WO2012041473A1

WO2012041473A1 - Method for marking glass

Info

Publication number: WO2012041473A1
Application number: PCT/EP2011/004800
Authority: WO
Inventors: Robert Bischoff; Thomas Rainer
Original assignee: Boraident Gmbh
Priority date: 2010-09-27
Filing date: 2011-09-26
Publication date: 2012-04-05
Also published as: DE102010046549A1

Abstract

The invention relates to a method for marking glass, in which a coating composition comprising at least one metal compound is applied in the form of a desired marking to a glass surface and the glass is subjected to a heat treatment in which metal ions diffuse from the coating composition into the glass volume and the heat treatment is carried out at a temperature in the range from 280°C to 320°C and the metal ions diffused in together with the glass matrix form a marking composed of fluorescent sites which marking is invisible in the visible wavelength range and fluoresces in the visible wavelength range under high-energy excitation, in particular on irradiation with UV light. The invention likewise relates to a marking in the glass volume underneath the glass surface, which marking is formed by fluorescent sites which are produced by metal ions which have diffused into the glass from the glass surface during a heat treatment, with the marking being invisible in the visible wavelength range and fluorescing so as to be visible to the eye on excitation, in particular illumination with UV light.

Description

Method for marking glass

The invention relates to a process for marking glass in which a coating composition comprising at least one metal compound is applied in the form of a desired marking to a glass surface and the glass is subjected to a heat treatment in which metal ions from the coating composition are subjected to heat treatment Diffuse glass volume into it. Markers of this type are known in the art and have been developed largely by the assignee of this invention. In such markings, a coating composition comprising a silver-metal compound is applied to float glass and the heat treatment causes diffusion of the silver ions into the glass volume, with the heat treatment applied here at temperatures above the glass transition temperature and / or at long temperatures Periods of heat treatment for several hours by the tin ions in the glass, which are present on a tin bath in the glass due to the float glass manufacturing process, causes a reduction of silver ions to metallic silver particles, which is a typical silver silver-brown irreversible Coloring in the glass volume, which is also called "sepia".

Compared to simple markings applied to the surface of a glass, e.g. By writing, stamping, scribing, lasering, engraving, etc., such a mark produced in the volume of the glass has the advantage of being highly secure against counterfeiting and of being protected against environmental influences.

CONFIRMATION COPY However, a disadvantage of such markings is that they are visible to the naked eye in the visible wavelength range (380 nm to 780 nm), namely as silver-typical yellow-brown discoloration and thus are considered aesthetically unpleasant. In addition, such markers are difficult to machine read due to their low contrast to the transparent glass environment, as is necessary, for example, in glass manufacturing for the purpose of documentation and / or quality assurance. Therefore, it also requires special reading to evaluate such markings. It is therefore the object of the invention to provide a marking method with which markings are introduced into glass which do not disturb aesthetically and are preferably machine-readable, but at least readable by the eye in the normal visible wavelength range. This object is achieved in that the diffused metal ions together with the glass matrix form a mark of fluorescence centers, which is invisible in the visible wavelength range and fluoresces by energetic excitation, in particular in the irradiation with UV light in the visible wavelength range.

Such a marking has the advantage that it is not visible to the human eye in the visible wavelength range, ie in particular in the range from 380 nm to 780 nm. Thus, such a mark is not perceived as disturbing because it can not be perceived.

For testing or other control purposes, however, the label can advantageously be made visible, namely, if it is excited by energetic excitation, for example by irradiation with UV light (wavelength less than 380 nm, preferably 254 nm) to fluoresce, wherein the fluorescence centers, the are arranged in the form of the desired marking in the glass, form a self-luminous marking, which in the visible wavelength range from the glass volume lights out and thus can be detected both by eye and by machine.

It is the essential core idea of the invention not only to allow metal ions to diffuse into the glass volume, as it is already known in the prior art, but to carry this out with a heat treatment, in particular a heat treatment specially adapted to the glass type, in a very defined temperature interval. that the metal ions are present not only as a simple ion accumulation, which at most produce a local refractive index change, but according to the invention form fluorescence centers.

Such fluorescence centers can form when the metal ions in the glass volume create a solid body with impurities (due to the metal ions) in which the individual energy levels of individual metal ions become energy bands having band gaps due to the multiplicity of metal ions in the otherwise insulating glass matrix which electrons can be excited, after which a radiation decay occurs with the emission of photons, which cause the fluorescence effect. Accordingly, according to the invention, such fluorescence centers form fluorophores locally corresponding to the desired marking form in the glass volume, ie, physical systems in which fluorescence occurs.

Accordingly, it is essential for the invention to tailor the heat treatment so that fluorescence centers are formed by the metal ions, but disadvantageous effects such as the abovementioned reduction are avoided.

In a variant which is preferred according to the invention, this can be carried out such that the heat treatment is carried out with a specific temperature and a temperature-adapted period of time which causes a certain minimum metal ion density in the glass matrix, at which fluorescence centers are formed. It has thus been found that fluorescence effects do not arise solely because metal ions are present in the glass matrix at all, but only when a certain minimum density is achieved by the diffusion. This means that at lower temperatures a longer diffusion time is needed, at higher temperatures, however, a shorter diffusion time. Temperature and time are thus two parameters that are coupled together to achieve fluorescence centers.

In this case, by no means can the temperature be increased as desired in order to shorten the time, since at too high temperatures, in particular above the glass transition temperature, disadvantageous effects such as the abovementioned reduction can occur. Accordingly, during the heat treatment, the temperature must remain below a typical maximum temperature for the type of glass, in particular the glass transition temperature.

The glass transformation temperature is given by the temperature at which the elastic properties of the glass change into viscoelastic properties. For flat glass (float glass), this temperature is for example about 530 degrees Celsius. Preference is given to working well below this temperature, in particular in order to exclude reduction effects with certainty, but nevertheless to effect diffusion. Also, the time must not be too long in order to achieve the largest possible metal ion density, since fluorescence extinction effects can occur if the density is too high , which is referred to as "quenching." It is therefore essential for a glass type used to adjust the appropriate parameters of temperature and time during the heat treatment to effect the formation of fluorescence centers rather than reduction or other adverse effects.

For flat glass as an exemplary glass type, it has been found, for example, that clearly reproduced results are obtained in the formation of fluorescence centers when the heat treatment is carried out at a temperature in the range of 250 ° C to 320 ° C, preferably 280 ° C to 320 ° C, particularly preferably at 290 ° C + - 10 ° C is performed, in particular wherein the heat treatment in this temperature interval over a period of at least one hour, but in particular for a period of time shorter than the time after which the metal ion density is too high and quenching prevents fluorescence. This maximum time can be determined empirically depending on the type of glass. With flat glass, for example, it lasts for less than 4 hours.

According to the invention, the height of the temperature and the duration of the heat treatment, in particular within certain specific limits, the fluorescence intensity of the marked glass region can be adjusted.

In the preparation of such a mark according to the invention in flat glass / float glass, in one possible embodiment, the coating composition is preferably applied on that side of the glass which has the lower tin ion density from both sides, thus, the so-called air side, but not the tin bath side , This ensures that there is only a low density of reducing ions in the vicinity of the mark.

Particularly preferably, a glass type can be used which does not provide any reducing ions for the diffused metal ions of the coating composition. For example, it may be glass types that are not applied to tin baths. A preferred type of glass is e.g. Borosilicate glass.

In a preferred embodiment, the glass to be marked with respect to its variety and the coating composition used with respect to its metal compound (s) are coordinated so that the glass in its glass matrix does not provide the ionic ions of the coating composition, reducing ions. In addition, with such a specific choice of glass and coating, the adjustment of the time and temperature parameters of the heat treatment proves to be less critical because of the adverse effect The metal ion reduction can not occur due to the principle. It can therefore be worked in a preferred development in such a targeted selection with a heat treatment above the glass transition temperature, in particular in order to abbreviate the time of the diffusion process. If a mark initially introduced invisibly into the glass volume is to be made visible later, eg for test purposes, it may be provided with a, in particular later, temperature treatment of the glass above a characteristic temperature for the glass, in particular the glass transformation temperature, which diffused into the glass To reduce metal ions by externally supplied or existing in the glass reducing ions to metal particles. It is thus possible to produce a color mark in the glass volume which can be recognized by the eye in the visible wavelength range, in particular where the color produced is typical for the metal compound used.

In particular, in this application, but also with general validity, it can also be provided that the glass used, in particular a float glass, a glass having a relatively tin-rich surface and a relatively low-tin surface and the coating composition is applied to the relatively tin-rich surface , It may also be contemplated to employ the effect of onset reduction on glasses having reducing ions or heat treated in a reducing atmosphere / environment for testing purposes to determine if the heat treatment is within a temperature interval properly tuned for the desired exclusive fluorescence center formation and / or or a correctly selected period of time. If it is determined in a test of the heat-treated glass that there are discernible discolorations in the glass in the mark produced, this is an indication that during the heat treatment a reduction with the reducing ions present or added in the glass has taken place and thus the Heat treatment with regard to temperature and / or time is not carried out correctly. was led. Such a glass can then be sorted out eg as part of a quality control as not usable.

In one embodiment, it can also be provided that the coating composition contains pigment particles or at least one dye, which are transferred to the glass during the marking process. In this case, only the metal ions preferably diffuse into the glass, while the pigment particles and / or dyes remain on the surface. It is thus possible to produce a superficial marking which is visible to the eye and a shape-identical marking in the volume of the glass which is not visible in the eye. Pigments and / or dyes may be adjuncts to optically facilitate the application of the label to the glass with the coating composition. After the diffusion process, they can be removed from the surface. According to the invention, it may be provided that the coating composition containing at least one metal compound, e.g. one or two metal salts and, if appropriate, binder comprises applied in the form of the desired marking by various possible method steps to the surface of a glass, in particular a flat glass pane. The application of the coating composition may e.g. an order of the composition in liquid or solid state. In this case, the thickness of the coating composition applied to the glass may preferably be in the range from 100 nm to 100 μm.

For example, the coating composition may be stamped onto the surface of the glass by a stamp corresponding to the shape of the desired label, or the coating composition is written onto the surface of the glass by a pencil in the desired shape.

The coating composition may also be applied to the glass by, for example, a transfer process such as printing or laser transfer a carrier material are transmitted to the surface of the glass by means of laser radiation, wherein the laser beam according to the carrier material of the desired shape. The coating composition may in this case be applied in a liquid but also in a solid layer state to the glass surface.

For example, the application of the coating composition may include adhering a self-supporting film of the coating composition to the glass surface, or the application of the

Coating composition an adhesion of a composite of the

Coating composition and a support film on the glass surface include. A film of the coating composition or the carrier film may preferably be self-adhesive here. The heat treatment mentioned at the outset can subsequently be carried out according to one of the aforementioned or also other application methods, e.g. by

Heating the marked glass, in particular a glass sheet in an oven. But it can also be provided that the heat treatment for

Diffusion is carried out by the laser beam, with which the

Coating composition is transferred to the surface of the glass. The transfer step is thus combined with the diffusion step by using a laser with which both can be performed.

Here, the laser intensity should be selected so that, depending on the type of glass, the necessary parameters mentioned above can be achieved in terms of temperature and time. Especially with glasses, such as borosilicate glass, which have no reducing ions, this laser-based application / diffusion can be made. The at least one metal compound in the coating composition may, for example, be copper, zirconium, praseodymium, cobalt or silver compounds.

The metal compounds used require no particular solubility in a solvent, but may be soluble. This facilitates the preparation of a variety of suitable coating compositions.

In a preferred embodiment of the invention, the

Coating composition in addition to the one metal compound used for the purpose of diffusion nor at least one other metal compound. This at least one other metal compound may e.g. serve to reduce the melting point of the coating composition and to accelerate the diffusion of the metal ions into the glass. Examples are potassium nitrate or borax, also in combination with silver nitrate.

If desired, the coating composition may further contain a reducing agent with which the metal ions of the metal compound are reducible in a subsequent temperature treatment at a higher temperature than that used for diffusion, if such subsequent reduction after the previous invisible marking is desired. Reducing agents preferably comprise copper and / or tin and / or iron and / or lead and / or cobalt and / or titanium compounds and / or complex systems such as iridium hexachloride and / or cyanoferrate. The reducing agents are able to diffuse into the glass and there strengthen the reduction process of the metal ions when the temperature required for the reduction is exceeded.

The concentration of the metal compound will usually range from 0.1 to 50, more preferably 1 to 30, most preferably 4 to 14, percent by weight of the coating composition.

Further advantages with regard to the formation of particularly homogeneous and stable layers can result if the coating composition is min. contains at least one additional substance with which the viscosity, the volume, the drying and evaporation rate, the wettability and / or the durability of the coating composition can be influenced. Examples of this are disinfectants in the case of the use of gelatin as a binder matrix or leveling agent to ensure a good and rapid spreading of the coating medium applied to the substrate, or viscosity increase and anti-settling compounds, which lead to a better durability of the coating medium and counter segregation and In the case of the application of the coating media as a paste effect a better layer uniformity.

The addition of drying regulators, such as silanes, also contributes to an improvement in the uniformity of the applied layer. Further advantages may result if the coating composition contains additives of dyes and / or pigments and / or of adhesion promoters and / or wetting agents. With dyes or pigments, the visibility of a layer applied to the glass can be increased. Furthermore, for example, in order to keep the surface tension of the coating media as low as possible and to be able to realize a coating without wetting disturbances on the glass or film surface, wetting agents and adhesion promoters can be used in the coating mixtures. As such, all wetting agents known per se from photographic emulsions or from other areas of coating technology, such as, for example, fluorosurfactants, disulphanes, relatively high molecular weight alkylaryl ethers, polyethylene glycols, etc., can be used.

The weight ratio of metal compound (s) and binder will vary depending on the mode of application of the coating composition. The binder (s) used must be present in an amount such that the bond matrix retains the adhesion of the metal compounds and other compounds contained in the coating media to the glass Surface is ensured. The metal compound-to-binder weight ratio will typically be selected in the range of 0.05 to 8000, more preferably in the range of 1 to 4000, depending on the intended application method. In special cases, however, other weight ratios could be suitable.

According to a first embodiment of the marking method according to the invention, the coating of the glass surface takes place by application (deposition) of the coating composition in the liquid or solid state, preferably by spraying, pouring, rolling, printing, knife coating or marking or laser marking with transfer media , Depending on the process, even curved and twisted surfaces can be evenly coated.

According to a further embodiment of the marking method according to the invention, the coating is carried out by application of the coating composition in the solid layer state. Preferably, this order comprises adhering a self-supporting film of the coating composition (thickness of the coating preferably 0.3 μm or larger) on the glass surface or a composite of the coating composition and a carrier film on the glass surface. Depending on the temperature stability, the carrier film can be removed again before or after the heat treatment. The film of the coating composition or the carrier film is preferably self-adhesive.

In a direct application of the coating composition, e.g. as a solution or pastes, they can be washed off again after the heat treatment. If desired, the binders can be optimized for effective removal by washing off.

In principle, all solvents which allow sufficiently high concentrations of dissolved or dispersed metal compounds are suitable as solvents for the coating composition. Preferred examples are ^water , alcohols, ketones or ethers and their mixtures. Particularly preferred Mixtures of water and a miscible organic solvent, for example a lower alcohol such as ethanol.

Depending on the application method, it is preferred if the solvents are miscible in addition to the solvent or dispersibility for the metal compounds and binders (polymers). In the case of the application of the coating media in the spray method with two-nozzle or multiple nozzle technique, this miscibility is required to a lesser extent. As binders, for example, known from the preparation of photographic emulsions ago natural polymers such. As gelatin, casein, albumin, polysaccharides, or artificial polymers such. As polyethylene glycols, polyvinyl alcohols, polyvinylpyrrolidones, cellulose actates, polyvinyl-formal and - butyrals, polystyrenes, copolymers of vinyl chloride and vinyl acetate, Hyaluronsäu- re, polyacryiates, etc. are used. Alternatively, mixtures of several binders may be used.

In the case of the use of films, for example, films of polycarbonate, polyethylene, polyethylene terephthalate, polyethylene naphthalate, Cellulosetri- acetate, polyvinyl chloride, polypropylenes, etc. may be used.

In the method using films as well as the other mentioned types of application of the coating media on the glass surface, a rapid drying of the applied coating media is advantageous. For this purpose, a coordination between the content of solvents in the coating medium, the rate and rate of application, the layer thickness and the evaporation rate of the solvent by means of known technological measures. The technological conditions should also be chosen such that the rate of drying is higher than the rate of crystallization of the dissolved metal compounds in order to obtain as small crystals of the metal compounds as possible. get bonds in the layer on the glass or on the films used. Small crystals of the metal compounds contribute significantly to the fact that the contact with the glass surface can be as intimate as possible. The layer thickness of the applied coating composition is also a parameter that affects the rate and rate of change. Suitable, non-limiting ranges are 50 nm to 50 μιτι, preferably 100 nm to 10 μιτι, more preferably about 1 -5 m.

Claims

claims

A process for marking glass in which a coating composition comprising at least one metal compound is applied to a glass surface in the form of a desired marking and the glass is subjected to a heat treatment in which metal ions from the coating composition diffuse into the glass volume, characterized in that the heat treatment is carried out at a temperature in the range of 280 ° C to 320 ° C and the diffused metal ions together with the glass matrix form a mark of fluorescence centers, which is invisible in the visible wavelength range and by energetic excitation, in particular by irradiation with UV light, fluoresces in the visible wavelength range.

A method according to claim 1, characterized in that the coating composition in the form of the desired label is applied by one of the following steps: a. The coating composition is stamped onto the surface of the glass by a die corresponding to the shape of the desired mark; b. The coating composition is written on the surface of the glass by a stick in the desired shape; c. The coating composition is transferred from a carrier material to the surface of the glass by means of laser radiation, the laser beam correspondingly illuminating the carrier material of the desired shape.

Method according to one of the preceding claims, characterized in that the heat treatment takes place for carrying out the diffusion by the laser beam, with which the coating composition is transferred to the surface of the glass.

4. The method according to any one of the preceding claims, characterized in that the heat treatment at a temperature in the range of 290 ° C plus / minus 10 ° C is performed, in particular over a period of at least one hour.

5. The method according to any one of the preceding claims, characterized in that the heat treatment is carried out with a temperature and a temperature-adapted period of time, which causes a minimum metal ion density in the glass matrix, are formed at the fluorescence centers, in particular the maximum metal ion density in does not exceed the glass matrix which results in a quenching of the fluorescence.

6. The method according to any one of the preceding claims, characterized marked, that the heat treatment is carried out at a temperature below the characteristic for the glass used transformation temperature.

7. The method according to any one of the preceding claims, characterized in that the glass to be marked and the coating composition used are coordinated so that the glass in its glass matrix, the metal ions of the coating composition does not provide reducing ions.

8. The method according to any one of the preceding claims, characterized in that with a temperature treatment of the glass above a temperature of 350 ° C or above a characteristic of the glass

Temperature, in particular the transformation temperature, the metal ions diffused into the glass are reduced by externally supplied or present in the glass reducing ions to metal particles and in the visible wavelength range recognizable by the eye color mark in the glass volume is generated.

9. The method according to claim 8, characterized in that the glass is checked for the performance of the heat treatment on the presence of recognizable by the eye color markers and the presence of the implementation of the heat treatment in an excessively high temperature range and / or at one closed for a long period of time.

10. The method according to any one of the preceding claims, characterized in that the coating composition comprises at least one metal compound in salt form.