EP0197886A1 - Process for manufacturing a flat light source - Google Patents

Abstract

The invention relates to a method for producing a flat lighting unit. The method according to the invention provides that light-guiding channels (16) in the form of transparent rods are arranged line by line on the top of a plate, that the top is covered with a casting compound and that the plate is removed from its underside as far as the casting compound has hardened, that only the light guide channels (16) remain enclosed on three sides by the casting compound forming a film (15).

Description

With regard to the German patent application P 34 34 806.9 or a subsequent application filed under the claim of the priority of this patent application, there is a lighting unit as state of the art in which light guide channels are arranged line by line, in the end faces of which light can be coupled in and along which the light from the light exit areas can be coupled out in the channel wall. The lighting unit there forms part of a scanning device for illuminating and optically scanning an areal template. In this scanning device, the lighting unit is used to illuminate the template in micro-rows, the light reflected from the template being detected column by column with the aid of light receiving elements. The illumination of individual micro-lines can be carried out uniformly over the length of the respective micro-line by continuously coupling light coupled into the micro-line-specific light guide channels on the face side along the respective light guide channel from its channel wall onto the micro line. However, it is also possible for the light to be coupled out successively along the longitudinal axis of the light-conducting channels, for example by means of a sound wave packet that stretches along the light-conducting channel.

The invention is based on a method for producing a flat lighting unit.

Such a lighting unit is described in the magazine "Electronics", Issue 24, 1984 on page 114. The known lighting unit is designed as an electroluminescent display unit, in which individually controllable pixels in the form of individually controllable electroluminescent elements are arranged in 256 rows and 512 columns in a display area. Control and driver electronics for controlling the individual pixels are also integrated in the known lighting unit. The construction depth of the known lighting unit is 0.8 inches (approx. 2 cm).

From US Pat. No. 3,238,859, a lighting unit is also known as part of a photocopying device. The known lighting unit contains a flat electroluminescent layer, which is arranged lying in a film arrangement between two transparent, electrically conductive film electrodes. By applying an alternating voltage to the foil electrodes, the electroluminescent layer is energetically excited so that it illuminates uniformly over its surface.

The invention has for its object to provide a method that enables the production of lighting units with at least line-wise controllable light emission in a very flat design and with comparatively few components; Another object is to enable the production of the flat lighting units in large numbers in a cost-effective manner while maintaining the same quality, with a particularly exact arrangement and design of the light guide channels having to be ensured.

To achieve this object, in a method for producing a flat lighting unit, light-guiding channels in the form of transparent rods are formed line by line on the top of a plate; the top of the plate is covered with a casting compound covering the light guide channels and filling the spaces between the light guide channels, and the plate is removed after the casting compound has hardened to such an extent that only the light guide channels remain enclosed on three sides by the casting compound.

The method according to the invention enables the production of a flat illumination unit with only a relatively small number of components due to the rods forming the light-guiding channels, the illumination unit being of a very flat construction as a result of the rods being thin. After curing, the casting compound forms a film which surrounds the light-guiding channels on three sides, so that only one side of the light-guiding channels is exposed for coupling out light fed into the light-guiding channels; the light guide channels are therefore well protected against external influences and are embedded in the film. Because the light guide channels are arranged on the plate beforehand, a high degree of accuracy can be achieved with regard to their later arrangement in the film.

In various applications for the lighting unit, transparency of the film may be desirable if, for. B. a template to be illuminated line by line through the film should be at least roughly visible or when using the lighting unit in a scanning device the film with the light guide channels is arranged closer to the original as light receiving elements. In these cases, it is to be regarded as advantageous if transparent material is used as the casting compound, the optical refractive index of which is lower than that of the light guide channels. This ensures that the film is transparent on the one hand and on the other hand the light guided in the light-guiding channels experiences total reflection in the border area between the light-guiding channels and the film, as a result of which stray light influences between adjacent light-guiding channels are prevented. A reduction in the effects of scattered light can also be achieved in an advantageous manner in that the light guide channels arranged on the top of the plate are mirrored with the casting compound before being coated.

A particularly inexpensive manufacture of the flat lighting unit according to the inventive method is achieved in that the light guide channels are pressed individually from transparent material and attached to the top of the plate in rows; the plate is detached from the encapsulated light guide channels after covering the light guide channels with the casting compound. To create micropoint-specific light exit areas, when pressing the light-guiding channels, additional notches can be pressed in on their surfaces facing away from the respective surface for fastening on the plate, at which the light coupled laterally into the light-guiding channels is coupled out of them.

A particularly high accuracy of the formation of the light guide channels with regard to their dimensions and their arrangement in the film formed by the casting compound is achieved in that the plate is made of transparent material and that the light guide channels are designed in the form of web-shaped elevations of the plate.

The plate is advantageously cast from transparent plastic using a die which is provided with depressions corresponding to the web-shaped elevations to be formed in the plate. This ensures a particularly precise arrangement and configuration of the web-shaped elevations or the later light-guiding channels in the film.

The transparent plate can be produced, for example, by injection molding, in that the die is used as a press die and the plate is injection molded.

It is particularly advantageous to use a photopolymerizable clear lacquer as a transparent plastic when casting the plate in the die and to harden it by exposure to light. Such a process step is known per se from the publication: "Philips Technical Review", volume 40, 1982, no. 10, page 290, in particular FIG. 4. The clear lacquer is pressed into the recesses of the die by means of a plexiglass pane and cured through the plexiglass pane by irradiation with ultraviolet light. In the method according to the invention, after the clear lacquer has hardened and the light-guiding channels have been cast, the plexiglass pane is detached from the cast light-guiding channels.

To produce the die, grooves are advantageously cut into a substrate layer, the depth and width of which correspond to the height and the spacing between the web-shaped elevations on the transparent plate to be formed; from the side of the substrate layer which has the grooves, a mold impression is obtained which forms the die.

A further solution to the problem stated above is, according to the invention, that a carrier plate with depressions arranged in rows on one side is pressed, the depth and width of which correspond to the cross-sectional dimensions of light guide channels, and that transparent material is introduced into the light guide channels to form the light guide channels. This variant of the method also makes it possible to produce a very flat lighting unit with only a few components, the light guide channels being embedded in the recesses in a well-protected manner against external influences.

If transparency of the carrier plate is desired, the carrier plate is pressed from transparent material, the refractive index of which is greater than that of the light guide channels; In this way it is achieved that the light guided in the light guide channels is totally reflected and no stray light can escape from the light guide channels. A reduction in the effects of scattered light is also advantageously achieved in that the carrier plate is mirrored on its side provided with the depressions before the introduction of the transparent material for the light guide channels.

The carrier plate with the depressions is advantageously produced by casting the carrier plate using a die, in that grooves are cut line by line in a substrate layer to produce the die, the depth and spacing of which corresponds to the cross-sectional dimensions of the light guide channels to be formed, from a first mold pressure is obtained from the side of the substrate layer having the grooves, and a second mold pressure is obtained from this, which forms the die. This process ensures an exact formation of the depressions for the light guide channels.

In order to create micropoint-specific light exit areas along the light-guiding channels, notches are cut into the substrate layer in columns in the transverse direction before the grooves are cut into the substrate layer be cut. These notches advantageously result in corresponding notches in the web-shaped elevations or the depressions, and thus in the processes involving the pressing of a transparent plate with web-shaped elevations, as well as in the process involving the formation of a carrier plate with depressions arranged in rows Light guide channels, so that light rays that are coupled into the end faces of the light guide channels are reflected at the notch surfaces facing the light source so that they strike the channel wall in the light exit area of the light guide channel approximately perpendicularly and can thus emerge therefrom. A uniform decoupling of light along the individual light-guiding channels is advantageously achieved in that the grooves are progressively cut into the substrate layer with increasing depth in the manufacture of the die.

According to a further development of the method according to the invention, the substrate layer itself can be formed in the form of a lacquer layer on a carrier layer.

In view of a high cutting accuracy when cutting the grooves and notches in the substrate layer, a metal plate, for example made of copper or aluminum, can alternatively be used for this.

A particularly simple and therefore inexpensive manufacture of the die for the process according to the invention is achieved in that a silicone rubber impression is used as the mold impression.

In a modification of this, a particularly high accuracy of the formation of the light guide channels with regard to their dimensions and their arrangement can be achieved by applying a conductive layer on the side of the substrate layer having the grooves in order to produce the mold impression, and that in a gaivan bath on the conductive layer, a metal layer is built up which, with sufficient thickness and free of the substrate layer, forms the mold impression (the die). In the case of a lacquer layer as the substrate layer, the conductive layer serves as the basis for the galvanic deposition of the metal layer. If the substrate layer consists of a metal plate, such as. B. of copper, the copper is etched away in the last step for producing the die and the conductive layer - for example a silver coating - serves to stop the etching process on the metal layer forming the die.

• Figuren 1A, 1 B bis 6A, 6B auf schematische Weise einzelne Verfahrensschritte zur Herstellung der flachen Beleuchtungseinheit dargestellt, wobei zunächst die lichtleitkanäle ausgebildet und anschließend in einer Folie vergossen werden; die
• Figuren 7A, 7B bis 9A, 9B zeigen im Hinblick hierauf alternative Teilschritte zur Ausbildung der Lichtleitkanäle mit Hilfe von photopolymerisierbarem Klarlack. Die
• Figuren 10A, 10B bis 15A, 15B zeigen einzelne Schritte einer weiteren Verfahrensvariante zur Herstellung der Befeuchtungseinheit, wobei die Lichtleitkanäle in Vertiefungen einer Trägerplatte eingebracht werden.
• Figur 16 zeigt schließlich einen Ausschnitt aus der fertig hergestellten Beleuchtungseinheit

To explain the method according to the invention are in the

• FIGS. 1A, 1B to 6A, 6B schematically depict individual method steps for producing the flat lighting unit, the light guide channels first being formed and then being cast in a film; the
• In view of this, FIGS. 7A, 7B to 9A, 9B show alternative sub-steps for forming the light-guiding channels with the aid of photopolymerizable clear lacquer. The
• FIGS. 10A, 10B to 15A, 15B show individual steps of a further method variant for producing the moistening unit, the light-guiding channels being introduced into depressions in a carrier plate.
• Figure 16 finally shows a section of the finished lighting unit

Regarding the sectional drawings shown in FIGS. 1A, 1B to 15A, 15B, it should be noted that the partial representations to the right of the dash-dotted dividing lines with respect to the left partial representations are each to be viewed at right angles to the plane of the drawing.

According to a first variant of the method according to the invention, a substrate layer consisting of a thin lacquer layer 2 is applied to a carrier layer 1 (FIGS. 1A, 1B), which can consist for example of a glass plate. In this lacquer layer 2, notches 3 are first cut into columns, which are progressively produced from column to column with greater notch depth. With a preferred gap between the notches 3 of approximately 0.5 mm, the notch depth is in the range from 0.004 mm to 0.5 mm. The notch surfaces 4 of the notches 3 are preferably at an angle of approximately 45 ° to the plane of the lacquer layer 2. In a second method step, grooves 5 with a preferably rectangular cross section are cut into the lacquer layer 2 in the transverse direction to the notches 3. The depth of cut for the grooves 5 is at least as large as that of the deepest cut notch. In view of the dimensions specified for the notches 3, the grooves 5 are preferably of a width of approximately 0.15 mm at a line spacing of approximately 0.5 mm (respectively from the center of a groove to the center of the neighboring groove). The carrier layer 1 with the lacquer layer 2 structured by the incisions forms wine master form.

In a next process step, a conductive layer 6 (shown here disproportionately thick) is applied to the lacquer layer 2, preferably in the form of a metal coating in a sputtering chamber. however, it is also possible to evaporate this metal coating. This process step serves to prepare the master mold for a subsequent electroplating process, in which a metal layer 7 (FIGS. 2A, 2B) is built up on the conductive layer 6 in a galvanic bath; preferred material for the metal layer 7 is nickel. The electroplating process is complete when the metal layer 7 reaches a thickness at which it fills the notches 3 and the grooves 5 in the lacquer layer 2 and otherwise forms a mechanically stable plate.

To reinforce the metal layer 7, it can be covered on its rear side facing away from the lacquer layer with an additional stabilizing layer 7a - (FIGS. 3A, 38) made of cast resin, for example. The metal layer 7 with the extremely thin conductive layer 6 and with the stabilization layer 7a on the rear side, after it has been removed from the lacquer layer 2, results in a die 8. With the aid of the die 8 which can be used as a press die, liquid transparent plastic can be used in an injection press 9 10 such as B. plexiglass or polycarbonate transparent plates 11 (Figure 4A, 4B), on the top 12 each row-like web-shaped elevations 13 are formed, which are provided in the transverse direction with notches 14 in columns. With regard to the arrangement and the dimensions of the web-shaped elevations 13 with the notches 14, the upper side 12 of the transparent plate 11 corresponds to the structure of the lacquer layer 2 of the master mold corresponding to FIG. 1A 1B.

In a subsequent process step, the transparent plate 11 is mirrored on its top 12 with the web-shaped elevations 13. Subsequently, the top 12 of the transparent plate 11 is covered with a casting compound 15 covering the web-shaped elevations 13 and filling the notches 14 and the spaces between the web-shaped elevations 13 (Figure 5a, 5B).

Once the casting compound 15 has hardened, the transparent plate 11 is removed, starting from its underside facing away from the upper side 12, until only the formerly web-shaped elevations 13 in the form of light guide channels 16 remain enclosed on three sides by the casting compound 15 (FIGS. 6A, 6B). . The plate 11 can be removed by a mechanical process, for example by grinding and subsequent polishing, or by a chemical etching process.

As an alternative to the method variant described above, the lighting unit can be completed following the method step shown in FIGS. 3A, 3B in accordance with the steps shown in FIGS. 7A, B to 9A, B. For this purpose, a photopolymerizable clear lacquer 21 is pressed into the recesses of the die 8 using a plexiglass plate 22. Subsequently, the clear lacquer 21 is irradiated through the plexiglass plate 22 with ultraviolet light 23, so that the clear lacquer 21 hardens to a transparent plate 11, which consists of a thin base plate 24 with rows of rows and notches 14 with web-shaped elevations 13 - (FIG. 8A , 8B). The die 8 is then released from the transparent plate 11 and the surface 25 of the transparent plate 11 thus produced is mirrored. In a subsequent process step, the plate 11 is coated on its mirrored surface 25 with a casting compound 15. After the casting compound 15 has hardened, the plexiglass plate 22 adhering to the transparent plate 11 is removed, so that apart from the very thin base plate 24, essentially only the web-shaped elevations of the transparent plate in the form of the light-conducting channels 16 remain enclosed on three sides by the casting compound 15 ( Figure 9A, 9B).

The casting compound 15 thus bids a film in which the light guide channels 16 with their notches 14 arranged in columns are embedded in rows. FIG. 16 illustrates this by means of a section of the lighting unit produced by the method according to the invention and consisting of the film 15 with the light-guiding channels 16, shown in a perspective view. Two parallel light beams 17 and 18 illustrate how light is coupled in laterally into the end faces of a light-guiding channel 16 due to the notches 14 of different depths in the light guide channel 16, a uniform coupling of the light from the light exit areas 19 and 20 in the channel wall of the light guide channel 16 is achieved over the longitudinal extent of the light guide channel 16.

To produce a lighting unit according to FIG. 16 in accordance with a further variant of the method according to the invention, in which the light-guiding channels consist of transparent material which is introduced or pressed into recesses in a carrier plate, reference is made below to FIGS. 10a, 10B to 15A, 15B.

As FIG. 10A, 10B shows, just like in the method variant described above, a master mold with grooves 5 and notches 3 is first produced. While a thin lacquer layer was formed as a substrate layer in the previously described method variant, the grooves 5 and notches 3 are cut into a metal plate 25, preferably made of copper, as shown in FIGS. 10a, 10B. In general, however, the alternative use of a lacquer layer or a metal layer as a substrate layer for cutting the grooves 5 and notches 3 is possible in both method variants.

In a further process step, a thin conductive layer 26, preferably made of silver, is applied to the side of the metal plate 25 provided with the grooves 5 and notches 3. A metal layer 27 is built up on this in a galvanic bath; preferred material for the metal layer 27 is nickel (FIG. 11 A, 11 B).

In a subsequent etching process, the metal plate 25 made of copper is etched away up to the conductive layer 26; the conductive layer 26 (silver) itself is resistant to the etchant used, so that the etching process ends as soon as the entire metal plate 25 has been etched away. The remaining metal layer 27 and the conductive layer 26 together form a first mold impression 28 (FIGS. 12A, 12B).

After electropolishing, a second mold impression 29 is produced from it in this way, as can be seen in FIGS. 13A, 13B. In terms of its surface structure, this second mold impression 29 corresponds to the metal plate 25 with the grooves 5 and notches 3 shown in FIGS. 10A, 10B.

The second mold impression 29 is used as shown in FIGS. 14A, 14B in an injection press 9 as a die 8. With the aid of this die 8, carrier plates 30 (FIGS. 12a, 12B) made of plastic 10 can be pressed in the injection press 9, the surface structure of which corresponds to that of the film 15 shown in FIG. The light guide channels 16 made of transparent material are then pressed into the depressions of the carrier plates 30 (FIGS. 15A, 15B).

The formation of the light guide channels 16 in the carrier plate 30 takes place in a corresponding manner, as described for the first method variant with reference to FIGS. 7A, 7B, preferably with the aid of photopolymerizable clear lacquer, which is pressed by means of a plexiglass plate. The clear lacquer is then irradiated through the plexiglass plate with ultraviolet light, so that the clear lacquer is cured and remains in the depressions of the carrier plate after removal of the plexiglass plate in the form of the light guide rods.

Within the scope of the invention, it is also possible to obtain the mold impressions from the substrate layer 2 or 25 using silicone rubber instead of by means of a galvanic process.

Depending on the control of the light guide channels, there are numerous possible uses for the lighting unit, for example as a two-dimensional lighting element, for example for optical scanning devices or as a high-resolution display.

Claims (19)

1. A method for producing a flat lighting unit, characterized in that light guide channels (16) in the form of transparent rods are formed line by line on the top (12) of a plate (11), that the plate (11) with one of the light guide channels (16) covering and the spaces between the light guide channels (16) filling casting compound (15) is covered and that the plate (11) after curing of the casting compound (15) is removed so far that only the light guide channels (16) on three sides of the casting compound (15) remain enclosed. 2. The method according to claim 1, characterized in that transparent material is used as the casting compound (15), the optical refractive index of which is lower than that of the light guide channels - (16). 3. The method according to any one of the preceding claims, characterized in that the light guide channels (16) arranged on the upper side (12) of the plate (11) are mirrored with the casting compound (15) before being coated. 4. The method according to any one of the preceding claims, characterized in that the light guide channels are individually pressed from transparent material and fastened on the top of the plate in a time-wise arrangement and that the plate is detached from the encapsulated light guide channels after coating the light guide channels with the casting compound. 5. The method according to any one of claims 1 to 3, characterized in that the plate (11) is made of transparent material and that the light guide channels (16) are designed in the form of web-shaped elevations (13) of the plate (11). 6. The method according to claim 5, characterized in that the plate (11) is cast from transparent plastic using a die (8) which is provided with the web-like elevations (13) to be formed in the plate (11) corresponding depressions. 7. The method according to claim 6, characterized in that the die (8) is used as a press die and the plate (11) is injection molded. 8. The method according to claim 6, characterized in that a photopolymerization clear coat (21) is used as the transparent plastic, which is hardened by exposure to light (23). 9. The method according to any one of claims 6 to 8, characterized in that for producing the die (8) in a substrate layer (2) rows of grooves (5) are cut, the respective depth and width of the height and the spacing between the web-shaped elevations - (13) on the transparent plate to be shaped - (11) and that a shape impression is obtained from the side of the substrate layer (2) which has the grooves (5) and which forms the die (8). 10. A method for producing a flat lighting device, characterized in that a carrier plate (30) is pressed with recesses arranged in rows on one side, the depth and width of which correspond to the cross-sectional dimensions of light-guiding channels (16), and that for forming the light-guiding channels (16 ) transparent material is introduced into the recesses. 11. The method according to claim 10, characterized in that the carrier plate (30) is pressed from transparent material whose optical refractive index is greater than that of the light guide channels - (16). 12. The method according to claim 10, characterized in that the carrier plate (30) is mirrored on its side provided with the depressions before the pressing in of the transparent material for the light guide channels (16). 13. The method according to any one of claims 10 to 12, characterized in that the carrier plate (30) is cast using a die - (8) that for the production of the die (8) in a substrate layer (25) rows of grooves (5) are cut, the depth and spacing of which corresponds to the cross-sectional dimensions of the light guide channels (16) to be formed, such that a first mold impression (28) and a second mold impression (29) from the side of the substrate layer (25) having the grooves (5) is obtained, which forms the matrix (8). 14. The method according to any one of claims 9 to 13, characterized in that before the grooves (5) are cut into the substrate layer (2 or 25) in the transverse direction, notches (3) are cut into columns in the substrate layer (2 or 25) will. 15. The method according to claim 14, characterized in that the notches (3) are progressively cut into the substrate layer (2 or 25) with increasing depth. 16. The method according to any one of claims 9 to 15, characterized in that the substrate layer in the form of a lacquer layer (2) is formed on a carrier layer (1). 17. The method according to any one of claims 9 to 15, characterized in that a metal plate (25) is used as the substrate layer. 18. The method according to any one of claims 9 to 17, characterized in that a silicone rubber impression is used as the mold impression. 19. The method according to any one of claims 9 to 17, characterized in that for producing the mold impression (8) on the grooves (5) having the side of the substrate layer (2) a conductive layer (6) is applied and that in a galvanic bath a metal layer (7) is built up on the conductive layer (6), which, with sufficient thickness, forms the mold impression (8) (the matrix) when it is free of the substrate layer (2).

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