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INVENTION
Patent of the Russian Federation RU2169667
METHOD OF OBTAINING A HIDDEN REVERSE IMAGE

METHOD OF OBTAINING A HIDDEN REVERSE IMAGE. KNOW HOW. INTRODUCTION. PATENT. TECHNOLOGIES.

INVENTION. METHOD OF OBTAINING A HIDDEN REVERSE IMAGE. Patent of the Russian Federation RU2169667

Applicant's name: St. Petersburg State Technological Institute
The name of the inventor: avrilenko IB; Eruzin AA; Ryazantsev SS; Udalov Yu.P.
The name of the patent holder: St. Petersburg State Technological Institute
Address for correspondence: 198013, St. Petersburg, Moscow Ave, 26, St. Petersburg State. Technological Institute (TU), ONTI and OIS
Date of commencement of the patent: 1999.05.11

The invention relates to the creation of reversible images that can be observed under certain physical conditions and made invisible in others. SUMMARY OF THE INVENTION: The hydrophilic regions in accordance with the image contours are created by a film having a thickness of 50-200 nM. The hydrophilic film is applied either in a glow discharge plasma at a constant or alternating current, or from a solution of a hydrophilic substance. In the case of a plasma chemical process, the hydrophilic film consists of metal oxide layers on the surface. Application mode: vacuum at partial pressure of air or argon 10 Pa, cathode material - steel, titanium, tungsten or aluminum, voltage at high-frequency discharge 400-1000 V, and for discharge of direct current voltage 1000-3000 V. Discharge current in both cases 0 , 1-1,0 A. In the case of using hydrophilic substances, the film consists of molecules of sucrose, magnesium chloride, calcium chloride or similar hydrophilic substances. The image appears due to optical contrast in an atmosphere of saturated water vapor between the areas covered with a water film (hydrophilic patches) and covered with droplets of water (hydrophobic patches). These features will ensure the reliability of protection of documents, securities from unauthorized reproduction and forgery.

DESCRIPTION OF THE INVENTION

The invention relates to methods for creating reversible images that can be observed under certain physical conditions and made invisible in others.

A method for creating reversible temperature sensitive images is known due to the different transparency and reflectivity of the inorganic or organic matter crystallized in a poly- or single-crystal state (US Pat. No. 5,837,348, priority of November 17, 1998) . In this patent, a film having a thickness of about 20 μm and consisting of microcapsules containing a low molecular weight substance (for example, behenic acid in a vinyl chloride-vinyl acetate shell) was heated to 100 ° C. (above the melting point of behenic acid) and rapidly cooled to room temperature. As a result, the image was recorded due to clouding of the microcapsules (during crystallization during the cooling, opal polycrystals are formed). Repeated heating to 80 ° C and slow cooling converted the microcapsules to a transparent state (crystallization under these conditions led to the formation of transparent single crystals in microcapsules). Due to the contrast of transparent and opal microcapsules, you can create an image. The disadvantage of this method of image creation is the need for heating in a rather narrow range of speeds, low resistance of the film from microcapsules to mechanical and radiation effects (in particular, to ultraviolet radiation). It is known to use for the same purposes heat-sensitive salts (for example, Ag 2 HgI 4 or Cu 2 HgI 4 ), which change their color when heated above 80 ° C. The use of these substances has, first of all, the drawback that they contain an environmentally hazardous element mercury. To fix these salts on the surface of the product is quite difficult.

On the other physical principle, the change in the optical properties of the surface is based on giving it hydrophilicity or hydrophobicity. Methods for imparting hydrophilic or hydrophobic properties are well known. This is either the application of hydrophilic compositions to the surface to maintain the transparency of the vehicle's mirror when water droplets fall-US Patent No. 5,594,585 , or the application of a vinyl polymer with a hydrophilic group on the surface ( US Pat. No. 5,624,627 ) or by conducting a dehydrochlorination reaction on the surface of the product ( US Patent No. 5,716,704 ). A similar result is obtained by synthesizing a hydrophilic substance on the semiconductor surface as a result of irradiation of an acid wetted layer with a KrF excimer laser - US Patent No. 5,741,628 . All these methods are characterized by a complex multi-operation technology and are not aimed at obtaining an image.

It is known to use hidden images to protect the trademark. They are created by complex printing techniques. Such as creating a multilayer coating with a hidden configuration that becomes visible at the time of transfer to a new medium ( US Patent 5,020,831) . This way of displaying the image dramatically complicates the verification of the authenticity of the average consumer, since it requires the use of special technical means and relevant knowledge.

The closest in terms of the technical essence of the invention is US Pat. No. 5,677,106, "Imprinting product with a tamperproof seal method of producing product" and US Pat. No. 5,642,530 "Non-fogging goggles." In the first invention, a hydrophilic and oleophilic film is applied to a lithographic printed circuit board as a result of a multi-stage process . The oleophilic layer is sensitive to light irradiation. Irradiation forms an image. The unexposed areas are chemically removed, which releases the porous hydrophilic surface. The image is created by wetting these areas with printing ink. The resulting image remains fixed after this. In US Pat. No. 5,642,530, a polyester or polycarbonate film is first formed on the surface of the spectacle glass, onto which a hydrophilic composition is then applied that reduces the contact angle of wetting the water to near zero. As a result, raindrops spread over the entire surface and the glasses glass remains transparent.

The disadvantages of the prototypes is that a multi-stage, long-term process is used to create the image (multi-stage when applying hydrophilic and hydrophobic layers, irradiation with electromagnetic radiation followed by chemical bleeding). Such processes are not environmentally safe. In addition, in patent 5642530 the surface on which the image is applied must be porous. At the same time, a permanently visible image is created, which is easily reproduced and forged by unauthorized reproduction.

The task of this development is to obtain and visualize the silhouette hidden images on the polished surface of glass, ceramic, polymer, mineral or metal products.

This is achieved by obtaining a latent reversible image by applying a thin hydrophilic film to the surface of the product with the desired contour, for which the article is placed in a glow discharge plasma or hydrophilic substance solution for the time necessary to obtain a hydrophilic film 50-200 nm in thickness. In addition, the hydrophilic film can be applied in plasma-chemical treatment in a glow discharge under vacuum at a partial pressure of air or argon of 10 Pa, cathode material - steel, titanium, tungsten or aluminum, voltage 400-1000 V for high-frequency discharge and 1000-3000 V for discharge Direct current, discharge current 0.1-1.0 A.

For the development of the image, the optical contrast between the hydrophilic and hydrophobic regions that occurs when it drips over the surface of the water, or the surface is covered with an oil film or a coloring pigment, or water droplets from the supersaturated water vapor (for example, during human respiration) condenses on the surface of the product. Hydrophilic films obtained by the plasmochemical method are resistant to the action of most chemical reagents and solvents except for hydrofluoric acid and a mixture of nitric and hydrochloric acids. Films applied from a solution of a hydrophilic substance are removed with an appropriate solvent. Silhouette is applied by any writing device or through a stencil.

The physical essence of the process of creating an image is that under vacuum discharge conditions, the surface of the article is bombarded with cathode metal ions and excited atoms, molecules and radicals of the plasma-forming gas. As a result, all sorbed dirt is removed from the solid surface. The surface atoms of the substrate with broken uncompensated bonds enter into a chemical interaction with ionized and excited plasma discharge particles. The process must be carried out until a very thin (thickness from 50 to 200 nm) layer containing atoms of the cathode material and components of the gaseous medium is formed on open surfaces (not protected by a mask-stencil). To do this, the process is conducted in a vacuum of 5-10 Pa and the discharge between the cathode and the anode occurs at a DC current of more than 1000 V and current strength of more than 0.1 A, or the discharge occurs at an alternating current of more than 400 V with a current strength of more than 0.05 A The parameters of the vacuum electric discharge (voltage, type of current - constant or variable, composition of the reaction gas, target-cathode distance) are determined by the material of the product. The cathode material can be any (steel, titanium, tungsten, aluminum, etc.). The processing time is determined by the desired degree of image contrast when developing. However, the thickness of the hydrophilic film should not exceed 200 nm. Otherwise, the hydrophilic film becomes visible and is relatively easy to erase from the surface. At the same time, hydrophilic films with a thickness of less than 200 nm have high adhesion and abrasion resistance. At a hydrophilic film thickness of less than 50 nm, there is no sufficient contrast in hydrophilic properties with an untreated surface.

The same result can be obtained by applying a hydrophilic film to the surface from the solution, which is then dried, and after drying forms a transparent hydrophilic film at predetermined areas of the surface.

In both cases, the thickness of the film must be so small that it does not give a visible optical contrast in comparison with the clean surface of the matrix, either in transmitted or reflected light, or under oblique illumination. With the naked eye, this film is not visible, but its affinity for water and other fluids differs from the untreated surface (ie from the cliched-in stencil).

To display (visualize) the image, it is necessary to hit the surface of a liquid or droplets of condensing vapor (for example, from human respiration), then due to the difference in the hydrophilicity of adjacent areas of the surface, the size and shape of the droplets will differ sharply, which provides optical contrast in reflected and transmitted light .

The proposed method is worked out on laboratory installations.

Example 1
On the nonfat surface of the product made of stainless steel, a mask-stencil with contours of the image or inscription was applied. The sample was placed in the evacuated chamber of a glow discharge device perpendicular to the flow of particles from the cathode. The cathode material is copper. A vacuum of 0.006 Pa was created and then air was introduced to a pressure of 10 Pa. After that, a high-frequency discharge was applied to the cathode at a frequency of 6 MHz (voltage 500 V, current 0.1 A) for 300 s. As a result, a metal oxide hydrophilic film was formed on the exposed surfaces of the steel product. The image becomes visible only after the appearance on the surface of droplets of water from saturated steam or oil contamination. Hydrophilic areas are covered under these conditions with a water film or very small droplets of water, while the rest of the surface is covered with large droplets. This creates an optical contrast in reflected light. The oil, on the contrary, does not wet the hydrophilic surface and creates an image negative with respect to the water developed. After cleaning the surface from traces of water or oil, the surface becomes again optically homogeneous (i.e., the image becomes invisible) and so can be repeated countless times.

Example 2
On the surface of the defatted window glass, a mask-stencil with cut out contours of the image or text is applied. The glass is then placed in the vacuum chamber of a glow discharge device of direct or alternating current perpendicular to the flow of particles from the cathode at a distance of 5-20 cm. A vacuum is created to 0.006 Pa, then a mixture of reaction gases is added according to Example 1 to a pressure of 1 Pa. After that, the DC voltage of 1500 V was applied to the cathode from titanium, and the amperage was 1 A. After 60 seconds, the discharge was stopped. As a result, a hydrophilic film formed on the surface of the glass, possessing all the properties of Example 1.

Example 3
A mask-stencil with image contours was applied to the surface of the polished granite. The sample was placed in a vacuum chamber of a glow discharge installation perpendicular to the flow of particles from the cathode of aluminum. A vacuum of 0.006 Pa was created and then up to 100 Pa of argon was allowed (possibly using the reaction gas of Example 1). The voltage was then applied to a cathode of 1000 V at a frequency of 50 Hz. After 200 s, a latent image is formed on the surface due to the formation of a hydrophilic metal oxide film according to Example 1.

Example 4
A text or a silhouette image was applied to the surface of the glass by any writing device or cliché, as a colorant in which any colorless hydrophilic substance having adhesion to glass (for example, a sucrose solution in water with a concentration of 5-50%) was used. The sample was then dried at a temperature of 100-200 ° C for 10 minutes. Then, a surplus of the "coloring" substance was washed off with a jet of water. The resulting invisible hydrophilic film became visible in saturated water vapor or under a stream of water similar to Example 1.

Example 5
On the surface of the porcelain glazed article, a text or a contour image was applied with a cliche on which a hydrophilic substance solution was placed. The composition of the solution: a saturated solution of magnesium chloride in 90% ethyl alcohol with the addition of glycerin (the ratio of volumes of alcohol solution and glycerin 4: 1). The sample was air dried for 3 minutes. The image became invisible, but manifested itself in a saturated water vapor.

Example 6
The same as in Example 5, but the composition of the solution: tsaponlak N 951 and calcium chloride in a ratio of 9: 1. The method of application and visualization is the same.

As can be seen in Examples 1-6, the goal is achieved by applying a hydrophilic film from the plasma and from the solution. The film obtained by the plasmochemical method has a high resistance to abrasion and radiation effects (especially to ultraviolet radiation). Films obtained from solutions (and, consequently, images based on them) have low resistance to abrasion and high resistance to radiation. Plasma-chemical films of Examples 1-3 do not dissolve in any known solvent, but can be removed by etching in hydrofluoric or hydrofluoric acid. Films from solutions of hydrophilic substances can be removed by boiling in water. The use of the invention makes it possible to obtain a latent reversible image on any solid polished surface.

CLAIM

1. A method of obtaining a latent reversible image by applying a thin hydrophilic film to the surface of the article with the desired contour, characterized in that the article is placed in a glow discharge plasma or hydrophilic substance solution for the time necessary to obtain a hydrophilic film 50-200 nm in thickness.

2. The method of claim 1, wherein the hydrophilic film is applied in a plasma-chemical treatment in a glow discharge under vacuum at a partial pressure of air or argon of 10 Pa, cathode material - steel, titanium, tungsten or aluminum, voltage 400-1000 V for high-frequency Discharge and 1000-3000 V for a discharge of direct current, discharge current 0.1-1.0 A.

print version
Date of publication 16.12.2006гг