JPH03183580A - Color thermal printer - Google Patents

Abstract

PURPOSE:To prevent generating of an image color shift and at the same time, expand an area of recording sheet where an image is thermally transferred by limiting the rotating torque of a platen roller which is made rotatable, constantly only during thermal transfer and thereby giving tension to the recording sheet using a grip roller as a basic element to transport the recording sheet forward and backward. CONSTITUTION:When a recording sheet P is returned in a B direction for thermal transfer, the rotating torque of a platen roller 1 is limited constantly by an adjustm,ent device such as a torque limiter, although a platen roller 1 is rotatably. Thus a back tension is slightly given to the recording sheet P transported in a B direction. As the platen roller 1 provided the recording sheet P with the back tension, adverse effects due to variations of different types are controlled and subsequently, and a color shift generating near the end of the recording sheet P is eliminated. A tension roller 11 is divided in sections in a shaft direction and each section gives its independent and equal tension to the recording sheet P. If the positional accuracy of the tension roller 11 is slightly low and rough, the oblique motion of the recording sheet P is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a color thermal printer. That is,
The present invention relates to a color thermal printer that forms a multicolor image by thermally transferring ink from an ink ribbon onto recording paper.

``Prior Art'' In general, in this type of color thermal printer, a thermal head is heated and pressed against a platen roller via a recording paper being conveyed and an ink ribbon, and multiple colors of ink on the ink ribbon are thermally transferred onto the recording paper in a surface-sequential manner. As a result, a multicolor image is formed.

In such color thermal printers, recording paper has conventionally been conveyed using a platen roller. That is, for example, Japanese Patent Application Laid-Open No. 63-94863 discloses a system in which a platen roller driven to rotate in forward and reverse directions serves as a reference for reciprocating the recording paper, and in addition, a tractor feeder is used in combination to transport the recording paper. Various recording paper conveyance systems based on platen rollers were adopted, such as those using fanfold paper.

"Problems to be Solved by the Invention" By the way, the following problems have been pointed out in such conventional color thermal printers.

First, the platen roller deforms and has a different shape during thermal transfer, that is, when the thermal head is pressed against it, and during non-thermal transfer, that is, when the thermal head is released from the pressure contact. If such a platen roller is used as a reference for conveying the recording paper, for example, an error will occur in the amount of reciprocal conveyance of the recording paper, which will cause transfer misalignment or color misregistration in the image thermally transferred to the recording paper, which will affect the image quality. It was a problem.

Second, since the platen roller is made of highly elastic rubber, it is difficult to maintain precision in its outer diameter, and its shape is likely to expand and deform due to heat from the thermal head. Therefore, it has been pointed out that the platen roller is unsuitable as a standard for conveying recording paper, which requires accuracy, small variation, and the like.

Thirdly, it has been pointed out that in recording paper conveyance systems that use separate reciprocating and multiple conveyance standards, poor conveyance accuracy occurs when reciprocating conveyance is repeated, that is, a difference in conveyance amount occurs. Color shift caused by these factors also occurs, which poses a problem in terms of image quality.

This point was pointed out in the conventional example.

In view of these circumstances, the present invention has been made to solve the problems of the conventional methods described above.The present invention has been made in order to solve the problems of the conventional methods described above. We propose a color thermal printer in which the platen roller is equipped with an adjusting means to limit the rotational torque only during thermal transfer, thereby preventing color misregistration of images and expanding the range of thermal transfer of recording paper. The purpose is to

"Means for Solving the Problems" Technical means of the present invention that are distantly related to this object are as follows.

In this color thermal printer, a thermal head is heated and pressed into contact with a platen roller via the recording paper and ink ribbon being conveyed, and multiple colors of ink on the ink ribbon are thermally transferred onto the recording paper sequentially, forming a multicolor image. Ru. This color thermal printer includes the following grip roller and tension roller.

The grip roller is disposed on the downstream side of the platen roller in the direction in which the recording paper is conveyed during thermal transfer, and is driven to rotate in forward and reverse directions while gripping the recording paper.

The tension roller is disposed upstream of the platen roller in the conveying direction, and applies tension to the recording paper being conveyed.

The grip roller serves as a reference for reciprocating the recording paper, and the platen roller is rotatable. Further, the platen roller is provided with an adjustment means that applies tension to the recording paper by limiting its rotational torque to a constant value only during thermal transfer.

"Function" Since the present invention consists of such means, it works as follows.

In this color thermal printer, the recording paper is transported back and forth using the grip roller as a reference. Then, a thermal head is brought into heat and pressure contact with the platen roller, and the ink of multiple colors of the ink ribbon is thermally transferred onto the recording paper sequentially, forming a multicolor image.

First, the grip roller serves as a reference for reciprocating conveyance, and the platen roller, which is deformed by pressure contact with the thermal head, only follows the conveyance of the recording paper, eliminating the error in the amount of reciprocal conveyance of the recording paper. Second, the grip roller does not expand or deform due to heat from the thermal head and has good outer diameter accuracy. Thirdly, since the grip roller is the only reference for reciprocating conveyance, the recording paper can be conveyed with excellent accuracy even if the reciprocating conveyance is repeated. These prevent color misregistration of images on recording paper.

Further, during thermal transfer, although the platen roller is rotatable, its rotational torque is limited to a constant level by an adjusting means, thereby applying tension to the recording paper being conveyed. Therefore, even if the edge of the recording paper comes off the tension roller as the thermal transfer progresses, no color shift occurs near the edge, and the thermal transfer range of the recording paper becomes wider.

"Example" The present invention will be described in detail below based on the example shown in the drawings.

First, its configuration will be explained in the order of the color thermal printer, its grip roller, platen roller, tension roller, and its functions.

For color thermal printers, see below.

FIG. 1 is an explanatory front view showing an embodiment of the present invention. In this color thermal printer, a thermal head 2 is heated and pressed against a platen roller 1 via a recording paper P and an ink ribbon R that are being conveyed, and ink of a plurality of colors of an ink ribbon R is thermally transferred onto the recording paper P in a field-sequential manner. A multicolor image is formed.

To explain these in detail, a platen roller 1 is arranged in the center of the printer body, and a thermal head 2 is arranged opposite to the platen roller 1 so as to be able to press against and separate from the recording paper P and the ink ribbon R. Further, a recording paper supply take-up reel 3 is arranged at the end of the printer body, and a recording paper P, which is an unused roll paper, is wound thereon.

From the supply side to the paper discharge side of the recording paper P, in order to form the transport path, the recording paper supply winding reel 3,
A feed roller 4 and a paper feed roller 5 that can be pressed against the feed roller 4, a grip roller 6 and a driven roller 7 that is pressed against the grip roller 6, a first paper sensor 8, a ribbon peeling roller 9, a platen roller 1 and the platen roller 1. Thermal head 2 that is pressed during thermal transfer, the ink ribbon guide roller 10 that is located slightly away from the conveyance path, the tension roller 11, and the driven roller 1 that is pressed against the tension roller 11.
2, a second paper sensor 13, a cutter 14, etc. are arranged. Through such a conveyance path, the recording paper P is sent out in the direction A in the figure, and then repeatedly conveyed back and forth several times between the opposite direction, the direction B in the figure. After thermal transfer is performed, the paper is discharged in the A direction.

The ink ribbon R is in the form of a film sheet with approximately the same width as the recording paper P, etc., and is coated with heat-melting pigment-based or heat-sublimating dye-based solid ink in the order of the three primary colors of yellow, magenta, and cyan over a fixed length. It is applied repeatedly every time. This ink ribbon R is unused and wound around the ink ribbon supply reel 15.
The ink ribbon is supplied from the ink ribbon and guided along with the recording paper P between the platen roller 1 and the thermal head 2 via the ink ribbon guide roller 10 . After the thermal transfer, the ink ribbon R is sequentially fed forward and separated from the recording paper P by a ribbon separation roller 9, after which the used ink ribbon is wound onto the ink ribbon take-up reel 16.

As shown in the figure, the thermal head 2 is pressed against the platen roller 1 during thermal transfer, and is separated from it during non-thermal transfer.

At the top of the thermal head 2, a large number of heating elements are provided, for example, in a line shape, and each dot is selectively heated by electricity.Such electricity heating generates a single color component, which is the hue image information of each of the three primary colors sent out. This is done based on the print data.

The paper feed roller 5 is held movable in two directions (up and down around a fulcrum S), and is pressed against the feed roller 4 as shown in the figure, or is lifted and separated from the feed roller 4, which is controlled by a sensor (not shown). Detected.

This is how a color thermal printer works.

Next, the grip roller 6 will be described.

The grip roller 6 is disposed downstream of the platen roller 1 in the direction B, which is the conveyance direction of the recording paper P during thermal transfer. The grip roller 6 is connected to a recording paper conveyance motor (not shown) such as a pulse motor via a timing belt or the like and is driven to rotate in forward and reverse directions, and grips the recording paper P between it and the driven roller 7. , which are transported back and forth in the A direction and the B direction. In addition, in order to ensure the transportation of such recording paper P with high precision and to prevent slips, etc.,
The grip roller 6 is set to have a high coefficient of friction on its surface. Specifically, it is a metal roller whose surface is blasted, a roller whose surface is sprayed or bonded with ceramic fine particles, or a rubber roller with a high coefficient of friction. etc. are used.

The grip roller 6 serves as a reference for reciprocating the recording paper P. In other words, in this color thermal printer, the torque of the grip roller 6 is set to be the highest during the conveyance path of the recording paper P, and is the only criterion for determining the amount of conveyance of the recording paper P in the A direction and the B direction. There is.

The grip roller 6 has this structure.

Next, the platen roller 1 will be described.

The platen roller l is rotatable to follow the conveyance of the recording paper P by the grip roller 6. The platen roller l is completely freely rotatable clockwise in the figure when the recording paper P is conveyed in six directions, that is, during non-thermal transfer in which the recording paper P is simply fed. On the other hand, when the recording paper P is conveyed in the B direction, that is, during thermal transfer when the recording paper P is returned, although the recording paper P can be rotated counterclockwise in the figure, its rotational torque is limited to a certain level, and the conveyed recording paper P It is designed to give a light back tension similar to a brake.

As an adjustment means for limiting the rotational torque and applying a predetermined tension in this manner, it is conceivable to attach a torque limiter or the like to the platen roller 1, for example. 2 and 3 are side sectional views showing such a mounting structure for the platen roller 1, with FIG. 2 showing one example and FIG. 3 showing another example.

First, in the example shown in FIG. 2, the platen roller shaft 17 and the torque limiter 18 are coaxially connected by a coupling 19.
A one-way clutch 20 is interposed within the coupling 19. That is, a drum-shaped platen roller 1
The platen roller shaft 17, which is a core metal, has its end projecting outward from the inner side plate frame 21 via a bearing.
Further, as described above, the torque limiter 18 with a predetermined torque required to apply tension to the recording paper P is fixed to the outer side plate frame 21'. The end of the platen roller shaft 17 and the torque limiter shaft 22 of the torque limiter 18 are coaxially connected by a coupling 19, and a one-way clutch 20 is provided within the coupling 19.

First, during non-thermal transfer, the one-way clutch 20 disconnects the platen roller shaft 17 and the torque trimmer 18, and the platen is rotated clockwise in the figure by the recording paper P being conveyed in the middle direction in FIG. A roller I is made freely rotatable in the same direction. On the other hand, during thermal transfer, the one-way clutch 20 is switched to continuously connect the two, and the platen roller is rotated counterclockwise in the figure as the recording paper P is conveyed in the direction B in FIG. The rotational torque of 1 is limited to a constant value by a torque limiter 18.

In the example shown in FIG. 3, the platen roller shaft 17 and the torque limiter 18 are connected via gears 23 and 24, and one-way clutches (not shown) are interposed at appropriate locations.

That is, a gear 23 is attached to the end of the platen roller shaft 17 that protrudes outward from the inner side plate frame 21 via a bearing.
is fixed. Further, the torque limiter 18 is attached to the outer side plate frame 21' via, for example, a one-way clutch (not shown), and the torque limiter shaft 22 is attached to the inner side plate frame 21 with a bearing (not shown).
The gear 2 is held on the shaft 22, and the gear 2 is
4 is fixed and meshes with the gear 23. However, the torque limiter 18 may be directly fixed to the outer side plate frame 21, and the one-way clutch may be interposed within the gears 23 and 24. Further, the functions of each member in the examples shown in FIG. 3 and the like are similar to those described above with respect to FIG.

The platen roller 1 has this structure.

Next, the tension roller 11 will be described.

The tension roller 11 is disposed on the upstream side of the platen roller I in the direction B, which is the conveyance direction of the recording paper P during thermal transfer. Then, tension is applied to the recording paper P being conveyed.

To explain these details in detail, FIG. 4 is a partially cutaway perspective view showing the mounting structure of the tension roller 1. As shown in FIG. 25 in the figure is a drive shaft, the end of this drive shaft 25 protrudes outward from the side plate frame 21, and the one-way clutch 26
A drive gear 27 is attached via the drive gear 27, and the drive gear 27 is connected to the above-mentioned recording conveyance motor. Drive shaft 25
A one-way clutch 28 is interposed between the mounting portion of the side plate frame 21 and the mounting portion of the side plate frame 21.

The tension roller 11 is attached to such a drive shaft 25 via a torque limiter 29. That is, the torque limiter 29 has one end, the core, fixed to the drive shaft 25, and the other end, the exterior, that is, the torque output end, fixed to the end of the tension roller 11. The tension roller 11 includes a core metal 30 and a bearing material 31 as an inner layer.
and a rubber material 32 as an outer layer, the end of the core metal 30 is fixed to the torque limiter 29 and is rotatable with respect to the drive shaft 25 inserted into the bearing material 31.

FIG. 5 is a partially cutaway perspective view showing a mounting structure in which two such tension rollers 11 are provided. That is, this tension roller 11 is divided into a plurality of parts in the axial direction, that is, in the width direction of the recording paper P, and in the example shown in FIG.
It is divided into two parts, each of which applies an independent and equal tension to the recording paper P. In the example shown in FIG. 5, two torque limiters 29 with the same set torque are arranged at a distance from each other in the center of the drive shaft 25, and both such torque limiters 2
Tension rollers 11 are individually attached to each side of the drive shaft 25 via 9. In the example shown in FIG. 5, the configuration of each other member is the same as that shown in FIG. 4, so the same reference numerals are given and the explanation thereof will be omitted. Further, the tension rollers 11 may be divided into three, four, or other plurality of rollers instead of one pair on both sides as in the example shown in FIG.

The tension roller 11 has this structure.

Next, the functions of the tension roller 11 will be described.

Since the tension roller 11 has the mounting structure shown in FIG. 4, it functions as follows. First, during non-thermal transfer, that is, when the recording paper P is conveyed in the incoming direction (see FIG. 1), tension is applied to the recording paper P as follows.

That is, the drive gear 27 is rotationally driven in the clockwise direction a in the figure by the recording paper conveyance motor, and the one-way clutch 26 continuously connects the drive gear 27 and the drive shaft 25 to rotate the drive shaft 25 in the direction a. Rotate it. Note that the one-way clutch 28 disconnects the attachment portion of the side plate frame 21 and the drive shaft 25, and functions as a mere hair ring.

The rotation of the drive shaft 25 is regulated to a low predetermined torque via the torque limiter 29 and transmitted to the tension roller 11, and the tension roller 11, which is rotationally driven in the direction a, applies a constant tension to the recording paper P. It is designed to give

The predetermined torque of the torque limiter 29, that is, the tension applied by the tension roller 11, is set to such an extent that the recording paper P, which is conveyed while being sandwiched between the grip roller 6 and the driven roller 7, does not slacken as described above. It is not so high and strong as to cause the recording paper P to slip between the rollers 7. Note that the surface circumferential speed of the tension roller 11 is set to be slightly faster than the surface circumferential speed of the grip roller 6.

On the other hand, the tension roller 11 is used during thermal transfer, that is, when the recording paper P
When the recording paper P is transported in the B direction (see FIG. 1), back tension is applied to the recording paper P as follows.

That is, the drive gear 27 is rotationally driven in the direction b, which is counterclockwise in the figure, by the recording paper conveyance motor, but since the one-way clutch 26 disconnects the drive gear 27 and the drive shaft 25, the rotation of the drive gear 27 is prevented. No drive is transmitted to the drive shaft 25. On the other hand, the one-way clutch 28 continuously switches between the mounting portion of the side plate frame 21 and the drive shaft 25, so that the drive shaft 25 is locked in the direction b and is fixed so as not to rotate. Since the drive shaft 25 is fixed in this way, the torque limiter 29
The tension roller 11 functions to limit the rotational torque of the tension roller 11 to a constant value, so that although the tension roller 11 can rotate in the b direction, its rotational torque is limited, and a light back tension like a brake is applied to the conveyed recording paper P. .

In this way, the tension roller 11 applies tension to the recording paper P conveyed in the A direction or the B direction, respectively. The aforementioned recording paper supply take-up reel 3 can also rotate freely in the counterclockwise supply direction in FIG. During directional conveyance, the recording paper P is rotationally driven in the winding direction clockwise in FIG. 1 with a low set torque that does not cause the recording paper P to sag.

The functions of the tension roller 11 are as follows.

The above is the explanation of the configuration, etc.

The operation etc. will be explained below.

This color thermal printer operates through the following steps: (1) a setting stage, (2) a thermal transfer stage for each color, (3) a paper discharge stage, and (4) a preparation completion stage. First, these will be explained with reference to FIG. 1 and the like.

(1) Setting stage After the recording paper P is loaded onto the recording paper supply take-up reel 3, the paper feed roller 5 is once lifted and separated from the feed roller 4. Thereafter, when the leading edge of the recording paper P is drawn between the two, the paper feed roller 5 is lowered and the leading edge of the recording paper P is brought into pressure contact with the feed roller 4. Then, a series of operations such as feeding the recording paper P and positioning the ink ribbon R are started.

That is, the feed roller 4. The grip roller 6, tension roller 11, etc. are rotationally driven, and the recording paper P is sent out from the recording paper supply take-up reel 3 via the platen roller I, and is conveyed in the direction A along the formed conveyance path. After the delivery roller 4 starts rotating counterclockwise in the figure, the rotation is stopped by an attached clutch 33 after a certain period of time has elapsed, and thereafter it can freely rotate.

The recording paper supply take-up reel 3 and the platen roller l are
During this time, it can freely rotate counterclockwise and clockwise in the figure. The tension roller 11 is driven to rotate clockwise in the figure with a low predetermined torque, and pinches the conveyed recording paper P between it and the driven roller 12 to apply tension and prevent it from sagging.

In this way, the recording paper P is rotated clockwise with the grip roller 6 as the only reference.
Due to the high frictional force on the surface, it is held between the driven roller 7 and conveyed exactly the desired length. For example, when thermal transfer is performed on A3 size paper, by controlling the rotational drive of the grip roller 6, that is, controlling the recording paper conveyance motor,
The leading edge of the recording paper P is conveyed to a position 420 mm away from the transfer position of the platen roller I in the A direction and then stopped.

The ink ribbon R is fed forward from the ink ribbon supply wheel 15 and stopped when the yellow ink reaches the thermal transfer position.

(2) Thermal transfer step for each color When a print command is issued thereafter, thermal transfer of the first color, yellow, is performed first.

That is, the thermal head 2 is pressed against the platen roller I via the ink ribbon R and the recording paper P, and the recording paper supply take-up reel 3 and the grip roller 6 are rotated clockwise and counterclockwise, respectively. Then, the recording paper P is conveyed in the B direction by the conveyance path and returned in the opposite direction to the previous feeding direction, and the ink ribbon R that is brought into close contact with the recording paper P is also conveyed together with it. Then, the heating element of the thermal head 2 is selectively energized and heated based on print data of a single color component of yellow, and the yellow ink applied to the ink ribbon R is thermally transferred to the recording paper P. Note that the recording paper supply take-up reel 3 is rotated clockwise in the figure with a low set torque to prevent the recording paper P from sagging. Although the platen roller l and the tension roller 11 can rotate counterclockwise, their rotational torque is limited to a certain level, and they apply a light bank tension like a brake to the conveyed recording paper P to prevent problems such as sagging. Preventing.

In this way, the recording paper P is rotated counterclockwise using the grip roller 6 as the sole reference during this thermal transfer, that is, when it is transported in the B direction, just as it was during the previous non-thermal transfer, that is, when it was transported in the A direction. Due to the high frictional force on the surface of the driven grip roller 6, it is held between the driven roller 7 and conveyed exactly the desired length. That is, by controlling the rotational drive of the grip roller 6, that is, by controlling the recording paper conveyance motor, the recording paper P has a printing area and printing length determined by the presence or absence of printing data, and a separation between the platen roller 1 and the ribbon separation roller 9. It is returned in the B direction by the total amount including the movement length, that is, by the amount previously conveyed in the incoming direction.

When the thermal transfer of the first color, yellow, is completed, the thermal head 2 is released from pressure contact with the platen roller l and separates, leaving a gap and retracting. Note that the used ink ribbon R is wound around the ribbon peeling roller 9 and removed from the recording paper P.
The ink ribbon is peeled off, sequentially fed forward, and wound onto the ink ribbon take-up reel 16.

Thereafter, thermal transfer of the second color, magenta, is performed. That is, the recording paper P is first fed in the input direction and stopped in accordance with the setting step (1) described above, and after the magenta ink is positioned on the ink ribbon R, the recording paper P is transferred to the B in accordance with the above-mentioned setting stage. The second color, magenta, is thermally transferred while being returned to the direction. Subsequently, the third color, cyan, is thermally transferred in the same manner.

(3) Paper discharge stage The thermal transfer of the third color cyan is completed, and the thermal head 2
When the recording paper P is separated from the platen roller 1, the recording paper P is in a state where it has been transported in the B direction and returned.

Therefore, the paper is ejected by largely feeding the recording paper P in the A direction and cutting it in accordance with the setting step (1) described above. That is, when the leading edge of the recording paper P is conveyed from the position of the cutter 14 in the direction A by a predetermined length, for example,
When thermal transfer is performed in three sizes, when the leading edge of the recording paper P is conveyed from the cutter 14 to a position of 420M,
The rotation of the grip roller 6 is stopped, and the cutter 14 is driven to cut the recording paper P into A3 size pieces.

(4) Preparation completion stage When the cutting by the cutter 14 is completed, the recording paper P for the next thermal transfer is rotated by the grip roller 6 so that its leading edge is, for example, 420 m from the transfer position of the platen roller l.
It is transported to the position m and enters the standby state.

This color thermal printer follows the steps of (1) setting stage, (2) thermal transfer stage for each color, (3) paper ejecting stage, and (4) preparation completion stage, and the ink of multiple colors of the ink ribbon R is printed on the recording paper P. The images are sequentially thermally transferred and superimposed to form a multicolor image.

Now, in this color thermal printer, color misregistration is prevented as follows.

First, the grip roller 6 serves as a reference for the reciprocating conveyance of the recording paper P, and the platen roller 1, which is deformed by pressure contact and separation from the thermal gutter 2, is only driven by the conveyance of the recording paper P. Therefore, the error between the reciprocating conveyance amount of the recording paper P that occurred when the platen roller l was used as the reference was
It will be resolved. Second, the grip roller 6 is transferred to the thermal
There is no expansion deformation due to heat from the throat 2, and the outer diameter accuracy is good.

Third, since the grip roller 6 is the only reference for reciprocating conveyance, it is not adversely affected by other conveying means, and the recording paper P can be conveyed with excellent accuracy even if the reciprocating conveyance is repeated a plurality of times. Fourthly, the tension roller 11 reliably prevents the recording paper P from sagging, and no error occurs in the thermal transfer position. This is the first of these. Second. Third. According to the fourth
Transfer misalignment of images on the recording paper P, that is, occurrence of color misalignment, is prevented.

In this color thermal printer, color misregistration is prevented in this way.

Further, in this color thermal printer, the thermal transfer range is widened as follows.

That is, during thermal transfer when the recording paper P is returned in the direction B, the platen roller 1 is rotatable, but its rotational torque is kept constant by adjusting means such as the torque limiter 18 (see FIGS. 2 and 3). It is designed to apply a light pack tension to the recording paper P conveyed in the B direction. Therefore, in the latter half of the thermal transfer for each color, the @(
If the rear end in the B direction (that is, the leading edge in the A direction) comes off the tension roller 11 in the B direction, and the thermal transfer is still continued, for example, if the print area and length are A3 size - cup, the following will occur. Become.

First, in such a case, if it is assumed that the platen roller 1 is completely free and rotatable regardless of the above, fluctuations in the winding load of the ink ribbon R and fluctuations in rotational speed due to the inertia of the platen roller 1 itself will occur. etc., adversely affect the conveyance of the recording paper P in the B direction, and the tension roller 11
Color misregistration will occur near the edge of the recording paper P that has come off.

In order to avoid this, it is necessary to restrict the thermal transfer range/printing range narrowly and exclude the area near the edge of the recording paper P, that is, the distance between the transfer position of the platen roller l and the tension roller 11 from the range. You won't get any more.

On the other hand, in this color thermal printer, in such a case, the platen roller 1 applies pack tension to the recording paper P as described above, so the adverse effects caused by various fluctuations are suppressed, and the occurrence of color misalignment near the edges of the recording paper P is prevented. Prevented. As a result, the recording paper P can be reliably thermally transferred to its edges, and the thermal transfer range and printing range are widened.

In this color thermal printer, the thermal transfer range is thus widened.

Furthermore, in this color thermal printer, skewing is prevented as follows.

That is, as described above, the tension roller 11 is divided into a plurality of parts in the axial direction, for example, into two parts in the example shown in FIG. 5, and each part applies an independent and equal tension to the recording paper P. Therefore, even if the positional accuracy of the tension roller 11 is somewhat poor and rough, for example, the axis of the tension roller 11 is not arranged parallel to the grip roller 6, which is the reference for conveyance of the recording paper P, the recording paper P Since independent and uniform tension is applied across the width, skewing is prevented.

As described above, the tension and back tension applied to the recording paper P conveyed in the input direction and the B direction are made uniform by the division, and skew does not occur.

On the other hand, in this case, if tension roller 1
Assuming that the recording paper P is not divided into pieces and is a single unit, there is a concern that the recording paper P may skew.

In this color thermal printer, skew feeding is prevented in this way.

The above is the explanation of the operation, etc.

"Others" Firstly, in this color thermal printer, the above-mentioned prevention of color misregistration is achieved only by a mechanical configuration.

In other words, the platen roller 1 and tension roller 1
1 is a mechanical rotation control system that combines a torque limiter 18 and a one-way clutch 20, a torque limiter 29 and a one-way clutch 26, 28, etc., as shown in FIGS. 2, 3, 4, 5, etc. is used, and an electrical rotation control method using a microcomputer, electromagnetic clutch, etc. is not used. Similarly, along with the grip roller 6, which has only a mechanical structure, the recording paper P
This prevents color misalignment.

Secondly, in this color thermal printer, since the conveyance path is formed in a nearly straight line, color misregistration and jamming can be prevented from occurring from this aspect as well.

That is, as shown in FIG. 1, the conveyance path of the recording paper P is as follows.
It is formed in a nearly horizontal straight line without any large U-shaped curves. Therefore, first of all, the amount of pressure and winding of the recording paper P around the platen roller 1, that is, the amount of bending of the recording paper P near the platen roller 1 is small, and the recording paper P transported by that amount is small.
This eliminates sagging and prevents color shift. Furthermore, since the conveyance path is straight, jamming of the recording paper P is naturally prevented.

Thirdly, in this color thermal printer, the first
As shown in the figure, roll paper is used as the recording paper P.
A return printing method is adopted in which thermal transfer is performed when returning to the direction, and an attempt is made to expand the thermal transfer range and printing range on the recording paper P as much as possible. However, the present invention is not limited to this, and if the thermal transfer range/printing range does not need to be expanded that much, cut paper may be used instead of roll paper as the recording paper P, and cut paper may be used instead of the supply winding reel 3 in a cassette. It is also possible to supply more of this. Of course in that case cutter 14
becomes unnecessary.

Fourthly, this color thermal printer is of a so-called full color type. That is, ink ribbon R
Three primary color inks of yellow, magenta, and cyan are applied to the recording paper P, and these are thermally transferred to the recording paper P to form a multicolor image. However, the present invention is not limited to this, and it is of course possible to use a method in which, for example, two colors of ink are applied to the ink ribbon R, and the two colors of ink are thermally transferred to form a multicolor image. It is conceivable to form a multicolor image using ink.

"Effects of the Invention" As explained above, the color thermal printer according to the present invention has a grip roller, which serves as a reference for reciprocating the recording paper, a rotatable platen roller, a tension roller, etc., and has the following features: Demonstrates the effect of

Firstly, since the grip roller rather than the platen roller serves as the reference for reciprocating conveyance, errors in the amount of reciprocal conveyance of the recording paper are eliminated. Second, the grip roller does not expand or deform due to heat from the thermal head and has good outer diameter accuracy. Thirdly, since the grip roller is the only reference, the conveyance accuracy is excellent even if the reciprocating conveyance is repeated. As a result, color misregistration in images is prevented and images of good quality can be obtained.

Furthermore, since the platen roller is equipped with an adjusting means that limits its rotational torque only during thermal transfer, tension is applied to the recording paper, and even if the thermal transfer progresses and the edge comes off the tension roller, color shift near the edge will not occur. This also has the effect of widening the thermal transfer range of the recording paper.

In this way, the problems that existed in this type of conventional example are completely eliminated, and the effects of the present invention are remarkable and great.

[Brief explanation of drawings]

FIG. 1 is an explanatory front view showing an embodiment of a color thermal printer according to the present invention. 2 and 3 are side sectional views showing the mounting structure of the platen roller, with FIG. 2 showing one example and FIG. 3 showing another example. FIG. 4 is a partially cutaway perspective view showing the mounting structure of the tension roller. FIG. 5 is a partially cutaway perspective view showing a mounting structure in which two tension rollers are provided. ■... 2... 6... 11... 18... P... R... Platen roller thermal head grip roller tension roller torque limiter (adjustment means) Recording paper ink ribbon 9 Figure F , 1 go” /

Claims (1)

[Claims] A thermal head is heated and pressed against a platen roller via the recording paper and the ink ribbon being conveyed, and multiple colors of ink on the ink ribbon are thermally transferred onto the recording paper in a surface-sequential manner to form a multicolor image. A color thermal printer comprising: a grip roller which is disposed downstream of the platen roller in the recording paper transport direction during thermal transfer, and which grips the recording paper and is driven to rotate in forward and reverse directions; and a tension roller disposed on the upstream side of the conveyance direction to apply tension to the recording paper being conveyed, the grip roller serving as a reference for reciprocating the recording paper, and the platen roller being rotatable. A color thermal printer characterized in that the platen roller is provided with an adjustment means that applies tension to the recording paper by limiting its rotational torque to a constant value only during thermal transfer.