Abstract:
An inner cover disposed on the underside of the free end of an open and closing cover that opens and closes a print medium container of a printer includes a protruding head having thickness is gradually narrower in the direction away from a platen roller. On said protruding head, a protruding part is disposed on a first surface opposing an adhesive layer during feeding a continuous label faces. The protruding part is adjacent to a portion of the outer circumference of the platen roller. A first rib is disposed on the surface of the protruding part. The first rib has a function of separating the continuous label from the outer circumference of the platen roller during back-feeding.

Description:
TECHNICAL FIELD 
     The present invention relates to a printer, for instance, a label printer configured to print desired information such as a character, a sign, a diagram, a bar code or so forth on a label continuous body. 
     BACKGROUND 
     A label printer is a type of printer exclusively for label printing. For example, the label printer is configured to rotate a platen roller to feed a label continuous body wound in a roll shape pinched at one end thereof between the platen roller and a thermal head, whereby printing the intended information on the label continuous body. 
     For example, Japan Laid-open Patent Application Publication No. 2008-62597 describes this type of label printer that a platen roller is rotatably disposed on a free end of an opening and closing cover for closing and opening a container of a label continuous body, and a thermal head is disposed on the interior of the label printer so as to face the thermal head when the opening and closing cover is set in a closed state. 
     SUMMARY OF THE INVENTION 
     Technical Problem 
     There is a type of label continuous body made in the form of a strip of continuous labels that does not include a liner but includes an adhesive agent layer on one surface thereof (linerless labels). In use of the linerless labels, the adhesive agent layer thereof is exposed. Hence, a part of a label printer, making contact with the adhesive agent layer, is made of non-adhesive material or is processed with non-adhesive treatment, whereby the linerless labels are prevented from easily sticking to the part. 
     However, in back feeding, which is a motion to feed the linerless labels reversely to a print feeding direction, the linerless labels are fed from a position corresponding to the thermal head to the upstream side in the print feeding direction while slightly sticking to the outer periphery of the platen roller. At this time, there are chances that the linerless labels are drawn into a gap between the platen roller and the opening and closing cover. Consequently, the linerless labels stick to the end of the opening and closing cover, and jam of the linerless labels occurs. Especially, such sticking-related jam easily occurs when the linerless labels are interposed and held between the thermal head and the platen roller for a long period of time. 
     The present invention has been made in view of the aforementioned technical background, and is intended to provide a technology whereby when a printer performs back feeding of a print medium including an adhesive agent layer on one surface thereof, the print medium can be prevented from sticking to an inner wall surface located upstream of a feed roller in a print feeding direction. 
     Solution to Problem 
     A printer according to a first aspect of the present invention includes a housing, a print medium container, an opening and closing cover, a feed roller, a print head, a protruding head, a protruding part, and a first ridge part. The print medium container is disposed in the housing and is configured to accommodate a print medium including an adhesive agent layer on one surface thereof. The opening and closing cover is pivotably supported by the housing, and is configured to open and close the print medium container. The feed roller is rotatably disposed on a free end of the opening and closing cover and is configured to feed the print medium. The print head is disposed to face the feed roller in the housing and is configured to print on the print medium. The protruding head is disposed on the free end of the opening and closing cover. The thickness of the protruding head gradually reduces in a separating direction from the feed roller. The protruding head includes a first surface, a second surface and a connecting part. The first surface opposes an adhesive agent layer of the print medium when the print medium is fed from the print medium container toward the feed roller in a closed state of the opening and closing cover. The second surface is adjacent to the print medium container in the closed state of the opening and closing cover. The connecting part is disposed on a tip of the protruding head and connects the first surface and the second surface. The protruding part is disposed on a feed roller side end of the first surface and protrudes in an intersecting direction with the first surface to face the feed roller. The first ridge part protrudes from a surface of the protruding part. 
     In a printer according to a second aspect of the present invention, a second ridge part may be disposed on the first surface of the protruding head and protrude therefrom. The second ridge part may extend in an intersecting direction with a lengthwise direction of the feed roller to continuously connect to the first ridge part. 
     In a printer according to a third aspect of the present invention, the second ridge part may end in a position between the feed roller and the connecting part. A third ridge part may be disposed on the first surface, protrude therefrom and is located on a side close to the connecting part away from the second ridge part on an extension of the second ridge part. 
     In a printer according to a fourth aspect of the present invention, a fourth ridge part may be disposed on the connecting part and protrude from a surface thereof. 
     In a printer according to a fifth aspect of the present invention, a fifth ridge part may be disposed on the second surface and protrude therefrom. 
     In a printer according to a sixth aspect of the present invention, the protruding head of the opening and closing cover may be integrally provided with a holding part configured to hold the feed roller. 
     In a printer according to a seventh aspect of the present invention, the housing may include a feed member that faces the first surface and being configured to form a feeding path for the print medium in the closed state of the opening and closing cover. The feed member may include a sixth ridge part on a surface thereof that faces the first surface. The sixth ridge part may protrude from a position that is adjacent to the first ridge part on the surface of the feed member. 
     In a printer according to an eighth aspect of the present invention, the housing may include a feed member and a pair of guide members. The feed member may face the first surface and be configured to form a feeding path for the print medium in the closed state of the opening and closing cover. The pair of guide members may be disposed inside the print medium container and be configured to guide a position of the print medium in a width direction. A gear member may be rotatably disposed on the feed member. The gear member may be configured to move one of the pair of guide members when the other of the pair of guide members is moved in the width direction of the print medium. 
     Advantageous Effects 
     According to the first aspect of the present invention, in back feeding of the print medium including the adhesive agent layer on one surface thereof; the print medium can be separated from the feed roller by the first ridge part. Hence, the print medium can be prevented from sticking to an inner wall surface located upstream of the feed roller in a feeding direction. 
     According to the second aspect of the present invention, in print feeding, even when the print medium approaches to the first surface in some operating situations, the adhesive agent layer of the print medium is allowed to makes contact with only a lesser number of parts. It is thus possible to reduce contact resistance occurring when the adhesive agent layer makes contact with the first surface. Hence, it is possible to inhibit or prevent occurrence of printing defects attributed to this contact of the adhesive agent layer. Additionally, in print feeding and back feeding of the print medium, the adhesive agent layer of the print medium can be inhibited or prevented from sticking to the first surface. Hence, it is possible to inhibit or prevent occurrence of jam attributed to this sticking of the adhesive agent layer. 
     According to the third aspect of the present invention, in print feeding, even when the print medium approaches to the first surface in some operating situations, the adhesive agent layer of the print medium is allowed to limitedly make contact with the first ridge part, the second ridge part and the third ridge part. It is thus possible to reduce contact resistance occurring when the adhesive agent layer makes contact with the first surface. Hence, it is possible to inhibit or prevent occurrence of printing defects attributed to this contact of the adhesive agent layer. Additionally, in print feeding and back feeding of the print medium, the adhesive agent layer of the print medium can be inhibited or prevented from sticking to the first surface. Hence, it is possible to inhibit or prevent occurrence of jam attributed to this sticking of the adhesive agent layer. Moreover, with the construction that the second ridge part and the third ridge part are spaced apart from each other, it is also possible to reduce the area that the adhesive agent layer of the print medium makes contact with the second ridge part and the third ridge part in back feeding of the print medium. Hence, it is possible to further enhance performance of feeding the print medium in back feeding. 
     According to the fourth aspect of the present invention, the adhesive agent layer of the print medium is allowed to limitedly make contact with the fourth ridge part on the connecting part. It is thus possible to reduce contact resistance occurring when the adhesive agent layer of the print medium makes contact with the connecting part in print feeding. Hence, it is possible to inhibit or prevent occurrence of printing defects attributed to this contact of the adhesive agent layer. Additionally, in print feeding of the print medium, the adhesive agent layer of the print medium can be inhibited or prevented from sticking to the connecting part. Hence, it is possible to inhibit or prevent occurrence of jam attributed to this sticking of the adhesive agent layer. 
     According to the fifth aspect of the present invention, the outer periphery of the print medium is allowed to make contact with only a lesser number of parts of the second surface when the print medium rotates within the print medium container. Hence, it is possible to reduce frictional resistance occurring in rotation of the print medium. 
     According to the sixth aspect of the present invention, the printer can be produced in smaller size than a construction that a member for holding the feed roller is separately disposed. 
     According to the seventh aspect of the present invention, it is possible to match the position of a trace formed on the print medium by the contact with the first ridge part and that of a trace formed on the print medium by the contact with the sixth ridge part. Hence, compared to a construction that the first ridge part and the sixth ridge part are displaced without facing each other, it is possible to reduce the number of lines left as traces of the ridge parts on the print medium. 
     According to the eighth aspect of the present invention, the printer can be produced in smaller size than a construction that the gear member is disposed on the bottom surface inside the housing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is an entire perspective view of a printer according to an exemplary embodiment of the present invention in a normal ejection mode. 
         FIG. 1B  is an entire perspective view of the printer shown in  FIG. 1A  in a separation ejection mode. 
         FIG. 2  is an entire perspective view of the appearance of a label continuous body and the printer shown in  FIGS. 1A and 1B  in an opened state of an opening and closing cover. 
         FIG. 3A  is a schematic configuration diagram of the printer shown in  FIG. 1A  in normal ejection. 
         FIG. 3B  is a schematic configuration diagram of the printer shown in  FIG. 1B  in separation ejection. 
         FIG. 4  is a perspective view of the opening and closing cover as seen from a gear side. 
         FIG. 5  is an enlarged perspective view of a protruding head of the opening and closing cover shown in  FIG. 4 . 
         FIG. 6  is a side view of the opening and closing cover shown in  FIG. 5 . 
         FIG. 7  is a perspective view of the opening and closing cover as seen from a paper container side. 
         FIG. 8  is a perspective view of major elements of the opening and closing cover and a feed plate. 
         FIG. 9  is a perspective view of the feed plate as seen from a side that is adjacent to a first surface of the protruding head of the opening and closing cover in a closed state of the opening and closing cover. 
         FIG. 10  is a perspective view of the opening and closing cover and the feed plate as seen from below. 
         FIG. 11  is a perspective view of the opening and closing cover, the feed plate and a paper guide mechanism as seen from below. 
         FIG. 12  is a schematic configuration diagram of the printer shown in  FIGS. 1A and 1B  in a printing step as seen from a lateral side. 
         FIG. 13  is an enlarged schematic configuration diagram of major elements of the printer shown in  FIG. 12 . 
         FIG. 14  is a schematic configuration diagram of the printer in another printing step subsequent to the printing step shown in  FIG. 12  as seen from the lateral side. 
         FIG. 15  is a schematic configuration diagram of the printer in yet another printing step subsequent to the printing step shown in  FIG. 14  as seen from the lateral side. 
         FIG. 16  is a schematic configuration diagram of the printer in a back feeding step as seen from the lateral side. 
         FIG. 17  is an enlarged schematic configuration diagram of major elements of a printer with a construction examined by the inventor of the present application in a back feeding step as seen from the lateral side. 
         FIG. 18  is an enlarged schematic configuration diagram of major elements of the printer shown in  FIG. 16 . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     This application claims priority to Japanese Patent Application No. 2014-165847 filed on Aug. 18, 2014, the entirety of which is hereby incorporated by reference in its entirety. 
     Based on drawings, an exemplary embodiment will be hereinafter explained in detail as an example of the present invention. In principle, the same constituent elements will be denoted by the same reference sign in the drawings for explaining the exemplary embodiment, and will not be explained repeatedly. Terms in the exemplary embodiment will be briefly explained as follows. The term “feeding” refers to a motion to feed a label continuous body (print medium) for a printing purpose. The term “feeding direction” (print feeding direction) refers to a direction in which the label continuous body is fed for a printing purpose, and specifically, a direction that the label continuous body is fed from a paper supplying part to a thermal head. The term “back feeding” refers to a motion to feed the label continuous body reversely to the feeding direction after printing of desired information on a desired label of the label continuous body whereby the other labels are reversely shifted such that the label next to the desired label is returned to a print starting position. The term “back feeding direction” refers to a direction in which the label continuous body is fed for a back feeding purpose, and specifically, a direction that the label continuous body is fed from a thermal head side to a paper supplying part side. The terms “separation ejection” and “normal ejection” are defined on the premise that “labels with a liner”, including a long strip of liner and a plurality of continuous labels temporarily attached to the liner at predetermined intervals, are used in a printer as a label continuous body. The term “separation ejection” refers to an ejection mode configured to eject the labels from the printer while the labels are separated from the liner one by one. On the other hand, the term “normal ejection” refers to an ejection mode configured to eject the labels from the printer without separating the labels from the liner. The normal ejection is applied not only to a situation that labels with a liner are ejected without separating the labels from the liner but also to a situation that other types of linerless labels used as a label continuous body are ejected. These other types of linerless labels include a strip of continuous labels without a liner and is configured to be fed while an adhesive agent layer on one surface thereof is exposed, a continuously produced sheet (continuous sheet) without a liner and does not include any adhesive agent layer thereon, and so forth. 
       FIG. 1A  is an entire perspective view of a printer according to the present exemplary embodiment in a normal ejection mode.  FIG. 1B  is an entire perspective view of the printer shown in  FIG. 1A  in a separation ejection mode.  FIG. 2  is an entire perspective view of the appearance of a label continuous body and the printer shown in  FIGS. 1A and 1B  in an opened state of an opening and closing cover. 
     As shown in  FIGS. 1A and 1B , a printer  1  according to the present exemplary embodiment is a portable label printer made in a flat cuboid shape, for instance. The printer  1  includes a body case  2 , an opening and closing cover  3 , a separation unit  4  and a front cover  5  (exemplary housing). The printer  1  is of a dual mode type configured to be capable of switching between normal ejection and separation ejection by itself. The printer  1  is not only usable with an ejection port facing upwards (in horizontal installation), but also usable with the ejection port facing sideward (in a vertical installation) by hooking a belt hook (not shown in the drawings) disposed on the bottom surface of the printer  1  on a belt of a worker or by attaching a shoulder belt (not shown in the drawings) to the printer  1  and then hanging the shoulder belt on the shoulder of the worker. 
     The body case  2  is a housing that composes part of the contour of the printer  1 . As shown in  FIG. 2 , the body case  2  includes a paper container  6  (exemplary print medium container) built in the interior thereof. The paper container  6  is a region for accommodating a label continuous body P wound in a roll shape. A pair of guide plates  7   a  (exemplary guide members) of a paper guide mechanism  7  is disposed in the interior of the paper container  6 . The paper guide mechanism  7  is a mechanism for supporting and guiding the label continuous body P in accordance with its width. As shown in  FIGS. 1A to 2 , a battery cover  8  is pivotably supported by one of the lateral surfaces of the body case  2  so as to take an opened position or closed position. 
     As shown in  FIG. 2 , the label continuous body P is, for instance, a strip of continuous labels (linerless labels) without a liner and includes an adhesive agent layer on one surface thereof and a release agent layer on the other surface thereof. The label continuous body P wound in a roll shape is accommodated in the paper container  6 . Location detection marks (not shown in the drawings) to indicate the locations of the labels are disposed on the adhesive agent side of the label continuous body P while being aligned along the lengthwise direction of the label continuous body P at predetermined intervals. A thermosensitive color developing layer is disposed on the front surface (located on the back side of the surface on which the adhesive agent layer is disposed, and is also referred to as a printing surface) of the label continuous body P. The thermosensitive color developing layer is configured to turn a predetermined color (black, red, etc.) when reaching a predetermined temperature range. 
     The opening and closing cover  3  is an opening and closing cover for closing and opening the paper container  6 . One lengthwise end of the opening and closing cover  3  (free end: lengthwise middle of the body case  2 ) is movable in directions separating from and approaching to the body case  2 , while the other lengthwise end thereof is pivotably supported by an opening and closing support shaft disposed on one lengthwise end of the body case  2 . The opening and closing cover  3  is biased in an opening direction (a direction in which the free end of the opening and closing cover  3  separates from the body case  2 ) by a torsion spring disposed on the opening and closing support shaft provided on the other lengthwise end thereof. 
     A platen roller  10  (exemplary feed roller) is rotatably supported by the free end of the opening and closing cover  3  so as to rotate in normal and reverse directions. The platen roller  10  is a feeder configured to feed the label continuous body P. The platen roller  10  extends along the width direction (short-side direction) of the label continuous body P. The platen roller  10  is made of, for instance, non-adhesive material such as silicone-contained resin or silicone rubber in order to prevent the adhesive agent of the label continuous body P from sticking thereto. A gear  10   b  is connected to one end of a platen roller shaft  10   a  of the platen roller  10 . When the opening and closing cover  3  is set in a closed state, the gear  10   b  is configured to be engaged with a gear and so forth (not shown in the drawings) disposed on the interior of the body case  2 , and be mechanically connected to a stepping motor for roller driving (not shown in the drawings) and so forth through the gear and so forth. 
     A separation pin  11  is disposed on the free end of the opening and closing cover  3  along and in the vicinity of the platen roller  10 . The separation pin  11  is a separation member and is supported at the both lengthwise ends thereof by the opening and closing cover  3 . When labels with a liner are used as a label continuous body, the separation pin  11  is configured to separate the labels from the liner. 
     A sensor  12  is disposed on a surface of a free end-side part of the opening and closing cover  3 . This surface opposes the label continuous body P. The sensor  12  is configured to detect the locations of the labels (the aforementioned location detection marks) of the label continuous body P. The sensor  12  is, for instance, a reflective photosensor or so forth. The sensor  12  includes a light emitter  12   a  and a light receiver  12   b.    
     When labels with a liner are used as the label continuous body P, the separation unit  4  is configured to separate labels from the liner of the label continuous body P in separation ejection, and then divide a feeding path for the label continuous body P into a feeding path for the liner and that for the labels. The separation unit  4  is disposed such that a nip roller  4   a  on the lengthwise tip thereof can be moved to a normal ejection position located inside the printer  1  and a separation ejection position located outside the printer  1 . The nip roller  4   a  is disposed so as to face the platen roller  10  in separation ejection. The nip roller  4   a  is configured to feed the liner inserted between the nip roller  4   a  and the platen roller  10  with the liner being pinched therebetween. The nip roller  4   a  is configured to rotate in conjunction with rotation of the platen roller  10 . 
     The front cover  5  is fixed to the body case  2  and composes part of the housing of the printer  1 . On the surface of the body case  2 , the front cover  5  covers a region that is adjacent to the opening and closing cover  3  and parts of the body case  2  that are located in the vicinity of the both lateral surfaces of the body case  2 . The front cover  5  includes a display  15 , operating buttons  16   a  and  16   b , an electric power button  17 , a cover open button  18 , a pair of release levers  19  and a cutter  20 . 
     The display  15  is a screen configured to display an operating command, a message and so forth. The display  15  is, for instance, an LCD (Liquid Crystal Display). The operating buttons  16   a  and  16   b  are buttons configured to operate the motion and setting of the printer  1 . The electric power button  17  is a button configured to turn on and off the electric power supply of the printer  1 . The cover open button  18  is a button configured to open the opening and closing cover  3 . The release levers  19  are configured to hold the separation unit  4  in the normal ejection position. When the release levers  19  are moved to approach each other, the holding of the separation unit  4  is releasable. The cutter  20  is configured to cut the label continuous body P that has been ejected in normal ejection. The cutter  20  is disposed on the tip of a part of the front cover  5 , i.e., the tip of a part that is adjacent to the opening and closing cover  3 , while extending from end to end of the tip in the short-side direction of the printer  1  (the axial direction of the platen roller  10 ). An ejection port is produced between the opening and closing cover  3  and the front cover  5 . 
     The internal structure of the printer  1  will be explained with reference to  FIGS. 3A and 3B .  FIG. 3A  is a schematic configuration diagram of the printer shown in  FIG. 1A  in normal ejection.  FIG. 3B  is a schematic configuration diagram of the printer shown in  FIG. 1B  in separation ejection. 
     A head bracket  27 , a thermal head  28  (exemplary print head), a coil spring  29 , the separation unit  4 , a feed plate  30  (exemplary feed member) and a battery container (not shown in the drawings) are installed adjacently to each other in the interior of the body case  2  while facing the paper container  6  and the platen roller  10 . 
     The head bracket  27  is configured to hold the thermal head  26  and the opening and closing cover  3  that is set in the closed state. The head bracket  27  is disposed so as to swing while facing the platen roller  10  when the opening and closing cover  3  is set in the closed state. When the platen roller shaft  10   a  of the platen roller  10  is fitted into a groove that is formed on the head bracket  27 , the opening and closing cover  3  is held by the head bracket  27 . The head bracket  27  is integrally provided with a press part  27   a . The press part  27   a  is located in a position (immediately below) that is adjacent to the cover open button  18 . When the cover open button  18  is pressed, the press part  27   a  is also pressed and swings, and thereby the holding of the opening and closing cover  3  by the head bracket  27  is released. When the holding of the opening and closing cover  3  is released, the opening and closing cover  3  is automatically opened by a biasing force of a torsion spring  31  disposed on an opening and closing support shaft  3   a  on the other lengthwise end thereof. 
     The thermal head  28  is printing means configured to print information, for instance, a character, a sign, a diagram, a bar code or so forth on the label continuous body P. The thermal head  28  is disposed on the head bracket  27  through a circuit board  32  while a printing surface thereof opposes a paper path. The thermal head  28  is adjacent to the platen roller  10  when the opening and closing cover  3  is set in the closed state. A plurality of heating resistors (heating elements), configured to generate heat by electric conduction, are disposed on the printing surface of the thermal head  28  while being aligned along the width direction (short-side direction) of the label continuous body P. The circuit board  32  is a wiring board configured to transmit a print signal to the thermal head  28 . 
     The coil spring  29  is configured to bias the head bracket  27  and the thermal head  28  toward the platen roller  10  when the opening and closing cover  3  is set in the closed state. The coil spring  29  is disposed on the back surface of the head bracket  27  (the back side of the surface to which the circuit board  32  is disposed). The head bracket  27  is pressed toward the platen roller  10  by the biasing force of the coil spring  29 . Hence, the platen roller shaft  10   a , fitted into the groove of the head bracket  27 , is also pressed and thereby the holding of the opening and closing cover  3  by the head bracket  27  is maintained. 
     The feed plate  30  is configured to form the paper path for feeding, toward the platen roller  10 , a part unwound in a sheet shape from the label continuous body P (see  FIG. 2 ) accommodated in the paper container  6  (note: the feed plate  30  will be described below). The battery container is configured to accommodate a battery for driving the printer  1 . The battery container is configured to be opened and closed by the aforementioned battery cover  8  (see  FIG. 2 ). A lithium-ion battery, for instance, is herein used as the battery. 
     The structure of the opening and closing cover  3  will be explained with reference to  FIGS. 4 to 7 .  FIG. 4  is a perspective view of the opening and closing cover as seen from the gear  10   b  side.  FIG. 5  is an enlarged perspective view of a protruding head of the opening and closing cover.  FIG. 6  is a side view of the opening and closing cover shown in  FIG. 5 .  FIG. 7  is a perspective view of the opening and closing cover as seen from the paper container side. 
     An inner cover  3   b  is detachably attached to the back side of the free end of the opening and closing cover  3  by screws N. The inner cover  3   b  is integrally provided with a protruding head  3   c . The protruding head  3   c  protrudes in a separating direction from the platen roller  10  disposed on the free end of the opening and closing cover  3 . The protruding head  3   c  has a thickness gradually reducing in the separating direction from the platen roller  10 . The protruding head  3   c  is integrally provided with holding parts  3   d  on the platen roller  10  side thereof. The holding parts  3   d  are disposed on the both lengthwise ends of the platen roller  10 . The holding parts  3   d  bend to enclose part of the outer periphery of the platen roller shaft  10   a . The platen roller shaft  10   a  (i.e., the platen roller  10 ) is rotatably held by the holding parts  3   d . Thus, the protruding head  3   c  is herein integrally provided with the member for holding the platen roller shaft  10   a  (the platen roller  10 ). Hence, compared to a construction that the member for holding the platen roller shaft  10   a  (the platen roller  10 ) is separately provided, the number of components can be reduced, and thereby, the printer  1  can be reduced in size and also in cost. 
     The protruding head  3   c  includes a first surface S 1 , a second surface S 2  located on the back side of the first surface S 1 , and a third surface S 3  (exemplary connecting part) located on the tip of the protruding head  3   c . The first surface S 1  is an internal wall surface configured to form the paper path of a part unwound in a sheet shape from the label continuous body P (feeding path in feeding and back feeding). The first surface S 1  opposes the adhesive agent layer of a part unwound in a sheet shape from the label continuous body P when the opening and closing cover  3  is set in the closed state. The aforementioned sensor  12  is disposed on the first surface S 1 . The protruding head  3   c  is integrally provided with a protruding part  3   e  on the platen roller  10 —side end of the first surface S 1  thereof. The protruding part  3   e  protrudes in an intersecting direction with the first surface S 1 , while facing part of the outer periphery of the platen roller  10  from end to end in the lengthwise direction of the platen roller  10 . 
     The second surface S 2  is an inner wall surface that is adjacent to the paper container  6  (i.e., the outer periphery of the label continuous body P wound in a roll shape) when the opening and closing cover  3  is set in the closed state. For example, the second surface S 2  has a curved shape along the outer periphery of the label continuous body P wound in a roll shape. The third surface S 3  is an inner wall surface configured to connect the first surface S 1  and the second surface S 2 . The extension of the third surface S 3  intersects with that of the first surface S 1  and that of the second surface S 2 . The third surface S 3  has, for instance, an approximately flat shape. It should be noted that the shape of the third surface S 3  is not limited to the flat shape and may be a curved shape. 
     The protruding head  3   c  includes a plurality of ribs R on its surface (the surface of the protruding part  3   e , the first surface S 1 , the second surface S 2  and the third surface S 3 ). The ribs R extend in intersecting directions with the lengthwise direction of the platen roller  10  while being aligned at predetermined intervals along the lengthwise direction of the platen roller  10 . Each rib R includes a first rib part R 1  (exemplary first ridge part), a second rib part R 2  (exemplary second ridge part), a third rib part R 3  (exemplary third ridge part), a fourth rib part R 4  (exemplary fourth ridge part) and a fifth rib part R 5  (exemplary fifth ridge part). 
     When seen from a lateral side of the opening and closing cover  3 , the first rib part R 1  of each rib R protrudes from the surface of the protruding part  3   e . When seen toward the first surface S 1 , the first rib part R 1  extends in an intersecting direction with the lengthwise direction of the platen roller  10 . In the extending direction of the first rib part R 1 , the platen roller  10 —side end of the first rib part R 1  ends in a shape sharpened toward the tip, whereas the first surface S 1 —side end continuously connects with the second rib part R 2 . 
     The aforementioned protruding part  3   e  is disposed on the both sides of the first rib part R 1  in the width direction (short-side direction). The protruding part  3   e  is configured to reduce the aspect ratio of the first rib part R 1  as described below, and also has a reinforcement function of enhancing the mechanical strength of the first rib part R 1  by holding the both sides of the leg of the first rib part R 1  in the width direction. 
     When seen from the lateral side of the opening and closing cover  3 , the second rib part R 2  of each rib R protrudes from the first surface S 1 . The second rib part R 2  is disposed in the vicinity of the protruding part  3   e . When seen toward the first surface S 1 , the second rib part R 2  also extends in the intersecting direction with the lengthwise direction of the platen roller  10 . In the extending direction of the second rib part R 2 , the end of the second rib part R 2  ends in a position between the platen roller  10  and the third surface S 3 . 
     When seen from the lateral side of the opening and closing cover  3 , the third rib part R 3  of each rib R protrudes from the first surface S 1 . When seen toward the first surface S 1 , the third rib part R 3  also extends along the feeding direction of the label continuous body P. The third rib part R 3  is disposed on the extension of the second rib part R 2 . However, the third rib part R 3  is disposed in the vicinity of the third surface S 3  located away from the second rib part R 2  without continuously connecting with the second rib part R 2 . In other words, a region without the ribs R exists between the second rib part R 2  and the third rib part R 3 . Thus, each rib R, extending along the feeding direction of the label continuous body P, is divided in a region between the platen roller  10  and the third surface S 3  on the first surface S 1  of the protruding head  3   c  of the opening and closing cover  3 . 
     When seen from the lateral side of the opening and closing cover  3 , the fourth rib part R 4  of each rib R protrudes from the third surface S 3  that is the tip surface of the protruding head  3   c . When seen toward the third surface S 3 , the fourth rib part R 4  also extends along the feeding direction of the label continuous body P. In the extending direction of the fourth rib part R 4 , one end of the fourth rib part R 4  continuously connects with the third rib part R 3  on the first surface S 1 , whereas the other end thereof continuously connects with the fifth rib part R 5  on the second surface S 2 . The protruding length (protruding height) of fourth rib part R 4  is longer (higher) than that of the first rib part R 1 , the second rib part R 2 , the third rib part R 3  and the fifth rib part R 5 . With this construction, in feeding the label continuous body P, a part unwound in a sheet shape from the label continuous body P is fed while being supported at two contact points (two locations), composed of the platen roller  10  and the fourth rib parts R 4 , in a range between the platen roller  10  and the third surface S 3 . 
     When seen from the lateral side of the opening and closing cover  3 , the fifth rib part R 5  of each rib R protrudes from the second surface S 2 . The protruding length (protruding height) of the fifth rib part R 5  is shorter (lower) than that of the first rib part R 1 , the second rib part R 2  and the third rib part R 3 . When seen toward the second surface S 2 , the fifth rib part R 5  extends along the rotational direction of the label continuous body P wound in a roll shape. With the fifth rib parts R 5  herein provided, when the label continuous body P wound in a roll shape rotates within the paper container  6 , the outer periphery of the label continuous body P is only allowed to make contact with a lesser number of parts (substantially contact with the fifth rib parts R 5 ) of the second surface S 2 . Hence, it is possible to reduce frictional resistance occurring in rotation of the label continuous body P wound in a roll shape. 
     The structure of the feed plate  30  of the printer  1  will be explained with reference to  FIGS. 8 to 11 .  FIG. 8  is a perspective view of major elements of the opening and closing cover and the feed plate.  FIG. 9  is a perspective view of the feed plate as seen from a side that is adjacent to the first surface of the protruding head of the opening and closing cover in a closed state of the opening and closing cover.  FIG. 10  is a perspective view of the opening and closing cover and the feed plate as seen from below.  FIG. 11  is a perspective view of the opening and closing cover, the feed plate and the paper guide mechanism as seen from below.  FIG. 8  illustrates the feed plate  30  in a transparent representation in order to show how the feed plate  30  and the protruding head  3   c  face each other. 
     When the opening and closing cover  3  is set in the closed state, the feed plate  30  is detachably screwed to the opening and closing cover  3  while facing the first surface S 1  of the protruding head  3   c  of the opening and closing cover  3 . The feed plate  30  includes a plurality of ribs Rb (exemplary sixth ridge parts) disposed on the surface thereof. The surface of the feed plate  30  is adjacent to the first surface S 1  of the protruding head  3   c . The ribs Rb extend in the intersecting direction with the lengthwise direction of the platen roller  10  while being aligned at predetermined intervals along the lengthwise direction of the platen roller  10 . The ribs Rb on the feed plate  30  are respectively disposed just in front of the ribs R on the first surface S 1  of the protruding head  3   c  in front of the feed plate  30 . With this construction, it is possible to match the contact positions between the ribs R and the label continuous body P with those between the ribs Rb and the label continuous body P. Hence, it is possible to match positions of traces formed on the label continuous body P by the contact with the ribs R with those of traces formed on the label continuous body P by the contact with the ribs Rb. Therefore, it is possible to reduce the number of lines left on the label continuous body P as traces of the ribs, compared to a construction that the ribs R and the ribs Rb are displaced without facing each other. 
     The feed plate  30  includes a support piece  30   a  disposed on approximately the middle of a lower edge (located on the bottom side in the body case  2 ) in the width direction (the lengthwise direction of the platen roller  10 ). The support piece  30   a  extends from part of the lower edge of the feed plate  30  toward the bottom surface in the interior of the body case  2 . As shown in  FIGS. 10 and 11 , the support piece  30   a  includes a pinion gear  7   b  (exemplary gear member) on the bottom surface of its tip. The pinion gear  7   b  is supported so as to rotate along the bottom surface in the interior of the body case  2 . As shown in  FIG. 11 , the pair of the guide plates  7   a  includes a pair of racks  7   c  on the bottom parts thereof. The racks  7   c  extend toward each other in a band shape. The pair of racks  7   c  is disposed to interpose the pinion gear  7   b  therebetween, while a plurality of teeth on the longer edge of each rack  7   c  are engaged with those of the pinion gear  7   b . With the construction, when one of the guide plates  7   a  is moved to one side in the width direction of the label continuous body P wound in a roll shape, the other of the guide plates  7   a  is oppositely moved to the other side in the width direction of the label continuous body P by the action of the pinion gear  7   b  and the racks  7   c . With the construction that the pinion gear  7   b  is disposed on the support piece  30   a  on the lower part of the feed plate  30 , the printer  1  can be produced in smaller size than by a construction that the pinion gear  6   b  is disposed on the bottom surface in the interior of the body case  2 . 
     An exemplary method of printing by the printer  1  will be explained with reference to  FIGS. 12 to 18 .  FIG. 12  is a schematic configuration diagram of the printer shown in  FIGS. 1A and 1B  in a printing step as seen from a lateral side.  FIG. 13  is an enlarged schematic configuration diagram of major elements of the printer shown in  FIG. 12 .  FIGS. 12 to 18  show an exemplary situation that the printer  1  is used in the vertical installation. 
     As shown in  FIG. 12 , a part unwound in a sheet shape from the label continuous body P accommodated in the paper container  6  is herein pinched between the thermal head  28  and the platen roller  10  through the fourth rib parts R 4  on the tip of the protruding head  3   c  of the opening and closing cover  3 . In this case, the adhesive agent layer of the part unwound in a sheet shape from the label continuous body P opposes the platen roller  10  and the first surface S 1  of the opening and closing cover  3  without being covered. By rotating the platen roller  10  under this condition, the part unwound in a sheet shape from the label continuous body P is fed in the feeding direction. Intended information is printed on the thermal labels of the label continuous body P at printing timing, set based on a timing signal detected by the sensor  12 , by causing the heating resistors of the thermal head  28  to heat and scan in response to a print signal transmitted to the thermal head  28 . With the protruding tip of the protruding head  3   c  of the opening and closing cover  3 , the part unwound in a sheet shape from the label continuous body P wound in a roll shape can be successfully separated from the label continuous body P regardless of the size of the label continuous body P, while being fed from the paper container  6  through the fourth rib parts R 4  on the tip of the protruding head  3   c  to the gap between the thermal head  28  and the platen roller  10 , both of which are located downstream in the feeding direction. 
     As shown in  FIGS. 12 and 13 , the adhesive agent layer of the part unwound in a sheet shape from the label continuous body P accommodated in the paper container  6  is fed while making contact with the fourth rib parts R 4  on the tip (the third surface S 3 ) of the protruding head  3   c  of the opening and closing cover  3 . In other words, with the fourth rib parts R 4  herein disposed, the adhesive agent layer of the label continuous body P is allowed to limitedly make contact with the fourth rib parts R 4  on the third surface S 3 . Therefore, it is possible to reduce contact resistance occurring when the adhesive agent layer of the part unwound in a sheet shape from the label continuous body P makes contact with the third surface S 3  in feeding. It is thereby possible to inhibit or prevent occurrence of printing defects attributed to this contact of the adhesive agent layer. Additionally, the adhesive agent layer of the part unwound in a sheet shape from the label continuous body P can be inhibited or prevented from sticking to the third surface S 3  in feeding. Hence, it is possible to inhibit or prevent occurrence of jam attributed to this sticking of the adhesive agent layer. Moreover, the part unwound in a sheet shape from the label continuous body P can be smoothly fed, and power for feeding the label continuous body P can be reduced. Hence, battery consumption of the printer  1  can be reduced. 
     Protruding length (protruding height) of the fourth rib parts R 4  is longer (higher) than that of the first rib parts R 1 , the second rib parts R 2  and the third rib parts R 3  on the first surface S 1  of the protruding head  3   c  of the opening and closing cover  3 . Hence, the part unwound in a sheet shape from the label continuous body P is supported at two contact points (two parts) composed of the fourth rib parts R 4  and the platen roller  10 . Normally in feeding, the adhesive agent layer of the part unwound in a sheet shape from the label continuous body P does not make contact with the first surface S 1 . However, even when the adhesive agent layer of the part unwound in a sheet shape from the label continuous body P approaches the first surface S 1  in some operating situations, the adhesive agent layer is allowed to limitedly make contact with the first rib parts R 1 , the second rib parts R 2  and the third rib parts R 3  due to the aforementioned support structure with two contact points. Accordingly, the adhesive agent layer of the part unwound in a sheet shape from the label continuous body P can be inhibited or prevented from sticking to the first surface S 1  in feeding. Hence, it is possible to inhibit or prevent occurrence of jam attributed to this sticking of the adhesive agent layer. Moreover, the part unwound in a sheet shape from the label continuous body P can be smoothly fed, and power for feeding the label continuous body P can be reduced. Hence, battery consumption of the printer  1  can be reduced. 
       FIG. 14  is a schematic configuration diagram of the printer in another printing step subsequent to the printing step shown in  FIG. 12  as seen from the lateral side.  FIG. 15  is a schematic configuration diagram of the printer in yet another printing step subsequent to the printing step shown in  FIG. 14  as seen from the lateral side. As shown in  FIG. 14 , a printed label part of the label continuous body P is ejected to the outside through the ejection port of the printer  1 . Thereafter, as shown in  FIG. 15 , the printed label part is cut off with the edge of the cutter  20 , while being pinched by fingers. 
       FIG. 16  is a schematic configuration diagram of the printer in a back feeding step as seen from a lateral side.  FIG. 17  is an enlarged schematic configuration diagram of major elements of a printer with a construction examined by the inventor of the present application in a back feeding step as seen from the lateral side.  FIG. 18  is an enlarged schematic configuration diagram of major elements of the printer shown in  FIG. 16 . 
     As shown in  FIG. 16 , back feeding for a part unwound in a sheet shape from the label continuous body P returns a leading label part of the label continuous body P, located next to the cut-off printed label part, to the printing position (the thermal head  28  side). 
     As shown in  FIG. 17 , if the protruding head  3   c  of the opening and closing cover  3  does not include the first rib parts on the platen roller  10 —side end of the first surface S 1 , this construction has the following risk in the back feeding step. That is to say, a part unwound in a sheet shape from the label continuous body P is drawn into a gap between the platen roller  10  and the protruding head  3   c  (region depicted with broken line A) when the part is fed from the position of the thermal head  28  toward the protruding head  3   c  while slightly sticking to the outer periphery of the platen roller  10 . Then, the part sticks to the platen roller  10 —side end of the protruding head  3   c , and accordingly jam occurs. Especially, such sticking-related jam easily occurs when the linerless labels are interposed and held between the thermal head  28  and the platen roller  10  for a long period of time. By contrast, in the present exemplary embodiment, as shown in  FIG. 18 , a part unwound in a sheet shape from the label continuous body P can be separated from the outer periphery of the platen roller  10  by the first rib parts R 1  when being fed from the position of the thermal head  28  toward the protruding head  3   c  while slightly sticking to the outer periphery of the platen roller  10 . In this case, the part unwound in a sheet shape from the label continuous body P can be separated from the outer periphery of the platen roller  10  on the back-feeding directional upstream side (feeding directional downstream side) of the region depicted with broken line A in  FIG. 17 . Therefore, the part unwound in a sheet shape from the label continuous body P can be prevented from being drawn into the gap between the platen roller  10  and the protruding head  3   c , and can be also prevented from sticking to the platen roller  10 —side end of the protruding head  3   c . Hence, occurrence of jam can be prevented in back feeding. 
     The height of the first rib parts R 1  and the shape of the platen roller  10 —side tip of the first rib parts R 1  are designed from the perspective of the aforementioned label separation function. If the first rib parts R 1  is disposed without the protruding part  3   e , it is inevitable for the first rib parts R 1  to have a large height and also have a high aspect ratio in order to achieve the aforementioned label separation function. Consequently, the mechanical strength of the first rib parts R 1  deteriorates, and this may result in deformation of the first rib parts R 1 . By contrast, in the present exemplary embodiment, the protruding part  3   e  is disposed and thereby the height (and the aspect ratio) of the first rib parts R 1  can be lowered than that in the construction without the protruding part  3   e . Hence, the first rib parts R 1  per se can be enhanced in mechanical strength. Additionally, the protruding part  3   e  is disposed on the both sides of the leg of each first rib part R 1  in the width direction such that each first rib part R 1  is interposed between adjacent regions of the protruding part  3   e . Hence, the first rib parts  121  can be enhanced in mechanical strength. In other words, the protruding part  3   e  exerts a function of a reinforcement member for the first rib parts R 1 . Based on the above, deformation of the first rib parts R 1  can be prevented. 
     In a back feeding step, the part unwound in a sheet shape from the label continuous body P sags in an approaching direction to the first surface S 1  of the protruding head  3   c . However, as shown in  FIG. 18 , the first surface S 1  includes the first rib parts R 1 , the second rib parts R 2  and the third rib parts R 3 . With this construction, the adhesive agent layer of the part unwound in a sheet shape from the label continuous body P is allowed to limitedly make contact with the first rib parts R 1 , the second rib parts R 2  and the third rib parts R 3 . Accordingly, the adhesive agent layer of the part unwound in a sheet shape from the label continuous body P can be inhibited or prevented from sticking to the first surface S 1  in the back feeding step. Hence, it is possible to inhibit or prevent occurrence of jam attributed to this sticking of the adhesive agent layer. Moreover, similarly in back feeding, the part unwound in a sheet shape from the label continuous body P can be smoothly fed, and power for feeding the label continuous body P can be reduced. Hence, battery consumption of the printer  1  can be reduced. Especially in the present exemplary embodiment, the second rib part R 2  and the third rib part R 3  are divided in each rib R. With this construction, it is even possible to reduce the area that the adhesive agent layer unwound in a sheet shape from the label continuous body P makes contact with the second rib parts R 2  and the third rib parts R 3  in the back feeding step. Therefore, it is possible to further enhance performance of feeding the label continuous body P in the back feeding step. 
     Based on the exemplary embodiment, the present invention made by the inventor of the present application has been specifically explained above. The exemplary embodiment disclosed in the present specification is exemplary only in all aspects and the present invention is not limited to the technology herein disclosed. In other words, the technical scope of the present invention should not be interpreted restrictively based on the explanation in the aforementioned detailed description, rather should be interpreted based on the description of claims, and encompasses equivalents of the technology described in the claims and all the changes made without departing from the gist of the claims. 
     For example, the aforementioned exemplary embodiment has explained that the present invention is applied to a dual mode printer usable for both of normal ejection and separation ejection. However, the application of the present invention is not limited to this, and is applicable to a printer usable exclusively for normal ejection. 
     Additionally, the aforementioned exemplary embodiment has explained that continuous labels (linerless labels) without a liner but include an adhesive agent layer on one surface thereof, are used as a print medium. However, the print medium is not limited to this. For example, a label continuous body that includes a plurality of labels temporarily attached to a long strip of liner (labels with a liner) or a continuously produced sheet without any adhesive agent layer (continuous sheet) is usable as the print medium, and not only a paper medium but also a film printable by a thermal head or so forth is usable as the print medium. The labels with a liner, the continuous sheet or the film can include location detection marks.