ES2354351B1 - OPTICAL AND / OR SOLAR LENS AND CORRESPONDING MANUFACTURING PROCEDURE. - Google Patents

Abstract

Ophthalmic and / or solar lens and corresponding manufacturing procedure. Ophthalmic and / or solar lens that comprises a substrate of a polymeric material and is coated with a hardener layer. On at least one of its surfaces is covered with a metal layer, a metal of the group formed by Cu, Ag, Al, Au, Ni, Ti, Cr, Mo, Pt, Rh, Zr and mixtures of the foregoing. The thickness of the metal layer is between 1 and 20 nm and the visible reflection of the lens is less than 10%. The lens has an abrasion resistance value greater than 5 BR, good aging resistance and square electrical resistivity on the coated surface of less than 20 ohm / sgr. The manufacturing process comprises a deposition stage, by physical vapor deposition with evaporation by electron gun, of the metallic layer.

Description

Ophthalmic lens and / or the corresponding manufacturing procedure.

Field of the Invention

The invention refers to an ophthalmic and / or polar lens, which comprises a substrate of a polymeric material, and is coated with a hardening layer. The invention also refers to a process for manufacturing an ophthalmic and / or solar lens according to the invention.

State of the art

The coating of lenses, and in particular ophthalmic lenses of a polymeric-organic nature, with hardener layers to improve their abrasion resistance is well known. This coating procedure is performed because the scratch resistance of this type of polymeric lens is much lower than that of mineral lenses. This hardener coating (lacquer) is usually applied by immersion in a bath (poly) siloxane, acrylic, methacrylic or polyurethane and subsequent curing in an oven at temperatures between 100 ° C and 130 ° C. Through this procedure hardener layers of thicknesses between 1 micron to 3 microns are obtained. Another possible technique to perform the hardening coating is by applying lacquers by the spinning technique with mechanical characteristics similar to the previous ones but with a productive process that only performs one lens face per stage.

For another, it is known to apply anti-reflective treatments AR to reduce reflection.To achieve this anti-reflective effect of visible light, a stack of several layers (typically between 1 and 6), of thicknesses between 10 nm to 150 nm each, is usually performed. This is usually done by PVD (Physical Vapor Deposition) techniques by electron gun or thermal evaporation although there are other techniques such as Plasma enhanced ChemicalVaporDeposition (PeCVD) or Sputtering.

The measurement of the abrasion resistance of a polymer ophthalmic lens is usually carried out in the industrial field by means of the so-called Bayer test of the company Colts Laboratories with operating procedure reference StandardL-11-10-08 and for the resistance to abrasion to the substrate of CR39 substrate. Thus, a value of BR = 10 means that the treated lens is 10 times more resistant to abrasion than a CR39 lens. In the present invention, this test has been used.

A test of measurement of the abrasion resistance under pressure of the lenses called SteelWool SW of the company Colts Laboratories with reference of operating procedure StandardL-1112-08 is also commonly used. This test is also used in the present invention.

On the other hand, ophthalmic and / or solar polymer-based lenses that incorporate an infrared fi lter are known. In some cases, the infrared filter is able to include absorbent pigments in polymeric, typically polycarbonate. However, the available materials are not limited and it is not possible to choose those materials that are optimal for ophthalmic lenses.

Summary of the invention

The object of the invention is to overcome these drawbacks. This purpose is achieved by an ophthalmic and / or solar lens of the type indicated at the beginning characterized in that at least one of its surfaces is covered with a metal layer, where the metal layer is a metal of the group formed by Cu, Ag, Al , Au, Ni, Ti, Cr, Mo, Pt, Rh, Zrymezclasde the above, and a thickness between 1 and 20 nm, and because the visible reflection of said lens, calculated according to ISO 8980-4 (Rv), is less than 10%, preferably less than 2.5%.

Indeed, the inclusion of a metallic layer of one of the indicated metals and within the indicated ranges has a high reflective effect of infrared radiation, specifically of infrared (IR) radiation termed solar according to the EN-1836 standard, which is included within the wavelength range of 780 nm (nanometers) and 2000 nm. In this way, it is possible to include in the lens a solar IR fi lter that acts mostly by reflection. Additionally, this metallic layer has suitable optical transmission properties in the visible spectrum, both for use in solar lenses and for use in non-solar ophthalmic lenses.

Additionally, this layer is suitable to act as one of the necessary layers in a structure of anti-reflective (or interferential) layers capable of reducing the amount of visible light that reflects the lens. The metal layer according to the invention is suitable to be part of this structure, which allows to simplify the total multilayer structure of the lens since this layer is able to perform two functions simultaneously.

Another additional advantage of this metallic layer is that it prevents the accumulation of static electricity in the lens, for example, generated by rubbing the polymer and the lens cleaning process.It is known that supercharged surfaces attract dust spots, which impairs the quality of vision. At present, attempts are being made to avoid the accumulation of static electricity in lails by including a transparent and transparent conduit of Tito (indium oxide and tin). However, the metal layer is much more efficient in this regard thanks to its lower electrical resistivity.

Preferably the metal layer is a metal of the group formed by Cu, Ag, Pt, AlyAu, and very preferably it is Ag.

Advantageously, the metal layer has a thickness between 5 and 15 nm.

In general, the metallic layer will be on one of the surfaces of the lens, however it could be applied on both sides of the lens (the inner shell and the outer shell). Likewise, there will usually be a single metallic layer as indicated, but the possibility could also be contemplated that, within a more complex multilayer structure, it would have included more than one metallic layer as indicated.

Preferably, between the hardened layer and the metallic layer, there is a first layer under the refractive index, which, advantageously, has a thickness of less than 200 nm.

Advantageously, between the first layer with a low index of refraction and the metal layer there is a first layer with a high index of refraction, which preferably has a thickness of less than 100 nm, and most preferably the thickness is between 20 and 50 nm.

Preferably on the metal layer there is a second layer of high refractive index which, advantageously, has a thickness of less than 100 nm, and most preferably the thickness is between 20 and 50 nm.

Advantageously, the first and second layers of the refractive index are of a material of the group consisting of oxides, nitrides or oxinitrides of Zr, Ti, Sb, In, Sn, Ce, Zn, Ta, Nb, Hf and mixtures of the above, and preferably ZrO2.

Preferably on the second layer of high refractive index there is a second layer of low refractive index which, advantageously, has a thickness of less than 200 nm. It is particularly advantageous if the thickness is between 20 and 50 nm.

Both the first and second layers of low refractive index are preferably SiO2.

Advantageously between at least one of the high refractive index layers and the metal layer there is an interface layer of a group material consisting of Si, Cr, Ti, Ni, Ni / Cr, SnO2, Al2O3, AlN, ZnO, SiOx, SiO / Cr, SiO2 / Al2O3, ITO, and MoO3. In the case of a material of the type SiO2 / Al2O3, it is advantageously the material called “Lima”, which is SiO2 with 5% of Al2O3. Preferably the interface layer has a thickness of less than 10 nm, and most preferably the thickness is between 1 and 3 nm.

Preferably on the hardener layer there is an initial interface layer, which is of a material of the group consisting of Si, Cr, Ti, Ni, Ni / Cr, SnO2, Al2O3, AIN, ZnO, SiOx, SiO / Cr, SiO2 / Al2O3 , ITO, and MoO3, and which has a thickness of less than 20nm. Particularly advantageous is the thickness between 5 and 15nm.

Advantageously, the lens has a primer layer between the substrate and the hardener layer.

A particularly advantageous embodiment of the invention consists of an ophthalmic and / or solar lens comprising a substrate of a polymeric material and is coated with a hardened layer and comprising, on the hardener layer, the following layer structure:

[a] an interphase layer of between 6 and 10 nm thick,

[b] a layer of interface of Crde between 1 and 3 nm thick,

[c] said metallic layer, of Ag, between 6 and 12 nm thick,

[d] a layer of interface of Crde between 1 and 3 nm thick,

[e] a high refractive index layer, of ZrO2, between 20 and 30 nm thick,

[f] a second layer of low refractive index, of SiO2, between 30 and 50 nm thick.

This structure is particularly interesting for solar lenses.

In general, it is advantageous that the lens always includes a hydrophobic outer layer, preferably perforated, which advantageously has a thickness between 2 nm and 40 nm.

Preferably, the lens according to the invention has a transmittance in the infrared solar IR spectrum and a transmittance in the visible TV spectrum, both calculated according to the EN 1836 standard, such that its TV / IR ratio is less than or equal to 1, with TV being less than 80%. This is particularly interesting for sun glasses.

Alternatively, the lens according to the invention preferably has a transmittance in the infrared solar spectrum IRR 80% and a transmittance in the visible spectrum TV, between 80% and 100%, both calculated according to EN 1836. This is the preferred case for non-solar lenses. In fact, it is ISO 8980-3 that stipulates the way of calculating the transmittance in the visible spectrum for non-solar ophthalmic lenses. However, the calculation method is the same as that used in the EN 1836 standard, so it is technically equivalent to refer to one or the other standard.

The lens coated with the structure according to the present invention has a visible reflection according to ISO 8080-4 Rv of less than 10%, and preferably less than 2.5%, on the surface where the solar infrared fi lter has been applied.

On the other hand, it is particularly advantageous for the lenses to meet a series of mechanical requirements (in particular abrasion resistance) and aging resistance (resistance to corrosion, resistance to ultraviolet rays) .In this regard, it is particularly advantageous for the lens to meet some (or all) of the following requirements:

-

Have an abrasion resistance value greater than 5, measured in Bayer Ratio (BR) units according to the Bayer test, according to the L-11-10-08 standard of Colts Laboratories.

-

Have a lower abrasion resistance value than 0.2, measured in units. Take the SteelWool test at 3kg for 1 minute and conforms to 0000, according to Colts Laboratories standard L-11-12-08.

-

Do not show visible deterioration after the tests of point 4.6.10.2 of resistance to immersion to saline solutions and point 4.6.10.1 of severe abrasion of MIL-F-48616A.

On the other hand, it is particularly advantageous for the lens to have a square electrical resistivity value on the coated surface of less than 20 Ω / sgr, measured according to the ASTMD-254 standard. Indeed, the metal layer has a decisive effect on the square electrical resistivity of the lens set. This electrical resistivity will depend directly on the thickness of the metal layer, so that an expert in the matter will be able to establish a correlation between the square electrical resistivity of the lens and the thickness of the metal layer, taking into account the nature of the metal chosen to form the metal layer. Therefore, the value of the square electrical resistivity of the lens can serve as an indicator of the reflective properties in the infrared spectrum of the lens, and will also serve as an indicator of the goodness of the lens's electrostatic properties.

The invention also aims at a manufacturing process for an ophthalmic and / or solar lens according to the invention characterized in that it comprises a deposition stage, by physical vapor deposition with evaporation by electron gun, on at least one of the lens surfaces, of a metal layer as indicated above.

Brief description of the drawings

Other advantages and characteristics of the invention can be seen in the following description, in which, without any limitation, some preferred embodiments of the invention are mentioned, mentioning the accompanying drawings. The figures show:

Fig. 1, a schematic view of a cross section of an embodiment of a lens according to the invention.

Fig. 2, a schematic view of a cross section of a solar infrared fi lter coating according to the invention.

Fig. 3, a schematic view of a cross section of another solar infrared fi lter coating according to the invention.

Detailed description of embodiments of the invention

Fig. 1 shows an example of a general structure of a lens according to the invention. The lens comprises a base of polymeric material on which there is a primer layer I. The continuation there is a hardening layer E on which the disposition of the solar filter is provided. This coating will then also fulfill other functions, since it can also fulfill other functions, since as a whole, it has anti-reflective properties of visible light, has anti-electrostatic properties (basically derived from the metal layer) and has adequate mechanical and anti-aging properties to comply with the different regulations. Finally, the lens has a hydrophobic outer layer H.

In Fig. 2, the detail of the coating R is shown, in what could be understood as the most complex case.The lower layer of the coating R is an initial interface layer IN 0. On the initial interface layer IN 0 there is a first layer of low index of refraction B1. Then there is a first layer of high index of refraction A1.

On the first layer of high index of refraction A1 a metallic layerM which has, above and below, an interface layer IN1.Next there is a second layer of high index of refractionA2 and, finally, there is a second layer of low index of refraction B2.

This scheme in Fig. 2 is, as already stated, the most generally complete case. It should be borne in mind, however, that not all layers have to be always present. In addition, it should be borne in mind that, although each of the layers has a main function, they all affect to a greater or lesser extent the optical and / or mechanical properties of the assembly.Porello, sometimes it can be the case that conceptually they are different layers, in practice they are made with the same material so that in practice they are physically a single layer.

In general, the layers of low refractive index B1yB2 and the layers of high refractive index A1yA2 are particularly important for achieving the mechanical properties of the lens, so it refers to scratch resistance, while the interface layers IN0, IN1 e IN2 are particularly important to achieve the adhesion, wear and barrier properties against oxidation and diffusion. However, all of them also have optical properties that can be used, such as to achieve the anti-reflective properties of the visible light of the assembly. For its part, the metal layer fulfills the basic function of being the solar IR fi lter by reflection, but it also has optical properties in the visible range that can be used to achieve the objectives of the lens assembly (for example the anti-reflective properties of visible light). This will, of course, depend on the materials and thicknesses used in each case.

In Fig. 3 another example of a coating is shown R. In this case the structure is simpler since it comprises only an initial interface layer IN0 on which an interface layer IN1 is directly located (ie there is not a first layer of low index of Refraction B1 or a first layer of high index of refraction A1) .On the interface layer IN1 is the metal layer My interface interface IN1. Continuation there is a high refractive index layer A2 and a layer under the index of refraction B2. The nomenclature A2 and B2 have been maintained for these layers to be consistent with two layers. since there are no "first layers" in this specific case. However, in this specific case, the metallic layer Mpuedasuplirel effect of the first layer of high refractive index A1 can be achieved.Also the initial interface layer IN0 also collaborates in this regard.

Claims (27)

1.Ophthalmic and / or polar lens, which comprises a substrate of a polymeric material, and is covered with a hardening layer, characterized in that at least one of its surfaces is covered with a metal layer, where metal is a metal layer of the group formed by Cu, Ag, Al, Au, Ni, Ti, Cr, Mo , Pt, Rh, Zrymixes of the above, and a thickness between 1 and 20nm, and because the visible reflection of said lens, calculated according to ISO 8980-4 (Rv), is 10% less.

2.

Lens according to claim 1, characterized in that said metallic layer is of a metal of the group formed by Cu, Ag, Pt, AlyAu, and preferably of Ag.

3.

Lens according to one of claims 1 or 2, characterized in that said metal layer has a thickness between 5 and 15 nm.

Four.

Lens according to any one of claims 1 to 3, characterized in that between said hardened layer and said metallic layer there is a first layer of low refractive index.

5.

Lens according to claim 4, characterized in that said first layer of low refractive index has a thickness of less than 200 nm.

6.

Lens according to one of claims 4 or 5, characterized in that between said first layer of low index of refraction and said metal layer there is a first layer of high index of refraction.

7.

Lens according to claim 6, characterized in that said first high refractive index layer has a thickness of less than 100 nm, preferably between 20 and 50 nm.

8.

Lens according to any of claims 1 to 7, characterized in that on said metallic layer there is a second layer of high refractive index.

9.

Lens according to claim 8, characterized in that said second layer of high refractive index has a thickness of less than 100 nm, preferably between 20 and 50 nm.

10.

Lens according to any of claims 6 to 9, characterized in that said first and second layers of high refractive index are from a group material consisting of oxides, nitrides or oxinitrides of Zr, Ti, Sb, In, Sn, Ce, Zn, Ta, Nb, Hf and mixtures of the foregoing, preferably ZrO2.

eleven.

Lens according to any of claims 8 to 10, characterized in that on said second layer of high refractive index there is a second layer of low refractive index.

12.

Lens according to claim 11, characterized in that said second layer of low refractive index has a thickness of less than 200 nm, preferably between 20 and 50 nm.

13.

Lens according to any of claims 4 to 12, characterized in that said first and second layers of low refractive index are SiO2.

14.

Lens according to any of claims 6 to 13, characterized in that between at least one of said layers of high index of refraction and said metal layer there is an interface layer of a material of the group formed by Si, Cr, Ti, Ni, Ni / Cr, SnO2, Al2O3, AlN, ZnO, SiOx, SiO / Cr, SiO2 / Al2O3, ITO, and MoO3.

fifteen.

Lens according to claim 14, characterized in that said interface layer has a thickness of less than 10 nm, preferably between 1 and 3 nm.

16. Lens according to any of claims 1 to 15, characterized in that on said hardening layer there is an initial interphase layer, where there is initial capacity of a material interface of the group formed by Si, Cr, Ti, Ni, Ni / Cr, SOO2, Al2O3, AlN, ZnO, SiOx, SiO / Cr, SiO2, SiO2, SiO2, SiO2, SiO2, SiO2 where the initial interface has a thickness of less than 20 nm, preferably between 5 and 15 nm.

17.

Lens according to any of claims 1 to 16, characterized in that it has a primer layer between said substrate and said hardener layer.

18.

Lens according to claim 1, characterized in that it comprises, on said hardener layer, the following layer structure:

[a] an interphase layer of between 6 and 10 nm thick, [b] a layer of interface of Crde between 1 and 3 nm thick, [c] said metallic layer, of Ag, between 6 and 12 nm thick, [d] a layer of interface of Crde between 1 and 3 nm thick, [e] a high refractive index layer, of ZrO2, between 20 and 30 nm thick, [f] a second layer of low refractive index, of SiO2, between 30 and 50 nm thick.

19.

Lens according to any of claims 1 to 18, characterized in that it comprises a hydrophobic outer layer, preferably perforated.

twenty.

Lens according to any one of claims 1 to 19, characterized in that it has a transmittance in the solar infrared spectrum IR and a transmittance in the visible spectrum TV, both calculated according to the standard EN 1836, such that its ratio TV / IRR is less than 1, TV being less than 80%.

twenty-one.

Lens according to any of claims 1 to 19, characterized in that it has a transmittance in the infrared infrared spectrum IRR 80% and a transmittance in the visible spectrum TV, between 80% and 100%, both calculated according to EN 1836.

22

Lens according to any of claims 1 to 21, characterized in that it has an abrasion resistance value greater than 5, measured in BR units according to the Bayer test, according to the L-11-10-08 standard of Colts Laboratories.

2. 3.

Lens according to any of claims 1 to 22, characterized in that it has an abrasion resistance value of less than 0.2, measured in units Make the test of Steel Woola 3kg for 1 minute and conforms 0000, according to Colts Laboratories Standard L-11-12-08.

24.

Lens according to any of claims 1 to 23, characterized in that it does not show visible deterioration after applying the tests of point 4.6.10.2 of resistance to immersion to saline solutions and of point 4.6.10.1 of severe abrasion of MIL-F-48616A standard consecutively.

25.

Lens according to any of claims 1 to 24, characterized in that it has a square electrical resistivity value on the coated surface of less than 20 Ω / sgr, measured according to ASTMD-254.

26.

Method of manufacturing an ophthalmic lens and / or only according to any of claims 1 to 25, characterized in that it comprises a deposition stage, by physical vapor deposition with evaporation by means of an electron gun, on at least one of the surfaces of said lens, of said metal layer.

SPANISH OFFICE OF THE PATENTS AND BRAND Application no .: 201130066 SPAIN Date of submission of the application: 21.01.2011 Priority Date: REPORT ON THE STATE OF THE TECHNIQUE 51 Int. Cl.: See Additional Sheet RELEVANT DOCUMENTS

Category

Documents cited Claims Affected

X

WO 2007 071723 A2 (ESSILOR INT et al.) 28.06.2007, pages 3-5; page 6, line 22 - page 8, 1-26

line 8; page 14, lines 7-15; page 18, lines 22-31; examples.

X

EP 1174734 A2 (KONISHIROKU PHOTO IND) 23.01.2002, paragraphs 69-70,74-75,91-94,103-105. 1-3.26

TO

WO 0155752 A1 (SOLA INT HOLDINGS et al.) 02.08.2001, pages 2-6,11-13,16. 1-26

TO

GB 2140581 A (AMERICAN OPTICAL CORP) 28.11.1984, pages 2-3, example 2. 1-26

Category of the documents cited X: of particular relevance Y: of particular relevance combined with other / s of the same category A: reflects the state of the art O: refers to unwritten disclosure P: published between the priority date and the date of priority submission of the application E: previous document, but published after the date of submission of the application

This report has been prepared • for all claims □ for claims no:

Date of realization of the report 25.02.2011

Examiner A. Urrecha Espluga Page 1/4

REPORT OF THE STATE OF THE TECHNIQUE Application number: 201130066 CLASSIFICATION OBJECT OF THE APPLICATION G02B1 / 10 (01.01.2006) G02C7 / 10 (01.01.2006) C23C14 / 20 (01.01.2006) C23C14 / 30 (01.01.2006) Minimum documentation sought (classification system followed by classification symbols) G02B, G02C, C23C Electronic databases consulted during the search (name of the database and, if possible, search terms used) INVENES, EPODOC, WPI, TXTUS, XPESP, NPL. State of the Art Report Page 2/4  WRITTEN OPINION Application number: 201130066 Date of Written Opinion: 25.02.2011 Statement

Novelty (Art. 6.1 LP 11/1986)

Claims Claims 4-16, 18, 20-25 1-3, 17,19, 26 IF NOT

Inventive activity (Art. 8.1 LP11 / 1986)

Claims Claims 1-26 IF NOT

The application is considered to comply with the industrial application requirement. This requirement was evaluated during the formal and technical examination phase of the application (Article 31.2 Law 11/1986).  Opinion Base.- This opinion has been made on the basis of the patent application as published. State of the Art Report Page 3/4  WRITTEN OPINION Application number: 201130066 1. Documents considered.- The documents belonging to the state of the art taken into consideration for the realization of this opinion are listed below.

Document

Publication or Identification Number publication date

D01

WO 2007 071723 A2 (ESSILOR INT et al.) 06/28/2007

D02

EP 1174734 A2 (KONISHIROKU PHOTO IND) 01/23/2002

D03

WO 0155752 A1 (SOLA INT HOLDINGS et al.) 02.08.2001

2. Statement motivated according to articles 29.6 and 29.7 of the Regulations for the execution of Law 11/1986, of March 20, on Patents on novelty and inventive activity; quotes and explanations in support of this statement The object of the invention is an ophthalmic and / or solar lens and the method of manufacturing said lens. Document D01 discloses an anti-reflective coating with antistatic properties for ophthalmic articles. In a preferred embodiment of said coating, it consists of five layers and comprises: a metal layer of a metal chosen from gold, platinum silver or mixtures thereof, preferably silver, and with a thickness less than or equal to 1 nm, and Four layers alternating materials of high refractive index (TiO2, ZrO2, Nb2O5, Y2O3, HfO2, Ta2O5, Si3N4.) and low refractive index (preferably SiO2). The substrate is preferably polymeric and has a primer and a hardening layer on it. The lens obtained has a hydrophobic outer layer, perfluorinated (pages 3-5; page 6, line 22-page 8, line 8; pages 14, lines 7-15, pages 18, lines 22-31; examples). Therefore, the technical object of claims 1-2, 17, 19 and 26 is not new in the light of what is disclosed in D01 (Art. 6 LP). Document D02 discloses an optical element comprising a polymeric substrate with a hardener layer on the same and a multilayer coating, in which one of the layers is metallic (aluminum, platinum, silver) and has a thickness of 1-10nm (paragraphs 69-70, 74-75, 91-94, 103-105). Therefore, the technical object of claims 1-3, 26 is novel in the light of what is disclosed in D02 (Art 6 LP). Document D03 discloses an anti-reflective coating for ophthalmic lenses. Said coating is placed on a polymeric substrate to which a hardener layer has been added and comprises a multilayer in which they alternate high refractive index materials (preferably TiO2 or ZrO2), low refractive index (SiO2) and a layer of a conductive material (ITO). The layers can be obtained by PVD. In a specific embodiment, a lens appears comprising a substrate on which a hardener layer has been added, and a 6 layer coating: ITO (4.4nm), SiO2 (51.6nm), TiO2 (15.5nm), SiO2 (27.8 nm), TiO2 (114.9 nm), SiO2 (81.3 nm), it is indicated that the high material Refractive index TiO2 can be replaced by ZrO2 and the resistivity of said lens is less than 10Ω / □ (pages 2-6, 11-13, 16). Dependent claims 4-16, 18, 20-25 do not contain any features that, in combination with the characteristics of the claims on which they depend meet the requirements of inventive activity. In what with respect to claims 4-16 and 18 the person skilled in the art knows that the stacking of layers in which they alternate High and low refractive index layers, with the materials and thicknesses used, improve the properties of anti-reflective coatings (documents D01, D03; specifically, the relevant parts thereof). The claims 20-25, relating to the values obtained for different properties in different tests, are considered to be they lack inventive activity since they are the result of the composition of the lens (Art. 8 LP). State of the Art Report Page 4/4