(a) Technical Field of the Invention 
     The present invention relates generally to a tamper-evident container structure, which comprises a plastic tray base and a cover that are attachable to each other with a first post and a second post coupled to each other, wherein the plastic tray base is provided on a circumference thereof with a first flange that is greater than a second flange provided along a circumference of the cover, so that unauthorized opening of the cover is prevented, unless a tear-off section that is formed at a predetermined location on a first protrusion with perforation lines provided on opposite sides of the tear-off section and a cut-off section formed between the perforation lines and the plastic tray base is torn to allow for opening and lifting of the cover, thereby providing a tamper evident effect. 
     (b) Description of the Prior Art 
     Various plastic containers that are made through vacuum forming are available, including boxes, cups, or bowls, which are fit for storage of food for keeping the food fresh. Such products are generally made of clear materials, allowing general consumers to see therethrough to observe food therein when they intend to purchase the food and this eliminates unnecessary arguing and quarrels after the sale. However, to inspect the food contained in such a container is intact and fresh, some consumers may open, without permission and authorization, the container to directly inspect the food. Some of such food containers, after being opened by the consumers, are not properly sealed to the original condition so that the food contained therein may get contaminated or spoiled. In addition, this may also lead to damage of the plastic container and affects the outside appearance of the container. Further, if it is not timely recognized that the package container has been tampered and opened, deterioration of the food contained therein would cause a waste of food and is also an economic burden of the shops. 
     Although temper evident containers are known, the conventional tamper evident containers often have a locking method that permits defeating the temper evident features using finger nails or pry tool to lift the cover. 
     In view of these problems, the present invention aims to provide a tamper-evident container, which provides a tamper evident effect to eliminate the drawbacks and deficiency of the prior art devices. 
     SUMMARY OF THE INVENTION 
     Thus, to prevent damage of the outside appearance of a plastic container and food contained in the container losing freshness resulting from unauthorized opening and tampering of the plastic container, the primary object of the present invention is to provide a tamper-evident container structure, which comprises a plastic tray base, a cover, a first protrusion section, a second protrusion section, a first post, a second post, perforation lines, and a cut-off section to provide a tamper indicating effect of ready identification of unauthorized opening or tampering. 
     To achieve the above objects, the present invention provides a tamper-evident container structure, which generally comprises a plastic tray base, the plastic tray base having one surface that is open and an opposite surface that is closed, the plastic tray base having an interior space in which at least one stop block is formed in such a way that the stop block circumferentially extends along an inner circumference of the plastic tray base, the plastic tray base having an outer circumference on which a first flange is formed in such a way that the first flange circumferentially extends around the plastic tray base; 
     a cover, which is coupled to the open surface of the plastic tray base to selectively close the plastic tray base, the cover having an outer circumference on which a second flange is formed in such a way that the second flange circumferentially extends around the cover and at least one downward-projecting block formed inboard and at an inner side of the second flange, length and width of the second flange being smaller than length and width of the first flange; 
     at least one first protrusion, which is formed at a predetermined location on the circumference of the plastic tray base, the first protrusion comprising at least one tear-off section formed at a predetermined location thereof, at least one perforation line being formed at a connection between the tear-off section and the first protrusion, a cut-off section being formed between the tear-off section and the plastic tray base, the tear-off section comprising at least one first post formed at a predetermined location thereof and a first recess; and 
     at least one second protrusion, which is formed at a predetermined location on the circumference of the cover, the second protrusion comprising at least one second post formed at a predetermined location thereof and a second recess, the second post and the first post being engageable with each other to tightly couple the first protrusion and the second protrusion to each other, the first recess and the second recess being in mating engagement with each other. 
     In the above-described first protrusion, the first protrusion has a middle section that comprises the tear-off section formed therein. 
     In the above-described tear-off section, the first post is formed on a surface of the tear-off section. 
     In the above-described first post, the first post has a lower portion on which an engagement block is formed to circumferentially extend along an inner circumference of the first post and the first post is a raised triangular block. 
     In the above-described second protrusion, the second post is formed on a surface of the second protrusion. 
     In the above-described second post, the second post has a lower end on which a projection block is formed to circumferentially surround the second post and the second post is a raised triangular block, so that engagement between the projection block and the engagement block couples the first post and the second post to each other. 
     In the above-described first recess, the first recess is arranged in a portion of the tear-off section of the first protrusion that is put into engagement with the second protrusion. 
     In the above-described second recess, the second recess is arranged in a portion of the second protrusion that is put into engagement with the tear-off section. 
     The foregoing objectives and summary provide only a brief introduction to the present invention. To fully appreciate these and other objects of the present invention as well as the invention itself, all of which will become apparent to those skilled in the art, the following detailed description of the invention and the claims should be read in conjunction with the accompanying drawings. Throughout the specification and drawings identical reference numerals refer to identical or similar parts. 
     Many other advantages and features of the present invention will become manifest to those versed in the art upon making reference to the detailed description and the accompanying sheets of drawings in which a preferred structural embodiment incorporating the principles of the present invention is shown by way of illustrative example. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of the present invention. 
         FIG. 2  is an exploded view of the present invention. 
         FIG. 3  is a schematic view showing a portion of the present invention. 
         FIG. 4  is a cross-sectional view showing a portion of the present invention. 
         FIG. 5  is a schematic view illustrating a recess of the present invention. 
         FIG. 6  is a view illustrating a use of the present invention. 
         FIG. 7  is a view illustrating a use of the present invention. 
         FIG. 8  is a view illustrating an embodiment of posts of the present invention. 
         FIG. 9  is a view illustrating an embodiment of protrusions of the present invention. 
         FIG. 10  is a view illustrating an embodiment of a plastic tray base and a cover of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following descriptions are exemplary embodiments only, and are not intended to limit the scope, applicability or configuration of the invention in any way. Rather, the following description provides a convenient illustration for implementing exemplary embodiments of the invention. Various changes to the described embodiments may be made in the function and arrangement of the elements described without departing from the scope of the invention as set forth in the appended claims. 
     Referring to  FIGS. 1 and 2 , which are respectively a perspective view and an exploded view of the present invention, as shown in the drawings, the present invention generally comprises a plastic tray base  1 . The plastic tray base  1  has one surface that is open and an opposite surface that is closed. The plastic tray base  1  has an interior space in which at least one stop block  11  is formed in such a way that the stop block  11  circumferentially extends along an inner circumference of the plastic tray base  1 . The plastic tray base  1  has an outer circumference on which a first flange  12  is formed in such a way that the first flange  12  circumferentially extends around the plastic tray base  1 . 
     A cover  2  is coupled to the open surface of the plastic tray base  1  to selectively close the plastic tray base  1 . The cover  2  has an outer circumference on which a second flange  21  is formed in such a way that the second flange  21  circumferentially extends around the cover  2  and at least one downward-projecting block  22  formed inboard and at an inner side of the second flange  21 . Length and width of the second flange  21  are smaller than length and width of the first flange  12 . 
     At least one first protrusion  3  is formed at a predetermined location on the circumference of the plastic tray base  1 . The first protrusion  3  has a middle section in which at least one tear-off section  31  is formed. At least one perforation line  32  is formed at a connection between the tear-off section  31  and the first protrusion  3  and a cut-off section  33  is formed between the tear-off section  31  and the plastic tray base  1 . At least one first post  34  is formed on a surface of the tear-off section  31 . The tear-off section  31  is provided, at a predetermined location thereof, with a first recess  35 . 
     At least one second protrusion  4  is formed at a predetermined location on the circumference of the cover  2 . At least one second post  41  is formed on a surface of the second protrusion  4 . The second protrusion  4  is provided, at a predetermined location thereof, with a second recess  42 . The second post  41  and the first post  34  are structured to mate and thus in coupled engagement with each other to couple the first protrusion  3  and the second protrusion  4  to each other. The first recess  35  and the second recess  42  are in mating engagement with each other. 
     In the structure of the first post  34  described above, the first post  34  has a lower portion that comprises an engagement block  341 , which, defining a groove, circumferentially extends along an inner circumference of the first post  34 . The first post  34  may be a triangular raised block. 
     In the structure of the second post  41  described above, the second post  41  is a triangular raised block and the second post  41  has a lower portion that comprises a projection block  411  formed thereon to circumferentially surround the second post  41 . Mutual mating engagement between the projection block  411  and the engagement block  341  couples and joins the first post  34  and the second post  41  to each other. 
     In the structure of the first recess described above, the first recess is arranged in a portion of the tear-off section of the first protrusion that is put into engagement with the second protrusion. 
     In the structure of the second recess described above, the second recess is arranged in a portion of the second protrusion that is put into engagement with the tear-off section. 
     Referring to  FIGS. 3 and 4 , which are respectively a schematic view showing a portion of the present invention and a cross-sectional view showing a portion of the present invention, as shown in the drawings, the plastic tray base  1  is closed and sealed through tight engagement between the stop block  11  and the downward-projecting block  22  and between the first flange  12  and the second flange  21 . In addition, the projection block  411  that is formed on the upper portion of the first post  34  and circumferentially surrounding the first post  34  and the engagement block  341  that is arranged on the upper portion of the second post  41  and circumferentially extends and surrounds an inner circumference of the second post  41  are structured to allow the projection block  411  and the engagement block  341  to mate and engage each other so as to couple the first post  34  and the second post  41  to each other thereby coupling the first protrusion  3  and the second protrusion  4  together to effectively and hermetically combine the plastic tray base  1  and the cover  2 . 
     As shown in  FIG. 5 , which is a schematic view illustrating a recess of the present invention, as shown in the drawing, the tear-off section  31  of the first protrusion  3  is provided with the first recess  35  at the connection thereof with the second protrusion  4 ; and the second protrusion  4  is provided with the second recess  42  at the connection thereof with the tear-off section  31 . Mating engagement between the first recess  5  and the second recess  6  makes the section protrusion  4  received and embedded in the first recess  35  so as to effectively prevent a user from lifting off the cover  2  by means of the second protrusion  4  using finger nails or pry tool, thereby achieving a tamper indicating effect. 
     Referring to  FIGS. 6 and 7 , which are views illustrating a use of the present invention, as shown in the drawings, the first protrusion  3  and the second protrusion  4  are coupled together through coupling between the first post  34  and the second post  41 . In an attempt to open the cover  2 , a user applies a force to the first protrusion  3  in a downward direction and also applies a force to the tear-off section  31  in an upward direction so that the forces that are opposite to each other and respectively in the upward and downward directions cause the tear-off section  31  to be torn along the perforation line  32  to the cut-off section  33  and thus lifted upward. Once the tear-off section  31  is completely torn, the cover  2  is free to open and lift. As such, positive evidence is provided for tampering indication of unauthorized opening and access. 
     Referring to  FIG. 8 , which is a view illustrating an embodiment of the posts of the present invention, as shown in the drawing, the first post  34  is formed on a surface of the tear-off section  31  and the first post  34  has an upper portion that comprises a projection block  411  that circumferentially surrounds the first post  34 . The second post  41  is provided on a surface of the second protrusion  4  and the second post  41  has an upper section that comprises an engagement block  341  circumferentially surrounding the second post  41 . Mating engagement between the projection block  411  and the engagement block  341  couples the first post  34  and the second post  41  to each other so as to have the first protrusion  3  and the second protrusion  4  tightly coupled to each other. 
     Referring to  FIG. 9 , which is a view illustrating another embodiment of the protrusions of the present invention, as shown in the drawing, the first protrusion  3  is arranged at one side, one corner, or any location of the plastic tray base  1  and the second protrusion  4  is correspondingly arranged at one side, one corner, or any location of the cover  2 . Coupling achieved between the first post  34  and the second post  41  couples the first protrusion  3  and the second protrusion  4  to each other to provide the same effect as described above. 
     Referring to  FIG. 10 , which is a view illustrating another embodiment of the plastic tray base and the cover of the present invention, as shown in the drawing, the plastic tray base  1  and the cover  2  are connected to each other in a pivoting manner at one side thereof for effectively closing or opening the plastic tray base  1 . 
     It will be understood that each of the elements described above, or two or more together may also find a useful application in other types of methods differing from the type described above. 
     While certain novel features of this invention have been shown and described and are pointed out in the annexed claim, it is not intended to be limited to the details above, since it will be understood that various omissions, modifications, substitutions and changes in the forms and details of the device illustrated and in its operation can be made by those skilled in the art without departing in any way from the claims of the present invention.
Disclosed is a tamper-evident container for food storage that uses a round male to female post lock on a single corner. After the cover is locked to the tray base, it requires breaking the corner tray tab to open the container. This tab tear off provides positive evidence of container opening to indicate the container has been opened or tampered with.