CA1178644A - High-potential brush polarizer - Google Patents
High-potential brush polarizerInfo
- Publication number
- CA1178644A CA1178644A CA000393517A CA393517A CA1178644A CA 1178644 A CA1178644 A CA 1178644A CA 000393517 A CA000393517 A CA 000393517A CA 393517 A CA393517 A CA 393517A CA 1178644 A CA1178644 A CA 1178644A
- Authority
- CA
- Canada
- Prior art keywords
- bristles
- charge
- corona
- conductive
- reference member
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05F—STATIC ELECTRICITY; NATURALLY-OCCURRING ELECTRICITY
- H05F3/00—Carrying-off electrostatic charges
- H05F3/04—Carrying-off electrostatic charges by means of spark gaps or other discharge devices
Landscapes
- Brushes (AREA)
- Electrostatic Charge, Transfer And Separation In Electrography (AREA)
Abstract
ABSTRACT
The maximum subcorona potential level to which a particular conductive bristle brush is able to regu1ate an electrostatic charge on charge-retaining material is sub-stantially increased by limiting the electrical current available to said particular conductive bristle brush from a potential source coupled to said brush to a level that is less than a magnitude necessary for corona generation.
The maximum subcorona potential level to which a particular conductive bristle brush is able to regu1ate an electrostatic charge on charge-retaining material is sub-stantially increased by limiting the electrical current available to said particular conductive bristle brush from a potential source coupled to said brush to a level that is less than a magnitude necessary for corona generation.
Description
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BACKC:ROUND-OF THE INVENTION
1. Field of the Invention The present invention relates to apparatus for establishing a relatively uniform charge level on charge-re*aining material, in general, and to such apparatus for establishing a uniform charge level on a moving web of such material, in particular.
BACKC:ROUND-OF THE INVENTION
1. Field of the Invention The present invention relates to apparatus for establishing a relatively uniform charge level on charge-re*aining material, in general, and to such apparatus for establishing a uniform charge level on a moving web of such material, in particular.
2 Descri tion of the Prior Art p The presence of electrostatic charges on charge-retaining materials causes problems m many industries. In the photographic indus-try, for exa~ple, electrostatic charges on potential photographs or film units within a light-tight film cassette containing a plurality of film units for use in an "instant" type photographic camera, such as that sold by Polaroid Corporation, Cambridge~ Massachusetts, under its registered trademark SX-70, will often cling to one another with such intensity as a result of the force of attraction developed by such electrostatic charges, that proper ejection of an exposed film unit ~rom said film cassette can be prevented if the effects of such charges are not controll~d. In the SX-70 photographic ilm units mentioned above, for example~ electrostatic charges are controlled by controlling the charge levels on components of said film prior to final film unit assembly.
A brush-like device may be employed to establish a desired electrostatic charge level on a moving web of charge-retaining material by ; passing said web through a relatively intense electrostatic field gener-ated by said device when it is electrically connected to a rclatively low ~ ' ~ 7~
potential DC source of suitable magnitude and polarity. A ~-similar but more limited disclosure o~ said brush-like device is contained at page 70 ln the February, 1980, issue oE "Re-search Disclosure." ~ -;
A limitation of electrostatic charge-controlling conductive bristle brush apparatus presently employed to estab-lish an electrostatic charge on charge-retaining material is -~
the inability to place an electrical potential on such a brush that is much in excess of 4.5KV without generating a corona on said conductive bristle brush. While corona might be accep-table in many charge-retaining material, charge-controlling applications, it is generally unsuitable for use with materials that are sensitive to light such as materials incorporated in many photographic products. In addition, corona produces ozone, and ozone has an odor that may be offensive to personnel in the vicinity of the corona source.
In accordance with one aspect of the present inven-tion, there is provided improved apparatus for regulating charges on charge-retaining materials, comprising: a common electrical conductor; means for esta~lish:ing an electrically conductive reference member; a predetermined number of elec~
trically conductive bristles supported over said reference ~ -member with one end of each of said bristles being in an elec-trically coupled relation to said common conductor, said bris-tles extending from their said one end toward said reference surface with the free ends of said bristles being adjacent said reference member; means for limiting the electrical cur-rent available to said bristles from said power supply to le~ than a magnitude necessary to establish a corona field between any of said predetermined number of electrically con-ductive bristles and said reference member; and a DC power . ~
source connected between said common electrical conductor and said reference member, the potential of said power source having a predetermined magnitude and polarity for establishing an electric field that will adjust the electrosta-tic charge to the desired charge level on charge-retaining material passed between said free bristle ends and said reference member, a magnitude that would otherwise produce said corona field between a conductive bristle and said reference member in the absence of sa-id current limiting means.
The current limiting means may take the form of such things as a current limiting resistor or the addition of more conductive bristles in parallel with existing conductive bris-tles that limit and absorb, respectively, current necessary for the generation of corona, thereby preventing corona gener-ation at said current limited c:onductive bristle brush.
According to another aspect of the present invention, there is provided apparatus for producing a charge of given magnitude on charge-retaining materials, said apparatus com-prising: an electrically conductive reference member; a conduc-tive brush arrangement having a common conductive member wi-th a plurality of conductive bristles having one end thereof electrically coupled to said common member and ex,~ended in generally parallel relation therefrom; means for mounting said brush arrangement over said reference member with -the -free ends of said bristles extending toward said member for charging charge-retaining material as it is advanced bet~!een said reference member and said bristles; means for coupling a DC source of power to said reference member and said brush arrangement to produce an electrical field therebetween, the power supply being capable of voltages in excess of the minimum voltage necessary to produce corona between said brush arrange-ment and said reference member; and means for limiting thecurrent flowing between said brush arrangement and said refer-ence surface to a value less than that occurring with corona at said minimum votlage level whereby said material may be charged to comparatively high levels by electrical fields in excess of s~id minimum corona voltage without producing corona.
According to a further aspect of the present inven-tion, there is provided a method of producing a relatively high charge on charge-retaining materials, comprising the steps of: advancing said charge-retaining material across an electrically conductive reference member; mounting a conduc-tive brush arrangement having a plurality of conductive bris-tles over said reference member with the free ends of said bristles extending toward said member for charging said charge-retaining material as it is advanced between said reference member and said bristles; applying across said reference member ~;
and said brush arrangement a potential in excess of the mini-mum voltage necessary to produce corona between sa:id brush arrangement and said reference member; and limiting the current flow between sald brush arrangement and said reference surface ~-to a value less than that occurring with said corona at said minimum voltage level whereby said material may be charged to comparatively high levels by electrical fields in excess of said minimum corona voltage without producing corona.
The invention will now be described in greater detail with reference to the accompanying drawings, in which: ~
Fig. 1 is a perspective view of a mechanical schema-tic ~;
of conductive bristle brush-type charge-controlling apparatus constructed in accordance with the prior art, and a moving web of charge-retaining material having its electrostatic -3a-charge controlled by said apparatus.
Fig. 2 is an equivalent electrical schematic of the conductive bristle brush-type electrostatic charge-controlling apparatus depicted in Fig. 1.
Fig. 3 is a graph of conductive bristle bruch current as a function of brush-to-backing roller voltage of the prior art charge-controlling apparatus of Figs. 1 and 2.
Fig. 4a is an electrical schematic diagram of conduc-tive bristle brush-type electrostatic charge-controlling ap-paratus that incorporates the inventive concept of thepresentinvention.
Fig. 4b is a schematic diagram of an additional con-ductive bristle brush connected in parallel with the conductive bristle brush schematically illustrated in Fig. 4a.
Fig. 4c is an electrical circuit that approximates the electrical ~pedance between the conductive bristle brush and the backing roller in Fig. 4a when additional bristles ~-are employed.
Fig. 5 is a graph of conductive bristle brush current as a function of brush-to-backing roller voltage of the charge-controlling apparatus of the present invention that is depicted in Fig. 4a.
In order to facilitate describing the preferred embodiments of the present invention, a brief description of `
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electrosta~ic charge-contxolling apparatu~ presently available in the prior art, over which the present invention is an improve-ment 9 will be provided.
Turning now to the drawings, in Figs. 1 and 2, a perspective vi w o~ prior axt charge controlling apparatus co~trolling the electrosta~ic charge on a movi~g web v~ charge-retai~ing material 10 and a~ e~uivalent electrical schematic o~
~aid apparatus are respectively depicted. ~ roll o~ charge-retaining material 10 is moved over rotatably mou~ted cylindrical rollers 12, 14, 16 and 18 in direction 20 at the desired rate of web 10 movement by suitable drive means ~not shown) coupled to said web 10.
~rush 22 is mouAtod in a ~ixed posi~ion and in a spac~d relation with respect to web 10 and backing roller 16. The con-~truction of brush 22 will be described helow in detail. For the presen~, however, it should b~ ~oted that bursh 22 does include a multiplicity o~ conductive bristles or ~ilaments 24 with an end of each o~ said filaments being ~lec~rically connected to common . electrical conductor 26. ~acking roller 16 i~ constructed o~
olcc~rically conductiv~ matoxials and said roll¢r 16 is conn~ctcd to gxound potential through path 28. The output of power supply or DC po~ntial source 30 is connected to common electrical : conductor 26 throu~h path 32~ The input of power supply 39 is connected o a source o~ ~lectrical ~ner0y at termi~al 34 (not sho~Yn) through path 36. Power supply 30 a~d ~round~d b~ck~ng xollcr lG arc conncct~d to th~ same ~round poten~ial. When power supply 30 is e~ergizedt a relatively in~enss elec~rostatic ~ield is established between the free ends o~ briskles 2~ of . brush 22 and grounded backing roller 16. The u~e o a multi : 30 plici~y o~ conduc~ive bristles or filamen~s in the ~orm o~
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brush 22 coupled to a suitabl~ potential sourc~ results in an electrostatic fi~ld being established between brush 22 and ~oller 16 by means o~ an electrial potential whose magnitude is substan-¦ tially less than that necessar~ ~or the generation of corona.
The reason for being able to e~ablish a ~ela~iv~ly intense ~ield ¦ with a rela~ively low voltage will be explained below in detail.
As web 10 is moved in direc~ion 20 o~er roller 16 between the ree ends of bristles 24 and grounded roller 16, through the relative}y inte~e elec~rostatic field established between said freP bristle ends and said roller 16, electrostatic charges retain~d by said web 10 are controlled or regulated by said electrostatic ~i~ld. The magnitude and polarity of the brush potcnl-ial supplicd by po~ontial source 30 is ostablishod be~orc web 10 is so moved, by empixically determinin~ the electrostatic fie}d intensity necessary for the desired degree of web 10 electrostatic charge regulation.
In the apparatus of Fi~s. 1 and 2, brush 22 is spac~d ¦ a finite distance ~rom moving web }0. By so spacing said ~rush 22 from said moving web 10, the magnitude o~ ~he poten~ial applied to said brush 22 must be increased in order to obtain the same electrostatic ~ield intensity over a sLmilar arranCJement where bru~h 22 was i~ actual contact with web lOo This is so because the brush-to-web spacing introduces an el ctrical Lmpedance o~ resistance to the generation o~ an electros~atic ~ield between these components. The elec~ros~a~ic charge level on w~b 10 can be propcrly rogulated at lower ~C po~en~ial wh~n I bxush ~2 is in direct contact with said web 10. However, i scratching of the surface of web 10 may occur and such scratching ~¦ may rend~x portions of w¢b 10 uselcss ~or incor~or~ion in ~n ~0 end prvduct.
Brushes employed to control the charge level on charge-retaining materials such as web 10 in Figs. 1 and 2 usually have a bristle or filament density in excess o~ 120,000 filaments per square inch and preerably in ex-cess of 150,000 filaments per square inch. The number of square inches of brush filaments and the physical dimensions of a particular brush are deter-mined by considering such factors as speed of web movement, the initial web ~
charge level and the type of material of which the web is formed. If, as in ;
the charge-controlling arrangement of Figs. 1 and 2, a web such as web 10 is ~ -moved over roller 16 at a relatively high rate of speed, it may be necessary to employ two or more commonly connected brushes and space them about the circumference of said roller 16 if a single brush is insufficicnt to esta-blish the desired web charge level.
Brush 22 in Figs. 1 and 2 includes a multiplicity of conductive bristles 2~ with each of said bristles having one end connected to common electrical conductor 26, as previously noted. Bristles 2~ of said brush 22 are circular in cross-section and are normally constructed of conductive mate-rials such as conductive nylon or stainless steel. Practically any conductive material may be employed for use as bristle material so long as its electrlcal resistance is 500 megohms or less. Low resistances are not necessary because, unlike a corona-generated field, only a minute amount of current is utilized;
primarily for leakage and for dipole orientation.
It is a well-known electrical phenomenon that more intense electro-static fields can be generated at sharp angle or small radius of curvature surfaces for the same applied potential than at smooth or large radius of curvature surfaces. The most useful conductive bristle brushes have bristle diameters :;
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of 50 microns.or less. With a bxistle o~ this size, the surface at the tip or free end o~ said bristle forms a surface with a radius that approaches zero. With a radius of this magnitude, a relatively in~ense electrostati~ field can be generated at the tip of such a bristle with a pot~ntial that is well below the approximately 4.5 KV DC l~vel where a corona would normally ~irst appear and very o~t~n at a potential o~ 1.5 KV DC.
In the operation of the prior art apparatus of Figs.
¦ 1 and 2, web 10 is moved between the free ends of conductive 1 10 bristle brush 22 and backi~g roller 16 in direction 14 by drive means (not shown~ for the purpose of having its electrostatic charge level regulated by the electrostatic field esta~lished bc~woon brush 22 ~nd roll~r 1~. Thc intonsity o~ ~his Eicld is dependent upon the magnitude o the voltage between said brush 22 and said roller 16~ For every bursh 22-to-roller 16 voltage level there is a corresponding brush current level.
As noted above, this brush curre~t is primarily to compe~sate ~ox curren~ leakage and ~or web charging. A graph 38 o~ con-ductive bris~le brush current as a ~unction o~ brush 22-to~
roller 16 voltage is shown in Fig. 3. As shown in Fig. 3, once brush 22 current increases to current level 40, said brush current remains relatively constant between brush-to-roller voltages 42 and 4~. ~owever, if the brush 22-to-roller 16 voltage is increased beyond voltage lev~l 44, corona will be generated at said brush 22, and brush 22 curren~ will increase in order ~o sustain said corona. The prcsenc~ of corona i6 unacceptable in many el~ctxostatic charge-regulating applica-i tions, especially when regulating electrostatic charges on light sensitive materials. The generatio~ o~ corona at a particular ¦ 30 brush 22-to-roller 16 voltage 1 vel limits the maximum i, , , , . ,_ . . ~
electrostatic charge level that can be established on, for example, web 10 by brush 22 to a charge level corresponding to said particular brush 22-to-roller 16 voltage level i~ the . presence o~ corona is to be avoided. Th~ elect~s~tic ~harge . 5 regulating apparatus o~ the present inve~tion substantially increases the charge level to which a charge on charge-retaining material ca~ be regulated without gen~xating an undesirable corona.
~urning now to the present invention and to Fig. 4a, where apparatus incorporating a preferred embodiment of said present invention is depicted. Fig. 4a is an electrical schematic diagram of conducti~e bristle brush-type electros~atic charge-co~trolliny apparatus tha~ incorporates the sub-corona electro-. s~atic chaxge level increasin~ apparatus o~ the present i~vention.
In Fig. 4a, brush 46 is mounted in a fixed position and in a spac~d rela~ion with respect o both web 48 and electrically . conductive, rotatably mounted cylindxical bac~.ing roller 50.
The construc~ion of brush 46 is the same as that o~ brush 22 . describ~d above in Figs. 1 and 2. As discussed above, a brush . 20 such as brush 46 in Fig. 4a includes a multiplicity of conductivebristles or filaments 42 with an end o~ each of said ~ilaments being electrically connected to common electrical conductor 54.
Backi~g rolle~ 50 is constructed o~ ~lectrically conductive material and said roller 50 is co~nected to g~ound potential : 25 throu~h path 56. The input o~ power supply 58 is connected to a sourcc o~ ~lect~ical ene~cJy ~t ~erminal 60 ~ot shown) through path 62~ Power supply 58 and grounded backing roller 50 are :~ . connected to the same ground poten~ialO The output of power supply or DC potential source 58 is connected to curre~t limiting . 30 mcans 6~ through path 66 a~ thc output of curre~t limitiny m~ans ~..
- ~7~6~
64 is co~nected tO common electrical conductor 54 o~ conductive bristle brush 46 through path ~.
~ s web of charge-retaining material ~8 is move~ in direction 70 between conductive bristl~ brush 46 and grounded backing roller 50, at the desired rate of web 48 movement, by suitable drive means (not shown) coupled to said web 58, the ¦ electros~atic charge level on web 48 is changed to the desired charge level by the relative}y intense electrostatic ~ield established betwee~ ~nergized condu tive bristle brush 46 and electrically conductive backing roller 50. I~ the electrostatic charge level sough~ to be established onr fox example, web 48 by brush 46 is larger than a predetermined value,co~ona will be ~nerated at said brush 46 wh~n the magnitude of thc electrical potential on said brush 46 supplied by power supply 58 equals or exceeds said predetermined value. By employing an embodiment of the inventive concept of the presen~ invention, ~he electrical j potential on said brush 46 may be substantially in~reased above said predetermined electrical pctehtial value without producing corona.
In order to produce and/or sustain a corona, it is essential that su~icien~ current or ions be m~de available for ~ movement between the corona-generating electrode and an electrl-: cally conductive reference member. By contrast, in the prior art ~ sub-corona conductive bris~le brush-type electrostatic charge-; 25 controlling appaxatus Q~ Figs. 1 and 2, ~or example, only a . minimal amount o~ curren~ is necessary for proper co~rol of electrostatic charg~s on a charge-retaining material. Whereas . current in the order of milliamps is necessary ~or corona, ~ conductive bristle brush curren~ in the ~eiyhborhood of lQ
¦ 30 microamps is sufficient for electrostatlc charge~controlliny puxposesO
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, ~17~64~
Whether or not corona will be generated at, for exampleg brush 46 in the electrostatic charge-controlling apparatus of Fig. 4A, is primarily dependent upon the number and size of bristles 52 of brush 46 as well as the magnitude of the potential applied to said brush 46. If the number of bristles in brush 46 is large enough, the desired electrostatic charge level may be obtained before corona develops. However, if corona should develop at a brush potential level necessary to obtain the desired electrostatic charge level on a charge-retaining material, said corona can be suppressed by limit-ing the available current to a level that is below that necessary to generate and/or sustain said corona.
Current limiting means 64 in Fig. 4a limits the current avai.lable to conductive bristle brush 46 from potential or power supply 58 to less than a level necessary for the generation of corona. Current limiting means 64 may take any number of different forms. In Fig. 4b, for example, current limiting means 64 of Fig. 4a takes the form of additional conductive bristles 72 in conductive bristle brush 74. It is useful to consider bristles 52 of conductive bristle brush 46 to be analogous to a multiplicity of resistors, of equal value, that are connected between path 66, that is connected to the high voltage output terminal of power supply 58, and ground path 56 in ~ig.
4a. Such an arrangement is represented by resistors 52a, 52bg 52c, etc. in Fig. 4c. Bristles 72 of brush 74 are connected in parallel with bristles 52, which is analogous to adding resistors 72a, 72b, etc. in parallel with resistors 52a, 52b, 52c, etc. in Fig. 4c. In accordance with conventional electric circuit theory, by adding bristles 72 (resistors 72a, 72b, etc.) in parallel with bristles 52 ~resistors 52a, 52b, ~ ;
- - ~ 3l7~36~
52c, etc.) current ~rom power supply 58 in Fig. 4a tha~ would otherwise ~low through bristles 52 and generate corona is shun~ed through bristles 72 thereby suppressing corona generation.
If the placement of additional conductive bristles in parallel with existing bristles is either inappropriate or un desirable, current limitiny means 64 in the charge-controlling apparatus o~ Fig. 4a may take the form o~ a current-limiting resistor. The ohmic valvP o~ ~he reslstance of said resistor i must also be }arge enough to limit cur~ent to a level below that i 10 necessary for th~ generation of corona in order to suppress any i corona that would otherwise be produced by, ~or example, brush . 52 in Fig. 4a.
Whcther il: is thc bristlc increasing techni4ue I illustrated in Figs. 4b and 4c, ox ~he current limiting resistor mentioned above, the degree to which current ~hrough a conductive i bristle brush must be limited to preclude the generation o~ corona 'i is de~ined by the graph 76 of conductive bristle brush current as a function of brush-to-roller voltage depicted in Fig. 5. As shown I in ~ig. 5, without additional bristles or a current }imitingresistor, corona would begin to develop at brush-to-roller voltage . 78 as brush current changed in accordance with graph 80 in said Fig. 5. However, by adding more conductive bristles or a current . limiting resistor in the manne~ described above, corona would not develop until increased brush-to-roll~x voltagP level 82 was establ.ished between bxush 46 and roller 50 as brush Gurxent . changed in accordance with graph 76 in ~ig. 5.
~ The term "elec~ros~atic ~ield" employed herein means ¦ one species of electric field.
It will be apparent to those skilled in the art from the ~oregoing description of my invention that various improv~ments ' .
~L~ 7 8~
and modifications can be made in it wi~hout departing from its true scope. The embodiments described herein are merely illus-trative and they should not be ~iewed as the only embodimen~s that might encompa~ my inventLon.
~, 'I
A brush-like device may be employed to establish a desired electrostatic charge level on a moving web of charge-retaining material by ; passing said web through a relatively intense electrostatic field gener-ated by said device when it is electrically connected to a rclatively low ~ ' ~ 7~
potential DC source of suitable magnitude and polarity. A ~-similar but more limited disclosure o~ said brush-like device is contained at page 70 ln the February, 1980, issue oE "Re-search Disclosure." ~ -;
A limitation of electrostatic charge-controlling conductive bristle brush apparatus presently employed to estab-lish an electrostatic charge on charge-retaining material is -~
the inability to place an electrical potential on such a brush that is much in excess of 4.5KV without generating a corona on said conductive bristle brush. While corona might be accep-table in many charge-retaining material, charge-controlling applications, it is generally unsuitable for use with materials that are sensitive to light such as materials incorporated in many photographic products. In addition, corona produces ozone, and ozone has an odor that may be offensive to personnel in the vicinity of the corona source.
In accordance with one aspect of the present inven-tion, there is provided improved apparatus for regulating charges on charge-retaining materials, comprising: a common electrical conductor; means for esta~lish:ing an electrically conductive reference member; a predetermined number of elec~
trically conductive bristles supported over said reference ~ -member with one end of each of said bristles being in an elec-trically coupled relation to said common conductor, said bris-tles extending from their said one end toward said reference surface with the free ends of said bristles being adjacent said reference member; means for limiting the electrical cur-rent available to said bristles from said power supply to le~ than a magnitude necessary to establish a corona field between any of said predetermined number of electrically con-ductive bristles and said reference member; and a DC power . ~
source connected between said common electrical conductor and said reference member, the potential of said power source having a predetermined magnitude and polarity for establishing an electric field that will adjust the electrosta-tic charge to the desired charge level on charge-retaining material passed between said free bristle ends and said reference member, a magnitude that would otherwise produce said corona field between a conductive bristle and said reference member in the absence of sa-id current limiting means.
The current limiting means may take the form of such things as a current limiting resistor or the addition of more conductive bristles in parallel with existing conductive bris-tles that limit and absorb, respectively, current necessary for the generation of corona, thereby preventing corona gener-ation at said current limited c:onductive bristle brush.
According to another aspect of the present invention, there is provided apparatus for producing a charge of given magnitude on charge-retaining materials, said apparatus com-prising: an electrically conductive reference member; a conduc-tive brush arrangement having a common conductive member wi-th a plurality of conductive bristles having one end thereof electrically coupled to said common member and ex,~ended in generally parallel relation therefrom; means for mounting said brush arrangement over said reference member with -the -free ends of said bristles extending toward said member for charging charge-retaining material as it is advanced bet~!een said reference member and said bristles; means for coupling a DC source of power to said reference member and said brush arrangement to produce an electrical field therebetween, the power supply being capable of voltages in excess of the minimum voltage necessary to produce corona between said brush arrange-ment and said reference member; and means for limiting thecurrent flowing between said brush arrangement and said refer-ence surface to a value less than that occurring with corona at said minimum votlage level whereby said material may be charged to comparatively high levels by electrical fields in excess of s~id minimum corona voltage without producing corona.
According to a further aspect of the present inven-tion, there is provided a method of producing a relatively high charge on charge-retaining materials, comprising the steps of: advancing said charge-retaining material across an electrically conductive reference member; mounting a conduc-tive brush arrangement having a plurality of conductive bris-tles over said reference member with the free ends of said bristles extending toward said member for charging said charge-retaining material as it is advanced between said reference member and said bristles; applying across said reference member ~;
and said brush arrangement a potential in excess of the mini-mum voltage necessary to produce corona between sa:id brush arrangement and said reference member; and limiting the current flow between sald brush arrangement and said reference surface ~-to a value less than that occurring with said corona at said minimum voltage level whereby said material may be charged to comparatively high levels by electrical fields in excess of said minimum corona voltage without producing corona.
The invention will now be described in greater detail with reference to the accompanying drawings, in which: ~
Fig. 1 is a perspective view of a mechanical schema-tic ~;
of conductive bristle brush-type charge-controlling apparatus constructed in accordance with the prior art, and a moving web of charge-retaining material having its electrostatic -3a-charge controlled by said apparatus.
Fig. 2 is an equivalent electrical schematic of the conductive bristle brush-type electrostatic charge-controlling apparatus depicted in Fig. 1.
Fig. 3 is a graph of conductive bristle bruch current as a function of brush-to-backing roller voltage of the prior art charge-controlling apparatus of Figs. 1 and 2.
Fig. 4a is an electrical schematic diagram of conduc-tive bristle brush-type electrostatic charge-controlling ap-paratus that incorporates the inventive concept of thepresentinvention.
Fig. 4b is a schematic diagram of an additional con-ductive bristle brush connected in parallel with the conductive bristle brush schematically illustrated in Fig. 4a.
Fig. 4c is an electrical circuit that approximates the electrical ~pedance between the conductive bristle brush and the backing roller in Fig. 4a when additional bristles ~-are employed.
Fig. 5 is a graph of conductive bristle brush current as a function of brush-to-backing roller voltage of the charge-controlling apparatus of the present invention that is depicted in Fig. 4a.
In order to facilitate describing the preferred embodiments of the present invention, a brief description of `
-3b-,. ,i,", ~ -:
electrosta~ic charge-contxolling apparatu~ presently available in the prior art, over which the present invention is an improve-ment 9 will be provided.
Turning now to the drawings, in Figs. 1 and 2, a perspective vi w o~ prior axt charge controlling apparatus co~trolling the electrosta~ic charge on a movi~g web v~ charge-retai~ing material 10 and a~ e~uivalent electrical schematic o~
~aid apparatus are respectively depicted. ~ roll o~ charge-retaining material 10 is moved over rotatably mou~ted cylindrical rollers 12, 14, 16 and 18 in direction 20 at the desired rate of web 10 movement by suitable drive means ~not shown) coupled to said web 10.
~rush 22 is mouAtod in a ~ixed posi~ion and in a spac~d relation with respect to web 10 and backing roller 16. The con-~truction of brush 22 will be described helow in detail. For the presen~, however, it should b~ ~oted that bursh 22 does include a multiplicity o~ conductive bristles or ~ilaments 24 with an end of each o~ said filaments being ~lec~rically connected to common . electrical conductor 26. ~acking roller 16 i~ constructed o~
olcc~rically conductiv~ matoxials and said roll¢r 16 is conn~ctcd to gxound potential through path 28. The output of power supply or DC po~ntial source 30 is connected to common electrical : conductor 26 throu~h path 32~ The input of power supply 39 is connected o a source o~ ~lectrical ~ner0y at termi~al 34 (not sho~Yn) through path 36. Power supply 30 a~d ~round~d b~ck~ng xollcr lG arc conncct~d to th~ same ~round poten~ial. When power supply 30 is e~ergizedt a relatively in~enss elec~rostatic ~ield is established between the free ends o~ briskles 2~ of . brush 22 and grounded backing roller 16. The u~e o a multi : 30 plici~y o~ conduc~ive bristles or filamen~s in the ~orm o~
: -4-~l~'7~6~
brush 22 coupled to a suitabl~ potential sourc~ results in an electrostatic fi~ld being established between brush 22 and ~oller 16 by means o~ an electrial potential whose magnitude is substan-¦ tially less than that necessar~ ~or the generation of corona.
The reason for being able to e~ablish a ~ela~iv~ly intense ~ield ¦ with a rela~ively low voltage will be explained below in detail.
As web 10 is moved in direc~ion 20 o~er roller 16 between the ree ends of bristles 24 and grounded roller 16, through the relative}y inte~e elec~rostatic field established between said freP bristle ends and said roller 16, electrostatic charges retain~d by said web 10 are controlled or regulated by said electrostatic ~i~ld. The magnitude and polarity of the brush potcnl-ial supplicd by po~ontial source 30 is ostablishod be~orc web 10 is so moved, by empixically determinin~ the electrostatic fie}d intensity necessary for the desired degree of web 10 electrostatic charge regulation.
In the apparatus of Fi~s. 1 and 2, brush 22 is spac~d ¦ a finite distance ~rom moving web }0. By so spacing said ~rush 22 from said moving web 10, the magnitude o~ ~he poten~ial applied to said brush 22 must be increased in order to obtain the same electrostatic ~ield intensity over a sLmilar arranCJement where bru~h 22 was i~ actual contact with web lOo This is so because the brush-to-web spacing introduces an el ctrical Lmpedance o~ resistance to the generation o~ an electros~atic ~ield between these components. The elec~ros~a~ic charge level on w~b 10 can be propcrly rogulated at lower ~C po~en~ial wh~n I bxush ~2 is in direct contact with said web 10. However, i scratching of the surface of web 10 may occur and such scratching ~¦ may rend~x portions of w¢b 10 uselcss ~or incor~or~ion in ~n ~0 end prvduct.
Brushes employed to control the charge level on charge-retaining materials such as web 10 in Figs. 1 and 2 usually have a bristle or filament density in excess o~ 120,000 filaments per square inch and preerably in ex-cess of 150,000 filaments per square inch. The number of square inches of brush filaments and the physical dimensions of a particular brush are deter-mined by considering such factors as speed of web movement, the initial web ~
charge level and the type of material of which the web is formed. If, as in ;
the charge-controlling arrangement of Figs. 1 and 2, a web such as web 10 is ~ -moved over roller 16 at a relatively high rate of speed, it may be necessary to employ two or more commonly connected brushes and space them about the circumference of said roller 16 if a single brush is insufficicnt to esta-blish the desired web charge level.
Brush 22 in Figs. 1 and 2 includes a multiplicity of conductive bristles 2~ with each of said bristles having one end connected to common electrical conductor 26, as previously noted. Bristles 2~ of said brush 22 are circular in cross-section and are normally constructed of conductive mate-rials such as conductive nylon or stainless steel. Practically any conductive material may be employed for use as bristle material so long as its electrlcal resistance is 500 megohms or less. Low resistances are not necessary because, unlike a corona-generated field, only a minute amount of current is utilized;
primarily for leakage and for dipole orientation.
It is a well-known electrical phenomenon that more intense electro-static fields can be generated at sharp angle or small radius of curvature surfaces for the same applied potential than at smooth or large radius of curvature surfaces. The most useful conductive bristle brushes have bristle diameters :;
,. ~
~ ~7 8~ ~ ~
of 50 microns.or less. With a bxistle o~ this size, the surface at the tip or free end o~ said bristle forms a surface with a radius that approaches zero. With a radius of this magnitude, a relatively in~ense electrostati~ field can be generated at the tip of such a bristle with a pot~ntial that is well below the approximately 4.5 KV DC l~vel where a corona would normally ~irst appear and very o~t~n at a potential o~ 1.5 KV DC.
In the operation of the prior art apparatus of Figs.
¦ 1 and 2, web 10 is moved between the free ends of conductive 1 10 bristle brush 22 and backi~g roller 16 in direction 14 by drive means (not shown~ for the purpose of having its electrostatic charge level regulated by the electrostatic field esta~lished bc~woon brush 22 ~nd roll~r 1~. Thc intonsity o~ ~his Eicld is dependent upon the magnitude o the voltage between said brush 22 and said roller 16~ For every bursh 22-to-roller 16 voltage level there is a corresponding brush current level.
As noted above, this brush curre~t is primarily to compe~sate ~ox curren~ leakage and ~or web charging. A graph 38 o~ con-ductive bris~le brush current as a ~unction o~ brush 22-to~
roller 16 voltage is shown in Fig. 3. As shown in Fig. 3, once brush 22 current increases to current level 40, said brush current remains relatively constant between brush-to-roller voltages 42 and 4~. ~owever, if the brush 22-to-roller 16 voltage is increased beyond voltage lev~l 44, corona will be generated at said brush 22, and brush 22 curren~ will increase in order ~o sustain said corona. The prcsenc~ of corona i6 unacceptable in many el~ctxostatic charge-regulating applica-i tions, especially when regulating electrostatic charges on light sensitive materials. The generatio~ o~ corona at a particular ¦ 30 brush 22-to-roller 16 voltage 1 vel limits the maximum i, , , , . ,_ . . ~
electrostatic charge level that can be established on, for example, web 10 by brush 22 to a charge level corresponding to said particular brush 22-to-roller 16 voltage level i~ the . presence o~ corona is to be avoided. Th~ elect~s~tic ~harge . 5 regulating apparatus o~ the present inve~tion substantially increases the charge level to which a charge on charge-retaining material ca~ be regulated without gen~xating an undesirable corona.
~urning now to the present invention and to Fig. 4a, where apparatus incorporating a preferred embodiment of said present invention is depicted. Fig. 4a is an electrical schematic diagram of conducti~e bristle brush-type electros~atic charge-co~trolliny apparatus tha~ incorporates the sub-corona electro-. s~atic chaxge level increasin~ apparatus o~ the present i~vention.
In Fig. 4a, brush 46 is mounted in a fixed position and in a spac~d rela~ion with respect o both web 48 and electrically . conductive, rotatably mounted cylindxical bac~.ing roller 50.
The construc~ion of brush 46 is the same as that o~ brush 22 . describ~d above in Figs. 1 and 2. As discussed above, a brush . 20 such as brush 46 in Fig. 4a includes a multiplicity of conductivebristles or filaments 42 with an end o~ each of said ~ilaments being electrically connected to common electrical conductor 54.
Backi~g rolle~ 50 is constructed o~ ~lectrically conductive material and said roller 50 is co~nected to g~ound potential : 25 throu~h path 56. The input o~ power supply 58 is connected to a sourcc o~ ~lect~ical ene~cJy ~t ~erminal 60 ~ot shown) through path 62~ Power supply 58 and grounded backing roller 50 are :~ . connected to the same ground poten~ialO The output of power supply or DC potential source 58 is connected to curre~t limiting . 30 mcans 6~ through path 66 a~ thc output of curre~t limitiny m~ans ~..
- ~7~6~
64 is co~nected tO common electrical conductor 54 o~ conductive bristle brush 46 through path ~.
~ s web of charge-retaining material ~8 is move~ in direction 70 between conductive bristl~ brush 46 and grounded backing roller 50, at the desired rate of web 48 movement, by suitable drive means (not shown) coupled to said web 58, the ¦ electros~atic charge level on web 48 is changed to the desired charge level by the relative}y intense electrostatic ~ield established betwee~ ~nergized condu tive bristle brush 46 and electrically conductive backing roller 50. I~ the electrostatic charge level sough~ to be established onr fox example, web 48 by brush 46 is larger than a predetermined value,co~ona will be ~nerated at said brush 46 wh~n the magnitude of thc electrical potential on said brush 46 supplied by power supply 58 equals or exceeds said predetermined value. By employing an embodiment of the inventive concept of the presen~ invention, ~he electrical j potential on said brush 46 may be substantially in~reased above said predetermined electrical pctehtial value without producing corona.
In order to produce and/or sustain a corona, it is essential that su~icien~ current or ions be m~de available for ~ movement between the corona-generating electrode and an electrl-: cally conductive reference member. By contrast, in the prior art ~ sub-corona conductive bris~le brush-type electrostatic charge-; 25 controlling appaxatus Q~ Figs. 1 and 2, ~or example, only a . minimal amount o~ curren~ is necessary for proper co~rol of electrostatic charg~s on a charge-retaining material. Whereas . current in the order of milliamps is necessary ~or corona, ~ conductive bristle brush curren~ in the ~eiyhborhood of lQ
¦ 30 microamps is sufficient for electrostatlc charge~controlliny puxposesO
'~
_g .
, ~17~64~
Whether or not corona will be generated at, for exampleg brush 46 in the electrostatic charge-controlling apparatus of Fig. 4A, is primarily dependent upon the number and size of bristles 52 of brush 46 as well as the magnitude of the potential applied to said brush 46. If the number of bristles in brush 46 is large enough, the desired electrostatic charge level may be obtained before corona develops. However, if corona should develop at a brush potential level necessary to obtain the desired electrostatic charge level on a charge-retaining material, said corona can be suppressed by limit-ing the available current to a level that is below that necessary to generate and/or sustain said corona.
Current limiting means 64 in Fig. 4a limits the current avai.lable to conductive bristle brush 46 from potential or power supply 58 to less than a level necessary for the generation of corona. Current limiting means 64 may take any number of different forms. In Fig. 4b, for example, current limiting means 64 of Fig. 4a takes the form of additional conductive bristles 72 in conductive bristle brush 74. It is useful to consider bristles 52 of conductive bristle brush 46 to be analogous to a multiplicity of resistors, of equal value, that are connected between path 66, that is connected to the high voltage output terminal of power supply 58, and ground path 56 in ~ig.
4a. Such an arrangement is represented by resistors 52a, 52bg 52c, etc. in Fig. 4c. Bristles 72 of brush 74 are connected in parallel with bristles 52, which is analogous to adding resistors 72a, 72b, etc. in parallel with resistors 52a, 52b, 52c, etc. in Fig. 4c. In accordance with conventional electric circuit theory, by adding bristles 72 (resistors 72a, 72b, etc.) in parallel with bristles 52 ~resistors 52a, 52b, ~ ;
- - ~ 3l7~36~
52c, etc.) current ~rom power supply 58 in Fig. 4a tha~ would otherwise ~low through bristles 52 and generate corona is shun~ed through bristles 72 thereby suppressing corona generation.
If the placement of additional conductive bristles in parallel with existing bristles is either inappropriate or un desirable, current limitiny means 64 in the charge-controlling apparatus o~ Fig. 4a may take the form o~ a current-limiting resistor. The ohmic valvP o~ ~he reslstance of said resistor i must also be }arge enough to limit cur~ent to a level below that i 10 necessary for th~ generation of corona in order to suppress any i corona that would otherwise be produced by, ~or example, brush . 52 in Fig. 4a.
Whcther il: is thc bristlc increasing techni4ue I illustrated in Figs. 4b and 4c, ox ~he current limiting resistor mentioned above, the degree to which current ~hrough a conductive i bristle brush must be limited to preclude the generation o~ corona 'i is de~ined by the graph 76 of conductive bristle brush current as a function of brush-to-roller voltage depicted in Fig. 5. As shown I in ~ig. 5, without additional bristles or a current }imitingresistor, corona would begin to develop at brush-to-roller voltage . 78 as brush current changed in accordance with graph 80 in said Fig. 5. However, by adding more conductive bristles or a current . limiting resistor in the manne~ described above, corona would not develop until increased brush-to-roll~x voltagP level 82 was establ.ished between bxush 46 and roller 50 as brush Gurxent . changed in accordance with graph 76 in ~ig. 5.
~ The term "elec~ros~atic ~ield" employed herein means ¦ one species of electric field.
It will be apparent to those skilled in the art from the ~oregoing description of my invention that various improv~ments ' .
~L~ 7 8~
and modifications can be made in it wi~hout departing from its true scope. The embodiments described herein are merely illus-trative and they should not be ~iewed as the only embodimen~s that might encompa~ my inventLon.
~, 'I
Claims (8)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. Improved apparatus for regulating charges on charge-retaining mate-rials, comprising:
a common electrical conductor;
means for establishing an electrically conductive reference member;
a predetermined number of electrically conductive bristles sup-ported over said reference member with one end of each of said bristles being in an electrically coupled relation to said common conductor, said bristles extending from their said one end toward said reference surface with the free ends of said bristles being adjacent said reference member;
means for limiting the electrical current available to said bristles from said power supply to less than a magnitude necessary to esta-blish a corona field between any of said predetermined number of electrically conductive bristles and said reference member; and a DC power source connected between said common electrical con-ductor and said reference member, the potential of said power source having a predetermined magnitude and polarity for establishing an electric field that will adjust the electrostatic charge to the desired charge level on charge--retaining material passed between said free bristle ends and said reference member, a magnitude that would otherwise produce said corona field between a conductive bristle and said reference member in the absence of said current limiting means.
a common electrical conductor;
means for establishing an electrically conductive reference member;
a predetermined number of electrically conductive bristles sup-ported over said reference member with one end of each of said bristles being in an electrically coupled relation to said common conductor, said bristles extending from their said one end toward said reference surface with the free ends of said bristles being adjacent said reference member;
means for limiting the electrical current available to said bristles from said power supply to less than a magnitude necessary to esta-blish a corona field between any of said predetermined number of electrically conductive bristles and said reference member; and a DC power source connected between said common electrical con-ductor and said reference member, the potential of said power source having a predetermined magnitude and polarity for establishing an electric field that will adjust the electrostatic charge to the desired charge level on charge--retaining material passed between said free bristle ends and said reference member, a magnitude that would otherwise produce said corona field between a conductive bristle and said reference member in the absence of said current limiting means.
2. The apparatus of claim 1 wherein said corona current limiting means is additional conductive bristles supported in the same general orientation as said predetermined number of electrically conductive bristles with an end of each of said additional bristles being in an electrically coupled relation to said common electrical conductor.
3. The apparatus of claim 1 wherein said corona current limiting means is an electrical resistor of a predetermined ohmic value and said resistor is connected in series between said power source and said predetermined number of electrically conductive bristles.
4. The apparatus of claim 1 wherein the diameter of each of said conductive bristles is equal to or less than 50 microns.
5. The apparatus of claim 1 wherein said conductive bristles are formed of conductive nylon.
6. The apparatus of claim 1 wherein said conductive bristles are formed of stainless steel.
7. Apparatus for producing a charge of given magnitude on charge-retaining materials, said apparatus comprising:
an electrically conductive reference member;
a conductive brush arrangement having a common conductive member with a plurality of conductive bristles having one end thereof electrically coupled to said common member and extended in generally parallel relation therefrom;
means for mounting said brush arrangement over said reference member with the free ends of said bristles extending toward said member for charging charge-retaining material as it is advanced between said reference member and said bristles;
means for coupling a DC sources of power to said reference member and said brush arrangement to produce an electrical field therebetween, the power supply being capable of voltages in excess of the minimum voltage necessary to produce corona between said brush arrangement and said reference member; and means for limiting the current flowing between said brush arrangement and said reference surface to a value less than that occurring with corona at said minimum voltage level whereby said material may be charged to comparatively high levels by electrical fields in excess of said minimum corona voltage without producing corona.
an electrically conductive reference member;
a conductive brush arrangement having a common conductive member with a plurality of conductive bristles having one end thereof electrically coupled to said common member and extended in generally parallel relation therefrom;
means for mounting said brush arrangement over said reference member with the free ends of said bristles extending toward said member for charging charge-retaining material as it is advanced between said reference member and said bristles;
means for coupling a DC sources of power to said reference member and said brush arrangement to produce an electrical field therebetween, the power supply being capable of voltages in excess of the minimum voltage necessary to produce corona between said brush arrangement and said reference member; and means for limiting the current flowing between said brush arrangement and said reference surface to a value less than that occurring with corona at said minimum voltage level whereby said material may be charged to comparatively high levels by electrical fields in excess of said minimum corona voltage without producing corona.
8. A method of producing a relatively high charge on charge-retaining materials, comprising the steps of:
advancing said charge-retaining material across an electrically conductive reference member;
mounting a conductive brush arrangement having a plurality of conductive bristles over said reference member with the free ends of said bristles extending toward said member for charging said charge-retaining material as it is advanced between said reference member and said bristles;
applying across said reference member and said brush arrangement a potential in excess of the minimum voltage necessary to produce corona between said brush arrangement and said reference member; and limiting the current flow between said brush arrangement and said reference surface to a value less than that occurring with said corona at said minimum voltage level whereby said material may be charged to comparatively high levels by electrical fields in excess of said minimum corona voltage without producing corona.
advancing said charge-retaining material across an electrically conductive reference member;
mounting a conductive brush arrangement having a plurality of conductive bristles over said reference member with the free ends of said bristles extending toward said member for charging said charge-retaining material as it is advanced between said reference member and said bristles;
applying across said reference member and said brush arrangement a potential in excess of the minimum voltage necessary to produce corona between said brush arrangement and said reference member; and limiting the current flow between said brush arrangement and said reference surface to a value less than that occurring with said corona at said minimum voltage level whereby said material may be charged to comparatively high levels by electrical fields in excess of said minimum corona voltage without producing corona.
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US22233281A | 1981-01-05 | 1981-01-05 | |
US222,332 | 1981-01-05 |
Publications (1)
Publication Number | Publication Date |
---|---|
CA1178644A true CA1178644A (en) | 1984-11-27 |
Family
ID=22831776
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
CA000393517A Expired CA1178644A (en) | 1981-01-05 | 1982-01-04 | High-potential brush polarizer |
Country Status (4)
Country | Link |
---|---|
EP (1) | EP0055984B1 (en) |
JP (1) | JPS57164757A (en) |
CA (1) | CA1178644A (en) |
DE (1) | DE3272402D1 (en) |
Families Citing this family (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4457256A (en) * | 1981-01-05 | 1984-07-03 | Polaroid Corporation | Precharged web coating apparatus |
US4761709A (en) * | 1984-10-29 | 1988-08-02 | Xerox Corporation | Contact brush charging |
DE3867141D1 (en) * | 1987-06-19 | 1992-02-06 | Till Keesmann | DEVICE FOR CHANGING THE STATIC, ELECTRICAL POTENTIAL THROUGH CORONATE DISCHARGE ON THE SURFACE OF A MOVING ELEMENT, MADE FROM INSULATING MATERIAL. |
JPH08315956A (en) * | 1995-05-18 | 1996-11-29 | Kasuga Denki Kk | Corona discharge treatment method of vessel, and device therefor |
DE102008018920A1 (en) * | 2008-04-15 | 2009-10-22 | Lindauer Dornier Gmbh | Pinning electrode arrangement |
Family Cites Families (9)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US2774921A (en) * | 1953-04-23 | 1956-12-18 | Haloid Co | Apparatus for electrostatically charging insulating image surfaces for electrophotography |
NL292836A (en) * | 1962-05-17 | |||
US3308344A (en) * | 1965-03-04 | 1967-03-07 | Ener Jet Corp | High voltage antistatic apparatus |
DE2120397A1 (en) * | 1970-04-27 | 1971-11-18 | Progil | Removal of static charges from plastic film |
US3730753A (en) * | 1971-07-30 | 1973-05-01 | Eastman Kodak Co | Method for treating a web |
JPS5038938B2 (en) * | 1972-01-14 | 1975-12-13 | ||
CH574176A5 (en) * | 1973-11-30 | 1976-03-31 | Gruenenfelder H El Ing Eltex E | |
JPS5418737A (en) * | 1977-07-12 | 1979-02-13 | Sharp Corp | Electrophotographic method |
US4213167A (en) * | 1978-03-31 | 1980-07-15 | Cumming James M | Planar gas and ion distribution |
-
1982
- 1982-01-04 DE DE8282100013T patent/DE3272402D1/en not_active Expired
- 1982-01-04 EP EP82100013A patent/EP0055984B1/en not_active Expired
- 1982-01-04 CA CA000393517A patent/CA1178644A/en not_active Expired
- 1982-01-05 JP JP54882A patent/JPS57164757A/en active Pending
Also Published As
Publication number | Publication date |
---|---|
JPS57164757A (en) | 1982-10-09 |
EP0055984A3 (en) | 1982-09-29 |
EP0055984A2 (en) | 1982-07-14 |
EP0055984B1 (en) | 1986-08-06 |
DE3272402D1 (en) | 1986-09-11 |
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