Patent Publication Number: US-10322594-B2

Title: Recording medium and manufacturing method of recording medium

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2016-043721, filed on Mar. 7, 2016, the entire contents of which are incorporated herein by reference. 
     FIELD 
     Embodiments of the present invention relate to a recording medium and a manufacturing method of a recording medium. 
     BACKGROUND 
     There are methods which, at the time of irradiating a recording medium in which a plurality of color developing layers of which threshold values of color developing temperature are different are laminated with laser light, form a full color image by varying strength of the laser light and an exposure time to the laser light in accordance with color to be developed. 
     Laser light with which a recording medium is irradiated is converted into heat, and the heat is propagated within the recording medium. The heat is propagated not only in a lamination direction in which color developing layers are to be laminated, but also in a direction orthogonal to the lamination direction. For this reason, as the heat is propagated from a laser spot of the laser light formed on the recording medium toward the inside of the recording medium, the heat is diffused in the direction orthogonal to the lamination direction. Accordingly, an area in the color developing layer where color is developed becomes larger than an area of the laser spot, and as a result a desired image cannot be formed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram showing an example of a schematic configuration of a recording medium according to the present embodiment. 
         FIG. 2  is a diagram for describing an example of a processing to make the recording medium according to the present embodiment develop color. 
         FIG. 3  is a diagram for explaining a problem, at the time of making a recording medium of a comparative example develop color. 
         FIG. 4  is a diagram showing an example of a configuration of the heat insulting layer which the recording medium according to the present embodiment has. 
         FIG. 5  is a diagram showing an example of a configuration of the heat insulting layer which the recording medium according to the present embodiment has. 
         FIG. 6  is a diagram showing an example of a configuration in which a first heat insulating layer of the heat insulting layer which the recording medium according to the present embodiment has is composed of air. 
         FIG. 7  is a diagram showing an example of a flow chart indicating a method for manufacturing the recording medium according to the present embodiment. 
     
    
    
     EMBODIMENT TO PRACTICE THE INVENTION 
     A recording medium of an embodiment has a substrate, a first color developing layer, a heat insulating layer, and a second color developing layer. The first color developing layer is laminated on the substrate and develops a first color at a temperature not less than a first threshold value. The heat insulating layer is laminated on the first color developing layer. The second color developing layer is laminated on the heat insulating layer, and develops a second color that is different from the first color at a temperature not less than a second threshold value that is higher than the first threshold value. The heat insulating layer has a first heat insulating layer of a first heat conductivity and a second heat insulating layer of a second heat conductivity that is higher than the first heat conductivity, which are laminated in a second direction orthogonal to a first direction in which the first color developing layer, the heat insulating layer, and the second color developing layer are laminated on the substrate. 
     Hereinafter, a recording medium according to the present embodiment and a manufacturing method of the recording medium will be described using the accompanying drawings. 
       FIG. 1  is a diagram showing an example of a schematic configuration of a recording medium according to the present embodiment. As shown in  FIG. 1 , a recording medium  100  has a substrate  10 , and a heat insulating layer  11 , a cyan color developing layer  12 , a heat insulating layer  13 , a magenta color developing layer  14 , a heat insulating layer  15 , a yellow color developing layer  16 , a protective layer  17  which are laminated on the substrate  10 . The recording medium  100  is manufactured by laminating the heat insulating layer  11 , the cyan color developing layer  12 , the heat insulating layer  13 , the magenta color developing layer  14 , the heat insulating layer  15 , the yellow color developing layer  16 , the protective layer  17  on the substrate  10  in this order. The heat insulating layer  11  contains heat insulating material which decreases heat transfer from the cyan color developing layer  12  to the substrate  10 . The cyan color developing layer  12  is a layer which is provided on the substrate  10  via the heat insulating layer  11  and contains temperature indicating material that develops cyan (an example of a first color) at a temperature not less than a low temperature threshold value t 1  (an example of a first threshold value). The heat insulating layer  13  is provided between the cyan color developing layer  12  and the magenta color developing layer  14 , and contains heat insulating material which decreases heat transfer from the magenta color developing layer  14  to the cyan color developing layer  12 . 
     The magenta color developing layer  14  is a layer which is provided on the cyan color developing layer  12  via the heat insulating layer  13  and contains temperature indicating material that develops magenta (an example of the first color or a second color) at a temperature not less than an intermediate temperature threshold value t 2  (an example of the first threshold value or a second threshold value) that is higher than the low temperature threshold value t 1 . The heat insulating layer  15  is provided between the magenta color developing layer  14  and the yellow color developing layer  16 , and contains heat insulating material which decreases heat transfer from the yellow color developing layer  16  to the magenta color developing layer  14 . The yellow color developing layer  16  is a layer which is provided on the magenta color developing layer  14  via the heat insulating layer  15  and contains temperature indicating material that develops yellow (an example of the second color) at a temperature not less than a high temperature threshold value t 3  (an example of the second threshold value) that is higher than the intermediate temperature threshold value t 2 . The protective layer  17  is provided on the yellow color developing layer  16 , and protects the heat insulating layers  11 ,  13 ,  15 , the cyan color developing layer  12 , the magenta color developing layer  14 , and the yellow color developing layer  16 . 
     The recording medium  100  of the present embodiment can reproduce a color of full colors by three colors of cyan which the cyan color developing layer  12  develops, magenta which the magenta color developing layer  14  develops, and yellow which the yellow color developing layer  16  develops. However, a recording medium of the present embodiment is not limited to the above-described structure, as long as a plurality of color developing layers which develop different colors at different temperatures are laminated via a heat insulating layer. 
     Next, an example of a processing for making the recording medium  100  according to the present embodiment develop color will be described using  FIG. 1  and  FIG. 2 .  FIG. 2  is a diagram for describing an example of the processing for making the recording medium according to the present embodiment develop color. 
     As shown in  FIG. 1 , a laser recording apparatus irradiates the recording medium  100  with laser light L when making the recording medium  100  develop color. At that time, the laser recording apparatus irradiates the recording medium  100  with the laser light L which has been condensed by a lens and so on, to form a laser spot SPT of a prescribed size on the recording medium. Heat generated by the laser light L with which the recording medium  100  has been irradiated is transferred from the laser spot SPT to the yellow color developing layer  16 , the magenta color developing layer  14 , and the cyan color developing layer  12 . 
     The cyan color developing layer  12 , the magenta color developing layer  14 , and the yellow color developing layer  16  are clear and colorless in an initial state in which heat is not applied to these layers, but these layers develop respective colors when heat is applied to these layers. In the present embodiment, the yellow color developing layer  16  develops color by heat of a temperature not less than the high temperature threshold value t 3 , as described above. The magenta color developing layer  14  develops color by heat of a temperature not less than the intermediate temperature threshold value t 2 . The cyan color developing layer  12  develops color by heat of a temperature not less than the low temperature threshold value t 1 . 
     Accordingly, when only the yellow color developing layer  16  of the recording medium  100  is made to develop color, as shown in (c) in  FIG. 2 , the laser recording apparatus irradiates the recording medium  100  with the laser light L of a first strength from the protective layer  17  side for a first time. The laser light L with which the recording medium  100  has been irradiated is converted into heat by the protective layer  17 , and the heat is transferred from the laser spot SPT formed on the protective layer  17  to the yellow color developing layer  16 , as heat of a temperature not less than the high temperature threshold value t 3 . By this means, the yellow color developing layer  16  develops yellow. At this time, the first time when the recording medium  100  is irradiated with the laser light L is made to be a short time, and the heat transfer from the yellow color developing layer  16  to the magenta color developing layer  14  is decreased by the heat insulting layer  15 , to prevent the magenta color developing layer  14  from developing color. 
     In addition, when only the magenta color developing layer  14  of the recording medium  100  is made to develop color, as shown in (b) in  FIG. 2 , the laser recording apparatus irradiates the recording medium  100  with the laser light L of a second strength that is weaker than the first strength from the protective layer  17  side for a second time that is longer than the first time. The laser light L with which the recording medium  100  has been irradiated is converted into heat by the protective layer  17 , and the heat is transferred from the laser spot SPT formed on the protective layer  17  to the magenta color developing layer  14 , as heat of a temperature that is not less than the intermediate temperature threshold value t 2  and is lower than the high temperature threshold value t 3 . By this means, the magenta color developing layer  14  develops magenta. At this time, the second time when the recording medium  100  is irradiated with the laser light L is made to be a time during which the heat is not transferred to the cyan color developing layer  12 , and the heat transfer from the magenta color developing layer  14  to the cyan color developing layer  12  is decreased by the heat insulting layer  13 , to prevent the magenta color developing layer  14  from developing color. Since the temperature of the heat which is transferred in the recording medium  100  is lower than the high temperature threshold value t 3 , the yellow color developing layer  16  does not develop color. 
     In addition, when only the cyan color developing layer  12  of the recording medium  100  is made to develop color, as shown in (a) in  FIG. 2 , the laser recording apparatus irradiates the recording medium  100  with the laser light L of a third strength that is weaker than the second strength from the protective layer  17  side for a third time that is longer than the second time. The laser light L with which the recording medium  100  has been irradiated is converted into heat by the protective layer  17 , and the heat is transferred from the laser spot SPT formed on the protective layer  17  to the cyan color developing layer  12 , as heat of a temperature that is not less than the low temperature threshold value t 1  and is lower than the intermediate temperature threshold value t 2 . By this means, the cyan color developing layer  12  develops cyan. At this time, the third time when the recording medium  100  is irradiated with the laser light L is made to be a time during which the heat is transferred to the cyan color developing layer  12 , to prevent defective color development of the cyan color developing layer  12 . Since the temperature of the heat which is transferred in the recording medium  100  is lower than the intermediate temperature threshold value t 2 , the yellow color developing layer  16  and the magenta color developing layer  14  do not develop color. 
     Next, a problem at the time of making a recording medium of a comparative example develop color will be described using  FIG. 3 .  FIG. 3  is a diagram for describing the problem, at the time of making the recording medium of the comparative example develop color. As shown in  FIG. 3 , a recording medium  200  of the comparative example has the substrate  10 , and a heat insulating layer  201 , the cyan color developing layer  12 , a heat insulating layer  202 , the magenta color developing layer  14 , a heat insulating layer  203 , the yellow color developing layer  16 , the protective layer  17  which are laminated on the substrate  10  in this order, in the same way as the recording medium  100  of the present embodiment. In the recording medium  200  of the comparative example, heat propagates not only in a direction (hereinafter called a longitudinal direction) in which the heat insulating layer  201 , the cyan color developing layer  12 , the heat insulating layer  202 , the magenta color developing layer  14 , the heat insulating layer  203 , the yellow color developing layer  16  and the protective layer  17  are laminated, but also in a direction (hereinafter, called a lateral direction) orthogonal to the longitudinal direction. For this reason, it is difficult to make a region of a desired size develop color. 
     Specifically, when the protective layer  17  is irradiated with the laser light L, as shown in  FIG. 3 , the laser light L with which the recording medium  200  has been irradiated is converted into heat by the protective layer  17 , and the heat is transferred from the laser spot SPT also in the lateral direction. And a range in which the heat is transferred in the lateral direction of the recording medium  200  becomes larger, as a distance from the laser spot SPT in the longitudinal direction becomes larger. For the reason, when the protective layer  17  is irradiated with the laser light L, the yellow color developing layer  16  develops color in a region of a size approximately equal to an area of the laser spot SPT. However, the cyan color developing layer  12  develops color in a region that is larger than the laser spot SPT, and thereby a desired image cannot be recorded. A spot diameter of the light L with which the recording medium  200  is irradiated is determined by a wavelength of the laser light L and performance of a lens, and thereby the spot diameter cannot be made not more than a prescribed spot diameter. Accordingly, in a color developing layer that is distant from the laser spot SPT, in order to make the color developing layer develop color in a region approximately equal to the laser spot SPT, it is necessary to reduce propagation of heat in the lateral direction in the recording medium  200 . 
     In the recording medium  100  of the present embodiment shown in  FIG. 4 , in the heat insulating layers  13 ,  15 , heat conductivity of the heat in the lateral direction is lower than heat conductivity of the heat in the longitudinal direction. That is, when heat is transferred from the yellow color developing layer  16  to the magenta color developing layer  14 , and when heat is transferred from the magenta color developing layer  14  to the cyan color developing layer  12 , the heat transfer in the lateral direction is reduced. By this means, since it is possible to transfer heat to a region of a size which is approximately equal to the laser spot SPT, in the magenta color developing layer  14  and the cyan color developing layer  12  which are distant from the laser spot SPT, it is possible to make the color development layer develop color in a region of a size which is approximately equal to the laser spot SPT, in each of the magenta color developing layer  14  and the cyan color developing layer  12 . 
       FIG. 4  is a diagram showing an example of a configuration of the heat insulating layer which the recording medium according to the present embodiment has. The heat insulating layer  13  has the same configuration as the heat insulating layer  15 . In the following description, the heat insulating layer  15  will be described. As shown in  FIG. 4 , in the heat insulating layer  15  which the recording medium  100  of the present embodiment has, first heat insulating layers  401  of a first heat conductivity λ 1 , and second heat insulating layers  402  of a second heat conductivity λ 2  that is higher than the first heat conductivity λ 1  are laminated in the lateral direction. That is, the heat insulating layer  15  has a structure in which the heat conductivity in the longitudinal direction is high and the heat conductivity in the lateral direction is low. By this means, when heat is transferred from the yellow color developing layer  16  to the magenta color developing layer  14 , since the heat propagation in the lateral direction in the heat insulating layer  15  can be reduced, an area in the lateral direction in which heat is transferred is approximated to the area of the laser spot SPT in the magenta color developing layer  14 , and accordingly, it is possible to form an image of a size that is approximate to the area of the laser spot SPT. 
     In addition, in the present embodiment, a thickness of the first heat insulating layer  401  in the lateral direction is not more than a half of a spot diameter of the laser spot SPT of the laser light L with which the recording medium  100  is to be irradiated. In addition, a thickness of the second heat insulating layer  402  in the lateral direction is not more than a half of the spot diameter of the laser spot SPT of the laser light L with which the recording medium  100  is to be irradiated. And as shown in  FIG. 4 , in the heat insulating layer  15 , the first heat insulating layers  401  and the second heat insulating layers  402  are alternately laminated in the lateral direction. That is, at least one of the first heat insulating layers  401  is contained in a region of the heat insulating layer  15  in which heat is propagated from the yellow color developing layer  16 , and the first insulating layers  401  and the second insulating layers  402  exist mixedly in the heat insulating layer  15 . By this means, it is possible to prevent that deviation in regions in which heat is propagated in the longitudinal direction is generated in the heat insulating layer  15 , and accordingly, in the magenta color developing layer  14 , a shape of a region in which heat is transferred is approximated to the shape of the laser spot SPT of the laser light L, and thereby it is possible to form an image approximate to the shape of the relevant laser spot SPT. 
       FIG. 5  is a diagram showing an example of a configuration of the heat insulating layer which the recording medium according to the present embodiment has. In the present embodiment, a plurality of the first heat insulating layers  401  are provided in a lattice shape in the lateral direction, as shown in  FIG. 5 . And a size (a length of one side of a lattice) of a lattice formed by the first heat insulating layers  401  is not more than a half of the spot diameter of the laser spot SPT of the laser light L with which the recording medium  100  is to be irradiated. And the second heat insulating layers  402  are respectively provided in openings of the first insulating layers  401  formed in a lattice shape. 
     Specifically, in the heat insulating layer  15 , a first layer  15 A and a second layer  15 B are laminated in the longitudinal direction. In the first layer  15 A, the first heat insulating layers  401  and the second heat insulating layers  402  are alternately laminated in an x-axis direction (an example of a third direction) out of the lateral direction. And in the second layer  15 B, the first heat insulating layers  401  and the second heat insulating layers  402  are alternately laminated in a y-axis direction (an example of a fourth direction) orthogonal to the x-axis direction out of the lateral direction. By this means, when the heat insulating layer  15  is seen from an irradiation source of the laser light L, a plurality of the first heat insulating layers  401  of the second layer  15 B and a plurality of the first heat insulating layers  401  of the first layer  15 A are provided in a lattice shape in the lateral direction. 
     In the heat insulating layer which the recording medium according to the present embodiment has, the first heat insulating layers  401  are provided in a lattice shape in the lateral direction, but without being limited to this, the second heat insulating layers  402  may be provided in a lattice shape in the lateral direction. In this case, the first heat insulating layers  401  are respectively provided in openings of the second heat insulating layers  402  formed in a lattice shape.  FIG. 6  is a diagram showing an example of a configuration in which the first heat insulating layers of the heat insulating layer which the recording medium according to the present embodiment has are composed of air. In the present embodiment, the first heat insulating layers  401  are composed of air existing in openings of the second heat insulating layers  402  that are formed in a lattice shape in the lateral direction (a plane direction) orthogonal to the longitudinal direction. Here, the first heat insulating layer  401  is formed of air, but the first heat insulating layer  401  has only to be formed of a member having heat conductivity that is lower than the second heat insulating layer  402 . 
     Next, an example of a flow of a manufacturing method of the recording medium  100  according to the present embodiment will be described using  FIG. 7 .  FIG. 7  is a diagram showing an example of a flow chart indicating the method for manufacturing the recording medium according to the present embodiment. 
     As shown in  FIG. 7 , a manufacturing apparatus to manufacture the recording medium  100  according to the present embodiment firstly prepares the substrate  10 , and laminates the heat insulating layer  11  on the substrate  10  (step S 701 ). Next, the manufacturing apparatus laminates the cyan color developing layer  12  on the heat insulating layer  11  (step S 702 ). Next, the manufacturing apparatus laminates the heat insulating layer  13  on the cyan color developing layer  12  (step S 703 ). The manufacturing apparatus laminates a first layer and a second layer on the cyan color developing layer  12  like the heat insulating layer  15  shown in  FIG. 5 . Here, the first layer and the second layer are respectively formed by laminating the first insulating layers  401  and the second insulating layers  402  in the lateral directions orthogonal to the longitudinal direction in which the cyan color developing layer  12  has been laminated. 
     Next, the manufacturing apparatus laminates the magenta color developing layer  14  on the heat insulating layer  13  (step S 704 ). Next, the manufacturing apparatus laminates the heat insulating layer  15  on the magenta color developing layer  14  (step S 705 ). At the time of laminating the heat insulating layer  15 , the manufacturing apparatus forms the heat insulating layer  15  by laminating the first layer  15 A and the second layer  15 B which have been respectively formed by laminating the first heat insulating layers  401  and the second heat insulating layers  402  in the lateral direction, in the same manner as in the heat insulating layer  13 . 
     Then, the manufacturing apparatus laminates the yellow color developing layer  16  on the heat insulating layer  15  (step S 706 ). Finally, the manufacturing apparatus laminates the protective layer  17  on the yellow color developing layer  16 , to manufacture the recording medium  100  (step S 707 ). 
     In this manner, according to the recording medium  100  according to the present embodiment, in the recording medium  100  in which a plurality of the color developing layers are laminated, prescribed heat insulating layers are respectively provided between a plurality of the color developing layers. Accordingly, in the color developing layer existing at a position distant from the laser spot SPT to be irradiated with the laser light L, it is possible to form an image of a size approximate to the size of the laser spot SPT. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.