Technical Field
The present invention relates to counterfeit preventing
structures and counterfeit preventing articles, which have
special optical effects.
5
Background Art
It is known to prevent from counterfeiting articles
which prevention of counterfeiting is required, such as
securities, certificates, and articles of upscale labels, by
10 adhering an element having difficult-to-copy optical effects.
Holograms, diffraction gratings, and multilayer interference
films are known as the elements having such optical effects.
Unauthorized reproduction can be prevented, since these
elements are difficult to be analyzed due to their micro
15 structures or complicated layer constructions.
Further, it is known to form a reflective layer in the
above-described holograms and the like is known for enhancing
the optical effects. More difficult-to-copy holographic
optical elements can be obtained by patterning this
20 reflective layer. For example, the holographic element
having the patterned reflective layer is adopted in bank
notes of various states/countries, as the counterfeit
preventing optical element.
The reflective layer can be patterned by a so-called
25 etching technique. Japanese Patent Laid-open No. 2003-
255115 discloses formation of a patterned mask by a printing
method and the like onto parts of the reflective layer to be
removed, followed by corrosive treatment of the reflective
layer (hereinafter, referred to as "demetallizing") (see
- 3 -
PTL1). However, counterfeit preventing effect of such
articles has been decreased, since similar effect can be
achieved by providing a patterned metal foil.
In regard to this problem, Japanese Patent Laid-open No.
2012-063738 proposes an optical element having a 5 reflective
layer which is totally registered to the diffraction
structure of a hologram, and has a high definition of 4000
dpi or more (see PTL2). This optical element is considered
to be difficult to copy, due to higher complexity and higher
10 definition. However, the pattern of high definition which
is difficult to copy can be detected only by observation
under a magnifying glass. It is difficult to confirm the
effect of the pattern by observation by the naked eye.
On the other hand, recently in the field of bank notes,
15 polymer bank notes involving a transparent polymeric
substrate is put to practical use. Therefore, observation
of counterfeit preventing optical element (a hologram, for
example) from two sides becomes an important genuineness
judging method. In view of the background described above,
20 counterfeit preventing optical elements exhibiting different
optical effects on front and back sides receive attention and
are required.
Citation List
25 Patent Literature
PTL1: Japanese Patent Laid-Open No. 2003-255115
PTL2: Japanese Patent Laid-Open No. 2012-063738
PTL3: International Patent Publication No. WO
2010/147185
- 4 -
PTL4: Japanese Patent Laid-Open No. H02-037301(1990)
PTL5: Japanese Patent Laid-Open No. 2007-329007
PTL6: Japanese Patent Laid-Open No. H01-291926(1989)
Summary of Invention
5 Technical Problem
The purpose of the present invention is to provide a
counterfeit preventing structure having different optical
effects on front and back sides wherein the effects can be
confirmed under observation with the naked eye.
10
Solution to Problem
The counterfeit preventing structure of the present
invention includes a micro-protrusion/depression reflective
layer causing structural color when irradiated with white
15 light. Different structural color can be generated dependent
on the medium covering the protrusion/depression structure,
even when the structure has the same shape.
The counterfeit preventing structure of the first
embodiment of the present invention comprises: a micro20
protrusion/depression reflective layer having a first surface
having micro-protrusions and micro-depressions and a second
surface opposite to the first surface and having microprotrusions
and micro-depressions; a first color-adjusting
layer provided on at least a part of the first surface and
25 in contact with the first surface; and a second coloradjusting
layer provided on at least a part of the second
surface and in contact with the second surface, wherein: the
first color-adjusting layer has a refractive index different
from a refractive index of the second color-adjusting layer;
- 5 -
the first and second surfaces of the microprotrusion/
depression reflective layer have microprotrusion/
depression surfaces causing structural colors by
reflecting, interfering, diffracting, scattering and/or
absorbing light of at least a portion of visible 5 e region;
optical effects obtained under observation from the side of
the first color-adjusting layer are different from optical
effects obtained under observation from the side of the
second color-adjusting layer; and the difference between
10 refractive indices of the first and second color-adjusting
layers are 0.1 or more. Here, the microprotrusion/
depression reflective layer may have the same
protrusion/depression shape on the first and second surfaces.
The micro-protrusion/depression reflective layer may have a
15 protrusion/depression shape which is rectangular in the
vertical cross-section, or alternatively, a
protrusion/depression shape in which a horizontal crosssectional
area varies monotonously from the top to the bottom.
Here, the micro-protrusion/depression reflective layer may
20 be provided at the part of the counterfeit preventing
structure, and the counterfeit preventing structure further
may comprise a protective layer covering the microprotrusion/
depression reflective layer and having the same
shape as the shape of the micro-protrusion/depression
25 reflective layer. It is preferable that the difference
between refractive indices of the first and second coloradjusting
layers is 0.2 or more. Further, wherein the microprotrusion/
depression reflective layer may consist of a
plurality of parts having different micro-protrusions and
- 6 -
micro-depressions. Here, the second color-adjusting layer
may consist of a plurality of parts having different
refractive indices, and at least one of the parts of the
second color-adjusting layer may have a refractive index
different from the refractive index of the first 5 coloradjusting
layer.
The counterfeit preventing article of the second
embodiment of the present invention comprises an article
including a transparent part and the counterfeit preventing
10 structure according to the first embodiment disposed on the
transparent part of the article. The article may comprise:
a personal authentication medium such as a card, a passport,
and a mobile phone; securities such as a bill and a bank
note; or a counterfeit preventing medium for brand protection.
15
Advantageous Effects of Invention
By adopting the above-described construction, it
becomes possible to provide a counterfeit preventing
structure having different optical effects on front and back
20 sides wherein the effects can be confirmed under observation
with the naked eye.
Brief Description of Drawings
Fig. 1 is a vertical cross-sectional diagram showing a
25 configuration example of the counterfeit preventing structure
according to the present invention;
Fig. 2 is a vertical cross-sectional diagram showing a
configuration example of the counterfeit preventing structure
according to the present invention;
- 7 -
Fig. 3 is a vertical cross-sectional diagram showing a
configuration example of the counterfeit preventing structure
according to the present invention;
Fig. 4A is a top-view showing a configuration example
of the micro-protrusion/depression reflective layer having 5 a
constitution that protrusions are aligned in a square
lattice;
Fig. 4B is a top-view showing a configuration example
of the micro-protrusion/depression reflective layer having a
10 constitution that protrusions are aligned in a hexagonal
closest packed lattice;
Fig. 5 is a vertical cross-sectional diagram showing a
configuration example of the counterfeit preventing structure
according to the present invention;
15 Fig. 6 is a vertical cross-sectional diagram showing a
configuration example of the counterfeit preventing structure
according to the present invention;
Fig. 7A is a vertical cross-sectional diagram showing
one step of the method for manufacturing the counterfeit
20 preventing structure according to the present invention;
Fig. 7B is a vertical cross-sectional diagram showing
one step of the method for manufacturing the counterfeit
preventing structure according to the present invention;
Fig. 7C is a vertical cross-sectional diagram showing
25 one step of the method for manufacturing the counterfeit
preventing structure according to the present invention;
Fig. 7D is a vertical cross-sectional diagram showing
one step of the method for manufacturing the counterfeit
preventing structure according to the present invention; and
- 8 -
Fig. 7E is a vertical cross-sectional diagram showing
one step of the method for manufacturing the counterfeit
preventing structure according to the present invention.
Description 5 of Embodiments
The counterfeit preventing structure of the present
invention comprises: a micro-protrusion/depression
reflective layer having a first surface having microprotrusions
and micro-depressions and a second surface
10 opposite to the first surface and having micro-protrusions
and micro-depressions; a first color-adjusting layer provided
on at least a part of the first surface and in contact with
the first surface; and a second color-adjusting layer
provided on at least a part of the second surface and in
15 contact with the second surface, wherein: the first and
second surfaces of the micro-protrusion/depression
reflective layer have micro-protrusion/depression surfaces
causing a structural color by reflecting, interfering,
diffracting, scattering and/or absorbing light of at least a
20 portion of visible region; the first color-adjusting layer
has a refractive index different from a refractive index of
the second color-adjusting layer; optical effects obtained
under observation from the side of the first color-adjusting
layer are different from optical effects obtained under
25 observation from the side of the second color-adjusting
layer; and the difference between refractive indices of the
first and second color-adjusting layers are 0.1 or more.
Fig. 1 shows a configuration example of the counterfeit
preventing structure comprising micro-protrusion/depression
- 9 -
reflective layer 20, first color-adjusting layer 10 covering
the whole of the first surface of the microprotrusion/
depression reflective layer 20 and extending to
the periphery of the micro-protrusion/depression reflective
layer 20, and second color-adjusting layer 30 covering 5 vering the
whole of the second surface of the microprotrusion/
depression reflective layer 20 and extending to
the periphery of the micro-protrusion/depression reflective
layer 20, wherein the first color-adjusting layer 10 is in
10 contact with the second color-adjusting layer in the
periphery of the micro-protrusion/depression reflective
layer 20.
When the counterfeit preventing structure is observed,
the structural color varies dependent on micro-protrusions
15 and micro-depressions in the micro-protrusion/depression
reflective layer 20, and refractive indices of the first
color-adjusting layer 10 and the second color-adjusting layer
30. The "structural color" in the present invention means a
color generated by reflected light, interfered light,
20 diffracted light and/or scattered light obtained by the
micro-protrusion/depression reflective layer, or a color
generated by absorption of light by the microprotrusion/
depression reflective layer 20.
If the ratio of the area of the top of protrusions in
25 the micro-protrusion/depression reflective layer 20 to the
area of the bottom of the protrusions ([area of the top of
protrusions]/[area of the bottom of protrusions]) is less
than 1.0, the observing surface of the microprotrusion/
depression reflective layer 20 can be interpreted
- 10 -
as a gradient structure in which a refractive index gradually
varies in the depth direction. Such protrusion/depression
shape has a horizontal cross-sectional area which
monotonously varies from the top to the bottom.
Specifically, such protrusion/depression shape 5 comprises
protrusions having a horizontal cross-sectional area which
monotonously increases from the top to the bottom, and
depressions having a horizontal cross-sectional area which
monotonously decreases from the top to the bottom. More
10 specifically, such protrusion/depression shape includes
shapes such as a circular cone, a pyramid, a truncated cone,
a truncated pyramid, a hemisphere, a hemi-ellipsoid, a half
circular cylinder (a circular cylinder with a semicircular
vertical cross-section), a triangular cylinder (a triangular
15 cylinder with a triangular vertical cross-section), spheroids
of sine curves or hyperbolas, and the like. In the present
specification, the "horizontal cross-section" means a crosssection
parallel to a principal plane of the counterfeit
preventing structure, and the "vertical cross-section" means
20 a cross-section perpendicular to a principal plane of the
counterfeit preventing structure. Here, the "vertical
cross-section" may be referred simply to as "cross-section".
The gradient structure absorbs electromagnetic waves.
The wavelength of the electromagnetic wave to be absorbed
25 varies dependent on the "depth/period ratio (D/P ratio)" of
the protrusions in the micro-protrusion/depression
reflective layer 20, and the refractive index of the material
existing in the gaps between the protrusions (air, the first
color-adjusting layer 10, or the second color-adjusting layer
- 11 -
30). Then, electromagnetic waves having wavelengths which
is not absorbed by the gradient structure are reflected or
scattered. The structural color is observed in the case
where the electromagnetic wave to be absorbed is visible
light. In the present invention, the "depth D" of 5 the
protrusions means a distance from the top of the protrusions
to the bottom part in a direction perpendicular to the
principal plane of the counterfeit preventing structure, as
shown in Fig. 1. On the other hand, the "period P" of the
10 protrusions mans a distance between the tops of two adjacent
protrusions in a direction parallel to the principal plane
of the counterfeit preventing structure, as shown in Fig. 1.
Further, in regard to the depressions, the "depth D" means a
distance from the top surface to the bottom apex of the
15 depressions in a direction perpendicular to the principal
plane of the counterfeit preventing structure, and the
"period P" means a distance between the bottom apices of two
adjacent depressions in a direction parallel to the principal
plane of the counterfeit preventing structure.
20 The electromagnetic wave is absorbed in a broader range
of wavelength, as increase of the D/P ratio of the protrusion.
If the D/P ratio is 0.5 or more, a black structural color is
observed, since the whole light in visible region is absorbed.
It is desirable that the D/P ratio is in a range from 0.01
25 to 0.5 for obtaining a chromatic structural color, although
the range depends on the shapes of the protrusions and the
like. Further, the D/P ratio in the above-described range
is preferable to prevent from diminishing or changing the
- 12 -
structural color caused by deformation due to external
factors (heat, pressure, or the like).
On the other hand, if the protrusions in the microprotrusion/
depression reflective layer 20 has a shape in
which the horizontal cross-sectional area does not vary 5 from
the top to the bottom, it is possible to generate a structural
color by interference. In this case, it is possible to
observe the structural color corresponding to the wavelength
of light emphasized by interference between light reflected
10 from the top surface of the protrusions in the microprotrusion/
depression reflective layer 20 and light reflected
from the bottom part which is different from the protrusions.
Also in this case, the structural color varies dependent on
the refractive index of the material existing in the gaps
15 between the protrusions (air, the first color-adjusting layer
10, or the second color-adjusting layer 30). In addition,
the refractive index of the first color-adjusting layer 10
is different from the refractive index of the second coloradjusting
layer 20, and therefore, optical path lengths in
20 the respective layers are different from each other.
Therefore, the wavelength of interfered light observed in the
side of the first color-adjusting layer 10 is different from
the wavelength of interfered light observed in the side of
the second color-adjusting layer 30, even if the shapes of
25 the protrusions and depressions on the front side of the
micro-protrusion/depression reflective layer 20 are the same
as the shapes on the back side. In other words, differently
colored indications can be obtained by observation from the
front and back sides. The shape in which the horizontal
- 13 -
cross-sectional area does not vary is a shape having a
rectangular vertical cross-section, and includes a prism (a
prism with a polygonal horizontal cross-section), a circular
cylinder (a circular cylinder with a circular horizontal
cross-section), an elliptical cylinder 5 (an elliptical
cylinder with an elliptical horizontal cross-section), and
the like.
Further, a structural color due to diffracted light can
be generated by forming a sub-wavelength structure in which
10 the protrusions in the micro-protrusion/depression
reflective layer aligned in the constant period less than the
wavelength of visible light. The sub-wavelength structure
can provide primary diffracted light in a broad viewing angle.
This makes it possible to improve visibility. Also in the
15 sub-wavelength structure, the structural color varies
dependent on the refractive index of the material existing
in the gaps between the protrusions (air, the first coloradjusting
layer 10, or the second color-adjusting layer 30).
The two-dimensional alignment of the micro20
protrusion/depression pattern in the microprotrusion/
depression reflective layer 20 may be a square
lattice shown in Fig. 4A, or in a hexagonal closest packed
lattice as shown in Fig. 4B, when diffracted light is utilized.
The square lattice shown in Fig. 4A is a structure obtained
25 with a plurality of first grooves extending one direction,
and a plurality of second grooves extending the direction
perpendicular to the direction in which the first grooves
extend. In the square lattice, one of the protrusions or
depressions is adjacent to four of the protrusions or
- 14 -
depressions. The hexagonal closest packed shown in Fig. 4B
is a structure in which one of the protrusions or depressions
is adjacent to six of the protrusions or depressions.
Besides, the protrusions and depressions may have other shape,
although the protrusions having a shape of a 5 quadrangular
pyramid are exemplarily shown in Figs. 4A and 4B. In
contrast to a structure consisting of a plurality of grooves
extending in one direction (corrugated sheet structure), the
structures shown in Figs. 4A and 4B can provide constant
10 diffracted light under observation from every arbitrary
direction due to two-dimensional isotropy, and thereby
excellent visibility can be obtained. In addition, the
diffraction indices of the first color-adjusting layer 10 and
second color-adjusting layer 30 are different from each other,
15 and thereby the optical path lengths in these layers are
different from each other, in the counterfeit preventing
structure of the present invention. Therefore, even if the
micro-protrusion/depression reflective layer 20 has
protrusions and depressions of the same shape on the front
20 and back sides, the emitting angle of the diffracted light
observed on the side of the first color-adjusting layer 10
is different from the emitting angle of the diffracted light
observed on the side of the first color-adjusting layer 30.
In other words, it is possible to emit diffracted light in
25 different angles, under observation from the front and back
sides.
When chromatic optical effects are obtained by
"absorption at arbitrary wavelength" or "interference at
arbitrary wavelength" due to a certain structure, diffracted
- 15 -
light caused by a periodic structure of protrusions and
depressions decreases the chromatic optical effects. This
is because the diffracted light exhibits variation in rainbow
colors dependent on observation angles. In this case, the
diffracted light may be suppressed by randomizing the 5 he period
of the micro-protrusion/depression pattern of the microprotrusion/
depression reflective layer 20. The "random
period" means a period having variation of about 10% to about
50% in comparison of an average period. It is preferable
10 to distribute the variation itself evenly (in other word,
randomly) throughout the surface of the microprotrusion/
depression reflective layer 20. Alternatively,
decrease in the chromatic optical effect caused by the
periodic structure of protrusions and depressions can be
15 avoided by setting the period of the microprotrusion/
depression pattern to make it difficult to observe
diffracted light in visible region, such as a sub-wavelength
period.
Further, a structural color caused by scattered light
20 can be generated from a scattering structure in which the
structure of protrusions and depressions in the microprotrusion/
depression reflective layer 20 is more
miniaturized. Mechanisms causing scattering by the
structure includes Rayleigh scattering, Mie scattering, and
25 diffraction scattering, for example. Also in the scattering
structure, scattering wavelength, scattering angle, and
scattering distribution varies due to difference in the
refractive indices of the first color-adjusting layer 10 in
contact with the first surface of the micro-
16 -
protrusion/depression reflective layer 20 and the second
color-adjusting layer 30 in contact with the second surface
of the micro-protrusion/depression reflective layer 20.
In every case in which any one of the above-described
mechanisms (absorption, interference, diffraction 5 and
scattering), the wavelength range and intensity of the
structural color caused by the counterfeit preventing
structure of the present invention may vary dependent on an
incident angle of a light source to the principal plane of
10 the counterfeit preventing structure and an observation angle
of an observer. Besides, the protrusions in the microprotrusion/
depression reflective layer 20 are explained above,
for an exemplary purpose. However, this is also the case
for the depressions in the micro-protrusion/depression
15 reflective layer 20. Besides, in the present specification,
the protrusions and the depressions may be collectively
referred to as "protrusion/depression shape", "microprotrusions
and micro-depressions", or "microprotrusion/
depression pattern".
20 When counterfeit preventing structure 100 shown in Fig.
1 is observed from the side of the first surface, light of
the first color is observed in region 110 in which the first
color-adjusting layer 10, the micro-protrusion/depression
reflective layer 20, and the second color-adjusting layer 30
25 are stacked, the first color being determined by the microprotrusion/
depression pattern of the microprotrusion/
depression reflective layer 20 and the refractive
index of the first color-adjusting layer 10. On the other
hand, if the difference in refractive indices between the
- 17 -
first color-adjusting layer 10 and the second color-adjusting
layer 30 is small in comparison with the difference in
refractive indices between the micro-protrusion/depression
reflective layer 20 and the first color-adjusting layer 10
or the second color-adjusting layer 30, smaller 5 reflectance
and small chromatic effects are obtained at the interface
between the first color-adjusting layer 10 and the second
color-adjusting layer 30 in region 120 where the microprotrusion/
depression reflective layer 20 does not exist.
10 Alternatively, it is possible to design to render the region
120 transparent. Besides, when the counterfeit preventing
structure 100 is observed from the side of the second surface,
light of the second color, determined by the microprotrusion/
depression pattern of the micro15
protrusion/depression reflective layer 20 and the refractive
index of the second color-adjusting layer 30, is observed in
region 110. On the other hand, the region 120 exhibits the
small degree of chromatic effects or is observed as a
transparent region, similarly to the above description.
20 Here, the first and second colors are different from each
other, due to difference in refractive indices of the first
color-adjusting layer 10 and the second color-adjusting layer
30. Therefore, the counterfeit preventing structure 100
provides images with different colors under observation from
25 the front and back sides.
In the micro-protrusion/depression reflective layer 20,
the protrusion/depression shape of the first surface may be
the same as the protrusion/depression shape of the second
surface. It is possible to make the protrusion/depression
- 18 -
shapes of the first and second surfaces identical by adopting
a so-called corrugated structure, if the shape of the
protrusions or the depressions is triangular prism
(triangular prism with a triangular vertical cross-section).
In the case where the protrusions and depressions 5 ns having
other shapes, it is possible to make the
protrusion/depression shapes of the first and second surfaces
identical by providing protrusions at the "white" squares of
so-called "checkerboard pattern" and depressions having a
10 corresponding shape to that of the protrusions at the "black"
squares. Alternatively, it is possible to make the
protrusion/depression shapes of the first and second surfaces
identical by alternately aligning rows consisting of a
plurality of protrusions and extending in one direction and
15 rows consisting of a plurality of depressions having a
corresponding shape to that of the protrusions and extending
in the same direction. Besides, the microprotrusion/
depression reflective layer 20 may have a uniform
thickness entirely.
20 Fig. 2 shows a counterfeit preventing structure 200
having a different constitution, which is similar to the
constitution shown in Fig. 1 except that the microprotrusion/
depression reflective layer 20 is provided on the
whole surface of the first color-adjusting layer 10.
25 When counterfeit preventing structure 200 shown in Fig.
2 is observed from the side of the first surface, light of
the first color is observed in both of: region 210 in which
the first color-adjusting layer 10, the microprotrusion/
depression reflective layer 20, and the second
- 19 -
color-adjusting layer 30 are stacked; and region 220 where
the second color-adjusting layer 30 does not exist. In
other words, the counterfeit preventing structure 200 is
observed as a body having a uniform color throughout the
whole surface, under observation from the side of the 5 first
surface. Besides, when the counterfeit preventing structure
200 is observed from the side of the second surface, light
of the second color, determined by the microprotrusion/
depression pattern of the micro10
protrusion/depression reflective layer 20 and the refractive
index of the second color-adjusting layer 30, is observed in
region 210. Further, light of third color, determined by
the micro-protrusion/depression pattern of the microprotrusion/
depression reflective layer 20 and the refractive
15 index of air, is observed in region 220. Here, the first to
third colors are different from each other, due to difference
in refractive indices of the first color-adjusting layer 10,
the second color-adjusting layer 30 and air. Therefore, the
counterfeit preventing structure 200 provides images, both
20 of shapes and colors of which are different from each other,
under observation from the side of the first surface and
observation from the side of the second surface.
Fig. 3 shows a counterfeit preventing structure 300
having a different constitution, which is similar to the
25 constitution shown in Fig. 2 except that the microprotrusion/
depression reflective layer 20 has hemispherical
protrusions convex to the second surface. The counterfeit
preventing structure shown in Fig. 3 can be obtained by
- 20 -
forming the first color-adjusting layer by a method utilizing
a monolayer particle film as set forth below.
The structural color under observation from the side of
the first surface is different from the structural color
under observation from the side of the second surface, 5 rface, even
if the refractive indices of the first color-adjusting layer
10 is the same as that of the second color-adjusting layer
30. This is because rates of change of horizontal crosssectional
area of the micro-protrusion/depression reflective
10 layer 20 in the first and second surface are different from
each other. In this constitutional example, the difference
in structural color based on asymmetry of the microprotrusion/
depression reflective layer 20 is further
emphasized by the difference in refractive indices of the
15 first color-adjusting layer 10 and the second color-adjusting
layer 30. In this constitutional example, the refractive
indices of the first color-adjusting layer 10 and the second
color-adjusting layer 30 are adjusted such that different
structural colors are observed from the front and back sides.
20 When counterfeit preventing structure 300 shown in Fig. 2 is
observed from the side of the first surface, light of the
first color is observed in both of: region 310 in which the
first color-adjusting layer 10, the microprotrusion/
depression reflective layer 20, and the second
25 color-adjusting layer 20 are stacked; and region 320 where
the second color-adjusting layer 20 does not exist. In
other words, the counterfeit preventing structure 300 is
observed as a body having a uniform color throughout the
whole surface, under observation from the side of the first
- 21 -
surface. Besides, when the counterfeit preventing structure
300 is observed from the side of the second surface, light
of the second color, determined by the microprotrusion/
depression pattern of the microprotrusion/
depression reflective layer 20 and the 5 refractive
index of the second color-adjusting layer 30, is observed in
region 310. Further, light of third color, determined by
the micro-protrusion/depression pattern of the microprotrusion/
depression reflective layer 20 and the refractive
10 index of air, is observed in region 320. Here, the first to
third colors are different from each other, due to difference
in refractive indices of the first color-adjusting layer 10,
the second color-adjusting layer 30 and air. Therefore, the
counterfeit preventing structure 300 provides images, both
15 of shapes and colors of which are different from each other,
under observation from the side of the first surface and
observation from the side of the second surface.
Fig. 5 shows a counterfeit preventing structure 500
having a different constitution in which the micro20
protrusion/depression reflective layer 20 has region 510
comprising protrusions having an approximately triangular
vertical cross-section and region 520 comprising
hemispherical protrusions convex to the side of the second
surface, and the second color-adjusting layer 30 is disposed
25 entirely on the second surface of the microprotrusion/
depression reflective layer 20. As such, the
micro-protrusion/depression reflective layer 20 may consists
of a plurality of parts comprising different microprotrusions
and micro-depressions. The protrusions in the
- 22 -
region 510 may be circular cones, polygonal cones, or
triangular prisms extending from front side to back side on
the paper surface (so-called corrugated structure wherein the
vertical cross-section is a triangle).
In the counterfeit preventing structure 500, 5 , the
structural color in the region 510 is different from the
structural color in the region 520 under observation from the
side of the first surface, since the rate of change in the
horizontal cross-sectional area of the micro10
protrusion/depression reflective layer 20 is different
between the first and second surface. Similarly, under
observation from the side of the second surface, the
structural color in the region 510 is different from the
structural color in the region 520. In this constitutional
15 example, the difference in structural color based on
asymmetry of the micro-protrusion/depression reflective
layer 20 is further emphasized by the difference in
refractive indices of the first color-adjusting layer 10 and
the second color-adjusting layer 30. In this constitutional
20 example, the refractive indices of the first color-adjusting
layer 10 and the second color-adjusting layer 30 are adjusted
such that different structural colors are observed from the
front and back sides.
When counterfeit preventing structure 500 shown in Fig.
25 5 is observed from the side of the first surface, light of
the first color is observed in region 510 comprising
protrusions having an approximately triangular vertical
cross-section, the first color being determined by the rate
of change in horizontal cross-sectional area of the
- 23 -
approximately triangular protrusions and the refractive index
of the first color-adjusting layer 10. On the other hand,
light of the second color is observed in region 520 comprising
hemispherical depressions, the second color being determined
by the rate of change in horizontal cross-sectional area 5 of
the hemispherical depressions and the refractive index of the
first color-adjusting layer 10. Besides, when observing
from the side of the second surface, light of the third color
is observed in region 510 comprising protrusions having an
10 approximately triangular vertical cross-section, the third
color being determined by the rate of change in horizontal
cross-sectional area of the approximately triangular
protrusions and the refractive index of the second coloradjusting
layer 30. On the other hand, light of the fourth
15 color is observed in region 520 comprising hemispherical
protrusions, the second color being determined by the rate
of change in horizontal cross-sectional area of the
hemispherical protrusions and the refractive index of the
second color-adjusting layer 30. Here, the first to fourth
20 colors are different from each other, due to difference in
cross-section, rate of change in horizontal cross-sectional
area, and refractive indices of the first color-adjusting
layer 10 and the second color-adjusting layer 20. Therefore,
the counterfeit preventing structure 500 provides images with
25 different colors, under observation from the side of the
first surface and observation from the side of the second
surface.
Fig. 6 shows a counterfeit preventing structure 600
having a different constitution, which is similar to the
- 24 -
constitution shown in Fig. 3 except that the second coloradjusting
layer 30 consists of first second color-adjusting
layer 31 and second second color-adjusting layer 32, the
refractive indices of which are different from each other.
As such, the second color-adjusting layer 30 may consists 5 of
a plurality of parts having different refractive indices.
In this case, at least one of the plurality of parts of the
second color-adjusting layer 30 has a refractive index
different from that of the first color-adjusting layer 10.
10 In the counterfeit preventing structure shown in Fig.
6, light of first color is observed in all of region 610
where the first color-adjusting layer 10, the microprotrusion/
depression reflective layer 20 and the first
second color-adjusting layer 31 are stacked, region 620 where
15 the first color-adjusting layer 10, the microprotrusion/
depression reflective layer 20 and the second
second color-adjusting layer 32 are stacked, and region 630
where the second color-adjusting layer 30 does not exist, the
first color being determined by the micro20
protrusion/depression pattern of the microprotrusion/
depression reflective layer 20 and the refractive
index of the first color-adjusting layer 10. In other words,
the counterfeit preventing structure 600 is observed as a
body having a uniform color throughout the whole surface,
25 under observation from the side of the first surface.
Besides, when observing from the side of the second surface,
light of the second color is observed in region 610, the
second color being determined by the microprotrusion/
depression pattern of the micro-
25 -
protrusion/depression reflective layer 20 and the refractive
index of the first second color-adjusting layer 31. On the
other hand, light of the third color is observed in region
620, the second color being determined by the microprotrusion/
depression pattern of the 5 microprotrusion/
depression reflective layer 20 and the refractive
index of the second second color-adjusting layer 32.
Further, light of the fourth color is observed in region 630,
the fourth color being determined by the micro10
protrusion/depression pattern of the microprotrusion/
depression reflective layer 20 and the refractive
index of air. Here, the first to fourth colors are different
from each other, due to difference in refractive indices of
the first color-adjusting layer 10, the first second color15
adjusting layer 31, the second second color-adjusting layer
32 and air. Therefore, the counterfeit preventing structure
500 provides images, both of shapes and colors of which are
different from each other, under observation from the side
of the first surface and observation from the side of the
20 second surface.
(Method for manufacturing a micro-protrusion/depression
structure)
For the micro-protrusion/depression structure of the
counterfeit preventing structure of the present invention,
25 it is practical to use a resin for constituting the first or
second color-adjusting layer, and to form a microprotrusion/
depression pattern onto the surface of the resin.
Hereinafter, a case where the micro-protrusion/depression
pattern is formed on the surface of the first color-adjusting
- 26 -
layer will be explained. Similar method can be adopted in
forming the micro-protrusion/depression pattern on the second
color-adjusting layer.
Typical methods for duplicating the microprotrusion/
depression pattern onto the surface of the 5 resin
continuously and on a large scale include "a coating method",
"a pressing method" described in Japanese Patent Laid-Open
No. H02-037301(1990), "a casting method" described in
Japanese Patent Laid-Open No. 2007-329007, and "a
10 photopolymer method" described in Japanese Patent Laid-Open
No. H01-291926(1989) (see PTL4 to PTL6).
A method for forming the first color-adjusting layer by
the coating method will be explained with reference to Figs.
7A-7E. First, the material of the first color-adjusting
15 layer 10 is applied onto a supporting substrate (not shown)
to form first precursor layer 15 having a flat surface, as
shown in Fig. 7A. In particular, it is preferable to adopt
a wet method, in order to reduce a manufacturing cost.
Further, the first precursor layer 15 may be formed by
20 applying the material diluted with a solvent, followed by
drying, in order to control the thickness of the resultant
first precursor layer 15. The useful material will be
described later.
The supporting substrate useful in the coating method
25 is preferably made from a material exhibiting low deformation
and decomposition due to application of heat, pressure,
and/or electromagnetic wave in formation of the microprotrusion/
depression pattern set forth below. Preferable
supporting substrates comprise film of organic resin, paper,
- 27 -
synthetic paper, plastic-composite paper, and resinimpregnated
paper. More preferable supporting substrates
is the film of organic resin. Useful organic resin includes
polyethylene terephthalate (PET), polyethylene naphthalate
5 (PEN), and polypropylene (PP).
The first color-adjusting layer 10 is formed by
contacting the resultant first precursor layer 15 with a
relief master (not shown) on which a relief shape has been
formed, and applying heat, pressure, light, and/or
10 electromagnetic wave, which is dependent on the material of
the first precursor layer 15, to transfer the inverted shape
of the relief master to the first precursor layer 15, as
shown in Fig. 7B. The relief shape on the relief master is
an inverted shape of the desired micro-protrusion/depression
15 pattern. If the first precursor layer 15 is made from
thermoplastic resin, it is preferable to apply heat and
pressure to the first precursor layer 15 in the state where
the first precursor layer 15 is in contact with the relief
master. If the first precursor layer is made from
20 thermosetting resin, it is preferable to first apply pressure
to the first precursor layer in the state where the first
precursor layer 15 is in contact with the relief master, to
transfer the shape, followed by application of heat. If the
first precursor layer is made from photocurable resin, it is
25 preferable to first apply pressure to the first precursor
layer in the state where the first precursor layer 15 is in
contact with the relief master, to transfer the shape,
followed by application of light or electromagnetic wave to
cure the photocurable resin. The application of heat in the
- 28 -
case where the thermosetting resin is used, and the
application of light or electromagnetic wave in the case
where the photocurable resin is used may be conducted in the
state where the first precursor layer 15 is in contact with
the relief master, or after separating the first 5 precursor
layer 15 from the relief master.
The first precursor layer 15 having a flat surface may
have a thickness in a range of from 0.1 m to 10 m.
Dependent on the method for forming the micro10
protrusion/depression pattern described below, protrusion of
the resin due to pressurizing and/or cockles may occur, if
the thickness of the first precursor layer 15 is too large.
On the other hand, it is difficult to obtain the desired
protrusion/depression pattern due to lack of flowability of
15 the material, if the thickness of the first precursor layer
15 is too small. Dependent on the shape of the desired microprotrusion/
depression pattern, the first precursor layer has
a thickness of preferably 1 to 10 times, more preferably 3
to 5 times, as large as the desired depth of protrusions and
20 depressions.
[0043]
Here, the relief master can be formed by any method
publicly known in the art. Further, by adopting a relief
master in a roll form, formation of the first precursor layer
25 15 onto the supporting substrate and formation of the first
color-adjusting layer 10 by using the relief master can be
carried out continuously.
Alternatively, the first color-adjusting layer 10 can
be formed by the "photopolymer method" (also referred to as
- 29 -
"a 2P method" or "a photosensitive resin method"). The
"photopolymer method" comprises the steps of casting
radiation-curable resin into the gap between a relief mold
(a mold for duplication of the micro-protrusion/depression
pattern) and a flat substrate (a plastic film and the 5 like),
curing the casted radiation-curable resin by radiation
(including visible light and ultraviolet light), and removing
the substrate and the cured resin film from the relief mold.
The protrusion/depression pattern having high definition can
10 be obtained by the "photopolymer method". Further, the
structure obtained by this method has a high accuracy in
formation of the protrusion/depression pattern, excellent
heat resistance, and excellent chemical resistance, in
comparison with the structure obtained by the "pressing
15 method" and "casting method" in which thermoplastic resin is
used. A method using a photocurable resin which is in a
solid state at the normal temperature or a radiation-curable
resin which exhibits high viscosity at the normal temperature,
and a method in which a releasing material is added between
20 the relief mold and the radiation-curable resin are known as
further novel methods.
Alternative methods for forming the microprotrusion/
depression pattern include a method utilizing a
monolayer particle film. For example, a monolayer particle
25 film in which spherical particles are two dimensionally
closest packed onto a plane can be used effectively. The
monolayer particle film can be obtained by aligning particles
having a uniform diameter. For example, the monolayer
particle film can be obtained by a method of slowly pulling
- 30 -
up a supporting substrate immersed in a solution of particles
at a constant rate (pull-up method). Alternatively, the
monolayer particle film can be manufactured by a method of
printing the "particulate ink" in which a binder resin is
added to a particulate-dispersed solution with 5 precisely
controlling the applying amount per unit area, to fix the
particulates onto a supporting substrate (printing method).
Further, it is possible to obtain a structure in which buttonshaped
protrusions are two dimensionally closest packed on a
10 plane, by applying thermal press treatment to a monolayer
particle film made of spherical particles of thermoplastic
material to deform the spherical particles to the flattened
state. Further, the monolayer particle film may be formed
from irregularly shaped particles having an approximately
15 uniform diameter. The monolayer particle film formed from
the irregularly shaped particles can provide: structural
color derived from a periodic structure dependent on twodimensional
filling ratio of the particles; and scattered
light derived from the shape of the irregularly shaped
20 particles. The micro-protrusion/depression pattern
obtained by using the monolayer particle film has an
advantage that the steady protrusion/depression shape is
obtained with high productivity.
Subsequently, onto the first color-adjusting layer 10
25 having the micro-protrusion/depression pattern is formed
reflective precursor layer 25, as shown in Fig. 7C.
The reflective precursor layer 25 can be formed by
applying highly bright reflective ink onto the first coloradjusting
layer 10, the ink containing particulates of the
- 31 -
reflective material which constitutes microprotrusion/
depression reflective layer 20, a solvent, and an
optional binder. The highly bright reflective ink can be
applied onto the first color-adjusting layer 10 by any of
known printing techniques such as an inkjet method, a 5 gravure
method, a micro gravure method, a roll coating method, and a
dip coating method. It is preferable to set the applying
amount of the ink to the extent that the microprotrusion/
depression pattern of the first color-adjusting
10 layer 10 is not filled up after drying the ink. In other
words, the applying amount of the ink is desirably set to the
extent that the micro-protrusion/depression pattern, to which
the micro-protrusion/depression pattern of the first coloradjusting
layer 10 is reflected, is formed on the upper
15 surface of the reflective precursor layer 25. It is
preferable that the thickness of the reflective precursor
layer 25, which is determined by the applying amount of the
ink, is not greater than a half (1/2) of the depth of the
micro-protrusion/depression pattern of the first color20
adjusting layer 10.
Further, it is desirable that the particulates of
reflective material in the highly bright reflective ink has
a particle diameter of not greater than a fifth (1/5) of the
25 period of protrusions and depressions of the microprotrusion/
depression pattern of the first color-adjusting
layer 10, and not greater than a fifth (1/5) of the depth of
protrusions and depressions of the microprotrusion/
depression pattern of the first color-adjusting
- 32 -
layer 10. A desirable reflectivity can be obtained, and
loss of structural color due to fill-up of the microprotrusion/
depression pattern of the first color-adjusting
layer 10 can be prevented, by adopting the particulates of
reflective material having the particle diameter 5 in the
above-described range.
Alternatively, the reflective precursor layer 25 can be
formed by a dry-coating method. The dry coating method
include any method publicly known in the art, such as a vacuum
10 deposition method, a sputtering method, and a CVD method.
The dry-coating method is preferable in that a thin film
having a uniform thickness can be obtained without burying
the micro-protrusion/depression pattern of the first coloradjusting
layer 10.
15 Subsequently, the reflective precursor layer 25 is
optionally patterned to form micro-protrusion/depression
reflective layer 20, as shown in Fig. 7D. It is possible to
use the reflective precursor layer 25 as the microprotrusion/
depression reflective layer 20 by omitting this
20 step, in the case where the micro-protrusion/depression
reflective layer 20 is provided on the whole surface of the
first color-adjusting layer 10 as shown in Fig. 2. Here,
the surface of the micro-protrusion/depression reflective
layer 20 which is in contact with the first color-adjusting
25 layer 10 is the first surface of the microprotrusion/
depression reflective layer 20. Further, the
surface opposite to the first surface and onto which second
precursor layer 35 (set forth below) will be formed is the
- 33 -
second surface of the micro-protrusion/depression reflective
layer 20.
The reflective precursor layer 25 can be patterned by a
wet-etching method using an etching liquid, or a dry-etching
method such as a plasma-etching method, and a reactive 5 active ion
etching method.
In the case where the micro-protrusion/depression
reflective layer 20 is formed on only partial region(s) of
the surface of the first color-adjusting layer 10, the micro10
protrusion/depression reflective layer 20 can be formed by:
a method of wet-applying the reflective material for
constituting the micro-protrusion/depression reflective
layer 20 pattern-wise onto the first color-adjusting layer
10; a method of dry-depositing the reflective material for
15 constituting the micro-protrusion/depression reflective
layer 20 pattern-wise onto the first color-adjusting layer
10 (see International Patent Publication No. WO 2010/147185);
or a method of previously disposing a patterned resist onto
the first color-adjusting layer 10, applying or depositing
20 the reflective material over the resist, and removing the
resist and the reflective material on the resist (a so-called
"lift-off method") (See PTL3).
Alternatively, the micro-protrusion/depression
reflective layer 20 may have an arbitrary pattern, or may
25 consist of a plurality of discrete parts. The counterfeit
preventing structure having such micro-protrusion/depression
reflective layer 20 can be considered as a counterfeit
preventing structure in which the microprotrusion/
depression reflective layer 20 is partially
- 34 -
provided. For example, an etching treatment after providing
an etching mask onto the reflective precursor layer 25 can
remove the part of the reflective precursor layer 25 which
is not covered with the etching mask. The etching mask can
be provided by any known printing method such as 5 gravure
printing, inkjet printing, and offset printing, or a
photolithography method utilizing photoresist material. The
micro-protrusion/depression reflective layer 20 having the
arbitrary pattern, or consisting of a plurality of discrete
10 parts can be formed by such methods.
Subsequently, the material of second color-adjusting
layer 30 is applied onto at least partial region(s) of the
micro-protrusion/depression reflective layer 20 and
optionally at least partial region(s) of the first color15
adjusting layer 10 to form the second color-adjusting layer
30 to obtain a counterfeit preventing structure. The
surface of the micro-protrusion/depression reflective layer
20 in contact with the second color-adjusting layer 30 is the
second surface of the micro-protrusion/depression reflective
20 layer 20. Fig. 7E shows an example where the second coloradjusting
layer 30 is formed on the whole surface of the
micro-protrusion/depression reflective layer 20 and on the
surface of the first color-adjusting layer 10 which is
positioned on the periphery of the micro25
protrusion/depression reflective layer 20.
Application of the material can be carried out by any
technique known in the art including printing methods,
transferring methods, and laminating methods. The useful
printing methods include an inkjet printing method, a gravure
- 35 -
printing method, a micro gravure printing method, a roll
coating printing method, and a flexographic printing method.
The transferring methods involve transferring a dye and/or a
pigment by applying heat or pressure. The laminating method
involve the step of adhering a light-transparent coating 5 oating or
film via an adhesive layer, onto the microprotrusion/
depression reflective layer 20, or the microprotrusion/
depression reflective layer 20 and the first
color-adjusting layer 10. If the coating or film to be
10 adhered has adhesive properties, the adhesive layer may not
be used. Further, in the case where plural types of the
second color-adjusting layers are used, the plural types of
the second color-adjusting layers can be formed by repeating
application of the material of each of the layers by the
15 above-described methods.
Fig. 7E shows an example that the second color-adjusting
layer 30 has a large thickness to the extent that the
protrusions and depressions of the microprotrusion/
depression reflective layer 20 and the first
20 color-adjusting layer 10 is totally filled up. In this
example, the second color-adjusting layer 30 has a nonuniform
thickness. However, the second color-adjusting layer 30 may
have a uniform thickness. In other words, the second coloradjusting
layer may have protrusions and depressions on its
25 upper surface. The second color-adjusting layer 30 may have
the flat or protrusion/depression upper surface, as long as
the second color-adjusting layer 30 has a sufficient
thickness to cause the above-described change in structural
color due to the refractive index in the vicinity of the
- 36 -
bottom of the depressions of the micro-protrusion/depression
reflective layer 20. Besides, surface treatments such as a
corona treatment, a flame treatment, and a plasma treatment
can be carried out to improve adhesion between the layers,
together with formation of each of the above-described 5 layers.
Alternatively, an adhesion anchoring layer (not shown) may
be optionally provided between two layers.
(Material of constituent layers)
The micro-protrusion/depression reflective layer 20 is
10 characterized by covering at least a part of the microprotrusion/
depression surface and reflecting electromagnetic
wave. In the case where light incident through the first
color-adjusting layer 10 or the second color-adjusting layer
30 set forth below is to be reflected, it is preferable to
15 form the micro-protrusion/depression reflective layer 20 from
metal, metal oxide, metal sulfide, or organic polymer. In
this case, it is preferable to set the difference of the
refractive indices of the first color-adjusting layer 10 and
the second color-adjusting layer from the refractive index
20 of the micro-protrusion/depression reflective layer 20 to not
less than 0.2. It becomes possible to obtain structural
color due to diffraction of the electromagnetic wave at the
interface between the first color-adjusting layer 10 and the
micro-protrusion/depression reflective layer 20, and the
25 interface between the second color-adjusting layer 30 and the
micro-protrusion/depression reflective layer 20, by setting
the difference in refractive index to not less than 0.2.
However, it is desirable to form the microprotrusion/
depression reflective layer 20 from a material
- 37 -
having opacifying properties, in order to exclude optical
effect on the back surface (the second surface for the first
surface, and vice versa). The "material having opacifying
properties" means a material having a total light
transmittance at a flat surface of not greater than 25%5 ,
preferably not greater than 10%.
Metal useful to form the micro-protrusion/depression
reflective layer 20 includes Al, Sn, Cr, Ni, Cu, Au, Ag, and
alloys thereof. Useful metal oxide includes, but not
10 limited to, Sb2 O3 , Fe2 O3 , TiO2 , CeO2 , PbCl2 , CdO, WO3 , SiO,
Si2 O3 , In2 O3 , PbO, Ta2 O3 , ZnO, ZrO2 , MgO, SiO2 , Si2 O2 , MgF2 ,
CeF3 , CaF2 , AlF3 , Al2 O3 , and GaO. Useful metal sulfide
includes, but not limited to, CdS and ZnS. Useful organic
polymer includes, but not limited to, polyethylene,
15 polypropylene, polytetrafluoroethylene, polymethyl
methacrylate and polystyrene. As necessary, the microprotrusion/
depression reflective layer 20 may be formed from
plural types of material. Alternatively, the microprotrusion/
depression reflective layer 20 may have a stacked
20 structure of a plurality of layers of different material.
The micro-protrusion/depression reflective layer 20 may have
an arbitrary pattern, or may consist of a plurality of
discrete parts, as described above.
The first color-adjusting layer 10 and the second color25
adjusting layer 30 can be formed from thermoplastic resin,
thermosetting resin, or photocurable resin. Useful
thermoplastic resin includes, but not limited to, acryl-based
resin, polyester-based resin, cellulose-based resin and
vinyl-based resin. Useful thermosetting resin includes, but
- 38 -
not limited to, urethane resin obtained by reaction between
acrylic polyol or polyester polyol having reactive hydroxyl
groups and polyisocyanate, melamine-based resin, epoxy resin,
and phenol-based resin. The material for forming the first
color-adjusting layer 10 and the second color-5 adjusting layer
30 can be selected in view of the factors that the material
has a sufficient flowability to allow formation by the
adopting production method, and that the resultant layer has
desired heat resistance and chemical resistance.
10 The photocurable resin useful in a photopolymer method
and the like can be obtained by using a composition utilizing
radical photopolymerization, a composition utilizing
cationic photopolymerization, or a composition utilizing both
of radical and cationic photopolymerization (a hybrid
15 polymerization-type composition).
The composition utilizing radical photopolymerization
contains a radically polymerizable monomer, oligomer, or
polymer, and a radical photopolymerization initiator. Here,
mixtures of two or more types of the radically polymerizable
20 monomer, oligomer, or polymer may be used. The radically
polymerizable monomer includes, but not limited to, 1,6-
hexanediol diacrylate, neopentyl glycol diacrylate,
trimethylolpropane triacrylate, pentaerythritol triacrylate,
pentaerythritol tetraacrylate, dipentaerythritol
25 pentaacrylate, and dipentaerythritol hexaacrylate. The
radically polymerizable oligomer includes, but not limited
to, epoxy acrylate oligomer, urethane acrylate oligomer, and
polyester acrylate oligomer. The radically polymerizable
polymer includes, but not limited to, acrylate-containing
- 39 -
urethane resin and acylate-containing epoxy resin. Useful
radical photopolymerization initiator includes, but not
limited to: benzoin-based compounds such as benzoin, benzoin
methyl ether and benzoin ethyl ether; anthraquinone-based
compounds such as anthraquinone and methyl 5 anthraquinone;
phenyl ketone-based compounds such as acetophenone,
diethoxyacetophenone, benzophenone, hydroxyacetophenone, 1-
hydroxycyclohexyl phenyl ketone, -aminoacetophenone, 2-
methyl-1-(4-methylthiophenyl)-2-morpholinopropane-1-one,
10 and Michler's ketone (4,4'-bis(dimethylamino)benzophenone);
benzil dimethyl ketal; thioxanthones; and acylphosphine
oxides.
The composition utilizing cationic photopolymerization
contains a cationically polymerizable monomer, oligomer, or
15 polymer, and a cationic photopolymerization initiator. The
cationically polymerizable monomer includes, but not limited
to, epoxy-containing monomer, oxetane-containing monomer,
and vinyl ethers. Cationically polymerizable oligomer or
polymer includes, but not limited to, epoxy group-containing
20 oligomer and epoxy group-containing polymer. The cationic
photopolymerization initiator includes, but not limited to,
aromatic diazonium salts, aromatic iodonium salts, aromatic
sulfonium salts, aromatic phosphonium salts, and metal salts
with mixed ligands.
25 The hybrid polymerization-type composition contains: a
radically polymerizable monomer, oligomer, or polymer; a
cationically polymerizable monomer, oligomer, or polymer; a
radical photopolymerization initiator; and a cationic
photopolymerization initiator. Here, aromatic iodonium
- 40 -
salts or aromatic sulfonium salts, which function as both of
the radical photopolymerization initiator and the cationic
photopolymerization initiator, may be used as a single
polymerization initiator.
In the above-described compositions, the content of 5 the
photopolymerization initiator is normally in a range of 0.1
to 15% by weight based on the total weight of the composition,
although it depends on the type of monomer, oligomer, or
polymer to be used. Further, the above-described
10 compositions may further contain a sensitizing dye, in
combination with the photopolymerization initiator. Further,
as required, the above-described compositions may further
contain a colorant such as a dye or a pigment, a cross-linking
agent, and/or various types of additives. The useful cross15
linking agent includes epoxy group-containing oligomer, or
epoxy group-containing polymer. The useful additive
includes any additive known in the art such as a
polymerization inhibitor, a leveling agent, an antifoaming
agent, an anti-sagging agent, an adhesion promoter, a coated
20 surface modifier, a plasticizer, and nitrogen-containing
compounds. Further, formability can be improved by adding
non-reactive resin to the radically photopolymerizable
composition, cationically photopolymerizable composition, or
hybrid polymerization-type composition.
25 Curing by cross-linking may be carried out by
introducing an ethylenically unsaturated group or a crosslinking-
reactive group into the resin obtained by the abovedescribed
method. In the case where the ethylenically
unsaturated group is utilized, cross-linking can be carried
- 41 -
out by the above-described radical photopolymerization
initiator or a thermal radical polymerization initiator. In
the case where the cross-linking-reactive group is utilized,
useful cross-linking agent includes, but not limited to,
isocyanate compounds, a silane-coupling agent, an 5 organic
titanate cross-linking agent, an organic zirconium crosslinking
agent, and an organic aluminate cross-linking agent.
Especially, the resin into which the ethylenically
unsaturated group is introduced is in a solid state at the
10 normal temperature and exhibits low tackiness (stickiness).
Thus, the resin into which the ethylenically unsaturated
group is introduced exhibits characteristics of low
contamination of the master, as well as excellent formability.
Alternatively, the first color-adjusting layer 10 and
15 the second color-adjusting layer 30 can be formed by applying
a liquid ink containing a film-forming material and drying
the ink. The useful film-forming material includes organic
compounds, inorganic compounds, and organic-inorganic
composite material. Useful organic compounds include, but
20 not limited to, acrylic resin, polyester resin, urethane
resin, epoxy resin, and melamine resin. Useful inorganic
compounds include, but not limited to, metal alkoxide such
as ethyl silicate, propyl silicate, and butyl silicate.
Useful organic-inorganic composite material includes
25 material in which the above-described organic and inorganic
compounds are chemically bonded.
In the present invention, the first color-adjusting
layer 10 has a refractive index different from that of the
second color-adjusting layer 30. Difference in refractive
- 42 -
index between the first color-adjusting layer 10 and the
second color-adjusting layer 30 is not less than 0.1,
preferably in a range from 0.2 to 0.4. However, in view of
the protrusion/depression structure to be used and the
desired optical effects, the difference in refractive 5 index
between the first color-adjusting layer 10 and the second
color-adjusting layer 30 may be appropriately adjusted. For
example, in the case of protrusion/depression structure
having a rectangular vertical cross-section, interference
10 between the top and bottom faces of the rectangle occurs.
Interference is caused by difference in optical path length
(product of the refractive index and the depth of the
structure) between two optical paths. Thus, taking the
optical path lengths into consideration, the refractive
15 indices of the first color-adjusting layer 10 and the second
color-adjusting layer 30 can be appropriately adjusted so as
to obtain desired structural color. In the case where the
second color-adjusting layer 30 consists of a plurality of
parts having different refractive indices, it is desirable
20 that difference of the refractive index of at least one of
the plurality of parts from the refractive index of the first
color-adjusting layer 10 is within the range described above.
By utilizing the first color-adjusting layer 10 and the
second color adjusting layer 20, difference in refractive
25 index of which is within the above-described range, different
optical effects can be obtained in observation from the first
color-adjusting layer and observation from the side of the
second color-adjusting layer, even when the micro-
43 -
protrusion/depression reflective layer 20 having the same
protrusion/depression shapes on the first and second surfaces.
The refractive indices of the first color-adjusting
layer 10 and the second color-adjusting layer 30 can be
adjusted by further inclusion of one or more types 5 of
particulates. The one or more types of particulates may be
organic particulates, inorganic particulates, or organicinorganic
composite particulates. The material of the
organic particulates includes, but not limited to, acrylic
10 resin, urethane resin, melamine resin, epoxy resin, vinyl
chloride resin, and vinyl acetate resin. The material of
the inorganic particulates includes, but not limited to,
metal oxide such as aluminum oxide, titanium oxide, cerium
oxide, yttrium oxide, zinc oxide, silicon oxide, tin oxide,
15 copper oxide, iron oxide, manganese oxide, holmium oxide,
bismuth oxide, cobalt oxide, and indium tin oxide (ITO), and
elemental metal. The organic-inorganic composite
particulates include, but not limited to, particulates made
from mixed material and particulates having a core-shell
20 structure. Alternatively, hollow particulates inside of
which gas is filled may be used. It is desirable that the
particulates to be used have an average particle diameter of
not greater than 100 nm, preferably in a range from 5 nm to
30 nm. The "average particle diameter" in the present
25 invention means a number-average value (n50) of primary
particle diameter of the particulates obtained by observation
with a transmission electron microscope (TEM). It becomes
possible to adjust the refractive indices of the first coloradjusting
layer 10 and the second color-adjusting layer 30,
- 44 -
along with controlling the strength of light scattering
caused by the particulates, preventing coating non-uniformity
due to reduced stability in dispersion of the particulates,
and preventing increase of the cost of the particulates.
Further, the first color-adjusting layer 10 and 5 the
second color-adjusting layer 30 may further contain a
colorant. The color-adjusting layer containing the colorant
can exhibit a more complicated color tone by combination of
the color provided by the colorant and the structural color.
10 A useful colorant includes, but not limited to, a pigment and
a dye which absorb or reflect a certain wavelength range of
visible light. The color-adjusting layer containing the
colorant desirably has a transmittance of not less than 50%
over the whole wavelength range of visible light which is not
15 less than 400 nm and not greater than 800 nm. The structural
color caused by the color-adjusting layer (the first coloradjusting
layer 10 and the second color-adjusting layer 30)
and the micro-protrusion/depression reflective layer 20 can
be observed from the outside, by adopting the above-described
20 range of transmittance.
The first color-adjusting layer 10 and the second coloradjusting
layer 30 desirably has a high surface hardness,
excellent resistance to wear, and excellent resistance to
scratching, since these layers may become the outmost layer
25 of the counterfeit preventing structure of the present
invention. Optionally, the counterfeit preventing structure
of the present invention may comprise a protective layer (not
shown) which covers the exposed surface of the first coloradjusting
layer 10 and/or the second color-adjusting layer
- 45 -
30, or the whole surface of the first color-adjusting layer
10 and/or the second color-adjusting layer 30. The
protective layer can be formed from thermoplastic resin,
thermosetting resin, photocurable resin, two-liquid-mixing
and curing resin, or hard coat material such as 5 silicone
resin and fluorine resin. The protective layer may further
contain an additive known in the art such as waxes or a
lubricant, in addition to the above-described material.
The protective layer may cover the exposed surface of
10 the micro-protrusion/depression reflective layer 20 which is
not covered with the first color-adjusting layer 10 or the
second color-adjusting layer 30. In this case, it is
desirable that the protective layer covering the exposed part
of the first surface of the micro-protrusion/depression
15 reflective layer 20 has a refractive index different from
that of the first color-adjusting layer 10, so that the region
where the first color-adjusting layer 10 is provided exhibits
a structural color different from that exhibited by the
region where the protective layer is in contact with the
20 micro-protrusion/depression reflective layer 20. Similarly,
it is desirable that the protective layer covering the
exposed part of the second surface of the microprotrusion/
depression reflective layer 20 has a refractive
index different from that of the second color-adjusting layer
25 30, so that the region where the second color-adjusting layer
30 is provided exhibits a structural color different from
that exhibited by the region where the protective layer is
in contact with the micro-protrusion/depression reflective
layer 20. In the case where the micro-protrusion/depression
- 46 -
reflective layer 20 is pattern-wise or consists of a
plurality of discrete parts, the protective layer may have
the same shape as that of the regions of the microprotrusion/
depression reflective layer 20.
An anti-reflective coating (not shown) may be 5 provided
onto the outmost surface of the counterfeit preventing
structure of the present invention, in order to improve
optical properties of the structure. Further, the
counterfeit preventing structure may be in the form of a
10 counterfeit preventing seal by further comprising an adhesive
layer (not shown) and a base layer (not shown), for the
purpose of enhancement of convenience. Alternatively, the
counterfeit preventing structure of the present invention can
be used in the form of a counterfeit preventing transfer foil
15 which has a function of transferring the structure from a
base layer (not shown). Further, the counterfeit preventing
structure of the present invention can be blended into a
paper, as long as the structure is observable from both sides.
Further, the present invention also relates to a
20 counterfeit preventing article comprising an article having
a transparent part, and the counterfeit preventing structure
disposed on the transparent part of the article. The article
having the transparent part includes: a personal
authentication medium such as various types of cards, a
25 passport, and a mobile phone; securities such as a bill and
a bank note; and a counterfeit preventing medium for brand
protection. The "personal authentication medium" in the
present invention means a medium on which personal
information is described or a medium in which the electronic
- 47 -
data of personal information is stored. The counterfeit
preventing structure is disposed on the transparent part of
the article, so that different optical effects are also
observable from the front and back sides, in the resultant
counterfeit preventing article. Therefore, it 5 is remarkably
difficult to counterfeit the above-described counterfeit
preventing article.
[Examples]
10 (Example 1)
To a transparent polyethylene terephthalate film having
a thickness of 23 m was applied an ink composition ("RL-9"
manufactured by KSM Co., Ltd.) by gravure printing, to obtain
a coating having a thickness of 1 m after drying.
15 Subsequently, a cylindrical master having a reversed
shape of the desirable micro-protrusions and microdepressions
was moved at a rate of 10 m/minute, and pressed
to the coating under a pressure of 2 kgf/cm2 (about 0.2 MPa)
at a temperature of 80C, to transfer micro-protrusions and
20 micro-depressions. Simultaneously with transferring, the
coating is irradiated with ultraviolet light emitted from a
high-pressure mercury lamp through a polyethylene
terephthalate for cuing the coating to which the microprotrusions
and micro-depressions had been transferred, to
25 obtain first color-adjusting layer 10. The energy density
of the ultraviolet light was 300 mJ/cm2. The resultant
micro-protrusions and micro-depressions had a grid structure
consisting of a plurality of parallel grooves having a depth
of 280 nm and disposed at a period of 400 mm, the vertical
- 48 -
cross-section perpendicular to the grooves having a shape
like a sine curve. The resultant first color-adjusting
layer had a refractive index of 1.43.
Subsequently, aluminum was deposited by a vacuum
deposition method onto the whole surface of the first 5 coloradjusting
layer 10 on which micro-protrusions and microdepressions
had been formed, to form microprotrusion/
depression reflective layer 20. The microprotrusion/
depression reflective layer 20 had a thickness of
10 50 nm on the flat parts of the first color-adjusting layer
10.
Subsequently, transparent resin having a refractive
index of 1.72 ("HX-101" available from Nissan Chemical
Industries, Ltd.) was applied onto the whole exposed surface
15 of the micro-protrusion/depression reflective layer 20 by a
roll coating method, and the coated film was dried to form
second color-adjusting layer 30 which covers the whole
surface of the micro-protrusion/depression reflective layer
20, to obtain a counterfeit preventing structure. The
20 second color-adjusting layer which was formed had a thickness
of 2 m in the flat parts.
(Comparative Example 1)
The procedure of Example 1 was repeated to obtain a
25 counterfeit preventing structure, except that the second
color-adjusting layer 30 having a thickness of 2 m and a
refractive index of 1.43 was formed by applying the ink
composition which had been used to form the first coloradjusting
layer 10 onto the micro-protrusion/depression
- 49 -
reflective layer 20 and irradiating the coated film with
ultraviolet light having an energy density of 300 mJ/cm2.
(Comparative Example 2)
The procedure of Example 1 was repeated to obtain a
counterfeit preventing structure, except that 5 transparent
resin having a refractive index of 1.5 ("HITAROID 7851"
available from Hitachi Chemical Co., Ltd.) was used for
forming the second color-adjusting layer 30.
(Comparison of Structural Color)
10 The color tone was visually evaluated under observation
from the direction perpendicular to the grooves of the
protrusion/depression structure and at the angle of 80° to
the principal plane of the counterfeit preventing structure,
in the counterfeit preventing structure. The results were
15 shown in Table 1 set forth below.
Table 1: Constitution and Structural Color of Counterfeit
Preventing Structures
Examples Refractive index
Color tone of structural
color
First
coloradjusting
layer
Second
coloradjusting
layer
Side of
first
coloradjusting
layer
(Side of
first
surface)
Side of
second
coloradjusting
layer
(Side of
second
surface)
Ex. 1 1.43 1.72 Blue Pink
- 50 -
C. Ex. 1 1.43 1.43 Blue Blue
C. Ex. 2 1.43 1.5 Blue Blue
As understood from Table 1, the counterfeit preventing
structure of Example 1 provided optical effects exhibiting
different color tones under observation from the front and
back sides. The counterfeit preventing structures 5 uctures of
Comparative Examples 1 and 2 exhibited the same color tone
under observation from the front and back sides, and no
special attributes were observed in these structures.
The optical effects exhibiting different color tones
10 under observation from the front and back sides are
especially effective in the case where the microprotrusion/
depression reflective layer 20 is disposed in the
part of the counterfeit preventing structure as shown in Fig.
1. If counterfeiting of these optical effects is intended,
15 supposed method might include the steps of: providing a
reflective layer, a first colored layer to be disposed onto
one surface of the reflective layer, and a second colored
layer to be disposed onto the other surface of the reflective
layer; and adhering the above three layers in a perfectly
20 registered state. However, counterfeiting for perfectly
reproduce the optical effects of the present invention is
difficult, since such perfect registering is very difficult.
Besides, examples exhibiting relatively sober color
tones of green and black colors are provided in the above25
described examples. However, it is possible to obtain
constitutions having greater design impression which provides
red color light with a metallic luster under observation from
- 51 -
the front side and green color light with a metallic luster
under observation from the back side, for example, by
selecting the constitution of the counterfeit preventing
structure (including the structure of the microprotrusion/
depression reflective layer 20, and 5 refractive
indices of the first color-adjusting layer 10 and the second
color-adjusting layer 30).
Reference Signs List
10 10 First color-adjusting layer
15 First precursor layer
20 Micro-protrusion/depression reflective layer
30 Second color-adjusting layer
31, 32 First and second second color-adjusting layers
15 100, 200, 300, 500, 600 Counterfeit preventing structure
110, 120, 210, 220, 310, 320, 510, 520, 610, 620, 630
Regions
- 52 -
WE CLAIM:
1. A counterfeit preventing structure comprising:
a micro-protrusion/depression reflective layer
having a first surface having micro-5 protrusions and
micro-depressions and a second surface opposite to the
first surface and having micro-protrusions and microdepressions;
a first color-adjusting layer provided on the at
10 least a part of the first surface and in contact with
the first surface; and
a second color-adjusting layer provided on the at
least a part of the second surface and in contact with
the second surface,
15 wherein:
the first color-adjusting layer has a refractive
index different from a refractive index of the second
color-adjusting layer;
the first and second surfaces of the micro20
protrusion/depression reflective layer have microprotrusion/
depression surfaces causing structure
colors by reflecting, interfering, diffracting,
scattering and/or absorbing light of at least a portion
of visible region;
25 optical effects obtained under observation from
the side of the first color-adjusting layer are
different from optical effects obtained under
observation from the side of the second color-adjusting
layer; and
- 53 -
the difference between refractive indices of the
first and second color-adjusting layers is 0.1 or more.
2. The counterfeit preventing structure according to Claim
1, wherein the micro-protrusion/depression 5 reflective
layer has the same protrusion/depression shape on the
first and second surfaces.
3. The counterfeit preventing structure according to Claim
10 1 or 2, wherein the micro-protrusion/depression
reflective layer has a protrusion/depression shape
which is rectangular in the vertical cross-section.
4. The counterfeit preventing structure according to Claim
15 1 or 2, wherein the micro-protrusion/depression
reflective layer has a protrusion/depression shape in
which a horizontal cross-sectional area varies
monotonously from the top to the bottom.
20 5. The counterfeit preventing structure according to any
one of Claims 1 to 4, wherein the microprotrusion/
depression reflective layer is provided at
the part of the counterfeit preventing structure, and
the counterfeit preventing structure further comprises
25 a protective layer covering the microprotrusion/
depression reflective layer and having the
same shape as the shape of the microprotrusion/
depression reflective layer.
- 54 -
6. The counterfeit preventing structure according to any
one of Claims 1 to 5, wherein the microprotrusion/
depression reflective layer consists of a
plurality of parts having different micro-protrusions
and micro-5 depressions.
7. The counterfeit preventing structure according to any
one of Claims 1 to 6, wherein the second color-adjusting
layer consists of a plurality of parts having different
10 refractive indices, and at least one of the parts of
the second color-adjusting layer has a different
refractive index from the refractive index of the first
color-adjusting layer.
15 8. A counterfeit preventing article comprising an article
including a transparent part and the counterfeit
preventing structure according to any one of Claims 1
to 6 disposed on the transparent part of the article.
20 9. The counterfeit preventing article according to Claim
8, wherein the article including the transparent part
is selected from the group consisting of a personal
authentication medium, securities, and a counterfeit
preventing medium for brand protection.
25
10. The counterfeit preventing article according to Claim
9, wherein the personal authentication medium includes
a description of personal information or stores
electronical data of personal information, and is
- 55 -
selected from the group consisting of a card, a passport,
and a mobile phone.
11. The counterfeit preventing article according to Claim
9, wherein the securities are selected from the grou5 p
consisting of a bill and a bank note.