HK1044590A1

HK1044590A1 - Method of fabrication of a device with optical layers

Info

Publication number: HK1044590A1
Application number: HK02104529A
Authority: HK
Inventors: Christoph Moelle; Thomas Küpper; Lars Bewig; Wolfram Maring; Jochen Heinz
Original assignee: Schott Ag
Priority date: 2000-06-17
Filing date: 2002-06-18
Publication date: 2002-10-25
Also published as: DE50113138D1; DE10029905A1; ATE376196T1; EP1164388A2; HK1044590B; EP1164388B1; EP1164388A3

Abstract

A process for producing a component that contains optical layers (2,3,4), comprises applying a number of optical layers onto a plastic substrate (1), using a chemical plasma impulse vaporization technique.

Description

The invention relates to an object consisting of a substrate of a plastic material and a number of optical layers.

A reflector consists of a basically funnel-like body, which is reflectively coated on its inner surface. Reflectors of this type are components of lights of all kinds, such as headlights. They consist of the materials glass, metal or plastic. The metal and plastic reflectors used in the automotive sector are equipped with a metallic reflective surface, which also reflects the heat radiation.

The range of such reflectors is very hot, resulting in temperatures of up to 200°C. If the reflectors are made of glass, there are no problems with the above temperatures.

Cold-coated reflectors made of glass substrates are now used for general lighting and theatre lighting, for example, where the cold-coated reflector only reflects visible radiation and transmits thermal radiation.

Due to the current headlamp geometry in vehicles with metallic coated reflectors, the infrared radiation reflected in this way results in locally high thermal loads on components that follow the radiation path, such as lenses, windshields, etc. Due to this load, these components must now generally be used as glass substrates and/or protected from thermal radiation by special coatings.

In the automotive industry, the weight saving is increasingly a concern, since a reduction in weight contributes to fuel savings. For this reason, efforts are being made to use plastic as a substitute for other materials, such as steel, as far as possible. However, this has not been possible in the case of the glass reflector, since the reflecting surface would have to be fitted with a cold-light mirror.

There are also known methods for the manufacture of articles, including plastic substrates with layers on them. One such method is described in DE 195 23 444 A1. A plastic is coated with a protective layer by means of a plasma-assisted CVD process (PICVD process) by means of an electrical high-frequency discharge at reduced gas pressure. The aim is to achieve the highest possible toughness of this layer to prevent splitting.

DE 197 03 538 A1 describes a process for modifying surfaces of PMMA substrates by applying a protective layer to the surface of the substrate to improve the adhesion of subsequent functional layers. The application of this protective layer is an additional step in the process and therefore entails additional effort and costs.

Other methods for applying thin layers to plastic substrates are described in DE 34 13 019 A1, EP 0 422 323 A1, DE 40 04 116 A1 and others. These include the adhesion of the layer applied to the substrate by the CVD or PICVD method.

DE 40 08 405 A describes the manufacture of optical coatings on a plastic substrate.

The methods used so far have not been satisfactory, and the necessary adhesive strength has not been achieved, but the objects so manufactured are in danger of dissolving the intermediate layer and thus the entire layer package, which may render the object unusable prematurely.

US-A-5369722 describes a method for the manufacture of waveguides that have a bonding layer.

The purpose of the invention is to specify a method by which a plastic substrate can be permanently and reliably coated with optical layers, in particular to achieve a permanent strength of the layers on the substrate and the layers between them.

This problem is solved by the characteristics of independent claim 1.

The inventors have recognized that permanent and reliable fixation of the interchangeable layers on the plastic and the interchangeable layers between them can be achieved by applying the interchangeable layers to the plastic substrate by a very specific process, namely the so-called PICVD process (chemical plasma-pulse evaporation).

In the PICVD methods used so far for applying layers to a substrate, the interface of the substrate is disturbed or destroyed by the energy load involved in its structure, which results in a reduction in the adhesion between the substrate and the adjacent layer. Accordingly, the inventors have recognized that the energy load associated with the plasma discharge must be minimized in order to increase the adhesion. This is both the amount of energy absorbed and the manner in which it is applied.

The invention makes it possible to exploit the inherent advantages of plastic, in particular its low weight and easy deformability, which play a special role in the automotive industry, as well as to avoid the hazards associated with glass splintering.

The high performance plastics are those that are stable up to a temperature of 100 degrees Celsius or more, where the PICVD process is advantageous because the substrate temperature is kept relatively low.

The following substances have proved particularly favourable as plastics: * Cycloolefin polymers (COP) * Cycloolefin copolymers (COC) * or derivatives thereof.

Several properties of COP and COC plastics make components made of COP-COC plastics with optical interference layer systems particularly suitable for use as optical components with/without compensation/coating: (i) high transparency with visible and infrared spectrum, low double refraction → low light losses and low heating due to heat absorption (ii) high thermal mould stability (iii) components made of COP/COC can be manufactured with similar precision to glass (iv) barrier effect, especially against water vapour → advantageous for good adhesion of shift systems

Due to the above characteristics, COP and COC plastics can replace glass substrates in many applications, opening up new possibilities in the design and design of optical systems.

The PICVD process provides a coating technology that is excellent for coating glass and other plastics. An example of this is a plastic reflector with cold reflection, which is of particular interest to the automotive industry. Cold-coated reflectors made of glass substrates are now found in the general lighting area or the theater lighting area.

The basic body of the reflector is thus made of plastic, as proposed, with all its advantages, notably low specific weight and easy deformability, and the problem of fragmentation is eliminated.

The invention also incorporates a reflective surface as a cold-light mirror, which is conveniently composed of multiple layers of different refractive coefficients, reflecting visible radiation and transmitting infrared radiation (cold-light mirror principle).

According to the invention, it has been shown that the alternating layers can be reliably and permanently fixed to the plastic when applied to the plastic substrate by a very specific method, namely by the plasma-pulse process or by chemical vaporization or by phase-pulse-chemical vaporization.

Due to the temperature load, only high-performance plastics that are stable to at least 100°C are better suited. To apply hard, durable cold light layer systems, usually high thermal loads of the substrate are required, which a plastic reflector cannot withstand without damage. Here the PICVD process is suitable, which as a pulsed process only causes a small energy input into the substrate and thus keeps the substrate temperature low. On the other hand, high pulse energy densities are generated in the plasmas, which produce hard and durable layers.Err1:Expecting ',' delimiter: line 1 column 349 (char 348)to a layer close to the next functional layer which is essentially the same or similar to the next inorganic layer.

The invention is applicable to all types of coating, the layer characteristics being controlled by the raw materials used and by the operating parameters of the plant, the layer characteristics being modifiable to a large extent, the intermediate layer being generally a so-called gradient layer composed of several layers, in which the layer near the substrate is essentially the same as the substrate and the layer far from the substrate is essentially the same as the functional layer.

The invention can also be used in the so-called remote PICVD procedure, where the plasma chamber and the coating chamber are known to be separated from each other.

The following is a detailed description of the invention: Figure 1 shows a body of the invention in a perspective cross-section. Figure 2 shows a device for coating a substrate in a schematic.

In Figure 1 a substrate is shown. On this one an intermediate layer 2 is applied. This has an adhesive mediator - anti-scratch function. It is reliably anchored to the substrate because it was applied to the substrate with minimal energy load according to the invention.

Intermediate layer 2 is a so-called gradient layer, made up of several individual layers of different composition, whereby the single layer near the substrate is essentially the same as substrate 1, while the upper, distant substrate layer is essentially the same as a subsequent layer.

The next layer is function layer 3, which performs optical functions, for example.

The end is a layer of deck 4.

The device shown in Figure 2 shall have the following components: A coating reactor 10 carries the substrate 1. You can see a microwave window 30, a microwave cavity 40, a gas inlet 50, and a substrate holder 60.

List of reference marks

1substrate2intermediate layer3functional layer4deck layer10coating reactor30microwave windows40microwave cavity conductor50gas inlet60substrate holder

Claims

A method for producing an object which comprises optical layers (3), comprising the following method steps:
1.1. a bonding agent layer (2) is formed on a substrate (1) made of cycloolefin polymers, i.e. COP, or cycloolefin copolymers, i.e. COC;

1.2. several optical layers (3) which form a cold-light reflector are applied to the bonding agent layer (2); characterized in that

1.3.the bonding agent layer (2) is arranged as a gradient layer between the substrate material and the material of the subsequent optical layer, with the gradient layer being formed from individual layers, starting from a layer which directly follows the substrate and is similar to the same as an organic chemical, up to a layer which is close to the next following optical layer (3) and is similar to the same as an inorganic chemical, and that

1.4. the bonding agent layer (2) and the optical layers (3) are formed by means of a plasma-pulse chemical vapor deposition, i.e. PICVD, with the total duration of the plasma action being at least 1/1000^th of the total action-free time interval during the plasma treatment and being at most equal to said time interval, and that

1.5. an action pulse of plasma action is between 0.1 and 10 ms, preferably between 0.5 and 5 ms.
A method according to claim 1, characterized in that the optical layers (3) have different refractive indexes.
A method according to one of the claims 1 to 2, characterized in that the coating rate during plasma action per unit of time and per unit of surface area is > 10 nanometres/min, preferably > 100 nanometres/min.