WO2008148642A1

WO2008148642A1 - Method for metal coating thermoplastic particles

Info

Publication number: WO2008148642A1
Application number: PCT/EP2008/056213
Authority: WO
Inventors: Rene Lochtman; Olaf Kriha; Norbert Schneider; Jürgen PFISTER; Norbert Wagner; Christian Exner; Klaus Hahn
Original assignee: Basf Se
Priority date: 2007-06-04
Filing date: 2008-05-21
Publication date: 2008-12-11
Also published as: TW200911900A

Abstract

The invention relates to a method for coating thermoplastic particles with a metal layer, wherein particles made of a thermoplastic are treated with a dispersion comprising metal particles, for example made of high-purity iron, in an organic dispersing agent, the organic dispersing agent is subsequently removed, and the coated thermoplastic particles are optionally subjected to a thermal treatment, the method being suited to provide durable new materials.

Description

Process for the metal coating of thermoplastic particles

description

The present invention relates to a process for producing coated, thermoplastic particles and to the use of surface-metallized particles for the production of moldings.

The prior art already describes several processes for the metal coating of thermoplastics via process steps such as metal evaporation or droplet deposition. The most commonly used thermoplastic polymers come from the group of acrylonitrile-butadiene-styrene copolymers and ABS blends. By contrast, the proportion of metal-coated polyolefins such as polyethylene or polypropylene has so far been low. The use of coatings for porous materials, small plastic particles and foams has so far been little studied. Metallized thermoplastics are used primarily in the automotive, housing, sanitary, packaging and electronics sectors.

To date, various physical, chemical and galvanic processes are available for coating. Purely physical processes such as the thermal spraying of metals are associated with a high temperature load for the plastic to be coated. These methods are therefore only of limited use for thermoplastics.

As a rule, chemical processes are initially based on an activation of the plastic surface via an etching process with a subsequent deposition of the metal layer. Due to the use of etchants, however, these methods are expensive and stressful for the environment.

For galvanic coatings, the use of electrically conductive plastics is an important prerequisite. Often, an indirect galvanic coating is used in which first chemically metallized and then the desired final layer of a metal is applied by electroplating.

In the field of thermoplastic foams non-metallic material layers are often applied in the literature to improve the mechanical and optical properties of moldings made of particle foams. This is done depending on the field of application, therefore, to give the foam part a smooth, decorative and / or abrasion-resistant surface.

In DE-A 197 31 393 the production of molded parts from ethylene-polypropylene (EPP) for e.g. Sun visors for motor vehicles described, wherein the plastic may have a coating.

EP-A 1 396 519 discloses a process for coating polystyrene foams (for example EPS) with a copper layer or a layer of different alloys, in which the metal powder is extruded with the thermoplastic mass.

DE-A 100 33 877 describes a process for coating foams with a polymeric covering layer, which is applied to the component in a liquid phase.

A coating of open-cell foams with metals is also described in DE-A 195 01 317, in which case a wet-chemical metallization is used.

From DE-A 37 24 156 a process for the production of hollow spheres is known in which a treatment with ceramic or metallic particles and pyrolysis or sintering takes place at temperatures of about 1000 ° C.

A disadvantage of the previously known methods is that the metallization of plastics is associated with high technical complexity and so far only massive components can be coated with adherent metal layers. Furthermore, the known methods for coating plastics are limited due to the non-conductivity and low temperature resistance of many thermoplastics.

Satisfactory methods for metallizing particle foams, especially with closed cells, which are inexpensive to carry out and can be used for different materials, however, are not yet known.

The invention has for its object to provide expandable particles or teilxpan- dierbare particles with metallic surfaces in order to achieve functional or decorative metallic surfaces on and / or in foams and thus the properties of a metal surface such as electrical and / or thermal conductivity, shielding electromagnetic radiation or higher-quality optical radiation and to combine the properties of the foam such as lightweight construction, thermal insulation and energy absorption. The object is achieved by a method for coating, in particular also propellant-containing thermoplastic particles with a partial or complete metal layer, in which the particles of a thermoplastic material with a dispersion containing, for example, metal particles in a (preferably organic) dispersing agent are treated, then the dispersant is removed and the coated thermoplastic particles are optionally subjected to a thermal treatment.

The present invention also relates to a process for producing expanded polystyrene foam bodies by producing pre-expanded particles of propellant-containing polystyrene and then foaming these particles in a closed mold, thereby welding the particles to the foam body. Expanded polystyrene foam bodies are so-called particle foams and are generally produced in a multi-stage process.

First, expandable polystyrene (EPS) is produced, which can be done by various methods:

a) by suspension polymerization of styrene (or other vinyl aromatic monomers or comonomers) in the presence of blowing agents, resulting in direct blowing agent-containing EPS particles;

b) by impregnating propellant-free polystyrene particles with the propellant under pressure in a heated suspension, the propellant diffusing into the softened particles; when the suspension is cooled under pressure, blowing agent-containing EPS particles are obtained;

C) in the so-called extrusion process by mixing the blowing agent into a polystyrene melt by means of an extruder or another mixing device; the propellant-containing melt is discharged under pressure and e.g. Granulated by means of underwater pressure granulation to form EPS particles.

In the subsequent process step, the so-called pre-foaming, the propellant-containing EPS particles are expanded by heating to give propellant-containing, partially expanded particles. They are stored in an embodiment for partial replacement of the propellant against air.

Finally, in a further method step, the so-called foaming, a mold which corresponds to the desired foam body is completely filled with the intermediately stored particles, sealed and steam-dried. beat. The particles expand again and weld together to the finished molded body made of EPS foam (particle foam).

As a thermoplastic, in the coating method, e.g. propellant-containing granules (e.g., EPS raw material) are used. The starting material can also be used in the form of prefoamed or even non-prefoamed propellant-containing particles.

As thermoplastics, e.g. Materials of polystyrene, polypropylene, acrylonitrile-butadiene-styrene polymers, polyethylene or mixtures of these plastics are used.

In the method of the invention, the thermoplastic particles may be e.g. made of raw material or partially expanded EPS (expanded polystyrene particle foam), EPP (expanded polypropylene particle foam) or EPE (expanded polyethylene particle foam) or other materials. The particles can have different shapes and sizes. You can e.g. a size (average diameter of the particles) of 0.1 mm to 30 mm, preferably from 0.1 mm to 15 mm, preferably 0.3 mm to 10 mm, in particular from 0.4 mm to 3 mm.

In a preferred embodiment of the invention, the particles contained in the dispersion used in the process of iron, zinc, nickel, copper, silver, tin, (and optionally also carbon) or mixtures thereof or alloys containing at least one of these metals. The use of carbonyl iron powder, ie. very finely divided and pure iron powder.

In a further embodiment, the chemically and / or electrolytically coatable particles contained in the dispersion preferably consist of so-called carbonyl iron, carbonyl nickel, copper and / or carbon (for example in the form of carbon black, graphite or carbon nanotubes) or mixtures from these particles.

The metal particles contained in the dispersion often have a nearly spherical shape and an average diameter of 0.01 .mu.m to 100 .mu.m, preferably 0.1 .mu.m to 50 .mu.m and particularly preferably from 1 to 10 .mu.m.

In a preferred embodiment of the invention, the dispersion used as dispersing agent contains a compound having a low boiling point or a high vapor pressure. It is possible, for example, to use carboxylic acid esters, such as ethyl acetate, aromatic solvents, such as toluene, benzene, xylene, aliphatic hydrocarbons, such as pentane, hexane and heptane, halogenated hydrocarbons, such as ethyl chloride, Methylene chloride or chloroform, aliphatic alcohols such as methanol, ethanol propanol, isopropanol or butanol, carboxylic acids such as acetic acid or water. As organic dispersing agent, it is preferable to use a carboxylic acid ester and optionally other auxiliaries.

The dispersion may also contain other auxiliaries, for. B maleic anhydride / styrene / polyethylene glycol comb polymers, PEG, PVP, metal salts (eg alkali metal or alkaline earth metal halides, sulfates, nitrates, carbonates, silicates), monodi- and triglycerides, mineral oil, paraffins, magnesium or calcium carbonate, Magnesium or calcium hydroxide, silicates and / or water.

The dispersion of the invention may e.g. contain the following components:

1 to 60 wt .-% dispersing agent, in particular from 10 to 60 wt .-% - 20 to 98 wt .-% chemically and / or galvanically coatable particles, and optionally 1 to 15 wt .-% of auxiliaries.

In a preferred embodiment of the invention, the dispersant can be removed at a pressure of 0.0001 mbar to 10 bar, in particular 0.01 mbar to 5 bar, in particular 0.1 mbar to 1 bar. The coated thermoplastic particles can be subjected to a thermal treatment at a temperature of 20 to 120 ⁰ C, this step can serve for a drying, but can also lead to (possibly additional) parts expansion.

When prefoaming the EPS particles are expanded in a conventional manner.

In the process, the dispersant can also be removed at a pressure of 0.001 to 1 bar.

The coated thermoplastic particles can be subjected to a thermal treatment at a temperature of 20 to 120 ⁰ C, preferably from 50 to 120 ⁰ C, in particular from 90 to 110 °.

In a further embodiment of the invention, the coated thermoplastic particles are subjected to a Dampfvorschäumverfahren at a temperature of 90 to 1 10 ⁰ C. The foaming of the thermoplastic particles already coated with a first chemically and / or electrolytically coatable particle (M1) produces polymer particles with a layer on the surface which contains less chemically and / or electrolytically coatable particles per unit area. In the method according to the invention, the thermoplastic particles can initially also be coated only with a partial metal layer. A second metal layer (MS2) can then also be applied to the thermoplastic particles coated with a first partial metal layer (MS1).

The invention also relates to the use of thermoplastic particles coated with a partial or complete metal layer for the production of moldings. The use takes place z. As for thermal insulation, as a material for shielding electromagnetic radiation or as a starting material for metal foams.

The invention also relates to moldings comprising the thermoplastic particles coated with a partial or complete metal layer and further auxiliaries and additives.

In a preferred embodiment of the invention, at least one second layer of a metal (MS2) is applied to the thermoplastic particles (prefoamed or not prefoamed) coated with a first chemically and / or electrolytically coatable particle layer (MS1). In this case, as the metal, e.g. Copper, silver gold, tin, nickel, chromium can be applied as second layer. For example, an electroless and / or galvanic secondary coating / metal deposition is possible.

The present invention also relates to the use of chemically and / or electrolytically coatable particles (layer) or the deposited thereon at least one metal layer coated thermoplastic particles, in particular produced as already described above, for the production of moldings. This can e.g. done by steam foaming.

The invention also provides for the use of thermoplastic particles coated with a partial or complete metal layer for the production of moldings.

The invention also relates to the use of thermoplastic particles coated with a partial or complete metal layer as thermal material

Insulation, as a material for shielding from electromagnetic radiation or as

Starting material for metal foams. The use of coated with a metal layer thermoplastic particles as an additional component for example, moldings or plates of non-metallized particle foams eg insulation boards is also an object of the invention. The thermoplastic particles may be of one or more chemically and / or galvanically coatable particle layers surrounded by a partial or complete layer, ie not necessarily means a complete enclosure.

The invention also relates to moldings comprising thermoplastic particles coated at least with a chemically and / or galvanically coatable particle layer or metal layer, as well as further auxiliaries and additives.

The shaped bodies contain the thermoplastic particles coated with a partial or complete metal layer and optionally further auxiliaries and additives.

The abovementioned objects are also achieved in that the surface of raw material particles (suitable blowing agent particles of thermoplastic polymers) of a prefoamed or non-prefoamed particle foam, preferably EPP (expanded polypropylene particle foam), EPS (expanded polystyrene particle foam) or EPE (expanded polyethylene particle foam ), be provided with a metal layer.

According to a preferred embodiment of the present invention, magnetisable particles in the form of carbonyl iron powder (CEP) particles are contained in the dispersion. The carbonyl iron powder (CEP) is preferably prepared by decomposition of iron pentacarbonyl. Various types of CEP are already known to those skilled in the art.

From hard and reduced CEP grades, surface treated types are derived in a variety of ways. For example, the most commonly treated carbonyl iron powders are silicate or phosphate coated, but other modifications are available. Another criterion for the differentiation of carbonyl selenium powders is the respective size distribution of the particles, which can have a significant influence on the application properties in the coating. The dispersed carbonyl iron powder particles preferably have a nearly spherical shape and an average diameter between 0.1 to 50, in particular 1 and 10 microns. In principle, however, all types of carbonyl iron powder are suitable for the invention. The exact selection depends on the conditions of use for the coating according to the invention.

The coated polymer particles can be converted, for example, into foamed moldings or semifinished products / cut foam made of particle foam. In the further coating of molded parts from the coated particles, the surface is closed and has only partially gusset spaces between the foam particles.

The deposition of the further coating materials takes place e.g. from the gas phase, liquid phase, solid phase or a phase mixture. Applied coating materials may again be metals such as e.g. Aluminum, copper, gold, silver, tin, chrome, and nickel. In order to ensure a uniform distribution of the coating material on the molded parts, e.g. a sputtering of the coating material during the coating process and / or a rotation / displacement of the foam. A variant is also the use of ultrasound. Another variant for atomization is the use of an air flow.

Various raw materials, including expanded polystyrene particle foam or prefoamed EPS beads, may be coated with, for example, an acrylate suspension containing carbonyl iron powder. These materials can then surprisingly be processed as standard materials. In particular, no abrasion of the CEP particles was observed in the molded parts produced. The welding of the particles in the finished molding was also very good.

The mechanical properties (such as flexural and compressive strength) were very good, as were the thermal insulation properties. There are numerous possible applications for the particles according to the invention:

• Insulating boards, e.g. EPS insulating boards, with magnetic properties, used to shield electromagnetic radiation

Particles according to the invention which can be electrolessly and / or galvanically metallized (use for shielding electromagnetic radiation, for decorative applications, as electrically and / or thermally conductive foams)

• Production of foams with improved heat-insulating properties by Fe particles in the μm range (see Neopor effect)

Production of metal foams, which can be used, for example, as crash absorbers, for example in motor vehicles.

The invention is explained in more detail by the figures 1 to 4 and by the following examples. In particular, two production variants are described:

Variant 1: (coating and subsequent foaming) EPS (expandable polystyrene, styrofoam) raw material is coated with a dispersion of CEP in a dispersing agent. Subsequently, the iron particle-coated EPS particles thus produced are foamed, for example in a conventional 3D mold. The molded part thus produced is characterized in that the metal particles are located between the welded foam particles and not in the interior of the particles. Of course, the CEP coating is also on the surface of the molding.

Variant 2: (coating after pre-foaming)

Pre-expanded expandable polystyrene is coated with a dispersion of CEP. The subsequently produced 3D molded parts have a similar but much denser metal coating than the molded parts according to variant 1. This method can be applied to all types of thermoplastic polymer particle foams (for example Neopolen from polypropylene, Neopor, etc.). In addition to CEP, other types of iron powder (water or gas atomized iron powder or reduced iron powder) or other metal powder (e.g., copper powder, zinc powder, nickel powder) may be used.

example 1

Styrofoam P326 (manufacturer: BASF AG) was coated with an antistatic agent K30 (secondary sodium alkanesulfonates, manufacturer BAYER AG). These particles were coated in a fluid coater (manufacturer: Hüttlin-WSC) with a solvent-containing carbonyl iron powder dispersion.

The dispersion consisted of 30% ethyl acetate, 5% Styroflex 2G66 (styrene-butadiene copolymer, manufacturer: BASF AG) as binder and 65% carbonyl iron powder SQ (manufacturer: BASF). The coating size for coating was 6655 g of styrofoam particles, the output of coated particles was 7847 g, so that 1192 g of carbonyl iron powder dispersion were applied by calculation. This corresponds to a coating content of about 15 wt .-%.

During the pre-foaming of the coated raw material, the good adhesion of the dispersion to the styrofoam particles prevented the abrasion of carbonyl iron powder. FIG. 1 and FIG. 2 show photographic representations of the particles according to the invention as enlargements (scanning electron micrographs).

There were excellent material properties for particle foams from particles coated in this way:

a) Pressure test according to the standard EN826

b) Bending strength from fracture test

c) thermal conductivity according to DIN 52612 (Poensgen)

Example 2

It is also possible to produce the prefoamed coated particle foams which have good mechanical properties from already prefoamed materials.

These materials are characterized in comparison to the materials produced according to process variant 1 in that the introduction of larger quantities of metal (for example CEP) into the foam body becomes possible.

The photograph in Figure 3 shows the cut edge of a material foamed to the block. The welding of the material is very good despite the dense coating with metal (CEP). The CEP is located here in particular at the welding points between the individual foam particles.

The photograph in FIG. 4 shows, on the one hand, the structure of a molded part made of styrofoam P326 which, after pre-foaming, was coated with a CEP suspension. The CEP is located almost exclusively between the individual foam beads. The beading is again very good despite the large amount of CEP applied. In the enlargement shown on the right side of FIG. 4, the regular arrangement of the cells can be clearly seen.

Claims

claims

1. A process for coating blowing agent-containing thermoplastic particles with a partial or complete metal layer, are treated in the particles of a thermoplastic with a dispersion containing metal particles in an organic dispersion medium, then the organic dispersant is removed and the coated thermoplastic particles optionally a thermal treatment be subjected.

2. Process according to claim 1, characterized in that particles of a prefoamed or non-prefoamed plastic are used as thermosplastic particles.

3. The method according to any one of claims 1 or 2, characterized in that as thermoplastic particles particles of polystyrene, polypropylene, acrylonitrile

Butadiene-styrene polymer, polyethylene or mixtures of these plastics are used.

4. The method according to any one of claims 1 to 3, characterized in that the thermoplastic particles of EPS (expanded polystyrene foam), EPP (expanded polypropylene particle foam) or EPE (expanded polyethylene particle foam) and have a size of 0.1 mm to 30 mm.

5. The method according to any one of claims 1 to 4, characterized in that the metal particles contained in the dispersion of iron, zinc, copper, silver, tin or alloys containing at least one of these metals.

6. The method according to any one of claims 1 to 5, characterized in that the metal particles contained in the dispersion of iron and / or copper and

Consist of carbon.

7. The method according to any one of claims 1 to 6, characterized in that the metal particles contained in the dispersion have a nearly spherical shape and a mean diameter of 0.1 to 50 microns.

8. The method according to any one of claims 1 to 7, characterized in that the metal particles contained in the dispersion consist of carbonyl iron powder.

9. The method according to any one of claims 1 to 8, characterized in that the dispersion contains as organic dispersant a carboxylic acid ester and optionally further auxiliaries.

10. The method according to any one of claims 1 to 9, characterized in that the dispersion contains 10 to 60 wt .-% dispersant, 20 to 98 wt .-% metal particles and optionally 1 to 15 wt .-% of auxiliaries.

1 1. A method according to any one of claims 1 to 10, characterized in that the coated thermoplastic particles are subjected to a thermal treatment at a temperature of 20 to 120 ⁰ C.

12. The method according to any one of claims 1 to 1 1, characterized in that the coated thermoplastic particles are subjected to a Dampfvorschäumverfahren at a temperature of 90 to 1 10 ⁰ C.

13. The method according to any one of claims 1 to 12, characterized in that the thermoplastic particles are initially coated only with a partial metal layer.

14. The method according to any one of claims 1 to 13, characterized in that on the coated with a first partial metal layer (MS1) thermoplastic particles at least a second metal layer (MS2) is applied.

15. Use of coated with a partial or complete metal layer thermoplastic particles prepared according to any one of claims 1 to 14 for the production of moldings.

16. Use of thermoplastic coated with a partial or complete metal layer thermoplastic particles prepared according to any one of claims 1 to 14 as a material for thermal insulation, as a material for shielding electromagnetic radiation or as a starting material for metal foams.

17. Shaped body containing the coated with a partial or complete metal layer according to claim 1 to 14 thermoplastic particles and other auxiliaries and additives.