Patent Application
20200009895
The present invention relates to a security ink pigment, a security ink, a printed matter, and a method of producing the security ink pigment.
Printed on a material to be printed is a coat which forms an image, which is a latent image not visually recognized with naked eyes under normal conditions but becomes a visual image visually recognized with the naked eyes under ultraviolet light irradiation, in order to enhance security of a printed matter for preventing forgery of the printed matter, for example. Ink used for printing the coat is referred to as a security ink, for example. A technique described in Patent Document 1 is an example thereof.
Techniques described in Patent Documents 2 and 3 relate to the invention described in the detailed description of the invention.
In the technique described in Patent Document 2, phosphor microparticles, which are perovskite-type oxides each having a composition expressed as a composition formula of BaSnO3 and converting light in an ultraviolet region into light in an infrared region, are used for enhancing power generation efficiency of a solar battery.
In the technique described in Patent Document 3, luminous particles, each of which is expressed as a general expression of Ba1-xSnAxO3, A being Li or Na and x satisfying 0<x<0.4, and which emit infrared light when being irradiated with UV light, are used for a security film. In the technique described in Patent Document 3, an average particle diameter of the luminous particles is preferably 0.3 to 5.0 μm.
A conventional technique typified by the technique described in Patent Document 1 contributes to a security enhancement of a printed matter. However, a lamp which emits ultraviolet light is easily available in recent years, so that it is often the case that the security enhancement of the printed matter cannot be sufficiently expected from the conventional technique typified by the technique described in Patent Document 1.
If a latent image formed by a coat printed on the material to be printed for the security enhancement of the printed matter becomes a visual image, it is desired that the visual image is clear.
The present invention is to solve these problems. A problem to be solved by the present invention is to enhance security of a printed matter, and make a visual image be clear if a latent image formed by a coat printed on a material to be printed for the security enhancement of the printed matter becomes the visual image.
A main constituent of a powder contained in a security ink pigment is a perovskite-type oxide which is expressed as a general formula of ABO3, A being mainly made of Ba and B being mainly made of Sn. The powder emits infrared fluorescence when being irradiated with ultraviolet excitation light. The perovskite-type oxide has a crystal lattice constant having a difference equal to or smaller than 0.002 angstrom from a theoretical crystal lattice constant of the perovskite-type oxide having a composition expressed as a composition formula of BaSnO3.
According to the present invention, a security of a printed matter is enhanced, and a visual image is clear if a latent image formed by a coat printed on a matter to be printed for the security enhancement of the printed matter becomes the visual image.
These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.
1.1 Printed Matter
A schematic diagram in
A printed matter 1000 illustrated in
The pigment 1040 is a fluorescent body emitting infrared fluorescence when being irradiated with ultraviolet excitation light. Accordingly, an image formed by the coat 1022 printed on the paper sheet 1020 is not visually recognized when not being irradiated with the ultraviolet light, and is not visually recognized with naked eyes even when being irradiated with the ultraviolet light. The image becomes a visual image when the image is irradiated with the ultraviolet light and taken with infrared camera. Accordingly, the image is helpful in enhancing the security of the printed matter 1000 for preventing forgery of the printed matter 1000, for example.
The pigment 1040 needs to be a fluorescent body having internal quantum efficiency (IQE) of 10% or more to make the visual image clear. The IQE serves as a barometer indicating the clearness of the visual image.
The pigment 1040 needs to be made up of powder having median diameter of 10 μm or less (D50) so that the coat 1022 is printed by a normal printing process and is flat and smooth. D50 serves as a barometer indicating print performance. However, the coat 1022 is printed by a normal printing process and is flat and smooth in some cases even when the pigment 1040 is made up of powder having median diameter D50 larger than 10 μm.
1.2 Security Ink
A schematic diagram in
A security ink 1100 illustrated in
When the security ink 1100 is used for printing the coat 1022, the security ink 1100 is applied to the paper sheet 1020, a volatile constituent contained in the vehicle 1122 is volatilized, and the pigment 1040 is firmly fixed to the paper sheet 1020 by the solid 1042 contained in the vehicle 1122.
1.3 Pigment
The pigment 1040 is made up of the powder emitting the infrared fluorescence when being irradiated with the ultraviolet excitation light.
A main constituent of the powder is a perovskite-type oxide. The powder may contain a small amount of accessory constituent.
The perovskite-type oxide has a composition expressed as a general formula of ABO3. A is mainly made of Ba. B is mainly made of Sn. A may contain an element other than Ba. For example, A may contain Zn. B may contain an element other than Sn. The perovskite-type oxide preferably has a composition expressed as a general formula of Ba1-xSnZnxO3, x satisfying 0≤x≤0.2.
The pigment 1040 illustrated in
The IQE of the pigment 1040 depends on an primary particle diameter which is a particle diameter of the primary particles 1202. A specific surface area reflecting the primary particle diameter needs to be equal to or larger than 0.079 m2/g and equal to or smaller than 10 m2/g so that the pigment 1040 is the fluorescent body having the IQE of 10% or more. It is considered that the IQE is reduced in a case where the specific surface area is larger than 10 m2/g and the primary particle diameter is too small by reason that a surface defect such as un unpaired electron dangling bond inhibits the fluorescent emission. It is considered that the IQE is reduced in a case where the specific surface area is larger than 0.079 m2/g and the primary particle diameter is too large by reason that the excitation light does not reach inside the primary particles 1202, so that efficiency of the fluorescent emission is reduced.
In addition, the IQE of the pigment 1040 depends on crystalline nature of the perovskite-type oxide. It is preferable that a difference of a crystal lattice constant of the perovskite-type oxide, which is the main constituent of the powder, from a theoretical crystal lattice constant of the perovskite-type oxide of 4.1163 having a composition expressed as a composition formula of BaSnO3 is equal to or smaller than 0.002 angstrom so that the pigment 1040 is the fluorescent body having the IQE of 10% or more.
Smoothness of the coat 1022 depends on an aggregated secondary particle diameter which is a particle diameter of the aggregated secondary particles 1200. D50 reflecting the aggregated secondary particle diameter need to be equal to or smaller than 10 μm so that the coat 1022 is printed by a normal printing process and is flat and smooth. A particle size distribution serving as a basis for calculation of D50, which is the particle size distribution diameter, is measured by a laser diffraction scattering method.
1.4 Production of Pigment
A heat-treated powder is prepared in Step S101 illustrated in
For the preparation of the heat-treated powder, powders of starting materials are prepared, the prepared powders of the starting materials are mixed with each other and mixed powder is prepared, and the prepared mixed powder is heat-treated. The powders of the starting materials contained in the mixed powder react to each other during the heat treatment. Each of the powders of the starting materials is an oxide of a constituent element constituting the perovskite-type oxide other than oxygen. The oxide of the constituent element may be replaced with a precursor which becomes the oxide of the constituent element during the heat treatment. The precursor is carbonate, nitrate, or oxalate, for example.
As illustrated in
In Step S102 subsequent to Step S101, when the condition described above occurs, a miniaturization process of reducing the size of D50 without drastically changing the specific surface area is performed on the prepared heat-treated powder. The pigment powder having the specific surface area ranging from 0.079 m2/g to 10 m2/g and D50 equal to or smaller than 10 μm is thereby obtained. When the condition described above does not occur, the heat-treated powder obtained without Step S102 may become the pigment powder without change. However, Step S102 may be performed to further enhance the print performance even when the condition described above does not occur.
In the miniaturization process, a classification or a wet dispersion is preferably performed. The wet dispersion may be a dispersion by a wet jet mill or a wet bead mill, or may be an ultrasonic dispersion. In the wet dispersion, cracking force is made to act on the heat-treated powder which has been dispersed in a dispersion medium, and the aggregated secondary particle constituting the heat-treated powder is cracked to be the smaller aggregated secondary particles or the primary particles.
When the classification is performed in the miniaturization process, small particles 1262 are extracted from particles 1260 constituting the heat-treated powder 1240, and a pigment powder 1242 is obtained, as illustrated in
When the wet dispersion is performed in the miniaturization process, aggregated secondary particle 1300 constituting a heat-treated powder 1280 is cracked to be small aggregated secondary particles 1302 or primary particles 1304, and a pigment powder 1282 is obtained, as illustrated in
When the dry grinding is performed by a disk mill or a hammer mill, for example, in the miniaturization process, aggregated secondary particle 1340 constituting a heat-treated powder 1320 is cracked to be small aggregated secondary particles 1342 or primary particles 1344, and a pigment powder 1322 is obtained, as illustrated in
1.5 Effect of Zn
It is predicted that Zn has a role as a sintering aid contributing to enhancement of wettability, for example. Accordingly, in the case where Zn is contained as illustrated in
A list of “BS/no miniaturization process” in Table 1 indicates a heat treatment temperature and a physical property value of the pigment powder for each of Examples 1 to 6 and Comparative Example 1 in which a perovskite-type oxide has a composition expressed as a composition formula of BaSnO3 and the miniaturization process has not been performed.
A list of “BSZ/no miniaturization process” in Table 1 indicates a heat treatment temperature and a physical property value of the pigment powder for each of Examples 7 to 12 and Comparative Example 2 in which the perovskite-type oxide has the composition expressed as a composition formula of Ba0.99SnZn0.05O3 and the miniaturization process has not been performed.
A list of “BS/classification” in Table 1 indicates a heat treatment temperature and a physical property value of the pigment powder for each of Examples 13 to 15 in which a perovskite-type oxide has a composition expressed as a composition formula of BaSnO3 and a classification has been performed in the miniaturization process.
A list of “BS/wet dispersion” in Table 1 indicates a heat treatment temperature and a physical property value of the pigment powder for each of Examples 16 to 18 in which a perovskite-type oxide has a composition expressed as a composition formula of BaSnO3 and a wet dispersion using a jet mill has been performed in the miniaturization process.
A list of “BS/dry grinding” in Table 1 indicates a heat treatment temperature and a physical property value of the pigment powder for each of Comparative Examples 3 to 5 in which a perovskite-type oxide has a composition expressed as a composition formula of BaSnO3 and a dry grinding using a disk mill has been performed in the miniaturization process.
In the Examples 1 to 6 and Comparative Example 1, powders of barium carbonate (BaCO3) and tin oxide (SnO2), which are starting materials, were weighed so that a molar ratio between barium (Ba) atom and tin (Sn) atom is 1:1, and the weighed powders were mixed and ground to obtain a mixed powder. The powders were mixed and ground by putting the weighed powders into a mortar and further putting an appropriate amount of ethanol into the mortar to obtain a paste-like material, and grinding the paste-like material until ethanol was volatilized and the dried mixed powder was obtained. The obtained mixed powder was put into a high-purity alumina crucible and sintered at a heat treatment temperature indicated by Table 1 in an air atmosphere to synthesize the heat-treated powder. In the Examples 1 to 6 and Comparative Example 1, the miniaturization process was not performed on the heat-treated powder which had been synthesized by a solid phase process, but the heat-treated powder which had been synthesized was adopted to the pigment powder without change.
In the Examples 7 to 12 and Comparative Example 2, the heat-treated powder was synthesized in a manner similar to Examples 1 to 6 and Comparative Example 1 except that powders of barium carbonate (BaCO3), tin oxide (SnO2), and zinc nitrate hexahydrate (Zn(NO3)2.6H2O), which are starting materials, were weighed so that a molar ratio between barium (Ba) atom, tin (Sn) atom, and zinc (Zn) atom is 0.995:1:0.005. Also in the Examples 7 to 12 and Comparative Example 2, the miniaturization process was not performed on the heat-treated powder which had been synthesized, but the heat-treated powder which had been synthesized was adopted to the pigment powder without change.
In the Example 13, the Example 14, and the Example 15, the heat-treated powder was synthesized in the manner similar to the Example 6, the Example 4, and the Example 1, respectively. In the Examples 13 to 15, the classification was performed on the heat-treated powder, which had been synthesized, to obtain the pigment powder. The classification was performed by an air classifier, turbo classifier TC15NS manufactured by Nissin Engineering Inc.
In the Example 16, the Example 17, and the Example 18, the heat-treated powder was synthesized in the manner similar to the Example 6, the Example 4, and the Example 1, respectively. In the Examples 16 to 18, the wet dispersion was performed on the heat-treated powder, which had been synthesized, to obtain the pigment powder. The wet dispersion was performed by a jet mill G-smasher (model code PML1000) manufactured by RIX CORPORATION. In the wet dispersion, ethanol was added to the heat-treated powder, which had been synthesized, to obtain slurry, and the dispersion processing was performed on the obtained slurry, and the slurry on which the dispersion processing had been performed was dried to obtain the pigment powder. An air injection pressure was 0.6 MPa in the dispersion processing. The processing was performed once.
In the Comparative Example 3, the Comparative Example 4, and the Comparative Example 5, the heat-treated powder was synthesized in the manner similar to the Example 6, the Example 4, and the Example 1, respectively. In the Comparative Examples 3 to 5, the dry grinding was performed on the heat-treated powder to obtain the pigment powder. The dry grinding was performed by a vibration disk mill RS200 manufactured by Retsch GmbH. A total number of rotations in the dry grinding was 1000 rpm.
The specific surface area, D50, the IQE, and the crystal lattice constant of the pigment powder of each of the Examples 1 to 18 and the Comparative Examples 1 to 5 were measured. The diameter calculated in terms of the specific surface area was obtained from the measured specific surface area, the difference of the crystal lattice constant was obtained from the measured crystal lattice constant, and the ratio of D50 to the diameter calculated in terms of the specific surface area was obtained from the obtained diameter calculated in terms of the specific surface area and the measured D50. Table 1 indicates results thereof. The diameter calculated in terms of the specific surface area 6/ρs is obtained using a density ρ=7.24 g/cm3 of BaSnO3 and the specific surface area s, and can be equated with the primary particle diameter. Moreover, shapes of particles constituting the pigment powders of the Examples 1 to 18 and the Comparative Examples 1 to 5 were observed by a scanning electron microscope.
The specific surface area was measured by a specific surface area measurement device Macsorb hm1208 manufactured by Mountech CO., Ltd. Nitrogen was used as an absorbent in the measurement, and an absorption temperature was 77 k.
D50 was measured by a laser diffraction/scattering particle diameter distribution measurement device LA950V2 manufactured by HORIBA, Ltd. In the measurement, the obtained pigment powder and an ultralow amount of dispersant were added to water, which was a dispersion medium, to disperse the pigment powder in the water. ARON A6114 manufactured by Toagosei Co., Ltd was used as the dispersant. ARON A6114 contains ammonium acrylate copolymer.
The IQE was measured by fluorospectrophotometer FP8600 manufactured by JASCO Corporation. An integrating sphere unit ISF834 of 60 mmφ and a fluorescent cell of 16 mmφ were used for the measurement, and a wavelength range of excitation light was set to 350 to 380 nm, and a measurement wavelength range of fluorescence was set to 750 to 1010 nm.
The crystal lattice constant was measured by an X-ray diffraction device D8 advance manufactured by Brucker Corporation. In the measurement, a crystal phase was identified by a powder X-ray diffraction (XRD) using CuKα ray to obtain an X-ray diffraction pattern, and a Reitveld analysis was performed on the obtained X-ray diffraction pattern using a crystal structure analysis software TOPAS, and the crystal lattice constant was refined to obtain the crystal lattice constant.
The difference of the crystal lattice constant was obtained by subtracting the theoretical crystal lattice constant of BaSnO3 of 4.1163 from the obtained crystal lattice constant.
The shapes of the particles were observed by a scanning electron microscope S-3400N manufactured by Hitachi High-Technologies Corporation. In the observation, an ultrasonic dispersion processing was performed for approximately 10 seconds on the small amount of pigment powder to which ethanol was added to obtain slurry, the obtained slurry was collected by a dropper, and the collected slurry was dropped on an observation stage to obtain a dry substance.
Evaluated were clearness of the coat containing the pigment powder of the Examples 1 to 18 and the Comparative Examples 1 to 5 and print performance of the pigment powder of the Examples 1 to 18 and the Comparative Examples 1 to 5. Table 2 indicates results thereof. A clearness A indicates that the coat is extremely clear. A clearness B indicates that the coat is clear. A clearness C indicates that the coat is dark. A print performance A indicates that the coat is flat and smooth to a finger touch. A print performance B indicates that the coat is almost flat and smooth to a finger touch. A print performance C indicates that the coat is rough to a finger touch. It is understood from the IQE indicated by Table 1 and the clearness indicated by Table 2 that the clearness tends to be enhanced with increase in the IQE, and the clearness becomes A or B in a case where the IQE is equal or higher than 10%. It is understood from D50 indicated by Table 1 and the print performance indicated by Table 2 that the print performance tends to be enhanced with decrease in D50, the print performance becomes A or B in a case where D50 is equal to or smaller than 10 μm, and the print performance becomes A in a case where D50 is equal to or smaller 5 μm.
The primary particles grow up as the heat treatment temperature changes from a low temperature to a high temperature. Accordingly, as illustrated in
As illustrated in
As illustrated in
As indicated by arrows 1400, 1402, 1404, 1406, 1408, and 1410 shown in
In contrast, as indicated by arrows 1412, 1414, and 1416 shown in
As illustrated in
The Example 4 and the Example 17 are different from each other in that the wet dispersion is not performed in the Example 4, however, the wet dispersion is performed in the Example 17. Accordingly, it is understood from the particle size distribution illustrated in
It is understood from the optical spectrum of excitation light and fluorescence illustrated in
It is understood from the X-ray diffraction pattern illustrated in
It is understood from the shapes of the particles constituting the pigment powder of the Example 4 illustrated in
It is also understood from the shapes of the particles constituting the pigment powder of the Example 6 illustrated in
The Example 4 and the Example 6 are different from each other in that the heat treatment temperature is 1422° C. in the Example 4, however, the heat treatment temperature is 1750° C. in the Example 6. In contrast, it can be grasped from the shapes of the particles constituting the pigment powder of the Example 6 illustrated in
The Example 4 and the Example 17 are different from each other in that the wet dispersion is not performed in the Example 4, however, the wet dispersion is performed in the Example 17. In contrast, it is grasped from the shapes of the particles constituting the pigment powder of the Examples 4 and 17 illustrated in
The ultraviolet light with which the powders are irradiated is ultraviolet light having a wavelength of 365 nm emitted from a handy UV light SLUV-6 manufactured by AS ONE Corporation. A distance from the light to the pigment powders is 5 cm, and illuminance is 130 LUX. The observation was performed using an infrared light viewer type 1700c manufactured by Japan Medical Services, Inc. in an infrared light camera.
The pigment powder of the Example 4, the pigment powder of the Example 7, the pigment powder of the Comparative Example 1, and a material powder, which has not been sintered yet, of the pigment powder of the Example 1 are put in bottles 1500, 1501, 1502, and 1503 illustrated in
It is understood from
The present invention has been shown and described in detail, the foregoing description is in all aspects illustrative and not restrictive. It is therefore understood that numerous modifications and variations can be devised without departing from the scope of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| PCT/JP2017/008721 | Mar 2017 | JP | national |
This application is a continuation application of PCT/JP2018/001377, filed Jan. 18, 2018, which claims priority to PCT/JP2017/008721, filed Mar. 6, 2017, the entire contents all of which are incorporated hereby by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2018/001377 | Jan 2018 | US |
| Child | 16552510 | US |
