DE1244345B - Method of bending glass sheets - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. Cl .:

C03b

C03B

German class: 32 a - 23 / 02- /

C03B 23-023

Number: 1 244 345

File number: J 25444 VI b / 32 a

Filing date: March 13, 1964

Opened on: July 13, 1967

The invention relates to a method for curving glass plates.

As is known, the change in shape is caused by a glass part heated above the transformation point learns, on the one hand by the distribution of the external forces acting on it, z. B. gravity, on the other hand, determined by the surface tension of the glass. Because this at a uniform temperature of the workpiece generally has the same value at every point on the surface Bending of plates normally only with the application of external compressive or tensile forces, mostly with With the help of bending molds or tools. The disadvantage of this procedure is once in the fact that a separate tool is required for each degree of curvature, on the other hand, that the quality a bare glass surface can be easily damaged by the pressed shape.

In contrast, the invention proposes a method in which the deformation is essentially caused only by the surface tension of the glass. In scientific research it was found that on the surface of glasses, e.g. B. by ion exchange, high pressure and can generate tensile stresses.

In the elastic range, such stresses can cause optical interference with sufficiently thin samples be detected. As our own experiments have shown, under certain conditions it succeeds with The help of artificially changed stress zones on the glass surface in the temperature range of the plastic Deformation of the glass, even at thicknesses of several millimeters, is unexpectedly strong Bend measure. The prerequisite for this is apparently that the relaxation of the stresses generated, e.g. B. due to diffusion or sintering processes, slow compared to the rate of deformation of the glass is going on. The method of the invention is that at least one Part of the glass surface a material change is made such that after heating the Tangential stresses on the surface of the glass to a temperature suitable for its deformation exist, which deviate from the surface tension on the opposite surface and at the specified temperature a ■ - in the case of non-permitted deformation - compared to the deformation duration have long relaxation time, so that the glass plate when heated to the said temperature curves essentially without the action of external forces.

For the production of the surface zones of different processes for bending glass plates

Applicant:

JENAer Glaswerk Schott & Gen.,

Mainz, Hattenbergstr. 10

Named as inventor:

Dr. Hubert Schröder, Wiesbaden

There are various options for changing this voltage. The known methods of alkali ion exchange can indeed achieve very high compressive or tensile stress values in individual cases, but their stability is because of the large increase in the diffusion rate above the transformation temperature generally not sufficient to carry out the process; also show up in some Glasses annoying side effects, such as B. opacities or cracks. A reliable, The method according to the invention, which is largely independent of the type of glass, consists in that on the glass surface thin layers (in preferably at least

»5 1 · 10 ~ ⁵ cm thickness) made of a material that has practically no ability to migrate on the same, the layers being selected or built up in such a way that they are under strong tensile or compressive stresses at least when heated. This can be achieved in a number of ways. If one chooses a layer material firmly adhering to the glass surface, the coefficient of thermal expansion of which is smaller than that of the glass, tensile stresses of increasing strength will occur in the layer as the temperature rises, which lead to a concave curvature of the coated glass surface above the transformation point. This is e.g. B. the case with layers which consist of oxides of Si, Ti, Zr, Th or Al. They are applied in a known manner either by vapor deposition in a vacuum or by hydrolytic and pyrolytic conversion of films deposited on the glass surface or vapors of dissolved compounds of the metals mentioned.

The occurrence of tensile stresses can also be caused or intensified by Produces layers of increased degree of porosity, which in the case of vapor deposition is due to the higher pressure of the Residual gas in the recipient as well as through simultaneous vapor deposition of soluble substances, when coated with liquid films due to higher proportions of volatile or

709 610/211

subsequently leachable components in the solution can be achieved. In the latter case are suitable as additives e.g. urea, camphor or ammonium chloride.

example 1

A plane parallel plate of 1 mm thickness of a mirror glass of the transformation point 545 ° C after thorough cleaning on one side by immersing and pulling up from a condensed Äthylsilikatlösung with addition of 2 weight percent urea with a uniform liquid film, for example, 5 x 10 ~ ⁵ cm thickness coated and dried briefly at 150 ° C. The remaining urea is then dissolved in water from the layer and circular disks are cut from the glass, which are heated as quickly as possible to 590 ° C. in an oven, preferably in a vertical position or hanging. After about half an hour, the platelets have assumed a concave curvature towards the layer side, which (depending on the thickness of the applied film) can be 3 m " ¹ and more.

A uniform coating with a liquid film causing the bend can also take place in a known manner by centrifuging the solution onto previously trimmed round disks. The maximum curvature that is obtained when a plane-parallel glass plate is covered on one side is, as a first approximation, proportional to d / D, where d and D mean the thickness of the thin layer or the glass plate, and depends on the degree of porosity of the layer and the selected laminate away.

Another way to produce temperature resistant Tensile stress in the glass surface consists in that in this by a chemical Leaching treatment creates micropores through which a silica enriched Layer of low density and expansion arises. The leaching of the usual soda-lime-silicate glasses takes place in a known manner particularly effectively when using weakly alkaline solutions of salts with the addition of inhibiting substances, such as. B. in German Patent 821,828.

Example 2

A Vio η solution of Na ₂ HAsO ₄ is mixed with 3 ° / o ⁿ / io solution of AlCl ₃ · 6H ₂ O and brought to pH 7.5 Äi. In the heated to 95 ° C solution to be treated, protected on one side with resist glass plates are immersed until at its surface a depleted layer of the optical thickness of 5 · 10 ^-5 cm is formed, which in the reflected light can be recognized by a blue interference color (2nd order). After rinsing and drying, the panels are cut to the desired format and the parts are heated in an approximately vertical position to 50 ° C above the transformation point of the glass until the curvature that can be achieved with the respective glass thickness is achieved.

The process also enables temperature-resistant compressive stresses to be generated on the Glass surface, which enable a convex curvature of the same to be produced. Suitable for this in particular layers of electropositive, polyvalent metals or low metal oxides, which are packed as closely as possible, preferably by vapor deposition, and deposited on the glass then oxidized by heating in air or oxygen. For example, Al, Si or Ti are suitable or SiO and TiO. The evaporation is preferably carried out until the condensed Layer has a light transmission (in the case of pure metals) of less than 30%. In the case of oxidation the metal or suboxide layers become largely translucent or even completely free of absorption. The layers can be oxidized before or during the heating of the glass to the deformation temperature. When diffusing in of the oxygen can then evidently the space required for the formation of the normal oxide lattice are not satisfied, so that this is under strong compressive stresses, which at the deformation temperature, a corresponding expansion of the glass surface bring about.

· * »..,"

Example 3

A circular disc of 60 mm diameter and 1 mm thickness is steamed at a pressure of 5 × 10 ^-6 Torr in 5 seconds with titanium, that the light transmittance is lowered to 6%. The platelet is then heated in an oven to 460 ° C. for 2 hours and then brought to a temperature which is 50 ° C. above the transformation point of the glass. The platelet curves convexly on the layer side and reaches a curvature of around 4 mr ¹ . Since the bending forces increase with the layer thickness d , the method also succeeds in locally varying the degree of curvature by changing d in a predetermined manner across the covered surface. If, in particular, d is decreased radially from a center point, a curvature in the manner of a (rotational) paraboloid can be achieved.

A particular advantage of the method is that the coating is optical at the same time Effects on the glass surface can be achieved, causing the glass to change its Can experience light transmission and / or its reflectivity.

According to known regulations of coating technology, this is achieved through the selection of materials with a correspondingly higher or lower refractive power compared to glass or through the use of absorbent laminates. For example, an anti-reflective coating of the glass surface can be achieved by applying a ZrO ₂ layer with an optical thickness of A / 4 or A / 2 and an additional SiO ₂ layer with an optical thickness of λ / 4. The layer thicknesses must be made larger by a corresponding factor in accordance with the reduction in the optical thickness caused by the contraction of the layer during the deformation of the glass during its manufacture.

The method according to the invention can be used for any flat glass that is not too thick and is mainly used for the production of cover plates, watch glasses, spectacle lenses and the like.

Claims (12)

Patent claims: 1. A method for bending glass plates, characterized in that at least part of the glass surface has a material Borrowed change is made such that after heating the glass to one of his Deformation suitable temperature tangential stresses exist on the surface, which deviate from the surface tension on the opposite surface and at the one mentioned Temperature one - in the case of non-permitted deformation - compared to the deformation duration have long relaxation time, so that the glass plate when heated to the said temperature curves essentially without the action of external forces. 2. The method according to claim 1, characterized in that thin on the glass surface Layers are applied from a material that has practically no migration capacity has the same, the layers being selected or constructed so that they are at least are under strong tensile or compressive stress when they are heated. ao 3. The method according to claim 2, characterized in that the thermal expansion coefficient of the layer material is smaller than that of the glass. 4. The method according to any one of claims 1 to 3, characterized in that layers can be produced with an increased degree of porosity on the glass surface, in particular with an additive volatile or subsequently leachable substances to the layer-forming starting materials. 5. The method according to claim 4, characterized in that on the glass surface by a chemical leaching treatment creates micropores through which one layer is lower Density and expansion arise. 6. The method according to claim 5, characterized in that the leaching of the glass surface made in weakly alkaline solutions with the addition of inhibiting substances will. 7. The method according to any one of claims 1 to 3, characterized in that layers electropositive, polyvalent metals or low metal oxides on the glass surface in dense packing, so that in the subsequent oxidation in air or Oxygen compressive stresses arise in the layer, which at the deformation temperature cause a concave curvature of the glass surface. 8. The method according to claim 7, characterized by the use of vapor-deposited Al, Si or Ti or SiO and TiO as starting material for the oxidized layers. 9. The method according to any one of claims 1 to 8, characterized in that the layer thickness the occupancy is varied locally in a predetermined manner, so that when the Glass deviations from the spherical curvature can be achieved. 10. The method according to claim 9, characterized in that the layer thickness of one Center decreases in the radial direction, so that a paraboloidal curvature of the glass is achieved. 11. Application of the method according to claims 1 to 10 for the production of arched Watch or eyeglass lenses. 12. The method according to any one of claims 1 to 10, characterized in that the for bending Serving layers are formed so that at the same time a change in the reflectivity and / or the light transmittance of the Glass is effected.