Abstract:
The present invention relates to an optical lens, in particular for use as a spectacle lens, having a lens element and a coating for producing an antistatic effect, said coating being applied onto the lens element and having a plurality of layers. Further, the antistatic effect is provided by two layers adjoining one another, wherein at least one of the two layers adjoining one another is formed in a non-stoichiometric fashion. Furthermore, the present invention relates to a method for producing a corresponding optical lens.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the priority of German patent application DE 10 2010 048 089.4, filed Oct. 1, 2010, and the priority of U.S. provisional application No. 61/388,984, filed Oct. 1, 2010. The entire contents of these priority applications are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to an optical lens, in particular for use as a spectacle lens, having a lens element and a coating for producing an antistatic effect, said coating being applied to the lens element and having a plurality of layers. 
     Furthermore, the present invention relates to a method for producing an antistatic coating having a plurality of layers for a lens element. 
     Antistatic spectacle lenses afford the advantage that dirt particles adhere to the spectacle lenses to a lesser extent on account of absent electrostatic attraction forces. Without an antistatic coating, a spectacle lens is soiled more rapidly and therefore has to be cleaned more often. Furthermore, the dirt is often difficult to remove. Therefore, in the case of the coating of spectacle lenses, a conductive and thus antistatic layer is usually inserted into the coating. For this purpose, hitherto an individual layer has been inserted into the antireflective coating of the spectacle lens. 
     One example of a coating can be gathered from the document US 2003/0179343 A1, for example. It describes a coating in which an antistatic layer composed of indium tin oxide (ITO) having a specific thickness is inserted into the antireflective coating. However, the insertion of such an ITO layer into the antireflective coating has certain disadvantages such as higher costs for the coating and impairment of the mechanical and optical properties of the antireflective coating. 
     Therefore, it is an object of the present invention to provide an antistatic coating for an optical lens, more particularly a spectacle lens, which can be integrated simply and cost-effectively into an antireflective coating of the optical lens. 
     BRIEF SUMMARY OF THE INVENTION 
     In accordance with a first aspect of the invention, therefore, there is provided an optical lens, in particular for use as a spectacle lens, having a lens element and a coating for producing an antistatic effect, said coating being applied to the lens element and having a plurality of layers, wherein the antistatic effect is provided by two layers adjoining one another, wherein at least one of the two layers adjoining one another is formed substoichiometrically. 
     In accordance with a second aspect of the invention, there is provided a method for producing an antistatic coating having a plurality of layers for a lens element, the method comprising the step of applying two layers adjoining one another are applied, wherein the antistatic effect is provided by the two layers adjoining one another, and wherein at least one of the two layers adjoining one another is formed substoichiometrically. 
     In this case, “substoichiometric” should be understood to mean that when the corresponding layer is applied, an oxygen inflow is kept lower than is necessary to obtain a stoichiometric ratio in the applied layer. Consequently, an oxygen deficiency prevails in the stoichiometric layer. 
     In this way, according to the invention, the antistatic effect is not obtained by means of a single layer made from conductive material but rather from a composite of two materials which produce a conductive interlayer or a conductive interface given suitable process control during the application of the layers. 
     As customary processes for producing such layers, PVD (Physical Vapour Deposition), e.g. the vaporization of solid substances by means of an electron beam, sputtering or arc vaporization, and also IBAD (Ion Beam Assisted Deposition), are known. However, all other physical vaporization processes with or without assistance of ions or plasma and also chemical processes such as CVD (Chemical Vapour Deposition) or the plasma-assisted variants thereof such as PECVD (Plasma Enhanced Chemical Vapour Deposition) or PICVD (Plasma Impulsed Vapour Deposition) are also possible. 
     By virtue of one of the two layers adjoining one another being formed in a substoichiometric fashion and the two layers having direct contact with one another, a conductive boundary layer can form between the two layers. An antistatic effect is produced by the conductivity of said boundary layer. If the materials of the two layers adjoining one another are used anyway for layers of the antireflective coating, particularly simple integration of an antistatic effect into an antireflective coating can be effected in this way. 
     In particular, according to the invention, there is provided an optical lens having a lens element and a coating for producing an antistatic effect, said coating being applied onto the lens element and having a plurality of layers, wherein the antistatic effect is provided by two layers adjoining one another, wherein the two layers adjoining one another are provided by a first substoichiometrically formed layer of TiO x , with x&lt;2, and a second layer of Al 2 O 3 . Thereby, the second layer is applied after the first layer. Hence, the second layer is positioned above the first layer. By this, the second layer is positioned farther away from the lens element than the first layer. 
     In particular, according to the invention, there is further provided a method for producing an antistatic coating having a plurality of layers for a lens element, comprising the following steps: 
     applying a first layer of TiO x , wherein the first layer is applied substoichiometrically with x&lt;2, and 
     applying a second layer of Al 2 O 3  onto the first layer. 
     In one refinement of the optical lens in accordance with the first aspect of the invention, it is provided that the two layers adjoining one another are provided by a first layer, which is produced from titanium oxide (TiO 2 ), and a second layer, which is produced from aluminium oxide (Al 2 O 3 ). 
     The materials TiO 2  and Al 2 O 3  are traditional materials for producing optical layer systems. In particular, TiO 2  as high refractive index material and Al 2 O 3  as low refractive index material are used on account of their high degree of transparency for producing antireflective coatings of optical lens elements. These layers act individually like customary oxidic layers without a significant conductivity. In the composite, however, such a coating can have a conductivity, which then has an antistatic effect. 
     In particular, it is provided in this case that the first layer, i.e. the layer produced from TiO 2 , is formed substoichiometrically. 
     The substoichiometric layer composition thus results as Ti &gt;1 O &lt;2  or TiO 2−y . In other words, the first layer is produced from TiO x  with x&lt;2.0, in particular 1.66&lt;x&lt;2. In particular, the first layer can be formed with an oxygen proportion of less than TiO 2 , in particular less than TiO 1.95 , in particular less than TiO 1.9 , in particular less than TiO 1.85 , but in particular with an oxygen proportion of more than TiO 1.66 , in particular more than TiO 1.7 , in particular more than Ti 1.75 , in particular more than TiO 1.85 . In particular, the substoichiometric composition of the first layer can be formed between TiO 1.66  and TiO 2 , in particular, it is formed between TiO 1.7  and TiO 1.95 , in particular between TiO 1.75  and TiO 1.9 , in particular between TiO 1.8  and TiO 1.85 . In particular, the first layer can be formed from, for instance, TiO 1.66 ; TiO 1.7 ; TiO 1.75 ; TiO 1.8 ; TiO 1.85 ; TiO 1.9 ; TiO 1.95 ; TiO 1.97 . Furthermore, the first layer can also be formed between TiO 1.66  and TiO 1.8 ; it can also be formed between TiO 1.8  and TiO 1.95 . 
     The application both of TiO 2  and of Al 2 O 3  with desired layer thicknesses is known in the prior art. By way of example, document EP 1 284 302 B1 discloses one possibility for producing TiO 2  sputtering targets. 
     In order to provide the first layer produced from TiO 2 , a PVD method, for example, can be applied. In this case, the substance Ti 3 O 5  is used as a customary starting substance for producing TiO 2 . In order to achieve a transparent oxidic TiO 2  layer, oxygen is normally concomitantly admitted into the vaporization chamber during the vaporization process. This process can additionally be assisted with ions in order to achieve particularly high refractive index and compact layers. With a specific evaporation rate and a specific quantity of oxygen which is concomitantly admitted into the vaporization area during vaporization, a stoichiometric layer, i.e. exactly TiO 2 , is normally obtained. With a slightly smaller oxygen inflow, the above-described substoichiometric layer with then Ti &gt;1.0 O &lt;2.0  is obtained. 
     In one refinement of the first aspect, it can be provided that the first layer is applied after the second layer. However, it is also possible for the second layer to be applied after the first layer. 
     In this case, the term “after” relates to the order of applying the layers to the optical lens element during the application process. If the lens element is designated in cross section as the bottommost layer, a succeeding layer is thus arranged further above. 
     If the first layer, i.e. the TiO 2  layer, is applied after the second layer, i.e. the Al 2 O 3  layer, care must be taken to ensure that initially there is still no oxygen excess in the vaporization area, in order that the TiO 2  layer remains substoichiometric and in order that the conductivity of the TiO 2  layer is also maintained. Therefore, the opposite order, i.e. the application of the Al 2 O 3  layer, i.e. the second layer, onto the TiO 2  layer, i.e. the first layer, affords an advantage since it is not necessary to consider the oxygen excess in the vaporization area. 
     In a further refinement, it can be provided that a third layer, which is produced from TiO 2 , is applied onto the second layer. A TiO 2 —Al 2 O 3 —TiO 2  coating thus results. 
     Furthermore, it can be provided that, upon opposite application of the first layer and the second layer, a fourth layer, which is produced from Al 2 O 3 , is applied onto the first layer. Consequently, an Al 2 O 3 —TiO 2 —Al 2 O 3  layer then results. 
     When applying the fourth layer, in this case care must be taken to ensure that said layer is applied by vapour deposition without oxygen additionally admitted into the vaporization area and without ion assistance. This ensures that in the boundary layer between the substoichiometric TiO 2  layer and the Al 2 O 3  layer, i.e. the first and second layers, no additional oxygen is incorporated which can reduce or prevent the conductivity by altering the substoichiometric TiO 2  layer in the direction of a stoichiometric TiO 2  layer. 
     In the method in accordance with the second aspect of the invention, too, it can be provided that the two layers adjoining one another are provided by a first layer, which is produced from TiO 2  and a second layer, which is produced from Al 2 O 3 . In particular, it is also possible in this case for the first layer to be formed substoichiometrically. 
     Furthermore, instead, the first layer can be applied after the second layer or the second layer can be applied after the first layer. 
     If the second layer is applied after the first layer, then a third layer, which is produced from TiO 2 , can be applied onto the second layer. 
     If the first layer is applied after the second layer, a fourth layer, which is produced from Al 2 O 3 , can be applied to the first layer. In this case it is provided, in particular, that the fourth layer is applied without additional oxygen and/or without ion assistance. 
     The method in accordance with the second aspect of the invention thus has the same advantages as the optical lens in accordance with the first aspect of the invention. 
     An antistatic effect is usually measured by means of an electric field strength measuring device at a defined distance. An antireflective layer without a conductive layer attains a field strength of several kilovolts (kV) after charging by means of a suitable material, for instance a brush or a cloth. An optical lens having a coating having an antistatic effect remains distinctly below a limit of one kV in the case of such charging. The antistatic effect of the coating present here has such a high dissipating capability that the charging remains almost zero. 
     It goes without saying that the features mentioned above and those yet to be explained below can be used not only in the combination respectively indicated, but also in other combinations or by themselves, without departing from the scope of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
       Exemplary embodiments of the invention are illustrated in the drawing and are explained in greater detail in the following description. In the figures: 
         FIG. 1  shows a schematic cross-sectional view of an optical lens in a first embodiment, 
         FIG. 2  shows a schematic cross-sectional view of an optical lens in a second embodiment, 
         FIG. 3  shows a schematic cross-sectional view of an optical lens in a third embodiment, 
         FIG. 4  shows a schematic cross-sectional view of an optical lens in a fourth embodiment, and 
         FIG. 5  shows a schematic flowchart of a method according to the invention in an embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows an optical lens  10  in an embodiment. The optical lens  10  has a lens element  12  provided with a coating  14 . The coating  14  has a plurality of layers  16  applied successively. 
     In particular, the coating  14  has a first layer  18 , which is formed from titanium oxide (TiO 2 ) in a substoichiometric ratio. In this case, the term “substoichiometric” denotes that an oxygen deficiency prevails; the composition therefore results as Ti &gt;1 O &lt;2 . A second layer  20 , which is produced from aluminium oxide (Al 2 O 3 ), is provided thereon. The substoichiometric first layer  18  and the second layer  20  together form a conductive boundary layer, which, on account of its conductivity, integrates an antistatic effect into the optical lens  10 . 
     The arrangement of the first layer  18  and the second layer  20  within the coating  14  need not necessarily be at a surface of the coating  14 . Lower layers  22  providing a further antireflective effect, for example, can be provided between the first layer  18  or the second layer  20  and the lens element  12 . Further upper layers  24 , for example a superhydrophobic termination layer (not illustrated), can be provided above the first layer  18  or the second layer  20 . 
     The designations “top” and “bottom” and “after” and “before” in this case relate to a process sequence  26 . The plurality of layers  16  of the coating  14  are applied to the lens element  12  successively. Accordingly, the lens element  12  forms a lower termination. A subsequently applied layer of the plurality of layers  16  is thus situated further away from the lens element  12  and thus further above than layers of the plurality of layers  16  that were applied earlier. 
     Consequently, in the embodiment illustrated, the antistatic effect is provided by two layers adjoining one another, namely the first layer  18  and the second layer  20 , wherein one of the two layers adjoining one another is formed in a substoichiometric fashion, namely the first layer  18 . 
       FIG. 2  illustrates a further embodiment of the invention.  FIG. 2  likewise shows an optical lens  10  having a lens element  12  with a coating  14 . The coating likewise comprises a plurality of layers  16 . In the embodiment illustrated in  FIG. 2 , the first layer  18  and the second layer  20  are applied in the opposite order. In this case, the second layer  20 , produced from Al 2 O 3 , is applied first and the first layer  18 , produced from TiO 2  in a substoichiometric ratio, is applied subsequently. 
     This embodiment also forms a conductive boundary layer between the first layer  18  and the second layer  20 , such that an antistatic effect is provided. Advantageously, the materials used are also customary for providing a coating having an antireflective effect, such that the antistatic effect can be integrated into an antireflective coating of a lens element  12  in a simple manner. 
       FIG. 3  shows a further embodiment of the invention. The embodiment illustrated in  FIG. 3  substantially corresponds to the embodiment illustrated in  FIG. 1 ; therefore, identical elements are designated by the same reference symbols and only the differences are discussed below. 
     In the embodiment in  FIG. 3 , a third layer  28 , which is likewise formed from TiO 2  in a substoichiometric ratio, is applied to the second layer. Consequently, both the first layer  18  and the second layer  20 , and the second layer  20  and the third layer  28  form a conductive boundary layer, such that the antistatic effect of the entire coating  14  is improved. 
       FIG. 4  shows yet another embodiment of the invention. The embodiment in  FIG. 4  substantially corresponds to the embodiment illustrated in  FIG. 2 , such that identical elements are identified by the same reference symbols. Only the differences are discussed below. 
     In the embodiment illustrated in  FIG. 4 , a fourth layer  30  composed of Al 2 O 3  is applied to the first layer  18 , which is provided from TiO 2  in a substoichiometric ratio. In this case, care should be taken to ensure that the fourth layer  30  is applied without additional oxygen, in order that the first layer  18  does not revert to a stoichiometric ratio. Once again, a conductive boundary layer is formed both between the first layer  18  and the second layer  20 , and between the first layer  18  and the fourth layer  30 , and the antistatic effect of the coating  14  is increased. 
       FIG. 5  shows a preferred embodiment of a method  32 . 
     The method  32  begins in a start step  34 , whereupon firstly, in a step  36 , a lens element  12  is provided. 
     Subsequently, in a step  38 , a layer composed of Al 2 O 3  is applied. This can be effected by means of one of the PVD, IBAD, CVD, PECVD or PICVD methods mentioned in the introduction. These methods are known in principle to the person skilled in the art. 
     Between steps  36  and  38 , in principle, other layers may also have been applied to the lens element. 
     The layer composed of Al 2 O 3  applied in step  38  then forms the second layer  20 . 
     In a step  40 , a layer composed of TiO 2  in a substoichiometric ratio is then applied directly to the second layer  20  applied in step  38 . 
     Such substoichiometric application can be effected for example by means of a PVD method configured as follows. A typical coating installation can be, for example, the “Boxcoater 1200 DLF” from Satisloh. Ti 3 O 5  is used as a starting substance. The application rate is approximately 0.4 nm/sec. It is effected in ion source operation with an END-Hall ion source Mark II+ with a discharge voltage of 160 volts and a discharge current of 2 amperes. In addition, 30 sccm O 2  (sccm=standard cubic centimeter per minute, corresponds to 1 ccm gas volume per minute under standard conditions, i.e. pressure of 101325 Pa, temperature of 0° C.) is concomitantly admitted during the vapour deposition. In order to obtain the substoichiometric Ti &gt;1 O &lt;2  layer, overall less than 40 sccm O 2  is concomitantly added to the coating area. 
     The layer applied in step  40  is then the first layer  18 . 
     Subsequently, a further layer composed of Al 2 O 3  without additional oxygen and ion assistance is applied to the first layer  18  in a step  42 . A coating as illustrated in  FIG. 4  is thus obtained, which has, besides its antireflective properties, additionally an antistatic effect and can be produced particularly simply without high additional costs. 
     Finally, the method ends in a step  44  and can subsequently begin anew.