets fly from the tip of the nozzle portion 10 to form characters and images on the recording medium 12. When the characters and images formed in the above process are sent to a position facing the ceramic substrate 6 by a paper feeding means (not shown), the control circuit synchronizes with the movement of the carriage 3 in the digit direction and a required electric signal is generated. Is input to the heating element 7. Then, only the portion of the already formed character or image where the shade change is desired is heated to change the shade.

Fig. 3 shows the control system for the change of shading, and CPU (control circuit) 20
A plurality of (three in the illustrated example) timers TM1, TM2, TM3 for setting the heating time are provided between the heating element driving circuit 21 and the heating element driving circuit 21. The heating element drive circuit 21 energizes the heating element 7 of the print head with the electric power PW for the time set by the timer.

The CPU 2 operates a predetermined one of the timers TM1, TM2 ... With different set times based on the grayscale information S. When the density is high, the heat application time is long, and when the density is low,
The heat application time is controlled to be short.

Further, FIG. 4 shows another structural example of a print head suitable for carrying out the present invention, 13 is a hybridized print head, and this print head 13 has a plurality of heating elements 14 and
It integrally has a plurality of ink droplet ejection nozzle portions 15 located below the heating element 14. Further, FIG. 5 shows an embodiment in which the nozzle 3 for cyan color, the nozzle portion 18 for magenta color, and the nozzle portion 19 for yellow color are arranged side by side on the carriage 3 in order to eject ink droplets for multicoloring. ing.

It should be noted that the ink used in the present invention may be any one as long as its density is improved or decreased depending on the amount of heat applied,
The ink is not particularly limited as long as it has the above-mentioned function.

Hereinafter, the present invention will be described with reference to examples of inks suitably used when carrying out the present invention. Dyes or pigments with hiding properties, hiding inks containing the vehicle as the main component, and microcapsules containing a foaming agent are dispersed in a colored ink in which dyes or pigments used in the field of recording or printing are dissolved or dispersed in a vehicle. The recording density can be changed from a dark color to a light color by applying heat by using the ejected ink. In the above case,
It is preferable to dye the wall of the capsule in the same color as the colored ink. On the other hand, the recording density can be changed from a light color to a dark color when heat is applied by using the jetting ink in which the color ink is made a light color and the concealing ink contained in the capsule is made a dark ink. Furthermore, the mechanism of the density change of the present ink will be described in detail when a jet ink that changes from a dark color to a light color is used. By ejecting the ejected ink from the nozzle portion onto the recording medium, the ejected ink adheres to and permeates the recording medium to obtain a dark-color recorded image. Further, by applying heat on the recorded image, the foaming agent in the microcapsules transferred to the recording medium is decomposed, the capsule wall is destroyed, the hidden ink hides the recorded image, and the dark recorded image becomes lighter. .

By appropriately selecting the type of the foaming agent, it is possible to produce microcapsules that can be destroyed at various temperatures, and by adjusting the addition amount of the microcapsules, it is possible to obtain extremely good gradation. Can be issued.

As the colorant used in the present invention, various dyes and pigments widely used in the fields of printing and recording can be used. The ink vehicle does not matter whether the ink type is water-soluble or water-insoluble, and water, oil, etc. can all be used.Ink viscosity, surface tension, penetrability into recording media, solubility or dispersibility of pigments, etc. It is also possible to add an activator, a filler, etc. for adjusting As the foaming agent, a thermally decomposable foaming agent and an easily volatile organic liquid are generally known, but in the present invention, the former one is preferably used and is a substance that chemically decomposes to generate a gas by heating. Among them, those satisfying the following conditions are preferably used. That is, (1) it can be stably dispersed or dissolved in the ink vehicle, (2) it is stable at room temperature and decomposes at 200 ° C or lower, (3) that the decomposed gas is not corrosive or toxic, (4) ) The decomposed gas has no unpleasant odor or contamination, and (5) the decomposed gas itself or its decomposed residue does not react with the ink material to cause discoloration or deterioration. Further, if necessary, a foaming auxiliary agent may be added in order to adjust the decomposition temperature of the foaming agent. Examples of the thermally decomposable foaming agent include bicarbonate such as sodium carbonate, carbonate such as ammonium carbonate, azide compound such as CaN ₆ , azodicarbonamide, N, N′-dinitropentaethylenetetramine and the like. . Examples of the foaming aid include lactic acid and guanidine ethanolamine carbonate.

The composition ratio of the hiding ink contained in the microcapsules is preferably in the range of 5 to 60 wt% of colorant, 40 to 95 wt% of vehicle, 0.1 to 10 wt% of foaming agent, and 0 to 10 wt% of foaming auxiliary agent. In addition, the composition ratio of the jet ink is 5 to 50
The range of wt%, vehicle 40 to 95%, capsule 5 to 50% is preferable.

Example 1. Titanium oxide 40 parts Diotatyl phthalate 60 parts Azodicarbonamide 5 parts Terephthaloyl chloride 0.4 parts The above composition was kneaded in a ball mill for 24 hours to obtain a white hiding ink. The ink was added to 400 ml of 0.5 wt% sodium bicarbonate water using a homomixer to obtain oil droplets having a particle size of 1 to 2 μ.
Emulsify and disperse. While continuing stirring, add 100 ml of 10% ethylene glycol, continue stirring for 10 minutes, and then spray dry using a spray dryer.
Polyester wall microcapsules (1) containing ˜2μ of white hiding ink containing a foaming agent were obtained.

Nigrosine 15 parts Oleic acid 60 parts Octyl oleate 15 parts Microcapsule (1) 10 parts The above composition was mixed and stirred to obtain a jet ink. When the ink obtained as described above was ejected from the nozzles, black clear recording having a reflection density of 1.1 was obtained on the recording paper. Furthermore,
When heat was applied by the heating element so that the recorded image was 150 ° C, the recorded image dropped to a reflection density of 0.7, and at 180 ° C, it was 0.
Fell to 4.

Example 2. Titanium oxide 40 parts Dioctyl phthalate 60 parts Azodicarbonamide 5 parts Ethanolamine 0.3 parts Terephthaloyl chloride 0.4 parts Microcapsules (2) were prepared from the above composition in the same manner as in Example 1.

Nigrosine 15 parts Oleic acid 60 parts Octyl oleate 15 parts Microcapsules (2) 10 parts A jetted ink was prepared from the above composition in the same manner as in Example 1 and recording was carried out to obtain a recorded image with a reflection density of 1.1. It was
Furthermore, when heated with a heating element, 0.1 at 100 ° C and 0.4 at 130 ° C.
The recording density decreased.

Example 3. Nigrosine 15 parts Oleic acid 60 parts Octyl oleate 15 parts Microcapsules (1) 5 parts Microcapsules (2) 5 parts The jetted ink record made from the above composition has a reflection density of 1.
Although it was 1, when the applied temperature was changed from 80 ° C to 180 ° C, the corresponding part was extremely favorably light-colored, and a high gradation recorded image was obtained.

〔effect〕

As is clear from the above description, according to the image forming method of the present invention, the first step of forming an image by applying the coloring ink to the recording medium by the inkjet method, and the image by the coloring ink according to the image information. It is characterized by having a second step of heating the ink to change the density of the image and promoting the drying of the ink, so that the nozzle diameter can be increased without reducing the nozzle diameter or the image forming speed. It is possible to obtain a high-quality image, to promote the drying of ink on the recording medium with a simple and inexpensive structure, and to faithfully and easily reproduce the gradation change and multicolor recording corresponding to the image information to form an image. An image forming method capable of performing the above is provided.

[Brief description of drawings]

FIG. 1 is a perspective view of an essential part showing an embodiment of a dot printer suitable for carrying out the image forming method of the present invention, FIG. 2 is a sectional view of a printing portion of the dot printer, and FIG. FIG. 4 is a block diagram schematically showing the system, FIG. 4 is a front view showing another embodiment of the print head, and FIG. 5 is a front view of a carriage having multicolor nozzles. 7 ... Heating element, 8 ... Ink, 10 ... Nozzle part, 11 ...
Piezoelectric element, 13 ... print head, 14 ... heating element, 15, 17, 1
8,19 …… Nozzle part.

Claims (1)

[Claims] 1. A first process of forming an image by applying a colored ink to a recording medium by an inkjet method, and heating the image by the colored ink according to image information to change the density of the image, and And a second step of promoting the drying of the ink.