RU2743423C1 - Method of producing inorganic luminescent compound with given fractional composition - Google Patents

Abstract

FIELD: optics.SUBSTANCE: invention can be used in production of materials having specified optical and physical properties and intended for authenticity control of valuable documents. To produce material based on inorganic luminescent compound of rare-earth metals, charge is prepared, solid-phase synthesis, washing and milling of finished product. Solid-phase synthesis is carried out in two steps. At the first stage, a complex is synthesized, containing a group II element of the periodic table, selected from Mg, Ca, Zn, Sr, element III of the group of the periodic table from the range of lanthanides Er, Yb, Tm, Ho; element IV of the group of the periodic table, selected from Ti, Si, Zr, Ge. At the second step, the end product is synthesized. Ground product is fractionated using track membranes by tangential filtration. Size of not less than 90 % of the particles of the obtained material is a given value selected within interval 0.1–50 mcm.EFFECT: invention enables to obtain an efficient inorganic luminescent substance with a given fractional composition for incorporation into paper, plastic, composite materials, printing inks and ink-jet compositions.3 cl, 1 ex

Description

The invention relates to the field of special materials with specified optical and physical properties, designed to control the authenticity of valuable documents, and used as fillers in paper, plastic and other composite materials, as well as as a pigment in printing paints, inkjet ink. The developed luminescent pigments are fine powders with special optical-physical properties, embedded in paper, plastic, adhesive layers or in printing ink to give the final product, for example, a counterfeit-proof printed product, additional special properties, such as UV and IR luminescence , anti-Stokes luminescence, IR absorption in a given spectral range and other properties.

These pigments can be used to give printed products both decorative and special, including hidden machine-readable, optical-physical properties - to protect these products from complete or partial counterfeiting and unauthorized copying. In the latter case, they can be designed for visual (organoleptic) or instrumental identification of the authenticity of protected printing products, such as banknotes and forms of securities, labels, excise and postage stamps, payment and identification documents, as well as passports, travel and other documents.

As a rule, special pigments based on inorganic luminescent compounds have an average particle size of 1 to 50 microns and are characterized by an inhomogeneous fractional composition, while the presence of large particles impairs the printing and technological properties of inks based on them.

For the normal operation of such compounds in the composition of paper or paints with thicknesses of layers of the carrier material from 1 to 100 microns (analogy with G&D patents), it is necessary to ensure the optimal amount of pigment in the layer, as well as to ensure their retention and stability of the dispersion, that is, to prevent their rejection from the carrier at all subsequent stages of the technological process and during the operation of the final products. On the other hand, the problem of rejection and / or insufficient retention and stability of the dispersion of pigments in paper or paints can be solved, inter alia, by the optimal choice of the fractional composition of the pigment.

The most common type of special pigments are pigments based on inorganic luminescent compounds, which have luminescence in the visible and / or IR ranges of the optical spectrum under the influence of UV, visible, IR radiation, or a combination of various exciting influences (the so-called signs of a complex principle of action).

In turn, the most common class of such compounds are substances with a crystal structure, activated by ions of rare earth metals (lanthanides).

As a rule, substances of this class have a sufficiently high hardness (from 6 to 9 on the Mohs scale), and do not tolerate mechanical grinding. Thus, an important task in the synthesis and subsequent production of these materials is to obtain crystals with a given particle size (fractional composition) without subsequent mechanical grinding and / or destruction.

The synthesis of such crystals can be described in three main phases:

- preparation and preparation of the charge;

- solid-phase crystal synthesis;

- pigment post-processing (grinding and washing).

Obviously, in order to exclude unnecessary mechanical action on the formed crystals, it is advisable to use a technology that ensures the production of crystals with a given fractional composition, and minimal mechanical action at the stage of post-processing and washing.

From the prior art, solutions US 4387112A, US 4047033A, RU 2379192, RU 2379195, RU 25256211, RU 2429272, RU 2401293, RU 2434926, RU 2516129 are known, describing a valuable document with marking based on a luminescent inorganic compound based on rare earth metals, having either narrow-band luminescence inherent in REM ions, or anti-Stokes luminescence in the visible range of the spectrum, or the property of re-emission in the near-IR range of the spectrum, or flare and photostimulated effects, or phosphorescence, or a combination of all of the above. However, this group of inventions does not disclose the need to use to solve the problem posed a method for producing a pigment with a given fractional composition, including ensuring the retention and stability of the dispersion of inorganic pigment in paper or printing ink, while not having a significant negative effect on the main special optical and physical properties pigment, in particular - luminescent.

In particular, it is known patent RU 2516129, publ. 05/20/2014, describing a fast kinetic infrared phosphor based on yttrium or lanthanum compounds, activated by trivalent ions of neodymium and praseodymium, which contains yttrium or lanthanum oxysulfide as a REE compound and has a chemical composition corresponding to the following empirical formula:

where Ln = Y, La; 2.5⋅10 ^-3 ≤х≤2⋅10 ^-2 ; 1⋅10 ^-5 ≤y≤5⋅10 ^-3 .

It has all the previously mentioned advantages and disadvantages of this type of phosphors.

Known solutions are set forth in the group of patents RU 2614980, RU 2610592, RU 2610767, RU 2614687, RU 2614688, RU 2614690, RU 2614693, RU 2615695, RU 2615696 describing the use of luminescent inorganic compounds based on rare earth metals for authenticity control of valuable documents, having luminescence in near-IR range of the spectrum under the influence of exciting radiation in the visible or IR range of the spectrum, and having the property of reducing the intensity (optical quenching) without changing the spectral composition of luminescent radiation under the influence of additionally applied radiation in the UV or visible range of the spectrum. This group of inventions also does not disclose the need to use a method for obtaining a pigment with a given fractional composition, which provides the required printing and technological properties of pigment-based paints, and does not negatively affect the main special optical-physical properties of a luminescent pigment.

In particular, patent RU 2615696, publ. 04/06/2017, characterizing a phosphor based on yttrium oxysulfide, activated with Tm ³⁺ ions, containing in the cation sublattice additionally as matrix cations one of La ³⁺ and Gd ³⁺ ions, and as co-activating ions a pair of ions of elements II and IV or II and V groups of D.I. Mendeleev and has a chemical composition corresponding to the following empirical formula:

where Ln is one of the La ³⁺ , Gd ³⁺ ions;

Me ¹ is one of the ions of the II group of D.I. Mendeleev - Ca ²⁺ , Sr ²⁺ , Ba ²⁺ ;

Me ² is one of the ions of elements IV (Ti ⁴⁺ , Zr ⁴⁺ , Si ⁴⁺ ) or V (Nb ⁵⁺ , Ta ⁵⁺ ) of the group of the Periodic Table of D.I. Mendeleev;

0 <x <0.80;

0.0025 <y <0.05;

0.01≤z <0.1;

0.005≤d <0.05.

Known patent RU 2614980, publ. 03/31/2017, characterizing the protective marking for instrumental control of the authenticity of the product, made on the basis of composite crystalline inorganic luminescent compounds of rare earth and alkaline earth elements, which has a chemical composition corresponding to the following empirical formula:

where Ln ¹ is one of the ions La ³⁺ , Gd ³⁺ , Y ³⁺ and / or any of their combinations; Ln ₂ - one of the ions YD ³⁺ , Er ³⁺ , Nd ³⁺ , Ce ³⁺ , Tm ³⁺ , But ³⁺ and / or any of their combinations;

Me ₁ - one of the ions Mg ²⁺ , Ca ²⁺ , Sr ²⁺ , Ba ²⁺ ;

Ме ₂ - one of the ions Ti ⁴⁺ , Zr ⁴⁺ , Si ⁴⁺ , Ge ⁴⁺ , Sn ⁴⁺ ;

0≤x≤0.60;

0.01≤y≤0.10;

0.005≤z≤0.05;

0≤n≤1;

0≤m≤1;

n + m = 1,

and the structure of the crystal structure, which is characterized by a high concentration of associated nonradiative trapping centers of free charge carriers formed around the luminescence centers, due to which the proposed marking has Stokes and / or anti-Stokes luminescence in the spectral range of 400-2500 nm, arising under the influence of exciting radiation lying in the spectral range of 700-1000 nm, and a change according to a given law of the intensity of luminescence without changing its spectral composition under the influence of stimulating radiation lying in the spectral range of 300-700 nm.

This invention does not describe a method for producing a substance with desired properties, nor does it disclose a method for producing a finely dispersed substance with micron and submicron particle sizes, and a pigment with a given fractional composition.

Closest to the claimed invention is the technical solution described in patent RU 2615696, publ. 04/06/2017, which characterizes a phosphor based on yttrium oxysulfide, activated by Tm ³⁺ ions, characterized in that it contains in the cation sublattice additionally one of the La ³⁺ and Gd ³⁺ ions as matrix cations, and a pair of ions as co-activating ions elements of II and IV or II and V groups of D.I. Mendeleev and has a chemical composition corresponding to the following empirical formula:

where Ln is one of the La ³⁺ , Gd ³⁺ ions;

Me ¹ is one of the ions of the II group of D.I. Mendeleev - Ca ²⁺ , Sr ²⁺ , Ba ²⁺ ;

Me ² is one of the ions of elements IV (Ti ⁴⁺ , Zr ⁴⁺ , Si ⁴⁺ ) or V (Nb ⁵⁺ , Ta ⁵⁺ ) of the group of the Periodic Table of D.I. Mendeleev;

0 <x <0.80;

0.0025 <y <0.05;

0.01≤z <0.1;

0.005≤d <0.05.

Patent RU 2615696 also describes a method for producing luminescent inorganic compounds based on rare-earth metals having luminescence in the near-IR spectral range under the influence of exciting radiation in the visible or IR spectral range, and possessing the property of reducing the intensity (optical quenching) without changing the spectral composition of luminescent radiation under exposure to additionally applied radiation in the UV or visible spectral range. The known method includes the operations of preparing a charge, solid-phase synthesis, washing and grinding the finished product.

The disadvantage of this method is the impossibility of obtaining pigments with a given fractional composition, which often leads to the impossibility of using pigments of this class for their intended purpose.

The objective of the present invention is to develop a method for producing inorganic special pigments based on rare-earth metals with a given fractional composition, devoid of the disadvantages of traditional methods of synthesis.

The technical result achieved by the implementation of the proposed invention is to obtain an effective inorganic luminescent substance with a given fractional composition, having luminescence of a given spectral composition in the wavelength range of 700-3000 nm under the influence of exciting radiation lying in the range of 700-1600 nm, and having the property of changing luminescence intensity without changing its spectral composition when exposed to stimulating radiation lying in the spectral range of 200-700 nm.

The specified technical result is achieved by the fact that in the method for producing a material based on an inorganic luminescent compound of rare-earth metal ions, including the preparation of a charge, solid-phase synthesis, washing and grinding the finished product, according to the invention, the solid-phase synthesis is carried out in two stages, and at the first stage the complex is synthesized Me ^III _x Me ^II yMe ^IV y,

where: Me ^II - an element of group II of the Periodic Table Mg, Ca, Zn, Sr;

Me ^III - an element of the III group of the Periodic table from the series of lanthanides Er, Yb, Tm, Ho;

Me ^IV - an element of group IV of the Periodic Table Ti, Si, Zr, Ge;

0.1≤X≤0.9;

0.01≤Y≤0.2;

while the initial oxides of the corresponding elements are mixed and calcined in the presence of Na ₂ CO ₃ at a temperature of 1100 ° C for 3 hours, the resulting oxide is ground to an average particle size of 1 μm, and used as a component of the charge, additionally containing elemental sulfur, lithium carbon dioxide, as well as Y ₂ O ₃ , from which the final product is synthesized at the second stage, while the charge is calcined at a temperature of 1250 ° C for 3 hours, the resulting cake is crushed and washed with a weakly acidic solution and distilled water to pH = 7, and at the final stage, the crushed product is fractionated twice using track membranes by the method of tangential filtration, while the size of at least 90% of the particles of the obtained material is a predetermined value selected within the range of 0.1 μm - 50 μm.

The resulting final substance, in which the elements Me ⁱⁿ -Me ⁿ -Me ^IV form separate associated complexes, providing effective optical quenching of IR luminescence during photostimulation in the visible and / or near IR spectral range.

To wash out the pigment, it is proposed to introduce an additional stage of pigment filtration through track membranes by the tangential filtration method. It is advisable to carry out this filtration method twice - through large and through small membranes - to isolate the required pigment fraction. The resulting inorganic luminescent compound has a particle size of 0.1 µm to 50 µm.

In one embodiment, it is carried out to obtain an inorganic luminescent substance with the possibility of luminescence of a given spectral composition in the wavelength range of 300-3000 nm under the influence of exciting radiation lying in the range of 300-1600 nm, and has the property of changing the luminescence intensity without changing its spectral composition when exposed to stimulating radiation lying in the spectral range of 200-700 nm.

In some embodiments, the method is carried out to obtain a material that is an inorganic luminescent compound based on ions of rare earth metals, characterized by anti-Stokes luminescence of green or red, or orange, or blue, or white glow under the influence of PC radiation in the wavelength range (800-1100 ) nm.

The resulting material can be incorporated into the substrate and / or applied to the surface of the information carrier, in particular, incorporated into a colorless marking that is indistinguishable on the surface and / or in the composition of the information carrier when viewed in daylight.

Marking can be applied to a cultural property or to a storage medium. This does not limit the list of physical bodies on which the indicated markings can be applied.

The information carrier on which the indicated marking can be applied is a banknote, excise stamp, postage stamp, passport, travel document, driver's license, identity card, security, plastic card, label, payment document. The specified list does not limit the list of objects representing information carriers on which the specified marking can be applied.

The proposed technical solution is illustrated by an example.

Example 1.

A method for producing an inorganic luminescent compound with optical modulation, with a particle size of 3 μm, having the following empirical formula:

(Y _0.98 Yb _0.01 Ca _0.005 Ti _0.005 ) 2O ₂ S

Solid-phase synthesis uses a two-stage synthesis:

1. A chemical compound with the structural chemical formula (Yb _0.50 Ca _0.25 Ti _0.25 ) ₂ O ₃ is formed by mixing and calcining the oxides of the starting materials (Yb ₂ O ₃ , CaO, TiO ₂ ) in the presence of soda at a temperature of 1100 ° C for 3 hours.

2. Obtained (Yb _0.50 Ca _0.25 Ti _0.25 ) ₂ O ₃ : Na ₂ O is ground in a ball mill to an average particle size of 1 μm, and is used as a component of the charge. Additional charge components - Y ₂ O ₃ , LiCO ₃ , S.

The resulting mixture is placed in magnesium crucibles and calcined in an inert gas atmosphere at a temperature of 1250 ° C for 3 hours. The resulting cake is extracted, crushed and washed with a weakly acidic solution and distilled water to pH = 7.

At the final stage, the required phosphor fraction (3 μm) is filtered through track membranes by tangential filtration in distilled water. First, filtration is carried out through a large membrane (track size 3 μm) to cut off the coarse fraction with a particle size of more than 3 μm. Then, filtration is carried out through a fine membrane (track size 2 μm) to remove fines.

The resulting fraction is dried in a drying oven until dusting.

Then the obtained inorganic luminescent compound with a fraction size of 3 μm is introduced into the composition of paper intended for subsequent printing of travel documents.

Claims (9)

1. A method of obtaining a material based on an inorganic luminescent compound of rare-earth metal ions, including preparation of a charge, solid-phase synthesis, washing and grinding the finished product, characterized in that the solid-phase synthesis is carried out in two stages, and at the first stage the complex Me ^III _X Me ^II _{Y is synthesized} Me ^IV _Y , where Me ^II is an element of group II of the Periodic Table Mg, Ca, Zn, Sr; Me ^III - an element of the III group of the Periodic table from the series of lanthanides Er, Yb, Tm, Ho; Me ^IV - an element of group IV of the Periodic Table Ti, Si, Zr, Ge; 0.1≤X≤0.9; 0.01≤Y≤0.2; while the initial oxides of the corresponding elements are mixed and calcined in the presence of Na ₂ CO ₃ at a temperature of 1100 ° C for 3 hours, the resulting oxide is ground to an average particle size of 1 μm and used as a component of the charge, additionally containing elemental sulfur, lithium carbonate , as well as Y ₂ O ₃ , from which the final product is synthesized at the second stage, while the charge is calcined in an inert gas atmosphere at a temperature of 1250 ° C for 3 h, the resulting cake is crushed and washed with a weakly acidic solution and distilled water to pH 7, and at the final stage, the crushed product is fractionated twice using track membranes by the tangential filtration method, while the size of at least 90% of the particles of the obtained material is a predetermined value selected within the range of 0.1-50 microns. 2. The method according to claim 1, characterized in that the result is a luminescent compound capable of luminescence of a given spectral composition in the wavelength range of 300-3000 nm under the influence of exciting radiation lying in the range of 300-1600 nm, and the property of changing the luminescence intensity without changing its spectral composition when exposed to stimulating radiation lying in the spectral range of 200-700 nm. 3. The method according to claim 1, characterized in that the result is a luminescent compound based on ions of rare earth metals, characterized by anti-Stokes luminescence of green, or red, or orange, or blue, or white luminescence under the influence of infrared radiation in the wavelength range 800-1100 nm.