Optical fibers with simplified adjustable light transmission and associated manufacturing process

Abstract

Optical fiber (2) comprising a body (4) made of a transparent or translucent material, which, when the optical fiber (2) is arranged as intended, has a light entry surface (5) designed and oriented for coupling light (L) from a light source (3) into the body (4), at least one light exit surface (6) designed and oriented for coupling the light (L) coupled into the body (4), and at least one interface (7) formed by an outer surface of the body (4) at which the light (L) is at least partially reflected and / or refracted on its way through the body (4) from the light entry surface (5) to the light exit surface (6);wherein at least one printing layer (8), preferably an opaque printing layer, is applied to and adjacent to the interface (7) to influence the optical reflection and / or refraction behavior of the light (L) at the interface (7), wherein the body (4) forms a base surface serving as a light entry surface (5), a top surface serving as a light exit surface (6) opposite the base surface, and a lateral surface bounded by the base surface and the top surface, serving as an interface (7) and extending circumferentially between the base surface and the top surface along a direction of rotation (U); characterized in that the printing layer (8) is formed by a circumferential printing of the body (4) and that the lateral surface serving as an interface (7) is continuously curved in the direction of rotation (U).

Description

[0001] The invention relates to a light guide and an associated manufacturing process. Automotive lighting without light guides is virtually unimaginable today. They are used for illuminating or backlighting electronic pixel matrix displays and pictograms on control elements in the interior, as well as for so-called function lights in the automotive interior and exterior, bathing the vehicle interior in ambient light, for example. This involves a considerable amount of effort.

[0002] Optical fibers have conquered areas previously reserved for classic reflective or refractive optics. Many functional lights in automotive exterior applications are now implemented using optical fiber technology: high-mounted third brake lights, taillights, mirror indicators, position lights, etc. Furthermore, optical fibers are used as a supporting design element. In the latter case, they are often integrated for styling reasons. Here, their primary purpose is to provide pleasant, unobtrusive light. The luminance levels are sometimes low, and the illumination merely facilitates orientation. The illuminated light-emitting surface is often exposed and can usually be touched. These are very often linear geometries with diffuse emission, designed to exhibit homogeneous luminance over long distances.Particularly in the area of ​​the dashboard and center console, there are numerous display and control elements: multifunction display, speedometer, radio and climate control unit, etc. Light guides are used here to backlight symbols and display elements (so-called searchlight) or to provide a surface backlight for an LCD.

[0003] In the case of LCD backlighting, the optical element, the "light guide," is typically a cuboid with a base area slightly larger than the visible area of ​​the display exposed by the aperture, typically 3.5 mm high. Materials used include transparent PMMA (polymethyl methacrylate, also known as Plexiglas) or polycarbonate. Light is coupled in via the side surfaces. Point light sources, usually located along one or two opposite sides, power the light guide. Light transmission within the light guide occurs via total internal reflection (TIR). To selectively couple out light, defects are created that prevent TIR reflection. These are usually diffusely scattering areas. Transparent base materials with transparent microspheres of slightly different refractive indices are commonly used for backlighting. These microspheres cause light to scatter in the forward direction.The targeted introduction of diffuse areas or scattering microstructures into transparent materials is achieved through partial roughening or subtractive processes. For a component manufactured using injection molding, there are several ways to implement this: The mold is roughened at the relevant points by etching, ablated using electrical discharge machining (EDM) or a laser beam, or the manufactured part is subsequently processed, which is comparatively complex and usually requires additional polishing steps.

[0004] Unlike when using volume-diffuse materials, the roughness or shape of the microstructure can be controlled at every point along the optical fiber. However, introducing these roughnesses or microstructures presents a challenge: reliable demolding of the optical fiber from the mold is jeopardized if multiple surfaces of the fiber, positioned at an angle to each other, are to be provided with roughnesses or microstructures by the mold. Often, the optical fiber can then only be manufactured in multiple parts. As a transparent optical component, the requirements for the tool, machine, and operator are particularly high: good molding of the structure, transparency without a yellow tint, no flow lines, and no contamination are essential.

[0005] At the front, rear, and sides, as well as in the interior of a car, you'll find lights that fulfill specific functions. Position lights or daytime running lights at the front, turn signals or marker lights at the sides, taillights or brake lights at the rear, and reading lights and ambient lighting in the interior are just a few examples. Since these lighting functions significantly influence the car's appearance, aesthetic considerations play a particularly important role. Light guides are therefore used strategically in the design process to enhance the visual appeal. The function can be performed entirely or partially by the light guide, depending on the requirements of the specific light fixture. In addition to ensuring homogeneous luminance along the entire length of the light guide, the fixture must also often meet legal photometric requirements.

[0006] Depending on the function, the required luminous intensities are very high and necessitate directional emission (in the sense of a narrow beam pattern). Furthermore, unlike LCD backlighting, the outer surface geometry very often requires curved shapes. Linear geometries are most common on the exterior. These include curved lines or rings. A diffusely scattering structure for light extraction is generally not feasible due to the required luminous intensities. Instead, notches or raised areas in the light-emitting surface are used to extract and emit the light in a directional manner.

[0007] The basic operating principle is otherwise very similar to LCD backlighting. One challenge here is to harmonize efficiency, luminance homogeneity, beam characteristics, and design (curvature). Each parameter influences the others and cannot be considered in isolation. As with LCD backlighting, the main task in the optical development of the light guide is to optimize the output structure – in this case, the depth and angle of the notches in the light-emitting surface. If, for process-related advantages, these notches are to be incorporated directly into the light-emitting surface of the light guide during the molding process, then, to ensure demolding of the manufactured part, the structuring of other surfaces of the part with three-dimensional features, such as notches or protrusions, or even microstructures, is generally precluded.

[0008] US 8 944 662 B2 discloses a light guide according to the preamble of claim 1. Light guides of this type are also known from US 8 708 543 B2 and DE 699 18 329 T2.

[0009] Against this background, the object of the invention is to provide an optical fiber that can be manufactured cost-effectively with greater design flexibility and whose optical effect, such as light transmission, can nevertheless be precisely controlled. This object is achieved by an optical fiber according to claim 1. An equally advantageous arrangement and a manufacturing method are each the subject of the dependent claims. Advantageous embodiments are each the subject of the dependent claims. It should be noted that the features listed individually in the claims can be combined with one another in any technologically meaningful way and demonstrate further embodiments of the invention. The description, particularly in conjunction with the figures, further characterizes and specifies the invention.

[0010] The optical fiber according to the invention comprises a body made of a transparent or translucent material; for example, the body is formed in one piece from a transparent or translucent thermoplastic, such as transparent polymethyl methacrylate or polycarbonate. If the optical fiber is arranged as intended, the body has a light-entry surface designed and oriented for coupling light from a light source into the body. If the optical fiber is arranged as intended, the body also has at least one light-emission surface designed and oriented for coupling the light coupled into the body. Furthermore, the body has at least one interface formed by an outer surface of the body, at which light is at least partially optically reflected and / or refracted on its path through the body from the light-entry surface to the light-emission surface.

[0011] According to the invention, at least one printing layer, preferably an opaque printing layer, is provided on and adjacent to the interface in order to influence the optical reflection and / or refraction behavior of the interface for the light coupled into the body at the point of application of the printing layer. Influence is understood, for example, to mean a change in the refractive behavior, but also a change in the spectral composition of the light reflected at the interface, for example, due to dispersion.For example, the pressure layer adjacent to the body's interface from the outside varies the total internal reflection condition for the light incident at the interface compared to an uncovered interface exposed to air on one side, so that at least a larger portion of the light coupled into the body is refracted at the interface and exits the body not through the intended light-emitting surface, but rather through the interface. The pressure layer can be applied to the entire interface; preferably, one or more pressure layers are applied only to specific areas of the interface. Preferably, more than 50% of the total interface is not covered by any of the pressure layers, and more preferably, it is completely uncovered. Each pressure layer can cover a self-contained portion of the interface. The light-emitting surface and the interface preferably form an acute or a right angle.

[0012] Because the optical conditions at the interface are influenced by one or more printing layers, the design freedom is greater compared to a variant where the interface is solely defined by the manufacturing process of the body. In the latter approach, for example, the need for non-destructive demolding restricts the freedom in designing the interface. For instance, introducing three-dimensional structures into the interface is problematic if their direction of extension clashes with the demolding direction. This is particularly critical if three-dimensional structures are already present elsewhere on the body, for example, in the light emission or light entry surfaces.

[0013] According to the invention, the body forms a base surface serving as a light entry surface, a top surface serving as a light exit surface opposite the base surface, and a lateral surface bounded by the base surface and the top surface, serving as a boundary surface and extending circumferentially between the base surface and the top surface along a circumferential direction, wherein the lateral surface serving as a boundary surface is printed circumferentially.

[0014] For example, the body is homogeneous and transparent, allowing the interface and the printed layer applied to it to be visible to the viewer through the top surface. This further increases design freedom and the possibility for aesthetic individualization, as even inaccessible, far-facing interfaces of the light guide contribute more to the overall optical impression, especially when the light source is switched off.

[0015] Preferably, the optical fiber has a penetration opening in both the base and top surfaces, with the penetration forming a penetration surface. For example, the penetration surface is not provided with a pressure layer.

[0016] According to the invention, the interface is continuously curved in the direction of rotation. Preferably, the interface forms a ruled surface that is continuously curved in one direction. A ruled surface, also called a rectilinear surface, is understood to be a surface swept out by a straight line moving in space. Preferably, the ruled surface is continuous in the direction of rotation, but not uniformly curved. For example, the ruled surface changes the direction of curvature along the circumferential direction and thus has convex and concave curved sections in the direction of rotation.

[0017] The light-entry surface and the light-emission surface are, for example, coated with a transparent or translucent material, or printed with a transparent or translucent material; preferably, they are uncoated, i.e., in particular, unprinted. Apart from any optional three-dimensional structures formed in the light-emission surface, the light-entry surface and the light-emission surface are, in a preferred embodiment, aligned parallel to each other.

[0018] Preferably, several printed layers with different colors are applied to the interface of the body of the optical fiber.

[0019] Preferably, the body is manufactured from a transparent thermoplastic using a thermally forming process.

[0020] Preferably, the light-emitting surface of the body has one or more three-dimensional structures, each consisting of planar surfaces that are angled towards each other and adjacent to one another. For example, the three-dimensional structure is a notch or a protrusion.

[0021] The invention further relates to an arrangement comprising a light source and a light guide in one of the previously described embodiments. For example, the arrangement is a functional light mounted on the exterior of the vehicle or a functional light arranged in the passenger compartment, such as a position light or daytime running light in the front area, a flashing light or marker light in the side area, a tail light or brake light in the rear area, or a reading light or ambient light in the passenger compartment.

[0022] For example, the light guide is integrated into the interior or exterior paneling of a motor vehicle. Preferably, the light-emitting surface forms a visible and tactile surface for an observer, such as a passenger.

[0023] The invention further relates to a method for manufacturing an optical fiber comprising the following steps. In one manufacturing step, a molded part is produced from a transparent or translucent thermoplastic using a thermal forming process, such as injection molding, in which the flowable thermoplastic is introduced into a cavity defined by a molding tool. The molded part produced by the solidification of the thermoplastic is a body which, when the optical fiber is arranged as intended, forms a light-entry surface designed and oriented for coupling light from a light source into the body and at least one light-emission surface designed and oriented for coupling the light coupled into the body.The body forms at least one interface defined by an outer surface of the body, at which light is at least partially reflected and / or refracted as it travels through the body from the light-entry surface to the light-emission surface. According to the invention, the body forms a base surface serving as a light-entry surface, a top surface serving as a light-emission surface opposite the base surface, and a lateral surface extending circumferentially between the base surface and the top surface along a direction of rotation, bounded by the base surface and the top surface. In a subsequent step, the formed part is demolded, for example, from the mold used in its production.

[0024] In a subsequent step, the interface is printed using an inkjet printing process, preferably using an inkjet digital printer with a robot that can be moved about more than 3 axes, for example 4 axes, for the relative positioning of the body and an inkjet printhead belonging to the inkjet digital printer.

[0025] According to the invention, at least one circumferential printing layer is produced, preferably at least one opaque printing layer, which is arranged on and adjacent to the interface and is intended to influence an optical reflection behavior or refraction behavior at the interface for the light coupled into the body.

[0026] According to a preferred embodiment of the method, a surface of the cavity of the forming tool, which forms the light-emitting surface, has one or more three-dimensional structures, each of which is formed from planar surfaces oriented at angles to one another and adjacent to each other. For example, the three-dimensional structure is a notch or a protrusion.

[0027] Preferably, the surface of the cavity forming the interface is continuously curved; in particular, the interface is designed as a curved ruled surface.

[0028] The following figures further illustrate the invention. The embodiment shown in the figures is to be understood as merely exemplary and represents only one preferred embodiment. They show: Fig. 1a a perspective view of a first, preferred embodiment of the arrangement 1 according to the invention; Fig. 1b a related detailed sectional view of the embodiment from Fig. 1; Fig. 2 a perspective view of a second, preferred embodiment of the arrangement according to the invention 1.

[0029] Fig. Figure 1a shows a first embodiment of the arrangement 1 according to the invention, comprising a light guide 2 and a light source 3. The light source 3 is, for example, a light-emitting diode, preferably one in SMD design, which is mounted on a printed circuit board (not shown) and electrically contacted. The light guide 2 of the arrangement 1 according to the invention has a body 4 made of transparent thermoplastic, which was produced as a molded part in a cavity of a molding tool (not shown) using a thermoforming process. The body 4 of the light guide 2 has a light entry surface 5 facing the light source 3, through which the light L generated by the light source 3 enters the body 4. The body 4 has a light exit surface 6 arranged parallel to and spaced apart from the light entry surface 5, from which the light L that has entered the body 4 exits.As the light passes through body 4, portions of it L are reflected and / or refracted at an interface 7 defined by the lateral surface of body 4. Interface 7 is formed by a lateral surface extending around the body 4 between the light-entry surface 5 (also called the base) and the light-emission surface 6 (also called the top surface). This lateral surface, or interface 7, is continuously curved in the direction of rotation U, with the radius and direction of curvature not being constant. The direction of rotation U runs parallel to both the light-entry surface 5 and the light-emission surface 6. The local refraction or refracting is determined by the lateral surface 5.The reflection behavior at the interface 7 depends not only on the angle of incidence L of the light present in the body 4, but also on the optical properties of the media adjacent to the interface 7, namely those of the thermoplastic of the body 4 on the one hand, and those of the medium applied to or adjacent to the outer surface on the other. Since large parts of the entire interface 7 or outer surface are only in contact with air, the reflection behavior or refraction behavior is determined, among other things, by the refractive index of the air, whereas the pressure layer 8 provided according to the invention and applied to the interface 7 influences the reflection behavior or refraction behavior at its application point, as shown in . Fig. 1b is shown.

[0030] This printed layer 8 is applied using a digital printing process with an inkjet printer (not shown) that has a robot movable along 4 axes for the relative positioning of the body 4 and an inkjet printhead belonging to the digital printer. Apart from the rasterization of the digital print, the printed layer 8 thus forms closed printed islands 8a, 8b. Consequently, printed island 8b is linear, while printed island 8a is planar. Printing with a printer adjustable along more than 3 axes not only enables improved printing of the three-dimensionally shaped interface 7 but also allows for circumferential or at least multi-sided printing of the body 4. Consequently, the printed layer 8, as shown in Fig. The printing island 8b shown in Figure 1a is designed such that it has an extent in the circumferential direction U that is more than half of the maximum circumference in the circumferential direction U of the body 4. In an embodiment not shown, two printing islands, each formed by a printing layer 8, are provided and are spaced apart from each other by more than half of the maximum circumference in the circumferential direction U of the body 4. To influence the direction of light emission from the light emission surface 6, this surface has several three-dimensional structures 9, 10, each formed from planar surfaces oriented at an angle to one another and adjacent to each other, such as a notch 10 or a protrusion 9.

[0031] Fig. Figure 2 shows a second embodiment of the arrangement 1 according to the invention, comprising a light guide 2 and a light source 3. The light source 3 is, for example, a light-emitting diode, preferably one in SMD design, which is mounted on a circuit board (not shown) and electrically contacted via this board. The light guide 2 of the arrangement 1 according to the invention has a body 4 made of a transparent thermoplastic, which was produced as a molded part in a cavity of a molding tool (not shown) using a thermoforming process. The body 4 of the light guide 2 has a light entry surface 5 facing the light source 3, through which the light L generated by the light source 3 enters the body 4.The body 4 has a light emission surface 6 arranged parallel to and spaced apart from the light entry surface 5, from which the light L entering the body 4 exits and which, in this embodiment, is completely flat. The body 4 also has a central opening 11 that opens into the light emission surface 6 and the light entry surface 5 and defines an opening surface 12 running substantially parallel to the lateral surface described below, which has no printed layer.

[0032] As the light passes through body 4, portions of it L are reflected and / or refracted at an interface 7 defined by the lateral surface of body 4. Interface 7 is formed by a lateral surface extending around the body 4 between the light-entry surface 5 (also called the base) and the light-emission surface 6 (also called the top surface). This lateral surface, or interface 7, is continuously curved in the direction of rotation U, with the radius and direction of curvature not being constant. The direction of rotation U runs parallel to both the light-entry surface 5 and the light-emission surface 6. The local refraction or refracting is determined by the lateral surface 5.The reflection behavior of the interface 7 depends, in addition to the angle of incidence L of the light present in the body 4, on the optical properties of the media adjacent to the interface 7, namely those of the thermoplastic of the body 4 on the one hand and those of the medium applied to or adjacent to the outer surface on the other. Since large parts of the entire interface 7 or outer surface are only in contact with air, the reflection behavior or refraction behavior is determined, among other things, by the refractive index of the air, whereas the pressure layer 8 provided according to the invention and applied to the interface 7 influences the reflection behavior or refraction behavior at its application point, as already shown from [reference]. Fig. Figure 1b illustrates this. This print layer 8 is applied using a digital printing process with an inkjet printer (not shown) that has a robot movable on 4 axes for the relative positioning of the body 4 and an inkjet printhead belonging to the digital printer. Apart from the rasterization of the digital print, the print layer 8 thus forms closed print islands 8b. The print islands 8b, extending parallel to each other, are linear in shape. Printing with a printer adjustable on more than 3 axes not only enables improved printing of the three-dimensionally shaped interface 7 but also allows for circumferential or at least multi-sided printing of the body 4. Consequently, the print layer 8, as shown in Figure 1b, can be used to create a three-dimensionally shaped interface 7. Fig. The two printed islands 8b shown are designed such that they have an extent in the circumferential direction U that is more than half the maximum circumferential circumference U of the body 4. Because the optical conditions at the interface 7 are influenced by one or more printed layers 8, the design freedom is increased compared to a variant in which the interface 7 is formed by the shaping manufacturing process of the body 4. In the latter variant, for example, the need for non-destructive demolding of the body 4 restricts the freedom in designing the interface 7. For example, the introduction of three-dimensional structures into the interface 7 is problematic if their direction of extension collides with the demolding direction.This is particularly critical if there are already 4 three-dimensional structures 9, 10 elsewhere in the body, such as in the light emission surface 6 of the first in . Fig. 1a shown embodiment of the arrangement 1 according to the invention.

Claims

[1] Optical fiber (2) comprising a body (4) formed from a transparent or translucent material, which, when the optical fiber (2) is arranged as intended, has a light entry surface (5) formed and oriented for coupling light (L) from a light source (3) into the body (4), at least one light exit surface (6) formed and oriented for coupling the light (L) coupled into the body (4), and at least one interface (7) formed by an outer surface of the body (4) at which the light (L) is at least partially reflected and / or refracted on its way through the body (4) from the light entry surface (5) to the light exit surface (6);wherein at least one printing layer (8), preferably an opaque printing layer, is applied to and adjacent to the interface (7) to influence the optical reflection and / or refraction behavior of the light (L) at the interface (7), wherein the body (4) forms a base surface serving as a light entry surface (5), a top surface serving as a light exit surface (6) opposite the base surface, and a lateral surface bounded by the base surface and the top surface, serving as an interface (7) and extending circumferentially between the base surface and the top surface along a direction of rotation (U); characterized by , that the printing layer (8) is formed by a circumferential printing of the body (4) and that the lateral surface serving as the interface (7) is continuously curved in the direction of rotation (U). [2] Light guide (2) according to claim 1, wherein the body (4) has a through-hole (11) opening into the light entry surface (5) and the light exit surface (6), which forms an inner circumferential surface (12). [3] Optical fiber (2) according to one of the preceding claims, wherein the interface (7) is a controlled surface continuously curved in the direction of rotation (U), or more preferably a controlled surface continuously but not uniformly curved in the direction of rotation. [4] Light guide (2) according to one of the preceding claims, wherein the light entry surface (5) and the light exit surface (6) are uncoated. [5] Optical fiber (2) according to one of the preceding claims, wherein several printed layers (8) having different colors are applied to the interface (7) of the body (4). [6] Optical fiber (2) according to one of the preceding claims, wherein the body (4) is produced from a transparent thermoplastic in a thermally forming process. [7] Light guide (2) according to one of the preceding claims, wherein the light exit surface (6) has one or more three-dimensional structures (9, 10) which are each formed from planar surfaces oriented at an angle to each other and adjacent to each other, such as a notch or protrusion. [8] Arrangement (1) comprising a light source (3) and a light guide (2) according to one of the preceding claims. [9] Arrangement (1) according to the preceding claim, wherein the light emission surface (6) of the body (4) forms a viewing surface and contact surface for an observer, for example a passenger. [10] Method for manufacturing an optical fiber (2) comprising the following steps: Producing a molded part from a transparent or translucent thermoplastic in a thermally forming process by introducing the thermoplastic into a cavity of a forming tool, wherein the molded part is a body (4) which, when the light guide (2) is arranged as intended, has a light entry surface (5) formed and oriented for coupling light (L) from a light source (3) into the body (4), at least one light exit surface (6) formed and oriented for coupling the light (L) coupled into the body, and at least one interface (7) formed by an outer surface of the body (4) at which the light (L) is optically at least partially reflected and / or refracted on its way through the body (4) from the light entry surface (5) to the light exit surface (6), wherein the body (4) has a base surface serving as a light entry surface (5), a surface serving as a light exit surface (6),forms a top surface opposite the base surface and a lateral surface bounded by the base surface and the top surface, serving as a boundary surface (7) and extending circumferentially between the base surface and the top surface along a direction of rotation (U); Demoldement of the mold; Printing the interface (7) in an inkjet printing process forming at least one printing layer (8), preferably at least one opaque printing layer, to influence the optical reflection behavior or refraction behavior of the light (L) at the interface (7), wherein the printing layer (8) is applied to and adjacent to the interface (7), characterized by , that the printing layer (8) is formed by a circumferential printing of the body (4) and that the lateral surface serving as the interface (7) is continuously curved in the direction of rotation (U). [11] Method according to the preceding claim, wherein the printing is carried out using an inkjet digital printer with a robot movable about more than 3 axes for the relative positioning of the body and an inkjet printhead belonging to the inkjet digital printer. [12] Method according to one of the two preceding claims, wherein a surface of the cavity forming the light emission surface (6) has one or more three-dimensional structures, each of which is formed from planar surfaces oriented at an angle to each other and adjacent to each other, such as a notch or elevation. [13] Method according to any one of the preceding claims 10 to 12, wherein a surface of the cavity forming the interface (7) is continuously curved, in particular a continuously curved ruled surface.

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