Patent Publication Number: US-6217019-B1

Title: Recording sheet package

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a recording sheet package for a thermal printer, especially for a direct thermal printer that directly heats a thermosensitive recording sheet to print an image thereon. 
     2. Background Arts 
     Thermal printers may be roughly classified into two types: direct thermal printing type and thermal transfer type. The thermal transfer type includes wax transfer type and sublimation type. For each type printer, a particular type of recording sheet is used. The wax transfer type printer melts or softens ink on ink film, and transfers it to the recording paper. The sublimation type printer sublimates or disperses dye of ink film onto the recording sheet. The recording sheet for the wax transfer type consists of paper coated with a smoothing layer. The recording sheet for the sublimation type consists of paper coated with polyester resin. 
     The thermosensitive recording sheet for the direct thermal printing is usually provided for a full-color printing. For example, JPA 61-213169 discloses a thermosensitive color recording sheet. The thermosensitive color recording sheet is constituted of a support layer and at least three coloring layers overlaid thereon which respectively develop cyan, magenta and yellow when heated up to different temperature ranges from each other. Thus, gradually increasing heat energies are applied to the thermosensitive recording sheet to develop three colors sequentially from the most thermosensitive coloring layer to the least thermosensitive coloring layer. Each coloring layer after developing color is optically fixed prior to the thermal coloring of the next coloring layer, so that the just colored layer may not develop color any more even while it is heated by the heat energies applied for the next coloring layer. For this optical fixation, ultraviolet rays of a predetermined wavelength range are applied to the thermosensitive recording sheet, to destroy the coloring ability of the colored layer. 
     Because of the photosensitivity to the ultraviolet rays, if the thermosensitive recording sheet is exposed to ambient light or light from a widely used fluorescent lamp or the like, for a certain time, the coloring ability is remarkably deteriorated. For this reason, the thermosensitive recording sheets must be preserved in a light-tight fashion. Moreover, since moisture has a great influence on printing quality in either type of recording sheet, it is desirable to protect the recording sheets from moisture as well as light even after they are loaded in the thermal printer, not to mention during their shipment and preservation. 
     To use the recording sheets, they are ordinarily loaded in a paper feeding cassette that is attached to a thermal printer. On loading the recording sheets in the paper feeding cassette, there have been risks of placing the recording sheets in a wrong posture, soiling the recording surface by the user&#39;s hand, or exposing the recording sheet to ambient light of an intolerable amount. Beside that, it has been uneasy to pile up the recording sheets neatly in the paper feeding cassette. If the recording sheets are loosely loaded, the recording sheets tend to get jammed in the printer. 
     To facilitate loading the recording sheets safely in a right posture, many types of recording sheet packages containing a pile of recording sheets in a casing have been suggested. JPA 5-116774 discloses a recording sheet package, wherein a portion of the casing is cut off along a line of cutting perforations to provide a paper feed-out opening for the recording sheet, and thereafter the package is loaded in a paper feeding cassette. The recording sheets are protected from light and moisture while being contained in the casing, and the users need not touch the recording sheets to load the recording sheets. However, the need for cutting the casing along the perforations makes this recording sheet package inconvenient. 
     Furthermore, in the recording sheet package of this prior art, an opening is formed through a bottom wall of the casing in connection to the paper feed-out opening concurrently with the paper feed-out opening being formed by cutting off the predetermined portion of the package casing. This bottom opening permits a push-up member to push up the recording sheets and presses the topmost recording sheet of the pile onto feed rollers that are inserted into the casing from upside of the paper feed-out opening. Therefore, this recording sheet package cannot sufficiently protect the recording sheets from light, moisture and dusts when it is unloaded from the paper feeding cassette. However, if the pile of recording sheets is not pressed onto these feed rollers by such a push-up member, the feed roller could not feed out the recording sheet when the remainder of recording sheets in the package reduces to a certain amount. Also, the piled recording sheets would be loosened, so the light-tightness and the moisture-tightness would be lowered as the remaining number of recording sheets decreases. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing, an object of the present invention is to provide a recording sheet package, which continues to protect the contained recording sheets from light, moisture and dusts, and prevents the pile of the recording sheets from loosening even after the remainder of recording sheets decreases. 
     To achieve the above and other object, according to the present invention, a recording sheet package containing a pile of recording sheets in a box-shaped casing is comprised of a paper feed-out opening formed in one end of the casing; a feed roller entrance formed through a top wall of the casing in connection to the paper feed-out opening, for allowing a feed roller of the paper feeding cassette or that of the thermal printer to access a topmost one of the piled recording sheets; a movable bottom plate on which the recording sheets are piled up, the movable bottom plate being disposed on a bottom wall of the casing that extends parallel to the top wall, so as to be able to flap up and down relative to the bottom wall; a push-up plate entrance formed through the bottom wall in connection to the paper feed-out opening, for allowing a push-up plate of the paper feeding cassette to push up the movable bottom plate and press the topmost recording sheet onto the feed roller; and a pressing plate disposed under the top wall so as to be able to flap up and down relative to the top wall, the pressing plate pressing the pile of recording sheets onto the movable bottom plate. 
     Because the pile of recording sheets is clamped between the movable bottom plate and the pressing plate, the recording sheets are maintained neat and tight even after the number of recording sheets in the casing reduces. 
     According to a preferred embodiment, the movable bottom plate is sized to be equal to or slightly larger than the recording sheet. By piling up the recording sheets with their recording surfaces oriented toward the movable bottom plate, the recording surface of the bottom recording sheet in the pile is kept in tight contact with the movable bottom plate, so is protected from ambient light. 
     According to a preferred embodiment, the casing is made from a cardboard paper having a moisture tight polymeric layer formed on one side thereof, such that the moisture tight polymeric layer is oriented outward of the casing. Thereby, the polymeric layer blocks ambient moisture from entering the interior of the casing, while the interior of the casing is maintained at an approximately constant humidity because of the moisture absorption property of the cardboard paper itself. 
     To protect the recording sheets, especially the thermosensitive recording sheets as having a specific photosensitivity, from being affected by ambient light, the cardboard paper preferably has a permeability of not more than 1% to light of a wavelength range from 300 nm to 500 nm. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects and advantages of the present invention will become apparent from the following detailed description of the preferred embodiments when read in connection with the accompanying drawings, which are given by way of illustration only and thus are not limiting the present invention, wherein like reference numerals designate like or corresponding parts throughout the several views, and wherein: 
     FIG. 1 is a perspective view of a recording sheet package according to an embodiment of the invention, and a paper feeding cassette for use with the recording sheet package; 
     FIG. 2 is an exploded perspective view of the recording sheet package of FIG. 1, wherein a casing of the recording sheet package consists of an outer casing member and an inner casing member; 
     FIGS. 3A,  3 B and  3 C are explanatory diagrams illustrating how to make the outer casing member of the recording sheet package; 
     FIGS. 4A,  4 B and  4 C are explanatory diagrams illustrating how to make the inner casing member of the recording sheet package; 
     FIG. 5 is a sectional view of the recording sheet package loaded in the paper feeding cassette; 
     FIG. 6 is an explanatory diagram illustrating a layered structure of a cardboard paper as a material of the casing of the recording sheet package; 
     FIG. 7 is an explanatory diagram illustrating a packing bag of the recording sheet package; 
     FIG. 8 is a perspective view of the paper feeding cassette in its closed position; 
     FIG. 9 is a schematic diagram illustrating the paper feeding cassette attached to a thermal printer with a CRT display device connected thereto; 
     FIG. 10 is an exploded perspective view illustrating a paper remainder indication device incorporated into the paper feeding cassette; 
     FIG. 11 is an enlarged perspective view of a paper remainder detection lever of the paper remainder indication device of FIG. 10; 
     FIGS. 12A,  12 B and  12 C are explanatory diagrams illustrating how the paper remainder indication device indicates the amount of the recording sheets that remainder in the recording sheet package; and 
     FIGS. 13A,  13 B and  13 C are explanatory diagrams illustrating how to make a casing of a recording sheet package according to a second embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In FIG. 1, a recording sheet package  10  contains a pile of recording sheets  11 , e.g. thermosensitive color recording sheets, in a flat box-shaped casing  12 . The recording sheet package  10  is loaded in a paper feeding cassette  27 , and the paper feeding cassette  27  is attached to a thermal printer to feed the recording sheets  11  one after another to the thermal printer. 
     As shown in FIG. 2, the casing  12  consists of a outer casing member  20  and an inner casing member  21  that is inserted into the outer casing member  20 . 
     As shown in FIGS. 3A to  3 C, the outer casing member  20  is made from a blanked piece of cardboard paper  13  by folding the cardboard paper  13  along folding lines  20   f  at an angle of 90°. Thereby, the cardboard paper  13  is sectioned into a top wall  20   a,  side walls  20   b  and  20   c,  and a pair of bottom wall halves  20   d  and  20   e.  By mating and bonding paste margins  20   g  of the bottom wall halves  20   d  and  20   e  to each other, the outer casing member of a flat rectangular barrel shape is provided. 
     As shown in FIGS. 4A to  4 C, the inner casing member  21  is also made from a blanked piece of the same cardboard paper  13  as the outer casing member  20 . By folding the blanked piece along folding lines  21   d  at an angle of 90°, the cardboard paper  13  is sectioned into a movable bottom plate  21   a,  an end wall portion  21   b  and a pressing plate  21   c.  Furthermore, by folding the pressing plate  21   c  inward along folding lines  21   f,  a pair of spring flaps  21   e  are provided. 
     The inner casing member  21  is inserted into the outer casing member  20  through an open end  32 . The end wall portion  21   b  of the inner casing member  21  closes the open end  32 , and extends beyond the open end  32  on either side of the casing  12  by a length equal to a thickness of the cardboard paper  13 . Thereby, the extended portions of the end wall portion  21   b  strike against end edges of the side walls  20   b  and  20   c  at the end of insertion of the inner casing member  21  into the outer casing member  20 , and stop the inner casing member  21  from sliding further into the outer casing member  20 . It is desirable to secure the inner casing member  21  to the outer casing member  20  through adhesive tapes or the like. 
     The movable bottom plate  21   a  is equal to or slightly larger than the recording sheet  11 , and is smoothly movable inside the outer casing member  20 . 
     The recording sheets  11  are piled in between the movable bottom plate  21   a  and the pressing plate  21   c.  Since the spring flaps  21   e  are bent into between the pressing plate  21   c  and the movable bottom plate  21   a,  the spring flaps  21   e  urge the recording sheets  11  toward the movable bottom plate  21   a  because of a stiffness of the cardboard paper  13 . Thus, the pile of the recording sheets  11  is held between the movable bottom plate  21   a  and the spring flaps  21   e.  The number of recording sheets  11  primary contained in the casing  12  depends on the thickness of the recording sheet  11 . 
     Especially for the thermosensitive recording sheet whose recording surface is photosensitive, it is preferable to orient the recording surfaces of the recording sheets  11  downward, i.e. toward the movable bottom plate  21   a.  Thereby, the recording surface of the bottommost recording sheet  11  of the pile is kept in tight contact with the movable bottom plate  21   a.  So the recording surfaces of the recording sheets  11  of the package  10  are prevented from being exposed to light. 
     Another open end  22  of the outer casing member  20  is used as a paper feed-out opening, so an end edge of the top wall  20   a  in the side of the paper feed-out opening  22  is partly cutout to provide a feed roller entrance  25  for permitting feed rollers  24  of the thermal printer to access the recording sheets  11 , as is implied in FIG.  5 . 
     The bottom wall halves  20   d  and  20   e  are each formed with a cutout  26   a  or  26   b  in connection to the paper feed-out opening  22 , and these cutouts  26   a  and  26   b  constitute a push-up plate entrance  26  when the bottom wall halves  20   d  and  20   e  are bonded to each other, as shown in FIG.  2 . As will be described in detail later, a push-up plate  28  of the paper feeding cassette  27  enters in the push-up plate entrance  26 , and pushes up the movable bottom plate  21   a  thereby to press the topmost recording sheet  11  onto the feed rollers  24 , as shown in FIG.  5 . 
     A cutout  30  formed in the end edge of the movable bottom plate  21   a  is for inserting a paper remainder detection lever  62  of the paper feeding cassette  27 , as shown in FIG.  5 . The paper remainder detection lever  62  detects an amount of the recording sheets  11  remaining in the recording sheet package  10 , as will be described in detail later. 
     The cardboard paper  13  has a layered structure, as shown in FIG. 6, that is usually constructed during the paper manufacturing. Since the recording sheet  11  is photosensitive, particularly to ultraviolet or near-ultraviolet rays, it is preferable to give a light shielding property to the cardboard paper  13 . Specifically, the cardboard paper  13  preferably has a permeability of not more than 1% to visible light and ultraviolet rays ranging from 300 nm to 500 nm in wavelength. For this purpose, at least one of paper layers contains light absorbing or screening materials such as carbon blacks, dyestuffs, or inorganic materials whose refractive index is not less than 1.50, e.g. titanium oxide, barium sulfate and calcium carbonate. It is preferable to color the outermost paper layer  13   a  that is oriented outward when the cardboard paper  13  is folded into the casing  12 , because it has the same effect as printing the outermost surface of the casing  12 . 
     It is also preferable to provide a polymeric layer  14  with a low vapor permeability on the outermost paper layer  13   a  by laminating, coating or printing. Thereby, the vapor permeability of the cardboard paper  13  and thus that of the casing  12  are lowered, so humidity inside the casing  12  varies less. This contributes to making the quality of prints more stable and independent of the humidity of the atmosphere. It is to be noted that the polymeric layer  14  is preferably provided only on one side of the cardboard paper  13 , that is, on the outermost paper layer  13   a.  By not providing such a moisture tight polymeric layer on the opposite surface of the cardboard paper  13  that is oriented inward of the casing  12 , the internal humidity of the casing  12  is kept constant due to the moisture retention of the cardboard paper  13 . As the moisture tight polymeric layer  14 , polyester film such as polyethylene terephthalate, vinylidene chloride, vinyl chloride, polypropylene, polyethylene, polyvinyl alcohol and their copolymers. Ordinarily, a sufficient moisture proof effect is obtained when the polymeric layer  14  has a thickness of 0.005 mm to 0.06 mm. More preferably, the thickness of the polymeric layer  14  is 0.01 mm to 0.03 mm. The weight of the cardboard paper  13  is preferably 180 g/m 2  to 650 g/m 2 , and more preferably 280 g/m 2  to 450 g/m 2 , in view of stiffness and processability. 
     As the casing  12  is formed from the layered cardboard paper  13  whose outer surface is coated with the moisture tight polymeric layer  14 , the recoding paper package  10  having the above configuration is superior in moisture proof, impact strength, and torsion strength. Moreover, since the inside surface of the casing  12  is not coated with such a moisture tight layer, the moisture absorption property of the cardboard paper  13  itself is effectively utilized for keeping the internal moisture condition of the casing  12  constant. 
     It is preferable to equalize the friction factor between the inside surface of the casing  12  and the recording sheet  11  to the friction factor between the recording sheets  11 , for the sake of stable feeding of the recording sheet  11 . Specifically, the friction factor between the inside surface of the casing  12  and the recording sheet  11  should not more than 20% differ from the friction factor between the recording sheets  11 . If the friction factor between the inside surface of the casing  12  and the recording sheet  11  is more than 20% larger than the friction factor between the recording sheets  11 , the last recording sheet  11  to feed would not smoothly slide out of the casing  12 . If, on the contrary, the friction factor between the inside surface of the casing  12  and the recording sheet  11  is more than 20% smaller than the friction factor between the recording sheets  11 , the recording sheets  11  tend to be fed out together from the casing  12 . 
     A label  29  indicating information on the recording sheets  11  contained in the casing  12  is put onto the outer surface of the casing  12 , e.g. on the bottom wall half  20   d  in the embodiment shown in FIG.  3 A. In this embodiment, a bar code  29   a  representative of the paper information is printed on the label  29 , so that the thermal printer can read the paper information from the bar code  29   a.  The paper information may include the type and format of the recording sheets  11  or heat-sensitivity or photo-sensitivity of the recording sheets  11 . 
     A bar code window  44  made of a transparent plastic is formed in a portion of a bottom wall  35   a  of the cassette body  35 , so that the bar code label  29  of the recording sheet package  10  loaded in the package chamber  38  is opposed to the bar code window  44 . 
     As shown in FIG. 7, the recording sheet package  10  is packed in a light-tight and moisture-tight packing bag  16  while it is on sale. The packing bag  16  is opened by cutting off a margin  16   a  along a cutting line  16   b.  To enable packing the recording sheet package  10  again in the packing bag  16 , a plastic sealing member  17  is provided along the cutting line  16   b  on opposite side of the margin  16   a.    
     To prevent the recording sheets  11  from slipping off the casing  12  after the recording sheet package  10  is taken out of the packing bag  16 , an adhesive tape  100  is put across the paper feed-out opening  22 . The adhesive tape  100  should be smoothly removable from the recording sheets  11  and the casing  12 . By putting the adhesive tape  100  across the paper feed-out opening  22 , the movable bottom plate  21   a  is kept in tight contact with the recording sheet  11 , so the recording sheets  11  are more tightly shielded from light and moisture. 
     As shown in FIGS. 1 and 8, the paper feeding cassette  27  is constituted of a cassette body  35  and a lid  36  that is mounted to the cassette body  35  through a hinge  37 . The lid  36  is opened to load the recording sheet package  10  in a package chamber  38  of the cassette body  35 . When the lid  36  is closed, engaging claws  39  of the lid  36  are engaged with a lock device  40  of the cassette body  35 , to keep the lid  36  in the closed position. By sliding an unlock button  41 , the lock device  40  is disengaged from the engaging claws  39 , so the lid  36  is unlocked. 
     To facilitate loading, the package chamber  38  is slightly larger than the recording sheet package  10 . A positioning projection  42  is formed on one side wall of the cassette chamber  38 . Correspondingly, a positioning mark  43  is provided on the recording sheet package  10  at the top wall  20   a  of the outer casing member  20 . The recording sheet package  10  is loaded in the package chamber  38  while putting the positioning mark  43  in opposition to the positioning projection  42 . 
     The push-up plate  28  is mounted in the package chamber  38  through a mounting device  46  that supports one end of the push-up plate  28 . Coiled springs  47  are mounted below another end of the push-up plate  28  to urge the push-up plate  28  to move upward. The push-up plate  28  is made of a resilient material, so the push-up plate  28  and the coiled springs  47  are pushed down by the recording sheet package  10  when the lid  36  is closed after the recording sheet package  10  is loaded in the package chamber  38 . In this closed position, the push-up plate  28  resiliently pushes up the movable bottom plate  21   a  of the recording sheet package  10 , as shown in FIG.  5 . 
     As shown in FIG. 5, a gap or slit  50  is provided between the cassette body  35  and the lid  36  on the side of the hinge  37 , to constitute a paper exit  50 . Behind the paper exit  50 , a recording sheet separating device  51  is provided for preventing a plurality of recording sheets  11  from being fed out concurrently. As shown in FIG. 1, a rubber block  52  is provided in a middle portion of the recording sheet separating device  51 . The rubber block  52  has a top surface  52   a  that is inclined in the paper feeding direction, and is protruded upward into a paper feeding path behind the paper exit  50 . If more than one recording sheet  11  are fed out from the recording sheet package  10 , the lower one of the recording sheets  11  is stopped from sliding out of the paper exit  50  because of the friction of the rubber block  52  against the recording sheet  11 . The recording sheet separating device  51  further has separating projections  53  on opposite sides of the rubber block  52   a.  Leading edges of the lower ones of those recording sheets  11  which are fed out together from the recording sheet package  10  strike against the separating projections  53 , so only the topmost recording sheet  11  can move past the recording sheet separating device  51 . 
     As shown in FIGS. 1 and 8, a pair of roller openings  55  are formed through the lid  36 , such that the feed roller entrance  25  of the recording sheet package  10  is located under the roller openings  55 . When the paper feeding cassette  27  is attached to a thermal printer, as shown for example in FIG. 9, the feed rollers  24  of the thermal printer  56  is brought into contact with the topmost recording sheet  11  of the recording sheet package  10  through the roller openings  55  and the paper entrance  25 . As the feed rollers  24  rotate in a paper feeding direction, the topmost recording sheet  11  is fed out from the recording sheet package  10  into the thermal printer  56 . 
     The recording sheet  11  after having a picture printed thereon through the thermal printer  56  is ejected onto the top wall of the lid  36  of the paper feeding cassette  27 . To guide and stop the ejected recording sheet  11  from dropping off, a pair of guide fences  57  and  58  are provided on the opposite sides of the top wall of the lid  36 . That is, the top wall of the lid  36  doubles as a paper ejection tray. 
     As shown in detail in FIG. 10, a paper remainder indication device  60  and a paper remain indication window  61  are provided in the paper feeding cassette  27 . The paper remainder indication device  60  is constituted of the paper remainder detection lever  62 , a paper remainder indication lever  63  and a holding plate  64 . As shown in FIG. 8, the paper remainder indication window  61  is constituted of a rectangular hole  65  formed through an end wall of the cassette body  35 , and a transparent plastic plate fitted onto the end wall in front of the rectangular hole  65 . 
     As shown in FIG. 11, the paper remainder detection lever  62  is an integral part consisting of a mounting shaft  62   a,  a detection arm  62   b  and an engaging fork  62   c  which are radially protruded from the mounting shaft  62   a.  The mounting shaft  62   a  is rotatably held in a bearing portion  67  that is provided on the bottom wall  35   a  of the cassette body  35 . 
     Referring back to FIG. 10, the paper remainder indication lever  63  consists of an engaging arm section  63   a  and an indication arm section  63   b  which extend orthogonally to each other, and is mounted rotatably on a pivot  35   c  that is provided on the bottom wall  35   a  of the cassette body  35 . The holding plate  64  is mounted on the paper remainder indication lever  63 , and is secured to the pivot  35   c  by a screw  74 . A coiled spring  70  that is suspended between this lever  63  and the bottom wall  35   a  urges the paper remainder indication lever  63  to rotate about the pivot  35   c  in a counterclockwise direction in FIG.  10 . 
     The engaging fork  62   c  of the paper remainder detection lever  62  is engaged with a pair of holes  68  and  69  that are formed through an end of the engaging arm section  63   a  of the paper remainder indication lever  63 . Thus, the rotational movement of the paper remainder detection lever  62  is transmitted to the paper remainder indication lever  63 . Since the indication arm section  63   b  is quite longer than the engaging arm section  63   a,  a small motion of the engaging arm section  63   a  is converted into a larger motion of a distal end of the indication arm section  63   b.  The distal end of the indication arm section  63   b  is bent rectangularly to provide an indicator blade  63   c,  and an indication label  71  is put on this indicator blade  63   c.  The indicator blade  63   c  is located behind the paper remainder indication window  61  such that the indication label  71  is partly viewed through the hole  65 . 
     As shown in FIG. 1, a distal end of the detection arm  62   b  protrudes upward through a cutout  28   a  of the push-up plate  28 , and comes to contact with the bottom of the pile of the recording sheets  11  when the recording sheet package  10  is loaded in the paper feeding cassette  27 . As the recording sheets  11  are sequentially fed out from the recording sheet package  10 , and thus the remaining number of recording sheets  11  decreases, the pile of the recording sheets  11  is pushed upward by the push-up plate  28  through the movable bottom plate  21   a.  As a result, the detection arm  62   b  moves upward while rotating about the shaft  62   a  in a counterclockwise direction in FIG.  10 . Thereby, the paper remainder indication lever  63  rotates in the counterclockwise direction according to the force of the coiled spring  70 , so the indicator blade  63   c  and thus the indication label  71  moves in a direction shown by an arrow in FIG.  10 . 
     As shown in FIGS. 12A to  12 C, the indication label  71  has a pattern printed thereon. The pattern consists of a first indication area  72  for indicating that there are not any recording sheets  11  in the recording sheet package  10 , and a second indication area  73  for indicating the remaining amount of recording sheet  11 . The whole first indication area  72  is colored in a single color, e.g. red, whereas the second indication area  73  sectioned diagonally into two triangular segments  73   a  and  73   b  of different colors, e.g. white and green. 
     Immediately after the recording sheet package  10  is newly loaded in the paper feeding cassette  27 , the indicator blade  63   c  is set in a position shown in FIG. 12A, wherein the lower green triangular segment  73   b  of the second indication area  73  occupies most of an area visible through the paper remainder indication window  61 . As the remaining amount of recording sheets  11  decreases, the indicator blade  63   c  moves toward a position as shown in FIG. 12B, wherein the second indication area  73  is still viewed through the paper remainder indication window  61 , but the upper white triangular segment  73   a  occupies most of the area visible through the hole  65 . That is, the occupation rate of the green segment  73   b  within the visible area of the paper remainder indication window  61  represents the amount of recording sheets  11  remaining in the paper feeding cassette  27 . After the last recording sheet  11  is fed out, the indicator blade  63   c  moves to a position shown in FIG. 12C, wherein the red first indication area  72  is placed behind the hole  65  of the paper remainder indication window  61 , indicating that there are not any recording sheets  11  in the paper feeding cassette  27 . 
     When making a print, a power switch  80  of the thermal printer  56  is turned on, and necessary commands are entered by operating some keys  77  of the thermal printer  56 . First, an image to print is displayed on an external display device  81 , such as a CRT monitor, connected to the thermal printer  56 . The image is displayed on the basis of image data that is sent from another device or read out from a memory medium, e.g. a smart media  78  inserted in a slot  79  of the thermal printer. The operator confirms the image to print on the display device  81 , and operates a print start key included in the keys  77 . 
     Then, the feed rollers  24  start rotating to feed the topmost recording sheet  11  in the recording sheet package  10  out of the paper feeding cassette  27  into the thermal printer  56 . The thermal printer  56  then prints the image on the recording sheet  11  according to a conventional three color frame sequential method. In this embodiment, the thermal printer  56  is a direct color thermal printer using the thermosensitive color recording sheet, so each color frame is recorded by heating the recording sheet  11  by a thermal head, and thereafter fixed by an optical fixing device. The recording sheet  11  having the image recorded thereon is ejected onto the lid  36  of the paper feeding cassette  27 . 
     As the remaining amount of the recording sheets  11  decreases, the movable bottom plate  21   a  of the casing  12  is pushed up by the push-up plate  28  of the paper feeding cassette  27 . Therefore, the topmost recording sheet  11  in the pile is always pressed onto the feed rollers  24 . On the other hand, the pressing plate  21   c  and the spring flaps  21   e  of the casing  12  keep on pressing down the recording sheets  11 . Therefore, the recording sheets  11  are kept in tight contact with each other, so the recording sheets  11  are well protected from moisture and extraneous light. Since the movable bottom plate  21   a  of the inner casing member  21  is kept in tight contact with the recording sheets  11 , the recording sheets  11  is protected from dust, even though the outer casing member  20  has the push-up plate entrance  26  in the bottom side thereof. 
     To use another type paper for printing, the paper feeding cassette  27  is detached from the thermal printer  56 , and the recording sheet package  10  is replaced by another type of recording sheet package. The half-used recording sheet package  10  can be packed again in the packing bag  16  and is sealed by closing the sealing member  17 , to preserve it while protecting it from moisture and light. 
     Although the casing  12  of the recording sheet package  10  is constituted of the inner and outer casing members  20  and  21 , it is possible to form a casing  91  from a single blanked piece  90  of cardboard paper, as shown in FIGS. 13A to  13 C. According to this embodiment, a pressing plate  91   d  is connected to a top wall  91   a.  An opening  92 , that provides a feed roller entrance and a paper exit as well, is formed between the top wall  91   a  and the pressing plate  91   d.  A pair of spring flaps  91   e  are connected to the pressing plate  91   d.  Also, an end wall portion  91   g  is connected to the top wall  91   a  on opposite side from the pressing plate  91   d,  and a movable bottom plate  91   h  is connected to the end wall portion  91   g.  Side walls  91   j  are connected to the top wall  91   a,  and bottom wall halves  91   k  are connected to the side walls  91   j,  in the same way as the outer casing member  20  of the first embodiment. 
     To form the casing  91 , the cardboard plate  90  is first folded along folding lines  91   f  to bend the spring flaps  91   e  downward, and then folded along folding lines  91   b  to place the pressing plate  91   d  under the top wall  91   a,  as shown in FIG.  13 B. Thereafter, the cardboard plate  90  is folded along folding lines  91 C at an angle of 90° to place the movable bottom plate  91   h  below the pressing plate  91   d  that is placed under the top wall  91   a,  as shown in FIG.  13 C. Then, a pile of recording sheets are inserted into between the pressing plate  91   d  and the movable bottom plate  91   h  with their recording surfaces oriented downward. 
     Next, the cardboard plate  90  is folded along folding lines  91   p  such that the side walls  91   j  and the bottom wall halves  91   k  are wrapped around the recording sheets and the movable bottom plate  91   h.  Thereafter, paste margins  91   m  of the bottom wall halves  91   k  are bonded to each other. Then cutouts  93   a  and  93   b  of the bottom wall halves  91   k  form a push-up plate entrance. 
     Although the bottom wall halves  20   d  and  20   e,  or  91   k  are approximately equal in size to each other, they may have different sizes from each other. The bonding position of the casing is not necessarily located in the bottom, but may be located in another position. For example, it is possible to locate the bonding position between a bottom wall portion and a side wall portion, or between a side wall portion and a top wall portion. 
     Although the recording sheets are fed out from the recording sheet package by the feed rollers that are provided in the thermal printer in the above embodiment, the recording sheet package of the present invention may be loaded in a paper feeding cassette having feed rollers incorporated therein. 
     The present invention is applicable to a recording sheet package for the thermal wax transfer type printer or the sublimation type thermal printer. 
     Thus, the present invention is not to be limited to the above embodiments but, on the contrary, various modification will be possible to those skilled in the art without departing from the scope of claims appended hereto.