DE3918859A1 - Coating for optical substrates - e.g. glass or plastic panels, has metal and dielectric layers - Google Patents

Abstract

A coating for optical substrates is formed by one or more basic elements, each consisting of a metal layer having at least one dielectric layer on both sides. USE/ADVANTAGE - The coating is useful on glass or plastic protective panels, goggles, neutral filters, etc., e.g., protective panels for VDUs. It has a surface resistivity of less than 500 ohms/square, has continuously variable transmission which is neutral in the visible range so that colour shifts are avoided, has a reflection of less than 1% in the 400-700nm. wavelength range and less than 0.5% in the 450-650 nm range to give neutral residual reflection with low dependency on the viewing angle, can be coated with plastics, uses inexpensive and controllable coating materials and has optimal reproducibility and stability.

Description

The invention relates to a coating for optical carriers according to the preamble of the first claim.

As optical carriers e.g. Used glass or plastics, their use as protective lenses, goggles, neutral filter or similar Find. Make a special application Protective screens for data display devices. Here is a wide banded reflex reduction desired, their reflection properties show only a slight dependence on the viewing angle, and which is also good electrical conductivity to the high electro to eliminate static fields from the front of the tube and electrical and magnetic stray fields from e.g. the time dampen lenlenk stage. In addition, the disc is certain se absorption in the visible spectral range, around the Contrast of the display increase and eye fatigue to prevent. There are different values depending on the picture tube the absorption felt as optimal.

Currently, the requirements can be met in that the side facing the viewer with a possibly conductive Broadband reflex reduction is provided, the substrate from a absorbent glass and faces away from the viewer a highly conductive layer is applied to the side.

This solution has the following serious disadvantages: Conductive reflections have surface resistances of  1 KΩ /, with which there is hardly any attenuation of the interference fields becomes.

Absorbent glasses are standard with only one transmis sion of approx. 30% or 60% available, the prices being Lich higher than with non-absorbent glasses and  especially with the highly absorbent variant delivery problems exist, since only a few manufacturers worldwide produce in are able. Well conductive materials, such as metals or ITO, have high refractive indices, so that the viewer turned and thus coated side a much higher Re flexion than the uncoated glass surface.

So far, there is no broadband solution for plastics Reflex reduction, good electrical conductivity and controllable Absorption made possible by the use of thin-film systems.

Coatings such as in EP 01 01 033, EP 01 45 201 and US 29 32 590 are not suitable the problems outlined in the following task to solve. The same applies to one of A. Thelen (Seminar 1986 on Glass Coating Technology) proposed system that a thin metal layer with an overlying dielek layer with a low refractive index.

The invention was based on the object of a thin-film system to develop, which with the known coating processes can be produced and has the following properties.

The surface resistance should be less than 500Ω /; attached a value of less than 100Ω /.

The transmission should be continuously adjustable and in sight range (400 nm λ 700 nm) should be as neutral as possible Avoid color shifts.

The reflection should be less than 700 nm in the 400 nm λ range 1% and in the range 450 nm λ 650 nm less than 0.5%. In doing so, the most neutral possible residual reflection is reduced Desired depending on the viewing angle.  

A coating of plastics should be made possible.

In addition, inexpensive and manageable Coating materials are used.

Optimal reproducibility and resistance to intended Tests are further requirements for the invention.

The task is identified by the distinctive part of the first Claim resolved. Claims 2 to 7 provide further Embodiments of the invention.

Realizing a lower sheet resistance d. H. high electrical conductivity, requires the use of a metal layer close. By varying the thickness of the metal layer the transmission can be adjusted continuously. It has to be done care is taken that only metals are used as metals which is as neutral as possible in the visible spectral range Have transmission and easy to control in thin layers are. These are the elements from Groups IIIB to VIIB and VIII of the periodic table.

However, metals generally have high reflectivity, i.e. Measures to reduce reflexes must be taken. To dielectric materials are used, such as fluorides Alkali and alkaline earth metals and the lanthanides and oxides the metals from groups III to VIII of the periodic table and the lanthanides.

The transmission of the system is essentially determined by the Thickness of the metal layer determined. This is in the range of a few nanometers, so interference effects in the layer themselves are negligible.  

Usually have simple combinations of absorbent Layers with dielectric, practically absorption-free Layers a highly asymmetrical reflection, i.e. a u. U. low residual reflection on one side with one high reflection correlated on the other hand. This he Appearance is very good for the intended applications disadvantageous.

The residual reflection of the side facing the viewer can can be significantly reduced by further dielectric Layers are introduced. But that makes it strong asymmetrical reflection of the system not eliminated. she will even significantly strengthened when you consider the thickness of the metal layer enlarged to resist transmission and area stood to decrease.

The effect of asymmetrical reflection can largely be eliminated when the metal layer determining the transmission in Sub-layers is split, with each sub-layer both adjacent to a dielectric. You can do single Grundele define elements and combine them. In this manner low transmission values can be displayed and a broadband low residual reflection facing the viewer th side with a low reflection of the opposite side realizable.

Additional dielectric layers can be between the basic elements ten to be introduced for improved optical adaptation. At Systems that represent a combination of basic elements, can dielectric common between the metal layers Layers exist.

For average transmission values in the range from approx. 20% to 60% the result is a relatively simple layer structure with only two Layers of metal. The first metal layer is directly adjacent the substrate, followed by a dielectric layer that second metal layer and a further dielectric layer.  

By changing the metal layer thicknesses in this area any transmission values can be set continuously, whereby only a slight change in the thickness of the dielectric is necessary is.

In the production of the layers, the substrate temperature Ts and also the coating rate have a great influence on the optical and electrical properties of the layers. For example, for Ts <280 ° C the surface resistance for a 4-layer system consisting of nickel and MgF ₂ with a transmission of approx. 30% is approx. 50 MΩ /. If the substrate temperature is reduced to approx. 250 ° C, the surface resistance drops to approx. 50Ω /.

In addition to nickel, other metals with a neutral transmission in the relevant spectral range can also be used. MgF ₂ as a dielectric can easily be replaced by SiO ₂ . This makes it possible to use cathode sputtering, which ensures even better layer adhesion and resistance to external attack.

The following table gives a selection of layer systems with the required properties:

For systems that contain tantalum, the transmission in An interesting course depending on the wavelength. It increases from approx. 25% at 400 nm to a value of approx. 60% at 700 nm. This can also result in the cathode ray tube Phosphors are used that have a high shortwave beam have a share of the solution. This is annoying in general and can be eliminate only by additional, complex filter measures.

Temperature-sensitive plastic substrates cannot be used with the optimal temperature for the coating can be processed.

A coating in the permissible temperature range up to approx. 100 ° C leads to poor layer adhesion and to undesirably high surface resistances. Therefore, an adhesive and barrier layer, for example made of SiO ₂ , CrO ₂ , Al ₂ O ₃ , TiO ₂ , Y ₂ O _{3, must also} be applied to the substrate as the first layer.

In addition to the significantly improved layer adhesion by that for the following layers compared to that Plastic surface, significantly changed condensation process Surface resistances in the range from 50Ω / to 100Ω / reached. Serve as an example for a transmission of approx. 30% and with Makrolon as substrate the following layer systems:

2 nm CrO₂ - 4.5 nm Ni - 80 mm MgF₂ - 5.5 nm Ni - 104 nm MgF₂
2 nm CrO₂ - 4.5 nm Ni - 78 mm SiO₂ - 5.2 nm Ni - 97 mm SiO₂

Referring to Figs. 1-4, the invention will be explained in more detail.

Show it:

Fig. 1 layer structure of a base element,

Fig. 2 the layer structure of two basic elements,

Fig. 3 layer structure corresponding to FIG. 1 with an additional metal layer,

Fig. 4 reflection as a function of wavelength; Comparison of the system according to the invention with the prior art.

In Fig. 1, a coating which consists of a basic element and in Fig. 2, which consists of two basic elements, is shown. The optical carrier is designated by 1 . This is coated with one or two basic elements, which each consist of a metal layer 2 or 3 and 4 , which are provided on both sides with 3 dielectric layers 5 to 10 or 11 to 22 . the number of dielectric layers in these examples is given as 3 on each side of the metal layers. However, there may also be more or less, just as the number of dielectric layers on both sides of the metal layer and for the individual basic elements may vary. The refractive indices of the dielectric layers are greatest for those layers which adjoin the metal layer and decrease with the distance therefrom.

Fig. 3 shows a layer structure of a base element accordingly the structure in Fig. 1, wherein the first layer applied to the optical carrier's is a metal layer 23 .

In FIG. 4, as an example, the reflections of the system according to Invention 24, consisting of 4.5 nm Ni - 80 nm MgF _{2 to} 5.2 nm Ni - 104 nm MgF _2, a system 25, which in the prior art Thelen was taken and consists of 17 nm Ni - 75 nm SiO ₂ , compared. Both examples are based on a trans mission of approx. 30%. The front and rear reflections of the two systems are shown depending on the wavelength. The curves 26 and 27 show the front and rear reflection 26 a and 27 a of the system 24 according to the invention, while the curves 28 and 29 show the front and rear reflection 28 a and 29 a of the system from Thelen 25 .

The advantage of the invention shown as an example Systems compared to the state of the art is clear here to see. The reflections are about an order of magnitude lower and the symmetry is in relation to the visible Spectral range significantly improved.

Claims (7)

1. Coating for optical carriers, consisting of one or more metal layers and dielectric layers, characterized in that one or more basic elements form the coating, each basic element consisting of a metal layer which is provided on both sides with at least one dielectric layer. 2. Coating according to claim 1, characterized in that the dielectric layers from the metal layer seen are arranged with a decreasing refractive index. 3. Coating according to one of claims 1 or 2, characterized characterized in that in such systems, which from there are several basic elements, the dielectric Layers between the metal layers of two reason elements are assigned to them together. 4. Coating according to one of the preceding claims, characterized in that the first on the optical Carrier applied layer is a metal layer. 5. Coating according to one of the preceding claims, characterized in that the metal layers made of metal len or alloys of groups IIIb to VIIb or VIII of the periodic table exist. 6. Coating according to one of the preceding claims, since characterized in that the dielectric layers in essentially from fluorides of alkali or alkaline earth metals or of lanthanides or of oxides of metals from groups III to VIII of the periodic table or of the lanthanides exist.   7. Coating according to one of the preceding claims, since characterized in that as a first layer a thin optically ineffective adhesive and barrier layer on the optical carrier is applied.