THERMAL TRANSFER TYPE COLOR PRINTER

Abstract: In a thermal transfer type color printer, an ink film (6) on which plural color inks are sequentially painted in its longitudinal direction is sequentially transported forward between an ink film supply roll (7) and winding roll (9a), while a printing paper (2) is repeatedly transported forward and backward in order to print out a color image by overlapping plural color inks. In color printing, the printing paper and ink film are partially overlapped and wound around a platen roller (5), and a thermal head (10) is pressed against the platen roller by sandwiching the ink film and printing paper therebetween so that the thermal head transfers the color inks on the printing paper. In order to prevent wrinkles from being formed on the ink film, tension applying means (16, 25 to 31, 101) applies tension force to the ink film by temporarily controlling or stopping revolution of the ink film supply roll. In addition, such tension force is also applied while the printing paper is transported backward, so that printing start position of each color ink is accurately coincided with printing position of the thermal head. Thus, a desirable color image can be printed out without color dislocation and without forming un-transferred portions thereof.

Description: The present invention relates to a thermal transfer type color printer, and more particularly to a thermal transfer type color printer which prints out a color image of high quality without color deviation. As a color printer for printing out the color image which is displayed on a display screen of a personal computer or a display screen for computer aided design (CAD) or computer aided manufacturing (CAM), the thermal transfer type color printer is conventionally known. This thermal transfer type color printer performs color printing by transferring color inks of plural colors painted on an ink film to a printing paper. This thermal transfer type color printer has relatively simple construction, so that it is advantageous in that this printer can save much time and labor in maintenance and management thereof. Hereinafter, description will be given with respect to an example of this thermal transfer type color printer by use of Figs. 1 to 3. In Fig. 1, 1 designates a printer unit. At rear face of this printer unit 1, a printing paper supply roll 3 by which a printing paper 2 is wound up is supported by a bracket 1a so that the roll 3 can freely revolve. As shown in Fig. 2, a plurality of feed holes 2a,... are disposed in a longitudinal direction at both edge portions of the printing paper 2. As shown in Fig. 1, the printing paper 2 which is pulled out from the supply roll 3 is partially wound and guided by a guide roller 4 and a platen roller 5, and then the printing paper 2 is pulled out from the printer unit 1. The above-mentioned guide roller 4 and platen roller 5 are provided for conveying the printing paper 2. Sprocket pins 4a, ... are formed at outer peripheral face of the guide roller 4, while other sprocket pins 5a, ... are formed at outer peripheral face of the platen roller 5. The diameters of those sprocket pins 4a and 5a are smaller than those of the feed holes 2a of the printing paper 2. In addition, those sprocket pins are provided in connection with the feed holes as shown in Fig. 2. The shaft edge of platen roller 5 is interconnected with a motor (not shown), so that the platen roller 5 can revolve around the shaft line thereof in a forward direction (i.e., Y1 direction) and in a negative direction (i.e., Y2 direction). This revolution of the platen roller 5 is transmitted to the roller 4 via a belt (not shown). This belt is wound by the guide roller 4 and platen roller 5 so that round speed of the guide roller 4 will be equal to that of the platen roller 5 but revolving direction of the guide roller 4 will be inverse to that of the platen roller 5. Meanwhile, under the above guide roller 4, an ink film supply roll 7 by which an ink film 6 is wound up is mounted so that this supply roll 7 can freely revolve. As shown in Fig. 3, the color inks of yellow, magenta and cyan colors are sequentially painted in turn on the ink film 6, wherein the yellow, magenta and cyan colors are the primary colors of color image printing. The ink film 6 which is pulled out from the supply roll 7 is partially wound around outer portion of the printing paper 2 which is partially wound by the platen roller 5. Further, the ink film 6 is wound up by an ink film winding roll (hereinafter, simply referred to winding roll) 9a of ink film transporting means 9. This ink film feeding means 9 is provided for transporting the ink film 6 in its longitudinal direction, wherein this means 9 comprises the winding roll 9a and a drive unit (not shown) which revolves the winding roll 9a in Y3 direction. Under the above-mentioned platen roller 5, a thermal head 10 is provided. This thermal head 10 is provided so that this thermal head can be pressed against and also separated from the outer peripheral face of the platen roller 5. In the case where this thermal head is pressed against the ink film 6 wound around the outer peripheral face of the platen roller 5 while the printing paper 2 is inserted between this ink film and the platen roller, this thermal head gives thermal pulses to the ink film 6 so that the color ink painted on the ink film 6 is transferred on the printing paper 2. In the thermal transfer type color printer having the above-mentioned constitution, the color printing is performed in accordance with the following procedure. First, the platen roller 5 is revolved in the forward direction (i.e., Y1 direction) so that the printing start position of the printing paper 2 is transported to the printing position of the thermal head 10, while the winding roll 9a of the ink film transporting means 9 is revolved in the Y3 direction so that the head position of the yellow color ink painted on the ink film 6 (see Fig. 3) will be coincided with the printing position of the thermal head 10. Next, the thermal head 10 is pressed against the ink film 6 which is wound around the outer peripheral face of the platen roller 5 via the printing paper 2. Then, the platen roller 5 is revolved forward, and the printing paper 2 is transported toward the printing paper discharging side in the state where the printing paper 2 is piled with the ink film 6. In this state, the thermal pulses are adequately given to the thermal head 10, so that the yellow color ink is transferred on the printing paper 2. After completing the yellow color printing as described above, the thermal head 10 is separated from the ink film 6. Next, the platen roller 5 is revolved in the forward direction so that the printing paper 2 will be separated from the ink film 6. Then, the platen roller 5 is revolved in the reverse direction (i.e., the Y2 direction) by the predetermined distance so that the printing paper 2 is transported toward the printing paper supplying side (i.e., the right side in Fig. 1), whereby the printing start position of the printing paper 2 is returned back to the printing position of the thermal head 10. At the same time, the winding roll 9a of the ink film transporting means 9 is slightly revolved in the Y3 direction so that the head position of magenta color ink painted on the ink film 6 (see Fig. 3) will be coincided with the printing position of the thermal head 10. Similar to the case of yellow color printing, the thermal head 10 is pressed against the ink film 6 and the platen roller 5 is revolved in the forward direction so that the magenta color ink is transferred on the printing paper 2. Thus, the magenta color printing is completed. Next, similar to the above-mentioned printing procedure, the printing paper 2 is transported in the reverse direction and the ink film 6 is transported. Then, the cyan color ink is transferred on the printing paper 2. As a result, the color image is printed on the printing paper 2. Meanwhile, in the case where the thermal head 10 transfers the ink of ink film 6 on the printing paper 2 in the conventional thermal transfer type color printer, the thermal contraction must be effected on the ink film 6 due to the heat generated by the thermal head 10, so that the ink film must be wrinkled. For this reason, the ink film 6 must be folded so that certain portion of the ink film will be adhered to the printing paper 2. When the thermal transfer is performed in such state, it is difficult to transfer the ink of the folded portion of the ink film 6 to the printing paper 2. Hence, the transferred image will have the color deviation ,or there will be the un-transferred portion of the image. So, there is a disadvantage in that the desirable image can not be obtained. This must be remarkably emerged as the color deviation of image in the color printing for transferring plural colors, which deteriorates the image quality. On the other hand, since the three color inks painted on the ink film 6 are sequentially transferred on the printing paper in the conventional thermal transfer type color printer, the platen roller 5 is reversely revolved to the predetermined position so that the printing position of the thermal head 10 will be repeatedly coincided with the printing start position. This deteriorates the accurate coincidence between the printing position of the thermal head 10 and the printing start position of the printing paper 2 at the printing start timing of each color, and this also lowers the precision for repeatedly transferring each color ink. Therefore, there is a problem in that the color image having high quality can not be obtained. More specifically, the feed holes 2a, ... of the printing paper 2 are matched with the sprocket pins 5a, ... of the platen roller 5, and the platen roller 5 is revolved forward and backward so that the printing paper 2 can move forward and backward along the outer peripheral face of the platen roller 5. When the platen roller 5 is revolved forward so that the thermal head 10 is pressed against the ink film 6 in the printing period, the frictional force in the Y2 direction as shown in Fig. 3 is applied between the printing paper 2 and the outer peripheral face of platen roller 5 or the ink film 6 due to the pressure applied by the thermal head 10. Thus, the printing paper 2 is transported in the Y4 direction shown in Fig. 2, wherein each of the sprocket pins 5a, ... is regularly matched with each of the feed holes 2a, ... thereof. On the contrary, in the case where the printing paper 2 is transported in the direction reverse to the Y4 direction (i.e., in the backward direction), the thermal head 10 is separated from the ink film 6 and the pressure thereof is released, so that the above frictional force will not be applied. For this reason, the printing paper 2 is transported in the state where each of the sprocket pins 5a, ... is irregularly matched with each of the feed holes 2a, ... thereof. Even when the platen roller 5 is revolved backward to the predetermined position, the printing paper 2 must be transported in the unstably deviated manner in the range of the difference between the inner diameter of feed hole 2a and the outer diameter of sprocket pin 5a. Therefore, it becomes impossible to coincide the predetermined printing position of the thermal head 10 with the printing start position. In order to prevent the wrinkles of ink film from being formed and also prevent the color dislocation from being occurred, the conventional printer (as disclosed in Japanese Patent Application No. 57-180335) provides tension applying means by which tension force is applied to the ink film in the printing. As for this tension applying means, electromagnetic brake which is driven to be on or off is used. In addition, in order to adjust braking force with slip control of such electromagnetic brake, the voltage applied to the brake is controlled to become lower than the rated voltage. However, due to the mechanical variation of the brake and voltage variation of power source, it is difficult to accurately adjust the tension force applied to the ink film. JP-68286 also discloses a multicolor printer which uses an electromagnetic brake as a tension applying means. It is accordingly a primary object of the present invention to provide a thermal transfer type color printer by which the wrinkles of the ink film due to the thermal contraction are prevented from being formed so that the transferred image will not include the density deviation, color deviation and un-transferred portion, whereby it becomes possible to certainly print out the desirable characters and colors having good image quality. According to the present invention, there is provided a thermal transfer type color printer comprising: (a) an ink film supply roll for supplying an ink film on which plural color inks are painted in turn; (b) a winding roll for winding up the ink film; (c) a platen roller for transporting a printing paper, the printing paper being partially wound around an outer peripheral face of the platen roller, while the ink film being partially wound around the platen roller via the printing paper; (d) a thermal head which can be pressed against and separated from the platen roller, the thermal head being pressed against the platen roller by putting the ink film and printing paper therebetween so that heat applied by the thermal head melts and transfers the color ink on the printing paper during color printing, the thermal head being separated from the platen roller after performing the color printing; (e) tension applying means for applying tension force to the ink film between the ink film supply roll and the thermal head while the thermal head is pressed against the platen roller, characterised in that the tension applying means is mechanically operable on the supply roll so as to continuously apply tension to the ink film while the thermal head is pressed against the platen roller. Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings wherein preferred embodiments of the present invention are clearly shown. In the drawings: Fig. 1 is a sectional view showing the mechanical constitution of the conventional thermal transfer type color printer; Fig. 2 is a plan view of the printing paper; Fig. 3 is a plan view of the color ink film; Fig. 4 is a diagrammatically sectional view showing mechanical constitution of thermal transfer type color printer according to a first embodiment of the present invention; Fig. 5 is a sectional view showing mechanical constitution of an ink film supply roll used in the first embodiment shown in Fig. 4; Figs. 4 and 5 are sectional views both designating the first embodiment of the present invention. In Fig. 5, 11 and 12 designate holding shafts each holding an ink film supply roll 7. These holding shafts 11 and 12 are mounted to the printer unit 1 in a manner that the shaft lines thereof coincide with each other, so that these holding shafts can freely revolve. Each of holding members 13 and 14 for holding the ink film supply roll 7 is mounted at each of shaft edges of the holding shafts 11 and 12 which face to each other. The ink film supply roll 7 is mounted between these holding members 13 and 14, and a coil spring 15 around the holding shaft 12 presses the roll 7 so that this roll 7 will be forced to be held between these holding members. Thus, the assembly of the holding shafts 11 and 12 and the ink film supply roll 7 can integrally revolve. A frictional clutch 16 is mounted at another shaft edge of the holding shaft 11. This frictional clutch 16 is constituted as follows: a clutch shaft 18 is fixed to the holding shaft 11 by a screw 17; and a frictional board 19 is mounted to this clutch shaft 18. The vertically sectional shape of the holding shaft 11 is formed like the letter "D", and the hole shape of the clutch shaft 18 is also formed like the letter "D". Hence, the frictional board 19 can slide on the clutch shaft 18 in its shaft direction, and this frictional board can also revolve with the clutch shaft. The shaft 18 has a frictional board portion 18a formed like a brim, and frictional member 20, frictional board 21 and frictional member 22 are mounted to certain portion of the clutch shaft 18 between the frictional board 19 and the frictional board portion 18a in a manner that these members can be removed therefrom. A coil spring 24 is arranged between the frictional board 19 and an adjusting nut 23, and this coil spring 24 presses the frictional board 19, frictional member 22, frictional board 21 and frictional member 20 to the frictional board portion 18a. The adjusting nut 23 is screwed to the clutch shaft 18, so that the pressure applied by the coil spring 24 can be adjusted by this nut. In Fig. 4, a lever 25 is mounted to a fulcrum 26 provided in the printer unit 1 in a manner that this lever can freely revolve around the fulcrum. At the tip edge portion of the lever 25, a projection 25a is formed, and this projection 25a has the shape matching with each of concave portions formed between teeth 21a, ... of the above-mentioned frictional board 21. In addition, the lever 25 is connected to a rod 28 by a connecting pin 27 which is arranged between the projection 25a and fulcrum 26. The rod 28 is moved in Y5 direction by an actuator 29, and this rod 28 is connected to this actuator 29 by a connecting pin 30. The actuator 29 is connected to a control equipment (not shown). At only a time when the thermal head 10 is pressed against the platen roller 5, the actuator 29 is operated. When the actuator 29 operates, the lever 25 revolves in Y6 direction around the fulcrum 26, so that the projection 25a is moved to be matched with one of the concave portions between the teeth 25a. Further, the lever 25 is connected to a coil spring 32 by a pin 31 arranged under the fulcrum 26, and this coil spring 32 is fixed at the printer unit 1. When the actuator 29 stops operating, the lever 25 is forced to be revolved in the direction reverse to the Y6 direction by such coil spring 32 so that the lever 25 will be separated from the frictional board 21. When the thermal head 10 is pressed against the platen roller 5 and then the printing is performed in the thermal transfer type color printer having the constitution as described heretofore, the projection 25a of the lever 25 is moved to be matched with one of the concave portions between the teeth 21a of the frictional board 21. For this reason, the ink film supply roll 7 is controlled by the frictional force generated between the frictional board 21 and frictional members 20, 22, so that the tension force is applied to the ink film 6 between the thermal head 10 and ink film supply roll 7. Thus, it is possible to prevent the thermal contraction due to the heat of thermal head 10 from being effected on the ink film 6, so that the wrinkles of the ink film 6 can be prevented from being formed. Therefore, the density deviation, color deviation and un-transferred portion of the image can be eliminated, so that it becomes possible to certainly print out the characters and colors having good image quality. Further, since the ink film 6 and printing paper 2 are transported together by the platen roller 5 in the printing, the winding roll 9a must wind up the ink film 6 having the length transported by the platen roller 5. Therefore, even if the tension force is applied to the ink film 6 between the ink film supply roll 7 and thermal head 10, the torque due to such tension force must not be additionally applied to the motor of the winding roll 9a. Meanwhile, when the printing is not performed, the lever 25 is separated from the frictional board 21 so that the ink film supply roll 7 is not controlled by the above frictional force. Hence, the tension force is not applied to the ink film 6. For this reason, the motor having the capacity similar to that of the conventional motor is sufficient, and the motor having large torque is not required. Therefore, the present first embodiment do have the merit in that the image having high image quality can be obtained without enlarging the scale of the motor driving the winding roll 9. As described heretofore, the first embodiment provides tension applying means which applies the tension force to the ink film between the ink film supply roll and thermal head when the thermal head is pressed against the platen roller. Hence, the printing is performed while the ink film is pulled. For this reason, the thermal contraction due to the heat of thermal head is prevented from being effected on the ink film. In other words, it is possible to prevent the wrinkles from being formed on the ink film. Thus, the first embodiment can demonstrate the first effect in which the desirable characters and colors having good image quality can be printed out. Further, as described before, the winding roll does not need the motor of large capacity. Therefore, the first embodiment can also demonstrate the second effect in which the color image having high image quality can be obtained without enlarging the capacity of motor for the winding roll.

Claims: A thermal transfer type color printer comprising: (a) an ink film supply roll (7) for supplying an ink film (6) on which plural color inks are painted in turn; (b) a winding roll (9a) for winding up said ink film; (c) a platen roller (5) for transporting a printing paper (2), said printing paper being partially wound around an outer peripheral face of said platen roller, while said ink film being partially wound around said platen roller via said printing paper; (d) a thermal head (10) which can be pressed against and separated from said platen roller, said thermal head being pressed against said platen roller by putting said ink film and printing paper therebetween so that heat applied by said thermal head melts and transfers said color ink on said printing paper during color printing, said thermal head being separated from said platen roller after performing the color printing; (e) tension applying means (16,25 to 31) operable to apply tension force to said ink film between said ink film supply roll and said thermal head while said thermal head is pressed against said platen roller, characterized in that the tension applying means is mechanically operable on said supply roll so as to continuously apply tension to said ink film while said thermal head is pressed against said platen roller. A thermal transfer type color printer according to claim 1 wherein said tension applying means includes a frictional clutch (16) mounted to a holding shaft (11) of said ink film supply roll, said frictional clutch working to thereby apply the tension force to said ink film at only a time when said thermal head is pressed against said platen roller. A thermal transfer type color printer according to claim 2 wherein said tension applying means further includes tension control means which contains actuator means (29,30 etc.) and a lever (25) having a projection (25a) at its tip edge portion, while said frictional clutch including a frictional board (21) and frictional member (20,22), said frictional board having plural teeth (21a) on its outer peripheral face and revolving around said holding shaft (11), said actuator means being activated so that said projection of lever is moved to be matched with one of concave portions between said teeth of frictional board during the color printing, whereby frictional force generated between said frictional board and said frictional member controls and intermittently stops revolution of said ink film supply roll via said frictional board so that the tension force is applied to said ink film during the color printing.

Inventors: OGITA, HIROMITSU, TOIDA, AKIKAZU
Applicants: SHINKO ELECTRIC CO. LTD.
Application year: 1988
Main classification: B41J17
IPC codes: B41J35, B41J17