JP2024088849A - Infrared luminescent ink composition, anti-counterfeiting printed matter and method for determining authenticity - Google Patents

Abstract

【assignment】
The present invention provides an infrared luminescent ink composition and an anti-counterfeiting printed matter that have luminescent properties that are difficult for counterfeiters to imitate and that have good luminescent intensity and acid resistance.
SOLUTION
The present invention is an infrared-emitting ink composition characterized in that a first infrared emitter and a second infrared emitter have the same emission wavelength range, the first infrared emitter has a higher emission intensity in at least one excitation wavelength range in each of the ultraviolet range, the visible light range, and the near-infrared range than the second infrared emitter, the second infrared emitter has higher acid resistance than the first infrared emitter, the first infrared emitter and the second infrared emitter have at least one excitation peak wavelength in each wavelength range, and at least one of the excitation peak wavelengths is different between the first infrared emitter and the second infrared emitter.
[Selected figure] Figure 5

Description

The present invention relates to anti-counterfeiting printed matter using infrared emitting materials.

There is a demand for advanced anti-counterfeiting and authenticity determination technologies to be added to anti-counterfeiting printed materials (hereinafter referred to as "anti-counterfeiting printed materials"), including banknotes, passports, revenue stamps, securities, identification documents, various tickets, and security labels. One of these anti-counterfeiting and authenticity determination technologies is a method in which an illuminant (hereinafter referred to as "infrared illuminant") is added that emits light in the near-infrared region invisible to the human eye when irradiated with light of a specific wavelength, and the illuminant is detected by a reading device to determine authenticity.

The infrared emitting material used in this method is white, has low coloring power, and is difficult to see, so a pattern with the infrared emitting material can be formed as a latent image. It can also be used in combination with other coloring pigments, which conceals the presence of the emitting material and makes it difficult to know that an infrared emitting material has been added. This feature can be overlooked in the event of counterfeiting or alteration, making accurate imitation difficult.

Examples of such infrared emitters include Nd _0.5 Yb _0.2 Na ₅ (WO ₄ ) ₄ and Nd _0.9 Yb _0.1 Na ₅ (MoO ₄ ) ₄ (for example, Patent Document 1), Nd _0.1 Yb _0.1 Gd _0.1 Y _0.7 PO ₄ (for example, Patent Document 2), Li(Nd,Yb)P ₄ O ₁₂ (for example, Patent Document 3), (Lu,Yb,Nd) ₂ O ₂ S (for example, Patent Document 4), Ca _k D ₁ (A _1-x-y ,Nd _x ,Yb _y ) ₂ (RO ₄ ) _m (D=Li, Ag, Al, Ga, In; A=Sc, Y, La, Gd, Lu, Al, Ga, In; R=Mo, W, V) (for example, Patent Document 5) is disclosed.

Japanese Patent Application Laid-Open No. 54-100991 Patent No. 3438188 Patent No. 2756852 JP 2010-132750 A JP 2011-21161 A

However, the infrared emitters described in Patent Documents 1, 2, and 3 are easily dissolved in water, and this tendency is particularly pronounced in acidic atmospheres. For this reason, there is a risk that the emission intensity will decrease significantly in humid or especially acidic atmospheres.

The infrared emitter described in Patent Document 5 has good chemical stability and good luminescence characteristics, but compared to the infrared emitter described in Patent Document 4, it has high luminescence intensity and high resistance to alkali, but relatively low resistance to acid, which raises concerns about its use in anti-counterfeiting printed materials that require robustness.

The infrared emitter described in Patent Document 4 has good chemical stability and good luminescence characteristics, but when compared to the infrared emitters described in Patent Documents 1, 2, 3, and 5, the emission intensity is actually lower for the same mass, and there is a problem that when high emission intensity is required, a relatively large amount (high content) must be used.

When a single material does not provide the desired characteristics, a method of mixing multiple materials is commonly used. However, when mixing two or more infrared emitters with different characteristics, depending on the combination of infrared emitters, the suitability of the infrared emitters may hinder each other's functional effects, resulting in a decrease in luminous intensity and acid resistance.

In addition, if two or more types of infrared emitters with excitation and emission characteristics in different wavelength ranges are mixed to produce two different emission characteristics, there is a risk that a person familiar with the luminescence phenomenon (a counterfeiter) could understand the emission characteristics and imitate similar emission characteristics by blending two or more types of infrared emitters with similar emission characteristics.

Furthermore, when two or more types of infrared emitters with excitation characteristics in different wavelength ranges are mixed, the emission characteristics of the infrared emitters can be read using two simple reading methods, so there is a risk that the luminescent material may be identified.

The present invention aims to solve the above problems by mixing two infrared emitters that have partially different excitation characteristics in the same wavelength range but have the same emission characteristics, which allows reading in a single wavelength range in the same way as when one type of infrared emitter is used, and by utilizing the partially different excitation characteristics to make the reading method more complex, it is difficult for counterfeiters to imitate the emission characteristics, and provides an infrared emitting ink composition and anti-counterfeiting printed matter that have good emission intensity and acid resistance.

The present invention is an infrared-emitting ink composition that contains at least a first infrared emitter and a second infrared emitter, the first infrared emitter and the second infrared emitter having substantially the same emission wavelength range, the first infrared emitter having a higher emission intensity in at least one excitation wavelength range in each of the ultraviolet range, the visible light range, and the near-infrared range than the second infrared emitter, the second infrared emitter having a higher acid resistance than the first infrared emitter, the first infrared emitter and the second infrared emitter having at least one excitation peak wavelength in each wavelength range, and at least one of the excitation peak wavelengths being different between the first infrared emitter and the second infrared emitter.

The present invention is an anti-counterfeiting printed matter characterized by having a printed image with a first information pattern formed from an infrared-emitting ink composition on at least a portion of a substrate.

The present invention is an anti-counterfeiting printed matter characterized in that the printed image further has at least one of a second information pattern formed by a second infrared-emitting ink composition containing a first infrared-emitting body or a third information pattern formed by a third infrared-emitting ink composition containing the second infrared-emitting body, adjacent to or close to the first information pattern.

The present invention is a method for determining the authenticity of an anti-counterfeit printed matter, comprising an irradiation step of irradiating a printed image with at least one of a first irradiation wavelength in a wavelength range that excites both a first infrared emitting element and a second infrared emitting element, or a second irradiation wavelength different from the first irradiation wavelength in a wavelength range that excites both, and a third irradiation wavelength in a wavelength range that excites the second infrared emitting element, which is different from the first irradiation wavelength and the second irradiation wavelength; a detection step of detecting the emission intensity for each irradiation wavelength of the printed image in the irradiation step; and a discrimination step of comparing the emission intensity detected in the detection step with the emission intensity of a genuine product and judging the authenticity based on whether it is within a reference value range of the emission intensity of a genuine product.

The present invention provides an infrared-emitting ink composition and anti-counterfeiting printed matter that have high luminescence properties, excellent acid resistance, and can be read in a single wavelength range in the same way as when a single type of infrared emitter is used, and that have luminescence properties that are difficult to imitate or identify by making the reading method more complex by utilizing some different excitation properties.

FIG. 1 is a diagram showing an example of an anti-counterfeit printed matter of the present invention. FIG. 1 is a diagram showing an example of an anti-counterfeit printed matter of the present invention. FIG. 1 is a diagram showing an example of an anti-counterfeit printed matter of the present invention. FIG. 2 is an example diagram showing a fluorescence spectrum of an infrared light-emitting body of the present invention. FIG. 2 is an example diagram showing an excitation spectrum of an infrared light emitter of the present invention. FIG. 13 is a diagram showing an example of a detection result according to the present invention. FIG. 2 is a diagram showing an example of the authenticity determination method of the present invention. FIG. 2 is a diagram showing an example of the authenticity determination method of the present invention. FIG. 11 is a diagram showing an example of a detection result according to the embodiment of the present invention. FIG. 2 is a diagram showing an example of the authenticity determination method of the present invention.

The following describes in detail the form for carrying out the present invention. Note that the present invention is not limited to the following embodiment, and should be understood to include various modified forms that are implemented within the scope that does not change the gist of the present invention.

(Embodiment)
An embodiment of the present invention will be described with reference to Fig. 1. As shown in Fig. 1, the anti-counterfeiting printed matter (1) of the present invention has, on at least a part of a substrate (2), a printed image (9) having a first information pattern (4) formed by an infrared emitting ink composition containing a first infrared emitter (7) and a second infrared emitter (8).

There are no particular limitations on the substrate (2) so long as it can be printed on, and it is preferably a material (substance) that does not absorb in the wavelength range absorbed or emitted by the infrared emitter, and known materials such as paper, plastic film, metal, foil, and other sheets, and molded products such as tags and cans can be used. For the same reason, there are no particular limitations on the color of the substrate (2), but when considering authenticity discrimination, it is preferable for the color to be one that does not absorb in the wavelength range absorbed or emitted by the infrared emitter.

(Printed image)
Next, the printed image (9) will be described. In Fig. 1 and Fig. 2, only the first information pattern (4) is included in the printed image (9), so the printed image (9) and the first information pattern (4) are the same. Fig. 1(a) shows an example in which the polygonal first information pattern (4) is formed on the substrate (2) by solid printing, but it may be formed by lines or halftone dots. In addition, as shown in Fig. 1(b) to Fig. 1(d), the shape of the first information pattern (4) is not particularly limited as long as it can detect infrared emission and be used for authenticity discrimination, and it can be formed in any shape such as a square, a circle, a triangle, etc.

Furthermore, the first information pattern (4) may be a figure or mark as shown in Fig. 2(a), or may be letters, numbers, or symbols as shown in Fig. 2(b). As shown in Fig. 2(c), it may be lines (curved lines or straight lines), colored patterns, basket weave patterns, etc., or as shown in Fig. 2(d), it may be code information such as a barcode or two-dimensional code.

As shown in FIG. 3(a), the printed image (9) may be formed such that the first information pattern (4) is adjacent to or close to the second information pattern (5) made of a second infrared-emitting ink composition having infrared emitting properties different from the infrared-emitting ink composition, or the first information pattern (4) and the second information pattern (5) are partially overlapped (not shown). As shown in FIG. 3(b), the printed image (9) may be formed such that the first information pattern (4) is surrounded by the second information pattern (5), or the second information pattern (5) is surrounded by the first information pattern (4).

Furthermore, as shown in FIG. 3(c), the printed image (9) may have a third information pattern (6) formed from an infrared emitting ink composition and a third infrared emitting ink composition having infrared emitting properties different from those of the second infrared emitting ink composition, formed adjacent to the first information pattern (4) and the second information pattern (5). In addition, the size of each information pattern is advantageous for authenticity determination in terms of infrared emitting detection by a detector, so that the larger the area ratio, the more advantageous it is for authenticity determination. The infrared emitting ink composition, the second infrared emitting ink composition, and the third infrared emitting ink composition will be described later.

In this specification, adjacent means that at least a portion of two adjacent information patterns touch or intersect, and close to each other means that two adjacent information patterns are not touching but are close to each other.

(Infrared emitter)
The infrared emitter used in the infrared emitting ink composition is characterized by absorbing light in a portion of at least one of the following wavelength ranges: the ultraviolet range from 200 nm to 400 nm, the visible range from 400 nm to 700 nm, and the near infrared range of 700 nm or more, and emitting light in the near infrared range of 800 nm or more. This wavelength range of absorption is called the "excitation wavelength." There may be two or more excitation wavelengths in each of the ultraviolet, visible, and near infrared wavelength ranges.

As infrared emitters with such characteristics, at least the infrared emitters shown in Patent Documents 1 to 5 can be used, as well as known infrared emitters with similar characteristics to the infrared emitters shown in Patent Documents 1 to 5. In all cases, at least one emission peak wavelength is in the wavelength range of 850 nm to 1100 nm that can be received by a silicon photodiode, and authenticity can be determined using a general-purpose detector. Most infrared emitters have multiple excitation wavelengths in each of the ultraviolet, visible, and near-infrared wavelength ranges.

As an embodiment of the present invention, _{the case where Li(Nd,Yb)P4O12 (Patent Document 3), (Lu,Yb,Nd)2O2S ( Patent Document} 4), and Ca _k Li _l (Nd _x ,Yb _y ) ₂ (WO ₄ ) _m (Patent Document 5) are used will be described as an example, but the present invention is not limited to the above-mentioned infrared emitters as long as there are two or more types of infrared emitters that have almost the same infrared emission characteristics and different other characteristics. Of course, the present invention is not limited to infrared emission, and the same method can be used for ultraviolet emission, visible emission, and upconversion emission.

Here, the infrared emitter shown in Li(Nd,Yb)P ₄ O ₁₂ (Patent Document 3) or Ca _k Li _l (Nd _x ,Yb _y ) ₂ (WO ₄ ) _m (Patent Document 5) is described as the "first infrared emitter (7)", and the infrared emitter shown in (Lu,Yb,Nd) ₂ O ₂ S (Patent Document 4) is described as the "second infrared emitter (8)". When comparing these infrared emitters in detail, the first infrared emitter (7) has a relatively high emission intensity compared to the second infrared emitter (8). On the other hand, the second infrared emitter (8) has a very high chemical resistance to acidic and alkaline chemicals compared to the first infrared emitter (7). Furthermore, compared to the second infrared emitter (8), the first infrared emitter (7) described in Patent Document 3 has low water resistance and acid resistance.

When providing an authenticity discrimination element based on infrared light emission to an anti-counterfeit printed matter (1), from the viewpoints of authenticity discrimination, economy, and printability, it is preferable to use a method that can obtain high luminescence intensity with a small amount of infrared light emitter. Therefore, it is preferable to use a first infrared light emitter (7) that has a relatively high luminescence intensity. However, the possibility of unintentional exposure to water, organic solvents such as alcohols, esters, and ethers, and acidic and alkaline chemicals cannot be denied. Since it is necessary to guarantee the authenticity even in the case of an anti-counterfeit printed matter (1) that has come into contact with or been exposed to such things, it is desirable for the authenticity discrimination element to have high chemical resistance.

When anti-counterfeiting printed matter (1) is normally used, it rarely comes into contact with water, organic solvents, or various chemicals, and contact with water, organic solvents, or various chemicals is an abnormal case. Such abnormal cases are hereafter referred to as "peculiar conditions." Therefore, if the type and blending ratio of the infrared emitter is selected based on the peculiar condition, it will be excessive performance in normal conditions, which will be disadvantageous in terms of economy and printability. Therefore, it is reasonable to set the type and blending ratio of the infrared emitter to be used based on normal use conditions, and take measures to guarantee authenticity even in peculiar conditions.

As a method for this, we have found a technique in which a first infrared emitter (7) with high luminous intensity is used as the main infrared emitter, and a second infrared emitter (8) is mixed in an appropriate ratio to guarantee authenticity in a special state. By using this method, it is possible to guarantee authenticity even in a special state while suppressing the blending ratio of the first infrared emitter (7) and the second infrared emitter (8) in the infrared emitting ink composition.

As a requirement of this method, the infrared emitters used in combination must have the same excitation wavelength and emission wavelength range, which are conditions for authenticity discrimination. In this regard, when authenticity discrimination is performed by using a mixture of the first infrared emitter (7) and the second infrared emitter (8), for example, when the excitation wavelength is 590 nm and the detection wavelength range is 850 nm or more, up to the detection range of a silicon photodiode, they show almost the same emission characteristics, and can be used in the same way as infrared emitting inks containing either of the infrared emitters alone.

The blending ratio of the first infrared emitter (7) with high luminous intensity and the second infrared emitter (8) with high chemical resistance may be determined according to the luminous intensity under the conditions for determining the authenticity of the anti-counterfeiting printed matter (1). For example, if the first infrared emitter (7) is completely lost under special conditions, authenticity must be guaranteed by the luminous intensity of the second infrared emitter (8) alone, and therefore a blending amount that exceeds at least the detection limit is required. The blending ratio of the first infrared emitter (7) and the second infrared emitter (8) with high chemical resistance in the infrared luminous ink composition may be a ratio that allows stable detection under normal conditions.

In addition, this embodiment is an example in which two types of infrared emitters, a first infrared emitter (7) and a second infrared emitter (8), are used, but three or more types of infrared emitters can be used as long as they do not affect the characteristics of the first infrared emitter (7) and the second infrared emitter (8) and are materials with the same excitation wavelength and emission wavelength range.

(Infrared emitting ink composition)
The infrared emitting ink composition is described below. The infrared emitting ink composition is composed of at least two types of infrared emitters, a first infrared emitter (7) and a second infrared emitter (8), and a varnish material, and depending on the varnish material, various adjusting agents such as a photopolymerization initiator, an auxiliary such as a drying agent, a dispersant, a gelling agent, a surfactant, and a lubricant are blended.

As coloring materials, organic or inorganic coloring pigments, luster pigments such as pearl pigments, functional materials such as magnetic materials and chromic materials, and extender pigments such as calcium carbonate, barium sulfate, and silicon oxide may be blended within the range where the infrared emission is not undetectable. In addition, when considering detection for authenticity determination, varnish materials and pigments that do not absorb light in the wavelength range equivalent to the excitation wavelength and infrared emission wavelength of the infrared emitter when authenticity determination is performed are preferable, and similar attention should be paid to the absorption characteristics of the photopolymerization initiator.

The type of infrared emitting ink composition is not particularly limited, and it can be any known ink such as offset ink, letterpress ink, flexo ink, screen ink, gravure ink, intaglio ink, inkjet ink, coating liquid, etc. In addition, the drying or polymerization method of the varnish material is not particularly limited, and known methods such as penetration drying, evaporation drying, oxidative polymerization, ionizing radiation drying, etc. can be used.

(Production method)
The method for producing the infrared emitting ink composition is not particularly limited as long as it is a method that can uniformly mix the components of the ink described above. When mixing the components in the method for producing the infrared emitting ink composition, for example, a mixer such as a planetary mixer, a tumbler, a bead mill, a sand mill, a stirrer, an agitator, a mechanical homogenizer, an ultrasonic homogenizer, a paint shaker, a V-type blender, a Nauta mixer, or a three-roll mill can be used.

(Printing method)
The method for applying the infrared emitting ink composition to the substrate (2) is not particularly limited, and any known application method can be used as long as it is a method that can apply an infrared emitting material, such as printing, such as offset printing, letterpress printing, flexographic printing, screen printing, gravure printing, intaglio printing, inkjet printing, or general coating including gravure coating.

(Second infrared emitting ink composition and third infrared emitting ink composition)
The second infrared-emitting ink composition differs from the infrared-emitting ink composition in that it contains a first infrared emitter (7) but does not contain a second infrared emitter (8). Moreover, the third infrared-emitting ink composition differs from the infrared-emitting ink composition in that it does not contain the first infrared emitter (7) but contains a second infrared emitter (8). Note that the materials such as varnish materials, color materials, and pigments, as well as the manufacturing method and application method, are the same as those of the infrared-emitting ink composition.

(acid resistance)
The acid resistance of the first information pattern (4) formed with the infrared emitting ink composition varies depending on conditions such as the infrared emitter used, the blending ratio of the infrared emitters, the properties of the ink binder, the printing film thickness, etc., but when it comes into contact with acid, the emission intensity is reduced by the first infrared emitter (7) which has a relatively low acid resistance. On the other hand, the second infrared emitter (8) has a high acid resistance and does not experience a large decrease in emission intensity compared to the first infrared emitter (7) even when it comes into contact with acid.

Therefore, by mixing the first infrared emitter (7) and the second infrared emitter (8), the second infrared emitter (8) compensates for the decrease in intensity of the first infrared emitter (7) under acidic conditions. Since the second infrared emitter (8) has a relatively low emission intensity compared to the first infrared emitter (7), the first infrared emitter (7) compensates for the emission intensity of the second infrared emitter (8) by mixing and using the first infrared emitter (7). Note that the change in emission intensity of the screen print and offset print when an infrared emitting ink composition in which the first infrared emitter (7) and the second infrared emitter (8) are mixed in any ratio is immersed in an acidic solution will be described in the examples below.

Next, the characteristics of the first infrared emitter (7) and the second infrared emitter (8) will be described. Figure 4 shows the fluorescence spectra of the first infrared emitter (7) and the second infrared emitter (8) when irradiated with orange light having a central wavelength of 590 nm as the excitation peak wavelength. Both the first infrared emitter (7) and the second infrared emitter (8) emit light in the near-infrared region from 950 nm to 1050 nm. This region is a wavelength range that can be detected by a small, inexpensive silicon photodiode.

Figure 5 shows the excitation spectra at the emission peak wavelengths of the first infrared emitter (7) and the second infrared emitter (8). The shapes of the excitation spectra of the first infrared emitter (7) and the second infrared emitter (8) are similar. However, the excitation peak wavelengths of the first infrared emitter (7) and the second infrared emitter (8) in the ultraviolet, visible, and near-infrared wavelength regions are shifted by several nm, and the half-widths at the excitation peak wavelengths in the ultraviolet region are different, with the most noticeable difference being the intensity difference of the excitation spectra around 300 nm.

The excitation spectrum in FIG. 5 is normalized for comparison of spectral shapes. In addition, the infrared emitting ink composition containing the first infrared emitter (7) and the second infrared emitter (8), and the third infrared emitting ink containing the second infrared emitter (8) may have excitation characteristics different from the excitation spectrum of the infrared emitter shown in FIG. 5 depending on the absorption characteristics of the varnish material, photopolymerization initiator, additives, auxiliaries, etc. used. This embodiment will be described in detail using the difference in excitation characteristics in the visible light region and the ultraviolet light region, but detection using the difference in excitation characteristics in the infrared region is also possible.

The excitation wavelength can be any wavelength that is absorbed by the infrared emitting material used, but the excitation wavelength that provides the highest emission intensity is preferable. Using an excitation wavelength in the visible light range has the advantage that the irradiation position of the light source can be visually confirmed, but the color pigments that can be blended are limited. The light source can be a tungsten lamp, halogen lamp, xenon lamp, deuterium lamp, mercury lamp, sodium lamp, or other lamp, and a filter can be used to extract only a specific wavelength range, or an LED or laser light source of a specific wavelength can be used.

(Detector)
The detector for detecting the infrared emission of the anti-counterfeiting printed matter (1) is not particularly limited as long as it is a sensor capable of detecting light in the infrared emission wavelength range. The sensor may be a semiconductor detector such as a silicon photodiode or an indium gallium arsenide photodiode, or a photoelectric conversion sensor such as a highly sensitive photomultiplier or an image intensifier. The detection method may be a linear or area-shaped arrangement of sensors to detect the infrared emission image. If the detection sensitivity is low, the detected light may be converted into an electrical signal and amplified. Depending on the sensitivity characteristics of the sensor used, it is preferable to attach an optical filter in front of the light receiving unit so as not to detect light other than the infrared emission of each information pattern. For example, when a silicon photodiode is used, a sharp cut filter that cuts visible light, for example, 850 nm or less, is attached.

The detector may be a combination of known photosensors, amplifiers, and A/D converters, and a judgment application may be constructed, or a commercially available device may be used. For example, the counterfeit prevention technology analysis device manufactured by Foster+Freeman Ltd. allows the light emission state to be visually observed as an image, and the NKC-1 and NKC-10 manufactured by Nemoto Specialty Chemicals Co., Ltd. allow the light emission to be detected as a numerical value in any unit.

(How to determine authenticity)
Next, the method for discriminating authenticity of an anti-counterfeit printed matter of the present invention will be described. As shown in Fig. 10, the method for discriminating authenticity of an anti-counterfeit printed matter of the present invention is characterized by comprising an irradiation step (E) of irradiating a printed image (9) of an anti-counterfeit printed matter (1) with at least one of a first irradiation wavelength (λ1) in a wavelength range that excites both a first infrared emitting body (7) and a second infrared emitting body (8) or a second irradiation wavelength (λ2) different from the first irradiation wavelength (λ1) in a wavelength range that excites both of them, and a third irradiation wavelength (λ3) in a wavelength range that excites the second emitting body (8) and different from the first irradiation wavelength (λ1) and the second irradiation wavelength (λ2), a detection step (D) of detecting the emission intensity of each irradiation wavelength of the printed image (9) in the irradiation step (E), and a discrimination step (J) of comparing the emission intensity detected in the detection step (D) with the emission intensity of a genuine product and discriminating authenticity based on whether it is within a reference value range of the emission intensity of a genuine product.

The authenticity determination method in this example can be performed using two irradiation wavelengths, at least one of the first irradiation wavelength (λ1) or the second irradiation wavelength (λ2), and the third irradiation wavelength (λ3). However, for better judgment, an example using three irradiation wavelengths, the first irradiation wavelength (λ1), the second irradiation wavelength (λ2), and the third irradiation wavelength (λ3), will be described. In addition, in the irradiation step (E) of this example, light in different excitation wavelength ranges, the first irradiation wavelength (λ1) of 590 nm, the second irradiation wavelength (λ2) of 254 nm, and the third irradiation wavelength (λ3) of 312 nm, is irradiated onto the anti-counterfeit printed matter (1).

The detection process (D) includes a first detection process (E-1) in which the first sensor (S1) detects the emission of the printed image (9) at a first irradiation wavelength (λ1), a second detection process (D-2) in which the second sensor (S2) detects the emission of the printed image at a second irradiation wavelength (λ2), and a third detection process (D-3) in which the third sensor (S3) detects the emission of the printed image at a third irradiation wavelength (λ3).

The discrimination process (J) compares the luminescence intensity in the detection process (D) with a predetermined reference value, and judges it to be genuine if it is within the range of the predetermined reference value. One example of a method of judgment is to set the output voltage of the luminescence intensity obtained by measuring a genuine product in advance as the reference value, set the allowable range as the reference value ± error centered on this reference value, and judge it to be "genuine" if the output voltage obtained from the object to be discriminated is between the maximum allowable value and the minimum allowable value, and judge it to be "false" if it is not within the allowable range. The setting of the reference value will be described later.

Alternatively, an emission intensity profile, which is the output waveform of the emission intensity of a genuine product measured in advance, can be used as a reference value, and pattern-matched with an emission intensity profile, which is the output waveform of the emission intensity of the object to be identified, and a match can be determined as "genuine." Note that with pattern matching, since a perfectly matching output waveform may not be formed depending on how the two output waveforms are superimposed, a threshold can be set within a range determined as the reference value, and a discrimination criterion can be set such that if the similarity falls within the set threshold range, the waveforms are determined to be the same. Here, the threshold can be set as appropriate.

Next, an example of a method for determining authenticity using the anti-counterfeit printed matter (1) shown in FIG. 3(c) will be described with reference to FIG. 6.

Figure 6 shows an example of how authenticity is determined by detecting the emission intensity profile of any one line (3) of the second information pattern (5), the first information pattern (4), and the third information pattern (6) when a first irradiation wavelength (λ1), a second irradiation wavelength (λ2), and a third irradiation wavelength (λ3) are irradiated onto an anti-counterfeit printed matter (1).

As described above, the first information pattern (4) is formed from an infrared emitting ink composition containing at least a first infrared emitting body and a second infrared emitting body, the second information pattern (5) is formed from a second infrared emitting ink composition containing the first infrared emitting body, and the third information pattern (6) is formed from a third infrared emitting ink composition containing the second infrared emitting body.

The first infrared emitter and the second infrared emitter have the same fluorescence (emission) wavelength range, the first infrared emitter has a higher emission intensity in at least one excitation wavelength range in each of the ultraviolet, visible, and near-infrared wavelength ranges than the second infrared emitter, the second infrared emitter has higher acid resistance than the first infrared emitter, the first infrared emitter and the second infrared emitter have at least one excitation wavelength peak in each wavelength range, and at least one of the excitation wavelength peaks is different between the first infrared emitter and the second infrared emitter.

When the first irradiation wavelength (λ1) is irradiated, a first emission intensity profile (L1) is shown, when the second irradiation wavelength (λ2) is irradiated, a second emission intensity profile (L2) is shown, and when the third irradiation wavelength (λ3) is irradiated, a third emission intensity profile (L3) is shown. The emission intensity may be a voltage value detected by a sensor, or data detected as an image may be processed and converted into a brightness value.

Figure 6 shows an example of an emission image and emission intensity profile of infrared emission of each information pattern when excitation light of three different wavelengths is irradiated to the anti-counterfeit printed matter (1). Figure 6 (a) shows a first infrared emission image (P1) when orange light having a peak wavelength of 590 nm, which is the first irradiation wavelength (λ1), is irradiated to the anti-counterfeit printed matter (1), as an example. Since the first infrared emitter (7) and the second infrared emitter (8) both absorb the first irradiation wavelength (λ1) and emit infrared light, all of the information patterns, the first information pattern (4), the second information pattern (5), and the third information pattern (6), can be detected as a white emission image. Furthermore, in the first emission intensity profile (L1), the first information pattern (4), the second information pattern (5), and the third information pattern (6) have the same intensity.

In addition, by adjusting the printing film thickness of each of the first information pattern (4), the second information pattern (5), and the third information pattern (6) and making the infrared emission intensity of each information pattern approximately the same, it is also possible to detect all of them as white luminescent images of the same brightness.

Figure 6 (b) is a second infrared emission image (P2) when the anti-counterfeiting print (1) is irradiated with ultraviolet light having a peak wavelength of 254 nm as the second irradiation wavelength (λ2). Since the first infrared emitter (7) and the second infrared emitter (8) both absorb the ultraviolet light of the second irradiation wavelength (λ2) and emit infrared light, the second information pattern (5), the first information pattern (4), and the third information pattern (6) can all be detected as nearly white emission images in the second infrared emission image (P2). However, since the emission intensities of the first infrared emitter (7) and the second infrared emitter (8) at the second irradiation wavelength (λ2) are slightly different, the emission intensities in the second emission intensity profile (L2) are in the order of second information pattern (5) < first information pattern (4) < third information pattern (6).

Figure 6 (c) is a third infrared emission image (P3) when the anti-counterfeit print (1) is irradiated with ultraviolet light having a peak wavelength of 312 nm as the third irradiation wavelength (λ3). The second infrared emitter (8) emits light, but the first infrared emitter (7) emits almost no light. Therefore, in the third infrared emission image (P3), the second information pattern (5) is hardly detected and is therefore black, the third information pattern (6) is white, and the first information pattern (4) is detected as a gray image indicated by diagonal lines, intermediate between the second information pattern (5) and the third information pattern (6). Furthermore, in the third emission intensity profile (L3), the emission intensity is also first information pattern (4) < third information pattern (6).

As described above, the method of detecting the three types of luminescence images or the three types of luminescence intensity profiles and discriminating between genuine and counterfeit can be a known method, such as a method of discriminating based on a certain degree of similarity using matching with a preregistered reference image or reference profile, or a method of setting a threshold value for the luminance value of the luminescence image and discriminating whether it falls within the range of the set value.

As a detection method, we have shown the difference in luminescence brightness (images) using three types of irradiation wavelengths, but it is clear that differentiation in luminescence brightness (images) is also possible using two types of irradiation wavelengths.

Next, another embodiment for identifying the anti-counterfeit printed matter (1) of the present invention will be described with reference to FIG. 7. Take the anti-counterfeit printed matter (1) shown in FIG. 1 as an example. The first information pattern (4) is formed from an infrared emitting ink composition in which a first infrared emitting body (7) and a second infrared emitting body (8) are appropriately mixed in any ratio.

As shown in FIG. 7, the anti-counterfeit print (1) is irradiated with light of 590 nm, which is a first irradiation wavelength (λ1), and the emission of the first information pattern (4) is detected by a first sensor (S1) in a first detection step (D1), the second detection step (D2) is irradiated with light of 254 nm, which is a second irradiation wavelength (λ2), and the emission of the first information pattern (4) is detected by a second sensor (S2), and the third detection step (D3) is irradiated with light of 312 nm, which is a third irradiation wavelength (λ3), and the emission of the first information pattern (4) is detected by a third sensor (S3), thereby detecting the emission of the excitation light with different wavelengths.

The light emitted by the first sensor (S1), the second sensor (S2), and the third sensor (S3) is photoelectrically converted and A/D converted, and is captured as a voltage value corresponding to the light emission intensity.

If the emission intensities of the first detection value (V1), the second detection value (V2), and the third detection value (V3) are low, the signal intensity is amplified by an amplifier as necessary, and the signal is transmitted to a computer that performs a determination step (J) for data processing as digital data via an A/D converter.

In the discrimination step (J), the comparison calculation unit of the computer compares the acquired first detection value (V1), second detection value (V2), and third detection value (V3) with a preset threshold value to discriminate between authenticity and counterfeit. The preset threshold value is an actual measurement value of the genuine product. For example, when the first threshold value (T1) for the first detection value (V1) is set, the second threshold value (T2) for the second detection value (V2) can be set as T2 = 5 x V1, and the third threshold value (T3) for the third detection value (V3) can be set as T3 = 2 x V1. Only when the first detection value (V1), second detection value (V2), and third detection value (V3) are all within the ranges of the preset first threshold value (T1), second threshold value (T2), and third threshold value (T3), the product is judged to be "genuine."

In other words, this is achieved by taking advantage of the difference in the excitation characteristics in the ultraviolet region between the first infrared emitter (7) and the second infrared emitter (8), separately irradiating the first infrared emitter (7) and the second infrared emitter (8) with ultraviolet light suitable for each emitter, and observing the change in emission intensity and/or brightness. It also becomes possible to detect imitations (counterfeits) that use similar materials other than the first infrared emitter (7) and the second infrared emitter (8).

Another embodiment of the method for determining the authenticity of an anti-counterfeit printed matter (1) of the present invention will be described with reference to FIG. 8. Take the anti-counterfeit printed matter (1) shown in FIG. 1 as an example. The first information pattern (4) is formed from an infrared emitting ink composition in which a first infrared emitting body (7) and a second infrared emitting body (8) are appropriately mixed in any ratio.

As an example, when irradiating light of 590 nm, which is the first irradiation wavelength (λ1), and detecting the emission intensity or acquiring the emission image, light of 254 nm, which is the second irradiation wavelength (λ2), and light of 302 nm, which is the third irradiation wavelength (λ3), are sequentially irradiated, the emission intensity or the brightness of the emission image changes according to the mixture ratio of the first infrared emitter (7) and the second infrared emitter (8).

For example, suppose that the first detection value (V1), which is infrared emission detected when a first information pattern (4) of an authentic anti-counterfeit print (1) is irradiated with light of 590 nm, which is the first irradiation wavelength (λ1), is 40 mV. The second detection value (V2) when the second irradiation wavelength (λ2) is irradiated in a state where the first irradiation wavelength (λ1) is irradiated is 4×40 mV (V1), and the third detection value (V3) when the third irradiation wavelength (λ3) is irradiated in a state where the first irradiation wavelength (λ1) and the second irradiation wavelength (λ2) are irradiated is 8×40 mV (V1), and each reference value is set.

In the case of an imitation printed matter applied with an infrared emitting ink composition containing only the first infrared emitting body (7), only the second infrared emitting body (8), or only a similar different illuminant, if a person who does not know the composition of the infrared emitting ink composition irradiates the printed matter with ultraviolet light of a wavelength that does not match the excitation characteristics of the blended infrared emitting body, the emission intensity or the brightness of the luminescent image will hardly change. For example, in the case of an imitation printed matter applied with a second infrared emitting ink composition containing only the first infrared emitting body (7), the first detection value (V1) is 40 mV, so it is similar, but the values of the second detection value (V2) and the third detection value (V3) are different from those of the genuine anti-counterfeit printed matter (1), so it can be determined to be an imitation.

That is, this can be achieved by utilizing the difference in the excitation characteristics in the ultraviolet region between the first infrared emitter (7) and the second infrared emitter (8) and irradiating them with excitation light of a wavelength that causes a difference in emission intensity, and observing the change in emission intensity and/or brightness. It also becomes possible to detect imitations (counterfeits) that use similar materials other than the first infrared emitter (7) and the second infrared emitter (8) or imitations (counterfeits) that use the first infrared emitter (7) and the second infrared emitter (8) alone.

Below, we will explain in detail the examples of the infrared emitting ink composition and anti-counterfeiting printed matter (1) of the present invention in accordance with the embodiment of the invention, but the present invention is not limited to these examples.

Example 1
In this Example 1, the infrared emitting ink composition was used as the screen ink composition, and the target design shown in FIG. 1(a) was used as the substrate (2) on wood-free paper (Shiraoi, manufactured by Nippon Paper Industries Co., Ltd.) using a 200 mesh printing plate, and anti-counterfeiting prints of various levels (1-1 to 1-4) were produced using a tabletop screen printer WHT3 manufactured by Mino Group Co., Ltd.

The infrared-emitting ink compositions were prepared by using Ca _k Li _l (Nd _x , Yb _y ) ₂ (WO ₄ ) _m as the first infrared emitter (7) and a product of Nemoto Specialty Chemical Co., Ltd. as the second infrared emitter (8) at different mixing ratios as shown in Table 1 below. As shown in Table 1, comparative infrared-emitting ink compositions containing the first infrared emitter (7) and the second infrared emitter (8) alone were prepared, and infrared-emitting printed matters (2-1, 2-2) were prepared as comparative anti-counterfeit printed matters under similar conditions.

(Luminescence Intensity Measurement)
To measure the infrared emission intensity of the anti-counterfeiting printed matter of each level (1-1 to 1-4) shown in Table 1 and the infrared luminescent printed matter (2-1, 2-2) as the comparative example of the anti-counterfeiting printed matter, a fluorescent reader NKC-10 manufactured by Nemoto Specialty Chemical Co., Ltd. was used. The measurement conditions were as follows: the emission detector was fixed at the distance where the maximum intensity was obtained on a reference plate made of a sintered compact made of 100% infrared emitter, and the infrared emission intensity was measured at this measurement distance.

For each level of anti-counterfeiting printed matter (1-1 to 1-4), measurements were taken at three points on one test sample for the acid resistance test, and the average of the three points was calculated. Next, each level of anti-counterfeiting printed matter (1-1 to 1-4) was immersed in a 3% hydrochloric acid solution for four hours, and the samples were washed with the solution and dried, and infrared emission intensity was measured in the same way as before the test. The infrared emission intensity (arbitrary units) before and after the acid resistance test are shown in Table 2.

As shown in Table 2, before the acid resistance test, the infrared-emitting printed matter (2-1) of the comparative example contains only the first infrared emitter (7), which has high emission intensity but slightly low acid resistance, and therefore has the highest emission intensity when not exposed to acid. On the other hand, the infrared-emitting printed matter (2-2) of the comparative example contains only the second infrared emitter (8), and therefore has the lowest emission intensity when not exposed to acid. The anti-counterfeiting printed matter (1-1 to 1-4) of each level, which contains a mixture of the first infrared emitter (7) and the second infrared emitter (8), has a lower emission intensity as the ratio of the first infrared emitter (7) decreases.

In addition, in terms of the infrared emission intensity ratio before and after the acid resistance test, the infrared-emitting printed matter (2-1) of the comparative example contains only the first infrared emitter (7), which has high emission intensity but slightly low acid resistance, and therefore the emission intensity decreased to about 70% of that before the acid resistance test. On the other hand, the infrared-emitting printed matter (2-2) of the comparative example contains only the second infrared emitter (8), which has high acid resistance, and therefore there was no significant decrease in emission intensity. It was confirmed that the anti-counterfeiting printed matter (1-1 to 1-4) of each level, which contains a mixture of the first infrared emitter (7) and the second infrared emitter (8), suppressed the decrease in emission intensity as the ratio of the first infrared emitter (7) decreased (the ratio of the second infrared emitter (8) increased).

(detection)
Next, as shown in Fig. 7, the anti-counterfeit printed matter (up to 1-1) was irradiated with orange light from a 590 nm LED, and the light emission was detected by sensor 1 (S1) equipped with a sharp cut filter that cuts out light under 850 nm, the light emission when irradiated with short-wave ultraviolet light of 254 nm from a UV lamp was detected by sensor 2 (S2), and the light emission when irradiated with medium-wave ultraviolet light of 302 nm was detected by sensor 3 (S3), and the detection values shown in Table 3 were obtained. Note that an InGaAs photodiode module C10439-11 was used as the sensor. The voltage values detected by each sensor were within the range of voltage values previously determined as threshold values, and the anti-counterfeit printed matter (1-1) was determined to be "genuine."

Example 2
Next, an offset ink composition was prepared as an infrared emitting ink composition. Note that the description of the same points as in Example 1 will be omitted.

As shown in Table 4, infrared emitting ink compositions of various levels were prepared by varying the mixing ratio of the first infrared emitter (7) and the second infrared emitter (8). The target design shown in FIG. 1(a) was used as the substrate (2) on fine paper (Kishu Paper Co., Ltd.) and offset printed to a print thickness of 1 μm ± 0.05 μm using a universal printability tester from Kumagai Riki Kogyo Co., Ltd., to produce anti-counterfeiting printed matter of various levels (1'-1 to 1'-4). Similarly, anti-counterfeiting printed matter of various levels (1'-1' to 1'-4') with a print thickness of 2 μm ± 0.05 μm was produced. As described above, comparative inks (B'-1, B'-2) shown in Table 4 were used to produce comparative infrared emitting printed matter (2'-1', 2'-2').

(Acid resistance test 2-1)
Next, an acid resistance test was performed according to JIS K 5701-1:2000 "Lithographic inks - Part 1: Test methods" 6.3.2 Acid resistance test. Each level of anti-counterfeit printed matter (1'-1 to 1'-4) was sandwiched between filter paper completely immersed in a 5% sulfuric acid solution, a load of 1 kg was placed on it, and the printed matter test piece was left in a sealed state for 10 minutes, and then dried at 50°C for 30 minutes. The infrared emission intensity of each level of anti-counterfeit printed matter (1'-1 to 1'-4) before and after the acid resistance test is shown in Table 4. Note that under the acid resistance test conditions of JIS K 5701-1:2000 "Lithographic inks - Part 1: Test methods", there was no decrease in emission intensity after the test as shown in Table 5.

(Acid resistance test 2-2)
Next, an evaluation of acid resistance stronger than the above-mentioned JIS standard was performed. This evaluation was performed because the robustness required for anti-counterfeiting printed matter such as banknotes, passports, and security printed matter is stronger than that of general printed matter, and therefore evaluation was performed by a severe immersion test. In this acid resistance test, each level of anti-counterfeiting printed matter (1'-1 to 1'-4) was immersed in a 3% hydrochloric acid solution for 4 hours, washed with the solution, dried, and then infrared emission intensity was measured. The infrared emission intensity of each level of anti-counterfeiting printed matter (1'-1 to 1'-4) after the acid resistance test is shown in Table 6.

As shown in Table 5, before the acid resistance test, the infrared emitting printed matter (2'-1) of the comparative example had the highest luminous intensity, and the luminous intensity decreased as the blending ratio of the first infrared emitter (7) decreased. After the acid resistance test, the infrared emitting printed matter (2'-1) of the comparative example was blended only with the first infrared emitter (7), which has high luminous intensity but slightly low acid resistance, so the luminous intensity decreased to about 40% of the initial intensity. On the other hand, the infrared emitting printed matter (2'-2) of the comparative example was blended only with the second infrared emitter (8), which has high acid resistance, so there was no decrease in luminous intensity. As shown in the anti-counterfeiting printed matter (1'-2 to 1'-4) in which the first infrared emitter (7) and the second infrared emitter (8) were mixed and blended, it was confirmed that the decrease in luminous intensity was suppressed as the ratio of the first infrared emitter (7) decreased (the ratio of the second infrared emitter (8) increased).

Similarly, the sample was immersed in a 1% hydrochloric acid solution for 4 hours, and the luminescence intensity ratio before and after the test was calculated, with the results shown in Table 6. In the case of 1% hydrochloric acid, the decrease in luminescence intensity after the test was less than in the case of 3%, but the trend was similar.

As shown in Table 7, the same test was performed on anti-counterfeit printed matter (1'-1' to 1'-4') with a print thickness of 2 μm. Compared to the anti-counterfeit printed matter (1'-1 to 1'-4), the rate of decrease in luminescence intensity after the acid resistance test was generally lower, but the smaller the proportion of the first infrared emitter (7), i.e., the larger the proportion of the second infrared emitter (8), the more suppressed the decrease in luminescence intensity, as in the case of 1 μm.

Therefore, by using a mixture of the first infrared emitter (7) and the second infrared emitter (8), it was possible to produce a luminescent printed matter that normally exhibits high luminescence intensity due to the effect of the first infrared emitter (7), and whose authenticity can be guaranteed due to the effect of the second infrared emitter (8) even in the case of being exposed to a special condition such as a chemical.

Example 3
In this Example 3, an offset ink composition containing an infrared emitting ink composition, a second infrared emitting ink composition containing only the first infrared emitting body (7), and a third infrared emitting ink composition containing only the second infrared emitting body (8) were prepared, and the first information pattern (4), the second information pattern (5), and the third information pattern (6) shown in FIG. 3(c) were printed on a wood-free paper (Shiraoi, manufactured by Nippon Paper Industries Co., Ltd.) as a substrate (2) using an offset proofing machine manufactured by Shimogaki Iron Works Co., Ltd., using each ink composition shown in Table 8, and an anti-counterfeiting printed matter (1) was printed. The first information pattern (4), the second information pattern (5), and the third information pattern (6) were colorless solid prints, and the printed patterns could not be visually recognized unless the difference in gloss was observed. In addition, the first information pattern (4), the second information pattern (5), and the third information pattern (6) were printed by adjusting the amount of ink transfer so that the infrared emitting intensity when irradiated with orange light was about the same.

(detection)
The anti-counterfeit printed matter (1) was sequentially irradiated with visible light of 485 to 610 nm obtained by filtering the light of a 100 W incandescent lamp, long-wave ultraviolet light emitted by an ultraviolet lamp having a central wavelength of 254 nm, and medium-wave ultraviolet light emitted by an ultraviolet lamp having a central wavelength of 312 nm, and infrared emission images were obtained under each irradiation condition using a CCD camera equipped with a sharp-cut filter that cuts out light under 850 nm.

(judgement)
As shown in FIG. 9(a), the first infrared emission image (P1) of each pattern when irradiated with visible light of 485 to 610 nm as the first irradiation wavelength (λ1) showed almost the same emission state for each information pattern (4, 5, 6). As shown in FIG. 9(b), the second infrared emission image (P2) of each pattern when irradiated with shortwave ultraviolet light of 254 nm as the second irradiation wavelength (λ2) showed that the second information pattern (5), the first information pattern (4), and the third information pattern (6) were all detected as almost white emission images. However, the emission intensity in the second emission intensity profile (L2) was second information pattern (5)<first information pattern (4)<third information pattern (6). 9(c), when ultraviolet light having a wavelength of 312 nm was irradiated as the third irradiation wavelength (λ3), the third infrared emission image (P3) of each pattern was detected as black, since the second information pattern (5) was hardly detected, the third information pattern (6) was detected as white, and the first information pattern (4) was detected as a gray image approximately between the second information pattern (5) and the third information pattern (6). Furthermore, the emission intensity in the third emission intensity profile (L3) was first information pattern (4) < third information pattern (6).

Next, pattern matching was performed between the reference values, which are the emission intensity profiles of the authentic product measured in advance, and the emission intensity profiles (L1, L2, L3) of the anti-counterfeit printed matter (1) shown in Figure 9. Since both emission intensity profiles match, the anti-counterfeit printed matter (1) was determined to be "authentic."

REFERENCE SIGNS LIST 1 Anti-counterfeit printed matter 2 Substrate 3 One line 4 First information pattern 5 Second information pattern 6 Third information pattern 7 First infrared emitting body 8 Second infrared emitting body 9 Printed image P1 First infrared emitting image when irradiated with a first irradiation wavelength (λ1) P2 Second infrared emitting image when irradiated with a second irradiation wavelength (λ2) P3 Third infrared emitting image when irradiated with a third irradiation wavelength (λ3) L1 First emission intensity profile when irradiated with a first irradiation wavelength (λ1) L2 Second emission intensity profile when irradiated with a second irradiation wavelength (λ2) L3 Third emission intensity profile when irradiated with a third irradiation wavelength (λ3) S Sensor

Claims (4)

An infrared emitting ink composition containing at least a first infrared emitter and a second infrared emitter,
The first infrared light emitter and the second infrared light emitter have substantially the same emission wavelength range,
The first infrared emitter has a higher emission intensity in at least one excitation wavelength range in each of the ultraviolet region, the visible light region, and the near-infrared region than the second infrared emitter;
the second infrared emitter has higher acid resistance than the first infrared emitter,
An infrared-emitting ink composition, characterized in that the first infrared emitter and the second infrared emitter have at least one excitation peak wavelength in each of the wavelength regions, and at least one of the excitation peak wavelengths is different between the first infrared emitter and the second infrared emitter. An anti-counterfeiting printed matter, characterized in that it has a printed image with a first information pattern formed on at least a portion of a substrate using the infrared emitting ink composition described in claim 1. An anti-counterfeiting printed matter according to claim 2, characterized in that the printed image further has at least one of a second information pattern formed by a second infrared-emitting ink composition containing the first infrared-emitting material or a third information pattern formed by a third infrared-emitting ink composition containing the second infrared-emitting material, adjacent to or close to the first information pattern. A method for determining authenticity of an anti-counterfeit printed matter according to claim 2 or 3, comprising the steps of:
an irradiation step of irradiating the printed image with at least one of a first irradiation wavelength in a wavelength range that excites both the first infrared light emitter and the second infrared light emitter or a second irradiation wavelength different from the first irradiation wavelength in a wavelength range that excites both of the first infrared light emitter and the second infrared light emitter, and a third irradiation wavelength in a wavelength range that excites the second infrared light emitter and different from the first irradiation wavelength and the second irradiation wavelength;
a detection step of detecting an emission intensity of the printed image for each irradiation wavelength in the irradiation step;
A method for determining authenticity, comprising a discrimination step of comparing the luminescence intensity detected by the detection step with the luminescence intensity of a genuine product and determining whether the luminescence intensity of the genuine product is within a standard value range.

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