Method for producing light guide bodies and use thereof in lighting unit
View Patent ↗The present invention relates to a method for producing light guide bodies and to their use in lighting units, for example for liquid crystal displays or for monitors. In particular, the present invention relates to a method for producing light guide bodies which have a thickness of at most 1 mm and contain at least 80 wt % of polymethyl methacrylate and no light-scattering constituents.
1. A method for producing a methacrylate-based light guide body having a thickness of between 100 μm and 1 mm, the method comprising extruding a methacrylate-based material in an apparatus followed by smoothing, to produce a methacrylate-based light guide body,
wherein the apparatus comprises
an extruder,
an optional melt pump,
an optional melt filter,
an optional static mixing element,
a flat film nozzle,
a smoothing mechanism comprising smoothing rolls,
and optionally a winder;
the flat film nozzle comprises a nozzle lip comprising control elements for adjusting the nozzle lip width, said control elements having a mutual separation of from 11 to 15 mm, such that a nozzle body has an external geometry which is adapted to the shape of the smoothing rolls;
a distance from a melt exit edge to a smoothing gap is 80 mm or less; and
at least 95 wt % of the methacrylate-based light guide body consists of PMMA, and it does not contain any impact modifiers.
2. The method according to claim 1 , wherein the flat film nozzle is aligned with a laser in relation to the smoothing mechanism, and a parallel deviation of the nozzle from the smoothing rolls, measured at the two ends of an outer side of the nozzle, has a maximum deviation of 3 mm.
3. The method of claim 1 , wherein a difference between the thinnest and thickest points of the light guide body is at most 5 μm.
4. The method of claim 1 , wherein a thickness deviation in the light guide body is at most 4%.
5. The method of claim 1 , wherein the nozzle and the roll have chromium surfaces, and these chromium surfaces have a roughness Ra of less than 0.08 μm.
6. The method of claim 2 , wherein a difference between the thinnest and thickest points of the light guide body is at most 5 μm.
7. The method of claim 2 , wherein a thickness deviation in the light guide body is at most 4%.
8. The method of claim 1 , wherein a thickness deviation in the light guide body is at most 3%.
9. The method of claim 2 , wherein the nozzle and the roll have chromium surfaces, and these chromium surfaces have a roughness Ra of less than 0.08 μm.
10. The method of claim 1 , wherein the nozzle body has an external geometry which is a complementary shape to the shape of the smoothing rolls.