JP2001081413A - Conductive coating - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an antistatic coating from which a reproducible, antistatic coating film free from environmental influence is obtained with its effect being continued permanently. SOLUTION: The antistaic coating composition comprises electrically conductive polymer particles and a film-forming polymer, wherein the electrically conductive polymer particles contain at least one electrically conductive polymer chosen from polyacetylene, polyaniline, polypyrrole, poly(paraphenylenevinylene) and the like, a flexible resin and a stabilizer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

FIELD OF THE INVENTION The present invention relates to compositions having an adjustable volume resistivity, and more particularly to their use in coatings as conductors with a selected volume resistivity on a substrate, the coating comprising: Including electrically conductive polymer particles and a film forming polymer.

[0002]

BACKGROUND OF THE INVENTION Conductive coatings having a selected volume resistivity on a substrate are important in many objects for providing or releasing charge. On the one hand, it limits the current flowing through or along the object,
On the other hand, the electrical resistance of the object and the coating must each be within a certain range in order to transfer the desired amount of charge fast enough. For this purpose, a coating is usually applied to the object such that the object as a whole has the desired resistance. If the object is made of a conductive material, the resistance of the coating that is continuously bonded to the material is preferably chosen high so that the coating actually determines the overall resistance. In the case of non-conductive objects, where a charge is generally applied or released through the coating, the resistance of the coating also determines the current that carries that charge.

[0003] Such coatings are generally formed from a composition that includes a non-conductive binder containing a finely dispersed conductive material.

[0004] Compositions for coatings for conductive rolls are known from US Pat. No. 5,597,652. The composition consists of nylon, urethane or rubber as binder and metal oxide or carbon as conductive material. The resistance of the coating formed from the composition depends on the ratio of binder to conductive material.

A disadvantage of this known composition is the poor controllability of the electrical resistance of the coating made from the composition. The resistance of the known composition actually takes two values depending on the concentration of the conductive material, and there is a steep transition trajectory between the two before a certain concentration known as the permeation threshold. One of the maximums is generally determined by the very high binder resistance. Another maximum is determined by the resistance of the conductive material forming a conductive passage therein prior to a certain concentration in the binder. The difference between the two maxima inferred from the resistivity of the material, as further defined below, can be very large, often reaching 10 ⁸ to 10 ¹¹ times. Suitable values for the use of a conductive roll, for example a charge conveyor roll, for the resistance of the coating are now precisely between the two maximum values mentioned above and are therefore in a steep transition trajectory. This makes it particularly difficult to reproducibly produce coatings with suitable desired electrical resistance from known compositions.

[0006] The resistance of a coating can also be affected by varying its thickness. However, the thickness of the coating is often constrained to a narrow range. On the one hand, the danger of short circuits due to pinholes or leakage must be avoided, which places a lower limit on the thickness. On the other hand, in the case of rolls that must be compressible, at least the coating must be sufficiently flexible to be able to follow the compression of the elastic coating without separating or breaking, which is related to the thickness. Set an upper limit. Such a change in thickness almost always has the potential to affect the resistance of the coating,
Or offer very little.

[0007] Conductive coatings having a selected volume resistivity on a substrate are important in many other applications.

[0008] Many objects are required to meet the increasing demands on, for example, antistatic properties. For many colored objects, antistatic properties are obtained by adding salts. The disadvantages of adding salt are that the effective range of the salt is closely related to the relative humidity, and that the salt will leach out over time.

[0009] Examples of the use of salt are found in carpets, antistatic clothing (gloves for clean room operations and for handling electronic components, etc.). Includes conductive coatings on the floor of the clean room and in areas where sensitive electronic components are used, where the charge is now released via copper pieces. This is because copper strips generally carry charge off very quickly.

[0010] Electrostatic charge is also a problem in polyester processing. For example, the rate at which PET is processed into a film is limited by the build up of static electricity during its processing and the fact that its rapid release can cause damage to PET films. Again, salts are used and coatings with tunable conductivity may provide a solution for more stable conduction levels.

Another application for coatings with tunable conductivity is a weakly conductive layer around an electrical conductor for conducting induced voltage. The use of carbon in this application is known. Here too, the disadvantages of the abrupt penetration threshold apply.

Another group of applications is created in areas where two connected objects, where potential large differences in voltage can occur, must be gradually brought to the same potential. Silver-containing adhesives are used to eliminate potential differences, but this is not only expensive, but also poorly adjustable in contact resistance.

[0013]

It is an object of the present invention to provide a composition wherein a coating on a substrate can be produced with a suitable and desirable range of volume resistivity as described for the object.

[0014]

This object is achieved by the fact that the electrically conductive polymer particles comprise a flexible carrier material, a conductive polymer and a stabilizer. It has been found that the specific resistance of a composition comprising a flexible carrier material, a conductive polymer and a stabilizer changes much more slowly with a change in the concentration of the conductive material as compared to known compositions. In particular, the compositions according to the invention do not show a sharp transition trajectory between high and low electrical resistance. With the composition according to the invention, the coating can be applied easily and reproducibly to the substrate, the electrical resistance of which at desired values in the layer thickness lies between the practically acceptable range. Have. An advantage of the composition according to the invention is that with it a permanent antistatic behavior can be achieved.

[0015]

DETAILED DESCRIPTION OF THE INVENTION A flexible carrier material is understood to be a material whose shape can be changed under the conditions of coating techniques known per se.

In the composition, the film-forming polymer acts as a binder, in which the electrically conductive polymer particles are dispersed to ensure conductive properties.

[0017] The electrically conductive polymer particles may be comprised of solid particles of an electrically conductive polymer, which may or may not be stabilized. The particles may also consist of stabilized electrically conductive particles on a carrier. Preferably, the electrically conductive polymer particles comprise a carrier, an essentially conductive polymer and a stabilizer. Such particles are described, for example, in EP-A-598.
592.

Essentially conductive polymers suitable for use in the composition according to the invention include, for example, polyacetylene, polyphenylene, poly (paraphenylenevinylene), polypyrrole, polyfuran, polythiophene, polyaniline and the conductive properties of these polymers. Substituted forms, as well as mixtures of two or more of the above compounds. Very suitable are polyaniline, polypyrrole, polythiophene and conductive substituted forms of these polymers, as well as 2
It is a mixture of the above. The intrinsically conductive polymer may be present in the composition according to the invention as such or bonded to a suitable carrier.

Carriers that can be used include, for example, alkyd resins, polyester resins, amino resins, phenol resins,
Polyurethane resin, epoxy resin, acrylate resin,
Cyclic rubbers, such as polyisoprene, polybutadiene, natural rubber, silicone resins, polyvinyl chloride, polyether, (poly) vinyl esters, such as polyvinyl acetate, polyolefins (eg, selected from the group comprising ethylene, propylene, butadiene and styrene) And a hydrocarbon resin, for example, a polymeric material selected from the group consisting of (co) polymers of cyclopentadiene.

Very suitable compositions are those in which the electrically conductive polymer particles and the film-forming polymer on the carrier are present in dispersed form in the dispersant. "Dispersion" is used herein to refer to any mixture of dispersants, including finely distributed conductive and / or film-forming polymers, fine enough for the intended application, such as dispersions, suspensions, and the like. It is understood that there are even turbids or solutions. The most suitable compositions are those in which the charged polymer particles and the film-forming polymer have been applied in the form of a stable aqueous dispersion.

[0021] Film-forming polymers suitable for use as binders in the composition are organic polymers capable of forming a film. Examples include polyvinylidene chloride, poly (meth) acrylate, polyurethane, polyester, alkyd resins, melamine-formaldehyde resins, polyvinyl acetate and polyvinyl alcohol. Most preferred are polymers that can be in the form of a dispersion in a dispersant, preferably in water, such as a latex, and that can form a film during and / or after removal of the dispersant. is there. Very suitable are polyurethane resins which have high abrasion resistance and are generally very flexible.

Very suitable for use in the compositions according to the invention are film-forming polymers which form films having a high flexibility, for example a reversible elastic elongation of at least 50%. The film-forming polymer is generally used in the form of a dispersion, and for environmental reasons is preferably used in the form of an aqueous dispersion. It must also be possible to disperse the conductive polymer in this dispersion.
One of skill in the art would readily be able to empirically select the appropriate combination of dispersants available for a particular film-forming polymer and a particular conductive polymer. In particular, most aqueous dispersions of the above organic polymers and essentially conductive polymers are widely known and available.

The substrate for application of the coating according to the invention can be both conductive and non-conductive. The conductive material is generally a metal, but may be a plastic filled with carbon or metal oxide. In the case of metallic materials, the invention preferably applies to non-corrosive metallic materials.

The invention also relates to an object comprising at least one substrate, which may or may not be conductive, provided with a coating according to claim 1. Here, the coating is bonded to the electrical conductor. The function of the electrical conductor is to transfer charge from the conductive coating to a location outside the substrate and the object containing the conductive coating. In order to transfer the charge supplied to the coating in a controlled manner, the electrical conductor, if it is a conductive substrate, can be directly bonded to the coating. However, for example, in the case of a non-conductive substrate, the conductor may be directly bonded to the substrate to release the charge stored on the coating or substrate in a controlled manner or to apply a charge to the substrate. Good. In all cases, the object according to the invention comprises a conductor for transferring charge to or from the object.

For producing a conductive object by applying a coating to a substrate, a method known per se is suitable. First of all, a composition according to the invention, preferably a dispersion of an essentially conductive polymer in a suitable dispersant, is produced.
Very suitable is the mixing of an intrinsically conductive polymer with a dispersion of a film-forming polymer. The dispersed mixture can then be applied to the substrate using methods known per se. Examples of such methods are dip coating, flow coating, air or airless spray, and application by rolls or brushes, optionally on electrostatically charged surfaces. Which method is chosen depends in part on economic factors, but many parts must be able to apply the coating at the desired thickness and with the smallest possible spread of thickness. It also depends on the requirements that must be met. If done manually, for example by dip coating in a relatively low viscosity composition or by electrostatic spraying, several thin layers can be applied. In industrial production, dip coating in a composition having a somewhat higher viscosity is a suitable method. After the composition has been applied, the applied layer is processed into a film.
This may be a simple removal of the solvent, but also an elevated temperature cure in the presence of a crosslinking agent. Suitable methods commonly used for the film-forming polymers described above are known to those skilled in the art.

The adhesion of the formed film to the substrate can be enhanced by adding an adhesion promoter known per se. If the substrate comprises rubber, it is also possible to apply the coating to a substrate where the substrate material has not yet been fully cured. Complete vulcanization of the rubber then takes place after the coating has been applied. This has been found to have a positive effect on the adhesion of the coating to the rubber. It is also possible to improve the adhesiveness by subjecting the substrate surface to a corona treatment. In addition, for example, flow promoters, thickeners and surfactants can be added to the composition to obtain the desired processing characteristics.

In the case of conductive substrates, the thickness of the coating must be such as to prevent the danger of short circuits.
In practice, a thickness of 20 μm has been found to be sufficient for this. Preferably, the thickness is greater than 50 μm,
More preferably, it is larger than 80 μm. A thickness of less than 400 μm is required for any desired elastic properties.
Preferably, the thickness is less than 200 μm, more preferably less than 150 μm.

For non-conductive substrates, the thickness of the coating is preferably between 0.01 and 20 μm. Preferably, the thickness is less than 10 μm, more preferably 5 μm
And even more preferably less than 2 μm.

The requirements imposed on the resistance and thickness of the coating determine the required volume resistivity ρ (Ω · m) of the coating material. The volume resistivity is the area A
Are placed on either side of the material to be measured and the resistance R from the measured current at a given voltage
Is measured by inferring Then, the volume resistivity is calculated as follows.

[Equation 1] ρ = R. A / 1 [Ω · m]

It has been found that the volume resistivity depends to some extent on the generated voltage (V) per unit (1) of the layer thickness. That is, the specific voltage (V _sp ) is as follows.

[Equation 2] V _sp = V / 1 [V / cm]

Suitable coating materials are from 1 × 10 ⁵ to
1 × 10 ¹¹ Ω · m, preferably 1 × 10 ^{6 to} 1 × ^{10 10}
Ω · m, most preferably from 1 × 10 ^{7 to} 1 × 10 ⁹ Ω · m (measured at a specific voltage of 25,000 V / cm). In particular, the last range can be achieved with great difficulty and certainly without reproducibility, using conductive coatings based on carbon.

Another advantage of the present invention is that high leakage voltages can be obtained by using the conductive coating according to the present invention. Specific leakage voltage (V _spb ) is defined herein as the specific voltage at which leakage occurs.

Preferably, the leakage voltage is higher than 400 V, which corresponds to a specific leakage voltage of more than 50,000 volt / cm for a layer thickness of 80 μm.

[0034]

The invention will now be described with reference to the following non-limiting examples.

EXAMPLE I A conductive composition based on an aqueous dispersion of polyurethane particles coated with polypyrrole (ConQuest XP 1000, from DSM) and an aqueous polyurethane dispersion as film-forming polymer (Uraflex UZ401, from DSM) Production of 25g of ConQuest XP 1000 (20% solids) with 11
3. 2.5 g Uraflex UZ 401 (40% solids) and
1 g of Dowanol DPnB (from Dow Chemical) was added. The conductive composition thus obtained is applied to a carbon-filled, and thus highly conductive, SBR rubber plate by 50 μm.
Applied as a thick wet layer. The coated substrate was then dried at 80C. The procedure for applying the coating was repeated four times on this substrate so as to obtain a coating having a final thickness of 80 μm. The electrical properties of the substrate coated in this way are measured by Selefec Mego
Measured by mmetre M1500P. One electrode was applied to the uncoated side of the substrate and one electrode was applied to the coated side. The resistance at 200 volts is 1.6 × 10 ⁹ Ω, which is 2.1 × 10 ⁹ Ω ·
corresponding to a volume resistivity of m. No leakage was measured up to 1400 volts. This corresponds to a specific voltage of 175,000 V / cm. Table 1 shows the results of other ratios.

[Table 1]

EXAMPLE II ConQuest XP 1000 and a 65% by weight solids hydroxyl-functional polyester (Uradil SZ255 G3Z-65, from DSM Resins) as film former (X) and a crosslinker (Cymel 350, from Dyno Cytec) Of conductive composition based on 577 g of Uradil SZ255 G3Z-65, 125 g of Cymel
350, 200 g of water and 100 g of isopropanol were added. As a result, a film former X having a solid content of 50% was formed. 90 g of film former X was added to 25 g of Co
Added to nQuest XP1000. The conductive composition thus obtained was applied to an aluminum plate as a wet layer having a thickness of 50 μm. The coated substrate is then heated to 125 ° C.
For 10 minutes. The procedure of applying the coating was repeated four times on the substrate to obtain a coating having a final thickness of 80 μm. The electrical properties of the substrate coated in this way can be measured using Selefec Megommet
Measured by re M1500P. One electrode was applied to the uncoated side of the substrate and one electrode was applied to the coated side. The resistance at 200 volts is 8.7 × 10 ¹¹ Ω, which is 1.1 × 10 ¹² Ω ·
corresponding to a volume resistivity of m. No leakage was measured up to 1400 volts. This corresponds to a specific voltage of 175,000 V / cm. Table 2 shows the results of other ratios.

[Table 2]

Comparative Example A Preparation of a conductive composition based on Polypyrrole (from Degussa), Aerosil OX-50 coated with Uradil SZ255 G3Z-65 and Cymel 350 Production of Aerosil OX-50 coated with polypyrrole
Ammonium persulfate granulation 97.8 g, was added to the dispersion of Aerosil OX-50 of 500g of water 2100 g. Next, a solution of 26.3 g of pyrrole in 1500 g of water was added. After overnight, the dispersion was brought to pH 11.9 with sodium hydroxide pellets, after which the polypyrrole-coated Aerosil OX-50 was filtered off. Then
The filtrate consisting of the polysilole-coated Aerosil OX-5 was finely dispersed in 2000 ml of water and the pH of the dispersion was brought to 2.0 with a solution of 100 g of paratoluenesulfonic acid in 100 g of water. pH 1
When it remained stable for 0 minutes, the polysilole-coated Aerosil OX-50 was filtered off and dried under a stream of nitrogen. Based on Aerosil OX-50 coated with polypyrrole
Aerosil OX-50 was coated in the production polypyrrole aqueous dispersion brute (1
57g), 809g of water, 31g of dispersant (Byk 19
0, from Byk Chemie) and 3 g of defoamer (Byk 028, Byk C
hemie) was added, after which the mixture was dispersed using a Dispermat with PVC spinning disks and glass beads (dispersion Y). 69 g of the film former X described in Example II were added to 25 g of dispersion Y.
The conductive composition thus obtained was applied to an aluminum plate as a wet layer having a thickness of 50 μm. The coated substrate was then cured at 125 ° C. for 10 minutes. The procedure of applying the coating was repeated four times on the substrate to obtain a coating having a final thickness of 80 μm. The electrical properties of the substrate coated in this way were measured with a Selefec Megommetre M1500P. One electrode was applied to the uncoated side of the substrate and one electrode was applied to the coated side. The resistance at 200 volts is 3.5 × 10 ¹¹ Ω,
This corresponds to a volume resistivity of 4.6 × 10 ¹¹ Ω · m. No leakage was measured up to 1400 volts. This corresponds to a specific voltage of 175,000 V / cm. Table 3 shows the results of other ratios.

[Table 3]

Comparative Example B Preparation of a Dispersion Based on Carbon (Dispersion Z) On 157 g of carbon, 809 g of water, 31 g of Byk 190
(Dispersant) and 3 g Byk028 (antifoam) were added, after which the mixture was dispersed using a Dispermat equipped with PVC rotating discs and glass beads. 23
9.5 g of film former X were added to 25 g of dispersion Z. The conductive composition thus obtained was applied to an aluminum plate as a wet layer having a thickness of 50 μm. The coated substrate was then cured at 125 ° C. for 10 minutes. The procedure of applying the coating was repeated four times on the substrate to obtain a coating having a final thickness of 80 μm. The electrical properties of the substrate coated in this way were measured with a Selefec Megommetre M1500P. One electrode was applied to the uncoated side of the substrate and one electrode was applied to the coated side. The resistance at 200 volts is 1.5 × 10 ¹¹ Ω, which corresponds to a volume resistivity of 7.9 × 10 ¹¹ Ω · m. Leakage was measured at 1000 volts. Table 4 shows the results of other mixing ratios in the dispersion.

[Table 4]

These examples show that when the composition according to the invention is used, 2 × 10 ⁵ at a specific voltage of 25,000 V / cm.
It clearly shows that a sufficiently tunable volume resistivity of 9.9 × ^{10 10} Ω · m can be obtained. The examples also show that the specific leakage voltage of the coating according to the invention is greater than 50,000 V / cm.
Example I further according to the invention has a specific resistance of 9.8x
It shows that coatings with specific leakage voltages greater than 175,000 V / cm can be produced in the range of 10 ^{6 to} 2.1 × 10 ⁹ Ω · m. Also, these examples show that when a flexible material is used as the carrier material (polyurethane in Examples I and II), a harder carrier material (Aerosil in Comparative Example A) is used.
It shows that a more gradual transition in volume resistivity is obtained.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C09D 165/02 C09D 165/02 173/00 173/00 179/00 179/00 181/00 181/00 ( 72) Inventor Johann Franz Gradas Antonius Janssen, Netherlands, 6165 A.P.Gerene, Marisstraat 11 (72) Inventor Pascal Maria Huberto Pierre Thyssen, Netherlands, 6191 XVV Beek, Orange Jzingel 88 (72) Inventor, Matthias Josef Gertruda Bronds The Netherlands, 6462 Seabuy Kerklaid, Thraxtrat 72

Claims (10)

[Claims] 1. A method of using a coating comprising electrically conductive polymer particles and a film-forming polymer on a substrate as an electrical conductor having a selected volume resistivity, wherein the electrically conductive polymer particles comprise a flexible carrier. A method comprising a substance, a conductive polymer and a stabilizer. 2. The conductive polymer is selected from the group consisting of polyacetylene, polyphenylene, poly (paraphenylenevinylene), polypyrrole, polyfuran, polythiophene, polyaniline and conductive substituted forms of these polymers, and mixtures of two or more of the above compounds. 2. Use according to claim 1, which is selected. 3. The method according to claim 1, wherein the conductive polymer is selected from the group consisting of polyaniline, polypyrrole, polythiophene and conductive substituted forms of these polymers, and mixtures of two or more of the above compounds. . 4. The carrier material according to claim 1, wherein the carrier material is flexible.
The use according to any one of claims 1 to 4. 5. A coating having a thickness of 0.01 to 400.
The use according to any one of claims 1 to 4, wherein the thickness is μm. 6. The method according to claim 1, wherein the electrically conductive polymer particles and the film-forming polymer are applied in the form of a dispersion.
The use according to any one of claims 1 to 5. 7. The use according to claim 6, wherein the dispersion is a stable aqueous dispersion. 8. A volume resistivity of 1 × 10 ^{5 to} 1 × 10 ¹¹ Ω.
The use according to any one of claims 1 to 7, wherein m is m. 9. A specific leakage voltage of 50,000 volt / cm
9. Use according to any one of the preceding claims, which is greater than. 10. An object comprising at least one conductive or non-conductive substrate provided with a coating according to claim 1, wherein the coating is bonded to an electrical conductor.