WO2007007077A1

WO2007007077A1 - Rear projection screen

Info

Publication number: WO2007007077A1
Application number: PCT/GB2006/002549
Authority: WO
Inventors: Roy Alexander; Keith Russell Irons
Original assignee: Ncast Limited
Priority date: 2005-07-09
Filing date: 2006-07-10
Publication date: 2007-01-18
Also published as: GB2436498B; GB0514135D0; GB2428307A; GB2436498A; GB0713477D0

Abstract

A rear projection screen material (1) comprises a layer of transparent film (2) and attached to at least one thereof a layer of a translucent film (4, 4’).

Description

REAR PROJECTION SCREEN

Field of the Invention

This invention relates to a rear projection screen and in particular to a screen for the projection and diffusion of images on to the rear thereof and viewed from the front or rear.

Background of the Invention

There are a number of scenarios where there is a requirement to view a screen from one side but to project images on to the screen from the other side. To achieve this a translucent screen must be used to capture and display the projected images.

Typically screens might use a diffuser, a fresnel or lenticular lens or the screen itself might be beaded in order to capture and display the image projected from the rear. These types of rear projection screens typically suffer from loss of image qualfty, bleaching by ambient light and loss of brightness as viewing angle increases.

In GB 1316395 a laminate is described for use simultaneously or separately, as a projection screen, writing surface, or a board for three dimensional magnetic markers comprising a light- reflective vinyl plastic layer bonded to a transparent polyvinyl fluoride film layer with the exposed surface of the polyvinyl film having either a roughened surface or a pattern of hemi-spherically shaped projections. The laminate includes a steel wire screen.

InJP 5150367 a screen comprising a soft polyvinylchloride sheet is described, a soft polyvinylchloride resin containing pearl pigments is applied to one side of the sheet, and is lined with a woven fabric.

In GB 1529838 a rear projection screen includes a light diffusing layer of wax mixed with a polymer, the polymer serving to increase the strength of the diffusion layer without affecting the optical properties of the wax. The type of wax used in this screen is non-film forming. One or both surfaces is mat or has optical element surface structure such as a lenticular, Fresnel or fly-eye structure).

A rear projection screen with improved projection and viewing qualities would be desirable.

Summary of the Invention

One aspect of the invention provides a rear projection screen material as specified in Claim 1.

Another aspect of the invention provides a process for the manufacture of a rear projection screen material as specified in Claim 20.

Yet another aspect of the invention provides a rear projection screen as specified in Claim 29.

Brief Description of the Drawings

In the drawings, which illustrate preferred embodiments of a rear projection screen according to the invention, and are by way of example:

Figure 1 is cross-section of a screen according to a first aspect of the invention;

Figure 2 is cross-section of a screen according to a second aspect of the invention;

Figure 3 is a schematic illustration of the process and apparatus for manufacturing the screen illustrated in Figure 1;

Figure 4 is a schematic illustration of the process and apparatus for manufacturing the screen illustrated in Figure 2; Figure 5 is a schematic representation of a rear projection screen mounted on a sheet of glass;

Figure 6 is an exploded view of the screen illustrated in Figure 1;

Figure 7a is a schematic illustration of the surface of the translucent film of the screen material;

Figure 7b is a schematic illustration of the surface illustrated in Figure 7a at ten times greater magnification;

Figure 8 is a trace illustrating the roughness of a rough surface of the translucent screen; and

Figure 9 is an illustration of the paths followed by light passing through a screen according to the invention.

Detailed Description of the Preferred Embodiments

Referring now to Figure 1, there is shown a screen material 1 comprising an inner-most layer 2 of transparent material which in the example is a polyvinylchloride (PVC) film, adhesive layers 3, 3' and outer layers 4, 4' of translucent material, which in the example is a polymeric translucent polyvinylchloride film, which in the example is a material known as vinyl etch due to one side of the film having an etched effect. The adhesive layers 3, 3' attach the inner-most layer 2 to the outer layers 4, 4'. In this example the adhesive layer is a composite part of the outer layers 4, 4' and adheres to the inner-most layer 2 when subjected to the process described with reference to Figure 3.

Referring now to Figure 2, a screen material comprises an inner-most transparent layer 11 of polyvinylchloride (PVC), adhesive layers 12, 12' and outer layers 13, 13' of vinyl etch. The adhesive layers 12, 12' attach the inner-most layer 11 to the outer layers 13, 13'. In this example the adhesive layer is a composite part of the outer layers 13, 13' and adheres to the inner-most layer 11 when subjected to the process described with reference to Figure 4. The screen material illustrated in Figure 2 includes an additional adhesive layer 14 on one or both of the outer surfaces of the outer layer 13, 13'. The provision of an adhesive layer 14 on the outer surface of one of the outer layers 13, 13' provides for the screen material to be applied to a surface such as a sheet of glass which might form part of a -window.

In the examples illustrated in Figures 1 and 2 the PVC film forming the inner-most transparent layer 11 is textured on both sides, the pattern of texture preferably being random. Some types of textured films are referred to as mark resistant film. The pattern may be embossed onto the film, typically using a weighted patterned roller. The pattern is illustrated in Figures 7a and 7b.

Figure 3 illustrates die apparatus required for and the process of manufacture of the screen material illustrated in Figure 1 and the process of manufacture. A roll 2'" of transparent PVC film 2 is arranged on a suitable dispenser. Similarly, rolls 3" of vinyl etch forming die outer layers 3, 3' are mounted on dispensers and located respectively above and below the PVC film 2. The three layers 2, 3 and 3' are brought together between rollers 5, 5' at a speed of 0.0208 to 0.04545 metres per second. The rollers 5, 5' press the layers together under a pressure of 40 to 80 pounds per square inch, and their temperature is raised to between 25 and 45 degrees C. The combination of temperature and pressure causes the adhesive 4, 4' to fuse the layers 3, 3' to the layer 2.

The apparatus and process illustrated in Figure 4 differs from that illustrated in Figure 3 in that a roll 14' of adhesive material 14 is arranged on a suitable dispenser beneatii the roll 12" of outer layer material 12. The adhesive material is fed between rollers 15, 15' in the manner as described with reference to rollers 5, 5' above.

The adhesive layer 14 is provided with a backing material on one side thereof. In the screen material 10 issuing from the rollers 15, 15' the adhesive 14 is more strongly adhered to the outer layer 12 than to the backing material 15 so that when the screen is to be attached to a window for example the backing material can be peeled off easily.

In the example die thickness of the inner-most layer 2, 11 is 500 microns widi the diickness of the vinyl outer layers 4, 4', 12, 12' being 80 microns. The thickness of the inner and outer layers is selected according to the rigidity of the resultant screen required. For example the inner-most layer 2, 11 may be between 225 and 500 microns and the outer-most layers may be between 50 and 200 microns.

In another embodiment of die screen material, one or both sides of die PVC film of the inner-most layer 2, 11 has a surface effect such as a sand grain effect. The surface effect causes air and/or adhesive pockets to be formed between the outer surface of die PVC film and the inner surface¹ of die outer layers 3, 3', 13, 13'. These air and/or adhesive pockets create boundaries thereby enhancing the refraction and scattering effects of die screen material. The surface effect may comprise a random pattern.

In another embodiment of die invention rather than the respective sheet materials being bonded together by an adhesive layer, diey are subjected to a combination of temperature and pressure which fuses together the inner and outer sheets.

Referring now to Figure 5, there is illustrated a screen comprising a window 21 having a glass pane 22 to one surface of which is applied a screen 20 of the type illustrated in Fig 2. A projector 23 projects an image onto one side 24 of the screen, the image being displayed on the odier side 25 of the screen. A free standing screen may be fabricated by mounting a sheet of screen material according to die invention in a frame. Alternatively, the screen material may be mounted on optically clear polycarbonate. Referring now to Figure 6, the screen material 1 comprising an inner-most layer 2 of transparent material which in the example is a polyvinylchloride (PVC) film, adhesive layers 3, 3' and outer layers 4, 4' of translucent material, which in the example is a polymeric translucent polyvinylchloride film, which in the example is a material known as vinyl etch due to one side 2' of the film having a roughed surface, which may result from an embossing or etching process. The surface 2" is substantially smooth in the example illustrated in this figure, although both surfaces 2' and 2" may be roughened. The adhesive layers 3, 3' attach the inner-most layer 2 to the outer layers 4, 4'. In this example the adhesive layer is a composite part of the outer layers 4, 4' and adheres to the inner-most layer 2 when subjected to the process described with reference to Figure 3.

Referring now to Figures 7a, 7b and 8, the roughened surface 2' has the effect of providing a nano-lens array in the screen material which scatters and diffuses light. The nano-lens array comprises a random distribution of nano-lens elements 6, each nano-lens element having the appearance of a dimple. The size of each nano-lens element is substantially random within maximum and minimum diameters of 150 to 375 micron. TypicaEy, the density of nano-lens elements 6 is between eight and sixteen elements per square millimetre of material and is preferably twelve per square millimetre of material distributed randomly and having depths varying between one and ten microns. Nano-lens elements each typically include smaller variations 7 in the order of one to three microns in depth and 0.1 to 100 micron in width. In this example the roughened surface T also includes score marks 8 which appear as substantially straight lines and are thought to occur due to the material being pulled through rollers.

Figure 8 illustrates the roughened surface 2' and it can be seen that the surface comprises a series of peaks and troughs as illustrated in Figure 8 occur. These peaks and troughs produce a broad scattering of light, which has a dual effect of providing a very wide viewing angle and scattering incident sunlight, which significantly reduces reflection and reducing bleaching of the image on projected onto the screen. Figure 9 illustrates the paths followed by light passing through the screen 1.

When compared to known rear projection screens, the screen material of the invention gives improved brightness, contrast, image clarity and viewing angle.

Claims

1. A rear projection screen material comprising a layer of transparent film and attached to at least one thereof a layer of a translucent Him.

2. A rear projection screen material as claimed in Claim 1, wherein the translucent film is a polymeric polyvinylchloride film.

3. A rear projection screen material as claimed in Claim 1 or 2, wherein the transparent film is a polyvinylchloride or a polyester film.

4. A rear projection screen material according to any preceding claim, wherein at least one surface of the transparent film has a surface effect

5. A rear projection screen material according to Claim 4, wherein the surface effect consists of a random pattern.

6. A rear projection screen material according to Claim 4 or 5, wherein the surface effect comprises an array of nano-scale lens elements.

7. A rear projection screen material according to Claim 6, wherein the distribution of nano- scale lens elements is between 8 and 16 elements per square millimetre.

8. A rear projection screen material according to Claim 7, wherein the distribution of nano- scale lens elements is twelve per square millimetre.

9. A rear projection screen material according to any of Claims 6 to 8, wherein the depth of nano-lens elements is between one and ten microns.

10. A rear projection screen material according to any of Claims 6 to 9, wherein a nano-lens element itself includes at least one surface effect.

11. A rear projection screen material according to Claim 10, wherein the depth of the surface effect is between one and three microns.

12. A rear projection screen material according to any of Claims 4 or 11, wherein the surface effect is a grain effect.

13. A rear projection screen material according to Claim 12, wherein the grain effect is a sand grain effect.

14. A rear projection screen material as claimed in any preceding claim, wherein the layers of translucent film are bonded to the respective surfaces of the transparent film by an adhesive layer.

15. A rear projection screen material as claimed in Claim 14, wherein the said adhesive is transparent.

16. A rear projection screen material as claimed in Claim 14 or 15, wherein the adhesive layer is applied to one of the transparent film and the translucent film before the said films are brought together.

17. A rear projection screen material as claimed in Claim 16, wherein the adhesive layer is applied to the translucent film before the transparent and translucent films are brought together.

18. A rear projection screen material as claimed in any preceding claim, wherein the transparent and translucent films are attached to each other by subjecting the layered material to a combination of temperature and pressure for a pre-determined duration.

19. A rear projection screen material as claimed in Claim 18, wherein the said combination of temperature and pressure for a pre-determined duration causes the adjacent surfaces of the transparent and translucent films to fuse together.

20. A process for the manufacture of a rear projection screen material as claimed in any of Claims 1 to 19, comprising the steps of: i. bring together layers of transparent and translucent film between pressure exerting means; ϋ. attaching the said layers together by exerting the layers when brought together to a predetermined pressure for a period of time.

21. A process according to Claim 20, comprising the further step of heating the layers of transparent film.

22. A process according to Claim 21, wherein heating occurs whilst the layers are being pressed together.

23. A process according to any of Claims 20 to 26, wherein the pressure is exerted on the layers by a pair of rollers.

24. A process according to Claim 23, wherein the layers are brought together by the said rollers.

25. A process according to any of Claims 20 to 24, wherein the said pressure is in the range of 40 to 80 pounds per square inch.

26. A process according to any of Claims 21 to 25, wherein the heating temperature is between 25 and 45 degrees C.

27. A process according to any of Claims 20 to 26, wherein the period of time is between 21 and 49 seconds for one metre of material to pass through the rollers.

28. A process according to any of Claims 24 to 27, wherein the material passes through the rollers at a speed of 0.0208 to 0.04545 metres per second.

29. A rear projection screen comprising a rear projection screen material as claimed in any of Claims 1 to 19.

30. A rear projection screen material substantially as described with reference to and as shown in Figures 1, 2 and 6 to 9 of the drawings.

31. A rear projection screen substantially as described with reference to and as shown in Figure 5.

32. A process of manufacturing a rear projection screen material substantially as shown in and as described with reference to Figures 3 and 4 of the drawings.