WO1992004985A1

WO1992004985A1 - Use of a conducting fibrous web and articles incorporating such a web

Info

Publication number: WO1992004985A1
Application number: PCT/NL1991/000184
Authority: WO
Inventors: Adam Paul Geel; Rudolf Gijsbertus Goossens; Dirk Albertus Bovenschen
Original assignee: Lantor B.V.
Priority date: 1990-09-21
Filing date: 1991-09-23
Publication date: 1992-04-02
Also published as: DE69105741T2; EP0549728B1; DE69105741D1; NL9002073A; EP0549728A1

Abstract

The invention relates to the use of a conducting fibrous web incorporated in a plastics article at or below the surface of said aricle for providing conduction for the electrostatic application of a coating to said surface.

Description

Title: Use of a conducting fibrous web and articles incorporating such a web

This invention relates to articles which are suitable for electrostatic application of a coating, more particularly a muffle coating, and to the use of a fibrous web for manufacturing such articles. Particularly in the automobile industry, there is a tendency to replace more and more metal parts by plastic parts with a view to improving weather resistance, increasing design options and saving weight. Plastics are also used increasingly in the manufacture of housings for various machines. One of the ongoing problems associated with the use of plastics is finishing the surface, in particular if this is to be done through a coating.

Heretofore, it has proved impossible to properly provide a finished surface in a single operation, as is possible with metal parts by means of muffling, painting or spraying.

Especially the porosity and the non-homogeneous structure of plastics surfaces leads to bubbles and other visible defects upon application of a lacquer, which necessitates an expensive finishing operation. Muffling further involves the problem of poor conductivity of the plastics, so that electrostatic coating, which is most desirable from an environmental point of view, is not properly possible, if at all.

A number of proposals have been made to enable the electrostatic application of a muffle coating. The abstract of Japanese patent application 52/14641 discloses embedding a metal powder at the back of the article to be coated. According to the abstract of Japanese patent application 59/89272, metal powder or fibres are provided in the article. The abstract of Japanese patent application 57/180638, finally, disloses the application of a conducting primer on the articles prior to electrostatic coating.

These methods have the disadvantage either that the properties of the article decline or that additional operations are necessary.

The object of the present invention is to provide a system in which the disadvantages of the prior art are not encountered.

Surprisingly, it has been found that a conducting fibrous web can be effectively used for providing the required electrostatic charge on a plastics article.

This invention accordingly relates to the use of a conducting fibrous web incorporated in a plastics article at or below the surface of the article for providing conduction for electrostatic application of a coating to said surface.

The fibrous web is preferably a web of metallized fibres, more particularly metallized plastics fibres.

The surface resistivity of the fibrous web as such must be kept as low as possible and is preferably less than l Ohm #. Suitable fibres are plastics fibres, preferably acrylic or polyester fibres, or glass fibres, which fibres have been metallized with nickel, copper or silver, or with alloys based on one.or more of these metals. It has been found that metallized fibres are appreciably more suitable for the present use than metal fibres, as metallized fibres yield an appreciably better conduction upon incorporation into the article. Moreover, metal fibres have the disadvantage that in the course of time the bond in the article deteriorates. Accordingly, although metal fibres can also be used, the use of metallized fibres is preferred.

The conducting fibrous web may consist of conducting fibres only, but it is also possible to use a combination of conducting and non-conducting fibres in the web. In that case, for obtaining good conduction, the length of the conducting fibres is preferably 40-60 mm. The web can be bonded thermically, chemically or mechanically. Optionally, a woven fabric can be used. To obtain optimum conduction, a combination is used of a web of metallized fibres which is in contact with a net of metal wires, for instance copper wires of a diameter of 0.05- 0.5 mm, which net can be relatively coarse, having for instance a mesh of 0.5-10 cm.

The present invention further relates to an article made from a plastics, suitable for electrostatic application of a coating, in particular a muffle coating, in which article an electrically conducting fibrous web has been incorporated at or below at least one of the surfaces thereof. The article according to the invention can comprise the above-described web at or just below its surface. If the web is located at the surface, the metallized fibres partly project through the plastics, so that the surface also has antistatic properties. The surface resistivity of the article can be low, for instance not more than 100, preferably not more than 10, more particularly not more than 1 Ohm #. This is very favourable for obtaining a surface to be coated electrostatically. Moreover, the advantage of a conducting surface is that the potential can be applied in a simple manner by means of a conducting tape which is provided on the surface, for instance adjacent or on the edge.

It is also possible to provide the conducting web just below the surface, for instance 100-400 μm below the surface. The article can be made from a thermoplastic or a thermosetting plastics. Examples of ther osetting plastics are phenolic resins, epoxy resins, polyester resins and polyurethane resins. Thermoplastics that can be used include the various "engineering plastics" such as polypropylene, ABS and related styrene polymers, polycarbonate, polyetherimide, polyphenylene oxide, polyphenylene sulfide and mixtures of such plastics. These plastics may also be reinforced with fibres. Known applications in this field are for instance articles made of fibre-reinforced polyester resin. The fibres to be used for the conducting fibrous web, and also for optional fibre reinforcement of the plastics, are, in particular, acrylic fibres, polyester fibres, glass fibres, carbon fibres and aramid fibres. Naturally, the choice of the fibres is partly determined by the temperatures the materials must be able to resist during manufacture and use.

The articles according to the invention can be made in different ways, depending on the materials to be used. Generally, in such systems a closed mould is used. The conducting fibrous web is introduced into a mould, optionally in combination with a fibrous web that can serve as a reinforcement of the plastics, for instance for the manufacture of a fibre-reinforced laminate. Suitable methods for manufacturing the articles according to the invention are SMC and RTM techniques. In SMC (Sheet Moulding Compounds) techniques, a so-called prepreg is introduced into the mould, whereupon the mould is closed and under the influence of pressure and temperature, the prepreg runs. The conducting web is already present in the mould and is subsequently impregnated with the prepreg. Another method is RTM (Resin Transfer Moulding) , in which a fluid resin, such as a thermosetting polyester resin, is injected into a closed mould already containing the conducting fibrous web and a fibrous web that can serve as a reinforcement of the plastics. Finally, it can be observed that it is also possible, in the case of. thermosetting systems, to use conventional laminate manufacturing techniques, in which all materials are applied by hand.

When utilizing a closed mould system, it is preferred that the fibrous webs to be used are provided with humidifiers and/or deaerators so as to improve the quality of the surface of the material. In this manner, a smooth plastics surface free of air-bubbles can be obtained.

The article with a conducting fibrous web at or below t?- surface is particularly suitable for electrostatic applicat._. n of a powdered coating, more particularly a muffle coating. Suitable powders are the conventional sinterable powders on a nylon, polyester, polyurethane or epoxy base. After the electrostatic application of the powdered coating, the lacquer is baked in a known manner. The invention is illustrated in and by the following examples which are not intended to limit the invention.

Example 1

A polyester needle web of about 100 g/m² consisting of 100% PBTP/PETP fibres, prefixed at 170°C at a pressure of about 4 g/cm², was laminated to a thermoprint bound web of about 35 g/m², consisting of 80% nickeled fibres and 20% PBTP/PETP fibres, with insertion between the webs of a polyester fabric of about 10 g/m² having per 5 cm diagonally applied copper wires of a diameter of 0.1 mm. Lamination was effected at 185°C at a line pressure of 18 N/cm. The web so obtained had a density of 0.48 g/cm³ measured at a pressure of 40 g/cm² and a surface resistivity measured over a length of 10 m of <0.1 Ohm #. The web was pressed as a surface web with SMC (on the basis of unsaturated polyester resin) to form a product of high surface smoothness and low porosity. Then the product was electrostatically coated with a polyester powdered coating. The coated product was hardened at 180°C. A homogeneous and smooth surface was obtained.

Example 2

40 g nickeled acrylic fibre was needled on a random polyacrylic needle web of 60 g/m² with interposition of a fabric of about 10 g/m² having per 5 cm diagonally applied copper wires of a diameter of 0.1 mm. The needle web so obtained had an elongation at break of more than 80% and a surface resistivity of <l Ohm #. The web was used as a surface web in the RTM process (on the basis of unsaturated polyester resin) . After hardening of the product and applying a potential difference between the conducting layer and the powder to be applied, the surface could be coated electrostatically.

Claims

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1. Use of a conducting fibrous web incorporated in a plastics article at or below the surface of said article to provide for conduction for electrostatic application of a coating to said surface.

2. Use as claimed in claim 1, wherein the fibrous web has been provided with metallized fibres.

3. use as claimed in claim 2, wherein the fibres have been metallized with nickel, copper, or silver, or with alloys based on one or more of these metals.

4. Use as claimed in claims 1-3, wherein the fibrous web has been provided with a net of metal wires.

5. An article manufactured from a plastics, suitable for electrostatic application of a coating, in particular a muffle coating, in which article an electrically conducting fibrous web has been arranged at or below at least one of the surfaces thereof.

6. An article as claimed in claim 5, wherein the fibrous web has been provided with metallized fibres.

7. An article as claimed in claim 6, wherein the fibres have been metallized with nickel, copper, or silver, or with alloys based on one or more of these metals.

8. An article as claimed in claim 6 or 7 , wherein the fibrous web has been provided with a net of metal wires.

9. An article as claimed in claims 6-8, wherein the fibrous web is disposed at the surface of the article and the surface resistivity is not more than 100, preferably not more than 10, more particularly not more than l Ohm #.

10. An article as claimed in claims 5-9, wherein the article has further been provided with a fibre reinforcement.