JPH10183037A - Water-soluble fluorescent ink and method for distinguishing water-soluble fluorescent ink - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable the recognition of an invisible or hardly visible print even when a fluorescent whitening agent is used as the fluorescent material to print on a printing medium contg. a flurescent whitening agent. SOLUTION: An absorbent material in an amount of 0.15-1.0wt.% having an absorption near at a wavelength of 700-850nm is added to a water-soluble fluorescent ink contg., as the main ingredients, water, a water-soluble resin, a hydrophilic org. solvent, and a fluorescent whitening agent excitable by ultraviolet rays from a black lamp. The ink is then used to print on a printing medium. The medium thus printed is exposed to ultraviolet rays, and the reflected light having wavelengths of 700nm or higher and light emitted by the ink are detected to check the existence of the ink, enabling the reading of print contents.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an invisible or invisible water-soluble fluorescent ink called invisible, and to a method for determining the water-soluble fluorescent ink from printed matter printed using the water-soluble fluorescent ink.

[0002]

2. Description of the Related Art For example, when address information is printed as a bar code on a mail to automatically sort the mail, or when a bar code is printed for security, if the bar code is visible, the address is displayed as the address. This is inconvenient because it overlaps and loses the meaning of security. For this reason, barcodes are printed using invisible or hardly visible fluorescent ink. Conventionally, such a fluorescent ink has, for example, a peak wavelength in the vicinity of 440 nm to 450 nm when irradiated with ultraviolet light (for example, it can be obtained by a black lamp having a peak wavelength in an ultraviolet region of 365 nm). It is known that a fluorescent dye such as a fluorescent whitening agent is dissolved in a solvent composed of, for example, water and a hydrophilic organic solvent, and a defoaming agent or a fungicide is added as required. Also, a fluorescent ink using a special fluorescent material that emits light at around 600 nm by irradiating ultraviolet light is known.

[0003]

SUMMARY OF THE INVENTION The former fluorescent ink is
Although a fluorescent whitening agent or the like is used as a fluorescent dye, the fluorescent whitening agent generally emits blue light when excited by irradiation with ultraviolet light. In addition, the fluorescent ink using the fluorescent whitening agent can perform printing invisible to a considerable density as visibility. In addition, it becomes slightly yellowish at a high concentration.
However, optical brighteners are also added to most ordinary white paper, so when printing with this fluorescent ink, the distinction between the ink portion and the paper portion can only be determined by the magnitude of the emission output. In other words, if the printing state is poor, a sufficient S / N ratio cannot be obtained, and if the printed place is a complementary color of blue or black characters are written, it is difficult to determine. there were. For this reason, there was a problem that it was not possible to print on white paper to which a fluorescent whitening agent was added using this fluorescent ink.

The latter fluorescent ink uses a special fluorescent material which emits light at around 600 nm by irradiating ultraviolet light. For example, Japanese Patent Publication No. 54-22335 discloses a method of irradiating ultraviolet light of 600 nm or less. Since the Eu-TTA (Europium-thenoyltrifluoroacetone chelate) phosphor that emits light at around 620 nm is used, the wavelength is significantly different from that of the fluorescent whitening agent. Therefore, a filter that transmits light at around 520 nm or more is used. By doing so, reading is possible even when printing on white paper. But,
In the case where the special fluorescent material is used, the fluorescent material is expensive, and there is a problem that the fluorescent ink has to be expensive.

Further, the black lamp has a characteristic spectrum from about 700 nm to about 800 nm under the influence of a mercury ray. Due to this effect, the reflected light of the black lamp is detected by the sensor even when there is no fluorescent material, and S
There is a problem that the / N ratio is reduced. In addition, as an inorganic material, there is a material that emits light in the visible region when irradiated with ultraviolet light, but the emission intensity is low, the response is poor, and the inorganic pigment does not dissolve in a solvent, so a stable dispersion system is required. There was trouble to do.

Therefore, the invention according to the first aspect of the present invention provides a printing method using a low-cost fluorescent whitening agent or the like as a fluorescent material, which makes it possible to perform printing that is invisible or hard to see, and furthermore, on a printing medium to which the fluorescent whitening agent is added. The present invention provides a water-soluble fluorescent ink capable of recognizing printed contents without being greatly affected by a fluorescent whitening agent on a print medium even when printing is performed.

Further, according to the second aspect of the present invention, invisible printing can be surely performed using an inexpensive fluorescent whitening agent or the like as a fluorescent material, and the printing is performed on a printing medium to which the fluorescent whitening agent is added. Provided is a water-soluble fluorescent ink capable of reliably recognizing printed contents with little influence of a fluorescent whitening agent on a print medium even when printing.

According to a third aspect of the invention, a fluorescent whitening agent or the like is added as a fluorescent material and the wavelength is 700 nm.
When printing is performed using a water-soluble fluorescent ink to which an absorbing material having an absorption of about 850 nm is added, the print is invisible or hardly visible on a print medium to which a fluorescent whitening agent is added. Provided is a method for determining a water-soluble fluorescent ink that can reliably recognize printed content without being affected by a whitening agent.

[0009]

According to the first aspect of the present invention,
As a main component, a water-soluble fluorescent ink containing water, a water-soluble resin, a hydrophilic organic solvent, and a fluorescent material excited by ultraviolet light, and a water-soluble fluorescent ink obtained by adding an absorbing material having an absorption wavelength of about 700 nm to 850 nm. is there.

According to a second aspect of the present invention, there is provided the water-soluble fluorescent ink according to the first aspect, wherein the absorbing material comprises 0.25 wt%.
That is, it is added in an amount of 1.0 wt% or less.

[0011] The invention according to claim 3 is characterized in that:
A water-soluble fluorescent ink containing water, a water-soluble resin, a hydrophilic organic solvent and a fluorescent material excited by ultraviolet light has a wavelength of 70.
A print medium printed using a water-soluble fluorescent ink to which an absorbing material having an absorption in the vicinity of 0 nm to 850 nm is added is irradiated with ultraviolet light, and reflected light having a wavelength of 700 nm or more and light emitted from the water-soluble fluorescent ink are emitted. It is to determine the presence or absence of fluorescent ink by detection.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. As the water-soluble fluorescent ink, a water-soluble fluorescent ink whose main component is water, a water-soluble resin, a hydrophilic organic solvent and a fluorescent material excited by ultraviolet rays, for example,
An ultraviolet excitation type water-soluble fluorescent ink in which a water-soluble resin and a water-soluble fluorescent whitening agent as a fluorescent material are dissolved in water and a hydrophilic organic solvent is used.
A water-soluble phthalocyanine dye (manufactured by Nippon Shokubai Co., Ltd.), which is an infrared absorber having an absorption of 50, is mixed. The amount of addition is such that the concentration of the water-soluble phthalocyanine dye is 0.25% by weight or more and 1.0% by weight or less.

As the water-soluble resin, a styrene acrylic resin neutralized with ammonia or monoethanolamine (for example, manufactured by Johnson Polymer Co., Ltd., or a styrene maleic acid resin neutralized with ammonia) can be used. Is added in an amount of 1 wt% to 15 wt%. Preferably, 1 wt% or more and 12.5 wt% or less are added. It is preferable that the amount of the water-soluble resin is large as the fluorescent ink.

As the hydrophilic organic solvent, for example, one kind or a mixture of polyhydric alcohols such as ethylene glycol, propylene glycol, diethylene glycol, polyethylene glycol, dipropylene glycol and glycerin is used. 10% by weight of this polyhydric alcohol to 5%
0 wt% is added. If necessary, auxiliary agents such as an antifoaming agent, a surfactant, a fungicide, and a preservative are added.

For example, as a water-soluble fluorescent whitening agent which is a fluorescent material excited by ultraviolet light, Mike manufactured by Mitsui Toatsu Co., Ltd.
rphor BS conc 200% (hereinafter referred to as BS), styrene acrylic resin (manufactured by Johnson Polymer Co., Ltd.) as a water-soluble resin, propylene glycol as a hydrophilic organic solvent, 700 nm ~ 8
Various water-soluble fluorescent inks having different mixing amounts were manufactured using EEX Color 702W (manufactured by Nippon Shokubai Co., Ltd.) as a water-soluble phthalocyanine dye which is an infrared absorber having an absorption at 50. Using a water-soluble fluorescent ink, printing was performed on a white private postcard as a printing medium by an on-demand type ink jet printer, and the light amount was measured using the light amount measuring device shown in FIG.
The viscosity of each water-soluble fluorescent ink is adjusted to about 10 cps, and the surface tension is adjusted to about 40 dyn / cm.

The light amount measuring device irradiates a private postcard 2 with ultraviolet light by using a black lamp 1 having a peak wavelength in an ultraviolet region of 365 nm, and reflects a reflected light from the private postcard 2 into a first condenser lens 3. And the first CCD 4 detects the light through the first CCD sensor 5 and the second condenser lens 6 and the second filter 7 detect the light through the second filter 7.

As the first filter 4, as shown in FIG. 2, an R-70 filter having a light transmission characteristic of transmitting a wavelength of 700 nm or more is used, and as the second filter 7, as shown in FIG. As shown, an L-42 filter having a light transmission characteristic of transmitting a wavelength of 420 nm or more is used. The EX color 702W has the light transmission characteristics shown in FIG.

Water-soluble fluorescent ink 1 (Comparative Example 1) Water-soluble resin amount: 5 wt% Hydrophilic organic solvent: 34 wt% Water: 57 wt% Surfactant: 1 wt% Defoamer: 0.2 wt% BS: 2 wt% Others ... 0.8 wt% water-soluble fluorescent ink 2 (Comparative Example 2) Amount of water-soluble resin ... 5 wt% Hydrophilic organic solvent ... 34 wt% Water ... 57 wt% Surfactant ... 1 wt% Defoamer ... 0.2 wt% BS ... 2 wt % Infrared absorber ... 0.1 wt% Others ... 0.7 wt% Water-soluble fluorescent ink 3 (Comparative Example 3) Water-soluble resin amount ... 5 wt% Hydrophilic organic solvent ... 34 wt% Water ... 57 wt% Surfactant ... 1 wt% Foaming agent: 0.2 wt% BS: 2 wt% Infrared absorber: 0.2 wt% Other: 0.7 wt% Water-soluble fluorescent ink 4 (Example 1) Water-soluble resin amount: 5 wt% Organic solvent ... 34 wt% Water ... 57 wt% Surfactant ... 1 wt% Defoamer ... 0.2 wt% BS ... 2 wt% Infrared absorber ... 0.25 wt% Other ... 0.65 wt% Water-soluble fluorescent ink 5 (Example) 2) Amount of water-soluble resin: 5 wt% Hydrophilic organic solvent: 34 wt% Water: 57 wt% Surfactant: 1 wt% Defoaming agent: 0.2 wt% BS: 2 wt% Infrared absorber: 0.5 wt% Other ... 3 wt% Water-soluble fluorescent ink 6 (Example 3) Water-soluble resin amount ... 5 wt% Hydrophilic organic solvent ... 33.5 wt% Water ... 57 wt% Surfactant ... 1 wt% Defoamer ... 0.2 wt% BS ... 2 wt% Infrared absorber: 1.0 wt% Other: 0.3 wt% Water-soluble fluorescent ink 7 (Comparative Example 4) Water-soluble resin amount: 5 wt% Hydrophilic organic solvent: 33.3 wt% Water 57 wt% Surfactant 1 wt% Antifoaming agent 0.2 wt% BS 2 wt% Infrared absorber 1.25 wt% Others 0.25 wt% More than 0.25 wt% of water-soluble fluorescent inks 1 to 7 are printed on private postcards. The result of the measurement by the light amount measuring device of FIG. 1 and the result of printing were examined for visibility, and the results shown in Table 1 were obtained.

[0019]

[Table 1]

In Table 1, the first CCD sensor 5
And the output of the second CCD sensor 8 is V (voltage). In the first CCD sensor output, ○ indicates good reading and X indicates poor. In addition, ○ in visibility indicates good as an invisible or hardly visible fluorescent ink, X indicates poor, and Δ indicates slightly poor.

As can be seen from Table 1, when the infrared absorbing agent is added in an amount exceeding 1 wt%, the color when the absorbing agent is dissolved (EEX Color 702W exhibits a dark green or brown color) becomes strong. Although it is sufficient as a fluorescent ink that is difficult to see, it is insufficient as a fluorescent ink that cannot be seen. Further, when the addition of the infrared absorbing agent was 0.2 wt% or less, the output of the first CCD sensor 5 exceeded 0.1 V, and the result that the reflected light of the black lamp 1 in the vicinity of 700 nm to 800 nm could not be cut sufficiently was obtained. . Therefore, when the addition of the infrared absorbent is 0.2 wt% or less, for example, when the postcard is conveyed at a relatively low speed of 2 m / sec or less or when the postcard is not conveyed, the printed contents can be read. However, if the postcard is conveyed at a relatively high speed exceeding 2 m / sec, the reading may be inaccurate. On the other hand, the addition of the infrared absorber was 0.25.
If it is not less than 0.1 wt%, the output of the first CCD sensor 5 will be 0.1 V or less,
Reading is possible without being affected by reflected light around 800 nm,
Even if the postcard is conveyed at a high speed exceeding 2 m / sec, the printed contents can be reliably read.

From the above, with the invisible fluorescent ink,
In addition, it has been found that it is desirable to add the infrared absorber in the range of 0.25 wt% to 1 wt% in order to reliably read the printed content during high-speed conveyance.

The output of the second CCD sensor 8 is for recognizing whether the light is emitted from the fluorescent ink or the fluorescent whitening agent on the paper, and detects an optical output having a wavelength of 420 nm or more.
Accordingly, the second CCD sensor 8 simultaneously detects the emission of the fluorescent substance in the fluorescent ink and the reflected light of the black lamp 1 of 700 nm or more. For example, when the water-soluble fluorescent ink 2 of Comparative Example 2 is used, the characteristics of the incident light to the second CCD sensor 8 are as shown in FIG. And the characteristics of the reflected light of 700 nm or more by the black lamp 1 are combined, and a large amount of the reflected light of 700 nm or more by the black lamp 1 is detected.

On the other hand, for example, when the water-soluble fluorescent ink 5 of the second embodiment is used, the characteristic of the incident light to the second CCD sensor 8 is, as shown in FIG. The characteristics are not affected by the reflected light. This is because the infrared absorber added to the fluorescent ink absorbs the reflected light of the black lamp 1 having a wavelength of 700 nm or more. Therefore, from the output result of the second CCD sensor 8, when the water-soluble fluorescent ink 5 according to the second embodiment is used, the printed content is reliably read without being affected by the reflected light of the black lamp 1 of 700 nm or more. We can see that we can do it. In the above-mentioned comparative examples and examples, the case where 2 wt% of BS, which is a water-soluble fluorescent whitening agent, was added, but the concentration-emission output characteristic of BS shows the characteristic as shown in FIG. , Actually 2.5wt5
Good degree.

From the above results, it can be seen that a water-soluble fluorescent ink containing water, a water-soluble resin, a hydrophilic organic solvent and a fluorescent material excited by ultraviolet light as main components has a wavelength of 700 nm or more.
By adding an absorbing material having an absorption around 850 nm, invisible or invisible printing can be performed, and even when printing on ordinary white paper to which a fluorescent whitening agent is added, the fluorescent whitening on the paper is performed. It is possible to recognize the printed content without being greatly affected by the agent, and more desirably, by adding the absorbing material to 0.25 wt% or more and 1.0 wt% or less, it is possible to reliably perform invisible printing, and furthermore, the Even when printing on normal white paper to which a whitening agent has been added, the printed content can be reliably recognized without being affected by the fluorescent whitening agent on the paper.For example, printing on a postcard Even if the postcard is conveyed at a high speed, the printed contents can be reliably read.

Next, as shown in FIG. 11, water, a water-soluble resin,
A water-soluble fluorescent ink containing a hydrophilic organic solvent and a fluorescent material excited by ultraviolet light has a wavelength of 700 nm to 850 n.
A method of printing an invisible barcode 22a with a water-soluble fluorescent ink to which an absorbing material having an absorption is added in the vicinity of m and using the reader shown in FIG. 8 to determine the presence or absence of the fluorescent ink will be described. As shown in FIG. 8, private postcard 2
2 and irradiates the printing surface of the barcode 22 a with ultraviolet light from the black lamp 21, and reflects the reflected light from the private postcard 22, while passing the first light through the first condenser lens 23 and the first filter 24. , And the other is detected by a second CCD sensor 28 through a second condenser lens 26 and a second filter 27.

As the first filter 24, as shown in FIG. 3, an L-42 filter having a light transmission characteristic of transmitting a wavelength of 420 nm or more is used, and as the second filter 27, as shown in FIG. As shown, an R-70 filter having a light transmission characteristic of transmitting a wavelength of 700 nm or more is used.

First, a private postcard 22 is conveyed, irradiated with ultraviolet light from a black lamp 21 and its reflected light is detected by a first CCD sensor 25 through a first condenser lens 23 and a first filter 24. . At this time, since the first filter 24 transmits only the wavelength of 420 nm or more,
The wavelength of 365 nm, which is the main component of the black lamp 1, is cut off. Further, the black lamp 1 has a unique spectrum around 700 nm to around 800 nm due to the influence of the mercury ray, and the reflected light is absorbed by the infrared absorbent in the fluorescent ink.

Therefore, when the first CCD sensor 25 reads the fluorescent ink of the barcode 22a, the fluorescent lamp has a peak at around 440 nm due to the fluorescent whitening agent contained in the fluorescent ink. 700 nm to 80
Since a unique mercury line spectrum around 0 nm occurs,
The wavelength characteristic of the fluorescent ink detected by the first CCD sensor 25 is as shown by the solid line graph a in FIG.
The total output of these is sent from the CD sensor 25. The output at this time is, for example, 1.2V.

When the white portion on the postcard 22 other than the barcode 22a is read by the first CCD sensor 25, the reflected light from the fluorescent brightener contained in the white portion and the mercury of the black lamp 1 According to the spectrum of the line, the wavelength characteristic of the reflected light from the white portion on the postcard detected by the first CCD sensor 25 becomes the characteristic shown by the dotted line b in FIG. Is output. The output at this time is 0.8V. At the stage of measurement by the first CCD sensor 25, there is not much difference in the output level, and it is possible to discriminate between a postcard containing a fluorescent brightener and another postcard not containing a fluorescent brightener. It is difficult to reliably determine whether a postcard is a white part or a fluorescent ink part.

The private postcard 22 is further conveyed, and its reflected light is detected by the second CCD sensor 28 through the second condenser lens 26 and the second filter 27. At this time, since the second filter 27 transmits only the wavelength of 700 nm or more, the reflected light from the fluorescent whitening agent having a wavelength of 365 nm, which is a main component of the black lamp 1, and having a peak near 440 nm is cut. Therefore,
The wavelength passing through the second filter 27 is 700 nm to 800 nm according to the spectrum of the mercury ray of the black lamp 1.
The nearby wavelengths are dominant.

When the fluorescent ink is detected, an infrared absorbent having an absorption wavelength around 700 nm to 850 nm is added to the fluorescent ink.
The wavelength near 0 nm is absorbed, and the reflected light from the black lamp 1 is suppressed. Therefore, the second CCD sensor 28
, The wavelength characteristic of the fluorescent ink detected is the characteristic shown by the solid line graph c in FIG. 10, and the output of the second CCD sensor 28 is 0.05 V.

On the other hand, the reflected light from the white part on the postcard 22 has no absorption by the infrared absorbing agent,
The wavelength characteristic of the reflected light from the white portion on the postcard detected by the CCD sensor 28 becomes the characteristic shown by the dotted line d in FIG. 10, and the influence of the reflected light in the vicinity of 700 nm to 800 nm by the mercury line spectrum of the black lamp 1. And the output of the second CCD sensor 28 becomes 0.3V.

As described above, the second CCD depends on the reflected light from the fluorescent ink or the reflected light from the white portion of the postcard 22.
Since the output level of the sensor 28 is significantly different, this second
From the output level of the CCD sensor 28, it is possible to reliably determine whether to read the fluorescent ink or to read other portions.

FIG. 12 is a flowchart showing the algorithm of the above-described determination processing. That is, first, S1
It is checked whether or not the detection output level of the first CCD sensor 25 is higher than a reference level, for example, 0.4 V. If the detection output level is not higher than the reference level (0.4 V), there is no fluorescent whitening agent component. It is determined that the postcard 22 has no barcode printed with the fluorescent ink. If the detection output level of the first CCD sensor 25 is equal to or higher than the reference level (0.4 V), it is determined that the postcard 22 has the fluorescent brightener component.

Subsequently, in S2, the second CCD sensor 2
It is checked whether or not the output level of No. 8 is a reference level, for example, 0.1 V or more. If the output level of the second CCD sensor 28 is lower than the reference level (0.1 V), it is determined that the portion is a portion printed by the fluorescent ink. Thus, the barcode 22a printed on the postcard 22 with the fluorescent ink can be reliably read.

In the above-described embodiment, Mike manufactured by Mitsui Toatsu Co., Ltd. is used as a fluorescent whitening agent excited by ultraviolet rays.
Although rphor BS conc 200% was used, the present invention is not limited to this, and other fluorescent whitening agents may be used.
In the embodiment described above, as the infrared absorber,
Although a water-soluble phthalocyanine-based dye such as EEX Color 702W was used, the present invention is not limited to this, and an absorption material having an absorption wavelength around 700 nm to 850 nm may be used. Further, a styrene acrylic resin was used as the water-soluble resin, but it is not necessarily limited to this, and PVP (polyvinylpyrrolidone) and P
VA (polyvinyl alcohol) or the like may be used.

Further, since the water-soluble fluorescent ink of the present invention contains an infrared absorbing material, for example, the printing section is irradiated with a light source in a wavelength region that is absorbed by the absorbing material. Since the light-absorbing area becomes black due to the absorption of light, it is possible to read the printed contents even by such a method.

[0039]

As described above, according to the first aspect of the present invention, since an absorbing material having an absorption wavelength of about 700 nm to 850 nm is added, an inexpensive fluorescent whitening agent or the like is used as the fluorescent material. Invisible or invisible prints can be made, and even when printed on a print medium to which a fluorescent whitening agent is added, the printed contents can be recognized without being greatly affected by the fluorescent whitening agent on the print medium. A water-soluble fluorescent ink can be provided.

According to the second aspect of the present invention, the amount of the absorbing material to be added is not less than 0.25% by weight and not more than 1.0% by weight. A water-soluble solution that allows invisible printing and prints on a print medium containing a fluorescent whitening agent without being affected by the fluorescent whitening agent. Can provide a fluorescent ink.

According to the third aspect of the present invention, a fluorescent whitening agent or the like is added as a fluorescent material,
When using a water-soluble fluorescent ink to which an absorbing material having an absorption in the vicinity of 00 nm to 850 nm is added, and printing is not performed on a printing medium to which a fluorescent whitening agent is added or hardly visible, the fluorescence on the printing medium is reduced. It is possible to provide a method for determining a water-soluble fluorescent ink that can reliably recognize printed contents without being affected by a brightener.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a light quantity measuring device for measuring a light quantity of fluorescent ink according to an embodiment of the present invention.

FIG. 2 is a graph showing light transmission characteristics of a first filter in the light quantity measuring device of FIG.

FIG. 3 is a graph showing light transmission characteristics of a second filter in the light quantity measuring device of FIG. 1;

FIG. 4 is a graph showing light transmission characteristics of an EX color 702W in the light quantity measuring device of FIG.

FIG. 5 is a graph showing incident light characteristics in Comparative Example 2 with respect to a second CCD sensor in the light quantity measuring device of FIG. 1;

FIG. 6 is a graph showing incident light characteristics in a second embodiment of the second CCD sensor in the light quantity measuring device of FIG. 1;

FIG. 7 is a graph showing concentration-emission output characteristics of a water-soluble fluorescent whitening agent, BS, added to the water-soluble fluorescent ink used in the embodiment.

FIG. 8 is a schematic configuration diagram of a reading device that reads a print content used in the embodiment.

9 is a graph showing wavelength characteristics of fluorescent ink detected by a first CCD sensor in the reader of FIG. 8 and wavelength characteristics of light reflected from a white portion on a postcard.

FIG. 10 is a graph showing wavelength characteristics of fluorescent ink detected by a second CCD sensor in the reader of FIG. 8 and wavelength characteristics of light reflected from a white portion on a postcard.

FIG. 11 is a diagram showing a private postcard on which the reader of FIG. 8 reads.

FIG. 12 is a flowchart showing a reading process by the reading device of FIG. 8;

[Explanation of symbols]

 21 black lamp 22 private postcard (printing medium) 24, 27 filter 25, 28 CCD sensor

Claims (3)

[Claims] 1. A water-soluble fluorescent ink containing water, a water-soluble resin, a hydrophilic organic solvent, and a fluorescent material excited by ultraviolet light as a main component, to which an absorbing material having an absorption wavelength in the vicinity of 700 to 850 nm is added. A water-soluble fluorescent ink, characterized in that: 2. The method according to claim 1, wherein the absorption material is 0.25 wt% or more and 1.0 or more.
2. The water-soluble fluorescent ink according to claim 1, wherein the ink is added in an amount of not more than wt%. 3. A water-soluble fluorescent ink containing water, a water-soluble resin, a hydrophilic organic solvent, and a fluorescent material excited by ultraviolet light as a main component, is added with an absorbing material having an absorption wavelength of around 700 nm to 850 nm. Irradiating the print medium printed with the water-soluble fluorescent ink with ultraviolet light, detecting reflected light having a wavelength of 700 nm or more and light emitted from the water-soluble fluorescent ink to determine the presence or absence of the fluorescent ink. Characteristic determination method of water-soluble fluorescent ink.