Patent Publication Number: US-2017357036-A1

Title: Relief structure and security medium

Description:
TECHNICAL FIELD 
     The present invention relates to a relief structure which is stuck or transferred to an article to prevent the counterfeiting of the article and a security medium having the relief structure. 
     BACKGROUND ART 
     There is disclosed a subtractive color filter that changes its color depending on an observation direction using a zero-order diffraction light (see Patent Literature 1). 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: JP-T 58-500916 
     SUMMARY 
     Technical Problem 
     However, when the structure disclosed in Patent Literature 1 is observed as it is, reflected light becomes so bright that the angular range over which a red or green color can be observed is narrow. 
     The object of the present invention is to provide a relief structure having a simple structure, capable of being manufactured with ease and at low cost, and capable of improving visibility, and a security medium having the relief structure. 
     Solution to Problems 
     To attain the above object, a relief structure according to an embodiment of the present invention includes a grating structure part having a grating formed at a predetermined angle, wherein the grating structure part includes a scattering structure part having a light scattering property. 
     Further, in the relief structure according to an embodiment of the present invention, the grating structure part includes a first unit structure part and a second unit structure part having a different configuration from that of the first unit structure part, and the scattering structure part is formed so as to produce a scattering effect by the different structures of the first unit structure part and second unit structure part. 
     Further, in the relief structure according to an embodiment of the present invention, the first unit structure part and the second unit structure part are formed according to phase information of a Fourier transformation pattern. 
     Further, in the relief structure according to an embodiment of the present invention, the second unit structure part is formed such that at least a part thereof is two-dimensionally shifted from the first unit structure part. 
     Further, in the relief structure according to an embodiment of the present invention, at least one of the first and second unit structure parts has the non-grating part in at least a part thereof. 
     Further, in the relief structure according to an embodiment of the present invention, at least a part of the second unit structure part is different in shape from the first unit structure part. 
     Further, in the relief structure according to an embodiment of the present invention, the grating structure part includes a first area having a first grating formed at a predetermined angle and a second area having a second grating rotated by a predetermined angle with respect to the first grating. 
     A security medium according to an embodiment of the present invention includes: 
     the relief structure; 
     a refractive index layer formed on the surface of the relief structure; and 
     an adhesive layer formed on the surface of the refractive index layer. 
     A security document according to an embodiment of the present invention includes the relief structure. 
     Advantageous Effects 
     According to the present invention, there can be provided a relief structure having a simple structure, capable of being manufactured with ease and at low cost, and capable of improving visibility, and a security medium having the relief structure. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a view illustrating a relief structure according to an embodiment of the present invention as viewed in a predetermined direction; 
         FIG. 2  is a view illustrating the relief structure according to the present embodiment as viewed in a direction rotated by 90° with respect to the predetermined direction; 
         FIG. 3  illustrates an example of a security medium including the relief structure according to the present embodiment in which a grating is formed according to phase information of a Fourier transformation pattern; 
         FIG. 4  illustrates a grating structure part including a scattering structure part according to a first embodiment; 
         FIG. 5  illustrates the grating structure part including the scattering structure part according to a second embodiment; 
         FIG. 6  illustrates the grating structure part including the scattering structure part according to a third embodiment; and 
         FIG. 7  illustrates the grating structure part including the scattering structure part according to another embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     A relief structure according to an embodiment of the present invention will be described below with reference to the accompanying drawings. 
       FIG. 1  is a view illustrating the relief structure according to an embodiment of the present invention as viewed in a predetermined direction.  FIG. 2  is a view illustrating the relief structure according to the present embodiment as viewed in a direction rotated by 90° with respect to the predetermined direction. 
     For example, in the present embodiment, a relief structure  1  includes a first area  1   a  constituting a background and a second area  1   b  constituting a character, as illustrated in  FIG. 1 . In the state illustrated in  FIG. 1 , the first area  1   a  includes a first grating  11  which is a vertical grating, and the second area  1   b  includes a second grating  12  which is a lateral grating obtained by rotating the vertical grating by 90°. 
     The first grating  11  has a grating pitch of 370 nm and a depth of 100 nm and constitutes the first area  1   a  which looks red in the state illustrated in  FIG. 1 . The second grating  12  has a grating pitch of 370 nm and a depth of 100 nm and constitutes the second area  1   b  which looks green in the state illustrated in  FIG. 1 . 
     When the thus formed relief structure  1  is rotated by 90° from the state illustrated in  FIG. 1  to the state illustrated in  FIG. 2 , the first grating  11  is turned into a lateral grating, and the second grating  12  is turned into a vertical grating which is at an angle of 90° with respect to the lateral grating. In this state illustrated in  FIG. 2 , the first grating  11  constitutes the first area  1   a  which looks green, and the second area  1   b  constitutes the second grating  12  which looks red. 
     In the present embodiment, the first and second gratings  11  and  12  are made to look red and green; alternatively, however, the first and second gratings  11  and  12  may be made to look like other colors by adjusting the grating pitch and depth. In this case, the grating pitch is preferably set to a length equal to or less than the wavelength (e.g., 500 nm) of a visible light. 
     When the thus formed relief structure  1  is observed as it is, reflected light becomes so bright that the angular range over which the red or green color can be observed is narrow. Therefore, in the present embodiment, a structure that scatters the reflected light is employed. As the structure for scattering the reflected light, a structure using a diffusion layer has conventionally been used; however, in such a structure, the thickness and the number of materials to be used are increased, resulting in increase in cost. Thus, in the present embodiment, a grating structure is used to scatter the reflected light. The following describes the scattering structure. 
     In the relief structure  1  according to the present embodiment, a grating is formed on a Fourier transformation pattern or the like to form a scattering structure part, whereby and diffusion functions can be realized by a relief shape alone. 
       FIG. 3  illustrates an example of a security medium  100  including the relief structure  1  according to the present embodiment in which a grating is formed according to phase information of a Fourier transformation pattern. 
     In the relief structure  1  included in the security medium  100  according to the present embodiment, when a grating structure part  10  is formed according to phase information of a Fourier transformation pattern  20 , a part of the grating structure part  10  is formed so as to have a different structure from that of the rest of the grating structure part  10  to thereby form a scattering structure part having a scattering effect. A refractive index layer is vapor-deposited on the surface of the Fourier transformation pattern  20  which the grating structure part  10  is formed. For example, in the present embodiment, a high refractive index layer  30  of zinc sulfide (ZnS) having a refractive index of 2.3 and a thickness of about 100 nm is deposited. The material of the high refractive index layer is not limited to zinc sulfide (ZnS), but may be any high refractive index material such as titanium oxide. For example, a heat seal layer  40  is formed on the high refractive index layer  30  as an adhesive layer. 
     The relief structure  1  and high refractive index layer  30  are stuck to an adherend  60  through the heat seal layer  40 . Examples of the adherend  60  include articles (i.e., also referred to as “security documents”) requiring counterfeiting prevention, such as an ID, a certificate, a passport, a bill, a cash voucher, a passbook, a public deed, and a brand protection label. 
     Although not illustrated, when the relief structure  1 , high refractive index layer  30 , and heat seal layer  40  are formed on a base material, a relief structure transfer foil can be obtained. The heat seal layer  40  of the relief structure transfer foil is brought into contact with the adherend  60 , followed by peeling-off of the base material, whereby the security medium  100  can be obtained. To facilitate the peeling-off of the base material of the relief structure transfer foil, a peeling layer may be provided between the base material and the relief structure  1 . The security medium  100  and relief structure transfer foil described above are not limited to the above configuration, but another configuration may be added thereto when needed. 
     The Fourier transformation pattern may be formed according to the method described in JP 2001-337584A or JP 2011-123266A. Further, as described in JP 2007-15196A, the relief structure  1  may be formed so as to allow observation of a predetermined image when a light from a point light source directly incident on the relief structure  1  applied with the Fourier transformation pattern or incident thereon after once reflected is observed through the relief structure  1 , or when a laser light transmitted through the relief structure  1  or a laser light transmitted through the relief structure  1  and then reflected is observed. 
       FIG. 4  illustrates the grating structure part including the scattering structure part according to a first embodiment. 
     The grating structure part  10  according to the first embodiment includes a first unit structure part  10   a  and a second unit structure part  10   b . The left-right or up-down position of the grating is two-dimensionally shifted between the first unit structure part  10   a  and the second unit structure part  10   b  in a plane constituting the grating according to phase information of the Fourier transformation pattern to thereby obtain the scattering structure part. For example, in the grating structure part  10  according to the first embodiment, assuming that the phase of the Fourier transformation pattern has two values: 0 and π, the first unit structure part  10   a  is formed at the phase 0 part, and the second unit structure part  10   b  is formed at the phase π part by shifting the second unit structure part  10   b  in the direction orthogonal to the grating line by a half of the grating pitch, as illustrated in  FIG. 4 . 
     As described above, in the relief structure  1  according to the present embodiment, the grating is formed according to phase information of the Fourier transformation pattern, so that it is possible to form the grating including the scattering structure part in a single process without addition of a diffusion layer. Thus, there can be provided a relief structure having a simple structure, capable of being manufactured with ease and at low cost, and having improved visibility. 
       FIG. 5  illustrates the grating structure part including the scattering structure part according to a second embodiment. 
     The grating structure part  10  according to the second embodiment includes a non-grating part in at least a part of the first and second unit structure parts  10   a  and  10   b . For example, in the grating structure part  10  according to the second embodiment, assuming that the phase of the Fourier transformation pattern has two values: 0 and π, the first unit structure part  10   a  is formed at the phase 0 part, and the non-grating part  10   c  where no grating is formed is set at the phase it part, as illustrated in  FIG. 5 . Thus, the scattering structure part is constituted by the first unit structure part  10   a , second unit structure part  10   b , and non-grating part  10   c . The non-grating part  10   c  may be provided in at least a part of the first and second unit structure parts  10   a  and  10   b.    
     As described above, in the relief structure  1  according to the present embodiment, the grating is formed according to phase information of the Fourier transformation pattern, so that it is possible to form the grating including the scattering structure part in a single process without addition of a diffusion layer. Thus, there can be provided a relief structure having a simpler structure, capable of being manufactured with ease and at low cost, and having improved visibility. 
       FIG. 6  illustrates the grating structure part including the scattering structure part according to a third embodiment. 
     The grating structure part  10  according to the third embodiment includes the first unit structure part  10   a  and the second unit structure part  10   b . The first unit structure part  10   a  and the second unit structure part  10   b  are formed so as to be shifted in the grating depth direction according to phase information of the Fourier transformation pattern and thus to have different shapes from each other, whereby the scattering structure part is obtained. For example, in the grating structure part  10  according to the third embodiment, assuming that the phase of the Fourier transformation pattern has two values: 0 and π, the first unit structure part  10   a  is formed at the phase 0 part, and the second unit structure part  10   b  different in shape from the first unit structure part  10   a  is formed at the phase π part by shifting the second unit structure part  10   b  by, e.g., 90 nm in the depth direction, as illustrated in  FIG. 6 . 
     As described above, in the relief structure  1  according to the present embodiment, the grating is formed according to phase information of the Fourier transformation pattern  20 , so that it is possible to form the grating including the scattering structure part in a single duplication process without addition of a diffusion layer. Thus, there can be provided a relief structure having a simple structure, capable of being manufactured with ease and at low cost, and having improved visibility. 
       FIG. 7  illustrates the grating structure part including the scattering structure part according to another embodiment. 
     In the grating structure part  10  according to the embodiment illustrated in  FIG. 7 , the grating is formed on a scattering pattern  50 . The scattering pattern  50  has a structure in which minute convex parts  51  formed on the surface thereof are used as scattering elements. Although the grating structure is formed only on the upper surface of the convex part  51  in the example of  FIG. 7 , it may be formed on a concave part  52 . That is, the grating structure may be formed on at least one of the convex part  51  and concave part  52 . 
     As described above, in the relief structure  1  according to the present embodiment, the grating is formed on the scattering pattern  50 , so that it is possible to form the grating including the scattering structure part in a single process without addition of a diffusion layer. Thus, there can be provided a relief structure having a simple structure, capable of being manufactured with ease and at low cost, and having improved visibility. 
     As described above, the relief structure  1  according to the present embodiment includes the grating structure part  10  having the grating formed at a predetermined angle, and the grating structure part  10  includes the scattering structure part  20  or  50  having a light scattering property. Thus, there can be provided a relief structure having a simple structure, capable of being manufactured with ease and at low cost, and having improved visibility. 
     Further, in the relief structure  1  according to the present embodiment, the grating structure part  10  includes the first unit structure part  10   a  and the second unit structure part  10   b  having a different configuration from that of the first unit structure part  10   a , and the scattering structure part  20  or  50  is formed so as to produce a scattering effect by the different structures of the first unit structure part  10   a  and second unit structure part  10   b . Thus, there can be provided a relief structure having a simpler structure and capable of being manufactured with ease and at low cost. 
     The first unit structure part  10   a  and second unit structure part  10   b  are formed according to phase information of the Fourier transformation pattern, allowing further improvement in visibility. 
     Further, in the relief structure  1  according to the present embodiment, the second unit structure part  10   b  is formed such that at least a part thereof is two-dimensionally shifted from the first unit structure part  10   a . Thus, there can be provided a relief structure having a simpler structure, capable of being manufactured with ease and at low cost, and having improved visibility. 
     Further, in the relief structure  1  according to the present embodiment, at least one of the first and second unit structure parts  10   a  and  10   b  has the non-grating part in at least a part thereof. Thus, there can be provided a relief structure having a simpler structure, capable of being manufactured with ease and at low cost, and having improved visibility. 
     Further, in the relief structure  1  according to the present embodiment, at least a part of the second unit structure part  10   b  is different in shape from the first unit structure part  10   a . Thus, there can be provided a relief structure having a simpler structure, capable of being manufactured with ease and at low cost, and having improved visibility. 
     Further, in the relief structure  1  according to the present embodiment, the grating structure part  10  includes the first area  1   a  having the first grating  11  formed at a predetermined angle and the second area  1   b  having the second grating  12  rotated by a predetermined angle with respect to the first grating  11 , allowing further improvement in visibility. 
     Further, the security medium according to the present embodiment includes the relief structure  1 , the high refractive index layer  30  formed on the surface of the relief structure  1 , the heat seal layer  40  formed on the surface of the high refractive index layer  30 . Thus, there can be provided a security medium having a simple structure, capable of being manufactured with ease and at low cost, and having improved visibility. 
     While the relief structure and security medium have been described by way of the several embodiments, the present invention is not limited to the above embodiments, and various combinations and modifications thereof are possible. 
     REFERENCE SIGNS LIST 
     
         
           1 : Relief structure 
           1   a : First area 
           1   b : Second area 
           11 : First grating 
           12 : Second grating 
           10 : Grating structure part 
           10   a : First unit structure part 
           10   b : Second unit structure part 
           20 : Fourier transformation pattern (scattering structure part) 
           30 : High refractive index layer 
           40 : Heat seal layer (adhesive layer) 
           50 : Scattering pattern (scattering structure part) 
           100 : Security medium