JPH0432746B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thermal transfer color printing device,
In particular, the present invention relates to a thermal transfer color printing device capable of producing many halftone colors.

As is well known, a thermal transfer color printing device performs multicolor printing by thermally transferring each color ink of a color ink film coated with a plurality of heat-melting color inks onto printing paper.

FIGS. 1A to 1D are diagrams showing examples of various color ink films currently used in this type of printing apparatus. Figure A shows the configuration of a roll-shaped color ink film 1 for the field sequential method.
Hot-melt inks of Y (yellow), M (magenta), and C (cyan) colors are alternately applied in strips on a polyester film with a thickness of 5 to 6 μm. When printing a single sheet of color, first the printing paper and the Y color ink are overlapped, the Y color ink is melted using the heat of the thermal head, and then transferred to the printing paper (usually plain paper). Next, return the printing paper to its original position, advance the color ink film 1, overlap the M color and the printing paper, print M color, and finally print C color in the same way. Print to complete color printing. In this way, each color is printed sequentially on a plane-by-plane basis, so it is called a plane-sequential method.

Further, FIG. 7B shows a sheet-like color ink film 2 used in place of the roll-like color ink film 1, in which sheet-like color ink films 2a, 2b, 2c of each color of Y, M, and C are sequentially attached to a printing paper. Color printing is performed in a field-sequential manner.

Furthermore, FIG.
Color inks of Y, N, and C colors are alternately applied to a predetermined length. First, the Y color and the printing paper are superimposed, and the thermal head is sequentially moved to the right to print one line. next,
The color ink film 3 is sequentially fed, the M color and the printing paper are superimposed, the M color is printed on the line, and finally the C color is printed on this line. In this way, for each row, Y→M→C
Printing is performed in this order, and color printing is performed. This method is called the line sequential method.

Figure D shows three-color parallel film 4 for the line-sequential method.
It is a figure showing a schematic structure of. Accordingly, in order to print Y→M→C for each line, it is sufficient to shift the film 4 in the vertical direction.

If these types of color ink films 1 to 4 are used, a total of seven colors, including three colors Y, M, and C, as well as red, blue-purple, green, and black, can be produced as shown in Figure 2. . In addition, black ink was added to the above-mentioned color ink films 1 to 4.

By the way, in recent years, as the demand for color printers has increased, seven colors are not enough, and the demand for color printers that can produce halftone colors has increased.

In order to produce such halftone colors, it is necessary to have gradations, and there are two conventional techniques: the area gradient method and the density gradation method.

First, the area gradation method is a method of producing gradations by constructing one pixel by a matrix of several dots, as shown in FIG. 3A and B. In the figure, one pixel 5 is constituted by a matrix of 3.times.3 dots, making it possible to print in 10 gradations from 0 to 9. In addition, an example of gradation level 3 is shown in FIG.

In such an area gradation method, the dot density of the thermal head must be increased due to resolution. As a result, the structure of the thermal head becomes complicated and expensive, and the peripheral circuitry and power supply capacity become large, resulting in an expensive color printing apparatus as a whole. Furthermore, since the dot density increases, the printing speed also decreases.

On the other hand, in the density gradation method, the amount of heat generated by the thermal head is changed to adjust the amount of melted color ink, thereby producing gradations. According to this method, it should be possible to produce a large number of gradations steplessly, but
In reality, it has been difficult to control the amount of heat generated, and it has been difficult to achieve stable gradations.

In view of the above circumstances, this invention provides a thermal transfer type color printing device that can produce gradation stably at low cost without increasing the density of the thermal head. It is characterized by

Embodiments of the present invention will be described below with reference to the drawings.

FIGS. 4A to 4D are diagrams showing the structure of a color ink film according to an embodiment of the present invention, and these diagrams correspond to A to D in FIG. 1, respectively.
The difference between these color ink films and the conventional color ink films shown in Fig. 1 is that in addition to the three colors Y, M, and C, W (white) is also used.
This is the point where colored ink is applied. That is, in the roll-shaped color ink film 11 for the field sequential method shown in FIG.
The sheet-like color ink film 12 for the field sequential method shown in FIG.
c, 12d. In addition, in the tape-shaped color ink film 13 for the line sequential method shown in FIG. In the four-color parallel film 14 for
Four color inks, M, C, and W, are applied in parallel.

FIGS. 5A to 5D are diagrams schematically showing color printing using the color ink films 11 to 14 described above.

In FIG. 1A, color ink film 11 is overlapped with plain paper 21, and color printing is performed in a field sequential manner. First, when one page of Y color is transferred to the plain paper 21, the plain paper 21 is returned to its original position, and the color film 11 is sequentially fed so that the plain paper 21 and the M color are superimposed, and one page of plain paper 21 is transferred to the plain paper 21. Transcription takes place. Thereafter, C and W colors are transferred in the same manner, and one sheet of color printing is performed. In this case, the thermal head 15 is adapted to perform transfer in units of one dot line.

Next, in the same manner as shown in FIG. 4B, the plain paper 22 is reciprocated three and a half times, and overprinting of four colors of Y, M, C, and W is performed. In this case, the sheet-like color ink films 12a to 12d are discarded every time one page is printed.

In FIG. 3C, a tape-shaped color ink film 13 and plain paper 23 are overlapped, and color printing is performed in a line-sequential manner. First, the Y color and the plain paper 23 are superimposed, and the thermal head 16 is sequentially moved to the right to transfer one line of Y color.The plain paper 23 remains in the same position, and the color ink film 13 and the thermal The head 16 is sent to the left, the M color and the plain paper 23 are overlapped, and one line of the M color is transferred in the same manner as above. Thereafter, when each color of C and W is transferred in the same manner, the plain paper 23 is sent upward by one line, and the next line is printed.

Next, in Figure 2, the four-color parallel film 1
By shifting 4 up and down, each color Y, M,
The only difference from the above line sequential method is that C, W and plain paper 24 are overlapped, and the rest is the same, so the explanation will be omitted.

According to this embodiment, white blends into or overlaps the seven base colors formed by the three colors of Y, M, and C inks, making it possible to express an intermediate color. For example, as shown in FIG. 6, pink P can be created by melting white W onto red R, which is formed by mixing Y and M colors.

Next, the effect of adding white ink,
A 2×2 dot area gradation method will be explained as an example.

First, with ink film of three colors Y, M, and C,
Each color can express five gradations according to the number of dots of 0, 1, 2, 3, and 4, so in total, 5 x 5 x 5 = 125 ... (1) colors can be realized.

Next, by adding W color ink,
Assuming that it is possible to achieve 1/2 gradation color for each color Y, M, and C, all four dots can produce 1/2 gradation color, so in the 2 x 2 dot area gradation method, each color Y, Both M and C can realize the following nine gradations.

0, 1/8, 2/8, 3/8, 4/8, 5/8, 6/
8, 7/8, 8/8 In this case, since it is possible to realize even numbers of molecules without overlapping white colors (for example, 4/8 can be achieved with 2 bits), the superposition of white colors is achieved by having odd numbers of molecules. You only need to overlap one dot for objects. For example, to achieve 5/8 of Y color, two dots of only Y color and one dot of Y color and W color overlapped.
All you have to do is form them individually.

Next, we will consider how many colors can be expressed using the above method. In this case, care must be taken if any one of the three colors Y, M, and C has 8/8. In this case, because there is no place to print W color (if W color is printed, 7/8
This is because combinations with other colors are restricted. On the other hand, in the case of 7/8 or less, it is possible to ensure at least one place where W color is printed, so all combinations are possible, and the number of combinations is 8×8×8=512.

Next, if any one color has 8/8, W
Combinations of gradations that do not include color dots, i.e., those where the molecules of the other two colors are even numbers (excluding 8/8)
Can only be combined with 3×4×
There are 4 = 48 ways.

Similarly, if two colors have 8/8, 3 × 4 = 12 ways, and if three colors have 8/8, 1
This makes it possible to express a total of 573 different colors.

From the above, it can be seen that by using an ink film of four colors of Y, M, C, and W, it is possible to express approximately 4.6 times as many colors as in the case of the conventional three colors of Y, M, and C.

In addition, each ink film 11 to 14 of this example
In addition to the four colors Y, M, C, and W, it is also possible to add black.

As described above, the present invention uses an ink film having white ink in addition to Y, M, and C three-color inks as a halftone color printing means, so that the following effects can be achieved.

(1) Even color printers that do not have area gradation can easily express halftone colors.

(2) In color printers with area gradation,
Halftone colors can be easily doubled or more.

(3) Halftone colors can be easily expressed without increasing the dot density of the thermal head.

[Brief explanation of drawings]

Figures 1A-D are diagrams showing examples of various color ink films used in conventional thermal transfer color printing devices, Figure 2 is a diagram for explaining subtractive color mixing of three colors Y, M, and C; 3A and 3B are conceptual diagrams showing an example of the area gradation method, FIGS. FIG. 6 is a diagram for explaining color printing using a film, and FIG. 6 is a diagram for explaining a method of expressing intermediate colors by thermal transfer of white ink. 11, 12, 13, 14...Color ink film, W...White ink.

Claims (1)

[Claims] 1. In a thermal transfer type color printing device that performs multicolor printing by thermally transferring each color ink of a color ink film coated with a plurality of heat-melting color inks by an area gradation method or a density gradation method, A thermal transfer color printing device characterized by adding white ink to a film and mixing the white ink with the color ink to produce halftone colors.