Ink composition using NANO copper compound having high near-infrared absorbency

Abstract

The present invention relates to an ink composition for printing a compound that absorbs near-infrared rays and, more specifically, to an ink composition for printing a copper compound having a maximum absorption wavelength in the near-infrared region. The ink composition for printing a copper compound according to the present invention can have a maximum absorption wavelength of 1000 nm or greater. In addition, the copper compound is applied as an inkjet ink by synthesizing into nanoparticles, and thus not only has a high absorption intensity in the near-infrared region but also has high dispersibility, and thus can be easily applied to offset printing. In addition, a printed product having excellent chemical resistance can be manufactured through post-treatment of a near-infrared absorber.

Description

Ink composition using nano copper compounds having high absorption capacity in the near-infrared region

[0001] The present invention relates to a near-infrared absorbing pigment and ink composition containing a copper compound in the form of nanoparticles as a near-infrared absorbent, which is a material that can be usefully used as a near-infrared absorbent having high absorption capacity in the wavelength range of the near-infrared region.

[0002] And, using a surfactant, an ink composition with excellent chemical resistance of a near-infrared absorbent was manufactured. The present invention relates to a technology for various uses and applications such as anti-counterfeiting, anti-tampering, and device detection of security products using the above-mentioned near-infrared absorption characteristics, including inkjet, offset, screen, and gravure printing.

[0003] Near-infrared absorbers generally refer to materials that absorb light in the wavelength range of 700 to 2,500 nm. They are invisible in daylight, but become visible through absorption / reflection in the near-infrared. Therefore, this technology is primarily applied to security-requiring items such as banknotes, checks, passports, bonds, and other securities. This section briefly describes the fields related to the present invention.

[0004] The nanoparticle-formulated copper compound synthesized by the present invention is applied to various fields such as inkjet, offset, screen, gravure, and intaglio printing, and is used as a near-infrared absorbing material for security products such as banknotes, security documents, passports, and checks to prevent counterfeiting or for device detection and identification. Since these security products are frequently handled by users, there is a risk of damage. Therefore, to ensure product safety and reliability, it is essential to develop a near-infrared absorbing composition with excellent chemical resistance, such as solvent resistance, acid resistance, and alkali resistance.

[0005] In general, there are various substances that absorb wavelengths in the near-infrared region, and they can be classified into near-infrared absorbing organic dye compounds and near-infrared absorbing inorganic pigment compounds.

[0006] Representative near-infrared absorbing organic dye compounds include azo, phthalocyanine, squarylnium, dimonium, cyanine, and dithiolene compounds, which absorb near-infrared wavelengths from 700 to 1000 nm depending on the type of substituent and the central metal. The central metal is a metal or metal oxide such as copper, nickel, zinc, vanadium, iron, manganese, lithium, or cobalt.

[0007] Near-infrared absorbing inorganic pigment compounds are mainly phosphate and pyrophosphate compounds, and research on alkaline phosphate compounds containing alkaline metals is currently in progress. Inorganic near-infrared absorbing pigments have a brighter appearance than organic near-infrared absorbing dyes, although this varies depending on the bonding metal, and are therefore also used as colorless near-infrared absorbers. Inorganic near-infrared absorbers exhibit differences in absorption performance depending on particle size. Metals such as copper, nickel, iron, titanium, and manganese are used as central metals, and lithium, sodium, and potassium are used as alkaline metals, and the nanoparticle-formed copper compound of the present invention falls into this category.

[0008] Near-infrared absorbing inorganic pigment compounds have higher stability than near-infrared absorbing organic dye compounds, have strong resistance to UV light and heat, and are chemically stable, so they do not easily deteriorate when used for a long period of time.

[0009] These near-infrared absorbing materials each have advantages and disadvantages in terms of near-infrared absorbance, light resistance, and heat resistance, depending on their physicochemical properties. However, they are selected and used according to their intended purpose. However, they have the characteristic of having a specific color.

[0010] While inkjet printers have many advantages over other types of printing and imaging, they require dyes that meet the conflicting requirements of not being dissolved within the ink medium or running or smudging excessively when printed on paper.

[0011] To prevent individual sheets of paper from sticking together after printing, the ink must dry quickly, but it must also not form clumps on the printer's fine nozzles. Storage stability is also important to prevent the formation of particles that could clog the printer's fine nozzles.

[0012] The present invention relates to a security printing ink composition having enhanced chemical resistance, which forms a nanoparticle-type near-infrared absorbent and a surfactant into a micelle structure while maintaining a nano size so as not to affect the micro-nozzle of a printer, and the purpose of the present invention is to provide a security printing ink composition having enhanced absorption characteristics and chemical resistance, which complements the shortcomings of existing organic near-infrared absorbents based on the inorganic near-infrared absorbent of the present invention.

[0013] In order to solve the above-described problem of the present invention, as an embodiment of the present invention, a security printing ink composition is provided, comprising a phosphate-based near-infrared absorbent having a particle size distribution of nanoparticles and containing one or more transition elements selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Hf, Ta, W, Re, Os, Ir, Pt and Au; and a surfactant, wherein the near-infrared absorbent and the surfactant form a micelle structure.

[0014] As another embodiment of the present invention, the particle size distribution of the near-infrared absorbent may be 10 to 1000 nm.

[0015] As another embodiment of the present invention, the near-infrared absorbent may be Cu2PO4(OH), preferably Cu2PO4(OH) having a libethenite crystal structure.

[0016] In another embodiment of the present invention, the surfactant is selected from the group consisting of polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monopalmitate, polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan tristearate, polyoxyethylene sorbitan monooleate, polyoxyethylene sorbitan trioleate, sorbitan monolaurate, sorbitane monostearate, sorbitan tristearate, sorbitan monooleate, sorbitane trioleate, It may be one selected from poloxamer 124, poloxamer 188, poloxamer 237, poloxamer 338, poloxamer 407, dodecylbenzenesulfonate, poly(4-vinylpyridine), sodium dodecylsulfonate, cetyltrimethylammonium bromide, polyvinylpyrrolidone, and octylphenol ethoxylate.

[0017] As another embodiment of the present invention, the nanoparticle-formed near-infrared absorbent may contain IR-absorbing transition element atoms or ions at a concentration of 20 to 40 wt%.

[0018] As another embodiment of the present invention, the nanoparticle-formed near-infrared absorbent may be included in an amount of 0.1 wt% to 40 wt% of the ink.

[0019] As another embodiment of the present invention, the ink composition may be for inkjet, offset, screen, gravure, or plate printing.

[0020] An ink composition using a nano copper compound manufactured according to the present invention has high absorption capacity in the near-infrared region, and has enhanced chemical resistance due to the formation of a micelle structure by a near-infrared absorbent and a surfactant.

[0021] Figure 1 is a near-infrared absorbance of the nanoparticle-ized copper compound of Synthesis Example 1.

[0022] Figure 2 is the near-infrared absorbance of the copper compound of comparative synthesis example 1.

[0023] Figure 3 shows XRD (X-ray diffraction) data of Synthesis Example 1.

[0024] Figure 4 shows EDS (Energy Dispersive Spectroscopy) data of Synthesis Example 1.

[0025] Figure 5 shows the particle size distribution table of Synthesis Example 1.

[0026] Figure 6 is an SEM photograph of the nanoparticle-ized copper compound of Synthesis Example 1.

[0027] Figure 7 shows the size of the SEM photograph of the nanoparticle copper compound of Synthesis Example 1.

[0028] Figure 8 is an SEM photograph of the copper compound of Synthesis Example 2.

[0029] Figure 9 shows the size of the SEM photograph of the copper compound of Synthesis Example 2.

[0030] Figure 10 is an SEM photograph of the copper compound of Synthesis Example 3.

[0031] Figure 11 shows the size of the SEM photograph of the copper compound of Synthesis Example 3.

[0032] Figure 12 is an SEM photograph of the copper compound of comparative synthesis example 1.

[0033] Figure 13 shows the size of the SEM photograph of the copper compound of comparative synthesis example 1.

[0034] The present invention relates to a printing ink composition of a copper compound having a maximum absorption wavelength in the near-infrared region, and the printing ink composition of a copper compound according to the present invention has a maximum absorption wavelength of 1000 nm or more.

[0035] In the expressions of the present invention, "ultraviolet" (UV) is used to designate a spectral range between 100 and 400 nm, "visible" (Vis) is used to designate a spectral range between 400 and 700 nm, "infrared" (IR) is used to designate a spectral range between wavelengths of 780 nm and 15000 nm, and near infrared (NIR) is used to designate a spectral range between wavelengths of 780 nm and 1400 nm (a range provided by the International Commission on Illumination (CIE)), which is cited in the literature [Sliney DH, Eye (the Scientific Journal of the Royal College of Ophtalmologists, 2016, 30(2), pages 222-229)].

[0036] The printing ink composition of the present invention comprises a phosphate-based near-infrared absorbent having a particle size distribution of nanoparticles and a surfactant, which contains at least one transition element, and the near-infrared absorbent and the surfactant form a micelle structure.

[0037] The transition element of the near-infrared absorbent may be at least one selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Hf, Ta, W, Re, Os, Ir, Pt and Au, and it is preferable that the near-infrared absorbent contains 20 to 40 wt% of the transition element or ion.

[0038] The surfactants that form the near-infrared absorber and the micelle structure are polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monopalmitate, polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan tristearate, polyoxyethylene sorbitan monooleate, polyoxyethylene sorbitan trioleate, sorbitan monolaurate, sorbitane monostearate, sorbitan tristearate, sorbitan monooleate, sorbitane trioleate. It may be at least one selected from poloxamer 124, poloxamer 188, poloxamer 237, poloxamer 338, poloxamer 407, dodecylbenzenesulfonate, poly(4-vinylpyridine), sodium dodecylsulfonate, cetyltrimethylammonium bromide, polyvinylpyrrolidone, and octylphenol ethoxylate.

[0039] The printing ink composition of the present invention, which synthesizes a copper compound as a near-infrared absorbent into nanoparticles and then applies it as a printing ink, exhibits high absorption intensity in the near-infrared region and has high dispersibility, making it suitable for offset printing. Furthermore, by forming a micelle structure using a surfactant, it is possible to produce printed matter with excellent chemical resistance.

[0040] The particle size distribution of the near-infrared absorbent included in the printing ink composition of the present invention is 10 to 1000 nm, and has the advantage of not having a concern about clogging the inkjet head due to the small nanoparticle size.

[0041] Furthermore, near-infrared absorbers that have been surface-treated with surfactants to form micelle structures have a size that is almost identical to that of near-infrared absorbers that have not been surface-treated, and likewise maintain a nanoscale size. Therefore, when using near-infrared absorbers that have been surface-treated with surfactants, they can be used as inkjet inks while maintaining the nanoscale size characteristic of nanoparticle-type near-infrared absorbers, while also exhibiting excellent chemical resistance.

[0042] The content of the near-infrared absorbent included in the printing ink composition of the present invention is 0.1 to 40 wt% of the total ink composition. If the content of the near-infrared absorbent exceeds 40 wt% of the ink, the content of the binder used in the production of the ink may be reduced, which may cause a problem in that the overall resistance of the ink is weakened.

[0043] The printing ink composition of the present invention is a security printing ink composition for inkjet, offset, screen, gravure, and plate printing.

[0044] Hereinafter, preferred embodiments of the present invention will be described in detail. However, the following embodiments are provided to enable those of ordinary skill in the art to fully understand the present invention, and may be modified in various other forms, and the scope of the present invention is not limited to the embodiments described below.

[0045]

[0046] [Synthesis Example 1]

[0047] To synthesize copper hydroxide phosphate nanoparticles, a 0.2 M aqueous copper sulfate solution was placed in a three-necked flask and stirred. A 0.2 M aqueous ammonium phosphate solution was then prepared in a beaker and stirred. The ammonium phosphate solution was added to the aqueous copper sulfate solution and stirred for 1 hour. Ammonia water was then added until the pH reached 5 to 7, followed by stirring. The mixture was stirred for 3 hours, maintaining the temperature at 100°C, until the reaction was complete. After the reaction was complete, the precipitate formed was filtered and washed.

[0048]

[0049] [Synthesis Example 2]

[0050] To synthesize copper hydroxide phosphate, a 0.2 M aqueous solution of copper nitrate was placed in a three-necked flask and stirred. A 0.2 M aqueous solution of ammonium phosphate was then prepared in a beaker and stirred. The ammonium phosphate solution was added to the copper nitrate solution and stirred for 1 hour. Ammonia water was then added until the pH reached 5 to 7, followed by stirring. While maintaining the temperature at 100°C, the mixture was stirred for 3 hours until the reaction was complete. After the reaction was complete, the precipitate formed was filtered and washed.

[0051]

[0052] [Synthesis Example 3]

[0053] To synthesize copper hydroxide phosphate, a 0.2 M aqueous solution of copper chloride was placed in a three-necked flask and stirred. A 0.2 M aqueous solution of ammonium phosphate was then prepared in a beaker and stirred. The ammonium phosphate solution was added to the aqueous copper chloride solution and stirred for 1 hour. Ammonia water was then added until the pH reached 5 to 7, followed by stirring. While maintaining the temperature at 100°C, the mixture was stirred for 3 hours until the reaction was complete. After the reaction was complete, the precipitate formed was filtered and washed.

[0054]

[0055] [Comparative Synthesis Example 1]

[0056] To synthesize copper hydroxide phosphate, a 0.1 M aqueous copper nitrate solution was placed in a 250 ml beaker and stirred. A 0.1 M aqueous sodium phosphate solution was then prepared and stirred in another beaker. The sodium phosphate solution was added to the copper nitrate solution and heated and stirred for 1 hour. The reaction was then carried out at 120°C for 8 hours using a high-temperature, high-pressure reactor. After the reaction was complete, the resulting precipitate was filtered and washed.

[0057]

[0058] Figure 1 shows the near-infrared absorbance of the nanoparticle copper compound of Synthesis Example 1. The near-infrared absorbing material according to the present invention has an absorbance difference in the visible light region and the near-infrared region of about 40 to 50%.

[0059] In this way, when the difference in absorbance between the visible light region and the near-infrared region is in the range of 40 to 50%, it has various advantages as a security material due to its bright color.

[0060] Figure 2 shows the near-infrared absorbance of the copper compound of Comparative Synthesis Example 1. The copper compound manufactured by Comparative Synthesis Example 1 has a difference in absorbance between the visible light region and the near-infrared region of about 30 to 40%, and it can be confirmed that it exhibits an absorbance in a lower region than the near-infrared absorbance of the nanoparticle-formed copper compound of Synthesis Example 1. Therefore, in the case of Synthesis Example 1, it can exhibit the desired near-infrared absorbance even with a lower content than Comparative Synthesis Example 1, and thus it can be seen to be superior in terms of usability as a security material.

[0061] Figure 3 shows the XRD of the nanoparticle-ized near-infrared absorbing material of Synthesis Example 1. The graph for Synthesis Example 1 is shown in red, and the graph of rebesenite corresponding to Cu2(PO4)(OH) as a standard is shown in blue. Since the XRD data of the nanoparticle-ized near-infrared absorbing material of Synthesis Example 1 and the graph of rebesenite show peaks at the same positions, it can be confirmed that they are the same material although they show differences in particle size distribution. Synthesis Examples 2 and 3 are also the same material as rebesenite, but show differences only in particle size distribution.

[0062] Specifically, the theoretical elemental analysis value of the crystal structure of Synthesis Example 1 is composed of approximately 53 wt% copper, 13 wt% phosphorus, and 33 wt% oxygen, and the actual elemental analysis value of the crystal structure of the copper compound synthesized by Synthesis Example 1 is approximately 50 wt% copper, 15 wt% phosphorus, 31 wt% oxygen, and other components. This shows that the basic composition may change depending on various factors and variables of the synthesis process, and it should be viewed that the copper compound of the present invention may not have quantitative properties, and has fluid values ​​in qualitative and quantitative components.

[0063] Figure 4 shows an EDS of a copper compound nanoparticle of Synthesis Example 1. EDS is a technique that is combined with an electron microscope to shoot electrons to collide with the surface of a sample and analyze the radiation (Characteristic X-rays) generated in the process. By measuring the energy of the X-rays generated at this time and matching it with the characteristic energy of the element, the element contained in the sample is analyzed. In Figure 4, the presence of the metallic element Cu can be confirmed in the EDS of the copper compound nanoparticle of Synthesis Example 1.

[0064] Figure 5 is a particle size distribution table of the nano-particle copper compound manufactured by Synthesis Example 1. Referring to the graph, the nano-particle copper compound manufactured by Synthesis Example 1 exhibits a particle size distribution of approximately 5 to 300 nm, and particles of 100 nm or less account for 70 to 80% of the distribution, confirming that it has been nano-particleized.

[0065] Figure 6 is an SEM photograph of the copper compound particles that were nanoparticleized in Synthesis Example 1, taken using a scanning electron microscope (SEM).

[0066] Figure 7 shows the particle size in an SEM photograph of the nanoparticle-ized copper compound particles of Synthesis Example 1. As seen in Figure 7, the particle size of the nano copper compound manufactured with copper sulfate is within the range of 20 to 150 nm, confirming that it has been nanoparticleized.

[0067] Figure 8 is an SEM photograph of the particles of the copper compound of Synthesis Example 2, measured using a scanning electron microscope (SEM).

[0068] Figure 9 shows the particle size in an SEM photograph of the copper compound particles of Synthesis Example 2. As seen in Figure 9, the particle size of the copper compound manufactured with copper nitrate is within the range of 4 to 5 μm, confirming that it is not nanoparticleized.

[0069] Figure 10 is an SEM photograph of the particles of the copper compound of Synthesis Example 3, measured using SEM.

[0070] Figure 11 shows the particle size in an SEM photograph of the copper compound particles of Synthesis Example 3. As seen in Figure 11, the particle size of the copper compound manufactured with copper chloride is within the range of 5 to 7 μm, confirming that it is not nanoparticleized.

[0071] The particles of the copper compound of Comparative Synthesis Example 1 were measured using a SEM (scanning electron microscope), and the SEM images and particle size distributions measured therefrom are shown in Figs. 12 and 13, respectively. As seen in Figs. 12 and 13, the particle size of the copper compound manufactured with copper chloride is within the range of 1 to 3 μm, confirming that it is not nano-particleized.

[0072] Compared to the copper compound synthesized in Synthesis Example 1, which was nano-sized in the nanometer range, the copper compounds synthesized in Synthesis Examples 2 and 3 and Comparative Synthesis Example 1 exhibit particle sizes in the micrometer range. Copper compounds having particle sizes in the micrometer range are not suitable for application to inkjet ink and offset printing because of the risk of inkjet heads being clogged due to the large particle size.

[0073]

[0074] [Experimental Example 1]

[0075] 5 g of the copper hydroxide phosphate synthesized in the above Synthesis Example 1 was dispersed in 100 ml of distilled water, 0.5 g of DBS (dodecylbenzene sulfonate sodium salt) was added, and then ultrasonic treatment was performed at 50°C for approximately 1 hour. After filtration, drying was performed to produce nanoparticles of copper hydroxide phosphate surface-treated with a surfactant.

[0076]

[0077] Manufacturing of ink for inkjet printers

[0078] [Example 1]

[0079] Using the nanoparticle copper hydroxide phosphate surface-treated with the surfactant obtained in Experimental Example 1 as a near-infrared absorbent, the raw material composed as shown in Table 1 below is dispersed and mixed using a Sambon mill, and then filtered with a 0.45 micron filter paper to prepare ink for inkjet.

[0080] Using the ink manufactured by the above method, printing is performed using an inkjet printer, and then the near-infrared absorption capacity is measured at 850 nm using a near-infrared absorption spectrum (Shimadzu / UV3101 PC).

[0081]

[0082] [Reference Example 1]

[0083] An inkjet ink was prepared in the same manner as in Example 1, except that the nanoparticle copper hydroxide phosphate obtained in Synthesis Example 1 was used as a near-infrared absorbent, and the near-infrared absorbance was measured.

[0084]

[0085] [Comparative Example 1]

[0086] An inkjet ink was prepared in the same manner as in Example 1, except that the copper hydroxide phosphate obtained in Comparative Synthesis Example 1 was used as a near-infrared absorbent, and the near-infrared absorbance was measured.

[0087]

[0088] DistinctionNear-infrared absorbent(g)Solvent(g)Surfactant(g)Antibacterial agent(g)Viscosity regulator(g)Distilled water(g)Reflectance(%)Example 110 (Experimental example 1)103117526.9Reference example 110 (Synthesis example 1)103117526.4Comparative example 110 (Comparative synthesis example 1)103117527.2

[0089] In order to confirm the characteristics of a near-infrared absorber as a security material, it is good to make the difference between the visible light portion and the near-infrared portion large, and it can function as a near-infrared absorber when the reflectance is 30% or less. As shown in Table 1 above, the reflectances of Example 1, Reference Example 1, and Comparative Example 1, which were prepared by using Synthetic Example 1, Experimental Example 1, and Comparative Synthetic Example 1 as a near-infrared absorber, are 26.4, 26.9, and 27.2% at 850 nm, respectively, indicating a reflectance of 30% or less.

[0090] Therefore, it was confirmed that there was no problem in using the nanoparticle copper hydroxide phosphate surface-treated with the surfactant obtained in Experimental Example 1 as a near-infrared absorbent.

[0091]

[0092] Manufacturing of ink for lithographic printing

[0093] [Example 2]

[0094] As a near-infrared absorbent, nanoparticle copper hydroxide phosphate surface-treated with the surfactant obtained in Experimental Example 1 was used to prepare ink for plate printing by mixing raw materials as shown in Table 2 below and kneading twice in a three-roll mill.

[0095]

[0096] [Reference Example 2]

[0097] An ink for plate printing was prepared in the same manner as in Example 2, except that the copper hydroxide phosphate obtained in Synthesis Example 1 was used as a near-infrared absorbent.

[0098]

[0099] [Comparative Example 2]

[0100] An ink for plate printing was prepared in the same manner as in Example 2, except that the copper hydroxide phosphate obtained in Comparative Synthesis Example 1 was used as a near-infrared absorbent.

[0101]

[0102] Distinctive component content (wt%) Binder Rosin-modified phenol resin 25 Near-infrared absorber Near-infrared absorber obtained in Experimental Example 1, Synthesis Example 1, and Comparative Synthesis Example 1 20 Filler Calcium carbonate 30 Other auxiliary agents Cobalt-based drying agent 1 Aliphatic hydrocarbon-based solvent 24

[0103] A test specimen was manufactured by printing with an inkjet ink manufactured by the method of Example 1, Reference Example 1, and Comparative Example 1, and an ink for plate printing manufactured by the method of Example 2, Reference Example 2, and Comparative Example 2, and the results of a chemical resistance test performed on the test specimen are shown in Table 3 below.

[0104] Wavelength 850 (nm) Inkjet ink Ink for plate printing Example 1 Reference Example 1 Comparative Example 1 Example 2 Reference Example 2 Comparative Example 2 Reflectance deviation (△%) Reflectance deviation (△%) Reflectance deviation (△%) Reflectance deviation (△%) Reflectance deviation (△%) Reflectance deviation (△%) Initial------Gasoline 0.46 2.78 4.5 10.34 2.14 4.19 Toluene 1.5 3 1.87 3.9 8 1.42 1.39 3.67 2% Sulfuric acid 6.88 29.74 40.13 6.73 28.0 138.5 45% Hydrochloric acid 7.6 35.48 45.38 7.38 34.97 42.42% Sodium hydroxide 6.5132.6235.226.1231.131.56 Artificial sweat 4.4127.4938.313.9726.8335.04

[0105] The reflectance of each of the inkjet near-infrared absorbing ink printed samples of Example 1, Reference Example 1, and Comparative Example 1 and the near-infrared absorbing ink printed samples for intaglio printing of Example 2, Reference Example 2, and Comparative Example 2 was measured, and the reflectance was measured after chemical treatment with gasoline, toluene, 2% sulfuric acid, 5% hydrochloric acid, 2% sodium hydroxide, and artificial sweat. When the reflectance of the untreated sample was set as the initial value, the deviation of the reflectance from the sample treated with each chemical is shown in Table 3.

[0106] In the case of the ink compositions of Examples 1 and 2, it can be confirmed that the reflectance after each chemical treatment has a reflectance deviation of 0.46 to 7.6% and 0.34 to 7.38%, respectively, compared to the initial value without chemical treatment. In Examples 1 and 2, the maximum values ​​of the reflectance deviation are 7.6% and 7.38%, respectively, and it can be confirmed that the reflectance deviation is not large at less than 8% compared to the initial value without chemical treatment even after chemical treatment, and this characteristic confirms that the chemical resistance to various chemicals is excellent.

[0107] In the case of the ink compositions of Reference Examples 1 and 2, it can be confirmed that the reflectance after each chemical treatment has a reflectance deviation of 1.87 to 35.48% and 1.39 to 34.97%, respectively, compared to the initial value without chemical treatment. It can be confirmed that the deviation is about 4.5 times larger than the reflectance deviation of Examples 1 and 2, with a maximum of less than about 36%.

[0108] In the case of the ink compositions of Comparative Examples 1 and 2, it can be confirmed that the reflectance after each chemical treatment has a reflectance deviation of 3.98 to 45.38% and 3.67 to 42.4%, respectively, compared to the initial value without chemical treatment. It can be confirmed that the deviation is about 6 times larger than the reflectance deviation of Examples 1 and 2, with a maximum of less than about 46%.

[0109] In the case of the near-infrared absorbent ink compositions of Examples 1 and 2, since they contain sodium dodecylbenzenesulfonate, which is an anionic surfactant, it can be confirmed that they exhibit excellent chemical resistance properties such as solvent resistance, acid resistance, and alkali resistance compared to Reference Examples 1 and 2 and Comparative Examples 1 and 2.

Claims

1. A security printing ink composition comprising a phosphate-based near-infrared absorbent having a particle size distribution of nanoparticles containing one or more transition elements selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Hf, Ta, W, Re, Os, Ir, Pt, and Au; and a surfactant, wherein the near-infrared absorbent and the surfactant form a micelle structure.

2. In paragraph 1, An ink composition for security printing, wherein the near-infrared absorbent is Cu2PO4(OH), Cu2PO4(OH) having a libethenite crystal structure.

3. In paragraph 1, An ink composition for security printing, wherein the particle size distribution of the above nanoparticle-ized near-infrared absorbent is 10 to 1000 nm.

4. In paragraph 1, The above surfactant is polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monopalmitate, polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan tristearate, polyoxyethylene sorbitan monooleate, polyoxyethylene sorbitan trioleate, sorbitan monolaurate, sorbitane monostearate, sorbitan tristearate, sorbitan monooleate, sorbitane trioleate, An ink composition for security printing, comprising at least one selected from among poloxamer 124, poloxamer 188, poloxamer 237, poloxamer 338, poloxamer 407, dodecylbenzenesulfonate, poly(4-vinylpyridine), sodium dodecylsulfonate, cetyltrimethylammonium bromide, polyvinylpyrrolidone, and octylphenol ethoxylate.

5. In paragraph 1, The above nanoparticle near-infrared absorbent is an ink composition for security printing containing IR-absorbing transition element atoms or ions at a concentration of 20 to 40 wt%.

6. In paragraph 1, An ink composition for security printing, wherein the content of the nano-particled near-infrared absorbent is 0.1 to 40 wt% of the total ink composition.

7. In paragraph 1, The above ink composition is an ink composition for security printing, which is for inkjet, offset, screen, gravure, and plate printing.

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