CA1036655A

CA1036655A - Process and apparatus for electrophotographic production of images

Info

Publication number: CA1036655A
Application number: CA210,858A
Authority: CA
Inventors: Eugen Mohn
Original assignee: Konica Minolta Inc
Current assignee: Konica Minolta Inc
Priority date: 1973-10-09
Filing date: 1974-10-07
Publication date: 1978-08-15
Also published as: DE2406161B2; JPS5089043A; FR2246898B2; FR2246898A2; CH564216A5; JPS5440021B2; DE2406161A1; SE7412647L; GB1468274A

Abstract

ABSTRACT OF THE DISCLOSURE
The disclosure relates to a method of producing pictures and an apparatus for carrying out the method and a use for the method. The present invention relates to a method of producing images in accordance with a master, which method is characterized by the fact that by exposure, as a function of the master, of a photoconductive layer onto or into said layer, there is produced a conductivity image which corresponds to the master and which is utilized to control, within a space adjacent said layer, an electrical field through which charged toner particles are moved, whereby the charge of toner particles which contact the said layer or a support for an image close to it is varied, and in a further method step, upon the disconnecting of the said electrical field, toner particles migrate in accordance with the master to the support for the image. The invention disclosed also concerns the use of the process for producing single coloured or multi-coloured pictures.

Description

1 1~3~i655 The present invention relate~ to a method of producing pictures. The invention refers to an apparatus for carrying " . -out the method and to a use of the method.
, For the production of pictures various electrophotographic I
i methods are already known~ In them a photoconductive layer I ~ ;
7 ,, iS imparted a uniform electrostatic charge and then exposed 7 l in accordance with a master copy. By the selective discharge ~ which takes place in this connection as a function of the y ~ master copy there is produced a latent electrostatic charge ~ image which corresponds to the master copy. This latent image 1' can be developed directly by known methods and then possibly ~2 il transferred to a support by the so-called image transfer process.
However, it is also possible to transfer the charge image to , I a suitable support by the so-called charge transfer process before it is developed and only then develop it~
!' However, there have also been proposed electrophotographic - processes which operate without the production of a latent electrostatic charge image. These methods are based on the ~ variable conductivity of a conductivity image corresponding ,~ to a master copy and produced in or on a photoconductive layer and electrolytic production of the image (cf. US Patent 3,130, `; 655). It has also been proposed to produce an electrostatic ;:~ charge image on the surface of a photoconductive layer as a ~i function of such conductivity image by means of a semiconductive ? , layer which is in close contact with the photoconductive layer

2~l (cf. UK Patent 797,027).
~ Finally, it is known to produce an image on a semi-2P I conductor by electrophoretic precipitation of colloidal 29 I particles (see the article "Methods for Producing Photographic 30 I! Images on Semiconductor Surfaces by Precipitation of Colloidal ¦
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3~i6~ l ~ticles arld by Electrophoresis," by ~. I. Bocllkareva, L. G. ,~
^ ' Paritskii and S. M. Ryvkin, A. F. Ioffe, Physicotechnical . i Institute, Academy of Sciences of the USSR, Leningrad, translated from Fizika i Tektnika Poluprovodnikov, Vol. 5, ,'l No. 5, pp. 900-903, May 1971).
Known electrophotographic processes for producing 7 ¦¦ ~mages have considerable disadvantages, particularly when 8 ! they serve for the production of colored images, for instance:
~ i~ 1. A high-voltage corona is required for the charging IU I of the photoconductive layer.
2. The high-voltage corona results in damage or impair- ¦ -ment to the photoconductive layer.
3. Undesired production of o~one.

4. Several transfer steps are necessary.

5. The production of e~act images is difficult or , complicated. i ;~
'~ 6. The exact repYoduction of half tones and mixed colors is very difficult due to the steep photographic , ;
; characteristic in these processes.
;! 7, If a paper provided with a photoconductive layer '; ~ is used in order to circumvent transfer steps, extremely complicated toner material is necessary in order to master the difficultieq of the electrophotographic process as a result 2~l, of the first and second partial images which have already ¦ ¦~
been produced on the paper. Electrolytic development of a conductivity image gives an image on the surface of the photo- 1 -~7 ' conductor, which image must then be transferred in an image ~ I transfer process. Furthermore, in this case each step, i.e.
29 ,l each partial image, requires a large amount of time, for 30 instance about 20 minutes. 5 Il . " :' ''', ~ 2- ~

`' ~Q3~i~5i5 8. Charge-transfer methods, while they permit almost simultaneous exposure and development, nevertheless require image transfers onto the final support which affords considerable difficulties in the production of exact images, for instance with respect to the exact covering of the individual partial color images.
m e object of the present invention is to provide a simple and rapidly operating method for the rapid and precise production of images, preferably for oolored images, and also an easily handled apparatus for carrying out the process which does not have the said disadvantages.
m e present invention relates to a method of producing images in accordance with a master, which method is characterized by the fact that by exposure, as a function of the master, of a photoconductive layer onto or into said layer, there is produced a conductivity image which corresponds to the master and which is utilized to control, within a spa oe adja oent said layer, an electrical field through which charged toner particles are moved, whereby the charge of toner particles which contact the said layer or a support for an image close to it is varied, and in a further method step, upon the disconnecting of the said electrical field, toner particles migrate in accordan oe with the master to the support for the image.
More particularly, the invention is a pro oe ss for electrophotographic image production from an original, in which a photoconductive layer is exposed in dependence upon the original and a conductivity image corresponding to the original is thereby produced on or in the layer. m e conductivity image controls a field produ oe d by two electrcdes in a spa oe between the photoconductive layer anda support iSprovided to support the image which is to be produced. Electrically charged toner particles are mLved by this field in the spa oe , the polarity of the charge of the toner particles being opposite to that of the electrode associated with the photoconductive layer in a positive process. m e electric field is subsequently made to break dcwn so that in the positive pro oe ss, toner particles migrate fram the ~ -3-., . .. , . ~ , 1~3f~6S5 photoconductive layer to the support and produce on it the image correspond-ing to the original and in a reversal process, the toner particles migrate from the support to the photoconductive layer and hen oe leave a negative image of the original on the support. m e pro oe ss is characterized in that a potential is applied at least to the circumferential surface of a cleaning roll which is moved over the support on which an image has just been produced in order to remove ex oe ss toner dispersion from the image. m e potential has the same polarity in relation to the earthed electrode on which the support is arranged as the charge of the toner particles used for producing 0 the image.
m e invention also relates to an apparatus for the carrying out of said process which is characterized by a first electrode and a second electrode, which electrodes may ke optionally connected to a source of voltage or to each other, the first electrode having associated with it a photoconductive layer which can ke exposed by imaging means in accordance with a master, and a support for an image is arranged on the second electrod~e and a medium having charged toner particles can be introduced in the spa oe between the two electrodes.
m e inventive aFparatus, more particularly, is used for carrying out the pro oe ss according to claim 1 and is comprised of a first and second electrode, switching means to connect these electrodes selectively to a so~r oe of voltage or to each other, and a photoconductive layer associated with the first electrode. Copying means is provided for copying an original onto the photoconductive layer, a support is arranged on the second electrode to support the image which is to be produced of the original, and means is prcvided for introducing charged toner particles into the spa oe between the photoconductive layer and the support. A cleaning roll is provided for the purpose of removing ex oe ss toner dis~ersion from an image which has just been produced, the cleaning roll being adapted to be displaceable relatively to and over the support for the image. m e apparatus is characterized in that at least the circumferential surfa oe of the cleaning roll is adapted to be oonnected to a voltage sour oe in such a manner that in relation to 3a-~:

1!:1!36~i55 an electrode on which the support for the imag~isarranged~ the circumferential surfa oe of the roll has a potential equal in polarity to the charge on the toner particles used for producing the image.
The invention also concerns the use of the said process for producing single-colored or multi-colored pictures.
The invention furthermore relates to pictures produ oe d by the said method.
The invention will ke explained in further detail kelow with reference to the drawing in which:
Fig. 1 is a schematic showing of the apparatus, not drawn to scale, Figs. la, lb, lc shcw three phases of the generation of the i~age, Fig. 2 shows a second diagrammatic emkodiment, Fig. 3 shows details of a first holding device of emkodiment of Fig. 2, Fig. 4 shows a portion of Fig. 3, Fig. 5 shows details of a second holding devi oe of the embodiment of Fig. 2, Fig. 6 is a diagrammatic representation of an apparatus for carrying out the process.
In all figures, corresponding parts have keen provided with the same referen oe numbers.
Fig. 1 is a diagrammatic view of a first embodiment of an apparatus for the carrying out of the said method. This figure shows merely the kasic construction of the arrangement in order to explain the mEnner of -operation and is not drawn to scale.
A first electrode 1 is formed by a transparent glass plate 2 which is oovered on one side by a thin, transparent, conductive layer 3.
m is conductive layer 3 can consist, for instance, of tin oxide, as is the case in the kncwn Nesa glasses. On the conductive layer 3 there is applied a photoconductive layer 4, for instan oe of panchromatically sensitized _4_ ~36655 `~ly-(N)-vinyl carbazole. The sensitizing can be effected, :j ., ; ' for instance, by adding a small amount of tetranitrofluorenone ^; I (TNF). The thickness of the photoconductive layer 4 is so -selected that it absorbs light in the visible spectral range and does so in such a manner that the light activates the layer in its entire thickness. For a layer of polyvinyl carbazole, 7 the thickness of the layer is preferably about 10 to 100 u.
! Facing the photoconductive layer 4 of the electrode 1 and equidistant at a slight distance therefrom, for instance a few tenths of a millimeter, there is arranged a second 7 1l electrode 5, for instance an aluminlm plate. A support 6 for an image, for instance a sheet of paper, lies on the second electrode 5 in good contact with it. The distance d between ~, the photoconductive layer 4 and the image support 6 is j ;;
- , preferably not greater than about 300 ~ and at most about 2mm.
,,As support 6 there is suitable a large number of materials which have suitable values of electric volume resistance and surface resistance. Thus, for instance, normal typewriter paper is well suited, but a plastic sheet, a plate of glass, a metallic foil or a textile material such as a woven or knitted fabric can also be used.
~. l In the space 7 between the photoconductive layer 4 : ; and the picture support 6 there is contained as medium a dispersion 8 of colored toner particles 9 in an organic liquid 10 of high ohmic value which assumes a given ZETA potential , .
`~ ~ as a result of the addition of a charge-control agent. In-'~7 ' formation as to suitable materials will be given later on.
From a master 11, for instance a slide, an image is pro-~ ¦ jected by optical focusing means 12 through the transparent 30 'l electrode 1 onto the photoconductive layer 4. As imaging !j ¦
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' 1~366S5 ~ans 12 there is suitable, fo~ instance, a slide projector ¦
, l~ having a source of light 12A, a condenser 12B, a color slide as master 11 and an objective 12C, which are only diagram-1 ' matically indicated in Fig. 1. However, other imaging means 5 ~l of ~nown type can be used which produce an image corresponding ~ to a master 11 on the photoconductive layer.
7 !1 For the reproduction of colored pic~ures, suitable P.~l partial color pictures and toner materials are used in successior ~. -~ '1 Further information will be given later on.
1DThe electrode 1 of the photoconductive layer 4 is connected via a switch 13 either to the one terminal~ in the I -present example the negative terminal, of a source of current 14, or to the second electrode 5. The second electrode 5 is connected to the other terminal, in this case to the positive terminal of the source of voltage 14, and preferably also to ground.
The dispersion 8 contains toner particles 9 preferably of the order of magnitude of 0.1 to 50 u. The organ~c liquid 10 preferably has a resistivity of about 106 _ 1014 ohm cm.
As color for the toner particles 9 there is selected for the ` production of colored images preferably in each case one of the sub~ctive primary colors cyan, magenta or yellow. The toner concentration can vary approximately within the range from ~ l 0.1 to 10 percent by weight. I
:~ The distance between the support 6 and the photo- !
i condùctive layer 4 is preferably approximately in the range of 7 ' ` 20J~ to 500JU. At least during a part of the exposure time ijl of the photoconductive layer 4 an electric field having a 2~ , field strength of about 1 to 100 volts/Ju is present between the two electrodes 1 and 5, depending upon the sensitivity of the photoconductive layer 4 as well as the charge of the toner .1 .
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3t~655 ~ticles. Color filters for the image produced on the photoconductive layer 4 are to be provided for the production ~ ;
of colored images, namely for the additive primary colors ' red, green and violet. There are suitable for this purpose, ; ,j for instance, the following Agfa-Gevaert separation filters:
~ red L599

7 I green U525 violet U438 ~ ' During the exposure time which, depending on the io ~ intensity, lies within the order of magnitude of about a few tenths of a second to a few seconds, the voltage amounting ~2 ,, to about 500-3000 volts is applied by means of the switch 13 i~ to the electrodes 1 and 5 in order to produce the said elec~
trical field. After the exposure the electrical field is dis-connected. i.e. the two electrodes are connected directly ~: ' with each other by actuating the switch 13. As a result of . ., .:
this, due to the action of the electrical field, an extremely `
rapid migration of the charged toner particles takes place.
Upon contact with the photoconductive layer 4 or with the i support 6, changes in charge of the corresponding toner particles occur. After removal of the previously applied voltage, i.e.
.`:?, after the two electrodes are connected with each other, a ~` migration of toner particles takes place to the surface of the , support 6 on which there is deposited a partial color image which corresponds to the conductivity image, corresponding to I ;
the master 11, of the photoconductive layer 4. ¦ ;-~7 l, A possible explanation for the conditions and processes occurring in the space 7 will be given now with reference to ~9 ,I Figs. la! lb, and lc.
30 1l In the first phase~ shown in Fig. la, the two elec-.~ ''' . .
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~a~3~;655 1 ~ ~~rodes 3 and 5 are directly connectecl witl-l each other ~ia the ? ;I switch 13 whicll is in its position 13'. The colored toner ` I particles 9 are in any desired distribution in the liquid 10.

; In the present example these toner particles are assumed to , have a positive charge.
!j i In the second phase, shown in Fig. lb, the two elec-trodes 3 and 5 are connected to the two poles of the source of voltage 14 via the switch 13 which is now in its position 13".
As a result of the exposure of the photoconductive layer 4, there is prodl~ced a conductivity ima~e which corresponds to the specific color separation of the master 11. Below the struct~re of the electric field in the space 7 which is de~
pendent on said conductivity image, the positive toner particles 9 (cf. Fig. la) migrate in the direction towards the elec-trode 4 and only those of them which strike a place on the photoconductive layer which has become conductive by the exposure will give off their positive charge. The particles 9~which impinge upon the nonconductive places retain their charge.
In the third phase, shown in Fig. lC, the two elec-trodes 4 and 5 are again directly connected with each other by the switch 13 which as been brough again into position 13' and the positive particles 9' migrate in the direction towards the electrode 5 which is at zero potential, they forming on the support 6 a color deposit 9" corresponding to the conductivity image of the photoconductive layer 4.
The formation of this color deposit takes place very rapidly, i.e. in less than one second after the switching of the switch 13 back into its original position 13'. The behavior of the toner particles has been described above with reference to Figs. la to lc only with regard to the two .," .

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' I 1~36655 I:
1 1I F icles 9 or 9' or 9". Of course, sirnilar behavior applies I -2 1I to the other particles in the dispersion 3.
3 I Thereupo~ the image support 6 is preferably pulled off ;~;
4 11 laterally, for instance together with the electrode 5.
5 ¦¦ The first partial color image obtained is dried preferably on 6 1l its surface, whereupon the process is repeated with another 7 ¦I color filter and corresponding toner material and the third 8 ¦¦ partial color image is produced on the image support 6 in

9 li analogous fashion with a third color filter and third toner

10 . materiaL. .~ .
~ For the production of the three partial color images, 12 1,l there is preferably maintained a specific sequence depending ,i on the properties of the toner materials, for instance the sequence yellow, magenta, cyan, which is customary in conven-tional color printing technique.
The photoconductive layer is preferably protected by 7 ,1 a thin protective layer against mechanical and chemical attack -; -1~ in order to obtain a longer life of use for this layer. Teflon, ~ SiO2 or else silicon nitrides are suitable, for instance, for 2~ , this protective layer.
Of course, the photoconductive layer 4 on the first ?2 1ll electrode 1 must be cleaned before each change in color, ;' l which, however, can easily be done due to the merely small 2~ quantity of dispersion 8.
Il The finished color image produced with all three 2n ¦¦ partial color images can furthermore be sprayed with a colorless 27 I lacquer in order to fix and increase the transparency and then 28 dried, for instance by passing it along a source of heat radiation.
~, For the protection of the photoelectric layer 4 upon its . I ~;, ~- .. ' ¦ ! . 1 Il _9_ Il ..... ' I J ~366S5 ~ ~posure an infral-e(i fi]ter can preferably be provided, whereby 2 11 the photoconductive layer 4 is protected against warTning up.
3 i11 At the same time an improvement of the reproduction of red in ~ colored pictures can be obtained hereby.
s The method described has a number of advantages over S 1l kno~n image-producing method~ which do not occur in this 7 ¦~ combination in any of the known methods, namely:
S ¦¦ 1. Possibility of being able to use ordinary paper 9 ~¦ as paper support, lQ ,~ 2. No charging of a photoconductive layer necessary,

11 11 3. No development of ozone,

12 l¦ 4. No problems in obtaining an exact registering of '3 il partial color images since the relative position of the original and of the copy is unchanged during each color process and can be otained for the differenct partial color images by simple mechanical stops. The picture support 6 remains on the electrode unchanged for all partial color images, 5. Excellent reproduction of half tones and mixed colors, ,i i 6. Direct production of images on the final image '; 1l support without transfer steps, 22 1 7. Separation of image on the support during the 2~ il breakd~wn - itself very short - of the electrical field within 2:~¦ fractions of a second.
25 1I Since on basis of Fig. 1 the development and manner ~6 1l of operation of the first embodiment of an apparatus for the 27 1~ carrying out of the said method has been described and 28 1 explained~ a second embodiment will now be described with 29 reference to Figs. 2 to 5.
30 ¦j In acccrdance with the seccnd embodiment, various . , . :

36~SS
thod steps tlecessary in ~he course of the production of a colored picture are ~acle automatic.
~ l The apparatus 100 shown in Fig. 2, is provided, as J 1l imaging means 12, with a slide projector the construction of i~ which is known and which is therefore only shown schematically.
6 I A color slide serving as master ll is inserted into the slide 7 I projector in the direction indicated by the arrow 15.
8 A shutter 16 is arranged behind the imaging means 12. As ~ shutter 16 there can be used a shutter which is known from use in cameras. The shutter 16 serves to set the exposure time 1i ll necessary for producing the conductivity image.
~2 1l One of three color filters 18, 19l 20 can be inter-

13 ! posed in the beam path 17 of the slide projector. Each of ~ I these color filters serves to produce the corresponding color ~ 1:
i~ ll separation or partial color image. As color filters 18, 19 -~
'.. ~l and 20 there are suitable, for instance, Agfa-Gevaerta 1 separation filters red: L599, violet: U438, and green: U525.
! , ? Preferably there can also be provided a gray filter which can ,~ ~ be inserted where necessary in the path of the beam of light in order to adjust the intensity of illumination in the case ~I,, of masters of different average brightness in such a manner -.2 ,~ that the same exposure time is always required, regardless L2î i~ of the ~aster.

2~ l~ Via a mirror 22 which is inclined 45 to the ~5 l horizontal, the beam path 17 is deflected downward onto the 26 1l¦ first electrode 1 bearing the photoconductive layer 4, which ~7 1¦ is arranged horizontally in a first holding device 23~ ;

28 I By means of a line 24 the first electrode 1 and its conductive 29 ¦ layer 3 are connected with the switch 13. The first electrode 1 1 30 ¦ can be connected via the switch 13 either with the one terminal l ". ', I ....

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~ , in this case the t-e~ative terminal, of the source of ~, 2 ¦I voltage 14 or via a line 25 with the second electrode 5. The 3 jl second electrode 5 is also connected with the second terminal ,i 4 j 14~, in this case the positive terminal of the source of ;
voltage 14, and with ground. The second electrode 5 is ~ conductively connected with a second holding device 26. The 7 second holding device 26 is supported for displacement in the 8 1 direction indicated by the double-ended arrow 28 horizontally 9 1 by guide means such as guide rails 27, The guide rails 27 1~ 1 are supported by bearing pedestals 29 on a base plate 30 of ! the apparatus 100. On the lefthand side of the guide rails 27 ~ there is provided a stop 31 which is preferably adjustable 13 l~, and by means of which the left end position of the second i~ ,I holding device Z6 can be adjusted in precisely reproducibLe i~ I manner.
'j On the righthand side of the guide rails 27, a loading l? , device 32 is provided. By means of the loading device 32, "' ~ a sheet of paper can be fed from a supply roll 33 to the second electrode 5 for each image to be produced~ By means of driven transport rollers 34, a strip of paper wound on the supply roll 33 is pulled off. By a cutting device 35 which is ~i , automatically actuated as a function of the desired format of 33 ll paper, a corresponding piece is cut off in each case from the 2~ li said strip and pushed by means of further driven transport ~5 1l rollers 36 onto the electrode 5 of the second hoLding device 26 26 ,I which is in its righthand end position. The second holding 2~ device 26 is preferably connected with a vacuum device (not shown in Fig. 2) by means of which the new sheet of paper is 29 fixed on the electrode 5 over suction holes. The apparatus 100 preferably also has a wetting means 37. The wetting means 37 - : :

` I 1~366SS l ;:
~ I inolude a storage tank 28 for the wetting agent 39, for instance¦
2 ¦ Isc~ r G manufactured by the Esso Company. -;
3 j By the wetting device 37 the paper 6 is saturated 4 1 with said wetting agent 39 so that upon the introduction of S ¦ the toner no solvent is removed from it by the paper since its 6 concentration would be changed thereby.
The storage tank 38 is connected via a line 40 with 8 a pump 41 which feeds the wetting agent 39 via a second line 42 9 to a two-way valve 43. As two-way valve 43 there is suitable ~10 ¦ an electromagnetically switchable valve of known construction.
111 From the two-way valve 43, a line 44 extends to a nozzle ,12 j arrangement 45 to which the second holding device 26 can be 13 I! passed. The apparatus 100 furthermore has a multiple toner ¦
i4 '¦ delivery device 46. Each individual color has its own conveyor r 1, part associated with it. A first stora~e tank 47' contains a 16 ' supply of the toner 48' for the first individual color. Via a ~17 , line 49' the toner 48' flows to a toner pump 50' and is fed i `
~ ~ by the latter via a line 51' to a two-way valve 52'. As two-way valve 52' there is preferably provided an electromagnetically ~ li actuatable valve. Upon the actua~ion of the two-way valve 52' ~l~l it conducts the toner 48 via a line 53 to an injection I ~-~ I! nozzle 54 at the end of the line 53 Upon nonactuation of I I
23 il the two-way valve 52' it conducts the toner 48' via a line 55' 24 j¦ back into the storage tank 47'.
25 ! In analogous fashion there are provided separate ~ storage tanks 47" and 47" ', toner pumps 50" and 50" ', 27 ¦¦ two-way valves 52" and 52" ', and injection nozzles 54" and 281 54" ', and the corresponding lines for the toner 48" and 48" ' 29 l for the second and third individual colors; cf. Fig. 4~
301 When the second holding device 26 is in its lefthand : *
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d position, there is a gap of, for instance, about 300~
2 I between the photoconductive layer ~ of the first electrode 1 :.: ! itl the first holding device 23 and the second electrode 5 in I the second holding device 26.
5 ¦The apparatus 100 also has a cleaning device 56 6 1 arranged lateral to the first holding device 23, as well as a drying device 57, the second holding device 26 being moved 8 1 past both of said devices. The cleaning device 56 contains a 9 ~ roller 58 which is movable downward,` for instance electro-10 1 magnetically, said roller being preferably provided with anelastic covering such as rubber or the like. The drying ,l device 57 can be provided, for instance, with heat radiators 13 1l and possibly with a blower.
Fig. 3 shows details of the first holding device 23.
;; l The first electrode l, with the photoconductive layer facing downward, is mounted in a frame 59. In the s~de part of the i , frame 59 there are arranged the ends of the lines 53', 53"
~ ,land 53" ' to which the injection nozzles 54', 54" and 55" ' Y respectively are connected.
2~ llAs can be noted from Fig. 4 which shows a portion of l ll Fig. 3 on a larger scale, the injection nozzles 54', 54" and ~- ~ 54" ' are so directed with respect to an oblique edge 60 23 Il of the first electrode 1 that the jet of toner liquid emerging ;1~ 2i !~ from them can ~low into the space lying below the photocon-` ¦ductive layer 4 and above the second electrode 5.
IlFig. 5 is a detail view of a second holding device 26.
27 ¦¦ 61 represents a wiper which consists, for instance, of a prcJ~ ¦
filed rubber provided with a sharp edge. The wiper 61 serves toi 29 clean the photoelectric layer 4 after the production of eachpartial color image during the movement of the second holding ~:"
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l ¦ d~v~ce 2~ towards the ri~llt. A cleaning roller 62 also serves 2 ¦ for ~he cleaning of the photocond~ctive layer 4.
3 ¦ Since the construction of the apparatus 100 has now ¦¦ been described with reference to Fig. 2 to 5, a description 5 1 will be given of the various method steps for the production ~;
6 of an image composed of three individual colors.
7 1. The second holding device 26 is brought into its 8 ri8hthand end position. The pump 41 and the pumps 50', 50"
9 and 50" ' are place in operation and the lamp 12A of the slide 10 1 projector is connected.
ll 2. By briefly connecting the drive member for the :- -12 ¦ transport rollers 34, a length of the strip of paper wound I ~ -3 11 on the supply roll 33 is pulled off.
3~ After reaching a given length, a suitable sheet of paper is cut from the paper strip by a brief actuating of 16 '', the cutting device 35. ¦ -li ', 4. The cut sheet is pushed onto the electrode 5 on j the holding device 26 by the connecting for a brief time of lS I the drive member of the transport rollers 36.
2~ 5. The vacuum device of the second holding device 26 21 1 is connected, the sheet of paper is drawn onto the electrode 5 2~ li and thereby fixed in its position on the electrode 5.
?3 1 6. The second holding device 26 is moved to the left, 2~ I! for instance by a motor acting via a rope, a rack or a 25 1I threaded spindle.
~6 ¦ 7. Only during the passage by the wetting device 37 27 ¦ is the two-way valve 43 actuated in such a manner that wetting 28 ¦ agent 39 is sprayed from the nozzle arrangement 45 onto the 29 ¦ surface of the sheet of paper lying the electrode 5.
30 ~ 8. Upon the first movement of the second holding ~' ' ~

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` 1~36655 ll ~ ¦1 ~Yice 26 below the first holding device 23, the two-way 2 1¦ valve 52' is actuated for the feeding of toner 48' for the 3 1I first color so that during the movement of the second holding device 26 until it reaches the stop 31, the space produced 5 ¦ between the photoconductive layer 4 and the second electrode 5 6 or the sheet of paper present on it is filled with the 7 first toner 48'.
8 9. The color filter 18 for the first color is 9 1 brought into the light path 17.
10. The switch 13 is switched to the terminal 14A of 11 cource of voltage 14 in order to produce the electrical field 12 ! in the space between the two electrodes.
13 jl 11. The shutter 17 is opened during the exposure 14 1¦ time Tl which is optimum for the first color, whereby a

15 ,i conductivity image corresponding to the first individual color

16 ,1 image of the master is produced in and on the photoconductive layer 4.
12. The switch 13 is switched in such a manner that , 1~ il now the first electrode 1 is connected with the second elec-~ ll trode 5. In fractions of a second there thereby takes place a 21 ~ deposit of color ~orresponding to the first individual color '? Il image on the support 6, i.e. on the sheet of paper lying on ~ the electrode 5.
24 11 13. The second holding device 26 is pulled away ¦i towards the right laterally from the first holding device 23, 26 il 1l1 whereby the wiper 61 and the cleaning roller 62 remove the 27 1 toner 48' from the photoconductive layer.
` 28 14. The cleaning device 56 is temporarily lowered 29 onto the passing support 6 and thus onto the sheet of paper bearing the first color deposit, whereby toner 48' which is ..
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ll adhering to the support 6 is wi.ped off.
? Ii 15. The seconcl llolding device 26 contimles to travel 3 ¦¦ towards the right to below the drying device 57 which is ;I temporarily connected and the first partial color image is 5 I thereby dried on its surface. ~:

h 1i 16. During the drying process the cleaning device 58 : .

I is at the same time freed of any adhering toner by the ~:

8 cleaning roller 62.

9 17. Upon the superficial drying, the first cycle lo during which th0 first partial color image has been produced 11 ¦ is eoncluded. ¦

12 ¦ In the seeond cycle the second color image is now 13 il produced in a manner similar to the first color image. I -4 1l 18. The holdi:ng device 26 is moved towards the left, and during its travel below the first holding device 23, the toner 48" for the second partial color image is fed by 7 I aetuation of the braneh valve 51".
, i 19. The color filter 19 for the second partial color image is brought into the beam path 17. i 2G j 20. The switch 13 is switehed to the terminal 14A of ~? !! the souree of voltage 14. 1 1 2, 'I 21. The shutter 16 is opened for the exposure time T2 28 il which is optimum for the second eolor, a conductivity image 24 lj eorresponding to the seeond eolor image being produeed in and/or 2sl on the photoeonduetive layer 4.
'6 22, The switeh 13 is switehed in sueh a manner that 27 the first eleetrode 1 is now eonneeted with the second elee-28 trode 5. In fraetions of a second there is thereby produced 29 a deposit of eolor eorresponding to the seeond partial 3D color image on the support 6, i.e. on the Rheet of paper

-17-.' I '~ ~
, 11 . - ~:
. ., - . , ready provided ~ith the first color image wh~ch is s~ill 2 ll resting on the electrode 50 3 ¦! 23, The second holding device 26 is pulled away ~ ll towards the right laterally from the first holding device 23 5 l¦ the wiper 61 and the cleaning roller 62 removing the toner s !1 48 from the photoconductive layer 4.
24. The cleaning device 56 is lowered onto the ¦
8 ¦ passing support 6 (the sheet of paper bearing the first and the I
9 second color deposits), whereby toner 48" still adhering to the I -support 6 is wiped off.
11 1 25. The second holding device 26 continues to travel 12 ¦¦ to the right to below the drying device 57 which is temporarily 3 ¦I connected and the second partial color image is thereby dried 4 l¦ on its surface. I -i5 ll 26~ During the drying process, the cleaning device 58 ~ I is simultaneously freed from any adhering toner by the cleaning 1~ ¦ roller 62.
lS ,i 27.~ Upon the drying of the surface, the second cycle 1 il during which the second ~lor image has been applied to the ~ l¦ color image is now also concluded.
21 ,l In similar fashion, one now proceeds with the third I -2 I toner 48" ' and the third color filter 20 and the optimum ¦ exposure time T3 for the third partial color image of the third 2~ ll cycle for the production of the third partial color image on 2~ the support 6 already bearing the first and the second partial ~6 ¦ color images, steps 27 to 36 now following analogously cor-27 responding to steps 18 to 27.
28 37, Finally the support 6 bearing all three color 29 ¦ images can be coated with an agent which increases the trans-parency and durability of the complete color image.
"
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1~36655 1 I ~
3~. Ihis is follo~ed by a final drying, wrlereupon tl~e ^ colored picture to be produced is finished.
- ~i The above steps 1 to 3~ can be achieved by manual . . , .
actuation of the various parts of the device 100 indicated ' or else by automatic actuation thereof. There is no difficulty 6 in designing the correspondir~ drives and controls on basis ' ~1 of the steps which have been described in detail. Thus the ¦ ;-1 8 ~ individual switch times for the movement of the second holding ¦ ~ ~-9 1l device 26, for the placing in operation of the coating device 32, ~3 the wetting device 37, the toner feed device 46, the cleaning 1 , device 56, the drying device 57 and the replacement of the ~ color filters can be controlled, for instance, by means of a ;- cam-controlled programming device.
-~ For the production of the photoconductive layer 4 - the following materials enter, for instance, into con-sideration: -; ! Organic polymers, such as polyvinyl carbazole, ;
~; " organic pigments in a suitable layer support, such as phthalo-: cyanin, or inorganic pigments in suitable layer supports, for ,. ,, I
1 instance cadmium sulfide, zinc oxide, etc. The layer support . ,. ,, 1 ;
consists of a suitable binder, for instance of acrylic resin, 2 styrene resin or similar substances.
;~ 2~ In the toner 48', 48" and 48" ' the particles may be ?4 ii charged positively or negatively. In case of reversed polarity of the Nesa glass acting as electrode 1 there is produced cor-Il responding to the particles on the support 6 a positive image 27 ,¦ and in case of the same polarity a negative image if a positive 29 is used in this connection as master. In corresponding manner, ¦ a negative master can be converted into a positive image~
As support 6 there can be used, for instance, ordinsry ,. ~
!l -` 3.~3~i6SS
~ 'I pewriter paper, plastic foil, for instance ~Iylar, 2 1! textile material, ~hether woven or kni~ted, glass plate, 3 1 aluminum foil or some other metal foil or plate.
4 j In order to obtain good image transparency, a film-¦I forming material is preferably applied to the support 6 after 6 Ij the production of the three individual color images. As such 7 ¦¦ film-forming material there is suitable a lacquer, for .. 8 ! instance any acrylic lacquer, a resin, for instance styrene resin~ a low-melting polymer, for instance polyethylene, or a O wax, for instance paraffin wax. The application can be ef-fected by customary technique1 for instance by spraying, 2 il coating, dipping or rolling.
il It should also be pointed out that by a change in i~l ! polarity of the charge of the particles 9 or of the source of ,, !!
i5 1 voltage 14, positive images can be produced from negative 6 ; masters and negative images from positive masters.
!l 17 i When the polarity of the electrode 3 is the same as the sign of the particle charge, a reversal process takes place, jl , ~, '5 l i.e. a negative image is produced from a positive master and ll a positive image from a negative master.
- ll If the polarity of the electrode 3 is opposite the 22 1l sign of the particle charge, no reversal process takes place, I
Il i , ll i.e. a positive master gives a positive image and a negative ?~ ¦- master gives a negative image.
25 ¦1 Information will now be given as to the nature, ¦ composition and production of substances which have proven ~7 1 advantageous for the production of images by the present process.
1st ExamPle:
1) Example of a photoconductor for the production - ~
of the photoconductive layer 4; -¦ A 20~u-thick layer of a mixture of polyvinyl carbazole 3~655 i' l ~ at~ ` percent by weigh~ tetranitrofluorenone as sensitizer.
2 , lb) Example of a toner 48' (first color: yellow)t 3 l 0.3 g Lithol-fast yellow 4R/1780 (BASF), as well as 4 l 0 04 g of an 8% solution of cobalt decanate in mineral 5 ¦ spirits are made up with Isopar G (ESSO) to lO0 g and dispersed -- 6 for lO mln. in a- high-frequency stirrer. In this way there is 7 produced a yellow toner with positively charged particles.
; lc) Example of a toner 48" (second color: magenta):
9 10 parts by weigh~ Fanal pink 322~2994 (BASF) are ¦~
lO l ground together with 90 parts by weight of Isopar G in a bead ~ , ball mill for 30 min. 4 g of this concentrate as well as j i ~2 il 0 04 g of an 8% solution of cobalt decanate in mineral spirits J i~l are made up to 100 g with Isopar G and dispersed in a high-~ ll frequency agitator for 10 min. In this way there is produced l~ ¦ a magenta toner with positively charged particles.
~ld) Example of a toner 48" ' (third color: cyan)~
1/5 parts by weight Savinyl blue GLS (Sandoz) and 5 1~ parts by weight Irgazin blue 3 GT (CIBA-GEIGY) are ground ~ , together with 90 parts by weight of Isopar G in a bead ball ; 2r~ mill for 30 min. 6 g of this concentrate and 0.04 g of an 8%
-I j cobalt decanate solution in mineral spirits are made up of to 100 g with Isopar G and dispersed for 10 min. in a high-~'3 1~ frequency agitator. In this way there is produced a cyan 2~ I toner with positively charged particles.
2s i! ld) Example of a wetting liquid 39:
26 1l As wetting liquid there is preferably used the same 1 27 li liquid as employed to produce the toner, and therefore, for ,. 28 ¦! instance, a hydrocarbon of high insulating power such as Isopar 29 G (ESSO).
le) Example for the production of the picture with ''' .' ".
Trade Mark ,' 111 I '' .

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substan oe s indicated under la to ld: After the wetting of the support 6 with the wetting liquid 39, the two electrodes 4 and 5 are caused to coincide and the spa oe 7 is filled with the yellow toner 48'. m e master 11 is projected for 6 sec. through a violet filter onto the photoconductor layer 4 and during the sa~!e time a voltage of -2.5 kv is applied to the NESA electrode 4. After the superficial drying of the first partial image and the cleaning of the photoconductor 4, the magenta toner 48" is introduced, the master 11 is projected through a ~ -green filter for 6 seconds and at the same time a voltage of -3 kv is applied to the NE5A electrcde 4. After again drying ànd cleaning, the cyan toner 48" ' is introduced, the master 11 is projected through a red filter for 6 sec. and at the same time a voltage of -1.5 kv is applied to the NESA electrode 4. The distance d between the surface of -~
.
the paper and the surface of the photoconductor is 160 u. After the drying and treatment with the fixing agent, a positive full-color image corresponding to the master 11 is produced on the support 6.
;~ 2nd Example:
2a) Example of a photoconductor 4:
B-phthalocyanin is muxed with a styrene acrylic resin as ` 20 binder and applied by coating in the form of a layer of a thickness of 5 u. The pigment/binder ratio is 3:10.
2b) E~amPle of a toner 48' (color black):
5 ml of *Hunt toner conoentrate (HUNT CHEMICAL CORPORATION) are ;~ diluted to 100 ~1 with Isopar G and mixed well by agitation. In thisway there is produced a black toner with positively charged particles.
2c) Example of the production of the image:
A black-white positive is projected as master 11 *Trade Mark '`' `:' - .
.' ' -; -22-~., ~' `

36i~S5 1 i , f~ ~6 sec. without color filter onto the photoconductor layer 2 1 4 and at the same time a voltage of -3 kv is applied to the 3 j ~ESA electrode 4. I~hen using the toner 48' of 2b there is ~ 4 1I produced on the support 6 a positive black-white image with good ¦I half tones which corresponds to the master ll. The distance d 6 is 200 u.
7 3rd Example:
8 3a) Example of a photoconductor 4: same as under la;
9 3b) Example of a toner 48' (first colorJ yellow)s 2 g of the printing color paste " Nagra 6" (SICPA) 1 !! as well as 0.04 g of 8% cobalt decanate solution in spirits 12 il of turpentine are made up to lO0 g with Isopar G and dispersed `. 13 1l for lO min. in a high-frequency agitator. A yellow toner i 1 ? 1! having positively charged particles is produced . , ~ . I
: 15 , 3c) Example of a toner 48" (second color: magenta):
., li 2 g of the printing color paste "Nagra red 28" (SICPA) as well as 0.04 g of 8% cobalt decanate solution in spirits of , ,~
~ ,, turpentine are made up to lO0 g with Isopar G and dispersed l ? il for lO min. in a high-frequency agitator. A magenta toner having positively charged particles is produced. I
~1 ,i 3d) Example of a toner 48" ' (third color: cyan):
22 ,¦ 2 of the printing color paste "Nagra blue 9" (SICPA) ~3 ~' as well as 0.04 g of 8% cobalt decanate solution in spirits of 24 ,~ t,urpentine are made up to lO0 g with Isopar G and disperesed ` !~ for lO min. in a high-frequency agitator. A cyan toner having 26 li positively charged particles is produced. ¦ ;

28 1 3e) Example of a wetting liquid 39: same as under ld.
¦ 3f) Example for the preparation of an image with the 29 substances indicated under 3a to 3e.
After the wetting of the image receiver with the wetting liquid 39, the two electrodes 4 and 5 are caused to Trade Mark ,. . , . - . .~ ~ ~ .
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3~5S
coincide and the space 7 is filled with the yellow tones 48'.
The master 11 -a colored slide- is projected for 6 sec.
through a violet filter onto the photoconductor layer 4 and a voltage of -2 kv is applied during the same time with the NESA electrode. After the drying of the surface of the first partial image and the cleaning of the photoconductor 4, the ~; magenta toner 48" is introduced, the master 11 is projected through a green filter for 6 sec. and at the same time a voltage of -1.8 kv is applied to the NESA electrode. After again drying and cleaning, the cyan tone 48" ' is introduced, -, the master 11 is projected for 6 sec. through a red filter, and at the same time a voltage of -0.9 kv is applied to the `
NESA electrode 4. The distance d is 200 u. After the drying ; and treating with the fixing agent there is produced on the support 6 a positive full-color image which corresponds to the :.~ .
master 11.
In the process of producing images described above, the excess toner dispersion which is left on the support after -production of a partial or full image on said support is removed `~
by means of a cleaning roll. According to an example, a cleaningroll is lowered for this purpose on to the support which is moved past underneath it so that the excess toner dispersion is sgueezed of~ the support.
` It has been found that regardless of the material used for the cleaning roll, when the roll is moved over the support it may itself become soiled with toner particles so that it must be cleaned before it is brought into contact with the next image. This involves a technical complication, preferably avoided, ~i especially in an automatic apparatus. In addition, it has been found that if a colour has just been deposited on the support, it is liable to be damaged as the cleaning roller is rolled over it because the roller is liable to remove not only excess ,.,,`1 :

., ' , ~3ti6~i5 toner dispersion but also toner particles which form part of the '~ image itself.
` The above mentioned disadvantages have been obviated and a simple process and simple apparatus has been provided for removing excess toner dispersion on an image which has just been produced without damaging the image itself.
In the present embodiment, for the electrophotographic production of images from an original, in which a photoconductive layer is exposed in dependence upon the original and a conductivity image corresponding to the original is thereby produced on or in this layer, which conductivity image serves to control a field produced by two electrodes in a space between the photoconductive layer and a support provided to support the image which is about .. . .
to be produced, this field causing the movement of electrically charged toner particles in the said space, the charge on the toner particles and the electrode associated with the photo-conductive layer being opposite in polarity in a positive process and identical in a reversal process. The electric field is subsequently made to break down with the result that in the positive process toner particles migrate from the photo-conductive layer to the support where they produce the image corresponding to the original and in the reversal process the toner particles migrate from the support to the photoconductive layer so that a negative image corresponding to the original is left on the support. This process is characterised in that a potential is applied at least to the circumferential surface of a cleaning roller which is moved over the support of an image which has just been produced in order to remove excess toner dispersion from said image. In relation to the earthed electrode on which the said support is mounted, the said potential has the same polarity as the charge of the toner particles used for producing the lmage.

!

lQ3f~SS

The invention relates also to an apparatus for . .
carrying out the said process, comprising a first electrode and a second electrode, switching means to connect these , electrodes selectively to a source of voltage or to each other, a photoconductive layer associated with the first electrode, copying means for copying an original on to the photoconductive layer, a support arranged on the second electrode for supporting ; the image which is to be produced from the original, and means for introducing charged toner particles into the space between the photoconductive layer and the support. For the pur~ose ~; of removing excess toner dispersion from an image which has ~ust been produced, a cleaning roller is provided, which roller is adapted to be displaceable over and relatively to the :, support for the image. The apparatus is characterised in that ~ ~-at least the circumferential surface of this cleaning roller is adapted to be connected to a source of voltage in such a manner that in relation to an electrode on which the said support for the image is arranged, the said circumferential surface has a potential of the same polarity as the charge of the toner particles used for producing the image.
Turning now to Figure 6, this figure is substantially similar to Fig. 2 previously described. It differs from the . , .
said Fig. 2 by the fact that a lead 58' is connected to the cleaning roll 58 which is made of conductive material, for example by means of a sliding contact (no~ shown). The said .. . .
lead 58' is connected by a switch 58" to a terminal 58"' of a voltage source 58"", the other terminal 58""' being earthed.
t ;`~ The switch 58" is closed while the cleaning roll 58 is rolled over the image support so that the roll 58 takes on the potential ` 30 of the terminal 58"' which, as already mentioned above, is , selected to have the same polarity as the charge of the toner particles used for producing the image.

- .- . -.
~ - 26 -.:' ' ' '- ' . .. ' ., ' ' ' ' 1C~3tj~SS
~- If a metal cleaning roll 58 is used, the voltage of the source 58"" is selected within a range of 100 to 1000 V, :-preferably 300 to 500 V. :
:~ The use of the above mentioned process provides the following advantages~
1. The cleaning roller 58 is not soiled by toner particles as it rolls over the image.
2. The image on the support is not damaged by :
'~ accidental detachment of toner particles. ~ ~.
; .
3. The bond between the image and the support is strengthened so that the image produced is made more resistant for further treatment.

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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. Process for electrophotographic image production from an original, in which a photoconductive layer is exposed in dependence upon the original and a conductivity image corresponding to the original is thereby produced on or in the said layer, which conductivity image controls a field produced by two electrodes in a space between the photoconductive layer and a support provided to support the image which is to be produced, electrically charged toner particles being moved by this field in the said space, the polarity of the charge of the toner particles being opposite to that of the electrode associated with the photoconductive layer in a positive process, and the electric field being subsequently made to break down so that in the positive process toner particles migrate from the photo-conductive layer to the support and produce on it the image corresponding to the original and in a reversal process the toner particles migrate from the support to the photoconductive layer and hence leave a negative image of the original on the support, which process is characterised in that a potential is applied at least to the circumferential surface of a cleaning roll which is moved over the support on which an image has just been produced in order to remove excess toner dispersion from said image which potential has the same polarity in relation to the earthed electrode on which the said support is arranged as the charge of the toner particles used for producing the image.

2. Apparatus for carrying out the process according to claim 1 comprising a first and second electrode, switching means to connect these electrodes selectively to a source of voltage or to each other, a photoconductive layer associated with the first electrode, copying means for copying an original on to the photoconductive layer, a support arranged on the second electrode to support the image which is to be produced of the original, and means for introducing charged toner particles into the space between the photoconductive layer and the support, a cleaning roll being provided for the purpose of removing excess toner dispersion from an image which has just been produced, which cleaning roll is adapted to be displaceable relatively to and over the support for the image, which apparatus is characterised in that at least the circumferential surface of this cleaning roll is adapted to be connected to a voltage source in such a manner that in relation to an electrode on which the said support for the image is arranged, the circumferential surface of the roll has a potential equal in polarity to the charge on the toner particles used for producing the image.