DE19700365A1 - Flexible, thermoformable, electrically conductive foils - Google Patents

Description

The invention relates to flexible, electrically conductive foils in thicknesses of 10 to 1000 microns, preferably 50 to 400 microns, which deforms thermally or mechanically can have high transparency and their effect regardless of the Humidity is. The foils are characterized by a transparent antistatic Coating from a mixture of 3,4-polyethylene dioxythiophene with an ther mixable or mechanically deformable binders. All come as polymer films thermoformable films (e.g. PA, PC, PU, PVC, PET, PEN, PS, PMMA, PP, PE) in Question. Applications find the films of the invention, for. B. for the packaging of electronic components where protection against electrostatic discharge particularly well received.

The use of electrically conductive, antistatic films for packaging sensitive goods has long been known. So z. B. for packaging electronic components or component groups (e.g. transistors and integrated Circuits) used electrically conductive foils to reduce the risk of electrostatic discharge, which destroy the electronic components could minimize. Even voltages below 100 V can become irreversible Cause damage and render the components unusable. Due to the increase The miniaturization of electronic components increases their sensitivity and the necessary protection against electrostatic discharge is becoming increasingly urgent.

When assembling printed circuit boards, for example, the electronic Components via so-called blister belts, d. H. thermoformed foil belts, which the Components included and sealed with narrow masking tapes, the processing tion machines fed at very high speeds. With this processing tion process loading packaging films made of organic polymers due to occurring friction on voltages up to a few kilovolts, which on the one hand leads to strong adhesion of the light components to the packaging film, or through subsequent discharge processes can destroy the components. A Protection against charging is imperative for this application.  

Protection against electrostatic discharge in the case of flammable or explosi filling goods are absolutely necessary. Also for the packaging of these critical filling goods the films according to the invention can be used.

It is state of the art for packaging by electrostatic discharge endangered goods (e.g. electronic components) the polymeric Ver equip packing foils with antistatic properties. This can be done either through a surface coating or by directly incorporating a conductive substance (e.g. conductive carbon black) or an ionic antistatic in the respective polymer. In the case of The use of conductive carbon black is the conductivity from a certain degree of filling with soot (Percolation point) through the developing soot network within art fabric-polymer matrix causes.

Soot-filled packaging films have good electrical / antistatic properties draw, but have the disadvantage that they are not transparent and therefore the view prevent on the packed goods. Furthermore, soot-filled films are only limited deep-drawable, because if stretched too much, especially in the corners of e.g. B. blister packaging, tears open the necessary soot network and thereby the conductivity get lost.

If ionic antistatic agents are added to the polymers, the resulting ones are Although packaging films are transparent, the antistatic agents only work when they are high Humidity.

From EP-A 302 304 and EP-A 339 340 it is known for the production of blister belts Use polycarbonate films that are transparent with electrically conductive polymers and are coated with an antistatic coating. Are suitable for. B. polypyrrole and polythio phene such as 3,4-polyethylene dioxythiophene. The manufacture of these coatings is known and uses the polymerization on which the conductive polymers are based the monomers on the film surface using suitable oxidizing agents such as Iron (III) salts. To produce the antistatic coating, however, are here  several process steps required and after the polymerization, the oxide agent z. B. can be removed from the coating with water.

It is also known (cf. EP-A 440 957) films with solutions or dispersions of conductive polythiophenes especially of 3,4-Polyethylenedioxythiophens transparent and antistatic coating. However, these layers cannot be mechanical or be thermally deformed.

The task therefore was to produce a flexible, electrically conductive film, the largely transparent, moisture-independent and thermal or mechanical is deformable and thus clear advantages over the previous state of Technology.

According to the invention this was achieved by coating polymer films with solutions and Dispersions of 3,4-polyethylene dioxythiophene with special organic Binders were combined. Polymer films with these transparent antista table coatings are thermally and / or mechanically deformable.

The preparation of the solutions or dispersions to be used according to the invention 3,4-polyethylene thioxythiophene is described in DE-OS 42 11 459.

Suitable binders are those which, during the thermal deformation of the be layered polymers themselves easily deformable, d. H. are soft. To be favoured therefore binders whose softening temperature is below the softening temperature of the coated polymer. In the case of mechanical deformation, the poly have high elongations at break, preferably <100%.

Examples of suitable binders for the process according to the invention are solutions gene and dispersions of homo- and copolymers of vinyl acetate, vinylidene chloride, methyl methacrylate, other acrylates and mixtures thereof.

Polyurethane latices are particularly suitable.  

Aqueous solutions or dispersions are preferably used.

Based on the solid content of conductive polymer, the coating contains solutions 50 to 4000 wt .-% of solid binder, preferably 100 to 2000% by weight.

In addition to water, the coating solutions can be water-miscible organic Solvents such as lower alcohols, methanol, ethanol, isopropanol, organic Amides, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, N-methylcapro lactam, ketones, acetone, methyl ethyl ketone, diacetone alcohol, ether, tetrahydrofuran, Contain dioxane.

Additions to increase the conductivity (e.g. sorbitol) are also possible (see EP-A 686 662).

The total solids content of the coating solutions is usually - in Dependence on the coating process used and the one to be achieved Coating thickness - between 0.1 and 50% by weight.

Suitable coating processes are e.g. B. spraying, printing (gravure, offset printing, screen printing), roller application process, curtain casting.

The dry layer thickness is usually between 0.05 and 100 μm, preferably 0.5 and 50 µm.

The thickness of the films is usually between 10 and 1000 μm, preferably 50 and 400 µm.

The polymeric carrier films can e.g. B. from the following thermoplastic polymers consist:  

PA = polyamide
PC = polycarbonate
PU = polyurethane
PVC = polyvinyl chloride
A-PET = amorphous polyethylene terephthalate
PEN = polyethylene naphthalate
PS = polystyrene
PMMA = polymethyl methacrylate
PP = polypropylene
PE = polyethylene
The plastic carrier films can have one or more layers, with individual layers being connected to one another by means of conventional laminating adhesive or intermediate layers.

The plastic carrier films can in their individual layers that of the films processing usual additives and auxiliaries, such as. B. lubricants, antiblocking agents, Antistatic agents, TiO₂, CaCO₃ contain.

The thermal deformation z. B. by deep drawing or by stamping Temperatures at which the film materials do not yet soften.

Examples Preparation of the 3,4-polyethylene dioxythiophene solution

20 g of free polystyrene sulfonic acid (M _n approx. 40,000), 21.4 g of potassium peroxodisulfate and 50 mg of iron (III) sulfate are placed in 2000 ml of water with stirring. 8.0 g of 3,4-ethylenedioxythiophene are added with stirring. The solution is stirred for 24 hours at room temperature. 100 g of anion exchanger (commercial product Bayer AG Lewatit MP 62) and 100 g of cation exchanger (commercial product Bayer AG Lewatit S 100), both moist with water, are then added and the mixture is stirred for 8 hours.

The ion exchangers are removed by filtration. It will be ready to use 3,4-polyethylene dioxythiophene solution with a solids content of approx. 1.2% by weight receive.

Comparative example

The 3,4-polyethylene dioxythiophene solution described above is made up to a 200 µm thick polycarbonate film of 30 × 30 cm² doctored, so that a dry layer thickness of 100 mg / m² results. The coated film has a surface resistance of 10⁴ Ω / Ψ. The film is then deformed by deep drawing at approx. 180 ° C. After After deep drawing, the antistatic coating has cracks and has deformed on the th places a surface resistance of <10¹⁰ Ω / Ψ. The antistatic effect is destroyed by the deep-drawing process.

example 1

A mixture of 6.5 g of the 3,4-polyethylene dioxythio described above phen solution, 3.0 g dimethylacetamide 10.0 g acetone, 5.0 g methanol, 3.0 g N-methyl pyrrolidone and 2.5 g polyvinyl acetate (Mowilith 50 commercial product from Hoechst) 30% in acetone is applied to a 200 µm thick polycarbonate film in about 60 µm wet  layer thickness doctored and dried. The coated film has a surface resistance of 10⁴ Ω / Ψ. The film is then deep drawn at approx. Deformed 180 ° C. After deep drawing, the antistatic coating points to the deformed areas have a surface resistance of 10⁴-10⁵ Ω / Ψ. The The antistatic effect of the layer is not adversely affected by deep drawing been.

Example 2

A mixture of 8.3 g of the 3,4-polyethylene dioxythiophene described above solution, 2.3 g of a 40% aqueous polyurethane solution (Bayderm Finish UD Commercial product from Bayer AG) and 0.5 g of N-methylpyrrolidone is in a wet layer thickness of approx. 60 µm on a 150 µm thick polycarbonate film and dried. The coated film has a surface resistance of 10³ Ω / Ψ. The The film is then deformed by deep drawing at approx. 180 ° C. After deep drawing hen the antistatic coating has a surface at the deformed points resistance from 10⁴-10⁵ Ω / Ψ. The antistatic effect of the layer is after the deep drawing.

Example 3

The procedure is as in Example 2, but the polycarbonate film is 200 µm thick Polyvinyl chloride film replaced. The coated film has a surface resistance stood at 3 × 10³ Ω / Ψ. The film is then deep drawn at approx. 180 ° C deformed. After deep drawing, the antistatic coating shows the deform Place a surface resistance of 2 × 10⁴ Ω / Ψ. The antistatic The effect of the layer is retained after the deep drawing.

Claims (6)

1. Thermally and mechanically deformable polymer film, characterized by a transparent antistatic coating made from a mixture of 3,4-polyethylene dioxythiophene with a thermally or mechanically deformable binder. 2. Film according to claim 1, characterized in that the polymer film on or can be multi-layered, with individual layers over adhesive or Bonding agent intermediate layers are interconnected. 3. Polymer film according to one of claims 1 and 2, characterized in that that it contains a polyurethane as a binder. 4. Use of the polymer film according to one of claims 1 to 3 for Ver pack of electrostatically sensitive components. 5. Use of the polymer film according to one of claims 1 to 3 for Manufacture of blister belts for packaging electrostatically sensitive Components. 6. Use of the polymer film according to one of claims 1 to 3 for ver pack of flammable or explosive goods.