DE102011088835A1 - Process for producing light-conducting bodies and their use in lighting units - Google Patents

Abstract

The present invention relates to a process for the production of optical waveguides with improved processability and their use in lighting units, e.g. for liquid crystal displays or monitors. In particular, the present invention relates to a process for the production of light-conducting bodies having a thickness of at most 1 mm, containing at least 80 wt .-% polymethyl methacrylate and no scattering particles.

Description

Field of the invention

The present invention relates to a process for the production of optical waveguides with improved processability and their use in lighting units, e.g. for liquid crystal displays or monitors.

In particular, the present invention relates to a process for the production of light-conducting bodies having a thickness of at most 1 mm, containing at least 80 wt .-% polymethyl methacrylate and no scattering particles.

State of the art

Light guide bodies are used in particular for surface illumination of various electronic objects, such as liquid crystal displays (LCD). Usually, light is radiated over an edge and decoupled normally to the propagation direction. Such light guide are the subject of EP 800 036 , The coupling of the light takes place in particular by structuring, which are provided in the surface of the plate.

Furthermore are off EP 656 548 Light guide known, use the polymer particles as a scattering body. The problem with these light-conducting bodies is their weathering resistance. In particular, intensive UV irradiation decomposes the polymer particles, so that UV irradiation leads to a yellow cast. This yellow tint is in turn very critical for use as a light guide, as a non-uniform color impression.

In addition, are out EP 1022129 Light guide known, which have a particle-free photoconductive layer of polymethyl methacrylate, to which a diffusely coated layer is applied. The diffused layer, which has a thickness in the range of 10 to 1500 microns, comprises barium sulfate particles. According to this principle, the light is passed over the PMMA layer, wherein the decoupling takes place through the diffuse layer. However, the light extraction can hardly be controlled because only the light is scattered normal to the propagation direction that has penetrated the boundary layer to the diffused layer. Accordingly, this is not a disturbance within the photoconductive layer, but a diffuse back reflection. In addition, the decrease in luminous intensity is very large, as the examples show.

Furthermore, light guide in DE-A 10 222 250 described. These light guide bodies show improved performance over the plates set forth above. However, the thickness of these, as well as the light guide body described above, at least 2 mm. For an increasing miniaturization of electronic devices, especially for aesthetic reasons, however, the smallest possible thickness of the light guide is desirable. A reduction in the plate thickness of the above-explained light guide leads to a very large decrease in the luminance with respect to the direction of extension of the incident light. As a result, a very inhomogeneous lighting is obtained, which is often unacceptable.

In the German patent application with the application number 102010062900.6 are light-conducting bodies having a thickness of 100 .mu.m to 1 mm of high-purity molding compositions based on methacrylate without process aid or Schlagzähmodifier described. Due to the pronounced brittleness of the light guide special demands are placed on the commercial production and further processing. For example, the light guide can be very difficult to cut or stamp on the desired formats. However, a prior art impact modifier counteracting these disadvantages would significantly degrade the optical properties of the light guide body.

task

In view of the prior art, it was an object of the present invention to provide a method for producing thin light guide available, with a very homogeneous illumination of relatively large areas can be achieved and can be processed simultaneously without tearing.

A further object of the invention was that the light guide bodies have particularly good yellow values even after prolonged use or after weathering.

Furthermore, the provision of lighting units containing light guide bodies with high energy efficiency, high illuminance and high reliability has been an object of the present invention.

Another object of the present invention was to provide a simple and inexpensive method for producing light bodies which can be easily adapted in size and shape to the requirements.

solution

These and other objects which are not explicitly mentioned, but which can be readily deduced or deduced from the contexts discussed hereinbelow, are solved by a novel process for producing methacrylate-based light-conducting bodies. These light guide bodies according to the invention have a thickness of between 100 μm and 1 mm. Furthermore, the method is characterized in that it is an extrusion process with subsequent smoothing. The plant used for this purpose according to the invention consists of at least the following components: an extruder, a flat film die, comprising a die lip, and a calender, in particular consisting of two smoothing rolls. In particular, the plant used according to the invention may also have the following optional components: a melt pump, a melt filtration, a static mixing element and / or a winder. In addition, the light guide body according to the invention are slightly impact modified.

It has been found, in particular, that not every impact modifier can be used in any desired concentrations equally for the production of the light-conducting bodies according to the invention. Suitable impact modifiers, or synonym impact modifiers, are characterized by their particle size and a refractive index adapted to the matrix. The impact modifiers used according to the invention are distinguished by the fact that their theoretical refractive index deviates not more than 0.02, preferably not more than 0.01, more preferably not more than 0.005 and very preferably not more than 0.003 from the theoretical refractive index of the thermoplastic matrix material of the light-conducting body.

The refractive index of polymers is a measurable quantity in principle. In the case of particles, in particular of particles which are often present with sizes in the nanometer range as Schlagzähmodifier, a direct measurement is hardly possible. In this case, the "theoretical refractive index" on which the invention is based can be applied. In the context of this invention, the refractive indices are therefore given as calculated values from these theoretical refractive indices. The following formula is used:

In the case of copolymers, the various repeating units are considered as having different homopolymers of the individual comonomers. Accordingly, the proportion of comonomers in the overall system is multiplied by the theoretical refractive index of a corresponding homopolymer. In the case of multi-phase systems, e.g. Block copolymers or core-shell polymers, the systems are considered such that no distinction between the individual polymer phases is made and the polymer would be present as a single phase. In this case, all components of all phases are considered together.

The theoretical refractive indices may be in J.Brandrup, EH Immergut, Polymer Handbook, 3rd Edition, Wiley, New York, 1989, Chapter VI, pp. 451-461 be read. The values disclosed herein are considered to be the basis of this invention. In the event that at this point a Range (such as 1.590 to 1.592 for polystyrene), the numerical average of this range is taken as the value (in the case of polystyrene, 1.591).

For a matrix material of pure PMMA with a theoretical refractive index of 1.4983, the theoretical refractive index of the impact modifier used according to the invention would thus be between 1.4783 and 1.5183, preferably between 1.4883 and 1.5083, particularly preferably between 1.4933 and 1 , 5033 and most preferably between 1.4953 and 1.5013.

In particular, the system used in the method according to the invention is characterized in that the flat film nozzle has a nozzle lip with adjusting elements for adjusting the die lip width, and the adjusting elements have a spacing of 5 to 20 mm, preferably 11 to 15 mm from each other. The gap of the die lip can be finely adjusted over the entire width of the die lip by means of the adjusting elements. In this context, one speaks of a so-called flex lip or Flexdüsenlippe.

The nozzle body used in the method according to the invention has an outer geometry which is adapted to the shape of the smoothing rollers ( 1 ). This may be a triangular or trapezoidal convergence of the nozzle body towards the nozzle lip. In addition, the flanks of the nozzle body can also be rounded so that they assume the shape of the smoothing rollers complementary. This may, as exemplified in 2 shown, also asymmetric only with respect to one of the two first smoothing rollers done.

Due to these shapes of the nozzle body, it is possible to set the distance from the melt outlet edge to the smoothing gap of less than 100 mm, preferably less than 80 mm and in special embodiments less than 60 mm. Surprisingly, it has been found that a particularly good film quality, in particular with regard to the surface quality, can be achieved by particularly small distances between the melt outlet edge and the smoothing gap.

The distance from the melt outlet edge to the smoothing gap is defined in the context of this invention as the distance ( 6 in 2 ) between the melt outlet edge and the point in the middle between the calender rolls, the smallest distance ( 7 in 2 ) has to the two smoothing rollers.

In particular, the present invention relates to a method in which the flat film die is aligned with respect to the calender by means of laser. This ensures that the parallel deviation of the nozzle from the smoothing rolls, measured at the two ends of a nozzle outside, has a maximum deviation of 3 mm, preferably 1 mm. The nozzle outer sides are the two flanks of the flat foil nozzle, each of which runs parallel to the two smoothing rolls.

In particular, the light guide bodies produced according to the invention are distinguished by the fact that the thickness deviation in the light guide body is at most 4%, preferably at most 3%. The thickness deviation is determined starting from the thinnest point of the light guide. A deviation of 3% thus means that the thickness of the thickest point of the light guide body may be at most 3% greater than the thickness of the thinnest point.

By means of the method according to the invention, it is possible to provide, in an unforeseeable manner, a thin light guide body with which a very homogeneous illumination of relatively large areas can be achieved.

Furthermore, the light guide produced by a method according to the present invention, a particularly high resistance to weathering, especially against UV irradiation.

Furthermore, the light guide over the entire surface a uniform color quality of the light extraction. This results in a particularly color-fast light. In particular, no yellowing arises with increasing distance from the light source. In addition, the brightness of the light guide can be adapted to different needs.

Surprisingly, it is possible to provide a lighting unit with a high energy efficiency, a high illuminance and a high reliability by means of a light guide body produced according to the invention.

The inventive method for producing light-guiding bodies is also particularly simple and inexpensive to perform.

Furthermore, the light guide body according to the invention have the advantage that they can be easily cut or punched to desired formats. Also in the extrusion of the light guide, the brittleness is so low that the risk of web breakage is minimized and the film is produced at high extrusion speed. The light guide can thus be processed with existing extrusion equipment and by known methods.

Detailed embodiment of the system used in the invention

The extrusion of polymers into films is well known and, for example, in Kunststoffextrusionstechnik II, Hanser Verlag, 1986, p. 125 ff. described. Here, further embodiments of the individual system components are executed.

In the method according to the invention, a hot melt is extruded from the die of the extruder to a gap between two smoothing rolls. The optimum temperature of the melt, for example, depends on the composition of the mixture and can therefore vary within wide limits. Preferred temperatures of the PMMA molding compound to the nozzle inlet are in the range of 150 to 300 ° C, more preferably in the range of 180 to 270 ° C and most preferably in the range of 200 to 260 ° C. The temperature of the smoothing rollers is preferably less than or equal to 150 ° C, preferably between 60 ° C and 140 ° C.

In one embodiment, the temperature of the nozzle is preferably selected to be higher than the temperature of the mixture prior to nozzle entry. The nozzle temperature is preferably set higher by 10 ° C., particularly preferably by 20 ° C. and very particularly preferably by 30 ° C., than the temperature of the mixture before the nozzle inlet. Accordingly, preferred temperatures of the die are in the range of 160 ° C to 330 ° C, more preferably 190 ° C to 300 ° C.

The calender used in the invention consists of two or three smoothing rollers. Smoothing rollers are well known in the art, with polished rollers used to obtain a high gloss. In the process according to the invention, however, other rolls can also be used as a smoothing roll. Through the gap between the two first smoothing rollers, a film is formed, which is the simultaneous cooling to a film. In 1 an embodiment with three smoothing rollers is shown schematically. It has surprisingly been found that a particularly good surface quality of the optical waveguide can be ensured by virtue of the fact that the nozzle and the roller have chrome surfaces, and in particular by the fact that these chrome surfaces have a roughness Ra (in accordance with FIG DIN 4768 ) smaller than 0.10 μm, preferably smaller than 0.08 μm.

The pressure with which the molten mixture is pressed into the nozzle, for example, can be controlled by the speed of the screw. The pressure is generally in a range of 40 to 150 bar, without limiting the inventive method thereby. Accordingly, the speed with which the films can be obtained according to the invention is generally greater than 5 m / min, in particular greater than 10 m / min.

To ensure a uniform melt delivery, a melt pump can be additionally installed in front of the surface foil nozzle.

So that the resulting film is largely free of impurities, a filter is optionally arranged before the melt enters the nozzle. The mesh size of the filter generally depends on the starting materials used and can accordingly vary widely. In general, they are in the range of 300 microns to 20 microns. It is also possible to arrange filters with several sieves of different mesh size in front of the nozzle inlet. These filters are commercially available. In order to obtain high-quality films, it is furthermore advantageous to use particularly pure raw materials.

Optionally, in addition, a static mixing element can be installed in front of the flat film nozzle. Through this, components such as pigments, stabilizers or additives can be mixed into the polymer melt or up to 5% by weight of a second polymer, for example in the form of a melt from a second extruder, can be mixed into the PMMA.

Matrix materials used according to the invention

The molding compositions used for producing the methacrylate-based light-conducting bodies produced according to the invention are molding compositions whose main thermoplastic constituent consists of at least 80% by weight, preferably at least 90% by weight and more preferably at least 95% by weight, of polymethylmethacrylate (hereinafter PMMA for short). These polymers are generally obtained by free radical polymerization of mixtures containing methyl methacrylate. In general, these mixtures contain at least 80% by weight, preferably at least 90% by weight and more preferably at least 95% by weight, based on the weight of the monomers, of methyl methacrylate. A particularly high quality in particular light guide, which consist essentially of polymethyl methacrylate.

In addition, these mixtures may contain further (meth) acrylates which are copolymerizable with methyl methacrylate. The term (meth) acrylates include methacrylates and acrylates as well as mixtures of both.

In addition to the (meth) acrylates set out above, the compositions to be polymerized may also contain other unsaturated monomers which are copolymerizable with methyl methacrylate and the abovementioned (meth) acrylates. These include, inter alia, 1-alkenes, acrylonitrile, vinyl acetate, styrene, substituted styrenes, vinyl ethers or divinylbenzene. All of the stated monomers are preferably used in a high purity.

The weight-average molecular weight M _{w of} the homo- and / or copolymers to be used according to the invention can vary within wide limits, the molecular weight usually being matched to the intended use and the method of processing of the molding composition. In general, however, it is in the range between 20,000 and 1,000,000 g / mol, preferably 50,000 to 500,000 g / mol, and more preferably 80,000 to 300,000 g / mol, without this being intended to restrict this. The weight average molecular weight is determined by gel permeation chromatography (GPC) against polystyrene standards.

Various poly (meth) acrylates can be used as matrix material for the production of the light guide body, which differ, for example, in molecular weight or in the monomer composition. Such particularly preferred molding compositions are commercially available under the trade name PLEXIGLAS ^® from Evonik Industries GmbH. In the context of this invention, matrix material is understood to be the material of the optical waveguide without the impact modifiers.

The molding compositions may contain conventional additives. These include, but are not limited to, antistatic agents, antioxidants, light stabilizers and organic phosphorus compounds, weathering agents and plasticizers. However, the amount of additives is limited to the purpose of use. The light-guiding bodies according to the invention preferably comprise at most 5% by weight and more preferably at most 2% by weight of additives, wherein light-conducting bodies which comprise substantially no additives surprisingly exhibit exceptional performance.

In a particular embodiment, the light guide is present as a multilayer, preferably as a two-layer laminate. In this case, a layer represents the PMMA optical waveguide with the composition according to the invention already embodied. In the particular embodiment, the optical waveguide is a coextrudate with at least one PMMA layer and at least one PVDF layer. The amounts stated above for the composition relate exclusively to the PMMA layer. The impact modifier is contained in the PMMA layer.

The light guide body

In addition to the method carried out are also the light guide, produced by the method according to the invention, and lighting units produced therefrom part of this invention. Such a lighting unit according to the invention comprises at least one light source and at least one light guide body. The matrix material of the optical waveguide consists of at least 80% by weight, preferably at least 90% by weight and particularly preferably at least 95% by weight, of PMMA and additionally contains impact modifiers as described above. In addition, the light guide body has a thickness between 100 .mu.m and 1 mm, preferably between 125 .mu.m and 750 .mu.m, particularly preferably in the range of 150 .mu.m to 600 .mu.m. on. The thickness here refers to the mean value of the smallest dimension of the optical waveguide measured perpendicular to the light propagation direction. The thickness can be determined by means of a loop micrometer or similar known devices.

kleiner 1 bevorzugt kleiner 0,75, besonders bevorzugt kleiner 0,5 und ganz besonders bevorzugt kleiner 0,3 ist. Preferably, the illumination units are distinguished by the fact that the thickness deviation in the light guide is at most 3% and the yellow value of the light guide (calculation in accordance with DIN 6167 for standard illuminant D65 / 10 °, in the measurement of the total spectral transmittance according to ISO 13468-2 the beam is perpendicular to the plane of the light guide body); Measurement according to DIN 5033 ) measured at

less than 1 is preferably less than 0.75, more preferably less than 0.5, and most preferably less than 0.3.

The light source is preferably one or more light-emitting diodes (LED). These are particularly preferably positioned on the edge of the light guide body. In particular, the light guide bodies of the present invention have at least one light introduction surface and at least one light exit surface, the light introduction surfaces preferably being one or more outer edges of the light guide body. In an alternative embodiment, the light can also be coupled over a large area prism. The coupling can be done via a so-called Encapsulant. For this purpose, a transparent, preferably crosslinked, soft polymer, such as a silicone or EVA between LED and light guide is attached to the edges. The radiation emerges from the LED, into the encapsulant, out there and into the light-guiding foil. Such an encapsulant represents an alternative to a prism for focusing the light from the possibly wider LED into the narrower edge of the light guide.

To illuminate the light introduction surface all known light sources can be used. Particular advantages can be achieved in particular by one or more light-emitting diodes. These can be z. B. in a frame on an edge, or an edge surface or end face, laterally of the surface to be indirectly illuminated, the light guide be arranged.

Depending on the arrangement of the light sources, in this case the light can be irradiated over all four edge surfaces. This may be necessary in particular for very large light-guiding bodies. In the case of smaller light-conducting bodies, one or two light sources are generally sufficient.

The light-introducing surface is capable of receiving light into the body, so that the light-conducting layer can distribute the introduced light over the entire light-emitting surface. The term light exit surface here denotes a surface of the light guide, which is suitable to emit light. The decoupling of light is preferably achieved by structuring in the surface of the light guide. Accordingly, the surface of preferred optical waveguide elements formed parallel to the light exit surface comprises a region with structures and an area without structures over which, if possible, no light is emitted. Therefore, preferred light guide bodies can deliberately emit light over very well defined areas of the surface, which light has been coupled in via the light introduction surface. Accordingly, the surface which is formed perpendicular to the light propagation direction, in addition to a light exit surface also have a surface over which only a small portion of the incident light is coupled out. A small proportion means that the luminance in this area of the surface is at most 20%, particularly preferably at most 10%, of the maximum luminance measured on the light exit surface. Areas with a low luminance do not count to the light exit surface.

In this case, the ratio of light exit surface to light introduction surface is generally at least 1, in particular at least 4, preferably at least 20 and particularly preferably at least 80. According to a preferred embodiment of the present invention, the light exit surface is perpendicular to the light introduction surface.

According to a preferred aspect of the present invention, the light guide body may take on a tabular shape, wherein the three extensions of the body have a different size.

The smallest extent here is the thickness of the board. The largest extent is defined as length, so that the third dimension represents the width. As a result, the light exit surface of this embodiment is defined by a surface corresponding to the product of length by width. The edge surfaces of the panel, each defined as the surface formed by the product of length times thickness or width times thickness, can generally serve as a light entrance surface. Preferably, the edge surfaces serving as the light entrance surface are polished.

The coupling-out of the light depends on the density of the structuring of the light-emitting surface or its roughness. The denser this structuring, the higher the probability of coupling light out of the light guide.

Such a light guide body preferably has a length in the range from 20 mm to 3000 mm, preferably from 30 to 2000 mm and particularly preferably from 50 to 1500 mm.

The width of this particular embodiment is generally in the range of 10 to 3000 mm, preferably 20 to 2000 mm, and more preferably 50 to 1000 mm.

In particular, the illumination unit according to the invention is characterized in that a part of the surface of the light guide body has structuring and a contrast exists between the structured surface of the light guide body and the non-structured surface of the light guide body.

The structuring can be obtained after the production of the films, for example by pressure or other mechanical effects. Furthermore, the patterning in the production of the films can be achieved by using rollers having a negative of structuring.

With respect to this invention, the shape of the structuring is not critical. It is essential that the light exit surface comprises impurities that are able to extract light. For example, points or notches can be applied. In addition, the light exit surface can also be roughened. The structurings usually have a depth in the range from 0.5 μm to 100 μm, in particular from 2 μm to 20 μm.

As already stated, the surface formed normal to the light propagation direction may also include regions without structures. Areas of the surface over which a slight, preferably no light outcoupling should take place, preferably have a roughness Ra of less than 0.10 μm, preferably less than 0.08 μm.

The density of the structuring can be chosen constant over the entire surface. Nevertheless, a fairly uniform luminance is achieved by the present invention.

Furthermore, it is possible to increase the density of the patterning with the distance to the light source in order to obtain a more uniform luminance. In comparison to conventional light guides, however, the change in density can be chosen to be much lower, since the light guides according to the invention have a more uniform luminance distribution per se.

The lighting units according to the invention are particularly used as Back Light Unit (BLU), Edge Lit Back Light Unit or Light Guide Panel (LGP).

The impact modifier

The impact modifiers used according to the invention can be based on very different chemical compositions. In addition to the chemical composition, very different polymer architectures can also be used. The impact modifiers can be crosslinked or thermoplastic. Furthermore, the impact modifiers can be present in particulate form, in particular also as core-shell or as core-shell-shell particles. Decisive for the method according to the invention and the light guide bodies according to the invention are, above all, the optical properties in relation to the theoretical refractive index and the concentration in the matrix material. For both features, the boundary regions according to the invention have already been explained above.

In addition, it has proved to be very advantageous, in particular with regard to a uniform color image in the light outcoupling, when particle-shaped impact modifiers have a particle diameter between 20 and 400 nm, preferably between 50 and 300 nm, particularly preferably between 100 and 285 nm and very particularly preferred between 150 and 270 nm. For larger particles, it can be due to light scattering effects to a less favorable in terms of the color-constant Lichtauskopplung result. The effect described can also be expected for particles smaller than 20 nm if they have a refractive index difference from the matrix and are present in large numbers. Blue light scatters more than light of yellow wavelength.

In this context, particle-shaped impact modifiers, which as a rule have a core-shell or core-shell-shell structure, are meant to be particulate. Thermoplastic Schlagzähmodifier contrast, have a different mechanism of action and are usually mixed with the matrix material. In the event that domains are formed, as for example in the use of Block copolymers occurs, apply to these domains whose size can be determined, for example, by electromicroscopy, corresponding preferred sizes as for the core-shell particles.

Starting from a pure PMMA matrix material or a matrix material, which is very similar to a pure PMMA at least in terms of the refractive index, there are various examples of thermoplastic impact modifiers. Such an example is aliphatic TPU (thermoplastic polyurethanes) such as are sold by Bayer, for example under the name Desmopan. Thus, in particular the TPU Desmopan ^® WDP 85784A, 85092A WDP, WDP 89085A and 89051D WDP, all of which have refractive indices of 1.490 to 1.500, suitable as an impact modifier for the inventive light guide body.

Another example for thermoplastic polymers for use in this invention as impact modifiers are methacrylate-acrylate block copolymers, particularly Acrylic TPE in which it is PMMA-poly n-butyl acrylate-PMMA triblock copolymers, and under the product name Kurarity ^® by the company Kuraray to be expelled. The poly-n-butyl acrylate blocks form nanodomains in the polymer matrix with a size between 10 and 20 nm.

The suitable crosslinked poly (meth) acrylate-based core-shell-shell impact modifiers for polymethacrylate matrix materials are well known. There are suitable descriptions of the synthesis for, Example in EP 1 332 166 and the EP 0 528 196 , It is the skilled person simply by means of the above-described calculation method of the theoretical refractive index to select or design a suitable Schlagzähmodifier.

The optical waveguides preferably contain between 0.3 and 45% by weight, preferably between 2.5 and 25% by weight, more preferably between 5 and 20% by weight and most preferably between 7.5 and 15% by weight impact modifier, if these are crosslinked particles, in particular core-shell or core-shell shell.

In the event that thermoplastic materials are used as impact modifiers, such as the listed aliphatic TPU or acrylic TPE, they are in a concentration between 3 and 40% by weight, preferably between 6 and 25% by weight and particularly preferably between 9 and 15 % By weight in the matrix material.

Examples

By means of film extrusion, light guide bodies are produced with the following compositions:
Example 1: 7.5% by weight Metablen ^® IR441 be extruded with 92.5% by weight of PLEXIGLAS ^® 7H. PLEXIGLAS ^® 7H has a refractive index of 1.491. Metablen ^® IR441 has a theoretical refractive index of 1.49 and particle sizes between 180 and 220 nm as the impact modifier. The difference between nD20 (Metablen ^® IR441) and nD20 (PLEXIGLAS ^® 7H) is 0.0014. An extruded optical fiber with a thickness of 500 microns has a very good optical appearance in terms of uniform light extraction and a uniform color distribution over the entire output surface.
Example 2: 15 wt% Metablen ^® IR441 be coextruded with 85% by weight of PLEXIGLAS ^® 7H. An extruded optical fiber with a thickness of 500 microns has a very good optical appearance in terms of uniform light extraction and a uniform color distribution over the entire output surface. In addition, this film can be processed more easily.
Comparative Example 1: 9.2 from 98 coextruded% by weight of an impact modifier consisting wt% n-butyl acrylate and 2% by weight of allyl methacrylate, and a particle size of about 60 nm 90.8% by weight of PLEXIGLAS ^® 7H. A coextruded light guide having a thickness of 500 μm has a poor optical appearance in terms of strong light scattering and a very strong yellowing.

Labels in the drawings

1 : Embodiment with three-roll calender and one-sided adapted die lip

2 : Clarification of the distances nozzle lip to calender

LIST OF REFERENCE NUMBERS

1

static mixer

2

flat film die

3

Nozzle lip (flex lip)

4

one-sided adapted outer geometry of the nozzle body

5

Calender made of three ( 1 ) or two ( 2 ) Smoothing rollers

6

Distance between the melt outlet edge and the point in the middle between the smoothing rollers

7

The smallest distance between the two smoothing rollers

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 800036 [0003]
• EP 656548 [0004]
• EP 1022129 [0005]
• DE 10222250 A [0006]
• DE 102010062900 [0007]
• EP 1332166 [0069]
• EP 0528196 [0069]

Cited non-patent literature

• J.Brandrup, EH Immergut, Polymer Handbook, 3rd edition, Wiley, New York, 1989, Chapter VI, pp. 451-461. [0016]
• Kunststoffextrusionstechnik II, Hanser Verlag, 1986, p. 125 ff. [0030]
• DIN 4768 [0033]
• DIN 6167 [0046]
• DIN 5033 [0046]

Claims (17)

Method for producing methacrylate-based light-guiding bodies with a thickness of between 100 μm and 1 mm, characterized in that the method is an extrusion method with subsequent smoothing, and in that the apparatus used consists of at least the following components: an extruder, a optional melt pump, an optional melt filtration, an optional static mixing element, a flat film die, a calender and optionally a winder, the flat film nozzle has a nozzle lip with adjusting elements for adjusting the nozzle lip width, and the adjusting elements have a distance of 11 to 15 mm to each other, the Nozzle body having an outer geometry that is adapted to the shape of the calender rolls, and the distance from the melt outlet edge to the calendering nip 80 mm or smaller, and that the light guide body has at least one layer consisting of a methacrylate-based matrix material and a Sc hugzähmodifier consists, wherein the impact modifier has a theoretical refractive index, which differs at most 0.02 from the theoretical refractive index of the matrix material. A method according to claim 1, characterized in that the flat film nozzle is aligned with respect to the calender by means of laser and that the parallel deviation of the nozzle to the calender rolls, measured at the two ends of a nozzle outside a max. Deviation of 3 mm. A method according to any one of claims 1 or 2, characterized in that the impact modifier has a core-shell or a core-shell-shell structure and a particle diameter between 20 and 400 nm, and that the impact modifier in a concentration between 0 , 3 and 45% by weight. A method according to claim 3, characterized in that the methacrylate-based layer contains 5 to 20% by weight of an impact modifier, that the impact modifier has a theoretical refractive index which deviates at most 0.005 from the theoretical refractive index of the matrix material, and that the particle diameter of the impact modifier between 50 and 300 nm is located. A method according to claim 4, characterized in that the methacrylate-based layer contains 7.5 to 15% by weight of an impact modifier, that the impact modifier has a theoretical refractive index which deviates at most 0.003 from the theoretical refractive index of the matrix material, and in that the particle diameter of the impact modifier is between 150 and 270 nm. A method according to any one of claims 1 or 2, characterized in that it is the impact modifier is a thermoplastic TPU or an acrylate-methacrylate triblock copolymer, and that the impact modifier is present in a concentration between 3 and 40% by weight. A method according to claim 6, characterized in that the methacrylate-based layer contains 6 to 25 wt% of a Schlagzähmodifiers, and that the impact modifier has a theoretical refractive index which deviates at most 0.005 from the theoretical refractive index of the matrix material. A method according to claim 7, characterized in that the methacrylate-based layer contains 9 to 15% by weight of an impact modifier, and that the impact modifier has a theoretical refractive index which deviates at most 0.003 from the theoretical refractive index of the matrix material. Method according to at least one of claims 1 to 8, characterized in that the difference between the thinnest and the thickest point of the light guide body is a maximum of 5 microns. A method according to any one of claims 1 to 9, characterized in that the thickness deviation in the light guide body is at most 4%, preferably at most 3%. A method according to any one of claims 1 to 10, characterized in that the nozzle and roller have chrome surfaces, and that these chrome surfaces have a roughness Ra less than 0.08 microns. Lighting unit comprising at least one light source and at least one light guide, characterized in that the light guide is produced according to the method of claim 1, at least 90 wt% consists of PMMA and contains a Schlagzähmodifier, wherein the impact modifier has a theoretical refractive index, the maximum 0, 02 differs from the theoretical refractive index of the matrix material, has a thickness between 100 .mu.m and 1 mm and the thickness deviation in the light guide body amounts to a maximum of 4%. Lighting unit according to claim 12, characterized in that the light guide body contains 0.1 to 15% by weight of a core-shell or a core-shell-shell impact modifier, wherein the impact modifier has a theoretical refractive index, the maximum of 0.003 of the theoretical refractive index of the matrix material differs, has a thickness between 125 microns and 750 microns, the maximum thickness deviation in the light guide is 3% and the yellowness of the light guide measured at τ _{[D65 / 10 °] is} less than 1, preferably less than 0.3. Lighting unit according to claim 12, characterized in that the light guide body contains 3 to 40% by weight of an aliphatic TPU or PMMA poly-n-butyl acrylate PMMA Triblockcopolymer impact modifier, wherein the impact modifier has a theoretical refractive index, the maximum of 0.003 of the theoretical Refractive index of the matrix material is different, has a thickness between 150 microns and 500 microns, the maximum thickness deviation in the light guide is 3% and the yellowness of the light guide measured at τ _{[D65 / 10 °] is} less than 1, preferably less than 0.3. Lighting unit according to at least one of claims 12 to 14, characterized in that a part of the surface of the light guide body has structuring. Lighting unit according to at least one of claims 12 to 15, characterized in that it is the light source to one or more light-emitting diodes (LED). Use of a lighting unit according to at least one of Claims 12 to 16 as a Back Light Unit (BLU), an Edge Lit Back Light Unit or a Light Guide Panel (LGP).

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