WO2002098583A2

WO2002098583A2 - Method for plasma deposition of polymer coatings

Info

Publication number: WO2002098583A2
Application number: PCT/RU2002/000238
Authority: WO
Inventors: Gleb E. Bugrov; Konstantin V. Vavilin; Sergei G. Kondranin; Elena A. Kralkina; Vladimir B. Pavlov
Original assignee: Plasma Tech Co., Ltd.
Priority date: 2001-06-04
Filing date: 2002-05-17
Publication date: 2002-12-12
Also published as: RU2190484C1; WO2002098583A3; WO2002098583B1; AU2002309363A1

Abstract

The method of plasma deposition of polymer coatings involves locating a sample to be treated in a discharge volume, filling a discharge chamber (1) by means of a working gas supply system (2) with a reactive gas containing at least one plasma polymerizable gas-monomer, and plasma generation in the discharge volume through the ignition and maintaining of a pulsed-periodic gas discharge with a periodically repeated sequence of pulses. During plasma polymerization of the gas-monomer, a polymer coating is deposited onto the surface of the sample. To do that, a pulsed-periodic discharge is used with the total current variation time of a separate pulse within the range of from 10-7 s to 10-1 s. The time interval between separate pulses in each sequence of pulses is selected within the range of from 10-5 s to 10-2 s. The invention allows the efficiency of plasma polymerization process to be increased and continuous processing to be enabled.

Description

METHOD FOR PLASMA DEPOSITION OF POLYMER COATINGS

Field of the Invention

The invention relates to the method of deposition coatings onto metal and dielectric substrates, in particulai-, it pertains to the plasma polymerization technology and plasma generation process.

Prior Art Various plasma polymerization methods and plasma generation methods are currently used in the plasma technology. For example, the European Patent EP 0 152 256 A2 (IPC G02 Bl/10, published

21.08.85) describes the method of plasma deposition of polymer coatings onto optical articles and the plasma generation method used for realization thereof. The objective of the method is to provide the surface of optical articles (such as lenses) with a polymer coating preventing water from adhesion during operation in a gaseous medium or air bubbles during operation in the water. The polymer coating is also developed for retarding the formation of oil or fat spots on the articles surfaces. The known method consists of igniting and maintaining a high- frequency discharge in the mixture of oxygen and hydrocarbons, preferably aliphatic hydrocarbons. A substrate is placed in the discharge plasma and a polymer coating possessing predetermined properties is formed by deposition from a discharge volume. The US Patent US 4,693,799 (IPC C07C3/24, published 15.09.87) discloses the method of deposition a polymer coating to a film, which is passed between electrodes through the discharge volume, within which plasma is generated by a pulsed discharge. The discharge volume is filled with a mixture of hydrocarbons or mixture of organometallic compounds. Plasma is maintained at a low temperature by selecting predetermined characteristics of the discharge: the voltage increment time for each discharge pulse must not exceed 100 ms and the one-pulse time, i.e. time between separate pulses, must not be less than 1 ms. The optimal discharge time characteristics are selected depending on a reactive gas or gas mixture used. The coating formed on the film in accordance with this process has low friction coefficient, possesses the properties of a grease lubricant, has increased service life and high strength, and, furthermore, the film does not need additional lubrication when employed.

Another method of plasma deposition of coatings (the international application WO 91/12092, IPC B05 D 3/06, 3/14, 3/00, 3/02, published 22.08.91) uses a low-temperature plasma for deposition a corrosion preventive coating on a steel substrate. Plasma is generated in a vacuum chamber, which is filled with a mixture of gaseous hydrocarbons, by igniting a DC voltage discharge, with the steel substrate functioning as a cathode. Anodes are located around the cathode and equipped with a magnetic system for generation of a magnetic field above the anodes. A reactive working gas is supplied together with an inert gas into the vacuum chamber both at the stage of preliminary treatment of the substrate and in the process ofdeposition an organosilane film.

The polymer coating formation method is described in the European application EP 0 002 889 A2 (IPC C08F 2/52, published 11.07.79) and involves plasma generation by igniting a glow discharge. A metal substrate onto which a polymer coating is deposited serves as a passive electrode. An opposite electrode is connected to a high-frequency voltage source. A fluorocarbon gas is used as a reactive gas-monomer.

The closest prior invention pertains to the polymer coating deposition method and to the plasma generation method for implementing the same, which are disclosed in the international application WO 99/27156 (IPC C23 C 16/44, published 03.06.99). The known method involves plasma polymerization of a coating deposited onto a metal surface by means of plasma generated by a DC gas discharge, including a pulsed discharge. To do so, a metal sample to be treated is placed on an anode, a discharge chamber is evacuated to a predetermined vacuum extent and a reactive gas mixture is supplied into the discharge chamber until a predetermined pressure is established within the discharge chamber. The reactive gas mixture is of the type containing unsaturated aliphatic hydrocarbon gas-monomer (acetylene) or fluorine-containing gas-monomer and non-polymerizable gas (nitrogen). The partial pressure of the non-polymerizable gas is selected to be in the range of 50-90% of the pressure of the reactive gas mixture. Voltage is supplied to electrodes for igniting an electric discharge, which provokes generation of plasma containing positive and negative ions and radicals of unsaturated aliphatic hydrocarbons and non-polymerizable gas. As a result, a hydrophilic or hydrophobic polymer coating is formed on the surface of anode and, accordingly, on the surface of the sample under treatment process. Such polymeric coating may be deposited to ceramic and polymer samples by means of plasma generated through a high-frequency discharge.

Although the known method allows a coating with an increased adhesion to be produced, which may be further painted, and this coating improves the corrosion resistance of metal surfaces, the process of deposition a polymer coating goes at a low rate and, as such, has a limited industrial application. Besides, in the process of deposition a coating from the reactive gas mixture containing acetylene and nitrogen, rather large macroparticles are formed owing to polymer agglomeration (dust). When landed on the sample under the treatment process or on the parts of a processing apparatus, macroparticles deteriorate the quality of the coating formed and affect the efficiency of units and systems of the processing apparatus. On the whole, such drawbacks hinder regulation of the continuous process for deposition polymer coatings under the conditions of industrial production.

Disclosure of the Invention

The objective of the present invention is directed to provide a method of plasma deposition of polymer coatings and to implementation of plasma generation method, which are adapted to ensure a high-rate plasma polymerization process for producing articles equipped with a polymer coating on the industrial scale and to reduce the concentration of (dust) macroparticles in a reaction volume. The given objective is directly connected to the increase in a discharge volume of a concentration of radicals used in the plasma polymerization process. Such radicals are produced in the process of generation of gas discharge plasma. Another objective set forth is to create conditions for regulating the properties of deposited coating through controlling the parameters of the gas discharge and adjusting the reactive gas composition.

The solution of the mentioned objectives allows the efficiency of the plasma polymerization process to be improved by increasing the concentration of radicals in the generated plasma, the continuity of processing to be facilitated, the processing parameters to be effectively controlled and the quality of the coating deposited to be improved.

The above mentioned technical results may be achieved through implementation of the method of plasma deposition of polymer coatings, which involves the following processes: locating of a sample to be treated in a discharge volume; filling a reaction chamber with a reactive gas containing at least one plasma polymerizable gas-monomer; generating plasma in the discharge volume by igniting and maintaining a gas discharge between discharge electrodes and deposition a polymer coating onto the surface of the sample to be treated in the process of plasma polymerization of the gas-monomer. According to the present invention, plasma is generated by igniting and maintaining a pulsed-periodic discharge with periodically repeated pulse sequence. Such form of a discharge is a particular case of a pulsed discharge. The total time of current variation for a separate pulsed discharge is selected to be in the range

7 1 • of from 10^" s to 10^" s, and time interval between separate pulses in each pulse sequence is within the range of from 10^"5 s to 10^"2 s. The pulsed-periodic discharge is of the type resulting from the action of periodically recurrent sequence of voltage pulses (pulse burst) upon a gas discharge interval. Each discharge pulse includes a voltage increment time and a time of action of a separate pulse at predetermined amplitude. The shape of a separate pulse may be close to a rectangular or it may be shaped as a length of a sinusoid of high-frequency or superhigh-frequency (microwave) bands. When a voltage of predetermined value is supplied to the discharge electrodes, a breakdown in the gas gap occurs. As a result of transition from the breakdown stage to the stationary pulsed discharge stage, the electron concentration is increased by several orders of the magnitude for a short period of time. The electronic energy at the transition stage is therefore considerably higher than in the stationary mode of a direct- voltage discharge. Considering that molecule excitation, ionization and dissociation processes depend to a larger extent on the average electronic energy, the efficiency of the mentioned processes at short voltage discharge pulses is substantially higher than at the stationary DC discharge. An increase in a dissociation rate results in a growth of the number (concentration) of radicals in the discharge and in an increased rate of a polymerization process. An essential increase in the polymerization rate occurs if the total current variation time for a separate pulsed discharge, including the voltage increment time and the time of a separate pulse, is not less than the time required for obtaining the maximal rate of formation of radicals of optimal composition (with respect to the required properties of the polymer coating to be formed). On the other hand, the total time of current variation for a separate discharge pulse must not be less than the time required for the transition of the discharge to the stationary mode with of DC discharge. It has been established from the results of tests that, on the basis of the above mentioned conditions, the total current variation time for a separate discharge pulse must be

7 1 selected in the range of from 10^" s to 10^" -s. On the other hand, the life time of radicals after elapsing of a voltage pulse is much longer than the life time of electrons, so the time interval between the voltage pulses must be longer than the time of exit of electrons from the discharge volume to the walls of the plasma reactor discharge chamber, but less than the life time of radicals in the discharge volume. The given condition provides for continuous generation of active particles (radicals) used for plasma deposition of polymer coatings. To comply with the said condition, according to the results of tests conducted, the time interval between separate pulses in each sequence of pulses must be selected in the range of from 10^"5 s to 10^"2 s. Thus, the high rate of a plasma polymerization process is ensured by continuous maintaining (during the sequence of voltage pulses) of a high concentration of radicals in the gas discharge plasma generated.

To provide for continuous processing and the required quality of a deposited coating, the time of each sequence of discharge pulses and the time interval between each of the pulse sequences following one another must be selected in the range of from 10^"4 s to 10 s.

The given condition is related to the fact that when the concentration of polymer chains in the gas discharge plasma reaches a predetermined value, the polymer chains agglomeration process results in the formation of macroparticles (dust) in the discharge volume. When fallen on the sample under treatment process or on the parts of the processing apparatus, these particles substantially deteriorate the quality of deposited coating, provoke premature failure of the units and systems of the processing apparatus and, on the whole, hinder the regulation of a continuous process of deposition polymer coatings during the employment of industrial equipment. To reduce the probability of forming macroparticles in the discharge volume, the time of sequence of discharge pulses must be consistent with the time required for forming in the gas discharge plasma of polymer particles of the size optimal for the desired properties of the deposited coating. The time interval between each of the pulse sequences (bursts) following one another must be consistent with the time required for exit of heavy dust macroparticles from the discharge volume. The fulfilment of the given conditions is connected with the above mentioned time range, which is appropriate both for the time of each sequence of discharge pulses and for the time interval between each of the sequences (bursts) of pulses following one another.

It should be further mentioned that the reactive gas (mixture of gases) used in the process of plasma deposition of a coating may contain an inert gas. Prior to deposition a polymer coating onto the sample surface to be treated, it is advisable that the mentioned surface be preliminarily cleaned and modified. Cleaning and modifying processes may be effected in a gas discharge plasma in the medium of inert and/or reactive gases. In this particular case, the sample surface cleaning and modification processes should be equally taken into account when the type of gas is to be chosen. For preliminary cleaning and modifying the sample surfaces, different types of discharges may be employed: DC discharge, pulsed discharge, high-frequency discharge or superhigh-frequency discharge. According to another embodiment of the invention, ion beams and radicals of inert and/or reactive gases may be used in sample surface precleaning and modifying procedures (mentioned alternative refers to both cleaning and modifying processes).

Prior to deposition a coating on the sample surface to be treated, a protective and/or intermediate adhesive coating may be preliminarily deposited, in particular, by plasma deposition method.

After deposition a polymer coating onto the sample surface, the coating surface may be modified, for example, by using gas discharge plasma in the medium of reactive gases. The coating surface may be modified by means of different types of discharges: DC discharge, pulsed discharge, high-frequency or superhigh-frequency discharge. The coating surface modification may be effectuated by using ion beams of inert and/or reactive gases. To improve the efficiency of the modifying process, radicals generated in reactive gas plasma may be additionally used.

To provide for continuous processing during plasma polymerization, it is advisable to clean at least one of the electrodes from film by heating it to its decomposition temperature. Such cleaning process may be also carried out by means of an accelerated ion beam.

It is appropriate to employ a hollow cathode as one of the electrodes used for plasma generation.

It is desirable to provide for continuous controlling of plasma parameters in the process of plasma polymerization by means of optical plasma radiation detecting system. The above mentioned results are also achieved by realizing the plasma generation method involving the following operations: filling of the discharge chamber with a reactive gas containing at least one plasma polimerizable gas-monomer, igniting and maintaining a gas discharge between discharge electrodes. According to the present invention, the pulsed discharge is ignited and maintained at a periodically recurrent sequence of pulses. The total time of current variation for a separate discharge pulse is selected in the range of from 10^" s to 10^"1 s, and the time interval between separate pulses in each sequence of pulses is selected in the range of from 10^"5 s to 10^"2 s.

The time of each discharge pulse sequence and the time interval between each of pulse sequences following one another is preferably in the range of from 10^"4 s to 10 s. The reactive gas (mixture of gases) may contain an inert gas. A hollow cathode may be employed as one of the electrodes used for plasma generation. Brief Description of Drawings

The features and advantages of the invention will become more evident by reference to the accompanying drawings, which illustrate the following:

Figure 1 is a schematic representation of a plasma generation apparatus used in the process of plasma deposition of polymer coatings;

Figure 2 is a schematic representation of the unit for continuous process of plasma deposition of polymer coatings;

Figure 3 is a graphic representation of dependence of amplitude variation (voltage U) of pulsed-periodic discharge during the time T of periodically repeating pulse sequences.

Data Certifying the Feasibility of the Invention

Described below is an example of embodiments of a cluster of inventions dealing with the method of plasma deposition of polymer coatings and plasma generation method used in the plasma deposition process, which are realized during operation of a plasmochemical processing apparatus.

The plasma generation apparatus (see Figure 1) used in the process of plasma deposition of polymer coatings is incorporated in a plasmochemical reactor and is composed of a vacuum discharge chamber 1, a working gas supply system 2 and a gas evacuation system 3. Discharge electrodes 4 located inside the discharge chamber 1 may be formed as aluminum plates arranged one opposite another and separated by a distance of 100 mm. Such embodiment is generally used when a high-frequency power supply system is employed, which is illustrated in Figure 1. The power supply system includes a pulsed-periodic signal source 5 for supplying signals composed of one or several high-frequency signals (the so- called RF burst). The pulsed-periodic signal source 5 is connected through a matching system 6 to electric terminals of the discharge electrodes 4. Another embodiment may use a power supply system for generating rectangular voltage pulses. In this instance, a pulsed voltage source (not shown in the drawing) is accordingly connected to an anode and to a cathode, with the latter being preferably a hollow cathode.

The plasmochemical aluminum foil processing apparatus illustrated in Figure 2 is composed of a loading vacuum chamber 7 containing a rolled aluminum foil 8, a chamber 9 for cleaning and modifying foil surface, a strengthening and corrosion preventive treatment chamber 10, a chamber 11 for plasma deposition of polymer coating onto the foil 8 in a pulsed-periodic discharge, a chamber 12 for modifying the surface of a polymer coating produced, and a chamber 13, where the treated foil is wound under vacuum onto a bobbin core 14. Drums 14 of a foil transportation system are arranged in the mentioned chambers 7, 9, 10, 11, 12 and 13.

The polymer coating deposition method and the plasma generation method employed in the coating deposition process were realized as follows. To generate high-frequency discharge plasma by means of an apparatus illustrated in

Figure 1, the vacuum discharge chamber 1 was subjected to evacuation by means of the gas evacuation system 3 until pressure in the chamber reached the value not in the excess of 0.13 Pa. The working gas, in particular acetylene and nitrogen mixture, was supplied into the discharge chamber 1 by means of the working gas supply system 2. When the discharge chamber lis filled with the working gas mixture up to the pressure of 26.6 Pa, with working gas supplying and discharge chamber evacuating processes being carried out in continuous mode of operation, the sequences of repetition voltage pulses were supplied to the flat aluminum electrodes 4 spaced by a 100-mm distance one from another from the source 5 of pulsed-periodic signals (with RF-burst) through the matching system 6. Each pulse was presented in the form of a length of sinusoid at the frequency of 13.56 MHz. As a result, a pulsed-periodic discharge with periodically repeated sequence of pulses was ignited in the discharge volume of the discharge chamber 1. Electrons are retained in the discharge volume by means of an outside magnetic system (not shown in the drawing), which generated a nonuniform stationary magnetic field decreasing from the walls to the center of the discharge chamber 1.

The amplitude variation (voltage U) of the pulsed-periodic discharge for time interval T of periodically repeated pulse sequences is exhibited in Figure 3. The pulse on the graphically presented dependence is formed as an arbitrary RF voltage pulse envelope. The parameters of a pulsed-periodic discharge are time t₁ of voltage increment in each pulse, time t₂ of a separate voltage pulse, time t₃ between separate pulses in each sequence (burst) of pulses, time t₄ of each pulse sequence, and time interval t₅ between each of the pulse sequences (bursts) following one another (see Figure 3). The sum of t_\ and t₂ is the total duration of current variation for each separate discharge pulse, which must be, according to the present invention, not less than the time demanded for providing a maximum radical formation rate and less than the time of transfer from the pulsed discharge stage to the stationary discharge stage (at direct discharge current). In compliance with the given condition, the sum of time t] and time t is selected within the range of from 10^"7 s to 10^"1 s. In the example under consideration tι=10^~7 s, t₂=10^"5 s. Time t is chosen in the range of from 10^"5 s to 10^"2 s. In the example under consideration t₃=1.8 • 10^"5 s. With such time interval between separate pulses in each pulse sequence, electrons exit from the discharge volume and radicals used for deposition the polymer coating remain in the discharge volume thereby providing a continuous processing. Also, by additionally selecting times t₄ and t₅ in the range of from 10^"4 s to 10 s, a required quality of deposited coating may be ensured and a continuous operating life of the processing equipment may be increased. The given results are closely related to the created conditions at which the macroparticle growth in the discharge volume is essentially limited and the exit of heavy microparticles during time intervals between the pulse sequences is provided. In the example of embodiment under consideration, time t₄ of each discharge pulse sequence and time interval t₅ between each of the pulse sequences following one another are 2 - 10^"4 s.

When mentioned conditions are provided during the current sequence of pulses, the working gas molecules are dissociated, radicals are formed and polymerized, and polymer chain growth to a predetermined size occurs, in compliance with predetermined required qualities, during the time of supplying the current pulse sequence. After an elapse of a pulse sequence time, macroparticles stop growing and exit from the discharge volume. The given process is periodically repeated during the pulse sequences (bursts) following one another.

It was established on the basis of tests conducted that (according to the present invention) the usage of pulsed-periodic discharge with periodically repeated sequence of pulses during plasma deposition of polymer coating and, accordingly, during realization of plasma generation method used for plasma deposition of coatings a polymer coating with predetermined characteristics was formed on the aluminum electrodes 4. The polymer film deposition rate exceeded by approximately two times the respective polymer film deposition rate in a commonly used RF discharge at the working frequency of 13.56 MHz. Moreover, on providing for a pulsed-periodic discharge with time t₄ of each discharge pulse sequence and time intervals t₅ of 2 • 10^"4 s between pulse sequences following one another, the size of macroparticles settled on the chamber walls has substantially reduced. The parameters of gas discharge plasma, including the temperature and composition of the working gas mixture, were controlled by the detected nitrogen-acetylene radiation spectrum. The polymerization rate was controlled by the intensity of the CH spectrum band; the gas mixture composition by the ratio of intensities of bands CH, N₂, CN, CO, O₂, H₂, of lines H, N, O; plasma concentration by the ratio of intensities of bands N₂, N₂ ⁺; gas temperature by the rotational structure of the band of the second positive system of nitrogen molecules. In the process of generation of high-frequency discharge plasma by means of an industrial processing apparatus illustrated in Figure 2, the plasma deposition of polymer coating and the gas discharge plasma generation processes were effectuated under similar conditions (with regard to the apparatus illustrated in Figure 1). The polymer coating was deposited onto the aluminum foil 8 transported through processing chambers 7, 9, 10, 11, 12 and 13 by drums 14 of the foil transportation system. During plasma deposition of coating in a pulsed-periodic discharge with periodically repeated pulse sequence, the aluminum foil was connected to the pulsed current source and served as anode. A hollow cathode (or a set of hollow cathodes) was used as a pulsed-periodic discharge cathode arranged above the moving aluminum foil 8. A magnetic system was arranged outside the chamber 12 for a nonuniform stationary magnetic field in the discharge volume (not shown in the drawing) in order to enhance plasma density and consequently dissociation and polymer deposition rates..

The roll of aluminum foil 8 to be treated was located in the loading chamber 7, which was subjected to evacuation to the pressure value not less than 0.133 Pa. The aluminum foil was transported by the drums 14 of the foil transportation system into the chamber 9 where the foil surface was subjected to the cleaning and modification procedures. Plasma cleaning and modification of the foil surface provide for improved quality in the future treatment processes, which is due to the essentially improved adhesion as compared to the known chemical methods. However, when the surface to be treated is heavily contaminated with oils, it must be preliminarily subjected to chemical treatment.

Plasma cleaning and modification of the surface to be treated may be effectuated in different type discharges: direct current, low-frequency discharge, high-frequency discharge, superhigh frequency (microwave) or pulsed discharge, including pulsed periodic discharge. The treatment process may be carried out in different gaseous media. As an example, plasma treatment of a surface may be carried out in air, inert and reactive gases under atmospheric and reduced pressure. During plasma treatment of surface the potential of rolled foil or sample of other shape is preferably 50 ÷ 1,000 V lower than that of plasma. The plasma cleaning and modification processes may be also effectuated under high vacuum conditions by exposing the surface to be treated to ion beams of inert and reactive gases. Such treatment may be effectuated in inert and/or reactive gas media. Also, the surface to be cleaned and modified may be additionally subjected to the action of charged particles in plasma medium in the presence of radicals. Preliminary cleaning and modification of the surface may be carried out, in particular, through the usage of radicals produced in the reactive gas plasma. Plasma and/or radical fluxes may be generated by the known methods and means, including high-frequency induction discharge, hollow cathode discharge, etc. It is expedient to use an extended gas discharge for cleaning and modifying a aluminum foil during implementation of mentioned methods and means. On completing the procedures of cleaning and modifying the surfaces of aluminum foil

8, the latter is transported into the chamber 10 for further strengthening and corrosion preventive treatment. Such additional pretreatment process is required in the cases when the sample surface requires protection from corrosion or an intermediate layer must be deposited for improving the adhesion between the surface of the material and the basic polymer coating to be deposited. Such intermediate layer may be synthesized in a direct current gas discharge, low frequency discharge, high frequency discharge, superhigh frequency discharge and pulsed discharge, including in a pulsed-periodic discharge.

The aluminum foil 8 is then transported by means of the drums 14 of the foil transportation system into the chamber 11 where a polymer film is deposited by plasma deposition method onto the aluminum foil 8 in a pulsed-periodic discharge with a periodically repeated pulse sequence. A pulsed-periodic discharge is provided in the chamber 11 by means of the system of stationary hollow cathodes arranged above the surface of aluminum foil 8 to be treated (not shown in the drawing). When a substantially large area is to be subjected to plasma deposition, flat nets may be used as cathodes which are arranged above the surface of foil 8. During plasma deposition of the coating, cathodes are heated for preventing the cathode working surfaces from being covered with the polymer film. The cathodes are heated to the film decomposition temperature. Another embodiment of the invention implies utilization of accelerated ion beams for cleaning the cathodes from the deposited film.

Electrons are trapped in the discharge volume of the chamber 11 by means of an outside magnetic system for generating a stationary magnetic field reducing from the walls to the center of the chamber 11.

Radiation spectrum controlling of plasma parameters and gas composition is performed during plasma polymerization process in the chamber 11 through the usage of an optical plasma radiation detecting system (not shown in the drawing). By controlling gas discharge plasma parameters, the parameters of a pulsed-periodic discharge and also times ti through t₅ (see Figure 3) may be changed within predetermined ranges, and gas composition in the chamber 11 may be regulated for obtaining required characteristics of the polymer film to be formed. The mentioned procedures are effectuated with the employment of a controlled pulsed power supply source and controlled working gas supply system units. It should be pointed out that the above mentioned embodiment of the invention using the processing apparatus illustrated in Figure 2 does not exclude the possibility of generating a pulsed-periodic discharge with a periodically repeated sequence of pulses not only with the usage of a rectangular voltage pulses but also by connecting the discharge electrodes to the source of pulsed-periodic signals with a high-frequency burst (identical to the apparatus shown in Figure 1).

After deposition of a polymer coating in the chamber 11 on the surface of aluminum foil 8, the latter is transported into the chamber 12 for modifying the surface of deposited coating. Modification of the surface of deposited polymer coating is performed in a gas discharge plasma in the reactive gas media. The potential of the aluminum foil 8 is set to be less than that of plasma by 50 ÷ 1,000 V.

Modification of the coating surface may be effectuated by exposing it to the DC discharge, pulsed discharge, high-frequency discharge or superhigh frequency discharge in different gas media such as air, inert and reactive gases under atmospheric and reduced pressure. Modification of the surface with a polymer coating thereon may be also realized under the vacuum conditions through the usage of ion beams of inert and/or reactive gases. Radicals generated in the reactive gas plasma may be additionally used for increasing the efficiency of the coating surface modification process. Plasma, ions and radicals may be generated by known methods and means, such as an inductive discharge, a discharge in a hollow cathode, etc.

Upon completion of a final treatment process in the chamber 12, the aluminum foil 8 is moved by drums 14 of the foil transportation system into the chamber 13 where the treated aluminum foil is wound onto a core 14 of a bobbin.

According to the present invention, the method of plasma deposition of a polymer coating and the plasma generation method through the usage of the industrial processing apparatus allow the rate of deposition the polymer film on the aluminum foil to be essentially increased (by approximately two times) owing to the increase of radical concentration in the generated plasma during the treatment procedure. Besides, a desired quality of the sputtered polymer coating, including the adhesiveness of the polymer film, and a predetermined operating life of the processing apparatus during the continuous plasma polymerization process are ensured. The mentioned results are achieved due to a substantial reduction of macroparticles (dust) concentration in the discharge volume. The realization of the methods, according to the present invention, in the processing plasma chemical apparatuses also allows the properties of the deposited polymer coating to be controlled by altering the parameters of a gas discharge and regulating the working gas composition. It should be also mentioned that the patentable method of plasma deposition of a polymer coating may be implemented without utilizing additional coating surface precleaning and modification procedures, preliminary strengthening and corrosion preventive treatment (deposition of protective and/or intermediate adhesion coating), as well as without further modification of the surface of deposited polymer coating. The aforesaid procedures are mentioned only in the preferred embodiment of the invention, which may be implemented by means of the industrial processing apparatus illustrated in Figure 2.

Industrial Application

The invention may be used in different processes for forming hydrophilic and hydrophobic coatings, corrosion preventive protective coatings, electrically insulating coatings, and adhesive polymer coatings on the surfaces of articles of different purposes. The method of plasma deposition of polymer coatings and plasma generation method may be realized by means of processing equipment, in particular, apparatuses providing operation of a plasmochemical reactor. In addition, the plasma generation method may be employed in different gas discharge units, in particulai-, in ion sources of different purposes.

Claims

What we claim is: 1. Method for plasma deposition of polymer coatings including placing a sample to be treated into a discharge volume, filling a discharge chamber (1) with a reactive gas containing at least one plasma polymerizable gas-monomer, plasma generation in the discharge volume through the ignition and maintaining of gas discharge between discharge electrodes (4) and deposition of polymer coating onto the surface of the sample in the process of plasma polymerization of said gas-monomer, is characterized in that plasma generation is effectuated by igniting and maintaining a pulsed-periodic discharge with periodically repeated sequence of pulses, with total time of current variation for a separate discharge pulse

7 1 being selected within the range of from 10^" s to 10^" s, and time interval between separate pulses in each sequence of pulses being within the range of from 10^"5 to 10^"2 s.

2. Method as claimed in claim 1, wherein the time of each sequence of discharge pulses and time interval between each of the pulse sequences following one another is selected to be within the range of from 10^" s to 10 s.

3. Method as claimed in claim 1 , wherein a reactive gas contains an inert gas.

4. Method as claimed in claim 1, wherein the surface of a sample to be treated is preliminarily cleaned and /or modified prior to deposition a polymer coating thereon.

5. Method as claimed in claim 4, wherein the processes of preliminary cleaning and modifying the surface to be treated are carried out in a gas discharge plasma in an inert gas and/or reactive gas medium.

6. Method as claimed in claim 4, wherein a DC discharge, pulsed discharge, high-frequency discharge, or superhigh-frequency discharge is used for preliminary cleaning and modifying the surface to be treated.

7. Method as claimed in claim 4, wherein ion beams of inert and/or reactive gases are used for preliminary cleaning and modifying the surface to be treated.

8. Method as claimed in claim 4, wherein radicals generated in reactive gas plasma are used for preliminary cleaning and modifying the surface to be treated.

9. Method as claimed in claim 1, wherein a protective and/or intermediate adhesive layer is deposited by plasma deposition method onto the surface of a sample to be treated prior to deposition of polymer coating thereon.

10. Method as claimed in claim 1, wherein the surface of a coating deposited onto the surface of a sample is subjected to modification.

11. Method as claimed in claim 10, wherein the coating surface modification process is effectuated in a gas discharge plasma in said reactive gas-monomer medium.

12. Method as claimed in claim 10, wherein DC discharge, pulsed discharge, high-frequency discharge or superhigh frequency discharge is used for modifying the coating surface.

13. Method as claimed in claim 10, wherein ion beams of inert and/or reactive gases are used for modifying the coating surface.

14. Method as claimed in claim 10, wherein radicals generated in a reactive gas plasma are used for modifying the coating surface.

15. Method as claimed in claim 1, wherein at least one of electrodes (4) is subjected to cleaning by heating it to coating decomposition temperature during the plasma polymerization process.

16. Method as claimed in claim 1, wherein at least one of electrodes (4) is subjected to cleaning by means of an accelerated ion beam during the plasma polymerization process.

17. Method as claimed in claim 1, wherein a hollow cathode serves as one of discharge electrodes (4).

18. Method as claimed in claim 1, wherein said plasma polymerization process is accompanied with plasma parameters control effectuated by means of an optical plasma radiation detecting system.

19. Plasma generation method including filling a discharge chamber (1) with a reactive gas containing at least one plasma polymerizable gas-monomer, with the following igniting and maintaining of a gas discharge between discharge electrodes (4), is characterized in that a pulsed discharge with periodically repeated pulse sequence is ignited and maintained, with total time of current variation for a separate discharge pulse being selected in the range of from 10^"7 s to 10^"1 s and time interval between separate pulses in each sequence of pulses being selected in the range of from 10^"5 s to 10^"2 s.

20. Method as claimed in claim 19, wherein the time of each sequence of pulses and the time interval between each of the pulse sequences following one another are selected in the range of from 10^"4 s to 10 s.

21. Method as claimed in claim 19, wherein a reactive gas contains an inert gas.

22. Method as claimed in claim 19, wherein a hollow cathode is used as one of the discharge electrodes (4).