Patent Publication Number: US-2023144762-A1

Title: Panel assembly, refrigerator, and home appliances

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 17/057,518, filed on Nov. 20, 2020, which is a National Stage application under 35 U.S.C. § 371 of International Application No. PCT/KR2019/014417, filed on Oct. 30, 2019, which claims the benefit of U.S. Provisional Application No. 62/757,721, filed on Nov. 8, 2018. The disclosures of the prior applications are incorporated by reference in their entirety. 
    
    
     TECHNICAL FIELD 
     The present specification relates to a panel assembly, a refrigerator including the same, and home appliances. 
     BACKGROUND 
     In general, refrigerators are home appliances for storing food at a low temperature in a storage space that is covered by a door. 
     For this, refrigerators cool the inside of the storage space by using cool air generated by being heat-exchanged with a refrigerant circulated through a refrigeration cycle to store foods in an optimum state. 
     Such a refrigerator is becoming larger and multifunctioned as dietary changes and user&#39;s preferences become more diverse, and thus, a refrigerator having various structures and convenience devices for user&#39;s convenience and freshness of stored foods has been introduced. 
     The storage space of the refrigerator may be opened/closed by the door. The refrigerators may be classified into various types according to an arranged configuration of the storage space and a structure of the door that opens and closes the storage space. 
     A separate accommodation space accessible from the outside may be provided in the door of the refrigerator. The accommodation space may be accessed by opening a partial auxiliary door or a home bar door without opening the entire refrigerator door through the above-described accommodation space. 
     Thus, frequently used foods may be stored in the separate accommodation space provided in the refrigerator door. Since the entire refrigerator door is not opened for accommodating food, there is an advantage of minimizing leakage of cold air inside the refrigerator. 
     However, even in such a structure, there is a problem in that the food is not checked unless the refrigerator door is opened. That is, the door should be opened to identify whether desired food is received in a space in the refrigerator or in a separate storage space provided in the door. If there is no desired food when opening the auxiliary door or the home bar, there is inconvenience to open the main door again. Here, there is a problem that unnecessary leakage of cold air occurs. 
     As a document for solving this problem, there is Korean Patent Publication No. 10-2016-0045545. 
     In the prior art document, disclosed is a refrigerator including: a cabinet in which a storage space is provided; a lighting device that illuminates the inside of the storage space; a door rotatably provided on the cabinet to open and close the storage space, defining an opening, and including a panel assembly having a front panel disposed on a front surface; and a controller allowing the lighting device to operate so that light is transmitted through the panel assembly so as to allow the storage space to be viewed from the outside of the door through the opening. 
     The front panel is made of a transparent material, and an insulation panel is disposed on a rear surface of the front panel. 
     According to the prior art document, when the lighting device is turned on, the light irradiated by the lighting device passes through the front panel made of the transparent material, and thus, a user may see the storage space through the front panel. 
     In the case of the prior art document, a vacuum space is defined between the front panel and the insulation panel, and a spacer is arranged between the front panel and the insulation panel. 
     In the case of the prior art document, a technique in which the spacer supports the insulation panel to prevent a central portion of the insulation panel from being bent is disclosed, but a technique of maintaining a constant gap across the front panel and the insulation panel by the spacer is not disclosed. 
     Also, in the case of the prior art document, when the lighting device is turned on, the light irradiated by the lighting device passes through the insulation panel and the front panel in sequence. However, since the spacer is disposed between the insulation panel and the front panel, there is a problem that the spacer between the insulation panel and the front panel is visible from the outside, and also, the prior art document does not disclose a technique for solving this problem. 
     Also, in the case of the prior art document, a hole for defining the vacuum space between the front panel and the insulation panel and a stopper for blocking the hole are disclosed. However, while the light irradiated by the lighting device sequentially passes through the insulation panel and the front panel, there is a concern that the hole and the stopper are exposed to the outside, and also, the prior art document does not disclose a technique for solving this problem. 
     Also, when a size of the spacer increases, possibility in which the gap between the front panel and the insulation panel is uniformly maintained is high. On the other hand, an area through which the light passes through the front panel is reduced by the spacer to reduce visibility. 
     According to the prior art document as described above, a technique for improving the visibility is not disclosed even if the gap between the front panel and the insulation panel is uniformly maintained. 
     SUMMARY 
     The embodiments provide a panel assembly, which is capable of being reduced in thickness while maintaining and improving thermal insulation performance and in which a gap between two panels adjacent to each other is uniformly maintained, a refrigerator, and home appliances. 
     The embodiments provide a refrigerator including a panel assembly, in which visibility of an inner space from the outside is improved by transmission of light while uniformly maintaining a gap between two panels, and home appliances. 
     A panel assembly according to one aspect includes: a first panel made of a glass material; a second panel spaced apart from the first panel and made of a glass material; a plurality of spacers provided between the first panel and the second panel so as to maintain a gap between the first panel and the second panel; a sealing member disposed between the first panel and the second panel for sealing a space between the first panel and the second panel; an exhaust hole provided in at least one of the first panel and the second panel so as to discharge air so that the space between the first panel and the second panel becomes a vacuum insulation space; and a cover member covering the exhaust hole. 
     The plurality of spacers may be spaced apart from each other in a first direction and a second direction crossing the first direction. The plurality of spacers may be disposed to be spaced apart from each other at a predetermined pitch in the first direction and the second direction. 
     The first panel may include a first area through which light is transmitted and a second area disposed outside the first area to restrict light transmission. A printed layer may be provided on a surface of the first panel facing the second panel, and the first area and the second area may be divided by the printed layer. The second area may be disposed to surround the first area. 
     The exhaust hole and the sealing member may be disposed to correspond to the second area. The exhaust hole and the sealing member may be disposed to face the second area. The first panel may have a size greater than that of the second panel. 
     The exhaust hole may be provided in the second panel. A getter for absorbing moisture may be provided in the exhaust hole. Alternatively, a getter for absorbing moisture may be provided at a position adjacent to the exhaust hole in the second panel. 
     The panel assembly may further include a third panel disposed at a side opposite to the second panel with respect to the first panel. The third panel may have a size greater than that of each of the first panel and the second panel. 
     The third panel may include a first area through which light is transmitted and a second area disposed outside the first area to restrict light transmission. The exhaust hole and the sealing member may be disposed to correspond to the second area. 
     An additional spacer may be provided between the third panel and the first panel. The additional spacer may be aligned with the spacer between the first panel and the second panel. The additional spacer may be disposed to face the spacer between the first panel and the second panel. 
     A gap between the third panel and the first panel may be less than a thickness of the first panel or a thickness of the third panel. 
     A contact area between the plurality of spacers and the first panel or a contact area between the plurality of spacers and the second panel may correspond to 0.01% to 0.05% of an area of the first panel or the second panel. 
     The sealing member may include a first portion disposed between the first panel and the second panel and a second portion disposed outside the first portion and having a thickness greater than that of the first portion. The sealing member may further include a third portion disposed outside the second portion to contact a side surface of the second panel. 
     A refrigerator according to another aspect includes: a cabinet provided with a storage space; and a door configured to open and close the storage space, the door being provided with a panel assembly. 
     The door may include a frame having an opening, and the panel assembly may be disposed to cover the opening. 
     The panel assembly may include: a first panel made of a glass material; a second panel spaced apart from the first panel, the second panel being made of a glass material; and a plurality of spacers disposed between the first panel and the second panel to maintain a gap between the first panel and the second panel, the plurality of spacers being disposed to be spaced apart from each other in a first direction and a second direction crossing the first direction. 
     The panel assembly may include: a sealing member disposed between the first panel and the second panel to seal a space between the first panel and the second panel; an exhaust hole provided in at least one of the first panel or the second panel to exhaust air so that the space between the first panel and the second panel serves as a vacuum insulation space; and a cover member configured to cover the exhaust hole. An insulation material may be provided in the frame and in contact with the second panel. 
     The first panel may include a first area through which light is transmitted and a second area disposed outside the first area to restrict light transmission. The exhaust hole and the sealing member may be disposed to correspond to the second area. At least a portion of the insulation material may be disposed to face the second area. 
     The refrigerator may further include a knock sensing device configured to contact the first panel and sense a knock input applied to the first panel. 
     The panel assembly may further include a third panel disposed at a side opposite to the second panel with respect to the first panel, wherein the third panel has a size greater than that of each of the first panel and the second panel. 
     The refrigerator may further include a knock sensing device configured to contact the third panel and sense a knock input applied to the third panel. 
     The refrigerator may further include a lighting unit provided in the door and configured to irradiate light. When a normal knock input is sensed by the knock sensing device, the lighting unit may be turned on while the door is closed to irradiate the light. The light may pass through the panel assembly. 
     A contact area between the plurality of spacers and the first panel or a contact area between the plurality of spacers and the second panel may correspond to 0.01% to 0.05% of an area of the first panel or the second panel. 
     The sealing member may include a first portion disposed between the first panel and the second panel and a second portion disposed outside the first portion and having a thickness greater than that of the first portion. The sealing member may further include a third portion disposed outside the second portion to contact a side surface of the second panel. 
     A home appliance according to further another aspect includes: a cabinet provided with an inner space; and a door configured to open and close the inner space, the door being provided with a panel assembly. 
     The door may include a frame having an opening, and the panel assembly may be disposed to cover the opening. 
     According to the proposed invention, there may be the advantage in that the thickness of the panel assembly is reduced while the insulation performance is maintained or increases. 
     Also, there may be the advantage in that the gap between the two adjacent panels is uniformly maintained during the assembly process or the use process of the panel assembly, and the possibility of damage due to the external force may be reduced. 
     Also, according to the present invention, the visibility of the inner space from the outside may be improved by light transmission while the gap between the two panels is uniformly maintained. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a perspective view of a panel assembly according to a first embodiment of the present invention. 
         FIG.  2    is a cutaway cross-sectional view taken along line  2 - 2  of  FIG.  1   . 
         FIG.  3    is a view illustrating a position of a getter in  FIG.  2    according to another embodiment. 
         FIG.  4    is a view illustrating a printed layer of a first panel according to the first embodiment of the present invention. 
         FIG.  5    is an enlarged view of a portion B of  FIG.  2   . 
         FIG.  6    is a view illustrating an arrangement of a spacer on a second panel according to the first embodiment of the present invention. 
         FIG.  7    is a view illustrating another example of the arrangement of the spacer according to the present invention. 
         FIG.  8    is a view illustrating various shapes of the spacer. 
         FIG.  9    is a view of a door to which a panel assembly is applied according to the first embodiment of the present invention. 
         FIG.  10    is an explode perspective view of  FIG.  9   . 
         FIG.  11    is a cross-sectional view taken along line A-A of  FIG.  9   . 
         FIG.  12    is a view illustrating another example of  FIG.  9   . 
         FIG.  13    is a sectional view taken along line B-B of  FIG.  9   . 
         FIG.  14    is a perspective view illustrating a state in which an injection hole is defined in the door according to the first embodiment. 
         FIG.  15    is a cross-sectional view of a panel assembly according to a second embodiment of the present invention. 
         FIG.  16    is a view of a door to which the panel assembly is applied according to the second embodiment of the present invention. 
         FIG.  17    is a cutaway cross-sectional view taken along line C-C of  FIG.  16   . 
         FIG.  18    is a cutaway cross-sectional view taken along line D-D of  FIG.  17   . 
         FIG.  19    is a cross-sectional view of a panel assembly according to a third embodiment of the present invention. 
         FIG.  20    is a cross-sectional view of a panel assembly according to a fourth embodiment of the present invention. 
         FIG.  21    is a view illustrating another example of  FIG.  20   . 
         FIG.  22    is a view of a door to which the panel assembly is applied to a refrigerator according to the first embodiment of the present invention. 
         FIG.  23    is a view of a state in which a door lighting unit is turned on in the refrigerator of  FIG.  22   . 
         FIG.  24    is a block diagram of the refrigerator of  FIG.  22   . 
         FIG.  25    is an exploded perspective view of a knock sensing device according to an embodiment of the present invention. 
         FIG.  26    is a cross-sectional view of a microphone module according to an embodiment of the present invention. 
         FIG.  27    is a view illustrating a state in which the microphone module is in contact with a panel assembly according to an embodiment of the present invention. 
         FIG.  28    is a view of a state in which the microphone module is in contact with the panel assembly of  FIG.  20   . 
         FIG.  29    is a cross-sectional view illustrating a state in which a door lighting unit is installed on a door according to an embodiment of the present invention. 
         FIG.  30    is a view illustrating another example in which the panel assembly is applied to the refrigerator according to the present invention. 
         FIG.  31    is a cutaway cross-sectional view taken along line E-E of  FIG.  30   . 
         FIG.  32    is a sectional view taken along line F-F of  FIG.  30   . 
         FIG.  33    is an enlarged view of a portion B of  FIG.  32   . 
         FIG.  34    is a view illustrating another example in which the panel assembly is applied to the refrigerator according to the present invention. 
         FIG.  35    is a view illustrating a state in which the panel assembly is applied to a cloth processor that is an example of a home appliance. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, some embodiments of the present invention will be described in detail with reference to the accompanying drawings. Exemplary embodiments of the present invention will be described below in more detail with reference to the accompanying drawings. It is noted that the same or similar components in the drawings are designated by the same reference numerals as far as possible even if they are shown in different drawings. In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted to avoid making the subject matter of the present invention unclear. 
     In the description of the elements of the present invention, the terms first, second, A, B, (a), and (b) may be used. Each of the terms is merely used to distinguish the corresponding component from other components, and does not delimit an essence, an order or a sequence of the corresponding component. It should be understood that when one component is “connected, “coupled” or “joined” to another component, the former may be directly connected or jointed to the latter or may be “connected”, coupled” or “joined” to the latter with a third component interposed therebetween. 
       FIG.  1    is a perspective view of a panel assembly according to a first embodiment of the present invention, and  FIG.  2    is a cutaway cross-sectional view taken along line  2 - 2  of  FIG.  1   . 
       FIG.  3    is a view illustrating a position of a getter in  FIG.  2    according to another embodiment.  FIG.  4    is a view illustrating a printed layer of a first panel according to the first embodiment of the present invention. 
     Referring to  FIGS.  1  to  4   , a panel assembly  10  according to a first embodiment of the present invention includes a first panel  11  and a second panel  13  disposed to be spaced apart from the first panel  11 . 
     The first panel  11  may be made of a glass material. The first panel  11  may be tinted glass. 
     The first panel  11  may have a thickness of about 3 mm to about 6 mm. The first panel  11  may be reduced in thickness to reduce a total thickness of the panel assembly  10 , thereby improving transmittance of light. The light transmittance may be related to visibility to be described later, and if the light transmittance is improved, the visibility may be improved. 
     If assuming a state in which the panel assembly  10  is used in a home appliance (see  FIG.  20   ), when the first panel  11  is made of tinted glass, if a lighting unit to be described later is turned on, light may pass through the first panel  11  to see an inner space of the home appliance. On the other hand, if the light unit is turned off, the seeing of the inner space of the home appliance may be restricted by the first panel  11 . 
     The first panel  11  may include a first surface  110   a  and a second surface  110   b  that is an opposite surface to the first surface  110   a.    
     When the panel assembly  10  is used in the home appliance, the panel assembly  10  may be fixed so that the first surface  110   a  defines an outer appearance of the home appliance. 
     The second panel  13  may be made of a glass material. A thickness of the second panel  13  may be the same as or different from a thickness of the first panel  11 . The thickness of the second panel  13  may be about 3 mm to about 6 mm. 
     The second panel  13  may be reduced in thickness to reduce the total thickness of the panel assembly  10 , thereby improving the light transmittance. 
     The second panel  13  may include a first surface  131  facing the second surface  110   b  of the first panel  11  and a second surface  131   b  that is an opposite surface of the first surface  131   a.    
     A low-emission coating layer  14  for reducing heat transfer due to radiation may be provided on the first surface  131   a.  Glass provided with the low-emission coating layer  14  may be referred to as low-ε glass. 
     In this embodiment, when the low-emission coating layer  14  is formed on the first surface  131   a  of the second panel  13 , the low-emission coating layer  14  may be prevented from being damaged while the panel assembly  10  is manufactured or used after the manufacturing. 
     As the low-emission coating layer  14  is formed on the second panel  13 , the thickness of the second panel  13  may be reduced to improve performance of the insulation glass. 
     The second panel  13  may be hard low-ε glass or soft low-ε. 
     The hard low-ε glass may be manufactured by spraying metal oxide (SnO 2 ) as a thermal coating material onto the glass surface and then performing a heat treatment process. The soft low-ε glass may be drafted by placing plate glass in a vacuum chamber and applying metals such as silver, titanium, and stainless steel in the form of multilayer thin film coating. 
     Alternatively, the second panel  13  may be transparent electrically conductive (TEC) glass formed by applying fluorine doped tin oxide (FTO) under an atmospheric pressure while using the same method as the hard low-ε glass. 
     A size of the first panel  11  may be larger than a size of the second panel  13 . For example, a horizontal length L 1  of the first panel  11  may be longer than a horizontal length L 2  of the second panel  13 . 
     A vertical length L 3  of the first panel  11  may be longer than a vertical length L 4  of the second panel  13 . 
     In the panel assembly  10 , positions of the first panel  11  and the second panel  13  may be determined so that a side surface of the second panel  13  and a side surface of the first panel  11  are spaced apart from each other. 
     Thus, the first panel  11  and the second panel  13  may be arranged in a stepped shape. 
     For example, a gap between the side surface of the first panel  11  and the side surface of the second panel  13  may be G 1 . 
     A screen-printed layer  112   a  may be provided on the second surface  110   b  of the first panel  11 . The printed layer  112   a  may be disposed along a circumference of the second surface  110   b  of the first panel  11 . 
     The printed layer  112   a  may restrict or block the light transmission. The first panel  11  may include a first area  111  through which light is transmitted and a second area  112  disposed outside the first area  112  to restrict the light transmission by the printed layer  112   a.  The second area  112  may be disposed outside the first area  111  and may be disposed to surround the first area  111 . 
     The second area  112  may transmit the light, but may have a light transmittance less than that of the first area  111  or may completely block the light. 
     The horizontal length of the first area  111  may be referred to as D 1 , and the vertical length may be referred to as D 2 . The horizontal length D 1  and the vertical length D 2  of the first area  111  may be the same or different from each other according to a kind of home appliances to which the panel assembly  10  is applied. 
     In  FIG.  4   , for example, the vertical length D 2  are greater than the horizontal length D 1  of the first area  111 . 
     A distance D 3  from an end of the first panel  11  to a boundary between the first area  111  and the second area  112  may be greater than a gap G 1  between an edge end of the first panel  11  and an edge end of the second panel  13 . 
     Thus, the printed layer  112   a  may face an edge portion of the second panel  13  as illustrated in  FIG.  2   . 
     The distance D 3  from the end of the first panel  11  to the boundary between the first area  111  and the second area  112  may vary depending on the type of home appliances to which the panel assembly  10  is applied. 
     Also, the distance D 3  from the end of the first panel  11  to the boundary between the first area  111  and the second area  112  may be the same or different from each other in a circumferential direction of the first panel  11 . 
     The low-emission coating layer  14  may be provided on the entire first area  111  of the first panel  11  and may be provided on a portion of the second area  112  or the entire second area  112 . 
     Since a portion of the second area  112  is in contact with a sealing member to be described later, the low-emission coating layer  14  may not be present. For example, the low-emission coating layer  14  may be formed from an outer end of the second area  112  to a position spaced apart by a predetermined distance. 
     The first panel  11  and the second panel  13  may be spaced apart from each other by a spacer  16 . 
     For example, the first panel  11  and the second panel  13  may be entirely spaced a predetermined interval from each other by a plurality of spacers  16  that are spaced apart from each other. 
     The spacer  16  may be, for example, any one of stainless steel, glass, and ceramic. 
     In this embodiment, when the panel assembly  10  is disposed to allow the light to be transmitted therethrough so that the inner space of the home appliance is seen, the spacer  16  may be preferably made of stainless steel. 
     When the spacer  16  is made of a stainless steel material, it may have excellent workability and less light reflection to minimize exposure of the spacer  16 , as well as improve visibility of the inner space of the home appliance by the panel assembly  10 . 
     On the other hand, when the spacer  16  is made of a glass material, the spacer  16  may appear white or a similar color due to diffuse reflection of light. Therefore, it is preferable that the spacer  16  is made of a stainless material in terms of the non-exposure of the spacer  16  and the visibility of the inner space of the home appliance. 
     A space between the first panel  11  and the second panel  13  may be a vacuum insulation space. An exhaust hole  132  may be defined in the second panel  13  so that the space between the first panel  11  and the second panel  13  becomes a vacuum insulation space. 
     Since air is exhausted through the exhaust hole  132 , the space between the first panel  11  and the second panel  13  may become the vacuum insulation space. 
     A gap between the first panel  11  and the second panel  13  may be designed in a range of 0.1 mm to 1 mm. 
     When the distance between the first panel  11  and the second panel  13  is greater than 1 mm, the spacer  16  for maintaining the distance between the first panel  11  and the second panel  13  may increase in thickness. 
     Since the spacer  16  is capable of transferring heat, when the thickness of the spacer  16  increases, the heat transfer amount by the spacer  16  in the panel assembly  10  increases to deteriorate thermal insulation performance. In addition, as the size of the spacer  16  increases, the area of the panel assembly  10 , through which the light is transmitted may be relatively reduced to deteriorate the visibility. 
     On the other hand, when a gap between the first panel  11  and the second panel  13  is less than 0.1 mm, a problem in which the first panel  11  and the second panel  13  are in contact with each other due to deformation of the first panel  11  or the second panel  13  while the air is exhausted through the exhaust hole  132  may occur. 
     However, according to this embodiment, if the distance between the first panel  11  and the second panel  13  is designed to be in the range of 0.1 mm to 1 mm, the gap between the first panel  11  and the second panel  13  may be maintained while preventing the thermal insulation performance and the visibility from being deteriorated. 
     Preferably, the gap between the first panel  11  and the second panel  13  may be designed in a range of 0.1 mm to 0.5 mm. 
     The exhaust hole  132  may be defined in a position spaced a predetermined distance inward from the edge end of the second panel  13 . However, in order not to expose the exhaust hole  132  to the outside, the exhaust hole  132  may be disposed at a position corresponding to the second area  112  of the first panel  11 . The exhaust hole  132  may be disposed to face the printed layer  112   a  of the first panel  11 . 
     A getter  17  for absorbing moisture in the vacuum insulation space may be disposed in the exhaust hole  132 . The getter  17  may be an evaporation type getter or a non-evaporation type getter. It is preferable to use the non-evaporation type getter in views of vacuum maintenance performance and simplification of the process. 
     The non-evaporation type getter may be a zirconium (Zr) alloy. For example, the getter  17  according to this embodiment may include zirconium (Zr), vanadium (V), iron (Fe), or the like. This getter  17  may adsorb hydrogen, water, carbon monoxide, carbon dioxide, nitrogen, and the like. 
     When air and moisture do not exist in the vacuum insulation space, thermal convection does not occur. A degree of vacuum in the vacuum insulation space may be 10 −3  Torr or less. 
     The exhaust hole  132  may be covered by a cover member  18 . The cover member  18  may be, for example, frit glass. 
     Alternatively, the getter  17  may be supported by a supporter (not shown), and at least a portion of the supporter may pass through the exhaust hole  132  and be disposed in the vacuum insulation space. That is, the getter  17  may be disposed in the vacuum insulation space. Even in this case, the cover member  18  may cover the supporter and a portion of the second surface  131   b  of the second panel  13 . 
     As another example, referring to  FIG.  3   , the second panel  13  may include an accommodation groove  131   d  in which the getter  17   a  is accommodated. The accommodation groove  131   d  may be disposed around the exhaust hole  132 . For example, the accommodation groove  131   d  may be formed by being recessed from the first surface  131   a  of the second panel  13  toward the second surface  131   b.    
     The accommodation groove  131   d  may be disposed at a position corresponding to the second area  112  of the first panel  11  so that the getter  17   a  accommodated in the accommodation groove  131   d  is prevented from being exposed to the outside. That is, the accommodation groove  131   d  may be disposed so as to face the printed layer  112   a  of the first panel  11 . 
     The panel assembly  10  may further include a sealing member  15  disposed between the edges of the first panel  11  and the second panel  13  to seal a space between the first panel  11  and the second panel  13 . 
     The sealing member  15  may be, for example, frit glass. That is, the sealing member  15  may be a glass sealant. 
     The sealing member  15  may be made of a material capable of being fired at a temperature of approximately 400° C. or less to prevent performance of the first panel  11  and the second panel  13  from being deteriorated during a firing process. 
     As an example, the sealing member  15  may be a lead-free glass composition and may include phosphorus pentoxide (P 2 O 5 ), vanadium trioxide (V 2 O 3 ), and tellurium. 
     Although not limited, the sealing member  15  may include 5% to 25% by weight of P2O5, 40% to 70% by weight of V25, 5% to 25% by weight of TeO2, 1% to 5% by weight of copper oxide (CuO), and 1% to 12% by weight of zinc oxide (ZnO), and 1% to 5% by weight of barium oxide (BaO). The sealing member  15  may be fired at a relatively low temperature by the composition of the sealing member  15 . 
     Also, the content of P 2 O 5 , V 2 O 5 , and TeO 2  in the sealing member  15  may satisfy the following relational expression so as to not only be fired at a low temperature, but also be lowered in crystallization tendency during the firing at a low temperature. 
       V 2 O 5 (wt %)/P 2 O 5 (wt %)&lt;3.5 
       P 2 O 5 (wt %)+TeO 2 (wt %)&gt;30 
     Also, in order to provide the sealing member  15  having excellent durability without including an inorganic filler or minimizing a content of the inorganic filler and also matching a coefficient of thermal expansion with the glass substrate so as to prevent peeling or breakage from occurring, the sealing member  15  may further include one or more of bismuth oxide (Bi 2 O 3 ), manganese dioxide (MnO 2 ), iron oxide (Fe 2 O 3 ), and silver oxide (Ag 2 O). 
       FIG.  5    is an enlarged view of a portion B of  FIG.  2   . 
     Referring to  FIG.  5   , a portion of the sealing member  15  may be disposed between the first panel  11  and the second panel  13 , and the other portion of the sealing member  15  may be in contact with a side surface  131   e  of the second panel  13  outside the second panel  13 . 
     That is, the sealing member  15  includes a first portion  151  disposed between the first panel  11  and the second panel  13  and a second portion  152  disposed outside the second panel  13 . Thus, a thickness of the second portion  152  (a thickness in an arrangement direction of the first panel  11  and the second panel  13 ) may be greater than a thickness of the first portion  151 . 
     As described in this embodiment, when the sealing member  15  is in contact with the side surface  131   e  of the second panel  13  outside of the second panel  13 , a contact area between the sealing member  15  and the second panel  13  and a contact area between the sealing member  15  and the first panel  11  may increase to increase in close contact strength by the sealing member  15 , thereby improving sealability. 
     Also, as the contact area between the sealing member  15  and the second panel  13  and the contact area between the sealing member  15  and the first panel  11  increase, an impact absorption of the sealing member  15  against an impact applied to the panel assembly  10  may increase. 
     An edge portion of the first surface  131   a  of the second panel  13  may be inclined. That is, the first surface  131   a  of the second panel  13  may include an inclined surface  131   c.    
     The inclined surface  131   c  may be inclined to move away from the second surface  110   b  of the first panel  11  toward the outside. 
     A portion of the first surface  131   a  of the second panel  13  is parallel to the second surface  110   b  of the first panel  11 , and the other portion (inclined surface  131   c ) of the first surface  131   a  of the second panel  13  is not parallel to the second surface  110   b  of the first panel  11 . 
     Thus, the sealing member  15  may further include a third portion  153  that connects the first portion  151  to the second portion  152  and is in contact with the inclined surface  131   c.    
     A thickness of the third portion  153  is greater than that of the first portion  151 . Due to the presence of the third portion  153  by the inclined surface  131   c,  the contact area between the sealing member  15  and the second panel  13  may further increase. 
     A width W (length from the first portion to the third portion) of the sealing member  15  may be set within a range of 3 mm to 15 mm. 
     Since heat is conducted by the sealing member  15 , when the width W of the sealing member  15  is greater than 15 mm in terms of heat conduction, a problem of deteriorating the thermal insulation performance occurs. On the other hand, when the width W of the sealing member  15  is less than 3 mm, there is a concern that the sealing performance of the vacuum insulation space is deteriorated. 
     Thus, as in this embodiment, when the width W of the sealing member  15  is set within the range of 3 mm to 15 mm, the sealing of the vacuum insulation space may be secured, and the thermal insulation performance may be prevented from being deteriorated. 
     Each of corners of the first panel  11  and the second panel  13  may be rounded at a predetermined curvature. 
     In a state in which the sealing member  15  is inserted between the first panel  11  and the second panel  13 , the first panel  11  and the second panel  13  may be pressed in a direction in which the first panel  11  and the second panel are close to each other to increase in coupling force between the sealing member  15  and the panels  11  and  13 . 
     If there is no inclined surface on the second panel  13 , the sealing member  15  may move into the vacuum insulation space while the first panel  11  and the second panel  13  are pressed in the direction in which the first panel  11  and the second panel  13  are close to each other. In this case, there is a problem that the sealing member  15  is in contact with the spacer  16  or is spread to the first area  111 . In this case, the first area  111  is reduced by the sealing member  15  to reduce the visibility. 
     However, as in the present invention, when the second panel  13  includes the inclined surface  131   c,  while the first panel  11  and the second panel  13  are pressed in the direction in which the first panel  11  and the second panel are close to each other, since the sealing member  15  moves to the portion at which the inclined surface  131   c  is formed, the movement of the vacuum insulation space may be minimized. 
       FIG.  6    is a view illustrating an arrangement of the spacer on the second panel according to the first embodiment of the present invention. 
     Referring to  FIGS.  2  and  6   , the spacers  16  may be spaced apart from each other in a first direction and may be spaced apart from each other in a second direction crossing the first direction. 
     For example, the plurality of spacers  16  may be arranged to be spaced apart in the vertical and horizontal directions. 
     The plurality of spacers  16  may be arranged to have a constant pitch P in the horizontal direction and may be arranged to have a constant pitch P in the vertical direction. 
     According to this arrangement, not only the plurality of spacers  16  may be arranged in the vertical line direction, but the plurality of spacers  16  may be arranged in the horizontal direction. The arrangement of the spacers in  FIG.  6    may be referred to as an orthogonal arrangement. 
     However, in the manufacturing process, while the plurality of spacers  16  are orthogonally arranged on the first panel  11  by a separate mechanism (not shown), the second panel  13  is seated on the plurality of spacers  16 . 
     Referring to  FIG.  6   , in the second panel  13 , the sealing member  15  may be disposed in an area  135  between a dotted line and an edge of the second panel  13 . The area  135  may also be referred to as a sealing member contact area. The contact area is disposed to surround the plurality of spacers  16 . In another aspect, the plurality of spacers  16  are disposed in an area inside the contact area, and the plurality of spacers  16  are spaced apart from the sealing member  15 . 
       FIG.  7    is a view illustrating another example of the arrangement of the spacer according to the present invention. 
     Referring to  FIG.  7   , the plurality of spacers  16  may be disposed to be spaced apart in the horizontal direction and the vertical direction. 
     For example, the plurality of spacers  163  in a first row may be disposed to be spaced a predetermined pitch P from each other in the horizontal direction. 
     The plurality of spacers  164  in a second row disposed below the first row may be disposed to be spaced a predetermined pitch P from each other in the horizontal direction. However, the plurality of spacers  163  in the first row and the plurality of spacers  164  in the second row may be disposed to be spaced a predetermined pitch P from each other without overlapping each other in the vertical direction. 
     In other words, the spacers  164  in the second row may be disposed on an area corresponding to the area between the two adjacent spacers  163  in the first row. The arrangement of the spacers in  FIG.  7    may be referred to as a diamond arrangement. 
       FIG.  8    is a view illustrating various shapes of the spacer. 
     (a) of  FIG.  8    illustrates one form of the spacer, and (b) of  FIG.  8    illustrates another form of the spacer. 
     Referring to (a) of  FIG.  8   , the spacer  16  may have a cylindrical shape or a shape similar to a cylinder. 
     Referring to (b) of  FIG.  8   , the spacer  16   a  may have a tube shape. That is, the spacer  16   a  may include an outer circumferential surface  161  and an inner circumferential surface  162 . A diameter OD of the outer peripheral surface  161  may be the same as or similar to a diameter of the cylindrical spacer. A diameter ID of the inner peripheral surface  162  may be less than the diameter of the cylindrical spacer. 
     In another aspect, the spacer  16   a  may have a cylindrical shape having a hollow. 
     Although  FIG.  8    illustrates that each of the spacers  16  and  16   a  has a smooth surface, this is merely an example. For example, it may be possible to form an unevenness on the surface of each of the spacers  16  and  16   a,  and the spacers  16  and  16   a  may have a polygonal pillar shape. 
     A maximum distance between the diameter of each of the spacers  16  and  16   a  or the outer circumferential surface and a line connecting two points to each other may be set within a range of 200 microns to 900 microns. 
     A contact area between one spacer  16  or  16   a  and the second panel  13  may be different depending on the shape of each of the spacers  16  and  16   a.    
     If the spacers  16  and  16   a  are concentrated into a certain area in relation to the second panel  13 , or the spacers  16  and  16   a  are not arranged evenly, possibility in which the spacers  16  and  16   a  are exposed to the outside may be high, and visibility of a certain area of the panel assembly may be significantly lowered due to the spacers  16  and  16   a.    
     However, as in this embodiment, when the spacers  16  and  16   a  are arranged at a predetermined pitch, the spacers  16  and  16   a  itself may be seen from the outside while maintaining the gap between the first panel  11  and the second panel  13  to improve the visibility of the panel assembly  10 . 
     In this embodiment, the diameter of each of the plurality of spacers  16  and  16   a  and the gap between the spacers may be determined so that the contact area between each of the plurality of spacers  16  and  16   a  and the second panel  13  corresponds to 0.01% to 0.05% of the area of the first surface  131   a  in the second panel  13 . 
     When the contact area between each of the plurality of spacers  16  and  16   a  and the second panel  13  is less than 0.01% of the area of the first surface  131   a  in the second panel  13 , the spacer  16  may not maintain the gap between the first panel  11  and the second panel  13  while air is removed from the space between the first panel  11  and the second panel  13 . In this case, a problem occurs in that the first panel  11  and the second panel  13  are in contact with each other (in view of maintaining the gap between the first panel and the second panel). 
     On the other hand, when the contact area between each of the plurality of spacers  16  and  16   a  and the second panel  13  is greater than 0.05% of the area of the first surface  131   a  in the second panel  13 , the spacers  16  and  16   a  may be exposed to the outside. That is, when light passes through the panel assembly  10 , the spacers  16  and  16   a  are visible to the outside, and the area through which the light is transmitted by the spacer  16  relatively decreases. Thus, there is a problem that the visibility of the inner space is deteriorated (in view of the visibility). 
     Also, since the areas of the spacers  16  and  16   a  increases, an amount of thermal conductivity by the spacers  16  and  16   a  may increase to deteriorate the thermal insulation performance (in view of the thermal insulation performance of the panel assembly). 
     However, as in this embodiment, when the contact area between each of the plurality of spacers  16  and  16   a  and the second panel  13  is set within the range of 0.01% to 0.05% of the area of the first surface  131   a  in the second panel  13 , there may be an advantage in that the visibility by the panel assembly  10  is improved while the gap between the first panel  11  and the second panel  13  is maintained. 
     The pitch of each of the adjacent spacers  16  and  16   a  may vary by a ratio of the contact area between each of the plurality of spacers  16  and the second panel  13  and the area of the first surface  131   a  in the second panel  13 , but may be determined within a range of approximately 20 mm to 60 mm. 
     The thickness of each of the spacers  16  and  16   a  is substantially the same as the gap between the first panel  11  and the second panel  13 . 
     The ratio between the pitch of each of the adjacent spacers  16  and  16   a  and the ratio of the contact area between each of the plurality of spacers  16  and the second panel  13  and the area of the first surface  131   a  of the second panel  13  may also be related to impact resistance of the first panel  11  and the second panel  13 . 
     Basically, a vacuum pressure is applied to the first panel  11  and the second panel  13 , which are in contact with the spacers  16  and  16   a.  In this state, even if an external impact is applied to the first panel  11  and the second panel  13 , the first panel  11  and the second panel  13  have to be prevented from being damaged. 
     As in this embodiment, when the contact area between each of the plurality of spacers  16  and  16   a  and the second panel  13  increases to 0.01% to 0.05% of the area of the first surface  131   a  in the second panel  13 , even if the external impact is applied to the first panel  11  and the second panel  13 , the damage of the first panel  11  and the second panel  13  may be minimized. Preferably, the contact area between each of the plurality of spacers  16  and  16   a  and the second panel  13  may satisfy a range of 0.025% to 0.03% of the area of the first surface  131   a  in the second panel  13 . 
     In summary, according to the spaced arrangement of the spacers  16  and  16   a  proposed in this embodiment, the panel assembly  10  may decrease in thickness while maintaining the thermal insulation performance by the area ratio of the spacers  16  and  16   a  and the second panel  13 , and the gap between the first panel and the second panel. 
     Also, the visibility of the inner space of the home appliance by the panel assembly  10  and the impact resistance to the external impacts may be improved. 
     Also, since the spacers  16  and  16   a  are not exposed to the outside, an aesthetic feeling of the panel assembly  10  itself may be prevented from being deteriorated. 
       FIG.  9    is a view of a door to which a panel assembly is applied according to the first embodiment of the present invention, and  FIG.  10    is an explode perspective view of  FIG.  9   .  FIG.  11    is a cross-sectional view taken along line A-A of  FIG.  9   ,  FIG.  12    is a view illustrating another example of  FIG.  9   , and  FIG.  13    is a sectional view taken along line B-B of  FIG.  9   . 
       FIG.  14    is a perspective view illustrating a state in which an injection hole is defined in the door according to the first embodiment. 
     In  FIG.  11   , it is illustrated that an insulation space is partially filled with an insulation material. 
     Referring to  FIGS.  9  to  14   , a panel assembly  10  according to this embodiment may be used for a door  30  of a home appliance. That is, the door  30  may include the panel assembly  10 . 
     The door  30  may further include a door frame  40  supporting the panel assembly  10  and a door liner  60  connected to the door frame  40 . The door frame  40  and the door liner  60  may be collectively referred to as a frame. 
     The door frame  40  may be made of, for example, a metal material. The door frame  40  may include a first opening  41 . The panel assembly  10  may cover the first opening  41 . 
     As the door frame  40  and the panel assembly  10  are made of different materials, in order to fix positions of the door frame  40  and the panel assembly  10  to each other, the door  30  may further include a bracket  50 . 
     A portion of each of the door frame  40  and the door liner  60  may be directly connected, and other portion may be connected by connection members  70  and  72 . For example, both sides of the door frame  40  may be directly connected to the door liner  60 , and upper and lower sides of the door frame  40  may be connected by connection members  70  and  72 . 
     The door frame  40 , the door liner  60 , and the connection members  70  and  72  may be collectively referred to as a frame assembly  90 . 
     The door liner  60  may include a second opening  61 . The panel assembly  10  may cover the second opening  61 . 
     The door liner  60  may include a bent portion  62  that is bent from the second opening  61  toward the door frame  40 . Alternatively, the door liner  60  may include a bent portion  62  extending toward the first opening  41 , and the bent portion  62  may define the second opening  61 . 
     The bracket  50  may be coupled to directly contact the door frame  40  and the panel assembly  10  or may be coupled while indirectly contacting the door frame  40  and the panel assembly  10  by an intermediate member. 
     The door frame  40  may be provided as a thin plate and may include a bent portion  42  that is bent inward from the first opening  41 . An inner region of the bent portion  42  substantially becomes the first opening  41 . 
     The panel assembly  10  may be disposed at the first opening  41  to cover the first opening  41  or may cover the first opening  41  from an outside of the first opening  41 . 
     A side surface of the panel assembly  10  may be in contact with the bent portion  42 . For example, the side surface of the first panel  11  may be in contact with the bent portion  42 . 
     The first panel  11  may define a portion of a front appearance of the door  30 . 
     A front surface (first surface) of the first panel  11  may define the same surface as a front surface of the door frame  40 , or a line passing through the front surface of the first panel  11  may pass through the front surface of the door frame  40 . Alternatively, the front surface of the first panel  11  and the front surface of the door frame  40  may be stepped. However, in this case, in order to prevent the first panel  11  from being damaged, the front surface of the first panel  11  may be disposed behind the front surface of the door frame  40 . 
     The bracket  50  may include a first portion  51  disposed to face the first panel  11 , a second portion  52  disposed to face the door frame  40 , and a third portion  53  connecting the first portion  51  to the second portion  52 . 
     The first portion  51  of the bracket  50  may face a rear surface (second surface) of the first panel  11 , and the second portion  52  of the bracket  50  may face a rear surface of the door frame  40 . 
     For example, the first portion  51  of the bracket  50  may be disposed to correspond to the second area  112  of the first panel  11 . That is, the first portion  51  of the bracket  50  may be disposed to face the second area  112  of the first panel  11 . 
     Thus, even if the panel assembly  10  is installed on the door  30 , the bracket  50  may be prevented from being exposed to the outside. 
     The first portion  51  of the bracket  50  may be provided with a coupling protrusion  54 , and the bent portion  42  may be provided with a protrusion slot (not shown) into which the coupling protrusion  54  is inserted. 
     A heater accommodation groove  502  may be defined in the first portion  51  of the bracket  50 . A heater  58  may be accommodated in the heater accommodation groove  502 . 
     The heater  58  may be fixed to the rear surface of the first panel  11  or be fixed to the first portion  51  of the bracket  50  by an adhesive tape (for example, an aluminum tape). Alternatively, an aluminum sheet may be attached to a portion corresponding to the heater  58  on the rear surface of the first panel  11 , and the heater  58  may be disposed to be in contact with the aluminum sheet. Even in this case, the heater  58  may be fixed to the bracket  50  by an adhesive tape (for example, an aluminum tape) while being accommodated in the heater accommodation groove  502 . 
     The heater  58  may prevent dew condensation from being generated by allowing a surface temperature of a peripheral portion of the side surface of the panel assembly  10  to increase. Heat of the heater  58  may be transferred to the first panel  11  and may also be transferred to the second panel  13  and the sealing member  15 . 
     In the case of this embodiment, since the panel assembly has a vacuum insulation space, a thickness of the panel assembly may be reduced compared to a structure in which a gas is filled between two panels. 
     When the panel assembly  10  according to this embodiment is applied to the structure of the existing door  30 , a gap between the panel assembly  10  and the bent portion  62  of the door liner  60  may occur by a reduced thickness of the panel assembly  10 . 
     If, without changing the structure of the existing door liner  60 , the panel assembly  10  according to this embodiment is used, as illustrated in  FIG.  11    and (a) of  FIG.  13   , the door  30  may further include an intermediate member  63  disposed in a spaced portion between the door liner  60  and the panel assembly  10 . 
     One side of the intermediate member  63  may be coupled to the door liner  60 , and the other side may be in contact with the panel assembly  10 . For example, the intermediate member  63  may be in contact with the rear surface (second surface) of the second panel  13 . 
     The intermediate member  63  may further include a contact portion  64  to increase in contact area between the intermediate member  63  and the second panel  13 . 
     Referring to  FIG.  12    and (b) of  FIG.  13   , as another example of the door liner  60 , the intermediate member may not exist as a separate member  63 , and the bent portion  62  of the door liner  60  may extend toward the second panel  13 , and the contact portion  64  may extend from the second panel  13 . 
     In either case, the door frame  40 , the door liner  60 , the bracket  50 , and the panel assembly  10  may define an insulation space P in which an insulation material  80  is filled. That is, the frame assembly  90  and the panel assembly  10  may define an insulation space P. 
     Referring to  FIG.  13   , the frame assembly  90  may be provided with a plurality of injection holes for injecting a foaming solution for forming the insulation material  80 . 
     For example, the plurality of injection holes may be defined to be spaced apart from a top surface  91  or a bottom surface of the frame assembly  90 . For example,  FIG.  13    illustrates that a first injection hole  92  and a second injection hole  93  are defined in the top surface  91  of the frame assembly  90 . 
     The first injection hole  92  and the second injection hole  93  may be disposed to face the insulation space P. The first injection hole  92  may face a space defined at one side of the panel assembly  10  in the insulation space P, and the second injection hole  93  may face a space defined at the other side of the panel assembly in the insulation space P. The foaming solution injected through the two injection holes  92  and  93  may not only flow in a horizontal direction in the insulation space P, but also flow in a downward direction so as to be filled into the insulation space P as a whole. 
     The contact portion  64  of the door liner  60  may be in contact with a position spaced a predetermined distance from an edge end of the second panel  13 . 
     The insulation material  80  may be in contact with the door frame  40 , the door liner  60 , and the bracket  50 . Also, the insulation material  80  may be in contact with a rear surface (second surface) of the second panel  13 . 
     A portion of the insulation material  80  may be in contact with the contact portion  64  to press the contact portion  64  toward the second panel  13 . Thus, the insulation material  80  between the contact portion  64  and the second panel  13  may be prevented from leaking. 
     Since the panel assembly  10  itself includes the vacuum insulation space, the thermal insulation performance may be maintained by the vacuum insulation space. On the other hand, since the outer surface of the panel assembly  10 , in particular, the sealing member  15  is capable of conducting heat, there is a need to prevent the thermal insulation performance due to the heat conduction. 
     In order to prevent deterioration in thermal insulation performance due to the heat conduction of the panel assembly  10 , the insulation material  80  may be in contact with the rear surface (second surface) of the second panel  13 . Also, the insulation material  80  may be in contact with a side surface of the second panel  13  and a portion of the sealing member  15 . 
     The insulation material  80  may be disposed to overlap the second panel  13  in a front and rear direction (which may be defined as an arranged direction of the panels). In order to secure the thermal insulation performance, the vertical or horizontal length (overlapping length) D 4  of the portion of the second panel  13  overlapping the insulation material  80  in the front and rear direction may be set within a range of 20 mm to 50 mm. 
     When the overlapping length of the insulation material  80  and the second panel  13  is less than 20 mm, a heat conduction blocking effect by the insulation material  80  is low, and thus, there is a concern that dew is generated on the surface of the panel assembly  10 . 
     On the other hand, when the overlapping length of the insulation material  80  and the second panel  13  is greater than 50 mm, there may be a disadvantage in that the area on which light is transmitted in the panel assembly  10  is reduced to reduce the visibility of the inner space. 
     However, as in the present invention, when the overlapping length D 4  of the insulation material  80  and the second panel  13  is set within the range of 20 mm to 50 mm, the visibility may increase, and thermal insulation performance may also be maintained. 
       FIG.  15    is a cross-sectional view of a panel assembly according to a second embodiment of the present invention. 
     Referring to  FIG.  15   , a panel assembly  10   a  according to this embodiment includes a first panel  211 , a second panel  212  disposed behind the first panel  211 , and a third panel  213  disposed in front of the first panel  211 . The third panel  213  may be disposed at an opposite side of the second panel  212  with respect to the first panel  211 . 
     The first panel  211  and the second panel  212  are spaced apart from each other by a plurality of spacers  221 , and a vacuum insulation space  216  between the first panel  211  and the second panel  212 ) is defined. 
     All the characteristics described in the first embodiment such as the thickness, the material, the low-emission coating layer of each of the panels described in the first embodiment, the gap between the first panel  11  and the second panel  13 , the degree of the vacuum of the vacuum insulation space, the size or shape of the spacer, the contact ratio of the spacer and the first or second panel, and the structure, the material, and the component of the sealing member may be equally or similarly applied to the second embodiment. 
     Thus, only characterized parts in the second embodiment will be described below. 
     The first panel  211  may include a first surface  211   a  that is a front surface and a second surface  211   b  that is a rear surface. The second panel  212  may include a first surface  212   a  that is a front surface and a second surface  212   b  that is a rear surface. The third panel  213  may include a first surface  213   a  that is a front surface and a second surface  213   b  that is a rear surface. 
     The first surface  212   a  of the second panel  212  may face the second surface  211   b  of the first panel  211 . The first surface  211   a  of the first panel  211  may face the second surface  213   b  of the third panel  213 . 
     An exhaust hole  211   c  for exhausting air may be defined in the first panel  211  to define a vacuum insulation space  216 . A getter  17  is disposed in the exhaust hole  211   c,  a getter  17  is installed at a position adjacent to the exhaust hole  211   c  in the first panel  211 , or a getter  17  is installed in the second panel  212 . 
     Also, a low-emission coating layer may be disposed on at least one of the first panel  211  or the second panel  212 . For example, the low-emission coating layer may be disposed on the first surface  211   a  or the second surface  211   b  of the first panel  211 , or the low-emission coating layer may be disposed on the first surface  212   a  of the second panel  212 . 
     The exhaust hole  211   c  may be blocked by the cover member  18 . In this case, the cover member  18  may cover the exhaust hole  211   c  between the third panel  213  and the first panel  211 . In this case, since the cover member  18  is protected by the third panel  213 , it may be prevented from being damaged by an external force. 
     A printed layer  214  may be disposed on the second surface  213   b  of the third panel  213 , and the exhaust hole  211   c  may be disposed to face the printed layer  214 . That is, the printed layer  214  of the third panel  213  and the exhaust hole  211   c  may be disposed to overlap each other in a front and rear direction. 
     The first panel  211  and the second panel  212  may have the same size. On the other hand, the third panel  213  may have a size greater than that of the first panel  211 . 
     A size relationship between the third panel  213  and the first panel  211  may be the same as the size relationship between the first panel  11  and the second panel  13  described in the first embodiment. 
     The third panel  213  may also include the first area and the second area, which are described in the first embodiment, by the printed layer  214  of the third panel  213 . 
     The vacuum insulation space  216  between the first panel  211  and the second panel  212  may be sealed by the first sealing member  222 . 
     The second surface  211   b  of the first panel  211  may include an inclined surface  211   d  inclined in a direction that is away from the second panel  212  toward an end side thereof. 
     The first surface  212   a  of the second panel  212  may include an inclined surface  212   c  that inclines in a direction that is away from the first panel  211  toward an end side thereof. 
     The second surface  211   b  of the first panel  211  and the first surface  212   a  of the second panel  212  except for the inclined surfaces  211   d  and  212   c  may be parallel to each other. 
     The first sealing member  222  may be disposed not only between the two parallel surfaces, but also may be disposed between the inclined surfaces  211   d  and  212   c.    
     Thus, the first sealing member  222  may include a first portion disposed between the two parallel surfaces and a second portion extending from the first portion and disposed between the inclined surfaces  211   d  and  212   c.    
     A thickness of the second portion is greater than that of the first portion. When the thickness of the second part is greater than that of the first part, contact areas between the first sealing member  222  and the first panel  211  and between the first sealing member  222  and the second panel  212  may increase to increase in contact strength by the first sealing member  222 , thereby improving sealability. 
     The third panel  213  may be spaced apart from the first panel  211  by a spacer  224 . The spacer  224  may also serve to seal a space between the first panel  211  and the third panel  213 . 
     An insulation space  217  may also be defined between the third panel  213  and the first panel  211 . The insulation space  217  may be a vacuum insulation space, an insulation space containing air, or an insulation space into which a gas for insulation (e.g., argon gas) is injected. 
     If the insulation space  217  between the first panel  211  and the third panel  213  is the vacuum insulation space, an additional exhaust hole may be defined in the first panel  211 , and the first panel  211  and the third panel  213  may be spaced apart from each other by a plurality of additional spacers. 
     A gap between the first panel  211  and the third panel  213  may be less than a thickness of the third panel  213  or the first panel  211 . 
     In this case, at least a portion of the additional spacer may overlap the spacer  221  disposed between the first panel  211  and the second panel  212  in a front and rear direction. As a result, it may be minimized that visibility is deteriorated by the spacers having a plurality of layers. 
     The gap between the first panel  211  and the third panel  213  may be equal to or greater than that between the first panel  211  and the second panel  212 . 
     The first surface  211   a  of the first panel  211  may include an inclined surface  211   e  that moves away from the third panel toward an end thereof. The spacer  224  may be in contact with the inclined surface  211   e.  Also, the spacer  224  may also be in contact with a side surface of the first panel  211 . 
     Thus, a contact area between the spacer  224  and the first panel  211  and a contact area between the spacer  224  and the third panel  213  may increase. 
       FIG.  16    is a view of a door to which the panel assembly is applied according to the second embodiment of the present invention,  FIG.  17    is a cutaway cross-sectional view taken along line C-C of  FIG.  16   , and  FIG.  18    is a cutaway cross-sectional view taken along line D-D of  FIG.  17   . 
     Referring to  FIGS.  16  to  18   , the door  200  according to this embodiment have the same structure as the structure of the door  30  according to the first embodiment except for a structure of a panel assembly  10   a,  and thus, the same structure is denoted by the same reference numerals, and the description of the first embodiment will be cited. 
     Thus, the door  200  according to this embodiment may also include a door frame  40  supporting the panel assembly  10   a  and a door liner  60  connected to the door frame  40 . Also, the door  200  may further include a bracket  50 . 
     The door frame  40  may include a first opening  41 , and the door liner  60  may include a second opening  61 . The panel assembly  10   a  may cover the first opening  41  and the second opening  61 . 
     The door liner  60  may include a bent portion  62  that is bent from the second opening  61  toward the door frame  40 . 
     The door frame  40  may be provided as a thin plate and may include a bent portion  42  that is bent inward from the first opening  41 . An inner region of the bent portion  42  substantially becomes the first opening  41 . 
     The panel assembly  10   a  may be disposed at the first opening  41  to cover the first opening  41  or may cover the first opening  41  from the outside of the first opening  41 . 
     When the panel assembly  10   a  is disposed inside the first opening  41 , a side surface of the panel assembly  10  may be in contact with the bent portion  42 . 
     For example, the side surface of the third panel  213  may be in contact with the bent portion  42 . 
     The third panel  213  may define a portion of a front appearance of the door  200 . That is, the panel assembly  10   a  may be installed on the door  200  so that the third panel  213  is disposed at the foremost side, and the second panel  212  is disposed at the rearmost side. 
     A front surface (first surface) of the third panel  213  may define the same surface as a front surface of the door frame  40 , or a line passing through the front surface of the third panel  213  may pass through the front surface of the door frame  40 . Alternatively, the front surface of the third panel  213  and the front surface of the door frame  40  may be stepped. However, in this case, in order to prevent the third panel  213  from being damaged, the front surface of the third panel  213  may be disposed behind the front surface of the door frame  40 . 
     The bracket  50  may include a first portion  51  disposed to face the third panel  213 , a second portion  52  disposed to face the door frame  40 , and a third portion  53  connecting the first portion  51  to the second portion  52 . 
     The first portion  51  of the bracket  50  may face a rear surface (second surface) of the third panel  213 , and the second portion  52  of the bracket  50  may face a rear surface of the door frame  40 . 
     For example, the first portion  51  of the bracket  50  may be disposed to correspond to the second area (area on which the printed layer is disposed) of the third panel  213 . That is, the first portion  51  of the bracket  50  may be disposed to face the second area of the third panel  213 . 
     Thus, even if the panel assembly  10   a  is installed on the door  200 , the bracket  50  may be prevented from being exposed to the outside. 
     The first portion  51  of the bracket  50  may be provided with a coupling protrusion  54 , and the bent portion  42  may be provided with a protrusion slot (not shown) into which the coupling protrusion  54  is inserted. 
     A heater accommodation groove  502  may be defined in the first portion  51  of the bracket  50 . A heater  58  may be accommodated in the heater accommodation groove  502 . 
     In the case of this embodiment, since the panel assembly  10   a  has a vacuum insulation space, a thickness of the panel assembly may be reduced compared to a structure in which a gas is filled between two panels. 
     When the panel assembly  10   a  according to this embodiment is applied to the structure of the existing door  30 , a gap between the panel assembly  10   a  and the bent portion  62  of the door liner  60  may occur by a reduced thickness of the panel assembly  10   a.    
     If, without changing the structure of the existing door liner  60 , the panel assembly  10   a  according to this embodiment is used, the door  30  may further include an intermediate member  63  disposed in a spaced portion between the door liner  60  and the panel assembly  10   a.    
     One side of the intermediate member  63  may be coupled to the door liner  60 , and the other side may be in contact with the panel assembly  10 . For example, the intermediate member  63  may be in contact with the rear surface (second surface) of the second panel  212 . 
     The intermediate member  63  may further include a contact portion  64  to increase in contact area between the intermediate member  63  and the second panel  212 . 
     As another example, the door liner  60  may be configured to include the same configuration as the intermediate member  63  by changing the structure of the door liner  60 . In this case, the door liner  60  may include a contact portion  64  for contacting the second panel  212 . 
     In either case, the door frame  40 , the door liner  60 , the bracket  50 , and the panel assembly  10   a  may define an insulation space P in which an insulation material  80  is filled. 
     The contact portion  64  of the door liner  60  may be in contact with a position spaced a predetermined distance from an edge end of the second panel  212 . 
     The insulation material  80  may be in contact with the door frame  40 , the door liner  60 , and the bracket  50 . Also, the insulation material  80  may be in contact with a rear surface (second surface) of the second panel  212 . A portion of the insulation material  80  may be in contact with the contact portion  64  to press the contact portion  64  toward the second panel  212 . Thus, the insulation material between the contact portion  64  and the second panel  212  may be prevented from leaking. 
     Since the panel assembly  10   a  itself includes the vacuum insulation space, thermal insulation performance may be maintained by the vacuum insulation space, but an outer surface of the panel assembly  10   a,  in particular, the sealing member  222  and the spacer  224  may be capable of the heat conduction, and thus, there is a need to prevent the thermal insulation performance by the heat conduction. 
     In order to prevent deterioration in thermal insulation performance due to the heat conduction of the panel assembly  10   a,  the insulation material  80  may be in contact with the rear surface (second surface) of the second panel  212 . Also, the insulation material  80  may be in contact with a side surface of the second panel  212 , the first sealing member  222 , and a portion of the spacer  16 . 
     The insulation material  80  may be disposed to overlap the second panel  212  in a front and rear direction (which may be defined as an arranged direction of the panels). In order to secure the thermal insulation performance, the vertical or horizontal length (overlapping length) D 4  of the portion of the second panel  212  overlapping the insulation material  80  in the front and rear direction may be set within a range of 20 mm to 50 mm. The technical meaning of the overlapping length D 4  of the insulation material  80  and the second panel  212  in the front and rear direction is the same as described in the first embodiment. 
       FIG.  19    is a cross-sectional view of a panel assembly according to a third embodiment of the present invention. 
     This embodiment is the same as the second embodiment except that there is a difference in distance between a first panel and a third panel at a position of a getter. Thus, only characterized parts in this embodiment will be described below. 
     Referring to  FIG.  19   , a panel assembly  10   c  according to this embodiment includes a first panel  211 , a second panel  212  disposed behind the first panel  211 , and a third panel  213  disposed in front of the first panel  211 . 
     The first panel  211  and the second panel  212  are spaced apart from each other by a plurality of spacers  221 , and a vacuum insulation space  216  between the first panel  211  and the second panel  212 ) is defined. 
     In this embodiment, an exhaust hole  212   e  may be defined in the second panel  212 . The exhaust hole  212   e  may be covered by the cover member  18 . The cover member  18  may cover the exhaust hole  212   e  at a side of the second surface  212   b  of the second panel  212 . 
     An accommodation groove  211   f  in which the getter  17  is accommodated may be defined in the second surface  211   b  of the first panel  211 . The accommodation groove  211   f  may be disposed to face the exhaust hole  212   e.  Alternatively, even if the accommodation groove  211   f  is not disposed to face the exhaust hole  212   e,  the accommodation groove  211   f  may be disposed at a position adjacent to the exhaust hole  212   e.    
     A printed layer  214  may be disposed on the second surface  213   b  of the third panel  213 , and the exhaust hole  211   c  and the getter  17  may be disposed to face the printed layer  214 . Thus, the accommodation groove  211   f,  the getter  17 , and the exhaust hole  212   e  may be prevented from being exposed to the outside by the printed layer  214  provided on the third panel  213 . 
     The first panel  211  and the second panel  212  may have the same size. On the other hand, the third panel  213  may have a size greater than that of the first panel  211 . 
     The third panel  213  may also include the first area and the second area, which are described in the first embodiment, by the printed layer of the third panel  213 . 
     The vacuum insulation space  216  between the first panel  211  and the second panel  212  may be sealed by the first sealing member  222 . The second surface  211   b  of the first panel  211  may include an inclined surface  211   d  inclined in a direction that is away from the second panel  212  toward an end side thereof. 
     The first surface  212   a  of the second panel  212  may include an inclined surface  212   c  that inclines in a direction that is away from the first panel  211  toward an end side thereof. 
     The second surface  211   b  of the first panel  211  and the first surface  212   a  of the second panel  212  except for the inclined surfaces  211   d  and  212   c  may be parallel to each other. 
     The first sealing member  222  may be disposed not only between the two parallel surfaces, but also may be disposed between the inclined surfaces  211   d  and  212   c.    
     Thus, the first sealing member  222  may include a first portion disposed between the two parallel surfaces and a second portion extending from the first portion and disposed between the inclined surfaces  211   d  and  212   c.    
     A thickness of the second portion is greater than that of the first portion. When the thickness of the second part is greater than that of the first part, contact areas between the first sealing member  222  and the first panel  211  and between the first sealing member  222  and the second panel  212  may increase to increase in contact strength by the first sealing member  222 , thereby improving sealability. 
     The third panel  213  may be spaced apart from the first panel  211  by a spacer  224 . 
     An insulation space  217   a  may also be defined between the third panel  213  and the first panel  211 . The insulation space  217   a  may be an insulation space into which a gas for insulation (e.g., argon gas) is injected. 
     The first surface  211   a  of the first panel  211  may include an inclined surface  211   e  that moves away from the third panel toward an end thereof. The spacer  224  may be in contact with the inclined surface  211   e.  Also, the spacer  224  may also be in contact with a side surface of the first panel  211 . Thus, a contact area between the spacer  224  and the first panel  211  and a contact area between the spacer  224  and the third panel  213  may increase. 
     A gap between the first panel  211  and the third panel  213  may be larger than a gap between the first panel  211  and the second panel  212 . 
       FIG.  20    is a cross-sectional view of a panel assembly according to a fourth embodiment of the present invention. 
     This embodiment is the same as the third embodiment except for a position of a getter and a position of an exhaust hole. Thus, only characterized parts in this embodiment will be described below. 
     Referring to  FIG.  20   , in case of a panel assembly  10   c  according to this embodiment, an exhaust hole  211   c  may be defined in a first panel  211 , and an accommodation groove  212   f  in which a getter  17  is accommodated may be defined in a second panel  212 . 
     The accommodation groove  212   f  may be disposed to face the exhaust hole  211   c.  Alternatively, even if the accommodation groove  212   f  is not disposed to face the exhaust hole  211   c,  the accommodation groove  212   f  may be disposed at a position adjacent to the exhaust hole  211   c.    
     A printed layer  214  may be disposed on the second surface  213   b  of the third panel  213 , and the exhaust hole  211   c  and the getter  17  may be disposed to face the printed layer  214 . Thus, the accommodation groove  212   f,  the getter  17 , and the exhaust hole  211   c  may be prevented from being exposed to the outside by the printed layer  214  provided on the third panel  213 . 
       FIG.  21    is a view illustrating another example of  FIG.  20   . 
     Contents of the display of  FIG.  21    may be equally applied to the structure of  FIG.  19   . 
     Referring to  FIG.  21   , the panel assembly  10   c  may further include a display  219 . The display  219  may be an LCD or an LED. 
     The display  219  may be disposed behind, for example, the third panel  213 . The display  219  may be disposed in a space  217   a  between the first panel  211  and the third panel  213 . The display  219  may be installed on a rear surface of the third panel  213 . 
     A signal cable  219   a  may be connected to the display  219 . The signal cable  219   a  may pass between the spacer  224  and the printed layer  214  and may be drawn out of the panel assembly  10   c.  As another example, a signal cable  219   b  connected to the display  219  may pass between the spacer  224  and the front surface of the first panel  211 . 
       FIG.  22    is a view of a door to which the panel assembly is applied to the refrigerator according to the first embodiment of the present invention,  FIG.  23    is a view of a state in which a door lighting unit is turned on in the refrigerator of  FIG.  22   , and  FIG.  24    is a block diagram of the refrigerator of  FIG.  22   . 
     Referring to  FIGS.  22  to  24   , a refrigerator  300  to which the panel assembly  10  according to this embodiment is applied may include a cabinet defining a storage space and doors  301  and  302  for opening and closing the storage space. 
       FIGS.  22  to  24    illustrate the panel assembly  10  according to the first embodiment, but it should be noted that the panel assemblies of the second to fourth embodiments described above may be applied to the refrigerator  300  in the same manner. 
     One or more doors  301  and  302  may open and close the storage space. Alternatively, the storage space may be divided into a refrigerating compartment and a freezing compartment, one door  301  may open and close the refrigerating compartment, and the other door  302  may open and close the freezing compartment. 
     The panel assembly  10  may be provided on the door  301 . 
     Since a structure of the door  301  is the same as the structure of the door  30  described in  FIG.  9   , a detailed description thereof will be omitted. 
     The door  301  may include a door storage space  303  in which foods are stored. The door storage space  303  may be a space defined by a basket coupled to the door  301 , a space defined between a plurality of baskets, or a space defined by a separate accommodation case. 
     The refrigerator  300  may include a door switch  403  for sensing the opening of the door  301 , a storage space lighting unit  401  that irradiates light to the storage space of the cabinet, and a controller  400  that controls the storage space lighting unit  401 . 
     The controller  400  may be turned on the storage space lighting unit  401  when the door switch  403  senses the opening of the door. When the storage space lighting unit  401  is turned on, a user may easily check the foods stored in the storage space. 
     The refrigerator  300  may further include a knock sensing device  410  for sensing a knock input to the panel assembly  10  and a door lighting unit  402  for irradiating light so that the door storage space  303  is seen from the outside. 
     When it is determined that the knock sensing device  410  senses a normal knock input, the controller  400  may turn on the door lighting unit  402 . That is, the door lighting unit  402  may be turned on in a state in which the door  30  is not opened. 
     For example, when the normal knock input is sensed, it may be a case that two knock inputs are sensed for a predetermined time. 
     As illustrated in  FIG.  22   , when the door lighting unit  402  is turned off, the door storage space  303  is not visible from the outside in front of the door  301 . On the other hand, when the door lighting unit  402  is turned on, as illustrated in  FIG.  20   , the door lighting unit  402  may irradiate light to the door storage space  303 , and some light sequentially pass through the panels of the panel assembly  10 . 
     Since light passes through the panel assembly  10 , the user may check the inside of the door storage space  303  from the outside of the door  301 . 
     When it is determined that the knock sensing device  410  senses a normal knock input, the controller  400  may turn on the storage space lighting unit  401 . 
     Alternatively, when the door lighting unit  402  is not provided in the door  301 , if it is determined that the normal knock input is sensed by the knock sensing device  410 , the storage space lighting unit  401  may be turned on. Even when the storage space lighting unit  401  is turned on, the light irradiated from the storage space lighting unit  401  may pass through the panel assembly  10  to confirm the inside of the door storage space  303  from the outside of the door  301 . 
     In the panel assembly  10 , light sequentially passes through the second panel  13  and the first panel  11 . As described above, the first panel  11  is divided into a first area  111  and a second area  112 . Here, the first area  111  is a viewing area through which light is transmitted, and the second area  112  is a non-viewing area through which the transmission of light is restricted. 
       FIG.  25    is an exploded perspective view of a knock sensing device according to an embodiment of the present invention,  FIG.  26    is a cross-sectional view of a microphone module according to an embodiment of the present invention, and  FIG.  27    is a view illustrating a state in which the microphone module is in contact with a panel assembly according to an embodiment of the present invention.  FIG.  28    is a view of a state in which the microphone module is in contact with the panel assembly of  FIG.  20   . 
     Referring to  FIGS.  25  to  28   , a knock sensing device  410  according to this embodiment is a device for sensing a knock input of a panel assembly  10  by a user. 
     The knock sensing device  410  may include a microphone module  421  that senses a knock input. 
     The knock sensing device  410  may further include a holder  423  in which the microphone module  421  is accommodated, an elastic member  424  pressing the holder  423  and the microphone module  421  toward the panel assembly  10 , and a support member  425  supporting the elastic member  424  and the holder  423 . 
     The microphone module  421  may include a microphone  4211  that directly senses sound waves and a microphone accommodation portion  4212  that accommodates the microphone  4211 . 
     The microphone  4211  directly senses the sound waves and is provided in a circular shape having a predetermined thickness so as to be fixed and mounted inside the microphone accommodation portion  4212 . 
     The microphone  4211  may include a sound wave receiving portion  4213  for receiving the sound waves, and the sound wave receiving portion  4213  may be disposed to face an opening  4214  of the microphone accommodation portion  4212 . The sound wave receiving portion  4213  may be disposed at one side of the microphone  4211 . 
     A signal line  4216  may be connected to the other side of the microphone  4211 , and the signal line  4216  may be directly or indirectly connected to the controller  400 . 
     The microphone accommodation portion  4212  is made of an elastic material such as rubber. For example, the microphone accommodation portion  4212  may be in contact with a rear surface  110   b  of the first panel  11  in the panel assembly  10 . 
     In practice, since a printed layer  114  may be present on the rear surface  110   b  of the first panel  11  in the panel assembly  10 , the microphone accommodation portion  4212  may be described as being in contact with the printed layer  114 . 
     Since a second area  112  of the first panel  11  is defined by the printed layer  114 , the microphone accommodation portion  4212  may be described as being in contact with a second area  112  of the first panel  11 . 
     The microphone accommodation portion  4212  may have an opening  4214  defined in one side adjacent to the microphone  4211  mounted inside the microphone accommodation portion  4212 , and a circular protrusion  4215  may be provided around the opening  4214 . Thus, the protrusion  4215  may be in close contact with the first panel  11 . 
     In a state in which the microphone accommodation portion  4212  and the first panel  11  are in close contact with each other by the protrusion  4215 , a sealed predetermined space may be defined between the opening  4214  and the sound wave receiving portion  4213 . 
     Thus, a front side of the contact space may be sealed by a medium, that is, the first panel  11 . Thus, vibration transmitted through the inside of the medium may allow air to vibrate in a predetermined space, and a sound wave caused by the vibration may be received by the microphone  4211 . 
     Due to this sealing, it may be possible to minimize introduction of external noise or vibration into the predetermined space. This may significantly reduce errors in knock input determination and a malfunction due to the external noise to improve a recognition rate of the knock input. 
     The holder  423  accommodates the microphone module  421 , and a module seating portion  4231  opened toward the first panel  11  may be provided. In a state in which the microphone module  421  is seated on the module seating portion  4231 , at least the protrusion  4215  may protrude further forward than a front surface of the holder  423 . 
     The holder  423  may have a holder slot  4232  through which the signal line connected to the microphone  4211  enters and exits. The holder slot  4232  may be opened at one side of the module mounting portion  4231 . 
     Also, a first elastic member fixing portion  423  may be provided on a rear surface of the holder  423  to protrude so that the elastic member  424  is fixedly mounted. The first elastic member fixing portion  423  may extend to pass through one end of the coil-shaped elastic member  424 . 
     A holder coupling portion  4234  having a hook shape and coupled to the support member  425  may be provided at each of both sides of the holder  423 . The holder  423  may be coupled to the support member  425  by the holder coupling portion  4234 . 
     Due to the hook shape of the holder coupling portion  4234 , movement of the holder  423  in an insertion direction toward the inside of the support member  425  may not be restricted by the hook shape of the holder coupling portion  4234 . The support member  425  is provided so that a front surface thereof is opened, and the holder  423  may be inserted through the opened front surface. 
     A second elastic member fixing portion (not shown) protruding so that the elastic member  424  is fixedly mounted may be disposed inside the holder  423 . The second elastic member fixing portion may be disposed on the same extension line as the first elastic member fixing portion  423  and be accommodated inside the elastic member  424 . 
     The microphone module  421  may be maintained in the state of being in close contact with the first panel  11  by the elastic member  424 . Particularly, the microphone module  421  may be remained in the state of being in close contact with the first panel  11  without changing a position thereof even due to an impact generated when the door  301  is opened or closed or due to an inertia during rotation of the door  301 . 
     A support member slot  4252  may be defined in one side of the support member  425 . The support member slot  4252  may be defined in the same extension line as the holder slot  4232 . Thus, a signal line passing through the holder slot  4242  may pass through the support member slot  4252 . 
     A support member fixing portion  4254  may be disposed on the other side of the support member  425 . The support member fixing portion  4254  may be provided to extend outward and be fixed to the door frame  40  or the connection members  70  and  72  or may be fixed to a separate case coupled to the door frame  40  or the connection members  70  and  72 . 
     Referring to  FIG.  28   , when the panel assembly  10   c  additionally includes a third panel  213 , the microphone module  421  may be disposed on an area corresponding to the printed layer  214  of the third panel  213 . For example, the microphone module  421  may be in contact with the printed layer  214  of the third panel  213 . 
       FIG.  29    is a cross-sectional view illustrating a state in which the door lighting unit is installed on a door according to an embodiment of the present invention. 
     Referring to  FIG.  29   , the door lighting unit  402  may be installed on the door liner  60 . 
     The door lighting unit  402  may include a case  441  and a cover  443  covering the case  411 . 
     The cover  443  may extend lengthily in a horizontal direction along the door liner  60 . The case  441  defines a space for accommodating a light emitting unit PCB  422  in which a plurality of light emitting units  442   a  are installed. 
     In the case  441 , a surface facing the light emitting unit PCB  442  may be round, and light irradiated from the light emitting unit  442   a  may be reflected through a rounded surface  441   a  having a predetermined curvature to travel toward the cover  443 . 
     A film for improving reflectance of light may be attached, or a coating layer may be disposed on the rounded surface  441   a.    
     The cover  443  may be provided so that the light reflected from the rounded surface  441   a  is transmitted. The cover  443  may be transparent or translucent so that light reflected and spread from the round surface  441   a  is transmitted. Therefore, the light passing through the cover  433  illuminates the door storage space in an indirect lighting manner and has the same effect as surface light emission. 
     The cover  443  may be attached with the film or coated to diffuse the light more effectively. 
     A portion of the light passing through the cover  443  may be irradiated to an auxiliary storage space  303 , and the other portion may be irradiated toward the second panel  13 . The light irradiated toward the second panel  13  may pass through the first panel  11  after passing through the second panel  13 . 
     When the first panel  11  defines an outer appearance of the refrigerator, the knock sensing device  410  may be in contact with the first panel  11 . As another embodiment, when the third panel  213  defines an outer appearance of the refrigerator, the knock sensing device  410  may be in contact with the third panel  213 . 
     The door lighting unit  402  may be disposed to be biased to either side of the door  301 , or a plurality of door lighting units  402  may be disposed to be symmetrical to each other in the door  301 . 
     In any case, some of the spacers  165  may be disposed closer to the door lighting unit  402  than other spacers  166  based on the plurality of spacers  16 . 
     As illustrated in  FIG.  29   , an amount of light or an intensity of light reaching to the spacer  165  disposed close to the door lighting unit  402  may be greater than an amount of light or an intensity of light reaching the spacer  166  disposed far from the door lighting unit  402 . 
     In views of visibility of the inner space of the home appliance, since it is preferable to minimize that the spacers  165  and  166  are exposed to the outside, a diameter (or size) D 5  of one spacers  165  disposed close to the door lighting unit  402 ) may be less than a diameter (or size) D 6  of the other spacer  166  disposed away from the door lighting unit  402 . 
       FIG.  30    is a view illustrating another example in which the panel assembly is applied to the refrigerator according to the present invention.  FIG.  31    is a cutaway cross-sectional view taken along line E-E of  FIG.  30   ,  FIG.  32    is a sectional view taken along line F-F of  FIG.  30   , and  FIG.  33    is an enlarged view of a portion B of  FIG.  32   . 
       FIG.  32    illustrates a positional relationship between a basket  505  and a second door  520  provided in a first door  512 . 
     Referring to  FIGS.  30  to  33   , a refrigerator  500  according to this embodiment may include a cabinet  501  including a storage space and a plurality of doors  510  and  540  for opening and closing the storage space. 
     The storage space may include a refrigerating compartment and a freezing compartment, and the plurality of doors  510  and  540  may include a refrigerating compartment door  510  and a freezing compartment door  540 . 
     For example, in this embodiment, the refrigerating compartment may be disposed above the freezing compartment. 
     The refrigerating compartment may be opened and closed by one or a plurality of refrigerating compartment doors  510 . In  FIG.  30   , as an example, two refrigerator compartment doors  510  are opened and closed as the refrigerator compartment door. 
     The freezing compartment may be opened and closed by one or more freezing compartment doors  540 . 
     The refrigerating compartment door  510  may include a first door  512  that opens and closes the refrigerating compartment and a second door  520  that is rotatable with respect to the first door  512 . 
     The first door  512  may include an opening  504  and a door storage space  506 . The door storage space  506  may be an inner space of the basket  505 , a space disposed between a plurality of baskets  505 , or a space defined by a separate case. 
     The second door  520  may open and close the opening  504 . The second door  520  may include a panel assembly  10 . The panel assembly  10  may cover at least a portion of the opening  504 . 
       FIGS.  30  to  32    illustrate that the second door  520  includes the panel assembly  10  according to the first embodiment, but it should be noted that the panel assemblies of the second to fourth embodiments described above may be applied to the second door  520  in the same manner. 
     The second door  520  may include a door frame  40   a  supporting the panel assembly  10   a  and a door liner  60   a  connected to the door frame  40   a.  Also, the second door  520  may further include a bracket  50   a.    
     Fundamental functions of the door frame  40   a,  the door liner  60   a,  and the bracket  50   a  may be the same as or similar to those mentioned in the first embodiment. 
     The door frame  40   a  may include a first opening  41   a,  and the door liner  60   a  may include a second opening  61   a.  The panel assembly  10  may cover the first opening  41   a  and the second opening  61   a.    
     The door liner  60   a  may include a bent portion  62   a  that is bent from the second opening  61   a  toward the door frame  40   a.  Alternatively, the door liner  60   a  may include a bent portion  62   a  extending toward the first opening  41   a,  and the bent portion  62   a  may define the second opening  61   a.    
     The door frame  40   a  may be provided as a thin plate and may include a bent portion  42   a  that is bent inward from the second opening  41   a.  An inner region of the bent portion  42   a  substantially becomes the second opening  41   a.    
     The panel assembly  10  may be disposed at the second opening  41   a  to cover the second opening  41   a  or may cover the second opening  41   a  from the outside of the second opening  41   a.    
     A side surface of the panel assembly  10  may be in contact with the bent portion  42   a.  For example, the side surface of the first panel  11  may be in contact with the bent portion  42   a.    
     The first panel  11  may define a portion of the front appearance of the second door  520 . A front surface (first surface) of the first panel  11  may define the same surface as a front surface of the door frame  40   a,  or a line passing through the front surface of the first panel  11  may pass through the front surface of the door frame  40   a.  Alternatively, the front surface of the first panel  11  and the front surface of the door frame  40   a  may be stepped. However, in this case, in order to prevent the first panel  11  from being damaged, the front surface of the first panel  11  may be disposed behind the front surface of the door frame  40   a.    
     The bracket  50   a  may include a first portion  51   a  disposed to face the first panel  11 , a second portion  52   a  disposed to face the door frame  40   a,  and a third portion  53   a  connecting the first portion  51   a  to the second portion  52   a.    
     The first portion  51   a  of the bracket  50   a  may face a rear surface (second surface) of the first panel  11 , and the second portion  52   a  of the bracket  50   a  may face a rear surface of the door frame  40   a.    
     For example, the first portion  51   a  of the bracket  50   a  may be disposed to correspond to the second area of the first panel  11 . That is, the first portion  51   a  of the bracket  50   a  may be disposed to face the second area of the first panel  11 . 
     Thus, even if the panel assembly  10  is installed on the second door  520 , the bracket  50   a  may be prevented from being exposed to the outside. 
     The first portion  51   a  of the bracket  50   a  may be provided with a coupling protrusion  54   a,  and the bent portion  42   a  may be provided with a protrusion slot (not shown) into which the coupling protrusion  54   a  is inserted. 
     A heater accommodation groove  502   a  may be defined in the first portion  51   a  of the bracket  50   a.  A heater  58  may be accommodated in the heater accommodation groove  502   a.    
     In the case of this embodiment, since the panel assembly  10  has a vacuum insulation space, a thickness of the panel assembly may be reduced compared to a structure in which a gas is filled between two panels. 
     When the panel assembly  10  according to this embodiment is applied to the structure of the existing second door  520 , a gap between the panel assembly  10  and the bent portion  62   a  of the door liner  60   a  may occur by a reduced thickness of the panel assembly  10 . 
     If, without changing the structure of the existing door liner  60   a,  the panel assembly  10  according to this embodiment is used, the second door  520  may further include an intermediate member  63   a  disposed in a spaced portion between the door liner  60   a  and the panel assembly  10 . 
     One side of the intermediate member  63   a  may be coupled to the door liner  60   a,  and the other side may be in contact with the panel assembly  10 . For example, the intermediate member  63   a  may be in contact with the rear surface (second surface) of the second panel  13 . 
     The intermediate member  63   a  may further include a contact portion  64   a  to increase in contact area between the intermediate member  63   a  and the second panel  13 . 
     As another example, the door liner  60   a  may be configured to include the same configuration as the intermediate member  63   a  by changing the structure of the door liner  60   a.  In this case, the door liner  60   a  may include a contact portion  64   a  for contacting the second panel  13 . 
     In either case, the door frame  40 , the door liner  60 , the bracket  50 , and the panel assembly  10  may define an insulation space in which an insulation material  80  is filled. 
     The contact portion  64   a  of the door liner  60   a  may be in contact with a position spaced a predetermined distance from an edge end of the second panel  13 . 
     The insulating material  80  may be in contact with the door frame  40   a,  the door liner  60   a,  and the bracket  50   a.  Also, the insulation material  80  may be in contact with a rear surface (second surface) of the second panel  13 . A portion of the insulating material  80  may be in contact with the contact portion  64   a  to press the contact portion  64   a  toward the second panel  13 . Thus, the insulation material may be prevented from leaking between the contact portion  64   a  and the second panel  13 . 
     Since the panel assembly  10   a  itself includes the vacuum insulation space, thermal insulation performance may be maintained by the vacuum insulation space, but an outer surface of the panel assembly  10   a,  in particular, the sealing member  222  may be capable of the heat conduction, and thus, there is a need to prevent the thermal insulation performance by the heat conduction. 
     In order to prevent deterioration in thermal insulation performance due to the heat conduction of the panel assembly  10 , the insulation material  80  may be in contact with the rear surface (second surface) of the second panel  13 . Also, the insulation material  80  may be in contact with a side surface of the second panel  13  and a portion of the sealing member  15 . 
     The insulation material  80  may be disposed to overlap the second panel  13  in a front and rear direction (which may be defined as an arranged direction of the panels). In order to secure the thermal insulation performance, an overlapping length D 4  of the insulation material  80  and the second panel  13  in a front and rear direction may be set within a range of 20 mm to 50 mm. The technical meaning of the overlapping length D 4  of the insulation material  80  and the second panel  13  in the front and rear direction is the same as described in the first embodiment. 
     Also, it is noted that the configuration and functions for transmitting light through the panel assembly by turning on the lighting unit by sensing the knock input described above may be applied to this refrigerator in the same manner. 
     As described above, if a thickness of the panel assembly  10  decreases, a size of the basket  505  may increase. When the size of the basket  505  increases, a volume of the door storage space defined by the basket  505  may increase. 
     For example, a portion of the basket  505  may pass through the opening  504  to protrude forward from a front surface of the first door  512 . As described above, even if the front surface of the basket  505  protrudes from the first door  512 , the basket  505  may not interfere with the panel assembly  10 . 
     Referring to  FIG.  32   , a portion of the basket  505  may be disposed on an area defined by the door liner  60   a.  That is, a front surface  505   a  of the basket  505  may be disposed adjacent to a rear surface of the panel assembly  10  (for example, the second panel  13 ). 
     Thus, the front surface  505   a  of the basket  505  may be disposed closer to the second panel  13  than one point of the door liner  60   a.    
     The front surface  505   a  of the basket  505  may be spaced apart from the second panel  13  to prevent the front surface  505   a  of the basket  505  and the second panel  13  from being in contact with each other. A spaced distance D 7  between the front surface  505   a  of the basket  505  and the second panel  13  may be greater than a thickness of the second panel  13 . 
     The spaced space between the front surface  505   a  of the basket  505  and the second panel  13  may provide a path for light irradiated from the door lighting unit  402 . 
     The front surface  505   a  of the basket  505  may be disposed in a space defined by an insulation material  80  provided in the insulation space P. 
     To prevent the basket  505  and the door liner  60   a  from interfering with each other during the rotation of the second door  520 , both side surfaces  505   b  of the basket  505  may be spaced apart from the intermediate member  63   a  of the door liner  60   a.  The intermediate member  63   a  may define a space in which the basket  505  is disposed. When the intermediate member  63   a  is integrated with the door liner  60   a,  the intermediate member  63   a  is referred to as an inner member defining a space in the door liner  60   a  in which the basket  505  is disposed (or it may also be referred to as the bent portion described above). 
     A horizontal distance from a rotation center of the second door  520  to one surface of both side surfaces  505   b  of the basket  505  may be greater than a maximum horizontal distance from the rotation center of the second door to the intermediate member (or the inner member) of the door liner  60   a  to prevent the basket  505  and the door liner  60   a  from interfering with each other during the rotation of the second door  520 . 
     A spaced distance D 8  between each of both side surfaces  505   b  of the basket  505  and the intermediate member  63   a  is greater than a spaced distance D 7  between the front surface  505   a  of the basket  505  and the second panel  13 . The spaced distance D 8  between each of both side surfaces  505   b  of the basket  505  and the intermediate member  63   a  may be determined based on a rotation trajectory of the second door  520  and the spaced distance D 7  between the front surface  505   a  of the basket  505  and the second panel  13 . 
     The spaced space between both side surfaces  505   b  of the basket  505  and the intermediate member  63   a  may provide a path for light irradiated from the door lighting unit  402 . 
     In  FIGS.  30  to  32   , the relationship between the panel assembly  10  and the door lighting unit  402  in the second door  520  has been described, but the related information may be applied equally even when the refrigerator includes one door. For example, the door lighting unit  402  may be disposed in the frame assembly  90  of the refrigerating compartment door or the freezing compartment door, and a size of each of the spacers may be determined according to the arrangement relationship between the door lighting unit  420  and the spacers. 
     A storage space lighting unit  401  may be provided in the cabinet  501 . The position of the storage space lighting unit  401  is not limited. For example, the storage space lighting unit  401  may be disposed at a front end (a position adjacent to the door) of the cabinet  501  or on a rear wall defining the storage space. 
     In this case, even when the door lighting unit  402  does not exist, if the storage space lighting unit  401  is turned on, the inside of the storage space may be visualized by the light of the storage space lighting unit  401 . 
     The storage space lighting unit  402  may be disposed on an upper wall of the cabinet  501 , a lower wall, or at least one of both sidewalls. 
     When the storage space lighting unit  402  is disposed on the wall defining the storage space, an amount of light or intensity of light reaching the other spacers disposed at the center of the panel assembly  10  may be greater than an amount or intensity of light reaching the spacer disposed at the outer side of the panel assembly  10 . 
     In this case, among the plurality of spacers, a diameter (or size) of the spacer disposed at the center of the panel assembly  10  may be less than a diameter (or size) of the spacer disposed on the outer side of the panel assembly. 
       FIG.  34    is a view illustrating another example in which the panel assembly is applied to the refrigerator according to the present invention. 
       FIG.  34    illustrates a side-by-side type refrigerator as an example. 
     Referring to  FIG.  34   , in the refrigerator  600  of this embodiment, a freezing compartment  603  and a refrigerating compartment  602  may be disposed at left and right sides. The freezing compartment  603  may be opened and closed by a freezing compartment door  620 , and the refrigerating compartment  602  may be opened and closed by a refrigerating compartment door  610 . 
     The refrigerating compartment door  610  may include the panel assembly  10  described above, and a structure of the refrigerating compartment door  610  may be the same as or similar to the structure of the door  30  described in  FIGS.  9  to  11   . 
       FIG.  34    illustrates that the refrigerating compartment door  610  includes the panel assembly  10  according to the first embodiment, but it should be noted that the panel assemblies of the second to fourth embodiments described above may be applied to the refrigerating compartment door  610  in the same manner. 
     Also, it is noted that the configuration and functions for transmitting light through the panel assembly by turning on the lighting unit by sensing the knock input described above may be applied to this refrigerator in the same manner. 
       FIG.  35    is a view illustrating a state in which the panel assembly is applied to a cloth processor that is an example of a home appliance. 
     Referring to  FIG.  35   , in the case of a cloth processor, an inner space  702  for processing such as sterilization and storage of clothes is provided, and the inner space  702  may be opened and closed by a door  710 . The door  710  may include the panel assembly  10  described above. 
     A structure of the door  710  according to this embodiment may be the same as or similar to the structure of the door described above. For example, the door of the home appliance may include a frame including an opening, and a panel assembly connected to the frame to cover the opening. An insulation material may be or may not be provided inside the frame. 
       FIG.  35    illustrates that the door  710  includes the panel assembly  10  according to the first embodiment, but it should be noted that the panel assemblies of the second to fourth embodiments described above may be applied to the door  710  in the same manner. 
     Also, it is noted that the configuration and functions for transmitting light through the panel assembly by turning on the lighting unit by sensing the knock input described above may be applied to this cloth processor in the same manner. 
     Also, although not presented in the this specification, if the home appliance includes the inner space and a door including the inner space and a door that opens and closes the inner space, the panel assembly of the present invention may be provided on the door, the configuration and functions for transmitting light through the panel assembly by turning on the lighting unit due to the sensing of a knock input may be applied in the same manner.