DE102015015516A1 - Screen and procedure for a free and a restricted view mode - Google Patents

Abstract

The invention relates to a screen (1) which can be operated in at least two operating modes B1 for a free viewing mode and B2 for a restricted viewing mode, comprising a planar-like backlight (2), which in the operating mode B1 for a free viewing mode light in a radiated unrestrained angular range, and which emits light in the restricted viewing mode B2 in a restricted angular range, a facing in front of the backlight (2) transmissive imager (5), for example an LCD panel, a viewing direction in front of the imager (5) located, plate-shaped light guide (3), which consists of a transparent plastic and scattering particles distributed therein, and lighting means (4) which are arranged laterally on narrow sides of the light guide (3), wherein in the operating mode B1, the lighting means (4) are turned off, so that from the back (2) outgoing and then penetrating through the transmissive imager (5) penetrating light substantially unaffected by the light guide (3) passes, and wherein in the operating mode B2, the lighting means (4) are turned on, so that the of the backlight (2) is superimposed by light penetrating into a restricted angular range and then penetrating through the transmissive imager (5), the light guide (3) now radiating over a large angular range, whereby the residual visibility of an image displayed on the transmissive imager (5) outside of said restricted angle range is reduced. Furthermore, a corresponding method is described.

Description

Field of the invention

In recent years, great progress has been made in broadening the viewing angle of LCDs. However, there are often situations in which this very large viewing area of a screen can be disadvantageous. Increasingly, information is also becoming available on mobile devices such as notebooks and tablet PCs, such as bank details or other personal information, and sensitive data. Accordingly, people need control over who can see this sensitive data; you have to be able to choose between a wide viewing angle to share information on your display with others, eg. B. when viewing holiday photos or for promotional purposes. On the other hand, they need a small viewing angle if they want to treat the image information confidentially.

State of the art

Supplementary films based on micro-blades have already been used for mobile displays to achieve their optical data protection. However, these slides were not (re) switchable, they always had to be placed by hand and then removed again. Also you have to transport them separately to the display, if you do not need them right now. A major disadvantage of the use of such lamellar films is also associated with the accompanying loss of light.

The US 6,765,550 describes such a screen by micro-blades. The biggest disadvantage here is the mechanical removal or mechanical attachment of the filter as well as the loss of light in the protected mode.

In the US 5,993,940 the use of a film is described, which has evenly arranged on its surface, small prism strips to achieve a privacy mode. Development and production are quite expensive.

In the WO 2012/033583 the switching between free and limited vision is generated by means of the control of liquid crystals between so-called "chromonic" layers. This creates a loss of light and the effort is quite high.

The font US 2009/0067156 discloses a variety of ideas for designing a lighting system and a display device. The there in the 3A and 3B shown variant uses in particular two backlights, so-called backlights, consisting of wedge-shaped light guides, and an LCD panel, the rear backlight 40 Mandatory a wide angle of illumination and the front backlight 38 imperative to produce a narrow illumination angle. However, the functionality remains unclear, as the backlight 38 To create a narrow illumination angle without the light with a wide illumination angle, which from the backlight 40 when passing through the backlight 38 is essentially converted into light with a narrow illumination angle.

To the design after 5 of the US 2009/0067156 It should be noted that both light guides 46 and 48 each produce "narrow light", ie light with a narrow illumination angle. The light of the light guide 48 becomes only through a complex to be created with prismatic submirror 50 in "wide light", ie light with a wide illumination angle, converted. This conversion extremely curtails the light intensity, since the light, which is initially emitted into a narrow illumination angle and is available as the only light, is then fanned out into a large illumination angle, generally the half space. As a result, depending on the parameters, the brightness is reduced by a factor of 5 or more (in terms of luminance). It is therefore a less relevant design.

In the embodiment according to 7 of the US 2009/0067156 A phosphor layer is absolutely necessary, this is to convert UV light into visible light. This effort is great and in the desire for sufficient light from the backlight to illuminate a LCD panel readable, very large intensities of UV light are needed. Thus, this is expensive, expensive and even from the shielding of the required UV radiation ago not practicable.

The US 2012/0235891 describes a very elaborate backlight in a screen. There according to 1 and 15 not only multiple optical fibers are used, but also other complex optical elements such as microlens elements 40 and prismatic structures 50 which transform the light from the rear lighting on the way to the front lighting. This is expensive and expensive to implement and also associated with loss of light. According to the variant 17 in the US 2012/0235891 produce both light sources 4R and 18 Light with a narrow illumination angle, with the light from the rear light source 18 only consuming in light with a large illumination angle, is converted. This complex transformation is - as already noted above - greatly brightness-reducing.

According to the JP 2007-155783 become special optical surfaces that are difficult to calculate and produce 19 used, which then divert light depending on the angle of light in different narrow or wide areas. These structures are similar to Fresnel lenses. There are also interfering edges which deflect light in undesired directions. Thus, it remains unclear whether really meaningful light distributions can be achieved.

After teaching the GB 2428128 A In order to obtain a limited view, additional light sources, which are clearly removed from the screen and which illuminate a hologram mounted on the screen, are used to superimpose side views with specific wavelengths. The disadvantage here is the required distance of the light sources from the screen and the effort to produce appropriate holograms.

In the US publication 2013/0308185 describes a special step-shaped optical fiber which emits light on a large area in different directions, depending on which direction it is illuminated from a narrow side. In interaction with a transmissive imager, z. As an LC display, thus a switchable between free and limited viewing mode screen can be generated. The disadvantage here is, inter alia, that the limited visual effect either only for left / right or up / down, but not for left / right / up / down can be generated simultaneously, as it is necessary for certain payment transactions. In addition, even in the restricted viewing mode from blocked viewing angles, a residual light is still visible.

Finally, that describes DE 10 2014 003 298 A1 Method and arrangement for optionally limiting the recognizability of images. For this purpose, a special optical element is necessary, which is at least 70% transparent to the light emanating from the screen, and which deflects laterally incident light from light sources into a restricted angular range in such a way that in directions alpha greater than gamma with gamma greater than 20 degrees to the surface normal of the screen, the light emanating from the screen is superimposed with the light deflected by the optical element, thereby substantially only the image displayed on the screen from angles beta less gamma to the surface normal of the Screen is fully visible.

The above-mentioned methods and arrangements generally have the disadvantage that they significantly reduce the brightness of the basic screen and / or require an active, but at least a special, optical element for mode switching and / or require costly and expensive manufacture and / or or reduce the resolution in freely viewable mode.

Description of the invention

It is therefore an object of the invention to describe a screen and a method by which a secure display of information can be realized by an optionally limited viewing angle, in a second mode, a free, if possible in the viewing angle unrestricted vision should be possible. The invention should be as inexpensive as possible to implement with simple means. In both modes, the highest possible resolution, particularly preferably the native resolution of the screen used, should be visible. Furthermore, only the least possible loss of light should be introduced through the solution.

• – eine flächenartig ausgedehnte Hintergrundbeleuchtung, die in der Betriebsart B1 für einen freien Sichtmodus Licht in einen nicht eingeschränkten Winkelbereich abstrahlt, und die in der Betriebsart B2 für einen eingeschränkten Sichtmodus Licht in einen eingeschränkten Winkelbereich abstrahlt,
• – einen in Betrachtungsrichtung vor der Hintergrundbeleuchtung angeordneten transmissiven Bildgeber, beispielsweise ein LCD-Panel oder ein anderer durchscheinender Lichtmodulator,
• – ein in Betrachtungsrichtung vor dem Bildgeber gelegener (d. h. mit oder ohne Abstand, z. B. 0 mm, 1 mm, 2 mm, 5 mm, 8 mm oder 10 mm zum transmissiven Bildgeber), plattenförmiger Lichtleiter, welcher aus einem transparenten, thermoplastischen oder thermoelastischen Kunststoff und darin verteilten Streupartikeln besteht, und
• – Leuchtmittel, die seitlich an Schmalseiten des Lichtleiters angeordnet sind,
• – wobei in der Betriebsart B1 die Leuchtmittel ausgeschaltet sind, so dass das von der Hintergrundbeleuchtung ausgehende und sodann durch den transmissiven Bildgeber hindurchdringende Licht im Wesentlichen unbeeinflusst durch den Lichtleiter hindurchtritt, und
• – wobei in der Betriebsart B2 die Leuchtmittel eingeschaltet sind, so dass das von der Hintergrundbeleuchtung in einen eingeschränkten Winkelbereich abgestrahlte und sodann durch den transmissiven Bildgeber hindurchdringende Licht von Licht überlagert wird, welches der Lichtleiter nunmehr flächig über einen großen Winkelbereich („groß” heißt in diesem Falle über einen Winkelbereich von mindestens 120 Grad oder mehr, bis nahezu zum Halbraum vor dem Lichtleiter) abstrahlt, wodurch die Restsichtbarkeit eines auf dem transmissiven Bildgeber dargestellten Bildes außerhalb des besagten eingeschränkten Winkelbereiches (deutlich) verringert oder sogar vollständig abgestellt wird.

This object is achieved according to the invention by a screen which can be operated in at least two operating modes B1 for a free viewing mode and B2 for a restricted viewing mode

• An areally extended backlight, which in the operating mode B1 radiates light into a non-restricted angular range for a free viewing mode, and which emits light in a restricted angular range in the operating mode B2 for a restricted viewing mode,
• A transmissive imager arranged in the viewing direction in front of the backlight, for example an LCD panel or another translucent light modulator,
• - a viewing direction ahead of the imager (ie, with or without spacing, eg, 0 mm, 1 mm, 2 mm, 5 mm, 8 mm, or 10 mm from the transmissive imager), a plate-shaped light guide made of a transparent, thermoplastic or thermoelastic plastic and scattering particles dispersed therein, and
• Illuminants, which are arranged laterally on narrow sides of the light guide,
• Wherein in the operating mode B1, the lighting means are switched off, so that the light emanating from the backlight and then penetrating through the transmissive imager passes through the light guide essentially uninfluenced, and
• - In the operating mode B2, the bulbs are turned on, so that the radiated from the backlight in a limited angular range and then penetrating through the transmissive imager light is superimposed by light, which now the light guide over a large angular range ("big" in this case about one Angle range of at least 120 degrees or more, to almost the half space in front of the light guide) radiates, whereby the residual visibility of an image displayed on the transmissive imager outside the said restricted angular range (significantly) reduced or even turned off completely.

In the operating mode B2, the image perceptible from oblique viewing directions blocked by the angle restriction is depending on the configuration of the lighting means 4 a gray or white surface, but usually not a black surface, since the light, which is the light guide 3 emits, even a black image content visibly outshines.

The areally extended backlight may be formed, for example, as in the scriptures WO 2015/121398 or even the US 2013/0308185 proposed. Other embodiments are of course possible.

Although such areal-extended backlight radiates light into a limited angular range in most known B2 mode configurations for a limited viewing mode, this directional selection is far from complete, resulting in being on a transmissive imager against such backlighting even from an oblique view, the image content can still be completely or largely recognized, albeit with low brightness and / or with a weak light-dark contrast. This still possible oblique view is completely or almost completely eliminated on account of the invention: by the superposition of the light emitted by the background illumination in a restricted angular range and then penetrating through the transmissive imager light with light, which now radiates the light guide over a large angular range, the residual visibility of an image displayed on the transmissive imager is reduced massively outside the said restricted angular range, often even completely turned off. Among other things, said residual visibility has to do with the fact that many LCD panels have a volume scattering and / or a scattering anti-glare surface which partially scatters the light arriving from behind and directed into restricted solid angle, whereby residual visibility is also given at oblique angles ,

As a rule, the plate-shaped light guide has a haze <10%, preferably <4%, measured according to FIG ASTM D1003 on. Also suitable as scattering particles are, in particular, titanium dioxide particles. However, other embodiments are possible, for example with particles of barium sulfate, with silsesquioxane particles or with crosslinked polystyrene particles or other types of particles. The scattering particles are generally distributed homogeneously, whereby the optical element has no inhomogeneous optical structure.

Furthermore, the plate-shaped light guide comprises at least two opposing large surfaces, which are arranged parallel or inclined to each other. A wedge-shaped structure is also possible, although parallel large areas are advantageous.

Sensible thicknesses of the light guide are typically between 0.5 mm and 4 mm inclusive. Other thicknesses may also be appropriate case-related.

• – einem flächigen Strahler, der vorzugsweise als Lichtleiter mit seitlich angeordneten Leuchtmitteln ausgebildet ist,
• – mindestens einem in den flächigen Strahler integrierten und/oder davor angeordneten Lichtkollimator (z. B. 2 gekreuzte BEF-Folien, 2 gekreuzte „Optical Lighting Films” (OLF) Typ 2301 von 3M^TM, und/oder einen oder mehrere Privacyfilter, z. B. Vikuiti von 3M^TM)
• – einem in Betrachtungsrichtung vor dem Lichtkollimator angeordneten plattenförmigen, transparenten (vorderen) Lichtleiter, welcher aus einem transparenten, thermoplastischen oder thermoelastischen Kunststoff und darin verteilten Streupartikeln besteht, sowie
• – (vordere) Leuchtmitteln, die seitlich an Schmalseiten des (vorderen) Lichtleiters angeordnet sind,
• – wobei in der Betriebsart B1 für einen freien Sichtbereich mindestens die (vordere) Leuchtmittel, und wahlweise auch der flächige Strahler eingeschaltet sind (d. h. wenn der flächige Strahler als Lichtleiter ausgebildet ist, werden selbstredend die Leuchtmittel des flächigen Strahlers eingeschaltet), und
• – wobei in der Betriebsart B2 für einen eingeschränkten Sichtbereich die (vorderen) Leuchtmittel aus- und der flächige Strahler eingeschaltet sind (d. h. wenn der flächige Strahler als Lichtleiter ausgebildet ist, werden ebenso die ihm zugeordneten Leuchtmittel eingeschaltet).

In advantageous embodiments, the backlight is off

• A flat radiator, which is preferably designed as a light guide with laterally arranged light sources,
• At least one light collimator integrated into the planar radiator and / or arranged in front of it (eg 2 crossed BEF foils, 2 crossed optical lighting films (OLF) type 2301 from 3M ^™ , and / or one or more privacy filters, e.g. B. Vikuiti from 3M ^™ )
• - A arranged in the viewing direction in front of the light collimator plate-shaped, transparent (front) light guide, which consists of a transparent, thermoplastic or thermoelastic plastic and dispersed therein scattering particles, as well as
• - (front) bulbs, which are arranged laterally on narrow sides of the (front) light guide,
• - Wherein in the operating mode B1 for a clear field of view, at least the (front) bulbs, and optionally also the flat radiator are turned on (ie if the flat radiator is designed as a light guide, of course, the bulbs of the flat radiator are turned on), and
• - Wherein in the mode B2 for a limited field of view, the (front) bulbs off and the flat radiator are turned on (ie if the flat radiator is designed as a light guide, also its associated bulbs are turned on).

For the (front) light guide and possibly the light guide of the flat radiator, the above-mentioned design options for the light guide above the imager apply analogously.

Advantageously used as scattering particles in the transparent light guides titanium dioxide particles having an average particle size of 150-500 nm in a concentration based on the weight of the respective optical fiber of 0.01-300 ppm by weight.

It is possible that the transparent light guides each consist of a matrix plastic A and scattering particles of a polymer B distributed therein, wherein the proportion of the scattering particles consisting of polymer B in each case 0.01 to 3 weight percent based on the matrix plastic A, and the refractive index nD (B) of the polymer B is at least 0.002 units above the refractive index nD (A) of the matrix plastic A.

Furthermore, it can bring advantages if on the upper side of the imager and / or on at least one of the large surfaces of the light guide in front of the imager means for reflection reduction, such as an anti-glare and / or an anti-reflection coating, are arranged. In particular, an antiglare coating in connection with the invention not only serves to reduce the direct reflections of external light spots, but rather also allows the scattered back reflection of the light emitted by the light guide in front of the imager to the imager.

In all the aforementioned embodiments, the said light sources can be LEDs or LED rows or laser diodes. Other variants are conceivable and are within the scope of the invention.

Particularly advantageously, the screen according to the invention finds use for entering or displaying confidential data, for example PIN PIN numbers, e-mails, SMS or passwords, at ATMs, payment terminals or mobile devices.

• – für die Betriebsart B1: Flächiges Abstrahlen von Licht in einen nicht eingeschränkten Winkelbereich für einen freien Sichtmodus, bevorzugt von einer flächenartig ausgedehnten Hintergrundbeleuchtung, oder alternativ
• – für die Betriebsart B2: Flächiges Abstrahlen von Licht in einen eingeschränkten Winkelbereich für einen eingeschränkten Sichtmodus, bevorzugt von einer (d. h., von der besagten) flächenartig ausgedehnten Hintergrundbeleuchtung,
• – Modulation des flächig abgestrahlten Lichtes, um diesem Licht Bildinformationen aufzuprägen, bevorzugt vermittels eines transmissiven Bildgebers, beispielsweise eines LCD-Panels oder einem Shutter,
• – Durchleiten des so modulierten Lichtes durch einen plattenförmigen Lichtleiter (in der Regel durch die Großflächen des Lichtleiter), welcher aus einem transparenten, thermoplastischen oder thermoelastischen Kunststoff und darin verteilten Streupartikeln besteht, wobei an den Schmalseiten des Lichtleiters Leuchtmittel seitlich angeordnet sind,
• – für die Betriebsart B1: Ausschalten der Leuchtmittel, so dass das flächig abgestrahlte und sodann mit den Bildinformationen modulierte Licht im Wesentlichen unbeeinflusst durch den Lichtleiter hindurchtritt, oder
• – alternativ für die Betriebsart B2: Einschalten der Leuchtmittel, so dass das flächig abgestrahlte und sodann mit den Bildinformationen modulierte Licht von Licht überlagert wird, welches der Lichtleiter nunmehr flächig über einen großen Winkelbereich abstrahlt („groß” heißt in diesem Falle über einen Winkelbereich von mindestens 120 Grad oder mehr, bis nahezu zum Halbraum vor dem Lichtleiter), wodurch die Restsichtbarkeit der Bildinformationen außerhalb des besagten eingeschränkten Winkelbereiches sehr deutlich verringert oder vollständig abgestellt wird.

The object of the invention is also achieved by a method according to the invention for displaying image information in at least two operating modes B1 for a free viewing mode and B2 for a restricted viewing mode, comprising the following steps:

• For the operating mode B1: flat emission of light into a non-restricted angular range for a free viewing mode, preferably from a planar-extended backlight, or alternatively
• For the operating mode B2: areal emission of light into a restricted angle range for a restricted viewing mode, preferably from a (in other words from said) areally extended backlight,
• Modulation of the surface-emitted light in order to impose image information on this light, preferably by means of a transmissive imager, for example an LCD panel or a shutter,
• Passing the thus modulated light through a plate-shaped light guide (usually through the large surfaces of the light guide), which consists of a transparent, thermoplastic or thermoelastic plastic and scattering particles distributed therein, wherein on the narrow sides of the light guide bulbs are arranged laterally,
• For the operating mode B1: switching off the lighting means, so that the light radiated in two dimensions and then modulated with the image information passes through the light guide substantially uninfluenced, or
• - Alternatively, for the operating mode B2: switching on the light source, so that the surface radiated and then modulated with the image information light is superimposed by light, which now broadcasts the light guide over a large angular range ("big" means in this case over an angular range of at least 120 degrees or more, to almost the half space in front of the light guide), whereby the residual visibility of the image information outside of said restricted angle range is very significantly reduced or completely turned off.

In operating mode B2, the image perceptible from oblique viewing directions blocked by the angle restriction is a gray or white surface, as a rule, but not a black surface since the light which the light guide emits is itself a black image content Visibly outshined.

If the surface emission of light is carried out by an areally extended backlight, then this can be formed, for example, as in the scriptures WO 2015/121398 or even the US 2013/0308185 proposed. Other embodiments are of course possible.

Although such areal-extended backlight radiates light into a limited angular range in most known B2 mode configurations for a limited viewing mode, this directional selection is far from complete, resulting in being on a transmissive imager against such backlighting even from an oblique view, the image content can still be completely or largely recognized, albeit with low brightness and / or with a weak light-dark contrast. This still possible oblique view is completely or almost completely eliminated on account of the invention: by the superposition of the light emitted by the background illumination in a restricted angular range and then penetrating through the transmissive imager light with light, which now radiates the light guide over a large angular range, the residual visibility of an image displayed on the transmissive imager is massively reduced outside of said restricted angle range.

The plate-shaped light guide generally has a haze of less than 10%, preferably less than 4%, measured according to ASTM D1003 , on. Also suitable as scattering particles are, in particular, titanium dioxide particles. However, other embodiments are possible, for example with particles of barium sulfate, with silsesquioxane particles or with crosslinked polystyrene particles or other types of particles.

• – einem flächigen Strahler, vorzugsweise einem Lichtleiter mit seitlich angeordneten Leuchtmitteln,
• – mindestens einem in den flächigen Strahler integrierten und/oder davor angeordneten Lichtkollimator (dieser Lichtkollimat besteht beispielsweise aus 2 gekreuzten BEF-Folien, 2 gekreuzten Optical-Lighting Films von 3M^TM, und/oder einem oder mehreren Privacyfiltern, z. B. Vikuiti von 3M^TM, oder einem 4way-Light Control Filter von Shin Etsu),
• – einem in Betrachtungsrichtung vor dem Lichtkollimator angeordneten plattenförmigen, transparenten (vorderen) Lichtleiter, welcher aus einem transparenten, thermoplastischen oder thermoelastischen Kunststoff und darin verteilten Streupartikeln besteht, (für die Ausgestaltung dieses (vorderen) Lichtleiters gelten die weiter oben gemachten Angaben zum Lichtleiter vor dem Bildgeber analog) sowie
• – (vordere) Leuchtmitteln, die seitlich an Schmalseiten des (vorderen) Lichtleiters angeordnet sind,
• – wobei in der Betriebsart B1 für einen freien Sichtbereich mindestens die (vorderen) Leuchtmittel, und wahlweise auch der flächige Strahler eingeschaltet sind (d. h., wenn der flächige Strahler als Lichtleiter ausgebildet ist, werden selbstredend die Leuchtmittel des flächigen Strahlers eingeschaltet), und
• – wobei in der Betriebsart B2 für einen eingeschränkten Sichtbereich die (vorderen) Leuchtmittel aus- und der flächige Strahler eingeschaltet sind (d. h., wenn der flächige Strahler als Lichtleiter ausgebildet ist, werden selbstredend die Leuchtmittel des flächigen Strahlers eingeschaltet).

In an advantageous embodiment, a background illumination is used for the two-dimensional emission of light in both modes B1 and B2, which consists of

• A flat radiator, preferably a light guide with laterally arranged light sources,
• At least one light collimator integrated in the planar radiator and / or arranged in front of it (this light collimat consists, for example, of 2 crossed BEF foils, 2 crossed 3M ^™ optical-lighting films, and / or one or more privacy filters, eg Vikuiti of 3M ^™ , or a 4way Light Control Filter by Shin Etsu),
• - A arranged in the viewing direction in front of the light collimator plate-shaped, transparent (front) light guide, which consists of a transparent, thermoplastic or thermoelastic plastic and dispersed therein scattering particles (for the design of this (front) light guide, the statements made above on the light guide apply before Imager analog) and
• - (front) bulbs, which are arranged laterally on narrow sides of the (front) light guide,
• - Wherein in the operating mode B1 for a clear field of view, at least the (front) bulbs, and optionally also the flat radiator are turned on (ie, when the planar radiator is designed as a light guide, of course, the bulbs of the flat radiator are turned on), and
• - In the mode B2 for a limited field of view, the (front) bulbs off and the flat radiator are turned on (ie, when the flat radiator is designed as a light guide, of course, the bulbs of the flat radiator are turned on).

Titanium dioxide particles having an average particle size of 150-500 nm in a concentration based on the weight of the respective optical waveguide of 0.01-300 ppm by weight are preferably used as scattering particles in all transparent light guides present.

Furthermore, it may be advantageous if on the upper side of the imager and / or on at least one of the large surfaces of the light guide in front of the imager means for reflection reduction, such as a Antiglare- and / or an antireflective coating, are arranged. In particular, an antiglare coating in connection with the invention not only serves to reduce direct reflections of external light spots, but rather also permits the scattered back reflection of the light emitted by the light guide in front of the image generator to the imager.

In all the aforementioned embodiments, the said light sources can be LEDs or LED rows or laser diodes. Other variants are conceivable and are within the scope of the invention.

For all embodiments, it holds true that each available optical waveguide has at least one light entry surface and at least one light exit surface, wherein the ratio of light exit surface to light entry surface is at least 4.

It is particularly preferred for the light guide (s) to use a concentration of scattering agents of titanium dioxide particles of 0.1-50 ppm by weight, preferably 0.1-10 ppm by weight. In this case, the titanium dioxide particles have an average particle size of 160 to 450 nm, more preferably from 170 to 400 nm. The Haze of the optical fiber, measured according to ASTM D1003, is in the range of 0.2 to 2%.

Behind the rearmost light guide the backlight, if there is a light guide, for example, a white and / or reflective surface may be arranged.

Furthermore, the optical waveguides can contain at least 40% by weight, preferably at least 60% by weight, of polymethyl methacrylate, based on their weight.

The planar radiator can be configured, for example, as a side-light, edgelight, direct LED backlight, edge LED backlight, as dark-field illumination, as an OLED or as another surface radiator.

In the screen according to the invention and also in the implementation of the method according to the invention may further be provided an electronic control, which gradually controls the transition between the operating modes B1 and B2 or vice versa by the backlight, the lighting and possibly other components are controlled accordingly. It can be provided that over a time course each time the brightness of one or more components (usually lighting means) is driven to zero, while at the same time the brightness of other components (usually other bulbs) increased to a maximum or a certain value is, and vice versa.

Furthermore, it can be provided in certain embodiments that the light guide is partially mirrored in front of the imager on its side facing the imager.

In this case, the intensity of the silver coating to compensate for differences in brightness in the operating mode B1 over the surface of the decoupled from the light guide light can be designed to vary, or only those areas are partially mirrored, in which the brightness has fallen below a predetermined limit without mirroring.

Furthermore, the comments and design variants, which have been described above for the screen according to the invention apply in analogous transmission for the inventive method.

Basically, the performance of the invention is maintained when the parameters described above are varied within certain limits.

Furthermore, the desired restricted angle ranges for the restricted view mode B2 can be independently defined and translated for the horizontal and vertical directions, respectively. For example, in the vertical direction, a larger angle (or perhaps no restriction at all) might be useful than in the horizontal direction, such as when ATMs are supposed to see something of different sizes while side-ins should be severely restricted. For POS payment terminals, on the other hand, due to security regulations, visibility restrictions in mode B2 are often necessary in both horizontal and vertical directions.

It is understood that the features mentioned above and those yet to be explained below can be used not only in the specified combinations but also in other combinations or alone, without departing from the scope of the present invention.

The invention will be explained in more detail below with reference to drawings, which also show features essential to the invention. It shows

1 a schematic diagram for the extraction of light, which is laterally coupled into an optical waveguide, in a large solid angle,

2 a schematic diagram for the passage of light, which results from a backlight, through a light guide,

3 a schematic diagram of the screen according to the invention of the operating mode B2 for a limited viewing mode in which the imager is illuminated with limited in solid angle light, wherein the modulated by the imager light of light from a light guide 3 is superimposed to enhance the privacy effect,

4 a schematic diagram of the screen according to the invention in the mode B1 for a free viewing mode in which the imager is illuminated with not limited in solid angle light, wherein the modulated by the imager light from light from a light guide 3 is superimposed,

5 a schematic diagram of an advantageous embodiment of a backlight 2 , shown here for operating mode B1 for a free viewing mode,

6 a schematic diagram of an advantageous embodiment of a backlight 2 , shown here for the operating mode B2 for a limited viewing mode,

7 an exemplary measurement graphs for the visibility when looking at a screen according to the invention in the mode B2, and

8th an exemplary measurement of the visibility when looking at a screen according to the invention in the mode B1.

The drawings are not true to scale and represent only schematic representations (usually sectional representations) again.

In 1 is a schematic diagram for the extraction of light, the side of bulbs 4 in a light guide 3 - shown here only as a small section in sectional view - coupled, is shown in a large solid angle. The small dots stylize scattering particles as scattering centers for the light, which laterally from the bulbs 4 is coupled. Due to total reflection, rays of the coupled-in light (bold lines) on the outer wall are returned to the light guide 3 thrown until they finally hit a scattering article to the desired coupling. The decoupling is stylized by a multitude of thin rays. The representation in 1 is highly stylized for better visibility; in reality there is a very large number of beam paths in the light guide 3 implemented.

2 shows a schematic diagram for the passage of light from a (not shown in the form of) backlight 2 due to a light guide 3 , The scattering particles play thereby a substantially negligible role, since the light from the backlight 2 comes from, ie not laterally through a narrow side of bulbs 4 is coupled and therefore not or hardly by total reflection in the light guide 3 is directed back and forth.

3 gives a schematic diagram of the screen according to the invention 1 in the B2 mode for a limited viewing mode, where the imager 5 is illuminated with limited in solid angle light, which by the imager 5 modulated light from light from a light guide 3 (shown with dashed arrows) is superimposed to enhance the privacy effect.

• – eine flächenartig ausgedehnte Hintergrundbeleuchtung 2, die in der Betriebsart B2 für einen eingeschränkten Sichtmodus Licht in einen eingeschränkten Winkelbereich abstrahlt,
• – einen in Betrachtungsrichtung vor der Hintergrundbeleuchtung 2 angeordneten transmissiven Bildgeber 5, beispielsweise ein LCD-Panel,
• – ein in Betrachtungsrichtung vor dem Bildgeber 5 gelegener (d. h. mit oder ohne Abstand zum transmissiven Bildgeber 5), plattenförmiger Lichtleiter 3, welcher aus einem transparenten, thermoplastischen oder thermoelastischen Kunststoff und darin verteilten Streupartikeln besteht, und
• – Leuchtmittel 4, die seitlich an Schmalseiten des Lichtleiters 3 angeordnet sind, (in 3 sind nur Leuchtmittel 4 an einer Seite eingezeichnet, diese können aber z. B. zusätzlich auch auf der gegenüberliegenden Schmalseite des Lichtleiters 3, oder an 3 oder sogar an 4 Schmalseiten vorhanden sein),
• – wobei in der Betriebsart B2 die Leuchtmittel 4 eingeschaltet sind, so dass das von der Hintergrundbeleuchtung 2 in einen eingeschränkten Winkelbereich abgestrahlte und sodann durch den transmissiven Bildgeber 5 hindurchdringende Licht (mit den fetten Pfeilen eingezeichnet in 3) von Licht (mit Strichlinien dargestellt) überlagert wird, welches der Lichtleiter 3 nunmehr flächig über einen großen Winkelbereich („groß” heißt in diesem Falle über einen Winkelbereich von mindestens 120 Grad oder mehr, bis nahezu zum Halbraum vor dem Lichtleiter 3) abstrahlt, wodurch die Restsichtbarkeit eines auf dem transmissiven Bildgeber 5 dargestellten Bildes außerhalb des besagten eingeschränkten Winkelbereiches (deutlich) verringert oder sogar vollständig abgestellt wird.

In the operating mode B2 are in the screen 1 So the following components are active:

• - an arealwide backlight 2 which emits light in a restricted angular range in the operating mode B2 for a limited viewing mode,
• - a viewing direction in front of the backlight 2 arranged transmissive imagers 5 for example, an LCD panel,
• A viewing direction in front of the imager 5 located (ie with or without distance to the transmissive imager 5 ), plate-shaped light guide 3 which consists of a transparent, thermoplastic or thermoelastic plastic and scattering particles distributed therein, and
• - Illuminants 4 , the side of narrow sides of the light guide 3 are arranged (in 3 are only bulbs 4 drawn on one side, but these can z. B. in addition also on the opposite narrow side of the light guide 3 , or be present at 3 or even at 4 narrow sides),
• - Where in the mode B2, the bulbs 4 are turned on, so that by the backlight 2 radiated into a restricted angular range and then through the transmissive imager 5 penetrating light (with the bold arrows drawn in 3 ) is superimposed by light (shown with dashed lines), which is the light guide 3 now flat over a large angular range ("big" means in this case over an angular range of at least 120 degrees or more, to almost the half space in front of the light guide 3 ), resulting in the residual visibility of one on the transmissive imager 5 displayed outside the said restricted angular range (significantly) reduced or even turned off completely.

In contrast, shows 4 a schematic diagram of the screen according to the invention in the mode B1 for a free viewing mode in which the imager is illuminated with unconstrained in solid angle light, wherein the modulated by the imager light from light from a light guide 3 is superimposed.

• – eine flächenartig ausgedehnte Hintergrundbeleuchtung 2, die in der Betriebsart B1 für einen freien Sichtmodus Licht in einen nicht eingeschränkten Winkelbereich abstrahlt,
• – einen in Betrachtungsrichtung vor der Hintergrundbeleuchtung 2 angeordneten transmissiven Bildgeber 5, beispielsweise ein LCD-Panel oder ein anderer durchscheinender Lichtmodulator,
• – ein in Betrachtungsrichtung vor dem Bildgeber 5 gelegener (d. h. mit oder ohne Abstand zum transmissiven Bildgeber 5), plattenförmiger Lichtleiter 3, welcher aus einem transparenten, thermoplastischen oder thermoelastischen Kunststoff und darin verteilten Streupartikeln besteht, und
• – Leuchtmittel 4, die seitlich an Schmalseiten des Lichtleiters 3 angeordnet,
• – wobei in der Betriebsart B1 die Leuchtmittel 4 ausgeschaltet sind, so dass das von der Hintergrundbeleuchtung 2 ausgehende und sodann durch den transmissiven Bildgeber 5 hindurchdringende Licht im Wesentlichen unbeeinflusst durch den Lichtleiter 3 hindurchtritt.

In the operating mode B1 are in the screen 1 So the following components are active:

• - an arealwide backlight 2 which, in the operating mode B1, emits light in a non-limited angular range for a free viewing mode,
• - a viewing direction in front of the backlight 2 arranged transmissive imagers 5 for example, an LCD panel or other translucent light modulator,
• A viewing direction in front of the imager 5 located (ie with or without distance to the transmissive imager 5 ), plate-shaped light guide 3 which consists of a transparent, thermoplastic or thermoelastic plastic and scattering particles distributed therein, and
• - Illuminants 4 , the side of narrow sides of the light guide 3 disposed
• - In B1 mode, the bulbs 4 are turned off, so that by the backlight 2 outgoing and then through the transmissive imager 5 penetrating light substantially unaffected by the light guide 3 passes.

As a rule, the plate-shaped light guide has a haze <10%, preferably <4%, measured according to FIG ASTM D1003 on. Also suitable as scattering particles are, in particular, titanium dioxide particles. However, other embodiments are possible, for example with particles of barium sulfate, with silsesquioxane particles or with crosslinked polystyrene particles or other types of particles. The scattering particles are usually distributed homogeneously, whereby the light guide 3 does not have an inhomogeneous optical structure.

Furthermore, the plate-shaped light guide contains 3 at least two opposing large surfaces, which are arranged parallel or inclined to each other. A wedge-shaped structure is possible, although parallel large areas are advantageous.

The extensive backlighting 2 can be formed, for example, as in the WO 2015/121398 proposed.

In addition shows 5 a schematic diagram of an advantageous embodiment of a backlight 2 , shown here for mode B1 for a clear view mode. According to shows 6 a schematic diagram of an advantageous embodiment of a backlight 2 , shown here for the operating mode B2 for a limited viewing mode.

• – einem flächigen Strahler 2a, der vorzugsweise als Lichtleiter mit seitlich angeordneten Leuchtmitteln 2b ausgebildet ist,
• – mindestens einem in den flächigen Strahler 2a integrierten und/oder davor angeordneten Lichtkollimator 2c (z. B. 2 gekreuzte BEF-Folien, 2 gekreuzte „Optical Lighting Films” (OLF) Typ 2301 von 3M^TM, und/oder einen oder mehrere Privacyfilter, z. B. Vikuiti von 3M^TM),
• – einem in Betrachtungsrichtung vor dem Lichtkollimator 2c angeordneten plattenförmigen, transparenten Lichtleiter 2d, welcher aus einem transparenten, thermoplastischen oder thermoelastischen Kunststoff und darin verteilten Streupartikeln besteht, sowie
• – Leuchtmitteln 2e, die seitlich an Schmalseiten des Lichtleiters 2d angeordnet sind,
• – wobei in der in 5 dargestellten Betriebsart B1 für einen freien Sichtbereich mindestens die Leuchtmittel 2e, und hier im Beispiel auch der flächige Strahler 2a eingeschaltet sind (d. h. wenn der flächige Strahler 2a als Lichtleiter ausgebildet ist, werden selbstredend die Leuchtmittel 2b des flächigen Strahlers 2a eingeschaltet), und
• – wobei in der in 6 dargestellten Betriebsart B2 für einen eingeschränkten Sichtbereich die Leuchtmittel 2e aus- und der flächige Strahler 2a eingeschaltet sind (d. h. wenn der flächige Strahler 2a als Lichtleiter ausgebildet ist, werden ebenso die Leuchtmittel 2b eingeschaltet).

Such a backlight 2 For example, it consists of

• - a flat radiator 2a , preferably as a light guide with laterally arranged bulbs 2 B is trained,
• - At least one in the flat radiator 2a integrated and / or arranged in front of light collimator 2c (eg 2 crossed BEF foils, 2 crossed optical lighting films (OLF) type 2301 from 3M ^™ , and / or one or more privacy filters, eg Vikuiti from 3M ^™ ),
• A viewing direction in front of the light collimator 2c arranged plate-shaped, transparent light guide 2d which consists of a transparent, thermoplastic or thermoelastic plastic and scattering particles distributed therein, as well as
• - Lamps 2e , the side of narrow sides of the light guide 2d are arranged
• - where in the in 5 illustrated operating mode B1 for a free field of view, at least the bulbs 2e , and here in the example also the flat radiator 2a are turned on (ie when the areal radiator 2a is designed as a light guide, of course, the bulbs 2 B of the flat radiator 2a switched on), and
• - where in the in 6 illustrated mode B2 for a limited field of view, the lighting means 2e off and the surface radiator 2a are turned on (ie when the areal radiator 2a is designed as a light guide, also the bulbs 2 B switched on).

For the light guide 2d apply the above-mentioned design options to the light guide 3 analogous.

The thick arrows on the bulbs 2 B and 2e such as 4 in the 3 . 5 and 6 indicate that they are turned on.

The bulbs are preferably (cold) white luminous LED lines.

Be advantageous as scattering particles in the transparent light guides 2d . 3 (possibly also 2 B ) Titanium dioxide particles having an average particle size of 150-500 nm used in a concentration based on the weight of the respective optical fiber of 0.01-300 ppm by weight.

It is also possible that the transparent light guides 2d . 3 (possibly also 2 B ) each consist of a matrix plastic A and scattering particles of a polymer B distributed therein, wherein the proportion of the scattering particles consisting of polymer B in each case 0.01 to 3 weight percent based on the matrix plastic A, and the refractive index nD (B) of the polymer B to at least 0.002 units above the refractive index nD (A) of the matrix plastic A.

Furthermore, it can bring benefits if on the top of the imager 5 and / or on at least one of the large surfaces of the light guide 3 are arranged for reflection reduction, such as an antiglare and / or an anti-reflective coating. In particular, a Antiglarebeschichtung used in connection with the invention not only the reduction of direct reflections of external light spots, but also allows the scattered back reflection of the imager 5 out of the light guide 3 radiated light.

An above-described, areally extended backlight 2 While, in most known B2 mode configurations, for a limited viewing mode, while emitting light into a limited angular range, this directional selection is far from complete, resulting in the presence of a transmissive imager 5 even from an oblique view, the image content can still be completely or largely recognizable before such a backlighting, albeit with low brightness and / or with a weak light-dark contrast. This still possible oblique view is completely or almost completely eliminated due to the invention: by the superposition of the backlight 2 radiated into a restricted angular range and then through the transmissive imager 5 penetrating light with light, which is the light guide 3 now radiated over a wide range of angles, the residual visibility of a on the transmissive imager 5 shown mass outside the said restricted angular range massively reduced.

This situation is for better understanding by means of measured values in the 7 and 8th visualized. So shows 7 a graph for the visibility when looking at an exemplary screen according to the invention in the operating mode B2, and 8th a graph for the visibility when looking at a screen according to the invention in the mode B1.

In both representations, the abscissa represents the viewing angle, measured from the center of the screen and relative to the perpendicular bisector, while the ordinate represents a relative luminance value for the luminance (without unit, since relative value). Similarly, for both drawings, the dashed trace represents the measurement for a white area in the center of the screen, while the solid trace shows the measurement for a black area in the center of the screen.

In 7 is clearly seen that in the operating mode B2 from oblique, blocked by the angle restriction insight directions from beyond +/- 30 degrees to the center perpendicular to the left and Right perceivable image in design of all bulbs as white LEDs (or LED lines) corresponds to a gray or white surface: Here is namely the contrast between black and white quasi canceled, since the light, which is the light guide 3 emits even a black image content visible gray or white outshines. With regard to the interpretation of the measurement curve, this means that the difference for looking at a black and a white surface is virtually absent from viewing angles beyond +/- 30 degrees left and right in relation to the mid-perpendicular in the embodiment of this measurement example, so that an image content is not more recognizable and the screen for oblique view is active. Compared with conventional technologies, the privacy in B2 mode is significantly improved. Although in this mode of operation due to the light guide 3 outgoing light, that of the imager 5 outgoing light, on which the image information is modulated, superimposed, also reduces its light-dark contrast. However, it is still large enough to show a clear, bright image from directions corresponding to small angles around the mid-perpendicular, for example less than 20 degrees.

In contrast, shows 8th in that in operating mode B1 a clear visual contrast can also be achieved from oblique angles, in particular because there is no superposition with light from the light guide 3 is present, as this does not emit light in this mode and that by the imager 5 penetrating light passes through virtually unaffected.

The method according to the invention can be explained analogously with reference to the drawings. For redundancy reasons, therefore, the description is not repeated here.

Both the above-described screen according to the invention and the method according to the invention make it possible to implement solutions which can be implemented well in order to reliably display information through an optionally restricted viewing angle, while in a further operating mode a free, as far as possible unobstructed viewing angle is possible. The invention can be realized inexpensively by simple means. In both modes, the native resolution of the imager used can be used. In addition, only a small or depending on the embodiment even no loss of light will be introduced through the solution.

The invention described above can advantageously be applied everywhere where confidential data is displayed and / or input, such as PIN entry or data display at ATMs or payment terminals or for password entry or reading emails on mobile devices.

In contrast to designs in the prior art, in which usually still a residual visibility is also available from oblique angles, the invention allows, depending on the configuration, the complete extinction of the residual visibility from blocked viewing angles.

LIST OF REFERENCE NUMBERS

B1

Operating mode for a free viewing mode

B2

Operating mode for a restricted viewing mode

1

screen

2

Backlight

2a

Flat radiator

2 B

Lamp

2c

light collimator

2d

plate-shaped light guide

2e

Lamp

3

plate-shaped light guide

4

Lamp

5

transmissive imager

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

• US 6765550 [0003]
• US 5993940 [0004]
• WO 2012/033583 [0005]
• US 2009/0067156 [0006, 0007, 0008]
• US 2012/0235891 [0009, 0009]
• JP 2007-155783 [0010]
• GB 2428128 A [0011]
• US 2013/0308185 [0012, 0018, 0032]
• DE 102014003298 A1 [0013]
• WO 2015/121398 [0018, 0032, 0069]

Cited non-patent literature

• ASTM D1003 [0020]
• ASTM D1003 [0034]
• ASTM D1003 [0067]

Claims (10)

Screen ( 1 ), which can be operated in at least two operating modes B1 for a free viewing mode and B2 for a restricted viewing mode, comprising - an areally extended backlighting ( 2 ), which emits light in an unrestricted angular range in the operating mode B1 for a free viewing mode, and which emits light in a limited angular range in the operating mode B2 for a restricted viewing mode, - one in the viewing direction in front of the backlight ( 2 ) arranged transmissive imagers ( 5 ), for example an LCD panel, - a viewing direction in front of the imager ( 5 ) located, plate-shaped light guide ( 3 ), which consists of a transparent, thermoplastic or thermoelastic plastic and scattering particles distributed therein, and - illuminant ( 4 ), which laterally on narrow sides of the light guide ( 3 ) are arranged, - wherein in the operating mode B1, the lighting means ( 4 ) are turned off so that the backlight ( 2 ) and then by the transmissive imager ( 5 ) penetrating light substantially unaffected by the light guide ( 3 ), and - wherein in the operating mode B2 the lighting means ( 4 ) are switched on, so that the of the backlight ( 2 ) radiated into a restricted angular range and then through the transmissive imager ( 5 ) penetrating light is superimposed by light, which the light guide ( 3 ) radiates now over a wide angular range, whereby the residual visibility of a on the transmissive imager ( 5 ) is reduced outside the said restricted angular range. Screen ( 1 ) according to claim 1, characterized in that the backlight ( 2 ) consists of - a flat radiator ( 2a ), preferably a light guide with laterally arranged light sources ( 2 B ), - at least one in the flat radiator ( 2a ) integrated and / or arranged in front of light collimator ( 2c ), - a viewing direction in front of the light collimator ( 2c ) arranged plate-shaped, transparent light guide ( 2d ), which consists of a transparent, thermoplastic or thermoelastic plastic and scattering particles distributed therein, and - illuminants ( 2e ), which laterally on narrow sides of the light guide ( 2d ) are arranged, - wherein in the operating mode B1 for a free field of view at least the lighting means ( 2e ), and optionally also the flat radiator ( 2a ) are switched on, and - wherein in the operating mode B2 for a limited field of view, the lighting means ( 2e ) and the flat radiator ( 2a ) are turned on. Screen ( 1 ) according to one of the preceding claims, characterized in that as scattering particles in the transparent light guides ( 2d . 3 ) Titanium dioxide particles having an average particle size of 150-500 nm in a concentration based on the weight of the respective optical fiber of 0.01-300 ppm by weight. Screen ( 1 ) according to one of claims 1 or 2, characterized in that the transparent light guides ( 2d . 3 ) each consist of a matrix plastic A and scattering particles of a polymer B distributed therein, wherein the proportion of the scattering particles consisting of polymer B in each case 0.01 to 3 weight percent based on the matrix plastic A, and the refractive index nD (B) of the polymer B to is at least 0.01 units above the refractive index nD (A) of the matrix plastic A. Screen ( 1 ) according to one of the preceding claims, characterized in that on the upper side of the imager ( 5 ) and / or on at least one of the large areas of the light guide ( 3 ) Means for reflection reduction, for example, an anti-glare and / or an anti-reflection coating, are arranged. Screen ( 1 ) according to one of the preceding claims, characterized in that at least the lighting means ( 2e . 4 ) LEDs or laser diodes are. Using a screen ( 1 ) according to one of claims 1 to 6 for the input or display of confidential data, for example PIN PIN numbers, e-mails, SMS or passwords, ATMs, payment terminals or mobile devices. Method for displaying image information ( 6 ) in at least two operating modes B1 for a free viewing mode and B2 for a restricted viewing mode, comprising the following steps: - for the operating mode B1: areal radiation of light in a non-restricted angle range for a free viewing mode, preferably of a planar-extended backlight ( 2 ), or alternatively - for the operating mode B2: areal emission of light in a restricted angular range for a restricted viewing mode, preferably of a planarly extended backlight ( 2 ) Modulation of the surface radiated light in order to impose image information on this light, preferably by means of a transmissive image generator (US Pat. 5 ), - passing the thus modulated light through a plate-shaped light guide ( 3 ), which consists of a transparent, thermoplastic or thermoelastic plastic and dispersed therein scattering particles, wherein on the narrow sides of the light guide ( 3 ) Illuminants ( 4 ) are arranged laterally, - for the operating mode B1: switching off the lamps ( 4 ), so that the surface radiated and then modulated with the image information light substantially unaffected by the light guide ( 3 ), or alternatively - for the operating mode B2: switching on the lighting means ( 4 ), so that the surface radiated and then modulated with the image information light is superimposed by light, which the light guide ( 3 ) radiates now flat over a large angular range, whereby the residual visibility of the image information outside of said restricted angular range is reduced. A method according to claim 8, characterized in that for the surface emitting of light in both modes B1 and B2, a backlight ( 2 ), which consists of - a flat radiator ( 2a ), preferably a light guide with laterally arranged light sources ( 2 B ), - at least one in the flat radiator ( 2a ) integrated and / or arranged in front of light collimator ( 2c ), - a viewing direction in front of the light collimator ( 2c ) arranged plate-shaped, transparent light guide ( 2d ), which consists of a transparent, thermoplastic or thermoelastic plastic and scattering particles distributed therein, and - illuminants ( 2e ), which laterally on narrow sides of the light guide ( 2d ) are arranged, - wherein in the operating mode B1 for a free field of view at least the lighting means ( 2e ), and optionally also the flat radiator ( 2a ) are switched on, and - wherein in the operating mode B2 for a limited field of view, the lighting means ( 2e ) and the flat radiator ( 2a ) are turned on. The method of claim 8 or 9, characterized in that as scattering centers (in all known transparent light guides 3 , possibly also 2d ) Titanium dioxide particles having an average particle size of 150-500 nm in a concentration based on the weight of the respective optical fiber of 0.01-300 ppm by weight.

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