KR20230080134A - Security pigment with dual color shifting function - Google Patents

Abstract

The present invention relates to a dual color conversion pigment comprising a first color conversion pigment and a second color conversion pigment, wherein the first color conversion pigment and the second color conversion pigment have a composite structure in which a dielectric layer is coated on both sides of the central layer, and the first color conversion pigment and the second color conversion pigment are observed as the same color or different colors depending on the viewing angle. The complex structure includes: a central layer; and dielectric layers formed on the upper and lower surfaces of the central layer, respectively, wherein the dielectric layers have a structure in which a first dielectric layer, a second dielectric layer, and a third dielectric layer are stacked, the first dielectric layer and the third dielectric layer are formed of the same metal oxide, the dielectric layer of the first color conversion pigment and the dielectric layer of the second color conversion pigment have the same optical thickness, and a security inks containing these dual color conversion security pigments may be used to form security elements which change color depending on the viewing angle. Accordingly, the present invention can be usefully used as a security element for visual identification when printing letters, numbers, characters, shapes, patterns, etc. on a security document.

Description

Security pigment with dual color shifting function}

The present invention relates to a dual color conversion security pigment, and more particularly, to a dual color conversion security pigment that appears as the same color or different colors depending on an observation angle.

[Assignment identification number] KOM2021_07

[Name of Department] Ministry of Strategy and Finance

[Research management institution] Korea Minting and Security Management Corporation

[Research project name] Securing future leading technology and advancing forgery and alteration technology

[Research Project Name] Creation of security ink for printing public security products and application solution IP

[Organizer] Korea Minting and Security Management Corporation

[Research period] 2021. 1. 01 ~ 2022. 12. 30. (2 years)

Hologram, watermark, security thread, silver thread for security products where forgery prevention is important, such as banknotes, securities, gift certificates, passports, ID cards, security labels, official documents, admission tickets, various tickets, and various containers and packaging Various security technologies such as security fiber, security ink, security printing, and color-shifting security elements are being applied.

Among them, the color conversion security element is a technology in which the observed color changes according to the viewing angle, and has the advantage of being able to easily identify authenticity with the naked eye without a separate authenticity identification device. has been developed

The color conversion effect cannot be reproduced by simple scanning and copying, so it is a very effective technology in terms of counterfeiting prevention. .

Various techniques have been proposed to counteract such counterfeiting. For example, US Patent No. 7611168 proposed a technique for enhancing security characteristics by combining a thin film interference layer and a diffraction pattern, and Korean Patent Publication No. 2004-0074073 Ho proposed a technique of disposing metal layers having different shades to achieve different shades. However, these technologies have disadvantages in that the implementation process is complicated, so the manufacturing cost is increased or the color conversion effect is insufficient.

To solve this problem, Korean Patent Registration No. 10-1534327 discloses a substrate, a concave pattern layer formed on the substrate and including a plurality of concave patterns, a color conversion layer formed on the concave pattern layer and changing color depending on the viewing angle, and the color A double color conversion security device comprising a protective layer covering an upper portion of the conversion layer so that it is not exposed to the outside, and characterized in that the color of the region where the concave patterns are formed and the background region where the concave patterns are not formed are different, Since a concave pattern is required to provide a color conversion effect, there is still a problem in that the implementation process is complicated.

Accordingly, a color conversion security element technology capable of providing more diverse visual effects through a simpler structure and implementation process is required.

Registered Patent No. 10-1534327 (registered on June 30, 2015)

In the present invention, it is intended to provide a dual color conversion security pigment that looks the same color in a normal view and different colors in a tilting view according to an observation angle.

One embodiment of the present invention for achieving the above object relates to a dual color conversion pigment comprising a first color conversion pigment and a second color conversion pigment.

The first color conversion pigment and the second color conversion pigment have a composite structure in which a dielectric layer is coated on both sides of a central layer, and the first color conversion pigment and the second color conversion pigment are observed as the same color according to a viewing angle, observed in different colors.

The composite structure includes a center layer and a dielectric layer respectively formed on top and bottom surfaces of the center layer, wherein the dielectric layer has a structure in which a first dielectric layer, a second dielectric layer, and a third dielectric layer are stacked, and the first dielectric layer and The third dielectric layer may be formed of the same metal oxide, and the dielectric layer of the first color conversion pigment and the dielectric layer of the second color conversion pigment may have the same optical thickness.

A refractive index of the second dielectric layer may be in the range of 1.47 to 2.0.

The refractive indices of the second dielectric layer of the first color conversion pigment and the second dielectric layer of the second color conversion pigment may differ by at least 0.4 or more.

The first dielectric layer and the third dielectric layer may include 5 to 20 wt% of Sn-TiO ₂ composite oxide and titanium dioxide (TiO ₂ ), respectively.

The Sn-TiO ₂ composite oxide may be prepared by mixing a Sn precursor and a Ti precursor.

The central layer may be formed of at least one of natural mica, synthetic mica, glass, alumina, silica, BiOCl and MgF ₂ .

The dual color conversion pigment of the present invention shows the same color seen from the front (vertical or normal view), but different colors from the side (inclined angle or tilting view), so that letters, numbers, characters, figures, In the case of printing with a pattern or the like, it can be usefully used as a security element for visual identification.

1 is a view for explaining color development according to the interference effect of color conversion pigments.
2 is a schematic cross-section of a composite structure of a first color conversion pigment and a second color conversion pigment.

Prior to a detailed description of the preferred embodiments of the present invention below, the terms or words used in the present specification and claims should not be construed as being limited to conventional or dictionary meanings, and meanings consistent with the technical spirit of the present invention. and should be interpreted as a concept.

Throughout this specification, when a certain component is said to "include", it means that it may further include other components without excluding other components unless otherwise stated.

Throughout this specification, “normal view” refers to observing an object at a vertical or near-vertical position, which means observing at an angle close to 0 degrees, and “tilting view” Means a case of observing the object to be observed at an oblique angle, preferably, it may be a case of observing at an inclination angle of 45 degrees.

Throughout this specification, "optical thickness" means the product of the refractive index and the actual thickness.

Throughout this specification, “%” used to indicate the concentration of a specific substance is (weight/weight)% for solid/solid, (weight/volume)% for solid/liquid, and liquid (weight/volume)%, unless otherwise specified. /liquid means (volume/volume)%.

Throughout this specification, since the refractive index of the dielectric used in the dual color conversion security pigment cannot be measured in practice, it was calculated using the theoretical refractive index and content ratio of a specific material.

Hereinafter, look at an embodiment of the present invention. However, the scope of the present invention is not limited to the following preferred embodiments, and those skilled in the art can implement various modified forms of the contents described herein within the scope of the present invention.

First, the dual color conversion pigment of the present invention includes a first color conversion pigment and a second color conversion pigment. Here, the first color conversion pigment and the second color conversion pigment included in the dual color conversion pigment are not in the form of a composition mixed together, but the first color conversion pigment and the second color conversion pigment are included separately from each other. do. That is, in the process of manufacturing and distribution before using the pigments, they are packaged separately from each other, and when the pigments are applied to the security document, each color conversion pigment may be printed on a different area of the security document.

The first color conversion pigment and the second color conversion pigment have a dual color conversion effect in which the same color or different colors are observed according to a viewing angle. More specifically, the same color is observed in normal view, and the first color conversion pigment and the second color conversion pigment are observed in different colors in tilting view. This characteristic comes from a structural difference between the first color conversion pigment and the second color conversion pigment, and will be described in detail below.

1 is a view for explaining color development according to the interference effect of color conversion pigments, and the structure and principle of interference effect pigments including color conversion pigments will be described with reference to FIG. 1 .

In the color conversion pigment, the first incident light (λ1) in the medium passes through the dielectric layer (coating layer) and is reflected at the interface with the central layer (substrate), and the transmitted light coming back to the medium and the first incident light (λ1) are parallel to the first incident light (λ1). 2 The color conversion effect can be found mathematically through the interference phenomenon between the incident light (λ2) and the reflected light reflected from the interface between the medium and the dielectric layer.

First, the simple geometric path difference between the first incident light λ1 and the second incident light λ2 is expressed as Equation (1) below.

In Equation (1), d is the thickness of the dielectric layer and φ is the incident angle. In addition, φ' is φ/n'', and n'' is a value obtained by dividing the refractive index (n) of the dielectric layer by the refractive index (n') of the medium.

In addition, here, the wavelength (λ') passing through the dielectric layer is a value obtained by dividing the incident light (λ) by the refractive index (n) of the dielectric layer, and is changed according to the refractive index of the dielectric layer. It is the same as Equation (2) below. In Equation (2), m is an interference order, which is 0 or a natural number.

Since the wavelength (λ') passing through the dielectric layer in Equation (2) is applied only to the 2d / cosφ' section, the amplified (constructive interference) wavelength (λ _max ) is equal to Equation (3) below, and incident light incident vertically For (φ = 0), it is the same as Equation (4).

From Equations (3) and Equations (4), two important clues to construct a dual color conversion security pigment can be obtained.

First, a normal view of the same color and a tilting view of different colors may be calculated and specified from changes in the refractive index (n) of the dielectric layer and the thickness (d) of the dielectric layer in the same interference order.

Second, as the interference order of the light path in the dielectric layer increases, a specific color of constructive interference repeatedly appears.

The present invention relates to a dual color conversion pigment having the same normal view color and different tilting view color based on the above first clue.

The first color conversion pigment and the second color conversion pigment constituting the dual color conversion pigment of the present invention have a composite structure in which dielectric layers are coated on both sides of the center layer.

2 is a schematic cross-section of the composite structure.

The composite structure, the center layer (110); and a dielectric layer 120 formed on the top and bottom surfaces of the center layer 110, respectively. The dielectric layer 120 includes a first dielectric layer 121, a second dielectric layer 122, and a third dielectric layer 123. It has a layered structure.

At this time, the composite structure may have a layered structure in which the dielectric layer 120 is formed only on the top and bottom surfaces of the center layer 110, as shown in FIG. 2, or similarly, the center layer 110 as well as the top and bottom surfaces This core may be formed in a core-shell structure in which the dielectric layer 120 forms a shell.

The center layer 110 may be at least one of natural mica, synthetic mica, glass, alumina, silica, BiOCl, and MgF ₂ . At this time, glass may be in a flake state, and alumina, silica, BiOCl, and MgF ₂ may be in a plate form. As the glass, for example, calcium aluminum borosilicate can be used.

The size of the particles forming the center layer 110 may have a top 90% particle size (D ₉₀ ) of 5 to 200 μm. If the top 90% particle size is too small, the aspect ratio (particle size to thickness (see FIG. 1)) lower, it is difficult to distinguish the dual color conversion effect phenomenon in which the tilting view colors of the first color conversion pigment and the second color conversion pigment are different, and if it is too large, there is a problem of poor printability when printing on a security document. It is preferable to use particles having a particle size.

The dual color conversion effect of the first color conversion pigment and the second color conversion pigment is represented by a difference in refractive index between the thickness of the dielectric layer 120 and the refractive index of the second dielectric layer 122 .

Specifically, the total optical thickness of the dielectric layer 120 of each of the first color conversion pigment and the second color conversion pigment is the same or similar, so that the same color appears in normal view, and the refractive index difference of each second dielectric layer 122 different colors in the tilting view.

The optical thickness of the dielectric layer 120 of the first color conversion pigment and the optical thickness of the dielectric layer 120' of the second color conversion pigment may be formed to be the same or similar. Accordingly, the same color may be observed in the normal view of the two color conversion pigments. Preferably, they may have the same optical thickness and the same interference order, because it may be difficult to implement the above-described dual color conversion effect if the interference orders are different from each other even if they have the same optical thickness.

At this time, since the refractive index of the center layer 110 is low, when the center layer 110 and the second dielectric layer 122 directly contact each other, the wave between the center layer 110 and the second dielectric layer 122 is reversed. The base surface reflection phenomenon, which is a reflection phenomenon, is weak, and thus, a problem in which saturation of the first color conversion pigment and the second color conversion pigment is lowered may occur. Therefore, in the present invention, in order to further improve the color visibility of the color conversion pigment, the first dielectric layer 121 having a refractive index exceeding 2.0 is first formed on the center layer 110, and then the second dielectric layer 122 is formed. .

In addition, when printing a pigment, it is generally used in the form of an ink composition mixed with a polymer resin. In general, the refractive index of the polymer resin is 1.4, and when the refractive index of the outermost dielectric layer in contact with the polymer resin approaches 1.4, the luminance is weak and the pigment Since it is difficult to apply as a security element due to low color visibility, in the present invention, the third dielectric layer 123 having a refractive index exceeding 2.0 is formed outside the second dielectric layer 122.

Among the dielectric layers 120 of the composite structure, the first dielectric layer 121 and the third dielectric layer 123 may be formed of the same metal oxide, and the metal oxide is a material having a refractive index exceeding 2.0, and thus the color It is possible to secure the luminance, chroma and color visibility of the conversion pigment.

Specifically, the metal oxide forming the first dielectric layer 121 and the third dielectric layer 123 includes Sn-TiO ₂ complex oxide and titanium dioxide (TiO ₂ ), among which the Sn-TiO ₂ complex oxide is 5 to 5 20 wt%. When such a metal oxide is used, it has a crystal structure in which Sn-TiO ₂ composite oxide is evenly dispersed inside titanium dioxide, so that the crystal lattice of titanium dioxide is formed in the rutile phase ( rutile phase), it is possible to increase the refractive index of the first dielectric layer 121 and the third dielectric layer 123 through a process of simply forming a dielectric layer.

It is preferable that the actual thickness of the first dielectric layer 121 and the third dielectric layer 123 is formed to be 40 to 60 nm in order to implement the above-described effect and the double color conversion effect.

Hereinafter, the first dielectric layer 121 and the third dielectric layer 123 will be described mainly in the case where they are formed of the same material, so the first dielectric layer 121 will be described, and this description will be the same for the third dielectric layer 123. can be applied

The first dielectric layer 121 may be formed by hydrolyzing a precursor of a metal oxide forming the first dielectric layer 121 on the center layer 110 . Specifically, a metal oxide coating layer may be formed by mixing the center layer 110 and a precursor solution including a metal oxide precursor.

More specifically, it may be performed by supplying a precursor solution to a solution containing a substrate forming the center layer 110 at a constant rate and reacting thereto. At this time, the reaction temperature may be 60 ~ 90 ℃, pH may be 1.5 ~ 2.0, if the pH is less than 1.5, the metal oxide is not attached to the surface of the center layer 110, it is difficult to form a coating layer, and if the pH exceeds 2.0, it is difficult to form a coating layer. Since the crystal lattice of titanium is not rutile, the basal surface reflection effect is weakened and the chroma of the color conversion pigment is lowered, so a pH adjuster such as sodium hydroxide may be used to maintain the pH within the above range during coating.

The precursor of the metal oxide may be SnCl ₄ as a tin precursor and TiOCl ₂ as a titanium precursor, and the precursor solution may be a mixture of these in an aqueous acid solution, and the aqueous acid solution may be an aqueous hydrochloric acid solution. Specifically, it may be a mixture of 3 to 10 wt% of a tin precursor, 50 to 70 wt% of a titanium precursor, and 23 to 43 wt% of an aqueous hydrochloric acid solution.

On the other hand, the second dielectric layer 122 determines the color of the color conversion pigment and, as described above, is a major factor that causes the first color conversion pigment and the second color conversion pigment to appear in different colors in the tilting view.

The second dielectric layer 122 is formed of a metal oxide different from that of the first dielectric layer 121 or the third dielectric layer 123 .

The refractive index of the second dielectric layer 122 may be 1.47 to 2.0, and when the refractive index of the first dielectric layer 122 is less than 1.47, the viewing angle at which an observer can observe one color is narrow, making it difficult to observe in normal view. , If it exceeds 2.0, there is a problem in that the color conversion effect does not appear because the color difference between the normal view and the tilting view is insignificant or the same color appears.

The second dielectric layer 122 may be formed of at least one metal oxide selected from the group consisting of SiO ₂ , Al ₂ O ₃ , TiO ₂ , ZrO ₂ , ZnO, Fe ₂ O ₃ and Fe ₃ O ₄ . At this time, it is more preferable to mix and use two or more metal compounds among the metal compounds listed above in an appropriate ratio to form a desirable refractive index of the second dielectric layer 122 .

The second dielectric layer 122 may be formed by mixing and reacting a precursor solution including a precursor of a metal oxide forming the second dielectric layer 122 after the coating of the first dielectric layer 121 is completed.

The second dielectric layer 122 may be directly processed in the same reactor after the coating of the first dielectric layer 121 is completed, or may be performed after washing and drying the substrate on which the coating of the first dielectric layer 121 is completed.

A metal oxide precursor for forming the second dielectric layer 122 is titanium oxychloride, titanium isopropoxide, titanium butoxide, titanium ethoxide, titanium sulfate, iron sulfate, iron chloride, iron nitrate, tetraethyl silicate, silicic acid. It may be at least one of sodium, silicon tetrachloride, aluminum chloride, sodium aluminate, aluminum sulfate, zirconium oxychloride, zirconium isopropoxide, zirconium butoxide, zirconium sulfate, zinc acetate, zinc chloride, zinc nitrate, and zinc sulfate, and , but not limited thereto.

A precursor solution for forming the second dielectric layer 122 may include a precursor of the metal oxide and an aqueous acid solution or an aqueous alkali solution.

When the second dielectric layer 122 is formed, the reaction temperature may be 60 to 90° C., the pH may be 6.5 to 7.5, and a pH adjusting agent such as hydrochloric acid or sodium hydroxide may be added during the reaction to maintain the pH.

At this time, as described above, the first color conversion pigment and the second color conversion pigment are included in the first color conversion pigment to implement a dual color conversion effect in which the same color is displayed in normal view and different colors are displayed in tilting view. It is preferable that the refractive index difference between the second dielectric layer 122 and the second dielectric layer 122' included in the second color conversion pigment has a difference of at least 0.4 or more. If the difference in refractive index is less than 0.4, the difference in color when observing the first color conversion pigment and the second color conversion pigment in a tilting view is insignificant, so that the dual color conversion effect is not implemented. Therefore, the difference in refractive index is at least 0.4 desirable.

In addition, while forming a refractive index difference between the second dielectric layer 122 included in the first color conversion pigment and the second dielectric layer 122' included in the second color conversion pigment to be 0.4 or more, as described above, the first color conversion In order to realize the same color in the normal view of the pigment and the second color conversion pigment, the dielectric layer 120 of the first color conversion pigment and the dielectric layer 120' of the second color conversion pigment have the same optical thickness as each other. The actual thickness of the second dielectric layer 122 included in the color conversion pigment and the second dielectric layer 122' included in the second color conversion pigment may be adjusted differently from each other.

Hereinafter, specific actions and effects of the present invention will be described through an embodiment of the present invention. However, this is presented as a preferred example of the present invention, and the scope of the present invention is not limited according to the examples.

[Production Example 1]

Precursor aqueous solution preparation step

First, 70 g of SnCl ₄ .5H ₂ O crystal particles were dissolved in 330 g of 10% aqueous hydrochloric acid solution, and 600 g of TiOCl ₂ aqueous solution (50% in terms of TiOCl ₄ ) was mixed and stirred to prepare a first precursor aqueous solution.

Next, 450 g of silicon dioxide powder having a medium particle size (D ₅₀ ) of 3 μm was added to 6 kg of a 30% sodium hydroxide aqueous solution and dissolved while heating, and 630 g of aluminum hydroxide having a medium particle size (D ₅₀ ) of 1.6 μm was added and stirred to stir the second precursor aqueous solution prepared.

491 g of anhydrous AlCl ₃ crystal particles were dissolved in 660 g of 10% hydrochloric acid aqueous solution, and 248 g of TiOCl ₂ aqueous solution was added and stirred to prepare a third precursor aqueous solution.

A fourth precursor aqueous solution was prepared by dissolving 129 g of anhydrous AlCl ₃ crystal particles in 300 g of 10% hydrochloric acid aqueous solution, adding 490 g of TiOCl ₂ aqueous solution and stirring.

dielectric layer coating step

First, 4L of deionized water and 400g of plate glass, which is a substrate for forming a center layer with a thickness of 1㎛ and a medium particle size (D ₅₀ ) of 20 to 40㎛, were mixed in a reactor, and the pH was adjusted to 1.7 using 10% aqueous hydrochloric acid solution, and then the pH was adjusted to 80 It was warmed up to °C.

Here, the first precursor aqueous solution was added at a rate of 1 ml / min, but the addition was stopped when the reflected color was white and a pale green (540 nm) interference color appeared to form a first dielectric layer on the surface of the substrate. At this time, an aqueous solution of sodium hydroxide was added to maintain the pH at about 1.7.

Next, co-stirring was performed for 30 minutes, and 30% sodium hydroxide aqueous solution was added to raise the pH to 7, followed by co-stirring for 10 minutes.

Here, the second precursor aqueous solution was added at a rate of 2 ml / min, but when the interference color of the normal view was purple (425 nm) of the second order of interference, the addition was stopped to form a second dielectric layer, and the pH during the reaction An aqueous hydrochloric acid solution was used to keep it at about 7.

Next, after co-stirring for 30 minutes, 10% aqueous hydrochloric acid was added to lower the pH to 1.7, followed by co-stirring for 10 minutes.

Here, the first precursor aqueous solution was added at a rate of 1 ml/min, but when the normal view turned green, the addition was stopped to form a third dielectric layer, and an aqueous sodium hydroxide solution was used to maintain the pH at about 1.7 during the reaction. did

Thereafter, the color conversion pigment having the first dielectric layer, the second dielectric layer, and the third dielectric layer formed on the upper and lower surfaces of the center layer is taken out of the reactor, dehydrated and washed three times, and then dried. The normal view is green and the tilting view is blue. The color conversion pigment of Example 1 was prepared.

[Production Example 2]

The color conversion pigments of Examples 2 to 6 and the color conversion pigments of Comparative Examples 1 and 2 were prepared by using the same method as in Preparation Example 1, but changing some processes as follows.

Example 2

A third precursor aqueous solution is used to form the second dielectric layer, and when the second dielectric layer is coated, the normal view is stopped when the second dielectric layer is purple, and when the third dielectric layer is coated, the normal view is green and the tilting view is cyan. did

Example 3

A third precursor aqueous solution is used to form the second dielectric layer, and when the second dielectric layer is coated, the normal view is stopped when the interference order is yellow (585 nm), and the third dielectric layer is coated. The normal view is blue and the tilting view is It was stopped when it was ultramarine blue.

Example 4

When the second dielectric layer was coated, it was stopped when the normal view was yellow (585 nm) of the first order of interference order, and when the third dielectric layer was coated, the normal view was stopped when it was blue and the tilting view was ultramarine blue.

Example 5

When the second dielectric layer was coated, it was stopped when the normal view was cyan (487 nm) of the second order of interference order, and when the third dielectric layer was coated, the normal view was stopped when it was yellow and the tilting view was blue.

Example 6

The third precursor aqueous solution is used to form the second dielectric layer, and when the second dielectric layer is coated, the normal view is stopped when the second dielectric layer is cyan (487 nm), and the normal view is yellow and the tilting view is yellow when the third dielectric layer is coated. It was stopped when it was light green.

Comparative Example 1

A fourth precursor aqueous solution was used to form the second dielectric layer, and the second dielectric layer was formed such that the calculated thickness of the second dielectric layer was 189 nm.

Comparative Example 2

When forming the first dielectric layer, the first dielectric layer was formed using the TiOCl ₂ aqueous solution instead of the first precursor aqueous solution.

[Experimental Example 1]

The refractive index of the second dielectric layer of each color conversion pigment prepared in Preparation Example 1 and Preparation Example 2 was calculated and listed in Table 1.

In addition, L * a * b * color coordinates in the normal view and the 45 degree tilting view of Examples 1 to 6, Comparative Example 1 and Comparative Example 2 using a CM-512M3 spectrophotometer (Minolta, Japan) It was measured, and the a* and b* values, which are indices of color, are listed in Table 1. In addition, the color was observed with the naked eye and described in the color item.

Refractive index of the second dielectric layer Normal view (0 degree) Tilting view (45 degrees) a* b* color a* b* color Example 1 1.55 -43 35 green 3 -36 blue Example 2 2.00 -40 28 green -32 -3 turquoise Example 3 2.00 4 -47 blue 25 -33 ultramarine blue Example 4 1.55 4 -44 blue 48 -35 purple Example 5 1.55 -5 60 yellow 7 -27 blue Example 6 2.00 -5 55 yellow -25 38 light green Comparative Example 1 2.10 -42 33 green -38 16 green Comparative Example 2 1.55 -27 21 green One -20 blue

Referring to Table 1, it can be seen that the colors of Example 1 and Example 2 are almost the same in the normal view, and the color difference is large in the tilting view. In addition, it was confirmed that the sets of Examples 3 and 4, and the sets of Examples 5 and 6 also show the same color in the normal view and different colors in the tilting view. It was confirmed that the same result was observed even when observed with the naked eye. Therefore, the combination of Example 1 and Example 2, the combination of Example 3 and Example 4, and the combination of Example 5 and Example 6 can be used as dual color conversion pigments. On the other hand, in the case of Comparative Example 1, normal It can be seen that there is no color conversion effect as it is observed as green in both the view and the tilting view. This is because the refractive index of the second dielectric layer exceeds 2.0. When the refractive index exceeds 2.0, the refractive index is too high, so that the normal view path difference and the tilting view path difference are less than the difference in wavelengths of visible light adjacent to each other. This is because there is no color change.

In the case of Comparative Example 2, there was a color change from green to blue, but the saturation was remarkably low, and it was difficult to observe the color change. In the structure, it is judged to be a problem that occurs because titanium dioxide does not form a rutile structure.

From these results, when the refractive index of the second dielectric layer is 2.00 or less and the refractive index of the first color conversion pigment and the second color conversion pigment differ by 0.4 or more, the same color appears in normal view and different colors appear in tilting view. I was able to confirm.

In addition, it was found that the metal oxide forming the first dielectric layer 121 and the second dielectric layer 123 is preferably a mixture of Sn-TiO ₂ composite oxide and titanium dioxide.

[Experimental Example 2]

In the color conversion pigments of Examples 1 to 6, the actual thickness, optical thickness, and interference order of the entire dielectric layer 120 were measured or calculated, and the refractive index, actual thickness, optical thickness, and interference order of the second dielectric layer 122 were measured. Orders were measured or calculated and summarized in Table 2. Among the items listed in Table 2, the calculated values were calculated using Equations (3) and (4).

dielectric layer (120) Second dielectric layer 122 real
Thickness (nm) optical
Thickness (nm) Interference order real
Thickness (nm) optical
Thickness (nm) refractive index Example 1 430 666 2 255 396 1.55 Example 2 333 666 2 198 396 2.00 Example 3 287 574 2 152 304 2.00 Example 4 370 574 2 196 304 1.55 Example 5 480 744 2 306 474 1.55 Example 6 372 744 2 237 474 2.00

Referring to the results of Tables 2 and 1 together, it can be seen that when the entire dielectric layer 120 has the same optical thickness, the same color is displayed in normal view. In addition, even if they have the same optical thickness, if the refractive indices of the second dielectric layer 122 are formed to be different from each other, it can be seen that different colors appear in the tilting view.

[Experimental Example 3]

Embodiments 1 and 2 were applied to different areas to print security elements, and pictures were taken observing them in a normal view (0 degree) and a tilting view (45 degrees), and the results are shown in FIG. 3 . Specifically, Example 1 was applied to the upper arrow and Example 2 to the lower arrow.

Referring to FIG. 3 , it was confirmed that Example 1 and Example 2 exhibited the same green color when observed in a normal view, whereas Example 1 exhibited a blue color and Example 2 exhibited a cyan color when observed in a tilting view.

The present invention is not limited to the specific embodiments and descriptions described above, and various modifications can be made by anyone skilled in the art without departing from the gist of the present invention claimed in the claims. and such modifications are within the protection scope of the present invention.

100: double color conversion security pigment 110: center layer
120: dielectric layer 121: first dielectric layer
122: second dielectric layer 123: third dielectric layer

Claims (6)

In the dual color conversion pigment comprising a first color conversion pigment and a second color conversion pigment,
The first color conversion pigment and the second color conversion pigment have a composite structure in which dielectric layers are coated on both sides of the center layer,
The first color conversion pigment and the second color conversion pigment are observed as the same color or different colors depending on the viewing angle,
The composite structure,
central layer; and
Including; dielectric layers respectively formed on the upper and lower surfaces of the center layer,
The dielectric layer has a structure in which a first dielectric layer, a second dielectric layer, and a third dielectric layer are stacked,
The first dielectric layer and the third dielectric layer are formed of the same metal oxide,
A dual color conversion pigment, characterized in that the dielectric layer of the first color conversion pigment and the dielectric layer of the second color conversion pigment have the same optical thickness as each other. According to claim 1,
The refractive index of the second dielectric layer is characterized in that the range of 1.47 ~ 2.0, dual color conversion pigment. According to claim 2,
The refractive index of the second dielectric layer of the first color conversion pigment and the second dielectric layer of the second color conversion pigment is at least 0.4 or more, characterized in that, the dual color conversion pigment. According to claim 1,
The first dielectric layer and the third dielectric layer each contain 5 to 20 wt% of Sn-TiO ₂ composite oxide and titanium dioxide (TiO ₂ ). Characterized in that, the dual color conversion security pigment. According to claim 4,
The Sn-TiO ₂ composite oxide is characterized in that prepared by mixing a Sn precursor and a Ti precursor, a dual color conversion security pigment. According to claim 1,
The central layer is formed of at least one of natural mica, synthetic mica, glass, alumina, silica, BiOCl and MgF ₂ , Dual color conversion security pigment.

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