JP2006346983A - Thermal printer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermal printer capable of executing edge-less print on a recording paper using one type of a platen roller, regardless of the recording paper. <P>SOLUTION: This thermal printer 1 can execute image printing from the front end 3a to the rear end 3b of the recorder paper 3 when the recording paper is carried in one arrow A direction. The thermal printer is arranged with a guide member 7 capable of guiding the rear end 3b of the recording paper 3 so as not to be away from the outer peripheral surface of the platen roller 2 by a prescribed distance, when the thermal head 9 is moved up to transfer the rear end 3b of the recording paper 3 in the other arrow B direction for a prescribed period. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a thermal printer, and more particularly to a thermal printer capable of printing a desired color image by reciprocating and transporting a recording sheet partially wrapped around a platen roller.

A conventional thermal printer is described in Patent Document 1. As shown in FIG. 6, a conventional thermal printer 30 has a cylindrical platen roller 31 and a thermal that can contact and separate (head up / down) with respect to the platen roller 31. A head 32 is disposed. FIG. 6 shows both the thermal head 32 in the head-down state and the thermal head 32 ′ in the head-up state (indicated by a two-dot chain line).
An ink ribbon 33 is routed between the platen roller 31 and the thermal head 32.
The ink ribbon 33 is wound around a take-up reel 33a and a supply reel 33b. Further, a recording paper 34 is disposed between the platen roller 31 around which the ink ribbon 33 is drawn and the thermal head 32, and the recording paper 34 is wound around the back surface thereof in close contact with the outer peripheral surface of the platen roller 31. ing.

The peripheral length of the outer peripheral surface of the platen roller 31 is formed longer than the length of the recording paper 34. For example, the platen roller 31 that can wind the recording paper 34 of A4 size is larger than A4 size A3. Although the recording paper 34 having a size cannot be wound, the recording paper 34 having an A5 size smaller than the A4 size can be wound.
Further, first to fourth contacts for pressing the recording paper 34 against the outer peripheral surface of the platen roller 31 so that the recording paper 34 wound around the outer peripheral surface is not displaced on the outer peripheral surface side of the platen roller 31. 35a to 35d are disposed.
The first to fourth contactors 35 a to 35 d are made of an elastic metal plate or the like, have a substantially U-shaped cross section, and are in elastic contact with the outer peripheral surface of the platen roller 31.

When a desired color image is printed on the recording paper 34, the platen roller 31 is rotated counterclockwise by the motor 36, and the uppermost recording paper 34 stored in the paper feeding cassette 37 is fed. Paper is fed to the platen roller 31 side by the roller 38.
Then, the leading end portion of the recording paper 34 is brought into pressure contact with the outer peripheral surface of the platen roller 31 by the first contactor 35a, and the thermal head 32 is headed down so that the ink ribbon 33 is pressed against the outer peripheral surface of the platen roller 31. Is done.

When the leading end of the recording paper 34 is conveyed between the thermal head 32 and the platen roller 31 with the head down, a plurality of heating elements (not shown) of the thermal head 32 are selected based on the print information. By generating heat, the ink of the ink ribbon 33 is printed on the recording paper 34, and a desired image is printed without borders on the entire surface of the recording paper 34.
JP 2003-39759 A JP 2003-39760 A

However, in the conventional thermal printer 30 as described above, the circumferential length of the outer peripheral surface of the platen roller 31 is formed longer than the length of the recording paper 34, and the entire length of the recording paper 34 is wound. The diameter dimension of the platen roller 31 is increased, and it is difficult to reduce the size of the thermal printer 30.
Further, when the length of the recording paper 34 is longer than the circumferential length of the platen roller 31, the recording paper 34 cannot be wound around the platen roller 31, so that the type of the platen roller 13 has to be exchanged.
The present invention has been made to solve the above-described problems. A thermal printer that can perform borderless printing on a recording sheet using a single platen roller regardless of the length of the recording sheet. The purpose is to provide.

As a first means for solving the above problems, a thermal printer according to the present invention includes a recording sheet, a cylindrical platen roller that can be wound around a part of the recording sheet and conveyed in one direction and the other direction, and the platen. It has a thermal head that can contact and separate (head up / down) from the roller,
It is possible to print an image on the entire surface from the front end portion to the rear end portion of the recording paper by the conveyance in the one direction, and after the image printing, the thermal head is raised up so that the rear end portion of the recording paper is A guide member capable of guiding the rear end portion of the recording paper from the outer peripheral surface of the platen roller so as not to be separated by a predetermined dimension or more when back-feeding in a different direction for a predetermined time is provided. To do.
Further, as a second means for solving the above-mentioned problem, a portion where the thermal head is headed down and pressed against the platen roller becomes the printing portion capable of image printing, and an outer peripheral surface of the platen roller is One pinch roller is disposed on the downstream side of the printing unit in the conveyance direction of the recording paper in the one direction, and the other pinch roller is disposed on the upstream side of the printing unit. A part of the recording paper is pressed and can be wound around the platen roller.
As a third means for solving the problem, the guide member is supported by the platen roller, and the recording paper is back-fed during the predetermined period during which the recording paper is back-feeded. At the same time, when the guide member rotates and at least the back-fed recording paper is brought into pressure contact with the other pinch roller, the guide member returns to the downstream home position from the printing unit. It is designed to do this.

As a fourth means for solving the above-mentioned problem, the guide member is always elastically biased in the one direction by an elastic member, and at least the back-fed recording sheet is the other pinch roller. When being pressed against each other, the home position is automatically returned by the urging force of the elastic member.
Further, as a fifth means for solving the above-mentioned problem, the guide member is supported by a rotation shaft of the platen roller so as to be rotatable, and a pair of arms extending to the outer peripheral surface side of the platen roller, A guide portion that bridges the pair of arm portions is formed, and a gap of a predetermined dimension is formed between the guide portion and the outer peripheral surface of the platen roller, and the back feed in the other direction is formed in the gap. The rear end side of the recording sheet is positioned so that the guide is possible.
Further, as a sixth means for solving the above-mentioned problem, the guide portion is formed with first and second inclined portions having substantially V shapes, and the apex at which the first and second inclined portions intersect with the first and second inclined portions. The said clearance gap is formed between the outer peripheral surfaces of a platen roller, It is characterized by the above-mentioned.

Further, as a seventh means for solving the above problem, the second inclined portion is characterized in that a front end portion of the recording sheet conveyed in the one direction is slidable.
As an eighth means for solving the problem, when the recording paper guided by the guide portion is back-fed for the predetermined time, the guide member stops rotating in the other direction. The recording paper to be back-fed is guided to the other pinch roller side.
Further, as a ninth means for solving the above-described problem, a roller support member that rotatably supports the one and the other pinch rollers is disposed, and the roller support member includes the one direction of the guide member. A first stopper portion capable of stopping rotation of the guide member and a second stopper portion capable of stopping rotation of the guide member in the other direction are formed with a predetermined interval. And

Further, as a tenth means for solving the above problem, the front end of the front recording sheet conveyed in the one direction with the guide member positioned at the home position during the image printing on the recording sheet. The portion slides on the second inclined portion and is guided to the one pinch roller side.
Further, as an eleventh means for solving the above-mentioned problem, a part of the recording paper is wound around the platen roller in a substantially U shape so as to be transported.

According to the present invention, it is possible to print an image on the entire surface from the front end to the rear end of the recording paper by conveying in one direction, and after printing the image, the thermal head is raised to move the rear end of the recording paper in the other direction. When backfeeding for a predetermined time, a guide member is provided that can guide the rear end of the recording paper from the outer peripheral surface of the platen roller so as not to exceed a predetermined dimension. Even without winding, the recording paper can be reliably back fed. Therefore, the diameter of the platen roller can be reduced, and a small thermal printer can be provided.
In addition, on the outer peripheral surface of the platen roller, one pinch roller is disposed on the downstream side of the printing unit in the recording paper conveyance direction in one direction, and the other pinch roller is disposed on the upstream side of the printing unit. Since a part of the recording paper can be wound around the platen roller by being pressed against the other pinch roller, a part of the recording paper to be fed back can be reliably wound around the platen roller. Color images can be printed.

The guide member is supported by the platen roller, and the guide member rotates together with the back-fed recording paper for a predetermined period during which the recording paper is back-fed so that at least the back-fed recording paper is the other. When pressed against the pinch roller, the guide member returns to the home position on the downstream side of the printing section, so the guide member does not get in the way when printing the image with the thermal head down. It has become.
The guide member is always elastically urged in one direction by the elastic member, and at least when the recording paper to be back fed is pressed against the other pinch roller, it automatically returns to the home position by the urging force of the elastic member. Therefore, a drive source for rotationally driving the guide member is not required, and a low-cost thermal printer with a reduced number of parts can be provided.

In addition, a gap of a predetermined size is formed between the guide portion and the outer peripheral surface of the platen roller, and the rear end side of the recording paper that is back-feeded in the other direction is positioned in the gap and can be guided. Therefore, the back end portion of the recording paper to be back-fed is not separated from the platen roller by a predetermined dimension or more, and reliable back-feeding can be performed.
Further, the guide portion is formed with first and second inclined portions that are substantially V-shaped, and a gap is formed between the apex at which the first and second inclined portions intersect and the outer peripheral surface of the platen roller. The recording paper can be reliably fed back without causing a problem such as paper jam.

In addition, since the front end portion of the recording paper conveyed in one direction is slidable in the second inclined portion, the second inclined portion ensures that the recording paper during image printing is placed on the other platen roller. I can guide you.
Further, when the recording paper guided by the guide portion is back-fed for a predetermined time, the rotation of the guide member in the other direction is stopped and the back-fed recording paper is guided to the other pinch roller side. Therefore, it is possible to reliably feed the recording paper back.

In addition, a roller support member that rotatably supports one and the other pinch rollers is disposed. The roller support member includes a first stopper portion that can stop the rotation of the guide member in one direction, and a guide member Since the second stopper portion capable of stopping the rotation in the other direction is formed at a predetermined interval, the guide member is moved from the first stopper portion to the second stopper by the back-fed recording paper. Rotate to the part. Therefore, the recording paper to be back-fed can be conveyed to the other pinch roller via the second stopper portion without any trouble such as paper jam.
Further, during image printing on the recording paper, the guide member is positioned at the home position, and the front end portion of the recording paper conveyed in one direction slides along the second inclined portion and is guided to the one pinch roller side. It is possible to reliably prevent problems such as paper jams on the recording paper during image printing.
In addition, since the recording paper is partly wound in a substantially U shape around the platen roller and can be conveyed, the recording paper of different types can be conveyed by one type of platen roller. Therefore, the diameter dimension of the platen roller can be reduced.

  Hereinafter, an embodiment of a thermal printer of the present invention will be described with reference to the drawings. 1 and 2 are cross-sectional views illustrating the main part of the thermal printer of the present invention, FIG. 3 is a side view illustrating the operation of the guide member according to the present invention, and FIGS. 4 and 5 are related to the present invention. It is a perspective view of the platen roller which attached the guide member.

First, a thermal printer 1 according to an embodiment of the present invention will be described with reference to FIGS. 1 to 5. A long platen roller 2 having a cylindrical shape is provided, and the platen roller 2 has both ends in the longitudinal direction. A rotating shaft 2a that protrudes from the portion with a predetermined length is formed.
The platen roller 2 supported by a frame side plate (not shown) and connected to a drive source such as a motor can be driven to rotate clockwise and counterclockwise. Yes.
A part of recording paper 3 made of thick paper such as photographic paper is wound around the outer peripheral surface of the platen roller 2 in a substantially U shape. It can be conveyed in the other direction.

The platen roller 2 has a printing portion 2b where a thermal head 9 to be described later comes down and press-contacts, and printing on the outer peripheral surface of the platen roller 2 in the direction of conveyance of the recording paper 3 in one direction of arrow A is performed. One pinch rollers 4 and 4 are disposed on the downstream side (left side in the drawing) from the portion 2b, and the other pinch rollers 5 and 5 are disposed on the upstream side (right side in the drawing) from the printing portion 2b.
The recording sheet 3 conveyed in one direction of the arrow A is configured such that the front end portion 3a is pressed against the outer peripheral surface of the platen roller 2 by one pinch roller 4 and is conveyed in the other direction of the arrow B. The recording paper 3 is configured such that the rear end 3 b is pressed against the outer peripheral surface of the platen roller 2 by the other pinch roller 5.
That is, the recording paper 3 that is pressed and sandwiched between the platen roller 2 by the one and the other pinch rollers 4 and 5 is wound around the platen roller 2 in a substantially U shape, and in one direction of the arrow A and the other of the arrow B. It can be transported in the direction.

As shown in FIGS. 4 and 5, the one and the other pinch rollers 4 and 5 are rotatable on a pair of roller support members 6 disposed at both ends in the longitudinal direction of the platen roller 2. It is supported on the outer peripheral surface so that it can be elastically contacted.
The one and the other pinch rollers 4 and 5 are rotatably supported at both ends in the longitudinal direction by frame side plates (not shown). Therefore, the movement of the roller support member 6 is regulated by the respective pinch rollers 4 and 5.
The one and the other pinch rollers 4 and 5 can be elastically contacted with the outer peripheral surface of the platen roller 2.
The roller support member 6 is formed with a first stopper portion 6a (the left side in the drawing) and a second stopper portion 6b (the right side in the drawing) at positions facing each other with an interval of a predetermined dimension on the upper side in the drawing. A part of the outer peripheral portion of the platen roller 2 is exposed between the first and second stopper portions 6a and 6b.

A guide member 7 made of a metal plate 7 is rotatably supported on the rotation shaft 2a of the platen roller 2 as shown in FIGS.
Then, when a thermal head 9 to be described later is raised and the recording paper 3 is back-fed in the other direction of the arrow B as shown in FIG. The guide can be guided so as not to be separated from the outer peripheral surface of the roller 2 by a predetermined dimension or more.

As shown in FIGS. 4 and 5, the guide member 7 is formed with a pair of arm portions 7 a, and the arm portions 7 a are respectively provided on the rotation shafts 2 a protruding from both end portions in the longitudinal direction of the platen roller 2. The platen roller 2 is rotatably supported and extends to the outer peripheral surface side.
The guide member 7 is formed with a long guide portion 8 that bridges between the pair of arm portions 7 a, and the recording paper 3 is inserted between the guide portion 8 and the outer peripheral surface of the platen roller 2. A possible gap of a predetermined dimension is formed.
As shown in FIG. 3, the guide portion 8 has a first inclined portion 8a on the left side and a second inclined portion 8b on the right side, and is substantially V-shaped.

The guide member 7 is always elastically biased in one direction of an arrow A by an elastic member (not shown). Therefore, before the recording paper 3 is fed to the platen roller 2 and during the conveyance of the recording paper 3 in one direction of the arrow A, the first inclined portion 8 a of the guide portion 8 is the first inclined portion 8 a of the roller support member 6. The movement is restricted by contacting the first stopper portion 6a.
The position where the guide member 7 is in contact with the first stopper portion 6 a on the downstream side of the printing portion 2 b in the conveyance direction in one direction of the arrow A is the home position of the guide member 7.

That is, the guide member 7 before the recording paper 3 is back-feeded in the other direction of the arrow B is located at the home position on the downstream side of the printing unit 2b in the conveying direction of the arrow A. Then, when the image printing to the rear end portion 3b of the recording paper 3 is completed in the direction indicated by the arrow A, the conveyance in the one direction of the recording paper 3 is stopped.
At this time, on the rear end portion 3b side of the recording paper 3, a spring back is generated to leave the outer peripheral surface of the platen roller 2, but the recording paper 3 is placed on the guide portion 8 of the guide member 7 located at the home position. The rear end 3 b side is guided so that the rear end 3 b of the recording paper 3 is not separated from the outer peripheral surface of the platen roller 2 by a predetermined dimension or more.

Further, the recording paper 3 in which the back feed in the other direction of the arrow B is started in the state where the guide member 7 is located at the home position, the rear end 3b side is not separated from the outer peripheral surface of the platen roller 2 by a predetermined dimension or more. In this way, the guide member 8 is guided by the guide portion 8. And while the recording paper 3 is back-fed for a predetermined time, it is conveyed with the guide member.
That is, since the guide member 7 can be rotated in the other direction of the arrow B against the urging force of an elastic member (not shown) by the recording paper 3 being back fed, the guide member 7 is driven. This eliminates the need for a driving source to reduce the number of parts and reduces the cost.

Further, the guide member 7 when the recording paper 3 pressed and sandwiched between the platen roller 2 and the other pinch roller 5 is fed in one direction of the arrow A is positioned at the home position on the downstream side of the printing unit 2b. is doing.
The recording sheet 3 fed in one direction has a front end 3 a that abuts against the second inclined portion 8 b and slides on the lower surface of the second inclined portion 8 b, so that the platen roller 2 and one pinch roller 4 It is designed to be clamped. Further, a thermal head 9 is disposed above the platen roller 2 shown in FIG. 1, and the thermal head 9 is composed of a long line head.
When the thermal head 9 is lowered, a portion where a plurality of heating elements (not shown) are formed can be pressed against the platen roller 2, and a portion where the heating elements are pressed is the printing unit 2b. .
The thermal head 9 is attached to a head mounting base 10 made of a highly heat conductive material with an adhesive or the like.

Further, on the right side of the head mounting base 10 shown in FIG. 1, a ribbon guide 11 capable of guiding an ink ribbon (not shown) wound around a supply reel (not shown) to the thermal head 9 side is disposed. A guide roller 12 capable of guiding an ink ribbon to a take-up reel (not shown) is disposed on the left side of the head mounting base 10.
The thermal head 9 is supported by a head support mechanism 13 on the upper side via a head mounting base 10 and can be brought into contact with and separated from the platen roller 2 (head up / down).

  The head support mechanism 13 includes a head support member 14 made of a highly heat conductive material such as an aluminum plate, and first and second rotating levers 15 and 16 made of iron plate or the like. As shown in FIG. A head mounting base 10 to which a thermal head 9 is fixed is attached to a flat head mounting portion 14 a formed on the left end portion side of the head support member 14.

A gap having a predetermined size is formed between the first and second rotating levers 15 and 16 to elastically hold the coil spring 17, and the lever portions 16 a and 17 a of the first and second rotating levers 15 and 16 are formed. The other end side on the right side of the figure and the other end side of the head support member 14 are supported by a support shaft 18 supported by a side plate on the frame side (not shown).
The head support mechanism 13 is rotated about the support shaft 18 as a fulcrum, so that the thermal head 9 moves up / down.

Image printing on the recording paper 3 by the thermal printer 1 of the present invention having such a configuration is performed by first moving the thermal head 9 up from the platen roller 2 by a predetermined size, for example, moving the platen roller 2 in one direction of arrow A. The recording paper 3 that is rotationally driven and pressed between the other pinch roller 5 and the platen roller 2 on the right side in the drawing is fed in one direction of an arrow A.
At this time, the guide member 7 is located at the home position on the downstream side of the printing unit 2b in the conveyance direction of the recording paper 3 with the arrow A.
The recording sheet 3 fed in one direction of the arrow A by the rotation of the platen roller 2 is such that the front end portion 3a slides on the lower surface side of the second inclined portion 8b of the guide portion 8 and the other pinch roller 5 side. Be guided to.

As a result, the front end portion 3a of the recording paper 3 is pressed and sandwiched between the other pinch roller 5 and the platen roller 2, and the front end portion 3a is conveyed in one direction of an arrow A as shown in FIG. The
At this time, a part of the recording paper 3 is wound around substantially half of the outer peripheral surface of the platen roller 2. That is, the recording paper 3 is conveyed by being partially wound around the platen roller 2 in a substantially U shape. Therefore, even the recording papers 3 having different lengths can be conveyed by one type of platen roller.

When the rear end portion 3b of the recording paper 3 fed in one direction of the arrow A is positioned downstream of the printing unit 2b, the rotation of the platen roller 2 is temporarily stopped. Then, based on a print command from the outside, the platen roller 2 is reversed in the other direction of the arrow B and the recording paper 3 is back-fed in the other direction.
Then, the guide member 7 that guides the rear end portion 3 b of the recording paper 3 so as not to be separated from the outer peripheral surface of the platen roller 2 by a predetermined dimension or more rotates together with the recording paper 3 to be fed back.

When the recording paper 3 is back-fed for a predetermined time, the other inclined portion 8b abuts on the second stopper portion 6b of the roller support member 6 and the guide member 7 that rotates in the other direction moves in the other direction. The rotation stops.
Then, the recording paper 3 to be back-fed slides on the guide portion 8, and the rear end portion 3b is guided to the other pinch roller 5 side via the second stopper portion 6b.
As a result, the rear end 3 b of the recording paper 3 is pressed and sandwiched between the other pinch roller 5 and the platen roller 2.

When the recording paper 3 slides on the guide portion 8 and is pressed between the other pinch roller 5 and the platen roller 2, the guide member 7 has a small frictional resistance with the recording paper 3, and an elastic member ( It automatically returns to the home position on the left side in the figure by the urging force (not shown).
Next, when the front end 3a is positioned on the printing unit 2b, the recording paper 3 back-feeding in the other direction of the arrow B temporarily stops the rotation of the platen roller 2 and the head support mechanism 13 is driven so that the thermal head 9 heads down.
Thereafter, the platen roller 2 is driven reversely in one direction of the arrow A, and the plurality of heating elements of the thermal head 9 are selectively heated based on the print information, whereby the recording paper 3 conveyed in the one direction of the arrow A. Then, the ink on the ink ribbon (not shown) is thermally transferred, and an image of a desired color is printed on the entire surface from the front end 3a to the rear end 3b of the recording paper 3, and the image is printed on the entire surface of the recording paper 3. (Borderless printing).

When printing a color image on the recording paper 3, the printing operation as described above is repeated a plurality of times, and inks of different colors on the ink ribbon are overprinted on the recording paper 3, so that a desired color image is printed. None can be printed.
In the thermal printer 1 of the present invention as described above, the back end portion 3b of the recording paper 3 is back-feeded in the other direction of the arrow B (the guide member 7 moves from the first stopper portion 6a to the second stopper portion 6b). Until the rear end 3b of the recording paper 3 is guided by the guide portion 8 of the guide member 7 so as not to be separated from the outer peripheral surface of the platen roller 2 by a predetermined dimension or more.

Therefore, the back-fed recording paper 3 can be reliably wound around the platen roller 2 with the rear end portion 3b guided to the other pinch roller 5, and the occurrence of problems such as cam removal can be prevented.
Further, according to the present invention, a part of the recording paper 3 is wound around the platen roller 2 in a substantially U shape and conveyed. Therefore, even if the length of the recording paper 3 is different, the platen roller 2 performs one direction or the other direction. The diameter can be made smaller than the platen roller 31 of the thermal printer 30 described in the conventional example. Therefore, the thermal printer 1 of the present invention can be downsized.

In the present invention, the guide member is described as being rotatably supported on the rotation shaft 2a of the platen roller 2. However, the guide member 7 is supported on the side plate on the frame side (not shown) to be rotatable. Things can be used.
The guide member 7 has been described as being elastically biased in one direction of arrow A by an elastic member (not shown) and automatically returning to the home position. However, the guide member 7 is driven to rotate by a cam member or the like. It may be the one made.

In addition, although the description has been given of the case where one and the other pinch rollers 4 and 5 are disposed, one and the other pinch rollers 4 and 5 may each be one.
Further, the feeding of the recording paper 3 before printing has been described by holding the front end portion 3a between the platen roller 2 and the pinch roller 5 and conveying it in one direction of arrow A. The end 3b may be pressed between the platen roller 2 and one pinch roller 4 and conveyed in the other direction of the arrow B.
Further, although the thermal printer 1 of the present invention has been described with respect to a thermal transfer printer using an ink ribbon (not shown), it may be one using thermal paper without using an ink ribbon.

It is principal part sectional drawing explaining the thermal printer of this invention. It is principal part sectional drawing explaining the thermal printer of this invention. It is a side view explaining operation | movement of the guide member concerning this invention. It is a perspective view of the platen roller which attached the guide member concerning this invention. It is a perspective view of the platen roller which attached the guide member concerning this invention. It is principal part sectional drawing of the conventional thermal printer.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Thermal printer 2 Platen roller 3 Recording paper 3a Front end part 3b Rear end part 4 One pinch roller 5 The other pinch roller 6 Roller support member 6a 1st stopper part 6b 2nd stopper part 7 Guide member 8 Guide part 8a 1st inclined part 8b 2nd inclined part
9 Thermal head 10 Head mount 13 Head support mechanism 14 Head support member 15 First rotation lever 16 Second rotation lever 17 Coil spring 18 Support shaft

Claims (11)

A recording sheet, a cylindrical platen roller that can be wound around a part of the recording sheet and conveyed in one direction and the other direction, and a thermal head that can contact (separate) the platen roller (head up / down) ,
It is possible to print an image on the entire surface from the front end portion to the rear end portion of the recording paper by the conveyance in the one direction, and after the image printing, the thermal head is raised up so that the rear end portion of the recording paper is A guide member capable of guiding the rear end portion of the recording paper from the outer peripheral surface of the platen roller so as not to be separated by a predetermined dimension or more when back-feeding in a different direction for a predetermined time is provided. Thermal printer.   A portion where the thermal head is headed down and press-contacted to the platen roller becomes a printing unit capable of printing the image, and the printing unit in the conveyance direction of the recording paper in the one direction is formed on the outer peripheral surface of the platen roller. One pinch roller is disposed on the further downstream side, and the other pinch roller is disposed on the upstream side from the printing unit, and a part of the recording paper is wound around the platen roller by being pressed against the one and the other pinch rollers. The thermal printer according to claim 1, wherein the thermal printer is enabled.   The guide member is supported by the platen roller, and the guide member rotates together with the back-fed recording paper during the predetermined period in which the recording paper is back-fed, so that at least the back feed 3. The guide member is configured to return to the downstream home position from the printing unit when the recording sheet to be pressed is pressed against the other pinch roller. To thermal printer.   The guide member is always elastically urged in one direction by an elastic member, and at least when the recording paper to be back fed is pressed against the other pinch roller, the urging force of the elastic member causes the home 4. The thermal printer according to claim 3, wherein the thermal printer automatically returns to the position.   The guide member is formed with a pair of arm portions that are rotatably supported by a rotation shaft of the platen roller and extend to the outer peripheral surface side of the platen roller, and a guide portion that bridges the pair of arm portions, A gap having a predetermined size is formed between the guide portion and the outer peripheral surface of the platen roller, and the rear end portion side of the recording paper that is back-fed in the other direction is positioned in the gap. The thermal printer according to claim 1, wherein the thermal printer is enabled.   The guide portion is formed with first and second inclined portions that are substantially V-shaped, and the gap is formed between an apex where the first and second inclined portions intersect with an outer peripheral surface of the platen roller. The thermal printer according to claim 5, wherein:   The thermal printer according to claim 6, wherein the second inclined portion is configured such that a front end portion of the recording sheet conveyed in the one direction is slidable.   When the recording paper guided by the guide portion is back-fed for the predetermined time, the guide member stops rotating in the other direction, and the back-fed recording paper is fed to the other pinch. The thermal printer according to claim 5, wherein the thermal printer is guided to a roller side.   A roller support member that rotatably supports the one and the other pinch rollers is disposed, and the roller support member includes a first stopper portion that can stop the rotation of the guide member in the one direction, and 9. The thermal printer according to claim 2, wherein the second stopper portion capable of stopping the rotation of the guide member in the other direction is formed with a predetermined interval. .   During the image printing on the recording paper, the guide member is located at the home position, and the front end portion of the front recording paper conveyed in the one direction slides on the second inclined portion, and the one pinch roller The thermal printer according to claim 7, wherein the thermal printer is guided sideways. 10. The thermal printer according to claim 1, wherein a part of the recording paper is wound around the platen roller in a substantially U shape so as to be transported.

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