CA2076094C

CA2076094C - Process and device for the production of a reflection-reducing coating on lenses

Info

Publication number: CA2076094C
Application number: CA002076094A
Authority: CA
Inventors: Alfons Zoller; Karl Matl; Rainer Gotzelmann; Gunther Sauer
Original assignee: Balzers und Leybold Deutschland Holding AG
Current assignee: Balzers und Leybold Deutschland Holding AG
Priority date: 1991-08-28
Filing date: 1992-08-13
Publication date: 2002-10-15
Anticipated expiration: 2012-08-13
Also published as: EP0529268B1; EP0529268A2; CA2076094A1; ES2094257T3; JPH05196803A; EP0529268A3; DE4128547A1; KR100278135B1; US5597622A; DE59207103D1

Abstract

The invention relates to a scratch-resistant coating for optical materials comprising synthetics as wall as to a process for the production of this coating. In order for the synthetic material, for example a CR39 lens, to be protected against scratches, first a very thin adhesion layer of SiO is applied, which is subsequently provided with a thick SiO2 layer.
Both layers are deposited in a vacuum chamber which comprises a vaporizer and a plasma source.

Description

PROCESS AND DEVICE FOR THE PRODUCTION OF A REFLECTION-REDUCING
COATING ON LENSES
The invention relates to a process and a device according to the preamble of Patent Claims 1 and 10.
With lenses the problem very often arises of applying a protective coating which is light-permeable and yet reflection-reducing. This applies for camera lenses as well as also for lenses of eye glasses. In the case of inept or careless handling by the user, eyeglasses can be subjected to extreme stress which cases scratching not only of synthetic glasses but also of silicate glasses. For surface damages as a rule sharp objects are responsible which are drawn across the surface under pressure. That can be, for example, sand with its sharp edges in a polishing cloth or the case of the glasses but also rough tissue.
Because they combine the property of low weight and greater resistance to breakage with the possibility of individual coloring, synthetic glasses are used increasingly more often.
However, they have the serious disadvantage that their surfaces which are considerably softer compared to silicate glasses are very susceptible to mechanical damage.
As a synthetic material for lenses duroplastics are used widely which comprise macromolecules chemically closely enmeshed with one another. They are most often very brittle at room temperatures. In addition, they are temperature stable, not weldable, insoluble, and only weakly swellable. One duroplastic preferred in lens systems used for eyeglasses is CR 39 which is a diallyldiethylene glycolcarbonate. Only very recently, apart from these synthetic materials used nearly exclusively in lens systems for glasses, other synthetic materials such as polymethylmethacrylate (PMMA), polystyrene (PS), and polycarbonate (PC) have been employed.
If, for example, a CR 29 synthetic is to be provided with an appropriate protective covering, the problems of detachment of the protective layer from the lens body, the difference in heat expansion of protective layer and lens body as well as in many cases the low temperature stability of the protective coating must be solved.
With silicate coatings the substrate is heated to a high temperature of approximately 300°C whereby sufficient energy is available for the coating molecules applied in a

- 2 -vapor deposition process in order to generate defect-free dense layers. In contrast, when producing a synthetic layer, the vapor deposition as a rule must be carried out at low temperature.
In order to make available the energy required in this case, the grown layers are bombarded with ions of an inert gas.
Additional ionization of the vapor particles and the reactive gas reinforces the densification process in the layer condensation.
Apart from these so-called ion-assisted deposition processes (IAD), the so-called plasma polymerization is also known in which during the layer formation the properties of the layer can be changed continuously so that, on the one hand, they are adapted to the synthetic surface from the aspect of the chemical structure and, on the other, form on the boundary to the air a glass-like structure which has a very high mechanical resistance.
A process for the production of transparent protective coatings comprising silicon compounds is already known which is used in the coating of synthetic substrates (DE-A-3 624 467 = EP-A-0 254 205). In this process a chemical vapor deposition takes place under the effect of a plasma (= plasma chemical vapor deposition) onto a polymerizable monomeric organic compound from the group of the siloxans and silazans wherein to the polymerization process oxygen is supplied in excess. The plasma is therein generated by means of high frequency between two electrodes of which the one has the function of a cathode and is connected with the substrates. Before the coating proper the substrates are exposed in an atmosphere comprising a noble gas to an ion bombardment by glow discharge in the presence of the organic compounds.
In another known process of plasma-enhanced coating of a substrate with a polymerizable silicon-comprising monomer the monomers are restricted to silans, silazans or disilazans and the plasma coating is carried out until a particular Taber wear index is attained (EP-A-O 52 870).
A device is also known (DE-C-3 931 713) with which optical lenses can be coated on both sides in a plasma-enhanced process. This device comprises two electrodes between which are disposed holding elements for the work pieces to be coated. The holding elements therein are at a defined electrical potential.
A similar process is known (EP-A-O 403 985) for the pretreatment of transparent synthetic substrates intended for vacuum coating. It has been found that through plasma

- 3 -bombardment of the substrate surface this surface is changed in such a way that the subsequence layer can be applied with a high degree of adhesive strength.
In a further device for the coating of substrates a vacuum chamber is provided with a substrate carrier disposed in it and having a plasma generator, a magnet and an electron emitter wherein, in addition, in the vacuum chamber a device for the generation of atoms, molecules or clusters of the materials for the generation of the layer on the substrates is disposed, which is located immediately next to the plasma generator and opposite the substrates (EP-90123712.3, K.Matl, W. Klug, A.
Zoller: Ion assisted deposition with a new plasma source, Paper presented at the Sec. PSE Conf., Garmisch-Partenkirchen 1990).
One advantage of this device reside therein that, in contrast to earlier devices of the ion-assisted deposition (IAD), it can act upon substrate holders having a diameter of approximately 1m with high plasma density.
Moreover, antireflection coatings are know which are applied onto synthetic lenses and comprise for example two layers of which the first layer is a Si02 layer and the second layer a Si0 layer (De-OS 27 39 044, Figure 1A).
Further, antireflection coatings are known comprising four or more descrete layers wherein for example, beginning at the substrate, the layer sequence is as follows: SiO, SiOz, CeOz, SiOz, CeOZ (DE-OS 38 18 341).
DE-A-39 09 654 describes a reflection-reducing system on substrates of plastic resin comprising a first layer of Si0 and a second layer of SiOz. Herein the second layer merely serves for improving the breaking strength and, therefore, has a thickness of only 10 nm to 60 nm.
A mar resistant coating formed on a substrate of plastics is also known wherein the coating has a thickness of 1 ~m to 10 um (US-A-3 811 753). However, the combination of mar-resistance and adhesive strength cannot be achieved with this coating.

- 3a -Further, it is known to apply a coating of 4 ~.m on lenses made of polymer which consists of vaporized glass, more specifically borosilicate glass (DE-A-25 38 982). Glass is made of Si02 to only 80 per cent. Further, the thickness of the base coating of Si0 and Si02 on which the glass is vaporized is not indicated.
With a further known reflection-reducing system consisting of two or three separate coatings first a homogenous layer of Si0 or an inhomogeneous coating of Si0 and a substance of a higher refractive index are applied to an object (DE-A-22 10 505). However, the degree of oxidation of the first Si0 layer is not indicated. Further, only the refractive index is inhomogeneous, but not the hardness of the layer.
It is also known to utilize Si0 having an optical thickness of h/4 and 1~/2 for reflection reducing of polycarbonate and other synthetic substrate materials (US-A-3 356 522; US-1-4 497 539). No distinction is made between coatings having good adhesive strength and abrasion-resistance properties.
With another known antireflection coating system for lenses of a synthetic polymer a first coating is made of a compound of Si0 and SiOZ having an index of refraction of 1,8 and an optical thickness of 1~/4 (=approximately 70 nm) and further coatings of Ti02, Ce02, A1z03 and Si02 having a refractive index of 1~/4 or 1~/2, respectively (DE-C-27 38 044).
Lastly, a process for the production of synthetic objects with hard coatings is also known, in which a layer based on silicon is disposed on a foundation material and onto this layer a Si02 film is applied (EP-A-O 266 225). The SiOz layer is herein applied by means of a vacuum vapor deposition process preferably in an ion-plating process.
The invention is based on the task of creating a scratch-resistant coating of eyeglasses, lenses and the like comprising a relatively soft synthetic material.
In one aspect the present invention provides an optical lens comprising a transparent plastic material substrate and a first layer of Si0 which is disposed directly on the substrate and which has a thickness of one atomic layer to 50 nm, and a second layer of SiOz on the first - 3b -layer. The second layer has a thickness of at least 500 nm and comprises at least two regions having different hardness, the region having the lower hardness being adjacent to the first layer.
In another aspect, the present invention provides a method for the production of a layer with nonhomogeneous hardnesses on a transparent plastic material substrate in a plasma coating installation. The method comprises the steps of:
First arranging one or more transparent plastic-material substrates in a substrate holder.
Si0 is then evaporated in an evaporator with simultaneous irradiation of the substrate with a plasma from a plasma source to form a layer of Si0 having a thickness of one atomic layer to 50 nm.
SiOz is then evaporated in an evaporator with simultaneous irradiation of the substrate with a plasma from a plasma source in which process either the plasma power and/or the gas pressure and/or the coating rate is altered so that a layer of Si02 having a thickness of at least 500 nm and having nonhomogeneous hardness is formed on the Si0 layer.
In yet another aspect, the present invention provides for an apparatus for performing the above method. The apparatus includes a chamber in which plasma can be generated, a substrate holder for holding one or more transparent plastic-material substrates, a plasma source opposite the substrate holder, an evaporator next to the plasma source containing SiO, an evaporator next to the plasma source containing Si02 granules, at least one ring magnet above the substrate holder, means for controlling the plasma power of the plasma sources, means for controlling the gas pressure, and means for controlling the coating rate of the evaporator containing Si02 granules.
The advantage achieved with the invention resides in particular therein that the tensions between the relatively soft synthetic substrate and the hard coating are decreased.

- 4 -The Si0 layer is selected to be of minimum thickness because SiO, for the application according to the invention, has optically undesirable properties and is therefore used primarily for the purpose of ensuring adhesion. With increasing layer thickness of Si0 the reflection increases. This leads to an increase of the oscillations of the reflections curve (r = f(~)) brought about by the succeeding thick SiOz layer. Moreover, Si0 is not absorption-free. A thin Si0 layer therefore keeps the undesirable reflections and absorption within reasonable limits and yet fulfils the requirements made of the adhesive strength.
The SiO2protective layer, in contrast, must be relatively thick, i.e. > 500 nm since otherwise the requirements made of the scratch-resistant are not met. Thinner SiOz layers at the given stress break down even if they are very hard. Moreover, they cause undesirable oscillations of the reflection curve. In the case of thicker Si02 layers the oscillations are also present, however, the wavelength interval of the minima and maxima becomes smaller with increasing layer thickness so that on visual inspection no disturbing interference effects can be observed.
Embodiment examples of the invention are depicted in the drawing and will be described in greater detail in the following.
Therein show:
Fig. 1 a two-layer configuration on a synthetic lens substrate;
Fig. 2 a three-layer configuration on a synthetic lens substrate;
Fig. 3 a seven-layer configuration on a synthetic lens substrate;
Fig. 4 a schematic representation of a plasma IAD process for the generation of thin layers.
In Figure 1 is depicted a lens substrate 1 of a synthetic material, for thickness CR 39, which is provided with a very thin Si0 layer 2 having a thickness of one atom up to 20 nm.
This layer 2 serves essentially for the purpose of effecting a better adhesion of a protective coating 3 with a

5 thickness of at least 500 rnn of Si02.
As has been found a Si02 layer applied directly adheres only poorly on synthetic materials. In so-called boiling tests coated substrates are cyclically imm~errrsed for a defined time in a boiling salt solution c~nprising for example 5% NaCl in water. They are subsequently plunged into cold water.
A layer of Si02 applied directly on a synthetic material be~mes very rapidly detached in such boiling tests, for example after 5 to 10 minutes. In fast, if a Si0 layer 2 is disposed between the Si02 layer 3 and the substrate of synthetic material which is coated under simultaneous plasma and ion bcanban~ent with a resistance vaporizer boat or an electron beam gun, the ( adhesion of the Si02 layer 3 increases considerably. Even after a boiling test lasting 40 minutes no impairments on layers 2 arid 3 could be detected.
With the thick Si02 layer 3 the wear properties are significantly improved relative to the synthetic substrate 1. CR 39, for example, has a harr~ness of approximately 180 to 200 N/mm2. Dense quartz, in contrast, has a hardness of 4500 N/nmn2. The hardness of the protective layer 3 can be adjusted in a very broad range via the plasma and coating parameters.
Thresh special plasma coatings harc~zess values of approximately 1000 N/imn2 up to nearly 4500 N/mm2 have so far been achieved.
The wear resistance increases basically with the hardness and the layer thicla~ess wherein at a layer thick~ss beginning at appr~ci~mately 3 to 8 ~mn a saturation effect in the wear resistance ocxurs as a fl~nction of the haxtlness. In the production of very haul and consequently brittle layers, strong tensions between layer and substrate are generated. For example CR 39 has a coefficient of thermal expansion of approximately 1 * 10'4/K while, in contrast, the coefficient of thermal expansion of quartz is almost negligible. Accordingly, a 70 mm CR 39 lens expands by approximately 0.4 mm at a temperature differexice of 80oC. The expansion of quartz, in contrast, is nearly 0. The tensions caused thereby make great dmnaryds made on tha adhesion of the layer. It is therefore useful to break down at least a part of the tensions in the layer itself. This is achieved via a hardness gradient i.e. the hardness increases frcen the interior on the substrata in the ~ztwar~d direction. For the production of the Si02 layer it is suggested to use as the starting material Si02 instead of a suboxide. Si02 can be vaporized with very laa vaporizer power. The temperature stress placed on

6 the sub:~trates can thereby be kept to a minimum during the production of the thick protective layer.
By insetting a layer 5 between the Si0 and the Si02 layer the oscillations in the reflection curve can be decreased considerably. This layer 5 has preferably an index of refraction smaller than the index of refraction of the substrate 1 and greater than the index of refraction of the protective layer 3. If CR 39 is used as the substraate and if the protective layer 3 oamprises Si02, the index of refraction of layer 5 is between 1.45 and 1.52. The thic3aless of layer 5 herein is approximately 80 to 120 rnn which at a wavelength of light of 550 rmi corresponds to a quarter wavelength.
~ this measure the oscillations due to the thiclmess of the layer 3 are atte~nxated.
Figure 3 depicts a variant in which as intermediate layer 6 a SiOx layer is used wherein x is a value between 1 and 2. On the Si02 layer 3 is disposed a carnbination of four father layers 7 to 10 which serve exclusively for the purpose of reducing the reflection. These layers ocanprise alternately Ta205 and Si02 wherein the uppermost layer is Si02.
The production of the layers takes place in the manner described in~the following and in conjunction with Figure 4.
In a standard vac:uuin installation 20 the layers are deposited by means of an electtron beam vaporizer 21 (see above Matl, Klug, Zoller). A plasma source 22 is herein disposed in the center and on the bottarn 23 of the installation 20 and directed onto an electrically insulating substrate holder 24. In the plasma soure-.e 22 is disposed a cylindrical electron-emitting LaB6 cathode 25 encompassed by a cylindrical anode 26 having a diameter of approximately 50 mm. A glow discharge pla~na is generated wherein a noble gas, primarily anon, is introduced via a line 28.
A cylindrical magnet coil 29 encloses the anode 26 and brings about that the possibility for movement of the electrons generated by the plasma is considerably increased in the axial direction and considerably decreased in the radial direction. The electrons mwe in spiral form about the magnetic field lines whereby the plasma reaches the coating chamber 20. On the top 30 of the coating cumber 20 and above the substrate holder 24 is provided an annular magnet coil 31 with an inner diameter greater than the diameter of the substrate holder. The magnetic field of this ring magnet 31

7 and the magnetic field of the cylinder coil 29 are superim~sed and form a guidance field for the electrons on their way frcan the cathode 25 heated indirectly by a heater 27 and fed, in turn, by the energy supply 32, as well as for the entire plasma between the plasma srntcce 22 and the substrate holder 24. In front of the dame-form substrate holder 24 is generated a dcane-form plasma boundary layer. Because the potential of the substrate holder 24 relative to the plasma is negative, the ions are accelerated out of the plasma botux3ary layer and bcm~ard a growing film which is thereby densified. A significant advantage of the production process in Car~parison to the conventional lAD processes with one ion source resides therein that tY~~e ions starting out of a plasma boundary layer forming parallel to the entire inner face of the substrate holder are acce7.erated over a short distance. In the case of an ion source where the acceleration takes place frcnn the bottoan of the chamber the conditions are different. In the device according to Figure 4 the ions frown the plasma botmdaiy layer are not influenced by collisions and energy losses. Moreover, the plasma extends over the entire area between the plasma source 22 and the substrate holder 24 so that the ion sour.~ce basically covers the same area as the substrate holder 24. With a conventional. ion sourve with grid extraction an extraction grid area is required corresporbding nearly to the beamed upon area on the substrate.
A reactive gas, for example 02, N2 is introduced into the Chamber 20 via a line 34. Due to the plasma in the chamber 20 it is ionized and activated.
The vaporized material 35 of the electron beam gun 21 must also pass through the plasma frcnn the substrate holder 24 so that it bec~es ionized and activated.
the plasma source 22 is electrically insulated from the chamber 20.
Apart frcmn the supplied discharge voltage one therefore in addition also obtains a potential difference between the s~ 22 and the chamber 20.
Tha source 22 assumes a variable positive potential relative to the Chamber 20 while the substrate holder 24 is nearly at the same potential as the chamber 20. The ion energy is determined by the potential difference between the anode tube 26 fed frarn a do current source 36 with a positive potential, and the substrate holder 24. The variable potential of source 22 is a function of the discharge voltage, the partial pressures of the gases

8 and the strength of the magnetic field. Thresh the positive floating potential of the electric field an electxic field is generated which reflects the electrons between source 22 and substrate holder 24. If they do not impinge on the anode tube 26 they are reflected on the cathode potential and can again crane out of the sue. Consequently, osc311ati.ng electron paths with an effective ionization and excitation of gas atcams and molecules are obtained. Due to the repulsion effect generated by the electric fields in the vicinity of the anode the plasma in front of the substrate holder 24 is dcanirsated by ions. This can be recognized by the potential of the substrate holder 24 which is approximately between 3 and 5 volts relative to the ( chamber wall 20. The discham~e parameters are up to 80 volts discharge voltage, 70 A discharge current, and 5 kW plasma power. The pressures are 1 x 10'4 to 8 x 10'4 mbars with a ratio of 02: Ar of up to 4 : 1. The described operation of the plasma source makes it possible to separate the plasma generation process frarn the vaporization process.
All vaporizable starting materials, for example oxides and fluorides, can be vaporized in the vaporizer 21 since no coupling between plasma source and vaporizer source exists.
For the vapor deposition of a scratch-resistant Si02 layer, Si02 ' granulate is used which is vaporized with electron beam generator 40 in the electron beam vaporizer 21. For this granulate a relatively low vaporizer power is required. In order to keep low the vaporizer power even in the case of highly refractive material for example Ta205 a multic~tp crucible with cups of ~ size is preferably used of which only one cx~p 41 is depicted. After pumping the chamber 20 down to a pressure of < 2 x 10'5 mbars the vapor deposition of the layer system is carried out.
The Sio adhesion layer is deposited at a rate of appznximately 0.1 rmys.
The pla~na source 22 is added simultaneously with the opexiing of a vaporizer diaphragm not shown. The source 22 is herein operated with pure azgon at a partial pressure of approximately 2.5 x 10'4 mbars. The discharge curreant is approximately 30 A at a discharge voltage of approximately 30 V. After obtaining the desired layer thickness the plasma source 22 is switched off simultaneously with the closing of the vaporizer diaphragm.
Subsequently, the vapor deposition of the thick Si02 protective layer takes place. Herein the plasma source 22 is also operated with argon.

~~ r ~~~~~~'~
The hardness of the Si02 layer is a ftmction of the plasma dischazge power i.e. current and voltage, the gas pressure, and the coating rate. The hardness gradient of the layer is adjusted with these parameters.
Especially low hardness values are achieved with low plasma power (< 1 kW) at relatively high pressure (approximately 6 x 10-4 mbars), and a high coating rate (appzroximately 5 x 10 nm/s). The greatest harr3ness values were achieved in experiments carried out with a plasma power of approximately 5 kW, at a pressure of 1.5 x 10'4 mbars and at a rate of 0.1 nttS/s. After the desired layer thic)mess has been arhi.eved, the plasma source 22 is switched off with the closing of the vaporizer diaphragm.
Subsequently, the vapor deposition of the first highly refractive layer Ta2o5 takes place. In principle, other highly refractive materials can also be used such as for example titanium oxide, zirconitan oxide, etc. In the highly refractive layers the plasma source 22 is also operated with argon at a pressure of approximately 2 x 10'4 mbars. In addition, oxygen is introduced into the chamber 20 through line 34 with a partial pressure of approximately 4 x 10'4 mbars. An oxygen inlet directly into the plasma source, analogously to inlet 28, is also possible. During the vapor deposition of the tantalwn pentoxide layer the plasma source is operated with a discharge pacer of approximately 5 kW. The coating rate is approximately 0.2 n~/s. The next layer Si02 is deposited in principle like the Si02 protective layer and specifically at a pressure of 2 x 10'4 mbars, a plasma power of apprrncimately 4 kW, and a coating rate of approximately 0.5 rm~/s.
The vapor deposition of the succeeding highly refractive layer takes place with the same parameters as the first highly refracaive layer. The last Si02 layer is deposited like the preceding Si02 layer.
The optimum production parameters of the ~ /4 SiC~ intermediate layer for the attenuation of the oscillations of the spectral curve disposed between the Sio layer arid the protective layer, are a ftinction of the hardness and, consequently, the index of refraction of the protective layer.
The following parameters are suitable: pressure approximately 2 x 10'4 mbars, plasma power approximately 4 kW, rate approximately 0.1 rm~/s.
It is understood that for the generation of atoms, molecu7.es or clusters of the materials, for example Sio or Si02, which are to be applied onto a synthetic lens or the like, instead of an electron beam vaporizer also a ~~ ~ ..~ ~.
to thermal vaporizer or a sp~xttexing cathode can be used. It is only esser~t3a1 that the plasma is generated in a device separated fran the electron beam gun, etc. Thereby that the plasma is generated in the plasma source 22 and the small particles to be applied in a vaporizer source 21, the uniformity of the coatis is especially high. Moreover, the coating parameters caa~ be adjusted largely ir~deper~dent-.ly of one ~, which is of great significaryoe for the product3.on of layers with tcxbghness gradients.
The substrate holder 24 whose lowpx edge is denoted by 33, can be rotated by means of a shaft 42. It can be provided on its underside with rnm~exnus lenses or the like to be cbated. Moreover, the substrate holder 24 ( can have a vaporizer protection not shoran which in the deposition of ir~sul.ating materials prevents the coating of a portion of the surface of the substrate holder with these insulating materials and consequently m~k~es possible the drainiryg of electrical charges via the substrate carrier.
Further details of the device according to Figure 4 can be found in German Patent A~lication P 40 20 158.9 and are therefore not described in i~rther detail.
When with an arrangement according to Fig. 4 the plasma power is put down in kW as a function of time this results in a straight line substantially linearly rising from 0,5 to 5,5 kW, whereas simultaneously the pressure falls almost linearly from 6 s 10 4 mbar to 1 ~ 10 4 mbar. At the same time the rate decre2ses from 5,5 nm/s to almost 0 nm/s.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An optical lens comprising a transparent plastic material substrate and a first layer of SiO which is disposed directly on the substrate and which has a thickness of one atomic layer to 50 nm, and a second layer of SiO2 on the first layer, characterized in that the second layer has a thickness of at least 500 nm and comprises at least two regions having different hardness, the region having the lower hardness being adjacent to the first layer.

2. The optical lens according to Claim 1, characterized in that the second layer has a thickness of 3000 to 10,000 nm.

3. The optical lens according to Claim 1, characterized in that the hardness of the second layer increases continuously from the first layer up to that surface of the second layer which faces away from the first layer.

4. The optical lens according to claim 1, characterized in that the hardness of the second layer increases from 500 N/mm2 to 4500 N/mm2.

5. The optical lens according to claim 1, characterized in that there is provided between the first layer and the second layer a third layer of a material whose refractive index is less than the refractive index of the substrate and greater than the refractive index of the protective layer.

6. The optical lens according to claim 5, characterized in that the third layer is composed of SiO
where 1 < x <= 2.

7. The optical lens according to claim 1, characterized in that a multilayer coating system is provided on the second layer.

8. The optical lens according to claim 7, characterized in that the coating system has four layers of which two layers are composed of Ta2O5 with two layers of SiO2.

9. The optical lens according to claim 1, characterized in that the first layer has a thickness of nm.

10. The optical lens according to claim 7, characterized in that the coating system has up to six layers of which up to three layers are composed of Ta2O5 and up to three layers of SiO2.

11. A method for the production of a layer with nonhomogeneous hardnesses on a transparent plastic material substrate according to claim 1 in a plasma coating installation, which method comprises the following steps:
arrangement of one or more transparent plastic-material substrates in a substrate holder;
evaporation of SiO in an evaporator with simultaneous irradiation of the substrate with a plasma from a plasma source to form a layer of SiO having a thickness of one atomic layer to 50 nm;
evaporation of SiO2 in an evaporator with simultaneous irradiation of the substrate with a plasma from a plasma source in which process one or more of plasma power, gas pressure and coating rate is altered so that a layer of SiO2 having a thickness of at least 500 nm and having nonhomogeneous hardness is formed on the SiO layer.

12. The method according to claim 11, characterized in that plasma discharge current increases with time.

13. The method according to claim 11, characterized in that the gas pressure decreases with time.

14. The method according to claim 11, characterized in that the evaporation rate decreases with time.

15. The method according to any one of claims 12 to 14 characterized in the that process is altered for about 15 minutes.

16. The method according to claim 12,characterized in that the plasma discharge current increases from about A to 100 A within a time interval of 5 to 20 minutes.

17. The method according to claim 13, characterized in that the gas pressure decreases from approximately 8 x 10 -4 mbar to 1 x 10 -4 mbar within a time interval of 5 to 30 minutes.

18. The method according to claim 14, characterized in that the power of the evaporator decreases within a time interval of 5 to 30 minutes so that the coating rate drops from 10 nm/s to 0.1 nm/s.

19. The method according to claim 11, characterized by the following steps:
a) a plasma discharge current which flows between a cathode and an anode increases from 10 A to 100 A within a time interval of about 5 minutes to 30 minutes;

b) simultaneously with the increase in the plasma discharge current, the pressure of the gas or gas mixture contained in vacuum chamber decreases from 8 x 10 -4 mbar to 1 x -4 mbar;
c) simultaneously with the increase in the plasma discharge current, power of the evaporator decreases.

20. An apparatus for performing the method according to claim 11, comprising;
a chamber in which plasma can be generated;
a substrate holder for holding one or more transparent plastic-material substrates;
a plasma source opposite the substrate holder;
an evaporator next to the plasma source containing SiO;
an evaporator next to the plasma source containing SiO2 granules;
at least one ring magnet above the substrate holder;
means for controlling plasma power of the plasma source;
means for controlling gas pressure; and means for controlling coating rate of the evaporator containing SiO2 granules.

21. The apparatus according to claim 20, characterized in that the plasma source has a cylindrical anode in which an electron emitter is situated and in that said cylindrical anode is surrounded by a cylindrical coil, a gas inlet being introduced into the interior of the cylindrical anode.

22. The apparatus according to claims 20 and 21, characterized in that the plasma source is electrically isolated from the vacuum chamber.