FI90324C - Process for producing an electrical conductive plastic product - Google Patents

Description

9Q324

Method for manufacturing an electrically conductive plastic product Forfarande for framstållning 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 do not conduct electricity per se, but they can be made electrically conductive for various 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 to the polymer, which are either electron accepting or donating. Thus, openings are created in the polymer chain, or extra electrons, which allow the electrical vix to pass along the conjugated chain. The electrical conductivity of the polymers can be adjusted, depending on the dopant content, so that it covers 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 conductive polymers. 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 doping of the polymer.

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Thus, as is previously known, the doping of polymers takes place in the formation of a product, e.g. FeCl3. Such a method becomes very expensive due to the special equipment for doping and, in addition, it is impractical and environmentally uneven because of the spread of toxic volatile gases in the environment.

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In order to solve this problem, attempts have also been made to develop special polymerization methods as well as to form mixtures of conducting polymers and other polymers which could be modified to dope. 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 formation of which is possible 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 the conductive polymer in the molten state until a homogeneous mass is obtained, from 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 producing an electrically conductive polymer product by doping, in which the doping takes place in connection with or even before the working of the polymer. The purpose of patent application FI-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

The method of working with Eras plastic pieces is compression molding. There are many ways to introduce the plastic mass into the mold, 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 comprising a plastic melting and dosing device (= injection unit) and a molding press (= sealing unit), a product-specific mold as well as 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 an injection-heated cylinder heated by an electric heating element-5, a helical screw is rotated 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 to decrease at the end of the screw with the non-return valve. At the rear end of the cylinder housing there is a feed hole and a funnel on top of it. 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-10 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 releases 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. in the nose of the cylinder, there is a hole which is either open or equipped with a valve. When the plastic has been melted in a sufficient amount, the screw stops and the nozzle of the 15 spraying units is driven into the spray channel hole in the mold. There is an opening in the middle of the mounting plate of the mold press. 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 piston, 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 with 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 cooled sufficiently the mold is opened. The machine is then ready for the next cycle. In most machines, a free opening is arranged under the formwork posts, where 25 products can fall onto the conveyor belt, for example. Most machines are horizontal to facilitate part removal. The cheapest mold solution is the so-called natural mold, in which the dividing plane follows the circumference of the largest projection of the extrudate and the extrudate, when cooled, easily slides out of the housing or away from the core. A channel is required between the nozzle of the injection molding and the mold housing, along which the 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, since, for example, the temperature of the mold must often be kept exactly constant and fairly 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 fish, 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 accurate in terms of the dimensions of the extrudate are usually made of heat-treated 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 inlets to ensure even filling. In these cases, the channel must be divided into multiple branches.

For details of injection molding machines and their molds, reference is made to handout 20 Properties, working 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). Their major consumer is the packaging industry (often disposable packaging such as jars, bottles, films). They are also used to make cheap transport and storage boxes, tins for drinking baskets. They are also used for more technical products when the properties are suitable. 30 destinations.

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The invention further relates to a method for manufacturing electrically conductive plastic products by doping a conductive polymer or a plastic mixture containing a conductive polymer in connection with the pushing of the product, when the pushing takes place by molding. The "conductive polymer" referred to in this application is also used as a dopable polymer, although it is not electrically conductive prior to doping.

It is preferable to make the plastic product internally from an electrically 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 use, 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 worked by injection molding by timing the doping in connection with the work.

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 dopant conductive polymer or

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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 with minimal 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 conductive polymer when it is in the molten state and the doping is timed to occur in connection with the work. In FI application 901632, doping was performed while working 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 conductor polymer or into the melt formed by the conductor polymer and the nitrile plastic in a manner which will be described in detail later in connection with the figure. The actual doping of Tålld takes place in 5 molds during the work and during and possibly after the 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. sulfonic acid having a suitable melting point).

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

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

The invention will now be described with reference to the accompanying drawing. Here, it 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 process 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 hopper 6 of the injection molding machine 4. The raw material mixture is then melted by means of a take-up screw 7 and introduced along the channel 8 into the mold 9. Liquid dopant 3a and / or gaseous is added to the molten conductive polymer mixture 2 'to the mold housing 10 in the mold housing 10. 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 channels 11 belonging to the mold 9. The mold can also be formed porous (not shown).

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

Claims (7)

8 90324 Patent claims A method 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 9) and the dopant (3a) are added to the doped conductive polymer (1) in the mold (9) or to the molten mixture of the doped conductive polymer (1) and the matrix plastic (2) through the mold channels (11) belonging to the mold (9). Process according to Claim 1, characterized in that the dopant is iodine. Process according to Claim 1 or 2, characterized in that the conductive polymer to be doped is a workable conducting polymer, preferably poly (3-octylthiophene). 15 Process according to one of Claims 1 to 3, characterized in that the matrix polymer in the doped plastic mixture containing the conductive polymer is polyethylene, polypropylene, polystyrene, PVC or EVA (ethylene vinyl acetate). Process according to one of Claims 1 to 4, characterized in that the molding takes place at a temperature of approximately 180 ° C, the matrix polymer being polyethylene, polystyrene, PVC or EVA. Process according to one of Claims 1 to 5, characterized in that the molding takes place at a temperature of approx. 195 ° C, the matrix polymer being polypropylene. Method according to one of Claims 1 to 6, characterized in that the molding takes place in connection with injection molding. 30 9 90 32 4