DE1497112A1 - An electrophotographic process for the production of positive or negative images by changing the color of dyes incorporated into a photoconductive layer - Google Patents

Description

PATENT DEPARTMENT LEVERKUSEN

Za / Pi ^{! a Mäl} * '965

Dr. Ü.x:;: l

An electrophotographic process for generating positive or negative images by changing the color of dyes incorporated into the photoconductive layer

The invention relates to an electrophotographic method sur optional generation of negative or positive images by color changes of dyes incorporated into a photoconductive layer, the layer being exposed imagewise and at the same time exposed to the action of charge carriers. The method according to the invention makes it possible to produce positive images or negative images on the layer using one and the same layer material, as desired. In addition, with the aid of the method according to the invention it is possible to produce images in a shorter time and in better quality than before.

The pictorial change of dyes under the simultaneous The effect of light and charge carriers is already known from American patent specification 3,082,085.

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The parbanderings always take place on those of the light made places, also from the German patent (F 43 790 IIa / 57b) known that for

the dyes known as sensitizers in combination with the corresponding semiconductors are suitable for this effect.

In the German patent specification (P 45 654 IXa / 57b)

is described that dyes, which subsequently to the Layer surface are applied, can be changed imagewise at the unexposed areas by grass discharges on the layer surface.

However, it was not enough to claim the practice quality of the images produced by the above methods in many cases they "manufacture ron pictures is especially complicated by the fact that even by relatively minor changes to the V-experiencing, such as the discharge conditions, in particular the electrode spacing of the Layer an image reversal can occur. As a result, one is forced to adhere to the prescribed processing conditions extremely precisely, which makes practical implementation considerably more difficult.

The invention is based on the object of developing an electrophotographic process which does not have the disadvantages of the known processes and which allows both negative and positive results in a reproducible manner

To make pictures.

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It has now been found that the changeability of the color a substance contained in the photoconductive layer by exposure and simultaneous action of charge carriers depends to an extraordinary extent on whether that is for the exposure used light contains wavelengths from the range of the basic lattice absorption of the semiconductor.

The basic lattice absorption is essentially the self-absorption of the semiconductor understood. Light from this wavelength range must have sufficient energy To raise electrons from the valence band to the conduction band. In the case of zinc oxide, light with a wavelength of about is sufficient 385 m / u and shorter these conditions. Light of these wavelengths supplies the zinc oxide with the energy required to raise the valence electrons into the conductivity band of about 3.2 eV.

This dependency is so great that the dyes come out of the basic lattice absorption range upon exposure to light with regard to the variability of their color under the conditions of the process can even be stabilized or vice versa expressed the changeability of the color of substances present in the photoconductive layer by simultaneous Exposure to light and charge carriers can be greatly accelerated if only for exposure such light is used that does not contain wavelengths from the basic grating absorption range. This finding is

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extremely surprising. So far, the professional world has been the Belief that the change in color is faster the more energetic the incident light. So is in the aforementioned American patent 3,082,085 the preferred use of UV light is indicated.

The above finding can now be used in the most varied of ways to produce negative or positive electrophotographic Images are applied. Negative images are understood to be those that result from a change in color the unexposed areas; in the case of positive images, conversely, those caused by a color change in the exposed areas develop.

1. Method of making positive images

In the simplest case, for example, a colored photoconductive one becomes Layer imagewise exposed using light that does not have wavelengths outside the basic lattice absorption range contains. In the case of photoconductive layers containing zinc oxide as a photoconductor, this would be e.g. Light from the visible or ultra-red part of the spectrum. A positive image of the original is obtained.

ORsGIMAL INSPECTED AS 44 - 4 -

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Is used for imagewise exposure light that contains only wavelengths from the basic lattice absorption range, i.e. when using zinc oxide as a photoconductor, uv light, no change in image is obtained with normal exposure times. Only with longer exposure times there is a slight bleaching of the unexposed areas.

If one uses Mischlich for the exposure, i.e. such what also contains wavelengths from the basic grating absorption range becomes a colored photoconductive layer on the Borders of the exposed and unexposed areas discolored, i.e. at the points where there is a jump in the conductivity of the photoconductive layer is present, finds an imagewise Change of shift instead. This effect is used according to an embodiment of the invention, which the use of unfiltered incandescent lamp light, i.e. that also contains UV light, is permitted. This embodiment is shown schematically in FIG. 1, which will be explained in more detail below. This is done simultaneously with the The original to be reproduced is projected onto a so-called auxiliary image with preferably the same light source. as Auxiliary images are suitable for example line or cross line grids. By, the exposure of the grid will be produced so-called conductivity jumps in the exposed parts of the photoconductive layer, which as further. explained above, in the absence of the help screen only to the

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Image borders arise. At the points where these conductivity jumps will take place, as already stated above, the layer changed image-wise. In this way an imagewise change in the entire exposed area is achieved. A particularly even discoloration is obtained if one takes care that the conductivity leaps over the exposed areas, which is achieved in a simple manner that the grid serving as an auxiliary image template during the exposure is moved.

2. Process for making negative images

The simplest case is imagewise exposure to light that only has wavelengths from the basic grating absorption range thus generally contains UV light. This possibility has already been mentioned above under (1) set out. One obtains after relatively long exposure times with simultaneous action of charge carriers an imagewise change in the unexposed areas of the photoconductive layer, i.e. a negative image of the original.

This process can be greatly accelerated if uniform at the same time as the exposure to UV light is exposed to such light that contains essentially no wavelengths from the basic grating absorption range.

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This embodiment is explained in more detail below Figure 2 shown schematically. Because the dye is more stable in the areas exposed imagewise to UV light is, the uniform exposure makes the photoconductive layer visible in the non-image-wise exposed areas changed .. You get a negative image of the original ·

For the uniform exposure of the photoconductive layer, light is used which has wavelengths from the basic grating absorption range contains, this uniform exposure must be done by an auxiliary image. The help picture has that above appearance specified under (1), i.e. the conductivity jumps explained above are produced and also achieved a uniform, visible change in the non-image-wise exposed parts of the photoconductive layer, i.e. a negative image of the original.

In this case the term "uniform exposure" is of course no longer correct, as this is now rasterized. Called Uniform Exposure however, it should be clearly stated that the exposure is not caused by the original to be reproduced he follows·

Negative images are obtained even if for the imagewise exposure a mixed light is used, which also has wavelengths outside the basic grating absorption range

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rich contains. In this case, the uniform exposure with or without an auxiliary image is also shown in the above carried out in the specified manner.

The known colored photoconductive layers can be used for the method according to the invention. For example, layers may be mentioned which consist of dispersions of finely divided photoconductors such as ZnO and IiO ₂ in film-forming resins or lacquers such as silicone resins, alkyd resins, nitrocellulose lacquers, etc., and which contain dyes in contact with the photoconductors. For example, if the layer contains ZnO as a semiconducting compound, these include rose bengal, bromophenol blue, eosin, erythrosin. Further useful layers are in the American patent

3,082,085 and the German patent specification

(F 43 790 IXa / 57b).

For example, if zinc oxide, which has a band edge distance of has about 3 »2 eV, used as a semiconducting material, the generation of positive images is radiation with wavelengths harmful in the area of 385 m / rev and below. The basic lattice absorption however, begins in its foothills at slightly larger wavelengths than 385 ni / U, so that depending on the type of zinc oxide used, the permissible wavelengths may vary somewhat. If, on the other hand, a negative image is to be produced, radiation acts in the Area of 385 m / rev and smaller.

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ORIGINAL EMSPECTED

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Incandescent lamps, xenon lamps or mercury vapor lamps, for example, can be used as light sources. For example, if the light source is a tungsten incandescent lamp, then the harmful UV component can be filtered out to generate a positive image on a colored ZnO layer »that the light source is preceded by an edge filter that only absorbs light with wavelengths greater than about 400 m / u lets through. Filters are preferably used which are particularly permeable in the absorption area of the dye, provided that they only hold back those wavelengths which correspond to the basic grating absorption. If, for example, rose bengal on ZnO is used as the dye, it is sufficient for the filter to clear the area between 430 and 600 m Ai or even only a part of it. Of the sub-regions, one in the vicinity of the absorption maximum of about 564 m / rev is of course particularly favorable. If, on the other hand, there are no filters, or insufficient filters, which absorb UV light, and a filament lamp is used as the light source, the UV component of the lamp can be reduced by operating the filament at a reduced radiation temperature. This can be achieved, for example, by not applying the full operating voltage to the lamp. Especially suitable are light bulbs having a filament temperature 1700 to 2200 ° C, preferably at about 2000 ⁰ G.

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If a negative image is to be produced on the same photoconductive layer, it is necessary that for the imagewise Projection a lamp is used, which has a light component in the basic lattice absorption range of the semiconductor Has. In the case of ZnO, a light source would have to be used, the emission of which is at least partially in the near UV lies. An Hg vapor lamp, for example, is provided for this purpose an only UV permeable filter in question. But also incandescent lamps that are operated at full intensity without a filter, create the negative effect. To accelerate the color change in the dark areas in the procedure specified under 2 The procedure can be such that, in addition to the imagewise illumination of the layer with UV light, the uniform exposure is also carried out Light from the absorption area of the dye is illuminated. In the case of Rose Bengal, these would be wavelengths between about 480 and 600 m / rev.

In general, direct exposure of the photoconductive layer from the front gives satisfactory results. If desired, the exposure of the layer with incandescent light * ie without a UV component can also be carried out through the carrier.

Enclosed are some possible embodiments of the Method according to the invention with reference to schematic drawings explained.

According to Fig. 1, the method for generating positive images is carried out, for example, that with the help of a Incandescent light projector (1) a slide (2) on the surface of a colored semiconductor layer (2) »which is on a metallized Plastic pad (4) is located, is projected.

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Simultaneously with the slide (2), a line slide (5) is placed on the Projected semiconductor surface. This line slide (5) is moved back and forth. Located opposite the layer surface an electrode (6) in the form of one or more tips or wires. The potential difference between electrode and Layer is now adjusted so that the electrode comes to spray. In this way, a positive image of the original is obtained.

According to Fig. 2, the method for generating negative images is carried out, for example, that with the aid of a projector (7), which emits light in the wavelength range of the basic lattice absorption of the semiconductor component in the layer, on the surface a colored semiconductor layer (3), which is on on a metalized plastic base, the image is located a slide is designed. At the same time with a second projector (8), the light in the wavelength range of Self-absorption of the dye but not in the area of the basic lattice absorption contains the semiconductor component, the entire layer (3) is illuminated. The dye just changes at the points that are not affected by the radiation in the basic lattice absorption range the semiconductor component are taken. A negative image is obtained.

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Example 1;

9, g of a photoconductive zinc oxide and 50 mg in alcohol Dissolved rose bengal are made into a paste in an agate mortar and then dried. The zinc oxide colored in this way is made into a paste with a solution of 0.75 g of a silicone resin in 10.5 g of toluene and ground in a ball mill for 1 hour. That Regrind is placed on a metalized plastic base one layer shed. After the layer has dried, it is grounded and applied to the surface using a 300 watt Projection lamp projects an image. A spherical Pt electrode is located opposite the photoconductive layer (0 = ^ 1 mm). The distance between the layer and the electrode is approximately 11 mm. The potential difference between corona electrode and Shift is 11-12 KV.

a) The full operating voltage of 220 volts is applied to the projection lamp. This corresponds to a filament temperature of about 2500 ⁰ G. The filament temperature was measured with the pyrometer. After a treatment period of several minutes, only the edges between light and dark parts are bleached.

b) The operating voltage, which has been reduced to around 120 volts, is applied to the projection lamp. This corresponds to a filament temperature of about 2000 ^° C. After 1.5 minutes, the bright image areas are completely bleached.

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ORIGINAL INSPECTED

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c) The full operating voltage of 220 volts is applied to the projection lamp. There is a in front of the projection lamp Edge filter, which only lets through light with wavelengths greater than 480 m / rev. After 1.5 minutes of treatment the bright areas are bleached in terms of image.

d) The test conditions are as in Example 1b or 1c. A mercury vapor lamp is now used over the incandescent light image a ÜV-Liohtbild projected. In front of the mercury vapor lamp there is a filter which only lets through wavelengths in the range between 300 and 400 m / u. On the from The dye does not fade in areas hit by UV light

Analogous results are found if instead of zinc oxide, for example, rutile and instead of rose bengal, for example

■ v

Bromophenol Blue, Diamond Fuchsin Red, and Eosin can be used. Experiments with compacts (as ZnO + dye without resin) resulted to very similar results. It can be seen from this that the type of resin used is only a relatively minor one Holle is playing.

Example 2:

The same experimental set-up is given as in Example 1a. In front of the projection lamp there are now different ones in sequence Interference filters are set with approximately the same permeability.

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The maximum permeability of the various filters is aexi wavelengths X ₁ * 442; λ ₂ = 474 ί X ₃ * 500; X ₄ * 540; ^ ₅ = 564; X ₆ »586; X _? »6O5f X ₈ = 654; JL _g = 675 nyu. With each filter, under otherwise identical conditions as in Example 1a, the layer is in each case subjected to an imagewise bleaching of the layer. In this way you get 9 different images. The experiment shows that the images that were made with filters 4, 5 and 6 give the best fading. The maximum absorption of Rose Bengal is also in this area. At X «442 m / u, only a weak one, at X- = 654 and X * 675 m / u, no fading effect is achieved. There, the absorption of rose bengal is negligible. Compare with IA Amick, RGA Review, Volume XX (1959) page 768, Fig. 11. From this it follows: If wavelengths from different spectral ranges are used, the dye bleaches the fastest in the spectral range of its maximum absorption.

Example 3:

A zinc oxide rose bengal layer of the same type as in example 1 is used Projected an image with the help of a mercury vapor lamp. In the beam path 1 filter (UGr 1} is switched on, the only light in Permits wavelength range between 300 myu and 400 m / rev. Opposite the photoconductive layer is a spherical Pt-BIe kt ro de Oüfwtmm). The distance between the layer and the electrode is 11 mm. The potential difference between the corona electrode

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and Schiclit is 11 to 12 KV. After a duration of treatment in about 6-10 minutes the dark areas of the image are faded. The result is a negative image of the Template. Longer times are therefore required to produce the negative image than to produce positive images.

Example 4 *

The same arrangement is used as in Example 3. The layer is, however, simultaneously still with light from the absorption area Bengal pink and illuminated with wavelengths greater than 480 m / u. The negative image is created in 1-2 minutes, i.e. in a much shorter time than in example 3

and in better quality.

Example 5 s

A layer of the same type as in Example 1 is used Otherwise the arrangement is as in example 1a, only now there is also a moving auxiliary image, consisting of individual light and dark strokes, projected. After a treatment period of 1.5-2 minutes, the bright areas of the image are faded.

Example 6 *

A layer with ZnO as the semiconductor component and Bengalroaa as the dye is used. With the help of a 300 watt lamp it will turn on the layer projects a bright circular disk. In the rays

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different interference filters are placed one after the other, Opposite the layer there is a Pt electrode at a distance of about 10 mm. The potential difference between layer and Electrode is 12 KV. At wavelengths of around 400 nyu and larger, the positive bending begins. Will a " Ιη, Ο, layer under the same conditions of imagewise exposure and exposed to the electrical charge carriers, the transition point is where the negative fading into positive fading passes, at around 440 and 470 nyu.

This experiment shows that the transition point at which the positive bending changes into negative bending depends on the semiconductor components in the layer. The band edge spacing of the ZnO is approximately 3.2 eV, which corresponds to a wavelength of 385 m / u. The band edge spacing of the In ₂ O is approximately 2.8 eV, which corresponds to a wavelength of approximately 440 m / u. The transition point from negative to positive bending is therefore both for ZnO and In ₂ O, at wavelengths which roughly correspond to the band edge spacing. The smaller the band edge distance, the longer the wavelengths the change from negative to positive bending occurs.

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Claims (6)

Claims; 1. Process for the electrophotographic production of Images using electrophotographic materials composed of a photoconductive layer on a base exist, under the simultaneous action of light and of charge carriers, the image immediately through a imagewise color change of substances contained in the photoconductive layer is made visible, characterized in that the imagewise exposure is carried out with light of such wavelengths lie outside the basic lattice absorption of the semiconductors present in the photoconductive layer, or that light is used for the imagewise exposure, which predominantly consists of such with wavelengths which lie outside the basic lattice absorption of the semiconductors, and then in the exposed Parts of the layer conductivity jumps are generated, in both cases an image-wise change in color the exposed areas takes place. 2. The method according to claim 1, characterized in that incandescent light sources are used for the imagewise exposure, the annealing temperatures between 1700 ⁰ O and 2200 ⁰ O are used. AG 44 - 17 - 9 0 9 8 13/1181 97- ΊΊΙ 3. The method according to claim 1, characterized in that for generating conductivity jumps at the same time an auxiliary image with strong light / dark contrasts is projected and moved with the actual image. 4. The method according to claim 1, characterized in that a photoconductive layer is used that has a colored Contains substance, and that the imagewise exposure to light .from the self-absorption range of the colored substance is carried out. 5. Process for the electrophotographic production of Images made using electrophotographic materials made up of a photoconductive layer consist of a base, with the simultaneous action of light and of charge carriers, the image being taken immediately made visible by an imagewise color change of substances contained in the photoconductive layer is, characterized in that such wavelengths are used for the imagewise exposure that the Basic lattice absorption correspond to the semiconductors present in the photoconductive layer, and that at the same time uniformly the whole shift additionally with light such Wavelengths is exposed which are outside the basic lattice absorption of the semiconductors present in the layer lying, with an imagewise change in the photographic layer on the non-imagewise exposed Places is generated. 9 0 9 8 13/1181 AG 44 - 18 - 6. The method according to claim 5, characterized in that that a photoconductive layer containing a colored substance is used, and that the uniform Exposure to light from the self-absorption region of the colored substance is carried out. AS 44 - 19 - 90 9813/1181