RU2641500C2 - Printed product with colour interference image - Google Patents

Abstract

FIELD: printing industry.SUBSTANCE: invention relates to printed products with a colour interference image printed on an inkjet printer by means of sedimentationally stable sol-gel ink in the form of a sol of crystalline titania nanoparticles of the anatase phase, allowing to obtain a colour interference image formed by at least one transparent in the visible spectral range by the refractive layer Xerogel of titanium dioxide with a thickness of 300 nm to 1 mcm, with a refractive index of more than 1.7 and a variable coloration as a function of and the thickness refractive layer prepared using a sol-gel ink in the form of a nanocrystalline titanium dioxide sol in solution of ethanol in water.EFFECT: possibility of inkjet printing of printed products with colour interference images on non-porous surfaces.5 cl, 3 dwg

Description

Technical field

The invention relates to printed products with a color interference image printed on an inkjet printer by means of sedimentation-stable sol-gel inks in the form of sols of crystalline titanium dioxide nanoparticles mainly in the anatase phase, which allows to obtain a color interference image formed by at least one refractive layer transparent in the visible region of the spectrum xerogel titanium dioxide with a thickness of 300 nm to 1 μm, with a refractive index of more than 1.7 and a varying color in depending on the thickness of the refractive layer.

State of the art

Color printing technology is booming and in less than 40 years it has gone from matrix printers with ink ribbon to 3D printers with the printing of bulk color materials, but the use of a color scheme for coloring CMYK or RGB dyes remains unchanged, which inevitably limits technological capabilities , and color rendition.

Color inkjet printing is the most common and affordable, but color inkjets and specialty papers are usually required to print color images for inkjet printing.

Moreover, inkjet inks of some colors are environmentally hazardous, for example, yellow inks are usually made using toxic cadmium compounds (Cd ²⁺ ), and color images printed with ordinary inkjet inks fade from exposure to sunlight, UV radiation and high temperatures.

In addition, high-quality color images by inkjet printing can be obtained only when using inks with certain physical properties (of a certain viscosity and surface tension) and on porous substrates (usually on special types of paper on which ink is absorbed but not fuzzy), which after ink dries usually deformed.

Known ink for an inkjet printer, and a method of inkjet printing with the suppression of 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 viscosity of the ink is from 1 to 5 cP at 25 ° C, and the content of X (%) of the substance 1, and the Y content (%) 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 the water-holding ability in an environment with a temperature of 23 ° C and a humidity of 45% and the 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, including a siloxane photopolymer containing titanium, intended for the manufacture of coatings with a high refractive index and 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 of 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 the specified first and second components is carried out until the completion of the formation of the specified titansiloxane 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 compiled 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 colorful layers of various colors on a surface of a printed material, 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 * [ (p _b -p _k ) / p _b ] ≤0.0007, where a is the raster step; b is the 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 on the substrate fluorescent dots of the image of printing inks are formed, which contain the pigments fluorescent when excited by a certain electromagnetic radiation, as well as non-fluorescent dots of the image of the 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 provides a grayscale image that 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)].

Known inks for color inkjet printing do not allow to obtain color interference images.

The phenomenon of interference in thin films is known, which is characterized in 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.

An important advantage of interference is the natural color reproduction, since the entire spectrum of sunlight is used to form the interference image, including the maximum possible number of colors and shades perceived by the human eye.

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.

Known scalable monochromatic interference on a smooth surface, formed either by the liquid phase or by a solid substrate with minimal roughness, for example, the artificial preparation of interfering layers on polished silicon and on solid organic polymers.

The phenomenon of interference in thin films is known, which is fundamental for the appearance of an iridescent effect when creating chameleon paints.

The appearance of color in the microstructures of photonic crystals and colloidal magnetic materials is known, however, all known methods of creation and 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 urgent 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 forming optical structures of nano-objects by inkjet printing methods.

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 viscosity and surfactants to reduce surface tension. This inevitably reduces the refractive index, due to an increase in the volume fraction of the organic part in the dry residue.

Known thin-film element with an interference layered structure for tamper-resistant papers, valuable documents and similar objects, containing 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 differ at least in the visible spectral region by 5 or more times, when observed in reflected light, the thin-film element has a metallic luster and a substantially neutral color, and when viewed in transmitted light is perceived at color in transmitted light the thin film element has a saturation C ^* _ab color defined in the CIELAB color space, 15. Two more of the glossy layers consist 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 two absorbing 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 C ^* _ab color saturation defined in the CIELAB color space of more than 20, preferably more than 25. The thin-film element when viewed at right angles is visible in transmitted green and has a C ^* _ab color of more than 30, preferably more 40, or - in transmitted light is visible yellow and has a color saturation C ^* _{ab of} more than 20, or - in transmitted light is visible in red and has a color saturation C ^* _{ab of} more than 20, preferably more than 30, or - in transmitted light is visible in blue and has a saturation color is the 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, including: the formation on the substrate of 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 composition of the image changes the size and refractive index of the 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 change the size and refractive index of the particles in the printed part of the array, and additionally contains a solvent that resizes 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 different from the rest of the image [RU 2013125497 G02B 1/00. Publ. 12/10/2014, WO 2012/061207 2012.05.10].

Known protective printing fluid and method of printing with nanoparticles, which allows to 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 onto 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 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. The 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].

No analogs of printed products obtained by color inkjet printing with colorless ink with nanoparticles were found in the scope of the search.

The known sol-gel processes are known as the technology of materials, including nanomaterials, including the production of sol with its subsequent transfer to gel, that is, to a colloidal system consisting of a liquid dispersion medium enclosed in a spatial network formed connected particles of a dispersed phase [https://ru.wikipedia.org/wiki/Zol-gel_process].

Sol (plural sol, 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].

Gels (unit gel, from lat. Gelo - “freeze”) are 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 the dispersed phase are not bound into the spatial structure, but freely participate in Brownian motion [http://dic.academic.ru/dic.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_protsecc].

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 the 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 in supercritical drying, in the preparation of cryogels, freeze-drying, and in the preparation of xerogels, convection subcritical drying .

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 (English 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.

The value of the zeta potential equal to 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 sol of rutile phase with an average particle diameter of less than 30 nm 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 steps: 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 С01G 23/047 2006-05-25].

Analogues of printed products with color interference images formed by at least one xerogel refractive layer transparent in the visible region of the spectrum and obtained by color inkjet printing with colorless ink with nanoparticles were not found in the scope of the search.

The closest prototype analogue in technical essence and the obtained technical result is a method for producing a titanium oxide sol, comprising the steps of: a) increasing the temperature of the reagent solution containing the titanium oxide precursor as a solvent for the reaction to a reaction temperature of 70 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 of C ₁ -C ₅ , a higher alcohol of C ₆ or more, ethylene glycol, and acetyl acetone. The lower alcohol is methanol, ethanol, propanol, isopropyl alcohol, butyl alcohol, isobutyl alcohol and / or 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. Moreover, the values of the refractive index 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 (i.e. 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 achieving 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 allow the formation of color interference nanostructures.

Tasks and technical result

The main objective of the invention is the ability to produce inkjet printing of printed products with color interference images on non-porous surfaces by means of specially prepared colorless sol-gel inks with the ability to observe color images in the reflected light of the visible spectrum, which in itself is especially unique to the inkjet printing method.

Technical results obtained by the implementation and use of the invention are:

- the manufacture of inkjet printing of printed products with color interference images in the form of optical film nanostructures of nanocrystalline sols of titanium dioxide with an accuracy of 10 nm, providing controlled interference, while usually inkjet printing focuses on micrometer manipulation of printed objects, and only in exceptional cases goes into the nanoscale;

- the manufacture of printed products using non-toxic inkjet inks based on chemically inert titanium dioxide, while classic inkjet colors are environmentally hazardous and include the use of toxic compounds such as Cd ²⁺ for a yellow cartridge;

- the manufacture of printed products by inkjet printing with color interference-colored images that do not fade from the action of sunlight and UV radiation, with high adhesion to a non-porous substrate;

- the manufacture of printed products with the possibility of reapplying ink for inkjet printing of refractive layers and reusing the substrate with the ability to remove the applied layers with aqueous solvents.

Disclosure of invention

A characteristic distinctive original feature of the invention is the use of inkjet printing to create color interference-colored printed images in the form of xerogel nanolayers of nanocrystalline titanium dioxide with high accuracy without the use of high temperatures and technically complex physical processes.

This became possible thanks to the use of special sol-gel inks based on a nanocrystalline sol of titanium dioxide of a predominantly anatase phase, during the natural drying of which optically monolithic coatings are formed in the form of a refractory xerogel layer of nanocrystalline titanium dioxide with a high refractive index (more than 2 in the entire range of visible light).

Controlling the thickness of the xerogel refractory layer of nanocrystalline titanium dioxide with an accuracy of 10 nm by means of a jet application of sol-gel ink allows to obtain color images in the entire color range of the visible light spectrum with controlled interference using only colorless ink.

The absence of dyes in the proposed sol-gel inks for color inkjet printing is highly promising from an environmental perspective, since the systems used based on nanocrystalline anatase titanium dioxide sols are non-toxic and bioinert.

According to the invention, when printing color interference-colored printed images by the inkjet method, it is proposed to use sol-gel ink prepared by the methods of solution chemistry for interference inkjet printing to create color interference images by the inkjet method, which makes it possible to create refractive coatings with a given thickness with an accuracy of 10 nm necessary to create color interference images even on unprepared smooth polymer films.

The proposed approach lays the foundation for the development of a fundamentally new direction in color printing and allows one to master new methods of color inkjet printing in the manufacture of printed products with the formation of optical nano-objects by widely available inkjet printing methods using conventional inkjet printers on non-porous substrates.

The problem is solved and the required technical result is achieved by the fact that in the manufacture of printed products with the inkjet method printed by color interference images for color inkjet printing using sol-gel ink containing nanocrystalline sol of titanium dioxide predominantly anatase phase in a solution of ethyl alcohol in water, characterized by at least 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 1-5 wt. %

the size of nanocrystalline particles of titanium dioxide 5-20 nm,

the average hydrodynamic particle diameter of the nanocrystalline sol of titanium dioxide is not more than 20 nm, mainly 15.8 nm,

the zeta potential of titanium dioxide nanoparticles is not less than +30 mV, mainly + 36 ± 5 mV,

the possibility of forming a transparent in the visible spectrum of the refractive layer of the xerogel of titanium dioxide with a thickness of 300 nm to 1000 nm with a refractive index of more than 1.7,

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

viscosity of not more than 2.5 MPa * s, mainly 2.1 MPa * s,

surface tension of not more than 30 nN / m, mainly 27 nN / m,

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

Used sol-gel ink for color interference inkjet printing containing nanocrystalline sol of titanium dioxide in a solution of ethyl alcohol in water, get in two stages:

at the first stage receive a nanocrystalline sol of titanium dioxide predominantly anatase phase in water,

and in the second stage, a sol-gel ink for color interference inkjet printing in the form of a nanocrystalline titanium dioxide sol in a solution of ethyl alcohol in water is obtained from a nanocrystalline titanium dioxide sol of a predominantly anatase phase in water, with the density, viscosity and surface tension required for inkjet printing.

A nanocrystalline sol of titanium dioxide of a predominantly anatase phase 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 anatase titanium oxide in water,

conducting temperature dehydration of amorphous titanium oxyhydroxide by heating to 70 ° C in an acidic environment,

by creating an acidic medium and holding at 80 ° C for 1 hour with an increase in the content of the crystalline phase of the anatase phase titanium oxide and obtaining a nanocrystalline titanium dioxide sol of a predominantly anatase phase with titanium dioxide crystal size of not more than 20 nm, mainly 5-20 nm, with the average hydrodynamic diameter of the sol particles is not more than 30 nm, mainly 15.8 nm, with the zeta potential of the sol particles not less than +30 mV, mainly + 36 ± 5 mV,

stabilization of the nanocrystalline sol of titanium dioxide predominantly anatase phase by protonization of the sol particles in the presence of nitric acid and holding for 1-2 weeks at room temperature with constant stirring to obtain a stable nanocrystalline sol of titanium dioxide predominantly anatase phase with an amorphous phase of titanium dioxide of not more than 5% with a titanium dioxide crystal size of 5–20 nm, mainly of the anatase phase, with an average hydrodynamic diameter of the sol particles of not more than 20 nm ety of 15.8 nm, a zeta potential of the sol particles is not less than +30 mV advantageously + 36,1 ± 5,3 mV.

Sol-gel ink for color interference inkjet printing in the form of a nanocrystalline sol of titanium dioxide in a solution of ethyl alcohol in water is obtained by:

adjusting the viscosity parameter of a nanocrystalline sol of titanium dioxide of a predominantly anatase phase in water to an index of not more than 2.1 MPa * s by concentrating a sol of nanoparticles of titanium dioxide of a predominantly anatase phase in water to a concentration of at least 8 wt. % by vacuum evaporation at a temperature of 50 ° C,

obtaining the required density and surface tension of the nanocrystalline sol of titanium dioxide predominantly anatase phase of not more than 25 mN / m by adding ethanol to a concentration of ethyl alcohol in water of not more than 70 mass. %

ensuring phase equilibrium between water and ethyl alcohol by homogenization for at least 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 of crystals of titanium dioxide predominantly anatase phase with an amorphous phase of titanium dioxide content of not more than 5%,

the concentration of nanocrystalline particles of titanium dioxide 1-5 wt. %

the size of nanocrystalline particles of titanium dioxide 5-20 nm,

the average hydrodynamic diameter of the sol particles is not more than 20 nm, mainly 15.8 nm,

the zeta potential of sol particles is not less than +30 mV, mainly + 36 ± 5 mV mV,

the possibility of forming a transparent in the visible spectrum of the refractive layer of xerogel nanocrystalline titanium dioxide with a thickness of 300 nm to 1 μm with a refractive index of more than 1.7,

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

viscosity of not more than 2.5 MPa * s, mainly 2.1 MPa * s,

surface tension of not more than 30 nN / m, mainly 27 nN / m In color interference inkjet printing using the sol-gel ink described above, at least one refractive layer of xerogel of nanocrystalline titanium dioxide, mainly of anatase phase, transparent in the visible spectral region, is formed on the substrate

- with a thickness of 300 nm to 1 μm,

- with a refractive index of more than 1.7, mainly more than 2,

- with changing color depending on the thickness of the refractive layer.

The formation of a xerogel refractory layer of nanocrystalline titanium dioxide of a predominantly anatase phase can be carried out using sol-gel ink in the form of a nanocrystalline titanium dioxide sol in a solution of ethyl alcohol in water not only by inkjet printing, but also by rolling, spraying or dipping methods.

Color management of images printed in detail by the above-described sol-gel ink in the form of predominantly anatase nanocrystalline titanium dioxide is carried out by forming a predetermined thickness value of the predominantly anatase nanocrystalline titanium dioxide thickness by:

layer-by-layer application of sol-gel ink to a predetermined xerogel refractive layer thickness,

a change in the concentration of the solid phase in the sol-gel ink,

using a set of sol-gel inks with a given concentration to form a certain thickness of the titanium dioxide xerogel refractive layer with a specific color

As a result of color inkjet printing with the above-described sol-gel ink in the form of a predominantly anatase nanocrystalline titanium dioxide, a printed product is obtained with a color interference image on the surface containing at least one refractive layer of at least one xerogel layer of a nanocrystalline titanium dioxide predominantly anatase phase with the thickness of the refractive layer from 300 nm to 1 μm, with a refractive index of the refractive layer of more than 1.7 and with a varying color Second, depending on the thickness of the refractive layer of nanocrystalline titanium dioxide xerogel.

Printed products with a color interference image are obtained on a non-porous smooth or polished surface with a minimum change in texture height along the z axis, for example, on a polyethylene (PET) film, on a surface resistant to ethyl alcohol and liquids with a pH value of at least 3, on a surface containing water-insoluble substrates on an opaque surface or a surface containing coatings of a Bragg mirror with preservation of color reproduction for at least 1 year.

Brief Description of the Drawings

In FIG. 1, 2, 3 show examples of color images printed on an inkjet printer obtained by interference in thin xerogel films of nanocrystalline titanium dioxide by sol-gel ink.

The implementation of the invention

In contrast to the known methods for creating an interference effect on solid materials, that is, the formation of thin-film refractive structures with a modified refractive index, which are usually realized using technically complex physical (laser, temperature or vacuum) exposure, the invention is based on the methods of solution chemistry.

The proposed method for producing sol-gel ink for color inkjet printing allows you to create thin (5-10 nm thick) interference refractive layers of environmentally friendly and biologically inert inorganic material (xerogel nanocrystalline titanium dioxide anatase form), which after application to the substrate provide two binding observation of the phenomenon of interference conditions, namely obtaining a refractive index above 1.7, that is, higher than that of a simple polymer (1.5), as well as the formation of refract ivnogo layer after drying with a specified nanoscale thickness, length complementary light waves of the visible spectrum from 300 nm to 1 micron up to 10 nm.

In this case, in contrast to the well-known highly refractive organic polymers, the viscosity parameter in sol-gel systems can be adjusted relatively simply by controlling the gelation stage. Moreover, in the case of a high degree of chemical protonization of the surface of the sol nanoparticles, the viscosity will be determined mainly by the concentration of the solvent, while sedimentation of the sol nanoparticles is then excluded.

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 sol-gel ink that makes them unique for use as a material for creating environmentally friendly interference color printing.

The color printed products obtained by the proposed technology have unique properties, such as the absence of color change over time, which is promising for the long-term storage of color images, since the main material (nanocrystalline titanium dioxide) is extremely stable, inert, and does not decompose for a long time.

Inkjet printing with the proposed highly refractive sol-gel inks allows the use of polymer substrates without prior modification and application of adhesive layers that are commonly used in inkjet printing.

Considering 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 image.

Among the many inorganic colloids that can be adapted to inkjet printing and actively used 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,

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

- 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 have shown, for the synthesis of nanocrystalline TiO ₂ particles _{of a} predominantly anatase phase from titanium alkoxides, titanium isopropylate is most preferable, which forms stable crystalline nuclei during hydrolysis.

The stage of ash formation, that is, the formation of a dispersed solid phase, 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 a number of 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 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, i.e. according to the principle of gelation:

Dehydrated Polycondensation:

or

Depropanol polycondensation:

The frequency 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 gel formation stage for interference inkjet printing by the proposed sol-gel inks proceeds directly on the substrate, since the main condition for gel formation 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.

Sol-gel ink for color interference inkjet printing 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 receive a nanocrystalline sol of titanium dioxide predominantly anatase phase in water,

and at the second stage, a sol-gel ink for color interference inkjet printing in the form of a nanocrystalline titanium dioxide sol in a solution of ethyl alcohol in water is obtained from a nanocrystalline titanium dioxide sol of a predominantly anatase form 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, the degree of protonization of the particle surface increases to a zeta potential of at least + 36 ± 5 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 nanocrystalline sol of titanium dioxide in water does not meet the criteria for inkjet printing, such as density, viscosity, and surface tension, in terms of rheology, therefore, at the second stage of the preparation of sol-gel inks for interference inkjet printing, the nanocrystalline sol of titanium dioxide 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 show that the most optimal for inkjet printing according to the dependence of the sol-gel ink parameters on the ethanol concentration in the nanocrystalline ash of titanium dioxide of the predominant anatase phase are sol-gel ink containing 70 wt. % ethanol.

It was also established that the stability of a nanocrystalline sol of titanium dioxide of a predominantly anatase phase sharply decreases 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 stability.

Inkjet printing with sol-gel ink can be carried out on any surface of 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.

Titanium dioxide anatase nanoparticles formed during the preparation of sol-gel inks have a purely 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 TiO ₂ particles 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.

The X-ray diffraction data of the synthesized TiO ₂ 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 inks. However, the addition of surfactants or polymers can lead to a significant loss of optical properties and stability for TiO ₂ printing 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 diameter of the nozzle while maintaining high stability of inkjet printing. Thus, the preparation of stable TiO ₂ sol-gel inks should occur in the pH range between 2 and 5.

The zeta potential of nanocrystalline TiO ₂ particles in sol-gel ink is predominantly +36 mV, which ensures a stable state of the sol.

To increase the crystallinity of sol particles and a 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 producing anatase is determined by using a pH closer to neutral, thus minimizing the effect of corrosive processes in printing.

The presence of a volatile solvent (ethanol) in the sol-gel ink contributes to the quick drying of the ink on the film.

Ethanol 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 ml 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 the surface topography is associated with a small particle size, which, according to the HRTEM 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 means of inkjet printing on a PET film, it is preheated to 70 ° C to increase the drying speed of the ink, but the use of volatile ethanol additive in the sol-gel inks used according to 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, tightly 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 with a newly filled 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 a sol-gel transition of the TiO ₂ ink during drying and 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 contact density between the xerogel particles themselves after the sol has dried, and, as a result, the gradient of mechanical hardness decreases 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.

Full-scale studies of inkjet printing of color interference images by the proposed sol-gel ink 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 1.85, 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.

Inkjet printing was carried out in a multi-pass technique. Each layer was completely dried after printing, so that the next layer was applied by the method of “wet on dry”.

The formation of an interference color image occurs in the process of condensation of the sol-gel ink on the surface of the substrate. Evaporation of the solvent and gelation of the nanocrystalline sol of titanium dioxide with the formation of the specified thickness of the xerogel layer of titanium dioxide provides the ability to control the color of the printed image as a result of controlled interference.

Full-scale studies have shown the practical possibility of forming an interference color image with the complete exclusion of temperature heating of the substrate for fixing ink, which positively affects the preservation of the morphology of the applied layer and significantly reduces warping of the substrate after the ink dries.

The low concentration of the solid phase of nanocrystalline titanium dioxide in the sol-gel provides high-precision positioning of the nanostructures of the xerogel of titanium dioxide with a high refractive index.

Color interference images printed by this method had a multicolor color with a high degree of detail.

The appearance of color is caused by the appearance of reflected light waves formed at the phase boundary of two materials with different refractive indices of TiO ₂ / air and TiO ₂ / polyethylene. Interfering with each other, they form a light wave complementary to the thickness of the layer that caused this phenomenon.

Thus, the appearance of a color shade is associated with the thickness of the applied xerogel layer of titanium dioxide, which according to the invention can be controlled by the number of layers applied.

Practically implementing the invention, for the first time it was possible to obtain a color image using colorless ink on an inkjet printer.

When using such colorless sol-gel inkjet inks and when using the proposed method of color interference inkjet printing, almost any color image painted in the entire visible range can be obtained. Some examples are presented in FIG. 1, 2, 3.

The uniqueness of the proposed color interference inkjet printing by the proposed sol-gel ink containing nanocrystalline sol of titanium dioxide of the predominantly anatase phase of the technology, the materials used and the images obtained by the new method consists in the possibility of using a conventional and inexpensive desktop inkjet printer for color interference printing.

The ability to adjust the rheological properties of the nanocrystalline sol of titanium dioxide and control its sol-gel transition provides a wide range of variation of the properties required to obtain sol-gel ink.

A nanocrystalline sol of titanium dioxide of a predominantly anatase phase, with an amorphous phase content of less than 5%, provides a manifestation of unique optical properties.

The condensation of the xerogel of titanium dioxide and its physical crosslinking with the surface of an unmodified PET film contributes to the excellent adhesion of the xerogel of titanium dioxide to the surface of a smooth substrate.

All this makes it possible to obtain unique color interference images with controlled color reproduction, formed on flexible and smooth polymer surfaces without the use of high-temperature heat treatment.

The uniqueness of the results lies in the practical ability to control inkjet interference printing, forming nanostructures of interference color images with high accuracy.

This was achieved only as a result of the creation of a fundamentally new approach for fixing ink for inkjet printing on a non-porous polymer substrate, as well as by a new method for the synthesis of nanocrystalline sols of titanium dioxide predominantly anatase phase.

The protonization of the surface of the particles of nanocrystalline sols of titanium dioxide increases the stability of the ink and the shift of the phase sol-gel transition during atmospheric drying.

As a result, scalable optical interference nanostructures were obtained for the first time by inkjet printing.

This is the basis for the use of soft chemistry in the creation of quantum communication objects and an effective platform for the transport of photons in the future.

High precision of application and unique optical characteristics of the obtained layers of titanium xerogel of predominantly anatase phase can be the basis for obtaining plenary waveguides, masking microembosse paper, as well as forming a wide-angle photoinduced panel as the basis for creating a photon / signal supercomputer.

A characteristic distinctive original feature of the invention is the use of nanocrystalline sol-gel systems to create controlled interference in thin films using colorless ink based on nanocrystalline titanium dioxide sols.

The controlled multilayer printing of highly refractive layers of titanium dioxide xerogel allows the creation of optical nanostructures on the surface of polymers, which, when interfering with interaction with visible light, lead to visual staining of images.

The presence of a highly refractive layer or xerogel layers of titanium dioxide, enclosed between air and a polymer substrate, allows you to select monochromatic light reflections that are complementary in wavelength with the thickness of this layer.

Considering the multiple number of colors in the visible spectrum, the color of the interference images created by the inkjet printer can be almost any.

The unique optical, morphological, and textural properties of the interference thin layers of titanium dioxide xerogel make it possible to put this into practice.

In this regard, the invention not only contributes to the creation of new color printing technologies, but also preserves the ecology of the environment and human health, protecting our planet.

To increase the color contrast, the substrate may be opaque or contain coatings such as a Bragg mirror.

For inkjet printing of color images, the proposed method used a polyethylene (PET) film of A4 format, 1.5 μm thick.

Image contrast was achieved using black film. Printing was carried out from a black cartridge, into which the sol-gel ink obtained by the above method was previously poured.

To print color images using the three-pass method, the settings used increased print quality, providing a twofold increase in ink.

To analyze the structure of the layers, medium-quality inkjet printing was used, which ensures the application of highly refractive layers with increased accuracy, but with less ink applied.

The printing was carried out by specially prepared files with masking of areas, as shown in Figure S4.

Applying a set of differently colored inks using the inkjet method is one of the main ways of forming color images.

Typically, ink color formation is achieved by combining CMYK or RGB colors.

According to the invention, a color printing technology using only inks that are completely safe to use is provided.

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 may be packaging materials, tags, bags or other printed materials known in the art. 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 foils 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.

An art image of a printed product can be made, configured, or simply saved as an electronic data file.

The artistic image may include data regarding the desired or specified colors for the respective elements of the product.

The dimensions and values disclosed in the description should not be understood 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 (5)

1. A printed product with a color interference image on the surface, characterized in that the color interference image is made in the form of at least one xerogel xerogel nanocrystalline titanium dioxide anatase phase with a refractive layer thickness of 300 nm to 1 μm, with a refractive index of the refractive layer of more 1.7, with a varying color depending on the thickness of the refractive layer obtained using sol-gel ink in the form of a nanocrystalline sol of titanium dioxide in a solution of ethyl alcohol in water. 2. A printed product with a color interference image on the surface according to claim 1, characterized in that the color interference image is obtained using sol-gel ink containing nanocrystalline sol of anatase phase titanium dioxide in a solution of ethyl alcohol in water at a concentration of about 1-10 wt. %, with an amorphous phase content of not more than 5%, with a crystal size of 5-20 nm anatase phase, with an average hydrodynamic particle diameter of not more than 30 nm, mainly 15.8 nm, with a zeta potential of at least +30 mV, + 36 ± 5 mV, with the possibility of forming a transparent xerogel refractive layer transparent in the visible spectrum from 300 to 1 μm thick with a refractive index of more than 1.7, with an ethanol concentration in water of not more than 70 wt.% With a predominant volume ratio of ethyl alcohol: water 3: 1 with a viscosity of not more than 2.5 mPa * s, mainly 2.1 mPa * s, with a surface tension of not more than 30 nN / m, mainly 27 nN / m, and a sedimentation stability of the sol of at least 1 year. 3. A printed product with a color interference image on the surface according to claim 1, characterized in that the color interference image is made on a non-porous smooth or polished surface with minimal change in texture height along the z axis, for example, on a polyethylene (PET) film, on a surface resistant to the effects of ethyl alcohol and liquids with a pH value of at least 3, on a surface containing water-insoluble substrates, on an opaque surface or a surface containing coatings of a Bragg mirror, s storing the color at least 1 year. 4. A printed product with a color interference image on the surface according to claim 1, characterized in that the color of the color interference image on the surface with the formation of a predetermined value of the thickness of the refractive layer is carried out by layer-by-layer application of sol-gel ink to the specified value of the thickness of the refractive xerogel layer, by changing the concentration of the solid phase in the sol-gel ink, or using sol-gel ink with a given concentration of the solid phase to form a certain thickness color refractory xerogel titanium dioxide with a certain color. 5. A printed product with a color interference image on the surface according to claim 1, characterized in that the color interference image on the surface is obtained using sol-gel ink containing anatase titanium dioxide nanoparticles 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 titanium dioxide crystal size of not more than 200 nm, concentration at titanium dioxide particles 1-5 wt.%, titanium dioxide nanoparticle size 5-20 nm, mainly 5-10 nm, average hydrodynamic diameter of titanium dioxide nanoparticles not more than 20 nm, mainly 15.8 nm, zeta potential of titanium dioxide nanoparticles not less than +30 mV, mainly +36 mV, the possibility of forming a transparent in the visible spectrum of the refractive layer of the xerogel of titanium dioxide with a thickness of 300 nm to 1 μm with a refractive index of more than 1.7, the concentration of ethyl alcohol in water is not more than 70 wt.% With a preferred ratio uh tyl alcohol: water 3: 1, viscosity no more than 2.5 MPa * s, mainly 2.1 MPa * s, surface tension not more than 30 nN / m, mainly 27 nN / m, sedimentation stability of sol of nanocrystalline particles of titanium dioxide not less 1 year

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