FR2836240A1 - Display screen for general public applications, has diffuser fixed to support and is located in focal plane of focusing components, and opaque layer including openings to allow focused light - Google Patents

Abstract

The screen has a support with focusing components. A diffuser (3) is fixed to the support and has an active face away from the support and located substantially in the focal plane of the focusing components. An opaque layer with thickness less than 20 micrometers thick includes openings to allow light focused by the components to pass through. An Independent claim is also included for a method of producing a display screen.

Description

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RETROPROJECTION SCREEN AND
ITS MANUFACTURING METHOD
The object of the invention is a rear projection screen for professional and consumer applications (television, picture walls, etc.).

 Such a screen is described in WO-A-00 67071. This request may be referred to for a discussion of the ideal properties of the screens and for the definitions of contrast, transmittivity and other parameters defining the screens.

 There is still a need for a rear projection screen, having contrast characteristics as good as those of WO-A-0067071, but which is of even simpler manufacture.

 The invention thus proposes, in one embodiment, a screen comprising a support with focusing elements and openings in the vicinity of the focusing points of the focusing elements, a diffuser having an active face turned towards the support and coated with an opaque layer, the opaque layer having openings in the vicinity of the focusing points of the focusing elements.

 In one embodiment, the opaque layer has a thickness of less than 10 micrometers, preferably less than 5 micrometers.

 Advantageously, the openings of the opaque layer have an area less than 10% or even 5% of the total surface of the screen.

1. 1 monodimensionnels, et les ouvertures du support présentent une surface supérieure à 15 %, voire 20% de la surface totale de l'écran. Dans un autre mode de réalisation, les éléments de focalisation sont bidimensionnels, et les ouvertures du support présentent une surface supérieure à 20%, voire 30% de la surface totale de l'écran. In one embodiment, the focusing elements are

1. 1, and the openings of the support have an area greater than 15%, or even 20% of the total area of the screen. In another embodiment, the focusing elements are two-dimensional, and the openings of the support have an area greater than 20% or even 30% of the total area of the screen.

 Advantageously, the support comprises a substrate with focusing elements and a layer having openings on the substrate. In this case, the layer having openings preferably has a thickness greater than or equal to 10 microns, or even greater than or equal to 20 microns.

 Preferably, the diffuser is a holographic diffuser.

 The invention also proposes a method of manufacturing a screen, comprising the steps of: - providing a support with focusing elements and openings in the vicinity of the focusing points of the focusing elements, - providing a diffuser having an active surface coated with an opaque layer;

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 - Application of the diffuser against the support, with the active face of the diffuser facing the support; and - forming apertures in the opaque layer by irradiation through the focusing elements.

 In one embodiment, the step of providing a support comprises: providing a substrate with focusing elements; depositing a layer on the substrate; and irradiating the layer through the focusing elements to form the openings in the vicinity of the focusing points of the focusing elements.

 In another embodiment, the step of providing a diffuser comprises: - the supply of a diffuser and - the application on the active side of the diffuser of an opaque layer by inkjet, flexography or silkscreen.

 Advantageously, the diffuser is a holographic diffuser.

 In one embodiment, the application step comprises: depositing an intermediate layer on the support, and applying the diffuser to the intermediate layer.

 In one embodiment, the intermediate layer is formed of an adhesive film and the deposition step comprises: - the application of the adhesive film on the support, and - the deposition of the film in the openings of the support.

 In this case, the intermediate layer may be formed of a thermoplastic film and the deposition step comprises: - the application of the thermoplastic film on the support, and - the deposition of the film in the openings of the support, the step application of the diffuser comprising heating the diffuser or the support.

 The intermediate layer may also be formed of an adhesive and the deposition step then comprises spraying the adhesive onto the support. In this case, the adhesive may be polymerizable and the spray is followed by a polymerization step in the openings by irradiation through the focusing elements. It is then advantageous that the step of applying the diffuser comprises irradiating the adhesive.

 It is also possible that the adhesive is microencapsulated and that the diffuser application step comprises the application of pressure.

 Other features and advantages of the invention appear in the description which follows of various embodiments of the invention, given by way of example and with reference to the figures which show:

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Figure 3 : écran du type holographique à microbilles comme éléments de focalisation ; Figures 4 et 5 : différents modes de collage du diffuseur holographique sur le substrat ; Figure 6 : écran très haut contraste à diffuseur classique Figure 7 : écran holographique à structure voisine de l'écran de la figure 6. Figure 1: holographic type screen according to the invention; Figure 2: another screen of the holographic type according to the invention;

Figure 3: screen of the holographic type with microbeads as focusing elements; Figures 4 and 5: different modes of bonding the holographic diffuser on the substrate; Figure 6: Very high contrast screen with conventional diffuser Figure 7: Holographic screen similar structure of the screen of Figure 6.

Figure 8: high-contrast screen diffusing structure with microbeads of a few microns in diameter.

 The characteristics of the screen are a contrast (C> 500) and a very high optical transmission (T0, 75), a high resolution if necessary for the intended application, a controlled directivity light emission increasing the screen brightness for the angles of vision interesting the application. At the exit of the Fresnel optics of the overhead projector, the back projection screen receives a collimated luminous flux that it focuses by a multitude of focusing elements in openings made in an opaque layer, at the exit of this opaque layer, lead to a controlled directivity light emission. The focusing elements are micro lenses, lenticulars or micro-beads.

 FIG. 1 illustrates the principle of the very high contrast holographic type screen, according to one embodiment of the invention. The substrate 1 with micro-focusing elements comprises a thick layer 2 with wide openings. The sum of the thicknesses of the substrate 1 and the layer 2 is equal to or very close to the focal length of the micro-focusing elements of the substrate 1.

 The holographic diffuser 3 blackened over its entire active surface, except at the focusing points of the micro-focusing elements of the substrate 1, is adhered to the outer face of the layer 2. At the focusing points, the holographic diffuser present in the openings of the black microlayer an active surface less than 10% or even 5% of the total screen area. Thus the holographic diffuser has its active face towards the projector as specified by the manufacturer; with the active face turned upside down towards the observer, the holographic diffuser emits abnormally high light at a high angle to the normal at the expense of the intermediate angles.

 The openings of the black microlayer made on the active surface of the holographic diffuser are therefore in contact with an air chamber; this protects the active holographic layer in the openings of the black microlayer from being in

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 contact with glue that would annihilate its diffusing properties with undesirable generation of "hot spot" in the transmitted images.

 On the outside, towards the observer, the screen may be provided with an anti-reflective layer.

 This screen of the holographic type is very innovative compared to the state of the art for which the holographic layer is stuck on a tinted substrate with optical transmission T = 0.5 which leads to an optical efficiency and a screen contrast limited.

 A method of manufacturing the screen of Figure 1 is as follows.

 On the substrate 1 provided with micro lenses or lenticulars on one side and of a thickness of a few tens of microns less than the focal length of the focusing elements, is applied by the known means (screen printing, etc ...) a layer of black ink a few tens of microns thick; the wide openings in the black layer 2 are produced for example by YAG laser irradiation (= 1060nm) focused by the focusing elements that concentrate the YAG energy in the black layer causing the local spraying thereof in the form of dust and smoked; the width of the openings is obtained by widening the YAG irradiation cone of the focusing elements.

 Another method of producing layer 2 is to coat a thick layer of positive photosensitive resin on substrate 1 and to irradiate it with UV rays through the focusing elements and then to develop it to generate the grooves or hollows around the points. of focus.

 Another method of producing the layer 2 is to lay on the substrate 1 a thick layer of a thermoplastic resin low melting temperature (<100 C) loaded graphite so opaque; then to make the openings (grooves or hollow) by YAG laser irradiation focused by the focusing elements; the blackened holographic diffuser is then glued by simple hot lamination on the layer 2.

 Another method of producing the layer 2 is to apply a thick layer of opaque liquid adhesive loaded with graphite and then after drying the YAG laser irradiated by the microelements to clear the openings of the layer 2. A Aqueous adhesive is good. The diffuser 3 is then laminated on the adhesive provided with its openings.

 In all cases, the openings in the thick layer are wide, relative to focusing of the focusing elements. In the case of single-dimensional focusing elements-splines or lenticular screens-the openings in the thick layer may have a size of up to 50% of the surface of the thick layer (or more exactly of the total area of the screen). A size greater than 20 or even 30% is appropriate.

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 In the case of two-dimensional, microlens, micro-bead or other-dimensional focal elements, the apertures in the thick layer may have a size of up to 50% of the surface of the thick layer (or more exactly of the surface area). total screen). A size greater than 15 or even 20% is appropriate.

 The openings in the thick layer can thus be obtained easily, without particular precautions in the manufacture. Compared to the solution proposed in WO-A-0067071, the manufacture is simpler; it is recalled that the openings proposed in this document have an area of 10% or less than 5% of the black layer.

 Moreover, the active surface of the holographic diffuser is blackened by known techniques such as inkjet, screen printing, flexography, etc.

 The black microlayer on the holographic active surface is very thin, a few microns thick at most, just matching the roughness of the active surface to limit the amount of black material to be sprayed later in the form of dust and fumes. The holographic diffuser thus blackened is adhered to the outer layer 2 avoiding any contact of the adhesive with the holographic active surface still blackened at this stage. Adequate bonding processes are described later in Figures 4 and 5 and above.

 Finally, the thin apertures at the point of focus are generated in the black microlayer applied to the holographic surface by a new YAG laser irradiation focused by the micro-focusing elements. Under the impact of the focused laser beam, the black microlayer is sprayed into the adjacent air chamber defined by the openings (grooves or troughs) of layer 2. Dusts from the spray are redeposited on the much larger surfaces delimiting the air chamber (greater than ten times at least in most cases) as the opening surface made in the black microlayer lying on the holographic surface. As a result, the redeposition of the dust does not generate a significant neutral filter on the passage of the light beam and therefore does not substantially reduce the optical transmission of the rear projection screen.

 In the case of lenticular focusing elements which generate grooves in the layer 2 emerging on both sides of the substrate, it is possible to avoid any redeposition of the dust by microcirculation of compressed air in the grooves of the layer 2 during the phase irradiation or YAG laser of the black microlayer applied to the holographic surface.

 Finally, the screen may be provided with an anti-reflection layer or glued on a transparent support itself provided with an external anti-reflection layer towards the observer.

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 In summary, the fluted or dug layer 2 only serves as support and protection by the air chambers for the holographic surface; this layer is not necessarily black, as explained with reference to Figure 2. The high contrast is obtained by the black micro-layer made directly on the open holographic surface at least at the focusing points for the passage of light. Thus, the two functions of the black layer of document WO-A-0067071 are separated: to ensure the presence of air in the vicinity of the points of the holographic diffuser through which the light directed towards the observer passes; and - to limit the contrast by blocking the light around these points of passage of the light.

The first function is provided by the thick layer; this mechanical function is obtained by manufacturing with higher tolerances. The second function is provided by the thin black layer deposited on the holographic screen. This optical function is easily obtained because of the small thickness of the corresponding black layer.

 FIG. 2 represents a variant of the holographic screen of FIG. 1 in that the deposition of the grooved or dug layer 2 is no longer necessary: the substrate 1 is provided directly on the face opposite to the spline focusing elements or hollow made according to the state of the art (molding, extrusion, thermoforming ...); this is possible because of the very wide positioning tolerance of these grooves or recesses relative to the focusing elements.

In other words, the large openings of the layer 2 of Figure 1 are formed directly in the substrate 1. Insofar as these openings have only a mechanical function, it is not necessary that they are arranged in a black or opaque layer.

 To illustrate the dimensions of the microstructures of the screen, consider for example a resolution of 40 lpi (lines per 25.4 mm): - periodicity and sizes of the focusing elements = 640 microns; - focal length = 2.2 mm; thickness of the layer 2 of FIG. 1: a few tens of microns-20 to 50 μm, for example; size of the openings of layer 2 of FIG. 1: 300 microns for example; - thickness of the black microlayer on the holographic surface: of the order of a micron to a few microns; size of the openings in the black microlayer = less than 32 μm or at most 64 μm in the case of splines (lenticular focussing), less than

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rieur à 140 am ou au plus 210 um dans le cas de creux (microlentilles de focalisation) ; - profondeur des cannelures ou creux dans le substrat 1 de la figure 2 : jusqu'à 500 m ; - taille des cannelures ou creux de la figure 2 : 300 um par exemple.

less than 140 am or not more than 210 um in the case of troughs (focusing microlenses); - depth of the grooves or recesses in the substrate 1 of Figure 2: up to 500 m; - size of the grooves or hollow of Figure 2: 300 um for example.

 It will be seen, as explained above, that the openings in the layer 2 of FIG. 1 or the grooves or recesses of FIG. 2 are larger than the openings in the black layer on the holographic diffuser.

 Figure 3 shows the new holographic projection screen using microbeads as focusing elements.

 The transparent substrate 1 with parallel faces serves to support the assembly. The microbeads are bonded to the substrate 1 according to the technique described in the Kodak-Pathé patent FR-A-959,731 of 10/10/49, except that the thermoplastic resin for bonding the beads is not blackened or graphite but remains transparent.

 Regarding the layer 2 and the holographic diffuser 3 blackened, everything is identical to what is described above (Figures 1 and 2).

 The optical index of the microbeads is chosen little higher than that of the thermoplastic adhesive to lead to a greater focal length allowing a consequent thickness of the layer 2; this facilitates the production of large openings in the latter and consolidates the cohesion of the assembly for the subsequent bonding of the diffuser 3.

 We will now describe with reference to FIGS. ? ? various methods of bonding the holographic diffuser 4. These methods apply to the bonding of a holographic diffuser for the manufacture of the screens shown in Figures 1 to 3.

They also apply to the collage of a holographic screen for the screen described in WO-A-0067071.

 FIG. 4 represents a gluing principle of the holographic diffuser 3.

 The high transparency adhesive film 4 is also used for bonding the different stages of LCD TV screens. The standard thickness adhesive film 4 (12 μm, 25 μm, ...) is laminated on the substrate 1 with or without the layer 2 - substrate of FIG. 1, FIG. 2 or FIG. Then, the film 4 stretched on the grooved or recessed structure / bumps is torn and pushed into the grooves or recesses of the substrate 1 under blowing compressed air scanning over the entire surface.

At the top of the bumps, the film 4 is maintained. Finally, the holographic diffuser 3 is glued by lamination without the film 4 coming into contact with the holographic active surface, in the vicinity of the points of passage of the light towards the observer. Since the film is transparent, the presence of the film or

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 fragments of films in the openings of the substrate 1 or the layer 2 is not a problem.

 A low melting point (80 C) EVA (Ethyl-Vinyl-Acetate) type thermoplastic film can replace the adhesive film 4. After blowing to tear and drive the thermoplastic film, the diffuser 3 is hot rolled (80 C) on the thermoplastic film 4 maintained on the bumps of the substrate 1. This is possible taking into account the temperature resistance of the holographic diffuser 3: 100 C for 240 hours.

 FIG. 5 represents the principle of bonding the diffuser 3 by micropulverisation of liquid adhesive or of various glues.

 On the substrate 1 or the layer 2 fluted or hollowed, is applied a thin adhesive layer 5 of the order of one micron or a few microns per micropulverisation swept over the entire surface.

 This adhesive layer may be: a simple aqueous adhesive; a thermoplastic adhesive on which the diffuser 3 will be hot rolled; - U.V glue; initially, it is polymerized in the grooves or recesses by U.V irradiation focused by the focusing elements; in a second step, the diffuser 3 is laminated on the substrate 1 under general U.V irradiation (at all angles) through the substrate 1 to polymerize the adhesive between the bosses of the substrate 1 and the diffuser 3; microencapsulated glue (capsules of the order of a few microns in diameter); under rolling pressure these capsules burst between the bosses of the substrate 1 and the diffuser 3 releasing the glue; at the bottom of the grooves or recesses, the capsules being under no pressure, the glue is not released and the active surface of the diffuser 3 is thus preserved; the microencapsulated adhesive may advantageously be of the U.V type to combine the pressure effects on the bosses and U.V hardening in the grooves or recesses.

 The holographic diffuser diffuses the light simply because of the roughness of the active surface. For a conventional diffuser, the scattering of light takes place in a thick layer of a few microns to a few tens of microns applied on a transparent support.

 Figure 6 shows the conventional diffuser screen with very high contrast and optical transmission. The substrate 1 does not have a fluted microstructure; the support of the conventional diffuser 3 is glued or laminated on the substrate 1. A black microlayer is applied to the outer surface of the diffuser 3 which is in the plane

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 focal point of the substrate focusing elements 1. The openings for the passage of light are made by laser irradiation YAG focused by the lenses; the surface of these openings represents 5 to 10% maximum of the total surface of screen. A substrate provided with an anti-reflection layer may be glued directly to the blackened diffuser 3 as a support.

 FIG. 7 represents a holographic diffuser screen that is close to the screen structure of FIG. 6.

The holographic diffuser 3 is stuck upside down on the substrate 1 without fluted structure; to restore the correct emissivity of the holographic layer with light from the low optical index to the strong index, the roughness of the holographic layer is filled and flattened by a higher optical index layer. This layer can be made by reactive plasma in low temperature (<60 C) plasma equipment and high flow rate (5000 / min deposition rate).

In this case, the indices can be the following: - optical index of the diffuser 3: 1, 4 - optical index of the evaporated layer: 1, 9 for a layer of Si3N4
2.2 for a TiO2 layer
2.2 for a layer of Ta2Os
The presence of the higher optical index layer ensures proper operation of the holographic diffuser-despite the absence of air in front of the active part of the diffuser.

 The external black microlayer responsible for the high contrast is produced and implemented as in the case of FIG.

 A support substrate provided with an anti-reflection layer can be glued directly to the blackened diffuser.

 FIG. 8 represents a high-contrast screen with diffusing structure with microbeads.

 The substrate 1 is provided with a thin black layer 2 (e <20 μm) having openings at the point of focus of the microlenses or lenticular of the substrate 1. The surface of these openings is 5 to 10% less than the total screen area. A layer of microbeads of glass or plastic a few microns in diameter is made on the entire surface by screen printing using as binder a U. V glue.

 Under U.V insolation focused by the focusing elements of the substrate 1, the U.V. glue is polymerized in the openings of the layer 2 causing the hardening and maintenance of the layer of microbeads in the openings. On the black layer, U. V glue not being polymerized due to the absence of U. V., the microbead layer can be removed for recovery. Director of light emission

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 by the screen is related to the optical index of the microbeads, the thickness of the layer of microbeads in the openings of the layer 2.

 The screen can be glued to an external support by means of a transparent adhesive film (identical to the adhesive film 4 of FIG. 4).

 The screen of FIG. 8 can also, because of the photopolymerization process used, be envisaged for the color by using colored microbeads; in this case, the projector sends only white light to the color screen.

 The method of producing the color screen is sequential like that used for the production of T.V screens.

 The screen of FIG. 8 can also be constructed sequentially to finally emit light with variable directivity from the center to the edges for example; for this, the screen production sequences involve microbeads of different index and microlayers of different thickness.

Claims (19)

 1. A screen comprising - a support (1) with focusing elements and openings in the vicinity of the focusing points of the focusing elements, - a diffuser (3) having an active face turned towards the support and coated with a opaque layer the opaque layer having openings in the vicinity of the focusing points of the focusing elements. 2. The screen of claim 1, characterized in that the opaque layer has a thickness of less than 10 micrometers, preferably less than 5 micrometers. 3. The screen of claim 1 or 2, characterized in that the apertures of the opaque layer have a surface less than 10% or even 5% of the total surface of the screen. 4. The screen of claim 1, 2 or 3, characterized in that the focusing elements are monodimensional, and in that the openings of the support have an area greater than 15% or even 20% of the total area of the surface. 'screen. 5. The screen of claim 1, 2 or 3, characterized in that the focusing elements are two-dimensional, and in that the openings of the support have an area greater than 20% or even 30% of the total area of the surface. 'screen. 6. The screen of one of claims 1 to 5, characterized in that the support comprises: - a substrate with focusing elements; a layer having openings on the substrate. 7. The screen of claim 6, characterized in that the layer having openings has a thickness greater than or equal to 10 microns, preferably greater than or equal to 20 microns. <Desc / Clms Page number 12>  8. The screen of one of claims 1 to 7, characterized in that the diffuser is a holographic diffuser. 9. A method of manufacturing a screen, comprising the steps of: - providing a support (1) with focusing elements and openings in the vicinity of the focusing points of the focusing elements, - providing a diffuser (3) having an active face coated with an opaque layer; - Application of the diffuser against the support, with the active face of the diffuser facing the support; and - forming apertures in the opaque layer by irradiation through the focusing elements. The method of claim 9, characterized in that the step of providing a support comprises:

 providing a substrate with focusing elements; depositing a layer on the substrate; and irradiating the layer through the focusing elements to form the openings in the vicinity of the focusing points of the focusing elements. 11. The method of claim 9 or 10, characterized in that the step of providing a diffuser comprises: - the supply of a diffuser and - the application on the active side of the diffuser of an opaque layer by inkjet, flexo or silkscreen. 12. The method of claim 9, 10 or 11, characterized in that the diffuser is a holographic diffuser. 13. The method of one of claims 9 to 12, characterized in that the application step comprises: - the deposition of an intermediate layer on the support, and - the application of the diffuser on the intermediate layer. 14. The method of claim 13, characterized in that the intermediate layer

 is formed of an adhesive film and in that the deposition step comprises: - the application of the adhesive film on the support, and - the deposition of the film in the openings of the support. <Desc / Clms Page number 13>

 15. The method of claim 13, characterized in that the intermediate layer is formed of a thermoplastic film and in that the deposition step comprises: - the application of the thermoplastic film on the support, and - the depression of the film in the openings of the support, the step of applying the diffuser comprising heating the diffuser or the support. 16. The method of claim 13, characterized in that the intermediate layer is formed of an adhesive and in that the deposition step comprises: - spraying the adhesive on the support. 17. The method of claim 16, characterized in that the adhesive is polymerizable and in that the spray is followed by a polymerization step in the openings by irradiation through the focusing elements. 18. The method of claim 16 or 17, characterized in that the adhesive is polymerizable and in that the step of applying the diffuser comprises irradiating the adhesive. 19. The method of claim 16, 17 or 18, characterized in that the adhesive is microencapsulated and in that the step of applying the diffuser comprises applying a pressure.