DE1522748A1 - Process for electrophoretic image reproduction - Google Patents

Description

Process for electrophoretic image reproduction

The invention relates to a method for image reproduction, in particular a method for image reproduction using of electrically photosensitive particles in the case of photoelectrophoretic ones Image reproduction systems.

Some time ago, an electrophoretic image display system suitable for displaying color images using photoconductive constituent particles has been proposed and which is described in Patent A (patent application X 37 IXa / 57e). In this image display system, differently colored, light-absorbing particles are suspended in a non-conductive liquid carrier. The suspension is placed between electrodes exposed to a potential difference and exposed to the image. After completing these stages, a selective particle

Migration takes place in the image display, which results in a visible image on one or both electrodes. An essential part of the system are the suspended particles, which are electrically photosensitive must, and obviously a useful change in charge polarity upon exposure versus activating electromagnetic radiation through interaction with one of the electrodes. With a monochrome

In the table system, particles of a single color are used, resulting in a single-colored image corresponding to conventional black-and-white photography. In a polychromatic system, natural images are obtained as mixtures of particles of two or more different colors, each opposing light
of a specific wavelength or a narrow range of wavelengths can be used. The particles used in this system must have both

k have an intense pure color, as well as strongly photosensitive be. The known pigments often lack the purity and brilliance of the color, they often lack one high degree of photosensitivity and / or the preferred relationship between peak spectral sensitivity and the peak photosensitivity necessary for use in such a system.

The object of the invention is therefore photoelectro-

90 9 8-4 471 A4 4

using phoretic image reproduction methods of photosensitive pigment particles in which the above listed ifiingel can be overcome. Another aim of the invention ordered M use to be highly photosensitive Particles in electrophoretic image display systems. Another object of the invention is to provide electrophoretic image reproduction methods in which Color images are generated. Another object of the invention is photoelectrophoretic image reproduction processes, where particles * have superior properties in terms of photographic (speed and color can be used over those of known pigments.

The above tasks and other benefits will be basically solved according to the invention in that in photoelectrophoretic image reproduction processes are used * the compounds of the general masses Foraiel

contain, in which X is substituted or lan-substituted _r mononuclear or omnuclear, aromatic or heterocyclic "groups with an ÖH substituent in ortho or" para position to the azo bond and Y is substituted or unsubstituted , mononuclear Öäer "iaelirkernige", "aromatic or heterocyclic groups mean.

ORIGINAL INSPECTED

9 0 ' "'. KI 1 L i _L

Compounds with the -N = N group are generally as azo compounds, for example azo dyes or pigments, and are generally used obtained from amine compounds by diazotization and coupling.

Within the broad class of aromatic and heterocyclic azo compounds, a number of subordinates were found Classes as particularly valuable for photoelectrophoretic image reproduction processes. These subclasses that used in accordance with the invention are as follows:

1. Compounds of the general formula

wherein R is a substituted or unsubstituted, mononuclear or polynuclear, aromatic or heterocyclic A group with an HO radical in ortho- or para-position to the azo bond, 2. Compounds of the formula

S 0? ⁿ Λ / · / 1 LkL _ΛΛΙΛ

ORIGINAL INSPECTED

where R is an aromatic group with several rings,
3. Compounds with phenyl or naphthyl groups as aromatic nuclei, in any available position

alternately
on the nucleus SSXJSSÄSX is substituted by OH or a group R, the group R having the general formula

-N = N

wherein X and Y are lower alkyl or hydroxy substituted lower alkyl groups, Z is a hydrogen or halogen atom, a lower alkyl, lower alkoxy, cyano or nitro group and η a positive one

Number from 1 to 4,

4. Compounds of the general formula

OH

It

N = N-Y

wherein X and Y are unsubstituted or substituted mean aromatic or heterocyclic radicals.

The subclasses of azo compounds listed above are preferred for use in photoelectrophoretic imaging processes because they are simple and

908044/1 ΑΛΑ

15227A8

are economical to manufacture, have a special pure and brilliant color and special are highly photosensitive. As the color and tint of the above compounds and their spectral and photosensitive excitability may vary Intermediate values of these variable values can be obtained by mixing some different compounds will.

As is known, azo dyes can be obtained in virtually any desired color. In monochromatic image reproduction, any color can be used to produce a two-color image, ie the color of the background material and the color of the compound used. While black and white images are usually preferred, images in other colors may be preferred for specific purposes, such as signs * or posters. An additive polychromatic system uses red, green and blue particles, while a subtractive system uses greenish-blue particles , magenta, and yellow particles can be used. Suitable photosensitive colored particles of each of these colors can be selected by the person skilled in the art from the compounds used according to the invention. It can be any suitable aromatic or heterocyclic

903844/1444

Azo compounds or mixtures thereof can be used.

Typical azo compounds in the context of the invention are:

2,4,6-Tris (N-ethyl-N-hydroxy-ethyl-p-aminophenylazo) - - (phloroglucin) ₂ -l, 3,5,7-tetrahydroxy-274 _T 6 _T 8-tetra (N- - methyl-N-hydroxyethyl-p-aminophenylazo) naphthalene; 1,3,5-trihydroxy-2,4,6-tri (3 * -nitro-N-methyl-N-hydroxymethyl 1-4'-aminophenylazo) benzene; 1,3,5-trihydroxy-2,4,6-tri (N-propyl-N-hydroxypropyl-4'-aminophenylazo) benzene; 1,3,5-trihydroxy-2,4,6-tri (3 ', 5'-dichloro-N-ethyl-N-hydroxyethyl--4 · aminophenylazo) benzene; S-methyl-l-phenyl ^ - (3'-

-pyrenylazo) -2-pyrazolin-5-one; 1- (3'-pyrenylazo) -2-hydroxy- -3-naphthanilide; l- (3'-pyrenylazo) -2-naphthol? l- (3'- Pyreneylazo) -2-phenol; 1- (3 x -pyrenylazo) -2-hydroxypyrene; 1- (3'-pyrenylazo) ^ -hydroxy-S-methyl-xanthene; 1- (3'-pyrenylazo) -2-hydroxyanthracene; 5- (3'-pyrenylazo) -4- hydroxy-1,2,3-triazole; 2,4,6-tris (3'pyrenylazo) phloroglucine; 2,4,6-tris (1'-naphthylazo-phloroglucinol; 2,4,6-tris- (2'-perylenylazo) -phloroglucinol; 2,4,6-tris (§'-phenylenylazo) -phloroglucine; 2,4,6-tris (1'-phenanthrenylazo) - -phloroglucine; 2,4,6-tris (1'-anthracenylazo) phloroglucine.

The compounds used according to the invention can be Manufacture according to the usual methods. The following examples are typical procedures for making the compounds, which are used according to the invention, described. Parts and percentages are based on weight, unless otherwise noted. The following examples

ORIGINAL tNSPECTED

9 0? ^q / L l 1 hf. i

However, games only give various preferred embodiments for the production of the invention connections used.

Example I.

About 4 parts of 3-aminopyrene were added to the sulfuric acid salt by stirring at room temperature with a mixture from about 12.5 parts of concentrated sulfuric acid

^v and about 6.5 parts of water for 20 minutes. The resulting suspension was diluted with about 200 parts of ice water. A concentrated aqueous solution of about 1.5 parts of sodium nitrite was then slowly added to this cold mixture. With stirring, a solution of about 1 part of phloroglucinol in about 50 parts of pyridine, about 100 parts of a 3N sodium hydroxide solution and about 250 parts of water was slowly added to this cold mixture. A black precipitate separated out. The mixture was made alkaline by adding 50% sodium hydroxide solution and then brought to room temperature. After standing for one hour, the mixture was acidified, heated to coagulate and the black precipitate filtered off. The dried solid was treated with about 200 parts of boiling ethanol and filtered hot. The product was then treated with warm, dilute sodium hydroxide solution, filtered, washed well with water and in

3Q

dried in a vacuum oven at about 70 ° C. The product consists of 2,4,6-tris- (3'-pyrenylazo) phloroglucinol with a melting point of approx. 278 - 284 ° C (decomp.)

Example 2

About 4 parts of 3-aminopyrene was transferred to the sulfuric acid salt by stirring at room temperature with a mixture of about 12.5 parts of concentrated sulfuric acid and about 6.5 parts of water for 20 minutes "The solution obtained was mixed with about 200 parts of ice water comparable thinned A . A concentrated aqueous solution of about 1.5 parts of sodium nitrite was then slowly added to this. The resulting suspension of the diazonium sulfate was slowly added to a cold solution of about 3.5 parts of 3-methyll-phenyl ^ -pyrazoline-S-one in about 150 parts of 3N sodium hydroxide solution. A brownish-red precipitate separated out. After warming to room temperature, the mixture was filtered, the precipitate was washed with water and dried in vacuo over phosphorus pentoxide. There was a quantitative yield of a red solid. Melting point 212 to 220 ⁰ C. yield by recrystallization from xylene crystals, melting point 244-246 ° C, from 3-methyl-l-phenyl-4- (3'-pyrenylazo) - - ■ ~ 2 pyrazolin-5-on exist,

S 5 9 8 4 h I 1 khk DRKSiNAL INSPECTED

Example 3

About 4.5 parts of 3-aminopyrene were obtained as in Example 1 diazotized. The diazonium sulfate slowly became a cooled solution of about 5 parts of 2-hydroxy-3-naphthanilif1 in about 50 parts of pyridine, about 100 parts of 3N sodium hydroxide and about 250 parts of water are added. The deposited precipitate was filtered off with Washed with water and dried in vacuo over phosphorus pentoxide. It became a dark purple colored solid which sintered at about 215 ° C and decomposed at about 282 ° C. By recrystallization from o-dichlorobenzene dark green-black crystals were obtained, which decompose at 305 to 308 ° C., and those from 1- (3'-pyrenylazo) -2 ~ hydroxy-3-naphthanilide exist.

Example 4

About 4.5 parts of 3-aminopyrene, diazotized as in Example 1, were coupled in a cold solution of about 3 parts of 2-naphthol in about 200 parts of 3N sodium hydroxide. The precipitate was filtered off, washed with water and dried in vacuo over phosphorus pentoxide. In this case, a dark-bordeäuxfarbiger solid which ats l- (3'-pyrenylazo) -2-naphthol is obtained with a melting point 190-205 ⁰ C.

Example 5 .

About 5 parts of N-ethyl-N-hydroxyathYl-p-phenylenedianiine were dissolved in about 150 parts of a 10% hydrochloric acid solution at 0 ° C. An aqueous solution containing about 1.5 parts was then slowly added to this cooled mixture Containing sodium nitrite was added. With stirring, the resulting cold mixture quickly became a solution of about 1 part 1,3,5-trihydroxybeHZol, which is in a solution from about 450 parts of water and about 150 parts of ammonium ^ Hydroxyd was dissolved, added. It imagined black precipitate which was filtered off, washed with water and dried. It became 2,4,6-Tris (N- -ethyl-N-hydroxyethyl-p-aminophenylazo) -phloroglucin obtain.

Example 6 .

The reaction was carried out as in Example 1, but N-methyl-N-hydroxyethyl-p-phenylenediamine and 1,3,5,7-tetrahydroxynaphthalene used. The product consists of 1,3,5,7-tetrahydroxy-2,4,6,8-tetra (N-methyl-N-hydroxyethyl-p-aminophenylazo) naphthalene.

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The reaction was carried out as in Example 1 except that 3-nitro-N-methyl-N-hydroxymethy1-4-phenylenediamine veniendet and l, 3 _r 5-trihydroxybenzene. The product is made

/// ι './· ^: ORIGINAL

off!, S / S

-hydroxymethy1-4'-aminophenylazo) -benzene.

In the accompanying figure is a transparent electrode, generally indicated by the reference number 1 shown, which in the case of this example consists of a layer of optically transparent glass 2, which is coated with a thin, optically transparent layer 3 of tin oxide, which is under the

V designation NESA glass is known. This electrode is hereinafter referred to as the "injection electrode". On the surface of the injection electrode 1 is coated a thin layer 4 of finely divided photosensitive particles dispersed in an insulating liquid carrier. As used herein, "photosensitive" or "photosensitive" refers to the properties of a particle which, after being attracted to the injection electrode,

^ of this under the influence of an applied electric Field migrates away when exposed to actinic electromagnetic radiation. One the detailed theoretical explanation of the mechanism of this operation is given in the above listed patent specification.; ..... (patent application X -37 IXa / 57e) given, which also in the present case should apply '. The liquid suspension ioa 4 can also

9 0 '- ¹ VV UI 1 /. / / _; .

ORlGINAi INSPECTED

a sensitizer and / or a binder for the Contain pigment particles that are at least partially soluble in the suspending or carrier liquid are, as will be discussed in detail below. Adjacent to the liquid suspension 4 is a second electrode 5, which is subsequently used as the blocking electrode is referred to, and with one side of the potential source 6 is connected by means of a switch 7. The opposite side of the potential source 6 is with the injection electrode 1 connected so that - if the Switch 7 is closed - an electric field between electrodes 1 and 5 through the liquid suspension 4 is created. An image projector consisting of a light source 8, a glass image 9 and a lens id is attached to the dispersion 4 a

To expose the original glass to be reproduced
image 9 soBXKEHäsi :. The electrode 5 is made in the form of a roller with an iron conductive central core Ii, which is connected to the potential source IS. The core ^

is with a layer of barrier electrode material 12 covered, which can consist of baryta paper. The pigment suspension is exposed to the image to be reproduced, while a potential is applied across the blocking and injection electrodes by closing the switch 7 will * The roller 5 will be used to roll over the top one Surface of the injection electrode 1 brought; where the

ßO 8 3 A4 / 1 hhly

ORIGINAL INSPECTED

Switch 7 is closed during the exposure period. This exposure to light causes the exposed pigment particles that were originally attracted to electrode 1 to migrate through the liquid and adhere to the surface of the barrier electrode, leaving behind them a pigment image on the injection electrode surface, which is a duplicate of the original glass or transparency image 9 represents. After exposure, the relatively volatile carrier liquid evaporates * leaving the pigment image behind. This pigment can then be fixed, for example by applying a layer over its upper surface or by means of dissolved binding material in the carrier liquid, for example a paraffin wax or another suitable binder which separates out of the solution when the carrier liquid evaporates. At about 3 to 6 wt -.% Of a paraffin binder in the carrier, good results revealed. The carrier liquid itself can consist of a paraffin wax or another suitable binder. On the other hand, the pigment image remaining on the injection electrode can be transferred to another surface and fixed thereon. As will be explained in detail below, both monochromatic and polychromatic image reproductions can be obtained by this system, depending on the type and number of those suspended in the carrier liquid

90S8U / 1U4 _0B1G1N AL INSPECTED

Pigments and the color of the light to which this suspension is exposed during the process is.

Any suitable insulating liquid can be used as a carrier for the pigment particles in the system will. Typical carrier liquids are decane, Dodecane, n-tetradecane, paraffin, beeswax or other thermoplastic substances, Sohio-odor-free-solution ^ medium 3440 (kerosene fraction from the Standard Oil Company of Ohio) and Isopar-G (long-chain, saturated, aliphatic Hydrocarbon from the Humble Oil Company of New Jersey). Image reproductions were of good quality with voltages in the range of 300 to 5000 volts in the device shown in the figure.

In a monochromatic system, particles become one single compound dispersed in the carrier liquid and exposed to a black and white image. Biea It gives ^

a monochrome picture that resembles a usual black-and-white photograph is equivalent to. In a polychromatic system, the particles are chosen so that those of different colors at different wavelengths in the visible spectrum according to their Address main absorption bands. The pigments must also be chosen in such a way. ^ .. that yours. , Spectral Sensitivity-.

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Speed curves show no significant overlap, so that there is a color separation and a subtractive multicolor Image reproduction results. In a typical multicolor subtractive system, the particle dispersion should contain bluish-green colored particles that are mainly sensitive to red light, magenta colored particles, mainly opposite Green light are sensitive, and yellow colored particles are primarily sensitive to blue light. When these particles are mixed in a carrier liquid, a black looking liquid results. When one or more of the particles is used to migrate from of the base electrode 11 migrate to an upper electrode, they leave behind particles that have one color result in an equivalent color of the light occurring. E.g. if they are exposed to red light, they migrate blue-green colored pigment particles, while the magenta colored and yellow pigments remain which combine to form red in the final image. In the same way, blue colors and green colors are reproduced by removing yellow and magenta, respectively. If white light strikes the mixture, wander all pigments, leaving the color of the white or transparent substrate behind. When no light exposure occurs, all pigments remain, which combine to form a black image.

9 C, '9- ν L "/. / 1 L! L

ORfGSNALINSPECTED

This represents an ideal method for subtractive Color image reproduction is to the extent that the particles are not just composed of a single component are, but also a twofold effect of the final image coloring and the photosensitive Exercise medium.

It has been found that the azo compounds described above are surprisingly effective when they are used in either monochrome or multicolor electrophoretic image display systems. Their good spectral sensitivity and their high photosensitivity result in dense, brilliant images.

All suitable, differently colored, photosensitive pigment particles with the desired spectral sensitivity together with the present compounds for the formation of a particle suspension in a carrier liquid for color image I playback can be used. About 2 to 10% by weight pigment gives good results. The addition less Amounts, generally between 0.5 and 5 mol%, of electron donors or acceptors to the suspensions can have significant increases in photosensitivity of the system.

9 0 ° ° '-, k I 1 U k U ^0Ri GWÄL INSPECTED

The following examples further illustrate the present invention with regard to the use of the Compounds of the general formula given above in electrophoretic image reproduction processes. Parts and percentages refer to the area unless otherwise noted. The following Examples illustrate various preferred embodiments of the electrophoretic image reproduction process £ according to the invention.

All of the following Examples 8-21 were used in executed a device of the type shown generally in the figure, the Fig 11 training mixture 4 on a NESA gas pad through which the Suspension took place. The NESA glass surface was in Series with a switch, a potential source and the conductive core of a roller with a coating of baryta paper connected on the surface. The roller had a P diameter of about 6.35 cm and was moving over the plate surface at a speed of about 1.45 cm moves every second. The panel was approximately 19 cm and was measured with a light intensity of 8,000 ft.-candles exposed on the light-coated NESA glass surface. All pigments with a relatively large particle size were ground in a ball mill for 48 hours to comminute their particle size, so that a

9 0 2 8> · ■ LI 1 ¹ A ι, h

ORiGlNALiHSPECTED

gave more stable dispersion which improves the resolution of the final image.

The examples listed in Table I give SpektralempfindlichkeitsUntersuchungen again _r as follows were carried out: About 7 parts of special pigment listed in column 2 of Table I were a kerosene fraction suspended in about 100 parts Sohio odor-free solvent-3440. This mixture Λ was spread onto the NESA glass injection electrode and a potential of the polarity and size listed in column 5 was applied to the barrier electrode. The exposure was to a lamp of 3200 ° K through a 0.30 step filter of neutral density to determine the sensitivity of the suspension to white light, and then Wratten-29-, -61-, and -47b- Filters individually placed over the light source in individual experiments to determine the sensitivity of the suspension to red, green and blue light. The ™ spectral sensitivity of the suspensions is given in columns 6 to 9 of Table I. Sensitivity is reported in ft.-candles obtained from a graph of optical density versus logarithm of exposure in ft.-candies. This is die'übliche method for the determination of a photosensitive material in photographic speed ^{l1. 11} The abbreviation "synth. ^M " means that the material was produced according to the method described above.

9 0 2 iU Λ / U '^ ORIGINAL INSPECTED

7 V -7 I ι Ί 7 8 6 O

Table I.

Example no.

formula

Roller paint manufacturing potent.

(Volt)

Sensitivity (f.C) Blue Green Red White

VIII

Black synth,

Black synth.

+5000 V 250 125 75 50 +2500 V 120 60 30th 30th +1000 V 60 20th 10 15th

+2500 V -2
-2500 V -1

250
900

-1

+1/3 +1/2

N = N

Il

00

77 7 I / V 7 8 6 0 6

example

I. __ ■

t p

formula

colour

Table II Roller '
potent.
(Volt) Empi
Embarrassing green RQt: IQO:
100 Manufacturing + 25QO V
-2500 V 500
500 125
200 500 » ■. Synth.

Red

XI

black

Synth.

'+2500 V
-2500 V

4000 3000 4Q0Q 3Q0Q

20QQ

7ViL7778606

Example no.

formula

Table III

colour

Manufacturing

Reel pot.
volt

Sensitivity (f: ■ © _<..); Blue green red white

black

Synth.

+2500 V

240

120

30th

30th

Synth.

Table IV

Example no.

formula

colour

Roller potentiometer. Manufacture <volts

Sensitivity (f.ei.)
Blue green red white

3OV

bluish-prot synth.

-2500 V +2500 V

1000
2000

700
2000

cn ro ro

In Example 15 below, a suspension was used from equal amounts of three differently colored ELgmenten produced, including the pigments in finely divided Form in Sohio-odorless-solvent-3440 Were dispersed so that the pigments about 8 wt .-% of the mixture resulted. This mixture is referred to as a "triple mixture". The mixture was examined by mounting it on a NESA glass pad and

^ as investigated in Example 8, with the exception that a multicolored Kodachrome transparency between the light source and the plate instead of the neutral one dense and Wratten filter was given. This projected a multicolored image onto the plate, when the roller is above the surface of the coated ; NESA glass substrate moved. It became a barite paper barrier electrode used, and the roll in the case of a negative Maintained potential of about 2500 volts with respect to the substrate. The roller was over the backing

ψ performed six times and was cleaned after each run. Potential and exposure were maintained throughout the six passes of the roller. After the six rounds, the image reproduction remaining on the base was examined _; borrowed density and color separation examined.

Example 15

The mixture of three consisted of a cyan pigment, Monolite

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Fast Blue GS / the alpha form of a metal-free phthalocyanine, those of E.I. duPont de Nemours & Co. available is, as a magenta pigment, the 3-methyl-r-phenyl-4- (3'- -pyrenylazo) ~ 2 ~ pyrazolin ~ 5-one and as a yellow pigment the Indofast Yellow Toner, a flavanthrone C.I. No. 70600 by Harmon Colors. This mixture of three resulted in a picture reproduction of good quality corresponding to the original.

The compounds according to the invention can be used alone Used to produce a monochrome image reproduction corresponding to the usual black and white photography will. Typical monochromatic image reproduction operations are shown in Examples 16-21 below. These single pigment suspensions were prepared in the same way as the three-part mixture described above exposed. The original image consisted of either 'a Kodachrome multicolor transparency or a usual black and white transparency.

Example 16 ,

About 7 parts of S-methyl-l-phenyl ^ - (3 '-pyrenylazo) -2- -pyrazolin-5-one were in about 100 parts of Sohio-odorless-solvent-S ^ O suspenäiert. The mixture was drawn up on the NESΑ glass base and a negative one Potential applied to the roller electrode. The plate was through a standard black and white transparency

909844 / Ί 444

exposed. The roller electrode was over the plate performed during the suspension. The one on the barrier electrode adhering particles were removed therefrom by cleaning, and the exposure step was repeated. It appears on the NESA glass surface an image corresponding to the Original. Since this pigment has a red color fairy, it occurs rendering as red and white on.

Example 17

About 8 parts 1- (3 '-pyrenylazo) ^ -hydroxy-S-naphthanilide were added in about 100 parts of Sohio noiseless solvent 344o suspended. The mixture was placed on the NESA glass pad drawn up and a negative potential applied to the roller electrode created. The plate was through a usual Black and white transparency at the same time as the passage exposed to the roller electrode via the plate. A reproduction corresponding to the original appears on the NESA glass surface. Because this pigment is a dark one If it is green-black in color, the image appears roughly black-and-white.

Example 18 \

About 8 parts of 1- (3'-pyrenylazo) -2-naphthol were approximately 100 parts of Sohio-odorless-solvent-3440 suspended « The mixture was drawn up onto the NESA glass support and a negative potential applied to the roller electrode

9 D 9 8 4 4/144 4

lays. The plate was through a standard black and white transparency exposed simultaneously with the passage of the roller electrode across the plate. It an image corresponding to the original appears on the Plate surface. Since this pigment is dark purple in color, the image appears purple and white.

Example 19

About 7 parts of 2,4,6-tris (1'-naphthylazo) phloroglucine were mixed with approximately 100 parts of Sohio 3440 Odorless Solvent. This dispersion was applied to the NESA surface drawn up and exposed while a negative potential of about 1000 volts is applied to the roller electrode was created. A picture corresponding to the original was made generated on the NESA surface. This image can be based on a white surface, e.g. ordinary paper, be transmitted. The result is a black and white image Of excellent quality.

Example 20

About 7 parts of 1,3,5,7-tetrahydroxy-2,4,6,8-tetra (N-methyl-N-hydroxyethyl-4 ^l -amino * phenylazo) naphthalene were mixed with about 100 parts of Sohio-Odorless Solvent 34400 mixed. This dispersion was drawn onto the NESA surface and exposed to a potential of about 1000 volts applied to the roller electrode. A corresponding picture

9 0RaU / -α ;; /. _{ΛηιΑίΝΜ mSPE} cTtf>

the original was formed on the NESA surface. This image can be used on a white surface, for example ordinary paper, transferred. A black and white picture of excellent quality is obtained.

Example 21

About 8 parts of i, 3,5-trihydroxy-2,4,6-tri (3'-nitro-N-methyl-N-hydroxymethyl ~ 4 -aminophenylazo) benzene were mixed with about 100 parts of Isopar-G. This dispersion was drawn onto the NESA surface and exposed while a potential of about 2500 volts was applied to the roller electrode. A picture according to the original results on the NESA surface.

As can be seen from the examples above, are the azo compounds very suitable for use in electrophoretic image reproduction process because their photographic speed, its density properties and Farh properties vary, a mixture may be more specific Pigments are preferred for many uses.

Although specific compounds and proportions have been given in the preceding examples, these can be varied by other suitable materials or in other proportions , in addition to other substances being added to the

90 98 44/1 UUk

Pigment masses for synergization. Increase or other Modification of their properties can be added. "The pigment compositions can be as desired according to the invention They can be dye-sensitized, or they can be both with other photosensitive materials organic as well as inorganic can be mixed.

■ 90 9 844 / U4-4-

Claims (1)

Claims (lj method for electrophoretic image reproduction, whereby a layer of a suspension is exposed to an applied electric field between at least one pair of electrodes, one of which is at least partially transparent, and at the same time this suspension is exposed to image reproduction through the transparent electrode with activating electromagnetic radiation, whereby a Pigment image is formed from migrating particles on at least one of the electrodes, characterized in that the suspension contains a plurality of finely divided particles of at least one color which consist of particles of the following photosensitive diazo pigments: a) Compounds of the general formula wherein R is an aromatic or heterocyclic radical with an HO group in ortho- or para-position to the azo bond,
co b) compounds of the general formula ORIGINAL INSPECTED where R is an aromatic group with several rings, c) Compounds with phenyl and naphthyl groups as aromatic nucleus, each available position of the nucleus being alternately substituted by HO groups and R groups where the groups R have the following general formula: -N = N wherein X and Y substituted lower alkyl or hydroxy substituted lower alkyl groups, Z hydrogen or halogen atoms, lower alkyl, lower alkoxy, cyano or nitro groups and η is a positive integer between 1 and 4, d) compounds of the general formula OU 0 C-X A / -K wherein X and Y are unsubstituted or substituted aromatic or heterocyclic radicals. 2 »Process according to claim 1, characterized in that the photosensitive pigment is a compound of the general formula ; 909844 / IA A4 ■ li = N-R wherein R is an aromatic or heterocyclic radical with a hydroxyl substituent in the ortho or para position mean for azo bond is used. 3. The method according to claim 1, characterized in that a compound of the general formula is used as the photosensitive pigment H
0. N
H
N
ι. ■ wherein R represents a multi-ring aromatic group is used. 4. The method according to claim 1, characterized in that 3-methyl-1-phenyl-4- (3'- pyrenylazo) -2-pyrazolin-5-one is used as the photosensitive pigment. 5. The method according to claim 1, characterized in that i- (3 • -Pyrenylazo) -2-hydroxy- -3-naphthanilide is used as the photosensitive pigment. 90 9 8AA / UU ■: 6. The method according to claim 1, characterized / that as photosensitive pigment 2,4,6-tris- {3'-pyrenylazo) -phloroglucin is used. 7. The method according to claim 1, characterized in that 2,4,6-tris (N-ethyl-N-hydroxyethyl-p ~ amino-phenylazo) phloroglucinol is used as the photosensitive pigment. 8. The method according to claim 1 to 7, characterized in that one electrode of the electrode pair consists of a blocking electrode. 9. The method according to claim 1 to 8, characterized in that a suspension containing a plurality of finely divided particles of at least two different colors in an insulating carrier liquid is used, wherein the particles of each color consist of a photosensitive pigment whose basic light absorption band practically coincides with its primary susceptibility to photosensitization. 909844 / T4 4 k Lee on the back