JPH10181164A - Ink ribbon cassette - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ink ribbon cassette capable of maintaining excellent print quality for a long period of time by improving remarkably traveling stabil ity of an ink ribbon by a method wherein catching of the ink ribbon around a roller, and fluctuation of back tension are eliminated. SOLUTION: The cassette 10 is constituted as follows; a pair of freely rotatable cores are stored in a cassette body; an ink ribbon 12 is wound between those cores; one side one is an unwinding core 20 and the other side one is a winding core 30. The ink ribbon 12 is led outside the cassette 10 in an approximately intermediate part of a pass line of the ink ribbon 12; a recessed part 13 for inserting a printing head printing on a recording medium by coaction with the ink ribbon 12 led outside is provided at a front end part of the cassette body; and at least one guide roller is respectively provided between the recessed part and the unwinding core 20 and between the recessed part and the winding core 20. In this case, while the ink ribbon 12 wound on the unwinding core 20 is unwound from an all wound state to an almost half wound state in printing, a sheet 14 of large frictional resistance in contact with an under side face of the ink ribbon 12 is provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink ribbon cassette mounted on a printer and used for printing on a predetermined recording medium in cooperation with a print head of the printer.

[0002]

2. Description of the Related Art Conventional ink ribbon cassettes include:
For example, the one described in JP-A-6-48003 is known. In this ink ribbon cassette, a pair of ribbon feed rollers whose surfaces in contact with the ink ribbon are formed of a material (rubber-like elastic material) having a large friction coefficient are provided on the winding side and the unwinding side. The angle at which the ink ribbon is wound around the roller is equal to or greater than the drive limit.

In order to provide an appropriate back tension to the running ink ribbon, a friction member for applying a brake to the rotation of the unwinding core is provided by a spring bias, and the inner surface of the bottom of the case of the ink ribbon cassette and the ink are fixed. 2. Description of the Related Art A sheet is interposed between an unwinding core around which a ribbon is wound.

[0004]

In the conventional ink ribbon cassette as described above, there is a problem that the ink ribbon is wound around the take-up roller while the ribbon is running due to the large friction coefficient of the roller. .

Further, variations in back torque occur due to accuracy errors and aging during the manufacture of the ink ribbon cassette or carriage, and variations in back tension resulting from this cause poor running of the ink ribbon and printing defects. was there.

Although contacting the sheet with the ink ribbon unwound from the unwinding core exerts a certain effect in providing back tension, if the winding state of the ink ribbon around the core varies. There is a portion that does not come into contact with the sheet, and the back tension is insufficient for the ink ribbon that is unwound from this portion, or the back tension is excessive for the portion where an excessive load is applied to the sheet, and in any case, it causes printing failure. I was

Furthermore, in the prior art, a friction sheet is provided on the inner surface of the bottom of the cassette so as to contact the lower side surface over the maximum winding diameter range of the ink ribbon wound on the unwinding core. When this configuration is adopted for the ink ribbon cassette, a friction sheet is similarly provided on the inner surface of the top of the other core which is the winding core. For this reason, the play of the unwind core and the take-up core inside the cassette becomes insufficient, and the running of the ink ribbon becomes unstable.

[0008]

SUMMARY OF THE INVENTION The present inventors have found that, in the above-described prior art, the ink ribbon is wound around the rollers or the back tension varies, so that the running stability of the ink ribbon is greatly impaired. As a result of repeated experiments and research to resolve the problem, while the ink ribbon wound around the unwinding core was unwound from full winding to almost half-wound during printing, it was wound while contacting a sheet with high frictional resistance. By configuring to be issued
The inventors have found that the above problem is solved, and have reached the present invention.

That is, according to the present invention, a pair of rotatable cores are housed in a cassette body, an ink ribbon is wound between the cores, one is an unwinding core, the other is a winding core, At approximately the middle of the ribbon pass line, the ink ribbon is led out of the cassette body, and printing is performed on a recording medium at the front end of the cassette body in cooperation with the ink ribbon led out. In an ink ribbon cassette provided with a concave portion for inserting a head, and at least one guide roller provided between the concave portion and the unwinding core and the winding core, the ink ribbon cassette is wound around the unwinding core. In addition, while the ink ribbon is unwound from a full-wound state to a substantially half-wound state during printing, a large frictional resistance comes into contact with the lower side surface of the ink ribbon. That the sheet, characterized in that is provided.

According to a preferred aspect of the present invention, the sheet is fixed to the inner surface of the bottom of the ribbon cassette. This enables double-sided printing.

The sheet is preferably formed of a material having a ratio of a coefficient of dynamic friction to a coefficient of static friction of 1/2 or more. Such materials include, for example, wool felt, polyurethane foam, and the like, and polyurethane foam is particularly suitable in consideration of the printing due to fluffing and the adverse effect on the thermal head.

According to another preferred embodiment of the present invention, the thickness of the sheet is 0.3 to 1.0 mm.

According to another preferred aspect of the present invention, the variation in the height position of the side surface of the ink ribbon wound on the unwinding core is within 4% of the ribbon width. In order to smoothly rotate the unwinding core around which the ink ribbon is wound, it is necessary to secure at least a fluctuation of the position of the ink ribbon + 2% (the gap between the unwinding core and the inner surface of the cassette body). If it is excessively large, it hinders stable running of the ink ribbon and may cause printing failure. Therefore,
In order to smoothly rotate the unwinding core while maintaining good running stability of the ink ribbon, it is preferable that the position fluctuation of the ink ribbon be within 4% of the ribbon width.

[0014]

FIG. 1 shows an ink ribbon cassette 10 according to an embodiment of the present invention. The ink ribbon cassette 10 is of a double-sided printing type which can be mounted upside down from the state shown in the figure, and is therefore symmetrical in the drawing. Also,
FIG. 1 is a top view showing the ink ribbon cassette 10 in a state where a cover is removed from a cassette body formed by joining a case and a cover.

A pair of cores 20 and 30 around which the ink ribbon 12 is wound are accommodated in the case 11, and in the state shown in the figure, the core 20 is an unwinding core and the core 30 is a winding core. . The ink ribbon 12 is guided from the unwinding core 20 by guide rollers 21, 22, 23, and 24, and furthermore, a substantially triangular protrusion formed on both sides of a concave portion 13 formed at the center of the front end of the case 10. After being guided to the tip of one of 25, 25,
3 is drawn out of the cassette. The other protrusion 3
The ink ribbon 12 guided by the leading end of the ink ribbon 5 and introduced again into the cassette is guided by the guide rollers 34, 33, 32 and 31 and wound around the winding core 30.

In a state where the ink ribbon cassette 10 is loaded on a carriage of a thermal transfer printer, a pair of rotating shafts on the carriage are composed of an unwinding core 20 and a winding core 30.
To engage. Then, the rotating shaft inserted and engaged with the winding core 30 is rotationally driven by an appropriate drive source, so that the ink ribbon 12 passes from the unwinding core 20 to the winding core 30 through the above-described pass line. The take-up core 20 is also driven and rotated in the same direction as the rotation drive direction of the take-up core 30. Further, a thermal head provided so as to be able to reciprocate along the platen together with the carriage is inserted into a concave portion 13 formed at the center of the front end of the ink ribbon cassette 10, and moves upward in FIG. The portion of the ink ribbon 12 which is led out is pulled up, and a predetermined printing is performed on a predetermined recording medium conveyed in synchronization with the traveling of the ink ribbon 12.

Since the configuration of the printer and the printing mechanism using the thermal transfer method are well known, they are not shown in the drawings and will be described only briefly.

Of the guide rollers 21 to 24 on the winding side and the guide rollers 31 to 34 on the winding side, the guide roller 32 on the winding side is a drive roller. That is, a drive shaft (not shown) provided on the carriage while the ink ribbon cassette 10 is loaded on the carriage is engaged with the drive roller 32, and the drive shaft is rotationally driven by an appropriate drive source. When driven, the driving roller 32 receives the driving force and rotates in the counterclockwise direction in the figure, and actively assists the running of the ink ribbon.

On the other hand, the guide roller 22 provided on the unwinding side opposite to the guide roller 32 has a rotating shaft (see FIG. 1) rotatably provided on the carriage when the ink ribbon cassette 10 is loaded on the carriage. (Not shown), but no drive source is connected to the rotating shaft, and the rotating shaft can only idle. In the present embodiment, as will be described later, the guide roller 22 on the unwinding side is maintained in a stationary state without substantially rotating even while the ink ribbon 12 is running.

The other guide rollers 21, 23, 24 and 31, 33, 34 are rotatably provided, and the friction between the peripheral surface thereof and the back coat (BC) surface of the ink ribbon 12 causes the ink ribbon 12 to rotate. It rotates with the traveling of.

FIG. 2 shows the unwinding core 20 and the unwinding core 20.
FIG. 3 is an enlarged vertical cross-sectional view of a portion including an ink ribbon 12 wound around the printer. As shown in FIG. 2, the ink ribbon 12 wound around the unwinding core 20 changes from a fully wound state (the state of the maximum winding diameter shown in FIG. 2) to a substantially half-wound state (the unwinding core and the winding core) during printing. While the winding diameter is approximately the same)
The sheet 14 is brought into contact with the lower side of the ink ribbon.
Is adhered to the inner surface of the bottom of the case 11. The sheet 14 in the illustrated embodiment is a urethane foam sheet having a thickness of 0.5 mm.

In this embodiment, the unwinding core 20
In the substantially semicircular region on the side (the right side in FIG. 2) close to the side surface of the case 11, the sheet 14 is stuck over a substantially half region on the outer peripheral side of the ink ribbon 12 in a fully wound state.
In the substantially semi-circular region on the center side of the case (the left side in FIG. 2), approximately half of the outer peripheral side of the sheet in the substantially semi-circular region on the side surface of the case is cut and adhered as a small width leaving only approximately half of the inner peripheral side. ing. This is because, as will be described later with reference to FIGS. 5 to 8, in the double-sided printing type ink ribbon cassette, the sheet 15 is similarly provided above the other core 30 so that the one core is fully wound. This is to prevent the outer peripheral end portion of the ink ribbon 12 from buffering with the sheet provided for the other core, and to secure a clearance between the core and the cassette main body. Similarly to the case side surface, the ink ribbon 12 may be stuck over a substantially half area on the outer peripheral side of the ink ribbon 12 in the fully wound state.

FIG. 3 shows the results of measuring the pull-out force of the ink ribbon 12 wound around the unwinding core 20 in the ink ribbon cassette without the sheet 14. That is,
If the sheet 14 is not provided, in the initial stage in which the ink ribbon 12 is unwound from the unwinding core 20, a pull-out area (about 20 gf), which is generally considered to cause printing defects
Below). In order to solve this problem, it is effective to provide a sheet having a large frictional resistance so as to come into contact with the unwinding core 20 and the lower side surface of the ink ribbon 12 wound around the unwinding core. Is provided over the entire winding range of the ink ribbon 12 in the wound state, the following new problem occurs.

That is, in the ink ribbon cassette of the double-sided printing type, the core 20 becomes the unwinding core and the core 30 becomes the winding core when mounted on the carriage in the state of FIG. Is the unwinding core, and the core 20 is the winding core. Therefore, FIG.
The sheet 14 is provided below the core 20 serving as the unwinding core in the state described above, and the sheet is provided above the core 30 on the side thereof. When the core 30 is used as the unwinding core, the sheet 14 is provided therebelow. The sheet is positioned to give a predetermined frictional resistance to the ink ribbon 12 unwound from the unwinding core.

In such a double-sided printing type ink ribbon cassette, when the sheet 14 is provided over the entire winding range of the ink ribbon of each of the cores 20 and 30, the sheet 14 is disposed below one core and above the other core. As a result, the height in the cassette becomes smaller by the sheet thickness from both sides thereof, and the play of the core in the cassette becomes insufficient. As shown in FIG. 2, the wound ink ribbon often has a wavy side surface. However, in order to smoothly rotate the unwinding core around which the ink ribbon is wound, it is necessary to use an ink ribbon. It is necessary to secure clearance as a play between the core and the inner surface of the cassette body, which is obtained by adding at least about 2% to the variation in the height of the side surface of the ink ribbon with respect to the width (%). The provision of 14 makes it difficult to secure such play.

Therefore, in the present invention, the ink ribbon 12 wound around the unwinding core 20 is brought into contact with the lower side surface of the ink ribbon 12 while being unwound from a fully wound state to a substantially half wound state during printing. The sheet 14 is attached to the inner surface of the bottom of the case 11, and the effect of providing the sheet 14 in this manner will be described with reference to FIGS.

FIG. 5 shows an unused ink ribbon cassette 10.
Shows the ink ribbon winding state of each core at
Substantially all of the ink ribbons 12 are wound around the unwinding core 20. As described above, on the side of the case, the ink ribbon 12 wound around the unwinding core 20 extends over a substantially half area on the outer circumference side, and on the center side of the case, only on a substantially half area on the inner circumference side. The lower side surface of the ink ribbon 12 is in contact with the sheet 14.

In this state, the core 3 serving as a winding core is
The sheet 15 is similarly adhered to the top inner surface of the cover 17 above the cover 17, but since the outer peripheral sides of the sheets 14, 15 at the center of the case are cut as described above,
The necessary clearance is secured without the outer peripheral end portion of the ink ribbon 12 completely wound around the unwinding core 20 being buffered with the sheet 15.

In this state, as printing is performed, the ink ribbon 12 is gradually unwound from the unwinding core 20, and the portion is wound up by the winding core 30. FIG. 6 shows a state in which the outer edge of the ink ribbon 12 wound around the unwind core 20 is the sheet 1.
4 shows a state in which it is barely mounted on the inner end of FIG. 5 to 6, the ink ribbon 12 is unwound from the unwinding core 20 in a state where the lower side surface is positioned on the upper surface of the sheet 14, so that the winding ribbon is slightly The side surface of the ink ribbon 12 wound around 30 is substantially horizontal.

When the ink ribbon 12 is further unwound from the state shown in FIG. 6, the outer peripheral end of the ink ribbon 12 wound around the unwinding core 20 is separated from the inner end of the sheet 14, so that the unwinding core 20 drops together. Subsequently, in this state, the ink ribbon 12 is
And is wound up by the take-up core 30. The height position of the take-up core 20 is changed from the position shown in FIG.
Therefore, as shown in FIG. 7, a step 16 corresponding to the thickness of the sheet 14 appears on the side surface of the ink ribbon 12 wound around the winding core 30 as shown in FIG. FIG. 8 shows a state in which printing of all the rolls has been completed and substantially all of the ink ribbons 12 have been rolled up by the roll-up core 30.

As described above, in the double-sided printing type ink ribbon cassette, the sheet 15 is adhered to the inner surface of the top of the cover 17 above the winding core 30 in the same manner as the unwinding core 20 side. The unwinding core 20 falls out of the unwinding core 20 at the moment when the outer diameter of the ink ribbon 12 becomes the same as the outer diameter of the ink ribbon wound up by the winding-up core 30 or immediately before that (FIG. 6 and FIG. 7), a step 16 is formed on the side surface of the ink ribbon 12 wound around the winding core 30, and the subsequent winding is performed so that the sheet 15 on the winding core 30 side escapes.

As described above, the ink ribbon 12 wound around the unwinding core 20 is unwound while being supported on the sheet 14 during printing from the fully wound state to the substantially half-wound state. However, since the ink ribbon 12 drops from the sheet 14 and is unwound in a non-contact manner with the sheet, a step 16 is generated on the side surface of the ink ribbon 12 wound around the winding core 30 in the double-sided printing type ink ribbon cassette, Thus, a predetermined clearance can be secured between the winding core 30 and the sheet 15.

The present inventors provided a sheet in which the sheet was provided over the entire winding range of the core (Comparative Example) and a sheet which was unwound while being in frictional contact with the sheet only from the fully wound state to the substantially half-wound state. When the clearance between the take-up core and the inner surface of the cassette main body after the completion of all-roll printing was measured using the two types of ink ribbon cassettes (Examples of the present invention), only the 0.2 mm average clearance was obtained in the former. In contrast, in the latter, a clearance of 0.5 mm average was obtained. Thus, according to the present invention, it has been proved that a sufficient play of the core is secured in the cassette, the rotation of the core becomes smooth, and the running of the ink ribbon can be stabilized.

After the printing of all the rolls of the ink ribbon cassette 10 is completed, the ink ribbon cassette in the state of FIG. 8 is removed from the carriage, turned over, and mounted on the carriage again, and the state of FIG. 9 is obtained. In this state, the core 30 serving as the unwinding core falls by its own weight, and the lower side surface of a region approximately half the outer periphery of the ink ribbon 12 wound around the core 30 extends over the entire surface (case side surface side) or the inner peripheral side thereof. It is supported on the sheet 15 only in a substantially half area (center side of the case). The operation when the ink ribbon 12 is unwound from this state is substantially the same as that described with reference to FIGS.

In the present invention, the ink ribbon 12 wound around the unwinding core 20 is unwound while being in frictional contact with the sheet 14 from the fully wound state to the substantially half-wound state. Is unwound in a non-contact manner, so that the sheet is not subjected to a frictional force in the latter half of printing. However, as shown in FIG. 3, there is no problem at all in the initial stage of unwinding because the shortage occurs in the pulling output. In the ink ribbon cassette of the present invention, the pull-out force when unwinding the ink ribbon 12 from the unwinding core 20 is as shown in FIG. 4, and a sufficient pull-out force is secured in all printing steps.

Although the essential requirements of the present invention have been mainly described above, preferred embodiments of the present invention will be described below.

As shown in FIG. 2, the lower side surface of the ink ribbon 12 wound around the unwinding core 20 is not a complete horizontal plane but is wavy due to an accuracy error, a secular change, or the like during the manufacture of the ink ribbon cassette 10. In many cases, the variation in the height of the side surface of the ink ribbon 12 in the wound state is preferably stopped within 4% of the ribbon width. As a result, the frictional force of the sheet 14 acts in a substantially half area on the outer peripheral side of the ink ribbon 12 wound around the unwinding core 20, and provides an appropriate back tension to the ink ribbon 12 sent out while receiving its own weight. Can be.

The following Table 1 shows that the variation in the height of the side surface of the ink ribbon 12 wound around the unwinding core 20 varies in the range of 3% to 5% with respect to the ribbon width. This shows the result of comprehensively judging the print quality with + 2% of backlash of the core in the cassette in order to ensure smooth rotation of the ink ribbon and run the ink ribbon stably. In this test, the sheet 14 was also used.
Using a 0.5 mm thick urethane foam sheet
The m-roll ink ribbon cassette was mounted on a Casio thermal transfer printer GX-710, and printing was performed on ordinary copy paper.

[Table 1] From these results, it is possible to provide an appropriate back tension to the ink ribbon 12 by controlling the variation in the height position of the side surface of the ink ribbon 12 wound around the unwinding core 20 within 4% of the ribbon width, thereby providing excellent printing. It has been demonstrated that quality can be maintained. In this example, a foamed urethane sheet was used as the sheet 14. Table 2 shows the results of a comparative test of the ink ribbon running stability and print quality when the sheet 14 was formed of various materials.

[Table 2] From the results shown in Table 2, it is understood that urethane foam and wool felt having a ratio of the coefficient of dynamic friction to the coefficient of static friction of 1/2 or more are suitable materials for the sheet 14.
When a hydrocarbon sheet and a urethane sheet are used, chatter occurs when the unwinding core 20 starts rotating,
The ink ribbon was not fed smoothly.
In the case where a wool felt sheet is used, fluffing caused by long-term use makes the running of the ink ribbon unstable and may adversely affect printing and the thermal head. Particularly preferred. In this example, the thickness of the urethane foam sheet 14 was 0.5 mm. Table 3 shows the results of a comparative test of the ink ribbon stability and the print quality by changing the thickness of the urethane foam sheet 14.

[Table 3] From the results shown in Table 3, it was confirmed that the thickness of the sheet 14 should preferably be in the range of 0.3 to 1.0. In a preferred embodiment of the present invention, at least the peripheral surface of the guide roller (stationary roller) 22 on the unwinding side and the guide roller (drive roller) 32 on the winding side have an ink contact with them when the ink ribbon travels. It is formed of a material such that the coefficient of friction (μ) with the ribbon BC surface is in the range of 0.2 to 0.8. A preferred example of such a material is ABS
(Acrylonitrile butadiene styrene). By forming these guide rollers 22 and 32 with a material that gives a friction coefficient of 0.2 to 0.8 between the ink ribbon BC surface and the ink ribbon BC, the guide roller (drive roller) 32 on the take-up side is provided with an ink ribbon. 12 is prevented from getting caught. Further, since the unwinding side guide roller 22 is formed of a low friction material giving such a friction coefficient,
When the ink ribbon 12 travels in accordance with the counterclockwise rotation of the take-up core 30 and the drive roller 32, the guide roller 22 generates a slip with the traveling ink ribbon 12 and substantially rotates. It is kept stationary without any change. For this reason, a brake is applied to the ink ribbon 12 passing through the stationary roller 22,
In addition to the frictional force caused by the contact with the ink ribbon 12, an appropriate back tension can be applied to the ink ribbon 12, so that the running of the ink ribbon 12 is further stabilized, and printing defects can be completely prevented. Further, the accumulation of the adhering portion, which has conventionally been a problem particularly in the unwinding side guide roller, can be solved by setting the coefficient of friction with the ink ribbon BC surface within the above range. The sheet 14
The material (coefficient of friction) of the stationary roller 22 is selected in an appropriate combination according to the type of the ink ribbon 12 to be used. Although one embodiment of the present invention has been described in detail above, the present invention is not limited to this embodiment, and various modifications can be made within the scope of the invention described in the claims. For example, in the above-described embodiment, the friction coefficient of the guide roller 22 with respect to the ink ribbon BC surface is set to a predetermined range so that the guide roller 22 is a stationary roller. It is also possible to constitute so that it may stop temporarily. The ink ribbon 12 used is
Depending on the type of sheet, even if the guide roller 22 is configured not to be a stationary roller but to be idle when the ink ribbon travels, it can be wound around the unwinding core 20 by appropriately selecting the material and thickness of the sheet 14. Ink ribbon sheet 12
It is possible to provide a predetermined back tension in the entire winding range.

According to the ink ribbon cassette of the present invention, the running stability of the ink ribbon can be remarkably improved, and excellent print quality can be maintained for a long period of time.

[Brief description of the drawings]

FIG. 1 is a top view showing a state in which a cover of an ink ribbon cassette according to an embodiment of the present invention is removed.

FIG. 2 is an enlarged vertical sectional view of a portion including an unwinding core and an ink ribbon wound around the unwinding core in the ink ribbon cassette of FIG. 1;

FIG. 3 shows a result of measuring a pull-out force of an ink ribbon unwound from an unwinding core in an ink ribbon cassette of a comparative example manufactured without providing a sheet in frictional contact with a lower side surface of the ink ribbon wound around the unwinding core. It is a graph shown.

FIG. 4 is an ink ribbon cassette of the present invention in which a sheet is provided so as to make frictional contact with the lower side surface of the ink ribbon while the ink ribbon wound on the unwinding core is unwound from a fully wound state to a substantially half-wound state. 3 is a graph showing the result of measuring the pull-out force of the ink ribbon in the same manner.

FIG. 5 is a cross-sectional view schematically showing a state where an unused ink ribbon cassette of the present invention is loaded on a carriage of a printer.

FIG. 6 is a cross-sectional view schematically showing a state in which substantially half an ink ribbon has been unwound from the unwinding core in the state of FIG. 5;

7 is a cross-sectional view schematically showing a state immediately after the ink ribbon is further unwound from the state of FIG.

FIG. 8 is a cross-sectional view schematically showing a state where printing of all volumes has been completed.

9 is a cross-sectional view schematically showing a state in which the ink ribbon in the state of FIG. 8 is mounted upside down.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Ink ribbon cassette 11 Case 12 Ink ribbon 13 Depression 14 and 15 Sheet 16 Step 17 Cover 20 Unwinding core 21 to 24 Guide roller (22 drive roller) 30 Take-up core 31 to 34 Guide roller (32 stationary roller)

Claims (6)

[Claims] A pair of rotatable cores are housed in a cassette body, and an ink ribbon is wound between these cores, one of which is an unwinding core and the other is a winding core. The ink ribbon is led out of the cassette body at substantially the middle of the cassette body, and a print head for printing on a recording medium is inserted into the front end portion of the cassette body in cooperation with the ink ribbon led out. The ink ribbon wound around the unwinding core in an ink ribbon cassette provided with a recess for the unwinding core and at least one guide roller provided between the recess and the unwinding core and the winding core, respectively. A sheet having a large frictional resistance that contacts the lower side surface of the ink ribbon is provided while the ink ribbon is unwound from a full winding state to a substantially half winding state during printing. Ink ribbon cassette, characterized in that. 2. The ink ribbon cassette according to claim 1, wherein said sheet is fixed to an inner surface of a bottom portion of said ribbon cassette. 3. The ink ribbon cassette according to claim 1, wherein the sheet is formed of a material having a ratio of a coefficient of dynamic friction to a coefficient of static friction of 1/2 or more. 4. The ink ribbon cassette according to claim 1, wherein said sheet is formed of a polyurethane foam. 5. The ink ribbon cassette according to claim 1, wherein said sheet has a thickness of 0.3 to 1.0 mm. 6. The ink ribbon cassette according to claim 1, wherein a variation in the height of the side surface of the ink ribbon wound around the unwinding core is within 4% of the ribbon width. .