Classifications

• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B23/00—Re-forming shaped glass
  • C03B23/02—Re-forming glass sheets
  • C03B23/023—Re-forming glass sheets by bending
  • C03B23/025—Re-forming glass sheets by bending by gravity
  • C03B23/0258—Gravity bending involving applying local or additional heating, cooling or insulating means
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B23/00—Re-forming shaped glass
  • C03B23/02—Re-forming glass sheets
  • C03B23/023—Re-forming glass sheets by bending
  • C03B23/0235—Re-forming glass sheets by bending involving applying local or additional heating, cooling or insulating means
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B29/00—Reheating glass products for softening or fusing their surfaces; Fire-polishing; Fusing of margins

Definitions

• the present invention relates to the techniques used for bending glass sheets comprising functional layers which modify their behavior, particularly in the heat treatments to which they are subjected.
• the behavior of the glass sheets subjected to a heat treatment leading to the bending of the latter is a function of their characteristics with respect to the thermal fluxes to which they are exposed. These flows are radiative, convective and conduction in very unequal proportions, and depend on the bending mode used. The fact remains that, in most cases, a very large part of the energy transmitted is by radiation. When these sheets are perfectly homogeneous over their entire surface, the only variations in conditions to which they are subjected come from their environment in the processing facilities.
• thermo masses are used, in other words elements associated with the frames, and whose role is to locally absorb part of the thermal fluxes, reducing thereby the energy absorbed by the glass.
• the presence of enamel coatings located on automotive glass is also a factor of thermal imbalance. Dark colored enamel absorbs much more than uncoated glass. The differences result in local overheating which can be compensated in particular by the use of the thermal masses indicated above.
• the glazing may have some forming defects due to the presence of these notched areas, they are located in locations, at the edge of the glazing, where they do not constitute excessive discomfort.
• the problem linked to glazings which do not offer uniform properties over their entire surface is much more troublesome when the parts of the glazing concerned are located in areas whose properties are regulated, in particular those which must be completely free of obstacle to the vision.
• the curved glass sheets comprise functional thin layers, in particular layers which modify the properties with respect to electromagnetic radiation, and in particular infrared. These are in particular the layers which reflect infrared radiation to limit the heating of vehicles exposed to the sun.
• the layers in question are composed of an assembly comprising at least one infrared reflecting layer, most often a metallic layer, in particular based on silver, a layer which is protected by thin dielectric layers.
• the application is made to flat glass sheets. This application can be carried out either directly at the exit of the glass production lines, or more frequently, and in particular for all applications requiring the implementation of vacuum deposition installations, of the "magnetron" type, in recovery of the previously produced glass sheets.
• the various functionalities conferred on automobile glazing lead to the provision of zones devoid of layers modifying the behavior vis-à-vis electromagnetic rays.
• the solution to this problem is, for glazing with an at least partially opaque layer (whether this results from reflection or absorption) to infrared radiation, which must have parts free of this layer, proceed first to complete bending on the sheets comprising a uniform layer, and once the bending is completed, secondly, to remove the layer on the parts which must be devoid of it.
• the means used for localized removal of the layer may vary depending in particular on the design of the zones which must be devoid of the layer in question. If mechanical abrasion means can be used to produce patterns having a certain extent, other types of means are necessary when the patterns are in the form of very small lines.
• one of the difficulties of proceeding according to the invention is to have to carry out the localized removal of the layer on a curved surface, the curvature of which can be relatively strong. Under these conditions, the elimination of the layer by mechanical or chemical means encounters obvious difficulties. On glazing with large curvature, removal by mechanical means is only possible insofar as the drawing of the zone devoid of layer is relatively simple. It is the same in a chemical removal mode, except to use photogravure techniques to form a pattern in a protective layer forming a screen, which is removed after the pattern has been produced by chemical attack. For simple patterns and not too curved glazing, mechanical means such as removal by brushing, if necessary with the help of masks can be envisaged.
• the choice of laser for localized elimination of the layer makes it possible to overcome certain difficulties linked to the curved shape treated.
• the means used to produce the laser ablation beam are not in contad with the surface, even if their location must take into account the shape of the treated sheet.
• the fact of ablating on non-flat surfaces requires some precautions.
• the laser beam, to present the maximum ef iciency, must be properly focused at the point of removal.
• the curvature of the treated sheet therefore requires that the laser source be at any point at practically constant distance from the point on which the impact takes place, or at least that the deviation from this distance remains within close limits although controlled.
• the power of the laser and the extent of the beam at the point of convergence having the highest power are chosen so as to lead to treatment as fast as possible.
• the operation must be part of the production cycles without introducing additional time, and without requiring the multiplication of treatment stations. Processing speed is therefore an important factor in the economy of the process.
• the convenience of the treatment preferably results in a single sweep of the surface to be treated.
• the points of impact being of substantially drastic shape, a certain overlap is necessary for the removal of the layer on the surface of a pattern extending in two dimensions.
• the structure of the radiation means that the energy is normally higher in the center of it.
• the energy distribution in the section of this radiation is of Gaussian type, maximum in the center and decreasing rapidly on the edges of the radiation.
• the size of the layer eliminated at the point of impact is not only a function of the cross-section of the radiation, but also of the power delivered in the plane of this impad.
• a wide but not very energetic ray can lead to a removal limited to a central zone of dimension much less than that of the section of this radiation.
• a very energetic beam can produce a removal over the entire section at the point of impact.
• the focal point impad usually has "effective" dimensions which do not exceed 200 / x.
• the radiation characteristics are chosen so that the power released and its location eliminates the layer without appreciably modifying the characteristics and in particular the surface condition of the glass substrate. It is known that laser beams are used in various operations in the glass industry.
• lasers are offered as tools for cutting sheets.
• the characteristics of these tools are obviously not suitable for the ablation of the thin layers envisaged according to the invention.
• Lasers have also been proposed to mark the glass. These modes of implementation are obviously excluded according to the invention. It is imperative that the treatment leaves the glass substrate intad. In particular the mechanical, but also the optical characteristics of these substrates must be kept practically unchanged.
• the usual glasses are transparent at certain wavelengths. In other words, for these wavelengths, the radiation dissipates very little energy in the glass. It is therefore particularly desirable not to risk damaging the glass substrate to choose such lasers.
• the attached figures illustrate the characteristics of transmission, absorption and reflection of glass sheets.
• Figure 1 is typical of the optical characteristics of a sheet of clear "float" silica-soda-lime glass, as a function of the wavelength of the incident radiation.
• the sheet considered is 2.1mm thick.
• the glass absorbs (3) little near infrared (700 to 2500nm). The absorption in the infrared only becomes significant for wavelengths greater than 2700nm (outside the limits of the graph).
• the transmission (1) is high, of the order of 90%, over the whole range of wavelengths shown.
• Figure 2 illustrates in the same way the behavior of a sheet of 2.1mm thick, coated with a layer reflecting the infrared.
• the layer in question is based on silver. It is of the type described in patent EP 0336257.
• the transmission (4) of the coated sheet decreases very rapidly for wavelengths greater than 800 nm.
• the reflection increases rapidly for infrared, whether the incident radiation is on the coated face (5), or on the opposite face (6).
• the absorption is, of course, very low when the radiation is directed onto the face carrying the layer (8). It is of the order of 15 to 20% when the radiation is directed on the other face (7).
• US Patent 5,728,994 illustrates in particular the use of this type of laser for the localized removal of an opaque layer disposed on a glass substrate.
• the aim pursued is the formation of a transparent pattern, capable of forming bright images.
• This patent proposes in particular the use of an Nd: YAG type laser whose wavelength is 1064 nm. It is specified that for these wavelengths the radiation is little absorbed by the glass.
• N ⁇ i YLF with wavelength from 1047 to 1053nm
• Nd glass at 1060nm
• Nd ⁇ AP at 1080nm
• Ho YLF at 2060nm
• Ho YAG at 2100nm
• Tm YAG at 2020nrn.
• Nd vanadates lasers are preferably used. The latter make it possible to keep effective pulse powers at high frequency.
• the lasers used must preferably have a wavelength such that the absorption in the glass remains limited so as not to modify the characteristics thereof.
• the radiation advantageously has a wavelength between 500 and 2500 nm, and preferably from 700 to 1500 nm.
• a laser whose wavelength and physical characteristics ensure that the interaction with the glass is sufficiently weak to cause no significant modification.
• This has the advantage of being able to ablate the radiation: being directed either on the side of the layer or on the side of the sheet which does not carry the reflective layer.
• the laser beam is directed through the glass sheet on the reflective layer. It is preferred insofar as this method of removal makes it possible to more completely eliminate the constituents of the layer.
• the power of the beam is maintained at a value which is not more than 10 6 J / s and preferably not more than 10 5 J / s.
• the power is not less than 10 3 J / s.
• the frequency of the pulses is chosen so as to obtain the best compromise in removal efficiency.
• the power applied per unit area can still be adjusted by focusing the beam appropriately.
• the other consequence of choosing the dimensions of the impad point is to determine the processing speed for a given surface.
• a particularity of the use of lasers for the removal of the layer is to allow the formation of patterns which may be of dimensions as small as necessary.
• the use of the laser allows the ablation of the layer along lines undetectable to the eye, for example whose width can be of the order of a few micrometers.
• the focusing of the beams is advantageously carried out on the layer to be removed in order to concentrate the power at this point.
• a deviation between the focus point and the layer is, of course, possible. However, this results in a decrease in power per unit area. In practice, it is preferable to keep this difference less than 15mm, and more advantageously less than 5mm. Given the curvatures of the most commonly produced glazings, it is necessary to provide means guaranteeing that the focusing point is maintained within the limits indicated above. Large glazing often has arrows of ten or more ointimeters or even more. If the removal is to be performed for example on the periphery of such glazing, it is understood that it is necessary to adjust the distance substantially constantly. Likewise for glazing with certain curvatures that are particularly accentuated, such as so-called panoramic windshields, it is necessary to ensure that the angle of incidence of the beam is kept substantially constant.
• a robot is advantageously used which allows adaptation to all the geometries of the glazing treated. Most often the laser source will be carried by the robot.
• the method of producing curved glazing comprising an infrared reflecting layer is described in more detail in the following examples.
• laminated windscreens are curved in the traditional way by gravity on frames. The two superimposed sheets are passed simultaneously through the bending oven. The face of the lower sheet numbered H, according to the traditional name, is coated with an infrared reflecting layer.
• This silver-based layer is of the type described in patent EP 0336257.
• the final glazing has at the location intended to receive the rain sensor (200mm from the upper edge of the glazing, and in the median axis) 22mm. arrow.
• the curvature in the orthogonal direction is less pronounced.
• the established conditions lead to a glazing meeting the nominal characteristics, with no optical defect detectable according to the usual tests.
• the optical distortions in reflection, at the location considered, measured in millidiopters are of the order of 2000.
• the sheet coated with the infrared reflecting layer has an area of 45mm in diameter, devoid of the layer and intended to receive the rain sensor. This zone is obtained by mechanical masking during the deposition of the layer.
• the glazings are curved under the previous conditions.
• the measurement in reflection this time shows a distortion corresponding to a value of 5000 millidiopters, clearly greater than that obtained previously.
• the irregularity of shape at the location devoid of a layer relative to the rest of the glazing is significant.
• This local deformation of the curved shape is not accepted by the builders.
• the sheets obtained with a uniform coating of the infrared reflecting layer, and which do not contain any defects, are then subjected to laser removal under the following conditions.
• the pulse durations are short to have the highest peak power. In the test carried out, the pulse duration is of the order of 10 ns.
• the beam is focused on a point of 200 ⁇ in diameter.
• the distance from the sheet to the source remains within the limits in question does not influence the treatment conditions.
• the local elimination of the layer in the latter case does not cause any modification of the bending.
• the efficiency of the removal of the layer is determined by X-ray fluorescence. Before removal the layer present of the order of 198 mg / m 2 of silver. After removal under the conditions indicated above, the same measurement shows a content which is less than 2 mgm 2 . In other words, the layer is completely eliminated.
• Ced is confirmed by the transmission measurement in the area thus treated. After removal, the light transmission in this area is approximately 86%, which corresponds to the transmission in the absence of a layer.
• Another series of tests is carried out on a windshield comprising the same type of layer as previously. This time the elimination of the layer corresponds to a network of lines forming a grid extending over a 180x180mm square. This pattern is intended to transmit radar waves to an on-board detector. The lines in this case are narrow enough that they are practically invisible to the naked eye. The width of the lines is less than 0.1mm. The horizontal and vertical spacing between the lines is 1mm.
• the optical distortion is measured less than lOOmillidioptries in transmission. If one proceeds to the formation of removal before bending, there is a much higher distortion, of the order of 400 millidiopters, which once again constitutes a defect with respect to the rest of the glazing in the zone considered. If the removal is carried out on the curved glazing, no deformation is introduced.
• the fineness of the lines is formed by means of the same laser but by focusing the beam so that the lines for removing the layer have a width of 90 micrometers. It is noted in this case that the laser is particularly well suited to the formation of such fine patterns. In this particular case, a masking operation is practically impossible.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Organic Chemistry (AREA)
• Joining Of Glass To Other Materials (AREA)
• Surface Treatment Of Glass (AREA)

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• 2003
  • 2003-12-23 BE BE2003/0680A patent/BE1015831A3/fr not_active IP Right Cessation
• 2004
  • 2004-12-16 EP EP04804884A patent/EP1765738A1/de not_active Ceased
  • 2004-12-16 WO PCT/EP2004/053538 patent/WO2005070841A1/fr not_active Ceased

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