JPH11170584A - Thermal transfer printer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the energy of a thermal head in order to enhance printing density, to prevent the printing omission caused by the folding wrinkles of an ink sheet generated by an increase and unbalance in the heating elongation of the ink sheet caused by executing printing offset left and right and to reduce the color shift of color printing. SOLUTION: Drive means 21, 31 driving the supply roll 2 and taking-up roll 3 of an ink sheet 1, a tension applying means 31 applying the front tension on the side of the ink sheet taking-up roll 3 to the printing position of the thermal head 4 of the ink sheet 1 and a tension applying means 21 applying back tension to the supply roll 2 are provided and the front tension applying means 31 changes over front tension on and after to tension stronger than that at the start time of printing on the way of printing.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal transfer printer, and by controlling the tension of an ink sheet at the time of printing, it is possible to reduce image quality, in particular, color omission due to wrinkling of the ink sheet and positional deviation between respective colors at the time of overlapping printing of color printing. We are trying to prevent it.

[0002]

2. Description of the Related Art FIG.
And FIG. 7 is a perspective view showing a configuration of a main part of a conventional thermal transfer printer disclosed in Japanese Unexamined Patent Publication (Kokai) Publication. 6 and 7,
Reference numeral 1 denotes an ink sheet on which yellow (Y), magenta (M), cyan (C), and black (K) inks are arranged on the surface of the base film 1a in a plane-sequential manner. Reference numeral 2 denotes a supply roll for supplying the ink sheet 1, and reference numeral 3 denotes a take-up roll for winding the ink sheet 1 from which ink after thermal transfer has been removed. 4 is a thermal head, 5 is a heating element of the thermal head 4, 6 is a peeling member provided on the thermal head 4 on the downstream side in the transport direction of the ink sheet 1, 7 is an ink sheet roller, 8 is a platen, and 9 is a printing paper. is there.

In the conventional thermal transfer printer, the ink sheet 1 and the printing paper 9 pass between the thermal head 4 and the platen 8 with
Is rotated so that the printing paper 9 and the ink sheet 1
It is conveyed by frictional force. At the same time, an electric signal is selectively applied to the heating element 5 of the thermal head 4, and the heating element 5 heats the ink sheet 1 and thermally transfers the ink to the printing paper 9 in accordance with the printing image. Further, the fed out ink sheet 1 is bent by the peeling member 6 and separated from the printing paper 9, and then wound up by the winding roll 3 through the ink sheet roller 7 in the direction of arrow W.

At this time, by selectively heating the thermal head 4 for printing, a part of the ink sheet 1 is heated and stretched as shown in FIG.
The heat extension part B of a occurs. The heated extension portion B is a material in which the material of the base film 1a of the ink sheet 1 is partially extended by heating, and is in a slack state as compared with a non-heated portion of the ink sheet 1.

FIG. 8 is an explanatory view showing a state in which folding and wrinkling have occurred in the ink sheet. 7 and 8, an arrow E indicates a weak tension of the ink sheet 1 generated at the heated extension portion B of the ink sheet 1. Arrow F is unstretched (unheated)
4 shows the winding tension of the ink sheet 1 generated at the portion of the ink sheet 1. G is a slack portion generated at the boundary between the heated extension portion B and the unheated portion. As described above, in the thermal transfer printing, the ink sheet 1 is loosened due to the heat elongation depending on the degree of heating during the thermal transfer. Then, at the boundary between the heated portion and the unheated portion, the ink slack portion G is in a swelled state. This phenomenon is particularly remarkable when the printing heating temperature of the thermal head 4 is increased in order to improve the printing density, and when half of the printing is performed in the scanning direction and the rest is unprinted.

In multicolor printing, the thermal head 4 is temporarily separated from the platen 8 at the start of the next color printing, and the printing paper 9 is printed.
And reset the ink sheet 1 with the ink sheet 1 at the head of the next color. When the thermal head 4 comes into contact with the platen 8 again at the start of the next color printing, the slack portion G is folded between the thermal head 4 and the platen 8, and a folding wrinkle H occurs. As a result, a problem occurs in which a fold W of the ink sheet 1 causes a portion K where an image is not transferred as shown in FIG. In FIG. 9, after the ink color of the ink sheet 1 is printed as magenta (M color),
An example in which a portion K in which the color of the next ink is not transferred to the head of cyan (C color) appears. Arrow J indicates the tension (back tension) of the ink sheet 1 on the supply roll 2 side.

[0007]

In the conventional thermal transfer printer as described above, the front tension on the take-up roll 3 side is increased, so that the slack portion G, which becomes a fold wrinkle, is extended to reduce the swelling. . But,
When the front tension (tensile force, ie, F + E) on the take-up roll 3 side is increased, the swelling of the slack portion G is reduced, but the weak tension E of the heated extension portion B of the ink sheet 1 and the unstretched (unheated) of the ink sheet 1 are caused. The difference from the normal tension F due to the winding of the ink sheet 1 generated in the portion becomes large.

For this reason, at the start of the next color printing, the thermal head 4 is brought into contact with the ink sheet 1 and the printing paper 9 sandwiched between the platens 8 to apply the front tension to start printing. Tension E
Is applied to the printing paper 9 through the ink sheet 1 and the printing paper 9 is slightly twisted. This movement position is the leading portion of the print, but at the rear end of the print, the amount of twisting movement is enlarged as shown in FIG. 10, causing color shift. Note that FIG. 10 shows an example in which the C color of the next color after the printing of the M color is shifted.

[0009]

According to the present invention, there is provided a thermal transfer printer for thermally transferring ink on an ink sheet on which ink is applied or printed in a face-to-face manner to a printing medium by a thermal head. Drive means for driving the take-up roll, tension applying means for applying a front tension on the take-up roll side of the ink sheet to the printing position of the ink sheet on the thermal head, and tension applying means for applying a back tension on the supply roll side. The tension applying means for the front tension switches the subsequent front tension to a tension higher than the tension at the start of printing during printing.

Further, in the above configuration, the back tension is switched to a tension lower than the tension at the start of printing by the tension applying means in response to the switching of the tension of the front tension of the ink sheet.

The switching of the tension is performed by gradually decreasing or gradually increasing the tension.

The drive means for the supply roll and the take-up roll of the ink sheet are DC motors, and these DC motors are used as tension applying means for applying front tension and back tension to the ink sheet by changing the applied voltage. It is a dual purpose.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 FIG. 1 is a configuration diagram showing a main part of a thermal transfer printer according to Embodiment 1 of the present invention. In the figure, reference numeral 1 denotes an ink sheet, and yellow (Y color) and magenta (M
Color), cyan (C color), and black (K color) inks are arranged in a plane-sequential manner. Reference numeral 2 denotes a supply roll for supplying the ink sheet 1, and reference numeral 3 denotes a take-up roll for winding the ink sheet 1 from which ink after thermal transfer has been removed. 4 is a thermal head, 5 is a heating element of the thermal head 4, 6 is a peeling member provided on the thermal head 4 on the downstream side in the transport direction of the ink sheet 1, 7 is an ink sheet roller, 8 is a platen, and 9 is a printing paper. is there.

Reference numeral 10 denotes a CP for controlling the thermal transfer printer.
U and 11 are drive control means for controlling the drive motors 21 and 31 of the supply roll 2 and the take-up roll 3. 2
Reference numerals 2 and 32 denote torque limiters provided between the drive motor 21 and the supply roll 2 and between the drive motor 31 and the take-up roll 3, respectively.
Denotes printing control means, and includes a thermal head 4, a platen 8
And the drive control means 11 and the like are controlled based on print data sent from a host computer (not shown).

FIG. 2 is a diagram showing the front tension of the ink sheet according to the first embodiment. In the figure, the vertical axis is the tension of the front tension, and the horizontal axis is the print length from the start to the end of printing. In the first embodiment, a signal is sent from the printing control means 12 to the torque limiter 32 so that the front tension of the ink sheet in the first half of the printing length is reduced and the front tension is increased in the second half of the printing length. , Changing its tension. In this tension change, the sudden change in the tension of the ink sheet as shown by the broken line in FIG. 2 is moderated by the extension elasticity of the ink sheet, but the thermal head 4 and the ink sheet during printing are alleviated. , Causing linear print unevenness in the print main scanning direction. Therefore, it is desirable to gradually and gradually change the tension as shown by the solid line in FIG.

As described above, by reducing the front tension of the ink sheet in the first half of the printing length, the heated and stretched portion of the ink sheet printed immediately before can be obtained.
Skew force S due to tension difference applied to unheated non-stretched part
Is reduced, the twist of the printing paper 9 through the ink sheet at the start of printing is reduced, and the color shift in the latter half of printing can be suppressed. Further, by increasing the front tension of the ink sheet in the latter half of the printing length, the slack portion G generated by the heating and stretching during printing is stretched, the amount of slack is suppressed, and the slack portion G is set when the next color printing is set.
The occurrence of non-transfer of an image due to the fold wrinkles H caused by entering between the thermal head 4 and the platen 8 can be reduced.

Embodiment 2 FIG. FIG. 3 is a diagram showing a change in the tension of the ink sheet according to Embodiment 2 of the present invention. FIG. 3A is the same as that showing the front tension of the first embodiment, and FIG. 3B shows the change of the back tension. In the first embodiment, when the front tension is increased in the second half of the printing length, the tension of the non-heated portions remaining at both ends of the ink sheet is applied from both sides toward the center of the ink sheet, and vertical wrinkles are generated on the ink sheet. Let it. When the vertical wrinkles multiply, the vertical wrinkles are folded between the thermal head 4 and the platen 8, and a non-printing line in the transport direction of the ink sheet occurs, thereby deteriorating the quality as a printed image. At this time, if the back tension is large, the wrinkles of the ink sheet grow rapidly. Therefore, FIG.
As shown in (b), if the back tension is reduced in accordance with the increase in the front tension, even if the ink sheet on the take-up roll 3 has a vertical wrinkle, the ink sheet on the supply roll 2 side will not be affected. It turned out that vertical wrinkles did not proliferate. Therefore, if the back tension is reduced in response to the increase in the front tension, it is possible to prevent the vertical wrinkles from being folded between the thermal head 4 and the platen 8.

Reducing the back tension in response to increasing the front tension during printing means increasing the difference in tension relative to the thermal head 4. Therefore, the position of the ink sheet easily changes with respect to the thermal head 4. In this case, the movement of the ink sheet with respect to the thermal head 4 can be prevented by gradually decreasing and gradually increasing the tension of the front tension and the back tension. This is particularly effective in eliminating printing unevenness in the scanning direction. Simultaneously performing the gradual decrease and the gradual increase simultaneously generates a relative tension difference with respect to the thermal head 4, so that the gradual decrease and the gradual increase are started with a slight time difference as shown in FIG. desirable.

Embodiment 3 FIG. 4 is a configuration diagram showing a main part of a thermal transfer printer according to Embodiment 3 of the present invention.
In the figure, 1 to 12 are the same as those in the first embodiment. 33 is a winding motor composed of a DC motor for driving and rotating the winding roll 3, and 23 is a supply roll 2
Is a supply motor composed of a DC motor that drives and rotates the motor. Here, a shunt or permanent magnet field DC motor is used.

In the first and second embodiments, the switching of the front tension and the back tension during printing is performed by the torque limiters 22 and 32, but the smooth increase and decrease of the tension are realized by the torque limiter. It was difficult to do. In the third embodiment, the winding motor 33 and the supply motor 23 are constituted by DC motors for smoothly increasing and decreasing the tension smoothly, and the switching of the tension from the printing control means 12 is performed via the DC motor drive control means 11. It is intended to be performed. Hereinafter, the tension control in the DC motor will be described.

Ink sheet 1 and printing paper 9 during printing
Is transported by a frictional force with the platen 8. The printing mechanism rotates the platen 8 at a predetermined rotation speed, and conveys the ink sheet 1 and the printing paper 9 at a constant speed V. When the winding motor 33 is driven to wind the ink sheet 1 at a speed V or higher with respect to the ink sheet 1 conveyed at the speed V,
The difference between the winding speed and the speed V is the front tension of the ink sheet 1 on the winding side. Similarly, when the supply motor 23 is driven so as to supply the ink sheet 1 at the speed V or less, the speed difference becomes the back tension on the supply side of the ink sheet 1. The rotation speed of the winding motor 33 and the supply motor 23, which are DC motors, can be easily changed by changing the applied voltage by the drive control unit 11.

FIG. 5 is a characteristic diagram of the DC motor, in which the horizontal axis represents torque, and the vertical axis represents rotation speed (rotation speed). In the figure, for a to b in the positive region, the DC motor rotates at a speed corresponding to the load from point a at a speed of 0 to point b at a no-load rotation speed. In the negative range b to c, since the torque becomes negative in a region where the rotation speed is larger than the point b of the no-load rotation speed, the rotation direction and the torque are opposite, and the DC motor operates as a brake. Taking advantage of this characteristic, the winding motor 33 uses the positive region of a to b,
, The winding of the ink sheet, the driving of the supply, and the control of the tension can be performed using the negative areas b to c.

As described above, the drive sources of the ink sheet take-up roll 3 and the supply roll 2 are constituted by the DC motors 33 and 23, and the driving and tension control of the DC motors 33 and 23 are performed.
By using the characteristic of the third embodiment, the drive control unit 11 performs the operation, so that the torque limiter 2 described in the first embodiment can be used.
This eliminates the need for 2 and 32, and makes it possible to switch the strength of the front tension and back tension of the ink sheet by smoothly increasing and decreasing the strength.

[0024]

As described above, according to the present invention, by increasing the front tension of the ink sheet in the latter half of printing, the slack portion of the ink sheet is stretched and the biting of the thermal head is prevented. Good image quality can be obtained.

Also, by reducing the back tension in response to increasing the front tension,
The occurrence of vertical wrinkles on the ink sheet is suppressed, and higher quality image quality can be obtained.

Also, by gently switching the tension, the latent movement of the ink sheet can be prevented, and an image quality with less color unevenness can be obtained.

Further, by performing the ink sheet conveyance and the tension control using the torque-rotation speed characteristic of the DC motor, more effective control can be performed with a simple configuration.

[Brief description of the drawings]

FIG. 1 is a configuration diagram illustrating a main part of a thermal transfer printer according to Embodiment 1 of the present invention;

FIG. 2 is a diagram illustrating a front tension tension of the ink sheet according to the first embodiment.

FIG. 3 is a diagram showing a change in tension of an ink sheet by a thermal transfer printer according to Embodiment 2 of the present invention.

FIG. 4 is a structural diagram showing a main part of a thermal transfer printer according to Embodiment 3 of the present invention.

FIG. 5 is a characteristic diagram of the DC motor according to the third embodiment.

FIG. 6 is a configuration diagram illustrating a main part of a conventional thermal transfer printer.

FIG. 7 is a perspective view showing a main part of a conventional thermal transfer printer.

FIG. 8 is an explanatory diagram showing a state in which folding wrinkles have occurred in the ink sheet.

FIG. 9 is a diagram illustrating a state in which print color omission has occurred due to folding and wrinkling of an ink sheet.

FIG. 10 is an explanatory diagram showing a state in which the printing paper is misaligned in printing.

[Explanation of symbols]

Reference Signs List 1 ink sheet, 2 supply roll, 3 take-up roll, 4 thermal head, 8 platen, 9 printing paper, 10 CPU, 11 drive control means, 12 print control means, 21, 31 drive motor, 22, 32 torque limiter, 23 , 33 DC motor, B Heat expansion part of ink sheet, E Weak tension generated in heat expansion part of ink sheet, F Normal tension generated in heat unaffected area of ink sheet, G Slack of heat affected area of ink sheet , H
Creases generated at the back of the heat-affected zone of the ink sheet.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Toshio Komori 2-3-2 Marunouchi, Chiyoda-ku, Tokyo Mitsubishi Electric Corporation

Claims (4)

[Claims] 1. A thermal transfer printer for thermally transferring, by a thermal head, ink on an ink sheet on which ink has been applied or printed in a face-to-face manner to a printing medium, a driving unit for driving a supply roll and a take-up roll for the ink sheet. A tension applying means for applying a front tension on the take-up roll side of the ink sheet and a tension applying means for applying a back tension on the supply roll side to a print position of the ink sheet on the thermal head; A thermal transfer printer wherein the front tension is switched to a tension higher than the tension at the start of printing on the way. 2. The thermal transfer printer according to claim 1, wherein the back tension is switched to a tension lower than the tension at the start of printing by the tension applying means in response to the switching of the front tension of the ink sheet. . 3. The thermal transfer printer according to claim 1, wherein the switching of the tension is performed by gradually decreasing or gradually increasing the tension. 4. A DC motor is used as a driving means for a supply roll and a take-up roll of the ink sheet, and these DC motors are used as tension applying means for applying front tension and back tension to the ink sheet by changing the applied voltage. The thermal transfer printer according to any one of claims 1 to 3, wherein the thermal transfer printer is also used.