CA1242166A - Process and apparatus for forming a polymerized coating on a substrate - Google Patents
Process and apparatus for forming a polymerized coating on a substrateInfo
- Publication number
- CA1242166A CA1242166A CA000459835A CA459835A CA1242166A CA 1242166 A CA1242166 A CA 1242166A CA 000459835 A CA000459835 A CA 000459835A CA 459835 A CA459835 A CA 459835A CA 1242166 A CA1242166 A CA 1242166A
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- Prior art keywords
- substrate
- electrode
- monomer
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- curvature
- Prior art date
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Classifications
-
- D—TEXTILES; PAPER
- D06—TREATMENT OF TEXTILES OR THE LIKE; LAUNDERING; FLEXIBLE MATERIALS NOT OTHERWISE PROVIDED FOR
- D06M—TREATMENT, NOT PROVIDED FOR ELSEWHERE IN CLASS D06, OF FIBRES, THREADS, YARNS, FABRICS, FEATHERS OR FIBROUS GOODS MADE FROM SUCH MATERIALS
- D06M10/00—Physical treatment of fibres, threads, yarns, fabrics, or fibrous goods made from such materials, e.g. ultrasonic, corona discharge, irradiation, electric currents, or magnetic fields; Physical treatment combined with treatment with chemical compounds or elements
- D06M10/04—Physical treatment combined with treatment with chemical compounds or elements
- D06M10/08—Organic compounds
- D06M10/10—Macromolecular compounds
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J7/00—Chemical treatment or coating of shaped articles made of macromolecular substances
- C08J7/12—Chemical modification
- C08J7/16—Chemical modification with polymerisable compounds
- C08J7/18—Chemical modification with polymerisable compounds using wave energy or particle radiation
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
- D21H23/00—Processes or apparatus for adding material to the pulp or to the paper
- D21H23/02—Processes or apparatus for adding material to the pulp or to the paper characterised by the manner in which substances are added
- D21H23/22—Addition to the formed paper
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- Chemical & Material Sciences (AREA)
- Health & Medical Sciences (AREA)
- Textile Engineering (AREA)
- Toxicology (AREA)
- General Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Medicinal Chemistry (AREA)
- Polymers & Plastics (AREA)
- Organic Chemistry (AREA)
- Engineering & Computer Science (AREA)
- Physical Or Chemical Processes And Apparatus (AREA)
- Treatments Of Macromolecular Shaped Articles (AREA)
- Polymerisation Methods In General (AREA)
- Paper (AREA)
- Diaphragms For Electromechanical Transducers (AREA)
- Other Resins Obtained By Reactions Not Involving Carbon-To-Carbon Unsaturated Bonds (AREA)
- Physical Vapour Deposition (AREA)
- Coating Of Shaped Articles Made Of Macromolecular Substances (AREA)
- Treatments For Attaching Organic Compounds To Fibrous Goods (AREA)
- Paints Or Removers (AREA)
- Addition Polymer Or Copolymer, Post-Treatments, Or Chemical Modifications (AREA)
- Chemical Or Physical Treatment Of Fibers (AREA)
Abstract
A PROCESS AND DEVICE FOR FORMING A POLYMERIZED COATING ON A
SUBSTRATE
ABSTRACT OF THE DISCLOSURE
To form a polymerized coating on a substrate, the surface of a substrate to be coated is placed in contact with a confined atmosphere containing a monomer or prepolymer in dispersed phase for giving rise to the coating polymer and a cold plasma is created by electric discharge in the confined atmosphere so as to create, from the monomer, reactive spe-cies which give rise to the polymerized coating. The electric discharge is an AC Corona discharge at a pressure close to atmospheric pressure between an electrode with a small radius of curvature and an electrode carrying the substrate, in a mixture of vapor phase monomer and an inert gas.
SUBSTRATE
ABSTRACT OF THE DISCLOSURE
To form a polymerized coating on a substrate, the surface of a substrate to be coated is placed in contact with a confined atmosphere containing a monomer or prepolymer in dispersed phase for giving rise to the coating polymer and a cold plasma is created by electric discharge in the confined atmosphere so as to create, from the monomer, reactive spe-cies which give rise to the polymerized coating. The electric discharge is an AC Corona discharge at a pressure close to atmospheric pressure between an electrode with a small radius of curvature and an electrode carrying the substrate, in a mixture of vapor phase monomer and an inert gas.
Description
Lo A_erocess and aeearatus for -forming a eolyme,rized coating _____su_str_t_ aAcKGRouND AND SUMMARY OF THE lNVENTION
The invention relates -to the formation of a polymerized carbonaceous coating on a substrate and i-t is particuLarly suitable for coating a substrate by polymerizing in situ fluorine-and carbon-containing monomers or prepoly-mers, vaporized or dispersed in an a-tmosphere in contact with 10 the substrate.
A process has already been proposed (US-A-4 188 426) for forming a polymerized coating on a substrate. The substrate to be coated is placed in contact with an atmosphe-re containing a monomer suitable to give rise to the coating 15 polymer and a cold plasma is crea-ted by electric discharge in the atmosphere so as to create -from the monomer, reactive species which polymerize on the substrate.
According to the specification o-f US-A-4 188 426, flow discharge or corona discharge may be used as elec-tric 20 discharge. The two phrases are used for designating discharge in an atmosphere at a very low pressure t10 microns of mercu-ry in the examples) and a-t frequencies in the radioelectric range (from 3 to 100 MFIz). For working in such a thin atmosphere, complex equipment must be used. It is practically impossible 25 to continuously treat moving material in the form of a strip or fiber of great length. The processing requires -times which are incompatible with industrial use.
US-A-4 188 426 may be regarded as representing -the current opinion according to which it is no-t possible to form 30 polymerized coa-tings in a cold plasma o-therwise than a-t very low pressures. This general opinion is outlined for example in a thesis by Hervé Carchano, Toulouse (1973), referring to - and summarizing prior work by others. According to Carchano, at a pressure of 3 torrs and above, the -thickness of the 35 coating which may be obtained is very small.
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The invention relates -to the formation of a polymerized carbonaceous coating on a substrate and i-t is particuLarly suitable for coating a substrate by polymerizing in situ fluorine-and carbon-containing monomers or prepoly-mers, vaporized or dispersed in an a-tmosphere in contact with 10 the substrate.
A process has already been proposed (US-A-4 188 426) for forming a polymerized coating on a substrate. The substrate to be coated is placed in contact with an atmosphe-re containing a monomer suitable to give rise to the coating 15 polymer and a cold plasma is crea-ted by electric discharge in the atmosphere so as to create -from the monomer, reactive species which polymerize on the substrate.
According to the specification o-f US-A-4 188 426, flow discharge or corona discharge may be used as elec-tric 20 discharge. The two phrases are used for designating discharge in an atmosphere at a very low pressure t10 microns of mercu-ry in the examples) and a-t frequencies in the radioelectric range (from 3 to 100 MFIz). For working in such a thin atmosphere, complex equipment must be used. It is practically impossible 25 to continuously treat moving material in the form of a strip or fiber of great length. The processing requires -times which are incompatible with industrial use.
US-A-4 188 426 may be regarded as representing -the current opinion according to which it is no-t possible to form 30 polymerized coa-tings in a cold plasma o-therwise than a-t very low pressures. This general opinion is outlined for example in a thesis by Hervé Carchano, Toulouse (1973), referring to - and summarizing prior work by others. According to Carchano, at a pressure of 3 torrs and above, the -thickness of the 35 coating which may be obtained is very small.
,~V,~ 1' irk
- 2 -It is an object of the invention -to overcome -the limita-tions of the prior known processes; it is a rnore specific object to remove use of a vacuum, so as to provide a solu-tion capable of being used industrially.
For that, it was necessary -to se-t aside earlier prejudices concerning the need to work a-t low pressure and to discover that corona discharge is accompagnied by phenomena very different from those which occur in a cold plasma created by radio frequency excita-tion. In particular, the Corona discharge is accompanied by an "electric wind" phenomenon which may be used wi-th advan-tage.
According to the presen-t invention, there is provided a process of in situ polymerizing a carbon-containing monomer or prepolymer on a subs-tra-te for forming an adherent coating thereon, comprising the steps oE placing said substrate in contact with said monomer or prepolymer dispersed in an atmosphere in contact with the substrate and contained in an enclosure under a pressure close to normal atmospheric pressure and generating a Corona discharge by applying an AC voltage between a first elec-trode having a small radius of curvature and a grounded second electrode, carrying the substrate and having a radius of curvature greater -than said small radius by several orders of magnitude, whereby reactive species are formed and driven by electric wind -toward said substrate for in situ polymeriza-tion on said substrate.
The term "Corona discharge" mus-t be cons-trued as designating the self-maintained discharge which takes place in a gas in the vicinity of an elec-trical conductor having a small radius of curvature subjected -to an intense non-uniform non-disruptive elec-tric field; that discharge is a luminescent discharge, is electrically and visually stable;
it is often associated with a discharge formed of so-called "streamers" which appears in the form of individual repetitive discharges.
The Corona discharge will be advantageously formed under AC current and s-truck between an electrode having a small radius of curvature and a counter elec-trode carrying the substra-te (and formed -thereby if it is conduc-ting), maintained at ground potential. Thus, elec-tric wind will always carry -the reactive species towards the substrate.
During the negative half wave, -the current will be formed of pulses corresponding to ionization phenomena in the stronger field zone, at a very high frequency. During the positive /
/
half wave, "aigrettes" or brush discharge occurs in the inter-electrode space and brings positive ions to the surface of the ;nsulating substrate, which causes breakages of atom chains and superficial spraying in the impact zone o-f the streamers 5 Thus, in a single operation, the surface of the substrate is activated, the monomer is polymerized in situ and -the polymer is bonded to the substrate by a phenomenon reLated to grafting.
It is probable that layers of an appreciable thickness are obtained in these conditions because the elec-10 tric wind projects the reactive species towards the substratewhich they reach with sufficient energy and before recombina-tion.
An AC electric current will be advantageously used in a frequency range less -than that currently called radio 15 frequency, i.e. below 100 KHz. A frequency of a few tens of KHz gives satisfactory resultsn However, for the sake of convenience, working may be directly at the industrial fre-quency of 50 Hz or 60 Hz. In this case, the Corona discharge starts as soon as the voltage reaches the value corresponding 20 to Paschen's law, i.e. a value depending on the pressure, on the interelectrode distance and on the gas mixed with the monomer (argon or helium in general). For current applications the voltage used will generally have an order of magnitude in the 10 volts range at atmospheric pressure.
With the invention a fluocarbon water-proofing fire-proofing and/or passivation coating may be formed on very different materials. In particular, such coatings may be for-med on threads, fibers, fabrics and more generally on all materials around which the discharge may take place and then 30 no particular precaution is required. The atmosphere may con-tain a significative oxygen content. Thus, threads, yarn or fibers of natural or artificial textile suchas polyester, po-lyamide, polyethylene, polyacrylonitrile may be treated.
When, as will be most often the case, a fluocarbon coating is of advantage, the monomer chosen will be a fluocar-. .
fir 3J.'L~;S~;
bon monomer capable of giving rise to reactive species~Several products among those known under the trademark FREON may be used and, among them, H2C = CF2 has given very satisfactory results. Monomers may also be used among those mentioned in US-A-4 188 426; tests carried ou-t with acrylic acid, formic acid, C ClF3 have proved sa-tisfactory.
Surface passivation of steel was also achieved in a SF6 atmosphere con-taining a small amount of ethyl methyl ketone.
In another use of the invention, odoriferous coatings have been achieved. In this case a carbon or fluocarbon monomer is used, for example tetrahydrogeraniol.
More specifically, according to the present inven-tion, there is provided a process of polymerizing a carbon containing monomer or prepolymer on a substrate comprising the steps of placing said substrate in contact with said monomer or prepolymer contained in an enclosure under a pres-sure close to normal atmospheric pressure and generating aCorona discharge between a first electrode having a small radius of curvature and a second electrode, carrying the substrate, and having a radius of curvature grea-ter than said small radius by several orders of magnitude, whereby reactive species are formed and driven by electric wind toward said substrate.
Also in accordance wi-th the present invention, there is provided a process of polymerizing a monomer Go~taining fluorine and carbon on a substrate, comprising: passing said substratelthrough a gaseous medium at substantially atmcs-- pa -pheric pressure, said medium comprising said monomer;
suppor-ting said substrate while in said medium wi-th an electrode having a large radius of curvature, pas-t an elongated electrode having a radius oE curvature lower than 1 mm, parallel to -the electrode supporting the substrate and at a dis-tance Erom 1 to 5 mm from said substrate; and maintaining an AC Corona discharge between the electrodes with a current value no-t exceeding 40 uA per cm of length of said elongated electrode.
` According to -the presen-t invention, there is also provided a process of polymerizing a carbon-fluorine monomer on a base paper shee-t or pattern fabric subs-trate for forming an adherent coating thereon, comprising the steps of placing said substrate in contact with said monomer dispersed in an atmosphere in contact with the substrate and con-tained in an enclosure under a pressure close to normal atmospheric pressure and generating an A.C. Corona discharge between a first electrode having a small radius oE curvature and a grounded second electrode, carrying the substrate, and having a radius of curvature greater than said small radius by several orders of magnitude, whereby reactive species are formed and driven by electric wind -toward said substrate Eor in situ polymerization on said substrate.
According to the present invention, there is also provided a device for polymerizing a carbon containing monomer or prepolymer onto a substrate, comprising an enclosure provided with means for flowing a substantially oxygen free flow of monomer or prepolymer in said enclosure in contact with the subs-trate on which a polymerized coating is to be Eormed while main-taining said enclosure at substantially normal atmospheric pressure; a grounded elec-trode wi-th a large radius of curvature supporting the substrate; an elonga-ted electrode having a sharp edge placed parallel -to the substrate where said substrate is supported - 4b -by said grounded electrode and a-t a distance from said grounded electrode of from 1 to 5 mm; electric supply means for providing, between the electrodes, an AC voltage of a value sufficient to create a Corona discharge at said substantially atmospheric pressure; and means for circulating said substrate over said grounded electrode.
The present invention Eurther relates to a device for polymerizing a carbon containing monomer or prepolymer onto a substrate, comprising an enclosure provided with means for flowing a monomer or prepolymer i.n said enclosure;
a grounded electrode with a large radius of curva-ture supporting the substrate on which a polymerized coating is to be formed; an electrode with a small radius of curvature placed parallel to the substrate; and electric supply means for providing, between the electrodes, an AC voltage of a value sufficient to create a Corona discharge a-t a pressure close to normal atmospheric pressure.
Preferably, the monomer or prepolymer is flowed in the enclosure along with a vector gas.
Whenever it is not indispensable to reduce the oxygen content to a very low value, it will be desirable to adop-t a pressure slightly less than the atmospheric pressure, so that possible leaks occur from the outside atmosphere of the workshop towards the inside of the enclosure and so that there is no dispersion in the workshop of toxic material coming from activation oE the monomer.
The invention will be better understood from the following non-restrictive description of preferred embodiments thereof, given by way of examples only.
SHORT DESCRIPTION OF TIE DRAWINGS
Figure 1 is a schematic representation of a device for continuous -treatment of a substrate in the form of a thread or porous strip, such as a fabric, by polymerization of a gaseous monomer ;
Figure 2 shows a modified device.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Referring to Figure 1, there is shown a device for 5 processing a substrate 10 in the form of a strip, which may be formed by a sheet of paper made from cellulose fiber, a woven or non-woven strip made from organic or inorgan;c material.
The device comprises an enclosure 12 having an inlet airlock 14 and an outlet airlock 16. The airlocks are each defined 10 by two walls having a slit through which the strip 10 passes.
Reduction of air ingress is obtained by means of flexible lips 18 fixed to the walls and rubbing against the strip. The internal volumes of the airlocks are connected to a -trap 20 for retaining decomposition products which may be harmful.
15 In order to further reduce the leaks of such products to the outside atmosphere, an additional collection space 22 having an extraction pump 24 and connected -to the trap 20 may be provided in the path of substrate 10 downstream of airlock 16.
The enclosure 12 contains means for creating a 20 Corona discharge comprising a rotating metal drum 26 connected to ground and supporting substrate 10. An electrode 28 is disposed in the enclosure in a position such that it presents a surface with a small radius of curvature (less than the ra-dius of drum 26 by several orders o-f magni-tude) facing the 25 zone of the substrate carried by the drum. In Figure 1, elec-trode 28 is formed by a blade whose edge is parallel to a generatrix of drum 26, at a distance of a few millimeters. A
wire may also be used as electrode having a diameter less than 2 mm. Several parallel wires may be provided in succession so 30 as to subject the substrate to several successive Corona discharges. Such a wire may be made from tungsten, molybdenum, titanium, vanadium or "monel" alloy and, rnore generally, from all metal materials, having catalytic properties or not, which resist corrosion. The electrode is fed by high vol-tage AC
35 generator 30. The generator is of a type which operates at a frequency less -than 100 KHz. It will usually supply a volta-ge of -the order of magnitude of 104 Vol-ts (-typically between 10 and 20 kV) when the distance between drum 26-forming the counter electrode-and electrode 28 is between 1 and 5 mm. The current supplied will typically be such tha-t travelling speeds of the substrate may be reached exceeding 1 m/mn.
Enclosure 12 is provided with means for supplying it with a monomer and vector gas (argon or helium in general) mixture and for renewing it.
In the embodiment of Figure 1, for the formation of a carbon-fluorinated polymer layer, such means comprise mixing means 32 which receives, through respective pressure reducers, argon from a cylinder 34 and CH2 = CF2 gas from a cylinder 36~
The mixture is supplied to the enclosure 12, at one end there-o-f, through a line fitted with a control valve 38. The enclo-sure has, opposite the intake pipe, a discharge pipe 40 ope-ning into a collecting receptacle ~2. The CH2 = CF2 content in the atmosphere is not critical. Oftentimes it will be pos-sible -to dispense with a vector gas. If necessary, it may be regulated permanently by monitoring the light absorption by thc atmos-phere by means o-f a photoabsorption photometer set to a spec-tral line characteristic of the monomer.
By way of example, tests have been carried out in a device containing a counter electrode -formed by a drum 10 cm in length and 6.5 cm in diameter, rotating wi-th a peripheral speed of 80 cm per minute. The electrode 28 was formed by a tungsten wire 250 microns in diameter. The generator 30 sup-plied a 50 Hz AC currentA In the embodiment as shown in Figure 1, it is not possible to hold the oxygen content a-t a very low value, due to air in-take through the seals. When the material to be treated is formed by a continuous film, for example of polyester, which has no-t undergone a previous surface activation treatment, the 2 content must be held very low. For that, a device may be adopted of the kind shown in Figure 2 in which -the parts corresponding to those in Figure 1 are designated by the same reference number. The feed and take up reels for subs-trate 10 are then placed inside the air-tight enclosure 12. The latter is first scavenged with vector gas (oxygen-free He or Ar), then supplied with a monomer or 5 prerJolymer mixture. Such a prepolymer mixture may be in liquid phase. If so, it must be supplied as a mist. The prepolymer may be dispersed in the form o-f a mist by an ul-trasonic gene-rator 44.
Particular conditions for processing several sub-10 strates will now be described and the corresponding resultswill be provided.
EXAMPLE 1 :
A cellulose fiber based paper 100 micron thick was used as substrate.
The voltage V between electrodes was 1~.7 kV. The distance between electrodes was 3 mm for an electrode length of 10 cm. The value I of the capacitive current was 200 PA.
The testing time t was 7 minutes A dark brown soft film was deposited, adhering well 20 to the surface of the substrate This deposit was not soluble in the usual solvents (alcohol, ace-tone), which shows that it was very cross-linked~ It had hydrophobic and dielectric pro-perties.
An interelectrode spacing d of 3 mm appeared optimum 25 in so far as the formation of the polymerized coating on the substrate and in so far as the proportion of the fluorinated links with respect -to the carbon links in the polymer were concerned.
With the above mentioned operating conditions, the 30 weight of the deposit per square centimeter of substrate was 0.8 x 10 4g/mn with a monomer flow rate of 117 cm3/mn.
EXAMPLE 2 :
The above test was repeated using a substrate of fabric 200 em -thick.
The best results were obtained for the following ~2~
operating conditions :
V = 15 kV
I = 130 PA
t = 20 mn d (interelectrode distance) = 3 mn The deposit obtained was quite adherent to the fabric and made it very hydrophobic.
EXAMPLE _ :
As substrate a polyethylene terephtalate film was 0 used having a thickness of 50 um.
V = 13 kV
I = 130 juA
d = 3 mn t = 15 mn The deposit obtained was 0.35 x 10 4 g/cm2/mn EXAMPLE 4 :
___________ A pure cellulose paper tor cotton fabric) was used as substrate having a thickness of 100 em. The voltage of the discharge was sine-shaped with a frequency of a few tens of 20 KHz. The interelectrode distance was 1 mm, the value of the current was a few tens of micro-amps~ the time duration of -the test was 20 mn.
A current of an odoriferous hydrocarbon formed by tetrahydrogeraniol : 5 t tCH ) -C - CH - CH - C - tCH ) - CH - CH OH ) OH OH OH OH
was formed as a mist in an ultrasonic chamber and introduced into the reactor in an argon flow. The droplets formed inside the bottle containing the tetrahydrogeraniol had an average 30 diame-ter close to 1 micron. As in -the previous cases, the flow of hydrocarbon was not a determining parameter for the length of time during which the active species remained in the reac-tor. The ultrasonic generator ~4 may be kept in permanent ope-ration at a frequency be-tween 1 and 10 k~lz. The Corona dischar-35 ge cause grafting of the molecule onto the substrate. The latter remained perfumed for about a month whereas -the same substrate treated with an aerosol, without Corona discharge, only remained perfumed for a few hours.
In the four above examples, an operating optimum 5 may be noticed as regards the distance d between the electro-de and the electric conditions.
It seems that this phenomenon may be explained by the following considerations .
The monomer molecule injected into the reactor is 10 electronically excited in the vicini-ty of the high voltage electrode by electron impact. The ions, radicals, molecules and atoms which are produced in an interelectrode space are conveyed by the electric wind from the high voltage electrode towards the counter electrode. on impact with the material, 15 the activated species react together and wi-th -the substrate, which results in grafting However, it will be readily under-stood that the life span of a chemical species depends on the interelectrode distance and electric wind speed parameters.
Thus the interelec-trode distance is an important parameter 20 for using to the best advantage the chemical reactivity of the species produced. If the distance becomes too high, the rate of growth decreases or even becomes zero : the voltage across the electrodes for main-taining the discharge probably causes destruction of the starting polymers or there is partial 25 recombination before the species reach the substrate. The distance will be generally between 1 and 5 mm.
'p-timum adjus-tment o-f the plasma polymerization process will take into account the thickness ox coating which is desired, the processing time and the value of the discharge 30 current. The value must in practice remain less than 30 ~A/cm at the usual speeds, o-f about 1 m/mn~ Higher speeds lead to operation with increased currents. jut, in practice, 40 JuA per cm of electrode length canno-t be much exceeded without risking arcing conditions, causing decomposition or ablation of -the 35 polymer formed.
For that, it was necessary -to se-t aside earlier prejudices concerning the need to work a-t low pressure and to discover that corona discharge is accompagnied by phenomena very different from those which occur in a cold plasma created by radio frequency excita-tion. In particular, the Corona discharge is accompanied by an "electric wind" phenomenon which may be used wi-th advan-tage.
According to the presen-t invention, there is provided a process of in situ polymerizing a carbon-containing monomer or prepolymer on a subs-tra-te for forming an adherent coating thereon, comprising the steps oE placing said substrate in contact with said monomer or prepolymer dispersed in an atmosphere in contact with the substrate and contained in an enclosure under a pressure close to normal atmospheric pressure and generating a Corona discharge by applying an AC voltage between a first elec-trode having a small radius of curvature and a grounded second electrode, carrying the substrate and having a radius of curvature greater -than said small radius by several orders of magnitude, whereby reactive species are formed and driven by electric wind -toward said substrate for in situ polymeriza-tion on said substrate.
The term "Corona discharge" mus-t be cons-trued as designating the self-maintained discharge which takes place in a gas in the vicinity of an elec-trical conductor having a small radius of curvature subjected -to an intense non-uniform non-disruptive elec-tric field; that discharge is a luminescent discharge, is electrically and visually stable;
it is often associated with a discharge formed of so-called "streamers" which appears in the form of individual repetitive discharges.
The Corona discharge will be advantageously formed under AC current and s-truck between an electrode having a small radius of curvature and a counter elec-trode carrying the substra-te (and formed -thereby if it is conduc-ting), maintained at ground potential. Thus, elec-tric wind will always carry -the reactive species towards the substrate.
During the negative half wave, -the current will be formed of pulses corresponding to ionization phenomena in the stronger field zone, at a very high frequency. During the positive /
/
half wave, "aigrettes" or brush discharge occurs in the inter-electrode space and brings positive ions to the surface of the ;nsulating substrate, which causes breakages of atom chains and superficial spraying in the impact zone o-f the streamers 5 Thus, in a single operation, the surface of the substrate is activated, the monomer is polymerized in situ and -the polymer is bonded to the substrate by a phenomenon reLated to grafting.
It is probable that layers of an appreciable thickness are obtained in these conditions because the elec-10 tric wind projects the reactive species towards the substratewhich they reach with sufficient energy and before recombina-tion.
An AC electric current will be advantageously used in a frequency range less -than that currently called radio 15 frequency, i.e. below 100 KHz. A frequency of a few tens of KHz gives satisfactory resultsn However, for the sake of convenience, working may be directly at the industrial fre-quency of 50 Hz or 60 Hz. In this case, the Corona discharge starts as soon as the voltage reaches the value corresponding 20 to Paschen's law, i.e. a value depending on the pressure, on the interelectrode distance and on the gas mixed with the monomer (argon or helium in general). For current applications the voltage used will generally have an order of magnitude in the 10 volts range at atmospheric pressure.
With the invention a fluocarbon water-proofing fire-proofing and/or passivation coating may be formed on very different materials. In particular, such coatings may be for-med on threads, fibers, fabrics and more generally on all materials around which the discharge may take place and then 30 no particular precaution is required. The atmosphere may con-tain a significative oxygen content. Thus, threads, yarn or fibers of natural or artificial textile suchas polyester, po-lyamide, polyethylene, polyacrylonitrile may be treated.
When, as will be most often the case, a fluocarbon coating is of advantage, the monomer chosen will be a fluocar-. .
fir 3J.'L~;S~;
bon monomer capable of giving rise to reactive species~Several products among those known under the trademark FREON may be used and, among them, H2C = CF2 has given very satisfactory results. Monomers may also be used among those mentioned in US-A-4 188 426; tests carried ou-t with acrylic acid, formic acid, C ClF3 have proved sa-tisfactory.
Surface passivation of steel was also achieved in a SF6 atmosphere con-taining a small amount of ethyl methyl ketone.
In another use of the invention, odoriferous coatings have been achieved. In this case a carbon or fluocarbon monomer is used, for example tetrahydrogeraniol.
More specifically, according to the present inven-tion, there is provided a process of polymerizing a carbon containing monomer or prepolymer on a substrate comprising the steps of placing said substrate in contact with said monomer or prepolymer contained in an enclosure under a pres-sure close to normal atmospheric pressure and generating aCorona discharge between a first electrode having a small radius of curvature and a second electrode, carrying the substrate, and having a radius of curvature grea-ter than said small radius by several orders of magnitude, whereby reactive species are formed and driven by electric wind toward said substrate.
Also in accordance wi-th the present invention, there is provided a process of polymerizing a monomer Go~taining fluorine and carbon on a substrate, comprising: passing said substratelthrough a gaseous medium at substantially atmcs-- pa -pheric pressure, said medium comprising said monomer;
suppor-ting said substrate while in said medium wi-th an electrode having a large radius of curvature, pas-t an elongated electrode having a radius oE curvature lower than 1 mm, parallel to -the electrode supporting the substrate and at a dis-tance Erom 1 to 5 mm from said substrate; and maintaining an AC Corona discharge between the electrodes with a current value no-t exceeding 40 uA per cm of length of said elongated electrode.
` According to -the presen-t invention, there is also provided a process of polymerizing a carbon-fluorine monomer on a base paper shee-t or pattern fabric subs-trate for forming an adherent coating thereon, comprising the steps of placing said substrate in contact with said monomer dispersed in an atmosphere in contact with the substrate and con-tained in an enclosure under a pressure close to normal atmospheric pressure and generating an A.C. Corona discharge between a first electrode having a small radius oE curvature and a grounded second electrode, carrying the substrate, and having a radius of curvature greater than said small radius by several orders of magnitude, whereby reactive species are formed and driven by electric wind -toward said substrate Eor in situ polymerization on said substrate.
According to the present invention, there is also provided a device for polymerizing a carbon containing monomer or prepolymer onto a substrate, comprising an enclosure provided with means for flowing a substantially oxygen free flow of monomer or prepolymer in said enclosure in contact with the subs-trate on which a polymerized coating is to be Eormed while main-taining said enclosure at substantially normal atmospheric pressure; a grounded elec-trode wi-th a large radius of curvature supporting the substrate; an elonga-ted electrode having a sharp edge placed parallel -to the substrate where said substrate is supported - 4b -by said grounded electrode and a-t a distance from said grounded electrode of from 1 to 5 mm; electric supply means for providing, between the electrodes, an AC voltage of a value sufficient to create a Corona discharge at said substantially atmospheric pressure; and means for circulating said substrate over said grounded electrode.
The present invention Eurther relates to a device for polymerizing a carbon containing monomer or prepolymer onto a substrate, comprising an enclosure provided with means for flowing a monomer or prepolymer i.n said enclosure;
a grounded electrode with a large radius of curva-ture supporting the substrate on which a polymerized coating is to be formed; an electrode with a small radius of curvature placed parallel to the substrate; and electric supply means for providing, between the electrodes, an AC voltage of a value sufficient to create a Corona discharge a-t a pressure close to normal atmospheric pressure.
Preferably, the monomer or prepolymer is flowed in the enclosure along with a vector gas.
Whenever it is not indispensable to reduce the oxygen content to a very low value, it will be desirable to adop-t a pressure slightly less than the atmospheric pressure, so that possible leaks occur from the outside atmosphere of the workshop towards the inside of the enclosure and so that there is no dispersion in the workshop of toxic material coming from activation oE the monomer.
The invention will be better understood from the following non-restrictive description of preferred embodiments thereof, given by way of examples only.
SHORT DESCRIPTION OF TIE DRAWINGS
Figure 1 is a schematic representation of a device for continuous -treatment of a substrate in the form of a thread or porous strip, such as a fabric, by polymerization of a gaseous monomer ;
Figure 2 shows a modified device.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Referring to Figure 1, there is shown a device for 5 processing a substrate 10 in the form of a strip, which may be formed by a sheet of paper made from cellulose fiber, a woven or non-woven strip made from organic or inorgan;c material.
The device comprises an enclosure 12 having an inlet airlock 14 and an outlet airlock 16. The airlocks are each defined 10 by two walls having a slit through which the strip 10 passes.
Reduction of air ingress is obtained by means of flexible lips 18 fixed to the walls and rubbing against the strip. The internal volumes of the airlocks are connected to a -trap 20 for retaining decomposition products which may be harmful.
15 In order to further reduce the leaks of such products to the outside atmosphere, an additional collection space 22 having an extraction pump 24 and connected -to the trap 20 may be provided in the path of substrate 10 downstream of airlock 16.
The enclosure 12 contains means for creating a 20 Corona discharge comprising a rotating metal drum 26 connected to ground and supporting substrate 10. An electrode 28 is disposed in the enclosure in a position such that it presents a surface with a small radius of curvature (less than the ra-dius of drum 26 by several orders o-f magni-tude) facing the 25 zone of the substrate carried by the drum. In Figure 1, elec-trode 28 is formed by a blade whose edge is parallel to a generatrix of drum 26, at a distance of a few millimeters. A
wire may also be used as electrode having a diameter less than 2 mm. Several parallel wires may be provided in succession so 30 as to subject the substrate to several successive Corona discharges. Such a wire may be made from tungsten, molybdenum, titanium, vanadium or "monel" alloy and, rnore generally, from all metal materials, having catalytic properties or not, which resist corrosion. The electrode is fed by high vol-tage AC
35 generator 30. The generator is of a type which operates at a frequency less -than 100 KHz. It will usually supply a volta-ge of -the order of magnitude of 104 Vol-ts (-typically between 10 and 20 kV) when the distance between drum 26-forming the counter electrode-and electrode 28 is between 1 and 5 mm. The current supplied will typically be such tha-t travelling speeds of the substrate may be reached exceeding 1 m/mn.
Enclosure 12 is provided with means for supplying it with a monomer and vector gas (argon or helium in general) mixture and for renewing it.
In the embodiment of Figure 1, for the formation of a carbon-fluorinated polymer layer, such means comprise mixing means 32 which receives, through respective pressure reducers, argon from a cylinder 34 and CH2 = CF2 gas from a cylinder 36~
The mixture is supplied to the enclosure 12, at one end there-o-f, through a line fitted with a control valve 38. The enclo-sure has, opposite the intake pipe, a discharge pipe 40 ope-ning into a collecting receptacle ~2. The CH2 = CF2 content in the atmosphere is not critical. Oftentimes it will be pos-sible -to dispense with a vector gas. If necessary, it may be regulated permanently by monitoring the light absorption by thc atmos-phere by means o-f a photoabsorption photometer set to a spec-tral line characteristic of the monomer.
By way of example, tests have been carried out in a device containing a counter electrode -formed by a drum 10 cm in length and 6.5 cm in diameter, rotating wi-th a peripheral speed of 80 cm per minute. The electrode 28 was formed by a tungsten wire 250 microns in diameter. The generator 30 sup-plied a 50 Hz AC currentA In the embodiment as shown in Figure 1, it is not possible to hold the oxygen content a-t a very low value, due to air in-take through the seals. When the material to be treated is formed by a continuous film, for example of polyester, which has no-t undergone a previous surface activation treatment, the 2 content must be held very low. For that, a device may be adopted of the kind shown in Figure 2 in which -the parts corresponding to those in Figure 1 are designated by the same reference number. The feed and take up reels for subs-trate 10 are then placed inside the air-tight enclosure 12. The latter is first scavenged with vector gas (oxygen-free He or Ar), then supplied with a monomer or 5 prerJolymer mixture. Such a prepolymer mixture may be in liquid phase. If so, it must be supplied as a mist. The prepolymer may be dispersed in the form o-f a mist by an ul-trasonic gene-rator 44.
Particular conditions for processing several sub-10 strates will now be described and the corresponding resultswill be provided.
EXAMPLE 1 :
A cellulose fiber based paper 100 micron thick was used as substrate.
The voltage V between electrodes was 1~.7 kV. The distance between electrodes was 3 mm for an electrode length of 10 cm. The value I of the capacitive current was 200 PA.
The testing time t was 7 minutes A dark brown soft film was deposited, adhering well 20 to the surface of the substrate This deposit was not soluble in the usual solvents (alcohol, ace-tone), which shows that it was very cross-linked~ It had hydrophobic and dielectric pro-perties.
An interelectrode spacing d of 3 mm appeared optimum 25 in so far as the formation of the polymerized coating on the substrate and in so far as the proportion of the fluorinated links with respect -to the carbon links in the polymer were concerned.
With the above mentioned operating conditions, the 30 weight of the deposit per square centimeter of substrate was 0.8 x 10 4g/mn with a monomer flow rate of 117 cm3/mn.
EXAMPLE 2 :
The above test was repeated using a substrate of fabric 200 em -thick.
The best results were obtained for the following ~2~
operating conditions :
V = 15 kV
I = 130 PA
t = 20 mn d (interelectrode distance) = 3 mn The deposit obtained was quite adherent to the fabric and made it very hydrophobic.
EXAMPLE _ :
As substrate a polyethylene terephtalate film was 0 used having a thickness of 50 um.
V = 13 kV
I = 130 juA
d = 3 mn t = 15 mn The deposit obtained was 0.35 x 10 4 g/cm2/mn EXAMPLE 4 :
___________ A pure cellulose paper tor cotton fabric) was used as substrate having a thickness of 100 em. The voltage of the discharge was sine-shaped with a frequency of a few tens of 20 KHz. The interelectrode distance was 1 mm, the value of the current was a few tens of micro-amps~ the time duration of -the test was 20 mn.
A current of an odoriferous hydrocarbon formed by tetrahydrogeraniol : 5 t tCH ) -C - CH - CH - C - tCH ) - CH - CH OH ) OH OH OH OH
was formed as a mist in an ultrasonic chamber and introduced into the reactor in an argon flow. The droplets formed inside the bottle containing the tetrahydrogeraniol had an average 30 diame-ter close to 1 micron. As in -the previous cases, the flow of hydrocarbon was not a determining parameter for the length of time during which the active species remained in the reac-tor. The ultrasonic generator ~4 may be kept in permanent ope-ration at a frequency be-tween 1 and 10 k~lz. The Corona dischar-35 ge cause grafting of the molecule onto the substrate. The latter remained perfumed for about a month whereas -the same substrate treated with an aerosol, without Corona discharge, only remained perfumed for a few hours.
In the four above examples, an operating optimum 5 may be noticed as regards the distance d between the electro-de and the electric conditions.
It seems that this phenomenon may be explained by the following considerations .
The monomer molecule injected into the reactor is 10 electronically excited in the vicini-ty of the high voltage electrode by electron impact. The ions, radicals, molecules and atoms which are produced in an interelectrode space are conveyed by the electric wind from the high voltage electrode towards the counter electrode. on impact with the material, 15 the activated species react together and wi-th -the substrate, which results in grafting However, it will be readily under-stood that the life span of a chemical species depends on the interelectrode distance and electric wind speed parameters.
Thus the interelec-trode distance is an important parameter 20 for using to the best advantage the chemical reactivity of the species produced. If the distance becomes too high, the rate of growth decreases or even becomes zero : the voltage across the electrodes for main-taining the discharge probably causes destruction of the starting polymers or there is partial 25 recombination before the species reach the substrate. The distance will be generally between 1 and 5 mm.
'p-timum adjus-tment o-f the plasma polymerization process will take into account the thickness ox coating which is desired, the processing time and the value of the discharge 30 current. The value must in practice remain less than 30 ~A/cm at the usual speeds, o-f about 1 m/mn~ Higher speeds lead to operation with increased currents. jut, in practice, 40 JuA per cm of electrode length canno-t be much exceeded without risking arcing conditions, causing decomposition or ablation of -the 35 polymer formed.
Claims (11)
1. A process of in situ polymerizing a carbon-containing monomer or prepolymer on a substrate for forming an adherent coating thereon, comprising the steps of placing said substrate in contact with said monomer or prepolymer dispersed in an atmosphere in contact with the substrate and contained in an enclosure under a pressure close to normal atmospheric pressure and generating a Corona discharge by applying an AC voltage between a first electrode having a small radius of curvature and a grounded second electrode, carrying the substrate and having a radius of curvature greater than said small radius by several orders of magnitude, whereby reactive species are formed and driven by electric wind toward said substrate for in situ polymerization on said substrate.
2. A process according to claim 1, wherein the pressure in said enclosure is slightly lower than atmospheric pressure.
3. A process according to claim 1, wherein said monomer is a carbofluorine monomer.
4. A process according to claim 1, wherein said monomer is H2C = CF2.
5. A process according to claim 1, wherein said monomer is odoriferous.
6. A process according to claim 1, wherein said discharge is generated by applying a voltage at a frequency lower than 100 kHz.
7. A process of polymerizing a monomer containing fluorine and carbon on a substrate, comprising: passing said substrate through a gaseous medium at substantially atmospheric pressure, said medium comprising said monomer;
supporting said substrate while in said medium with an electrode having a large radius of curvature, past an elongated electrode having a radius of curvature lower than 1 mm, parallel to the electrode supporting the substrate and at a distance from 1 to 5 mm from said substrate, and maintaining an AC Corona discharge between the electrodes with a current value not exceeding 40 uA per cm of length of said elongated electrode.
supporting said substrate while in said medium with an electrode having a large radius of curvature, past an elongated electrode having a radius of curvature lower than 1 mm, parallel to the electrode supporting the substrate and at a distance from 1 to 5 mm from said substrate, and maintaining an AC Corona discharge between the electrodes with a current value not exceeding 40 uA per cm of length of said elongated electrode.
8. A device for polymerizing a carbon containing monomer or prepolymer onto a substrate, comprising an enclosure provided with means for flowing a substantially oxygen free flow of monomer or prepolymer in said enclosure in contact with the substrate on which a polymerized coating is to be formed while maintaining said enclosure at substantially normal atmospheric pressure; a grounded electrode with a large radius of curvature supporting the substrate an elongated electrode having a sharp edge placed parallel to the substrate where said substrate is supported by said grounded electrode and at a distance from said grounded electrode of from 1 to 5 mm; electric supply means for providing, between the electrodes, an AC voltage of a value sufficient to create a Corona discharge at said substantially atmospheric pressure; and means for circulating said substrate over said grounded electrode.
9. A device according to claim 8, wherein said means for circulating said substrate move said substrate into and out of said enclosure through slots in walls of said enclosure and means connected to said walls and rubbing on said substrate for limiting gas leaks through said slots.
10. A device according to claim 8, wherein said grounded electrode is in the shape of a rotating drum and said electrode having a sharp edge is a knife blade electrode having an edge parallel to a generatrix of the drum.
11. A process of polymerizing a carbon-fluorine monomer on a base paper sheet or pattern fabric substrate for forming an adherent coating thereon, comprising the steps of placing said substrate in contact with said monomer dispersed in an atmosphere in contact with the substrate and contained in an enclosure under a pressure close to normal atmospheric pressure and generating an A.C. Corona discharge between a first electrode having a small radius of curvature and a grounded second electrode, carrying the substrate, and having a radius of curvature greater than said small radius by several orders of magnitude, whereby reactive species are formed and driven by electric wind toward said substrate for in situ polymerization on said substrate.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FR8312576 | 1983-07-29 | ||
| FR8312576A FR2549869B1 (en) | 1983-07-29 | 1983-07-29 | METHOD AND DEVICE FOR PERFORMING IN SITU POLYMERIZATION OF FLUOCARBON MONOMERS ON A SUBSTRATE |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1242166A true CA1242166A (en) | 1988-09-20 |
Family
ID=9291250
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000459835A Expired CA1242166A (en) | 1983-07-29 | 1984-07-27 | Process and apparatus for forming a polymerized coating on a substrate |
Country Status (7)
| Country | Link |
|---|---|
| EP (1) | EP0133832B1 (en) |
| JP (1) | JPS6090225A (en) |
| AT (1) | ATE24941T1 (en) |
| CA (1) | CA1242166A (en) |
| DE (1) | DE3462054D1 (en) |
| FI (1) | FI77879C (en) |
| FR (1) | FR2549869B1 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5449383A (en) * | 1992-03-18 | 1995-09-12 | Chatelier; Ronald C. | Cell growth substrates |
Families Citing this family (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4844979A (en) * | 1986-02-13 | 1989-07-04 | Minnesota Mining And Manufacturing Company | Shaped polymeric articles having improved receptivity to organic coatings |
| AU640345B2 (en) * | 1988-05-17 | 1993-08-26 | Commonwealth Scientific And Industrial Research Organisation | Hydrophilic non-swelling multilayer polymeric materials and process for their manufacture |
| WO1989011500A1 (en) * | 1988-05-17 | 1989-11-30 | Commonwealth Scientific And Industrial Research Or | Hydrophilic non-swelling multilayer polymeric materials and process for their manufacture |
| DE3827628A1 (en) * | 1988-08-16 | 1990-03-15 | Hoechst Ag | METHOD AND DEVICE FOR THE SURFACE PRE-TREATMENT OF A MOLDED BODY MADE OF PLASTIC BY MEANS OF AN ELECTRIC CORONA DISCHARGE |
| DE3827629A1 (en) * | 1988-08-16 | 1990-03-15 | Hoechst Ag | METHOD AND DEVICE FOR THE SURFACE PRE-TREATMENT OF SINGLE OR MULTILAYER MOLDING MATERIAL BY MEANS OF AN ELECTRIC CORONA DISCHARGE |
| DE3827631A1 (en) * | 1988-08-16 | 1990-02-22 | Hoechst Ag | SELF-SUPPORTING AREA WITH AT LEAST ONE STRUCTURED SURFACE |
| DE3827632A1 (en) * | 1988-08-16 | 1990-03-08 | Hoechst Ag | Self-supporting sheet-like article having at least one structured surface |
| DE3827630A1 (en) * | 1988-08-16 | 1990-02-22 | Hoechst Ag | AREA OF A SUBSTRATE AND A COATING AND METHOD FOR THE PRODUCTION THEREOF |
| EP1754547A3 (en) * | 1998-10-27 | 2007-05-30 | E. I. du Pont de Nemours and Company | In situ fluoropolymer polymerization into porous substrates |
| FR3043679B1 (en) * | 2015-11-12 | 2021-07-23 | Aptar Stelmi Sas | PROCESS FOR TREATING AN ELASTOMERIC PACKAGING ELEMENT, AND PACKAGING ELEMENT THUS TREATED. |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4131691A (en) * | 1977-09-22 | 1978-12-26 | Surface Activation Corporation | Coating a substrate by glow discharge graft polymerization |
| US4188426A (en) * | 1977-12-12 | 1980-02-12 | Lord Corporation | Cold plasma modification of organic and inorganic surfaces |
-
1983
- 1983-07-29 FR FR8312576A patent/FR2549869B1/en not_active Expired
-
1984
- 1984-07-26 FI FI842989A patent/FI77879C/en not_active IP Right Cessation
- 1984-07-27 CA CA000459835A patent/CA1242166A/en not_active Expired
- 1984-07-27 JP JP59158533A patent/JPS6090225A/en active Pending
- 1984-07-30 AT AT84401592T patent/ATE24941T1/en not_active IP Right Cessation
- 1984-07-30 DE DE8484401592T patent/DE3462054D1/en not_active Expired
- 1984-07-30 EP EP84401592A patent/EP0133832B1/en not_active Expired
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5449383A (en) * | 1992-03-18 | 1995-09-12 | Chatelier; Ronald C. | Cell growth substrates |
Also Published As
| Publication number | Publication date |
|---|---|
| EP0133832A1 (en) | 1985-03-06 |
| FI77879B (en) | 1989-01-31 |
| FR2549869A1 (en) | 1985-02-01 |
| FR2549869B1 (en) | 1986-07-11 |
| DE3462054D1 (en) | 1987-02-19 |
| FI77879C (en) | 1989-05-10 |
| JPS6090225A (en) | 1985-05-21 |
| FI842989A0 (en) | 1984-07-26 |
| FI842989A (en) | 1985-01-30 |
| EP0133832B1 (en) | 1987-01-14 |
| ATE24941T1 (en) | 1987-01-15 |
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