Method for manufacturing an injection molding insert and injection molding insert

Abstract

The invention relates to a method for manufacturing an injection mold insert (1000), in particular for injection molding optical components of motor vehicle lighting devices, comprising at least the following steps: - Deployment (100) of a deployment body (1), - Molding (200) a special surface topography (12) into a surface (11) of the insert body (1), and - electroless plating (300) of the surface (11) of the insert body (1) by a nickel dispersion coating (2) comprising polytetrafluoroethylene particles (23) dispersed in a nickel matrix (22).

Description

[0001] The present invention relates to a method for manufacturing an injection mold insert and a corresponding injection mold insert for injection molding optical components of motor vehicle lighting devices. STATE OF THE ART

[0002] Optical components for automotive lighting systems are typically manufactured using injection molding. Examples include individual lenses, microlens assemblies, reflectors, diffusers, diffractive and holographic elements, antireflective structures, optical fibers, light guides, thick-walled optics, and end caps. A crucial characteristic of such optical components is their surface condition, which significantly influences their functionality with regard to light manipulation. Smooth surfaces are required for high-efficiency individual lenses or reflectors, while precise roughness levels or specific surface patterns are necessary for light-diffusing elements or microlens assemblies. The surface condition of the molded optical components is directly determined by the surface condition of the corresponding molds, which must therefore meet stringent quality requirements.The mold is typically equipped with an insert that features the desired surface topography for casting. Since optical components for automotive devices are generally mass-produced, the tool life of the mold inserts, and especially their surface finish, should be very long-lasting.

[0003] Two main problems arise when injection molding optical components with micro-surface structures. First, the injection-molded components adhere to the surface structure of the mold insert, making demolding more difficult or even causing warping of the components during demolding. Furthermore, contaminants accumulate in the microstructures on the surface of the inserts, particularly residues of additives intended to facilitate demolding, such as stearic acid. Such contaminant accumulation leads to a progressive deterioration of the surface quality of the molded parts and necessitates regular cleaning intervals, which, in industrial mass production, result in undesirable production downtime. DISCLOSURE OF THE INVENTION

[0004] The object of the present invention is to provide an injection molding insert for the durable and high-precision injection molding of optical components of motor vehicle lighting devices and a method for its manufacture.

[0005] This problem is solved by a method according to claim 1 and an injection molding insert according to claim 8 of the present invention. Advantageous embodiments of the invention are defined in the dependent claims.

[0006] The invention discloses the technical teaching that the method for manufacturing the insert comprises at least the following steps: - Provision of a deployment body, - Molding a special surface topography into a surface of the insert body, and - Electroless plating of the surface of the insert body by means of a nickel dispersion coating comprising polytetrafluoroethylene particles dispersed in a nickel matrix.

[0007] The invention utilizes the synergistic properties of nickel dispersion coatings, combining the high hardness, corrosion resistance, and dimensional accuracy of electroless nickel coatings with the non-stick effect of PTFE particles acting as an embedded dry lubricant. The PTFE particles significantly reduce the adhesion of the molded components and contaminants. In particular, the use of additional auxiliary materials intended to facilitate demolding can be completely eliminated in the injection molding process. Consequently, the application of the nickel dispersion coating to the injection mold insert facilitates the demolding process and ensures a permanently contamination-free mold surface, thus enabling significantly more uninterrupted production cycles than were possible with conventional inserts based on the prior art.

[0008] Electroless nickel plating is an autocatalytic process in which the reduction of nickel ions in a solution and the deposition of the nickel coating are carried out by the oxidation of a chemical compound present in the solution itself, i.e., a reducing agent such as hydrogenated sodium hypophosphite, which provides electrons. Unlike electroplating, it is not necessary to pass an electric current through the plating solution to form the nickel deposit. Electroless nickel plating creates homogeneous coatings, regardless of the topography of the workpiece surface, and, depending on the catalyst, can even be applied to non-conductive surfaces. Electroless nickel coatings exhibit a very dense microstructure and are therefore suitable as corrosion protection for the molded part.The composition of electroless nickel coatings typically includes nickel and a certain amount of phosphorus. The co-deposition and integration of PTFE particles results in a nickel dispersion coating with randomly distributed PTFE particles in the nickel matrix, offering excellent functionality for injection molding.

[0009] In particular, the surface of the insert is plated with a nickel dispersion coating comprising 5 to 25 vol% PTFE particles, the PTFE particles having a diameter in the range of 0.5 µm to 5 µm. The PTFE particles are typically round.

[0010] Furthermore, the surface of the insert is plated with a nickel dispersion coating with a thickness of 1 µm to 100 µm. The thickness depends on the detailed dimensions of the surface topography to be plated. Microtopographies, for example, for injection molding diffuser optics or microlens assemblies, require thin coatings to maintain the spatial resolution of the surface topography, while thicker coatings are particularly useful for smoothing unwanted surface roughness, for example, for injection molding mirror-like reflector optics.

[0011] After plating, the insert can be heat-treated at a temperature of 200 °C to 300 °C for a period of 1 to 10 hours. Such heat treatment results in a significant hardening of the nickel dispersion coating and consequently improves its resistance to mechanical wear. Immediately after plating, the electroless nickel exhibits an amorphous microstructure, which is transformed by the heat treatment into crystalline nickel and a hard nickel phosphide phase.

[0012] Preferably, the surface topography is formed on the insert by laser milling or mechanical machining, particularly to a spatial resolution in the range of 0.5 µm to 10 µm. Laser milling with pulsed laser sources, especially ultrashort pulses in the femtosecond range, is suitable for patterning surfaces made of different materials with a lateral resolution significantly below 10 µm, or, in the case of periodic surface structures, even in the submicrometer range using multi-beam interference techniques. Laser milling is based on the physical process of laser ablation, i.e., the sublimation of an irradiated material volume. Laser milling can be applied to shaped bodies with complex three-dimensional surface contours.

[0013] Furthermore, the invention relates to an injection molding insert for injection molding optical components of motor vehicle lighting devices, wherein the insert is produced by one of the preceding embodiments of the inventive method, wherein the surface topography is specifically designed for injection molding a Fresnel optic, a microlens optic, a light guide optic, a diffuser optic or a reflector optic. PREFERRED EXECUTION FORM

[0014] Further details, properties and advantages of the subject matter of the invention are disclosed in the following description of the respective figures, which exemplify a preferred embodiment of the manufacturing process and the injection molding insert according to the invention. Fig. Figure 1 is an illustration of the first step of the method according to the invention. Fig. 2 is an illustration of the second step, and Fig. Figure 3 illustrates the third step and an application according to the invention.

[0015] The Fig. Figures 1-3 show schematic cross-sections of a segment of an insert body 1.

[0016] The deployment of 100 units of the operational body 1 is in Fig. Figure 1 illustrates the first step of the inventive method. The insert body 1 is advantageously manufactured from tool steel by milling and / or electrical discharge machining. The surface 11 is oriented towards the cavity of the corresponding mold and must therefore be functionalized according to the inventive method to provide the desired surface quality of the components to be formed. The topography of the surface 11 of the insert body 1, as provided, is determined by the machining process, namely the surface waviness and the various orders of magnitude of surface roughness.

[0017] Fig. Figure 2 illustrates the second step of the inventive method, namely the shaping 200 of the special surface topography 12 into the surface 11 of the insert body 1, in this case by means of laser milling. For this purpose, the laser beam 3 travels along programmed paths over the surface 11 and results in local material ablation with high spatial resolution, for example in the range of 1 µm to 10 µm. The laser beam 3 generally operates in a pulsed mode, for example with femtosecond pulses. Advantageously, a multi-beam laser unit is used for high surface ablation rates. The surface topography 12 in the example of Fig. Figure 2 features the Fresnel rings 13, indicating that the device is intended for injection molding Fresnel lenses for automotive lighting devices. Beyond the example illustrated here, laser milling is suitable for generating a wide variety of patterns on complex three-dimensional molded body surfaces for various applications, such as micrometer-sized patterns for molded parts with refractive or diffusing properties, or for holographic applications.

[0018] Fig.Figure 3 illustrates the third step of the inventive process, namely the electroless plating 300 of the surface 11 of the insert body 1 with the nickel dispersion coating 2, comprising PTFE particles 23 dispersed in a nickel matrix 22, which ultimately produces the injection molded insert 1000 according to the invention. The special surface topography 12, representing a Fresnel lens, is well preserved by the nickel dispersion coating 2, which is an advantage of the electroless plating process. The enlarged view of the nickel dispersion coating 2 shows the PTFE particles 23 randomly distributed within the nickel matrix 22. On the coating surface 21, the PTFE particles 23 provide the desired non-stick properties, thus preventing the injection-molded components and contaminant particles from adhering.If the injection molding insert 1000 wears out during operation, the PTFE particles 23 initially embedded appropriately under the coating surface 21 ensure proper functionality of the injection molding insert 1000 throughout its entire service life.

[0019] The present invention is not limited by the embodiment described above, which is shown only as an example and can be modified in various ways within the scope of protection defined by the appended claims. Reference symbol list 1000 deployment 1 insert 11 Insert body surface 12 Surface topography 13 Fresnel ring 2 coating 21 Coating surface 22 Nickel matrix 23 PTFE particles 3 Laser beam 100 Deployment of the deployment unit 200 Images of surface topography 300 plating

Claims

Method for manufacturing an injection mold insert (1000), in particular for injection molding optical components of automotive lighting devices, comprising at least the following steps: - providing (100) an insert body (1), - forming (200) a special surface topography (12) into a surface (11) of the insert body (1), and - electroless plating (300) of the surface (11) of the insert body (1) by a nickel dispersion coating (2) comprising polytetrafluoroethylene particles (23) dispersed in a nickel matrix (22). Method according to claim 1, characterized in that the surface (11) is plated by a nickel dispersion coating (2) comprising a proportion of 5 vol.% to 25 vol.% polytetrafluoroethylene particles (23) (300). Method according to claim 1 or 2, characterized in that the surface (11) is plated by a nickel dispersion coating (2) comprising polytetrafluoroethylene particles (23) with a diameter of 0.5 µm to 5 µm (300). Method according to one of the preceding claims, characterized in that the surface (11) is plated by a nickel dispersion coating (2) with a thickness of 1 µm to 100 µm (300). Method according to one of the preceding claims, characterized in that the insert (1000) is heat-treated after plating (300) for a period of 1 hour to 10 hours at a temperature of 200 °C to 300 °C. Method according to one of the preceding claims, characterized in that the surface topography (12) is formed by laser milling or mechanical processing (200). Method according to one of the preceding claims, characterized in that the surface topography (12) is formed with a spatial resolution of 0.5 µm to 10 µm (200). Injection mold insert (1000) for injection molding optical components of motor vehicle lighting devices, characterized in that the mold is produced by a method according to one of the preceding claims. Injection molding insert (1000) according to claim 8, characterized in that the surface topography (12) is designed for injection molding a Fresnel optic, a microlens optic, a light guide optic, a diffuser optic or a reflector optic.

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