Thermal transfer apparatus equipped with a curved ink ribbon separation bar

Abstract: In an ink ribbon separation device for use with a thermal transfer apparatus having a separation bar (6), the shape of the separation bar (6) is such that the thickness (C) of the bar in an ink ribbon travelling direction is greater at its center in the direction orthogonal to the ink ribbon travelling direction than that (S) at the ends thereof. The center bulges in a downstream direction in a bow shape at a rate of 10 to 200 µm with respect to a toner width of 100 mm.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the uniform separation of an ink ribbon of a thermal transfer apparatus, and more particularly, to a thermal transfer apparatus equipped with ink ribbon uniform separation means, which prints an image on an image receiving sheet by way of an ink ribbon and through use of a thermal head, the means reliably and simultaneously separating the ink ribbon at all points in a widthwise direction thereof. 2. Description of the Related Art Figure 10 is a perspective view showing the principal elements of a thermal transfer apparatus to which the present invention is applied. In Figure 10, reference numeral 1 designates a thermal head; 2 designates a platen disposed opposite to the thermal head 1; 3 designates a pair of conveyor rollers for carrying an image-receiving sheet 4; 5 designates an ink ribbon; 6 designates a separation bar; 7 designates a guide roller for the ink ribbon 5; and 8 designates a core for taking up the ink ribbon 5. In this thermal transfer apparatus, after ink has been thermally transferred to the image-receiving sheet 4 from the ink ribbon 5 by the application of heat to the thermal head 1, the image-receiving sheet 4 is separated from the ink ribbon 5. The separation bar 6 is provided for simultaneously separating the ink ribbon 5 from the image-receiving sheet 4 at all points in a widthwise direction. Despite the aforementioned configuration, the prior art suffers from a problem that the ink ribbon 5 fails to simultaneously separate from the image-receiving sheet 4 at all points in the primary scanning direction (i.e., the widthwise direction of the ink ribbon or the image-receiving sheet) after the printing operation. This is attributable to a tendency that in the existing thermal transfer apparatus, slight tension is applied to the center of the ink ribbon and the image-receiving sheet, while strong tension is applied to the side edges of the image-receiving sheet. Accordingly, since uneven tension is applied to the ink ribbon and the image-receiving sheet in the widthwise direction thereof, they are quickly separated at the side edges or slowly separated at their center in an upstream direction, thus resulting in irregularities in the separation of the ribbon from the sheet. In the event of such separation irregularities, ink is unevenly transferred to the image-receiving sheet, resulting in an ink transfer failure. Japanese Patent Unexamined Publication No. Hei.09-39349 describes a thermal transfer apparatus according to the preamble of claim 1, wherein a separation bar has a thickness in its center differing from that of the ends thereof, but fails to quantitatively disclose the thickness; the purpose of the curved separation bar is to avoid wrinkles in the ink ribbon. A similar structure is shown in JP-A-07-266649. In both prior art cases, the central part of the separation bar protrudes toward the thermal head. SUMMARY OF THE INVENTION The present invention has been made in view of the foregoing circumstances, and an object of the present invention is to solve the foregoing problem in the prior art, and to provide an ink ribbon separation device for use with a thermal transfer apparatus, the device being capable of preventing a transfer failure due to a separation failure. To achieve the foregoing object, there is provided a thermal transfer apparatus according to claim 1. Embodiments of the invention are defined in dependent claims 2 to 10. As mentioned above, the thermal transfer apparatus prevents nonuniform separation of the ink ribbon from the sheet in the widthwise direction by changing tension of the ink ribbon in the widthwise direction at a position downstream of the thermal transfer apparatus so that uniform tension is applied, which results in prevention of a transfer failure. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a top view showing a separation bar according to a first embodiment of the present invention; Figure 2 is a top view showing a separation bar according to a second embodiment of the present invention; Figure 3 is a front view showing a separation bar according to the second embodiment of the present invention; Figure 4 is a front view showing a separation bar according to the fourth aspect of the present invention; Figure 5 is a side view showing a guide roller for guiding an ink ribbon according to a first example of the sixth aspect of the present invention; Figure 6 is a side view showing a guide roller for guiding an ink ribbon according to a second example of the sixth aspect of the present invention; Figure 7 is a side view showing a core for taking up an ink ribbon according to a first example of the seventh aspect of the present invention; Figure 8 is a side view showing a core for taking up an ink ribbon according to a second example of the seventh aspect of the present invention; Figure 9 is a schematic representation showing an ink ribbon press member which is formed of a material of highly frictional coefficient and which is interposed between a thermal head and a separation bar, according to an eighth aspect of the present invention; and Figure 10 is a perspective view showing the principal elements of a thermal transfer apparatus to which the present invention is applied. DETAILED DESCRIPTION OF THE INVENTION Preferred embodiments of the present invention will be described in detail by reference to the accompanying drawings. An explanation will be principally given of embodiments comprising a separation bar 6, a guide roller 7 for an ink ribbon, and a core 8 for taking up the ink ribbon, all of which have unique shapes. Figure 1 is a top view showing a separation bar according to a first embodiment of the present invention. According to the first embodiment, the thickness of a separation bar 6a in an ink ribbon travelling direction is greater at its center C in a direction orthogonal to the ink ribbon travelling direction than that at the ends S thereof, and the separation bar bulges in a downstream direction in the form of a bow shape. In short, the separation bar 6a bulges at its center in a width direction and tapers down to its ends. As a result, the center C of the separation bar 6a applies the maximum tension to the ink ribbon 5 positioned downstream of the thermal head 1, and the tension symmetrically diminishes toward the ends S of the separation bar 6a. There exists a correlation relating to a difference in thickness between the center C and the ends S. As a result of several experiments, the desirable relationship between a toner width and the amount of protuberance of the center C of the separation bar 6a was found to be a rate of 10 - 200 µm (particularly preferably, a rate of 30 to 100 µm) with respect to a toner width of 100 mm. Accordingly, in the present embodiment, the center C should bulge at a rate of 50 to 500 µm, more preferably at a rate of 200 µm, with respect to a toner width of 330 mm. As a result, uniform tension is applied to the ink ribbon and the image-receiving sheet in their widthwise direction, preventing nonuniform separation of the ink ribbon from the sheet in an upstream position relative to the separation bar. Figure 2 is a top view showing a separation bar according to a second embodiment of the present invention. A spacer 9 is interposed between the center C of a separation bar 6b in a direction orthogonal to an ink ribbon travelling direction and the thermal head 1. The ends S of the separation bar 6b are screwed to the thermal head 1, thus curving the separation bar 6b in a direction designated by arrow F toward the side of the thermal head 1. By virtue of such a configuration, the center C applies the maximum tension to the ink ribbon in an upstream position relative to the separation bar 6b, and the tension symmetrically diminishes toward the ends S, as in the case of the separation bar shown in Figure 1. Coupled with the tensile characteristics of the thermal transfer apparatus, uniform tension is eventually applied to the ink ribbon and the image-receiving sheet in their widthwise direction, thus preventing them from being nonuniformly separated from each other in an upstream position relative to the separation bar. The difference between the thickness of the center C of the separation bar and that of the ends S is the same as that of the separation bar shown in Figure 1. As a result of several experiments, the desirable relationship between a toner width and the amount of protuberance of the center C of the separation bar 6a was found to be a rate of 10 - 200 µm (particularly preferably, a rate of 30 to 100 µm) with respect to a toner width of 100 mm. Accordingly, in the present embodiment, the center C should be bulged at a rate of 50 to 500 µm, more preferably at a rate of 200 µm, with respect to a toner width of 330 mm. As a result, uniform tension is applied to the ink ribbon and the image-receiving sheet in their widthwise direction, preventing nonuniform separation of the ink ribbon from the sheet in an upstream position relative to the separation bar. Figure 3 is a front view showing a separation bar 6c according to the third aspect of the present patent invention. The lower end of the separation bar 6c in the vertical direction has such a configuration that its center CU in a direction orthogonal to an ink ribbon travelling direction is lower than its ends SU by an amount of "t." Through use of the separation bar 6c having such a configuration, the center portion CU applies the maximum tension to the ink ribbon 5 in an upstream position relative to the separation bar 6c, and the tension symmetrically diminishes towards the ends SU. Coupled with the tensile characteristics of the thermal transfer apparatus, uniform tension is eventually applied to the ink ribbon and the image-receiving sheet in their widthwise direction, thus preventing them from being nonuniformly separated from each other in an upstream position relative to the separation bar. The difference between the thickness of the center CU of the separation bar 6c and that of the ends SU of the same is the same as that of the separation bar shown in Figure 1. Figure 4 is a front view showing a separation bar 6c according to the fourth aspect of the present invention. The center C of the separation bar 6c is formed so as to have a low frictional coefficient in a widthwise direction. The center C applies the maximum tension to the ink ribbon 5 positioned in a downstream position relative to the thermal head 1, and the tension symmetrically diminishes toward the ends S of the separation bar 6c. By virtue of the foregoing configuration, even if the ink ribbon and the image-receiving sheet are withdrawn in the downstream direction by uniform force, the maximum withdrawing force is exerted on the area of the ink ribbon 5 around the center C in an upstream position relative to the separation bar 6c, and the force symmetrically diminishes towards the ends S. Coupled with the tensile characteristics of the thermal transfer apparatus, uniform tension is eventually applied to the ink ribbon and the image-receiving sheet in their widthwise direction, thus preventing them from being nonuniformly separated from each other in an upstream position relative to the separation bar. The method of reducing the frictional coefficient of the center of the separation bar according to the present embodiment includes a method of covering with Teflon coating the hatched center portion of the separation bar 6c with respect to its widthwise direction (about half the entire width). Figure 5 is a side view showing a guide roller 7a for an ink ribbon according to the first example of the sixth aspect of the present invention. The guide roller 7a according to the first example bulges at the center C, and the thickness of the guide roller 7a decreases continuously toward the ends S thereof. The center C of the guide roller 7a applies the maximum tension to the ink ribbon 5 in an upstream position relative to the guide roller, and the tension symmetrically diminishes towards the ends S of the guide roller. There exists a correlation relating to a difference between the center C and the ends S. As a result of several experiments, the desirable relationship between a toner width and the diameter of the guide roller 7a was found to be a rate of 10-200 µm (particularly preferably, a rate of 30 to 100 µm) with respect to a toner width of 100 mm. The greater the width of the guide roller, the larger the diameter of the same. Accordingly, according to the first example, the center C of the guide roller 7a bulges at a rate of 50 to 500 µm, more preferably at a rate of 200 µm, with respect to a toner width of 330 mm. As a result, the center C applies the maximum tension to the ink ribbon 5 positioned in a downstream position relative to the thermal head 1, and the tension symmetrically diminishes toward the ends S of the guide roller 7a. Coupled with the tensile characteristics of the thermal transfer apparatus, uniform tension is eventually applied to the ink ribbon and the image-receiving sheet in their widthwise direction, thus preventing them from being nonuniformly separated from each other in an upstream position relative to the separation bar. Figure 6 is a side view showing a guide roller 7b for an ink ribbon according to the second example of the sixth aspect of the present invention. The guide roller 7b according to the second example bulges at the center C, and the thickness of the guide roller 7b decreases stepwise toward the ends S thereof. The center C of the guide roller 7a applies the maximum tension to the ink ribbon 5 in a downstream position relative to the thermal head 1, and the tension symmetrically diminishes towards the ends S of the guide roller. The correlation between the thickness of the center C and the thickness of the ends S is the same as that of the guide roller shown in Figure 5. By virtue of the foregoing configuration, the maximum withdrawing force is exerted on the area of the ink ribbon 5 around the center C in an upstream position relative to the thermal head 1, and the force symmetrically diminishes towards the ends S. Coupled with the tensile characteristics of the thermal transfer apparatus, uniform tension is eventually applied to the ink ribbon and the image-receiving sheet in their widthwise direction, thus preventing them from being nonuniformly separated from each other in an upstream position relative to the separation bar. Although the guide roller 7a, which is shown in Figure 5 and has its greatest thickness at the center C and the thickness decreases continuously toward the ends S thereof, is troublesome to manufacture, the guide roller 7b having a profile such as that shown in Figure 6 is easy to manufacture. In effect, even the latter guide roller 7b sufficiently prevents nonuniform separation of the ink ribbon from the image-receiving sheet. Figure 7 is a side view showing a core 8a for taking up an ink ribbon according to the first example of the eighth aspect of the present invention. The take-up core 8a according to the first example bulges at the center C in the widthwise direction, and the diameter of the take-up roller 8a decreases continuously toward the ends S thereof. The center C applies the maximum tension to the ink ribbon 5 positioned in a downstream position relative to the thermal head 1, and the tension symmetrically diminishes toward the ends S of the take-up roller 8a. The difference in thickness between the center C and the ends S should be set to 0.4 to 2 mm or thereabouts, preferably 0.6 to 1.4 mm, or e.g., 1.0 mm. By virtue of the foregoing configuration, the maximum withdrawing force is exerted on the area of the ink ribbon around the center C, and the force symmetrically diminishes towards the ends S. Coupled with the tensile characteristics of the thermal transfer apparatus, uniform tension is eventually applied to the ink ribbon and the image-receiving sheet in their widthwise direction, thus preventing them from being nonuniformly separated from each other in an upstream position relative to the separation bar. Figure 8 is a side view showing a core 8b for taking up an ink ribbon according to the second example of the eighth aspect of the present invention. The take-up roller 8b according to the second embodiment bulges at the center C, and the thickness of the take-up roller 8b decreases stepwise toward the ends S thereof. With this configuration, the center C of the take-up roller 8b applies the maximum tension to the ink ribbon 5 in a downstream position relative to the thermal head 1, and the tension symmetrically diminishes towards the ends S of the guide roller. The correlation between the thickness of the center C and the thickness of the ends S is the same as that of the guide roller shown in Figure 7. By virtue of the foregoing configuration, the maximum withdrawing force is exerted on the area of the ink ribbon 5 around the center C, and the force symmetrically diminishes towards the ends S. Coupled with the tensile characteristics of the thermal transfer apparatus, uniform tension is eventually applied to the ink ribbon and the image-receiving sheet in their widthwise direction, thus preventing them from being nonuniformly separated from each other in an upstream position relative to the separation bar. Although the take-up roller 8a, which is shown in Figure 7 and has its greatest thickness at the center C and the thickness decreases continuously toward the ends S thereof, is troublesome to manufacture, the take-up roller 8b having a profile such as that shown in Figure 8 is easy to manufacture. In effect, even the latter take-up roller 8b sufficiently prevents nonuniform separation of the ink ribbon from the image-receiving sheet. Figure 9 is a side view showing a structure of the tenth aspect of the present invention. More specifically, the structure comprises an ink ribbon press member 10 having a high frictional coefficient interposed between the thermal head 1 and the separation bar 6d. Although the press member 10 may be provided at each end of the separation bar 6d, the press member 10 should be provided over the entire widthwise surface of the separation bar 6d in order to ensure prevention of quick separation of the ink ribbon from the image-receiving sheet. Since the ink ribbon is reliably prevented from being quickly separated from the sheet in the area between the thermal head 1 and the separation bar 6d, a transfer failure stemming from a separation failure can be prevented. The ink ribbon press member 10 having a high frictional coefficient according to the second embodiment may be formed from spongy material such as a foaming urethane. The foregoing embodiments show examples of the present invention. Needless to say, the present invention is not limited to these examples. For example, it is more effective to combine together two or more of the aforementioned elements: that is, the separation bar of any one of the first to fifth aspect or a separation bar formed by combination thereof; the guide roller of the sixth or seventh aspect; the take-up core of the eighth or ninth aspect; and the ink ribbon press member of the tenth aspect. In such a case where the foregoing elements are used in combination, they exert influence on one another. For this reason, contrary to a case where they are used solely, the elements should be used so as to slightly reduce the numerical values mentioned above. All the foregoing descriptions are predicated on a thermal transfer apparatus in which small tension is exerted on the center of the ink ribbon and strong tension is exerted on the sides of the same. In some types of thermal transfer apparatus, a few thermal transfer apparatus exist wherein small tension is exerted to the sides of the ink ribbon and strong tension is exerted to the center of the same, in a manner opposite to that of the foregoing type of thermal transfer apparatus. In such a case, according to the idea of the present invention, the separation bar, the guide roller, and the ink-ribbon take-up core have structures completely opposite to those of the corresponding elements mentioned previously. More specifically, in such a case, the thermal transfer apparatus will be constructed as follows. Constitution of each component of a thermal transfer apparatus in which strong tension is exerted on the center of an ink ribbon and weak tension is exerted to the sides of the ink ribbon: (1) A separation bar has such a shape that the thickness of the bar in an ink ribbon travelling direction ribbon is greater at the ends of the bar in the direction orthogonal to the ink ribbon travelling direction, than that at the center of the bar, and the bar bulges in a downstream direction in the form of a reverse bow shape. The bar is formed into the reverse bow shape at a rate of 10 to 200 µm with respect to a toner width of 100 mm. (2) Spacers are interposed between the thermal head and the ends of the separation bar in a direction orthogonal to an ink ribbon travelling direction, and the center of the separation bar is curved toward the thermal head. The bar is curved at a rate of 10 to 200 µm with respect to a toner width of 100 mm. (3) The bottom of the separation bar in the vertical direction has such a shape that the bottom portions of the bar at both ends in the direction orthogonal to an ink ribbon travelling direction are lower than the bottom portion of the bar at the center thereof. The bottom of the bar descends at a rate of 10 to 200 µm with respect to a toner width of 100 mm. (4) In the area of the separation bar which comes into contact with the ink ribbon, the ends of the bar have a frictional coefficient smaller than that of the center in the direction orthogonal to the ink ribbon travelling direction. (5) In the area of the separation bar which comes into contact with the ink ribbon, the ends of the bar are covered with Teflon coating. (6) A guide roller for guiding the ink ribbon is formed into a pincushion or stepped shape. More specifically, in the axial direction of the roller, the guide roller has at its center a smaller diameter and at its ends a greater diameter. The roller is formed so as to become tapered at a rate of 10 to 200 µm with respect to a toner width of 100 mm. (7) A core for taking up an ink ribbon is formed into a pincushion or stepped shape. More specifically, in the axial direction of the core, the take-up core has at its center a smaller diameter and at its ends a greater diameter. (8) An ink ribbon press member having a high frictional coefficient is interposed between a thermal head and the separation bar. As mentioned previously, an existing thermal transfer apparatus causes a transfer failure stemming from a separation failure, because no consideration is paid to variable control of tension in an ink ribbon in its width direction. In contrast, as has been described in detail, the present invention allows for variable control of tension in the ink ribbon in its widthwise direction and has the remarkable effect of being able to realize an ink ribbon separation apparatus which prevents a transfer failure stemming from a separation failure.

Claims: A thermal transfer apparatus, equipped with an ink ribbon uniform separation bar, (6), comprising: a thermal head (1); the separation bar (6) having a bow shape and extending in a direction orthogonal to the ink ribbon (5) travelling direction, characterized by the separation bar (6) defining the bow shape at a location where the separation bar contacts the ink ribbon, wherein the bow shape is defined by a rate of 10 to 200 µm with respect to a toner width of 100 mm, so that a uniform tension is applied to the ink ribbon at said location where the ink ribbon is separated from the image receiving sheet. The thermal transfer apparatus of claim 1, wherein said bow shape is defined by the thickness of the separation bar (6a) in the ink ribbon travelling direction, the thickness being greater at the center of the bar in a direction orthogonal to the ink ribbon travelling direction than that at ends of the bar, and the center bulges in a downstream direction. The thermal transfer apparatus of claim 1, wherein said bow shape is defined by a spacer (9) interposed between the thermal head (1) and the center to the separation bar (6b) in a direction orthogonal to an ink ribbon travelling direction, the ends of the separation bar (6b) being curved toward the thermal head (1). The thermal transfer apparatus of claim 1, wherein said bow shape is defined by the bottom of the separation bar (6c) in the vertical direction having such a shape that a bottom portion at the center of the bar (6c) in a direction orthogonal to an ink ribbon (5) travelling direction is lower than that at ends of the bar (6c). The thermal transfer apparatus of claim 1, wherein the same function of the bow shape for applying a uniform tension to the ink ribbon is realized by a flat separation bar (6c) in which an area (Cu) which comes into contact with an ink ribbon (5) has a frictional coefficient at the center of the bar in an ink ribbon travelling direction smaller than that at ends of the bar. The thermal transfer apparatus as defined in claim 5, wherein the center of the area of the separation bar (6c), which comes into contact with the ink ribbon, is covered with Teflon coating. The thermal transfer apparatus of claim 1, further comprising a guide roller (7a, 7b) for guiding the ink ribbon (5); wherein the guide roller (7a, 7b) has a spindle or stepped shape and has at its center a thickness greater than that at the ends thereof in an axial direction of the roller. The thermal transfer apparatus as defined in claim 7, wherein the guide roller having the spindle or stepped shape is formed at a rate of 10 to 200 µm with respect to a toner width of 100 mm. The thermal transfer apparatus of claim 1, further comprising a core (8a, 8b) for taking up an ink ribbon (5), wherein the core (8a, 8b) has a spindle or stepped shape and has at its center a thickness greater than that at the ends thereof in an axial direction of the core. The thermal transfer apparatus of claim 1 comprising: an ink ribbon press member (10) having a high frictional coefficient and being interposed between the thermal head (1) and the separation bar (6d).

Inventors: KINJYO KAZUAKI, SAWANO MITSURU, KINJYO, KAZUAKI, SAWANO, MITSURU
Applicants: FUJI PHOTO FILM CO LTD, FUJI PHOTO FILM CO., LTD.
Application year: 1998
Main classification: B41J2
IPC codes: B41J17, B41J2, B41J35