FI90324B - A method of making an electrically conductive plastic product - Google Patents

Description

9Q324

Process for the manufacture of an electrically conductive plastic product Förfarande för framställning av en elledande plastprodukt 5

The invention relates to a method for manufacturing an electrically conductive plastic product by doping a conductive polymer or a mixture of a conductive polymer and a matrix plastic in a molten state.

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 application No. 168,620, the aim of which is to obtain a stable dispersion of a conductive polymer in a thermoplastic polymer, the shaping of which is possible while maintaining optimal 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 patent application FI-901632 discloses for the first time a method for manufacturing an electrically conductive polymer product by doping, in which the doping takes place in connection with or even before the processing of the polymer. The purpose of patent application F1-901632 is to provide a method for doping a conductive polymer in which the properties of the conductive polymer can be modified as desired and which is stable. 25

One method of machining plastic parts is molding. The introduction of the plastic mass into the mold can take place in many different ways, of which injection molding or injection molding, as it is also called, is the most common method. Injection molding can be used to produce dimensionally accurate, complex and completely similar products.

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Injection molding requires an injection molding machine, which includes a plastic melting and dosing device (= injection unit) and a mold press (= sealing unit), a product-specific mold 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-5, 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 in the middle stage 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 plastic mass. 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 15 injection units is driven into the injection channel hole in the mold. For this purpose, the mounting plate of the mold press has an opening in the middle. At the rear end of the screw there is a hydraulic 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) in its passage, which prevents the molten mass from flowing back along the threads of the screw.

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In the sealing unit, the plastic mass is injected into the mold under very high pressure. The maximum pressure of the spraying unit is of the order of 500 bar. 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 traced under the mold tables, where 25 products 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 follows the circumference of the largest projection of the extrudate and the extrudate, when solidified, easily slides out of the housing or off the top of the core. 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. 30 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. Cooling and tempering devices, for example, are required as a peripheral device in connection with injection molding, because, for example, the temperature of the mold often has to be kept exactly constant and quite hot.

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The injection mold must be dimensioned to withstand the injection pressure and the closing pressure without changing its shape. The maximum pressure given by the spraying unit is 1500-2000 bar, which is rarely needed. The pressure also decreases in the ducts and mold cavities, but the mold must still withstand hundreds of bars. If there is a part of the mold which moves outwards at this point, it must be locked mechanically or by a hydraulic cylinder when the mold is closed. Molten durable plastic penetrates cracks of less than 0.1 mm under pressure. (Thermoplastic and rubber penetrate an even smaller gap.) Mold parts that are important for the dimensions of the extrudate are usually made of annealed steel or hardened. Sometimes surfaces are nitrated or hard chromated if the surface requirements are high. The surfaces of the mold housing must meet the surface requirements of the product. The molds may have many nests or the large extruders have many mass entry points to ensure even filling. In these cases, the channel must be divided into multiple branches.

For details on injection molding machines and their molds, reference is made to handout 20 Properties, processing methods and use of plastics, Training Center for Engineering Organizations, INSKO, dipl.ins. Mikael Boedeker).

All thermoplastic plastics can be extruded in a mold. Two groups are often discussed: general or bulk plastics and engineering plastics. Universal plastics usually refer to plastics costing FIM 4-25 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 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. 30 destinations.

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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 compression 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.

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.

The object of the invention is to provide a method by which conductive polymers can be processed by injection molding by timing the doping in connection with the processing.

In order to achieve the above objects, the method according to the invention is mainly characterized in that the conductive polymer or the mixture of conductive polymer and matrix plastic is introduced into the mold in the molten state and the dopant is added to the moldable conductive polymer or molten mixture of dopable conductive polymer and matrix plastic.

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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 mold base can be used as the equipment with minor modifications.

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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, doping was performed when processing the product, e.g. in connection with an extruder, in which case the dopant was added to the extruder before pressing into the mold.

90324 6 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 conductive polymer or into the melt formed by the conductive polymer and the matrix plastic in a manner which will be explained in detail later in connection with the figure. In this case, the actual doping takes place in 5 molds during machining and during and possibly after shaping of the product.

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

The invention can be used to make any plastic product with possible electrical conductivity.

The invention will now be described with reference to the figure of the accompanying drawing. This is not intended to limit the invention to the details of the figure.

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The figure shows an embodiment of the invention in connection with an applied injection molding method in which a dopant is added to a molten conductive polymer mixture while the mixture is in the mold through special channels in the mold.

In the figure, a conducting polymer 1 or a mixture 2 'of conductive polymer 1 and matrix plastic 2 is added to the feed hopper 6 of the injection molding machine 4. The raw material mixture is then melted by means of a feed screw 7 and introduced into the mold 9 along the channel 8. Liquid dopant 3a and / or gaseous is added to the molten conductive polymer mixture 2 'in the mold 9 in the mold housing 10. The dopant 3a is introduced into the mold 9 via line 12 13. In the mold, the raw material mixture is pressed in the mold housing 10. The press is cooled and then removed in a manner known per se.

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The dopant 3a is added to the molten conductive polymer mixture 2 'through the channels 11 belonging to the mold 9. The mold can also be formed porous (not shown).

. The following are claims, within the scope of which the details may vary within the scope of the inventive idea 5.

Claims (7)

A process for producing an electrically conductive plastic product by doping a conductive polymer or a mixture of a conductive polymer (1) and a matrix plastic (2) in a molten state, characterized in that the conductive polymer (1) or the mixture of conductive polymer and matrix plastic (2) is passed in a molten state in a mold (9) and dopant (3a) is added in the mold (9) in the dopable conductive polymer (1) or in the doped conductive polymer (1) meltable dopable and matrix plastic (2) mixture. via mold channels (11) belonging to mold (9). 2. A method according to claim 1, characterized in that the dopant is iodine. Method according to claim 1 or 2, characterized in that the dopable conductive polymer is a processable conductive polymer, advantageously poly (3-octylthiophene). 4. A process according to any one of claims 1-3, characterized in that the matrix polymer in the plastic composition which can be doped containing conductive polymer is polyethylene, polypropylene, polystyrene, PVC or EVA (ethylene vinyl acetate). Process according to any of claims 1-4, characterized in that the molding takes place at a temperature of about 180 ° C when the matrix polymer is polyethylene, polystyrene, PVC or EVA. 25 Process according to any of claims 1-5, characterized in that the molding takes place at a temperature of about 195 ° C when the matrix polymer is polypropylene. 30 Process according to any of claims 1-6, characterized in that the molding takes place in connection with injection molding.