JPH0281676A - Halftone image recording method - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a thermal transfer recording method, and in particular to a method that makes it possible to easily record halftone images by controlling the heating temperature and time of the heating resistor element of the print head. The present invention relates to a halftone image recording method.

[Prior Art] Conventionally, ink sheets used in this type of thermal transfer recording method are
It has a structure in which an ink layer is provided directly on the base material, and by one heat generation of the heat generating resistor element, the ink in the heat generating portion of the ink sheet is peeled off and transferred onto the recording paper at once. For this reason,
The recorded dots on the recording paper can only obtain two values, black and white.

In recent years, the recording targets required of these recording devices have become more sophisticated, from text to images and from monochrome to color. However, since the above-mentioned conventional technology cannot achieve faithful halftone expression, the above-mentioned requirements have not been met. It is difficult to realize this.

For this reason, as an example of a method for obtaining a halftone image, there is a dye method in which the number of dots constituting one pixel of printing is changed, but a decrease in recording resolution is unavoidable.

The present invention provides a recording method that uses a novel thermal transfer recording ink sheet and applies appropriate recording energy to form halftone images with excellent resolution and good reproducibility even on plain paper.

[Means for Solving the Problems] According to the present invention, an ink sheet for thermal transfer recording is provided, in which an adhesive layer is provided on a base material, and microcapsules encapsulating a coloring material inside are coated on the adhesive M. , a printing head having a heating resistor element is pressed, and recording energy applied from the heating resistor element is changed stepwise according to the image to heat it, thereby reproducing a smooth halftone image on plain paper. It is possible.

The present invention will be explained in detail below with reference to the drawings.

FIG. 1 is a schematic sectional view showing the structure of an ink sheet used in the halftone image recording method of the present invention. An adhesive layer 3 is coated on a base material 1, and microcapsules 2 encapsulating a coloring material are arranged thereon. As the base material 1, capacitor SA, PET film, etc. are usually used. The adhesive layer 3 for bonding the base material 1 and the microcapsules 2 may be made of polyamide resin, polyester resin, or the like.

FIG. 1(b) is a schematic cross-sectional view of the microcapsule 2. FIG. The microcapsules 2 have a diameter of about 2 to 12 μm, and the coloring material 4 is wrapped in a shell 5. The coloring material 4 consists of a dye, a binder, a low melting point agent, etc. For example, dyes 1 to 2, binder 0
．． 1 to 10, and the low melting point substance can be comprised in the range of 1 to 99. Usually the weight ratio of shell and coloring material is 1.5~l:
About too much is enough.

In the above configuration, the microcapsules heated by the print head from the substrate side will melt to a different degree depending on the applied recording energy (heating energy of the heating resistor element), and if the energy is high, a large number of microcapsules will melt. When the energy is low, a small number of microcapsules melt more strongly, and the extent to which the coloring material inside the microcapsules is transferred to the recording medium also differs depending on the heat generation energy. As a result, the amount of color material transferred to the recording paper, that is, the size and density of the recording pixels, can be controlled as a function of the heat energy of the thermal head.

Furthermore, by widely distributing the melting point of the microcapsules within a temperature range corresponding to the heat generation energy from the heating resistor element, the heat generation energy and the degree of melting of the microcapsules become correlated over a wide temperature range. The stepwise heat generation energy from the body element corresponding to the pixel corresponds in a wide range to the extent of the coloring material to be transferred, and as a result, the density reproduction range and density variation on the recording paper can be improved.

The melting point of the microcapsules can be adjusted by the content of a low melting point agent in the colorant and/or the constituent materials of the shell, and can also be adjusted, for example, by changing the mixing ratio of glycerin and gelatin.

It is also possible to substantially change the melting point by changing the shell thickness and the melting heat energy.

Similarly, this can also be done by changing the thickness of the microcapsules.

Next, a method of changing heat generation energy by a heat generating resistor element in a stepwise manner according to an image according to the method of the present invention will be described.

FIG. 2 shows an example of a circuit diagram for heating a plurality of heating resistor elements in a thermal head in stages. In the figure, reference numeral 6 denotes a plurality of heat generating resistor elements within the thermal head, which are connected to a transistor 7 that turns on and off the heat generation of the resistor elements. Reference numeral 8 denotes a CPU, which stores image signals on a shift register 9, and further specifies tone signals for forming a halftone image to a strobe pulse control circuit 10. When both the digital signal output from the shift register 9 and the digital signal output in pulse form from the strobe pulse control circuit 1O are output, current flows from the AND circuit 11 to the transistor 7, and the emitter and collector of the transistor 7 The potential difference between them disappears, and the heating resistor element 6 generates heat.

Halftone images are recorded using the ink sheet and electric circuit configured as described above. In other words, the ink sheet and the recording paper are overlapped and moved while pressing the thermal head inside the printer from the base material side of the ink sheet, and the heating resistor element inside the thermal head is heated step by step. Toned image recording is performed, and at this time, the coloring material inside the microcapsules is transferred to the recording paper according to the heat energy of the thermal head. As a result, the amount of color material transferred to the recording paper, that is, the size and density of the recording pixels, can be controlled as a function of the heat energy of the thermal head.

Incidentally, generally known means can be used to prepare the ink sheet for thermal transfer recording according to the present invention.

[Example] Three types of microcapsules, yellow, magenta, and cyan, were prepared by an interfacial polymerization method, and the blending ratio of shell materials was varied so that the melting points of the capsules were distributed in a temperature range of 80 to 150°C.

The obtained microcapsules had a particle size of 1 to 10 μm, and the weight ratio of the shell to the coloring material was about 1:10.

To create an ink sheet, polyethylene terephthalate (CPET) with a thickness of 6 μm was used as a base material, and polyester resin was added on top of this using a ball mill using toluene as a solvent.
The mixed solution was coated with a bar coater to a thickness of about 1 μm to form an adhesive layer. The microcapsules prepared above were sprinkled on the adhesive layer before it was dry. After removing excess ink particles that did not adhere to the adhesive layer, it was sufficiently dried to obtain an ink sheet for thermal transfer recording.

FIG. 4 shows the sheet obtained. In the figure, 1 is a base material, 12, 13, and 14 are microcapsules in which coloring materials of three primary colors of yellow, magenta, and cyan are internally encapsulated, and 3 is an adhesive layer.

Yellow, magenta, and cyan ink colors are distributed on the ink sheet as shown in the diagram.

When we performed a solid image printing test on plain paper using a thermal head constructed from the circuit shown in Figure 2, we found that the recording density was affected by the thermal energy generated by the thermal head, as shown in Figure 3. The image changed accordingly, and beautiful midtones were recorded. (The heating temperature was approximately 80 to 200°C.) In other words, the relationship between the current pulse to the heating resistor element of the thermal head and the recording density is as shown in Figure 3, as can be seen from the solid line in the figure. In addition, in the ink sheet used in the halftone image recording method of the present invention, by changing the recording energy applied to the heating resistor element in stages, the recording density of the solid image also changes in stages, so that the halftone image can be recorded. Image recording was realized. On the other hand, when using a conventional ink sheet with an ink layer formed directly on the base material, even if the recording energy applied to the heating resistor element is changed stepwise as shown by the dotted line in the figure, Since the recording density did not change accordingly but changed rapidly, it was impossible to record halftone images.

Next, the obtained ink sheet for thermal transfer recording shown in FIG. 4 is superimposed on the recording paper and moved by a paper feeding system, and the ink sheet of the yellow coloring area is first printed using the same device as that used in the above printing test. A yellow halftone image is formed on the recording paper using the same method, and then the recording paper is returned to the standard position. Next, a magenta halftone image is formed, and then a cyan halftone image is formed, thereby creating a full-color density gradation. It was possible to record halftone images with good reproducibility.

[Effects of the Invention] As explained above, a heating resistor is applied to an ink sheet for thermal transfer recording in which an adhesive layer is provided on a base material, and microcapsules containing a coloring material are coated on the adhesive layer. A smooth halftone image can be recorded on plain paper with good reproducibility by pressing the print head having the element and heating it by changing the recording energy applied from the heating resistor element in stages according to the image. It becomes possible. According to the present invention, a complicated device is not required, and the device can be made smaller and lower in cost.

[Brief explanation of the drawing]

FIG. 1(a) is a cross-sectional view of an ink sheet used in the halftone image recording method of the present invention, FIG. 1(b) is a cross-sectional view of microcapsules in the ink sheet, and FIG. FIG. 3 is a circuit diagram for stepwise heating a plurality of heating resistor elements in a thermal head to be used. FIG. 4 is a diagram showing the relationship between energizing pulse width and recording density. FIG. 4 is a diagram showing the configuration of an ink sheet for full-color recording used in the halftone image recording method used in the embodiment of the present invention, and (a) is a schematic plan view. FIG. 3B is a schematic front cross-sectional view. l...Base material 2...Microcapsule 3...Adhesive layer 4...Color material 5...Shell 6...Heating resistor element 7...Transistor 8...CPU 9...・Shift register IO...Strobe pulse control circuit II...AND circuit 12...Microcapsule 13 filled with yellow coloring material...Microcapsule 14 filled with magenta coloring material...Cyan color Microcapsules encapsulating materials Patent applicant Canon Co., Ltd.

Claims (1)

[Scope of Claims] 1) An ink sheet for thermal transfer recording in which an adhesive layer is provided on a base material, and microcapsules encapsulating a coloring material inside are coated on the adhesive layer, and a heating resistor element is provided on the ink sheet. A halftone image, characterized in that a halftone image is formed on a recording medium by pressing a print head and heating the recording energy applied from the heating resistor element by changing it in stages according to the image. Recording method. 2) The halftone image recording method according to claim 1, wherein the melting point of the microcapsules is widely distributed within a temperature range corresponding to the stepwise recording energy from the heating resistor element.