Patent Publication Number: US-10315440-B2

Title: Platen unit and printer

Description:
TECHNICAL FIELD 
     The present invention relates to a thermal printer that performs printing while nipping and feeding a band-shaped continuous label sheet using a thermal head and a platen roller. 
     BACKGROUND ART 
     In the prior art, a linerless label adapted to save resources has been employed as a band-shaped continuous label sheet. The linerless label does not have a liner sheet (release sheet) on which an adhesive layer on a back surface of a label substrate is temporarily attached. 
     A thermal printer  1  for such a linerless label has a feeder unit  3  of a linerless label  2 , a detection unit  4 , and a print unit  5  as illustrated in  FIG. 10 . 
     The linerless label  2  is wound in a roll shape and is loaded on the feeder unit  3 . As illustrated in the partially enlarged view of  FIG. 10 , the linerless label  2  has a band-shaped label substrate  7 , an adhesive layer  8  formed on a back surface of the label substrate  7 , an underlying heat-sensitive color developing layer  9  formed on a front surface of the label substrate  7 , and an overlying release layer  10 . 
     In this manner, since the release layer  10  is formed on top of the linerless label  2 , the adhesive layer  8  comes into contact with the release layer  10  by winding the linerless label  2  in a roll shape. Therefore, even when a roll of the linerless label  2  is loaded on the feeder unit  3 , it is possible to continuously feed the linerless label  2  without sticking between inner and outer layers. 
     The linerless label  2  continuously discharged from the feeder unit  3  is fed to the print unit  5  from the feeder unit  3 . The detection unit  4  and a guide roller  11  that guides the linerless label  2  are provided in the middle of a feeding path of the linerless label  2  from the feeder unit  3  to the print unit  5 . 
     The detection unit  4  has a mark sensor  12  such as a transparent optical sensor to detect a relative position of the linerless label  2  with respect to the print unit  5  by sensing a position detection mark (not shown) printed on the linerless label  2  in advance at a predetermined pitch. 
     The print unit  5  has a thermal head  13  and a platen roller  14 . The linerless label  2  continuously discharged from the feeder unit  3  is fed to a gap between the thermal head  13  and the platen roller  14 . 
     In the print unit  5 , the linerless label  2  is nipped and fed by rotating the platen roller  14 , and printing of predetermined contents is performed on a surface of the label substrate  7  by supplying data to a heating element  15  of the thermal head  13  and developing a heat-sensitive color developing layer  9  formed on the surface of the label substrate  7 . 
     The linerless label  2  is cut out along a line of perforations (not shown) formed on the linerless label  2  at a predetermined pitch and is issued as a single tag of the linerless label  2 A. Alternatively, the printed linerless label  2  may be cut out at a predetermined pitch using a cutter such as a movable blade or a fixed blade to issue a single tag of the linerless label  2 A. 
     In the thermal printer  1  having such a configuration, a releasable material such as silicone rubber is used on the platen roller  14  coming into contact with the adhesive layer  8  of the back surface of the linerless label  2  to guarantee non-adhesiveness. In addition, a downstream-side wraparound prevention member  16  having non-adhesiveness similar to that of the platen roller  14  is provided in a downstream side of the feeding direction from the platen roller  14 . 
     It is desirable to design a gap between the downstream-side wraparound prevention member  16  and the platen roller  14  as small as possible. Meanwhile, if the platen roller  14  is detachably installed considering maintainability, and the gap between the downstream-side wraparound prevention member  16  and the platen roller  14  is excessively small, the downstream-side wraparound prevention member  16  may interfere in installation or removal of the platen roller  14 . 
     In this regard, a technique has been proposed, in which the downstream-side wraparound prevention member  16  is assembled with a platen bearing that rotatably supports the roller shaft  140  of the platen roller  14 , and the platen bearing is detachably installed in the support member provided in a device housing as a fixing portion, so that the platen roller  14  and the downstream-side wraparound prevention member  16  are unitized into a single assembly, and the single assembly is detachably installed in the device housing (see JP 09-314948 A). 
     In the technique of JP 09-314948 A, a pair of notches are formed on an outer circumference of the platen bearing, and the downstream-side wraparound prevention member  16  is assembled with a pair of notches. In addition, the platen bearing is inserted into a concave portion of the support member and is fixed by rotating a pair of notches of the platen bearing in synchronization with the downstream-side wraparound prevention member  16 . 
     SUMMARY OF INVENTION 
     Even in backward feeding of the linerless label  2 , the linerless label  2  may stick to the platen roller  14 . For this reason, similar to the platen roller  14 , it is conceived that an upstream-side wraparound prevention member having non-adhesiveness may also be provided in the upstream side of the feeding direction from the platen roller  14 . 
     Similar to the downstream-side wraparound prevention member  16 , it is desirable to design a gap between the upstream-side wraparound prevention member and the platen roller  14  as small as possible. However, if the gap is excessively small, installation or removal of the platen roller  14  may become difficult. 
     In this regard, in addition to the platen roller  14  and the downstream-side wraparound prevention member  16 , the upstream-side wraparound prevention member may also be unitized into an assembly. However, since the platen roller  14  is interposed between the downstream-side wraparound prevention member  16  and the upstream-side wraparound prevention member, interference may be generated in any one of the downstream-side wraparound prevention member  16  and the upstream-side wraparound prevention member when the platen bearing is fixed in the support member, and it may be difficult to smoothly perform installation or removal. 
     In view of the aforementioned problems, it is therefore an object of the present invention to provide a thermal printer capable of facilitating smooth installation or removal even when the upstream-side wraparound prevention member is unitized in addition to the platen roller and the downstream-side wraparound prevention member. 
     According to a first aspect of the present invention, there is provided a thermal printer including: a thermal head and a platen roller configured to perform printing while nipping and feeding a linerless label; a downstream-side wraparound prevention member disposed on a downstream side of a feeding direction, the downstream-side wraparound prevention member being configured to prevent the linerless label from rolling up to the platen roller; an upstream-side wraparound prevention member disposed on an upstream side of the feeding direction, the upstream-side wraparound prevention member being configured to prevent the linerless label from rolling up to the platen roller; a fixing portion configured to rotatably support a roller shaft of the platen roller; and a support member configured to detachably support the fixing portion, wherein the downstream-side wraparound prevention member is assembled with the fixing portion fixedly in a rotational direction of the roller shaft, the upstream-side wraparound prevention member is assembled rotatably with respect to the roller shaft, and the downstream-side wraparound prevention member and the upstream-side wraparound prevention member are provided with a restriction mechanism, the restriction mechanism is configured to restrict relative rotation of the upstream-side wraparound prevention member with respect to the downstream-side wraparound prevention member. 
     According to a second aspect of the present invention, at the thermal printer according to the above-described first aspect, the support member is provided with a fixing concave portion for fixing the fixing portion, the downstream-side wraparound prevention member is positioned by inserting the fixing portion into the fixing concave portion in a predetermined direction and thereafter rotating the downstream-side wraparound prevention member and the fixing portion around the roller shaft, and the upstream-side wraparound prevention member is positioned in a predetermined position by inserting the fixing portion into the fixing concave portion while rotation of the upstream-side wraparound prevention member is restricted by the restriction mechanism so as not to approach the downstream-side wraparound prevention member. 
     According to a third aspect of the present invention, at the thermal printer according to the above-described first aspect, the support member is provided with a fixing concave portion for fixing the fixing portion, the downstream-side wraparound prevention member is positioned by inserting the fixing portion into the fixing concave portion in a predetermined direction and thereafter rotating the downstream-side wraparound prevention member and the fixing portion around the roller shaft, and the upstream-side wraparound prevention is positioned with assistance in rotation to a predetermined position by inserting the fixing portion into the fixing concave portion while rotation of the upstream-side wraparound prevention member is restricted by the restriction mechanism so as not to be apart from the downstream-side wraparound prevention member. 
     According to a forth aspect of the present invention, at the thermal printer according to the above-described third aspect, the thermal printer further includes an engagement portion provided with a slope surface, the slope surface being configured to rotate the upstream-side wraparound prevention member toward the predetermined position by abutting on the upstream-side wraparound prevention member when the fixing portion is inserted into the fixing concave portion. 
     According to a fifth aspect of the present invention, at the thermal printer according to the above-described forth aspect, the engagement portion is provided with a pair of engagement surfaces, the pair of engagement surfaces have different angles and position the upstream-side wraparound prevention member by engaging in different places of the upstream-side wraparound prevention member. 
     According to a sixth aspect of the present invention, at the thermal printer according to the above-described forth aspect, a portion of the upstream-side wraparound prevention member that abuts on the slope surface by inserting the fixing portion into the fixing concave portion is placed in the upstream side with respect to a center axis of the roller shaft. 
     According to the aspects of the present invention, even when the upstream-side wraparound prevention member is unitized in addition to the platen roller and the downstream-side wraparound prevention member, it is possible to position the upstream-side wraparound prevention member so as not to generate interference in installation of the platen roller and smoothly perform installation or removal of the platen roller. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic side view illustrating a configuration of a thermal printer according to an embodiment of the invention; 
         FIG. 2  is a schematic perspective view illustrating a configuration of a platen unit having a downstream-side wraparound prevention member and an upstream-side wraparound prevention member installed in a platen roller; 
         FIG. 3  is an exploded perspective view illustrating the platen unit; 
         FIG. 4  is a schematic perspective view illustrating a configuration of the thermal printer; 
         FIG. 5  is an explanatory diagram for describing how to mount the platen unit on a support member by holding only a downstream-side plate portion; 
         FIG. 6  is an explanatory diagram for describing how to mount the platen unit on the support member by holding only the downstream-side plate portion; 
         FIG. 7  is an explanatory diagram for describing how to mount the platen unit on the support member by holding only the downstream-side plate portion; 
         FIG. 8  is an explanatory diagram for describing how to mount the platen unit on the support member by holding only the downstream-side plate portion; 
         FIG. 9  is an explanatory diagram for describing how to mount the platen unit on the support member by holding the downstream-side plate portion and the upstream-side plate portion; and 
         FIG. 10  is a schematic side view illustrating a thermal printer of the prior art. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Embodiments of the present invention will now be described in detail with reference to the accompanying drawings. 
     Referring to  FIG. 1 , a thermal printer  1   a  according to an embodiment of the invention includes a feeder unit  3  of a linerless label  2 , a detection unit  4 , and a print unit  5   a . Note that, in  FIGS. 1 and 2 , like reference numerals denote like elements as in a thermal printer  1  of the prior art illustrated in  FIG. 10 , and they will not be described repeatedly. 
     Referring to  FIG. 1 , the print unit  5   a  is provided with a downstream-side wraparound prevention member  16  placed in a downstream side of a feeding direction of the linerless label  2  (hereinafter, simply referred to as a “downstream side”) with respect to the platen roller  14  and an upstream-side wraparound prevention member  17  placed in an upstream side of the feeding direction of the linerless label  2  (hereinafter, simply referred to as an “upstream side”) with respect to the platen roller  14 . 
     As illustrated in  FIG. 2 , the downstream-side wraparound prevention member  16  and the upstream-side wraparound prevention member  17  are assembled with a roller shaft  140  of the platen roller  14  to form the platen unit  30 . 
     Note that the platen roller  14  is formed of a releasable material such as silicone rubber to guarantee non-adhesiveness. Similar to the platen roller  14 , non-adhesiveness is also provided on surfaces of the downstream-side wraparound prevention member  16  and the upstream-side wraparound prevention member  17  coming into contact with a back surface of the linerless label  2 . 
     Referring to  FIG. 3 , the platen unit  30  has a pair of holding bearings  31 , a pair of platen bearings  32 , a gear unit  33 , and a pair of retainers  34  in addition to the platen roller  14 , the downstream-side wraparound prevention member  16 , and the upstream-side wraparound prevention member  17 . 
     Toward a feeding direction of the linerless label  2 , a rotational shaft portion  141  rotatably supported by the holding bearing  31  and the platen bearing  32 , and an engagement groove  143  engaged with the retainer  34  are sequentially provided toward an open end in the roller shaft  140  placed in the left side of the platen roller  14 . 
     In addition, toward the feeding direction of the linerless label  2 , a rotational shaft portion  141  rotatably supported by the holding bearing  31  and the platen bearing  32 , a D-cut portion  142  cut in a D-shape and provided with a gear portion  33 , and an engagement groove  143  engaged with the retainer  34  are sequentially provided toward an open end in the other end side of the roller shaft  140  placed in the right side of the platen roller  14 . 
     The holding bearing  31  has an engagement protrusion  311  assembled with the upstream-side wraparound prevention member  17  and a flange portion  312 , and is annularly installed in left and right rotational shaft portions  141  of the roller shaft  140  while the engagement protrusion  311  faces inward. 
     The upstream-side wraparound prevention member  17  has a left bracket  171  assembled with the holding bearing  31  annularly installed in the left rotational shaft portion  141 , a right bracket  172  installed in the holding bearing  31  annularly installed in the right rotational shaft portion  141 , and an upstream-side plate portion  173  stretching between the left and right brackets  171  and  172 . 
     The left bracket  171  is provided with an installation hole  174 , and the right bracket  172  is provided with an installation groove  178 . The installation hole  174  and the installation groove  178  are assembled with the engagement protrusions  311  of the left and right holding bearings  31 , respectively. 
     As a result, the upstream-side wraparound prevention member  17  is provided independently from rotation of the platen roller  14  (roller shaft  140 ) while a gap between a circumferential surface of the platen roller  14  and the upstream-side plate portion  173  is appropriately maintained. 
     The platen bearing  32  has an engagement protrusion  321  assembled with the downstream-side wraparound prevention member  16 , a fixing portion  322  supported by the support member  43 , and a flange portion  323  provided between the engagement protrusion  321  and the fixing portion  322 . The platen bearing  32  is annularly installed in each of the left and right rotational shaft portion  141  of the roller shaft  140  next to the holding bearing  31  while the engagement protrusion  321  faces inward. 
     The downstream-side wraparound prevention member  16  has a pair of installation brackets  161  respectively assembled with the platen bearings  32  annularly respectively installed in the left and right rotational shaft portions  141  and a downstream-side plate portion  162  stretching between a pair of installation brackets  161 . 
     Flat cutting is performed for the engagement protrusion  321  of the platen bearing  32  to form a pair of flat-cut faces, and the installation bracket  161  is provided with an engagement hole  163  engaged with the engagement protrusion  321 . The installation brackets  161  are assembled with the engagement protrusions  321  of each of the left and right platen bearings  32  through the engagement holes  163 . 
     As a result, the downstream-side wraparound prevention member  16  is provided independently from rotation of the platen roller  14  (roller shaft  140 ) while a gap between a circumferential surface of the platen roller  14  and the downstream-side plate portion  162  is appropriately maintained. 
     The platen bearing  32  and the downstream-side wraparound prevention member  16  are fixed in a rotational direction with respect to the roller shaft  140  and are rotated in synchronization with each other around the platen roller  14  (roller shaft  140 ). 
     The downstream-side wraparound prevention member  16  is assembled with the platen bearing  32 , and the upstream-side wraparound prevention member  17  is assembled with the holding bearing  31 . Since the platen bearing  32  and the holding bearing  31  are members independent from each other, the downstream-side wraparound prevention member  16  and the upstream-side wraparound prevention member  17  are rotated around the platen roller  14  (roller shaft  140 ) independently from each other. 
     Referring to  FIG. 4 , the thermal printer  1   a  is provided with a casing  40  which includes a lower casing  41  and an upper cover  42  that openably/closably covers an upper part of the lower casing  41  with the rear side of the lower casing  41  as a fulcrum. Note that  FIG. 4  shows the thermal printer  1   a  in which the platen unit  30  is removed. 
     The upper cover  42  has a thermal head  13  provided with a heating element  15 , and the lower casing  41  provided with a feeding unit  3  that rotatably supports and houses a roll of the linerless label  2 . 
     The lower casing  41  is provided with a pair of support members  43  where the platen unit  30  is mounted. The pair of support members  43  are positioned where face the heating element  15  while the upper cover  42  is closed. In addition, a first engagement portion  44  that positions the upstream-side wraparound prevention member  17  of the platen unit  30  and second and third engagement portions  45  and  46  that position the downstream-side wraparound prevention member  16  of the platen unit  30  are provided between the pair of support members  43 . 
     First, how to mount the platen unit  30  on the support members  43  by holding the downstream-side plate portion  162  of the downstream-side wraparound prevention member  16  will be described in detail with reference to  FIGS. 5 to 8 . 
     Referring to  FIG. 5 , the support member  43  is provided with an insertion portion  431  opened upward and a fixing concave portion  432  that supports the fixing portion  322  of the platen bearing  32 . 
     Flat cutting is performed for opposite sides of the fixing portion  322  of the platen bearing  32 . In addition, an interval L 1  of the insertion portion  431  is slightly larger than a small diameter L 2  (the interval between the opposite flat-cut faces) of the fixing portions  322 . A diameter M 1  of the fixing concave portion  432  is set nearly equal to a large diameter M 2  of the fixing portion  322 . 
     By inserting the fixing portion  322  from the insertion portion  431  to the fixing concave portion  432  while the flat-cut faces of the fixing portion  322  are vertically erected, as illustrated in  FIGS. 6 and 7 , and then rotating the fixing portion  322  around the roller shaft  140 , as illustrated in  FIG. 8 , the installation brackets  161  assembled with each of the platen bearings  32  (the downstream-side wraparound prevention member  16 ) are positioned, so that the fixing portions  322  are fixed to the fixing concave portions  432  of the support members  43 . 
     Note that, in  FIGS. 6 and 7 , the downstream-side wraparound prevention member  16  and the second and third engagement portions  45  and  46  are not illustrated. In  FIG. 8 , the upstream-side wraparound prevention member  17  and the first engagement portion  44  are not illustrated. 
     As illustrated in  FIG. 3 , each of the left and right brackets  171  and  172  of the upstream-side wraparound prevention member  17  is provided with a rotation restrictor  175  engaged with the downstream-side plate portion  162  of the downstream-side wraparound prevention member  16  from its back surface side. 
     The downstream-side wraparound prevention member  16  and the upstream-side wraparound prevention member  17  are rotatable independently from each other. On the other hand, when the rotation restrictor  175  is engaged with the downstream-side plate portion  162  from its back surface, the rotation of the upstream-side wraparound prevention member  17  is restricted relatively to the downstream-side wraparound prevention member  16  to prevent the downstream-side plate portion  162  of the downstream-side wraparound prevention member  16  from being apart from the upstream-side plate portion  173  of the upstream-side wraparound prevention member  17  more than necessary. 
     As a result, as illustrated in  FIG. 5 , the upstream-side end portion of the upstream-side plate portion  173  is placed in the upstream side from a center axis of the roller shaft  140  in mounting of the platen unit  30  while the flat-cut faces of the fixing portion  322  are vertically erected. 
     As illustrated in  FIG. 6 , the first engagement portion  44  of the lower casing  41  is provided with a slope surface  441  that abuts on the upstream-side end portion of the upstream-side plate portion  173  when the platen unit  30  is mounted. 
     The slope surface  441  has an approximately arc cross section, and its upstream side is smoothly elevated. The slope surface  441  has a curvature gentler than that of the locus of the upstream-side end portion of the upstream-side plate portion  173  for rotation of the upstream-side wraparound prevention member  17 . As a result, when the platen unit  30  is mounted, a force is exerted from the slope surface  441  to the upstream-side end portion of the upstream-side plate portion  173 , so that the upstream-side wraparound prevention member  17  is rotated in the arrow direction of  FIG. 6 , that is, such that the upstream-side plate portion  173  is shifted to the upstream side. 
     Note that, when the platen unit  30  is mounted, an operator may rotate the upstream-side wraparound prevention member  17  in the arrow direction of  FIG. 6 , that is, such that the upstream-side plate portion  173  is shifted to the upstream side. In this case, as the upstream-side plate portion  173  abuts on the slope surface  441 , a force is exerted from the slope surface  441  to the upstream-side end portion of the upstream-side plate portion  173  as indicated by the arrow direction of  FIG. 6 . Therefore, it is possible to assist an operator to rotate the upstream-side wraparound prevention member  17 . 
     As the first engagement portion  44 , a horizontal engagement surface  442  is provided in the upstream side of the slope surface  441 , and a vertical engagement surface  443  is provided in the downstream side of the slope surface  441 . When the upstream-side end portion of the upstream-side plate portion  173  is deviated from the slope surface  441  by the rotation of the upstream-side wraparound prevention member  17 , the upstream-side positioning portion  176  provided in the left bracket  171  with a gap from the upstream-side end portion of the upstream-side plate portion  173  abuts on the slope surface  441 , and the upstream-side wraparound prevention member  17  is rotated similarly. 
     The left bracket  171  is provided with a downstream-side positioning portion  177  with a gap from the upstream-side positioning portion  176 . When the center axis of the roller shaft  140  reaches a predetermined position as the platen unit  30  is mounted, the upstream-side positioning portion  176  is engaged with the horizontal engagement surface  442  of the first engagement portion  44 , and the downstream-side positioning portion  177  is engaged with the vertical engagement surface  443  of the first engagement portion  44  as illustrated in  FIG. 7 , so that the upstream-side wraparound prevention member  17 , that is, the upstream-side plate portion  173  is positioned in a predetermined position in the left side. 
     As illustrated in  FIG. 3 , the right bracket  172  is also provided with the upstream-side positioning portion  176  and the downstream-side positioning portion  177 . Similarly, in the right bracket  172 , the upstream-side positioning portion  176  is engaged with the horizontal engagement surface  442  of the first engagement portion  44 , and the downstream-side positioning portion  177  is engaged with the vertical engagement surface  443  of the first engagement portion  44 , so that the upstream-side wraparound prevention member  17 , that is, the upstream-side plate portion  173  is positioned in a predetermined position in the right side. 
     As a result, the upstream-side wraparound prevention member  17 , that is, upstream-side plate portion  173  is positioned in both right and left sides. 
     Referring to  FIG. 8 , the installation bracket  161  of the downstream-side wraparound prevention member  16  is provided with an upstream-side positioning portion  164  that abuts on the second engagement portion  45  when the platen unit  30  is mounted. The second engagement portion  45  extends to the upstream side and has an elastic piece  451  that deforms as the upstream-side positioning portion  164  abuts and a horizontal engagement surface  452  formed in the open end of the elastic piece  451 . 
     The installation bracket  161  is provided with a downstream-side positioning portion  165  with a gap from the upstream-side positioning portion  164 . As the downstream-side wraparound prevention member  16  fixed to the fixing portion  322  in a rotational direction is rotated in the arrow direction of  FIG. 7 , the upstream-side positioning portion  164  is engaged with the horizontal engagement surface  452  of the second engagement portion  45 , and the downstream-side positioning portion  165  is engaged with the third engagement portion  46  as the horizontal engagement surface as illustrated in  FIG. 8 , so that the downstream-side wraparound prevention member  16 , that is, the downstream-side plate portion  162  is positioned in a predetermined position. 
     As a result, the fixing portion  322  is fixed to the fixing concave portion  432  of the support member  43 , and the platen roller  14  is installed in a predetermined position. 
     Subsequently, how to mount the platen unit  30  on the support members  43  by holding the downstream-side plate portion  162  of the downstream-side wraparound prevention member  16  and the upstream-side plate portion  173  of the upstream-side wraparound prevention member  17  will be described in detail with reference to  FIG. 9 . 
     When an operator holds both the downstream-side plate portion  162  of the downstream-side wraparound prevention member  16  and the upstream-side plate portion  173  of the upstream-side wraparound prevention member  17 , the downstream-side plate portion  162  and the upstream-side plate portion  173  abut on each other as illustrated in  FIG. 9 . 
     The downstream-side plate portion  162  and the upstream-side plate portion  173  serve as a restriction mechanism for restricting relative rotation so as not to allow the upstream-side wraparound prevention member  17  to approach the downstream-side wraparound prevention member  16 . 
     While rotation is restricted so as not to allow the upstream-side wraparound prevention member  17  to approach the downstream-side wraparound prevention member  16 , that is, while the downstream-side plate portion  162  and the upstream-side plate portion  173  abut on each other, the fixing portion  322  is inserted into the fixing concave portion  432  through the insertion portion  431  by vertically erecting the flat-cut surface of the fixing portion  322 . As a result, the left and right brackets  171  and  172  of the upstream-side wraparound prevention member  17  are guided to a position where the upstream-side positioning portion  176  is engaged with the horizontal engagement surface  442  of the first engagement portion  44 , and the downstream-side positioning portion  177  is engaged with the vertical engagement surface  443  of the first engagement portion  44  as illustrated in  FIG. 7 . 
     As a result, the upstream-side wraparound prevention member  17 , that is, the upstream-side plate portion  173  is positioned in a predetermined position without operator&#39;s consciousness. Then, by rotating the downstream-side wraparound prevention member  16  to the downstream side, the downstream-side wraparound prevention member  16 , that is, the downstream-side plate portion  162  is positioned in a predetermined position. 
     As described above, according to this embodiment, the thermal printer  1   a  includes the thermal head  13  and the platen roller  14  that perform printing while nipping and feeding the linerless label  2 , the downstream-side wraparound prevention member  16  disposed on the downstream side of the feeding direction to prevent the linerless label  2  from rolling up to the platen roller  14 , the upstream-side wraparound prevention member  17  disposed on the upstream side of the feeding direction to prevent the linerless label  2  from rolling up to the platen roller  14 , the fixing portion  322  (platen bearing  32 ) that rotatably supports the roller shaft  140  of the platen roller  14 , and the support member  43  that detachably supports the fixing portion  322 . The downstream-side wraparound prevention member  16  is assembled with the fixing portion  322  fixedly in the rotational direction of the roller shaft  140 , and the upstream-side wraparound prevention member  17  is rotatably assembled with the roller shaft  140 . In addition, the downstream-side wraparound prevention member  16  and the upstream-side wraparound prevention member  17  are provided with the downstream-side plate portion  162  and the rotation restrictor  175  as a restriction mechanism for restricting relative rotation of the upstream-side wraparound prevention member  17  with respect to the downstream-side wraparound prevention member  16 . 
     In this configuration, even when the upstream-side wraparound prevention member  17  is unitized in addition to the platen roller  14  and the downstream-side wraparound prevention member  16 , it is possible to position the upstream-side wraparound prevention member  17  so as not to generate interference in installation of the platen roller  14  and smoothly perform installation or removal of the platen roller  14 . 
     According to this embodiment, the support member  43  is provided with the fixing concave portion  432  for fixing the fixing portion  322 . The downstream-side wraparound prevention member  16  is positioned by inserting the fixing portion  322  into the fixing concave portion  432  in a predetermined direction (while the opposite flat-cut faces are vertically erected) and thereafter rotating the downstream-side wraparound prevention member  16  and the fixing portion  322  around the roller shaft  140 . In addition, the upstream-side wraparound prevention member  17  is positioned in a predetermined position by inserting the fixing portion  322  into the fixing concave portion  432  while rotation of the upstream-side wraparound prevention member  17  is restricted by a restriction mechanism including the downstream-side plate portion  162  and the upstream-side plate portion  173  so as not to approach the downstream-side wraparound prevention member  16 . 
     In this configuration, if the platen unit  30  is mounted on the support members  43  while an operator holds both the downstream-side plate portion  162  of the downstream-side wraparound prevention member  16  and the upstream-side plate portion  173  of the upstream-side wraparound prevention member  17 , it is possible to position the upstream-side wraparound prevention member  17 , that is, the upstream-side plate portion  173  in a predetermined position in the left side without operator&#39;s consciousness. 
     According to this embodiment, the support member  43  is provided with the fixing concave portion  432  for fixing the fixing portion  322 . The downstream-side wraparound prevention member  16  is positioned by inserting the fixing portion  322  into the fixing concave portion  432  in a predetermined direction (while the opposite flat-cut faces are vertically erected) and thereafter rotating the downstream-side wraparound prevention member  16  and the fixing portion  322  around the roller shaft  140 . The upstream-side wraparound prevention member  17  is positioned with assistance in rotation to a predetermined position by inserting the fixing portion  322  into the fixing concave portion  432  while rotation of the upstream-side wraparound prevention member  17  is restricted by a restriction mechanism including the downstream-side plate portion  162  and the rotation restrictor  175  so as not to be apart from the downstream-side wraparound prevention member  16 . 
     In this configuration, as the platen roller  14  is installed, the downstream-side wraparound prevention member  16  and the upstream-side wraparound prevention member  17  are positioned. Therefore, it is possible to easily install the platen roller  14  without considering positions of the downstream-side wraparound prevention member  16  and the upstream-side wraparound prevention member  17 . 
     According to this embodiment, the thermal printer  1   a  has the first engagement portion  44  provided with the slope surface  441  that abuts on the upstream-side wraparound prevention member  17  by inserting the fixing portion  322  into the fixing concave portion  432  and rotates the upstream-side wraparound prevention member  17  to a predetermined position. 
     In this configuration, it is possible to guide the upstream-side wraparound prevention member  17  to a predetermined position using a simple structure as the platen roller  14  is mounted. 
     According to this embodiment, the first engagement portion  44  is provided with a pair of engagement surfaces (the horizontal and vertical engagement surfaces  442  and  443 ). The pair of engagement surfaces have different angles and position the upstream-side wraparound prevention member  17  by engaging in different places of the upstream-side wraparound prevention member  17 . 
     In this configuration, it is possible to accurately position the upstream-side wraparound prevention member  17  using the horizontal and vertical engagement surfaces  442  and  443 . 
     According to this embodiment, a portion of the upstream-side wraparound prevention member  17  that abuts on the slope surface  441  by inserting the fixing portion  322  into the fixing concave portion  432  is placed in the upstream side with respect to the center axis of the roller shaft  140 . 
     In this configuration, it is possible to smoothly guide the upstream-side wraparound prevention member  17  to a predetermined position as the platen roller  14  is installed. 
     Although embodiments of this invention have been described hereinbefore, the aforementioned embodiments are just a part of applications of this invention, and are not intended to limit the technical scope of this invention to specific configurations of the aforementioned embodiments. 
     With respect to the above description, the contents of application No. 2014-175687, with a filing date of Aug. 29, 2014 in Japan, are incorporated herein by reference.