EP0462019B1 - Device for displaying or projecting images or the like - Google Patents

Description

The invention relates to a device for viewing or projecting images or the like, comprising an external outlet face covered by a transparent coating and resistant to abrasion.

Display devices, such as cathode ray tubes and liquid crystal displays, have a transparent front wall, most often made of glass. The image is formed on one side of this wall and is observed on the other side.

The quality of the image observed depends on the physical properties of the material of the wall and its state, in particular the state of the external face.

Likewise, a projection device usually includes an output objective and the quality of the projected image may be degraded by a poor condition of the external surface of the projection objective.

The invention makes it possible to reduce the dependence on external disturbances of the state of the external surface of the transparent front wall of the display device or the state of the external face of the projection objective.

It is characterized in that the abrasion-resistant layer comprises at least one of the following materials: adamantine carbon, Y₂O₃, Al₂O₃, tin and indium oxide with implantation of oxygen. The transparent front wall of the display or projection device is covered with a transparent layer of an abrasion-resistant material, of a hardness substantially greater than that of the material constituting the front wall or the objective, and / or a conductive transparent material.

An anti-abrasive layer reduces the risk of alteration, for example by scratches, of the external face of the front wall or of the lens. A conductive layer makes it possible to prevent the external face attracting dust by accumulation of static electricity.

These provisions are particularly useful when viewing or projecting high resolution images, in particular of high definition television. Indeed, in the latter case, with a total number of lines of the order of 1000 and approximately 1000 points per line, the number of points of the image being of the order of 10⁶, the image elements or pixels are of small dimensions and it follows that alterations, in particular by scratches or by dust, of the external observation or projection face can appreciably deteriorate the image viewed or projected.

In a preferred embodiment, one and / or the other of the abrasion-resistant or conductive layers is associated with an anti-reflection layer making it possible to reduce the coefficient of reflection of ambient light on the external display or display surface. projection.

If several layers are provided, the anti-abrasion layer will preferably be the outer layer.

In one embodiment, a single layer is provided which is both abrasion-resistant and conductive. This layer is for example a conductive tin and indium oxide, the anti-abrasion function of which is achieved by surface densification by implantation of oxygen ions.

It has been found that good results are obtained by using adamantine carbon as an anti-abrasion material. Indeed, this material is not very rough, has a hardness of between 1,500 and 4,000 Kg / mm² and is chemically inert. It is preferable to choose a small thickness, less than 100 Å, so as not to alter the quality of transmission of the transparent wall or of the objective to be protected.

The mechanical and optical properties of adamantine carbon can be adjusted if it is mixed with selected quantities of hydrogen. In particular, the refractive index can be chosen at will between 1.9 and 2.1 with a rate of hydrogen atoms of between 35 and 55%. The advantage of the adjustable choice of the value of the refractive index is that it is thus possible to easily associate an anti-reflection layer with said layer of adamantine carbon.

Adamantine carbon also constitutes a filter opposing the transmission of ultraviolet radiation.

Adamantine carbon can be deposited on a glass wall - generally previously coated with conductive and / or anti-reflective layers - by a chemical vapor deposition method using a plasma starting from a hydrocarbon such than methane CH₄. Of course, other methods of deposition of adamantine carbon are possible: bombardment of a graphite target placed opposite the wall to be covered, combustion of acetylene and hydrogen in the presence of oxygen, etc.

• la figure 1 est un schéma d'un appareillage de dépôt de carbone adamantin sur la dalle d'un tube de télévision selon l'invention,
• la figure 2 est un schéma représentant un autre appareillage de dépôt de carbone adamantin sur la face frontale d'un tube de télévision,
• la figure 3 est un schéma d'une partie de la face frontale de la dalle d'un tube de télévision selon l'invention, et
• la figure 4 est un diagramme illustrant certaines propriétés du tube de la figure 3.

Other characteristics and advantages of the invention will appear with the description of some of its embodiments, this being carried out with reference to the drawings in which:

• FIG. 1 is a diagram of an apparatus for depositing adamantine carbon on the slab of a television tube according to the invention,
• FIG. 2 is a diagram showing another apparatus for depositing adamantine carbon on the front face of a television tube,
• FIG. 3 is a diagram of part of the front face of the panel of a television tube according to the invention, and
• FIG. 4 is a diagram illustrating certain properties of the tube of FIG. 3.

In general, the invention consists in placing on the front face, visible, of a device for viewing or projecting images, a layer of a material opposing abrasion and / or of a conductive material. . Of course, the added layer is transparent.

In addition, it is preferable that the anti-abrasion and / or conductive layer be associated with an anti-reflection layer.

In what follows we will only refer to a cathode ray tube for high definition television. Such a tube has a glass envelope ending, towards the front, by a slab with a front display face.

It is preferable to provide a single layer performing the function of abrasion-resistant and electrically conductive. For this purpose, a tin and indium oxide (ITO) is used, the surface density of which is of great value thanks to an implantation of oxygen carried out by ion bombardment.

This treatment minimizes the risk of scratches. In addition, for an anti-reflection effect, it would be preferable to treat this oxide in such a way that it has a refractive index equal to the square root of the index of the glass constituting the slab of the tube.

Of course, the thickness of the tin and indium oxide layer is sufficiently small, of the order of 10⁻⁶ to 2 x 10⁻⁶ cm (100 to 200 Å), so that it is transparent. . However, this layer remains transparent up to a thickness of the order of 5 x 10⁻⁵ cm (5000 Å) or more.

For the anti-abrasion function, it is preferable to use adamantine carbon having a structure analogous to that of diamonds. In this case, the adamantine carbon, deposited at a thickness of between 4 x 10⁻⁸ and 10⁻⁶ cm (4 A and 100 Å), constitutes the last layer deposited on a layer of conductive and / or anti-reflective ITO.

Adamantine carbon has an amorphous structure, is chemically inert and has a hardness of between 1,500 and 4,000 Kg / mm²; it can be deposited by several techniques. Preferably, the so-called PCVD technique will be used which consists in placing the slab of the tube 10 in an enclosure 11 (FIG. 1) inside which CH₄ methane or another hydrocarbon is introduced and a microwave plasma 12 is formed which cracks the hydrocarbon molecules. Thus hydrogen is separated from carbon; this latter material is deposited on the target 10 _a that constitutes the external face of the slab of the tube.

A deposit of adamantine carbon with a thickness of 2 x 10⁻⁷ to 5 x 10⁻⁷ cm (20 to 50 Å) is obtained in a few tens of seconds.

It may be advantageous for the deposited layer 13 to contain hydrogen. For this purpose the quantity of hydrogen can be adjusted by limiting the proportion of the hydrocarbon molecules which are cracked.

The refractive index of adamantine carbon is between 1.9 and 2.1 if the proportion of hydrogen atoms is between 35 and 55%.

Hat étant la proportion d'atomes d'hydrogène en %.The mechanical properties also depend on the amount of hydrogen. They also depend on the growth rate of the adamantine carbon layer. Thus for a deposit whose growth is 6 x 10⁻⁷ cm (60 Å) / minute the Knoop HK hardness is expressed by the following formula. $$\text{HK (Kg / mm²) = 50 x Hat (\%) - 250}$$

Hat being the proportion of hydrogen atoms in%.

In a variant (FIG. 2) the slab 10 ′ of the tube is placed in an enclosure 11 ′ inside which a high vacuum is produced of the order of 1.33 x 10⁻⁴ Pa (10⁻⁶ torr) . Opposite slab 10 ′ is a graphite target 14. The face of this target which is opposite the external face of the slab 10 ′ is bombarded with ions which tear off carbon ions coming to deposit on the substrate.

In both cases the substrate 10, 10 ′ is heated to a temperature of the order of 200 to 300 ° C.

It is also possible to form adamantine carbon by combustion in the oxygen of a hydrocarbon with hydrogen, the slab being heated to a temperature of the order of 800 ° C. One can also consider a conventional diamond growth technique which consists in heating the slab to a temperature between 600 and 1100 ° C in an enclosure inside which is introduced a tungsten filament heated to 2000 ° C by current flow, this enclosure containing a mixture of 98.5% hydrogen, 1% methane CH₄ and 0.5%, oxygen.

In Figure 3 there is shown schematically an outer surface coating 15 of slab 10 of tube television. On the glass substrate 10, with a refractive index equal to 1.54, is deposited a layer 16 of titanium oxide TiO₂, with a refractive index 2.4 and of thickness 7 x 10⁻⁷ cm (70 , 1 Å), then a layer 17 of silica thickness 5.37 x 10⁻⁶ cm (537 Å) and of index 1.45, then another layer 18 of titanium oxide TiO₂ of thickness 6.093 x 10⁻⁵ (6093 Å), then another layer 19 of silica 6.8 x 10⁻⁶ cm thick (680 Å) and finally adamantine carbon 13 thick 10⁻⁶ cm (100 Å).

Of course, adamantine carbon, index 1.9, can be replaced by ITO.

Layers 16 to 19 have an index adaptation role allowing the anti-reflection function.

With a structure of the type shown in FIG. 3, it has been found that the reflection losses are between 0.5 and 2% for visible radiation. These losses are represented on the diagram of FIG. 4 where the wavelength λ (1 Å = 10⁻⁸ cm) of the light has been plotted on the abscissa and the losses R by reflection on the ordinate.

These reflection losses are valid for incidences below 45 °. The losses increase significantly for higher incidences.

For the anti-abrasion effect the adamantine carbon can be replaced by transparent amorphous carbon or by another hard oxide such as Y₂O₃ or Al₂O₃ (alumina).

Finally, it should be noted that both adamantine carbon and ITO can be used, which poses no particular problem because of the equality of the indices of these materials. In one embodiment, the abrasion-resistant layer is adamantine carbon and it is covered by a thin film of hard and conductive ITO.

Claims (6)

1. Device for displaying or projecting images, including an external exit face (15) covered with a transparent and abrasion-resistant coating (13), characterized in that the anti-abrasion layer includes at least one of the following materials: adamantine carbon, Y₂O₃, Al₂O₃, oxygen-implanted indium tin oxide.
2. Device according to Claim 1, in which the anti-abrasion layer includes adamantine carbon, characterized in that the said layer contains hydrogen.
3. Device according to Claim 1 or 2, characterized in that, the anti-abrasion layer including adamantine carbon, the thickness of the adamantine carbon layer lies between 4 x 10⁻⁸ cm and 10⁻⁶ cm (4 and 100 Å).
4. Device according to any one of the preceding claims, characterized in that the external exit face is covered with a conductive transparent coating.
5. Device according to any one of the preceding claims, characterized in that the external face furthermore has an anti-refection coating.
6. Device according to any one of the preceding claims, characterized in that the anti-abrasion layer is the external layer.

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