WO2020161184A1

WO2020161184A1 - Optical unit for backlighting a display

Info

Publication number: WO2020161184A1
Application number: PCT/EP2020/052858
Authority: WO
Inventors: Oliver Jakoby; Boris ECKERT; Peter Bolte; Helmut Marquardt; Stefan Keul
Original assignee: Continental Automotive Gmbh
Priority date: 2019-02-08
Filing date: 2020-02-05
Publication date: 2020-08-13
Also published as: DE102019201647A1

Abstract

In the method according to the invention for producing an optical unit for backlighting a display, the optical unit comprises a plurality of optical films (F). A film stack (FB) having at least two films is formed with a first contour and is beveled on at least one edge (S4). At least one additional film (R) is formed with a second contour that is adapted to the first contour (S5). The additional film is inserted in the beveled part of the film stack (S6).

Description

description

Optical unit for the background lighting of a display

The present invention relates to a method for producing an optical unit for the backlighting of a display. The invention further relates to an optical unit produced using the method for the background lighting of a display and a display with such a background lighting.

Liquid crystal displays (LCDs) are used in many areas of technology, for example in entertainment electronics, for displaying images on mobile phones or in vehicle technology for instrument clusters, for displaying an infotainment system or as an imaging unit for head-up Displays.

The display is based on mutually independent segments with liquid crystals that change their alignment when an electrical voltage is applied and thus influence the polarization direction of incident light. In this way, the permeability for polarized light that is generated with a backlight and another polarization filter changes on a polarization filter.

In the background lighting for LCDs that is common today, light-emitting diodes (LED) are used. These can be attached to the side of a light guide and scattered forward through it. In this case, a plurality of separate, stacked optical films are usually provided between the light guide and the liquid crystal layer in order to avoid scattering and deflection of the Light to ensure the most homogeneous possible illumination of the display surface. On the opposite side of the light guide, a reflector is often provided in order to deflect light which does not initially propagate from the light guide in the direction of the liquid crystal layer in this direction and thus to increase the brightness and the efficiency of the display.

The stack of films of optical films used for homogeneous illumination of the display surface is currently usually produced by superimposing several prefabricated films in the final assembly of the backlight, for example by successively positioning the individual films on the light guide, aligning them and fixing them in a holding frame.

For this purpose, the individual optical foils are tailored to size and procured and processed. This is technically, logistically and cost-wise not the best solution and is very expensive. Furthermore, the individual foils can generate tinsel through friction with one another, which can interfere with the image generated by the display. Each of the individual foils must also be fixed separately in order to prevent any other potential noise generation in the event of vibrations, for example.

Furthermore, WO 2005/024473 A2 describes how to hold a stack of two or more optical foils together before inserting them into the display frame by gluing them to one another by means of an adhesive positioned outside the viewing area of the foils.

It is an object of the present invention to provide a method for producing an optical unit which is improved in comparison for the background lighting of a display, as well as a corresponding optical unit for the background lighting of a display and a display with such a background lighting.

This object is achieved by a method for producing an optical unit for the backlighting of a display having the features of claim 1, an optical unit according to claim 9 and a display according to claim 11. Preferred embodiments of the invention are the subject of the dependent claims.

In the method according to the invention for producing an optical unit for the background lighting of a display, the optical unit comprises a plurality of optical films. A stack of foils comprising at least two foils is formed with a first contour and bent at at least one edge, so that a lid-shaped stack of foils with a reshaped, bent part with an at least partially circumferential edge is produced. At least one further film is introduced into the lid-shaped film stack.

This creates a mechanically stable arrangement which prevents the foils from slipping against one another or with respect to a light guide located in between. Furthermore, the penetration of dirt can be prevented or at least reduced.

According to an advantageous embodiment, film material for the at least two films of the film stack is arranged one above the other. A stack of foils comprising at least two foils is formed from the foil material arranged one above the other isolated. The individual foils in the foil stack are then connected to one another at the edges.

This significantly simplifies the final assembly, since only a single component is handled instead of several foils. Furthermore, the friction between the films is excluded, so that the formation of tinsel and image disturbances based thereon are avoided. Finally, measures to reduce noise by handling only one component instead of several individual foils are easier to implement.

The individual foils in the foil stack are advantageously pressed together and thereby thermally fused to one another at the edges.

Likewise, the individual foils can advantageously also be connected to one another at the edges in the foil stack by means of an adhesive process.

In this case, the individual foils are preferably punched out in the shape and size required for the display lighting and connected in the foil stack after the punching by the adhesive process.

Likewise, the individual foils can also be cut out in the shape and size required for the display lighting by means of a thermal fusion cutting process and connected by the cutting process by melting the edge phase in the foil stack.

The thermal enamel is advantageous here

cutting process a laser cutting process or an ultrasonic cutting process. A reflector film and a light guide are preferably introduced into the cover-shaped film stack. Accordingly, an optical unit according to the invention for the background lighting of a display comprises a film stack having at least two films, wherein

a stack of foils comprising at least two foils and having a first contour is shaped and bent at at least one edge in such a way that a lid-shaped stack of foils with a reshaped, bent part having an at least partially circumferential edge is present; and

- At least one further film is introduced into the lid-shaped film stack.

A display according to the invention has a background lighting with an optical unit according to the invention.

The background lighting of the display preferably has a light guide and a reflector designed as a reflector film, the reflector film being introduced into the bevelled part of the film stack and the light guide being arranged between the reflector film and the film stack. Further features of the present invention will become apparent from the following description and the appended claims in conjunction with the figures. Figure overview

Fig. 1 shows a flow chart for the inventive

Method for producing an optical unit for the backlighting of a display;

Fig. 2 shows schematically the production of an inven

optical unit according to the invention consisting of a folded, made of several connected foils on facing foil stack and a reflector foil inserted into this; and

Fig. 3 schematically shows a backlight with an optical unit according to the invention.

Figure description

For a better understanding of the principles of the present invention, embodiments of the invention are explained in more detail below with reference to the figures. The same reference characters are used in the figures for elements that are the same or have the same effect and are not necessarily described again for each figure. It goes without saying that the invention is not restricted to the illustrated embodiments and that the features described can also be combined or modified without departing from the scope of the invention as defined in the appended claims.

FIG. 1 shows a flow chart of a method according to the invention for producing an optical unit for the background lighting of a display. No individual, pre-assembled foils are used here. Instead, in a first method step S1, film material is stacked one on top of the other in a large sheet format for the various films. The sheet format is typically rectangular and is preferably selected so that several of the required foils can be produced from one sheet. Depending on the material properties of the respective film material, however, instead of being in large-format sheets, it can also be present on a roll and unrolled from it.

In a second method step S2, a stack of foils comprising the foils is separated from the stacked foil material (S2). Different methods can be used for this. In this way, the foils can be punched out with the desired contour and size in punching processes with punching tools corresponding to the desired shape. Laser, ultrasonic, water jet or plasma cutting processes can also be used, for example.

The individual foils in the foil stack are then in a third process step S3 by thermal fusing or by an additional adhesive process, e.g. after punching, joined together at the edges. The film composite produced in this way can then be assembled in one piece as part of the final assembly of the backlight.

The connection of the individual foils can also take place during the cutting process, if the edge phase of the foil stack is melted using a suitable cutting process, for example a laser or ultrasonic cutting process. Finally, it is also conceivable that the foil first to connect enmaterial and only then to separate.

The stack of foils produced has, for example, two or three foils stacked one on top of the other. The foils used can have different optical properties.

For example, so-called diffusion foils or diffuser foils are used for the background lighting, which ensure a homogeneous scattering of the light that is emitted directly by LEDs or a light guide used as a light source. Such diffusion films are typically translucent with high transmission values for the irradiated light, but are not completely transparent and appear cloudy. For example, depending on the configuration, between zero and three diffusion foils can be used.

Likewise, prism films can be used, for example, which are highly transparent and can be used with a microprismatic surface to optimize the illumination. For example, a prism sheet or two prism sheets with prism structures arranged perpendicular to one another can be used.

A combination of different types of film, for example two prismatic films with one diffusion film, can also be used.

In a fourth method step S4, the foil stack is then bent at the edges by hot forming, so that the restoring force of the foils is eliminated and the foil stack then permanently has a lid-like shape. This can also be done as part of a punching and bending process, in which the Foil stack is punched in a suitable contour and then folded.

Furthermore, in a fifth method step S5, which is independent of the previous method steps and can therefore take place after, during or before these other method steps, at least one further film with a smaller contour adapted to the dimensions of the lid-shaped film stack is reshaped. In particular, this further film can be a reflector film.

In a sixth method step S6, this is pushed into the lid-shaped stack of foils so that the foils are prevented from slipping against one another. In particular, a reflector foil can be introduced into the folded part of the foil stack, with a light guide arranged between the reflector foil and the foil stack also becoming part of this arrangement, so that a mechanically stable optical unit is created for the background lighting of a display. In this case, the ingress of dirt can be prevented by the circumferential edge.

The folding of the stack of foils can also be done on just one, two or three sides, depending on the overall structure. Thus, when the light originating from the LEDs is coupled into the light guide from the side, the area of the coupling point can be left out of the fold.

FIG. 2 shows schematically the production of an optical unit according to the invention, consisting of a beveled stack of foils comprising three connected foils and a reflector foil inserted therein. Foil sheets with foil material FM for the three foils are arranged one above the other, the foil material initially still being present separately. After separation from the stacked film material, there are then three films F with the dimensions required for the background lighting of the display, which are then passed on for further processing. Further foils can be produced from the excess remainder FR of the foil material, as long as the size of the remainder allows this. After the fusing or gluing, a film composite FB consisting of the three films is then present, this being initially plane-parallel in the example shown. A cover-shaped composite film FD is then produced by folding the edges of the film stack. After the reflector film R has been introduced into this lid-shaped film stack FD, a mechanically stable optical unit OE is then present, and further optical elements, not shown here, can be arranged between the reflector film and the folded film stack.

FIG. 3 schematically shows a backlight with such an optical unit according to the invention, which can be used for an electronic display element, in particular in the form of a liquid crystal display. The liquid crystals are typically arranged between two glass layers, polarizers being arranged above and below the glass layers. This structure is familiar to the person skilled in the art and is therefore not shown in the figure.

In the illustrated embodiment, the backlight has a light source L, a plate-shaped one

Light guide LL a lid-shaped film composite FD with two optical films F for optimizing the illumination and a reflector film R on. But this is only an example Embodiment, for example, more than two foils and several reflector foils can also be present.

The light source L preferably generates white light and can in particular have an arrangement with a large number of light-emitting diodes (LEDs), but other designs are also possible, for example with one or more fluorescent tubes. In particular in the case of display systems in which a small overall thickness is desired, the light source is positioned laterally as shown and the light from the light source is deflected by the light guide LL onto the actual display element. In order to enable the light originating from the LEDs to be coupled into the light guide, the cover-shaped film composite FD on the LEDs is not folded.

The film composite FD contains optical films F for optimizing the illumination, whereby various optical properties of the background light can be influenced. One or more diffuser foils, additional polarizer foils or prism foils, each having a series of prism-shaped ribs on their surface, can be provided. On the side of the light guide LL opposite the foil composite FD, a reflector foil R is provided which deflects light that does not initially propagate from the light guide in the direction of the liquid crystal layer in this direction and thus increases the brightness of the display.

Claims

1) A method for producing an optical unit for the backlighting of a display, wherein the optical unit comprises a plurality of optical films, characterized in that

- a stack of foils (FB) comprising at least two foils is formed with a first contour and folded (S4) on at least one edge, so that a lid-shaped stack of foils (FD) is produced with a deformed folded part having an at least partially circumferential edge; and

- At least one further film (R) is introduced into the lid-shaped film stack (S 6).

2) The method according to claim 1, wherein

- Foil material (FM) for the at least two foils (F) of the foil stack (FB) is arranged one above the other (S1);

- A film stack (FB) comprising at least two films is separated (S2) from the film material arranged one above the other; and

- The individual foils in the foil stack (FB) are connected to one another at the edges (S3).

3) The method according to claim 2, wherein the individual foils in the foil stack (FB) are pressed together and are thereby thermally fused together at the edges.

4) Method according to claim 2, wherein the individual foils in the foil stack (FB) are connected to one another at the edges by an adhesive process. 5) Method according to claim 4, wherein the individual foils are punched out in the shape and size required for the display lighting and are connected in the foil stack (FB) after the punching by the gluing process.

6) The method according to claim 5, wherein the individual foils are cut in the shape and size required for the display lighting by means of a thermal fusion cutting process and are connected by the cutting process by melting the edge phase in the foil stack (FB).

7) The method according to claim 6, wherein the thermal

Fusion cutting process is a laser cutting process or an ultrasonic cutting process.

8) Method according to one of the preceding claims, wherein a reflector film (R) and a light guide (LL) are introduced into the lid-shaped film stack.

9) Optical unit for the backlight of a

Displays comprising several optical films, characterized in that

- a stack of foils (FD) comprising at least two foils (F) is shaped with a first contour and bent at at least one edge in such a way that a lid-shaped foil stack (FD) with a reshaped, bent part with an at least partially circumferential edge is present; and

- At least one further film (R) is introduced into the lid-shaped film stack (FD). 10) Optical unit according to claim 9, wherein the film stack (FD) has a reflector film (R) and a light guide (LL). 11) Display that is backlit with an optical

Unit according to claim 9 or 10.

12) display according to claim 11, wherein the backlight has a light guide (LL) and a reflector, which is designed as a reflector film (R), wherein the reflector film is brought into the folded part of the film stack and the light guide between the reflector film and the Foil stack is arranged.