DE10240605A1 - Coating thermoplastic foam mouldings with metallic layers, comprises controlling the thermal capacity of the particles or droplets that are used for coating - Google Patents

Abstract

A process for coating thermoplastic foam mouldings with a metallic cover layer, comprises controlling the thermal capacity of the particles or droplets that are used to coat the foam, so it is less than that required to melt the surface of the molding, or so foam or polymer melting is no deeper than 0.0001-5 mm. A process for coating thermoplastic foam mouldings with a metallic cover layer, comprises controlling the thermal capacity of the particles or droplets that are used to coat the foam, so it is less than that required to melt the surface of the molding, or so foam or polymer melting is no deeper than 0.0001-5 mm. The mouldings consist of particle foam, e.g. expanded polypropylene, polyethylene, or polystyrol. The coating material is applied in the solid, liquid or gaseous phase, or as a mixture of phases, and the foam is cooled during the coating process. The coating process takes place at a pressure of 10-8 to 10 bar, and layer thicknesses of 0.1 micronsm to 2 mm are achieved. The metal coatings consist of e.g. aluminum, copper, gold, silver, chromium nickel, copper bronze, tin, zinc, or nickel.

Description

The invention relates to a method for the metallization of surfaces by applying a metal layer on the surface of Particles made of particle foams by deposition of metals using heated metallic sources.

According to the state of the art already a variety of thermoplastics over various Process provided with metal coatings. Approximately 90% of those used here thermoplastic polymers come from the group of ABS and ABS blends. The amount on polyolefins has so far been very low and the use of porous substances and foams are minimal. Metallized plastics are used especially in the automotive, sanitary, Packaging and electronics area. Various are available for coating Choice of physical, chemical and galvanic processes. Purely physical processes such as thermal spraying are possible with a high temperature load of the plastic to be coated. These procedures are for Thermoplastics can only be used to a limited extent. Chemical processes are based first on an activation of the plastic surface via an etching process with subsequent deposition the metal layer. Due to the use of etching agents such as Chromic sulfuric acid these processes are very polluting and, moreover, cost-intensive. For galvanic Coatings is a conductive plastic Requirement. Most frequently indirect galvanic coating is used, initially with chemical is metallized and then galvanically the desired one Final layer is applied.

In the field of foams, to improve the mechanical and optical properties of molded parts made of particle foams, these are often coated with non-metallic materials in order to give the foam part a smooth, decorative or abrasion-resistant surface, depending on the application. In the area of trim or add-on parts for motor vehicles is like in DE 19731393 described the production of half-shells from EPP with lamination with foils or textiles for sun visors a common structure. In DE 10033877 describes a method for coating foams with a polymeric top layer which is applied to the component in a liquid phase. The coating of open-cell foams with metals is in DE 19501317 described, a wet chemical metallization being used here.

The disadvantage is that the metallization of plastics is connected with a lot of effort and so far only massive components are coated with adhesive metal layers can. Furthermore, the use of the methods for coating plastics due to the non-conductivity and the low temperature resistance many plastics limited. For coating foams are wet chemical and thus environmentally harmful processes for antistatic equipment open-cell foams used. Metallization process of closed-cell particle foams as functional components or EMC (electromagnetic compatibility) components such as electronics housings or Packaging are used and through the formation of a Faraday Cage that Preventing the penetration of electromagnetic waves are not known.

The invention is therefore the object based on particle foams with metallic surfaces provided with functional or decorative metallic surfaces to achieve these foams and thus the properties of a metal surface like conductivity or higher Appearance and the properties of the foam such as lightweight construction and Connect energy absorption.

This is solved by the fact that the surface of components made of particle foams, preferably EPP (expanded Polypropylene particle foam), EPS (expanded polystyrene particle foam) or EPE (expanded polyethylene particle foam) with a metal layer is provided, this at the moment of connection with the foam has such a low heat capacity that no thermal damage of the foam and / or only near the surface of the foam be melted by the applied metal layer.

The foams to be coated lie as molded parts foamed from foam particles or semi-finished / cut foam in front. When coating molded parts, the surface is closed and only partially has gusset spaces between the foam particles. One option here is roughening the surface to create pores and undercuts to improve the Liability during the coating process. With cut foam are on the surface of the foam the cell walls of the Foam particles at least partially damaged, causing a partial Exposing the cell structure and thus an open pore structure and undercuts on the surface to increase the adhesive strength of coatings are given.

The deposition of the coating materials takes place from the gas phase, liquid phase, Solid phase or a mixture of phases. Coating materials used can Metals such as aluminum, copper, gold, silver, chrome-nickel, copper-bronze his.

A preferred variant is the metal liquefaction from resistance-heated sources or be heated boats or coils. The vaporized or melted drops of material can be deposited on the foam under normal pressure or negative pressure. The thermal capacity of the coating materials is regulated via the temperature, drop size of the coating materials and the amount dispensed. The distance between the source of the materials for surface coating and the foam to be coated also has an influence on the temperature of the coating particles / drops hitting the foam. A variant is also the cooling of the coating drops / particles over this distance and / or the cooling of the foam to be coated. Dispensing quantity, drop size and temperature are set so that the foam to be coated is not thermally damaged. A variant for improving the adhesion is a temperature control which allows areas close to the surface to melt through the coating material directly during the coating process. In order to ensure a uniform distribution of the coating material, the coating material is atomized during the coating process and / or the foam is rotated / shifted. A variant here is the use of ultrasound. Another variant for atomization is the use of an air stream.

Significant advantage of the procedure is the use of a purely physical process which the Coating of thermoplastic particle foams with low Melting point allowed in the range 100-200 ° C. Furthermore, no chemical pretreatment steps for the foams are required. Due to the surface properties of the Particle foam is with mechanical pretreatment or without Pretreatment achieved sufficient adhesion. It can Components made with functional or decorative metallic surfaces and thus the requirements for a metal surface and Requirements regarding lightweight construction and energy absorption are met.

Embodiment:

The top layer ( 1 ) is about metal evaporation, drop formation ( 4 ) or formation of fine particles from a heated source ( 3 ) on the particle foam molded part ( 2 ) applied. Adhesion to the foam surface takes place via surface interactions, by embedding the metal layer in undercuts in the surface, which is partly due to the foam structure or interstices between foam particles or, in the case of cut foam, through the cell structure of the foam particles, but also through surface treatment / roughening or melting through the coating materials can be reinforced. In addition, undercuts or melting areas close to the surface bring about a positive fit and mechanical anchoring with areas of the metal layer.

Claims (20)

Process for coating molded parts made of thermoplastic foams with a metallic cover layer, characterized in that the components, particles or drops of the coating material have a thermal capacity when they strike the molded part surface during the coating process, which a. is smaller than the heat capacity required for melting the molded part surface and / or b. have a heat capacity which causes the foam or polymer surface to melt through the coating material in areas near the surface with a depth of between 0.0001 mm to 5 mm. A method according to claim 1, characterized in that molded parts from particle foams, especially EPP, EPE, EPET or EPS can be coated. Method according to one or more of the preceding claims characterized in that the top layer material deposited on the foam in gas, liquid, solid or mixed phase is deposited. Method according to one or more of the preceding claims characterized that the top layer from a heated source as a material carrier via metal evaporation, Drop formation or formation of fine particles on the particle foam molded part be applied. Method according to one or more of the preceding claims characterized in that the top layer materials in the form of liquid droplets the foam is deposited and this has a diameter between 0.01 μm and have 2.0 mm. Method according to one or more of the preceding claims characterized that the cover layer materials are melted by means of current flow become. Method according to one or more of the preceding claims characterized that during the coating process the coating materials as aerosol are present and / or atomized become. Method according to one or more of the preceding claims, characterized in that during the coating process, the loading layering materials are atomized using ultrasound. Method according to one or more of the preceding claims characterized that during of the coating process the foam part a shift or experiencing rotation. Method according to one or more of the preceding claims characterized in that between the generation of the top layer particles and the appearance on the foam surface a cooling of the Metal particles to a temperature below or in the range of Melting temperature of the foam takes place. Method according to one or more of the preceding claims characterized that during of the coating process, the foam part is cooled. Method according to one or more of the preceding claims characterized that during the components, particles to be deposited during the coating process or drops of coating materials are cooled. Method according to one or more of the preceding claims, characterized in that the coating process takes place at a pressure between 10 ^-8 and 10 bar. Method according to one or more of the preceding claims characterized in that layer thicknesses between 0.1 μm and 2.0 mm are generated. Method according to one or more of the preceding claims characterized that as evaporation materials for the top layer Metals such as aluminum, copper, gold, silver, chrome-nickel, copper-bronze, Tin, zinc, or nickel can be used. Method according to one or more of the preceding claims characterized in that the molded parts to be coated from particle foams such as EPP (expanded polypropylene particle foam), EPS (expanded Polystyrene particle foam) or EPE (expanded polyethylene particle foam) are built up. Method according to one or more of the preceding claims characterized in that the molded parts to be coated have a defined Roughness or surface structure by mapping a corresponding molding tool surface structure have, such as lattice structures that form-fit anchoring of the improve metallic particles. Method according to one or more of the preceding claims characterized in that the foam molding surface has no spray marks. Method according to one or more of the preceding claims characterized that the first top layer as an intermediate layer for further Treatment and / or coating steps is used. Method according to one or more of the preceding claims characterized in that a copper and / or nickel layer is applied and a chrome layer is applied galvanically in the subsequent step becomes,