Process for the manufacturing of low reflection coating

p0001The present invention relates to a reflection-reducing layer and a method for producing a coating with this reflection-reducing layer and a substrate, in particular safety glass having this coating.

p0002By reflection of visible and non-visible spectral of sunlight, the efficiency of solar light utilization decreases for example in solar heat absorbers or photovoltaic modules, which have as a cover a glass pane. The same applies to greenhouse glazing, which should be generally designed so that with increasing exposure to light, the interior is heated accordingly. Usually, thermally toughened glass sheets thereon antireflection coatings are used for the said glass constructs.

p0003There are anti-reflection from the prior art layers or so-called. Antireflection coatings of magnesium fluoride known. Here, the refractive index of the magnesium fluoride corresponds ideally to the formula (refractive index glass)^1/2 for a very good anti-reflective effect. However, magnesium fluoride is not very resistant to weathering, so the use of these layers, for example, for photovoltaic modules and greenhouse glasses, is severely restricted.

p0004Another example of anti-reflective coatings are those which are applied by the sol-gel method.

p0005Here, the substrate to be coated is immersed in a solution that contains the main film component, usually bound to organic radicals. In the subsequent drying process, the layer component remains on the substrate together with the organic remains. These layers are initially very soft and scratch-prone.

p0006Conventionally, a mixture is used as a starting solution, the silica dispersed in particle sizes in the nanometer range contains. After applying the mixture on the substrate are usually one or more annealing steps. In this case, layers are formed, which contain hollow spaces, so that the refractive index of the layer is lowered in comparison to the refractive index of the bulk material. Depending on the temperature load remain different sized cavities at which scatters the light.

p0007Similar Entspieglungsschichten can be achieved by spraying with solutions and subsequent annealing steps. While a good Schichtdickenuniformität of up to +/- 1% is achieved in the dip coating generally, the layer thickness of +/- 5% are common in the spraying process variations. The antireflection effect depends on the product of refractive index of the layer x layer thickness. Thus, the spray is only suitable for the preparation of optically uniform anti-reflective coatings.

p0008A disadvantage of the immersion coating is that on the one hand, due to either not or only be coated with a different layer thickness due to the different flow behavior near the edge in comparison with the substrate center and the other by a necessary suspension of the wheel, portions of the disc. Another disadvantage of the dip coating is to be conditionally that optically magnified by the expiry of the coating solution on the glass surface adhered thereto particles. All of these effects result in partial areas of the coated substrate must be discarded. Another disadvantage of the dip coating, the subsequent high temperature treatments which are additionally required due to the sensitivity to scratching of the untempered layer, even if the coated glass pane is thermally tempered, for example at 600 ° C.

p0009A further possibility to design the surface of a glass substrate antireflective, is the etching of the surface of a glass sheet, wherein in the etched layer of the mixture of the remaining glass and air takes the desired value for the reduction in reflection. Such etched glass panels etched with hydrofluoric acid. This process requires extensive precautions to ensure safe and environmentally neutral operation. The etchant itself liberates volatile fluorinated substances as hindering the formation of ozone in the upper atmosphere.

p0010A disadvantage of the layers additively or subtractively produced from solutions or dispersions is their relatively open pore structure. This results in the known processes layers with cavities in the range of several to 100 nanometers. The cavities are open toward the surface and can eg., Water or dirt from the environment record. This leads to optical degradation and / or corrosion.

p0011With interference layers systems continue to be significantly higher reflection losses reach than with single layers. In addition to higher demands on the Schichtdickenuniformität and the fact that multiple layers are generally associated with higher production costs than single layers, layer packages reduce such light reflection in the designated range of wavelengths of light. In areas outside of the antireflection layers act reflection increasing.

p0012To a very wideband antireflection z. B. from the ultraviolet to reach up into the infrared region of the solar spectrum, a lot of layers alternating refractive indices in the interference layer package must be superimposed deposited. A so-called broadband coating with interference layers is therefore very expensive.

p0013It is an object of the present invention to provide a single layer with a reduction in reflection over the entire spectrum of sunlight available to be produced environmentally friendly and inexpensive and has excellent resistance to external influences.

p0014This object is achieved with the method of the present invention.

p0015The present invention relates to a process for preparing a reflection-reducing coating on a transparent substrate containing at least one layer containing silicon, oxygen, carbon and hydrogen, is deposited on at least one side of the substrate and subsequently in said at least one layer of carbon and hydrogen content is reduced.

p0016The present invention also relates to a reflection-reducing layer.

p0017It has been found according to the invention that voids in an entirely different mechanism and in another embodiment than from liquids additive or subtractive layers produced by reduction of the carbon and hydrogen content in the at least one layer on the substrate in the layer itself. While arise dimension of the aforementioned processes cavities in the range of the order of several to several tens of nanometers to add a few hundred nanometers, it is possible in the present process to reduce the hydrogen and carbon content so that voids are formed in atomic scale and remain which are approximately homogeneously distributed through the layer.

p0018This leads to a considerable reduction of the reduction of the refractive index against the Siliciumdioxidumgebung, whereby the transmission of sunlight is increased broad-band through the layer. Simultaneously, the layer is precisely because of the homogeneous defect formation significantly less susceptible, such. As compared to a water absorption from the environment.

p0019The single coating produced according to the invention has excellent stability and can usually the thermal tempering process of glass upstream process steps, such as cutting or edging, survive without damage. The formation of the layer on the substrate is carried out conveniently in biasing an uncoated transparent substrate, so that no additional energy input for the production of a non-reflective safety glass is required.

p0020The coating produced by this invention has excellent anti-reflection effect with respect to sun light radiation in the wavelength range from 300 nm to 2500 nm, wherein the transparent substrate has a refractive index n of n> 1.4 and having at least one layer has a refractive index n 'of n' <1.32 ,

p0021In a preferred embodiment of the method according to the invention is first at least a single layer, 5 - 30 atomic% of silicon, 20 - 60 atom% of oxygen, 2-30 atomic% of carbon and 2 - contains 30 atomic% hydrogen, on a transparent structured substrate.

p0022In the subsequent process step, the carbon content is preferably reduced, preferably to <15 at%, in particular <5 atomic% of carbon and hydrogen content to <20 atomic% of hydrogen, and in particular <10 atomic% of hydrogen without any appreciable peripheral cavities (pores) having an average diameter arise> 5 nm.

p0023is preferably in the layer of the porosity of pores having an average pore diameter of> 3 nm less than 10% by volume, in particular less than 4% by volume.

p0024The at least one layer may, depending on the subsequent use of the coated transparent substrate, on both sides of the substrate, either sequentially or simultaneously, be deposited.

p0025In a further preferred embodiment of the method according to the invention at least one layer in a layer thickness in the range of 5 is - 400 nm is deposited on the substrate. In particular, the layer thickness is 50-200 nm, and most preferably it is 60-150 nm.

p0026The method of the invention deposited on the transparent substrate at least one layer is subsequently subjected to a treatment, is reduced in the said at least one layer of the carbon and hydrogen content. This step is preferably carried out by at least one layer is annealed.

p0027It has been found in practice that an annealing of the layer at a temperature in the range 250-800 ° C can be carried out for a period of less than 30 minutes. Particularly good reflection-reducing layer is obtained when at a temperature in the range of a maximum of 700 ° C for a period of time with heating and holding time of less than 15 minutes is annealed.

p0028In an alternative embodiment of the method according to the invention the reduction of the carbon and hydrogen content in the at least one layer can be carried out without annealing in the presence of oxygen. Preferably, an oxygen plasma is used.

p0029In this case, the layer thickness is ≤ 250 nm, preferably 30-250 nm, especially 50-150 nm for the duration of the oxygen treatment, the substrate temperature is between room temperature and 350 ° C preferably between 180 ° C and 350 ° C.. While the rate of oxygen removal with increasing substrate temperature to 180 ° C increased considerably, at substrate temperatures> 180 ° C is only observed a slight increase in the carbon removal rate.

p0030The transparent substrate is, generally to glass, laminated glass, and in particular float glass panes. However, also suitable are plastic plates or plastic films, in particular those plastic foils which are inserted during the production of laminated glass between the glass sheets.

p0031includes the deposition of the at least one layer containing silicon, oxygen, carbon and hydrogen, on the substrate can be effected by a PVD process, a CVD process or a combination of both processes.

p0032In a preferred embodiment of the inventive method the at least one layer by sputtering silicon or silicon dioxide is deposited in a reactive gas atmosphere. As a reactive gas, a mixture of alkenes and / or alkenes with oxygen, argon and / or oxygen can be used.

p0033It is further preferred, the reactive gas admix silicon-containing gases, wherein the concentration of which constitutes ≤ 5 atomic% of the total gas flow.

p0034Alternatively, the deposition of the at least one layer containing silicon, oxygen, carbon and hydrogen, by a CVD process, preferably plasma enhanced, are deposited on the substrate.

p0035In a preferred embodiment, the gas space contains a mixture of oxygen, at least one silicon-containing compound and / or carbon-containing compound and / or a noble gas. The silicon-containing compound preferably contains at least one oxygen atom directly bonded to the silicon atom.

p0036The plasma CVD process can be excited by radiofrequency and / or microwave radiation. The excitation radiation can be supplied to the plasma continuously or time-limited pulses.

p0037In a particular preferred embodiment, the plasma excitation is operated in pulsed mode. With this procedure, one reaches the representation of the layer composition in the form of a gradient, where the pulse interval is used for to control the composition of the layer. Shorter pulse intervals have an increase of carbon content in the layer under otherwise identical deposition result. Merely by variants of the pulse pause, the construction of a gradient is possible.

p0038In this embodiment, the pulse duration in the range of 0.1 to 10 ms and the pulse pause is varied in the ratio 1: 1 to 1: 500 is set for the pulse duration.

p0039The layer may also be an arrangement of a plurality of series connected deposition sources are deposited. The substrate passes through different deposition sources, which layer source builds for source. Through variations in the gas composition and / or the duration of the pulse pause as gradient layers can be produced.

p0040In a preferred layer structure of the carbon and hydrogen content is reduced with increasing distance from the substrate surface in the anti-reflective layer. The change in concentration can be carried out continuously or in jumps. In a preferred embodiment, an anti-reflection layer is deposited in two parts on at least one side of the substrate, which substrate-near part, S₁, Prior to the removal of carbon from the film, from 5 to 30 atomic% silicon, 20 - 60 atom% of oxygen, 2-30 atomic% of carbon - preferably ≥ 15 atomic% of carbon - and 2 - 30 atomic% of hydrogen - preferably ≤ 15 atomic% hydrogen - covers and more distant from the substrate layer, S₂, 20 - includes 20 atomic% hydrogen - 35 atomic% silicon, 40 - 67 atomic% oxygen and 0 - 15 atomic% of carbon and. 5 The ratio of the layer thicknesses of the two areas dS₁: dS₂ is preferably>. 5

p0041The surface of at least one layer may be finally adjusted hydrophobic. This hydrophobization is effected by a further treatment in at least one of silicon and carbon-containing plasma.

p0042Another hydrophobization may be effected by a further cover layer is deposited, consisting essentially of carbon and fluorine.

p0043The thickness of the cover layer should be at least 0.3 nm. The carbon and fluorine-containing layer can also be deposited by a plasma treatment in a flouriertem hydrocarbon.

p0044The benefits of Hydrophobisierungsschicht is that water or other hydrophilic media can not or only with difficulty interacting with the layer. The ease of purification of the layer and its longevity increases. In addition, the hydrophobic layer or surface layer causes water condensed only in large drops and run this from a little obliquely inclined substrate rapidly. Thus, the light transmission is ensured from the atmosphere already from early in the morning even with condensation (dew). The overall efficiency of a solar collector (heat or electricity) or integrated over time light transmission of greenhouse disc increases.

p0045The inventive anti-reflection layer is disposed on a transparent substrate having a refractive index n of n> 1.4 has. The reflection-reducing layer contains silicon, oxygen, carbon and hydrogen and has a refractive index n 'of n' <1.32 on. The reflection-reducing layer can be produced by the inventive process. The layer is characterized in that the pore proportion of pores with a mean diameter of> 3 nm less than 10% by volume, preferably less than 4% by volume amounts.

p0046The reflection-reducing layer may comprise in a preferred embodiment, a continuously or intermittently varying carbon concentration, wherein the concentration of carbon in the vicinity of the air side of the layer is smaller than in the vicinity of the substrate.

p0047In a further embodiment, an additional Hydrophobisierungsschicht of ≥ 0.3 nm thickness is applied onto the reflection-reducing layer. Preferably, the Hydrophobisierungsschicht comprises at least 50 atomic% carbon.

p0048The produced by the method according to the invention the coating is particularly suitable for substrates, such as safety glasses, z. B. toughened, which are used for example in the construction of greenhouses and solar modules. One example is a cover for a solar collector with thermal and / or photovoltaic operation with an inventively coated toughened.