RU2650138C2 - Colorless sol-gel ink for ink-jet printing iridescent holographic images and method for producing thereof - Google Patents

Abstract

FIELD: polygraphic industry.

SUBSTANCE: invention relates to sol-gel ink for ink-jet printing of iridescent holographic images on holographic paper or on a micro-embossed surface. Sol-gel ink comprises a nanocrystalline titanium dioxide sol of an anatase phase with an amorphous phase content of not more than 5 wt% in water and 60-70 wt% of ethyl alcohol. Solid content of said titanium dioxide sol in the ink is 1-5 wt%. Sol-gel ink has a surface tension of at least 25 mN/m, not more than 50 mN/m and a viscosity of not less than 2.1 mPa⋅s, not more than 20 mPa⋅s. Sol-gel ink is produced in two stages. At the first stage, the nanocrystalline titanium dioxide sol is obtained in water using a solution of titanium isopropoxide and 2-propanol, crystal formation and protonation. At the second stage, the sol-gel ink in the form of a nanocrystalline titanium dioxide sol in a solution of ethyl alcohol in water with the viscosity and surface tension required for ink-jet printing is produced from the nanocrystalline titanium dioxide sol in water.

EFFECT: invention provides a non-toxic ink based on chemically inert and environmentally safe titanium dioxide and environmentally acceptable ethyl alcohol and the possibility of a technologically simple and quick (no more than 5 minutes) ink-jet printing by conventional ink-jet printers unique and individual color iridescent holographic images on micro-embossed or holographic paper.

5 cl, 8 dwg, 1 tbl

Description

The invention relates to inorganic chemistry, in particular to the production of a sedimentation-stable sol of crystalline titanium dioxide nanoparticles, mainly in the anatase phase, used as colorless sol-gel ink for inkjet printing of color rainbow holographic images, which allows to print using inkjet printing products with color rainbow holographic images formed by at least one nanocrystalline xerogel refractory xerogel layer transparent in the visible region of the spectrum titanium dioxide having a thickness of 30 nm to 1 micron, with a refractive index of 1.7 and a color changing color depending on the thickness of the refractive layer xerogel.

Color printing technology is developing rapidly and in less than 40 years it has overcome the path from matrix printers with ink ribbon to 3D printers with the printing of bulk color materials, but the use for ink sets based on CMYK or RGB color schemes remains unchanged, which inevitably limits both technological capabilities and color reproduction. At the same time, ink for inkjet printing of some colors is environmentally hazardous, for example, yellow ink is usually made using toxic cadmium compounds (Cd ²⁺ ), in other cases, chromium, mercury and lead ions are used, and color images printed with ordinary inkjet method fade from the action of sunlight, UV radiation and high temperatures. In addition, it is possible to obtain high-quality color images using inkjet printing only on porous substrates (usually on special types of paper), which usually dry out after the ink dries.

Modern inkjet devices use several fundamentally different types of ink [http://smart-t.ru/page.php?id=9]:

- Water-based ink,

- Oil based ink,

- Solvent based inks (Solvent and EcoSolvent).

In water-based inks, the main component by volume is water with a small proportion of glycerol and solvent to obtain the viscosity and surface tension of the ink required for inkjet printing. In accordance with the nature of the coloring agent contained in them, water-based inks are divided into two main groups: dye-based ink (Dye) and pigment (Pigment).

The dye-based ink is completely dissolved in a liquid medium, which is given a very intense color and provides maximum optical properties due to light absorption and uniform distribution. Images printed with dye-based inks are particularly bright, but in most cases they are easily washed off with water and are not highly resistant to UV radiation.

Pigment ink is a suspension of small particles of colored inorganic pigment. They give color as well as Dye ink by absorbing light. But since the pigment is not dissolved in the medium, part of the light entering the surface is scattered by it. This explains the reduced brightness compared to dye-containing inks. Pigment inks are much more resistant to sunlight and moisture. Sometimes immersion of the print in water (without mechanical impact on the surface) does not lead to visible blurring of the image, and in combination with a moisture-resistant medium, the image can be used outdoors without additional protection.

The coloring component of oil ink is always pigment. These inks provide very high image quality and at the same time resistance to the negative effects of the environment (water and sunlight) for a fairly long time (about 1 year). Oil inks dry quickly, do not have a tendency to spread, which makes it possible to obtain prints of high definition, contrast and the desired color rendition, they are used in devices with piezoelectric heads, but they are not popular because of the high price and also as well as water-based inks require media with a special coating. Solvent-based inks usually contain chemically aggressive and environmentally hazardous substances, most often based on cyclohexanone, and pigment is always the coloring agent. Such inks do not require the use of coated materials (although specialized solvent printing materials will undoubtedly improve image quality).

Unlike images made with water and oil inks, which retain their qualities for no more than a year without surface protection, the invariance of “solvent” prints is observed for 3 years, and sometimes more.

The use in chemical solvent printing of less harmful chemical compositions for humans and the environment, which, nevertheless, provides a reliable connection of the pigment with the surface of the print medium. The use of eco-solvent ink has also reduced the cost of the printing devices themselves through the use of housings for the printheads and elements of the ink supply system from less expensive materials.

Standard solvent inks have been replaced by less environmentally hazardous, but no less effective in terms of print quality and print stability in use, eco-solvent inks that do not contain hazardous solvents, but well-known eco-solvent inks usually have a low resistance to intense abrasion.

Inkjet printing requires fine-tuning the viscosity and surface tension of the ink or fine-tuning the printer for a specific ink composition. In most cases, additives such as glycerin are used to increase the viscosity and surfactants to reduce surface tension, but this inevitably reduces the refractive index, due to an increase in the volume fraction of the organic part in the dry residue.

Known ink for an inkjet printer and an inkjet printing method with suppressing the phenomenon of twisting of printed materials and stable ejection, including 62-77 wt. % water, 10-18 wt. % dye, 2.0-15 wt. % water-soluble organic substances, including X (%) water-soluble organic matter 1, and Y (%), water-soluble organic matter 2. Moreover, the ink viscosity is from 1 to 5 cP at 25 ° C, and the content of X (%) of substance 1 and the content Y (%) of substance 2 satisfies the ratio of formulas (I) and formula (II): (I) 0.15≤Y / X≤0.9; (II) 15 wt. % ≤X + Y≤32 wt. % Compound 1 is a water-retaining water-soluble organic compound having a difference between a water-holding ability in an environment with a temperature of 23 ° C. and a humidity of 45% and a water-holding ability in an environment with a temperature of 30 ° C. and a humidity of 80% at 36% or less. Compound 2 is a water-soluble organic compound other than dye and water-soluble organic compound 1 [RU 2329288 C09D 11/00, B41J 2/01, B41M 5/00 Publ. July 20, 2008, WO 2005/087879 (September 22, 2005)].

Known ink, device and method of inkjet printing with ink viscosity of 100 mPa⋅s or less based on 50 to 80 wt. % organic solvent capable of evaporation from printed ink. The paint includes a UV curable material polymerizable by the free radical polymerization mechanism, a photoinitiator and a dispersible colorant. The radiation curable material contains a UV curable oligomer having a polyester, urethane or epoxy backbone, a molecular weight of 500 to 4000 and a viscosity of 0.5 to 20 Pa · s at 60 ° C. The ink jet printing apparatus for said ink includes a printing mechanism, a device for evaporating the solvent from the ink, and a UV radiation source. The inkjet method using this ink provides coatings on substrates, including non-porous surfaces, with increased resistance to solvents and dry friction [RU 2561095 C09D 11/00, C09D 11/10, B41J 2/00, B41J 11/00 Publ. . 08/20/2015, WO 2011/021052 2011.02.24].

A known method of obtaining a composition of polysiloxane and organic titanate comprising a siloxane photopolymer containing titanium, designed to produce a coating with a high refractive index and is resistant to abrasion to protect spectacle lenses made from organic glasses, which includes, as the first component of the photopolymer, anhydrous alkoxysilane hydrolyzate obtained by hydrolysis organosilane. As a second component, the photopolymer contains a titanium carboxylic acid ester having the formula (RCOO) nTiR '(4-n) (I), where N is an integer from 1 to 4 inclusive, R is the number of hydrogen atoms or alkyl groups with 1- 5 by carbon atoms, and R 'represents a hydrogen atom, a hydroxyl group, or an alkoxy group of 1-5 C atoms. The reaction of these first and second components is carried out until the formation of the specified titanium siloxane photopolymer in the absence of added water. After adding water and hydrolysis of the hydrolyzable groups, further polymerization takes place to obtain a stable aqueous sol containing 20-30% by weight of TiO ₂ relative to the weight of the solid materials of the final composition [US 5357024 C08G 77/58; C08G 79/00; C08K 5/09; C08L 83/04; C09D 183/04; C09D 183/14; 1994.10.18].

Known printed product, including a substrate and an image printed by a combination of colors of six inks of different colors. Each of the colors is defined by a predetermined ink ratio having a full tone of a given color and a halftone of a given color. Each of the six inks has a combined color difference dE of the full tone L-C-H-a-b of not more than 2. Ink is combined on the product to produce colors other than six ink colors. Each of the six inks has a combined color difference of dE halftone of no more than 3. Each of the six colors contains one or two pigments. A method of printing an article on an analog printing device includes preparing an electronic data file of a given artistic image, including the specified colors for the corresponding elements of the artistic image. Perform test printing of the artistic image by printing a data file using a digital printing device. Printer settings are combined with an electronic art image file. Provide multiple print locations with copies of the combined parameters by setting up a printing device and an electronic file containing visualization of the art image. Using the combined settings of the printing device and the electronic data file of the artistic image, copies of the product are printed dotwise, forming a complete picture of the composed image [RU 2468923 V41M 1/14 Publ. 12/10/2012, WO 2009/083857 2009.07.09].

A known method of manufacturing multicolor printing reproductions, which consists in sequentially applying to the surface of the printed material colorful layers of different colors, carrying monochromatic raster images with different raster lines, according to which, to improve the quality of reproduction, the raster lineature for each monochromatic image is selected from the dependence a / b * [ (r _b- r _k ) / r _b ] ≤0.0007, where a is the raster pitch; b distance from the observer’s eye to the image in question; p _b - reflection coefficient of the printed material; p _to the reflection coefficient of the corresponding paint [RU 2043199 V41M 1/14 Publ. 09/10/1995].

Known grayscale image obtained by printing on a substrate, which consists of at least two types located in the form of a raster image points of different colors. The desired color is obtained by mixing the colors of the dots of the image, and fluorescent image dots of printing inks are formed on the substrate, which contain pigments fluorescent when excited by a certain electromagnetic radiation, as well as non-fluorescent image dots of printing inks containing color, non-fluorescent pigments when excited by a certain electromagnetic radiation. Moreover, these fluorescent image points and non-fluorescent image points are placed on a substrate in a checkerboard pattern relative to each other. This ensures the obtaining of a grayscale image, which is distinguished by high gloss and close to real color rendition [RU 2264296 В41М 1/14 В41М 3/14 B42D 15/10 Publ. November 20, 2005, WO 03/011606 (February 13, 2003)].

The phenomenon of interference in thin films is known, which is characterized by the fact that at the phase boundary of materials differing in optical density, a reflected beam is formed with a wavelength equal to the thickness of the material layer with a large refractive index (RI), which is perceived by the human eye as monochromatic color. In particular, interference is observed in soap bubbles (air / surfactant in water), in the iris of the multilayer structure of nacre. However, the saturation of the color, which is responsible for the contrast of the resulting image, largely depends on the magnitude of the difference in the refractive indices of the applied layer and the substrate used. To enhance this effect, attempts were made to modify polymers using various nanoscale crystalline substances. Such approaches made it possible to obtain a high refractive index for organic polymers, however, the optical properties of organic polymers deteriorated sharply due to the lack of a homogeneous distribution of components between themselves and technologically unsolved problems of forming films of a given thickness with an accuracy of 10 nm, complementary to the structure of the light wavelength .

An alternative to physical methods for producing interference films (by laser spraying, thermal calcination, laser excitation of metals in oxygen with the formation of oxide layers, vacuum deposition of “masks”, etc.) can be the preparation of inorganic polymer films by solution chemistry methods. In particular, the technology of low-temperature sol-gel synthesis, which makes it possible to obtain monolithic film crystalline materials at low temperatures and atmospheric pressure, is considered the greatest prospect. Langlet et al. Showed the application of this technology in the field of creating TiO ₂ coatings for optics and creating photocatalytic coatings on films.

All known methods of creating interference are not suitable for color inkjet printing.

Inorganic colloids are currently actively used for the film printing of biosensors and electronics, but their application for inkjet color printing is unknown. However, until now, the capabilities of inkjet printing have been focused by the microrange, that is, by the formation of image elements at the micron level, greater than the wavelengths of light. Therefore, it is relevant to develop previously unknown inkjet printing technologies for inorganic nanostructures with an accuracy of up to 10 nm in thickness to create the basis for the development of a new stage in the development of color inkjet printing and to develop fundamentally new interference methods for the formation of optical structures of nano-objects by inkjet printing methods.

A thin-film element with an interference layered structure for counterfeit papers, valuable documents and similar objects is known, comprising at least two translucent absorbing layers and at least one dielectric separation layer located between at least two absorbing layers . Each of the two absorbing layers consists of a material having a complex refractive index N, the real part n and the imaginary part k of which, at least in the part of the visible region of the spectrum, differ 5 or more times, when observed in reflected light, the thin-film element has a metal luster and essentially neutral color, and when observed in transmitted light it is perceived in color, in transmitted light the thin-film element has a color saturation C ^* _ab defined in the CIELAB color space of more than 15. Two p the absorbing layers are composed of different materials, the real part n1 and the imaginary part k1 of the material of one of the two absorbing layers differ 5 or more times, at least in the visible part of the spectrum, and the real part n2 and the imaginary part k2 of the material of the other the two absorbent layers differ by 8 or more times, preferably 10 or more times, particularly preferably 15 or more times. One of the absorbing layers or both of the absorbing layers are made of silver or aluminum. The dielectric separation layer is made of SiO _x or MgF ₂ . In transmitted light, the thin film element has a chroma C ^* _ab, determined in CIELAB color space, more than 20, preferably greater than 25. The thin film element when viewed vertically - is visible in transmitted light and has a green color saturation C ^* _ab of more than 30, preferably more than 40, or - in transmitted light is visible yellow and has a color saturation of C ^* _{ab of} more than 20, or - in transmitted light is visible in red and has a color saturation of C ^* _{ab of} more than 20, preferably more than 30, or - in transmitted light is visible in blue and has a saturation veto C ^* _ab of more than 20, more preferably 30 or thin-film element in transmitted light and visible color shows the color change effect. The thin film element may be combined with a color filter, preferably with a color print layer or a color spray layer. The thin-film element is combined with a relief structure, in particular deposited on a diffraction relief structure or micro-optical relief structure [RU 2514589 B42D 15/00 Publ. 04/27/2014, WO 2011/032665 2011.03.24].

A known method of obtaining diffracting images in crystalline colloidal arrays comprising: forming on the substrate an ordered periodic array of particles, where the array of particles diffracts in the wavelength band, depending on the viewing angle; printing the image composition into parts of the array in the image configuration; shifting the wavelength band of the diffracted radiation and / or changing the refractive index in the printed part of the array, so that the printed part diffracts the radiation with a wavelength band and reflection intensity different from the rest of the array; and fixing the printed part of the array in such a way that the printed part of the array diffracts the radiation and displays an image. The image composition resizes and the refractive index of particles in the printed part of the array, resulting in a shifted wavelength band diffracted by the printed part of the array. The composition of the image contains monomers that resize, and the refractive index of the particles in the printed part of the array, and further comprises a solvent that resizes the particles having a core-shell structure by changing the size and refractive index of the particle shells. The composition of the outer layer of the coating provides for the coalescence of the particles of the array in the printed part to obtain a film showing the image in the printed part, where the rest of this is almost colorless. The printing step includes applying the image composition by xerographic printing, inkjet printing, flexographic printing, silk screen printing, metallography or intaglio printing. The image composition provides a shift of the diffraction wavelength of a part of the array in the image printed using the image composition, so that part of the array in the image printed using the image composition diffracts the radiation at a wavelength other than the rest of the image [EN 2013125497 G02B 1/00 Publ. . 12/10/2014, WO 2012/061207 2012.05.10].

Known protective printing fluid and a method of printing with nanoparticles, which protect printed materials from fake reprints, for example, in the manufacture of banknotes, stocks, checks and other valuable papers. The printing fluid for printing through narrow nozzles on objects, in particular in the manufacture of banknotes, stocks, checks, contains a carrier medium and nanoparticles of metal salts in the form of crystalline solid particles with an average diameter of less than 300 nanometers, fluorescent or phosphorescent when excited by UV radiation of range A , B or C or visible light. The emitted fluorescence or phosphorescence radiation does not lie in the frequency range of visible light, the frequency range of the excitation and the frequency range of the emission are shifted in frequency. Nanoparticles contain subsidizing additives of at least one type with a range of excitation frequencies and a range of emission frequencies for fluorescence or phosphorescence. A printing method includes the operation of supplying the above-described printing fluid through one or more narrow nozzles. The supply of printing fluid (s) is carried out through several narrow nozzles, the nozzles being individually or in groups regulated with respect to the presence or absence of the supply of printing fluid. The nozzles individually or in a group are regulated with respect to the duration or intensity of the outflow of the printing fluid [RU 2312882 C09K 11/08, C09D 11/00, B41J 2/00, B41M 3/14 Publ. December 20, 2007, WO 03/052025 06/26/2003].

The known sol-gel processes are known (sol-gel process) - technologies for producing materials, including nanomaterials, including the production of sols with their subsequent translation into a gel, that is, into a colloidal system consisting of a liquid dispersion medium enclosed in a spatial grid, formed by the connected particles of the dispersed phase, [https://ru.wikipedia.org/wiki/Zol-gel_process].

Sol (plural sols, from Latin solutio - solution) is a highly dispersed colloidal system (colloidal solution) with a liquid (lyosol) or gaseous (aerosol) dispersion medium, in the volume of which another (dispersed) phase is distributed in the form of liquid droplets , gas bubbles or small solid particles, the size of which lies in the range from 1 to 100 nm [phttps: //ru.wikipedia.org/wiki/Zoli]

(ед. ч. гель, от лат. gelo - «застываю») - структурированные системы, состоящие из высокомолекулярных и низкомолекулярных веществ. Наличие трехмерного полимерного каркаса (сетки) сообщает гелям механические свойства твердых тел: отсутствие текучести, способность сохранять форму, прочность и способность к деформации (пластичность и упругость), [https://ru.wikipedia.org/wiki/Гели].

(unit, gel, from Latin gelo - “freeze”) - structured systems consisting of high molecular weight and low molecular weight substances. The presence of a three-dimensional polymer skeleton (mesh) informs the gels of the mechanical properties of solids: lack of fluidity, ability to maintain shape, strength and deformability (ductility and elasticity), [https://ru.wikipedia.org/wiki/Gels].

In contrast to gels, in sols, particles of a dispersed phase are not bound into a spatial structure, but freely participate in Brownian motion [http://dic.academic.ru/dic.nsf/nanotechnology/449/Zol]. Most gels are known to be thermodynamically unstable; during aging due to isothermal recondensation or recrystallization, the coagulation structure that is reversible with respect to the mechanical action degenerates into an irreversible condensation-crystallization structure. In addition, many gels are prone to syneresis - volume reduction with the release of the liquid phase as a result of spontaneous compaction of the structural network [http://www.xumuk.ru/encyklopedia/958.html].

The general name “sol-gel process” (sol-gel technology, sol-gel method) ”unites a group of methods for the preparation (synthesis) of materials from solutions, the essential element of which is gel formation at one of the stages of the process. The most famous variant of the sol-gel process is based on the processes of controlled hydrolysis of compounds, usually alkoxides M (OR) _x (M = Si, Ti, Zr, V, Zn, Al, Sn, Ge, Mo, W, etc.) or the corresponding chlorides, in an aqueous or organic, often alcoholic, environment [hereinafter https://ru.wikipedia.org/wiki/Zol-gel_process]. At the first stage of the sol-gel process of the hydrolysis and polycondensation reaction lead to the formation of a colloidal solution - sol - particles of hydroxides, the size of which does not exceed several tens of nm. An increase in the volume concentration of the dispersed phase or other changes in external conditions (pH, solvent replacement) lead to intensive contact formation between particles and the formation of a monolithic gel in which the solvent molecules are enclosed in a flexible but sufficiently stable three-dimensional network formed by hydroxide particles. Concentration of sols followed by gelation is carried out by dialysis, ultrafiltration, electrodialysis, evaporation at relatively low temperatures or extraction. It is known that the processes of solvent removal from the gel (drying) play an extremely important role in the sol-gel process. Depending on the method of their implementation, various synthesis products (xerogels, ambigels, cryogels, aerogels) can be obtained.

Airgel is the common name for all gels with a low solids content, the pores of which are filled with air, in a narrower sense, they are characterized by the fact that they are used for supercritical drying, for cryogels they are freeze-dried, and convection subcritical for xerogels .

Ambigel is a product of drying an aqueous or organic gel at atmospheric pressure, characterized, in contrast to xerogel, by low density values approaching the density of airgels.

Xerogel is a product of drying aqua or alcohol at atmospheric pressure under conditions leading to the collapse (collapse) of macropores and a significant increase in the density of the material [http://thesaurus.rusnano.com/wiki/article2155].

Common features of these products are the preservation of nanoscale structural elements and fairly high values of specific surface area (hundreds of m ² / g), although their bulk density can differ hundreds of times. Most sol-gel synthesis products are used as precursors in the preparation of oxide nanopowders, thin films for coating optical lenses or ceramics. In disperse systems, a double electric layer appears on the particle surface (at the particle – dispersion medium interface) [http://www.photocor.ru/theory/zeta-potential/]. A double electric layer is an ion layer formed on the surface of a particle as a result of adsorption of ions from a solution or dissociation of surface compounds. The particle surface acquires a layer of ions of a certain sign, uniformly distributed over the surface and creating a surface charge on it. Theories of the double electric layer are widely used to interpret surface phenomena, but there are no direct methods for measuring potentials at the boundary of the adsorption layer. To quantify the magnitude of the electric charge in the double electric layer, the zeta potential is widely used. The zeta potential is not equal to the adsorption potential or surface potential in the double electric layer. However, the zeta potential is often the only available way to evaluate the properties of a double electric layer. When a particle moves, the double electric layer breaks. The place of the gap when moving the solid and liquid phases relative to each other is called the slip plane. The slip plane lies on the boundary between the diffuse and adsorption layers, or in the diffuse layer near this boundary. The potential on the slip plane is called the electrokinetic or zeta potential (ζ potential). In other words, the zeta potential is the potential difference between the dispersion medium and the fixed layer of liquid surrounding the particle [http://thesaurus.rusnano.com/wiki/article2155]. The importance of the zeta potential is that its value can be associated with the stability of colloidal dispersions. The zeta potential determines the degree and nature of the interaction between the particles of the dispersed system. For molecules and particles that are small enough, a high zeta potential will mean stability, i.e. the solution or dispersion will be stable with respect to aggregation. When the zeta potential is low, attraction exceeds repulsion, and dispersion stability will be violated. So, colloids with a high zeta potential are electrically stabilized, while colloids with a low zeta potential tend to coagulate or flocculate. A zeta potential value of 30 mV (positive or negative) can be considered as a characteristic value for the conditional separation of low-charged surfaces and high-charged surfaces. The greater the electrokinetic potential, the more stable the colloid. It is known that at values of the zeta potential from 0 to ± 30 mV, poor stability of colloidal systems is observed (coagulation or flocculation is possible), and at values greater than ± 30 mV, good stability of colloidal systems [http://thesaurus.rusnano.com/wiki / article2155].

A known method of producing water dispersible nanoparticles of sols of titanium dioxide rutile phase rutile with an average particle diameter of less than 30 nm of high purity in an aqueous medium that does not have ionic impurities and is used for optical materials having a high refractive index and having a high dielectric constant and dispersibility in solvents without any any ionic impurities such as Cl ^- , NO ₃ ^- , SO ₄ ^-2 , comprising the following stages: production of a mixed solvent from water and hydrogen peroxide; hydrolysis of titanate peroxide and hydrothermal treatment of the solution with dissolution of titanate peroxide and the formation of a titanium dioxide sol [US 2006110319 C01G 23/047 2006-05-25].

The closest in technical essence and the obtained technical result analogue prototype sol-gel ink and the method for their preparation is a method for producing a titanium oxide sol, which includes the steps of: a) increasing the temperature of the reagent solution containing the titanium oxide precursor as a solvent for the reaction to the reaction temperature 70 up to 95; b) obtaining a titanium oxide sol with the addition of an acid catalyst with a reagent solution and carrying out a sol-gel reaction while removing the solvent for the reaction from it; and c) drying the prepared sol by freeze-drying, normal pressure drying, or vacuum drying and re-dispersing the dried titanium in a dispersion solvent. The sol-gel reaction when removing the solvent for the reaction in stage b) is carried out at a temperature of from 70 to 95 ° C. The solvent for the reaction and the solvent for dispersion is the same or different one or more solvents selected from the group consisting of water, a lower alcohol from C ₁ -C ₅ , a higher alcohol C ₆ or more, ethylene glycol, and acetyl acetone. The lower alcohol is methanol, ethanol, propanol, isopropyl alcohol, butyl alcohol, or isobutyl alcohol or and the higher alcohol is polyvinyl alcohol. The titanium oxide precursor is one or more compounds selected from the group consisting of titanium, tetraethoxysilane tetraisopropoxy titanium, titanium tetrabutoxy zirconium, titanyl chloride, titanyl sulfate and oxytitanyl sulfate. An acid catalyst is one or more compounds selected from the group consisting of nitric acid, sulfuric acid, hydrochloric acid, and acetic acid. The acid catalyst is added in an amount of 11 to 30 parts by weight based on 100 parts by weight of the titanium oxide precursor. One or more inorganic salts selected from the group consisting of NaCl, KCl, NaBr and KBr, or one or more surfactants selected from the group consisting of sodium dodecyl sulfate, cetyltrimethyl ammonium bromide and cetyl trimethyl ammonium chloride are added to the reagent solution in step a) in an amount of from 1 to 10 parts by weight, based on 100 parts by weight of the titanium oxide precursor. Primary particles of titanium dioxide having an average diameter of from 1 to 20 nm in the crystalline form of anatase or rutile. Secondary titanium dioxide particles have an average diameter of 200 nm or less. The titanium dioxide sol has a solids content of from 8 to 50 wt. % The composition for coating glasses, industrial safety glasses or leisure glasses contains a sol of titanium dioxide in an amount of from 10 to 70 wt. % [WO 2007073043 2007-06-28 C01G 23/047 prototype].

The technology for producing sols of crystalline titanium dioxide nanoparticles according to the prototype WO 2007073043 involves the implementation of multi-stage operations aimed at obtaining functional sol-gel powder and film materials. The steps for preparing the powder include hydrolysis followed by protonization and further precipitation using drying. At the same time, the refractive index values obtained in the prototype, not exceeding 1.6, allow us to concentrate the field of application of the coatings obtained on the basis of TiO ₂ nanocrystalline sols exclusively as antireflective (that is, bleaching!) And UV protective layers for glasses for various functional purposes. However, the technology of the prototype WO 2007073043 does not allow to obtain colloids based on crystalline titanium dioxide without using the stage of complete dehydration or drying. This, in turn, does not allow to achieve high values of the refractive index (more than 1.7) in the entire visible range even after the introduction of a volatile solvent and, therefore, does not mask the microembosity (microte etched) diffracting polymers.

Known methods for the formation of holographic images based on the diffraction and interference of light waves.

The founder of holography is considered to be Dennis Gabor, a professor at London State College, who received the first hologram in 1947.

Holography (from the Greek. Holos - complete, complete and grapho - I write, draw, draw) is a special photographic method in which images of three-dimensional objects are recorded and then restored, which are highly similar to real ones. Such a photographic record is called a hologram. The author of the term “holography” D. Gabor emphasized that the method allows you to register complete information about the investigated object. Holography began to develop rapidly and acquired great practical importance after, as a result of fundamental research in quantum electronics, performed by Soviet physicists N.G. Basov and A.M. Prokhorov and American scientist Charles Townes, in 1960, the first laser was created. Initially, holographic images were formed in laser light, in particular, the first portrait of a person was shot using a ruby laser in 1967. The beginning of fine holography was laid by the work of Emmett Leith and Juris Upatnieks of the Michigan Institute of Technology (USA), who received in 1962 the first volumetric transmission hologram reconstructed in laser light. The work of Academician Yu.N. Denisyuk, made in the 60-70s of the XX century. He first received reflective holograms that allow reproducing three-dimensional images in ordinary, white light. In 1969, Stephen Benton of Polaroid Research Laboratories (USA) made a transmission hologram visible in ordinary white light. The holograms invented by Benton were called rainbow, as they shimmer with all the colors of the rainbow that make up the white light. Benton's discovery made it possible to begin mass production of inexpensive holograms by “stamping” (stamping) interference patterns on plastic. Rainbow holograms of this type are widely used today to protect against forgery of documents, bank cards, etc. Thanks to Benton, rainbow holography has gained popularity in wide sections of society. An excellent feature of rainbow holographic images is the formation of periodic structures (with different refractive indices) on the surface of any material using microembossing (micro-embossing). Rainbow holograms (Benton holograms) do not require the use of expensive photopolymer varnishes, technologically they can be easily scaled. Such holograms are widely used in a wide variety of applications, ranging from authentication and optical data storage to interferometry, particle capture and phase conjugation. The classic process of making a rainbow hologram is laborious and multi-stage. First, a master hologram is made, which is recorded by laser recording, direct processing, or electron beam lithography, on a thin layer of photoresist, after which the photoresist is dried, unexposed areas are removed using a laser of continuous radiation. A metal matrix is made from the obtained stencil, on which the lavsan film is then rolled, and transferred to the surface holographic relief of the cured polymers. The whole process of obtaining a rainbow holographic image can last several days. Moreover, for the manufacture of master holograms, strict control of temperature and vibration isolation is necessary. Accordingly, affordable and fast printing of individual rainbow holographic images is not yet known today. Given the complexity of manufacturing rainbow holography, scalability is achieved by pressing a template matrix into the surface of polymers, latexes and various varnishes that dry out under the influence of temperature, oxidation and / or ultraviolet curing to obtain a micro microembossed (micro embossed) surface. Thus, either a holographic film (i.e., a film having a variable 3D structure) or a single image with a holographic effect in the form of text or image is obtained. The process of transferring a matrix pattern to a polymer tape usually takes from several hours to several days, depending on the complexity of the layout design.

A known method of forming a holographic embossed pattern, consisting of the stages: A. recording a holographic pattern on a photosensitive plate by means of laser holography for manufacturing an optical mask of a holographic pattern; B. duplication of the holographic pattern from the optical plate to the metal plate to obtain a metal plate with a holographic pattern; C. Transfer of a laser holographic pattern from a metal plate to the information layer of a water-soluble film with the formation of an embossed holographic pattern; D. transferring the holographic pattern from the metal plate to the information layer of the water-soluble film and forming a relief holographic pattern on the surface of the base material by supplying water to the water-soluble film with the formation of a holographic pattern on the surface of the base material or on the surface of the workpiece having a complex shape; E. the formation on the surface of the relief holographic pattern of an additional protective layer with acrylic acid or polyester material with a thickness of 0.01 μm to 100 μm [US 8118960 B2 B01J 19/08; B32B 37/02; B41M 5/025 2010-01-07 WO 2007 CN 71181 20071205].

A known method for producing a protective laminated embossed or embossed hologram, comprising an optionally transparent substrate having two sides, at least one of the two sides, or itself embossed or having a layer with an embossed layer of HRI material with a high visual resolution with a refractive index not less than 0.3 higher than that of the relief material bordering the embossed side or the embossed layer, which includes the following stages: a) conditioning the outer surface of the inorganic material layer HRI with a high im visual resolution with an alkaline solution or acidic solution; b) drying the outer surface of the HRI inorganic material layer with high visual resolution; c) applying a layer of adhesive composition on the conditional outer surface of an inorganic HRI layer with high visual resolution; and d) laminating the outer surface of the HRI material layer with a high visual resolution of the material with a transparent polymer film [WO 2009037332 B32B 27/14; B32B 3/30; B42D 15/10; C09J 5/02; G03H 1/02; G09F 3/02 2009-03-26 US 20070973934 P 20070920].

A known method of manufacturing transparent products comprising microrelief images, such as holograms or a diffraction grating, covered at least partially by a layer of material having a refractive index different from the refractive index of a transparent layer of about 0.2 units, which consists of the steps of: applying to a transparent a film of a carrier layer with a separation layer, embossing the surface of the separation layer to obtain a microrelief image; applying liquid to the microrelief image to form a transparent layer of refraction, which increases the visibility of at least a portion of the image; applying an adhesive layer to a transparent refractive layer. In this case, the refractive layer has a refractive index that differs from the refractive index of the transparent layer by about 0.2 or more units. The liquid is applied by the coating method or by the printing method: flexography, gravure printing, gravure printing, offset, gravure, offset, rotational gravure. The liquid has a viscosity in the range of about 15 to about 50 centistokes, preferably in the range of about 21 to about 27 centistokes, it is applied in an amount of about 0.5 to about 2.0 g / m ² , preferably 0.8 to about 1, 2 g / m ² . The refractive layer is formed from a liquid containing at least one material from the group BiOCl, Sb ₂ O _5, TiO ₂ -SnO ₂ -ZrO ₂ and ZnO ₂ Sb ₂ O ₅ in the form of dispersions, solutions, suspensions, and emulsions, and refractive the layer has a thickness of from about 0.3 to 3.0 microns, preferably from 0.5 to 1.0 microns [US 6468380 B05D 1/28; B05D 7/24; G02B 5/18; G03H 1/02; G03H 1/18; 2002-10-22].

Holographic interference images are currently usually obtained on widely available, holographic paper in the market. Holographic paper is an optically variable device that changes the appearance of the image depending on the light source, light angle and viewing angle. The images themselves are reproduced on the surface of the paper, or other substrate, by the original holographic matrix by micro-embossing of the coating on the surface of the paper. The surface is then metallized in a vacuum to provide a very bright, shiny, metallic luster that produces a rainbow-colored holographic image and makes it visible. Holographic paper is printed using special inks that dry out as a result of oxidation and / or UV curing. In addition, paints that dry when solvents or water are removed are used.

Widespread in computer publishing is currently inkjet printing on decorative paper with an attractive appearance. Greeting cards, folders, presentations, business cards, labels, tags, posters, stationery, artwork, etc., digital printing are mass-produced today in the office and at home on inkjet printers. Inkjet printing typically uses water based or solvent based inks. Water-based inkjet inks do not combine well with holographic paper, because the polymer or metallized surface of holographic paper is poorly wetted by water and does not absorb moisture well. Solvent-based inkjet inks are more compatible with holographic paper, but solvents commonly used in inkjet inks, such as ethyl acetate, methyl ketone and acetone, are dangerous to humans and the environment, and often require special conditions when used. Therefore, they are trying to solve the compatibility problem of water-based inks widely used in inkjet printing with holographic paper by developing special coatings of holographic paper.

Known intended for inkjet printing coating holographic paper containing a primer layer, a primary and secondary layer. The secondary layer includes a plurality of microscopic pores, which are preferably 1 to 6 μm in diameter, to allow ink jet ink to enter the coating during printing. The coating is compatible with water based paints and solvent based paints. The pores serve to fix the inkjet ink, preventing them from spreading upon drying and accelerate the drying speed of the ink. In addition, the second layer is porous enough to absorb the ink as it dries. The deeper the second layer, the faster it dries. The primer layer of holographic paper is made of a material of the group consisting of acrylic, polyester, urethane, and vinyl resins and nitrocellulose, and the secondary layer of the group of polyvinyl alcohol, gelatin, cellulose, acrylic resins and polyvinyl propylene and has many mechanically formed microscopic pores located on it to provide space for fixing and absorbing inkjet ink [US 6458449 V41M 5/52; B41M 5/00 Publ. 2002-10-01].

The most common known method for producing rainbow holograms is to create on the surface a usually thermoplastic microrelief substrate on which diffraction of visible light occurs. Most often, the diffraction relief is obtained by embossing the surface of a thermoplastic substrate, for example, a thermoplastic polymer film. This process occurs as a result of the contact of a stamp from a solid material with a substrate. In this case, the corresponding microrelief in mirror image is engraved on the surface of the stamp [Pat. US 3,578,845 (Brooks et al.)]. It is known that the diffraction effect is higher, the greater is the difference between the refractive indices of the substrate substance and the external environment. Therefore, often the surface of the microrelief is covered with thin layers of reflective materials, such as aluminum, copper, gold, etc. Alternatively, the surface of the microrelief is coated with thin layers of high refractive index transparent materials such as zinc sulfide, iron oxide, lead oxide, zinc selenide, cadmium sulfide, titanium dioxide, zinc oxide, lead chloride, cerium oxide, cadmium oxide, neodymium oxide or oxide aluminum. Substrates coated with transparent coatings with a high refractive index are often used as anti-counterfeiting elements in various products, such as, for example, bank cards.

The microrelief embossing process can be implemented using an engraved shaft, as described in US Pat. U.S. 4,913,858 and 5,164,227 (Miekka et al). In this case, a substrate in the form of a continuous web is passed between the engraved shaft and the support shaft. The thermoplastic layer on the substrate is heated to the required temperature, which ensures the embossing process under pressure, or the directly engraved shaft is heated. Distinguish between "soft embossing" (soft embossing) and "hard embossing" (hard embossing). In the first case, the embossing process is carried out before coating with a high refractive index. "Hard embossing" is carried out through the coating with a high refractive index. Translucent coatings with a high refractive index (for example, ZnS or TiO ₂ ) cause a greater thickness than metal coatings to obtain a brighter diffraction pattern. Typically, the thickness of the ZnS coating is 400-600 angstroms, while the aluminum coating has a thickness of 200 angstroms or less. In addition, translucent coatings are much harder than metal coatings. ZnS has a Mohs hardness of 4.5 compared to 2.75 for aluminum. This requires a higher embossing pressure, which, accordingly, necessitates the use of more powerful equipment for embossing the microrelief.

The most common method for producing films with a thermoplastic layer is a thermoplastic layer, for example, applying thermoplastic varnish from solutions or aqueous dispersions to the surface of polyethylene terephthalate or polypropylene films using known methods, such as gravure printing, air knife, doctor blade and others.

High refractive index coatings are usually applied by vacuum deposition. In this case, it is very important that no volatile substances remain in the composition of the relief layer, which will evaporate during the evacuation process and create defects on the surface of the material. An important point is that in the process of vacuum deposition of a coating with a high refractive index, there is a need to process a sufficiently large amount of film, which is due to the technical parameters of the vacuum deposition process - a high speed is required (500 m / min) and some time is needed to stabilize the process , significantly limits the production of small quantities of products, which is very important in the production of protected products in small runs.

It is known to obtain substrates with a relief layer by the method of production of coextruded films, as described in US Pat. U.S. 7,157,135 (Wolfgang Decker at al). The relief layer in the coextruded film should have at least 10 ° C lower melting point than the base substrate. The thickness of the relief layer varies in the range of 0.1-2.0 μm with a thickness of the base substrate of 7-120 μm.

The common technical disadvantages of the known methods for producing rainbow holograms on the surface of a usually thermoplastic microrelief substrate are the technological complexity and insecurity of the microrelief from mechanical stresses, so they are forced to develop various ways to protect rainbow holographic images.

Known optically variable protective device containing at least the first and second superimposed on each other diffraction or holographic structures that form optically variable effects, while at least the first structure has a surface relief microstructure, the second structure forming optically variable effects is visible through the first structure. The first structure that forms optically variable effects contains a discrete metal layer or contains a reflective layer formed by a dielectric material with a high refractive index, essentially a purely lattice structure in combination with a dielectric layer with a high refractive index, and the second structure that forms optically variable effects contains either a classical hologram, or a zero-order diffraction device, or a fresnel structure. Moreover, the first and second structures that form optically variable effects contain complementary zero-order diffraction devices and form orthogonal holographic images, usually created by classical holography. The second structure, which forms optically variable effects, contains a surface relief microstructure and an opaque reflective layer. The first and second surface relief microstructures were obtained by different processes, either by scanning interferometry, or lithographic interferometry, or electron beam lithography, or classical rainbow lithography. A method of manufacturing a protective device involves providing at least a first and a second superimposed diffraction or holographic structures forming optically variable effects, wherein at least the first structure has a surface relief microstructure, the second structure forming optically variable effects is visible through the first structure. Each structure forming optically variable effects is formed by embossing the corresponding surface embossed microstructure into an embossing layer, in which the embossing layer contains varnish or embossing polymer. Each microstructure is obtained through another process of creating the original and layered on top of each other using an intermediate laminating UV curing adhesive [RU 2004 129 336 B42D 15/10 publ. 05/10/2005 WO 03/082598 10/09/2003].

Known information-protective label made on a paper or polymer basis with the possibility of fixing it on a unit of goods, on which a bar code is printed that carries identification and content information, which additionally contains a diffractive copy protection element having a surface microrelief that creates the effect of optical diffraction, made on a metallized polymer carrier deposited on the base of the label. The surface microrelief, which creates the effect of optical diffraction, of the diffractive copy protection element, is made directly on the polymer basis of the label, which is metallized, its base on the side attached to the product contains an adhesive layer. The label is coated with a protective seal in the form of microlines and / or microtext, an invisible ink glowing in the light of a UV detector or visible through a red optical filter, and the surface microrelief, which creates the effect of optical diffraction, is a Benton hologram or a diffraction grating made by electron beam holography [RU 9 542 G09F 3/00 Publ. March 16, 1999].

The technical disadvantages of the known analogues that are eliminated by the implementation of the patented object are the technological complexity and the duration of the production of holograms in a single copy, the need for complex expensive equipment.

A known method of creating a protective hologram, including the operation of creating the desired image, recording a hologram from the desired image, creating a metal matrix from the hologram of the desired image, then replicating the protective hologram on the surface of the polymer film by stamping it with a matrix, according to which to increase manufacturability beforehand, before making the matrix for replicating holographic images of the desired image, consisting of a series of single images, on the floor surface of a dimensional film, an operation is performed to create a metal matrix from each single holographic image, an electrically conductive layer is applied to the surface of the polymeric material, then by the mechanical recombination method, which embosses the existing electrically conductive layer on the surface of each metal image with a single image in turn, a common matrix is made, which includes a series of holographic images and recreates the desired image mirror, and the operation of replication is protective th hologram on polymer film by embossing to operate her general matrix [RU 2258248 G03H 1/26, G03H 1/00, G06K 19/00 Publ. 08/10/2005 Conventional priority 06/19/2001 UA 2001064261 PCT WO 02/103457 (12/27/2002)]. The disadvantage of this method is its lack of manufacturability, due to the need to create an electrically conductive layer on the surface of the matrix. To create an electrically conductive layer on the surface of the matrix, a chemical nickel plating operation is used. This operation, firstly, is not sufficiently controlled, therefore, the layer has a different thickness over the area of the matrix, and secondly, it is very complex in terms of technology and quite expensive, which limits the use of the above method.

The production of today's rainbow-colored holograms is increasing annually, but the technology of affordable and fast printing of small-volume and individual images with a rainbow holographic effect has not yet been unknown.

The objective of the technical result of the invention is:

- obtaining non-toxic inks for color inkjet printing of unique rainbow holographic images based on chemically inert and environmentally friendly titanium dioxide and an environmentally acceptable aqueous solution of ethyl alcohol;

- providing the possibility of technologically simple, fast (no more than 5 minutes) inkjet printing with ordinary inkjet printers of unique and individual color rainbow holographic images on microembos or holographic paper by means of specially prepared colorless sol-gel inks with the possibility of subsequent observation on the surface of unique rainbow holographic images in reflected in the light of the visible spectrum, which can be used for instant protection of documents, printing surnames , Photos, personalized printing holograms on the document name, create a personalized souvenir and printed production of consumer, secure printing of registered transport tickets, individual invitations to events;

- the formation by means of inkjet printing of optical film nanostructures of xerogel nanocrystalline titanium dioxide with an accuracy of 10 nm, and a refractive index of more than 1.7;

- obtaining rainbow holographic images that do not fade from the action of sunlight and UV radiation;

- providing the ability to re-apply ink for inkjet printing of rainbow holographic images and reuse of the substrate with the ability to remove deposited layers of rainbow holographic images with aqueous solvents.

Typical distinctive results of the implementation of the invention are:

- the preparation and use of colorless sol-gel inks containing nanocrystalline sol anatase with an amorphous phase content of not more than 5%, with a high refractive index of more than 1.7 in the entire visible range of the spectrum after drying, applied to holographic paper or microembos using an inkjet printer ;

- the formation of colorless colorless sol-gel inks containing nanocrystalline anatase sol with an amorphous phase content of not more than 5%., a nanoscale coating in the form of printed text, numbers or drawings, hereinafter - images coated with transparent polymers or varnishes with a refractive index of less than 1.6 with the creation of an optical effect of masking free from sol-gel-printed ink images of areas of holographic paper or microembossed surface and selective display of printed sol-g spruce ink rainbow holographic images;

- surface protection of the rainbow holographic image with a coating of transparent polymers or varnishes;

- the ability to quickly and technically simple to obtain through conventional inkjet printers unique images with a rainbow holographic effect with full preservation of the diffraction effect and optical transparency in the visible range of light;

- the possibility of using inkjet printing technology to create unique rainbow holographic images by conventional inkjet printers by forming nanocrystalline titanium dioxide xerogel nano-layers on holographic paper with high accuracy without using high temperatures and technically complex physical processes;

- technically simple control of the thickness of the xerogel refractive layer of nanocrystalline titanium dioxide with an accuracy of 10 nm by inkjet printing with the possibility of obtaining color rainbow holographic images in the entire color range of the visible light spectrum with controlled interference using the same colorless sol-gel ink;

- the absence of toxic dyes in the proposed sol-gel ink for inkjet printing of rainbow holographic images;

- high prospects for the practical implementation of the proposed solutions from the environmental side, since the systems used based on nanocrystalline sols of anatase titanium dioxide are non-toxic and bioinert.

The practical obtaining of previously unattainable technical results became possible only when using the original specially prepared colloidal dispersion of a nanocrystalline sol of titanium dioxide with a high refractive index in the entire visible range corresponding to the rheological properties of inkjet inks. This was made possible thanks to the creation and use of special colorless sol-gel inks based on a nanocrystalline sol of titanium dioxide of a predominantly anatase phase, during natural drying of which optically transparent monolithic coatings are formed in the form of highly refractive xerogel layers of nanocrystalline titanium dioxide with a refractive index of more than 1.7 in all range of visible light.

According to the invention, a fundamentally new method for preparing colorless sol-gel ink for inkjet printing of rainbow holographic images, which makes it possible to create refractive coatings with a given thickness with an accuracy of 10 nm, is necessary for the selective masking of rainbow microembossed materials with a refractive index of less than 1.6.

The proposed sol-gel inkjet ink for rainbow holographic images lays the foundation for the development of a fundamentally new direction of inkjet printing of rainbow holographic images and allows one to master new methods of forming optical nano-objects by widely available inkjet printing methods using conventional inkjet printers on non-porous microembossed substrates and holographic paper.

The problem is solved and the required technical result is achieved by the fact that the sol-gel inkjet ink for printing rainbow holographic images on holographic paper or on a microembossed (microte embossed) surface contains nanocrystalline anatase sol with an amorphous phase content of not more than 5%. in a solution of ethyl alcohol in water, characterized by at least one of the following group of properties:

the presence of titanium dioxide nanoparticles in the form of crystals of titanium dioxide of a predominantly anatase phase with a content of an amorphous phase of titanium dioxide of not more than 5%,

the concentration of nanocrystalline particles of titanium dioxide is not less than 1 wt. %

the size of the nanocrystalline particles of titanium dioxide is not more than 100 nm,

the average hydrodynamic particle diameter of the nanocrystalline sol of titanium dioxide is not more than 100 nm, mainly 15.8 nm,

the zeta potential of titanium dioxide nanoparticles is not less than +10 mV, mainly + 36.1 ± 5.3 mV,

the possibility of forming a transparent in the visible spectrum of the refractive layer of xerogel titanium dioxide with a thickness of 30 nm to 1000 nm with a refractive index of more than 1.75,

the concentration of ethyl alcohol in water is not more than 70 wt. % with a predominant ratio of ethyl alcohol: water 3: 1,

the duration of sedimentation stability of the nanocrystalline sol of titanium dioxide for at least 1 year.

At the same time, sol-gel inkjet ink for printing rainbow holographic images on holographic paper or on a microembossed surface has:

viscosity no more than 20 MPa * s, mainly 2.1 MPa * s,

surface tension of not more than 50 nN / m, mainly 27 nN / m.

Ink sol-gel for inkjet printing of rainbow holographic images on holographic paper or on a microembossed surface in the form of a nanocrystalline sol of titanium dioxide, in a solution of ethyl alcohol in water, is obtained in two stages, at the first stage, a nanocrystalline anatase sol with an amorphous phase content of not more than 5 % in water, and in the second stage, a sol-gel inkjet ink is obtained from a nanocrystalline titanium dioxide sol in water in the form of a nanocrystalline titanium dioxide sol in a solution of ethyl alcohol in water with the viscosity and surface tension required for inkjet printing.

Nanocrystalline anatase sol with an amorphous phase content of not more than 5%. in water is obtained by obtaining a solution of titanium alkoxide by mixing titanium isopropoxide and 2-propanol, hydrolysis of titanium alkoxide to form stable crystalline nuclei of titanium dioxide predominantly anatase phase in water, conducting temperature dehydration of amorphous titanium oxyhydroxide by heating to 70 ° C in an acidic environment, creating an acidic environment and exposure at 80 ° C for 1 hour with an increase in the content of the crystalline phase of titanium oxide predominantly anatase phase and obtaining nanocrystalline sol d titanium oxide of a predominantly anatase phase, with a crystal size of titanium dioxide of not more than 100 nm, mainly 5-20 nm, with an average hydrodynamic diameter of sol particles of not more than 100 nm, mainly 15.8 nm, with a zeta potential of sol particles of not less than +10 mV mainly + 36.1 ± 5.3 mV, stabilizing the nanocrystalline sol of titanium dioxide by protonization of the sol particles in the presence of nitric acid and holding for no more than 1-2 weeks at room temperature with constant stirring to obtain a stable nanocrystalline sol of dio titanium oxide of a predominantly anatase phase in water, characterized by: a content of an amorphous phase of titanium dioxide of not more than 5%, a crystal size of titanium dioxide of 5-100 nm, a predominantly anatase phase, an average hydrodynamic diameter of sol particles of not more than 100 nm, mainly 15.8 nm, a zeta-potential of particles sol not less than +10 mV predominantly + 36.1 ± 5.3 mV.

Nanocrystalline anatase sol with an amorphous phase content of not more than 5% in a solution of ethyl alcohol in water is obtained by adjusting the viscosity parameter of a nanocrystalline titanium dioxide sol in water to an index of not more than 20 MPa * s by concentrating a sol of titanium dioxide nanoparticles in water to a concentration of at least 8 wt . % by vacuum evaporation at a temperature of 50 ° C, obtaining the required surface tension of a nanocrystalline sol of titanium dioxide not more than 50 nN / m by adding ethyl alcohol to a concentration of ethyl alcohol in water of not more than 70 mass. %, ensuring the phase equilibrium between water and ethyl alcohol by homogenization for no more than 12 days to obtain a nanocrystalline sol of titanium dioxide predominantly anatase in a solution of ethyl alcohol in water, characterized by at least one of the following group of properties: the presence of nanocrystalline particles of titanium dioxide in the form crystals of titanium dioxide with a content of an amorphous phase of titanium dioxide of not more than 5%, a concentration of nanocrystalline particles of titanium dioxide of not less than 1 wt. %, the size of nanocrystalline particles of titanium dioxide 5-100 nm, the average hydrodynamic diameter of the sol particles is not more than 100 nm, mainly 15.8 nm, the zeta potential of the sol particles is not less than +10 mV, mainly + 36.1 ± 5.3 mV mV , the possibility of forming a transparent in the visible spectrum of the refractive layer of xerogel of nanocrystalline titanium dioxide with a thickness of 30 nm to 1 μm with a refractive index of more than 1.75, the concentration of ethyl alcohol in water is not more than 70 mass. % with a predominant volume ratio of ethyl alcohol: water 3: 1, a viscosity of not more than 20 MPa * s, mainly 2.1 MPa * s, a surface tension of not more than 50 nN / m, mainly 27 nN / m.

Obtained sol-gel inks using conventional inkjet printers allow printing rainbow holographic images on holographic paper or on a microembossed surface in two stages: at the first stage, sol-gel is printed on ink on a holographic paper or on a microembossed surface with ink containing a nanocrystalline titanium dioxide sol in an ethyl solution alcohol in water, optically transparent images with a refractive index of more than 1.7 in the entire visible range of the spectrum after they dry I indicated the sol-gel ink, and in the second stage the surface of the holographic paper or on the microembossed surface with the sol-gel ink printed on it is coated with an optically transparent polymer or varnish with a refractive index of not more than 1.6, with the creation of an optical masking effect free of printed sol-gel ink images of areas of a holographic paper or microembossed surface and selective display of sol-gel ink-printed rainbow holographic images Eden.

In this case, when printing sol-gel images with ink on holographic paper or on a microembossed surface, at least one refractive layer of xerogel of nanocrystalline titanium dioxide with a thickness of 30 nm to 1 μm and a refractive index of more than 1.7 is transparent in the visible region of the spectrum , with varying color depending on the thickness of the refractive layer.

The color of rainbow holographic images is controlled by forming a predetermined thickness of the xerogel refractive layer of nanocrystalline titanium dioxide by layer-by-layer application of sol-gel ink to a predetermined thickness of the xerogel refractive layer, by changing the concentration of the solid phase in sol-gel ink using a set of sol-gel ink from a predetermined concentration for the formation of a certain thickness of the refractive layer of xerogel titanium dioxide with a specific color.

In FIG. 1 shows graphs of surface tension and viscosity versus ethanol content in a titanium dioxide sol.

In FIG. Figures 2 and 3 show photos of microembossed (micro-embossed) polymer films used for inkjet printing of rainbow holographic images.

Figure 4 shows the stages of visualization of a layer of titanium dioxide on the surface of a holographic microembossed polymer film with obtaining rainbow holographic text and / or images in the process of inkjet printing.

In Fig. 5, ESM images of films based on titanium dioxide on the surface of holographic paper are presented, deposited by the vacuum method (a, b) and we offer the method of inkjet printing (c, d).

In FIG. Figure 6 shows SEM images of coatings after five tests of cross sections and energy dispersive analysis of films based on titanium dioxide deposited on the surface of holographic paper by the vacuum method (a, b) and the proposed inkjet printing method (c, d).

In FIG. 7a shows the reflection spectrum of the TiO ₂ film (a) and the refractive index of the nanocrystalline TiO ₂ layer obtained by the jet method in the visible light region (b).

In FIG. Figure 8 shows the designer text (a) and image (b) received on a computer screen, printed with a layer of titanium dioxide on holographic paper, images and polymer-coated color holographic images.

In contrast to the known methods for creating rainbow holographic images, which are usually realized using technically complex physical (laser, temperature or vacuum) effects, the proposed invention is based on the methods of solution chemistry.

The proposed colorless sol-gel inkjet inks for rainbow holographic images and the method for their production allow creating thin interference refractive layers of environmentally friendly and biologically inert inorganic material (xerogel of nanocrystalline titanium dioxide), which, after application to the substrate, provide two phenomena of rainbow holography required for observation conditions, namely, obtaining a refractive index above 1.7, that is, higher than that of a simple polymer (1.5), as well as f formation of a refractive layer after drying with a given nanoscale thickness, complementary to the visible wavelength of the light spectrum from 300 nm to 1 μm with an accuracy of 10 nm.

In this case, in contrast to the well-known highly refractive organic polymers, the viscosity parameter required for inkjet printing in the sol-gel systems of the proposed sol-gel inks can be set up in a relatively simple way by controlling the gelation stage. In the case of a high degree of chemical protonization of the surface of the sol nanoparticles, the viscosity of the proposed sol-gel ink can be controlled by the concentration of the solvent in water to prevent sedimentation of the sol nanoparticles.

The rheological properties of the proposed sol-gel inks required for ink-jet printing are adjusted by controlling the phase sol-gel transition and introducing volatile solvents, primarily ethyl alcohol (hereinafter, ethanol), into the composition of the sol-gel ink. It is this advantage of the proposed colorless sol-gel ink that makes them unique for use as a material for creating environmentally friendly inkjet printing of color rainbow holographic texts and images. Printing products with rainbow holographic texts and images obtained using the sol-gel ink technology have unique properties, such as the absence of color change over time, which is promising for long-term storage of color holographic images, since the main material of images (nanocrystalline titanium dioxide) is extremely It is stable, inert and does not decompose for a long time.

Inkjet printing with the proposed highly refractive sol-gel inks allows the use of ordinary holographic paper and polymer substrates without first modifying and applying the binder layers that are commonly used in inkjet printing. Given the ability of many inorganic sols (colloids) to resuspend, the proposed printing technology is universal and can be reused when re-applying the image to a polymer substrate or to a previously made holographic image. Among the many inorganic colloids that can be adapted to inkjet printing and are actively used right now, only a few can be classified as highly refractive, highly transparent and not expensive to use, for example ZrO ₂ , TiO ₂ , ZnO.

Most preferred of these is titanium dioxide TiO ₂ , for the following reasons:

- the preparation of crystalline sol-gel systems of titanium dioxide is quite well understood,

- the refractive index of titanium dioxide in the anatase phase is 2.61,

- xerogel nanocrystalline titanium dioxide is completely transparent in the visible region of the world,

- titanium dioxide easily crystallizes under conditions of temperature dehydration, since it almost always has a crystalline core,

- a high value of the isoelectric point (I.E.P. = 5.9) allows to obtain highly stable, sedimentation-stable titanium dioxide sols.

As the studies of the authors showed, for the synthesis of nanocrystalline TiO ₂ particles from titanium alkoxides, titanium isopropylate is most preferable, which forms stable crystalline TiO ₂ nuclei _of predominantly anatase phase during hydrolysis. The stage of ash formation, that is, the formation of a dispersed solid phase of TiO ₂ nanocrystalline particles, includes successively the stages of hydrolysis and condensation as a mechanism for the formation and growth of nanoparticles.

Schematically, the interaction of alcoholates with water (hydrolysis reaction) can be represented as follows (where R is an alkoxide radical, for example C ₃ H ₇ O):

≡Ti-OR + H ₂ O → ≡Ti-OH + R- (OH)

≡Ti-OH + RO-Ti → ≡Ti-O-Ti≡ + R- (OH)

≡Ti-OH + OH-Ti → ≡Ti-O-Ti≡ + H ₂ O

The use of titanium isopropylate as an inorganic precursor has several significant advantages. One of the most important is the possibility of stepwise hydrolysis, by regulating the synthesis conditions.

or

Due to the high reactivity of such a precursor, its use is carried out with the addition of various organic modifiers that prevent aggregation processes.

In this particular case, aggregation was prevented by protonating the surface of titanium dioxide nanoparticles with the addition of nitric acid.

After hydrolysis proceeds, the mechanisms of condensation are responsible for the formation of sol. They proceed according to the following reactions:

a) alkoxylation:

≡ Ti-OH + iC ₃ H ₇ O-Ti≡ → ≡ Ti-O-Ti≡ + iC ₃ H ₇ OH

b) oxidation:

≡Ti-OH + OH-Ti≡ → ≡Ti-O-Ti≡ + H ₂ O

c) olation:

The key role in the further structuring is played by polycondensation processes that promote the formation of hybrid bonds and the formation of ordered structures in the form of a gel array according to the gelation principle:

Dehydrated Polycondensation:

or

Depropanol polycondensation:

It was established that the periodicity of such structures substantially depends on many parameters and synthesis conditions. The formation of such bond bridges determines the presence of nanostructures in such materials and their final properties, causing the occurrence of the sol-gel transition in the TiO ₂ system.

The gelation stage during inkjet printing of rainbow holographic images by the proposed sol-gel inks proceeds directly on the substrate (on the surface of microembossed or holographic paper), since the main condition for gelation is an increase in the density of the coagulation contact, which is achieved by the natural removal of a volatile solvent, mainly ethanol. Otherwise, gelling may occur inside the ink cartridge, which is unacceptable for ink jet stability.

The colorless sol-gel ink according to the invention for inkjet printing of color rainbow holographic images in the form of a nanocrystalline sol of titanium dioxide in a solution of ethyl alcohol in water is prepared in two stages: at the first stage, a nanocrystalline anatase sol with an amorphous phase content of not more than 5% is obtained. predominantly anatase phase in water, and in the second stage, a sol-gel ink for color interference inkjet printing is obtained from a nanocrystalline sol of titanium dioxide in water in the form of a nanocrystalline sol of titanium dioxide in a solution of ethyl alcohol in water with the density, viscosity and surface tension required for inkjet printing .

To prepare a nanocrystalline sol of titanium dioxide in water, two solutions are first prepared:

for the first solution, 3-16 ml of titanium isopropoxide and 12-50 ml of 2-propanol are used. This concentration provides a solids content in the final sol-gel ink at a level of 1-5 wt. %;

to prepare a second solution, 0.7-2.4 ml of nitric acid is added to 100 ml of water and the mixture is heated to 70 ° C to initiate the process of temperature dehydration and increase the content of the crystalline phase, after which the first is gradually added to the second solution with stirring.

The introduction of acid promotes a change in the pH of the solution, which is responsible for the process of crystal formation and an increase in the ionic strength of the solution, contributing to an increase in the mobility of the molecules and accelerate the dissolution of the molecular "coat" of ligands and ions of crystalline TiO ₂ nuclei. As a result of this, the degree of protonization of the particle surface increases to a zeta potential value of at least + 36.1 ± 5.3 mV, which ensures high stability of colloidal particles and leads to the required size of the formed crystalline formations of titanium dioxide at a level of about 5-20 nm, mainly of the anatase phase . The resulting mixture was kept for 1 hour at a temperature of 80 ° C, after which it was sealed with a film and kept for 1-2 weeks at room temperature with stirring. Long exposure helps to achieve equilibrium of the colloidal system of the sol and a gradual increase in the content of the crystalline phase to an indicator of at least 95% relative to the solid phase.

The resulting solution of a nanocrystalline sol of titanium dioxide in water does not meet the criteria for inkjet printing, such as density, viscosity and surface tension, in its rheological parameters, therefore, at the second stage of the preparation of sol-gel ink for interferential inkjet printing, nanocrystalline anatase sol with an amorphous phase content of not more than 5 % in water is modified with a volatile solvent, mainly ethyl alcohol (ethanol).

The predominant choice of ethanol as a volatile solvent is due to its low surface tension, economic cheapness and affordability, the ability to pre-solvate in water without destroying the double electric layer of micelles of the synthesized nanocrystalline sol of titanium dioxide. To obtain the viscosity index required for inkjet printing, the synthesized sol of titanium dioxide is first concentrated by evaporation in a rotary evaporator under pressure at 50 ° C to bring the concentration of the solid phase of TiO ₂ to a concentration of at least 8 mass. % This is necessary to bring the viscosity parameter of the finished sol-gel ink to a level of at least 2.1 MPa * s, in order to ensure the possibility of squeezing a drop of ink from the nozzle of the print head of an inkjet printer. To obtain the surface tension required for inkjet printing, sol-gel ink, an aqueous solution of sols of nanocrystalline titanium dioxide is mixed with ethanol, mainly following the stoichiometry of H ₂ O / Ethanol 1: 3. This stoichiometry determines the set of required density and surface tension of at least 25 mN / m. The resulting solution is homogenized for at least 12 days to achieve phase equilibrium between the solvents.

The main rheological characteristics of the sol-gel ink depending on the ethanol content are presented in Table 1, where the Z parameter was calculated based on the equation: Z = √ (d⋅σ⋅δ) / η, where δ is the density, d is the nozzle diameter, and σ is surface tension, η - viscosity.

These data allow us to establish that the most optimal for inkjet printing according to the dependence of the sol-gel ink parameters on the ethanol concentration in the nanocrystalline titanium dioxide sol of the predominant anatase phase are sol-gel ink containing about 70 wt. % ethanol. It was also found that the stability of the nanocrystalline sol of titanium dioxide decreases sharply with the addition of ethanol of more than 70 wt. % This is due to the fact that ethanol changes the structure of the double electric layer of TiO ₂ particles, sharply lowering their sedimentation stability.

Inkjet printing with sol-gel ink can be carried out on the surface of almost any material that meets the conditions of inkjet printing, however, to obtain thin interfering layers, the substrate must meet the following basic conditions:

- have a non-porous, mostly smooth or polished surface with a minimal change in the height of the texture along the z axis,

- be resistant to ethanol and liquids with a pH value of at least 3,

- contain water-insoluble substrates.

The titanium dioxide anatase nanoparticles formed during the preparation of sol-gel inks have a pure crystalline structure with an average crystallite size of about 5 nm, which corresponds to the direction of the interlayer distance of the body-centered tetragonal structure of anatase. The nanocrystallization of the lattice of particles of titanium dioxide is extremely important for obtaining interference in thin films as already noted. High resolution transmission electron microscopy (HRTEM) confirms the presence of a single crystalline phase with a high degree of crystallinity. X-ray diffraction data for the synthesized titanium dioxide particles show diffraction peaks at angles of 25.411 (101), 37.911 (004), 48.011 (200), 54.011 (105), 54.911 (211) and 62.811 (204), which also confirms the anatase TiO ₂ phase of co an average crystallite size of no more than 5 calculated by the Scherrer equation. These data are completely consistent with the data of transmission electron microscopy and electron diffraction.

For printing thin interference layers - film uniformity is critical to product reliability, and inks containing stabilized colloidal nanoparticles are necessary for liquid phase thin film deposition. For oxide particles, surfactants are most often used to stabilize colloidal ink. However, the addition of surfactants or polymers can lead to a significant loss of optical properties and stability for titanium dioxide-based printed films. In the study, a simple pH control approach was used to protonize the surface and increase the stability of sol particles in order to achieve high homogeneity of the formed layers. The protonization of the surface of the sol particles significantly shifts the critical point of gelation, preventing the development of coagulation contact between the particles. As a result, the structure formation by the polycondensation mechanism begins to occur when the interaction force is 10 ^-11 -10 ^-10 N / contact, when the distance between the particles decreases to 10 ^-9 m. This approach can significantly reduce the nozzle diameter while maintaining high inkjet printing stability. Thus, the preparation of stable TiO ₂ sol-gel inks should occur in the pH range between 2 and 5. The zeta potential of nanocorrystalline particles of titanium dioxide in sol-gel ink is predominantly +36 mV, which ensures a stable state of the sol. To increase the crystallinity of the sol particles and the corresponding increase in the refractive index of the solid phase, the ionic strength of the solution was increased by introducing a compound with a high dissociation constant in the form of inorganic nitric acid (K _a = 24). Considering that the protonating agent is able to influence the phase composition of TiO ₂ during crystallization of amorphous sol particles, this choice was due to the ability of nitric acid to contribute to the formation of the most photoactive phase of anatase.

The most popular polymorphic modifications of TiO ₂ - rutile, anatase and brookite have similar refractive indices, but the advantage of obtaining anatase is determined by using a pH closer to neutral, thereby minimizing the effect of corrosion processes in the print. The presence of a volatile solvent (ethyl alcohol) in the sol-gel ink contributes to the quick drying of the ink on the film or on the surface of holographic paper. Ethyl alcohol plays a very important role, because it is the main factor affecting the rate of evaporation of the solvent. A low concentration of ethanol can contribute to slow drying of the ink on the substrate, coalescence, and an unpredictable change in morphology, while an excess concentration of ethanol leads to a decrease in particle stability due to the destruction of the double isoelectric layer.

For experiments, we used the widespread Canon Pixma IP2870 desktop printer, with standard PG745, CL-746 cartridges. The print head integrated in the cartridge had a droplet size of 2 PL and a nozzle diameter of 1.280 μm. After washing, the cartridge was filled with TiO _{2 with} prepared sol-gel ink, without further modification. No design changes were made to the design of the printer and cartridge. Viscosity was determined with a Brookfield HA / HB viscometer, and surface tension with a Kyowa DY-700 tensiometer. To control the color of the image obtained after drying the sol of the refractive layer of the xerogel of titanium dioxide, it is necessary to form even homogeneous layers in order to achieve the interfering effect in solid thin films. To study the relief of the deposited structures, atomic force microscopy (AFM) was used to scan the surface relief. According to the profilogram of AFM images, it was found that the change in the relief, regardless of the number of layers applied, changes by no more than 20 nm in the range up to 1 μm. Such a surface completely provides the conditions for the occurrence of interest in thin films of xerogel of titanium dioxide and can be used for color printing technology using the inkjet method of optical nanostructures. The change in surface topography is associated with a small particle size, which, according to the TEMP and SEM data, predominantly has a size of 1-5 nm and does not exceed 10-15 nm. This proves that sol-gel inkjet printing based on a nanocrystalline sol of titanium dioxide predominantly of the anatase phase in an aqueous solution of ethyl alcohol is easily achievable with the high accuracy necessary for constructing the interfering layers of individual elements of color interference images.

It is known that in order to obtain images by inkjet printing on an RT film, it is preheated to 70 ° C to increase the drying speed of the ink, but the use of volatile ethanol additives in the sol-gel inks used in the invention does not require this, despite the fact that the evaporation rate below 70 ° C. The solvent removal gradient of the proposed and used sol-gel inks makes it possible to obtain a dense uniform film of highly refractive titanium dioxide xerogel. According to SEM, the nanoparticles of the resulting titanium dioxide xerogel are spherical aggregates of predominantly 5-10 nm in diameter, densely packed together. The results of profilometric analysis show that the film has a curved surface with a slight roughness, which indicates the high compactness of the aggregated nanoparticles forming the layers during slow drying. A more detailed analysis of the surface texture provides AFM images for different layers shows that the superposition of the layers does not lead to a change in the surface structure due to the "healing" of defects of the previous layer, again filled with sol. The continuity of the layers confirms the absence of surface cracking, which can occur during quick drying of the layers and uneven application of the material to the surface, which is in good agreement with classical methods of application. To determine the correspondence to the determined thicknesses of the xerogel layer of titanium dioxide from the reflection spectra, scanning electron microscopy of ultrahigh resolution (SEM - HC) was used. For this, the substrate was subjected to a perpendicular cut in the direction of movement of the print head. To determine the interface of the TiO ₂ substrate, in order to determine the true thickness of the xerogel layer of titanium dioxide, we used energy dispersive analysis with a color contrast function. As a result, the formation of even layers of titanium dioxide xerogel close to perfect condition was observed, which indicates the impeccability of the printing technology and the sol-gel ink composition used. According to the data obtained, high uniformity in the thickness of the xerogel of titanium dioxide and consistency between different measurements is achieved. In addition, it was found that the thickness of the xerogel layers of titanium dioxide is the same along the perimeter, regardless of the number of applications. It is also clearly seen that the obtained titanium dioxide layers have close contact with the surface of the substrate. This is due to the occurrence of the sol-gel transition of the sol-gel ink during drying and the condensation of the sol into a dense xerogel layer. The particle size of the xerogel of titanium dioxide, not exceeding 20 nm, allows the deposition of the proposed sol-gel ink with high penetration.

The study of the mechanical properties of inkjet coatings of xerogel titanium dioxide on the surface of plastic films was performed using a texture analyzer.

It is known that the microhardness of xerogel films deposited from solutions is a key indicator, since the use of soft chemistry usually leads to a loss of mechanical resistance due to the formation of a high porosity of the xerogel layer. In addition, inkjet printing on such non-porous surfaces, such as glass and polymers, causes a number of difficulties not only due to the coalescence of the droplets, but also because of the low adhesion of the dry xerogel layer to the glass and polymer substrate. Studies have shown a decrease in mechanical strength by a factor of 2 (for the 7th layer relative to the first), which may be due to the relatively low density of contact between the xerogel particles themselves after the sol has dried, and, as a result, a drop in the mechanical hardness gradient with increasing xerogel layer thickness.

It is also known that layer-by-layer deposition of a sol can cause deformation of previous layers, complicating the process of obtaining hierarchical structures, therefore, to increase the mechanical strength of xerogels, heat treatment is used at 300-500 ° C, increasing the degree of crystallinity and initiating the occurrence of interfacial interactions with subsequent sintering. Obviously, the effect of such high temperatures makes it impossible to deposit layers of titanium dioxide water sol applied by conventional methods on polymer substrates. The use of the inventive sol-gel inkjet ink in the form of a nanocrystalline sol of titanium dioxide of a predominantly anatase phase in a solution of ethyl alcohol in water makes it possible to obtain thin xerogel layers from the sol with regulation of thickness up to 10 nm at room temperature with strong bonding of individual xerogel layers to each other with a friend. Field studies of inkjet printing of color rainbow holographic images by the colorless sol-gel inks offered by the paper showed that, despite the structural features of titanium dioxide xerogel layers formed by wet solution chemistry, their optical properties turned out to be similar to the optical properties of calcined titanium dioxide xerogels. Synthesized sol-gel inks can be classified as promising highly refractive coatings, given that in the entire visible range this refractive index does not fall below 1.75, which, given the high uniformity of deposition during the sol-gel transition, indicates the prospects of their use as real substitutes for organic refractive polymers . The following reagents can be used to produce inkjet inks based on titanium dioxide sols:

- organic and inorganic precursors of titanium, hydrolyzed in the aquatic environment. For example, titanium isopropoxide 97%;

- volatile solvents that do not destroy the double electric layer of titanium dioxide particles and increase the drying speed of dispersions. For example, ethanol> 96%;

- protonating agents based on easily dissociating compounds, for example inorganic acids. In particular, nitric acid (~ 65%);

- medium for stabilization of colloidal nanoparticles, ensuring the preservation of the zeta potential at a level of at least 20 mV, for example water, with a resistance of at least 50 MΩ * cm.

To obtain a surface masking coating of the titanium dioxide layer, organic compounds polymerizing under the influence of external influences (temperature, oxygen, air humidity, UV, etc.) and having a refractive index of not more than 1.6, for example, isobutyl methacrylate, can be used as a lacquer layer. 97% dispersed in 99.6% acetone. TiO ₂ nanoparticles are synthesized by hydrolysis of titanium isopropoxide in deionized water with vigorous stirring (1000 rpm) and using nitric acid as a protonation agent.

To regulate surface tension and viscosity, an aqueous sol solution is mixed with ethanol. The dependence of surface tension and viscosity as a function of the ethanol content in the ash is shown in FIG. one.

The resulting solution was homogenized for 12 days to complete solvation. The resulting sol was evaporated in a rotary evaporator under reduced pressure at 50 ° C. Viscosity was determined with a Brookfield HA / HB viscometer and surface tension with a Kyowa DY-700 strain gauge. The obtained sol-gel TiO ₂ ink was applied onto commercially available microrelief PET films manufactured by Pakvizhn LLC with a thickness of 20 μm, having the following microrelief embossing and a refractive index of 1.41 (A = 400 nm). The film was not pretreated and no layers were applied on it, modifying its surface. To print the obtained sol-gel titanium dioxide ink, we used a Canon Pixma IP-2840 desktop office printer with a drop volume of 2 square meters. For this, the holographic film was fixed on a regular sheet of A4 format, providing the required paper thickness. The sol-gel ink was placed in the cartridge without further modification. The thickness of the obtained xerogel layer of nanocrystalline titanium dioxide during inkjet printing with sol-gel ink after drying in air and removal of solvents did not exceed 500 nm s, the refractive index of at least 1.75 ± 0.08 in the entire visible spectral region. After drying, the surface of the holographic microthermal film with a xerogel layer of nanocrystalline titanium dioxide deposited on the surface was covered with an acrylic varnish layer consisting of a 1: 1 solution of isobutyl methacrylate in acetone using a 30 cm long Mayer rod made of nickel wire with a diameter of 10 mm and a wire thickness of 6 μm. The thickness of the smooth glossy transparent coating obtained from the varnish layer after drying did not exceed 4 μm with a refractive index of 1.34 (for a light beam of 400 nm). The time of complete drying of the varnish layer with the formation of the finished holographic rainbow image did not exceed 30 minutes. Powder X-ray diffraction data using Bruker D8 Advance was used to confirm the dry solids composition of the anatase film after drying the sol-gel ink.

To study the xerogel layers of nanocrystalline titanium dioxide, sprayed using a scanning electron microscope (SEM) with a cross-section function, including energy dispersive analysis, after complete drying in a vacuum desiccator, the film was examined without additional sputtering with an ultrahigh resolution of 1 nm using a Magellan 400L electron microscope (Field Emission Inc.).

Optical reflection measurements at normal incidence were performed to obtain the refractive indices of the xerogel layer of nanocrystalline titanium dioxide in the range of 400-800 nm. For this experiment, a confocal optical scheme was organized. Incident unpolarized light from a halogen lamp (HL-2000-FHSA) that was focused on the film surface through a 50x microscope objective (Mitutoyo M plan ARO, N.A. 0.55). The reflected light was collected using the same optics and then analyzed using a spectrometer (HORIBA LabRam HR) with a cooled CCD camera (Andor DU 420A-OE) and 150 g of a 1 mm diffraction grating.

The spectra obtained were normalized to the known spectrum of a halogen lamp. The transmission spectra of the hologram of the inkjet method were measured using a Cary 8454 UV-VIS with a diode array system. TA.XTPlus texture analyzer (Stable Micro Systems, UK) operating in the horizontal friction system (A / HFS) mode was used to determine the shear strength of TiO ₂ films (test speed: 2.5 mm S-1 and distance: 95 mm ) The spectra obtained were normalized to the known spectrum of a halogen lamp. The practical implementation of the invention allows to obtain rainbow holograms of any shape using an inkjet printer of the proposed sol-gel ink. To do this, it is necessary to mask the surface of a holographic microembossed sol-gel film with high refractive index (HRI) in the right places.

The steps for visualizing a titanium dioxide layer on the surface of a holographic microembossed polymer film to produce rainbow holographic text and / or images during inkjet printing are shown in Fig. 4. As mentioned above, holographic paper is known as an optically variable device, in which the image varies depending on light source, light angle, and from the viewing angle. A rainbow holographic image reproduced on the surface of a holographic paper or other microembossed substrate is a reproduction of the original holographic matrix on a microembossed (micro embossed) coating of holographic paper. The refractive index (RI) of such a holographic microembossed paper, which is usually obtained from a UV-curable polymer, is usually in the range of 1.3-1.59. The usual preservation of the microrelief of materials with the same RI from fats and moisture from air is usually carried out by metallizing the surface under vacuum to obtain a bright, shiny metallic luster that improves the holographic image and makes it visible, or the microstructure is coated with a transparent dielectric layer with a high refractive index by vacuum deposition or with using polymers with a refractive index of RI of at least 1.7. This feature of maintaining the diffraction effect of rainbow holography is used in the invention to obtain rainbow holograms with predetermined images by using the proposed sol-gel ink for inkjet printing. The special sol-gel inks described above were prepared based on an aqueous colloidal solution of nanocrystalline titanium dioxide. The application of sol-gel ink to the surface of an open holographic paper or other microembossed surface creates a nanometer highly refractive layer after drying, which prevents the diffraction effect from disappearing from the use of varnish or a polymer layer with a low refractive index (Fig. 4). Local storage of rainbow holographic images is ensured by several parameters implemented in this invention:

1) the refractive index of the micro-embossed film or holographic paper and the transparent lacquer coating is close or identical;

2) the average refractive index for xerogel of nanocrystalline titanium dioxide, applied by inkjet printing, more than 1.7 in the entire visible range of light;

3) an optically transparent xerogel layer of nanocrystalline titanium dioxide, formed by inkjet printing and a transparent coating layer of a polymer or varnish do not change the light transmission, fully preserving the diffraction effect - the basis of rainbow holography;

4) the xerogel layer of nanocrystalline titanium dioxide formed by inkjet printing and the coating layer of the polymer or varnish have high adhesion to the substrate.

Almost any image and text can be obtained under the above conditions. In addition, given the high porosity of the layer of titanium dioxide nanoparticles and their hydrophilic properties, it is possible to apply conventional inkjet inks to the upper layers with a high refractive index, thus combining several optical effects in thin layers. To maintain high contrast and increase the optical effect of rainbow holography, it is important to apply a transparent dielectric layer with a high refractive index. Inks based on a nanocrystalline titanium dioxide sol fully meet these requirements, and after drying form an optically transparent coating with a high refractive index of more than 1.7. The main property of these nano-products is a high degree of crystallinity and the ability of the phase sol-gel transition during drying under natural atmospheric conditions without the use of high temperatures. Obtaining titanium dioxide using the methods of solution chemistry without annealing stage, as well as achieving a refractive index of 1.7 ± 0.1 xerogel of titanium dioxide in the visible region by previously known methods was impossible. Typically, a calcined nanocrystalline titanium dioxide powder dispersed in a polymer is used, but this approach is not suitable for inkjet printing and does not allow the formation of thin layers with uniform accurate nanodistribution of the refractive phase.

According to the invention, low-temperature sol-gel synthesis is used to produce nanocrystalline titanium dioxide with a refractive index of 1.75 at 400 nm. To prevent the photocatalytic effect of titanium dioxide on the organic phase, the titanium dioxide layer is varnished, which prevents contact between the photocatalyst and water molecules, makes it inactive and safe for the substrate for a long time. At the same time, an experimental possibility was found to obtain a nanocrystalline sol of titanium dioxide ₂ , using only nitric acid as a protonating agent without any stabilizers. To reduce surface tension and increase the drying speed of sol-gel inks, we modified the process for producing nanocrystalline sols of titanium dioxide ink, adapting their physicochemical properties for inkjet printing and uniform application. The absence of commonly used organic stabilizers, such as polymers and surfactants, contributes to the rapid condensation of the nanocrystalline sol of titanium dioxide during the evaporation of the solvent, providing high adhesion to the microrelief surface, providing a sol-gel transition of the nanocrystalline sol of titanium dioxide to xerogel directly on the substrate. As a result, higher adhesion of nanocrystalline titanium dioxide to the substrate is achieved compared to using conventional vacuum deposition, as shown in FIG. 5.

In the images of FIG. 5 it is clearly seen that there is an extremely weak adhesion of the TiO ₂ coating applied by vacuum technology to embossed holographic paper (a, b), in comparison with the adhesion of the TiO ₂ coating applied by the proposed inkjet printing method (c, d). This is due to the fact that the vacuum deposition method requires the preliminary activation of a microembossed holographic surface in an oxygen plasma stream with the formation of active hydroxyl groups on the polymer surface, in contrast to the formation of sol-gel coatings that provide physical crosslinking on the surface during drying.

These findings are confirmed by cross-sectional data obtained after applying TiO _{2 in} various ways (Fig. 6). To assess the adhesive properties of the coating, the peeling was tested using a classic adhesive tape. The results of tests of cross sections and energy dispersive analysis (EMF) of films based on titanium dioxide deposited on the surface of holographic paper by the vacuum method (a, b) and the proposed inkjet method (c, d) show high adhesion properties of TiO ₂ films. applied by an inkjet printer according to the proposed method of inkjet printing (Fig. 6). This is confirmed by the EMF profilogram, where it is clearly seen that the active TiO ₂ layer deposited in vacuum is easily separated from the substrate. It was found that after five adhesion tests using an adhesive tape test, the continuity of the coating obtained according to the invention is maintained at 50%. TiO ₂ coatings are not crosslinked with the polymer substrate after vacuum deposition, which facilitates its easy separation, and resistance to mechanical stress is impaired. The proposed colloidal sol-gel inks are more resistant to external mechanical stress and provide high adhesion of titanium dioxide films to the surface of holographic paper. The EMF profilography image for a sol-gel titanium dioxide printed on an inkjet printer illustrates the continuity and complete preservation of the coating after five adhesive tape tests, as well as the close contacts between the applied TiO ₂ layer and the polymer substrate without prior hydroxylation of the substrate surface.

The optical properties of inkjet-printed nanocrystalline titanium dioxide, such as the reflection and dispersion spectra of the refractive index, are shown in Fig. 7. Since the coating under study was located between two isotropic media (air and 2 mm fused silica substrates), at certain radiation wavelengths, one can observe reflection of the minima in the spectra (for example, the radiation is not “seen” but is actually reflected from the “virtual” boundary between the substrate and air). The reflection coefficient for the air-glass boundary is shown as a red dotted line in FIG. 7a. The reflectance maxima in FIG. 7a correspond to the positive interference of a certain wavelength of radiation reflected from the air-printed layer, the boundary of the glass-printed layer. Thus, from the experimental data on the reflection coefficients, one can obtain the refractive index of the film dispersion. This relationship is shown in FIG. 7, where the scatter of experimental values for the refractive indices obtained from a large series of experiments makes it possible to estimate the refractive index 1.75 ± 0.08 of a nanocrystalline titanium dioxide layer obtained by the jet method in the entire visible spectral region. The high refractive index of the nanocrystalline titanium dioxide layer obtained by the jet method (RI ~ 1.75), unlike polymer holographic paper (RI ~ 1.41), leads to masking of the microrelief surface compared to the varnished areas, which preserves light diffraction by machined parts. It was experimentally established that the optical density of the coatings formed by the TiO ₂ jet method is on a par with calcined materials.

These properties were used to reproduce rainbow holographic images (Fig. 8) by selectively applying the proposed sol-gel ink with a high refractive index RI (more than 1.7) on an inkjet printer on ordinary holographic paper, followed by applying a varnish layer with a low RI ( 1.34) by means of the Maer rod. The disappearance of the iridescent holographic effect in the area not exposed to the proposed TiO ₂ sol-gel ink is due to the fact that the refractive indices of the Banton holographic paper (1.41) and the lacquer layer (1.34) are close to each other, which leads to the fact that light cannot interfere at the boundary between these phases and passes through the structure of the layers without changing. On the other hand, the presence of an intermediate thin, transparent layer of a nanocrysallic xerogel layer of titanium dioxide with a high refractive index leads to the preservation of the holographic effect of the microembossed (microrelief) surface. This not only causes reflection at the interface between the holographic paper and varnish, but also increases the intensity of the reflected beam, increasing the main rainbow holographic effect. The brightness of the image is determined solely by the technical features of the inkjet printer and depends on its resolution. In FIG. 8c) it is clearly seen that after applying a highly refractive xerogel layer of nanocrystalline titanium dioxide and subsequent formation of a third layer with a low refractive index, the holographic effect does not change its brightness and fully reproduces printed images of the text and pattern in the form of rainbow holographic images. The presence of an intermediate thin xerogel layer of nanocrystalline titanium dioxide with a high refractive index deposited by inkjet printing over holographic paper increases the reflection coefficient by an average of two orders of magnitude compared to holographic paper coated only with polymer varnish. The transparency of the final heterostructure in the visible region remains unchanged, even a 2% increase in the light transmission of the resulting heterostructure is observed.

The high mechanical strength of TiO ₂ coatings and their adhesion to PET holographic paper is confirmed by test results to determine the coefficient of friction. It was found that the interaction force between the film and TiO _{2 of} holographic paper, 0.557 ^min , is close to the interaction of varnish with pure PET, 0.637. This proves the high affinity of the films and their high stability, as a conventional organic substrate. The range of measurement of the friction coefficient depending on the thickness of the deposited xerogel layer of nanocrystalline titanium dioxide corresponds to the contact interaction of classical organic polymers.

In this regard, high adhesion of the layers to each other is ensured. The optimum required ethanol content was determined experimentally, in a volume of at least 60%, in accordance with the data of optical transparency, achieving a masking effect, and rheological properties of sol-gel inks of the most optimal properties for inkjet printing of rainbow holographic images.

The implementation of the invention shows an effective and cost-effective strategy for the development of inkjet printing of individual rainbow holograms using ordinary, widespread holographic paper. This became possible due to the use of an inkjet printer to form a xerogel layer of nanocrystalline titanium dioxide with a high refractive index, which, after coating it with a varnish layer, provides a protective function for the microrelief, while maintaining the diffraction effect of rainbow holography in the treated area. The formed heterostructure does not change the optical transparency and, therefore, maintains the contrast of the image. Moreover, in comparison with the traditional TiO ₂ vacuum deposition technology, the proposed sol-gel method provides high adhesion and the formation of a dense heterostructure with increased mechanical strength.

The proposed method can significantly expand the visualization capabilities of rainbow holographic images and greatly simplifies the manufacturing process. Typically, ink color formation is achieved by combining CMYK or RGB colors. According to the invention, a color printing technology using only ink is completely safe for use. At the same time, the proposed sol-gel inks significantly expand the possible choice of substrates for application, including the use of flexible polymer substrates and smooth solids, which makes application in a format practically unlimited, and greatly facilitates the technology of application of interference structures controlled up to 10 nm .

As printed products, packaging materials, tags, bags or other printed materials known in the art can be made. The substrate may be any material that is used in the printing industry as a substrate. Substrates may include polymer films and other polymeric materials, various types of paper, ranging from thin tissue paper to corrugated cardboard, kraft paper, coated folders. Metallic films and metal foil can also be used as a substrate. The main substrate may be coated with preparations known in the printing industry to obtain a printed artistic image. The printed product may receive a protective and decorative finish after the artistic image is printed on the substrate. The printed substrate can be further processed in the manufacturing process of the package, or the process of processing ends with printing.

The shape of the rainbow holographic images of the printed product can be made, configured, or simply saved as an electronic computer data file.

The dimensions and values disclosed in the description should not be construed as strictly limited to the listed exact numerical values. On the contrary, unless otherwise specified, each such size is intended both to indicate the value given in the description and to the functionally equivalent range of this value. For example, a size disclosed as “20 nm” means “approximately 20 nm”.

All documents cited in the detailed description of the invention, in the relevant part, are included here as reference information; reference to any document should not be construed as recognition that this document discloses the present invention. If any meaning or definition of a term in the description contradicts any meaning or definition of the same term in the document included as reference, then the meaning or definition of the term given in the description should be defining. Although specific embodiments and / or individual features of the present invention have been described herein, it will be apparent to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. Therefore, the appended claims are intended to cover all such changes and modifications that are within the scope of this invention.

Claims (7)

1. Sol-gel inkjet ink for printing rainbow holographic images on holographic paper or on a microembossed surface, including nanocrystalline anatase phase titanium dioxide sol with an amorphous phase content of not more than 5 wt. % in water and the quantitative content of the solid phase in sol-gel ink is 1-5 wt.%, and ethyl alcohol in an amount of 60-70 wt. %, and sol-gel ink has a surface tension of at least 25 mN / m, no more than 50 mN / m and a viscosity of at least 2.1 mPa⋅s, no more than 20 mPa⋅s. 2. Sol-gel ink according to claim 1, characterized in that they contain nanocrystalline anatase sol with an amorphous phase content of not more than 5 wt.% In a solution of ethyl alcohol in water, and at least one of the following group of properties: the presence of titanium dioxide nanoparticles in the form of crystals of titanium dioxide predominantly anatase phase with a content of an amorphous phase of titanium dioxide of not more than 5 wt.%, a concentration of nanocrystalline particles of titanium dioxide of not less than 1 wt. %, the size of the nanocrystalline particles of titanium dioxide is not more than 100 nm, the average hydrodynamic diameter of the particles of the nanocrystalline sols of titanium dioxide is not more than 100 nm, mainly 15.8 nm, the zeta potential of titanium dioxide nanoparticles is not less than +10 mV, mainly +36.1 ± 5 , 3 mV, the possibility of forming a transparent in the visible spectrum of the refractive layer of xerogel titanium dioxide with a thickness of 30 to 1000 nm with a refractive index of more than 1.75, the concentration of ethyl alcohol in water is not more than 70 wt. % with a predominant ratio of ethyl alcohol: water 3: 1, the duration of sedimentation stability of nanocrystalline sol of titanium dioxide for at least 1 year. 3. Sol-gel ink according to claim 1, characterized in that they have: a viscosity of not more than 20 mPa⋅s, mainly 2.1 mPa⋅s, surface tension of not more than 50 mN / m, mainly 27 mN / m. 4. The method of obtaining sol-gel ink for inkjet printing of rainbow holographic images on holographic paper or on a microembossed surface according to claim 1, which consists in the fact that at the first stage, an anatase nanocrystalline sol with an amorphous phase content of not more than 5 wt. % in water using a solution of titanium isopropoxide and 2-propanol in a concentration that provides a solids content of sol-gel ink of 1-5 wt. %, crystal formation and protonization by the addition of this solution to an aqueous solution containing nitric acid, in an amount that ensures the degree of protonization of the particles to a zeta potential of at least +10 mV, mainly + 36.1 ± 5.3 mV, and exposure to tight closure and stirring for 1-2 weeks, at the second stage, the obtained nanocrystalline sol of anatase titanium dioxide is mixed and homogenized in water with ethyl alcohol, taken in an amount providing sol-gel ink with a surface tension of at least 25 mN / m and no more than 50 mN / m and a viscosity of at least 2, 1 mPa⋅s, not more than 20 mPa⋅s. 5. The method according to p. 4, characterized in that the nanocrystalline anatase sol with an amorphous phase content of not more than 5 wt.% In water is obtained by obtaining a titanium alkoxide solution by mixing titanium isopropoxide and 2-propanol, hydrolysis of titanium alkoxide with the formation of stable crystalline dioxide nuclei predominantly anatase phase of titania in water, the temperature of dehydration of amorphous titanium oxyhydroxide heating to ⁷⁰ ° c in an acidic medium, creating an acidic environment and heating at 80 ° c for 1 hour with increasing sod holding the crystalline phase of titanium oxide predominantly anatase phase and obtaining a nanocrystalline sol of titanium dioxide predominantly anatase phase with a crystal size of titanium dioxide of not more than 100 nm, mainly 5-20 nm, with an average hydrodynamic particle diameter of sol not more than 100 nm, mainly 15.8 nm , with a zeta potential of sol particles of at least + 10 mV, mainly + 36.1 ± 5.3 mV, stabilization of a nanocrystalline sol of titanium dioxide by protonization of sol particles in the presence of nitric acid and holding no more than 1-2 weeks at room temperature with constant stirring to obtain a stable nanocrystalline sol of titanium dioxide predominantly anatase phase in water with an amorphous titanium dioxide phase content of not more than 5 wt.%, with a size of crystals of titanium dioxide 5-100 nm, mainly anatase phase, with an average hydrodynamic diameter sol particles of not more than 100 nm, mainly 15.8 nm, with a zeta potential of sol particles of not less than +10 mV, mainly + 36.1 ± 5.3 mV.

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