FI90325B - A method of making an electrically conductive plastic product - Google Patents

Description

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Method for producing an electrically conductive plastic product 'v-' * · - ~ For the production of plastic products 5

The invention relates to a method for manufacturing an electrically conductive plastic product in connection with injection molding, in which the product is formed from a molten plastic mixture so that the raw material is plasticized in a cylinder by means of a feed screw and injected into a mold.

10 Plastics and other polymers are not conductive in themselves, but can be made electrically conductive for a variety of applications. Electrically conductive polymers can be prepared from organic polymers with long chains of conjugated double bonds. The amount of silicon electrons in the double bonds can be influenced by the addition of certain dopants (dopants) to the polymer, which are either electron accepting or donating. Thus, gaps, or extra electrons, are created in the polymer chain, which allow an electric current to flow along the conjugated chain. The electrical conductivity of polymers can be adjusted depending on the dopant content to cover almost the entire conductivity range from insulators to metals. Such electrically conductive polymers have many interesting applications, e.g., EM1 applications and ESD-20 applications.

Conductive polymeric and organic conductors are generally insoluble, cannot be melted or shaped, and in some cases are unstable to oxygen, moisture, and high temperatures, which is why doping at high temperatures has not been successful in the past. Until now, it has therefore not been possible to thermoplastically treat or modify the conducting polymers in any way. There have been reports of the meltability of some individual conducting polymers, but their conductivity has been very poor. After doping, the polymer is generally insoluble and can no longer be modified, which is why doping has traditionally been performed after the polymer has been modified.

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It is thus known that the doping of the polymers takes place after the treatment, i.e. the formation of the product, e.g. with FeCl3. Such a method becomes very expensive due to the special equipment for doping and, in addition, it is impractical and environmentally unfriendly because toxic volatile gases are released into the environment.

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To solve this problem, attempts have also been made to develop specific polymerization methods and to form mixtures of conductive polymers and other polymers which could be modified after doping. However, the conductivity has generally been too low.

With regard to the state of the art related to the present invention, reference is made to EP Patent Publication No. 168,620, the aim of which is to obtain a stable dispersion of a conductive polymer in a thermoplastic polymer which can be shaped while maintaining optimum conductivity. The aim of this publication is also the possibility of stabilization after dispersion. In this EP, a thermoplastic polymer is mixed (dispersed or dissolved) with a conductive polymer in a molten state until a homogeneous mass is obtained, after which the solvent is removed. The matrix polymer is stated to be polyether, polyester, polyvinylene chloride, polyamide, etc. The doping according to the publication takes place in solution or by ultrasound. Additives are also added to improve workability.

Applicant's earlier F1 application 901632 discloses for the first time a method for producing an electrically conductive polymer product by doping, wherein the doping takes place during or even before the processing of the polymer. The purpose of FI application 901632 is to provide a method for doping a conductive polymer, where the properties of the conductive polymer can be modified as desired and which is stable.

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Injection molding or injection molding, as it is also called, is the most common method of making plastic parts. Injection molding can be used to produce dimensionally accurate, complex and completely similar products.

30 Injection molding requires an injection molding machine with a plastic melting and dosing device (= injection unit) and a mold press (= sealing unit), a product-specific mold 3 90325 and a cooling system. The machine usually consists of two main parts, an injection unit and a shut-off unit mounted on a common base. In the injection unit, in a cylinder heated by electric resistors, a helical screw rotates by the force of an electric or hydraulic motor. The depth of the screw threads is greatest at the beginning and decreases * 5 in the middle and continues small at the end of the screw where the non-return valve is located. There is a feed hole at the back of the cylinder liner and a funnel on top. The raw material is poured into the hopper and the rotating screw pulls the raw material with it. The plastic then melts due to cylinder heating and friction. At the start of plasticization (melting), the screw is in the front position in the cylinder. The screw can move backwards as it passes the molten 10 plastic masses past. A chamber is formed in front of the tip of the screw, into which the molten plastic wraps. At the front end of the chamber, i.e. the nose of the cylinder, there is a hole which is either open or equipped with a valve. When a sufficient amount of plastic has been melted, the screw stops and the nozzle of the injection unit is driven into the injection channel hole in the mold. To do this, there is an opening in the middle in the mounting plate of the closing unit. At the rear end of the screw there is a hyd-15 ratchet cylinder which gives an injection pressure of up to 1500-2000 bar on a standard machine. The screw acts as a piston because it has a non-return valve (so-called ring) at its tip, which prevents the molten mass from flowing back along the threads of the screw.

In the sealing unit, the plastic mass is injected into the mold under very high pressure. The maximum pressure of the spray unit is of the order of 500 kp / cm2. A plastic mass is injected into the mold and when it has solidified sufficiently the mold is opened. The machine is then ready for the next cycle. Most machines have a free opening under the mold tables, where the product can fall onto a conveyor belt, for example. Most machines are horizontal to facilitate part removal. The cheapest mold solution is the so-called natural mold, where the dividing plane 25 follows the circumference of the largest projection of the extrudate and the extrudate, when solidified, easily slides out of the housing or out of the boil. A channel is required between the nozzle of the injection molding machine and the mold housing, along which molten plastic flows into the housing. The channel can be e.g. conical and at its simplest the channel continues as a cone to the surface of the extrudate and connects to it. Special ejection systems are required for the mold to remove the extrudate. A considerable amount of heat enters the mold with the molten mass, which must be transported away and cooled. As a peripheral device in connection with injection molding, e.g.

4 90325 Cooling and tempering equipment, as, for example, the temperature of the mold often has to be kept exactly constant and fairly hot. For details on injection molding machines, reference is made to the handout Properties of Plastics, Machining Methods and Use, Training Center for Engineering Organizations, INSKO, dipl.ins. Mikael Boedeker).

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All thermoplastic plastics can be injection molded. Two groups are often discussed: general or bulk plastics and engineering plastics. General purpose plastics generally refer to plastics costing FIM 4-6 / kg, eg LDPE (LD polyethylene), HDPE (HD polyethylene), PP (polypropylene), PS (polystyrene), SB (styrene butadiene) and PVC (polyvinyl chloride). The major consumer of these 10 is the packaging industry (often disposable packaging such as jars, bottles, films). They are also made into cheap transport and storage boxes, beverage baskets, etc. They are also used for more technical products when the properties are suitable. to.

More particularly, the invention relates to a method of manufacturing electrically conductive plastic products by doping a conductive polymer or a plastic mixture containing a conductive polymer in connection with the processing of the product when the processing takes place by injection molding. In this application, the term "conductive polymer" is also used for a polymer to be doped, although it is not yet electrically conductive prior to doping.

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It is preferable to make the plastic product from an internally conductive polymer or a mixture of such a polymer and a matrix plastic. In this case, the electrical conductivity of the product can be precisely adjusted to the desired application, either by changing the composition of the polymer mixture or by varying the degree of doping.

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The object of the invention is to provide a method by which injection-molded plastic products can be produced from an electrically conductive polymer.

In order to achieve the above-mentioned objects, the method according to the invention is mainly characterized in that in the method a solid dopant or alternatively a dopant mixed / attached to the material is added to the melting conductive polymer of the injection molding machine. after plasticization before injection into the mold to provide electrical conductivity.

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Preferred embodiments of the invention have the features of the subclaims.

The advantage of the invention is that the doping method according to it is very easy to implement. The existing standard device-10 base can be used as a minor modification.

The invention utilizes the realization of FI application 901632 that doping can be performed by adding a doping agent to the conducting polymer while it is in the molten state and the doping is timed to occur during processing. In FI application 901632 15 doping was performed when processing the product, e.g. in connection with injection molding. The present invention has discovered new ways of manufacturing electrically conductive products in connection with injection molding.

The present invention provides a novel method for doping a conductive polymer in the molten state. According to the invention, the dopant can be introduced into the melt mixture either mixed with the conductive polymer, mixed with the matrix plastic, or the dopant can be added directly to the conductive polymer or to the melt formed by the conductive polymer and the matrix plastic. In all cases, the dopant is mixed with the plastic before the product is compressed.

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The oxidizing or reducing dopant may be either a gas (e.g., iodine vapor), a liquid (e.g., liquid sulfonic acid), or a solid (e.g., a sulfonic acid having a suitable melting point).

The polymer used may be any melt processable dopable polymer, e.g. poly (3-octylthiophene) and any processable polymer as the matrix material.

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The dopant is added to the conductive polymer or mixture of the conductive polymer and the matrix polymer during or after melting.

The invention can be used to make any plastic product 5 having electrical conductivity.

In the following, the invention will be described with reference to the figure of the accompanying drawing, various embodiments of the invention. This is not intended to limit the invention to the details of the figures.

The figure shows an embodiment of the invention in connection with an applied injection molding process in which a dopant is added by means of an extruder to a molten conductive polymer mixture in a mixing device before injection into a mold.

In the embodiment of the invention according to the figure, only the conducting polymer 1 or a mixture of the conducting polymer 1 and the matrix plastic 2a is added to the feed hopper 15 6 of the injection molding machine 4. This mixture is plasticized, as described above, in the cylinder 5 by means of a feed screw 7. The dopant is added to the molten conductive polymer blend 1,2 in a mixing device 11 located in the injection molding machine 4 between the cylinder 5 and the channel 8 leading to the mold 9. The mixture is then passed through a channel 8 into a mold 9, where it is pressed in the housing 10 of the mold 20. The press is cooled and then removed in a manner known per se.

According to the embodiment according to the figure, the solid dopant 3 alone or the dopant 3 mixed / attached to the material 2b is added by means of an extruder 15 to the molten conductive polymer mixture 1,2a in the mixing device 11 before injection into the mold 9. The extruder 15 has a feed screw 16 which feeds the dopant 3 and any material 2b to the mixing device 11.

The following are claims, within the scope of which the details may vary within the scope of the inventive idea.

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Claims (6)

A process for producing an electrically conductive plastic product in connection with injection molding, in which the product is formed by a molten plastic mixture such that the raw material is plasticized in a cylinder by means of a feeding screw (7) and sprayed in a mold (9), characterized in hence, in the process, solid dopant (3) or alternatively a dopant (3) mixed with / attached to some material is added by means of an extruder (15) to a mixing device (11) in an extruder (4) in molten conductive polymer to be doped or in a molten mixture (1,2a) of conductive polymer to be doped and a matrix plastic (1,2) after the plasticization that has taken place in the cylinder (5) of the extruder (4) prior to spraying into the mold (9 ) to achieve conductivity. Method according to claim 1, characterized in that the dopant is iodine. 3. A method according to claim 1 or 2, characterized in that the conductive polymer to be doped is a processable conductive polymer, advantageously poly (3-octylthiophene). 20 4. A process according to any of claims 1-3, characterized in that the matrix polymer in the plastic mixture to be doped and containing conductive polymer is polyethylene, polypropylene, polystyrene, PVC (polyvinyl chloride) or EVA (ethyl vinyl acetate). 25 Process according to any of claims 1-4, characterized in that the spraying of the plastic mass into the mold takes place at a temperature of about 180 ° C when the matrix polymer is polyethylene, polystyrene, PVC (polyvinyl chloride) or EVA (ethyl vinyl acetate). Process according to any of claims 1-5, characterized in that the injection of the plastic mass into the mold takes place at a temperature of about 195 ° C when the matrix polymer is polypropylene.