WO2009115285A2

WO2009115285A2 - Device for signs

Info

Publication number: WO2009115285A2
Application number: PCT/EP2009/001941
Authority: WO
Inventors: Daniele Danieli
Original assignee: Ddue S.R.L.
Priority date: 2008-03-20
Filing date: 2009-03-17
Publication date: 2009-09-24
Also published as: ITMI20080480A1; WO2009115285A3

Abstract

A device comprising the following parts: a light guiding plate in thermoplastic material, a light source adjacent to at least one edge of the light guiding plate, a reflecting surface placed along the surface of the light guiding plate, called herein lower surface, which is opposite to that from which the light is emitted, on the lower surface of the light guiding plate, hollow elements, having a cone- or truncated cone shape and a circular or elliptic base are present. The arrangement of the hollow elements in the directions both parallel and perpendicular with respect to the edge of the light guiding plate is such that, for a length of 2.54 cm in each of the two directions, the number of said hollow elements is comprised between 3 and 25.

Description

DEVICE FOR SIGNS

The present invention relates to flat or curved plates, lighted by light sources placed on one or more edge lits showing surfaces having an improved brightness that is uniform on the whole lighted surface of the plate.

More specifically, the present invention relates to plates formed of a thermoplastic polymer, preferably acrylic polymers, obtainable with a process that can be scaled up in a simple way.

The plates according to the present invention are usable for preparing lighted signs, even of remarkable sizes.

Devices formed of plates having light sources on one or more edges are known in the prior art. They are used for uniformly lighting signs. These devices, called "backlight units" or "edge light units", are generally formed of a light guiding plate capable to diffuse light on the surfaces of the device. For this purpose the plate can include suitable additives, or one or both surfaces of the plate can be satinized, or dot-print treated.

USP 5,584,556 describes a device for diffusing the light comprising a light guiding plate, a light diffusing plate positioned on the upper surface of the light guiding plate (by viewing the device from the top) , a reflecting surface placed on or adjacent to the lower surface of the light guiding plate, a light source placed on one or both the opposite sides of the light guiding plate (see the Figures of this patent) . The lower surface of the light guiding plate has a series of small protrusions, or of small cavities, or a series of grooves having rough surfaces. The figures illustrate that said protrusions, or cavities, or grooves are arranged according to lines which are parallel to the side of the light guiding plate that is lit by the light source. This architecture can also be in the form of dots aligned according to parallel lines, wherein the dot density increases as the distance from the light source increases. The devices described in this patent however do not show surfaces with a high brightness .

Patent application WO 02/101,448 describes a light guiding plate comprising a series of horizontal V-shaped grooves. They are positioned perpendicularly to the light source placed on one or both the opposite sides of the plate. The grooves are spaced and placed along the light diffusion direction. Both the groove width and the groove depth are gradually increased as the distance from the light source increases (see in particular Figures 11 and 12 of the patent application) . Besides the horizontal grooves a second series of V-shaped grooves, perpendicular to the previous ones, can be present, thus forming a reticule. The distance among the perpendicular grooves is reduced as their distance from the light source increases. According to this patent application a good light uniformity on the plate surface is obtained by using a series of grooves forming a reticule. The drawback is that, if the reticule is not used, a good light uniformity cannot be obtained.

USP 5,779,338 relates to a device for surface lighting formed of a light-guiding plate of transparent material, a light source placed along one edge lit of the device, a light diffusion plate placed on the surface of the light guiding plate from which the light is emitted and a reflecting plate placed on the surface of the light guiding plate that is opposite to the surface with the diffusion plate. On the surface facing the reflecting plate, a series of hollow elements having a conical or polygonal pyramid shape, is drawn. In the first and in the second embodiment of said patent, see Figures from 2 to 5 , both the angle called alpha represented in Fig. 3 by the cone vertex and the angle called beta at the base of the cone must satisfy precise conditions. In the third embodiment, see Fig. 6 of the patent, no conditions for the angles are set. The hollow elements are filled with diffusing material. The surfaces of the device described in this patent do not show a high brigthness.

Patent application WO 2007/147,517 in the name of the Applicant, describes a device for surface lighting comprising a light guiding plate, a light source placed on at least one edge lit of the light guiding plate, and a reflecting surface placed on a surface of the light guiding plate. On the surface of the light guiding plate facing the reflecting plate there is a series of grooves drawn parallel to the edge of the light guiding plate in contact with the light source. The grooves are hollow-shaped and their overall surface, measured by the projections on the lower plate surface, is comprised between 10% and 60% of the plate surface. The devices described in this patent application show surfaces with high brightness and uniform light intensity. However, from the industrial or commercial point of view, it is requested to make available devices that with the same supplied power can provide improved brightness. As a matter of fact, in order to reduce energy consumption, the ratio between the sign brightness and the power absorbed from the light source, must be the highest as possible.

Furthermore, there is a need to have available devices used for the lighted signs whose manufacture is more and more easy from an industrial point of view.

The need was felt to have available a "backlight unit" and/or "edge lit unit" device having the following combination of properties: uniform lighting of the surfaces, even for lighted signs having relatively large surfaces, for example having size of 500x700 mm, or 1,000x700 mm, or 1,000x1,800 mm, etc., obtainable by a simplified industrial process, improved sign brightness, compared with the devices of the prior art, the source lighting power being equal. The Applicant has surprisingly and unexpectedly found a device solving the above mentioned technical problem.

An object of the present invention is a "backlight unit" and/or "edge lit unit" device comprising: a light guiding plate, in thermoplastic material, having a surface from which light is emitted or light emitting surface and on the opposite side of the plate a surface called lower surface, a light source, adjacent to at least one edge of the light guiding plate, a reflecting surface, placed on the lower surface of the light guiding plate, on the lower surface of the light guiding plate hollow elements having a cone or truncated cone shape and a circular or elliptic base are arranged in both parallel and perpendicular directions with respect to the edge of the light guiding plate facing the light source, the number of said hollow elements for a length in each of said directions equal to 2.54 cm is comprised between 3 and 25.

Preferably for a length equal to 2.54 cm (1 inch) in the direction parallel and perpendicular with respect to the edge of the light guiding plate adjacent to the light source, the number of hollow elements is comprised between 4 and 15, more preferably 5-10.

In a preferred embodiment of the present invention, for a light guiding plate with a thickness of 10 mm, the above cone-shaped or truncated cone-shaped hollow elements have the following dimensions : height, or depth of the hollow elements, is comprised between about 0.05 mm and about 3 mm, preferably between 0.1 mm and 2 mm, the dimensions of the base, that is the diameter when the base is a circle, or the longer axis when the base is an ellipse, is comprised between about 0.05 mm and about 3 mm, preferaby 0.1 mm-2 mm.

In the device of the present invention instead of one light source, two light sources are preferably used, placed on opposite lateral edges of the light guiding plate. Light sources placed on all the sides of the light guiding plate can also be used.

The light guiding plate dimensions can have very reduced formats, such as the A4 format, up to a very large one, for example it can have a width of 2 m and any length, even up to a length of 10 m. Preferably the light guiding plate has sizes 500 mm (width) x 700 mm (length), or 700mm x 1,000 mm, or 1,000mm x 2,000 mm.

The thickness of the light guiding plate generally ranges from about 5 mm up to about 60 mm, preferably from about 8 mm to about 15 mm. When the light guiding plate show a high thickness, preferably about 45-60 mm, both the height and the base size of the hollow elements can be optionally increased. The height, for example, can be up to 5 mm. The same value can be reached for the base diameter or the longer axis of the ellipse of the base.

Preferably both the longitudinal and transversal sections of the light guiding plate are rectangular.

Generally the hollow elements have a rough surface.

The base of the hollow elements besides being circular or elliptic, can be also polygonal. In this case the hollow elements have a pyramid- or truncated pyramid shape.

In this embodiment the polygonal base is preferably square or rectangular. In said casees two opposite sides can also show a rounded profile. When the base is rectangular, the opposite rounded sides are the smaller ones. When the base is polygonal, the base dimension is given by the square diagonal or, respectively by the rectangle diagonal. The diagonal length is comprised between about 0.05 mm and 3 mm, preferably 0.1 mm-2 mm.

Preferably the number of the hollow elements increases as the distance from the light source increases. Alternatively, or contemporaneously, it is also possible to change also the sizes of the hollow elements depending on the distance from the light source.

Generally the bases of the hollow elements are not in contact with each other. The reflecting surface is made of any material reflecting light, for example a white surface can be used. Thermoplastic polymers, for example foam PVC, as FOREX^®; metal sheets, in particular an aluminum sheet, or aluminum composites, as DIBOND^®, can be used as reflecting surface.

According to another embodiment of the present invention in place of the reflecting surface, a transparent thermoplatic material sheet can also be used. In this way the advertising signs with two lighted surfaces are obtained.

The polymeric thermoplastic material of the light guiding plate can be for example a (meth) acrylic (co) polymer, poly- ethylenterephthalate, polyethylenterephthalate modified with a glycol, such as for example diethylenglycol, butandiol, hexandiol and 1 , 4-cyclohexan dimethanol; polycarbonate, etc.. Mixtures of various thermoplastic materials can also be used. In particular the (meth) acrylic thermoplastic (co) polymer can be formed of an alkyl (meth) acrylate homopolymer or of a copolymer derived from an alkyl (meth) -acrylate with at least one monomer having one or more ethylene type unsaturations . As alkyl (meth) acrylate, those wherein the alkyl has from 1 to 8 carbon atoms, preferably from 1 to 4 carbon atoms, for example methyl-, ethyl-, propyl-, isopropyl- and butyl- (meth) acrylate, can be mentioned. A particularly preferred monomer is methyl methacrylate . Preferably the termoplastic polymer is formed of methyl methacrylate homopolymers or copolymers of methylme- thacrylate with (meth) acrylic esters or (meth) acrylic acids, in particular methylmethacrylate/alkylacrylate copolymers, preferably ethyl acrylate. The (meth) acrylic thermoplastic (co) polymer comprises from 70% to 100% by weight of alkyl methacrylate and from 0% to 30% by weight, preferably from 3% to 10% by weight, of one or more comonomers containing one or more ethylene unsaturations. The monomers containing one or more ethylene unsaturations are for example selected from C₁-C₈ alkyl-acrylates, styrene, styrene substituted, acrylonitrile, methacrylonitrile, C₁-C₈ alkyl methacrylates different from the alkyl methacrylate used as main comonomer, hydroxyalkyl acryl- ates and methacrylates, alkoxyalkyl or aryloxyalkyl acrylates and methacrylates wherein the alkyl group has from 1 to 4 carbon atoms, acrylamide, methacrylamide, acrylic acid, me- thacrylic acid, maleimides and dimethacrylates of C₁-C₄ alkylen glycol. The acrylic copolymers can be obtained by the known processes, for example by suspension or mass polymerization. The polymerization takes place in the presence of a chain transfer agent, as for example di-unsaturated monocyclic terpe- nes and monounsaturated bicyclic terpenes, as for example ter- pinolene; mercaptanes, as tert-dodecyl mercaptane .

The lower surface of the light guiding plate can optionally show a zone adjacent to the light source which does not contain hollow elements. Generally the width of this zone ranges from 2 cm to 10 cm, preferably from 3 cm to 5 cm. The purpose of this zone is to form in the luminous sign a frame, that is generally not lighted. When the light guiding plate is made of acrylic polymer, preferably polymethylmethacrylate, the frame appears opaque.

The light guiding plate according to the present invention is obtainable by extrusion, casting, or compression molding.

The preparation by casting is carried out in the case of acrylic polymers.

Preferably the light guiding plate edges are polished according to known techniques .

On one or more of the edges of the light guiding plate that are not adjacent to the light source, a reflecting film can be placed, for example a polyester film, for example a Scotch 3M^® polyester tape 850 film, or a reflecting aluminum film, etc ..

The thermoplastic polymer of the light guiding plate can optionally contain light diffusing fillers. They can be of organic and inorganic polymeric type. The polymeric fillers, for example PTFE, have average sizes between 0.1 and 200 micron, preferably from 0.1 micron to 50 micron, more preferably from 1 micron to 15 micron. The amount of organic fillers is between 5 ppm and 1,000 ppm, preferably from 100 ppm to 200 ppm. The inorganic fillers, for example barium sulphate, have average sizes between 0.1 micron and 50 micron, preferably between 0.5 micron and 10 micron. Their amount by weight is in the range 0.01% - 2%, preferably 0.1% -0.8%, still more preferably 0.1% - 0.6%.

Optionally, the hollow elements can be present also on the light emitting surface of the light guiding plate. In another embodiment said surface can optionally be matted.

The hollow elements on the surface of the light guiding plate can be formed by using the conventional equipments available in the art, for example they can be made by laser incisions .

Lighted signs are obtained by positioning on the light surface of the device of the present invention a sheet, generally of plastic material, with an advertising message.

The light source used in the device of the present invention to lit the sign can be of any type, for example it can be formed of a series of LED, generally placed on one or more edges of the device .

It is a further object of the present invention luminous signs comprising the "backlight unit" or "edge lit unit" device according to the present invention.

The devices can also be used for preparing LCD devices, for example screens .

It has been surprisingly and unexpectedly found by the Applicant that with the device of the present invention it is possible to obtain an uniform lighting of the surface, without using, as indicated in the prior art, or light diffusing plates or hollow elements filled with light diffusing materials, or hollow elements having a geometrical shape such that its angles meet specific ranges.

Tests carried out by the Applicant have surprisingly and unexpectedly shown that, the power supplied by the light source being the same, with the device of the present invention an uniform and a more intense lighting of the sign is achieved in comparison with the devices of the prior art, for example those described in the patent application WO 2007/147,517.

Tests carried out by the Applicant have also shown that by increasing in the device of the present invention the number of hollow elements comprised in a length of 2.54 cm above the present upper limit of 25, it is observed a remarkable lowering of light diffused homogeneity on the emitting surface of the light guiding plate.

The following Examples illustrate the invention and do not limit the application scope thereof. EXAMPLES Light system

The light system used is formed of two LED strips, placed on two opposite edges of the light guiding plate, said LEDs having an overall power of 56 W.

Determination of the light intensity diffused on the emitting surface of the light guiding plate

A luxmeter RS 180-7133 model is used.

The luxmeter is moved along a line perpendicular to the two lit edges. At interval points the distance of the luxmeter from one of the edges and the light intensity are measured. EXAMPLE 1

Measurement of the light intensity on the emitting surface of a "backlight unit" device according to the present invention

The device consists of a light guiding plate having 500 mm (width) x 700 mm (length) and 10 mm thickness. On one surface of the plate, by using a laser device, cone-shaped concave elements are made by engraving the light guiding plate surface. Said cone-shaped hollow or concave elements have a base diameter between 0.8 mm and 1.1 mm and heigth between 0.7 mm and 1.0 mm. The cone-shaped hollow elements are arranged in directions parallel and perpendicular with respect to the edge of the light guiding plate adjacent to the light source such that, for a length in each of the two directions equal to 2.54 cm, there is a number of hollow elements comprised between 4 and 7. The cone-shaped hollow elements show a rough surface.

It is calculated that the total area taken by the bases of these grooves is not lower than 7% and not higher than 17% with respect to the lower surface of the plate.

A reflecting surface is placed on the surface of the light guiding plate engraved with the cone shaped hollow elements, by using a white FOREX^® (foam PVC) plate.

By using the above described method of determination of light intensity, light intensities on the emitting surface of the device of the example have been measured. The light intensities are reported in Table 1. EXAMPLE 2 Comparative

Measurement of the light intensity on the emitting surface of a "backlight unit" device according to WO 2007/147,517

The used device consists in a light guiding plate having 500 mm (width) x 700 mm (length) and 10 mm thichness sizes. On the lower surface of the plate grooves are made by using a laser equipmennt . Said grooves have an average width of 1 mm and depth of 0.2 mm. The grooves are spaced in such a way that the total area, measured from the projections of the hollow grooves on the plate surface, is equal to 28% with respect to the total plate surface. The grooves show a rough surface.

A reflecting surface constituted of a white FOREX^® (foam PVC) plate is placed on the surface of the light guiding plate bearing the grooves.

The light intensities have been measured as in Example 1 and are reported in Table 2.

Table 2 shows that the light intensity on the emitting surface of the device of the prior art is uniform but it is lower than that of the device of the invention.

By comparing the data obtained with a device according to the present invention with that of the prior art, it is found that by using the same light source, an increase of light intensity, of about 18-20%, is observed. TABLE 1

TABLE 2

Claims

A "backlight unit" and/or "edge lit unit" device comprising the following parts: a light guiding plate, in thermoplastic material, having a surface from which light is emitted, or light emitting surface, and on the opposite side of the plate a surface called lower surface, a light source, adjacent to at least one edge of the light guiding plate, a reflecting surface, placed on the lower surface of the light guiding plate, on the lower surface of the light guiding plate hollow elements having a cone or truncated cone shape and a circular or elliptic base are arranged in both parallel and perpendicular directions with respect to the edge of the light guiding plate facing the light source, the number of said hollow elements for a length in each of the two directions on the lower surface equal to 2.54 cm, is comprised between 3 and 25.

A device according to claim 1, wherein, for a light guiding plate with a thickness of 10 mm, the cone-shaped or truncated-cone shaped hollow elements are characterized by the following dimensions: the height is comprised between about 0.05 mm and about 3 mm, the diameter when the base is a circle, or the longer axis when the base is an ellipse, is comprised between about 0.05 mm and about 3 mm. A device according to claims 1-2, wherein two light sources are placed on the opposite lateral edges of the light guiding plate .

A device according to claims 1-3, wherein the sizes of the light guiding plate range from the format A4 up to 2 m of width, with length up to 10 m. A device according to claims 1-4, wherein the thickness of the light guiding plate ranges from about 5 mm up to about 60 mm, preferably from about 8 mm to about 15 mm.

6. A device according to claims 1-5, wherein both the longitudinal and transversal sections of the light guiding plate are rectangular.

7. A device according to claims 1-6, wherein the hollow elements have a rough surface .

8. A device according to claims 1-7, wherein the hollow elements, have a polygonal base and a pyramid shape or truncated-pyramid shape.

9. A device according to claim 8, wherein the polygonal base is square or rectangular.

10. A device according to claims 1-9, wherein for a length equal to 2.54 cm in the direction parallel and perpendicular with respect to the edge of the light guiding plate adjacent to the light source, the number of hollow elements is comprised between 4 and 15.

11. A device according to claims 1-10, wherein the number of the hollow elements increases as the distance from the light source increases.

12. A device according to claims 1-11, wherein the bases of the hollow elements are not in contact with each other on the lower surface of the light guiding plate.

13. A device according to claims 1-12, wherein the reflecting surface is formed of materials selected from thermoplastic polymers, metal sheets, or aluminum composites.

14. A device according to claims 1-13, wherein in the place of the reflecting surface, a plate in transparent thermoplastic material is used.

15. A device according to claims 1-14, wherein the polymeric thermoplastic material of which the light guiding plate is made is a (meth) acrylic (co) polymer, polyethylente- rephthalate, modified polyethylenterephthalate, polycarbonate or mixtures thereof .

16. A device according to claims 1-15, wherein the zone of the lower surface of the light guiding plate adjacent to the light source does not contain hollow elements.

17. A device according to claim 16, wherein the width of the zone not containing hollow elements, measured in direction perpendicular to the edge of the plate adjacent to the light source, ranges from 2 cm to 10 cm.

18. A device according to claims 16-17, wherein the light guiding plate is made of acrylic polymers.

19. A device according to claims 1-18, wherein the edges of the light guiding plate are polished.

20. A device according to claims 1-19, wherein on one or more of the edges of the light guiding plate wherein the light source is not present, a reflecting film is placed.

21. A device according to claims 1-20, wherein the light guiding plate contains light diffusing fillers, of polymeric and/or inorganic type .

22. A device according to claim 21, wherein the polymeric fillers have average sizes comprised between 0.1 micron and 200 micron.

23. A device according to claims 21-22, wherein the amount of organic fillers is comprised between 5 ppm and 1,000 ppm.

24. A device according to claim 21, wherein the inorganic fillers have average sizes comprised between 0.1 micron and 50 micron.

25. A device according to claim 24, wherein the amount by weight of the inorganic fillers is in the range 0.01%-2%.

26. A device according to claims 1-25, wherein the hollow elements are present on the surface of the light guiding plate from which the light is emitted, or the surface is matted.

27. Lighted signs and LCD devices comprising the devices according to claims 1-26.