METHOD OF PREPARING A CONDUCTIVE PLASTIC PRODUCT WITH THE BLOWING METHOD

Abstract: The invention is concerned with a method of preparing a conductive plastic product with the blowing method wherein the product is formed from a melt plastic mixture by means of an annular extrusion nozzle and blast gas. Conductive polymer or a plastic mixture containing conductive polymer to be doped is lead to the extrusion nozzle and blast gas is lead inside the product to be formed which blast gas contains doping agent in gas form to achieve conductivity.

Description: Method of preparing a conductive plastic product with the blowing method The invention is concerned with a method of preparing a plastic product by the blowing method wherein the product is formed from a melt plastic mixture by means of an annular extrusion nozzle and blast gas. More in detail, the invention is concerned with a method of preparing conductive plastic products by doping of a conductive polymer or of a plastic mixture containing a conductive polymer in connection with the working of the product when the working is carried out with the blowing method. The good isolating properties of plastics have in some cases restricted their use, for example because static electricity has been collected in packages prepared of plastic. Static electricity has increased the adhesion of films to each other in the production processes of plastics and thus made the winding properties worse. The package products charged with static electricity can in the use cause situ¬ ations of danger for example a risk of explosion. Spiking may cause dangerous situations, especially in solvents to be held in plastic barrels and in other inflam¬ mable fluids. Static electricity in package materials also increases the contamination of the packages during storage. In packages with sensitive electronic components it is very important to avoid spiking and forming of static electricity. Three methods are mainly used for treating plastics to be conductive or antistatic of which one way is to add metallic powder or soot among the isolating and non- conductive plastic to achieve conductivity. The problem with this is that there shall be so much added particles uniformly distributed that they touch each other. In this case also the conductivity curve will have bends, in other words, at low concentrations there is no conductivity and after a given threshold value the conductivity is high. Another possibility to treat plastics to be antistatic is to treat the surface of the plastic product either with corona charging or with given chemicals. The problem with the corona charging is that the effect is maintained only for a short time. The problem with the chemical surface treatment is its dependence on humidity. The surface resistance of a plastic product thus treated depends on the air humidity around the product. The third possibility is to coat the plastic product with a thin metalhc layer. The problem with this method is that the product is very brittle, the surface is sensitive and the conductivity curve has bends. The best way is to make the plastic product of a polymer that is conductive in itself or from a mixture of such polymer and a matrix plastic. Then the conduc¬ tivity of the product can be exactly controlled in accordance with the wished use either by changing the composition of the polymeric mixture or by altering the doping degree. Generally it has not been possible to work up products made by conductive polymers. The most conventional way of preparing the wished products has been to form the product in connection with the polymerization. From for example the Patent Publication DE 3716284 there is known a method of preparing a film wherein anilin is polymerized electro-chemically and a polyanilin film is formed on the anode. Plastic films are most usually prepared with the blowing method, with the plane film method or with calandering. Conductive plastic products has generally been prepared with the plane film method in which case there has been mixed carbon black, metallic particles or other conductive material with the basic plastic to be formed in melt state and to work up the thus received mixture. Such methods have been presented for example in the Patent Publications EP-240976, wherein a polyolefine layer and an aciylate polymer containing carbon black has been coextruded, in the Patent Publication JP-59093644 wherein antistatic plastic has been prepared by coextruding of a polystyrene or an ABS plastic (acryle nitrile butadiene styrene) and a polystyrene that has been made conductive by means of carbon black. It is known in itself to combine a working of a plastic product by blowing with a chemical treatment. Thus, a treatment of polypropene with ozone is known from the Patent Publication JP-60250938-A, wherein ozone gas is lead inside the film bubble to be blown. The aim of the treatment is to improve the surface prop¬ erties of polypropene. The Patent Publication GB-2083404 in turn presents mixing of perfumes with the blast gas when blowing of films or bags to decrease smelling problems of plastic products. The object of the invention is to produce a method by which conductive poly¬ mers can be worked by blowing by timing the doping in connection with the working. The method of the invention is mainly characterized in that a plastic mixture containing conductive polymer to be doped is lead to the extrusion nozzle and inside the product to be formed there is lead blast gas that contains material in gas form that dopes the conductive polymer to achieve conductivity. The advantageous embodiments of the invention have the characteristics of the subclaims. In the method, melt conductive polymer is pressed by means of an annular form to a product in tube form inside which a gas pressure is maintained. In the method, dopant, in gaseous form, is lead among this gas. The dopant can also be such a solid or fluidic substance that gasifies in the blast gas. The doping of the conductive polymer is carried out when it is in melt state after which the plastic mixture is cooled. The advantage of the invention is that the doping method of it is very easy to carry out. The device to be used can be an already existing standard device with minor changes. Films, tubes, bodies and other products that can be prepared with the blowing method can be prepared with the method of the invention. Conductive polymers are used for example as conductive or antistatic films, surface heating conductors, heating films, flexible eletrodes and detecting elements, batteries and raw material for batteries and accumulators, semi- conductive components in solar cells and as catalysts. Especially the films prepared with the method of the invention can be used as raw materials in preparing products for EMI (electric magnetic interference) and ESD (electric static discharge) applications. In the following the invention is explained in detail by means of the enclosed figures 1-3 which are not meant to restrict the invention. Figs 1-2 present different embodiments of the invention and Fig.3 the activation of the doping. In Fig. 1 the doping has been presented in connection with preparing of a plastic film with the blowing method. In Fig. 2 the doping has been presented in connection with a form blowing method. In Fig. 3 there has been presented an activation of the doping after the blowing of the film. In Fig. 1 the doping has been presented in connection with preparing of a plastic film with the blowing method. Etiher a conductive polymer or a mixture of a conductive polymer and a matrix plastic is introduced in the feedhopper (2) of the extruder (1). The screw (3) of the extruder feeds melt plastic to the nozzle (4). The task of the nozzle (4) is to form a thin tube of the melt plastic inside which blast gas is lead from a filling opening (5), that contains gaseous dopant. A film bubble (7) is formed from the plastic mixture (6) by the effect of the blast gas inside which bubble the doping gas can affect the conductive polymer. After cooling and solidifying the plastic film is lead by means of guiding plates (8) to draw-in rollers (9) and further to the winding (10). In Fig. 2 the doping has been presented in connection with a mould blowing method. Conductive polymer or a mixture of a conductive polymer and a matrix plastic is introduced in the feedhopper (2) of an extruder (1). The screw (3) of the extruder feeds melt plastic to the nozzle (4). In the nozzle (4) the fabricate (7) of the product is formed from the plastic mixture (6) inside the mould (8). The mould (8) and the fabricate (7) inside that is blown in the next stage to the final product (9) whereat the blast gas (5) contains gaseous dopant. The doping gas among the blowing gas can affect the conductive polymer that is in melt stage and dope that. The activation of the doping has been presented in Fig. 3 after the blowing of the film. The device and its function is in other respects the same as in figure 1, but there is in addition to that devices (11) for external activation of the doping.

Claims: Claims 1. Method of preparing a conductive plastic product with the blowing method in which method the product is formed of a melt plastic mixture by means of an annular extrusion nozzle and blast gas, characterized in that conductive polymer or a plastic mixture containing conductive polymer to be doped is lead to the extrusion nozzle and blast gas is lead inside the product to be formed which blowing gas contains doping material in gas form to achieve conductivity. 2. Method of claim 1, characterized in that the plastic coming from the extrusion nozzle is formed to a film tube inside which doping gas is lead. 3. Method of claim 1, characterized in that the plastic coming from the extrusion nozzle is lead to a blowing mould and the mould blowing gas contains doping gas. 4. Method of any of claims 1-3, characterized in that the doping gas is iodine or ozone. 5. Method of any of claims 1-4, characterized in that the conductive polymer is a conductive polymer that can be worked, preferably poly(3-octyltiophen). 6. Method of any of claims 1-5, characterized in that the plastic mixture to be doped is a mixture of a conductive polymer and a matrix plastic. 7. Method of claim 6, characterized in that the matrix polymer is polyethene, polypropene, PVC or EVA (ethene vinyl acetate). 8. Method of claim 7, characterized in that the matrix polymer is polyethene and the tempearure of the extruder nozzle is below 200°C. 9. Method of claim 7, characterized in that the matrix polymer is polypropene and the temperature of the extruder nozzle is ca 200-220°C. 10. Method of any of claims 1-9, characterized in that the doping is followed by a separate activation step of the dopant.

Inventors: KAERNAE TOIVO, KOKKONEN TIMO, LAAKSO JUKKA, KAERNAE, TOIVO, KOKKONEN, TIMO, LAAKSO, JUKKA
Applicants: NESTE OY
Application year: 1992
Main classification: B29C49
IPC codes: B29C47, B29C49