FI116626B - A process for precipitating conductive polymer coatings in supercritical carbon dioxide - Google Patents

Description

116626

METHOD FOR THE DEPOSITION OF LEADING POLYMER COATINGS IN supercritical carbon dioxide

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to conductive polymer composites.

In particular, the present invention relates to methods for improving the electrical conductivity of the surface layer of thermoplastic polymer products.

2. Brief Summary of the Prior Art 15

The supercritical phase of carbon dioxide (scCO2) occurs at temperatures above +31 ° C and above 7.3 MPa. Supercritical CO 2 is a solvent for many organic, especially non-polar, molecules, and is capable of reversibly swelling various polymers, i.e. has a plasticizing effect. Due to these known properties, scOO2 can act as a carrier phase for transporting small molecules to the polymer matrix. The major factors that influence the efficiency of material transport are the solubility of these small molecules in scCO2 and ·:; diffusion kinetics of scC02 within the matrix material. The solubility of the molecule in scCO2 can be improved using a suitable co-solvent such as ethyl or methyl alcohols, acetone or water. The main advantages of liquid or supercritical CO 2 over most commonly used organic solvents are its non-flammability, non-toxicity, low cost and adjustable solvent power.

30; ' 'There are several techniques for making electrically conductive otherwise insulating polymeric products or their surfaces. The conventional method is to blend electrically conductive fillers into the polymer. The bulk electrical conductivity thus obtained depends on the filler material used, but the surface conductivity is typically less than that expected from the bulk properties of the composite material. In addition, the mechanical properties and processability of matrix polymers are generally reduced.

Another solution where the conductivity of the surface is essential is the use of electrically conductive coatings. These include solid metal films and solvent-based coatings containing a conductive phase and a polymeric binder. One demanding aspect associated with most coatings is their adhesion to the base material. Other aspects include corrosion of the metal coating films and the formed layers and, in certain cases, the emission and reflectivity of the electromagnetic radiation.

Intrinsically conductive polymers such as polyaniline, poly-pyrrole and polythiophenes are a new class of relatively conductive materials. In their electrically conductive form, they are generally insoluble and non-meltable materials. Thus, in order to provide highly conductive and mechanically satisfactory composites with insulating materials, solubilization treatment in organic solvents and on-site polymerization of the conductive phase are generally employed.

U.S. Patent 6,214,260 is one example of an on-site polymerization of an electrically conductive elastomeric foam. Initially, "· *: the preformed polyurethane foam is treated with an oxidant solution in a supercritical solvent to allow the foam to swell and to distribute the oxidant substantially uniformly to the foam wall and supports.

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As described in Example 2 of the patent, the polyurethane foam is first swollen with iron (III) trifluoromethanesulfonate in a supercritical carbon dioxide solution, followed by contacting the thus impregnated foam with a pyrrole solution in supercritical carbon dioxide [35] to polymerize to a polypyrrole.

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In Tang M. et al., European Polymer Journal 39 (2003) p. The polymerization is accomplished by doping the impregnated base polymer with an oxidant by immersing it in an aqueous or acetonitrile solution of FeCl 3.

However, there is no method that can be used to precipitate an electrically conductive polymer or to provide a polymer surface quickly and efficiently without harmful waste, whereby insulating polymers can be industrially processed for various purposes requiring materials with an electrically conductive surface.

In processes using on-site polymerization, the major disadvantage is that a large amount of organic waste is generated. A partial solution to this problem has been presented by Tang et al., Supra, who used supercritical carbon dioxide to impregnate polystyrene with pyrrole. Thereafter, the pyrrole was polymerized in oxidant water or acetonitrile baths. Still, a large amount of an inorganic (iron chloride) oxidant solution was formed with contaminant polymerization residues.

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SUMMARY OF THE INVENTION

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: "*; 25 The above and other drawbacks of the prior art can be corrected by the process of the present invention wherein the polymeric product is first treated with a monomer-containing scCO 2 -containing phase (method step 1) followed by an oxidant-containing. containing a phase capable of polymerizing said monomer to form an electrically conductive polymer on the insulating polymer (method step 2) .The polymerization reaction occurs predominantly in or near the surface layer of the monomer-containing matrix, which is swollen with scCO2. Polymerization residues such as unreacted mono-** mer and oxidant can be removed from the matrix by treatment thereafter with pure scCO2 or a mixture of scCO2 and a suitable co-solvent.

Instead of supercritical CO 2, high pressure liquid CO 2 close to the supercritical state can also be used. This is a viable option, especially in the oxidation step (method step 2).

The use of organic solvents is minimized since each step of the process uses only carbon dioxide and less than 101%, preferably less than 11%, of a suitable co-solvent. Suitable co-solvents include, but are not limited to, lower alcohols, acetone, and water.

The perfect solution to the prior art waste problem is to exclude a bath based on an inorganic aqueous solvent or organic solvent using carbon dioxide as the only actual solvent in the process.

Suitable monomers include aniline, pyrrole, thiophenes and substituted derivatives thereof, which may be polymerized using chemical oxidation polymerization.

The thickness of the conductive layer can be adjusted by varying the treatment time, monomer and oxidant concentrations, scCO2-25 phase pressure and temperature, and between process steps 1 and 2. . pressure-reducing speed.

The surface structure of the composite thus obtained consists essentially of overlapping networks of a matrix phase and a conductive phase. The surface layer is 30 highly adhesive and has the best electrical and mechanical properties.

The foregoing features of the present invention will become apparent to those skilled in the art from the detailed description and examples.

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DETAILED DESCRIPTION OF THE INVENTION

In applications requiring electrical conductivity, various otherwise electrically insulating thermoplastic and thermosetting polymers are used.

5 Common application areas include protection against static discharge (ESD) and electromagnetic interference (EMI) attenuation. There are quite different requirements for conductivity between the two applications: Protection against static discharges is considered to be optimal for materials with a surface resistivity of about 10 6 to 10 8 ohms, whereas for material attenuation of electromagnetic interference the material generally requires less than 10'1 ohm * cm bulk resistivity. Intrinsically conductive polymers have proven to be useful in both fields.

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In many cases, only the electrical conductivity of the surface is relevant, and various coating methods are available to meet the electrical conductivity requirement of the surface. The reason for using different coating methods is (i) saving the conductive material because it is generally expensive compared to the matrix polymer, and more importantly (ii) the critical material of the matrix polymer; integrity of properties. Such critical features are: ·: mechanical performance and processability.

«I *«> 25 A good example of such a product is textile fabric. The fabrics are woven or knitted from fibers that have been spun treated to provide precisely controlled properties. Another example of a textile fabric is non-woven fabric.

* · 30 By melt blending electrically conductive materials, for example naturally occurring conductive polyaniline salt, into fiber-forming polymers such as polyesters and polyamides, it is not generally possible to obtain ··. satisfactory mechanical properties. This is due to the extremely rigid nature of the electrically conductive polymer itself and the lack of phase compatibility at the microscopic level. According to another embodiment, the fibers are drawn from a solution containing a fiber-forming polymer and an electrically conductive polymer. This results in much finer microstructures, but the process treats large amounts of volatile organic solvent.

5 Coating of conventional textile fibers (polyesters, polyamides) has been found to be the most suitable way to manufacture fibers for ESD protection and in some cases also for EMI protection. However, it is a very challenging task to form a rigid conductor-resistant coating on a flexible base material fiber. Various (possibly reactive) sprayed, dipped and brushed coatings have been used, but they have a limited durability and are generally very expensive. In addition, a considerable part of the expensive coating is lost in the process. The solution to the durability problem is to use on-site polymerization of the fiber surface 15 according to the sequential process steps 1 and 2 above, since the resulting composite surface structure consists essentially of interlaced networks of matrix and conductive phases. The fibers so treated may be filaments, yarns or wide textile structures formed from these filaments or yarns.

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In the present invention, the on-site polymerization is carried out according to the process shown in Example 1 below and Figure 1. In general example 1, a polyester textile web is being treated. The invention is in no way limited to the treatment of fibers or fabrics. One suitable base material is a flexible sheet material which is not made by a textile process such as a belt or the like. This material may be an elastomeric material, or the elastomer may be on its surface, which is treated as described above. Optimal treatment time (typically 15-20 min): 30 depends on process conditions (7, p) and concentrations of reactants (monomer, oxidant).

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Example 1. General description of the method.

1. The polyester fabric roll S is sealed in pressure vessel 1 (polymerization reactor). The roll is held in place during processing.

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Method Step 1: 2. Liquid carbon dioxide is pumped from CO 2 tank 2 to pressure vessel via heater 10 and CO 2 pump 9 and stabilized to 10 + 35 ° C and 9 MPa (supercritical state) pressure in vessel 1. Liquid pyrrole monomer (0.011% by weight) is pumped From the 11 monomer tanks 3 to the container 1. The low-power mixer 8 in the pressure vessel 1 keeps the fluid phase in circulation.

15 3. Supercritical carbon dioxide diffuses into the polyester fiber. The mono-mer is transported through the fabric fibers swollen with scC02. The conditions are maintained for about an hour.

4. The fluid content of the pressure vessel 1 (carbon dioxide, excess monomer) is allowed to flow through the heater 12 to the recovery system (separator 4) at a lower hydrostatic pressure. After half an hour excess pressure vessel 1 has fallen to about 0.1 MPa. When the supercritical phase pressure is lowered and the gaseous CO 2 phase appears, the monomer separates as a liquid in separator 4. The CO 2 is liquefied again and stored, preferably recycled to form a new supercritical solvent phase. In Figure 1, the CO 2 is led back to the CO 2 tank by the return line 5 · from the separator 4. 30 along. The return line 5 has a condenser 13 from which the CO 2 is returned to the tank. The monomer may be introduced from the bottom of the separator 4 '* into the intermediate container 6 and may be reused in process step 1.

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Process Step 2: 5. The pressure vessel 1 is filled with a mixture of supercritical or liquid carbon dioxide and an oxidant pumped from the oxidant tank 7, for example the same pump 11 used to pump the monomer. A suitable co-solvent (cosolvent) may be used to make the oxidant soluble in CO 2, in which case the co-solvent may be pumped from the oxidant tank 7 together with the dissolved oxidant. Organic acid may be added to adjust the pH of the mixture to 10 and as a dopant.

6. Chemical oxidation polymerization begins on the surface of the fibers. The reaction is allowed to continue for at least 15 minutes, or until the desired yield is obtained without over-oxidation of the product. The optimal polymerization time depends on the concentrations of polymerizable monomer and oxidant used. The reaction is quenched in the following steps.

7. Allow the fluid contents of the vessel (carbon dioxide, excess oxidant, co-solvent, organic acid) to flow into the recovery system (separator 4) at a lower hydrostatic pressure. As the supercritical phase pressure drops, the gaseous CO 2 phase separates from liquids and solids. All ingredients are recovered. The gaseous CO 2 can be recycled as above. The remaining oxidant remains dissolved in the co-solvent / ··. and can be reused in the solution of the new process step 2.

30 Extraction: 8. The supercritical or liquid carbon dioxide is pumped from the CO 2 tank into 2 pressure vessels 1. The polymerization reaction is stopped and the excess reactants are extracted from the fabric S.

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The present invention can be applied to many polymer base materials. It has been shown that supercritical carbon dioxide swells most thermoplastics at temperatures close to their glass transition temperature. The monomeric affinity of the base materials varies widely depending on the chemical functionality available and can therefore be adjusted with minor chemical (or physico-chemical) modifications. The base materials may be rigid or flexible, partially crosslinked or elastomeric.

Possible base material polymers include, but are not limited to: - thermoplastic polyesters such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT) and polytrimethylene terephthalate (PTT), - polyamides such as PA 6, PA 6.6, 15 - polycarbonate (PC), PMMA), - polyolefins such as polymethylpentene (PMP), polyethylene (PE), polypropylene, ethylene propylene diene (EPDM), their copolymers, functional analogues and mixtures thereof, 20 - polyvinyl chloride (PVC), - cycloolefin copolymer (COC) and Copolymers of styrene and their mixtures with other thermoplastics; styrene-ethylene-butadiene-styrene copolymer (SEBS): acrylonitrile-butadiene-styrene copolymer (ABS), ··. 25 - polyurethanes.

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Suitable monomers include aniline, pyrrole, thiophene and substituted derivatives thereof, which may be polymerized using chemical oxidation polymerization. These substituted derivatives include, but are not limited to, methyl pyrrole, methoxyaniline, 2,2-bithiophene, 3-alkylthiophene and 3,4-ethylenedioxythiophene.

Suitable oxidants for the above monomers are well known in the art [from scientific publications in the art and include, but are not limited to, v: 35 peroxides, peroxide sulfates, and ferric salts. Preferred oxidizing agents are '; specific organic iron (III) salts, in particular sulfonic acid salts, 116626 10 for which their counterions also act as effective and stable dopant in naturally conductive polyanilines, polypyrroles and polythiophenes.

Particularly useful are Fe (III) p-toluenesulfonate and Fe (III) trifluoromethanesulfonate, which has a higher solubility in supercritical fluid solvents containing ethanol as a co-solvent as described in the aforementioned U.S. Patent 6,214,260.

The first supercritical or liquid carbon dioxide phase may contain both an oxidizing agent and a separate dopant if it is necessary to increase the conductivity of the polymerized polymer to the desired level. In process step 1, various peroxides and peroxide sulfates may be used together with the dopant acids to prepare the electrically conductive form of the polymer.

In particular, organic sulfonic acids such as dodecylbenzenesulfonic acid (DBSA), paratoluene sulfonic acid (PTSA) and camphorsulfonic acid (CSA) are used to protonate the electrically conductive polymer to its electrically conductive form and the electrical stability of the electrically conductive polymer phase. These dopants can be used ... together with an oxidant in the first phase of supercritical or liquid CO2.

As far as possible, the polymeric surface obtained in the process of the invention may, in a separate process step, be made electrically conductive, conductive, dopant, such as an acid (e.g., DBSA, CPA or PTSA), to conduct to raise it to the desired level, or to improve its electrical or mechanical properties.

| t; Examples 2-5 are provided to illustrate the versatility of the method. In each example, the weight gain of the sample is given in grams and percentages. These values include the simultaneous weight loss of the matrix poly 116626 11 m due to the removal of low molecular weight substances. The yield of the process is shown as the calculated power of C.E. = [polymerized monomer / monomer feed prior to monomer recovery] by weight basis.

Example 2.

The polyester (PET) woven fabric (192 g) was sealed in a 7 liter 10-liter reactor. 10 ml of pyrrole was injected into the bottom of the vessel and liquid carbon dioxide was pumped into the reactor until equilibrium was reached (Γ = + 40 ° C, p = 9.0 MPa). These conditions were maintained for 45 minutes. The vessel pressure was reduced to approximately 1 MPa / min. Excess pyrrol (8.1 ml) was collected from the separator system (Figure 1).

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12 g of Fe (III) trifluoromethanesulfonate in 100 ml of ethanol was injected into the vessel. Liquid carbon dioxide was pumped in and the pressure was raised to 13.1 MPa (Γ = + 40 ° C). After 2 hours, the pressure was reduced and excess ethanol-oxidant-20 was collected from the separator. The reactor was again pressurized with pure carbon dioxide to remove traces of monomer and oxidant from the fabric. The fabric had a black, highly adherent and uniform • layer; · Polypyrrole trifluoromethanesulfonate coating.

The coating had a surface resistivity of about 5-102Q / square as measured by two-point test equipment. The weight of the fabric had increased by about Am = 1.15 g (s 0.6%). Excluding PET weight loss, the calculated power of the pyrrole polymerization C.E. = [polymerized monomer / monomer feed] was 3% prior to recovery of excess monomer.

Example 3.

Non-woven fabric (80 g) made of polyamide 6 (nylon) was sealed in a seven liter reactor. 30 ml of pyrrole was injected into the bottom of the vessel and liquid carbon dioxide was pumped from the reactor until a steady state (11 = + 40 ° C, p = 9.7 MPa) was reached. These conditions were maintained for 50 minutes. The vessel pressure was reduced at approximately 1 MPa / min. Excess pyrrol (22 mL) was collected from the separator system (Figure 1).

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70 g of Fe (III) trifluoromethanesulfonate in 200 ml of ethanol was injected into the vessel. Liquid carbon dioxide was pumped in and the pressure was raised to 10.0 MPa (Γ = + 40 ° C). After 75 minutes, the pressure was reduced and excess ethanol-oxidant-10 was collected from the separator. The reactor was again pressurized with pure carbon dioxide to remove traces of monomer and oxidant from the fabric. The fabric had a black, highly adherent and uniform poly (pyrrolitrifluoromethane sulfonate) coating deposited on the surface of the fabric (/ ¾ = 102 ° / square, Am = 1.72 g = 2%, C.E. = 1.5%).

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Example 4.

A 7 liter reactor was charged with 178 g of PET fabric.

The procedure of Example 1 was repeated using ethylene dioxide thiophene (EDOT) as a monomer (7 ml EDOT in 20 ml ethanol). ·· The monomer impregnation time and conditions were: f = 45 min, 7 = ...: + 40 ° C, p = 9.5 MPa. (Process Step 1) 25 g of Fe (III) p-toluenesulfonate in 80 mL of ethanol (Process Step 2) was used as the oxidizing agent. The polymerization conditions were: t = 105 min, T- + 40 ° C, p = 9.7 MPa. The fabric had a layer deposited on the surface: dark blue, very tacky and uniform PEDOT-p-toluenesulfonate coating (ps = 105 Ω / square, Am = 0.23 g = 0.13%, CE = if: 1.0%) .

Example 5.

A seven liter reactor was charged with 50 g of clear polycarbo-35 sodium (Lexan 9034) strips (0.9 mm χ 10 mm χ 60 mm). Strips: placed in a rack so that the fluid phase was applied uniformly and directly to all surfaces.

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The procedure of Example 1 was repeated using pyrrole as a monomer and acetone as a co-solvent (7 ml pyrrole in 20 ml acetone). The impregnation time and conditions for the monomer were: t = 80 min, T = + 80 ° C, 5 p = 14.5 MPa. (method step 1)

55 g of Fe (III) trifluoromethanesulfonate in 200 ml of ethanol was used as the oxidizing agent (process step 2). The polymerization conditions were: t = 130 min, T = + 80 ° C, p = 12.0 MPa. The fabric had a black, highly adherent and uniform coating of polypyrrole trifluoromethanesulfonate (/ ¾ = 107 Ω / square, Am = 0.15 g = 0.3%, C.E. = 0.6%) on the surface of the fabric.

The invention is practically suitable for increasing the electrical conductivity of any polymeric matrix surface that can be treated under supercritical or liquid conditions of carbon dioxide, on-site polymerization of a naturally conductive polymer, and at least after surface treatment with at least after finishing or a polymer blend. The invention is particularly suitable for antistatic treatment of textiles, sheets and belts, but it should be understood that the invention is not. . not limited to the aforementioned basic materials and applications.

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Claims (15)

116626 14 A process for forming an electrically conductive polymeric surface on 5 solid polymeric base materials (S), comprising the following sequential steps: 1. treating a solid polymeric base material (S) in a pressure reactor (1) with a first supercritical or liquid carbon dioxide containing monomer to 2. removing a first supercritical or liquid carbon dioxide phase from the reactor (1) together with any monomer residues, 3. introducing a second supercritical or liquid carbon dioxide phase containing the oxidizing agent into the reactor (1) and 4. performing an on-site oxidation polymerization of the monomer in the polymer substrate with an oxidizing agent to form an electrically conductive polymeric surface on the polymer substrate (S), 5. removing one of the supercritical or liquid carbon dioxide phases from the reactor. I 4 * i i 4 »f Process according to Claim 2, characterized in that, after removal of the second carbon dioxide phase, the process comprises the following: Step 4: 6. Removing the traces of reactants from the parent material (S) in the third phase of supercritical or liquid carbon dioxide. Process according to Claim 2, characterized in that the removal is effected by introducing into the reactor (1) a third carbon dioxide phase in contact with the basic material (S) in the reactor. Process according to claim 1, 2 or 3, characterized in that the monomer is selected from pyrrole, a substituted pyrrole derivative such as methylpyrrole, aniline, a substituted aniline derivative such as methoxyaniline, thiophene, and a substituted thiophene derivative such as 2,2 '. -bithiophene, 3-alkylthiophene or 3,4-ethylenedioxythiophene. Process according to one of Claims 1 to 4, characterized in that the oxidizing agent is selected from ferric salts, peroxides and peroxide sulfates. Process according to Claim 5, characterized in that the ferric salt is an organic salt of a sulfonic acid, such as Fe (III) p-toluenesulfonate or Fe (III) trifluoromethanesulfonate. Process according to any one of the preceding claims, characterized in that the second carbon dioxide phase contains an additional solvent which increases the solubility of the oxidizing agent in said phase, the amount of additional solvent preferably being less than 101%, preferably less than 11%. Process according to one of Claims 2 to 7, characterized in that the third carbon dioxide phase contains an additional solvent which increases the solubility of the oxidizing agent in said phase. Process according to claim 7 or 8, characterized in that the co-solvent is selected from lower alcohols, acetone and water. revenge. 25 A method according to any one of the preceding claims, characterized by -! * · ;;; The polymer base material (S) to be treated comprises polymeric fibers, in particular synthetic fibers, such as polyamide or polyester fibers. 30 A method according to claim 10, characterized in that the polymeric base material (S) to be treated is a textile having polymeric fibers in its structure, such as a woven fabric or knit or non-woven fabric. 35 • st i 116626 16 Method according to one of the preceding claims, characterized in that the polymeric base material (S) is a flexible sheet-like material, such as a belt, for example a material having an elastomer on its surface. 5 Process according to any one of the preceding claims, characterized in that the first carbon dioxide phase and / or the second carbon dioxide diphase is taken from a pressure reactor to a separation step in which the carbon dioxide pressure is lowered to separate the reactant residues from the carbon dioxide. Process according to Claim 13, characterized in that the carbon dioxide extracted from the pressure reactor (1) is recycled to the pressure reactor, where it forms a phase in a new cycle of successive stages. * 't »' i - * * 116626 17