Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D1/00—Processes for applying liquids or other fluent materials
  • B05D1/62—Plasma-deposition of organic layers
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01T—SPARK GAPS; OVERVOLTAGE ARRESTERS USING SPARK GAPS; SPARKING PLUGS; CORONA DEVICES; GENERATING IONS TO BE INTRODUCED INTO NON-ENCLOSED GASES
  • H01T19/00—Devices providing for corona discharge
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D7/00—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials
  • B05D7/22—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials to internal surfaces, e.g. of tubes
  • B05D7/227—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials to internal surfaces, e.g. of tubes of containers, cans or the like

Definitions

• the invention relates to a process of forming organic coatings within a corona discharge.
• a corona discharge is produced by capacitatively exciting a gaseous media lying between two spaced electrodes, at least one of which is insulated from the gaseous media by a dielectric barrier.
• corona discharge is limited in orgin to alternating currents.
• corona discharge is a high voltage, low current phenomenon with voltages being typically measured in kilovolts and currents measured in milliamperes.
• a corona discharge may be maintained over wide ranges of pressure and frequency, although approximate atmospheric pressures and frequencies substantially above power transmission values are typically employed.
• Electrodeless discharge When dielectric barriers are employed adjacent each of two spaced electrodes in achieving a corona discharge, the discharge phenomenon is frequently termed an electrodeless discharge, whereas when a single dielectric barrier is employed to insulate a single electrode, the resulting phenomenon is frequently termed a semicorona discharge. Both the terms electrodeless discharge and semicorona discharge are intended as species designations for corona discharge.
• a completely unrelated and electrically distinct discharge phenomenon is a glow discharge, which is sometimes confused with corona discharge by those having only casual acquaintance with electrical discharge phenomena, since both corona discharge and glow discharge yield a soft or diffused visual display.
• Glow discharge is produced by ionization of low pressure gaseous media using bare electrodes in contact therewith. Pressures are typically maintained well below 5 mm. Hg in order to benefit from reduced voltage requirements in accordance with Paschens law. Operation at or near atmospheric pressure as in the case of corona discharge is precluded by arcing.
• glow discharge is not a capacitive phenomenon, it may be produced by either direct or alternating current.
• lower voltages and frequencies are typically employed with glow discharge than are typical with corona discharge.
• a third, completely distinct form of gaseous electrical discharge is electrical arcing, which is a high current, low voltage phenomenon.
• Arcing occurs when two conductive surfaces of dissimilar electrical potential sufficiently ionized the gaseous media in association therewith to form a conductive ionic path therebetween.
• Arcing is 3,415,683 Patented Dec. 10, 1968 visually dissimilar from a corona discharge in that the former is 'areally limited and exhibits distinct boundaries whereas the latter exhibits a soft or diffused appearance.
• corona discharge is capable of activating certain specific chemical reactions.
• organic materials in vapor form may be deposited in a corona discharge to yield organic coatings physically resembling polymers formed by conventional chemical techniques.
• organic vapors not generally polymerizable by chemical techniques may be deposited as coatings in the presence of a corona discharge.
• organic coatings laid down in a corona discharge are more thickly deposited on substrate asperities than on relatively smooth substrate areas. The process is practicable over a Wide range of pressure conditions.
• the invention may be practiced under any set of conditions in which a corona discharge is maintainable.
• certain corona discharge producing conditions offer distinct procedural advantages and are preferred.
• a corona discharge may be maintained over a wide range of pressure conditions without arcing.
• Atmospheric and near-atmospheric pressures offer particular advantages in avoiding the use of expensive pressure control equipment. Pressures of 0.2 to 10 atmospheres generally define the preferred limits of operation.
• a corona discharge can be generated using only an alternating current.
• high frequencies are preferred since the phenomenon is capacitive in nature. Frequencies ranging from 2,0 c.p.s. to 500,000 c.p.s. are contemplated.
• a preferred frequency range is from 3,000 c.p.s. to 10,000 c.p.s.
• the current voltage and power utilized in generating a corona discharge for a specific coating process will vary over wide limits depending on the thickness of the dielectric barrier or barriers employed, the electrode spacing, and the nature of the gaseous media lying within the discharge area. As a general rule, more complex materials will absorb more energy than less complex materials. The inert gas argon, for example, will absorb much less energy than air. In an electrodeless application utilizing two quartz barriers of 2 mm. thickness separated by a 4 mm. spacing, the voltage should suitably be maintained at 12 to 15 kilovolts. In a semicorona application,
• a single quartz barrier having 4 mm. thickness is required to operate at equivalent voltages.
• the energy used is proportioned to the coating thickness deposited.
• corona discharge attacks an organic material
• the exact chemical mechanism by which a corona discharge attacks an organic material is not known. In acting on monomeric organic materials, polymerizable by conventional chemical techniques, it would appear that the products obtained by corona discharge resemble the polymeric materials which could be obtained by conventional chemical processes.
• the materials which can be deposited by corona discharge activation are not limited to those polymerized by known chemical processes. Corona discharge may, for example, deposit polymer resembling coatings when a vapor of methane, benzene, toluene, or any other generally unpolymerizable organic material is passed therethrough. Generally, better yields are obtained with materials known to be polymerizable by conventional chemical techniques.
• the substrate on which the coating is deposited may vary within wide limits.
• the substrate being coated may be employed as a bare electrode separated from an insulated electrode.
• the substrate is preferably employed as a ground electrode.
• a semicorona discharge is generated between the insulated electrode and the substrate acting as the ground electrode.
• Coating material lying between the substrate and the insulated electrode is deposited on the substrate.
• the thickness and uniformity of the coating deposited can be controlled by regulating the gap between the insulated electrode and the substrate. The coating thickness is proportionately greater in any area where the gap is reduced, since the potential gradient is higher.
• the substrate to be coated is, of course, unsuitable for use as an electrode itself and two electrodes must be employed.
• One or both of the electrodes may be insulated to provide a dielectric barrier between the spaced electrodes.
• An organic vapor and the substrate are both positioned within the corona between the electrodes.
• the substrate may either be coated while moving through the corona or while remaining stationary therein.
• the organic vapor may be either circulated through the corona or allowed to remain stagnant within the discharge.
• the maintenance of a corona discharge is dependent on the potential gradient between electrodes. With higher voltages the electrodes may be more widely spaced.
• the minimal spacing between electrodes is determined either by the dielectric breakdown of the insulation barrier, resulting in arcing, or by the electrodes becoming too closely spaced to conveniently position the substrate and coating material therebetween. Using 2 to 4 mm. thickness of quartz in the form of either one or two dielectric barriers, it has been determined that electrode spacings of 1 to 5 mm. are convenient.
• the wire In coating conducting indefinite length articles elongated along a single axis, such as wire, it is generally preferred to employ the wire as a bare electrode, preferably a ground electrode and to concentrically position an annular insulated electrode about the wire.
• the can In dealing with cylindrical conductive articles, as for example cans, it is preferred to employ the can as a bare ground electrode and to position an insulated electrode concentrically within the can.
• the coatings laid down in a corona discharge may be fully cured therein or may be subjected to subsequent treatments to complete the cure.
• polymeric coatings exhibit three separate stages of cure. In the first stage the coating is adhesive. Coatings cured only to the adhesive stage may be useful in combination with laminating processes. In a second stage of curing, coatings are not tacky but are still extractable by solvents indicating less than a complete cure. Nontacky, incompletely cured coatings are conveniently handled and yet may be subsequently rendered adhesive by heat or solvent treatment. Completely cured polymeric coatings are nonadhesive and insoluble in most solvents. Coating cure treatments employing temperatures up to 250 C. are specifically contemplated by this invention.
• Example 1 An open ended, previously weighed tin can of the type conventionally employed to package foods and beverages having an inside diameter of 64 mm. and a length of 4% inches is suitably grounded. A glass insulated electrode having an outside diameter of 59 mm. and a length of 8 inches is centered within the tin can. A vapor conduit is connected between the base of the tin can and a pressure tank of butadiene. A sealing element including an exhaust conduit is placed on the top of the tin can to prevent diffusion of air between the can and the insulated electrode. The valve on the pressure tank is opened and the flow rate of gaseous butadiene controlled to 13 cc./ min. The flow rate is determined at approximately atmospheric pressure and a room temperature of 25 C.
• the system is purged for four minutes to remove any air from between the insulated electrode and the tin can.
• An alternating current of 13 kv. peak is applied to the electrode and can generating a soft, diffused corona.
• a frequency of 10,000 c.p.s. is employed.
• the coating process is continued 3 minutes at 320 watts.
• the tin can is removed from the corona coating apparatus and subjected to a temperature of 200 C. for a period of 4 minutes.
• the coated can is again weighed and determined to have received 0.031 gram of coating material. It is noted that the can coating is somewhat thicker along the longitudinal seam.
• Example 2 The process of Example 1 is repeated using the tin can as the high potential electrode and the insulated electrode as a ground.
• the coated can is noted to have a thicker coating along the longitudinal seam.
• Example 3 An open ended tin can and insulated electrode of the type described in Example 1 are similarly arranged.
• the space between the insulated electrode and the tin can is connected by fluid conduits to a source of butadiene and a source of argon.
• Argon is used to purge the system and subsequently butadiene is supplied at a fiow rate of 700 cc./min. and argon at a flow rate of 1150 cc./min.
• a voltage of 13.9 kv. peak at 10,000 c.p.s. is supplied to the insulated electrode while the tin can is grounded.
• the corona discharge is maintained for 10 minutes with a power input of 114.5 watts.
• the tin Upon removal from the coating apparatus, the tin can is subjected to an after-treatment as described in Example 1.
• the coated can is noted to have a thicker coating along the longitudinal seam.
• Example 4 An open ended, previously weighed tin can and insulated electrode of the type described in Example 1 are similarly arranged.
• the system is purged with argon and coating material is subsequently supplied to the system by bubbling argon through liquid toluene.
• a voltage of 20.2 kv. peak at 10,000 c.p.s. is supplied to generate a corona discharge.
• the corona is maintained 3 minutes with a power input of 272.5 watts.
• the tin can Upon removal from the coating apparatus, the tin can is subjected to an after-treatment as described in Example 1. The coated can is again weighed and determined to have received 0.0052 gram of coating material.
• the coated can is noted to have a thicker coating along the longitudinal seam.
• Example 5 A tin can having a length of 4% inches, an inside diameter of 64 mm., an open top and a closed bottom is suitably connected to electrical ground.
• Two glass fluid inlet tubes are positioned within the tin can and extending near the bottom.
• An insulated electrode having a bottom outside diameter of 55 mm. and a top outside diameter adjacent the can top of 59 mm. is mounted within the can with the bottom end of the insulated electrode spaced 3.5 mm. from the end of the can.
• Duct sealing material is hand molded between the insulated electrode, the can top, and the inlet tubes. The duct sealing material is left spaced from the exterior walls of the inlet tubes an amount suflicient to allow vapor to exhaust.
• the inlet tubes are connected by suitable fluid conduits to a source of butadiene and argon.
• the space between the insulated electrode and the can is purged for fifteen minutes using argon.
• the fiow of butadiene and argon are controlled to provide respective flow rates of 150 cc./min. and 1150 cc./min.
• a 10.9 kv. peak voltage at 10,000 c.p.s. is applied to the insulated electrode to generate a corona discharge. The discharge is maintained for 15 minutes with a power input of 164 watts.
• the coated can is noted to be more thickly coated along the seam.
• Example 6 An electrodeless coating process is performed utilizing an outer electrode comprising a glass cylinder having a wall thickness of 1.5 mm. and an inside diameter within the discharge area of 42 mm. A length of the glass cylinder is exteriorly coated with a transparent, conductive coating of tin oxide to define the discharge area.
• the glass tube above the electrical discharge area is provided with an exhaust conduit connected to a vacuum pump, and below the discharge area the glass tube forms a glass mixing and heating pot having two inlet conduits.
• a second glass tube Mounted concentrically within the first glass tube is a second glass tube, forming an inner electrode, having a similar wall thickness and an outside diameter of 35 mm.
• the inside surface of the glass tube is similarly lined with the tin oxide.
• the interior of the inner electrode is filled with copper shavings in which a metal encased thermometer is mounted.
• a 1 inch wide, 40 inches long, and mils thick strip of asbestos paper is spirally wound about the outer surface of the inner electrode.
• the inlet conduits of the heating and mixing pot are connected to sources of metacresol and argon.
• the system is purged with argon while the mixing pot is maintained at 250 C.
• the metal encased thermometer in the inner electrode reads 150 C.
• the system is reduced to a pressure of 300 mm. Hg.
• a corona discharge is established using a voltage of 7 kv. peak at 10,000 c.p.s.
• the corona is maintained 20 minutes with a power input of 34 watts.
• a visible deposit is formed at the end of 10 minutes and at the end of 20 minutes the deposit is dry to the touch.
• Example 7 The coated asbestos paper strip obtained from Example 6 is heated to 125 C. in air. The strip is subsequently placed in toluene. None of the coating is extractable by toluene.
• Example 8 The coated strip of Example 8 is divided into two portions. One portion of the strip is soaked in toluene for 5 minutes while another portion is soaked in methylethyl :ketone for 5 minutes. In each case the coating discolored the solvent indicating that the coating is not completely cross-linked and may be further cured.
• Example 10 The process of Example 8 is repeated using a inch wide strip of polytetrafiuoroethylene. A corona discharge is maintained using a voltage of 9.0 kv. peak at 10,000 c.p.s. The corona is continued 15 minutes with a power input of 45 watts. The resultant product displays a tacky, adherent coating.
• Example 11 A coating apparatus as described in Example 6 is modified by theaddition of a water cooling jacket adjacent the outer electrode.
• the apparatus is connected to a source of acrylonitrile vapor and a source of argon.
• a strip of kraft paper 10 mils thick, 1 inch wide, and approximately 40 -inches long is spirally mounted adjacent the exterior surface of the inner electrode.
• the system is purged and operated using the same sequence of steps described in Example 6.
• a flow rate of 0.4 cc./-min. liquid acrylonitrile is maintained together with 25 cc./min. argon measured at atmospheric pressure and 25 C.
• the space between the inner and outer electrodes is maintained at 600 mm. Hg during coating.
• a corona discharge is maintained between the electrodes using a voltage of 7 to 10 kv. peak over a period of 8 minutes.
• a power input of 50 watts is maintained.
• the kraft paper is noted to have a light brown coating which extends throughout the thickness of the paper and is visible on each face.
• the coating is noted to be nonadhesive to touch.
• the coated paper is noted to be insoluble in toluene and soluble in methyl ethyl ketone.
• Example 12 An annular electrode is formed from an "eight inch long quartz tube having an outside diameter of 6 mm. and an interior diameter of 3 mm. by placing a silver outside conductive coating on the tube.
• a 20 gauge Wire is centered within the quartz electrode and suitably grounded.
• the glass tube is provided with means conducting vapor to the lower end thereof and is suitably provided with a gas exhaust at the upper end.
• a butadiene vapor is conducted upwardly through the tube at a flow rate of 8 cc./ min. measured at 25 C. and atmospheric pressure.
• the silver, outer electrode is connected to a source of alternating current at a voltage of 20 kv. peak so that a corona discharge is formed.
• the corona discharge is continued 2 minutes with a power input of 50 watts.
• the resulting product is a coated wire having a hard, insoluble coating.
• Example 13 A wire is coated as in Example 12, except that the wire is connected to a source of alternating current and the silver electrode is grounded. A similar product is obtained.
• a process of coating within a desired zone comprisin introducing an organic vapor within the zone
• a process of coating between two electrodes, at least one of which is dielectrically insulated, comprising:
• a process of coating an electrically conductive substrate utilizing a dielectrically insulated electrode comprising:
• a process of coating an electrically conductive substrate utilizing a dielectrically insulated electrode comprising:
• a process according to claim 8 wherein the pressure between the substrate and the insulated electrode is maintained at approximately atmospheric pressure.
• a process of coating a cylindrical, electrically conductive substrate utilizing a dielectric insulated electrode comprising:
• a process of coating an open-ended tin can having a longitudinal seam comprising:
• a process of selectively coating a substrate having a protuberance on the surface thereof to be coated comprising:
• a process of coating an indefinite length, electrically conductive article comprising:
• a process of coating a paper substrate comprismg:
• a process of providing a polymeric coating on paper at atmospheric pressure comprising:

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• Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• Plasma & Fusion (AREA)
• Treatments Of Macromolecular Shaped Articles (AREA)
• Physical Or Chemical Processes And Apparatus (AREA)
• Application Of Or Painting With Fluid Materials (AREA)
• Resistance Heating (AREA)

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Citations (4)

• 1964
  • 1964-09-23 US US398798A patent/US3415683A/en not_active Expired - Lifetime
• 1965
  • 1965-09-20 FR FR31962A patent/FR1515841A/fr not_active Expired
  • 1965-09-21 NL NL6512263A patent/NL6512263A/xx unknown
  • 1965-09-22 CH CH1308165A patent/CH441062A/de unknown
  • 1965-09-22 DE DE19651546972 patent/DE1546972A1/de active Pending
  • 1965-09-22 GB GB40455/65A patent/GB1105946A/en not_active Expired

Patent Citations (4)

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