NO128733B - - Google Patents

Description

Method and apparatus for electrophoretic

imaging.

in

The present invention relates to a method for photoelectrophoretic imaging where a suspension of electrically photosensitive particles, containing an electrically photosensitive pigment, in a carrier liquid is exposed to an electric field applied over two electrodes, at least one of which is at least partially translucent, the image being formed by exposing the suspension to an image with a source of activating electromagnetic radiation through the translucent electrode.

Furthermore, the invention relates to an apparatus for carrying out the method, comprising a device for applying an electric field over a suspension of finely divided particles between two electrodes, at least one of which is at least partially encased, a source for activating radiation and a device for exposing the drug suspension to an image pattern of the activating radiation.

Although many photographic systems are known today, all suffer

of some deficiency. Many require excessively expensive and complicated pre-treatment of the photosensitive media, while others suffer from insufficient resolution, photographic speed, spectral sensitivity and the like. In addition to the aforementioned shortcomings

with many of the current photographic systems, additional post-processing is usually required to produce a visible

image from the latent image, which is produced in the photosensitive medium after it has been exposed to light.

Can photographic systems be used today for production

of color images, the complexity of the material and the process steps is further increased to an incredible degree. Not only are far more complex multi-layered photosensitive media required,

often consisting of as many as from svv to nine very thin layers of different materials of varying chemical composition, but in addition to this, the material requires a large number of further processing steps and careful control of each of these steps becomes much more critical than with ordinary varieties -white systems.

Although imaging systems based on particle migration techniques have previously been proposed, these systems have proven to be so insensitive to light, produce such poor images and are so complicated, complicated and difficult to produce that they have never been commercially accepted. These earlier systems used composite particles comprising at least two and usually several layers of different materials such as, for example, photoconductive cores with varying resistivity, l.vsf.

it was previously believed that the production of a light-filtering effect was necessary to prevent mutual influence between the oarticles and oscillation in the system as well as to perform other functions. However, the French have unexpectedly and surprisingly found that this composite layer structure is not only unnecessary,

but even undesirable and that single-component particles produced from photosensitive pigments can be used instead, to produce Ise-excellent ■ results under ■ conditions as described below.

These earlier systems, known for example from the U.S. patent-script 2.9^0.8^7, have also proved so insensitive to light and imperfect in color rendering that they have never been commercially accepted.

This had the result, because in the earlier particles, ordinary photoconductors were used which mostly had relatively broad (even panchromatic) spectral sensitivity or photoconductors made colour-sensitive, that they were provided with a colored coating without regard to the color of the photoconductor. This colored coating was used to provide a light-reflecting effect in order to make the articles selectively spectrally sensitive, and at the same time impart the correct color to the particles. Although previously used<p>articles contained additional types of material, even the simplest particles resulted in poor results because the two functions of the layers were incompatible and, at best, their characteristics had to be chosen by compromise. On

on the one hand, the layer should have a high optical density to provide .

the image a good final color, while on the other hand high density tends to even further reduce the light transmission effect of the layer like a filter. According to the invention, it has now been found, quite unexpectedly and surprisingly, that with a large number of photosensitive pigment particles such filter layers are completely unnecessary and in fact undesirable because they reduce the sensitivity of the system. Instead, it has been found that the natural selective spectral light absorption that imparts the color appearance to each of the different colored particles also contributes to their movement in the imaging system.

The method according to the invention is characterized by the fact that particles are used where the pigment is both the primary electrically photosensitive component and the particles' primary colourant.

The device according to the invention is characterized by the fact that the second electrode is a blocking electrode whose surface is formed by a material that has a specific resistance of at least 10 7 ohm/cm 2 , that the distance between the electrodes is less than 25 microns and that the applied electric field has a field strength of at least 12 volts per

micron.

The invention will now be described with reference to the accompanying drawings, in which:

Fig. 1 and IA show side views of simple exemplary systems

for carrying out the invention.

Figs. 2A, 2B, 2C and 2D show schematic partial views of the sequence of events that take place during the execution of the imaging

the process..

The size and shape of the elements in the drawings must not be taken as actual sizes nor proportional to the actual sizes, as many elements have been purposely extended in size and shape in order to provide a more complete and clear description of the invention.

Referring to figure 1, a translucent is seen

electrode generally denoted by 11 as in the present

example is made of a layer of translucent glass 12

coated with a thin optically transparent layer 13 of tin oxide, commercially available under the trade name "NESA" glass.

This electrode shall hereafter be referred to as the "introduction electrode".

On the introduction electrode there is a thin layer of finely divided photosensitive particles dispersed in an insulating liquid carrier. With regard to the expression "photosensitive", it is understood in this context any particle which, once attracted to the introduction electrode, will migrate away from it again under the influence of an applied electric field when exposed to actinic electromagnetic radiation. However, a detailed theoretical explanation of the likely mechanism of the invention will be given below. The liquid suspension 14 may also contain a light-sensitive agent and/or a binder for the pigment particles, which is at least partially soluble in the suspension or carrier liquid, as will be explained in more detail later. Above the liquid suspension is another electrode 16 which is connected to one pole of a voltage source 17 across a switch 18. The opposite pole of the voltage source 17 is connected to the introduction electrode 11 so that when the switch 18 is closed, an electric field will be applied across over the liquid suspension 14 by means of the electrodes 11 and 16. An image projector consisting of a light source 19, a transparent (film) 21 and a lens 22 is arranged for exposure of the dispersion 1H by means of a slide of the original transparent 19 to be reproduced. It should be noted here that the introduction electrode 11 does not necessarily have to

be optically translucent, but that the electrode 16 can instead

be optically translucent and the exposure can be carried out through it from above as shown in fig. 1.

According to the embodiment as shown in fig. IA, identical numbers are used for identical parts of the device which is the same as shown in fig.l, with the exception that the electrode 16 is produced in the form of a roll 23 which has a conductive central core 24 connected to the voltage source 17. The core is covered with a layer of barrier electrode material 26 which can for example be barite paper. In both of the embodiments shown (Fig. 1 and IA), the pigment suspension is exposed to the image to be reproduced, while a potential is applied across the blocking and insertion electrodes, when the switch 18 is closed.

According to fig. In the 1A embodiment, the roller 23 is rolled across the top surface of the lead electrode 11 with the switch 18 closed during the exposure period. This light exposure causes exposed pigment particles which were originally attracted to the electrode 11 to migrate through the liquid and adhere to the surface of the barrier electrode, leaving a pigment image on the surface of the lead electrode, which image is a copy of the original film 19- According to fig. In the 1 embodiment, the blocking electrode 16 can then be removed from the surface of the pigment suspension 1H, after which the relatively volatile carrier liquid evaporates and leaves the pigment image. This pigment image must then be fixed in place, for example by placing a coating over its top surface or with the help of a dissolved binder in the carrier liquid such as narafin wax or other suitable binders which fall out of the solution when the carrier liquid evaporates.3 - 6%<p> arafin wax in the carrier liquid has been found to give good results. The carrier liquid itself can be melted paraffin wax or other suitable binders in a liquid state, which are self-adhesive after cooling and returning to a solid state. Alternatively, the pigment image left on the insertion electrode can be transferred to another substrate and attached to this. As explained in more detail later, the system can produce both monochromatic and multichromatic images depending on the number of pigments suspended in the carrier liquid as well as the color of the light to which the suspension is exposed during the process.

Pig. 2A to 2D show in detail an assumed theoretical ionization mechanism for the system with the pigment particle size and carrier fluid thickness greatly exaggerated for illustrative purposes. As the system has experimentally proven to be usable, there is of course no intention of limiting the invention to this working theory which is only presented to clarify the invention. In the figures shown, the same numbers are used to identify parts of

the system which are identical to those in fig. 1 and IA. In fig. 2A

it is seen that the pigment dispersion, denoted by 14, consists of an insulating carrier liquid 27 in which charged pigment particles 28a, 28b, 28c and so on are suspended. The pigment particles 28 have a net electrostatic charge when they are suspended in the carrier liquid 27, which is believed to be due to the free-concentration electrical relationship between the particles and the liquid. The charge is captured or bound either inside the pigment body or at its surface. The net charge can be either positive or negative, in which case, however, a circled negative charge in each pigment particle has been used to schematically suggest that trapped negative charge carriers give the particular particle a net negative electrostatic charge. When the switch 18 is open and no potential is applied across the electrodes 11 and 16 in the system as shown in fig. 2A, the suspended particles 28 appear only to assume arbitrary positions in the carrier fluid 27. However, when the switch 18 is closed, whereby the conductive surface 13 of the electrode 11 is made positive relative to the rear surface of the barrier electrode 16, negatively charged particles in the system will tend to move towards the electrode 11, while any positively charged particles in the system will move towards the blocking electrode 16. However, the presence of any positively charged particles in the system and their movement therein will be disregarded to facilitate the explanation of the movement of the negatively charged particles in the carrier fluid. As the pigment particles 28 are non-conductive in the absence of actinic irradiation, they migrate down to contact with or close to the introduction electrode 11, and remain in this position under the influence of the applied electric field until they are subjected to exposure by means of activating electromagnetic irradiation. In reality, these particles are bound to the surface of the introduction electrode 11 until the exposure takes place, because the particles 28 are sufficiently non-conductive in suspension in their unexposed state to prevent the introduction of positive charges from the surface 13 of the electrode 11 into the particles. Particles bound to the surface 13 form the potential imaging particles of the final image to be reproduced on the surface.

When light photons 31 (Fig. 2) are generated by means of, for example, the projector, which exposes the system to the image to be reproduced, they are absorbed by the photosensitive pigment particle 28b and "create" hole-electron pairs of charge carriers inside the particle by to raise them to a conducting energy band.. As the charge carriers have just been formed by the cycle of the light photons 31 (fig. 2C),

have they not had the opportunity to be captured in charge traps inside the pigment body 28b such as the circled negative charge carrier. Accordingly, these newly formed charge carriers can be considered mobile in nature and are shown in the drawing with non-circled plus-minus signs. Due to the fact that an electric field is impressed across the particles by means of potential impressed across the electrode 16

and the conductive surface 13 of the electrode 11, the hole-electron pairs formed inside these particles are forced to separate before they can unite, with the negative charge carriers moving towards the surface 13, while the positive charge carriers move up towards the electrode 16.

As the initially formed charge carriers are in a mobile state,

can the negative charge carriers near the pigment electrode touch

surface move across the very short distance out of pigment particle 28b to surface 13, as indicated by the small arrow, leaving the pigment particle with a net positive charge. As the particle 28b now carries a net negative charge, it is pushed away from the positive surface 13 in the electrode 11 and attracted by the negative blocking electrode 16, as it moves as indicated by the arrow 32 in fig. 2D. Accordingly, any particles such as 28B on surface 13 that are exposed to electromagnetic radiation of a wavelength to which they are sensitive (that is, a wavelength that will cause hole-electron pairs to form within the particles) will move away from surface 13 up to the surface of the electrode 16 and will leave behind such particles as 28C, which are either not exposed at all, or not exposed to electromagnetic rays to which they are sensitive. If, therefore, all particles in the system are sensitive to some wavelength of light, and the system is exposed to an image of white light, a positive image will be formed on the surface 13 of the electrode 11 by the removal of bound particles from its surface in the exposed area and that bound particles remain in unexposed areas. The system is thus able to produce a photographic negative image on the surface 16, as only particles in exponential regions move up towards this surface.

When particles such as 28b move up through the liquid carrier 27

from the surface 13 towards the electrode 16, it must be assumed that the new charge carriers go into charge carrier traps, and this has been schematically indicated by showing the holes circled in the circle in fig. 2D.

Consequently, the particle now contains one trapped electron and two

trapped holes that give a net charge of plus 1.

It should be clear at this point in the description that

are certain preferred characteristics of the electrodes 11 and 16. These are that the electrode 11 will preferably be able to receive introduced electrons from the bound particle 28b when exposed to light, to enable a net change in charge polarity on the particle, and that the electrode 16 will preferably be a blocking electrode which is unable to introduce electrons into the particle 28b at more than a very slow rate, when it comes into contact with the surface of the electrode 16. If all polarity in the system is reversed, the electrode 11 will obviously preferably become capable of receiving introduced holes from bound particles after exposure to light, and the electrode 16 will preferably be a blocking electrode incapable of introducing holes into the particles at more than a very slow rate when they contact the surface thereof electrode. According to this preferred embodiment, the electrode 11 can be composed not only of ordinary conductive material such as tin oxide, copper, copper iodide, gold or the like, but can also include many semi-conducting materials such as raw cellophane which is not ordinarily considered a conductor, but which is nevertheless capable of receiving introduced charge carriers of the correct polarity under the influence of the applied field. Even highly insulating materials such as polytetrafluoroethylene can be placed over the surface of the lead electrode and still be usable because charge leaving the particles originally bound to this surface, after exposure, can simply move out of the particles and remain on the insulating surface and thereby allow the exposed particles to migrate. However, the use of more conductive materials is preferable because it allows a cleaner charge separation in that charge leaving the particles after exposure can move into the underlying surface and away from the particle in which it was produced. This also prevents possible charge accumulation on the electrode, which tends to reduce the field between the electrodes. On the other hand, the preferred embodiment of the blocking electrode 16 is such that it prevents or greatly reduces the introduction of electrons (or holes, depending on the original polarity of the charge on the particle) into the particle 28b when it reaches the surface of this electrode. Consequently, the surface of this electrode facing the carrier liquid 27 can, in the preferred

embodiment be either an insulator or a semiconductor which will not allow the passage of sufficient charge carriers under the influence of the applied field to discharge the particles originally bound to it, thereby preventing the particles from oscillating in the system. Although this barrier electrode will allow the passage of some charge carriers through it to the particles, it will still be considered to belong to the class of preferred materials if it does not allow the deposition of sufficient charge carriers to discharge the particle to the opposite polarity because even a discharged particle will tend to - to stick to the blocking electrode using Van der Waals forces. Also material

ales that do not fall into the preferred class may be used<*>,

but they tend to lead to oscillation of the particles in the system, resulting in lower image density, poorer image quality, image reversal and similar errors, the degree of such errors in most cases being dependent on how far the material used differs from the preferred class of materials in electrical properties.

The use of this blocking electrode constitutes an important feature of the invention as it prevents the articles from oscillating between the electrodes and enables the use of individual composite, uncoated photosensitive pigment particles in the system, which at the same time significantly improves the image quality.

Baryte paper and other suitable materials can be used as

coating on the surface of the blocking electrode and can be moistened on the back side, with ordinary tap water or coated with a layer of electrically conductive material. Baryte paper consists of panir coated with barium sulfate suspended in a gelatino<p>solution.

Although the blocking electrode has been essentially described

in connection with a barite paper blocking electrode, any material having a specific resistance of about 10 7 ohms/cm 2 or more may be used. Typical materials in this resistance range that have been used in one or more of the devices described in the drawings include cellulose acetate and polyethylene coated paper, cellophane, nitrocellulose, polystyrene, polytetrafluoroethylene and polyethylene terephthalate.

The terms "blocking electrode" and "introduction electrode" must

in this context is understood and interpreted through the description and requirements. As described in more detail below, the system can

is used in connection with particles that initially assume a net positive charge or net negative charge and even with systems where the <p>articles in the suspension apparently assume charges of both polarities.

Although the following insulating carrier fluids are usable in the system: decane, dodecane, N-tetradecane, molten paraffin, molten beeswax or other molten thermoplastic materials, "Sohio" odorless solvent (a kerosene extract) as well as "Isopar G" (a long chain saturated aliphatic hydrocarbon ) then any suitable insulating liquid can be used. The social voltage used in the system is not critical and good image quality has been produced with, for example, voltage varying from 300 to 1500 volts in the apparatus shown in fig. let.

Depending on the particular intended use of the system

the liquid suspension 14 may contain one, two, three or even more different particles of different color and with different spectral sensitivity ranges. Thus, for example, in a monochromatic system, the particles contained in the imaging fluid 14 may actually be any color in which it is desired to produce the final image, such as gray, black, blue, red, yellow, and so on, and the particular point or area of their spectral sensitivity is relatively unimportant as long as they show reactivity in one or another area of the visible spectrum, which can be measured with the help of an ordinary emission source. In a monochromatic system, the pigment can actually vary in reactivity from one with a very narrow sensitivity band all the way to one that has a panchromatic sensitivity. In polychromatic systems, the particles can be selected so that particles of different colors correspond to different wavelengths in the visible spectrum, thus enabling phase separation. It should be noted, however, that this separation in spectral reactivity into particles including different colors is not necessary in all cases, and that in some cases it may actually be considered undesirable. Thus, for example, in a monochromatic black-and-white system where it is desirable to produce a very intense black image, it may be advantageous to produce this result by using two or more differently colored pigments in the system, which when combined will provide a black image. In this last case, considerable overlapping and even coincidence of the spectral sensitivity curves of the different pigments can be tolerated and can even be drawn as

that all the pigments used in the system will be receptive in approximately the same way to commonly available light sources which are not uniformly panchromatic in their light emission. If a white light is used, then it is clear that this overlap is not necessary.

In a preferred panchromatic system, the particles are selected

so that those of different color correspond to different wavelengths in the visible spectrum corresponding to their main absorption and further so that their spectral sensitivity curves have no significant overlap, which thus allows color separation and subtractive multi-colour imaging.

Several different particles are used, namely a cyan (blue) colored particle which is mainly sensitive to red light, a magenta (red) colored particle which is mainly sensitive to green light and a yellow colored particle which is mainly sensitive to blue light. While this is the simplest combination, additional particles having different absorption maxima can be added to improve color synthesis. When mixed together in the carrier liquid, these particles produce a black liquid and when one or more particles are caused to migrate from the bottom electrode 11 towards the upper electrode, they leave behind particles which produce a color equivalent to that of the incident light source. Thus, exposure to red light will cause cyan pigments to migrate, leaving behind magenta and yellow pigments which in combination form red in the final image. In the same way, blue and green light will be reproduced by removing yellow and magenta respectively,

and naturally if white light falls on the charge, all the pigments will migrate, leaving behind the color of the white or transparent substrate. Without exposure, all pigments are left behind which in combination form black. It should be noted that this is an ideal technique for subtractive color imaging in that<p>the articles are not only each made of one component, but that in addition to this they perform a double function in that they serve both as a color medium for the finished image and as photosensitive medium for the system. Consequently, the system in its action represents the ultimate in eliminating the composite nature of previous methods of subtractive color imaging.

Regardless of whether the system is used to reproduce a monochromatic or a polychromatic image, it is desirable to use pigment particles that are relatively small in size, because small particles produce better and more stable pigment dispersions in the liquid carrier and are also able to produce images with greater sharpness than would be possible with larger particles. Even where the pigments are not commercially available in small particle size, this must be reduced using common techniques, for example extended paint in a wedge mill or similar. When the particles are suspended in the liquid carrier, they can assume a net electro-

static charge so that they are attracted to one of the electrodes in the system, depending on the polarity of this charge in relation to the electrodes' charge. It is not necessary that the particles assume only one charge polarity, but instead the particles can be attracted to both electrodes. Some of the particles will first move towards the introduction electrode, while others move towards the blocking electrode in this type of system. However, this particle migration takes place evenly over the entire area covered by the two electrodes, and the effect of imaging, exposure-induced migration is added to this. It should then be clear that the apparent bipolarity of the suspension does not in any way affect the image-forming property of the system except for the fact that it uniformly removes part of the particles from the system before the image-forming adaptation of the particle migration takes place. In other words, the above-mentioned behavior causes a part of the suspended particles to be removed from the system as possible image formers. The effect of removing part of the particles as possible image formers in the system can be easily overcome by simply preparing the original particle suspension with a sufficiently high concentration so that the system is able to produce sharp images. It has also been found that with some suspensions of this type both species of potential polarity can be applied to the electrodes during imaging.

Although some of the photosensitive pigment materials used in this invention can be used in conventional methods that work on a photoconductive principle, it is believed that another type of photoreactive mechanism is present because it has generally been found that the spectral reactivity of the materials is much narrower and their sensitivity is much higher when they are used in a liquid carrier form than when they are used in other forms that include photoconductive reactivity.

Addition of small amounts (typically varying from 0.5 to 5 mole percent) of electron donors or acceptors to the suspension, with the choice depending on whether the particles attracted to the input electrode are positive or negative, has given a clear increase in the photosensitivity of the system which described in the examples. This effect is believed to be due to either the removal of free charge carriers from the system or from an original charge built up on the

surface of the particles.

Any suitable, differently colored, photosensitive pigment particle having the desired spectral reactivity can be used to form the pigment mixture in the carrier liquid for color imaging. The photosensitive pigment can, for example, be of a polymeric nature. The percentage content of pigment in the insulating liquid carrier is not critical, but as an example it can be noted that from 2 to 10% by weight have been tried and have given good results.

In a particularly preferred form of the method, the electrode to which the image particles migrate is repeatedly brought into contact with the particle suspension during the continuous application of potential and image exposure with cleaning of the electrode between each contact. This technique has been found to produce a clear improvement in the color balance of the produced image and generally to improve the accuracy of color reproduction in the system. Three to eight repetitions of the contact have generally been shown to produce results that cannot be further improved by further treatment. The improved form of imaging process can be performed by repeatedly rolling the electrode 23 in figure 1a over the particle suspension the desired number of times with wiping at the wheel of a cleaning brush in contact with the upper surface of the roll or by manual cleaning. Four (to seven) coats of the roller in this manner produce good results. As mentioned above, once a particle image is formed on one of the electrodes, it can be attached thereto by spraying a binder, by applying a coating, or by including a binder solution in the liquid suspension medium. In most cases, however, it will be found advantageous to transfer the image from the electrode and attach it to another substrate so that the electrode can be reused. Such a transfer can be accomplished by lifting the image using an adhesive surface such as for example "Scotch brand" cellophane tape or preferably by means of electrostatic field transfer. Electrostatic transfer can be carried out, for example, by carrying out the de-filming process as described in connection with Fig. IA, and then allowing another roll to pass above the particle image formed on the electrode 11, which roll is held at a potential which has the opposite polarity to that of the first electrode ktrode

(roll 23). If the second electrode roll is coated with a sheet of baryta paper, this will take up the entire image as the electrode roll is rolled over it.

Although different electrode distances can be used, distances of less than 25 microns extending down even to the point where the electrodes make contact with each other, as in the case of the roller electrode in fig. IA, a particularly preferred form of the invention in that such distances produce better sharpness and far better color separation results than what is produced with a greater distance when these distances are used under the above-mentioned voltages. This improvement is believed to be due to the high field strength across the suspension during imaging.

The following examples are given to illustrate the invention. All the subsequent examples were carried out in an apparatus of the general type shown in fig. IA with the image mixture 14 coated on a "NESA" glass through which the exonation was carried out. The glass surface was connected in series with a switch, a voltage source

and the conducting central part of a roll coated with baryta paper on the surface. The roll had a diameter of approx. 64 mm and was moved across the electrode surface at a speed of 1.45 cm. per second. The electrode surface used was approx. 8 cm. square and was exposed to a light intensity of l800 normal light. Unless otherwise specifically mentioned, 7% by weight of the pigment mentioned in each example was suspended in "Sohio odorless Solvent 3440" and the applied voltage was 2500 volts. All particles which, when purchased, had too large a particle size, were ground for 48 hours in a ball mill in order to produce a more stable dispersion and thereby improve the sharpness of the finished image. The exposure was made with a 3200° K lamp through a 0.30 neutral density step v/edge filter to measure the sensitivity of the suspensions to white light. Then "Wratten" filters Nos. 29, 6l and 47b were each draped over the light source in separate experiments to measure the sensitivity of the suspension to red, green and blue light respectively.

The relative sensitivity of the suspensions indicated in reactivity numbers is derived from the number of steps in the step wedge filter ("step wedge filter") that could be distinguished in the images obtained through this filter. Thus, where one step was visible in the image, the sensitivity was 1, where two were visible, it was 2, and where three were visible, it was 4, where 4 was visible, it was 8, etc. Many were tried with raster copy ('' line codv") or continuous toning media. ("tone subjects") and everyone who was tested in this way produced good quality images with both types of media.

Example I.

"Locarno Red X-1686", CI. No. 15865, 1-(4'-methyl-5'-chloroazobenzene-2'-sulfonic acid)-2-hydroxy-3-naphthenic acid was ground in a ball mill, dispersed in "Sohio,,solvent and<p>robed on light- sensitivity. The pigment showed the same reactivity whether the roll was made positive or negative to the "NESA" glass electrode. The relative sensitivity of the suspension to blue light was 2, to green light 8, to red light 0, and to white 32.

Example II.

"Watchung Red B", a barium salt of 1-(4'-methyl-5'-chloroazo-benzene-2'-sulfonic acid)-2-hydroxy-3-naphthenic acid, CI. No. 15865 was tested with positive tension on the roller. This pigment showed a sensitivity of 1 to blue light, 4 to green light, 0 to red light and 32 to white light.

Example III.

"Permagen Red L Toner 51-500", 1-(4'-methyl-5.'-chloroazobenzene-2*-sulfonic acid)-2-hydroxy-3-naphthenic acid, CI. No. 15865 was tested with both positive and negative voltage on the roller and found to give the same reactivity to both, which suggested bipolarity in the suspension. The reactivity was as follows: 8 for blue light, 32 for green light, 0 for red light and 64 for white light.

Example IV.

"Napthol Red B", 1-(2'-methoxy-5'-nitrophenylazo)-2-hydroxy-3"-nitro-3-naphthanilide, CI. No. 12355, was tested with positive voltage on the roll and gave the following reactivity : opposite blue light 1, opposite green 4, opposite red 0 and opposite white 16.

Example V.

"Duol Carmine" the calcium pigment color of an azo dye, 1-(4'-methylazobenzene-2'-sulfonic acid)-2-hydroxy-3-naphthenic acid, CI. No. 15850, was tested with positive voltage on the roll and showed the following sensitivity: to blue light 5, to green light 16,

opposite red light 1 and opposite white light 64.

Example VI.

"Bonadur Red B", an insoluble azo dye, was tried

with positive tension on the roller. The pigment is a dye, described in CI. No. 15865, with hydrogen substituted for sodium in the compound to render it insoluble. The dispersion showed the following sensitivity: to blue light 2, to green light 8,

opposite red light 2 and opposite white light 64.

Example VII.

"Calcium Lithol Red", the calcium pigment of an azo dye, 1-(2'-azonatalene-1'-sulfonic acid)-2-naphthol, CI. No. 15630, was tested with positive voltage on the roll and showed a sensitivity of 1 to blue light, 4 to green light, 0 to red light and 16 to white light.

Example VIII. '

"Indofast Double Scarlet Toner", a Dyrantron type pigment was tested with positive voltage on the roll and showed a sensitivity of 4 to blue light, 8 to green light, 0 to red light and 32 to white light. The pigment is a polynuclear aromatic with the following

chemical structure:

Example IX.

"Quindo Magenta RV-6803" a quinacridone nigment with

following structural formula:

was tested with positive voltage on the roller and showed a sensitivity of 2 to blue light, 16 to green light, 0 to red light and 128 to white light.

Example X.

"Indofast Brilliant Scarlet Toner", 3,4,9,10- (N,N'-(p-Methoxyphenyl)-imido)-perylene, CI. No. 71140 was tested with positive polarity on the roll and showed a sensitivity of: 32 to blue light, 64 to green light, 0 to red light and 128 to white light.

Example XI.

"Indofast Red MV-6606", a thioindoxyl nigment with the following structural formula:

(dichlorothiondigo).

was tested with positive voltage on the roll and gave a sensitivity of

2 against blue light, 8 against green light, 0 against red light.and

32 opposite white .light.

Example XII.

"Vulcab East Red BBE Toner 35-2201": 3,3'-dimethoxy-4,4-bof enyl-bis(1 "-phenyl i- 3"-nety 1-4 !'-azo-2"-pyrazoline- 5"-on). C.I.

no. 21200 was Drøvet with both positive and negative accuracy now on the roll. With positive polarity, the sensitivity was 16 to blue light, 32 to green light, 0 to red light and 64 to white light. With negative polarity: 8 for blue light, 12 for green light, 0 for red light and 32 for white light.

Example XIII.

Reversal of the phenomenon indicated by the suspension

according to t-xample XII was found to occur when a suspension of

"Pyrazolone Red B Toner", CI. No. 21120, was tested with both positive and negative polarity on the roll. This suspension showed a white light sensitivity of 16 with negative polarity and 4 with positive polarity.

Example XIV.

"Cyan Blue GTNF", betaformeh of copper phthalocyanine, CI.

No. 74160, was<p>robbed with positive voltage on the coil and gave a sensitivity to blue light of 1, to green light 1, to red light 16 and to white light 32.

Example XV.

The alpha form of the pigment according to Example XIV (trade name: "Cyan Blue XR") was driven with positive voltage on the roll and gave a sensitivity of 1 to blue light, 4 to green light, 16 to red light and 32 to white light.

Example XVI.

"Monolite Fast Blue G.S." the alpha form of metal-free phthalocyanine, CI. No. 7^100 was tested with positive tension on the roll and gave a sensitivity of 1 to blue light, 8 to green light, 32 to red light, and 64 to white light.

Example XVII.

The test of Example XVI was repeated except that 3 mole percent of 2,4,7-trinitro-9-fluorenone was added to the "Monolit Fast Blue" suspension, which gave a two-fold increase

1 photographic speed in the suspension.

Example XVIII.

The test of Example XVI was repeated except that 2 mole percent of benzonitrile was added to the suspension, which gave a 3-fold increase in photographic speed.

Example XIX.

The pigment of Example XVI was changed to the alpha form by painting in o-dichlorobenzene and found to have a sensitivity of i to blue light, 4 to green light, 32 to red light and 64 to white light with positive potential on the roll.

Example XX.

Methyl violet, an acid fo^fortungstic molybdic acid pigment of triphenylmethane dye, 4-(N,N',N'-trimethylaniline)-methylene-N", N"-dimethyl laniline chloride, CI. No. 42535 was tested with positive polarity on the roller and was found to have a reactivity of 0 to blue light, 1 to green light, 1 to red light and 8 to white light.

Example XXI.

A suspension of "Indofast Violet" pigment, dichloro-9,18-isoviolanthrone, CI. No. 60010 was<p>robed with positive potential on the roll and gave a sensitivity of 0 for blue light, 8 for green light, 0 for red light and 32 for white light.

Example XXII.

"Diane" blue, 3,5'-methoxy-4,4'-diphenyl-bis(1"-azo-2"-hydroxy-3"-naphthanilide), CI. No. 21180 was tested with positive potential on the roll and showed a sensitivity of 0 to blue light,

1 for green light, 8 for red light and 16 for white light.

Example XXIII.

A polychloro-substituted copper phthalocyanine, CI. No. 74260 was tested with positive voltage on the coil and gave 0 for blue light, 0 for green light, 16 for red light and 32 for white light.

Example XXIV.

A sample of "Indanthrene Brilliant Orange R.K.", 4,10 dibromo-6,12-anthanthrone, CI. No. 59300 was tested with negative voltage on the roll and showed the following sensitivity: 4 to blue light, 16 to green light, 0 to red light and 32 to white light.

Example XXV.

"Algol Yellow CC", 1.2.5.6.-di-(C,C'-diphenyl)-thiazolan-traquinone, CI. No. 67300 was tested with a positive roll and showed the following reactivity: 2 to blue light, 0 to green light,

0 for red light and 8 for white light.

Example XXVI.

The test according to Example XXIII was repeated with exception

of 2 mole percent 2,4,7_trinitro-9_fluorenone being added to the pigment suspension consisting of "Algol Yellow", which gave a fourfold increase in photographic speed.

Example XXVII.

"Indofast Yellow Toner", flavanthrone, CI. No. 70600 was examined with a positive roll and showed the following reactivity: 16 for blue light, 4 for green light, 0 for red light and 64 for white light. With a negative roll, the reactivity was: 8 for blue light, 2 for green light, 0 for red light, and 32 for white light.

Example XXVIII.

"Indofast Orange Toner", a benzimidazole pigment, CI.

No. 71105 was tested with a positive roll and gave the following reactivity:

0 for blue light, 8 for green light, 16 for red light and 32 for white light.

Example XXIX.

Bright "Cadmium Orange Concentrate", a cadmium selenide pigment, CI. No. 77196 was tested with a negative roll and gave the following reactivity: 80 for blue light, 0 for green light, 20 for red light and 160 for white light.

Example XXX.

1-cyano-2,3~phthaloyl-7,8-benzopyrrocoline was synthesized according to the first method given for its synthesis (see: Journal of the American Chemical Society: "Reactions of Naohtoquinones with Malonic Ester and its analogs. III, 1-Substituted Phthaloyl and Phthaloylbenzopyrrocolines". 5•March 1957, page 1215)- This yellow compound was tested with a negative roll and showed the following reactivity: 0 for red light, 8 for green light, 16 for blue light and 16 for white light.

Example XXXI.

A suspension comprising equal amounts of "Watchung Red B"

(see Example II), "Monolite East Blue G.S." (see Example XVI) and the yellow pigment according to Example XXX in "Sohio" solvent was prepared with a total amount of pigment of 8% by weight of the suspension. These pigments are respectively magenta, cyam and yellow. The mixture hereinafter referred to as "wood mixture" was smeared on a "NESA" glass plate and exposed under the same conditions as described in connection with Example I except that a "Kodachrome" film was placed between the white light source and the "NESA" the glass so that a colored image was projected onto the composite wood as the roller moved across the "NESA" glass. Here, too, a barite paper blocking electrode was used and the roll was held at a negative potential of approx. 2,500 volts in relation to the substrate. The roller was rolled six times over the substrate and cleaned between each pass. After the sixth roll, an excellent, fully colored image was left on the glass surface. The voltage and exposure were maintained at all times during the six times of rolling.

Example XXXII.

A suspension comprising equal amounts of "Watchung Red B", "Algol yellow G.C." and "Monolite East Blue G.S." in "Sohio" solvent was prepared with a total amount of pigment of approx. 7 percent by weight. The mixture was applied to a "NESA" glass and exposed under the same conditions as described in Example I except that the "Kodachrome" film was placed between the white light source and the "NESA" glass so that a colored image was projected onto the wood mixture as the roller moved over the "NESA" glass. Here too, a barite paper blocking electrode was used and the roll was held at a negative potential of 2500 volts in relation to the introduction electrode. After the roller had passed over the lead-in electrode, a subtractive color image appeared on the lead-in electrode. This experiment was repeated using cellophane-cellulose acetate and polyethylene-coated paper, polystyrene, polystyrene, polytetrafluoroethylene and polyethylene terephthalate as barrier electrode surfaces instead of baryta paper. All these materials gave good results, the first three materials the best.

Example XXXIII.

The test according to Example XXXII was repeated with the exception that 2 mole percent 2,4,7_trinitro-9-fluorenone was added to the wood mixture, which gave four. times increase in photographic speed.

Examples XXXIV - XXXIX.

Six different pigment-wood mixture suspensions were prepared, each comprising equal amounts of three different pigments in "Sohio", odorless solvent as described above with a total pigment content of 7% by weight.

In Example XXXIV, the wood composite was prepared from "Duol Carmine" (see Example V), "Algol yellow" (see Example XXV) and "Monolite Fast Blue" (see Example XVI).

In example XXXV, the wood composition consisted of "Watchung Red B"

(see Example II), "Monolit Fast Blue G.S. (Example XVI) and "Velvaglow Fluorescent" pigment which is mainly sensitive to blue light.

In Example XXXVI, the wood composition consisted of "Monolite Fast Blue G.S.", "Lermon Cadmium Yellow", CI. No. 77196 a cadmium sulphide oigment sensitive mainly to blue light, as well as "Watchung Red B".

The wood composition in Example XXXVII consisted of "Monolite East Blue G.S.", "Indofast Yellow Toner" (Example XXVII) and "Watchung Red B".

The wood mixture in Example XXXVIII consisted of "Cyan Blue Toner G.T.N.C" (Example XIV), "Algol yellow (Example XXV) and "Watchung Red B".

The wood mixture in Example XXXIX consisted of "Indofast yellow

Toner", "Cyan Blue Toner" (Example XIV) and Watchung Red B".

Each of these six wood material mixtures was tested for imaging properties according to the technique described in Example XXXII and found to give good quality color images.

Example XL.

A wood suspension was prepared, comprising equal amounts of "Watchung Red B", "Monolite Fast Blue G.S." and the yellow pigment described in Example XXX in "Sohio" solvent with a total pigment content of 8% by weight. The suspension was tested according to the procedure described in Example XXXII and gave good color images with well-separated colours.

Examples XLI - XLIII.

In each of the following examples, a suspension was prepared comprising equal amounts of the two differently colored pigments in "Sohio" solvent with 6% by weight of total pigment.

In Example XLI, the pigments were "Algol Yellow" and "Cyan Blue Toner GTNP".

In Example XLII "Watchung Red B" and Cyan Blue Toner GTNF".

In Example XLIII “Watchung Red B” and “Monolite Fast Blue

G. S." .

The three two-pigment suspensions, when exposed to two- and three-color images containing respectively blue and red, green and red, and green and red according to the method of Example XXXII, were found to give two-color images of blue and red -, green and red, and green and red parts of the original image on the upper electrode (roll) in the imager.

Claims (4)

1. Process for photoelectrophoretic imaging where a suspension of electrically photosensitive particles, containing an electrically photosensitive pigment, in a carrier liquid is exposed to an electric field applied over two electrodes, at least one of which is at least partially translucent, the image being formed by the suspension is exposed to an image with a source of activating electromagnetic radiation through the translucent electrode, characterized in that particles are used where the pigment is both the primary electrically photo-sensitive component and the particles' primary colourant. 2. Method in accordance with claim 1, characterized in that particles are used which consist almost entirely of the electrically photosensitive pigment. 3. Apparatus for carrying out the method in accordance with claim 1 or 2, comprising a device for applying an electrical field over a suspension of finely divided particles between two electrodes, at least one of which is at least partially translucent, - a source of activating radiation as well as a device for exposing the particle suspension to an image pattern of the activating radiation, characterized in that the second electrode is a blocking electrode whose surface is formed by a material that has a 7 2 specific resistance na at least 10 ohm/cm, that the distance between the electrodes is less than 25 microns and that the applied electric field has a field strength of at least 12 volts per micron. 4. Apparatus in accordance with claim J> .~characterized in that the blocking electrode's surface facing the image-forming suspension is made of particulate barium sulfate suspended in gelatin.